Peiris, Bemini Hennadige Janath (2006-12). Resource allocation in DS-CDMA systems with side information at the transmitter. Doctoral Dissertation. Thesis uri icon


  • In a multiuser DS-CDMA system with frequency selectivity, each user??????s spreading
    sequence is transmitted through a different channel and the autocorrelation and
    the cross correlation properties of the received sequences will not be the same as
    that of the transmitted sequences. The best way of designing spreading sequences
    for frequency selective channels is to design them at the receiver exploiting the users??????
    channel characteristics. By doing so, we can show that the designed sequences outperform
    single user AWGN performance.
    In existing sequence design algorithms for frequency selective channels, the design
    is done in the time domain and the connection to frequency domain properties
    is not established. We approach the design of spreading sequences based on their
    frequency domain characteristics. Based on the frequency domain characteristics of
    the spreading sequences with unconstrained amplitudes and phases, we propose a
    reduced-rank sequence design algorithm that reduces the computational complexity,
    feedback bandwidth and improves the performance of some existing sequence design
    algorithms proposed for frequency selective channels.
    We propose several different approaches to design the spreading sequences with constrained amplitudes and phases for frequency selective channels. First, we use the
    frequency domain characteristics of the unconstrained spreading sequences to find a
    set of constrained amplitude sequences for a given set of channels. This is done either
    by carefully assigning an already existing set of sequences for a given set of users or by
    mapping unconstrained sequences onto a unit circle. Secondly, we use an information
    theoretic approach to design the spreading sequences by matching the spectrum of
    each user??????s sequence to the water-filling spectrum of the user??????s channel.
    Finally, the design of inner shaping codes for single-head and multi-head magnetic
    recoding channels is discussed. The shaping sequences are designed considering them
    as short spreading codes matched to the recoding channels. The outer channel code
    is matched to the inner shaping code using the extrinsic information transfer chart
    In this dissertation we introduce a new frequency domain approach to design
    spreading sequences for frequency selective channels. We also extend this proposed
    technique to design inner shaping codes for partial response channels.

publication date

  • December 2006