Darmstadt, Techn. University, Diss., 2002.

There are two important techniques, automatic repeat request (ARQ) and forward error control (FEC), in error control systems. ARQ uses redundancy for detecting errors. While an error is detected in a transmitted code word, the receiver requests the transmitter to re-transmit the corrupted code word and the transmitted code word with detected error is discarded. However, the transmitted code word with detected error still contains a lot of information. ARQ schemes require a feedback channel. FEC relies on the controlled use of redundancy in the transmitted code word to detect and correct errors. Whether the decoding of the received code word is successful, no further processing is performed at the receiver. Therefore, FEC requires only a one-way link between the transmitter and receiver. In error control systems, a powerful FEC, turbo coding, was first proposed in 1993. Its performance was investigated by simulation to be close to the Shannon limit. Hybrid ARQ (HARQ) systems after properly combining the ARQ techniques and FEC techniques, can be classified into type-I, type-II and type-III, and its performance can be elevated far more than ARQ systems. HARQ adopts the FEC methods to detect and correct the error patterns caused in the process of transmission. While errors are detected in the demodulated signals at receiver and fail to be corrected, the receiver will activate ARQ mechanism to request the transmitter to retransmit related information to achieve an error-free transmission. In this thesis, a feasible type-II hybrid ARQ algorithm is proposed. Performance of the proposed algorithm is evaluated and analyzed by computer simulations. Compared with the traditional HARQ algorithms, the proposed algorithm can offer better performance in delay time and number of retransmissions with approximate throughput.

The problem of the efficient use of Hybrid Automatic-Repeat-reQuest (Hybrid-ARQ) in wireless communication has attracted a considerable amount of research. In this thesis, the use and implementation of turbo codes as the Forward Error Correction (FEC) code for Hybrid-ARQ is investigated. The major accomplishments of the research include both the analysis and implementation of turbo Hybrid-ARQ. The thesis begins by obtaining a tractable bound for the performance of turbo codes with M-ary Quadrature-Amplitude-Modulation (M-ary QAM). The research considers the design problem of turbo coded Hybrid-ARQ optimized for AWGN and fading channels. The design problem of turbo Hybrid-ARQ in wideband channels is considered and an optimization strategy is proposed based on Orthogonal-Frequency-Division- Multiplexing (OFDM). The research also presents a novel rate scalable encoder structure that optimal selects a disparate but optimal pair of component codes given the channel conditions. A second part of the thesis considers the implementation of turbo Hybrid-ARQ in Very Large Scale Integration (VLSI ) systems. A design for a single architecture for Type-I and Type-II turbo Hybrid-ARQ is suggested in addition to approaches for improving performance of the Soft-Output-Viterbi-Algorithm(SOVA) decoder core. The research also proposes a SOVA decoder architecture that exploits reliability information to select between the SOVA and bi-directional SOVA.

No description available.

The objective of this dissertation is to investigate incremental redundancy low-density parity-check (IR-LDPC) codes for hybrid forward error correction / automatic repeat request (HybridARQ) schemes. Powerful capacity-approaching IR-LDPC codes are one of the key functional elements in high-throughput HybridARQ schemes and provide a flexible rate-compatible structure, which is necessary for low-complexity HybridARQ schemes. This dissertation first studies the design and performance evaluation of IR-LDPC codes, which have good error rate performance at short block lengths. The subset codes of the IR-LDPC codes are compared to conventional random punctured codes and multiple dedicated codes. As a system model for this work, an adaptive LDPC coded system is presented. This adaptive system can confront the nature of time-varying channels and approach the capacity of the system with the aid of LDPC codes. This system shows remarkable throughput improvement over a conventional punctured system and, for systems that use multiple dedicated codes, provides comparable performance with low-complexity at every target error rate. This dissertation also focuses on IR-LDPC codes with a wider operating code range because the previous IR-LDPC codes exhibited performance limitation related to the maximum achievable code rate. For this reason, this research proposes a new way to increase the maximum code rate of the IR-LDPC codes, which provides throughput improvement at high throughput regions over conventional random punctured codes. Also presented is an adaptive code selection algorithm using threshold parameters. This algorithm reduces the number of the unnecessary traffic channels in HybridARQ schemes. This dissertation also examines how to improve throughput performance in HybridARQ schemes with low-complexity by exploiting irregular repeat accumulate (IRA) codes. The proposed adaptive transmission method with adaptive puncturing patterns of IRA codes shows higher throughput performance in all of operating code ranges than does any other single mode in HybridARQ schemes.

Automatic Repeat-reQuest (ARQ) schemes are extensively used in communication systems and computer networks to achieve reliable transmission. Using space-time codes (STCs) with multiple input multiple output (MIMO) or multiple input single output (MISO) systems is an effective way to combat multipath fading, which is the most severe impairment for wireless communication systems. STCs are designed to use the rich scattering multipath environment provided by using multiple transmit antennas. The work done in this thesis focuses on the use of ARQ schemes with non-orthogonal space-time block codes (NOSTBCs) based on Reed Solomon codes. The truncated-selective ARQ (TS-ARQ) scheme is considered and three novel hybrid ARQ (HARQ) schemes are proposed. Simulation results reveal that, compared to using TS-ARQ with orthogonal space-time block codes (OSTBCs), using NOSTBCs with any of the three proposed HARQ schemes can provide significant gains in terms of dropped packet rate and spectral efficiency at the cost of increased decoding complexity. The performance can be further improved by using the water filling principle to adaptively allocate transmit power among transmit antennas.

International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada / We study the reliable (acknowledged) operation (i.e., ARQ scheme) of CFDP (CCSDS File Delivery Protocol) over single-hop space link. We focus on the immediate NAK mode, as specified in [1], under the assumption that PDU error events of forward and backward channels are statistically independent. We point out the problem of duplicated retransmissions due to the long propagation delay and analyze throughput efficiency. We also present modeling and analysis of the average time taken for the delivery of a file with an arbitrary size, which are more rigorous than currently available heuristics.

Asynchronous Transfer Mode (ATM) protocol was designed to support real-time traffic steams over high quality links like fiber optics where the transmission error is extremely low. ATM performs poorly in an error-prone environment such as wireless communications. The purpose of this research is to investigate error control schemes in wireless ATM (W-ATM) to support real-time service, such that the physical layer error conditions are handled in lower layers under ATM transport layer. Automatic Repeat reQuest schemes (ARQ) and Forward Error Correction (FEC) have been widely used for reliable data transmissions. However, the current existing ARQ schemes can potentially introduce unbounded delay in high error rate environments like W-ATM network due to the lack of delay control mechanism. As a result, they are not appropriate for real-time data communications in which there are strict packet delay requirements. In this dissertation, we explored the issues related to W-ATM area. Adaptation of FEC, specifically Reed-Solomon code, to channel error conditions in W-ATM is investigated. The quality-of-service (QoS)-aware error control algorithm is originated and its performance is evaluated. The algorithm is further simplified to make it more suitable for practical applications. The requirements of ARQ applicability for real-time communication environment like W-ATM is extensively analyzed. An ARQ scheme, called D-bit protocol, is developed to satisfy the real-time requirements. The scheme supports reliable packet discarding while allowing retransmissions without compromising user-level QoS for real-time stream applications. Simulations show the effectiveness and liveness of the protocol. / Ph. D.

The key challenge in mobile ad-hoc network (MANET) is the design of routing protocol which adapting their behavior to frequency with rapid changes in the network. As we have known, there are two main kinds of routing protocols in MANET: proactive and reactive routing protocol; and in addition, authors [1] proposed to use location information provided by positioning devices such as global positioning systems (GPS) to assist routing. We wonder whether the assumption of all devices in the communication area have the GPS ability is reasonable; furthermore, a GPS-enabled device has its own limitation on working areas; for example, the GPS ability cannot work in the indoor environments. In this paper, (1) we tried to addition the mechanism of probing routing redirection/discovery at routing protocol in AODV. Using overheard node avoid route breaking and select route batter than origin.(2)we tried to use the property of GPS to solve the routing problems in MANET, which like broadcast storm in the route discovery, device power saving and optimal one-hop destination, channel reuse rate, and optimal routing path. According to 802.11 specification, the best way to reach the goal of device power saving is putting device into the sleep mode. In this routing protocol, we let most mobile devices stay in the sleep mode until it sends or receives data or acts as an intermediate node to forward data. Last, we use simulations and implementation to validate the effectiveness of our design.

This thesis considers the analysis of system performance and resource allocation for a coded OFDM system over frequency selective fading channels. Due to the inseparable role taken by channel coding in a coded OFDM system, an information theoretical analysis is carried out and taken as the basis for the system performance and throughput. Based on the results of the information theoretical analysis, the optimal system BER performance of a coded OFDM system is first shown to converge to the outage probability for large OFDM block lengths. Instead of evaluating the outage probability numerically, we provide in this thesis a simple analytical closed form approximation of the outage probability for a coded OFDM system over frequency selective quasi-static fading channels. Simulation results of the turbo-coded OFDM systems further confirm the approximation of the outage probability. By taking the instantaneous channel capacity as the analytical building block, system throughput of a coded OFDM system is then provided. With the aim to compare the performance difference between adaptive and uniform resource allocation strategies, the system throughput of different allocation schemes under various channel conditions is analyzed. First, it is demonstrated that adaptive power allocation over OFDM sub-carriers at the transmitter achieves very little gain in terms of throughput over a uniform power distribution scheme. Theoretical analysis is then provided of the throughput increase of adaptive-rate schemes compared with fixed-rate schemes under various situations. Two practical OFDM systems implementing rate-compatible-punctured-turbo-code-based (RCPT-based) hybrid automatic-repeat-request (Hybrid-ARQ) and redundancy incremental Hybrid-ARQ protocols are also provided to verify the analytical results.