9:30, SPCOM-L10.1
COMPARISON OF DIGITAL MULTI-CARRIER WITH DIRECT SEQUENCE SPREAD SPECTRUM IN THE PRESENCE OF MULTIPATH
S. ZHOU, G. GIANNAKIS, A. SWAMI
We compare single user digital Multi-Carrier Spread Spectrum modulation with Direct Sequence Spread Spectrum in the presence of frequency-selective multipath fading. We derive closed-form expressions for the bit error probability and show that MC-SS is more robust to multipath fading than is DS-SS.

9:50, SPCOM-L10.2
EM-BASED ACQUISITION OF DS-CDMA WAVEFORMS FOR RADIOLOCATION
R. ILTIS, S. KIM, A. THOMAS
A handshaking protocol for radiolocation is considered using DS-CDMA packet transmission. The expectation - maximization (EM) algorithm is employed for code delay acquisition. It is shown that the systematic application of EM on the flat-fading channel yields a parallel interference cancellation (PIC)-based technique for acquisition. On the frequency-selective channel, it is necessary to jointly estimate both the code delays and multipath coefficients. The EM approach in this latter case yields an algorithm that combines PIC with an eigendecomposition/eigenvalue maximization step for channel identification.

10:10, SPCOM-L10.3
LOW COMPLEXITY ANTI-JAM SPACE-TIME PROCESSING FOR GPS
W. MYRICK, J. GOLDSTEIN, M. ZOLTOWSKI
This paper investigates the performance of reduced rank space-time processors in the context of anti-jam mitigation for an M-Code based GPS receiver utilizing a circular array. Several adaptive processing algorithms are discussed utilizing power minimization techniques. It is assumed an INS (Inertial Navigation System) or direction finding algorithm is incorporated into the receiver for satellite look direction based algorithms. Reduced rank space-time processing is accomplished via the innovative Multistage Wiener filter (MSWF). It is demonstrated that the MSWF does not require matrix inversion, thereby reducing computational complexity. The processing algorithms are compared in terms of available degrees of freedom and distortion of the GPS cross correlation function (CCF).

10:30, SPCOM-L10.4
NARROW-BAND INTERFERENCE SUPPRESSION IN DIRECT SEQUENCE SPREAD SPECTRUM SYSTEMS USING A LATTICE IIR NOTCH FILTER
J. CHOI, N. CHO
This paper proposes an algorithm for the suppression of narrow-band interference in direct sequence spread spectrum (DSSS) systems, based on the open loop adaptive IIR notch filtering. The center frequency of the interference is monitored on-line by the adaptive lattice IIR notch filter in [6] or by time-frequency analysis in [3]. The power of the interference signal is also estimated from the adaptive filters. Another lattice IIR notch filter is placed in front of the receiver, the notch of which is controlled by the frequency estimate to remove the interference. However, the IIR notch filter with the zeros on the unit circle also removes the information signal at the notch frequency while removing the interference and causes data distortion. Hence, the depth of the notch should also be adjusted for the trade-off between data distortion and effective interference reduction. The objective function for adjusting the depth of the notch is defined as the overall signal to noise ratio (SNR). The SNR is expressed as a function of filter parameters and the notch depth that maximizes the SNR is found. Simulation results show that the proposed algorithm yields better performance than the existing FIR notch filter [3] and the conventional FIR LMS algorithm with very long taps [1].

10:50, SPCOM-L10.5
SEMIBLIND DECISION-FEEDBACK MULTIUSER INTERFERENCE CANCELLATION BASED ON THE MAXIMUM LIKELIHOOD PRINCIPLE
M. BUGALLO, J. MÍGUEZ, L. CASTEDO
This paper addresses the problem of interference suppression in Direct Sequence Code Division Multiple Access (DS CDMA) systems. We propose a novel semiblind Decision Feedback (DF) receiver based on the Maximum Likelihood (ML) principle that simultaneously exploits the transmission of training sequences and the statistical information concerning the unknown transmitted symbols. The Space Alternating Generalized Expectation Maximization (SAGE) algorithm allows an efficient iterative implementation of the receiver. Computer simulations show that the resulting multiuser detector attains practically the same performance as the theoretical DF Minimum Mean Square Error (MMSE) receiver.

11:10, SPCOM-L10.6
SEMI-BLIND SPACE-TIME CHIP EQUALIZER RECEIVERS FOR W-CDMA FORWARD LINK WITH CODE-MULTIPLEXED PILOT
F. PETRE, G. LEUS, M. ENGELS, M. MOONEN, H. DE MAN
In the forward link of W-CDMA systems, the multipath propagation channel destroys the orthogonality of the spreading codes and therefore causes multi-user interference. In this paper, we propose new training-based and semi-blind space-time chip equalizer receivers for the forward link of W-CDMA systems with a continuous code-multiplexed pilot. Both Least-Squares (LS) algorithms for block processing and Recursive Least-Squares (RLS) algorithms for adaptive processing are derived. The proposed receivers can track fast fading multipath channels and outperform the RAKE receiver with perfect channel knowledge. For full system load, the training-based and semi-blind approach have exactly the same performance. However, for low to medium system load, the semi-blind approach outperforms the training-based approach.