A system and apparatus includes an optical masking unit that is configured for applying a user's mask code. The mask code has a code length of at least equal to a number of users. A light source unit is coupled to the optical masking unit. The light source unit includes a number of coherent lasers. The number of coherent lasers is at least equal to half the number of users. Each of the coherent lasers is configured for operation at a different specific prescribed operating frequency. A modulation unit is configured for applying the user's data to the coherent lasers. An optical combiner unit is operable for combining outputs of the coherent lasers to an optical fiber input.

Disclosed is an air conditioner. The air conditioner of the present disclosure includes: a plurality of indoor units configured to be distributed and installed in a plurality of floors in a building; a controller configured to monitor and control the plurality of indoor units; and a wireless communication unit configured to transmit and receive data by the controller, the plurality of indoor units, and one outdoor unit by using a wireless communication method; wherein the wireless communication unit comprises a transmitter and a receiver using a Sub-GHz band frequency, wherein the transmitter includes: an optical orthogonal code generating unit configured to first cipher source data using an optical orthogonal code; and a narrow-band chaotic signal generating unit configured to secondarily cipher by using a chaotic signal, wherein the data is sequentially encrypted through the optical orthogonal code generating unit and the narrowband chaotic signal generating unit and then transmitted.

An optical transmitter, an optical receiver, and an optical transmission method are disclosed. The optical transmitter includes an optical signal generator, N spreaders, N pairs of data modulators, and a combiner, where the optical signal generator generates N optical carriers; an i.sup.th spreader spreads an i.sup.th optical carrier, to obtain a spread optical signal having two subcarriers; splits the spread optical signal into a first optical signal and a second optical signal; and delays the second optical signal to obtain a third optical signal; an i.sup.th pair of data modulators modulate the first optical signal and the third optical signal to obtain a pair of modulated optical signals, transmit the pair of modulated optical signals to the combiner, where the pair of modulated optical signals reaching the combiner differ by 1/(4 fsi) in time domain; and the combiner combines, into one optical signal, N pairs of modulated optical signals.

An optical transmitter, an optical receiver, and an optical transmission method are disclosed. The optical transmitter includes an optical signal generator, N spreaders, N pairs of data modulators, and a combiner, where the optical signal generator generates N optical carriers; an i.sup.th spreader spreads an i.sup.th optical carrier, to obtain a spread optical signal having two subcarriers; splits the spread optical signal into a first optical signal and a second optical signal; and delays the second optical signal to obtain a third optical signal; an i.sup.th pair of data modulators modulate the first optical signal and the third optical signal to obtain a pair of modulated optical signals, transmit the pair of modulated optical signals to the combiner, where the pair of modulated optical signals reaching the combiner differ by 1/(4 fsi) in time domain; and the combiner combines, into one optical signal, N pairs of modulated optical signals.

Aspects of the present disclosure provide a scheme for generating a multiple access (MA) signal that include mapping each of at least one stream of bits to generate a set of modulated symbols and transmitting the set of modulated symbols. The spreading signatures that are selected to map the at least one stream of bits are selected, at least in part, based on a set of compatibility rules. The spreading involves mapping each stream of bits using a respective spreading signature from a set of spreading signatures to generate a respective set of modulated symbols, wherein real spreading signature components of the spreading signatures are orthogonal to each other and imaginary spreading signature components of the spreading signatures are orthogonal to each other.

An air conditioner is provided that includes a plurality of indoor units configured to be distributed and installed in a plurality of floors in a building; a controller configured to monitor and control the plurality of indoor units; and a wireless communication unit configured to transmit and receive data by the controller, the plurality of indoor units, and one outdoor unit using a wireless communication method. The wireless communication unit comprises a transmitter and a receiver using a Sub-GHz band frequency. The transmitter includes an optical orthogonal code generator configured to first cipher source data using an optical orthogonal code, and a narrow-band chaotic signal generator configured to secondarily cipher using a chaotic signal. The source data is sequentially encrypted through the optical orthogonal code generator and the narrowband chaotic signal generator and then transmitted.

Aspects of the subject disclosure may include, a coupler having a first member coupled to a transmission medium, a first component coupled to the first member, a second member coupled to the transmission medium, and a second component coupled to the second member. The first component can facilitate transmission of first signals via the first member, and the second component can facilitate transmission of second signals via the second member. The first signals and the second signals can in turn induce electromagnetic waves that propagate along the transmission medium without requiring an electrical return path. Other embodiments are disclosed.

Free-space communication systems and methods are provided. The systems include a transmitter that combines multiple sets of radio-frequency-modulated optical carrier frequencies for transmission across free space using multiple transmission apertures. Different sets of signals are filtered to form single sideband signals. The different sets of single sideband signals are then combined to form dense wavelength division multiplexed signals. In addition, combined sets of signals of different polarizations can be combined. A receiver can include a single receive aperture.

Aspects of the present disclosure provide a scheme for generating a multiple access (MA) signal that include mapping each of at least one stream of bits to generate a set of modulated symbols and transmitting the set of modulated symbols. The spreading signatures that are selected to map the at least one stream of bits are selected, at least in part, based on a set of compatibility rules. The spreading involves mapping each stream of bits using a respective spreading signature from a set of spreading signatures to generate a respective set of modulated symbols, wherein real spreading signature components of the spreading signatures are orthogonal to each other and imaginary spreading signature components of the spreading signatures are orthogonal to each other.

Aspects of the subject disclosure may include, a coupler having a first member coupled to a transmission medium, a first component coupled to the first member, a second member coupled to the transmission medium, and a second component coupled to the second member. The first component can facilitate transmission of first signals via the first member, and the second component can facilitate transmission of second signals via the second member. The first signals and the second signals can in turn induce electromagnetic waves that propagate along the transmission medium without requiring an electrical return path. Other embodiments are disclosed.