Joint Frequency and Timing Recovery for MSK-Type Modulation

We investigate a novel nondata-aided method for jointly estimating timing and carrier frequency offset in MSK-type modulation. The algorithm has a feedforward structure and lends itself to a simple digital implementation. Its estimation accuracy depends on a design parameter that may be varied to trade performance for computational complexity. Setting the parameter to unity yields a synchronization scheme already known in the literature. Computer simulations are used to assess the synchronizer performance on AWGN Rayleigh fading channels with MSK and Gaussian MSK modulation

Carrier-Frequency Estimation for Transmissions over Selective Channels

This paper deals with carrier-frequency estimation for burst transmissions over frequency-selective channels. Three estimation schemes are proposed, all based on the use of known training sequences. The first scheme employs an arbitrary sequence and provides joint maximum-likelihood (ML) estimates of the carrier frequency and the channel response. Its implementation complexity is relatively high but its accuracy achieves the Cramer–Rao bound. The second scheme is still based on the ML criterion, but the training sequence is periodic, which helps to reduce the computational load. The third scheme also employs periodic sequences, but its structure comes from heuristic reasoning. Theoretical analysis and simulations are employed to assess the performance of the three schemes

Channel Estimation for the Downlink of the UMTS TDD Component

The time-division duplex (TDD) component of the universal mobile telecommunications system (UMTS) employs synchronous code-division multiple-access techniques with orthogonal spreading codes to provide protection against cochannel interference. In the presence of multipath propagation, however, the code orthogonality is lost and multiaccess interference is generated at the receiver. In such conditions, an estimate of the channel impulse response is required for reliable detection. In this paper, we propose and compare two pilot-assisted schemes for channel estimation in the downlink of the UMTS-TDD system. Both algorithms also provide estimates of the users' energies, which are needed to perform multiuser detection. Theoretical analysis and computer simulations are used to assess the channel estimation performance in terms of mean-squared errors and bit-error rate. It is shown that the accuracy of the proposed estimators attains the Cramer-Rao bound at intermediate/high signal-to-noise ratios

Channel Estimation and Tracking for MC-CDMA Signals

This paper investigates the impact of channel estimation errors in the uplink and downlink of a multicarrier code-division multiple-access system. Pilot blocks are periodically inserted into the downlink data stream to perform a least-squares channel estimation. It is shown that a single-user minimum-mean-square-error (MMSE) detector endowed with the proposed channel estimator has relatively low complexity, good performance and is robust to estimation errors even under full-loaded conditions. In the uplink scenario channel estimates are computed through a least-mean-square algorithm and are passed to a linear MMSE multi-user detector or a parallel interference cancellation (PIC) receiver. Simulations indicate that in this case the system performance depends heavily on the quality of the channel estimates, meaning that they are particularly critical

Channel Acquisition and Tracking for DS-CDMA Uplink Transmissions

This paper deals with channel acquisition and tracking for the uplink of direct-sequence code-division multiple access systems. The transmission medium is characterized by multipath propagation, and the goal is to estimate the time-varying channel impulse response (CIR) for a new user entering the system. Channel acquisition is pursued through maximumlikelihood techniques. The resulting scheme may be too complex in some applications, as it requires the online inversion of a large matrix. Therefore, we also consider a simpler solution based on the least-squares (LS) criterion. Channel tracking is performed through weighted LS methods. At each signaling interval, the CIR estimate is updated using data decisions and exploiting the inverse of the interference covariance matrix to mitigate the near–far problem. Performance is assessed by simulation in a scenario inspired by the frequency-division duplexing component of the universal mobile telecommunications system. The acquisition/ tracking algorithms are found to be resistant to multiuser interference and suitable for transmissions over fast-fading channels