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Communications, IEEE Transactions on

Issue 5 • Date May 2010

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Displaying Results 1 - 25 of 33
  • IEEE Transactions on Communications - Cover

    Page(s): c1 - c2
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    Freely Available from IEEE
  • Comment on "Accurate approximations to the sum of generalized random variables and applications in the performance analysis of diversity systems

    Page(s): 1313 - 1314
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (121 KB) |  | HTML iconHTML  

    Closed-form expressions of the precisely accurate error probability are given for equal gain diversity in generalized fading distributions, namely ??-?? and ??-??, considered by da Costa and Yacoub. View full abstract»

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  • Lattice precoding and pre-distorted constellation in degraded broadcast channel with finite input alphabets

    Page(s): 1315 - 1320
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (231 KB) |  | HTML iconHTML  

    In this letter, we propose a novel transmission scheme based on lattice precoding and pre-distorted constellation for the two-user AWGN degraded broadcast channel. In the proposed scheme, the lattice precoding is used for the weaker user to cancel the interference from the stronger user. The predistorted constellation is also proposed for the stronger user to overcome the nonlinear distortion due to the lattice precoding. Numerical results show that the achievable rate of the proposed transmission scheme is beyond the achievable rate region of the superposition coding and successive interference cancelation with finite input alphabets. View full abstract»

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  • Multiuser switched diversity scheduling systems with per-user threshold

    Page(s): 1321 - 1326
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (215 KB) |  | HTML iconHTML  

    A multiuser switched diversity scheduling scheme with per-user feedback threshold is proposed and analyzed in this paper. The conventional multiuser switched diversity scheduling scheme uses a single feedback threshold for every user, where the threshold is a function of the average signal-to-noise ratios (SNRs) of the users as well as the number of users involved in the scheduling process. The proposed scheme, however, constructs a sequence of feedback thresholds instead of a single feedback threshold such that each user compares its channel quality with the corresponding feedback threshold in the sequence. Numerical and simulation results show that thanks to the flexibility of threshold selection, where a potentially different threshold can be used for each user, the proposed scheme provides a higher system capacity than that for the conventional scheme. View full abstract»

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  • Coherent max-log decision fusion in wireless sensor networks

    Page(s): 1327 - 1332
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (291 KB) |  | HTML iconHTML  

    In this letter, we revisit the problem of distributed coherent decision fusion for wireless sensor networks where the sensors make independent decisions on the hypothesis under test and forward their decisions over noisy fading channels to the fusion center. We propose a novel fusion rule which is obtained by applying the max-log approximation to the optimal fusion rule. Furthermore, we provide a unified performance analysis of binary decision fusion which is applicable to the optimal fusion rule and various suboptimal fusion rules such as the max-log, maximal ratio combining, equal gain combining, and Chair-Varshney fusion rules. Our results show that the proposed max-log fusion rule outperforms all previously proposed suboptimal fusion rules and has a close-to-optimal performance. View full abstract»

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  • Convergence conditions for decentralized optimal traffic engineering in connectionless networks

    Page(s): 1333 - 1337
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (398 KB) |  | HTML iconHTML  

    This letter proposes a new and comprehensive set of convergence conditions for a distributed optimal traffic engineering method for connectionless networks. The method was originally proposed in, but we show in this letter that the convergence conditions accompanying the method in are not comprehensive and work only in some conditions. More precisely, it is shown that the adaptation laws in will misbehave in some situations. Consequently, they can not achieve optimal resource allocation. This letter presents the correct form of the convergence conditions under which the adaptation laws can effectively lead to optimal network utilization. View full abstract»

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  • Fiber hartley transform and optical indirect computation of discrete cosine transform

    Page(s): 1338 - 1343
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (389 KB) |  | HTML iconHTML  

    We present a recursive approach to implement the Discrete Hartley Transform in the optical domain by using a passive fiber network of asymmetric couplers, without phase shifters. The optical implementation of Discrete Cosine Transform is also derived, resulting in effective and flexible tools for optical data compression and signal processing. View full abstract»

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  • Extended multilevel prime codes for optical CDMA

    Page(s): 1344 - 1350
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (330 KB) |  | HTML iconHTML  

    In this paper, a new family of "multilevel" wavelength-time codes with expanded code cardinality, flexible code length, zero autocorrelation sidelobes, and the maximum cross-correlation function of any arbitrary positive integer n is constructed and analyzed. Besides having asymptotically optimal cardinality, the new codes can be partitioned into n levels, such that the cross-correlation function between any two code matrices in level l is at most l, where 1 ¿ l ¿ n. The hardlimiting performance of these multilevel codes is analyzed algebraically. Our results show that the unique partitioning property of these multilevel codes supports a trade-off between code cardinality and performance for meeting different system requirements, such as user capacity and throughput. View full abstract»

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  • Asymptotic error analysis of diversity schemes on arbitrarily correlated rayleigh channels

    Page(s): 1351 - 1355
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (236 KB) |  | HTML iconHTML  

    Asymptotic error rate expressions are derived for multi-branch equal gain combining and selection combining operating on arbitrarily correlated Rayleigh fading channels. These closed-form solutions are used to provide rapid and accurate estimation of the error rates in large signal-to-noise ratio regions. More importantly, they reveal additional insights into the transmission characteristics of linear diversity combining schemes operating on correlated Rayleigh fading channels. It is shown that the asymptotic error rates over correlated branches can be obtained by scaling the asymptotic error rates over independent branches with a factor, det(M), where det(M) is the determinant of the normalized channel correlation matrix. This relationship is valid for both coherent and noncoherent signalings. A similar relationship is also established for the outage probabilities of fading wireless systems employing multi-branch diversity reception. View full abstract»

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  • Performance evaluation of a multi-branch tree algorithm in RFID

    Page(s): 1356 - 1364
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (533 KB) |  | HTML iconHTML  

    Reading efficiency is one of the key factors to evaluate Radio Frequency Identification (RFID) systems. For the system using multi-branch protocols, the performance would be better if the tags are properly divided into multiple groups. This paper firstly gives the closed-form of system efficiency for binary tree algorithm. Based on the theoretical analysis, the optimal branches number is derived. An efficient multi-branch tree (EMBT) algorithm is proposed subsequently, along with a tag number estimation algorithm and performance evaluation. Both theoretical analysis and simulation results indicate that multi-branch tree algorithm has better performance than the conventional binary tree algorithm. System identification efficiency of the proposed method can achieve above 45%, while that of the binary tree algorithm is only 34.8%. View full abstract»

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  • Low-complexity decoding for non-binary LDPC codes in high order fields

    Page(s): 1365 - 1375
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (423 KB) |  | HTML iconHTML  

    In this paper, we propose a new implementation of the Extended Min-Sum (EMS) decoder for non-binary LDPC codes. A particularity of the new algorithm is that it takes into accounts the memory problem of the non-binary LDPC decoders, together with a significant complexity reduction per decoding iteration. The key feature of our decoder is to truncate the vector messages of the decoder to a limited number nm of values in order to reduce the memory requirements. Using the truncated messages, we propose an efficient implementation of the EMS decoder which reduces the order of complexity to ¿(nm log2 nm). This complexity starts to be reasonable enough to compete with binary decoders. The performance of the low complexity algorithm with proper compensation is quite good with respect to the important complexity reduction, which is shown both with a simulated density evolution approach and actual simulations. View full abstract»

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  • On the design of LDPC code ensembles for BIAWGN channels

    Page(s): 1376 - 1382
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB) |  | HTML iconHTML  

    Existing design methods for irregular Low-Density Parity-Check (LDPC) codes over the additive white Gaussian noise channel are based on using asymptotic analysis tools such as density evolution in an optimization process. Such a process is computationally expensive particularly when a large number of constituent variable node degrees are involved in the design. In this paper, we propose a systematic approach for the design of irregular LDPC codes. The proposed method, which is based on a pre-computed upper bound on the fraction of edges connected to variable nodes of degree 3, is considerably less complex than the conventional optimization approach. Through a number of examples, we demonstrate that using our method, ensembles with performance very close to those devised based on optimization, can be designed. In addition to having very good performance, the number of constituent variable node degrees in the designed ensembles is only three or four. This, in some cases, is much smaller than the corresponding number for optimization-based designs with similar performance. View full abstract»

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  • Quasi-cyclic LDPC codes: an algebraic construction

    Page(s): 1383 - 1396
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1023 KB) |  | HTML iconHTML  

    This paper presents two new large classes of QC-LDPC codes, one binary and one non-binary. Codes in these two classes are constructed by array dispersions of row-distance constrained matrices formed based on additive subgroups of finite fields. Experimental results show that codes constructed perform very well over the AWGN channel with iterative decoding based on belief propagation. Codes of a subclass of the class of binary codes have large minimum distances comparable to finite geometry LDPC codes and they offer effective tradeoff between error performance and decoding complexity when decoded with low-complexity reliability-based iterative decoding algorithms such as binary message passing decoding algorithms. Non-binary codes decoded with a Fast-Fourier Transform based sum-product algorithm achieve significantly large coding gains over Reed-Solomon codes of the same lengths and rates decoded with either the hard-decision Berlekamp-Massey algorithm or the algebraic soft-decision Kotter-Vardy algorithm. They have potential to replace Reed-Solomon codes in some communication or storage systems where combinations of random and bursts of errors (or erasures) occur. View full abstract»

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  • Optimized low-delay source-channel-relay mappings

    Page(s): 1397 - 1404
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (525 KB) |  | HTML iconHTML  

    The three-node relay channel with a Gaussian source is studied for transmission subject to a low-delay constraint. A design algorithm for joint source¿channel mappings is proposed and numerically evaluated. The designed system is compared with reference systems, based on modular source and channel coding, and the distortion-rate function for the Gaussian source using known achievable rates for the relay channel. There is a significant gain, in terms of decreased power, in using the (locally) optimized systems compared with the reference systems. The structure of the resulting source mapping and the relay mapping is visualized and discussed in order to gain understanding of fundamental properties of optimized systems. Interestingly, the design algorithm generally produces relay mappings with a structure that resembles Wyner-Ziv compression. View full abstract»

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  • Power series quantization for noisy channels

    Page(s): 1405 - 1414
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (311 KB) |  | HTML iconHTML  

    A recently proposed method for transmission of correlated sources under noise-free conditions, power series quantization (PSQ), uses a separate linear or nonlinear predictor for each quantizer region, and has shown to increase performance compared to several common quantization schemes for sources with memory. In this paper, it is shown how to apply PSQ for transmission of a source with memory over a noisy channel. A channel-optimized PSQ (COPSQ) encoder and codebook optimization algorithms are derived. The suggested scheme is shown to increase performance compared with previous state-of-the- art methods. View full abstract»

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  • Estimation of cubic nonlinear bandpass channels in orthogonal frequency-division multiplexing systems

    Page(s): 1415 - 1425
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (430 KB) |  | HTML iconHTML  

    Modeling and compensation of nonlinear communication channels has long been an important research topic in digital communications. A nonlinear bandpass channel is commonly modeled by a baseband equivalent Volterra series which relates the complex envelopes of the channel input and output. In this paper, we propose a novel method to estimate the frequency-domain baseband equivalent Volterra kernels of cubically nonlinear bandpass channels in orthogonal frequencydivision multiplexing (OFDM) systems. We recognize that the input signal for an OFDM system employing QAM or PSK modulations satisfies the properties of a kind of random multisine signal. By exploring the higher-order auto-moment spectra of the random multisine signal, a computationally efficient algorithm for determining the frequency-domain baseband equivalent Volterra kernels is derived. The obtained kernel estimates are optimal in the minimum mean square error (MMSE) sense. The proposed method can be used to estimate nonlinear bandpass channels for OFDM systems employing pure QAMs, pure PSKs, or a mixture of QAMs and PSKs. The effectiveness of the proposed method is demonstrated by applying it to estimate the nonlinear bandpass channel of an example OFDM system. Nonlinear channel compensators based on the Volterra model can benefit from the proposed method. View full abstract»

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  • Noise correlation in compact diversity receivers

    Page(s): 1426 - 1436
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (565 KB) |  | HTML iconHTML  

    The impact of antenna mutual coupling on signal correlation in multi-antenna receivers has been studied in great detail. By contrast, there has been little work on how mutual coupling affects noise. In this paper we present a noise model for a diversity receiver that includes noise generated by the antennas, front-end amplifiers, and other receiver components. This model shows that noise in a compact diversity receiver may be spatially correlated. Expressions relating noise correlation to properties of the antennas and amplifiers are derived and its impact on the outage probability of an optimal diversity combiner is studied. Examples illustrating the relationship between mutual coupling and noise correlation demonstrate how different noise sources may impact performance in profoundly different ways. View full abstract»

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  • On the robustness of dirty paper coding

    Page(s): 1437 - 1446
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (377 KB) |  | HTML iconHTML  

    A dirty-paper channel is considered, where the transmitter knows the interference sequence up to a constant multiplicative factor, known only to the receiver. Lower bounds on the achievable rate of communication are derived by proposing a coding scheme that partially compensates for the imprecise channel knowledge.We focus on a communication scenario where the signal-to-noise ratio is high. Our approach is based on analyzing the performance achievable using lattice-based coding schemes. When the power of the interference is finite, we show that the achievable rate of this lattice-based coding scheme may be improved by a judicious choice of the scaling parameter at the receiver. We further show that the communication rate may be improved, for finite as well as infinite interference power, by allowing randomized scaling at the transmitter. View full abstract»

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  • Distance-based node activation for geographic transmissions in fading channels

    Page(s): 1447 - 1456
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1176 KB) |  | HTML iconHTML  

    In wireless multi-hop packet radio networks (MPRNs) that employ geographic transmissions, sleep schedules or node activation techniques may be used to power off some nodes to conserve energy. We consider the problem of selecting which nodes should power on to listen to a scheduled transmission when the channel suffers from random fading. We choose the objective of maximizing the expected value of the distance covered in a single transmission between a transmitter and the farthest receiver that successfully receives the packet, under a constraint on the expected number of receivers that turn on. Since there is a tradeoff between the distance of a node from the transmitter and the probability that the node receives the message correctly, we propose to use node-activation based on link-distance (NA-BOLD). We investigate optimal and sub-optimal NA-BOLD schemes and compare their performance with that of schemes that use a constant sleep schedule for every node within some radius of the transmitter. Our results show that the proposed NA-BOLD schemes achieve significantly larger transmission distances than conventional schemes. View full abstract»

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  • Statistical channel model based on α-stable random processes and application to the 60 GHz ultra wide band channel

    Page(s): 1457 - 1467
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (549 KB) |  | HTML iconHTML  

    In this paper, we introduce a statistical model of the ultra wide band channel impulse response at 60 GHz. The novelty of our model is to consider the transfer function as an α-stable random process. It leads to a characterization of the channel by a deterministic measure that can be estimated from observed transfer functions. We present the theoretical framework of our proposed solution and the necessary tools to estimate the characteristic measure and generate the impulse responses. Simulations based on 2 GHz wide channel measurements in the 60 GHz band show the validity of our model. View full abstract»

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  • Information theoretic capacity of cellular multiple access channel with shadow fading

    Page(s): 1468 - 1476
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB) |  | HTML iconHTML  

    In this paper, we extend the well-known model for the Gaussian Cellular Multiple Access Channel originally presented by Wyner. The first extension to the model incorporates the distance-dependent path loss (maintaining a close relevance to path loss values in real world cellular systems) experienced by the users distributed in a planar cellular array. The density of base stations and hence the cell sizes are variable. In the context of a Hyper-receiver joint decoder, an expression for the information theoretic capacity is obtained assuming a large number of users in each cell. The model is further extended to incorporate the log-normal shadow fading variations, ensuring that the shadowing models are fairly comparable to the free space model. Using these fair models the effect of the shadow fading standard deviation on the information theoretic capacity of the cellular system is quantified. It is observed that a higher standard deviation results in lower capacity if the mean path loss is appropriately adjusted in order to model the mean loss due to the physical obstacles causing the shadow fading. The results validate that larger cell sizes and a higher standard deviation of shadowing (with appropriately adjusted mean path loss) results in lower spectral efficiency. View full abstract»

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  • Variable-rate M-PSK communications without channel amplitude estimation

    Page(s): 1477 - 1484
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (546 KB) |  | HTML iconHTML  

    Channel estimation at the receiver side is essential to adaptive modulation schemes, prohibiting low complexity systems from using variable rate and/or variable power transmissions. Towards providing a solution to this problem, we introduce a variable-rate (VR) M-PSK modulation scheme, for communications over fading channels, in the absence of channel gain estimation at the receiver. The choice of the constellation size is based on the signal-plus-noise (S+N) sampling value rather than on the signal-to-noise ratio (S/N). It is analytically shown that S+N can serve as an attractive simpler criterion, alternative to S/N, for determining the modulation order in VR systems. In this way, low complexity transceivers can use VR transmissions in order to increase their spectral efficiency under an error performance constraint. As an application, we utilize the proposed VR modulation scheme in equal gain combining (EGC) diversity receivers. View full abstract»

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  • Joint estimation of I/Q imbalance, CFO and channel response for MIMO OFDM systems

    Page(s): 1485 - 1492
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (383 KB) |  | HTML iconHTML  

    In this paper, we study the joint estimation of inphase and quadrature-phase (I/Q) imbalance, carrier frequency offset (CFO), and channel response for multiple-input multipleoutput (MIMO) orthogonal frequency division multiplexing (OFDM) systems using training sequences. A new concept called channel residual energy (CRE) is introduced. We show that by minimizing the CRE, we can jointly estimate the I/Q imbalance and CFO without knowing the channel response. The proposed method needs only one OFDM block for training and the training symbols can be arbitrary. Moreover when the training block consists of two repeated sequences, a low complexity two-step approach is proposed to solve the joint estimation problem. Simulation results show that the mean-squared error (MSE) of the proposed method is close to the Cramer-Rao bound (CRB). View full abstract»

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  • Network resource allocation for competing multiple description transmissions

    Page(s): 1493 - 1504
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (410 KB) |  | HTML iconHTML  

    Providing real-time multimedia services over a besteffort network is challenging due to the stringent delay requirements in the presence of complex network dynamics. Multiple description (MD) coding is one approach to transmit the media over diverse (multiple) paths to reduce the detrimental effects caused by path failures or delay. The novelty of this work is to investigate the resource allocation in a network, where there are several competing MD coded streams. This is done by considering a framework that chooses the operating points for asymmetric MD coding to maximize total quality of the users, while these streams are sent over multiple routing paths. The framework is based on the theoretical modeling where we consider two descriptions and high source coding rate region approximated within small constants. We study the joint optimization of multimedia (source) coding and congestion control in wired networks. These ideas are extended to joint source coding and channel coding in wireless networks. In both situations, we propose distributed algorithms for optimal resource allocation. In the presence of path loss and competing users, the service quality to any particular MD stream could be uncertain. In such circumstances it might be tempting to expect that we need greater redundancy in the MD streams to protect against such failures. However, one surprising aspect of our study reveals that for large number of users who compete for the same resources, the overall system could benefit through opportunistic (hierarchical) strategies. In general networks, our studies indicate that the user composition varies from conservative to opportunistic operating points, depending on the number of users and their network vantage points. View full abstract»

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  • Average power reduction for MSM optical signals via sparsity and uncertainty principle

    Page(s): 1505 - 1513
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB) |  | HTML iconHTML  

    Multiple subcarrier modulation is an appealing scheme for high-data rate optical communication. However a major drawback is its low average power efficiency. While subcarrier reservation is a common approach to combat this problem, little is known about the performance of algorithms that utilize subcarrier reservation. By combining properties of sparse signals with an abstract form of the Uncertainty Principle related to multiple subcarrier signals, we design an effective iterative method for constructing average-power-efficient multicarrier signals. Unlike most existing subcarrier reservation methods, our method provides a guaranteed bound for the achievable average power reduction as well as guaranteed rates of convergence. Numerical simulations demonstrate the performance of the proposed method. View full abstract»

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Aims & Scope

IEEE Transactions on Communications focuses on all telecommunications including telephone, telegraphy, facsimile, and point-to-point television by electromagnetic propagation.

 

 

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Meet Our Editors

Editor-in-Chief
Robert Schober
University of British Columbia