JPH10322759A - Carrier wave channel shared cellular mobile communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To consider effect exerted to the frequency utilization efficiency of a frequency duplex re-utilization system and to decide the channel set of a macro cell and a micro cell by combining and using the frequency duplex re- utilization system and a usual system in the case that a signal channel number included in one carrier wave is equal to or more than a channel set number. SOLUTION: In the macro cell 1 of a transmission FS wave adjacent to the macro cell 2 (radius R1 ) of the transmission FA wave, the service area (radius R2 of micro cell 3) of the transmission Fa wave of the same carrier wave as the transmission FA wave and smaller transmission power is provided together. The micro cell 3 is realized by using the same transmission Fa wave as the transmission FA, wave of the macro cell 2 theoretically even inside the macro cell 1. Thus, the micro cell 3 is provided together inside the macro cell 1, the service of uniform call amount density is realized and total call amount density is substantially improved by the macro cell 1 and the micro cell 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system, that is, a cellular mobile communication system in which a signal channel is switched each time a mobile unit moves in a microcell having a different carrier frequency. More specifically, the present invention relates to a cellular mobile radio system using a frequency multiple access (FDMA) system in combination with a code division multiple access (CDMA) system and a time division multiple access (TDMA) system. The present invention relates to a mobile radio communication system which is provided in parallel with a system, shares a carrier frequency band with each other, and is suitable for receiving communication services of both systems with a single portable device.

[0002]

2. Description of the Related Art A wide area mobile telephone system has heretofore been known as a cellular public mobile telephone system and has already been widely used worldwide. In addition, Japanese Patent Publication No. 7-46877
As described in "Mobile Radio Communication System" (hereinafter referred to as "Document 1"), a macro cell of a wide area mobile telephone system is superimposed with a micro cell of a private radio telephone system, and the two systems share the same frequency channel band. There is also known a system suitable for receiving communication services of both systems with one portable device. Kinoshita et al., "Frequency sharing between wide-area cordless telephone and urban cellular mobile telephone: frequency channel double reuse method", IEICE Transactions BI
I, Vol. J76-BII, No. 6, pp. 487
−495, June, 1993 (hereinafter referred to as Reference 2), which is scientifically named “frequency double reuse system”, in which common and different frequency bands are mounted on the same portable device. This is a single portable system that can be designed with higher frequency utilization efficiency than the mode portable system.

[0003] The above-mentioned system is an FDMA system or a TD for a narrow band.
It is based on the MA method. The reason is that it is assumed that the number of carriers included in the entire frequency band allocated to a certain area is sufficiently larger than the number of cells using different carriers, that is, the number of carrier channel sets (ignoring so-called division loss. Range). That is, in the above method, the ratio of the number of carrier waves and the number of channel sets included in the all allocated frequency bands is 1
Assuming the case where the frequency becomes 0 or more, the arrangement of the carrier frequencies of the microcell system is determined so that the frequency use efficiency is increased.

However, in the CDMA system and the wideband TDMA system, the number of signal channels included in one carrier increases (from 7 to about 35), and the ratio of the number of all carriers to the number of channel sets becomes 10 or less, and the frequency double retransmission is performed. The effect of the "use method" on the frequency use efficiency cannot be ignored.

[0005]

SUMMARY OF THE INVENTION CDMA and wideband TD
In the case of the MA method, it is necessary to determine the channel set of the macro cell and the micro cell in consideration of the influence of the above factors on the frequency use efficiency of the “frequency double reuse method”.

[0006] Specifically, when the number of signal channels included in one carrier is equal to or greater than the number of channel sets, how to use the "frequency double reuse system" is realized, and
The issue is how to improve the frequency use efficiency.

[0007]

According to the present invention, when the number of signal channels included in one carrier is equal to or greater than the number of channel sets as described above, the "frequency double reuse system" is used.
And the conventional system to improve the frequency use efficiency. That is,
By means of mixing the carrier with the conventional "frequency double reuse system" in a conventional manner, this "frequency double reuse system"
Take advantage of the fact that the frequency use efficiency is higher than that of a mere conventional system.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

FIG. 2 shows the principle of the "frequency double reuse system". In the macro cell 1 carrier F _B adjacent to the macrocell 2 (radius R ₁₎ of the carrier F _A, the radius R of the carrier F _A and the same carrier wave by transmission power is smaller than the base station carrier F _a service area of (microcell 3 ₂ ) is conceptually shown. When the transmission power of the base station is P and the distance to the receiving point is R, the received signal strength S is approximately given by the following equation (Equation 1).

[0010]

(Equation 1)

It is known that α in (Equation 1) can be approximated by α = 3.5 in UHF band urban area propagation and α = 4.5 in typical in-building propagation (Reference 2). This figure is
In principle, the carrier F _{A of the} macro cell 2 also in the macro cell 1
Show that it is possible realize a micro cell 3 using the same carrier F _a and. The reason is that the signal strength near the transmitting antenna (base station) as shown in (Equation 1) causes the interference I
This is because a stronger region exists.

Hereinafter, a description will be given using a conventional hexagonal cell model for the theoretical analysis. Assuming that a shift parameter on the oblique coordinate axis using the same carrier is (i, j), the number of channel sets not using the same carrier = class size C is given by the following equation (Equation 2).

[0013]

(Equation 2)

In the ordinary cellular system, the frequency of the same carrier is not reused in this cluster. However, Reference 2
As described above, in the "frequency double reuse system", the same carrier frequency is reused by the micro cells in this cluster with a small amount of power.

FIG. 3 shows the dependence of the signal strength / interference ratio S / I on the cluster size C at the cell edge in FIG. The macro cell system and the micro cell system are superimposed uniformly on an infinite plane, and the calculation is performed by the formula (5) of Reference 2 on the assumption that all cells are in use (with equal communication quality). Here, β = J / I is the ratio of self-interference I and mutual interference J of both systems. The case where β = 1 is interesting, and the S / I is degraded by 3 dB as compared with the conventional frequency allocation (allocation to different frequency bands) system.

If one of the systems has a small number of base stations at the beginning of introduction, β is generally small, but β becomes large at the end of introduction. In the conventional method (Reference 2), as shown in FIG. 3, the number of clusters is increased to keep S / I (that is, communication quality) constant. However, when the cluster C is small (C ≦ 4) as in the CDMA or the wideband TDMA system, the S / I can no longer be kept constant by the conventional method (FIG. 3). In particular, in the CDMA system, practicality is studied even when C = 1, and in that case, it is necessary to reconsider whether the “frequency double reuse system” can be applied.

Table 1 shows the CDMA system and the broadband TDM.
The specification example of the A method is shown.

[0018]

[Table 1]

AMPS in Table 1 is a specification of the US FDMA system, and GSM is a specification of the European wideband TDMA system. CDMA in Table 1 shows an example of a direct spreading method using a PN code. The allocated frequency bandwidth W is 10
At 30 MHz and 30 MHz, half are used for transmission and the rest are used for reception. CDMA system and wideband TDM
The A method indicates that the number of telephone channels included in one carrier is equal to or greater than the number C of clusters.

The present invention shows a method in which the "frequency double reuse method" is effective (the frequency use efficiency is kept high) even in the above case.

FIG. 4 shows a hexagonal cell model where C (i, j) = C (1,1) = 3. For the macro cell, three waves of carrier frequencies F _A , F _B , and F _C are used. For the microcells, the carrier wave _Fa is used with low power except for the white portion. Even in the microcell using the carrier F _A , the periphery (部 of the radius R ₁ and 75% in area) uses the carrier Fa. To maintain uniform throughout a micro cell radius R _2, in the micro-cells of the carrier F _A, slightly higher setting the transmission power P ₂₂ than the carrier frequency F _B, F _C microcells in the transmission power P ₂₁ . Asada, Kinoshita et al. "Basic Study on CDMA Mobile Communication System I" IEICE, 2nd meeting, MMIN9
6-02, pp. 7-14, on April 20, 1996 (hereinafter referred to as Reference 3), the transmission powers P21, P22
Is shown.

In the white part, the carrier frequencies _Fb and _Fc are used. In this case, the number of carriers is now 2 and the cluster C2 of microcells cannot be realized, and microcells that cannot be serviced with the same communication quality are generated in the cluster. In simple FDMA and narrowband TDMA conventional method that assumes (Document 2), since the number of carrier waves is sufficiently larger than the number of clusters C, adjacent carrier _{F D, F E, F F} , F G, ·
Could supply F _d , F _e , F _g ,. But C
In a cellular system in which a so-called division loss becomes a problem in DMA or wideband TDMA, the above problem becomes prominent.

The invention, F _A, F _B, using a carrier F _D adjacent to F _D in the white part of the macro cell in low power F _d to complete the cluster microcell, uniform microcell within the macrocell Provide services. Example 1 of FIG.
Shows the carrier arrangement of this embodiment in comparison with the conventional method. If you look in part, the use of the F _d is mix conventional methods in the "frequency double reuse scheme".

However, it is clear that the frequency reuse efficiency of the "mixed frequency double reuse system" is improved as compared with the conventional method having the same communication capacity (B = _Ba , M = _Ma).
And).

FIG. 5 shows a cell model where C (i, j) = (1,0) = 1. All adjacent macro cells have carrier F _A
You are using Peripheral part of macro cell (75% in area)
The microcell (radius R ₂ ) of the carrier F _a of low power is further added to the peripheral part ( _１ ／ of the radius R ₁ , 25
To -6.25 = 18.75%) are used microcell carrier F _a (increase slightly transmit power to equal the radius R ₂ in). However, the conventional "frequency double reuse system" can no longer be used for white portions.

The present invention uses conventional methods for this white area. That is, the “frequency double reuse method” and the conventional method are mixed. Embodiment 2 of FIG. 1 shows the frequency array method of the present invention in the above cell model in comparison with a conventional method. This "mixed frequency double reuse system" has clearly improved frequency use efficiency as compared with a mere conventional method. 75% of macro cells
And the microcell system uses carrier waves F _a and F _b (the number of carrier waves =
This is because 2) can be used.

In other words, the present invention is effective in a service area where so-called division loss is a problem. In other words, when the number of carriers allocated to a certain area is divided by the number of clusters C to obtain a fraction (not an integer), an area where a uniform call traffic cannot be maintained occurs. Normally, this is assigned to a macro cell with a large telephone call volume. In the present invention, a microcell system is provided in such a macrocell, and a service of uniform call density is realized by using the carrier and the present invention, and the total call density is dramatically improved by both systems. .

As described above, the CDMA system and the broadband TD
In the MA system, it is not possible to increase the cluster size at the end of the introduction of the microcell system and set the communication quality equal to the initial stage (= non-introduction period).

That is, it is necessary to design a macro system on the premise that a micro cell system is provided. The frequency use efficiency ηr in this case is shown in the following equation (Equation 3) in comparison with the conventional method.

[0030]

(Equation 3)

Here, W is the carrier bandwidth, M is the number of signal channels contained in one carrier, C is the cluster size, Ce
Is the number of carriers added to the microcell (1 in the embodiment of FIG. 1), and the suffix a indicates that of the conventional system to be compared. It is apparent from FIG. 1 that ηr of (Equation 3) becomes 1 or more. After that, it is necessary to design both systems so that the communication quality does not deteriorate even at the end of the introduction compared to the initial stage. For example, the cell radius R ₁ increases the base station power of the macro cell and so kept equal to R ₁ a.

It is apparent that the present invention can be similarly applied to the sector cell system as shown in Document 1 without being shown in the embodiments.

[0033]

According to the present invention, which is an extension of the conventional "frequency double reuse method", the "mixing method of the conventional method and the conventional method" has higher frequency utilization efficiency than the simple conventional method. Further, the present invention is particularly effective when the number of signal channels included in one carrier is large and the cluster size of the system is small, as in the case of the CDMA system and the wideband TDMA system.

[Brief description of the drawings]

FIG. 1 is a diagram showing a carrier arrangement according to embodiments 1 and 2 of the present invention in comparison with a mere conventional method.

FIG. 2 is a diagram showing a relationship between a radio field intensity and a cell radius in a macro cell and a micro cell.

FIG. 3 is a diagram showing signal strength versus interference in a system in which both a macro cell system and a micro cell system are provided in accordance with an introduction situation β.

FIG. 4 shows the arrangement of carriers in the macro cell system.
The figure which showed C = 3 in a square cell model.

FIG. 5 shows the arrangement of carriers in the macrocell system.
The figure which showed C = 1 in the square cell model.

[Explanation of symbols]

1, 2, 4 ... macrocell, 3 ... micro cell, P _21, P
₂₂ ... transmission power, R _1, R ₂ ... radius.

Claims (1)

[Claims] In a cellular mobile communication system that repeatedly reuses the same carrier, a plurality of communication channels per carrier are provided, and a cellular mobile communication system having a different cell radius is provided in a service area of the cellular mobile communication system. A mobile communication system in which both mobile communication systems share essentially the same carrier frequency band, wherein at least one extra carrier is smaller in radius than the number of cells using different carriers, that is, the number of carrier channel sets. A cellular mobile communication system for use in a system channel set.