Frequency setting method and apparatus for radio transmission apparatus

Abstract: A frequency setting system for a radio transmission apparatus of the type transmitting a signal in the form of bursts and changing transmission frequency burst by burst. A frequency division data generator (30) feeds both a frequency division data signal representative of a frequency division number and a strobe signal representative of frequency setting to a frequency synchesizer (20). A strobe pulse is fed to the frequency synthesizer immediately after the end of the preceding burst. The frequency division data signal for the next burst can then be sent at any time in the period between that strobe pulse and the end of the burst to which it relates. The timings for generating the frequency division data signal and strobe signal do not need to be determined with regard to the locking time of the frequency synthesizer which is dependent on the kind of the synthesizer, and the frequency, etc.

Description: The present invention relates to a frequency setting method and apparatus, for a radio transmission apparatus of the type transmitting a signal in intermittent bursts and changing the transmission frequency burst by burst. Radio transmission apparatus of the type described include apparatus which determines the transmission frequency in response to the output of a frequency synthesizer which is implemented with a PLL (Phase Locked Loop) system. Specifically, the frequency synthesizer changes the frequency of its output by changing a frequency division number. The frequency division number is given as a frequency division data signal which is applied to the frequency synthesizer. Examples of such apparatus are found in European Patent Application EP-A-0 295 515 and United Kingdom Patent Application GB-A-2 015 277. In the prior art frequency setting method, a strobe signal may also be applied to the frequency synthesizer to constitute a control datum for determining the timing of the frequency division number. A problem with this method is that the locking time necessary for the frequency synthesizer to lock the phase varies with the kind of synthesizer, the size of the change in frequency between successive bursts, and so forth. It follows that the timings for feeding the frequency division data signal and subsequent strobe signal to the frequency synthesizer have to be controlled in matching relation to a particular configuration of the apparatus. The present invention in its various aspects is defined in the independent claims below, to which reference should now be made. Advantageous features of the invention are set forth in the appendant claims. The invention will be described in more detail, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a timing chart representative of a prior art frequency setting method for a radio transmission apparatus; Fig. 2 is a block diagram schematically showing a radio transmission apparatus for practising preferred embodiments of the present invention; Fig. 3 is a block diagram schematically showing a frequency synthesizer included in the apparatus of Fig. 2; Fig. 4 is a block diagram schematically showing a variable frequency divider included in the frequency synthesizer of Fig. 3; Fig. 5 is a timing chart representative of a preferred embodiment of the present invention; and Fig. 6 is a timing chart representative of an alternative embodiment of the present invention. To better understand the present invention, a brief reference will be made to a prior art frequency setting method, shown in Fig. 1. Specifically, Fig. 1 shows a burst signal transmitted from a radio transmission apparatus, and a frequency division data signal and a strobe signal which are applied to a frequency synthesizer. The burst signal is shown as having three bursts 101 to 103 to which are assigned three different frequencies f₁, f₂ and f₃, respectively. Since the frequency differs from one burst to another as mentioned, it is set burst by burst. For the burst 103, for example, the frequency f₃ is set by feeding frequency division data 103A included in the frequency division data signal, and then a strobe 103B included in the strobe signal. Generally, PLL type frequency synthesizers need a certain locking time t for locking the phase. Hence, an arrangement is made such that the delivery of the frequency division data and the strobe to the synthesizer is completed a period of time t before the time when the associated burst begins. However, the locking time t of the frequency synthesizer depends on the kind of synthesizer, the size of the change in frequency between successive bursts, and so forth, as discussed earlier. This results in complicated control over the timings of the frequency division data and strobes. Referring to Fig. 2, there is shown a radio transmission apparatus to which preferred embodiments of the present invention are applied and which assigns a different frequency to each burst. As shown, the radio transmission apparatus, generally 1, has a transmitter 10 for generating a radio signal, and a PLL type frequency synthesizer 20 for setting the transmission frequency of the transmitter 10. A frequency division data generator 30 feeds to the frequency synthesizer 20 a frequency division data signal and a strobe signal which provides the synthesizer 20 with a frequency division setting timing. A switch 40 switches on and off the output of the transmitter 10 to generate bursts while delivering them to an antenna 50. A controller 60 controls the operation timings of the frequency division data generator 30 and switch 40. As shown in Fig. 3, the frequency synthesizer 20 has a variable frequency divider 21, a phase comparator 22, a reference signal oscillator 23, a low pass filter 24, and a VCO (Voltage Controlled Oscillator) 25. The VCO 25 delivers a signal whose frequency is variable to the transmitter 10 via a terminal 26. The variable frequency divider 21 receives the frequency division data from the frequency division data generator 30 via a terminal 27 and the strobe signal via a terminal 28. Fig. 4 shows a specific construction of the variable frequency divider 21. As shown, the variable frequency divider 21 has a programmable counter 210, a latch 211, and a shift register 212. 17-bit frequency data, for example, which is representative of a frequency division number, is serially fed via the terminal 27 to the shift register or 17-bit shift register 212. After all 17-bit frequency data has been fed to the shift register 212, a strobe signal is applied to the latch 211 via the terminal 28. The frequency data lodged in the shift register 212 is applied to the programmable counter 210 to have its frequency changed thereby, so that the output frequency of the frequency synthesizer 20 itself is changed. A clock is fed to the shift register 212. In Fig. 3, the clock is not shown because the clock and the frequency division data are usually fed in a pair. The frequency synthesizer 20 may be implemented by LSI "µPD2833C" available from NEC Corporation, Japan. A preferred embodiment of the present invention practicable with the above construction will be described. Fig. 5 shows timings at which the illustrative embodiment generates a burst signal, a frequency division data signal, and a strobe signal. Let the following description concentrate on a burst 203 included in the burst signal by way of example. The burst 203 has a frequency f₃ which is set by a strobe 203B which is included in the strobe signal. As Fig. 5 indicates, the strobe 203B is fed to the frequency synthesizer 20 at a time t ₂ when the burst 202 immediately preceding the burst 203 has ended, i. e., immediately after the beginning of a non-transmission interval. Further, frequency division data 203A included in the frequency division data signal for setting the frequency of the burst 203 of interest begins to be fed at a time when a burst 201 two bursts ahead of the burst 203 has ended, i. e., immediately after a strobe 202B has been delivered at a time t ₁ which is just after the beginning of a non-transmission interval. The controller 60, therefore, causes the strobe signal and subsequent frequency division data signal to be fed in synchronism with the timings at which the switch 40 is in an OFF state. In this configuration, while the output of the transmitter 10 is switched on and off by the switch switch 40, the frequency is set such that the different frequencies f₁ to f₃ are assigned to the bursts 201 to 203, respectively. As stated above, the illustrative embodiment determines the operation timings with no regard to the locking time which is dependent on the kind of frequency synthesizer, the frequency, and so forth, whereby the control is simplified. Moreover, the frequency synthesizer does not need a high-speed clock because the entire non-transmission interval is usable as the locking time t , so that the design is easy and the carrier-to-noise (C/N) ratio is easy to improve. Further, the interval between successive strobes is fully available for the delivery of the frequency division data, meaning that the signal speed of the frequency data can be lowered. This is successful in reducing the interference between data signals which is apt to occur in the event of interchange of high-speed data, thereby eliminating the need for expensive cables such as shielded cables for signal lines. Hence, the apparatus is inexpensive and simple in construction. Referring to Fig. 6, an alternative embodiment of the present invention will be described. The operation timings shown in Fig. 3 are provided by the controller 60, as follows. Assume a burst 302, for example, which is included in a burst signal and has a frequency f₂. In this particular embodiment, frequency data 302A included in a frequency division data signal for setting the frequency f₂ begins to be fed at a time t ₃ when a burst 301 immediately preceding the burst 302 has begun. A strobe 302B for setting the frequency f₂ is fed at a time when the burst 301 has ended, i. e., at a time t ₄ which is just after the beginning of the non-transmission interval. The controller 60, therefore, causes the frequency division data signal and strobe signal to be delivered in synchronism with the operation timings of the switch 40. Specifically, while the output of the transmitter 10 is switched on and off by the switch 40, the different frequencies f₁ to f₃ are assigned to the bursts 301 to 303, respectively. The advantages attainable with the alternative embodiment shown and described are comparable with those which have been stated in relation to the previous embodiment. In summary, it will be seen that the present system provides a frequency setting method which allows the operation timings of a radio transmission apparatus to be determined without regard to the locking time of a frequency synthesizer which is dependent on the kind of the synthesizer, and the frequency, etc. The method, therefore, promotes simple control over a radio transmission apparatus.

Claims: A frequency setting method for radio transmission apparatus which transmits a signal in intermittent bursts, the transmission frequency changing burst by burst, the method comprising the steps of: generating a frequency division data signal representative of a frequency division number, and a control datum for setting the frequency; and feeding a frequency division data signal for defining the frequency of a burst, and thereafter feeding a control datum to set the frequency for that burst; and in which the control datum is fed immediately after the end of the preceding burst which precedes the burst in respect of which the frequency is to be set. A method according to claim 1, including beginning to feed the frequency division data signal immediately after the control datum which sets the frequency in respect of the said preceding burst. A method according to claim 1, including beginning to feed the frequency division data signal immediately after the beginning of the said preceding burst. Frequency setting apparatus for radio transmission apparatus which transmits a signal in intermittent bursts, the transmission frequency changing burst by burst, the frequency changing apparatus comprising: means (30) for generating a frequency division data signal representative of a frequency division number, and a control datum for setting the frequency; and means (27,28) for feeding a frequency division data signal for defining the frequency of a burst, and thereafter feeding a control datum to set the frequency for that burst; and in which the feeding means (28) feeds the control datum immediately after the end of the preceding burst which precedes the burst in respect of which the frequency is to be set. Apparatus according to claim 4, in which the feeding means (27) begins to feed the frequency division data signal immediately after the control datum which sets the frequency in respect of the said preceding burst. Apparatus according to claim 4, in which the feeding means (27) begins to feed the frequency division data signal immediately after the beginning of the said preceding burst. Apparatus according to claim 4, 5 or 6, in which the generating means comprises frequency synthesizer means (20) having a predetermined locking time for generating said local frequencies in response to control data, and in which the period between the control datum and the beginning of the burst in respect of which the frequency is being set is longer than the said predetermined locking time. An apparatus comprising: transmitter means (10) for successively transmitting at least first and second bursts at predetermined intervals and changing the frequencies of the first and second bursts in response to local frequencies; frequency synthesizer means (20) having a predetermined locking time for generating the local frequencies in response to control data; means (30) for generating a frequency division data signal which is used for setting the frequency of the second burst following the first burst; means (27) for feeding the frequency division data signal between the ends of the first and second bursts; and means (28) for applying a first control datum to the frequency synthesizer means between the end of the first burst and a particular time which is ahead of the second burst, the period between the particular time and the beginning of the second burst being longer than the predetermined locking time.

Inventors: SHIMIZU HIROYUKI, SHIMIZU, HIROYUKI, SHIMIZU, HIROYUKI, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1990
Main classification: H03J5
IPC codes: H04J4, H04J13, H03J5