Channel Estimation for Code Division Multiple Access Combined with Space Time Block Coding

Abstract

In this paper, we present a combination of code division multiple access, space time block coding and orthogonal frequency division multiplexing technology. Also, the channel estimator related to this combination is proposed. In code division multiple access system, as the number of users increases the performance decreases. To overcome this problem, we apply space time block coding to improve the performance of the system. This approach is valid for non time dispersive channels. In the case of time dispersive channels, the problem of inter-symbol interference occurs. To cancel the inter-symbol interference, we use orthogonal frequency division multiplexing technology to transform the time dispersive channel into a number of non time dispersive channels. In this case, the received signal is simply decoded. To further improve the performance, channel estimator has to be very efficient. Therefore, we propose channel estimator based on the pilot symbols inserted periodically into the orthogonal frequency division multiplexing transmitted frame. At the receiver, interpolation filtering with specific gain and cutoff frequency is used to estimate the channel at all locations corresponding to orthogonal frequency division multiplexing frame. Several examples of real and estimated channels with different Doppler shifts are addressed. Simulation results of these examples show high performance and robustness of our approach.