Abstract: A module and system are provided for reducing or suppressing ringing occurring in a digital signal to be transmitted. A transmission module Ma includes a transmitter 200a configured to transmit a digital signal, a transmission antenna 100a constituted by a metal plate, or by a conductor formed on an insulator, the transmission antenna 100a being configured to be electromagnetically or magnetically coupled to a reception antenna 100b of a non-contact reception module Mb for digital communication, and a resistor 400a connected in series between the transmitter 200a and the transmission antenna 100a. The resistor 400a has such a resistance value that the resistor 400a entirely blunts a waveform of the digital signal outputted from the transmitter 200a so as to reduce or suppress ringing occurring in the digital signal. The blunted digital signal is to be inputted into the transmission antenna 100a.

Abstract: Ringing occurring in a digital signal to be transmitted, is reduced or suppressed. A transmission module Ma includes a transmitter 200a configured to transmit a digital signal, a transmission antenna 100a constituted by a metal plate, or by a conductor formed on an insulator. The transmission antenna 100a is configured to be electromagnetically or magnetically coupled to a reception antenna 100b of a non-contact reception module Mb for digital communication. A resistor 400a is connected in series between the transmitter 200a and the transmission antenna 100a. The resistor 400a has such a resistance value that the resistor 400a entirely blunts a waveform of the digital signal outputted from the transmitter 200a so as to reduce or suppress ringing occurring in the digital signal. The blunted digital signal can be inputted into the transmission antenna 100a.

Abstract: A first electronic device of a first user programmed to: connect, with a second electronic device of a second user over a first peer-to-peer wireless network link; send, to the second electronic device, a first unique code generated by the first electronic device, corresponding to a first user identifier of the first electronic device; receive, from the second electronic device, a second unique code generated by the second electronic device, corresponding to a second user identifier of the second electronic device; store, the second unique code, and second metadata associated with the second electronic device including the time, proximity or duration of interaction; retrieve, from a coupled backend database stored in a cloud, a third unique code of an electronic device, uploaded to the coupled backend database stored in the cloud; and display, a notification on the first electronic device, if the third unique code matches the second unique code.

Abstract: Methods, systems, and mobile devices for providing users with social media-related information about other users based on the relative geographic locations of the users.

Abstract: Methods, systems, and mobile devices for providing users with social media-related information about other users based on the relative geographic locations of the users.

Abstract: A host device uses an intermediate frequency determined based on frequencies of a second-order nonlinear intermodulation distortion component and a harmonic component which are generated in an analog optical link connected to the host device, for example, an analog optical link of a distributed antenna system (DAS), and precompensates for the second-order nonlinear intermodulation distortion component and the harmonic component generated in the analog optical link.

Abstract: A method for profile matching includes receiving a plurality of user profiles, each user profile comprising traits of a respective user. The method includes receiving a preference indication for a first user profile of the plurality of user profiles. The method also includes determining a potential match user profile of the plurality of user profiles based on the preference indication for the first user profile. The method also includes presenting the potential match user profile to a second user.

Abstract: Embodiments of the invention include electronic communications devices having a memory in near field communication device, a memory arbitrator and a host processor. The near field communication (NFC) devices are configured to receive data and drive power from the communication signal. The memory arbitrator is connected to the NFC device and the memory. The memory arbitrator is also configured to access the memory in response to an access request from the NFC device. Additionally, the memory is configurable to be accessed by both the host processor and the NFC device according to embodiments of the present invention.

Abstract: Provided is a receiver for processing VSB signal. The receiver includes a first equalizer/decoder unit and a second equalizer/decoder unit. The first equalizer/decoder unit performs a first equalizing operation, first TCM decoding and first RS decoding on a received symbol to output a first dibit. The second equalizer/decoder unit performs a second equalizing operation, second TCM decoding and second RS decoding on the received symbol to output a transport stream. The first dibit is provided as a priori information for a soft-decision operation of the second TCM decoding.

Abstract: Embodiments of the invention include electronic communications devices having a memory in near field communication device, a memory arbitrator and a host processor. The near field communication (NFC) devices are configured to receive data and drive power from the communication signal. The memory arbitrator is connected to the NFC device and the memory. The memory arbitrator is also configured to access the memory in response to an access request from the NFC device. Additionally, the memory is configurable to be accessed by both the host processor and the NFC device according to embodiments of the present invention.

Abstract: A frequency and data synchronization control system through the 8VSB SFN DTx modulation prevents the deterioration of the digitally broadcasted receiving sensitivity caused by a discrepancy of the frequency or data between the receiver of the digital broadcasting signal and the distributed translator or between distributed translators.

Abstract: A method of providing a service at a remote terminal including receiving information broadcast by a commercial radio station in a broadcast radio channel; discriminating an identifier of an application within the received broadcast information; initiating an authentication process for authenticating broadcast information received via the broadcast channel; and in response to a positive authentication, enabling use of information received via the broadcast radio channel by the identified application.

Abstract: The communication device comprising a voice communicating implementer, an incoming communication ID implementer, a payment monetary value data transmitting implementer, a remaining monetary value data updating implementer, an automated supplementary monetary value data adding implementer, and a simultaneous implementation implementer.

Abstract: An embodiment of the invention provides an electronic device. The electronic device includes a digital-to-analog converter (DAC), a transmitter front-end (TX FE), an amplifier, an analog-to-digital converter (ADC), and a swap circuitry. The TX FE has a first and a second input end coupled to a first and a second output end of the DAC, respectively. The ADC has a first and a second input end coupled to a first and a second output end of the amplifier, respectively. The swap circuitry is configured to couple the first and second output ends of the DAC to a first and a second input end of the amplifier in a normal state, respectively, and couple the first and second output ends of the DAC to the second and first input ends of the amplifier in a swapped state, respectively.

Abstract: An apparatus and method for transmitting digital broadcast signal are provided. The apparatus includes a group formatter to format a data group including mobile service data, where the group formatter further maps the mobile service data into a data group of interleaved format, adds N training sequences into a corresponding location of the data group of interleaved format, adds signaling data into the data group of interleaved format, inserts place holder bytes for MPEG header and non-systematic Reed-Solomon (RS) parity into the data group of interleaved format, and deinterleaves the mobile service data in the data group of interleaved format, a non-systematic RS encoder to non-systematic RS encode the mobile service data in the formatted data group and insert non-systematic RS parity obtained from the non-systematic RS encoding into the formatted data group.

Abstract: A single sideband mixer is constructed with digital logic elements such as T-type flip-flops and inverters and with FETs, and the resulting mixer circuit simultaneously improves control over the frequency resolution, noise floor and operating frequency range. The use of this group of elements also allows the mixer circuit to be easily realized in an integrated circuit.

Abstract: A Wireless Regional Area Network (WRAN) receiver comprises a transceiver for communicating with a wireless network over one of a number of channels, and an Advanced Television Systems Committee (ATSC) signal detector for use in forming a supported channel list comprising those ones of the number of channels upon which an ATSC signal was not detected. The ATSC signal detector comprises a matched filter that matches to at least a modulated version of an ATSC field sync signal for detecting the presence of an incumbent ATSC broadcast signal.

Abstract: A signal receiving apparatus includes: a receiver which receives at least two types of broadcasting signals included in a plurality of channels; and a controller which controls the receiver to search a current channel according to one type of a broadcasting signal used for a previous channel search and to search a current channel according to another type of a broadcasting signal if the channel is not searched, to thereby set an automatic channel.

Abstract: A carrier recovery apparatus usable with a VSB receiver and a method thereof. The carrier recovery apparatus is capable of recovering a carrier even though a pilot signal may be corrupted due to multi-path characteristics of a channel. Accordingly, the carrier recovery apparatus performs a BECM (Band Edge Component Maximization) algorithm on upper and lower sidebands of a received signal to generate phase information therefrom. The phase information is combined in a combiner. Since the BECM algorithm is performed on the upper and lower sidebands, it is possible to execute the carrier recovery even through the upper sideband of a received signal may be corrupted. Therefore, the carrier recovery apparatus can prevent performance degradation of the VSB receiver caused by corruption in the pilot signal.

Abstract: A VSB communication system or transmitter for processing supplemental data packets with MPEG-II data packets includes a VSB supplemental data processor and a VSB transmission system. The VSB supplemental data processor includes a Reed-Solomon coder for coding the supplemental data to be transmitted, a null sequence inserter for inserting a null sequence to an interleaved supplemental data for generating a predefined sequence, a header inserter for inserting an MPEG header to the supplemental data having the null sequence inserted therein, a multiplexer for multiplexing an MPEG data coded with the supplemental data having the MPEG header added thereto in a preset multiplexing ratio and units. The output of the multiplexer is provided to an 8T-VSB transmission system for modulating a data field from the multiplexer and transmitting the modulated data field to a VSB reception system.

Abstract: Disclosed are circuits, techniques and methods for removing one or more harmonics from a waveform that has been mixed with a local oscillator. In one particular example, such a waveform may also be mixed with a second local oscillator at a different frequency and combined with the first mixed waveform to suppress and/or substantially remove the one or more harmonics.

Abstract: A VSB communication system or transmitter for processing supplemental data packets with MPEG-II data packets includes a VSB supplemental data processor and a VSB transmission system. The VSB supplemental data processor includes a Reed-Solomon coder for coding the supplemental data to be transmitted, a null sequence inserter for inserting a null sequence to an interleaved supplemental data for generating a predefined sequence, a header inserter for inserting an MPEG header to the supplemental data having the null sequence inserted therein, a multiplexer for multiplexing an MPEG data coded with the supplemental data having the MPEG header added thereto in a preset multiplexing ratio and units. The output of the multiplexer is provided to an 8T-VSB transmission system for modulating a data field from the multiplexer and transmitting the modulated data field to a VSB reception system.

Abstract: The disclosure can provide methods and systems for autocalibrating a transceiver. The method can include upconverting a bandpass input signal by mixing the bandpass input signal with a first local oscillator signal to form an initial transmitter signal. The initial transmitter signal can be looped back to a receiver and downconverted with a second local oscillator signal having a frequency that is different from the first local oscillator to form an intermediate frequency signal. At least one of a gain and a phase of the transmitter can be adjusted based on a transmitter image sideband of the intermediate frequency signal to generate a calibrated transmitter signal having minimized transmitter image sideband.

Abstract: A transmitter includes a first amplifier to amplify an in-phase oscillator signal to produce an in-phase mixing signal and a second amplifier to amplify a quadrature-phase oscillator signal to produce a quadrature-phase mixing signal. A first mixer mixes the in-phase mixing signal with a first information signal to produce a first output signal. A second mixer mixes the quadrature-phase mixing signal with a second information signal to produce a second output signal. The first output signal and an inverted second output signal are summed to produce a transmitter output signal that includes an image signal caused by a phase imbalance between the in-phase and quadrature-phase mixing signals. An image monitor monitors the image signal and reduces or eliminates the phase imbalance by independently adjusting a phase of the in-phase mixing signal and/or a phase of the quadrature-phase mixing signal. Consequently, a power of the image signal is reduced or eliminated.

Abstract: In a signal processing circuit (3) for a contactlessly communicating communication partner device (1), there are provided a transmitted-signal path (9) and a received-signal path (10), the received-signal path (10) branching off from a branch point (AP) present on the transmitted-signal path (9), a filter stage (11) and a matching stage (12) connected downstream of the filter stage (11) being provided on the transmitted-signal path (9), the filter stage (11) having a resonant frequency that is in a frequency range the center frequency value of which matches an upper sideband frequency, and the branch point (AP) being situated between the filter stage (11) and the matching stage (12).

Abstract: A phase tracking system includes a source of an input signal representing a received symbol. A phase rotator has a first input terminal which is responsive to the input signal, a second input terminal which is responsive to a phase correction signal, and an output terminal which produces a phase adjusted output signal. A decision element generates an ideal signal representing the received symbol in response to the phase adjusted output signal. A phase adjuster, which has full phase wrap-around capability, generates the phase correction signal in response to the phase difference between the phase adjusted output signal and the ideal signal.

Abstract: A Wireless Regional Area Network (WRAN) receiver comprises a transceiver for communicating with a wireless network over one of a number of channels, and an Advanced Television Systems Committee (ATSC) signal detector for use in forming a supported channel list comprising those ones of the number of channels upon which an ATSC signal was not detected. The ATSC signal detector comprises a matched filter that matches to at least a modulated version of an ATSC field sync signal for detecting the presence of an incumbent ATSC broadcast signal.

Abstract: A VSB communication system or transmitter for processing supplemental data packets with MPEG-II data-packets includes a VSB supplemental data processor and a VSB transmission system. The VSB supplemental data processor includes a Reed-Solomon coder for coding the supplemental data to be transmitted, a null sequence inserter for inserting a null sequence to an interleaved supplemental data for generating a predefined sequence, a header inserter for inserting an MPEG header to the supplemental data having the null sequence inserted therein, a multiplexer for multiplexing an MPEG data coded with the supplemental data having the MPEG header added thereto in a preset multiplexing ratio and units. The output of the multiplexer is provided to an 8T-VSB transmission system for modulating a data field from the multiplexer and transmitting the modulated data field to a VSB reception system.

Abstract: A VSB communication system or transmitter for processing supplemental data packets with MPEG-II data packets includes a VSB supplemental data processor and a VSB transmission system. The VSB supplemental data processor includes a Reed-Solomon coder for coding the supplemental data to be transmitted, a null sequence inserter for inserting a null sequence to an interleaved supplemental data for generating a predefined sequence, a header inserter for inserting an MPEG header to the supplemental data having the null sequence inserted therein, a multiplexer for multiplexing an MPEG data coded with the supplemental data having the MPEG header added thereto in a preset multiplexing ratio and units. The output of the multiplexer is provided to an 8T-VSB transmission system for modulating a data field from the multiplexer and transmitting the modulated data field to a VSB reception system.

Abstract: A VSB communication system or transmitter for processing supplemental data packets with MPEG-II data packets includes a VSB supplemental data processor and a VSB transmission system. The VSB supplemental data processor includes a Reed-Solomon coder for coding the supplemental data to be transmitted, a null sequence inserter for inserting a null sequence to an interleaved supplemental data for generating a predefined sequence, a header inserter for inserting an MPEG header to the supplemental data having the null sequence inserted therein, a multiplexer for multiplexing an MPEG data coded with the supplemental data having the MPEG header added thereto in a preset multiplexing ratio and units. The output of the multiplexer is provided to an 8T-VSB transmission system for modulating a data field from the multiplexer and transmitting the modulated data field to a VSB reception system.

Abstract: The present invention provides a novel symbol timing recovery method for VSB receivers. Systems are described that comprise a timing error detector (TED) that produces an exact symbol timing error even in the presence residual carrier phase offset, loop filter that controls the characteristics of acquisition and tracking of digital PLL loop, Voltage/Numerically Controlled Oscillator (VCO/NCO) that adjusts the sampling instant and phase, A/D converter that samples a continuous VSB input signal, and a interpolating squared root raised cosine filter that performs both matched filtering and a compensation of constant timing offset of quarter symbol caused by the invented TED. The timing error detector in this invention comprises an envelope detector, band pass filter, squaring block, high pass filter, and decimator.

Abstract: In a dual-channel HD radio receiver, when the broadband filter channel is compromised, the broadband channel is inactivated and the narrowband channel is activated. By mixing the signals of the two channels during the change, undesirable audio artifacts can be minimized.

Abstract: The invention relates to a receiver (1, 49, 51, 52, 54) for receiving RF signals. The known receiver comprises a phase-locked loop which is controlled by the stereo pilot. Because of unwanted frequency changes, a sampling rate converter precedes the stereo decoder. Filtering operations within a complex range can be performed by means of the invention.

Abstract: This signal detection method detects an output signal indicating data information contained at least in two sideband waves from an input signal having a carrier and at least two sideband waves accompanying the carrier. The method includes a cut off step for cutting off a sideband wave positioned at the high frequency side or the low frequency side as compared to the carrier from the at least two sideband waves and a square detection step for outputting an output signal by performing square detection of an input signal having one of the sideband waves which has been cut off.

Abstract: Methods and systems for robust single sideband LO generation are disclosed. Aspects of one method may include generating LO output signals where a VCO may generate a signal that may be used to generate a first pair of signals and a second pair of signals. The first pair of signals, with a frequency of 1.8 GHz, may be 90° out of phase With each other, and the second pair of signals, with a frequency of 800 MHz, may be 90° out of phase with each other. The second pair of signals may be linearly amplified and low-pass filtered. The filtered signals may be mixed with the first pair of signals to generate the LO output signals. A corner frequency for the low-pass filter may be substantially 1.5 times the frequency of a fundamental frequency for the signal to be filtered. Various embodiments of the invention may generate differential output signals, including the LO output signals.

Abstract: A method and system for calibrating a quadrature modulator. The method includes: determining a set of sideband calibration frequencies; for each sideband calibration frequency out of the set of sideband calibration frequencies: inputting an input signal having the sideband calibration frequency to the quadrature modulator; measuring a sideband signal power level; determining at least one calibration parameter in response to phase and gain imbalances expected at the measured sideband signal power level.

Abstract: A transmitter shifts a baseband data signal having a bandwidth of 2?M using a tone signal having a frequency ?M, which centers a sideband of the data signal at zero frequency. The transmitter then filters the shifted signal to filter out the non-centered sideband, and then adds the tone signal to form a composite signal. The transmitter upconverts the composite signal during a first operational mode using a RF signal having a frequency ?C equal to a center frequency of a channel. In a second operational mode, the transmitter upconverts a DC level using the same RF signal. The upconverted DC level can be used as a continuous wave carrier signal having a frequency ?C. The transmitter has a single RF oscillator to output both a SSB signal centered at frequency ?C during the first mode and a carrier signal of frequency ?C during the second mode.

Abstract: In a signal processing circuit (3) for a contactlessly communicating communication partner device (1), there are provided a transmitted-signal path (9) and a received-signal path (10), the received-signal path (10) branching off from a branch point (AP) present on the transmitted-signal path (9), a filter stage (11) and a matching stage (12) connected downstream of the filter stage (11) being provided on the transmitted-signal path (9), the filter stage (11) having a resonant frequency that is in a frequency range the center frequency value of which matches an upper sideband frequency, and the branch point (AP) being situated between the filter stage (11) and the matching stage (12).

Abstract: A mechanism for initiating contact with someone, via a telecommunications system, who is in the admirer's proximity, but whose identity or telecommunications address (e.g., telephone number, e-mail address, etc.) is unknown. The illustrative embodiments enable the user to use what information he does know about the admired person—the admiring person's distinguishing characteristics—to get a telecommunications address through which the initial contact can be made.

Abstract: An audio broadcast receiving apparatus and an audio broadcast receiving method implemented by the audio broadcast receiving apparatus are disclosed. A tuner simultaneously receives a radio wave in a specific frequency band of the analog audio broadcast and a radio wave of the digital audio broadcast transmitted in parallel with the analog audio broadcast in the specific frequency band. A demodulator retrieves the intended audio information by demodulating the signal received by the tuner. An analog receiving signal bandpass filter selectively passes the receiving signal corresponding to the analog audio broadcast radio wave. An analog receiving signal amplifier outputs an output signal representing an amplified receiving signal that has passed the analog receiving signal bandpass filter to the demodulator, and the gain of the amplifier is controlled in accordance with the level of the same output signal.

Abstract: A chopper-direct-conversion (CDC) radio receiver includes a phase-alternating mixer receiving an antenna input signal and at least one local oscillator signal and generating a double sideband signal in a single mixing step. The phase-alternating mixer may be implemented by two parallel mixers each mixing the input signal with one of two local oscillator signals and an adder receiving and summing outputs from the two parallel mixers, by a track-and-hold circuit sampling the input signal based upon the local oscillator signal, or by a window averaging circuit averaging the input signal across a period of the local oscillator signal. The CDC architecture is suitable for fabrication on a single chip and offers solutions to virtually all problems found in conventional direct-conversion receivers.

Abstract: A transmitter upconverts a SSB data signal during a first operational mode using a RF upconverting signal having a frequency that is offset from a center frequency of a channel (?C) by an amount that depends on the data signal's SSB bandwidth (?M). In a second operational mode, the transmitter upconverts a tone signal having a frequency ?M using the same RF upconverting signal. The upconverted tone signal can be used as a continuous wave (CW) carrier signal having a frequency ?C. The transmitter has a single RF oscillator to output both a SSB signal centered at frequency ?C during the first mode and a carrier signal of frequency ?C during the second mode.

Abstract: For the noise reduction of an audio signal generated by stereo-demultiplexing of a frequency-modulated stereo multiplex signal (SFM(t)) a filtering within the signal path to generate the stereo difference signal (ud(t)) is performed that determines a weight with which the upper sideband (ud,u(t)) and the lower sideband (ud,l(t)) of the amplitude modulated stereo-difference signal are weighted with different weighting factors that are dependent on the frequency.

Abstract: Briefly, in accordance with an embodiment of the invention, a method and apparatus to transfer information is provided, wherein the method includes transferring information between at least two wireless devices using a waveform that includes a first sinusoidal signal and a second sinusoidal signal, wherein the second sinusoidal signal has more zero-crossings than the first signal and wherein a duration of the first sinusoidal signal is less than a duration of the second sinusoidal signal.

Abstract: A free-running sample rate converter and a large spanning, non-linear pre-equalizer are employed before a timing recovery loop within a wireless receiver chain, while forward and feedback equalization after the timing recovery loop (at and around the input of a sync detector) is also retained. A channel identifier produces a channel estimate from the PN511 training sequence within the received wireless signals, with the pre-equalizer employing the resulting channel estimate to equalize the received signals being passed to the timing recovery loop, improving the signal quality for carrier and timing recovery and decoding to increase the probability of successful decoding while enabling the use of fast tracking forward and feedback equalizers for decoding.

Abstract: The present invention provides a method and device for determining the sideband ratio of a superconducting mixer using a comb generator. The method includes the steps of: (a) tentatively adjusting the sideband ratio of a mixer for calibration of an output of the comb generator; (b) determining the signal intensity of a pseudo-celestial signal oscillator for calibration of the output of the comb generator; (c) repeating the steps (a) and (b) to derive the relation between the sideband radio of the mixer for the comb-generator output calibration and the intensity of a pseudo-celestial signal; (d) calibrating the output of the comb generator; and (e) obtaining the sideband ratio of the mixer to be measured.

Abstract: A sinusoidal RF carrier is modulated for the transmission of digital binary data streams through the amplitude suppression of carrier wavelets. These wavelets are defined between zero crossover positions representing zero energy locations. This modulation is accomplished when the carrier is slightly amplitude modulated with a modulation signal that is equal in frequency to the carrier itself and the modulation always begins or ends upon the exact zero voltage crossing point of the RF cycle phase. The modulation is applied as a slight shift of the amplitude of any single cycle, each cycle representing a single bit of data. A single cycle of RF will either represent a “1” or “0” depending upon the amplitude of the cycle, relative to other adjacent cycles in the same carrier.

Abstract: The system for recovering symbol timing offset and carrier frequency error from an orthogonal frequency division multiplexed (OFDM) signal includes a receiver circuit for receiving an OFDM modulated signal representing a series of OFDM symbols, and providing a received signal to an output thereof. A peak development circuit is included for developing a signal having a plurality of signal peaks representing symbol boundary positions for each received OFDM symbol, where each of the signal peaks is developed responsive to an amplitude and phase correspondence produced between the leading and trailing portions of each of the received OFDM symbols. The system includes a circuit for enhancing the signal peak detectability, which includes a circuit for additively superimposing and then filtering the signal peaks, to produce an enhanced signal peak having an improved signal-to-noise ratio.

Abstract: A vestigial-sideband (VSB) signal is down-converted to generate a VSB signal including a carrier frequency offset from zero frequency by an amount greater than the bandwidth of the VSB signal. The carrier of this final I-F signal has a carrier offset from zero-frequency, which carrier offset exceeds the highest modulating frequency of the VSB signal and is adjusted to a prescribed carrier offset value. The down-converted VSB signal is digitized to generate a digital multiplicand signal for a digital multiplier circuit. The digital multiplier circuit is supplied a digital multiplier signal descriptive of a system function composed of a constant term and a second harmonic of the carrier frequency offset from zero frequency. Digital product signal from the digital multiplier circuit is descriptive of a double-sideband amplitude-modulation final I-F signal in the digital regime, which DSB AM final I-F signal is subsequently detected to generate a baseband demodulation result.

Abstract: A method and apparatus is provided for locking a local oscillator to a reference oscillator. The reference oscillator is arranged to transmit a signal containing two reference pilot tones in a signal sideband. The apparatus samples the received signal and makes a frequency shifted copy where the shift is equal to the expected separation between the reference tones. The non-shifted and shifted signals are then combined in the frequency domain to constructively reinforce one of the reference pilot tones which is then searched for. Once the tone has been identified, a correction to the local oscillator frequency is calculated. The apparatus may be of particular use in a radio telemetry system in which it is important that the frequency of the local oscillators in the transmitters and receivers are very accurately matched to each other and where, in order to reduce interference, all the clocks used in the system are locked to a master clock.