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WiMAX system adjust the signal modulation and coding scheme on the basis of Signal to Noise ratio (SINR) condition of the radio link. When the radio link quality is high the highest modulation sceme and light coding is used giving the system more capacity. During a signal fade or long signal path the wiMAX system can shift to a lower order modulation sceme with heavier coding to maintain the connection quality and link stability.
So we have SNR = 22 dB the modulation is 64 QAM
SNR= 16 dB modulation 16 QAM
SNR= 9 dB modulation QPSK and
SNR = 6 dB modulation BPSK
The IEEE 802.16 standard speaks about this also
you can find various papers in this forum itself.......
Try to search for Adaptive Modulation for the conceptual understanding.
Yes, for uplink SNR the Base station calculates SNR by received power while for downlink the subscriber station calculates and sends the requirement of its particular suitable burst profile....
Typical calculation can be --------
If Pr is received power in dBm then.
SNR(dB) = Pr(dBm) – No(dBm)
Where No (dBm) is the noise power in dBm, Assume, the carrier bandwidth is B, the receiver noise figure is F, the spectral efficiency is rb/B and the coding gain Gc
Then the SNR for coded modulation with data rate rb can be obtained by
SNR (dB)= 10 log[(Pr/No)x(rb/B)] -Gc
Where No (dBm) = -174(dBm) + 10 log B + F (dB)
Where Gc is normally considered as 5dB.
Actually WiMax uses the technique of OFDM in which we have the Orthogonal frequencies to modulate oure data. Thats changes the technique of modulation in WiMAx
If you have a frame with 30 symbols duration i think that the modulation scheme remains the same for all the symbols because logically and if we examine the OSI Model , frame will take delimitor in second layer (link)whereas the modulation will be in physical layer.
Added after 46 seconds:
Hi
If you have a frame with 30 symbols duration i think that the modulation scheme remains the same for all the symbols because logically and if we examine the OSI Model , frame will take delimitor in second layer (link)whereas the modulation will be in physical layer.
Added after 1 hours 47 minutes:
Hi
If you have a frame with 30 symbols duration i think that the modulation scheme remains the same for all the symbols because logically and if we examine the OSI Model , frame will take delimitor in second layer (link)whereas the modulation will be in physical layer.
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