OFDM-based WLAN systems are originally used for nearly static environment. But in the trend of user-convenience, if we want to support mobility, the most important issue is the Doppler effect caused by the object velocity. We investigate how the Doppler effect, signal-to-noise ratio (SNR) and imperfect estimation of channel impulse response (CIR) and the maximum Doppler shift fd influence the final bit error rate (BER) under the simulation environment, modified WLAN 802.11a specification. For these effects, we give some simulation results and conclusions. If CIR and df are known with the same number of multipath, we can see some phenomenon. First, the BER is dominated by AWGN noise. Second, under the same channel delay spread, the higher the object velocity is, the more serious the BER is. Third, under the same the object velocity, the more serious the BER is. If CIR is known instead of fd, under the same error percentage of fd and the same number of multipath, the lesser the velocity is the lesser the BER curve changes. If fd is known instead of CIR with the same number of multipath, the longer the channel delay spread is, the more serious the BER is.

国立情報学研究所で電子化したコンテンツで使用している。

The goal of this thesis was to implement a DVB-T receiver on Coresonic’s DSP-processor and attempt to evaluate how to design a receiver that is robust against very strong echoes with a long delay. Long delayed echoes is very common in Single Frequency Networks (SFN) which is why focus was put on finding algorithms that work well in SFN.The thesis involved analyzing different algorithms involved in making a DVB-T receiver where the focus was to find a good channel estimation algorithm. The thesis also included programming the DSP-processor and making some smaller modifications to their hardware solution to integrate their error correction hardware. After finding relevant articles with promising algorithms a small transmitter, channel and receiver was modeled in Matlab in order to try the different algorithms. After testing the different algorithms some of the simpler ones were first implemented to quickly get a working receiver. The implementation was however time consuming and all of the most appropriate algorithms to better avert the effects of long and strong echoes where not implemented. This means some algorithms where only analyzed and discussed.The receiver performance is tested and simulated in Coresonic’s DSP simulator. The receiver does not fully meet the requirements set by NorDig when it comes to handling long delay spread echoes with a magnitude of 0db when tested in the DSP processor simulator. The receiver is however able to handle the Ricean channel at a SNR of 19 Db and Rayleigh channel at an SNR of 24 Db.This report is the result of the final thesis of a Master of Science in Computer Engineering at Linköpings Tekniska Högskola. The thesis was performed at Coresonic AB in Mjärdevi Linköping.