CDMA receiver

Details CDMA receiver CDMA receiver

2000-04-20

2004-10-12

Pham, Chi (Department: 2667)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S342000, C370S320000, C375S150000, C455S063100, C455S501000, C455S517000, C455S067110, C455S067130, C455S570000

Reexamination Certificate

active

06804215

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a receiver of a code-division multiple access system and, in particular, to a receiver of a code-division multiple access system intended to improve a reception quality.
In a conventional mobile communication system such as a mobile telephone, use has been made of a multiplexing system such as a time division multiple access (TDMA) system or a frequency division multiple access (FDMA) system. However, in response to a growing demand for effective use of frequencies following an increase in number of subscribers and for multimedia communications, attention is directed to a code division multiple access (hereinafter abbreviated to CDMA) system as a multiplexing system for a next-generation mobile telephone. The CDMA system is a technique for simultaneously carrying out a plurality of communications by the use of signals in a same frequency band by means of the spread spectrum technique. In a CDMA mobile communication system using the above-mentioned technique, a plurality of users occupy a same frequency and a same time and modulate communication data by the use of spread codes assigned to the users to identify the users. The spread codes of the users are orthogonal to one another. Therefore, at a receiving side a multiplexed signal obtained by multiplexing all user's communication data is multiplied by a spread code used by each user in a same phase so as to extract communication data of a desired user.
In the CDMA mobile communication system, a communication quality is determined by orthogonality of communication data signals of all users multiplexed In the same frequency. Practically, however, due to variation in a propagation condition, the orthogonality can not completely be maintained. Therefore, when the signal of the desired user is demodulated a signal component of another user is undesiredly contained to result in deterioration in signal quality. In order to avoid the deterioration in signal quality, the receiving side measures a ratio between a signal reception level and an interference reception level for the desired user and requests a transmitting side to change transmission power so as to satisfy a predetermined ratio. In this approach, a transmission level is increased at the transmitting side in order to maintain a predetermined signal-to-interference ratio (hereinafter abbreviated to SIR) at a CDMA receiver in the CDMA mobile communication system. However, increase in transmission level prevents the reduction in power consumption at a terminal and the improvement in degree of multiplexing into the same frequency. In order to solve the above-mentioned problem, attention is directed to an interference removing technique. In the interference removing technique, an interference wave, i.e., a signal component other than that of a desired user is removed from a communication data signal received. Thus, it is possible to improve a reception signal quality even in a low SIR condition.
Hereinafter, description will be made of a CDMA receiver using the interference removing technique. Herein, it is assumed that the CDMA receiver performs an interference removing operation of a multistage type in which interference removal is repeatedly carried out in three stages for three users.
FIG. 1
shows the structure of a conventional CDMA receiver for carrying out interference removal in a multistage fashion. The CDMA receiver comprises a reception timing detecting section
10
for detecting reception timings of three users and, in correspondence to the reception timings, interference estimating sections in each stage. The interference estimating sections includes first- through third-stage interference estimating sections
11
11
through
11
13
corresponding to the reception timing of a first user, first through third-stage interference estimating sections
11
21
through
11
23
corresponding to the reception timing of a second user, and first- through third-stage interference estimating sections
11
31
to
11
33
corresponding to the reception timing of a third user. The CDMA receiver further comprises residual signal producing sections
12
1
and
12
2
.
A multiplexed signal
13
received by the CDMA receiver is supplied to the reception timing detecting section
10
, the first-stage interference estimating sections
11
11
through
11
31
, and the residual signal producing section
12
1
. The multiplexed signal
13
is a frame signal composed of a plurality of slots. At a predetermined position in the frame, a pilot symbol as predetermined pattern data is added before or after an information symbol of a predetermined length. The reception timing detecting section
10
detects the pilot symbol added to the multiplexed signal
13
to detect data reception timings of desired users. The reception timings thus detected are supplied as reception timings
14
1
through
14
3
to the first-stage interference estimating sections
11
11
through
11
31
, the second-stage interference estimating sections
11
12
through
11
32
, and the third-stage interference estimating sections
11
13
through
11
33
individually for the users, i.e., individually for the reception timings. In synchronism with the reception timings
14
1
through
14
3
detected by the reception timing detecting section
10
for the individual users, the first-stage interference estimating sections
11
11
through
11
31
multiply the multiplexed signal
13
by spread codes assigned to the individual users to extract data signals of the desired users, respectively. The data signals thus extracted are supplied as user signals
15
1
through
15
3
to the second-stage interference estimating sections
11
12
through
11
32
in a subsequent stage, respectively. In addition, the first-stage interference estimating sections
11
11
through
11
31
multiply the extracted user data signals again by the spread codes assigned to the users. Thus, signal components of the users contained in the multiplexed signal
13
are reproduced to obtain reproduction signals
16
1
through
16
3
which are supplied to the residual signal producing section
12
1
. The residual signal producing section
12
1
is supplied with the multiplexed signal
13
in addition to the reproduction signals
16
1
through
16
3
and produces a residual signal
17
obtained by subtracting the reproduction signals
16
1
through
16
3
from the multiplexed signal
13
. The residual signal
17
is used as an input signal to be subjected to interference removal in the second stage.
The residual signal
17
is supplied to the second-stage interference estimating sections
11
12
through
11
32
and the residual signal producing section
12
2
.In synchronism with the reception timings
14
1
through
14
3
detected by the reception timing detecting section
10
for the individual users, the second-stage interference estimating sections
11
12
through
11
32
multiply the residual signal
17
supplied thereto by the spread codes individually assigned to the users to despread the residual signal. Resultant signals (or despread signals) are weak in signal level. Therefore, in order to minimize errors produced in transmission-path estimation required upon demodulation, the user signals
15
1
through
15
3
supplied from the first-stage interference estimating sections
11
11
through
11
31
are added to the resultant signals to produce added user signals increased in ratio of the signal components of the desired users. Thus, data signals of the desired users are extracted. The data signals thus extracted are supplied as user signals
18
1
through
18
3
to the third-stage interference estimating sections
11
13
through
11
33
in a subsequent stage, respectively. In addition, the second-stage interference estimating sections
11
12
through
11
32
subtract, from the user data signals extracted thereat as demodulation signals, signal components corresponding to the user signals
15
1
through
15
3
previously added and multiply results of extraction again by the spread codes assigned to the users, r

Affiliated with

Also associated with

Rating

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

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

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3259249