Reliable Communications under Limited Knowledge of the Channel

  • Author / Creator
    Yazdani, Raman
  • For successful correction of errors in a digital communication system, information about the channel, such as timing, noise power, fading gain, etc., should normally be available at the receiver. To this end, most receivers use channel parameter estimation and timing recovery modules. However, these modules are costly in terms of overhead, occupied chip area, power dissipation, and are usually imperfect. Thus, the need for high-speed communication systems motivates finding other solutions. In this thesis, we seek efficient coding solutions for reliable communication under limited channel and timing information. We address the problem by considering three important scenarios: First, we consider Gaussian channels with unknown noise power at the receiver. By using low-density parity-check (LDPC) codes, we propose a robust decoding method which provides better performance compared to the existing methods. Second, we consider decoding on wireless fading channels where the fading gain and/or noise power are unknown at the receiver. Most modern error-correcting codes require soft metrics, usually log-likelihood ratios (LLRs), to be calculated at the receiver. This calculation is cumbersome on fading channels especially when the fading gain is unknown. Thus, we first propose an LLR accuracy measure, propose an efficient approximate LLR calculation technique, and then show that the performance under approximate LLRs is extremely close to that of exact LLRs. Third, we seek practical coding for channels with imperfect timing at the receiver. In vast majority of the coding schemes invented, perfect synchronization is assumed between the transmitter and receiver. In most communication systems, however, achieving perfect synchronization is not possible. This leads to random symbol insertions and deletions in the received signal and poses a great challenge for error correction since conventional error-correcting codes fail at these situations. In this thesis, we propose a practical coding strategy which allows recovering insertions, deletions, and substitution errors without sacrificing the transmission resources.

  • Subjects / Keywords
  • Graduation date
    Fall 2012
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.