TABLE OF CONTENTS In satellite communication systems, as a rule, many users are active at the same time. The problem of simultaneous communications between many single or multipoint satellite users, however, can be solved by using Multiple Access (MA) technique. Since the resources of the systems such as the transmitting power and the bandwidth are limited, it is advisable to use the channels with complete charge and to create a different MA to the channel. This generates a problem of summation and separation of signals in the transmission and reception parts, respectively. Deciding this problem consists in the development of orthogonal channels of transmission in order to divide signals from various users unambiguously on the reception part. There are five the following principal forms of MA techniques:
Frequency Division Multiple Access (FDMA) is a scheme where each concerned LES or MES is assigned its own different working carrier radio frequency inside the spacecraft transponder bandwidth.
Time Division Multiple Access (TDMA) is a scheme where all concerned Earth stations use the same carrier frequency and bandwidth with time sharing, non-overlapping intervals.
Code Division Multiple Access (CDMA) is a scheme where all concerned Earth stations simultaneously share the same bandwidth and recognize the signals by various processes, such as code identification. Actually, they share the resources of both frequency and time using a set of mutually orthogonal codes, such as a Pseudorandom Noise (PN) sequence.
Space Division Multiple Access (SDMA) is a scheme where all concerned Earth stations can use the...
