Results

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Figure 31 shows the BER. The two curves with BER values between 10-4 and 0.5 is the results when using AWGN only. The three flat curves with BER at about 10-4 to 10-5 is the results when using burst noise only.Up to a SNR at about 5-10 dB, the BER is affected mainly by AWGN. When the SNR increases, the BER starts to depend on burst noise only. The BER function has now reached the saturation area where the BER almost doesn’t decrease anything when the SNR is increased. When the signal amplitude starts to get higher than the burst amplitude, as we increase the SNR further, the curves again starts to decrease rapidly.

Bit error rate function for AWGN and burst errors
Figure 31 - Bit error rate function for AWGN and burst errors.

Figure 32 shows the CLR. As in Figure 31, the two curves at higher CLR is when adding AWGN only and the three flatter curves at lower CLR is when adding burst noise only.

Cell loss function for AWGN and burst errors
Figure 32 - Cell loss function for AWGN and burst errors.

The flatter curves show that the CLR for IB transmission (ATM over MPEG) is lower (about 4-6 times) than the CLR for OOB transmission (ESF) at 3.088 Mbps and higher (about 1.5-2 times) than the CLR for OOB transmission at 41.712 Mbps, when only burst noise is added to the channel.

As can be seen in Figure 32, the CLR at 41.712 Mbps is lower for OOB transmission than IB transmission. This is because there are about 3.5 ATM cells in each RS coded MPEG2-TS packet and each one of the ATM cells in the ESF is RS coded separately. If one Reed-Solomon coded MPEG2-TS packet can’t be corrected, all 3.5 ATM cells are lost, while if one Reed-Solomon coded ATM cell in the ESF can’t be corrected, only that ATM cell is lost.

The CLR for OOB transmission starts to decrease rapidly at about 15 dB less SNR than the CLR for IB transmission. This is due to the lower SNR needed for QPSK than for 64-QAM to achieve the same CLR (or BER).

Table 3 shows the approximate SNR and CLR at the different breakpoints where the plots of the curves start to decrease significantly.

SNR at breakpoint CLR at breakpoint
ATM (AWGN): 5 dB 10
ATM over MPEG (AWGN): 16 dB 3.5
ATM (Burst, 3.088 Mbps): 43 dB 10-3
ATM (Burst, 41.712 Mbps) 42 dB 2*10-4
ATM over MPEG (Burst): 59 dB 1.5*10-4

Table 3 - SNR and CLR at different breakpoints for the four curves.