In this contribution we derive a union bound of the bit error ratio (BER) in wireless multiple input multiple output (MIMO) data transmission systems using maximum likelihood (ML) receivers. A novel channel model is used to take into account channel correlation. Relying on the Euclidean distance between different transmit signals, we show that the error performance is governed by a few so-called error types (ET). Simulation results are shown for a 4x4 MIMO system with BPSK modulation and for a 2x2 MIMO system with 16QAM modulation for several channel correlations. Our union bound becomes tight for low BER for all MIMO systems under investigation.

Recently many space-time coding schemes for multiple antenna systems (MIMO) have been proposed in order to achieve high data rates when transmitting over wireless channels. However, most of such schemes rely on maximum likelihood (ML) detection, which can become quite complex when many antennas are involved and higher modulation schemes are utilized. On the other hand, the high diversity gains of MIMO channels are easily lost when low-complexity receivers like ZF or MMSE are applied. It is thus of utmost importance to look for low-complexity receivers which achieve almost ML performance. In this paper, a new scheme for approximate ML detection for typical flat Rayleigh fading channels is proposed, achieving ML performance in the area of bit error ratio between 10/sup -4/ and 0.1 as it is of interest in wireless communications. The proposed scheme allows the transmission of 64QAM schemes on 4/spl times/4 antenna schemes with a detection complexity of only 1% of a brute force ML receiver.

In this paper we present a family of quasi-orthogonal space-time codes for correlated MIMO (multi-input/multi-output) channels using four and eight transmit antennas when only partial channel state information is sent back to the transmitter. Transmit diversity is improved up to nearly the optimum diversity value. This high diversity can be exploited with zero forcing receivers as well as with maximum-likelihood receivers.

We propose an adaptive modulation scheme for wireless MIMO systems. The main goal of this scheme is to maximize the bit rate for a fixed target BER. The MIMO channel is split up into several independent channels (subspaces) by a singular value decomposition. On each of these independent channels, the modulation format is adapted to the subchannel SNR. The proposed algorithm allocates appropriate modulation schemes from 2PSK to 256QAM to each subchannel. The channel is assumed to be quasi static flat Rayleigh fading, perfectly known at both ends of the link. Mean data rates that can be obtained are presented as a function of the mean SNR, keeping BER below a target value of, e.g., 10/sup -3/ for spatially uncorrelated and partially correlated channels without using any error correcting code.

Image coding using the discrete wavelet transform can attain very good results compared to traditional methods. In fact, most of the best known results for image coding have been related to the DWT. A simple scheme to code the DWT coefficients is the embedded zero-tree wavelet algorithm by Shapiro (1993). The embedded zero-tree wavelet can exploit both the similarity among subbands and the sparseness of the subbands. We propose a new simple image coder based on the DWT. The DWT coefficients are coded in bitplanes. Each bi-level pixel is coded in a context formed by its parental and surrounding pixels. In this way, both the similarity and the sparseness among subbands are exploited. We show the experimental results, both in terms of distortion measurement and visual comparison, and compare them to well-known methods.

A new pseudo-random generator for decimal numbers is presented. A sequence of decimal digits is obtained by combining a binary and a quinary maximal-length sequence generated by feedback shift-register circuits. The autocorrelation sequence (ACS) of the resulting decimal sequence is calculated; it shows that linear dependencies are extremely small. Finally, guidelines are developed for choosing feedback polynomials which yield low cross correlation between various sequences of decimal digits.