Coordinated Multipoint Schemes Research Articles

Uplink CoMP Transmission for Cellular-Connected UAV Networks

In this letter, we study the coordinated multipoint (CoMP) scheme in the uplink cellular-connected UAV network. By considering the LoS and NLoS components in air-to-ground (A2G) transmission, we adopt the strongest average received signal strength (RSS)-based CoMP scheme. We then develop an analytical framework to evaluate the network performance in terms of coverage probability and area spectral efficiency (ASE) for the case of two cooperative base stations (BSs), followed by an extension to a generalized number of cooperative BSs. Compared to the CoMP scheme with single UAV tier and Non-CoMP baseline, the considered CoMP scheme is able to leverage favored Line-of-Sight (LoS) transmission, lower path loss and BS cooperation gain.

Selective interference alignment and neutralization in coordinated multipoint using multiuser MIMO

SummaryIn wireless communication, the concept of coordinated multipoint (CoMP) transmission is more attractive, and it transpired the notion based on interference management techniques. Interference alignment (IA) and interference neutralization (IN) methods can substantially align and neutralize the interference signals. The existing work in the CoMP transmission using multiuser multi‐input and multi‐output (MU‐MIMO) had long‐held problems such as specific limit of intercell (ICI) and cochannel interference (CCI) cancelation that contain low performance in cell‐edge users. The proposed framework of the transmission signal in selective interference alignment and neutralization (SIAN) CoMP MU‐MIMO system transmits multiple data streams in multipath by using downlink coordination between base stations and receiver side. This work contributes the individual perspectives to implement the IA and IN to align and cancel the interfered signals at the receiver side. Once the perspectives mentioned above are executed, zero‐forcing (ZF) and rechanneling filter are applied on the receiver side to eliminate residual ICI. In addition, spectral efficiency significantly improves the achievable data rate and enhances the performance of cell‐edge users and reduces the CCI at the receiver side. Furthermore, the antenna configuration signals are decoded to get the exact version of interference‐free signals with null path loss of signal transmission. The effectiveness of the proposed framework analyzes and verifies the numerical evaluation of the achievable degree of freedom. Finally, the simulation demonstrates the comparison of the proposed CoMP scheme with MIMO ZF and non‐CoMP schemes, which significantly improve the performance of spectral efficiency for cell‐edge users.

Ground-to-Air Communications Beyond 5G: A Coordinated Multipoint Transmission Based on Poisson-Delaunay Triangulation

This paper designs a novel ground-to-air communication scheme to serve unmanned aerial vehicles (UAVs) through legacy terrestrial base stations (BSs). In particular, a tractable coordinated multi-point (CoMP) transmission based on the geometry of Poisson-Delaunay triangulation is developed, which provides reliable and seamless connectivity for UAVs. An effective dynamic frequency allocation scheme is designed to eliminate inter-cell interference by using the theory of circle packing. For exact performance evaluation, the handoff probability of a typical UAV is characterized, and then the coverage probability with handoffs is attained. Simulation and numerical results corroborate that the proposed scheme outperforms the conventional CoMP scheme with three nearest cooperating BSs in terms of handoff and coverage probabilities. Moreover, as each UAV has a fixed and unique CoMP BS set, it avoids the real-time dynamic BS searching process, thus reducing the feedback overhead.

Distributed fronthaul-constrained joint transmission design and selection using augmented consensus-based dual decomposition

User-centric coordinated multipoint (CoMP) joint transmission (JT) is a novel technique to manage interference and enhance system performance with single frequency reuse, where user equipment (UE) communicates with their closest transmission points (TPs). Unfortunately, in coherent JT, requirement of strict network synchronization accuracy makes it difficult and expensive to be practically deployed. The noncoherent JT has therefore received growing attention since it requires less strict network synchronization accuracy compared to its coherent counterpart as it does not require the signal to be phase-aligned at the receiver. Moreover, cell-free massive MIMO, which is regarded as combining CoMP with massive MIMO systems, has recently been touted as a solution for avoiding intercell interference and provide uniform coverage over a large area. However, the operational costs of CoMP, such as the associated control signaling and communication overhead and the increase of network complexity, could prevent the practical implementation of CoMP. A distributed joint transmission CoMP (JT-CoMP) scheme is proposed herein that allows distributed design and selection of cooperating transmission nodes. To maximize user capacity, the proposed distributed consensus optimization problem assumes spectrum underlay transmission is used so that the solution can achieve non-orthogonal multiple access (NOMA) for cell-free user centric JT-CoMP systems. The proposed algorithm is different from others in the literature because it solves a design problem that involves a coupling constraint that no existing algorithm can solve. Analytical results based on spectral graph theory are given to prove its convergence and characterize its rate of convergence. The more practical scenario is further considered, where limited fronthaul capacity is also included in the problem. A successive convex approximation (SCA) method is used to solve the resulting nonconvex problem, which is shown to maximize spectral efficiency. Simulation results are provided to show that the performance of both proposed distributed algorithms (that address problem without and with fronthaul constraint) is comparable to its centralized counterpart.

Unified Analysis of Coordinated Multipoint Transmissions in mmWave Cellular Networks

This article performs a unified analysis of three coordinated multipoint (CoMP) transmission strategies in the downlink of mmWave cellular networks, including the fixed-number base station (BS) cooperation (FNC), the fixed-region BS cooperation (FRC), and the interference-aware BS cooperation (IAC). We first develop a comprehensive framework for CoMP operation in cellular networks, and investigate the network performance under a Poisson point process (PPP) model together with mmWave spectrum. To show what fraction of users in the network achieve target reliability for a given signal to interference-plus-noise ratio (SINR)/signal-to-interference ratio (SIR), we derive the SINR/SIR meta distributions, and further obtain the coverage probability as well as mean local delay for the three cooperation strategies. A pivotal intermediate step to compute the performance metrics is the derivation of joint distributions of distances between a typical user and cooperative BSs. Our analysis demonstrates that parameters of blockage have a significant influence on the network performance for the three CoMP schemes. We find that the FRC scheme makes more users achieve the given link reliability for the scenario with a low density of BSs, while the IAC scheme provides better performance for the network with a high density of BSs. Moreover, the optimal CoMP scheme can be approximately selected by considering the nearest distance from the serving BS to user and the radius of the approximate line-of-sight (LoS) region in the cellular networks.

A resource efficient scheme for backhaul‐constrained coordinated multipoint cellular networks

AbstractThe coordinated multipoint (CoMP) is a promising set of techniques that deals with inter‐cell interference differently than the conventional interference mitigation schemes. This unique approach can effectively mitigate or even exploit the interference, turning it into a useful signal. The CoMP was first introduced in Release‐11 by Third Generation Partnership Project (3GPP) for the fourth generation (4G) long term evolution‐advanced (LTE‐A) systems, enhanced in subsequent releases and recently incorporated as one of the fifth generation (5G) component technologies. In this article, we propose two techniques aiming to improve the performance of existing CoMP schemes. First, we examine the impact of constraint backhaul on the cell coordination and propose an optimal CoMP mechanism that adaptively switches between joint transmission (JT) and coordinated beamforming (CBF) CoMP schemes taking into consideration the average sum rate and the available backhaul capacity. Next, we present a backhaul overhead reduction scheme for CoMP enabled networks, which extends the performance gains of adaptive CoMP scheme. Simulation results suggest that proposed adaptive scheme outclasses conventional CoMP schemes and offers a spectrally efficient solution with increased average user throughput and sum rate.

Base Station Coordination Scheme for Multi-Tier Ultra-Dense Networks

In this paper, we consider a relative received link power (RRLP)-based coordinated multi-point (CoMP) joint transmission (JT) in the multi-tier ultra-dense networks (UDN). In this CoMP scheme, we identify the cooperating base stations (BSs) by comparing the average received link power (ARLP) of the neighbouring BSs with respect to the BS having the strongest ARLP (i.e., the main link BS) to a user. To analyze the performance of this CoMP scheme in the downlink multi-tier UDN, we first approximate the received signal power distribution, and derive the coverage probability using stochastic geometry. After revisiting the area spectral efficiency (ASE) to make it more suitable for CoMP transmission in UDN, we also analyze the ASE and the network energy efficiency (NEE). Using simulations, we validate the derived coverage probability, and investigate the CoMP performance in multi-tier UDN. Our simulations show that the RRLP-based CoMP scheme can outperform the fixed number of strongest BS-based CoMP scheme in the high BS density regime. Our study of the NEE performance reveals that not only the RRLP-based CoMP scheme is more efficient than conventional non-CoMP transmission scenario, but also its NEE performance improves with the average number of cooperating BSs.

A Novel Coordinated Multipoint Scheme With Zero Guard Interval for ATSC 3.0 Single Frequency Networks

Advanced Television Systems Committee (ATSC) has issued ATSC 3.0 as the standard for the next-generation of Digital Terrestrial Television (DTT) broadcasting. ATSC 3.0 introduces several new features including Layered Division Multiplexing (LDM) that is a form of Non-Orthogonal Multiple Access (NOMA). ATSC 3.0 supports the legacy Single Frequency Networks (SFN), where the Guard Interval (GI) is considered to overcome the multipath as well as the asynchronous reception from different transmitters. Considering the huge distances between the DTT broadcasters, the GI overhead could be comparable to the data size, making the control/data ratio unfavorable. This paper proposes the association of Coordinated MultiPoint (CoMP) in SFN with NOMA-LDM. A novel formation of the channel matrix is provided that jointly includes the asynchronous channel's cross correlations for further joint detection of the signals at the receiver. The purpose is to enhance the coverage and spectral efficiency while avoiding hectic guard intervals or directional antennas. The capacity region is derived in an information theoretic framework based on exploiting the asynchronous channels' memory and correlation. We show that the spectral efficiency can exceed that of the non-coordinating schemes, provided that the proper receiver is equipped with the proposed channel matrix formation. Our extensive simulations validate that our proposed association of CoMP-SFN with NOMA-LDM provides a considerable boost in the coverage and channel reliability, while increasing the spectral and power efficiency.

Cooperative resource management for C-V2I communications in a dense urban environment

Cellular-based vehicle-to-everything (C-V2X) is one of the emerging and promising techniques to support vehicular communications by enabling both safety-critical and non-safety services. C-V2X communications is a core solution to manage and advance future traffic safety and mobility. In this paper, we design a cellular-based vehicle-to-infrastructure (V2I) communications model for a Manhattan dense urban environment that has many roads deployed in the cell edge region, which results in severe co-channel interference (CCI). Thus, we aim to utilize two cooperative interference management schemes such as dynamic inter-cell interference coordination (ICIC) and coordinated multipoint (CoMP) to mitigate interference and to improve communication reliability. We evaluate the performance of the interference management schemes based on various performance indexes, such as vehicle UE average throughput, vehicle UE received interference, and vehicle UE outage probability. By effectively implementing the dynamic ICIC scheme, we achieve an immense reduction in CCI, which results in the improvement of user (UE) received signal quality. Moreover, we employ coordinated scheduling (CS) CoMP scheme to further mitigate the interference among cells. Finally, by implementing both dynamic ICIC and CS CoMP schemes simultaneously, a meaningful level of performance enhancement is achieved.

Air-to-Air Communications Beyond 5G: A Novel 3D CoMP Transmission Scheme

In this paper, a novel $3$D cellular model consisting of aerial base stations (aBSs) and aerial user equipments (aUEs) is proposed, by integrating the coordinated multi-point (CoMP) transmission technique with the theory of stochastic geometry. For this new $3$D architecture, a tractable model for aBSs' deployment based on the binomial-Delaunay tetrahedralization is developed, which ensures seamless coverage for a given space. In addition, a versatile and practical frequency allocation scheme is designed to eliminate the inter-cell interference effectively. Based on this model, performance metrics including the achievable data rate and coverage probability are derived for two types of aUEs: {\it i)} the general aUE (i.e., an aUE having distinct distances from its serving aBSs) and {\it ii)} the worst-case aUE (i.e., an aUE having equal distances from its serving aBSs). Simulation and numerical results demonstrate that the proposed approach emphatically outperforms the conventional binomial-Voronoi tessellation without CoMP. Insightfully, it provides a similar performance to the binomial-Voronoi tessellation which utilizes the conventional CoMP scheme; yet, introducing a considerably reduced computational complexity and backhaul/signaling overhead.

Coordinated Multi-Point Transmission: A Poisson-Delaunay Triangulation Based Approach

Coordinated multi-point (CoMP) transmission is a cooperating technique among base stations (BSs) in a cellular network, with outstanding capability at inter-cell interference (ICI) mitigation. ICI is a dominant source of error, and has detrimental effects on system performance if not managed properly. Based on the theory of Poisson-Delaunay triangulation, this paper proposes a novel analytical model for CoMP operation in cellular networks. Unlike the conventional CoMP operation that is dynamic and needs on-line updating occasionally, the proposed approach enables the cooperating BS set of a user equipment (UE) to be fixed and off-line determined according to the location information of BSs. By using the theory of stochastic geometry, the coverage probability and spectral efficiency of a typical UE are analyzed, and simulation results corroborate the effectiveness of the proposed CoMP scheme and the developed performance analysis.

A CoMP-Based outage compensation solution for heterogeneous femtocell networks

In wireless cellular networks, self-healing is one of the three functionalities for self-organizing networks, and it has four major components: fault detection, fault diagnosis, fault response and fault recovery. In this paper, we propose a cell outage compensation mechanism (fault response scheme) using a network cooperation scheme in a heterogeneous network environment with densely deployed Femto Base Stations (FBSs). The network cooperation scheme for FBSs uses the Coordinated Multi-Point (CoMP) transmission and reception with joint processing technique where the main purpose of cooperation among FBSs is to guarantee service to UEs even in cases where their primary FBSs or their backhauls fail. The objective of our proposed mechanism is to maximize the total users’ throughput taking into consideration the spectrum and power constraints. Therefore, different clustering methods are studied and analyzed to improve the performance of the network cooperation scheme. Simulation results show that our proposed network cooperation scheme using CoMP can improve the Femto User Equipment (FUE) throughput by more than 30% compared to a non-cooperation solution for self-healing, and CoMP schemes with spectral clustering and k-means clustering algorithms can improve FUE throughput by up to 50%. Moreover, the proposed CoMP operation schemes prevent service rate from dramatic drop when FBSs fail.

Anywhere Decoding: Low-Overhead Uplink Interference Management for Wireless Networks

Inter-cell interference (ICI) is one of the major performance-limiting factors in the context of modern cellular systems. To tackle ICI, coordinated multi-point (CoMP) schemes have been proposed as a key technology for next-generation mobile communication systems. Although CoMP schemes offer promising theoretical gains, their performance could degrade significantly because of practical issues such as limited backhaul. To address this issue, we explore a novel uplink interference management scheme called anywhere decoding, which requires exchanging just a few bits of information per coding interval among the base stations (BSs). Despite the low overhead of anywhere decoding, we observe considerable gains in the outage probability performance of cell-edge users, compared to no cooperation between BSs. Additionally, asymptotic results of the outage probability for high-SNR regimes demonstrate that anywhere decoding schemes achieve full spatial diversity through multiple decoding opportunities, and they are within 1.5 dB of full cooperation.

Adaptive CoMP with Spatial Phase Coding for Interference Mitigation in the Heterogeneous Network

This paper proposes an adaptive coordinated multi point (CoMP) scheme using pre-coding in order to improve the reliability of wireless communication systems based on orthogonal frequency division multiplexing (OFDM). In the conventional scheme, the received signal to noise ratio (SNR) of the mobile is degraded due to the interference signal. Therefore, the bit error rate (BER) performance is degraded, as is, the reliability of the system, due to inter-cell interference (ICI). Therefore, the BER performance of the system is reduced and the transmitter must perform unnecessary re-transmission. The proposed scheme uses the CoMP scheme to improve reliability in a heterogeneous network (HetNet) system. Additionally, the proposed scheme uses the constructive spatial phase coding (SPC) scheme to mitigate the received SNR reduction due to the interference signal. Therefore, the proposed scheme can prevent performance degradation caused by the interference signal. When a mobile is located in the cell edge, the transmission signal is distorted by the transmitted signal from the adjacent cell. The proposed scheme can reduce the SNR of the interference signal by using the destructive SPC scheme. Therefore, this scheme can improve the reliability of the system. The simulation results show that the BER performance of the proposed scheme is better than that of the conventional scheme. As a result, the proposed scheme improves the reliability of systems by adaptively applying the CoMP and SPC schemes.

A Cache-Aided Communication Scheme for Downlink Coordinated Multipoint Transmission

Content caching at the base stations (BSs) is a promising strategy that can provide improved quality-of-service (QoS) provisioning for content-centric services, and at the same time reduce instantaneous backhaul payload. This paper focuses on the applications of the caching mechanism in the downlink of coordinated multipoint (CoMP) transmission, where the collaborating BSs cooperatively serve the user equipments (UEs). A cache-aided transmission scheme for downlink CoMP with limited local cache resources at the BSs is proposed to improve QoS provisioning in terms of outage performance. In order to cache files more efficiently while guaranteeing the QoS, the contents are divided into two sets, a popular set and a less popular set, according to their popularity profile following the Zipf model. The popular files are cached at all the BSs, while the less popular files are cached only at part of the BSs in a cache cluster subject to the strategy design. Furthermore, based on the popularity of the requested files, UEs are categorized into two groups and the notion of request competition between the two groups is introduced. The corresponding request competition model and admission probabilities for transmission requests are analyzed. Based on the request competition model, the best cache placement strategy for the popular and less popular sets that minimizes the average outage probability is derived. Numerical results show that the proposed cache-aided CoMP scheme outperforms the baseline traditional caching strategies in terms of the average transmission outage.

Capacity Analysis of Joint Transmission CoMP With Adaptive Modulation

Joint transmission (JT)-based Coordinated Multipoint (CoMP) systems achieve high performance gains by allowing full coordination among multiple cells, transforming unwanted intercell interference into useful signal power. In this paper, we present an analytical model to perform adaptive modulation for a typical JT CoMP system, consisting of three transmission points, under a target bit error rate (BER) constraint. Probability density functions of the signal-to-interference-plus-noise ratio (SINR) are derived for different JT CoMP schemes, and based on them, closed-form expressions for the average spectral efficiency (ASE) are obtained when adopting continuous-rate adaptive modulation. The study of ASE is also extended for the case of discrete-rate modulations, where the performance comparison of different practical quantized modulation schemes is carried out.

Coverage Performance of Joint Transmission for Moving Relay Enabled Cellular Networks in Dense Urban Scenarios

Communication plays a significant role in terms of providing connectivity for urban users as well as sensors in smart cities. It has been shown that better communication capability for vehicular users can be obtained by introducing moving relays (MRs). With MRs, it is possible for macro base stations and moving relays to serve non-vehicular macro-users by performing coordinated multipoint (CoMP) joint transmission (JT). A bias-based CoMP scheme for MR enabled cellular network is analyzed in this paper. Motivated by antenna design constraints, in this paper, we assume that the outdoor antenna system of the MR can only be used for the moving backhaul link, i.e., the in-vehicle antenna system is also serving the non-vehicular macro-users. Using the stochastic geometry approach, a tractable model of the network is proposed. Based on the proposed model, integral expressions for CoMP-JT probability and coverage probability of non-vehicular macro user equipment are derived. Simulations verify the accuracy of the derived expressions. The results show that the probability for macro user equipment to be served with CoMP-JT is up to 70% when the intensity of MRs is ten times that of MBSs. This paper also includes a performance comparison among the analyzed scheme and related works. CoMP-JT with MRs provides better coverage performance for nearby macro user equipment. It can be found that the coverage gain of CoMP increases when the intensity of MRs increases within a certain range. Simulation results provide insights for practical system design in smart cities, such as the optimal MR intensity and the feasibility for opening access of MRs to macro user equipment.

Performance Analysis of CoMP in Ultra-Dense Networks with Limited Backhaul Capacity

Coordinated multipoint (CoMP) transmission provides an effective way to mitigate inter-cell interference as well as improve network performance in ultra-dense networks (UDNs). However, applying coordination among access points (APs) requires high backhaul capacity (BC), which becomes a bottleneck for employing CoMP. Considering a downlink UDN with limited BC, this paper conducts performance analysis of two CoMP schemes including joint transmission (JT) and coordinated scheduling/beamforming (CS/CB) from three aspects: a typical user's perspective, a typical AP's perspective and a network perspective. Firstly, the coverage probability (CP) and ergodic capacity (EC) of a typical user are characterized. Secondly, per-AP backhaul consumption is explicitly quantified and the successful serving probability (SSP) of a typical AP is proposed to capture its robustness to limited BC. Additionally, we propound effective ergodic capacity (EEC) to consider performance gain and backhaul consumption simultaneously from a global perspective. Further, the approximated expressions of all the performance metrics are given so that the impact of cluster size and AP density can be overtly observed. Numerical results illustrate that JT outperforms CS/CB in the case of high BC threshold, small cluster size or high AP density and a comparative smaller size is preferable for both two schemes for practice.

D2D Enhanced Co-Ordinated Multipoint in Cloud Radio Access Networks

Coordinated multipoint (CoMP) is an efficient technique to increase cell-edge coverage probability and throughput in cloud radio access network (C-RAN). In this paper, we integrate device-to-device (D2D) communications with CoMP by applying a distance based mode selection rule for downlink users in C-RAN, exploiting the proximity of D2D communications to improve system spectral efficiency. Using stochastic geometry, we first derive the signal-to-interference ratio distribution at a typical downlink user and a typical D2D receiver when two types of CoMP schemes, namely, zero-forcing beamforming (ZFBF) and noncoherent joint transmission (NC-JT), are applied in C-RAN. In addition, we analytically compare ZFBF and NC-JT using rate coverage probability. Meanwhile, we analyze the effect of D2D communications on enhancing the area spectral efficiency (ASE) of CoMP enabled C-RAN system. Numerical results show that increasing the co-operative cluster size would potentially degrade the system ASE when the network is heavily loaded. Furthermore, it is observed that enabling D2D mode in C-RAN can effectively offload the traffic of C-RAN and provide significant ASE gains if mode selection threshold is properly designed. Lastly, it is analytically demonstrated that spectrum resources can be better exploited by D2D users if they coexist with ZFBF enabled radio units (RUs) rather than NC-JT enabled RUs.

On energy efficient design for dynamic CoMP transmission in K-tier heterogeneous cellular networks

Motivated by the objective of pursuing revenue, improvement in coverage and reduction in energy cost for wireless communication networks have been of great significance for mobile operators. Therefore, heterogeneous cellular networks (HCNs) and Coordinated Multipoint (CoMP) transmission are considered as promising solutions to enhance the performances of wireless communication systems. This paper analyzed the K-tier HCNs with a dynamic downlink CoMP scheme, in which the flexible clusters of cooperative stations are determined by a connecting threshold 0. Using stochastic geometry, the coverage probability (CP) and energy efficiency (EE) of a K-tier HCN operating under this scheme are derived, based on which the trade-off between CP and EE is discovered and discussed. Simulation results show the validity of our derivations. The proposed schememay significantly reduce energy consumption sacrificing a small amount of CP, and outperforms the fixed scheme as well. The CP-EE trade-off are also revealed, whichsuggests suitable trade-off points between CP and EE that will deliver the maximum economic profitability. Tendencies discovered in this paper may provide the operators with opportunities for further optimization in pursuit of economic profitability.