The Research Of HARQ Technique In Mobile Communication Systems

On the mobile communication systems, the effects of multipath fading channel may weaken the performance, and lead into the co-existence of random errors and burst errors. The reliability of data communications can not be achieved if these problems can not be solved, and the QoS (quality of service) can not be satisfied either. Hybrid ARQ technology is the combination of FEC (forward error correction) and ARQ (automatic repeat request). This kind of system not only has the ability of error correction, but also has the ability of detecting errors which can not be corrected. Hybrid ARQ technique was first designed in the early of 1960's and gains comprehensive research during the latest four decades. 3GPP and 3GPP2 both treat HARQ as a key technique of high rate downlink data services. On the platform of 3G communication systems, this paper studies the hybrid ARQ techniques.We first introduce the CDMA2000 1x EV-DO system, which is a specification of high rate packet data communication. Then on the platform of EV-DO, we study the application of different kinds of hybrid ARQ schemes. After the discussion of the classic HARQ schemes, we pay our attention to the hybrid ARQ schemes which is based on the method of pre-code: one scheme is based on the pre-equalization of multipath fading channels, we put forward a improved scheme of pre-equalization and enhance the high rate downlink packet data services; and the other is based on the rearrangement of constellation in multilevel modulation. We introduce these new schemes into EV-DO system, and improve its performance.