Abstract: A digital GMSK filter for use for frequency modulation of a carrier signal in a GMSK transmission system is described. The GMSK filter uses a large number of individual current sources, whose current values are individually weighted. The current sources are driven via a control logic module using a shift register with a thermometer code, such that this results in a total current with a Gaussian characteristic, which is converted across a resistor to a voltage and drives a voltage controlled oscillator (VCO). The filter provides exact implementation of the sample values, virtually without any quantization error, and requires only a small chip area for its implementation.

Abstract: The present invention is an apparatus and method for performing a Gaussian Minimum Shift Keying baseband modulation based on a reference phase to be simplified. The invention mainly comprises: a memory unit storing a plurality of parameters and their corresponding tabular data of a low pass Gaussian filter, the parameters and their corresponding tabular data being simplified in advance; the low pass filter being used for reducing the bandwidth of the apparatus and increasing the utilization of the bandwidth; and a processing unit based on the input digital data and the tabular data in the memory unit to generate the digital in-phase signal In and the digital quadrature-phase signal Qn.

Abstract: A phase modulator for direct wideband linear phase modulation of a microwave continuous wave carrier signal which is suitable for many analog and digital phase or frequency modulation techniques. Linear phase modulation range in excess of 360 degrees is provided as a result of linear variation in the modulating signal. A conditioned baseband modulating signal is injected into a highly linear fractional range phase shifter, operating at a subharmonic of the desired output frequency. A nonlinear circuit is used to perform frequency and instantaneous phase multiplication, thus expanding the linear phase modulation range to greater than 360 degrees at the desired output frequency. With special conditioning of the baseband modulating signal, the phase modulator can be made frequency agile in ultra-small frequency steps, without requiring a stable, frequency agile reference signal or frequency synthesizer.

Abstract: For the purpose of estimating the frequency shift of a CPFSK signal (x(t)), a variable, integer delay parameter D is introduced. The respective CPFSK signal (x(t)) is scanned at intervals k·T+&tgr;, T being the scanning period, k a scanning index and &tgr; a delay constant. For the intervals k·T+&tgr;, intermediate signal values (z(k)) are determined from the scanning values (x(k)) of the CPFSK signal (x(t)) obtained for the intervals k·D·T+&tgr; and [k−1]D·T+&tgr; depending on said parameters. The estimated value (&ngr;) for the frequency shift is then obtained from a number of L0 intermediate signal values (z(k)) that have previously been determined for the intervals i·D·T+&tgr; (i=0 . . . L0−1).

Abstract: The invention is a method whereby a digital data bearing signal, comprising a single frequency generated by encoding a nonreturn-to-zero (NRZ) signal so as to cause it to have no frequency spread, is added to the signals presently being transmitted over cellular telephone systems. The signal to be added is comprised of a single frequency, which alternates in phase at coded time intervals. The channels (1, 3) presently in use have bandwidth limits specified by regulatory authorities, which have a small guard space (2, 4) between them. The single frequency signal, which carries data at high data rates, can be added between these channels in a way that will not interfere with the channels in use. Frequency-hopping spread-spectrum is used to further reduce any interaction between channels.

Abstract: A wireless communication system operates a power amplifier (422) in an earth terminal (400) in a non-saturated mode of operation to transmit communication signals over a communication uplink to a communication satellite (100). The satellite operates a power amplifier (186, 188) in a saturated mode of operation to transmit communication signals over a communication downlink to terminal (400). Operating the amplifiers in the different modes of operation increases efficiency.

Abstract: A VCO modulator controller including a ROM memory storing a number of waveform maps, a counter coupled to the ROM memory and capable of developing a sequence of ROM addresses, a temporal bit generator responsive to a data stream to develop a next bit Nb, a current bit Cb, and a past bit Pb, control circuitry developing a digital waveform signal from selected waveform maps in the ROM memory using the Nb, Cb, and Pb bits and the sequence of ROM memory outputs, and a DAC that converts the digital waveform signal to an analog VCO control signal that encodes said data stream.

Abstract: The invention reduces transient peaks in signals transmitted in CDMA communication systems. A plurality of spread spectrum data signals are combined into a combined signal having fluctuating power level corresponding to the combination of the data signals. The combined signal is modulated to produce an RF signal for transmission. The average power of the combined signal is measured over a selected time period. The combined signal power level is adaptively limited to a calculated power level based at least in part on the measured power.

Abstract: A transmitter has a phase modulator and a phase locked loop that has a relatively high powered voltage controlled oscillator. The phase locked loop has a phase sensitive detector for comparing a phase comparison frequency derived from the voltage controlled oscillator output with a phase modulated intermediate frequency carrier derived from the phase modulator. The phase modulator has a reference frequency source, means for deriving four quadrature phase components of the reference frequency produced by the source and phase selection means controlled by complex modulation means for deriving the phase modulated intermediate frequency carrier by random interpolation between the four quadrature components.

Abstract: A method and apparatus for performing fractional minimum shift key modulation for a very small aperture terminal. A signal with a fractional modulation which appears to be frequency shift key is generated in the indoor unit. The outdoor unit employs a novel multiplication method to translate this signal to a minimum shift key modulated signal for satellite transmission.

Abstract: The circuit for combined operation of a mobile radio with GMSK and 8-PSK modulation includes a transmission PLL for GMSK operation, and a direct modulator for 8-PSK operation. A transmission oscillator in the transmission PLL is also used as a synthesizer oscillator for the direct modulator. The modulation in the transmission PLL is suppressed for this purpose. The circuit allows cost-effective implementation while retaining the advantages of a transmission PLL.

Abstract: A form of modulation that is variable in terms of its number of steps is provided in a mobile communication system using a digital modulation of a modulation carrier. The number of steps of the modulation in the respective digital transmission channel is thereby adaptively matched to the respectively existing transmission conditions during operation such that a largely constant error probability is achieved in this transmission channel. The modulation method is to be preferably applied in a mobile communication system with combined time-division multiplex/frequency-division multiplex multiple access methods (TDMA/FDMA).

Abstract: The invention relates to a TDMA method, transmitter and receiver, wherein a training sequence is modulated and superposed on a data signal to thereby generate a TDMA burst. Thereby, the training sequence can be made longer and is always available during data reception, such that longer channel impulse responses can be measured. In the transmitter, the training sequence is separately modulated in a modulating means (3) before being superposed on the data signal. The receiver comprises an extracting means (11) for extracting the superposed training sequence and a cancelling means (9) for cancelling the training sequence from the data signal to be detected.

Abstract: A method and apparatus for predicting signal values for signals that have not yet been received wherein the information stream transmitted has been divided into a first stream and a second stream. A first Q component is predicted based on values stored in a state memory for the first bit stream. A first I component is predicted using the first predicted Q component and a previous bit from the state memory for the first bit stream. Then, a second Q component is predicted based on values in the state memory for the second bit stream. A second I component is then predicted using the second predicting Q component and the previous bit from the second bit stream. The first I component and the second Q component are added to obtain a combined I value and the first Q component and the second I component are added to obtain a combined Q value.

Abstract: A shape modulation transmit loop with digital frequency control permits spectral shaping of a digital pulse stream (12) by controlling the slew rate of the transition signal (16) between successive pulses. The loop is formed when the digital data stream is fed into an up/down counter (152) whose output is coupled to a programmable memory means (154), such as RAM, EEPROM, flash memory or similar electronic storage means. The output (108) of the programmable memory (154) forms a first input to an adder (112) which drives an accumulator (52) with specified steps. Values corresponding to the desired waveform (70) are stored in a lookup table (60) which is coupled to a digital-to-analog conversion circuit (64) which uses the values in the lookup table (60) to construct a sine wave output signal (70) corresponding to the frequency set by the current specified step of the up/down counter (152).

Abstract: Circuitry for modulating the frequency of a carrier signal with data signals for high frequency radio transmission, which includes a MSK generator for generating a series of in-phase (I) signals and an associated series of quadrature (Q) signals corresponding to the data signals to be transmitted. A first shift register receives binary input from the I signals generated with the MSK generator, the binary input being indicative of the sign orientation of the generated I signals from the MSK generator. A second shift register receives binary input from the Q signals generated with the MSK generator, with the binary input being indicative of the sign orientation of the generated Q signals from the MSK generator.

Abstract: A uniform amplitude modulator includes in-phase component & quadrature component generation units and a modulated signal generation unit. The in-phase component & quadrature component generation units receive data represented by phase information and generate in-phase and quadrature components as analog signals. The modulated signal generation unit receives the in-phase and quadrature components and generates a modulated signal whose amplitude is uniform. One of the in-phase component & quadrature component generation units is constituted by a device for outputting an analog signal having any one of three, predetermined positive and negative values associated with the phase information, and 0. The other is constituted by a device for outputting an analog signal associated with the phase information.

Abstract: An MSK modulator which performs an accurate MSK modiation with high speed digital data is provided. When a to-be-modulated digital signal is provided from a code generator 1, a bidirectional shift register 2 allows a bit-row with sixteen bits to shift in circulation in a direction determined in accordance with a logic value of the supplied digital signal. Weighting adders 3I and 3Q weight and add logic values of the fifth to twelfth least significant bits in the bit row and logic values of the first to eighth least significant bits in the bit row. Two analog signals each of which is generated by the weighting adders 3I and 3Q are out of phase to each other by (&pgr;/2) radians. The analog signal generated by the weighting adder 3I is multiplied by a signal generated by a first local oscillator 7, whereas the analog signal generated by the weighting adder 3Q is multiplied by a signal generated by a phase shifter 8. An adder 9 adds these multiplication results to generate an MSK modulation wave.

Abstract: The invention relates to a sensor for a measuring an electrochemical corrosion potential comprising a sensor tip, a conductor electrically connected to the sensor tip, an insulating member which surrounds the conductor, a connecting member which surrounds the conductor; and a sleeve which fits over the sensor tip, the insulating member, and the connecting member, the sleeve having inner threads which engage with corresponding outer threads on at least one of the sensor tip and the connecting member.

Abstract: A method and apparatus for demodulating and decoding an MSK signal utilizing synchronous accumulation and simultaneous synchronization of reference carrier and MSK data clocks enables a GPS correlator channel in a multi-channel GPS receiver to be used for processing MSK signals. The PRN code epochs are synchronized with the MSK data clocks and the process of de-spreading with a PRN code is disabled in order to obtain coherent MSK demodulation without corrupting the MSK signal with a PRN code within the channel.

Abstract: A direct modulation phase lock loop (PLL) a voltage controlled oscillator (VCO) (114). A divider (118) has a first divider input coupled to the VCO and a second divider input to receive a modulation inducing divisor sequence. A phase detector (102) has a first detector input coupled to the divider to receive the output thereof, and a second detector input to receive a reference input. A tuning circuit (306, 406) is coupled to the phase detector and the VCO, the tuning circuit responsive to a variable DC reference potential such that the tuning circuit has a frequency response that is constant over the modulation bandwidth whereby the PLL is a type 1 PLL with low modulation distortion.

Abstract: A signal modulator includes a digital signal processor, an address buffer, a counter, and a first memory device. The digital signal processor is adapted to receive digital data at a receive sampling rate and define a code word based on a subset of the digital data. The address buffer is coupled to the digital signal processor and adapted to receive the code word and store a base address. The counter is adapted to increment an address offset at a transmit sampling rate. The transmit sampling rate is a multiple of the receive sampling rate. The first memory device has a plurality of memory locations and is adapted to receive the base address and the address offset and provide a first waveform data sample from the memory location addressed by the base address and the address offset. A method for modulating a signal includes receiving digital data at a receive sampling rate. The time interval between digital data samples defines a bit interval. A code word is determined based on a subset of the digital data.

Abstract: A method and apparatus for performing fractional minimum shift key modulation for a very small aperture terminal. A signal with a fractional modulation which appears to be frequency shift key is generated in the indoor unit. The outdoor unit employs a novel multiplication method to translate this signal to a minimum shift key modulated signal for satellite transmission.

Abstract: The present invention includes a method for generating a GMSK modulating signal from a serial digital data bit stream whereby the GMSK modulating signal modulates a carrier frequency signal associated with a GMSK transmitter of a digital communications system. Specifically, the method includes converting each set of m consecutive data bits of the bit stream into a parallel symbol, whereby there are 2.sup.m possible symbols. Each symbol is generally defined as (B.sub.-(m-1). . . B.sub.0), where B.sub.0 is the current data bit and B.sub.-(m-1) is the mth previous data bit with respect to B.sub.0. Next, a corresponding phase advance is assigned to each of the 2.sup.m symbols, each phase advance being substantially equivalent to a percent phase advance contributed by the m consecutive data bits of each symbol. Also, four corresponding accumulated phases are assigned to each of the 2.sup.m symbols, each accumulated phase being derived from a multiple of 90 degrees.

Abstract: Apparatus for generating the family of PSK (phase shift keyed) modulations, which include BPSK (binary PSK), QPSK (quaternary PSK), MSK (minimum shift keying) and the like. The carrier is generated with the desired digital information already phase-modulated onto it by directly introducing a phase shift or delay onto the error path of a phase-locked loop. causing the phase-locked loop to create the phase modulation. The [proposed scheme differs from common practice approaches, which are usually implemented by linear synthesis (an AM technique); rather, it] invention employs direct nonlinear synthesis (an FM technique). The invention [yields good phase precision with arbitrary spectral shaping under the constraint of constant envelope signaling. It] permits the connection of the output of a simple, inexpensive VCO (voltage controlled oscillator) directly to a system's antenna without the need for intervening circuit elements such as phase splitters, mixers, and the like which is applicable to [.

Abstract: In order to provide a digital GMSK modulator operating sufficiently stably without aliasing distortion even with a sampling rate of twice of that of input signal, a quasi-GMSK modulator of the invention comprises: integration means (105) for integrating an input signal; filtering means (106, 107) for performing a digital Gaussian filter manipulation of output of the integration means with a low sampling rate of twice or more of a data rate of the output of the integration means; a phase modulator (107, 108 and 111) for obtaining a continuous wave phase-modulated with output of the filtering means; and a limiter (112) for limiting amplitude of the continuous wave within a fixed value.

Abstract: A modulated clock MSK modulator that separately modulates a sinusoidal clock signal by square wave I and Q digital data signals prior to the I and Q data signals being modulated onto a carrier wave signal. Mixers or applicable biphase switches are utilized to impress the I and Q digital data signal information onto the clock signal by inverting or non-inverting the clock signal on separate I and Q data rails to create I and Q modulated clock signals separated in phase. The I channel data modulated clock signal and the Q channel data modulated clock signal are then separately applied to a conventional quadraphase modulator to be separately modulated onto a carrier wave signal, and the summed together to be transmitted.

Abstract: A system and method for encoding and transmitting data with a spread-spectrum packet-switched system. Data to be transmitted by a packet transmitter are encoded for privacy and to restrict intelligent receipt of the data to the intended recipient. The encoded data is demultiplexed into sub-data-sequence signals which are spread-spectrum processed and then combined as a multichannel spread-spectrum signal. The multichannel spread-spectrum signal is concatenated with a header to output a packet-spread-spectrum signal which is transmitted over radio waves to a packet receiver. The packet receiver obtains timing for the multichannel spread-spectrum signal from the header. The multichannel spread-spectrum signal is then despread and multiplexed as received-encoded data. The received-encoded data is decoded by the intended recipient and stored in a receiver memory for output.

Abstract: In a modulating system, a converting unit generates first and second quadrature signals based on a transmission data signal in synchronous with a transmission clock signal. First and second filters perform band limitation to the first and second quadrature signals to generate first and second band-limited quadrature signals. An oscillator generates a sine wave signal and a phase shifter phase-shifts the sine wave signal from the oscillator to generate first and second phase-shifted sine wave signals. A phase difference between them is .pi./2, and the first phased-shifted sine wave signal precedes the second phased-shifted sine wave signal in the phase. First and second multipliers multiply the first and second phase-shifted sine wave signals by the first and second band-limited quadrature signals to generate first and second multiplied signals, respectively. An adder synthesizes the first and second multiplied signals to generate an synthesis signal.

Abstract: A system and method are provided in which a phase modulation generator is used to modulate the output signal of a DDS with a modulation index, h/N. The phase-modulated. DDS output drives a PLL, which is an upconversion stage for a radio transmitter, with the modulated DDS signal as the PLL's reference. The output of the PLL will have a modulation index of h. Consequently, the frequency band of the DDS output is significantly narrower than the frequency band of upconversion stages used in conventional transmitters, and there are significantly less spurious emissions in the transmitted signal. However, a transmitter employing the present phase-modulated DDS-driven PLL topology can still transmit over a relatively wide frequency band.

Abstract: A method for generating minimum shift keying (MSK) modulation signals with relatively reduced energy sidelobes relative to known methods. In one embodiment, a second derivative of the phase waveform is taken and convolved with a selectable smoothing function and integrated twice to generate a smooth phase waveform S2D.sub.-- MSK (i)=where .o slashed. (i)=.pi. i d(i)/2T. In the alternate embodiment, the sidelobe energy can be varied by simply changing the smoothing function, which can be stored in a lookup table. In the embodiment, the MSK modulation signal has a constant amplitude envelope allowing it to be transmitted using class C amplifiers. Since the embodiment provides continuous phase derivatives, the frequency and thus the sidelobe energy is sufficiently reduced to minimize interference with cosite equipment and nearby communication channels bands.

Abstract: A transceiver uses feedback control to monitor a transmitted continuous phase modulation (CPM) waveform, such as a spread spectrum CPM waveform, and adjust the modulation index in response thereto. Codewords are selected from a table according to a data signal and applied to a pulse shaping network. The pulse shaping network outputs a CPM waveform to a prefilter. The prefilter is connected to an FM modulator, such as a voltage controlled oscillator. In one embodiment, a correlator in the transceiver monitors the transmitted waveform during times when the transceiver is not receiving signals, and provides a correlation signal to a feedback control circuit. The feedback control circuit dynamically adjusts the gain of the prefilter, and may comprise, e.g., a second order tracking loop filter. The feedback control signal thereby tracks the amplitude of the transmitted waveform and adjusts the output gain of the prefilter so as to maintain a constant signal envelope.

Abstract: A Gaussian Minimum Shift Keying modulator that provides direct modulation of a carrier signal, produced by a single microwave high power voltage controlled oscillator. A continuous phase frequency shift keyed modulated signal with a modulation index of 0.5 is produced at the desired output frequency using a full 360 degree linear continuous phase modulator, controlled by a linear baseband signal that is the integral of the binary baseband information signal. This modulated signal is used as the reference signal for a phase locked high power voltage controlled oscillator. The phase locked loop provides frequency tracking and Gaussian spectral shaping to the modulated output signal.

Abstract: A communications system includes a vector modulator controller receiving a data stream and developing a vector modulator control signal by GMSK waveform synthesis and a transmitter having a vector portion controlled by the vector modulator control signal. The vector modulator controller includes: (1) ROM memory storing a plurality of waveform maps including an alternating map, a constant map, a monotonic sine map, and a monotonic cosine map; (2) a counter coupled to the ROM memory and capable of developing a sequence of ROM addresses; (3) a temporal bit generator responsive to a data stream, the temporal bit generator developing a next bit Nb, a current bit Cb, and a past bit Pb from the data stream; (4) control circuitry to develop a digital waveform signal from selected waveform maps in the ROM memory; and (5) a pair of DACs responsive to the digital waveform signal and operative to output a vector modulator control signal that encodes the data stream.

Abstract: Coherent modulation schemes for CPM signals. The disclosed schemes avoid the error probability increase due to the differential encoding by using a coherent encoder. A simple demodulator can be implemented by using a Nyquist-3 CPM scheme with coherent encoding. Such a scheme can be demodulated in substantially the same manner as signals modulated using M-PSK.

Abstract: A remote ground terminal transmitter for transmitting a modulated data signal having a constant envelope amplitude. The remote ground terminal transmitter comprises a source of data signals, a modulator for providing a carrier signal, receiving a data signal from the source of data signals, and modulating the carrier signal with the received data signal so as to produce a constant envelope minimum shift key modulation signal. The transmitter further comprises a power amplifier which operates in the saturation mode to amplify the modulated carrier signal produced by the modulator to the desired power level.

Abstract: Methods and systems for determining a cosine (I) or sine (Q) component for the purpose of modulating a digital signal in radiocommunication systems are disclosed. Exemplary embodiments describe how such determinations may be performed using digital signal processing techniques to improve component accuracy, while reducing the amount of processor memory (e.g., DSP memory) used to accomplish this task. Phase information from a sampled signal is used to access one or more tables containing component values, or a combination of a component base values and difference values between consecutive base values. The phase information can be used derive an offset value from the difference values, which offset value is added to a component base value to provide a component value for output. This has the effect of reducing the amount of memory consumed while maintaining high resolution.

Abstract: A modulated clock MSK modulator that separately modulates a sinusoidal clock signal by square wave I and Q digital data signals prior to the I and Q data signals being modulated onto a carrier wave signal. Mixers or applicable biphase switches are utilized to impress the I and Q digital data signal information onto the clock signal by inverting or non-inverting the clock signal on separate I and Q data rails to create I and Q modulated clock signals separated in phase. The I channel data modulated clock signal and the Q channel data modulated clock signal are then separately applied to a conventional quadraphase modulator to be separately modulated onto a carrier wave signal, and the summed together to be transmitted.

Abstract: Device for continuous phase modulation, produced from a frequency synthesizer including a variable oscillator and a phase-locked loop with, in series, a frequency division circuit, a phase comparator and a low-pass filter. In order to reduce modulation in the loop, the modulation is applied not only to the input of the synthesizer but also, in compensation, in the loop. In order to eliminate the modulation residue in the loop, a control signal for the oscillator is derived by a circuit which performs a correlation between the residue of the modulation and the output signal from a filter producing the same filtering effect as the loop, and which receives the modulation signal from the input of the synthesizer.

Abstract: A technique for modulating and demodulating CPM spread spectrum signals and variations of CPM spread spectrum signals. A transmitter divides a signal data stream into a plurality of data streams (such as I and Q data streams), independently modulates the I and Q data streams using CPM or a related technique, and superposes the plurality of resultants for transmission. A receiver receives the superposed spread spectrum signal and simultaneously attempts to correlate for a plurality of chip sequences (such as I and Q chip sequences), and interleaves the correlated I and Q data streams into a unified signal data stream. In one embodiment, a spread spectrum transmitter comprises a plurality of lookup tables for storing spread spectrum code chip sequences, at least one preamble code chip sequence, and at least one fill code chip sequence. An output from each of the tables is provided to a selection circuit (e.g.

Abstract: A method and apparatus for digitally phase modulating and frequency upconverting communication signals to an intermediate frequency, producing the IF output with only digital hardware and without the use of digital to analog converters, analog multipliers (mixers) or power combiners. A digital phase modulator provides an in-phase and a quadrature output, each of which is coupled to one input of a relatively simple multi-bit to single-bit delta-sigma data converter. The output from the converter is a pair of single-bit digital output signals. Each such single-bit output is inverted and both the inverted single-bit output and the non-inverted single-bit output of both the in-phase and the quadrature outputs are coupled to a 4:1 multiplexer. One of these four inputs is then selected by a modulo-4 counter. The modulo-4 counter is incremented at a rate that is selected based upon the desired IF frequency.

Abstract: A method and corresponding apparatus for error correction of MSK-coded data receives a signal (101) partitionable into adjacent frames (111,113) each subdividable into three tridents (103, 105, 107). A first sample quality metric (225) applicable to a p (123) of the signal (101) associated with a last trident (107) of the tridents of a first frame (111) of the adjacent frames (111, 113) is synthesized, and a second sample quality metric (227) applicable to a portion (125) of the signal (101) associated with a first trident (103') of the tridents of a second frame (113) following the first frame (111) is synthesized. Each of the first and second sample quality metrics (225, 227) have a magnitude dependent on a time that the associated portion (123) of the signal (101) has a magnitude exceeding an average magnitude (127) of the signal (101).

Abstract: Binary and Quadrature Feher's (F)-Modulation/Amplification with significantly reduced envelope fluctuations and peak radiation, increased power efficiency and transmit power delivered by connected RF (radio frequency), Infrared (IR) and other devices. A subclass of these systems has a constant envelope. Extraordinary power advantages, robust BER performance and linearly or nonlinearly amplified narrow spectrum without the pitfalls of conventional BPSK and DBPSK is attained. The FBPSK improved efficiency transmitter is compatible with conventional BPSK receivers. FBPSK modems are based on using quadrature structure where Q channel data is inserted in quadrature with I channel data. The Q channel data is the same as the I channel but is offset by one half bit (Tb/2). Further improvement in the spectrum is attained using correlation between I and Q channels. FBPSK modem is shown to meet the IEEE 802.11 specified spectral mask (-30 dB point) for wireless LAN, and leads output power gain of 6.

Abstract: A surface acoustic wave (SAW) device is described that comprises a piezoelectric medium using input and output transducers for launching and detecting a surface acoustic wave on the piezoelectric medium. In particular, a device is described that uses a special combination of transducers for the direct generation of a coded minimum shift keyed (MSK) waveform from an input impulse waveform. The same device is used for the direct detection of an input MSK waveform in order to generate an impulse waveform with sidelobe characteristics similar to those expected from a specific code. The SAW device provides the advantages of MSK encoded waveforms for spread spectrum applications and the advantage of implementing such entirely on a SAW substrate.

Abstract: A method for tuning an RF bandpass filter, especially a combiner filter (10.sub.1, 10.sub.2. . . 10.sub.n) belonging to a GSM system, in which an RF signal having a certain nominal carrier frequency (f.sub.c) is inputted into the RF bandpass filter and a medium frequency of a pass band of the RF bandpass filter is tuned depending on an RF power propagating through the bandpass filter or on an RF power reflected from an input of the bandpass filter. For an easier tuning of the filter and for a tuning accuracy better than before, (a) a carrier is modulated by a signal causing a first predetermined offset (+.DELTA.f), of the carrier frequency, (b) a medium frequency, at which the power propagating through the filter is at the maximum or the power reflected from the input of the filter is at the minimum, is searched for for the bandpass filter, (c) the first medium frequency obtained at stage (b) is stored, (d) the carrier is modulated by a signal causing a second predetermined offset (-.DELTA.

Abstract: In the modulation and demodulation of a plurality of frequency separated channels on a radio frequency carrier by digitally coded speech or data, the speech or data is modulated on a digitally generated sub-carrier by quadrature phase shift keying and after conversion to analogue form the modulated sub-carrier is mixed with an RF carrier of fixed frequency to produce the signal for transmission. Reception and demodulation of the transmitted signal are effected by the reverse processes. Frequency multiplication is effected after the digital to analogue conversion by producing analogue samples of very short duration and applying them to a suitable filter. Frequency division during the analogue to digital conversion is effected by sub-sampling.

Abstract: In a transmitting apparatus, information signal frame position information is supplied from a transmission line frame control unit in a frame constructing unit to an information signal frame control unit provided within a frame constructing unit. In a reception apparatus, information signal frame position information is supplied from transmission line frame control unit provided within a frame analyzing unit to an information signal frame synchronization detection protecting unit provided within a frame analyzing unit. n information signal frames having a length which results from dividing the data area of the transmission line frame by n are located at an arbitrary position within the data area of the transmission line frame and a stuff control is effected on every information signal frame. Also, a value of n which yields a stuff ratio in which a residual jitter can be prevented from being increased is selected by transmitting a single information signal by using n information signal frames.

Abstract: An MSK receiver includes a downconverter for downconverting the received MSK signals. The phase drift or phase error per bit of the message preamble is determined. The reference carriers are generated, and the phase of the reference signals is adjusted during message demodulation under the control of the estimated rate of phase change across the preamble portion. In accordance with another aspect of the invention, the downconverted MSK signal burst is digitized and the digitized burst signal is stored in memory, following which it is read repeatedly so that bit timing, start-of-message timing, carrier phase, and carrier drift processing may be performed in a desired sequence, using all the available information for more accurate demodulation. According to a yet further aspect of the invention, a second order tracking loop is used to adjust the phase of the demodulation reference signals.