Systems and methods for a non-data-aided (NDA) approach to advanced OFDM timing are provided. This approach allows for accurate OFDM symbol timing and synchronization by avoiding inter-symbol interference (ISI) in multipath environments where an earliest arriving signal may not be the strongest signal. The NDA approach may rely on generating and applying a bias correction to a combined correlation result of the multi-path signals.

A system that incorporates aspects of the subject disclosure may perform operations including, for example, receiving, via an antenna, a signal generated by a communication device, detecting passive intermodulation interference in the signal, the interference generated by one or more transmitters unassociated with the communication device, and the interference determined from signal characteristics associated with a signaling protocol used by the one or more transmitters. Other embodiments are disclosed.

Disclosed is a blind authentication method for a frequency selective fading channel based on belief propagation. The method includes: transmitting carrier signals to a frequency selective fading channel with multiple paths, where each carrier signal includes an authentication signal, a pilot signal and an information signal performing BKIC processing on a carrier signal in each path to obtain a target signal, and performing differential signal processing on the target signal to obtain a target authentication signal, obtaining a reference signal based on a key and the pilot signal in each path performing the differential signal processing on the reference signal to obtain a reference authentication signal, and calculating a correlation between the target authentication signal and the reference authentication signal to obtain a test statistic; and comparing the test statistic with a prescribed threshold to determine whether the carrier signal path can pass authentication.

A method of selecting a codebook is disclosed. The method is performed in a network node and includes: determining whether to use single-user multiple-input-multiple output, SU-MIMO, or multi-user multiple-input-multiple output, MU-MIMO, in a cell (C1) controlled by the network node, and selecting, based on the determining, a first codebook or a second codebook for use in communication with a communication device within the cell (C1). The first codebook is configured for SU-MIMO communication and the second codebook is configured for MU-MIMO communication. A network node, computer program and computer program product are also disclosed.

Techniques are described for carrier frequency offset (CFO) and channel estimation of orthogonal frequency division multiplexing (OFDM) transmissions over multiple-input multiple-output (MIMO) frequency-selective fading channels. A wireless transmitter forms blocks of symbols by inserting training symbols within two or more blocks of information-bearing symbols. The transmitter applies a hopping code to each of the blocks of symbols to insert a null subcarrier at a different position within each of the blocks of symbols, and a modulator outputs a wireless signal in accordance with the blocks of symbols. A receiver receives the wireless signal and estimates the CFO, and outputs a stream of estimated symbols based on the estimated CFO.

The present disclosure provides a radio communication apparatus, a radio communication system, a radio communication method, and a program capable of demodulating signals at appropriate reception timings. A radio communication apparatus 11 includes: a measurement unit 111 configured to measure delay profiles of a plurality of frequency bands; and a determination unit 112 configured to determine a path timing of a first frequency band f.sub.1 based on a time difference between a first time t.sub.m1 indicating a time of a maximum amplitude in the first frequency band f.sub.1 of the plurality of frequency bands and a second time t.sub.m2 indicating a time of a maximum amplitude in a second frequency band f.sub.2 of the plurality of frequency bands.

A radio frequency transmission system and methods for mitigating multipath radio frequency interference are disclosed. Embodiments include a first helical antenna having a first radius and operable to receive a first electromagnetic signal, and a second helical antenna having a second radius and operable to receive a second electromagnetic signal. Further embodiments include a phase adjuster configured to receive the first electromagnetic signal as an input signal, apply an adjustable phase delay to the input signal, and output an adjusted electromagnetic signal. Still further embodiments include a signal combiner configured to receive the adjusted electromagnetic signal and the second electromagnetic signal and output a combined electromagnetic signal.

A system that incorporates aspects of the subject disclosure may perform operations including, for example, receiving, via an antenna, a signal generated by a communication device, detecting passive intermodulation interference in the signal, the interference generated by one or more transmitters unassociated with the communication device, and the interference determined from signal characteristics associated with a signaling protocol used by the one or more transmitters. Other embodiments are disclosed.

Systems and methods for a non-data-aided (NDA) approach to advanced OFDM timing are provided. This approach allows for accurate OFDM symbol timing and synchronization by avoiding inter-symbol interference (ISI) in multipath environments where an earliest arriving signal may not be the strongest signal. The NDA approach may rely on generating and applying a bias correction to a combined correlation result of the multi-path signals.

Disclosed is a blind authentication method for a frequency selective fading channel based on belief propagation. The method includes: transmitting carrier signals to a frequency selective fading channel with a plurality of paths, where each of the carrier signals includes an authentication signal, a pilot signal and an information signal, and the authentication signal is superimposed on the pilot signal; receiving the carrier signals, performing blind known interference cancellation (BKIC) processing on a carrier signal in each of the plurality of paths of the frequency selective fading channel to obtain a target signal, and performing differential signal processing on the target signal to obtain a target authentication signal, where in the BKIC processing, a pilot signal in the each of the plurality of paths is cancelled through a belief propagation technique by using a prior probability density function and a Tanner graph of the target signal; obtaining a reference signal based on a key and the pilot signal in the each of the plurality of paths, performing the differential signal processing on the reference signal to obtain a reference authentication signal, and calculating a correlation between the target authentication signal and the reference authentication signal to obtain a test statistic; and comparing the test statistic with a prescribed threshold to determine whether the carrier signal in the each of the plurality of paths can pass authentication.