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     

Soft handoff algorithms for CDMA cellular networks

This paper discusses the design of soft handoff algorithms for cellular communication systems. The handoff process is modeled as a hybrid system and handoff design is cast as an optimization problem based on such a model. Performance is evaluated in terms of call quality, average number of active base stations, average number of active set updates, and average amount of interference. A soft handoff algorithm, which achieves a tradeoff between these performance criteria, is obtained using principles of dynamic programming. One key feature of the algorithm is that it incorporates the effects of mobility and shadow fading in the handoff decision. Different diversity combining schemes are considered including selective combining, equal gain combining (EGC), and various optimized combining (OC) methods in the soft handoff mode. For EGC and OC, Wilkinson's and Schwartz and Yeh's methods are used to compute the statistics for the power sum of the signals. Simulation results indicate that the performance of the handoff algorithm is a function of the different combining schemes and of the different methods used to compute the statistics of the power sum. Moreover, it is observed that interference cancellation is important in order for the algorithm to be viable for cellular systems which experience interference due to using nonorthogonal multiple access.     

TOA-based robust location algorithms for wireless cellular networks

Caused by Non-Line-Of-Sight (NLOS) propagation effect, the non-symmetric contamination of measured Time Of Arrival (TOA) data leads to high inaccuracies of the conventional TOA based mobile location techniques. Robust position estimation method based on bootstrapping M-estimation and Huber estimator are proposed to mitigate the effects of NLOS propagation on the location error. Simulation results show the improvement over traditional Least-Square (LS) algorithm on location accuracy under different channel environments.     

Call admission and handoff control in multi-tier cellular networks: algorithms and analysis

In this paper, we investigate a call-admission and handoff-control framework for multi-tier cellular networks. We first propose and compare Call-Admission Control (CAC) algorithms based on the cell-dwelling time, by studying their impact on the handoff-call dropping and new-call blocking probabilities and the channel partitioning between the two tiers. Our results show that a simple, cell-dwelling-time-insensitive algorithm performs better under various mixes of user mobilities and call types. Moreover, there is an optimal channel partition of the overall spectrum between the tiers which minimizes the dropping and blocking probabilities for the two different CAC algorithms studied in this paper. Once the call is admitted into the network, we propose and compare various handoff- queuing strategies to reduce the call dropping probability. We show that implementing a queuing framework in one of the tiers (especially the upper, i.e., macrocellular, tier), results in a significant reduction in the dropping probability.     

Design and analysis of parallel file downloading algorithms in peer-to-peer networks

It is well known that the method of parallel downloading can be used to reduce file download times in a peer-to-peer (P2P) network. There has been little investigation on parallel download and chunk allocation for source peers with random service capacities. The main contribution of this paper is to address the problem of efficient parallel file download in P2P networks with random service capacities. A precise analysis of the expected download time is given when the service capacity of a source peer is a random variable. A general framework is developed for analyzing the expected download time of a parallel download and chunk allocation algorithm, and is applied to the analysis of several algorithms. Two chunk allocation algorithms for parallel download are proposed. It is observed that the performance of parallel download can be significantly improved by using the method of probing high-capacity peers. One such algorithm is proposed and its expected parallel download time is analyzed. The performance of these parallel file download algorithms in P2P networks with random service capacities are compared. The above parallel download algorithms are extended to multiple file download by dividing source peers into clusters. It is noticed that there is an important issue of optimal parallelism which minimizes the combined effect of intracluster and intercluster overhead of parallel download and load imbalance.     

Design and analysis of cooperative wireless data access algorithms in multi-radio wireless networks

In the future, most mobile nodes will have multiple radio interfaces, and this feature can be exploited to reduce the transmission cost in wireless data access applications. In this work, we propose cooperative poll-each-read (CoopPER) and cooperative callback (CoopCB) wireless data access algorithms with strong consistency in multi-radio wireless networks. In addition, we investigate CoopPER and CoopCB in heterogeneous wireless networks where CoopPER and CoopCB nodes are mixed. Extensive simulations are done to show the effects of access-to-update ratio, data access pattern, cache size, and cooperation range. Simulation results demonstrate that CoopPER and CoopCB can significantly reduce the expensive transmission cost over wireless links.     

Real-time mobility tracking algorithms for cellular networks based on Kalman filtering

We propose two algorithms for real-time tracking of the location and dynamic motion of a mobile station in a cellular network using the pilot signal strengths from neighboring base stations. The underlying mobility model is based on a dynamic linear system driven by a discrete command process that determines the mobile station's acceleration. The command process is modeled as a semi-Markov process over a finite set of acceleration levels. The first algorithm consists of an averaging filter for processing pilot signal, strength measurements and two Kalman filters, one to estimate the discrete command process and the other to estimate the mobility state. The second algorithm employs a single Kalman filter without prefiltering and is able to track a mobile station even when a limited set of pilot signal measurements is available. Both of the proposed tracking algorithms can be used to predict future mobility behavior, which can be, useful in resource allocation applications. Our numerical results show that the proposed tracking algorithms perform accurately over a wide range of mobility parameter values.     

Call-on-hold for improving the performance of dynamic channel-assignment strategies in cellular networks

Efficient use of the limited radio spectrum is of paramount importance to supporting the ever-increasing number of mobile terminals. There is a need for devising complementing techniques to improve the performance of dynamic channel-assignment (DCA) algorithms to increase the capacity of cellular systems. In this paper, we study the concept of call-on-hold to improve the performance of a class of DCA algorithms called coordinated assignment without measurement (CAWM). DCA algorithms such as the Geometric strategy, the Nanda-Goodman strategy, the borrowing with directional channel locking (BDCL) strategy, and the two-step dynamic priority (TSDP) strategy fall into the CAWM class. To gain insight into the CAWM DCA algorithms, we simulated those algorithms and monitored carrier availability and failure to assign a channel characteristics in a cell. After observing these characteristics, we formulated a hypothesis as follows: If a new or handoff call is put on hold for a short while in a cell in the absence of an available channel, it is highly likely that the local base station will soon find a channel for the call. In the proposed approach, a DCA algorithm is said to have failed to assign a channel to a call only if a waiting call is delayed for longer than a threshold period called maximum delay. Our simulation-based study shows that it is possible to significantly reduce failure rates of the CAWM class of DCA algorithms by putting those calls on hold which would otherwise be blocked or dropped. The impact of small values of maximum delay on the average delay suffered by all calls in a network is negligible, but the reduction in failure rate is significant. We have explained how the call-on-hold idea can be easily integrated with the GSM system.     

Dynamic segmentation of cellular networks for improved handover performance

One of the most important initial steps, inherent in the planning procedure of cellular networks, is their segmentation in operational parts that is performed at different levels corresponding to the hierarchy and topology of the network. The major goal of this procedure is the efficient deployment of the system and management of the distributed segmented parts while minimizing the signaling overhead in the network. As we show here, it can take place even during the operational phase of the network when certain shortcomings appear. In this work, we present an approach based on graph theory for the segmentation of cellular networks at the Base Station Controller (BSC) level that achieves a significant increase in the performance of the network. In particular, with the proposed method, both the handover attempts when a mobile station is moving to a cell belonging to a different BSC as well as the corresponding handover failure rate are decreased significantly, allowing for a continuous network upgrade. Copyright © 2007 John Wiley & Sons, Ltd.     

Performance of received power and traffic-driven handover algorithms in urban cellular networks

This article presents an investigation of the handover algorithms suitable for implementation in urban mobile cellular networks based on TDMA. More precisely, the class of received power and traffic-driven handover algorithms, which are based on absolute and relative measured values of received power and on actual traffic load, is analyzed. The algorithms usually investigated in the literature (and often implemented in actual mobile networks) belong to this class. We show the performance of traditional algorithms, and also propose some new ones, in an effort to reduce the probability of dropout due to sudden changes of received power and to distribute the traffic load over several cells; they show performance improvements with respect to those previously known from the literature. The performance of the different handover algorithms is evaluated by means of a simulation tool that allows the consideration of complex scenarios, suitable mobility and propagation models, power control, cell sectorization, nonuniform user distribution, and so on. The metrics used for performance comparison are the outage, blocking, dropout, and satisfaction probabilities, whose different definitions are discussed in the article, and the average number of handovers per call. Several urban scenarios, characterized by uniform and nonuniform traffic distributions, are taken into account. Our results show that one of the proposed algorithms, based on traffic estimates, yields the best performance of all the considered scenarios.     

On the performance of packet-switched cellular networks for wireless data communications

Cellular frequency reuse is known to be an efficient method to allow many wireless telephone subscribers to share the same frequency band. However, for wireless data and multi-media communications optimum cell layouts differ essentially from typical solutions for telephone systems. We argue that wireless radio systems for bursty message traffic preferably use the entire bandwidth in each cell. Packet queuing delays are derived for a network with multipath fading channels, shadowing, path loss and discontinuously transmitting base stations. Interference between cells can be reduced by appropriately scheduling transmissions or by spatial collision resolution.Portions of this paper have been presented at the IEEE International Conferences on Personal Indoor Mobile Radio Communications (PIMRC) of 1993 in Yokohama and 1994 in The Hague.     

Unified performance analysis with exact solutions for uplink non-orthogonal multiple access system-based cellular networks

This research presents a unified performance analysis methodology for the power domains of uplink non-orthogonal multiple access (NOMA) system consisting of a base station and an arbitrary number of users over Rayleigh fading channels. The study derives exact closed-form expressions for key performance metrics, such as outage probability (OP), symbol error rate (SER), outage capacity (OC), average channel capacity (AVC), and amount of fading, using binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) modulations. The analysis encompasses all necessary channel parameters for evaluating the performance of an uplink NOMA system. The theoretical and simulation results completely supported one another. Furthermore, the results were compared with experiments in the literature using similar parameters. The proposed system was determined to increase performance by 40% for OP, 62% for SER, and 4.74 times for AVC at SNR = 20 dB. Finally, this study introduced exact solutions that can significantly accelerate NOMA systems analysis by exploiting the information in the existing database for analytical design processes in communications theory.     

Performance analysis of cellular networks

Dynamic channel allocation can reduce the probability of blocking in cellular telephone networks. However, more is needed to achieve optimal performance. The author aims at estimating the minimal blocking probability for some simple cellular networks. Some dynamic channel allocation strategies are analyzed, the optimal performance (obtained by dynamic allocation and flow control) of some very simple networks is computed, and simple bounds on optimal performance are presented. These results lead to a better understanding of cellular networks and can be used to evaluate new control algorithms     

Deploying AL-FEC protection with online algorithms for multicast services over cellular networks

Reliability control is a key concern on the evolution of mobile multicast services. To this direction, the use of forward error correction (FEC) on the application layer is widely adopted in several mobile multicast standards. FEC is a feedback free error control method, where the transmitter introduces in advance redundant information within the source data to enable receivers recovering arbitrary data erasures. On multicast delivery where retransmission-based error recovery methods are not efficient, the most suitable error control method is the use of application layer forward error correction (AL-FEC) codes. In this work, we introduce novel AL-FEC deployment policies over mobile multicast environments utilizing online algorithms. We aim at the efficient application of AL-FEC protection with RaptorQ codes over multicast delivery in the context of competitive analysis. We provide a competitiveness analysis model of AL-FEC application over mobile multicast environments. Furthermore, we propose two online algorithms adjusting the introduced redundancy of AL-FEC protection according to several FEC encoding parameters and constraints of mobile multicast delivery.     

Call admission control for voice/data integrated cellular networks: performance analysis and comparative study

In this paper, we propose a new call admission control scheme called dual threshold bandwidth reservation, or DTBR scheme. The main novelty is that it builds upon a complete sharing approach, in which the channels in each cell are shared among the different traffic types and multiple thresholds are used to meet the specific quality-of-service (QoS) requirements. We present a detailed comparative study based on mathematical and simulation models, and quantitatively demonstrate that the DTBR is capable of providing the QoS guarantee for each type of traffic, while at the same time leading to much better channel efficiency. We further show that the DTBR scheme with elastic data service can offer both service guarantee and service differentiation for voice and data services, and enhance the bandwidth utilization.     

调制识别算法及性能分析

为了提高信号调制识别的性能,以信号的六阶和四阶累积量作为识别特征,研究了一种基于高阶累积量的调制识别算法.分析了最大似然调制识别算法和高阶累积量调制识别算法的性能.并在高斯信道和平衰落信道下对其性能进行了仿真,仿真表明,在一般通信环境下,基于累积量的调制识别算法具有较强的稳健性和实用性.     

User-level performance of channel-aware scheduling algorithms in wireless data networks

Channel-aware scheduling strategies, such as the Proportional Fair algorithm for the CDMA 1xEV-DO system, provide an effective mechanism for improving throughput performance in wireless data networks by exploiting channel fluctuations. The performance of channel-aware scheduling algorithms has mostly been explored at the packet level for a static user population, often assuming infinite backlogs. In the present paper, we focus on the performance at the flow level in a dynamic setting with random finite-size service demands. We show that in certain cases the user-level performance may be evaluated by means of a multiclass Processor-Sharing model where the total service rate varies with the total number of users. The latter model provides explicit formulas for the distribution of the number of active users of the various classes, the mean response times, the blocking probabilities, and the throughput. In addition we show that, in the presence of channel variations, greedy, myopic strategies which maximize throughput in a static scenario, may result in sub-optimal throughput performance for a dynamic user configuration and cause potential instability effects.     

Advanced analysis methods for 3G cellular networks

The operation and maintenance of the third generation (3G) mobile networks will be challenging. These networks will be strongly service driven, and this approach differs significantly from the traditional speech dominated in the second generation (2G) approach. Compared to 2G, in 3G, the mobile cells interact and interfere with each other more, they have hundreds of adjustable parameters, and they monitor and record data related to several hundreds of different variables in each cell. This paper shows that a neural network algorithm called the self-organizing map, together with a conventional clustering method like the k-means, can effectively be used to simplify and focus network analysis. It is shown that these algorithms help in visualizing and grouping similarly behaving cells. Thus, it is easier for a human expert to discern different states of the network. This makes it possible to perform faster and more efficient troubleshooting and optimization of the parameters of the cells. The presented methods are applicable for different radio access network technologies.     

波带交换新算法及其性能分析

由于波带交换在减少交换结构端口数、降低控制面复杂度和光交叉连接费用方面具有实际的意义,因而引起了人们广泛的关注.文章提出了两种新的波带交换算法并且做了相应的性能分析.