QAM constellation coder - transmitting a file The file with size 6 MB is transmitted in 100 seconds using a constellation coder QAM with a constellation of 6 bit/symbol 

$ { M = 10^6, B = 8} $

Tasks:

1. What is the signal bandwidth if the band exceedance factor is 0.5?

$W_m = (1+α)R_s$ 

$W_m = (1+0.5)*80 000 = 120k$ 

2. What is the signal sampling frequency at the modulator output if the oversampling ratio equals 3.

$ T_S = 6*0.0000020833 = 0.0000125 $

$ n = T_s / T_p $

$ 3 = 0.0000125 / T_p  = 0.00000416666 = 4.17 µs$

$ F_p = 1/T_s =&gt; F_p = 239808.15 Hz = 240 kHz  $

3. How numerous is the set of symbols of the constellation used?

$ M = 2^k $

$ k = 6 $

$ M = 2^6 = 64 $

4. What is the modulation performance?

$ R_b / W_m = 480k / 120k = 4 $

5. How long will the signal transmission last if the band exceedance factor is 1.

And this is the only task I have no idea how to do. Any suggestions?

I would also be very grateful I you check the other tasks, if they were done correctly, or if I made any mistakes. Thank you in advance!
Since the bandwidth stays constant at 120 kHz, the symbol rate needs to be reduced: $$R_s = W_m/(1+\alpha) = 120000/2 = 60000 \text{ symbols per second.}$$

Then the bit rate is $R_b = 6R_s=360,000 \text{ bits per second.}$

The transmission duration is then $$T = \frac{48 \times 10^6 \text{ b}}{360 \times 10^3 \text{ b/s}} = 133.3 \text {s}.$$