ransmitting a spread-spectrum signal with the unique key for that specific radio. To all other radios this signal would appear only as Networks small additional interference since such signals are designed to combat jam- ming. Only the radio that is receiving signals with its own unique spread- spectrum carrier would receive the transmitted signal and relay it on to the next radio in the designated route. This next hop in the route is again done by transmitting a spread-spectrum signal using the key unique to this next radio. Destination and routing information is assumed to be attached to the message. It is common practice in communication networks to acknowledge the receipt of messages. The failure to receive an acknowledgment causes a retransmission of the message. In multihop networks, where messages are relayed one or more times, acknowledgments may be used for each relay (hop-by-hop), from the final destination to the source (end-to-end), or both. The above generic decentralized network might represent terrestrial dig- ital radios in a tactical battlefield environment where radios may drop out of the network due to jamming and/or direct attack. Centralized network control may make such a network system too vulnerable. Hence we have considered here a system with minimal network control and synchroniza- tion requirements. 2.1.2 Centralized (Multipoint-to-Point) Networks Military communication satellites are usually processing satellites that can despread, demodulate, decode, reformat, and route through various down- link antenna beams the uplink spread-spectrum signals from various mobile and stationary terminals [4]. Generally, such a satellite is the central node in a star network as sketched in Figure 2.6 where the satellite serves as the Figure 2.6. Star network. Multiple Access Figure 2.7. Fully connected star networks. central controller for the network. This type of radio network is the oppo- site extreme from the terrestrial radio network described in the previous section. For the star network the cen