The Chinese ground forces (army and naval infantry) have been practicing the use of electronic jamming of enemy communications. This was an old Soviet tactic, which led to the development of frequency hopping radios in the West. The Chinese jammers appear to only work against older (non hopping) radios. Thus, if the Chinese are training to fight someone equipped with that older equipment, who could the enemy be? North Korea? Then again, there are jammers that can interfere with frequency hopping radios. These are pretty high tech items, and it would appear that China might now have such equipment, and is testing it in simulated combat conditions.