ISSN:1124-318X    

DOI:10.1002/ett.4460130502

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2002

数据来源: WILEY

摘要:

AbstractAfter discussing basic possibilities to exploit the spatial dimension for wireless communications, a vector transmission model for MIMO channels is taken to investigate the potential of the spatial dimension for MC‐CDMA. For frequency‐selective channels it is shown that the spreading component of MC‐CDMA may already provide enough diversity, so that it gets more important to use the spatial component offered by MIMO channels for parallel transmis

ISSN:1124-318X    

DOI:10.1002/ett.4460130503

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2002

数据来源: WILEY

摘要:

AbstractMulticarrier code‐division multiple access (MC‐CDMA) first appeared in the literature in 1993. It combines conventional code‐division multiple access (CDMA) and orthogonal frequency‐division multiplexing (OFDM), and has several variants that depend on how this combination is done. Although there have been a significant number of publications on MC‐CDMA since its introduction, the literature is still very fragmented, and the terminologies used by different authors are inconsistent. In addition, there are also a number of confusions concerning the detection of MC‐CDMA signals on frequency‐selective channels. As an attempt to achieve mis goal, this paper gives a comprehensive review of MC‐CDMA, describes its different variants, and reviews the receiver techniques for orthogonal MC‐CDMA. It also discusses the relative merits of MC‐CDMA and of multicarrier time‐division multiple access (MC‐TDMA) and orthogonal frequency‐division multiple access (OFDMA) which are the two omer multiple access techniques usable in conjunction with

ISSN:1124-318X    

DOI:10.1002/ett.4460130504

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2002

数据来源: WILEY

摘要:

AbstractIn this paper, both the concept and the demonstrator implementation of an advanced airport data link is described which is used for data exchange between pilots and controllers in future surface movement guidance and control systems on airports. To fulfil future airport capacity requirements, the proposed data link has to be a high capacity, high rate data link. Therefore, the data link design is based on multi‐carrier code‐division multiple‐access which is a flexible and highly efficient multiple‐access transmission technique suitable for mobile communications in fading conditions. Both simulation results with typical aeronautical channel scenarios and bit error rate measurements using the demonstrator hardware show the suitability of multi‐carrier code‐division multiple‐access for aeronautical communications within the airport and its vicinity. Moreover, implementation effects which degrade the performance are identified and countermeasures are proposed and investigated. The results show that a reduction of the implementation loss of up to 2 dB is achievable by applying appropriate co

ISSN:1124-318X    

DOI:10.1002/ett.4460130505

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2002

数据来源: WILEY

摘要:

AbstractA novel efficient algorithm is proposed for the optimisation of capacity assignment in a MC‐CDMA system with an additional frequency division multiplexing component. Based on an estimate of the frequency‐selective channel, the algorithm optimises the assignment of the sub‐bands to the users with respect to the overall system capacity. Moreover, in the optimisation process the algorithm can efficiently cope with a given prioritisation among classes of user‐services, i.e. user‐groups, identified on the basis of a certain demand, such as throughput, tolerable delay and/or error rate etc. From an initial random solution, the algorithm proceeds progressively towards the optimisation of the target function, yielding, in general, a local optimum. By trying a few different initial solutions a very good approximation of the global optimum can be obtained. Futhermore, the algorithm complexity grows only as the square of the number of carriers. Simulation results show that its application provides a very significant gain in the downlink performance of the overall system or of the prioritised us

ISSN:1124-318X    

DOI:10.1002/ett.4460130506

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2002

数据来源: WILEY

摘要:

AbstractThis paper deals with spreading sequences selection for downlink and uplink Multi‐Carrier Code Division Multiple Access (MC‐CDMA) systems with the aim of minimizing the dynamic range of the transmitted multicarrier signal envelope and the multiple access interference. The crest factor of orthogonal and non‐orthogonal sequences are compared analytically and by simulation for downlink and uplink phase shift keying MC‐CDMA transmissions. Then, in order to minimize the multiple access interference produced by frequency selective channels, an optimized spreading sequence allocation procedure is presented. Finally, a selection of the spreading codes which jointly reduces the multiple access interference and the crest factor is proposed for downlink MC‐CDM

ISSN:1124-318X    

DOI:10.1002/ett.4460130507

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2002

数据来源: WILEY

摘要:

AbstractCommunication standards based on coherent data demodulation require an accurate estimation of the channel in order to ensure a reliable transmission. This is a difficult task especially for fast fading channels caused by high‐speed mobile units. In this paper, we compare different nonblind and blind channel estimation approaches for OFDM related systems. Since most blind channel estimators are known to be extremely complex or sensitive towards certain system parameters, we present a novel algorithm which delivers sufficient estimates with comparatively little effort. Furthermore, an iterative channel estimation scheme is shown that leads to significant performance improvements particularly for high speed propagation

ISSN:1124-318X    

DOI:10.1002/ett.4460130508

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2002

数据来源: WILEY

摘要:

AbstractIn this paper, a non‐data‐aided maximum a posteriori (MAP) channel estimation technique for OFDM systems employing M‐PSK modulation scheme is proposed. The technique requires a convenient representation of the discrete multipath fading channel based on the Karhunen‐Loeve orthogonal expansion and estimates the complex channel parameters of each subcarriers iteratively in frequency domain using the Expectation‐Maximization (EM) algorithm. Pilot symbols are employed to choose reliable initial values of the unknown channel parameters. An analytical expression is derived for the exact Cramer‐Rao lower bound of the proposed MAP channel estimator. Moreover, robustness of estimator to changes in channel correlation and signal‐to‐noise ratio is also analyzed. The performance is presented in terms of the mean‐square error and the uncoded symbol error rate for a system employing QPSK signaling. Computer simulations demonstrate that the performance of OFDM systems using coherent demodulation based on our channel estimation can be signi

ISSN:1124-318X    

DOI:10.1002/ett.4460130509

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2002

数据来源: WILEY

摘要:

AbstractThis paper derives the Maximum Likelihood (ML) algorithm for jointly estimating Direction Of Arrival (DOA) and delay path characteristics of multipath propagation by using array antennas whose elements are placed on a circular circumference. The algorithm is especially made of in a quasi‐synchronous Multi‐Carrier (MC) / Code Division Multiple Access (CDMA) systems in order to achieve the optimal diversity effect. The estimated channel characteristics may be used in Multiple Access Interference (MAI) cancellation or suppression, which remains as the subject of future study. Assuming in the acquisition period, e. g. the preamble period of packet transmission, mutually orthogonal codes are assigned to the set of multiple carrier channels of the CDMA users and the assignments are cyclically shifted from one symbol period to another. Each of the received carrier channel signals at each of the antenna elements is correlated on the time axis with the orthogonal code assigned to each user and in this way the data characterizing the radio wave propagation from each of the users can be separately supplied to the algorithm to follow. The algorithm performs a 2‐dimensional Discrete Fourier Transform (DFT) on the signal sequence thus supplied from the antenna elements and the carrier channels, giving a sufficient statistic by which the DOA and delay path characteristics can be estimated for each of the multiple paths from each of the users. Use of the estimation is demonstrated to obtain the optimal weights for frequency‐space diversity and significant improvement in Bit Error Rate (BER) performance was observed over the conventional way of obtaining the

ISSN:1124-318X    

DOI:10.1002/ett.4460130510

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2002

数据来源: WILEY

摘要:

AbstractThis paper proposes a novel array‐antenna‐assisted Doppler spread compensator for orthogonal frequency division multiplexing (OFDM), which is sensitive to fast time‐variation of the radio propagation channel. In the proposed compensator, a linear array antenna is installed on top of the vehicle. The compensator estimates the received signal at a certain point on the linear array antenna by using space domain interpolation. Because the relative position of the estimated receiving point with respect to the ground does not change during the effective symbol duration of an OFDM signal, the time variation due to the movement of the vehicle can be compensated for. Computer simulation shows that the compensator can compensate for the bit error rate performance degradation due to time‐variation of the channel when the velocity of the vehicle is up to 180km/h and a two‐element array antenna is used at the carrier frequency of 600 MHz. The bit error rate performance can be further improved by using a four‐element ar

ISSN:1124-318X    

DOI:10.1002/ett.4460130511

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2002

数据来源: WILEY