JPH0412660B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a regenerative repeater for phase modulated signals. Simultaneous detection and delayed detection are widely used for demodulating phase keyed signals (PSK). In particular, since the latter does not require carrier signal regeneration, a simple demodulator can be constructed by allowing some deterioration (about 1.4 dB). However, on the contrary, since there is no carrier phase synchronization function, the delay time error of the delay line (Te seconds: the century value is the symbol period T), the temperature change G/deg), and the intermediate frequency fo (even though it is called RF) Good) fluctuation △ω _IF generates a steady phase difference θe [rad] expressed by the following equation. θe2πfo×(Operating temperature range)×G×T+2πfo・Te
+△ω _IF・Te Therefore, it cannot be used in places where these various quantities fluctuate rapidly. In particular, narrowband communication methods for satellite communications (e.g. (SCPC; Single Channel Per
carrier), the previous Δω _IF is large compared to the transmission rate R, and the conventional delay detection circuit suffers from extremely large deterioration. Furthermore, deterioration due to the shift between the transmission carrier shift and the center frequency of the reception bandpass filter (corresponding to the filter bank as described later in the case of digital processing) is not eliminated. An object of the present invention is to provide a repeater intended to absorb such deterioration. According to the present invention, demodulating K-phase phase modulation information,
A repeater that re-modulates and transmits using a separately determined modulation method detects the phase difference between the current received signal and the received signal one symbol before.
a phase difference detector for detecting phase information, a phase error detector for subtracting a quantized value with a step size of (2π/K) of the phase difference from the phase difference, and an output of the phase error detector. A smoothing low frequency filter,
a phase shifter that shifts the phase of the current received signal, the phase of the phase difference detector output, or the received signal one symbol before in accordance with the output phase amount of the low frequency filter output; and re-modulating and relaying the detected K-phase phase information, and at the same time, transmitting the output of the low-band transmitter to the transmitting side according to a separately determined method, and controlling the transmitting carrier frequency on the transmitting side. A repeater having the following characteristics is obtained. Next, the present invention will be explained in detail with reference to the drawings. First, we will discuss countermeasures against deterioration of delayed detection due to IF deviation. FIG. 1 is a block diagram of a conventionally known delay detector. In the figure, 2 is a delay circuit with a symbol period T, and 1 is a phase difference detector that detects the phase difference between the current received signal (terminal 203) and the received signal one symbol before (terminal 204). Terminal 100 is a received signal input terminal, and terminal 101 is a differential detection output terminal. In recent years, digitalization of demodulators has progressed, and there has been a demand for delay detection systems that utilize digital processing. In this case, the transmitted signal is subjected to multiplicative detection at almost the same frequency as the transmitted carrier to obtain a complex baseband signal x(t), which is converted into a complex digital signal X(kT) (k= (integer) and perform delayed detection through digital processing. FIG. 2 shows a block diagram of the product detector 3. In the figure, 35 is an oscillator with the same frequency as the transmission carrier, 30 and 31 are double balanced mixers (multipliers), 32 is a π/2 transfer shifter, 3
3 and 34 are low frequency converters, and 36 and 37 are A/D converters. Since the real part and imaginary part of the complex digital signal X (kT) are outputted from the output terminals 102 and 103, respectively, both terminals will be collectively referred to as a terminal 104. FIG. 3 is a block diagram showing a circuit that receives a complex digital signal X (kT) and performs delayed detection through digital processing, and the configuration is exactly the same as that in FIG. 1. 2
is a delay circuit, in this case using digital memory. 1 is a phase difference detector which obtains the current received signal X(kT) and the received signal X((k-1)T) one symbol before from terminals 203 and 204, and 1) T) is its complex conjugate value X ^*
((k-1)T) (only inverting the polarity of the imaginary part) is obtained from 11 conjugate circuits (circuits whose output is x _R -j _XI when the input is x _R +j _XI ), and the The phase change of F→F→=X(kT)×X ^* ((k-1)T) is obtained using the complex multiplier 10. A vector F→ is output to the output terminal 105. The vector F→ and the transmission code change are identified as follows.

[Table] →
However, arg〓F〓 indicates the argument of vector F from e ^jo .
Figure 4 illustrates the above table. As an identification circuit corresponding to this figure, a read-only memory (ROM) can be used which uses the complex digital value F→ of the terminal 105 as an address and outputs the phase change identification value of the corresponding transmission code. FIG. 5 is a block diagram of an embodiment of a carrier offset absorption type delay detector. Reference numbers 1 and 2 in the figure are the same as 1 and 2 in FIG. 1, respectively. When a 4-phase PSK wave _is input to the circuit shown in FIG.
1, 2) are obtained. Here, only △ω _IF was considered as a factor in the deterioration of delayed detection. 4 in Figure 5 is the above formula △ω _IF
This phase error detector detects only T and consists of an identification circuit 40 shown in FIG. 4 and a phase difference detector 1' which obtains the phase difference between its input and output signals. Above θo(t)
Since the value of the first term on the right side is the same as the output of the discrimination circuit 40, the output θo of the phase difference detector 1' becomes θe=π/2l+△ω _IF・T−π/2l=△ω _IF T . If the received signal is in a distortion-free and noise-free state, the obtained θe corresponds to a steady phase error, but generally there is distortion and noise in the received input signal. Therefore, the steady phase error must be found from the average value E{θe(t)} of θe(t). The low-pass wave generator 50 performs the averaging. The polarity of E{θe(t)} thus obtained is inverted by the inverter 51 and becomes −E{θe(t)}.
E{θe(t) between X(kT) and X((k-1)T)
}
Since there is a steady phase error of
It turns out that it is sufficient to rotate the phase of (kT) by -E{θe(t)}. Therefore, it is sufficient to rotate (add) the phase by the inverter output value using the phase shifter 52. As a result, block 52,
It can be seen that 1, 40, 1', 50, and 51 constitute a first-order feedback control system. In this case, △ω _IF T
In order to make θe(t) equal to θe(t), the feedback control system must include a perfect integrator in the loop. For this reason, it is desirable that the low-pass wave generator 50 be a perfect integrator. Block 5 in FIG. 5 is a block diagram drawn on a phase basis, but on a complex digital value basis, block 5 becomes as shown in FIG. 6. That is, the output of block 1' is a vector e ^j 〓 ^e(t) .
Therefore, the imaginary part extractor 55 extracts only the imaginary part of e ^j 〓 ^e(t) = cosθe (t) + jsinθe (t), and sinθe
(t) θe(t) is extracted, this output is integrated by 50 real input integrating circuits, and the output is inverted by an inverter to become −E{θe(t)}. 54 is ROM
outputs e ^-jE {〓 ^e(t) }. 53 is a complex multiplier,
The input signal X (kT) is multiplied by e ^-jE {〓 ^e(t) }, and
The phase of (kT) will be rotated by -E{θe(t)}. As described above, by using a delay detector as shown in FIG. 5, deterioration of the delay detection circuit can be absorbed. Next, let us consider the case of group demodulation of regenerative relay for sanitary purposes. In this case, the transformer multiplexer technology used for analog-to-digital conversion of terrestrial telephone lines, that is, conversion from FDM lines to TDM lines, is promising.
This technology allows the FDM line to handle the SSB signal of one telephone line.
By taking advantage of the fact that they are arranged regularly at 4KHz, the group band signal can be sampled at high speed.
A digital baseband signal for each channel is obtained by a filter bank using FFT (Fast Fourier Transform). Figure 7 shows this situation. 700 is a transformer multiplexer with multiple SCPC (Single Channel) input terminals.
An FDM input is applied in which the waves are aligned with a carrier spacing of approximately ΔB. From this signal, a digitized complex baseband signal of each channel is obtained from the output terminal 108. At this time, each SCPC wave of the FDM signal is regularly △B
If they are lined up with carrier spacing of
The baseband signal of each channel obtained at 08 has no frequency offset. In the case of sanitary SCPC, the RF is in the 4 to 30 GHz band and its frequency stability is not very high, so it cannot be expected that the carriers transmitted independently by each station will be lined up regularly. Therefore, a frequency offset occurs in the baseband signal of each channel. This frequency offset can be demodulated without any problem by using the delay detector described above. However, since a transformer multiplexer is a type of bandpass filter bank, the input signal carrier shifts from the center frequency of this bandpass filter, causing odd symmetrical frequency distortion. As a result, the baseband signal of each channel becomes full of orthogonal interference. A reliable way to absorb this is to control the carrier frequency on the transmitting side. As this control signal, there is a low frequency filter output of the delay detector shown in FIG. This output outputs a value proportional to △ω _IF , so this value is sent back to the transmitting side, and by controlling the transmitting carrier frequency according to this value, the center frequency of the bandpass filter and the carrier frequency can be adjusted. can absorb deviations. Moreover, for this reason, there is no need for a special frequency offset detector or the like on the receiving side. FIG. 8 is a block diagram of one embodiment of the present invention. 30
0 is an antenna of a repeater, and a received signal is guided to a terminal 107 by a circulator 301. 250 is a bandpass filter for the channel desired to receive. 3 indicates the product detector shown in FIG. Here, 250 and 3 (150) may be considered as one output of the transformer multiplexer shown in FIG. Reference numeral 9 denotes a delay detector shown in FIG. 5, the detection output of which is outputted to a terminal 101, and the output of the low frequency detector 50 is outputted to a terminal 106. 6 is a transmitting section of the repeater, and the detection output and the output of the low frequency wave filter 50 are added to the transmission buffer 61, and in this buffer, the detection output 90 and the low frequency wave filter 50 are added as shown in FIG. The outputs are arranged in the order of output 91. This data is sent by the next transmitter 62 to the transmit antenna 300. Next, on the transmitting side, 302 is an antenna, 30
3 is a circulator, and the received signal is sent to the receiving section 8, demodulated by a demodulator 80 as data, and a demultiplexer 81 separates and extracts the low frequency filter output value from the received data. Reference numeral 7 denotes a transmitter which raises the output of the intermediate frequency band transmitter 70 to the RF band using an RF band oscillator 72 and guides it to the antenna 302.
At this time, the frequency of the oscillator 72 is controlled in accordance with the low frequency band output from the demultiplexer 81. It should be noted that it is not necessary to send back the low frequency device output information very frequently, and the amount of data for this is negligible compared to relay data. Note that in this embodiment, the demodulated and reproduced information may be retransmitted anew in the SCPC format, or may be retransmitted through multiple channels together in the TDM format. FIGS. 10 and 11 are block diagrams of another embodiment of a carrier offset absorption type delay detector. Components in each figure correspond to like reference numerals of components in FIG. Figures 5 and 10
The difference between this figure and FIG. 11 is the position of the phase shifter 52. Since the phase difference detector 1 is a subtracter that detects a phase difference, even if the phase shifter 52, which also works as a simple adder, is moved to its output side (the first
(Fig. 0) Furthermore, even if the polarity is changed (omitting the inverter 51) and the input terminal is transferred to another input terminal (Fig. 11), exactly the same function can be realized. As described above, according to the present invention, it is possible to provide a repeater that can perform group demodulation of a plurality of SCPC waves with uneven carrier spacing without significant deterioration.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional delay detection circuit, FIG. 2 is a block diagram of a multiplicative detector for demodulating by digital processing, and FIG. 3 is a block diagram of a delay detection circuit for complex digital signals. Figure 4 shows
Figures 5 and 6 are diagrams for explaining the contents of a detection output identification circuit for 4-phase PSK, and Figures 5 and 6 are block diagrams for explaining a carrier offset absorption type delay detector. Figure 7 is a diagram for explaining a transformer multiplexer. FIG. 8 is a block diagram showing an embodiment of the present invention, and FIG. 9 is a diagram showing a transmission data matrix of a repeater according to the present invention. 10th
11 are block diagrams for explaining another example of a carrier offset absorption type delay detector. In the figure, 1... Phase difference detector, 2... Delay circuit, 3... Multiplier detector, 4... Phase error detector, 9... Carrier offset absorption type delay detector, 50... Low frequency Wave device, 51...Inverter,
52... Phase shifter, 61... Transmission buffer,
62... Transmitter, 70... Intermediate frequency band transmitter, 7
2... Oscillator, 80... Demodulator, 81... Demultiplexer, 250... Band pass filter, 3
00,302... antenna, 301,303...
A circulator, 700 . . . a transformer multiplexer is shown, respectively.

Claims (1)

[Claims] 1. In a repeater that demodulates K-phase phase modulation information, re-modulates it using a separately determined modulation method, and transmits the signal, detects the phase difference between the current received signal and the received signal one symbol before. a phase difference detector that detects K-phase phase information by detecting K-phase phase information; a phase error detector that subtracts a quantized value using (2π/K) of the phase difference as a step size from the phase difference; a low-pass filter for smoothing the output of the detector, and a low-pass filter for smoothing the phase of the current received signal, the phase of the phase difference detector output, or the phase of the received signal one symbol before. It includes a phase shifter that shifts the phase according to the output phase amount of the output, and at the same time re-modulates and relays the detected K-phase phase information, the low-frequency shifter output is transmitted to the transmitting side using a separately determined method. A repeater characterized in that it transmits signals back to the transmitter and controls the transmitting carrier frequency on the transmitting side.