Practical space-time radio method for CDMA communication capacity enhancement
First Claim
1. 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; and
h) demodulating the spatially filtered subsequent set to obtain a symbol from the original information signal.
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Accused Products
Abstract
A practical way to enhance signal quality (carrier to interference. C/I) in both up and downlink of wireless point to multi-point CDMA service implements basic radio direction finding techniques to allow for optimal diversity combining in an antenna array employing large number of elements. This approach is facilitated through the use of very small bit counts arithmetic and capitalizing on finite alphabet signal structure (Walsh symbols, for example in IS-95 CDMA) or a known training sequence. Alternate implementations can use floating point data representations. The method facilitates ASIC implementation, thereby enabling distributed processing to achieve the required computation practicality. The method utilizes the uplink channel data to determine the downlink spatial structure (array beams) to enhance downlink C/I and hence, increase downlink capacity. The preferred embodiment is optimized to IS-95 , however, any signal that has either a finite alphabet or a training sequence built in can utilize the same idea. The use of the known signal structure facilitates simple array response vector determination and eliminates the necessity for covariance matrix calculation and analysis. Hence, this approach can be utilized for GSM and TDMA wireless air-interfaces as well.
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Citations
32 Claims
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1. A method for wireless communication comprising:
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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; and h) demodulating the spatially filtered subsequent set to obtain a symbol from the original information signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. In a wireless communication system comprising a mobile unit and a base station having an N-element antenna array, a method for efficiently determining at the base station a spatial channel of the mobile unit, the method comprising:
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a) 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) performing step (a) 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) calulating the matrix product C=AH B, 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) determining from the matrix C a spatial direction of a signal part originating from the mobile. - View Dependent Claims (10, 11, 12)
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13. 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. - View Dependent Claims (14, 15, 16, 17, 18)
- transmitting an information signal from a mobile unit;
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19. A method for wireless communication comprising:
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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; 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. - View Dependent Claims (20, 21, 22, 23, 24, 25)
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26. A CDMA base station comprising:
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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; and a RAKE receiver coupled to the receiving beamformer, wherein the RAKE receiver produces from the spatially filtered signals an information signal. - View Dependent Claims (27, 28, 29, 30)
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31. A base station in a wireless CDMA communication system, the base station comprising:
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a) an antenna array comprising N antenna elements; b) a set of N radio frequency transceivers coupled to the N antenna elements; and c) an adaptive beamformer coupled to the N radio frequency transceivers, wherein the adaptive beamformer generates spatial beams selected from a set of calculated beams comprising narrow beams and broad beams, wherein the narrow beams overlap with, and are phase matched to the broad beams, and wherein the spatial beams control relative phases of signals transmitted by the transceivers from the antenna elements. - View Dependent Claims (32)
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Specification