JP3129808B2 - Terminal device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminal device connected to a center device via a telephone line and transmitting data to the center device.

[0002]

2. Description of the Related Art When transmitting data to a telephone line, it is necessary to set the level of the transmitted data to a level determined by technical standards. As is well known, the transmission level has a maximum level of 0 dBm or less and an average level of -15 ± L dBm or less. Note that L is a line transmission loss.

[0003] When data is transmitted to a center device at a transmission level that does not satisfy such conditions, the transmitted data may not be properly received by the center device. No acknowledgment signal (ACK) indicating that has been properly received is not returned.

In a conventional terminal device, a line transmission loss of a telephone line to which the terminal device is connected is measured, and in consideration of the line transmission loss, a data transmission level that satisfies the technical standard is fixed. To transmit data at this fixed transmission level.

[0005]

As described above, in the conventional terminal device, line transmission loss is measured and data is fixedly transmitted at a data transmission level in consideration of the line transmission loss. Since the transmission loss varies depending on the telephone line to which the terminal device is connected, a complicated operation of measuring the line transmission loss for each telephone line to which the terminal device is connected and adjusting the data transmission level is required. In particular, this is a major obstacle when constructing a system for connecting a large number of terminal devices.

As a method for solving such a problem, a circuit for automatically detecting a current or the like of a telephone line, estimating a line transmission loss, and automatically adjusting a data transmission level can be considered. The incorporation of such a circuit in the device has the problems that the circuit configuration becomes complicated and the price increases.

[0007] The present invention has been made in view of the above,
An object of the present invention is to provide a terminal device capable of transmitting data accurately regardless of line transmission loss.

[0008]

In order to achieve the above object, a terminal device of the present invention is a terminal device connected to a center device via a telephone line and transmitting data to the center device. Transmission means for transmitting data to the center device via the communication device, reception determination means for detecting whether or not the center device has received the transmission data in response to transmission of data to the center device by the transmission means; When the reception determination unit detects that the transmission data has not been received, the transmission level of the transmission data is increased, and the ratio of the signal pause time to the signal transmission time of the transmission data is increased. Control means for controlling the transmission data to be retransmitted to the center device.

[0009]

According to the terminal device of the present invention, when it is detected that the data transmitted to the center device via the telephone line cannot be received by the center device, the transmission level of the transmission data is increased and the signal of the transmission data is increased. The ratio of the signal suspension time to the transmission time is increased, and the transmission data is retransmitted to the center device.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a terminal device according to one embodiment of the present invention. The terminal device shown in FIG. 1 is connected to a center device (not shown) via the telephone line 1, and transmits data to the center device and receives data from the center device.

The telephone line 1 is connected to an interface unit 2, to which a transmitting unit 3 is connected via a transmission level switching unit 4 and a receiving unit 6 is directly connected. The transmitting unit 3 is connected to the control unit 7 via the transmission time switching unit 5, and the receiving unit 6 is also connected to the control unit 7.

The transmission level switching section 4 is a section for switching the transmission level of the transmission data from the transmission section 3, and the transmission time switching section 5 is a section for switching the transmission time of the transmission data. More specifically, the transmission time switching unit 5 returns an acknowledgment signal (ACK) indicating that the data has been received from the center device, even though the data has been transmitted to the center device via the telephone line 1. In a case where the transmission level is not changed, when the transmission level switching unit 4 switches the transmission level of the transmission data to be increased under the control of the control unit 7, the ratio of the signal pause time to the signal transmission time of the transmission data is increased. And resend the transmitted data,
Thereby, the average level of the transmission data when the transmission level is increased is controlled so as to be the same as the average level of the transmission data before the transmission level is increased, so as not to exceed the average level in the above-mentioned technical standards. is there. Next, the operation will be described with reference to the timing chart shown in FIG. 2 and the flowchart shown in FIG.

The terminal device shown in FIG. 1 is connected to the center device via the telephone line 1, for example, as shown in FIG.
When transmitting the data "B, C", the transmission unit 3 of the terminal device transmits the data at the normal transmission time and the normal low transmission level by the transmission time switching unit 5 and the transmission level switching unit 4 under the control of the control unit 7. (Step 1 in FIG. 3)
10). For example, in the present embodiment, the signal transmission time T1 is 1
00 ms, a signal stop time T2 of 100 ms is selected as a normal transmission time, and -12 dBm is selected as a normal low transmission level. In this case, the average transmission power is half of the signal transmission power, ie, -12 dBm to 3 dBm.
As a result, the above-mentioned technical standard can be satisfied despite the line transmission loss and can be applied to any telephone line without level adjustment.

As described above, first, when the terminal device transmits data to the center device via the telephone line 1 at a normal transmission time and transmission level, for example, the signal level of the transmission data is large due to a large line transmission loss. Greatly attenuates,
The reception level cannot be secured in the center device,
If the line quality is poor and the noise level is high, the S / N at the center device is degraded, and as a result, the center device cannot correctly receive the transmission data from the terminal device,
The center device will not return an acknowledgment signal (ACK) to the terminal device. In such a case, in FIG.
Although the center device returns a negative acknowledgment signal (NAK) instead of an acknowledgment signal (ACK),
Such a negative acknowledgment signal (NAK) is not always returned, and there may be no response.

When transmitting data to the center device as described above, the terminal device transmits an acknowledgment signal (A) from the center device.
It is checked whether or not CK) has been returned, that is, whether or not the center device has succeeded in receiving (step 12).
0). This is determined by returning the negative acknowledgment signal (NAK) from the center device or by the center device not responding, as described above.

When an acknowledgment signal (ACK) is returned from the center device and it is determined that the center device has succeeded in reception, the process is terminated as shown in FIG. If the device has not succeeded in receiving, the terminal device controls the transmission level switching unit 4 via the control unit 7 to switch the transmission level of the transmission data to a high level, and controls the transmission time switching unit 5. Then, the transmission time is switched to the transmission time longer than the signal transmission time (steps 130 and 140). In this embodiment, -9 dBm is set as the high transmission level, and the signal transmission time T
3 is set to 100 ms, and the signal suspension time T4 is set to 300 ms. In this case, the average transmission power is の of the signal transmission power, that is, −15 dB which is 6 dBm lower than −9 dBm.
Bm, which satisfies the above technical standard regardless of the line transmission loss.

Next, the terminal device sets the transmission level to a high level as described above, and retransmits the transmission data for which the transmission time has been set long to the center device via the telephone line 1 (step 150). In this case, the center device receives a signal at a level 3 dBm higher than the initial low transmission level, so that the problems of insufficient sensitivity and S / N can be solved, data can be received accurately, and the center device receives a positive signal. A response signal (ACK) is returned to the terminal device. Therefore, the check of whether or not the center device has properly received the data (step 160) also succeeds in the reception. If the reception is not properly performed by the center device, an error occurs (step 170). In this case, retransmission may be repeated a plurality of times.

As described above, when data is retransmitted, the data transmission time increases to 400 ms, which is twice the normal time, but this is because data reception in the center device is performed accurately. In other cases, the data is transmitted in a normal short transmission time, so that there is no particular problem.

The setting of the transmission level and the transmission time at the time of data retransmission can be variously performed by considering the reception performance of the center device and the transmission time in terms of the system. For example, in the above-described embodiment, the high transmission level is set to -3.
In the case of dBm, the signal transmission time T3 is set to 100 ms.
The signal pause time T4 may be set to 1.5 s or more. In this case, the average transmission power is 1/16 of the signal transmission power.
Or less, ie, -1 to -12 dBm or lower, -1 dBm
It can be 5 dBm or less.

[0021]

As described above, according to the present invention,
When it is detected that the data transmitted to the center device via the telephone line cannot be received by the center device, the transmission level of the transmission data is increased, and the ratio of the signal pause time to the signal transmission time of the transmission data is increased. Then, since the transmission data is retransmitted to the center device, the data transmission level is increased and retransmitted even if the center device cannot properly receive the data due to a large line transmission loss, for example. Although the center device can receive data accurately, such an increase in the level can be performed without increasing the average transmission power due to the increase in the ratio of the signal transmission time, so that the technical standard can be satisfied. . In addition, the troublesome work of adjusting the data transmission level for each telephone line as in the related art is not required, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a terminal device according to an embodiment of the present invention.

FIG. 2 is a timing chart showing waveforms of the terminal device shown in FIG.

FIG. 3 is a flowchart showing the operation shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Telephone line 3 Transmission part 4 Transmission level switching part 5 Transmission time switching part 6 Receiving part 7 Control part

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) H04M 11/00-11/10 H04B 3/04 H04L 1/00

Claims (1)

(57) [Claims] 1. A terminal device connected to a center device via a telephone line and transmitting data to the center device, comprising: a transmitting means for transmitting data to the center device via a telephone line; In response to data transmission to the center device, reception determination means for detecting whether the center device was able to receive the transmission data, and reception determination means for detecting that the center device could not receive the transmission data, Control means for increasing the transmission level of the transmission data, increasing the ratio of the signal pause time to the signal transmission time of the transmission data, and retransmitting the transmission data to the center device. A terminal device characterized by the above-mentioned.