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  • Articles  (30)
  • CDMA  (30)
  • Springer  (30)
  • National Academy of Sciences
  • 1995-1999  (30)
  • 1975-1979
  • Electrical Engineering, Measurement and Control Technology  (30)
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  • Articles  (30)
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  • Springer  (30)
  • National Academy of Sciences
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  • 1
    Electronic Resource
    Electronic Resource
    Performances of acquisition schemes for CDMA systems with complex signature sequences (1995)
    Springer
    International journal of wireless information networks 2 (1995), S. 27-39 
    Details
    ISSN: 1572-8129
    Keywords: CDMA ; acquisition ; complex sequences
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper investigates the acquisition performance of code-division multiple-access communication systems using deterministic complex signature sequences. Unlike most earlier studies, performances are obtained in the presence of multiple user interference, and the results can be applied to complex as well as binary signature sequences. Two serial search acquisition schemes are considered. The first scheme assumes that there is no data in the reference user's signal until the acquisition is achieved. The second scheme allows data modulation in the reference user's signal during the acquisition process. Probability of detection and probability of false alarm of both schemes are obtained without using the Gaussian approximation. Instead, a discrete approximation of the probability density function of the MUI is used in performance evaluations. Numerical results are presented for example sets of Gold, 4-phase, and FZC sequences. They show that complex and binary sequences have comparable acquisition performances. Results also show significant degradation of acquisition performances as the number of users increases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01464196
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  • 2
    Electronic Resource
    Electronic Resource
    Performance of antenna diversity multiuser receivers in CDMA channels with imperfect fading estimation (1996)
    Springer
    Wireless personal communications 3 (1996), S. 91-110 
    Details
    ISSN: 1572-834X
    Keywords: Multiuser receivers ; diversity reception ; fading channels ; CDMA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The performance of antenna diversity coherent and differentially coherent linear multiuser receivers is analyzed in frequency-nonselective Rayleigh fading CDMA channels with memory. The estimates of the complex fading processes are utilized for maximal-ratio combining and carrier recovery of the coherent multiuser receiver. To analyze the impact of channel estimation errors on the receiver performance, error probability is assessed directly in terms of the fading rate and the number of active users, showing the penalty imposed by imperfect channel estimation as well as the fading-induced error probability floor. The impact of fading dynamics on the differentially coherent decorrelating receiver with equal-gain combining is quantified. While performance of multiuser receivers at lower SNR is determined by both the fading dynamics and the number of active CDMA users, performance at higher SNR is given by an error probability floor which is due to fading only and has the same value as in a single-user case. The comparison of the two receiver structures indicates that the coherent decorrelating receiver with diversity reception may be preferable to the differentially coherent one in nonselective fading CDMA channels with memory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333925
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  • 3
    Electronic Resource
    Electronic Resource
    Space-time optimum combining for CDMA communications (1996)
    Springer
    Wireless personal communications 3 (1996), S. 73-89 
    Details
    ISSN: 1572-834X
    Keywords: Adaptive arrays ; interference cancellation ; CDMA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper it is shown how spatial and temporal processing can be combined to increase the capacity of CDMA-based wireless communications systems. Degrees of freedom provided by space-time processing can be exploited to combat both fading and co-channel interference (the near-far effect). Specifically, we formulate and study the following methods: (1) space-time diversity, (2) cascade optimum spatial-diversity (RAKE) temporal, (3) cascade optimum spatial-optimum temporal, and (4) joint domain optimum processing. It is shown that, due to its interference cancellation capability, optimum combining provides significantly better performance than diversity processing. In particular, it is shown that in a typical CDMA scenario with two antennas, the joint domain optimum combining system provides at least a 25% increase in capacity over diversity processing. Optimum combining may be applied to compensate for imperfect power control of the signals received at the base station.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333924
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  • 4
    Electronic Resource
    Electronic Resource
    Activity detection in a multi-user environment (1996)
    Springer
    Wireless personal communications 3 (1996), S. 149-174 
    Details
    ISSN: 1572-834X
    Keywords: CDMA ; activity detection ; multi-user detection ; non-Gaussian noise ; distribution-free detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The detection of a weak stochastic signal in multi-variate impulsive noise is investigated. The signal is that of a new user in a Code-Division Multiple-Access multi-user system. A particular type of transformation noise is considered: the trasmitted signal vector is modified by a linear transformation prior to signal detection thereby yielding a signal process and noise process that are dependent from component to component of the recieved vector. The linear operator is designed to combat multiple-access interference. The effect of such a transformation is studied by deriving the efficacies and asymptotic relative efficiencies of several detectors. Both linear and non-linear cross-correlator detector structures are examined. The performance of the detectors is determined for two types of non-Gaussian noise: additive channel noise and residual multiple-access interference noise. The numerical results are consistent with previous findings and motivate the investigation of a hybrid detector which is composed of a combination of the linear correlator and the polarity coincidence correlator. The asymptotic normality of the test statistics under study is also investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333928
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  • 5
    Electronic Resource
    Electronic Resource
    Exploiting Macrodiversity with Distributed Antennas in Micro-Cellular CDMA Systems (1999)
    Springer
    Wireless personal communications 9 (1999), S. 179-196 
    Details
    ISSN: 1572-834X
    Keywords: CDMA ; integrated wireless access networks ; distributed antenna diversity ; personal communication systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We consider the use of distributed antennas to increase the capacity and peak data rate achievable in a microcellular CDMA system with limited bandwidth. In additon to the diversity against Rayleigh fading achievable by use of microdiversity among nearly co-located transmit or receive antennas, we exploit macrodiversity against shadow fading that more widely separated antennas permit. We report on antenna configurations for both directional and omni-directional antennas that provide the most uniform signal-to-interference ratio coverage, averaged over a large number of position vectors drawn from a spatially uniform distribution of mobiles. Call capacities and peak transmission rates are determined for an integrated system carrying traffic at different constant rates, where processing gain and the transmission rate are selected to satisfy a common chip rate. For the downlink a 5.5 dB capacity gain can be achieved for 64 kb/s calls using four antennas located on the diagonals of each square cell. A bandwidth of 5 MHz allows two or more calls to be simultaneously supported at data rates up to 512 kb/s, as opposed to only 128 kb/s for three co-located antennas. On the uplink we distinguish between the computationally simpler equal-gain combining of the antenna signals and the possibly more complex maximum-ratio combining. With equal gain combining we achieve a peak data rate of 128 kb/s and a capacity gain of 2.5 dB relative to equal gain combining of three nearly co-located antenna signals. With maximum ratio combining the peak uplink rate can be as high as 512 kb/s and the capacity is increased by 2.0 dB relative to the maximum-ratio combining of three co-located antennas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018354918175
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  • 6
    Electronic Resource
    Electronic Resource
    A distributed link scheduling algorithm for CDMA packet radio networks (1995)
    Springer
    International journal of wireless information networks 2 (1995), S. 61-70 
    Details
    ISSN: 1572-8129
    Keywords: Distributed algorithms ; spread-spectrum ; CDMA ; packet radio network
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A distributed algorithm for the conflict-free channel allocation in CDMA (code division multiple access) networks is presented. Dynamic adjustment to topological changes is also considered. Though the schedules produced by our algorithm are not optimal with respect to link schedule length, the algorithm is simple and practical. The link schedule length minimization problem is NP-complete. Here the length of a link schedule is the number of time slots it uses. The algorithm guarantees a bound 2Δ — 1 time slots on the TDMA cycle length, where Δ is the maximum degree of a station (i.e., maximum number of stations that a station can reach by radio links) in the network. The message complexity of a station isO(Δ).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01464456
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  • 7
    Electronic Resource
    Electronic Resource
    Information Capacity of the Space Division Multiple Access Mobile Communication System (1999)
    Springer
    Wireless personal communications 11 (1999), S. 131-159 
    Details
    ISSN: 1572-834X
    Keywords: mobile communications ; information capacity ; SDMA ; CDMA ; adaptive MMSE receivers ; multisensor receivers ; antenna arrays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract An expression for the Shannon capacity lower bound of the space division multiple access (SDMA) mobile communication channel with interference is shown. The bound is tightly approaching the Shannon capacity of the orthogonal SDMA system over Gaussian channel with no interference. The information capacity of the SDMA system with adaptive MMSE receivers is presented as well. The SDMA system with MMSE receivers achieves at least 50% of the orthogonal SDMA system capacity for the input signal to noise ratio of practical interest in cellular mobile communications (10–30dB).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018679827153
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  • 8
    Electronic Resource
    Electronic Resource
    Smart Antennas with Two-Dimensional Array Configurations for Performance Enhancement of a Joint Detection CDMA Mobile Radio System (1999)
    Springer
    Wireless personal communications 11 (1999), S. 89-108 
    Details
    ISSN: 1572-834X
    Keywords: smart antennas ; CDMA ; system performance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Smart antennas for base stations of cellular mobile radio systems offer the potential of system performance enhancement by taking advantage of the directionally inhomogeneous signal reception at the receiver. In this paper, two-dimensional array configurations employed at the uplink receiver of a joint detection CDMA (JD-CDMA) mobile radio system are investigated. This smart antenna concept can be split up into a novel channel estimator and data detector which incorporate explicitely the information of the direction-of-arrival (DOA) of signals emerging from users assigned to the considered base station. Proceeding from channel models that model the directional inhomogeneity of the mobile radio channel with single DOAs, the link level performance of a JD-CDMA mobile radio system using this smart antenna concept is evaluated for the rural propagation environment. The performance evaluation is based on Monte Carlo simulations of data transmission and average bit error rates versus the average signal to noise ratio per net information bit are presented for different array configurations. Although these results should be considered as upper bounds for the link level performance, they reveal the advantages of implementing two-dimensional array configurations at the uplink receiver of a JD-CDMA mobile radio system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018607024631
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  • 9
    Electronic Resource
    Electronic Resource
    A Decision Feedback Reverse Link Receiver Implementation for IS-95 CDMA Communications (1999)
    Springer
    Wireless personal communications 11 (1999), S. 209-217 
    Details
    ISSN: 1572-834X
    Keywords: IS-95 ; CDMA ; communications ; receiver ; implementation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract An implementation of a reverse link receiver for IS-95 CDMA (Code-Division Multiple-Access) communications that applies decision feedback to the decoding of the received signal is presented. Decision feedback is used in order to improve BER performance by making use of additional information that conventional receiver designs generally ignore. Qualitative analysis and computer simulation of the hardware components of the proposed implementation shows that it can be built as a single integrated circuit using present day technology. The design presented here does not include the RF front-end of the receiver, does not consider the effects of multipath and fading on system performance, and assumes perfect power control.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018366426668
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  • 10
    Electronic Resource
    Electronic Resource
    Performance of a coded multi-carrier DS-CDMA system in multi-path fading channels (1995)
    Springer
    Wireless personal communications 2 (1995), S. 167-183 
    Details
    ISSN: 1572-834X
    Keywords: CDMA ; multi-carrier modulation ; frequency hopping ; hybrid FH/DS ; adaptive transmission ; modulation for fading channels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Multi-carrier DS-CDMA has been considered as an effective scheme for reducing multiple access interference in quasi-synchronous transmission. The scheme allows the reduction of multiple access interference by transferring the orthogonality property of the signals into the frequency domain where the orthogonality property is robust to relative chip offsets between the spreading codes of the various users. However in multi-path channels, the multi-carrier technique results in frequency non-selective fading in the sub-channels, due to the narrower bandwidth, hence a reduction of the capability of the spread spectrum signal to mitigate the effect of multi-path propagation. In this paper, we consider the use of a Reed-Muller code with soft decision decoding to regain the corresponding loss in performance, and compare the resulting system with a single carrier DS-CDMA system. The effect of system parameters such as the number of sub-channels is investigated through numerical calculation and simulation, from which a number of system design criteria are arrived at.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01099536
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  • 11
    Electronic Resource
    Electronic Resource
    Blind Multiuser Detection with Array Observations (1998)
    Springer
    Wireless personal communications 6 (1998), S. 179-196 
    Details
    ISSN: 1572-834X
    Keywords: multiuser communications ; blind identification ; array signal processing ; CDMA ; adaptive receivers.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Cochannel interference is usually a major limitation to the performance of mobile wireless systems. Examples of different forms of cochannel interference include multi-access interference in CDMA systems and cochannel interference resulting from frequency reuse in TDMA systems. In order to mitigate the interference from other users we present a blind multiuser receiver which utilizes array observations and performs both spatial and temporal processing of the received signal. The presented technique is completely blind in the sense that no signature sequences, channel state or spatial location needs to be known a priori, nor use of a training sequences, channel state or spatial location needs to be known a priori, nor use of a training sequence is required for the adaptation. The diversity introduced by the array observations can be efficiently combined with the use of CDMA signature sequences. After initial convergence, a reliable estimate of the combined temporal and spatial signature for each user is provided that can be employed by a multiuser receiver of lower complexity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008844620736
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  • 12
    Electronic Resource
    Electronic Resource
    The Linear Prediction Method of Fading Channel Estimation for the Rake Receiver with Impulsive Interference (1998)
    Springer
    Wireless personal communications 6 (1998), S. 233-248 
    Details
    ISSN: 1572-834X
    Keywords: spread spectrum ; CDMA ; Rake receiver ; fading channel ; linear predictor ; adaptive algorithm ; impulsive interference
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Parameter estimation of the multipath and fading channel is investigated for the Rake combiner used in a CDMA system with coherent demodulation. A linear predictor is proposed to obtain a better estimation. Since the industrial interference environment is generally impulsive, a parallel LMS adaptive algorithm is proposed to reduce the impact of impulsive noise on predictor weights adjustment. Performance analysis and computer simulations are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008854708341
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  • 13
    Electronic Resource
    Electronic Resource
    Decorrelating detectors for quasi-synchronous CDMA (1996)
    Springer
    Wireless personal communications 3 (1996), S. 129-147 
    Details
    ISSN: 1572-834X
    Keywords: CDMA ; decorrelating ; multiuser detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract To date, two forms of spread spectrum code division multiple access (CDMA) have been considered in the literature. Either synchronous CDMA, where all users are both chip and bit synchronized relative to each other, or asynchronous CDMA, where all users are neither chip nor bit synchronized relative to each other. Between these two extremes lies quasi-synchronous CDMA (QS-CDMA) where users are not chip synchronized but are approximately bit synchronized. Quasi-synchronous CDMA arises in microcell systems where the combined propagation time and delay spread produces a variation in the round trip delay time limited to a few chips. Detection of QS-CDMA at the base station is considered. It is shown that memoryless detection can be achieved by appending blank chips to the user's spreading codes. Two decorrelating detectors are proposed and analyzed. The first uses a matched filter bank to produce a discrete time signal, and the second uses a single oversampling integrate-and-dump filter to produce a discrete time signal. For the first detector, each matched filter is synchronized to its respective user, and for the second detector, the integrate-and-dump filter is synchronized to the base station transmissions. The performance of the two detectors is shown to be approximately equal provided the integrate-and-dump filter is sampled at least two times the chip rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333927
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  • 14
    Electronic Resource
    Electronic Resource
    Interference cancellation for a multicellular CDMA environment (1996)
    Springer
    Wireless personal communications 3 (1996), S. 1-15 
    Details
    ISSN: 1572-834X
    Keywords: CDMA ; multiuser communications ; interference cancellation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper considers the performance of adaptive interference cancellation applied to a CDMA microcellular environment, by employing a circular cell geometry and a closed form expression for the Bit Error Rate of a CDMA system with interference cancellation to analyze the effect of out-of-cell interference. Results are presented which indicate that out-of-cell interference will severely limit the benefits of interference cancellation in a multicellular system. Attempts to cancel all out-of-cell interference will further degrade performance. However, the use of selective interference cancellation in which only the strongest out-of-cell interferers are cancelled may result in significant performance enhancement. These results agree closely with those obtained using a hexagonal geometry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333920
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  • 15
    Electronic Resource
    Electronic Resource
    Performance analysis of linear joint equalization and multiple access interference cancellation for multitone CDMA (1996)
    Springer
    Wireless personal communications 3 (1996), S. 17-36 
    Details
    ISSN: 1572-834X
    Keywords: CDMA ; multitone ; joint detection ; receiver design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In [18] the combination of multitone modulation with direct sequence spectrum spreading has been introduced. The performance of a correlation receiver with diversity has been evaluated for a multipath channel in the presence of a multiple access interference (MAI) using the Gaussian assumption. In the present paper we analyze the problem of joint equalization and cancellation of the multipath and multiple access interferences for these multitone CDMA (Code Division Multiple Access) systems. A linear structure is first investigated for a mean square error (MSE) criterion. In order to understand the potential of the system we study the steady-state behavior of the joint equalizer-canceler. The investigation is carried out for a joint device following a bank of matched filters and assuming perfect carrier phase and timing recovery. An exact expression for the bit error probability of BPSK symbols before and after cancellation, is obtained in the form of an integral The performance of the joint device is investigated for different types of channels. The resistance to the near-far effect is also demonstrated. Then adaptive structures are derived from a least square approach. Their performance is demonstrated by means of computer simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333921
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  • 16
    Electronic Resource
    Electronic Resource
    Convergence analysis of a CM array for CDMA systems (1996)
    Springer
    Wireless personal communications 3 (1996), S. 37-53 
    Details
    ISSN: 1572-834X
    Keywords: Constant modulus ; CDMA ; smart antenna
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The incorporation of directional sensitivity, provided by so-called adaptive antennas is useful in suppressing interfering signals that arise from spatially distinct mobile sources. The problem is that in a cellular radio environment where multipath exists, the standard adaptive antenna using reference signals may not properly lock on the desired signal. This is because the signal correlation matrix processed by the antenna may then be close to singular and standard algorithms fail. Also, most standard algorithms need to cooperate with the receiver for the spatial discrimination of signals. A smart antenna utilizing a blind algorithm is of interest since the antenna may not need to get any feedback from a receiver for the adjustment of weight coefficient for spatial processing and can stand alone to be plugged into any kind of receiver structure. In this paper, we address the convergence property of a Constant Modulus Algorithm which is a blind algorithm and, if employed, can provide no need for an antenna to cooperate with a receiver attached. By identifying a relationship between the weight coefficients and output signal amplitude, we also evaluate the performance of such a stand-alone antenna plus a CDMA matched filter reception. Our results show that for a three element CM array, the BER of a desired user with the other interfering users is much better than a conventional correlation receiver for a single user case since the array suppresses interferences and achieves array gain in SNR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333922
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  • 17
    Electronic Resource
    Electronic Resource
    Feasibility of Spectrum Sharing Between Fixed and Mobile Radio Systems (1999)
    Springer
    Wireless personal communications 9 (1999), S. 31-55 
    Details
    ISSN: 1572-834X
    Keywords: spectrum sharing ; CDMA ; mobile radio ; fixed service
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract General techniques are presented to investigate the feasibility of spectrum sharing between a DS-CDMA mobile radio system and a fixed point-to-point microwave link. The limitations of a spectrum sharing arrangement are identified for specific system parameters. Initial results indicate that, for the systems considered, spectrum sharing will be difficult to implement in many environments and that the spectrum sharing arrangement is limited by the mobile radio system performance, in particular the reverse mobile link. However it is shown that the coordination requirements of the two systems converge when the mobile transmission power is increased. When excision suppression is used to remove fixed service interference at a mobile receiver, it may have an adverse effect on the mobile system performance due to a degradation in the correlation characteristics of the received signal. The degradation in the received signal depends on the width and centre frequency of the excised interference relative to the mobile signal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018323213193
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  • 18
    Electronic Resource
    Electronic Resource
    The therapy of Percy Comms: A dialogue on PCS issues (1995)
    Springer
    International journal of wireless information networks 2 (1995), S. 123-132 
    Details
    ISSN: 1572-8129
    Keywords: Personal communication system ; microcells ; CDMA ; DCS ; intelligent multimode terminal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Most papers, single or multi-author, expound concepts, theories, and experimental results from a particular standpoint. This article is fundamentally no different, but it does discuss aspects of PCS in a dialogue form using two characters; a personal communications engineer, called Percy Comms, and his therapist, Dr. Mike Cellular. Because the characters are fictitious the author is able to break away from the formal, almost legalistic style of most papers to use a form of dialogue that is not unknown between PCS engineers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01577277
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  • 19
    Electronic Resource
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    Broadband-CDMA overlay (1995)
    Springer
    International journal of wireless information networks 2 (1995), S. 197-221 
    Details
    ISSN: 1572-8129
    Keywords: CDMA ; multiple access ; spread spectrum ; wireless communications
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A Broadband Code Division Multiple Access (B-CDMA) technique is presented that will overlay the existing cellular telephone spectrum (825 to 894MHz). The overlay will provide additional capacity to the network while allowing high quality voice and high speed data services to be coexistent with the existing cellular services (AMPS and TDMA). The advantages of using B-CDMA in a fading environment are analyzed. The low level of mutual interference between the existing cellular telephone system and the B-CDMA overlay system is shown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01538146
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  • 20
    Electronic Resource
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    A decorrelating detector for use with antenna arrays (1995)
    Springer
    International journal of wireless information networks 2 (1995), S. 239-246 
    Details
    ISSN: 1572-8129
    Keywords: CDMA ; antenna arrays ; multiuser detection ; spread spectrum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper addresses the problem of synchronous CDMA communications when, due to bandwidth limitations, signature waveforms have relatively large correlations. A receiver which uses the multiple received signals available from an antenna array is proposed and its performance analyzed. This receiver may be interpreted as a multichannel extension of the decorrelating detector and therefore shares its immunity to near-far effects. The receiver uses the discrimination afforded by the antenna array to effectively reduce the correlation between users' transmitted signals thereby avoiding the reduction in performance which occurs in the single channel decorrelator when signature correlations become significant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01538148
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  • 21
    Electronic Resource
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    Improved base station circular antenna array receiver for wireless CDMA systems (1996)
    Springer
    International journal of wireless information networks 3 (1996), S. 187-194 
    Details
    ISSN: 1572-8129
    Keywords: Antenna arrays ; CDMA ; array interpolation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A Spatial interpolation technique for the upsampling of uniform circular arrays (UCAs), beyond spatial aliasing, is considered. The UCA interpolation algorithm is used as a preprocessing procedure in the reverse link to improve the performance of a cellular code division multiple access (CDMA) system. The motivation is to enhance the system's capacity and array resolution and reduce the fading and coupling effects with minimal receiver hardware and cost. At the base station, we propose to place the antenna elements uniformly on an imaginary circumference farther apart thanλ/2, whereλ is the free-space wavelength. The resulting UCA possesses superior resolution, less coupling effects than a corresponding UCA with the same number of elements and circumferential spacing less than or equal toλ/2, and possibly higher diversity gain. In order to increase the system's capacity and eliminate any spatial aliasing, we propose to interpolate the UCA to within the spatial Nyquist rate. This is achieved by placing a virtual antenna element halfway on the circumference between every two adjacent antenna elements. Simulations results are provided to support our claims.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02109334
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  • 22
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    An Evaluation Model for Integrated Services on Wireless Broadband CDMA Networks (1999)
    Springer
    Wireless personal communications 10 (1999), S. 137-153 
    Details
    ISSN: 1572-834X
    Keywords: CDMA ; Markov chains ; Integrated Services protocol ; throughput ; delay
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper proposes a performance evaluation approach for integrated voice and data services on a broadband code division multiple access (CDMA) network. For random access schemes, the dynamic behavior of a CDMA channel infers that we must be cautious with a performance judgment. We must be especially careful when choosing a mathematical model that has to include the effect of dynamic error rates. The approach shown in this paper is to employ a Poisson error model that takes the occurrence of errors as a Poisson process with the occurring rate dependent on the channel traffic. Based on this assumption, we developed a continuous-time Markov chain model to evaluate the throughput and delay performance. This approach can certainly apply to the evaluation of many integrated services protocols.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018329015533
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  • 23
    Electronic Resource
    Electronic Resource
    A Systolic Array Implementation of the One-Shot Decorrelating Detector Used for Mobile CDMA Communications (1999)
    Springer
    Wireless personal communications 11 (1999), S. 219-229 
    Details
    ISSN: 1572-834X
    Keywords: CDMA ; one-shot ; systolic ; detector ; implementation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A systolic array implementation of the one-shot decorrelating detector algorithm designed for Code-Division Multiple-Access (CDMA) spread spectrum communication systems used in mobile communications environments is developed. This detector has the advantage that it is near-far resistant, that is, it minimizes the interference effects that near-end users have on far-end users. However, its implementation requires the on-line inversion of the correlation matrix between the desired and interfering users. For this reason, a systolic computation approach is chosen to help solve the problem of fast on-the-fly matrix inversion. Performance of the proposed implementation is assessed via digital computer simulation. The implementation methodology presented here leads to a VLSI implementation structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018371312382
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  • 24
    Electronic Resource
    Electronic Resource
    Spreading Codes Generator for Wireless CDMA Networks (1998)
    Springer
    Wireless personal communications 7 (1998), S. 69-88 
    Details
    ISSN: 1572-834X
    Keywords: CDMA ; pseudo random generator ; orthogonal codes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The prime characteristic of spread spectrum modulated signals is that their bandwidth is greater than the information rate. In this way a redundancy is introduced that allows the severe levels of inteference inherent in the transmission of digital information over radio and satellite links to be overcome. Current spread spectrum applications are primarily in military communications; nevertheless, there is growing interest in this technique for third generation mobile radio networks (UMTS, FPLTS, etc.) with open discussion regarding the practicality of using a multiple access system based on spread spectrum techniques (CDMA). However, in order to support as many users in the same bandwidth as other multiple access techniques such as TDMA or FDMA, it is important how to generate large families of sequences that present low cross-correlation. The aim of this paper is to describe a spreading codes generator that can produce a large number of PN sequences with good properties of auto- and cross-correlation. Moreover, the codes generated shows high unpredictability and good statistical behaviour. This also allows the implementation of some features that are common on military networks such as message privacy (increasingly important in commercial networks) without additional cost. The structure presented shows itself to be advantageous for high speed generation of codes at a low cost, low power consumption (allowing longer life for batteries), small size and simplicity of implementation, essential ingredients for commercial equipment. Another attractive feature is its structural parallelism, useful in VLSI implementations. All of these features render it potentially suitable for the implementation of channel bandwidth sharing systems in future wireless personal communications networks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008860715309
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  • 25
    Electronic Resource
    Electronic Resource
    Analysis of an Approximate Decorrelating Detector (1998)
    Springer
    Wireless personal communications 6 (1998), S. 97-111 
    Details
    ISSN: 1572-834X
    Keywords: CDMA ; multiuser detection ; decorrelating detector ; linear demodulation ; co-channel interference.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper an approximate decorrelating detector is analyzed on the basis of a first order approximation to the inverse crosscorrelation matrix of signature waveforms. The approximation is fairly accurate for systems with low crosscorrelations and is exact in the two-user synchronous case. We present an exact as well as approximate analysis of the bit-error-rate performance of this detector on a channel that is subject to flat fading, and also specifically for the case of random signature waveforms. The detector outperforms the conventional matched filter receiver in terms of BER. The approximate decorrelator (while not being near-far resistant like the decorrelating detector) is fairly robust to imperfections in power control. Power trade-off regions are identified which characterize the significant advantage that the approximate decorrelator provides over the matched filter receiver. The reduced complexity of the approximate decorrelator and performance gains over the conventional matched filter makes it a viable alternative for implementation in practical CDMA systems, in particular in those where the signature waveforms span many symbol intervals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008852822553
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  • 26
    Electronic Resource
    Electronic Resource
    Performance Comparison of Multiuser Detectors with Channel Estimation for Flat Rayleigh Fading CDMA Channels (1998)
    Springer
    Wireless personal communications 6 (1998), S. 137-160 
    Details
    ISSN: 1572-834X
    Keywords: CDMA ; multiuser detection ; fading channel estimation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Since the conventional detector performs poorly in bandwidth-efficient Code Division Multiple Access (CDMA) systems, several multiuser detectors were proposed recently. In this paper, we compare performance of the decorrelator, the two-stage detector (2S), and the decision-feedback detector (DF) for the Rayleigh flat fading synchronous CDMA channel. First, assuming perfect channel estimation, we show that the 2S and the DF have much lower bit error rate (BER) than the decorrelator, and prove that the ideal DF has unity Asymptotic Multiuser Efficiency (AME). Furthermore, we evaluate the performance of these detectors in the presence of channel mismatch. We model the Rayleigh flat fading channel as the second order Auto Regressive (AR) process, and use the Kalman filter as the channel estimator. The lower bounds on the BER of the 2S and the DF are derived. The analytical results and the simulations show that the estimation error accumulated due to cancellation of other users limits the performance of the 2S and the DF. Therefore, in the presence of channel mismatch, the decorrelator offers comparable or even better performance than more complex decision-feedback and two-stage detectors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008805006624
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  • 27
    Electronic Resource
    Electronic Resource
    Space-Time Optimum Combining for CDMA Overlay for Personal Communications Systems (1998)
    Springer
    Wireless personal communications 6 (1998), S. 295-309 
    Details
    ISSN: 1572-834X
    Keywords: adaptive antennas for wireless ; overlay ; CDMA ; interference cancellation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The requirement to suppress narrowband interferences in CDMA communication stems from the overlay concept, i.e., coexistence of different types of signals in the same frequency band. This paper describes the performance analysis of a direct-sequence (DS) CDMA personal communication system sharing a common spectrum with narrowband microwave radio links in the 1.85 to 1.99 GHz band. The coexistence of these two systems within the same frequency band will improve the overall spectrum efficiency, but will also cause interference to both systems. In this paper it is shown that joint spatial and temporal optimum combining provides an efficient means of improving the performance of the DS-CDMA system through cancellation of the narrowband signal and the co-channel interferences. The proposed space-time architecture provides degrees of freedom for both diversity and interference cancellation. It is shown that the joint space-time receiver is robust with respect to the narrowband interference signal bandwidth and its carrier frequency offset from the DS-CDMA carrier frequency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008883722614
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  • 28
    Electronic Resource
    Electronic Resource
    Performance of a CDMA System with an Adaptive Receiver and a New Family of Complex Valued Spreading Sequences (1998)
    Springer
    Wireless personal communications 7 (1998), S. 111-134 
    Details
    ISSN: 1572-834X
    Keywords: CDMA ; complex spreading sequences
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper presents the results of a capacity evaluation for a direct-sequence (DS), code-division, multiple access (CDMA) system over both an additive white Gaussian noise (AWGN) channel and a Rayleigh fading channel. The system considered uses an adaptive receiver. The performance of sets of sequences from various binary and complex valued families is examined. The performance of the system is measured in terms of the total efficiency, and it is shown that the new sequence sets offer higher system capacity and lower signal-to-noise power spectral density ratios.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008888810320
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  • 29
    Electronic Resource
    Electronic Resource
    Hybrid acquisition of direct sequence CDMA signals (1996)
    Springer
    International journal of wireless information networks 3 (1996), S. 55-65 
    Details
    ISSN: 1572-8129
    Keywords: Hybrid acquisition ; CDMA ; sequential detection ; MSPRT
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In direct sequence code division multiple access (DS-CDMA) systems, signal acquisition is necessary before communication can commence. Recent work has shown that the problem of acquisition may be even more restrictive than the problem of error control in limiting the capacity and performance of these systems. Passive matched filters and parallel search schemes have been shown to be able to acquire signals rapidly, but they do so at the cost of high or prohibitive complexity. In contrast, straight serial search schemes have lower complexity but acquire the signal much more slowly. In this paper, we studyhybrid active correlation schemes that provide flexibility in the trade-off between acquisition speed and complexity. These techniques test several phases concurrently and either decide that a particular phase is correct, in which case the decision is verified by a binary hypothesis test, or that none of the phases are correct, in which case another group of phases is tested. Two new hybrid acquisition schemes are presented; the first is based on a fixed-sample-size weighted MAP test, and the second is based on anM-ary sequential hypothesis test called MSPRT. It is shown that the weighted MAP-based scheme hypothesis test called MSPRT. It is shown that the weighted MAP-based scheme outperforms a standard MAP-based scheme. It is also shown that considerable performance gain can be obtained using sequential testing. In particular, it is shown through numerical examples that MSPRT-based schemes are several times faster than corresponding fixed-sample-size schemes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02106662
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  • 30
    Electronic Resource
    Electronic Resource
    Performance analysis of a slotted CDMA ALOHA network (1996)
    Springer
    International journal of wireless information networks 3 (1996), S. 195-202 
    Details
    ISSN: 1572-8129
    Keywords: CDMA ; ALOHA ; Markov analysis ; equilibrium point analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract ALOHA is a simple and efficient way of allowing many machines with bursty data streams to communicate with a central computer. For cases where machines are equally likely to transmit to one another, CDMA ALOHA, which allows for full connectivity, may be a better multiple access protocol than slotted ALOHA through a central machine. This paper first describes a model for a fully connected, full duplex, and slotted CDMA ALOHA network where the “receiver-based code” access protocol is used. The stations can send data to, and receive data from, different stations simultaneously. The model is analyzed using discrete-time Markov chain, and some numerical results are presented. For a system with a large number of users where Markov analysis is impractical, equilibrium point analysis is used to predict the stability of the system and determine the throughput as well as the delay performance of the system when it is stable. It is shown that a CDMA slotted ALOHA network has a much better performance compared to simple slotted ALOHA networks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02109335
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