Massive multiple-input-multiple-output (MIMO) systems use few hundred antennas to simultaneously serve large number of wireless broadband terminals. It has been incorporated into standards like long term evolution (LTE) and IEEE802.11 (Wi-Fi). Basically, the more the antennas, the better shall be the performance. Massive MIMO systems envision accurate beamforming and decoding with simpler and possibly linear algorithms. However, efficient signal processing techniques have to be used at both ends to overcome the signaling overhead complexity. There are few fundamental issues about massive MIMO networks that need to be better understood before their successful deployment. In this paper, we present a detailed review of massive MIMO homogeneous, and heterogeneous systems, highlighting key system components, pros, cons, and research directions. In addition, we emphasize the advantage of employing millimeter wave (mmWave) frequency in the beamforming, and precoding operations in single, and multi-tier massive MIMO systems.

https://www.mdpi.com/2079-9292/6/3/63/pdf

Massive MIMO Wireless Networks: An Overview

Heterogeneous network deployment is considered to be among the most promising approaches to meet the demand for increasing communication capacity. The concept is that of increasing the number of cells while reducing their size to provide different layers of coverage. This paper proposes a coordinated method to face the interlayer and intralayer interference caused by the overlapping of heterogeneous cells. The aim is to exploit the benefits of both enhanced intercell interference coordination (eICIC) and coordinated multipoint (CoMP) approaches and to limit, at the same time, their drawbacks by means of their optimized joint use. The idea devised here is to build an ad hoc CoMP system on top of a basic eICIC mechanism. Therefore, the analysis focuses on the dynamic selection of users and cells involved in CoMP operations, with the goal of minimizing the unfulfilled data rate requests (UDRRs). Due to the computational complexity of the optimal solution, we propose a heuristic procedure and validate its accuracy by providing a comparison with the optimal numerical solution. In particular, our results show that the proposed method outperforms other benchmark solutions in terms of UDRRs and signaling overhead.

An Optimized CoMP Transmission for a Heterogeneous Network Using eICIC Approach

Time-domain enhanced inter-cell interference coordination (eICIC) is an effective technique to reduce the cross-tier inter-cell interference (ICI) in long term evolution (LTE)-based heterogeneous small cell networks (HetSCNs). This paper first clarifies two main communication scenarios in HetSCNs, i.e., macrocells deployed with femtocells (macro-femto) and with picocells (macro-pico). Then, the main challenges in HetSCNs, particularly the severe cross-tier ICI in macro-femto caused by femtocells with closed subscribe group (CSG) access or in macro-pico caused by picocells with range expansion are analyzed. Based on the prominent feature of dominant interference in HetSCNs, the main idea of time-domain interference coordination and two basic schemes in the eICIC standardization, i.e., almost blank subframe (ABS) and orthogonal frequency division multiplexing symbol shift are presented, with a systematic introduction to the interactions of these techniques with other network functions. Then, given macro-femto and macro-pico HetSCNs, an overview is provided on the advanced designs of ABS-based eICIC, including self-optimized designs with regard to key parameters such as ABS muting ratio, and joint optimized designs of ABS-based eICIC and other radio resource management techniques, such as user association and power control. Finally, the open issues and future research directions are discussed.

Time-domain ICIC and optimized designs for 5G and beyond: a survey

Heterogeneous networks (HetNets) are intended to offer wide area coverage and high data rate transmission by deploying small cells besides macrocells. Device-to-device (D2D) communication as an underlay of cellular network enriches local service and offloads base station. In this paper, we target the video transmission demanded by picocell edge users (PEUEs), who suffer from low quality channel due to the inter-cell interference from macrocell and long physical distance from picocell. Moreover, the wireless channels are burst-loss prone for upper layer applications such as video on demand (VoD), which makes the traditional channel coding such as forward error correction (FEC) insufficient. In this paper, we address these issues and propose a cooperative video transmission scheme to improve PEUEs' received video quality by constructing two transmission paths from picocell to each PEUE. The two transmission paths are the direct transmission from pico-eNB (i.e., base station) to PEUE and a relay-assisted path by means of D2D communication for frame recovery, respectively. Reference frame selection and unequal error protection are adopted to further improve the overall performance. Extensive simulations are conducted and results demonstrate that the proposed scheme outperforms state-of-the-art scheme in Config.4b scenarios defined by 3GPP.

Device-to-device assisted video frame recovery for picocell edge users in heterogeneous networks

Heterogeneous networks (HetNets) are intended to offer wide area coverage and high data rate transmission by deploying small cells besides macrocells. One way to improve the system throughput is intercell interference coordination. The coordination methods in literature use the system throughput as the only selection criteria without considering each user's data rate requirement and investigate the intercell interference only during the period when small cell's edge users are served. In this paper, we propose an algorithm to maximize the users' data rate satisfaction ratio in HetNet leveraging on the two existing intercell interference coordination schemes ABS and CoMP. Intensive simulations are conducted and the results demonstrate that our proposed scheme achieves considerable gains over competing schemes in terms of the data rate satisfaction ratio and the system capacity in Config.4b scenarios defined by 3GPP.

Intercell Interference Coordination under Data Rate Requirement Constraint in LTE-Advanced Heterogeneous Networks

As one of the key technical challenges in long term evolution (LTE)-Advanced heterogeneous networks (HetNets) is intercell interference coordination, many different schemes, such as coordinated multipoint (CoMP) and almost blank subframe (ABS) schemes, have been proposed in this field. Different cells are pushed to cooperate to eliminate intercell interference in CoMP coordinated beamforming, but performance is heavily dependent on the quality of channels. ABS schemes allow highpower cells to transmit almost blank subframes, and avoid interference with low-power cell edge users, which will in turn result in reduced high-power cell throughput as cost. An adaptive ABS-CoMP scheme in an LTE-Advanced HetNet is proposed, which combines both the ABS and CoMP coordinated beamforming schemes to eliminate intercell interference, and adaptive transmits signals in different ways. It is assumed to improve system throughput and mitigate signaling overhead and computational complexity. The results from simulations demonstrated that the proposed scheme outperformed the ABS and CoMP schemes, and achieved considerable system throughput gains in Config.4b scenarios defined by 3GPP.

An adaptive ABS-CoMP scheme in LTE-Advanced heterogeneous networks

We present an improved beamforming method based on the signal-to-leakage-and-noise ratio (SLNR) for downlink multi-user multi-stream MIMO systems in this paper, which further take into account the co-channel interference. The simulation results demonstrate that the proposed method outperforms the original SLNR criterion and achieves considerable gains in BER performance.

Wei Luo

Papers

An adaptive ABS-CoMP scheme in LTE-Advanced heterogeneous networks

An Improved Beamforming Method Based on SLNR for Downlink Multi-user Multi-stream MIMO System