Adaptive Hybrid ARQ System Using Turbo Product Codes with Hard/Soft Decoding

Abstract

The bit error rate (BER) performance of turbo product codes (TPC) has been considered extensively in the literature. However, other performance metrics such as throughput can be more informative in particular systems. In this letter, the throughput performance of hybrid automatic repeat request (HARQ) is considered using TPC with iterative hard and soft decision decoding. Monte Carlo simulation and semi-analytical solutions are developed to evaluate the throughput of HARQ-TPC system for a wide selection of codes. The obtained results reveal that the coding gain advantage of the soft over hard decoding is reduced significantly when throughput is adopted as the performance metric, and it actually vanishes completely for some codes. When adaptive coding is used, the soft decoding advantage is limited to about 1.4 dB.Index Terms-Hybrid automatic repeat request, turbo product codes, subpacket systems, error detection, iterative decoding. I. INTRODUCTIONT URBO product codes (TPC), alternatively referred to as block turbo codes, are powerful forward error correction (FEC) codes that can provide high coding gain [1]. TPC are constructed by serially concatenating two linear block codes separated by an interleaver [2]. TPC support a wide range of codeword sizes and code rates, and they are included in some recent communication standards such as the IEEE-802.16 for fixed and mobile broadband wireless access systems [3] and the IEEE-1901 for broadband power line networks [4].The ultimate coding gain of TPC is achieved by performing a number of soft-input soft-output (SISO) iterative decoding processes that are applied to each row and column in the codeword matrix, which requires considerable computational power [5]. Consequently, reducing the computational complexity of TPC has received significant attention in the literature as reported in [5], [6] and the references listed therein. The computational complexity constraint of TPC becomes even more severe for systems that employ automatic repeat request (ARQ) protocol because particular packets have to be retransmitted, and hence decoded several times. The techniques that employ both FEC and ARQ are usually referred to as hybrid ARQ (HARQ) [7].In the literature, Al-Dweik et al. [5], [8], [9] proposed new techniques to reduce the SISO decoders complexity Manuscript

Link adaptation for wireless video communication systems

“…In this project, an adaptive TPC HARQ scheme with packet combining is proposed to maximize system throughput based on the channel condition. Preliminary results show that system complexity and power consumption can be reduced while maintaining the system throughput unchanged [5].…”

“…The adaptation process is performed to maximize the system throughput by changing the codeword size and code rate based on the channel condition. Based on our evaluation of the T-HARQ system, we observed that system complexity and power consumption can be reduced while maintaining the system throughput unchanged [5]. In the second part of the PhD project, we plan to find out an optimum power assignment per retransmission for the T-HARQ system such that for a given throughput value the total consumed power is minimized.…”

On the performance of adaptive HARQ with no channel state information feedback

“…In our work in [12] a power optimization algorithm is proposed to minimize the transmit energy under throughput constraints. The main motivation for adopting this approach is the unique behavior of several HARQ systems where the throughput varies in a staircase manner as a function of the signal-to-noise ratio (SNR) [13]- [16]. The staircase behavior of the throughput implies that the transmit power can be controlled eruptively to minimize the total transmit energy while maintaining the throughput unchanged.…”

Low Complexity Hybrid ARQ Using Extended Turbo Product Codes Self-Detection

“…In the second phase, the receiver verifies if the FEC process was successful, and then sends a message to the transmitter to retransmit the packet if the FEC process was unsuccessful; otherwise, the message informs the transmitter to send the next packet in the transmitter buffer. In general, most of the work reported in the literature performs the bit error correction and packet error detection (PED) as two independent processes where the FEC is implemented at the Physical Layer (PHY) while the PED is performed at the Data Link Control (DLC) layer [5], [6]. Because the FEC and PED are implemented at two different layers, the interaction between the two FEC and PED operations is considered as a cross-layer cooperation.…”

“…The PED is usually performed using cyclic redundancy check (CRC) codes [5], [6]. The generic implementation of the CRC process is based on a linear feedback shift register (LFSR) that performs the polynomial division process of the serial data input.…”