Frequency-hopped spread-spectrum random access with retransmissioncutoff and code rate adjustment

A transmission policy for frequency-hopped spread-spectrum random-access communication systems in which the retransmission of a blocked packet at each station is determined as a function of that station's own collision experience is examined. For stability considerations and for channel throughput increase, the information packet is encoded by a Reed-Solomon code. An equilibrium analysis is used to show that undesirable bistable behaviour can be avoided if packets are rejected after a certain number of transmission attempts and the code rate is adjusted accordingly. The region of code rate and number of transmission attempt pairs that guarantees the network stability are investigated. The packet rejection probability, average packet delay, and maximum stable throughput are evaluated     

Routing strategies for maximizing throughput in LEO satellite networks

This paper develops routing and scheduling algorithms for packet transmission in a low Earth orbit satellite network with a limited number of transmitters and buffer space. We consider a packet switching satellite network, where time is slotted and the transmission time of each packet is fixed and equal to one time slot. Packets arrive at each satellite independently with a some probability during each time slot; their destination satellite is uniformly distributed. With a limited number of transmitters and buffer space on-board each satellite, contention for transmission inevitably occurs as multiple packets arrive at a satellite. First, we establish the stability region of the system in terms of the maximum admissible packet arrival rate that can possibly be supported. We then consider three transmission scheduling schemes for resolving these contentions: random packet win, where the winning packet is chosen at random; oldest packet win, where the packet that has traveled the longest distance wins the contention; and shortest hops win (SHW), where the packet closest to its destination wins the contention. We evaluate the performance of each of the schemes in terms of throughput. For a system without a buffer, the SHW scheme attains the highest throughput. However, when even limited buffer space is available, all three schemes achieve about the same throughput performance. Moreover, even with a buffer size of just a few packets the achieved throughput is close to that of the infinite buffer case.     

Performance study of hybrid spread-spectrum random-accesscommunications

A numerical study of the performance of hybrid direct-sequence slow-frequency-hopped spread-spectrum random-access schemes using Reed-Solomon forward-error control coding is performed. The performance measures of interest are the maximum numbers of simultaneous transmitters that can be tolerated in the vicinity of a receiver at a desirable level of the bit (or symbol) error probability, the normalized throughput, and the packet error probability. For the case where all simultaneous signals have the same received power levels, a critical comparison of the performance of direct-sequence, frequency-hopped, and hybrid spread-spectrum systems with the same overall bandwidth expansion is conducted with respect to the above performance measures, and ranges of parameters, for which each system outperforms the others, are identified. It is also established that hybrid spread-spectrum random-access schemes have considerably higher throughput than the uncoded nonspread-spectrum ones, for the desired range of values of the packet error probability     

蓝牙分组传输性能分析与自适应分组选择策略

分析了蓝牙2．0＋EDR新规范定义的3种调制方式在AWGN信道下的位错误率与平均接收信噪比的关系，推导了ACL分组的重传概率与平均接收信噪比的函数表达式。通过分组的重传概率与特性分析了ACL分组的传输性能，包括平均吞吐量、平均重传次数、平均传输时延等。提出了AWGN信道下的自适应分组选择策略，通过在不同的信噪比情况下选择合适的分组类型进行传输而获得最大吞吐量，给出了进行分组类型切换的信噪比门限值。分析结果与提出的策略适用于蓝牙数据传输性能的优化。     

A diversity combining DS/CDMA system with convolutional encodingand Viterbi decoding

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     

Throughput of nonpersistent inhibit sense multiple access with capture

The throughput of an FM mobile radio channel employing a nonpersistent multiple access protocol with inhibit sensing to provide packet data transmission is presented. With FM capture, the variations in received packet power due to propagation loss and multipath allow a packet to be successfully received in the presence of interfering packets, thus increasing the throughput over FM without capture.<>     

Throughput of strongly interfering slow frequency-hopping networks

With the increasing use of short-range wireless devices for high-data-rate communication in the shared frequency bands, the level of interference can be expected to increase. The ability to estimate the performance degradation of these devices due to increasing interference is, therefore, important. In this paper, the throughput of devices that perform frequency hops after each transmitted packet in order to achieve diversity is investigated. The system model allows for an analysis of systems where packets of variable durations are used, and the throughput derivation is based on the assumption that collisions result in a total loss of the data in the colliding packets. The resulting expression for the throughput is given as a function of the number of frequency channels used for frequency hopping, the number of interfering networks, the durations of the packet types available, and the probability of networks selecting a certain packet type for transmission. An approximation of the exact expression for the throughput is also derived, and the results are applied to an example system consisting of Bluetooth piconets.     

Performance of packet-switched fiber-optic frequency-hoppingmultiple-access networks

A packet-switched frequency-hopping multiple-access (FO-FHMA) communication system based on bus topology is proposed and investigated. In this arrangement, access to the optical medium for the network subscribers is provided via frequency-hopping (FH). The proposed FH technique in this analysis takes advantage of the Reed-Solomon (RS) codes to encode information packets and, consequently, to combat possible burst errors at the receiver. At user locations, encoded subpackets are frequency-hopped with the aid of a phase modulator, using a preassigned FH pattern for transmission over the optical medium. At the receiver site, a balanced phase discriminator/detection device followed by a frequency-dehopping receiver is used to recover the desired information. An alternative receiver structure, where the received signal is heterodyned prior to dehopping, is also proposed. The implications of this coherent detection are consequently discussed. Performance measures in terms of throughput and probability of incorrect decoding for chip synchronous model with asynchronous transmission characteristic in the absence of side information are obtained to assess the viability of the proposed packet-switched fiber-optic multiple-access communication system. Numerical results are presented when short RS codes are utilized as FH assignment codes     

Network-assisted diversity for random access wireless networks

A novel viewpoint to the collision resolution problem is introduced for wireless slotted random access networks. This viewpoint is based on signal separation principles borrowed from signal processing problems. The received collided packets are not discarded in this approach but are exploited to extract each individual user packet information. In particular, if k users collide in a given time slot, they repeat their transmission for a total of k times so that k copies of the collided packets are received. Then, the receiver has to resolve a k×k source mixing problem and separate each individual user. The proposed method does not introduce throughput penalties since it requires only k slots to transmit k colliding packets. Performance issues that are related to the implementation of the collision detection algorithm are studied. The protocol's parameters are optimized to maximize the system throughput     

一种新的基于虚拟队列的无线多播网络编码调度策略

网络编码由于其传输效率高的特性,近年来在无线多播网络中得到广泛的应用。针对无线多播网络中丢包自动重传效率低的问题,该文提出一种新的基于虚拟队列中数据包到达时间的编码调度策略(CSAT)。在CSAT策略中,为了提高编码效率,采用虚拟队列来存放初始以及未被所有接收者接收到的数据包。考虑到队列的稳定性,CSAT策略按照一定的比率从主次队列选择发送;在次队列发送数据包时,结合了编码和非编码两种方式,根据数据包到达队列的先后,选取能够使较多数据包参与编码的方式发送。仿真结果表明,该文所提的CSAT编码调度策略在有效提高了数据包传输效率的同时,提高了网络的吞吐量并降低了平均等待时延。     

利用BCH纠错编码实现对蓝牙广播性能的改善

为减少重传次数、提高蓝牙在噪声环境下的广播数据传输性能,提出了对蓝牙广播数据分组采用BCH码进行纠错编码的方法.根据蓝牙广播分组重传概率与平均接收信噪比的关系,分别提出了采用BCH纠错编码的广播数据分组和蓝牙原有的广播数据分组在加性高斯白噪声信道下的自适应分组选择策略,即通过在不同的信噪比情况下选择不同的分组类型进行传输以得到最少的广播重传次数和最大的传输吞吐量.比较结果表明采用BCH纠错编码方法的广播性能要明显优于蓝牙原有的广播性能.     

High throughput slotted ALOHA packet radio networks with adaptivearrays

The authors consider the use of a multiple-beam adaptive array (MBAA) in a packet radio system. In an MBAA, a given set of antenna elements is used to form several antenna patterns simultaneously. When it is used in a packet radio system, an MBAA can successfully receive two or more overlapping packets at the same time. Each beam captures a different packet by automatically pointing its pattern toward one packet while nulling other, contending packets. It is shown how an MBAA can be integrated into a single-hop slotted ALOHA packet radio system, and the resulting throughput is analyzed for both finite- and infinite-user populations     

Dynamics of TCP traffic over ATM networks

Investigates the performance of transport control protocol (TCP) connections over ATM networks without ATM-level congestion control and compares it to the performance of TCP over packet-based networks. For simulations of congested networks, the effective throughput of TCP over ATM can be quite low when cells are dropped at the congested ATM switch. The low throughput is due to wasted bandwidth as the congested link transmits cells from “corrupted” packets, i.e., packets in which at least one cell is dropped by the switch. The authors investigate two packet-discard strategies that alleviate the effects of fragmentation. Partial packet discard, in which remaining cells are discarded after one cell has been dropped from a packet, somewhat improves throughput. They introduce early packet discard, a strategy in which the switch drops whole packets prior to buffer overflow. This mechanism prevents fragmentation and restores throughput to maximal levels     

Packet throughput in slotted ALOHA DS/SSMA radio systems withrandom signature sequences

Packet throughput figures are obtained for direct sequence spread spectrum multiple access (DS/SSMA) slotted ALOHA radio systems where all users employ random signature sequences from bit-to-bit within all transmitted packets. These calculations use an improved Gaussian approximation technique which gives accurate bit error probabilities and also incorporates the effect of bit-to-bit error dependence within each packet in the multiaccess interference environment. Numerical results are given for packets which employ varying amounts of block error control, and a comparison is made with results obtained by other methods which ignore the effects of bit-to-bit error dependence within each packet in the multiaccess interference environment. Numerical results are given for packets which employ varying amount of block error control, and a comparison is made with results obtained by other methods which ignore the effects of bit-to-bit error and/or employ less-accurate Gaussian approximations to the probability of data bit error. Maximum throughput per unit bandwidth figures are calculated which compare favorably to similar figures for narrowband signaling techniques     

Performance evaluation of CSMA/ID MAC protocol for IP over WDM ring networks

In this paper, a packet pre‐classification media access control protocol based on a carrier sense multiple access with idle detection (CSMA/ID) scheme is investigated for supporting IP packets over all‐optical WDM ring networks. The purpose of the protocol is to increase throughput and to decrease the packet transmission delay of IP packets over optical networks in a metropolitan area network. This protocol avoids both packet collision and packet fragmentation. In order to improve the utilization of the network, the packets transmitted from a local area network are first pre‐classified into various class queues of an access point (AP) according to their length. After checking the available space based on the wavelength received by the receivers of the AP, the packets in the queues are transmitted. An analytical model is developed to evaluate the performance of the protocol, with simulation results showing good network efficiency. The proposed network has short‐term variations that introduce unfairness conditions. This problem could be overcome by assigning a quota on individual queues to allow all queues fair access. Copyright © 2008 John Wiley & Sons, Ltd.     

Performance analysis of a random packet selection policy formulticast switching

This paper studies a random packet selection policy for multicast switching. An input packet generates a fixed number of primary copies plus a random number of secondary copies. Assuming a constant number of contending packets during a slot, the system is modeled as a discrete time birth process. A difference equation describing the dynamics of this process is derived, the solution of which gives a closed form expression for the distribution of the number of packets chosen. Then this result is extended to the steady state distribution through a Markov chain analysis. It is shown that the old packets have larger fanout than the fresh packets and the copy distribution of the mixed packets is determined. The packet and copy throughput taking into account the old packets have been obtained. We determined the mean packet delay as well as an upperbound for packet loss probabilities for finite buffer sizes. The asymptotic distribution of the number of packets is also given for large switch sizes under saturation by applying results from the renewal theory. Finally, simulations are done to determine the performance of the switch under mixed (unicast plus multicast) traffic     

Reduced-rate retransmissions for spread-spectrum packet radio multimedia networks

A reduced-rate retransmission (RRR) scheme is proposed for improving the throughput performance of spread-spectrum packet radio networks. The scheme takes advantages of the available multi-rate scalable source coding techniques. It assumes that several versions of a data packet with different sizes (number of information bits) are available. The transmission of a packet starts from its full-size version. If the full-size version is not correctly received, its half-size version is used in the retransmission. If further retransmissions are needed, the quarter-size version and so on are used. The shrunk packets are transmitted either in a minislot if the processing gain is kept the same, or occupying a slot duration by increasing the processing gain proportionally. In both cases, the effective signal to interference ratio for a packet is increased. As a result, the system throughput is improved. Theoretical and numerical results are provided in this paper which illustrate the throughput improvement. Another advantage of the proposed RRR scheme is that the packet-size reduction provides finer granules for link adaptation. Therefore, it is especially suitable for multimedia applications for which codes of variable rate for the source data are available and which can tolerate gracefully degraded quality of service. The performance of the proposed scheme in fading channels is also addressed.     

High-speed buffer management for 40 gb/s-based photonic packet switches

We develop a method of high-speed buffer management for output-buffered photonic packet switches. The use of optical fiber delay lines is a promising solution to constructing optical buffers. The buffer manager determines packet delays in the fiber delay line buffer before the packets arrive at the buffer. We propose a buffer management method based on a parallel and pipeline processing architecture consisting of (log/sub 2/N+1) pipeline stages, where N is the number of ports of the packet switch. This is an expansion of a simple sequential scheduling used to determine the delays of arriving packets. Since the time complexity of each processor in the pipeline stages is O(1), the throughput of this buffer management is N times larger than that of the sequential scheduling method. This method can be used for buffer management of asynchronously arriving variable-length packets. We show the feasibility of a buffer manager supporting 128 /spl times/ 40 Gb/s photonic packet switches, which provide at least eight times as much throughput as the latest electronic IP routers. The proposed method for asynchronous packets overestimates the buffer occupancy to enable parallel processing. We show through simulation experiments that the degradation in the performance of the method resulting from this overestimation is quite acceptable.     

Optimal Bandwidth Assignment on Up- and Downlinks of Satellite with Buffer Capacity

This paper considers a satellite communication system with the slotted ALOHA access mode where the satellite is assumed to have on-board regeneration ability and the finite buffer capacity for storing noncollided packets from the uplink. The system is analyzed with the downlink bandwidth restricted to1/Lof the uplink bandwidth, and with the conventional slotted ALOHA system whereL = 1and the buffer size at the satellite is equal to zero. Maximum throughput and throughput-delay characteristics of this system are analytically obtained. The satellite is given an optimal buffer size to achieve maximum throughput and minimum packet transmission delay. It is shown that the constraints that lead to the downlink bandwidth being lower than the uplink bandwidth do not necessarily result in throughput penalties in a buffered satellite system. Furthermore, when the total bandwidth which can be divided between up- and downlinks is given, if two or three times that of the downlink is assigned to the uplink and if the satellite has buffer storage space only for a few packets, we show that maximum throughput of the system will be improved about 40 percent with little change in delay characteristics in comparison with that of the conventional slotted ALOHA system where the given total bandwidth is equally divided between up- and downlinks.     

CSMA local radio networks with BPSK modulation in Rayleigh fading channels

Calculation of the throughput of a carrier sense multiple access (CSMA) packet radio network with capture over slow Rayleigh-fading channels is presented. The effects of capture on the throughput of the system are related to the modulation and coding technique of the transmission system, the general distribution of terminals in the area and the length of the transmitted packets. BPSK modulation and BCH coding are considered.<>