JP3231904B2 - Channel assignment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a channel allocation system for a mobile communication system, and more particularly to a channel allocation system capable of improving the frequency use efficiency in TDMA mobile communication.

[0002]

2. Description of the Related Art In TDMA radio communication, as shown in FIG. 10, a transmission wave 1-a emitted from one radio base station is time-divided into several slots, each of which is used for communication with another party. b, 1-c, and 1-d. Therefore, a radio channel specified by a set of a carrier frequency and a slot number is a unit of allocation.

In a conventional autonomous distributed dynamic channel allocation method for allocating a radio channel without monitoring by an upper station and exchanging control information with another radio base station, (1) each radio channel has The base station searches for an available wireless channel (free channel) free from interference according to a fixed and uniform channel number, and allocates the first found free channel. (2) In the past, priority is given to the wireless channel that has been least affected by interference. Such methods have been taken.

[0004]

However, in a system in which the radio base stations are not synchronized on a frame-by-frame basis, the radio base stations A and B having a positional relationship of causing interference with each other are, for example, shown in FIG. Assuming that slots on the same carrier are used as shown in FIG. 11, every time one slot is used by the station A, two slots are interfered by the station B, so that the frequency use efficiency is reduced. The conventional wireless channel allocation algorithm has a problem that it is not possible to avoid adverse effects on the frequency utilization efficiency when using the same frequency channel asynchronously as described above.

[0005] Further, at the time of call generation, if the determination is made one by one until an available channel is found to determine whether or not an allocation candidate channel is affected by interference, the time required to select a radio channel increases. According to the following procedure, a method of narrowing down the connection time by narrowing down the allocation candidate wireless channels is performed.

That is, as shown in FIG. 12, each wireless base station periodically searches for an idle time zone of a wireless device or a search for a wireless communication channel using a dedicated wireless device (determination of idle / in use). This is performed with reference to the ranking table 12-1. Generally, the order of the periodic channel search follows the number assigned to the wireless channel common to all wireless zones. The wireless channel determined to be free here is registered in the free channel table 12-2 as an allocation candidate at the time of call generation.

[0007] When a call occurs in the local station wireless zone, one of the wireless channels registered in the idle channel table 12-2 is selected, the interference wave reception level is measured again, and it is determined that the wireless channel is idle. For example, the wireless channel is allocated. On the other hand, when it is determined that the wireless channel is in use, the next candidate is selected from the empty channel table, and the above procedure is repeated. FIG. 13 (a) is a flow chart of each of the above procedures.
(B).

[0008] In the above-described conventional wireless channel allocation method for performing a periodic channel search, just like the wireless channel allocation method for not performing a periodic free channel search, in the case of asynchronous frames between wireless base stations, There is a problem that the frequency use efficiency is reduced.

The present invention has been made to solve such a conventional problem, and has as its object to improve the frequency use efficiency in TDMA communication.

[0010]

According to the present invention, the above-mentioned object is solved by the means described in the claims.

That is, the present invention comprises a plurality of radio base stations and a radio terminal located in a radio zone of each radio base station, and each radio base station can use a plurality of carriers. And selecting a carrier used for communication from the plurality of carriers and a slot in a TDMA signal transmitted using each carrier from the plurality of carriers between the radio base station and the radio terminal to perform time division multiple access (TDMA). In a wireless communication system that performs communication, when a call occurs in a wireless zone of a wireless base station, the wireless base station calculates the number of slots used by its own station for each carrier, and the number of used slots is large. This is a channel assignment method for assigning a call generated preferentially from an unused slot on a carrier.

[0012]

According to the present invention, a channel is allocated from a radio channel on a carrier having a large number of slots in use, and a periodic channel search is performed. In addition, there is an operational effect that it is possible to improve a decrease in frequency utilization efficiency due to a slot shift in the case of frame asynchronous between wireless base stations.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example in which the system of the present invention is applied to a wireless communication system that does not perform a periodic channel search will be described as a first embodiment.

FIG. 1 is a flowchart showing a control procedure according to the first embodiment of the present invention. As shown in FIG. 6 (a), the radio base station, the call that caused raw, whether there are remaining channels
And, if there are channels, the highest allocation priority
Select a new channel. The channel is not receiving interference
If available, use the carrier in the table shown in FIG.
Increase the number of slots by 1 and assign
Change the allocation priority. At the end of communication,
As shown in (b), the number of used slots of the corresponding carrier
, And assign priority order in descending order of the number of used slots
Change place. When channel switching between wireless zones occurs
In the same way as above,
Change and assign priority in the order of the number of used slots
To change. As described above, according to the procedure of FIG. 1, the search order table in which the number of used slots for each carrier and the priority of channel assignment (the order of the carrier with the largest number of used slots) is recorded as shown in FIG. To update. At this time, in the same carrier, as shown in FIG. 3, priorities are given according to the numbers given to the slots in time.

When a call is generated in the radio zone of the radio base station in the radio channel use condition and the interference condition as shown in FIG. The measurement is started (if no free channel is found, the interference wave reception levels of 4-5 of the used interference slot 2 and 4-6 of the used interference slot 1 are measured after 4-1). According to the priority of allocation, measurement is performed in the order of slots 4-2, 4-3, and 4-4 to find an empty slot 4-4, and when this is allocated, the procedure of FIG. I do.

Next, a case where the present invention is applied to a wireless communication system for performing a periodic channel search will be described as a second embodiment. FIGS. 5A, 5B, and 5C are flowcharts showing the control procedure of the present embodiment.

As shown in FIGS. 3 (b) and 3 (c), each time a radio base station generates / ends a call (and switches channels between radio zones), each radio base station has a format as shown in FIG. The search order table that records information on the number of used slots for each carrier and the search order of the channel search (in order of the number of used slots) is updated.

On the other hand, each radio base station periodically performs the processing shown in FIG. 5A, and measures the interference wave reception level using an idle radio in accordance with the search order of the table shown in FIG. , Is determined to be free / in use. As for the search order between slots on the same carrier, the search is performed in a temporal order, as in the first embodiment described above.

As a result of the interference wave reception level measurement → empty / busy determination, those determined to be empty are registered in an empty channel table having a format shown in FIG. As the number of wireless channels registered in the free channel table (= free channel table size), one suitable for the system is set for each system.

The channel search is performed until the empty channel table is filled or until all the wireless channels have been searched. At the time of call generation (and at the time of channel switching between wireless zones), it is checked whether the wireless channels in the idle channel table are being used one by one or whether they are idle, and the idle wireless channel is checked. If found, assign the wireless channel and, as described above,
Update the table.

Hereinafter, as an example of the operation of the present invention, 6 ch
A case where the system of the present invention is applied to a TDMA wireless communication system will be described. In a system with an available channel table size of 3, when the radio base station is in a radio channel use situation and interference situation as shown in FIG. Start measurement.

In the order of slots 4-2, 4-3, and 4-4,
A search is performed, and the free channel 4-4 is registered in the free channel table. Hereinafter, the search order is the carrier 4-5, 4
Although -6, the search for 4-5 is performed, and the empty slots 4-7 and 4-8 are registered in the empty channel table.
The search in this cycle ends when the free channel table is filled.

[0023]

As described above, according to the method of the present invention, it is possible to realize the separation of the radio channel from the peripheral radio zone on a carrier unit basis, and the interference from the peripheral radio zone in the frame asynchronous system between radio base stations. There is an advantage that deterioration of frequency use efficiency due to waves can be improved.

In the 4ch TDMA system, assuming that the radio base stations A and B use carriers f ₁ and f ₂ as shown in FIG. 8A, the next time a call is generated at the radio base station A , applying invention, is allocated to FIG (B) of 8-1 by <br/> urchin slot f ₁ of available slots in the base station B is a 8-2 and 8-3, the number thereof is but still 2, without applying the present invention, when assigning the slots 8-4 f ₂ as shown in FIG. (c), the number of available slots in the base station B is 0, the radio base station B The call that has occurred becomes a call loss.

FIG. 9 shows the result of a simulation performed for the procedure of the second embodiment of the present invention. The simulation conditions are asynchronous, 110 wireless zones, 4 slots × 10 carriers, 3 wireless zones repeated, and applied traffic 7.2 Erlang per wireless zone. It can be seen that the call loss rate is improved by about 10 to 50% compared to a system in which the search is performed in the same order at each base station.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a control procedure according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a search order table.

FIG. 3 is a diagram illustrating slot numbers.

FIG. 4 is a diagram illustrating an example of a state of a wireless channel.

FIG. 5 is a flowchart showing a control procedure according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating an example of a search order table.

FIG. 7 is a diagram illustrating an example of an empty channel table.

FIG. 8 is a diagram illustrating an effect of the present invention.

FIG. 9 is a diagram showing a simulation result of the second embodiment.

FIG. 10 is a diagram illustrating an example of use of slots in TDMA wireless communication.

FIG. 11 is a diagram illustrating an example of slot interference in TDMA wireless communication.

FIG. 12 is a conceptual diagram of a channel assignment process of a mobile communication system that performs a periodic channel search.

FIG. 13 is a flowchart showing channel allocation processing of a conventional mobile communication system that performs a periodic channel search.

[Explanation of symbols]

 4-1, 4-5, 4-6 slot usage 4-2-4-4, 4-7-4-9 slots

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04B ^7/ 24-7/26 102 H04Q ^7/ 00-7/38

Claims (1)

(57) [Claims] 1. A radio base station comprising: a plurality of radio base stations; and a radio terminal located in a radio zone of each radio base station, wherein each radio base station is capable of using a plurality of carriers; Radio for performing time division multiple access (TDMA) communication by selecting a carrier to be used for communication from the plurality of carriers and a slot in a TDMA signal transmitted using each carrier from the plurality of carriers between a base station and the radio terminal. In a communication system, when a call is generated in a wireless zone of a wireless base station, the number of slots used by the wireless base station in its own station is calculated for each carrier. A channel assignment method characterized by assigning a call that has occurred preferentially from a used slot.