Computer Science - Networking - Discussion

Please explain SS/TDMA?

Can any one explain this question in detail please?

Introduction:

Imagine there are three users who want to communicate with three different receivers. It's a one to one communication process. Now consider that the satellite can service only one request at a time. Thus if all three users communicate simultaneously it might create problems. To solve this problem we have a concept of multiple accessing. FDMA(Frequency division MA) TDMA(Time division MA), CDMA(Code Division MA) Space Division MA etc.
TDMA.

Each of these MA have there own merits and demerits. TDMA accessing scheme allows a user to access the entire bandwidth only for a certain period of time. Thus a single carrier frequency is shared among different users. The data is send in the form of bursts of information rather than in an continuous fashion. The frame contains Reference Bits/preamble(Guard Time+CBTR+UW+SIC) +data +Q(Postamble). Preamble contains system identification and synchronization data which is shared to a master station. Now Each user would send data in the form of burst in allocated time. Thus in this way multiple users can utilize on single career frequency . Such a type of accessing is also called MULTIPLE CHANNEL PER CARIER (MCPC).

SS/TDMA
Now in earlier times usually in 1980's the multiplicity of high-powered beams were utilized effectively. However, it increases the interconnection complexity. Using TDMA we can send data to satellite or satellite can send data to the earth station (uplink and downlink) however there is now interconnection between these two. To provide an interconnection between uplink and downlink narrow high power beams (satellite spot beams) are synced with burst transmission signal to multiple destinations by TDMA. Such systems contains onboard real time microwave switch operated in sync with TDMA. Using this technique same carrier frequency could be reused at a different geographical location without channel interference.