Adegbenga B. Awoseyila

Robust time-domain timing and frequency synchronization for OFDM systems

A robust and efficient technique for frame/symbol timing and carrier frequency synchronization in OFDM systems is presented. It uses a preamble consisting of only one training symbol with two identical parts to achieve reliable timing and frequency accuracy in the time-domain, over a wide frequency estimation range which can be up to half of the signal sampling frequency. Also, it has a low complexity which is adaptive to the degree of channel distortion. Computer simulations in the Rayleigh fading ISI channel show that the proposed method achieves superior performance to existing techniques in terms of timing and frequency accuracy. Also, its operation in the time-domain helps to achieve faster synchronization convergence.

Improved preamble-aided timing estimation for OFDM systems

An improved method for estimating the frame/symbol timing offset in preamble-aided OFDM systems is presented. It uses a conventional preamble structure and combines autocorrelation techniques with restricted crosscorrelation to achieve a near-ideal timing performance without significant increase in complexity. Computer simulations show that the method is robust in both AWGN and fading multipath channels, achieving better performance than the existing methods.

Low complexity time-domain channel and delay spread estimation for OFDM systems

A low complexity time-domain channel estimation scheme for OFDM systems is presented. It uses a training symbol (preamble) to estimate the channel impulse response (CIR) in the presence of timing synchronization errors. Its computational complexity is much lower than that of the popular MMSE technique and this can be further reduced if there is prior knowledge of the channel delay spread. Consequently, channel delay spread estimation is also addressed by using threshold setting on the optimized CIR. Computer simulations show that the proposed scheme achieves near-ideal accuracy in quasi-static channels.

Signal-to-Noise Ratio Estimation Algorithm for Advanced DVB-RCS Systems

This paper presents a signal-to-noise ratio (SNR) estimation algorithm for advanced Digital Video Broadcasting-Return Channel via Satellite (DVB-RCS) systems using adaptive coding and modulation (ACM) in the reverse link of broadband satellite systems. Due to the absence of a repetitive pilot symbol structure, SNR estimation has to be performed using the fixed symbol preamble data. Moreover, sporadic nature of data traffic on the return link causes variation in interference level from slot to slot and, therefore, the estimation has to be done within one traffic slot duration. Hence, it becomes necessary to use a combination of data-aided (DA) and decision-directed (DD) algorithms so as to make use of traffic data. A non-data-aided (NDA) estimator that was previously proposed by the authors for binary phase shift keying (BPSK) and QPSK schemes is extended to 8-PSK in a decision directed manner. This estimator shows improved performance over existing estimators. The inherent bias of DD approach at low values of SNR is reduced by using a hybrid approach, i.e., using the proposed estimator at moderate/high values of SNR and the moments-based estimator (M2M4) at low values of SNR. Overall improved performance of the proposed hybrid estimator, in terms of accuracy and complexity, makes it an attractive choice for implementing ACM in advanced DVB-RCS systems.

Signal-to-noise ratio estimation algorithm for adaptive coding and modulation in advanced digital video broadcasting-radar cross section satellite systems

This paper presents a signal-to-noise ratio (SNR) estimation algorithm for advanced digital video broadcasting- return channel via satellite (DVB-RCS) systems using adaptive coding and modulation (ACM). Due to the absence of a repetitive pilot symbol structure, SNR estimation has to be performed using the fixed symbol preamble data. Moreover, sporadic nature of data traffic on the return link causes variation in interference level from slot to slot and, therefore, the estimation has to be done within one traffic slot duration. Hence, it becomes necessary to use a combination of data-aided and decision-directed (DD) algorithms so as to make use of traffic data. A non-data-aided estimator that was previously proposed by the authors for binary and quadrature phase shift keying schemes is extended to 8-PSK in a decision directed manner. The inherent bias of DD approach at low values of SNR is reduced by using a hybrid approach, that is, using the proposed estimator at moderate/high values of SNR and the moments-based estimator (M2M4) at low values of SNR. Overall improved performance of the proposed hybrid estimator, in terms of accuracy and complexity, makes it an attractive choice for implementing ACM in advanced DVB-RCS systems.

On acquisition and tracking methods for SC-FDMA over satellite

In this paper we address the main opportunities and challenges related to the use of a single carrier frequency division multiple access (SC-FDMA) waveform over a geostationary (GEO) satellite return link. More in details the impact of the satellite round-trip delay on SC-FDMA synchronisation acquisition is discussed and a possible solution for an efficient log-on procedure is proposed. The effects of satellite uplink channel impairments on SC-FDMA synchronization tracking are also analyzed and a set of timing, frequency and phase offsets estimation algorithms is proposed to be efficiently used in the context of satellite return link. In addition, also a reference architecture for SC-FDMA system focused on synchronization aspects is proposed.

Threshold Detection Analysis for OFDM Timing and Frequency Recovery

Some recently proposed robust methods for time-domain timing and frequency synchronization in OFDM systems incorporate the use of cross-correlation based threshold detection in their timing adjustment and joint time-frequency algorithms. In this paper, we analyze the threshold criterion used and derive its theoretical performance. This translates into a better characterization of these OFDM synchronization algorithms, leading to a closer match between design expectations and practical performance. Computer simulations show a strong agreement between theoretical predictions and numerical results.

Simplified Expressions for APSK Error Performance

The amplitude phase shift keying (APSK) constellation adopted by the second g eneration standard for digital video broadcasting via satellite (DVB-S2), represents a power- and spectrally-efficient modulation scheme suitable for an effective digital transmission over non-linear satellite channels. In this paper, an analytical evaluation of the performance of APSK constellations in additive white Gaussian noise is performed and a simplified expression to approximate the error probability is presented. The expression accounts for a number of symbols, equal to the number of concentric rings in the constellation. It is shown to significantly reduce the computational complexity associated with previously known error performance expressions, while closely predicting the error rates in the relevant signal-to-noise ratio (SNR) range.

Spectrally efficient waveforms for the return link in satellite communication systems

In this paper, we study the applicability of terrestrial mobile waveforms in the return link of a high throughput satellite (HTS) communication system. These include orthogonal frequency division multiple access (OFDMA), single-carrier frequency division multiple access (SC-FDMA) and filter bank multi-carrier (FBMC). Key solutions to the challenges in a geostationary orbit (GEO) satellite channel, such as synchronization and non-linear distortion, are presented. A global-positioning-system-(GPS)-based approach for synchronization acquisition is proposed, while suitable algorithms are studied for timing/frequency offset estimation and synchronization tracking. The spectral and power efficiencies of the schemes are optimized by means of an intermodulation interference (IMI) cancelling receiver, and these are compared to state-of-the-art time division multiple access (TDMA). Finally, end-to-end simulations validate the system performance.

Enhanced Channel Estimation for DVB-S2 Systems

The aim of this paper is to study the potential improvement in nonlinear channel distortion and link quality estimation based on evolved pilots especially suited for the estimation of nonlinearities. In contrast to the constant-envelope pilots specied in the current DVB-S2 standard, a multilevel pilot design is proposed wherein pilots are taken from the same constellation as the user data. Simulation results indicate that amplier distortion and eective signal-to-noise ratio (SNR) at the demodulator input can be estimated more accurately for higher-order modulation than is achievable using constant-envelope pilots. Enhanced nonlinear channel equalization improves the bit error performance and improved SNR estimation can help to improve the threshold setting for adaptive coding and modulation procedure.