Telecommunications & Signal Processing Laboratory

Thesis Abstracts, 1990-1992

Kai Ming Cheung
Generalized Likelihood Commutation Signaling for Indoor Communications
M.Eng. Thesis, December 1992
Supervisor: H. Leib

Using the Generalized Likelihood (GL) principle, a receiver structure of relatively low complexity is developed for indoor wireless communication channels. The receiver, which is robust against channel models, provides a performance close to optimal in the GL sense. The GL receiver combines naturally both channel estimation and data detection and therefore it is ideal for transmission systems which operate over unknown channels. The effects of multipath induced intersymbol interference (ISI) on the channel estimation process are mitigated by employing the technique of commutation signaling. In addition, by union bounding technique, it is shown that with sufficient bandwidth expansion, the probability of having significant ISI on the data detection process can be made arbitrarily small. Furthermore, a simplified GL receiver is proposed to combine binary commutation signaling with DPSK modulation scheme. The error performance of such a receiver under perfect channel estimation over multipath Rayleigh and Lognormal fading channels is presented and the performance degradation due to incorrect channel estimation is investigated via computer simulations.

Patrick Beirouti
Automatic Repeat Request on Fading Channels
M.Eng. Thesis, May 1992
Supervisors: H. Leib and S. D. Morgera

Automatic repeat request (ARQ) is a widespread technique for error control in data communication systems. This research examines the performance of conventional ARQ schemes over fading channels. The basic Gilbert-Elliott two-state Markov model is used to represent these channels. This basic model is recursively extended to a 2n-state Markov chain suitable for n-bit block codes. Using this 'Extended Gilbert-Elliot' model, an approximation of the throughput efficiency of the conventional ARQ schemes is derived. This approximation is particularly valid for slow fading channels. Furthermore, performance plots are obtained, showing the effects of channel fading on throughput efficiency: ARQ performance deteriorates with slower fading, or alternatively, higher channel memory. Consequently, frequency-hopped codeword transmission is explored, a technique by which channel memory can be reduced. Throughput performance of frequency-hopped ARQ systems is derived, which shows significant potential improvements over systems with no frequency hopping.

William James McCausland
Distortion Free Compression of Musical Scores
M.Eng. Thesis, December 1991
Supervisors: H. Leib and S. D. Morgera

Music notation represents what a composer creates. This research is concerned with the problem of compression, without distortion, of complete scores of musical pieces. The musical score source has many interesting characteristics which set it apart from other information sources; for example, it is a collection of parallel 'parts'; the durations of symbols (notes) are variable; and the transitions between notes in different parts need not be simultaneous. These distinguishing features are discussed and incorporated into the procedure described in this work. The research consists of three parts. The first is the design of a representation system allowing musical scores to be stored on digital media. The second is the development of a simple music editor and the compilation of two pieces of music. The third is the design and implementation of a compression algorithm. Significantly higher compression ratios are achieved using the designed algorithm vis--vis those achieved using a standard general data compression algorithm.

Kenneth Mark Aleong
A Technique for Combining Equalization with Differential Detection
M.Eng. Thesis, August 1991.
Supervisors: H. Leib and P. Kabal

A technique for combining equalization and differentially coherent detection is proposed for use in wireless communication when carrier phase recovery is difficult. A decision-feedback differentially coherent scheme, which generates an improved reference phase, is combined with a linear equalizer and the LMS algorithm is used to adapt the equalizer to an unknown channel. In addition, the proposed receiver is simulated for various two-dimensional signal constellations over multipath channels. It is shown that for high SNR, the degradation of this structure is negligible with respect to combined coherent detection and equalization. Therefore, this equalized differentially coherent detection scheme can be used when carrier phase tracking (i.e. coherent detection) is difficult and intersymbol interference is a major obstacle.