Practical space-time radio method for CDMA communication capacity enhancement

In a wireless communication system comprising a mobile unit and a base station having an N-element antenna array, a system for efficiently determining at the base station a spatial channel of the mobile unit, the system comprising:

• a) means for calculating a transform of a symbol as received from a first antenna of the antenna array, wherein the calculation produces a first M-dimensional vector having complex valued components, where M is a number of predetermined symbols in a symbol alphabet;
• b) means for performing said calculating simultaneously and in parallel for the symbol as received from N−1 additional antennas in the array, thereby producing a matrix B containing N row vectors of dimension M;
• c) means for calculating the matrix product C=AHB, where each of L columns of the matrix A is an N-dimensional vector containing a response of the N antenna array in one of L predetermined directions relative to the array;
• and
• d) means for determining from the matrix C a spatial direction of a signal part originating from the mobile.

A method for wireless communication comprising:

• transmitting an information signal from a mobile unit;
• receiving the transmitted signal with an array of N antenna elements to yield a set of N received signals;
• spatially correlating the N received signals with the contents of an antenna array calibration table to obtain directional information about the mobile unit, wherein the stored calibration table comprises complex valued elements having 1-bit-plus-sign real part and 1-bit-plus-sign imaginary part, whereby spatial correlation is facilitated;
• and spatially filtering subsequent received signals from the mobile unit in accordance with the directional information to obtain corresponding transmitted information signals, wherein spatially filtering comprises filtering through multiple narrow beams, whereby fading is mitigated.

A method for wireless communication comprising:

• transmitting uplink information signals from a set of mobiles;
• receiving the uplink signals with an array of N antenna elements to yield a set of N received signals;
• processing the N received signals to obtain spatial information about the mobiles, wherein the processing comprises identifying a known-structure sequence in the received signals;
• calculating downlink beamforming information based upon the spatial information, wherein the beamforming information comprises assigning each of the mobiles to one of a set of downlink beams, wherein the set of downlink beams comprises wide beams for nearby mobiles and narrow beams for distant mobiles, and wherein the wide beams overlap the narrow beams;
• and
• transmitting downlink information signals to the mobiles in accordance with the calculated downlink beamforming information.

A CDMA base station comprising:

• an antenna array comprising N antenna elements;
• a set of N receivers coupled to the N antenna elements to produce N incoming signals;
• a set of N despreaders coupled to the N receivers, wherein the despreaders produce from the N incoming signals N despread signals corresponding to a single mobile unit;
• a set of N symbol transformers coupled to the N despreaders, wherein the transformers produce complex-valued outputs from the despread signals;
• a spatial correlator coupled to the N symbol transformers, wherein the correlator correlates the complex-valued outputs with stored array calibration data to produce beamforming information for multiple signal parts associated with the mobile unit;
• a receiving beamformer coupled to the spatial correlator and to the N receivers, wherein the receiving beamformer spatially filters the N incoming signals in accordance with the beamforming information;
• a RAKE receiver coupled to the receiving beamformer, wherein the RAKE receiver produces from the spatially filtered signals an information signal;
• compensation circuits for correcting phase and amplitude imbalances of transmit and receive channels.

A method for wireless communication comprising:

• a) transmitting from a mobile unit a code modulated signal obtained by modulating original symbols by a predetermined pseudo-noise sequence, wherein the original symbols represent an original information signal;
• b) receiving at a base station antenna array N complex valued signal sequences received in parallel from N corresponding antenna elements;
• c) correlating in parallel each of the N signal sequences with the pseudo-noise sequence to select N received signals comprising N received symbols corresponding to a common one of the original symbols;
• d) transforming in parallel the N received symbols to obtain N complex-valued transformer outputs;
• e) correlating collectively the N transformer outputs with a set of complex array calibration vectors to obtain spatial information, wherein each array calibration vector represents a response of the antenna array to a calibration signal originating in a predetermined direction relative to the base station;
• f) repeating steps (b),(c),(d),(e) to obtain spatial information about multiple signal components;
• g) spatially filtering a subsequent set of N complex valued signal sequences in accordance with the spatial information about multiple signal components;
• h) demodulating the spatially filtered subsequent set to obtain a symbol from the original information signal;
• and
• i) determining a main angle-of-arrival of the transmitted signal by calculating a center of gravity of a histogram of angle-of-arrival signal samples.

A method for wireless communication comprising:

• a) transmitting from a mobile unit a code modulated signal obtained by modulating original symbols by a predetermined pseudo-noise sequence, wherein the original symbols represent an original information signal;
• b) receiving at a base station antenna array N complex valued signal sequences received in parallel from N corresponding antenna elements;
• c) correlating in parallel each of the N signal sequences with the pseudo-noise sequence to select N received signals comprising N received symbols corresponding to a common one of the original symbols;
• d) transforming in parallel the N received symbols to obtain N complex-valued transformer outputs;
• e) correlating collectively the N transformer outputs with a set of complex array calibration vectors to obtain spatial information, wherein each array calibration vector represents a response of the antenna array to a calibration signal originating in a predetermined direction relative to the base station;
• f) repeating steps (b),(c),(d),(e) to obtain spatial information about multiple signal components;
• g) spatially filtering a subsequent set of N complex valued signal sequences in accordance with the spatial information about multiple signal components;
• h) demodulating the spatially filtered subsequent set to obtain a symbol from the original information signal;
• and
• i) identifying from a histogram of angle-of-arrival signal samples multiple scattering zones and an angle spread for each of the scattering zones.

A method for wireless communication comprising:

• a) transmitting from a mobile unit a code modulated signal obtained by modulating original symbols by a predetermined pseudo-noise sequence, wherein the original symbols represent an original information signal;
• b) receiving at a base station antenna array N complex valued signal sequences received in parallel from N corresponding antenna elements;
• c) correlating in parallel each of the N signal sequences with the pseudo-noise sequence to select N received signals comprising N received symbols corresponding to a common one of the original symbols;
• d) transforming in parallel the N received symbols to obtain N complex-valued transformer outputs;
• e) correlating collectively the N transformer outputs with a set of complex array calibration vectors to obtain spatial information, wherein each array calibration vector represents a response of the antenna array to a calibration signal originating in a predetermined direction relative to the base station;
• f) repeating steps (b),(c),(d),(e) to obtain spatial information about multiple signal components;
• g) spatially filtering a subsequent set of N complex valued signal sequences in accordance with the spatial information about multiple signal components;
• h) demodulating the spatially filtered subsequent set to obtain a symbol from the original information signal;
• and
• i) measuring CIR and using the measured CIR to identify time-of-arrival information.

A method for wireless communication comprising:

• a) transmitting from a mobile unit a code modulated signal obtained by modulating original symbols by a predetermined pseudo-noise sequence, wherein the original symbols represent an original information signal;
• b) receiving at a base station antenna array N complex valued signal sequences received in parallel from N corresponding antenna elements;
• c) correlating in parallel each of the N signal sequences with the pseudo-noise sequence to select N received signals comprising N received symbols corresponding to a common one of the original symbols;
• d) transforming in parallel the N received symbols to obtain N complex-valued transformer outputs;
• e) correlating collectively the N transformer outputs with a set of complex array calibration vectors to obtain spatial information, wherein each array calibration vector represents a response of the antenna array to a calibration signal originating in a predetermined direction relative to the base station;
• f) repeating steps (b),(c),(d),(e) to obtain spatial information about multiple signal components;
• g) spatially filtering a subsequent set of N complex valued signal sequences in accordance with the spatial information about multiple signal components, wherein spatially filtering comprises filtering through multiple narrow beams, whereby fading is mitigated;
• and
• h) demodulating the spatially filtered subsequent set to obtain a symbol from the original information signal.

A method for wireless communication comprising:

• a) transmitting from a mobile unit a code modulated signal obtained by modulating original symbols by a predetermined pseudo-noise sequence, wherein the original symbols represent an original information signal;
• b) receiving at a base station antenna array N complex valued signal sequences received in parallel from N corresponding antenna elements;
• c) correlating in parallel each of the N signal sequences with the pseudo-noise sequence to select N received signals comprising N received symbols corresponding to a common one of the original symbols;
• d) transforming in parallel the N received symbols to obtain N complex-valued transformer outputs;
• e) correlating collectively the N transformer outputs with a set of complex array calibration vectors to obtain spatial information, wherein each array calibration vector represents a response of the antenna array to a calibration signal originating in a predetermined direction relative to the base station;
• f) repeating steps (b),(c),(d),(e) to obtain spatial information about multiple signal components;
• g) spatially filtering a subsequent set of N complex valued signal sequences in accordance with the spatial information about multiple signal components, wherein spatially filtering comprises filtering through beams with different polarization;
• and
• h) demodulating the spatially filtered subsequent set to obtain a symbol from the original information signal.

A method for wireless communication comprising:

• transmitting uplink information signals from a set of mobiles;
• receiving the uplink signals with an array of N antenna elements to yield a set of N received signals;
• processing the N received signals to obtain spatial information about the mobiles, wherein processing the N received signals to obtain spatial information comprises calculating a center of gravity of a histogram of angle-of-arrival signal samples;
• calculating downlink beamforming information based upon the spatial information, wherein the beamforming information comprises assigning each of the mobiles to one of a set of downlink beams, wherein the set of downlink beams comprises wide beams for nearby mobiles and narrow beams for distant mobiles, and wherein the wide beams overlap the narrow beams;
• and
• transmitting downlink information signals to the mobiles in accordance with the calculated downlink beamforming information.