Methods, systems, and apparatus, including computer programs encoded on a computer storage medium for receiving, by a first device, a first signal from a second device, the first signal including a carrier signal modulated with a first modulation signal. Detecting a frequency of the carrier signal by performing a carrier extraction (CAREX) process on the first signal. Adding a second modulation signal to the carrier signal of the first signal to produce a combined signal, wherein the second modulation signal is a transpositional modulation (TM) signal and the first modulation signal is a non-TM signal. Transmitting the combined signal.

An apparatus for estimating carrier frequency offset includes a notch frequency setting circuit, N notch filters, an M.sup.th power circuit, a spectrum generating circuit, a peak frequency determining circuit, a comparing circuit, and a frequency offset determining circuit. The notch frequency setting circuit sets different notch-frequencies for the notch filters, which generate N filtered signals by filtering an input signal. The M.sup.th power circuit performs an M.sup.th power calculation on the N filtered signals to generate N M.sup.th power filtered signals. The spectrum generating circuit generates N M.sup.th order spectra for the N M.sup.th power filtered signals. The peak frequency determining circuit determines respective peak frequencies of the N M.sup.th order spectra. The comparing circuit identifies an optimal peak frequency from the N peak frequencies. The frequency offset determining circuit determines an estimated carrier frequency offset according to the optimal peak frequency.

An apparatus for estimating carrier frequency offset includes a notch frequency setting circuit, N notch filters, an M.sup.th power circuit, a spectrum generating circuit, a peak frequency determining circuit, a comparing circuit, and a frequency offset determining circuit. The notch frequency setting circuit sets different notch-frequencies for the notch filters, which generate N filtered signals by filtering an input signal. The M.sup.th power circuit performs an M.sup.th power calculation on the N filtered signals to generate N M.sup.th power filtered signals. The spectrum generating circuit generates N M.sup.th order spectra for the N M.sup.th power filtered signals. The peak frequency determining circuit determines respective peak frequencies of the N M.sup.th order spectra. The comparing circuit identifies an optimal peak frequency from the N peak frequencies. The frequency offset determining circuit determines an estimated carrier frequency offset according to the optimal peak frequency.

Systems and methods for transpositional modulation and demodulation are provided. One such method for generating a signal includes the steps of providing a look-up table having a plurality of quarter-cycle waveforms, each of said quarter-cycle waveforms associated with a respective input level; receiving an input signal; and outputting quarter-cycle waveforms associated with levels of the received input signal. Systems for transpositional modulation are also provided. One such system for generating a signal includes a look-up table having a plurality of quarter-cycle waveforms. Each of the quarter-cycle waveforms are associated with a respective input level, and the look-up table is configured to receive an input signal, and output quarter-cycle waveforms associated with levels of the received input signal.

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for modulating and demodulating transpositional modulated (TM) signals. One aspect features a method of modulating a carrier signal that include the actions of generating a TM signal by generating a sinusoidal signal, and modulating the sinusoidal signal based on a data signal to provide the TM signal. Inserting the TM signal into a carrier signal to provide a TM modulated carrier signal. Modulating the TM modulated carrier signal with a non-TM signal to provide a combined signal. Transmitting the combined signal.

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium for receiving, by a first device, a first signal from a second device, the first signal including a carrier signal modulated with a first modulation signal. Detecting a frequency of the carrier signal by performing a carrier extraction (CAREX) process on the first signal. Adding a second modulation signal to the carrier signal of the first signal to produce a combined signal, wherein the second modulation signal is a transpositional modulation (TM) signal and the first modulation signal is a non-TM signal. Transmitting the combined signal.

A microprocessor includes a memory, an input/output port and a switch controller. Transmission data, a spread code and an inverted code are stored in the memory. The switch controller generates a spread spectrum signal by calling up either of the spread code or the inverted code in accordance with a bit of the transmission data. A switch connected to the input/output port is switched on and off based on the spread spectrum signal. In addition, an antenna is connected to the input/output port via a coupler. An oscillation circuit includes a reference oscillator and a BPF and inputs a harmonic of a reference signal to the coupler as a carrier wave.

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium for receiving, by a first device, a first signal from a second device, the first signal including a carrier signal modulated with a first modulation signal. Detecting a frequency of the carrier signal by performing a carrier extraction (CAREX) process on the first signal. Adding a second modulation signal to the carrier signal of the first signal to produce a combined signal, wherein the second modulation signal is a transpositional modulation (TM) signal and the first modulation signal is a non-TM signal. Transmitting the combined signal.

Disclosed is a Link 16 terminal having a receiver and a transmitter. The receiver may be configured to process received signals in a receive mode to produce digitized samples, which may then be processed in a digital signal processor. The transmitter may be configured to produce a transmit signal that is provided to an antennas for transmission during transmit mode. The transmit signal may also be provided to the receiver in transmit mode to produce digitized samples of the transmit mode, may then be processed in a digital signal processor for compliance with requirements for Link 16 transmissions.

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium for receiving, by a first device, a first signal from a second device, the first signal including a carrier signal modulated with a first modulation signal. Detecting a frequency of the carrier signal by performing a carrier extraction (CAREX) process on the first signal. Adding a second modulation signal to the carrier signal of the first signal to produce a combined signal, wherein the second modulation signal is a transpositional modulation (TM) signal and the first modulation signal is a non-TM signal. Transmitting the combined signal.