Scheduling and adaptive transmission for the downlink in 4G systems

In this paper, we propose a system suitable for efficient packet data transmission using the Internet Protocol (IP) in wireless 4G systems. It consists of a hybrid type-II Automatic Repeat reQuest (ARQ) scheme combined with an Adaptive Modulation System (AMS) and a time slot scheduler supplied by channel predictions. It is referred to as predictive HARQ-II/AMS. The performance of the system in a fast fading downlink channel is investigated through simulations where in particular, BER and throughput performance are studied. The proposed system is compared to two simpler systems. One has access to channel predictions and uses adaptive modulation but does not employ error correction and retransmission at the link layer (referred to as predictive AMS). The other has no access to the channel prediction but use HARQ-II/AMS in a blind way (referred to as blind HARQ-II/AMS). The results show that with perfect channel prediction both predictive AMS and predictive HARQII/AMS satisfy the BER requirements with some advantages to the former in terms of efficient usage of channel capacity. However, with imperfect channel prediction a retransmission protocol is required to meet the BER requirement making predictive HARQ-II/AMS the winner.