JPH04213931A - Mobile telephone set - Google Patents

Abstract

PURPOSE:To simplify the constitution of a mobile telephone set employing the communication system to measure an electric field strength of an adjacent cell by an idle slot by forming a transmission slot, a reception slot and the idle slot in time division. CONSTITUTION:The electric field strength of an adjacent cell is measured by changing only a 2nd local oscillation circuit 34 in a 1st local oscillation circuit 6 and the 2nd local oscillation circuit 34 processing a reception signal.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile telephone device, and more particularly to a mobile telephone device suitable for application to a cellular type mobile telephone device.

0002

2. Description of the Related Art A so-called cellular system has been put into practical use in communication systems with mobile bodies, such as car telephone systems. This cellular system divides the communication area into multiple cells, and each cell has a base station (fixed station).
A base station is provided to communicate with mobile objects within the cell. In this case, each mobile unit performs transmission and reception with the base station, and also receives control signals to determine which cell base station it can communicate with. That is, for example, in the case of a car telephone system using a digital line, the slot configuration when each mobile body accesses the base station is as shown in FIG. 4, a transmission slot T from the mobile body and a reception slot R at the mobile body. , and idle slot I are repeated in sequence, each slot being several ms. A communication method with such a slot configuration is TDMA (Time
Division Multiple Access
) method.

[0003] In the period of idle slot I,
Measures the electric field strength of the cell currently communicating with the adjacent cell. That is, a control signal transmitted from a base station of an adjacent cell is received in idle slot I, and the field strength (RSSI) is determined from the reception level of this control signal.
l Strings Indicator). In this case, each cell is assigned a frequency (channel) of a control signal for determining field strength, and adjacent cells are set to have different frequencies of control signals. Based on this determination, if the electric field strength of the currently communicating cell is stronger, communication with the same base station is continued, and if the electric field strength of the adjacent cell is stronger, it is determined that the neighbor cell has approached the base station. Then, a command to switch to communication with a base station of an adjacent cell is transmitted to the base station. When switching to communication with this adjacent cell, after transmitting this command, the communication is switched to communication with the adjacent cell at a predetermined timing based on an instruction from the base station side.

FIG. 5 shows the configuration of a transmitting/receiving device on the mobile body side in which such communication is performed. In the figure, 1 indicates a transmitting/receiving antenna, and the signal f received by this antenna 1 is
R is supplied to a band pass filter (BPF) 3 that constitutes a receiving circuit via a changeover switch 2, and this BPF 3
is supplied to a mixer 5 via an amplifier 4. Also,
In the figure, 6 indicates a local oscillator as a frequency synthesizer for selecting a reception channel, and the oscillation output fS of this oscillator 6 is
is supplied to the mixer 5 via the bandpass filter 7. The oscillation frequency fS of this oscillator 6 is fR + fi1
(fi1 is the first intermediate frequency). In this case, the local oscillator 6 also serves as an oscillator for selecting a transmission channel, which will be described later.

[0005] Then, the output fR of the amplifier 4 in the mixer 5
The oscillation output fS of the oscillator 6 is mixed with the first intermediate frequency signal fi1 of the received signal. Then, this intermediate frequency signal is supplied to a mixer 9 via a bandpass filter 8, and this mixer 9 generates an oscillation output fi1 of the local oscillator 10.
-fi2 (fi2 is the second intermediate frequency), and the mixed output is passed through the bandpass filter 11 to the output terminal 1.
2, a second intermediate frequency signal fi of a received signal of a predetermined channel;
2 is obtained, and this second intermediate frequency signal fi2 is supplied to a subsequent received signal processing circuit (not shown).

Further, the baseband transmission signal obtained at the input terminal 21 is supplied to a modulation circuit 22, and this modulation circuit 2
2 modulates the transmission signal based on the oscillation output fTL of the oscillator 23, and supplies this modulated output to the mixer 24. The mixer 24 is supplied with the oscillation output fS of the oscillator 6,
By mixing this oscillation output fS and the transmission signal, a transmission signal fT of a predetermined channel is obtained. The transmission signal fT of this predetermined channel is passed through a bandpass filter 25 and an amplifier 2.
6 and the changeover switch 2 to the antenna 1, and is transmitted from the antenna 1.

Here, the oscillation output fS of the oscillator 6 is (f
R + fi1), and the received signal fR
The frequency difference of the transmission channel between the transmission signal fT and the transmission signal fT is ΔF
Then, the oscillation output fTL of the oscillator 23 is (fi1+Δ
F). With this configuration, by simply changing the oscillation frequency fS of the oscillator 6 according to the channel used for communication between the base station and the mobile object, the receiving channel and the transmitting channel can be linked with the frequency difference ΔF. and change. Therefore, one local oscillator can serve both as a reception channel selection local oscillator and a transmission channel selection local oscillator, making it possible to easily configure a mobile communication device (telephone device).

[0008]

[Problems to be Solved by the Invention] However, in a mobile communication device having such a configuration, it is necessary to change the oscillation frequency of the local oscillator 6 for selecting a transmission/reception channel in the idle slot I to the transmission slot T and the reception slot R. was there. That is, as mentioned above, since reception and transmission can be performed with the same oscillation frequency of the oscillator 6, there is no need to change the oscillation frequency of the oscillator 6 in the transmission slot T and the reception slot R, but in the idle slot I, each cell It was necessary to receive a control signal at a predetermined frequency for each time, and it was necessary to switch to a reception frequency corresponding to this control signal. Therefore, by changing the oscillation frequency of the oscillator 6, during each idle slot I, the reception frequency is switched from one corresponding to the reception signal fR to one corresponding to the control signal, and after receiving this control signal, the reception frequency is switched again. It was necessary to change the reception frequency corresponding to the reception signal fR, and it was necessary to change the oscillation frequency of the oscillator 6 twice within one slot. Here, the length (time) of each idle slot I
When there is a sufficient amount of time, there is time to change the oscillation frequency of the oscillator 6, but in reality each slot is several ms long, so the local oscillator for receiving channel selection and the local oscillator for transmitting channel selection are used in this way. It was difficult to measure the electric field strength of adjacent cells in a configuration in which a single local oscillator was used. In particular, the oscillation frequency of oscillator 6 is several hundred MH
It was impossible to switch such a high frequency oscillation signal at high speed.

An object of the present invention is to integrate a local oscillator for receiving channel selection and a local oscillator for transmitting channel selection into one.
To enable reliable measurement of electric field strength in an idle slot with a communication device of a simple configuration that can be used individually.

0010

[Means for Solving the Problems] The present invention provides a communication system in which, as shown in FIG. 1, for example, a transmission slot, a reception slot, and an idle slot are formed in a time-division manner, and the electric field strength of an adjacent cell is measured in the idle slot. In a mobile telephone device according to the present invention, a first local oscillation circuit (6) and a second local oscillation circuit (34) are provided, the oscillation frequency of the first local oscillation circuit (6) is fixed, and the oscillation frequency of the first local oscillation circuit (6) is fixed. At the same time, the oscillation frequency of the second local oscillation circuit (34) is switched between receiving in the receiving slot and measuring the electric field strength in the idle slot, and The oscillation frequency of the second local oscillation circuit (34) is mixed with the received signal mixed with the oscillation frequency of the local oscillation circuit (6) to perform reception and measurement of electric field strength.

[0011]

[Operation] By doing this, there is no need to change the oscillation frequency of the first local oscillation circuit in the idle slot, and only the oscillation frequency of the second local oscillation circuit needs to be changed. Therefore, for example, if the transmission slot is after the idle slot, the oscillation frequency of the second local oscillator circuit in the idle slot is changed from that corresponding to the frequency of the received signal to that of the control signal required in the idle slot. It is only necessary to change the oscillation frequency of the second local oscillation circuit to one that corresponds to the frequency of the received signal during the next transmission slot, and to change the oscillation frequency of the second local oscillation circuit to one that corresponds to the frequency of the received signal during the next transmission slot. You will be able to afford to receive.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. In these FIGS. 1 to 3, FIGS. 4 and 5
The same reference numerals are given to corresponding parts, and detailed explanation thereof will be omitted.

FIG. 1 is a configuration diagram showing a mobile telephone device of this embodiment mounted on a mobile body, which is applied to a cellular mobile telephone system like the conventional example, and has a transmission slot T and a reception slot R. This is applied to a TDMA telephone system in which the idle slot I and the idle slot I are formed in a time-division manner. In this case, the configuration on the transmitting side is the same as the conventional one (FIG. 5). In this example, the signal fR received by the antenna 1 is supplied to the mixer 5 via the changeover switch 2, bandpass filter 3, and amplifier 4. This received signal fR and a transmitted signal fT to be described later are transmitted at a frequency around 800 MHz, and the bandpass filter 3 sets the center frequency of the passed signal to approximately 800 MHz, which corresponds to this received signal fR. In this mixer 5, an oscillation output fS (
=fR +fi1) to produce the first intermediate frequency signal fi1
get.

The first intermediate frequency signal fi1 output from the mixer 5 is supplied to the movable contact 43 of the changeover switch 40 via the low-pass filter 31. Here, the cutoff frequency of the low-pass filter 31 is approximately 800 MHz. Further, the changeover switch 40 connects the first fixed contact 41 and the movable contact 43 when the slot is the receiving slot R, and connects the second fixed contact 42 and the movable contact 43 when the slot is the idle slot I. Then, the received signal obtained at the first fixed contact 41 of the changeover switch 40 is supplied to the first fixed contact 51 of the changeover switch 50 via the bandpass filter 32. This bandpass filter 32 sets the center frequency of the passing signal to 9, which corresponds to the first intermediate frequency fi1.
The frequency shall be approximately 10kHz. In addition, the second switch of the changeover switch 40
The received signal obtained at the fixed contact 42 is directly supplied to the second fixed contact 52 of the changeover switch 50. Then, the received signal obtained at the movable contact 53 of the changeover switch 50 is supplied to the mixer 33. Further, in the figure, reference numeral 34 indicates a local oscillator, which is configured as a frequency synthesizer, and supplies its oscillation output to the mixer 33. In this case, the oscillation output of the local oscillator 34 is changed between the reception slot R and the idle slot I.

Then, the mixer 33 mixes the received signal obtained at the movable contact 53 of the changeover switch 50 with the oscillation output of the oscillator 34 to obtain a second intermediate frequency signal fi2, and the second intermediate frequency signal fi2 is bandpassed. It is supplied to an output terminal 36 via a filter 35. In this case, the bandpass filter 35 sets the center frequency of the passed signal to about 455 kHz.

Other parts are shown in FIG. 5 as a conventional example.
It is configured similarly to a mobile telephone device.

Next, the operation of communication using this mobile telephone device will be explained with reference to FIGS. 2 and 3.

As shown in FIG. 2A, the communication system used in this device is a TDMA system in which a transmission slot T, a reception slot R, and an idle slot I are formed in a time-division manner. The oscillation output of the local oscillator 6 for
It is assumed that the frequency fS is constant in all slots. This frequency fS is expressed as the sum of the first intermediate frequency fi1 and the frequency fR of the receiving channel. And oscillator 3
The oscillation frequency of 4 is fi1- in reception slot R.
fi2, and by mixing this frequency signal fi1-fi2 with the first intermediate frequency signal fi1, the second intermediate frequency signal f
i2 is obtained, and this second intermediate frequency signal fi2 is outputted to the output terminal 36.
and supplies it to the subsequent circuit. Here, in this receiving slot R, the movable contacts 43, 53 of the changeover switches 40, 50 are in a connected state with the first fixed contacts 41, 51, respectively, so the first intermediate frequency signal fi1 is filtered through the bandpass filter. 32 to a mixer 33. In this case, the bandpass filter 32 uses the first intermediate frequency signal fi
Since only one band is passed through, only the received signal fR of the predetermined channel is sent to the output terminal 36 as the second intermediate frequency signal f.
It is extracted as i2.

When it is idle slot I, the oscillation frequency of the oscillator 34 is fi1-fi2+Δf
and change it by Δf. Here, Δf is the difference between the reception frequency fR and the control signal frequency fa of the adjacent cell. When the idle slot I is selected, the movable contacts 43 and 53 of the changeover switches 40 and 50 are connected to the second fixed contacts 42 and 52, respectively, so that the first intermediate frequency signal fi1 is transmitted to the bandpass filter 32. It is supplied to the mixer 33 without going through it. Therefore, in the idle slot I, the first intermediate frequency signal fi1 is not subjected to image removal by the band pass filter 32, and contains image frequencies that are not cut by the low pass filter 31.

Here, regarding this image frequency, FIG.
To explain using, the control signal frequency fa of the adjacent cell
When centering on , there are fa -2 above and below this frequency fa.
Theoretically, image frequencies of fi2 and fa+2fi2 exist. In this case, in actual cellular mobile phone systems, the control signal frequencies of each cell are not spaced at equal intervals; the lower image frequency fa -2fi2 and the upper image frequency fa -2fi2 are Channel settings are made such that only one of the image frequencies fa+2fi2 exists. Therefore, the control signal frequency fa and the lower image frequency fa −2fi2
When receiving the band in which the control signal frequency fa and the upper image frequency fa+2fi2 exist, one side receives only the control signal frequency fa. The received power is
That is, it can be determined that the weaker received electric field strength is the electric field strength when only the control signal frequency fa is received.

In this example, this fact is utilized to determine the electric field strength of the control signal frequency fa of the adjacent cell. For example, as shown in FIG. 2, only the control signal frequency fa is received in a certain idle slot I. Then, in the next idle slot I, a signal containing the upper image frequency fa+2fi2 is received. Then, the strength of the electric field strength of the received signal at each idle slot I obtained at the output terminal 36 is determined, and the one with the weaker electric field strength (in this example, the electric field strength at the first idle slot I) is selected from that of the adjacent cell. Judged as received electric field strength.

[0022] For example, when the received field strength of this adjacent cell is compared with the field strength of the signal currently being received in reception slot R, and it is determined that communication can be better with the base station of the adjacent cell, Communication is switched to the base station of this adjacent cell.

In this way, the reception field strength of the adjacent cell is determined using the idle slot I, but in this example, only the oscillation frequency of the oscillator 34 is changed in the idle slot I, so that the transmission/reception channel selection is The oscillation frequency of the local oscillator 6 does not change in any slot, and even if the reception frequency is changed in the idle slot I, the oscillation frequency of the local oscillator 6 does not change in any slot. There are no negative effects. Therefore, it is not necessary for the receiving circuit to be in a state where it can receive the signal fR in the transmission slot T that follows the idle slot I, but it is only necessary that it be in a state in which it can receive the signal fR in the reception slot R that follows the transmission slot T. . For this reason, Figure 2
As shown in , the time T from the start of each idle slot I until just before the end of the period of this idle slot I
1, the oscillation frequency of the oscillator 34 on the receiving circuit side is changed from fi1-fi2 to fi1-fi2+Δf. Then, when this time T1 has elapsed and the oscillation frequency of the oscillator 34 reaches fi1-fi2+Δf, the received electric field strength of the control signal frequency fa of the adjacent cell is determined. Then, during the elapse of time T2 from this time until the end of the next transmission slot T, the oscillator 34 on the receiving circuit side
The oscillation frequency of is returned to fi1-fi2 again.

By changing the oscillation frequency of the oscillator 34 in this way, the change in the oscillation frequency required for receiving the control signal of the adjacent cell in the idle slot I can be adjusted between each idle slot I and this idle slot I. It only needs to be done in the next transmission slot T, and compared to changing the oscillation frequency of the oscillator 34 only in the idle slot I, the time to change the oscillation frequency is almost double, and the oscillation frequency can be changed with a margin. The electric field strength of adjacent cells can be determined stably. Further, since the oscillator 34 that changes the oscillation frequency is a second local oscillator, its oscillation frequency is significantly lower than that of the oscillator 6, which is the first local oscillator. Here, when the oscillation frequency is low, the time required for changing the oscillation frequency is short, and from this point as well, there is a margin for changing the oscillation frequency, and the electric field strength of the adjacent cell can be determined stably.

From these points, according to the transmitter/receiver of this example, despite the simple configuration in which the oscillator for transmitting and receiving channel selection is shared, it is possible to stably determine the electric field strength of the adjacent cell in a short idle slot I. can. Further, transmission in the transmission slot T can also be performed stably without being affected by the determination of the electric field strength of the adjacent cell in the idle slot I.

[0026]

According to the present invention, despite the simple configuration in which the oscillator for transmitting and receiving channel selection is shared, it is possible to stably determine the electric field strength of an adjacent cell in a short idle slot. Accordingly, it is possible to simplify the configuration of a telephone device suitable for a type of mobile telephone system.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of a mobile telephone device of the present invention.

FIG. 2 is a timing diagram illustrating an embodiment of the mobile telephone device of the present invention.

FIG. 3 is a characteristic diagram illustrating an embodiment of the mobile telephone device of the present invention.

FIG. 4 is an explanatory diagram showing a slot configuration of a TDMA system.

FIG. 5 is a configuration diagram showing an example of a conventional mobile telephone device.

[Explanation of symbols]

1 Antenna 5 Mixer 6 Oscillator 32 Bandpass filter 33 Mixer 34 Oscillator 35 Bandpass filter 36 Output terminal 40 Selector switch 50 Selector switch

Claims (1)

[Claims] 1. A mobile telephone device employing a communication method in which a transmission slot, a reception slot, and an idle slot are formed in a time-division manner, and the electric field strength of an adjacent cell is measured in the idle slot. A second local oscillation circuit is provided, the oscillation frequency of the first local oscillation circuit is fixed, reception in the reception slot and electric field strength measurement in the idle slot are performed, and the second local oscillation circuit is provided with a second local oscillation circuit.
The oscillation frequency of the local oscillation circuit is switched between reception in the reception slot and measurement of the electric field strength in the idle slot, and the reception signal mixed with the oscillation frequency of the first local oscillation circuit is mixed with the second one. A mobile telephone device that mixes the oscillation frequencies of local oscillation circuits to perform reception and field strength measurement.