Abstract: A method of estimating jitter for a DFS can include determining a plurality of linear equations, wherein each linear equation corresponds to, at least in part, a combination of multiplier and divisor attributes for setting an output frequency of the DFS, identifying maximum and minimum values for the slope component and the vertical axis intercept component from the plurality of linear equations, providing an equation for determining minimum jitter given, at least in part, an input frequency, and providing an equation for determining maximum jitter given, at least in part, an input frequency. A linear equation can be derived for estimating jitter of the DFS according to a specified input frequency and a specified value of the divisor attribute of the DFS. The linear equation further can depend upon the minimum jitter and the maximum jitter.

Abstract: An electronic device includes an analog-to-digital converter adapted to receive a radio-frequency signal and adapted to provide therefrom a digital signal, wherein the radio-frequency signal may include an interference signal. The electronic device has a controller adapted to perform a digital measure on the digital signal and adapted to generate therefrom a selection signal having a first value indicating a non-interference condition in the radio-frequency signal and having a second value indicating an interference-condition in the radio-frequency signal. A selector is adapted to transmit the digital signal in case the selection signal has the first value and to transmit a signal replacing the digital signal in case the selection signal has the second value.

Abstract: For voltage values (observed noise sequence) in an electronic power line (communication medium) which are obtained at a predetermined interval, initial values of noise characteristics based on a statistic of the observed noise sequence itself are decided by a moment method (S301 to S307), the noise characteristics (state transition probabilities and state noise power) for maximization of the likelihood of the observed noise sequence are obtained from the initial values by MAP (Maximum A Posteriori) estimation using a Baum-Welch algorithm (S309 to S312), a state sequence is estimated from the obtained noise characteristics, and an impulsive noise at each time point is detected.

Abstract: A new method of performing interference estimation to allow the data packets to be efficiently delivered in an OFDM system. The interference estimation is performed on average over each frame for each mobile station individually in both frequency and time domains. Based on the estimated interference, the CIR can be determined by the BTS based on channel response estimates made by the BTS, or by the MS based on channel response estimates made for the uplink assuming a symmetrical channel. Numerical results show that the CIR estimation error could be very small if a sub-channel is considered as the minimum transmission unit. In terms of the aggregate throughput, the interference estimation method can provide a significant gain.

Abstract: A side channel attack resistance evaluation apparatus includes: a measurement section that measures side channel information leaking from an encryption device to be evaluated; a noise removal section that removes noise from the measured side channel information using a band-pass filter (BPF); a passband determination section that determines the passband of the band-pass filter; and a DSCA (Differential Side-Channel Analysis) evaluation section that evaluates resistance against the differential side channel analysis. The passband determination section preferably has a DFT processing section and a power spectrum analysis section, or has a DFT processing and a DFA processing section.

Abstract: A multi-tone transceiver including: a transform component, a tone selector, an error detector, an aggregator and an oscillator. The transform component transforms received communications from the time domain to the frequency domain. The tone selector selects a sub-set of the received tones which exhibit an elevated signal-to-noise ratio (SNR) as a clock recovery tone set (CRTS) and drops and add tones to the CRTS as required by changes in the SNR of the individual tones. The error detector detects phase errors in each received tone of the CRTS. The aggregator calculates an average aggregate phase error from all tones in the CRTS. The oscillator controls clocking of the transceiver. The oscillator is responsive to the average aggregate phase error to adjust a clock phase in a direction which reduces a phase error with a clock on the opposing transceiver.

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: An apparatus and a method for selecting a receiver for demodulating a reception signal at a reception end having a plurality of receivers are provided. The method includes determining, a mean and a standard deviation of Signal-to-Noise Ratios (SNRs) of the receivers are determined, estimating a Doppler frequency, determining a statistical value of a modulation order of subframes received in advance, determining SNR estimation values of the receivers based on the determined mean and standard deviation of the receivers, the estimated Doppler frequency, and the determined statistical value of the modulation order of the received subframes, selecting one receiver having a largest SNR estimation value among the determined SNRs of the receivers, and demodulating a reception signal using the selected receiver.

Abstract: A signal to noise power ratio estimation system for multi-carrier communication includes a phase rotator, a power estimator, a channel gain calculator, an average and selection device, a combination and calculation device and a decibel (dB) transformation device. The signal to noise power ratio estimation system makes use of a transmit parameter signaling or pilot subcarriers to blindly assist in the signal to noise power ratio estimation to accordingly gain an estimated signal to noise power ratio accurately, and thus a communication system can be calibrated to a preferred condition.

Abstract: Orthogonal frequency division multiplexing (OFDM) has become a popular transmission method for high speed wireless radio transmission, due to its potential for low complexity of transmitters and receivers. A method and apparatus are contemplated for cancelling additive sinusoidal disturbances of a known frequency in OFDM receivers which arise e.g. from clock signals that are present for frequency reference, mixer control, and A/D converter control, as well as harmonics and mixing products of those periodic signals, coupling into some point in the receiver chain and appearing as rotating complex exponentials superimposed to complex baseband receive signals. According to the inventive method and apparatus an estimation of an amplitude and phase of a disturbing superimposed tone with a known frequency is obtained and the amplitude and phase estimation is used to cancel the spurious tone preventing a degradation of receiver sensitivity while achieving low implementation complexity.

Abstract: A signal detection apparatus includes electronics configured to receive an RF input and to process the RF input applying a decision rule that is a normalized quantity to determine if a man-made signal is present or if only noise is present while achieving a constant false alarm rate.

Abstract: A communication receiver which applies signal processing for quantitatively estimating receive signal factors such as communication channel quality, signal characteristics, and overall system received bit error rate (BER) or packet error rate (PER) and which applies a general algorithm for mapping these estimated factors to control receiver performance and minimize power consumption.

Abstract: Embodiments of a system for determining and optimizing the performance a signaling system are described. During operation, the system captures or measures a single-bit response (SBR) for the signaling system. Next, the system constructs an idealized inter-symbol-interference-free (ISI-free) SBR for the signaling system which is substantially free of inter-symbol-interference (ISI). The system then calculates an ISI-residual from the captured SBR and the idealized ISI-free SBR. Next, the system constructs a calibration bit pattern for the signaling system that is based substantially on the ISI-residual. Finally, the system uses the calibration bit pattern to calibrate, optimize and determine an aspect of the performance of the signaling system.

Abstract: There is provided a jitter injection apparatus that generates an output signal having an injected jitter. The jitter injection apparatus includes a first oscillator that generates a first periodic signal, a second oscillator that generates a second periodic signal having a period different from that of the first periodic signal, and a switching section that switches which of the first periodic signal and the second periodic signal is output at every predetermined timing and outputs the switched periodic signal as the output signal.

Abstract: A communications system permits bandwidth configurability using a linear frequency modulated (LFM) waveform for transmitter/receiver synchronization. The system permits enhancement of MIL-STD-1553 data buses, and is likewise applicable to any bandwidth-configurable modem.

Abstract: The present invention provides a method for simplifying a probabilistic rate adaptation procedure in a wireless communication system, which comprises calculating a conditional probability density function of SNR of a transmitted signal by the probabilistic rate adaptation procedure, to generate an SNR estimation result, taking logarithm on the SNR estimation result to generate a logarithm result, and partitioning SNR values into a plurality of regions according to the logarithm result, to generate a discrete function from the SNR estimation result.

Abstract: A system for testing a communications link. A system includes a transmitter, a receiver, a digital communications link, and a service processor. The digital communications link includes a plurality of lanes through which the transmitter is coupled to the receiver. During an operating mode of the digital communications link and during otherwise normal system operation, the service processor (a) switches a selected one of the plurality of lanes from the operating mode to a test mode, (b) performs an eye scan of the selected lane, (c) stores data corresponding to the eye scan of the selected lane, and (d) returns the selected lane to the operating mode.

Abstract: Systems and methods are presented for measuring power levels of primary and interfering signals as well as noise, particularly for satellite transmitted signals. A typical method comprises the steps of receiving a signal comprising a primary signal, an interference signal and noise, demodulating the primary signal to remove a carrier frequency, decoding the primary signal to obtain symbols, estimating a power level of the primary signal based upon the demodulated and decoded primary signal. Additionally, an ideal primary signal can be generated from the carrier power and frequency and the symbols and subtracted from the received signal to produce the noise and interference signal. The noise and interference power is then estimated from the noise and interference signal.

Abstract: Techniques for deriving sample timing for multiple signal instances received on multiple antennas for a given propagation path. In one scheme, a DLL is maintained for each path, and each DLL tracks the timing of the best signal instance for the assigned path. In another scheme, a DLL is maintained for each path, and each DLL tracks the average timing of the multiple signal instances for the assigned path. To reduce timing jitter, the SINR of a signal instance may be estimated for a number of different time offsets. The loop filter for the DLL is initially updated in the normal manner. If a change in the time offset used for the sample timing is detected, then the SINRs for the new and prior offsets are compared. The new time offset is used if the associated SINR is better. Otherwise, the prior time offset is retained and used.

Abstract: A method of examining the eligibility of a modulation and coding scheme includes determining a range of pseudo signal-to-noise ratio (pseudo-SNR) corresponding to a range of packet correct rate (PCR) acceptable for a transmitter, obtaining a first score of a positive acknowledgement (ACK) and a second score of a negative acknowledgement (NACK) according to the range of pseudo-SNR and the range of PCR, applying weighting to a score of a response message, which is one of an ACK message and a NACK message, and a pseudo-SNR corresponding to an immediately preceding response message when receiving the response message, for generating a pseudo-SNR corresponding to the response message, and examining the eligibility of a modulation and coding scheme in use according to the pseudo-SNR corresponding to the response message.

Abstract: Disclosed herein are methods of processing transmissions in a wireless communication system to detect whether a transmission unit contains transmitted data, systems for processing transmissions in a digital communications system to detect the same, receivers for processing transmissions in a wireless communications system and computer readable media implementing a method for processing the same. In one embodiment, a method of processing transmissions in a wireless communication system to detect whether a transmission unit contains transmitted data includes: generating an averaged function of bit reliability indicators from a plurality of received samples and applying a test to compare an average of ln cos h(·) (natural logarithm of the hyperbolic cosine) values for the reliability indicators, with a factor proportional to an average signal-to-disturbance ratio of the plurality of samples to determine if the transmission unit contains transmitted data.

Abstract: To select a rate for a transmitter in a communication system, a receiver obtains a channel response estimate and a received SINR estimate for the transmitter, e.g., based on a pilot received from the transmitter. The receiver computes a hypothesized SINR for the transmitter based on the channel response estimate and the received SINR estimate. The receiver then selects a rate for the transmitter based on (1) the hypothesized SINR and (2) characterized statistics of noise and interference at the receiver for the transmitter, which may be given by a probability density function (PDF) of SINR loss with respect to the hypothesized SINR. A look-up table of rate versus hypothesized SINR may be generated a priori for the PDF of SINR loss. The receiver may then apply the hypothesized SINR for the transmitter to the look-up table, which then provides the rate for the transmitter.

Abstract: A pre-coding/decoding method and apparatus for data transmission between a transmitting end and a receiving end is provided. The pre-coding method for data transmission through Time Division Duplexing (TDD) in a mobile communication system includes estimating downlink channel state information based on an uplink sounding signal, and pre-coding a data symbol and a reference signal based on the estimated downlink channel state information.

Abstract: A device and method for effectively judging a communication quality in a communication system and a program used for the judgment. A communication device generates a four-value FSK symbol by adding a redundant bit to a bit of the most important part of encoded audio data. The symbol containing the redundant bit is set so that the symbol value is the maximum value of the minimum value of the four values which may be obtained. A reception device R receives the FSK modulation wave, restores the symbol, counts the number of redundant bits contained in the restored symbol and having incorrect values, decides whether to perform a bad frame masking process and what kind of bad frame masking process is to be performed, and executes the decided process. Thus, it is possible to accurately or rapidly judge the communication quality with a simple configuration.

Abstract: An encoded serial data bit error analyzer captures the actual waveform of an encoded serial data stream associated with a bit error so that a user may readily validate the cause of the bit error. An encoded serial data stream decoder in the analyzer is modified to provide a signal for a trigger system when a characteristic of a bit error failure is detected. A power splitter produces a pair of incident encoded serial data streams from a programmable test signal, one of which is input to a device under test and the other is input to the analyzer. A re-transmitted encoded serial data stream from the device under test is input to another channel of the analyzer. The encoded serial data stream decoder provides an “error detected” output when a condition occurs in the re-transmitted encoded serial data stream indicative of a bit error. The “error detected” output is used as a trigger signal to capture the incident and re-transmitted encoded serial data waveforms surrounding the detected bit error.

Abstract: A method and apparatus for compensating a modulation imbalance effect in a communication device. In one embodiment, at least three sets of modulation imbalance parameters (MIPs) are estimated by executing an auto balance sequence. The at least three sets of MIPs correspond to a baseband signal configured to have at least three configurable frequencies, each of the at least three sets of MIPs corresponds to one of at least three configurable frequencies. The auto balance sequence is configured to provide an offset signal generated within a communication device to trigger generation of each one of the at least three configurable frequencies. The at least three sets of MIPs are filtered to select a filtered set. The modulation imbalance effect is compensated by using the filtered set to reduce distortion of the baseband signal in the communication device.

Abstract: A system that incorporates teachings of the present disclosure may include, for example, a controller to: determine crosstalk coupling characteristics between a plurality of lines of a Digital Subscriber Line (DSL) system connected to a plurality of modems based on a transition between a full power mode and one or more other modes, and provide the determined crosstalk coupling characteristics to one or more of the plurality of modems for performance of at least one of pre-coding a transmitted signal and processing a received signal along a line of the plurality of lines, where the pre-coding and processing is performed based at least in part on the determined crosstalk coupling characteristics, and where the pre-coding of the transmitted signal and the processing of the received signal reduce effects of fluctuating crosstalk. Other embodiments are disclosed.

Abstract: In accordance with the present invention, novel methods for adaptive receiver design and related parameter estimation techniques for efficient and non-coherent reception of ultrawideband signals are presented. Efficient estimation of maximum excess delay of the channel for enabling many useful adaptation techniques is additionally provided. Also, noise power estimation which significantly improves the performance of the receivers is presented.

Abstract: The present invention relates to a system for calculating a digital quality index (DQI), which provides a rating on a predetermined scale, indicative of the impairments in a received quadrature amplitude modulated (QAM) signal in a CATV cable system. The DQI system utilizes bit error rates prior to and after forward error correction to calculate the DQI value. To increase the calculation rate, the bit error rates can be estimated using voltage errors, signal to noise ratios and/or average corner error metrics.

Abstract: In a network for digital data packet transmission, reception quality of received data packets is sensed (111) by a remote terminal (101). Thereupon, a bit string indicative for the sensed reception quality is generated (112). This bit string or a compressed version of this bit string is transferred (114) in real-time over a management channel to a first central processing unit (121) in a network node (102) where the bit string is compacted or processed. By processing the bit string, the first central processing unit (121) may determine impulse noise characteristics. Alternatively, the bit string or a compressed or compacted version thereof may be forwarded to a second central processing unit (131) in a network manager (103) that processes the bit string and determines impulse noise characteristics.

Abstract: A public safety communications network uses asymmetric channels for receiving requests for data from a mobile client over a narrowband land mobile radio system (LMRS) channel and delivering wideband data over a digital television (DTV) network channel to a DTV datacast receiver with the mobile client. An emergency operations center connected to the LMRS receives and processes the data requests and forwards the requested data. DTV network stations have a data multiplex insertion system for inserting the requested data into a DTV signal. The DTV network may be a public television network. An addressing system identifies unique mobile client addresses and unique mobile client group addresses and selects a DTV transmitter for delivering response messages in accordance with the addresses. A forward error correction (FEC) regulation system is used in transmitting requested data with FEC strength regulated as a function of historical bit-error-rate or receive power for a geographical location.

Abstract: A method of automatically determining a far-end crosstalk (FEXT) and near-end crosstalk (NEXT) transfer function in communication lines such as Digital Subscriber Lines (DSL). In a first phase, an input test signal with a known power density spectrum (PSD) covering a frequency range of interest is transmitted at the near end of line A while a received signal or noise-related quantity or PSD is measured at both the near end and far end of line B. In a second phase, transmission of the test signal is stopped, and a received signal or noise-related quantity or PSD is again measured at both ends of line B. In a third phase, the FEXT/NEXT transfer function is determined based on the measurements of the first and second phases.

Abstract: A system and method of detecting the location and magnitude of multi-path echoes in a channel impulse response by going through the channel impulse magnitude response only once and detecting all the multi-path echoes, both location and magnitude, according to certain threshold criteria. The impulse magnitude response samples are processed on-the-fly (on demand) and do not require the storage of the entire channel impulse magnitude response which makes it ideal for ASIC implementation.

Abstract: A method for determining a quantized channel vector in a terminal of a Multiple Input Multiple Output communication system includes determining a channel quality of a channel between a base station and the terminal and determining the quantized channel vector from a plurality of quantized channel vectors based on the determined channel quality. The determined quantized channel vector provides a predefined channel property value.

Abstract: In a wireless communication system, a method and apparatus for noise estimation of a received OFDM communication signal, wherein the signal comprises a data frame with a preamble having at least one long training field (LTF) containing two substantially similar OFDM symbols, comprise examining the LTF for substantially similar OFDM symbols. The noise power in the signal is estimated and the received signal power is measured. The signal to noise ratio is calculated and the signal power is determined by subtracting the noise power from the signal noise.

Abstract: A mobile terminal device for performing multi-carrier communication with a base station device can improve communication quality while reducing the data amount without lowering accuracy of feedback information.

Abstract: The present disclosure proposes a method for channel estimation with excellent accuracy for a large variety of channel conditions and with low computational complexity. The method represents a specific combination of a plurality of linear channel estimation schemes. A resulting hybrid channel estimator may retain the low complexity of the constituent estimators while performing same or better than each of the constituent estimators. The proposed simplified hybrid estimator may provide very close error rate performance to the optimal Wiener estimator over a wide range of channel scenarios.

Abstract: Transmission power relative to a propagation path having a variation in gain is controlled to increase communication channel capacity, and a data rate is controlled in accordance with the variation of the increased communication channel capacity. In order to increase the communication channel capacity, the transmission power is determined so that the sum of noise power (=received noise power/propagation path gain) converted into one at a transmitter and the transmission power becomes constant. As a result, contrary to the background art, the transmission power is controlled to be reduced when the propagation path gain decreases and to be increased when the propagation path gain increases.

Abstract: A method implemented by a user equipment includes selecting a first estimate of a signal-to-noise (SNR) ratio, calculating a first amplitude and first noise variance, calculating a second amplitude and a second noise variance, calculating a second SNR, calculating a resolution value, adjusting the first SNR, and performing estimation iterations until the resolution value is equal to a predetermined value.

Abstract: The present invention provides a transceiver for receiving and transmitting data over a network, and a method for testing the same. In particular, the present invention provides a physical layer transceiver having a built-in-self-test (BIST) device that allows for, among other things, pulse density/width variation and jitter control.

Abstract: Time correlation of signal to distortion characteristics is achieved by acquiring time domain data for a frequency band representing a communication signal, the communication signal having multiple channels. The time domain data is simultaneously converted to frequency and demodulation domain data in sequential time blocks. The frequency and demodulation domain data are processed to obtain respectively frequency and demodulation domain measurements. The resulting measurements are displayed simultaneously as a function of time for all the time blocks and/or for a selected one of the time blocks. An ACLRogram display provides a display having a time axis and a frequency axis in the form of bars spanning the frequency band for each time block with each bar being divided into frequency sub-bands representing a main channel and adjacent side channels, the shading of each segment of the bar representing a measurement value for that segment.

Abstract: Methods are described for identifying a dominant impairment on a communication channel impaired by an interference issue. The methods include systematic examination of total power loading, systematic examination of signal power reduction, statistical examination of communication channel noise power, and systematic examination of interleaver effectiveness. Each relates to automatically diagnosing and characterizing distortion-based interference issues by monitoring the performance of a communication channel during a testing procedure. These methods enable a technician or engineer to remotely diagnose distortion-based interference issues relatively quickly without having to use external test equipment and without having to deploy technicians to various locations within the cable plant. A system by which these methods can be implemented is also disclosed.

Abstract: A receiver for a communications link includes a receiver module and a host receiver. These two components can be tested independently. In one embodiment, the receiver module is characterized with respect to noise and distortion. The noise performance can be determined by comparing input and output signals of the receiver module, to determine the relative noise of the receiver module. The distortion performance can be determined by comparing the distortion of input and output signals of the receiver module, using a reference host receiver that includes an equalizer. The host receiver can be tested by using a reference receiver module.

Abstract: A method and a device are provided for crosstalk evaluation of a channel, wherein the channel is represented and/or modeled by a multiple-input-multiple-output (MIMO) system connecting a first network component with at least one second network component. The MIMO system contains first coefficients associated with transmission lines that are in particular associated with crosstalk. The crosstalk contains a near-end crosstalk (NEXT) portion and a far-end crosstalk (FEXT) portion. The first network component sends a signal to one second network component; the far-end crosstalk portion and the near end crosstalk portion are evaluated.

Abstract: Detection of a process state change includes, in each of a number of filters having differing time constants, generating an estimated average process state from observed samples of the process. A number of state change decisions are generated by comparing each of the number of estimated process states with a respective one of a number of threshold values. It is then decided that the process has changed state if any one or more of the state change decisions indicates that the process has changed state.

Abstract: A noise estimation apparatus and method thereof includes an evaluation circuit, a first calculation circuit, a second calculation circuit, and a mean calculation circuit. The evaluation circuit is utilized for determining which constellation point on a constellation diagram each received symbol in a communication signal corresponds to for purposes of generating a relevant evaluated symbol and outputting an evaluated signal. The first calculation circuit is for generating an error output signal according to the communication signal and the evaluated signal, wherein the error output signal includes a plurality of error calculation values. The second calculation circuit is utilized for adjusting at least a portion of the plurality of error calculation values of the error output signal in order to output an adjusted error output signal. The mean calculation circuit is utilized for averaging the adjusted error output signal in order to generate a noise estimation result.

Abstract: According to method and apparatus embodiments taught herein, power control feedback is generated for a control channel signal that is received in conjunction with a reference channel signal based on the reference channel's signal strength or quality, and an estimate of a gain factor relating the control and reference channel signals. By way of non-limiting example set in a Wideband CDMA (WCDMA) context, the reference channel signal comprises a Common Pilot Channel (CPICH) signal and the control channel signal comprises a Fractional Dedicated Physical Channel (F-DPCH) signal that is transmitted at an (unknown) power gain relative to the CPICH signal.

Abstract: The present invention implements a method and system for dynamically adapting the modulation and coding scheme for radio links in a wireless communications network based on a retransmission environment model in order to maximize throughput and most efficiently allocate bandwidth resources. The present invention encompasses a refined calculus and methodology for deriving the link adaptation thresholds in a retransmission environment using a complex model and analysis of the retransmission environment. The present invention holds particular application for wireless data communications as opposed to real time data services because it is based on a retransmission model applicable primarily for data services. A critical component of this new link adaptation system is a “no transmission” cutoff mode that is selected for SIR below a base threshold value. This new mode prevents system instability and misallocation of bandwidth in a wireless communication system.

Abstract: A modem uses information from prior calls in a current call if the current communication line is similar to the communication line of a prior call. During modem training, the current communication line is compared to a communication line used during at least one prior call. If the characteristics are substantially similar, stored data mode information from the prior call(s) is used to design a signal constellation for use during the current call's data mode. If the number of prior calls exceeds a value, then the signal constellation may be designed using previously stored data mode information without using information from the current call's training mode. If the number of prior calls does not exceed the value, then the signal constellation may be designed using the previously stored data mode information and information from the current call's training mode.

Abstract: A signal processing system compensates for the relative phase difference between multiple frequency bands so that the combination of the bands is constructive throughout a substantial portion of the band overlap or crossover region. In one embodiment, a signal combining system may include a comparator for determining a relative phase difference between the two signals within a predefined crossover region, a phase adjusting element for adjusting a phase of one of the two signals; and a combiner for combining the phase-adjusted signal and the other of the two signals.