Cross-layered retransmission schemes for TCP-based services

Various retransmission schemes for wireless communication systems have been used to improve performance such as reliability and throughput. Each retransmission scheme is designed to improve the performance according to characteristics of each layer of protocol stacks, such as delay components and error control. Especially, a cross-layered retransmission scheme has been proposed to maximize the spectral efficiency by combining a retransmission scheme and adaptive modulation and coding (AMC). However, the cross-layered retransmission scheme is designed for performance improvement at the wireless access networks. The end-to-end performance is not taken into account for modeling of the cross-layered retransmission schemes. It is difficult to design retransmission schemes for the end-to-end performance improvement. In this paper, we analyze the delay and the throughput at the transport layer for the end-to-end performance when a system uses a cross-layered retransmission scheme and the transmission control protocol as the reliable transmission protocols. We also propose a cross-layered retransmission strategy, AMC combined with automatic repeat request (ARQ) and hybrid ARQ (HARQ), to improve end-to-end throughput. From the evaluation results, it is shown that the proposed cross-layered retransmission strategy is suitable for delay insensitive services that require high throughput.     

A spread slotted CDMA/ALOHA system with hybrid ARQ for satellitemultiple access

We propose and investigate a new type of satellite multiple access protocol that combines the characteristics of the spread slotted (SS)-ALOHA protocol, code division multiple access (CDMA), and the hybrid automatic repeat request (ARQ) error controlling and retransmission scheme, in order to increase the throughput by reducing the number of retransmissions and to keep the bit error rate (BER) of the satellite link low when the channel experiences heavy traffic. The main feature of our proposed system is the utilization of two different fields in the analysis of the satellite multiple access problem. Since the hub now possesses the forward error correction (FEC) capability to correct errors that appear after the CDMA despreading of the packets, the satellite does not need to ask so often for the retransmission of erroneous packets and will ask for retransmission only when the FEC error correcting capability is exceeded. This paper also presents the adaptive optimization of the balance between the CDMA processing gain and FEC coding gain in order to obtain a better throughput for the SS-CDMA/ALOHA with hybrid ARQ protocol for satellite multiple access. The optimization is made with the constraint of keeping the bandwidth of the transmitted packets constant during all times. According to this, the effective throughput of the protocol (information bits over total transmitted bits ratio) is improved by adaptively changing the CDMA and FEC codes used in the transmission. This adaptive optimization is done by observing the channel status or load and increasing or decreasing both coding schemes' gains. Computer simulations show the performance of the proposed multiple access scheme     

Parity retransmission hybrid ARQ using rate 1/2 convolutional codeson a nonstationary channel

A parity retransmission hybrid automatic repeat request (ARQ) scheme is proposed which uses rate 1/2 convolutional codes and Viterbi decoding. A protocol is described which is capable of achieving higher throughputs than previously proposed parity retransmission schemes. The performance analysis is based on a two-state Markov model of a nonstationary channel. This model constitutes a first approximation to a nonstationary channel. The two-state channel model is used to analyze the throughput and undetected error probability of the protocol presented when the receiver has both an infinite and a finite buffer size. It is shown that the throughput improves as the channel becomes more bursty     

Adaptive A-MPDU retransmission scheme with two-level frame aggregation compensation for IEEE 802.11n/ac/ad WLANs

The aggregate MAC protocol data unit (A-MPDU) is one of the significant frame aggregation schemes to improve the performance for high-rate IEEE 802.11n/ac/ad wireless local area networks (WLANs). However, the performance of the A-MPDU scheme does not meet the user expectations because the frame length of the retransmitted A-MPDU will be inevitably and sharply reduced due to the effect of the lost subframe on the number of the aggregatable subframes (i.e., the aggregation level). To overcome this problem, an adaptive A-MPDU retransmission scheme with the two-level frame aggregation compensation is proposed. In this scheme, when the aggregation level of the retransmitted A-MPDU frame dramatically decreases, one of the appropriate two-level aggregation strategies is adaptively employed to compensate the length of the retransmitted A-MPDU frames according to the theoretical analysis of the throughput performance for the conventional A-MPDU scheme and two strategies of the two-level aggregate frame respectively. Simulations using ns-3 platform are performed and the results demonstrate that the proposed adaptive A-MPDU retransmission scheme can achieve higher throughput and medium access control (MAC) layer efficiency.     

Throughput performance of memory ARQ schemes

We present a throughput analysis for the memory automatic repeat request (ARQ) schemes with self-decodable frame retransmissions, taking into account frame header and frame acknowledgment failure probability. A lower bound on the throughput is obtained for a very general class of schemes which encompasses many of those proposed in the literature. Numerical results are given for several example systems, and suitable header and acknowledgment forward error correction (FEC) encodings are determined     

Adaptive Modulation and Coding with Selective Retransmission under OFDM signaling

In this paper, we present bandwidth efficient selective retransmission method in conjunction with adaptive modulation and coding (AMC) scheme for OFDM waveform. In the proposed method, when a packet failure occurs, receiver requests retransmission of information symbols prone to error corresponding to the low signal-to-noise ratio (SNR) sub-carriers of OFDM modulation. The selective retransmission avoids unnecessary retransmission and AMC chooses a proper modulation and coding scheme with an objective to maximize the throughput. Our method achieves higher throughput as compared to conventional retransmission methods such as Chase combining hybrid automatic repeat reQuest (CC-HARQ) and incremental redundancy hybrid automatic repeat reQuest (IR-HARQ). We also provide the throughput and delay analysis of the proposed method for non-truncated ARQ. The simulation results demonstrate throughput gain without significant impact on delay as compared to the conventional retransmission approaches.     

A novel adaptive hybrid ARQ scheme for wireless ATM networks

This paper describes the design and performance of a novel adaptive hybrid ARQ scheme using concatenated FEC codes for error control over wireless ATM networks. The wireless links are characterized by higher, time‐varying error rates and burstier error patterns in comparison with the fiber‐based links for which ATM was designed. The purpose of the hybrid ARQ scheme is to provide a capability to dynamically support reliable ATM‐based transport over wireless channels by using a combination of our ARQ scheme (called SDLP) and the concatenated FEC scheme. The key ideas in the proposed hybrid ARQ scheme are to adapt the code rate to the channel conditions using incremental redundancy and to increase the starting code rate as much as possible with the concatenated FEC, maximizing the throughput efficiency. The numerical results show that our proposed scheme outperforms other ARQ schemes for all SNR values. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hybrid Error Control Using Retransmission and Generalized Burst-Trapping Codes

On most real channels hybrid error control schemes are expected to provide a throughput higher than that of automatic repeatrequest (ARQ) systems and a reliability better than forward error correction (FEC) systems. On compound channels, channels with a mixture of random and burst errors, generalized burst-trapping (GBT) codes seem to be quite effective for FEC. In this paper, a hybrid scheme with Go BackNARQ as the retransmission component and GBT code as the FEC component, is described. Its performance is analyzed in terms of throughput efficiency and undetected error probability and is compared with that of a forward-acting GBT code. Numerical calculations of the parameters are presented to illustrate the performance.     

Multidestination Protocols for Satellite Broadcast Channels

Two retransmission procedures, the go-back-N(GBN) scheme and the selective repeat (SR) scheme, have been analyzed for data transfer from one transmitter to many receivers. We consider transfer of error-controlled bulk data over a satellite broadcast channel. Two retransmission strategies, the dynamic retransmission group reduction (DRGR) technique and the fixed retransmission group (FRG) technique, are proposed. We study the GBN and SR schemes for both strategies. Analytic expressions are derived for the throughput performance of the GBN scheme and of the SR scheme with infinite resources, while discrete event simulation is used to estimate the throughput of the selective repeat scheme with finite resources. Only the SR scheme using the DRGR technique provides acceptable performance for high-speed bulk data transfer. For the DRGR technique, the throughput falls logarithmically with an increase in the number of receivers. In contrast, the throughput for the FRG technique falls exponentially with an increase in the number of receivers.     

Optimal design of hybrid FEC/ARQ schemes for TCP over wireless links with Rayleigh fading

In this paper, we investigate interactions between TCP and wireless hybrid FEC/ARQ schemes. The aim is to understand what is the best configuration of the wireless link protocol in order to guarantee TCP performance and channel efficiency. Interactions between TCP and different link layer mechanisms are evaluated by means of an analytic model that reproduces: 1) a Rayleigh fading channel with FEC coding, 2) a generic selective repeat ARQ Protocol, and 3) the TCP behavior in a wired-cum-wireless network scenario. The analytic model is validated-by means of ns-based simulations. The analysis represents a contribution to the optimal design of link layer parameters of wireless networks crossed by TCP/IP traffic. The main findings can be summarized as follows: 1) fully reliable ARQ protocols are the best choice for both TCP performance and wireless link efficiency and 2) optimal values of FEC redundancy degree from the point of view of energy efficiency maximizes TCP performance as well.     

Selective-repeat-ARQ schemes for broadcast links

The authors propose retransmission error control schemes for broadcast channels. In their selective-repeat-ARQ (automatic repeat request) method, they incorporate some aspects of implementation that they believe were ignored by all the previous work. Based on this protocol, they also propose a type-2 hybrid ARQ scheme that uses parity retransmission. They apply the dynamic programming optimization technique of Wang and Silvester (1987), with some modification, to their schemes. Analysis shows that their schemes outperform all the existing schemes. As special cases of their proposed schemes, the authors can obtain point-to-point ARQ schemes which also outperform all the existing point-to-point schemes. Thus, their schemes extend the useful range of retransmission error control schemes for these channels     

An Enhanced A-MSDU Frame Aggregation Scheme for 802.11n Wireless Networks

The main goal of the IEEE 802.11n standard is to achieve a minimum throughput of 100 Mbps at the MAC service access point. This high throughput has been achieved via many enhancements in both the physical and MAC layers. A key enhancement at the MAC layer is frame aggregation in which the timing and headers overheads of the legacy MAC are reduced by aggregating multiple frames into a single large frame before being transmitted. Two aggregation schemes have been defined by the 802.11n standard, aggregate MAC service data unit (A-MSDU) and aggregate MAC protocol data unit (A-MPDU). As a consequence of the aggregation, new aggregation headers are introduced and become parts of the transmitted frame. Even though these headers are small compared to the legacy headers they still have a negative impact on the network performance, especially when aggregating frames of small payload. Moreover, the A-MSDU is highly influenced by the channel condition due mainly to lack of subframes sequence control and retransmission. In this paper, we have proposed an aggregation scheme (mA-MSDU) that reduces the aggregation headers and implements a retransmission control over the individual subframes at the MSDU level. The analysis and simulations results show the significance of the proposed scheme, specifically for applications that have a small frame size such as VoIP.     

Performance of a type-II hybrid ARQ protocol in slotted DS-SSMApacket radio systems

The application of a type-II hybrid ARQ protocol in a slotted direct-sequence spread-spectrum multiple-access (DS-SSMA) packet radio system is investigated. Both the static performance and the dynamic performance of such a system are analyzed. In the physical layer, packet error and packet success probabilities are computed using the improved Gaussian approximation technique, which accounts for the bit-to-bit error dependence within a packet. In the data-link layer, two-dimensional Markov chains are employed to model the system dynamics. Based on this model, the performance of the type-II hybrid ARQ protocol is upper and lower bounded by considering, respectively, a superior scheme and an inferior scheme. Steady state throughput and delay performances of the two bounding schemes are obtained. Moreover, it is shown that for each fixed input load, there is an optimal retransmission probability under the finite user population assumption. Bounds on this optimal retransmission probability are also given     

Trellis Coded Hybrid Selective Repeat ARQ Schemes for Point-to-Multipoint Communication over Rayleigh Fading Channels

In this paper, the hybrid selective repeat (SR) automatic repeat request (ARQ) scheme using trellis coded modulation (TCM) proposed by Tellambura and Bhargava [21] is generalized to point-to-multipoint communications for Rayleigh fading channel. Analytical expressions are derived for the throughputs of the point-to-multipoint communication schemes with and without code combining technique. Numerical results show that the protocol using code combining technique yields better throughput than the protocol without code combining and the throughputs decrease when the number of receivers and the value of erasure threshold increase. When the number of receivers equals 1, the scheme without code combining becomes the point-to-point communication scheme proposed in [21].     

一种面向实时业务的Ad Hoc网络MAC协议

为降低AdHoe网络中实时业务的端到端时延,提出了基于802．11DCF的改进协议。协议采用3种机制降低实时业务的时延：面向路径的连续转发机制将RTS中的转发信息携带在ACK中发送,给实时业务提供较高的接入优先级;标签交换机制使得中间节点可以在MAC层获取转发信息,加快了实时业务数据包的转发速度;重传控制机制减少了无效传输的超时数据包。仿真结果表明,在重负载条件下,改进协议中实时业务的时延比802．11DCF有大幅度的下降,网络吞吐量也有所提高。     

Adaptive source rate control for real‐time wireless video transmission

Hybrid ARQ schemes can yield much better throughput and reliability than static FEC schemes for the transmission of data over time-varying wireless channels. However these schemes result in extra delay. They adapt to the varying channel conditions by retransmitting erroneous packets, this causes variable effective data rates for current PCS networks because the channel bandwidth is constant. Hybrid ARQ schemes are currently being proposed as the error control schemes for real-time video transmission. An important issue is how to ensure low delay while taking advantage of the high throughput and reliability that these schemes provide for. In this paper we propose an adaptive source rate control (ASRC) scheme which can work together with the hybrid ARQ error control schemes to achieve efficient transmission of real-time video with low delay and high reliability. The ASRC scheme adjusts the source rate based on the channel conditions, the transport buffer occupancy and the delay constraints. It achieves good video quality by dynamically changing both the number of the forced update (intracoded) macroblocks and the quantization scale used in a frame. The number of the forced update macroblocks used in a frame is first adjusted according to the allocated source rate. This reduces the fluctuation of the quantization scale with the change in the channel conditions during encoding so that the uniformity of the video quality is improved. The simulation results show that the proposed ASRC scheme performs very well for both slow fading and fast fading channels. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sequential decoding with an efficient partial retransmission ARQstrategy

The authors present and analyze an efficient partial retransmission automatic repeat request (ARQ) strategy using convolutional coding and sequential decoding in conjunction with code combining. In the proposed ARQ scheme, whenever a packet of data needs to be retransmitted that packet is not repeated entirely as in the case of conventional full retransmission ARQ strategies. Instead, symbols of that packet are repeated a few at a time, sequentially, as needed, hence making a more effective use of the channel. It is shown that partial repetitions and code combining still yields an increase of the apparent Pareto exponent of sequential decoding, as in the case of full repetition-code combining. A throughput analysis shows that the partial retransmission ARQ strategy yields a substantial throughput improvement over the full retransmission-code combining ARQ strategies     

Separate codes on type-II hybrid ARQ systems

A hybrid automatic repeat request (ARQ) system (HARQ-II) with parity retransmission for error correction, which combines ARQ and forward error correction is discussed, and the successful application of these codes to HARG-II is illustrated. A method of constructing the codes whereby conventional BCH codes can be changed into separable codes is proposed. A scheme is presented that has the advantages that, the code lengths are always made equal and that even in parity retransmission new information symbols can be sent along with the necessary parity-check symbols. The performance of the proposed schemes on the binary symmetric channel is discussed. The numerical results show that they outperform conventional schemes     

Performance of ATM networks under hybrid ARQ/FEC error controlscheme

In ATM networks, fixed-length cells are transmitted. A cell may be discarded during the transmission due to buffer overflow or detection of errors. Cell discarding seriously degrades transmission quality. This paper analyzes a hybrid automatic repeat request/forward error control (ARQ/FEC) cell-loss recovery scheme that is applied to virtual circuits (VCs) of ATM networks. FEC is performed based on a simple single-parity code, while a Go-Back-N ARQ is employed on top of that. Both throughput efficiency and reliability analysis of the hybrid scheme are presented. In the process we investigate the interactive effects of the network parameters (number of transit nodes, traffic intensity, ARQ packet length, …) on the performance. The analysis provides a method for optimizing the FEC code size for a given network specification