JPH08223086A - Radio communication system with line condition guide function - Google Patents

Abstract

PURPOSE: To enable a service user to perform satisfactory communication again after restoration of the line state by previously reporting the probability of line disconnection and the restoration estimated time to the service user. CONSTITUTION: In the communication system, a user terminal equipment and/or a base station equipment is provided with a circuit 1 which estimates the average extent of attenuation in accordance with the long-time variance of the reception signal intensity, a circuit 2 which distinguishes between attenuation owing to rainfall and attenuation owing to shielding in accordance with short- time variance of the reception signal intensity and estimates the extent of attenuation owing to rainfall, a circuit 4 which estimates the present strength of rainfall in accordance with the extent of attenuation owing to rainfall, and a circuit 5 which estimates the future rainfall condition in accordance with the present strength of rainfall. If there is the probability of line disconnection, the alarm indicating this probability and the restoration estimated time are reported to the service user.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite communication system such as a fixed satellite communication system, a mobile communication system and a satellite broadcasting system, and a wireless communication such as a fixed wireless system and a terrestrial wireless system such as a terminal subscriber wireless system. It relates to the system, and in particular to the guidance of the line status.

[0002]

2. Description of the Related Art In a mobile communication system, the line margin is small due to system restrictions and the signal strength is severely deteriorated by propagation. The quality is not good enough. Therefore, in the conventional technique, when the received signal strength becomes smaller than a predetermined value, a warning sound is emitted for the purpose of avoiding the line disconnection or informing the user of the possibility of the line disconnection. It calls the user's attention. In addition, in the conventional technology for fixed satellite communication systems and satellite broadcasting systems, the line status and the received image quality are constantly monitored, and if the signal strength deterioration due to propagation is large, it is announced that the line status is currently bad. .

[0003]

In recent satellite communication systems, especially mobile satellite communication systems, non-GSO satellites are used for the purpose of reducing propagation delay time or reducing propagation loss. The system using is attracting attention. In such a system, it is considered to use a high frequency such as 20/30 GHz for the feeder link between the communication satellite and the ground fixed station due to the problem of frequency sharing with other systems. However, in such a frequency band, signal attenuation due to rainfall is large, and there is a high risk of disconnection. On the other hand, in future satellite communication systems, it is required to form part of wideband ISDN (B-ISDN) not only in fixed satellite communication but also in mobile satellite communication. In such a system, since it is necessary to perform high-speed and wideband transmission, the antenna system is required to have high directivity and satellite tracking function. Therefore, especially in a system using a mobile terminal, it is necessary to use a high frequency such as 20/30 GHz to realize the above function. Therefore, it is assumed that future satellite communication systems will be strongly affected by rainfall attenuation not only on the feeder link but also on the service link directly connected to the mobile station.

In the prior art, when the signal quality is inevitably inevitably caused at a specific position in the service area, such as the shielding attenuation due to a building, the service user should move in the direction in which the received signal strength is high. Although it is effective because it encourages the communication, it predicts the risk of line disconnection for the deterioration of signal quality that may occur in an arbitrary or relatively wide area within the service area due to natural phenomena such as rain attenuation. However, even if the service user tries to communicate again, if the line condition is not recovered, communication is impossible, and there is a problem that the service user is not useful as information.

Degradation of propagation phenomena such as rain attenuation, fading, and scintillation can be considered as a factor of the natural phenomenon that causes the deterioration of the line quality at any place in the service area. However, in the frequency band of 1 GHz or higher used for wireless communication, the influence of scintillation is small, so rain attenuation and fading are problems in wireless communication services.

According to the present invention, among natural phenomena, in particular, when the signal strength is deteriorated due to rain attenuation, the service user is likely to be disconnected, and the recovery expected time is notified in advance. An object of the present invention is to provide a wireless communication system having a line status guidance function that allows a service user to wait for recovery of the line status and try again good communication.

[0007]

In order to achieve the above-mentioned object, the present invention provides a user terminal equipment or base station equipment of a communication system, or both equipments, with a long-term variation and a short-term variation of a received signal strength. The current rainfall attenuation is calculated from this, and the current rainfall intensity is estimated from this to estimate the state of the propagation path in the future.
It has a configuration characterized in that it has a function of notifying a service user in advance of a line disconnection and a predicted recovery time.

[0008]

According to the present invention, when the communication line is likely to be disconnected, the service user is notified in advance of the possibility of the line disconnection and the expected recovery time of the line state. Therefore, if the line is disconnected, or if the line condition deteriorates significantly, the service user must wait for the line condition to recover and perform good communication again without unnecessarily attempting to restart communication. You can

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a first embodiment according to the present invention when a non-GSO satellite is used and a mobile satellite communication service centering on a telephone service and a low speed data service is assumed. In such a system, the service link has an L band (1.5 GHz to 1.6 GHz) or S band.
Frequencies in the (2.5 GHz to 2.6 GHz) band are often used, but due to the problem of frequency sharing with other systems, the Ku band (12 GHz to 14 GHz) is used for the feeder link.
It is conceivable to use a high frequency such as z) or Ka band (20 GHz to 30 GHz). In the low frequency band such as the L band or the S band, there is almost no influence of the rain attenuation, but in the high frequency such as the Ku band or the Ka band, as shown in FIG. Deteriorates the line quality. Therefore, in this example, a circuit for estimating the state of the current and future propagation paths and a circuit for notifying the possibility of disconnection and the expected recovery time are provided only to the gateway earth station.

In FIG. 1, reference numeral 1 is a long-term fluctuation measuring circuit for recording long-term fluctuations in received signal strength from a satellite, and 2 is short-time fluctuation measurement for recording short-term fluctuations in received signal strength. Circuit. As the received signal, a signal for communication may be used, or a beacon wave from a satellite may be used. When estimating the rain attenuation from the received signal strength, it is necessary to distinguish it from the shield attenuation, especially in land mobile communication. 1 and 2 are circuits for this purpose. In general, shield attenuation can be well described by a knife-edge model with a metal plate. According to the knife edge model, in the case of shield attenuation, as shown in FIG. 3, the received signal strength oscillates immediately before the attenuation starts, and then rapidly attenuates. On the other hand, in the case of rain attenuation, the received signal strength does not oscillate immediately before the attenuation starts. However, since the additional noise due to the propagation increases, the received signal strength greatly varies due to the noise. By using this fact, the long-term fluctuation measuring circuit 1 records the long-term fluctuation to determine the average attenuation amount from the normal received signal strength, and the short-term fluctuation measuring circuit 2 measures the short-term fluctuation. From the situation, it is possible to estimate the amount of attenuation due to rainfall by determining whether it is due to shielding or rain. An alarm signal generating circuit 3 outputs an alarm signal when the amount of rainfall attenuation exceeds a predetermined value from the system margin.

Reference numeral 4 is a circuit for estimating the rainfall intensity from the rainfall attenuation amount. According to ITU-R Report 721-3 (ITU, 1990), the relationship between the rainfall attenuation amount g _R (dB / km) per km and the rainfall intensity R (mm / h) is expressed by the following formula.

[0012]

## EQU1 ## g _R = K _R ^a (1) k = [k _H + k _V + (k _H −k _V ) cos ² θ cos 2τ] / 2 (2) a = [k _H a _H + k _V a _V + ( _{k V a H + k V a} V) cos 2 θ cos2τ ] / 2K (3) where, theta is the angle of elevation, tau is the tilt angle of the polarization with respect to the horizontal plane. Further, k _H , k _V , a _H , and a _V are given for each frequency as shown in Table 1.

[0013]

[Table 1]

Therefore, in a particular satellite communication system, the frequency to be used, the elevation angle of the satellite, and the tilt angle of polarization are given in advance. If the average length in the height direction of the rain cloud is L _C , the length L _P of the radio wave passing through the rain cloud is

## EQU2 ## It is given by L _P = L _C / sin θ (4). From the above, the rainfall attenuation amount g _R per 1 km is obtained by dividing the rainfall attenuation amount estimated using the circuits 1 and 2 by L _P , and if the inverse transformation of equation (1) is applied, the rainfall intensity The estimated value R of is calculated.

Reference numeral 5 is a circuit for estimating the continuation of rainfall in the future. When the estimated value R of the present rainfall intensity becomes larger than a predetermined value, the estimated value of the present rainfall intensity is shown. From this, we estimate the time that is expected to continue raining in the future, which is stronger than the predetermined rainfall intensity. It has been shown that the average duration of rainfall follows a lognormal distribution as shown in equation (4).

[0016]

(Equation 3) Here, s and m are the standard deviation and average value of ln (x). The median μ and variance σ of the lognormal distribution are
Using s and m,

[0017]

[Equation 4] Is represented. These are functions of the rainfall intensity R and are shown in FIG.
As shown in, the log-log graph is a straight line.

Utilizing these conditions, the duration of heavy rain is estimated as follows. First, μ and σ are obtained from the current estimated rainfall intensity value R using FIG. Next, using the obtained μ and σ, Equation (6) and Equation (7)
The inverse transformation of is performed and s and m are calculated. Finally, the formula
Using (5), calculate the time when heavy rainfall is expected to continue at a constant risk rate P _A. That is,

(Equation 5) The duration T such that FIG. 5 shows an example of estimating the duration of rainfall. From FIG. 5, assuming that the current rainfall intensity R is 50 mm / h and the risk rate is 10%, for example, the time period during which heavy rain of 50 mm / h or more continues is estimated to be about 12 minutes. If the current rainfall intensity R is 25 mm / h and the risk rate is 30%, the estimated value of the duration of heavy rain of 50 mm / h or more is about 10 minutes. In this way, the estimation circuit 5 estimates the time when heavy rain is expected to continue in the future.

Reference numeral 6 is an alarm based on the outputs of the alarm issuing circuit 3 and the rainfall duration estimation circuit 5 that the service user may be disconnected due to rainfall and the expected recovery time of the line. Is an information sending circuit for sending the.

As described above, in the present embodiment, the current and future propagation path states are estimated from the average received power fluctuation and the short-time received power fluctuation, and when there is a risk of line disconnection, The service user is informed of the possibility of line disconnection and the estimated recovery time.

In a system that provides a mobile satellite communication service centering on high-speed data services such as B-ISDN and Asynchronous Transfer Mode (ATM) transmission using Non-GSO satellites, both the feeder link and the service link are provided. To K
It is possible to use a high frequency such as the u band or the Ka band. In such a case, by adding the circuit shown in the first embodiment not only to the gateway (gateway) earth station but also to the user terminal equipment, the state estimation of the current and future propagation paths can be performed by the feeder link and the service. It is possible to issue the information to the service user by performing the link separately.

FIG. 6 shows a second embodiment according to the present invention. In the system as described above, instead of installing additional circuits in both the gateway earth station and the user terminal equipment, the gateway earth station is provided with: 2 circuits for 1, 2 and 4
Estimate the amount of rain attenuation of beacon waves from satellites by using the system, and using the fluctuation measurement circuits 1-1 and 2-1.
By subtracting the rainfall attenuation amount of the beacon wave estimated using the fluctuation measurement circuits 1-1, 2-1 from the rainfall attenuation amount of the received signal wave for communication estimated by using The rain attenuation of only the service link is estimated.
This is because the signal for communication causes rain attenuation in both the service link and the feeder link, but the beacon wave from the satellite is attenuated only by the rain in the feeder link part, so by calculating the difference between the two, It takes advantage of the fact that rainfall attenuations at feeder links and service links can be estimated separately. Reference numeral 7 is a service link / feeder link rainfall attenuation estimation circuit for this purpose. In this embodiment, the rain attenuation in the feeder link and the service link are separately estimated in this way, and the state of the future propagation path is estimated separately for the feeder link and the service link, so that the service user Is issuing information to.

[0023]

As described above, according to the present invention, when the line condition becomes extremely bad due to rain,
The service user is notified in advance of the line status alert as well as the time when the line status is expected to recover, so the user does not need to unnecessarily try to restart communication, and the line status is restored. It becomes possible to wait for a good communication. In addition, the number of unnecessary calls in the communication system is reduced, which is effective for effective use of the system.

[Brief description of drawings]

FIG. 1 is a system diagram (a) showing a first embodiment according to the present invention.
3 is a block diagram (b).

FIG. 2 is a characteristic diagram showing a rainfall attenuation amount per 1 km.

[Fig. 3] Fig. 3 is a characteristic diagram showing how a building attenuates shielding.

FIG. 4 is a characteristic diagram for obtaining the median and standard deviation of a lognormal distribution.

FIG. 5 is a diagram showing an example in which a predicted duration of rainfall is estimated.

FIG. 6 is a system diagram (a) showing a second embodiment according to the present invention.
Is a block diagram (b).

[Explanation of symbols]

 A, B users 1,1-1,1-2 long-term fluctuation measuring circuit 2,2-1,2-2 short-time fluctuation measuring circuit 3 alarm issuing circuit 4,4-1,4-2 rain issuing circuit 5 Rain duration estimation circuit 6 Information transmission circuit 7 Service link / Feeder link Rain attenuation estimation circuit

Claims (1)

[Claims] 1. A circuit for measuring a long-term fluctuation of a received signal strength and estimating an average attenuation amount of the signal strength in at least one of a user terminal equipment and a base station equipment in a wireless communication system, and a received signal strength A circuit that measures short-term fluctuations and distinguishes between attenuation due to rainfall and attenuation due to shielding to estimate the amount of rainfall attenuation, and a circuit that issues an alarm when the amount of rainfall attenuation exceeds a predetermined value. , A circuit that estimates the current rainfall intensity from the amount of rain attenuation, a circuit that estimates the future rainfall situation from the current rainfall intensity, a warning that the service user may be disconnected, and a recovery forecast It is equipped with a circuit for sending out the time, estimates the current state of the propagation path, and if there is a risk of line disconnection, informs the terminal user in advance of the possibility of line disconnection and the expected recovery time. A wireless communication system having a channel condition information functions, characterized in that it is configured to.