Transmission method, transmitter and receiver

Details Transmission method, transmitter and receiver Transmission method, transmitter and receiver

1999-02-19

2003-02-11

Pham, Chi (Department: 2631)

Pulse or digital communications

Transmitters

C375S225000, C375S130000, C375S146000

Reexamination Certificate

active

06519292

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transmission method, a transmitter and a receiver, which is preferably applied to a cellular radio-communication system such as a portable telephone system.
2. Description of the Related Art
A conventional cellular radio-communication system is constituted so that an area for which communication services are provided is divided into cells of a desired size, a base station serving as a fixed radio station is set in each of the cells, and a portable telephone serving as a mobile radio station performs radio communication with a base station in a cell in which the portable telephone is present.
In the above case, various communication systems are considered between a portable telephone and a base station. Typical systems are the code division multiple access (CDMA) system and the time division multiple access (TDMA) system.
The CDMA system is a communication system for transmitting a narrow-band modulated wave (primary modulation) by spectrum-spreading the frequency bandwidth of the wave (secondary-modulating) and thereby, widening the width up to several tens of times or more, in which every communication is performed by using the same radio carrier so that multiple access can be realized by assigning an independent spread code to each communication channel and thereby assigning the same wide frequency band to a multiplicity of communication channels. The receiving side can restore transmission information by reverse-spreading the signal of a desired channel, thereby recognizing signals of other channels as noises and extracting only a purposed primary-modulated wave, and demodulating the wave.
The transmitter and receiver of a cellular radio-communication system for transmitting or receiving a digital signal in accordance with the CDMA system are described below by referring to
FIGS. 1 and 2
. In this connection, the transmitter and receiver shown in
FIGS. 1 and 2
are mounted on, for example, the base station of a portable telephone system or a portable telephone and used for the up communication from the portable telephone to the base station or the down communication from the base station to the portable telephone.
As shown in
FIG. 1
, symbol
1
denotes the transmitter of a cellular radio-system according to the DS(Direct Spread)-CDMA system (hereafter simply referred to as CDMA system) as a whole. In
FIG. 1
, a case is assumed in which a communication environment using the same frequency band for all adjacent cells, that is, the so-called state in which the number of repetitions of frequency is “1” is set and an information bit stream S
1
is transmitted at a bit rate of 8 K[bit/sec] desired by a user by using a bandwidth of 1.024[MHz].
The transmitter
1
first inputs the information bit stream S
1
of a bit rate of 8K[bit/sec] to an encoding section
2
. The encoding section
2
generates a transmission symbol stream S
2
of 16K[Coded bit/sec] encoded at an encoding rate of ½ by applying the convolutional encoding which is one of error corrections to the information bit stream S
1
and rearranging the sequence of transmission symbols thereby obtained at random (rearranging of the sequence is hereafter referred to as interleaving) and transmits the stream S
2
to a spread-code multiplier
3
.
The spread-code multiplier
3
generates a transmission symbol stream-S
3
spread to 1024K[Chip bit/sec] by multiplying the 16K[Coded bit/sec] transmission symbol stream S
2
by a spread code C
1
having a spreading ratio (hereafter referred to as SP) of 64 supplied by a spread-code generating section
4
and supplies the stream S
3
to a long-code multiplier
5
. In this case, the spread-code multiplier
3
assigns the same frequency band to 64 channels by using 64 types of PN codes orthogonal to each other.
In this case, in the transmitter
1
, the spread code C
1
having an SP corresponding to the bit rate of the information bit stream S
1
is assigned by the spread-code generating section
4
when channel assignment is requested. Therefore, when the bit rate of the information bit stream S
1
is 16K[bit/sec], the spread code C
1
having an SP of 32 is assigned.
The long-code multiplier
5
performs scrambling by multiplying the transmission symbol stream S
3
by a long code C
2
intrinsically set to each base station supplied from a long-code generating section
6
so that crosstalk does not occur even if the same spread code C
1
is used for adjacent cells and transmits a transmission symbol stream S
4
of 1024K[chip/sec] thereby obtained to a symbol mapping section
7
.
In this case, because the number of repetitions of frequency is “1”, the same frequency band is used for adjacent cells and moreover, the same frequency band is used for the spread code C
1
. Therefore, by using the long code C
2
intrinsically provided for each base station, the interference between adjacent cells is prevented. That is, in the case of a CDMA cellular radio-communication system, the spread codes C
1
used for portable telephones are orthogonal to each other in the same cell. However, there is not orthogonal relation between adjacent cells.
The symbol mapping section
7
generates a transmission signal S
5
showing each piece of symbol information by a phase value by applying the binary phase-shift keying (BPSK) modulation processing to the transmission symbol stream S
4
successively input and transmits the signal S
5
to a transmission circuit
8
.
The transmission circuit
8
generates a transmission signal S
6
of a predetermined frequency channel by filtering the transmission signal S
5
, then transforming the signal S
5
into an analog signal, and multiplying the transmission signal transformed into an analog signal by a high frequency, and thereby frequency-converting the analog transmission signal into a desired frequency band (e.g. approx. 800[MHz]), and amplifies the signal S
6
to a predetermined power and thereafter transmits the signal S
6
through an antenna
9
.
Moreover, as shown in
FIG. 2
, the receiver
10
receives the transmission signal S
6
transmitted from the transmitter
1
through an antenna
11
and inputs the signal S
6
to a receiving circuit
12
as a reception signal S
11
. The receiving circuit
12
fetches a base band signal by amplifying the reception signal S
11
up to a predetermined level and then, frequency-converting the signal S
11
, moreover fetches a BPSK-modulated reception signal S
12
by filtering the base band signal and then, transforming the signal S
12
into a digital signal, and transmits the signal S
12
to a bit-stream extracting section
13
.
The bit-stream extracting section
13
fetches symbol information by applying the BPSK demodulation processing to the reception signal S
12
and transmits the symbol information to a long-code multiplier
14
as a reception symbol stream S
13
of 1024K[chip/sec].
The long-code multiplier
14
receives a long code C
3
same as that generated in the long-code generating section
6
at the transmission side from a long-code generating section
15
and performs descrambling by multiplying the reception symbol stream S
13
by the long code C
3
. Thereby, the long-code multiplier
14
generates a reception symbol stream S
14
of 1024K[chip/sec] same as the transmission symbol stream S
3
generated at the transmission side and transmits the stream S
14
to a spread-code multiplier
16
.
The spread-code multiplier
16
generates a spread code C
4
same as the spread code C
1
generated by the spread-code generating section
4
at the transmission side with the spread-code generating section
17
, reverse-spreading the spread code C
4
by multiplying the reception symbol stream S
14
of 1024K[chip/sec] by the spread code C
4
, and transmits a reception symbol stream S
15
of 16K[Coded bit/sec] thereby obtained to a decoding section
18
.
The decoding section
18
returns the sequence of

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