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Selected Areas in Communications, IEEE Journal on

Issue 8 • Date Aug. 2000

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  • Guest editorial wideband CDMA I

    Publication Year: 2000 , Page(s): 1341 - 1343
    Cited by:  Papers (1)
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    Freely Available from IEEE
  • Wideband code division multiple access

    Publication Year: 2000 , Page(s): 1344 - 1354
    Cited by:  Papers (28)  |  Patents (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (182 KB)  

    To satisfy ever-increasing demands for higher data rates, as well as to allow more users to simultaneously access the network, interest has peaked in what has come to be known as wideband code division multiple access (WCDMA). We discuss those basic characteristics of WCDMA waveforms that make them attractive for high data rate transmission over wireless and mobile channels. We emphasize how the choice of spread bandwidth affects the bit error rate of the system, as well as how it affects the reliability of various subsystems, such as those that perform coarse acquisition and adaptive power control. We then discuss how some of the waveforms being considered for cellular WCDMA systems differ from those in use in the narrowband CDMA cellular system, and emphasize, as an example, multicarrier CDMA. Finally, we discuss other potential enhancements to WCDMA systems, such as the use of interference suppression at the receiver, or multiple antennas at the transmitter. View full abstract»

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  • Turbo-coded ARQ schemes for DS-CDMA data networks over fading and shadowing channels: throughput, delay, and energy efficiency

    Publication Year: 2000 , Page(s): 1355 - 1364
    Cited by:  Papers (10)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (163 KB)  

    Modified ARQ (automatic-repeat-request) techniques based on turbo coding are investigated for asynchronous DS-CDMA (direct-sequence code-division multiple-access) data networks under shadowing and frequency selective fading channel conditions. The throughput, delay, and energy efficiency performance of standard ARQ, metric combining, and RCPT (rate compatible punctured turbo) coded ARQ schemes are compared via simulations. The RCPT/ARQ schemes are shown to outperform the other two schemes in terms of both throughput and energy efficiency at the cost of larger delay and complexity. In addition, maximum network throughput is investigated for different ARQ schemes under energy constraints. View full abstract»

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  • Suppression of multiple narrowband interferers in a spread-spectrum communication system

    Publication Year: 2000 , Page(s): 1365 - 1374
    Cited by:  Papers (9)  |  Patents (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (242 KB)  

    We consider the problem of estimating and suppressing many unknown independent and time-varying interferers in a spread-spectrum communication system. The interferers are assumed to be present in a wide frequency range. In order to detect, estimate, and track the interference, we use a bank of hidden Markov model filters operating in the frequency domain. The hidden Markov model filters' outputs are then used to suppress the existing interference. The computational complexity of our scheme is only linear in the number of interferers. The simulation studies show that our proposed novel schemes adapt quickly in tracking the time-varying nature of the interference. View full abstract»

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  • The TD-CDMA based UTRA TDD mode

    Publication Year: 2000 , Page(s): 1375 - 1385
    Cited by:  Papers (71)  |  Patents (56)
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    The third-generation mobile radio system UTRA that has been specified in the Third Generation Partnership Project (3GPP) consists of an FDD and a TDD mode. This paper presents the UTRA TDD mode, which is based on TD-CDMA. Important system features are explained in detail. Moreover, an overview of the system architecture and the radio interface protocols is given. Furthermore, the physical layer of UTRA TDD is explained, and the protocol operation is described. View full abstract»

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  • Interference considerations for the time division duplex mode of the UMTS Terrestrial Radio Access

    Publication Year: 2000 , Page(s): 1386 - 1393
    Cited by:  Papers (36)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (284 KB)  

    The air interface of the UMTS Terrestrial Radio Access (UTRA) covers both a frequency division duplex (FDD) part for the paired bands and a time division duplex (TDD) part for the unpaired bands of the UMTS spectrum. The Universal Mobile Telecommunication System (UMTS) is the 3rd-generation mobile communication system. This paper presents an interference evaluation of the UTRA TDD. Since both uplink and downlink share the same frequency in TDD, the signals of the two transmission directions can interfere with each other. This interference can occur between two mobile stations or between two base stations within one carrier or between two operators. The interference between uplink and downlink is evaluated by system simulations. Synchronization and coordination requirements of UTRA TDD are evaluated based on the results. View full abstract»

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  • Adaptive nonuniform phase-shift-key modulation for multimedia traffic in wireless networks

    Publication Year: 2000 , Page(s): 1394 - 1407
    Cited by:  Papers (52)  |  Patents (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (255 KB)  

    The characteristics of mobile wireless communication channels fluctuate for many reasons, including movement of the radios, changes in path attenuation, and variations in interference. Several adaptive signaling techniques have been proposed for use in wideband code-division multiple-access (CDMA) systems including adaptive data rates, adaptive spreading code rates, discontinuous transmission, and multicode CDMA. We introduce adaptive signaling techniques that use nonuniform phase-shift-key (PSK) modulation. These techniques have several advantages for use in CDMA communications, and they support multimedia transmission by simultaneously delivering different types of traffic, each with its own required quality of service. The signaling methods that we propose deliver a basic message at a specified error rate and simultaneously deliver an additional message by exploiting any extra capability that is available. We show that by adapting the location of the points in a PSK constellation, the throughput can be maximized for the additional message while maintaining an acceptable error rate for the basic message. Responses to larger changes in channel quality are accomplished by adapting the PSK constellation size, signaling rate, and error-correcting code. Examples of adaptive signaling schemes that employ nonuniform PSK constellations are presented, including an application to a cellular CDMA system. View full abstract»

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  • The performance of direct-sequence spread spectrum with complex processing and quaternary data modulation

    Publication Year: 2000 , Page(s): 1408 - 1417
    Cited by:  Papers (8)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (270 KB)  

    The receiver processing that is often employed for direct-sequence spread spectrum with quaternary data modulation operates separately on in-phase and quadrature components of the spread-spectrum signal. Previous results on complex quaternary sequences, which are also referred to as four-phase sequences, provide a strong motivation to employ alternative processing methods that permit the receiver to benefit from the correlation properties of these sequences. With this goal in mind we present receiver architectures that use complex processing and are capable of demodulating the signals proposed for the third-generation mobile cellular code-division multiple-access systems. The performance of the proposed receiver architecture with complex processing is shown to be determined by the complex aperiodic correlation functions for the spreading sequences. Comparisons are made with systems in which the quaternary sequences are derived from pairs of common binary spreading sequences and the receiver employs separate in-phase and quadrature processing. We find that in spite of their superior periodic crosscorrelation properties, the previously developed quaternary sequences do not provide significantly smaller error probabilities in multiple-access systems. View full abstract»

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  • Uplink performance evaluation of multicode DS/CDMA systems in the presence of nonlinear distortions

    Publication Year: 2000 , Page(s): 1418 - 1428
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (314 KB)  

    This paper investigates the behavior of multicode direct sequence code division multiple access (DS/CDMA) systems in the presence of nonlinear distortions caused by high power amplifiers. The performance of the multicode system can be degraded due to a large variation in the envelope of the multicode signal. A technique that uses a small number of parallel transmitted sequences is proposed for combating the nonlinearity. This technique ran be modified to have a constant envelope for achieving further performance improvement. Comprehensive comparisons are made for different systems, based on both theoretical analysis and computer simulation. Our study shows that the technique employing a few parallel transmitted sequences, in conjunction with quasi-ML (maximum likelihood) detection, and the use of the modified scheme, are very effective for combating the nonlinearity. View full abstract»

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  • Dynamic assignment of orthogonal variable-spreading-factor codes in W-CDMA

    Publication Year: 2000 , Page(s): 1429 - 1440
    Cited by:  Papers (107)  |  Patents (29)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (251 KB)  

    This paper presents an optimal dynamic code assignment (DCA) scheme using orthogonal variable-spreading-factor (OVSF) codes. The objective of dynamic code assignment is to enhance statistical multiplexing and spectral efficiency of W-CDMA systems supporting variable user data rates. Our scheme is optimal in the sense that it minimizes the number of OVSF codes that must be reassigned to support a new call. By admitting calls that would normally be blocked without code reassignments, the spectral efficiency of the system is also maximized. Simulation results are presented to show the performance gain of dynamic code assignment compared to a static assignment scheme in terms of call blocking rate and spectral efficiency. We also discuss various signaling techniques of implementing our proposed DCA scheme in third-generation wideband CDMA systems. View full abstract»

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  • Multiple access protocol for integration of variable bit rate multimedia traffic in UMTS/IMT-2000 based on wideband CDMA

    Publication Year: 2000 , Page(s): 1441 - 1454
    Cited by:  Papers (47)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    The UMTS terrestrial radio access (UTRA), based on a wideband DS-CDMA technique, fully supports the UMTS requirements and has flexible support for real-time, variable-bit-rate services, as well as an efficient packet mode. This paper presents a description and a performance evaluation of a medium access protocol which may be used in the UTRA system to provide constant-bit-rate (voice), variable bit-rate (video), and low priority data services. The performance evaluation of voice and data services has been carried out by a suitable analytical approach. Simulation results are also shown in order to validate analytical predictions. View full abstract»

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  • Distributed sample acquisition-based fast cell search in inter-cell asynchronous DS/CDMA systems

    Publication Year: 2000 , Page(s): 1455 - 1469
    Cited by:  Papers (2)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (418 KB)  

    We introduce a fast fell-search scheme based on the distributed sample acquisition (DSA) technique for inter-cell asynchronous DS/CDMA systems. The proposed DSA scheme enables the long-code acquisition extremely fast even without employing any passive matched filter which used to dominate synchronization circuit complexity in asynchronous DS/CDMA systems. In the DSA-based asynchronous DS/CDMA system, each base station spreads its DQPSK-modulated long-code generator information with an assigned short-period igniter sequence, and broadcasts it as a common pilot signal. A mobile station first identifies and acquires the igniter sequence of the cell group currently located, then detects the conveyed long-code generator information by despreading the acquired igniter sequence, thereby identifying and synchronizing the long-code of the current cell. The mean acquisition time of this proposed DSA-based inter-cell asynchronous DS/CDMA system, evaluated under the assumption that each of 512 cell-specific long-codes is a 10-ms segment (38400-chips for the chip rates of 3.84 Mchips/s) of complex Gold codes of period 2/sup 18/-1 and the igniter sequence (or, group code) set is composed of 7 complex orthogonal Gold codes of period 256, turned out even shorter than that of the inter-cell synchronous DS/CDMA systems employing the conventional serial search method. Furthermore, simulation results showed that the DSA scheme employing a passive matched filter is much superior in terms of acquisition time and robustness, to the 3GPP W-CDMA synchronization scheme having comparable complexity. View full abstract»

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  • Cell search in W-CDMA

    Publication Year: 2000 , Page(s): 1470 - 1482
    Cited by:  Papers (72)  |  Patents (102)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (327 KB)  

    In a CDMA cellular system, the process of the mobile station searching for a cell and achieving code and time synchronization to its downlink scrambling code is referred to as cell search. Cell search is performed in three scenarios: initial cell search when a mobile station is switched on, idle mode search when inactive, and active mode search during a call. The latter two are also called target cell search. This paper presents algorithms and results for both initial and target cell search scenarios for the wideband CDMA (W-CDMA) standard. In W-CDMA, the cell search itself is divided into five acquisition stages: slot synchronization, frame synchronization and scrambling code group identification, scrambling code identification, frequency acquisition, and cell identification. Initial cell search needs all five stages, while target cell search in general does not need the last two stages. A pipelined process of the first three stages that minimizes the average code and time acquisition time, while keeping the complexity at a reasonable level, is considered. The frequency error in initial cell search, which may be as large as 20 kHz, is taken care of by partial symbol despreading and noncoherent combining. Optimization of key system parameters such as the loading factors for primary synchronization channel, synchronization channel, and common pilot channel for achieving the smallest average code and time acquisition time is studied. After code and time synchronization (the first three stages), a maximum likelihood (ML)-based frequency acquisition method is used to bring down the frequency error to about 200 Hz. The gain of this method is more than 10 dB compared to an alternative scheme that obtains a frequency error estimate using differential detection. View full abstract»

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  • Channel acquisition for wideband CDMA signals

    Publication Year: 2000 , Page(s): 1483 - 1494
    Cited by:  Papers (24)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (310 KB)  

    The scenario considered is one where a single new user is to be acquired on the reverse link by the base station, and where the channel parameters of the interfering users are known. Following a minimum mean squared error (MMSE) strategy for suppressing the multiaccess interference, the parameter estimation problem is posed in a maximum likelihood framework, To reduce complexity, the solution is implemented in two stages: first, the estimated tap delays are restricted to be at chip spacings; second, the number of taps is reduced by allowing for arbitrary spacing between them. The performance of the proposed techniques is studied through numerical simulations. It is shown that significant gains can be obtained by exploiting the structure of the interference and acquiring the channel parameters jointly. View full abstract»

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  • Experiments on coherent adaptive antenna array diversity for wideband DS-CDMA mobile radio

    Publication Year: 2000 , Page(s): 1495 - 1504
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (299 KB)  

    In wideband direct sequence code division multiple access (W-CDMA), employing an adaptive antenna array is a very promising technique to reduce severe multiple access interference (MAI) from high rate users. A four-antenna pilot symbol-assisted coherent adaptive antenna array diversity (PSA-CAAAD) receiver comprising an adaptive antenna array based on a minimum mean squared error (MMSE) criterion and a RAKE combiner is implemented in preliminary laboratory and field experiments. There are two important design concepts of the PSA-CAAAD receiver. The first is that the adaptive antenna array forms an antenna beam for each resolved propagation path and tracks only slow changes in the directions of arrival (DOAs) and average powers of the desired and interfering user signals. The second is that the RAKE combiner tracks the instantaneous changes in channel conditions and coherently combines the signals of the desired user propagating along the resolved paths to maximize the instantaneous signal-to-interference plus background noise power ratio (SINR). This paper presents, both by laboratory and field experiments, the effectiveness of PSA-CAAAD receiver as a powerful means to reduce severe MAI from high rate users, and that it is more effective than using a space diversity receiver with the same number of antennas in the W-CDMA reverse link. View full abstract»

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  • Performance of a spatio-temporal matched filter receiver for DS/SSMA communications

    Publication Year: 2000 , Page(s): 1505 - 1515
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (341 KB)  

    A spatio-temporal matched filter receiver for direct-sequence spread-spectrum multiple-access (DS/SSMA) communications with aperiodic random quadriphase spreading sequences is derived, and the system performance is analyzed. It is shown with the method of characteristic functions that the cross-correlation coefficients between the desired user's and the interfering users' spreading sequences tend, in distribution, to independently and identically distributed circularly symmetric complex Gaussian random variables as the processing gain goes to infinity. Based on this Gaussian approximation, the structure of the spatio-temporal matched filter receiver is derived and a bit error rate formula is obtained. Using Monte-Carlo simulations, as well as analytical methods, it is shown that the spatio-temporal matched filter receiver achieves a significant performance improvement over the conventional, temporal, and spatial matched filter receivers by effectively suppressing the multiple access interference. View full abstract»

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  • Performance of RAKE reception in dense multipath channels: implications of spreading bandwidth and selection diversity order

    Publication Year: 2000 , Page(s): 1516 - 1525
    Cited by:  Papers (94)  |  Patents (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (274 KB)  

    We develop an analytical framework to quantify the effects of the spreading bandwidth (BW) on spread spectrum systems operating in dense multipath environments in terms of the receiver performance, the receiver complexity, and the multipath channel parameters. The focus of the paper is to characterize the symbol error probability (SEP) performance of a RAKE receiver tracking the L strongest multipath components in wide-sense stationary uncorrelated scattering (WSSUS) Gaussian channels with frequency-selective fading. Analytical SEP expressions of the RAKE receiver are derived in terms of the number of combined paths, the spreading BW and the multipath spread of the channel. The proposed problem is made analytically tractable by transforming the physical RAKE paths, which are correlated and ordered, into the domain of a "virtual RAKE" receiver with independent virtual paths. This results in a simple derivation of the SEP for a given spreading BW and an arbitrary number of combined paths. View full abstract»

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  • Experimental evaluation of combined effect of coherent RAKE combining and SIR-based fast transmit power control for reverse link of DS-CDMA mobile radio

    Publication Year: 2000 , Page(s): 1526 - 1535
    Cited by:  Papers (9)  |  Patents (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (305 KB)  

    The combined effect of coherent RAKE combining using the weighted multislot averaging (WMSA) channel estimation filter and closed-loop fast transmit power control (TPC) in the 4.096 Mchip/s direct sequence code division multiple access (DS-CDMA) mobile radio reverse link is experimentally evaluated. The WMSA channel estimation filter utilizes periodically transmitted pilot symbols (four pilot symbols are time-multiplexed in each 40-symbol time slot). Its observation period is extended to 2-K slots in order to improve the accuracy of the channel estimation. The fast TPC is based on the measurement of signal-to-interference plus background noise ratio (SIR) using pilot symbols. Laboratory experiments show that the use of the K=2 WMSA channel estimation filter reduces the required E/sub b//I/sub 0/ at the average BER of 10/sup -3/ by approximately 0.5 dB compared to use of the linear interpolation filter, and that the required E/sub b//I/sub 0/ is minimized when the SIR measurement interval is M=10 symbols (one slot TPC delay). It was also clarified that SIR-based TPC works satisfactorily when two users with different information data rates, i.e., SF, independently employ fast TPC. Field experimental results obtained in an area nearby Tokyo showed that the average BER of 10/sup -3/ is achieved at the target E/sub b//I/sub 0/ per antenna of approximately 2.5 dB by using four-finger branch RAKE and two-branch antenna diversity. Although the target E/sub b//I/sub 0/ to achieve same BER, when there is one interfering user with a fourfold greater transmit power than that of the desired user that independently employs fast TPC, is almost the same as that in the single-user case, the mobile transmit power is increased by 1.0-2.0 dB due to the increased MAI. These results indicate that the combination of coherent RAKE combining and fast TPC works well in practical multipath fading channels. View full abstract»

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  • A generalized RAKE receiver for interference suppression

    Publication Year: 2000 , Page(s): 1536 - 1545
    Cited by:  Papers (94)  |  Patents (87)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (241 KB)  

    Currently, a global third-generation cellular system based on code-division multiple-access (CDMA) is being developed with a wider bandwidth than existing second-generation systems. The wider bandwidth provides increased multipath resolution in a time-dispersive channel, leading to higher frequency-selectivity. A generalized RAKE receiver for interference suppression and multipath mitigation is proposed. The receiver exploits the fact that time dispersion significantly distorts the interference spectrum from each base station in the downlink of a wideband CDMA system. Compared to the conventional RAKE receiver, this generalized RAKE receiver may have more fingers and different combining weights. The weights are derived from a maximum likelihood formulation, modeling the intracell interference as colored Gaussian noise. This low-complexity detector is especially useful for systems with orthogonal downlink spreading codes, as orthogonality between own cell signals cannot be maintained in a frequency-selective channel. The performance of the proposed receiver is quantified via analysis and simulation for different dispersive channels, including Rayleigh fading channels. Gains on the order of 1-3.5 dB are achieved, depending on the dispersiveness of the channel, with only a modest increase in the number of fingers. For a wideband CDMA (WCDMA) system and a realistic mobile radio channel, this translates to capacity gains of the order of 100%. View full abstract»

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  • SSDT-site selection diversity transmission power control for CDMA forward link

    Publication Year: 2000 , Page(s): 1546 - 1554
    Cited by:  Papers (47)  |  Patents (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (218 KB)  

    This paper proposes site selection diversity transmission power control (SSDT), an advanced form of transmission power control (TPC) for CDMA forward link, SSDT realizes site selection transmission diversity instead of full site transmission diversity used in conventional TPC during soft hand over (SHO) mode. The major intention of the site selection is to mitigate interference caused by multiple site transmission done at conventional TPC. Simulation results indicated that the higher the capacity gain of SSDT is in comparison to conventional TPC, the lower the mobile station (MS) speed is. Capacity gain of about 55% for a pedestrian MS is achieved by SSDT in case of MS reception diversity and 6 finger RAKE reception. This paper also presents the benefits of SSDT in terms of its high path capturing efficiency and the mitigation of power imbalance among active BSs due to TPC command reception error. View full abstract»

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Aims & Scope

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

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Muriel Médard
MIT