Carrier aggregation intermodulation distortions in Advanced Systems
Achieving greater throughput in telecommunications requires increasing bandwidth. However, due to scarcity in carrier frequencies, the required bandwidth may not be available in a contiguous band. LTE Advanced uses multiple bands for one single user, which is known as carrier aggregation [1]. However, power amplifier’s efficiency can only be achieved when operated in the nonlinear mode, in which multiple bands will lead to intermodulation distortions (IMD). The consequence can be a severe desensitization of the own receiver. Predistortion is one of the methods used for mitigating intermodulations.
Some of the predistortion methods perform the following steps:
- extract the IMD to be mitigated from the output;
- demodulate it;
- modulate it again at IMD carrie;
- add it (with opposite phase) to the main signal before amplification [2]. Then be cancellation between IMDs generated in the power
- amplifier by the main signal and those reintroduced from output will be noticed. However, such cancellation will be possible only if the 2 IMDs have opposite phases.
In this project we analyse the consequences of carrier aggregation intermodulation distortions in LTE-Advanced and we design and hardware implement an IMD carrier generator, which will output a linear combination of used frequency carriers.
References:
- Zukang Shen et al., Overview of 3GPP LTE-Advanced Carrier Aggregation for 4G Wireless Communications, in IEEE COMMUNICATION MAGAZINE, February 2012
- Mahmoud Abdelaziz et al., Low-Complexity Subband Digital Predistortion for Spurious Emission Suppression in Noncontiguous Spectrum Access, in IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 64, NO. 11, november 2016