We are replacing a "RF modem + Router system" with a Software Defined Receiver. After analyzing the receiving and sent signals we found out that an IPv4 UDP packets have been sent and received. The packets have a source IP like: 188.8.131.52 and the destination IP changes (its sometimes 184.108.40.206 and sometimes broadcast 220.127.116.11) Now the "Software Defined Receiver" is placed inside a PC. As we don't have a router anymore how can we send the obtained IP packets to the destination IP's or broadcast?
You don't need a router if the traffic is sent to IP's within the same subnet. As long as the subnet mask is the same for all hosts in the network they will listen to the broadcast IP and will respond to ARP requests.
You don't need a router to move traffic within the same subnet, that's all layer 2 transport with MAC addresses resolved with ARP.
There are software routers out there-- you could also use a small Linux VM to act as a basic router. You can check out a tutorial here.