Saturday, May 14, 2011

Relay-Assisted Mobile WiMAX

There are two major technological and social trends significantly changing people’s lives: wireless communications and the Internet. Leveraging these two trends, worldwide interoperability for microwave access (WiMAX) creates a new utility enabling the development of new services and new Internet business models. In particular, the full potential of WiMAX will be realized when it is used for innovative nomadic and mobile broadband applications. With the finalization of the IEEE 802.16e standard and upcoming test and certification of WiMAX products, mobile broadband services are becoming a reality. The 802.16e standard provides broadband wireless Internet Protocol (IP) access to support a variety of services (such as voice, data, and multimedia) on virtually any device. The operation of WiMAX is currently limited to a number of licensed frequency bands below 6 GHz for reliably supporting non-line-of-sight (NLoS) operations. The 802.16e standard has also become a part of the IMT-2000 family.
WiMAX is often quoted as combining long transmission ranges (e.g., in a macrocell) with high data capacities (multi megabit per second throughput to end users). Power and spectral efficiency is key to a successful WiMAX deployment. The mobile WiMAX physical (PHY) layer is based on scalable orthogonal frequency division multiple access (SOFDMA) technology, which enables flexible channelization. The new technologies employed by mobile WiMAX result in higher data transfer rates, simpler mobility management, and lower infrastructure costs compared to current 3G systems. The underlying scenario for mobile WiMAX is an outdoor environment with multiple users within a cell. Hence scheduling (allowing a fair and efficient distribution of resources) and interference (from intracell and intercell) become important issues.
Radio relaying can address many of the challenges faced in the deployment of mobile WiMAX and its potential benefits. The relay system targets one of the biggest challenges in next generation mobile wireless access (MWA), namely the provision of high data rate coverage in a cost-effective and ubiquitous manner. Within a multihop relay network, a multihop link can be formed between the base station (BS) and a distant mobile station (MS) using a number of intermediate relay stations (RS). To avoid interference between the relay links, the simplest approach is to assign unique radio resources to each link. Using this approach, the multihop users will rapidly drain the system of valuable radio resource. The wireless medium is a precious infrastructure commodity and the situation is especially acute at lower frequencies (where the radio signal propagation characteristics are more favorable) when a significant amount of radio spectrum is needed to provide ubiquitous wireless broadband connectivity. Spectrum predictions for future cellular networks indicate large shortfalls by 2010, if not before. Hence the above approach can only be used for a very small number of very high-value MSs, or in applications where spectral efficiency is not vital, such as military or disaster relief communication networks. Given its commercial applications, relaying in the context of WiMAX must conserve radio spectrum and emphasize the need for high spectral efficiency. Enhancing radio resource efficiency is a key challenge in a competitive business development.
We focuses on the efficiency of relay transmission. We present leading edge techniques, and merge both theoretical analysis and practical application for a mobile WiMAX system with multihop relay. Directional distributed relaying is then proposed to achieve high data throughput with reduced demands on radio resource.
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