Using space time codes on FDMA/TDMA based system with soft and hard handoff algorithms

A simple scheme that provides transmit diversity using two antennas was introduced by Alamouti (1998). This scheme was extended by Tarokh (1998, 1999) to several transmit and receive antennas. The scheme includes a joint design of coding, modulation and antenna diversity and is called Space Time Coding (STC). In general in a STC scheme, data is encoded by channel codes such as trellis or block codes and the encoded data are split into N streams that are simultaneously transmitted using N transmit antennas. The received signal at each receive antenna is a linear superposition of the N transmitted signals perturbed by noise, but, with the knowledge of the channel, the receiver can extract the information and enjoy diversity gain comparable to that achieved by receive diversity. In this paper, we consider a new scheme of combining Space Time Codes for transmit diversity and Maximal Ratio Receive Combining for receive diversity in an array of base stations in a cellular system to accomplish soft handoff, even in FDMA/TDMA type systems. The base stations, using one or more antennas are sharing common channels with neighboring cells and thus are able to implement soft handoff. It is shown that this scheme provides an improved performance, under the criterion of coverage area, relative to the hard handoff scheme implemented in a typical FDMA/TDMA cellular system.