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Cognitive Wireless Systems (UKIWCWS), 2009 First UK-India International Workshop on

Date 10-12 Dec. 2009

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  • [Front cover]

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  • [Title page]

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  • A diversity analysis for block-fading Amplify-and-Forward systems

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (190 KB) |  | HTML iconHTML  

    In this paper, we deal with the performance of nonorthogonal Amplify-and-Forward (NAF) protocols over block-fading channels. In contrast with previous studies, which assume that the channel remains constant over the whole cooperative frame, here we relax this constraint and assume a block fading channel which changes during the cooperation. Despite this additional channel diversity degree, channel inversion amplification schemes are unable to increase the diversity gain of the system due the high correlation between the two simultaneous diversity branches. We propose a fixed gain amplification factor which efficiently uses the additional diversity degree of the channel and recovers the diversity loss associated with channel inversion schemes. The diversity analysis is based on some well-defined capacity bounds which follow the diversity order of the true capacity. View full abstract»

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  • A hybrid energy detection approach to spectrum sensing

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    This paper introduces a hybrid energy detection approach to spectrum sensing in cognitive radio. Conventional energy detection technique (with N samples) is based on two hypotheses - i) where all N are signal samples corrupted by noise, ii) where all N are noise-only samples. Based on these two hypotheses a threshold is set for declaring a given N-sample signal as belonging to either of the two cases. This paper considers those cases which occur in practice - M samples out of N being signal corrupted with noise and the rest being noise-only, 0 ≤ M ≤ N, thus covering the conventional two hypotheses as well. The method described here, referred to as “hybrid energy detection”, proposes a combination of a 32-sample detector with a 16-sample detector which yields an improvement in performance in most such mixed signal-noise cases. The “hybrid energy detection” method requires certain thresholds to be set, in order to maximize the gain. We use simulated annealing to find those threshold values. The cost function used for simulated annealing takes into consideration the ratio of sensing time interval to transmit time interval in the secondary user. View full abstract»

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  • A new degree distribution for LT codes for broadcasting in ad-hoc network using network coding

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (227 KB) |  | HTML iconHTML  

    In this paper we consider a network in which one of the nodes wants to send a packet to all the other nodes in the network by broadcasting the packet. At each instant one of the nodes acts as a source and transmits a packet which has to be received by all the other nodes in the network We propose a new distribution for LT codes to perform network coding in a distributed manner. Using LT codes which are fountain codes for Network coding at source independent backbone with our particular distribution decreases the number of transmission required to broadcast the packet. Also this distribution allows a better control on the average degree of encoded packets. We carry out simulations to corroborate our idea. View full abstract»

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  • A novel multiple access scheme using MSE-OFDM for uplink

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (122 KB) |  | HTML iconHTML  

    This paper presents a novel multiple access scheme for uplink of future mobile communications using MultiSymbol Encapsulated Orthogonal Frequency Division Multiplexing (MSE-OFDM). MSE-OFDM is a bandwidth efficient OFDM scheme, where a number of OFDM symbols are grouped together as a frame and protected by one single cyclic prefix (CP). This reduces the extent of redundancy caused by the CP and increases the bandwidth efficiency of the system. In the proposed scheme, a number of OFDM symbols from one user are grouped and one cyclic prefix is used for a group of symbols. Thus, we can get better spectral efficiency as compared to conventional OFDMA. The FFT size is also reduced, which improves the robustness to synchronization errors and reduces the PAPR. View full abstract»

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  • Adaptive subcarrier and bit allocation techniques for MIMO-OFDMA based uplink cognitive radio networks

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (129 KB) |  | HTML iconHTML  

    We propose an adaptive radio resource allocation algorithm for a multiple-input multiple-output (MIMO) orthogonal frequency division multiple access (OFDMA) based uplink cognitive radio network (CRN). The CRN has multiple secondary users (SUs) coexisting with multiple primary users (PUs). The aim is to admit as many SUs as possible in various subcarriers while ensuring no interference is leaked to PUs. This is achieved by letting the SUs to transmit signals through the null-space of the channels seen between SUs and the primary network basestation (PNBS). Subcarriers are allocated based on the correlation coefficient of the left singular vector of the MIMO channels seen between various SUs and the secondary network basestation (SNBS). Once the SUs are allocated in various subcarriers, the radio resource management in terms of power and bit allocation is performed on a per user basis using an integer linear programming framework. The performance of the algorithm has been evaluated using simulation results. View full abstract»

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  • An efficient spectrum mobility management strategy in cognitive radio networks

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (222 KB) |  | HTML iconHTML  

    In this paper, we propose to design a spectrum mobility strategy using Fuzzy Logic System for cognitive radio networks (CRN). The proposed strategy enables cognitive radios (CR) to vacate the spectrum if primary user (PU) needs it back or to adjust its transmit power in order to avoid interference with PU or nearby CR. Using our scheme, CR switches between the bands only if it is not able to modify its transmit power within the tolerable interference limits. Thus, our work is divided in two modules, one with the priority to control CR transmit power within tolerable range and second to switch to another frequency band in order to avoid interference. Simulated results show that using our proposed fuzzy power control scheme, we can decrease transmit power consumption and achieve lower number of spectrum handovers. View full abstract»

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  • Application of distributed MIMO waterfilling algorithm for broadband channels and its performance in the presence of CSI errors

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    A method for the application of the MIMO iterative waterfilling algorithm for broadband channels is presented. The modified game-theoretic problem formulation and its Nash equilibrium are presented, along with conditions for its existence and uniqueness and for the convergence of the distributed algorithm. The method is verified using a simple design example. The performance of the MIMO iterative waterfilling algorithm in the presence of errors in the channel state information (CSI) is also presented. View full abstract»

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  • BER performance of regenerative multi-antenna cooperative relay network in Rayleigh fading channel

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    BER performance of cooperative relay network, employing infrastructure based fixed relays having multiple antennas has been investigated. Closed form expression for average BER has been derived, when destination is assumed to perform selection combining of the signals, received from direct path and through relay path. BER expressions are derived for both the cases of selection and maximum ratio combining at the relay terminal. The effect of relay placement on the system performance has also been studied under different path loss conditions. View full abstract»

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  • Clustered and leveled disjoint multipath routing algorithm for wireless sensor networks

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (323 KB) |  | HTML iconHTML  

    As the complexity of the wireless sensor networks increase, in routing protocols increase. Since energy efficiency is the primary criteria in performance of the network, any saving in energy is highly desirable. Sensor networks consists of nodes in which have limited computational power and are limited in energy resource. The transmission of data packets to the base station with the minimum possible energy and least possible delay are the goals of efficient routing algorithms. The data collected by each node is communicated through the network to the base station which processes it to gather information about the network or to detect an event in the environment. In this paper we propose a new routing scheme which exploits the redundancy and geometrical properties of the wireless network. The approach we take is to combine the ideas of directional flooding, leveling, clustering and disjoint multipath routing to achieve an optimal routing scheme in terms of average energy consumed and total number of transmitted packets. Processing and structuring of the network before the implementation of the directional flooding algorithm improves the performance considerably when compared to the implementation of directional flooding algorithm without any preprocessing. We carry out extensive experimentation and simulations to corroborate our claims. View full abstract»

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  • Cognitive radio as common information exchange reference model for interoperability between hetrogeneous networks

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    This paper presents the application of cognitive radio (CR) in interoperability between two heterogeneous networks. We have used CR as a common information exchange platform to ensure interoperability between IEEE 802.11b (Wi-Fi) and IEEE 802.16a (Wi-Max) networks in the same shared frequency band. CR is used to link these two networks which are considered out of reach from each other. We compare the performance of complete network in different scenarios simulated with varying number of constant bit raThis paper presents the application of cognitive radio (CR) in interoperability between two heterogeneous networks. We have used CR as a common information exchange platform to ensure interoperability between IEEE 802.11b (Wi-Fi) and IEEE 802.16a (Wi-Max) networks in the same shared frequency band. CR is used to link these two networks which are considered out of reach from each other. We compare the performance of complete network in different scenarios simulated with varying number of constant bit rate (CBR) applications. Different matrices for comparison are throughput, end to end delay and jitter. Further to this, equal traffic is generated to compare the throughput of Wi-Max and Wi-Fi subnets.te (CBR) applications. Different matrices for comparison are throughput, end to end delay and jitter. Further to this, equal traffic is generated to compare the throughput of Wi-Max and Wi-Fi subnets. View full abstract»

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  • Collaborative spectrum sensing in OFDM-based Cognitive Radio

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    The rapid increase in the number of wireless devices highlights the importance of intensive dynamic use of the available spectrum. One technology to implement dynamic spectrum access is Cognitive Radio (CR). One of the main challenges of CR is gaining spectrum awareness, thus being able to undertake reliable and sufficiently sensitive spectrum sensing. In this paper, an OFDM-based CR system exploiting the inherent cyclic prefix (CP) and idle period of the transmission signals is proposed, assuming a realistic fading channel. Furthermore, collaborative spectrum sensing has been studied based on the proposed methodology, in the presence of Rayleigh fading and log-normal distributed shadowing. The simulation results indicate that the probability of detection can be significantly improved while maintaining the level of interference protection to the primary users by including the CP and idle period in the sensing time in both slow and fast fading channels. Moreover, collaboration of multiple secondary users improves the sensitivity of the sensing algorithm in terms of minimum detectable SNR. The analyses provided in this paper show that collaboration among 10 users facilitates detection at lower SNR levels up to -10 dB with 0.9 probability of correct detection and 0.1 probability of false alarm. View full abstract»

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  • Collaborative spectrum sensing: Optimising the number of collaborating users

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    In the IEEE 802.22 standard, the spectrum sensing mechanism is identified as a key functionality of a cognitive radio. Due to the channel uncertainty, a single cognitive user, in most cases, can not make a reliable decision and hence collaboration or cooperation of and among multiple users is required. However, when large number of cognitive users are collaborating with each other, the bandwidth requirements for sending their result to the fusion centre tends to be very large. In this paper, a metric for spectrum efficiency is defined and used for the optimisation of collaborative spectrum sensing. An optimisation algorithm is presented to calculate the optimal number of collaborating cognitive users with the aim to maximise overall spectrum efficiency by satisfying certain constraints in terms of global probability of detection and probability of false alarm. Numerical results show that for maximum spectrum efficiency collaboration of only a subset of the available cognitive users is required. View full abstract»

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  • Combined phase and code optimization for PAPR reduction in M-ary CI/MC-CDMA system

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (620 KB) |  | HTML iconHTML  

    This paper proposes a high capacity M-ary modulation based carrier interferometry/multicarrier code division multiple access (CI/MC-CDMA) system with reduced peak-to-average power ratio (PAPR). The new method simultaneously supports high and low data rate transmission. The implementation is done by allocating all sub-carriers to the users who transmit high data rate and alternate odd and even subcarriers are assigned to the other sets of users transmitting at low data rate. The usage of alternate sub-carriers suggests to split CI codes in odd and even parts leading to an increase in capacity. PAPR reduction is achieved through the combined use of (1) phase shift of subcarriers, odd CI code using odd sub-carriers by an amount of -π/2M, odd CI using even sub-carriers by an amount of -π/2M -π/2, even CI code using odd sub-carriers by -π/2M -π, and even CI code using even subcarriers by -π/2M -3π/2, all measured with respect to orthogonal codes supporting high data rate transmission and (2) left and right cyclic shift of the code pattern by an amount of one to three chips. Trellis coding is then applied for further improvement in PAPR values. Complementary cumulative distribution function (CCDF) for PAPR values are reported for different values of M through extensive simulation results. View full abstract»

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  • Cooperative change detection using physical layer fusion

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    This work presents a new approach to spectrum sensing for cognitive radios with multiple sensors under a change detection framework. Physical layer fusion is used at the fusion center in order to implement a cumulative sum based change detection algorithm. Two channel models, AWGN and quasi static block-fading, are considered for the channel between the sensors and the fusion center. Analytical expressions are obtained for determining the false alarm rate and worst case detection delay performance. Simulation results are presented to highlight the performance of the scheme. It is shown that this scheme achieves a performance close to that of a centralized change detection scheme in the case of an AWGN channel. View full abstract»

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  • Cooperative compressive spectrum sensing by sub-Nyquist sampling

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    Compressive Sensing (CS) is a novel framework shows that a Qb-point discrete time signal that is k-sparse, can be exactly recovered by using small amounts of linear projections. In this paper, we propose an aliasing-based distributed compressive spectrum sensing technique for Cognitive Radio (CR) networks. We firstly model the spectrum aliasing phenomenon as a linear projection from the ideal sampled spectrum to the sub-sampled spectrum. Then the necessary conditions for jointly reconstructing the spectrum without aliasing are provided. Rather than using separate compression device, the Analog-to-Digital Converters (ADCs) in our proposed method perform data compression as well as sampling. More important, with multiple receivers operating at sub-Nyquist sampling rates, the fusion centre can effectively recover the spectrum without aliasing. View full abstract»

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  • Cooperative spectrum sensing protocols in cognitive radio based on energy detection

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    Spectrum sensing is the most important task of a cognitive radio network that aims to opportunistic spectrum access (OSA), whereas it has been shown that cooperative spectrum sensing improves the performance of a secondary network. Recently, the idea of relaying has been introduced as a method for improving the detection of primary users in cognitive radio. In this paper, we propose a novel cooperative spectrum sensing protocol that exhibits improved performance compared to existing protocols. In this protocol, decision fusion is used to reach a final decision based on the decisions made in each time slot at the secondary user with the lower detection probability. An analysis, as well as simulation results are provided to demonstrate the improved performance of the proposed protocol compared to existing ones. View full abstract»

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  • Design issues in wide scanning range cognitive radios

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    Cognitive radios are being looked upon as the solution for the spectrum scarcity problem. Mitigating spectrum scarcity requires robust spectrum sensing receivers and frequency adaptive transmitters. Wideband cognitive radios are more attractive as they provide a wider range of secondary communication opportunities. They are accompanied by issues at the frontend architecture level, baseband distribution and spectrum sensing in the receivers. At a network level, the success of wideband cognitive radios are dependent on the network topology. This paper discusses these problems and provides guidelines for solving them. View full abstract»

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  • Dynamic spectrum allocation technique in cognitive radio networks

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (197 KB) |  | HTML iconHTML  

    We propose a novel algorithm to model the dynamic channel allocation problem in cognitive radio networks. In the proposed work, we define a unique model to assign priorities to the secondary users based on the required Quality of Service and on the interference delay to minimize the switching of secondary users. The proposed scheme also mitigates the delay of the licensed primary users due to minimized switching. View full abstract»

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  • Information theoretic analysis of cooperative relay in cognitive radio

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    Motivated by the inefficient usage of the licensed spectrum across many frequency bands, cognitive radio (CR) was proposed to promote the spectrum utilization by opportunistically exploiting the existence of spectrum “holes.” Under this new paradigm, cognitive (unlicensed) user is allowed unobtrusive access to a channel exhibiting negligible primary (licensed) user activity. Cooperative communication is increasingly regarded as a way to address hidden terminal issues and to improve spatial diversity for the same spectrum frequency band. In this paper, we investigate two scenarios of cooperation: cooperative transmission of primary traffic by cognitive users (cognitive relaying) and cooperative transmission between cognitive nodes. The first scenario focuses on one cognitive transmitter which has the option to relay traffic of the primary assuming that the primary is oblivious to its presence and thus exclude the possibility of spectrum leasing. While the latter investigates a spectrum-rich node that is selected as the relay node to improve the performance between the source and the destination. To demonstrate the feasibility and performance of cooperative relay for cognitive radio, numerical results based on information theory approach are provided in order to discuss the advantages and limits of the two strategies. View full abstract»

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  • Light Cognitive Radio enabled inter operator Flexible Spectrum Usage for IMT-Advanced

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    In this paper we propose a mechanism to enable Flexible Spectrum Usage (FSU) in Local Area (LA) indoor deployment scenario of International Mobile Telecommunications-Advanced (IMT-A) with several operators in the given geographical area. The proposed scheme is referred to as policy assisted light Cognitive Radio (CR) enabled FSU, because it follows the CR cycle and considers policy as an important element to assist FSU. It facilitates allocation of spectrum from a common pool in flexible manner and ensures coexistence of several operators in the given geographical area on the shared spectrum. It also provides an autonomous, self adjustable and scalable solution for the emerging large scale indoor deployment of Home eNode-Bs (HeNBs). View full abstract»

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  • MIMO two-way relaying in frequency selective environment using OFDM

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    This paper presents Orthogonal Frequency Division Multiplexing (OFDM) based two-way relaying scheme to communicate between two nodes S1 and S2 via MIMO Relay Station (RS) in a frequency selective environment. This scheme relies on two-hop relaying approach which uses two orthogonal channel resources to transmit and receive a signal. This scheme requires the channel state information (CSI) only at RS. Spatial filtering is implemented at the RS for transmit and receive processing which is evaluated using zero forcing (ZF) and minimum mean squared error (MMSE) criterion. MATLAB simulations are conducted to evaluate the validity of the algorithm using both criterions in presence of frequency selective environment. The simulation results depict that the algorithm under defined conditions performs better in a frequency selective fading environment with the use of OFDM. Also, the BER performance evaluated through spatial filtering done using MMSE is found to be better than its ZF counterpart. View full abstract»

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  • Minimax Probability Machine Regression for wireless traffic short term forecasting

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    Traffic can reflect the latent rules and characteristics of the wireless network. Through researching, we found that the more accurate traffic prediction, the higher efficiency, utilization rate of network bandwidth and QoS can be guaranteed. Therefore, how to construct predictive models of wireless network traffic exactly is a major research topic. In this paper, Minimax Probability Machine Regression (MPMR) is proposed for forecasting wireless network traffic in 802.11 networks. Experiment provides the performance of the forecasting model and gives some comparative analysis. It evidences that the model is feasible. And compared with SVM, MPMR can not only obtain an efficient and satisfactory prediction efficiency but also less errors than SVM. View full abstract»

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