Finite User Population Research Articles

Entropy Analysis of Broadband Wireless Access Systems

A Broadband Wireless Access (BWA) system consists of a base station and a set of $M$ users within its antenna sector, with $N$ simultaneously active users, $0\le N\le M$ , working in Point-to-Multipoint (PMP) mode. We model this system as family of Birth–Death Processes (BDPs), with size $M+1$ , in equilibrium, indexed by system utilization parameter $\rho$ , ratio of its primary birth and death rates. Relying on the fundamental concepts of system information $i$ and system entropy $S=E(i)$ , we develop an entropy analysis of BWA systems. Thereby, by definition, the system entropy, as the mean value of system information, is the uncertainty, related to the system. Taking system information as loss function, we identify risk and uncertainty, related to the system. Using the maximization of entropy, given the average number $\overline{N}$ of active users, we promote belt-zone of deviation from maximum uncertainty and a function of relative risk, regarding $\overline{N}$ , for a BWA system. This analysis is illustrated on BWA systems with finite user population, such as the binomial $M$ -server BWA systems, modeled by the family of BDPs with binomial distribution, and the delay single-server BWA systems, modeled by the corresponding family of BDPs; both systems represent private networks.

Performance Analysis on Partial Channel Sharing of Cognitive Networks with Finite User Population

摘要: 认知网络中动态信道共享是提高频谱资源利用率的关键。针对有限用户数下多认知网络共存场景，该文建立3维马尔科夫链部分信道共享模型，仿真分析用户有/无信道切换功能下认知网络间部分信道共享的性能。分别就阻塞概率、强迫终止概率、切换概率和系统吞吐量等，与静态频谱分配策略和分级共享策略进行比较仿真测试，结果表明，采用部分信道共享策略的系统在容忍较小的切换概率和强迫终止概率下可以获得较大的系统吞吐量。 关键词: 认知无线电 / 有限用户数 / 马尔科夫链模型 / 信道共享

Performance Analysis of Cognitive Radio Spectrum Access with Different Primary User Access Schemes

The cognitive access process based on different access schemes of the primary user in the spectrum sharing system of cognitive radio is studied. In the cognitive system with finite user population, the primary users access the licensed channels through random access, real-reservation access, pseudo-reservation access and non-random access. The cognitive users access the licensed channels without interfering the primary users. Their access process is modeled using the three-dimensional continuous Markov model. The performance analysis is presented with variation of the number of cognitive users. It is known from the simulated results that the handoff probability, the blocking probability and the forced termination probability of the cognitive users increase with the increase of the number of cognitive users. It is also found that the random access scheme has the highest handoff probability. And the real-reservation access scheme has the highest blocking probability and forced termination probability. In addition, the non-random access scheme has the maximum channel utilization.

On spectral properties of finite population processor shared queues

We consider sojourn or response times in processor-shared queues that have a finite population of potential users. Computing the response time of a tagged customer involves solving a finite system of linear ODEs. Writing the system in matrix form, we study the eigenvectors and eigenvalues in the limit as the size of the matrix becomes large. This corresponds to finite population models where the total population is \(N\gg 1\). Using asymptotic methods we reduce the eigenvalue problem to that of a standard differential equation, such as the Hermite equation. The dominant eigenvalue leads to the tail of a customer’s sojourn time distribution.

Performance analysis of finite population fractional guard channel policies in mobile cellular networks

This paper investigates an analytical model of a channel allocation algorithm with a finite population of users in mobile cellular networks. The recursive formulas are derived for the new call blocking and handoff dropping probabilities of the Finite Population Fractional Guard Channel policies. The Fractional Guard Channel policy reserves a non-integral number of guard channels for handoff calls by rejecting new calls that depend on the current channel occupancy. The effect of users' mobility on the maximum system capacity is achieved when the Finite Population Uniform Fractional Guard Channel (FPUFGC) policy is evaluated. It is shown that FPUFGC policy performs better than Finite Population Guard Channel policy under the low handoff/new traffic ratio. An optimal parameter of FPUFGC minimises the blocking probability subject to the constraint on the dropping probability. Numerical results show that the proposed policy gives an improved system performance, compared to the most commonly used handover algorithms.

Multiple Access Algorithms Without Feedback Using Combinatorial Designs

A new class of multiple access algorithms for systems without feedback is introduced and analyzed. A finite population of users is assumed, where each user transmits a packet R times within the next N time slots (and all packets have an equal length of one slot). To improve the performance achieved by randomly selecting these R slots, user codes are invoked such that any two users will only transmit simultaneously in at most one slot, i.e., 2-(N, R, 1) designs. We argue that in most cases, the set of user codes can be generated easily using cyclic designs and provide a method to select T user codes from the set of user codes SN,R in case the user population consists of T |SN,R|, can still benefit from these user codes in two different manners. Closed formulas that express the success probability of a packet are provided for all population setups. Finally, a comparison with the random selection strategy demonstrates the performance gain realized by the new multiple access algorithms and some engineering rules to optimize the performance are provided.

Analysis of cognitive radio spectrum access with finite user population

A new loss model for cognitive radio spectrum access with finite user population are presented, and exact solution for the model and its approximation for computation scalability are given. Our model provides the investigation of the delay performance of a cognitive radio system. We study the delay performance of a cognitive radio system under various primary traffic loads and spectrum band allocations.

Average packet delay of CSMA/CA with finite user population

In this paper, a simple closed form solution for the packet delays of the basic carrier sense multiple access with collision avoidance system is derived. Simulation results confirm the applicability and correctness of the derivation.

Average packet delay of CSMA/CA with finite user population

In this paper, a simple closed form solution for the packet delays of the basic carrier sense multiple access with collision avoidance system is derived. Simulation results confirm the applicability and correctness of the derivation.

Performance analysis of buffered R-ALOHA systems using tagged user approach

In this paper, R-ALOHA systems with propagation delay, finite buffer capacity and finite user population are analyzed using Tagged User Approach. The system throughput, message response time, message delay-time distribution and message blocking probability are obtained. It is assumed that each message consists of a random number of packets with a general distribution, and each user have a finite buffer capacity. To maintain the fairness to all users, it is assumed that each message in the buffer is transmitted independently that is, a user has to release the reserved slot after finishing the transmission of a message even if it has more messages waiting in the buffer. The analysis can be extended to R-ALOHA systems with infinite buffer capacity straightforwardly. The accuracy of the analysis is verified by simulations.

A MAC Protocol for New and Handoff Calls with Finite Population

A MAC protocol for new and handoff calls with a finite population of users, rather than with an infinite user population as in dynamic channel reservation scheme (DCRS), is considered. Similar to DCRS, we divide the wireless channels into shared channels and reserved channels. The handoff calls access any available channel with probability of one, while the new calls access a shared channel with probability of one and access a reserved channel with a request probability. We propose three simpler formulae than that used in the existing DCRS in setting the request probability. In addition, the handoff calls in our proposed protocol are allowed to queue in a finite buffer. To evaluate the system performance, a mathematical model based on queuing theory, rather than a simulation method used in DCRS, is developed. It is a general model that can be adopted for any types of request probabilities including DCRS. Suggestions of how to get the optimum values of the design parameters are also given.

Performance of a shared packet wireless network with interactive data users

This paper studies the user-perceived performance of a shared packet wireless network for interactive data applications such as Web-browsing. We have defined a new measure: the Equivalent Circuit Rate (ECR) for a user in a shared access network is the dedicated access circuit rate that would be required by the user in order to have an equivalent user experience. The ECR measure is intuitive, useful and robust. We present a simple analytical model based on a closed queueing network with a finite population of interactive data users whose traffic can be modeled as ON/OFF traffic with feedback. The analytical results are consistent with our detailed simulations, where we study TCP-based Web traffic simulations for an EDGE (Enhanced Data Rates for GSM Evolution) TDMA system using realistic workload models. Our study incorporates constant bit-rate channels, variable bit-rate channels, as well as mixed user groups with different channel conditions. We show that a shared wireless network is well characterized by simple parameters that depend only on mean statistics, for a broad range of scenarios. ECR is well approximated by R × (1 - U), where U is the utilization and R is the effective shared channel rate; this result holds even if different user groups have different rates or the channel rates are variable. These results will be useful in network dimensioning, admission control, and for defining quality of service targets for different user groups.

Performance Analysis of Buffered CSMA/CD Systems

This paper presents a new approximation approach, called tagged user approach (TUA), for the queueing analysis of slotted CSMA/CD systems with a finite user population having either finite or infin...

Performance and stability analysis of buffered slotted ALOHA protocols using tagged user approach

This paper presents a new approximation approach to analyze slotted ALOHA (S-ALOHA) systems with finite user population having either finite or infinite user buffer capacity. By assuming a symmetric channel, the performance analysis of the overall system is determined by the performance of an arbitrarily selected user, called the tagged user. The service time distribution for the tagged user buffer is found using a state flow graph. This distribution is then applied to the queueing analysis of the tagged user using available classical queueing theory results. The proposed approach can be applied to analysis of systems with a very large user population and user buffer capacity. The distributions and mean values of the important performance indices such as waiting time, queue size, and interdeparture time are obtained. The stability of the system with infinite buffer capacity is also studied. The region of transmission probability p in which the system is always stable and has best performance is obtained. Though the system with finite buffer capacity is considered to be always stable, a comprehensive analysis of the equilibrium points in the system is presented. The analysis presented will allow a proper choice of transmission probability so that the system always operates at the desired equilibrium point.

Performance of a type-II hybrid ARQ protocol in slotted DS-SSMA packet radio systems

The application of a type-II hybrid ARQ protocol in a slotted direct-sequence spread-spectrum multiple-access (DS-SSMA) packet radio system is investigated. Both the static performance and the dynamic performance of such a system are analyzed. In the physical layer, packet error and packet success probabilities are computed using the improved Gaussian approximation technique, which accounts for the bit-to-bit error dependence within a packet. In the data-link layer, two-dimensional Markov chains are employed to model the system dynamics. Based on this model, the performance of the type-II hybrid ARQ protocol is upper and lower bounded by considering, respectively, a superior scheme and an inferior scheme. Steady state throughput and delay performances of the two bounding schemes are obtained. Moreover, it is shown that for each fixed input load, there is an optimal retransmission probability under the finite user population assumption. Bounds on this optimal retransmission probability are also given.

Dynamic control of time slot assignment in multiaccess reservation protocols

The authors consider the dynamic control of time slot assignment in reservation protocols for multiaccess channels employing frame structures similar to those investigated by Roberts and others. Such protocols are particularly suitable for channels with long propagation delays, such as satellite channels. Fixed length frames are dynamically divided on a frame by frame basis into reservation subframes with minislots for reservation requests transmitted by slotted Aloha random access, and data subframes with reserved time slots for data packet transmissions. Formulating the problem as a Markov decision process, the authors derive the optimal time slot assignment policy, which makes use of complete state information of the finite user population, and obtain the delay-throughput performance. Results show that the optimal policy provides substantial performance improvements over fixed assignment policies. Furthermore, a heuristic dynamic assignment policy called the MF policy is proposed that is much easier to derive and implement, particularly for large networks, while maintaining performance very close to the optimal. Both of these dynamic policies depend on system state information, which the authors propose to estimate using a generalised pseudo-Bayesian estimator. The use of this estimator results in only a small reduction in performance.

Performance analysis of CSMA with priority acknowledgments (CSMA/PA) on noisy data networks with finite user population

An analytical procedure is developed to calculate delay and throughput performance of CSMA/PA (carrier sense multiple access with priority acknowledgments). Time-axis slotting and Markov chain analysis are used to determine the channel backlog per cycle. A cycle includes information packet access and transmission time followed by acknowledgment transmission or time-out. Throughput and delay performance are then calculated in terms of the number of network terminals, the network packet error probability, the packet generation rate, and the mean information packet retransmission delay. Fixed-length information and acknowledgment packets are assumed. Calculated results show excellent agreement with measured delay and throughput performance for two distinct five-node intrabuilding power line networks operating at data rates from 1.2 to 9.6 kb/s.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>