Research Letter Throughput of Type II HARQ-OFDM/TDMUsingMMSE-FDE in aMultipath Channel

Packet services are dominant in future broadband wireless communications, where hybrid automatic repeat request (HARQ) is used for error control [1]. HARQ schemes combine error detection and forward error correction to make more efficient use of the channel. In type I HARQ, all the necessary parity bits are sent with each transmission. However, type II HARQ sends only the error detection parity bits, while the error correction parity bits are retransmitted upon request if the decoder detects errors. Therefore, with type II HARQ scheme a higher throughput can be achieved. Wireless channel is characterized as a multipath propagation environment (i.e., frequency selective fading channel). Orthogonal frequency division multiplexing (OFDM) is attractive due to its robustness against multipath channel, while a drawback is its high peak-to-average power ratio (PAPR) [2]. OFDM with rate compatible punctured turbo (RCPT) coded HARQ [3] gives a good throughput. However, in type II HARQ-OFDM the uncoded packet is send first and consequently, neither coding nor frequency diversity gain is available. In essence, OFDM-based scheme (e.g., multicarrier CDMA) with type II HARQ [4] that efficiently exploits the channel frequency selectivity in the first transmission is preferable. Most of the work in this area preclude the power requirement of multicarrier signaling due to high PAPR. In this paper, we present the use of OFDM combined with time division multiplexing (OFDM/TDM) using minimum mean square error frequency domain equalization (MMSE-FDE) [5] with type II HARQ to exploit the channel frequency selectivity. In type II HARQ OFDM/TDM during the first uncoded transmission the channel frequency selectivity is exploited through MMSE-FDE to increase the throughput of conventional OFDM with a lower PAPR. The paper is organized as follows. Section 2 describes the system model. The performance is presented in Section 3. Section 4 concludes the letter.