L a b R e s e a r c h
Theses - D.K. Asano
Ph.D. Thesis: CPM Transceivers Using a Limiter-Discriminator in Fading Channels
In this thesis, a communication system that uses Continuous Phase Modulation and a limiter-discriminator detector is examined. The problem of design for such a system is divided into three parts: receiver, transmitter and coding. Conventional receiver structures, including matched filtering, equalization and sequence estimation, are examined and found to provide little performance improvement due to the random fading effects and the non-linear properties of the detector. Examination of the error events shows that the errors are related to the magnitude of the fading. Using this information results in a new, robust processor structure which provides a significant performance improvement.
On the transmitter side, the effects of the modulation index and transmitter pulse shape are studied. For several transmitter pulse shapes, the optimal modulation index is found. It is also found that the performance is related to the correlation between the possible transmitted waveforms. The pulse shapes are compared in terms of error rate performance and bandwidth. The rectangular pulse shape is found to be the best. Gaussian Minimum Shift Keying is examined as an example of partial response signalling. The performance is found to be much worse than full response schemes. Even though there is some memory in partial response schemes, the memory cannot be efficiently used because of the distortion caused by the detector.
The suitability of the fading channel for coding is examined and found to be much like a random error channel. Codes designed using the Hamming distance criterion are examined and found to perform well. Compensation for the negative aspect of coding, namely the reduction in information rate, is examined by using two techniques: reduced bandwidth coding and Trellis Coded Modulation (TCM). The reduced bandwidth coding technique proves to be better than TCM in the fading channel case, thus indicating that Hamming distance is a better design criterion than Euclidean distance. For TCM codes, it is found that the Euclidean distance criterion is reasonable except at high signal-to-noise ratios, where an average Euclidean distance is found to lead to better code performance.
M.A.Sc. Thesis: Phase Smoothing Functions for Continuous Phase Modulation
In this thesis, the problem of signal design for continuous phase modulation is examined. Using the performance measures of effective bandwidth and minimum distance, the optimal tradeoffs are derived to give a family of signals. The optimization is carried out for various receiver observation intervals for both full and partial response signalling. In some cases, the optimization is not possible using the available tools so a family of signals based on the optimal ones is introduced to give some insight into the problem. The tradeoffs that result between bandwidth and bit error rate are then compared as a function of the receiver observation interval and as a function of the memory length of the signalling scheme. Then the signals obtained by the optimization process are compared to well known signals in terms of their tradeoffs. Finally, for equal values of minimum distance the power spectra are compared in terms of out-of-band power and percent bandwidth. The signals obtained by the optimization process are found to have good spectral properties near the center frequency but slightly worse performance farther away when compared to the well known signals.
Theses - Students
Kazuyuki Morioka, DEng. Thesis (2014/9):
Application of Continuous Phase Modulation to Wideband Wireless Systems
Summary (in Japanese) [HTML]
Satoshi Yamazaki, DEng. Thesis (2011/9):
Receiver performance and adaptive equalization for an unequal error
protection code system in a mobile communication environment
Summary (in Japanese) [PDF]