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Communications Letters, IEEE

Issue 1 • Date January 2011

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Displaying Results 1 - 25 of 37
  • Table of contents

    Page(s): c1 - c4
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    Freely Available from IEEE
  • Staff List

    Page(s): c2
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    Freely Available from IEEE
  • Photonic CDMA Systems with Security Physical Layers

    Page(s): 1 - 3
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (431 KB) |  | HTML iconHTML  

    Cryptographic schemes based on classical information transmission and physical entities are addressed. This scheme provides ways to detect the extent of eavesdropping and does not entirely rely on computational complexity. Its implementations in photonic code division multiple access (CDMA) systems are suggested and secure key distributions under multiplexing environments are examined. View full abstract»

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  • NAT-Compatibility Testbed: An Environment to Automatically Verify Direct Connection Rate

    Page(s): 4 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB) |  | HTML iconHTML  

    In this article, an NAT-compatibility testbed is designed to automatically conduct the repeated experiments, collect the test results, and verify the direct connection rate (DCR) of any NAT traversal programs. Achieving a high DCR is important because using relays may unnecessarily increase the bandwidth cost, processing load of the relay servers, and the end-to-end packet delay. The NAT-compatibility testbed is constructed with 4 components: two peers, an automatic execution mechanism, NAT devices, and signaling/intermediate servers such as STUN, TURN, and SIP. It is also called the fully meshed testbed because the test result of all NAT combinations is a square. It measures the DCR of ICE, KeyStone, and PJNATH as 53.7%, 59.87%, and 50.93%, respectively. Experimental results show that asymmetric and unexpected direct connectivity check results occur in the real Internet. In order to enhance NAT traversal capability, the findings, like "port prediction" and "call-role sensitivity problem," are also described in the experimental results. View full abstract»

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  • Packet Error Probability in a Three-Branch Diversity System with Majority Combining

    Page(s): 7 - 9
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (142 KB) |  | HTML iconHTML  

    In this paper, we derive a closed-form expression for the packet error probability in a three-branch diversity transmission scheme with distinct bit error probabilities in each branch and a majority combining technique implemented on a data link layer. Based on the derived expression and its approximate form, we also demonstrate that the proposed technique reduces the packet error probability by a factor numerically equal to one third of the packet size, compared to the conventional selection combining. View full abstract»

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  • Symbol Error Probability of QAM with MRC Diversity in Two-Wave with Diffuse Power Fading Channels

    Page(s): 10 - 12
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (225 KB) |  | HTML iconHTML  

    In the context of two-wave with diffuse power (TWDP) fading scenarios, this letter analyzes the average symbol error probability (SEP) of rectangular quadrature amplitude modulation (QAM) for single- and multi-channel receptions. Specifically, novel exact expressions are derived for the average SEP in nondiversity and maximal-ratio combining (MRC) schemes. Our derived SEP results apply to general operating scenarios with distinct TWDP fading parameters and arbitrary number of diversity branches. View full abstract»

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  • Frequency Planning Scheme Based on Interference Coordination for OFDM-Relay Systems

    Page(s): 13 - 15
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (441 KB) |  | HTML iconHTML  

    A novel intra-cell frequency planning scheme based on interference coordination is exploited for cellular Orthogonal Frequency Division Multiplexing (OFDM)-Relay systems. In this strategy, a factor RI is introduced to model the interference in the 2nd slot. According to RI and the signal-to-interference-plus-noise ratio, the scheduler groups all the users into three sets. Furthermore, the total spectrum in the 2nd slot is divided into three parts based on the size of user sets, so that the frequency recourses in access links are reused properly. Simulation results show that the proposed method enhances the system performance in terms of both system capacity and cell edge users' SINR, with low overheads and computational complexity. View full abstract»

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  • A New Lower Bound on Range-Free Localization Algorithms in Wireless Sensor Networks

    Page(s): 16 - 18
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (174 KB) |  | HTML iconHTML  

    This letter examines the lower bound on localization error, which is an important performance measure for localization algorithms. Unlike some previous works based on the circular coverage model, we consider a more realistic scenario where radio propagation is subject to log-normal shadow fading. In this letter, we present an analytical expression for the distribution of lower bound on localization error for any range-free localization algorithm in WSNs. Finally, the derivation is validated through simulations. View full abstract»

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  • Gradient-Based Threshold Adaptation for Energy Detector in Cognitive Radio Systems

    Page(s): 19 - 21
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB) |  | HTML iconHTML  

    Cognitive Radio (CR) systems have been proposed to enable flexible use of the frequency spectrum in future generations of wireless networks. These are expected to detect spectrum bands that are not actively used by licensed (primary) users and provide unlicensed (secondary) users access to these bands. In this context it is important for the CR systems to promptly react to changes in the operating environment and to adapt to the changing patterns of spectrum use. This motivates the work presented in this paper, which studies adaptation of the detection threshold for energy-based spectrum sensing in dynamic scenarios under constraints imposed on the probabilities of missed detection and false alarm. View full abstract»

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  • Symbol Error Probability of Two-Way Amplify-and-Forward Relaying

    Page(s): 22 - 24
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (234 KB) |  | HTML iconHTML  

    The overall outage probability (OOP) and symbol error probability (SEP) of a two-way amplify-and-forward (AF) relaying system are investigated. Tight closed-form expressions for the OOP and average SEP are derived for single-relay two-way AF systems. Further, in the case of multiple-relay two-way relaying, a tight closed-form expression for the OOP and an asymptotic approximation to the average SEP are obtained, respectively. Using these expressions, one can evaluate the outage and SEP performance of a two-way relaying system easily and fast. View full abstract»

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  • On Modeling Malware Propagation in Generalized Social Networks

    Page(s): 25 - 27
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB) |  | HTML iconHTML  

    A hybrid malware on smart phones can be propagated by both end-to-end messaging services via personal social communications and short-range wireless communication services via spatial social interactions. Inspired from epidemiology, we propose a novel differential equation-based model to analyze the mixed behaviors of delocalized infection and ripple-based propagation for the hybrid malware in generalized social networks consisting of personal and spatial social relations. Validated by simulations, our model serves as the very first analytical model successfully approximating the complicated propagation behaviors of the hybrid malware. View full abstract»

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  • Secure Network Coding in DTNs

    Page(s): 28 - 30
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (150 KB) |  | HTML iconHTML  

    The application of network coding can significantly improve the performance of message delivery in delay tolerant networks, assuming all participants behave honestly. However, if some nodes of the network are compromised, the adversary can launch pollution attack and this way can destroy large amount of data with small effort. Current solutions against pollution attack require public key infrastructure, that is often not available in mobile ad-hoc networks. Our proposal allows packets to verify each other, hence an intermediate node can decide whether these packets can be encoded together without authenticating the source. View full abstract»

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  • Fast Mobility Management for Delay-Sensitive Applications in Vehicular Networks

    Page(s): 31 - 33
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (339 KB) |  | HTML iconHTML  

    This letter presents a fast IP mobility management scheme in vehicular networks where multiple wireless network interfaces are used to perform the fast handover without packet loss. In order to do that, the IETF standard HMIPv6 has been extended, where multiple simultaneous tunnels between the HMIPv6 MAP and the mobile gateway are dynamically constructed. The architecture for supporting multiple tunnels has been designed, and both mathematical analysis and simulation have been done for performance evaluation. View full abstract»

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  • SER Analysis of the Mobile-Relay-Based M2M Communication over Double Nakagami-m Fading Channels

    Page(s): 34 - 36
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (259 KB) |  | HTML iconHTML  

    It has been shown that mobile-to-mobile (M2M) communications, where scatters are both around the transmitter and the receiver, may experience more severe channel fading than the fixed-to-mobile (F2M) communications. Double Nakagami-m fading is adopted to provide a realistic description of the M2M channel. By using the moment generating function (MGF) based approach, the exact symbol error rate (SER) expression, which can be numerically evaluated, is derived for the considered mobile-relay-based M2M system. Moreover, the asymptotic SER bound is provided at a high SNR regime for the insight of our approach. According to our analysis, an asymptotic diversity order of 2 × min(m1, m2) can be achieved in case of independent identically distributed (i.i.d) channels. Numerical studies illustrate that analytic results exactly match the simulations. View full abstract»

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  • A Simple and Robust Equal-Power Transmit Diversity Scheme

    Page(s): 37 - 39
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (222 KB) |  | HTML iconHTML  

    Spatial diversity techniques are now used in most wireless communications systems to improve robustness to signal fading. On the downlink of cellular systems, low-cost requirements of the user terminal tend to favor transmit diversity over receive diversity, and Alamouti's transmit diversity technique appears today in most wireless communications systems standards. But in terms of the total transmit power, Alamouti's technique loses 3 dB with respect to optimum transmit diversity which requires perfect Channel State Information (CSI) at the transmitter. In this paper, we introduce a simple transmit diversity technique that relies on simple power measurements at the receiver which comes very close to optimum transmit diversity performance when assuming perfect CSI is available at the transmitter while relaxing the transmit power requirements by 3 dB. In this technique, the same power is transmitted from the two antennas and the phase difference of the signals received from the two channels is constrained to be smaller than π/N, where N is a predefined parameter. Its performance is studied in narrowband fading channels, in OFDM systems operating on frequency-selective channels, and in the presence of channel estimation errors. View full abstract»

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  • Blind Detection for Primary User Based on the Sample Covariance Matrix in Cognitive Radio

    Page(s): 40 - 42
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (315 KB) |  | HTML iconHTML  

    In this letter, a new blind sensing method based on the Cholesky factorization of the sample covariance matrix is presented for cognitive radios (CR). The proposed method overcomes the noise uncertainty problem of the energy detector (ED) and can also perform well without information about the channel, the primary signal and the noise power. Most importantly, unlike other detectors based on the sample covariance matrix (including the covariance absolute value (CAV), the maximum-minimum eigenvalue (MME), and the maximum eigenvalue trace (MET) detectors), the decision threshold for the proposed detector can be determined using an exact non-asymptotic expression without any asymptotic assumptions on the sample size and the sample dimension. Numerical simulations show the superiority of the new detector to the CAV, MME and MET detectors. View full abstract»

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  • Impact of Limiting Number of Links on the Lifetime of Wireless Sensor Networks

    Page(s): 43 - 45
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (294 KB) |  | HTML iconHTML  

    The lifetime of wireless sensor networks (WSNs) is optimized if the traffic within the network is adjusted in a way that all nodes dissipate their energies in a balanced fashion. To balance the energy dissipation, nodes split their flows and these flows are forwarded to different nodes acting as relays. In consequence some nodes have too many incoming and/or outgoing links. In this letter we investigate the impact of limiting the number of incoming and outgoing links of nodes on the network lifetime of WSNs through a Mixed Binary Linear Programming (MBLP) framework. Our results show that the decrease in WSN lifetime is less than 1.0% if the limits on the number of incoming and outgoing links are not lower than three. View full abstract»

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  • Closed-Form BER Analysis of Alamouti-MRC Systems with ICSI in Ricean Fading Channels

    Page(s): 46 - 48
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (233 KB) |  | HTML iconHTML  

    In this letter, we derive an exact closed-form expression for the bit error rate (BER) of an M-ary quadrature amplitude modulation (QAM) multiple-input multiple-output (MIMO) 2×NR system that employs Alamouti's space time block code (STBC) transmission and maximal ratio combining (MRC) reception, when imperfect channel state information (ICSI) is considered in a Ricean fading channel. An approximate yet accurate expression for the BER is also provided when a strong line of sight (LOS) component is considered. It is observed that the loss of orthogonality of Alamouti's code due to ICSI leads to a non-negligible noise enhancement. View full abstract»

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  • An Iterative Hungarian Algorithm Based Coordinated Spectrum Sensing Strategy

    Page(s): 49 - 51
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (171 KB) |  | HTML iconHTML  

    Coordinated spectrum sensing ensures Cognitive Radio systems to get the usability of every channel within the entire spectrum of interest by assigning terminals to detect different channels simultaneously. This letter proposes an optimized channel-assignment strategy for coordinated spectrum sensing based on an Iterative Hungarian Algorithm. Simulation results show that the proposed strategy performs excellently in improving the overall sensing performance of the system. View full abstract»

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  • Toward Increasing Packet Diversity for Relaying LT Fountain Codes in Wireless Sensor Networks

    Page(s): 52 - 54
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (190 KB) |  | HTML iconHTML  

    Diversity is a powerful means to increase the transmission performance of wireless communications. For the case of fountain codes relaying, it has been shown previously that introducing diversity is also beneficial since it counteracts transmission losses on the channel. Instead of simply hop-by-hop forwarding information, each sensor node diversifies the information flow using XOR combinations of stored packets. This approach has been shown to be efficient for random linear fountain codes. However, random linear codes exhibit high decoding complexity. In this paper, we propose diversity increased relaying strategies for the more realistic and lower complexity Luby Transform code in a linear network. Results are provided herein for a linear network assuming uniform imperfect channel states. View full abstract»

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  • Performance Analysis of Wireless Systems from the MGF of the Reciprocal of the Signal-to-Noise Ratio

    Page(s): 55 - 57
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (189 KB) |  | HTML iconHTML  

    A class of wireless problems is characterized by the availability of the moment generating function (MGF) of the reciprocal of the signal-to-noise ratio. We show how to compute the average error rates and outage probability in this case. The result allows a simple, accurate numerical calculation of the average error rate by using the Gauss-Legendre numerical quadratures. We also derive the exact bit error rate of multihop relays for the special case where the fading index of each hop is an odd multiple of one-half. View full abstract»

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  • Joint Transmit/Receive Antenna Selection for MIMO Systems: A Real-Valued Genetic Approach

    Page(s): 58 - 60
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (225 KB) |  | HTML iconHTML  

    This study proposes a new antenna selection (AS) method using the real-valued genetic algorithm (RVGA) to improve the channel capacity of multiple-input/multiple-output (MIMO) systems. By defining a score function based on channel capacity, AS can be formulated as an optimization problem over a multidimensional real space, and solved by implementing the RVGA method. The simulation results show that the performance of the proposed RVGA AS provides approximately the same achievable rates as the optimal exhaustive search (ES) AS, while maintaining a moderate computational load. View full abstract»

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  • Routing Selection with Overloading Cancellation for Multihop Cellular Systems

    Page(s): 61 - 63
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (234 KB) |  | HTML iconHTML  

    Instead of the traditional cellular system, the multihop cellular architecture with multiple distributed relay stations (RSs) can potentially augment coverage, data rates, and quality of service (QoS). However, the RS overloading matter may cause a system malfunction. In this letter, the RS overloading problem is considered and a simple routing selection with overloading cancellation is proposed for enhancing system capacity and QoS. View full abstract»

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  • Increasing the One-Hop Progress of Nearest Neighbor Forwarding

    Page(s): 64 - 66
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (179 KB) |  | HTML iconHTML  

    Nearest neighbor forwarding (NNF) intends to maximize throughput in wireless networks. However, NNF suffers from low one-hop progress and may therefore significantly increase end-to-end delay. The spatial efficiency (SE), i.e., the expectation of the ratio of progress to interference area associated with one hop, is introduced in order to quantify this trade-off. The problem of low progress is addressed by maximizing the one-hop SE, subject to the central angle γ, determining the forwarding area. By this, the optimal balance between minimizing the interference area and maximizing progress is found. Then, this analysis is extended by considering a Poisson point process, driven by some traffic intensity, on the interference area. Furthermore, the traffic aware γ*-NNF strategy is proposed which adapts γ to the traffic intensity in order to maximize SE. Simulation results show a significant reduction of the end-to-end delay if γ*-NNF is used. View full abstract»

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  • Exact Decoding Probability Under Random Linear Network Coding

    Page(s): 67 - 69
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (174 KB) |  | HTML iconHTML  

    In this letter, we compute the exact probability that a receiver obtains N linearly independent packets among K ≥ N received packets, when the sender/s use/s random linear network coding over a Galois Field of size q. Such condition maps to the receiver's capability to decode the original information, and its mathematical characterization helps to design the coding so to guarantee the correctness of the transmission. Our formulation represents an improvement over the current upper bound for the decoding probability, and provides theoretical grounding to simulative results in the literature. View full abstract»

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George K. Karagiannidis
Aristotle University of Thessaloniki
Greece