Coordinated Multipoint Research Articles

Green energy driven cellular networks with JT CoMP technique

Concerns about global warming and increasing number of base stations (BSs) leading to rising energy consumption have prompted extensive research effort focusing on energy efficiency (EE) issue for cellular networks. As a result, cellular operators are increasingly deploying renewable energy (RE) sources in BSs as a promising way to reduce the on-grid consumption and operational expenditure. In this paper, we propose a novel framework on green energy driven cellular networks aiming to maximize the utilization of the green energy and minimize the grid energy consumption considering stochastic traffic demand profile. Each BS is equipped with renewable energy generators, such as solar panel along with a set of batteries as an energy storage device and also connected to commercial grid supply. In addition, joint transmission (JT) coordinated multi-point (CoMP) transmission technique is integrated with the proposed model for selecting the best serving BSs for a user equipment (UE). The prime goal is to quantify the EE of various selection schemes namely, distance based, SINR based and SINR–distance based JT CoMP techniques under the proposed network model. Provision of sleep mode approach in BSs is also considered. A thorough investigation in the downlink of LTE-Advanced (LTE-A) cellular system is carried out for evaluating EE performance of the proposed framework under a wide range of network settings. Numerical results validate the proposed network models demonstrating a considerable enhancement in network EE compared to other counterparts.

Coordinated beamforming for heterogeneous small‐cell networks with a non‐ideal backhaul

In this article, intra- and inter-cell interference caused by the non-ideal backhaul in coordinated multipoint (CoMP) are studied. A recursive estimation-based zero-forcing beamforming (RE-ZFBF) scheme is proposed to mitigate the interference. Based on an initial value, the RE-ZFBF scheme recursively approximates the beamformer variation between two consecutive time points by exploiting the temporal channel correlation. In contrast to a previous work, the authors convert the original non-convex constraint quality-of-service problem to an unconstrained convex one, by optimising the estimation of the beamformer error, rather than the beamforming power. It is shown that the proposed scheme can mitigate at most half the intra- and inter-cell interference, enhance the ZFBF performance, and outperform the existing works for CoMP with a non-ideal backhaul in heterogeneous small-cell networks.

User-Centric Multi-RATs Coordination for 5G Heterogeneous Ultra-Dense Networks

This column reviews the concept of user-centric access, which permits the network to tailor a “follow me” virtual cell for a user via multipoint coordination in a UDN environment. We further discuss the feasibility of extending such a virtual cell by considering tight integration of heterogeneous RATs exposed to the user, by taking the context information and instantaneous status of the user device into account. In particular, we conceive an edge/fog computing platform capable of acquiring and jointly processing information from multiple heterogeneous RATs and the users. Such a framework may have great potential to play key roles in 5G and beyond, in terms of realizing truly flexible radio access that can be customized for each individual user in the network.

NASH: Navigation-Assisted Seamless Handover Scheme for Smart Car in Ultradense Networks

In the vehicular network, the smart car provides variously network services via user equipment (UE). However, the services might be interrupted since the handover procedure of the UE is performed frequently. The existing handover decision schemes in cellular networks are mostly based on received signal strength (RSS) to make the handover decision. However, these schemes suffer from a ping-pong effect and, as a result, perform unnecessary handovers incurring extra signaling overhead and packet loss, which is even more exaggerated in the ultra-dense environment. The failure probability of the handover procedure will increase when the velocity of the car is fast. Therefore, in this paper we propose a navigation-assisted seamless handover (NASH) scheme for reducing unnecessary handovers and the ping-pong effect. NASH uses the massive Multiple Input Multiple Output (MIMO) technique to perform the bicasting scheme and then it utilizes coordination multi-point (CoMP) and carrier aggregation (CA) mechanisms in the handover procedure to avoid the packet loss problem and enhance throughput. Moreover, a dynamic time to trigger (TTT) mechanism is proposed according to the velocity of the car. The simulation results show that the proposed scheme has a better performance in terms of handover latency, packet loss, network throughput, handover failure probability, and the number of unnecessary handovers.

Joint virtual edge-clustering and spectrum allocation scheme for uplink interference mitigation in C-RAN

Fractional Frequency Reuse (FFR) and Coordinated MultiPoint (CoMP) processing are two of the conventional methods to mitigate the Inter-Cell Interference (ICI) and to improve the average Signal-to-Interference-plus-Noise Ratio (SINR). However, FFR is associated with low system spectral efficiency and CoMP does not take any action to mitigate the inter-cluster interference. In this article, we study the challenges and problems of the current interference management techniques and explain why the clustering and spectrum allocation must be studied jointly. Then, in the context of Cloud Radio Access Network (C-RAN), we propose a joint virtual clustering and spectrum allocation scheme, called Cloud-CFFR, to address such problems. With respect to both FFR and CoMP, Cloud-CFFR decreases the complexity, delay, and ICI while increasing the system spectral efficiency. Since the system performance in cell-edge regions relies on the cooperation of different Virtual Base Stations (VBSs), there is no service interruption in handling handovers; moreover, in order to address the unanticipated change in capacity demand, a flexible spectrum management technique is proposed which dynamically changes the subband boundaries based on the number of active users in the clusters. Simulation results confirm the validity of our analysis and show the benefits of this novel uplink solution compared to the traditional schemes.

Performance analysis of capacity based Coordinated Multipoint (CoMP) handover scheme in Long Term Evaluation-Advanced (LTE-A) network

Coordinated Multipoint (CoMP) has been chosen in Release 11 as the best technique to improve both cell coverage and quality. However, the issue regarding the saturation on the system throughput in highly congested network leads to the system capacity overload. Thus, the existing CoMP handover scheme in LTE-A is not accommodating the conditions of the CoMP technique available. A capacity based CoMP handover scheme is proposed for better system capacity management. In CoMP, the coordination schemes are well developed in conjunction to improve overall quality for the user using MATLAB software. Performance analysis results show that capacity based CoMP handover scheme provides better Signal-to-Interference-plus-Noise Ratio (SINR) and reduces the number of unnecessary handover causes better handover performance.

Resource Allocation for CoMP in Cellular Networks With Base Station Sleeping

Base station sleeping (BSS) can result in significant reduction in energy consumption of cellular networks during low traffic conditions. We show that the coverage loss due to BSS can be compensated via coordinated multi-point (CoMP) -based transmission in a cluster of base stations. For a BSS with CoMP-based system, we propose various BSS patterns to achieve suitable trade-offs between energy savings and throughput. We formulate the CoMP resource allocation and $\alpha -$ Fair user scheduling as a joint optimization problem. We derive the optimal time fraction and user scheduling for this problem and use it to formulate a simplified BSS with CoMP optimization problem. A heuristic that solves this problem is presented. Through extensive simulations, we show that suitable trade-offs among energy, coverage, and rate can be achieved by appropriately selecting the BSS pattern, CoMP cluster, and rate threshold.

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.

Overview of CoMP Clustering in UDN

System throughput and resource utilization can be improved in ultra-dense networks (UDN) by deploying a large number of small base stations. However, base stations are very close in UDN, which will cause serious interference between base stations. To solve this problem, coordinated multi-point (CoMP) has been improved, which has the ability to reduce inter-cell interference and to improve data rate. However, the complexity of cooperation among all cells is very high. Therefore, it is necessary to construct small-size cooperation clusters. This article analyzes one of the key challenges of CoMP application in UDN—optimal CoMP clustering. Firstly, the background knowledge of CoMP is introduced. Secondly, we focus on the classification and summarization of the latest achievements in clustering research and the objective and challenges faced in the design of CoMP clusters. Finally, the future research directions and potential methods of CoMP clustering are discussed.

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.

A Technique for Cloud Based Clustering and Spatial Resource Reuse and Scheduling of 3D In-Building Small Cells Using CoMP for High Capacity CRAN

In this paper, we propose a technique for cloud coordinated clustering and scheduling of small cells, i.e., femtocells, in CRAN to improve capacity and spectral efficiency in 3D in-building environments. Control-and user-plane of each cell is decoupled. The clustering technique consists of two levels of clustering such that level 1 clustering defines an initial 3D femtocell cluster size. Level 2 clustering defines a cooperating set of femtocells per floor within each level 1 cluster to explore joint transmission coordinated multipoint (CoMP) during off-states of their transmit power. Femtocells are split at the MAC layer, and a mechanism is presented to model the bandwidth and latency fronthaul constraints. We derive the system level aggregate capacity, spectral efficiency, and energy efficiency. We then develop a heuristic algorithm and discuss its scheduler implementation. With numerical and simulation results, we show with an example scenario that the proposed technique can achieve the maximum CoMP capacity gain of 44% per building and 32.15% in overall system level. Finally, we demonstrate that the proposed technique can achieve the performance requirements of 5G cellular systems and point out the significance and further research issues.

Performance Analysis of Dynamic Re-Clustering and Resource Allocation in Ultra Dense Network

Coordinated multi-point (CoMP) is a key technology to mitigate inter-cell interference, which can significantly improve the cell edge performance and system throughput. In addition, the choice of the cells within cluster will directly affect the effect of CoMP, and especially, it may cause the increase of the number of dissatisfied users in the system. To minimize dissatisfied users in the ultra-dense network (UDN) application scenario, based on the control-data separation architecture model, a clustering algorithm is studied to improve the SINR and throughout. Then, load balancing is developed and the overall percentage of unsatisfied users are reduced obviously. Furthermore, a dynamic resource allocation scheme is proposed by defining a factor $\alpha $ and applied to optimize the performance of system, which is compared with load balancing under the conditions of a different clustered size and density of users. The experiments prove that the performance of load balancing is more sensitive to the change of clustered size than resource allocation, and the load balancing has overwhelming advantage compared with resource allocation in the dense deployment scenario. However, when the density of users becomes sparser, resource allocation performs better, which gives important meanings for future UDN.

A novel benefit-tree based dynamic clustering algorithm of comp in dense network

We focus here on the Energy Efficiency (EE), and propose an improved dynamic clustering algorithm that is incorporated into Coordinated MultiPoint (CoMP) with sleeping mode. Thanks to the frame structure of Benefit-tree employed in dynamic clustering of CoMP, the proposed algorithm can significantly improve the EE by choosing the most energy efficient competitive clustering strategy. At the same time, it can save energy by sleeping the underutilized base stations in the cellular network. In the performance simulation for EE, the proposed algorithm provides 10% higher in EE than the existing algorithm.

Mobility analysis of CoMP-based ultra-dense networks with stochastic geometry methods

This paper conducts mobility analysis in Coordinated multipoint (CoMP) based ultra-dense networks (UDNs) where channel state information (CSI) is outdated due to feedback delay. To depict the impac...

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.

Multiple carrier frequency offsets and multipath channels estimation for coordinated multi-point FBMC systems

Filter bank multicarrier (FBMC) systems are active candidates for the physical layer of the fifth generation of wireless communication networks (5G). The combination of FBMC system with the coordinated multipoint (CoMP) has been proposed to improve the performance of mobile terminals (MT) located at the cell edge. Accurate estimation of carrier frequency offset (CFO) and channel has great importance in communication systems. In this paper, a data-aided joint maximum likelihood (ML) CFO and channel estimation is proposed for the downlink of CoMP. Notably choosing the proper training sequences from Hadamard matrix for different base stations (BSs) reduces the complexity of estimator. Additionally joint CFO correction and channel equalization has been studied at the MT. Finally, we evaluate the efficacy of the presented algorithms using simulation.

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.

Optimal scheduling of coordinated multipoint transmissions in cellular networks

SummaryIn this paper, we study the optimal scheduling problem in coordinated multipoint (CoMP) transmission–based cellular networks. We consider joint transmission and coordinated scheduling together in CoMP transmission–based cellular networks and develop an optimization framework to compute the optimal max‐min throughput and the optimal scheduling of the transmissions to the users. The optimization problem is found to be a complex linear program with number of variables in for a cellular network of N users and K cells. We solve the optimization problem for several network instances using an optimization tool. The numerical results show that the optimal CoMP transmission provides a significant throughput gain over a traditional transmission. We find that in optimal scheduling the fraction time of coordinated scheduling is higher than that of joint transmission. To solve the optimization problem without any optimization tool, we propose a heuristic algorithm. The performance of the heuristic algorithm is evaluated and found to be provided throughput around 97% of the optimal throughput. Further, we extend the optimization framework to study joint scheduling and power allocation (JSPA) problem in CoMP transmission–based cellular networks. We numerically solve the JSPA problem for the network instances and demonstrate that the optimal power allocation at the base stations is not binary for a significant fraction of time of scheduling. However, the gain in max‐min throughput by the optimal JSPA technique over the optimal scheduling technique is not significant.

Affinity Propagation Based CoMP Clusters for Dense Small Cell Networks with Backhaul Constraints

Dense small cells have been considered as a promising solution for improving system throughput in 5G networks. When a large number of small cells are overlapped, serious inter-cell interference (ICI) becomes one of the major technical challenges. Coordinated multi-point (CoMP) is an effective technology to mitigate ICI. In this paper, we study affinity propagation based CoMP cluster for dense small cell networks with backhaul constrains. The graph based static clusters and affinity propagation based clusters are formed so as to achieve good performance and reduce complexity. By taking into account the hybrid CoMP mode, the optimal problem which maximizes the system throughput with the limit-capacity backhaul has been formulated. An effective hybrid CoMP cluster strategy is gained by solving the optimal problem. The simulation results demonstrate that the proposed scheme could enhance average throughput.

Molecular recognition by multiple metal coordination inside wavy-stacked macrocycles

Most biological and synthetic receptors for small organic molecules employ a combination of relatively weak intermolecular interactions such as hydrogen bonds. A host compound that utilizes stronger yet reversible bonding in a synergistic manner could realize precise recognition, but the regulation and spatial arrangement of such reactive interaction moieties have been a challenge. Here, we show a multinuclear zinc complex synthesized from a macrocyclic ligand hexapap, which inwardly arranges labile metal coordination sites for external molecules. The metallomacrocycle forms a unique wavy-stacked structure upon binding a suitable length of dicarboxylic acids via multipoint coordination bonding. The saddle-shaped deformation and dimerization realize the differentiation of the interaction moieties, and change of guest-binding modes at specific metal coordination sites among the many present have been achieved utilizing acid/base as external stimuli.