JPH10336146A - Method for designing radio line of cdma mobile communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To guarantee the quantity of an outgoing line for transmission from a base station by designing a radio line based on mutual relation among the rate of the transmission power of a design object channel in whole power which is transmitted from a base station, a margin to be added to the required reception power of the object channel in a cell end and the rate in terms of a place where the object channel cannot satisfy required quality. SOLUTION: A CDMA mobile communication system is a mobile communication system where plural radio base stations 11 and mobile stations 12 are mutually execute communication through the use of a CDMA system. Designing is executed through the use of relation which is calculated by using a prescribed condition. Remains obtained by subtracting power which is assigned to a communication channel from whole transmission power from the radio base stations are divided and assigned to the reporting channel and the simultaneous call channel of a control channel. Then, an interference margin in a cell end is set by a prescribed calculation diagram. Finally, the transmission power of the design object channel is calculated from a set margin value, etc., and set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio base station and a code division multiple access (hereinafter referred to as CDMA (Coding
CDMA configured by a plurality of mobile stations performing communication using a scheme called "de Division Multiple Access").
The present invention relates to a radio channel design method for a mobile communication system, and more particularly to a radio channel design method for a CDMA mobile communication system that can guarantee the quality of a downlink transmitted from a base station.

[0002]

2. Description of the Related Art Mobile communication systems, such as mobile phones and car phones, which are currently in widespread use, divide an entire service area into relatively small radio zones called cells to provide services. Such a system is called a cellular system. For example, the radius of one cell is set to about 1 to 2 km.

A radio wave transmitted at a certain transmission power from a transmission point propagates in space while attenuating and reaches a reception point. The amount of attenuation received by a radio wave is such that it increases as the distance between the transmission point and the reception point increases. On the other hand, a receiving point needs a certain or more received power to demodulate a received radio wave with a required quality. Therefore, if the cell radius is increased to increase the area covered by one base station, or to reduce the number of base stations required to cover a certain area, the base station and the mobile station require A higher power transmitter must be provided. Conversely, if the cell radius is reduced to reduce the area covered by one base station, or if the capacity is increased by increasing the number of base stations to cover a certain area, the base station and the mobile station And the required transmission power is reduced.

As described above, in mobile communication in which information is wirelessly transmitted between a base station and a mobile station, setting of a cell radius and setting of transmission power are extremely important issues. Then, based on the above-described properties, the maximum transmission power of the mobile station or the transmission power or the maximum transmission power of a plurality of channels transmitted from the base station is set, or the request for the given transmission power or capacity is set. The design in which the cell radius is set from is referred to as radio channel design. Conventional frequency division multiple access (hereinafter referred to as FDMA (Frequency Division Multi
ple Access) or a time division multiple access (hereinafter abbreviated as TDMA (Time Division Multiple Access)) mobile communication system. This is described in detail in Chapter 4 of "Mobile Communication," (Kagaku Shimbun, September 1992), and the description is omitted here.

On the other hand, the CDMA system is a system in which each user shares the same radio frequency band by using different spreading codes. The channel is constituted by a spreading code. In a communication system using this CDMA system, all other communication using the same frequency band cause interference. That is, if the same frequency band is used in all cells, a very large number of communications in all cells become interference sources, and the total amount of interference is independent of which spreading code is used by each user for communication. It has the feature that the communication quality is determined.

A cellular mobile communication system employing a CDMA system as a radio access system will be referred to as a CDMA cellular system. From the viewpoint of CDMA cellular design, it is important to design the subscriber capacity of each cell, the coverage (cell radius) of each cell, and the transmission power of the base station and the mobile station. The line design in the CDMA cellular system is to calculate a target subscriber capacity for each cell and transmission power for obtaining coverage for each cell, or to calculate a traffic density given under a condition where transmission power is given. This is a design that calculates the subscriber capacity and coverage for each cell required for processing with a certain quality. As described above, CDs in which all other communications using the same frequency band cause interference
Due to the characteristic peculiar to the MA system, in CDMA cellular, there is a trade-off between capacity and transmission power for coverage. In a radio channel design in a TDMA or FDMA system which is a conventionally used radio access method, a design is performed based on a relationship between coverage and transmission power. Therefore, there has been a serious problem that the conventional radio channel design method cannot be directly applied to the radio channel design of CDMA cellular, which must perform radio channel design in consideration of the relationship with the capacity.

[0007] From such a background, literature (Andrew J. Vit
erbi, "CDMA, principles of spreadspectrum communicat
ion, "Addison-Wesley, Massachusetts, 1995), describes in detail the uplink and downlink channel design of CDMA cellular systems. The capacity can be increased by allowing a larger amount of interference.
Coverage decreases, such as capacity, coverage,
The relationship between the transmission powers is explained. Also, it is explained that the capacity of the downlink is limited by the total transmission power of the base station, but since the capacity, coverage, and transmission power of the uplink are not clarified,
Downlink design was not possible.

Further literatures (Ono, Adachi, "DS-CDMA"
Uplink capacity and transmission power, "IEICE Transactions on Information Technology B-II, Vol.J79-B-II, No.1, pp.17-25, January 1996) In consideration of the above, an attempt is made to improve the accuracy of the uplink line design, but no mention is made of the downlink line.

[0009] On the other hand, considering future mobile multimedia communication in which video on demand, WWW browsing, and the like are performed in a mobile environment, it is expected that traffic on the downlink will be overwhelmingly greater than that on the uplink. Further, management of mobility of a mobile station, which is the most important function in mobile communication, is performed via a downlink control channel. For example, when the power of the mobile station is turned on, the mobile station searches for and receives a control channel transmitted from the base station to specify the zone in which the mobile station is located, and performs operations such as location registration. Further, even when the mobile station moves to another zone as the mobile station moves, the mobile station detects that it has moved by measuring the reception power of the control channel transmitted from the base station. Thus, the downlink control channel plays an extremely important role in the cellular system.

[0010]

However, as described above, the conventional method of designing a radio channel of a mobile communication system using the FDMA or TDMA system is directly applied to CDMA.
It cannot be used in cellular. Furthermore, until now CDM
Circuit design techniques in A Cellular have evolved for the uplink. For the downlink, line design could not be performed because the relationship between capacity, coverage, and transmission power had not been clarified so far. This means that it is not possible to guarantee the quality of the downlink control channel transmitted from the base station, and there are many places where outgoing and incoming calls cannot be made even within the zone. There was an unfavorable problem.

[0011] The present invention has been made in view of the above,
An object of the present invention is to provide a radio channel design method for a CDMA mobile communication system that can guarantee the quality of a downlink transmitted from a base station in a CDMA mobile communication system.

[0012]

To achieve the above object, the present invention according to claim 1 comprises a radio base station and a plurality of mobile stations communicating with the radio base station by code division multiple access. A radio channel design method for a CDMA mobile communication system, comprising: adding a ratio of transmission power of a channel to be designed to total power transmitted from a radio base station to required reception power of a channel to be designed at a cell edge. The gist is to design a radio channel based on a mutual relationship between a margin to be set and a location ratio at which a channel to be designed cannot satisfy required quality.

According to the first aspect of the present invention, the ratio of the transmission power of the design target channel to the total transmission power of the base station, the margin to be added to the required reception power of the design target channel at the cell edge, and the design Since the radio channel design is performed based on the mutual relationship between the location ratios where the target channel cannot satisfy the required quality, the transmission power of the base station can be set so as to satisfy a predetermined location ratio.

[0014] The present invention described in claim 2 is the same as claim 1.
In the invention described above, the radio channel design sets a ratio of transmission power of a channel to be designed to the total power transmitted from the radio base station, and the set ratio and the channel to be designed satisfy required quality. Calculate the margin to be added to the required received power of the channel to be designed at the cell edge from the required value of the locational ratio that cannot be satisfied, and calculate the transmission power of the design channel using this calculated margin The gist of the procedure is to perform the procedure.

According to the second aspect of the present invention, the ratio of the transmission power of the design target channel to the total transmission power of the base station is set, and this ratio and the location where the design target channel cannot satisfy the required quality. From the required value of the ratio and the margin added to the required reception power of the design target channel at the cell edge, and using this margin to calculate the transmission power of the design channel, a given target is set. It is possible to obtain highly reliable downlink quality that satisfies the subscriber capacity.

Further, the present invention according to claim 3 provides the invention according to claim 1.
In the described invention, the radio channel design sets a margin to be added to a required reception power of a channel to be designed at a cell edge, and the value of the set margin and a channel to be designed satisfy required quality. The gist is that the procedure is to set the ratio of the transmission power of the channel to be designed to the total power transmitted from the radio base station from the required value of the locational ratio that cannot be satisfied.

According to the third aspect of the present invention, a margin to be added to the required reception power of the channel to be designed at the cell edge is set, and the value of this margin and the channel to be designed satisfy the required quality. In order to set the ratio of the transmission power of the design target channel to the total transmission power of the base station from the required value of the locational ratio that cannot be used, the reliability is set so that the transmission power of each given channel can be satisfied. High downlink quality can be obtained.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the radio channel design is such that the transmission power of the channel to be designed occupies the total power transmitted from the radio base station and the cell edge. Set a margin to be added to the required received power of the channel to be designed, and calculate the local ratio where the channel to be designed cannot satisfy the required quality from the set ratio and the value of the margin, The setting process of the ratio and the margin in the total power and the calculation of the local ratio are repeated so that the obtained local ratio approaches the required value with sufficient accuracy, and the local ratio is sufficient. The gist is that the transmission power of the design target channel is calculated by using the ratio and the margin in the total power when the accuracy approaches the required value.

According to the present invention, the ratio of the transmission power of the design target channel to the total transmission power of the base station and the margin added to the required reception power of the design target channel at the cell edge are set. Setting, and calculating the locational ratio at which the design target channel cannot satisfy the required quality from the ratio and the value of the margin, and calculating the total power so that the locational ratio approaches the required value with sufficient accuracy. The process of setting the ratio and the ratio of the margin and the calculation of the location ratio are repeated, and when the location ratio approaches the required value with sufficient accuracy, the design target channel is calculated using the ratio and the margin to the total power. , It is possible to obtain highly reliable downlink quality that satisfies the given total transmission power.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a CDMA mobile communication system to which a radio channel design method according to one embodiment of the present invention is applied. The mobile communication system shown in FIG. And the mobile station 12 communicate with each other using the CDMA system.

In the radio channel design method for the CDMA mobile communication system configured as described above, the ratio of the transmission power of the channel to be designed to the total power transmitted from the radio base station, ξ, The relationship between the margin M added to the required received power and the local ratio P _outage where the channel to be designed cannot satisfy the required quality will be described.
In the present embodiment, the relationship between them is obtained by computer simulation. The outline of the computer simulation is shown below.

(1) Cell / sector selection Propagation loss based cell / sector selection (2) Propagation environment Distance attenuation (constant α), shadowing (standard deviation σ),
No instantaneous fluctuation (3) Orthogonal code The effect of orthogonalization within the own sector is expected to be γ = 0.5 on average.

(4) Transmission power of base station It is assumed that the base station always transmits at the maximum transmission power.
Therefore, the amount of interference received by a mobile station is determined only by the position of the own station, and does not depend on the number or location of other mobile stations.

Now, channels transmitted from a base station (all J stations) with unit power are received by a certain mobile station, and those arranged in descending order of received power are denoted as R ₁ , R ₂ ,..., R _J. . Assuming that the total transmission power of the base station is P and the ratio of the power allocated to the channel to the total transmission power is ξ, E _b / I ₀ (E _b is information 1 of the own communication wave) corresponding to the quality of the channel. Energy per bit, I ₀ is the power density of the interference wave)

(Equation 1) It is. Here, N ₀ is the thermal noise power density of the receiver, and B is the transmission speed of the channel. X is a variable representing an amount corresponding to the ratio of the total interference amount to the interference from the own sector.

(Equation 2) Defined. If this falls below the required value (E _b / I ₀ ) _req , it is defined as deterioration,

(Equation 3) And can be transformed. For the purpose of modifying the condition shown in Expression (3) so as to be expressed by the same expression regardless of the cell radius, a required reception level E _b | Cell-edge at the cell edge is introduced as a reference value.

FIG. 4 shows the relationship between the required reception level at the cell edge and other values.

N _O is the thermal noise power density of the receiver, I _0max is the maximum allowable interference power density at the cell edge,
I _0max is M times N ₀ .

Further, I _0max is _set to a required value of quality (E _b / I
₀ ) req times the required reception level at the cell edge E _b | Ce
ll-edge is obtained.

Also, the ratio of E _b | Cell-edge to N ₀ is _expressed as (E _b / N
₀ ) Represented as Cell-edge.

From the figure,

(Equation 4) Can be expressed as However, it is _{C 0 = pg / (E b} / I 0) req.

By computer simulation, x and y are actually calculated, and the deterioration rate for a given M is calculated. In the computer simulation, α = 3.8, σ _s =
It is a 6-sector configuration at 10 dB. FIG. 2 shows the relationship between the local deterioration rate and the power distribution ratio.

Next, a procedure for executing a radio channel design based on the obtained relation will be described with reference to numerical examples.

First, a wireless channel design procedure according to an embodiment will be described. This example is an example of a case where the radio circuit design is started at the request of the subscriber capacity.

The ratio 送信 of the transmission power of the channel to be designed to the total power transmitted from the radio base station is set as follows. In the present embodiment, a downlink control channel will be described as an example. As a control channel, a broadcast channel (B
Consider two types, CCH) and paging channel (PCH). The BCCH is a common control channel used to broadcast common control information and the like to a plurality of mobile stations existing in the own zone. On the other hand, the PCH is a channel used to notify the incoming call to the mobile station. FIG. 3 shows how transmission power is distributed by the base station. In FIG. 3, π of the entire transmission power is allocated for the communication channel. The setting of π is determined from the request of the subscriber capacity. The subscriber capacity increases as π increases. The relationship between π and subscriber capacity is described, for example, in the literature, Andrew.
J. Viterbi, "CDMA Principles of Spread Spectrum Co
mmunication, "Addison-Wesley, Massachusetts, 1995, there is a detailed description, and the description is omitted. It is assumed that ξ _BCCH and ξ _PCH of the entire transmission power are respectively allocated to _BCCH and _PCH.
The required E _b / I ₀ for H and PCH are (E _b /
_Assuming that I ₀ ) _BCCH and (E _b / I ₀ ) _PCH and the transmission rates are B _BCCH and B _PCH , respectively, the ratio of ξ _BCCH to ξ _PCH is

(Equation 5) It is. In this document, ξ _BCCH : ξ _PCH = 1: 1 is used as an example for numerical calculation for ease of explanation. Also, π = 0.8 is used. From the above, ξ _BCCH = 0.1,
ξ _PCH was set to 0.1.

Next, referring to FIG. 2, an interference margin M (including a shadowing margin) at the cell edge is set. B
For both CCH and PCH, spreading factor pg = 256, required E
Assuming that _b / I ₀ = 5 dB, C ₀ = 80.95.
From か ら_BCCH = ξ _PCH = 0.1, both ξC ₀ =
8.095. From FIG. 2, about 5 dB is obtained as the value of M for satisfying the location ratio of 5%.

Finally, the transmission power of the design target channel is calculated. The setting of the transmission power itself can be executed in the same procedure as the calculation performed in the conventional wireless channel design. For example, the calculation is performed as follows.

[0037]

## EQU6 ## Transmission power = thermal noise power of receiver + required SIR +
Propagation loss at cell edge + margin M + mobile station antenna gain + base station antenna gain + feeding loss at base station Next, a radio channel design procedure according to another embodiment will be described. This example corresponds to an example in which a radio channel design is started after transmission power of each design target channel is given.

In this case, first, a margin M to be added to the required received power of the channel to be designed at the cell edge is set. This can be calculated using the formula used in the above description. That is,

## EQU7 ## Transmission power = thermal noise power of receiver + required SIR +
Using the relationship of propagation loss at the cell edge + margin M + mobile station antenna gain + base station antenna gain + feeding loss at the base station, the following equation is obtained.

[0039]

## EQU8 ## Margin M = Transmission power−Thermal noise power of receiver−
Required SIR-propagation loss at cell edge-mobile station antenna gain-base station antenna gain-feeding loss at base station Assuming that M = 5 dB is obtained as a result of the above calculation, the description will be continued below. Using FIG. 2, ξC ₀ = 7.5 is obtained as a value on the horizontal axis corresponding to M = 5 dB and the local deterioration rate 5%. Both BCCH and PCH have a spreading factor pg = 256,
Assuming that the required E _b / I ₀ = 5 dB, C ₀ = 80.95. Therefore, ξ _BCCH = ξ _PCH = 7.5 / 80.95 =
0.09265 is obtained.

Next, a radio channel design procedure according to another embodiment will be described. This example corresponds to a design example in which the operation is started after the total transmission power of the wireless base station is given.

In this case, since the total transmission power of the radio base station is given, the ratio of the transmission power of the channel to be designed to the total power transmitted from the radio base station is determined. The transmission power of the channel is determined. Therefore, the margin M to be added to the required received power of the channel to be designed at the cell edge is

## EQU9 ## Margin M = Transmission power−Thermal noise power of receiver−
It is calculated from required SIR-propagation loss at cell edge-mobile station antenna gain-base station antenna gain-feed loss at base station. Therefore, ξ and M have a one-to-one correspondence.

For example, starting from a small {or a large} and performing a search as follows,
This is a method for executing a radio line design. Set ξ to an appropriate value. Next, the margin M

Calculated from the following equation: Margin M = transmission power−thermal noise power of receiver−required SIR−propagation loss at cell edge−mobile station antenna gain−base station antenna gain−feeding loss at base station. Next, referring to FIG. 2, the local ratio P at which the channel to be designed cannot satisfy the required quality
Seeking _outage . This procedure is repeated until _{Poutage approaches the} required value with sufficient accuracy.

Using the resulting ξ or M,
The transmission power of the channel to be designed, for example, using ξ,

## EQU11 ## The transmission power of the channel to be designed = ξ × the total transmission power of the radio base station is obtained, and the design is completed.

[0044]

As described above, according to the first aspect of the present invention, the ratio of the transmission power of the design target channel to the total transmission power of the base station and the required reception power of the design target channel at the cell edge are reduced. Since the radio channel design is performed based on the mutual relationship between the added margin and the location ratio where the design target channel cannot satisfy the required quality, the CDM
A It becomes possible to set the transmission power of the base station so as to satisfy a predetermined location ratio in the downlink of the mobile communication system, it is possible to guarantee the quality in the downlink,
Thereby, high reliability can be provided for the quality of the downlink. Further, since the transmission power of the base station is set to the optimum value, it is effective in economicalization of the base station device in a low traffic area and an increase in capacity in a high traffic area.

According to the second aspect of the present invention, the ratio of the transmission power of the design target channel to the total transmission power of the base station is set, and this ratio and the location where the design target channel cannot satisfy the required quality are set. From the required value of the ratio, a margin to be added to the required received power of the design target channel at the cell edge is calculated, and the transmission power of the design channel is calculated using this margin. Reliable downlink quality that satisfies the user capacity can be obtained.

According to the third aspect of the present invention, a margin to be added to the required received power of the channel to be designed at the cell edge is set, and the value of this margin and the channel to be designed satisfy the required quality. Since the ratio of the transmission power of the design target channel to the total transmission power of the base station is set based on the required value of the locational ratio that cannot be achieved, it is highly reliable so that the transmission power of each given channel can be satisfied. The quality of the downlink can be obtained.

According to the present invention, the ratio of the transmission power of the design target channel to the total transmission power of the base station and the margin added to the required reception power of the design target channel at the cell edge are set. Then, from the ratio and the value of the margin, a locational ratio at which the design target channel cannot satisfy the required quality is calculated, and the total power is set to a value close to a required value with sufficient accuracy. The process of setting the occupation ratio and the margin and calculating the locational ratio are repeated, and the ratio and the margin in the total power when the locational ratio is close to a required value with sufficient accuracy are used to design the channel to be designed. Since the transmission power is calculated,
It is possible to obtain highly reliable downlink quality that satisfies the given total transmission power.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a CDMA mobile communication system to which a radio channel design method according to an embodiment of the present invention is applied.

FIG. 2 is a graph showing an example of the interrelationship between a local deterioration rate, a ratio of transmission power, and a margin value.

FIG. 3 is a diagram for explaining an example of distribution of transmission power of a wireless base station.

FIG. 4 is a diagram showing a relationship between reception levels at a cell edge.

[Explanation of symbols]

 11 wireless base station 12 mobile station

Claims (4)

[Claims] 1. A radio channel design method for a CDMA mobile communication system comprising a radio base station and a plurality of mobile stations communicating with the radio base station by code division multiple access, the transmission power of a channel to be designed. Of the total power transmitted from the radio base station, the margin added to the required received power of the channel to be designed at the cell edge, and the location where the channel to be designed cannot satisfy the required quality. A radio channel design method for a CDMA mobile communication system, comprising: designing a radio channel based on a mutual relationship between the radio channel and the mobile terminal. 2. The radio channel design sets a ratio of transmission power of a channel to be designed to the total power transmitted from a radio base station, and the set ratio and a channel to be designed satisfy a required quality. Calculate the margin to be added to the required received power of the channel to be designed at the cell edge from the required value of the locational ratio that cannot be satisfied, and calculate the transmission power of the design channel using this calculated margin 2. The method according to claim 1, wherein the step is performed. 3. The radio channel design sets a margin to be added to a required reception power of a channel to be designed at a cell edge, and the value of the set margin and a channel to be designed satisfy required quality. 2. The method according to claim 1, wherein a step of setting a ratio of the transmission power of the channel to be designed to the total power transmitted from the radio base station is set based on a required value of a location ratio that cannot be satisfied. A radio channel design method for a CDMA mobile communication system. 4. The radio channel design includes a ratio of transmission power of a channel to be designed to the total power transmitted from a radio base station and a margin to be added to required reception power of a channel to be designed at a cell edge. Is calculated, and from the set ratio and the margin value, the locational ratio at which the channel being designed cannot satisfy the required quality is calculated, and the obtained locational ratio is calculated with sufficient accuracy to the required value. The setting process of the ratio and the margin in the total power and the calculation of the local ratio are repeated so as to be close to the total power, and the local ratio occupies the total power when the local ratio approaches the required value with sufficient accuracy. 2. The radio channel designing method for a CDMA mobile communication system according to claim 1, wherein the transmission power is calculated by using a ratio and a margin to calculate transmission power of a design target channel. Law.