In this paper, we develop a framework for user association in infrastructure-based wireless networks, specifically focused on flow-level cell load balancing under spatially inhomogeneous traffic distributions. Our work encompasses several different user association policies: rate-optimal, throughput-optimal, delay-optimal, and load-equalizing, which we collectively denote α-optimal user association. We prove that the optimal load vector ρ*that minimizes a generalized system performance function is the fixed point of a certain mapping. Based on this mapping, we propose and analyze an iterative distributed user association policy that adapts to spatial traffic loads and converges to a globally optimal allocation. We then address admission control policies for the case where the system is overloaded. For an appropriate system-level cost function, the optimal admission control policy blocks all flows at cells edges. However, providing a minimum level of connectivity to all spatial locations might be desirable. To this end, a location-dependent random blocking and user association policy are proposed.

Relay is one of the key features being considered for IMT-Advanced systems. The relay architectures defined in IEEE 802.16m and 3GPP LTE-Advanced are optimized only for non-mobile relay, i.e., the Relay Station is attached to a designated Base Station and becomes a part of the fixed access network. A mobile relay architecture, where relay may switch attached BS according to operation demand, will promise more resilient relay deployment. In this paper, we first highlight three use cases where mobile relays can offer useful deployment options. Next, we propose an enhanced handover mechanism for relay-based group mobility by extending the IEEE 802.16m specification on relay. To this end, we describe the handover architecture for mobile relay highlighting the C-plane and U-plane enhancements required in order to support group mobility of mobile stations. Using illustration and comparisons, we show that mobile relay will offer significant benefits of signaling overhead reduction and provide users seamless mobility experience compared to fixed relays.

In this study, the authors consider the benefits of mobile terminals (MTs) with different access points (APs) for uplink and downlink transmission to conserve MTs’ energy. In traditional cellular networks, an MT is typically associated with a single AP. However, as wireless networks evolve, heterogeneous and/or overlay deployment scenario become viable and an MT can be associated with different APs for uplink and downlink transmission. The authors call this ‘dual APs association’. The authors show that allowing dual APs association provides a significant gain on the uplink system capacity and/or the uplink transmit power savings. As a specific example of the use of dual APs, the authors focus on relay networks and show that considering the relay cost further increases the benefits of this approach. Based on extensive simulations using IEEE 802.16m relay network Evaluation Methodology, the authors demonstrate that dual APs can improve the uplink harmonic capacity by 350% or reduce the uplink transmit power by 7 dB. The authors note, however, that there exists a signalling cost in implementing dual APs association, which needs be overcome to achieve these substantial performance improvements.

Since mobile devices are equipped with limited battery power, it is essential to have efficient power management mechanisms in mobile broadband networks such as mobile WiMAX that enable always on connectivity and provide high throughputs. In recent times Voice over IP (VoIP) has emerged as an important and dominant application in broadband mobile networks such as WiMAX. VoIP traffic is uniquely characterized by small packets sent regularly at periodic intervals and are bound by strict latency requirements for satisfactory user experience. This paper presents novel mechanisms to achieve enhanced power saving during a VoIP session by exploiting unique characteristics of VoIP traffic in next generation mobile WiMAX networks based on IEEE 802.16m standard. The analytical model and simulation results indicate that proposed methods reduce the average power consumption during a VoIP call by up to 70% compared to the existing IEEE 802.16m draft specifications. Moreover, the simulation results closely match our proposed analytical model.

WiMAX technology, based on IEEE 802.16 standard, is a promising broadband wireless technology for future 4G network. WiMAX provides radio access with centralized control, where bandwidth resources are managed and allocated by base station (BS) for both uplink (UL) and downlink (DL). Current WiMAX standard defines several bandwidth request (BWReq) mechanisms to serve a variety of applications, which however may not be efficient for on-off bursty traffic patterns. In this paper, we propose a novel adaptive polling service (aPS), with the advantage of significantly reducing the signaling overhead associated with the bandwidth request process without compromising the delay performance of real-time applications. Extensive simulations demonstrate that aPS outperforms existing scheduling services in terms of overall efficiency for a wide range of applications.

Video broadcast and mobile TV have received significant interests from both academia and industry recently. The emerging mobile WiMAX (802.16e) is capable of providing high data rate and flexible quality of service (QoS) mechanisms, making the support of mobile TV very attractive. However, how to efficiently deliver video broadcast over WiMAX is not straightforward, especially in the multi-BS mode. The multi-BS mode requires multiple BSs to be synchronized in the transmission of common multicast/broadcast data. In this paper, we first identify the key design issues for video broadcast over WiMAX in the multi-BS mode. Then, we present an end-to-end solution which fully addresses key issues such as synchronization, energy efficiency and robust video quality. Moreover, we propose a methodology to optimize the coverage, the spectrum efficiency and the video quality. Results show that our proposed scheme can significantly improve the coverage and spectrum efficiency while satisfying video quality requirements.

This paper presents survivability mechanisms that attempt to improve the overall restoration efficiency of dynamic link restoration in optical WDM mesh networks. The proposed mechanisms make use of network state information such as link load in order to identify critical network sections (such as links or segments) that are subsequently protected by selectively assigning backup capacity ahead of failures. The first approach, termed "threshold based selective link restoration", utilizes existing link load information to identify critical links, and the second approach, termed "threshold based selective segment restoration", employs data-analysis techniques to identify critical segments. The overall goal of the proposed algorithms is to improve the restoration efficiency by providing a trade-off between proactive protection and reactive restoration. The experimental results indicate that under high loads, the proposed approaches maintain a consistent restoration efficiency that is at least 10% when compared to dynamic restoration.