JPH0411143B2 - - Google Patents

Description

Detailed Description of the Invention [Summary] When a unique word non-detection signal is input to the delta M decoder, the delta M decoder receives 1's and 0's instead of pulses encoded by delta modulation.
A circuit that prevents clipping noise by applying alternating pattern pulses.

[Industrial application field]

The present invention relates to an improvement of a delta M decoder for meeting lines used, for example, in TDMA satellite communication systems.

In recent years, communication between a master station, a slave station, and each slave station is performed via a satellite repeater using TDMA (time division multiple access).

FIG. 4 is a diagram showing an example of a TDMA frame structure.

As shown in the figure, a super frame starts from, for example, 64 frames, and one frame starts from, for example, 10 basic frames.
One basic frame consists of a synchronization burst section and a data burst section for a master station and five slave stations.

Each of these synchronization burst parts includes a unique word (hereinafter abbreviated as UW) signal, and the slave station synchronizes its own UW with the master station's UW, and this synchronization
Extract the required data burst using UW.

Also, the meeting signal is 32 in the 10th basic frame.
However, the time slot for the master station's meeting signal is assigned to the odd-numbered frame in the super frame, and the slave station is assigned to the even-numbered frame, so the communication between the master station and slave stations is bidirectional. Communication is possible, but since the same frame is used between slave stations, the pre-talk method is used. Further, the meeting signal is converted into pulses (hereinafter referred to as encoding path) encoded by delta modulation (hereinafter abbreviated as ΔM).

Here, ΔM compares the current amplitude value of the analog signal with the quantized amplitude value one sample before, and when it is higher than the previous value, it is 1, and when it is lower, it is 0.
The analog signal is encoded using a binary code of It is requested.

[Conventional technology]

Figure 5 shows a block diagram of a conventional example of a ΔM decoder.
FIG. 6 shows an explanatory diagram of the operation of FIG. 5.

Therefore, the operation of FIG. 5 will be explained with reference to FIG. 6, where the numbers in FIG. 6 indicate the waveforms of the portions with the same numbers in FIG.

In Figure 5, a repeater on a satellite (not shown)
For example, a 24Mbps burst signal was received from
The slave station converts the signals into parallel signals of 3 Mbps x 8 columns, for example, and writes them into the random access memory in the speed converter 1. Each of these signals is read out at 4 Kbps, for example, and the 8 columns of parallel signals are converted to 32 Kbps by a parallel/serial conversion circuit P/S, and code pulses as shown in FIG. 5 are applied to the decoder 3.

Therefore, the pulse generator 3-3 detects whether the input code pulse is 1 or 0, and if it is 1, it will generate a pulse with a predetermined pulse width and positive amplitude (referred to as a step size), and if it is 0, it will generate a pulse with a negative step size. The pulse is superimposed on the previously sent pulse to obtain a waveform as shown by the left arrow in FIG.

Note that when the 1 and 0 consecutive detector 3-1 detects, for example, three consecutive 1's or 0's in the input code pulse, the detected pulse is changed to the step size controller 3-2.
In addition, the output of the pulse generator 3-2 is superimposed on the output of the pulse generator 3-3, and the step size is doubled, for example, to reduce errors with the actual analog signal.

The obtained waveform is shaped by a waveform shaping section 3-4 comprising an integrator and a low-pass filter, and an analog signal is sent to the outside.

[Problem that the invention seeks to solve]

However, when the synchronization is lost and the burst disappears, the code pulse applied to the pulse generator 3-3 becomes 0 continuously, but it does not immediately become 0, but as shown in Figure 6. , a waveform that decreases at a predetermined step size is generated by the waveform shaping section 3-4.
added to.

For this reason, sudden changes are extracted and sent to the outside, creating a harsh sound (called clip noise).
There is a problem that occurs.

[Means for solving the problem] The above problem is solved by means 1 for generating an alternating pattern of 1 and 0 in a delta M decoder for a meeting line used for TDMA satellite communication, as shown in Fig. 1.
4, when a pulse consisting of each data burst encoded by delta modulation or a unique word non-detection signal indicating that the unique word signal included in each data burst unit cannot be detected is input. is achieved by the clip noise prevention circuit of the present invention having a selection means 15 which selects pulses of an alternating pattern and applies them to the delta M decoder 3 during the input period of the data burst corresponding to the undetected unique word signal. resolved.

[Effect]

In the present invention, when a UW non-detection signal is input,
An alternating pattern is added to the ΔM decoder 3 instead of a code pulse. The signal obtained by ΔM decoding of this alternating pattern repeats increases and decreases in the same steps, so when it passes through the waveform shaping section 3-4, it becomes only a DC component and no clip noise occurs.

〔Example〕

The contents of the present invention will be specifically explained below with reference to illustrated embodiments. Note that the same reference numerals indicate the same objects throughout the figures.

Fig. 2 is a block diagram of one embodiment of the present invention;
The figure shows an explanatory diagram of the operation of FIG.

Therefore, the operation shown in FIG. 2 will be explained with reference to FIG.

In FIG. 2, a speed converter (not shown) converts an input burst signal into a burst signal of a predetermined frequency and outputs it, but a delay of about one frame occurs during this operation. This output is converted from parallel data to serial data via a parallel/serial conversion circuit P/S2 and is applied to the selector 5.

A UW detection unit (not shown) detects a UW signal from an input burst signal. When the UW detection signal indicating that the UW signal has been detected is applied to the selector 5, the selector 5 selects the output of the parallel/serial conversion circuit P/S2, and also indicates that the UW signal has not been detected. When the UW non-detection signal shown in FIG. Add.

Therefore, as shown in FIG.
However, when it passes through this circuit, a constant level of DC is obtained.

That is, since there are no abrupt change components, unpleasant clipping noise can be prevented.

Note that when the input burst signal is momentarily interrupted, the UW non-detection signal is applied to the selector 5, but as mentioned above, the input burst signal is delayed for a certain period of time in the speed converter (not shown), so the selector 5
It is possible to reliably cut out the burst signal corresponding to the UW undetected signal.

Also, when the error rate of the input burst signal is very bad, a UW non-detection signal is applied to the selector 5, so the corresponding burst signal is cut off by the selector 5 to reliably prevent clipping noise that occurs at this time. I can do it.

〔Effect of the invention〕

As explained in detail above, when synchronization is lost,
By adding the pattern 101010... to the ΔM decoder, only the DC component is output, so
This has the effect of preventing unpleasant clipping noise.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the principle of the present invention, Fig. 2 is a block diagram of an embodiment of the present invention, Fig. 3 is an explanatory diagram of the operation of Fig. 2, and Fig. 4 is a diagram showing an example of a TDMA frame structure. , FIG. 5 is a block diagram of a conventional example, and FIG. 6 is an explanatory diagram of the operation of FIG. In the figure, 2 is a parallel/serial conversion circuit, 3 is a ΔM decoder, 4 is a pulse generator, and 5 is a selector.

Claims (1)

[Claims] 1. A delta-M decoder for a meeting line used in a TDMA satellite communication system, comprising means 14 for generating an alternating pattern of 1's and 0's, and each data burst usually encoded by delta modulation. When a unique word non-detection signal indicating that the unique word signal included in each data burst unit could not be detected, the input period of the data burst corresponding to the non-detected unique word signal is input. a selection means 15 for selecting pulses of the alternating pattern and applying them to the delta M decoder 3;