Multiple Access
Technique
- To Transmit a signal from one
user to another, the information must be sent over a channel that is
possibly shared with many others users simultaneously transmitting their
own signals.
- A key issue therefore regards
ways in which this communication channel is partitioned among the various
users such that each receiver is able to accurately recover the signal the
sender intended to transmit.
- There is a need for techniques
that allow the multiple users to share the same frequency especially as
wireless telecommunication continues to increase in popularity.
Currently three types of schemes are used
- Time division Multiple Access (
TDMA)
- Frequency division Multiple
Access (FDMA)
- Code division Multiple Access (
CDMA)
Time division Multiple Access (TDMA):
Time Division Multiple Access is a channel access method for
shared medium networks. It allows several users to share the same frequency
channel by dividing the signals into different time slots. The users transmit
in rapid succession, one after the others, each using his own time slots . this
allows multiple station to share the same transmission medium while using only
the part of its bandwidth they require.
In other words in TDMA system, each user uses the whole channel
bandwidth for a fraction of time.
TDMA is a type of time division multiplexing, with the special
point that instead of having one transmitter connected to one receiver, there
are multiple transmitters.
·
Non-continuous transmission
makes handoff simpler.
·
Slots assigned
cyclically can be assigned on demand in dynamic TDMA.
·
Less stringent power
control than CDMA due to reduced intra cell interference.
·
Cell breathing is more
complicated. • Complex frequency/slot allocation.
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