Showing papers in "Wireless Communications and Mobile Computing in 2007"

A survey on congestion control for mobile ad hoc networks

Abstract: Congestion control is a key problem in mobile ad hoc networks. The standard congestion control mechanism of the Transmission Control Protocol (TCP) is not able to handle the special properties of a shared wireless multi-hop channel well. In particular, the frequent changes of the network topology and the shared nature of the wireless channel pose significant challenges. Many approaches have been proposed to overcome these difficulties. In this paper, we give an overview over existing proposals, explain their key ideas and show their interrelations. Copyright © 2007 John Wiley & Sons, Ltd.

An adaptive energy-efficient and low-latency MAC for tree-based data gathering in sensor networks

Abstract: Summary A specific characteristic of sensor network applications is that the major traffic consists of data collection from various sensor source nodes to a sink via a unidirectional tree. In this paper, we propose DMAC, an energy efficient and low latency MAC that is designed and optimized for such data gathering trees in wireless sensor networks. We first show that previously proposed MAC protocols for sensor networks that utilize activation/sleep duty cycles suffer from a data forwarding interruption problem, whereby not all nodes on a multihop path to the sink can be notified of data delivery in progress, resulting in significant sleep delay. DMAC is designed to solve the interruption problem, by giving the active/sleep schedule of a node an offset that depends upon its depth on the tree. This scheme allows continuous packet forwarding because all nodes on the multihop path can be notified of the data delivery in progress. DMAC also adjusts node duty cycles adaptively according to the traffic load in the network by varying the number of active slots in an schedule interval. We further propose a data prediction mechanism and the use of more to send (MTS) packets in order to alleviate problems pertaining to channel contention and collisions. Our simulation results as well as experimental results with the Mote platform show that by exploiting the applicationspecific structure of data gathering trees in sensor networks, DMAC provides significant energy savings and latency reduction while ensuring high data reliability. Copyright © 2007 John Wiley & Sons, Ltd.

Radio frequency identification: technologies, applications, and research issues

Abstract: A radio frequency identification (RFID) system is a special kind of sensor network to identify an object or a person using radio frequency transmission. A typical RFID system includes transponders (tags) and interrogators (readers): tags are attached to objects/persons, and readers communicate with the tags in their transmission ranges via radio signals. RFID systems have been gaining more and more popularity in areas such as supply chain management, automated identification systems, and any place requiring identifications of products or people. RFID technology is better than barcode in many ways, and may totally replace barcode in the future if certain technologies can be achieved such as low cost and protection of personal privacy. This paper provides a technology survey of RFID systems and various RFID applications. We also discuss five critical research issues: cost control, energy efficiency, privacy issue, multiple readers' interference, and security issue. Copyright (c) 2006 John Wiley & Sons, Ltd.

On efficacy of Rayleigh‐inverse Gaussian distribution over K‐distribution for wireless fading channels

Abstract: For studying performance characteristics of radio channels, the knowledge about the probability density function (pdf) of fading–shadowing effects is essential. K-distribution corresponding to Rayleigh–gamma distribution (RGD) is widely used to approximate a more realistic Rayleigh–lognormal distribution (RLD) which does not have a closed form expression. A new composite Rayleigh-inverse Gaussian distribution (RIGD), an alternative to K-distribution, is analyzed with regards to its suitability and effectiveness in radio channels. Detailed investigations are made to study the performance characteristics of RIGD and K-distribution (RGD) in terms of Kullback–Leibler (KL) measure of divergence. Based on these investigations, it is found that RIGD is better suited for capturing fading–shadowing aspects of radio channels instead of K-distribution. Copyright © 2006 John Wiley & Sons, Ltd.

A brief survey of self‐organization in wireless sensor networks

Abstract: Summary Many natural and man-made systems exhibit self-organization, where interactions among components lead to system-wide patterns of behavior This paper first introduces current, scientific understanding of self-organizing systems and then identifies the main models investigated by computer scientists seeking to apply self-organization to design large, distributed systems Subsequently, the paper surveys research that uses models of self-organization in wireless sensor networks to provide a variety of functions: sharing processing and communication capacity; forming and maintaining structures; conserving power; synchronizing time; configuring software components; adapting behavior associated with routing, with disseminating and querying for information, and with allocating tasks; and providing resilience by repairing faults and resisting attacks The paper closes with a summary of open issues that must be addressed before self-organization can be applied routinely during design and deployment of senor networks and other distributed, computer systems Copyright © 2007 John Wiley & Sons, Ltd

Binary-Offset-Carrier modulation techniques with applications in satellite navigation systems

Abstract: An important aspect in designing the modulation scheme for various satellite systems, such as the modernized GPS and Galileo, is to obtain good spectral properties and suitable spectral shaping. For example, in the future satellite navigation systems, some of the main goals are: low interference with the existing GPS signals, good root-mean-square (RMS) bandwidth, good time resolution (in order to allow the separation between channel paths and to decrease the synchronization errors) etc. Starting from the recently proposed cosine- and sine-BOC modulation families for GPS and Galileo systems, we introduce a new, generalized family, denoted here by double-BOC (DBOC) modulation. We derive and analyze the properties of the power spectral densities (PSD) and autocorrelation functions (ACF) of the DBOC modulation with various orders, we show its relationship with BPSK, sine- and cosine-BOC modulations, and we illustrate via several examples how to choose optimally the parameters of this new modulation family, according to different optimization criteria. The examples are targeting at applications such as the design of suitable modulations for Galileo open service (OS) and public regulated service (PRS) signals, but the authors believe that the DBOC concept might be useful to other satellite-based applications, when the available bandwidth is large enough. Copyright © 2006 John Wiley & Sons, Ltd.

New direction of broadband wireless technology

Abstract: Summary The most important technical challenge for the realization of 4G mobile networks is twofold: (a) to overcome the highly frequency-selective fading channel and (b) to significantly reduce the transmit power from mobile terminals. Recently, it has been shown that the application of frequency-domain equalization (FDE) can take advantage of channel frequency-selectivity and improve the transmission performance of single-carrier (SC) as well as multicarrier (MC) signal transmissions. Either SC or MC can be used for the downlink (base-to-mobile) to achieve almost the same bit error rate (BER) performance. However, for the uplink (mobile-to-base) applications, SC transmission is more appropriate since it has less peak power. For broadband data transmissions, transmit power reduction is a very important issue. Applying wireless multi-hop technique is a possible solution to this issue. In this paper, we will discuss about some important 4G wireless techniques. Copyright © 2007 John Wiley & Sons, Ltd.

An overview of scalable video streaming

Abstract: During the past two decades, video coding technology has matured and stat-of-the-art coding standards have become very important part of the video industry. Standards such as MPEG2 [16] and H.264/AVC [20] provide strong support for digital video transmission, storage and streaming applications.

A survey on analytic studies of Delay‐Tolerant Mobile Sensor Networks

Abstract: This paper presents a survey of analytic studies on the Delay-Tolerant Mobile Sensor Network (DTMSN). We first give an overview of the analytic study on DTMSN, by identifying several key design components, that is, nodal mobility model, data delivery scheme, and queue management scheme. Then, several representative analytic models of DTMSN are exemplified and discussed in detail, with thorough comparison presented and possible open research issues enumerated. We expect that this paper will provide a deep understanding of the characteristics of DTMSN, and at the same time reveal the key design issues in its modeling and performance analysis, leading to useful insights for future theoretic study and protocol design. Copyright © 2007 John Wiley & Sons, Ltd.

Evaluating MobySpace-based routing strategies in delay-tolerant networks

Abstract: Because a delay-tolerant network (DTN) can often be partitioned, routing is a challenge. However, routing benefits considerably if one can take advantage of knowledge concerning node mobility. This paper addresses this problem with a generic algorithm based on the use of a high-dimensional Euclidean space, that we call MobySpace, constructed upon nodes' mobility patterns. We provide here an analysis and a large-scale evaluation of routing schemes using MobySpace by replaying real mobility traces. The specific MobySpace evaluated is based on the frequency of visits of nodes to each possible location. We present simulation results for single-copy and multi-copy routing strategies that use MobySpace as a means to route bundles or to control flooding. We show that routing based on MobySpace can achieve good performance compared to a number of common algorithms.

Delay/disruption tolerant mobile ad hoc networks: latest developments

Abstract: There is much research activity in the emerging area of delay/disruption tolerant networks (DTN) in the past few years. DTNs pose many new challenges, and protocols designed for wired Internet or wireless mobile ad hoc networks do not work properly in DTNs. Routing is one of the key components in DTNs and the message ferry (MF) approach has been drawn a lot of attention to support routing in DTNs. Besides the underlying routing protocols, issues in transport layer are also very important and need to be addressed for DTNs. Recently, many new routing protocols, including unicast using the MF approach, inter-region routing and multicast, have appeared in the literature. There are also a few works addressing issues in the transport layer. This paper provides an overview on recent developments including message ferrying, multicast support, inter-region routing, and transport layer issues. It also points out some open research issues and intends to motivate new research and development in this area. Copyright © 2007 John Wiley & Sons, Ltd.

Simultaneous mobility: analytical framework, theorems and solutions

Abstract: The original Mobile IP (MIP) protocol does not perform Route Optimisation but uses Home Agents to forward traffic. Thus, it does not have problems with simultaneous mobility, that is, the special case when both end hosts are mobile and move at about the same time. However, MIP for IPv6 (MIPv6) uses binding updates that are sent directly to a correspondent node. Session Initiation Protocol based mobility management (SIPMM) and MIP with location registers (MIP-LR) also use direct binding updates between a mobile host and a correspondent node. Thus, MIPv6, MIP-LR and SIPMM are vulnerable to the simultaneous mobility problem. In this paper, we analyse the simultaneous mobility problem and solution mechanisms, and propose new ways for MIPv6, MIP-LR and SIPMM to handle simultaneous mobility. Copyright © 2006 John Wiley & Sons, Ltd.

A practical analysis of communication characteristics for mobile and distributed pollution measurements on the road

Abstract: Summary Measuring environmental data in city areas has become an important issue for municipalities due to several climate directives. As fixed measuring stations are inflexible, cost-intensive, and limited to monitoring a specific spot, we developed a distributed environmental monitoring network called Environmental Monitoring in Metropolitan Areas (EMMA). This architecture is based on the delay tolerant networking approach and can be integrated into existing Public Transportation Networks (PTNs). Buses or other vehicles can be equipped with sensor nodes that gather data and forward messages. In order to evaluate the basic ideas of this project we performed a series of real-world experiments. Besides analyzing the behavior of 802.11-based Wireless Local Area Network (WLAN) between moving vehicles in a controlled environment, we also evaluated the communication performance in urban environments. Moreover, we examined the qualification of a Disruption Tolerant Networking (DTN) implementation for spreading measurement results throughout the network. The suitability of EMMA’s architecture has been successfully demonstrated by these experiments. Copyright © 2007 John Wiley & Sons, Ltd.

A time‐based adaptive retry strategy for video streaming in 802.11 WLANs

Abstract: Video streaming over time-varying, error-prone wireless LANs (WLANs) poses many challenges One problem is that WLANs are designed without awareness of the characteristics of application data, which causes performance degradation in a noisy or congested environment In this paper, we propose a time-based adaptive retry (TAR) mechanism for MPEG-like video streaming over 80211 wireless networks TAR dynamically determines whether to send or discard a packet based on its retransmission deadline instead of adopting a static retry limit uniformly over all the packets Our approach can adapt the retry limit for each individual packet, thus providing indirect unequal error protection over different types of video frames Analytical and simulation results show that TAR significantly improves video quality and saves channel bandwidth We also describe a preliminary software-based implementation of TAR and use it to demonstrate the practicality of the proposed approach Copyright © 2007 John Wiley & Sons, Ltd

Review of content-aware resource allocation schemes for video streaming over wireless networks

Abstract: Summary As wireless technology evolves towards its fourth generation (4G) of development, the prospect of offering multimedia services such as on-demand video streaming and video conferencing to wireless mobile clients becomes increasingly more viable. The eventual success of such applications depends on the efficient management of the limited system resources while taking into account the time-varying wireless channel conditions as well as the varying multimedia source content. In this paper, we review some of the recent advances in cross-layer design schemes, which aim at providing significant gains in performance for video streaming systems through contentaware resource allocation. Advances in both, real-time video streaming, where the video is encoded and transmitted in real-time, as well as, on-demand video streaming, where the video is pre-encoded in a media server, are considered. Copyright © 2007 John Wiley & Sons, Ltd.

Capacity of MIMO channels in the presence of co-channel interference

Abstract: This paper presents analytical results on the capacity of multiple-input-multiple-output (MIMO) fading channels in the presence of co-channel interference (CCI). We consider the scenario in which the desired and CCI users are all subject to Rayleigh fading. We assume that channel realizations of both the desired and CCI users are known at the receiver. Moreover, we consider the case where the transmitter does not have any CSI and as such equal-power allocation among transmit antennas is used. Given this setup, we derive the moment generating function (MGF) and the mean of the mutual information (MI). We then study the complementary cumulative distribution function of the MI using a Gaussian approximation. Finally, we present and discuss numerical examples to illustrate the mathematical formalism and to show the effect of various parameters on the capacity of MIMO channels in the presence of CCI. Copyright © 2006 John Wiley & Sons, Ltd.

Generalization of signcryption for resources‐constrained environments

Abstract: Traditional signcryption is not feasible for some information security scenarios, though it is a new cryptographic primitive that simultaneously fulfills both the functions of signature and encryption. Generalized signcryption is an adaptive primitive which achieves both secrecy and authenticity or provides them respectively by a generic structure. The notions related to generalized signcryption such as syntax, correctness, and security are proposed in the paper. A practical generalized signcryption scheme ECGSC is evaluated carefully also. The formal proofs for the unforgeability and confidentiality of ECGSC in the Random Oracle model are provided. To give a solution for multiple user settings, an efficient multicast scheme is also designed. ECGSC will seamlessly switch to the Elliptic Curve Digital Signature Algorithm (ECDSA) or a provable secure asymmetric encryption scheme when recipient's keys or sender's keys are absent. Compared with other schemes, it saves 9–14% communication costs in the signcryption mode. It also saves 78–82% computational costs. Copyright © 2007 John Wiley & Sons, Ltd.

An algebraic approach to generate super‐set of perfect complementary codes for interference‐free CDMA

Abstract: Summary This paper introduces an algebraic approach to generate the super-set of perfect complementary (PC) codes suitable for new generation CDMA applications, characterized by isotropic multiple access interference (MAI) free and multipath interference (MI) free properties. The code design methodology proposed in this paper takes into account major impairing factors existing in real applications, such as MAI, MI, asynchronous transmissions, and random signs in consecutive symbols, such that a CDMA system using the generated codes can insure a truly interferencefree operation. Two important facts will be revealed by the analysis given in this paper. First, implementation of an interference-free CDMA will never be possible unless using complementary code sets, such as the PC code sets generated in this paper. In other words, all traditional spreading codes working on an one-code-per-user basis are not useful for implementation of an MAI-free and MI-free CDMA system. Second, to enable the interference-free CDMA operation, the flock size of the PC codes should be made equal to the set size of the codes, implying that a PC code set can support as many users as the flock size of the code set. A systematic search has been carried out to generate the super-set of various PC codes with the help of carefully selected seed codes belonging to distinct sub-sets. This paper will also propose an implementation scheme based on multi-carrier CDMA architecture and its performance is compared by simulations with the ones using traditional spreading codes. Copyright © 2006 John Wiley & Sons, Ltd.

Performance analysis of coded cooperation diversity in wireless networks

Abstract: Diversity is an effective technique in enhancing the link quality and increasing network capacity. When multiple antennas cannot be used in mobile units, user cooperation can be employed to provide transmit diversity. In this paper, we analyze the error performance of coded cooperation diversity with multiple cooperating users. We derive the end-to-end bit error probability of coded cooperation (averaged over all cooperation scenarios). We consider different fading distributions for the interuser channels. Furthermore, we consider the case of two cooperating users with correlated uplink channels. Results show that more cooperating users should be allowed under good interuser channel conditions, while it suffices to have two cooperating users in adverse interuser conditions. Furthermore, under bad interuser conditions, more cooperating users can be accommodated as the fading distribution becomes more random. Copyright © 2006 John Wiley & Sons, Ltd.

Cluster-based information processing in wireless sensor networks: an energy-aware approach†

Abstract: Summary Emerging Wireless Sensor Network (WSN) applications demand considerable computation capacity for in-network processing in resource limited WSN environments. To achieve the required processing capacity under energy consumption constraints, collaboration among sensors through parallel processing methods emerges as a promising solution. Although such methods have been extensively studied in wired networks of processors, its counterpart for WSNs remains largely unexplored. In this paper, a localized task mapping and scheduling solution for energyconstrained applications in WSNs, Energy-constrained Task Mapping and Scheduling (EcoMapS), is presented. EcoMapS guarantees energy consumption constraints while minimizing schedule length. EcoMapS incorporates channel modeling, concurrent task mapping, communication and computation scheduling, and sensor failure handling algorithms. Simulation results show significant performance improvements of EcoMapS over existing mechanisms in terms of minimizing schedule lengths subject to energy consumption constrains. Copyright © 2007 John Wiley & Sons, Ltd.

A study on the PAPRs in multicarrier modulation systems with different orthogonal bases

Abstract: This paper studies the peak-to-average power ratios (PAPRs) in multicarrier modulation (MCM) systems with seven different orthogonal bases, one Fourier base and six wavelet bases. It is shown by simulation results that the PAPRs of the Fourier-based MCM system are lower than those of all wavelet-based MCM (WMCM) systems. A novel threshold-based PAPR reduction method is then proposed to reduce the PAPRs in WMCM systems. Both numerical and simulation results indicate that the proposed PAPR reduction method works very effectively in WMCM systems. Copyright © 2006 John Wiley & Sons, Ltd.

A client‐side design and implementation for push to talk over cellular service

Abstract: This paper proposes a client architecture for the push to talk over cellular (PoC) service based on the open mobile alliance (OMA) PoC specifications v1.0 release. We show that most standard VoIP modules can be reused for the PoC client, and the VoIP software can be easily extended to support PoC service. Then we present the detailed message flows between the PoC client and other network entities in the PoC system. A PoC client prototype has been implemented in the Industrial Technology Research Institute (ITRI) and National Chiao-Tung University (NCTU) Joint Research Center. Copyright © 2006 John Wiley & Sons, Ltd.

Generation of bivariate Nakagami-m fading envelopes with arbitrary not necessary identical fading parameters

Abstract: In this paper, a generation procedure of two correlated Nakagami-m random variables for arbitrary fading parameters values (not necessary identical) is described. For the generation of two correlated Nakagami-m samples, the proposed method uses the generalized Rice distribution, which appears in the conditional distribution of two correlated Nakagami-m variables. This procedure can be applied to simulate diversity systems such as selection combiners, equal-gain combiners, and maximal-ratio combiners as well as multiple-input multiple-output (MIMO) receiver systems, in Nakagami-m channels. Copyright © 2006 John Wiley & Sons, Ltd.

UMTS security : system architecture and hardware implementation

Abstract: Universal mobile telecommunication system (UMTS) has specified security mechanisms with extra features compared to the security mechanisms of previous mobile communication systems (GSM, DECT). A hardware implementation of the UMTS security mechanism is presented in this paper. The proposed VLSI system supports the Authentication and Key Agreement procedure (AKA), the data confidentiality procedure, and the integrity protection procedure. The AKA procedure is based on RIJNDAEL Block Cipher. An efficient RIJNDAEL architecture is proposed in order to minimize the usage of hardware resources. The proposed implementation performs the AKA procedure within 76 µs comparing with the 500 ms that UMTS specifies. The data confidentiality and the integrity protection is based on KASUMI Block Cipher. The proposed KASUMI architecture reduces the hardware resources and power consumption. It uses feedback logic and positive-negative edge-triggered pipeline in order to make the critical path shorter, without increasing the execution latency. The S-BOXes that are used from RIJNDAEL and KASUMI block ciphers have been implemented with combinational logic as well as with ROM blocks. Copyright © 2006 John Wiley & Sons, Ltd.

Investigation of multicast‐based mobility support in all‐IP cellular networks

Abstract: To solve the IP mobility problem, the use of multicast has been proposed in a number of different approaches, applying multicast in different characteristic ways. We provide a systematic discussion of fundamental options for multicast-based mobility support and the definition and experimental performance evaluation of selected schemes. The discussion is based on an analysis of the architectural, performance-related, and functional requirements. By using these requirements and selecting options regarding network architecture and multicast protocols, we identify promising combinations and derive four case studies for multicast-based mobility in IP-based cellular networks. These case studies include both the standard any-source IP multicast model as well as non-standard multicast models, which optimally utilize the underlying multicast. We describe network architecture and protocols as well as a flexible software environment that allows to easily implement these and other classes of mobility-supporting multicast protocols. Multicast schemes enable a high degree of flexibility for mobility mechanisms in order to meet the service quality required by the applications with minimal protocol overhead. We evaluate this overhead using our software environment by implementing prototypes and quantifying handoff-specific metrics, namely, handoff and paging latency, packet loss and duplication rates, as well as TCP goodput. The measurement results show that these multicast-based schemes improve handoff performance for high mobility in comparison to the reference cases: basic and hierarchical Mobile IP. Comparing the multicast-schemes among each other the performance for the evaluated metrics is very similar. As a result of the conceptual framework classification and our performance evaluations, we justify specific protocol mechanisms that utilize specific features of the multicast. Based on this justification, we advocate the usage of a source-specific multicast service model for multicast-based mobility support that adverts the weaknesses of the classical Internet any-source multicast service model. Copyright © 2006 John Wiley & Sons, Ltd.

Self‐adaptive routing protocols for integrating cellular networks, WLANs, and MANETs

Abstract: A growing need to have ubiquitous connectivity has motivated our research to provide continuous connection between various wireless platforms such as cellular networks, wireless local area networks (WLANs), and mobile ad hoc networks (MANETs). In this paper, we consider integration at the routing layer and propose two adaptable routing protocols (IRP-RD and IRP-PD) that exploit topology information stored at the fixed network components (cellular base stations and WLAN access points) for the route discovery and maintenance processes. Our proposed protocols can provide connectivity to the cellular network and/or WLAN hotspots through multihop routing, while differ in the gateway discovery approach used. In IRP-RD, multihop routes to gateways to the cellular network or WLAN hot spots are discovered on demand, while in IRP-PD out of coverage users proactively maintain routes to the gateways. Furthermore, proposed protocols can be used in any heterogeneous scenario, combining a cellular network and WLANs operating in infrastructure or ad hoc (MANET) mode. We provide simulation results that demonstrate the effectiveness of the proposed integrated routing protocols and show the advantages and drawbacks of each gateway discovery approach in different heterogeneous scenarios. Copyright © 2006 John Wiley & Sons, Ltd.

Hidden Markov modeling and macroscopic traffic filtering supporting location-based services

Abstract: In this study, we present a technique that combines pattern recognition techniques with cellular signaling measurements and more precisely information extracted from Abis air interface in GSM network. The pattern recognition is applied to measurement reports that mobile terminal (MT) sends to its serving base station (BS). Modeling of these reports is performed by hidden Markov model (HMM) while employing clustering large applications (CLARA) as clustering method. The accurate results during MT velocity estimation located inside a probe vehicle show the potential of the method when applied to large scale of MTs in order to estimate basic parameters for road traffic. Copyright © 2006 John Wiley & Sons, Ltd.

Localized energy efficient routing in mobile ad hoc networks

Abstract: We consider the problem of localized energy aware routing in mobile ad hoc networks. In localized routing algorithms, each node forwards a message based on the position of itself, its neighbors and the destination. The objective of energy aware routing algorithms is to minimize the total power for routing a message from source to destination or to maximize the total number of routing tasks that a node can perform before its battery power depletes. In this paper we propose new localized energy aware routing algorithms called OLEAR. The algorithms have very high packet delivery rate with low packet forwarding and battery power consumption. In addition, they ensure good energy distribution among the nodes. Finally, packets reach the destination using smaller number of hops. All these properties make our algorithm suitable for routing in any energy constrained environment. We compare the performance of our algorithms with other existing energy and non-energy aware localized algorithms. Simulation experiments show that our algorithms present comparable energy consumption and distribution to other energy aware algorithms and better packet delivery rate. Copyright © 2006 John Wiley & Sons, Ltd.

Mobile location estimation for DS-CDMA systems using self-organizing maps

Abstract: In this paper, a self-organizing map (SOM) scheme for mobile location estimation in a direct-sequence code division multiple access (DS-CDMA) system is proposed As a feedforward neural network with unsupervised or supervised and competitive learning algorithm, the proposed scheme generates a number of virtual neurons over the area covered by the corresponding base stations (BSs) and performs non-linear mapping between the measured pilot signal strengths from nearby BSs and the user's location After the training is finished, the location estimation procedure searches for the virtual sensor which has the minimum distance in the signal space with the estimated mobile user Analytical results on accuracy and measurement reliability show that the proposed scheme has the advantages of robustness and scalability, and is easy for training and implementation In addition, the scheme exhibits superior performance in the non-line-of-sight (NLOS) situation Numerical results under various terrestrial environments are presented to demonstrate the feasibility of the proposed SOM scheme Copyright © 2006 John Wiley & Sons, Ltd