JPH1084369A - Terminal device and line access method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To prevent a center station from allocating channels when accessing and communicating with one of a plurality of channels, and to provide a data collision probability between terminal devices. It is an object of the present invention to enable communication with less traffic. SOLUTION: A channel is randomly selected, a monitoring tuner is set for the selected channel, and a signal strength is monitored. When the signal strength is equal to or lower than a predetermined value over a monitoring period measured by a timer, the channel is used. If it is confirmed that the transmission is not performed, the frequency of the modulator is set to the frequency and the transmission is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminal device for performing data communication and a line access method suitable for the terminal device. More specifically, the present invention relates to a method in which a plurality of terminal devices use one of a plurality of channels. The present invention relates to a multi-channel access-type terminal device for performing communication by means of communication and a line access method thereof.

[0002]

2. Description of the Related Art When a plurality of terminal devices communicate using one channel from among a plurality of channels, a line access method is TDMA: Time Division Multiple.
Access (time division multiple access) method or FDMA: Freque
ncy Division Multiple Access
The method is common.

In the TDMA system, a plurality of channels are created by dividing a signal in the same frequency band by time, a transmitting side sends a signal in a time slot of a vacant channel, and a receiving side synchronizes with the channel. In the time slot (time slot). That is, in the TDMA system, a line is time-divided (fixed-length time slot allocation).
Is divided into a plurality of channels.

On the other hand, in the FDMA system, a frequency band is divided at a fixed frequency interval to create a plurality of channels, a transmitting side selects a vacant channel and sends a signal, and a receiving side transmits a signal to itself. A signal is extracted by identifying a certain channel by frequency. That is, in the FDMA system, a line is divided into a plurality of channels by a frequency band.

[0005] In either the TDMA system or the FDMA system, the center station must determine which terminal device uses which channel (time slot or frequency band) every time communication is performed. In addition, the center station needs to know the allocation status of all channels, and the load is concentrated on the center station. In addition, in order to allocate a channel to a terminal device, an exchange between a center station / terminal device for channel allocation / release is required.

Furthermore, in the case of the TDMA system, it is necessary to synchronize the time slot between the center station and the terminal device. For example, in a CATV (Cable Television) network or the like, the distance between the center station and the terminal device is limited. Since the distance is close to 100 km, there is a disadvantage that the propagation delay between the two must be calculated and synchronized.

In the case of the FDMA system, although there is no need for synchronization, if the terminal device secures a channel at the beginning of communication, the channel is occupied until the communication is completed (even if no data is actually flowing). However, there is a drawback that another terminal device cannot use the channel.

On the other hand, as a line access method in which the center station does not perform channel allocation, ATM: Asynchronous
There is a Transfer Mode (asynchronous transfer mode) method. In this ATM system, a line is divided into 53-byte cells in a time-division manner and transferred in cell units, and a terminal device that has obtained a cell sets the cell to “in use”. Instead of being allocated, communication is performed by acquiring an empty cell by itself.

[0009] In the case of the ATM system, although there is no load assigned to the center station, in a CATV network or the like, the distance between terminal devices becomes close to 200 km at the maximum, and cell propagation delay cannot be ignored. For example, the propagation delay of a coaxial cable is
It is on the order of 8 microseconds per km, and a propagation distance of 200 km will result in a 1.6 ms delay. On the other hand, if the transmission rate is 1.5 Mbps, a 53-byte cell is transmitted in 282 microseconds. As a result, even if one terminal device is using a cell, another terminal device located at a position distant from the terminal device recognizes the cell as an empty cell, and the two terminal devices simultaneously use the cell. That is, a collision will occur.

[0010] In Japanese Patent Publication No. 6-20189,
If all channels are in use when the terminal device starts communication, the center station retains the identification number of the terminal device that started communication, and when a free channel is created, the identification number is held. A method of notifying a terminal device having the above is disclosed. According to this method, the terminal device can secure the channel immediately after the channel becomes free, and the channel can be allocated first to the terminal device that has attempted to start communication first. However, this does not solve the disadvantage that the channel assignment load is concentrated on the center station.

Further, Japanese Patent Application Laid-Open No. 58-59648 discloses that a terminal device that secures a channel temporarily suspends and uses the channel when the channel is not used temporarily. It is disclosed that the channel is secured again afterwards. This method also does not solve the disadvantage that the channel allocation load is concentrated on the center station.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned technical problems, and when a center station accesses one of a plurality of channels to perform communication, a center station is provided. It is an object of the present invention to provide a terminal device and a line access method that do not perform channel assignment and enable communication with a low probability of data collision even when the distance between the terminal devices is long.

[0013]

In order to achieve the above-mentioned object, the present invention is configured as follows.

That is, the present invention randomly selects one of a plurality of channels, confirms that the randomly selected channel is not used by another terminal device on the transmission path, and uses the selected channel. The data is transmitted using the channel confirmed not to exist.

According to the present invention, the terminal device randomly selects one of the plurality of channels and transmits data after confirming that the channel is not used. Since line access without load can be realized and a channel is selected at random, the probability of data collision between terminal devices can be reduced.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION
A terminal device of a multi-channel access method for performing communication using any one of transmission channels formed of a plurality of channels, and a selection unit for randomly selecting one of the plurality of channels, A confirmation unit for confirming that the randomly selected channel is not used by another terminal device on the transmission path, and a transmission unit for transmitting data using the channel confirmed to be unused. According to the first aspect of the present invention, it is possible to realize line access without a channel allocation load by the center station and to select a channel at random, so that the probability of data collision between terminal devices is reduced. Can be reduced.

According to a second aspect of the present invention, the confirmation means includes:
Monitoring means for monitoring the signal strength of the randomly selected channel, and setting means for setting a monitoring period to be monitored by the monitoring means, wherein the signal strength of the randomly selected channel over the monitoring period is When the strength is equal to or less than the predetermined strength, the channel is confirmed not to be used by another terminal device on the transmission path. According to the invention of claim 2, the channel selected at random is monitored. Since monitoring is performed over a period, the probability of data collision between terminal devices can be further reduced.

According to a third aspect of the present invention, the selecting means includes:
When a channel selected at random is used by another terminal device on the transmission path, the other channel except the channel is selected at random, and according to the invention of claim 3, Since a new channel can be selected one after another without selecting a channel in use again, the time required to access the line can be reduced.

The invention according to claim 4 of the present invention is used when a transmission path is composed of a plurality of channels, and each terminal device on the transmission path communicates using one of the channels. A line access method, comprising: a selecting step of randomly selecting one of the plurality of channels; and confirming that the randomly selected channel is not used by another terminal device on the transmission path. And a transmitting step of transmitting data using a channel confirmed not to be used. According to the invention as set forth in claim 4, a line access without a channel allocation load by the center station is provided. Can be realized, and a channel is randomly selected, so that the probability of data collision between terminal devices can be reduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration diagram showing an example of a communication network including a terminal device according to one embodiment of the present invention.

This communication network is, for example, a CATV network for performing data communication, in which a center station 1 and a plurality of terminal devices 2 perform communication via a transmission line 3, and a line access method according to the present invention. Is applied when the terminal device 2 transmits data to the center station 1. In this embodiment, the description will be made by applying the FDMA method.

That is, the transmission line 3 is frequency-divided as shown in FIG. 2, and FIG. 2A shows an “up” frequency region for carrying data from the terminal device 2 to the center station 1. FIG. 2B shows a “downstream” frequency domain in which data is transmitted from the center station 1 to the terminal device 2, and these are hereinafter referred to as an uplink channel and a downlink channel.

The upstream channel is further divided into 100 frequency regions, each of which is assigned a channel number from "0" to "99". Each of the 100 frequency regions is referred to as an "uplink channel". Called.

The terminal device 2 transmits data to the center station 1 using one of the uplink channels. That is, data communication from the terminal device 2 to the center station 1 is performed using the FDMA method.

FIG. 3 is a schematic block diagram of the terminal device 2 according to the present invention. The terminal device 2 receives the distribution mixer 4 and the data transmitted by the center station 1 using the downlink channel. A receiving unit 5, a transmitting unit 6 for transmitting data to the center station 1 using an uplink channel, a memory 7 for storing data to be transmitted and received data, and a CPU 8 for controlling the operation of the entire terminal device And a bus 9.

FIG. 4 is a block diagram showing the internal configuration of the transmitting section 6 of the terminal device 2 in FIG.

The transmitting section 6 includes a control section 10 for controlling the operation of the entire transmitting section, a monitoring tuner 11 for receiving the frequency of the selected channel, and a monitoring section 12 for monitoring the signal strength from the monitoring tuner 11. , A transmitter 13 for encoding data, generating a transmission packet, and the like;
A modulator 14 for modulating a transmission packet at a frequency of an uplink channel designated by 0, and a random number generator 15 for generating a random number
And a timer 16 for measuring a monitoring period for monitoring the signal strength.

In this embodiment, in order to realize a line access without a channel allocation load by the center station 1 and to reduce the probability of data collision between the terminal devices 2, one of a plurality of channels is used. Transmitting data using a channel selected at random, confirming that the randomly selected channel is not used by another terminal device 2 on the transmission path 3, and confirming that the channel is not used. It is.

Also, the channel selected at random is
Confirmation of not being used by another terminal device 2 is performed as follows. That is, the signal strength of a randomly selected channel is monitored, and when the signal strength is equal to or less than a predetermined strength over a monitoring period set as described later, it is confirmed that the channel is not used. is there.

In transmitting data to the center station 1, the terminal device 2 first uses a random number generator 15 as a selecting means to set "0" to "99" corresponding to the channel number of the uplink channel. A random number in the range up to is generated, a channel is randomly selected, and it is confirmed as follows that the randomly selected channel is not used by another terminal device 2 on the transmission line 3.

A random number generator 15 as setting means generates a random number in a range between a minimum value and a maximum value of a predetermined monitoring period of the uplink channel to set a monitoring period. The monitoring unit 12 monitors the signal strength of the selected channel, and when the signal strength is equal to or less than a predetermined strength over the monitoring period measured by the timer 16, the control unit 10 that constitutes the checking unit performs the selection. It confirms that the assigned channel is not being used.

[0033] The transmitter 13 and the modulator 14 constituting the transmitting means transmit data using the channel which has been confirmed not to be used.

When a randomly selected channel is used, the control unit 10 controls each unit to randomly select a channel again and confirms that the selected channel is not used. This operation is repeated.

As described above, the terminal device 2 randomly selects a channel, confirms that the selected channel is not used by another terminal device 2, and transmits data using that channel. The station 1 does not need to perform channel assignment, thereby preventing concentration of load on the center station 1 and eliminating exchange between the center station / terminal device for channel assignment / release.

Furthermore, since channels are selected at random, for example, in a configuration in which channels are selected with regularity, there is a possibility that a plurality of terminal devices 2 may select the same channel and keep colliding. In the present invention, there is no such a possibility, and the probability of collision can be reduced.

When the signal strength of the channel selected at random is equal to or less than a predetermined strength over the monitoring period,
Since data is transmitted after confirming that the channel is not used, the probability of data collision can be further reduced as compared with a configuration in which a monitoring period is not provided. In particular, to avoid collisions due to propagation delays, this monitoring period
It is preferable to set so as to be larger than the maximum propagation delay derived from the maximum terminal distance of the communication network.

FIG. 5 is a diagram showing a packet format used for transmitting data using an uplink channel in the present embodiment.

The packet 17 has a unique word (U
W), synchronization byte (SYNC), terminal ID (TID),
It consists of a length field (LEN), a data part and a CRC.

The unique word (UW) is used for retrieving a packet in the center station 1 by repeating a predetermined bit pattern. Synchronous byte (SY
NC) is a byte having a predetermined bit pattern, and indicates that a byte after this is a meaningful field. The terminal device 2 has a unique terminal ID (TI
D) is assigned in advance, and the terminal ID of the packet 17
In (TID), the terminal ID (TID) of the terminal device 2 that is the transmission source of the packet is written. The length field (LEN) indicates the length of the data part, and the CRC is for checking a bit error from the start of the terminal ID (TID) to the end of the data part.

Next, the operation when the terminal device 2 having the above configuration transmits data to the center station 1 will be described with reference to the flowchart of FIG.

First, it is determined whether or not there is data to be transmitted in the memory 7 according to the transmission command (step 1). If there is data to be transmitted, the CPU 8 informs the control unit 10 in the transmission unit 6 of that fact. And the control unit 10 instructs the random number generator 15 to generate a random number in a range from “0” to “99” corresponding to the channel number of the uplink channel, and Select (Step 2).

The control unit 10 controls the monitoring tuner 11 based on the random number from the random number generator 15, and sets the receiving frequency of the monitoring tuner 11 to the frequency of the upstream channel corresponding to the random number (step 3).

The control unit 10 again instructs the random number generator 15 to generate a random number in a range between the minimum value and the maximum value of the predetermined monitoring period of the uplink channel, and sets the monitoring period at random (step). 4). As described above, it is desirable that the minimum value of the monitoring period is set to be larger than the maximum propagation delay derived from the maximum terminal distance of the communication network. Note that as another embodiment of the present invention, the monitoring period may be a fixed time.

The control unit 10 activates the timer 16 based on the random number from the random number generator 15 so as to time out when the monitoring period for the random number has elapsed (step 5).

The monitoring section 12 receives the signal from the monitoring tuner 11 and keeps informing the control section 10 whether or not the signal strength is equal to or higher than a predetermined strength, that is, whether or not there is a signal. If the control unit 10 is notified by the monitoring unit 12 that the strength is equal to or higher than the predetermined strength, that is, that there is a signal before the timer 16 times out (step 6), the control unit 10 determines that the channel is being used and determines that the channel is in use. Is stopped (step 10), and the process is restarted from step 2.

When starting over, the random number for channel setting in step 2 is set to a channel number that has not been selected before. In this way, by randomly selecting a channel number that has not been selected,
The time until the line can be accessed can be reduced without selecting the channel in use again. Note that as another embodiment of the present invention, a channel may be randomly selected from the already selected channels, including the selected channels.

If the timer 16 times out without the control unit 10 notifying the existence of a signal having a predetermined strength or more from the monitoring unit 12 (step 7), the control unit 10 can confirm that the channel is not used. As a result, the frequency of the modulator 14 is set to the frequency of the uplink channel (step 8).

Next, the control unit 10 notifies the CPU 8 via the bus 9 that transmission is possible. The CPU 8 generates a packet excluding a unique word (UW), a synchronization byte (SYNC), and a CRC from the data in the memory 7, further instructs the memory 7 and the control unit 10 to transmit, and the control unit 10 Upon receiving the instruction, the transmitter 13 is instructed to transmit.

As a result, the packet in the memory 7 is sent to the transmitter 13, and the transmitter 13 calculates and adds a CRC to the packet, encodes the packet, and then transmits the unique word (U
W) and a synchronization byte (SYNC).
Send to 4. The modulator 14 modulates the packet from the transmitter 13 at the frequency set in Step 8 and
To complete the transmission (step 9).

As described above, according to this embodiment,
Instead of the center station 1 controlling the line access of the terminal device 2, each terminal device 2 can compete and perform access control, thereby preventing the load from being concentrated on the center station 1. And exchange between the center station / terminal device for channel allocation / release is not required.

In this embodiment, since the FDMA system is used, the synchronization between the center station 1 and the terminal device 2 becomes unnecessary.

In the above embodiment, a channel is acquired for each communication. However, as another embodiment of the present invention, a channel may be acquired for each packet. In this case, it is possible to prevent one terminal device from continuously occupying the channel.

In the above-described embodiment, the channel waits until the monitoring period elapses before accessing the channel. However, as another embodiment of the present invention, access is made immediately without providing a monitoring period. In this case, although the probability of collision increases, the delay time until data transmission can be reduced.

Although the above embodiment is applied to the FDMA system, another embodiment of the present invention may be applied to the TDMA system. In this case, the frequency of the monitoring tuner is fixed. The signal strength of a time slot corresponding to a channel selected at random is monitored, and the monitoring period is a multiple of the period of the time slot.

[0056]

As described above, according to the present invention, one of a plurality of channels is selected at random, and data is transmitted after confirming that the channel is not used. No need for channel assignment,
As a result, it is possible to prevent concentration of the load on the center station, and it becomes unnecessary to exchange between the center station / terminal device for channel allocation / release.

Further, according to the present invention, since a channel is selected at random, the probability of data collision between terminal devices can be reduced, and a channel selected at random is monitored over a monitoring period. Therefore, the possibility of data collision between terminal devices can be further reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a communication network according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating frequency allocation in the communication network of FIG. 1;

FIG. 3 is a diagram illustrating an internal configuration of the terminal device of FIG. 1;

FIG. 4 is a block diagram of a transmission unit in FIG. 3;

FIG. 5 is a diagram showing a packet format from a terminal device to a center station.

FIG. 6 is a flowchart illustrating a transmission operation of the terminal device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Center station 2 Terminal device 3 Transmission line 6 Transmitting unit 10 Control unit 11 Monitoring tuner 12 Monitoring unit 14 Modulator 15 Random number generator

Claims (4)

[Claims] 1. A multi-channel access terminal device for performing communication using any one of a plurality of channels of a transmission line, wherein one of the plurality of channels is randomly selected. Selecting means for selecting, a confirming means for confirming that the randomly selected channel is not used by another terminal device on the transmission path, and data using the channel confirmed to be unused. A terminal device, comprising: transmitting means for transmitting. 2. The monitoring device according to claim 1, wherein the checking unit includes a monitoring unit that monitors a signal strength of a channel selected at random, and a setting unit that sets a monitoring period during which monitoring is to be performed by the monitoring unit. The terminal device according to claim 1, wherein when the signal strength of the randomly selected channel is equal to or less than a predetermined strength, the terminal device confirms that the channel is not used by another terminal device on the transmission path. 3. The method according to claim 1, wherein the selecting unit is configured to, when the randomly selected channel is being used by another terminal device on the transmission line, randomly select another channel other than the selected channel. 3. The terminal device according to 1 or 2. 4. The transmission path is composed of a plurality of channels,
A line access method in which each terminal device on the transmission path performs communication using one of the channels, and a selecting step of randomly selecting one of the plurality of channels, A confirmation step of confirming that the randomly selected channel is not used by another terminal device on the transmission path; and a transmission step of transmitting data using the channel confirmed to be unused. A line access method, comprising: