Michiel Petrus Lotter

A multiple trellis coded Q/sup 2/PSK system for wireless local loop applications

The code design and performance evaluation of multiple trellis-coded modulation (MTCM) codes for application to a Q/sup 2/PSK micro-cellular wireless local loop access system are investigated. The paper formulates extended design criteria for MTCM code design based on the analysis of burst errors. Based on this criteria, the design of new 4-state codes for Q/sup 2/PSK is presented, and the bit error rate performance of these code designs, assuming coherent detection and perfect clock recovery are studied by means of simulation. It is demonstrated through computer simulation results that coding gains in excess of 13.0 dB at a bit error probability of 10/sup -5/ can be achieved with the designed MTCM coded system, relative to the uncoded system under the conditions present in a micro-cellular wireless local loop network. Furthermore, the benefits of using channel state information (CSI) in conjunction with MTCM are also considered.

An optimum interference mitigating combining scheme for the CDMA downlink with the same complexity as MRC

This letter presents a new optimum interference mitigating combining (OIMC) scheme for the code-division multiple-access downlink RAKE receiver. The OIMC scheme optimizes the RAKE weights and maximizes the signal-to-interference-plus-noise ratio (SINR) at the RAKE combiner output. Unlike other interference mitigation schemes, the new scheme does not need to estimate the interference or data correlation matrix (and its inverse) of the received signal to render a reliable and low complexity receiver. The OIMC scheme mitigates interference by inversely proportionately weighting the finger output by its associated interference power, while simultaneously mitigating multipath fading. The interference power is found to be directly related to the fingers associated multipath channel gain, rendering the OIMC scheme with the same order of complexity as a maximal ratio combining (MRC) scheme. Under realistic channel conditions, simulation results show that the proposed OIMC scheme always outperforms MRC with a gain of up to more than 1 dB.

Rake receiver performance for CDMA downlink

This paper presents a closed-form expression of the average SIR of the optimum CDMA downlink Rake receiver (1) for identically independently distributed (iid) Raleigh fading and a tight bound for the non-iid case. It shows that the average SIR decreases as the number of multipaths, L, increases and achieves its minimum when the channel multipath intensity profile (MIP) is constant. This paper also proves, both in theory and with simulations that the BER increases as L increases, and that it is a convex function of the multipath channel gains and achieves its maximum when the channel MIP is constant. In addition, this paper derives a decision threshold for MRC, which results in a non-optimum Rake, to determine if a multipath is to be combined without loss of SIR. In summary, this paper proves, against conventional wisdom, that a Rake receiver for the CDMA downlink does not achieve the Lth order diversity gain. In fact, its performance varies inversely to an Lth order diversity system, such as CDMA uplink. L MPIs. In this paper, we derive a closed form expression for the average SIR of the IMOC for iid Raleigh fading channels. This average SIR is found to be monotonically decreasing as L increases. For the non-iid Raleigh fading channels, we derive a lower bound for the SIR and this bound is tight when applied to the SIR for the iid case. The bound is also proved to be minimized when the channel MIP is constant. The paper shows both in theory and in simulations that BERs of both the IMOC and MRC obtain their maximum when the channel MIP is constant and increase as L increases. Therefore, the BER of a Rake receiver with either IMOC or MRC in the presence of MPI behaves in an opposite way to the BER with a diversity gain of order L where the BER decreases as L increases and obtains its minimum when the channel MIP is constant.