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Communications, IEEE Transactions on

Issue 8 • Date Aug. 2005

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Displaying Results 1 - 25 of 33
  • Table of contents

    Publication Year: 2005 , Page(s): c1 - c4
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  • IEEE Transactions on Communications publication information

    Publication Year: 2005 , Page(s): c2
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  • Maximum Spread of D -Dimensional Multiple Turbo Codes

    Publication Year: 2005 , Page(s): 1237 - 1242
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB) |  | HTML iconHTML  

    This letter presents the mathematical framework involved in the determination of an upper bound of the maximum spread value of a D -dimensional turbo code of frame size N . This bound is named the sphere bound (SB). It is obtained using some simple properties of Euclidian space (sphere packing in a finite volume). The SB obtained for dimension 2 is equal to \sqrt 2N . This result has already been conjectured. For dimension 3, we prove that the SB cannot be reached, but can be closely approached (at least up to 95%). For dimensions 4–6, the construction of particular interleavers shows that the SB can be approached up to 80%. Moreover, from the SB calculation, an estimate of the minimum Hamming weight of the weight-two input sequence is derived. View full abstract»

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  • Amplitude and Sign Adjustment for Peak-to-Average-Power Reduction

    Publication Year: 2005 , Page(s): 1243 - 1247
    Cited by:  Papers (5)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    In this letter, we propose a method to reduce the peak-to-mean-envelope-power ratio (PMEPR) of multicarrier signals by modifying the constellation. For M -ary phase-shift keying constellations, we minimize the maximum of the multicarrier signal over the sign and amplitude of each subcarrier. In order to find an efficient solution to the aforementioned nonconvex optimization problem, we present a suboptimal solution by first optimizing over the signs, and then optimizing over the amplitudes given the signs. We prove that the minimization of the maximum of a continuous multicarrier signal over the amplitude of each subcarrier can be written as a convex optimization problem with linear matrix inequality constraints. We also generalize the idea to other constellations such as 16-quadrature amplitude modulation. Simulation results show that by an average power increase of 0.21 dB, and not sending information over the sign of each subcarrier, PMEPR can be decreased by 5.1 dB for a system with 128 subcarriers. View full abstract»

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  • General Formula for Transmit Power Rise in CDMA Systems With Fast Power Control

    Publication Year: 2005 , Page(s): 1248 - 1251
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    Transmit power rise (TPR) in code-division multiple-access (CDMA) systems can be defined as the ratio of the average transmit power to the average receive power, where the average total channel power attenuation is assumed to be one. The TPR has been practically used in the universal mobile telecommunications system radio network planning for modeling of the joint impact of the fast power control, the propagation channel power attenuations, and the antenna diversity. In this letter, we present a general analytical formula for the calculation of TPR in CDMA systems with fast power control, for an arbitrary multipath power profile, arbitrary numbers of transmit and receive antennas, and arbitrary maximum transmit power. View full abstract»

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  • Performance Analysis of Predetection EGC in Exponentially Correlated Nakagami- m Fading Channel

    Publication Year: 2005 , Page(s): 1252 - 1256
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB) |  | HTML iconHTML  

    Using a Gil-Palaez lemma-based approach, we derive a general expression for the bit-error rate of a predetection equal gain combining receiver for coherent binary phase-shift keying modulation in exponentially correlated, Nakagami- m fading channel for an arbitrary number of branches. The obtained expressions are different for even and odd numbers of branches. Numerical results have been corroborated with simulations. View full abstract»

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  • Capacity of UWB Impulse Radio With Single-User Reception in Gaussian Noise and Dense Multipath

    Publication Year: 2005 , Page(s): 1257 - 1262
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    In this letter, we derive the capacity of ultra-wideband impulse radio (IR) systems employing optimal single-user reception. The environment in which the evaluation is set is that of a dense multipath and equal energy levels for interfering users, where multiple-access interference can be modeled as Gaussian. The investigation covers both binary and M -ary pulse position modulation approaches, employing either hard or soft decoding, and is targeted to low-signal-to-noise ratio/low-power environments where IR is supposed to work. View full abstract»

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  • Improvement and Analysis of Iterative Decision- Feedback Differential Demodulation

    Publication Year: 2005 , Page(s): 1263 - 1268
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB) |  | HTML iconHTML  

    In this letter, we consider iterative decision-feedback differential demodulation (iterative DFDM), which was proposed previously as a low-complexity solution for power-efficient transmission over flat fading channels without channel state information at the receiver. We devise a modified demodulator (inner decoder), which improves both the achievable bit-error rate performance and the convergence of iterative DFDM without increasing complexity. We also establish an equivalent decoder model for iterative DFDM which enables a convergence analysis by means of extrinsic information transfer charts. View full abstract»

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  • Pulse Position Amplitude Modulation for Time-Hopping Multiple-Access UWB Communications

    Publication Year: 2005 , Page(s): 1269 - 1273
    Cited by:  Papers (39)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    In this letter, we propose a new modulation scheme called pulse position amplitude modulation (PPAM) for ultra-wideband (UWB) communication systems. PPAM combines pulse position modulation and pulse amplitude modulation to provide good system performance and low computational complexity. The channel capacity of PPAM is determined for a time-hopping multiple-access UWB communication system. The error probability and performance bounds are derived for a multiuser environment. View full abstract»

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  • Estimators Using Noisy Channel Samples for Fading Distribution Parameters

    Publication Year: 2005 , Page(s): 1274 - 1277
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    The problem of estimating parameters of two main fading distributions, Ricean and Nakagami- m , is considered. Unlike most previous estimators which are designed to use samples from a noiseless channel, new estimators which use noise-corrupted samples are proposed. Both maximum-likelihood designs and moment-based designs are considered. The performances of the new estimators are examined and compared with those of previous estimators derived in the literature. Numerical results show the superiority of the new estimators for operation in noisy channels. View full abstract»

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  • Narrowband Interference Mitigation in Impulse Radio

    Publication Year: 2005 , Page(s): 1278 - 1282
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    Impulse radio (IR) systems have drawn attention during the last few years. These systems are planned to coexist with narrowband systems without interfering them. Nevertheless, the narrowband systems can cause interference which may jam the IR receiver. This letter analyzes a low-complexity narrowband interference (NBI)-mitigation algorithm for IR systems, based on minimal mean-square error combining. Theoretical analysis reveals that these algorithms nearly eliminate the NBI. The concept is also extended to the case where the receiver has more correlators than channel taps. View full abstract»

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  • A Simple Adaptive Coding Scheme for Multiuser Interference Suppression in Ultra-Wideband Radio Transmissions

    Publication Year: 2005 , Page(s): 1283 - 1287
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB) |  | HTML iconHTML  

    In this letter, we introduce a simple co-decoding scheme for ultra wideband (UWB) impulse radio systems impaired by multiuser interference (MUI). The proposed scheme exhibits an adaptive capability with respect to MUI degrading effects and, depending on the MUI level, it may switch from a hard-detection operating mode to a soft-detection one. So doing, the presented scheme is able to gain resistance against near–far effects. Several numerical tests support the conclusion that the presented scheme outperforms conventional ones currently planned for noise-limited UWB systems up to orders of magnitude in MUI-limited application scenarios. View full abstract»

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  • Reduced-Complexity Decoding of LDPC Codes

    Publication Year: 2005 , Page(s): 1288 - 1299
    Cited by:  Papers (281)  |  Patents (60)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (784 KB) |  | HTML iconHTML  

    Various log-likelihood-ratio-based belief-propagation (LLR-BP) decoding algorithms and their reduced-complexity derivatives for low-density parity-check (LDPC) codes are presented. Numerically accurate representations of the check-node update computation used in LLR-BP decoding are described. Furthermore, approximate representations of the decoding computations are shown to achieve a reduction in complexity by simplifying the check-node update, or symbol-node update, or both. In particular, two main approaches for simplified check-node updates are presented that are based on the so-called min-sum approximation coupled with either a normalization term or an additive offset term. Density evolution is used to analyze the performance of these decoding algorithms, to determine the optimum values of the key parameters, and to evaluate finite quantization effects. Simulation results show that these reduced-complexity decoding algorithms for LDPC codes achieve a performance very close to that of the BP algorithm. The unified treatment of decoding techniques for LDPC codes presented here provides flexibility in selecting the appropriate scheme from performance, latency, computational-complexity, and memory-requirement perspectives. View full abstract»

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  • Multistage Iterative Decoding With Complexity Reduction for Concatenated Space–Time Codes

    Publication Year: 2005 , Page(s): 1300 - 1309
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB) |  | HTML iconHTML  

    Space–time encoders exploiting concatenated coding structures are efficient in attaining the high rates available to large-dimensional multiple-transmitter, multiple-receiver wireless systems under fading conditions, while also providing maximal diversity benefits. We present a multistage iterative decoding structure that takes full advantage of the concatenated nature of the transmission path, treating the modulator and channel stages as an additional encoder in serial concatenation. This iterative decoder architecture allows an encoder employing decoupled coding and modulation to reach the performance of coded modulation systems. It also admits reduced-complexity decoding with a computational load that is nonexponential in the number of antennas or the transmission bit rate, and makes practical decoding for large transmitter arrays possible. The performance curves for these methods follow the shape of the Fano bound, with only a modest power penalty. View full abstract»

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  • Combined Coding and Training for Unknown ISI Channels

    Publication Year: 2005 , Page(s): 1310 - 1322
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB) |  | HTML iconHTML  

    The traditional method of sending a training signal to identify a channel, followed by data, may be viewed as a simple code for the unknown channel. Results in blind sequence detection suggest that performance similar to this traditional approach can be obtained without training. However, for short packets and/or time-recursive algorithms, significant error floors exist due to the presence of sequences that are indistinguishable without knowledge of the channel. In this paper, we reconsider training-signal design in light of recent results in blind sequence detection. Specifically, we consider the tradeoff between the complexity of receiver processing and the amount of training overhead required. More generally, we design training codes which combine modulation and training. In order to design these codes, we find an expression for the pairwise error probability of the joint maximum-likelihood (JML) channel and sequence estimator. This expression motivates a pairwise distance for the JML receiver based on principal angles between the range spaces of data matrices. The general code-design problem (generalized sphere packing) is formulated as the clique problem associated with an unweighted, undirected graph. We provide optimal and heuristic algorithms for this clique problem. For both long and short packets, we demonstrate that significant improvements are possible by jointly considering the design of the training, modulation, and receiver processing. View full abstract»

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  • Performance of Filterbank and Wavelet Transceivers in the Presence of Carrier Frequency Offset

    Publication Year: 2005 , Page(s): 1323 - 1332
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (544 KB) |  | HTML iconHTML  

    In this paper, we investigate the performance of a generic filterbank transceiver in the presence of a carrier frequency offset. We propose a theoretical model to compute the error probability in the case of a generic frequency-selective channel. Moreover, the proposed method is also extended to deal with nonuniform, i.e., wavelet, transceivers. The accuracy of the model is evaluated by means of computer simulations, using several types of filterbank transceivers. Systems based on cyclic prefix (CP) and zero padding (ZP) are considered to avoid interblock interference (IBI) in frequency-selective channels. The analytical results obtained with the proposed method allow us to quickly compare different systems, characterized by a different filterbank selectivity, as well as by different methods to combat IBI (ZP or CP). View full abstract»

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  • Energy-Efficient Scheduling for Wireless Sensor Networks

    Publication Year: 2005 , Page(s): 1333 - 1342
    Cited by:  Papers (54)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (480 KB) |  | HTML iconHTML  

    We consider the problem of minimizing the energy needed for data fusion in a sensor network by varying the transmission times assigned to different sensor nodes. The optimal scheduling protocol is derived, based on which we develop a low-complexity inverse-log scheduling (ILS) algorithm that achieves near-optimal energy efficiency. To eliminate the communication overhead required by centralized scheduling protocols, we further derive a distributed inverse-log protocol that is applicable to networks with a large number of nodes. Focusing on large-scale networks with high total data rates, we analyze the energy consumption of the ILS. Our analysis reveals how its energy gain over traditional time-division multiple access depends on the channel and the data-length variations among different nodes. View full abstract»

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  • Analytical Modeling of Offset-Induced Priority in Multiclass OBS Networks

    Publication Year: 2005 , Page(s): 1343 - 1352
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB) |  | HTML iconHTML  

    In this paper, we present for the first time an analytical model that quantifies the mechanism by which offset size affects priority in multiclass optical-burst switching (OBS) systems. Using the model, we derive an exact expression for the distribution of the number of bursts that contend with an arriving burst. The model is applicable to systems in which each class has an arbitrary burst-length distribution and an arbitrary offset size. We also derive accurate approximate expressions for the burst-blocking probability of premium-class traffic, as well as expressions for the sensitivity of premium-class performance to offset jitter and variations in the arrival rates of each class. In a case study, we find that scaling up a system in terms of the number of wavelengths and the traffic load significantly improves not only the burst-blocking performance of the premium class, but also its sensitivity to lower class traffic variations. We also use the model to dimension and provision the system to guarantee a minimum level of premium-class blocking and premium-class robustness to low-class load variations. View full abstract»

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  • Proportional Fair Space–Time Scheduling for Wireless Communications

    Publication Year: 2005 , Page(s): 1353 - 1360
    Cited by:  Papers (31)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB) |  | HTML iconHTML  

    We extend the proportional fair (PF) scheduling algorithm to systems with multiple antennas. There are K client users (each with a single antenna) and one base station (with n_R antennas). We focus on the reverse link of the system, and assume a slow-fading channel where clients are moving with pedestrian speed. Qualcomm's original PF scheduling algorithm satisfies the PF criteria only when the communication is constrained to one user at a time with no power waterfilling. However, the original PF algorithm does not generalize easily when we have n_R receive antennas at the base station. In this paper, we shall formulate the PF scheduling design as a convex optimization problem. One challenge is in the optimal power allocation over the multiantenna multiaccess capacity region, which is still an open problem. For practical consideration, we consider multiuser minimum mean-square error processing at the base station. To obtain first-order insight, we propose an asymptotically optimal PF scheduling solution. Using the proposed PF solution for a multiantenna base station, the system capacity is enhanced by exploiting the multiuser selection diversity, as well as the distributed multiple-input multiple-output configuration. It is found that the PF scheduler achieves a good balance between fairness and system capacity gain. View full abstract»

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  • Performance of DPSK Signals With Quadratic Phase Noise

    Publication Year: 2005 , Page(s): 1361 - 1365
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    Nonlinear phase noise induced by the interaction of the fiber Kerr effect and amplifier noises is a quadratic function of the electric field. When the dependence between the additive Gaussian noise and the quadratic phase noise is taken into account, the error probability for differential phase-shift keying signals is derived analytically. Depending on the number of fiber spans, the signal-to-noise ratio penalty is increased by up to 0.23 dB, due to the dependence between the Gaussian noise and the quadratic phase noise. View full abstract»

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  • Fair Multiuser Channel Allocation for OFDMA Networks Using Nash Bargaining Solutions and Coalitions

    Publication Year: 2005 , Page(s): 1366 - 1376
    Cited by:  Papers (182)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB) |  | HTML iconHTML  

    In this paper, a fair scheme to allocate subcarrier, rate, and power for multiuser orthogonal frequency-division multiple-access systems is proposed. The problem is to maximize the overall system rate, under each user's maximal power and minimal rate constraints, while considering the fairness among users. The approach considers a new fairness criterion, which is a generalized proportional fairness based on Nash bargaining solutions and coalitions. First, a two-user algorithm is developed to bargain subcarrier usage between two users. Then a multiuser bargaining algorithm is developed based on optimal coalition pairs among users. The simulation results show that the proposed algorithms not only provide fair resource allocation among users, but also have a comparable overall system rate with the scheme maximizing the total rate without considering fairness. They also have much higher rates than that of the scheme with max-min fairness. Moreover, the proposed iterative fast implementation has the complexity for each iteration of only O(K^2N\log _2 N+K^4) , where N is the number of subcarriers and K is the number of users. View full abstract»

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  • Differential MMSE: A Framework for Robust Adaptive Interference Suppression for DS-CDMA Over Fading Channels

    Publication Year: 2005 , Page(s): 1377 - 1390
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (600 KB) |  | HTML iconHTML  

    The linear minimum mean-squared error (MMSE) criterion is known to provide adaptive algorithms for interference suppression in direct-sequence (DS) code-division multiple-access (CDMA) systems. However, standard MMSE adaptation is not robust to fast fading, being unable to compensate for rapid channel variations. In this paper, we provide a framework for deriving robust adaptive algorithms in this setting based on a new differential MMSE (DMMSE) criterion, which is a constrained optimization problem in which the quantity to be tracked is the ratio of the data appearing in two successive observation intervals. When applied to a DS-CDMA system with short spreading waveforms (i.e., with period equal to the symbol interval) operating over a flat-fading channel, the DMMSE criterion avoids tracking the fades, exploiting the negligible variation of the fading gain over two consecutive symbols. For frequency-selective fading, the DMMSE criterion is extended to provide a new eigenrake receiver which provides interference suppression and diversity combining without requiring explicit information regarding the desired user's propagation channel. View full abstract»

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  • Spectral-Encoded UWB Communication Systems: Real-Time Implementation and Interference Suppression

    Publication Year: 2005 , Page(s): 1391 - 1401
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB) |  | HTML iconHTML  

    This paper considers a particular implementation of an ultra-wideband communication system that uses spectral encoding as both the multiple-access scheme and the interference-suppression technique. The main advantage of this technique is that the transmitted signal spectrum can be conveniently shaped to suppress narrowband interference and to not cause noticeable interference to overlaid systems. An extensive analysis of a possible implementation of this system by using surface acoustic-wave models is presented, and general expressions for the system performance are obtained. Numerical results show that a significant improvement in the system performance is obtained when the proposed interference-suppression method is used. View full abstract»

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  • Free-Space Optical MIMO Transmission With Q -ary PPM

    Publication Year: 2005 , Page(s): 1402 - 1412
    Cited by:  Papers (114)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB) |  | HTML iconHTML  

    The use of multiple laser transmitters combined with multiple photodetectors (PDs) is studied for terrestrial, line-of-sight optical communication. The resulting multiple-input/multiple-output channel has the potential for combatting fading effects on turbulent optical channels. In this paper, the modulation format is repetition Q -ary PPM across lasers, with intensity modulation. Ideal PDs are assumed, with and without background radiation. Both Rayleigh and log-normal fading models are treated. The focus is upon both symbol-/bit-error probability for uncoded transmission, and on constrained channel capacity. View full abstract»

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  • Space–Time Code Design for CPFSK Modulation Over Frequency-Nonselective Fading Channels

    Publication Year: 2005 , Page(s): 1413
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (35 KB)  

    We derive a novel space–time code-design criterion for continuous-phase frequency-shift keying (CPFSK) over frequency-nonselective fading channels. Our derivation is based on a specific matrix that is related to the input symbols of the CPFSK modulators. With this code-design criterion, we propose a simple interleaved space–time encoding scheme for CPFSK modulation over frequency-nonselective correlated fading channels to exploit potential temporal and spatial diversity advantages. Such an encoding scheme consists of a ring convolutional encoder and a spatial encoder, between which a convolutional interleaver is placed. A decoding algorithm that generates symbol metrics for the Viterbi decoder of convolutional codes from the spatial modulation trellis is examined. Simulation results confirm that the advantages of combination of the interleaved convolutional encoding (for temporal diversity) and the spatial encoding (for spatial diversity) are promising for various system parameters. 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