Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-08-17
2003-04-08
Le, Thanh Cong (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C375S142000, C375S145000, C455S440000
Reexamination Certificate
active
06546258
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a communication apparatus for receiving a plurality of signals from a plurality of base stations respectively and selecting one of them, which is the most suitable base station, to thereby communicate with the selected one.
2. Description of the Related Art
There is a communication apparatus adopting a CDMA (Code Division Multiple Access) method. By this CDMA method, the transmission signal is narrow-band-modulated and is further spread-spectrum-modulated by using a spread code series, to be thereby transmitted as a communication signal having a wide band. By performing such a spread spectrum modulation, it is possible to improve the capability of eliminating a disturbance wave and an interference wave, as compared with an ordinary narrow band modulating method. Further, by performing the spread spectrum modulation using the different spread code series for each user, a large number of users can commonly use the same frequency band to communicate with the other party. Namely, a so-called multiple access is enabled. Because such an advantageous feature is appreciated, the CDMA method is remarked as a basic technique for the movable body communication system in the next generation.
By the way, in the field of the movable body communication system adopting the CDMA method which has been already engaged in the business e.g., in the field of the portable telephone, such a system structure is employed that a large number of base stations, which are wire-line-connected to a communication line controlling station, are constructed to be distributed for each area (service area) and that a wireless communication is performed between the communication apparatus (portable telephone), which each user possesses, and each base station. By automatically detecting the closest base station to the portable telephone of each user from among the large number of base stations and then by communicating with the detected base station, it is possible to establish a good communication even if each user is moving.
In order to automatically detect the closest base station, the portable telephone may have a receiving circuit as shown in
FIG. 5
, for example.
In
FIG. 5
, in order to establish an asynchronous communication between the portable telephone and a certain base station among a large number of base stations, respective one of the base stations is identified by a downstream scramble code. The total: number of scramble codes usable here is 512. Those 512 scramble codes are divided into 32 groups, and the number of the scramble codes in each group is 16 (since 512 [codes] is divided by 32 [groups], 512÷32=16 [codes]). By using this group division, a cell search is performed.
Each base station spread-spectrum-modulates and transmits the assigned scramble code group identification short code and the scramble code. This transmitted electric wave is received by the portable telephone, so that it is possible to detect from which base station the received electric wave is.
In the receiving circuit show in
FIG. 5
, an electric wave from a base station is received by an antenna
1
, and a reception signal thereof is amplified by an RF (Radio Frequency) circuit
2
and is supplied to multipliers
3
and
4
. To the multiplier
3
, a code series for inverse-spreading, which is generated by a spread series generator
6
, is supplied. To the multiplier
4
, a code series for inverse-spreading, a phase of which is shifted by &pgr;/2 by a phase shift circuit
5
, is supplied.
An inverse-spreading circuit is constituted by the multipliers
3
and
4
, the phase shift circuit
5
and the spread series generator
6
. The in-phase component (I component) generated by the multiplier
3
and the orthogonal component (Q component) generated by the multiplier
4
are supplied through low pass filters
7
and
8
respectively to a correlation calculating circuit and a complex matched filter
11
.
The complex matched filter
11
detects the I component and the Q component supplied from the low pass filters
7
and
8
. A scramble code synchronous detecting circuit
12
synchronous-detects (or synchronous-captures) the scramble code on the basis of this wave component detection result. Further, a scramble code group ID detecting circuit
13
detects the scramble code group identification short code IDn of the base station, on the basis of this synchronous detection result.
Namely, as the scramble code synchronous detecting circuit
12
performs the synchronous-detection as mentioned above, one scramble code group identification short code IDn is generated from among
32
scramble code group identification short codes ID
1
to ID
32
. The scramble code group ID detecting circuit
13
detects the group, to which the base station belongs, on the basis of this scramble code group identification short code IDn.
A scramble code generating circuit
14
sequentially generates
16
scramble codes CODE
1
to CODE
16
, which belong to this detected scramble code group identification short code IDn, and supplies them to the correlation operating circuit
9
.
The correlation operating circuit
9
obtains the correlation between (i) the scramble code CODEm and (ii) the I component and the Q component from the low pass filters
7
and
8
respectively, each time when the scramble code CODEm among the
16
scramble codes CODE
1
to CODE
16
is supplied from the scramble code generating circuit
14
, and supplies the correlation value Rm obtained by this correlating operation, to a scramble judging circuit
15
. Through the correlation operating circuit
9
, the I component and the Q component are supplied to a phase correcting circuit
10
, so that the decoding process is performed by the phase correcting circuit
10
and finally a reception output is generated.
The scramble code judging circuit
15
judges that the identification of the base station (e.g., the synchronous capture) is completed if the correlation value Rm reaches or exceeds a predetermined threshold value THD while comparing the correlation value Rm with the threshold value THD. Then, the data communication or voice communication by using the pertinent receiving circuit is started. On the other hand, the scramble code judging circuit
15
judges that an appropriate base station is not detected if the correlation value Rm does not reach the threshold value THD. Then, the scramble code synchronous detecting circuit
12
performs the synchronous detection again, and the processes of synchronous-capturing as described above are repeatedly performed until the base station is identified.
However, in the above described communication apparatus, by detecting the scramble code group identification short code IDn from, the received electric wave, the groups are narrowed down to one group, to which the base station transmits this electric wave belongs. Further, by selecting one scramble code CODEm belonging to this one group, the closest base station is identified.
Accordingly, it takes a long time period to search the closest base station. Namely, in addition to the requirement of selecting the scramble code group, it is necessary to repeat the above mentioned various processes, 16 times at the maximum in order to select one scramble code CODEm from among the 16 scramble codes CODE
1
to CODE
16
, even after the group identification short code IDn is detected.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a communication apparatus and a communication method, which can speedily specify an appropriate base station from among a plurality of base stations.
The above object of the present invention can be achieved by a communication apparatus for communicating with one base station among a plurality of base stations. The communication apparatus is provided with: a present position detecting device for detecting a present position of the communication apparatus and outputting present position information indicative of
Akimoto Takayuki
Kodama Yasuteru
Nohara Manabu
Okamura Masahiro
Shioda Takehiko
Cong Le Thanh
Ewart James D
Morgan & Lewis & Bockius, LLP
Pioneer Corporation
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