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Communications Letters, IEEE

Issue 9 • Date September 2012

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Displaying Results 1 - 25 of 52
  • Table of contents

    Publication Year: 2012 , Page(s): c1 - c4
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    Freely Available from IEEE
  • Staff list

    Publication Year: 2012 , Page(s): c2
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  • HARQ Feedback in Spectrum Sharing Networks

    Publication Year: 2012 , Page(s): 1337 - 1340
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB) |  | HTML iconHTML  

    This letter studies the throughput and the outage probability of spectrum sharing networks utilizing hybrid automatic repeat request (HARQ) feedback. We focus on the repetition time diversity and the incremental redundancy HARQ protocols where the results are obtained for both continuous and bursting communication models. The channel data transmission efficiency is investigated in the presence of both secondary user peak transmission power and primary user received interference power constraints. Finally, we evaluate the effect of secondary-primary channel state information imperfection on the performance of the secondary channel. Simulation results show that, while the throughput is not necessarily increased by HARQ, substantial outage probability reduction is achieved in all conditions. View full abstract»

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  • Hierarchical Space Shift Keying for Unequal Error Protection

    Publication Year: 2012 , Page(s): 1341 - 1344
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB) |  | HTML iconHTML  

    In this letter, we introduce the concept of enabling unequal error protection (UEP) with space shift keying (SSK)-type modulation that encodes the source information entirely in the antenna indices. Unique characteristics associated with SSK-type modulation as compared with conventional pulse/quadrature amplitude modulation (PAM/QAM) are discussed in the context of UEP design. Three general design concepts for two-level and three-level UEP are presented. Simulation results confirm the multilevel bit protection capabilities of the proposed hierarchical spatial constellation designs. View full abstract»

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  • A Novel PAPR Reduction Scheme for SC-OFDM with Frequency Domain Multiplexed Pilots

    Publication Year: 2012 , Page(s): 1345 - 1348
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (266 KB) |  | HTML iconHTML  

    In this letter, a novel data-pilot multiplexing scheme with reduced peak to average power ratio (PAPR) is introduced for single carrier (SC)-orthogonal frequency division multiplexing (OFDM) systems. In the proposed scheme, phases of SCOFDM symbols are rotated adaptively such that PAPR is reduced and circular shifts are introduced in the time domain (TD). To index the amount of phase rotation applied at the transmitter, a sequence of pilot symbols, which is unique for each phase rotation angle, is chosen from a predetermined set and multiplexed with the phase rotated SC-OFDM symbols in the frequency domain. Simulation results indicate that the proposed method can reduce the PAPR dramatically, and yield superior bit error rate (BER) performance compared to conventional methods. View full abstract»

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  • Cross Layer Adaptation with QoS Guarantees for Wireless Scalable Video Streaming

    Publication Year: 2012 , Page(s): 1349 - 1352
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (101 KB) |  | HTML iconHTML  

    In this paper, a cross-layer adaptation scheme is proposed for quality of service (QoS) provision in the scalable video streaming of high definition (HD) content. The cross-layer parameters, which contain the video rate, payload length of a packet, the mode of modulation and coding scheme (MCS), can be dynamically adapted to minimize distortion of a video streaming under the given delay bound. Based on the channel quality and rate-distortion parameters, the proposed scheme formulates the problem of parameter selection into an optimization problem. Simulation results show that our approach guarantees video quality under QoS constraints. View full abstract»

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  • Linear Equalization for Multicode MC-CDMA Downlink Channels

    Publication Year: 2012 , Page(s): 1353 - 1356
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (127 KB) |  | HTML iconHTML  

    We investigate multirate multicarrier code-division multiple-access (MC-CDMA) downlink systems with multicode transmission. Specifically, we design a new linear equalizer that outperforms the minimum mean-squared error (MMSE) per-carrier equalizer, without requiring the spreading codes of the interfering users. The complexity of this new linear equalizer is similar to that of the MMSE per-user equalizer, which however needs the spreading codes of the interfering users. Simulation results validate the effectiveness of the proposed equalizer, especially when there are few interfering users. View full abstract»

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  • Low Complexity Wiener Filtering in CDMA Systems Using a Class of Pseudo-Noise Spreading Codes

    Publication Year: 2012 , Page(s): 1357 - 1360
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (158 KB) |  | HTML iconHTML  

    Code division multiple access (CDMA) has become a widely adopted technology for wireless communications, particularly in mobile third generation systems (3G) and global positional system (GPS). In CDMA, a particular class of pseudonoise (PN) spreading codes yields a code-set Grammian with only two distinct eigenvalues. For these spreading codes, we propose a computationally efficient method for signal detection using Wiener filtering. Our approach relies on a matrix inversion step, where we gain in computational efficiency by using the Sherman-Morrison-Woodbury formula. The resulting approach involves significantly less computational load compared to popular approaches like Conjugate Gradient (CG) method and the (traditional) Cholesky decomposition. View full abstract»

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  • A Two-Dimensional Signal Space for Intensity-Modulated Channels

    Publication Year: 2012 , Page(s): 1361 - 1364
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (402 KB) |  | HTML iconHTML  

    A two-dimensional signal space for intensity-modulated channels is presented. Modulation formats using this signal space are designed to minimize average and peak power for a fixed minimum distance between signal points. The uncoded, high-signal-to-noise ratio, power and spectral efficiencies are compared to those of the best known formats. The new formats are simpler than existing subcarrier formats, and are superior if the bandwidth is measured as 90% in-band power. Existing subcarrier formats are better if the bandwidth is measured as 99% in-band power. View full abstract»

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  • Constrained Interleaving of Turbo Product Codes

    Publication Year: 2012 , Page(s): 1365 - 1368
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (146 KB) |  | HTML iconHTML  

    Constrained interleaving is presented to improve the performance of turbo product codes. Traditional row/column interleaving achieves the highest possible minimum distance while ignoring the error coefficients, whereas uniform interleaving focuses on reducing the error coefficients while ignoring the minimum distance. Constrained interleaving achieves the highest possible minimum distance thereby forcing error coefficients of all contributions below the highest achievable minimum distance to zero while simultaneously lowering the error coefficients of the remaining contributions close to those of uniform interleaving. We present a lower bound for the error rate with constrained interleaving, and demonstrate using 2D and 3D SPC codes that the bound can be approached reasonably well with a constrained interleaver that is only 2 to 3 times the size of a row/column interleaver. Constrained interleaving performs better than row/column interleaving and the improvement becomes more significant with increasing order of SPC. While uniform interleaving typically uses large interleaver sizes and creates an undesirable error floor, constrained interleaving performs better at much shorter interleaver sizes and eliminates the error floor. View full abstract»

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  • Non-Uniform 2-Slot Constellations for Relaying in Butterfly Network with Imperfect Side Information

    Publication Year: 2012 , Page(s): 1369 - 1372
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (154 KB) |  | HTML iconHTML  

    There are two key aspects affecting the performance of butterfly network with wireless network-coded relaying. The first one is the amount of Complementary Side Information (C-SI) at destinations and the second is given by a parametric Multiple-Access channel performance of source constellation alphabets. In this paper we show that theNon-uniform 2-slot (NuT) constellations, proposed originally for bi-directional relaying in the 2-Way Relay Channel (2-WRC), are suitable also for the butterfly network, combining the favorable parametric channel performance with the potential to increase the reliability of required C-SI (necessary for successful decoding at the final destination). Possessing both these qualities, the NuT alphabets surpass again the conventional linear modulation schemes, extending further the scope of their potential application. View full abstract»

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  • Distribution of Diagonal Elements of a General Central Complex Wishart Matrix

    Publication Year: 2012 , Page(s): 1373 - 1376
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (159 KB) |  | HTML iconHTML  

    We consider a general central complex Wishart matrix derived from non-circular complex Gaussian vectors. We present a technique for evaluation of the probability density, cumulative distribution, and moment generating functions of the joint distribution of the diagonal elements of the Wishart matrix. We give examples of application of the obtained results. View full abstract»

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  • OFDM PAPR Reduction by Shifting Null Subcarriers Among Data Subcarriers

    Publication Year: 2012 , Page(s): 1377 - 1379
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (238 KB) |  | HTML iconHTML  

    This proposed method reduces the peak-to-average power ratio (PAPR) of multi-carrier transmission, by exploiting null-subcarriers. Compared with the Partial Transmit Sequence Simulated Annealing (PTS-SA) method, the proposed method yields better PAPR reduction performance while consuming the same computation complexity and less channel side information (CSI). The proposed method also demonstrates better bit-error-rate (BER) performance and much lower computation complexity than Null-Switching when CSI is available. Meanwhile, our method is compatible with the current commercial systems and can incorporate with most other PAPR-reduction methods (such as partial transmit sequences, selective mapping, tone injection, trellis shaping). View full abstract»

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  • CRoWN: Content-Centric Networking in Vehicular Ad Hoc Networks

    Publication Year: 2012 , Page(s): 1380 - 1383
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (271 KB) |  | HTML iconHTML  

    Content-centric networking is a new paradigm conceived for future Internet architectures, where communications are driven by contents instead of host addresses. This paradigm has key potentialities to enable effective and efficient communications in the challenging vehicular environment characterized by short-lived connectivity and highly dynamic network topologies. We design CRoWN, a content-centric framework for vehicular ad-hoc networks, which is implemented on top of the IEEE 802.11p standard layers and is fully compliant with them. Performance comparison against the legacy IP-based approach demonstrates the superiority of CRoWN, thus paving the way for content-centric vehicular networking. View full abstract»

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  • On the Achievability of Interference Alignment for Three-Cell Constant Cellular Interfering Networks

    Publication Year: 2012 , Page(s): 1384 - 1387
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (334 KB) |  | HTML iconHTML  

    For a three-cell constant cellular interfering network, a new property of alignment is identified, i.e., an interference alignment (IA) solution obtained in a user-cooperation scenario can also be applied to a non-cooperation environment. By using this property, an algorithm is proposed by jointly designing transmit and receive beamforming matrices. Analysis and simulation results show that more degrees of freedom (DoF) can be achieved compared with conventional schemes in most cases. View full abstract»

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  • Improving TCP Performance over Optimal CSMA in Wireless Multi-Hop Networks

    Publication Year: 2012 , Page(s): 1388 - 1391
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (226 KB) |  | HTML iconHTML  

    Optimal CSMA (oCSMA) has been receiving extensive attentions for its provable optimality in throughput and fairness without message passing over wireless multi-hop networks. However, recent studies suggest that TCP over oCSMA performs poorly, hindering the deployment of oCSMA in real networks. In this letter, we show that just a simple, additional virtual queue at the MAC layer can significantly improve TCP performance when oCSMA is used as the underlying MAC. Through testbed-based experiments, we demonstrate that with our virtual queueing scheme, TCP flows achieve near-optimal throughput performance in various scenarios. View full abstract»

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  • A New Power Allocation Method for Parallel AWGN Channels in the Finite Block Length Regime

    Publication Year: 2012 , Page(s): 1392 - 1395
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    We investigate power allocation methods over AWGN channels in order to maximize the lower bound of the achievable rate, which is a more practical measure than channel capacity in the finite block length regime. Since the objective function of the optimization problem to solve is not concave, a part of the objective function is relaxed into a Taylor series expansion. Using the modified objective function, we propose a modified water-filling scheme to maximize the lower bound of the achievable rate with given power constraints, and verify the convergence of the proposed method. Numerical results show that the proposed scheme outperforms the conventional water-filling method in the finite block length regime. View full abstract»

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  • Distance Based Thresholds for Cluster Head Selection in Wireless Sensor Networks

    Publication Year: 2012 , Page(s): 1396 - 1399
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (143 KB) |  | HTML iconHTML  

    Central to the cluster-based routing protocols is the cluster head (CH) selection procedure that allows even distribution of energy consumption among the sensors, and therefore prolonging the lifespan of a sensor network. We propose a distributed CH selection algorithm that takes into account the distances from sensors to a base station that optimally balances the energy consumption among the sensors. NS-2 simulations show that our proposed scheme outperforms existing algorithms in terms of the average node lifespan and the time to first node death. View full abstract»

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  • Fast Scheduling for Delay Minimization in UWB Wireless Networks

    Publication Year: 2012 , Page(s): 1400 - 1403
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB) |  | HTML iconHTML  

    We study the optimal scheduling problem for delay minimization subject to traffic demand, transmit power and Signal-to-Noise-plus-Interference Ratio (SNIR) constraints in rate-controlled Ultra-Wideband (UWB) wireless networks. We first formulate the Linear Programming (LP) problem where the number of variables is exponential in the number of the links. We then propose the heuristic algorithm called Exclusion Region and Utility Maximization based Column Generation Method (EXUM-CGM) to solve the problem rapidly and efficiently. In EXUM-CGM, we decompose the large scale problem into two sub-problems, Restricted Master Problem (RMP) and Pricing Problem (PP). We adapt the exclusion region concept commonly used in UWB systems to the initialization of the RMP. Since the PP formulation is a non-linear integer programming problem, we propose a heuristic algorithm based on utility maximization. Through the simulations, we show that EXUM-CGM decreases the runtime of the exponential LP problem significantly while achieving very close-to-optimal solutions. View full abstract»

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  • ISAR: Improved Situation-Aware Routing Method for Wireless Mesh Backbones

    Publication Year: 2012 , Page(s): 1404 - 1407
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (227 KB) |  | HTML iconHTML  

    Due to the increasing performance requirements of wireless access services, adaptive interference resistant routing is crucial for providing reliable access and high bandwidth services via wireless mesh networks. In this letter, we propose an improved method for situation-aware routing, which extends the existing routing protocols via a refined situation-aware routing metric and a greedy load-balancing routing scheme. Simulation results demonstrate that the proposed method can achieve a higher throughput with lower transmission delay compared to previous routing schemes. View full abstract»

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  • Secrecy Rate for MISO Rayleigh Fading Channels with Relative Distance of Eavesdropper

    Publication Year: 2012 , Page(s): 1408 - 1411
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (198 KB) |  | HTML iconHTML  

    In this letter, we extend the results of secure transmission with artificial noise over multiple-input single-output (MISO) wiretap channels. There is a case such that the transmitter knows the relative distance of the eavesdropper. That is, it knows the distance from itself to the eavesdropper divided by its distance to the legitimate receiver. The study found that when the transmitter utilizes information about the relative distance of the passive eavesdropper, the system can achieve a significant increase in its secrecy rate. This work may be useful evaluating a secure communication system in where a secure-zone is enforced and is accessible, exclusively, to the legitimate receiver. View full abstract»

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  • Link Adaptation for Energy-Efficient Transmission with Receiver CSI

    Publication Year: 2012 , Page(s): 1412 - 1415
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (122 KB) |  | HTML iconHTML  

    This paper derives link adaptation solutions for different wireless communications channels, maximizing the energy efficiency. These solutions account for the transmission as well as processing power consumption. The minimum energy consumption is achieved by solving an optimization problem, which we prove to be quasi-convex. We show that a convex function characterizes the average number of retransmissions when errors are due to channel noise or fading. We also derive closed-form approximations of the optimal link parameters for Rayleigh and Nakagami channels. These indicate that the target outage probability is only a function of the packet length. View full abstract»

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  • An Efficient Time Synchronization Scheme for Broadband Two-Way Relaying Networks Based on Physical-Layer Network Coding

    Publication Year: 2012 , Page(s): 1416 - 1419
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (134 KB) |  | HTML iconHTML  

    We present an efficient time synchronization scheme for broadband two-way relaying networks based on two-phase physical layer network coding. Especially, a preamble structure is proposed in this letter for the synchronization. The synchronization approach exploits the preamble in frequency domain and time domain to effectively separate the mixed signals, and jointly estimate timing-offsets and channel parameters, respectively. Numerical results confirm that the suggested method is superior to the conventional scheme, and is very suitable for the synchronization in broadband two-way relaying networks based on two-phase physical layer network coding. View full abstract»

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  • Optimal Energy-Efficient Power Allocation for OFDM-Based Cognitive Radio Networks

    Publication Year: 2012 , Page(s): 1420 - 1423
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (145 KB) |  | HTML iconHTML  

    This letter investigates the energy-efficient power allocation for orthogonal frequency division multiplexing (OFDM) based cognitive radio networks (CRNs). The problem is to maximize the energy-efficiency measured using the "throughput per Joule" metric subject to the total transmit power and interference constraints. It is then transformed into an equivalent convex problem using parametric programming. Furthermore, an optimal iterative algorithm based on convex optimization theory and parametric programming is proposed. The numerical results show that the proposed optimal algorithm can achieve higher energy-efficiency than that obtained by solving the original problem directly because of its non-convexity. Energy-efficiency maximization can also achieve a good tradeoff between capacity and energy in CRNs. View full abstract»

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  • Impact of Rate Control on the Performance of a Cognitive Radio Ad-Hoc Network

    Publication Year: 2012 , Page(s): 1424 - 1427
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (141 KB) |  | HTML iconHTML  

    Location awareness allows to define a concurrent transmission region where a primary and a secondary networks can coexist. In this paper we investigate the impact of channel rate control on the performance of a cognitive radio ad hoc network overlaying an infrastructure-based system. The proposed algorithm adequately adjusts the secondary user rate to be as large as possible while respecting a given constraint on the achievable primary rate. As a consequence, the rate control scheme expands the concurrent transmission region and increases the average rate of the secondary users, without affecting the primary. Numerical results show that it is possible to increase the throughput of the cognitive ad-hoc network and therefore increase the efficiency of the spectrum utilization. View full abstract»

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George K. Karagiannidis
Aristotle University of Thessaloniki
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