Wireless Communications

Driven by the visions of Internet of Things and 5G communications, recent years have seen a paradigm shift in mobile computing, from the centralized mobile cloud computing toward mobile edge computing (MEC). The main feature of MEC is to push mobile computing, network control and storage to the network edges (e.g., base stations and access points) so as to enable computation-intensive and latency-critical applications at the resource-limited mobile devices. MEC promises dramatic reduction in latency and mobile energy consumption, tackling the key challenges for materializing 5G vision. The promised gains of MEC have motivated extensive efforts in both academia and industry on developing the technology. A main thrust of MEC research is to seamlessly merge the two disciplines of wireless communications and mobile computing, resulting in a wide-range of new designs ranging from techniques for computation offloading to network architectures. This paper provides a comprehensive survey of the state-of-the-art MEC research with a focus on joint radio-and-computational resource management. We also discuss a set of issues, challenges, and future research directions for MEC research, including MEC system deployment, cache-enabled MEC, mobility management for MEC, green MEC, as well as privacy-aware MEC. Advancements in these directions will facilitate the transformation of MEC from theory to practice. Finally, we introduce recent standardization efforts on MEC as well as some typical MEC application scenarios.

A Survey on Mobile Edge Computing: The Communication Perspective

It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

The vision of next generation 5G wireless communications lies in providing very high data rates (typically of Gbps order), extremely low latency, manifold increase in base station capacity, and significant improvement in users’ perceived quality of service (QoS), compared to current 4G LTE networks. Ever increasing proliferation of smart devices, introduction of new emerging multimedia applications, together with an exponential rise in wireless data (multimedia) demand and usage is already creating a significant burden on existing cellular networks. 5G wireless systems, with improved data rates, capacity, latency, and QoS are expected to be the panacea of most of the current cellular networks’ problems. In this survey, we make an exhaustive review of wireless evolution toward 5G networks. We first discuss the new architectural changes associated with the radio access network (RAN) design, including air interfaces, smart antennas, cloud and heterogeneous RAN. Subsequently, we make an in-depth survey of underlying novel mm-wave physical layer technologies, encompassing new channel model estimation, directional antenna design, beamforming algorithms, and massive MIMO technologies. Next, the details of MAC layer protocols and multiplexing schemes needed to efficiently support this new physical layer are discussed. We also look into the killer applications, considered as the major driving force behind 5G. In order to understand the improved user experience, we provide highlights of new QoS, QoE, and SON features associated with the 5G evolution. For alleviating the increased network energy consumption and operating expenditure, we make a detail review on energy awareness and cost efficiency. As understanding the current status of 5G implementation is important for its eventual commercialization, we also discuss relevant field trials, drive tests, and simulation experiments. Finally, we point out major existing research issues and identify possible future research directions.

Next Generation 5G Wireless Networks: A Comprehensive Survey

The increasing demand of mobile Internet and the Internet of Things poses challenging requirements for 5G wireless communications, such as high spectral efficiency and massive connectivity. In this article, a promising technology, non-orthogonal multiple access (NOMA), is discussed, which can address some of these challenges for 5G. Different from conventional orthogonal multiple access technologies, NOMA can accommodate much more users via nonorthogonal resource allocation. We divide existing dominant NOMA schemes into two categories: power-domain multiplexing and code-domain multiplexing, and the corresponding schemes include power-domain NOMA, multiple access with low-density spreading, sparse code multiple access, multi-user shared access, pattern division multiple access, and so on. We discuss their principles, key features, and pros/cons, and then provide a comprehensive comparison of these solutions from the perspective of spectral efficiency, system performance, receiver complexity, and so on. In addition, challenges, opportunities, and future research trends for NOMA design are highlighted to provide some insight on the potential future work for researchers in this field. Finally, to leverage different multiple access schemes including both conventional OMA and new NOMA, we propose the concept of software defined multiple access (SoDeMA), which enables adaptive configuration of available multiple access schemes to support diverse services and applications in future 5G networks.

Non-orthogonal multiple access for 5G: solutions, challenges, opportunities, and future research trends

In this paper, a new multiuser detection scheme combining decorrelating detection and multicarrier transmission is proposed and analyzed in a frequency-selective Rayleigh fading channel. The bit error probability and asymptotic multiuser efficiency are derived and compared for the proposed and the conventional decorrelating detector scheme. From the numerical results, it is shown that the proposed scheme achieves better BER performance and lower computational complexity than the conventional decorrelating detector. It is also shown that the proposed scheme is more robust than the conventional scheme when there is partial narrowband interference, and alleviates near-far problem more effectively.

Performance of a multicarrier decorrelating multiuser receiver for a DS/CDMA system

Improving downlink CDMA capacity has been an area of intensive research for the past decade, especially as the downlink has become the capacity limiting link. Multi-antenna technologies are an obvious candidate for increasing the downlink capacity, but successfully decoding spatially multiplexed signals is very challenging in an interference-limited environment, such as that of CDMA cellular systems. In this paper, a simple and novel MIMO-CDMA system design is developed, in which users are assigned to a transmit antenna either without regard to channel knowledge (static) or based on antenna selection feedback bits (dynamic). These proposed antenna partitioning techniques have a minimal increase in complexity and require only small changes to existing CDMA standards. The outage probability and capacity of the proposed systems are derived and it is shown that they outperform conventional CDMA systems regardless of the number of antennas or antenna partitioning technique.

Antenna partitioning for multiuser MIMO-CDMA

This paper proposes a new strategy combining interference alignment (IA) and rate splitting for a three user interference channel with a cognitive transmitter. Although a half of available dimensions are sacrificed to align interference signals from other users in conventional IA, the proposed scheme recycles the sacrificed dimensions with the help of a cognitive transmitter. The achievable rate region and generalized degrees of freedom are derived. Compared with conventional IA, the proposed scheme improves achievable rate and generalized degrees of freedom.

Interference alignment with rate splitting in a three-user interference channel with a cognitive transmitter

The number of available worker nodes for distributed computing can be limited and varying in wireless networks with noisy channels. However, the conventional straggler mitigation schemes ensure perfect reconstruction only when the number of worker nodes is more than a predetermined number, called the recovery threshold. When the number of worker nodes is less than the recovery threshold, the conventional schemes show a poor reconstruction performance. To facilitate distributed computing in noisy channels, leveraging the tensor product representation and frame quantization theory, we propose a novel straggler mitigation scheme for distributed matrix multiplication. The proposed scheme offers a reasonable reconstruction performance even when the number of worker nodes is varying and limited. By analyzing the computation error, we figure out the conditions required for encoding and decoding frame design, which suggest using uniform tight frames for encoding and their Moore-Penrose inverse for decoding. The superiority of the proposed scheme to the conventional straggler mitigation schemes when the number of available worker nodes is limited is verified by simulations.

Distributed Matrix Multiplication Based on Frame Quantization for Straggler Mitigation

This paper considers the effect of variation of load resistance, as a function of the amount of charged energy in battery, in magnetic wireless power transfer. We calculate load resistance as a function of time, and show that load resistance increases as the receiver acquires energy over time. Unlike the previous studies that considered the resonance frequency of transmitter and receiver as a fixed value, so that it remains unchanged once it has been set, it is shown that the resonance frequency changes as load resistance varies. To avoid performance degradation due to the unmatched resonance frequencies between transmitter and receiver, we employ feedback from the receiver. Considering the cost of feedback, there is a trade-off between the number of feedbacks that the receiver sends and the collected energy at the receiver. For a point-to-point system model, the optimal feedback interval that maximizes the received energy is found. The numerical results show that the proposed protocol collect more energy compared to the conventional magnetic wireless power transfer systems.

Wan Choi

Papers

Performance of a multicarrier decorrelating multiuser receiver for a DS/CDMA system

Antenna partitioning for multiuser MIMO-CDMA

Interference alignment with rate splitting in a three-user interference channel with a cognitive transmitter

Distributed Matrix Multiplication Based on Frame Quantization for Straggler Mitigation

Maximizing Received Energy in Magnetic Resonance Wireless Power Transfer Using Feedback