In 6G network with extreme MIMO a potential misalignment exists between UE-centric rank selection and the internal link adaptation state of the gNB, specifically the outer loop link adaptation offset. Since this misalignment leads to inefficient resource utilization and degraded quality-of-service, it must be avoided. We present a novel adaptive rank selection algorithm that allows the gNB to dynamically influence the rank selection of the UE to bridge this gap. Our solution incorporates a gNB-configurable rank selection margin, α, which imposes a minimum required throughput gain to justify selecting a higher rank. This margin constrains the greedy rank selection by the UE, and helps aligning it with the link adaptation state of gNB. System-level results confirm that our method outperforms the conventional greedy baseline, boosting XR capacity from 14 to 15 users per cell and delivering consistent UE throughput gains across all measured percentiles for best-effort file transfer traffic.

While extended reality (XR) applications are expected to be one of the cornerstone use cases for the 6G mobile communications system, the actual performance and capacity results for XR in 6G are yet to be rigorously established. This paper bridges this gap by developing a detailed system model for a candidate 6G network and using it for evaluating the performance of XR applications through extensive system-level simulations. We investigate three enablers for the 6G networks: new spectrum utilization, extreme multiple-input multiple-output (MIMO) methods, and advanced radio resource management (RRM) techniques. Our results demonstrate a 3 times XR capacity improvement over 5G baselines at 3.5 GHz using enhanced CSI feedback framework and advanced RRM techniques. Furthermore, by utilizing the new 7 GHz upper-mid band spectrum with extreme MIMO and a larger bandwidth, XR capacity can be further improved by approximately a factor of 10, supporting more than 50 users per cell. These findings provide the first quantitative evidence of 6G’s potential for XR and offer a crucial baseline for future 6G development.

Conventional hybrid automatic repeat request (HARQ) uses single-bit feedback to boost retransmission reliability; however, its limited granularity restricts advanced link adaptation (LA) for optimizing performance beyond reliability. This paper presents a novel LA approach for retransmissions in 6G networks, targeting spectral efficiency (SE) optimization through effective modulation and coding scheme selection within the HARQ framework. In a dense urban setting with urban macro cell deployment and file transfer protocol model 3 (FTP3) traffic, our optimal LA solution improves average downlink (DL) physical resource block utilization by 31.37 % over Chase combining (CC), a gain inherently linked to SE optimization. Following 3GPP release 18 study item technical report's recommendation to include LA information in HARQ feedback, we address feedback design limitations of the optimal solution with a quantized LA metric. This metric is incorporated into our novel enriched HARQ feedback (EHF) at the user equipment, enabling EHF to surpass single-bit conventional feedback that only conveys transport block decoding status. Evaluated under varying feedback bit counts and LA quantization levels, our design achieves significant gains-e.g., a 20.26 % increase over CC in average DL throughput per FTP3 packet with 4-bit feedback-offering flexibility in application-specific bit sizing.

Sub-band full duplex (SBFD) is a novel duplexing scheme that enables concurrent uplink (UL) and downlink (DL) transmission on non-overlapping frequency resources within an unpaired carrier. Earlier studies indicated that to unleash the full potential gain of SBFD, the radio frame configuration must be adapted to traffic load condition and network characteristics. This paper proposes a centralized deep reinforcement learning framework, based on soft actor-critic for discrete action setting (SAC-Discrete), with a modified prioritized replay mechanism, to train a model that dynamically determines the best frame configuration based on cells' buffer statuses. This method aims to maximize the geometric mean of user throughput, ensuring fairness across all users in both link directions. Simulation results demonstrate that our proposed solution improves UL performance by maximizing the geometric mean of user throughput under varying offered loads.

Cellular mobile networks have enabled several new use cases with their rapid development, and they are now considered for mission-critical and even military applications with 5G, their latest commercially available version. However, it is of utmost importance that communication channels operate in a secure and reliable manner for these purposes. Smart jammers pose a significant threat due to their accessibility, strong potential for causing service disruptions, and their difficulty in detection. This issue can be reduced by hopping between frequencies, making it harder for a malicious actor to disrupt communication. In this study, the handover mechanism, which is a supported feature in all commercial devices according to 3GPP standards, is evaluated as a frequency hopping technique in terms of feasibility and performance at preventing the attack. The proposed method is proven effective, as it can switch frequencies every second while keeping data interruptions below 75 ms for 99% of the time.

This paper investigates a dynamic packet scheduling algorithm designed to enhance the eXtended Reality (XR) capacity of fifth-generation (5G)-Advanced networks with multiple cells, users, and services. The scheduler exploits the newly defined protocol data unit (PDU)-set information for XR traffic flows to enhance its quality-of-service awareness. To evaluate the performance of the proposed solution, advanced dynamic system-level simulations are conducted. The findings reveal that the proposed scheduler offers a notable improvement in increasing XR capacity up to 45%, while keeping the same enhanced mobile broadband (eMBB) cell throughput as compared to the well-known baseline schedulers.

This paper presents a dynamic inter-cell interference coordination (ICIC) technique that enhances extended reality (XR) capacity, while minimizing the impact on enhanced mobile broadband (eMBB) traffic in a multi-cell multi-user network. The network identifies victim XR users based on their experienced performance and dynamically coordinates with aggressor cells for muting in specific transmission time intervals to alleviate interference for the victim users. Extensive dynamic system-level simulations demonstrate the effectiveness of the proposed ICIC scheme, achieving a 22-32% gain in XR capacity while incurring a degradation of 12-22% in average eMBB cell throughput.

The introduction of sub-band full duplex (SBFD) with simultaneous downlink and uplink transmissions has the potential to improve the uplink performance as compared to traditional static time division duplexing (TDD) with sparse uplink resources. However, SBFD benefits are limited by cross-link interferences caused by the simultaneous uplink and downlink transmissions. This paper proposes to dynamically reduce the 5G base station (gNB) transmission power during SBFD slots to mitigate the gNB self- and gNB-to-gNB-interferences, as well as corresponding link adaptation enhancements to unleash the full potential of such techniques. The SBFD system-level performance is evaluated with different levels of power reduction under varied offered load conditions for urban macro (UMa) and dense urban (DU) environments. Results indicate that for the DU, applying a 10 dB gNB transmit power reduction for SBFD slots leads to a 187% improvement of cell-edge user uplink throughput under high offered load (compared to static TDD). For UMa, at most 4 dB SBFD gNB transmit power reduction is recommended for improving the cell-edge uplink throughput while still ensuring downlink acceptable data rates.

This paper presents a performance evaluation of sub-band full duplex (SBFD) for an indoor office environment. SBFD has the potential to improve packet latency by utilizing non-overlapping uplink and downlink frequency resources simultaneously. To evaluate the SBFD performance, system- level simulations are conducted with different packet sizes and varied offered load conditions. The simulation results reveal a clear dependence of SBFD performance on the packet size of the traffic model. For small packet cases, up to 55% improvement of the average packet latency in the uplink and up to 24% in the downlink is achieved in SBFD, as compared to static TDD, when a 90 dB ratio of self-interference mitigation (RSI) is ensured. For large packet cases, including an uplink-only slot in the SBFD frame structure has the potential to improve the uplink latency, even though this adjustment leads to increased downlink latency. Furthermore, simulation results indicate that the has a noticeable impact on the SBFD performance in the downlink.

In this paper, we address the joint performance of eXtended reality (XR) and best-effort enhanced mobile broadband (eMBB) traffic for a 5G-Advanced system. Although XR users require stringent throughput and latency performance, operators do not lose significant additional network capacity when adding XR users to an eMBB-dominated network. For instance, adding an XR service at 45 Mbps with a 10 ms packet delay budget yields close to a 45 Mbps drop in eMBB capacity. In an XR-only network layer, we show how the capacity in a number of supported XR users depends significantly on the rate but also the latency budget. We also show how the XR service capacity is significantly reduced in the mixed service setting as the system goes into full load and other-cell interference becomes significant. The presented results can be used by cellular service providers to assess their networks’ performance of XR traffic based on their current eMBB performance or as input to dimensioning to be able to serve certain XR traffic loads.

Extended Reality (XR) applications introduce challenging requirements for radio mobile systems in terms of capacity and latency. At the same time, XR devices needs to minimize power consumption to extend battery lifetime and limit dissipated heat. Addressing capacity and latency requirements without excessively increasing power consumption of user devices requires the evolution of 5G power saving schemes. In this work, we propose an Adaptive DRX (ADRX) scheme and design a control policy to optimally adjust active duration of the DRX cycle in order to satisfy XR requirements and minimize energy consumption. To this end, we formulate the problem of selecting the user active time as a stochastic online optimization problem and present a control policy to optimally solve it. Numerical results confirm that the proposed solution increases the number of satisfied users and reduce power consumption compared to standard DRX mechanism. In particular, in a Dense Urban scenario where standard DRX cannot fulfill the requirements of any XR user, ADRX can serve up to 4-5 users per cell with 10% power saving gain.

Uplink power control plays a significant role in maintaining a good signal quality at the serving cell while minimizing interference to neighboring cells, thus maximizing the system performance. Traditionally, a single value open-loop power control (OLPC) parameter, P0, is configured for all the user equipments (UEs) in a cell, and often same setting is used for similar cells. Recent studies have demonstrated that optimal P0depends on many factors, which yields a complex multidimensional optimization problem and there are no efficient approaches known to solve it under practical system-level settings. In this paper, we propose a solution based on reinforcement learning (RL) where each BS autonomously adjusts its P0setting to maximize its throughput performance. As compared to conventional sub-optimal approach, our solution encompasses a smart clustering of UEs, where each cluster specifies its own P0. The proposed solution is evaluated by extensive system level simulations, where our results demonstrate a potential performance enhancement as compared to the baseline proposals.

5G New Radio (NR) incorporates numerous beam-based novel features such as beam management procedures for selecting the best serving gNB beam, recovery from beam failures, beam-based inter-cell mobility support and advanced UEs with multiple directional panels. In this paper, we study the joint performance of all these techniques for a macro cellular scenario at 28 GHz with special emphasis on how the UE antenna design influences the system-level performance. It is shown that the full benefits of 5G can be delivered with the introduction of multiple directional antenna panels at the UE side. We also introduce a mechanism for controlling the UE antenna panel switching. Our results from advanced dynamic system-level simulations indicate excellent performance with handover failure rates on the order of 0.01-0.03%, and beam failure rates at 0.04%, for UE speeds as high as 60 km/h. The median SINR gain of using four directional antenna panels at the UE equals 6 dB as compared to Omni UEs.

The fifth generation (5G) new radio supports a diversity of network deployments. The industrial factory (InF) wireless automation use cases are emerging and drawing an increasing attention of the 5G new radio standardization groups. Therefore, in this paper, we propose a service-aware time division duplexing (TDD) frame selection framework for multi-traffic deployments. We evaluate the performance of the InF network deployments with the state-of-the-art 3GPP modeling assumptions. In particular, we consider the dynamic TDD mode along with optimized uplink power control settings. Multi-traffic coexistence scenarios are also incorporated such that quality of service (QoS) aware dynamic user scheduling and TDD link selection are introduced. Extensive system level simulations are performed in order to evaluate the performance of the proposed solutions, where the proposed QoS-aware scheme shows 68% URLLC outage latency reduction compared to the QoS-unaware solutions. Finally, the paper offers insightful conclusions and design recommendations on the TDD radio frame selection, uplink power control settings and the best QoS-coexistence practices, in order to achieve a decent URLLC outage latency performance in the state-of-the-art InF deployments.

Several Medium Access Control (MAC) based beam management procedures have been adopted in the 3rd Generation Partnership Project (3GPP) to support beam-based communication in 5G New Radio (NR). These connected mode beam management functionalities include beam tracking, beam failure detection and beam failure recovery. This paper provides a detailed system-level performance analysis of beam management procedures for Frequency Range 1 (FR1) macro-cellular environments. Assumptions which are left open for User Equipment (UE) implementation are also discussed. Extensive system-level performance results for metrics such as beam failure probability, beam failure recovery, and beam time-of-stays are presented. We observe excellent beam management performance for UEs that are not about to experience handovers. On the other hand, UEs at the cell-edge are subject higher values, but still on an acceptable failure probability level of 1-2% for UE speeds up to 30 kmph.

In this paper, we present an extensive system-level assessment of 5G New Radio (NR) uplink performance for a dense macro deployment at 28 GHz carrier frequency. As is demonstrated, the uplink transmit power control (TPC) configuration has significant influences on the end-user performance and cell capacity, and therefore must be carefully configured. Effects of having advanced terminals with multiple directional antenna panels are studied and compared to the performance of having simpler users with omnidirectional antennas. It is found that having advanced terminals with three or four directional antenna panels offers 15% higher cell capacity and 100% improvement in the 5%-ile cell-edge outage user throughput as compared to omni-terminals. The paper also provides guidelines for setting of the critical TPC poarameters, and their related dependencies.

Unlicensed spectrum operation mandates the performance of channel access mechanisms to ensure the absence of transmissions by other unlicensed radio access technologies. Packets are prone to be impacted by these mechanisms as transmissions might be delayed. In this paper, we first analyse the impact of unexpected and sporadic IEEE 802.11ax interference on a New Radio-Unlicensed (NR-U) deployment in an industrial environment. Given the need for improvement in such scenarios, frequency diversity techniques are proposed to fulfil tight latency-reliability requirements and combat the impact of 802.11ax interference. A multi-channel NR-U system in which, at least, one of the channels is free of IEEE 802.11ax interference is studied. The paper shows that multi-channel techniques with a lack of flexibility in the channel selection exhibit modest benefits in scenarios with the presence of sporadic interference. A scheme with flexible channel selection is proposed and verified as the preferred option for stringent latency and reliability applications.

The ultra-reliable and low-latency communication (URLLC) is the key driver of the current 5G new radio standardization. URLLC encompasses sporadic and small-payload transmissions that should be delivered within extremely tight radio latency and reliability bounds, i.e., a radio latency of 1 ms with 99.999% success probability. However, such URLLC targets are further challenging in the 5G dynamic time division duplexing (TDD) systems, due to the switching between the uplink and downlink transmission opportunities and the additional inter-cell cross-link interference (CLI). This paper presents a system level analysis of the URLLC outage performance within the 5G new radio flexible TDD systems. Specifically, we study the feasibility of the URLLC outage targets compared to the case with the 5G frequency division duplexing (FDD), and with numerous 5G design variants. The presented results therefore offer valuable observations on the URLLC outage performance in such deployments, and hence, introducing the state-of-the-art flexible-FDD technology.

Dual connectivity for reliability is considered one of the most important enablers of ultra-reliable low-latency communication in fifth-generation cellular systems. In this paper, we focus on downlink dual connectivity, proposing two methods that prevent unnecessary duplicates transmissions to enhance spectral efficiency when using data duplication. In the first method, the duplicates of packets already successfully delivered to the terminal are promptly dropped from the transmission queues of the involved base stations thanks to an uplink indication provided by terminal itself. In the second method, the transmission of duplicates from the secondary node is enforced only upon a failure of the master node. The performance of the two proposed schemes is evaluated in terms of i) achievable packet reliability within the 1-ms latency target of ultra-reliable low-latency communication, and ii) resource-block utilization via system-level simulation campaigns. The results show that, in the investigated scenario, the second proposal can support a four-times higher offered load with respect to the baseline approach.

Accurate downlink link adaptation is a major challenge for ultra-reliable and low-latency communications (URLLC) as a consequence of the random and unpredictable load variations at the interfering cells. To address this problem, this paper introduces enhancements to the channel quality indicator (CQI) measurement and reporting procedures for 5G New Radio (NR). The goal is to accurately estimate and report the lower percentiles of the user channel quality distribution. First, a simple and efficient technique is proposed for filtering the channel quality samples collected at the user equipment and, accordingly, estimating tail signal-to-interference-and-noise (SINR) performance. Second, a new CQI reporting format is introduced which better guides downlink scheduling and link adaptation decisions of small URLLC payloads at the gNB. The benefits of the proposed solutions are evaluated via advanced system-level simulations, where it is shown that the proposed solutions significantly outperform existing CQI measurement and reporting schemes. For instance, the 99.999% percentile of the experienced latency is reduced from 1.3 ms to 0.86 ms for the case when URLLC traffic is multiplexed with enhanced mobile broadband (eMBB) traffic.

Communications over the unlicensed spectrum are susceptible to be delayed by mandatory channel access mechanisms. Based on the need for improving the latency-reliability performance of New Radio-Unlicensed for supporting new usecases, such as industrial applications, different types of channel access are evaluated in this paper. By using asynchronous and demand-driven channel access, it is shown that approximately 50% of the delay experienced by a downlink packet is due to listen before talk (LBT). Furthermore, UEs might be blocked by an unsuccessful uplink LBT losing the opportunity to transmit their previously scheduled data. As an alternative, synchronous channel access is evaluated. By using a coordinated LBT among the nodes, the channel access delay is reduced to a constant value. However, UEs can still be blocked when initiating their uplink transmissions due to neighbours transmissions. Motivated by this fact, an approach in which a central node is in charge of the frame selection is proposed. Therefore, all the nodes in the system are coordinated in both the channel access and the frame configuration. In this case, a latency reduction of 70% as compared to the previously mentioned alternatives is achieved at high loads and 99.9999% reliability.

In this paper, the performance impact of several high-reliable and low-latency communications technology enablers in the unlicensed spectrum for standalone operation is evaluated. Firstly, a comparison between MulteFire (MF) and New Radio-Unlicensed (NR-U) is established. It is shown that higher sub-carrier spacings and shorter processing times provide clear latency reduction benefits. Additionally, different transmission time intervals (TTI) durations are evaluated. Shortening the TTI duration decreases the latency by a factor of 5.75 at 99.99% reliability and reduces the uplink Listen Before Talk (LBT) blocking probability by 18%. The possibility of having multiple switching points during the frame is also evaluated. It is concluded that having multiple switching points provides a latency reduction mainly due to the reduction of the number of channel accesses and the reduced gaps within the frame. A time-diversity technique to cope with high uplink LBT blocking probability is also evaluated. By combining the aforementioned features, a latency reduction factor of 31 is achieved when optimized NR-U and MulteFire performances are compared.

Dynamic time division duplexing (TDD) is envisioned as a vital transmission technology of the 5G new radio, due to its reciprocal propagation characteristics. However, the potential cross-link interference (CLI) imposes a fundamental limitation against the feasibility of the ultra-reliable and low latency communications (URLLC) in dynamic-TDD systems. In this work, we propose a near-optimal and complexity-efficient CLI suppression scheme using orthogonal spatial projection, while the signaling overhead is limited to B-bit, over the back-haul links. Compared to the state-of-the-art dynamic-TDD studies, proposed solution offers a significant improvement of the URLLC outage latency, e.g., ~-199% reduction, while boosting the achievable capacity per the URLLC packet by ~+156%.

Dynamic time division duplexing (TDD) is one of the major novelties of the 5G new radio standard. It notably improves the network resource utilization with sporadic directional packet arrivals. Although, the feasibility of the ultra-reliable and low-latency communications (URLLC) within such deployments is critically challenged, mainly due to the crosslink interference (CLI). In this work, we propose a semistatic and computationally-efficient TDD radio frame adaptation algorithm for 5G macro deployments. Particularly, we first identify the quasi-static variance of the cross-cell traffic buffering performance, with various CLI co-existence conditions. Accordingly, a common radio frame pattern is dynamically estimated based on the filtered multi-cell traffic statistics. Our system-level simulation results show that the proposed solution achieves a highly improved URLLC outage performance, i.e., offering ~ 40% reduction gain of the achievable URLLC outage latency compared to perfect static-TDD, and approaching the optimal interference-free flexible-TDD case; though, with a significantly lower control overhead size.

This paper addresses the problem of down-link centralized multi-cell scheduling for ultra-reliable lowlatency communications in a fifth generation New Radio (5G NR) system. We propose a low-complexity centralized packet scheduling algorithm to support quality of service requirements of URLLC services. Results from advanced 5G NR system-level simulations are presented to assess the performance of the proposed solution. It is shown that the centralized architecture significantly improves the URLLC latency. The proposed algorithm achieves gains of 99% and 90% URLLC latency reduction in comparison to distributed scheduling and spectral efficient dynamic point selection.

5G networks should support heterogeneous services with an efficient usage of the radio resources, while meeting the distinct requirements of each service class. We consider the problem of multiplexing enhanced mobile broadband (eMBB) traffic, and grant-free ultra-reliable low-latency communications (URLLC) in uplink. Two multiplexing options are considered; either eMBB and grant-free URLLC are transmitted in separate frequency bands to avoid their mutual interference, or both traffic share the available bandwidth leading to overlaying transmissions. This work presents an approach to evaluate the supported loads for URLLC and eMBB in different operation regimes. Minimum mean square error receivers with and without successive interference cancellation (SIC) are considered in Rayleigh fading channels. The outage probability is derived and the achievable transmission rates are obtained based on that. The analysis with 5G new radio assumptions shows that overlaying is mostly beneficial when SIC is employed in medium to high SNR scenarios or, in some cases, with low URLLC load. Otherwise, the use of separate bands supports higher loads for both services simultaneously. Practical insights based on the approach are discussed.

5th generation radio networks should efficiently support services with diverse requirements. For achieving better resource utilization, the sharing of the radio channel between the different services is an attractive solution. While the downlink multiplexing can be well accomplished with dynamic scheduling, efficient multiplexing of enhanced mobile broadband (eMBB) and ultra-reliable low-latency communications (URLLC) in uplink is still an open problem. In particular, we consider the case of URLLC using grant-free allocation for sporadic transmissions, multiplexed on shared resources with eMBB with high data volume. Since the moment in which a grant-free transmission occurs is not known, URLLC and eMBB transmissions overlay. Power control settings are then assessed as a way to manage the performance trade-off between the services. Due to the complexity of 5G new radio, the evaluation is based on advanced system level simulations. Insights regarding the configuration of fractional power control settings upon the coexistence of the different services are presented.

The fifth generation (5G) of the wireless communication networks supports wide diversity of service classes, leading to a highly dynamic uplink (UL) and downlink (DL) traffic asymmetry. Thus, dynamic time division duplexing (TDD) technology has become of a significant importance, due to its radio frame flexibility. However, fully dynamic TDD systems suffer from potentially severe inter-cell cross link interference (CLI). In this paper, we propose a novel inter-cell radio frame coordination (RFC) scheme based on sliding codebook for fully dynamic TDD 5G networks. Proposed coordination scheme simultaneously addresses two optimization objectives of minimizing the average CLI while reliably maximizing the achievable DL/UL capacity, by virtually extending the RFC degrees of freedom through a sliding phase-offset RFC codebook design. Compared to the state-of-the-art TDD studies, the proposed scheme shows significantly improved ergodic capacity, i.e., at least ~ 140% gain under both the TCP and UDP protocols, and with much less signaling overhead, limited to B-bit. The paper offers valuable insights about how to most efficiently pre-mitigate potential CLI in Macro TDD systems.

This paper introduces a preemptive rank offloading scheduling framework for joint ultra-reliable low-latency communications (URLLC) and enhanced mobile broadband (eMBB) traffic in 5G new radio (NR). Proposed scheduler dynamically adapts the overall system optimization among the network-centric ergodic capacity and the user-centric URLLC one-way latency, based on the instantaneous traffic and radio resources availability. The spatial degrees of freedom, offered by the transmit antenna array, are fully exploited to maximize the overall spectral efficiency. However, when URLLC traffic buffering is foreseen, proposed scheduler immediately enforces scheduling pending URLLC payloads through preemption-aware subspace projection. Compared to the state-of-the-art schedulers from industry and academia, proposed scheduler framework shows significant scheduling flexibility in terms of the overall ergodic capacity and URLLC latency performance. The presented results therefore offer valuable insights of how to most efficiently multiplex joint URLLC-eMBB traffic over the 5G NR spectrum.

We address the problem of resource allocation and packet scheduling for a mixture of ultra- reliable low-latency communication (URLLC) and enhanced mobile broadband (eMBB) traffic in a fifth generation New Radio (5G NR) networks. A novel resource allocation method is presented that is latency, control channel, hybrid automatic repeat request (HARQ), and radio channel aware in determining the transmission resources for different users. This is of high importance for the scheduling of URLLC users in order to minimize their latency, avoid unnecessary costly segmentation of URLLC payloads over multiple transmissions, and benefit from radio channel aware multi-user diversity mechanisms. The performance of the proposed algorithm is evaluated with an advanced 5G NR compliant system level simulator with a high degree of realism. Simulation results show promising gains of up to 98% latency improvement for URLLC traffic and 12% eMBB end-user throughput enhancement as compared to conventional proportional fair scheduling.

In this paper, we study the performance of ultra- reliable low-latency communication (URLLC) for cellular standalone systems in unlicensed bands. Our focus is on the 5 GHz band, adopting a system model in coherence with the MulteFire standard, which essentially is a variant of LTE (Long Term Evolution) for unlicensed band operation. We show that especially the mandatory Listen Before Talk (LBT) procedure suppose a challenge for achieving low latency communication. Our theoretical analysis indicated that the impact of the LBT procedure prior to downlink transmissions can be significant, taking values of 3-25 ms for the considered offered load levels. Furthermore, our advanced dynamic system-level simulations show that the time spent performing LBT often accounts for 18\%-42\% of the packet latency budget, depending on the considered outage level and offered traffic. Therefore LBT represents a major challenge for achieving URLLC-alike performance in unlicensed spectrum.

5G new radio is envisioned to support three major service classes: enhanced mobile broadband (eMBB), ultra-reliable low-latency communications (URLLC), and massive machine type communications. Emerging URLLC services require up to one millisecond of communication latency with 99.999% success probability. Though, there is a fundamental trade-off between system spectral efficiency (SE) and achievable latency. This calls for novel scheduling protocols which cross-optimize system performance on user-centric; instead of network-centric basis. In this paper, we develop a joint multi-user preemptive scheduling strategy to simultaneously cross-optimize system SE and URLLC latency. At each scheduling opportunity, available URLLC traffic is always given higher priority. When sporadic URLLC traffic appears during a transmission time interval (TTI), proposed scheduler seeks for fitting the URLLC-eMBB traffic in a multi-user transmission. If the available spatial degrees of freedom are limited within a TTI, the URLLC traffic instantly overwrites part of the ongoing eMBB transmissions to satisfy the URLLC latency requirements, at the expense of minimal eMBB throughput loss. Extensive dynamic system level simulations show that proposed scheduler provides significant performance gain in terms of eMBB SE and URLLC latency.

In this paper, we discuss the achievable transmission rates over collision-prone radio resources shared by a number of devices, representative of novel Internet-of-Things (IoT) scenarios. We consider Maximum Ratio Combining (MRC) and Minimum Mean Square Error (MMSE) receivers at the base station, and derive the relationship between target failure probability and saturation rate, which represents the maximum achievable rate over shared resources in the interference limited regime. MRC receiver is shown to be sensitive to the presence of statistically relevant interferers operating over the same resources, rapidly leading to rate saturation. The MMSE receiver adds a tier of protection to collisions thanks to its interference suppression capabilities, suffering for a rate penalty only in case of a high number of users. A realistic system analysis in an indoor hotspot scenario validates the analytical trends and suggests insights on practical link adaptation strategies.

A centralized joint cell selection and scheduling policy for ultra-reliable low latency communication (URLLC) is studied in this paper for the 5G new radio (NR). A low complexity cell association and scheduling algorithm is proposed, while maintaining attractive performance benefits. By being able to centrally control from which cells the different users are instantaneously scheduled, we show that the undesirable queuing delays for URLLC traffic can be significantly reduced. The proposed solution is evaluated in a realistic multi-cell, multi-user, dynamic network setting in line with the 5G NR system design specifications, and calibrated against 3GPP NR assumptions. The presented performance results show promising gains, where the proposed centralized solution can accommodate 38% higher traffic offered load than a traditional distributed network implementation, while still fulfilling the challenging reliability and latency targets for URLLC.

This work is related to 5G new radio concept design, with focus on ultra-reliable and low latency communication (URLLC) use cases. We mainly target to achieve the stringent latency and reliability requirements for transmissions over the air interface, such as 99.999% success probability within 1 ms. Meeting these requirements in an efficient way, that is, without draining the network capacity is one of the main challenges for the new radio standardization. In this work, we propose a scheme to perform blind retransmissions on shared radio resources together with the application of successive interference cancellation to receive remaining non-decoded data with low delay penalty. The method avoids control errors and extra delays existent on feedback-based retransmission schemes. The investigations also show that blind retransmission on shared resources is more resource efficient than a conservative single shot transmission, depending on the number of users sharing the resources.

In this paper, we present an exhaustive system level analysis of using preemptive scheduling for latency critical traffic in coexistence with mobile broadband for the 3GPP 5G New Radio. Enhanced recovery and HARQ retransmission mechanisms exploiting base station a priori knowledge of punctured radio resources from using preemptive scheduling are proposed. It is demonstrated that a scheme with HARQ multi-bit feedback and selective retransmission of punctured resources is an attractive solution. Furthermore, the performance sensitivity from using either fully interleaved or frequency-first code block layouts is assessed. The impact on the mobile broadband performance is evaluated at TCP-level, studying both the penalty on throughput and smoothened TCP round trip time to assess how preemptive scheduling affects the end-to-end performance of other traffic.

ONE5G (E2E-aware Optimizations and advancements for the Network Edge of 5G New Radio) is an European funded collaborative project, aiming at designing Radio Access Network (RAN) enhancements to address the multiplicity of services and deployment scenarios for 5G. The project will build upon the specification already defined in 3GPP to propose advanced link techniques and optimization schemes taking into account an end-to-end (E2E) performance view. This paper describes the scenarios considered in the project and the set of uses cases considered, as well as the approach to define Key Performance Indicators reflecting the E2E performance. The technical areas investigated in the project are presented, as well as the planned prototypes.

Ultra-reliable and low latency communication (URLLC) presents the most challenging use cases for fifth generation (5G) mobile networks. Traditionally the focus for mobile broadband has been to optimize the system throughput for high speed data traffic. However the optimization criteria for URLLC should focus on achieving small packets transmissions under strict targets such as 99.999% reliability within 1 ms. Power control is one candidate technology component for improving reliability and latency. In this work we investigate the power control for grant-free URLLC transmissions through extensive system level simulations in a urban outdoor scenario. We initially compare different settings for open loop power control (OLPC) with full and with fractional path loss compensation. Then we evaluate whether power boosting the retransmission can reduce the probability of packets delays under the 1 ms constraint. We also discuss the practical implication of applying power boosting. With full path loss compensation and boosting retransmissions, we show that a URLLC load such as 1200 small packets per second per cell can be achieved in the considered scenario.

This paper presents solutions for efficient multiplexing of ultra-reliable low-latency communications (URLLC) and enhanced mobile broadband (eMBB) traffic on a shared downlink channel. Such a scenario presents multiple challenges in the context of radio resource scheduling, link adaptation and inter-cell interference, which are identified and addressed throughout the paper. Specifically, a joint link adaptation and resource allocation technique is proposed that dynamically adjusts the block error probability (BLEP) of the URLLC payload transmissions in accordance with the instantaneous experienced load per cell. Extensive system-level simulations of the downlink performance show promising gains of this technique, reducing the URLLC latency from 1.3 ms to 1 ms at the 99.999% percentile, with less than 10% degradation of the eMBB throughput performance as compared to conventional scheduling policies.

Multiple transmit and receive antennas can be used to increase the number of independent streams between a transmitter-receiver pair, or to improve the interference resilience property with the help of linear minimum mean squared error (MMSE) receivers. An interference aware inter-cell rank coordination framework for the future fifth generation wireless system is proposed in this article. The proposal utilizes results from random matrix theory to estimate the mean signal-to-interference-plus-noise ratio at the MMSE receiver. In addition, a game-theoretic interference pricing measure is introduced as an inter-cell interference management mechanism to balance the spatial multiplexing vs. interference resilience trade-off. Exhaustive Monte Carlo simulations results demonstrating the performance of the proposed algorithm indicate a gain of around 40% over conventional non interference-aware schemes; and within around 6% of the optimum performance obtained using a brute-force exhaustive search algorithm.

Unique Word Discrete Fourier Transform -spread - Orthogonal Frequency Division Multiplexing (UW DFT-s-OFDM) waveform replaces the Cyclic Prefix (CP) with a known sequence which is contained in the symbol itself rather than being appended to it. In this paper, we propose a new UW DFT-s-OFDM design which aims at exploiting such known sequence at the tail of the signal for tracking the variations of the radio channels on a symbol basis, thus overcoming the limited flexibility of DFT-s-OFDM waveforms in multiplexing reference sequences and data. Further, we also present a criterion for efficiently selecting the reference sequences to be adopted by users experiencing fast time-varying channel conditions. Initial simulation results show the capability of the proposed design of improving the link performance of high speed users, even without additional overhead.

This paper presents enhancements for lowering the handover interruption time in future wireless networks. We propose a selective data forwarding for the handover preparation phase, and the integration of the make-before-break procedure with the synchronous random access-less handover. To evaluate our proposals, we analyze the handover timing for typical and variable values of the user equipment and e-NodeB processing times, and X2 interface latencies. Our results show that the processing delays, reconfiguration times, and the X2 latency should be simultaneously reduced to minimize the data interruption time. Selective data forwarding during the handover preparation reduces the data interruption time by 18 % compared to the basic random access less handover with typical network delays. Make-before-break is the most suitable handover type for future low-latency applications, as it achieves zero data interruption independent of the latency of handover steps.

In this paper, we present an inter-cell interference subspace coordination scheme for multiple-input multiple-output communications. The method relies on downlink precoding design for distributed multi-cell multi-user networks. In the proposed method, receivers benefit from minimum-mean square error structure. Each receiver separates the received signal space into desired/interference sub-spaces. The key idea in this contribution is to employ precoding algorithms at the transmission-end with the objective of jointly projecting transmitted signal over desired subspace and aligning most of the interference onto predefined interference subspaces at the interfered receiver end. This idea works with only local channel state information available at transmitter-side and benefits from low computational complexity. Simulation results show that the proposed method offers about 28\% throughput enhancements in networks with high dominant interference regimes.

A reliable feedback channel is vital to report decoding acknowledgments in retransmission mechanisms such as the hybrid automatic repeat request (HARQ). While the feedback bits are known to be costly for the wireless link, a feedback message more informative than the conventional single-bit feedback can increase resource utilization efficiency. Considering the practical limitations for increasing feedback message size, this paper proposes a framework for the design of flexible-content multi-bit feedback. The proposed design is capable of efficiently indicating the faulty segments of a failed large-size data packet thanks to which the transmitter node can reduce the retransmission size to only include the initially failed segments of the packet. We study the effect of feedback size on retransmission efficiency through extensive link-level simulations over realistic channel models. Numerical result present significant savings in retransmission resources offered by the proposed flexible-content feedback design.

Radio networks are at the brink of a transformation in order to meet new requirements for high data and device densities expected for the Internet-of-Things (IoT) era. Cloud technology is positioned to be a key element in building effective 5G radio networks, so-called Cloud RANs. In this paper, we focus on Cloud RAN architectural benefits in relation to synchronous handovers without random access; an important enabler for ultra-low latency and ultra-high reliability services for high mobility IoT applications. We analyze the performance of Cloud RAN architectures and introduce a new concept for reducing the handover preparation time. Compared to today's distributed RAN architectures, we show a handover preparation time reduction of up to 60% for a wide range of interface and processing latency assumptions.

In this paper, we present a punctured scheduling scheme for efficient transmission of low latency communication (LLC) traffic, multiplexed on a downlink shared channel with enhanced mobile broadband traffic (eMBB). Puncturing allows to schedule eMBB traffic on all shared channel resources, without prior reservation of transmission resources for sporadically arriving LLC traffic. When LLC traffic arrives, it is immediately scheduled with a short transmission by puncturing part of the ongoing eMBB transmissions. To have this working efficiently, we propose recovery mechanisms for punctured eMBB transmissions, and a service-specific scheduling policy and link adaptation. Among others, we find that it is advantageous to include an element of eMBB-awareness for the scheduling decisions of the LLC transmissions (i.e. those that puncture ongoing eMBB transmissions), to primarily puncture eMBB transmission(s) that are transmitted with low modulation and coding scheme index. System level simulations are presented to demonstrate the benefits of the proposed solution.

5G downlink Inter-Cell Interference Coordination (ICIC) has a twofold objective: to better exploit the benefits of ICIC in coherence with the rest of Radio Resource Management (RRM) principles in 5G; and to support new 5G service classes and their coexistence in a multi-service setting. We propose on-demand Power Boosting and Inter-cell Coordination (PB-IC) to meet high reliability and low latency requirements of critical data without compromising the spectral efficiency of the rest of traffic. PB-IC is demonstrated to provide similar latency gains as the classical frequency reuse, but much lower impact to the enhanced Mobile BroadBand (eMBB) traffic. Results demonstrate that the tail of the latency distribution is reduced as much as 100% in the 10^-4 percentile, achieving comparable gains to static frequency reuse. At the same time, the degradation in eMBB throughput is minimized, reaching a 14% loss instead of the 50% observed with static ICIC. We discuss the standardization effort required for having PB-IC supported, with considerations of the measurement requirements to the UE and the infrastructure backhaul latencies.

The fifth generation (5G) cellular network demands new solutions to meet, in an efficient way, the stringent targets for ultra-reliable and low latency communication (URLLC), such as 1-10-5reliability within 1 ms. In a wireless system, the control signaling of the scheduling process is also a source of errors and delays. Semi-persistent scheduling (SPS) is an option to reduce the signaling, leading to lower latency and improved transmission reliability. However, conventional SPS still applies grant signaling to schedule the retransmission. In this work it is proposed an alternative scheme in which a group of users shares a pre-scheduled resource for retransmission. The benefit is that it provides a retransmission opportunity without needing a scheduling control information. Besides that, if the pre-scheduled resource can not be reallocated, the sharing mechanism avoids excessive capacity loss. It is demonstrated through a simple analytical model that, for right grouping sizes and initial transmission error rates, the target error probability e.g. 10-5can be achieved. It is also shown that the suggested scheme can provide improved resource efficiency compared to a single conservative transmission which also avoids re- scheduling.

In this paper we present our latest findings on dynamic user-centric scheduling for a flexible 5G radio design, capable of serving users with highly diverse QoS requirements. The benefits of being able to schedule users with different transmission time intervals (TTIs) are demonstrated, in combination with a user-centric multiplexing of control and data channels. The proposed solution overcomes some of the shortcomings of LTE-Advanced in terms of scheduling flexibility and performance. In general it is found that using short TTIs is advantageous at low to medium offered traffic loads for TCP download to faster overcome the slow start phase, while at higher offered traffic loads the best performance is achieved with longer TTIs. Using longer TTI sizes results in less control overhead (from scheduling grants), and therefore higher spectral efficiency. The presented analysis leads to the conclusion that a future 5G design shall include support for dynamic scheduling with different TTI sizes to achieve the best performance.

This study compares the amount of control signaling required by traditional network-controlled mobility management with the one required by user equipment autonomous cell management operations in a real-life highway scenario. The scenario is covered by macros and densely-deployed small cells. Different strategies for preparing the small cells for autonomous operations are studied. Our results show that traditional dual connectivity requires an average of 4.9 messages, per user per second, to be exchanged between the user equipment and the network, and 11.6 messages between e-NodeBs. On the other hand, autonomous cell management operations considerably decrease the amount of signaling. The highest reductions can be achieved by preparing all cells along the highway, cutting the signaling overhead by 92 % over the air, and 39 % between e-NodeBs. Furthermore, the approach of applying a newly developed window-based feature for preparing the cells brings significant benefits.

In Dual Connectivity (DC), a User Equipment (UE) can be configured with two radio access nodes in order to aggregate the available resources at both nodes. As with dual connectivity each node has independent radio resource management, the maximum power allocation at the UE can be easily exceeded and the interference can be increased. Hence, the power distribution among the carriers needs to be optimized and has to minimize the required coordination among the nodes. In this paper we propose an optimal power allocation based on the load of the cells and cell effective interference. Additionally, we determine criteria for configuration of UEs with dual connectivity. The simulation results show performance improvement by the proposed algorithm with respect to the achieved user throughput. Performance gains (threefold gain in median user throughput) are evident in low as well as high loads in the cell.

Besides coping with the increasing demand of broadband services, 5th Generation (5G) radio access technology is expected to support mission critical communication (MCC) services targeting very low latencies. In this paper, we investigate the feasibility of the usage of an early Hybrid Automatic Repeat reQuest (HARQ) feedback for reducing the latency of acknowledged transmissions without disregaring spectral efficiency. As enabler of such early feedback, a new technique for predicting the decoder outcome before decoding occurs, is proposed. This technique is intended to generate an early ACK/NACK, or an uncertain feedback in case a reliable prediction cannot be achieved. Simulation results show a very limited occurrence of false positives and false negatives, and uncertain feedback rates not exceeding 6% when adaptive modulation and coding (AMC) and a 10% Block Error Rate (BLER) target is assumed. A correct early ACK/NACK can be generated for around 90% of the transmissions or more.

Achieving the trade-off between coverage, ultra-low latency and capacity is a major challenge for a 5th Generation (5G) wide area concept, especially when operating in Time Division Duplex (TDD) mode. In this paper, we focus on the design of the Guard Period (GP) which is needed to accommodate the transition between downlink (DL) and uplink (UL) transmissions in a 5G TDD wide area system operating at below 6 GHz carrier frequencies. The necessity of serving cell edge users with long propagation delays while coping with latency constraints may lead to a large GP overhead, thus reducing the resource utilization in the cell. We propose a distance-dependent scheduling technique which is meant at reducing the GP overhead while ensuring sufficient coverage. Numerical analysis shows the benefits of the proposed techniques in terms of available radio resources, especially for very large cells operating with short frames.

Network-Assisted Interference Cancellation and Suppression (NAICS) receivers have appeared as a promising way to curb inter-cell interference in future dense network deployments. This investigation compares the performance of a NAICS receiver with successive interference cancellation capabilities, known as Symbol-Level Interference Cancellation (SLIC), with respect to a baseline Minimum Mean Square Error-Interference Rejection Combining (MMSE-IRC) receiver. The study is carried out on a dense, clusterized small cell network, illustrating to which extent NAICS can overcome the additional interference associated with such deployments. Moreover, we analyse how much the data rates could be potentially improved by estimating the throughput with ideal cancellation of the dominant interferer. The results point to limited gains of up to 12% in the coverage data rates when NAICS is used, and that the instantaneous throughput might increase up to 100% in the most favourable case, falling significantly below the estimated 200% maximum gain with ideal cancellation.

Network-Assisted Interference Cancellation and Suppression (NAICS) receivers have appeared as a promising way to curb inter-cell interference in future dense network deployments. This investigation compares the performance of a NAICS receiver with successive interference cancellation capabilities, known as Symbol-Level Interference Cancellation (SLIC), with respect to a baseline Minimum Mean Square Error-Interference Rejection Combining (MMSE-IRC) receiver. The study is carried out on a dense, clusterized small cell network, illustrating to which extent NAICS can overcome the additional interference associated with such deployments. Moreover, we analyse how much the data rates could be potentially improved by estimating the throughput with ideal cancellation of the dominant interferer. The results point to limited gains of up to 12% in the coverage data rates when NAICS is used, and that the instantaneous throughput might increase up to 100% in the most favourable case, falling significantly below the estimated 200% maximum gain with ideal cancellation.

Massive MIMO (mMIMO) antenna array and Grid of Beams (GoB) are one of the key components for 5G to achieve high spectral efficiency and coverage. System level simulations are necessary to optimally intergrate the components of 5G system. Simulations with mMIMO antenna array involve handling large matrices, which results in increased simulation time typically upto several days depending on the size of the antenna array. However, GoB are fixed wideband beams and the receiver sees only the effective channel which is a combination of the channel and the GoB. Therefore, for system level simulations it is sufficient to general only the effective channel. In this paper, we propose a simulation model to directly generate the effective channel based on the 3GPP 3D channel model. It is shown that for the simulation of urban macro cells scenario specified in TR 38.913, the computational effort can be reduced by a factor of 1000. Furthermore, simulations show that very high SINR and user throughput values are achievable through GoB.

Mobility performance and the impact of handover data interruption times in real scenarios are studied by means of field measurements in an operational LTE network. Both slow- and high-speed scenarios are analyzed by collecting results from two different areas: Aalborg downtown and the highway which encircles the same city. Measurements reveal that the terminal is configured by the network with different handover parametrization depending on the serving cell, which indicates the use of mobility robustness optimization. Although the network is dominated by three-sector sites, no intra-site handovers are observed in the city center as cells on the same site often cover different non-crossing street canyons. Moreover, no handover failures are experienced in the measurements which confirms robust LTE mobility performance. The average interruption time, which is at least equal to the handover execution time, lays within a 24-29ms interval. Nevertheless, examples of delays larger than 100ms are occasionally observed. The studied scenarios are replicated in a system level simulator to investigate whether simulations are capable of reproducing similar mobility performance.

This study evaluates whether last versions of Long Term Evolution with dual connectivity are able to support the latency and reliability requirements for the upcoming vehicular use-cases and time-critical applications. Data interruption times during handovers and cell management operations are evaluated by means of system level simulations for a high-speed scenario. The scenario models a highway covered by a macro layer and an ultra dense network of small cells distributed on both sides of the road. Results reveal that for single connectivity, and due to the large amount of handovers, terminals are unable to exchange data with the network about 5% of the time. This time is considerably reduced if dual connectivity with split bearer architecture is adopted, with less than 1%of time in data interruption. However, when adopting secondary cell group architecture, the relative data interruption time increases up to 6.9%.

It is generally recognized that efficient multiplexing of users with highly diverse requirements needs a flexible frame structure. For a new 5th generation mobile networks (5G) air interface, the hybrid automatic repeat request (HARQ) solution should also be revised to harvest all possible performance benefits that can be obtained with a flexible frame structure. In this paper, we outline a number of HARQ enhancements and design principles for a 5G wide area solution. This includes a flexible asynchronous HARQ scheme with options for dedicated per-link configurations of feedback timing and multi-bit richness. Among others, the proposed solution supports asymmetric link operation, network implementations with different fronthaul latencies, and multi-bit feedback to facilitate variable block length HARQ retransmissions for improved resource utilization. Numerical results are presented for different link configurations.

It is well recognized in the literature that the performance of the hybrid automatic repeat request (HARQ) transmission can be improved by adapting the transmission parameters through exploiting extra information from the receiver over the feedback channel. This introduces new degrees of freedom for a more flexible per-link optimized transmission. This paper proposes a framework considering the practical aspects of such feedback design and analyzes better resource utilization by retransmission techniques in the 5th generation mobile networks (5G) technology. We propose to generate a decoder state information (DSI) feedback at the receiver side and to enable using this information at the encoder side where retransmission parameters will be set to meet an optimal target block error rate. The savings in retransmission resources can then be utilized for transmission of other packets. The systemlevel simulation results show the attractive enhancement of ~8% average throughput gain by using only one extra feedback bit per HARQ process compared to conventional HARQ approach.

In this paper we present a novel configurable 5G time division duplex (TDD) frame structure, including a flexible scheduling (resource allocation) framework for wide area scenarios. The unavoidable tradeoffs between coverage, latency, and capacity are studied with the objective of deriving a 5G air interface solution that is capable of serving users with highly diverse service requirements. Among others, it is shown that coverage challenged users will experience larger latency, while other users can still be served with shorter latency if adopting the proposed 5G solution. Achieving low latency, does, however, come at cost of lower spectral efficiency, so our solution includes control mechanisms for determining on a per user basis if the link shall be optimized for latency or capacity.

The contention-based (CB) transmission is a promising solution for small data packets transmission in 5G uplink. In this paper, a Non-Orthogonal Coded Access (NOCA) scheme, called ZC-NOCA, is proposed for CB transmission in 5G uplink. For ZC-NOCA, the codes generated by Zadoff-Chu (ZC) sequences is used to spread the data bit over the Orthogonal Frequency Division Multiple (OFDM) symbols. Different with LTE, where ZC sequences keep inter-cell orthogonal, ZC-NOCA use both non-orthogonal and orthogonal sequences for spreading. A CB transmission channel design with ZC-NOCA for 5G uplink is presented, to combine the advantages of both orthogonal and non-orthogonal schemes. The link level performance of ZC-NOCA is investigated by using two types of multi user detection (MUD) receiver considering the user detection performed by preamble or directly by the spreading codes. The study show ZC-NOCA allow a large number of user overloading and enable massive connections employed with CB transmission. Compare to orthogonal code access scheme, with larger code book length ZC-NOCA enables to support more than 10x user connections with acceptable link performance loss in CB transmission.

Zero-tail Discrete Fourier Transform-spread OFDM (ZT DFT-s-OFDM) modulation replaces the Cyclic Prefix (CP) with a low power tail whose length can be dynamically configured to cope with the instantaneous delay spread of the channel. In this paper, we discuss the reference sequence design for ZT DFT-s-OFDM. Our proposed approach is based on a deliberate distortion of the known Zadoff-Chu (ZC) sequences aiming at adapting them to the ZT DFT-s-OFDM waveform while preserving their attractive properties. A numerical analysis confirms the validity of our design in generating ZT DFT-s-OFDM reference sequences with zero autocorrelation, limited cross-correlation, flat frequency response and low Peak-to-Average Power Ratio (PAPR).

Dual connectivity (DC) allows user equipments (UEs) to receive data simultaneously from different eNodeBs (eNBs) in order to boost the performance in a heterogeneous network with dedicated carrier deployment. Yet, how to efficiently operate with DC opens a number of research questions. In this paper we focus on the case where a macro and a small cell eNBs are inter-connected with traditional backhaul links characterized by certain latency, assuming independent radio resource management (RRM) functionalities residing in each eNB. In order to fully harvest the gain provided by DC, an efficient flow control of data between the involved macro and small cell eNBs is proposed. Moreover, guidelines for the main performance determining RRM algorithms such as UE cell association and packet scheduling are also presented. It is demonstrated how proper configuration of the proposed flow control algorithm offers efficient trade-offs between reducing the probability that one of the eNBs involved in the DC runs out of data and limiting the buffering time. Simulation results show that the performance of DC over traditional backhaul connections is close to that achievable with inter-site carrier aggregation (CA) and virtually zero-latency fronthaul connections, and in any case it is significantly higher compared to the case without DC.

This paper addresses distributed interference management in downlink of multi-cell multiple- input multiple-output (MIMO) time division duplex (TDD) networks. Each user is associated with a user-centric cluster of base stations (BSs), which cooperatively serve the user through CoMP joint transmission. Clusters of different users possibly share some BSs such that they may overlap, being coupled by interference and transmit power constraints at each BS. Our objective is the design of BSs clustering and precoding matrices per-user in order to maximize the weighted sum-rate of the system by controlling the interference and the power spent at BSs. In contrast to previous works where all channel matrices in the system are needed, we propose a distributed procedure whereby only channel matrices towards a limited number of candidate BSs per user are required while interference is still controlled by using the signal received from an uplink transmission. For an LTE-compliant dense deployment of 2×2 MIMO BSs/users, results show gains of 6-16% in terms of sum-rate and 49-84% in terms of 5%-tile per-user rate (depending on the maximum cluster size) as compared to distributed BS-disjoint clustering schemes.

A mobility performance sensitivity analysis is presented for Dual Connectivity cases where the users can be served simultaneously by a macro and a small cell. The performance is assessed for the 3GPP generic simulation scenario and for two site-specific cases, with the aim of comparing the results coming from these different scenarios. The site-specific scenarios are based on detailed three-dimensional topography map data and advanced ray-tracing techniques. It is generally found that the first order statistics and overall conclusions are in good alignment for the considered environments. However, there are also a number of differences in the obtained performance results for the different cases, e.g. in terms of small cell time-of-stay statistics. The explicit modeling of streets and building topology, propagation in street canyons, etc., is found to have an important impact on the mobility performance. Especially the time-of-stay statistics and the location of handover failures differ between generic 3GPP case and the site-specific modeling scenarios. So in conclusion, trends and observations from simulations based on the 3GPP scenario are valuable, but should be supplemented by results from site-specific scenarios, as additional performance-determining effects are more accurately represented for such cases.

This study considers a downlink cell association and scheduling mechanism for an LTE-Advanced network with a centralized architecture, featuring a central baseband (BB) pool and distributed small cells at the remote site. In the proposed solution, the BB pool determines the user-cell association to increase the network performance. A simple suboptimal algorithm with reduced complexity is used on a per time instant basis. The challenges associated to the user measurement reports and the interference variablity are discussed. Compared to the usual case where users connect to the cell providing the highest received power and scheduling is performed independently within the cells, the proposed algorithm can provide up to a 70% median data rate gain.

Simulations play a key role in validating new concepts in cellular networks, since most of the features proposed and introduced into the standards are typically studied by means of simulations. In order to increase the trustworthiness of the simulation results, proper models and settings must be provided as inputs to the simulators. It is therefore crucial to perform a thorough validation of the models used for generating results. The objective of this paper is to compare measured and simulated mobility performance results with the purpose of understanding whether simulation models are close to reality. The presented study is based on drive tests measurements and explicit simulations of an operator network in the city of Aalborg (Denmark) - modelling a real 3D environment and using a commonly accepted dynamic system level simulation methodology. In short, the presented results show that the simulated handover rate, location of handovers, radio link failures, and signal/interference level statistics match well with measurements, giving confidence that the simulations produce realistic performance results.

The objective of this paper is to propose traffic steering solutions that aim at optimizing the end- user throughput. Two different implementations of an active mode throughput-based traffic steering algorithm for Heterogeneous Networks (HetNet) are introduced. One that always forces handover of the active users towards the cell offering the highest throughput, and a second scheme that aims at maximizing the systems sum throughput. Results show that the first option brings the best performance at the cost of more than three handovers per user per second for high-load cases. The second option offers slightly lower traffic steering gains at a considerably lower cost in terms of number of handovers. The gain in terms of increased average session throughput for the second option equals 32% at low-load, 18% at medium-load, and 7% at high-load conditions. The gain in the fifth percentile user session throughput is generally higher, reaching values of 36% and 18% for the medium- and high-load conditions.

In this paper we present a 5G frame structure designed for efficient support of users with highly diverse service requirements, including mobile broadband (MBB) data, mission critical communication (MCC), and massive machine communication (MMC). The proposed solution encompasses flexible multiplexing of users on a shared channel with dynamic adjustment of the transmission time interval (TTI) in coherence with the service requirements per link. This allows optimization of the fundamental trade-offs between spectral efficiency, latency, and reliability for each link. The frame structure is based on in-resource physical layer control signaling that follows the corresponding data transmission for each individual user. The principle of in-resource control signaling has numerous advantages; it presents a highly flexible and scalable solution, it allows joint beamforming for control and data transmission, as well as efficient time-frequency inter-cell interference coordination. Numerical results are presented, including simple comparison against LTE.

In this paper, we investigate the operation of eICIC in a realistic deployment based on site specific data from a dense urban European capital area. Rather than the classical semi-static and common network-wide configuration, the importance of having highly dynamic and distributed mechanisms that are able to adapt to local environment conditions is revealed. We propose a promising opportunistic cell association algorithm and a generalized method for fast muting adaptation. The performance results show that the traditional semi-static eICIC configuration leads to modest gains in realistic deployments, whereas the set of proposed fast dynamic eICIC algorithms leads to capacity gains on the order of 35-120% depending on the local environment characteristics. In the analysis of the performance results for the site specific use case, it is furthermore highlighted how those deviate from typical findings from 3GPP standardized HetNet scenarios.

Dual Connectivity (DC) has been studied and proved to be an effective solution to deal with the fragmented resources in deployment scenarios where the macro and small cells use different frequency carriers. The performance of DC has mainly been analyzed using generic network models such as those proposed by the 3GPP. However, the benefits of DC in real networks have not been proved. In this paper, we investigate the performance of DC in a realistic deployment from a big European city. Additionally, a novel opportunistic cell selection technique is also proposed. Results show that DC does improve the performance in this realistic layout. Due to the uneven load distribution observed in realistic deployments, DC is able to provide fast load balancing gains also at relatively high load - and not only at low load as typically observed in 3GPP scenarios. For the same reason, the proposed cell selection technique that aims at performing intra-layer load balancing shows promising benefits in this irregular deployment.

The support of mission-critical communication (MCC) opens the possibility to implement a broad range of novel applications. V2X communication for traffic safety and automation is, among others, one of these innovative applications expected to bring big benefits to society: accidents are prevented, driving times are reduced, and carbon dioxide is saved. In this regard, we first present a system model and fundamental definitions of reliability, latency and availability. Relying on these definitions, a systematic review of requirements for the huge variety of V2X applications is provided, including insights into the expected evolution towards autonomous driving. The many challenges introduced by V2X use cases are emphasized and compared to today's wireless system capabilities. Finally, we give our vision on the design of future radio technologies for the support of this kind of communications.

The arrival of mission critical applications in the context of vehicular, medical and industrial wireless communications calls for reliability constraints never seen before in cellular systems. Enhanced Inter-Cell Interference Coordination (eICIC) has been widely investigated in the context of LTE-A Heterogeneous Networks, but always with load balancing and resource partitioning purposes. Given the broad range of new use cases targeting ultra high reliability, we propose the use of on-demand eICIC for reducing the BLER of the retransmissions of critical users while minimizing the impact to the rest of the network. Combined with a ROot Cause Aware HARQ (ROCA-HARQ), which provides additional information when a transmission fails, the joint mechanism is relevant for any LTE/LTE-A deployment and can be easily implemented in a real network. System-level simulations show attractive BLER reductions up to 80% with little impact in throughput performance (loss in user throughput below 6%).

Dual connectivity (DC) is a promising technique to boost the user throughput performance by allowing user equipments (UEs) to receive data simultaneously from a macro cell and a small cell. In order to ensure high degree of realism and practical relevance of the results, we investigate the performance of DC in a realistic deployment based on three-dimensional data from a dense urban European capital area, assuming realistic flow control on the backhaul connections between the macro and small cell eNBs. It is found that the configuration of UEs with DC plays a critical role in the performance of DC under realistic conditions. A modified opportunistic cell association algorithm is proposed. Simulation results show that with proper configuration of UEs with DC, the performance of DC exhibits similar gains as observed in generic 3GPP scenarios.

In scenarios where the macro and small cells are deployed at different carrier frequencies, dual connectivity (DC) is a promising technique to serve the users with higher data rates. In this paper we focus on the case where the macro and small cell eNBs are inter-connected with traditional backhaul connections characterized by certain latency, assuming independent radio resource management (RRM) functionalities residing in each eNB. In order to fully harvest the gain provided by DC, an efficient flow control of data between the involved macro and small cell eNBs is proposed. It is demonstrated how proper configuration of the proposed flow control algorithm offers trade-offs between reducing the probability that one of the eNBs involved in the DC runs out of data and limiting the buffering time in the corresponding eNB. Simulation results show that the performance of DC over traditional backhaul connections is close to that achievable with inter-site carrier aggregation (CA) and virtually zero-latency fronthaul connections.

This article compares the potential performance gains from downlink scheduling and interference mitigation in an LTE-Advanced dense small cell network. The study combines theoretical considerations and system-level simulations with a dynamic traffic model and different offered loads. It is shown that intra-cell scheduling can provide a 22% throughput gain in a narrow traffic load region, while the plausible gains from an ideal inter-cell resource management mechanism can be greater than 50% for a wider range of traffic loads, reaching 300% for some of the cases. The results from this research provide valuable insight for the design of resource management algorithms targeted to small cell scenarios on dedicated carriers.

This paper aims at the theoretical modeling of different packet schedulers in Long Term Evolution-Advanced (LTE-A) systems. For that purpose, an abstract Radio Resource Management (RRM) framework has been developed, considering Proportional Fair (PF) and cross-Component Carrier scheduling. To validate our work, extensive system level simulations have been conducted for different ratios of users with Carrier Aggregation (CA) capabilities. The associated results confirm that the proposed model satisfactorily captures the main properties of the aforementioned scheduling metrics without any need for explicit design at a subframe resolution; hence, making it a promising candidate for a convenient scheduler implementation in simulators with simplified RRM modeling.

In this paper we introduce a laboratory emulation setup for evaluation of Long Term Evolution (LTE) mobility performance in a co-channel heterogeneous network (HetNet). The setup consists of two eNodeB emulators, signal faders and release 9 LTE User Equipment (UE). It is shown how the LTE HetNet mobility performance varies depending on load conditions and the configuration of UE reporting events. Pico cell outbound handover to the macro cell are found to be particular challenging, especially for higher UE speeds. Finally, we discuss the prospects of the emulation setup and how it can be exploited to conduct further experiments towards gaining additional understanding of HetNet mobility performance for LTE UEs.

With uplink inter-site carrier aggregation (CA), it is possible to configure a user equipment (UE) to transmit on multiple layers (macro and small cells) simultaneously, each of which may exhibit different radio channel characteristics. This introduces new challenging issues such as how to configure the UEs with CA and how to assign UEs on different layers. In this paper, we propose an uplink inter-site CA configuration algorithm by taking some of the key factors into considerations (i.e., cell load conditions, UE transmission power constraint, and potential interference to other cells) when deciding whether UEs should be configured with uplink inter-site CA or not. Simulation results show that with proper configuration of UEs to operate with uplink inter-site CA, good user throughput gain compared to the case without inter-site CA can be achieved at low load due to larger bandwidth accessibility, but the CA gain decreases as the load increases.

This paper studies how to best utilize two carriers (F1 and F2) in a heterogeneous network (HetNet) where both macro and small cells are deployed. Two well known multi-cell cooperation techniques are applied: enhanced inter-cell interference coordination (eICIC) on carriers that are co-channel deployed at both macro and small cells and inter-site carrier aggregation (CA) between carriers that are separately deployed at macro and small cells. Extensive performance results with different carrier deployment strategies with/without multi-cell cooperation are presented under realistic time-variant traffic conditions. For the considered HetNet scenario, the carrier deployment strategy resulting in the best downlink end-user throughput performance is found to be co-channel for low load conditions, and one carrier deployed at the macro and two carriers deployed at small cells (called hybrid deployment #2 in our study) for high load conditions. Introducing multi-cell cooperations in the form of eICIC and inter-site CA between the macro and small cells can significantly improve the performance for co-channel and hybrid deployment #2 at high load and low load conditions, respectively.

This paper aims at evaluating different mechanisms for providing Inter-Frequency (IF) Load Balancing (LB) in multi-layer heterogeneous deployments. More specifically, the performance of IF mobility management based on signal quality measurements is compared against a load-dependent Traffic Steering (TS) framework that triggers IF mobility events only if load imbalance is detected. To evaluate the joint interaction of the aforementioned schemes with more advanced LB features, system level simulations have been conducted with and without Carrier Aggregation (CA) capable users. Results have shown that although quality-based handoff procedures can act as a passive TS mechanism, they are costly in handovers and measurements gaps. The developed TS scheme utilizes cell neighbor measurements more efficiently, achieving significant handover reduction. Finally, CA makes the proposed framework even more attractive, since its careful parameterization becomes less relevant and load imbalances can be tackled by the packet scheduler as well.

Enhanced Intercell Interference Coordination (eICIC) techniques boost the performance of co-channel deployments of macro and small cells. However, features like the Almost Blank Subframes (ABS) are intended to be semistatically configured, due to the limited amount of information and the intrinsic delay over the X2 inter-cell interface. In this paper we investigate dynamic solutions for the allocation of the muted resources with small cells in the form of Remote Radio Heads (RRH), connected to the macro cell through a low latency interface. A simple eICIC framework for intercell Radio Resource Management in macro-RRH cases is developed. Based on minimal information collection, we propose an algorithm that adjusts the ABS ratio on a fast basis, aiming at balancing the instantaneous load betweeen the macro and the RRH layer. Performance results with bursty traffic and low and high load conditions show that the dynamic algorithm provides gains of 40-50% both in 5%-ile and 50%-ile user throughput compared to the semi-static case.

In this paper we study uplink open loop power control (OLPC) optimization for co-channel Heterogenous Network (HetNet) scenarios with macro and pico cells under fractional load conditions. Two methods for automatic OLPC optimization are proposed, motivated and compared against manual approach. It is found that the OLPC parameters at the pico-layer can be computed as a function of the OLPC parameters at the macro-layer, taking the load at the different cells into account. It is shown that using such a methods results in good overall system level performance. We contribute with in-depth analysis of dependencies between OLPC parameters, cells load, throughput performance and other metrics used to describe network operation on system level.

In this paper we analyze the mobility performance for an LTE Heterogeneous Network with macro and pico cells deployed on different carriers. Cases with/without downlink inter-site carrier aggregation are investigated. Extensive system level simulations are exploited to quantify the performance. It is shown that not only does the use of inter-site carrier aggregation offer higher end-user throughput, but also several benefits in terms of improved mobility performance. Among others, it is shown that the performance becomes less sensitive to the setting of mobility parameters when inter-site carrier aggregation is used, while still keeping the handover signaling burden at an acceptable level. The probabilities of radio link failures, handover failures, and unnecessary handovers (also known as ping-pongs) are kept at a minimum for proposed the solution.

This paper investigates the potentials of traffic steering in the Radio Resource Control (RRC) Idle state by evaluating the Absolute Priorities (AP) framework in a multi-layer Long Term Evolution (LTE) macrocell scenario. Frequency priorities are broadcast on the system information and RRC Idle users can be steered towards higher priority carriers whenever coverage allows it. However, such an approach may overload the prioritized layers. For that purpose, an enhanced scheme is proposed, where priorities are adjusted on a user basis and are provided to the terminal via the connection release signaling. The priority adjustment is based on both the Composite Available Capacity (CAC) and the radio conditions of the candidate layers. Compared to broadcast AP, the proposed scheme achieves better load balancing performance and improves network capacity, given that the User Equipment (UE) inactivity periods are not significantly long. Finally, better alignment between the RRC Connected and Idle mobility procedures is observed, guarantying significant decrease of handovers/reselections and potential battery life savings by minimizing the Inter-Frequency (IF) measurement rate in the RRC Idle.

Enhanced Inter Cell Interference Coordination (eICIC) for co-channel deployments of pico cells throughout a macro cell layout is studied. In particular, we analyze a scenario where only some macro cells have picos deployed, while other macro cells have no small cells. The challenge for such highly irregular scenarios is how to operate eICIC, and especially how to coordinate macro-cell muting. Our analysis shows that for eICIC to provide gain in such scenarios, it is recommended to use fully time aligned traditional Almost Blank Subframes (ABS) in the macro-cells with picos, while first tier surrounding macro cells shall use low-power ABS. For such cases, user throughput gains of 30%-40% are still achievable. Moreover, it is demonstrated that if macro muting patterns are not fully time aligned, it causes additional interference fluctuations in the network, resulting in less efficient link adaptation and radio-aware packet scheduling.

Heterogeneous networks (HetNets) have been extensively discussed in 3GPP to further enhance the system throughput of traditional well-planned macrocell deployment. In this paper, we consider a HetNet scenario consisting of macro eNBs and low-power nodes implemented as remote radio heads (RRHs) or picos with dedicated carrier deployment. Collaborative inter-site carrier aggregation (CA) is proposed in scenarios with macro+RRH deployment to make an efficient use of the fragmented spectrum from multiple cells. While in scenarios with macro+pico deployment, UEs can only connect to either the macrocell or the picocell using simple cell range expansion (RE). Extensive system-level simulations have been conducted to investigate the performance gains that can be achieved with intersite CA under different traffic models and user distributions. Results show that using inter-site CA between the macrocell and the small cell obviously offers higher throughput due to larger bandwidth accessibility for the terminals, especially in low load.

Enhanced Inter-Cell Interference Coordination (eICIC) techniques are targeted to improve the system and cell-edge throughput of Heterogeneous Networks (HetNets) in LTE-Advanced systems. In order to protect pico UEs from the strong macro interference, the macro eNB can either stop data transmission or simply reduce the transmission power during certain subframes. In this paper, we investigate the impact of reducing the transmission power in LTE HetNets. We evaluate the tradeoff among macro transmission power, cell load and system and cell-edge throughput, with bursty and non-bursty traffic. Moreover, we address some of the technical and standardization challenges related to having a time-varying transmission power. Based on the results, we provide guidance on how to best configure the network to achieve the full potential of the eICIC concept in dynamically changing environments.

Enhanced Inter-Cell Interference Coordination (eICIC) for co-channel deployment of pico-cells throughout a macro-cell layout is a promising solution to increase system capacity and network coverage in Long Term Evolution (LTE)-Advanced systems. The use of both pico-cell Range Extension (RE) and time domain eICIC (TDM muting) in this scenario has been proved to provide high gains compared to the traditional homogeneous network. Nevertheless, performance results in literature assume ideal Common Reference Signals (CRS) interference cancellation in the pico-UEs during Almost Blank Subframes (ABS), i.e., receivers are capable of perfectly suppressing all CRS interference from all neighbour cells. In this paper we investigate the impact of non-ideal CRS Interference Cancellation (IC) in eICIC systems. We propose a simple RSRP-based CRS IC criterion not requiring any extra signaling. The performance is evaluated and compared to the ideal case in the downlink by means of extensive system level simulations that follow the 3GPP guidelines. Results confirm that TDM eICIC can still provide significant gains when realistic CRS IC is considered.

Heterogeneous Networks (HetNet) have been recognized as a key enabler for providing high data rates. However, co-channel deployed HetNet will experience inter-layer interference, and hence calls for use of enhanced Inter-Cell Interference Coordination (eICIC) to solve such interference problems. In order to achieve the full performance benefits of eICIC, its corresponding configuration parameters shall be carefully adjusted. In this paper we study how sensitive the HetNet performance is for different eICIC parameters in different HetNet scenarios, and provide guidelines on how to set them. Among others, it is concluded how the spatial UE distribution, the used propagation models, and pico eNB transmit power settings influence the performance and the optimal eICIC parameter choice.

This paper addresses carrier-based inter-cell interference coordination (CB-ICIC) among LTE femtocells operating on a single carrier. CB-ICIC is in many ways linked to the widely investigated dynamic channel assignment problem, which is often studied in the context of graph coloring. The investigation revolves around the sensible definition of the underlying graph, i.e. the network model, rather than focusing on the coloring algorithms and their properties. Ultimately, we posit that improper online graph-coloring suffices and is actually preferable. In short, settling for less-than-optimal configurations avoids uncontrolled service interruptions. Such disruptions tend to raise understandable concerns when it comes to fully autonomous selection of operational CCs. Our results dispel such concerns by showing that conservative methods can achieve most of the benefits of unrestricted off-line coloring algorithms with a very modest number (2-3) of CCs to choose from.

In this paper macro performance in a co-channel macro and femto setup is studied. Measurements are performed in a live Universal Mobile Telecommunication System (UMTS) network. It is concluded that femto interference does not affect macro downlink (DL) performance as long as the macro Received Signal Code Power (RSCP) is stronger than femto RSCP. We also conclude that a macro escape carrier is a robust DL interference management solution. In uplink (UL) direction it is shown that a single femto UE close to macro cell can potentially cause a noise rise of 6 dB in the surrounding macro cell. In order to limit the noise rise from femto UEs, femto UE power capping and lowering femto common pilot channel (CPICH) power is recommended. The consequence is less uplink interference towards the macro, but also decreased femto coverage. Measurements close to macro cell centre showed femto coverage radius smaller than 5 meter - with realistic power settings. This makes co-channel femto deployment less promising in dense macro environments with good macro RSCP coverage.

Different technical solutions are enabling the move from macro-only scenarios towards heterogeneous networks with a mixture of different base station types. In this paper we focus on multi-layer LTE-Advanced networks, and especially address aspects related to co-channel interference management. The network controlled time-domain enhanced inter-cell interference coordination (eICIC) concept is outlined by explaining the benefits and characteristics of this solution. Extensive system level performance results are presented with bursty and non-bursty traffic to demonstrate the eICIC concepts ability to dynamically adapt according to the traffic conditions.

The performance of enhanced Inter-Cell Interference Coordination (eICIC) for Long Term Evolution (LTE)- Advanced with co-channel deployment of both macro and pico is analyzed. The use of pico-cell Range Extension (RE) and time domain eICIC (TDM muting) is combined. The performance is evaluated in the downlink by means of extensive system level simulations that follow the 3GPP guidelines. The overall network performance is analyzed for different number of pico-eNBs, transmit power levels, User Equipment (UE) distributions, and packet schedulers. Recommended settings of the RE offset and TDM muting ratio in different scenarios are identified. The presented performance results and findings can serve as input to guidelines for co-channel deployment of macro and pico-eNBs with eICIC.

Co-channel deployment of Closed Subscriber Group (CSG) home-cells or Home E-UTRAN NodeBs (HeNBs) will create coverage holes for macro connected user that is not part of the CSG. In this paper, we address the problem of detecting the macro-cell coverage hole and protecting the macro-users that are located inside such a coverage hole. To reduce the impact of HeNB interference on the macro-cell performance, the HeNBs can be partially muted on some subframes, leading to Time Domain (TDM) muting. With TDM muting, macro-users in the coverage hole can be protected by scheduling them only on the muted subframes that are free of HeNB interference. Different methods for coverage hole detection are considered, and their performance is evaluated under the downlink transmission of a Long Term Evolution (LTE) network. These methods are based on user measurements. Recommendations on the coverage hole detection will be provided based on the obtained results.

This paper aims at analyzing the mobility performance in heterogeneous 3GPP (3rd Generation Partnership Project) Long Term Evolution (LTE) networks. The main objective is to analyze the behavior of LTE macro/pico co-channel networks with different mobility parameters, such as the “Time-To-Trigger” (TTT). For this purpose, a system simulator has been utilized to assess the performance. The system must have different settings depending on the user velocity and on which cell-layer user is being serviced. Additionally, we have considered scenarios with a mixture of users moving freely or constrained to a hotspot, and different pico cell deployments.

LTE-Advanced is the evolutionary path from LTE Release 8. It is designed to significantly enhance the performance of LTE Release 8 in terms of higher peak data rates, improved system capacity and coverage, and lower latency. These enhancements allow LTE-Advanced to meet or exceed the IMT-Advanced requirements and are being considered as part of LTE Release 10. In this paper, some of the physical layer enhancement techniques for LTE-Advanced have been studied including carrier aggregation (CA), uplink multi-cluster scheduling, and uplink multi-user multiple-input multiple-output (MU-MIMO) with non-overlapping allocations. A system-level simulation was conducted to investigate the performance gains that can be achieved in uplink CA with multi-cluster scheduling and MU-MIMO. Simulation results show that with proper differentiation between power-limited and non-power-limited LTE-A users, multi-cluster scheduling with CA has similar coverage performance as in Rel'8, but can achieve substantial gains in average user throughput compared with Rel'8. MU-MIMO can further improve the throughput performance, especially when MU-MIMO is combined with multi-cluster scheduling.

This paper addresses the interference management problem in the context of LTE-Advanced femtocells. Due to the expected large number of user-deployed cells, centralized network planning becomes increasingly less viable. Consequently, we consider an architecture of autonomous decision makers. Our main contribution in this paper, denominated Generalized Autonomous Component Carrier Selection (G-ACCS), is a distributed carrier-based inter-cell interference coordination scheme that represents one step towards cognitive radio networks. The algorithm relies on expected rather than sensed interference levels. This approach facilitates scheduler-independent decisions, however, it can lead to overestimation of the interference coupling among cells when the resources are not fully utilized. Acknowledging this fact, G-ACCS leverages the power domain to circumvent the restrictive nature of expected interference coupling. This work focuses on the downlink and also provides an extensive characterization of the network performance as a function of the topology as well as the often overlooked temporal traits of traffic. We compare G-ACCS with other carrier-based solutions, including the simplest universal reuse strategy. The encouraging simulation results demonstrate that G-ACCS achieves an efficient and fair distribution of resources in all considered traffic and deployment conditions. More importantly, this is attained in a truly autonomous fashion, without any explicit parametrization.

In this paper we analyse the downlink performance of a rank adaptive multiple input multiple output (MIMO) system in a busty traffic cellular network. A LTE-Advanced system with multiple component carriers was selected as a study case. To highlight the advantage of using MIMO techniques, we used a single input multiple output (SIMO) system as a baseline for performance comparison. The gain mechanisms of the MIMO system over the SIMO system are investigated and their characteristic at different traffic load conditions are highlighted. The simulation results are used to verified our proposed model to predict the performance of the SIMO and MIMO systems in a bursty traffic network.

Carrier aggregation (CA) is one of the key features for LTE-Advanced. By means of CA, two or more component carriers (CCs) can be aggregated to form a much wider transmission bandwidth up to 100 MHz in order to meet the IMT-Advanced requirements. With CA, it is possible to schedule a user equipment (UE) on multiple component carriers simultaneously. From radio resource management (RRM) perspective, CC selection plays an important role in optimizing the system performance with CA. In this paper, we investigate the uplink resource allocation for LTE-Advanced Systems, i.e., how to assign CCs to different users, and how to do the power scaling for each user. A pathloss threshold based CC selection algorithm is proposed to distinguish between power-limited and non-power-limited LTE-Advanced UEs, and assign only one CC to power-limited LTE-Advanced UEs, while assign multiple CCs to non-power-limited LTE-Advanced UEs. Simulation results show that the derived pathloss threshold works effectively and efficiently compared to other thresholds, and the proposed CC selection algorithm can achieve much better performance in terms of cell edge, average, and cell center user throughput compared to blindly assigning all LTE-Advanced UEs on all CCs.

Dynamic spectrum approaches are steadily gaining momentum, especially in the context of femtocells. Yet designing efficient, stable, fair and scalable distributed algorithms is no easy feat, specially if the cells in a wireless network tend to act selfish and independently. Game Theory is a powerful toolbox which models the interaction of autonomous agents. In this paper we present a game theoretic model for a dynamic spectrum sharing framework recently proposed for femtocells. Our analysis includes cases where femtocells compete for spectrum as well as cooperative cases towards a common goal. The system level simulation results show that strict adherence to the game-theoretic selfish behavior performs poorly compared to the non-adherent rules which balance altruism and rational egoism. The main conclusion is that practical solutions should be guided but not limited by purely theoretical assumptions.

In this paper we investigate uplink carrier aggregation in the context of dense residential deployments of LTE-Advanced Femtocells. Previous work in the literature based on macro-cells suggested considering UE power limitations to infer which UEs should be allowed to employ multiple component carriers. However, due to the very small radius of femtocells, UEs are not expected to become power-limited at all. We propose a decentralized scheme with limited signalling requirements that incorporates power control information, not only to guide the UE-specific carrier selection procedure, but also to capitalize on the inherent power spectral density and path loss differences in order to minimize inter-cell interference. We present a series of system level simulation results which provide strong evidence that our scheme delivers substantial gains in terms of coverage compared to existing solutions without sacrificing the SINR.

The Macro offload of closed mode 3G Femtocells is studied; i.e. how much of downlink macrocellular traffic can be moved to a Femtocell layer. Taking the 3GPP dense urban reference model as our starting point we show that the combination of adaptive Femtocell power calibration together with a Macro-user frequency allocation method that considers the SINR difference between the mixed and a Macro-only carrier, improves offload. Additionally, the total number of carriers available to the operator is important for the offload potential. It is confirmed that a macro-only carrier is a desirable deployment strategy. At a 25% HNB penetration rate in apartments, 7% of the network traffic can be offloaded in the two-carrier case. This improves to 15% when three carriers are available. With Femto-aware macro-user carrier allocation, the offload performance improves further to 20% with 2 carriers.

With full channel state information (CSI) available, it has been shown that carrier aggregation (CA) in the downlink can significantly improve the data rate experienced at the user equipments (UE) [1], [2], [3], [4]. However, full CSI feedback in all component carriers (CCs) requires a large portion of the uplink bandwidth and the feedback information increases linearly with the number of CCs. Therefore, the performance gain brought by deploying CA could be easily hindered if the amount of CSI feedback is not thoroughly controlled. In this paper we analyze several feedback overhead compression schemes in CA systems. To avoid a major re-design of the feedback schemes, only CSI compression schemes closely elated to the ones specified in LTE-Release 8 and LTE-Release 9 are considered. Extensive simulations at system level were carried out to evaluate the performance of these feedback schemes in various traffic load conditions. Different scenarios were considered to answer the questions of when and why these CSI feedback compression schemes can be applied in CA.

The increasing popularity of the femtocell concept has revamped the interest in dynamic interference coordination techniques for dense and uncoordinated deployments of low- power home base stations. One of the proposed schemes for 4G OFDMA femtocells is known as Autonomous Component Carrier Selection (ACCS). ACCS capitalizes on the carrier aggregation framework of LTE-Advanced to curb inter-cell interference levels. Albeit being exclusively based on downlink information, previous contributions attested the effectiveness of the scheme in the uplink as well. This paper extends the initial argumentation by including uplink information into the component carrier selection process. We assess and discuss the uplink performance of two proposed variants of ACCS via extensive system level simulations. The striking conclusion based on the results is that the mere addition of uplink information, which is difficult to estimate in the real world, does not provide substantial performance improvements.

This paper is focused on interference mitigation for LTE-Advanced multi-layer networks with macro and HeNBs. The autonomous HeNB power setting in the downlink is studied for different HeNB access methods. Our studies show that using the so-called escape carrier configuration and autonomous HeNB power setting is a promising strategy for enabling gradual introduction of user-deployed HeNBs in existing macro-layer networks.

Interference management for co-channel deployment of macro-cells and closed subscriber group (CSG) home-cells (HeNBs) are studied. We especially address the downlink macro-layer coverage-hole problem, where HeNBs may create too high interference to nearby macro-users, unless active interference management is applied. Interference management techniques based on HeNB power setting and partial Time Domain (TDM) muting of HeNBs are studied. Cases with TDM muting require optimization of the macro-cell packet scheduler, including taking into account that the interference level varies significantly at the users as function of the enforced muting pattern for the HeNBs. During subframes where HeNBs are muted, some interference is still generated due to the fact that signals like common reference signals are still to be transmitted. It is therefore studied how much the HeNB interference from muted subframes shall be reduced for TDM muting to perform better than schemes with simple HeNB power reduction.

This paper focuses on reducing the uplink overhead caused by Acknowledgement (ACK)/Non-acknowledgement (NACK) signaling in an Long Term Evolution (LTE)-Advanced system. Such a system typically aggregates multiple Component Carrier (CC)s to obtain a wide bandwidth. Usually it has much larger feedback overhead than the single-CC system, and hence reducing the overhead is of special importance. A technique called ACK/NACK bundling has been used for the overhead reduction of the ACK/NACK signaling. Along with the overhead reduction, the downlink performance is also degraded. The tradeoff between the downlink performance and the overhead is analyzed under various load conditions and antenna configurations. The presented results can be used for selecting the proper bundling scheme based on specific system setting.

Long Term Evolution (LTE)-Advanced is expected to aggregate multiple Component Carrier (CC)s to fulfil the high data rate requirement. It may serve users with different capabilities in accessing these CCs, e.g., some can access all CCs, whereas some may operate on only one CC. This gives challenges to the packet scheduler to maximize the system performance over all CCs. In this paper we provide a mathematical model of the log-measure utility in an LTE-Advanced system, and give proof that our previously developed cross-CC Proportional Fair (PF) packet scheduler maximizes this utility. System level simulations are performed, which confirm that cross-CC PF scheduling offers much higher utility than independent PF and channel blind schedulers. This scheduler is then generalized to adjust the resource sharing among users. It can trade off between average cell throughput and cell edge user throughput. However, any adjustment in the resource sharing leads to a loss in utility.

Carrier aggregation (CA) is one of the most distinct features for LTE-Advanced systems, which can support a much wider transmission bandwidth up to 100 MHz by aggregating two or more individual component carriers (CCs) belonging to the same (intra-band) or different (inter-band) frequency bands. With CA, it is possible to schedule a user equipment (UE) on multiple CCs simultaneously. From radio resource management (RRM) perspective, CC selection plays an important role in optimizing the system performance, especially in the case of inter-band CA where the radio propagation characteristics of each CC can be different. In this paper, we investigate the downlink resource allocation for inter-band CA, i.e., how to assign carrier(s) to different UEs. A simple yet effective G-factor based carrier selection algorithm, which takes both traffic load and radio channel characteristics into considerations, is proposed with the objective to guarantee good coverage for Rel'8 UEs and robustness for Rel'10 UEs. Simulation results show that our proposed G-factor based carrier selection algorithm can achieve much better coverage performance compared to the least-load carrier selection in scenarios with relatively high inter-site distance and relatively high frequency separation between carriers, at the expense of some marginal average user throughput loss.

The recent introduction of carrier aggregation in LTE-Advanced enables new possibilities in designing frequency domain interference reduction and management schemes. These methodologies are of extreme interest in the case of dense and uncoordinated deployments of femtocells. In such scenarios, dense deployment of cells coupled with the scarcity of frequency resources may lead to a potentially disruptive amount of interference, which severely affects the performance of the system. This contribution presents a novel method inspired by graph and coalitional game theories. The proposed algorithm consists of a set of distributed and scalable rules for building coalitions; these rules essentially resolve the conflicts among avid femtocells competing for a limited amount of resources. The proposed scheme has been designed by targeting localized reconfigurations, thus avoiding reconfiguration storms in the network. Furthermore, the rules governing the resource redistribution ensure overall system performance improvements while maintaining a certain degree of fairness among the competing nodes. Simulation results prove the effectiveness of the proposed method.

This paper focuses on the performance evaluation of LTE uplink in presence of bursty data traffic. First, the performance of different power control (PC) strategies in different load conditions is evaluated. It is shown that the optimal PV policy depends on the load in the network and/or in the own cell. Simulation results demonstrate that in low load conditions applying no PC (or alternatively using fractional PC) can provide significant gains compared to full compensation PC. The gain is achieved both in terms of average and percentile user throughput performance. However, when also considering medium-to-high load conditions fractional PC can guarantee the best trade-off between peak data rates and cell edge performance. Finally, the performance of LTE uplink when assuming different system bandwidths and Rx antenna configurations is evaluated as a function of the network load. In general, larger system bandwidths can guarantee higher peak data rates, while increasing the number of Rx antenna elements is especially beneficial for cell-edge performance.

It has been identified in numerous contributions that dynamic interference coordination is very appealing in case of dense and uncoordinated deployments of home eNBs, also known as femtocells. One of the proposed schemes for LTE-Advanced is known as Autonomous Component Carrier Selection (ACCS). Previous contributions presented extensive downlink performance results attesting the effectiveness of ACCS. Nonetheless, the uplink has its own set of specificities, such as the use of Fractional Power Control (FPC). In this light, the purpose of this paper is two-fold: (i) Provide qualitative and quantitative answers to questions such as what is the impact of FPC on femtocells and how to best configure it. (ii) Evaluate in detail the uplink performance of ACCS under realistic power control settings. Using results derived from extensive uplink system level simulations we show that the behavior of FPC when applied to femtocells is significantly different from that seen on macrocells. In addition we demonstrate that ACCS is equally attractive and applicable to the uplink even though most decisions are based on UE downlink measurements.

This paper provides an assessment of 3GPP standardized LTE/LTE-A uplink power control procedures in case of a co-channel operation of different types of base stations. Especially the case of femtocell deployment with an overlaying macrocell is considered. Imperfections of the currently accepted procedures in case of such networks are pointed and a modified solution is proposed. It is shown that in case of heterogeneous networks more cell-specific configuration can lead to 8% and 14% performance improvements in capacity and coverage of local cells respectively, without harm for overlying macrocells. The evaluation of the proposed scheme has been done on case of a macro and femto co-channel deployment, but should be also valid for other cell types.

in this paper we address the problem of reducing the feedback for the downlink transmission in multi-carrier systems. In these systems multiple Component Carriers (CCs) are aggregated together to form a wide spectrum. Consequently, a large feedback overhead is required to report the channel quality information over such a wide bandwidth. We first generalize two existing feedback reduction techniques, and then propose a new one. These techniques use different feedback schemes across the CCs, or allow some CCs to be un-reported, for the purpose of reducing the amount of feedback. Performance for the investigated techniques is evaluated in a realistic system setting with different traffic conditions and terminal categories. Based on the obtained results, the selection of proper feedback reduction technique under different load conditions can be made. The findings are useful for reducing the feedback overhead in future generation wireless communication systems that operate over multiple CCs.

Carrier aggregation (CA) has been proposed to aggregate two or more component carriers (CCs) to support a much wider transmission bandwidth for LTE-Advanced systems. With carrier aggregation, it is possible to schedule a user equipment (UE) on multiple component carriers simultaneously. In this paper, we evaluate the performance of uplink CA in LTE-Advanced systems with different CC allocation schemes. We first present the radio resource management (RRM) framework of multi-component carrier LTE-Advanced systems, with special attention on CC selection, adaptive transmission bandwidth, and uplink power control. Simulation results show that with CA and advanced CC selection algorithm, the cell edge user throughput of LTE-Advanced UEs maintains the same as Rel'8 UEs, but substantial performance gains can be achieved in terms of average and cell center user throughput, especially in low load traffic conditions.

For the future LTE-Advanced network, one of the requirements in the uplink (UL) direction is to enhance the celledge user performances. Coordinated multi-point reception in the UL is one of the techniques being investigated to further improve the performance of LTE networks. With the help of the information coordination through the links between the sites and advanced receivers the UL performance can be improved. The simulation results show that, with the ideal interference cancellation, inter-Site maximum ratio combining, and optimized closed-loop and open-loop fractional power control, there are about 27% gains for the 5% outage user throughput and 12% gains for the average user throughput. As shown in this paper, these gains from UL macro-scopic multi-cell combining between sites are achieved for optimized power control, ideal interference cancellation receivers, and X2 with no delay and high bandwidth.

Low-power home base stations, also known as femtocells, are one of the strong candidates for high data rate provisioning in indoor environments. Unfortunately, the benefits are not without new challenges in terms of interference management and efficient system operation. In this paper we take a closer look at several aspects associated with the deployment of LTE-Advanced home eNBs under two different access policies: closed subscriber group (CSG) and open subscriber group (OSG). Our results are derived from extensive downlink system level simulations. We limit our scope to dense-urban deployment of femtocells assuming dedicated carriers, i.e. no interference to/from the macro layer. Particularities of each access mode are discussed under different hard frequency re-use configurations. Our results indicate that an OSG deployment is indeed able to cut short the lower end of the SINR distribution when universal frequency re-use is employed. However, when other re-use configurations are considered, OSG no longer guarantees improved SINR conditions. In addition, we present additional results for the autonomous component carrier selection (ACCS) concept introduced in earlier contributions, providing strong suggestions that the scheme yields attractive performance benefits independently of the access policy selected by the operator. Finally, we point out that uplink results including realistic power control settings need to be considered before definitive conclusions can be safely drawn.

Abstract-In this paper we focus on resource allocation for next generation wireless communication systems with aggregation of multiple Component Carriers (CCs), i.e., how to assign the CCs to each user, and how to multiplex multiple users in each CC. We first investigate two carrier load balancing methods for allocating the CCs to the users- Round Robin (RR) and Mobile Hashing (MH) balancing by means of a simple theoretical formulation, as well as system level simulations. At Layer-2 we propose a simple cross-CC packet scheduling algorithm that improves the coverage performance and the resource allocation fairness among users, as compared to independent scheduling per CC. The Long Term Evolution (LTE)-Advanced is selected for the case study of a multi-carrier system. In such a system, RR provides better performance than MH balancing, and the proposed simple scheduling algorithm is shown to be effective in providing up to 90% coverage gain with no loss of the overall cell throughput, as compared to independent scheduling per CC.

In this paper we focus on LTE-Advanced with backward compatibility, which serves a mixture of LTE-Advanced and LTE-Rel'8 users. Aggregation of multiple component carriers (CCs) to form a wide spectrum is assumed in order to fulfill the bandwidth requirement for the next generation systems, thereby leading to a multi-carrier system. Although a LTE-Advanced user can simultaneously access all the CCs, a LTE-Rel'8 user is restricted to operate on a single CC at a time. Different methods for balancing the load across these CCs will affect the system performance. This is investigated through both analytical methods and system level simulations. Bearing in mind that the LTE-Advanced users are scheduled on more CCs than the LTE-Rel'8 users, we propose a simple cross CC packet scheduling algorithm that improves the resource allocation fairness among the two categories of users. This simple scheduling algorithm is shown to be effective in providing better coverage performance with no loss of the overall cell throughput, as compared to independent scheduling per CC.

In this paper we focus on LTE-Advanced performance under bursty traffic conditions, and devote our effort to the different methods for balancing the load across multiple carriers. These carriers are the component carriers (CCs) that belong to the same carrier frequency. They are bonded together in order to fulfill the requirement of wide spectrum in LTE-Advanced. We first derive the analytical model for a bursty birth-death traffic model with fixed payload size for OFDMA with different frequency domain packet schedulers. Applying this model for a multi-carrier system, we compute the performance for different system setups. The obtained analytical results are verified using extensive system level simulations. Based on the analytical and simulation results, it is suggested to assign the users on all CCs if a cell is not heavily loaded. Otherwise, assign each user with only one CC using the load balancing method of Round Robin is preferable, in the sense that it maintains good performance with low uplink overhead.

In a multi-component carrier LTE-Advanced system, a user can simultaneously be scheduled on all component carriers (CCs). For the base station to perform radio channel aware packet scheduling, each user ideally has to feedback information corresponding to all CCs. This results in a potentially high amount of uplink overhead. Furthermore, a user in a power limited situation may experience outage because of insufficient power for the required feedback. In this paper we first propose several techniques at different layers for the overhead reduction, as well as protecting the users from being in the outage situation. Afterwards, we show how these techniques can be integrated in a LTE-Advanced system. A weighted proportional fair scheduler is also proposed to maintain good performance with a reduced amount of overhead. Extensive simulation results are presented in the end for analyzing the proper trade-off between performance and overhead reduction and outage protection.

The explosive growth of mobile communications on one hand and the overly crowded and expensive spectrum on the other hand have fueled hot debates on spectrum sharing techniques, anticipating fundamental changes in spectrum regulation. A key point of the discussions has been the need for empirical tests and validation of even the simplest spectrum sharing proposals already available. In this paper, inspired by IEEE 802.11 WLANs, the authors employ carrier sense multiple access with collision avoidance (CSMA/CA) in an LTE-Advanced framework and compare the achieved performance with that of an ordinary LTE-Advanced system employing static frequent reuse schemes. The analysis is performed by means of system level simulations in Local Area networks where the e-NodeBs (eNB) may be randomly placed without any prior considerations to minimize inter-cell interference. Average and cell-edge user throughput results show that the contention based approach, despite its beautiful simplicity, wastes resources due to random back-off timers and hidden nodes. In nearly all cases, well known frequency reuse alternatives are more interesting options.

Uncoordinated deployment of eNBs in local area environments will benefit from having support for dynamic frequency re-use mechanisms also known as "autonomous component carrier selection", where each eNB dynamically selects to use only a subset of the available component carriers (i.e. using from one component carrier up to the maximum number of available component carriers). Component carriers are selected autonomously by each eNB depending on the offered traffic, interference coupling with neighboring cells, etc. In this contribution we propose a simple and distributed scheme based on so-called background interference matrices (BIMs) for autonomous component carrier selection. Extensive numerical simulation campaigns indicate that the proposed scheme effectively allows each eNB to select the most attractive frequency configuration; improving average user capacity and boosting cell edge performance considerably.

The main source of interference in OFDMA system in downlink is inter-cell interference, which can severely limit the throughput of users near the cell edge. The inter-cell interference coordination (ICIC) is one method to improve the performance. In this paper autonomous inter-cell interference avoidance schemes under fractional load (FL) conditions in the downlink for 3rd generation partnership project (3GPP) long term evolution (LTE) are proposed. The proposed schemes do not require any inter-cell signaling for ICIC; rather the decision about the allocation of the spectrum in order to avoid the inter- cell interference is taken based on the information available within the cell itself. We show that the schemes for spectral resource selection is important for FL scenario to avoid high BLER. The proposed schemes further improve the SINR condition therefore higher cell throughput and coverage are realized.

This paper focuses on the Physical Downlink Control Channel (PDCCH) and describes the impact of its realistic constraints. Specifically, the impact on the performance of the UTRAN LTE FDD downlink and on the QoS provisioning is studied. It is described, when adopting a QoS-aware packet scheduling policy, how scheduling limitations due to control channel may affect the scheduler behavior. It is shown that the system level performance degradation could be kept negligible utilizing the dynamic link-adaptation mechanisms available on the control channel and adopting careful control channel-related design solutions. Therefore, assuming a proper dimensioning in terms of OFDM symbols reserved for control, the PDCCH could simply be modeled for LTE FDD system level simulation purposes by limiting the number of PDCCH allocations. Such a number primarily depends on the system bandwidth.

LTE-advanced systems, which aim to provide high data rate wireless services, have received world-wide researching interests nowadays. In this paper, the performance of fixed frequency reuse with different reuse factors is studied in LTE-advanced systems. Performance is measured in terms of both average cell throughput and cell edge user throughput. It is found that a properly chosen reuse factor with respect to cell size (which leads to different level of inter-cell interference), can offer up to 30% gain in average cell throughput and much higher gain for cell-edge user throughput in local area (LA). This high gain from frequency reuse makes it attractive for future LTE-advanced systems.

This paper presents a dynamic spectrum sharing algorithm to minimize the inter-cell interference, so as to achieve a high system performance. This algorithm operates in a self-organized manner without the need of any centralized control, thereby is especially useful in local area (LA) where the enhanced-NodeBs (eNB) are close and coordination among them is hard or expensive to achieve. Results show that with very limited signaling between the eNBs, the proposed algorithm can effectively improve the system performance, and it can even overcome the performance with fixed frequency plan.

Evolved (E-) UTRA is currently being standardized as a long term evolution (LTE) of the 3GPP radio access technology. One of the goals of E-UTRA is to achieve 2-4 times the spectral efficiency and user throughputs compared to HSUPA/HSDPA. Support for fast link adaptation based on adaptive modulation & coding (AMC) is one of the features being introduced in the E-UTRA specifications to enhance the uplink spectral efficiency. This paper focuses on the performance evaluation of fast AMC in E-UTRA uplink compared to link adaptation schemes that only slowly adapt to the varying channel and interference conditions. It is shown that despite measurement errors and the high variability of uplink inter-cell interference, fast AMC can boost the capacity of E-UTRA uplink by approximately 20% to 25%.

UTRAN Long Term Evolution (LTE) architecture shall support end-to-end quality of service (QoS). To maintain the QoS of in-progress sessions in a cell it is important to admit a new radio bearer only if all the existing sessions and the new bearer can be guaranteed QoS according to their requirements. Hence admission control (AC) has an important role to play for QoS provisioning. In this paper we propose an AC algorithm for LTE uplink utilizing the fractional power control formula agreed in 3GPP. The proposed AC algorithm is compared with a reference AC algorithm. It is shown that at 10% unsatisfied user probability the carried traffic gain of the proposed AC algorithm can be up to around 29% over the reference AC algorithm. Furthermore, the proposed AC algorithm inherently tunes itself for varying load conditions without additional complexity.

Long term evolution (LTE) architecture shall support end-to-end quality of service (QoS). For the QoS support and service differentiation it is important that the admission control and packet scheduling functionalities are QoS-aware. In this paper a combined admission control and a decoupled time-frequency domain scheduling framework for LTE uplink is presented. The proposed framework is shown to effectively differentiate QoS user classes in a mixed traffic scenario.

UTRAN long term evolution is currently under standardization within 3GPP with the aim of providing a spectral efficiency 2 to 4 times higher than its predecessor HSUPA/HSDPA release 6. Single carrier FDMA has been selected as multiple access for the uplink. This technology requires the subcarriers allocated to a single user to be adjacent. The consequence is a reduced allocation flexibility which makes it challenging to design effective packet scheduling algorithms. This paper provides a search-tree based channel aware packet scheduling algorithm and evaluates its performance in terms of throughput and noise rise distributions. It is shown that, despite measurement errors and high inter-cell interference variability, the proposed algorithm can increase the uplink capacity by 24% for the macro 1 scenario and 19% for the macro 3 scenario.

UTRAN long term evolution is currently under standardization within 3GPP with the aim of providing a spectral efficiency 2 to 4 times higher than its predecessor HSUPA/HSDPA release 6. Single carrier FDMA has been selected as multiple access for the uplink. This technology requires the subcarriers allocated to a single user to be adjacent. The consequence is a reduced allocation flexibility which makes it challenging to design effective packet scheduling algorithms. This paper proposes a channel aware packet scheduling algorithm which exploits the bandwidth flexibility offered by the system to perform an allocation which closely resembles the frequency domain envelope of the metric to be optimized. Compared to a fixed bandwidth approach, the proposed algorithm provides a greater flexibility given the inbuilt adaptation to different scenarios and loads, as well as an improvement in term of performance for the Macro 3 case. In this case the uplink capacity is increased by approximately 20% in average cell throughput and 10% in UE outage compared to a fixed bandwidth channel aware approach.

3GPP has recently agreed on an Open Loop Power Control (OLPC) for the uplink in UTRAN Long Term Evolution. The power control configuration determines the level of interference in the system, but requires to be tuned depending on the propagation scenario, user's bandwidth, etc. A reliable knowledge of the interference would be very useful for the operator to determine the maximum link budget for a certain coverage performance. In this paper we propose a novel algorithm to use the Overload Indicator for an automatic adjustment of the OLPC parameters to achieve the desired interference operating point, showing its potential compared to an a priori setting.

UTRAN long term evolution is currently being standardized in 3GPP with the aim of more than twice the capacity over high-speed packet access. The chosen multiple access for uplink is single carrier FDMA, which avoids the intra-cell interference typical of CDMA systems, but it is still sensitive to inter-cell interference. As a result, the role of the power control becomes decisive to provide the required SINR, while controlling at the same time the interference caused to neighboring cells. This is the target of the fractional power control (FPC) algorithm lately approved in 3GPP. This paper evaluates in detail the impact of a FPC scheme on the SINR and interference distributions in order to provide a sub-optimal configuration tuned for both interference- and noise-limited scenarios.

This paper addresses advanced radio resource management (RRM) algorithms for multiple-input multiple-output (MIMO) transmission schemes in downlink OFDMA systems. The analysis covers the main RRM mechanisms including MIMO rank adaptation and time-frequency packet scheduling. The UTRAN Long Term Evolution (LTE) system is used as case study. System-level performance analysis is presented for 2 times 2 and 4 times 4 spatial-multiplexing, single-user MIMO transmission schemes in typical macro- and micro-cell scenarios including the effects of limited and imperfect CQI feedback from the terminals. We show that time-frequency domain RRM schemes can be successfully adapted and optimized for operations with high-rate adaptive MIMO transmission schemes.

In this paper we present the results on performance evaluation of 6-sector-site deployment and compare against 3-sector-site deployment in the downlink UTRAN LTE systems. To facilitate the performance evaluation a quasi-dynamic multicell system level simulator that follows the 3GPP UTRAN LTE specifications has been used. A significant gain in the order of 88% in site capacity is achieved by changing the 3-sector- site deployment by 6-sector-site deployment. A mixed network topology with a combination of 3 and 6-sector-site deployment has been also considered and its potential benefits investigated. The 6-sector deployment in the mixed network topology can be a viable option to meet high traffic demands in localized areas such as hot spots, yielding a capacity gain in the 6-sector sites in the order of 95 % to 110 %.

In this paper we introduce orthogonal frequency division multiple access (OFDMA) downlink general packet scheduling methods for throughput fairness control among users. The investigation is based on the 3GPP UTRAN long term evolution (LTE) and a decoupled time/frequency domain packet scheduler approach is used. It is shown that fairness can be effectively controlled with frequency domain metric weighting or time domain priority set scheduling (TD-PSS) depending on the number of users in the cell. Furthermore we introduce a principle of metric decoupling between time and frequency domain schedulers that is fundamental for maximizing throughput control. The algorithms are simulated in best effort (BE) and constant bit rate (CBR) users conditions. They are shown to provide coverage gains of up to 60% for a cell throughput loss of 5 % over the well known time-frequency domain proportional fair scheduler.

Dynamic time-frequency domain packet scheduling algorithms in the shared channel of downlink Orthogonal Frequency Division Multiple Access (OFDMA) systems have been shown to achieve high multi-user diversity scheduling gains. However, the flexibility is obtained at the cost of additional control signaling for which the availability of resources is limited. This article addresses the effects of control signaling resources limitation as well as the effects of terminal control signaling decoding errors on the performance OFDMA packet scheduling algorithms.

Handover is one of the key functionalities which tries to keep a user equipment (UE) connected to the best base station (eNodeB). Handover is usually based on the downlink received signal strength (RSS) and carrier-to-interference ratio (CIR) measurements. Processing of the handover measurement is usually done in Layer 1 (LI) and Layer 3 (L3) by the UE, and handover is initiated by the serving eNodeB if certain event criteria are met. L3 filtering can be done in linear domain or decibel (dB) domain. A hard handover algorithm based on the downlink RSS and CIR measurements along with linear and dB domain L3 filtering has been studied by using a dynamic system level simulator for a 3GPP UTRAN LTE recommended scenario. The results suggest that RSS measurement with linear or dB domain L3 filtering is a better criterion for handover in terms of reduced number of handovers for a small penalty on the downlink CIR.

This paper evaluates the hard handover performance for UTRAN LTE system. The focus is on the impact that received signal strength based hard handover algorithm have on the system performance measured in terms of number of handovers, time between two consecutive handovers and uplink SINR for a user about to experience a handover. A handover algorithm based on received signal strength measurements has been designed and implemented in a dynamic system level simulator and has been studied for different parameter sets in a 3GPP UTRAN LTE recommended simulation scenario. The results suggest that a downlink measurement bandwidth of 1.25 MHz and a handover margin of 2 dB to 6 dB are the parameters that will lead to the best compromise between average number of handovers and average uplink SINR for user speeds of 3 kmph to 120 kmph.

UTRAN LTE uplink is a SC-FDMA based system currently under development within 3GPP. The decision of basing the system on the packet switched technology attracts a lot of attention about the possible designs of resource allocation strategies. In this work we propose an algorithm which distributes the available bandwidth proportionally to the channel conditions while meeting the SINR target by means of power control. A simple resource allocation scheme which is fair with respect to bandwidth allocation is used as baseline reference. The comparison is carried out in terms of SINR distribution, user throughput and cell throughput. The results show that the proposed algorithm, when combined with slow power control, is able to improve the average cell throughput by approximately 23% with almost no reduction of the 5% outage average user throughput.

In this paper we analyze the downlink OFDMA system-level performances of a 2times2 dual-stream MIMO multiuser transmission scheme under the assumptions of partial and noisy channel quality indicator (CQI) feedback available from the terminals. The effects on the CQI feedback of the terminal measurement and estimation errors, quantization errors, uplink reporting format and delays are included. Two reduced CQI reporting schemes are evaluated in macro and microcell scenarios when operating in combination with a MIMO outer loop link adaptation (OLLA) and a MIMO aware frequency domain packet scheduling (FDPS) algorithm. We show that, by using OLLA and with a proper choice of the CQI reporting scheme for dual-stream MIMO, the required CQI feedback overhead can be reduced by 90% while limiting the cell throughput losses to less than 10%.

In this paper we propose a modification to Shannon capacity bound in order to facilitate accurate benchmarking of UTRAN long term evolution (LTE). The method is generally applicable to wireless communication systems, while we have used LTE air-interface technology as a case study. We introduce an adjusted Shannon capacity formula, where we take into account the system bandwidth efficiency and the SNR efficiency of LTE. Separating these issues, allows for simplified parameter extraction. We show that the bandwidth efficiency can be calculated based on system parameters, while the SNR efficiency is extracted from detailed link level studies including advanced features of MIMO and frequency domain packet scheduling (FDPS). We then use the adjusted Shannon capacity formula combined with G-factor distributions for macro and micro cell scenarios to predict LTE cell spectral efficiency (SE). Such LTE SE predictions are compared to LTE cell SE results generated by system level simulations. The results show an excellent match of less that 5-10% deviation.

In this paper, we investigate methods for improving an OFDMA system simulator in terms of trade-off between complexity and radio channel implementation accuracy. Fast fading and SINR calculations are the most resource consuming tasks of a system simulator. In order to decrease their complexity, it is proposed to reduce the number of calculated channel transfer function (CTF) realizations according to the time and frequency correlation properties of the simulated radio channel. Besides, we highlight that the upsampling of the channel impulse response (CIR), which is needed for the fast Fourier transform (FFT) application, may introduce major errors in the channel frequency statistics if it is done by simple brute force grid alignment (BFGA) method. To achieve better results we introduce a low complex upsampling method which reduces the simulation inaccuracies significantly. The possibility to trade complexity for precision is shown. It is possible for instance to divide the fast fading and SINR calculation complexity by 50 while keeping a reasonable simulation accuracy.

In this study we analyze the downlink OFDMA system level performance for three different channel quality indicator (CQI) reporting schemes. The effect of terminal measurement and estimation errors, quantization from formatting and compression, and uplink reporting delays and detection errors are included. We find that a simple threshold-based CQI scheme provides an attractive trade-off between downlink system level performance and uplink CQI signaling overhead, as compared to using a best-M scheme. When applied to the UTRAN LTE system in a 10 MHz bandwidth, we find that a frequency domain packet scheduling gain of 40% is achievable with a CQI word size of only 30-bits. Finally, the effect of applying a so-called outer loop link adaptation algorithm is reported.

In this paper we investigate the performance of frequency domain packet scheduling (FDPS) under fractional load (FL), based on the UTRAN long term evolution downlink. Under FL, the packet scheduler does not need to transmit on entire system bandwidth due to lack of traffic in the network, which leads to an improvement in the user experienced SINR. System-level simulations show that the proportional fair scheduler tries to optimize resource allocation by avoiding transmission on frequencies that are experiencing severe interference. As an example, FDPS can provide a gain of 4 dB in SINR over the round-robin scheduler, when the load is equal to 25%. The observed interference control is achieved without any centralized management. Further, FDPS under FL can provide an effective trade-off between cell throughput and coverage. The FDPS performance is dependent on the ability of link adaptation to track variations in interference. This ability is reduced when the frequency usage pattern is changing rapidly over time.

In this paper we evaluate the performance of downlink channel dependent scheduling in time and frequency domains. The investigation is based on the 3GPP UTRAN long term evolution (LTE) parameters. A scheduler framework is developed encompassing frequency domain packet scheduling, HARQ management and inter-user fairness control. It is shown that by dividing the packet scheduler into a time-domain and a frequency-domain part the fairness between users can be effectively controlled. Different algorithms are applied in each scheduler part, and the combined performance is evaluated in terms of cell throughput, coverage, and capacity. We show that frequency-domain packet scheduling can provide a gain of around 35% in both throughput and coverage over opportunistic time-domain only scheduling. Furthermore, it is shown that by using an equal throughput scheduler, coverage can be improved by 100% at the expense of a 5% loss in average cell throughput in comparison with the proportional fair scheduler.

This paper presents HSDPA performance evaluation in an urban micro cell environment with outdoor base station antenna heights below roof-top level (10 m) and both outdoor and indoor pedestrian mobiles (3 km/h). A path loss model which accounts for the 3D geometry of the radio environment is used, thus allowing the simulation of indoor user locations at different building floor levels. The single user throughput evaluation is carried out using realistic HSDPA link-level simulations combined with the newly obtained statistics of the geometry factor in the considered micro cell environment. The results with 80% HSDPA power and 15 HS-PDSCH multi-codes showed median single-user throughput in the range of 4.8 Mbps/cell. It was also found that ground floor areas can be served with up to 5% better median throughputs compared to the outdoor and high (top) floor areas

This study devises a simple mathematical model that predicts the number of beams that maximizes system capacity for different WCDMA network configurations. The ideal number of beams to be synthesized within a cell by an antenna array (AA) with a fixed number of elements at the base station (BS) is primarily influenced by the average antenna gain and the relative power allocated to the secondary common pilot channel (S-CPICH) transmitted on each directional beam. It is shown that for a fixed maximum Node-B transmit power the overall system capacity gain in the downlink (DL) provided by switched beam forming (SBF) decreases with the cell size, that is, as more power is needed by the pilot channels to assure coverage. Predictions from our model are compared with simulation results obtained from a detailed dynamic system level simulator in order to be validated. A remarkably good match is observed

We analyse the downlink (DL) cell throughput for a WCDMA system using switched beamforming (SBF) with 4-element antenna array at the base station (node-B) and dual antenna (2Rx) user equipment (UE). We investigate the performance as a function of the penetration rate of 2Rx UEs. The performance assessment is conducted with dynamic system simulations, which are supplemented with simple theoretical analysis. Code blocking (CB) occurs when a UE is denied access in the cell due to lack of a DL channelisation code under the primary scrambling code for that cell. When the code-blocking problem is circumvented, it is observed from the simulation results that at 100% penetration rate of 2Rx UEs, the combined feature offers more than the multiplicative gain in the capacity improvement. The numerical result obtained from the theoretical analysis complements the simulation results. The SBF-2Rx code-unrestricted (CU) capacity gain is 327% compared to a 3-sector single directional antenna transmission at the node-B and single antenna reception at the UE

Cell specific algorithms for dynamic sharing of transmit power and channelization codes between HSDPA and Release'99 dedicated channels on the same carrier are proposed. A fast node-B based HSDPA power allocation algorithm is derived, which is able to track the fast power control fluctuations of dedicated channels. Fast channelization code allocation is handled by the centralized RNC. The presented performance results show an improved utilization of the transmission resources. The cell throughput is improved significantly by using these algorithms as compared to using semi-static allocation schemes previously published in the open literature.

The functional split between the centralized radio network controller (RNC) and the base station (node-B) presents new challenges and opportunities for implementing QoS control for HSDPA. In this paper we present different options for implementing QoS over HSDPA, and we focus particularly on the shared responsibility between the QoS aware algorithms at the RNC and the node-B. Different strategies for QoS aware node-B packet schedulers are discussed. The paper is concluded with network performance results for different services over HSDPA, ranging from simple best effort traffic, to constant bit rate streaming, and voice over IP. For these services we show capacity gains of up to 40% from using QoS-aware packet scheduling.

This paper describes the attributes of the COST 259 directional channel model that are applicable for use in the design and implementation of macrocellular mobile and portable radio systems and associated technology. Special care has been taken to model all propagation mechanisms that are currently understood to contribute to the characteristics of practical macrocellular channels and confirm that large scale, small scale, and directional characteristics of implemented models are realistic through their comparison with available measured data. The model that is described makes full use of previously published work, as well as incorporating some new results. It is considered that its implementation should contribute to a too) that can be used for simulations and comparison of different aspects of a large variety of wireless communication systems, including those that exploit the spatial aspects of radio channels, as, for example, through the use of adaptive antenna systems

This study addresses the performance of a wideband code-division multiple-access mobile communications system with beamforming antenna arrays (AAs) at the base station, synthesizing a grid of beams. In order to fully exploit the capacity gain from beamforming without jeopardizing the stability of the system, a directional power-based admission control (AC) scheme is applied. Due to the higher capacity offered by beamforming techniques, shortage of orthogonal channelization codes in the downlink becomes an increasingly important factor, which may result in blocking of users before the interference power limit is reached. The problem of channelization code shortage is addressed, and a solution based on splitting the cell into several code regions is proposed. For a network with circuit switched data services operated at 64 kb/s, the capacity gain for an eight-element AA is found to equal a factor of 2.5 for a universal mobile telecommunications equivalent system, with one channelization code set per cell. The capacity gain is limited by severe channelization code shortage under these circumstances. This problem is solved by deploying a cell splitting strategy with multiple code regions, which subsequently results in a capacity gain increase to a factor of 3.4. Furthermore, the soft capacity mechanism associated with partial deployment of AAs in a subset of the cells in the network is also addressed. It is demonstrated that a hot spot cell with AAs also helps increase the capacity of the surrounding cells with conventional sector antennas when using a power-based AC strategy.

Capacity increases promised by multiple-input multiple-output (MIMO) systems mostly depend on the spatial correlation properties of the radio channel. The paper investigates the connection between these properties and the capacity figures. It first derives the correlation coefficient between two antenna elements as a function of their spacing, the power azimuth spectrum (PAS), the azimuth spread (AS) and the mean angle of incidence of the waves, for three different types of PAS, namely uniform, truncated Gaussian and truncated Laplacian. With the help of the established relations, correlated flat-fading MIMO channels are generated, whose capacity performance and effective degrees of freedom (EDOF) are investigated for two power allocation schemes, water-filling and uniform. The impact of channel estimation errors is also evaluated.

The performance of uplink synchronous WCDMA systems for low dispersive environments is evaluated at network level. The capacity increase is computed for the particular case of UMTS, taking into account the impact of effects like the code shortage, the number of receiver antennas, the penetration rate, and the use of soft handover. This is done theoretically and by means of a dynamic simulator, which considers more realistic conditions. Theoretical calculations match the simulation results. According to the results generated for speech service, the main problem in uplink synchronous WCDMA systems is the code shortage. For Pedestrian A environments with the most realistic conditions uplink synchronous WCDMA provides a 9.6% capacity gain. However, a very high potential exists for situations where this code shortage can be solved, i.e. 35.8% capacity gain assuming no code restriction.

The downlink performance enhancement provided by dual antenna terminals in a WCDMA network is evaluated. A UMTS network is taken as a case study and the behaviour of conventional power based radio resource management algorithms is discussed for both circuit and packet switched services. The aim is to clarify: (i) what the available capacity gain is; (ii) whether it is possible to capture this capacity gain without any higher layer overhead; and (iii) how the capacity is distributed among the users. A theoretical analysis of the dependency of the capacity gain upon the proportion of dual antenna terminals is conducted and the outcome matches the simulation results. Moreover, the impact of soft handover on the performance gain is considered. Furthermore, it is shown that the system becomes hard limited due to lack of channelisation codes, rather than excessive interference.

Empirical results characterizing the joint statistical properties of the local azimuth spread (AS), the local delay spread (DS), and the shadow (slow) fading component are presented. Measurement data from typical urban, bad urban, and suburban (SU) environments have been analyzed. It is found that a log-normal distribution accurately fits the distribution function of all the investigated parameters. The spatial autocorrelation function of both AS, DS, and shadow fading can be modeled with an exponential decay function. However, for SU environments the spatial autocorrelation function is better characterized by a composite of two exponential decaying functions. A positive cross correlation is found between the AS and the DS, while both parameters are negatively correlated with shadow fading. All essential parameters required for the implementation of a simulation model considering the joint statistical properties of the AS, DS, and shadow fading are provided.

Theoretical and experimental studies of multiple-input/multiple-output (MIMO) radio channels are presented. A simple stochastic MIMO model channel has been developed. This model uses the correlation matrices at the mobile station (MS) and base station (BS) so that results of the numerous single-input/multiple-output studies that have been published in the literature can be used as input parameters. The model is simplified to the narrowband channels. The validation of the model is based upon data collected in both picocell and microcell environments. The stochastic model has also been used to investigate the capacity of MIMO radio channels, considering two different power allocation strategies, water filling and uniform and two different antenna topologies, 4/spl times/4 and 2/spl times/4. Space diversity used at both ends of the MIMO radio link is shown to be an efficient technique in picocell environments, achieving capacities within 14 b/s/Hz and 16 b/s/Hz in 80% of the cases for a 4/spl times/4 antenna configuration implementing water filling at a SNR of 20 dB.

This study investigates the application potential of the SAGE (space-alternating generalized expectation-maximization) algorithm to jointly estimate the relative delay, incidence azimuth, Doppler frequency, and complex amplitude of impinging waves in mobile radio environments. The performance, i.e., high-resolution ability, accuracy, and convergence rate of the scheme, is assessed in synthetic and real macro- and pico-cellular channels. The results indicate that the scheme overcomes the resolution limitation inherent to classical techniques like the Fourier or beam-forming methods. In particular, it is shown that waves which exhibit an arbitrarily small difference in azimuth can be easily separated as long as their delays or Doppler frequencies differ by a fraction of the intrinsic resolution of the measurement equipment. Two waves are claimed to be separated when the mean-squared estimation errors (MSEEs) of the estimates of their parameters are close to the corresponding Cramer-Rao lower bounds (CRLBs) derived in a scenario where only a single wave is impinging. The adverb easily means that the MSEEs rapidly approach the CLRBs, i.e., within less than 20 iteration cycles. Convergence of the log-likelihood sequence is achieved after approximately ten iteration cycles when the scheme is applied in real channels. In this use, the estimated dominant waves can be related to a scatterer/reflector in the propagation environment. The investigations demonstrate that the SAGE algorithm is a powerful high-resolution tool that can be successfully applied for parameter extraction from extensive channel measurement data, especially for the purpose of channel modeling.

The applicability of the SAGE (space-alternating generalized expectation-maximization) algorithm to the estimation of time variant radio channels is demonstrated. This algorithm allows one to separate the complex multi-dimensional optimization problem required to compute the estimate of the parameters characterizing the impinging waves, i.e. their delay, incidence azimuth, Doppler frequency, and complex amplitude, into separate one dimensional optimization processes that can be performed sequentially. The performance of the scheme, i.e. its convergence behavior and its accuracy, is investigated in synthetic and real channels.