JPH03117142A - Phase modulation and demodulation system - Google Patents

Abstract

PURPOSE:To improve the accuracy of phase estimate and phase correction by obtaining an optimum complex number base band signal at a synchronizing point based on plural complex number base band signals at preceding and succeeding several sample points with respect to the sample point of a synchronizing signal in response to the sampling point. CONSTITUTION:When a complex number base band signal is sampled from a reception signal synchronously with a synchronizing signal, the reception signal is sampled at a sampling frequency of a prescribed multiple of the synchronizing signal and an optimum complex number base band signal at the synchronizing point is obtained from plural complex number base band signals at preceding and succeeding several sample points of the sample point of the synchronizing signal based on the sampling point. Thus, the validity of the value per symbol is improved and the entire accuracy of phase estimate and phase correction is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to a phase keying demodulation (PSKI system), and particularly relates to the demodulation system.

[Prior Art 1 A demodulation method in the PSK method is described, for example, in the following document.

[4800/2400 standardized for general switched telephone networks]
bit/s modem Data communication in telephone networks V series Recommendation J (:1 JTT RED BOOK, Japan ITU
Murano/Kaikai Association "Disicle signal processing in information and communications" Shokodo P32-90 Hajime Namiki [Storage-Bulk demodulation method for wireless short packets] Journal of the Institute of Electronics and Communication Engineers Vol. 1. J67-B No, l pp
5461, 1984: Binsei - "QP for land mobile communication using linear square estimation method"
SK synchronous detection method” Journal of the Institute of Electronics and Communication Engineers Vol. 72-
B II No, 4 pp125-132.198
9 Honda, R. Kobayashi "Study on computational demodulation method of PSK signal" Institute of Electronics and Communication Engineers Technical Report C5-87-109pp57-
In order to demodulate the 64°987 PSK modulated signal and obtain transmission data,
A method is used in which a carrier wave is regenerated from a received signal and synchronous detection is performed using this. In this case, the carrier wave is used to extract the complex baseband signal from the received signal, but if the carrier wave is not reproduced as one that completely absorbs fluctuations (fading, etc.) in the received signal on the transmission path, the receiving side The complex baseband signal is obtained as a complex band signal on the transmitting side subjected to phase fluctuation. This is because a carrier wave regeneration circuit that is originally suitable for regenerating a carrier wave with a long time constant is used to estimate phase fluctuations that fluctuate very quickly. For this reason, various methods have been proposed to accurately guarantee the phase fluctuation of the received signal on the transmission path. For example, a method uses the linear square estimation method to estimate phase fluctuations due to facing from the received complex baseband signal and obtains phase synchronization. These methods include converting into temporary complex baseband signals, cutting out these signals as burst signals for several symbol rates, and sequentially performing phase estimation and phase compensation.

[Problems to be Solved by the Invention] In the above-mentioned methods, the value of the complex baseband signal obtained in synchronization with the synchronization signal is trusted, and the value of the complex baseband signal of the burst signal is determined from the complex baseband signal of several symbols. It estimated the phase shift (error) and performed phase compensation. However, phase fluctuations on the transmission path, such as phase fluctuations due to fading, are so severe that they occur even within one symbol, and the complex baseband signal sampled at the point synchronized with the synchronization signal is reliable. There is no guarantee, and phase error correction using only the complex baseband signal at this synchronization signal point was not accurate.

An object of the present invention is to eliminate the above-mentioned drawbacks and provide a phase modulation demodulation method that obtains an optimal complex baseband signal at a synchronization point.

[Means for Solving the Problems] The phase modulation method according to the present invention converts an image signal into binary data, modulates the data in accordance with phase information of a carrier wave, converts it into a passband signal, and transmits the signal to a transmission path. a transmission means for transmitting;
means for receiving the passband signal from a transmission path, multiplying the signal by a carrier wave, converting it into a complex baseband signal, detecting a synchronization signal from the received signal, and reproducing binary data from the complex baseband signal using the signal; In a phase modulation demodulation system having a transmission path and a receiving means having a means for correcting a phase shift received during conversion to a complex baseband signal, the received signal is sampled at a sampling period that is a predetermined times the synchronization signal, and one symbol is obtained. A complex baseband signal is obtained at a sample point synchronized with the synchronization signal within the rate and multiple sample points before and after it, and from the values of these multiple complex baseband signals, the complex baseband signal at the synchronization point within the l symbol rate is calculated. presume.

[Example] Hereinafter, the present invention will be specifically explained based on examples thereof.

In the present invention, when sampling a complex baseband signal from a received signal in synchronization with a synchronization signal, the received signal is sampled at a sampling frequency that is a predetermined times that of the synchronization signal, and synchronization is performed within one symbol rate based on this sambling point. The optimum complex baseband signal at the synchronization point is determined from the values of a plurality of complex baseband signals at several samples before and after the sample point of the signal.

Figure 1 shows the overall configuration of the PSK system. The transmission system is 2(i
-7- data is converted into phase information by an encoder lO, and the X and Y components of the phase angle are passed through transmission filters (waveform shaping filters) 12 and 14 with raised cosine characteristics to convert them into a complex baseband signal S. After that, the respective orthogonal carrier waves cos (wctl) are input to the modulator 16.

sin (wct) and add these to convert into a bus band signal S2, which is sent to the transmission line 18. By the way, in general, the basic equation of phase modulation is expressed as follows, when the sending signal is S (tl).

S (t) = sin (wcJ 〇(t)) = cos
θ(tl ・sin (wc41 + sinθ(L)
・cos(wc41(1) where cos e [t), sinθIt) is
These are X and Y components each corresponding to a phase angle θ, and they are transmitted while changing at a symbol rate 'r (transmission rate).

Wc is the angular frequency of the carrier wave. In reality, the X and Y components that change at the symbol rate T are input to a waveform shaping filter and transmitted, so the transmitted waveform is 5(t)=Σh(t-1T)・caSe(TI Si
n fwc-tl] knee 00 +Σh (t-j ・T) ・sinθ(T) ・co
s (wc tIJ knee (1) Wi= caSe (T)+, j Sinθ('r
). Here, h (tl is the impulse response of the waveform shaping filter, and Wi is the complex number representation of the X and Y components.

Now, the transmitted waveform transmitted in this manner is affected by amplitude fluctuations, phase fluctuations, and transfer functions of the transmission line in the transmission system, and is therefore received by the reception system as follows.

r(tl=a Re(ΣWi l gft-u) i+
(u-i41dul=-sen・exp(-jwo・t−jΔwo・t−jθ.11.
,,, (31, where g (tl is the transmission characteristic of the transmission system, △WO is the frequency offset, θ0 is the phase jitter,
a is the amplitude variation.

The processing on the receiving side is ΔWQ+θ. , a to find Wi from r(t). In reality, the transmission characteristics of the transmission system g it) are determined by the automatic equalizer 24 of the reception 1p1), and a is determined by the AGC 20 (Aul;
GajnControl). Therefore,
Here, only correction of phase fluctuations in the received signal due to fluctuations in the transmission path will be considered. For simplicity, it is assumed that the amplitude characteristics and the transmission characteristics of the transmission system have been corrected, and the receiving system demodulator 22 is
G(: 20 output signal with carrier wave sin (wctlc
os (multiply by wctl and receive filters 22a, 2
2b to demodulate into a complex baseband signal. The complex baseband signal is expressed as follows.

Z (t) = S (tl ・exp f−j△wo−
t-jOo), (4)=Sft)・exp(-,i
tΔ wo・shiten 〇. )) Here, 211;l is
The complex baseband signal obtained directly from the received signal, S
(tl is the complex baseband signal at the time of transmission. Therefore, ΔWo=frequency offset, θ.・If the phase jitter is estimated, Ht)・exp 1. JΔWot+Jθ. )
By calculating S ftl can be obtained.

In addition, if the synchronization signal is accurate, h (Tlsjnθ(T) can be obtained and the transmitted signal can be regenerated. Here, △Wo=
Frequency offset and θ. : Methods for estimating and correcting phase jitter include, for example, a method that uses a linear square estimation method to estimate and correct phase fluctuations due to fading from a received complex baseband signal, and a method that uses a carrier wave (reference wave) fixed in advance on the receiving side. A method may be used in which the received signal is converted into a provisional complex baseband signal using this signal, and these signals are extracted as burst signals of several symbol rates and subjected to sequential timing, phase estimation, and phase compensation.

By the way, these methods rely on the value of the complex baseband signal obtained in synchronization with the synchronization signal, and estimate the phase shift (error) in the burst signal from the complex baseband signal for the number of symbols. The phase correction section 28 performs estimation, and the phase correction section 26 performs phase compensation. but,
Phase fluctuations on the transmission path, such as phase fluctuations due to fading, are so severe that they occur even within one symbol, and there is no guarantee that the complex baseband signal sampled at the point synchronized with the synchronization signal is reliable. Therefore, correction of the phase error using only the complex baseband signal at the synchronization signal point is not accurate.

Therefore, in this embodiment, when obtaining a complex baseband signal within 1 symbol, multiple complex baseband signals are obtained at 1 within 1 symbol rate, rather than using only the complex band signal synchronized with the synchronization signal, and the synchronization is determined from these values. This is to find the optimal complex baseband signal at a point. For this reason, the received signal is sampled at a sampling frequency that is a predetermined times higher than the synchronization signal. The complex baseband correction section 32 (FIG. 4) performs the above processing.

FIG. 2 shows the relationship between the samples used in the complex baseband correction section 32 (to be described later) of the phase correction section 26 and symbol reto. The complex Besband signal at the synchronization point nT is Zn
T, data before and after ZnT-i.

It is expressed as ZnT+i. i is a number smaller than the number of samples N within the symbol rate. As an example, when calculating the average value of a complex baseband signal within l symbols and making it the complex baseband of that symbol point, m (m < N) samples before and after the point synchronized with the synchronization signal are used. The arithmetic operation shown in FIG. 3 is performed to calculate an arithmetic average, and this is used as a corrected complex baseband signal ZnT.

Note that here, an arithmetic average value is used as the complex baseband signal, but other weighted averages, moments, medians, etc. may also be calculated and used.

FIG. 4 shows an example of a circuit configuration for implementing the complex baseband correction section 32 of this example. Here, the 2m complex baseband signals of FIG. 2 output from the reception filter are sequentially stored in two 2m buffers B, .about.B.

When the synchronization signal SS is detected, the data D in the 2m buffers is read into the complex band signal correction processing section 32, and
The processing shown in FIG. 3 is performed.

That is, the phase correction unit 26 manually adjusts Znt to 100
1. Perform the calculation At of the averaging process and obtain f1021Pn
t is output to the determination section 30.

FIG. 5 shows the circuit configuration of a second embodiment of the complex baseband correction section according to the present invention. Here, 2m reception filters (F, -F
2b) is provided, and each time the synchronization signal (SS1) is detected, the complex baseband signal 21 output from these plurality of filters is extracted by the complex band signal correction processing section 34, and the processing 3 in FIG. 3 is performed. For the receiving filter group with different phases, use filters whose frequency characteristics have a raised cosine characteristic and a phase delay in which each filter output is delayed by exactly l samples.This is similar to the circuit shown in Fig. 4. Operationally they are exactly the same.

In order to demodulate the PSK modulated signal and obtain transmission data as described above, it is necessary to multiply the received signal by a carrier wave and extract a complex baseband signal by using a reception filter. In this case, if the carrier wave does not completely absorb fluctuations (fading, etc.) in the received signal on the transmission path, the complex baseband signal on the receiving side can be obtained as the complex band signal on the transmitting side that has undergone phase fluctuations. It will be done. For this reason,
Various methods have been proposed for accurately compensating for phase fluctuations on the transmission path of received signals. However, these methods rely on the value of the complex baseband signal obtained in synchronization with the synchronization signal, and perform phase compensation by estimating the phase fluctuation from the complex baseband signal for several symbols before and after it. . However, in phase fluctuations on a transmission path, such as phase fluctuations due to fading, fluctuations occur even within one symbol, and correction using only the complex baseband signal sampled at the point synchronized with the synchronization signal is difficult. was not accurate.

According to the first embodiment, when sampling a complex baseband signal from a received signal in synchronization with a synchronization signal, the first and second signals are sampled at a sampling frequency that is a predetermined times that of the synchronization signal, and this sampling This method calculates the optimal complex baseband signal at the synchronization point from the values of multiple complex baseband signals at several sample points before and after the sample point of the synchronization signal based on the point, improving the effectiveness of the value per symbol. However, the accuracy of phase estimation and phase correction as a whole is also improved.

[Effects of the Invention] According to the present invention, when sampling a complex baseband signal from a received signal in synchronization with a synchronization signal, the received signal is sampled at a sampling frequency that is a predetermined times that of the synchronization signal, and this sampling point is Based on this, the optimal complex baseband signal at the synchronization point is determined from the complex baseband signal values of several sample points before and after the sample point of the synchronization signal, and the effectiveness of the value per l symbol is This also improves the accuracy of phase estimation and phase correction as a whole.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the phase modulation demodulation method according to the present invention; FIG. 2 is an explanatory diagram of averaging processing for obtaining multiple complex baseband signals within one symbol rate according to the present invention; FIG. is a flowchart of the averaging process according to the present invention, FIG. 4 is a circuit diagram showing a first embodiment of the averaging process according to the present invention, and FIG. 5 is a circuit diagram showing a second embodiment of the averaging process according to the present invention. It is a circuit diagram. Main parts, tatami explanatory diagram B, ~B 2ffi-delay device F1 ~ F2 +++-1 reception filter 6 AGC circuit demodulator automatic equalizer, phase correction section, phase error estimation section judgment section, complex baseband correction processing section

Claims (1)

[Claims] 1. Transmitting means for converting an image signal into binary data, modulating the binary data in accordance with phase information of a carrier wave, converting it into a passband signal, and transmitting the same to a transmission path; The passband signal is received from the transmission path, the passband signal is multiplied by a carrier wave, converted to a complex baseband signal, a synchronization signal is detected from the received signal, and the synchronization signal is used to convert the complex baseband signal to the complex baseband signal. In a phase modulation demodulation method having a means for reproducing binary data and a receiving means having a means for correcting a phase shift received on a transmission line and during conversion to a complex baseband signal, Sample at twice the sampling period, calculate the complex baseband signal at the sample point synchronized with the synchronization signal within 1 symbol rate, and multiple sample points before and after it, and from the values of these multiple complex baseband signals, calculate the 1 symbol rate. A phase modulation demodulation method characterized by estimating a complex baseband signal at a synchronization point within 2. In the method according to claim 1, when estimating an appropriate complex baseband signal at a synchronization point from the plurality of complex baseband signals, the average, weighted average, median, moment, and maximum value of the plurality of values are estimated. , minimum value, etc., and the optimum value among them is set as the value of the complex baseband signal. 3. In the system according to claim 1, in order to extract the plurality of complex baseband signal points from the received signal in synchronization with the synchronization signal, a plurality of buffers for holding the output of the reception filter are provided, and the synchronization signal A phase modulation demodulation method that is characterized by comparing the contents of these buffers at timings synchronized with , and determining the optimal value of a complex baseband signal.