Downlink Coordinated Multipoint Research Articles

On the Application of Quasi-Degradation to Network NOMA in Downlink CoMP Systems

The application of network non-orthogonal multiple access (N-NOMA) technique to coordinated multi-point (CoMP) systems has attracted significant attention due to its superior capability to improve connectivity and maintain reliable transmission for CoMP users simultaneously. Based on the concept of quasi-degraded channel for N-NOMA, this paper studies the precoding design for downlink N-NOMA scenarios with two base stations (BSs) equipped with multiple antennas. In specific, under quasi-degraded channels, simple linear precoding based N-NOMA can achieve the same minimal total transmission power as theoretically optimal but complicated dirty paper coding (DPC) scheme, when the users’ target rates and minimal transmission power of each BS are given. In this paper, the channel quasi-degradation (QD) condition is first rigorously derived for the scenario with single CoMP user and two NOMA users. The closed-form optimal precoders for N-NOMA under quasi-degraded channels are also provided. Then, based on QD condition, a novel hybrid N-NOMA (H-N-NOMA) scheme is proposed, which is a mixture of N-NOMA and conventional zero-forcing beamforming (ZFBF) scheme. Further, for the scenarios with more users, a low-complexity QD based user pairing (QDUP) algorithm is proposed, which is then combined with H-N-NOMA to make a novel scheme termed H-N-NOMA/QDUP into being. Numerical results are presented to reveal the impact factors on QD channels, and also demonstrate the superior performance of the proposed H-N-NOMA/QDUP scheme. It is shown that the proposed H-N-NOMA/QDUP scheme can effectively exploit the benefit of multi user diversity.

Stochastic Geometry Based Modeling and Analysis on Network NOMA in Downlink CoMP Systems

Stochastic Geometry Based Modeling and Analysis on Network NOMA in Downlink CoMP Systems

Performance Evaluation of Downlink Coordinated Multipoint Joint Transmission under Heavy IoT Traffic Load

Emerging 5G network cellular promotes key empowering techniques for pervasive IoT. Evolving 5G-IoT scenarios and basic services like reality augmented, high dense streaming of videos, unmanned vehicles, e-health, and intelligent environments services have a pervasive existence now. These services generate heavy loads and need high capacity, bandwidth, data rate, throughput, and low latency. Taking all these requirements into consideration, internet of things (IoT) networks have provided global transformation in the context of big data innovation and bring many problematic issues in terms of uplink and downlink (DL) connectivity and traffic load. These comprise coordinated multipoint processing (CoMP), carriers’ aggregation (CA), joint transmissions (JTs), massive multi-inputs multi-outputs (MIMO), machine-type communications, centralized radios access networks (CRAN), and many others. CoMP is one of the most significant technical enhancements added to release 11 that can be implemented in heterogonous networks implementation approaches and the homogenous networks’ topologies. However, in a massive 5G-IoT device scenario with heavy traffic load, most cell edge IoT users are severely suffering from intercell interference (ICI), where the users have poor signal, lower data rates, and limited QoS. This work is aimed at addressing this problematic issue by proposing two types of DL-JT-CoMP techniques in 5G-IoT that are compliant with release 18. Downlink JT-CoMP with two homogeneous network CoMP deployment scenarios is considered and evaluated. The scenarios used are IoT intrasite and intersite CoMP, which performance evaluated using downlink system-level simulator for long-term evolution-advanced (LTE-A) and 5G. Numerical simulation scenarios were results under high dense scenario—with IoT heavy traffic load which shows that intersite CoMP has better empirical cumulative distribution function (ECDF) of average UE throughput than intrasite CoMP approximately 4%, inter-site CoMP has better ECDF of average user entity (UE) spectral efficiency than intrasite CoMP almost 10%, and intersite CoMP has approximately same ECDF of average signal interference noise ratio (SINR) as intrasite CoMP and intersite CoMP has better fairness index than intrasite CoMP by 5%. The fairness index decreases when the users’ number increase since the competition among users is higher.

Study of Handover Techniques for 4G Network MIMO Systems

For the upcoming 4G systems, network multiple-input multiple-output (MIMO) and inter-cell interference coordination (ICIC) are two of key techniques adopted in 4G systems to mitigate the serious inter-cell interference (ICI) and improve coverage and cell-edge throughput. Network MIMO is referred to as coordinated multi-point (CoMP) in LTE-A. In this paper, we propose a simulation platform to analyze the handover issue for downlink CoMP transmissions in LTE-A cellular systems. Among the variety of ICIC strategies, we apply the widely adopted soft frequency reuse (SFR) and the fractional frequency reuse (FFR) schemes. Both schemes are based on the idea of applying a frequency reuse factor of one in cell-center areas, and a higher reuse factor in cell-edge areas. Therefore, the ICI is reduced at the expense of the available frequency resources for each cell.

Exploiting non‐orthogonal multiple access in downlink coordinated multipoint transmission with the presence of imperfect channel state information

SummaryIn this paper, the impact of imperfect channel state information (CSI) on a downlink coordinated multipoint (CoMP) transmission system with non‐orthogonal multiple access (NOMA) is investigated since perfect knowledge of a channel cannot be guaranteed in practice. Furthermore, the channel estimation error is applied to estimate the channel information wherein its a priori of variance is assumed to be known. The impact of the number of coordinated base stations (BSs) on downlink CoMP NOMA is investigated. Users are classified into one of two groups according to their position within the cell, namely, cell‐center user (CCU) and cell‐edge user (CEU). In this paper, ergodic capacity and sum capacity for both CCU and CEU are derived as closed forms. In addition, various experiments are conducted with different parameters such as SNR, error variance, and power allocation to show their impact on the CoMP method. The results show that CoMP NOMA outperforms the CoMP orthogonal multiple access (OMA) wherein the condition of the channel impacts the performance of CoMP NOMA less. It is worth noting that a higher number of coordinated BSs enhances the total capacity of CoMP NOMA. Finally, the performance analysis is validated due to the close accordance between the analytical and simulation results.

Intelligent User-Centric Networks: Learning-Based Downlink CoMP Region Breathing

In the presence of irregular transmission/reception point (TRP) topologies and non-uniform user distribution, the user-to-node association optimization is a rather challenging process in real user-centric networks, especially for the joint transmission aided coordinated multipoint (CoMP) technique. The grade of challenge further escalates, when taking the dynamic user scheduling process into account in order to enhance the system capacity attained. To tackle the above-mentioned problem, we holistically optimize the system by conceiving joint user scheduling and user-to-node association. Then, for the sake of striking a significantly better balance between the network capacity and coverage quality, we propose a generalized reinforcement learning assisted framework intrinsically amalgamated both with neural-fitted Q-iteration as well as with ensemble learning and transfer learning techniques. Consequently, a powerful policy can be found for dynamically adjusting the set of TRPs participating in the joint transmission, thus allowing the CoMP-region to breathe, depending on both the temporal and geographical distribution of the tele-traffic load across the network. To facilitate the prompt learning of the global policy supporting flexible scalability, the overall network optimization process is decoupled into multiple local optimization phases associated with a number of TRP clusters relying on iterative information exchange among them. Our simulation results show that the proposed scheme is capable of producing a policy achieving a network-edge throughput gain of up to 140%$ and a network capacity gain of up to 190% under the challenging scenario of having a non-uniform geographical UE distribution and bursty traffic.

User clustering and resource allocation in downlink CoMP with NOMA

In coordinated multipoint (CoMP) system, the cell-edge performance is improved by minimizing inter-cell interference (ICI) through coordination of resources. Additionally, the non-orthogonal multiple access (NOMA) has been introduced as a promising candidate to further enhance the throughput of next generation wireless communication systems. NOMA allows multiple users to access the wireless channel in the same bandwidth simultaneously, however at different transmit power. In joint transmission NOMA in CoMP (JT-NOMA-CoMP), multiple cells jointly transmit data to users using the same time-frequency resources, which significantly improves the system performance. In this paper, we present a low-complexity user clustering and resource allocation strategy in downlink JP-NOMA-CoMP system with multiple antenna. Based on computer simulation, we show that the proposed approach outperforms the conventional JP-OMA-CoMP and single antenna JP-NOMA-CoMP in terms of achievable sum rate.

Deep Learning in Downlink Coordinated Multipoint in New Radio Heterogeneous Networks

We propose a method to improve the performance of the downlink coordinated multipoint (DL CoMP) in heterogeneous fifth generation new radio (NR) networks. The standards-compliant method is based on the construction of a surrogate CoMP trigger function using deep learning. The cooperating set is a single-tier of sub-6 GHz heterogeneous base stations operating in the frequency division duplex mode (i.e., no channel reciprocity). This surrogate function enhances the downlink user throughput distribution through online learning of non-linear interactions of features and lower bias learning models. In simulation, the proposed method outperforms industry standards in a realistic and scalable heterogeneous cellular environment.

Enhancing User Fairness in NOMA for Downlink CoMP Networks

Enhancing User Fairness in NOMA for Downlink CoMP Networks

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.

QoS priority‐based coordinated scheduling and hybrid spectrum access for femtocells in dense cooperative 5G cellular networks

AbstractA third‐generation partnership project long‐term evolution system uses the concept of a 2‐tier heterogeneous network, where low‐power and short‐range femtocells are laid under macrocells to fulfill the quality of service (QoS) requirements of users and to boost overall network throughput. However, cochannel deployment gives rise to the problem of cross‐tier interference that significantly deteriorates the performance of the cellular network. The coordinated multipoint (CoMP) transmission scheme is proposed as a promising solution to alleviate cross‐tier interference by doing cooperation among the neighbor base stations. In this paper, we propose a QoS priority‐based coordinated scheduling and hybrid spectrum access (QoS‐CSaHSA) scheme for downlink CoMP transmission in 2‐tier networks. The proposed QoS‐CSaHSA scheme dynamically reduces the femtocells' power requirements by considering the neighbor cell interference, and it also balances the macrocell load by switching the femtocells to HA mode. Moreover, it can reduce unnecessary muting of the base stations because it only enables the coordinated scheduling CoMP when there is no other possibility to reduce the cross‐tier interference. System‐level simulation results prove the validity of the proposed QoS‐CSaHSA scheme in a heterogeneous network environment. Compared with the existing schemes that operate the femtocells in a closed‐subscriber group without considering users' QoS requirements, the proposed scheme almost doubles the cell‐edge user throughput and reduces the packet loss rate and call‐blocking probability.

Performance Analysis of Downlink Coordinated Multipoint Joint Transmission in Ultra-Dense Networks

Ultra-dense networks (UDNs) are one of the key enabling techniques for implementation of 5G wireless communication systems, and inter-cell interference is a major issue in UDNs. Coordinated Multipoint Joint Transmission (CoMP-JT) helps reduce inter-cell interferences. However, due to randomly and densely distributed access entities in UDNs, many challenging issues need to be dealt with to implement CoMP-JT in UDNs. In this article, we aim to address the issues on how to achieve maximal per area spectral efficiency in UDNs based on CoMP-JT technology. The performance of UDNs with different joint transmission schemes are evaluated with the help of computer simulations to show the effective deployment schemes of small cells.

Optimal Dynamic Point Selection for Power Minimization in Multiuser Downlink CoMP

This paper examines a coordinated multi-point transmission/reception system where multiple base-stations (BSs) employ coordinated beamforming to serve multiple mobile-stations (MSs). Under the dynamic point selection mode, each MS can be assigned to only one BS at any time. This paper then presents a solution framework to optimize the BS associations and coordinated beamformers for all MSs. With target signal-to-interference-plus-noise ratios at the MSs, the design objective is to minimize either the weighted sum transmit power or the per-BS transmit power margin. Since the original optimization problems contain binary variables indicating the BS associations, finding their optimal solutions is a challenging task. To circumvent this difficulty, we first relax the original problems into new optimization problems by expanding their constraint sets. Based on the nonconvex quadratic constrained quadratic programming framework, we show that these relaxed problems can be solved optimally. Interestingly, with the first design objective, the obtained solution from the relaxed problem is also optimal to the original problem. With the second design objective, a suboptimal solution to the original problem is then proposed, based on the obtained solution from the relaxed problem. Simulation results show that the resulting jointly optimal BS association and beamforming design significantly outperforms fixed BS association schemes.

Time-fluctuation error influence on downlink CoMP performance in mobile fronthaul

Time-fluctuation error influence on downlink CoMP performance in mobile fronthaul

Double Side Signal Splitting SWIPT for Downlink CoMP Transmissions With Capacity Limited Backhaul

This letter studies power allocation for simultaneous wireless information and power transfer in downlink coordinated multipoint (CoMP) systems. A central unit (CU) conveys data and channel information to multiple radio remote units (RRUs) via a capacity-limited backhaul. We provide a dual polarized (DP) antenna-based double side signal splitting method. Specifically, signals are split up into information decoding part [user equipment (UE) data transmitted from CU] and energy harvesting part (deterministic data created at RRUs), which are transmitted and received via vertical and horizontal polarizations of DP antennas, respectively. Normal beamformers (such as zero forcing and maximum ratio transmission) are used to reduce complexity. The problem is to maximize the sum rate satisfying per-UE received power, per-backhaul-link capacity, and per-RRU power transmission constraints. The results are provided to verify the effectiveness of the proposed scheme.

Precoding Design with Joint Dynamic Channel Assignment and Band Selection Techniques for Downlink CoMP OFDMA Systems

Multi cell transmission can prevent the multi-cell interference by localizing the signals at different sub-band for the downlink (DL) localized orthogonal frequency division multiple access (OFDMA) systems. However, the synchronized errors, such as carrier frequency offset (CFO), will induce the challenging problems of interference due to the non-orthogonality between the subcarriers and cells. In this paper, we propose the novel precoding design with joint dynamic channel assignment and band selection techniques for DL coordinated multipoint (CoMP) OFDMA systems with CFO effect. Further, a two-stage pre-processing technique is proposed to eliminate the above interference problems and reduce the computational complexity of the cell-edge users for DL CoMP OFDMA systems. Moreover, the central unit can assign the resource dynamically to enhance the link quality. Therefore, the dynamic channel on/off assignment techniques and the dynamic band selection techniques are proposed to enhance the bit error rate (BER) performance. Simulation results confirm that the proposed precoding transceiver provides excellent BER and lower computational complexity of the cell-edge communication than the conventional block diagonalization technique.

Dynamic Cooperative Base Station Selection Scheme for Downlink CoMP in LTE-Advanced Networks

Coordinated Multi-Point (CoMP) transmission is a technique proposed to enhance the spectral efficiency and system throughput in an interference limited cellular networks. In CoMP joint processing (JP) scheme multiple base stations (BSs) are coordinately transmit data streams to each user. As more than two base stations are involved, abundant spatial resources are exploited and more backhaul spectrum for JP cooperation is required. The backhaul architecture for CoMP JP is crucial to provide low latency, unlimited capacity, less power consumption, and perfect synchronization among the BSs. However, satisfying all these constraints is impossible as the number of cooperative BSs increases for each user. In this paper, a dynamic cooperative base station selection scheme is proposed to reduce the backhaul load for CoMP user by selecting the appropriate number of coordinated BSs from the CoMP cluster to ensure the certain quality of service (QoS). In particular, for cell edge user the number of cooperative BSs per user has been selected in order to achieve reduced overhead and the allocation of backhaul capacity is performed under the max---min fairness criterion. Simulation results show that the proposed selection scheme achieves significant performance improvement than other transmission modes in terms of the average sum rate per backhaul use and minimal total power consumption.

Proportional-Fair Resource Allocation for Coordinated Multi-Point Transmission in LTE-Advanced

Coordinated multi-point (CoMP) transmission and reception are introduced as a promising technology in the 3GPP LTE-advanced standard, to manage interference, improve the overall system performance, and enhance system reliability. In this paper, a resource allocation problem is studied for downlink CoMP coordinated beamforming systems, where each base station (BS) serves its own mobile stations. Multiple-input-multiple-output (MIMO) transmit precoding and resource allocation are linked to the underlying proportional-fair scheduling to ensure a good trade-off between cell-average and cell-edge user spectral-efficiency. Due to the coupled interference among mobile stations, the resulting proportional-fair resource allocation optimization problem becomes nonconvex. To solve for optimal operating point for MIMO CoMP network, a parallel successive convex approximation-based algorithm is introduced. The introduced scheme enables all BSs to update their optimization variables in parallel by solving a sequence of strongly convex subproblems. Closed-form expressions of the locally optimal solution in both the high and low signal-to-noise regimes are characterized. The performance of the introduced scheme is also investigated through simulations. Numerical results show the efficiency of the introduced algorithm.

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.

Downlink CoMP resource allocation based on limited backhaul capacity

Coordinated Multi-Point (CoMP) transmission is put forward in the Long Term Evolution-Advanced (LTE-A) system to improve both average and cell-edge throughput. In this paper, downlink CoMP (DL-CoMP) resource allocation scheme based on limited backhaul capacity is designed to take a tradeoff between system throughput and fairness. Resource allocation of proportional fairness based on querying table is proposed. It updates RB allocation matrix when center cell has completed resource allocation and delivers the matrix to adjacent cells for their own RB allocation. Furthermore, Water-Filling algorithm based on adaptive water level (AWF) is used for power allocation to boost system fairness. In this paper, performance of downlink CoMP based on limited backhaul capacity and single-point transmission is contrasted, and results indicate that CoMP dramatically enhances system throughput and spectral efficiency. Moreover, AWF power allocation scheme obtains higher system fairness than conventional Water-Filling (WF) algorithm, although it gets slightly lower system throughput. Finally, this paper discussed that the system performance is partially affected by the percentage of CoMP resource.