The fifth-generation wireless technology is primarily designed to address a wide range of use cases mainly categorized into the enhanced mobile broadband, ultra-reliable and low-latency communication, and massive machine-type communication segments. To efficiently serve some other use cases whose requirements lie in-between these main use cases, the 3rd generation partnership project (3GPP), in Rel-17, introduce support for the reduced capability new radio (NR) devices known as RedCap with lower cost and complexity compared to legacy 5G devices. The considered complexity reduction techniques are associated with degraded link performance and coverage for the physical channels. Particularly, for the physical downlink control channel (PDCCH), which requires careful consideration, the reduction of the user equipments’ (UEs) complexity and the associated coverage loss can lead to an increase in the PDCCH blocking probability. This, in turn, can impact either the latency or the network capacity depending on the scenario. In this paper, we investigate the PDCCH blocking probability metric for RedCap devices. Specifically, we evaluate the performance of blocking probability in terms of various parameters including the number of users, size of downlink control information, size of control resource set, and the number of PDCCH candidates. Our results demonstrate that the PDCCH blocking probability increases by reducing the number of antenna branches, the number of PDCCH candidates, control resource set, and by increasing the number of scheduled UEs. We also show that the impact of reducing the DCI size is marginal on the PDCCH blocking probability. Finally, we discuss potential solutions and design guidelines for reducing the PDCCH blocking probability.

The 5th generation (5G) new radio (NR) is designed to support a wide range of use cases, requirements, and services from enhanced mobile broadband (eMBB) to ultra-reliable low-latency communications (URLLC). NR signals are designed to meet stringent requirements, and in particular the physical down-link control channel (PDCCH) which requires careful consideration. In this paper, we provide a comprehensive analysis on the PDCCH blocking probability in a network where multiple users need to be scheduled for receiving downlink control information. We evaluate the performance of blocking probability in terms of various network parameters including number of users, size of the control resource set (CORESET), and PDCCH aggregation levels (ALs). Our analysis reveals fundamental tradeoffs and key insights for efficient network design in terms of PDCCH blocking probability.

Utilizing the abundant bandwidth in millimeter wave frequency bands is an interesting option to enable wireless communication services with challenging latency and reliability requirements for factory automation. Nevertheless, millimeter wave bands have less favorable propagation properties compared to lower bands, which impacts the coverage negatively. In this paper, we show that millimeter wave bands can fulfill extreme latency and reliability requirements with much higher system capacity than mid-band frequencies by means of beamforming, large antenna arrays, and network densification. This makes millimeter wave bands suitable for providing ultra-reliable low-latency communication services for factory automation. However, we find that small beam misalignments due to channel state information error can degrade the system capacity substantially.

In Release 13 the Third Generation Partnership Project (3GPP) developed the Narrowband Internet of Things (NB-IoT). It is a cellular technology providing wireless connectivity to machine-type services and applications. In 3GPP Releases 14 and 15, NB-IoT evolved to meet the requirements defined for a fifth generation (5G) communications system in 3GPP and in the International Telecommunications Union Radiocommunication (ITU-R) sector. This paper introduces NB IoT in the context of 3GPP's recent work on 5G. It presents the ITU-R International Mobile Telecommunication 2020 (IMT 2020) and 3GPP 5G performance requirements. A complete evaluation of the NB IoT performance for each of these requirements is presented, and it is shown that NB IoT meets the 5G performance requirements for massive IoT (mIoT) services.

This paper describes the elements of the uplink sub-PRB resource allocation, which in Rel-15 was added to the set of functionalities LTE provides for Machine-Type Communications. The high capacity demands of machine-type services, the continuous aim for lowering the device power consumption, and the need of performing more efficient uplink transmissions at low signal-to-noise ratio (SNR) regimes, have in 3GPP LTE-M Release 15 been addressed by introducing sub-PRB transmissions over PUSCH. In principle, it refers to an uplink resource allocation with finer granularity than a 180-kHz physical resource block (i.e., allocations based on sets of less than 12 adjacent 15-kHz subcarriers). The sub-PRB feature can be used to improve the uplink transmission quality of devices placed in difficult access locations at remote distances. Besides increasing the PUSCH spectral efficiency, the sub-PRB feature offers other benefits such as lowering the code rates and decreasing the device power consumption.

Narrowband Internet of Things (NB-IoT) is a new radio access technology, recently standardized in 3GPP to enable support for IoT devices. NB-IoT offers a range of flexible deployment options and provides improved coverage and support for a massive number of devices within a cell. In this paper, we provide a detailed evaluation of the coverage performance of NBIoT and show that it achieves a coverage enhancement of up to 20 dB when compared with existing LTE technology.

While a heterogeneous network increases the system performance in terms of coverage and capacity, if it is deployed without being well planned and without making use of optimized configurations, it could potentially lead to tough requirements on the mobility performance. The system level simulations shows that in typical scenarios the small separated cell deployment (each low power node is deployed as a separate cell) meets mobility requirements from the regular network operations perspective. However, in challenging mobility scenarios, small separated cell deployment might suffer from the degradation in mobility performance due to the non-optimal handover settings. The proposed combined cell deployment (low power nodes and macro cell use the same cell identity) provides an effective alternative to improve mobility in terms of reduced handover numbers and improved transmission robustness for handover signaling, therefore simplifying the network planning and management.

Carrier aggregation has enabled LTE to efficiently utilize wide and fragmented spectrum to provide high data rate services to end users' benefits. We investigate the challenges of providing reliable multi-carrier hybrid automatic repeat request (HARQ) and timely periodic channel state information (CSI) feedbacks from terminals aggregating multiple component carriers in LTE networks. We consider unified and reliable uplink control channel designs to carry multi-carrier HARQ and periodic CSI feedback messages simultaneously. Care is taken in the designs to reduce the detection complexity on the network side, which also improves its detection reliability relative to existing LTE signalling schemes.

Successive interference cancellation (SIC) is a well-known technique for mitigating interference. For multiple-layer reception, hard-decision SIC with perfect per-layer rate control has been proven to be a capacity-achieving scheme. In practice, however, due to imperfect rate control and signaling constraints, there is a potential for certain variants of SIC techniques to achieve better performance than the conventional hard-decision SIC approach. In this paper, the benefits of various SIC techniques are studied. We show that a soft SIC scheme that passes information iteratively between equalizer, demodulator, and decoder enhances MIMO reception in downlink LTE.

In this letter, a multistage group detection (MSGD) approach to nonlinear equalization is proposed. At each stage, symbols are divided into groups, and maximum-likelihood detection (MLD) within the group is performed. The MLD process identifies a number of promising group values. It is constrained to only consider candidate symbol values identified in the previous stage. Groups are formed by combining groups from the previous stage. For example, symbols are detected one at a time, then two at a time, then four at a time, and so on. The last stage is a form of constrained maximum-likelihood sequence detection (MLSD). The overall demodulation process can be viewed as approximate MLSD, and results show that near-MLSD performance is possible with reasonable complexity. While the High Speed Downlink Packet Access (HSDPA) cellular system is used as an example, the approach can be applied other situations, including the Long Term Evolution (LTE) uplink and MIMO.

In this paper, we study how the capacity and coverage of voice over internet protocol (VoIP) in the WCDMA uplink can be improved by using advanced base station receivers capable of multi-user detection (MUD). To avoid the complexity of joint-detection, a multi-stage successive interference cancellation (SIC) detector or parallel interference cancellation (PIC) detector is used as an implementation of MUD. To further reduce complexity, time-division multiplexing (TDM) is used to separate user groups in time so that MUD can focus on a smaller number of overlapping signals. SIC or PIC cancels a number of temporarily detected user signals from the receive signal before detecting another user signal. A temporarily detected user signal can be regenerated based on demodulated data or decoded data, and based on hard-decision values or soft-decision values. We find that a two-stage SIC or PIC process improves VoIP performance significantly and having more detection stages beyond two does not further improve performance by much. The improved performance allows a VoIP user to reduce the average transmit power, which translates to VoIP capacity and coverage increases. Furthermore, we find that the individual user performance is not sensitive to its detection order. We also quantify the relative performance between the various signal regeneration schemes considered. As expected, post-decoding interference cancellation (IC) offers a significant gain over pre-decoding IC. Furthermore, we find that post-decoding IC is robust to traffic load variations. Also, soft-decision based cancellation achieved the best performance. However, the performance improvement is small compared to hard-decision based cancellation. Finally, we see that MUD can work with G-Rake to suppress one dominant other-cell interfering signal, e.g., due to a high-data-rate user in another cell.

Direct-sequence code-division multiple-access (DSCDMA) cellular systems, such as wideband CDMA (WCDMA), are limited in performance by interference. Linear equalization, such as generalized Rake (G-Rake) receivers and transversal chip equalizers, can theoretically provide significant gains in performance by suppressing interference. In this paper, an adaptive G-Rake receiver is developed, employing practical algorithms for finger placement and weight computation. Finger placement is determined by selecting delays from a candidate set using a "maximal-weight" criterion. Weight computation includes estimation of an impairment covariance matrix using a parametric approach. While described in the context of the downlink, these algorithms can be used in the uplink as well. Both single-antenna and dual-antenna receivers are considered. Link and system performance are evaluated for the downlink, showing significant gains in high-rate coverage.

In this paper, we study the performance of transmit diversity schemes in a wideband code-division multiple-access (WCDMA) system. We consider a space-time transmit diversity (STTD) scheme using the Alamouti code and a simple switch transmit diversity (STD) scheme in which the transmitter selects instantaneously the best antenna for transmission. Receiver impairment is generally modeled as a colored, complex Gaussian process, which gives rise to temporal and spatial correlations. First, we extend the G-Rake formulation to process a STTD signal, accounting for the space-time code structure as well as the temporal and spatial correlations of the impairments. The performance of STTD and STD for a WCDMA system is then evaluated. We show that STTD improves the coverage of low-to-medium rate services significantly for users at cell edge compared to the scheme without transmit diversity. Such improvements are observed even when the channels already have diversity through multipath and multiple receive antennas. Thus, STTD is well suited for broadcast when feedback from mobiles is not available. For high-data-rate availability, however, using one feedback bit to allow the STD scheme to transmit only on the better antenna achieves significantly better performance compared to STTD. This is because sending the desired signal through one radio channel makes it easier for linear equalizers to restore orthogonality. For mobiles dominated by self-interference due to loss of orthogonality, better equalization results in much improved data rates.

The system benefits of using an advanced dual-branch diversity receiver at the mobile terminal are studied in a Wideband Code-Division Multiple-Access (WCDMA) cellular system. The receiver considered is an extension of the generalized Rake (G-Rake) receiver which provides a form of array processing. In addition to exploiting the temporal correlation in receiver impairments and the orthogonality between spreading codes, spatial correlation is also accounted for in the formulation of finger combining weights. We show that this dual-branch G-Rake receiver, even with a pessimistic antenna configuration, has a potential to increase the system capacity, relative to the conventional single-branch Rake receiver, by 94% for voice communications. For data communications, high-data-rate availability can be significantly improved. This allows a HSDPA user at the cell border to enjoy a data rate close to 4 Mbps in dispersive channels. For end-user performance of TCP/IP applications, users with a dual-branch G- Rake receiver experience significantly higher packet bit rates and shorter download times.

Own-cell interference limits capacity and coverage in the WCDMA enhanced uplink, and the use of interference cancellation (IC) techniques is required to provide high-data-rate availability. For a typical uplink WCDMA system with mixed traffic generated by few high-data-rate users and many low-rate users (e.g., voice users), this paper considers an IC receiver that cancels the high-data-rate signals prior to low-rate traffic reception. The IC receiver provides substantial capacity gains and the benefits of cancellation can be seen as increased achievable data rate for a fixed voice load and/or increased voice load for a target data load. For example, with a data rate of 1.5 Mbps, voice capacity gains are between 60% and 80%. In low voice load, the achievable data rate exceeds 3.5 Mbps. Due to the nature of traffic in WCDMA networks and the option of a short transmission time interval (TTI) for high-data-rate transmission in WCDMA Release 6, this IC scheme is an attractive solution for implementation in base station receivers. In addition, this paper considers also an uplink receiver that cancels the control channels of all users in the cell. Capacity gains are substantial in cells highly loaded with low-rate users

In the downlink of direct-sequence code-division multiple-access (DS-CDMA) cellular systems, system capacity is limited by multiuser interference. This interference can be suppressed at the receiver by interference whitening approaches such as chip equalization and generalized RAKE (G-RAKE) reception. In this paper, we show how these advanced receivers can increase system capacity. First, the G-RAKE receiver formulation is extended to include soft handoff and other-cell interference. Then, voice capacity is evaluated, including the effects of fast fading, interference correlation, power control, orthogonality properties of own-cell signals, and soft handoff. Numerical results for the wideband CDMA system show that when the channel is dispersive, advanced receivers improve capacity by 30-34%

In this paper, successive intracell interference cancellation (IIC) of the wideband-code division multiple access (W-CDMA) signal at the mobile unit is considered. Three new interference cancellation techniques suitable for the downlink of any CDMA system with orthogonal spreading are proposed. No prior knowledge of users' spreading codes or even their spreading factors are required for interference cancellation. A new term, effective spreading code, has been introduced, which is defined as the interfering user physical code as seen by the desired user within the desired user symbol duration. The mobile receiver estimates the effective spreading codes of the interfering users regardless of their spreading factors using fast Walsh transform (FWT) correlators (instead of the regular correlators) and uses this information to suppress the intracell multiuser interference. Three different interference-suppressing techniques are studied: subtraction; combined interfering signal projection; and separate interfering signal subspace projection. The complexity of the proposed techniques is low compared to conventional interference cancellation techniques. For a W-CDMA system and the IMT-2000 vehicular channel model, a capacity increase of up to 150% of the original (without IIC) system capacity is shown.

This paper describes the physical layer for a high penetration paging (HPP) mode, that is a highly integrated adjoint to a cellular system. Through the use of very low rate coding and periodically inserted synchronization bursts, the HPP mode enables a cellular user to locate and maintain a minimal communication link with a cellular network at 15 to 20 dB below the normal operating signal to noise ratio (SNR). In this paper, the ANSI-136 air interface standard is used as the underlying cellular system. The same concept can be extended to other systems as well.

The benefit of generalized RAKE reception to downlink system capacity is studied. System capacity is evaluated for certain cell and user outage probabilities. Fast fading, noise correlation, power control, and soft handoff are all included in our study. The site selection diversity transmission (SSDT) approach to power allocation between soft handoff links is shown to be optimal in the sense that it minimizes total transmit power to a given user. Numerical results show that G-RAKE receivers can improve system capacity by as much as 30-45% in a highly dispersive channel.

Currently, a global third-generation cellular system based on code-division multiple-access (CDMA) is being developed with a wider bandwidth than existing second-generation systems. The wider bandwidth provides increased multipath resolution in a time-dispersive channel, leading to higher frequency-selectivity. A generalized RAKE receiver for interference suppression and multipath mitigation is proposed. The receiver exploits the fact that time dispersion significantly distorts the interference spectrum from each base station in the downlink of a wideband CDMA system. Compared to the conventional RAKE receiver, this generalized RAKE receiver may have more fingers and different combining weights. The weights are derived from a maximum likelihood formulation, modeling the intracell interference as colored Gaussian noise. This low-complexity detector is especially useful for systems with orthogonal downlink spreading codes, as orthogonality between own cell signals cannot be maintained in a frequency-selective channel. The performance of the proposed receiver is quantified via analysis and simulation for different dispersive channels, including Rayleigh fading channels. Gains on the order of 1-3.5 dB are achieved, depending on the dispersiveness of the channel, with only a modest increase in the number of fingers. For a wideband CDMA (WCDMA) system and a realistic mobile radio channel, this translates to capacity gains of the order of 100%.

In a CDMA cellular system, the process of the mobile station searching for a cell and achieving code and time synchronization to its downlink scrambling code is referred to as cell search. Cell search is performed in three scenarios: initial cell search when a mobile station is switched on, idle mode search when inactive, and active mode search during a call. The latter two are also called target cell search. This paper presents algorithms and results for both initial and target cell search scenarios for the wideband CDMA (W-CDMA) standard. In W-CDMA, the cell search itself is divided into five acquisition stages: slot synchronization, frame synchronization and scrambling code group identification, scrambling code identification, frequency acquisition, and cell identification. Initial cell search needs all five stages, while target cell search in general does not need the last two stages. A pipelined process of the first three stages that minimizes the average code and time acquisition time, while keeping the complexity at a reasonable level, is considered. The frequency error in initial cell search, which may be as large as 20 kHz, is taken care of by partial symbol despreading and noncoherent combining. Optimization of key system parameters such as the loading factors for primary synchronization channel, synchronization channel, and common pilot channel for achieving the smallest average code and time acquisition time is studied. After code and time synchronization (the first three stages), a maximum likelihood (ML)-based frequency acquisition method is used to bring down the frequency error to about 200 Hz. The gain of this method is more than 10 dB compared to an alternative scheme that obtains a frequency error estimate using differential detection.

In this paper, blind intra-cell interference cancellation (IIC) of the W-CDMA signal at the mobile unit is considered. Two new blind interference cancellation techniques suitable for the downlink of any CDMA system are proposed. The receivers are blind in the sense that no prior knowledge of users' spreading codes or even their spreading factors are required. The mobile receiver estimates the effective spreading codes of the interfering users regardless of their spreading factors using fast Walsh transform (FWT) correlators and uses these information to cancel out the intra-cell multi-user interference. The complexity of the proposed techniques is low compared to conventional interference cancellation techniques. Simulation results show a capacity increase of up to 50 % of the original (without IIC) system capacity or up to 10 dB signal to Gaussian noise ratio gain at a fixed capacity (the inter-cell interference is modeled as a Gaussian noise).

Tail bits and tail-biting are the two commonly used methods for terminating the trellis of convolutional codes. In this paper, we evaluate the relative performance of these two options by comparing their performance in a variety of cases. Suboptimal decoding algorithms for the tail-biting case are proposed. Puncturing is proposed as an alternative method to prevent the rate loss when tail bits are used. The performance of several puncturing schemes are evaluated. In addition, we explore the bit error rate of these schemes as a function of position of bits in a block.