Effect of code acquisition on the performance of blind spreading factor detection in a WCDMA system | |
| Author | Wavegedara, K. C. B. |
| Call Number | AIT Thesis no.TC-01-15 |
| Subject(s) | Code division multiple access Spread spectrum communications Broadband 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-01-15 |
| Abstract | In WCDMA systems, variable data rate communication is utilized. The spreading factor (SF) of a user is allowed to change when a frame starts. The user includes the rate information in the control channel using transport format combination indicator (TFCI). The rate information bits are encoded and interleaved over the whole radio frame of 10 ms and hence, at the receiver decoding and deinterleaving have to be carried out in order to detect the information. Thus, the data rate and the SF can be detected only after a 10 ms delay. In addition to delay, using TFCI overhead to carry the rate information consumes transmission capacity. By using blind detection the user equipment can save network resources required for transmitting TFCI bits. Therefore, it becomes very important to detect the spreading factor of the physical data channel without using TFCI bits transmitted in the physical control channel. In this thesis, performance analysis of autocorrelation based blind spreading factor detection technique proposed by Juntti, Pajukoski, (2000) for WCDMA system is considered. The channel delay estimation required in spreading factor detection is carried out using minimum variance based code acquisition scheme (proposed by Latva-aho et al., 1998). The effect of code acquisition errors to the performance of SF detection is studied. The performance of the autocorrelation based SF detection technique and minimum variance based code acquisition scheme has been studied over a frequency selective Rayleigh fading channel with real parameters of WCDMA systems. It was found that the performance obtained from the SF detection algorithm is very poor in .frequency selective fading channel environment. However, significantly improved performance has been obtained when the algorithm is modified to utilize multipath combining. The performance of SF detection algorithm highly degrades with number of interfering users. It was observed that as number of users increases, the difference of the performance of SF detection between using minimum variance based acquisition and using perfect code acquisition increases. However, even with perfect code acquisition, it is not possible to get acceptable performance for number of users above fifteen. Therefore, the degradation of the performance due to the code acquisition errors is not an important factor. Furthermore, the SF detection algorithm shows poor performance in the presence of high near-far problem. It was found that the performance of the minimum variance based code acquisition scheme is poor for long observation intervals. However, much better performance has been achieved for short observation intervals. The result obtained from simulations is opposite to that presented in the literature for a simpler channel model with two multipath components separated by five chip intervals. In this thesis, a channel model with nine multipaths components, which are closely spaced, has been used. This is the probable reason for the results obtained. The minimum variance based code acquisition scheme outperforms the conventional matched filter based scheme for large number of interfering users. Further, it was found that the performance of matched filter based scheme severely deteriorates as near-far ratio increases, while the minimum variance based acquisition scheme shows high near-far resistance. |
| Year | 2001 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. TC-01-15 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Department of Information and Communications Technologies (DICT) |
| Academic Program/FoS | Telecommunications (TC) |
| Chairperson(s) | Makelainen, Kimmo; |
| Examination Committee(s) | Sharma, A.B. ;Rajatheva, R.M.A.P. ; |
| Scholarship Donor(s) | Government of Finland ; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2001 |