Demodulator of receiver

Details Demodulator of receiver Demodulator of receiver

2000-08-25

2004-02-24

Phu, Phoung (Department: 2634)

Pulse or digital communications

Receivers

Angle modulation

C375S326000, C375S279000, C329S304000

Reexamination Certificate

active

06697440

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a demodulating apparatus of a receiver, and more specifically to a demodulating apparatus of a receiver for demodulating a PSK modulated signal obtained by time-multiplexing a digital signal modulated in a 2-phase, 4-phase, and 8-phase PSK modulation system in a hierarchical transmission system, etc. by using a carrier regenerated by carrier regeneration means, and outputting an I-Q symbol stream data.
BACKGROUND ART
A digital satellite TV broadcast in a plurality of modulation systems in which different necessary C/Ns are required, for example, in a hierarchical transmission system in which an 8 PSK modulated wave, a QPSK modulated wave, and a BPSK modulated wave are time-multiplexed and repeatedly transmitted for each frame has been developed for practical use.
FIG. 8
shows an example of the configuration of one transmission frame in the hierarchical transmission system. One frame includes a frame synchronous signal pattern (predetermined 20 symbols are actually used as a frame synchronous signal in 32 symbols) formed by 32 BPSK-modulated symbols, a TMCC (transmission and multiplexing configuration control) pattern for transmission multiplexing configuration identification formed by 128 BPSK-modulated symbols, a superframe identification pattern formed by 32 symbols (predetermined 20 symbols are actually used as a superframe identification signal in 32 symbols), a main signal having 203 8 PSK (trellis codec 8 PSK) modulated symbols, a 4-symbol burst symbol signal (BS) obtained by BPSK-modulating a pseudo random noise (PN) signal, a main signal having a 203 8 PSK (trellis codec 8 PSK) modulated symbols, a 4-symbol burst symbol signal (BS) obtained by BPSK-modulating a pseudo random noise (PN) signal, a main signal having 203 QPSK-modulated symbols, a 4-symbol burst symbol signal (BS) obtained by BPSK-modulating a pseudo random noise (PN) signal, a main signal having 203 QPSK-modulated symbols, and a burst symbol signal (BS) having 4 BPSK-modulated symbols in this order.
Here, the mapping for each modulation system on the transmission side will be described below by referring to
FIGS. 9A-9C
.
FIG. 9A
shows a signal point arrangement at the I-Q phase (an I-Q vector or an I-Q signal space diagram) when the 8 PSK modulation system is used. In the 8 PSK modulation system, a 3-bit digital signal (abc) can be transmitted as 1 symbol, and there can be 8 combinations of bits forming 1 symbol, that is, (0 0 0), (0 0 1), (0 1 0), (0 1 1), (1 0 0), (1 0 1), (1 1 0), and (1 1 1). These 3-bit digital signals are converted into the signal point arrangements
0
through
7
in the I-Q phase on the on the transmission side as shown in FIG.
9
A. The conversion is referred to as 8 PSK mapping.
In an example shown in
FIG. 9A
, the bit string (0 0 0) is converted into the signal point arrangement ‘
0
’, the bit string (0 0 1) is converted into the signal point arrangement ‘
1
’, the bit string (0 1 1) is converted into the signal point arrangement ‘
2
’, the bit string (0 1 0) is converted into the signal point arrangement ‘
2
’, the bit string (1 0 0) is converted into the signal point arrangement ‘
3
’, the bit string (1 0 0) is converted into the signal point arrangement ‘
4
’, the bit string (1 0 1) is converted into the signal point arrangement ‘
5
’, the bit string (1 1 1) is converted into the signal point arrangement ‘
6
’, and the bit string (1 1 0) is converted into the signal point arrangement ‘
7
’.
FIG. 9B
shows the signal point arrangement at the I-Q phase when a QPSK modulation system is used. In the QPSK modulation system, a 2-bit digital signal (de) can be transmitted as 1 symbol, and there can be 4 combinations of bits as a symbol. They are (0 0), (0 1), (1 0), and (1 1). In the example shown in
FIG. 9B
, for example, the bit string (0 0) can be converted into the signal point arrangement ‘
1
’, the bit string (0 1) can be converted into the signal point arrangement ‘
3
’, the bit string (1 1) can be converted into the signal point arrangement ‘
5
’, and the bit string (1 0) can be converted into the signal point arrangement ‘
7
’.
FIG. 9C
shows the signal point arrangement when a BPSK modulation system is used. In the BPSK modulation system, a 1-bit digital signal (f) can be transmitted as 1 symbol. In the digital signal (f), for example, the bit (0) is converted into the signal point arrangement ‘
0
’, and the bit (1) is converted into the signal point arrangement ‘
4
’. The relationship between the signal point arrangement and the arrangement number in each modulation system is defined such that the signal point arrangement is equivalent to the arrangement number based on the 8 BPSK.
The I axis and the Q axis of the QPSK and the BPSK in the hierarchical transmission system match the I axis and the Q axis of the 8 PSK.
Eight frames shown in
FIG. 8
form one superframe. In the area of 20 predetermined symbols of a frame synchronous signal pattern in each frame, a well-known 20-bit digital signal pattern (referred to as W
1
) is BPSK-mapped. In the area of 20 predetermined symbols of a superframe identification signal pattern as a leading frame in a superframe, a well-known 20-bit digital signal pattern (referred to as W
2
) different from W
1
is BPSK-mapped. In the area of 20 predetermined symbols of a superframe identification signal pattern in each frame other than the leading frame in a superframe, a well-known 20-bit digital signal pattern (referred to as W
3
, and obtained by inverting each bit of W
2
) is BPSK-mapped.
In the receiver for receiving a digital modulated wave (PSK modulated wave) in the hierarchical transmission system, the intermediate frequency signal of a signal received by a reception circuit is demodulated through orthogonal detection by a demodulating circuit, thereby obtaining two sequences of I-Q base band signals (hereinafter, the I-Q base band signal can also be referred to as I-Q symbol stream data) indicating the momentary value for each symbol off the I axis and the Q axis orthogonal to each other. However, when there is a shift in phase between the carrier before the modulation of an input of the demodulating circuit and the reference carrier regenerated in the demodulating circuit, the received signal point of the modulated I-Q base band signal is phase-rotated toward the transmission side. Therefore, the digital signal transmitted on the transmission side cannot correctly recover if the data is input as it is to the decoder and PSK-mapped.
Each of the burst symbol signals (BS) shown in
FIG. 8
is obtained by resetting the PN code generator having a predetermined configuration at the starting position of the initial burst symbol signal (BS) in a frame on the transmission side, shifting the output according to the symbol clock at each period in the transmission frame configuration, and performing a BPSK mapping process.
The demodulating circuit uses a burst symbol signal (BS) as a pilot signal for amendment of the phase of the reference carrier, and allows the phase of the carrier in the state before the modulation of the received signal to match the phase of the reference carrier, thereby setting the absolute phase such that the signal point of the I-Q base band signal output from the demodulating circuit as matching the signal point on the transmission side.
FIG. 10
shows, the configuration of the demodulating circuit of the receiver for receiving the PSK modulated wave in the conventional hierarchical transmission system. A demodulating circuit
1
shown in
FIG. 10
obtains an I-Q base band signal by orthogonally detecting the intermediate frequency signal of a received signal.
10
denotes a carrier regeneration circuit for regenerating two reference carriers f
c1
(=cos &ohgr;t), and f
c2
(=sin &ohgr;t) whose frequencies and phases are synchronized with those of the carrier in the state before the modulation of the input of the demodulating circuit
1
, and whose phases are 90° shifted to each other to be orthogonal to each other.
2
and
3
denote multipliers f

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