SYSTEM FOR REDUCING INTERFERENCE IN ELECTRONIC DEVICES CAUSED BY DISCONTINUOUS TRANSMISSION RADIOTRANSMITTERS Field of the Invention This invention relates to radio terminals using pulse or discontinuous transmission, where there is a potential for these pulse transmissions to cause electromagnetic interference in electronic devices . BACKGROUND OF THE INVENTION Modern radio communication systems often involve the transmission of digital information. These systems often transmit information packets in pulses, in such a way that the transmitter is active, then inactive, and then again active. One advantage of such a pulsed / discontinuous transmission system is that while a transmitter, for example, a terminal, is not in transmission, other terminals can transmit using the same carrier frequency thus allowing a single radio receiver to be tuned to the carrier frequency to receive several transmissions. Such a system is based on the multiple time division access (TDMA), in which a set of remote terminals share the same carrier frequency when transmitting in different periodic timeslots. An example of such a system is specified in the IS-54 standard of the Association of Telecommunications Industries, more commonly known as North American digital cellular radio. In the IS-54, a remote terminal, which is a digital cellular phone, transmits information during a time period of approximately 6.6 ms in each structure of 20 ms; that is, at a structure speed of 50 Hz with a work factor of 33%. During a transmission rate of 6.6 ms, the power level remains substantially constant, except for variations of less than about 3 dB due to the modulation of the information in the carrier. This modulation occurs at 24 ksymbols / s, a speed much greater than the speed of the structure. During the remaining 13.4 ms of the 20 ms structure, the phone does not transmit. Digital cell phones are increasingly used indoors and it is common for the radio terminal to be deployed near home electronic devices, such as televisions. Sometimes demodulation-amplitude occurs in these other electronic devices which often results in unwanted interference. Typically, this happens as follows. The RF emission is collected by a circuit driven and coupled to a diode or transistor junction. The junction rectifies the RF and the surrounding circuits provide low pass or band pass filtering (often to the voice band, if these are audio frequency circuits). This greatly removes the variations in the RF carrier frequency due to the modulation of the information and leaves mainly only the coarse variation due to the pulse at intervals of the carrier. If this waveform that interferes with the baseband is coupled to the ac in the surrounding circuitry, what is obtained is a rectangular waveform with a value of dc0, a period of 20 ms, a working factor of 33% , and a peak-to-peak voltage or current level related to the RF power level of the emission. Note that this demodulation process is not very sensitive to small changes in the carrier frequency. Such a waveform can cause a great problem of disturbance effects; for example, a 50 Hz rectangular waveform can be heard in audio circuits as an annoying buzzing sound. This type of interference can also occur in hearing aids. A similar problem arises in radio systems that are not necessarily TDMA systems in which the RF emission of a terminal is discontinuous; for example, in systems that make use of voice activity detection (VAD). The problem is similar, except that the pulse characteristic can be irregular instead of periodic. SUMMARY OF THE INVENTION In order to reduce the effects on interference, it is advantageous to make the RF emission of the radio terminal continuous or as continuous as possible (focus of a 100% work factor). Accordingly, an object of the present invention is to provide a system for reducing the interference caused to electronic devices by discontinuously transmitting radio terminals which does not result in significant capacity losses of the radio system. According to one embodiment of the present invention, a radio terminal transmits data on its assigned carrier frequency during its allocated time quota for communications. When it has finished its transmission, it changes frequency to another specific carrier frequency, which can be called "carrier of wasted energy" and continues radiating at the same power level. For example, in TDMA systems, the terminal will transmit on the wasted energy carrier during the time quotas not allocated for communications for that terminal. Typically, this radiation is not used for communication; the energy is simply "wasted" on this carrier frequency as a way to ensure that this radiation is emitted by the terminal during normally unused timeslots. In this way, the thick variations in the RF envelope of the carrier are reduced at very short time intervals as necessary to momentarily turn off the RF emission while the carrier frequency is switched to and from the wasted energy carrier. This allows the carrier frequency allocated for the communication to be used by other radio terminals for communication during those timeslots, as for example in a conventional TDMA system, while the discontinuous / boost nature of the levels of radio frequency is considerably reduced. power emitted. It should be noted that the present invention is not limited to a TDMA system and can be applied to other systems using discontinuous transmission, for example, systems using Time Division Duplex Transmission (TDD) or using speech activity detection . Accordingly, according to a broad aspect of the invention, a radio transmitter is provided which decreases the level of fluctuations in the power levels emitted by such a transmitter even when such a terminal transmits information on a discontinuous basis. Thus, according to the present invention, a discontinuous transmission transmitter transmits information on a discontinuous basis while maintaining a relatively constant emission level as compared to a transmitter that ceases transmission when there is no information to be transmitted. Preferably, all radio terminals in the radio system use the same wasted energy carrier, without taking into account which carrier frequencies are assigned to them for communications. In this way, only one carrier frequency becomes useless for communications over a broad system base, which has a relatively insignificant impact on the capacity of the system if there are many frequencies carrying communications in the system. In accordance with a broad aspect of the invention, there is provided a wireless telecommunication system using discontinuous transmission of information, a method for reducing the resulting interference in electronic devices caused by a transmitter comprising the steps of a) determining when it is about to be transmitted information; b) tune the transmitter to a carrier frequency used for communication when information is about to be transmitted; and c) tuning said transmitter to another carrier frequency, when the information is not to be transmitted. According to another aspect of the invention, there is provided a discontinuous transmission transmitter comprising a carrier frequency generator to generate a first carrier frequency to be transmitted when the information is about to be transmitted and to generate a second carrier frequency to be transmitted when the information is not transmitted. is about to be transmitted; and a controller for driving said carrier frequency generator to generate said first carrier frequency when the information is about to be transmitted and to generate said second carrier frequency when the information is not to be transmitted. BRIEF DESCRIPTION OF THE DRAWINGS The present invention, together with other objects and additional advantages thereof, will be better understood from the following description of the exemplary embodiments with reference to the drawings in which: The figure is an exemplary illustration of RF emission from a conventional IS-54 terminal. Figure Ib is an illustration of the resulting interference waveform found in an interfered device after the demodulation-amplitude and filtering of the RF waveform of FIG. Figure 2a is an exemplary illustration of the RF emission of an IS-54 terminal modified according to an embodiment of the present invention. Figure 2b is an illustration of the resulting interference waveform found in an interfered device after the demodulation-amplitude and filtering of the RF waveform of Figure 2a. Figure 3 is an illustration of the frequency plan of a typical digital cellular radio system. Figure 4 is a block diagram representative of the RF circuits of a terminal according to an embodiment of the invention. Fig. 5 is a block diagram showing further details of the terminal of Fig. 4. Fig. 6 is an illustration of the RF emission of a conventional IS-95 terminal. Figure 7 is an illustration of the emission of
RF of an IS-95 terminal according to one embodiment of the present invention. Figure 8 is an illustration of the emission of
RF of a multiple access terminal by frequency hopping according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED MODALITIES In the illustration of FIG. 1, a conventional IS-54 digital cellular terminal emission is shown. Emissions occur periodically at 20 ms intervals such as 100. There are three communication time quotas in each interval. During the allocated time quota for its communications 101, the terminal in question transmits information by modulating an assigned carrier frequency for communications fc 105. During this time slot of 6.66 ms, the average level of transmitted RF power is P 106, and there are small variations of a few decibels in the power 107 due to modulation. These variations take place at the signaling speed of 24 ksymbols / s. During the other two timeslots 102 and 103, the terminal is not transmitting, so that the carrier frequency fc can be used up to two other terminals in the immediate vicinity. Figure Ib shows an example of a resultant interference waveform arising from undesired amplitude demodulation that occurs in an interfered device subject to the emission of FIG. In this example, the emission of the figure has been rectified, which we will call the RF emission waveform, which causes the envelope detection. Typically, this happens in a transistor or diode semiconductor that rectifies the junction within the interfered device. The resulting interference waveform has passed through a low pass filter with a cut-off frequency somewhere substantially above 50 Hz and substantially below 24000 Hz. This occurs due to the capacitance of circuits or parasitic capacitances in a transistor. This causes the high-frequency components to be removed on the carrier frequency and the modulation rate. Finally, the resulting interference waveform has been coupled to ac with a cutoff frequency substantially below 50 Hz which causes the DC component to be removed without significant distortion of the rectangular waveform. This occurs in a capacitively coupled circuit path. Such rectification, filtering and ac coupling tends to occur in many electronic circuits found in home electronics, particularly audio preamplifier circuits that could be found in hearing aids, broadcast band radio receivers and television equipment. The resulting interference waveform 110 is a rectangular wave that follows the envelope of the original RF emission. The period T 112 is 20 ms, and the portion of the period where the waveform 114 is positive is 6.66 ms. We can define the work factor d as the fraction of the period in which the resulting interference waveform is positive. In this case, d = 33%. The peak-to-peak amplitude A 116 of the resulting interference waveform 110 is a function of the power P in the RF interference waveform during the time slot 101. Note that the interference waveform The resultant is relatively insensitive to changes in the original carrier frequency fc resulting, for example, from the transfer. Although the TDMA emissions of an IS-54 terminal have been used in this example, it would be appreciated by those skilled in the art that emissions from another type of TMDA radio terminals, such as those corresponding to the European cellular digital system known as GSM, they would cause similar effects, with different period, factor of work and amplitude. The average power of the resulting interference waveform is a measure of its ability to cause unwanted effects, for example, a perceptible hum in an audio device. For a rectangular waveform this power can be easily calculated and is proponal to A * "d (ld) In this example, the power is proponal to 0.222 A. For the constant amplitude A, the power is maximum when d = 0.5 (square wave) and approaches 0 to the extent that d approaches either 0 or 100%, therefore, if d can be made close to 100%, the ability of the interference to make undesired effects can be substantially reduced. The illustration of Figure 2a shows the emission of a modified IS-54 digital cellular terminal that incorporates the system of the present emission.The emissions occur periodically at intervals of 20 ms 200. During the quota of time allocated for its communications 201, the terminal in question transmits information by modulating the carrier frequency of the communications fc 205. During this time slot of approximately 6.66 ms, the average RF power level is P 206, the same as in the figure the, with small variations in power due to modulation. These variations take place at the signaling speed of 24 ksymbols / s. Unlike FIG. 1, during the other two timeslots 202 and 203, the terminal also transmits at the power level P, but the frequency designated as a "wasted energy carrier" has been switched fw 208. The terminal can continue to modulate the fw carrier with random, pseudorandom, or fixed bit patterns during time shares 202 and 203. However, as an alternative, the carrier may be irradiated af "without modulation, if the amount of interference produced in such devices results from differences in power levels because the lack of modulation is relatively minor. There are two very shperiods of time on 210 and 212 of only a fraction of a millisecond each, during which, as a practical matter, the emission stops while the transmitter switches between fc and f ", to avoid radiation interference on other carrier frequencies of communications in the system. Alternatively, it may be possible to leave the RF power level as P during the periods e and e2, if there is no oppnity to interfere with the radio system's receivers since they are not receiving information during these periods of time. Figure 2b shows the resulting interference waveform 220 that could arise in an interfered device subject to the emission of Figure 2a. The resulting interference waveform 220 is a rectangular wave that follows the envelope of the original RF emission. Period T 222 is 20 ms, as in Figure Ib, but the work factor d is close to 100%. Specifically, d = l- ((the + e2) / T). If the = e2 = 0.2 milliseconds, then d = 98%. The amplitude demodulation process is not very sensitive to the change in the carrier frequency from fc to fw if the change in the carrier frequency is only a small percentage. The peak-to-peak amplitude A 226 of the resulting interference waveform 220 is a function of the power P in the RF emission waveform during the timeslots 201-203, is the same as in the figure Ib. Since the work factor d is now 98%, the power in the resulting interference waveform is now proponal to 0.0196A which is only about 9% when much of the power as in the case of the figure Ib. Although it is assumed that the waveforms in the example are perfectly rectangular for simple calculations, it should be noted that the substantial reduction in interference occurs even if the filtering causes the baseband waveform to be non-rectangular. Figure 3 shows an example of a system frequency plan for a TDMA radio system incorporating an aspect of the present invention. The frequency plan in the example is based on the spectrum assigned in N America for cellular radio systems. In any given jurisdiction, there are two radiocell systems, known as A and B, operated by different service providers. In this plan, 416 carrier frequencies 310 spaced at 30 KHz intervals are available to the service provider A to allocate radio terminals to be used for communications to the fixed base stations or cell sites operated by the service provider A The carrier frequency fc referred to in Figure 2a for a specific call could be any of these carrier frequencies. Another individual carrier frequency of 824.01 MHz is designed as the wasted energy carrier 312 for the service provider system A. The radio terminals are switched to radiate on this carrier frequency during timeslots when they are not communicating with cell sites. This carrier frequency is used by all the radio terminals in system A, without taking into account which particular carrier frequency coming from set 310 is using a given terminal at the time of communications. Similarly, 416 carrier frequencies 320 spaced at 30 KHz intervals are available to the service provider B to be assigned to radio terminals to be used for communications to the fixed base stations or cell sites operated by the service provider. B. The carrier frequency fc referred to in Figure 2a for a specific call could be any of those carrier frequencies. Another individual carrier frequency of 824.01 MHz is designed as the wasted energy carrier 312 for the service provider system B. Note that in this example, it is the same frequency that is used by system A for this purpose. Since no useful communication occurs in the wasted energy carrier, a single carrier frequency can be shared by both service providers in order to minimize the number of carriers not available for communications. The parasitic antennas formed by the circuit paths on a typical circuit panel, for example, would tend to have a wideband response. In this example, in the worst case the change in the carrier frequency coming from a carrier frequency of communications to the wasted energy carrier frequency is only 3%, which would have a negligible effect on the amplitude demodulation process in the most of the devices interfered with. It will be appreciated by those skilled in the art that the wasted energy carrier could be chosen in place of another carrier frequency, not necessarily one at the edge of the band allocated for the radio service. In addition, as a practical matter, there could be more than one carrier frequency designated as a wasted energy channel for each system. This would have the effect of reducing the aggregate power of many radio terminals appearing on any particular carrier frequency as observed, say, by a fixed cell site receiver, and can reduce such practical problems as intermodulation at the site receiver. cell phone. The various wasted energy carrier frequencies could be pre-programmed at the radio terminals, and randomly or sequentially selected by each terminal, or they could be assigned by the use of messages sent to the radio terminals by the base stations or cell sites. In this particular example, frequency 312 chosen as the wasted energy carrier is one not currently allocated for use in communications by service providers either A or B in North America. Therefore, there is no direct loss in the capacity of the system due to its assignment to another purpose. As a practical matter, the carrier frequency of 824.04 MHz adjacent to this carrier may also be useless due to the interference of the adjacent channel. Nevertheless, even in this case, the service provider A has only lost one channel of the 416, which represents a relatively insignificant loss of capacity.
Figure 4 shows a block diagram of an RF transceiver of the terminal according to a preferred embodiment of the invention. In the transmitter chain (TX), the baseband signal source TX 400 of the terminal is first mixed with an intermediate frequency (LO) local oscillator (LO) 401 in the mixer 402 to generate a modulated IF signal 403. The IF signal 403 is amplified and filtered at 404 and then moved by frequency to an RF carrier frequency, for example fc, by the carrier frequency generator 405, which is controlled by a control signal 406. In the figure 5 an example of the carrier frequency generator is shown in detail. The RF signal at the output of 405 is amplified at a higher power in the power amplifier 407 before being sent to the TX port of the duplexer 408. The signal is transmitted out through the antenna 409 which is connected to the antenna port of the duplexer. Similarly, in the receiver chain (RX) the RF signal is first received by the antenna 409 and then goes to the duplexer 408, and to the low noise amplifier (LNA) 410. The RF signal at the LNA output 410 shifts by frequency to the IF in the mixer 411 via the RF LO 412 which is normally a programmable synthesizer. The IF signal at the output of the mixer 411 is amplified and filtered at 413 and then moved by frequency towards the baseband frequency on the mixer 414 by the LO of IF 415. It will be appreciated by those skilled in the art that in other components are often included in the practice and other implementations of an RF transceiver are possible. Although the implementation of a terminal RF transceiver may change, the basic function remains the same as shown in Figure 4. Figure 5 is a block diagram showing additional components of a terminal according to a preferred embodiment of the invention. present invention. Only the transmission chain is shown and an example of a carrier frequency generator 405 is shown in more detail. Figure 5 also shows a handset 565, a microcontroller 550 and components for providing power to the terminal as will be discussed below. In Figure 5, the carrier frequency generation 405 comprises a mixer 505, two local oscillators, 506 and 520, and a switch 521 that selects which LO is applied to the mixer 505. During the communication period 201, the switch 521 selects the RF LO 506 for frequency shifting the IF signal towards a desired carrier frequency fc. The RF LO 506 is a variable local oscillator source, eg, a programmable synthesizer, which in this example generates a frequency equal to f -f? F, where fc is selected from the available communication channels. During periods 202 and 203, switch 521 selects LO 520 to frequency shift the IF signal toward the wasted energy carrier frequency fw for transmission. The LO 520 is a fixed local oscillator source that generates a frequency equal to fw-flf, assuming that only one carrier frequency of wasted energy is allocated. It should be apparent to one skilled in the art that an equivalent alternative is to have the local oscillator 520 tuned to a frequency equal to fw + f? F and to the RF LO by tuning to a frequency equal to fc + f? F with a mixer appropriate In operation, the controller (550) scales to the switch 521 between the RF LO 506 and 521, or in other words, selects whether the transmitter transmits to fc or fw, depending on whether or not there is information to be transmitted. Since the terminal of Figure 5 transmits RF energy almost all the time, it consumes more electrical energy than a conventional TDMA terminal. This higher power consumption reduces the communication time if a terminal is energized by a battery. However, in fixed wireless access applications, the terminals usually include an AC power adapter energized by the power supply of the AC mains with a battery backup used only in the case of a power failure of the AC mains. Therefore, high power consumption is not a significant problem for fixed wireless access terminals unless there is an AC failure. Accordingly, the preferred embodiment of the invention shown in Figure 5 will operate in a power saving mode during AC power failure. As shown in Figure 5, an AC sensor will detect an AC power failure, will toggle the switch 533 to select the battery as the power source during such power failure, and will send a signal 535 to the controller 550 to switch the terminal to energy saving mode. When operating in the energy saving mode, the switch 521 will not be connected to the LO 520 during periods 202 and 203 and, in addition, the energy to the entire Tx chain may be decreased during periods 202 and 203 as well. Accordingly, in the energy saving mode, a terminal of the preferred embodiment transmits the same RF signal and consumes the same amount of electrical energy as a conventional terminal. Although the terminal would generate the same amount of interference to domestic electronic devices in the energy-saving mode as a conventional terminal, it would not be a serious problem since most domestic electronic devices can not function during an AC power failure. In addition, such a system can be configured with a switch, for example, a user-selectable switch, which will prevent operation in energy saving mode, for example, if the user is related to interference to such devices such as auxiliary devices. hearing, etc. Such a switch can alternatively be operated remotely by a control signal sent over the radio link from a control center in the wireless network. The present invention is not limited only to TDMA radio systems, but is also applicable to other systems that make use of discontinuous transmission or detection of voice activity. Thus, FIG. 5 shows a voice activity detection module (VAD) 570 for detecting whether speech generated by the headset 565 actually exists. The VAD 570 then sends an indication to the microcontroller whether speech is presented or not, while send all signals from the handset to the baseband block and IF 560. It should be noted that the voice activity detection block 570 is not required unless the system performs voice activity detection. Figure 6 shows the periods of the RF emission of a terminal that uses multiple access by code division (CDMA) according to the IS-95 standard of the Industrial Telecommunications Association for CDMA digital cellular terminals. The system is designed to take advantage of pauses in the voice to increase the capacity of the system. An IS-95 terminal contains means for detecting outgoing voice activity. During the periods in which the voice information 610, 611 is presented, the terminal continuously transmits on a communication carrier frequency fc. During a period in which there is a pause in voice 612, the terminal goes to a discontinuous transmission mode. In this mode, other information is transmitted, for example, control information and / or information about the noise level of the background audio, on the fc in bursts of 2.5 ms 613, 614 and 615, one burst every 20 ms interval 616, 617, 618. These bursts represent a reduced amount of information compared to the voice information and are transmitted in irregular positions in the 20 ms intervals. In a CDMA system, the capacity (the number of terminals that a carrier frequency can share) is improved by reducing the average energy present in the channel. Therefore, the capacity of the IS-95 system is increased by this discontinuous transmission mode, since the average energy added in the frequency fc observed by a base station or cell site receiver due to many terminals operating on the carrier frequency fc, they are reduced when the terminals (asynchronously to each other) use this mode. However, as a result, the demodulation-amplitude interference discussed above potentially occurs in an electronic device close to a given radio terminal subject to the RF interference waveform of this emission, as the gross fluctuations every 20 ms during periods of pauses in the voice they cause undesired effects. Figure 7 illustrates emissions from a modified IS-95 radio terminal employing one aspect of the present invention. During periods in which voice information 710, 711 is presented, the terminal continuously transmits on a communication carrier frequency fc, as in Figure 6. During a period in which there is a pause in voice 712, the terminal goes to a mode different. In this mode, a small amount of information is transmitted over fc in bursts of 2.5 ms 713, 714 and 715, with one burst occurring, in irregular positions, at intervals of every 20 ms 716, 717, 718, as in Figure 6. However, during the remaining time intervals 720, 721, and 722 of the periods 716, 717 and 718, the terminal is switched to a wasted energy carrier fw and radiates at the same energy level as it transmits when using the carrier fc . As a practical matter, there may be very brief periods (not shown) before and after each burst 720, 721 and 722 where the RF emission must be turned off while the frequency is switched to or from fw. If these periods are much shorter than the duration of bursts 713, 714 and 715 (2.5 ms), then the total work factor during the voice pause is closer to 100% than in the case of Figure 6, and therefore, as noted above, the effects of interference are reduced. Still another embodiment of the present invention is particularly suitable for a type of TDMA system that uses frequency hopping and VAD, as shown in Figure 8. In this case, during periods when the information is about to be transmitted 810, the terminal The radio transmits information about a set of carrier frequencies fl - fn 812 when jumping in a pseudo - random sequence from carrier to carrier and transmitting some information about each carrier. In such a system, the capacity of the system is increased by reducing the amount of time a given terminal is transmitting over frequencies fl - fn. In this way, there is a reduced probability that two terminals that use the same specific frequency at the same time and "collide". The amount of time spent in the transmission of the fl-fn frequencies can be reduced by the use of discontinuous transmission. During the periods in which the information does not have to be transmitted 814, for example when the means for detecting the voice activity indicate a pause in the voice, and when other information, for example, information about the noise level of the background audio and / or control information that does not need to be transmitted, the terminal is switched to a wasted energy carrier fw 816 and continues to irradiate at the same energy level it was using before this period. In this way, the working factor of the RF envelope of the emission coming from a radio terminal is almost 100%, while the actual use of the communication carriers fl - fn, and therefore the capacity of the system. , remains the same as in discontinuous, conventional frequency jump systems. It will be appreciated by those skilled in the art that in a radio system employing both TDMA and another form of discontinuous transmission such as Voice Activity Detection, the present invention can be applied to both the TDMA quotas and the discontinuous transmission within a given TDMA time quota. For example, in a typical system, a radio terminal would be assigned to a communications quota that occurs regularly in a structure. The application of the present invention would involve having the terminal switched to a bearer of wasted energy and continuing irradiation during other timeslots of the structure. With the VAD, the terminal may also not be able to transmit information during its own quota of time if no voice information is presented. The application of the present invention would involve having also the switched terminal to a wasted energy carrier and continuing the irradiation during its own time quota during periods when no voice information is presented, and when no other information needs to be transmitted. With reference to Figure 5 it should be noted that other components, which are included in such a terminal are not shown, and other implementations are possible. The controller determines whether there is information to be transmitted according to the TDMA, detection of voice activation or other protocols responsible for discontinuous transmission, as is known in the art. In some TDMA systems, the experiments suggest that the performance of the terminal of Figure 5 is improved if, during the time periods in which the transmitter does not transmit information, the wasted energy carrier is modulated with pseudo-random data that approximates the type of modulation that occurs when information is transmitted. Such pseudorandom data may be produced by the controller and sent to the baseband block through a control signal (not shown), or may be produced directly in the baseband block as is also known in the art. It will be appreciated by those skilled in the art that alternative implementations may be possible; for example, if the RF LO 506 is able to move the frequency rapidly between fw-fIF and fc-fiF during the intervals 210 and 211, then the switch 521 and the LO 520 are unnecessary. In this case, the carrier frequency generator 405 would only comprise the mixer 505 and a fast-moving RF LO controlled by the controller. Also, as another alternative particularly suited to situations in which the amount of interference produced in interfered devices results from differences in energy levels because the modulation of the carrier frequency can be ignored, then the carrier frequency generator 405 can be configured as follow. The LO 520 produces the entire signal of f "to be amplified directly by the power amplifier 507. In this case, only the RF LO 506 is connected to the mixer 505 and the switch 521 is moved in such a way that it is connected either to the LO 520 or to the output of the mixer 505 to the power amplifier 507 depending on whether the information is transmitted or not. As an alternative embodiment, the present invention can be adopted for use in a Fl-null or quadrature modulation implementation. It should be noted that although the preferred embodiment of the invention has been addressed with respect to its application in a particular type of interference caused in home electronic devices, the invention can also be used to reduce other forms of unwanted interference resulting from discontinuous transmissions. Numerous other modifications, variations, and adaptations may be made to the embodiments of the invention described above without departing from the scope of the invention as defined in the claims.