JPH11168419A - Antenna diversity system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna diversity system with which a radio signal can be stably received by switching and selecting an antenna, based on received electric field intensity (RSSI-P). SOLUTION: When any radio signal is not received yet, a plurality of antennas 20a and 20b are successively switched at certain time intervals corresponding to a reference clock CLOCK, and carrier sense is performed by any antenna with which a high reception level can be provided. When the received electric field intensity through the relevant antenna under carrier sense gets higher than a prescribed threshold, with such a state as a trigger, the received electric field intensity provided from the respective antennas is compared by a comparator 13, the antenna to provide the highest received electric field intensity is selected, the relevant radio signal is received by using the relevant antenna, and relevant radio data are satisfactorily and stably received while using the antenna of the highest received electric field intensity to the reception end of the relevant radio signals (data).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna diversity system for receiving a radio signal by switching a plurality of antennas, and more particularly, to selecting an antenna used for receiving a radio signal based on a received electric field strength (RSSI-P). About the method of doing.

[0002]

2. Description of the Related Art In radio communication such as mobile communication, a plurality of radio signal paths are generated due to reflection of radio waves between a transmitter 1 and a receiver 2 as shown in FIG. Suffers from fading, and the reception condition deteriorates. A diversity reception method is known as a technique for reducing the effects of such fading, and an antenna diversity method for switching a plurality of antennas to receive a radio signal is known as one of the diversity reception methods. .

In the antenna diversity system, for example, as shown in FIG. 7, a receiver 2 has two antennas 2a and 2b.
The antennas 2a and 2b are switched to select an antenna having a good reception state and receive a radio signal. Here, in the conventional antenna diversity system, the antennas 2a and 2b are switched by using the deterioration of the reception state and the deterioration of the reception error rate (packet error rate) of the radio signal as a trigger.

[0004]

However, in the method of switching the receiving antenna triggered by the deterioration of the receiving state, a situation occurs in which the antenna is switched during the reception of the radio signal (data). There is a problem that a reception error occurs. Further, in the method of switching the receiving antenna triggered by the deterioration of the reception error rate of the radio signal, the processing for calculating the error rate at a certain time interval is performed. There has been a problem that the state cannot be maintained in a good state.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an antenna diversity system capable of receiving radio signals stably.

[0006]

In the antenna diversity system according to the present invention, when a radio signal is not received, a plurality of antennas are sequentially switched at a certain time interval. Career sense is available. When the received electric field strength of the antenna becomes equal to or more than a predetermined threshold value by performing the carrier sense as described above, using this as a trigger, the received electric field strength obtained from each antenna is compared, and the antenna having the largest received electric field strength is determined. The selected radio signal is received using the selected antenna. As a result, the antenna having the maximum received electric field strength is used until the reception of the radio signal (data) is completed, and the radio data can be satisfactorily and stably received.

Here, the received electric field strength (RSSI-P) is a signal obtained by continuously amplifying the received radio wave (for example, several tens μV → several V). Carrier sense (reception of radio signal)
Is detected. It should be noted that the present invention is a pager, a mobile phone,
It can be applied to various wireless communication devices, including mobile communication devices such as mobile computers,
The number of antennas is not limited to two and can be applied to a wireless communication device including two or more antennas.

[0008]

FIG. 1 shows an example of a diversity circuit according to the antenna diversity system of the present invention. This diversity circuit includes an A / D converter 10,
First register 11, second register 12, comparator 1
3, RSSI detector 14, first timing generator 1
5, the second timing generator 16, the first OR circuit 1
7, a second OR circuit 18.

The A / D converter 10 and the RSSI detector 14 receive a received electric field strength (RSSI-
P) is input to the first timing generator 15, and a reference clock CLOCK is output from a clock generation circuit (not shown) to the first timing generator 15.
Is entered. Further, the antenna selection signal ANTSEL-P is output from the second OR circuit 18, and the antenna switch 1 is switched in accordance with the antenna selection signal ANTSEL-P.
9 is two antennas 20 provided in the wireless communication device
a or 20b is switched to the antenna used for reception.

This embodiment is applied to a pager for wirelessly receiving packet data. The structure of the packet data is as shown in FIG. From the top of the packet, the packet includes a call name including a call address and the like, a preamble including a synchronization signal and the like, and a C for performing an error check.
It includes an RC, various flags, a main message forming data contents, and a CRC for performing error checking. Here, the receiving circuit of the wireless receiver, when receiving (carrier sense) the call name located at the head of the packet, the received electric field strength increases sharply, and when this received electric field strength exceeds a predetermined threshold value, this is used as a trigger. The diversity circuit performs a sequence for selecting an antenna as described later. Note that the preamble period (10 μsec in this example) is set longer than the processing time (9.5 μsec in this example) for selecting and determining an antenna according to the sequence.
This telegram following the preamble is reliably received by the selected antenna.

The diversity circuit shown in FIG. 1 uses an antenna 20a and an antenna 20a according to a procedure as shown in FIG.
b). First, the RSSI detector 1
4 constantly monitors the received field strength (RSSI-P) (step S1), and does not output enable to the second timing generator 16 when the RSSI-P is less than a predetermined threshold. As a result, the first timing generator 1
5, via the first OR circuit 18 and the second OR circuit 18, the antenna selection signal ANTSEL- whose binary value switches at a predetermined time interval based on the reference clock CLOCK.
P is input to the antenna switch 19, and the two antennas 20a and 20b are switched at the predetermined time interval (step S2). In this state, the A / D converter 10 operates, but the registers 11 and 12 are in an inactive state, and the comparison process according to the outputs of these registers is not performed.

As described above, even when the RSSI-P is less than a predetermined threshold value (ie, a state where carrier sense is not performed), antenna switching is performed at a fixed time interval, so that high reception performance is exhibited. be able to. For example, as shown in FIG. 4, even when the reception state is poor due to fading of the antenna 20b, a good reception state can be obtained by switching to the antenna 20a, and the carrier sense is reliably performed to drop the packet data. It is possible to receive without receiving.

When a received electric field strength (RSSI-P) equal to or greater than the threshold value is obtained by one of the antennas 20a and 20b, the RSSI detector 14 outputs an enable signal to the second timing generator 16 and triggers it. To perform an antenna selection sequence. As a result, the A / D converter 10 and the registers 11 and 12
The A / D converter 10 operates according to the LOCK, and at the initial timing, the received electric field strength (RSSI-P) obtained by the reception by one antenna (for example, 20a) is digitized by the A / D converter 10 and the first register 11 (Step S3), and at the next timing, the antenna is switched to the other (step S4), and the reception field strength (RS) obtained by the reception by the other antenna (for example, 20b) is obtained.
(SI-P) is digitized by the A / D converter 10 and latched in the second register 12 (step S).
5). This antenna switching (step S4)
Is performed by the same processing as in step S2.

The comparator 13 determines whether the register 1
The received electric field intensity values latched by the registers 1 and 12 are compared (step S6). If the received electric field intensity value latched by the register 11 exceeds the received electric field intensity value latched by the register 12, the comparator 13 outputs The signal is output by the second OR circuit 18 to switch the polarity of the antenna selection signal ANTSEL-P, and the antenna switch 19 switches the receiving antenna to the other (step S7).

That is, at the first timing, the antenna 2
Field strength (RSSI-
If P) exceeds the received electric field strength (RSSI-P) obtained by the reception by the antenna 20b at the next timing, it is switched again to the antenna 20a at which the high electric field strength is obtained, and at the first timing. The received electric field strength (RSSI-P) obtained by the reception by the antenna 20a is
When the received electric field strength is equal to or less than the received electric field strength (RSSI-P) obtained by the reception by the antenna 20b at the next timing, the higher electric field strength of the antennas 20a and 20b is maintained while the antenna 20b currently used is kept as it is. Is selected as the receiving antenna. Note that the selection determination process is completed before the main message receiving process as described above, and the main message can be received using an antenna that can obtain a higher electric field strength.

The enable output from the RSSI detector 14, which triggers the start of the antenna selection sequence, is maintained until the reception of the packet data ends (the carrier sense ends), whereby the packet data is selected and determined. The reception is continued by the antenna that has been set. That is, as shown in FIG.
An antenna capable of carrier sensing is selected from Oa and antenna 20b, and the packet data is received using this antenna. As described above, since antenna switching is not performed during reception of certain data, a reception error due to antenna switching does not occur in the data, and stable and good reception can be performed.

Here, during the data reception after the antenna is selected and set, the received field strength (RSSI-RS) is such that the magnitudes of the latch values of the registers 11 and 12 are reversed.
If the fluctuation of P) occurs, the antenna may be switched during data reception.
In order to prevent such a situation, the reception electric field strength (R
SSI-P) is set to a certain high value within a range capable of maintaining the required carrier sense sensitivity so as not to fall below the fluctuating threshold value of SSI-P.
It is preferable that the enable output from the RSSI detector 14 is maintained until the reception of the data is completed. If the threshold cannot be set relatively high,
Received electric field strength (RSSI-
A circuit for counting the fluctuation frequency of P) is added, so that instantaneous fluctuations are canceled and stable reception is maintained, and antenna switching is performed again only for fluctuations of a frequency that cannot be ignored. I just need.

[0018]

As described above, according to the antenna diversity system according to the present invention, when a radio signal is not received, a plurality of antennas are sequentially switched at a certain time interval to obtain a high reception level. Carrier sense with an antenna, when the carrier sensed in this way and the received electric field strength by the antenna becomes a predetermined threshold or more,
By using this as a trigger, the antenna having the highest received electric field strength is used until the end of the reception of the radio signal, so that the radio signal can be satisfactorily and stably received.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a diversity circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of packet data according to an embodiment of the present invention.

FIG. 3 is a flowchart illustrating a procedure of an antenna switching process according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating an operation of antenna switching according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating an antenna switching operation according to an embodiment of the present invention.

FIG. 6 is a diagram illustrating fading by conventional multipath.

FIG. 7 is a diagram illustrating the principle of antenna diversity.

[Explanation of symbols]

11, 12: register, 13: comparator, 14
... RSSI detector, 19 ... antenna switcher,
20a, 20b ... antenna, RSSI-P ...
Received electric field strength, ANTSEL-P ... antenna selection signal,

Claims (1)

[Claims] In an antenna diversity system in which a plurality of antennas are switched to receive a radio signal, when a radio signal is not received, a plurality of antennas are sequentially switched to receive a radio signal and reduce the electric field received by any of the antennas. Triggered by being equal to or greater than a predetermined threshold value, comparing received electric field strengths obtained from each antenna, selecting an antenna having the highest received electric field strength, and performing reception of the radio signal using the antenna. An antenna diversity system.