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PHYSICS (576 journals)

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Journal Cover Physical Communication
  [SJR: 1.375]   [H-I: 15]   [1 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1874-4907
   Published by Elsevier Homepage  [2817 journals]
  • Models, statistics, and rates of binary correlated sources
    • Abstract: Publication date: Available online 19 April 2016
      Source:Physical Communication
      Author(s): Marco Martalò, Riccardo Raheli
      This paper discusses and analyzes various models of binary correlated sources, which may be relevant in several distributed communication scenarios. These models are statistically characterized in terms of joint Probability Mass Function (PMF) and covariance. Closed-form expressions for the joint entropy of the sources are also overviewed. The asymptotic entropy rate for very large number of sources is shown to converge to a common limit for all the considered models. This fact generalizes recent results on the information-theoretic performance limit of communication schemes which exploit the correlation among sources at the receiver.


      PubDate: 2016-04-21T23:28:35Z
       
  • Full-duplex communication for future wireless networks: Dynamic resource
           block allocation approach
    • Abstract: Publication date: Available online 13 April 2016
      Source:Physical Communication
      Author(s): Chandan Pradhan, Garimella Rama Murthy
      In this paper, we discuss a full-duplex (FD) communication scenario, where multiple FD user equipments (UEs) share same spectrum resources (or resource blocks) simultaneously. The FD eNodeB deploys digital precoding and successive interference cancellation with optimal ordering algorithm, to allow coexistence of multiple UEs in downlink and uplink, respectively. The sharing of same resource blocks, results in co-channel interference (CCI), in downlink of a UE, from uplink signals of other UEs. To mitigate the interference, a smart antenna approach is adopted. The approach includes using multiple antennas at UEs to form directed beams towards eNodeB and nulls towards other UEs. However, the approach fails when the UEs due to their mobility align themselves in the same direction with respect to the eNodeB (eNB). In this paper, we propose a dynamic resource block allocation (DRBA) algorithm for avoiding CCI due to mobility of UEs, sharing the spectrum resource, in a FD communication scenario. The proposed algorithm shows significant improvement of the quality of service (QoS) of the communication links.


      PubDate: 2016-04-17T22:34:31Z
       
  • Special issue on D2D-based offloading techniques
    • Abstract: Publication date: Available online 8 April 2016
      Source:Physical Communication
      Author(s): Vincenzo Mancuso, Omer Gurewitz



      PubDate: 2016-04-08T18:19:31Z
       
  • ECM and SAGE based joint estimation of timing and frequency offset for
           DMIMO-OFDM system
    • Abstract: Publication date: Available online 8 April 2016
      Source:Physical Communication
      Author(s): Sucharita Chakraborty, Debarati Sen
      Distributed multiple-input multiple-output (DMIMO) technology is a key enabler of coverage extension and enhancement of link reliability in wireless networks through distributed spatial diversity. DMIMO employs classic relay channels in between the source and the destination to opportunistically form a virtual antenna array (VAA) for emulating cooperative diversity. Use of multiple antennas at the relays further increases capacity and reliability of the relay-destination channel through multiplexing and diversity of MIMO antennas respectively. In such network, the signal received at the destination is characterized by multiple timing offsets (MTO) due to different propagation delay and multiple carrier frequency offsets (MCFO) due to independent oscillators of the relays. Hence, synchronization becomes a crucial issue in DMIMO in order to realize the distributed coherence. In this paper, we address joint estimation of MCFO and MTO in DMIMO orthogonal frequency division multiplexing (OFDM) with MIMO configuration at the relays for estimate-and-forward (EF) relaying protocol. Two iterative algorithms, based on expectation conditional maximization (ECM) and space alternating generalized expectation-maximization (SAGE) are proposed for joint estimation in presence of inter carrier interference (ICI). The robustness of both the estimators to ICI is evaluated by mathematical analysis and supported by extensive simulations. The performance of the proposed estimators are assessed in terms of mean square error (MSE) and bit error rate (BER). The theoretical Cramer-Rao lower bound (CRLB) of estimator error variance is also derived.


      PubDate: 2016-04-08T18:19:31Z
       
  • Guest Editorial for the special issue on Self-optimizing Cognitive Radio
           Technologies
    • Abstract: Publication date: Available online 22 March 2016
      Source:Physical Communication
      Author(s): Muhammad R.A. Khandaker, Kai-Kit Wong, Haitao Zhao, Shamik Sengupta



      PubDate: 2016-03-23T14:07:14Z
       
  • Time reversal acoustic communication receivers: DSP implementation and
           fast channel estimation
    • Abstract: Publication date: Available online 15 March 2016
      Source:Physical Communication
      Author(s): Sergio Matiz Romero, Mohsen Badiey, Aijun Song
      A communication system is implemented on digital signal processors (DSPs) for the underwater acoustic environment. The implemented receiver uses time reversal multi-channel combining followed by a single-channel decision feedback equalizer. Periodic channel estimation is employed to track the channel fluctuations. These techniques are used to mitigate time-varying inter-symbol interference, which is the main challenge in the underwater acoustic channel at operating frequencies greater than 10 kHz. Various optimization tasks are performed to reduce the receiver computational complexity. A fast implementation of the matching pursuit algorithm is tested on the DSP platform. Its performance, in terms of accuracy and run-time, is compared with that of the basic matching pursuit algorithm. Experimental results of the transmission and demodulation of binary phase-shift keying signals at three different symbol rates were obtained in the local Delaware Bay. The low bit error rates demonstrate the effectiveness of our implementation.


      PubDate: 2016-03-18T13:41:49Z
       
  • A fractional path-loss compensation based power control technique for
           interference mitigation in LTE-A femtocell networks
    • Abstract: Publication date: Available online 15 March 2016
      Source:Physical Communication
      Author(s): Sawsan Ali Saad, Mahamod Ismail, Rosdiadee Nordin, Afaz Uddin Ahmed
      Introduction of Femtocells in heterogeneous network enhances the capacity, indoor coverage of the existing macrocell based network. It also allows high-speed data services for the multi-media application and software. However, in dense co-channel deployment scenarios femtocells cause severe interference to the neighbouring cells users. In this paper, a downlink-power-control scheme is presented for femtocell with no overhead signalling exchange with the macrocell. The femtocell adjusts the transmit power subject to home user equipment (HUE) measurements. The minimum level of transmit power is determined by the target Signal to Interference and Noise Ratio (SINR) of femtocell user that is set according to the required Quality of Service (QoS) of the femtocell users. The system level simulations confirm that, the proposed scheme reduces the outage probability of the nearby macrocell user equipment (MUE) up to 16.7% compared to fixed power setting, while maintaining the spectral efficiency of femtocell users. Furthermore, the transmit power can be reduced by 52.6% which leads to power effective solution of the interference scenario.


      PubDate: 2016-03-18T13:41:49Z
       
  • Inherent diversity combining techniques to mitigate frequency selective
           fading in chaos-based DSSS systems
    • Abstract: Publication date: Available online 3 March 2016
      Source:Physical Communication
      Author(s): Stevan M. Berber, Ankur K. Gandhi
      Analysis of communication systems with combiners, assuming flat fading channels, is well-known. However, this analysis for a chaos-based DSSS system with a frequency selective channel, giving proper mathematical model and derived expressions for the probability of error, practically does not exist. This paper presents the theoretical model of a chaos-based DSSS system assuming frequency selective channel that is composed of a primary channel and a number of secondary channels. In order to investigate the consequences of delays on signal transmission in these channels, this paper uses presentation of signals in discrete time domain and theoretical frame of discrete time stochastic processes. The channel is represented by a modified Saleh-Valenzuela model, which results in a number of delayed signal replicas at the receiver side. For the sake of explanation, the delays are assumed to remain in a chip interval. For the sake of comparison, the theoretical models and derived expressions are confirmed by the simulation of the system.


      PubDate: 2016-03-08T11:01:57Z
       
  • From conceptual to operational: Over-the-air-programming of land mobile
           radios
    • Abstract: Publication date: Available online 24 February 2016
      Source:Physical Communication
      Author(s): Jeremy Carter, Eric Grommon, Phil Harris
      Programming, management, and interoperability of land mobile radios within the public safety sector has long been a salient issue for policymakers, practitioners, service vendors, and scholars. Despite receiving substantial attention in the form of government expenditure and agency task forces, there has only been moderate advancement in this concerning area. Recently, as part of a U.S. Department of Justice-funded effort, an innovative technology known as wireless broadband over-the-air-programming (OTAP) has been translated from a conceptual model to an operational deployment. OTAP technology holds significant promise to enhance the management of public safety communications via land mobile radios. This research presents the concept of OTAP, the engineering behind the recently developed broadband enabled OTAP prototype, and conceptualizes how this technology can impact the processes used to facilitate public safety interoperability within the context of portable radio programming.


      PubDate: 2016-02-26T17:49:59Z
       
  • Editorial Board
    • Abstract: Publication date: March 2016
      Source:Physical Communication, Volume 18, Part 2




      PubDate: 2016-02-20T15:28:40Z
       
  • Cooperative spectrum sensing protocols and evaluation with IEEE 802.15.4
           devices
    • Abstract: Publication date: Available online 10 February 2016
      Source:Physical Communication
      Author(s): Tahir Akram, Tim Esemann, Horst Hellbrück
      Spectrum Sensing is one of the important tasks for wireless devices. By sensing the spectrum, wireless devices sense their radio environment and perform spectrum access accordingly to reduce collisions. Due to radio propagation effects and inherent noise in the measurements, performance of todays wireless technologies with individual spectrum sensing cannot solve the hidden node problem. Cooperative sensing is seen as a way to improve the performance of wireless devices improving the radio bandwidth utilization and minimizing interference among wireless devices. To the best of our knowledge, this is the first work which provides protocols for cooperative sensing and presents experimental results with IEEE 802.15.4 devices. We present and implement protocols and applications for primary, secondary and cooperative users with a dedicated control channel. Thereby, the secondary user receiver serves as a first cooperative node in the system which reduces collisions between primary and secondary users. We evaluate the system performance with receiver sensing and additional cooperative nodes. We also propose a mechanism to extend the protocol for multiple secondary users sharing the same control channel. Based on the evaluations, we also provide recommendations for usage of cooperative sensing with focus on IEEE 802.15.4.


      PubDate: 2016-02-15T14:14:26Z
       
  • Editorial Board
    • Abstract: Publication date: March 2016
      Source:Physical Communication, Volume 18, Part 1




      PubDate: 2016-02-15T14:14:26Z
       
  • PHYCOM editorial for 2015
    • Abstract: Publication date: March 2016
      Source:Physical Communication, Volume 18, Part 1
      Author(s): Ian F. Akyildiz



      PubDate: 2016-02-15T14:14:26Z
       
  • Analytical study of a service discovery system based on an LTE-A D2D
           implementation
    • Abstract: Publication date: Available online 1 February 2016
      Source:Physical Communication
      Author(s): Salam Doumiati, Hassan Artail
      This work adapts the paradigm of Cloud Computing over the framework of Device-to-Device (D2D) proximity-based communications in order to offer proximity services to LTE network subscribers, and offload major traffic from the core network. Our proposed work introduces a platform in which mobile devices can offer network services to other nearby devices, and thus act as service end points, or mobile cloudlets. Devices seeking particular services can discover these providers and communicate with them directly, but with the help of the LTE network whose role is limited to assisting in the service provider discovery process. D2D can introduce several positive aspects within any community, through 1) helping tourism by making it seamless to obtain needed services; 2) improving social ties among the society members; and 3) helping the economy through creating a more conducive environment for thriving personal-level businesses. From an implementation point of view, our solution is in line with the 3GPP standards, utilizes the 3GPP-proposed network elements designated for offering proximity based services, and introduces no changes to the rest of the LTE system. Our experimental results proved the effectiveness of our system in helping mobile users discover needed services offered by nearby providers, and therefore communicate directly in a peer-to-peer fashion.


      PubDate: 2016-02-10T17:04:30Z
       
  • Performance evaluation of chaotic spreading sequences in a multi-user
           MIMO-OFDM system
    • Abstract: Publication date: Available online 29 January 2016
      Source:Physical Communication
      Author(s): Asma Ahmadinejad, Siamak Talebi
      A transmission with an acceptable performance is an important issue and is a topic of immense interest in wireless communications. In this paper, we propose an innovative solution which hires chaos theory in a “multiple-input-multiple-output, orthogonal frequency division multiplexing, code-division multiple-access (MIMO OFDM-CDMA)” system. The main goal is to improve performance by using chaotic systems as spreading codes. Since autocorrelation is an important criterion in selecting spreading codes, we investigate the autocorrelations of chaotic codes so as to choose proper sequences for spreading. Simulation results have shown that this method has better performance in comparison with other spreading codes such as the Walsh-Hadamard (WH) codes. In other word, bit-error rate has been refined and more possible code sequences are available.


      PubDate: 2016-01-31T14:58:03Z
       
  • Performance evaluation of backhaul bandwidth aggregation using a partial
           sharing scheme
    • Abstract: Publication date: Available online 21 January 2016
      Source:Physical Communication
      Author(s): Valentin Burger, Michael Seufert, Tobias Hoßfeld, Phuoc Tran-Gia
      To cope with the increasing demand of mobile devices and the limited capacity of cellular networks mobile connections are offloaded to WiFi. The access capacity is further increased, by aggregating bandwidth of WiFi access links. To analyse the performance of aggregated access links we model the most simple case of two cooperating systems interchanging capacities using an offloading scheme. The resulting analytic model is computed by means of a two-dimensional birth and death process. It can be used to seamlessly evaluate the performance of systems between partitioning and complete sharing. This allows to optimize the setting of thresholds dependent on the load of the cooperating system. Furthermore the benefit of aggregating bandwidth in different scenarios with homogeneous and heterogeneous workloads is quantified.


      PubDate: 2016-01-24T13:32:11Z
       
  • Unleashing the secure potential of the wireless physical layer: Secret key
           generation methods
    • Abstract: Publication date: Available online 16 January 2016
      Source:Physical Communication
      Author(s): Ahmed Badawy, Tarek Elfouly, Tamer Khattab, Amr Mohamed, Mohsen Guizani
      Within the paradigm of physical layer security, a physical layer characteristic is used as a common source of randomness to generate the secret key. This key is then used to encrypt the data to hide information from eavesdroppers. In this paper, we survey the most recent common sources of randomness used to generate the secret key. We present the steps used to extract the secret key from the estimated common source of randomness. We describe the metrics used to evaluate the strength of the generated key. We follow that with a qualitative comparison between different common sources of randomness along with a proposed new direction which capitalizes on hybridization of sources of randomness. We conclude by a discussion about current open research problems in secret key generation.


      PubDate: 2016-01-20T12:50:06Z
       
  • Cooperative spectrum sharing MIMO systems with successive decoding
    • Abstract: Publication date: Available online 14 January 2016
      Source:Physical Communication
      Author(s): Nikolaos I. Miridakis, Dimitrios D. Vergados, Angelos Michalas
      A spectrum sharing system with primary and secondary nodes, each equipped with an arbitrary number of antennas, is investigated. Particularly, the outage performance of an underlay cognitive system is analytically studied, in the case when the end-to-end ( e 2 e ) communication is established via an intermediate relay node. To better enhance the e 2 e communication, successive interference cancellation (SIC) is adopted, which compensates for both the transmission power constraint and the presence of interference from primary nodes. Both the relay and secondary receiver perform unordered SIC to successively decode the multiple streams, whereas the decode-and-forward relaying protocol is used for the e 2 e communication. New closed-form expressions for the e 2 e outage performance of each transmitted stream are derived in terms of finite sum series of the Tricomi confluent hypergeometric function. In addition, simplified yet tight approximations for the asymptotic outage performance are obtained. Useful engineering insights are manifested, such as the diversity order of the considered system and the impact of interference from the primary nodes in conjunction with the constrained transmission power of the secondary nodes.


      PubDate: 2016-01-15T11:19:49Z
       
  • Further results on multicarrier MFSK based underwater acoustic
           communications
    • Abstract: Publication date: Available online 2 January 2016
      Source:Physical Communication
      Author(s): Xingyu Cai, Lei Wan, Yi Huang, Shengli Zhou, Zhijie Shi
      Multicarrier M -ary frequency shift keying (MFSK), a parallel transmission of multiple MFSK data streams, is one basic reference scheme for underwater acoustic communications due to low-complexity incoherent processing at the receiver and ease of implementation. In this paper, we provide some further results for multicarrier MFSK based on the recent development of coherent orthogonal frequency division multiplexing (OFDM) schemes. Specifically, we adopt an OFDM based representation, develop a residual Doppler shift compensation approach at the receiver, and present different ways of computing the soft likelihood information for multicarrier MFSK transmissions in combination with nonbinary channel coding. As compared with coherent OFDM, simulation and semi-experimental results show that multicarrier MFSK has consistent performance in channels with different numbers of paths and in environments with different types of external noise.


      PubDate: 2016-01-05T07:28:30Z
       
  • Impact of the knowledge of nodes’ positions on spectrum sensing
           strategies in cognitive networks
    • Abstract: Publication date: Available online 22 December 2015
      Source:Physical Communication
      Author(s): Andrea Abrardo, Marco Martalò, Gianluigi Ferrari
      In this paper, we focus on cognitive wireless networking, where a primary wireless network (PWN) is co-located with a cognitive (or secondary) wireless network (CWN). The shared frequency spectrum is divided into disjoint “subchannels” and each subchannel is “freely” assigned (in a unique way) to a node of the PWN, denoted as primary user equipment (PUE). We assume that the nodes of the CWN, denoted as cognitive user equipments (CUEs), cooperate to sense the frequency spectrum and estimate the idle subchannels which can be used by the CWN (i.e., assigned to CUEs) without interfering the PWN. The sensing correlation among the CUEs is exploited to improve the reliability of the decision, taken by a secondary fusion center (FC), on the occupation status (by a node of the PWN) of each subchannel. In this context, we compute the mutual information between the occupation status and the observations at the FC, with and without knowledge of the positions of the nodes in the network, showing a potential significant benefit brought by this side information. Then, we derive the fusion rules at the FC: our numerical results, in terms of the network-wise probabilities of missed detection (MD) and false alarm (FA) at the secondary FC, indicate a significant performance improvement when knowledge of the CUEs’ positions is available at the secondary FC, confirming the mutual information-based theoretical prediction.


      PubDate: 2015-12-24T02:25:39Z
       
  • On the existence of an MVU estimator for target localization with
           censored, noise-free binary detectors
    • Abstract: Publication date: Available online 22 December 2015
      Source:Physical Communication
      Author(s): Arian Shoari, Alireza Seyedi
      The problem of target localization with censored noise-free binary detectors is considered. In this setting only the detecting sensors report their locations to the fusion center. It is proven that if the radius of detection is unknown to the fusion center, a minimum variance unbiased (MVU) estimator does not exist. Also it is shown that when the radius is known the center of mass of the possible target region is the MVU estimator among estimators that are invariant under Euclidean motion. In addition, a sub-optimum estimator is introduced whose performance is close to the MVU estimator but is preferred computationally. Moreover, for the case when the radius of detection is unknown a sub-optimum estimator is proposed that performs close to the Clairvoyant estimator. Furthermore, minimal sufficient statistics have been provided, both when the detection radius is known and when it is not. Simulations confirmed that the derived MVU estimator outperforms several heuristic location estimators.


      PubDate: 2015-12-24T02:25:39Z
       
  • Random neural network based novel decision making framework for optimized
           and autonomous power control in LTE uplink system
    • Abstract: Publication date: Available online 17 December 2015
      Source:Physical Communication
      Author(s): Ahsan Adeel, Hadi Larijani, Ali Ahmadinia
      This paper presents a novel decision making framework for cognitive radio networks. The traditional continuous process of sensing, analysis, reasoning, and adaptation in a cognitive cycle has been divided into two levels. In the first level, the process of sensing and adaptation runs over the radio transmission hardware during run-time. In the second level, the process of analysis and reasoning runs in the background in offline mode. This arrangement offloads the convergence time and complexity problem of reasoning process during run-time. For implementation of the first level, a random neural network (RNN) based controller trained on an open loop case based database on the cloud has been designed. For the second level, a genetic algorithm (GA) based reasoning and an RNN based learning has been developed. The proposed framework is used to address the uplink power control problem of long-term evolution (LTE) system. The performance of RNN is compared with artificial neural network (ANN) and state-of-the-art fractional power control (FPC) scheme in terms of essential cognitive engine (CE) design requirements, capacity, and coverage optimization (CCO). The simulation results have shown that RNN based CE can achieve comparable results with faster adaptation, even subject to severe environment changes without the need of retraining.


      PubDate: 2015-12-20T01:30:36Z
       
  • Route selection for interference minimization to primary users in
           cognitive radio ad hoc networks: A cross layer approach
    • Abstract: Publication date: Available online 17 December 2015
      Source:Physical Communication
      Author(s): Surajit Basak, Tamaghna Acharya
      An opportunistic routing problem in a cognitive radio ad hoc network is investigated with an aim to minimize the interference to primary users (PUs) and under the constraint of a minimum end-to-end data rate for secondary users (SUs). Both amplify-and-forward (AF) and decode-and-forward (DF) relaying techniques are considered for message forwarding by SU nodes in the network. Unlike popular transmit power control based solutions for interference management in cognitive radio networks, we adopt a cross layer approach. The optimization problem is formulated as a joint power control, channel assignment and route selection problem. Next, closed form expression for transmission power is derived and corresponding channel selection scheme and routing metric are designed based on this solution. The proposed route selection schemes are shown to depend not only on gains of the interference channels between SUs and PUs but also on the values of the spectrum sensing parameters at the SU nodes in the network. Two distributed routing schemes are proposed based on our analysis; (i) optimal_DF and (ii) suboptimal_AF. The routing schemes could be implemented using existing table driven as well as on demand routing protocols. Extensive simulation results are provided to evaluate performance of our proposed schemes in random multihop networks. Results show significant reduction in PUs’ average interference experience and impressive performance as opportunistic routing schemes can be achieved by our schemes compared to traditional shortest path based routing schemes. Performance improvement is also reported over prominent recent schemes.


      PubDate: 2015-12-20T01:30:36Z
       
  • Self-interference cancellation in full-duplex wireless with IQ imbalance
    • Abstract: Publication date: Available online 19 December 2015
      Source:Physical Communication
      Author(s): Manabu Sakai, Hai Lin, Katsumi Yamashita
      To achieve full-duplex wireless communication, the most essential issue is to eliminate in-band self-interference caused by simultaneous transmission and reception. In this paper, we investigate the impact of transmitter IQ imbalance on digital signal processing (DSP)-assisted analog self-interference cancellation, where two transmitters are used for transmission and cancellation, respectively. Our result implies that the transmitter IQ imbalance results in residual self-interference after conventional DSP-assisted analog cancellation, which still has a much higher power compared to the desired signal. Then, a baseband cancellation signal generated by widely linear (WL) filtering is proposed to effectively handle the transmitter IQ imbalance, and the optimal WL filter and the adaptive algorithm to obtain them can be derived. The impact of receiver IQ imbalance on the proposed adaptive algorithm is analyzed, and we show that the algorithm is capable of obtaining the same optimal WL filter despite receiver IQ imbalance. In addition, for practical implementation, we propose an adaptive algorithm based on the augmented complex least mean squares (ACLMS) method to obtain the WL filter, where no information about the transmitter and receiver IQ imbalances is needed. The steady state behaviors of the proposed adaptive algorithms are analyzed and the performance bounds are derived. Numerical simulation results confirm the validity and superior performance of the proposed ACLMS algorithm in various practical scenarios of transmitter and receiver IQ imbalances. Also, the tolerance of the proposed algorithm to other transceiver impairments was investigated using simulations.


      PubDate: 2015-12-20T01:30:36Z
       
  • DSP based real-time single carrier underwater acoustic communications
           using frequency domain turbo equalization
    • Abstract: Publication date: Available online 2 December 2015
      Source:Physical Communication
      Author(s): Bo Peng, Hefeng Dong
      In this paper, a DSP based real-time single carrier underwater acoustic communication system is developed. The designed receiver system operates in frequency domain for low complexity equalization. The turbo principle is incorporated into channel equalization and channel estimation processes to improve the system reliability. The channel is treated as stable within each small block and iteratively estimated based on LMS method and soft information provided by channel decoder. The soft LMS channel estimation is able to achieve better performance than conventional phase compensation scheme in single carrier frequency domain system. The receiver system is implemented on a floating point DSP running at 350 MHZ. Through careful optimization, the real-time processing is achieved with sufficient margin for both single-hydrophone receiver and multi-hydrophone systems. The designed system has been tested by both tank experiment and sea trials and achieves satisfied performance.


      PubDate: 2015-12-06T20:49:01Z
       
  • Radio access technology selection in heterogeneous networks
    • Abstract: Publication date: Available online 2 December 2015
      Source:Physical Communication
      Author(s): Kinda Khawam, Samer Lahoud, Marc Ibrahim, Mohamad Yassin, Steven Martin, Melhem El Helou, Farah Moety
      The migration of wireless networking towards the 5G era is distinguished by the proliferation of various Radio Access Technologies (RAT). As no existing technology can be surrogated by another one, the coexistence of today wireless networks is the best solution at hand when dealing with the incessantly growing user demand for bandwidth. Hence, in this heterogeneous environment, users will be able to utilize services through diverse RATs. RAT selection is crucial and must be designed astutely to avoid resource wastage. In this paper, we consider the downlink of a heterogeneous network with two broadband RATs: a primary RAT such as LTE, and a secondary RAT such as WiFi. We start by formulating a centralized approach for the RAT selection as an optimization problem. Then, two distributed approaches are proposed for adequate RAT selection: first, we put forward distributed heuristic algorithms based on the peak rate perceived by users from available RATs. Second, we devise a distributed RAT selection scheme portrayed as a non-cooperative game with a learning-based algorithm to reach the Nash Equilibriums of the RAT selection game. Extensive simulation results show that the proposed distributed algorithms give efficient results compared to the centralized optimal approach. The analysis of the simulation results enables to define pertinent use cases that delimit the scope of the proposed optimal centralized and distributed approaches.


      PubDate: 2015-12-06T20:49:01Z
       
  • Editorial Board
    • Abstract: Publication date: December 2015
      Source:Physical Communication, Volume 17




      PubDate: 2015-12-01T19:27:12Z
       
  • Doppler-aided localization of mobile nodes in an underwater distributed
           antenna system
    • Abstract: Publication date: Available online 1 December 2015
      Source:Physical Communication
      Author(s): Patrick Carroll, Katherine Domrese, Hao Zhou, Shengli Zhou, Peter Willett
      In this paper, we consider a problem of localizing a moving object in the context of an underwater distributed antenna system. All the distributed nodes record the time-of-arrivals of a single message from the moving object and obtain the Doppler speed estimates used in the decoding process. Conventional methods have relied only on the time-of-arrival measurements to obtain position estimates, on top of which filtering methods can be further applied for tracking purposes. In this work, we explore the usefulness of Doppler speed information. The combination of time-of-arrival measurements and Doppler speed estimates associated with a single message enhances the accuracy of position estimation and provides an estimate of the velocity of the mobile object. A Kalman Filter (KF) and a Probabilistic Data Association Filter (PDAF) are further implemented processing the point estimates. Simulations show that the proposed Doppler-aided methods improve both the point estimation and tracking filter performance, which is verified using data from pool tests.


      PubDate: 2015-12-01T19:27:12Z
       
  • Inter-cellular scheduler for 5G wireless networks
    • Abstract: Publication date: Available online 1 December 2015
      Source:Physical Communication
      Author(s): Cédric Gueguen, Mahdi Ezzaouia, Mohamad Yassin
      Enhancing the Quality of Experience (QoE) in wireless networks is a crucial issue. Many acknowledged works focus on intra-cellular scheduling. They have shown that when the channel impairment is taken into consideration by the opportunistic scheduling approaches, it allows to reach higher throughputs and, for the most efficient ones, a higher fairness. However, if some of these works provide results near to optimum considering a single cell, high QoE cannot be guaranteed for scenarios where the cells are overloaded. In this article, we propose a new inter-cellular scheduler able to help the overloaded cells thanks to a dynamic cell bandwidth allocation. Our resource allocation technique is based on an adequate emergency parameter called Mean Cell Packet Delay Outage Ratio (MCPDOR). Performance evaluation shows that the proposed scheduler widely outperforms existing solutions in various scenarios. A variant of our solution that does not consider MCPDOR is also proposed and evaluated.


      PubDate: 2015-12-01T19:27:12Z
       
  • Special issue on radio access network architectures and resource
           management for 5G
    • Abstract: Publication date: Available online 23 November 2015
      Source:Physical Communication
      Author(s): J. Pérez-Romero, X. Lagrange, J. Nasreddine, J. Marquez-Barja



      PubDate: 2015-11-27T18:45:13Z
       
  • SDN/NFV-enabled satellite communications networks: Opportunities,
           scenarios and challenges
    • Abstract: Publication date: Available online 10 November 2015
      Source:Physical Communication
      Author(s): R. Ferrús, H. Koumaras, O. Sallent, G. Agapiou, T. Rasheed, M.-A. Kourtis, C. Boustie, P. Gélard, T. Ahmed
      In the context of next generation 5G networks, the satellite industry is clearly committed to revisit and revamp the role of satellite communications. As major drivers in the evolution of (terrestrial) fixed and mobile networks, Software Defined Networking (SDN) and Network Function Virtualisation (NFV) technologies are also being positioned as central technology enablers towards improved and more flexible integration of satellite and terrestrial segments, providing satellite network further service innovation and business agility by advanced network resources management techniques. Through the analysis of scenarios and use cases, this paper provides a description of the benefits that SDN/NFV technologies can bring into satellite communications towards 5G. Three scenarios are presented and analysed to delineate different potential improvement areas pursued through the introduction of SDN/NFV technologies in the satellite ground segment domain. Within each scenario, a number of use cases are developed to gain further insight into specific capabilities and to identify the technical challenges stemming from them.


      PubDate: 2015-11-18T16:16:32Z
       
  • What will interference be like in 5G HetNets?
    • Abstract: Publication date: Available online 23 October 2015
      Source:Physical Communication
      Author(s): Janne Riihijärvi, Petri Mähönen, Marina Petrova
      In this paper we discuss challenges in interference modeling for performance analysis of future wireless networks. We show through detailed numerical and simulation case studies as well as through measurements that many of the commonly used models result in potentially highly inaccurate predictions of interference and performance. In particular, we identify correlations in node locations, three-dimensional structure of future network deployments, and complexity of in-building and inter-building radio propagation as key domains where further research is needed. We also discuss in detail potential approaches to be taken as starting points for new research in these domains.


      PubDate: 2015-11-18T16:16:32Z
       
  • On achievable rate of massive MIMO multiple access channels via virtual
           representation
    • Abstract: Publication date: Available online 27 October 2015
      Source:Physical Communication
      Author(s): Yun Xue, Jun Zhang, Shi Jin, Xiqi Gao
      This paper investigates the uplink achievable rates of massive multiple-input multiple-output (MIMO) systems in correlated fading channels via virtual representation. The fast fading MIMO channel matrix is assumed to have a Rayleigh-distributed random component with variance profile. Under the minimum mean-squared error receiver employed, we first derive the first and second asymptotic moments of signal-to-interference-plus-noise ratio (SINR). Then, we propose that the probability distribution function of SINR, which can be well approximated by a Gamma distribution. Finally, we derive a lower bound on the SINR and approximation of achievable rate. Numerical results demonstrate that both the lower bound on the SINR and the approximated rate apply for a finite number of antennas and remain tight.


      PubDate: 2015-11-18T16:16:32Z
       
  • On error rate performance of multi-cell massive MIMO systems with linear
           receivers
    • Abstract: Publication date: Available online 4 November 2015
      Source:Physical Communication
      Author(s): Haiquan Wang, Meijun Zhou, Ruiming Chen, Wei Zhang
      For an uplink of multi-cell multiuser (MU) Multiple-Input, Multiple-Output (MIMO) system, where each cell has a Base Station (BS) with M antennas and K users with single antenna, the Zero-Forcing (ZF) decoder and the Minimal Mean-Square Error (MMSE) decoder are considered. Upper bounds, lower bounds on Pair-wise Error Probability (PEP) of these decoders are derived. Moreover, analytic expressions of approximations on PEP are given. These show that, if the BS knows Channel State Information (CSI) in its own cell only and does not have CSI in other cells, error floors will occur even when Signal-to-Noise Ratio (SNR) goes to infinity for both the ZF decoder and the MMSE decoder, while these error floors disappear when M goes to large. All theoretical results above are confirmed by simulations. Especially, the approximations of PEP match up with simulation results very well.


      PubDate: 2015-11-18T16:16:32Z
       
  • A survey on 5G: The next generation of mobile communication
    • Abstract: Publication date: Available online 11 November 2015
      Source:Physical Communication
      Author(s): Nisha Panwar, Shantanu Sharma, Awadhesh Kumar Singh
      The rapidly increasing number of mobile devices, voluminous data, and higher data rate are pushing to rethink the current generation of the cellular mobile communication. The next or fifth generation (5G) cellular networks are expected to meet high-end requirements. The 5G networks are broadly characterized by three unique features: ubiquitous connectivity, extremely low latency, and very high-speed data transfer. The 5G networks would provide novel architectures and technologies beyond state-of-the-art architectures and technologies. In this paper, our intent is to find an answer to the question: “what will be done by 5G and how?” We investigate and discuss serious limitations of the fourth generation (4G) cellular networks and corresponding new features of 5G networks. We identify challenges in 5G networks, new technologies for 5G networks, and present a comparative study of the proposed architectures that can be categorized on the basis of energy-efficiency, network hierarchy, and network types. Interestingly, the implementation issues, e.g., interference, QoS, handoff, security-privacy, channel access, and load balancing, hugely effect the realization of 5G networks. Furthermore, our illustrations highlight the feasibility of these models through an evaluation of existing real-experiments and testbeds.


      PubDate: 2015-11-18T16:16:32Z
       
  • Design and implementation of spectrum sensing for cognitive radios with a
           frequency-hopping primary system
    • Abstract: Publication date: Available online 30 September 2015
      Source:Physical Communication
      Author(s): Sanjeev Gurugopinath, Raghavendra Akula, Chandra R. Murthy, R. Prasanna, Bharadwaj Amruthur
      In this work, spectrum sensing for cognitive radios is considered in the presence of multiple Primary Users (PU) using frequency-hopping communication over a set of frequency bands. The detection performance of the Fast Fourier Transform (FFT) Average Ratio (FAR) algorithm is obtained in closed-form, for a given FFT size and number of PUs. The effective throughput of the Secondary Users (SU) is formulated as an optimization problem with a constraint on the maximum allowable interference on the primary network. Given the hopping period of the PUs, the sensing duration that maximizes the SU throughput is derived. The results are validated using Monte Carlo simulations. Further, an implementation of the FAR algorithm on the Lyrtech (now, Nutaq) small form factor software defined radio development platform is presented, and the performance recorded through the hardware is observed to corroborate well with that obtained through simulations, allowing for implementation losses.


      PubDate: 2015-10-03T16:11:04Z
       
  • QPSK waveform for MIMO radar with spectrum sharing constraints
    • Abstract: Publication date: Available online 25 September 2015
      Source:Physical Communication
      Author(s): Awais Khawar, Ahmed Abdelhadi, T. Charles Clancy
      Multiple-input multiple-output (MIMO) radar is a relatively new concept in the field of radar signal processing. Many novel MIMO radar waveforms have been developed by considering various performance metrics and constraints. In this paper, we show that finite alphabet constant-envelope (FACE) quadrature-pulse shift keying (QPSK) waveforms can be designed to realize a given covariance matrix by transforming a constrained nonlinear optimization problem into an unconstrained nonlinear optimization problem. In addition, we design QPSK waveforms in a way that they don’t cause interference to cellular system, by steering nulls towards a selected base station (BS). The BS is selected according to our algorithm which guarantees minimum degradation in radar performance due to null space projection (NSP) of radar waveforms. We design QPSK waveforms with spectrum sharing constraints for stationary and moving radar platform. We show that the waveform designed for stationary MIMO radar matches the desired beampattern closely, when the number of BS antennas N BS is considerably less than the number of radar antennas M , due to quasi-static interference channel. However, for moving radar the difference between designed and desired waveforms is larger than stationary radar, due to rapidly changing wireless channel.


      PubDate: 2015-09-25T14:26:58Z
       
  • Multiple trellis-coded modulation, per-survivor processing and
           Reed-Solomon coding in the presence of phase noise
    • Abstract: Publication date: Available online 25 September 2015
      Source:Physical Communication
      Author(s): Markku Kiviranta, Aarne Mämmelä
      The aim of this paper is to consider trellis coded modulation (TCM) in the presence of phase noise. The starting point is a two-dimensional 32 point cross (32-CR) signal set that has served as a benchmark for other power and bandwidth efficient modulation schemes. Per-survivor processing (PSP) is used for carrier phase estimation, and both the phase acquisition (transient state) and phase tracking (steady state) performances are considered in an additive white Gaussian noise (AWGN) channel, in which phase offset or time varying phase noise is introduced. Based on the theoretical and simulation results it can be said that the 32-CR constellation is itself more sensitive to a phase error rather than the PSP algorithm. Due to the phase error the TCM scheme becomes a catastrophic code. Possible solutions include stringent phase noise requirements for oscillators, multiple trellis-coded modulation (MTCM) and concatenated TCM and Reed-Solomon (RS) coding. Our simulation results show that a simple combined MTCM, PSP and RS scheme has around 3 dB advantage at compared to the pure TCM and PSP in the presence of phase noise. A semianalytical approach is used for performance evaluation, and the method is a particularly convenient tool to determine the rate of RS coding in detail.


      PubDate: 2015-09-25T14:26:58Z
       
  • Direction Finding of rogue Wi-Fi access points using an off-the-shelf
           MIMO-OFDM receiver
    • Abstract: Publication date: Available online 25 September 2015
      Source:Physical Communication
      Author(s): Asaf Tzur, Ofer Amrani, Avishai Wool
      Elimination of rogue Access Points (APs) is a challenging security goal of growing interest and practical importance. However, even when network administrators suspect that such devices are indeed present to attack their organization, physically locating their whereabout is an intricate task. In this work a method is suggested for implementing autonomous Direction Finding (DF), i.e., an apparatus for passively identifying the Angle-of-Arrival (AoA) of a received Wi-Fi signal, using a standard off-the-shelf Wi-Fi receiver. Modern wireless communication standards, such as Wi-Fi (e.g. IEEE 802.11n), are based on Orthogonal Frequency Division Multiplexing (OFDM) and Multiple-Input Multiple-Output (MIMO) technologies. The key contribution of the current work is an approach of employing the multiple receiving antennas jointly with OFDM Channel State Information (CSI) as the basis for implementing an interferometry DF tool. This approach is theoretically investigated via numeric analysis, and practically validated by a working prototype. The performance of the prototype was evaluated both in the laboratory, in a sterile environment, as well as in field trials. In realistic indoor setting the prototype was able to acquire the AoA with a median error of 8–15 degrees.


      PubDate: 2015-09-25T14:26:58Z
       
  • Error exponent analysis of energy-based Bayesian decentralized spectrum
           sensing under fading
    • Abstract: Publication date: Available online 7 September 2015
      Source:Physical Communication
      Author(s): Sanjeev Gurugopinath, Chandra R. Murthy, Vinod Sharma
      This paper considers decentralized spectrum sensing, i.e., detection of occupancy of the primary users’ spectrum by a set of Cognitive Radio (CR) nodes, under a Bayesian set-up. The nodes use energy detection to make their individual decisions, which are combined at a Fusion Center (FC) using the K -out-of- N fusion rule. The channel from the primary transmitter to the CR nodes is assumed to undergo fading, while that from the nodes to the FC is assumed to be error-free. In this scenario, a novel concept termed as the Error Exponent with a Confidence Level (EECL) is introduced to evaluate and compare the performance of different detection schemes. Expressions for the EECL under general fading conditions are derived. As a special case, it is shown that the conventional error exponent both at individual sensors, and at the FC is zero. Further, closed-form lower bounds on the EECL are derived under Rayleigh fading and lognormal shadowing. As an example application, it answers the question of whether to use pilot-signal based narrowband sensing, where the signal undergoes Rayleigh fading, or to sense over the entire bandwidth of a wideband signal, where the signal undergoes lognormal shadowing. Theoretical results are validated using Monte Carlo simulations.


      PubDate: 2015-09-12T11:10:35Z
       
  • A novel user pairing scheme for functional decode-and-forward multi-way
           relay network
    • Abstract: Publication date: Available online 11 September 2015
      Source:Physical Communication
      Author(s): Shama N. Islam, Salman Durrani, Parastoo Sadeghi
      In this paper, we consider a functional decode and forward (FDF) multi-way relay network (MWRN) where a common user facilitates each user in the network to obtain messages from all other users. We propose a novel user pairing scheme, which is based on the principle of selecting a common user with the best average channel gain. This allows the user with the best channel conditions to contribute to the overall system performance. Assuming lattice code based transmissions, we derive upper bounds on the average common rate and the average sum rate with the proposed pairing scheme. Considering M -ary quadrature amplitude modulation with square constellation as a special case of lattice code transmission, we derive asymptotic average symbol error rate (SER) of the MWRN. We show that in terms of the achievable rates, the proposed pairing scheme outperforms the existing pairing schemes under a wide range of channel scenarios. The proposed pairing scheme also has lower average SER compared to existing schemes. We show that overall, the MWRN performance with the proposed pairing scheme is more robust, compared to existing pairing schemes, especially under worst case channel conditions when majority of users have poor average channel gains.


      PubDate: 2015-09-12T11:10:35Z
       
  • Outlier-aware cooperative spectrum sensing in cognitive radio networks
    • Abstract: Publication date: Available online 9 September 2015
      Source:Physical Communication
      Author(s): Gaurav Kapoor, Ketan Rajawat
      This paper considers the problem of cooperative spectrum sensing in cognitive radio networks (CRN). Communication in CRNs may be disrupted due to the presence of malicious secondary users (SU) or channel impairments such as shadowing. This paper proposes a spatio-frequency framework that can detect and track malicious users and anomalous measurements in CRNs. The joint problem of spectrum sensing and malicious user identification is posed as an optimization problem that aims to exploit the sparsity inherent to both, spectrum occupancy and malicious user occurrence. Proposed scheme obtains improved performance by utilizing node location information, and can handle missing or inaccurate location information, and noisy SU reports. A distributed block-coordinate descent-based algorithm is proposed that is shown to outperform the state-of-the-art PCA-based approach, and is flexible enough to defeat a variety of attacks encountered in SU networks. An online algorithm, that can handle incorporate multiple SU readings sequentially and adapt to time-varying channels, primary user, and malicious user activity, is also proposed and shown to be consistent. Simulation results demonstrate the efficacy of the proposed algorithms.


      PubDate: 2015-09-12T11:10:35Z
       
  • A low complexity detection/decoding algorithm for NB-LDPC coded PRCPM
           system
    • Abstract: Publication date: Available online 11 September 2015
      Source:Physical Communication
      Author(s): Xiying Liu, Shancheng Zhao, Xiao Ma
      This paper studies the combination of non-binary low-density parity-check (NB-LDPC) codes and M -ary partial response continuous phase modulation (PRCPM). A low-complexity joint detection/decoding algorithm is proposed, which is referred to as the Max-Log-MAP/ X -EMS algorithm. In this joint algorithm, the CPM detector is implemented by the Max-Log-MAP algorithm while the LDPC decoder is implemented by the Extended Min-Sum (EMS) algorithms. Three kinds of EMS algorithms, including D -EMS, T -EMS, and M -EMS algorithms, are compared, which are referred to as X -EMS algorithm for convenience. Simulation results show that the Max-Log-MAP/ X -EMS algorithm performs as well as the traditional iterative detection/decoding algorithm based on the BCJR algorithm and the QSPA algorithm, but with lower complexity. In addition, comparison of the proposed NB-LDPC coded PRCPM system with the eBCH coded PRCPM system is given, which shows the performance advantages of our system.


      PubDate: 2015-09-12T11:10:35Z
       
  • A DEC-MDP model for joint uplink/downlink resource management in
           OFDMA-based networks
    • Abstract: Publication date: Available online 5 September 2015
      Source:Physical Communication
      Author(s): Ahmad M. El-Hajj, Dusit Niyato, Zaher Dawy
      With the advent of mobile services with asymmetric and symmetric quality of service (QoS) requirements, traditional single link resource allocation techniques have started to show some limitations in handling the complex requirements. To address these issues, joint uplink/downlink resource management approaches were recently introduced where both communications links are jointly considered in the resource management process. One direct consequence of this coupling is a modification of the underlying queueing behavior since the decision making process in one direction in terms of transmission rate now depends on the performance achieved in the opposite direction. In this paper, we present a modeling approach of the decision making process that takes place under the joint uplink/downlink resource management framework. Using decentralized Markov decision processes (DEC-MDP) as a model and gradient ascent methods as an optimization technique, we formulate and solve the joint uplink/downlink decision making process. The uplink and downlink of each user are considered as agents. Assuming certain subcarrier and power allocation schemes, we investigate the resource usage in the uplink and downlink to achieve a certain delay balancing constraint where the total delay in the uplink and downlink is bound by a pre-determined threshold. The approach followed starts by modeling the problem in hand using DEC-MDPs. After discussing the different aspects of the model, the solution using gradient ascent is described. Simulation results illustrate the different dimensions of the problem and their impact on the resource management process.


      PubDate: 2015-09-07T10:11:29Z
       
  • Performance evaluation of improved double-threshold energy detector over
           Rayleigh-faded sensing and imperfect reporting channels
    • Abstract: Publication date: Available online 21 August 2015
      Source:Physical Communication
      Author(s): Ramtin Rabiee, Kwok Hung Li
      Cognitive radio (CR) has been viewed as a promising solution to spectrum scarcity. In order to design a reliable CR system, many improvements have been proposed to enhance spectrum sensing performance of secondary users (SUs) in a CR network (CRN). Sensing reliability and transmission throughput of SUs are two important performance criteria, which should be optimized to enhance signal protection of primary user (PU) as well as spectrum utilization rate. In this paper, we consider Rayleigh-faded sensing channels and SUs use improved energy detector (IED) to make their local decisions. The final decision is made in a fusion center (FC) through the cooperative spectrum sensing (CSS) scheme with erroneous reporting channels. We show that the improved double-threshold energy detector (IDED) outperforms the conventional energy detector (CED) in terms of the total error rate. Furthermore, we evaluate the transmission throughput of the CRN through various ED schemes with detection constraints over both perfect and imperfect reporting channels. We show that the IDED has the highest achievable throughput among different ED schemes over imperfect reporting channels.


      PubDate: 2015-08-25T08:35:52Z
       
  • Communicate to illuminate: State-of-the-art and research challenges for
           visible light communications
    • Abstract: Publication date: Available online 24 August 2015
      Source:Physical Communication
      Author(s): Ozgur Ergul, Ergin Dinc, Ozgur B. Akan
      In the near future, the available radio-frequency (RF) bandwidth will not be sufficient to meet the ever increasing demand for wireless access. Visible light communication (VLC) is an alternative method to reduce the burden of RF-based communication, especially in indoor communications. 70 % of the communication is indoors, and light emitting diode (LED) arrays are spreading for illumination purposes thanks to their low energy and higher lifetime. VLC can be realized as a secondary application in LED arrays that are placed for lighting. In this way, some of the wireless traffic can be sent using light, with less cost and less carbon footprint. For these reasons, VLC attracts significant research interests. We provide an extensive survey of the current literature by outlining challenges and future research areas in order to facilitate future research in this area.


      PubDate: 2015-08-25T08:35:52Z
       
  • Editorial Board
    • Abstract: Publication date: September 2015
      Source:Physical Communication, Volume 16




      PubDate: 2015-07-27T14:07:38Z
       
  • The combination of aggregation, ARQ, QoS guarantee and mapping of
           Application flows in Very High Throughput 802.11ac networks
    • Abstract: Publication date: Available online 17 July 2015
      Source:Physical Communication
      Author(s): Oran Sharon, Yaron Alpert
      We investigate the performance of the IEEE 802.11ac MAC layer Aggregation schemes in light of QoS guarantee with the use of an ARQ protocol, and in very high PHY rates. The investigation is done in different models of mapping Application flows into Traffic Streams and Access Categories. We show that when the IEEE 802.11ac ARQ protocol is used with relatively high bit error rates, it is not effective to use the full aggregation capability. Second, we show that there is not one best model of mapping Application flows into Traffic Streams and Access Categories. In particular, using two Access Categories is sometimes less efficient than using one.


      PubDate: 2015-07-19T08:33:46Z
       
  • Optimal downlink power allocation in cellular networks
    • Abstract: Publication date: Available online 9 July 2015
      Source:Physical Communication
      Author(s): Ahmed Abdelhadi , Awais Khawar , T. Charles Clancy
      In this paper, we introduce a novel approach for power allocation in cellular networks. In our model, we use sigmoidal-like utility functions to represent different users’ modulation schemes. Each utility function is a representation of the probability of successfully transmitted packets per unit of power consumed by a user, when using a certain modulation scheme. We consider power allocation with utility proportional fairness policy, where the fairness among users is in utility percentage i.e. percentage of successfully transmitted packets of the corresponding modulation scheme. We formulate our power allocation optimization problem as a product of utilities of all users and prove that it is convex and therefore the optimal solution is tractable. We present a distributed algorithm to allocate base station powers optimally with priority given to users running lower modulation schemes while ensuring non-zero power allocation to users running higher modulation schemes. Our algorithm prevents fluctuation in the power allocation process and is capable of traffic and modulation dependent pricing policy. This can be used to flatten traffic and decrease the service price for users. We also compare our results with a benchmark algorithm and show that our algorithm performs better in allocating powers fairly to all users without dropping any user in order to maximize performance.


      PubDate: 2015-07-15T05:16:53Z
       
  • Analysis of degrees of freedom under mixture Gaussian model in cognitive
           radio systems
    • Abstract: Publication date: September 2015
      Source:Physical Communication, Volume 16
      Author(s): Ahsan-Abbas Ali , Shuangqing Wei
      We propose a mixture-Gaussian model for a cognitive radio channel to analyze the interplay between the interference in the system and the degrees-of-freedom (DOF), i.e., the average number of channel uses per transmission frame, used by the secondary user (SU) for communications in the long run. In contrast to the conventional studies, we assume that the SU receiver (SU-RX) does not precisely know whether the primary-user (PU) transmitter is on or off. Due to this assumption the resulting interference channel is mixture-Gaussian. Our objective is to find the optimal sensing threshold and sensing time for the signal detector used by the SU transmitter (SU-TX). Our formulation of the optimization problem reflects the trade-off between SU-TX’s DOF for communications and that for detection. Both the DOFs affect PU’s interference to SU, and SU’s interference to PU. The latter interference causes PU performance degradation, which is kept within tolerable range as a constraint. As a further contribution, we define interference regimes for SU performance on the basis of PU transmission power level. We also address the scenario when PU receiver uses the nearest neighbor decoding while wrongly anticipating that the channel is Gaussian. Finally, we demonstrate that even if SU-TX’s signal detector performs suboptimally, SU can still achieve the optimal detector’s performance in the high interference regime by adjusting the sensing parameters.


      PubDate: 2015-07-09T01:54:33Z
       
 
 
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