In this paper, the effect of spatial diversity on the throughput and reliability of wireless networks is examined. Spatial diversity is realized through multiple independently fading transmit/receive antenna paths in single-user communication and through independently fading links in multiuser communication. Adopting spatial diversity as a central theme, we start by studying its information-theoretic foundations, then we illustrate its benefits across the physical (signal transmission/coding and receiver signal processing) and networking (resource allocation, routing, and applications) layers. Throughout the paper, we discuss engineering intuition and tradeoffs, emphasizing the strong interactions between the various network functionalities.

We consider turbo-trellis-coded transmission over fading multiple-input-multiple-output (MIMO) channels with transmit diversity using space-time block codes. We give a new view on space-time block codes as a transformation of the fading MIMO channel towards a Gaussian single-input-single-output (SISO) channel and provide analytical results on the BER of space-time block codes. Furthermore, we describe the concatenation of Turbo-TCM with a space-time block code and show that in addition to the transmit diversity substantial benets can be obtained by turbo iterations as long as the channel is time-varying during transmission of a coded block or frequency hopping is applied. Finally, a double iterative scheme for turbo equalization and turbo decoding of the concatenation of Turbo-TCM and space-time block code in frequency-selective MIMO channels is described. Keywords Turbo-TCM, Turbo equalization, Space-Time Codes, Transmit Diversity. I.

We give an introduction to wireless systems with multiple transmit and receive antennas. Using multiple antenna systems is motivated by results on the capacity of multiple-input-multipleoutput (MIMO) channels. We describe different approaches to exploit these capacities like Bell Labs Layered Space-Time Architecture (BLAST), which we append by FEC coding and turbo processing, and transmit antenna diversity using space-time codes. The focus of the paper is on space-time codes. We describe the diversity effect of space-time trellis codes and space-time block codes using equivalent channel models and discuss if the MIMO channel capacity can be fully exploited using those techniques.

We present space-time turbo equalization methods for complex trellis coded modulation (TCM) signals transmitted over broadband wireless channels, which is characterized by severe multipath fading. The multipath fading channel, protected by a TCM encoder/decoder pair, is described as a convolutional encoder and the received signal is viewed as the output of a serially concatenated coding system. It is wellknown that in the narrowband transmission case, the equivalent encoder model for the channel can be represented by reasonable complexity and optimum symbol detection is achieved by iterative equalization/decoding schemes where soft-information is shared between the constituent decoders. However, for fixed wireless systems operating at high data rates, the multipath delay spread becomes large which makes direct application of trellis based equalization methods impossible.

This paper presents a space-time turbo (iterative) equalization method for TCM signals over broadband wireless channels. For fixed wireless systems operating at high data rates, the multipath delay spread becomes large, making it impossible to apply trellis based equalization methods. The equalizer proposed here consists of a broadband beamformer which processes antenna array measurements to shorten the observed channel impulse response, followed by a conventional scalar turbo equalizer. Since the applicability of trellis based equalizers is limited to additive white noise channels, the beamformer is required to preserve the whiteness of the noise at its output. This constraint is equivalent to requiring that the FIR beamforming filters must have a power complementarity property. The power complementarity property imposes non-negative definite quadratic constraints on the beamforming filters, so the beamformer design is expressed as a constrained quadratic optimization problem. The composite channel impulse response at the beamformer output is shortened significantly, making it possible to use a turbo equalizer for the joint equalization and decoding of trellis modulated signals. The proposed receiver structure is simulated for two dimensional TCM signals such as 8-PSK and 16-QAM and the results indicate that the use of antenna arrays with only two or three elements allows a large decrease in the channel SNR needed to achieve a 10-4 bit error rate.