Carrier aggregation intermodulation distortions in Advanced Systems

Achieving greater throughput requires increasing bandwidth. However, due to frequency’s scarcity, the necessary bandwidth may not be available in one contiguous band. LTE Advanced use multiple bands for one user: that is carrier aggregation [1]. However power amplifier’s efficiency is only possible in the nonlinear mode, in which multiple bands will lead to intermodulation (IMD) distortions. The consequence can be severe desensitization of own receiver. The predistortion is one of the method used for mitigating intermodulations.

Some of the predistortion methods  follow the following steps: extract the IMD to be mitigated from the output , demodulate it, modulate it again at IMD carrier and add it (with opposite phase) to main signal before amplification [2]. There will then be cancellation between IMDs generated in the power amplifier by the main signal and those reintroduced from output. However that cancellation will be possible if those 2 IMDs has opposite phases.

In this project we analyse the consequences of carrier aggregation intermodulation distortions in LTE-Advanced and we design and implement (hardware implementation) an IMD carrier generator, which will output a linear combination of used frequency carriers.

References:

  1. Zukang Shen et al., Overview of 3GPP LTE-Advanced Carrier Aggregation for 4G Wireless  Communications, in IEEE COMMUNICATION MAGAZINE, February 2012
  2. 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
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