無線通信的多接技術 - 劃時多接

• TDMA (Time Division Multiple Access)

EXAMPLE:

Consider The Previous GSM TDMA/FDD GSM system. If 8 voice channels are supported on a single radio

channel, find the number of simultaneous users that can be accommodated in GSM.

SOLUTION:

N=(25x1000-2x100)/200x8=992, and N=(25x1000)/200x8=1000 for no guardband.

Preamble

Information Message

Trail Bits

Slot #1

Slot #2

Slot #3

Slot #N

Trail Bits

Information Data

Guard Period

Sync. Bits

TDMA Frame Structure

N=m(Bt-2Bg)/Bc

N: Number of Channels.

m: Maximum number of TDMA users per each radio channel.

Bt:Total Spectrum Allocation.

Bg:Guard Band.

Bc:Channel Bandwidth.

One TDMA Frame : Tf

Efficiency of TDMA:=(1-bOH/ bT)x100%.

bOH : The number of overhead bits per frame.

bT : The total number of bits per frame(=TfR),

where Tf is the frame duration and R is the

channel bit rate.

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