JPH02233029A - Mobile communication system for same frequency time division transmission and reception - Google Patents

Abstract

PURPOSE:To evade interference and disturbance by receiving a channel having possibility to give interference and disturbance to a communication channel, measuring the reception level of a time slot of 2 series and selecting a time slot of a series with a high reception level as a time slot of its own station. CONSTITUTION:When a communication request takes place between a base station 1 and a mobile station 2 while a mobile station 4 and a base station 3 make communication at a frequency F2, the base station 1 receives a radio wave in the frequency F2 having a relation of giving interference to the frequency F1 prior to the start of communication. Then the base station 1 measures an average reception level of the transmission block of the base station 3 and the transmission block of the mobile station 4 respectively and sends the result in a time slot synchronously with the time slot with a high level. The mobile station 2 uses the time slot, selected for the transmission by the base station 1 because the station 2 synchronously with the base station 1 and uses other time slot as the transmission time slot.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a technology for reducing interference from peripheral stations in a mobile communication system that uses the same frequency and alternates transmission and reception in a time-division manner. .

(Prior Art) In two-way mobile communication, it is common for mobile stations and base stations to transmit at different frequencies. On the other hand, if the transmission frequencies of the mobile station and base station are the same frequency,
There is a communication method in which transmission and reception are performed alternately by time division. For example, this converts an audio signal into a digital code and uses the formula 1
The code is divided every 0 milliseconds (the divided Sawata code is called a block) and is transmitted alternately between the mobile station and the base station in block units. Since the time (time slot) in which the mobile station and the base station can each transmit is the maximum of the entire block, the code transmission rate of the block should be twice the rate when voice is converted into digital code. This method has the following advantages:

(1) Normally, flF filters are required for the transmitting band and the receiving band, but since these are the same frequency, the R
Only one F filter is required.

(2) When the transmission frequencies of the mobile station and the base station are different, in order to prevent the transmission waves from entering the reception band in the mobile station or base station equipment and suppressing the sensitivity of the receiver, It is necessary to keep the frequencies of the transmitted wave and the received wave (in other words, the transmitted waves of the mobile station and the base station) sufficiently apart. For this reason, such a system can only be used when there is availability in two sufficiently distant frequencies (bands). On the other hand, in the same frequency time division transmission/reception system, if there is at least one matching frequency (band), it can be used.

Although this method has such advantages, it also has the following drawbacks.

In FIG. 3, 1.3 is a base station and 2.4 is a mobile station. The frequency used by base station 1 and mobile station 2 is F1.
, it is assumed that the frequency used by the base station 3 and the mobile station 4 is F2. When F and F2 are on the same frequency, if a radio wave from another station with a high level comes in as interference while the own station is receiving, it becomes co-channel interference and causes interference noise. F,
Even if F2 and F2 have different frequencies, if a high-level F2 radio wave enters as interference while F2 is being received, sensitivity will be suppressed in the receiver, which will interfere with communication.

By the way, base station antennas are generally installed at high places such as on steel towers, but mobile station antennas are often installed at low positions of 1 to 2 meters from the ground surface. Therefore, for example, the level of interference that the base station 1 receives is higher from the base station 3 than from the mobile station 4. On the other hand, the interference that mobile station 2 receives from base station 3 is smaller than the interference that base station 1 receives from Moe's base station 3. When mobile stations 1 and 4 are close to each other, the interference received by mobile station 2 from mobile station 4 may be greater than the interference received by mobile station 2 from base station 3. That is, interference between base stations and between mobile stations is the most problematic. In order to avoid this interference, F and F at the base station and mobile station must be
It is necessary to synchronize the timing of transmission and reception of the two. This is because by synchronizing, when mobile station 2 is transmitting, other mobile stations 4 are also transmitting, and when base station 1 is transmitting, other base stations 3 are also transmitting. This is because there is no need to consider interference between mobile stations and between base stations. However, this requires that the base stations first synchronize with each other and then the mobile stations synchronize with these base stations. In conventional techniques for synchronization between base stations, it is necessary to provide a control station separate from the base station, and to provide a control line from this control station to each base station for synchronization. In addition, in the case of a failure in the transmission line that transmits the control line between the control station and the base station, the transmission line may be automatically switched, and in this case, the transmission delay time will be different, so it is necessary to resynchronize. There is.

For these reasons, not only a control line but also a device to monitor whether synchronization is maintained and a device to automatically resynchronize if synchronization is lost is required, which has the disadvantage of high cost. . Furthermore, if base stations that cause interference with each other are installed and operated by different communication companies, it may be difficult to connect control stations and control lines to the base stations of these different companies.

(Problems to be Solved by the Invention) An object of the present invention is to avoid interference between base stations and mobile stations without requiring a control line for synchronization between base stations, and to avoid interference between base stations and mobile stations. The purpose of the present invention is to provide a split transmission/reception mobile communication system.

(Means for Solving the Problems) A feature of the present invention for achieving the above object is a mobile communication system that uses the same frequency and performs transmission and reception in a time-division manner using two series of time slots arranged alternately. In,
Prior to the start of communication, a channel that may cause interference to the communication is received, and when the channel is in communication, the time slot with the higher reception level among the alternate transmission time slot series of that channel. This is a same-frequency time-division transmitting/receiving mobile communication system that uses the same time slot sequence as the own station's time slot sequence.

(Operation) When a mobile station and a base station attempt to start communication, the present invention monitors a channel that may cause interference to the communication channel, and measures the reception level of the time slot of alternate transmission and reception on that channel. , the time slot with the higher level is set as the transmission time slot of its own station.

As already explained, the level of interference waves received by the base station is higher from other base stations than from other mobile stations. Therefore, the timeslots that are more strongly received at the base station are the timeslots of other base station transmissions. Therefore, by setting the time slot with the higher reception level as the transmission time slot of the own station, it is possible to automatically synchronize with other base stations. While the conventional technology requires control lines and the like for synchronization between base stations, the present invention does not require these devices and lines.

In addition, if the base stations are sufficiently far apart and mutual interference between base stations is not a problem, the mobile station can use the time slot with the higher reception level as its own transmission time slot in the same way as above. , interference with mobile station reception can be avoided.

(Example) FIG. 1 is a diagram for explaining the same frequency time division transmission and reception system seen from a certain specific station, 10-It to-2,...
・IO-5 is a transmission code block obtained by dividing the transmission code into blocks, 2L,, 2o-2, -20-4 is a received reception code block, IL,, -114 is a transmission code block lL+, 10-2, "10-4 is transmitted in the time slot, 2L+. 21-2. -21-4 is the time slot in which received code blocks 20-, 2L2, -20-4 are received.

For example, taking base station 3 as an example, time slots IL,...
-IL4 is the time slot that the base station 3 is transmitting and the mobile station 4 is receiving, and 2L,, 2L2, -2L4 is the time slot that the mobile station 4 is transmitting and the base station 3 is receiving. .

Now, an example will be described in which a communication request occurs between the base station 1 and the mobile station 2 while the mobile station 4 and the base station 3 are communicating on the frequency F2. However, it is assumed that 1X2 is in a relationship that causes interference to communication in F1.

Before starting communication, the base station 1 first receives radio waves from F2, which interferes with F. As shown in Fig. 1, the received radio waves of F2 are transmitted by base station 3,
IL2, -11-4 and 21-+ transmitted by mobile station 4
, 21-2, . . . 21-4 are alternately arranged. Base station 1 has 11-+, 11-2. ...11-4
and the average reception levels of 2L, 2L2, -2L4 are measured, it is determined which one has the higher level, and the data is transmitted in a time slot synchronized with the time slot with the higher level. Since mobile station 2 is synchronized with base station 1,
The time slot selected by the base station 1 for transmission is set as a receiving time slot, and the other time slots are set as transmitting time slots.

FIG. 2 shows an example of the configuration of a base station, in which 30 is a handset;
1 is a control circuit, 32 is a transmitting circuit, 33 is a receiving circuit, 34
is an antenna common circuit, and 35 is an antenna. When starting communication, the control circuit 31 controls the receiving circuit 33 to receive F2. The receiving circuit 33 receives 21-1. 11-1. 21-2. The reception level is measured every time slot 11-2- and reported to the control circuit 3l. 3l takes the average for each alternate time slot and determines the time slot with the highest average level.

Next, the control circuit 31 controls the transmitting circuit 32 and receiving circuit 33 to transmit and receive on the F1 channel.

At the same time, the control circuit 3l controls the transmitting circuit 32 to use the time slot synchronized with the high reception level time slot as the transmission time slot, and to use the time slot synchronized with the low reception level time slot as the reception time slot. Controls the receiving circuit 33.

The mobile station 2 has a configuration similar to that shown in FIG. 2, and uses the base station's transmission time slot as the reception time slot,
A communication path with the base station 1 is configured by using the reception time slot of the base station as the transmission time slot.

By the way, even if base station 1 receives radio waves from F2, which interferes with F1, if there are no other base stations or mobile stations nearby, or even if there are, they are not using F2. Sometimes there is no reception level at F2. In this case, the timing of the transmission and reception time slots cannot be determined using the method described above.

However, in this case, since there is no interference wave, it means that transmission and reception can be performed at any timing. Therefore, the base station 1 selects an arbitrary timing as a transmission time slot, and determines a reception time slot accordingly.

(Effects of the Invention) As explained above, a channel that may cause interference to a communication channel is received, the reception levels of the two time slots are measured, and the time slot of the series with the higher reception level is automatically selected. By selecting the time slot as the station time slot, the time slot that is likely to be subject to high interference is not selected as the receiving time slot.
Since it can be used as a transmission time slot, there is an advantage that interference can be avoided.

While conventional techniques require communication lines and devices for synchronization between base stations to obtain similar effects, the present invention has the advantage of not requiring these.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating a same frequency time division transmission and reception system according to the present invention, FIG. 2 is a configuration example of a base station, and FIG. 3 is a model diagram of a mobile communication system. 2, 4: Mobile station, transmission code block, reception code block, reception time slot, transmission time slot 3]; control circuit; 33; reception circuit; 35; antenna. 1, 3; base station, IL,, IL,, -IL5; zo-,, 20-2, =20-4; 21-1. 2
1-2, -21-. + :11-,. 11-2,
""11-4;30; handset, 32; transmitting circuit, 34; antenna common circuit,

Claims (1)

[Claims] In a mobile communication system that uses the same frequency and performs transmission and reception in a time-division manner using two series of time slots arranged alternately, the possibility of causing interference to the communication is determined prior to the start of the communication. When a certain channel is received and the channel is in communication, among the alternate transmission time slot series of that channel,
A same-frequency time-division transmitting/receiving mobile communication system characterized in that the same time slot series as the time slot series with a higher reception level is used as the time slot series of the local station.