Performance improvement of the HDR system due to hybrid ARQ

One of the main improvements that the 1xEV-DO (IS-856) standard adds to the original HDR proposal is the hybrid automatic repeat request (H-ARQ) mechanism. The H-ARQ scheme combines error correction, error detection, soft packet combining and incremental redundancy. H-ARQ reduces the required forward link SINR and thereby improves overall system capacity, particularly in mobile environments. We present simulation results comparing the aggregate throughput of CDMA HDR systems with and without H-ARQ. We find that H-ARQ gives greatest gain at moderate to high mobile speeds and also at cell-edge locations, where the mean received Ec/Io is small. The addition of H-ARQ more than doubles the aggregate throughput for mobile speeds above 21 km/h.