The design and investigation of a 4-QAM-OFDM-CDMA transmitter-receiver to obtain low peak to average power ratio in wireless communications | |
| Author | Ginige, Thilak |
| Call Number | AIT Diss no.TC-02-01 |
| Subject(s) | Wireless communication systems Code division multiple access |
| Note | A dissertation submitted in partial fullfillment of the requirements for the degree of Doctor of Engineering, School of Advanced Technologies |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation; no. TC-02-01 |
| Abstract | This thesis deals with the Peak to Average Power Ratio (P APR) problem of the OFDM-CDMA systems, which have attractive properties for high transmission rate data, to be used in future wireless communication applications. The following P APR reduction techniques with a new 4-QAM-OFDM-CDMA transmitter-receiver design are proposed for downlink in mobile communication. First, an OFDM-CDMA transmitter and a receiver design with 4-QAM modulation are proposed to limit number of input data combinations. Limitation of input data combinations to a small number makes it possible to reduce probability of high P APR occurances of any spreading code. Therefore we propose to select codes with low P APR values to be used and that technique is investigated. BER performance of this receiver is obtained for an A WGN as well as for a frequency non-selective fading channel. Performance of Turbo codes is also obtained to achieve better performance for A WGN and multi-path fading channel. Next, using proposed 4-QAM-OFDM-CDMA system, a low P APR spreading code selection method is proposed. This technique can be applied to any spreading code set such as Walsh Hadarmard, Gold Codes, m-sequences etc. Further, it is shown that this technique is capable of limiting the P APR level of an 80 sub-carrier single user OFDMCDMA system to 6dB with m-sequences although theoretically maximum possible P APR level of such a system is 19dB (10 log10 (N)). Next, the Dynamic Spreading Code Allocation technique for P APR Reduction in OFDM-CDMA systems with 4-QAM modulation is proposed for the down-link in mobile communication. With the proposed technique, the P APR level of a system with 10 users and 64 sub-carriers using 64 chip Walsh-Hadamard (WH) codes, can be limited to 15dB while maintaining P APR level of a single user, system to 12 dB. However, the worst case theoretical maximum levels of such sytems could go up to 18.1 dB and 28.ldB respectively. Although 64 chip WH codes are employed to evaluate the performance it can be generalized to all other sets of spreading codes. For BER and P APR level performance verification and comparison was carried out to show the advantages of the P APR reduction schems proposed first. Also for the dynamic spreading code selection method, performance was evaluated by using graphs of P APR level vs probability of exceeding that P APR level. In addition to that the worst case P APR bounds are obtained and compared for ordinary and proposed systems. Finally, the BER comparison with an P APR reduction method of amplitude clipping and forward error correction coding (AL-FEC) is obtained. The research work was further extended, by proposing a spreading code sharing M'ary PSK CDMA system and a spreading code sharing multi-carrier M'ary PSK CDMA (SCS-MPSK-MC-CDMA) system concepts. The main advantage of the latter system is low P APR values can be obtained with similar BER performance under the same conditions of a conventional M'ary PSK multi-carrier CDMA system. P APR profiles of these systems as well as BER performance have been obtained and how proposed P APR reduction techniques can be applied are discussed. It can be seen that the proposed 4-QAM-OFDM-CDMA transmitter-receiver design can be applied to wireless communication systems with A WGN or multi-path fading channels. The proposed P APR reduction methods also can be used with the 4- QAM-OFDM-CDMA system as well as SCS-MPSK-MC-CDMA systems. Since MPSK systems are extremely sensitive to phase errors, proposed SCS-MPSK-MC-CDMA system can be applied to indoor wireless systems with larger number of users having low P APR levels compared to conventional system. |
| Year | 2002 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation; no. TC-02-01 |
| Type | Dissertation |
| School | School of Advanced Technologies (SAT) |
| Department | Department of Information and Communications Technologies (DICT) |
| Academic Program/FoS | Telecommunications (TC) |
| Chairperson(s) | Rajatheva, R.M.A.P.;Ahmed, Kumar M.; |
| Examination Committee(s) | D. N. Batanov, D.N.; Erke, Tapio;Imai, Hideki; |
| Scholarship Donor(s) | Government of Finland; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2002 |