Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1998-12-15
2003-08-05
Ton, Dang (Department: 2666)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S441000
Reexamination Certificate
active
06603754
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a base station transmission system in a mobile communication system, and more particularly, to a base station transmission system in a CDMA (Code Division Multiple Access) mobile communication system and a method for processing a baseband signal using the same, which can provides a baseband signal less susceptible to noise and maximize a channel capacity.
2. Background of the Related Art
In general, in the mobile communication system, there are transmission or reception signal of baseband, intermediate frequency band, and radio frequency band depending on a frequency band of the signal. The baseband is a frequency band occupied by an original information signal before modulation. Therefore, the baseband is a frequency band of which lowest frequency is near to 0 or containing a direct current component. The intermediate frequency band is a frequency band to which a baseband frequency to be transmitted to outside of the station is increased by adding a local oscillator frequency in a frequency converter in a base station and, opposite to this, to which a radio frequency received from outside of the station is decreased by subtracting the local oscillator frequency in the frequency converter. The radio frequency band is a frequency band for use in radio communications within an electromagnetic spectrum range from 10 KHz to 300 GHz.
FIG. 1
illustrates a block diagram showing a related art basestation transmission system in a CDMA mobile communication system.
Referring to
FIG. 1
, the related art basestation transmission system in a CDMA mobile communication system is provided with a channel card unit
1
, a buffer unit
2
, and a baseband signal processing unit
3
, each of which has a PCB form. The channel card unit
1
is provided with four CDMA modem
11
~
14
, each having a CDMA basestation modem unit
10
for band spreading a received digital voice signal according to a CDMA recommendations(for example, IS-95 family), a digital combining unit
20
a
or
20
b
for combining digital signals from the CDMA basestation modem unit
10
transmitted through alpha, beta, gamma paths, a digital/analog converting unit
30
a
or
30
b
for converting the digital signal from the digital combining unit
20
a
or
20
b
into an analog signal, a low pass filter
40
a
and
40
b
for removing unnecessary frequency band in view of a signal characteristic from the signal from the digital/analog converter
30
a
or
30
b,
and an amplifier
50
a
or
50
b
for amplifying a signal from the low pass filter
40
a
or
40
b
to a required level. The buffer unit
2
is provided with amplifiers
61
~
66
equal to the channel card units
1
in number, each for separating analog signals provided through I, and Q channels from the amplifier
50
a
or
50
b
into sectors of alpha, beta, and gamma. The baseband signal processing unit
3
is provided with accumulators
70
a
~
70
f
each for accumulating an analog signal from the buffer amplifier
61
~
66
, phase equalizers
80
a
~
80
f
each for regulating a phase characteristic of a signal from the accumulator
70
a
~
70
f
to suit to a CDMA signal characteristic, low pass filters
90
a
~
90
f
each for removing an unnecessary frequency band from a signal from the phase equalizer
80
a
~
80
f
to satisfy a cut offset characteristic, and intermediate amplifiers
100
a
~
100
f
each for receiving a signal from the low pass filter
90
a
~
90
f
and amplifying to a required level for easy modulation in I & Q modulation type(one of QPSK modulation type). The back planes
110
a
and
110
b
in
FIG. 1
denote unitary PCBs, which is one of transmission mediums used in place of cable in data transmission between the channel card unit
1
, the buffer unit
2
and the baseband signal processing unit
3
, each in a PCB form, in the basestation transmission system. As shown in
FIG. 1
, output terminals on the channel card unit
1
are connected to the back plane
110
a,
and output terminals on the buffer unit
2
are connected to the back plane
110
b.
The operation of the related art basestation transmission system in a CDMA mobile communication system will be explained.
A voice signal encoded in a vocoder is provided to one of the CDMA modem
11
~
14
in the voice channel card unit
1
as an 8 bit data bus. Each of the CDMA modems
11
~
14
, two or four are provided on one board, provides one communication channel. In the related art, the CDMA modem
11
or
14
spreads a voice signal into a digital baseband signal of 1.2288 Mcps, selects I or Q channel, and provides to the digital combining unit
20
a
or
20
b
at up to 9600 bps through three channels of alpha, beta, gamma. The digital combining unit
20
a
or
20
b
receives the baseband signal split into three alpha, beta, and gamma paths for each of the I and Q channels from one CDMA modem
11
and
14
, subjects to digital combining, and provides to the digital/analog converter
30
a
or
30
b
in 10 bit units. Then, the digital/analog converter
30
a
or
30
b
converts the received digital signal into an analog signal suitable for radio transmission. The low pass filter
40
a
or
40
b
removes unnecessary bands in view of a signal characteristic from the analog signal of 1.2288 MHz from the digital/analog converter
30
a
or
30
b
. The amplifier
50
a
or
50
b
provides the analog signal from the low pass filter
40
or
40
b
to the buffer amplifier
61
~
66
in the buffer unit
2
separate for three alpha, beta, and gamma paths for each of the I and Q channels through the back plane
110
a.
The buffer amplifier
61
~
66
in the buffer unit
2
provides the analog signal to the baseband signal processing unit
3
separate for three alpha, beta, and gamma paths for each of the I and Q channels through the back plane
110
b
. Each of the accumulators
70
a
~
70
f
in the baseband signal processing unit
3
accumulates the analog signal from the buffer amplifier
61
~
66
and provides to the phase equalizer
80
a
~
80
f
Each of the phase equalizers
80
a
~
80
f
adjusts a phase characteristic of a signal from the accumulator
70
a
~
70
f
to suit to a CDMA signal characteristic and provides to the low pass filter
90
a
~
90
f.
The low pass filter
90
a
~
90
f
removes unnecessary bands from the phase adjusted CDMA baseband signal to satisfy a cut offset characteristic and provides to the intermediate amplifier
110
a
~
100
f.
The intermediate amplifier
100
a
~
100
f
amplifies the CDMA baseband signal, and then converted into a radio frequency for transmission, and transmitted through a basestation antenna.
However, in the related art CDMA basestation transmission system, the baseband signal is susceptible to noise during the baseband signal provided from the buffer unit
2
through the back plane
100
b
is accumulated in the accumulator in the baseband signal processing unit
3
. This is because the baseband signal provided through the back plane
110
b
is an analog signal susceptible to noise. The demerit significantly affects a forward capacity of the system, which can be a great cause of a communication quality degradation when the communication is busy. That is, the related art basestation transmission system has a limit in improvement of a communication quality through improvement of a baseband signal characteristic improvement.
A maximum number of the CDMA modems
11
~
14
mountable on the channel card unit
1
is four under the present level of a basestation transmission system supporting technique. The basestation transmission system of the Qualcomm in U.S.A. can supports 2 CDMA modems, and the STAREX-CMX of the LG Information and Communication, Ltd. can supports 4 CDMA modems. As one CDMA modem provides on communication channel, the basestation transmission system with the channel card unit, the buffer unit, and the baseband signal processing unit shown in
FIG. 1
should be kept extended for an increased transmission rate of the baseband signal. However, the extension results in a complicated st
Fleshner & Kim LLP
LG Electronics Inc.
Ton Dang
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