Doppler Spread Estimation Research Articles

Doppler Spread Estimation in Mobile Communication Systems

A new technique based on the auto-correlation function is described for the estimation of the Doppler spread in mobile communication systems. We first propose to divide a uncertainty region of Doppler spread into multiple frequency bins. Based on the given multiple bins the correlator compares the estimated value at a certain time index to the theoretical exact value and then decides which bin the Doppler spread is estimated in. The certain time index can be optimized to give the largest decision region among multiple bins. We derive the optimum time index algorithm to give the largest decision region for each bin based on Rayleigh fading channel. We also apply the same Doppler spread estimator to the Rician case with the slight transformation of the received signal. We show that the proposed technique is not affected significantly by the Rician factor and the SNR degradation with the reasonable number of samples for estimation which is not the case of other estimators given in the literature.

Reliable Doppler-spread estimation using an evolutionary algorithm for underwater acoustic communications over channels with frequency-selective fading

There is a pressing need for reliable wideband underwater acoustic communication for enhanced performance of diver communications, underwater networks, control links to ROVs and data links to remote sensors and AUVs. The performance of such links is compromised by the doubly-spread acoustic channel, where multipath time-delay spread causes inter-symbol interference due to frequency-selective fading and Doppler-spread results in additional signal distortion and temporal variation of the channel characteristics. However, if the channel characteristics can be estimated accurately, especially the Doppler-spread, many of these problems can be resolved. Doppler-spread occurs because the Doppler velocity may be different on each path. The paper describes a method for improved-reliability Doppler spread estimation of channels that experience frequency-selective fading. The method uses a wideband sounding signal to overcome the frequency selective fading and the estimation of the Doppler spread is obtained from this complex waveform using multi-layered optimization based on evolutionary algorithms. The method has a wide dynamic range and can estimate the Doppler shift of weak multipath components in the presence of strong multipath components. The accuracy of the Doppler-spread estimate is not limited by the short duration of sounding signal and the method performs well even in the presence of significant noise.

Doppler spread estimation in mobile radio systems

In this letter, Doppler spread estimation in digital mobile radio systems is described. A maximum-likelihood approach is derived, and used to develop suboptimal approaches with lower complexity. The proposed algorithms rely on periodic channel estimation and can be used in both TDMA and CDMA systems.

Designs for pilot-symbol-assisted burst-mode communications with fading and frequency uncertainty

High performance and reasonable complexity have made pilot-symbol-assisted modulation (PSAM) of great practical interest in mobile communications. However, no previous work has investigated PSAM in burst-mode operation which is commonly encountered in multiple-access schemes (time-division or slow-frequency-hopped system). This paper examines the burst structure design problem in a frequency-flat fading environment. The explicit relationship between error performance and the design parameters, including pilot allocation, frequency offset, Doppler spread, and modulation scheme, is explored. Periodic pilot insertion commonly used for continuous transmission produces degraded performance in burst-mode operation. A new, unequal-pilot-spacing burst architecture is proposed in this paper to achieve better error performance. This work also focuses on the potential performance improvement of a frequency offset estimator and a Doppler spread estimator. The results show that an improvement up to 2.5 dB in SNR/bit can be attained by a Doppler spread estimator. A significant frequency offset can produce an irreducible error floor or a severe reduction in the throughput rate if no compensation is implemented. The performance degradation investigated in this paper can be used to determine the specification of the frequency offset estimator and the Doppler spread estimator used in conjunction with PSAM.