The investigation of Trellis coded-modulation and turbo Trellis coded-modulation schemes for Rayleigh multipath fading channels | |
| Author | Nguyen Hoang Ha |
| Call Number | AIT Thesis no.TC-97-5 |
| Subject(s) | Mobile communication systems Digital communications |
| Note | A thesis submitted in partial fulfillment of the requirement for the degree of Master of Engineering. |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. TC-97-5 |
| Abstract | Coded-modulation technique combines coding and modulation in one process in order to provide both error correcting and spectral saving capabilities. This technique is therefore very attractive for digital mobile communications, where the effect of fading, especially multipath fading needs to be reduced and the bandwidth usage needs to be optimized. In this thesis two different coded-modulation techniques were investigated together with various equalization methods for frequency-selective Rayleigh fading channel and significant improvement in error performance was obtained. Trellis coded-modulation (TCM) is well known as a bandwidth efficient coding scheme over additive white Gaussian noise (AWGN) channel. However, not much has been done for its application over frequency selective fading channel . A system model is analyzed in order to apply TCM schemes for this type of channel. The model is based on separate equalizers and TCM decoders, and a symbol interleaver. Several soft-output algorithms for equalizing multipath fading channel are considered in combination with both Viterbi and maximum a posteriori probability (MAP) decoding of TCM. Our simulation results show that with the proper choice of algorithm for equalizing multipath fading channel, TCM schemes achieve large coding gain over uncoded system with the same spectral efficiency. Coding gains of up to 4dB and 8dB were observed at BER level of 10ยท4 . The astonishing performance of a new coding technique, turbo coding, has been reported widely by many researchers, but in most of the work turbo codes were investigated with binary modulation over A WGN channel or flat fading channel. Two approaches in applying turbo codes with multilevel modulation over AWGN channel are considered in this thesis. The first approach is merely the natural combination of turbo codes with multilevel modulation and is called the pragmatic approach. The second one is the extension of binary turbo codes by replacing component recursive systematic convolutional codes by recursive systematic TCM codes. This approach is referred to as turbo trellis coded-modulation (TTCM). It takes the advantages of both near Shannon limit error performance of turbo codes and spectral saving of TCM. Our simulation results are presented for both approaches and it is shown that T-TCM gives the best performance compared to any other scheme having the same spectral efficiency. More importantly, the system model used for TCM is extended to investigate the performance of T-TCM schemes over frequency-selective fading channel. Basically the T-TCM decoder is kept unchanged as in case of A WGN channel. In order to do that a modified MAP (Max-Log-MAP) algorithm is selected for the equalizer so that the logarithm of probability for each symbol is available at the input of T-TCM decoder. Our work is completely new for the application of turbo codes with high spectral efficiency modulation over frequency-selective fading channel. Simulation results show that the error performance of the proposed system is much better than any other coded-modulation schemes in the past for this type of channel. |
| Year | 1997 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. TC-97-5 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Department of Information and Communications Technologies (DICT) |
| Academic Program/FoS | Telecommunications (TC) |
| Chairperson(s) | Premanandana Rajatheva |
| Examination Committee(s) | Makelainen, Kimme;Zhang, Jian-Guo |
| Scholarship Donor(s) | Government of Finland. |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 1997 |