VSAT DATA-NETWORKS

Two general methods have been used to provide random access packet communications in very small-aperture (VSAT) data networks: spread spectrum (or CDMA) and ALOHA. In this paper we review the use of satellite channels for such networks and discuss certain basic aspects of the architecture of VSAT data networks. Although spread spectrum and ALOHA have different origins and are sometimes represented as competing technologies, they can in fact be characterized as different ways of viewing the same low-dimensional signals in a high-dimensional signal space. After a brief introduction to the architecture of VSAT networks we show how a simple linear transformation of conventional ALOHA packets leads to signals identical in all respects to the most common form of spread-spectrum signals. We call the result of this transformation spread ALOHA. There are two practical consequences of this theoretical result. First, for the case of small earth stations it is not possible to find an access technique with a higher throughput than spread ALOHA. Second, the use of different spreading sequences for different users in a packet network using spread spectrum is not necessary for user separation. © 1990 IEEE