236 research outputs found
Kalman filter equalization for QPSK communications
The discrete complex Kalman filter is considered as an equalizer for quadrature phase shift keyed (QPSK) systems in the presence of additive noise and intersymbol interference (ISI). For a known linear time-invariant channel with finite duration impulse response, the finite n-dimension complex Kalman filter equalizer is able to reduce the degradation caused by ISI. When the channel is unknown, an adaptive Kalman equalizer is used in which the channel complex tap gains are estimated by decision feedback. A two component multipath channel QPSK system is used as an example. Using the Chernoff upper bound to calculate the error probabilities, the computer simulation shows that both the Kalman filter equalizer and adaptive equalizer have a better performance than the integrate-and-dump correlator with no equalizer --Abstract, page ii
Shuttle Ku-band signal design study
Carrier synchronization and data demodulation of Unbalanced Quadriphase Shift Keyed (UQPSK) Shuttle communications' signals by optimum and suboptimum methods are discussed. The problem of analyzing carrier reconstruction techniques for unbalanced QPSK signal formats is addressed. An evaluation of the demodulation approach of the Ku-Band Shuttle return link for UQPSK when the I-Q channel power ratio is large is carried out. The effects that Shuttle rocket motor plumes have on the RF communications are determined also. The effect of data asymmetry on bit error probability is discussed
Kalman Filter Equalization For QPSK Communications
The discrete complex Kalman filter is considered as an equalizer for quadrature phase-shift keyed (QPSK) systems in the presence of additive noise and InterSymbol interference (ISI). When the channel is unknown, an adaptive Kalman equalizer is used in which the channel complex tap gains are estimated by decision feedback. Copyright © 1976 by The Institute of Electrical and Electronics Engineers, Inc
Performance Degradation Due To Specular Multipath Intersymbol Interference
Plots of performance degradation are used to compare the effects of fading and intersymbol interference in a two-component specular multipath digital communications channel. Similar plots are then used to compare two practical receivers designed to combat the interference. Degradation plots are shown to allow easy identification of each receiver\u27s range of usefulness, as well as identification of variance bounds demanded of channel parameter estimates which the receivers require. Copyright © 1973 by The Institute of Electrical and Electronics Engineers, Inc
Equalization Of QPSK Data Transmission In Specular Multipath
This paper gives performance results for transversal-filter equalization of Quadri phase phase-shift-keyed (QPSK) signals with two-component multipath and demodulator phase error. An analytical expression for optimum, minimum mean-square-error tap weights in terms of the multipath and signal parameters is given. Probability of error results for no equalization and equalization with adaptive decision-feedback tap-weight adjustment are compared. The results show that significant improvement can be obtained with relatively simple equalizer structures. Copyright © 1974 by The Institute of Electrical and Electronics Engineers, Inc
Digital data transmission over mobile radio channels
The aim of this work is to study data transmission over a microwave
digital mobile radio channel at 900 MHz, where the channel is subjected
to multipath fading. Besides the fading, the other impairments assumed
here are additive noise, co-channel interference and adjacent channel
interference. Two modulation techniques are investigated in this work,
namely Quadrature-Amplitude-Modulation (QAM) and Quadrature-Phase-Shift-
Keying (QPSK). The channel is characterised digitally, assuming multipath
Rayleigh fading in the presence of noise. The detection process
studied here are near-maximum likelihood schemes: non-linear equalisation
methods are also considered in detail.
The thesis is also concerned with carrier synchronisation and channel
estimation under conditions of Rayleigh fading. Since the carrier
syncn,honisation is a most important requirement in mobile radio, a
Digital Phase Locked Loop (DPLL) technique has been designed and investigated
in the form of a feedback digital synchronisation system. Two
types of channel estimation technique, namely feedforward and feedback
estimators, are also investigated in this work. The feedback estimator
is modified by the addition of a digital control system, in order to
reduce its delay, and to cope with rapidly fading signals. Successful
carrier synchronisation is demonstrated by the use of space diversity.
The study was completed using models of the component parts of the system,
and by the use of extensive computer simulations to analyse the system
under various operating conditions
New bounds on RAKE structures for DS-CDMA over frequency-selective Rayleigh fading channels
An upper bound is derived for the probability of error in an asynchronous binary direct-sequence spread-spectrum multiple-access communications system operating over frequency selective Rayleigh fading channels. A coherent RAKE receiver with predetection selective diversity combining is considered. The performance of a multipath-combining receiver is determined for the case of multiple interfering transmitters. Furthermore, the performance of the system is determined in terms of parameters of the signature sequences. These parameters can be used as guides in selecting sequences for the system. The bounds agree with the exponential portion of a normal distribution in which the interfering interference components subtract from the signal amplitude. The results obtained are verified by simulation.Peer ReviewedPostprint (published version
Doppler-corrected differential detection system
Doppler in a communication system operating with a multiple differential phase-shift-keyed format (MDPSK) creates an adverse phase shift in an incoming signal. An open loop frequency estimation is derived from a Doppler-contaminated incoming signal. Based upon the recognition that, whereas the change in phase of the received signal over a full symbol contains both the differentially encoded data and the Doppler induced phase shift, the same change in phase over half a symbol (within a given symbol interval) contains only the Doppler induced phase shift, and the Doppler effect can be estimated and removed from the incoming signal. Doppler correction occurs prior to the receiver's final output of decoded data. A multiphase system can operate with two samplings per symbol interval at no penalty in signal-to-noise ratio provided that an ideal low pass pre-detection filter is employed, and two samples, at 1/4 and 3/4 of the symbol interval T sub s, are taken and summed together prior to incoming signal data detection
A review of modulation techniques for use in a satellite multipath environment
Modulation techniques for use in satellite multipath environmen
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