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:

  1. extract the IMD to be mitigated from the output;
  2. demodulate it;
  3. modulate it again at IMD carrie;
  4. add it (with opposite phase) to the main signal before amplification [2]. Then be cancellation between IMDs generated in the power
  5. 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:

  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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