Multicarrier systems have shown better performance measures when system parameters (power, bits etc.) are optimized over different frequencies with respect to the channel gain factor. On the other hand stringent wireless spectrum constraints requiring inter-system spectrum sharing are giving birth to peak-power constrained multicarrier systems like MB-OFDM (A. Batra et al., 2004) based UWB system that rely on limiting peak emission power in order to inhibit interference with other systems using the same frequency spectrum. Power optimization for such systems must incorporate the additional peak-power constraint and at the same time respect the crucial time constraints of a very high data-rate system like that of UWB. This work addresses both of these issues by first analytically solving the peak power constrained BER minimizing power allocation problem and finally an important contribution comes in the development of a simplistic implementation algorithm which is found to converge faster than some recently proposed solutions based on iterative waterfilling for optimal power allocation in peak-power constrained systems.

The capacity approaching performances (Richardson et al., 2001) of different types of low density parity check (LDPC) codes have led them to undergo extensive research in recent years. Along with asymptotic performances analysis, the optimization of 'irregularity' profile for different channels and the performance analysis of practical finite-length codes has also been extensively explored. With multi-carrier communications becoming the physical layer choice for many emerging wireless systems, a feasible solution for optimizing the irregularity profile of irregular LDPC codes for a frequency selective channel is a problem of particular importance and interest. This paper proposes a simple-to-implement greedy 'check' allocation (GCA) based method for the construction of BER-optimized irregular LDPC codes using the criterion of Gallager upper bound (Gallager, 1962) for probabilistic decoding. A comparison of our GCA algorithm with some existing works (Mannoni et al., 2002) on the irregular LDPC codes optimization for multicarrier systems based on the classical Gaussian approximation of the 'density evolution' approach, shows that the same irregularity behavior can be achieved with a much simpler method.

The recent adoption of ultra-wideband (UWB) technology for applications involving short-range very high data- rate wireless communication necessitates efficient allocation of system resources (bits, power etc.) because of the stringent spectral mask constraints. The multiband-OFDM(MB-OFDM) based UWB proposal permits usage of adaptive resource allocation over different sub-carriers so as to efficiently respond to the frequency-selective nature of the UWB channel.This paper proposes a new discrete bit-allocation methodology that results in minimizing power consumption for a fixed throughput and which appears to converge to the optimal solution faster than most known optimal discrete bit-loading methods. With peak- power-constraint and channel gain factor given for a sub-carrier, the sufficient condition for determining maximum permissible number of bits is also established. While earlier bit-loading algorithms have mostly targeted the ADSL-type systems, UWB application scenario is targeted in this paper to seek the total energy improvement factor with respect to a non-adaptive UWB system. However, the allocation methodology can be used for any multi-carrier based system.

In this paper, we present first ideas on how highly time and frequency selective channels may be modeled using wavelet decomposition. This approach is compared to a previously developed channel model using Karhunen-Loeve decomposition. We focus our study on OFDM systems, but this means no restriction with respect to the application of such a modeling technique.

This paper addresses the design and performance of time-recursive receivers for diversity based communication systems with flat Rayleigh or Ricean fading. The paper introduces a general state-space model for such systems, where there is temporal correlation in the channel gain. Such an approach encompasses a wide range of diversity systems such as spatial diversity, frequency diversity, and code diversity systems which are used in practice. The paper describes a number of noncoherent receiver structures derived from both sequence and a posteriori probability-based cost functions and compares their performance using an orthogonal frequency-division multiplex example. In this example, the paper shows how a standard physical delay-Doppler scattering channel model can be approximated by the proposed state-space model. The simulations show that significant performance gains can be made by exploiting temporal, as well as diversity channel correlations. The paper argues that such time-recursive receivers offer some advantages over block processing schemes such as computational and memory requirement reductions and the easier incorporation of adaptivity in the receiver structures.

We propose an optimum turbo channel estimation algorithm for OFDM systems on highly selective fading channels. This algorithm performs an iterative estimation of the multiplicative fading channel according to the maximum a posteriori criterion. It requires a convenient representation of the highly time and frequency selective fading channel based on the Karhunen-Loeve expansion theorem. It also optimally takes into account the coded structure of the data symbols in the estimation process thanks to the Bahl (1974) algorithm.