JPH02237231A - Base station selecting system of mobile communication system and mobile terminal - Google Patents

Abstract

PURPOSE:To prevent the wasteful use of a battery and a frequency by permitting a mobile terminal to estimate the reception power of an incoming radio line in respective peripheral base stations and selecting the base station based on said reception power in a mobile communication system in which zones different in a size coexist. CONSTITUTION:The mobile terminal 20 periodically receives signals from a base station a10', a base station b11 and a base station c12, and obtains a propagation loss from the difference of transmission power and the reception power of an outgoing radio line, which has actually been received, at every base station from a base station transmission power code in the signals. Then, the reception power of the incoming radio line in respective base stations is obtained from the difference of the maximum transmission power of the mobile terminal 20 and the propagation loss. At the start time of communication, the base station with least propagation loss is selected, and whether it can execute communication based on the reception power of the incoming radio line in the base station or not is decided. When it is decided to be communicable, a connection request is given. Thus, the wasteful use of the battery and the frequency can be prevent in the mobile communication system where the zones different in the size coexist.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a base station selection method and a mobile terminal for a mobile communication system, and particularly to a base station selection method and a mobile terminal for a small zone type (cellular type) mobile communication system. Regarding the terminal.

[Conventional technology]

The conventional base station selection method for general mobile communication systems is
When a mobile terminal selects a base station, it simply selects the base station that received the downlink radio link signal transmitted by the base station with the strongest reception power [References Z.C. Fuller (Z. C. Fluhr), “Adpanst.
Advanced Mobile Phone Service Control Architecture
ne Service: Control Archit
The Bell System Technical Journal
al Journal), January 1979, 62-6
3 pages].

Recently, as a new trend in small zone mobile radio systems such as car telephone systems, demand for mobile terminals that can be carried by subscribers has increased. Since such mobile terminals are strongly required to be small and lightweight, the battery cannot be made very large. In other words, an important issue when accommodating mobile terminals in a mobile communication system is battery saving technology. As a particularly effective battery saving technique, transmission power control is well known in which the transmission power of a mobile terminal is controlled according to propagation loss to maintain it at the minimum level necessary for making a phone call. Applying this technology to car phone systems, for example,
If the mobile terminal is far from the base station or is behind a building or mountain, and the propagation loss is large, the transmission power level will be increased. When the transmission power loss decreases due to the transmission power loss, it is conceivable to lower the level of transmission power to save battery power.

In the method of saving battery by transmitting power control, when starting a call by making or receiving a call, or when performing zone switching (handoff) during a call, by selecting a base station with the lowest possible propagation loss, the battery can be saved as much as possible. Battery saving effect can be obtained. This means that if the transmission power of each base station is approximately equal, as in the current car phone system, selecting the base station with the strongest downlink radio link reception power will minimize the propagation loss and maximize the transmission power. This will result in a teri-saving effect.

[Problem to be solved by the invention]

In the base station selection method and mobile terminal of the conventional mobile communication system described above, since the transmission power of each base station is approximately equal,
It is constructed based on the principle that propagation loss can be minimized by selecting the base station with the strongest downlink radio channel reception power. However, at present, in order to meet the rapidly increasing demand for small zone mobile communication systems, zones are becoming increasingly fragmented in urban areas where traffic is concentrated. For example, the distribution of car phone traffic in Tokyo is highly concentrated around Chiyoda and Aoyama, and to deal with this, NTT (Nippon Telegraph and Telephone Corporation) has subdivided zones within Tokyo to reduce subscriber capacity. We are trying to increase this number. Similarly, zone fragmentation is progressing in major cities around the world. This situation began in August 1986.
It is introduced in detail on pages 91 to 104 of the magazine "Nikkei Electronics" published on the 11th of May.

In future mobile communication systems, at least in urban areas with a large number of subscribers, it is essential to introduce microzone systems with extremely small zone radii, although the number of base stations will increase significantly and system costs will increase. I can say that. However, although the system cost may be slightly higher in urban areas, such a micro-zone system is not economically viable in suburban areas where the number of subscribers is not so large, so the service will continue with a small-zone system like the current system. It turns out. In this way, by using a system that uses micro zones in urban areas and small zones in suburban areas, an efficient system can be constructed for service areas where the area density of subscribers varies.

By the way, in a mobile communication system where zones of significantly different sizes coexist, each base station is given transmission power according to the size of the zone, resulting in a large difference in the transmission power of the base stations. . If there is a large difference in the transmit power of base stations in this way, there will be no correlation between the received power of the downlink radio link and the propagation loss. Therefore, by applying the conventional base station selection method as is, Even if a user selects the base station with the strongest received power for the downlink wireless link, it does not mean that the base station with the smallest propagation loss has been selected, and even if Hatteri Saving is performed using transmission power control technology, sufficient effects will not be obtained. The problem is that it cannot be done.

Furthermore, when a mobile terminal with low transmission power is located in a zone of a base station with high transmission power, a significant difference occurs between the transmission power of the base station and the transmission power of the mobile terminal. In such a case, even if the conventional base station selection method 2 is applied as is and the mobile terminal selects the base station with the strongest downlink wireless link reception power and the reception power is sufficient for making a phone call, ,
It is expected that there will be frequent cases where calls cannot be made due to insufficient reception power of the uplink radio link at the base station. In such a case, after the mobile terminal actually transmits a calling signal or an incoming call response signal, it becomes clear that a call cannot be made, resulting in the problem of wasted battery and frequency.

An object of the present invention is to select a base station with the smallest propagation loss in order to obtain the maximum battery saving effect using transmission power control technology in a mobile communication system where zones of different sizes coexist, and An object of the present invention is to provide a base station selection method for a mobile communication system that prevents wasteful use of batteries and frequencies by determining in advance whether a call is possible or not, and a mobile terminal that implements the method.

[Means to solve the problem]

The present invention is a base station selection method for a mobile communication system that covers a service area with a plurality of base stations, in which each base station broadcasts a signal informing mobile terminals of its transmission power, and the mobile terminals The propagation loss between each peripheral base station and the mobile terminal is calculated from the transmission power of the base station and the reception power of the actually received downlink radio link, and the transmission loss between each peripheral base station and the mobile terminal is calculated from the transmission power of the mobile terminal and the transmission power of the base station. The method is characterized in that the received power of the uplink radio link is estimated, and the base station is selected and communicated with based on the received power of the uplink radio link.

The present invention also provides a means for determining the transmission power of each peripheral base station, and a means for determining the reception power of a downlink radio link from each peripheral base station, in a mobile terminal of a mobile communication system that covers a service area with a plurality of base stations. means for determining the propagation loss between the respective peripheral base stations from the transmission power and the reception power of the downlink radio link; and means for determining the propagation loss between the uplink radio links at each peripheral base station from the transmission power and the transmission power of the mobile terminal. It is characterized by comprising: means for estimating the received power of the line; and means for comparing the received power of the uplink radio line with a predetermined threshold.

[Operation] As described above, in order to obtain the maximum battery saving effect through transmission power control, it is necessary to always select a base station with the minimum propagation loss.

However, if there is a large difference between the transmission powers of the base stations, it is not possible to determine the magnitude of the propagation loss just by comparing the received power of the downlink radio link from each base station. Generally, in mobile communication systems, the base station and mobile terminal use the same antenna for transmission and reception, so there is a propagation loss in the downlink radio link from the base station to the mobile terminal, and the propagation loss in the uplink radio link from the mobile terminal to the base station. It is considered that the propagation loss is the same. Therefore, if the mobile terminal can know the transmission power of each base station, it can directly calculate and compare the propagation loss from the difference between the transmission power and the reception power of the downlink radio link.
The base station with the minimum propagation loss can be selected.

Furthermore, from the difference between the maximum transmission power of the mobile terminal and the propagation loss,
By estimating the received power of the uplink radio channel at this base station, it can be determined in advance whether or not it is possible to communicate with this base station.

That is, if the estimated received power of the uplink wireless channel is greater than the minimum required received power for making a call, it is determined that the call is possible. Furthermore, if the estimated received power of the uplink wireless line is less than the minimum required received power for making a call, it is determined that the call is not possible.

Here, methods for a mobile terminal to know the transmission power of each base station include a method in which the base station broadcasts a signal indicating the current transmission power, or a method in which each base station is given a base station ID that allows it to know the transmission power. One possible method is to provide this in advance. The former method is suitable for a system in which the base station's transmission power is changed depending on the situation, and the latter method is suitable for a system in which the base station's transmission power is fixed.

In the present invention, a mobile terminal in standby or in communication receives the downlink radio link of each surrounding base station, and calculates the propagation loss from the difference between the transmission power and the received power of the actually received downlink radio link for each base station. , the received power of the uplink radio link at each base station is determined from the difference between the maximum transmission power of the mobile terminal and the propagation loss. When starting a call, the base station with the lowest propagation loss is selected, and it is determined whether the call is possible based on the received power of the uplink wireless link at this base station. If it is determined that the call is possible, a connection request is made. , if it is determined that a call is not possible, the connection request is prohibited.

Also, if a base station appears during a call that provides a propagation loss smaller than that of the currently connected base station, that base station is selected as a candidate for zone switching, and the path loss of the currently connected base station is changed. It is determined whether to perform zone switching based on the values of the propagation loss of the base station, the received power of the uplink radio link at the currently connected base station, and the received power of the uplink radio link at the new base station.

In this way, the mobile terminal uses transmission power control technology to select the base station with the smallest propagation loss so as to obtain the maximum battery saving effect, and also determines in advance whether or not it is possible to communicate with that base station. By doing so, you can prevent wasting battery and frequency.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a mobile communication system for explaining an embodiment of the base station selection method of the present invention.

The base station alo, the base station bll, and the base station C12 have current transmission powers Pa, P. , P, and transmits base station information including a base station transmission power code.

The mobile terminal 20 in standby is connected to base station a10 and base station b1.
1.Receive the signal from the base station cl2 periodically, and calculate the transmission power Pa, Pb, PC from the base station transmission power code in the signal.
, and the received power E a of the actually received downlink wireless link
Find 4nl+E b4m+E C4m. And transmission power P. , Pb, PC and downlink wireless link received power E
From the difference between a-im+E b-sm+E c-em, the propagation loss L. of each base station is determined. ,L. , Lc. Furthermore, the maximum transmission power P1 of the mobile terminal 20 and the propagation loss L, , Lb
, LC, the received power E1 of the uplink radio channel at each base station is E m -+b + E1. seek.

When starting a call by making or receiving a call, the mobile terminal 20 uses the propagation loss L. of each base station. ．． L,. The base station with the smallest propagation loss is selected by comparing Lc, and the reception power of the uplink radio link at that base station is compared with the minimum reception power P required for making a call. For example, in Figure 1, Lb<L
8 If Lc, select base station bll and select E m-
Compare pb and Pth. If E≧P, it is determined that a call is possible and a calling signal or an incoming call response signal is transmitted. Also E ffl. If b < P th, it is determined that a call is not possible, and transmission of a calling signal or an incoming call response signal is prohibited.

During a call, as well as during standby, the mobile terminal 20 periodically loses the propagation loss L. ．． Lb. Find Lc. Then, the propagation loss (L,) of the currently connected base station (base station b11) and other propagation losses (L. and LC) are compared, and the propagation loss (L,) of the currently connected base station (base station b11) is compared. If a base station appears that provides a propagation loss smaller than It is determined whether zone switching is possible based on the received power of the uplink radio link at the base station and the received power of the uplink radio link at the new base station.

As described above, according to this embodiment, each base station broadcasts a signal informing the mobile terminal of its transmission power, and the mobile terminal
The propagation loss between each peripheral base station and the mobile terminal is calculated from the transmission power of the surrounding base station and the received power of the actually received downlink radio link, and the transmission loss between each peripheral base station and the mobile terminal is calculated from this propagation loss and the transmission power of the mobile terminal. The received power of the uplink radio link at the station is estimated, and based on this received power of the uplink radio link, a base station is selected and communicated with.

FIG. 2 is a block diagram of an embodiment of a mobile terminal of the present invention.

This mobile terminal includes an antenna 21, a duplexer 22, a receiving circuit 24 that functions as a means for determining the transmission power of each peripheral base station 10 and IL 12, and a receiving circuit 24 that determines the received power of the downlink radio link from each peripheral base station. A reception power measurement circuit 23 functions as a means for determining the propagation loss between each peripheral base station from the transmission power and the reception power of the downlink radio link, and a calculation unit 25 functions as a means for determining the propagation loss between the transmission power and the reception power of the downlink radio link. an arithmetic unit 29 that functions as a means for estimating the received power of an uplink wireless line at each peripheral base station from the electric power; and an arithmetic unit 2;
a memory 26 that stores the propagation loss calculated by 5 and the received power of the uplink radio link estimated by the calculator 25; a control unit 27 that functions as a means for comparing the received power of the uplink radio link with a predetermined threshold; It has a transmitting circuit 28 and an out-of-service area indicator lamp 30.

Next, the operation of this mobile terminal will be explained.
, IL 12 is assumed to be transmitting base station information including a base station transmission power code indicating a value of transmission power and a base station ID.

For example, base station information transmitted by the base station 10 is input to the received power measuring circuit 23 and the receiving circuit 24 via the antenna 21 and duplexer 22 of the mobile terminal 20 in standby or on a call. The received power measuring circuit 23 measures the received power of the downlink radio channel and outputs the result to the calculator 25. The receiving circuit 24 outputs the transmission power and base station ID obtained from the base station transmission power code in the base station information to the arithmetic unit 25. The computing unit 25 calculates the transmission Sta loss from the difference between the value of the transmission power of the base station and the value of the reception power of the downlink radio link,
It is stored in the memory 26 along with the base station ID. Arithmetic unit 29 calculates the uplink radio channel reception power at the base station from the difference between the maximum transmission power of the mobile terminal and the propagation loss output from computing unit 25, and stores it in memory 26 together with the base station ID.

The control unit 27 controls the received power measuring circuit 23 and the receiving circuit 24 so that the base station ID, propagation loss, and received power of the uplink radio link of all peripheral base stations are determined.

In the case of a call origination or an incoming call response, the control unit 27 selects the base station with the lowest propagation loss based on the contents of the memory 26, and compares the received power of the uplink radio link at this base station with the minimum received power required for making a call. to determine if it is possible to make a call. If it is determined that a call is possible, the control unit 27 controls the transmitting circuit 28 to transmit a calling signal or an incoming call response signal. If it is determined that a call is not possible, the control unit 27 turns on the out-of-service area indicator lamp 30 and prohibits the transmission of a calling signal or an incoming call response signal.

During a call, the control unit 27 periodically compares the propagation loss of the currently connected base station in the memory 26 with the propagation loss of other base stations, and selects a propagation loss smaller than the propagation loss of the currently connected base station. When a base station that causes loss appears, that base station is considered a candidate for zone switching, and the propagation loss of the currently connected base station, the propagation loss of the new base station, and the ``two radios'' of the currently connected base station are determined. Based on the received power of the line and the received power of the uplink radio link at the new base station, it is determined whether the switching is to be performed. If it is determined that zone switching is to be performed, the transmitting circuit 28 is controlled to start zone switching control for that base station.

[Effects of the Invention] As described above in detail, according to the present invention, even in a mobile communication system where zones of different sizes coexist, a mobile terminal can obtain maximum battery saving effect using transmission power control technology. By selecting the base station with the smallest propagation loss so that communication is possible, and determining in advance whether or not it is possible to communicate with that base station, it is possible to prevent wasted time and frequency.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a mobile communication system for explaining an embodiment of the base station selection method of the present invention, and FIG. 2 is a block diagram of an embodiment of a mobile terminal of the present invention. 10... Base station a 11... Base station b 12... Base station C 20... Mobile terminal 21... Antenna 22... Dual unit 23... Received power measuring circuit 24... Receiving circuit 25... Arithmetic unit 26... Memory 27... Control unit 28... Transmitting circuit 29 ... Arithmetic unit 30 ... Out of range indicator lamp E l-+m+ E b. +11+E Cim”
・Received power L of the downlink radio link at the mobile terminal. ．． L. ,Lc......propagation loss P. ,P. ，
PC...Transmission power E Ill -sa +
Ep. ,E,,U. ...Received power of uplink wireless link at base station

Claims (2)

[Claims] (1) A base station selection method for a mobile communication system that covers a service area with multiple base stations, in which each base station broadcasts a signal informing the mobile terminal of its transmission power, and the mobile terminal selects nearby bases. The propagation loss between each peripheral base station and the mobile terminal is calculated from the transmission power of the station and the reception power of the actually received downlink radio link, and the transmission loss at each peripheral base station is calculated from the propagation loss and the transmission power of the mobile terminal. A base station selection method for a mobile communication system, characterized in that the received power of an uplink radio link is estimated, and a base station is selected and communicated with based on the received power of the uplink radio link. (2) in a mobile terminal of a mobile communication system that covers a service area with a plurality of base stations, means for determining the transmission power of each peripheral base station; means for determining the reception power of a downlink wireless link from each peripheral base station; means for determining a propagation loss between the respective peripheral base stations from the transmission power and the reception power of the downlink radio link; A mobile terminal for a mobile communication system, comprising: means for estimating power; and means for comparing received power of the uplink radio channel with a predetermined threshold.