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Channel Estimation for TD-HSPA

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Basic working principle of the Steiner channel estimator.




Sandro Belfanti
Karim Badawi


Hasler Foundation




Time division synchronous code division multiple access (TD-SCDMA) is a 3GPP standard that has been launched successfully in China only few years ago. A corresponding evolved 3.5G standard TD-HSPA has been specified for future high-speed packet data transmission, its TDD nature allows it to master asymmetric services more efficiently than other 3G standards. Up- and downlink resources are flexibly assigned according to traffic needs, which is helpful in an environment with increasing data traffic, which tends to be asymmetric (mobile Internet).

Due to strong multipath fading present in the mobile environment, powerful equalizers are required to reverse the effect of the multipath channel. To that end, these equalizers typically rely on accurate channel estimates, estimated from known transmit symbols. Since TD-SCDMA invests a considerable portion of the transmitted data to send known training sequences like pilot symbols and midambles, this information has to be fully and efficiently utilized to obtain a reliable channel estimate.

In this project, different channel estimation algorithms for TD-SCDMA have been analyzed and compared with focus on future hardware implementations. Particular attention was paid to the special structure of the midambles, which are constructed as a superposition of cyclically shifted basic midambles. This structure can be exploited to reduce the implementation complexity considerably by using the Steiner channel estimator which based on a FFT computation.