共查询到18条相似文献,搜索用时 571 毫秒
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针对RC-LDPC码编码的自适应增余型重传(IR-HARQ)系统,构造了码率范围从0.1到0.9,码率间隔为0.1的速率匹配低密度奇偶校验(RC-LDPC)码族,并基于多载波链路预测的互信息(MI)模型,准确预测了系统最少应重传的校验码元数,可以根据每次传输的信道状况采用不同的调制方式,能在很宽的信噪比范围内提高系统信息传输的有效性。 相似文献
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为了提高分等级网络中次用户通过机会频谱接入获得的有效吞吐率,提出了一种基于信道质量的鲁棒机会频谱接入策略.该策略利用信道质量信息和信道占用信息做出传输决策,使得次用户在信道感知结果为空闲和占用时分别以不同的信道质量门限选择传输机会发起传输,充分利用了信道质量好的传输机会.结合该策略,建立了以对主用户的干扰为约束条件,最大化次用户有效吞吐率的优化问题,并考虑到了信道传播特性统计参数存在不准确估计的情况,对该接入策略的门限进行了鲁棒性设计.仿真结果表明:所提出的鲁棒机会频谱接入策略能够显著提高次用户的有效吞吐率. 相似文献
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阐述一种星座图可调的自适应调制方案,并在Beyond ITM-2000的相关参数下进行了性能仿真。该方案能克服移动无线信道时变衰落特性对传输性能的影响,在信道的传输质量满足一定误码率要求的前提下,根据无线信道衰落情况,使调制方式在四相移相键控调制(Quaternary Phase Shift Keying,QPSK)、正交幅度调制(Quadrature Amplitude Modulation,QAM)包括8QAM,16QAM,32QAM,64QAM,128QAM,256QAM之间自如切换。仿真结果表明,该系统方案可以有效地适应无线信道的时变衰落,不但能增加系统平均吞吐量,而且能提高频谱利用率。 相似文献
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混合自动重传请求(Hybrid Automatic Repeat Request,HARQ)技术是保障数据可靠传输最有效的差错控制技术。在本文中,采用不规则重复码(Irregular Repeat Accumulate,IRA)码作为前向纠错码,得出了在AWGN信道下的吞吐率。仿真结果表明,IRA码在HARQ系统中的吞吐率接近turbo码,但译码复杂度远远低于Turbo码。 相似文献
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数据通信最初是在有线网上发展起来的,通常要求较大的带宽和较高的传输质量.对于有线连接,数据传输的可靠性是通过重传来实现的.当前一次尝试传输失败时,就要求重传数据分组,这样的传输机制就称之为ARQ(自动请求重传).在无线传输环境下,信道噪声和由于移动性带来的衰落以及其他用户带来的干扰使得信道传输质量很差,所以应该对数据分组加以保护来抑制各种干扰.这种保护主要是采用前向纠错编码(FEC),在分组中传输额外的比特.然而,过多的前向纠错编码会使传输效率变低.因此,一种混合方案HARQ,即ARQ和FEC相结合的方案被提出了.本文对移动通信系统HARQ技术做了详细的研究. 相似文献
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《Vehicular Technology, IEEE Transactions on》2005,54(4):1415-1425
Many rate-adaptive MAC protocols have been proposed in the past for wireless local area networks (LANs) to enhance the throughput based on channel information. Most of these protocols are receiver based and employ the RTS/CTS collision avoidance handshake specified in the IEEE 802.11 standard. However, these protocols have not considered the possibility of bursty transmission of fragments in the corresponding rate adaptation schemes. In this article, a rate-adaptive protocol with dynamic fragmentation is proposed to enhance the throughput based on fragment transmission bursts and channel information. Instead of using one fragmentation threshold in the IEEE 802.11 standard, we propose to use multiple thresholds for different data rates so more data can be transmitted at higher data rates when the channel is good. In our proposed scheme, whenever the rate for the next transmission is chosen based on the channel information from the previous fragment transmission, a new fragment is then generated using the fragment threshold for the new rate. In this way, the channel condition can be more effectively used to squeeze more bits into the medium. We evaluate this scheme under a time-correlated fading channel model and show that the proposed scheme achieves much higher throughput than other rate-adaptive protocols. 相似文献
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Incremental-redundancy hybrid automatic repeatrequest (IR-HARQ) schemes are proposed in several wireless standards for increased throughput-efficiency and greater reliability. We investigate transmit power and modulation order adaptation strategies for the IR-HARQ schemes over correlated Rayleigh fading channels using semi-Markov decision processbased model. In order to jointly analyze physical layer and link layer, transmitter model incorporates a finite-size buffer that receives randomly varying traffic from a higher layer application. It is assumed that channel variations can be modeled with a firstorder Markov chain. We show that the optimal transmission power and rate adaptation laws under buffering delay and packet overflow constraints can be obtained using the framework of semi-Markov decision process. We discuss three different adaptation models for the IR-HARQ schemes and compare their performances with the non-adaptive scheme. It is shown that unique optimal policy exists for each case and it can be computed using linear programming approach. This optimal policy is then applied for realistic channel fading and incoming traffic samples to evaluate its performance for both hard-decision and softdecision decoding. Simulation results in general point out that substantial power savings can be achieved using adaptation and also if the transmission-delay requirements are relaxed. 相似文献
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Hybrid ARQ with selective combining for fading channels 总被引:10,自引:0,他引:10
We propose and analyze a hybrid automatic repeat request (ARQ) with a selective combining scheme using rate-compatible punctured convolutional (RCPC) codes for fading channels. A finite-state Markov channel model is used to represent the Rayleigh fading channels. We show that the hybrid ARQ with selective combining yields better performance than the generalized type-II ARQ scheme for fading channels. Furthermore, simulation results of real-time video time division multiple access (TDMA) transmission system are given. Better video quality can be obtained by our proposed scheme, with a bounded delay. Analytical results of throughput and packet error rate (PER) are compared to the simulated results. Our analysis based on a finite-state Markov channel model, is shown to give good agreement with simulations 相似文献
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This paper proposes a common interleaving method associated with independent channel‐encoding among transmitter antenna branches in orthogonal frequency and code division multiplexing based on multiple‐input multiple‐output (MIMO) multiplexing to achieve an extremely high throughput such as 1 Gbps using a 100 MHz bandwidth. This paper also investigates the average packet error rate performance as a function of the average received signal energy per bit‐to‐background noise power spectrum density ratio (Eb/N0). We found that the loss in the required average received Eb/N0 of the proposed method is only within approximately 0.3 dB in up to a 12‐path Rayleigh fading channel, using 16QAM and Turbo coding with a coding rate of 5/6. We also clarify that even for a large fading correlation among antenna branches, 1 Gbps is still possible by increasing the transmission power. Therefore, the proposed method reduces the processing rate to 1/4 in the turbo decoder with only a slight loss in the required average received Eb/N0. 相似文献
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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. 相似文献
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《Journal of Visual Communication and Image Representation》2008,19(8):520-528
In this paper, we present a novel scalable video transmission strategy over multi-input multi-output (MIMO) wireless systems with time-varying channel capacity. It is a great challenge to simultaneously guarantee the QoS for video delivery and maximize the system throughput over time-varying MIMO channel. We demonstrate that, by making full use of estimated channel state information (CSI) through feedback, a cascade of adaptive operations can be designed to satisfy maximum throughput for scalable video over MIMO systems. These operations include power allocation based on water-filling (WF), adaptive channel selection (ACS), and novel throughput maximizing power reallocation (PR). The proposed ACS transmission scheme enables overall increase in data throughput among enhancement layers by adaptively launching base layer bit-stream to proper sub-channel. Then, after initial power allocation with WF and proper adaptive mode selection, we obtain the surplus power across enhancement layer sub-channels which can be reallocated to some sub-channels by the proposed PR scheme. With such power reallocation, certain enhancement layers will be able to reach new level of QAM modulation through PR so as to maximize the system data throughput. We present in this paper some detailed analysis on these adaptive operations. We also present some simulation results to demonstrate that maximum throughput video transmission over MIMO wireless systems indeed can be achieved based on scalable video coding (SVC) and a sequence of appropriately designed adaptive operations. 相似文献
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The authors propose and study an adaptive error-control coding scheme for binary digital FM (BFM) mobile radio transmission. The scheme employs code combining through packet retransmissions. The number of transmissions of a packet is in proportion to the channel fading/noise levels, which is in contrast to time diversity techniques where a fixed number of repetitions of a data packet is performed even in the absence of channel errors. Furthermore, the receiver uses received signal envelopes as channel state information, which significantly improves the throughput and bit error rate (BER) performance. Performance of the proposed scheme is analyzed for frequency-flat Rayleigh fading channels with additive white Gaussian noise (AWGN), co-channel interference and random FM noise 相似文献