A receiver of the present invention addresses the need for improved interference suppression without the number of transmissions by the power control system being increased, and, to this end, provides a receiver for a CDMA communications system which employs interference subspace rejection to tune a substantially null response to interference components from selected signals of other user stations. Preferably, the receiver also tunes a substantially unity response for a propagation channel via which a corresponding user's signal was received. The receiver may be used in a base station or in a user/mobile station.

Interference suppression in cdma systems

Ground-based pseudolites support accurate determination of mobile receiver (401) locations by broadcasting CDMA signals (202) interleaved by a TDMA system. Pseudolites synchronize signal transmissions with an accurate timing reference, such as can be derived from GPS satellites (201). Adjacent pseudolites broadcast CDMA signals at different times, eliminating near-far signal interference between pseudolites. A mobile receiver, typically a cellular telephone, receives and enables determination of times of arrival (TOA) of the pseudolite signals. A location processor associated with the mobile receiver may access an internal database of pseudolite locations, or pseudolite location information may be encoded in pseudolite transmissions. The location processor uses pseudolite location information and TOA to determine mobile receiver location. The TDMA pseudolite-based system may augment the GPS to provide more accurate location information than is available from the GPS alone.

Pseudolite-augmented gps for locating wireless telephones

This paper presents a new approach to GPS-based navigation which offers significant improvement in antijam capability over traditional designs. The algorithms may be implemented at low cost in software in existing and future GPS receivers using, as inputs, postcorrelation I and Q data and, optionally, raw data from other sensors. Traditional systems are not optimal at high jammer-to-signal (J/S) ratios as a consequence of modular design, use of traditional fixed-gain or gain-scheduled tracking loops, and use of artificial moding logic. The approach described here employs a nonlinear filter that operates efficiently at all J/S levels. Filter gains continuously adapt to changes in the J/S environment, and the error covariance propagation is driven directly by measurements to enhance robustness under high jamming and dynamics conditions. Extended-range correlation may be optionally included to increase the code tracking loss-of-lock threshold under high jamming scenarios. Computational complexity is comparable to an extended Kalman filter. Results of hardware-in-the-loop simulations are presented which demonstrate improvements of 15 dB or more in antijam capability relative to traditional designs.

A deeply integrated adaptive GPS-based navigator with extended range code tracking

Spread spectrum receiver architectures and methods are described for reducing interference, particularly the interference observed at a user-end terminal in a W-CDMA 3G mobile communications system. Interpath interference which arises due to non-zero cross and auto correlation of more than one spreading code is suppressed by estimating a transmitted signal stream, or a plurality of such signal streams in the case of a plurality of multipath components, respreading this estimated signal and subtracting non-orthogonal interference contributions from a received signal. The techniques provide an improved bit error rate or equivalently, enhanced capacity for a digital mobile communications network.

Receiver processing systems

According to a first broad aspect of the present invention, there is provided a novel communication system having a forward link comprising: at least one base station which transmits multiple radio frequency (RF) signals; and a mobile station, the mobile station including: a receiver for receiving the RF signals; means for converting the RF signal to an intermediate frequency (IF) signal; means (704) for sampling the IF signal to generate a digital signal, the digital signal having a data component; means (712) for canceling co-channel and or cross-channel interference in the digital signal by projecting the IF signal into a subspace orthogonal to a subspace of the interference component and multiplying this projection with the digital signal; and means (710) for acquisition and tracking of the digital signal.

Interference cancellation in a signal

A spread spectrum signal demodulator receives a received signal including a plurality of spread spectrum signals, and comprises at least one signal strength suppressing means, which reduces a correlation signal outputted from a first correlation detecting means or replica signals until the correlation signal has been traveled through a replica signal generating means, a replica signal subtracting means and a second correlation detecting means. According to the invention, it is possible to improve interference cancellation capacity with a computational effort substantially comparable to that in a prior art replica signal cancellation system and improve interference cancellation performance with increasing number of interference cancellers irrespective of the magnitude of the correlation. With a sufficient number of interference cancellers provided, it is possible to obtain the same effect as obtainable with prior art decorrelation in a real time processing irrespective of the correlation magnitude.

Yoshio Takeuchi

Papers

Spread spectrum signal demodulator