Certain features relate to a remote antenna unit having a multi-stage isolation sub-system for isolating uplink and downlink signal paths. A multi-stage isolation sub-system in the remote antenna unit can include a first stage device that is configured to generate a cancellation signal for canceling unwanted downlink signals received at the uplink antenna. The isolation sub-system can also include a second stage device configured to generate a cancellation signal that attenuates residual noise and intermodulation products generated in the downlink path and received in the uplink path. The multi-stage isolation sub-system can combine the cancellation signals with signals received on the uplink path in order to cancel or attenuate downlink leakage signals and residual noise present on the uplink path.

Systems and methods are provided for adaptive equalization, for example for use with coherent optical reception. The equalizer has a loop for updating taps of an adaptive linear filter forming part of the equalizer. In the loop, an error calculator calculates an error, a gradient calculator calculates a gradient of the error or filtered error. One or more gradient filters are used to filter the gradient, and the filtered gradient is used to update the taps of the adaptive linear filter. A reduction in self oscillation in the equalizer is achieved by separating the frequencies with channel features that change with time and scaling them up to speed up convergence of the equalizer.

Systems and methods are provided for adaptive equalization, for example for use with coherent optical reception. The equalizer has a loop for updating taps of an adaptive linear filter forming part of the equalizer. In the loop, an error calculator calculates an error, a gradient calculator calculates a gradient of the error or filtered error. One or more gradient filters are used to filter the gradient, and the filtered gradient is used to update the taps of the adaptive linear filter. A reduction in self oscillation in the equalizer is achieved by separating the frequencies with channel features that change with time and scaling them up to speed up convergence of the equalizer.

Certain features relate to a remote antenna unit having a multi-stage isolation sub-system for isolating uplink and downlink signal paths. A multi-stage isolation sub-system in the remote antenna unit can include a first stage device that is configured to generate a cancellation signal for canceling unwanted downlink signals received at the uplink antenna. The isolation sub-system can also include a second stage device configured to generate a cancellation signal that attenuates residual noise and intermodulation products generated in the downlink path and received in the uplink path. The multi-stage isolation sub-system can combine the cancellation signals with signals received on the uplink path in order to cancel or attenuate downlink leakage signals and residual noise present on the uplink path.

Certain features relate to a remote antenna unit having a multi-stage isolation sub-system for isolating uplink and downlink signal paths. A multi-stage isolation sub-system in the remote antenna unit can include a first stage device that is configured to generate a cancellation signal for canceling unwanted downlink signals received at the uplink antenna. The isolation sub-system can also include a second stage device configured to generate a cancellation signal that attenuates residual noise and intermodulation products generated in the downlink path and received in the uplink path. The multi-stage isolation sub-system can combine the cancellation signals with signals received on the uplink path in order to cancel or attenuate downlink leakage signals and residual noise present on the uplink path.

Apparatuses and methods in a communication system are disclosed. A signal is received. The signal comprises demodulation reference information. The apparatus compute estimates of the channel and of interference-plus-noise vectors. The interference-plus-noise vectors are used as input for choosing a tapering matrix and for determining shrinkage target matrix and parameter. An interference plus noise covariance matrix estimator is computed and used in an equalizer, which has as input an estimate of the interference-plus-noise covariance matrix.