JP2928623B2 - Point-multipoint transmission method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a point-multipoint transmission system suitable for use in a star-type or bus-type transmission line composed of an optical fiber and a multi-branch coupler.

[Prior Art] Points such as a star type composed of an optical fiber and a multi-branch coupler shown in FIG. 4 and a bus type shown in FIG.
To perform 1: N point-to-multipoint transmission using the multipoint transmission method, a time division multiplex method is used. The downlink signal from the main device 1 to the plurality of slave devices # 1 to #n does not cause any problem even in a general time division multiplexing system, but the uplink signals from the slave devices # 1 to #n are , The received signals may overlap and reception may not be possible. FIG. 6 shows an example in which there are three slaves, and an overlap occurs between slaves # 1 and # 2. In order to avoid this, non-signal sections (guard times) as shown in FIG. 7 are provided on both sides of the transmission signal of each slave device to prevent signal overlap.

[Problems to be Solved by the Invention] By the way, the guard time requires an interval longer than the maximum delay difference caused by the distance of each slave device, and the longer the distance difference, the longer the guard time is required. Therefore, there is a problem that the time during which a signal can be transmitted effectively is reduced by the guard time, and the transmission efficiency is reduced.

The present invention has been made in view of the above problems, and has as its object to provide a point-to-multipoint transmission system capable of reducing guard time and increasing transmission efficiency.

[Means for Solving the Problems] In order to solve the above problems, according to the first aspect of the present invention, point-to-multipoint transmission for exchanging signals between a main device and a plurality of slave devices is provided. In the method, a delay amount indication signal for instructing a delay amount for each slave device is provided in the downlink signal to each slave device, and a reference timing for the downlink signal is set in advance for each slave device, and each slave device is set. The apparatus transmits an uplink signal after a delay time corresponding to the delay amount instruction signal from the reference timing, and sets the delay amount instruction signal to indicate a predetermined position in the occupation time of the uplink signal, The slave device transmits only the specific pattern signal as an uplink signal at a timing according to the delay amount indication signal, and the main device measures a time position at which the specific pattern is detected. Thus, the delay amount of the slave device is recognized, and the value of the delay amount indication signal of the slave device is determined from the result.

The invention according to claim 2 is characterized in that the last timing of the downlink signal is used as the reference timing.

In the invention according to claim 3, the delay amount indication signal is a multiple of a clock cycle of the transmission signal, a multiple of a predetermined integer multiple of the clock cycle, or a predetermined integer multiple of the clock cycle. It is characterized by being expressed in multiples.

In the invention according to claim 4, in a case where the downstream signal and the upstream signal are bidirectionally transmitted by time division multiplexing, the slave device which transmits the upstream signal first after the completion of the downstream signal has the delay. It is characterized in that the value of the amount indication signal is set to the delay amount 0.

[Operation] According to the first, second and third aspects of the present invention, the time when the uplink signal from the slave device is transmitted according to the delay time according to the delay amount instruction signal and the specific pattern signal is received by the main device is measured. By doing so, the delay amount of the slave device can be accurately known, so that even if the guard time is shortened, the uplink signals do not overlap.

Further, in the invention according to claim 4, for a slave device that first sends an uplink signal after the termination of a downlink signal, the value of the delay amount instruction signal is set to 0 and the main device of the specific pattern signal Is measured.

Embodiment FIG. 1 is a timing chart for explaining an embodiment of the present invention. In this embodiment, the time division multiplexing of the downlink signal and the uplink signal using the same
This is an example when the present invention is applied to the M transmission system.

In the figure, three slave devices # 1 to #
delay amount indicating bits τ1, τ indicating the delay amount corresponding to n
2, τ3 are assigned. Each of the slave units # 1 to # 3 has its own delay amount indication bit τ1, τ assigned to this downlink signal.
2, .tau.3, and transmits an uplink signal at a timing delayed from the determined position (reference timing) of the downlink reception signal by the value indicated by the delay amount indication bit. The reference timing at this time may be any position as long as it is a fixed position of the downlink reception signal, but in the example of FIG. 1, the last timing of the downlink signal is used as a reference (corresponding to the invention of claim 2). Then, for example, the delay amount instruction value τ1 of the device # 1 = 0, the delay amount instruction value τ2 of the slave device # 2 = T1 + 2 (t1−t2), the slave device #
If the delay instruction value τ3 of 3 is set to τ3 = T2 + 2 (t2−t3), the guard time is reduced as shown in FIG. Note that Ti (i is an integer) is the occupation time of the signal of the i-th slave device, and ti is the delay time between the i-th slave device and the main device.

FIG. 2 shows a modification of the above embodiment, in which reference timings for downlink signals are set at different intervals for each slave device. The delay amount indicating bit indicates the amount of delay from each reference timing.
In the case of this example, the instruction value of the delay amount can be made smaller than that of the example of FIG. 1, so that the number of bits is reduced and the number of bits of the downlink signal can be reduced.

Further, the delay amount indication bit may be set as a multiple of a clock cycle used for transmission / reception of the transmission line code or a multiple of a positive integer of the clock cycle. In this case, there is an advantage that the delay timing can be easily and accurately recognized in the device by using only the counter. Further, when the delay amount indication value is set as an integral multiple of the clock cycle as a unit, the number of bits for indicating the delay amount is greatly reduced, and there is an advantage that the number of bits required for the downlink signal is reduced. However, in this case, a guard time is necessary because of a setting error shorter than the unit time, but if the unit is not extremely large, the guard time can be shortened, so that there is no practical problem (the invention of claim 3). Corresponding to).

As described above, the guard time can be reduced as in the case shown in FIG.

Although the above description has been made with the TCM transmission method, the present invention can be similarly applied to other methods, for example, a case where a downstream signal is transmitted using another line or another wavelength of an optical fiber.

Next, a method of measuring the installation position of each slave device or the amount of signal delay on the master device side will be described with reference to FIG.

FIG. 3 shows a case where measurement is performed for slave device # 2. First, main device 1 sets instruction value τ2 of the delay amount so as to be approximately at the center of the upstream signal occupation time of slave device # 2. In the slave device # 2, a synchronization pattern (a fixed bit pattern for synchronization and transmitted at the head of the normal signal) or a short signal of only a specific signal is used as a measurement signal (specific pattern), and the delay amount is determined. Indication bit τ2
Are transmitted according to the delay amount specified by the slave device (the slave device # in FIG. 3).
2). The main device 1 receives this uplink signal and detects a synchronization pattern or a measurement signal composed of a specific signal. Then, the delay amount for the slave device # 2 is recognized from the detection time.

By the way, the position of the measurement signal varies depending on the installation position of the slave device, that is, the signal delay amount. However, since the measurement signal consists of only a synchronization pattern or a specific signal, the guard time is equivalent before and after the occupation time of the slave device. Will be obtained. In the example shown in FIG. 3, the delay time instruction bit τ2 is set to correspond to the center of the occupation time, so that a guard time is obtained before and after the measurement signal by about の of the occupation time. Accordingly, by appropriately providing the value of the delay amount indication bit and the occupation time of the uplink signal, a sufficient guard time can be secured, and the delay amount can be measured favorably without overlapping the signal of the adjacent slave device. And using this measurement result,
The instruction of the delay amount in each of the communication systems described above can be set correctly, and communication with a small guard time can be performed.

Also, when the TCM transmission method (time division multiplexing communication method) is adopted and the measurement is performed on the slave device # 1 (slave device that sends out the first uplink signal after the downlink signal ends), the delay amount Even if the value of the indication bit is set to 0, there is no upstream signal before the slave device # 1, so that the guard time in the forward direction is automatically secured and good measurement is possible. At this time,
Since almost the entire occupation time of the signal of the slave device can be set as the guard time in the backward direction, it is possible to measure even a longer delay amount, that is, a slave device installed far away.

The measurement of the delay amount is generally performed prior to communication with the slave device.

4. Effect of the Invention As described above, according to the present invention, the point-
Guard time when multipoint transmission is performed by time division multiplexing can be reduced, and transmission efficiency can be improved.

Here, the delay amount instruction signal is set so as to indicate a predetermined position in the occupation time of the uplink signal, and the slave device transmits only the specific pattern signal at the timing according to the delay amount instruction signal. The main device measures the time position at which the specific pattern is detected, thereby recognizing the delay amount of the slave device, and determining the value of the delay instruction signal of the slave device from the result. Therefore, the optimum setting can be performed without knowing the installation position of the slave device.

Further, if the delay amount indication signal is represented by a multiple of the clock cycle of the transmission signal, a multiple of a predetermined integral multiple of the clock cycle, or a multiple of a predetermined integer multiple of the clock cycle, the slave device becomes complicated. It is possible to recognize the delay timing of the upstream signal with high accuracy without providing a simple circuit.

[Brief description of the drawings]

FIG. 1 is a timing chart for explaining one embodiment of the present invention, FIG. 2 is a timing chart for explaining a modification of the embodiment, and FIG. 3 is a description of another modification of the embodiment. FIG. 4 is a block diagram illustrating a point-multipoint star-type connection, FIG. 5 is a block diagram illustrating a point-multipoint bus-type connection, and FIG. FIG. 7 is a timing chart for explaining a conventional communication method, and FIG. 7 is a timing chart for explaining a conventional communication method when a guard time is provided. 1... Main device, # 1 to #n...

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04L 12/40

Claims (4)

(57) [Claims] In a point-multipoint transmission system for transmitting and receiving signals between a main unit and a plurality of sub units, a delay indicating a delay amount for each sub unit in a downlink signal to each of the sub units. Amount indication signal is provided, and a reference timing for the downlink signal is preset for each slave device, and each slave device sends an uplink signal after a delay time corresponding to the delay amount indication signal from the reference timing, The delay amount instruction signal is set to indicate a predetermined position in the occupation time of the uplink signal, the slave device sends only the specific pattern signal as an uplink signal at a timing according to the delay amount instruction signal, By measuring the time position where the specific pattern is detected in the main device,
A point-to-multipoint transmission method, characterized in that the delay amount of the slave device is recognized, and the value of the delay amount indication signal of the slave device is determined from the result. 2. The point-multipoint transmission system according to claim 1, wherein the last timing of the downlink signal is used as the reference timing. 3. The delay amount indicating signal is represented by a multiple of a clock cycle of a transmission signal, a multiple of a predetermined integral multiple of a clock cycle, or a multiple of a predetermined integer multiple of a clock cycle. The point-to-multipoint transmission system according to claim 1 or 2, wherein: 4. In a case where a downstream signal and an upstream signal are transmitted in a bidirectional manner by time division multiplexing, a slave device which first transmits an upstream signal after the completion of the downstream signal, delays the value of the delay amount indication signal. 4. The point-multipoint transmission system according to claim 1, wherein the amount is set to zero.