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Practical space-time radio method for CDMA communication capacity enhancement
| Details |
Inventors: Scherzer, Shimon B.;
Assignee: Adaptive Telecom, Inc. (Campbell, CA); Metawave Communications Corporation (Redmond, WA)
Primary Examiner: Bost; Dwayne
Assistant Examiner: Gelin; Jean A
Attorney, Agent or Firm:
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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DETAILED DESCRIPTION Although the following detailed description contains many specifics for the purposes of illustration, anyone of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention.
Accordingly, the following embodiments of the invention are set forth without any loss of generality to, and without imposing limitations upon, the claimed invention.
FIG.
1 provides a general view of the system architecture of a base station according to the present invention.
The base station comprises a receiving antenna array 10 having N antenna elements.
Preferrably, the number N of antenna elements is approximately 16.
In this embodiment, the system also comprises a separate antenna array 15 for transmission.
Using antenna duplexers, however, the arrays can be combined, as is well known in the art.
The embodiment allows for low cost duplexers and antenna filters since beam forming requires much less power per element to provide the required effective radiated power (ERP).
Each of the N antenna elements is coupled to a corresponding one of a set of N conventional receivers 101.
Each receiver down-converts an incoming signal in frequency and digitizes it to produce a received signal having I & Q (in phase and quadrature) signal components.
In this embodiment, the receivers are coherently tuned by a common local oscillator 104 to allow for both phase and amplitude data measurement, thereby producing, at any given instant, an N-dimensional received signal vector having complex valued components.
Alternatively, a calibration signal of fixed frequency can be injected to all receiver channels simultaneously with the received signal, allowing for continuous estimation of the phase and amplitude difference among the receivers.
The calibration signal can be differentiated from the received signal since it is not spread and can have a very low level since its integration can be very long.
Specific relevant receiver designs are presented in U
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Telecommunications 
