ISSN:1124-318X    

DOI:10.1002/ett.4460060102

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

年代:1995

数据来源: WILEY

ISSN:1124-318X    

DOI:10.1002/ett.4460060103

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

年代:1995

数据来源: WILEY

ISSN:1124-318X    

DOI:10.1002/ett.4460060104

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

年代:1995

数据来源: WILEY

ISSN:1124-318X    

DOI:10.1002/ett.4460060105

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

年代:1995

数据来源: WILEY

摘要:

AbstractThis work presents a direct sequence spread‐spectrum multiaccess (DS/CDMA) receiver that employs integrated structure of staged decoder and CCI (co‐channel interference) canceller, when multilevel coded modulation is used and the system undergoes fading channel. We exploit the attractive multistage decoding method of multilevel coding. Each stage decoding is jointly done with the data estimation process and thus replicas of CCI can be formed with high precision, which ultimately results in performance improvement without any additional decoding delay or circuit complexity. We have chosen appropriate multilevel 8‐PSK coded modulation schemes for the integrated receiver of staged decoder and CCI canceller in fading channels. Computer simulation results show the significant coding gain that can be achieved by the proposed scheme in comparison with the conventional scheme. The effect of estimation error as well as unequal power is also investi

ISSN:1124-318X    

DOI:10.1002/ett.4460060106

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

年代:1995

数据来源: WILEY

摘要:

AbstractAn asynchronous code‐division multiple access (CDMA) system with adaptive transmitters and receivers is considered. It is assumed that the adaptive receiver and transmitter have no knowledge of the signature waveforms and timing of other users. The concept of adaptive transmitter is based on feedback information from the corresponding receiver. The information obtained from the receiver is used to calculate the optimum transmitter signature. The signatures are adaptively adjusted according to the MSE criterion during the training period as well as during data transmission. CDMA systems employing the adaptive transmitters in the presence of multiple access interference achieve the matched filter bound with no interference. The proposed CDMA system are tested by simulation over a channel with multiple access interference and additive white gaussian nois

ISSN:1124-318X    

DOI:10.1002/ett.4460060107

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

年代:1995

数据来源: WILEY

摘要:

AbstractIn this paper we consider a multi‐sensor detection problem in both additive white Gaussian noise (AWGN) and fading channels with the users using the channel based on a code division multiple access (CDMA) scheme. Several multi‐sensor detectors that have been studied previously do offer good performance; however, these detectors require the knowledge of the signal energies and these have to be estimated. Such an estimation might not be feasible in fading and time‐varying channels. We show how the linear optimal detector can then be simplified to obtain a decorrelating detector which does not require the knowledge of the users' signals. We show that this decorrelating detector performs almost as well as the linear optimal detector in an AWGN channel. We further investigate its performance in single‐path and frequency‐selective slowly fading channels. In a slowly fading channel when there is multi‐user interference, the conventional detector reaches a saturation point beyond which no improvement in performance can be obtained. We show that the performance of the decorrelating detector does not depend on the other users' energies and hence on the other users' fading characteristics. We further show that a decorrelating detector can be used to obtain a Rake type of receiver in frequency‐selective fa

ISSN:1124-318X    

DOI:10.1002/ett.4460060108

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe probability of error is determined for an uncoded coherent direct‐sequence spread‐spectrum system with rake reception operating in a specular multipath fading environment. Bounds on the probability of error for a convolutionally‐coded system are also calculated through the use of the union bound. The model that is utilized contains a large number of paths divided into groups across the signalling interval. The rake is assumed to be locked onto the direct path and one strong path from each of a subset of the other groups. The probability of error is calculated using the characteristic function to determine the effect of various system parameters such as the processing gain and the number of rake branches. Comparisons are made with results obtained through the standard Gaussian assumption. Finally, further analytic results are presented for the rake receiver in the low signal‐to‐noise ra

ISSN:1124-318X    

DOI:10.1002/ett.4460060109

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

年代:1995

数据来源: WILEY

摘要:

AbstractFrequency hopping (FH) spread spectrum is a well known technique used in communications systems to provide protection against interference such as jamming. With fast FH (FFH) (one or more hops per transmitted data symbol), powerful and robust methods for diversity combining have been developed as an additional jamming countermeasure. These same techniques can be applied to reduce the effects of multiple access interference, and so can be considered for civilian CDMA applications. Although the performance of a FFH communications system can be degraded considerably by fading, few results exist which show the effects of fading on the diversity combining process. In this paper, both analytic and simulation results are presented for several diversity combining methods in a Rayleigh fading channel, which is often considered to be the worst case. The performance of these combining methods in fading is compared with that in AWGN and multitone interference to determine which methods are effective against these degradations.

ISSN:1124-318X    

DOI:10.1002/ett.4460060110

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

年代:1995

数据来源: WILEY

摘要:

AbstractA DS CDMA satellite uplink with power control error is considered. CDMA system performance is normally interference limited, and, in an additive, white, Gaussian noise channel, with many users, sufficient processing gain, and effective power control, individual users typically experience the average performance over all users. In this case, the other users appear as the equivalent of additional Gaussian noise and each user experiences the same environment. An alternative measure of performance under fading conditions is the probability of outage. For coded signals, the fading must be averaged over all the symbols in the code word. For properly interleaved signals and i.i.d. Rayleigh fade statistics, the average must be performed over a chi‐squared variate. The probability of outage, defined as the probability that the decoded bit error rate exceeds a specified threshold, is monotonic with the probability that the chi‐squared variate is less than a specified threshold. We derive upper and lower bounds on the outage probability for soft decision decod

ISSN:1124-318X    

DOI:10.1002/ett.4460060111

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

年代:1995

数据来源: WILEY