Variable bit allocation for FH-CDMA wireless communication systems

In the wireless indoor environment, the channel may vary slowly as users and the interferers may move at slow speeds. A frequency hopped CDMA (FH-CDMA) system can adapt to the different interference levels in hopping patterns and assign the slots different bit rates to increase the system capacity. We show that the maximum throughput bit rate/channel assignment problem is NP-hard. Several practical ad hoc bit allocation algorithms are designed based on the insights derived from exhaustive searches. The algorithms that achieve the most system capacity perform interference avoidance. Users concentrate their throughput in a small fraction of the slots with low interference by transmitting large signal constellations, while avoiding the channels with large interference. Simulations show that the flexibility of users to adjust their bit rates to the interference environment can significantly increases the system capacity. 1. This work is funded by Motorola Inc., under the terms of a university partnerships in research grant. 2. Corresponding author.