Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
2002-10-30
2004-07-27
Maung, Nay (Department: 2684)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S147000, C375S349000
Reexamination Certificate
active
06768769
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mobile communication system based on the principles of CDMA (Code Division Multiplex Access), and more particularly to a receiving circuit in a mobile terminal in a mobile communication system based on the principles of CDMA.
2. Description of the Related Art
In recent years, mobile communication systems are finding a growing number of subscribers and are required to increase their capacity to accommodate subscribers. One approach to an increased capacity to accommodate subscribers is a technique known as CDMA in which one frequency band is shared by signals spread by a plurality of mathematically orthogonal codes.
In a CDMA mobile communication system, the receiving circuit of each mobile terminal has a plurality of finger receivers for inversely diffusing transmitted data in association with respective multiple paths. The transmitted data are inversely diffused by the finger receivers and then synthesized with each other.
FIG. 1
of the accompanying drawings shows in block form a finger receiver which is being experimentally studied by the inventors of the present application.
As shown in
FIG. 1
, the finger receiver comprises an inverse diffuser
1
for complex-inverse diffusing transmitted data at each chip rate for five points of −1/2&pgr;, −1/4&pgr;, 0&pgr;, +1/4&pgr;, +1/2&pgr; at 16.384 MHz with respect to a reference point, a symbol accumulative adder
2
for accumulating and adding the data complex-inverse diffused by the inverse diffuser
1
in each symbol rate interval with respect to the above five points, a symbol power calculator
3
for converting the symbol data accumulated and added by the symbol accumulative adder
2
into power values and outputting the power values, a slot power accumulative adder
4
for accumulating and adding the power values for the five points outputted from the symbol power calculator
3
in a slot rate interval, a maximum value detector
5
for detecting one of the five complex-inverse diffusing points where the accumulated slot power value is maximum, based on the result produced by the slot power accumulative adder
4
, and a symbol data selector
6
for outputting, to a circuit at a later stage (not shown), the accumulated and added data at the point where the power value is maximum, which has been detected by the maximum value detector
5
, of those the symbol data accumulated and added by the symbol accumulative adder
2
.
Operation of the finger receiver shown in
FIG. 1
will be described below.
FIG. 2
of the accompanying drawings is a flowchart of the operation of the finger receiver shown in
FIG. 1
, and
FIG. 3
of the accompanying drawings shows received data, illustrating how the finger receiver shown in
FIG. 1
operates.
When data transmitted from a base station facility (not shown) is received in step S
101
, the inverse diffuser
1
inversely diffuses the transmitted data at a chip rate of 4.096 MHz using an inversely diffusing code in step S
102
. In step S
102
, the chip rate is divided into four timings, and the transmitted data is inversely diffused for five points of −1/2&pgr;, −1/4&pgr;, 0&pgr;, +1/4&pgr;, +1/2&pgr; at 16.384 MHz.
Then, the symbol accumulative adder
2
accumulates and adds the data complex-inverse diffused by the inverse diffuser
1
in each symbol rate interval with respect to the above five points in step S
103
.
The symbol power calculator
3
converts the symbol data accumulated and added by the symbol accumulative adder
2
into power values and outputs the power values in step S
104
.
The slot power accumulative adder
4
accumulates and adds the power values at the five points outputted from the symbol power calculator
3
in one time slot rate interval in step S
105
.
Then, the maximum value detector
5
detects one of the five complex-inverse diffusing points where the accumulated slot power value is maximum, based on the result produced by the slot power accumulative adder
4
in step S
106
.
Thereafter, the point detected by the maximum value detector
5
is supplied to the symbol data selector
6
. The symbol data selector
6
has been supplied with symbol data in a slot next to the slot where the accumulated slot power value is maximum as detected by the maximum value detector
5
.
The symbol data selector
6
outputs, to a circuit at a later stage, the accumulated and added data at the point where the power value is maximum, which has been detected by the maximum value detector
5
, i.e., the accumulated and added data at the point where the accumulated power is maximum as detected in the preceding slot, of those symbol data accumulated and added by the symbol accumulative adder
2
in step S
107
.
As described above, the chip rate is divided into a plurality of timings, and a received power is calculated at each of the timings. Data in a next slot at the timing where the received power is maximum is extracted and outputted to the circuit at the later stage for thereby increasing the quality of received data.
In a receiving circuit having finger receivers of the type described above, one of the five complex-inverse diffusing points where the accumulated slot power value is maximum is detected on the basis of the result produced by the slot power accumulative adder. If the transmitted data is burst data as in a paging channel (PCH), then the point where the accumulated slot power value is maximum is detected at a noise level for a slot free of received data, and data at the point detected as having the maximum value is extracted from the accumulated and added symbol data in a next slot and outputted to the circuit at the later stage. Therefore, an optimum complex-inverse diffusing point is not selected in the next slot, resulting in a degraded received-data quality.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a receiving circuit which is capable of increasing the quality of received data even if transmitted data is burst data as in a paging channel.
To achieve the above object, there is provided in accordance with the present invention a receiving circuit comprising an antenna and a radio unit for receiving data, a plurality of finger receivers for inversely diffusing the data received by antenna and the radio unit in association with respective multiple paths, and a synthesizer for synthesizing datan inversely diffused by the finger receivers, each of the finger receivers comprising means for dividing a reception timing in each predetermined interval into a plurality of timings, inversely diffusing the received data at each of the timings, detecting one of the timings where a reception level is highest based on the inversely diffused data, and outputting data in a next interval at the detected timing.
Each of the finger receivers may comprise means for deciding whether there is received data or not based on the reception level at the timing where the reception level is highest, outputting the data in the next interval at the timing where the reception level is highest if it is determined that there is received data, and outputting the data in the next interval at the timing of presently outputting the data if it is determined that there is no received data.
Each of the finger receivers may comprise an inverse diffuser for dividing a chip rate into a plurality of reception timings and complex-inverse diffusing data received via the antenna and the radio unit at each of the reception timings, a symbol accumulative adder for accumulating and adding the data complex-inverse diffused by the inverse diffuser in each symbol rate interval at each of the reception timings, a symbol power calculator for converting symbol data accumulated and added by the symbol accumulative adder into power values and outputting the power values, a slot power accumulative adder for accumulating and adding the power values at the reception timings outputted from the symbol power calculator in a slot rate interval, a maximum value
Lele Tanmay
Maung Nay
NEC Corporation
Scully Scott Murphy & Presser
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