Bertrand Muquet

MIMO Link Adaptation in Mobile WiMAX Systems

Mobile WiMAX systems are based on the IEEE 802.16e specifications, which include two mandatory MIMO profiles for the downlink. One of these is Alamoutis space-time code (STC) for transmit diversity, and the other is a 2times2 spatial multiplexing MIMO scheme. In this paper, we compare the two schemes assuming that the latter employs maximum-likelihood detection. The analysis shows that at the same spectral efficiency, Alamoutis STC combined with maximum-ratio combining (MRC) at the receiver significantly outperforms the 2times2 spatial multiplexing scheme at high values of the signal-to-noise ratio (SNR). Next, selection of a MIMO option is included in link adaptation to maximize network capacity, and operating SNR regions are determined for different modulation, coding and MIMO combinations.

Diversity, interference cancellation and spatial multiplexing in MIMO mobile WiMAX systems

Multiple input multiple output (MIMO) techniques are an essential part of the IEEE 802.16e-2005 specifications, which form the basis of mobile WiMAX systems. In this paper, we first discuss the tradeoffs between diversity, interference cancellation and spatial multiplexing in MIMO systems, and we compare optimum combining (OC), maximum-ratio combining (MRC) and interference cancellation for different numbers of receive antennas. Then, we focus on the two mandatory MIMO profiles in the IEEE specifications (Alamoutis STC and the 2x2 spatial multiplexing scheme) and compare them when the first is combined with MRC at the receiver. The analysis obtained using the ITU pedestrian B channel in ideal conditions indicates that the two schemes lead to similar performance when they are operated at the same spectral efficiency

Chapter 8 – WiMAX Implementation

Publisher Summary This chapter focuses on the schemes from current and future IEEE 802.16 specifications. It describes the schemes existing in current IEEE 802.16e specifications and discusses briefly the solutions proposed for IEEE 802.16m. It provides the benefits of UL-MIMO together with a new method, namely, tile-switched diversity (TSD), which benefits from transmit diversity without any channel knowledge at the transmitter side. UL-MIMO techniques are introduced in the standards to provide additional gains on the uplink link budget compared to single transmit antenna schemes. In addition to the STC based on Alamouti scheme, the current WiMAX specifications include CDD as the transparent UL transmission technique. Although this technique does not require specific detection mechanism at the base station, it suffers from performance loss in specific channels like near line of side ones. In this contribution, this chapter presents an alternative transparent transmission technique, which has similar performance to CDD in channel conditions where CDD is thought to perform well and does not suffer from performance loss as CDD in specific channel conditions. Moreover, it studies the effect of second transmit antenna in the front-end design and shows that it possible to realize second transmission path in mobile stations with a small cost increase.