Base station receiver equipment

Details Base station receiver equipment Base station receiver equipment

1996-03-22

1997-11-04

Chin, Wellington

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

370342, 370360, 375347, 455135, 455137, 455138, 455273, H04B 7216

Patent

active

056847939

DESCRIPTION:

BRIEF SUMMARY
This application claims benefit of international application PCT/FI94/00239 filed Jun. 6, 1994, published as WO94/30025 Dec. 22, 1994.


BACKGROUND OF THE INVENTION

The invention relates to a rake-type CDMA base station receiver equipment, comprising a number of correlators each having a received signal as its input, a number of diversity combiners, and means for measuring the quality of the received signal.
CDMA is a multiple access method based on the spread spectrum technique, and it has been applied recently in cellular radio systems due to its several advantages, such as spectral efficiency.
In CDMA each signal consists of an individual pseudorandom sequence, which modulates the baseband frequency while spreading the band of the data signal. Data signals of a number of users are transmitted simultaneously on the same frequency band. Users are distinguished from each other by a pseudorandom sequence called a spreading code. Correlators provided in the receivers are synchronized with a desired signal, which they recognize on the basis of the spreading code, and restore the original band of the signal. On arriving at the receiver, signals having another spreading code do not correlate in an ideal case, but retain their wide band and thus appear as noise in the receivers. One aims at selecting the spreading codes used by the system in such a way that they are orthogonal with respect to each other, i.e. do not correlate with each other.
The properties of CDMA differ from those of the traditional TDMA and FDMA multiple access methods in many ways. One major difference lies in the attitude of CDMA towards multipath propagation of a signal over a radio path. In the radio traffic between a mobile station and a base station in a typical cellular network environment, signal components propagate over several paths between a transmitter and a receiver. This multipath propagation is mainly due to reflections of the signal from the surrounding surfaces. In the traditional FDMA and TDMA systems, multipath propagation is a major factor deteriorating the quality of a connection, and therefore methods improving the received signal quality, such as equalizers, have been developed to compensate for it. In CDMA, multipath propagation can be utilized.
A so-called rake receiver is used widely as a receiver solution in CDMA, which receiver comprises one or more rake branches or correlators. Rake branches are independent receiver units, the function of which is to assemble and demodulate one received multipath-propagated signal component. The implementation of a rake branch is described more closely in Modern Communications and Spread Spectrum, Chapter 12, G. Cooper, C. McGillem, McGraw-Hill, New York 1986. In addition to rake branches intended for signal reception, the CDMA receiver typically comprises at least one separate searcher branch, the function of which is to search out different signal components of a signal transmitted by a desired spreading code, and detect the phases of the signal components. Each rake branch can be controlled so as to be correlated with a signal component propagated over a different path, whereby each signal component arrives at the receiver with a slightly different delay. The control of the rake branches takes place by indicating a desired spreading code and its phase to the correlator. As the signal components propagate over different paths, they often also fade independently of each other. In a traditional CDMA receiver, signals from a number of correlators are preferably combined, which results in a high-quality signal irrespective of the multipath propagation over the radio path. Accordingly, multipath propagation can be utilized as diversity gain.
Due to the mobile character of a radio telephone, the propagation environment between the base station and the radio telephone varies continuously. The strength and number of multipath-propagated signals vary with the location of the radio telephone. Changes and movements occurring in the environment also affect the propagation of radio waves.

REFERENCES:
patent: 4530087 (1985-07-01), Yamamoto
patent: 4984247 (1991-01-01), Kaufmann et al.
patent: 5109390 (1992-04-01), Gilhousen et al.
patent: 5166952 (1992-11-01), Omurg et al.
patent: 5237586 (1993-08-01), Bottomley
patent: 5293398 (1994-03-01), Hamao et al.
patent: 5305349 (1994-04-01), Dent
Cooper, G. et al., Modern Communications and Spread Spectrum, Chapter 12: "Detection of Spread-Spectrum Signals", McGraw-Hill, New York, 1986, pp. 345-375.

Affiliated with

Also associated with

Rating

Base station receiver equipment does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Base station receiver equipment, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Base station receiver equipment will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1838980