I stand corrected (one of our local PD's was recorded for the show, not live so that's why I though that)
From their wiki page:
In order to deliver live footage from the field to A&E's master control in New York City, the production uses bonded cellular technology.[12] This allows for a far less constrained and expensive production than would be possible using traditional satellite or microwave transmission technologies.[8] The bonded cellular system used on the show is designed and manufactured by AVIWEST. The system is supplied and supported by their US technology partner, VidOvation - Lake Forest, CA.