Showing papers in "Wireless Personal Communications in 2010"
TL;DR: Analytical closed-form expressions for the cyclic cumulant polyspectra of linearly digitally modulated signals affected by fading, carrier frequency and timing offsets, and additive Gaussian noise are derived, along with a condition for the oversampling factor to avoid aliasing in the cycle and spectral frequency domains.
Abstract: Modulation classification is an intermediate step between signal detection and demodulation, and plays a key role in various civilian and military applications. In this correspondence, higher-order cyclic cumulants (CCs) are explored to discriminate linear digital modulations in flat fading channels. Single- and multi-antenna CC-based classifiers are investigated. These benefit from the robustness of the CC-based features to unknown phase and timing offset. Furthermore, the latter provides significant performance improvement due to spatial diversity used to combat the fading effect. Classifier performances are investigated under a variety of channel conditions. In addition, analytical closed-form expressions for the cyclic cumulant polyspectra of linearly digitally modulated signals affected by fading, carrier frequency and timing offsets, and additive Gaussian noise are derived, along with a condition for the oversampling factor to avoid aliasing in the cycle and spectral frequency domains.
83 citations
TL;DR: A new predictive handover framework is proposed that uses the neighbor network information to generate timely the link triggers so that the required handover procedures can appropriately finish before the current link goes down.
Abstract: Next-generation wireless networks should be able to coordinate and integrate different communication systems. It has been a challenging problem to support a seamless handover in these diverse wireless network environments. Link level triggers can provide information about events which can help handover decision and layer 3 entities better streamline their handover related activities. In most conventional layer 2 triggering approaches, a pre-defined threshold for a specific perspective such as the received signal strength is used. This may cause too late or too early handover executions. In this paper we propose a new predictive handover framework that uses the neighbor network information to generate timely the link triggers so that the required handover procedures can appropriately finish before the current link goes down. First we estimate a required handover time for the given neighbor network conditions, then using a predictive link triggering mechanism the handover start time is dynamically determined to minimize handover costs. The handover costs are analyzed in terms of the total required handover time and the service disruption time. The numerical analysis and simulation results show that the proposed method significantly enhances the handover performance in heterogeneous wireless networks.
83 citations
TL;DR: This paper proposes a Route Stability based QoS Routing (RSQR) protocol in Mobile Ad Hoc Networks (MANETs) which is an extension of QoS routing with throughput and delay constraints which shows performance improvements in terms of packet delivery ratio, control overhead and average end-to-end delay.
Abstract: To provide high quality communications service among mobile wireless devices is basically a challenging task in wireless ad hoc networks. In this paper, we propose a Route Stability based QoS Routing (RSQR) protocol in Mobile Ad Hoc Networks (MANETs) which is an extension of QoS routing with throughput and delay constraints. Ensuring a data path to be valid for sufficiently longer period of time is a very difficult problem in MANET due to its highly dynamic nature. We propose a simple model for computing link stability and route stability based on received signal strengths. By including some extra fields in route request/reply packets, the route stability information can be utilized to select a route with higher stability among all the feasible routes between a given source destination pair. Further, inclusion of a signal strength based admission control enhances the performance of the routing. Results of our experiments show performance improvements in terms of packet delivery ratio, control overhead and average end-to-end delay in comparison with a QoS routing protocol proposed by Q. Xue and A. Ganz.
83 citations
TL;DR: A serverless, forward secure and untraceable authentication protocol for RFID tags that can search a particular tag efficiently without server’s intervention and is secured against major security threats.
Abstract: One of the recent realms that gathered attention of researchers is the security issues of Radio Frequency Identification (RFID) systems that have tradeoff between controlled costs and improved efficiency. Evolvement and benefits of RFID technology signifies that it can be low-cost, efficient and secured solution to many pervasive applications. But RFID technology will not intermingle into human lives until prevailing and flexible privacy mechanisms are conceived. However, ensuring strong privacy has been an enormous challenge due to extremely inadequate computational storage of typical RFID tags. So in order to relieve tags from responsibility, privacy protection and security assurance was guaranteed by central server. In this paper, we suggest serverless, forward secure and untraceable authentication protocol for RFID tags. This authentication protocol safeguards both tag and reader against almost all major attacks without the intervention of server. Though it is very critical to guarantee untraceability and scalability simultaneously, here we are proposing a scheme to make our protocol more scalable via ownership transfer. To the best of our knowledge this feature is incorporated in the serverless system for the first time in pervasive environments. One extension of RFID authentication is RFID tag searching, which has not been given much attention so far. But we firmly believe that in near future tag searching will be a significant issue RFID based pervasive systems. So in this paper we propose a serverless RFID tag searching protocol in pervasive environments. This protocol can search a particular tag efficiently without server's intervention. Furthermore they are secured against major security threats.
62 citations
TL;DR: This paper proposes an energy-efficient group key management scheme called Topological Key Hierarchy (TKH), which generates a key tree by using the underlying sensor network topology with consideration of subtree-based key tree separation and wireless multicast advantage.
Abstract: A sensor network operating in open environments requires a network-wide group key for confidentiality of exchanged messages between sensor nodes. When a node behaves abnormally due to its malfunction or a compromise attack by adversaries, the central sink node should update the group key of other nodes. The major concern of this group key update procedure will be the multi-hop communication overheads of the rekeying messages due to the energy constraints of sensor nodes. Many researchers have tried to reduce the number of rekeying messages by using the logical key tree. In this paper, we propose an energy-efficient group key management scheme called Topological Key Hierarchy (TKH). TKH generates a key tree by using the underlying sensor network topology with consideration of subtree-based key tree separation and wireless multicast advantage. Based on our detailed analysis and simulation study, we compare the total rekeying costs of our scheme with the previous logical key tree schemes and demonstrate its energy efficiency.
52 citations
TL;DR: Two novel Weighted Markov Chain (WMC) approaches based on rank aggregation are proposed in this paper, in which a favorite network is selected as the top one of rank aggregation result fused from multiple ranking lists based on decision factors.
Abstract: Vertical handover decision making is one of the key problems in heterogeneous networks environment. In IEEE 802.21 standard, a Media Independent Handover (MIH) framework is proposed to improve user experience of mobile devices by facilitating handover in heterogeneous networks with measurements and triggers from link layers. However, vertical handover decision making can benefit from the information more than link layers. In this paper, an Enhanced Media Independent Handover (EMIH) framework is proposed by integrating more information from application layers, user context and network context. Given such information, there is also another important problem on how to select a favorite network. Two quite important problems from realistic scenario are as follows: (1) how to make use of partial knowledge due to incomplete value measurement on decision factors; (2) how to deal with robustness problem due to inaccurate measurement on decision factors. In order to tackle these problems, two novel Weighted Markov Chain (WMC) approaches based on rank aggregation are proposed in this paper, in which a favorite network is selected as the top one of rank aggregation result fused from multiple ranking lists based on decision factors. Moreover, an entropy weighting method, combined with WMC approach, is studied. The simulations demonstrate the effectiveness of these proposed approaches.
45 citations
TL;DR: This paper develops mathematical models that result in expressions for the characteristic function of the time required to complete exchanges of an arbitrary number of MIH signaling messages between a mobile node and a remote mobility manager.
Abstract: The IEEE 802.21 Media Independent Handover (MIH) working group is developing a set of mechanisms to facilitate migration of mobile users between access networks that use different link-layer technologies. Among these are mobility managers that create and process signaling messages to facilitate handovers. The MIH signaling architecture being developed in the Internet Engineering Task Force (IETF) allows any transport layer protocol to carry MIH messages. The IETF has considered using the unreliable but lightweight transport available with the User Datagram Protocol (UDP) as well as the reliable stream-oriented transport with congestion control offered by the Transmission Control Protocol (TCP). In this paper we develop mathematical models that result in expressions for the characteristic function of the time required to complete exchanges of an arbitrary number of MIH signaling messages between a mobile node (MN) and a remote mobility manager (MM). Our models also provide expressions for the average amount of overhead associated with MIH message exchanges due to retransmissions either by the MIH signaling entities or by the transport-layer protocol. In addition, we provide simulation results that confirm the results from the mathematical model and illustrate the effect of varying transport parameters such as the TCP maximum retransmission timeout.
34 citations
TL;DR: The contribution of the paper is the development of a simple distributed algorithm that allows mobile nodes to autonomously navigate through the field and improve the area coverage.
Abstract: Reliable monitoring of a large area with a Wireless Sensor Network (WSN) typically requires a very large number of stationary nodes, implying a prohibitive cost and excessive (radio) interference. Our objective is to develop an efficient system that will employ a smaller number of stationary nodes that will collaborate with a small set of mobile nodes in order to improve the area coverage. The main strength of this collaborative architecture stems from the ability of the mobile sensors to sample areas not covered (monitored) by stationary sensors. An important element of the proposed system is the ability of each mobile node to autonomously decide its path based on local information (i.e. a combination of self collected measurements and information gathered by stationary sensors in the mobile's communication range), which is essential in the context of large, distributed WSNs. The contribution of the paper is the development of a simple distributed algorithm that allows mobile nodes to autonomously navigate through the field and improve the area coverage. We present simulation results based on a real sparse stationary WSN deployment for the coverage improvement scenario.
33 citations
TL;DR: Analytical and simulation results demonstrate that the proposed methods are effective in terms of spectrum mask regulation, total degradation, complementary cumulative probability function versus PAPR threshold, and bit error rate in presence of nonlinear distortion.
Abstract: This paper proposes an effective tone reservation method with null subcarriers (TRNS) to reduce the peak to average power ratio (PAPR) for so-called WiMAX system. The TRNS method utilizes a part of null subcarriers in guard band to reduce the PAPR, which satisfies the spectrum mask regulation and avoids bandwidth sacrifice. Furthermore, this paper analyzes the properties of order statistics of orthogonal frequency division multiplexing (OFDM) signals. A type of low complexity TRNS method (LC-TRNS) is proposed to solve problems of the TRNS method, including high complexity and the performance degradation under low predefined threshold. Finally, a joint nonlinearity reduction scheme by predistortion and TRNS method is proposed. Not only the nonlinear distortion in the WiMAX system is reduced, but also the good tradeoff between power efficiency and system performance is achieved. Both analytical and simulation results demonstrate that those proposed methods are effective in terms of spectrum mask regulation, total degradation, complementary cumulative probability function versus PAPR threshold, and bit error rate in presence of nonlinear distortion.
33 citations
TL;DR: The living lab method as combined here with a user-driven approach is an example of how designers can carry out and gain from working with people as co-creators in design projects.
Abstract: The paper presents the set up of a Living Laboratory in a city of North Denmark exploring mobile support for everyday life with diabetes. Background and definitions of the living lab method is presented together with descriptions of the technical setup, applications and explorations. The living lab method was practiced over two iterations--one in 2008 and one in 2009. 17 diabetes families, 9 service providers, researchers and ICT-consultants has participated in the activities. The results present how the living lab method provides an open platform for exploring technology in naturalistic settings combined with controlled activities, technical set up, support and data collection. The meetings of users, researchers, developers, and service providers in the living lab showed how living labs are an open platform supporting interactive learning among participants on technological innovations. The living lab method as combined here with a user-driven approach is an example of how designers can carry out and gain from working with people as co-creators in design projects.
33 citations
TL;DR: A uniform balancing energy routing protocol which allows the distribution of energy load among any sensor nodes; thus extends network lifetime and outperforms some protocols given in the literature.
Abstract: In wireless sensor network, the power supply is, generally, a non-renewable battery. Consequently, energy effectiveness is a crucial factor. To maximize the battery life and therefore, the duration of network service, a robust wireless communication protocol providing a best energy efficiency is required. In this paper, we present a uniform balancing energy routing protocol. In this later the transmission path is chosen for maximizing the whole network lifetime. Every transmission round, only the nodes which have their remaining energies greater than a threshold can participate as routers for other nodes in addition to sensing the environment. This choice allows the distribution of energy load among any sensor nodes; thus extends network lifetime. The experimental results shows that the proposed protocol outperforms some protocols given in the literature.
TL;DR: The proposed spatial simulation model is derived from a non-realizable lognormal reference model with given correlation properties by using Rice's sum-of-sinusoids, and it is pointed out that Gudmundson’s correlation model results in an infinite LCR.
Abstract: The focus of this paper is on the higher order statistics of spatial simulation models for shadowing processes. Such processes are generally assumed to follow the lognormal distribution. The proposed spatial simulation model is derived from a non-realizable lognormal reference model with given correlation properties by using Rice's sum-of-sinusoids. Both exact and approximate expressions are presented for the level-crossing rate (LCR) and the average duration of fades (ADF) of the simulation model. It is pointed out that Gudmundson's correlation model results in an infinite LCR. To avoid this problem, two alternative spatial correlation models are proposed. Illustrative examples of the dynamic behavior of shadow fading processes are presented for all three types of correlation models. Emphasis will be placed on two realistic propagation scenarios capturing the shadowing effects in suburban and urban areas.
TL;DR: The new design adjusts the TR signal by a way to support ultra-wide bandwidth and provides better matching to the UWB spectral mask with better temporal focusing features.
Abstract: The experiments of time reversal (TR) technique with ultra-wideband (UWB) signals are conducted in indoor propagation channel by using time-domain technique. The UWB propagation channel response of a typical indoor environment is measured and time reversal technique is applied for signal transmission. The characteristics of the TR scheme for different propagation scenarios, line-of-sight (LOS) and non-LOS with different wideband receiving antennas are evaluated. The measurement results of signals focusing gain, temporal sidelobes and average signal energy for different propagation scenarios are presented. The spectral analysis of TR-UWB signals is conducted and an inherent bandwidth limit of the classical TR-UWB scheme is observed. To overcome the bandwidth restrictions, novel design architecture is proposed. The new design adjusts the TR signal by a way to support ultra-wide bandwidth and provides better matching to the UWB spectral mask with better temporal focusing features.
TL;DR: The results obtained by calculations show that the performance improvements are significant for reducing average intercarrier-interference (ICI) power and increasing the ratio of average signal power to average ICI power (SIR).
Abstract: This paper is focused on the problem of reducing the intercarrier-interference (ICI) power in the transmission over Orthogonal Frequency Division Multiplexing Systems (OFDM) using pulse shaping methods. A new pulse was proposed here and it was investigated in terms of ICI interference. It appears to be suitable for transmission in OFDM systems with carrier frequency offset. The results obtained by calculations show that the performance improvements are significant for reducing average intercarrier-interference (ICI) power and increasing the ratio of average signal power to average ICI power (SIR).
TL;DR: This paper deduces approximate capacity formulae for closed-loop transmit diversity schemes that are generalizations of the closed- loop schemes included in UTRA FDD specification and calculates approximation error and shows that the approximation is tight for flat Rayleigh fading environments with and without fast transmit power control.
Abstract: Transmit diversity techniques have received a lot of attention recently, and open-loop and closed-loop downlink transmit diversity modes for two transmit antennae have been included into universal terrestrial radio access (UTRA) frequency division duplex (FDD) specification. Closed-loop modes provide larger system capacity than open-loop modes, but they need additional side information of the downlink channel in the transmitter. In FDD systems this requires a separate feedback channel. Quantization of channel state information (CSI) in closed-loop transmit diversity schemes decreases the performance when compared to a closed-loop system where the transmitter has access to complete CSI. In this paper, we analyze the effect of quantization of CSI and deduce approximate capacity formulae for closed-loop transmit diversity schemes that are generalizations of the closed-loop schemes included in UTRA FDD specification. Moreover, we calculate approximation error and show by simulations that our approximation is tight for flat Rayleigh fading environments with and without fast transmit power control.
TL;DR: A novel tractable multi-cell mobility model for wireless cellular networks under the general assumptions that the cell dwell times induced by mobiles’ mobility and call holding times are modeled by using a general distribution instead of exponential distribution is presented.
Abstract: Multi-cell mobility model and performance analysis for wireless cellular networks are presented. The mobility model plays an important role in characterizing different mobility-related parameters such as handoff call arrival rate, blocking or dropping probability, and channel holding time. We present a novel tractable multi-cell mobility model for wireless cellular networks under the general assumptions that the cell dwell times induced by mobiles' mobility and call holding times are modeled by using a general distribution instead of exponential distribution. We propose a novel generalized closed-form matrix formula to support the multi-cell mobility model and call holding time with general distributions. This allows us to develop a fixed point algorithm to compute loss probabilities, and handoff call arrival rate under the given assumptions. In order to reduce computational complexity of the fixed point algorithm, the channel holding time of each cell is down-modeled into an exponentially distributed one for purposes of simplification, since the service time is insensitive in computing loss probabilities of each cell due to Erlang insensitivity. The accuracy of the multi-cell analytic mobility model is supported by the comparison of the simulation results and the analytic ones.
TL;DR: A novel approach in adjusting the step size of the CMA using the fuzzy logic based outer loop controller is presented in this paper, which obtains a more robust training process for the simple CMA algorithm.
Abstract: The Constant Modulus Algorithm (CMA), although it is the most commonly used blind equalization technique, converges very slowly. The convergence rate of the CMA is quite sensitive to the adjustment of the step size parameter used in the update equation as in the Least Mean Squares (LMS) algorithm. A novel approach in adjusting the step size of the CMA using the fuzzy logic based outer loop controller is presented in this paper. Inspired by successful works on the variable step size LMS algorithms, this work considers designing a training trajectory that it overcomes hurdles of an adaptive blind training via controlling the level of error power (LOEP) and trend of error power (TOEP) and then obtains a more robust training process for the simple CMA algorithm. The controller design involves with optimization of training speed and convergence rate using experience based linguistic rules that are generated as a part of FLC. The obtained results are compared with well-known versions of CMA; Conventional CMA, Normalized-CMA [Jones, IEEE conference record of the twenty-ninth asilomar conference on signals, systems and computers (Vol. 1, pp. 694---697), 1996], Modified-CMA [Chahed, et al., Canadian conference on electrical and computer engineering (Vol. 4, pp. 2111---2114), 2004], Soft Decision Directed-CMA (Chen, IEE Proceedings of Visual Image Signal Processing, 150, 312---320, 2003) for performance measure and validation.
TL;DR: An exact method is employed to analyze the bit error rate (BER) performances of differential chaos shift keying (DCSK) communication system over fading channels and the Gaussian approximation (GA) method is compared with the exact method.
Abstract: An exact method is employed to analyze the bit error rate (BER) performances of differential chaos shift keying (DCSK) communication system over fading channels. The exact BER performances of DCSK in Nakagami-m Rayleigh and Rician fading channels are derived, respectively. The Gaussian approximation (GA) method is compared with the exact method. The numerical results and simulation results for the two methods are presented and are compared in the fading channels, respectively. These results support our theoretical analysis.
TL;DR: It is argued that the use of convergence layers and the development of adaptive network protocols is a promising approach to enable low end devices to participate in heterogeneous network architectures.
Abstract: Wireless sensor networks and wireless mesh networks are popular research subjects. The interconnection of both network types enables next-generation applications and creates new optimization opportunities. However, current single-gateway solutions are suboptimal, as they do not allow advanced interactions between sensor networks (WSNs) and mesh networks (WMNs). Therefore, in this article, challenges and opportunities for optimizing the WSN-WMN interconnection are determined. In addition, several alternative existing and new interconnection approaches are presented and compared. Furthermore, the interconnection of WSNs and WMNs is used to study challenges and solutions for future heterogeneous network environments. Finally, it is argued that the use of convergence layers and the development of adaptive network protocols is a promising approach to enable low end devices to participate in heterogeneous network architectures.
TL;DR: This paper proposes a mobility model that does not assume any radio propagation environments and movement patterns of a mobile node, and devise a statistical compensation method to initiate link layer triggers in a timely manner considering the given handover signaling delay bound.
Abstract: Cross layer handover schemes are expected to provide seamless services to users on the move. To achieve this goal, a link layer must timely trigger handover protocols of upper layers so that they can finish necessary handover procedures before current wireless link terminates. Therefore, a mobile node needs an appropriate model to predict impending handover to generate link layer triggers in time. In this paper, we propose a mobility model that does not assume any radio propagation environments and movement patterns of a mobile node. Through statistical analysis of the received signal strength index (RSSI) datasets measured in various radio propagation environments, we validate that an adaptive autoregressive process can be used as a handover prediction model. With the proposed model, we also propose a link layer triggering scheme. Since the prediction process inevitably introduces errors, we devise a statistical compensation method to initiate link layer triggers in a timely manner considering the given handover signaling delay bound. Simulation results show that the error compensation method can significantly decrease the rate of late link layer triggers with the reasonable increase in the false alarm rate.
TL;DR: In this paper a new access control model, relation based access control (RelBAC), is provided for context-aware environment with a domain specific Description Logic to formalize the model.
Abstract: Context-aware computing is an important aspect of the pervasive computing environment and its various dynamic context information brings new challenges to access control systems. In this paper a new access control model, relation based access control (RelBAC), is provided for context-aware environment with a domain specific Description Logic to formalize the model. The novelty of RelBAC is that permissions are formalized as binary relations between subjects and objects which could evolve with the dynamic contexts. The expressive power of RelBAC is illustrated in a case study of a project meeting event.
TL;DR: This work focuses on the role and the information of the components of the RTMS, which provides the means for profile modelling, the acquisition of monitoring/discovery/context information, and the negotiation and selection of configurations, based on information deriving from policies, as well as the profiles and the context.
Abstract: In the era of wireless communications, Beyond the 3rd Generation (B3G), a network operator (NO) should satisfy numerous requirements, namely, personalisation, context awareness, always best connectivity, ubiquitous service provision and seamless mobility. A NO can efficiently satisfy the requirements by relying on the different radio networks of its heterogeneous infrastructure, and potentially on other cooperating networks. In this respect, the NO should possess advanced management mechanisms for driving its users to the most appropriate networks that satisfy the requirements. The presentation of such a management system is the specific contribution of this paper. The system is called Reconfigurable Terminal Management System (RTMS). In general, it provides the means for profile modelling, the acquisition of monitoring/discovery/context information, and the negotiation and selection of configurations, based on information deriving from policies, as well as the profiles and the context. Our work focuses on the role and the information of the components of the RTMS. Concrete functionality for accomplishing the role is also presented. Nevertheless, the system is open to the integration of alternate functionality. Our discussion includes a business case that presents in high-level terms the role of the management system, a detailed description of the components of the management system and results that show the efficiency of the management schemes. A summary and further research challenges, conclude this article.
TL;DR: Through analysis and simulation evaluation, it is demonstrated that multiuser transmission with a scheduling algorithm and single-user transmission with enhanced spatial multiplexing achieve enhanced performance by exploitingMultiuser diversity in the space and time domains.
Abstract: By adopting multiple-input-multiple-output (MIMO) antenna technologies, IEEE 802.11 wireless LANs are evolving into high speed systems. While only one user can transmit at a time in the conventional IEEE 802.11 systems, we investigate the possibility of multiuser transmission by using MIMO antennas, which is now known as multiuser MIMO. The multiuser MIMO technique enables multiple users to receive packets over the downlink simultaneously, but it should be carefully used in the IEEE 802.11 systems for interoperation with non-MIMO legacy terminals. Through analysis and simulation evaluation, we demonstrate that multiuser transmission with a scheduling algorithm and single-user transmission with enhanced spatial multiplexing achieve enhanced performance by exploiting multiuser diversity in the space and time domains. Especially, when the number of stations is large, multiuser transmission shows better performance than enhanced single-user transmission.
TL;DR: This paper considers user scheduling in conjunction with receive antenna selection and proposes simplified and suboptimal user scheduling algorithms for both BD and SO with the objective of sum rate maximization.
Abstract: Block diagonalization (BD) and successive optimization (SO) are two suboptimal but more practical (compared to dirty paper coding (DPC)) orthogonal linear precoding techniques for the downlink of multiuser MIMO systems. Since the numbers of users supported by BD or SO for a given number of transmit antennas are limited, BD or SO should be combined with scheduling so that a subset of users is selected at a given time slot while meeting the dimensionality requirements of these techniques. On the other hand, receive antenna selection (RAS) is a promising hardware complexity reduction technique. In this paper, we consider user scheduling in conjunction with receive antenna selection. Since exhaustive search is computationally prohibitive, we propose simplified and suboptimal user scheduling algorithms for both BD and SO. For BD, we propose capacity and Frobenius-norm based suboptimal algorithms with the objective of sum rate maximization. Starting from an empty set, each step of proposed algorithms adds the best user from the set of users not selected yet until the desired number of users have been selected. Proposed receive antenna selection works in conjunction with user scheduling to further enhance the sum rate of BD. For SO, a Frobenius-norm based low complexity algorithm is proposed, which maximizes the ratio of the squared Frobenius norm of the equivalent channel (projected to the joint null space of the previously selected users) to the sum of the squared Frobenius norms of the previously selected users' preprocessed channels. Simulation results demonstrate that the proposed algorithms achieve sum rates close to exhaustive search algorithms with much reduced complexity. We also show that in addition to reduced hardware complexity at the receiver, antenna selection enhances multiuser diversity gain that is achieved with user scheduling.
TL;DR: Simulation results show that the proposed STC schemes achieve better multiplexing-diversity tradeoffs than the existing conventional schemes.
Abstract: In this work, we introduce a new space---time coding (STC) paradigm which is based on the joint design of quasi-orthogonal space---time block code (Q-OSTBC) and the successive interference cancellation (SIC) detector. Based on the proposed principle, two high-rate Q-OSTBCs for three and four transmit antennas are designed. The symbols of the proposed Q-OSTBCs are of judiciously designed diversity order which can be effectively exploited by the SIC based receiver to cancel interference as well as to obtain diversity gain. The proposed SIC-amenable STC's amicable quasi-orthogonal structure also lends itself to efficient low-complexity linear decoding. Simulation results show that the proposed STC schemes achieve better multiplexing-diversity tradeoffs than the existing conventional schemes.
TL;DR: A novel algorithm for the identification of NLOS propagation using both angle and time estimates leads to enhanced versions of the Time of Arrivals and Angle of Arrival positioning methods, which increases the upgrade flexibility and minimizes the implementation cost.
Abstract: Positioning algorithms and their implementation in mobile networks are being investigated in the literature due to their importance in location services. Nowadays, the need for superior accuracy has cast attention to hybrid positioning techniques. In this paper, we introduce a novel algorithm for the identification of NLOS propagation using both angle and time estimates, which leads to enhanced versions of the Time of Arrivals and Angle of Arrivals positioning methods. Furthermore, a novel GSM procedure for the implementation of the latter techniques is proposed. In contrast to specified network-based GSM solutions (U-TDOA), the proposed requires minimum modifications in the GSM Phase 2+ infrastructure and protocol stack, and therefore increases the upgrade flexibility and minimizes the implementation cost. The proposed GSM positioning procedure has been experimentally validated using a GSM emulator and the modified signalling messages given by a measurement tool of the emulator are exhibited. Finally, the enhanced cost functions are experimentally evaluated using several GSM-like, high-capacity simulation environments and the results have shown significant reduction of the location error compared to the conventional techniques.
TL;DR: It is considered that each cell can search respective optimal order chirp basis to replace exponential basis to suppress ICaI, and optimal interference restricted combination equalizer based on the Fractional Fourier Transform is proposed to suppressICeI.
Abstract: Transmission over wireless time-varying channels can lead to inter-carrier interference (ICaI) and inter-cell interference (ICeI) in multiple-input multiple-output orthogonal frequency division multiplexing systems. In this paper, it is considered that each cell can search respective optimal order chirp basis to replace exponential basis to suppress ICaI, and optimal interference restricted combination equalizer based on the Fractional Fourier Transform is proposed to suppress ICeI. Furthermore, a novel equivalent channel estimation algorithm is used to improve system simulation efficiency. The simulation results demonstrate the effectiveness of proposed approach.
TL;DR: This paper analyzes the complexity-performance trade-off of several heuristic near-optimum multiuser detection approaches applied to the uplink of synchronous single/multiple-input multiple-output multicarrier code division multiple access (S/MIMO MC-CDMA) systems and shows that unitary Hamming distance search MuD (uH-ds) approaches reach the best convergence rates.
Abstract: This paper analyzes the complexity-performance trade-off of several heuristic near-optimum multiuser detection (MuD) approaches applied to the uplink of synchronous single/multiple-input multiple-output multicarrier code division multiple access (S/MIMO MC-CDMA) systems. Genetic algorithm (GA), short term tabu search (STTS) and reactive tabu search (RTS), simulated annealing (SA), particle swarm optimization (PSO), and 1-opt local search (1-LS) heuristic multiuser detection algorithms (Heur-MuDs) are analyzed in details, using a single-objective antenna-diversity-aided optimization approach. Monte- Carlo simulations show that, after convergence, the performances reached by all near-optimum Heur-MuDs are similar. However, the computational complexities may differ substantially, depending on the system operation conditions. Their complexities are carefully analyzed in order to obtain a general complexity-performance framework comparison and to show that unitary Hamming distance search MuD (uH-ds) approaches (1-LS, SA, RTS and STTS) reach the best convergence rates, and among them, the 1-LS-MuD provides the best trade-off between implementation complexity and bit error rate (BER) performance.
TL;DR: This contribution deals with the review of the main physical layer techniques for encrypting the information and the proposal of a new physical layer technique ensuring secure communication in a full wireless environment.
Abstract: Due to the enormous spreading of applied wireless networks, security is actually one of the most important issues for telecommunications. One of the main issue in the field of securing wireless information exchanging is the initial common knowledge between source and destination. A shared secret is normally mandatory in order to decide the encryption (algorithm or code or key) of the information stream. It is usual to exchange this common a priori knowledge by using a "secure" channel. Nowadays a secure wireless channel is not possible. In fact normally the common a priori knowledge is already established (but this is not secure) or by using a non-radio channel (that implies a waste of time and resource). The information is encrypted by means of a private key that must be known by both the transmitter and the receiver. One of the main weak point about security is the private key exchanging interval. The key cannot be public and cannot be known a priori. The problem is how to exchange this private key through a totally secure wireless channel. This contribution deals with the review of the main physical layer techniques for encrypting the information and the proposal of a new physical layer technique ensuring secure communication in a full wireless environment. The information is modulated, at physical layer, by the thermal noise experienced by the link between two terminals. A loop scheme is designed for unique recovering of mutual information. The probability of error/detection is analytically derived for the legal users and for the third unwanted listener (passive or active attacker). Both the case of passive and active attacks have also been implemented and simulated by using Matlab-Simulink software. The analytical results have been compared to the simulated ones. All the results show that the performance of the proposed scheme yields the advantage of intrinsic security, i.e., the mutual information cannot be physically demodulated (passive attack) or denied (active attack) by a third terminal.
TL;DR: Some theoretical and practical issues and research directions in the field of wireless communications and networking that are common to most if not all application areas are presented.
Abstract: Scientific and technological innovations of the last few decades in the field of wireless telecommunications and networking have enabled a wide area of applications and services in healthcare, transportation, environmental protection, infotainment, industrial automation, homeland security, smart urban environments and other disparate fields. At the same time the complexity and criticality of these systems creates many technical challenges in their design, development and operation. This paper reviews a number of important application fields of wireless communications and networking and discusses recent results, key challenges and unsolved issues in each one of them. It goes on to present some theoretical and practical issues and research directions in the field of wireless communications and networking that are common to most if not all application areas. These include theoretical link and network capacity limits, cognitive radio and cognitive networking, programming and in-field reprogramming of wireless devices, and complex system design inspired by biology and physics.