Active Digital Cancellation of Transmitter Induced Modulated Spur Interference in 4G LTE Carrier Aggregation Transceivers
Sprache des Titels:
Proceedings of the Vehicular Technology Conference (VTC Spring 2016)
Mobile user equipments supporting Long Term Evolution (LTE) - carrier aggregation (CA) face several new unpredicted issues when operating in frequency division Duplex mode. This paper addresses the transmit (Tx) modulated spur problem, a new issue, that appears in LTE-CA transceivers. Due to the presence of several mixers and dividers to support different bands and CA scenarios, many harmonics are generated on the chip. Unavoidable crosstalk between these harmonics can generate an unwanted continuous wave spur around the Tx frequency. Once this spur appears at the chip area where the receive (Rx) local oscillator resides, it downconverts the undesired portion of the Tx signal which leaked through the duplexer to the Rx baseband. This interference, referred to as Tx modulated spur, causes a severe degradation of the signal-to-noise Ratio (SNR) of the wanted signal. To mitigate such, we propose an active digital cancellation architecture which utilizes the known information of the Tx signal. An equivalent baseband model of the Tx modulated spur is presented from which the digital cancellation architecture is derived. Simulations show that the proposed architecture cancels the Tx interference and improves the SNR of the wanted signal significantly.