JPH0595312A - Radio transmission system - Google Patents

Abstract

PURPOSE:To prevent occurrence of aborted information by allowing a terminal station to increase a transmission probability in response to a transmission wait time so as to reduce the transmission wait time when a signal is sent to a center station with the transmission probability stored in advance. CONSTITUTION:A terminal station is provided with a means 15 receiving notice information and extracting it and with a means 18 storing a transmission probability P for transmission to a preset center station, and with a means 16 starting transmission with a stored transmission probability P when the notice information from the center station represents an idle incoming channel and awaiting the transmission with a probability (1-P) when the information indicates a busy channel. Moreover, the terminal station increases the stored transmission probability P in response to the length of a transmission wait time. The terminal station measures the transmission wait time to increase more the transmission probability as the transmission wait time is set longer thereby reducing the frequency of occurrence of the transmission waiting with the probability (1-P) and suppressing further extension of the transmission wait time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication system composed of a plurality of terminal stations and a central station which controls these terminal stations, and in particular, transmits signals from each terminal station to the central station by random access. Wireless transmission system.

[0002]

2. Description of the Related Art In a mobile communication system provided with a plurality of terminal stations and a central station, random access is used as a technique in which a large number of terminal stations multiplex a radio channel of the same frequency in a so-called uplink from the terminal station to the central station. There is a method. In this random access method, throughput is reduced due to collisions of transmission signals from a plurality of terminal stations, and therefore an access method is adopted which reduces collisions and improves throughput.

As a method corresponding to this access method,
An empty line control method can be mentioned. In this skyline control method, the central station detects whether the upstream channel is in use or is idle and notifies it to the terminal station, and when one terminal station is using the upstream channel, suppresses signal transmission from other terminal stations. This is a way to avoid signal collisions. However, even with this method, when the uplink channel changes from being in use to being empty,
Signal collisions are likely to occur because a plurality of terminal stations waiting for transmission simultaneously send signals. In order to avoid this signal collision, a certain probability value P (hereinafter P is referred to as a transmission probability) is stored in the terminal station in advance, and a large number of terminals when transmission prohibition is changed to transmission permission by the transmission probability P are stored. There is a method to reduce the simultaneous signal transmission from the station.

A P-persistent ICMA method, which is a typical method of the sky line control method considering the transmission probability, will be described below with reference to the drawings.

FIG. 3 shows a time chart of signal transmission between a central station and a terminal station in this wireless transmission system, and FIG.
3 is a flowchart showing a signal transmission operation of a terminal station.

The up signal from the terminal station to the central station and the down signal 31 from the central station to the terminal station are slotted, and the slot of the up signal and the slot of the down signal are synchronized. Transmission prohibition / permission information 33 for controlling the transmission of the terminal station is added to the end of each slot 32 constituting the downlink signal 31. The central station monitors the upstream channel in each slot 32, and as shown in FIG.
In the slot in which the upstream signal from B is detected, the transmission prohibition / permission information 33 of the same slot of the downlink signal is prohibited (B).
To prevent transmission of other terminal stations in the next slot to avoid signal collision. The terminal stations 2 and 3 which have generated the upstream information for the central station are prohibited from transmitting / permitting information 3 from the central station.
When 3 indicates that the transmission is prohibited, the transmission prohibition / permission information 33 is continuously monitored until the transmission is permitted (I). When the transmission is permitted, the terminal stations 2 and 3 determine whether to start transmission or wait for transmission in the next slot according to the stored transmission probability P. As a result, the terminal station 2 starts transmission with a probability of P, and the terminal station 3 waits for transmission with a probability of 1-P.

In this way, it is possible to avoid the simultaneous signal transmission of a plurality of terminal stations when the transmission prohibition is changed to the transmission permission, and it is possible to reduce the occurrence of signal collision. The terminal station 3 waiting for transmission waits for only one slot and then transmits the transmission prohibition / permission information 33 again.
To monitor. At this point, if transmission is permitted, processing according to the transmission probability P is performed as before, and if transmission is prohibited, the above processing is performed again from the beginning after a lapse of random time.

[0008]

In order to prevent congestion in radio signal transmission, it is preferable to set a threshold for the transmission waiting time, and terminal stations exceeding this threshold should discard the transmission of uplink information. As a result, in a system with a long maximum transmission delay, there is a problem that the number of terminal stations that discard uplink information increases and the reliability of the system deteriorates.

As described above, in the conventional system, the value of the transmission probability P is fixed even for a terminal station that has been waiting for a long transmission at a certain point, so that the transmission waiting is performed with the probability 1-P as before. The transmission waiting time was likely to be extended. As a result, the maximum transmission delay time of the system becomes long and there is a high possibility that the uplink information may be discarded.

The object of the present invention is to make the value of the transmission probability P variable according to the transmission waiting time, thereby shortening the transmission waiting time and shortening the maximum transmission delay time of the system,
It is to reduce the possibility of discarding upstream information.

[0011]

According to the present invention, a central station and a plurality of terminal stations are connected by a slotted wireless circuit, and the central station is used when an upstream channel from the terminal station is available. Means to detect whether or not
A means for notifying the terminal station of this detection result as notification information on the downlink channel is provided, and the terminal station receives the notification information and extracts it, and transmits to the preset central station. Means for storing the transmission probability P, and when the broadcast information from the central station indicates that the uplink channel is idle, transmission is started at the transmission probability P, and the broadcast information indicates that the uplink channel is in use. In this case, in the wireless transmission system including means for waiting for transmission with probability 1-P, the terminal station stores the transmission probability P
Is provided according to the length of the transmission waiting time.

The terminal station can be provided with means for counting the number of slots waiting for transmission and means for increasing the transmission probability P to be stored in advance by the number of slots counted by this means.

[0013]

The terminal station measures the transmission waiting time and increases the transmission probability P as the transmission waiting time becomes longer. As a result, the frequency of waiting for transmission with the probability 1-P is reduced, and it is possible to suppress further extension of the transmission waiting time. Therefore, it is possible to shorten the maximum transmission delay time of the system and reduce the possibility of discarding the uplink information.

[0014]

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

FIG. 1 shows the configuration of a terminal station according to an embodiment of the present invention.
FIG. 2 shows the configuration of the central station.

The terminal station includes an antenna 11, a transmission / reception distributor 12 that distributes a transmission signal and a reception signal, a transmission unit 13 that encodes and modulates uplink information and generates an uplink signal, and transmits the uplink information. Upstream information buffer 14 to be stored
A receiving unit 15 that demodulates and decodes the received downlink signal to extract downlink information; a terminal station control circuit 16 that determines transmission start according to transmission / reception timing control and transmission probability; The transmission waiting slot number counter 17 for counting the number of elapsed slots (hereinafter referred to as the transmission waiting slot number) and the transmission probability determination storage circuit 18 for determining and storing the transmission probability based on the transmission waiting slot number are provided.

Here, the feature of this embodiment is that the number of transmission waiting slots is counted by the transmission waiting slot number counter 17 and stored in the transmission probability determination storage circuit 18 as the number of transmission waiting slots increases. This is to increase the value of the transmission probability P.

Next, the configuration of the central station will be described. The central station is
An antenna 21, a transmitter / receiver / distributor 22 that distributes a transmission signal and a reception signal, a transmitter 23 that encodes and modulates downlink information to generate a downlink signal, and whether an uplink channel is in use or is idle. Upstream signal detection circuit 24 for checking
And a receiving unit 25 that demodulates and decodes the received upstream signal and extracts the upstream signal, and central station control that sets downlink signal transmission prohibition / permission information 33 according to the detection results of the transmission / reception timing control and the upstream signal detection circuit. Circuit 26
With. This central station configuration is the same as the conventional one.

Next, the transmission prohibition / permission information setting operation of the central station of this embodiment will be described. The transmission prohibition / permission information setting operation of this central station is the same as the conventional signal transmission time chart shown in FIG. The central station control circuit 26 causes the upstream signal detection circuit 24 to check whether the upstream channel is in use or free in each slot. If the slot is in use, the transmission unit 23 is instructed to set the transmission prohibition / permission information 33 at the end of the same slot in the downlink signal to the transmission prohibition (B). ) To order. In this way, the central station sets the transmission prohibition / permission information of each slot and notifies it to the terminal station.

Next, the transmission probability determining operation at the terminal station will be described. When the terminal station control circuit 16 detects that uplink information has occurred and is stored in the uplink information buffer 14, the terminal station control circuit 16 resets the transmission waiting slot number counter 17 to "0" at that time and activates the counter. .. Thereafter, the transmission waiting slot number counter 17 counts the number of elapsed slots until a transmission signal is transmitted. The transmission probability determination storage circuit 18 is provided with a table showing the correspondence between the transmission wait slot number and the transmission probability value P shown in Table 1 below, and each time the transmission wait slot number counter 17 updates the transmission wait slot number. The transmission probability value P corresponding to is determined and stored. The above-described transmission probability determination operation is performed immediately after the slot is transferred, and the transmission probability determination operation is completed before the transmission probability value P is used in the signal transmission operation.

[0021]

[Table 1] Next, the signal transmission operation from the terminal station will be described. The operation of the terminal station at this time is similar to the signal transmission operation of the conventional example shown in FIG. That is, when the terminal station control circuit 16 detects that uplink information has occurred and that information has been stored in the uplink information buffer 14, the receiving unit 15 receives the downlink signal from the central station and prohibits transmission of the downlink signal. The permission information 33 is taken out. If this information is transmission prohibition, the transmission unit 13 is instructed to prohibit transmission of uplink information, and thereafter, the transmission prohibition / permission information 33 is continuously monitored until the transmission is permitted. When the transmission is permitted or the transmission is changed from the transmission prohibited to the transmission permitted, the transmission waiting value or the transmission start is determined based on the transmission probability value P after the completion of the transmission probability determining operation stored in the transmission probability determining circuit 18. ,
When it is determined that the transmission is started, the transmission unit 13 is instructed to start the transmission in the next slot, and the transmission unit 13 transmits the uplink information. When it is determined that the transmission is to be waited, the transmission of the uplink information to the transmission unit 13 is prohibited, and the transmission prohibition / permission information 33 of the next slot is monitored. When the transmission is permitted, the operation according to the transmission probability value P is performed again. When the transmission is prohibited, the above operation is repeated from the beginning after waiting a random time.

As described above, in Table 1, the transmission probability value P is set to be larger as the number of transmission waiting slots is larger, so that the transmission probability can be made larger for a terminal station having a longer transmission waiting time. As a result, it is possible to stochastically prioritize the transmission / transmission of the terminal station having a long transmission waiting time over the terminal station having a short transmission waiting time.

Although the table shown in Table 1 is used in this embodiment, any other table can be used as long as the transmission probability value P is corresponding to a larger number of transmission waiting slots.

[0024]

As described above, according to the present invention, the transmission probability P becomes higher as the terminal station has a longer transmission waiting time. Therefore, the frequency of waiting for transmission with the probability 1-P can be reduced and the transmission waiting time can be further extended. Can be suppressed. As a result, it is possible to reduce the possibility of exceeding the transmission waiting time threshold value and discarding the uplink information, and to use another table.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a terminal station according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a central station of an embodiment of the present invention.

FIG. 3 is a signal transmission time chart of a conventional terminal station.

FIG. 4 is a time chart of a signal transmission operation of a conventional central station.

[Explanation of symbols]

 11, 21 Antenna 12, 22 Transmission / reception distributor 13, 23 Transmission unit 14 Upstream information buffer 15, 25 Reception unit 16 Terminal station control circuit 17 Transmission waiting slot number counter 18 Transmission probability determination memory circuit 24 Upstream signal detection circuit 26 Central station control Circuit 31 Downlink signal 32 Slot 33 Transmission prohibition / permission information

Claims (2)

[Claims] 1. A center station and a plurality of terminal stations are connected by a slotted wireless circuit, and the center station detects whether or not an upstream channel from the terminal station is available or in use. And means for notifying the terminal station of this detection result as notification information on the downlink channel, the terminal station receiving and notifying this notification information, and transmitting to a preset central station. And a means for storing the transmission probability P for performing the above, and when the broadcast information from the central station indicates the availability of the uplink channel, the transmission is started at the transmission probability P, and the broadcast information indicates that the uplink channel is in use. In the wireless transmission system including means for waiting for transmission with probability 1-P, the terminal station increases the stored transmission probability P according to the length of transmission waiting time. Radio transmission system characterized by comprising a. 2. The wireless transmission system according to claim 1, wherein the terminal station comprises means for counting the number of slots waiting to be transmitted, and means for increasing the transmission probability P to be stored in advance by the number of slots counted by this means.