PN code tracking for STBC transmit diversity RAKE receivers in closely spaced multipath environments

Conventional early-late-gate (ELG) pseudo-noise (PN) code tracking shows poor performance in closely spaced multi-path environments where multiple path separation is less than 1.5 times PN chip interval for example. Fock et al. (Dec. 2001) proposed an efficient PN code tracking scheme for a RAKE receiver with a single transmit antenna and a single receive antenna by canceling the self-interference coming from the closely spaced adjacent multipaths. However, a general trend for 3G or future wireless communication system development is to employ multiple transmit and multiple receive antennas instead of a single transmit antenna. The space time block code (STBC) in S. Alamouti (Oct. 1998) is one of popular transmit antenna diversity schemes. In this paper we propose a PN code tracking algorithm for the STBC transmit diversity system under 3GPP specifications, extending the work by Fock et al. (Dec. 2001). Channel estimation for the transmit diversity system is provided with the aid of primary common pilot channel (P-CPICH) pattern. Simulations show that the proposed algorithm can eliminate the effects of the adjacent paths and can make an improvement in the root mean square (RMS) of the timing error compared to system without transmit diversity, e.g., 2 dB in chip-energy-to-noise-density ratio E_c/N₀ at RMS = 0.1.