Showing papers in "Wireless Personal Communications in 2007"
TL;DR: This paper focuses on the technology behind a HAPS communications system, how this has developed, and compares it to the terrestrial and satellite equivalents.
Abstract: This paper looks into the relatively new field of high altitude platform stations. HAPS is seen as a `middle ground' between the terrestrial and satellite cases, and aims to exploit of the advantages of both types of system. Since HAPS is such a new field, this paper focuses on the technology behind a HAPS communications system, how this has developed, and compares it to the terrestrial and satellite equivalents. One important area that is being investigated is the applications for which HAPS should be used. This is a critical issue if a significant business case is to be made for HAPS. Worldwide HAPS projects and research issues are also highlighted. Finally, the review concludes with the remarks on the future of HAPS for wireless communications systems.
94 citations
TL;DR: This article introduces context aware systems in mobile computing environments, review the basic mechanisms underlying the operation of such systems, and discusses notable work and important architectures in the area.
Abstract: In this article, we report software architectures for context awareness in mobile computing environments, sensor centric systems and discuss context modeling issues. Defining an architecture for supporting context-aware applications for mobile devices explicitly implies a scalable description of how to represent contextual information and which are the abstraction models capable of handling such information. Using sensors to retrieve contextual information (e.g., user location) leads to a sensor network scheme that provides services to the applications level. Operations for capturing, collating, storing, and disseminating contextual information at the lowest level and aggregating it into increasingly more abstract models qualify the context-aware systems. In this article, we introduce context aware systems in mobile computing environments, review the basic mechanisms underlying the operation of such systems, and discuss notable work and important architectures in the area.
92 citations
TL;DR: Simulation experiments show that CC caching mechanism achieves significant improvements in cache hit ratio and average query latency in comparison with other caching strategies.
Abstract: In this paper, we present a scheme, called Cluster Cooperative (CC) for caching in mobile ad hoc networks. In CC scheme, the network topology is partitioned into non-overlapping clusters based on the physical network proximity. For a local cache miss, each client looks for data item in the cluster. If no client inside the cluster has cached the requested item, the request is forwarded to the next client on the routing path towards server. A cache replacement policy, called Least Utility Value with Migration (LUV-Mi) is developed. The LUV-Mi policy is suitable for cooperation in clustered ad hoc environment because it considers the performance of an entire cluster along with the performance of local client. Simulation experiments show that CC caching mechanism achieves significant improvements in cache hit ratio and average query latency in comparison with other caching strategies.
69 citations
TL;DR: This paper describes the 802.21 framework and a Media-independent Pre-Authentication (MPA) mechanism currently under discussion within the IRTF that can further optimize handover performance and describes a test-bed implementation and experimental performance results of the combined mobility technique.
Abstract: Dual-mode handsets and multimode terminals are generating demand for solutions that enable convergence and seamless handover across heterogeneous access networks. The IEEE 802.21 working group is creating a framework that defines a Media Independent Handover Function (MIHF), facilitates handover across heterogeneous access networks, and helps mobile users experience better performance during mobility events. In this paper, we describe this 802.21 framework and also summarize a Media-independent Pre-Authentication (MPA) mechanism currently under discussion within the IRTF that can further optimize handover performance. We discuss how the 802.21 framework and the MPA technique can be integrated to improve handover performance. Finally, we describe a test-bed implementation and validate experimental performance results of the combined mobility technique.
65 citations
TL;DR: A novel pulse shape is suggested to decrease the Inter-Carrier Interference (ICI) in an Orthogonal Frequency Multiplexing System (OFDM) due to frequency offset.
Abstract: A novel pulse shape is suggested to decrease the Inter-Carrier Interference (ICI) in an Orthogonal Frequency Multiplexing System (OFDM) due to frequency offset. Furthermore several Nyquist- I pulses recently found are also used for the same purpose. Simulation results are compared for the average ICI and for the signal to interference ratio (SIR) for the pulses under consideration. The sensitivity of the ICI to the used pulse shape and the effectiveness of the proposed pulse shape are reported.
62 citations
TL;DR: A practical UMTS–WLAN interworking architecture based on 3GPP standards is presented and a seamless handoff scheme that guarantees low delay and low packet loss during UMTS-WLAN handoff is proposed.
Abstract: Interworking issues between Universal Mobile Telecommunication System (UMTS) and Wireless Local Area Network (WLAN) have become a great matter of interest as an increasing number of mobile internet users require broadband wireless access to IP services in the wide area. In this paper, we present a practical UMTS---WLAN interworking architecture based on 3GPP standards and propose a seamless handoff scheme that guarantees low delay and low packet loss during UMTS---WLAN handoff. For low handoff delay, the proposed handoff scheme performs pre-registration and pre-authentication processes before layer 2 handoff. Moreover, it uses packet buffering and forwarding functions in order to reduce packet loss during the handoff period. On the above basis, detailed signaling procedures are presented, together with system requirements when a mobile terminal moves from UMTS to WLAN and vice-versa. Numerical results show that the proposed scheme performs well with respect to signaling cost, handoff delay, and packet loss compared with conventional schemes.
59 citations
TL;DR: By using the genetic algorithm based on fuzzy decision-making, some modifications have been implemented to the incorporated slots which lead to even more enhancement in the antenna bandwidth which is larger than that of a corresponding unslotted rectangular microstrip antenna or a conventional E-Shaped patch antenna.
Abstract: In this paper a novel form of the familiar E-shaped patch antenna is presented. In the presented approach, by using the genetic algorithm (GA) based on fuzzy decision-making, some modifications have been implemented to the incorporated slots which lead to even more enhancement in the antenna bandwidth. The MOM (Method of Moment) is employed for analysis at the frequency band of 1.8GHz---2.6GHz by the optimization parameters of supply locations and slot dimensions. In the implemented fuzzy system, inputs are parameters like population, and outputs are parameters like recombination to produce the next generation. Fuzzy inference system (FIS) is used for the control of GA parameters. The design is also optimized by successive iterations of a computer-aided analysis package and experimental modifications. Prototype antenna, resonating at wireless communication frequencies of 1.88 and 2.37 GHz, has been constructed and experimental results are in relatively good agreement with the analysis. Dimensions of the modified slots for bandwidth enhancement, while maintaining good radiation characteristics, have been determined and the obtained antenna bandwidth of 36.7% is larger than that of a corresponding unslotted rectangular microstrip antenna or a conventional E-Shaped patch antenna. Details of the antenna design approach and experimental results are presented and discussed.
46 citations
TL;DR: A novel cross-layer architecture that provides context-awareness, smart handoff and mobility control in heterogeneous wireless IP networks, and Tramcar, a smart and practical system, which is more capable of dealing with 4G challenges.
Abstract: The integration of a multitude of wireless networks is expected to lead to the emergence of the fourth generation (4G) of wireless technologies. Under the motivation of increasing the levels of user satisfaction while maintaining seamless connectivity and a satisfactory level of QoS, we design a novel cross-layer architecture that provides context-awareness, smart handoff and mobility control in heterogeneous wireless IP networks. We develop a Transport and Application Layer Architecture for vertical Mobility with Context-awareness (Tramcar). Tramcar presents a new approach to vertical handoff decisions, which is not exclusively based on network characteristics but also on higher level parameters which fall in the application and transport layers. Tramcar is tailored for a variety of different network technologies with different characteristics and has the ability of adapting to changing environment conditions and unpredictable background traffic. Furthermore, Tramcar allows users to identify and prioritize their preferences. Tramcar is a smart and practical system, which is more capable of dealing with 4G challenges. Simulation results demonstrate that Tramcar increases user satisfaction levels and network throughput under rough network conditions and reduces overall handoff latencies.
44 citations
TL;DR: The empirical results reveal that Mobile IP yields the highest handoff delay among the three mobility protocols, and that SIP and SCTP yield 33 and 55% lower handoff delays respectively compared to Mobile IP.
Abstract: Over the last decade, we have witnessed a growing interest in the design and deployment of various network architectures and protocols aimed at supporting mobile users as they move across different types of networks. One of the goals of these emerging network solutions is to provide uninterrupted, seamless connectivity to mobile users giving them the ability to access information anywhere, anytime. Handoff management, an important component of mobility management, is crucial in enabling such seamless mobility across heterogeneous network infrastructures. In this work, we investigate the handoff performance of three of the most widely used mobility protocols namely, Mobile IP, Session Initiation Protocol (SIP), and Stream Control Transmission Protocol (SCTP). Our empirical handoff tests were executed on an actual heterogeneous network testbed consisting of wired, wireless local area, and cellular networks using performance metrics such as handoff delay and handoff signaling time. Our empirical results reveal that Mobile IP yields the highest handoff delay among the three mobility protocols. In addition, we also found that SIP and SCTP yield 33 and 55% lower handoff delays respectively compared to Mobile IP.
43 citations
TL;DR: The quasi-optimality of the proposed backoff enhancement for IEEE 802.11 DCF that requires information only about the network size and that is quasi-optimal under all traffic loads is proved analytically and numerical results show that it increases, both the throughput and fairness, of IEEE IEEE.
Abstract: Existing backoff scheme's optimization of IEEE 802.11 DCF MAC protocol consider only saturated networks or asymptotic conditions. In real situations, traffic is bursty or streamed at low rates so that stations do not operate usually in saturated regime. In this work, we propose and analyze a backoff enhancement for IEEE 802.11 DCF that requires information only about the network size and that is quasi-optimal under all traffic loads. We first analyze the performance of DCF multiple access scheme under general load conditions in single-hop configuration and we provide an accurate delay statistics model that consider the self-loop probability in every backoff state. We prove then the short-term unfairness of the binary exponential backoff used in IEEE 802.11 by defining channel capture probability as fairness metric. Motivated by the results on fairness, we introduce the constant-window backoff scheme and we compare its performance to IEEE 802.11 DCF with Binary exponential backoff. The quasi-optimality of the proposed scheme is proved analytically and numerical results show that it increases, both the throughput and fairness, of IEEE 802.11 DCF while remaining insensitive to traffic intensity. The analysis is then extended to consider the finite queuing capacity at nodes buffers using results from the delay analysis. NS2 simulations validate the obtained results.
43 citations
TL;DR: A modified and refined genetic algorithm to find the exact solutions to the complex, multi-modal, multivariate and highly nonlinear likelihood function and its performance is the best among popular ML-based DOA estimation methods.
Abstract: Maximum likelihood (ML) direction-of-arrival (DOA) estimation algorithm is a nearly optimal technique. In this paper, we present a modified and refined genetic algorithm (GA) to find the exact solutions to the complex, multi-modal, multivariate and highly nonlinear likelihood function. With the newly introduced features such as intelligent initialization and the emperor-selective mating scheme, carefully selected crossover and mutation operators, and fine-tuned parameters such as the population size, the probability of crossover and mutation, the GA-ML estimator achieves fast global convergence. The GA-ML estimator has been compared with various DOA estimation methods in a variety of scenarios, and the simulation results demonstrate that in most scenarios the proposed GA-ML estimator is the fastest and its performance is the best among popular ML-based DOA estimation methods.
TL;DR: This work discusses recent and on-going standardization activities within IEEE, IETF, and 3GPP toward seamless homogeneous as well as heterogeneous mobility support.
Abstract: The challenge to provide seamless mobility in the near future emerges as a key topic in various standardization bodies. This includes first of all the support of seamless handover between homogeneous networks. Distinct technologies--such as IEEE 802.11WLANs (Wi-Fi) and IEEE 802.16 MANs WiMAX--have recently augmented such support to existing standards to enable seamless homogeneous handover. Cellular networks, in contrast, already included this inherently from the start. Currently considerable effort goes into coupling of different radio access technologies. Therefore, the second key topic in standardization is seamless heterogeneous handovers. IEEE, IETF, as well as 3GPP consider different approaches toward architectures and protocols enabling seamless mobility management. In this work, we discuss recent and on-going standardization activities within IEEE, IETF, and 3GPP toward seamless homogeneous as well as heterogeneous mobility support.
TL;DR: A novel QoS routing algorithm based on Simulated Annealing (SA_RA) is proposed, which first uses an energy function to translate multiple QoS weights into a single mixed metric and then seeks to find a feasible path by simulated annealing.
Abstract: Multi-constrained quality-of-service routing (QoSR) is to find a feasible path that satisfies multiple constraints simultaneously, which is a big challenge for mobile ad hoc networks (MANETs) where the topology may change constantly. It has been proved that such a problem is NP-complete. Heuristic algorithms with polynomial and pseudo-polynomial-time complexities are often used to deal with this problem. However, existing solutions, most of which suffered either from excessive computational complexities or from low performance were proposed only for wired networks and cannot be used directly in wireless MANETs. In this paper a novel QoS routing algorithm based on Simulated Annealing (SA_RA) is proposed. This algorithm first uses an energy function to translate multiple QoS weights into a single mixed metric and then seeks to find a feasible path by simulated annealing. The paper outlines simulated annealing algorithm and analyzes the problems met when we apply it to QoSR in MANETs. Theoretical analysis and experiment results demonstrate that the proposed method is an effective approximation algorithms showing better performance than the other pertinent algorithm in seeking the (approximate) optimal configuration within a period of polynomial time.
TL;DR: This paper compares the effect of measured and simulated radio maps on the accuracy of two different methods of wireless network based localisation and indicates that, although the propagation model used underestimated the signal strength by up to 15 dB at certain locations, there was not a signigicant reduction in localisation performance.
Abstract: Indoor wireless network based client localisation requires the use of a radio map to relate received signal strength to specific locations. However, signal strength measurements are time consuming, expensive and usually require unrestricted access to all parts of the building concerned. An obvious option for circumventing this difficulty is to estimate the radio map using a propagation model. This paper compares the effect of measured and simulated radio maps on the accuracy of two different methods of wireless network based localisation. The results presented indicate that, although the propagation model used underestimated the signal strength by up to 15 dB at certain locations, there was not a signigicant reduction in localisation performance. In general, the difference in performance between the simulated and measured radio maps was around a 30% increase in rms error.
TL;DR: This work proposes an optimal pricing strategy, based on which the service provider can regulate the overall network behavior, that enforces fairness under the constraint of an equal access probability in wireless access systems.
Abstract: Wireless access based on slotted Aloha with selfish users may result in very inefficient use of the system resources. To impose cooperation and fairness in such systems, we propose an optimal pricing strategy, based on which the service provider can regulate the overall network behavior. As the users' utility incorporates the price paid for using the spectrum, by striving to improve their own performance, the users act to optimize the overall network performance. Our analysis is based on a game theoretic framework, and we consider both the simple collision model for packet reception, as well as multipacket reception capabilities for the physical layer. The proposed pricing strategy enforces fairness under the constraint of an equal access probability.
TL;DR: In this paper, an energy-aware data aggregation scheme (EADA) for grid-based wireless sensor networks with a mobile sink is proposed and simulations show that the proposed routing scheme outperforms the coordination-based data dissemination scheme (CODE).
Abstract: Wireless sensor networks (WSNs) are made up of many small and highly sensitive nodes that have the ability to react quickly. In WSNs, sink mobility brings new challenges to large-scale sensor networks. Almost all of the energy-aware routing protocols that have been proposed for WSNs aim at optimizing network performance while relaying data to a stationary gateway (sink). However, through such contemporary protocols, mobility of the sink can make established routes unstable and non-optimal. The use of mobile sinks introduces a trade-off between the need for frequent rerouting to ensure optimal network operation and the desire to minimize the overhead of topology management. In this paper, in order to reduce energy consumption and minimize the overhead of rerouting frequency, we propose an energy-aware data aggregation scheme (EADA) for grid-based wireless sensor networks with a mobile sink. In the proposed scheme, each sensor node with location information and limited energy is considered. Our approach utilizes location information and selects a special gateway in each area of a grid responsible for forwarding messages. We restrict the flooding region to decrease the overhead for route decision by utilizing local information. We conducted simulations to show that the proposed routing scheme outperforms the coordination-based data dissemination scheme (CODE) (Xuan, H. L., & Lee, S. Proceedings of the Sensor Networks and Information Processing Conference, pp. 13---18, 2004).
TL;DR: A power-aware multicast routing protocol (PMRP) with mobility prediction for MANETs and simulation results show that the proposed PMRP outperforms MAODV.
Abstract: A mobile ad hoc network (MANET) is a dynamically reconfigurable wireless network that does not have a fixed infrastructure. Due to the high mobility of nodes, the network topology of MANETs changes very fast, making it more difficult to find the routes that message packets use. Because mobile nodes have limited battery power, it is therefore very important to use energy in a MANET efficiently. In this paper, we propose a power-aware multicast routing protocol (PMRP) with mobility prediction for MANETs. In order to select a subset of paths that provide increased stability and reliability of routes, in routing discovery, each node receives the RREQ packet and uses the power-aware metric to get in advance the power consumption of transmitted data packets. If the node has enough remaining power to transmit data packets, it uses the global positioning system (GPS) to get the location information (i.e., position, velocity and direction) of the mobile nodes and utilizes this information to calculate the link expiration time (LET) between two connected mobile nodes. During route discovery, each destination node selects the routing path with the smallest LET and uses this smallest link expiration time as the route expiration time (RET). Each destination node collects several feasible routes and then selects the path with the longest RET value as the primary routing path. Then the source node uses these routes between the source node and each destination node to create a multicast tree. In the multicast tree, the source node will be the root node and the destination nodes will be the leaf nodes. Simulation results show that the proposed PMRP outperforms MAODV (Royer, E. M. & Perkins, C. E. (1999). In Proceedings of the ACM MOBICOM, pp. 207---218, August 1999.) and RMAODV (Baolin, S. & Layuan, L. (2005). In Proceeding of the 2005 IEEE International symposium on microwave antenna, propagation and EMC technologies for wireless communications, Vol. 2, pp. 1514---1517, August 2005.).
TL;DR: It is shown that rotated signal constellations with component interleaving improve the performance of M-PSK significantly as compared to the unrotated one over Rayleigh and Ricean fading channels.
Abstract: In this paper, the modulation diversity is used to improve the performance of M-PSK modulation over fading channels. Modulation diversity can be achieved by rotating the signal constellation and using component interleaving. We derive symbol error probability expressions for rotated uncoded M-PSK over Ricean fading channels and obtain optimal rotation angles for M-PSK (M = 2, 4, 8). We show that rotated signal constellations with component interleaving improve the performance of M-PSK significantly as compared to the unrotated one over Rayleigh and Ricean fading channels. For example, when the ratio of the direct path power to the multipath signal power, K is 0 and 10, 8 and 1.5 dB gains are obtained, respectively, at a symbol error probability of 10?3 for 8PSK modulation. We also show that as K gets larger, the gain obtained by the rotation rapidly decreases. We develop a new asymmetric 8PSK signal constellation obtained from two QPSK signal constellations that are optimally rotated by different angles. This asymmetric 8PSK and also the rotated 8PSK signal constellation together with component interleaving are applied to four-state trellis-coded schemes. Simulation results show that these new schemes provide good performance improvements over the original TCM schemes and previous relevant works over Rayleigh and Ricean fading channels.
TL;DR: This paper proposes a cooperation enhancement mechanism using “Neighborhood WatchDog” to generate “Trust Token” based on the first-hand observation to prevent non-cooperative vehicles from tampering packet relaying in the network.
Abstract: As one special case of the Mobile Ad Hoc Networks (MANET), vehicular ad-hoc networking (VANET) is featured by its high mobility and constantly changing topology. In VANET, nodes can work properly only if the participating vehicles cooperate with each other during communications. However, as a distributed network, individual vehicles might be non-cooperative for their own benefits. In order to prevent non-cooperative vehicles from tampering packet relaying in the network, we propose a cooperation enhancement mechanism using "Neighborhood WatchDog" to generate "Trust Token" based on the first-hand observation. Therefore, trust relationships and packet-acceptance decisions of the receiving nodes are based on the instant observation and the token-proved relaying behavior of the benign neighboring vehicles. With the inherit mapping between the Electronic ID of one vehicle and its public key, keys can be distributed on-the-fly. As a network layer solution, the cooperation enhancement mechanism proposed in this paper is built on the top of our previous proposed Media Access Control (MAC) protocol: Relative Position Based-MAC (RPB-MAC).
TL;DR: The simulation results indicate that EACLE outperforms a conventional scheme such as EAD (Energy-Aware Data-centric routing) in terms of communication success rate and energy consumption.
Abstract: In this paper, we propose a new energy efficient clustering scheme with transmission power control named "EACLE" (Energy-Aware CLustering scheme with transmission power control for sEnsor networks) for wireless sensor networks, which are composed of the following three components; "EACLE clustering" is a distributed clustering method by means of transmission power control, "EACLE routing" builds a tree rooted at a sink node and sets the paths from sensor nodes taking energy saving into consideration, and "EACLE transmission timing control" changes the transmission timing with different levels of transmission power to avoid packet collisions and facilitates packet binding.
With an indoor wireless channel model which we obtained from channel measurement campaigns in rooms and corridors and an energy consumption model which we obtained from a measurement of a chipset, we performed computer simulations to investigate the performance of EACLE in a realistic environment. Our simulation results indicate that EACLE outperforms a conventional scheme such as EAD (Energy-Aware Data-centric routing) in terms of communication success rate and energy consumption. Furthermore, we fully discuss the impact of transmission power and timing control on the performance of EACLE.
TL;DR: In this article, the authors apply some cryptology (such as public key infrastructure, hashing chain and digital signature) to propose a realistic mobile ticket system such that fairness, non-repudiation, anonymity, no forging, efficient verification, simplicity, practicability and obviate the embezzlement issues can be guaranteed.
Abstract: Advances in wireless network technology and the continuously increasing users of Personal Trusted Device (PTD) make the latter an ideal channel for offering personalized services to mobile users. In this paper, we apply some cryptology (such as public key infrastructure, hashing chain and digital signature) to propose a realistic mobile ticket system such that fairness, non-repudiation, anonymity, no forging, efficient verification, simplicity, practicability and obviate the embezzlement issues can be guaranteed. On the basis of PTD is more portable and personal than personal computer, we gradually perceived that the widely used PTD will present huge commerce profits for mobile ticket service provider and it is convenient to the PTD user.
TL;DR: A new tapered beamforming function for sidelobe reduction in the uniform concentric circular arrays (UCCA) is proposed, based on tapering the current amplitudes of the rings in the array, where all elements in an individual ring are weighted in amplitude by the same value and the weight values of different rings are determined by a function that has a normalized-gaussian probability density function variation.
Abstract: In this paper, a new tapered beamforming function for sidelobe reduction in the uniform concentric circular arrays (UCCA) is proposed. This technique is based on tapering the current amplitudes of the rings in the array, where all elements in an individual ring are weighted in amplitude by the same value and the weight values of different rings are determined by a function that has a normalized-gaussian probability density function variation. This novel tapering window is optimized in its parameters to have the lowest possible sidelobe level that may reach 43 dB below the main lobe and these optimum weights are found to be function of the number of elements of the innermost ring and the number of rings in the array. The proposed tapering window can be modified to compensate the gain reduction due to tapering when compared with the uniform feeding case.
TL;DR: Simulation results indicate an improvement in parameters such as connection and handover blocking probabilities, which justifies the enhancement in the overall usage of network resources when connections are handled separately.
Abstract: Current trends in cellular telecommunications suggest the incorporation of Wireless Local Area Networks (WLANs) as supplementary access technologies into the existing cellular infrastructure. Overlay network architectures are expected to improve both service provision and resource utilization under the condition that sophisticated architectural options are followed. Many proposals suggest that all active connections be handled through the same access network technology. However, this is not believed to be efficient in a heterogeneous environment. Therefore, a mechanism that allows each connection of a terminal to be served by different radio access technology is introduced. Based on a tight coupling architecture for interworking between Universal Mobile Telecommunications System (UMTS) and WLANs, the proposed scheme combines a sophisticated decision mechanism with flexible connection management in a way that ensures seamless service continuity during handover. The performance of the system is evaluated using a detailed simulation model and compared against existing architectures. Simulation results indicate an improvement in parameters such as connection and handover blocking probabilities, which justifies the enhancement in the overall usage of network resources when connections are handled separately.
TL;DR: It is shown how set partitioning can be used to design multiple uncorrelated fading waveforms enabling the simulation of Rayleigh fading channels, and shows that the sample average of the generated waveforms results in a deterministic process.
Abstract: In this paper, we introduce a new technique for the design of high-performance Rayleigh fading channel simulators. The proposed design method uses set partitioning --- a technique, which plays a key role in the design of trellis-coded modulation schemes. We show how set partitioning can be used to design multiple uncorrelated fading waveforms enabling the simulation of Rayleigh fading channels. For the important case of isotropic scattering, we show that the sample average of the generated waveforms results in a deterministic process, the autocorrelation function (ACF) of which tends to the zeroth-order Bessel function of the first kind as the number of sample functions increases. The proposed procedure is completely deterministic. The comparison with a stochastic procedure using Monte Carlo techniques will be made. A study of the performance shows clearly that the new technique using set partitioning outperforms by far existing Monte Carlo methods.
TL;DR: In a saturated network, participation in forwarding provides the high-data rate node with significant benefits in throughput and media-access-delay, while increasing the number of bits-per-joule even if it is the only node participating in data forwarding as suggested in this paper.
Abstract: We introduced the use of two-hop forwarding to increase the throughput of an 802.11 network in our earlier work (Narayanan et al., Proceedings of IEEE WCNC'05, March 2005). Other researchers have also considered the benefits of forwarding in the 802.11 infrastructure mode to increase the total network throughput. But the high-data rate node that forwards data for other nodes will have to spend its energy transmitting this data. Previous work on forwarding implicitly assumed that in an enterprise network, the collective good is sufficient to justify this increased energy expense. However, it is important to address the advantages and the cost of participating in such schemes from the individual forwarding node's perspective. Since a node cannot know whether there are other high-data rate nodes in the network capable and willing to forward data, it needs to assume that it is the only node with the capability to do so. In this paper, we focus our analysis on the cost benefit for such a forwarding node. We quantify the throughput improvement, medium access delay reduction and energy consumption for the forwarding node in a saturated network. The analysis and simulation results demonstrate that in a saturated network, participation in forwarding provides the high-data rate node with significant benefits in throughput and media-access-delay, while increasing the number of bits-per-joule even if it is the only node participating in data forwarding as suggested in this paper. The increase in the bits-per-joule is due to the reduction in the total amount of time needed by the high data rate node to transmit a given number of its own application bits. This results in savings in energy expenditure for the forwarding node. Based on these benefits, we conclude that it is unequivocally in the interest of a high data rate node to participate in two-hop forwarding schemes in 802.11 networks.
TL;DR: A model to analyze the throughput and delay performance of the EDCA mechanism under non saturation conditions is presented and it can be used to analyze generic source models, as it neither makes any assumption on the source’s arrival process nor requires all packets be of the same length.
Abstract: In this paper, we present a model to analyze the throughput and delay performance of the EDCA mechanism under non saturation conditions. The main strength of our model is that it can be used to analyze generic source models, as it neither makes any assumption on the source's arrival process nor requires all packets be of the same length. Simulation results confirm the accuracy of our model under a variety of realistic source models, including (i) typical arrival processes for voice, video, and data traffic, and (ii) packet length distributions derived from measurements.
TL;DR: The proposed algorithm reduces the handover rate by around 50% and thus improves the network resource efficiency as compared to that based on signal strength thresholds only.
Abstract: In future generation mobile cellular systems, position location of mobile terminal is expected to be available. In this paper, we propose an initiation algorithm for intersystem handover based on the combination of position location of mobile terminal and the absolute signal strength thresholds. Global System for Mobile communication (GSM) and Universal Mobile Telecommunication Systems (UMTS) networks are considered for interworking. The proposed algorithm reduces the handover rate by around 50% and thus improves the network resource efficiency as compared to that based on signal strength thresholds only.
TL;DR: In this study, multiuser detection in code division multiple access (CDMA) was performed by using neural network (NN) and parallel interference cancellation (PIC), which got better BER performance than the three stage PIC receiver in AWGN channel, and almost same PIC performance with the three stages PIC receivers in the Rayleigh fading channel.
Abstract: In this paper, multiuser detection in code division multiple access (CDMA) was performed by using neural network (NN) and parallel interference cancellation (PIC). Neural network is used as a front-end stage of one stage PIC circuit. PIC is a classical technique in multi user detection process and its bit error rate (BER) performance is not good in one stage for most of the applications. For improving its BER performance, generally multi stage PIC which has high computational complexity is used. In this study, we have got better BER performance than the three stage PIC receiver in AWGN channel, almost same BER performance with the three stages PIC receiver in the Rayleigh fading channel.
TL;DR: This paper considers the error performance of an uncoded multiple-input-multiple-output (MIMO) wireless system with antenna selection at the transmitter and maximal ratio combining (MRC) at the receiver end.
Abstract: This paper considers the error performance of an uncoded multiple-input-multiple-output (MIMO) wireless system with antenna selection at the transmitter and maximal ratio combining (MRC) at the receiver end. Exact closed-form expressions are derived for symbol error probability of the aforementioned scheme in independent and identically distributed (i.i.d) Nakagami-m fading channels.
TL;DR: The way that the CW (Contention Window) size is calculated after a successful transmission is modified and the effect of the CW size on performance and fairness is studied to show that the performance of DCF with this modification is better, specially, for traffics in which throughput is the most important parameter.
Abstract: IEEE 802.11 is a widely used standard for MAC and PHY layers of WLANs. Unfortunately, the access methods offered in this standard cannot support QoS (Quality of Service) for real-time traffics. Using multimedia applications over WLANs is increasing and, on the other hand, it seems that the access methods employed in this standard causes high variations in delay or jitter and wastes bandwidth due to collisions. There are many methods to enable DCF--basic access method in 802.11--with service differentiation and QoS. The difficulty in majority of these methods is unfair bandwidth allocation among low and high priority traffics at high loads resulting starvation for low priority traffics. In this paper, we modify the way that the CW (Contention Window) size is calculated after a successful transmission and study the effect of the CW size on performance and fairness. Results of our simulations show that the performance of DCF with this modification is better, specially, for traffics in which throughput is the most important parameter. Besides, this method provides better fairness among low and high priority traffics. We also employ a scheme to enable 802.11 with service differentiation which grants dynamic priority to low priority traffics to prevent starvation, specially, in high loads.