JournalTOCs

Physical Communication

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ISSN (Print) 1874-4907
Published by Elsevier

[2556 journals]

Cooperation within the Small Cell: The indoor, correlated shadowing case
- Abstract: Publication date: Available online 10 May 2013
  Source:Physical Communication
  Author(s): Vasileios K. Sakarellos , Dimitrios Skraparlis , Athanasios D. Panagopoulos
  The deployment of Small Cells in fourth generation (4G) communication systems is aimed at providing significant capacity improvements and higher availabilities. However, the design of Small Cell systems in indoor environments is especially challenging due to high shadowing attenuation induced by clutter and human blockage. This paper studies node cooperation and multiple relaying and proposes novel analytical formulas for the outage probability of cooperative Small Cells suffering from shadowing. The channel fading gains are modelled as correlated lognormal random variables, in order to reflect the properties of indoor propagation environments. Various cooperative strategies are considered, taking into account the use of one or two Relays and different receiver combining techniques. In addition, the relative performance of each cooperative configuration and the benefit of cooperation over non-cooperation are investigated. Finally, interesting and useful insights are produced regarding the impact of the correlated lognormal environment parameters on the configuration of cooperative Small Cells.
  
  PubDate: 2013-05-11T14:02:09Z
A history-aware greedy channel restoration scheme for cognitive radio-based LTE networks
- Abstract: Publication date: Available online 9 May 2013
  Source:Physical Communication
  Author(s): Arash Azarfar , Jean-François Frigon , Brunilde Sansò
  Cognitive radio-based Long Term Evolution (LTE) networks benefit from the powerful features of cognitive Radios (CR), such as learning and reconfigurability, enabling them to perform, if required, channel switching to a channel with higher quality. This process of searching and sensing other channels is a restoration (recovery) process where the objective is to find the best channel in the shortest time. We propose in this paper a history-aware greedy restoration scheme triggered not only when the quality of the current operating channel of the user goes below a threshold, but at regular intervals. Based on the state of the current channel, our scheme computes the optimal number of channels to be sensed in this restoration period and this number is dynamically updated after each channel sensing result. Intrinsic features of learning and history-awareness of CRs are used to create the list of channels to be sensed based on the channels’ background and historical information. The sensing order improves the restoration mechanism by providing a shorter restoration time or a restored channel with a higher quality. We show that the proposed combined scheme provides improvements for the CR-based LTE network’s throughput, compared to other restoration schemes which work based on only greediness or history-awareness.
  
  PubDate: 2013-05-11T14:02:09Z
Towards an optimal transmission of SDUs in IEEE 802.16e WiMAX systems
- Abstract: Publication date: June 2013
  Source:Physical Communication, Volume 7
  Author(s): Yaron Alpert , Jonathan Segev , Oran Sharon
  In this paper we address the mutual influence between the PHY layer budding blocks (FEC blocks) and the MAC level allocations in the Uplink and Downlink of IEEE 802.16e systems, and address methods to increase the overall PHY and MAC combined efficiency. We evaluate the efficiency of several schemes for the transmission of Service Data Unit (SDU) packets through Protocol Data Units (PDUs) in physical Bursts. The optimality criterion is the Goodput. When using the Convolutional Turbo Code, Bursts are composed of FEC blocks that have a direct influence on the probability of bits being received successfully, and thus on the Goodput. In the first scheme, every SDU is transmitted as a stand-alone PDU. In the second scheme, the Burst is first divided into PDUs in a way that maximizes the Goodput, assuming the transmission of a bit stream (and not SDUs). Then the SDUs are mapped into the PDUs with possible Fragmentation/Packing. The optimal size of the PDUs is computed by an O ( 1 ) running time algorithm, an important feature because this algorithm is a part of the scheduler in the BS. The results show that when the estimation of the FEC success probability is accurate, SDUs should be mapped into optimal size PDUs in reliable channels. For unreliable channels it is better to transmit each SDU as a separate PDU. When the estimation of the FEC success probability is not accurate, it is always better to transmit SDUs as separate PDUs.
  
  PubDate: 2013-04-25T14:05:03Z
Self organized energy efficient position aided relays in LTEA
- Abstract: Publication date: June 2013
  Source:Physical Communication, Volume 7
  Author(s): Shahid Mumtaz , Du Yang , Valdemar Monteiro , Christos Politis , Jonathan Rodriguez
  Energy is an expensive commodity in Long term Evolution-Advanced networks (LTEA). In recent years many researchers have proposed different approaches to minimize energy consumption in LTEA. Relays and the Self Organized Network (SON) technologies are an attractive solution to cost reduction, and to minimize energy utilization in LTEA. SON has the potential for self-configuring, self-optimizing, self-healing and minimizing the energy consumption in the network and by deploying Relay Nodes (RNs) it enhances the capacity, the diversity and fairness in the network. In this paper we consider the self-optimizing and self-healing properties of SON and propose a novel energy efficient SON based position aided relay algorithm. The proposed algorithm is capable of reducing the energy consumption by 50% in the best case scenario. A System Level Simulator (SLS) is used to evaluate the performance of the proposed algorithm through numerical results.
  
  PubDate: 2013-04-25T14:05:03Z
Performance of multi-user transmitter preprocessing assisted MIMO system over correlated frequency-selective channels
- Abstract: Publication date: June 2013
  Source:Physical Communication, Volume 7
  Author(s): Prabagarane Nagaradjane , Yuvika Ashwina Rajan , Prasaanth Muralidharan , Sabarish Karthik Vivek Sarathy
  In this contribution we present the performance of a multi-user transmitter preprocessing (MUTP) assisted multiple-input multiple-output (MIMO) space division multiple access (SDMA) system, aided by double space time transmit diversity (DSTTD) and space time block code (STBC) processing for downlink (DL) and uplink (UL) transmissions respectively. The MUTP is invoked by singular value decomposition (SVD) which exploits the channel state information (CSI) of all the users at the base station (BS) and only an individual user’s CSI at the mobile station (MS). Specifically, in this contribution, we investigate the performance of multi-user MIMO cellular systems in frequency-selective channels from a transmitter signal processing perspective, where multiple access interference (MAI) is the dominant channel impairment. In particular, the effects of three types of delay spread distributions on MUTP assisted MIMO SDMA systems pertaining to the Long Term Evolution (LTE) channel model are analyzed. The simulation results demonstrate that MUTP can perfectly eliminate MAI in addition to obviating the need for complex multi-user detectors (MUDs) both at the BS and MS. Further, SVD-based MUTP results in better achievable symbol error rate (SER) compared to popularly known precoding schemes such as block diagonalization (BD), dirty paper coding (DPC), Tomlinson–Harashima precoding (THP) and geometric mean decomposition (GMD). Furthermore, when turbo coding is invoked, coded SVD aided MUTP results in better achievable SER than an uncoded system.
  
  PubDate: 2013-04-25T14:05:03Z
Coupled PHY, MAC and repetition scheduling in IEEE 802.16 WiMAX systems
- Abstract: Publication date: June 2013
  Source:Physical Communication, Volume 7
  Author(s): Yaron Alpert , Jonathan Segev , Oran Sharon
  We address some issues related to the mutual influence between the PHY layer budding blocks (FEC blocks ), the MAC level allocations, and repetition, in IEEE 802.16e/WiMAX systems, in order to increase the overall combined efficiency. We suggest three methods to use repetition: two are based on the increased transmission success probability due to the transmission and decoding of several copies of the same data, and one is based on signal adding and the decoding of one copy with a larger SNR. The last method turned out to be the most efficient one. We show quantitatively that repetition is efficient mainly in low SNRs where otherwise transmissions are not possible, and in particular in negative SNRs. However, there are cases where using repetition is more efficient than using a stronger Modulation/Coding scheme without repetition. Finally, we also show that repetition shall be used with several Modulation/Coding schemes, and not just with QPSK-1/2 as the IEEE 802.16e/WiMAX standard mandates.
  
  PubDate: 2013-04-25T14:05:03Z
Editorial Board
- Abstract: Publication date: June 2013
  Source:Physical Communication, Volume 7
  
  PubDate: 2013-04-25T14:05:03Z
Potential games for energy-efficient resource allocation in multipoint-to-multipoint CDMA wireless data networks
- Abstract: Publication date: June 2013
  Source:Physical Communication, Volume 7
  Author(s): Stefano Buzzi , Alessio Zappone
  The problem of noncooperative resource allocation in a multipoint-to-multipoint CDMA cellular network is considered in this paper. The considered scenario is general enough to represent several key instances of modern wireless networks such as a multicellular network, a peer-to-peer network (interference channel), and a wireless network equipped with femtocells. In particular, the problem of joint transmit waveforms adaptation, linear receiver design, and transmit power control is examined. Several utility functions to be maximized are considered, and, among them, we cite the received SINR, and the transmitter energy efficiency, which is measured in bit/J, and represents the number of successfully delivered bits for each energy unit used for transmission. Resorting to the theory of potential games, noncooperative games admitting Nash equilibria in multipoint-to-multipoint cellular networks regardless of the channel coefficient realizations are designed. Computer simulations confirm that the considered games are convergent, and show the huge benefits that resource allocation schemes can bring to the performance of wireless data networks.
  
  PubDate: 2013-04-25T14:05:03Z
Enabling next generation small cells through femtorelays
- Abstract: Publication date: Available online 23 April 2013
  Source:Physical Communication
  Author(s): Ian F. Akyildiz , Elias Chavarria-Reyes , David M. Gutierrez-Estevez , Ravikumar Balakrishnan , John R. Krier
  Today’s society is driven by ever-growing information needs, which cause increased demand for ubiquitous and very high speed wireless communications. In search for the urgent need of improved coverage and capacity, cellular networks are currently undergoing a major transformation from an architecture comprised of thoroughly planned macrocell base stations (MBSs) to a much more heterogeneous architecture where the macrocell network is underlaid by one or several tiers of unevenly deployed small cells. However, this new set of technologies is not exempt of several challenges. Backhaul is still an unresolved issue, i.e. which is the best technology for the small cell to reach the core network. In the case of uncoordinated co-channel deployments where the macrocell and small cell tier share the spectrum (e.g. femtocells or metrocells), the interference is also a major problem. In this paper, a new concept and architecture called femtorelays is introduced as a novel solution for next generation small cell problems. A femtorelay is a small cell access point that enables improved cellular coverage within indoor environments while increasing the overall system capacity through spatial frequency reuse. Working as an open-access small cell, it provides dual-backhaul connectivity to the core network for registered and unregistered users. One of the backhaul connections is the internet-based, and the second one is the relay-based operating on spectrum owned by the wireless carrier. The radio interference between macrocell and small cell is overcome by servicing the macrocell interfering users at the femtorelay. Unlike the traffic from subscribers, this traffic will be forwarded to the network through the relay-based backhaul. The internal architecture, the approach employed to make the technology fit in existing networks, and future evolution of the basic femtorelays for larger scenarios are also presented. Finally, performance results show the potential of this technology to outperform other existing solutions.
  
  PubDate: 2013-04-25T14:05:03Z
An extended 3-dimensional channel model for polarized antenna array
- Abstract: Publication date: Available online 23 April 2013
  Source:Physical Communication
  Author(s): Mei-fang Jing , Rui-ping Wei , Xin Su , Shao-hui Sun , Rakesh Tamrakar
  Based on existing 3-Dimensional (3-D) channel model developed by WINNER II/+, we propose an extended 3-D channel model, which takes the vertical velocity component and polarized array structure into account. The distributions of several channel parameters are verified through simulation. Furthermore, initial system-level simulation results for 3D-MIMO transmission scheme are presented in this paper.
  
  PubDate: 2013-04-25T14:05:03Z
Inter-cell spectrum efficiency improvement technology
- Abstract: Publication date: Available online 23 April 2013
  Source:Physical Communication
  Author(s): Zhaohua Lu , Xiaodan Zhang , Huahua Xiao , Dengkui Zhu , Kun Liu
  Improvement of inter-cell spectrum efficiency is a valuable research topic in mobile communication system, which impact cell edge user experience especially. According to current research results, three methods to deal with inter-cell interference to improve inter-cell spectrum efficiency, including inter-cell interference randomization, inter-cell interference cancellation and inter-cell interference co-ordination. This paper analyses three important inter-cell spectrum efficiency improvement technologies: soft frequency reuse (SFR), uplink power control, downlink coordinated multi-point transmission/reception (CoMP), and relative research progress.
  
  PubDate: 2013-04-25T14:05:03Z
Three schemes for wireless coded broadcast to heterogeneous users
- Abstract: Publication date: March 2013
  Source:Physical Communication, Volume 6
  Author(s): Yao Li , Emina Soljanin , Predrag Spasojević
  We study and compare three coded schemes for the single-server wireless broadcast of multiple description coded content to heterogeneous users. The users (sink nodes) demand different numbers of descriptions over links with different packet loss rates. The three coded schemes are based on the LT codes, growth codes, and randomized chunked codes. The schemes are compared on the basis of the total number of transmissions required to deliver the demands of all users, which we refer to as the server (source) delivery time. We design the degree distributions of LT codes by solving suitably defined linear optimization problems, and numerically characterize the achievable delivery time for different coding schemes. We find that including a systematic phase (uncoded transmission) is significantly beneficial for scenarios with low demands, and that coding is necessary for efficiently delivering high demands. Different demand and error rate scenarios may require very different coding schemes. Growth codes and chunked codes do not perform as well as optimized LT codes in the heterogeneous communication scenario.
  
  PubDate: 2013-04-13T15:35:01Z
Real-time delay with network coding and feedback
- Abstract: Publication date: March 2013
  Source:Physical Communication, Volume 6
  Author(s): Eleni Drinea , Lorenzo Keller , Christina Fragouli
  We consider the problem of minimizing delay when broadcasting over erasure channels with feedback. A sender wishes to communicate the same set of μ messages to several receivers. The sender can broadcast a single message or a combination of messages at each timestep, through separate erasure channels. Receivers provide feedback as to whether the transmission was received. If, at some time step, a receiver cannot identify a new message, delay is incurred. Our notion of delay is motivated by real-time applications that request progressively refined input, such as the successive refinement of an image encoded using multiple description coding. Our setup is novel in that it combines coding techniques with feedback information to the end of minimizing delay. We show that it allows Θ ( μ ) benefits as compared to previous approaches for offline algorithms, while feedback allows online algorithms to achieve smaller delay compared to online algorithms without feedback. Our main complexity result is that the offline minimization problem is N P -hard both under scheduling and coding algorithms. However we show that coding does offer delay and complexity gains over scheduling. We also discuss online heuristics and evaluate their performance through simulations.
  
  PubDate: 2013-04-13T15:35:01Z
The role of coding in the choice between routing and coding for wireless unicast
- Abstract: Publication date: March 2013
  Source:Physical Communication, Volume 6
  Author(s): Ramakrishna Gummadi , Laurent Massoulie , Ramavarapu Sreenivas
  We consider the benefits of coding in wireless networks, specifically its role in exploiting the local broadcast property of the wireless medium. We first argue that for unicast, the throughput achieved with network coding is the same as that achieved without any coding. This argument highlights the role of a general max-flow min-cut duality and is more explicit than previous proofs. The maximum throughput can be achieved in multiple ways without any coding, for example, using backpressure routing, or using some centralized flow scheduler that is aware of the network topology. However, all such schemes, in order to take advantage of the local broadcast property, require dynamic routing decisions for choosing the next hop for each packet from among the nodes where it is successfully received. This choice seems to depend critically on feedback signaling information like queue lengths, or ARQ. In contrast, note that the use of network coding can achieve the same without such feedback, in exchange for decoding overhead. A key issue to be resolved in making a comparison between routing and coding would be how critical feedback signaling is, for the throughput of routing policies. With this motivation, we first explore how feedback at a given node affects its throughput, with arbitrary rates of its one-hop neighbors to the destination. Static routing policies which are essentially feedback independent, are considered. An explicit characterization of the optimal policies under such a feedback constraint is obtained, which turns out to be a natural generalization of both flooding and traditional routing (which does not exploit local broadcast, because the next hop is fixed prior to the transmission). When losses at the receivers are independent (still allowing for dependencies on transmissions by two different nodes, to model interference), the reduction in capacity due to constraining the feedback is limited to a constant fraction ( e − 1 = 37 % ) of the coding capacity, and gets arbitrarily close to optimal as the unconstrained capacity goes to zero. We also extend this analysis to a layered multihop network and also compare the throughput of flooding to backpressure via simulations for a layered network assuming independent losses. Finally, if there are dependencies in the losses seen by receivers from a single broadcast, the reduction could be arbitrarily bad, even with just two hops.
  
  PubDate: 2013-04-13T15:35:01Z
Editorial Board
- Abstract: Publication date: March 2013
  Source:Physical Communication, Volume 6
  
  PubDate: 2013-04-13T15:35:01Z
PHYCOM Editorial for 2012
- Abstract: Publication date: March 2013
  Source:Physical Communication, Volume 6
  Author(s): Ian F. Akyildiz
  
  PubDate: 2013-04-13T15:35:01Z
Implementation of physical-layer network coding
- Abstract: Publication date: March 2013
  Source:Physical Communication, Volume 6
  Author(s): Lu Lu , Taotao Wang , Soung Chang Liew , Shengli Zhang
  This paper presents the first implementation of a two-way relay network based on the principle of physical-layer network coding (PNC). To date, only a simplified version of PNC, called analog network coding (ANC), has been successfully implemented. The advantage of ANC is that it is simple to implement; the disadvantage, on the other hand, is that the relay amplifies the noise along with the signal before forwarding the signal. PNC systems in which the relay performs XOR or other denoising PNC mappings of the received signal have the potential for significantly better performance. However, the implementation of such PNC systems poses many challenges. For example, the relay in a PNC system must be able to deal with symbol and carrier-phase asynchronies of the simultaneous signals received from multiple nodes, and the relay must perform channel estimation before detecting the signals. We investigate a PNC implementation in the frequency domain, referred to as FPNC, to tackle these challenges. FPNC is based on OFDM. In FPNC, XOR mapping is performed on the OFDM samples in each subcarrier rather than on the samples in the time domain. We implement FPNC on the universal soft radio peripheral (USRP) platform. Our implementation requires only moderate modifications of the packet preamble design of 802.11a/g OFDM PHY. With the help of the cyclic prefix (CP) in OFDM, symbol asynchrony and the multi-path fading effects can be dealt with simultaneously in a similar fashion. Our experimental results show that symbol-synchronous and symbol-asynchronous FPNC have essentially the same BER performance, for both channel-coded and non-channel-coded FPNC systems.
  
  PubDate: 2013-04-13T15:35:01Z
Joint MMSE designs for analog network coding and different MIMO relaying schemes: A unified approach and performance benchmarks
- Abstract: Publication date: March 2013
  Source:Physical Communication, Volume 6
  Author(s): Jialing Li , Enoch Lu , I-Tai Lu
  To gain understanding of the analog network coding and different MIMO relaying schemes and to facilitate the scheme selection, there is a need for a unified approach and performance benchmarks. In this paper, analog network coding, direct transmission, Two-Hop relaying, and cooperative relaying schemes are analyzed and compared. A unified approach, the novel generalized iterative approach, is proposed for jointly designing the MMSE MIMO processors (including precoders, relay processors and decoders) for these schemes. Numerical results show that for each scheme, there exist system and channel parameter regime(s) where it is the most desirable among the four schemes. Performance benchmarks, physical insights and some guidelines for MIMO relaying scheme selection are presented.
  
  PubDate: 2013-04-13T15:35:01Z
Analysis and performance of network decoding strategies for cooperative network coding
- Abstract: Publication date: March 2013
  Source:Physical Communication, Volume 6
  Author(s): Jawad Manssour , Tafzeel ur Rehman Ahsin , Slimane Ben Slimane , Afif Osseiran
  In this work, we present two new low-complexity network decoding strategies for cooperative network coding in a multiple-access relay channel scenario. For these two strategies, Selection and Soft Combining and Majority Vote Network Decoding, along with the optimal joint network decoding, we derive expressions for bit error probability performance as a function of the signal-to-noise ratio (SNR) of the different Rayleigh fading links, and show the tightness of the derived bounds through simulation results. The two proposed schemes provide a similar bit error probability (BEP) performance compared to the optimal scheme, while having significantly lower complexity. Further, we study the effect of user pairing on the error performance by considering different SNRs on the user and relay links towards the destination. It is also shown that the error performance of the different schemes follows the same trend for a given user pairing strategy.
  
  PubDate: 2013-04-13T15:35:01Z
Introduction to the Special Issue on Network Coding and its Applications to Wireless Communications
- Abstract: Publication date: March 2013
  Source:Physical Communication, Volume 6
  Author(s): David Haccoun , Muriel Médard , Emina Soljanin , Raymond W. Yeung
  
  PubDate: 2013-04-13T15:35:01Z
Physical-layer network coding: Tutorial, survey, and beyond
- Abstract: Publication date: March 2013
  Source:Physical Communication, Volume 6
  Author(s): Soung Chang Liew , Shengli Zhang , Lu Lu
  The concept of physical-layer network coding (PNC) was proposed in 2006 for application in wireless networks. Since then it has developed into a subfield of network coding with wide implications. The basic idea of PNC is to exploit the mixing of signals that occurs naturally when electromagnetic (EM) waves are superimposed on one another. In particular, at a receiver, the simultaneous transmissions by several transmitters result in the reception of a weighted sum of the signals. This weighted sum is a form of network coding operation by itself. Alternatively, the received signal could be transformed and mapped to other forms of network coding. Exploiting these facts turns out to have profound and fundamental ramifications. Subsequent works by various researchers have led to many new results in the domains of (1) wireless communication, (2) information theory, and (3) wireless networking. The purpose of this paper is fourfold. First, we give a brief tutorial on the basic concept of PNC. Second, we survey and discuss recent key results in the three aforementioned areas. Third, we examine a critical issue in PNC: synchronization. It has been a common belief that PNC requires tight synchronization. Recent results suggest, however, that PNC may actually benefit from asynchrony. Fourth, we propose that PNC is not just for wireless networks; it can also be useful in optical networks. We provide an example showing that the throughput of a passive optical network (PON) could potentially be raised by 100% with PNC.
  
  PubDate: 2013-04-13T15:35:01Z
On the solvability of single rate 2-pair networks — A cut-based characterization
- Abstract: Publication date: March 2013
  Source:Physical Communication, Volume 6
  Author(s): Kai Cai , K.B. Letaief , Pingyi Fan , Rongquan Feng
  In this paper, we propose a subnetwork decomposition/combination approach to investigate the single rate 2-pair problem. It is shown that the solvability of a single rate 2-pair problem is completely determined by four specific link subsets, namely, A 1 , 1 , A 2 , 2 , A 1 , 2 and A 2 , 1 of its underlying network. As a result, an efficient cut-based algorithm to determine the solvability of a single rate 2-pair problem is presented.
  
  PubDate: 2013-04-13T15:35:01Z
Function computation via subspace coding
- Abstract: Publication date: March 2013
  Source:Physical Communication, Volume 6
  Author(s): Nikhil Karamchandani , Lorenzo Keller , Christina Fragouli , Massimo Franceschetti
  This paper considers function computation in a network where intermediate nodes perform randomized network coding, through appropriate choice of the subspace codebooks at the source nodes. Unlike traditional network coding for computing functions, that requires intermediate nodes to be aware of the function to be computed, our designs are transparent to the intermediate node operations.
  
  PubDate: 2013-04-13T15:35:01Z
Active topology inference using network coding
- Abstract: Publication date: March 2013
  Source:Physical Communication, Volume 6
  Author(s): Pegah Sattari , Christina Fragouli , Athina Markopoulou
  Our goal, is to infer the topology of a network when (i) we can send probes between sources and receivers at the edge of the network and (ii) intermediate nodes can perform simple network coding operations, i.e., additions. Our key intuition is that network coding introduces topology-dependent correlation in the observations at the receivers, which can be exploited to infer the topology. For undirected tree topologies, we design hierarchical clustering algorithms, building on our prior work in Fragouli et al. (2006). For directed acyclic graphs (DAGs), first we decompose the topology into a number of two-source, two-receiver (2-by-2) subnetwork components and then we merge these components to reconstruct the topology. Our approach for DAGs builds on prior work on tomography in Rabbat et al. (2006), and improves upon it by employing network coding to accurately distinguish among all different 2-by-2 components. We evaluate our algorithms through simulation of a number of realistic topologies and compare them to active tomographic techniques without network coding. We also make connections between our approach and alternatives, including passive inference, traceroute, and packet marking.
  
  PubDate: 2013-04-13T15:35:01Z
New results on performance analysis of opportunistic regenerative relaying
- Abstract: Available online 3 April 2013
  Publication year: 2013
  Source:Physical Communication
  
  In this paper, we investigate an opportunistic relaying scheme where the selected relay assists the source-destination (direct) communication. In our study, we consider a regenerative opportunistic relaying scheme in which the direct path may be unusable, and takes into account the effect of the possible erroneously detected and transmitted data at the selected relay. We first derive the signal-to-noise (SNR) statistics for each hop, which are used to determine accurate closed form expressions for end-to-end bit-error rate (BER) of binary phase-shift keying (BPSK) modulation and end-to-end outage probability for a transmission rate R over Rayleigh fading channels. Furthermore, we evaluate the asymptotical performance and deduce the diversity order. Finally, we validate our analysis by showing that performance simulation results coincide with our analytical results over linear network architecture.
  
  PubDate: 2013-04-05T20:05:03Z
Rate-lossless PAPR reduction in per-subcarrier antenna selection OFDM systems
- Abstract: Available online 22 March 2013
  Publication year: 2013
  Source:Physical Communication
  
  We propose a generalised rate-lossless technique for reducing the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing systems employing antenna selection on a per-subcarrier basis. The proposed technique, which is from the family of the active constellation extension (ACE) approaches to PAPR reduction, exploits the nulled subcarriers (for a given antenna) that arise through the antenna selection process to reduce the PAPR by introducing a controlled level of distortion to these subcarriers. We demonstrate that known PAPR reduction methods are unsuitable for per-subcarrier antenna selection systems, which motivates our modifications. We then show that our proposal achieves a much lower PAPR than traditional ACE methods for the given systems. Moreover, we demonstrate through a detailed theoretical analysis of the bit-error rate and a simulation analysis of the distortion transmitted on the nulled subcarriers, that the interference to the data signal caused by this distortion will not hinder practical system performance. Finally, we show that the efficacy of the proposed technique increases with the number of transmit antennas.
  
  PubDate: 2013-03-24T15:08:00Z
Complexity reduced detection for MIMO–OFDMA uplink with distinct frequency offsets from each user
- Abstract: Available online 16 March 2013
  Publication year: 2013
  Source:Physical Communication
  
  In this work, we propose a relatively low-complexity iterative algorithm for the detection of transmitted symbols at the uplink of a multiple-input multiple-output (MIMO) orthogonal frequency-division multiple-access (OFDMA) system. The algorithm allows distinct frequency-offsets (FO)s between each user and the base-station (BS). FOs cause inter-carrier-interference (ICI), which degrades the performance of the receiver and increases the computational-complexity to decode the transmitted symbols. In order to decrease the computational-complexity at each receive antenna the proposed algorithm accounts for the interference of subcarrier k onto only ± D nearby subcarriers and ignores the interference on remaining subcarriers. This yields a banded structured ICI matrix, which is exploited to design a low-complexity soft-interference-cancellation minimum mean-squared error (SIC-MMSE) equalizer. The effects of ignoring the subcarriers are compensated for by increasing the number of receive antennas. Simulation results show that for an uncoded system the bit-error-rate (BER) performance of the proposed algorithm outperforms the MMSE equalization and is very much close to the no FO scenario. Moreover, when convolution encoding is incorporated in the proposed algorithm outperforms the coded MMSE equalizer only after first iteration.
  
  PubDate: 2013-03-16T15:07:31Z
Joint user grouping and frequency allocation for multiuser SC-FDMA transmission
- Abstract: Available online 6 March 2013
  Publication year: 2013
  Source:Physical Communication
  
  This paper proposes strategies for user pairing and frequency allocation for a virtual multiple-input multiple-output (V-MIMO) single-carrier frequency division multiple access (SC-FDMA) transmission over intersymbol interference (ISI) channels. N u users, equipped with a single antenna each, compose one pair/group and transmit their data in the same frequency band to the base station (BS), equipped with multiple antennas. Multiuser equalization is applied at the BS. The pairs ( N u = 2 ) are either transmitting in subsequent time slots in a time division multiple access (TDMA) scheme using all available bandwidth or in different frequency chunks in a frequency division multiple access (FDMA) scheme. A generalization for N u > 2 users, called user grouping, is given for the FDMA scheme. For the optimization of joint frequency allocation and pairing/grouping, a low complexity solution is proposed and evaluated by simulations for the uplink of Long Term Evolution (LTE). As optimization criteria, the capacity of the resulting V-MIMO channel and the bit error rate (BER) after equalization are evaluated, respectively. The simulation results show that the proposed algorithms yield significant gains compared to random user pairing and frequency allocation and that using BER as an optimization criterion yields a significantly better performance.
  
  PubDate: 2013-03-08T15:14:10Z
A fuzzy extension of VIKOR for target network selection in heterogeneous wireless environments
- Abstract: Available online 24 February 2013
  Publication year: 2013
  Source:Physical Communication
  
  In a highly integrated ubiquitous wireless environment, the selection of a network that can fulfill end-users’ service requests while keeping their overall satisfaction at a high level, is vital. The wrong selection can lead to undesirable conditions such as unsatisfied users, weak Quality of Service (QoS), network congestions, dropped and/or blocked calls, and wastage of valuable network resources. The selection of these networks is performed during the handoff process when a Mobile Station (MS) switches its current Point of Attachment (PoA) to a different network due to the degradation or complete loss of signal and/or deterioration of the provided QoS. Traditional schemes perform the handoff necessity estimation and trigger the network selection process based on a single metric such as Received Signal Strength (RSS). These schemes are not efficient enough, as they do not take into consideration the traffic characteristics, user preferences, network conditions and other important system metrics. This paper presents a novel multi-attribute vertical handoff algorithm for heterogeneous wireless networks which achieves seamless mobility while maximizing end-users’ satisfaction. Two modules are designed to estimated the necessity of handoff and to select the target network. These modules utilize parallel Fuzzy Logic Controllers (FLCs) with reduced rule-set in combination with a network ranking algorithm developed based on Fuzzy VIKOR (FVIKOR). Simulation results are provided and compared with a benchmark.
  
  PubDate: 2013-02-28T13:34:44Z
Single-carrier frequency domain adaptive antenna array for uplink multi-user MIMO transmission in a cellular system
- Abstract: Available online 24 February 2013
  Publication year: 2013
  Source:Physical Communication
  
  In this paper, single-carrier frequency domain adaptive antenna array (SC-FDAAA) for the uplink multi-user multiple-input multiple-output (MIMO) transmission in a cellular system is studied. By employing AAA weight control in frequency domain, the base station (BS) can suppress the multi-user interference (MUI) and therefore realize multi-user SC transmission. In addition, channel frequency selectivity can be exploited to obtain the frequency diversity (or the multi-path diversity). The frequency domain signal-to-interference-plus-noise-ratio (SINR) after weight control is investigated and the computational complexity of the proposed receiver is analyzed. In numerical simulations, cellular structure using the frequency reuse is assumed and the effect of co-channel interference (CCI) is considered. The performance of the SC uplink multi-user MIMO transmission using SC-FDAAA is testified and compared with other multi-user detection schemes. The link capacity (maximum number of users/cell) and cellular link capacity (link capacity/frequency reuse factor) are also be evaluated.
  
  PubDate: 2013-02-28T13:34:44Z
On the use of frequency-domain cross-layer diversity techniques to cope with lost packets
- Abstract: Available online 24 February 2013
  Publication year: 2013
  Source:Physical Communication
  
  The Quality of Service (QoS) requirements for modern broadband wireless systems can be very high, with small error rates and delays. To preclude significant degradation on the spectral efficiency, these systems also require high throughputs. Lost packets, either due to errors or collisions, are usually discarded and need to be retransmitted, leading to performance degradation. An efficient alternative to simple retransmissions is to combine the signals associated to different transmission attempts. This paper analyses two time diversity approaches to cope with lost packets that are relatively similar at physical layer but treat different packet loss causes: a low-complexity diversity combining ARQ scheme (Automatic Repeat reQuest) employed in a TDMA (Time Division Multiple Access) architecture; and a Network Diversity Multiple Access (NDMA), which is a multi-packet reception approach able to separate multiple mobile terminals transmitting simultaneously in one slot using temporal diversity. This paper combines the use of these techniques in Single Carrier Frequency Domain Equalization (SC-FDE) systems, which are widely recognized as the best candidates for the uplink of future broadband wireless systems. It aims to present a comparison among the approaches focusing on error rate, throughput and delay performances, not discarding the implementation complexity issues.
  
  PubDate: 2013-02-28T13:34:44Z
Joint physical network coding and LDPC decoding for two way wireless relaying
- Abstract: Available online 9 February 2013
  Publication year: 2013
  Source:Physical Communication
  
  In this paper, we investigate the joint design of channel and network coding in bi-directional relaying systems and propose a combined low complexity physical network coding and LDPC decoding scheme. For the same LDPC codes employed at both source nodes, we show that the relay can decodes the network coded codewords from the superimposed signal received from the BPSK-modulated multiple-access channel. Simulation results shown that this novel joint physical network coding and LDPC decoding method outperforms the existing MMSE network coding and LDPC decoding method over AWGN and complex MAC channel.
  
  PubDate: 2013-02-12T10:47:07Z
Near optimal performance joint semi-blind channel estimation and data detection techniques for alamouti coded single-carrier (SC) MIMO communication systems
- Abstract: Available online 16 January 2013
  Publication year: 2013
  Source:Physical Communication
  
  In this paper, two novel joint semi-blind channel estimation and data detection techniques are proposed and investigated for Alamouti coded single-carrier (SC) multiple-input multiple-output (MIMO) communication system using Rayleigh flat fading channel model. In the first novel semi-blind technique, blind channel estimation can be performed by using singular value decomposition (SVD) of received output autocorrelation matrix and training based channel estimation for orthogonal training symbols can be performed by using orthogonal pilot maximum likelihood (OPML) algorithm. Further using, that semi-blind channel estimate and received output, data detection is performed by using Maximum likelihood (ML) detection. Finally we derived new training symbols from error covariance matrix of estimated data and known orthogonal training symbols, which further applied to OPML algorithm for final channel estimate. In the second novel semi-blind technique, blind channel estimation can be performed by using matrix traingularization based on householder QR decomposition (H-QRD) of received output autocorrelation matrix instead of SVD decomposition. Other steps are same as the first novel technique to calculate data detection and final channel estimation. Simulation results are presented under 2-PSK, 4-PSK, 8-PSK and 16-QAM data modulation schemes using 2 transmitters and different combinations of receiver antennas to investigate the performances of novel techniques compare to conventional whitening rotation (WR) and rotation optimization maximum likelihood (ROML) based semi-blind channel estimation techniques. Result demonstrates that novel techniques outperform others by achieving near optimal performance.
  
  PubDate: 2013-01-19T15:06:06Z
PHY modulation/rate control for fountain codes in 802.11a/g WLANs
- Abstract: Available online 2 January 2013
  Publication year: 2013
  Source:Physical Communication
  
  In this paper we consider the joint performance of fountain codes and 802.11a/g PHY modulation/coding. We consider optimality both in terms of maximizing goodput and minimizing energy, and results are presented for both theoretical and experimental channel models. In contrast to studies in cellular networks, we find that in 802.11a/g WLANs the cross-layer approach of a higher-layer fountain coding with a PHY layer modulation and FEC coding can yield very limited gains, and the PHY modulation/rate that optimizes the uncoded multicast performance is also close to optimal for fountain-coded multicast traffic over a wide-range of network conditions. This is potentially an important observation as it indicates that in 802.11a/g WLANs cross-layer design for multicast rate-control would bring few benefits and PHY layer modulation/rate-control can be carried out without regard to the use of fountain coding at higher layers.
  
  PubDate: 2013-01-03T15:05:45Z
A fuzzy admission control scheme for high quality video delivery over underlay cognitive radio
- Abstract: Available online 20 December 2012
  Publication year: 2012
  Source:Physical Communication
  
  In much of the traditional tight admission control algorithms for video cognitive users in cognitive networks, cognitive users are admitted sequentially based on the strict quality of service and interference constraints imposed on the cognitive and primary users respectively. The sequential admittance of cognitive users may impose some form of the queuing delay for time-sensitive cognitive users which may be unacceptable. On the other hand, traditional admission control schemes do not consider the quality of experience (QoE) of video users for admitting newly incoming ones. For addressing these issues and obtaining a more flexible quality-centric admission control policy by which the admission system can admit eligible cognitive users in parallel, and to cope with uncertainties in the acceptable levels of the video quality for different cognitive users (which may use different softwares/hardwares with different capabilities) and interference levels imposed on the primary users, a soft admission control (SAC) technique (named FQAC) is proposed by which the admission probability level for the parallel cognitive users can intelligently be controlled based on some linguistic input variables. Numerical analysis has been performed to validate the efficiency of the proposed quality-aware SAC mechanism.
  
  PubDate: 2012-12-22T18:04:59Z
Resource allocation in relay-assisted MIMO MAC systems with statistical CSI
- Abstract: Available online 20 December 2012
  Publication year: 2012
  Source:Physical Communication
  
  In this work, the issue of non-cooperative resource allocation in the uplink of a relay-assisted MIMO MAC (multiple input multiple output multiple access channel) system with statistical CSI (channel state information) is considered. The mobile transmitters pursue individual achievable ergodic rate maximization, whereas the relay aims at optimizing the global performance of the system. The problem is formulated as a Stackleberg game with the relay as the leader, and the multiple access users as the followers. Moreover, necessary and sufficient conditions for beamforming optimality at the relay are derived, which simplifies the resource allocation process. Finally, numerical results corroborate the theoretical findings.
  
  PubDate: 2012-12-22T18:04:59Z
Efficient coupled PHY and MAC use of physical Bursts in WiMAX/IEEE 802.16e networks
- Abstract: Available online 26 September 2012
  Publication year: 2012
  Source:Physical Communication
  
  We address several issues related to the efficient use of Bursts in WiMAX/IEEE 802.16e systems. We look on the relation between the PHY layer budding blocks (FEC blocks) and the allocation of MAC level frames (PDUs) over these FEC blocks. In particular, we show how to transmit a given amount of MAC level data bits over a given Burst in order to maximize the number of successfully transmitted data bits in the Burst. We also compute, given an amount of data bits to transmit, what is the Burst size that maximizes each of the following three performance criterion: the number of successfully transmitted data bits in the Burst, the maximum ratio between the number of successfully transmitted data bits to the Burst size, and the number of successfully transmitted data bits per PHY slot. For the first problem the paper shows how to optimally divide the Burst into PDUs and shows that sometimes it is more efficient to use less reliable Modulation/Coding schemes. For the second problem the paper shows that using the PHY slots efficiently is the best criterion to consider.
  
  PubDate: 2012-12-18T18:05:18Z
Optimal design of perfect DFT sequences
- Abstract: Available online 23 October 2012
  Publication year: 2012
  Source:Physical Communication
  
  In this paper, we propose a novel scheme to construct a large set with N ( N + 1 ) perfect sequences of length N , derived from an Inverse Discrete Fourier Transform (IDFT) of Chu and maximum-length sequences. This optimum set of perfect periodic autocorrelation sequences has a maximum absolute value of periodic cross-correlation strictly lower than N and close to the well known lower bound SQRT( N ). Moreover, we present a method to transform these perfect sequences into orthogonal sequences. A similar method is also proposed to obtain optimum bipolar codes derived from an alternative set of N 2 perfect sequences. In the design of perfect sequences, the difficulty is to achieve both low cross-correlation and low peak-to-average power ratio (PAPR). Many of the proposed perfect DFT sequences should have low PAPR and thus can be applied in an OFDM–CDMA (Orthogonal Frequency-Division Multiplexing–Code Division Multiple Access) communication system or in a simple CDMA communication system. Alternatively, the proposed perfect DFT sequences may be useful for pre-coded mapping in OFDM communication systems or for the design of radar waveform diversity sets.
  
  PubDate: 2012-12-18T18:05:18Z
Statistical distributions of instantaneous power and peak-to-average power ratio for single-carrier FDMA systems
- Abstract: Available online 12 November 2012
  Publication year: 2012
  Source:Physical Communication
  
  This paper analyzes the distributions of instantaneous power and peak-to-average power ratio (PAPR) for single-carrier frequency-division multiple-access (SC-FDMA) signals, where localized FDMA (LFDMA) and interleaved FDMA (IFDMA), as well as a block-interleaved FDMA (B-IFDMA) are considered as a part of the discrete Fourier transform (DFT)-precoded orthogonal frequency-division multiple access (OFDMA) systems adopted in the recent mobile communications standard. Comparisons of analytical and simulation results show a good match in terms of both the measures, which confirms the validity of the analytical framework developed in this work.
  
  PubDate: 2012-12-18T18:05:18Z
Secure communications over opportunistic-relay channels
- Abstract: Available online 19 November 2012
  Publication year: 2012
  Source:Physical Communication
  
  In this paper, we derive information-theoretic performance limits for secure communications over two classes of discrete memoryless relay channels. We consider two different communication scenarios over a four node wireless network comprising a source–destination pair, a relay node and a malicious node eavesdropping on the link between the relay and the destination. In both scenarios, the relay is (1) opportunistic in the sense that, it utilizes the communication opportunity to transmit its own message to the destination; and (2) constrained to secure its communication from the external eavesdropper. We present a novel achievability scheme, namely layered coding, to simultaneously deal with cooperation, cognition and confidentiality. We derive inner bounds on the capacity region for the two communication scenarios, and characterize the rate-penalty for satisfying the security constraints on the messages. Outer bounds are derived using auxiliary random variables which enable single-letter characterization. We also compare the opportunistic-relay models to the classical cognitive radio network setup. Finally, we discuss some of the advantages and drawbacks of our coding strategy in comparison to those in the existing literature, which provides interesting insights into the relative merits of the methods employed in this work for obtaining the capacity bounds.
  
  PubDate: 2012-12-18T18:05:18Z
Model and comparative analysis of reduced-complexity receiver designs for the LTE-advanced SC-FDMA uplink
- Abstract: Available online 19 November 2012
  Publication year: 2012
  Source:Physical Communication
  
  Due to its favorable peak-to-average power ratio (PAPR), a single-carrier frequency-division multiple access (SC-FDMA) scheme has been chosen for the 3GPP Long Term Evolution Advanced (LTE-A) uplink, as opposed to the orthogonal frequency-division multiple access (OFDMA) scheme used in the downlink. SC-FDMA, however, is prone to suffer from the effects of inter-symbol interference. When combined with multiple-input multiple-output (MIMO) transmission, the complexity of optimal detection for SC-FDMA grows exponentially with the product of the number of transmitting antennas and the channel length. A means to reduce the complexity is to equalize the channel in frequency domain (FDE) first, similar to OFDM, followed by detection in time domain, using well-developed standard receivers for flat fading MIMO channels. Apparently, these reduced-complexity two-stage receivers suffer from a rate loss as a consequence of their simplifying design assumptions. In this paper, we provide an extensive model of SC-FDMA transmission with FDE. Based on this model, we derive the achievable rates of four reduced-complexity two-stage receivers within the mismatched receiver framework in terms of generalized mutual information (GMI). The rate expressions allow to assess the rate loss as compared to the optimal receiver for varying channel parameters such as channel length and spatial correlation. It is shown, for instance, that a distributed subcarrier mapping which is beneficial from a frequency diversity point of view, substantially deteriorates the achievable rates. It is also explained how this loss can be compensated for by combining time domain detection with frequency domain interference cancelation.
  
  PubDate: 2012-12-18T18:05:18Z
Price-based interference control for two-tier femtocell networks
- Abstract: Available online 26 November 2012
  Publication year: 2012
  Source:Physical Communication
  
  This paper presents a novel price-based interference control scheme for two-tier femtocell networks, aiming to limit the interference from femtocell users to marcocell base station (MBS). Assuming that the MBS protects itself by pricing the interference power from the femtocell users, the femtocell users set their transmission powers by competitively selecting the interference power fractions under the constraint of the total tolerable interference. The problem of femtocell users’ competitive interference occupation process is cast into a non-cooperative interference power purchase game, and the existence and uniqueness of the Nash equilibrium is proved. Then, a distributed interference power fraction iterative algorithm is developed to find the Nash equilibrium of the game, and the convergence analyses in both synchronous and asynchronous case are presented. The distributed implementations are also shown. Simulation results show the convergence of the interference power fraction iterative algorithm and the effectiveness of the proposed interference control scheme.
  
  PubDate: 2012-12-18T18:05:18Z
Modeling and analysis of the radio wave depolarization in urban environments
- Abstract: December 2012
  Publication year: 2012
  Source:Physical Communication, Volume 5, Issue 4
  
  Depolarization is herein investigated for urban radio propagation. First, a theoretical study on some fundamental depolarizing mechanisms along one path, involving single and double reflection as well as wedge diffraction, is presented. Significant parameters impacting on XPR (cross polarization ratio) as the oblique incidence angle on walls or streets orientation with regards to the transmitter–receiver axis are studied thanks to simple theoretical models. XPR is also analyzed using deterministic propagation simulations in a realistic typical urban environment. The conclusions drawn in the theoretical study for single phenomena are also observed at the scale of several streets combining several paths: XPR decreases in proportion to these parameters change. These observations have been confirmed by polarimetric measurements conducted in Tokyo which are given in the last part.
  Highlights ► Useful keys are given to understand the physics of depolarization in urban areas. ► Use of matrix formalism permits a clear separation of depolarizing factors. ► Depolarization depends on the street orientation and incident elevation angle.
  
  PubDate: 2012-12-18T18:05:18Z
Receive antenna selection in diversely polarized MIMO transmissions with convex optimization
- Abstract: December 2012
  Publication year: 2012
  Source:Physical Communication, Volume 5, Issue 4
  
  In this paper, we present a low complexity approach to receive antenna selection for capacity maximization, based on the theory of convex optimization. By relaxing the antenna selection variables from discrete to continuous, we arrive at a convex optimization problem. We show via extensive Monte-Carlo simulations that the proposed algorithm provides performance very close to that of the optimal selection based on an exhaustive search. We consecutively optimize not only the selection of the best antennas but also the angular orientation of individual antenna elements in the array for a so-called true polarization diversity system. Dual- and triple-polarized antenna structures are a very good solution for realizing compact devices and also robust against many imperfections as compared to spatially separated antenna structures. Effectively we extend our work from two dimensional antenna structures to three dimensions. We model such polarized antenna systems and then apply convex optimization theory for selecting the best possible antennas in terms of capacity maximization. Channel parameters like transmit and receive correlations, and cross-polarization discrimination ( XPD ) are taken into consideration while modeling polarized systems. We compare our results with the Spatially Separated (SP) MIMO with and without selection by performing extensive Monte Carlo simulations. We found that by using a convex optimization algorithm, the performance of multiple polarized systems can be significantly enhanced. For certain channel conditions we observe that triple polarized systems increase the performance significantly compared to dual-polarized and spatially separated systems. We observed that applying selection at the receiver only boosts the performance in Non-Line of Sight (NLOS) channels compared to Line of Sight (LOS) channels.
  
  PubDate: 2012-12-18T18:05:18Z
Tri-polarized MIMO systems in real-world channels: Channel investigation and performance analysis
- Abstract: December 2012
  Publication year: 2012
  Source:Physical Communication, Volume 5, Issue 4
  
  Polarized multi-antenna systems are an effective solution for reducing inter-antenna spacing while still maintaining low inter-antenna correlation. Traditionally, only dual-polarized antenna systems are used for polarized transceivers. In this paper, tri-polarized antenna systems are investigated. Starting from the polarization mechanisms in the wireless propagation channel, it is shown that dual-polarized MIMO systems show high sensitivity to the transmitter and receiver orientation, which may be very critical in practical applications. Tri-polarized MIMO systems are introduced as a solution to obtain a robust MIMO performances, which are independent of the transmitter and receiver orientation. The performances of dual- and tri-polarized MIMO systems are evaluated on real-world measured channels, and the limits of each of these systems is highlighted.
  
  PubDate: 2012-12-18T18:05:18Z
Tri-polarized spectrum sensing based on an experimental outdoor-to-indoor cognitive-radio scenario
- Abstract: December 2012
  Publication year: 2012
  Source:Physical Communication, Volume 5, Issue 4
  
  Compared to classical spatially separated multiple antenna system, cross-polarized co-located antenna systems are an interesting way to reduce equipment size while reducing the inter-antenna correlation. In this paper the spectrum sensing of a Cognitive Radio (CR) system taking advantage of polarization diversity under Rayleigh fading is investigated and compared to an equivalent system using spatial diversity. This analysis is based on a theoretical formulation applied to a real-world scenario. For this purpose, an outdoor-to-indoor measurement campaign at a frequency of 3.5 GHz is realized, where an indoor secondary user senses the signals received from an outdoor primary base station. The signals received at each antenna are first combined and then applied to an energy detector. The theoretical expressions are simulated in the measurement context. The detection probability behavior as a function of distance between the Primary Transmitter (PTx) and the Secondary Terminal (STE) and the inter-antenna correlation effect on the sensing performance are studied.
  
  PubDate: 2012-12-18T18:05:18Z
The effect of polarization separation on the performance of Candecomp/Parafac-based vector sensor array processing
- Abstract: December 2012
  Publication year: 2012
  Source:Physical Communication, Volume 5, Issue 4
  
  In this paper we generalize the polarization separation measure introduced by Compton (1981) [2] for collocated sources, to the case of two sources with distinct DOAs recorded on a vector sensor array. We give a geometrical interpretation of this new measure and show that this polarization separation becomes essential for source estimation accuracy when the angular separation is insufficient.
  
  PubDate: 2012-12-18T18:05:18Z
Study of the asymptotic Cramér–Rao Bound for the COLD uniform linear array
- Abstract: December 2012
  Publication year: 2012
  Source:Physical Communication, Volume 5, Issue 4
  
  In this paper, we study the Cocentered Orthogonal Loop and Dipole pairs Uniform Linear Array (COLD-ULA) which is sensitive to the source polarization in the context of the localization of time-varying narrow-band far-field sources. We derive and analyze nonmatrix expressions of the deterministic Cramér–Rao Bound ( CRB (COLD) ) for the direction and the polarization parameters under the assumption that all the sources are lying in the azimuthal plane. We denote this bound by ACRB (COLD) , where the “A” stands for Asymptotic, meaning that the presented results are derived under the assumption that the number of sensors is sufficiently large. While, to our knowledge, closed-form (nonmatrix) expressions of the CRB (COLD) for multiple time-varying polarized sources signal do not exist in the literature, we show that the ACRB (COLD) takes a closed-form (nonmatrix) expression in this context and is a good approximation of the CRB (COLD) even if the number of sensor is moderate (about ten), if the source signals are not spatially too close. Our approach has two important advantages: (i) the computational complexity of the proposed closed-form of the bound is very low, compared to the brute force computation of a matrix-based deterministic CRB in case of time-varying model parameters and (ii) useful informations can be deduced from the closed-form expression on the behavior of the bound. In particular, we prove that the ACRB (COLD) for the direction parameter is not affected by the knowledge or the lack of it concerning the polarization parameters. Another conclusion is that with a COLD-ULA, more model parameters can be estimated than for the uniformly polarized ULA without degrading the estimation accuracy of the localization parameter. Finally, we also study the ACRB (COLD) for a priori known complex amplitudes.
  
  PubDate: 2012-12-18T18:05:18Z
Editorial Board
- Abstract: December 2012
  Publication year: 2012
  Source:Physical Communication, Volume 5, Issue 4
  
  PubDate: 2012-12-18T18:05:18Z
Polarization in Wireless Communications
- Abstract: December 2012
  Publication year: 2012
  Source:Physical Communication, Volume 5, Issue 4
  
  PubDate: 2012-12-18T18:05:18Z