Improving the performance of mobile broadcasting systems using multiple base stations and distributed space?time codes

Error performance of distributed space-time codes used for mobile broadcasting systems consisting of multiple base stations is analysed. The base stations are assumed to operate in a simulcast mode, that is they simultaneously transmit the same message using the same carrier frequency. Mobile users within the intersection of the coverage areas, thus, enjoy a small probability of shadowing and a high probability of at least one line-of-sight (LOS) link. In effect, the base stations establish a virtual multiple-antenna system. The use of a distributed space-time code offers an additional spatial diversity gain. Considering a single user with a fixed (random) position, the impact of shadowing and LOS components on the error performance of the system is analysed and compared with a conventional multiple-antenna system with co-located transmit antennas. Specifically, the analysis shows that already a single LOS link significantly improves the overall system performance. In the case of shadowing, huge diversity gains are obtained in the distributed system. In a system with co-located transmitters, however, the performance improvements compared with a single-antenna system are rather small, when shadowing is taken into account. Altogether, it can be concluded that systems with distributed transmitters are typically superior to conventional multiple-antenna systems (due to macroscopic diversity), and that distributed space-time codes are superior to conventional simulcasting (due to microscopic diversity)