Frame Synchronization for Variable-Length Packets

A cognitive radio can sense its environment and adapt some of its features, such as carrier frequency, transmission bandwidth, transmission power, and modulation, thus allowing dynamic reuse of the available spectrum. Due to their high degree of adaptability to environmental variations, cognitive radios are expected to utilize packet-based transmission with variable-length frames. Packet-based transmission requires the receiver to perform frame synchronization, an important enabling step that allows adaptation in cognitive radios. However, proper metrics to characterize the performance of frame synchronization for transmission of variable-length frames are currently unavailable. To address this issue, we put forth two performance metrics, namely the expected duration to complete frame synchronization and the probability of correct acquisition within a given duration. We then develop analytical expressions for these important metrics. This paper advances our understanding of frame synchronization for the continuous transmission of variable-length frames and for bursty transmission.     

一种多优先级变长调度星载IP交换机交换结构的设计

针对星载IP交换机中硬件资源使用受限的情况,设计实现了一种具有8个优先级、采用指针复制和变长分组调度机制的大容量共享存储交换结构,给出了电路的具体组成、关键调度算法和工作流程.使用Xilinx V4sx55 FPGA实现了完整的8×8交换结构,电路共占用了164K字节片上存储器资源和5982个4输入查找表,可以满足三模冗余设计要求.在系统工作主频为100MHz、片外采用SRAM、数据位宽为64的情况下,交换结构的峰值吞吐率可以达到1.6Gbps;片外采用133MHz DDR存储器、位宽为64时,交换结构的峰值吞吐率可以达到4.25Gbps;该交换单元进行多级扩展后,可以满足10Gbps以上的系统设计需求.     

The Knockout Switch: A Simple, Modular Architecture for High-Performance Packet Switching

A new, high-performance packet-switching architecture, called the Knockout Switch, is proposed. The Knockout Switch uses a fully interconnected switch fabric topology (i.e., each input has a direct path to every output) so that no switch blocking occurs where packets destined for one output interfere with (i.e., block or delay) packets going to different Outputs. It is only at each output of the switch that one encounters the unavoidable congestion caused by multiple packets simultaneously arriving on different inputs all destined for the same output. Taking advantage of the inevitability of lost packets in a packet-switching network, the Knockout Switch uses a novel concentrator design at each output to reduce the number of separate buffers needed to receive simultaneously arriving packets. Following the concentrator, a shared buffer architecture provides complete sharing of all buffer memory at each output and ensures that all packets are placed on the output line on a first-in first-out basis. The Knockout Switch architecture has low latency, and is self-routing and nonblocking. Moreover, its Simple interconnection topology allows for easy modular growth along with minimal disruption and easy repair for any fault. Possible applications include interconnects for multiprocessing systems, high-speed local and metropolitan area networks, and local or toll switches for integrated traffic loads.     

Scheduling Algorithms for a Slotted Packet Switch with either Fixed or Variable Length Packets

We address the problem of congestion resolution in optical packet switching (OPS). We consider a fairly generic all-optical packet switch architecture with a feedback optical buffer constituted of fiber delay lines (FDL). Two alternatives of switching granularity are addressed for a switch operating in a slotted transfer mode: switching at the slot level (i.e., fixed length packets of a single slot) or at the burst level (variable length packets that are integer multiples of the slot length). For both cases, we show that in spite of the limited queuing resources, acceptable performance in terms of packet loss can be achieved for reasonable hardware resources with an appropriate design of the time/wavelength scheduling algorithms. Depending on the switching units (slots or bursts), an adapted scheduling algorithm needs to be deployed to exploit the bandwidth and buffer resources most efficiently.     

A novel Variable-Length Code for robust video coding

A novel Variable-Length Code （VLC）, called Alternate VLC （AVLC）, is proposed in this letter, which employs two types of VLC to encode source symbols alternately. Its advantage is that it can not only stop the symbol error propagation effect, but also correct symbol insertion errors and avoid symbol deletion errors, so the original sequence number of symbols can be kept correctly, which is very important in video communication.     

基于单程建路的高效快速双向标签交换路径生成算法

双向标签交换路径(LSP)是多协议标签传输应用(MPLS-TP)网络技术的重要组成部分,但现有的双向LSP生成算法因双程建路而在控制开销和用时方面导致冗余。为此,该文提出一种基于单程建路的高效双向LSP生成算法(EAEBL),在保障建路效果的前提下,通过控制消息的一次单程正向传递完成双向LSP的生成,从而减少建立双向LSP的控制开销和用时而且能够加快启动数据分组的传递。理论分析验证了EAEBL算法的有效性,仿真结果显示：与现有的4种双向LSP生成算法相比,EAEBL算法的建路控制开销和用时分别减少了14.7%和50%以上,数据分组在源LSR的等待时间则被减至趋近于0。     

适用于MPEG2视频解码的VLD设计

提出了一种新的适用于ＭＰＥＧ２视频解码的变字长解码（ＶＬＤ）结构,根据ＭＰＥＧ２变字长码表的特点,通过合理的码字分割解决码字的存储问题,采用桶式移位器,使得每个时钟能处理一个码字。     

Algorithm for Scheduling Variable-Length Messages in WDM Networks

In this paper, we develop and analyze a simple algorithm for scheduling variable length messages in WDM networks with a passive star coupler. We base our schemes on a star topology with centralized control and use a scheduling algorithm similar to the process management in UNIX system. Every node and message have a scheduling priority associated with them. By comparing our algorithm with random select algorithm, we find that significant improvement in performance can be achieved with very little extra cost.     

实现变长分组交换的星载交换机中队列管理器的FPGA设计

针对星载交换机中硬件资源消耗受限的情况,该文设计实现了一种可以进行变长分组调度的队列管理器电路,详细介绍了各个模块的设计思想和工作流程。使用Verilog HDL编程实现各个模块的功能,并通过ModelSim前仿真得出,该电路逻辑可实现,能够满足队列管理器的功能设计要求,具有较高的效率。     

一种PIN开关调制器

介绍了一种用FET作为开关的高性能PIN开关调制器的工作原理和设计方法。给出了实际应用调制器的波形。     

一种新的多分组联合译码方法

多分组译码目前有两种方式:分集合并和码字合并。但是这两种方法都是利用信道的 输出值,即译码之前的信道符号来合并。考虑到FEC的纠错功能,提出了输出联合码字合并的方法。 该方法将FEC译码器的输出值看作是传输分组经过较好信道后的一个输出分组,将其与重传分组进行 合并译码。理论推导和仿真结果证明新方法可以极大地降低系统的传输延时,同时没有增加系统的复 杂度。     

Entropy Coding With Variable-Length Rewriting Systems

This paper describes a family of codes for entropy coding of memoryless sources. These codes are defined by sets of production rules of the form almacr rarr bmacr, where a is a source symbol, and lmacr, bmacr are sequences of bits. The coding process can be modeled as a finite-state machine (FSM). A method to construct codes which preserve the lexicographic order in the binary-coded representation is described. For a given constraint on the number of states for the coding process, this method allows the construction of codes with a better compression efficiency than the Hu-Tucker codes. A second method is proposed to construct codes such that the marginal bit probability of the compressed bitstream converges to 0.5 as the sequence length increases. This property is achieved even if the probability distribution function is not known by the encoder     

An Enhanced SOA-Based Double-Loop Optical Buffer for Storage of Variable-Length Packet

To extend the buffer depth of a fiber loop optical buffer, we have experimentally demonstrated an enhanced semiconductor optical amplifier (SOA)-based dual-loop optical buffer (DLOB) for storing variable-length optical packets. We have theoretically derived constraints governing the buffer depth of the DLOB, in which the SOA not only provides a nonlinear phase shift in the loop to implement the buffer function but also compensates for the fiber loop attenuation during long-time storage. It is found that the maximum allowable length of a stored packet to avoid the counter-propagation packet collision inside the SOA depends on the SOA bias position as well as the length of the fiber loop. To demonstrate the effectiveness of the proposed enhanced configuration, we have successfully demonstrated the storage of 2.5-Gbps variable-length packets even when the length of the input packet exceeds the corresponding length of the fiber loop. Another unique advantage of the proposed enhanced DLOB configuration is that it can also overcome the problem of power leakage of the stored packet due to a directional gain difference of single SOA and gain saturation. Index     

An Efficient Variable-Length Code Construction for Iterative Source-Channel Decoding

We present a novel variable-length code (VLC) construction which exhibits an inherent error correcting capability due to the exclusive presence of codewords with even Hamming weight. Besides error robustness, the proposed code construction features a similar codeword length distribution as Golomb-Rice codes, and therefore, in particular for sources with exponentially distributed symbols, has good source compression properties at the same time. We show that in a source channel coding framework with outer source encoding, inner channel encoding with a recursive convolutional code, and iterative decoding the proposed VLC construction can lead to significant performance improvements compared to fixed-length source encoding with optimized mappings. In particular, simulation results for the AWGN channel verify that for Gauss-Markov sources a performance close to the theoretical limit can be achieved.     

A Method for Classifying Packets into Network Flows Based on GHSOM

Recently, various applications and services are used in the Internet. Load balancing the increasing network traffic in real time can improve the network quality. The flow control technologies become much more important than before. Our research proposes an intelligent network flow identifying method, which is based on the neural network algorithm, GHSOM. In this paper, we suggest to utilize the structural classification of GHSOM for training the properties of packets, such as timestamp, source and destination. Based on our proposed normalization, IP network flows can be formed autonomously during the learning process. The combination use of the new normalization with the GHSOM can divide a flow to several sub-IP flows. This paper indicates that a flow shall consist of several sub-IP flows, and sub-IP flow shall consist of several IP packets. The experiments show that IP packets can be divided to flow and sub-IP flow classes properly. Furthermore, those repeated jumbo sub-IP flows can be used to discover communicating errors or abnormal attacks.     

A MAC-Layer Retransmission Technique for Collided Packets in Wireless Sensor Network

Efficient transmission of data for reducing collisions in sensor network is the most significant way of enhancing the network performance and achieving lifetime maximization. In this paper, we have proposed a novel data retransmission strategy for unsuccessfully transmitted packets in case of uniform and variable data rate applications. For applications with uniform data rate, a fixed number of retransmission attempts are assigned to each packet and the retransmission probability gradually reduces according to 1-Truncated Geometric Distribution after every collision. For variable data rate applications with normalized data rate $N$ , our strategy reduces the priority of the collided packets using $N$ -Truncated Geometric Distribution. After fixed unsuccessful attempts with first priority, the packets are retransmitted with reduced priority so as to avoid engaging of network resources for long duration. Moreover, our both strategies aim to improve the usual retransmission mechanism of Standard ZigBee/IEEE 802.15.4 by replacing it with our innovated scheme. The simulation shows that our proposed retransmission technique outperforms the Standard ZigBee with GTS in terms of average energy consumption, network throughput, average number of retransmission attempts and network performance.     

HSDPA中的分组调度算法

HSDPA系统采用了AMC、HARQ、快速调度等技术以支持有效的数据业务,因此对传统的调度算法提出了新的挑战,分组调度成为影响系统性能的一个重要因素.介绍了两种针对HSDPA系统的调度算法：自适应正比公平算法（APF）和M-LWDF算法,并简单分析了它们的性能.     

Conditional Run-Length and Variable-Length Coding of Digital Pictures

In earlier publications, we have presented two coding schemes which take into account the conditional statistics of input signals. In the first scheme, the codewords are assigned in such a way as to provide a signal with long runs of zeros and ones. In the second scheme, each picture element is coded by variable-length codewords according to the values of previously transmitted PEL's. In this paper, by providing further results, we examine these coding schemes in greater detail. The performance of both schemes in terms of entropy and bit rate are compared with an optimum predictive coder. The simulation results indicate that these schemes have a significant advantage over standard predictive encoders. Methods to reduce the storage requirement for the encoder and decoder codebooks are also discussed.     

A New Scheme to Avoid Collisions for Broadcast Packets in Wireless LANs

This paper proposes a new approach to avoiding collisions for broadcast packets in distributed wireless LANs. The basic idea is to use in-band pulses to convey the medium access control information for broadcast packets. The new approach extends the basic functionality of the IEEE 802.11 distributed coordination function (DCF) from the unicast case to the broadcast case and significantly improves the broadcasting efficiency in wireless LANs.