Rate-optimal DSP synthesis by pipeline and minimum unfolding

This paper presents a rate-optimal scheduling for real-time DSP algorithms. By using pipelining and unfolding techniques, the parallel characteristics of recursive DSP algorithms can be exploited. A novel unfolding technique is developed to unravel all concurrency in the recursive data flow graph. A perfect rate unfolded data flow graph is also introduced, which can cause a fully static rate optimal functional pipeline schedule. Experimental results have shown that the proposed method can always yield rate-optimal designs with a smaller unfolding factor compared to previous studies     

Collision-aware design of rate adaptation for multi-rate 802.11 WLANs

One of the key challenges in designing a rate adaptation scheme for IEEE 802.11 wireless LANs (WLANs) is to differentiate bit errors from link-layer collisions. Many recent rate adaptation schemes adopt the RTS/CTS mechanism to prevent collision losses from triggering unnecessary rate decrease. However, the RTS/CTS handshake incurs significant overhead and is rarely activated in today's infrastructure WLANs. In this paper we propose a new rate adaptation scheme that mitigates the collision effect on the operation of rate adaptation. In contrast to previous approaches adopting fixed rate-increasing and decreasing thresholds, our scheme varies threshold values based on the measured network status. Using the "retry" information in 802.11 MAC headers as feedback, we enable the transmitter to gauge current network state. The proposed rate adaptation scheme does not require additional probing overhead incurred by RTS/CTS exchanges and can be easily deployed without changes in firmware. We demonstrate the effectiveness of our solution by comparing with existing approaches through extensive simulations.     

Relay-volunteered multi-rate cooperative MAC protocol for IEEE 802.11 WLANs

In IEEE 802.11, the rate of a station (STA) is dynamically determined by link adaptation. Low-rate STAs tend to hog more channel time than high-rate STAs due to fair characteristics of carrier sense multiple access/collision avoidance, leading to overall throughput degradation. It can be improved by limiting the transmission opportunities of low-rate STAs by backoff parameters. This, however, may cause unfair transmission opportunities to low-rate STAs. In an attempt to increase overall throughput by volunteer high-rate relay STAs while maintaining fairness, we propose a new cooperative medium access control (MAC) protocol, relay-volunteered multi-rate cooperative MAC (RM-CMAC) based on ready to send/clear to send in multi-rate IEEE 802.11. In the RM-CMAC protocol, we show that the effect of hogging channel time by low-rate STAs can be remedied by controlling the initial backoff window size of low-rate STAs and the reduced transmission opportunity of low-rate STAs can be compensated by the help of volunteer high-rate relay STAs. We analyze the performance of RM-CMAC, i.e., throughput and MAC delay, by a multi-rate embedded Markov chain model. We demonstrate that our analysis is accurate and the RM-CMAC protocol enhances the network throughput and MAC delay while maintaining the fairness of low-rate STAs.     

高效的用于CMMB的LDPC解码器设计

本文设计了高效率的支持两个码率的CMMB标准的LDPC解码器。论文采用分层修正最小和算法和存储器压缩技术减少存储器资源的使用;采用备份存储器方法,仅用很少的存储器代价,解决CMMB的LDPC码存在的存储器读写冲突;采用硬件资源复用,可以同时处理1/2码率和3/4码率,减少资源消耗。本文设计的LDPC解码器,在SMIC 0.18 m工艺下进行了综合,综合结果显示,解码器的面积8.55mm2,功耗215.4mW。     

Auxilliary computations for perceptron networks

In this study we consider a multilayer perceptron network with sigmoidal activation and trained via the backpropagation algorithm. The output of all neurons is collected and a simple linear regression is performed. It is shown that untrained networks with randomly chosen coefficients perform comparably with fully trained networks. This result casts a new light on the role of activation functions, the impact of dimensionality, and the efficacy of training algorithms such as backpropagation.     

Rate-optimal fair power allocation in complex field network coded relay communications

In this paper, we consider the complex field network coded relay assisted communication (CFNC-RAC) channel. Although CFNC-RAC is spectrally efficient, its bit error rate performance is degraded by multi-access interference, which can be improved by appropriately allocating the user and relay powers. Since the fairness is an important factor for a practical multi-user communication system, we have proposed a rate-optimal fair power adaptation (ROFPA) technique in this work. The proposed ROFPA policy not only aims to maximize the average achievable sum-rate of CFNC-RAC under the use of the decode and forward relaying but also intends to satisfy the average rate-fairness restriction while taking the total power constraint and the network topology into account. We formulate the ROFPA as a non-convex optimization program and then derive an analytical solution for it. Extensive performance evaluation and numerical simulations validate that ROFPA method can provide significant sum-rate with considerable user fairness when compared to symbol-error-rate optimized (SER-OPT) policy proposed by Eritmen et al. (Wirel Netw, 2015. doi:10.1007/s11276-015-0924-1).     

利用network coding的多速率多播最大吞吐量问题研究

本文研究了利用network coding的多速率多播最大吞吐量问题.与以往研究重点集中在单速率多播中的network coding研究工作不同,本文考虑了链路的异构性问题并采用多速率多播来解决该问题.首先文中形式化地描述了多速率多播最大可得吞吐量问题,并证明了在分层独立和层速率固定条件下,利用network coding的多速率多播最大吞吐量问题是NP-hard类问题,同时给出了最大吞吐量的上界.此外本文同时也研究了分层相关和层速率可变情况下的最大吞吐量问题.     

Imprecise computations

The imprecise computation technique has been proposed as a way to handle transient overload and to enhance fault tolerance of real-time systems. In a system based on this technique, each time-critical task is designed in such a way that it can produce a usable, approximate result in time whenever a failure or overload prevents it from producing the desired, precise result. This paper describes ways to implement imprecise computations, models to characterize them and algorithms for scheduling them. An imprecise mechanism for the generation and use of approximate results can be integrated in a natural way with a traditional fault-tolerance mechanism. An architectural framework for this integration is described     

Stochastic approximation based on-line algorithm for fairness in multi-rate wireless LANs

It is well known that IEEE 802.11 based MAC provides max–min fairness to all nodes even in a multi-rate WLAN. However, the max–min fairness may not always be the preferred fairness criteria as it significantly reduces overall system throughput. In this paper, we explore the proportional fairness and the time fairness. First, we obtain a condition that must be satisfied by the attempt probabilities to achieve proportional fairness. Using this condition, we propose a stochastic approximation based on-line algorithm that tunes attempt probabilities to achieve proportional fairness. The proposed algorithm can be implemented in a distributed fashion, and can provide optimal performance even when node uses a rate adaptation scheme. Next, we show that the time fairness is a special case of weighted max–min fairness with the weight for a node is equal to its transmission rate. Thus, the existing algorithms to achieve weighted max–min fairness can be used to achieve time fairness as well. This exposition also demonstrates that the proportional fairness and the time fairness are not the same contrary to what was conjectured. Performance comparison of various fairness criteria is done through ns-3 simulations. Simulation results show that time fair schemes achieve the highest throughput, and the sum of logarithm of individual node’s throughputs under the time fairness is close to that under a proportionally fair scheme.     

多码率LDPC码高速译码器的设计与实现

低密度奇偶校验码(LDPC码)以其接近香浓极限的性能得到了广泛的应用.如何在.FPGA上实现多码率LDPC码的高速译码,则是LDPC码应用的一个焦点.本文介绍了一种多码率LDPC码及其简化的和积译码算法;设计了这种多码率LDPC码的高速译码器,该译码器拥有半并行的运算结构和不同码率码共用相同的存储单元的存储资源利用结构,并以和算法与积算法功能单元同时工作的机制交替完成对两个码字的译码,提高了资源利用率和译码速率.最后,本文采用该结构在FPGA平台上实现了码长8064比特码率7/8、6/8、5/8、4/8、3/8五个码率的多码率LDPC码译码器.测试结果表明,译码器的有效符号速率达到200Mbps.     

多速率自适应技术在Ir协议中的应用研究

在RRU设备的组网过程中,由于新设备的引入,需要兼容多种速率的光接口,多速率自适应技术不需要人为对RRU设备的光接口速率进行干预.以TI公司的TLK6002为例,研究了RRU设备光接口多种速率自适应的难点,给出了进行速率自适应的流程图和方法.使用本方法的RRU设备,自动进行光接口速率的调整,能够大大降低网络建设中的难度...     

自适应多码率语音编码流的可靠传输

自适应多码率语音编码已入选为第三代移动通信系统的语音压缩编码方案。本文提出了一种适合压缩语音传输的联合信源信道编码方法并对其性能进行了统计比较。利用压缩语音比特流中的固用冗余的信道译码算法是本文的研究重点。仿真结果表明利用信源冗余信息的信道译码器可以获得较大的编码增益。本文所用的信道编码方案为适合语音传输的卷积码。     

Compressed sensing based multi-rate sub-Nyquist sampling system

Signal sampling is a vital component in modern information technology. As the signal bandwidth becomes wider, the sampling rate of analog-to-digital conversion(ADC) based on Shannon-Nyquist theorem is more and more high and may be beyond its capacity. However the analog to information converter(AIC) based on compressed sensing(CS) is designed to sample the analog signals at a sub-Nyquist sampling rate. A new multi-rate sub-Nyquist sampling(MSS) system was proposed in this article, it has one mixer, one integrator and several parallel ADCs with different sampling rates. Simulation shows the signals can be reconstructed in high probability even though the sampling rate is much lower than the Nyquist sampling rate.     

The multi-hop multi-rate wavelength division multiplexing ring

Transparency of the optical layer offers the possibility to design a network that operates at varying transmission bit rates. While variable bit rate interfaces are being tested and will soon provide the possibility to optimally select the transmission rate for each optical channel, the potential advantages of relying upon multiple transmission rates in the optical network have yet to be fully explored. In this paper, we define the concept of multi-hop and multi-rate (M&M for short) network in which the tributary signal is transmitted over a concatenation of optical channels, with each optical channel operating at its own transmission rate. The optimal rate of each optical channel is determined by a number of factors including the end node's interface, amount of multiplexed traffic and cost of the network components. The potential advantages provided by the M&M network when compared to first generation optical networks (i.e., SONET/SDH), to single- and multi-hop (constant bit rate) optical networks, are discussed in general and demonstrated numerically in a WDM ring. Presented results show that the network cost reduction achieved by the M&M design is a function of the cost ratio between the optical bandwidth (wavelengths) and the optical terminals     

Modeling of systems with overflow multi-rate traffic

The article proposes an analytical method for determining occupancy distribution and blocking probability in systems which are offered overflow traffic composed of multi-service traffic streams. The described analytical model enables determination of parameters of traffic overflowed from primary groups in hierarchically constructed telecommunication networks. The proposed method is based on an appropriate modification of the Kaufman-Roberts recursion for the full-availability group with multi-rate traffic and uses the modified Fredericks & Hayward’s approximation. Additionally, an approximate method for dimensioning systems with multi-service overflow traffic is also presented. The analytical results of the blocking probability and the results obtained in the dimensioning processes calculated using the presented methodology are compared with the data obtained from the system simulation process.     

W-CDMA 多业务传输中的码片均衡技术

介绍了一种新的W-CDMA中的抗多径接收技术,即码片均衡技术,它特别针对视频点播等高速业务,适用于下行链路多业务传输。并研究了码片均衡器的现状,探讨了码片均衡的发展趋势。     

A Cooperative Channel Assignment protocol for multi-channel multi-rate wireless mesh networks

Wireless mesh networks (WMNs) are considered as one of the outstanding technologies that provide cost-effective broadband Internet accesses to users. The off-the-shelf IEEE 802.11 PHY and MAC specifications support both multi-channel and multi-rate capabilities. However, designing an efficient channel assignment protocol that exploits both available channels and data rates is a critical issue to overcome the network performance degradation. In multi-rate wireless networks, high-rate links may severely suffer from throughput degradation due to the presence of low-rate links. This problem is often referred to as performance anomaly. In this paper, we design a Cooperative Channel Assignment (CoCA) protocol to consider the performance anomaly problem in multi-channel multi-rate WMNs. Based on the proposed family architecture, CoCA exploits the Estimated Delivery Time (EDT) metric and an efficient balancing algorithm. Using the EDT metric, CoCA performs channel assignments to form Multi-channel Multi-hop Paths (MMPs) so that CoCA separates high-rate links from low-rate links over different channels and increases the channel diversity. In addition, CoCA considers the performance anomaly problem and throughput fairness during channel assignments by utilizing the balancing algorithm. We evaluated the performance of CoCA through extensive simulations and found that CoCA outperforms existing well-known channel assignment protocols for WMNs.     

光电跟踪伺服系统的输入多采样率满意控制

针对成像跟踪器低采样率帧频特性对光电跟踪伺服系统控制性能的影响,提出了一种基于输入多采样率控制原理的满意PID控制器.应用输入多采样率控制原理,提高了控制系统的稳定度,减小了跟踪器的低采样率帧频特性对系统跟踪性能的影响.将输入多采样率PID控制器的参数求解转换为满足极点约束和方差约束的多目标满意优化问题,从而使伺服系统的跟踪性能满足指定的快速性和精度指标要求.对所提出方法的有效性进行了实验验证,结果表明:在成像跟踪器的输出帧频为25Hz的条件下,所提出的输入多采样率满意PID控制器能够减小光电跟踪伺服系统工作模式切换带来的超调和振荡,对0.5Hz正弦信号的动态跟踪精度能够提高2个像素点;能够有效降低成像跟踪器的低采样率帧频特性对伺服系统控制性能的影响,提高了系统跟踪目标的稳定性、动态性和跟踪精度.