Thorsten Petermann

Is blind channel estimation feasible in mobile communication systems? A study based on GSM

We compare the effect of blind and nonblind channel estimates on the performance of Global System for Mobile communications (GSM) receivers. More precisely, we investigate whether two blind approaches, based on higher order statistics (HOS), can compete with two conventional methods, exploiting training sequences. For blind and nonblind estimates of six fast and slowly fading mobile radio channels, we give simulated bit error rates (BERs), after Viterbi detection, in terms of the signal-to-noise ratio (SNR). We also study the influence of cochannel interferers at different values of the signal-to-interference ratio (SIR). Averaged over the six channel examples, we demonstrate that the blind channel estimation algorithm eigenvector approach to blind identification (EVI) leads to an SNR loss of 1.2-1.3 dB only, while it saves the 22% overhead in GSM data rate caused by the transmission of training sequences. Since just 142 samples are used for blind channel estimation, we consider this performance outstanding for an approach based on HOS.

Impact of blind versus non-blind channel estimation on the BER performance of GSM receivers

We investigate in this paper whether the HOS-based blind channel estimation method EVI (eigenvector approach to blind identification) can compete with the nonblind cross-correlation-based scheme used in state-of-the-art GSM receivers (Global System for Mobile communication). For blind, non-blind, and ideal estimates of COST-207 mobile radio channels, we give simulated bit error rates (BER) after Viterbi detection in terms of the mean signal-to-noise ratio (SNR). Averaged over three COST-207 propagation environments, EVI leads to a mean SNR loss of 1.2 dB only, while it saves the 22% overhead in the GSM data rate due to the transmission of training sequences. Since just 142 samples are used for channel estimation, we consider this performance outstanding for an approach based on HOS.

Blind and nonblind turbo estimation for fast fading GSM channels

Wireless communication systems such as global system for mobile (GSM) communications are playing a growing role for data transmission. In order to ensure reliable transmission, the channel impulse response has to be estimated accurately. This is a difficult task particularly for fast fading channels caused by high-speed mobile units. We deal with the application of nonblind and blind channel estimation approaches to identify the full rate data Traffic CHannel (TCHF9.6) of GSM. We present a new iterative channel estimation scheme leading to a significant performance improvement especially for high-speed propagation with Doppler frequencies up to 500 Hz. Furthermore, it is shown that blind channel estimation schemes could be as efficient as nonblind methods when regarding bit error rates (BERs) after channel decoding in terms of the E~/sub b//N/sub 0/ ratio. Moreover, a solution for the scalar ambiguity inherent in all blind estimation approaches is suggested.

Blind turbo channel estimation in OFDM receivers

Finite-alphabet-based blind channel estimation in OFDM systems is known to be extremely complex due to an exhaustive search to be performed over a tremendous number of channel coefficient combinations. In, this paper, we present a novel blind channel estimator which dramatically reduces this number of coefficient combinations to be checked without a significant deterioration in estimation quality. Hence, the new low complexity approach enables the application of blind channel estimators based on the finite alphabet set even if the transmitted data are high-rate modulated. Furthermore, we show that the performance of blind channel estimation can be improved by an iterative process based upon the capabilities of channel coding. Using bit error rates, the algorithm is tested with simulations and compared to other blind and nonblind channel estimators.

Iterative blind and non-blind channel estimation in GSM receivers

Channel estimation plays a leading role in wireless communication systems such as GSM (Global System for Mobile communications). Putting the main emphasis on investigating the application of non-blind and blind channel estimation approaches to the identification of a full rate data Traffic CHannel (TCH/F9.6), we present a new idea of an iterative channel estimation based upon the capabilities of channel coding. We show that this method leads to a significantly improved performance especially for high speed propagations with Doppler frequencies up to 500 Hz. Giving the bit error rates (BERs) before and after channel decoding in terms of the E~/sub b//N/sub 0/ ratio, we show, furthermore, that blind channel estimation schemes could be as efficient as non-blind methods.

Blind channel estimation in GSM receivers: a comparison of HOS and SOCS based approaches

Due to the solution of an eigenvalue problem, a common drawback of all blind estimation algorithms is the interference of the estimated channel impulse response caused by an unknown complex factor. Since maximum likelihood sequence estimation (MLSE) requires the knowledge of the exact channel characteristics, we present in this paper a method based on a linear mean square error (MSE) solution which enables the estimation of this factor using a-priori information of the source signal. On the assumption of COST-207 mobile radio channels, we compare the blind channel estimation approaches with the non-blind cross-correlation method (CC) used in state-of-the-art GSM receivers (Global System for Mobile communications) and give the bit error rates (BER) after Viterbi detection in terms of the signal-to-noise ratio (SNR). Finally, we also study the influence of non-Gaussian co-channel interference (CCI) on the blind and non-blind estimation schemes.

Blind GSM channel estimation under channel coding conditions

As a fundamental component of the global system for mobile communications (GSM), channel coding aims at improving speech and data transmission quality when the signal encounters disturbances. We put the main emphasis on investigating the application of blind channel estimation approaches based on second order statistics and/or higher order statistics to the identification of a full rate data traffic channel (TCH/F9.6). Giving the bit error rates after equalization and channel decoding in terms of the E~/sub b//N/sub 0/ ratio, we show that there are blind channel estimation algorithms which are almost as efficient as non-blind methods even if the disturbance is non-Gaussian.

Iterative Blind Channel Estimation for OFDM Receivers

Finite-Alphabet based blind channel estimation in OFDM systems is known to be extremely complex due to an exhaustive search to be performed over a tremendous number of channel coefficient combinations. In this paper, we present a novel blind channel estimator which dramatically reduces this number of coefficient combinations to be checked without a significant deterioration in estimation quality. Hence, the new low complexity approach enables the application of blind channel estimators based on the finite alphabet set even if the transmitted data are high-rate modulated. Furthermore, we show that the performance of blind channel estimation can be improved by an iterative process based upon the capabilities of channel coding. Using bit error rates, the algorithm is tested with simulations and compared to other blind and nonblind channel estimators.

A study on the application of blind turbo channel estimators to ofdm related systems

Communication standards based on coherent data demodulation require an accurate estimation of the channel in order to ensure a reliable transmission. This is a difficult task especially for fast fading channels caused by high-speed mobile units. In this paper, we compare different nonblind and blind channel estimation approaches for OFDM related systems. Since most blind channel estimators are known to be extremely complex or sensitive towards certain system parameters, we present a novel algorithm which delivers sufficient estimates with comparatively little effort. Furthermore, an iterative channel estimation scheme is shown that leads to significant performance improvements particularly for high speed propagations.