A TDMA network of 5 earth stations shares a single transponder equally. The fram

Question

A TDMA network of 5 earth stations shares a single transponder equally. The frame duration is 2 ms, the preamble time per station is 20 m s, and guard bands of 5 m s are used between bursts. Transmission bursts are QPSK at 30 Mbaud. a. Calculate the number of 64-kbps voice channels that each TDMA earth station can transmit.
b. If the earth stations send data rather than digital speech, what is the transmission rate of each earth station?
c. What is the efficiency of the TDMA system expressed as Efficiency = (message bits sent)/(maximum number of possible bits that could have been sent)?

Explanation / Answer

Given,   Frame length = 2ms =2000s

               Preamble Time = 20s

               Gaurd Time = 5s

               Transmission Burst = 30Mbaud QPSK

               No. Of Earth Stations = 5

  a. No.Of voice channels can be obtained asfollows,

               2000 = (5 * 20) + (5*5) + (5*T )

               T = (2000 - 100 - 25) /5

                  = 375 s

      Thus, 60 Mbit/S ˜60bits/s

      Thus, 375 s ˜22500 bits

      We have 128 bits forsatellite channel

      Thus, no. of VoiceChannels = 22500/128 = 175

   b. Transmission Rate

       Total No. of bitstransmitted by 5 earth stations = 22500

        Transmissionrate for each station = 22500/5 = 4500

   c. Efficiency = (message bits sent) /(maximum number of possible bits that could have be sent)

                     =175 / 22500 = 0.077 %

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