JPS6313540A - Channel selection method for mobile data terminal equipment - Google Patents

Abstract

PURPOSE:To minimize the probability of collision by giving information of polling number in each channel from a center side and allowing each terminal equipment to select a channel in a probability that the number of loads to each channel is equal to each other. CONSTITUTION:Terminal equipments T1-T4 make communication with a center respectively, two channels are used and equipments T1-T4 select any channel to send a connection request signal to start communication. Then polling is applied from the center to the terminal equipment and the terminal equipment sends a data in response to a polling signal. when plural terminal equipments send a connection request signal at the same time in the same channel with a polling number of 0, collision takes place and the connection request is not sent correctly. Suppose that the number of communication terminal numbers in the channel 1 is less than that in the channel 2, the channel 2 has many collisions. Thus, the traffic of a connection request signal in the access slot of each channel is made equal. Thus, the collision probability of the connection request signal is minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a channel selection method for mobile data terminals in a mobile radio data communication system in which a large number of terminals share a plurality of frequency channels.

(Prior Art) The ultimate purpose of communication is to enable each of the mobile hermits to own a terminal and to secure communications no matter where they are. However, in order to satisfy such requirements, a large amount of frequency resources are required. In order to provide mobile communication services to a large number of users in response to such demands, it is necessary to develop a mobile data communication system that can efficiently accommodate data terminals with extremely small amounts of data. . As an efficient method of accommodating terminals in such a system where the amount of traffic per terminal is small, there is a method of polling only terminals that are communicating. In this method, the center polls only the terminals that are communicating. There is also a method in which the center transmits a specific polling number for a terminal that wants to start a new communication, and the terminal can transmit a connection request signal only when that number is transmitted from the center. An example of such a method is the patent [Communication method] filed in July 1985 (Application number 6O-1).
62228). On the other hand, when the number of terminals becomes extremely large, the wireless channels that accommodate them must also be thick. For this purpose, there are two methods: one uses a wide-band, high-speed channel, and the other uses a plurality of narrow-band channels. The method of using a wideband channel is easy to control, but it also causes a lot of noise and requires a large transmission output from the terminal, which poses a problem when providing services to portable terminals. Therefore, the present invention describes a scheme using multiple narrowband channels. With multiple narrowband channels, how to select a channel becomes a major problem. Another big problem is at what timing to transmit to each channel. Such a multi-channel data communication system has not yet been put into practical use, but there is a teleterminal system at the research stage. In this system, each channel is divided into slots, and each terminal transmits to its own slot by random access. Regarding channel selection, the center side sends free channel information, and the terminal selects a channel and transmits based on that information. This method is described in detail in a research report on teleterminals published by the Teleterminal System Study Group of the Ministry of Posts and Telecommunications in August 1985.

(Problem to be solved by the invention) However, if the channels to be used are determined in this way, traffic will concentrate on the free channels notified by the center, and the load distribution between channels will not be effective, which will cause problems. Collisions will increase. An object of the present invention is to eliminate the drawbacks of the conventional channel selection method described above, and to provide a channel selection method that minimizes collisions in a system in which polling is performed by providing access slots in a plurality of channels. It is in.

(Means for Solving the Problem) In the present invention, in a mobile radio data communication system in which a large number of data terminals share a plurality of channels, a base station polls only those terminals that are currently communicating on each channel. , a communication system in which a terminal attempting to start a new communication can transmit a connection request signal only when a specific polling number called a predetermined access slot arrives, and the base station uses a control channel to Notify each terminal of the number of terminals communicating in the channel, and when each terminal attempts to start communication, select a channel with probability such that the traffic amount of the access slot is equal for each channel. The above problem is solved by using a channel selection method characterized by the following.

(Function) When data terminals start communication, random access is inevitable unless communication channels are assigned to all terminals.

This comes from the fact that each terminal cannot know what state the other terminals are in. In order to minimize the probability of collision under such conditions, the best way is to equalize the loads on access slots in all channels. For a system in which the center polls only communicating terminals for each channel, the actual capacity of access slots differs for each channel depending on the number of polls. For this reason, in the present invention, information on the number of polls in each channel is sent from the center side, and the terminal selects a channel with a probability that the load on each channel is equal.

(Example) FIG. 2 shows the configuration of a system in which the present invention is used. The terminals T1 to T4 communicate with the center C, respectively. The number of channels is two, and each terminal selects one of the channels, transmits a connection request signal, and starts communication. When the connection is completed, the center polls the terminal, and the terminal transmits data in response to the polling signal. A connection request signal can be sent only when the polling number is 0. If multiple terminals simultaneously transmit connection request signals on the same channel when the polling number is 0, a collision will occur and the connection requests will not be transmitted correctly. This problem is more likely to occur as the number of balls on the channel increases. This is because when many terminals are polled, the interval between the arrival of polling number O becomes longer, and the probability that multiple connection requests will occur during that time increases.

Therefore, if the number of communication terminals in channel 1 is smaller than the number of communication terminals in channel 2, collisions are more likely to occur in channel 2. Therefore, it is desirable for the terminal to access channel 2 with a higher probability. This situation can be seen in the third
As shown in the figure. In order to minimize the collision probability, the traffic amount of connection request signals in the access slots of each channel (the shaded portion of the channel (upper F in the figure)) may be made equal. An algorithm for this purpose in an embodiment of the present invention is shown in FIG. First, the center uses the lower control channels to broadcast the number of terminals currently polling in each channel. A terminal that is about to start communication decides which channel to use based on this information. Considering the access slot as one polling, P
Channel i with i polls has 1/(A
There are polling slots at a rate of *Pi+1). However, A is the average message length. Therefore, if we set (N is the number of channels) and control to select channel i with probability Qi = 1/(f9*(A*Pi+1 '')'), we can equalize the traffic volume of polling slots in each channel. This allows the probability of connection request signal collision to be minimized.

If the amount of traffic is uneven, the probability of collision on the channel with the highest amount of traffic becomes extremely high, and the overall throughput decreases.

The average message length A may be broadcast by the center or may be stored in the terminal in advance.

(Effects of the Invention) As described in detail above, according to the present invention, a plurality of channels are provided, each channel is provided with an access slot, connection is made, and connected terminals are polled. It is possible to provide a terminal calling method that minimizes the probability of collision in a system that is similar to the above.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a flowchart showing the operation of one embodiment of the present invention, Fig. 2 is a block diagram showing an example of the configuration of a system in which the present invention is used, and Fig. 3 is an implementation of the present invention. 5 is a timing chart for explaining an example operation using a signal format on a channel. C...Center, Tl~T4...Terminal.

Claims (1)

[Claims] In a mobile radio data communication system in which many data terminals share multiple channels, a base station polls only those terminals that are currently communicating on each channel, and polls terminals that are about to start new communication in advance. In a channel selection method for a mobile data terminal using a communication method that allows a connection request signal to be transmitted only when a specific polling number as a defined access slot arrives, the base station communicates on each channel using a control channel. The number of terminals in the access slot is notified to each terminal, and when each terminal attempts to start communication, it selects a channel with probability such that the traffic amount of the access slot is equal for each channel. Channel selection method for mobile data terminals.