Resource allocation for multiple classes of DS-CDMA traffic

We consider a packet data direct-sequence code-division multiple-access (DS-CDMA) system which supports integrated services. The services are partitioned into different traffic classes according to information rate (bandwidth) and quality of service (QoS) requirements. Given sufficient bandwidth, QoS requirements can be satisfied by an appropriate assignment of transmitted power and processing gain to users in each class. The effect of this assignment is analyzed for both a single class of data users and two classes of voice and data users. For a single class of data users, we examine the relationship between average delay and processing gain, assuming that ARQ with forward error correction is used to guarantee reliability. The only channel impairment considered is interference, which is modeled as Gaussian noise. A fixed user population is assumed and two models for generation of data packets are considered: (1) each user generates a new packet as soon as the preceding packet is successfully delivered and (2) each user generates packets according to a Poisson process. In each case, the packets enter a buffer which is emptied at the symbol rate. For the second traffic model, lowering the processing gain below a threshold can produce multiple operating points, one of which corresponds to infinite delay. The choice of processing gain which minimizes average delay in that case is the smallest processing gain at which multiple operating points are avoided. Two classes of users (voice/data and two data classes) are then considered. Numerical examples are presented which illustrate, the increase in the two-dimensional (2-D) capacity region achievable by optimizing the assignment of powers and processing gains to each class     

On Multiple Traffic Type Integration over Wireless TDMA Channels with Adjustable Request Bandwidth

A new medium access control (MAC) protocol for mobile wireless communications is presented and investigated. We explore, via an extensive simulation study, the performance of the protocol when integrating voice, video and data packet traffic over a wireless channel of high capacity (referring to an indoor microcellular environment). Depending on the number of video users admitted into the system, our protocol varies: a) the request bandwidth dedicated to resolving the voice users contention, and b) the probability with which the base station grants information slots to voice users, in order to preserve full priority for video traffic. We evaluate the maximum voice capacity and mean access delay, as well as the aggregate channel throughput, for various voice and video load conditions, and the maximum voice capacity, aggregate channel throughput and average data message delays, for various video, voice and data load conditions. As proven by the comparison with a recently introduced efficient MAC scheme (DPRMA), when integrating voice and video traffic our scheme obtains higher voice capacity and aggregate channel throughput. When integrating all three traffic types, our scheme achieves high aggregate channel throughput in all cases of traffic load.     

Modeling dynamic channel allocation in multicellular communicationnetworks

Future cellular mobile communication networks will exploit microcellular architectures and dynamic channel allocation in order to meet the rapidly increasing traffic demand. In this paper, an analytical model has been developed in order to evaluate the performance of maximum packing, a dynamic channel allocation scheme for cellular communication networks. Specifically, a finite number of users has been assumed, moving in a geographical region, covered by a finite set of cells. The considered users are characterized by a variable degree of mobility, which allows both variable sized cells and different user speeds to be analyzed. The model, based on queueing networks, allows the evaluation of the main system performance parameters in terms of blocking probability of new calls, handoff blocking probability, forced termination probability, unsuccessful probability, and throughput. Performance predictions are confirmed by simulation in a wide range of load conditions and user mobility     

Analytic forward link performance of pilot-aided coherent DS-CDMAunder correlated Rician fading

This paper presents a methodology for analyzing the forward link performance of a pilot-aided coherent DS-CDMA system under correlated Rician fading. In the forward link of a CDMA system, orthogonal modulation is usually used to minimize the self-interference. To maintain the orthogonality and reduce the receiver complexity, a common pilot channel (shared by all users) is employed to provide the reference for coherent demodulation. A tradeoff shows that a higher pilot ratio yields good channel estimates but takes away some capacity from traffic users, while a lower pilot ratio results in poorer channel estimates and leads to higher traffic power per user. This paper derives the analytical error performance, which includes (1) imperfect channel estimation by the pilot channel, (2) a very general channel model where correlations between paths as well as Rician fading are considered, and (3) interference patterns due to multiple paths and the surrounding base stations' transmissions. This paper also considers self-interference due to the loss of orthogonality caused by pulse shaping     

Free access stack algorithms for microcellular radio systems

We evaluate the data traffic performance of a centralized packet access protocol for microcellular radio systems supporting both speech and data users. A time-slotted radio channel is assumed. Speech contention is decoupled from data contention to give speech priority over data. A free access stack algorithm is used for handling data contention. An out-slot access scheme is used in which the slots are divided into user-information transmission slots and contention slots for sending transmission requests. The contention slots are subdivided in minislots to improve the access capacity. The out-slot algorithm performances are compared with the performances of a previously proposed in-slot one in which all slots can be used for sending user information. A memoryless channel, with capture and errors, is considered. The effects of speech traffic on data performance are evaluated. Moreover, the paper presents a method for evaluating the packet error probability of a packet cellular system. This method is used for evaluating the proposed algorithm in a microcellular system. An access technique with coordinated operation among cochannel cells is studied. The effects of sectorization on data performances and protocol unfairness are investigated. Different frequency reuse factors are taken into consideration     

Interference suppression for space-time coded CDMA via decision-feedback equalization

A single-user receiver structure is proposed for space-time coded code-division multiple-access (CDMA) downlink in a multiuser frequency-selective channel. This structure is a two-dimensional (2-D) decision-feedback equalizer (2D-DFE) whose filters are optimized based on the MMSE criterion to mitigate noise, intersymbol interference (ISI), and multiuser interference (MUI) with a moderate complexity. By modeling the spreading codes of the interfering users as random sequences, system performance was evaluated using the Gaussian approximation. Two models for the desired user's spreading sequence have been considered and compared. Our numerical results show that in both cases the 2D-DFE exhibits significant performance improvement over the standard space-time coded RAKE, especially in interference-limited conditions. It is also observed that the gain obtained by using DFE in a MISO channel is less that in a SISO channel and this problem can be solved by providing diversity at the receiver.     

Performance Analysis of Statistical Voice/Data Multiplexing Systems with Voice Storage

In this paper the performances of four statistical voice/data multiplexers are analyzed and compared. The structures of these multiplexers are based on the newly proposed queueing, frame management, and integrated flow control methods. For the queueing purpose, two separate finite voice and data buffers are used to queue voice and data packets independently. For frame management, four versions of master frame management are considered. As for the integrated flow control algorithm, speech coding techniques such as variable rate coding and embedded coding are considered. To evaluate the performances of the multiplexers, analytical formulations are made from the equivalent queueing models of the proposed systems. Then, numerical results on the performance of the multiplexers are obtained by using the Gauss-Seidel iteration method. These results show that there exist tradeoffs between data and voice traffic performances for a given input traffic load and the output channel rate.     

A Service Differentiated MAC Protocol for OFDM/TDMA Wireless Systems

1IntroductionAkey goal to achievein next generation wireless net-works is to develop an efficient method to allocate thescarce bandwidth resources among users of differenttypes of traffic in a wireless multi media network. Theentityincharge of performingthat taskisthe MACpro-tocol , which must be able to support various classes oftraffic while guaranteeing their required Quality of Ser-vice (QoS) .Ref .[1] proposes a MACprotocol for ultrahigh-speed radio access system. The new protocol isb…     

A new approach for medium-access control for data traffic and itsadaptation to the GSM general packet radio services

The inhibit sense multiple access with polling (ISMA/P) is a packet-based medium-access control scheme for statistical multiplexing of data users over a single slotted channel of a time-division multiple-access (TDMA) cellular system. In ISMA/P, the central base station (BS) asserts control over the users by polling data in smaller blocks. This enables ISMA/P to attain a near ideal, steady, and high throughput and low-mean delay performance, which is not usually achievable by contention-reservation-based MAC schemes. In this paper, we describe the ISMA/P algorithm and provide a detailed simulation study of it over a global system for mobile communications (GSM)-like slotted channel for a traffic model adopted from European Railways applications. This study shows that ISMA/P can achieve a steady throughput of 90% over a large range of load. A number of practical advantages of ISMA/P, such as elimination of channel hogging, incorrect channel sensing, battery saving, etc., are also elaborated     

A dynamic packet reservation multiple access scheme for wireless ATM

The dynamic packet reservation multiple access (DPRMA) scheme, a medium access control protocol for wireless multimedia applications, is proposed and investigated. DPRMA allows the integration of multiple traffic types through a single access control mechanism that permits users to specify their immediate bandwidth requirements. The primary feature of DPRMA is the dynamic matching of the traffic source generation rates with the assigned portion of the channel capacity. This is accomplished by a control algorithm that regulates the actual amount of channel capacity assigned to users. To support multimedia communication, channel capacity assignments are prioritized by traffic type. The performance of the scheme is evaluated and the scheme is shown to perform well in a system with voice, video conferencing, and data users present. It is also shown to provide improved performance over a system with a modified version of the packet reservation multiple access (PRMA) scheme. Furthermore, several system parameters are studied and optimized.     

Traffic model and performance analysis for cellular mobile radio telephone systems with prioritized and nonprioritized handoff procedures

A traffic model and analysis for cellular mobile radio telephone systems with handoff are described. Three schemes for call traffic handling are considered. One is nonprioritized and two are priority oriented. Fixed channel assignment is considered. In the nonprioritized scheme the base stations make no distinction between new call attempts and handoff attempts. Attempts which find all channels occupied are cleared. In the first priority scheme considered, a fixed number of channels in each cell are reserved exclusively for handoff calls. The second priority scheme employs a similar channel assignment strategy, but, additionally, the queueing of handoff attempts is allowed. Appropriate analytical models and criteria are developed and used to derive performance characteristics. These show, for example, blocking probability, forced termination probability, and fraction of new calls not completed, as functions of pertinent system parameters. General formulas are given and specific numerical results for nominal system parameters are presented.     

A model for channel sharing in land mobile radio dispatch services

A modeling approach to the problem of channel sharing in land mobile radio dispatch services, which is based on real life traffic data, is presented. In order to apply the GI/G/1 queueing model, the first step consists in identifying a message arrival process for each user by means of observed available data. It is then shown how to use simple approximation formulas to evaluate the expected waiting time, when two or more independent users must share a common channel. GPSS simulations were performed to verify that the proposed approach is suitable to practical applications.     

Integrating Voice, Video, and E-mail Data Packet Traffic over Wireless TDMA Channels with Errors

In this paper, we explore, via an extensive simulation study, the performance of a new medium access-control (MAC) protocol when integrating voice, video, and e-mail data packet traffic over a wireless channel of high capacity, with errors. Depending on the number of video users admitted into the system, our protocol varies (a) the request bandwidth dedicated to resolving the voice users contention and (b) the probability with which the base station grants information slots to voice users, in order to preserve full priority for video traffic. We evaluate the voice and video packet-dropping probabilities for various voice and video load conditions and the average e-mail data message delays. Our scheme achieves high aggregate channel throughput in all cases of traffic load despite the introduction of errors in the system.     

Data traffic‐based analysis of delay and energy consumption in cognitive radio networks with and without resource reservation

A new opportunistic cross‐layer MAC protocol involving channel allocation and packet scheduling for cognitive radio networks is proposed. Cognitive radio allows secondary users (SUs) to exploit the available portions of the licensed spectrum bands without interfering with primary users. In particular, we consider a cognitive radio system, where SUs are equipped with two transceivers: a control transceiver and a software‐defined radio transceiver. Data traffic characteristics of SUs are considered to ameliorate system performance. So, we propose a mechanism of resource reservation to improve QoS requirements that favors successful SUs to transmit data during x time slots without interfering with primary users. The key novelty of this paper is giving priority for SUs with important data traffic and which frequently solicits data channels to transmit for the remaining time of the ongoing time slot and for the next time slots directly after checking the channel availability. We develop a new analytical model to evaluate delay parameter for two scenarios with and without resource reservation and we then investigate the impact of those scenarios on the energy consumption. We show through simulations that cognitive radio performances increase noticeably with the proposed scheme. Copyright © 2014 John Wiley & Sons, Ltd.     

Towards an end-to-end delay analysis of wireless multihop networks

In wireless multihop networks, end-to-end (e2e) delay is a critical parameter for quality of service (QoS) guarantees. We employ discrete-time queueing theory to analyze the end-to-end (e2e) delay of wireless multihop networks for two MAC schemes, m-phase TDMA and slotted ALOHA. In one-dimensional (1-D) networks, due to the lack of sufficient multiplexing and splitting, a space–time correlation structure exists, the nodes are spatially correlated with each other, and the e2e performance cannot be analyzed as in general two-dimensional networks by assuming all nodes independent of each other. This paper studies an 1-D network fed with a single flow, an extreme scenario in which there is no multiplexing and splitting. A decomposition approach is used to decouple the whole network into isolated nodes. Each node is modeled as a GI/Geo/1 queueing system. First, we derive the complete per-node delay distribution and departure characterization, accounting for both the queueing delay and access delay. Second, based on the departure process approximation, we define a parameter to measure the spatial correlation and its influence on the e2e delay variance. Our study shows that traffic burstiness of the source flow and MAC together determines the sign of the correlation.     

Queueing study of a 3-priority policy with distinct servicestrategies

A discrete-time, single server, 3-queue system is presented and analyzed. A distinct service strategy, namely the consistent-gated (c-G), 1-limited (L) and head-of-line (HoL), is applied to each of the queues (c-G/L/HoL policy). It is shown that this queueing system provides for an accurate analytical model for a DQDB station, as well as a means for an approximate evaluation of the correlation associated with key traffic processes in that network. In addition, the developed queueing system could be useful for the modeling of the queueing behavior of an ATM link shared by high-priority, low priority and control traffic. Through an asymptotic analysis under heavy low-priority traffic, the worst case performance for the high priority traffic is determined. Furthermore, it is illustrated that the asymptotic analysis provides for a potentially tight delay bounding technique. Finally, the delay performance of the developed queueing system is compared to that of a similar system in which one of the queues receives 1-limited service and the other two exhaustive (HoL^-/L/HoL⁺ policy)     

Performance of DS-CDMA receivers with MRC in nakagami-m fading channels with arbitrary fading parameters

The receivers that combine spatial antenna diversity with temporal multipath diversity are known as two-dimensional (2-D) RAKE receivers. In this paper, we consider the outage probability and the bit error rate performance of a coherent binary phase shift keying 2-D RAKE receiver in the context of an asynchronous direct sequence (DS)-code division multiple access (CDMA) system operating in a Nakagami-m fading channel with real and arbitrary fading parameters. The closed-form expressions derived for the two wireless performance measures are easily evaluated numerically and enable the link designer to examine the effects of system parameters, such as the number of receive antennas, RAKE fingers per antenna, and asynchronous CDMA users in the cell, as well as channel conditions, such as the amount of fading in the combined paths and the multipath intensity profile of the channel on the link performance. In addition, the diversity loss due to correlated fading among the spatially separated RAKE fingers is quantified.     

Power Control Using Two-Level Channel Inversion for Data Traffic in a Cellular CDMA System: Performance and Optimal Design

In this paper, we propose and analyze a simple adaptive uplink power control scheme, called two-level channel inversion, for data traffic in a cellular CDMA system. The basic idea is to reduce out-cell interference by reducing the rate of, or even suspending, transmission when the wireless channel is in a bad condition. We first describe the scheme in detail, and then present a probabilistic analysis model for evaluating the system performance. With this model, we determine the queueing delay and system throughput. Numerical results show that in comparison with the traditional channel inversion scheme, the two-level channel inversion scheme can substantially improve system throughput at a moderate cost of extra queueing delay. Finally, we present a design algorithm to optimize the overall performance while maintaining each user's quality of service (QoS).     

Approximate performance analysis of heavily loaded slotted downlink channel in a wireless CDMA system supporting integrated voice/data services

This paper is concerned with the performance analysis of a slotted downlink channel in a wireless code division multiple access (CDMA) communication system with integrated packet voice/data transmission. The system model consists of a base station (BS) and mobile terminals (MT), each of which is able to receive voice and/or data packets. Packets of accepted voice calls are transmitted immediately while accepted multipacket data messages are initially buffered in first in, first out (FIFO) queues created separately for each destination. The BS distinguishes between silence and talkspurt periods of voice sources, so that packets of accepted data messages can use their own codes for transmission during silent time slots. To fulfill QoS requirements for both traffic types, the number of simultaneous packet transmissions over the downlink channel must be limited. To perform this task, a fair, single-priority multiqueueing scheduling scheme is employed. Discrete-time Markov processes are used to model the system operation. Statistical dependence between queues is the main difficulty which arises during the analysis. This dependence leads to serious computational complexity. The aim of this paper is to present an approximate analytical method which enables one to evaluate system performance despite the dependence. Therefore, it is assumed that the system is heavily loaded with data traffic, and a heuristic assumption is made that makes the queueing analysis computationally tractable. Typical system performance measures (i.e., the data message blocking probability, the average data throughput and delay) are evaluated, however, due to the accepted heuristic assumption, the analysis is approximate and that is why computer simulation is used to validate it.     

Analysis of Traffic Distribution and Blocking Probability in Future Wireless Networks

Future wireless networks are envisioned to provide good quality multimedia services to mobile users anywhere at anytime. Traditional analysis of teletraffic in such networks assumes that call arrivals follow a Poisson process, as each cell is being modeled as an M/G/c/c queueing system. This does not reflect the real situation since handoff traffic arrivals are not generally Poissonian. In this paper, we propose to model each cell in future wireless networks as a G/G/c/c queueing system. As such a model has not been explicitly addressed in the literature, our main contribution is to propose a solution which enables to evaluate both traffic distribution and blocking probability within each cell of the service area. Result analysis reveals that coefficient of variation of call arrivals has more impact on the network performance than coefficient of variation of channel holding time.