Integrated access and backhaul (IAB) is envisioned as a possible solution to address the need for network densification in situations where fiber connection is not viable. In Release 18, 3rd generation partnership project (3GPP) will take another step on extending IAB capabilities. With mobile IAB (mIAB), IAB nodes can be deployed within vehicles, e.g., buses. As in every new technology, performance assessment and evaluation of the impact of interference is of interest for industry and academia. In this paper, we present contributions on those topics. First, we evaluate the performance of mIAB compared to fiber-connected deployments. Moreover, we study the impact of interference on the performance of mIAB networks and propose a solution based on inserting silent slots on the time division duplex (TDD) frame pattern. According to our simulation results, mIAB is capable of improving performance of onboard user equipments (UEs) without harming too much the quality of service (QoS) of surrounding UEs. Furthermore, we show that the TDD frame pattern should be carefully designed to account for scenarios with different levels of interference.

This work studies the application of a reconfigurable intelligent surface (RIS) in a cloud radio access network (C-RAN) targeting the reduction of resource usage while providing adequate capacity. We investigate if an RIS can contribute to improve the trade-off between the downlink system spectral efficiency (SE) and energy consumption of a multi-base-station (BS) multi-user single-RIS setup by means of link activation, radiated power control, and operational power mode decisions that can benefit from RIS-enhanced radio channels. For this purpose, we optimize the activations jointly with BS and RIS beamforming for maximum energy efficiency (EE) under a centralized approach and subject to SE, power, fronthaul capacity, and RIS phase-shift constraints. The associated mixed-boolean non-linear problem is solved using monotonic and semidefinite relaxation methods integrated in a Branch-Reduce-and-Bound procedure. Simulations show that the RIS helps to increase the EE of a C-RAN w.r.t. its non-RIS-aided and fully-connected versions by 30% and 80%, respectively.

While the problems of sum-rate maximization and sum-power minimization subject to quality of service (QoS) constraints in the multiple input multiple output interference broadcast channel (MIMO IBC) have been widely studied, most of the proposed solutions have neglected the user scheduling aspect assuming that a feasible set of users has been previously selected. However, ensuring QoS for each user in the MIMO IBC involves the joint optimization of transmit/receive beamforming vectors, transmit powers, and user scheduling variables. To address the full problem, we propose a novel formulation of a rate-constrained sum-utility maximization problem which allows to either deactivate users or minimize the QoS degradation for some scheduled users in infeasible scenarios. Remarkably, this is achieved avoiding the complexity of traditional combinatorial formulations, but rather by introducing a novel expression of the QoS constraints that allows to solve the problem in a continuous domain. We propose centralized and decentralized solutions, where the decentralized solutions focus on practical design and low signaling overhead. The proposed solutions are then compared with benchmarking algorithms, where we show the effectiveness of the joint scheduling and transceiver design as well as the flexibility of the proposed solution performing advantageously in several MIMO IBC scenarios.

In this article we deal with total transmit power minimization problem in SC-FDMA system constrained to Quality of Service (QoS) and user satisfaction constraints. Through algebraic manipulations we were able to convert an integer nonlinear optimization problem in an Integer Linear Problem (ILP) so as to obtain the optimal solution. Motivated by the high computational to obtain the optimal solution, we propose a low computational complexity suboptimal solution. The results obtained through computational simulations show that the proposed solution presents satisfactory results regarding both outage rate and energy consumption.

In this paper we study radio resource allocation for cooperative networks with multiple relay and destination nodes employing orthogonal frequency-division multiple access. Resource allocation in our scenario is composed of relay selection, subcarrier pairing and assignment as well as transmit power allocation. Motivated by the increased concern about energy resource efficiency, we propose the total energy efficiency optimization in a cooperative scenario subject to quality of service constraints. Although the formulated problem is integer and non linear, we managed to optimally solve the problem by applying an iterative algorithm. Motivated by the high computational complexity to obtain the optimal solution, we propose a low-complexity suboptimal solution. Through computational simulations, we study the impact of the quality of service and circuit power on the proposed solutions.

Massive multiple‐input multiple‐output technology has been considered a breakthrough in wireless communication systems. It consists of equipping a base station with a large number of antennas to serve many active users in the same time–frequency block. Among its underlying advantages is the possibility to focus transmitted signal energy into very short‐range areas, which will provide huge improvements in terms of system capacity. However, while this new concept renders many interesting benefits, it brings up new challenges that have called the attention of both industry and academia: channel state information acquisition, channel feedback, instantaneous reciprocity, statistical reciprocity, architectures, and hardware impairments, just to mention a few. This paper presents an overview of the basic concepts of massive multiple‐input multiple‐output, with a focus on the challenges and opportunities, based on contemporary research.

Abstract In order to keep and/or expand its share of the wireless communication market and decrease churn, it is important for network operators to keep their users (clients) satisfied. The problem to be solved is how to increase the number of satisfied non‐real time (NRT) and real time (RT) users in the downlink of the radio access network of an orthogonal frequency division multiple access system. In this context, the present work proposes a method to solve the referred problem using a unified radio resource allocation (RRA) framework based on utility theory. This unified RRA framework is particularized into two RRA policies that use sigmoidal utility functions based on throughput or delay and are suitable for NRT and RT services, respectively. It is demonstrated by means of system‐level simulations that a step‐shaped sigmoidal utility function combined with a channel‐aware opportunistic scheduling criterion is effective toward the objective of user satisfaction maximization. Copyright © 2014 John Wiley & Sons, Ltd.

Researches in Power Control (PC) schemes are fundamental to provide efficient algorithms and understand their behavior in Device-to-Device (D2D) scenario. The aim of the current study is to investigate Open Loop Power Control (OLPC), Closed Loop Power Control (CLPC) and indicate Soft Dropping Power Control (SDPC) like an alternative PC scheme to D2D communications underlaying a cellular network. We briefly review PC schemes, suggest a new point of dynamic offset compensation factor σ setting the issue in CLPC and evaluate its performance in terms of spectral and power efficiency. Results demonstrate that SDPC keeps a reasonable spectral efficiency and provides a gain of 70 % in power efficiency in relation Long Term Evolution (LTE) PC schemes for cellular communications, and the factor σ = 0.8 can modify the behavior of CLPC because increases the Signal to Interference-plus-Noise Ratio (SINR) of the worst users.

For systems with reuse factor less than one, the co- channel interference can drastically reduce the gain of primary networks, which limits the whole system performance. This paper exploits the selection of Downlink (DL) or Uplink (UL) band to be reused by a Device-to-Device (D2D) link. The band selected by the method is based on a radio distance metric, such as received power. Despite being a simple concept, results have shown that band selection can effectively mitigate the interference caused by D2D communications in a Long Term Evolution (LTE) network. Therefore, the coexistence of cellular and D2D communication modes becomes possible in time, frequency, and space.

Device-to-Device (D2D) communication is seen as a promising technology to increase the capacity of current wireless systems without extra electromagnetic spectrum bands. However, before starting a D2D communication, Mobile Stations (MSs) must be aware of their neighbors, through a discovery process. While operating in cellular networks, such process may benefit from the network-assistance. In this paper, we propose a method based on the available network power measures to improve the discovery process. Results show that our proposal is less complex but still outperforms traditional methods when considering the time to detect all neighbors.

Device-to-Device (D2D) communications underlying cellular networks are a way to increase the network capacity and potentially save the battery lifetime of closely located physical devices. However, D2D communications can generate significant interference to the cellular network when the same resources are shared by both systems. Therefore, the design of Power Control (PC) schemes is required to keep the interference under control, get energy-efficient transmissions and protect cellular devices. In this work, we investigated operating points of the Soft Dropping Power Control (SDPC) and Open-Loop Power Control (OLPC) schemes for energy efficiency of cellular and D2D communications in uplink OFDMA systems. Results indicate that the SDPC performs better for cellular links and OLPC provides higher gains for D2D links in terms of energy efficiency. While high values of pathloss compensation factor α have been widely used in OLPC studies for the LTE standard, α ∊ {0.4, 0.5} has provided high energy efficiency gains for D2D links. Also, by properly setting the parameters of the OLPC applied to D2D links in uplink and considering the most favorable scenario for sharing resources in all cells, the minimum cost for having spectral efficiency gains for D2D communications represents an impact of 11 % on the system spectral efficiency of cellular communications.

In order to expand its market share and decrease churn, cellular network operators want to achieve the maximum possible number of satisfied clients. In this paper, we propose to solve the problem of user satisfaction maximization using an utility- based dynamic resource assignment algorithm that uses a sigmoidal utility function combined with either Orthogonal Random Beamforming (ORB) or Fixed Switching Beamforming (FSB). System-level evaluations of the downlink of an Orthogonal Frequency Division Multiple Access (OFDMA) system with real-time services demonstrate that there is an optimal number of spatial beams to be used by ORB and FSB, that FSB outperforms ORB with lower complexity, and also that the proposed joint resource assignment and beamforming outperforms other classical techniques found in the literature.

More and more Coordinated Multi-Point (CoMP) systems are attracting interest as a means to improve the performance of conventional cellular networks, particularly thanks to the joint processing approach. However, the large amount of signaling and computer operations required deserves special attention regarding both backhaul and radio resources constraints. Partitioning the set of transmission points into clusters is likely to reduce this coordination cost, but the search for the best formations of clusters may lead to expressive further computational efforts. Herein we introduce a novel approach, the Clustering-based Assignment Algorithm (CbAA), to cluster dynamically the transmission points on the downlink in order to transmit coherently to multiple users. When compared to static clustering, the proposed CbAA provided expressive gains in terms of system spectral efficiency. Compared to state-of-the-art dynamic clustering approaches, CbAA can waive the exhaustive search over all possible formations as well as the repetitive precoder calculations during the clustering procedure.

Space Division Multiple Access (SDMA) grouping algorithms are usually employed in order to find a suitable set of User Equipments (UEs) for spatial multiplexing. The largest SDMA group is not always the best SDMA group in a given transmission such that higher gains might be achieved by dynamically adjusting the SDMA group size. Besides, algorithms that balance the Signal to Interference-plus-Noise Ratio (SINR) among different links might ensure a certain level of link quality and so provide a more reliable communication for the scheduled UEs. This paper provides system-level analyses for strategies of Radio Resource Allocation (RRA) in Coordinated Multi-Point (CoMP) systems, which consider dynamic SDMA grouping, joint precoding and power allocation for SINR balancing. Our results show that Sequential Removal Algorithms (SRAs) and SINR balancing provide gains of system spectral efficiency.

The International Telecommunications Union established through the International Mobile Telecommunications-Advanced a set of requirements for high performance 4rd Generation communication systems and, with the aim of meeting such requirements, 3rd Generation Partnership Project Long Term Evolution (LTE) is considering a set of enhancements, referred to as LTE-Advanced. In LTE-Advanced context, Coordinated Multi-Point (CoMP) communication appears as a promissing technology to boost system throughput and to allow for an efficient Resource Allocation (RA). In this paper, we study RA algorithms that exploit coordination in the Downlink (DL) of CoMP systems to implement adaptive frequency reuse and so improve system throughput. We show through system-level analyzes that quite high throughput gains are achieved through intelligent RA.

In this paper, we consider a system based on Orthogonal Frequency Division Multiple Access (OFDMA) and investigate the benefits of combining the Satisfaction Oriented Resource Allocation (SORA) algorithm, which aims at maximizing the number of satisfied users in a system, and Orthogonal Random Beamforming (ORB), which provides spatial multiplexing gains and has low computacional complexity, low signaling demands, and high transparency to the User Equipment. Our investigations have shown that considerable gains in terms of throughput and user satisfaction can be achieved by combining SORA and ORB.

Space Division Multiple Access (SDMA) is a promising solution to improve the spectral efficiency of future mobile radio systems. However, finding the group of MSs that maximizes system capacity using SDMA is a complex combinatorial problem, which can only be assuredly solved through an Exhaustive Search (ES). Because an ES is usually too complex, there are several sub- optimal SDMA grouping algorithms to solve this problem. Such algorithms, however, usually depend on the preceding matrices of candidate SDMA groups and are also considerably complex. In this work, an SDMA grouping algorithm is proposed for the downlink of multi-user multiple input multiple output systems. It is based on the spatial correlation and gains of the MSs' channels in the SDMA group, thus not depending on preceding and having low complexity. The proposed algorithm is formulated as a convex quadratic optimization problem and is efficiently solved by convex optimization methods. It is analyzed considering zero-forcing precoding and it is shown to almost achieve the performance of an ES for the SDMA group that maximizes the system capacity.

In this work, a sub-optimal space division multiple access (SDMA) grouping strategy is proposed for the downlink of multi-user MIMO systems. It uses a new spatial compatibility check metric to estimate the grouping efficiency without needing to compute MIMO filter weights, thus reducing the complexity of SDMA grouping. Moreover, an iterative variant of the block diagonalization for throughput maximization algorithm is proposed, which can be employed to select the number of streams allocated to each user as to increase the sum capacity of the SDMA group. The proposed SDMA strategy is compared through simulation with single-user transmission, random grouping, and exhaustive search, and it is shown to have a good performance-complexity trade-off

The capacity of GERAN is expected to be limited by interference, particularly in urban areas, and by the quality of service (QoS) requirements demanded by the users. Smart antenna arrays employing beamforming techniques, commonly known as adaptive antennas (AA), are an efficient technology in mitigating interference in urban areas with low azimuth spread. In EGPRS, the packet data service of GERAN, resource scheduling is responsible for multiplexing users on shared physical channels in order to best fulfill QoS requirements. By using more efficient scheduling algorithms, the resulting QoS is enhanced and, ultimately, it may be exchanged for capacity. In this work, the QoS and capacity gains provided by an AA system and two scheduling algorithms in several EGPRS system configurations are shown. Furthermore, it is demonstrated that, when combined, a tighter reuse scheme, a base station AA system, and an enhanced scheduling algorithm can result in a capacity gain of up to approximately 450% over the reference scenario.