Radio telephone apparatus with frequency divider used during emission and stopped during reception

Abstract: A radio telephone apparatus of the TDMA/TDD system includes a frequency division orthogonal modulator (111) including a frequency divider (210) for dividing by four a local signal having a frequency which is four times that of the intermediate frequency to obtain a carrier having a frequency shifted from that of the local signal by 90°. The signal to be modulated is subjected to an orthogonal modulation in mixers (203A, 203B) according to the carrier wave to produce an intermediate frequency carrier. The operation of the modulator is stopped in a signal reception state by a signal at a power down terminal (209) to prevent the intermediate frequency carrier from being produced. Signal transmission and reception are conducted using carriers having different frequencies. By these measures cochannel interference from the transmitter entering the receiver in the same housing is reduced.

Description: The present invention relates to a radio telephone apparatus, and in particular, to a radio telephone apparatus operating according to a digital radio telephone system. A mobile communication system is established on the premise of utilization of frequencies as a limited resource. As a radio telephone system increasing the frequency utilization efficiency, there has been proposed a digital radio system adopting the time division multiple access (TDMA) and the time division duplex (TDD) communication. In the TDMA/TDD system, digital communications are implemented according to the TDMA connection system in which a plurality of radio stations use a frequency based on time division and the TDD communication system accomplishing bidirectional communications usually called ping-pong communications. In mobile communications using the TDMA/TDD system, transmission and reception of signals are conducted in the ping-pong or duplicated manner by use of a frequency between a base station and a mobile telephone set in a period of time, namely, a pair of time bands assigned to a TDMA frame as a basic element for communications. In the TDMA/TDD system using the single frequency for the ping-pong communications as above, an identical IF carrier frequency is employed for transmission and reception in a radio section of the apparatus, which consequently causes a problem of a co-channel interference in the housing thereof. Heretofore, the difficulty has been coped with as follows, for example. Power to the transmission amplifier is turned off, an antenna change-over switch is arranged to prevent a transmission radio wave from entering the receiver section, or the receiver section is shielded to prevent an intermediate frequency (IF) carrier and the transmission carrier from adversely influencing the receiver section. However, according to the known technology, even if the preventive provisions above are effected, it has been impossible to prevent the occurrence of the co-channel interference in the identical housing. European Patent Application EP-A-0 496 498 was published on 29th July 1992, which is after the priority date claimed in the present application. That application describes a time-division duplex radio transceiver which transmits and receives on the same frequency using a common antenna and an antenna switching circuit. In the second embodiment shown in Figure 2, the transmitter section and the receiver section both use an IF frequency of 200MHz. The 200MHz local oscillator frequency required in the transmitter section is obtained from an 800MHz oscillator by dividing the frequency in two series-connected circuits which each divide the frequency by two. The operation of the frequency divider is stopped in the reception state. The invention is defined in claim 1 below to which reference should now be made. Advantageous features are set forth in the appendant claims. The invention will be described by way of example with reference to the drawings, in which: Fig. 1 is a signal timing chart showing an example of the operation of communication frames in the TDMA/TDD system and an example of communications between a private or personal station (PS) and a base station (BS) in this system; Fig. 2 is a schematic diagram showing the configuration of an example of the TDMA/TDD telephone communication system; Fig. 3 is a block diagram schematically showing the constitution of a radio section in a radio telephone apparatus of the TDMA/TDD system according to the related art; Fig. 4 is a block diagram showing the configuration of an embodiment of the radio telephone apparatus in accordance with the present invention; and Fig. 5 is a block diagram illustratively showing the configuration of an example of a frequency division orthogonal modulator shown in Fig. 4. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the accompanying drawings, description will be given in detail of an embodiment of the radio telephone apparatus in accordance with the present invention. Prior to the description of the apparatus of the embodiment, for an easy understanding of the apparatus, a radio telephone communication system of the TDMA/TDD system and a radio telephone apparatus of the prior art will be briefly described. Fig. 2 shows an example of the system configuration of the radio telephone communication system to which the TDMA/TDD system is applied, while Fig. 1 is a signal timing chart showing an example of communications between a personal station (PS) and a base station (BS). As shown in a signal format A of Fig. 1, according to the TDMA/TDD system, a frame on a frequency fc is partitioned into a transmission slot part or field and a reception slot field. Moreover, each of the slots are subjected to a time division in accordance with the number of private stations. Namely, in this example, the transmission slot field is subdivided into transmission slots T1 to T4 and the reception slot field is split into reception slots R1 to R4 according to the time division. Each private station uses a transmission slot and a reception slot beforehand assigned thereto for communications. For example, a radio station PS1 communicates the transmission slot T1 and the reception slot R1 with a base station BS. As a result, a four-channel simultaneous communication can be accomplished in a configuration of Fig. 2 including four private stations PS1 to PS4 and a base station BS 501 connected via subscriber lines 701 to an exchange 601. In Fig. 1, a signal timing chart B shows the operation of telephone communications simultaneously carried out via four channels between four private stations and the base station in conformity with the TDMA/TDD system. Each of the private station is a radio telephone apparatus such as a cordless telephone set, whereas the base station is a connecting device for establishing links between the exchange 601 and the private stations. As shown in the signal timing chart B of Fig. 1, to prevent transmission waves from interfering with each other, the private stations PS1 to PS4 adopt the transmission slots T1 to T4 respectively assigned thereto in advance to conduct signal transmissions to the base station BS. When the communicating private terminals PS1 to PS4 are set to the reception state, the base station similarly sends signals thereto by use of the respective reception slots R1 to R4. As described in conjunction with Figs. 1 and 2, the identical carrier frequency is adopted for the time-division communications in the TDMA/TDD system. Referring next to Fig 3, description will be given of a radio section to which the TDMA/TDD is applied according to the prior art. In this regard, in the private and base stations, radio sections respectively thereof have the same construction. Consequently, the configuration will be described, by way of example, for the structure of the radio section of the private section. As can be seen from Fig. 3, the radio section is primarily subdivided into a transmission part or section 110 and a reception section 120. In the radio section of each of these sections 110 and 120, there are used identical transmission intermediate frequency (IF), send/receive RF frequency, and RF local frequency. In the transmitter section 110, an IF orthogonal modulator 115 receives a frequency of IF local f1 signal from an IF local oscillator 116. The oscillator 116 oscillates, on receiving time-division signals I and Q of the transmission slot T1, a frequency identical to the intermediate frequency. The modulator 115 then carries out an orthogonal modulation on the IF local f1 signal by two ring modulators 117 each including a diode, thereby outputting a transmission IFf1 signal to a transmission mixer 113. The mixer 113 modulates the received IFf1 signal according to the frequency fRF from an RF local oscillator 130 so as to send a resultant transmission wave fc to an RF transmission amplifier 114. The amplifier 114 amplifies the signal fc to deliver a resultant signal to an antenna switch 131. In this situation, since the antenna switch 131 has been changed over to a side of the transmission section 110, a transmission wave 132 is outputted from the antenna 132. According to the TDMA/TDD system as above, since the identical carrier frequency is used for the signal transmission and reception, in order to prevent the transmission wave from directly entering the receiver section 120, the antenna switch 131 is arranged to achieve the change-over operation. When the transmission is finished, the transmission part 110 sets the antenna switch 131 to a side of the receiving part 120. This accordingly prevents the cochannel interference with any other private station and inhibits the cochannel interference from occuring in the same housing due to the transmission signal having a frequency identical to the reception signal. Next, the receiver section 120 receives via a receiving slot R1 a reception carrier signal from the base station. The carrier signal has the frequency fc of the transmission frequency. This signal is passed through a reception RF filter 124 to obtain a signal free from noises and the like. The obtained signal is amplified by an RF reception amplifier 123 so as to send an amplified signal to a reception mixer 122. The mixer 122 demodulates the reception carrier fc according to a frequency fRF from the RF local oscillator 130, which is also used to conduct the RF modulation in the transmission. The demodulated frequency IFf2 is transmitted to a demodulator 121, which then produces therefrom demodulated baseband I and Q signals. As above, in the radio section of the related art associated with the TDMA/TDD system, the identical carrier frequency fc and the same intermediate frequencies IFfl and IFf2 are used for the signal transmission and reception. Consequently, when designing the radio section of the TDMA/TDD system, it is necessary to appropriately suppress the cochannel interference in which the transmission wave enters the receiving part in the same housing. Specifically, the cochannel interference is considered to be caused by the transmission wave entering the RF receiver unit 120 via the RF transmission amplifier 114 and the antenna change-over switch 131, the signal entering the RF receiver section 120 from the transmission mixer 113, or the transmission intermediate frequency entering the RF receiver unit 120 from the mixer 131. In consequence, according to the related technology shown in Fig. 3, in order to decrease the cochannel interference level in the identical housing, power to the transmission amplifier 114 is turned off, the antenna change-over switch 131 is adopted to prevent the transmission wave from entering the receiving part 120, or the receiving section 120 is shielded to prevent the transmission signal IFfl and the output from the transmission mixer 113 from entering the receiver part 120, thereby avoiding the occurrence of the interference. However, the construction of the radio section of Fig. 3 cannot completely suppress the interference and hence the reliability and performance of the radio telephone apparatus are considerably deteriorated. Next, description will be given of an embodiment of the radio telephone apparatus in accordance with the present invention. Fig. 4 is a block diagram showing an embodiment of the radio section of the radio telephone apparatus according to the present invention. In this configuration, the same reference numerals are assigned to the same components as those of Fig. 3, and the system constitution as well as the communication sequences are the same as those shown in Figs. 1 and 2. In this connection, the system constitution and the communication sequences shown in Figs. 1 and 2 are employed only as examples for describing the embodiment. Naturally, the number of private stations and the like are not restricted by the embodiment. According to this embodiment, in place of the orthogonal modulator 115 including the ring modulators 117 shown as the related art in Fig. 3, a frequency division orthogonal modulator 111 is used. When a divider (x 1/4) thereof is turned off, the orthogonal modulator 111 stops outputting the intermediate frequency signal Fig. 5 is a block diagram of the frequency division orthogonal modulator 111 using the divider (x 1/4). In Fig. 5, a local input terminal 205 receives from an IF local oscillator 112 as an input thereto a signal having a frequency which is four times that of the intermediate frequency IF. A clock buffer 201 receives as a buffer input thereto a local signal from the local oscillator 112 and then supplies the divider 210 with a clock signal CK and an inverse clock signal CK having a phase which is inverse to that of the clock signal CK. The divider 210 receives the local signal to generate therefrom an IF carrier signal having a phase shifted from that of the local signal by 90° . The divider 210 includes two D flip flop circuits 202A and 202B. Clock terminals CK and CK respectively thereof are connected to the clock buffer 201. PD terminals controlling operations of the respective circuits are connected to a power down terminal 209. In addition, terminals D , D, Q , and Q of the flip flop circuit 202A are connected to terminals Q, Q , D , and D of the flip flop circuit 202B, respectively. Moreover, clock output terminals  and  of the flip flop 202A are respectively connected to clock input terminals  and  of a double balance mixer 203A; whereas clock output terminals  and  of the flip flop 202B are respectively connected to clock input terminals  and  of a double balance mixer 203B. In this embodiment, by setting the power down terminal 209 to an L level, the operation of the frequency divider 210 can be stopped. Consequently, it is possible to completely stop the generation of the signal of the intermediate frequency component IFf1 as an output from the modulator. The double balance mixers 203A and 203B receive as inputs thereto a channel I from a terminal 206 and a channel Q from a terminal 207, respectively. Signals received from these channels are mixed therein according to the clock signal from the divider 210. Each mixer 203 has two output terminals. As shown in Fig. 5, these terminals of the respective mixers are connected to each other via two resistors. Intermediate points between the resistors are connected to associated input terminals of an adder 204. As a modulator output, there is produced from an output terminal 208 of the adder 204 a signal of intermediate frequency component IFf1. As above, according to this embodiment, the operation of the divider 210 is supervised by changing the logic level of the power down terminal 209. Namely, when the operation of the divider 210 is stopped, the IFf1 signal interfering with the demodulator 121 is interrupted. Consequently, even when the RF local fRF is operating in the receiving state, the transmission wave fc does not appear in the output signal from the transmission mixer 113. This prevents the cochannel interference of the transmission wave fc with the receiver section 120. In signal reception, when the divider 210 of the modulator 111 is stopped so as to interrupt the IFfl signal, the power of the RF transmission amplifier 114 is turned off, and the antenna switch 131 is set to the side of the receiver section 120, the cochannel interference is completely prevented from occurring in the housing. In addition, according to the embodiment, since a frequency division orthogonal modulator is employed in place of an orthogonal modulator, the frequency of the intermediate frequency signal IFf1 is different from that of the intermediate frequency signal IFf2, which consequently prevents the cochannel interference from occurring. While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by those embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope of the present invention.

Claims: Radio telephone apparatus for conducting communications in accordance with the TDMA/TDD system, the telephone apparatus having a transmission section (110) and a receiving section (120), and the transmission section comprising a local signal generator (112) for generating a local oscillatory signal of a first frequency, and a frequency-division orthogonal modulator (111) comprising a frequency divider (210) and a mixer (203A, 203B); and in which the frequency divider (210) is coupled to the local signal generator to divide the frequency of the local oscillatory signal to provide an IF carrier signal at a second frequency which is less than the first frequency, the mixer (203A, 203B) is coupled to the frequency divider to modulate orthogonal input signals (I,Q) onto the IF carrier signal to produce an intermediate frequency signal for subsequent conversion to RF for transmission, and the frequency divider is selectively operable to supply or not to supply an IF carrier signal, and is responsive to the apparatus being in a reception state not to supply an IF carrier signal. Apparatus according to claim 1, in which the frequency divider generates two output IF carrier signals respectively 90 degrees apart in phase. Apparatus according to claim 1 or 2, in which the frequency divider divides by four. Apparatus according to claim 3, in which the frequency divider includes two flip-flop circuits (202A, 202B). Apparatus according to claim 4, in which the flip-flop circuits are D-type flip-flop circuits. Apparatus according to any preceding claim, in which the receiving section operates with an intermediate frequency which is different from the intermediate frequency in the transmission section. Apparatus according to any preceding claim, in which the output of the transmission section and the input of the receiving section are coupled to a common antenna section (132) through an antenna switching circuit (131), and when the antenna switching circuit couples the antenna to the transmission section (110) the frequency divider (202A, 202B) is rendered operative and when the antenna switching circuit couples the antenna to the receiving section (120) the frequency divider is rendered inoperative.

Inventors: HARA TOSHIHIRO, HARA, TOSHIHIRO, HARA, TOSHIHIRO, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1992
Main classification: H04B7
IPC codes: H04B7, H04J3, H04B1, H04L5, H04M1