Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1999-03-16
2002-05-07
Pham, Chi (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S150000, C375S152000, C375S343000, C370S515000
Reexamination Certificate
active
06385232
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a synchronization detection device and its method, and more particularly, is suitably applied to a cellular radio communication system that allows asynchronous communication between base stations according to the direct sequence-code division multiple access (DS-CDMA) system.
2. Description of the Related Art
The DS-CDMA system is a multiplexing system using spread codes and its application to the cellular radio communication system has been vigorously under study as one of the radio access systems of the future mobile communication system. In the cellular radio communication system, an area to provide communication service is divided into cells with a desired size and a base station as a fixed station is provided in each cell and a communication terminal device which is a mobile station is connected by radio to the base station having the best communication state.
In such a cellular radio communication system, a method to search a base station to which the mobile station is connected is generally called a cell search. In this DS-CDMA cellular radio communication system, in order that the base stations use the same frequency, timing of spread code included in the received signal should be trapped simultaneously with this cell searching.
This cellular radio communication system using the DS-CDMA system can be classified into two types: a synchronous system between base stations in which temporal synchronization is performed among all base stations; and asynchronous system between base stations in which time synchronization is not conducted. Since the synchronous system between base stations is regulated by the IS-95 Standard, an absolute reference time is set in each base station using radio waves of the global positioning system (GPS) and thus, temporal synchronization will be performed among base stations. In this system, base stations transmit the same long code as the spread code at timing different from each other based on the absolute reference time. And thus, at the time of cell search, the mobile station can search the base station to be connected only by trapping the timing of a long code.
On the other hand, in the asynchronous system between base stations, base stations transmit a different long code in order to identify base stations, and accordingly, at the time of cell search, it is necessary for the mobile station to detect timing of the long code as well as the type of the long code. Therefore, in the case of asynchronous system between base stations, there is a problem that the time required for cell search becomes longer as compared with the synchronous system between base stations. However, as contrary to the above, in the asynchronous system between base station, since it is unnecessary to receive GPS radio wave, service area can be widened to areas where GPS radio wave can not reach. Therefore, if the cell search problem can be solved, this system is very effective.
As a method to speed up the cell search in the asynchronous system between base stations, several methods can be considered. One of these methods is that of transmitting a common short code among base station as well as a long code and a group identification short code to specify the long code group, and of detecting the timing and code type of the long code to be transmitted based on these short codes. In the following explanations, the method to detect the code timing and code type will be referred to as identification.
More specifically, the base station has a signal generation unit
1
of the control channel as shown in
FIG. 1
, and it forms transmission data in which long code, common short code and group identification short code are combined by using the signal generation unit
1
, and transmits the transmission data through the control channel. At first, a first multiplier
2
sequentially spreads input information bit S
1
having the value such as “1” with the common short code CSC having comparatively short cycle, that is common in each base station, and outputs spread data S
2
to a second multiplier
3
. In the second multiplier
3
, long code LC having the longer cycle than the common short code CSC is entered and the spread data S
2
is successively spread using the long code LC and the spread data S
3
is output to an adder
5
.
In this connection, this long code LC is very specific to every base station and base stations are identified by this long code LC. And a long code enable signal SCE is entered into AND circuit
4
, and by setting this long code enable signal LCE to the level “L” at a fixed cycle, the long code LC to be supplied to the second multiplier
3
will be masked over the segment of level “L”. Thus, the spread data S
3
to be sent from the second multiplier
3
is not spread out in the long code LC over the segment on which long code enable signal LCE has the level “L”. Hereinafter, the segment over which the long code LC is masked is referred to as masked segment.
On the other hand, group identification short code GISC, that shows the group of long codes LC to be used in the signal generation unit
1
and has the same cycle as the common short code CSC, is entered into the third multiplier
6
. And this third multiplier
6
spreads out information bit S
4
having such as the value “1” with this group identification short code GISC and outputs spread data S
5
to the adder
5
. In this connection, the spread data S
5
will be formed on the masked segment of long code LC.
The adder
5
, by adding these spread data S
3
and S
5
, forms transmission data S
6
for transmitting by the control channel. Thus, by transmitting this transmission data S
6
by the control channel via the transmission circuit and antenna (not shown in FIG.), the transmission signal containing long code LC, common short code CSC and group identification short code GISC is be transmitted from the base station.
At this point, the timing of long code LC, common short code CSC and group identification short code GISC included in the transmission signal transmitted from the base station will be shown in
FIGS. 2A
to
2
C. As shown in
FIGS. 2A
to
2
C, common short codes CBC exist repeatedly in the transmission signal. Also long codes LC exist repeatedly in the transmission signal. However, the long code LC is masked just over the segment synchronized with the common short code CSC at the cycle T
MK
. Moreover, in the masked segment of the long code LC, since the spread data S
5
is added, group identification short code GISC exists over that masked segment.
In the case of receiving the transmission signal containing codes (CSC, GISC and LC) by the mobile station at the above timing and identifying the long code LC included in the transmission signal, firstly the common short code CSC existing over the masked segment is detected from the received signal to detect the timing of long code LC. When it is detected, the type of group identification short code GISC existing over the masked segment is determined. In this case, the group identification short code GISC shows the group of long code LC included in the received signal, and if the type of group identification short code GISC can be identified, the candidate of long code LC can be specified to that group.
Accordingly, after the group identification short code GISC is determined, the type of long code LC included in the received signal can be identified by narrowing down the candidate onto the long code LC in the group which the group identification short code GISC indicates and sequentially confirming whether these are candidates or not. With this arrangement, since the number of candidates can be decreased by the group identification short code GISC, the time required to judge the type of long code LC can be shortened as compared with the case of making all long codes LC as candidates.
At this point, the synchronization detection device to identify long code LC included in the received signal according to the above method will be shown in FIG.
3
. In this
FIG. 3
Maioli Jay H.
Pham Chi
Phu Phuong
Sony Corporation
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