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Date 28-30 April 2008

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Displaying Results 1 - 25 of 91
  • [Front cover]

    Publication Year: 2008
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  • Symposium Committee

    Publication Year: 2008 , Page(s): 1
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  • 2008 IEEE Sarnoff Symposium

    Publication Year: 2008 , Page(s): 1
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  • [Copyright notice]

    Publication Year: 2008 , Page(s): 1
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  • Technical sessions

    Publication Year: 2008 , Page(s): 1 - 11
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  • Cognitive Sensing Based on Side Information

    Publication Year: 2008 , Page(s): 1 - 6
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (277 KB) |  | HTML iconHTML  

    We study a sensing algorithm for cognitive radios based on Bayesian energy detection while utilizing available side information. The side information available to the cognitive user can consist of: (i) spatial locations of the cognitive and primary receivers, (ii) received power of the primary-signal at the cognitive user, and (iii) a priori transmission probability of the primary user. Considering several scenarios with different combinations of side information, we derive the respective, optimal detection thresholds for the cognitive user. Numerical results using these thresholds show significant performance improvement based on the side information. Specifically, information on spatial locations can help stabilize the performance for a wide range of the primary activity factor. Highly skewed a priori primary-transmission probability further helps improve the performance dramatically. View full abstract»

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  • Improved 3-dB Subgroup based Algorithm for Optimal Discrete Bit-Loading

    Publication Year: 2008 , Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB) |  | HTML iconHTML  

    Aggressive trends in higher throughput and QoS demands along with the increasing constraints on resources-at- hand (available bandwidth, peak emission power, processing delay etc.) require efficient and fast algorithms for resource allocation with no compromise in performance. For more than a decade, huge amount of research-work has been dedicated to improve the convergence time of discrete bit-loading algorithms for optimal allocation of bits to different sub-carriers of a multi- carrier system with respect to the channel response. Recently we proposed by Mahmood, A. and Jaffrot, E., (2006) the 3-dB Subgroup based allocation methodology which gives us the first insight into an underlying pattern of allocation, based upon which an algorithm can be devised for optimal discrete bit allocation using the Gap approximation factor for practical systems. In this work, we reduce further the complexity incurred by the 3-dB subgroup algorithm with no compromise on performance. The exact number of execution cycles of our improved algorithm over a simple scalar processor is compared to that of a recently proposed by Papandreou, N. and Antonakopoulos, T., (2005) algorithm for optimal discrete bit-loading to verify the fast convergence of our algorithm. View full abstract»

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  • Selective Broadcasting in Multi-Hop Cognitive Radio Networks

    Publication Year: 2008 , Page(s): 1 - 5
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (303 KB) |  | HTML iconHTML  

    Cognitive networks enable efficient sharing of the radio spectrum. Control signals used to setup a communication are broadcast to the neighbors in their respective channels of operation. But since the number of channels in a cognitive network is potentially large, broadcasting control information over all channels will cause a large delay in setting up the communication. Thus, exchanging control information is a critical issue in cognitive radio networks. This paper deals with selective broadcasting in multi-hop cognitive radio networks in which, control information is transmitted over pre-selected set of channels. We introduce the concept of neighbor graphs and minimal neighbor graphs to derive the essential set of channels for transmission. It is shown through simulations that selective broadcasting reduces the delay in disseminating control information and yet assures successful transmission of information to all its neighbors. It is also demonstrated that selective broadcasting reduces redundancy in control information and hence reduces network traffic. View full abstract»

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  • Distributed Dynamic Frequency Allocation In Wireless Networks Under Time-Varying User Activities

    Publication Year: 2008 , Page(s): 1 - 5
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (210 KB) |  | HTML iconHTML  

    We propose a framework to analyze the performance of the distributed dynamic frequency allocation algorithm introduced in [1] in the presence of time-varying activity of clusters. In our network model, nodes are grouped into a number of clusters. Each cluster chooses its transmission frequency band based on its knowledge of the interference that it experiences. Furthermore, each cluster can be in active or inactive mode according to a two-state Markov model. We derive conditions on the convergence of the algorithm in mean and variance using stochastic analysis. Additional simulation studies verify the results of stochastic modeling and the performance of the algorithm. View full abstract»

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  • Extending the Scope of the Resource Admission Control Subsystem (RACS) in IP Multimedia Subsystem Using Cognitive Radios

    Publication Year: 2008 , Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1031 KB) |  | HTML iconHTML  

    This paper highlights issues relating to signaling of IMS traffic, and how a truly seamless converged network may be achieved using cognitive radio technology. In this paper we propose implementation of the Resource Admission Control Subsystem (RACS) in IMS using cognitive radios to achieve the required flexibility in resource allocation across different networks. Our proposed model enables the RACS to have an extended 'view' of available networks and resources. The end result is that the scope of the RACS is greatly increased, and resource reservation and QoS management by the RACS is also greatly increased. View full abstract»

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  • Protecting MANETs from Spurious CTS Attacks with Randomized Carrier Sensing

    Publication Year: 2008 , Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (549 KB) |  | HTML iconHTML  

    The request-to-send and clear-to-send (RTS/CTS) exchange has been used in mobile ad-hoc networks (MANETs) to alleviate the hidden and exposed terminal problems. In such an exchange, the so-called network allocation vector (NAV) indicates the current and future state of the channel. Unfortunately, this technique may suffer from virtual jamming by malicious nodes in the network. For example, malicious nodes may send periodic Spurious CTS (SCTS) packets with the sole purpose of forcing other nodes to update their NAV values and preventing them from using the channel. In this paper, we investigate the effect of such SCTS attacks and propose a solution, termed carrier sensing based discarding (CSD). The CSD scheme serves as an add-on to the original RTS/CTS-based medium access control schemes such as IEEE 802.11 DCF MAC. We further demonstrate the performance of our proposed scheme through analysis and the ns2 simulator. View full abstract»

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  • Rate Splitting Issue for Finite Length Raptor Codes

    Publication Year: 2008 , Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (223 KB) |  | HTML iconHTML  

    In this paper, we discuss the rate splitting issue for the design of finite length Raptor codes, in a joint decoding framework. We show that the choice of a rate lower than usually proposed for the precede enables to design Raptor codes that perform well at small lengths, with almost no asymptotic loss. We show in particular that the error floor can be greatly reduced by properly choosing the rate splitting between the precede and the LT code. Those behaviors are demonstrated both on the BEC and the BIAWGN channel. View full abstract»

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  • Performance and Power Spectrum Calculations for Convolutionally Coded Generalized MSK with Two Symbol Periods Pulse Shape Duration

    Publication Year: 2008 , Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (303 KB) |  | HTML iconHTML  

    We show that by applying a cascaded convolutional encoder using two stages of coding, the last being a double repetition code, to "preceded" generalized minimum-shift keying (MSK) signals with pulse shape of duration two symbol periods a significant improvement in power and spectral efficiency is achieved. With only a double repetition code, it is shown that the signal has a power spectrum identical to uncoded MSK-like. When outer encoder is applied to improve the power efficiency, the bandwidth expansion is just a reciprocal of the outer encoder rate. It is demonstrated that considering performance, bandwidth and receiver complexity, generalized MSK signal coded using our special cascaded convolutional codes is an improvement over MSK and generalized MSK coded with "optimum" convolutional codes for the same code rate and receiver complexity reported previously for the same modulation scheme. View full abstract»

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  • Performance Prediction for Turbo Codes in MIMO Wireless Systems

    Publication Year: 2008 , Page(s): 1 - 5
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (317 KB) |  | HTML iconHTML  

    In multiple-input multiple-output (MIMO) systems, accurately predicting performance prior to data transmission remains a difficult problem. This paper proposes an algorithm to predict the bit error rate (BER) and packet error rate (PER) of a MIMO system with turbo coding. First, we modify the union bound (UB) with the help of Craig's formula to make it more amenable to random channels. Second, we extend a method to compute turbo code distance spectrums to accommodate puncturing and code termination. We apply this version of the UB and the distance spectrums to a MIMO system, and produce an algorithm to predict performance. In our results, we show tight bounds at lower, and practical, BERs and PERs. View full abstract»

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  • Closed-form approximation of Coded BER in QAM-based BICM Faded Transmission

    Publication Year: 2008 , Page(s): 1 - 5
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (329 KB) |  | HTML iconHTML  

    In this paper we develop closed-form approximations for the coded BER in bit-interleaved coded modulation (BICM) transmission over Rayleigh fading channels. To obtain the desired expressions we apply the so-called saddle point approximation and use analytical forms of the probability density functions (PDF) of the reliability metrics. Numerical examples illustrate the accuracy of the proposed method. View full abstract»

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  • Fast Simulation for the Performance Evaluation of LDPC Codes using Fast Flat Histogram Method

    Publication Year: 2008 , Page(s): 1 - 5
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (183 KB) |  | HTML iconHTML  

    The quality of transmission in digital communication systems is usually measured by frame error rate (FER). The time taken by standard Monte Carlo (MC) simulation to estimate the FER increases exponentially with the increase in signal-to-noise ratio (SNR). In this correspondence, we present an Adaptive Importance Sampling (AIS) technique inspired by statistical physics called fast flat histogram (FFH) method to evaluate the performance of LDPC codes with a reduced simulation time. The FFH method employs Wang Landau algorithm based on a Markov Chain Monte Carlo (MCMC) sampler and we managed to decrease the simulation time by a factor of 13 to 173 for LDPC codes with block lengths up to 2640 bits. View full abstract»

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  • Receiver design for turbo codes used in an impulsive noise environment

    Publication Year: 2008 , Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (369 KB) |  | HTML iconHTML  

    Turbo codes allow reliable data communication at signal-to-noise ratios very close to those predicted by Shannon. Further, breaking up the decoding task so that separate decoders work on the two constituent codes, passing extrinsic information between them, greatly simplifies the implementation of the decoder. Traditionally, the statistical model for noise used in the design and analysis of the decoder is the additive white Gaussian noise (AWGN) model. However many practical applications present situations where the AWGN model for noise is clearly sub-optimum. Optimum performance for a spread spectrum system when the noise is non-Gaussian in nature is possible by augmenting the traditional turbo decoder with a nonlinear preprocessor. A computationally efficient version of such a receiver for reliable decoding of turbo coded, direct-spread data in non-Gaussian noise is investigated here. The noise is represented using Middleton class-A model and a parametric receiver is designed. Performance of such a scheme based on the system bit error rate is studied. View full abstract»

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  • Impact of Topology-dependent and independent Mobility Models on the Connectivity of Wireless Networks

    Publication Year: 2008 , Page(s): 1 - 5
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (291 KB) |  | HTML iconHTML  

    The performance of the algorithms developed for wireless ad hoc and sensor networks is strictly dependent upon the changes in the physical topology of such networks. In this work, the connectivity and average path length of a static wireless network is studied in the presence of overlaying mobile nodes. A topology-based mobility model is proposed and the performance is empirically compared with traditional mobility models, such as random walk, for grid, random, and degree- limited initial topologies for different network sizes. It is shown that the connectivity of randomly distributed wireless networks can significantly be improved even with a single additional mobile node. View full abstract»

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  • A Receiver-Oriented Rate-Adaptation Strategy for Improving Network Efficiency in Mobile Ad-Hoc Networks

    Publication Year: 2008 , Page(s): 1 - 5
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (292 KB) |  | HTML iconHTML  

    This article investigates the efficacy of a novel receiver-oriented adaptive-rate system for sustaining the quality of a randomly fluctuating wireless link at a prescribed level in generalized multipath fading channels. Multilevel hierarchical modulations inherently have a limited ability to facilitate passive rate-adaptation, and this attribute is exploited to improve the effective bit transmission rate at low and moderate carrier-to-noise ratios. In our scheme, the multiresolution source data is first matched to the unequal bit error protections of a multiresolution modulation, and in the presence of adverse channel conditions, the "less important" bits from the demodulated symbols are dropped in order to maintain the link bit error rate at the desired level. One of the salient features of our proposed link adaptation strategy is that it neither rely nor require any feedback of channel quality estimates from the receiver to the sender, and the performance improvement is achieved without dynamically altering the signal constellation size at the transmitter or by using error control coding with incremental redundancy. Moreover, the proposed link adaptation strategy can still be effective even in a rapidly time-varying environment since the received signal strength of each symbol at the demodulator input is used to decide on which demodulated bits of that symbol should be retained, and thus our rate adaptation is operated at the symbol level. The duality between the problems of finding 'optimal signaling in a delay constrained or unknown time-varying channels' and 'optimal signaling for broadcast/multicast channels' is also established. View full abstract»

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  • Wireless, Mesh & Ad Hoc Networks; Military Convoy Location and Situation Awareness

    Publication Year: 2008 , Page(s): 1 - 5
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (317 KB) |  | HTML iconHTML  

    Vehicular ad-hoc networks have become an emergent research topic as vehicle-to-vehicle communications (V2V) offer some unique advantages. These advantages include a slow/stopped vehicle advisor capability (which advises the driver when any vehicle ahead is stopped or traveling slower than 20 mph), an emergency electronic brake light (which notifies the driver when a vehicle ahead is suddenly braking hard), a lane change and blind spot advisor, an intersection collision warning, and a forward collision avoidance capability with automatic braking. The intent is to use these emergent commercial applications for the military and to improve the communication between military vehicles in various tactical situations. This paper adds to this area of study with some new practical findings pertaining to vehicular networks, specifically convoy communications and unmanned vehicle control. Besides considering of principles and rules of military convoys, experiments and simulations with military scenarios are necessary to improve vehicular networking for the military use. Global Positioning Systems (GPS) tracing has become a key point in this field as we look at GPS traces and their effects on throughput improvement and reliability on vehicular communications. These issues were analyzed through experiments using the ORBIT testbed. View full abstract»

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  • Issues and Improvements in TCP Performance over Multihop Wireless Networks

    Publication Year: 2008 , Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    TCP performance in contention-based multi-hop wireless networks is shaped by two main factors, which are unlike the wired network case. First, the maximum throughput for a given topology and flow pattern is reached at an optimal congestion window. We provide an improved analysis of this effect. Second, the control traffic uses higher proportion of the channel bandwidth than in the wired case. Our results show that the much smaller TCP ACKpackets consume channel resource comparable to the much longer data packets, over high-speed connections. Motivated by this understanding, we reformulate and enhance an existing idea for improving TCP performance by further lowering the number of control packets. Extensive simulations show that our strategy increases the TCP throughput up to 205% compared to the regular TCP, in long-hop wireless networks and 35% in a complex network. View full abstract»

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  • An Algorithm for Sensing Coverage Problem in Wireless Sensor Networks

    Publication Year: 2008 , Page(s): 1 - 5
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (720 KB) |  | HTML iconHTML  

    Wireless sensor networks (WSNs) have been widely studied and usefully employed in many applications such as monitoring environment, embedded system and so on. In WSNs, substantial nodes are deployed randomly over the entire desired area; therefore, the sensing regions of different nodes may be partially overlapped. This is referred to as the sensing coverage problem. In this paper we first define a maximum sensing coverage region problem (MSCR) in WSNs and then solve the problem by the proposed algorithm. In our method, the maximum monitored area fully covered by a minimum active sensors. The main design features are: selecting a small number of delegated sensor nodes by identifying and removing redundant nodes in high-density networks and assigning them an off-duty operation while guarantees the whole area is k-covered, to make sure all events occurred in that area can be accurately and timely detected. We apply the proposed algorithm to improve LEACH, a hierarchical protocol for WSNs and develop a simulation program to evaluate the performance of the algorithm. View full abstract»

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  • Implementation of the Distributed Hash Tables on Peer-to-peer Networks

    Publication Year: 2008 , Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (137 KB) |  | HTML iconHTML  

    This paper is an examination of the Koorde distributed hash table protocol, "an extension of the Chord protocol" and "a scalable peer-to-peer lookup service" designed to be employed by Internet applications. The Koorde extension uses deBruijn graphs to improve the efficiency of the basic Chord algorithm. The two protocols are described and their basic operation are constructed in Java classes so that their operation may be analyzed and compared using simulations that is developed to roughly represent common communication sessions between peers over the Internet. Simulations are run comparing the hop counts of accessing different numbers of possible nodes and percentages of live nodes using the Chord or its Koorde extension. View full abstract»

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  • Forwarding Strategies for Uplink Gaussian Multi-source Multi-relay Network

    Publication Year: 2008 , Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB) |  | HTML iconHTML  

    In this paper, we introduce the multi-source multi- relay channel model. In this model, the transmit signals of all users are received at multiple distinct relays. Each of these transmit signals can be either decoded or amplified at any one or a combination of the relays and then forward to the destination. For both decode-and-forward and amplify-and-forward strategies applied at the relays, we provide schemes to compute their achievable regions respectively. The achievable regions for both strategies are then compared by numerical simulations in both symmetric and asymmetric channel scenarios. Our numerical results show that when the power constraints of the relays are small, we can achieve larger rates by using decode-and-forward. Further, decode-and-forward is strictly optimal for the maximal sum rate since it can achieve the capacity outer bound. When the power constraints of the relays are large, amplify-and-forward outperforms decode-and-forward in general. For decode-and- forward, the optimal rates are achieved by forwarding the signals using the maximal power available at the relays. However, for amplify-and-forward, the power should be carefully adjusted to maximize the achievable rates. View full abstract»

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  • Multicast Planning for Mission-Critical Networks

    Publication Year: 2008 , Page(s): 1 - 5
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (595 KB) |  | HTML iconHTML  

    In this paper, considering user vicinity information, maximum tolerable unwanted traffic, and routing overhead, we introduce a new two-stage multicast group planning technique which has many applications in tactical networks (TN) used in the future battlefield networks (FBN). We formally define channelization problem with respect to no false exclusion and minimum false inclusion requirements. We address: (i) selection of the number of multicast groups, (ii) adaptation of the mapping algorithms to the networks with different characteristics, and (Hi) reduction of the computational complexity of the mapping algorithms. Our approach results in scalable group configurations based on the availability of resources in the network. Simulation results show that it is cost-effective and generates multicast groups of smaller sizes, which are easier to maintain especially in mobile ad hoc networks (MANETs), than other greedy approaches for the same amount of unwanted traffic per user. View full abstract»

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