共查询到20条相似文献,搜索用时 31 毫秒
1.
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 相似文献
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Packet access using DS-CDMA with frequency-domain equalization 总被引:2,自引:0,他引:2
The next-generation mobile communications system is anticipated to support very high-speed data rates exceeding several tens megabits per second. In this paper, we consider high-speed downlink packet access for direct-sequence code-division multiple access (DS-CDMA) as in third-generation wideband code-division multiple-access systems. Adaptive modulation and coding (AMC), multicode operation and hybrid automatic repeat request (HARQ) will be the enabling technologies. With such high-speed data transmissions, however, multicode operation severely suffers from the loss of orthogonality among the spreading codes since the wireless channel becomes severely frequency-selective. In this paper, we apply frequency-domain equalization (FDE) based on minimum mean-square error (MMSE) criterion instead of conventional rake combining for receiving the packet. A new MMSE-FDE weight is derived for packet combining. The throughput in a frequency-selective Rayleigh-fading channel is evaluated by computer simulation for Chase combining and incremental redundancy (IR) packet combining. It is shown that the use of MMSE-FDE for the reception of multicode DS-CDMA packet gives an improved throughput irrespective of the channel's frequency-selectivity. 相似文献
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The wireless medium may cause substantial packet losses, rendering Transmission Control Protocol (TCP) inefficient. We propose a cross-layer solution by combining link-layer retransmission techniques and a solution for TCP packet reordering. It is costly to conduct link-layer retransmission with the constraint of orderly packet delivery. We require the link layer to provide reliable packet delivery, but without orderly delivery guarantee, thus transforming the problem of high packet error rates to the problem of packet reordering. The latter is dealt with by enhancing TCP with a solution for packet reordering. We justify our design by analyzing both general scenarios and the case of IEEE 802.11n. Our simulation results demonstrate that the proposed method is effective in improving TCP connection goodput in wireless networks. 相似文献
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本文采用TURBO码为纠错码,在分析传统的反馈重传方式的基础上,将分块传输系统和码合并技术相结合,提出了一种新型HARQ系统,并为其设计了新型交织器。新型HARQ系统将每帧数据多次重传合并,转化为在一帧的多个分块之间合并,不需要重传。该系统大幅度降低了重传次数、交织的时延和平均迭代次数,实现了数据的实时通信;译码器接收的数据在解扩之前充分合并,更加有效地利用了软信息;该系统还省去了常用Ⅰ型HARQ系统中必须使用的收发端复杂的反馈重传控制和庞大的存储器;新型HARQ系统巾TURBO码的最小距离增加为原来的许多倍。通过理论分析和仿真比较了新型HARQ系统和Ⅰ型HARQ系统的性能,结果证明了新型HARQ系统性能的优越性。新型HARQ系统为第三代无线通信技术提供了一种较好地选择。 相似文献
5.
LIU Fang KONG Jian WANG Wen-bo LIU Yuan-anBeijing University of Posts Telecommunications Beijing P.R.China 《中国邮电高校学报(英文版)》2005,12(1)
1 Introduction With the proliferation of the World Wide Web (WWW)in our daily life, a number of wireless data services[1] suchas voice, audio, video streaming, file and web downloadingalso need to be supported in the wireless access networks.To bring the WWW traffic to the wireless mobile devices, itis important that a suitable protocol or standard is chosen tocater to the growing demands of data services over wirelesschannels which could handle a wide variety of multimediatraffic with … 相似文献
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《Vehicular Technology, IEEE Transactions on》2009,58(9):4795-4804
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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. 相似文献
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无线网络中,节点发送的数据分组传输失败后,执行重传机制。传统的重传机制ARQ由于在一次重传中只能发送一个丢失的数据分组,因此传输效率比较低。利用网络编码技术和AQR重传机制,我们可以在重传中使用网络编码,广播发送由多个丢失数据分组编码得到的编码分组,从而提高重传效率。本文中我们提出一种将网络编码应用于多个发送方多个接收方(MSMR)无线网络中的算法RMBNC。理论推导和仿真分析验证了我们提出的算法的有效性。 相似文献
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In this paper, we present a discrete time Markov chain based analytical framework for the study of Direct-Sequence Code-Division-Multiple-Access (DS-CDMA) with slotted ALOHA random access protocols (DS-CDMA-S-ALOHA) for packet Personal Communications Networks (PCNs). It incorporates both the random access and the random errors associated with DS-CDMA-S-ALOHA protocols into a unified framework. The key feature is that it distinguishes between the two stages in the transmission process, namely the access stage and the reception stage, which characterize the random access and the random errors associated with DS-CDMA-S-ALOHA protocols respectively. Two DS-CDMA-S-ALOHA protocols are presented and analyzed. The performance of the protocols and the effects of the design parameters, namely the packet retransmission probability and the forward error correction code rate of the Bose-Chaudhuri-Hocquenghem (BCH) block codes are evaluated numerically and compared with a bandwidth equivalent conventional multi-channel slotted ALOHA system. The results show that, by proper design, the DS-CDMA-S-ALOHA protocols can double the throughput with respect to that of a bandwidth equivalent conventional multi-channel slotted ALOHA system. 相似文献
11.
We study packet combining techniques for retransmission schemes over intersymbol interference (ISI) channels. Two types of combining schemes are investigated, namely, maximum-likelihood combining (MLC) and iterative combining (IC). By first employing a precoding technique and then by interpreting the ISI channel as a trellis code, the transmissions of the same data packet at different times through the channel can be treated as the parallel concatenation of recursive trellis codes. If interleavers are used in between retransmissions, "turbo" coding gains can be achieved by iterative equalization. It is shown that IC provides excellent performance and outperforms other forms of combining in terms of frame error rate performance both analytically and through simulations 相似文献
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This paper proposes an efficient packet selection algorithm, called Weight Pick, for improving the efficiency of a network coding based multicast retransmission protocol in mobile communication networks. Unlike existing packet selection algorithms, Weight Pick introduces the concept of a dynamic combination number in performing network coding. Based on this concept, a base station dynamically determines the number of packets combined or encoded in a retransmission packet based on the current packet receiving status of users and the combination number for each retransmission packet can be different. In packet selection, Weight Pick attempts to find an encoding combination whose weight is not less than (C ? 1) for every user, where C is the combination number of that retransmission packet. Simulation results show that Weight Pick can significantly improve the retransmission performance as compared with existing packet selection algorithms in terms of both packet loss ratio and packet transmission delay. 相似文献
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In this paper, we propose an aware-based adaptive opportunistic retransmission control scheme for wireless multimedia Mesh
networks. The proposed scheme provides maximum retransmission count optimization based on environment-aware to improve packet
relay probability. The scheme discriminates the types of packet loss in wireless link by means of environment information
and selects the retransmission count by taking the IEEE 802.11 wireless channel characteristics into consideration. Furthermore,
the maximum retransmission count of MAC is adjusted adaptively. Extensive simulations demonstrate that the proposed scheme
significantly reduces packet collision probability and packet loss rate, and thus improves network throughput. 相似文献
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Jui Teng Wang 《Wireless Personal Communications》2007,43(4):1051-1055
A distributed adaptive rate system for wireless packet networks is proposed. Compared to the centralized adaptive rate system
that needs to know the packet retransmission probability to maximize the throughput, this system need not know the packet
retransmission probability in advance and can achieve the optimal adaptive rate system that maximizes the throughput for wireless
packet networks. 相似文献
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A time diversity automatic repeat-request (ARQ) scheme is investigated for a slotted narrowband DS/CDMA wireless data network over a Nakagami fading channel. Numerical results reveal that the proposed adaptive retransmission diversity with packet combining provides a considerable advantage over the conventional slotted DS/CDMA ALOHA at the expense of a slight increase in implementation complexity 相似文献
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On reducing the rate of retransmission in time-varying channels 总被引:1,自引:0,他引:1
For data communications in time-varying channels such as wireless channels, the dynamic channel fluctuations often cause high frame-error rates. When the link layer detects that a frame is in error, conventionally, the frame is dropped and retransmission of the frame is requested. Based on the fact that the erroneous frames still contain useful information, several schemes have been proposed, such as packet combining and incremental redundancy, which retain and utilize the erroneous frames to improve retransmission performance. In this paper, we address two questions: 1) how much information is still useful in the erroneous frame; and 2) how to design a retransmission scheme to make efficient use of such information. We model this scenario (retransmission with an erroneous frame available at the receiver) as communication with side information at the receiver, and for a class of time-varying channels, the compound block interference channels, we derive with information-theoretic arguments the minimum information rate sufficient for retransmission to recover the erroneous frame. Motivated by the theoretical results, we propose an embedded channel coding/modulation structure together with a rate-adaptive retransmission scheme. Performance results indicate significant improvements over existing retransmission schemes in both additive white Gaussian noise and quasi-static Rayleigh fading channels. 相似文献
19.
Averaged diversity combining is applied to an asynchronous DS/CDMA system using convolutional encoding and Viterbi decoding. A cyclic redundancy check (CRC) code is included in the scheme to trigger retransmission requests. Multiple received packets are combined on a bit by bit basis to form a single, more reliable packet. The error correcting decoder operates on the combined packet, as opposed to the most recently received individual packet (e.g., as in a type-I hybrid ARQ protocol), substantially increasing the probability of acceptance with each additional transmission. We show that the proposed technique allows a significant increase in the CDMA system capacity, throughput, and reliability 相似文献