Abstract: Systems and methods are disclosed herein for a Convex Reduction of Amplitude (CRAM) based processing scheme for a Multiple Input Multiple Output (MIMO) Orthogonal Division Multiplexing (OFDM) transmitter system. In one embodiment, a method performed by a processing system for a MIMO OFDM transmitter system comprises precoding frequency-domain input signals to provide frequency-domain precoded signals for multiple subcarriers. The method further comprises processing the frequency-domain precoded signals in accordance with a CRAM-based processing scheme to provide time-domain precoded signals for respective transmit branches of the MIMO OFDM transmitter system. The CRAM-based processing scheme uses projection matrices for the subcarriers, respectively, to project clipping energy into a null space of the MIMO OFDM transmitter system. Further, the projection matrices are a function of static or semi-static information that defines the null space of the MIMO OFDM transmitter system.

Abstract: A method, system and apparatus are disclosed. A system including at least one wireless device and a network node configured to communicate with the at least one wireless device is provided. The network node includes an antenna array including a plurality of antennas. The network node is configured to determine at least one precoding matrix based on a Douglas-Rachford splitting convex optimization model between a per-antenna power constraint and a Multi-User Interference (MUI) requirement for evening the output power of the plurality of antennas of the antenna array. The network node is configured to cause transmission to the at least one wireless device using the antenna array based at least in part on the at least one precoding matrix.

Abstract: A method and network node for implementing a channel reciprocity transform for multiple frequency beamforming are disclosed. According to some aspects, a method in a network node includes determining an average angular spectral density (ASD) based at least in part on a Fast Fourier transform (FFT) of an uplink received vector for each of multiple subcarriers from at least one antenna polarization. The method includes resampling the average ASD at a wavelength for a subcarrier of the multiple subcarriers in a downlink sub-band. The method also includes determining a frequency-transposed channel estimate for the downlink sub-band based at least in part on an inverse Fast Fourier transform (IFFT) of the resampled average ASD. The method also includes beamforming a signal to the WD in the downlink sub-band using the determined frequency-transposed channel estimate.

Abstract: A method is disclosed for reduction of peak-to-average power ratio (PA-PR) of transmission using multiple-input multiple-output (MIMO) from a transmitter. The method comprises defining a rank-extended MIMO transmission towards one or more intended receivers and one or more virtual receivers (wherein the one or more virtual receivers reside in a null space of a MIMO channel between the transmitter and the one or more intended receivers), generating a rank-extended MIMO signal for the rank-extended MIMO transmission (wherein the rank-extended MIMO signal comprises an intended receiver signal portion and a virtual receiver signal portion), determining a clipping signal for the rank-extended MIMO signal, and generating a PAPR reduced MIMO signal by combining the rank-extended MIMO signal with a projection of the clipping signal onto the null space of the MIMO channel. In some embodiments, the method further comprises transmitting the PAPR reduced MIMO signal over the MIMO channel.

Abstract: A method and network node for forward distortion correction for time domain beam forming are provided. According to one aspect, a method in a network node includes filtering cach signal output by the time domain beamformer by a band stop filter, the band stop filter including a stop band overlapping a pass band of the signal output by the time domain beamformer. The method also includes filtering each signal output by the time domain beamformer by a group delay filter in electrical parallel with a band stop filter, the group delay filter providing a group delay to the signal output by the time domain beamformer. The method also includes subtracting an output of each band stop filter from an output of a corresponding group delay filter.

Abstract: Methods and systems are described for reducing interference on radio units from passive intermodulation (PIM) distortion. Base station radio units can have multiple antennas, each receiving and sending communications over various frequencies. Embodiments under the present disclosure can identify the source of PIM and then reduce power of the aggressor downlink carriers on the impacted antennas. This can reduce the PIM that desensitizes the uplink receivers.

Abstract: A method, network node and wireless transceiver, for implementing iterative downlink passive intermodulation (PIM) spatial avoidance algorithms are provided. According to one aspect, a method in a wireless transceiver includes determining an uplink signal power. The method also includes determining an estimate of a downlink PIM subspace that minimizes a cost function that depends on the uplink signal power and a previous estimate of the downlink PIM subspace.

Abstract: A method in a network node and an apparatus for determining passive intermodulation (PIM) characteristics at the network node are provided. According to one aspect, a method includes capturing signals from each of at least one antenna port at a first time and a second time. The method includes determining a first covariance matrix based on signals captured at the first time. The method also includes determining a second covariance matrix based on signals captured at the second time. The method further includes determining a difference matrix, the difference matrix being based on a difference between the first and second covariance matrices, the difference matrix corresponding to changes in PIM between the first time and the second time.

Abstract: A method and radio in a network node for passive intermodulation (PIM) downlink subspace acquisition. According to one aspect, a method includes determining a downlink projection matrix that is formed using the downlink beamforming weights and determining a first downlink interference covariance matrix estimate for a current downlink orthogonal frequency division multiplexed, OFDM, symbol based at least in part on multiplying the downlink projection matrix by a scaling factor that is dependent on the passive intermodulation, PIM, power generated in one or more uplink channels.

Abstract: A network node is provided. The network node includes processing circuitry configured to determine at least one Convex Reduction of Amplitude, CRAM, projection matrix based at least in part on a signal subspace of scheduled wireless devices, and optionally cause transmission based at least in part on the at least one CRAM projection matrix.

Abstract: A method of a wireless communication transmitter is disclosed for peak-to-average power ratio (PAPR) control of communication symbols with N time-domain signal samples for transmission via each of M antenna elements. The method comprises: applying a PAPR cost function f(x) which has a proximal operator with closed form and is differentiable in an interval, and the proximal operator comprises a parameter lambda for tuning; selecting a value for lambda to perform a trade-off between PAPR and at least one other characteristic of the wireless communication transmitter; selecting a precoding for the collection of samples as a solution to an optimization problem for the selected value for lambda, wherein the optimization problem comprises minimization of an overall cost function comprising at least the PAPR cost function, and wherein solving the optimization problem comprises using the proximal operator of the PAPR cost function.

Abstract: Systems and methods are disclosed herein for a Convex Reduction of Amplitude (CRAM) based processing scheme for a Multiple Input Multiple Output (MIMO) Orthogonal Division Multiplexing (OFDM) transmitter system. In one embodiment, a method performed by a processing system for a MIMO OFDM transmitter system comprises precoding frequency-domain input signals to provide frequency-domain precoded signals for multiple subcarriers. The method further comprises processing the frequency-domain precoded signals in accordance with a CRAM-based processing scheme to provide time-domain precoded signals for respective transmit branches of the MIMO OFDM transmitter system. The CRAM-based processing scheme uses projection matrices for the subcarriers, respectively, to project clipping energy into a null space of the MIMO OFDM transmitter system. Further, the projection matrices are a function of static or semi-static information that defines the null space of the MIMO OFDM transmitter system.

Abstract: Systems and methods are disclosed herein that relate to Peak-to-Average Power Ratio (PAPR) reduction in a MIMO OFDM transmitter system. In some embodiments, a method of operation of a transmitter system includes, for each carrier of two or more carriers, performing precoding of frequency-domain input signals for the carrier to provide frequency-domain precoded signals for the carrier, the frequency-domain input signals for the carrier being for a plurality of transmit layers for the carrier, respectively. The method further includes processing the two or more pluralities of frequency-domain precoded signals for the two or more carriers, respectively, in accordance with a multi-carrier processing scheme to provide a plurality of multi-carrier time-domain transmit signals for a plurality of antenna branches, respectively, of the MIMO OFDM transmitter system.

Abstract: Systems and methods are disclosed herein that relate to Peak-to-Average Power Ratio (PAPR) reduction in a MIMO OFDM transmitter system. In some embodiments, a method of operation of a transmitter system includes, for each carrier of two or more carriers, performing precoding of frequency-domain input signals for the carrier to provide frequency-domain precoded signals for the carrier, the frequency-domain input signals for the carrier being for a plurality of transmit layers for the carrier, respectively. The method further includes processing the two or more pluralities of frequency-domain precoded signals for the two or more carriers, respectively, in accordance with a multi-carrier processing scheme to provide a plurality of multi-carrier time-domain transmit signals for a plurality of antenna branches, respectively, of the MIMO OFDM transmitter system.

Abstract: A method and network node for detection of passive intermodulation (PIM) are disclosed. According to one aspect, a method includes determining values of a covariance matrix based at least in part on uplink signals received by the network node radio. The method also includes determining a plurality of uplink (UL) channel 5 eigenvalues based at least in part on an eigen-component acquisition technique. The method further includes determining a presence or absence of PIM based at least in part on a plurality of the UL channel eigenvalues.

Abstract: A method of a wireless communication transmitter is disclosed for peak-to-average power ratio (PAPR) control of communication symbols with N time-domain signal samples for transmission via each of M antenna elements. The method comprises: applying a PAPR cost function f(x) which has a proximal operator with closed form and is differentiable in an interval, and the proximal operator comprises a parameter lambda for tuning; selecting a value for lambda to perform a trade-off between PAPR and at least one other characteristic of the wireless communication transmitter; selecting a precoding for the collection of samples as a solution to an optimization problem for the selected value for lambda, wherein the optimization problem comprises minimization of an overall cost function comprising at least the PAPR cost function, and wherein solving the optimization problem comprises using the proximal operator of the PAPR cost function.

Abstract: A method and radio in a network node for passive intermodulation (PIM) downlink subspace acquisition. According to one aspect, a method includes determining a downlink projection matrix that is formed using the downlink beamforming weights and determining a first downlink interference covariance matrix estimate for a current downlink orthogonal frequency division multiplexed, OFDM, symbol based at least in part on multiplying the downlink projection matrix by a scaling factor that is dependent on the passive intermodulation, PIM, power generated in one or more uplink channels.

Abstract: Systems and methods are disclosed herein that relate to Peak-to-Average Power Ratio (PAPR) reduction in a MIMO OFDM transmitter system. In some embodiments, a method of operation of a transmitter system includes, for each carrier of two or more carriers, performing precoding of frequency-domain input signals for the carrier to provide frequency-domain precoded signals for the carrier, the frequency-domain input signals for the carrier being for a plurality of transmit layers for the carrier, respectively. The method further includes processing the two or more pluralities of frequency-domain precoded signals for the two or more carriers, respectively, in accordance with a multi-carrier processing scheme to provide a plurality of multi-carrier time-domain transmit signals for a plurality of antenna branches, respectively, of the MIMO OFDM transmitter system.

Abstract: A first radio node for uplink and downlink co-scheduling is provided. The first radio node includes processing circuitry containing instructions executable to configure the first radio node to: determine a scheduling restriction for joint uplink and downlink scheduling based on passive intermodulation (PIM) generated during simultaneous uplink and downlink communications where the uplink communications corresponds to communications from a second radio node to the first radio node, and perform communications according to the scheduling restriction.

Abstract: Systems and methods are disclosed herein that relate to Peak-to-Average Power Ratio (PAPR) reduction in a MIMO OFDM transmitter system. In some embodiments, a method of operation of a transmitter system includes, for each carrier of two or more carriers, performing precoding of frequency-domain input signals for the carrier to provide frequency-domain precoded signals for the carrier, the frequency-domain input signals for the carrier being for a plurality of transmit layers for the carrier, respectively. The method further includes processing the two or more pluralities of frequency-domain precoded signals for the two or more carriers, respectively, in accordance with a multi-carrier processing scheme to provide a plurality of multi-carrier time-domain transmit signals for a plurality of antenna branches, respectively, of the MIMO OFDM transmitter system.