On the Design of Space-time Codes Employing Multiple Trellis Coded Modulation

| Space-time (ST) codes have shown considerable promise for reliable transmission, at relatively high data rates, over wireless fading channels in systems employing multiple transmit and receive antennas. Here, we consider the design of space-time codes employing multiple trellis coded modulation (MTCM). In MTCM, each trellis branch corresponds to multiple symbol transmissions from each transmit antenna. This structure is shown to be necessary for achieving maximum transmit diversity gain when using trellis codes with parallel paths. Systematic code search procedures with low complexity are described based on the properties of ST-MTCM codes. By properly labeling the trellis branches, we illustrate that the overall coding gain can be made larger than that achieved by conventional ST-TCM codes with the same throughput and the same number of states. We also demonstrate that optimization using the diierent design criterion needed for quasi-static at fading and fast at fading channels typically leads to diierent ST-MTCM codes. as an eeective way to fully exploit both transmit diversity and receive diversity to overcome the impairments of wireless fading channels. Good ST codes are typically designed by jointly considering the error correction coding gain and diversity gain possible with proper modulation. Hence, reliable, high data rate, transmissions over fading channels are enabled. In 1], two examples of smart-greedy space-time codes are very brieey presented. These smart-greedy codes employ multiple trellis coded modulation (MTCM), in which each trellis branch corresponds to multiple symbol transmissions from each transmit antenna. The majority of the discussions in 1] focus on conventional trellis coded modulation (TCM) (i.e., only one symbol per trellis branch for each transmit antenna). Concatenated smart-greedy ST codes were recently considered in 14]. In this paper, we show that when trellis codes have parallel paths, it is not possible to achieve maximum transmit diversity gain by using conventional TCM. In these cases, ST-MTCM codes should be applied. For ST-MTCM codes, our design procedure attempts to label the trellis branches so that the coding redundancy is

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