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Communications, IEEE Transactions on

Issue 1 • Date Jan. 2004

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Displaying Results 1 - 25 of 35
  • Table of contents

    Publication Year: 2004 , Page(s): 1
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    Freely Available from IEEE
  • IEEE Transactions on Communications Society publication information

    Publication Year: 2004 , Page(s): 0_2
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  • Partially concatenated convolutional codes

    Publication Year: 2004 , Page(s): 1 - 5
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    We present a new concatenated code construction. The resulting codes can be viewed as intermediate between parallel and serially concatenated convolutional codes. Proper partitioning of the outer code sequence provides a new degree of freedom for code design. Various methods are considered to analyze code properties. View full abstract»

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  • Condensed table of Huffman coding, a new approach to efficient decoding

    Publication Year: 2004 , Page(s): 6 - 8
    Cited by:  Papers (12)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (112 KB) |  | HTML iconHTML  

    This letter introduces a new technique for designing and decoding Huffman codes. The key idea is to define a condensed Huffman table (CHT) that is smaller than the ordinary Huffman table and which leads to fast decoding. For example, the new approach has been shown to reduce the memory consumption by a factor of eight, compared with the single-side grown Huffman table. View full abstract»

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  • Efficient weight vector representation for closed-loop transmit diversity

    Publication Year: 2004 , Page(s): 9 - 16
    Cited by:  Papers (8)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    For a closed-loop transmit (Tx) diversity, the Tx weights are calculated at a receiver, and fed back to a transmitter. As the number of Tx antennas increases, the potential gain of closed-loop Tx diversity may be significant. However, the amount of feedback information, which is the number of Tx weights that should be fed back, linearly increases, and the performance improvement of a closed-loop Tx diversity system may not be as significant as expected due to delay in the feedback process. Thus, an efficient Tx weight representation, which can reduce the amount of feedback information, is needed. In this letter, a Tx weight vector representation is presented, and its performance is analyzed. Analysis shows that this weight vector representation, referred to as basis selection, significantly reduces the amount of feedback information with little performance degradation. View full abstract»

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  • Effective SNR for space-time modulation over a time-varying Rician channel

    Publication Year: 2004 , Page(s): 17 - 23
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB) |  | HTML iconHTML  

    Rapid temporal variations in wireless channels pose a significant challenge for space-time modulation and coding algorithms. This letter examines the performance degradation that results when time-varying flat fading is encountered when using trained and unitary space-time modulation. Performance is characterized for a channel having a constant specular component plus a time-varying diffuse component. A first-order autoregressive (AR) model is used to characterize diffuse channel coefficients that vary from symbol to symbol, and is shown to lead to an effective signal-to-noise ratio (SNR) that decreases with time. Differential modulation is shown to have an advantage in effective SNR over trained unitary modulation at high power. Simulation results are provided to support our analysis. View full abstract»

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  • RAKE reception with unequal power path signals

    Publication Year: 2004 , Page(s): 24 - 27
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    This letter analytically determines the effects of selective diversity on the performance of a RAKE receiver in dense multipath channels featuring an arbitrary power delay profile. The approach devised permits assessing the symbol-error probability of the RAKE receiver with simple computations, and determining the influence on system behavior of different power delay profiles and number of resolved paths, as well as signal bandwidth. View full abstract»

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  • Statistical modeling of W-CDMA signals for use over frequency-selective multipath channels

    Publication Year: 2004 , Page(s): 28 - 30
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB) |  | HTML iconHTML  

    This letter presents a mathematical model for the statistics of wideband code-division multiple-access signals which experience multipath fading. The statistics are obtained from numerically generated signals, and are then modeled with an offset noncentral chi distribution with three degrees of freedom. The mathematical model is tested against the numerically generated data by the use of a chi-square goodness-of-fit test. View full abstract»

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  • Impact of RF impairments on a DS-CDMA receiver

    Publication Year: 2004 , Page(s): 31 - 36
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB) |  | HTML iconHTML  

    This letter provides an analysis of the impact of classical radio frequency (RF) front-end impairments (RF mismatch and direct current (dc) offset) on the performance of direct-sequence code-division multiple-access (DS-CDMA) receivers; such issues are of particular importance in the case of zero intermediate-frequency (Zero-IF) receivers. Using a standard expression of the baseband signals as well as basic properties of spreading codes used in DS-CDMA communications, we show that the consequence of such RF mismatch and dc offset is essentially a degradation of the wanted signal's level and an increase of the noise power. We give closed-form expressions (in Eb/N0 form) for both. The results are then shown to be in accordance with numerical simulations utilizing the codes of the universal terrestrial radio access in the frequency-division duplex mode downlink standard. View full abstract»

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  • Line strip spot-diffusing transmitter configuration for optical wireless systems influenced by background noise and multipath dispersion

    Publication Year: 2004 , Page(s): 37 - 45
    Cited by:  Papers (32)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB) |  | HTML iconHTML  

    In this letter, we propose and evaluate a novel optical wireless configuration that employs a multibeam transmitter in conjunction with a narrow field-of-view direction diversity receiver. Such a configuration overcomes the drawbacks and combines the advantages of both types of optical wireless links, including line-of-sight and diffuse transmission. A multibeam transmitter placed on the communication floor was adopted to produce multiple diffusing spots on the middle of the ceiling in the form of a line strip. The design goal is to reduce the effect of intersymbol interference and to improve the signal-to-noise ratio (SNR) when the system operates under the constraints of background noise and multipath dispersion. Simulation results show that our line strip multibeam transmitter (LSMT) with only three branches diversity gives about 23 dB SNR improvement over the conventional system. The results also show that the multipath dispersion, which induces pulse spread, is significantly reduced when the LSMT with diversity detection is used. View full abstract»

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  • Multiple-symbol double-differential detection based on least-squares and generalized-likelihood ratio criteria

    Publication Year: 2004 , Page(s): 46 - 49
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    Two algorithms for double-differential detection of multiple phase-shift keying modulation are proposed, based on a least-squares criterion and a generalized-likelihood ratio test, respectively. While both algorithms take advantage of the performance gain obtained by observing the received signal over an observation interval longer than that required for symbol-by-symbol detection, the former has the important advantage of reduced implementation complexity, whereas the latter offers better performance. View full abstract»

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  • BER performance of dual predetection EGC in correlative Nakagami-m fading

    Publication Year: 2004 , Page(s): 50 - 53
    Cited by:  Papers (29)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB) |  | HTML iconHTML  

    In this letter, an approach to the evaluation of the error performance in dual predetection equal-gain combining (EGC) systems over correlated Nakagami-m fading channels is presented. Deriving an infinite series representation for the characteristic function of the sum of two correlated Nakagami-m variables, a closed-form formula is extracted for binary phase-shift keying and coherent binary frequency-shift keying, while several other modulation schemes are studied, capitalizing on a Parsevals's theorem-based approach, previously published. Numerical results and simulations are also presented to illustrate the proposed mathematical analysis and to point out the effect of the input signal-to-noise ratio unbalancing, the fading severity, and the fading correlation on the system's error performance. View full abstract»

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  • V.92: the last dial-up modem?

    Publication Year: 2004 , Page(s): 54 - 61
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB) |  | HTML iconHTML  

    Ever since the first dial-up modems appeared in the 1960s, their obsolescence has been repeatedly predicted. However, contrary to such predictions, dial-up modems thrived in the 1980s and 1990s as a result of the slow rollout of residential digital services and the unprecedented growth of internet and remote access. Since the first 300 b/s dial-up modem standard (V.21), modem speeds have increased steadily. Most recently, International Telecommunications Union (ITU) Recommendation V.90 (1998) takes advantage of the direct digital-network connection of an internet service provider (ISP) remote-access server to achieve speeds of more than 50 kb/s downstream (from ISP to a user). However, for upstream transmission (from a user to ISP), V.90 employs the older V.34 modulation (1994), which typically delivers on the order of 30 kb/s. A new ITU modem standard called V.92 increases upstream rates to above 40 kb/s, again by taking advantage of pulse code modulation connections. In this paper, we present the transmission scheme that has been adopted for V.92. It involves a generalization of Tomlinson-Harashima precoding. We predict that V.92 will be the last dial-up modem standard. However, we have to wonder whether we might be falling into the same trap into which many others have fallen in the past. The future will be the judge!. View full abstract»

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  • On the design of MIMO block-fading channels with feedback-link capacity constraint

    Publication Year: 2004 , Page(s): 62 - 70
    Cited by:  Papers (148)  |  Patents (33)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB) |  | HTML iconHTML  

    In this paper, we propose a combined adaptive power control and beamforming framework for optimizing multiple-input/multiple-output (MIMO) link capacity in the presence of feedback-link capacity constraint. The feedback channel is used to carry channel state information only. It is assumed to be noiseless and causal with a feedback capacity constraint in terms of maximum number of feedback bits per fading block. We show that the hybrid design could achieve the optimal MIMO link capacity, and we derive a computationally efficient algorithm to search for the optimal design under a specific average power constraint. Finally, we shall illustrate that a minimum mean-square error spatial processor with a successive interference canceller at the receiver could be used to realize the optimal capacity. We found that feedback effectively enhances the forward channel capacity for all signal-to-noise ratio (SNR) values when the number of transmit antennas (nT) is larger than the number of receive antennas (nR). The SNR gain with feedback is contributed by focusing transmission power on active eigenchannel and temporal power waterfilling . The former factor contributed, at most, 10log10(nT/nR) dB SNR gain when nT>nR, while the latter factor's SNR gain is significant only for low SNR values. View full abstract»

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  • Blind multiuser detection in uplink CDMA with multipath fading: a sequential EM approach

    Publication Year: 2004 , Page(s): 71 - 81
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB) |  | HTML iconHTML  

    We consider joint channel estimation and data detection in uplink asynchronous code-division multiple-access systems employing aperiodic (long) spreading sequences in the presence of unknown multipath fading. Since maximum-likelihood (ML) sequence estimation is too complex to perform, multiuser receivers are proposed based on the sequential expectation-maximization (EM) algorithm. With the prior knowledge of only the signature waveforms, the delays and the second-order statistics of the fading channel, the receivers sequentially estimate the channel using the sequential EM algorithm. Moreover, the snapshot estimates of each path are tracked by linear minimum mean-squared error filters. The user data are detected by a ML sequence detector, given the channel estimates. The proposed receivers that use the exact expressions have a computational complexity O(2K) per bit, where K is the number of users. Using the EM algorithm, we derive low-complexity approximations which have a computational complexity of O(K2) per bit. Simulation results demonstrate that the proposed receivers offer substantial performance gains over conventional pilot-symbol-assisted techniques and achieve a performance close to the known channel bounds. Furthermore, the proposed receivers even outperform the single-user RAKE receiver with Nyquist pilot-insertion rate in a single-user environment. View full abstract»

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  • Contention resolution in random-access wireless networks based on orthogonal complementary codes

    Publication Year: 2004 , Page(s): 82 - 89
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    This paper proposes a new method for contention resolution in random-access wireless networks. Using orthogonal complementary codes to design access-request packets, users can reserve channel access successfully, even in severe contentions. Collisions among access-request packets can be resolved and exploited, whereas collisions among data packets are avoided. System throughput and delay performance can be enhanced, because random-access contention becomes transparent. Specifically, system throughput approaches the offered load up to the maximum value one with improved average packet delay performance. A joint layer design approach is proposed with both the physical layer signal-detection algorithm and the medium access-control layer random-access protocol. The performance is analyzed with the consideration of signal detection errors. Simulations are performed to demonstrate its superior performance. View full abstract»

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  • Group-orthogonal multicarrier CDMA

    Publication Year: 2004 , Page(s): 90 - 99
    Cited by:  Papers (55)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB) |  | HTML iconHTML  

    In the presence of frequency-selective multipath fading channels, code-division multiple access (CDMA) suffers from multiuser interference (MUI) and intersymbol interference (ISI); but when properly designed, it enjoys multipath diversity. Orthogonal frequency-division multiple access (OFDMA) is MUI-free, but it does not enable the available channel diversity without employing error-control coding. On the other hand, coded OFDMA may achieve lower diversity than a CDMA system employing the same error-control codes. In this paper, we merge the advantages of OFDMA and CDMA to minimize MUI effects, and also enable the maximum available diversity for every user. In our group orthogonal multicarrier CDMA (GO-MC-CDMA) scheme, groups of users share a set of subcarriers. By judiciously choosing group subcarriers, we guarantee that every user transmits with maximum diversity. MUI is only present among users in the same group, and is suppressed via multiuser detection, which becomes practically feasible because we assign a small number of users per group. Performance is analyzed, and simulations are carried out to illustrate the merits of GO-MC-CDMA relative to existing alternatives. View full abstract»

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  • MU-MIMO channel adapted precoding for MAI/ISI-free uplink burst transmission

    Publication Year: 2004 , Page(s): 100 - 109
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    This paper considers the uplink of a multiuser direct-sequence code-division multiple-access communication system based on burst transmission over frequency-selective channels. A new precoding method is presented that is able to take benefit from the space diversity introduced at the mobile transmitters and at the common receiver. User-specific spreading codes are designed so that filters matched to the total impulse responses can remove completely the interference and maximize the signal-and-interference-plus-noise ratios. It is analytically proved that an infinite number of solutions is available to orthogonalize the system. Three particular solutions are considered. A progressive solution is firstly proposed to provide orthogonality in a simple way. Then a near-optimum solution is proposed to orthogonalize the system while attempting to reduce the total transmitted power. The minimization of the total transmitted power is a complex problem of nonlinear optimization that can only be solved using an iterative algorithm. The third solution proposed is based on an iterative algorithm. Those three solutions are analyzed in term of their different performance for a varying number of transmit and receive antennas. A comparison is also provided with a system using a conventional set of binary codes and linear or decision-feedback minimum mean-square error joint detection. It is shown that the near-optimum and iterative solutions are the only ones that are able to fully benefit from the space diversity. View full abstract»

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  • Merging multicarrier CDMA and oscillating-beam smart antenna arrays: exploiting directionality, transmit diversity, and frequency diversity

    Publication Year: 2004 , Page(s): 110 - 119
    Cited by:  Papers (5)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB) |  | HTML iconHTML  

    In this paper, a novel merger of multicarrier code-division multiple access (MC-CDMA) and smart antenna arrays is introduced. Here, a group of Q carriers in the MC-CDMA system is applied to its own M-element smart antenna array at the base station (BS). The smart antennas are located in close proximity to one another. We generate a transmit diversity gain at the receiver by carefully moving (oscillating) the antenna array's pattern. The pattern oscillation is achieved by applying appropriate time-varying phases to array elements of each smart antenna. The beam pattern oscillation ensures a mainlobe at the position of the intended user and small oscillations in the beam pattern. This beam pattern oscillation leads to a time-varying channel with a controllable coherence time; hence, a transmit diversity benefit, in the form of a time diversity benefit, is available at the receiver. Employing MC-CDMA with the proposed smart antenna at the BS, we achieve: 1) directionality which creates high network capacity via space-division multiple access; 2) a transmit diversity gain which supports high performance at the receiver in the mobile unit; and 3) increased capacity and performance via MC-CDMA's ability to support both CDMA and frequency diversity benefits, respectively. View full abstract»

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  • Space-time dynamic signature assignment for the reverse link of DS-CDMA systems

    Publication Year: 2004 , Page(s): 120 - 129
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB) |  | HTML iconHTML  

    Multiple-access interference is one of the major impediments in the reverse link of code-division multiple-access (CDMA) systems, due to the synergy of the users' spreading codes, transmission delays, and the channel characteristics. A space-time dynamic signature-assignment (DSA) algorithm was briefly described by the authors in a previous paper. In this paper, we further elaborate on the space-time DSA approach and its receiver structure for the reverse link of direct-sequence (DS)-CDMA systems using multiple antennas at the receiver. The space-time DSA dynamically assigns the users' spreading codes and transmission delays, i.e., to assign the user signatures, in order to minimize mutual crosscorrelations. In assigning the signatures, the DSA adopts a low-complexity iterative algorithm which utilizes channel information and aims to maximize the signal-to-interference-plus-noise ratio of the poorest performing user at the base station. Analytic results as well as further simulation results are provided to support our arguments. View full abstract»

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  • Harmonic mean and end-to-end performance of transmission systems with relays

    Publication Year: 2004 , Page(s): 130 - 135
    Cited by:  Papers (230)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB) |  | HTML iconHTML  

    Closed-form expressions for the statistics of the harmonic mean of two independent and identically distributed gamma variates are presented. The probability density function of the harmonic mean of two F variates is also derived. These statistical results are then applied to study the performance of wireless communication systems with nonregenerative relays over flat Nakagami fading channels. More specifically, outage probability formulas for noise-limited systems as well as systems affected by interference are obtained. Furthermore, general expressions for average bit-error rates are also derived. Finally, comparisons between regenerative and nonregenerative systems are presented. Numerical results show that the former systems clearly outperform the latter ones for low average signal-to-noise ratios (SNRs). They also show that the two systems have similar performance at high average SNRs. View full abstract»

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  • Recursive short-data-record estimation of AV and MMSE/MVDR linear filters for DS-CDMA antenna array systems

    Publication Year: 2004 , Page(s): 136 - 148
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB) |  | HTML iconHTML  

    The presence of the desired signal during estimation of the minimum mean-square error (MMSE)/minimum-variance distortionless-response (MVDR) and auxiliary-vector (AV) filters under limited data support leads to significant signal-to-interference-plus-noise ratio (SINR) performance degradation. We quantify this observation in the context of direct-sequence code-division multiple-access (DS-CDMA) communications by deriving close approximations for the mean-square filter estimation error, the probability density function of the output SINR, and the probability density function of the symbol-error rate (SER) of the sample matrix inversion (SMI) receiver evaluated using both a desired-signal-"present" and desired-signal-"absent" input covariance matrix. To avoid such performance degradation, we propose a DS-CDMA receiver that utilizes a simple pilot-assisted algorithm that estimates and then subtracts the desired signal component from the received signal prior to filter estimation. Then, to accommodate decision-directed operation, we develop two recursive algorithms for the on-line estimation of the AV and MMSE/MVDR filter and we study their convergence properties. Finally, simulation studies illustrate the SER performance of the overall receiver structures. View full abstract»

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  • Precise error-rate analysis of bandwidth-efficient BPSK in Nakagami fading and cochannel interference

    Publication Year: 2004 , Page(s): 149 - 158
    Cited by:  Papers (68)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    The bit-error rate (BER) of bandlimited binary phase-shift keying in a fading and cochannel interference (CCI) environment is derived for the case of perfect coherent detection. The fading-and-interference model assumed is general and of interest for microcellular system studies. The model allows both desired signal and interfering signals to experience arbitrary amounts of fading severity. A precise BER expression is derived using a characteristic function method. Using this accurate analytical result, the impact of the interfering users' fading severity on the desired user-error rate is examined. The BERs obtained under perfect coherent detection are also valid as lower performance bounds for practical realizable receivers where ideal coherent detection is difficult to implement. The error-rate performance of a novel bandwidth-efficient pulse shape is determined for the general fading and CCI environment. Analysis and numerical results show that the new pulse can provide better BER performance than the widely used raised-cosine pulse. View full abstract»

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  • A robust digital baseband predistorter constructed using memory polynomials

    Publication Year: 2004 , Page(s): 159 - 165
    Cited by:  Papers (284)  |  Patents (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    Power amplifiers (PAs) are inherently nonlinear devices and are used in virtually all communications systems. Digital baseband predistortion is a highly cost-effective way to linearize PAs, but most existing architectures assume that the PA has a memoryless nonlinearity. For wider bandwidth applications such as wideband code-division multiple access (WCDMA) or wideband orthogonal frequency-division multiplexing (W-OFDM), PA memory effects can no longer be ignored, and memoryless predistortion has limited effectiveness. In this paper, instead of focusing on a particular PA model and building a corresponding predistorter, we focus directly on the predistorter structure. In particular, we propose a memory polynomial model for the predistorter and implement it using an indirect learning architecture. Linearization performance is demonstrated on a three-carrier WCDMA signal. View full abstract»

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  • Frame Synchronization for Coded Systems Over AWGN Channels

    Publication Year: 2004 , Page(s): 166
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (33 KB)  

    Frame Synchronization for Coded Systems Over AWGN Channels T. Cassaro and C. N. Georghiades For the additive white Gaussian noise channel, we consider the problem of frame synchronization for coded systems. We present an algorithm that takes advantage of soft information provided by a soft decoder to produce an enhanced estimate of the frame boundary. To reduce complexity, a companion algorithm is introduced that is a hybrid of the optimal uncoded frame synchronizer introduced by Massey and the list synchronizer introduced by Robertson. The high-complexity coded maximum-likelihood frame synchronizer used by Robertson will accordingly be replaced by our algorithm, which operates on decoder-provided soft decisions. The algorithm begins by obtaining a list of high-probability starting positions via the log-likelihood function of the optimal uncoded frame synchronizer. Then, a test \delta is used to decide if the decision of the optimal uncoded frame synchronizer is sufficient, or whether list synchronization is required. If the test chooses in favor of using the optimal uncoded synchronizer, the estimate is obtained with relative ease. Otherwise, list synchronization is performed and statistics provided by the decoder are used to resolve the frame boundary. Monte Carlo simulations demonstrate that the frame-synchronization error rate (the probability of the synchronizer making an error) achieves the lower bound for signal-to-noise ratio values exceeding 1 dB. 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