Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2000-05-30
2004-01-27
Yao, Kwang Bin (Department: 2667)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S342000
Reexamination Certificate
active
06683861
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a CDMA mobile communication system, a searcher circuit and a communication method. More particularly, the invention relates to a CDMA mobile communication system, a searcher circuit and a communication method realizing a Code Division Multiple Access (CDMA) communication by combining outputs of a finger circuit performing dispreading for a reception signal.
2. Description of the Related Art
In CDMA mobile communication which has been expected as a mobile communication in the next generation, a radio wave reaching to a mobile station from a base station is distributed into several fractions due to influence of buildings and the like. Therefore, there are a plurality of radio waves reaching to the mobile station. Respective radio waves causes delay.
In order to realize the CDMA communication, a path search function for recognizing a plurality of radio waves distributed by correlators of respective base stations and a Rake function for combining data of a plurality of finger circuits, each of which performs dispreading for a plurality of distributed radio waves are necessary.
When the mobile station moves, a hand over may be performed. The hand over includes a diversity hand over, in which cells are switched, and a soft hand over, in which sectors are switched.
As shown in
FIG. 8
, the diversity hand over, in which the cells are switched, is a switching operation to be caused when a device
100
as the mobile station is positioned at a position where a cell
61
and a cell
62
overlap, for switching from a condition receiving a transmission signal of the base station of lower reception power to a condition receiving a transmission signal of the base station of higher reception power. For example, an operation, in which the device
100
as the mobile station switches receiving condition from a condition receiving a transmission signal from a base station
61
a
corresponding to the cell
61
, to a condition receiving a transmission signal from a base station
62
a
corresponding to the cell
62
, is the diversity hand over.
In this case, since a plurality of antennas receive signals simultaneously, reception state of the device
100
is switched from a receiving condition of the transmission signal of the base station
61
a
to a receiving condition of the transmission signal of the base station
62
a
without momentaneous interruption of communication. Here, “cell” is a area where the transmission signal from the base station reaches. By presence of a plurality of cells, mobile communication in wide range can be realized.
In contrast to this, the soft hand over, in which the sectors are switched, is operation for switching receiving condition when the device
100
as the mobile station is located at a position where a sector
601
and a sector
602
overlap, from a condition receiving a transmission signal of an antenna of lower reception power to a condition receiving a transmission signal of an antenna of higher reception power, as shown in FIG.
9
. For example, the operation for switching from the condition receiving the transmission signal from an antenna ANT
1
corresponding to the sector
601
to the condition receiving the transmission signal from an antenna ANT
2
corresponding to the sector
602
.
In this case, since the signals are received from a plurality of antennas simultaneously, communication can be switched from the receiving condition of the transmission signal of the antenna ANT
1
to the receiving condition of the transmission signal of the antenna ANT
2
without momentaneous interruption. Here, “sector” is a range of reaching the transmission signal from one antenna of the base station
60
a
. Assuming that three antennas ANT
1
to ANT
3
are provided for one base station
60
a
, three sectors
601
to
603
are present within the cell of the base station. In this case, by differentiating directionalities of the three antennas, three sectors are provided within the same cell.
Operation of the mobile station upon performing the foregoing diversity hand over and soft hand over (which may be referred to as “hand over” as generally referred to), will be discusses with reference to the drawings.
FIG. 1
is a block diagram showing an internal construction of the mobile station. In
FIG. 1
, there is shown a construction of the major part of the mobile station upon diversity hand over.
The device
100
as the mobile station receives transmission signals
3
and
4
of radio wave from the base stations
61
a
and
62
a
by means of an antenna
5
. The received signals
3
and
4
are converted into a chip rate by a radio portion
6
. The transmission signal of the base station
61
a
converted into the chip rate is despread by a correlator
7
for the base station
61
a
and the radio wave of the base station
62
a
is despread by a correlator
8
for the base station
62
a
. These correlators
7
and
8
have function for shifting a phase for a signal which is received and demodulated, per a given interval, and establish correlation between the phase shifted signal and a known data (spread code). Then, the correlators
7
and
8
output delay profile data.
For the signals of respective base stations
61
a
and
62
a
despread in the correlators
7
and
8
, peak detection of a signal level (power) is performed by a searcher circuit
9
for recognizing a plurality of distributed signals.
A plurality of recognized signals are assigned to a finger circuit
10
for the base station
61
a
and a finger circuit
11
for the base station
62
a
. Then data after dispreading by respective finger circuits
10
and
11
are combined by a Rake circuit
12
for outputting a decoded data
13
.
Here, an internal construction of the typical searcher circuit
9
is shown in FIG.
10
. Referring to
FIG. 10
, the searcher circuit
9
is constructed with a peak detection circuit
91
a
for detecting a peak value with respect to the delay profile data provided corresponding to the correlator
7
, a peak detection circuit
91
b
for detecting a peak value with respect to the delay profile data provided corresponding to the correlator
8
, and assigning portion
92
for assigning the peak values detected by the peak detections circuits
91
a
and
91
b
to the finger circuits
10
and
11
. With such construction, the peak values of the delay profile data for the reception signal is assigned to the finger circuit.
Here, if a plurality of radio waves separately arriving should have the same interference if transmitted from the same radio wave transmission source. However, when radio waves transmitted from different radio wave transmission sources are to be combined as in the hand over, magnitudes of interference should be different at different radio wave transmission source. For example, magnitudes of interference are differentiated in such a manner that the radio wave transmitted from one transmission source is as illustrated in FIG.
11
A and the radio wave transmitted from the other transmission source is as illustrated in FIG.
11
B.
Consideration is given for the case where the reception signals shown in
FIGS. 11A and 11B
are combined in the Rake circuit
12
. In this case, if the reception signals are combined by simple addition and if the arriving signal levels are different, the signal of lower reception power may be extinguished by the signal of higher reception power. Namely, since the peak value
15
of the base station
61
a
is lower than or equal to a noise level of the base station
62
a
, the signal from the base station
61
a
is extinguished as shown in FIG.
12
. Then, the finger circuit, output of which is not used, can be present to waste the power consumed by such finger circuit.
On the other hand, since the base station spreads the transmission signal with a unique spread code, if the output data of the correlators of the base stations
61
a
and
62
a
are combined, it becomes impossible to identify the base station corresponding to the peal value as shown in FI
NEC Corporation
Scully Scott Murphy & Presser
Yao Kwang Bin
LandOfFree
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