Honglin Hu

Relay technologies for WiMax and LTE-advanced mobile systems

Relay technologies have been actively studied and considered in the standardization process of next-generation mobile broadband communication systems such as 3GPP LTE-Advanced, IEEE 802.16j, and IEEE 802.16m. This article first introduces and compares different relay types in LTE-Advanced and WiMAX standards. Simulation results show that relay technologies can effectively improve service coverage and system throughput. Three relay transmission schemes are then summarized and evaluated in terms of transmission efficiency under different radio channel conditions. Finally, a centralized pairing scheme and a distributed pairing scheme are developed for effective relay selection. Simulation results show that the proposed schemes can maximize the number of served UE units and the overall throughput of a cell in a realistic multiple-RS-multiple-UE scenario.

Wireless mesh networking : architectures, protocols and standards

ARCHITECTURES Wireless Mesh Networks: Issues and Solutions MultiRadio MultiChannel Mesh Networks IEEE 802.11-Based Wireless Mesh Networks PROTOCOLS Routing in Wireless Mesh Networks Medium Access Control in Wireless Mesh Networks Security in Wireless Mesh Networks Scalability in Wireless Mesh Networks Load Balancing in Wireless Mesh Networks Cross-Layer Optimization for Scheduling in Wireless Mesh Networks Multimedia Communications over Wireless Mesh Networks Multiple Antenna Techniques for Wireless Mesh Networks STANDARDIZATION AND ENABLING TECHNOLOGIES Standardization of Wireless LAN Mesh Networks in IEEE 802.11s IEEE 802.16 WiMAX Mesh Networking Cognitive Radio and Dynamic Spectrum Management Wireless Mesh Networks Case Study: Fire Emergency Management and Market Analysis Wireless Mesh Networks for Public Safety and Disaster Recovery Applications INDEX

Self-configuration and self-optimization for LTE networks

With the rapid growth of mobile communications, deployment and maintenance of cellular mobile networks are becoming more and more complex, time consuming, and expensive. In order to meet the requirements of network operators and service providers, the telecommunication industry and international standardization bodies have recently paid intensive attention to the research and development of self-organizing networks. In this article we first introduce both the market and technological perspectives for SONs. Then we focus on the self-configuration procedure and illustrate a self-booting mechanism for a newly added evolved NodeB without a dedicated backhaul interface. Finally, mobility load balancing as one of the most important selfoptimization issues for Long Term Evolution networks is discussed, and a distributed MLB algorithm with low handover cost is proposed and evaluated.

Intracluster Device-to-Device Relay Algorithm With Optimal Resource Utilization

Device-to-device (D2D) communications help improve the performance of wireless multicast services in cellular networks via cooperative retransmissions among multicast recipients within a cluster. Resource utilization efficiency should be taken into account in the design of D2D communication systems. To maximize resource efficiency of D2D retransmissions, there is a tradeoff between multichannel diversity and multicast gain. In this paper, by analyzing the relationship between the number of relays and minimal time-frequency resource cost on retransmissions, we derive a closed-form probability density function (pdf) for an optimal number of D2D relays. Motivated by the analysis, we then propose an intracluster D2D retransmission scheme with optimized resource utilization, which can adaptively select the number of cooperative relays performing multicast retransmissions and give an iterative subcluster partition algorithm to enhance retransmission throughput. Exploiting both multichannel diversity and multicast gain, the proposed scheme achieves a significant gain in terms of resource utilization if compared with its counterparts with a fixed number of relays.

Distributed Antenna Systems: Open Architecture for Future Wireless Communications

This chapter presents a survey of information theoretic results available on DAS in cellular systems. The treatment focuses on the derivation of the sum-rate of different inter-cell and intra-cell communications strategies for both uplink and downlink. A simple symmetric family of cellular models in which the inter-cell interferences are emerging from a the adjacent cells only is considered. Although hardly realistic, this family of models accounts for essential parameters of cellular systems such as inter-cell interference and fading. Whenever computation of the sum-rate is intractable or yields little insight into the problem, asymptotic performance criteria (e.g. extreme-SNR parameters) are evaluated. Emphasis is placed on the assessment of benefits of cooperation among APs (i.e. joint detection/precoding).The rapid growth in mobile communications has led to an increasing demand for wideband high data rate communications services. In recent years, the Distributed Antenna System (DAS) has emerged as a promising candidate beyond 3G and 4G mobile communications. Distributed Antenna Systems: Open Architecture for Future Wireless Communications is a comprehensive technical guide that covers the fundamental concepts, recent advances and open issues of the DAS. The topic is explored with various key challenges in diverse scenarios, including architecture, capacity, connectivity, scalability, medium access control, scheduling, dynamic channel assignment and cross-layer optimization. The primary focus of this book is the introduction of concepts, effective protocols, system integration, performance analysis techniques, simulations and experiments, and more importantly, future research directions in the DAS. The first part of the book introduces DAS fundamentals, including channel models and theoretical issues, examining the capacity of the DAS with different structures. Concentrating on the MAC and protocols for the DAS, the second part of the book includes information on distributed signal processing, optimal resource allocation, cooperative MAC protocols, cross layer design, and distributed organization. The third part presents case studies and applications of the DAS, including experiment, RF engineering, and applications.

Double proportional fair user pairing algorithm for uplink virtual MIMO systems

In this letter, we study the user pairing algorithms for uplink virtual multiple-input multiple-output (V-MIMO) systems, and propose a new double proportional fair (D-PF) algorithm for user pairing of the uplink V-MIMO systems. The proposed D-PF algorithm uses the PF criterion to decide the first user, and a modified PF criterion is suggested to choose the pairing user. Simulation results show that the proposed D- PF algorithm outperforms the conventional determinant formula (DF) algorithm in terms of both throughput and fairness performances. Moreover, if compared with the conventional single PF (S-PF) algorithm, the proposed D-PF algorithm achieves a fairly good trade-off between the throughput and fairness, being able to trade with 5% throughput loss for 15% fairness enhancement.

Mobile cellular networks and wireless sensor networks: toward convergence

In recent years, machine-to-machine (M2M) communications, which do not need direct interactions from human beings, are booming to meet the fast-increasing requirements of datacentric wireless services and applications. Mobile cellular networks (MCN) and wireless sensor networks (WSN) are evolving from heterogeneous networks to converged networks, in order to support M2M communications. In this article, we investigate and discuss key technical challenges and opportunities for the convergence of MCN and WSN. We propose that the mobile terminals in MCN act as both sensor nodes and gateways for WSN in the converged networks. We evaluated the performance gain, and our simulation results show that better system performance, in terms of throughput, delay, and network lifetime, can be achieved in WSN by using interactive optimization with MCN.

An efficient random access scheme for OFDMA systems with implicit message transmission

Random access channel (RACH) is usually used for initial channel access, bandwidth request, etc. In this paper, we analyze the throughput and access delay performance of the RACH in an orthogonal frequency division multiple access (OFDMA) system. A closed-form expression of the RACH throughput is presented and its mean access delays under both binary exponential and uniform backoff policies have also been derived. Moreover, to further improve the utilization of RACH in an OFDMA system, we propose a novel message transmission scheme in a shared RACH. The message in the proposed scheme can be sent implicitly in the cyclic-shifted preambles which make the transmission much more reliable in a contention based RACH. Meanwhile, performance of the preamble detection has also been improved by the redundant information conveyed in messages. Finally, simulation results will demonstrate performance gains of the proposed scheme.

Null Space-Based Precoding Scheme for Secondary Transmission in a Cognitive Radio MIMO System Using Second-Order Statistics

In this paper, we propose a null space-based precoding scheme for secondary transmission in a cognitive radio multiple-input multiple-output (CR-MIMO) network under the assumption that time-division-duplex is employed by the primary transmission. First, the secondary transmitter periodically senses the transmitted signals from the primary users and estimates the corresponding covariance matrix. Then, subspace techniques are utilized to estimate the noise subspace of this covariance matrix, and the dimension of the noise subspace is estimated using information theory criteria (AIC or MDL). Finally, the obtained null space is used as the precoding matrix for the secondary transmission, which effectively avoids the interference induced by the secondary transmission at the primary users. Moreover, the achievable capacity of the secondary MIMO channel by the proposed scheme is derived. Simulations are performed to show the efficacy of the proposed scheme.

Energy-Efficient Coordinated Scheduling Mechanism for Cellular Communication Systems with Multiple Component Carriers

The energy consumption in radio access network is expected to increase significantly as the network expends to fulfill the explosively growing data traffics. However, when evaluating the energy saving mechanisms, the impact on other performance metrics such as spectral efficiency, should also be taken into account. In this paper, based on the multiple component carrier (CC) feature specified in Long Term Evolution-Advanced (LTE-A) systems, an energy-efficient coordinated scheduling mechanism is proposed to reduce the energy consumption in cellular networks by dynamically switching off CCs and base stations (BS) according to load variations, with special attention on the switching off order and BS transmit power adjustment to maintain service continuity of downlink users. Both the energy and spectral efficiency of the system under the proposed scheduling mechanism are analyzed. Simulation results show that when data traffics are below a quarter of the system capacity, with the proposed scheme more than half of the network power consumption can be saved, while the requirements for user data rate, service continuity, network coverage and spectral efficiency are guaranteed.