Coordinated Multipoint Networks Research Articles

Covert performance enhancement in NOMA enabled CoMP network with optimal RIS selection

In this paper, we consider the covert rate maximization problem for the cell edge user in a reconfigurable intelligent surface (RIS) aided downlink non-orthogonal multiple access (NOMA) network with coordinated multipoint (CoMP) transmission in the presence of channel estimation errors. We derive the analytical expression for the detection error probability (DEP) at the adversary (Willie) assuming the worst case scenario where they employ optimal detection threshold. With the derived analytical expression, we propose an optimal RIS selection scheme to boost the covert rate. To further improve the covert performance, we optimize the NOMA power allocation coefficients and phase shifts of the selected RIS subject to the target rate and covertness constraints. Simulation results demonstrate the improvement in covert rate and robustness offered by the proposed scheme in the presence of channel estimation errors over other benchmarks.

Energy and Delay Guaranteed Joint Beam and User Scheduling Policy in 5G CoMP Networks

Massive Multi-Input Multi-Output (MIMO) and Coordinated MultiPoint (CoMP) technologies in Cloud-RAN (C-RAN) architecture become inevitable trend due to the advent of next-generation mobile applications, which are traffic-intensive, such as ultra high definition (UHD) video. In this paper, we study a joint beam activation and user scheduling problem in a 5G cellular network with massive MIMO and CoMP utilizing orthogonal random beamforming technique. This paper aims to minimize total Remote Radio Heads’ (RRHs’) energy expenditure in a dynamic C-RAN architecture while ensuring finite service time for all user traffic arrivals in the communication coverage. We leverage Lyapunov drift-plus-penalty framework to transform an original long-term average problem into a series of per-slot modified problems. Since the provided per-slot problem is combinatorial and nonlinear optimization problem, we are inspired by a greedy algorithm to design energy and delay guaranteed joint beam activation and user scheduling policy, namely BEANS. We prove that the proposed BEANS ensures finite upper bounds of average RRH energy consumption and average queue backlogs for all traffic arrival rates within constant ratio of capacity region and all energy-delay tradeoff parameters. These proofs are the first attempt to theoretically demonstrate guarantees of energy and queue bounds in a framework consisting of possibly negative submodular objective function and non-matriod constraints. Finally, via extensive simulations, we compare the capacity region and energy-queue backlog tradeoff of BEANS with optimal and existing algorithms, and show that BEANS attains up to 65% of energy saving for the same average queue backlog compared to the algorithms which do not take traffic dynamics and energy consumption into considerations.

Generalized Coordinated Multipoint Framework for 5G and Beyond

The characteristic feature of 5G is the diversity of its services for different user needs. However, the requirements for these services are competing in nature, which impresses the necessity of a coordinated and flexible network architecture. Although coordinated multipoint (CoMP) systems were primarily proposed to improve the cell edge performance in 4G, their collaborative nature can be leveraged to support the diverse requirements and enabling technologies of 5G and beyond networks. To this end, we propose generalization of CoMP to a proactive and efficient resource utilization framework capable of supporting different user requirements such as reliability, latency, throughput, and security while considering network constraints. This article elaborates on the multiple aspects, inputs, and outputs of the generalized CoMP (GCoMP) framework. Apart from user requirements, the GCoMP decision mechanism also considers the CoMP scenario and network architecture to decide upon outputs such as CoMP technique or appropriate coordinating clusters. To enable easier understanding of the concept, popular use cases, such as vehicle-to-everything (V2X) communication and eHealth, are studied. Additionally, interesting challenges and open areas in GCoMP are discussed.

Performance Analysis of an Energy-Efficient Clustering Algorithm for Coordination Networks

The mechanism of Coordinated Multi-Point (CoMP) can improve the spectral efficiency of the 4G and 5G cellular network, and also can reduce transmitting power of base stations (BSs). However, CoMP requires a large amount of energy due to extra signal processing and backhaul traffic. In this paper, an energy-efficient algorithm based on optimal dynamic clustering mechanism (ODCEM) for CoMP networks is proposed, which aims to minimize the overall network energy consumption. In the ODCEM, cells are pre-ordered in descending order according to their traffic load increments. The cell with lowest load increment is selected to switch off. Then, users in selected cell are handed over to other neighboring cells if quality of service (QoS) for users can be guaranteed. After that, the selected cell is switched off to conserve network energy. The remaining cells in each CoMP cluster will be evaluated after the previous order is updated. The simulation results show that the energy efficiency of ODCEM schemes is significantly higher than that of fixed CoMP algorithm in terms of SINR and traffic loads. Furthermore, the ODCEM algorithm can achieve better energy efficiency with lower computational complexity according to the performance evaluation of user association and BS switching off.

Research on Grouping Methods in CoMP Networks

Coordinated multi-point (CoMP) networks are inter-cell cooperation mechanisms specifically proposed to enhance transmission of users at cell edge. Therefore, selection appropriate group of cells to provide better transmission service is an important research topic in CoMP networks. In this paper, we proposed two grouping methods in CoMP networks including: (1) the arriving user accesses the same empty channels of his best and second best link quality cells and (2) if there are no same empty channels from his best and second best link quality cells, allow the arriving user to access one of the empty channels from his best or second best link quality cells. Simulation Results show that the proposed model can effectively evaluate influences of system performance of these two grouping methods.

Optimization of 5G Virtual Cell Based Coordinated Multipoint Networks Using Deep Machine Learning

Providing seamless mobility and a uniform user experience, independent of location, is an important challenge for 5G wireless networks. The combination of Coordinated Multipoint (CoMP) networks and Virtual- Cells (VCs) are expected to play an important role in achieving high throughput independent of the mobile’s location by mitigating inter-cell interference and enhancing the cell-edge user throughput. Userspecific VCs will distinguish the physical cell from a broader area where the user can roam without the need for handoff, and may communicate with any Base Station (BS) in the VC area. However, this requires rapid decision making for the formation of VCs. In this paper, a novel algorithm based on a form of Recurrent Neural Networks (RNNs) called Gated Recurrent Units (GRUs) is used for predicting the triggering condition for forming VCs via enabling Coordinated Multipoint (CoMP) transmission. Simulation results, show that based on the sequences of Received Signal Strength (RSS) values of different mobile nodes used for training the RNN, the future RSS values from the closest three BSs can be accurately predicted using GRU, which is then used for making proactive decisions on enabling CoMP transmission and forming VCs.

On the Performance of Security-Based Nonorthogonal Multiple Access in Coordinated Multipoint Networks

The conventional nonorthogonal multiple access (NOMA) strategy has secrecy challenge in coordinated multipoint (CoMP) networks. Under the secrecy considerations, this paper focuses on the security-based NOMA system, which aims to improve the physical layer security issues of conventional NOMA in the coordinated multipoint (NOMA-CoMP) networks. The secrecy performance of S-NOMA in CoMP, that is, the secrecy sum-rate and the secrecy outage probability, is analysed. In contrast to the conventional NOMA (C-NOMA), the results show that the proposed S-NOMA outperforms C-NOMA in terms of the secrecy outage probability and security-based effective sum-rate.

On the Performance of a Multi-Tier NOMA Strategy in Coordinated Multi-Point Networks

Non-orthogonal multiple access (NOMA) is a promising multiple access technique for fifth-generation mobile networks. In this letter, a novel multi-tier NOMA (TNOMA) scheme is proposed for a coordinated multi-point (CoMP) network. This TNOMA scheme aims to improve the coverage of high data rate services in a CoMP network, especially for the case when access points are not able to serve all of the users in the network. To bench-mark the TNOMA scheme against one-tier NOMA-CoMP, the effective sum-rate performances are evaluated. The results show that the performance difference between one-tier only NOMA-CoMP and multi-tier NOMA-CoMP is influenced by the transmission-nodes-selection threshold value ( $\epsilon _{k}$ ) and the target data rate.

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 the Performance of Opportunistic NOMA in Downlink CoMP Networks

In this letter, an opportunistic NOMA (ONOMA) scheme is proposed in a coordinated multipoint (CoMP) system. Compared with the conventional joint-transmission (JT) NOMA in CoMP, the main purpose of the ONOMA scheme is to advance the capability of the CoMP system and the effectiveness of the successive-interference-cancellation (SIC) decoding process. The relationship between the topology of the ONOMA cells and the sum-rate of CoMP network is analyzed. Meanwhile, the outage probability of ONOMA system is derived and evaluated in an ideal case and nonideal case, respectively. In the numerical results, the sum-rate and the outage performance of the proposed ONOMA CoMP are compared with the JT-NOMA CoMP and it is shown that the proposed ONOMA scheme outperforms the conventional JT-NOMA scheme in CoMP system.

Joint transmission in cellular networks with CoMP—Stability and scheduling algorithms

Due to the current trend towards smaller cells, an increasing number of users of cellular networks reside at the edge between two cells; these users typically receive poor service as a result of the relatively weak signal and strong interference. Coordinated Multi-Point (CoMP) with Joint Transmission (JT) is a cellular networking technique allowing multiple Base Stations (BSs) to jointly transmit to a single user. This improves the users’ reception quality and facilitates better service to cell-edge users. We consider a CoMP-enabled network, comprised of multiple BSs interconnected via a backhaul network. We formulate the OFDMA Joint Scheduling (OJS) problem of determining a subframe schedule and deciding if and how to use JT in order to maximize some utility function. We show that the OJS problem is NP-hard. We develop optimal and approximation algorithms for specific and general topologies, respectively. We consider a time dimension and study a queueing model with packet arrivals in which the service rates for each subframe are obtained by solving the OJS problem. We prove that when the problem is formulated with a specific utility function and solved optimally in each subframe, the resulting scheduling policy is throughput-optimal. Via extensive simulations we show that the bulk of the gains from CoMP with JT can be achieved with low capacity backhaul. Moreover, our algorithms distribute the network resources evenly, increasing the inter-cell users’ throughput at only a slight cost to the intra-cell users. This is the first step towards a rigorous, network-level understanding of the impact of cross-layer scheduling algorithms on CoMP networks.

SINR Evaluation for Improved Practical Coordinated Multi-point Clustering

Coordinated multipoint (CoMP) networks cooperatively process user equipment (UE) to eliminate inter-cell interference. CoMP networks convert the interfering signals into useful information by controlling the interference among adjacent cells. This is important for UE at the cell edge. This paper examines deployment of CoMP networks and investigates how CoMP communications can enhance the signal-to-interference and noise ratio (SINR) in practical inter-site and intra-site networks. In addition, we propose weighted clustering according to the average number of active users in the sector. Priority in forming clusters is given to sectors with more users. This reduces the error caused by the uniform UEs distribution assumption used by many researchers. We consider real city topography, terrain data, and UEs distribution to evaluate the received power and estimate the SINR improvement in real CoMP networks.

Feedback Generation for CoMP Transmission in Unsynchronized Networks with Timing Offset

Coordinated multipoint (CoMP) transmission is a promising technique in long term evolution (LTE) systems to provide coverage and broadband communication for cell edge user equipments (UEs). However, as signals from multiple transmitters may reach the UE at different times, CoMP networks might experience high time offsets, leading to significant performance loss in closed-loop transmission. In this paper we show that spacing between reference signals (RSs) imposes a phase offset on the transmit covariance matrix in presence of timing offset (TO), affecting the feedback generation. The promised advantages of closed-loop CoMP transmission vanish in presence of TO due to improper precoding matrix index (PMI) selection. Keeping the phase shift close to zero, reliable PMI selection can be guaranteed and as a result near optimum performance is achieved for closed-loop CoMP transmission in unsynchronized networks with TO present.

A Multi-Cell Coordinated Scheduling Algorithm Based on Delta-CQI for CoMP Network Systems

In the coordinated scheduling/beamforming of coordinated multi-point (CoMP) systems, a multi-cell coordinated scheduling algorithm is proposed for inter-cell interference coordination and cell-edge users’ throughput enhancement. The concept of Delta-CQI is introduced to indicate the interference level experienced by users in one cell when the users in adjacent cells of the cooperation region using different precoding vectors. Adjacent base stations exchange the information of Delta-CQI which is fed back from the users in each cell and calculate the weighted interference factor, then the user scheduling is performed by the multiple cells in the cooperative cell set along with the priority factor given by the proportional fairness scheduling algorithm used in each cell. The proposed multi-cell coordinated scheduling algorithm considers the user interference among different cells to improve the data rate of users in cell edge, which gives a good tradeoff between system fairness and spectrum efficiency. Beside that, the overhead of the control information exchange among coordinated cells are reduced by the Delta-CQI feedback and exchange.

Coordinated Multipoint Transmission with Limited Backhaul Data Transfer

When the joint processing technique is applied in the coordinated multipoint (CoMP) downlink transmission, the user data for each mobile station needs to be shared among multiple base stations (BSs) via backhaul. If the number of users is large, this data exchange can lead to a huge backhaul signaling overhead. In this paper, we consider a multi-cell CoMP network with multi-antenna BSs and single antenna users. The problem that involves the joint design of transmit beamformers and user data allocation at BSs to minimize the backhaul user data transfer is addressed, which is subject to given quality-of-service and per-BS power constraints. We show that this problem can be cast into an \ell_0-norm minimization problem, which is NP-hard. \changedv{Inspired by recent results in compressive sensing, we propose two algorithms to tackle it. The first algorithm is based on reweighted \ell_1-norm minimization, which solves a series of convex \ell_1-norm minimization problems. In the second algorithm, we first solve the \ell_2-norm relaxation of the joint clustering and beamforming problem and then iteratively remove the links that correspond to the smallest transmit power. The second algorithm enjoys a faster solution speed and can also be implemented in a semi-distributed manner under certain assumptions.} Simulations show that both algorithms can significantly reduce the user data transfer in the backhaul.

A Utility-Based Joint Resource Allocation Approach for Multi-Service in CoMP Networks

Coordinated multi-point (CoMP) joint transmission is considered as a key technique to mitigate inter-cell interference and improve the cell-edge performance in 3GPP LTE-Advanced. In this paper, a utility-based joint resource allocation approach is proposed to support CoMP joint transmission in orthogonal frequency division multiple access systems. Two different utility functions are considered with diverse quality of service provisioning. The objective is to maximize the sum utility of a clustered CoMP network, considering mixed real-time voice over IP (VoIP) and best-effort (BE) traffic patterns. A centralized joint resource allocation algorithm is proposed by decoupling the optimization problem into per-subchannel subproblems. Further more, a greedy user selection based low-complexity algorithm is proposed for practical implementation. For the sake of performance comparison, the proportional-fair based joint scheduling, as well as two non-coordinated scheduling schemes are also evaluated. Via system-level simulation we show that the proposed algorithms not only substantially improve the cell-edge spectrum efficiency of BE users, but also significantly decrease the packet drop ratio and call outage ratio of VoIP users.

Busy Burst Enabled Coordinated Multipoint Network with Decentralized Control

A novel decentralized coordinated multipoint (CoMP) technique facilitated by receiver feedback is proposed. If multiple base stations (BSs) access the same radio resource; downlink transmissions from one BS cause co-channel interference (CCI) towards towards users served by neighboring BSs. To mitigate CCI in a multiple-input-multiple-output (MIMO) network, the mobile station (MS) scheduled in a tagged cell (i.e. the active user) emits a busy burst (BB) on a time-multiplexed feedback slot, applying the precoder used earlier for receiving data. Prior to transmission a neighboring BS must scan the feedback slot using the spatial precoder(s) intended for data transmission. Consequently, in a time division duplex (TDD) system the channels of the data and the feedback slots become reciprocal. Therefore, by listening to the feedback slot, a neighboring BS can predetermine the CCI potentially imposed towards the active user for each of its available precoders. This information enables the BS to select spatial precoders autonomously so that CCI is limited to a predetermined threshold. Simulation results demonstrate that the proposed technique achieves 20% increase in spectral efficiency, 6-fold increase in cell-edge user throughput, and 40% reduction in transmitted energy, compared to transmit beamforming without interference coordination.