A simple correlated channel model for ultrawideband (UWB) multiple-antenna systems is proposed. The authors show that a single numerical value of the spatial correlation coefficient is sufficient to accurately model the performance of UWB spatial multiplexing systems in an indoor environment. The appropriate value of the correlation coefficient is selected by ensuring a close match between the bit error rate results achieved on the proposed correlated channel and those on the measured indoor channel. The authors also experimentally confirm that the performance substantially degrades in the presence of high values of spatial correlation for a range of spatial multiplexing receivers, and quantify the relationship between this degradation and the value of the spatial correlation coefficient. Thus, a route for the development of the existing standards for singleantenna UWB channels to the multiple-antenna regime is provided here.

Cooperation among network nodes provides transmit diversity in cases where wireless transmitters, due to size and power limitation, cannot support multiple antennas. We consider cooperation among A4 nodes, where each node achieves space diversity by using other nodes' antennas as relays. Cooperation among nodes has been shown to achieve impressive bit error rate (BER) gains as compared to a noncooperative system while maintaining the same information rate, transmit power, and bandwidth [I, 2,3,4]. Firstly, this paper formulates an optimum, centralised power allocation scheme appropriate for a cooperative network that employs transparent relaying. It will be shown that the proposed allocation scheme significantly outperforms the equal power allocation scheme, e.g., by up io 5 dB for a 3-user case at a bit error rate of Secondly, this paper proposes a distributed power aIlocation scheme where each node independently calculates its power allocation factors, and it will be shown that it converges to the optimum allocation yielded by the centralised approach. Finally, this paper presents a distributed power allocation algorithm to optimise the BER performance of cooperative networks only with partial knowledge of the channel state information (CSI) of the non-adjacent nodes.

Abstract-Orthogonal Frequency Division Multiplexing (OFDM) significantly reduces receiver complexity in wireless broadband systems and therefore has recently been proposed for use in wireless broadband multi-antenna (MIMO) systems. The performance of maximum likelihood detector in MIMO-OFDM system is optimal, however, its complexity, especially with higher order constellation is prohibitive. A number of other detectors, both linear and non-linear, may offer substantially lower complexity, however, their performance is significantly lower. This paper proposes a class of lattice-reduction-aided (LRA) receivers for MIMO-OFDM systems that can achieve near maximum likelihood detector performance with low complexity. Performance comparisons between LRA receiver and other popular receivers, including linear receivers and V-BLAST in both independent and correlated channels, are provided. It will be shown that the performance of LRA receiver is superior as compared to other sub-optimal detection methods, especially when the channel is correlated.

In this paper, a number of ultrawideband (UWB) multiple-input multiple-output (MIMO) spatial multiplexing systems are presented and their error performance is analysed. For both model-based and measured UWB channels, the performance of various MIMO detectors is evaluated under the multiband orthogonal frequency division multiplexing (MB-OFDM) regime. Contrary to expectation, the results demonstrate that significant spatial diversity can be extracted, in addition to linear data-rate scaling, despite the large frequency diversity inherent in the UWB channel. It is shown that nonlinear detection schemes with reasonable complexity can provide considerable diversity gain, in contrast to well-known linear receivers. Thus, the proposed UWB spatial multiplexing schemes not only increase the data rate but also provide significant diversity gain and improved error rate performance.