Leonid Krasny

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.

Doppler spread estimation for wireless mobile radio systems

In this paper, efficient and practical approaches for Doppler spread estimation in wireless mobile radio systems are described. A hypothesis-testing approach, given the channel autocorrelation estimate, is utilized for Doppler spread estimation. The channel autocorrelation is estimated slot-by-slot using the knowledge of the channel estimates over the known fields of a TDMA burst, and averaged over several slots to reduce the effect of noise. In practical systems, the Doppler spread must be estimated in the presence of frequency offsets between the transmitter and the receiver. Hence, an algorithm that decouples Doppler spread estimation from automatic frequency compensation (AFC) is also presented. In addition to the mean estimation error performance, the convergence and the tracking ability of the algorithms are evaluated via simulation using ANSI 136 Rev-B modulation and signal transmission format.

System-level performance gains of per-antenna-rate-control (S-PARC)

Currently, there is a high level of interest in MIMO antenna systems, such as per-antenna-rate-control (PARC), for enhancing the data rates for the HSDPA provision of the WCDMA standard. Recent studies have shown that PARC may be improved by adaptively selecting the number of transmitted substreams (the MIMO mode) and the antenna subset from which the substreams are transmitted to better match propagation conditions. In this paper we evaluate the system-level performance of S-PARC for HSDPA. We show that S-PARC achieves significant gains with respect to conventional (non-selective) PARC as well as receive diversity systems, even in the presence of spatially correlated fading. We demonstrate the importance of MIMO mode and antenna selection in correlated fading, and show that without it, a performance loss with respect to receive diversity can occur.

Performance of time of arrival estimation based on signal eigen vectors

Multiple signal identification and classification (MUSIC) is a well known approach to time of arrival estimation of band-limited signals received through multi-path channels. MUSIC uses the eigen vectors of the correlation matrix for the received data that are associated with noise components. We compare the performance of MUSIC to an algorithm that is based on the eigen vectors associated with the signal components of this correlation matrix. The performance comparison is made using a simple two path channel model where the second path delay is assumed known and the statistics of the error in measuring the delay of the first path are compared. The optimal algorithm for this estimation problem is the maximum-likelihood algorithm (ML) and the performance of MUSIC and the signal eigen vectors algorithm are compared to the ML approach.

Delta modulation for channel feedback in transmit diversity systems

In a wireless communication system with multiple transmit antennas, knowledge of the channel at the transmitter can be used to increase link and system capacity. In a frequency division duplex system, the channel may be estimated by the receiver and communicated back to the transmitter for use in future transmissions. Efficient schemes that achieve channel feedback in this manner are of interest. We present a channel feedback scheme that uses delta modulation to encode channel information efficiently by exploiting the temporal correlation of the wireless channel. A system with multiple transmit antennas and a single receive antenna is used to evaluate the performance of the channel feedback scheme. The effect of feedback channel errors on system performance is shown. The presented method is found to be advantageous for channels with low to moderate Doppler frequencies.

Enhanced time of arrival estimation with successive cancellation

Two methods for accurate estimation of time or angle of arrival that use successive cancellation techniques are presented. The first method performs successive cancellation with a correlation approach used for each iteration. The second method uses the multiple signal identification and classification (MUSIC) approach for each iteration. The first method exhibits enhanced performance as compared to straight-forward correlation techniques and has lower complexity than high resolution techniques such as MUSIC. The method also performs better than Capons (1969) minimum variance method and MUSIC when the total time duration of the received signal is small or when the signal-to-noise ratio is low. The second method performs better than MUSIC and Capons minimum variance approach but is more complex than both of them. The methods are explained in the context of time of arrival estimation.

Wave-number estimation in an ocean waveguide

The optimal (by the criterion of maximum likelihood function) algorithm is applied to the problem of estimating the wave numbers of normal modes in an ocean waveguide. This algorithm has a high-resolution property, takes into account availability of correlated spatial noise, does not require prior modal decorrelation, is suitable for a horizontal array of any shape, and permits one to attain the potential wave-number estimation accuracy limit (Cramer–Rao bound). Numerical simulations for the Pekeris model of an ocean waveguide are presented, demonstrating that the optimal algorithm can essentially (more than ten times) improve the wave-number estimation performance relative to those one for the MUSIC algorithm. Wave-number estimation by the optimal algorithm requires searching for the global extremum of some goal function. It is connected, in common, with known computing difficulties and the absence of sufficiently well-developed computing algorithms. Algorithms based on the signal eigenvectors property o...

Transceiver design and performance evaluation of MIMO systems with forward link channel knowledge

We study multiple input multiple output (MIMO) antenna systems in a frequency selective channel with complete forward link channel knowledge based on a discrete frequency domain model. An optimal transmit and receive architecture in terms of maximizing the MIMO channel capacity is first described, followed by the practical considerations of linear pre-filter, encoder, modulation and receiver designs. Simulations focused on cases with more transmit than receive antennas demonstrate the great potential ability of such systems to exploit both the coherent array gain and the spatial multiplexing gain using a fairly simple receiver.

Improved packet data performance for WCDMA using multi-antenna techniques

Multi-antenna systems have been proposed to improve data rates for third-generation networks, such as the highspeed downlink shared channel (HS-DSCH) packet-data mode in the WCDMA system. We consider the impact of incorporating two multiple transmit antenna systems into HS-DSCH. The first uses transmit diversity with channel knowledge at the transmitter together with a single receive antenna, while the second is an open-loop scheme with multiple transmit and receive antennas. In dispersive propagation environments, multiple access and intersymbol interference, resulting from multicode and multi-antenna transmissions, must be handled appropriately to avoid limiting overall performance. We show, through system simulations, that improved system and user throughputs can be obtained in realistic channel conditions due to the combined effects of channel and multiuser diversity.

Performance of successive cancellation techniques for time of arrival estimation

Two successive cancellation methods for estimation of time or angle of arrival were presented by Krasny and Koorapaty (1986) and their performance was investigated for multipath channels with uncorrelated paths components. In this paper, the performance of the methods is investigated over channel models that have been designed to simulate real-world environments and have been extensively used for evaluating cellular positioning methods in standardization bodies. The first method performs successive cancellation with a correlation approach used for each iteration. The second method uses the multiple signal identification and classification (MUSIC) approach for each iteration. It is shown that the method based on the correlation approach outperforms MUSIC and Capons (1969) minimum variance approach for many cases of interest. The performance for the methods are investigated in the context of time of arrival estimation.