Abstract: A communication system (10) includes a transmitter (20) having programmable signals (46, 58, 60, 80) which can be used to adjust transmitter-caused quadrature-phase signal imbalances. A receiver (18) of the system (10) is remotely located from the transmitter (20) and generates a signal quality statistic (102, 112) that is monitored in a slow-tracking feedback loop to formulate commands which indicate how to program the programmable signals (46, 58, 60, 80). This receiver (18) performs its signal quality statistic monitoring while a data stream (36) is being extracted from a received communication signal.

Abstract: A digital communication receiver (10) includes a magnitude-based symbol synchronizer (38) which separates complex phase attributes from magnitude attributes. The phase attributes are processed by a phase processor (78) which identifies clock adjustment opportunities. The magnitude attributes are processed by a magnitude processor (76) that generates a phase error estimate signal (82), which in turn drives a clock generator (24) in a phase locked loop (54) to achieve symbol synchronization in a non-data-directed manner. An additional adjustment feedback loop (114, 128) includes a phase error offset generator (52) and operates in conjunction with the phase locked loop (54) to allow the phase locked loop (54) to achieve lock and a robust operating point in spite of distortion in a received input analog signal (12).

Abstract: A phase-noise compensated digital communication receiver (40, 40', 40") includes a carrier tracking loop (56) which imposes a transport delay on a carrier tracking loop signal (60) before that signal (60) is fed back upon itself. The carrier tracking loop (56) includes a phase rotator (58) that rotates a down-converted digital communication signal (50) by a phase determined by a phase-conveying signal (72). A carrier tracking loop signal is obtained from the carrier tracking loop and delayed in a delay element (82) by a duration that compensates for the transport delay. A phase rotator (84) then rotates the delayed carrier tracking loop signal through a phase value determined by the phase-conveying signal (72) to obtain an open-loop phase signal (86) from which data are extracted. Different embodiments of the receiver (40, 40', 40") are provided to accommodate adaptive equalizer (54) issues.

Abstract: A constrained-envelope digital-communications transmitter circuit (22) in which a binary data source (32) provides an input signal stream (34), a phase mapper (44) maps the input signal stream (34) into a quadrature phase-point signal stream (50) having a predetermined number of symbols per unit baud interval (64) and defining a phase point (54) in a phase-point constellation (46), a pulse-spreading filter (76) filters the phase-point signal stream (50) into a filtered signal stream (74), a constrained-envelope generator (106) generates a constrained-bandwidth error signal stream (108) from the filtered signal stream (74), a delay element (138) delays the filtered signal stream (74) into a delayed signal stream (140) synchronized with the constrained-bandwidth error signal stream (108), a complex summing circuit (110) sums the delayed signal stream (140) and the constrained-bandwidth error signal stream (108) into a constrained-envelope signal stream (112), and a substantially linear amplifier (146) amplifies

Abstract: A digital communication system (20) communicates using a polar amplitude phase shift keyed (P-APSK) phase point constellation (70, 70', 70"). Pragmatic encoding is accommodated using the constellation (70, 70', 70") to simultaneously communicate both encoded and uncoded information bits (69, 51). The constellation (70, 70', 70") has an even number of phase point rings (74) and equal numbers of phase points (72) in ring pairs (75, 76, 77). Encoded information bits (69) specify secondary modulation and uncoded information bits (51) specify primary modulation. The constellation (70, 70', 70") is configured so secondary sub-constellations (78) include four phase points (72) arranged so that two of the four phase points (72) exhibit two phase angles at one magnitude and the other two of the four phase points (72) exhibit phase angles that are at another magnitude. The difference between the phase angles at different magnitudes within a secondary sub-constellation (78) is constant.

Abstract: A communication system (11) uses concatenated coding in which an inner code is configured to match the needs of an outer code. The inner code is implemented through a pragmatic trellis coded modulation encoder (18) and decoder (34). A parser (50) of the encoder (18) distributes fewer than one user information bit per unit interval (66) to a convolutional encoder (58) which generates at least two convolutionally encoded bits for each user information bit it processes. Exactly one of the convolutionally encoded bits is phase mapped (56) with at least two user information bits during each unit interval (66). The decoder (34) detects a frame sync pattern (48) inserted into the user information bits to resolve phase ambiguities. Phase estimates are convolutionally decoded (100) to provide decoded data estimates that are then used to selectively rotate the phase estimates prior to routing the phase estimates to a slice detector (118).

Abstract: A digital communication system (20) communicates using a polar amplitude phase shift keyed (P-APSK) phase point constellation (70, 70'). Pragmatic encoding and puncturing is accommodated. The pragmatic encoding uses the P-APSK constellation (70, 70') to simultaneously communicate both encoded and uncoded information bits. The P-APSK constellation (70, 70') has an even number of phase point rings (74, 76) and equal numbers of phase points (72) in pairs of the rings (74, 76). Encoded bits specify secondary modulation and uncoded bits specify primary modulation. The constellation (70, 70') is configured so that secondary modulation sub-constellations (78) include four phase points (72) arranged so that two of the four phase points (72) exhibit two phase angles at one magnitude and the other two of the four phase points exhibit phase angles that are at another magnitude. The difference between the phase angles at different magnitudes within a secondary sub-constellation (78) is constant.

Abstract: A communication system (10) includes a rotationally invariant pragmatic trellis coded modulator (18) and demodulator (34). The modulator (18) partitions information bits (20) into primary (42) and secondary (44) data streams. The secondary data stream (44) is convolutionally encoded (70) then fed to the LSB of a phase mapper (76). The phase mapper (76) is arranged so that all pairs of adjacent phase data are generated from pairs of opposing polarity LSB inputs. The primary data stream (42) is differentially encoded through a dual channel differential encoder (50). The demodulator (34) convolutionally decodes (90) the secondary stream, then re-encodes (96) secondary stream estimates. The re-encoded secondary stream estimates are used to remove (102) the secondary modulation from phase value estimates. Adjusted phase value estimates are phase demodulated (104) and differentially decoded using a dual channel differential decoder (106).

Abstract: A digital demodulator (10) reads symbol samples into a memory buffer (38) that can be played forward and backward into a phase locked loop (48). During an initial non-data directed symbol timing estimating phase (56) the demodulator (10) achieves an approximate frequency synchronization and starts to achieve phase synchronization on an incoming stream of symbols. During a first forward readout pass (58) of stored samples, the phase locked loop (48) begins the frequency and phase convergence. During subsequent pass (60) using a reverse readout of stored samples, phase locked loop (48) continues to converge toward zero phase error. Then another forward pass (66), phase locked loop (48) achieves usable frequency and phase synchronization of carrier and begins valid data extraction.

Abstract: A communication system (10) includes a rotationally invariant pragmatic trellis coded modulation (PTCM) encoder (18) and decoder (34). The PTCM encoder (18) partitions information bits (20) into primary (42) and secondary (44) data streams. A pilot bit (56) is inserted into the secondary data stream (44) during each frame (46). The secondary stream (44) then receives rate 1/2 convolutional encoding (60) that is punctured to a rate of 9/16. The primary data stream (42) is differentially encoded (50). The encoded primary and secondary streams are concurrently phase mapped (70) using an 8-PSK constellation so that an effective code rate of 5/6 results. The PTCM decoder (34) convolutionally decodes (84) the secondary stream, then re-encodes secondary stream estimates using a systematic, transparent convolutional encoder (88). The pilot bit is evaluated (92) in the re-encoded symbol estimates (90) to detect and correct any secondary stream inversion that may have occurred due to phase ambiguity.

Abstract: A digital communication receiver (#10) takes one complex sample (#20) of a baseband analog signal (#12) per symbol. A rectangular to polar converter (#44) separates phase attributes of the complex samples from magnitude attributes during coarse symbol synchronization (#28). A phase processor (#48) identifies clock adjustment opportunities which occur when relatively large phase changes take place between consecutive symbols. A magnitude processor (#46) influences symbol timing only during clock adjustment opportunities. The magnitude processor (#46) advances symbol timing in a phase locked loop when decreasing magnitude changes are detected during clock adjustment opportunities and retards symbol timing when increasing magnitude changes are detected during clock adjustment opportunities during coarse symbol synchronization (#28).

Abstract: A digital communication receiver (10) takes one complex sample (20) of a baseband analog signal (12) per symbol. A rectangular to polar converter (26) separates phase attributes of the complex samples from magnitude attributes. A phase processor (28) identifies clock adjustment opportunities which occur when relatively large phase changes take place between consecutive symbols. A magnitude processor (32) influences symbol timing only during clock adjustment opportunities. The magnitude processor (32) advances symbol timing in a phase locked loop when decreasing magnitude changes are detected during clock adjustment opportunities and retards symbol timing when increasing magnitude changes are detected during clock adjustment opportunities. An interpolator (66) may be used to estimate magnitude values between samples so that magnitude change is determined between sampled magnitude values and estimated magnitude values.

Abstract: A selectable demodulator (32) operates in the phase domain to implement a coherent demodulation path (40) and a differentially coherent demodulation path (42). The coherent path (40) includes a differential encoder circuit (46) to produce coherently demodulated differential data. Magnitude converters (62, 62') convert phase errors in each path into magnitude values. A comparison circuit (66) compares magnitude values from the two paths (40, 42) and selects the path encountering the least phase error. A selection circuit (60) provides data codes demodulated in accordance with the selection.

Abstract: Symbols (18) of a burst (12) are sub-divided into symbol sections (20). Each symbol section (20) is sampled and converted into polar coordinates. A buffer bank (38) selectably delays the samples and replays a preamble (14). A demod bank (40) includes a coherent demod (58) and several differential demods (60). Each differential demod (60) processes its own stream of symbol sections (20). The differential demods (60) feed a preamble detector (66) and a symbol synchronization circuit (62). The symbol synchronization circuit (62) identifies the symbol section (20) which yields the smallest magnitude of frequency errors. This symbol section (20) is processed by the coherent demod (58) to acquire carrier phase and recover data. The coherent demod (58) is implemented in the phase domain so that only oscillation signal phase data need be generated in phase locked loops.

Abstract: A communication system (10) includes a modulation section (12) and a demodulation section (14). The modulation section (12) performs frequency modulation in accordance with a frequency trajectory signal (28, 30, 32). An intersymbol interference (ISI) prediction filter (20) adjusts the amplitude of the frequency trajectory signal (28, 30, 32) in response to data code (16) sequences being conveyed over a plurality of symbols (18). More frequent data changes in the sequence of the data codes (16) lead to greater amplitudes in the frequency trajectory signal. The demodulation section (14) applies a distorted phase signal to a decision circuit (38). The distorted phase signal conveys a received phase (46) that includes ISI. Due to the equalization applied by the ISI prediction filter (20), the received phase (46) approximates a target phase (40, 42) in spite of the ISI.

Abstract: In despreading a received spread spectrum signal, spread by means of a linear feedback shift register, the signal is demodulated and filtered and then applied to a predictor for estimating the length, connection polynominal and contents in accordance with the Berlekamp-Massey iterative algorithm. The estimates are then applied to a local LFSR to produce a despreading random signal which is mixed with the received signal to remove the spreading factor. The instantaneous total energy of the output signal is measured and when the estimations are correct, the total energy will exceed a predetermined limit and a signal is supplied to the predictor to indicate that the estimates are correct.

Abstract: The addition of a low softening point glass of Tg 300.degree.C and optionally a blowing agent, to a reinforced thermosetting composite material gives fire retardant properties to the product. Smoke emission on burning is less than for halogenated fire retardant additives. A preferred embodiment is GRP sheet containing a powdered phosphate glass and a blowing agent.

Abstract: An isocyanate-based polymeric foam material having dispersed therein a particulate low-softening point inorganic oxide glass having a transformation temperature of not greater than 300.degree.C, and optionally a blowing agent which is capable of liberating a non-flammable gas on heating above a temperature in the range 150.degree. to 400.degree.C.