Packet-error probability analysis for unslotted FH-CDMA systemswith error-control coding

In frequency-hopped (FH) code-division multiple-access (CDMA) systems, a number of users can transmit their packets simultaneously by using quasi-orthogonal FH patterns (codes). In applications where time is unslotted, the symbol-error probability is not the same for each symbol because the number of interfering users varies throughout the packet duration. Packet-error probability for such systems is evaluated by first enumerating all possible interference states and then averaging the packet-error probability associated with each of these states. The use of Reed-Solomon error-control coding is assumed. The computational task for this evaluation is enormous. Therefore, upper bounds and an alternate less-detailed approximate model are developed for easier computation. This approximate model generates results that are very close to those obtained using the authors' first model (1988) for the cases in which those results are computable. The conclusions of this study confirm the observation, originally made elsewhere, that the widely used threshold-based model for other-user interference is not an accurate one     

Hit statistics in FH-CDMA unslotted packet networks

This correspondence is concerned with the statistical dependence of hits due to multiple-access interference in the time-unslotted frequency-hopping (FH) packet networks. Relying on the technique of joint probability generating functions (PGFs), we give a formal proof that if the ratio of the number of interfering packets to the number of frequency slots K/q is held constant, hits due to multiple-access interference are asymptotically independent as q/spl rarr//spl infin/. We also derive expressions for the correlation coefficients of hits in the packet.     

非时隙CDMA分组网络吞吐量性能分析:统一的方法

CDMA分组网络性能主要受限于信道中同时传输的其它分组的干扰.与时隙CDMA分组网络相比,非时隙CDMA分组网络所受到的干扰情况更加复杂.本文提出了一种非时隙CDMA分组网络的干扰分析模型,并采用递归方式建立了网络吞吐量性能分析的统一方法.在此基础上,分析了网络节点突发固定长度分组和突发可变长度分组两种情况下的网络吞吐量性能,并讨论了扩频增益和分组传输方式对网络性能的影响,给出了相应的数值结果.文章最后进一步讨论了吞吐量的上下界问题.与前人提出的马尔可夫模型相比,采用本文提出的方法可以得到更为准确的吞吐量性能.     

Performance analysis of unslotted fiber-optic code-divisionmultiple-access (CDMA) packet networks

This paper examines code-division multiple-access (CDMA) techniques used in unslotted fiber-optic packet networks. Since the inherent properties and signal processing of the conventional communication channels are different from those of the fiber-optic channels, new code sequences must be constructed for fiber-optic applications. In unslotted systems, the exact solution is very difficult to obtain. Therefore, two approximation methods are presented to analyze the performance of such systems. Simulation is performed to verify the accuracy of the results     

Blocking probability analysis for packet circuit emulation services

Standardization of pseudo-wire and circuit emulation services on IP packet networks is underway. The ability to quickly find circuits in networks supporting circuit emulation is directly computed using blocking probability analysis. When all of the sequenced flows have the same maximum packet size, i.e., they are homogeneous, blocking probabilities are computed using Erlang's B formula. This paper describes analysis tools for the heterogeneous case and introduces the concept of steady-state fragmentation blocking probability, which controls the size of state transition diagrams used in the analysis. Simulation results using these tools are presented.     

General probability density function of packet service times for computer networks

The letter presents derivations of a generalised probability density and distribution functions of packet service times for computer communication networks. Included in the derivation are the effects of message segmentation into packets and the effects of control traffic. We also present the first and the second moments of the packet service times. These expressions can be used in modelling and analysis of computer networks by assigning appropriate values to various parameters.     

Performance analysis of unslotted CSMA/CA in wireless networks

In this paper a novel analytical model for the saturation throughput of unslotted Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA) in wireless networks is proposed. A fixed point procedure is developed based on the interaction of the Physical layer (PHY) and the Medium Access Control sub-layer (MAC). The output of the Clear Channel Assessment (CCA), i.e. idle or busy medium in the neighborhood of a node, serves as a feedback mechanism for the dynamical scheduling rate controlled by the back-off procedure. The PHY is described by a renewal process between successful transmissions with failed attempts and collided packets in between. A semi-Markov process of the internal states of a node is used as a model for the MAC. An event-driven simulator for the non-beacon enabled IEEE Std 802.15.4?MAC is developed to verify the numerical results of the analytical method. A detailed analysis of the idle period after a transmission is carried out based on the proposed analytical approach. The probability that the CCA senses the channel idle depends clearly on the actual back-off stage and the first back-off expiration after a transmission cannot be modeled by a exponential distribution when a finite number of nodes are in contention. The output of the event-driven simulations confirms both statements in great detail and the saturated throughput evaluated with the analytical procedure is verified by event-driven simulations.     

Topological analysis of packet networks

The author describes a unified approach for the topological analysis of nonhierarchical and hierarchical packet networks. The approach differs from previous approaches in adopting an end-to-end mean delay objective and including a variety of practical routing constraints. These include limits on the number of paths allowed in a route, limits on the number of hops allowed in a path, and constraints due to prevalent virtual circuit implementations. For a broad range of networks, quantitative analysis based on this approach provides new insights into the complex relationships between network topology and routing and delay constraints. It is shown that the sole use of a network average delay criterion often leads to network designs that exhibit poor end-to-end mean delays for some node pairs, and that it is possible to configure networks that meet an end-to-end mean delay objective for every node pair at little or no additional cost     

Throughput and packet error probability of cellularfrequency-hopped spread-spectrum radio networks

The authors characterize multiple-access interference for cellular mobile networks, in which users are assumed to be Poisson-distributed in the plane and use frequency-hopped spread-spectrum signaling with a transmitter-oriented assignment of frequency-hopping patterns. Exact expressions for the bit error probabilities are derived for binary coherently demodulated systems without coding. Approximations for the packet-error probability are derived for coherent and noncoherent systems and these approximations are applied when forward-error-control coding is used. In all cases, the effects of varying interference power are accurately taken into account according to some propagation law. Numerical results are given in terms of bit-error probability for the exact case and throughput for the approximate analyses. Comparisons are made with previously derived bounds, and it is shown that these tend to be very pessimistic     

The probability of multiple correct packet receptions indirect-sequence spread-spectrum networks

We provide methods to evaluate the probabilities P(l, m-l|K), l=0, 1, ..., m and m⩽K of exactly l correct packet receptions in a group of m receivers, given that K packets are transmitted simultaneously from users employing direct-sequence spread spectrum (DS/SS) signalling schemes. This quantity is useful for the design and performance evaluation of protocols for admission control and dynamic code allocation in multiple-access spread spectrum packet radio networks intended for terrestrial or satellite applications. The evaluations are carried out for DS/SS networks employing BPSK modulation with coherent demodulation and convolutional codes with Viterbi decoding. Systems with geographically dispersed receivers and systems with colocated receivers are considered. Approximations based on the independent receiver operation assumption (IROA) and the Gaussian multivariate distribution are developed, and their accuracy is checked against the exact expressions derived for synchronous systems. The joint first error event approximation (JFEEA) is also developed for coded systems and compared to the IROA     

Analysis of unslotted direct-sequence spread spectrum multipleaccess network with packet combining

A packet combining scheme is investigated for an unslotted random access code division multiple access network over a frequency selective Rayleigh fading channel. It is shown that this simple diversity combining mechanism is highly advantageous for systems which can both tolerate a certain delay and operate over highly time-varying channels     

The probability of multiple correct packet reception in codedsynchronous frequency-hopped spread-spectrum networks

We present a computationally efficient method of evaluating the probability of multiple correct packet reception in coded synchronous frequency-hopped spread-spectrum (FHSS) networks. We show that the approximation using the independent receiver operation assumption (IROA), which has been frequently employed in the literature without rigorous validation, produces reasonable results in most network load conditions when compared to the exact computations derived from our proposed method. Specifically, the expected value of the absolute error was in the range of 0.0055%-18.21% in the investigated scenarios     

Energy-based interference analysis of heterogeneous packet radio networks

While the use of radio technology for wireless data communications has increased rapidly, the wide variety of radio interfaces being used has made interference investigations hard to perform. With that in mind, we present a novel approach for analyzing packet radio communications, applicable to interfering heterogeneous networks, which leads to tractable analytical expressions. The core of the approach is an analytical framework modeling each network with individual properties for the packet types and the channel sets used, while taking path loss between all network nodes into account. Furthermore, we present a derivation of closed-form expressions for the throughput of the networks, thus allowing for the investigation of important mechanisms limiting network and system performance. The expressions enable fast and flexible analysis to be performed without extensive computer simulations or measurement campaigns. To illustrate the use of the framework and the strength of the closed-form expressions, we analyze a heterogeneous example system consisting of one IEEE 802.11b network and multiple Bluetooth networks that use multiple packet types. In the analysis, we also take the adjacent channel interference into account when calculating network throughput as functions of the number of interferers in the system.     

WDM-based packet networks

We discuss design considerations for wavelength division multiplexing (WDM)-based packet networks. In the near term, such networks are likely to consist of WDM links connected using some form of electronic multiplexing. The focus of this article is on the joint design of the electronic and optical layer with the objective of simplifying the network and reducing the protocol stack. To that end, we discuss the benefits of optical flow switching, network reconfiguration, traffic grooming, and optical layer protection. We also discuss the state of all-optical packet networking with particular focus on local area network technology     

Markov-based channel characterization for tractable performance analysis in wireless packet networks

Finite-state Markov chain (FSMC) models have often been used to characterize the wireless channel. The fitting is typically performed by partitioning the range of the received signal-to-noise ratio (SNR) into a set of intervals (states). Different partitioning criteria have been proposed in the literature, but none of them was targeted to facilitating the analysis of the packet delay and loss performance over the wireless link. In this paper, we propose a new partitioning approach that results in an FSMC model with tractable queueing performance. Our approach utilizes Jake's level-crossing analysis, the distribution of the received SNR, and the elegant analytical structure of Mitra's producer-consumer fluid queueing model. An algorithm is provided for computing the various parameters of the model, which are then used in deriving closed-form expressions for the effective bandwidth (EB) subject to packet loss and delay constraints. Resource allocation based on the EB is key to improving the perceived capacity of the wireless medium. Numerical investigations are carried out to study the interactions among various key parameters, verify the adequacy of the analysis, and study the impact of error control parameters on the allocated bandwidth for guaranteed packet loss and delay performance.     

差错信道下无线局域网丢包率性能分析

分析了AWGN（加性高斯白噪声）信道和瑞利衰落信道下无线局域网DCF（分布式协调功能）丢包率性能，推导出差错信道下使得吞吐量最大的最优分组长度闭式解并且证明了最优解的惟一性。研究结果表明，差错信道中不同调制方式和分组长度对丢包率性能有重要影响，根据信道状态调整分组长度能够获得最大的系统吞吐量。     

Performance analysis of data packet discarding in ATM networks

Data performance in ATM networks should be measured on the packet level instead of the cell level, since one or more cell losses within each packet is equivalent to the loss of the packet itself. Two packet-level control schemes, packet tail discarding and early packet discarding, were proposed to improve data performance. In this paper, a new stochastic modeling technique is developed for performance evaluation of two existing packet-discarding schemes at a single bottleneck node. We assume that the data arrival process is independent of the nodal congestion, which may represent the unspecified bit-rate traffic class in ATM networks, where no end-to-end feedback control mechanism is implemented. Through numerical study, we explore the effects of buffer capacity, control threshold, packet size, source access rate, underlying high-priority real-time traffic, and loading factor on data performance, and discuss their design tradeoffs. Our study shows that a network system can he entirely shut down in an overload period if no packet-discarding control scheme is implemented, under the assumption that there are no higher layer congestion avoidance schemes. Further, unless with sufficiently large buffer capacity, early packet discarding (EPD) always outperforms packet tail discarding (PTD) significantly under most renditions. Especially under the overload condition, EPD can always achieve about 100% goodput and 0% badput, whereas the PTD performance deteriorates rapidly. Among all the factors, the packet size has a dominant impact on EPD performance. The optimal selection of the EPD queue control threshold to achieve the maximum goodput is found to be relatively insensitive to traffic statistics