High-level synthesis for low power based on network flow method

We propose an effective algorithm for power optimization in behavioral synthesis. In previous work, it has been shown that several hardware allocation/binding problems for power optimization can be formulated as network flow problems and cand be solved optimally. However, in these formulations, a fixed schedule was assumed. In such a context, one key problem is that given an optimal network flow solution to a hardware allocation/binding problem for a given schedule, how to generate a new optimal network-flow solution rapidly for a local change of the given schedule. To this end, from a comprehensive analysis of the relation between network structure and flow computation, we devise a two-step procedure: Step 1) a max-flow computation step which finds a valid (maximum) flow solution while retaining the previous (maximum flow of minimum cost) solution as much as possible and Step 2) a min-cost computation step which incrementally refines the flow solution obtained in Step 1, using the concept of finding a negative cost cycle in the residual graph for the flow. The proposed algorithm can be applied effectively to several important high-level optimization problems (e.g., allocations/bindings of functional units, registers, buses, and memory ports) when we have the freedom to choose a schedule that will minimize power consumption. Experimental results (for bus synthesis) on benchmark problems show that our designs are 4%-40% more power-efficient over the designs produced by a random-move based solution and a clock-step based optimal solution, which is due to a) exploitation of the effect of scheduling and b) optimal binding for every schedule instance. Furthermore, our algorithm is about 2.6 times faster in run time over the full network flow based (optimal) algorithm, which is due to c) our novel (two-step) mechanism which utilizes the previous flow solution to reduce redundant flow computations.     

Reducing bandwidth consumption at startup of media transmissions

One of the primary objectives for media-on-demand systems is the reduction of bandwidth requirements. In this article we show a way how some bandwidth can be saved at the beginning of a media stream transmission. This saving is accomplished by omitting segments at their first transmission if the second transmission is in due time. To increase the number of omissions we propose an algorithm which optimizes the transmission schedule for this aim without modifying its maximum bandwidth requirement.     

Deadline-aware scheduling of cooperative relayers in TDMA-based wireless industrial networks

In this paper we consider a scenario in which a set of source nodes wishes to transmit real-time data packets periodically to a central controller over lossy wireless links, while using a TDMA-based medium access control protocol. Furthermore, a number of relay nodes are present which can help the source nodes with packet retransmissions. The key question we consider in this paper is how to schedule the TDMA slots for retransmissions while taking advantage of the relay nodes, so that the average number of packets missing their deadlines is minimized. We provide a problem formulation for the general deadline-aware TDMA relay scheduling problem. Since the design space of the general problem is large, we also present one particular class of restricted TDMA relay scheduling problems. We suggest and numerically investigate a range of algorithms and heuristics, both optimal and suboptimal, of the restricted scheduling problem, which represent different trade-offs between achievable performance and computational complexity. Specifically, we introduce two different Markov Decision Process (MDP) based formulations for schedule computation of the restricted TDMA relay scheduling problem. One MDP formulation gives an optimal schedule, another (approximate) formulation gives a sub-optimal schedule which, however, comes very close to the optimal performance at much more modest computational and memory costs.     

Data buses take flight

We discuss feasible design methods for implementing the reliable MIL-STD-1773 data buses that use mature optoelectronic devices. To guarantee reliable data transmission over the data bus, we present three efficient modulation techniques that can be used to reduce the complexity of optical transceivers and the processing time at each receiver, compared with using the modulation scheme recommended by MIL-STD-1773. We will also describe the design of electro-optic active couplers for AFO data buses and present the design consideration of AFO transmitters and a wavelength-division-multiplexing scheme.     

Smoothing variable-bit-rate video in an internetwork

The burstiness of compressed video complicates the provisioning of network resources for emerging multimedia services. For stored video applications, the server can smooth the variable-bit-rate stream by transmitting frames into the client playback buffer in advance of each burst. Drawing on prior knowledge of the frame lengths and client buffer size, such bandwidth-smoothing techniques can minimize the peak and variability of the rate requirements while avoiding underflow and overflow of the playback buffer. However, in an internetworking environment, a single service provider typically does not control the entire path from the stored-video server to the client buffer. This paper presents efficient techniques for transmitting variable-bit-rate video across a portion of the route, from an ingress node to an egress node. We develop efficient techniques for minimizing the network bandwidth requirements by characterizing how the peak transmission rate varies as a function of the playback delay and the buffer allocation at the two nodes. We present an efficient algorithm for minimizing both the playback delay and the buffer allocation, subject to a constraint on the peak transmission rate. We then describe how to compute an optimal transmission schedule for a sequence of nodes by solving a collection of independent single-link problems, and show that the optimal resource allocation places all buffers at the ingress and egress nodes. Experiments with motion-JPEG and MPEG traces show the interplay between buffer space, playback delay, and bandwidth requirements for a collection of full-length video traces     

视频流点播Dynamic Batched Patching算法研究

本文提出了一个新的视频流点播传输策略,用以解决现有传输策略中存在的系统资源利用率低,QoS较差等问题.该策略的思想是服务器根据用户请求到达时刻,按动态批处理的方式来接纳并服务请求用户,每组用户必须同时从一个或两个信道接收视频内容.文中对本策略的性能进行了理论推导与定量分析,并与现有传输策略作了性能比较,最后采用仿真实验对前面的理论分析与比较进行了验证.理论分析及实验结果表明该策略是一个简单高效的传输策略,适合任意规模的点播应用.     

A timestamp-sensitive scheduling algorithm for MPEG-II multiplexersin CATV networks

To achieve smooth display of MPEG-II programs in the residential cable TV networks, we present a timestamp-sensitive scheduling algorithm for MPEG-II multiplexers. The deadline-driven scheduler maintains, for each program stream, a counter and a timestamp to record and determine how many transport stream (TS) packets should be transmitted before the current scheduling cycle ends. The decoding timestamp (DTS) of TS packets is used to update the counter in order to prevent deadline violation. This algorithm is compared numerically with the timestamp-insensitive algorithm which runs constant-bit-rate (CBR) scheduling. The trace-driven simulation shows that the deadline violation of our timestamp-sensitive scheduling is much lower than CBR's and well controlled for programs with various degrees of burstiness. We also show that the algorithm can be further improved by adding a scheme to prevent buffer underflow and overflow at multiplexers and set-top-boxes, respectively     

Approximation algorithm for minimal convergecast time problem in wireless sensor networks

In this paper we consider how to collect data from sensors deployed in the Euclidean plane in a time-efficient way. We assume that all sensors could adjust their transmission ranges and aggregate data received from other sensors. We adopt a collision-free transmission model using proper schedules for data transmission. We study the problem of finding the schedule under which data from all sensors could be transmitted to the data sink in the minimal time. We propose an approximation algorithm for this NP-hard problem whose performance ratio is bounded by a constant. This significantly improves the existing approximation algorithm that does not have a constant performance ratio.     

Energy-efficient packet transmission over a wireless link

The paper considers the problem of minimizing the energy used to transmit packets over a wireless link via lazy schedules that judiciously vary packet transmission times. The problem is motivated by the following observation. With many channel coding schemes, the energy required to transmit a packet can be significantly reduced by lowering transmission power and code rate and therefore transmitting the packet over a longer period of time. However, information is often time-critical or delay-sensitive and transmission times cannot be made arbitrarily long. We therefore consider packet transmission schedules that minimize energy subject to a deadline or a delay constraint. Specifically, we obtain an optimal offline schedule for a node operating under a deadline constraint. An inspection of the form of this schedule naturally leads us to an online schedule which is shown, through simulations, to perform closely to the optimal offline schedule. Taking the deadline to infinity, we provide an exact probabilistic analysis of our offline scheduling algorithm. The results of this analysis enable us to devise a lazy online algorithm that varies transmission times according to backlog. We show that this lazy schedule is significantly more energy-efficient compared to a deterministic (fixed transmission time) schedule that guarantees queue stability for the same range of arrival rates.     

An On-Line Scheduler over Hard Real-Time Communication System

By thorough research on the prominent periodic and aperiodic scheduling algorithms,anon-line hard real-time scheduler is presented,which is applicable to the scheduling of packets over a link.This scheduler,based on both Rate Monotonic,pinwheel scheduling algorithm Sr and Polling Serverscheduling algorithms,can rapidly judge the schedulability and then automatically generate a bus tablefor the scheduling algorithm to schedule the packets as the periodic packets.The implementation of thescheduler is simple and easy to use,and it is effective for the utilization of bus link.The orderly executionof the bus table can not only guarantee the performance of the hard real time but also avoid the blockageand interruption of the message transmission.So the scheduler perfectly meets the demand of hard real-time communication system on the field bus domain.     

Optimal transmission scheduling over a fading channel with energy and deadline constraints

We seek to maximize the average data throughput of a single transmitter sending data over a fading channel to a single user class. The transmitter has a fixed amount of energy and a limited amount of time to send data. Given that the channel state determines the throughput obtained per unit of energy expended, the goal is to obtain a policy for scheduling transmissions that maximizes the expected data throughput. We develop a dynamic programming formulation that leads to an optimal transmission schedule, first where the present channel state is known just before transmission, and then to the case where the current channel state is unknown before transmission, but observed after transmission and evolves according to a Markov process. We then extend our approach to the problem of minimizing the expected energy required to send a fixed amount of data over a fading channel given deadline constraints.     

VoIP transmission mechanism based on TCP

As the widespread employment of firewalls on the Internet, user datagram protocol (UDP) based voice over Internet protocol (VoIP) system will be unable to transmit voice data. This paper proposed a novel method to transmit voice data based on transmission control protocol (TCP). The method adopts a disorder TCP transmission strategy, which allows discontinuous data packets in TCP queues read by application layer directly without waiting for the retransmission of lost data packets. A byte stream data boundary identification algorithm based on consistent overhead byte stuffing algorithm is designed to efficiently identify complete voice data packets from disordered TCP packets arrived so as to transmit the data to the audio processing module timely. Then, by implementing the prototype system and testing, we verified that the proposed algorithm can solve the high time delay, jitter and discontinuity problems in standard TCP protocol when transmitting voice data packets, which caused by its error control and retransmission mechanism. We proved that the method proposed in this paper is effective and practical.     

Error Protection and Interleaving for Wireless Transmission of JPEG 2000 Images and Video

The transmission of JPEG 2000 images or video over wireless channels has to cope with the high probability and burstyness of errors introduced by Gaussian noise, linear distortions, and fading. At the receiver side, there is distortion due to the compression performed at the sender side, and to the errors introduced in the data stream by the channel. Progressive source coding can also be successfully exploited to protect different portions of the data stream with different channel code rates, based upon the relative importance that each portion has on the reconstructed image. Unequal error protection (UEP) schemes are generally adopted, which offer a close to the optimal solution. In this paper, we present a dichotomic technique for searching the optimal UEP strategy, which lends ideas from existing algorithms, for the transmission of JPEG 2000 images and video over a wireless channel. Moreover, we also adopt a method of virtual interleaving to be used for the transmission of high bit rate streams over packet loss channels, guaranteeing a large PSNR advantage over a plain transmission scheme. These two protection strategies can also be combined to maximize the error correction capabilities.     

The Performance of Multicarrier CDMA for the Correlated Rayleigh Fading Channel

We present an new method for the analytical calculation of the error probability in a Rayleigh fading channel with correlated fading amplitudes. Even though the method can be applied for more general problems, we restrict ourselves on the investigation of a multicarrier CDMA transmission. The frequency correlation between the fading amplitudes of the carriers is given by the delay power spectrum of the channel. We generalize the well-known analytical expressions for the pairwise error probability of the uncorrelated Rayleigh channel to this case of correlated fading. This probability can be expressed in a closed form by an integral over a finite interval which can be easily evaluated numerically. We present some examples to show how much of the diversity of a code remains useful if the transmission channel does not provide an arbitrary degree of diversity.     

Optimal erasure protection for scalably compressed video streams with limited retransmission.

This paper shows how the priority encoding transmission (PET) framework may be leveraged to exploit both unequal error protection and limited retransmission for RD-optimized delivery of streaming media. Previous work on scalable media protection with PET has largely ignored the possibility of retransmission. Conversely, the PET framework has not been harnessed by the substantial body of previous work on RD optimized hybrid forward error correction/automatic repeat request schemes. We limit our attention to sources which can be modeled as independently compressed frames (e.g., video frames), where each element in the scalable representation of each frame can be transmitted in one or both of two transmission slots. An optimization algorithm determines the level of protection which should be assigned to each element in each slot, subject to transmission bandwidth constraints. To balance the protection assigned to elements which are being transmitted for the first time with those which are being retransmitted, the proposed algorithm formulates a collection of hypotheses concerning its own behavior in future transmission slots. We show how the PET framework allows for a decoupled optimization algorithm with only modest complexity. Experimental results obtained with Motion JPEG2000 compressed video demonstrate that substantial performance benefits can be obtained using the proposed framework.     

基于DSFCI-tree的分布式数据流频繁闭合模式挖掘

频繁闭合模式集可惟一确定频繁模式完全集且数据量要小几个数量级。根据分布式数据流的特点,提出了一种挖掘频繁闭合项集的算法,该算法采用K叉树形结构,以叶子节点接收各条数据流,创建DSFCI_tree结构来存贮各条数据流中的每段闭合模式,然后逐层往上合并更新,从而在根节点可得整个分布式数据流的频繁闭合模式。     

Efficient algorithms for scheduling data broadcast

With the increasing acceptance of wireless technology, mechanisms to efficiently transmit information to wireless clients are of interest. The environment under consideration is asymmetric in that the information server has much more bandwidth available, as compared to the clients. It has been proposed that in such systems the server should broadcast the information periodically. A broadcast schedule determines what is broadcast by the server and when. This paper makes the simple, yet useful, observation that the problem of broadcast scheduling is related to the problem of fair queueing. Based on this observation, we present a log‐time algorithm for scheduling broadcast, derived from an existing fair queueing algorithm. This algorithm significantly improves the time‐complexity over previously proposed broadcast scheduling algorithms. Modification of this algorithm for transmissions that are subject to errors is considered. Also, for environments where different users may be listening to different number of broadcast channels, we present an algorithm to coordinate broadcasts over different channels. Simulation results are presented for proposed algorithms.     

Optimal communication in bluetooth piconets

Bluetooth is a low-power, low-cost, short-range wireless communication system operating in the 2.4-GHz industrial, scientific, and medical (ISM) band. Bluetooth links use frequency hopping whereby each packet is sent on a single frequency while different packets are sent on different frequencies. Further, there are a limited number of packet sizes. We show that we can exert indirect control over transmission conditions by choosing the packet size transmitted over each frequency as a function of the channel conditions. Our goal then is to provide a packet-size-selection algorithm that can maximize the throughput in a Bluetooth piconet in the presence of lossy wireless channels. We first develop a renewal-theory-based mathematical model of packet transmission in a frequency-hopping system such as a Bluetooth piconet. We use this model to show that a threshold-based algorithm for choosing the packet lengths maximizes the throughput of the system. We provide an algorithm that determines the optimal thresholds efficiently. We show the optimality of this algorithm without using standard optimization techniques, since it is not clear that these techniques would be applicable given the functions involved. Using simulations, we observe that this strategy leads to significantly better throughput as compared to other baseline strategies, even if the assumptions made to prove optimality are relaxed.     

Deterministic collision free communication despite continuous motion

We present a deterministic solution for nodes in a mobile wireless ad hoc network to communicate reliably and maintain local neighborhood information. The nodes are located on a two-dimensional plane and may be in continuous motion. In our solution we tile the plane with hexagons. Each hexagon is assigned a color from a finite set of colors. Two hexagons of the same color are located sufficiently far apart so that nodes in these two hexagons cannot interfere with each other’s broadcasts. Based on this partitioning we develop a periodic deterministic schedule for mobile nodes to broadcast. This schedule guarantees collision avoidance. Broadcast slots are tied to geographic locations instead of nodes and the schedule for a node changes dynamically as it moves from tile to tile. The schedule allows nodes to maintain information about their local neighborhood. This information in turn is used to keep the schedule collision-free. We demonstrate the correctness of our algorithm, and discuss how the periodic schedule can be adapted for different scenarios. The periodic schedule, however, does not address the problem of initial neighbor discovery at start-up. We give a separate algorithm for this problem of initially discovering nodes present within communication range at start-up.     

Advances and Challenges with Data Broadcasting in Wireless Mesh Networks

Wireless mesh networks have become a promising means to provide low-cost broadband access. Many WMN applications require broadcasting data (IPTV etc.) over the WMN. This article studies how efficient data broadcast, measured in terms of broadcast latency, can be realized by exploiting two features of WMNs: the use of multiple transmission rates at the link layer and the use of multiple radio interfaces on each node. We demonstrate that by exploiting these features, broadcast latency can be reduced severalfold compared to the current default practice in wireless LANs of using the lowest transmission rate for broadcast traffic. We also discuss two important insights we have gained from our investigation. First, we find that when multiple radio interfaces are used, a channel assignment algorithm designed for unicast traffic may often perform poorly for broadcast flows. Second, we find that the efficiency of a transmission rate for reducing broadcast latency can be reasonably predicted by the product of the transmission rate and its coverage area.