Performance of turbo codes with multilevel modulation over frequency selective fading channels using turbo equalization | |
| Author | Chantri Polprasert |
| Call Number | AIT Thesis no.TC-00-11 |
| Subject(s) | Algorithms Wireless communication systems |
| Note | A thesis submitted in partial fulfillment of the requirement for the degree of Master of Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. TC-00-11 |
| Abstract | In wireless communications, it is conventionally known that data transmission in band-limited channels is subjected to intersymbol interference (ISI) distortion, which, if left uncompensated, causes high error rates. This requires a good equalizer to deal with it. Recently, the concept of iterative process has successfully been applied in many applications such as in the decoding of turbo codes called turbo decoding and in the equalization called turbo equalization. Raphaeli and Zarai ( 1998) combines the iterative process in both equalization and decoding and its performance is about 0.8 dB from the ISI channel capacity. Turbo codes (Berrou et al., 1993) gives near Shannon-limit error correcting capability, however most of the work related to them consider only BPSK modulation, which results in low data rate transmission. One approach is to map the turbo codes into high spectral efficiency modulation such as M-PSK or M-QAM. Moreover, Franz and Bauch (1999) investigates the performance of the convolutional codes over the ISI channel using turbo equalization where an approach that transforms the log-likelihood ratio (LLR) from bit level into symbol level is proposed. In this thesis, we will make use of the excellent performance of turbo equalization and turbo codes to combat the degradation due to the effect of ISL The combined turbo equalization and turbo decoding receiver is developed here. The approach proposed in (Franz and Bauch, 1999) will be modified and applied to this combined receiver. The objective is to transform the information from turbo decoder from bit level into symbol level before sending them back to the equalizer to implement turbo equalization. The performance of turbo codes with multilevel modulation using the combined receiver will be investigated over the frequency selective Rayleigh fading channel in terms of bit error rate (BER) as a function of Eb/No over different types of information block size, encoder constraint length, modulation scheme. Furthermore, a suboptimum soft-output algorithm (SSA) (Li et al., 1995), which requires only a forward recursion under a constraint of a fixed decision delay will be applied to the equalizer denoted by a suboptimum softoutput equalizer (SSE) to compare the performance with Max-log-MAP algorithm. From the simulation results, it is seen that only 3 iterations are sufficient to obtain an excellent BER performance when using this combined turbo equalization and turbo decoding receiver. When comparing between the system using the Max-Log-MAP equalizer and the SSE, although both give the similar performance, the SSE is more complex than the MaxLog- MAP equalizer. |
| Year | 2000 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. TC-00-11 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Department of Information and Communications Technologies (DICT) |
| Academic Program/FoS | Telecommunications (TC) |
| Chairperson(s) | Rajatheva, R.M.A.P. ; |
| Examination Committee(s) | Ahmed, K.azi M.;Makelainen, Kimmo ; |
| Scholarship Donor(s) | Self Support; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2000 |