JPH01256234A - Base station selecting circuit - Google Patents

Abstract

PURPOSE:To surely discriminate a base station with the best condition even in the presence of selective fading at a high speed by selecting a base station whose reception signal power is received strongly among base stations whose error is less as the base station with the best communication condition. CONSTITUTION:A microprocessor 50 constitutes a control means to select a base station whose reception signal power is received strongest by a detector 60 and an A/D converter 70 as the base station with the best condition among base stations whose signal is received without any error detected by an error correction decoder 40 or detected at least with less error. Thus, the control to be connected to the base station with the best condition is attained without talking the observing time longer.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a base station selection circuit, and particularly to a base station selection circuit for realizing a base station selection method in a mobile terminal of a mobile communication system with a small zone configuration such as a car phone. The present invention relates to a base station selection circuit.

[Conventional technology]

Mobile communication systems such as car telephones employ a small zone configuration in which a service area is covered by multiple base stations. In such small zone systems, handoff functionality is required to continue service to mobile terminals that move across zones to different zones during a call. As one implementation form of such handoff, a method for measuring the received signal power from each base station at a mobile terminal and connecting to the strongest base station is proposed in the patent application "Digital Mobile Communication System and mobile terminal”
It is described in.

[Problem to be solved by the invention]

Although the above embankment proposal has various advantages,
However, there is still room for improvement in the following points.

In other words, the method of using received signal power as an evaluation standard has the advantage of being able to determine zone boundaries relatively accurately, but it is not the correct evaluation standard when there is selective fading, which is well known in high-speed digital communications. It is not. For example, under aging conditions (as shown in Figure 3, selectivity is such that multiple radio waves arrive at the mobile terminal and the delay time difference is large), even if the received signal power is strong, due to interference, the correct digital signal cannot be received. It is known that demodulation cannot be performed.

On the other hand, as a more direct signal quality evaluation standard, there is a method using error rate as an evaluation standard, which is used in diversity technology or the like. Since this method ultimately requires a small error rate, it is the most direct observation method and can be said to be the more desirable method.

Therefore, it is conceivable to introduce this into the mobile communication system as described above.

However, this method also has problems. The reason is that if you try to provide service even in areas with poor radio wave conditions, in areas with good conditions such as wide roads, no errors will occur even if you reach the boundary of the service area, and therefore no handoffs will occur. An example of this situation is shown in FIG. 3(b). In FIG. 3 (bl), if a service is to be provided to a back alley with poor propagation conditions, it is necessary to set the transmission power so that the electric field strength at position X becomes the service limit.

In this case, a terminal communicating with base station A moving along the main street will not detect the deterioration until it reaches point Y. This is not a problem when the number of users is small, but if the number of users increases and there are users using the same frequency in distant zones, the frequency will change even if you approach that zone. The problem is that there are users who do not change the information, causing interference.

An object of the present invention is to provide an improved base station selection circuit that can realize a base station selection method in a mobile terminal, etc. using a communication quality evaluation method that solves these problems, and thereby provides a base station selection circuit that can be used even under selective fading. The goal is to connect to a base station with truly good communication quality, avoid interference with other users, and quickly determine the base station with the best conditions.

[Means to solve the problem]

The present invention provides a base station selection circuit for selecting a base station with which a mobile terminal that can receive signals from a plurality of base stations in a mobile communication system with a small zone configuration communicates, the circuit comprising: a received signal power measuring means for measuring the received signal power from possible base stations; an error detecting means for detecting errors in the received signal; The present invention is characterized by comprising a control means for selecting a base station whose received signal power is strongly received by the measuring means as a base station with good communication conditions.

[Effect]

In the present invention, the received signal power is used as the basic standard for communication quality evaluation, and the error rate is introduced as an evaluation standard only when the error rate is extremely large despite the high received signal power, and is used in conjunction with the received signal power. We will adopt this method. By doing this, it is possible to control the connection to the base station with the best conditions without requiring a very long observation time.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

An embodiment of the present invention is shown in FIGS. 1 and 2. FIG.

The embodiment shown in FIG. 1 is an implementation of the communication quality evaluation method according to the present invention in a mobile terminal, and FIG. 1 shows only the part of the terminal configuration that is related to the detection of received signal quality. FIG. 2 shows an algorithm for actually evaluating communication quality and transmitting a handoff request.

As shown in FIG. 1, in the circuit of this embodiment, that is, a mobile communication system with a small zone configuration, a mobile terminal (specifically, a mobile terminal capable of receiving signals from a plurality of base stations)
A circuit for selecting the best base station to communicate with (for example, a car phone) is connected to an input terminal 10 to which a received signal is manually input.
0, a mixer 10, a synthesizer 80 that supplies a carrier signal to the mixer 10, a bandpass filter 20, and a demodulator (to which the output of the bandpass filter 20 is applied)
DEM) 30 and an error correction decoder (DEC).
OD) 4o, a detector 60 that detects the output of the bandpass filter 20, and an A/D that converts the detected output from A/D.
It has a converter 70 and a microprocessor 50.

The error correction decoder 40 and the A/D converter 70 are each connected to a microprocessor 50, the synthesizer 80 is connected to the microprocessor 50, and the microprocessor 50 is connected to a terminal 10.
1, a handoff request signal, which will be described later, is sent out.

The detector 60 and the A/D converter 70 constitute a detection means for detecting the received signal power from a base station with which the mobile terminal can communicate, that is, a received signal power measuring means, and the error correction decoder 40 constitutes an error detection means for detecting errors in the received signal.

Furthermore, the microprocessor 50 includes an error correction decoder 40
Among the base stations that were able to receive the signal without detecting any errors, or at least the base stations that were detected as having few errors, the one with the strongest received signal power was received by the wave detector 60 and the A/D converter 70. It constitutes a control means for selecting a base station as a base station with the best conditions.

In this way, the circuit for selecting the best base station with which a mobile terminal should communicate, which can receive signals from a plurality of base stations in a mobile communication system with a small zone configuration, is capable of communicating with the mobile terminal. The system includes a detector 60 and an A/D converter 70 as means for measuring the received signal power from a base station, and an error correction decoder 40 as an error detection means for detecting errors in the received signal. A microprocessor 50 as a control means that selects the base station from which the received signal power is the strongest in the received signal power detection among the base stations detected as having few errors in the error detection as the base station with the best communication condition. have

In this circuit configuration, received signal power is used as the basic standard for evaluating communication quality, and in addition to this, error rate is introduced as an evaluation standard only in certain cases.

This is done from the following viewpoints.

In other words, when simply using the error rate as an evaluation standard and applying it uniformly to base station selection, the method using the error rate as the evaluation standard is preferable as an evaluation standard because it is closest to the final communication quality, but it is not accurate. The difficulty is that the received signals from a large number of vias are required to estimate the error rate. especially,
When conditions are good, the observation time must be extremely long in order to determine the most favorable base station. Furthermore, under selective fading, where errors occur even though the received signal power is high, errors tend to increase rapidly. Therefore, in the above configuration, the evaluation criteria based on both the received signal power and the error rate described above are used in combination.

Further, to explain the operation, in FIG. 1, a received signal inputted from an input terminal 100 is multiplied by a carrier signal from a synthesizer 80 by a mixer 10, and then passed through a bandpass filter 20 to extract a desired signal. Ru. This output is demodulated by a demodulator 3° and then subjected to error correction by an error correction decoder 40. Error correction decoder 40 outputs an uncorrectable pulse to microprocessor 50 if there is an error that cannot be corrected. At the same time, the received signal is detected by the wave detector 60 to obtain the received signal power, which is converted into a digital signal by the A/D converter 70 and input to the microprocessor 50. The microprocessor 50 determines the base station with the best reception conditions according to the procedure shown in FIG. 2, and transmits a handoff request to the base station if necessary.

Concrete hands! +[ is as follows.

In FIG. 2, in step 321, channel setting is executed, and then in step S22, in this example, it is determined whether there is an error.

That is, first, the frequency of the synthesizer 80 is set to receive the signal of the control channel, which may be the control channel of any base station (step 52).
1). Then, the correction pulse from the error correction decoder 40 is input, and if there is an uncorrectable error, that is, if the answer to step S22 is Yes, the received signal power of that station is not stored; Skip S23,
If the correction is successful, the received signal power of that station is memorized (
Step 523). This operation is performed for all control channels (steps 321 to 524), and when this is completed, the base station with the strongest received signal power among the received signal powers of the stored base stations is determined (step 525).
). The process then proceeds to determination step 326, and if the answer is No, the process returns to step S21, but if the base station is different from the base station in communication, a handoff request signal is output from the terminal 101 ( Step 527
).

By doing so, it is possible to control the base station to always connect to and communicate with the base station with the best conditions.

Furthermore, regarding the time required to select a base station, it is possible to control the connection to the base station with the best conditions at high speed, without requiring a very long observation time.

In the above explanation, the base stations that were able to receive the signal without detecting an error by the error detection means are selected as targets for selection, and the received signal power detection means selects the base station with the strongest received signal power (the base station from which the signal was received the most). Although the base station is interpreted as a base station with good communication conditions, as described above, the base station to be selected may be a base station detected to have few errors.

In addition, the determination of uncorrectability by the decoder of an error correction code can be easily realized with a commonly used block code, and when a convolutional code is used,
For example, in the case of Viterbi decoding, the probability of decoding can be easily determined by observing the bus metric.

Furthermore, although this embodiment has been described as an example in which communication quality is evaluated on the mobile terminal side, similar processing can also be performed on the network side that combines a base station and a switching center. In this case, each base station receives the signal from a specific terminal, performs error correction and measures the received signal power, and collects this information at the exchange to determine the base station with the best conditions. good.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a base station selection circuit that can quickly and reliably determine the base station with the best conditions even when there is selective fading. Further improvements can be made to the above-mentioned proposal.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an example of a control algorithm of the control means in FIG. FIG. 10...Mixer 20...Band pass filter (BPF) 30...Demodulator (DEM) 40...Error correction decoder 50...Microprocessor 60...Detector 70...A/ D converter 80...Synthesizer 100...Input terminal 101...Terminal Attorney Yoshiyuki Iwasa Figure 1 Figure 2

Claims (1)

[Claims] (1) A base station selection circuit for selecting a base station with which a mobile terminal should communicate, which is capable of receiving signals from multiple base stations in a mobile communication system with a small zone configuration, and is capable of communicating with the mobile terminal. a received signal power measuring means for measuring the received signal power from a base station; an error detecting means for detecting errors in the received signal; 1. A base station selection circuit comprising control means for selecting a base station from which a received signal power is strongly received by the means as a base station with good communication conditions.