Integrating data traffic into a CDMA cellular voice system

Part one of this paper analyzes the effects of data traffic integration into a CDMA cellular voice system. The figure of merit used for the quality of service seen by the voice users is measured by the probability of blocking. The CDMA system under consideration is a power controlled, cellular architecture in which blocking occurs when the total interference level exceeds the background noise level by 10 dB [1]. It is shown that the introduction of data can be done at little or no increase in the probability of blocking on the voice users. In part two we propose and analyze a protocol which achieves the efficient integration of data by maximizing the utilization of the resources and minimizing the delay experienced by the voice users. The proposed protocol admits data traffic into the CDMA cellular system based on the current aggregate voice interference level, and allows for the efficient integration of voice and data without degrading the quality of service for the delay-critical voice traffic. A Markovian model for this protocol is developed, evaluated and compared to computer simulation results.     

Up- and Downlink Admission/Congestion Control and Maximal Load in Large Homogeneous CDMA Networks

This paper proposes scalable admission and congestion control schemes that allow each base station to decide independently of the others what set of voice users to serve and/or what bit rates to offer to elastic traffic users competing for bandwidth. These algorithms are primarily meant for large CDMA networks with a random but homogeneous user distribution. They take into account in an exact way the influence of geometry on the combination of inter-cell and intra-cell interferences as well as the existence of maximal power constraints of the base stations and users. We also study the load allowed by these schemes when the size of the network tends to infinity and the mean bit rate offered to elastic traffic users. By load, we mean here the number of voice users that each base station can serve.     

Performance analysis of voice/data cellular CDMA with SIR-based admission control

In this paper, we analyze the performance of a signal-to-interference ratio (SIR)-based admission control strategy on the uplink in cellular code-division multiple-access (CDMA) systems with voice and data traffic. Most studies in the current literature to estimate CDMA system capacity with both voice and data traffic do not take into account admission control based on SIR constraints. Here, we present an analytical approach to evaluate the outage probability for voice traffic, the average system throughput, and the mean delay for data traffic in a voice/data CDMA system, which employs an SIR-based admission control. We make two main approximations in the voice call outage analysis-one based on the central limit theorem (CLT) and the other based on the Fenton's method. We apply the Fenton's method approximation to compute the retransmission probability and the mean delay for data traffic, and the average system throughput. We show that for a voice-only system, a capacity improvement of about 30% is achieved with the SIR-based admission control as compared with the code availability-based admission control. For a mixed voice/data system with 10 Erlangs of voice traffic, an improvement of about 40% in the mean delay for data is shown to be achieved. Also, for a mean delay of 50 ms with 10 Erlangs of voice traffic, the data Erlang capacity improves by about 50%.     

Interference analysis and capacity for forward link 3G CDMA network with adaptive antennas

In code division multiple access (CDMA) systems, the capacity of forward link (FL) communication to mobile receivers is limited primarily by co‐channel interference (CCI). Adaptive antenna arrays (AAAs) that use antenna arrays along with advanced signal processing at the base station (BS) have been proposed to mitigate this limitation. For a 3G CDMA cellular network, where each BS equipped with an AAA serves mixture of voice and data users within its coverage, we study FL capacity and investigate the effects of different factors (array topology, multipath angle spread, data rate, and beamforming algorithm) on this capacity under Rayleigh fading channel. By modeling the instantaneous signal‐to‐interference power ratio received at the mobile, we derive the system outage equation that considers blocking of either desired voice or data user. Simulation results show that for the same element spacing and number of antenna elements per cell, the uniform circular array (UCA) topology results in larger capacity than the sectorized uniform linear array (ULA) topology does, and that a larger angle spread or data user rate reduces FL capacity. Copyright © 2007 John Wiley & Sons, Ltd.     

Admission policies for integrated voice and data traffic in CDMApacket radio networks

The authors derive optimal admission policies for integrated voice and data traffic in packet radio networks employing code division multiple access (CDMA) with direct-sequence spread spectrum (DS/SS) signaling. The network performance is measured in terms of the average blocking probability of voice calls and the average delay and packet loss probability of data messages. The admission scheme determines the number of newly arrived voice users that are accepted in the network so that the long-term blocking probability of voice calls is minimized. In addition, new data arrivals are rejected if the mean delay or the packet loss probability of data exceeds a desirable prespecified level. A semi-Markov decision process (SMDP) is used to model the system operation. Then, a value iteration algorithm is used to derive the optimal admission control. Two models for the other-user interference of the CDMA system are considered: one based on thresholds and another based on the graceful degradation of the CDMA system performance, and their performance is compared. These admission policies find application in emerging commercial CDMA packet radio networks including cellular networks, personal communication networks, and networks of LEO satellites for global communications     

Capacity, throughput, and delay analysis of a cellular DS CDMAsystem with imperfect power control and imperfect sectorization

An analytical model is developed to evaluate the performance of a cellular slotted DS CDMA system in terms of user capacity, throughput, and delay for the reverse link, i.e., from mobile to base station, considering interference from both home cell and adjacent cells. The user capacity is studied for voice communications and the throughput and delay are investigated for data communications. The effect of both imperfect power control and imperfect sectorization on the performance is investigated. It is shown that the system is rather sensitive to small power control errors and that voice activity monitoring and sectorization are good methods to improve the performance of cellular DS CDMA systems     

Cognitive radio CDMA networking with spectrum sensing

In this paper, the performance of cognitive radio (CR) code division multiple access (CDMA) systems is analyzed. More precisely, CR users belong to a cognitive radio network (CRN), which coexists with a primary radio network (PRN). Both CRN and PRN are CDMA‐based, with colocated base stations. Soft hand off and power control are considered in both the CRN and the PRN. Upon the development of an accurate simulator for a representative three‐cell cellular scenario, we evaluate the performance of the proposed CR system in terms of outage probability, blocking probability and average data rate of secondary users. Three different spectrum sensing techniques are. Two new schemes, based on interference limit, are proposed and compared with an existing adaptive spectrum sensing scheme. Spectrum activity measurements and spectrum sharing decisions have been considered for evaluating the performance of the three schemes. The paper proposes a new CR‐CDMA networking model and a simulation testbed for evaluating performances of secondary users and primary users in terms of outage, blocking, BER and average data rate in the presence of soft hand‐off and power control. For comparison purposes, the analysis in the absence of spectrum sensing is also investigated.Copyright © 2012 John Wiley & Sons, Ltd.     

Packet CDMA versus dynamic TDMA for multiple access in anintegrated voice/data PCN

A comparative evaluation of dynamic time-division multiple access (TDMA) and spread-spectrum packet code-division multiple access (CDMA) approaches to multiple access in an integrated voice/data personal communications network (PCN) environment are presented. After briefly outlining a cellular packet-switching architecture for voice/data PCN systems, dynamic TDMA and packet CDMA protocols appropriate for such traffic scenarios are described. Simulation-based network models which have been developed for performance evaluation of these competing access techniques are then outlined. These models are exercised with example integrated voice/data traffic models to obtain comparative system performance measures such as channel utilization, voice blocking probability, and data delay. Operating points based on typical performance constraints such as voice blocking probability 0.01 (for TDMA), voice packet loss rate 10^-3 (for CDMA), and data delay 250 ms are obtained, and results are presented     

Optimal strategies for admitting voice and data traffic in networks of LEO satellites using CDMA

Efficient policies are derived for admitting voice and data traffic into networks of low-earth-orbit (LEO) satellites using code-division multiple-access (CDMA) with direct-sequence spread-spectrum (DS/SS) signaling. The satellites act as bent-pipes; no on-board processing or intersatellite links are present. Dual satellite diversity is used to mitigate the effects of shadowing. The policies assume a movable boundary form, allocate optimally the CDMA capacity (PN codes) to voice and data users, and can increase significantly the number of users served while satisfying their bit error rate (BER) requirements. In contrast to direct admission policies that do not take into consideration the statistical features of the traffic, the new policies do account for the different nature of voice and data traffic and the history of prior transmissions/admissions. Two priority schemes are considered: voice users have higher priority than data users, or voice and data users have the same priority. A modified version of our policies can handle two classes of data users: one with high priority which requires real-time delivery and another with low priority that can be queued; the BER requirements of the two data types may differ. Optimal policies have lower voice blocking rates and data packet error rates than direct admission policies.     

Adaptive S-ALOHA CDMA as an alternative way of integrating servicesin mobile environments

Code-division multiple-access (CDMA) schemes appear to be very promising access techniques for coping with the requirements of third-generation mobile systems, mainly because of their flexibility. This paper proposes an adaptive S-ALOHA DS-CDMA access scheme as a method for integrating nonreal-time (i.e., Internet applications) and real-time (i.e., voice) services in a multicell scenario by exploiting the potentials of CDMA under time-varying channel load conditions. The adaptive component makes data terminals autonomously change their transmission rate according to the total (voice+data) channel occupancy, so that the minimum possible data delay, which can be analytically obtained by defining a birth-death process, is almost always achieved. Moreover, by means of a simplified cellular model, the proposed algorithm revealed the same behavior, i.e., it tries to select the most suitable transmission rate at any time slot, when it is affected by intercell interference and even by power control imperfections. Finally, in order to gain more insight into the potentials of such an access strategy, the adaptive S-ALOHA CDMA scheme is then compared to a reservation time-division multiple-access (TDMA)-based protocol (PRMA++), showing the benefits of the CDMA-based solution in terms of capacity, flexibility, and data delay performance     

Software radio architecture with smart antennas: a tutorial onalgorithms and complexity

There has been considerable interest in using antenna arrays in wireless communication networks to increase the capacity and decrease the cochannel interference. Adaptive beamforming with smart antennas at the receiver increases the carrier-to-interference ratio (CIR) in a wireless link. This paper considers a wireless network with beamforming capabilities at the receiver which allows two or more transmitters to share the same channel to communicate with the base station. The concrete computational complexity and algorithm structure of a base station are considered in terms of a software radio system model, initially with an omnidirectional antenna. The software radio computational model is then expanded to characterize a network with smart antennas. The application of the software radio smart antenna is demonstrated through two examples. First, traffic improvement in a network with a smart antenna is considered, and the implementation of a hand-off algorithm in the software radio is presented. The blocking probabilities of the calls and total carried traffic in the system under different traffic policies are derived. The analytical and numerical results show that adaptive beamforming at the receiver reduces the probability of blocking and forced termination of the calls and increases the total carried traffic in the system. Then, a joint beamforming and power control algorithm is implemented in a software radio smart antenna in a CDMA network. This shows that, by using smart antennas, each user can transmit with much lower power, and therefore the system capacity increases significantly     

基于SIR和语音业务优先级的联合功率/速率控制

本文针对综合语音和数据蜂窝系统的上行链路,提出了一种基于SIR和语音业务优先级的联合功率和数据速率控制算法(SIRPBCPRC)。该算法是一种分布式算法,容易实现;并且在进行资源分配时考虑了语音业务的实时性,给予语音用户更高的优先级。理论分析和仿真表明,SIRPBCPRC方案通过降低数据用户数据速率和发射功率来减少对语音用户的干扰,从而降低了语音用户的中断概率,达到语音业务的通信质量要求。同时,由于CDMA系统是干扰受限系统,所以采用该算法时,随着数据用户产生的干扰的降低,语音用户的发射功率也会随之降低。     

CDMA蜂窝系统中基于模糊神经网络的反向链路功率控制

CDMA是一个干扰受限系统,反向链路功率控制对于克服“远近效应”和增加系统容量是非常重要的.本文提出了一种基于模糊神经网络(FNN)的自适应闭环功率控制算法,该算法动态地调整功率控制增量,使基站接收到的每个用户的发射功率相等.仿真结果表明,由于模糊神经网络能够较好地识别反向链路的时变特性,FNN功率控制算法比传统的固定步长功率控制方法取得了更好的控制性能和更大的系统容量.而且,FNN能够通过神经网络训练自动地调整隶属度函数和模糊规则,从而适合于实现在线系统识别和自适应控制.     

Optimum Power Assignment for Maximum Throughput in CDMA Personal Communication Systems with Integrated Voice/Data Traffic

A CDMA personal communication system with integrated voice/data traffic is considered, in which the link error performance is controlled according to the voice error rate requirement, and the acceptable data traffic error rate is ensured by ARQ. Optimum power assignment (or allocation) between voice and data users is investigated to maximize the total system throughput. A graphical method (the tangent method) is described to obtain this optimum power allocation. The maximum throughput is expressed as a function of other system parameters. The tangent method is further used to measure the impact of transmission quality on the maximum data throughput. Numerical results and a design example are given for a power controlled wideband IS-95 type wireless personal communication system.     

Capacity Analysis for Connection Admission Control in Indoor Multimedia CDMA Wireless Communications

In this paper, the capacity analysis for connection admission control is presented for the reverse-link transmission of a packetized indoor multimedia wireless communication system using direct sequence code division multiple access (DS/CDMA). Since CDMA is interference limited, the signal-to-interference-plus-noise ratio criterion is used to check if there is enough system resources (i.e., the CDMA channels and received signal power) for each new connection request. Taking into account the stochastical nature of multimedia traffic, the effective bit rate is used to characterize the resources required by each mobile user and a linear approximation is then used to find the total resources required by all the mobile users already admitted to the system and the new connection request. Transmission errors due to both base station buffer overflow and wireless channel impairments are considered. The capacity of multimedia traffic is determined in such a way that the utilization of the system resources is maximized and, at the same time, the required transmission bit error rate and transmission delay of all users admitted to the system are guaranteed. Computer simulation results are given to demonstrate the performance of the proposed method for capacity analysis.     

Joint admission/congestion control for wireless CDMA systemssupporting integrated services

A new data traffic control scheme is developed for maintaining the packet error rate (PER) of real-time voice traffic while allowing nonreal-time data traffic to utilize the residual channel capacity of the multi-access link in an integrated service wireless CDMA network. Due to the delay constraint of the voice service, voice users transmit their packets without incurring further delay once they are admitted to the system according to the admission control policy. Data traffic, however, is regulated at both the call level (i.e., admission control) and at the burst level (i.e., congestion control). The admission control rejects the data calls that will otherwise experience unduly long delay, whereas the congestion control ensures the PER of voice traffic being lower than a specified quality of service (QoS) requirement (e.g., 10 ^-2). System performance such as voice PER, voice-blocking probability, data throughput, delay, and blocking probability is evaluated by a Markovian model. Numerical results for a system with a Rician fading channel and DPSK modulation are presented to show the interplay between admission and congestion control, as well as how one can engineer the control parameters. The tradeoff of using multiple CDMA codes to reduce the transmission time of data messages is also investigated     

Implementing interference cancellation to increase the EV-DO Rev A reverse link capacity

This article provides the principles and practice of how interference cancellation can be implemented on the EV-DO Rev A reverse link. It is shown that applying interference cancellation to CDMA achieves the multiple access channel sum rate capacity for either frame synchronous or asynchronous users. The per user SINR gain from space-time interference cancellation translates directly into a CDMA capacity gain of the same factor, allowing EV-DO Rev A to support more users with higher data rates. We demonstrate how interference cancellation can be added to base station processing without modifying user terminals, EV-DO standards, or network coverage. We present commercially viable receiver architectures for implementing interference cancellation with the asynchronism and H-ARQ of EV-DO RevA, and explain why closed loop power control can operate the same way it does today. Network level simulations over a wide range of channels confirm that interference cancellation offers significant capacity gains for all users, while maintaining the same link budget and system stability.     

PMCAP/CDMA协议在语音与数据混合业务中的应用研究

该文将CDMA移动通信系统上行信道中的一种MAC协议PMCAP／CDMA协议应用到语音与数据混合业务的情况，对协议建立数学模型，并对性能进行理论计算和仿真。为了保证对语音请求的优先分配，将PN码集分为语音可用码集，数据可用码集及语音与数据的预防码集。提出了新的动态码集分配方案。仿真表现，该方案较固定码集方案更好地提高了系统的综合性能，而负指数码字分配方案提供了语音与数据性能的很好折衷。     

An uplink CDMA system architecture with diverse QoS guarantees forheterogeneous traffic

The uplink access control problems for cellular code-division multiple-access (CDMA) systems that service heterogeneous traffic with various types of quality-of-service (QoS) and use multicode CDMA to support variable bit rates are addressed. Considering its distinct QoS requirements, class-I real-time traffic (e.g., voice and video) is differentiated from class-II non-real-time traffic (e.g., data). Connection-oriented transmission is achieved by assigning mobile-oriented code channels for class-I traffic, where each corresponding mobile needs to pass an admission test. Class-II traffic is transmitted in a best-effort manner through a transmission-rate request access scheme which utilizes the bandwidth left unused by class-I traffic. Whenever a mobile has class-II messages to transmit, the mobile requests code channels via a base station-oriented transmission-request code channel, then, according to the base station scheduling, the transmission is scheduled and permitted. Addressed are the admission test for class-I connections, transmission power allocation, and how to maximize the aggregate throughput for class-II traffic. The admission region of voice and video connections and the optimum target signal-to-interference ratio of class-II traffic are derived numerically. The performance of class-II traffic transmissions in terms of average delay is also evaluated and discussed     

Erlang Capacity of a Voice/Data Cellular CDMA Uplink System Using Prioritized Admission Control and Adaptive Power Control

A CDMA uplink system that carries both voice and data traffic is investigated. The reservation-based admission control scheme is used to prioritize voice mobiles, and the truncated channel inversion power control scheme is used by data mobiles to improve system capacity. The performance of the system is measured by the Erlang capacity. Two methods of determining the Erlang capacity are presented. The first method decouples the analysis of blocking and outage performance, thus simplifying numerical search. The second method takes into account the impact of mobile traffic fluctuations on interference statistics, and thus yields more accurate results. Numerical results are provided that show significant differences between the two methods. Finally, the Erlang capacities of the system are compared for different power control schemes.