Improved ACLR by Cancellation Carrier Insertion in GFDM Based Cognitive Radios

Generalized Frequency Division Multiplexing (GFDM) is a recent multicarrier modulation technique with low out-of-band radiation that makes it an attractive choice for the PHY layer of cognitive radio. In orthogonal frequency division multiplexing (OFDM) the out of band leakage is around -13 dB; with raised cosine or root raised cosine pulses, the out of band leakage of a GFDM system is -35 dB. To improve the adjacent channel leakage ratio (ACLR) even further, a technique of inserting cancellation carriers is implemented. Cancellation carriers are inserted at the vicinity of interference avoidance notch and are designed such that these cancellation carriers mitigate the interference from other subcarriers to the adjacent band. With this technique the out of band leakage is lowered to around -65 dB. This stunning improvement in the GFDM adjacent channel leakage ratio satisfies stringent FCC requirements for cognitive radio transmissions in TV white space scenarios.