Jerome A. Gansman

Optimum and suboptimum frame synchronization for pilot-symbol-assisted modulation

Pilot-symbol-assisted modulation (PSAM) is a method to reduce the effects of fading in mobile communications by periodically inserting known symbols in the data stream. The receiver uses these pilot symbols to derive its amplitude and phase reference. One aspect of this procedure which has not received much attention in the literature is the method used by the receiver to locate the pilot symbols. This paper uses optimum frame synchronization techniques to develop two synchronizers for PSAM systems; one is based on a standard maximum likelihood (ML) estimation formulation, and the other is a sequential testing algorithm. Both methods use a simple quadratic correlation filter with an energy correction factor. Simulation results and a theoretical analysis are presented.

Single frequency estimation with non-uniform sampling

A new frame structure is proposed for pilot symbol assisted modulation (PSAM) systems which includes a small number of known pilots at the start of each frame. This facilitates the estimation of large frequency offsets without aliasing. Cramer Rao lower bounds and the exact ML estimates are derived for AWGN and Rayleigh fading channels. Finally, simulations show that the ML estimator has much better performance than existing reduced complexity estimators when applied to this sparse observation model.

A study of non-uniform pilot spacing for PSAM

Pilot symbol assisted modulation (PSAM) achieves coherent demodulation in a fading environment by inserting known symbols into the data stream. The receiver uses these pilot symbols to estimate its amplitude and phase reference. Although the pilots are typically spaced uniformly, adding extra consecutive pilot symbols allows one to estimate a large frequency offset on the channel. This work uses computer simulations to investigate the bit error probability (BEP) of PSAM with various non-uniform frame structures. It is shown that for higher Doppler rates, a non-uniform frame structure yields a lower BEP than a comparable uniform frame. Furthermore, in the presence of an unknown frequency offset, a non-uniform frame performs much better because it can estimate and remove the frequency offset prior to compensating for the fading process.

Multidimensional multirate DOA estimation in beamspace

This paper presents a beamspace version of ESPRIT for uniform rectangular arrays that supports closed-form 2-D angle estimation, automatically couples the two components of the source directions, and works with any front end beamformer. The proposed algorithm is based on the observation that beamspace noise eigenvectors can be transformed to vectors that are bandpass and have spectral nulls at the inband source locations. This facilitates multirate processing (involving modulation to baseband, filtering, and decimation) and yields a space with dimensionality equal to the number of beams used to probe the subband rather than the number of elements in the sensor array. The MUSIC algorithm can be applied to this noise subspace. Alternatively, a transformation matrix can be computed a priori, which maps the beamspace signal eigenvectors to the corresponding signal subspace that has the ESPRIT structure. The TLS-ESPRIT algorithm is then modified to obtain the two directions for each source from a single eigenvalue-eigenvector pair. Hence, they are automatically coupled.

Frame synchronization for PSAM on Rayleigh fading channels

Pilot symbol assisted modulation (PSAM) is a method to reduce the effects of fading in mobile communications by periodically inserting known symbols in the data stream. The receiver uses these pilot symbols to derive its amplitude and phase reference. One aspect of this procedure which has not received much attention in the literature is the method used by the receiver to locate the pilot symbols. This paper satisfies that need by investigating optimum and sub-optimum frame synchronization techniques for the case of an M-QAM data symbol set and a PSK pilot sequence.

High Efficiency Narrowband Wireless Modems for ITS Applications

The Intelligent Transportation System (ITS) relies heavily on data communications systems to link field equipment such as traffic sensors, changeable message signs and incident response vehicles with traffic operations centers. This paper has two main purposes. The first is to present a review of data communications concepts essential in the design of wireless modems for the ITS 220 MHz spectral allocations. The second is to propose an architecture for such modems which offers spectral efficiency much higher than that available in current products. The new modem architecture is implemented using the combination of a digital signal processor, discrete electronics, and high level software. All sophisticated signal processing is implemented in software to provide both high performance and flexibility. The system forms an ideal testbed for the design of future enhancements and modifications to fit specific ITS applications. A prototype has been constructed and subjected to full bench testing. Preliminary field testing has been performed and more is in progress.

Maximum likelihood frame synchronization for PSAM

Pilot symbol assisted modulation (PSAM) is a method to reduce the effects of fading in mobile communications by periodically inserting known symbols in the data stream. The receiver uses these pilot symbols to derive its amplitude and phase reference. In this paper, standard maximum likelihood (ML) estimation techniques are used to derive optimum synchronization structures for AWGN and slow Rayleigh fading.

Further synchronization results for PSAM systems

This paper investigates the affect of a frequency offset on the bit error probability of pilot symbol assisted modulation in frequency non-selective slow Rayleigh fading. Traditionally, the Wiener filter is designed to estimate both the fading induced multiplicative distortion and the frequency offset. However, it is shown that altering the frame structure to include consecutive pilot symbols and compensating for the frequency offset prior to Wiener filtering greatly improves the system performance.

A Comparative Synchronizers Study of a Class of PSAM Frame

Pilot symbol assisted modulation (PSAM) is amethod to reduce the effects of fading in mobilecommunications by periodically inserting knowing symbolsin the data stream. The receiver uses the pilot symbols to estimate channel state information. In orderto do this, the pilot symbols must first be located inthe noisy received sequence. This paper investigates theperformance of a class of PSAMs frame synchronizers which have the form of a quadratic correlationfilter and threshold test. Computer simulations are usedto show that these synchronizers can be designed to havea robust performance over a large range of Doppler spreads and SNR, to achieve anarbitrarily high probability of correct acquisition, andto maintain low computational complexity.

2-D angle estimation in beamspace featuring multidimensional multirate eigenvector processing

Zoltowski and Kautz (see IEEE Tran. on Signal Processing, May 1994 and IEEE Signal Processing Letters, Jan. 1994) developed a beamspace domain based 1D angle estimation scheme for uniform linear arrays that allows one to solve for the arrival angles of plane waves via the roots of a small order polynomial and works with any type of front end beamformer. This paper extends their approach to the more general case of 2D angle estimation with a uniform rectangular array (URA) of sensors. The approach is based on the fact that the telescoped beamspace noise eigenvectors exhibit a bandpass characteristic. Therefore, multidimensional multirate processing can be performed to ultimately yield a small dimensional signal subspace. A novel version of ESPRIT can then be applied to effect closed-form 2D angle estimation and automatically couple the two components of the source directions. Simulations demonstrating the efficacy of the approach are presented.<<ETX>>