Standalone Omron CP1L PLC to DCS system via Ethernet connection and wireless network

Hi all,

I am currently undergoing a project in which I am required to establish a communication link between a DCS system and a standalone PLC. After careful inspection of the site, I have decided to establish this connection wirelessly. However, I am still undecided on which wireless communication protocol I should use. Could you please help me out on this?
Note: 1. The standalone PLC and the DCS network modules are approximately a distance of 200m apart.
2. Site is an industrial site and thus outdoor conditions of communication medium will have to be met (antenna/router/etc. will be exposed).
3. Efficient data transmission and receiving is crucial as the PLC controls machinery.

Your help will be very much appreciated.