Performance analysis of LLR combining HARQ for MIMO systems in Mobile WiMAX

The use of hybrid automatic-repeat-request (HARQ) with multi-antenna systems (MIMO) promises high throughput with high reliability in broadband wireless communication systems. One of the combining methods in MIMO-HARQ is by directly optimizing the log-likelihood ratio (LLR) values instead of compensating the multiple signal-to-interference-and noise power ratios (SINRs) as in conventional combining method. The problem of this approach is that the receiver complexity is significantly increased along with the order of the modulation used. This paper proposed simplified implementation of the MIMO-HARQ with LLR combining method under the IEEE 802.16e Mobile WiMAX system. Proposed scheme are verified using ITU-B Pedestrian and ITU-A Vehicular channel model with various modulation order. Simulated packet error rate (PER) results show that the simplified method paired with CTC has greater performance, yet lower complexity, compared to original direct method paired with CC.