KR970007361B1 - Frequency controlling system - Google Patents

Abstract

None.

Description

[Name of invention]

Frequency control system

[Brief Description of Drawings]

1 shows a series of adjacently located transport channels through which multiple modulated information signals are transmitted simultaneously.

2 is a graphic showing a single signal transmitted on a single transmission channel representing a signal received by a radiotelephone having the frequency control system of the present invention.

3 shows a signal similar to the signal of FIG. 2 but shifted to a frequency that partially exceeds the band pass of the filter circuit of the radiotelephone.

4A and 4B are graphic representations of a weak strength modulated information signal transmitted over a transmission channel when a large amount of noise is present.

5 is a graphic showing a single channel when transmitting a modulated information signal and also transmitting a pseudo signal.

6A and 6B show two adjacently located transmission channels when a weak strength signal is transmitted on a first transmission channel and a strong strength signal is transmitted on the channel adjacent to the channel.

7 is a block diagram of a frequency control system of the present invention.

8 is a block diagram of a transceiver, such as a cellular radiotelephone, including the frequency control system of the present invention.

9 is a logic flow diagram illustrating a method of the present invention.

Detailed description of the invention

[Background of invention]

The present invention relates generally to an automatic frequency control system, and more particularly to an automatic frequency control system that operates in response to the detection of an information-containing signal of a desired characteristic.

A communication system for transmitting information between two locations includes a transmitter and a receiver, which are interconnected by a transmission channel when transmitting an information signal.

In one type of communication system, namely a wireless communication system, a transmission channel includes a radio frequency channel interconnecting a transmitter and a receiver. In order to transmit an information signal called a baseband signal on a radio frequency channel, the baseband signal must be converted into a form that can be transmitted on a radio frequency channel. This conversion process is called modulation, where the baseband signal is a radio frequency electromagnetic wave. The frequency of the radio frequency electromagnetic waves is a value within a frequency value range that defines the radio frequency channel. Radio frequency electromagnetic waves are commonly referred to as carrier signals and carrier signals once modulated with a baseband signal are referred to as modulated information signals, where the information content of the modulated information signal refers to a frequency range called the modulation spectrum at or near the carrier signal frequency center. Occupy. Once the baseband signal is modulated with a carrier signal, the final modulated information signal is transmitted through free space on the radio frequency channel to transmit information between the transmitter and receiver of the communication system.

Various techniques have been developed for modulating baseband signals into carrier signals. Examples of such modulation techniques include amplitude modulation (AM), frequency modulation (FM), phase modulation (PM), and complex modulation (CM).

A receiver in a wireless communication system receives a modulated information signal transmitted over a radio frequency channel. The receiver includes circuitry for reproducing an information signal from a modulated information signal transmitted over a radio frequency channel when the circuit includes or does not include a circuit for detection. The process of detecting or reproducing the baseband signal is called demodulation. Typically, the receiver includes a circuit (demodulation circuit) for performing a demodulation process and further includes a down conversion circuity. The down conversion circuit converts the modulated information signal in the direction of frequency attenuation to properly operate the demodulation circuit.

Each of the plurality of transmitters modulates a signal and transmits it over different radio frequency channels. In order to demodulate only one desired signal by the demodulation circuit of the receiver, the receiver further includes a tuning circuit that demodulates only signals in a desired frequency range. Such a tuning circuit includes a filter circuit forming a frequency pass band and passes only a signal having a frequency component within a frequency defined by the pass band of the filter circuit. The receiver further includes a filter circuit for inhibiting passage of the signal generated during down conversion and demodulation of the received signal.

The optical frequency range over which the modulated information signal is transmitted is called the electromagnetic frequency spectrum. The electromagnetic frequency spectrum is divided into frequency bands, each of which defines a frequency range of the electromagnetic frequency spectrum. The frequency band is further divided into channels called transmission channels. In order to minimize interference between simultaneously transmitted and modulated information signals, radio frequency signal transmission is adjusted in any of the frequency bands of the electromagnetic frequency spectrum. A 200 MHz frequency band portion of the electromagnetic frequency spectrum (extended between 800 MHz and 1000 MHz) is allocated for wireless telephone communication. Wireless telephony communication may be performed by a wireless telephone utilized in a cellular communication system. Such a radiotelephone includes circuitry for simultaneously transmitting and receiving a modulated information signal, thereby allowing bidirectional communication between the radiotelephone and receivers located far away from each other.

A detailed description of cellular communication systems is available in "1989 Memory Cellular Telecommunation Systems" published by W. William W. Lee in 1989, in the Bell Systems Technology Journal volume published in January 1979, and in "No. 1". Mobile telephone service "and" Cellular Systems Mobile Station Compatibility Protocol "published in Volume IS-3-D, published by the Electronics Industry Association in 1987.

In general, cellular communication systems are achieved by placing numerous base stations spaced apart throughout the region. Each base station includes circuitry for receiving a modulation information signal sent by a radiotelephone and circuitry for transmitting the modulated information signal to the radiotelephone. The modulated information signal between the radiotelephone and the base station can be transmitted in bidirectional communication.

Care must be taken to select the location of each base station of the cellular communication system so that at least one base station is within the transmission range of the radiotelephone located at any location throughout the area. Since base stations are located throughout the region, earth stations are associated with their respective base stations. Earth stations located in relation to each of the base stations that are spaced apart are referred to as " cells ", where a plurality of cells each associated with the base station forms a zone surrounded by a cellular communication system. A wireless telephone located within the boundaries of a cell of a cellular communication system transmits a modulated information signal to at least one base station and receives a modulated information signal from the at least one base station.

Typically, communication between a wireless telephone and a base station occurs on a control channel where data such as data that the base station refers to, for example, broadband data (eg, 8 kilobits per second data), is transmitted to the wireless telephone. Such data includes instructions for the wireless telephone to receive and transmit signals on a feature radio frequency channel called a voice channel. When operating on a voice channel, the base station transmits the voice information along with the Supervisory Audio Tone (SAT) signal to the wireless telephone. In some cellular communication systems with enhanced performance, the base station transmits voice information along with a DigiTai Supevisory Audio Tone (DSAT) signal. SAT signals are described in detail in this document. The DSAT signal is 100 bits of data per second under a voice signal functionally similar to the SAT signal. For example, a DSAT signal consists of 24-bit digitally encoded words that are repeated continuously at 100 bits per second. While the DSAT signal has the advantage of being passed through a reduced bandwidth channel, the SAT synth cannot pass through a reduced bandwidth channel. In particular, when received by the wireless telephone and properly detected, each of the signals represents a communication between the base station and the wireless telephone.

Although many wireless telephones simultaneously transmit modulated information signals at different transmission frequencies (i.e., each of the multiple wireless telephones can simultaneously modulate the baseband signal while the signals are transmitted on different radio frequency channels), Each modulated information signal occupies a portion of a frequency band (ie, a radio frequency channel). Even if the signal is transmitted at the same frequency or overlapping of signals that are simultaneously transmitted by frequency drift of one or more signals is not allowed, any overlapping modulation may be achieved by overlapping the simultaneously transmitted and modulated information signals. It is also possible to prohibit detection of the information signal.

In order to prohibit the overlapping of the modulated information signal transmitted simultaneously, the transmission channel defined within the frequency band allocated for radiotelephone communication is divided into a 30 KHz channel in the United States and a 25 Hz channel in Japan. Plans have been developed to divide the transmission channel into 10KHz channels in the United States and 12.5KHz channels in Japan. By reducing the channel bandwidth, the number of channels transmitting the signal is increased. This increases the telephone calling capacity of the shellular communication system.

Minimize frequency drift of any transmitted signal, regardless of whether the signals are transmitted over a transmission channel of 30, 25, 12.5, 10 KHz, or any other frequency bandwidth, to prevent overlapping of the transmitted and modulated information signal shall. Frequency drift of the transmitted signal is caused by a change in the oscillation frequency of a commonly used oscillator, generating (or down converting) electromagnetic waves (i.e., carrier signals) that modulate the information signal. And environmental changes such as supply voltage changes.

By reducing the channel bandwidth to increase the capacity of the cellular communication system, there is a need to make the frequency drift of the transmitted signal much smaller, even though the reduced small frequency drift is allowed.

Frequency control systems and methods for minimizing frequency drift problems are known and frequently utilized in many existing communication systems. In general, an oscillator composed of a transmitter and a radio pair is configured, or an apparatus for controlling the ambient state is included so that the change in the ambient state does not change the oscillator frequency by a magnitude. The characteristic frequency of the selected oscillator is utilized as the reference frequency at which the other oscillator is "locked", that is, maintained at relative frequency.

As a specific example of cellular wireless telephony described above, an oscillator is formed that forms each circuit portion of a base station located throughout the region (typically, the reference oscillator of the base station is an "ovenizd" oscillator). The oscillation frequency can be maintained in the device controlling the ambient conditions so as to precisely control the oscillation frequency of the radio frequency signal generated thereby the characteristic frequency exhibiting the minimum drift.

The radiotelephone located within the signal transmission range transmitted by the base station utilizes the carrier signal frequency of the radio frequency signal transmitted by the base station to the radiotelephone as the frequency at which the radiotelephone oscillator is registered, so that the oscillator frequency of the radiotelephone oscillator is registered. To control. The reference frequency determined by the carrier signal frequency of the radio frequency signal transmitted by the base station is a reference frequency and down conversion circuit in which the transmission frequency of the radiotelephone is offset so that the signal transmitted by the radiotelephone is exactly the same as the base station frequency. The oscillation signal supplied to the mixing circuit of can be utilized by the radio telephone as the reference frequency to be synchronized. This system is commonly referred to as an automatic frequency control (AFC) system.

Existing automatic frequency control systems enable or disable AFC operation depending on the level strength of the received signal. When the received signal level is below the threshold level, the frequency control system of the receiver is disabled. When the received signal level is above the threshold level, the frequency control system of the radiotelephone receiver is enabled. When the frequency control system is enabled, the reference oscillator frequency of the radiotelephone is adjusted in accordance with the incoming signal received for the purpose of correcting the radiotelephone frequency to the base station frequency. When the frequency control system is disabled, the reference oscillator frequency is not adjusted by the frequency control circuit.

In the case of a cellular radiotelephone, a received signal strength indicator (RSSI) signal is used to enable or disable the operation of the automatic frequency control system. Typically, cellular radiotelephones generate a received signal strength indicator (RSSI) signal which is a DC voltage proportional to the power level of the signal received by the receiver. When the signal strength is above the threshold level as indicated by the RSSI signal, the AFC is enabled; Conversely, if less, the AFC is disabled. This determination of the RSSI level is made after the control channel is selected or when the radiotelephone activates the voice channel. Control channel scan and selection processes, voice channel transmissions, RSSI signals and other calling process functions will be described in more detail.

While the frequency control system is suitable for accurately determining the carrier signal frequency of the transmitted signal, the frequency control system may operate improperly in various situations.

First, because the frequency control system operates only when the RSSI signal is above a predetermined level, the signal received by the radiotelephone receiver smaller than the minimum power level is not utilized as a reference to which the reference oscillator of the radiotelephone is synchronized. This occurs despite the fact that the AFC circuit can achieve frequency synchronization with incoming incoming signals having a level below the AJF threshold level. The threshold level cannot simply be reduced because the weakest signal level at which synchronization is occurring is usually below the level at which RSSI can determine to clean up the signal strength. At weak signal levels, the RSSI signal becomes nonlinear, the RSSI signal does not necessarily have dynamic range, and the noise received by the receiver fluctuates the RSSI signal, all of which described above degrades the accuracy of the RSSI signal.

In addition, respond to signal strength indicating that the presence of a spurious signal (a signal generated by another service, a signal caused by intermodulation, or a pseudo response from a wireless telephone) is "synchronized" at an incorrect frequency. To operate the frequency control system.

In addition, when the signal is not received by the radiotelephone and the noise exceeds a certain level, the frequency control system is "synchronized" to the wrong frequency.

In addition, a frequency control system that operates in response to a signal strength indication when a simultaneously transmitted signal on a recognized channel frequency drifts to a desired transmission channel is " synchronized " with a signal that frequency drifts to the desired transmission channel.

Moreover, when a signal transmitted simultaneously to a channel adjacent to a signal transmitted on the desired transmission channel is much larger in size than a signal transmitted on the desired transmission channel, the frequency control system operating in response to the signal strength indication is a much larger signal. Are "synchronous".

Therefore, a frequency control scheme is required that operates to determine the oscillation frequency of the oscillator of the radio telephone only when the signal received by the radio telephone is the desired information signal.

[Summary of invention]

The present invention provides a frequency control system for correcting a frequency difference between a transmitter and a receiver that operates in response to detection of transmitted information-bearing signals of a desired characteristic.

The present invention provides a frequency control system that can be operated to determine the frequency only when a signal containing information of a desired characteristic is detected so as to be utilized as a reference for a signal supplied to a receiver.

The present invention provides a method for maintaining a receiver oscillator frequency of a receiver unit at a desired frequency related to the oscillation frequency of a signal transmitted to the receiver unit.

According to the present invention, a frequency control system is described which is operative to maintain the receiver oscillation frequency of the receiver unit at a desired frequency related to the oscillation frequency of the signal transmitted to the receiver unit. The frequency control system includes at least one variable frequency oscillator oscillating at the receiver oscillation frequency and receives a signal transmitted to the receiver unit. The signal detector detects when the signal transmitted to and received from the receiver unit is an information-bearing signal with desired characteristics.

In response to the detection by the signal detector of the information-bearing signal with the desired characteristics, the receiver oscillation frequency of the variable frequency oscillator maintains the receiver oscillation frequency in relation to the oscillation frequency of the signal transmitted to the receiver unit.

Detailed description of the invention

A portion of the frequency band assigned to the cellular radiotelephone is shown in FIG. 1, where the vertical axis 10 is dBm and the horizontal axis 14 is kilohertz (approximately, axis 10 is volts, watts or amplitude). The frequency band portion shown is divided into adjacently located channels 18, 22, 26, 30, 34, 38 and 42. The vertically extending line in the figure indicates the boundaries between adjacent channels of the channels 18-42.

Channels 18, 22, 26, 30, and 42 are conventional bandwidths, such as the 30 KHz bandwidth transmission channels of the frequency bands allocated for wireless telephony in the United States, or 25KHz bandwidth transmission channels of the frequency bands assigned to wireless telephones in Japan. Channels 34 and 38 are reduced bandwidth compared to the bandwidth sizes of channels 18-30 and 42 and are the same as the 10 KHz bandwidth channel proposed for use in the United States and the 12.5 KHz bandwidth channel proposed for use in Japan. It illustrates a transmission channel utilized in an increased turbulence wireless telephony communication system.

Signals are sent on respective channels 18-42. A signal is transmitted on channel 18 that includes modulation spectrum 46 centered around carry frequency 48.

A signal is transmitted on channel 22 including modulation spectrum 50 centered around the carrier frequency (and). It is centered around carrier frequency 56 on channel 26.

The signal including the modulation spectrum 54 is centered around the carrier frequency 60 on the channel 30. The signal including the modulation spectrum 62 is centered around the carrier frequency 64 on the channel 34. The signal, including the modulation spectrum, is centered around the center carrier frequency 68 on channel 38. The signal, including the modulation spectrum 66, is centered around the carrier frequency 68 on the channel 38. The signal, including the modulation spectrum 70, is centered around the carrier frequency 72 on the channel 42.

The signals transmitted on channels 18, 22, 26 and 42 represent modulated information signals including conventional bandwidth voice signals (and SAT signals); Signals transmitted on channels 34 and 38 indicate modulated information signals, including speech signals of reduced bandwidth (and DSAT signals), which are transmitted on channels 18-26 and 34-42. Channels 18-26 and (wing-42) are referred to as voice channels, signals 46-70 represent various magnitudes indicating that the signal received by the receiver changes the signal strength.

The signal transmitted on channel 30 represents a modulated information signal including a control signal of conventional bandwidth (in the United States, such a control signal consists of 10 kilobits of data per second and in Japan the control signal is typically per second 8 kilobits of data). Since the control signal is transmitted on the channel 30, the channel 30 is called a control channel. The control signal consisted of a magnitude smaller than the signal magnitude transmitted on channels 18-26 and 38-42. The bandwidth of the control channel, such as control channel 30, is a bandwidth similar to that of the conventional channel, such as voice channels 18-26 and 42.

2 shows a single transmission channel similar to that of FIG. 1, where the vertical axis 80 is dBm and the horizontal axis 24 is kilohertz (again, the vertical axis can be in volts or watts). Frequency 90 represents a single signal received by a receiver, such as a receiver of a radiotelephone down-converted by the down conversion circuit described above. Lines 92 and 96 extending to the reception shown by hatch lines in the figure indicate the cut-off frequency of the receiver filter circuit, such as the filter circuit of the receiver tuning circuit.

Although the signal is shifted downward by the receiver down conversion circuit as long as the signal bandwidth is within the bandwidth of the filter circuit of the receiver, the form of the modulation spectrum is via a transmission channel such as any channel 18-42 in FIG. It is in the same form of modulation spectrum as it is transmitted. When the receiver down conversion circuit typically includes a mixer circuit, the center frequency 90 of the down converted signal depends on the frequency of the mixed signal supplied to the mixer circuit. Frequency control of the mixed signal that forms the oscillation signal generated by the receive oscillator needs to ensure that the center frequency of the final down converted signal is within the band pass of the filter circuit of the receiver.

FIG. 3 shows a graphic similar to that of FIG. 2, with the vertical axis 100 being dBm and the horizontal axis 104 being kilohertz (again, the vertical axis can be in volts or watts). Modulation Spectrum (08) And a signal composed of the carrier frequency 110 represents a signal similar to that of FIG. 2 and frequency downconverted by the down conversion circuit. Lines 112 and 116 extending to the reception shown as hatch lines are similar to lines 92 and 96 in FIG. 2 indicating the cutoff frequency of the filter circuit of the receiver. As shown, part of the signal exceeds the cut off frequency of the filter. This is caused by the frequency error of the oscillation frequency of the oscillator of the receiver circuit. Frequency error causes the final downconverted signal to be frequency offset from the center frequency of the filter band pass. The portion of the signal 108 that is not within the band pass of the filter is not passed by the filter and the information content of the signal 108 is distorted when the signal portion is truncated. The passband amplitude and phase response of the filter also distorts the information content of the signal. The amount of distortion depends on the amount of frequency error of the local oscillator, and the larger the frequency error, the greater the distortion. In order to keep the distortion below a certain amount, the frequency error has to keep the magnitude of the bandpass below a certain percentage. When the voice channel bandwidth is reduced, small frequency errors keep the distortion below an acceptable range because the band pass must be reduced. Since this frequency change of the oscillator causes a signal, such as signal 108, in which the signal information content is distorted or completely lost outside the filter circuit band pass of the receiver, the oscillation frequency change of the oscillator of the receiver should be minimized. do.

Frequency control system operation minimizes the frequency difference between the oscillation frequency of the oscillator of the receiver and the oscillation frequency of the signal generated by the remote transmitter (base station in the cellular communication system). Since the oscillation frequency of the oscillator of the base station is much more conveniently controlled to prohibit changes in the oscillation frequency, such a frequency control system is utilized to form part of many conventional radiotelephones to automatically control the frequency of the oscillator of the radiotelephone. do.

Existing frequency control systems compare the IF signal frequency with the reference frequency, generate a correction signal, and use the correction signal to correct the local oscillator of the receiver. The above-mentioned criterion is a circuit composed of a resonator (quartz or ceramic resonators) having high frequency stability or includes a frequency reference signal and constitutes a comparator.

In this system, the IF signal from the limiter is applied to the comparator (the frequency divider is used in the IF signal path). When a base station signal is present, the IF signal frequency indicates the base station frequency and the local oscillator frequency. Since the base station has very high frequency stability, most of the IF signal frequency change is due to the local oscillator frequency drift, so the correction signal changes in response to the local oscillator frequency. In the absence of a base station signal, the IF signal frequency is a random frequency determined by the upper and lower cutoff frequencies of the IF bandpass filter. A randomly varying correction signal appears at the output terminal of the comparator. If this signal is applied to the local oscillator for frequency correction, the local oscillator frequency is randomly varied. To prohibit this, conventional frequency control systems disable frequency control when no signal is present. This disables frequency control only when the RSSI signal performed is below the threshold by enabling frequency control only when the RSSI signal level is above a certain turnover.

4A is a graphical depiction of a single transport channel 124. Similar to the graphics shown in FIGS. 1-3, the vertical axis 128 is dBm (or may be volts or watts) and the horizontal axis is kilohertz. Vertically extending lines 136 and 140, shown as hatch lines, indicate the boundaries of the transmission channel 124. When the signal transmitted to the channel 124 includes one of a voice signal or a control signal, the transmission channel 124 forms one of the voice channel or the control channel. Signal 124 is a small and small strength signal in size.

Line l48 shows a Gaussian or white noise. The noise magnitude is much greater than the magnitude of the modulation spectrum 144 of the signal, both the signal and noise contained on the transmission channel 124 are frequency-processed and passed by the filter circuit of the receiver.

If the RSSI level of the received signal (information signal summed with noise) is higher than the threshold level, the existing frequency control system is enabled. However, since noise masks the information signal, the frequency detected by the frequency control system, which is the carrier frequency of the received signal, is actually a randomly varying frequency. Using such a frequency to synchronize the oscillator of the radiotelephone, the radiotelephone oscillator randomly changes the frequency.

The graphic depicted in FIG. 4B includes a similar number of transport channels 124 similar to the graphic in FIG. 4A and having boundaries indicated by lines 136 and 140. Preference including the modulation spectrum 144 and carrier frequency 164 is transmitted on channel 124. In FIG. 4B, the noise provided on the channel is not constant but is maximal at the frequency indicated by l56, as indicated by curve 154. Again, if the RSSI level of the received signal is higher than the threshold level, the existing frequency control suspend is enabled. However, the frequency detected by the frequency control system to be the carrier frequency is the frequency indicated by 156 rather than the net carrier frequency 146 of the information signal. Using this frequency to synchronize the radio telephone oscillator will synchronize the radio telephone oscillator to the incorrect frequency.

A similar situation occurs when there is no information signal received by the receiver and only the noise indicated by lines 148 and 156 is received.

5 is a graphic depicting a single transmission channel having a boundary indicated by lines 168 and 172 extending to reception shown by hatch lines. Again, similar to the graphic of the figure, the vertical axis 176 is dBm (also the vertical axis may be volts or watts) and the horizontal axis 180 is kilohertz. The transmission channel 164 may be one of the voice or control channel when the signal including the modulation spectrum (mouth input) and the carrier frequency 186 includes one of the voice signal or the control signal.

5 shows a second signal including a modulation spectrum l92 and a center frequency 194 representing a cloth signal. The maximum signal strength of the pseudo signal is greater than the maximum signal strength of the desired information signal and the maximum signal strength of the pseudo signal is located at the carrier frequency 196 of the pseudo signal. When the pseudo signal is a power level of sufficient magnitude to cause the RSSI signal to be above a threshold level, the pseudo signal carrier is not the net carrier frequency 188 of the information signal in order for the frequency detected by the frequency control system to be the carrier frequency. It is better to be at the frequency 194.

FIG. 6A shows a graphic similar to the graphic of the figures, with the vertical axis 200 being dBm (the vertical axis may be watts or watts) and the horizontal axis 202 being kilohertz. Two adjacent transmission channels 204 and 208 are shown, where channel 204 is the frequency bandwidth with the boundaries indicated by lines 212 and 216 extending to the reception shown as hatch lines and channel 208 is It is a frequency bandwidth with boundaries indicated by vertically extending lines 216 and 220 shown as hatch lines. The transmission channels 204 and 208 are signals comprising the modulation spectrum 224 and the carrier frequency 226 transmitted on voice or channel 204, including the control channel and the modulation spectrum transmitted on channel 208. 228 and the carrier frequency 230 include voice or control signals, respectively.

As shown, the signal transmitted on channel 208 is much larger than the signal transmitted on channel 204. Since the magnitude of the signal transmitted on channel 208 is too large compared to the magnitude of the signal transmitted on channel 204, after downconversion to an intermediate frequency, a larger signal, even if distorted as shown in FIG. The component part of appears. FIG. 6B is similar to FIG. 6A but shows a frequency down converted signal in graphic form and is filtered by the filter circuit of the radiotelephone receiver. The signal transmitted on channel 204 is down converted and passed in a non-distorted form as shown in modulation spectrum 224B and carrier frequency 226B. Much larger signals transmitted on the transmission channel 2058 are down converted and partially passed, as shown by the modulation spectrum 228B and the carrier frequency 230B. The signal is partially passed by the radiotelephone receiver filter circuit because it has only finite rejection in adjacent channels. When the passed signal is at a power level sufficient to cause the RSSI signal to be above a threshold level, the adjacent channel signal carrier rather than the forward carrier frequency 226B of the information signal in order for the frequency detected by the frequency control system to be the carrier frequency. It is preferable to be the frequency 230B.

The frequency control system of the present invention generates the frequency control signal only when the desired information signal is detected, thereby prohibiting the error display of the reference frequency of the received signal as described with reference to the figures of FIGS. The presence of excessive noise (FIGS. 4A and 4B), pseudo signals (FIG. 5) and adjacent channel interference (FIGS. 6A and 6B) prohibits proper reception of transmitted information signals. By disabling the frequency control system when the actual desired information signal is not detected by the receiver, the control system is not "synchronized" with the incorrect frequency.

7 is a simplified block diagram of the frequency control system of the present invention. The signal received by the receiver and frequency down-converted to the intermediate frequency level is supplied to frequency comparator 306 and demodulator 308 on line 304. The frequency comparator 304 compares the frequency of the signal supplied on the line 3 a with the frequency of the oscillation signal supplied to the frequency comparator on the line 310. Frequency comparator 306 generates a signal on line 312 in response to the comparison.

Demodulator 308 demodulates the signal supplied on line 314 and generates a demodulation signal on line 316. Line 316 is connected to an information signal detector 320 that operates to form when the demodulated signal is the desired information signal. When information signal detector 320 detects the presence of the desired scene, a signal is generated on line 324. Lines 324 and 312 are connected to frequency controller 332.

The frequency controller 332 generates an output signal on the line 338 supplied to the oscillator 344 to convert the oscillation frequency of the oscillator 344 in response to the signal value supplied to the line 388. The frequency controller 332 generates a signal on the line 338 to convert the oscillation frequency of the oscillator 344 only during the time when the signal on the line 324 indicates the presence of the desired information signal. Since the frequency controller 332 generates a signal on the line 338 to change the oscillation frequency of the oscillator 344 only when the information signal of the desired characteristic is supplied on the line 304, the distortion or lack of the information signal causes the oscillator ( 344) change of oscillation frequency is prohibited.

8 is a block diagram of a transceiver 400 coupled with a frequency control system of the present invention. In particular, the block diagram of FIG. 8 illustrates a wireless telephone operating in a conventional or improved capacity cellular communication system. However, the frequency control system of the present invention can be operated as a receiver (eg, a pager) as well as many different transceivers.

The transceiver 400 includes an antenna 404 for receiving a transmitted radio frequency signal. Antenna 404 generates a signal on line 408 that indicates the signal received by antenna 404. Line 408 is connected to band pass filter 412 for passing a desired frequency signal. In an embodiment of the invention, the pass band of filter 412 is between 843 and 870 MHz.

Filter 412 generates a filtered signal on line 416 that is supplied to radio frequency amplifier / mixer 420. A single circuit amplifier / mixer 420 is shown as amplifier 422 and mixer 424, respectively. Amplifier 422 amplifies the signal supplied on line 416 and the amplified signal is supplied to mixer 424. The oscillation signal generated by oscillator 430 is provided to mixer 424 on line 428. Mixer 424 mixes the signal frequencies amplified by amplifier 422 downward to generate a mixed signal on line 432. The signal frequency generated on line 432 is referred to as " 11F " (first intermediate frequency signal). The signal generated on line 432 is similar to the signal supplied on line 416, but amplifies and shifts the frequency downwards (circuit 420 consists only of a mixer circuit or an amplifier / filter / mixer combination). Circuit)

The signal generated on line 432 is supplied with a filter 436 which generates a filtered signal on line 440. In an embodiment of the invention, filter 436 includes a passband centered at a frequency of about 55 MHz. The filter signal generated on line 440 is supplied to an intermediate frequency amplifier 444 which generates an amplified signal on line 448. The amplified signal generated on line 448 is second mixed mixer 452. Mixer 452 receives an oscillation signal generated by oscillator 460 that is alternately connected to 2d LO oscillator synthesizer 462. In an embodiment of the invention, oscillator 460 oscillates at 54.540 MHz. Generate an oscillating signal of frequency.

Mixer 452 generates a signal on line 460 that is a 460 KHz frequency in this embodiment and refers to it as a "2d IF" frequency. Line 460 is in turn connected to filter 468 or filter 472. Filter 468 includes a pass band of conventional bandwidth (30 KHz in the United States and 25 KHz in Japan) and filter 472 includes a pass band of reduced bandwidth (10 KHz in the United States and 12.5 KHz in Japan). Filter 468 generates a filtered signal on line 476 when it receives a signal generated on line 464. Similarly, filter 472 generates a filtered signal on line 480 when a signal generated on line 464 is supplied to filter 472. The filtered preference generated on line 476 or the filtered signal generated on line 480 is supplied to intermediate frequency amplifier 484. Amplifier 484 (consisting of several series stages) generates an amplified signal on line 488. In addition, amplifier 484 includes circuitry for generating a signal on line 492 indicative of the magnitude of the supplied signal. The signal generated on line 492 is called a received signal strength indicator (RSSI) signal.

The amplified signal generated on line 488 is supplied to filter 494 and the filtered signal generated on line 488 is generated on line 496. The filtered signal generated on line 496 is supplied to limiter 500 (consisting of several series stages) which generates a voltage limited signal on line 504. In addition, similar to amplifier 484, limiter 500 includes circuitry for generating a signal on line 506 indicating the signal magnitude supplied to it. The signal generated on line 506 is similar to the signal generated on line 492, referred to as a received signal strength indicator (RSSI) signal.

The signal generated on line 504 is supplied to FM demodulator 508 and the signal generated on line 510 is supplied to automatic frequency control (AFC) unit 512. The AFC unit 5112 is conventional and operates as described above. The FM demodulator 508 demodulates or reproduces the information content of the signal supplied on the line 504. FM demodulator 508 receives (Rx) generates a signal on line 516 to which voice processor circuit 518 is supplied and to receive (Rx) data interface circuit 520.

RSSI signals generated on lines 492 and 506 are supplied to RSSI circuit 522. RSSI circuit 522 generates a signal on line 526 in response to signal values supplied on lines 492 and 506. Line 526 is connected to A / D converter 530 which converts an analog signal into a digital signal on line 534.

The voice processor circuit 518 may be comprised of, for example, an integrated circuit, which performs functions such as de-emphasis, expansion, volume control (and muting), and the like. The signal output by voice processor circuit 518 on line 588 is supplied to receiver 542.

The data interface 520, which is also configured as an integrated circuit, interfaces the data signal supplied on the line 516 to the processor 546 on the line 550. The interface 520 is further connected to the bus (and additionally the speech processing circuit 518). Data interface 520 performs functions such as SAT detection DSAT status and 8 kilobit data per second decoding.

Processor 546 receives the input signal (RSSI signal level indication) on line 534 as well as line 550 and includes a signal generated on line 546 by AFC unit 512. Processor 546 is also coupled to bus 554.

The bus 554 interconnects the processor 546 to the transmit (Tx) data interface circuit 562 and the transmit (Tx) voice processing circuit 566 as well as the processing circuit 510 and the data interface unit 520. Circuit 562 is similar to circuit 520 but performs the same functions as SAT signal generation, DSAT signal generation, and 8 kilobit decode encoded per second. Tx data interface 562 is similar to circuit 520 but performs functions such as SAT signal generation, DSAT signal status and initial 8-kilobit decoding encoding. Tx data interface 562 is connected by line 568 to receive signals formed by Rx data interface 520 and to receive signals from processor 546 on line 569. Circuit 566 is similar to circuit 518 but performs functions such as preemphasis, compression, maximum deviation limit, and splatter filtering.

Bus 554 is coupled to display 570 and keypad 574 to input manual input to processor 546 and display information generated therefrom.

Processor 546 is connected to bus 576 to interconnect processor and reference oscillator 580 and programmable synthesizer 584. When the data interface circuit 520 detects the presence of valid information, excitation SAT signal or 8 kilobits per second, the detection is supplied to the processor 546. The software algorithm implemented in processor 546 detects the presence of a DSAT signal. In response to the signal detection, processor 546 generates a signal on bus 576 to oscillate reference oscillator 580 in a manner represented by the signal generated by AFC unit 512 on line 558. Change the frequency.

When valid information (i.e., SAT signal, 8 kilobits per second data, or DSAT signal) is not detected by the software algorithm implemented by the data interface circuit 520 or the processor 546, the processor 546 oscillator No signal is generated on bus 576 to change the oscillation frequency of 580. Since the oscillation frequency of the reference oscillator is not changed unless a voice or data signal is received by the receiver of the radiotelephone, an undesirable signal (e.g., small, the state described in relation to FIGS. 4-6). An error frequency change is not caused in response to receiving.

Oscillator 580 generates an oscillation signal on line 588 which is fed to 2d LO oscillator synthesizer 580, programmable synthesizer 584 and AFC unit 5112. Altering the oscillator frequency of oscillator ω o changes the oscillation frequency of oscillator 460 and oscillator 430 (connected to synthesizer 584 programmable by line 592.) Generated by oscillator 580 and The oscillation signal supplied to the unit 512 is compared with the signal supplied to the AFC unit 5l2 on the line 526 (not shown inside the division and comparison circuit of the unit 512) and occurs on the line 558. The signal to be indicative of the comparison like a conventional AFC unit.

8 shows a transmitter of a wireless telephone. Since the transmitter is conventional, a description thereof has been omitted, but in the figure, a signal (signal from the speaker 598) generated by the Tx data interface circuit 562 and the Tx voice processing circuit on the line 596 is received. The transmitter is shown. The transmitter is an offset synthesizer 600, an offset oscillator 604, an offset mixer 608 (supplied with an oscillation signal generated by the oscillator 430 and amplified by the amplifier 612), filter 616, excitation An excimer 620, an amplifier 624, an aberrant coupler 628, and a filter 632 (both filters 632 and 412 form a duplexer).

The output power of the signal generated by the transceiver 400 is controlled by the power control unit 634 which is provided with an input signal generated by the RF detector 640 and the processor 546 on the line 644. Offset synthesizer 600 is further connected to line 588 to receive the oscillation signal generated by oscillator 580.

Referring now to the logic flow chart of FIG. 9, a method for maintaining the receiver oscillation frequency of the receiver unit at a desired frequency relative to the oscillation frequency of the signal is described. First, as indicated by block 700, a signal is sent to the receiver unit. Next, as shown by block 704, the time when the signal transmitted to the receiver unit includes an information bearing signal of a desired characteristic is detected. Next, as shown by block 708, the receiver oscillation frequency of the variable frequency oscillator is changed to remain at the receiver oscillation frequency that is related to the generation frequency of the signal.

While the present invention has been described in connection with the drawings, it will be apparent to those skilled in the art that modifications and variations of the present invention can be made without departing from the scope of the present invention. Therefore, the present invention is not limited to the above embodiments but includes all the techniques which have been modified and changed based on the present invention.

Claims (9)

A frequency control system for a radio receiver unit operating in a wireless communication system that transmits a data management signal prior to or simultaneously with a voice signal, the frequency control system receiving a modulated signal at the radio receiver unit and oscillating at the receiver oscillation frequency. A variable frequency oscillator for generating an electrical signal indicative of an electrical signal, and operatively coupled to receive an electrical signal from the mask frequency oscillator to detect when the modulated signal includes the data management signal of a selected value. A signal detector for generating a management signal-detected signal when the management signal is the selected value, and operatively coupled to the signal detector and the variable frequency oscillator to generate the management signal-detected signal when the preference detector generates the management signal-detected signal. Oscillation frequency of the modulated signal And a frequency controller that adjusts the oscillation frequency of the variable frequency oscillator to a relative frequency relationship of and forbids adjusting the oscillator frequency when the signal detector does not generate the management signal-detected signal. Frequency control system. 2. The frequency control system of claim 1, wherein said modulated signal comprising said data-management signal as a voice signal comprises a signal transmitted on a control channel. 2. The frequency control system of claim 1, wherein the modulated signal comprising the data-management signal comprises a signal transmitted on a voice channel. 2. The frequency control system of claim 1, wherein the modulated signal comprising the data-management signal comprises a frequency modulated signal. The frequency control system of claim 1, wherein the frequency controller comprises a device for calculating a difference signal indicating a frequency difference between the receiver oscillation frequency and the oscillation frequency of the modulated signal. 6. The frequency control system of claim 5, wherein the frequency controller generates a frequency corrected output signal. 7. The apparatus of claim 6, wherein the frequency corrected output signal is variable in response to the signal detector detecting the modulated signal comprising the data-management signal to generate the management-detected signal. A frequency control system, characterized in that applied to the frequency oscillator. 12. The frequency control system of claim 1, wherein the variable frequency oscillator comprises a demodulation circuit to demodulate a received modulated signal. 9. The frequency control system of claim 8, wherein the frequency controller displays a frequency characteristic for passing a signal within a first frequency bandwidth or a second frequency bandwidth.