An introduction to spread spectrum

M ODERN military communications systems are , increasingly adopting the digital method of transmitting information. In a digital communications (or data) link, the information to be sent is represented by a sequence of electronic pulses. In the simplest form of digital signal transmission, these pulses are referred to as binary digits, or “bits.” Each pulse, or bit, is the smallest amount of data that can be communicated, and the messages to be sent ‘are composed of larger sets of these bits. The manner in which message information is imparted to the data bits is the subject of information modulation, a topic well covered in most basic texts on communications.” The subject addressed here is the reliable detection, at the communications receiver, of the individual bits when interference is present, so that the information carried by the sequence of data bits can be recovered. The time duration of a data bit implies a minimum bandwidth capability for the communications link. Thus, it is important to understand the basic concept of bandwidth involved in any criteria for reliable reception.