Abstract: The present invention relates to an apparatus and a method for compensating carrier feedthrough in a quadrature modulation system. In order to suppress the carrier feedthrough, and minimize and compensate the carrier feedthrough, differences of baseband differential input DC voltages in an in-phase as well as a quadrature-phase are simultaneously adjusted to 0 or a certain slight voltage difference by a simple analog circuit. Therefore, it is possible to suppress carrier feedthrough using a simple analog type apparatus for compensating carrier feedthrough, and simply achieve an apparatus for carrier feedthrough using a variety of quadrature modulators.

Abstract: A network device comprises a PSK modulator that PSK modulates a header portion of a data packet at a first effective throughput and that PSK modulates outbound data at a second effective throughput to form a PSK modulated payload. A symbol modulator symbol modulates the outbound data at a third effective throughput to form a symbol modulated payload. A modulation selection unit forms a payload portion of the data packet based on at least one of the PSK modulated payload and the symbol modulated payload.

Abstract: A distortion compensating circuit is provided in which, in the polar modulation system, while suppressing increase of compensation data and increase of the circuit scale, a modulated signal can be correctly expressed, or low-distortion characteristics of a power amplifier can be realized. Based on a steady characteristic compensating circuit 11 which stores an output signal amplitude and output phase characteristics with respect to a control voltage in a steady state, amplitude adjustment is executed on amplitude information r11(t) on which amplitude correction is performed, by a first amplitude information adjusting portion 13, whereby the output-response characteristics of an output signal amplitude of an amplifier with respect to a change of the control voltage can be improved.

Abstract: DQPSK modulator control is provided using a single monitor photodiode with a selectively injected dither tone. The dither tone signal is sequentially injected into arm modulators and/or to a modulator driver port in time slots. A tapped signal at the output of the modulator is monitored synchronously with injected dither (I arm, Q arm, or phase modulator in third slot). The recovered dither output from a single photodiode is processed in the same sequence as the dither injection to adjust the bias to the optimal point: I-arm at the null point, Q-arm at the null point, and phase modulator at the quadrature point. This technique can be used for any control where the rate of change of the monitored condition due to systemic or environmental conditions (e.g., temperature, aging, etc.) is slow enough to allow time slot dither injection, monitor, and control.

Abstract: On a radio frequency signal path a transmission phase shifter causes a phase shift. From a first end of said phase shifter comes a first sample, and from a second end of said phase shifter comes a second sample. Another phase shifter changes the phase of the second sample by the same magnitude as said transmission phase shifter. A measurement circuit combines the phase-shifted second sample with a phase-inverted version of the first sample to produce an output indicative of a power level of the original signal on the radio frequency signal path.

Abstract: The present invention relates to an amplitude modulation apparatus, an amplitude limiting method, and a transmission apparatus for performing amplitude limitation on an orthogonally modulated signal. The amplitude modulation apparatus, the amplitude limiting method, and the transmission apparatus enable peak value suppression of a transmission wave with a simple structure. An amplitude limiting apparatus that performs amplitude limitation on an orthogonally modulated signal includes first amplitude limiting means (31, 32) for limiting to predetermined amplitudes the amplitudes of an I-component and a Q-component of the orthogonally modulated signal that are orthogonal to each other, and second amplitude limiting means (33-41) for performing further amplitude limitation on the I-component and the Q-component according to the difference between the amplitude-limited I-component and Q-component obtained by the first amplitude limiting means.

Abstract: A harmonic-rejection modulation device is provided, which includes a phase splitter, a low pass filter, and a modulator. Based on a square wave, the phase splitter generates a plurality of unfiltered local oscillating signals having phase angles of 0°, 30°, 90°, 120°, 180°, 210°, 270° and 300°, respectively. The low pass filter filters the high frequency components of the unfiltered local oscillating signals to generate a plurality of local oscillating signals having phase angles of 0°, 30°, 90°, 120°, 180°, 210°, 270° and 300°, respectively. The modulator modulates a baseband signal with the local oscillating signals, wherein the third harmonics of the local oscillating signals are eliminated by the modulation process of the modulator. The invention also provides a method of modulating a baseband signal.

Abstract: A method and apparatus modulate a polarity of a burst of pulses of the impulse radio signal using a first pseudo noise sequence generated by a shift register and a position of the burst of pulses using a second pseudo noise sequence generated by the shift register.

Abstract: A circuit 30 for upsampling and upconverting a high rate signal that is divided into M in phase (I) symbols and M quadrature (Q) symbols. A Nyquist filter 32 upsamples by a factor of k each of the 2M symbols in parallel during one system clock period (CP). The filter 32 has a plurality of 2kM filter components 40, 42, that each provides a continuous output. A plurality of multipliers 50, 52 each upconverts a filter component output with a carrier wave signal 46, 48 that is output from a numerically controlled oscillator 44. A plurality of adders 54 each adds the output of two multipliers 50 to recombine corresponding I and Q samples to output kM samples during a CP. For continuous phase modulation, N parallel bits are input into the filter 32, upsampled in one CP, and accumulated and modulated 82 in parallel in one CP. For analog processing, M (I) and M (Q) symbols are input into an FIR filter 77a, 77b for upsampling, and decimated at a MUX/DAC block 78 for subsequent analog upconversion.

Abstract: Embodiments of an apparatus for sample rate conversion are described. Various embodiments include an interpolator configured to interpolate a digital input data stream by using values of an interpolation phase shift control quantity to generate a digital output data stream, a computing stage configured to compute values of the interpolation phase shift control quantity, and an enabling/disabling stage configured to selectively disable the interpolator while keeping the computing stage enabled.

Abstract: A modulator includes a micro-electromechanical resonator device configured to receive an input signal and generate two output signals in response thereto, wherein the two signals having a predetermined phase relationship therebetween. The modulator further includes a switching system configured to selectively pass one of the two signals to an output of the modulator in an alternating fashion in response to phase modulation data.

Abstract: There are included a first quadrature modulation part (5) that divides an input signal into an I signal and a Q signal having a phase orthogonal to the phase thereof and uses a baseband frequency to perform frequency conversions of the I and Q signals, thereby performing a quadrature modulation; and a second quadrature modulation part (8) that uses in-phase and quadrature carriers of FM frequencies, which are 90 degrees out of phase with respect to each other, to perform frequency conversions of the I and Q signals, which are generated by the first quadrature modulation part (5), thereby performing a quadrature modulation.

Abstract: A system for controlling a power supplied to a load from a radio frequency amplifier system includes a radio frequency signal generator adapted for generating a radio frequency signal, an amplifier to which the radio frequency signal is supplied and that amplifies the radio frequency signal into a radio frequency power signal, a power coupler connected to the amplifying member for coupling the radio frequency power signals, where the power coupler includes a summing connection adapted for connection to the load and a compensating connection adapted for connection to a dissipative element. A first control value generating member is adapted for receiving a signal proportional to a power output from the power coupler at the summing connection and is adapted for generating a first control signal for controlling the amplifier or a current supply that supplies current to the amplifier.

Abstract: A system and method for communicating signals over a noisy channel is provided wherein an input signal may be sampled and modulated to make the signal more noise insensitive. In accordance with one embodiment, of the invention, an signal code modulation (SCM) scheme may be used wherein digital and analog signals representing the original signal are generated. In another embodiment, an original modulated signal may be demodulated and then remodulated using a more robust modulation scheme. The system may be used to a variety of applications including wireless internet access.

Abstract: A modulation/demodulation apparatus according to an embodiment of the present invention includes a sine wave generating circuit configured to output two sine waves which are orthogonal to each other and have equal amplitude, an orthogonal modulator connected to the sine wave generating circuit and configured to modulate the sine waves to generate a modulated signal, a detecting section configured to detect amplitude fluctuation in the modulated signal, a multiplying section configured to multiply the modulated signal and the amplitude fluctuation detected by the detecting section together, and an orthogonal demodulator configured to demodulate the modulated signal multiplied with the amplitude fluctuation by the multiplying section to generate a demodulated signal.

Abstract: Direct digital QAM modulation at an RF frequency is obtained from digitally synthesized RF signals which are generated for use as the two vectors. The two vectors are individually controlled in phase and summed to provide a combined phase and amplitude modulation that forms the modulated signal. The synthesized RF signal is generated from a higher reference frequency using a variable pulse stretching technique implemented with programmable delay lines. The amount of the pulse stretch in each cycle is controlled by a phase increment value. Pulse stretching can be extended beyond one cycle by pulse swallowing, allowing the generation of an RF signal from DC up to and including the input reference frequency. Phase modulation is added by digital control of the pulse stretching according to the phase modulation data bits.

Abstract: Briefly, in accordance with one or more embodiments, a transmitter comprises four phase modulators to provide four path phase modulation. The phase modulators modulate local oscillator signals with control signals derived from quadrature baseband data to be transmitted to result in four phase modulated signals. The four phase modulated signals may be combined to provide a pulse position and pulse width modulated signal that may have a constant, or nearly constant, amplitude. The frequency spectrum of the control signals have narrower bandwidths and greater out of band attenuation resulting in higher suppression of out of channel and out of band noise.

Abstract: Methods provide for the amount of information encoded by spectral keying into a UWB symbol having a plurality of modulation symbol times, to be increased by operating two or more frequency band carriers simultaneously during at least one of a plurality of modulation symbol times. In one aspect of the present invention, once a frequency resource, such as a carrier, has been used during a given modulation symbol time, those frequency resources are not used again within that UWB symbol. A method of transmitting symbols, includes providing (302) data to be transmitted, determining (304), which frequency carriers, if any, of a set of n frequency carriers, are to be turned on during each of n modulation symbol times, and turning on (306) each of the determined frequency carriers during each of the modulation symbol times, and wherein each frequency carrier is turned on only once during the transmission of the symbol.

Abstract: An active 90-degree phase shifter with LC-type emitter (source) degeneration is provided, which is practiced in an integrated circuit. The phase shifter comprises a first differential amplifier, having one first signal output end and comprising an inductor, a first transistor and a second transistor, wherein the inductor is connected to the emitters (sources) of the first and the second transistors; and a second differential amplifier, having one second signal output end and comprising a capacitor, a third transistor and a fourth transistor, wherein the capacitor is connected to the emitters (sources) of the third and the fourth transistors. Wherein the bases (gates) of the first and the fourth transistors are signal input ends, and the bases (gates) of the second and the third transistors are coupled together.

Abstract: A novel apparatus and method for a fully digital quadrature architecture for a complex modulator. The complex modulator can substitute for existing prior art analog quadrature modulator structures and those based on a digital polar architecture (r, ?). The modulator effectively operates as a complex digital-to-analog converter where the digital inputs are given in Cartesian form, namely I and Q representing the complex number I+jQ, while the output is a modulated RF signal having a corresponding amplitude and phase shift. The phase shift being with respect to a reference phase dictated by the local oscillator, which is also input to the converter/modulator. Several embodiments are provided including modulators incorporating dual I and Q transistor arrays, a single shared I/Q transistor array, modulators with single ended and differential outputs and modulators with single and dual polarity clock and I/Q data signals.

Abstract: The present invention relates to a polar modulation apparatus and method, in which an in-phase and a quadrature-phase signal are processed in the analog domain to generate an analog signal corresponding to a derivative of a phase component of said polar-modulated signal. The analog signal is then input to a control input of a controlled oscillator (40). As an example, the processing may be based on a differentiate-and-multiply algorithm in the analog domain. Thereby, phase and envelope signals are generated in the analog domain and bandwidth enlargement due to the processing of the polar signals and corresponding aliasing can be prevented to obtain a highly accurate polar-modulated output signal.

Abstract: A modulation system includes a modulator configured to employ a modulation mechanism on data. The mechanism includes a signal constellation configured to map sub-carriers which include a signal to be modulated. The signal constellation has a plurality of points asymmetrically disposed on a circle about an origin and a point at the origin wherein a number of sub-carriers becomes variable over different symbol intervals. Corresponding demodulators and corresponding methods are also disclosed.

Abstract: A pulse modulator generates a pulse-modulated signal by pulse-modulating and amplifying the amplitude component of an input signal. A low-pass filter filters the pulse-modulated signal from the pulse modulator, and generates an amplified amplitude signal which is obtained by amplifying the amplitude component. An error corrector generates a corrected amplitude signal by correcting an error of the amplified amplitude signal from the low-pass filter by using the amplitude component of the input signal. A mixing unit generates the output signal by mixing the corrected amplitude signal from the error corrector and the phase component of the input signal.

Abstract: A digital modulator performs BPSK on differential data, filters it, and outputs the resultant data. A determining unit determines a combination of continuous two values of differential data. In a waveform generator, waveform generation rules are set for each of the combinations. On the basis of the waveform generation rule corresponding to the combination determined by the data determining unit, the waveform generator sequentially outputs a digital waveform signal.

Abstract: Systems and methods for receiving layered modulation for digital signals are presented. An exemplary apparatus comprises a tuner for receiving a layered signal and producing a layered in-phase signal and a layered quadrature signal therefrom, an analog-to-digital converter for digitizing the layered in-phase signal and the layered quadrature signal and a processor for decoding the layered in-phase signal and the layered quadrature signal to produce one or more discrete layer signals.

Abstract: Systems and methods are disclosed for feeder link configurations to layered modulation. One feeder link system employs feeder link spot beam to antennas in distinct coverage areas to enable frequency reuse. Another system employs narrow beam width feeder link antenna to illuminate individual satellites also enabling frequency reuse. Yet another system uses layered modulation in the feeder link. Another feeder link system employs a higher order synchronous modulation for the satellite feeder link than is used in the layered modulation downlink signals.

Abstract: A direct division modulator is provided. The direct division modulator includes a symbol mapper converting the input data from a binary bitstream to a desired frequency deviation, such as where the frequency deviation data encodes the information from the bitstream. A converter generates a divide value using the desired frequency deviation information, and a summer adds an average value to the divide value. A converter quantizes the divide value and shapes quantization noise associated with the quantized divide value. A divider modulates a reference signal with the quantized divide value and generates an output signal.

Abstract: A modulator (10) and method provides a programmable phase rotation for supporting different modulation formats and different phase rotations. The modulator (10) includes a programmable symbol counter (32) and symbol phase rotation logic (31) operatively responsive to programmable phase rotation size data (36) and programmable counter size data (30). The modulator (10) can be used to communicate with different modulation formats employing different phase rotation conventions as used in different communication systems. The symbol phase rotation logic (31) produces rotated in-phase data (20) and rotated quadrature data (22) in response to receiving at least received symbol data (24), programmable phase rotation size data (36), and symbol count data (32) based on programmable counter size data (30). According to another embodiment, the phase rotations of the modulator (10) may be dynamically selectable such that the phase rotations may be selected to accommodate changes in channel characteristics in real time.

Abstract: An apparatus and method for generating piecewise linear phase transitions during a phase transition interval of a first signal to control controlling the phase/frequency of a second signal. The initiation point, duration and shaping parameters of the piecewise linear phase transitions are selected to control adjacent channel emissions in the second signal.

Abstract: The digital Intermediate Frequency (IF) modulator applies to various modulation types and offers a simple and low cost method to implement a high-speed digital IF modulator using field programmable gate arrays (FPGAs). The architecture eliminates multipliers and sequential processing by storing the pre-computed modulated cosine and sine carriers in ROM look-up-tables (LUTs). The high-speed input data stream is parallel processed using the corresponding LUTs, which reduces the main processing speed, allowing the use of low cost FPGAs.

Abstract: It is possible to calibrate an I(Q) signal without interrupting the modulation operation of an orthogonal modulation device. The orthogonal modulation device includes: an adder for outputting a pseudo noise superimposed signal obtained by adding the I(Q) signal to a pseudo noise PN; a signal conversion section for mixing the pseudo noise superimposed signal with a local signal of a predetermined local frequency and outputting a converted signal; a phase shifted local signal multiplier for multiplying the local signal whose phase has been changed by a phase shifted device with the converted signal; a pseudo noise multiplier for multiplying the output of the phase shifted local signal multiplier with the pseudo noise; an integrator for integrating the output of the pseudo noise multiplier; and an error measurement section for measuring the error of the I(Q) signal according to the output of the integrator.

Abstract: A quadrature modulator includes a local oscillator oscillating at an oscillation frequency equal to 4/(2N+1) times a carrier frequency where N is a natural number, a frequency conversion block for multiplying the oscillation frequency by a factor of (2N+1)/2, a divider for dividing the multiplied oscillation frequency to output a pair of orthogonal carrier waves, first and second multipliers for modulating the carrier waves with a digital baseband signal, and an adder for adding the modulated carrier waves to output a carrier signal having the carrier frequency. The frequency conversion block includes a divider for dividing the oscillation frequency, N frequency mixers cascaded from one another and a band-pass-filter, which are cascaded in this order.

Abstract: Radiofrequency apparatus and method including at least one transmitter and/or receiver of a useful signal S0, at least one device adapted to the application of a coefficient N to the useful signal S0. The method includes modulating the useful signal S0 with a frequency Fm, transposing the modulated signal S1 to a frequency Fm+Fol, and multiplying the transposed, modulated signal S3 by a coefficient N in order to obtain a signal S4 at a transmission frequency Fe.

Abstract: An IQ modulator's performance is optimized through determination of suitable control parameters by the application of known DC biases as the I and Q inputs. Also known are the relative amplitude and actual phase of the sine and cosine carriers to be modulated before they are summed. It is shown that by measuring an RMS voltage Atotal an appropriate number of times for a related combination of the applied DC biases in conjunction with the other known input parameters, a number of behavior parameters that are indicative of mixer performance can be discovered through analysis, such as the solution of a system of linear equations. The combination of behavior parameters may be assigned a Figure Of Merit (FOM) that can be taken as an indication of the degree to which mixer operation approaches ideal behavior. The control parameters may be perturbed over a selected range, and the extraction of the behavior parameters repeated.

Abstract: Methods, apparatus and systems for implementing an algorithm for N-symbol noncoherent processing of M-ary DPSK signals in a pilotless, wireless system is provided. The algorithm is carried out with (N?1) recurrent steps (iterations) plus a decision step. Each iterative step includes simple trigonometrical transformation of quadrature components of the current symbol and summation of the transforms with results of the previous step. A final N-symbol decision regarding the current transmitted symbol corresponds to the vector of maximum length, calculated after the (N?1)-th step of the iterative procedure. The general algorithm is optionally implemented with one or more intersymbol processors, one or more memory blocks for saving results of the intersymbol processors, and a decision block. In addition, shift registers for quadrature components of the received signal may be utilized.

Abstract: An IQ modulator's performance is optimized through determination of suitable control parameters by the application of known DC biases as the I and Q inputs. Also known are the relative amplitude and actual phase of the sine and cosine carriers to be modulated before they are summed. It is shown that by measuring an RMS voltage Atotal an appropriate number of times for a related combination of the applied DC biases in conjunction with the other known input parameters, a number of behavior parameters that are indicative of mixer performance can be discovered through analysis, such as the solution of a system of linear equations. The combination of behavior parameters may be assigned a Figure Of Merit (FOM) that can be taken as an indication of the degree to which mixer operation approaches ideal behavior. The control parameters may be perturbed over a selected range, and the extraction of the behavior parameters repeated.

Abstract: The invention relates to processes and devices which make it possible to directly modulate an RF carrier with a quadrature signal. It consists in filtering (504) this quadrature signal around zero so as to introduce alternately (507, 508) on each of the channels a low-frequency subcarrier that will serve as reference. Each of these channels is alternately demodulated in a synchronous manner (519) cosine-wise and sine-wise. The demodulation signal is filtered (523) so as to recover the subcarrier marred by modulation errors. The measurement of these errors (524) allows feedback correction (503) of the quadrature signal. It makes it possible to perform the major part of the operations in the digital processor (501) and enables direct vector modulation to be made possible at millimeter frequencies.

Abstract: An active 90-degree phase shifter with LC-type emitter (source) degeneration is provided, which is practiced in an integrated circuit. The phase shifter comprises a first differential amplifier, having one first signal output end and comprising an inductor, a first transistor and a second transistor, wherein the inductor is connected to the emitters (sources) of the first and the second transistors; and a second differential amplifier, having one second signal output end and comprising a capacitor, a third transistor and a fourth transistor, wherein the capacitor is connected to the emitters (sources) of the third and the fourth transistors. Wherein the bases (gates) of the first and the fourth transistors are signal input ends, and the bases (gates) of the second and the third transistors are coupled together.

Abstract: The present invention involves a transmitter for transmitting two levels of data in a hierarchical transmission system. The transmitter has encoders, a modulator, an adjuster, and an up converter. The first encoder has a first output and capable of providing digital information based on a first level of data on the first output. The second encoder has a second output and is capable of providing digital information based on a second level of data on the second output. The modulator is coupled to the first encoder and has I and Q outputs. The adjuster is coupled to the modulator and second encoder and modifies signals on the I and Q outputs of the modulator to produce transmission I and transmission Q outputs. The up converter is coupled to the adjuster and is capable of transmitting broadcast radio signals based on the transmission I and transmission Q outputs. The modulator may include a root raised cosine filter and/or a QPSK modulator.

Abstract: A transmitter in which modulator output signal values are generated by a multi-level modulation method. The transmitter comprises a look-up table for storing a pre-defined number of values corresponding to data symbols and representing a signal or a pulse format, registers for selecting values representing the signal or the pulse format to be used to defined in-phase and quadrature component values, and adders for defining the modulator output signal values by summing the in-phase and quadrature component values while the number of the in-phase and quadrature component values to be summed is determined by a number of inter-dependent symbols.

Abstract: The invention concerns a device for producing a phase and amplitude modulated signal (G) suitable for radio transmission via an antenna (30), based on the EER technique and means (20) for temporal clamping of a phase controlling signal (D) and an amplitude controlling signal (F) so that the phase modulating component is synchronized with the amplitude modulating component in the output signal (G).

Abstract: The present invention is a filtering apparatus in an 8 Phase Shift Keying (8PSK) system. The filtering apparatus comprises a ?/16 phase shift module, a weight distribution module, and a combination module. The ?/16 phase shift module is used for shifting a second vector from a 3?/8 phase shift module with ?/16 radians to generate a corresponding third vector. The weight distribution module is used for distributing a plurality of selected weights to a predetermined distribution waveform and storing a plurality of corresponding weighted distribution waveforms. The combination module, according to the third vector, is used for determining which weight distribution waveforms to be selected from the weight distribution module and combining the selected weighted distribution waveforms to generate a modulation signal. The filtering apparatus and method of the present invention may save a lot of memory in the filtering process.

Abstract: A system to communicate digital data symbols with higher than QPSK modulation comprises a transmitter and receiver. The transmitter comprises, a modulator and circuitry to split and encode the data into a first block of more significant bits and a second block of less significant bits for modulating by. The receiver receives digital data bits by iterative determination of soft estimates of bits followed by a hard decision as to what bit was intended, and comprises a first processor to provide first soft estimates of bits of the received signal, and a second processor to decode the first soft estimates and to provide second soft estimates of the bits.

Abstract: A method for reducing out-of-band emission in an AM transmitter for digital transmission includes generating, from a digital modulation signal, an amplitude signal and a phase-modulated radio frequency signal configured to control the AM transmitter. A digital modulation process is used in which a hole is formed around a 0/0 point so that a zero crossing is avoided by a substantial margin in a vector diagram representation. Thereby a respective bandwidth of the amplitude signal and the phase-modulated radio frequency signal is limited so that the out-of-band emission decreases as a function of a shoulder distance achievable by the AM transmitter at a rate where a spectrum mask is not exceeded.

Abstract: 8PSK modulation methods and apparatuses are provided. In a first embodiment, product factors of symbol vectors and a coefficient of a shape filter are stored in a table and compressed by 8 times based on a law of a trigonometric function, wherein a method of table looking-up is used to replace a multiplication operation. In a second embodiment, all states of 8PSK modulation are stored in a table after shape filtering, and then the data of the states stored in the table are compressed based on a corresponding relationship of a law of a trigonometric function and an electrical level diversity, and then a table looking-up operation is performed. In a third embodiment, new modulated vectors are stored in a modulated phase table after simple 8PSK modulation and phase rotation, the modulated phase table is compressed by 4 times, and new modulated vectors are obtained by a table looking-up operation and data processing. Then, shape filtering is performed by utilizing a RAM coefficient filter.

Abstract: The invention concerns a wideband modulator using a PLL synthesizer, which can match the frequency characteristic and prevent degradation in modulation accuracy even in the presence of a variation in the manufacture of circuit components. In a wideband modulator which modulates the division ratio of a frequency divider by using a modulating signal generated by a modulating signal generator and outputs a modulated carrier signal from a VCO, calibration data from a calibration data generator are input via a selector. The amplitude value of an ac component of each modulating signal, either appearing on the output of a loop filter or demodulated by a demodulator, is converted to a digital value by way of an A/D converter. The difference between the two is detected and a control signal FCR to eliminate the difference is generated in order to correct the frequency characteristic of a PLL or a pre-distortion filter.

Abstract: A communication apparatus operating under a back scattering system involving processes of QPSK modulation is provided. The apparatus includes: a first signal channel for acquiring a first reflected wave by getting an incoming radio wave directly reflected without wave passage through any phase shifter; a second signal channel for acquiring a second reflected wave having a phase shifted by ?/2 relative to the phase of the first reflected wave through two-way wave passage through a first phase shifter alone; a third signal channel for acquiring a third reflected wave having a phase shifted by ? relative to the phase of the first reflected wave through two-way wave passage through the first and a second phase shifter; and a fourth signal channel for acquiring a fourth reflected wave having a phase shifted by 3?/2 relative to the phase of the first reflected wave through two-way wave passage through the first through a third phase shifter.

Abstract: An apparatus and method for transmitting and receiving a communication signal includes selecting a pulse shape for a continuous phase modulated waveform, encoding specific information into the waveform to form a communication signal and transmitting the communication signal. The system receives the transmitted communication signal and samples the received signal at a specified rate, the sample rate being less than the symbol rate, enabling reconstructing the waveform and extracting encoded information at sub sample per symbol rates, thereby reducing the reliance on high speed wideband analog to digital converters (ADC) for high speed applications.

Abstract: A system and method for compensating for the time delay between the in-phase I and the quadrature Q paths of a digitally modulated transmitter incorporating an analog quadrature modulator is disclosed. The time delay between the in-phase I and the quadrature Q paths is computed and used to calibrate a set of interpolation filters in the forward path that compensate for this delay, reducing the frequency dependent degradation in performance of the analog quadrature modulator. The disclosed system and method provides improved compensation of gain, phase and DC offsets in the analog quadrature modulator over a broader bandwidth. Fractional delay interpolation filters may be used to estimate the delay between the in-phase and quadrature paths. This eliminates the need for a factory calibration procedure, speeding up manufacture and reducing costs.

Abstract: A QPSK modulation scheme uses a data spreading mechanism to rob a relatively limited portion of available transmitter power, and inject into the QPSK waveform a prescribed amount of carrier signal power, through which detection and non-regenerative extraction of the carrier at the receiver may be achieved without incurring a signal-to-noise degradation penalty. In addition, the injected carrier-based modulation scheme of the invention may employ high performance forward error correction coding, to significantly reduce the signal power required for achieving a very low energy per bit-to-noise density ratio (Eb/N0)—on the order of one to zero dB.