Quadrature-quadrature phase-shift keying (Q/sup 2/PSK) is a spectrally efficient modulation scheme which utilizes available signal space dimensions in a more efficient way than two-dimensional schemes such as QPSK and MSK (minimum-shift keying) It uses two date shaping pulses and two carriers, which are pairwise quadrature in phase, to create a four-dimensional signal space and increases the transmission rate by a factor of two over QPSK and MSK However, the bit error rate performance depends on the choice of pulse pair With simple sinusoidal and cosinusoidal data pulses, the E/sub b//N/sub 0/ requirement for P/sub b/(E)=10/sup -5/ is approximately 16 dB higher than that of MSK Without additional constraints, Q/sup 2/PSK does not maintain a constant envelope, however, a simple block coding can provide a constant envelope This coded signal substantially outperforms MSK and TFM (time-frequency multiplexing) in bandwidth efficiency Like MSK, Q/sup 2/PSK also has self-clocking and self-synchronizing ability An optimum class of pulse shapes for use in Q/sup 2/PSK format is presented One suboptimum realization achieves the Nyquist rate of 2 b/s/Hz using binary detection >

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Quadrature-quadrature phase-shift keying

A quantum communication system including an emitter and a receiver, the emitter including an encoder and at least one photon source and being configured to pass a signal pulse and a reference pulse, which are separated in time, through the encoder and output the signal pulse and the reference pulse. The reference pulse has a higher probability of containing more than one photon than the signal pulse. The receiver includes a decoder and at least one detector for measuring the signal pulse and the reference pulse.

Quantum communication system

A transmitter encodes a number 2N data bits by using N data bits to select one of 2N levels of a cosine wave and the other N data bits to select one of 2N levels of a sine wave. The modulation attains the cosine wave levels at instants offset by half an N-bit symbol interval with respect to the sine wave levels, and is called Offset QAM (OQAM). A received OQAM signal is amplified, filtered and digitized at a sampling rate of preferably only one sample per N-bit half-symbol interval. Successive N-bit half-symbols comprise information modulated alternately on a cosine and a sine carrier wave. The receiver may remove this successive rotation by applying successive derotations of successive digitized samples by like amounts. The derotated samples are then correlated with known sync half-symbols. The sync correlations determine a set of channel coefficients describing the dependence of each digitized sample on one or more unknown half-symbols. The computed channel estimates are then used to predict the expected received sample values for all possible sequences of successive unknown half-symbols that are to be decoded. Received samples are then compared with all possible expected values and a measure of disagreement or error metric computed. That sequence with the lowest cumulative error metric is used to determine the decoded symbol output. In other aspects of the invention, dual mode transmitters and receivers are disclosed that enable different types of modulation to be alternatively utilized in a same apparatus.

Transmitter/receiver for gmsk and offset-qam

Systems and methods for orthogonal frequency division multiplexing are provided. In one embodiment, a multi-carrier modem comprises: a receiver configured to de-modulate symbols from at least one of a plurality of spectrally overlapping carrier signals to produce a receiver output; a transmitter configured to modulate symbols onto at least one of a plurality of the spectrally overlapping carrier signals; a processor coupled to the transmitter, wherein the processor outputs data for transmission by the transmitter, wherein the processor applies an inverse Fourier transform to the data transmitted by the transmitter; the processor coupled to the receiver, wherein the processor applies a Fourier transform to the receiver output; and a controller programmed to instruct the transmitter to transmit at least one symbol representing a request for bandwidth allocation on a first carrier; wherein the controller is further programmed to determine when a collision has occurred on the first carrier.

Systems and method for orthogonal frequency divisional multiplexing

A compact low-power radio frequency (RF) transceiver with a built-in antenna provides wireless communication between a computer and another device. A direct conversion receiver together with a voltage controlled oscillator, phase lock loop circuits, digitally controlled divider circuits and a patch antenna are packaged into a compact enclosure, having dimensions within the PCMCIA format. In some embodiments, the transceiver enters a sleep mode whenever it is idle in order to further conserve power. In other embodiments, a signature detector enables the transceiver to distinguish between noise and valid messages by recognizing a signature word embedded in the data packet.

Radio tranceiver for data communications

A suppressed carrier signal is offset quadrature phase shift key modulated so the reference carrier phase is stepped 90° in the same direction in synchronism with sequential bits of a serial data stream and is further bi-phase modulated in response to the binary data source having first or second binary values. A coherent receiver responds to the suppressed carrier signal to establish an equivalent sequence of stepping reference phases at the carrier frequency. The reference phases synchronously rotate in 90° increments in the same direction as the suppressed carrier reference, being permitted a four-fold initial phase ambiguity (0°, 90°, 180°, and 270°). The rotating reference phase is compared in a bi-phase manner with the appropriate component of the suppressed carrier signal to derive sequential d.c. polarities indicative of the binary bit values during the sequential binary data bits.

F. A. Wissel

Papers

QPSK Suppressed carrier with rotating reference phase