Torgny Palenius

Reduced Complexity Detectors for Continuous Phase Modulation Based on a Signal Space Approach

Optimum detectors for CPM use in general a large number of filters in order to calculate the optimum metrics. In this paper, we propose correlation detectors that calculate its metrics in a subspace of the signal space. The subspace is selected such that the asymptotic error performance is optimized for the given dimensionality. We focus on noncoherent detectors but show also some results for coherent detectors. The subspace metric calculation is combined with previously published reduced complexity decoding algorithms such as the SAN(B) and RSSD algorithms. Optimum subspace correlation detectors with different number of filters are found for both binary and quaternary CPM schemes. Their error performance on an AWGN channel is derived analytically through the use of a minimum Euclidean distance approach and is also simulated through the symbol error probability. Comparison is done with the optimum detectors. A close agreement between minimum distance and simulated symbol error probability is found for all considered detectors. We find that in most cases only 4 to 6 matched filters are needed in order to obtain a performance that is close to optimum. This corresponds to at least a five-fold reduction in number of filters and with the reduced complexity search algorithms for making symbol decisions this leads to a dramatic reduction in overall complexity.

A noncoherent CPM-detector which uses a reduced set of basis functions

A suboptimum noncoherent detector for partial response CPM (continuous phase modulation) is studied. The number of filters in the filter bank is reduced by using a limited signal space in the CPM detector. It is found that the number of dimensions in the mismatched detector can be considerably reduced. For a quaternary 2RC scheme with h=1/3, the number of filters is reduced from 32 to eight with a loss of about 0.5 dB in error performance. SAN(B), a limited tree search algorithm, is used for the symbol decision.<<ETX>>

Optimized Search Window Alignment for A-GPS

The best performance of assisted-global positioning system (A-GPS) positioning is obtained when fine time assistance is provided to the terminal, i.e., when information on the GPS time of week is provided, and is accurate to within a few microseconds. This paper presents a new method for the minimization of the size of the coarse acquisition (C/A) code search windows, around their so-provided window centers. The method accounts for 1) the geometrical shape of the initial region where the terminal is known to be located; 2) the location of the radio base station; and 3) the azimuth and elevation angles of each space vehicle. Benefits include a reduced computational complexity of the GPS signal acquisition or a corresponding sensitivity enhancement.