Department Publications

HKU Scholars Hub: Gaussian Despreading Chip Waveform for Coherent Code Tracking in DS/CDMA Systems Skip navigation HKU Login Guest Login Home Publications Researchers Staff Research Postgraduates Organizations Grants Datasets Deposit Data HKUL Research Data Management Theses Patents Community Service File Download There are no files associated with this item. Supplementary Appears in Collections: Electrical & Electronic Engineering: Conference papers Conference Paper: Gaussian Despreading Chip Waveform for Coherent Code Tracking in DS/CDMA Systems Show simple item record Show full item record Export item record Title Gaussian Despreading Chip Waveform for Coherent Code Tracking in DS/CDMA Systems Authors Thayaparan, SWang, JNg, TS Issue Date 1999 Citation Proc. International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC'99, …

This paper presents the code tracking performance on the use of weighted chip despreading PN sequence in a coherent delay locked tracking scheme for direct-sequence spread-spectrum (DS/SS) systems. In the delay locked loop (DLL), the conventional rectangular chip waveform for early and late despreading PN sequences is replaced by a weighted exponential chip waveform. The chip weight (/spl gamma/) is tuned to optimise the DLL performance. The early-late spacing is considered as one chip time. This scheme is analysed for both ideal and band limited received signals in the presence of additive white Gaussian noise.

This paper presents the performance comparison on the use of general non-linear dectors in a non-coherent delay locked tracking scheme for direct-seuence spreqd-spectrum systems. In the dalay locked loop (DLL), the square law-enevelope detectors are replaced by a full wave (even) nth - law detectors and this scheme is analysed in the presence of additive white gaussian noise. The tracking error of the DLL is compared for different values of n (n=0.5, 1, 2, 3, respectively). The results shows that the tracking error of the DLL can be reduced further in low signal to nose power ratio region by using the full wave (even) nth -law detectors for n<2 when compare with using the square law enevelope detectors (n=2).

An adaptive Viterbi algorithm, derived from a dynamic estimate of the fading channel is used for the decoding of a convolutional coded 16 QAM system in a mobile environment. The estimates are obtained by a sequence of known pilot symbols embedded in the data stream, and perform compensation for Rayleigh fading. The likelihood criterion in the Viterbi decoder is also modified by these channel estimates through a metric weighting function. We demonstrate through computer simulations, that our new technique achieves a BER improvement of 7-10 dB at P/sub e/=10/sup -3/ in a fast flat Rayleigh fading environment compared to an uncoded system. The BER performance of our new technique in a co-channel interference (CCI) controlled environment is also studied, and the results show that it may achieve a 40% to 85% improvement in capacity over the standard modem scheme for the new US digital cellular …

We apply baseband pulse shaping techniques for /spl pi//4 QPSK in order to reduce the spectral regeneration of the bandlimited carrier after nonlinear amplification. These Feher's patented techniques, namely, /spl pi//4 FQPSK (superposed QPSK) and /spl pi//4 CTPSK (controlled transition PSK), may also be noncoherently demodulated. Application of these techniques is in fast fading, power efficient channels, typical of the mobile radio environment. Computer simulation and experimental studies demonstrate that with these baseband waveshaping techniques, carrier envelope fluctuations are significantly reduced, and the out-of-band power after nonlinear amplification is suppressed by up to 20 dB compared to /spl pi//4 QPSK. In frequency noninterleaved land or satellite mobile radio systems operating in a nonlinear, fading and ACI (adjacent channel interference) environment, these techniques may achieve 20 …

An adaptive Viterbi algorithm, derived from a dynamic estimate of the fading channel, is used for the decoding of a convolutional coded 16-QAM system in a mobile environment. The estimates are obtained by a sequence of known pilot symbols embedded in the data stream, and perform compensation for Rayleigh fading. The likelihood criterion in the Viterbi decoder is also modified by these channel estimates through a metric weighting function. We demonstrate, through computer simulations, that our new technique achieves a BER improvement of 7-10 dB at P,= 10-’in a fast flat Rayleigh fading environment compared to an uncoded system. The BER performance of our new technique in a CCI controlled environment is also studied, and the results show that it may achieve an 80 percent improvement in spectral utilization over the standard modem scheme for the new US. digital cellular system, ii/l-DQPSK.

New methods for generating additional capacity from the limited available spectrum for digital mobile, cellular and personal communications systems are introduced. Techniques for the improvement of spectral efficiency and capacity with modulation schemes currently in use are first investigated. The adoption of more spectrally efficient multilevel modulation formats to yield further improvements in capacity is then undertaken.

A coded 16-quadrature amplitude modulation (QAM) scheme with digital channel sounding, convolutional coding, and space diversity is introduced for improving the spectral utilization of digital cellular systems. A combined estimate of channel reliability is obtained from the diversity branches, and is used to modify the likelihood criterion of the Viterbi decoder. This is an extension of the authors previous decoding techniques to include multiple diversity paths. They investigate the bit error rate performance of this scheme in fast fading channels corrupted by additive white Gaussian noise and cochannel interference through computer simulations. The results show that in a cellular environment, this scheme may achieve an improvement in capacity of 30% compared to the pi /4-DQPSK method with diversity reception.<>

The application of two baseband pulse shaping techniques to improve the spectral efficiency obtained by pi /4-DQPSK (differential quadrature phase shift keying) in a nonlinearly amplified land mobile environment is examined. The spectral and bit error rate (BER) performance of these techniques is studied through computer-aided design techniques. It is demonstrated that, by using the shaping methods considered. pi /4-QORC (quadrature overlapped raised cosine) and pi /4-CTPSK (controlled transition PSK), the spectral regeneration after nonlinear amplification can be reduced significantly. Thus, the schemes studied allow closer channel spacing compared to pi /4-DQPSK, the current standard modem scheme for the US digital mobile communications system.<>

The spectral/power efficiency and performance of the pi /4-quadrature phase-shift keying (QPSK) modems (American and Japanese digital cellular emerging standards) are studied and briefly compared to GMSK modems (proposed for European Digital European Cordless Telephone System) (DECT) and Group Special Mobile System (GSM) cellular standards). Improved filtering strategies and digital pilot aided (digital channel sounding) techniques are considered for pi /4-QPSK and for other digital modems. More spectrally efficient modem trends and some research results for future cellular/mobile (land mobile) and satellite communication systems applications are also highlighted.<>

A new modulation technique, π/4-Controlled Transition PSK (π/4-CTPSK), suitable for non-linearly amplified digital mobile satellite communications systems is introduced. This technique is derived from π/4-QPSK, the modulation scheme adopted as the new U.S. and Japanese digital cellular standard. The π/4-CTPSK modulated carrier is shown to undergo significantly less spectral regeneration after non-linear amplification compared to π/4-QPSK, leading to more efficiant utilization of the available power and spectrum. A principal application of π/4-CTPSK is for systems which may require differential or discriminator detection, such an low bit-rate satellite and land mobile radio communications.

An adaptive Viterbi algorithm, derived from a dynamic estimate of the fading channel, is used for the decoding of a convolutionally coded 16 QAM system in a mobile environment. The new technique achieves a BER (bit error rate) performance improvement of 8 dB at P/sub e/=10/sup -3/ in a fast flat Rayleigh fading environment compared to an uncoded system with pilot symbol aided compensation. The BER performance of the new technique in a cochannel interference (CCI) controlled environment is also presented. Results indicate that the 16 QAM scheme achieves significant improvements in spectral and power efficiency when compared to the emerging US standard, which will use pi /4-DQPSK for digital cellular systems.<>

The performance of Miller coded pilot aided modulation systems is studied by computer-aided design techniques. It is shown that the use of this nonredundant code may improve the bit error rate (BER) performance of pilot aided modulation schemes over similar uncoded coherent and noncoherent systems. Miller coded random data have a spectral density about 12 dB lower than uncoded data at and around the unmodulated carrier frequency. The use of this code reduces the interference between the data spectrum and the pilot tone, and hence improves the BER performance. This improvement is significant, particularly in low bit-rate systems where a relatively wide bandpass filter is required for pilot extraction and successful compensation for fading and Doppler shift caused phase variations. This improved BER performance is obtained with no redundancy, but at the cost of some spectral efficiency.<>