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  • Articles  (840)
  • Chemistry  (409)
  • Engineering  (392)
  • CDMA  (39)
  • Electrical Engineering, Measurement and Control Technology  (840)
  • 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
    Spread Spectrum Technique to Improve the Performance of Radio over Fibre for Microcellular GSM Networks (2000)
    Springer
    Wireless personal communications 14 (2000), S. 133-146 
    Details
    ISSN: 1572-834X
    Keywords: radio over fibre ; microcellular networks ; CDMA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper presents a GSM-specific assessment of the performance of a radioover fibre link between a remote antenna unit and GSM base station. Theintermodulation distortion (IMD) has been analysed for a system using thesubcarrier multiplexing (SCM). A novel technique using direct sequence spreadspectrum is proposed to minimize the IMD by decreasing the signal amplitudeprior to a direct modulation of a laser diode. The results show that theoptical fibre microcellular is outperforming the full wireless system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008957200405
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  • 5
    Electronic Resource
    Electronic Resource
    Implementation of the Decorrelating Receiver for Asynchronous DS-CDMA Systems over Multipath Fading Channels (2000)
    Springer
    Wireless personal communications 15 (2000), S. 79-95 
    Details
    ISSN: 1572-834X
    Keywords: CDMA ; multiuser detection ; multipath fading channel ; decorrelating detector
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper presents a decorrelating detector for DS-CDMAasynchronous systems over multipath fading channels. The decorrelatingreceiver applies the inverse correlation matrix of signature waveformsto detect the received signal. A procedure for finding such an inversematrix is developed. This procedure employs the reciprocal basis,derived from the basis of normalized user signatures, to cancelsimultaneously both the multiuser and the intersymbolinterference. The proposed multiuser detector operates over a finitedetection window, and the only restriction imposed on the set of signaturesis that the signatures must be independent at the receiver end. If the channelis slowly variant, the detectorcan be very efficient for high bit rate transmissions. Theoreticalbounds for the multiuser interference are obtained. Simulationresults, in which both binary and non-binary sequences are used,reveal that the behaviour of the detector approaches the single userbound when an adequate set of signatures is employed. The reducedcomplexity of this detector indicates that it could be a good candidatefor practical implementation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008959121461
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  • 6
    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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  • 7
    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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  • 8
    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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  • 9
    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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  • 10
    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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