The brainwave control is not suddenly emerged, but it has been established for a long time, and the new methodology is always invented and added.
The research of EEG started from the wired electrode, hence the brainwave control should be originated from the wired technology. It intrinsically elucidates the brain disorder by the wave pattern, which is advanced to cure its disease by irradiation, though dramatically evolved to cause the disorder in the brain. The EEG and biofeedback have been continued as the treatment in public, though its malfunction and misuse was concealed at some point, because it was classified by the US government, which also indicates this technology is too dangerous to be publicly available.
The brain control was openly discussed and reported initially, though disappeared in 1980s, implying there was highly likely a fundamental breakthrough in 1970s, to establish the technology to cause the disorder in the brain. It was started from the wired but evolved to the wireless, which also highly likely occurred in 1970s. The wired electrode even has a distance, hence the wireless is not far away to be progressed. Looking back the history, the wired electrode was also evolved from the plugin to the skull, onto the shaved skull, eventually to the multiple electrodes on the head. In the current technology, the brainwave can be read and sent by the system similar to the headset.
All in all, the distance is not a problem, especially to send the electromagnetic wave to the brain. The transmitting antenna is an issue to this matter, as the very low frequency requires a long antenna to send. As well known, that kind of antenna has been a huge structure, though the long antenna is not necessarily straight, hence the modern machine is not always enormous. The sufficient length can be achieved by winding.