Question

I have a doubt regarding time division multipluxing.
In GSM we are using time division multiplexing.
In time division multiplxing, there is timeslots foreach signel. But while using GSM mobiles, we are getting a continues flow of data, but actually we are not transmitting it continuesly rite??

How do we get continues signal even if transmission is done using TDM.

Answer 1

The simple answer is that you’re not receiving a continuous flow of data. What you are receiving is short bursts of data close enough together that they seem to form a continuous stream.

In case you care, the specific numbers for GSM are that it starts with 4.615 ms frames, each of which is divided into 8 timeslots of .577 ms. So, a particular mobile handset receives data for .577 ms, then waits for ~4 ms, then receives data for another .577 ms, and so on. There’s a delay of 3 time slots between receiving and transmitting, so it receives data, then ~1.8 ms later, it gets to transmit for .577 ms.

The timing is close enough together that even if (for example) the signal gets weak and/or there’s interference for a few ms, and a particular hand-set misses receiving data for one time slot won’t necessarily be audible. When the signal is lost for about 20 ms, most people can start to perceive it as actual signal loss. Losses shorter than that will result in lower sound fidelity, but not necessarily as actual loss of signal.

It’s also worth noting that most of the newer (3G, 4G, LTE) systems work entirely differently, being based on CDMA instead of TDMA.