Adaptive modulation techniques for OFDM-CDMA based 4G mobile networks | |
| Author | Wasantha, Muthuthanthrige Kumudu |
| Call Number | AIT Thesis no.TC-02-10 |
| Subject(s) | Modulation theory Code division multiple access |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. TC-02-10 |
| Abstract | Ever increasing demand for high speed data transmission with mobility due to the quantum advancement in multimedia applications used in this information era day to day life has created a huge burden on the limited radio frequency bandwidth available for wireless communication. OFDM - CDMA (Orthogonal Frequency Division Multiplexing - Code Division Multiple Access) with adaptive modulation techniques is one of the most promising technologies for high speed data transmission over wireless channels due to its favourable properties to overcome many channel impairments. Quadrature Amplitude Modulation (QAM), Phase Shift Keying (PSK) and Multi-h Continuous Phase Modulation schemes are investigated in this study as adaptive modulation techniques. A pilot symbol assisted channel estimation method is used to estimate the channel quality and to decide the suitable modulation format to meet the targeted Bit Error Rate (BER) of 1 o-04 or better. BER performance of M-ary QAM (M=2, 4, 16), M-ary PSK (M=2, 4, 8) and M-ary MHPM (M=2, 4) modulation schemes in OFDM-CDMA system under different channel conditions and with different number of CDMA users has been investigated and presented in this thesis. In general higher order modulation schemes can accommodate only few number of CDMA users and more noise resilient lower order modulation schemes can support more number of CDMA users. Based on the results of the OFDM-CDMA system with fixed modulation schemes and the corresponding estimated channel CNR, OFDM-CDMA systems with adaptive modulation schemes were simulated. The simulation results show that an adaptive modulation based system can use the available spectrum more efficiently than fixed modulation based system under varying channel conditions while maintaining a targeted BER performance criterion. Further simulation results show that irrespective of modulation scheme i.e., whether QAM, PSK or MHPM, any higher order modulation format need better channel condition than a lower order format to maintain the same BER performance. In poor channel conditions all adaptive systems end up with the lowest order modulation scheme available in the system. There is no specific advantage in terms of BER performance in limiting modulations formats to one category in adaptive systems such as adaptive PSK, adaptive QAM etc., but in terms of hardware and software it is easier to implement such a system than an adaptive system having many different modulation schemes such as QAM, PSK and MHPM. |
| Year | 2002 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. TC-02-10 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Department of Information and Communications Technologies (DICT) |
| Academic Program/FoS | Telecommunications (TC) |
| Chairperson(s) | Fernando, W. A. C. ; |
| Examination Committee(s) | Ahmed, K. M. ;Erke, T. ; |
| Scholarship Donor(s) | Sonera Corporation, Finland; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2002 |