JPS60119156A - Msk rectangular synchronization detecting circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an M S K (Minin+++m 5hi
Regarding an orthogonal synchronous detection circuit used for demodulating a ft Keying signal, the band of a loop filter is changed in accordance with the electric field strength.

PRIOR ART AND PROBLEMS Digitization of mobile radio voice communications, such as telephones, is lagging behind other fields. One of the reasons is that audio is ADM.
, ADPCM, etc., if encoded and transmitted, the band would be too wide and the existing FM channel separation (2
This is because the frequency exceeds 5KHz. However, since the MSK transmission method with a modulation index of 0.5, which is a type of phase continuous FSK, is efficient, it is possible to transmit using the existing FM channel.

In general, demodulation methods include (11-discriminator method, (2) delayed detection method, and (3) orthogonal synchronous detection method, each of which has its advantages and disadvantages.The orthogonal synchronous detection method (3) for MSK signals Japanese Patent Publication No. 55-73164
However, this method has the best static characteristics. However, this method has a locked loop (PLL) for carrier wave regeneration, which causes problems, such as multipath fading caused by reflections from buildings in the case of mobile radio, and rapid amplitude fluctuations (relay rate) when these signals are combined and received. There is a problem that PLL cannot follow up due to the occurrence of fading.

Since the methods of [f], ) and [2] do not have a closed loop, the time response to electric field fluctuations is fast, and they are convenient in cases where the electric field strength fluctuates sequentially, such as in mobile radio. However, when the electric field strength is constant, the error rate and other state characteristics are approximately 6 dB for the method (1,1), and approximately 3r]B for the method (2), compared to the method (3). Because it is inferior,
It would be ideal if measures against electric field fluctuations could be applied to the orthogonal synchronous detection method in step 3).

Purpose of the Invention The present invention attempts to improve the dynamic tracking characteristics of the loop filter used in the PLL of a quadrature synchronous detection circuit by changing the band of the loop filter according to the electric field strength. be.

Structure of the Invention The present invention relates to a synchronous (MSK orthogonal synchronous detection circuit composed of a general transmission wave regeneration circuit, a data regeneration circuit, and a clock regeneration circuit), which is used in a phase locked loop for carrier wave regeneration of the synchronous carrier wave regeneration circuit. The feature is that a control circuit is provided to control the bandwidth of the loop filter so that it is wide when the received electric field is high and narrow when the received electric field is low, and this will be explained in detail below with reference to the illustrated embodiment. Explain.

Embodiment of the invention FIG. 1 is a block diagram showing an embodiment of the invention, in which 1 represents M.
This is an SK quadrature synchronous detection circuit. This circuit] is composed of a synchronous carrier recovery circuit 2, a data recovery circuit 3, and a clock recovery circuit 4. Synchronization (general transmission wave regeneration circuit 2 has input MSK
1SK1 low transmission It has a phase-locked loop PLL for obtaining a synchronized reproduction general transmission wave (reference carrier wave). This P L
L is phase comparator 11.12, low pass filter (LP
F)14. ．． 15, phase comparator 16 (exclusive OR circuit), phase comparator (exclusive OR circuit) 17, loop filter 18a, L8b, voltage controlled oscillator (VCO) 19
, and provides the phase comparator 11 with a general transmission wave that is 90 degrees out of phase with the phase comparator 12 through a 90 degree phase shifter 13 . This is to obtain the sine synchronous detection output sin at the output of L P F 1.4 and the cosine synchronous detection output cos at the output of the LPF 15. These outputs sin, c
For example, if the P1-rate is 16 Kbps, the os has components of 3 Kbps each.

The fact that the demodulated output can be obtained by inputting the two synchronous detection outputs with a phase difference of 90 degrees to the data reproducing circuit 3 is detailed in the aforementioned Japanese Patent Laid-Open No. 55-73164, etc. Although omitted here, as a phase-locked loop, these two signals are multiplied and combined by the phase detector 16 to create a doubled sine wave signal sin 2θ, which is input to the phase comparator 17. There is a point. This phase comparator 1
The other input of 7 is the clock C from the clock recovery circuit 4.
It is K2. This clock CK2 is a cosine wave of the same frequency synchronized with the output of the phase comparator 16.

The reason for using this clock CK2 is to remove the modulation component included in the output of the phase comparator 16 and input only the phase error component of the general transmission wave to the loop filter 18a or]8b.The clock regeneration circuit 4 A clock CKI for stripe data reproduction is also created.

Loop filter] 8a or 1.8b band-limits the above error component and feeds it back to the VCO 19. 20 is a switch for switching either of these loop filters 18a, 1.8b according to the electric field strength; this part is related to the present invention.

That is, the loop filter +-82 has a wide band and is used when the electric field is high. On the other hand, the loop filter 18b has a narrow band and is used when the electric field is low. A switching signal CT L corresponding to the high or low received electric field is obtained from the electric field strength detection circuit 5.

This circuit 5 can utilize, for example, the carrier squelch detection circuit shown in FIG. The figure shows the outline of the receiver, 31
is an antenna, 32 is a high frequency amplifier that amplifies a signal in the 400 MHz band, 33 is a mixer, and 34 is a center frequency 4.
A 55 KHz intermediate frequency filter, and 35 an intermediate frequency amplifier with a limiter.

FIG. 3 shows static characteristics comparing the error rates of the loop filters 18a and 8b. Characteristic A (dashed line) using loop filter 1.8a with a wide band is loop filter 1.
It is worse than characteristic B (solid line) using 8b. However, since the band is wide, the response is good, and when the error rate is high and the electric field is high, the loop filter 18a is used to increase the response, and Q is applied so that it can follow rapidly changing fading. On the other hand, when the electric field is low and the error rate worsens, a loop filter 181) with a narrow band is used to prevent deterioration of line quality. One guideline for the switching levels of the loop filters 18a and 18b is a shield error rate in the range of 10 to 10. The one-dot chain line is an example of this, and is set to 10-4. However, when three or more types of loop filters are used, these switching levels are set in multiple stages.

A' and B' in FIG. 4 are dynamic characteristics, and C is a static characteristic (total characteristics including switching) shown in FIG. 3 for comparison. The dynamic characteristic A'B' of this orthogonal synchronous detection method is saturated at a certain error rate, and beyond this point it does not improve even if the receiver's curry health increases. This is due to fading accompanied by rapid level fluctuations, which causes AM-
This is because PM conversion occurs and a phase error occurs. When the fading frequency is 40 Hz and the 1iI transmission frequency is 400 MH2, the dynamic characteristics are saturated at an error rate of about 10. Therefore, if the loop filter is switched from 181) to 182 in the previous stage to widen the band, the characteristics will change from B' to A' of the filter 181), extending to a value better than 10. Therefore, by switching the loop filters 18a and 18b, the static characteristics of the error rate deteriorate slightly, but the dynamic characteristics are improved, which is the second aspect of the present invention.
This is an advantage.

FIG. 5 shows a concrete example of the loop filters 1.8a and 18b. In this example, resistors R1, R2 and capacitor C are shared by both filters, and resistor R3 is used (switch 2
0 off) constitutes a wide band loop filter 18a, and also bypasses the resistor R3 (switch 20 on) to configure a narrow band loop filter 1.8b. The constants of each element are, for example, R1-10 = Ω, R2 = IKΩ, R3 = 100
Ω, C-1 μF.

Effects of the Invention As described above, according to the present invention, the band of the loop filter of the phase-locked loop for carrier wave recovery of the quadrature coherent detection circuit that demodulates the MSK signal is controlled to be wide when the electric field is high and narrow when the electric field is low. Therefore, the followability is improved, the dynamic characteristics of the error rate are also improved, and it is possible to make the digitization of a car phone that is used while passing through a built-up area even more practical.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing a part of a receiver, and FIG. 3 is a block diagram showing an embodiment of the present invention.
FIG. 4 is a static characteristic diagram of the K-quadrature synchronous detection circuit, FIG. 4 is a dynamic characteristic diagram thereof, and FIG. 5 is a circuit diagram showing a specific example of a loop filter. In the figure, 1 is an MSK quadrature synchronous detection circuit, 2 is a synchronous 1 forwarding regeneration circuit, 3 is a data regeneration circuit, 4 is a clock regeneration circuit, 5 is a field strength detection circuit, PLL is a phase locked loop, 18a, 18b is a loop filter, and 20 is a changeover switch thereof. Applicant Fujitsu Limited Representative Patent Attorney Minoru Aoyagi

Claims (1)

[Claims] In an MSK quadrature synchronous detection circuit composed of a synchronous 1 general transmission regeneration circuit, a data regeneration circuit, and a black and vine regeneration circuit, the bandwidth of the loop filter used in the phase-locked loop for carrier wave regeneration of the synchronous IM transmission regeneration circuit. An MSK orthogonal synchronous detection circuit comprising a control circuit that controls the received electric field to be wide when the received electric field is high and narrow when the received electric field is low.