Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1999-07-23
2003-05-20
Ghebretinsae, Temesghen (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S150000, C375S347000
Reexamination Certificate
active
06567462
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to radio communications apparatus and methods of communicating data using radio signals. More specifically, the present invention relates to receivers that recover data for at least one of a plurality of users from spread spectrum radio signals. Furthermore, the present invention relates to a method of recovering data for at least one of a plurality of users from spread spectrum radio signals.
Data is communicated using code division multiple access systems (CDMA) by combining the data with a user specific spreading code and transmitting the combination to a receiver using radio signals. At the receiver, the data is recovered from the radio signals by comparing the received sampled radio signals with a user specific spreading code that is known to the receiver. Similarly, a plurality of transmitters operatively coupled to a corresponding plurality of user data sources can be configured to contemporaneously communicate data from the transmitters to the receivers which detect the data by comparing the radio signals with the user specific spreading code uniquely associated with each of the users.
A result of combining the data with a user specific spreading code is that the bandwidth obtained from the resulting radio signals is greater than that obtained by radio signals carrying data alone. Accordingly, the frequency bandwidth occupied by code division multiple access signals is often greater than a coherence bandwidth of the radio communications channel through which the signals are transmitted. Code division multiple access communicated radio signals provide an advantage because the signals themselves exhibit frequency diversity, and different parts of the bandwidth of the radio signals suffer from fading independently.
Code division multiple access is used in second generation mobile radio telephone systems, and is now being proposed for third generation mobile radio telephone systems. A characteristic of a frequency bandwidth in which radio signals are transmitted in second and third generation mobile radio telephone systems is that the radio signals travel between the transmitters and the receivers of the system through a plurality of paths. As a result, data symbols regenerated from the received signals exhibit inter symbol interference that must be cancelled in order for the data to be recovered.
A further advantage of code division multiple access is that radio signals traveling through each of the paths that reach the receiver may be individually resolved and the radio signal energy for each of these signals can be recovered and combined to facilitate detection of the communicated data. A receiver that operates in this way to detect radio signals traveling through individual paths is known as a rake receiver. A rake receiver is provided with a plurality of rake fingers. Each rake finger is configured to correlate the received signals with the user specific spreading code. Each one of the fingers of the rake receiver is assigned to one of a plurality of temporal displacements corresponding to one of a plurality of paths through which the radio signals reach the receiver.
A further known receiver for CDMA spread spectrum radio signals is described in a published article entitled “Blind Adaptive 2D Rake Receiver for DS-CDMA Based on Space-Frequency MVDR Processing,” by Zoltowski et al., which is known to have been submitted for publication to the IEEE Journal on Transactions on Signal Processing, June 1996, and is currently available on the Internet. This article discloses a rake receiver operatively associated with an array of antennas that are configured to provide spatial diversity and antenna gain with respect to the detected radio signals. Furthermore, each of the rake fingers operates to correlate the received signals and to form a frequency domain representation of the correlated signals to detect and recover data from the detected radio signals. This rake receiver is referred to in the following description as a two dimensional space-frequency rake receiver.
Mobile radio telecommunications systems are configured to use an allocated portion of the radiofrequency spectrum as efficiently as possible. The ability of a receiver of CDMA radio signals to recover data in the presence of contemporaneously detected radio signals substantially contributes to the efficiency of CDMA communication systems.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an improved receiver for detecting and recovering data communicated using code division multiple access, and an improved method of detecting and recovering data communicated using code division multiple access, which overcome the above-mentioned disadvantageous of the heretofore known receivers and methods of this type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a receiver for recovering data, for at least one of a plurality of users, from spread spectrum radio signals that include radio signals representative of a combination of data and a data spreading code associated with the at least one of the plurality of users and a combination of a predetermined sequence of pilot data and a pilot spreading code. The improvement includes a plurality of antennas, with each one of the antennas configured to detect a different version of the radio signals. A base band conversion device is electrically coupled to the antennas and configured to generate, for each version of the radio signals, a version of baseband signal samples representative of the respective version of the radio signals. A data recovery device is configured to: correlate each version of the baseband signal samples with respect to the pilot spreading code to obtain respective versions of correlated pilot spreading code signal samples; form at least one covariance matrix from a frequency domain representation of a predetermined temporal window of the respective versions of the correlated pilot spreading code signal samples; correlate each version of the baseband signal samples with respect to the data spreading code to obtain respective versions of correlated data spreading code signal samples; form a frequency domain representation of each version of the correlated data spreading code signal samples; and detect the data from the frequency domain representation of each version of the correlated data spreading code signal samples in combination with the at least one covariance matrix.
With the foregoing and other objects in view there is also provided, in accordance with the invention, a receiver for recovering data, for at least one of a plurality of users, from spread spectrum radio signals that include radio signals representative of a combination of data and a data spreading code associated with the at least one of the plurality of users and a combination of a predetermined sequence of pilot data and a pilot spreading code. The improvement includes a plurality of antennas. Each one of the antennas is configured to detect a different version of the radio signals. A base band conversion device is electrically coupled to the antennas and configured to generate, for each version of the radio signals, a version of baseband signal samples representative of the respective version of the radio signals. A data recovery device includes a plurality of rake detectors. Each one of the rake detectors is electrically coupled to the base band conversion device to obtain a respective version of the base band signal samples. Each one of the rake detectors has: a correlation device to correlate the respective version of the base band signal samples with the data spreading code to obtain correlated data spreading code signal samples and to correlate the respective version of the base band signal samples with the pilot spreading code to obtain correlated pilot spreading code signal samples, and a frequency conversion device electrically coupled to the correlation device to generate a frequency domain representation of the corr
Brunner Christopher
Haardt Martin
LandOfFree
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