A method is provided for detecting an access zone configuration of a downlink wireless transmission received from a wireless network by a receiver. The method includes steps of activating the receiver, synchronizing the receiver with the wireless network, detecting, by the receiver after the step of synchronizing, a received access zone of the downlink wireless transmission, determining a base symbol of the detected access zone, ascertaining a first gap and a second gap from repetitive information contained within the determined base symbol, concluding, from the ascertained first and second gaps, that the detected access zone is part of a multiple access zone configuration, and registering, after the step of concluding, the receiver with the wireless network.

Methods, systems, and apparatus, including computer programs encoded on computer-storage media, for compensating for frequency-dependent I-Q imbalance. In some implementations, a radio receiver includes an in-phase mixer configured to generate an in-phase (I) signal and a quadrature mixer configured to generate a quadrature (Q) signal. A first analog-to-digital (A/D) converter is configured to generate first digital samples from one of the I signal and the Q signal. A second analog-to-digital (A/D) converter is configured to generate second digital samples from the other of the I signal and the Q signal. A compensation system includes a feedback loop configured to compensate for frequency-dependent I-Q imbalance based on results, for each of multiple of the first digital samples, of cross-correlation of the first digital sample with each of multiple of the second digital samples.

A receiver circuit includes a quadrature signal generator to generate an in-phase (I) signal and a quadrature (Q) signal from a local oscillator signal and an IQ phase sense and control circuit to generate a phase adjustment code responsive to a phase error between quadrature signals generated by a plurality of mixers. The receiver circuit also includes a phase corrector to adjust a phase difference between the I and Q signals from the quadrature signal generator to generate corrected I and Q signals to be provided to the plurality of mixers.

A spatial position-dependent I/Q domain modulation method, dual domain modulation method and multiple access communication method are provided. The methods eliminate the dependence of physical layer secure communication on channel state information, and realize the function that a receiver at an expected position can communicate normally, while an eavesdropper at other positions cannot receive a signal or can only receive a wrong signal. The security capability of a wireless communication system is improved from the spatial dimension. The multiple access communication method can realize the distinguishing of multiple users according to precise spatial position points. Even if a plurality of users are located in the same sector in an angular domain, as long as the spatial positions of these users are different, the method can be used to perform multiple access communication, thereby further improving the spatial multiplexing rate of the system and increasing the system capacity.

A radio receiver device is arranged to receive a radio signal modulated with a data packet including an address portion. The radio receiver comprises: a synchronisation circuit portion arranged to produce synchronization information corresponding to the data packet; a demodulation circuit portion comprising a correlator, wherein said demodulation circuit portion is arranged to receive the radio signal and to produce an estimate of the address portion comprising a plurality of demodulated bits using said correlator and the synchronisation information; an address checking circuit portion arranged to receive the plurality of demodulated bits, to check said plurality of demodulated bits for a predetermined bit pattern, and to produce a match flag if it determines that the plurality of demodulated bits corresponds to the predetermined bit pattern. The radio receiver device is arranged such that, upon detecting an upcoming timeout event, the demodulation circuit portion sends a timeout warning signal to the address checking circuit portion using a handshaking channel therebetween; said address checking circuit portion being arranged such that, if it receives the timeout warning signal, it stops checking the plurality of demodulated bits for the predetermined bit pattern.

An optical transmitter (102,200) is operable to generate an optical signal (260) by modulating a number N of frequency divisional multiplexing (FDM) subcarriers using transformed digital signals which are determined by applying a pseudo FDM (pFDM) transformation to preliminary digital signals representative of multi-bit symbols. Rather than experiencing the effects of the number N of FDM channels, the optical signal experiences the effects of a different number M of pFDM channels, where MN. In some examples, the number M of pFDM channels is less than the number N of FDM channels, and frequency-dependent degradations may be averaged across different symbol streams. In other examples, the number M of pFDM channels is greater than the number N of FDM channels, and different symbol streams may experience different frequency-dependent degradations. An optical receiver (102,300) is operable to apply an inverse pFDM transformation to recover estimates of the multi-bit symbols.

An optical transmitter (102,200) is operable to generate an optical signal (260) by modulating a number N of frequency divisional multiplexing (FDM) subcarriers using transformed digital signals which are determined by applying a pseudo FDM (pFDM) transformation to preliminary digital signals representative of multi-bit symbols. Rather than experiencing the effects of the number N of FDM channels, the optical signal experiences the effects of a different number M of pFDM channels, where MN. In some examples, the number M of pFDM channels is less than the number N of FDM channels, and frequency-dependent degradations may be averaged across different symbol streams. In other examples, the number M of pFDM channels is greater than the number N of FDM channels, and different symbol streams may experience different frequency-dependent degradations. An optical receiver (102,300) is operable to apply an inverse pFDM transformation to recover estimates of the multi-bit symbols.

An estimating apparatus for bias drift of a transmitting end modulator, a compensating apparatus, a receiver and a method are disclosed. Estimation and compensation of the bias drift are performed directly at the receiving end according to phase recovered received signals, with no need of providing an extra bias control circuit at the transmitting end. Estimating and compensating for the bias drift includes recovering received signals by removing a frequency difference and a phase difference between a transmitting end laser and a receiving end laser producing phase recovered received signals, estimating the bias drift of the transmitting end modulator according to the phase recovered received signals and compensating the bias drift of the transmitting end modulator in a receiver.

A receiver is presented, such that the receiver may be configured to receive transmissions in accordance with a continuous waveform and to relock quickly on a received transmission when the transmitter is switched or a change in the waveform parameters is made. The receiver may be configured to support reception of a shared channel and/or of a channel allocated for SCPC usage and may be modified while used (e.g., dynamic SCPC). In addition, a satellite communication system is presented, the satellite communication system comprising at least one receiver in accordance with the above-described receiver. The satellite communication system may be configured to utilize the receiver's characteristics for at least the purpose of achieving a highly efficient return link channel.

A receiver signal is sampled at a sampling rate equivalent to a chip rate at which chips of a known signal are timed. The resulting receiver signal samples are segmented into receiver signal segments, which are filtered by respective matched filters that are matched to known signal segments segmented from the known signal. Indexes are assigned to elements of the resulting filter response sequences to define an array thereof. Frequency transforms are computed of elements of the filter response sequences in respective columns of the array. Indexes are assigned to elements of the resulting frequency response sequences to define another array thereof. Channel effects imparted on a radio signal are jointly estimated from characteristics of the other array at which at least one local maximum is located.