JPH07143549A - Radio channel retrieval system - Google Patents

Abstract

PURPOSE:To provide a radio channel retrieval system for shortening time required for retrieving an idle channel without lowering frequency efficiency. CONSTITUTION:All the channels are not defined as a retrieval target but the retrieval target channel is limited to one part of all the channels and when there is a channel satisfying required quality in the limited retrieval target channels, the channel at the lowest quality is allocated among those channels satisfying the required quality but when there is no channel satisfying the required quality in the limited retrieval target channels, a generated call is judged as a call loss. As examples for selecting the retrieval target channels, there are a method for selecting all the required number of channels at random and a method for selecting a retrieval start channel and selecting the required number of channels in the order of arrangement or the like.

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 that applies dynamic channel allocation (DCA), which allocates available channels among all wireless channels according to the occurrence of a call.

[0002]

2. Description of the Related Art Desired wave-to-interference wave power ratio (CIR) and desired wave-to-noise power ratio (C
NR), bit error rate (BER), etc., but CIR is used as the quality in the following description. The concept is the same when the quality is defined by other than CIR.

As a conventional technique, a method of allocating all channels to a call that satisfies the required quality found first as a search target (First Available (FA) method), and searching all channels A method of assigning the lowest quality level channel among the channels that meet the required quality among all channels to the generated call (minimum margin method)
There are two methods.

Two methods will be described below. In the explanation, the total number of channels is 24 and the required CIR is 20.
dB.

FIG. 1 shows dynamic channel allocation (D
CA: Dynamic Channel Assign
is a configuration of a mobile communication system that assigns a wireless channel according to the “ment”. From the channels (24 channels) used in the system, each base station (A, B, C) selects and allocates a radio channel having a CIR value of 20 dB or more according to the occurrence of a call. For the sake of explanation, the numbers shown in FIG. 2 are given to the wireless channels. CIR value is 20d
If there is no wireless channel of B or higher, the call is lost in any method.

Now, assume that a call originates at the terminal e in the zone of the base station A, and the CIR value of each radio channel at that time is as shown in FIG. In FIG. 3, it is assumed that the wireless channel number 5 is assigned for communication with the terminal a.

(1) When the first available (FA) method is applied In the FA method, the search order is set in a certain direction as shown in FIG. 4, but the search is started in order to avoid bias in the wireless channels used. It is common to choose the channel randomly. The case where the search start channel is the radio channel number 1 and the radio channel number 18 in FIG. 2 will be described.

Since the required CIR is 20 dB, 20 dB when the search start channel is the radio channel number 1.
Radio channel number 7 (CI
An R value of 40 dB) is assigned to the terminal e (FIG. 5). The search start channel is the wireless channel number 18
In the case of, the wireless channel number 19 (CIR value 25d
B) is assigned to terminal e (FIG. 6).

As described above, in the FA method, a radio channel to be randomly assigned is selected from radio channels satisfying the required CIR.

On the other hand, the required CIR is as close as possible (required CIR
Assigning a wireless channel (of the wireless channels that satisfy IR) means that the same channel is repeatedly used at a short distance when viewed from the whole system.
It is desirable because it improves the frequency utilization efficiency.

Therefore, the FA method has a drawback that the frequency utilization efficiency is lowered.

(2) When the minimum margin method is applied The minimum margin method is a method of searching all the wireless channels and allocating the wireless channel having the worst CIR value among the wireless channels satisfying the required CIR. When the CIR value of the wireless channel is as shown in FIG. 3, the wireless channel number 1
1 (CIR value 21 dB) is assigned to the terminal e (FIG. 7).

According to the minimum margin method, the same channel can be repeatedly used at a short distance.
The frequency utilization efficiency can be improved as compared with the method A. However, since it is necessary to search all channels, there is a problem that the processing time for determining the allocated channel becomes a problem, and the connection delay time from the call generation to the wireless channel allocation becomes long.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a radio channel search system which can reduce the time required for a free channel search without lowering the frequency utilization efficiency.

[0015]

A feature of the present invention for achieving the above object is that it is composed of a plurality of base stations and terminals located in a radio zone formed around the base stations. Regarding the allocation of radio channels used for communication between stations and terminals, selection of radio channels to be allocated in a communication system in which base stations or terminals select and allocate radio channels that satisfy the desired quality in response to the occurrence of a call. Each time, the number of channels less than the total number of channels is selected as a search target, the channel quality is measured for all the search target channels, and if one or more channels in the search target channels satisfy the required quality, Is a radio channel search that allocates the channel with the lowest quality level among the channels that meet the required quality to the generated call. In the equation.

[0016]

The present invention restricts the search target channels to a part of all the channels without making all the search targets, and is required when there is a channel satisfying the required quality in the restricted search target channels. Of the channels that satisfy the quality, the channel with the lowest quality level is assigned, and if there is no channel that satisfies the required quality in the restricted search target channels, the call that occurs is lost.

This is different from the conventional technique in that the search target channel is limited and the search target channel is searched by the minimum margin method.

[0018]

EXAMPLES Examples of the present invention will be described. In this section as well, quality shall be specified by CIR.

Search target channels are 1/2 of the total number of channels
The case will be described in the first embodiment. The case where the number of search target channels is ¼ of the total number of channels will be described in the second embodiment. The channel search order is the same as that shown in FIG.

[0020]

[First Embodiment] In the system shown in FIG.
The base station A selects a radio channel to be allocated when a call occurs at.

A case where the CIR value of each radio channel at the time when a call originates at the terminal e is as shown in FIG. 8 will be described. Since the required CIR is 20 dB now, the radio channels satisfying the required CIR are shaded in FIG.

According to the present invention, the number of search target channels is limited first, but in the present embodiment, since the search target channels are limited to 1/2 of all channels, the number of search target channels is 1.
It becomes 2. The search target channel is searched by the minimum margin method, that is, the wireless channel having the worst CIR value among the wireless channels satisfying the required CIR is assigned.

When the CIR value of each radio channel is as shown in FIG. 8, if the search start channel is the first channel,
The channels to be searched are the first to twelfth channels (enclosed by thick lines in FIG. 8), and among the seventh channel, eighth channel, tenth channel, and eleventh channel that satisfy the required CIR, the CIR value Low 11th
A channel (CIR value 21 dB) is allocated.

On the other hand, when the search start channel is the 15th channel, the search target channels are the 15th to 24th channels.
Of the 15th channel, the 19th channel, the 22nd channel, the 23rd channel, and the 24th channel, which are the channels and the 1st to 2nd channels (enclosed by the thick line in FIG. 9) and satisfy the required CIR, CI
The 22nd channel with a low R value (CIR value 24 dB) is allocated.

According to the minimum margin method, all the wireless channels are searched and the wireless channel 11 (CIR value 21 dB) is allocated. However, by applying the minimum margin method for 1/2 of the total number of wireless channels, , Required C
A radio channel having a relatively low CIR value can be selected from radio channels satisfying the IR, that is, the repeating distance of the same radio channel can be shortened, and frequency utilization efficiency can be improved. In addition, the time required to search the wireless channel is half that of the worst CIR method.
Can be reduced to.

[0026]

[Second Embodiment] Similar to the first embodiment, a case will be described in which the CIR value of each radio channel at the time when a call occurs at the terminal e is as shown in FIG. Required CIR
The wireless channels that satisfy the conditions are shaded in FIG. In this embodiment, since the number of search target channels is limited to 1/4 of all channels, the number of search target channels is 6.

If the search start channel is the fifth channel, the search target channels are the fifth to tenth channels (enclosed by the thick line in FIG. 10), and the required CI is obtained.
Of the seventh channel, eighth channel, and tenth channel that satisfy R, the eighth channel (C
An IR value of 24 dB) is assigned.

If the search start channel is the 16th channel, the search target channels are the 16th to 21st channels.
Becomes a channel (enclosed by the thick line in FIG. 11),
Channel 19 (CIR that satisfies only the required CIR)
The value 25 dB) is assigned.

According to the minimum margin method, all the radio channels are searched and the radio channel 11 (CIR value 21 dB) is allocated. However, by applying the minimum margin method to 1/4 of all the radio channels in this way, , Required C
A radio channel having a relatively low CIR value can be selected from radio channels satisfying the IR, that is, the repeating distance of the same radio channel can be shortened, and frequency utilization efficiency can be improved. In addition, the time required for wireless channel search is 1/4 that of the worst CIR method.
Can be reduced to.

On the other hand, when the search start channel is the first channel, the search target channels are the first to sixth channels (enclosed by the thick line in FIG. 12), and the required CI is obtained.
Since no channel satisfies R, the generated call is lost. Although there are channels other than the search target channels that satisfy the required CIR, the call loss was caused because the number of search target channels was limited.

Since the search start channel is randomly determined, it can be considered that the radio channels in use are averaged among all the channels. Therefore, if the number of search target channels is sufficiently large and there are no assignable channels (radio channels that satisfy the required CIR) in the search target channels, it is considered that the number of assignable channels is small in other channels as well. . Therefore, by limiting the number of search target channels and applying the minimum margin method among them, the same effect as the worst CIR method (frequency utilization efficiency improvement by repeatedly using the same radio channel at a sufficiently close distance) can be obtained. To be In addition, the search processing time, that is, the connection delay time can be shortened as compared with the minimum margin method in which all wireless channels are measured.

[0032]

As described above, according to the present invention, there is an advantage that a high frequency utilization efficiency can be realized with a short radio channel search time.

FIG. 13 shows the result of computer simulation comparing the conventional method with the present invention. In the simulation, the total number of channels was set to 72, and in the area formed by the regular hexagonal zones as shown in FIG. 14, the relation between the call volume and the call loss rate per zone was obtained for the FA method and the present invention. In FIG. 13, FA (72) is the case of FA method for all channels (72 channels), and TS = 72, TS = 36, TS = 24, TS = 1.
In the present invention, the number of search target channels is 72 (all channels), 36 (1/2), and 24 (1 /).
3), 18 (1/4) and 12 (1/6). TS = 72 is the same as the conventional minimum margin method.

From FIG. 13, it is understood that if the number of channels to be searched is 18 (1/4 of all channels) in the present invention, a frequency utilization factor substantially equal to that of the conventional FA method can be obtained. In this case, the channel search time is 1/4 of the minimum margin method. Further, when the number of search target channels is set to 36 (1/2 of all channels) in the present invention, the search processing time can be halved as compared with the minimum margin method that searches all 72 channels. It can be seen that the utilization efficiency is only reduced by about 10%.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a mobile communication system to which the present invention is applied.

FIG. 2 is a diagram showing the numbers of wireless channels.

FIG. 3 is a diagram showing a CIR value of each wireless channel.

FIG. 4 is a diagram showing a wireless channel search order.

FIG. 5 is a diagram illustrating a conventional technique, a diagram illustrating a case where a search start channel is channel number 1 in the FA method, and a shaded portion represents an assigned channel.

FIG. 6 is a diagram illustrating a conventional technique, a diagram illustrating a case where a search start channel is a channel number 18 in the FA method, and a shaded portion represents an assigned channel.

FIG. 7 is a diagram for explaining a conventional technique, in which hatching represents allocated channels in the minimum margin method.

FIG. 8 is a diagram for explaining the first embodiment of the present invention, in which shaded areas represent wireless channels that satisfy the required CIR, and thick lines represent search target channels.

FIG. 9 is a diagram for explaining the first embodiment of the present invention, in which shaded areas represent wireless channels that satisfy the required CIR, and bold lines represent search target channels.

FIG. 10 is a diagram illustrating a second embodiment of the present invention,
Shaded cells represent wireless channels that satisfy the required CIR, and bold lines represent search target channels.

FIG. 11 is a diagram illustrating a second embodiment of the present invention,
Shaded cells represent wireless channels that satisfy the required CIR, and bold lines represent search target channels.

FIG. 12 is a diagram illustrating a second embodiment of the present invention,
Shaded cells represent wireless channels that satisfy the required CIR, and bold lines represent search target channels.

FIG. 13 is a diagram illustrating an effect of the present invention.

FIG. 14 is a diagram illustrating a computer simulation model for confirming the effects of the present invention.

[Explanation of symbols]

 a, b, c, d, e terminal A, B, C base station

Claims (3)

[Claims] 1. A base station is composed of a plurality of base stations and terminals located in a radio zone formed around the base stations. A call channel is assigned to a radio channel used for communication between the base station and the terminal. In a communication system that selects and allocates a wireless channel that satisfies the desired quality at the base station or terminal depending on the occurrence of, the number of channels less than the number of previous channels is searched for each selection of the wireless channel to be allocated. , The channel quality is measured for all the channels to be searched, and if one or more channels satisfy the required quality in the channels to be searched, the channel with the lowest quality level is generated among the channels that satisfy the required quality. A wireless channel search method characterized by allocating to established calls. 2. The selection of the search target channel is performed by randomly determining a search start channel of channels arranged in a predetermined order, and selecting a required number of channels from the channel in order of arrangement. The wireless channel search method according to claim 1. 3. The wireless channel search method according to claim 1, wherein the search target channel is selected randomly from all channels.