Diversity Analysis for Frequency-Selective MlMO-OFDM Systems With General Spatial and Temporal Correlation Model

Abstract

In the low signal-to-noise ratio regime, the performance of concatenated coding schemes is limited by the convergence properties of the iterative decoder. Idealizing the model of iterative decoding by an indepen- dence assumption, which represents the case in which the codeword length is infinitely large, leads to analyzable structures from which this perfor- mance limit can be predicted. Mutual information-transfer characteristics of the constituent coding schemes comprising convolutional encoders and soft-in/soft-out decoders have been shown to be sufficient to characterize the components within this model. Analyzing serial and parallel concate- nations is possible just by these characteristics. In this paper, we extend the method of extrinsic information transfer charts that is limited to the case of a concatenation of two component codes, to the case of multiple turbo codes. Multiple turbo codes are parallel concatenations of three or more constituent codes, which, in general, may not be identical and may not have identical code rates. For the construction of low-rate codes, this concept seems to be very favorable, as power efficiencies close to the Shannon limit can be achieved with reasonable complexity. Abstract—In this paper, we present quasi-chaotic schemes for secure digital communication systems, designed over Galois fields with optimal randomness properties. Schemes with the maximum output sequence length (all-zero input response) are presented for different Galois fields. Two coefficients are used to quantitatively measure the proximity of the behavior of these schemes with respect to the ideal white-noise behavior. The proposed schemes outperform those presented by Frey in his paper, and achieve the optimal quasi-chaotic properties available for a given chaotic digital scheme. The proposed schemes have also a very little loss in bit-error rate performance, so that they are a good alternative to the design of systems for which encryption and error correction are important joint goals. They can be implemented with time-variant coefficients in order to highly improve the cryptographic properties of the transmission. Abstract—In this paper, the effect of a general spatial and tem- poral fading correlation structure on the performance of coded mul- tiple-input multiple-output-orthogonal frequency-division multiplexing (MIMO-OFDM) systems is studied. The analysis handles an arbitrary joint transmit-receive spatial correlation model, including the non-Kronecker model. An upper bound on the maximum achievable diversity order for frequency-selective MIMO-OFDM systems with general temporal and spatial correlation is derived. Furthermore, a space-time-frequency code design that can achieve the upper bound for any arbitrarily cor- related channel scenario is provided. The general framework of the analysis includes space-frequency-coded systems as a special case. For the space-frequency-coded MIMO-OFDM system, it is shown that any space-frequency code designed to achieve full diversity in the indepen- dent fading channel can achieve full diversity in an arbitrary spatially correlated channel. The derived analytical results are consistent with those in the existing literature for special correlation structures. Extensive simulation results are provided to confirm the theoretical analysis. Abstract—A new modulation method for linear space-time codes is pro- posed, based on using constellations of different sizes for different symbols. It is shown that the proposed method significantly reduces the complexity of the sphere-decoding algorithm. The complexity reduction is more pro- nounced in high-rate codes, where each code matrix carries a large number of symbols. We also show that the choice of constellation size provides a tradeoff between performance and complexity. Using this, some guidelines for choosing constellation size are presented. As one introduces more con- stellation disparity in the code, the complexity is further reduced, while the performance loss grows. Typically, a complexity reduction of one to two or- ders of magnitude can be achieved at the expense of about 3 dB coding gain. We suggest modification in our design to reduce this loss to about 2 dB.