Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. It is common to integrate multiple radios into a single communication system. For example, smartphones may have radios to support cellular communication, WiFi, GPS, and Bluetooth®, etc., with each radio operating on a different frequency band. Even for systems that have just a single radio, the radio may be a frequency division duplex (FDD) system in which the transmit (Tx) and receive (Rx) links simultaneously operate on different frequency bands. In these systems, the strongest interference on an Rx signal of a victim receiver may be induced by self-jamming leakage of Tx signals that are simultaneously transmitted by one or more aggressor transmitters of the systems. The Tx signals may leak to the Rx path through the finite isolation between the Tx and Rx paths. For example, in a system containing a 3GPP Long Term Evolution (LTE) radio and a WiFi radio, non-linearities present in the transmitter chain, such as in an up-converter or a power amplifier (PA) of the LTE transmitter, may generate spectral re-growth that falls in the Rx frequency band of the WiFi receiver as a leakage signal. Even when the Tx leakage signal occupies a different frequency band from the Rx signal, the Tx leakage signal may cause co-channel interference on the intended Rx signal due to non-linearities in the Rx chain. For example, non-linear behavior in the radio frequency (RF) down conversion components, such as non-linear excitation of low noise amplifiers (LNA), mixers, switches, filters, data converters, etc., operating on the Tx leakage signal may generate interference in the Rx frequency band. The effects of the self-jamming interference due to the non-linearities of the Tx or the Rx chains are degradation in the performance of the communication systems.
In a communication system affected by self-jamming interference, the Tx waveforms that generate the interference may be determined. Hence, the communication system may reconstruct the interference component of the Rx signal at the victim Rx chain via an adaptive non-linear interference cancellation (NLIC) scheme. For example, an NLIC module may generate, based on the baseband Tx signal of an aggressor transmitter, an estimate of the interference in the baseband Rx signal at a victim receiver due to the Tx/Rx non-linearities. The Rx chain may remove the estimated interference from the baseband Rx signal to cancel or to mitigate the interference.
Often, there may be self-jamming interference signals from multiple aggressor transmitters. For example, a multiple-input multiple-output (MIMO) LTE transceiver may transmit Tx signals on the same frequency from multiple antennas. Each of the antennas may generate an interference signal of different power to a victim receiver, such as a Wireless Local Area Network (WLAN) receiver. Another scenario for multiple self-jamming interference may occur in an LTE transceiver that uses uplink carrier aggregation, where different carriers of the uplink Tx bandwidth may generate multiple interference signals that are different harmonics of the carriers. For example, a third harmonic from a first carrier and a second harmonic from a second carrier may overlap with the Rx signal of a WLAN receiver. Multiple self-jamming interference signals may also be found in simultaneous transmissions from a Global System for Mobile (GSM) transceiver and an LTE transceiver of a smartphone, where the multiple interference signals on the victim receiver may be generated by different mechanisms. In these systems, the NLIC module of the victim receiver may attempt to reconstruct the interference component of the Rx signal by estimating an aggregate sum of the multiple interference signals from multiple Tx signals. However, estimating the sum of the multiple interference signals may become complex when the multiple interference signals are generated by different mechanisms and may be of different power. In addition, it may be difficult to scale such implementation as the number of interference signals changes. As such, there is a need for an NLIC solution that is simpler, scalable, and more robust when there are multiple aggressor transmitters.
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