Performance evaluation of a joint CDMA/NC-PRMA protocol forwireless multimedia communications

A joint code division multiple access and noncollision packet reservation multiple access (CDMA/NC-PRMA) technique is proposed and investigated as an uplink protocol for the third-generation (3G) mobile systems. Being the underlying time division multiple access (TDMA) architecture of the CDMA transmissions, NC-PRMA enables the base station (BS) to have a centralized control over the slot allocation policy. In order to reduce the multiple access interference (MAI) variation in a CDMA transmission, two different slot assignment schemes, referred to as load-balancing (LB) and power-grouping (PG) schemes, are proposed and evaluated. Simulation results show that considerable improvement can be achieved over the joint CDMA/PRMA scheme, in which the MAI variation is reduced by way of a dynamic permission probability for contending terminals. Especially when an imperfect power control mechanism is considered, the proposed PG assignment scheme achieves significant performance advantages     

Performance analysis of CDMA with imperfect power control

The standard correlation receiver for code-division multiple access (CDMA) systems is susceptible to the near-far problem. Power control techniques attempt to overcome near-far effects by varying transmitted power levels to ensure that all signals are received with equal power levels. Since these algorithms cannot perfectly compensate for power fluctuations in a mobile communications channel, the capacity of the system is reduced for a given bit-error rate (BER). This paper examines the performance of a CDMA system using imperfect power control by extending analytical techniques that account for multiple access interference. Single cell capacity is compared with systems employing perfect power control     

Numerical analysis of joint CDMA/PRMA protocol based on equilibriumpoint analysis

Numerical expressions to assess the performance of a joint direct sequence code division multiple access/packet reservation multiple access (CDMA/PRMA) protocol are presented. Simulation of CDMA/PRMA systems with narrowbeam antennas is also applied to support the proposed technique     

卫星通信系统中的多址接入协议

简述了卫星通信中多址协议的分类和影响多址协议性能的因素,重点介绍了三种预约多址协议PRMA-HS、PRMA/CDMA和Butst Reservation CDMA,并分析了它们的性能.     

Effect of imperfect power control on cellular code division multiple access system

An analytical model is developed to evaluate the performance of a cellular direct-sequence code division multiple access (DS CDMA) system with a perfect as well as an imperfect power control scheme and without power control considering the near-far effect. The effect of the three schemes on the performance is compared.<>     

A medium access control scheme for TDD-CDMA cellular networks with two-hop relay architecture

In this paper, we propose a multihop medium access control (mMAC) scheme for time division duplexing-code division multiple access (TDD-CDMA) cellular networks with two-hop relay architecture to support packet data transmission. The proposed mMAC is based on joint CDMA/PRMA (packet reservation multiple access) protocol and it includes BCH code selection, power control and multihop relaying. Simulation results reveal that cellular networks with two-hop relay architecture with the proposed mMAC scheme can substantially provide a good performance as well as larger cell coverage as compared to conventional TDD-CDMA single-hop cellular networks.     

Delta modulation based prediction for access control in integratedvoice/data CDMA systems

In this paper, we propose access control protocols for integrated voice/data code division multiple access (CDMA) systems that are based on estimating the residual capacity available for data users. The data model considered in the analysis is suitable for non-transparent services (e.g., e-mail, file transfer, store-and-forward facsimile, etc.). The residual capacity is derived from the feasibility condition for power control using an adaptive prediction technique based on delta modulation. The analysis is extended for the case of imperfect power control. Two access control protocols are considered: modified delta modulation with scheduled access (MDM-S) and modified delta modulation with random access (MDM-R). Comparisons with earlier proposed protocols reveal a better performance in terms of average throughput for data for a given system capacity and outage probability     

Performance of DS-CDMA with imperfect power control operating overa low earth orbiting satellite link

The analysis of both the performance and capacity of direct sequence CDMA in terrestrial cellular systems has been addressed in the technical literature. It has been suggested that CDMA be used as a multiple access method for satellite systems as well, in particular for multispot beam low Earth orbit satellites (LEOS). One is tempted to argue that since CDMA works well on terrestrial links, it will nominally work as well on satellite links. However, because there are fundamental differences in the characteristics of the two channels, such as larger time delays from the mobile to the base station and smaller multipath delay spreads on the satellite channels, the performance of CDMA on satellite links cannot always be accurately predicted from its performance on terrestrial channels. In the paper, the authors analytically derive the performance of a CDMA system which operates over a low Earth orbiting satellite channel. They incorporate such effects as imperfect power control and dual-order diversity to obtain the average probability of error of a single user     

Admission control for variable spreading gain CDMA cellular system with imperfect power control and shadowing

Variable spreading gain (VSG) CDMA is the prime transmission scheme for supporting multiple services for the next generation cellular systems. As different services have different quality of service and data rate requirements, admission control is essential in safeguarding the performance of different services in VSG‐CDMA cellular systems in harsh wireless environment. In this paper, we propose an admission control scheme for multiple services VSG‐CDMA cellular system in a practical multi‐cell environment where there exist adverse effects due to imperfect power control and shadowing. Rather than with a fixed bound as in previous studies, the admission bound in our scheme is based on the probability distribution of total intra‐cell power (P_in) and other‐cell interference power (I_other). This is used to estimate the blocking probability by utilizing a simple and accurate approximation that incorporates the random nature of P_in and I_other. Evaluation of the impact of power control error to the mean and standard deviation of P_in and I_other, we performed and compared the blocking probability with fixed admission bound scheme in an integrated voice/data environment. Our work has enabled the calculation of the blocking probability and capacity of different mobility users having different power control errors under shadowing. Copyright © 2006 John Wiley & Sons, Ltd.     

CDMA systems in fading channels: admissibility, network capacity,and power control

We study the admissibility and network capacity of imperfect power-controlled code-division multiple access (CDMA) systems with linear receivers in fading environments. In a CDMA system, a set of users is admissible if their simultaneous transmission does not result in violation of any of their quality-of-service (QoS) requirements; the network capacity is the maximum number of admissible users. We consider a single-cell imperfect power-controlled CDMA system, assuming known received power distributions. We identify the network capacities of single-class systems with matched-filter (MF) receivers for both the deterministic and random signature cases. We also characterize the network capacity of single-class systems with linear minimum-mean-square-error (MMSE) receivers for the deterministic signature case. The network capacities can be expressed uniquely in terms of the users' signal-to-interference ratio (SIR) requirements and received power distributions. For multiple-class systems equipped with MF receivers, we find a necessary and sufficient condition on the admissibility for the random signature case, but only a sufficient condition for the deterministic signature case. We also introduce the notions of effective target SIR and effective bandwidth, which are useful in determining the admissibility and hence network capacity of an imperfect power-controlled system     

Handoff effect on packet reservation multiple access (PRMA) in microcellular system

Packet reservation multiple access (PRMA) has been proposed for third-generation wireless information networks by D.J. Goodman and S.X. Wei (see ibid., vol.40, p.170-6, 1991). The mobile-initiated handoff has been proposed to disperse the base station (BS) burden, which is increased by the small microcell radius. However, increased contentions, due to handoff, affect the overall performance of PRMA, even though these frequent handoffs do not burden the BS. We analyze the handoff effect on PRMA performance under a microcellular system, both voice-only and combined voice-and-data systems. A steady state voice-terminal model with handoff is proposed. System-equilibrium equations are derived using the proposed model. The system performance is evaluated, using a Markov analysis method, in terms of packet-dropping probability, data-packet delay, and throughput. The change of performance under handoff show the impact of handoff on PRMA.     

High data-rate packet communications for cellular networks usingCDMA: algorithms and performance

The advantages of code division multiple access (CDMA) for cellular voice have become well known, and IS-95-based systems have now been widely deployed. Attention is now focused on higher data-rate packet services for cellular systems. Although many packet multiple access schemes have been studied over the years, researchers have often studied single cell performance and ignored reuse. Moreover, direct sequence spread spectrum (DSSS) has been considered unsuitable for high data-rate packet multiple access since spreading limits the permitted data rates, DSSS requires large overhead (preambles) for acquisition and requires closed-loop power control. In this paper, we describe a scheme for high data-rate packet service using CDMA that addresses all of the above problems and has been standardized in Revision B of IS-95. A low rate fundamental code channel is maintained that eliminates the need for long preamble and provides closed-loop power control. Reuse is managed by the infrastructure through a “burst-level” admission control based on load and interference-level measurements at the base stations and mobiles. We report on the feasibility of such a burst-mode packet data service for cellular CDMA networks. The focus is not only on the performance of high data-rate users, but also on the impact on voice users sharing the CDMA band. We propose a multitiered performance analysis methodology consisting of a mix of static simulations, dynamic simulations at different time scales, and analytic methods to address the various feasibility issues: impact on coverage; capacity; power control; and effectiveness of burst admission algorithms. Based on the current study, we can conclude that the proposed approach is well suited for third-generation wideband CDMA systems being considered for standardization throughout the world     

Multiuser receiver scheme for full‐rate space–time coded CDMA system with imperfect estimation

By introducing a full‐rate space–time coding (STC) scheme, a synchronous CDMA (code division multiple access) system with full‐rate STC is given, and the corresponding uplink performance is investigated in Rayleigh fading channel with imperfect estimation. Considering that existing STC‐CDMA system has high decoding complexity, low‐complexity multiuser receiver schemes are developed for perfect and imperfect estimations, respectively. The schemes can make full use of the complex orthogonality of STC to reduce the high decoding complexity of the existing scheme, and have linear decoding complexity compared with the existing scheme with exponential decoding complexity. Moreover, the proposed schemes can achieve almost the same performance as the existing scheme. Compared with full‐diversity STC‐CDMA, the given full‐rate STC‐CDMA can achieve full data rate, low complexity, and partial diversity, and form efficient spatial interleaving. Thus, the concatenation of channel coding can effectively compensate for the performance loss due to partial diversity. Simulation results show that the full‐rate STC‐CDMA has lower bit error rate (BER) than full‐diversity STC‐CDMA systems under the same system throughput and concatenation of channel code. Moreover, the system BER with imperfect estimation are worse than that with perfect estimation due to the estimation error, which implies that the developed multiuser receiver schemes are valid and reasonable. Copyright © 2010 John Wiley & Sons, Ltd.     

Multidimensional PRMA with prioritized Bayesian broadcast-a MACstrategy for multiservice traffic over UMTS

Multidimensional packet reservation multiple access is proposed as a medium-access control (MAC) strategy for the uplink channel of the UTRA (UMTS terrestrial radio access) time-division/code-division multiple-access (TD/CDMA) mode to benefit from efficient statistical multiplexing on the large common pool of available resources (i.e., slots defined both in time and code domain). A prioritized Bayesian broadcast algorithm is derived to stabilize multidimensional packet reservation multiple access (MD PRMA) and to allow for access delay discrimination of four different access classes. Access delay spread can be selected, and trading voice-dropping ratio against data-access delay is possible. To control multiple-access interference, Bayesian broadcast can be combined with load-based access control. The performance of both frequency-division duplex (FDD) and time-division duplex (TDD) mode is evaluated, the latter particularly relevant for TD/CDMA. For mixed voice, Worldwide Web (WWW) browsing, and e-mail traffic, the UMTS WWW model is used, while the e-mail traffic model is derived here     

Optimising delay and throughput in packet-switched CDMA networkwith collision resolution using stack algorithm

The authors address the effect of code division multiple access (CDMA) on the performance of wireless packet-switched networks. Although CDMA can enhance throughput, the delay at small traffic loads suffers from bandspreading. For imperfect signal separation at the receiver, performance benefits from CDMA may be lost. The capacity of the particular stack algorithm addressed for collision resolution can be enhanced from 0.32 to ~0.40 if a 10 dB spreading gain with perfect signal separation is employed     

CRDA: a collision resolution and dynamic allocation MAC protocol tointegrate data and voice in wireless networks

One key requirement for radio access in advanced, third generation (3G) mobile communication systems is the ability to accommodate a variety of services via a flexible and efficient medium access control (MAC) protocol. The paper presents and evaluates a new multiple access protocol termed CRDA (collision resolution and dynamic allocation), which has the potential to meet the above requirement. CRDA is basically a slotted packet-reservation multiple access technique with dedicated reservation slots, which allows the main shortcoming of previous PRMA schemes, i.e., contention, to be overcome through the integration in the MAC protocol of a code-division multiple-access (CDMA) transmission mode used to access the reservation slots. This prevents collisions during the reservation phase and enhances channel throughput, notably in the case of mixed voice/data traffic. Our simulations of the CRDA MAC integrate voice channels with data sources, generating what we call advanced data traffic, which has a very similar shape to the actual traffic generated by World Wide Web (WWW) applications. The standard assumption of Poissonian data traffic is also considered. Our conclusion is that the CRDA MAC protocol satisfactorily accommodates both types of traffic     

Power imbalance effects on packet CDMA

This paper presents an analysis of packet code-division multiple-access (CDMA) with single user receivers and power level variations. The power level variations are due to imperfect power control. The teletraffic is modeled as an M/G/∞ queueing system. Average error rates and outage probabilities that a user sees are evaluated for a single cell CDMA system. The effects of power level variations are investigated using a combination of an approximation and an upper bound, and the loss in traffic capacity is evaluated. Numerical results for CDMA systems with different processing gains and coding gains are presented. It is shown that imperfect power control reduces significantly the CDMA teletraffic capacity, and much has to be gained by improving the power control schemes. The methods and results of this work could be used for quantifying the required accuracy of power control in CDMA and for evaluation of the capacity loss due to power control errors     

Traffic handling capability of a broadband indoor wireless networkusing CDMA multiple access

CDMA (code division multiple access) may be an attractive technique for wireless access to broadband services because of its multiple access simplicity and other appealing features. In order to investigate the traffic handling capabilities of a future network providing a variety of integrated services, this paper presents a study of a broadband indoor wireless network supporting high-speed traffic using CDMA multiple access. The results are obtained through the simulation of an indoor environment and the traffic capabilities of the wireless access to broadband 155.5 MHz ATM-SONET networks using the mm-wave band. A distributed system architecture is employed and the system performance is measured in terms of call blocking probability and dropping probability, the impacts of the base station density, traffic load, average holding time, and variable traffic sources on the system performance are examined. The improvement of system performance by implementing various techniques such as handoff, admission control, power control and sectorization are also investigated     

Performance of a joint CDMA/PRMA protocol for mixed voice/datatransmission for third generation mobile communication

A joint code-division multiple-access/packet-reservation multiple-access (CDMA/PRMA) technique is proposed and investigated as a candidate for an uplink protocol for third generation mobile communication systems. Access to the radio channel is controlled such that compared to random access CDMA, interference variance is reduced and throughput increased. Mixed voice/data traffic is investigated for an isolated cell only, whereas voice-only traffic is also investigated in a cellular environment with a regular hexagonal cell structure. Intercell interference is assumed to be Gaussian, and only the average interference level is considered     

Packet-length adaptive CLSP/DS-CDMA: performance in burst-error correlated fading channels

The authors analyze throughput-delay performance of an unslotted channel load sensing protocol (CLSP)/direct sequence (DS)-code division multiple access (CDMA) packet radio network (PRN) with adaptive packet length over burst-error correlated fading channels. CLSP controls the packet access in uplink of unslotted ALOHA/DS-CDMA systems so that contention is avoided and throughput is maximized. However, due to high uncertainty of radio channels, the performance of CLSP/DS-CDMA PRN may suffer from notable degradations. Using theoretical analysis and simulation, the authors show that in highly correlated fading environments adapting the length of radio packets to fading conditions significantly improves system performance and energy efficiency of mobile terminals. In their modeling, they study the relation between the fade statistics and the packet length in correlated Rayleigh fading channels. The effects of reception diversity, imperfect transmit power control (TPC), and user mobility are considered. The results are used to develop simple, energy-efficient, and robust adaptation mechanisms.