Investigation of STBC and TSTD Transmitter Diversity Effect Considering Frequency and Time Diversity in Spread OFDM Broadband Packet Wireless Access

摘要

This paper investigates the effects of the Space-Time Block Code (STBC)transmitter diversity and Time Switched Transmitter Diversity (TSTD) schemes while simultaneouslyconsidering the time diversity effect derived from hybrid automatic repeat request (ARQ) with packetcombining and the frequency diversity effect for forward link Spread Orthogonal Frequency DivisionMultiplexing (OFDM) packet wireless access in a broadband multiparth fading channel. Simulationresults show that when the frequency diversity gain in Spread OFDM through frequency-domainspreading and channel coding plus interleaving in the frequency domain and the time diversity gainthrough hybrid ARQ are obtained, the additional transmitter diversity gain through STBC becomes verysmall, due to the decreasing pilot signal energy per transmitter branch. The results also show thatTSTD, which simply switches the transmission branch alternately, improves the required averagereceived signal energy per symbol-to-noise power spectrum density ratio by approximately 1.0 and 0.5dB compared to one-branch transmission, when the maximum number of retransmissions in hybrid ARQ isthree, without and with antenna diversity reception, respectively, in a 12-path Rayleigh fadingchannel with the root mean squared delay spread of 0.3 μsec and maximum Doppler frequency of 20 Hz.