Pulse or digital communications – Spread spectrum
Reexamination Certificate
1998-12-04
2002-06-04
Chin, Stephen (Department: 2734)
Pulse or digital communications
Spread spectrum
C375S146000, C375S147000, C375S150000, C455S442000
Reexamination Certificate
active
06400750
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a base station system, a data transmission method of a multicarrier CDMA/FDM hybrid system, and a mobile communication system using the same, and in particular to an improved base station system, data transmission method, and a mobile communication system using the same which are capable of increasing the number of mobile stations supported in a cell when using a multicarrier CDMA method by differently setting a modulation mode of a traffic signal in accordance with the number of the mobile stations in a cell.
2. Description of the Conventional Art
The multicarrier CDMA system and data transmission method is disclosed in the U.S. Pat. No. 5,521,937 entitled “Multicarrier direct sequence spread system and method”. In the patent, the DSSS(Direct Sequence Spread Spectrum) in which the spectrum of a user data is spread using a PN(Pseudo noise) code is transmitted to various different frequency channels, a receiver receives the signals at each frequency channel and then combines the received signals for thereby demodulating it. In this mobile communication receiver, it is possible to obtain a combining gain and signal processing gain from the diversity of channel characteristics the frequency channels.
FIG. 1
illustrates a base station system supporting a K mobile stations and using four carrier waves in the mobile communication system using the multicarrier CDMA method.
In the drawings, reference numeral
102
represents an exchange,
104
represents a base station system,
106
represents a base station control apparatus,
108
represents a pilot signal modulation apparatus,
110
represents a paging signal modulation apparatus,
112
-
1
through
112
-K represent traffic signal modulation apparatuses,
114
-
1
through
1144
represent combining units,
116
-
1
through
116
-
4
represent BPSK(Binary Phase Shift Keying) modulators,
118
represents a radio frequency(RF) combining unit,
120
represents an amplifier, and
122
represents an antenna.
The exchange
102
communicates with the base station control apparatus
106
in the base station
104
. The base station control apparatus
106
controls the pilot up signal modulation apparatus using a CDMA/FDM(Frequency Division Multiplexing), the paging signal modulation apparatus
110
and the K number of the traffic signal modulation apparatuses
112
-
1
through
112
-K.
The pilot signal modulation apparatus
108
outputs the first, second, third and fourth signals, which are the same pilot pseudo noise (PN) code.
The paging signal modulation apparatus
110
outputs the first, second, third and fourth paging signals, which are the same paging spread spectrum signals. Here, the paging spread spectrum signal is obtained by multiplying the paging information data bit inputted from the base station control apparatus and the paging PN code.
In the K-number of the traffic signal modulation apparatuses
112
-
1
through
112
-K, four traffic spread spectrum signals are generated by multiplying the four user data bits and the traffic PN code in parallel, and four spread spectrum signals are output to first, second, third and fourth traffic signals.
The first through fourth combiners
114
-
1
through
114
-
4
sum the first through fourth pilot, paging, and the K number of the traffic signals, respectively.
The first through fourth BPSK modulators
116
-
1
through
1164
modulate the outputs of combiners
114
-
1
through
114
-
4
to the radio frequency using the frequencies f
1
, f
2
, f
3
. The RF(Radio Frequency) modulated by the first through fourth BPSK modulators
116
-
1
through
116
-
4
are combined by the RF combiner
118
. In addition, the output from the RF combiner
118
is amplified by the amplifier
120
and is transmitted through the antenna
122
.
When the frequency transmitted through the antenna
122
is received at a predetermined terminal, the terminal converts each spread spectrum signal received in a carrier frequency into a base band frequency. The codes allocated to the terminal are multiplied and despread. In addition, the above-described terminal combines the despread signals using a maximal-ratio combiner for thereby demodulating the user data.
Here, the pilot signal modulation apparatus
108
and the first through fourth BPSK modulators
116
-
1
through
1164
are the elements of the multicarrier pilot signal modulation apparatus. The paging signal modulation apparatus
110
and the first through fourth BPSK modulators
116
-
1
through
1164
are the elements of the multicarrier paging modulation apparatus. The traffic signal modulation apparatuses
112
-
1
through
112
-K and the first through fourth BPSK modulators
116
-
1
through
116
-
4
are the elements of the multicarrier signal modulation apparatus.
In the mobile communication system of the multicarrier CDMA, the number of code chips per data bit is reduced by the number of the carriers compared to the mobile communication system of a single carrier CDMA using the identical bandwidth. In the cellular mobile phone system of the CDMA, orthogonal codes are used for distinguishing mobile stations at the link from the base station to the mobile station. The number of orthogonal codes is the same as the number of the code chips per data bit.
Therefore, the number of the codes for distinguishing the mobile stations which may be used for the mobile communication system of the multicarrier CDMA is reduced by times the number of the carriers compared to the single carrier mobile communication system using the identical bandwidth.
In the mobile communication system of the multicarrier CDMA using four carrier frequencies having the construction as shown in
FIG. 1
, the number of the code chips per data bit is reduced by ¼ compared to the mobile communication system of the single carrier method.
Therefore, the number of the orthogonal codes which may be allocated to each mobile station is reduced by ¼ as well. In the base station of the mobile communication system of the multicarrier method, in order to support the same number of the mobile stations as the number of the mobile stations which may be used in the base station of the mobile communication system using the single carrier method, the code allocated to each mobile station should be a code which is not orthogonal to each other. Namely, a quasi-orthogonal functions or a random sequence should be used instead of the orthogonal function for distinguishing the mobile stations. However, if the quasi-orthogonal function or the random sequence is used, since the interference between the mobile stations in the same cell is increased, the bit error rate is increased for thereby degrading the performance of the system.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a base station system and a data transmission method of a multicarrier CDMA/FDM hybrid system and a mobile communication system using the same which overcome the aforementioned problems encountered in the conventional art.
It is another object of the present invention to provide a base station system of a multicarrier CDMA, a data transmission method and a mobile communication system using the same which are capable of controlling a lot number of mobile stations by distinguishing the mobile stations using orthogonal codes at a link from a base station to a terminal of a cellular system using the multicarrier CDMA and removing interference from signals transmitted to the other mobile stations in the same cell.
In order to achieve the above objects, there is provided a base station system which includes a base station control apparatus connecting with an exchange, a pilot signal modulation apparatus for generating a spread spectrum modulated pilot signal as many as the number of carriers in accordance with a control of the base station control apparatus, a paging signal modulation apparatus for generating spread spectrum modulated paging signals as many as the number of carriers in accordance with a co
Im Duck-Bin
Lee Dong-Wook
Chin Stephen
Electronics and Telecommunications Research Institute
Liu Shuwang
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