Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
2000-10-13
2003-05-13
Corrielus, Jean (Department: 2631)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
27
Reexamination Certificate
active
06563881
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a communication method in digital radio communication suitable for application to a radio communication system such as a radio telephone system using, for example, a cellular scheme, and to a transmitter and a receiver to which the communication method is applied.
BACKGROUND ART
As a conventional communication scheme for sharing a wide frequency band among a plurality of users and conducting communication efficiently, such as a radio telephone system, there is, for example, the DS-CDMA (Direct Sequence-Code Division Multiple Access) scheme. In this DS-CDMA scheme, a transmission signal sequence is spread (multiplied) by a code to generate a wide band signal, and this signal is transmitted. Furthermore, on a receiving side, a received signal is multiplied by the same spreading code as that of the transmission side to yield an effect called despreading. Only a desired signal component is thus extracted out of the received signal.
FIG. 1
shows a transmission configuration in a cellular radio communication system to which the conventional DS-CDMA scheme has been applied. An information bit stream obtained at an input terminal
1
is subjected to processing such as coding and interleaving in a coding unit
2
, then supplied to a multiplier
3
, and multiplied and spread therein by a code intended for channel assignment obtained at a terminal
3
a
. The spread bit stream is randomized in a multiplier
4
of a subsequent stage by a long code obtained at a terminal
4
a
, and thereafter mapped in a symbol mapping unit
5
to a transmission symbol. As for this mapping method, there are various techniques depending on the communication scheme.
The transmission signal mapped in the symbol mapping unit
5
is multiplexed in an adder
6
with transmission signals of other systems as occasion demands, supplied to a transmission processing unit
7
, subjected to high frequency processing such as modulation therein, thereafter converted in frequency to a frequency band to be radio-transmitted, and radio-transmitted from an antenna
8
.
Assuming now that the information bit stream obtained at the input terminal
1
is, for example, 8 kbps, it is encoded in the coding unit
2
with a coding rate 1/2. The bit rate of the coded bit becomes 16 kbps. If the coded bit is spread with a spreading factor
64
in the multiplier
3
, a bit stream of 1024 kcps (where cps represents Chip Per Second) is obtained. If the information bit stream is different in bit rate, the bit rate of the transmission signal can be made constant by changing the spreading factor to be used in the multiplier
3
.
Furthermore, as for other transmission systems added in the adder
6
as well, various information bit streams can be mixed as information bit streams supplied to the coding units
2
of respective transmission systems, provided that the bit stream of the transmission signal supplied to the adder
6
is constant.
A configuration for receiving the signal subjected to the transmission processing using the conventional DS-CDMA scheme will now be described by referring to
FIG. 2. A
signal of a predetermined frequency band received by an antenna
11
is subjected to frequency conversion in a reception processing unit
12
to form an intermediate frequency signal. The received signal thus subjected to the frequency conversion is demodulated to yield a baseband symbol sequence. Out of this symbol sequence, a received bit stream is extracted in a bit extraction unit
13
. The received bit stream thus extracted is supplied to a multiplier
14
, and multiplied and descrambled by a long code obtained at a terminal
14
a
. The multiplied output of the multiplier
14
is supplied to a multiplier
15
, and multiplied by a despreading code obtained at a terminal
15
a
. Despreading processing is thus conducted, and a coded bit stream is obtained. The coded bit stream is decoded in a decoding unit
16
, and an information bit stream is obtained at a terminal
17
.
If a signal of the case where the above described information bit stream of 8 kbps is transmitted as the bit stream of 1024 kcps is received by the configuration of
FIG. 2
, then the signal is despread in the multiplier
15
with a despreading factor
64
and an information bit stream of 8 kbps is obtained. Furthermore, if the despreading factor of the despreading code obtained at the terminal
15
a
is changed, then an information bit stream of a different bit rate can be coped with.
In the description given so far, the case where information bit streams of a plurality of bit rates are mixed and radio-transmitted by using the DS-CDMA scheme has been described. Also in the case where they are radio-transmitted by using the TDMA (Time Division Multiple Access) scheme, however, it is also possible to mix information bit streams of a plurality of bit rates.
FIG. 3
is a diagram showing the structure of one frame in the case of 8-TDMA structure in which one frame is formed of 8 time slots ranging from slot
1
to slot
8
.
Assuming now slots to be assigned in the case where the transmission rate per slot is 8 kbps, for example, slots
1
and
2
are respectively assigned to users A and B having a transmission rate of 8 kbps and communication of the transmission rate of 8 kbps is conducted by using the slot
1
or
2
. Furthermore, two slots composed of slot
3
and slot
4
are assigned to a user C having a transmission rate of 16 kbps and communication of 16 kbps is conducted. Furthermore, four slots composed of slots
5
through
8
are assigned to a user D having a transmission rate of 32 kbps and communication of 32 kbps is performed. According to the transmission rate at the time of a transmission request from each user, a base station or the like thus sets the number of slots in one frame to each user variably. As the result, it is possible to cope with the TDMA scheme by accommodating information bit streams having a plurality of bit rates mixedly and radio-transmitting them.
Furthermore, in the case where radio transmission is performed using a multi-carrier scheme called OFDM (Orthogonal Frequency Division Multiplex) scheme, for example, the configuration shown in
FIG. 4
of a prior art is used as the transmission configuration. This configuration is a configuration applied to DAB (Digital Audio Broadcasting). An information bit stream obtained at a terminal
21
is subjected to processing such as coding in a coding unit
22
, and thereafter mapped to transmission symbols in a symbol mapping unit
23
. The transmission symbols are supplied to a mixing circuit
24
, and multiplexed with other transmission data therein. As for the multiplexing conducted here, transmission data are simply coupled in series to generate a multiplexed symbol stream. For example, if symbols having 64 ksps per channel are multiplexed by 18 channels, then the transmission rate of the multiplexed symbol stream becomes 64 ksps×18=1152 ksps.
This multiplexed symbol stream is subjected to symbol rearrangement performed by frequency interleaving in a frequency conversion unit
25
. As a result, symbols of respective channels are scattered. The rearranged symbol stream is converted into a multi-carrier signal arranged on the frequency axis by inverse Fourier transform processing in an inverse Fourier transform circuit (IFFT circuit)
26
. The output of this IFFT circuit
26
is subjected to radio transmission processing in a radio processing unit
27
, and radio-transmitted in a predetermined frequency band.
As for a configuration of the receiving side of this multi-carrier signal, a signal of a desired frequency band received by an antenna
31
is converted to a baseband signal in a reception processing unit
32
as shown in FIG.
5
. Here, the baseband signal component of the multi-carrier signal is a signal having information pieces arranged on the frequency axis. Therefore, the multi-carrier signal is supplied to a fast Fourier transform circuit (FFT circuit)
33
and subjected to Fourier transform processing. As a result, subca
Sakoda Kazuyuki
Suzuki Mitsuhiro
Yamaura Tomoya
Corrielus Jean
Ghulamali Qutub
Maioli Jay H.
Sony Corporation
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