Spread-Spectrum Packet Radio Using Narrowband Headers

Abstract

Transmitting the header of a packet using narrowband signaling coupled with an associated channel access protocol such as ALOHA or carrier-sense multiple-access (CSMA), followed by the data portion of the packet as a spread-spectrum signal with a spreading sequence that is common to all nodes in the network, provides several advantages over using either narrowband or wideband techniques exclusively. For example, all network nodes can obtain channel traffic loading and destination information by examining only the narrowband headers. Wideband synchronization is facilitated by using the end of the header transmission as a time index for wideband signal acquisition. Long signature sequences minimize the probability that two or more wideband packets will be transmitted with their sequences aligned, while avoiding the requirement that each receiver search for several different sequences as in a transmitter-oriented protocol. A common signature sequence facilitates packet broadcasting and simplifies transmitter and receiver design. Flow control can be implemented by monitoring the CSMA narrowband channel and insuring that the network offered rate remains below the saturation point. Finally, adaptive interference cancellation is simplified. The analysis shows that the system has similar throughput performance to a wideband-only network provided that the headers are short compared to the total packet length. This system was granted U.S. Patent 5,022,046.