JPH0223748A - Radio communication system - Google Patents

Abstract

PURPOSE:To attain data transmission in an absolute phase modulation system by transmitting a modulation wave which is obtained by means of periodically inserting a non-modulated part into a phase modulated wave obtained by making transmission data into a frame and extracting the non-molduated part from a reception wave on a reception side. CONSTITUTION:A modulator 2 phase-modulates a code which is made into the frame in a non-modulated code F that is periodically inserted into transmission data Dr on a transmission side 1 and transmits it. On the other hand, the reception side demodulates the transmission modulation wave Rf in a demodulator 3 and a frame synchronization circuit 4 synchronizes the demodulation data by the non-modulated part F and outputs reception data DR which has been frame-synchronized to outside. The reception modulation wave Rf is sampled by the pulse PF of frame synchronization in a switch 5 so as to extract a non-modulated wave RfF. A filter 6 extracts the non-modulated wave RfF and a reference carrier C for demodulation is obtained, whereby it is supplied to the demodulator 3. Thus, a non-linear processing can be removed from the encoding processing of the reception wave, and data transmission in the absolute phase modulation system without differential modulation can be executed.

Description

[Detailed Description of the Invention] [Summary] Regarding a wireless communication system that transmits digital data by phase modulating it, it is possible to reduce the code error rate of data by making transmission using absolute phase modulation possible, and when code error correction is introduced. The aim is to create a wireless communication system that can improve demodulation performance during transmission, by periodically inserting non-modulated parts into the framed phase-modulated wave of the transmitted data, and on the receiving side, the frame of the demodulated data is synchronized at a constant rate. The received wave is sampled with periodic pulses, the unmodulated portion is extracted from the received wave, and filtered to reproduce the reference carrier wave, and the received wave is multiplied by the reproduced reference carrier wave and demodulated to obtain frame-synchronized received data. Configure to output.

Also, a signal that is periodically inserted into the framed phase modulated wave of the transmission data is a modulated wave with a certain pattern, and on the receiving side, the signal is driven by a pulse with a certain period to synchronize the frame of the demodulated data, and the signal is modulated in the certain pattern. The reference carrier wave is regenerated by inversely modulating the received wave with the output of a pattern generator that generates the same pattern for the wave.

[Industrial application field]

The present invention relates to a wireless communication system that transmits digital data with information added to the phase, such as multi-level quadrature amplitude varying ill Q A M and four-phase phase shift shifting 11QPSK, and particularly relates to a method for regenerating a stable reference carrier wave on the demodulation side. This invention relates to enabling transmission using absolute phase modulation, reducing the code error rate of received data, and improving demodulation performance when code error correction is introduced.

The demodulation method that receives a multilevel phase modulated wave and restores the transmitted data is generally a synchronous detection demodulation method that restores the original transmitted data by comparing the phase of the received signal with a reference carrier wave with no phase fluctuation. It is being carried out according to A reference carrier wave for this synchronous detection is regenerated from a received signal, and it is desired that the method of reproducing the reference carrier wave be small and stable. Further, normally, since there is phase uncertainty in the reproduced carrier wave, in order to avoid this, a differential encoder is provided on the transmitting side and a differential decoder is provided on the receiving side. In this differential encoder and decoder, when a code error occurs on the transmission path, the number of error pulses is doubled, causing deterioration of the received code error rate.

Furthermore, when introducing an error correction method that adds redundant bits to transmission data, there is generally a fixed upper limit on the number of error pulses that can be tolerated within a block for block codes and within a constraint length for convolutional codes.

Therefore, the error correction ability of the differential encoder/decoder when two consecutive code errors occur is significantly lower than the ability when a random code error occurs. Therefore, in order to prevent two consecutive pin errors from occurring in wireless communication systems that incorporate error correction, it is strongly desired to introduce a transmission system that uses phase modulation without using a differential encoder/decoder.

[Conventional technology]

Generally, multi-level quadrature amplitude modulation 1@QAM and four-phase phase shift keying Q
In phase modulated waves such as PsK and binary phase shift keying BPSK, carrier frequency components are not generated when the probability of occurrence of the code "do 0" in the transmitted data is guaranteed to be equal. Therefore, the phase modulation wave on the receiving side When reproducing a reference carrier signal from a modulated wave, it is necessary to perform nonlinear processing such as inverse modulation, frequency multiplication, and baseband multiplication (Costas) on the received signal.

Further, the order of nonlinear processing varies depending on the modulation method, and for example, in the case of four-phase PSK (QPSK), fourth-order nonlinear processing is required.

On the other hand, this nonlinear processing causes phase uncertainty in the reproduced reference carrier wave. For example, in the case of 4-phase PSK (QPSK), carrier waves with four types of phases are regenerated every 90 degrees,
The phase at which the signal is reproduced is undefined depending on the initial state.

If this phase uncertainty exists, demodulated data may be inverted or replaced, making it impossible to demodulate correct data. Traditionally, differential encoders/decoders are used to avoid this problem. A differential encoder/decoder is a device that, when phase modulating input transmission data, assigns a modulation phase so that the transmission information is placed on the difference between the phase of the previous carrier signal and the phase of the current signal. . For example, when the transmission information is "0", the carrier wave signal is sent out in the same phase as the previous phase, and when the transmission information is "1", it is sent out in the opposite phase, which is the inversion of the previous phase. .

Then, on the receiving side, the reverse operation is performed, that is, if the phase of the current received signal is the same as the previous phase, it is determined as "0",
If the phase is opposite, it is determined as "1".

In addition, in order to reduce the jitter (phase fluctuation) of the recovered carrier wave, a special code is inserted on the transmitting side at a ratio of, for example, 1 symbol in 32 symbols, so that the probability of occurrence of data with codes "0" and "1" is equal. I'm doing it like that. By doing this, the spectrum of the modulated signal is prevented from concentrating near the carrier frequency, thereby reducing the jitter of the reproduced carrier wave.

FIG. 6 is a block diagram of an example of a carrier recovery circuit according to the prior art. This figure shows a conventional example in the case of 16-value QAM, and FIG. 7 is an explanatory diagram for explaining its operation.

In the conventional reference carrier regeneration circuit shown in FIG. 6, the oscillation output of the voltage controlled carrier oscillator VCOIA is split into waves with a phase difference of π/2 by a splitter 2A, and the input is received by a multiplier 31^ and a multiplier 32A. The signals are multiplied by 16-level QAM IF large inputs and demodulated respectively. The demodulated outputs of the two series are each sent to a receiving filter 41.
Through A and 42A, the level is identified by four discriminators I to ■, and the signal is processed by an adder to form a phase detector with four stable points every 90 degrees, and the error signal of the detection output is The oscillation phase of the VCOIA is controlled through a loop filter 8^.

Furthermore, since the input signal is 16-value QAM, there are inconvenient signal points in a phase detector having four stable points every 90 degrees. The explanatory diagram of FIG. 7 shows a space diagram of signals in only the first quadrant, and the other three quadrants have the same form although not shown. As shown in Figure 7, there are four signal points in the first quadrant, but only the phase error from the two signal points indicated by diagonal lines is used, and the other two signal points have phase errors. In order to
, the timing is selected by the selection control signal obtained by rectifying at 52A, level discrimination at Vl, and addition.
The configuration is such that a nonlinear operation is performed to eliminate the frimbufrosop 7.

[Problem to be solved by the invention]

As mentioned above, the conventional carrier wave regeneration method requires nonlinear processing of the error signal of the phase detector using a selection control signal, resulting in large-scale circuitry and problems such as difficulty in adjustment. .

Although not shown in the figure, as mentioned above, if a differential encoder is installed on the transmitting side, a differential decoder is required on the receiving side. There is a problem of deterioration.

Furthermore, code errors caused by differential encoders/decoders have the property of occurring in two consecutive bits, so even if an error corrector such as a convolutional encoder is introduced, its effectiveness cannot be fully demonstrated. There is a problem.

An object of the present invention is to provide a wireless communication system that solves these problems.

[Means to solve the problem]

This problem is solved by transmitting data n on the transmitting side, as shown in Figure 1.
A periodic non-modulated part F is added to the phase modulated wave that frames t.
The receiving side samples the received modulated wave Rf with a frame synchronization pulse 11F, extracts the non-modulated part RfF from the received wave Rf, and filters it to reproduce the reference carrier wave C for demodulation. However, this problem is solved by the present invention, which detects and demodulates the received wave Rf using the reproduction reference carrier C and outputs the received data D and l.

In the principle diagram of FIG. 1 showing the configuration of the wireless communication system of the present invention, 1 is a system in which one non-modulated part F or a certain pattern P is inserted for every certain number (N-1) of transmission data D, and a certain number of This is a framing circuit that periodically outputs N framed data.

2 is a modulator that performs phase modulation to determine the phase of a carrier signal using the output code of the framing circuit 1 and outputs it as a transmission modulated wave Rf.

Reference numeral 3 denotes a demodulator that multiplies the received modulated wave Rf, which has received the output of the modulator 2, by a reproduction reference carrier C, which will be described later, performs synchronous detection, demodulates the signal, and outputs data.

4 performs frame synchronization on the output data of the demodulator 3 using its non-modulated portion F or constant pattern P, outputs the frame synchronized received data D7 to the outside, and simultaneously outputs the pulse pv used for frame synchronization. This is a frame synchronization circuit.

Reference numeral 5 denotes a switch that turns on/off the received modulated wave Rf according to a frame synchronization pulse INF output from the frame synchronization circuit 4, samples it, and outputs the sampled signal.

Reference numeral 6 denotes a filter that extracts only the unmodulated carrier wave Rf from the sampled received modulated wave Rf output from the switch 5.

The carrier wave Rfr output from the filter 6 is then supplied to the demodulator 3 as a reproduction reference carrier wave C.

[Effect]

In the present invention, the modulator 2 phase-modulates the non-modulated code F or the framed code of a fixed pattern P, which is periodically inserted into the transmission data ay by the framing circuit 1 on the transmitting side. The transmitting modulated wave Rf is received and demodulated on the receiving side, and frame-synchronized received data D+t is outputted to the outside, but the received modulated wave Rf is sampled by the frame synchronizing pulse INF at the switch 5 and is then demodulated on the transmitting side. When a modulated wave with a fixed pattern P is inserted in the framing circuit 1, the reference carrier wave C for demodulation is obtained by extracting the unmodulated wave RfF (after inverse modulation) with the filter 6, so there is no need for coding processing of the received wave. Linear processing can be eliminated. Therefore, there is no phase uncertainty in the reproduced reference carrier C for demodulation. As a result, data transmission using an absolute phase modulation method other than differential modulation becomes possible.

Therefore, with a differential encoder/decoder, the code error rate of demodulated data will not deteriorate, and even if an error corrector such as a convolutional encoder is introduced, its effect will not be insufficient. problem is resolved.

〔Example〕

FIG. 2 is a block diagram showing the configuration of the wireless communication system according to the first embodiment of the present invention, and FIG. 3 is a time chart for explaining its operation. Figure 5 is a block diagram showing the configuration of a wireless communication system according to a second embodiment of the present invention.

In the first embodiment shown in FIG. 2, the framing circuit 1 inserts a non-modulated portion F so that one frame is composed of 32 symbols and one symbol is non-modulated for every 31 symbols of the transmission data D. A non-modulating section (F
) is a framing circuit by insertion.

The modulator 2 is composed of, for example, a 4-phase PSK modulator, and as shown in the time chart of FIG.
A total of 1 frame is a 32-symbol code, which is a 1-symbol unmodulated code F, and a 4-phase P that determines the four phases of the carrier signal.
Demodulator 3 on the receiving side performs SK modulation and generates a transmitted modulated wave Rf.
Output to.

The demodulator 3 is configured with a 4-phase PSK demodulator corresponding to the modulator 2 on the transmitting side, receives the 4-phase PSK transmission modulated wave from the transmitting side, and filters the received 4-phase PSK modulated wave as described below. Vessel 6
Multiply the output of the reproduced reference carrier wave, perform synchronous detection, and demodulate.
The demodulated data is output to the frame synchronization circuit 4.

The frame synchronization circuit 4 consists of a frame counter that is reset every time it counts 32 symbol clocks for one frame, and a timing pulse is output once every 32 symbols to establish frame synchronization. When not, the sampling timing is swept. And the sampling timing is exactly the unmodulated part F of the received signal.
When the timing pulse pF matches, a correct demodulation operation is performed by the timing pulse pF at that time, and frame synchronization is established. Once frame synchronization is established, the sweep is stopped and normal synchronization protection operations are performed. In this embodiment, synchronization is established by sweeping a maximum of 31 symbols.

The frame synchronization circuit 4 establishes frame synchronization by detecting the unmodulated portion F from the output data of the demodulator 3, and outputs the frame-synchronized received data D to the outside. ■ Sampling pulse l) F of the time chart in Figure 3 used was switched to
Output to.

The switch 5 is composed of, for example, a diode switch,
■Turn on/off the received modulated wave Iff that received the transmitted modulated wave with ■sampling pulse, which is equal to the period of the frame synchronization pulse output from the frame synchronization circuit 4; ■sampled received modulated wave Rf.

is output to the filter 6.

The filter 6 is composed of, for example, a single-tuned band-pass filter, and extracts only the unmodulated carrier wave C from the sampled received modulated wave Rf output from the switch 5, and demodulates it as the reproduction reference carrier wave C. Supply to vessel 3. For the filter 6, if a problem arises in its fractional band, stability, tracking characteristics with respect to frequency changes, etc., a tracking type filter as shown in FIG. 4 can be used. The tracking type filter shown in Fig. 4 is a PLL (Phase Locked Lo
OP), and a zero-order hold circuit 62 is added to the output of a phase detector PD 61. The zero-order hold circuit 62 converts the phase error voltage of the phase detector PD 61 into the switch SW every time the sampling pulse p arrives.
It operates so that the previous error voltage continues to be held in the capacitor C while the pulse p disappears. As this sampling pulse p, the output pF of the frame synchronization circuit 4 mentioned above is used. Therefore, the fourth
The tracking type filter shown in the figure replaces the switch 5 and filter 6 shown in FIG.

As described above, in the first embodiment of the present invention shown in FIG. The receiving side receives the transmitted modulated wave Rf which has been subjected to 4-phase PSK modulation at step 2, samples the received modulated wave Rf at switch 5, and extracts it at filter 6 to obtain the reference carrier wave C for demodulation. Nonlinear processing can be eliminated in wave encoding processing.

Therefore, there is no phase uncertainty in the reproduced reference carrier C for demodulation. As a result, in this embodiment, data transmission using an absolute phase modulation method that does not use a differential encoder/decoder is possible, and the bit error rate of demodulated data deteriorates. Even if an error corrector is introduced,
There is no problem that the effect cannot be fully demonstrated.

Furthermore, in the second embodiment shown in FIG. 5, the one-symbol signal inserted into the 31-symbol transmission data D by the transmitting-side framing circuit 1 is not a non-modulated code, but a fixed pattern of modulated pulses P. is inserted as a frame synchronization signal. On the receiving side, a pattern generator 7 is provided which generates pulses with exactly the same pattern as the fixed pattern of frame synchronization signal P inserted on the transmitting side.
The inverse modulator 8 modulates the frame synchronization signal portion Rf of the received modulated wave Rf in the opposite direction by the output of the inverse modulator 8 .

As a result, an unmodulated signal is obtained at the output of the inverse modulator 8, and the unmodulated signal is sampled by the sampling switch 5 using the frame synchronization pulse pr from the frame synchronization circuit 4, thereby creating a frame of the received modulated wave. A recovered carrier wave C is obtained by extracting and filtering the synchronization pattern portion. Note that a trigger pulse for determining the start of the pattern generator 7 is also obtained from the frame synchronization circuit 4.

As described above, in the second embodiment shown in FIG. 5 as well, nonlinear processing can be eliminated in the code processing of the received wave, similarly to the first embodiment shown in FIG. Therefore, the reproduced reference carrier C for demodulation
has no phase uncertainty. As a result, data transmission using an absolute phase modulation method instead of differential modulation becomes possible, and differential encoders/decoders degrade the code error rate of demodulated data, and convolutional encoders and other error correction Even if a device is introduced, there is no problem in that the effect cannot be fully demonstrated.

〔Effect of the invention〕

As described above, according to the present invention, nonlinear processing can be eliminated from the code processing of the received signal, so that there is no phase uncertainty in the reproduced reference carrier wave for demodulation. As a result, data transmission using an absolute phase modulation method instead of differential modulation becomes possible, and the code error rate of demodulated data does not deteriorate due to differential encoder/decoder, and errors caused by convolutional encoders etc. If a corrector is introduced, the demodulation performance can be sufficiently improved.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram showing the configuration of a wireless communication system according to the present invention. FIG. 2 is a block diagram showing the configuration of a wireless communication system according to a first embodiment of the present invention. FIG. A time chart for explaining the operation of the embodiment, FIG. 4 is a block diagram of a tracking type filter having a different configuration from the filter of the first embodiment of the present invention, and FIG. 5 is a second embodiment of the present invention. FIG. 6 is a block diagram showing the configuration of an example wireless communication system. FIG. 6 is a block diagram of a reference carrier recovery circuit of a conventional wireless communication system. FIG. 7 is an explanatory diagram of the operation of the conventional reference carrier recovery circuit. In the figure, 1 is a framing circuit on the transmitting side, 2 is a modulator, 3 is a demodulator on the receiving side, 4 is a frame synchronization circuit, 5 is a sampling switch, 6 is a filter, 7 is a pattern generator, and 8 is a receiver. is the inverse modulator on the side.

Claims (1)

[Claims] 1. Transmit a modulated wave (Rf) that frames (1) transmit data (D_T) and performs phase modulation (2), receives the modulated wave on the receiving side, multiplies it by a reference carrier wave, and demodulates it. (3) In a wireless communication system that outputs received data (D_R) with frame synchronization (4), a non-modulated portion (F) is periodically added to the framed phase modulated wave of the transmitted data (D_T). Insert (1) and send,
On the receiving side, the received wave (Rf) is sampled (5) with a pulse (p_F) of a constant period to achieve frame synchronization (4) of the demodulated data, and the unmodulated portion (Rf_F) is sampled from the received wave.
) by extracting and filtering (6) the reference carrier (C
), multiplies the reproduced reference carrier wave (C) and received wave (Rf), demodulates (3), and outputs received data (D_R) with frame synchronization (4). . 2. The signal that is periodically inserted (1) into the framed phase modulated wave of the transmission data (D_T) is a modulated wave (P) with a certain pattern, and the receiving side performs frame synchronization (4) of the demodulated data. The received wave (Rf) is inversely modulated (8) by the output of a pattern generator (7) which is driven by pulses of a certain period and generates the same pattern as the modulated wave (P) of the certain pattern. (C) The wireless communication system according to item 1, characterized in that the wireless communication system reproduces.