Automatic-repeat-request error control schemes

Error detection incorporated with automatic-repeat-request (ARQ) is widely used for error control in data communication systems. This method of error control is simple and provides high system reliability. If a properly chosen code is used for error detection, virtually error-free data transmission can be attained. Various types of ARQ and hybrid ARQ schemes, and error detection using linear block codes are surveyed

Collaborative HARQ Schemes for Cooperative Diversity Communications in Wireless Networks

Wireless technology is experiencing spectacular developments, due to the emergence of interactive and digital multimedia applications as well as rapid advances in the highly integrated systems. For the next-generation mobile communication systems, one can expect wireless connectivity between any devices at any time and anywhere with a range of multimedia contents. A key requirement in such systems is the availability of high-speed and robust communication links. Unfortunately, communications over wireless channels inherently suffer from a number of fundamental physical limitations, such as multipath fading, scarce radio spectrum, and limited battery power supply for mobile devices. Cooperative diversity (CD) technology is a promising solution for future wireless communication systems to achieve broader coverage and to mitigate wireless channels’ impairments without the need to use high power at the transmitter. In general, cooperative relaying systems have a source node multicasting a message to a number of cooperative relays, which in turn resend a processed version message to an intended destination node. The destination node combines the signal received from the relays, and takes into account the source’s original signal to decode the message. The CD communication systems exploit two fundamental features of the wireless medium: its broadcast nature and its ability to achieve diversity through independent channels. A variety of relaying protocols have been considered and utilized in cooperative wireless networks. Amplify and forward (AAF) and decode and forward (DAF) are two popular protocols, frequently used in the cooperative systems. In the AAF mode, the relay amplifies the received signal prior to retransmission. In the DAF mode, the relay fully decodes the received signal, re-encodes and forwards it to the destination. Due to the retransmission without decoding, AAF has the shortcoming that noise accumulated in the received signal is amplified at the transmission. DAF suffers from decoding errors that can lead to severe error propagation. To further enhance the quality of service (QoS) of CD communication systems, hybrid Automatic Repeat-reQuest (HARQ) protocols have been proposed. Thus, if the destination requires an ARQ retransmission, it could come from one of relays rather than the source node. This thesis proposes an improved HARQ scheme with an adaptive relaying protocol (ARP). Focusing on the HARQ as a central theme, we start by introducing the concept of ARP. Then we use it as the basis for designing three types of HARQ schemes, denoted by HARQ I-ARP, HARQ II-ARP and HARQ III-ARP. We describe the relaying protocols, (both AAF and DAF), and their operations, including channel access between the source and relay, the feedback scheme, and the combining methods at the receivers. To investigate the benefits of the proposed HARQ scheme, we analyze its frame error rate (FER) and throughput performance over a quasi-static fading channel. We can compare these with the reference methods, HARQ with AAF (HARQ-AAF) and HARQ with perfect distributed turbo codes (DTC), for which correct decoding is always assumed at the relay (HARQ-perfect DTC). It is shown that the proposed HARQ-ARP scheme can always performs better than the HARQ-AAF scheme. As the signal-to-noise ratio (SNR) of the channel between the source and relay increases, the performance of the proposed HARQ-ARP scheme approaches that of the HARQ-perfect DTC scheme

An adaptive coding scheme with code combining for mobile radio systems

10.1109/25.260765IEEE Transactions on Vehicular Technology424469-476ITVT

Trellis coded modulation techniques

The subject of this thesis is an investigation of various trellis coded modulation (TCM) techniques that have potential for out-performing conventional methods. The primary advantage of TCM over modulation schemes employing traditional error-correction coding is the ability to achieve increased power efficiency without the normal expansion of bandwidth introduced by the coding process. Thus, channels that are power limited and bandwidth limited are an ideal application for TCM. In this thesis, four areas of interest are investigated. These include: signal constellation design, multilevel convolutional coding, adaptive TCM and finally low-complexity implementation of TCM. An investigation of the effect of signal constellation design on probability of error has led to the optimisation of constellation angles for a given channel signal to noise ratio and a given code. The use of multilevel convolutional codes based on rings of integers and multi-dimensional modulation is presented. The potential benefits of incorporating several modulation schemes with adaptive TCM which require a single decoder are also investigated. The final area of investigation has been the development of an algorithm for decoding of convolutional codes with a low complexity decoder. The research described in this thesis investigated the use of trellis coded modulation to develop various techniques applicable to digital data transmission systems. Throughout this work, emphasis has been placed on enhancing the performance or complexity of conventional communication systems by simple modifications to the existing structures

The development of an error-correcting scheme for use with a six-tone HF modem

This thesis describes the development of an error correcting system for a H.F. modem employing 6-tone Multi-Frequency Shift Keying (MFSK) as its modulation scheme. The modulation scheme was chosen to be compatible with equipment already in service and to eliminate the need to modify the existing communications infrastructure. A convolutional code together with either Viterbi decoding or Fano decoding is chosen to provide the error correction because of the potential power of such codes and because it is possible for these combinations of code and decoding method to work with any alphabet size. To detect whether correction has been successful a Cyclic Redundancy Check (CRC) is embedded within the data block before encoding.A method of using a convolutional code to provide variable rate is presented. The method uses a systematic code so that it is possible for the scheme to have a quick look to see if the first data transmission has been received error free. A search for good codes is undertaken and the effect the alphabet size has on the code spectra discussed. It is shown that a good generator sequence for a binary code is also a good generator sequence for non-binary codes.To decode the convolutional code both the Viterbi maximum likelihood decoder and the Fano sequential decoder are studied. It is argued that the Fano sequential decoder is the better choice for this application because it makes better use of system resources which will be limited in the field equipment. It is also shown that the performance of multi-level codes is better than binary codes and that an alphabet size of around 6 is optimum.The throughput of the variable rate scheme and a number of fixed rate schemes is examined. It is shown that the variable rate scheme provides the best throughput at all data rates and that the throughput improvement at the higher data rates is greatest. The effect of interleaving is also examined and results presented.To support the variable rate scheme a protocol is developed that can be used on practical H.F. channels. The potential problems with errors on both the forward and return channel are analysed and mechanisms to deal with these built-in

Packet data communications over coded CDMA with hybrid type-II ARQ

This dissertation presents in-depth investigation of turbo-coded CDNIA systems in packet data communication terminology. It is divided into three parts; (1) CDMA with hybrid FEC/ARQ in deterministic environment, (2) CDMA with hybrid FEC/ARQ in random access environment and (3) an implementation issue on turbo decoding. As a preliminary, the performance of CDMA with hybrid FEC/ARQ is investigated in deterministic environment. It highlights the practically achievable spectral efficiency of CDMA system with turbo codes and the effect of code rates on the performance of systems with MF and LMMSE receivers, respectively. For given ensemble distance spectra of punctured turbo codes, an improved union bound is used to evaluate the error probability of ML turbo decoder with MF receiver and with LMMSE receiver front-end and, then, the corresponding spectral efficiency is computed as a function of system load. In the second part, a generalized analytical framework is first provided to analyze hybrid type-11 ARQ in random access environment. When applying hybrid type-11 ARQ, probability of packet success and packet length is generally different from attempt to attempt. Since the conventional analytical model, customarily employed for ALOHA system with pure or hybrid type-I ARQ, cannot be applied for this case, an expanded analytical model is introduced. It can be regarded as a network of queues and Jackson and Burke\u27s theorems can be applied to simplify the analysis. The second part is further divided into two sub topics, i.e. CDMA slotted ALOHA with hybrid type-11 ARQ using packet combining and CDMA unslotted ALOHA with hybrid type-11 ARQ using code combining. For code combining, the rate compatible punctured turbo (RCPT) codes are examined. In the third part, noticing that the decoding delay is crucial to the fast ARQ, a parallel MAP algorithm is proposed to reduce the computational decoding delay of turbo codes. It utilizes the forward and backward variables computed in the previous iteration to provide boundary distributions for each sub-block MAP decoder. It has at least two advantages over the existing parallel scheme; No performance degradation and No additional computation