# Performance Comparisons of Broadband Power Line Communication Technologies
## 4 BER Comparisons and Discussion
### Simulation Results and Discussion
The required SNR to obtain \(10^{-3}\) for the BER is \(-11.7\) dB at six iterations. Next, the performance change according to the diversity number at each modulation is investigated. The BER results for the whole values of \(DV_{n}\) are shown in Figure 17, where the iteration number is set to 6. The BER performance improves as \(DV_{n}\) increases. In Figure 17a, to obtain a BER of \(10^{-3}\) in QPSK mode, an SNR of 0.3 dB is required with \(DV_{n}=2\) and an SNR of \(-3.3\) dB with \(DV_{n}=3\). Thus, an SNR improvement of 3.6 dB is obtained owing to the diversity number increasing from 2 to 3. However, the performance improvement obtained from the diversity becomes small when the diversity number becomes large. For example, when the diversity number increases from 9 to 10, an SNR improvement of 0.4 dB is obtained. The other modulations, 16 QAM and \(\pi/4\)-DQPSK, show a similar trend. Figure 17b shows the BER results for 16 QAM mode. The BER hardly decrease even with a large SNR when \(DV_{n}=1\). However, when \(DV_{n}\geq 2\), the BER decreases rapidly as the SNR increases. Without diversity, a bit may be not recovered even at a high SNR due to a deep notch in the channel,  
Figure 16: BER results for Mini DF. Figure 12:0 BER results for IoT PLC with \(\pi/4\)-DQPSK modulation: (**a**) \(DV_{n}=3\); and (**b**) \(DV_{n}=15\). but in the presence of diversity, copies of the bit can make the bit correctable. At BER=\(10^{-3}\), an SNR improvement of 2.95 dB is obtained with a \(DV_{n}\) increase from 2 to 3. When \(DV_{n}\) increases form 9 to 10, an SNR improvement of 0.31 dB is observed at BER=\(10^{-3}\). In Figure 17c, the BER results for \(\pi/4\)-DQPSK mode are shown. Comparing the BER performance of \(\pi/4\)-DQPSK mode with that of the other modes at every \(DV_{n}\), the BER performance of \(\pi/4\)-DQPSK is better than that of 16 QAM but is worse than that of QPSK. Figure 12:1 BER results of IoT PLC for the whole \(DV_{n}\): (a) QPSK mode; (b) 16 QAM mode; and (c) \(\pi/4\)-DQPSK mode. HPGP uses CTC for the FEC. Thus, iterative decoding is used as in IoT PLC. Figure 18 shows the BER results for HPGP. BER values are given at Interactions 2, 4, 6, and 8. As the iterations increase, the BER difference between iterations decreases. The block size for STD and HS modes is 2080, while the block size of MINI mode is 544. The falling slope of the BER curve in Figure 18a is less steep than those in the other modes, because the block size at the MINI mode is smaller. The STD mode makes four copies for the coded bits while HS makes two copies. Thus, the STD mode outperforms the HS mode in terms of the BER. At a BER of \(10^{-3}\), the STD mode requires an SNR of \(-5.7\) dB while the HS mode requires 1.3 dB. The MINI mode has the most copies for the coded bits, but the BER performance at high SNR is not better than the STD mode because of the small input block size. The BER results for HS PLC are shown in Figure 12:2 For the performance evaluation of HS PLC, the best and worst modes in terms of the BER are considered. The FEC in HS PLC does not use iterative decoding. Figure 19a shows the BER results for the NORMAL mode. An error floor is present and the BER does not fall below 0.02 in the NORMAL mode. There is no diversity in the NORMAL mode. In the DV mode, the BER decreases as the SNR increases due to the high diversity of 12 at the expense of the transmission rate, but the falling slope of the BER is not as rapid as that of IoT PLC or HPGP, which uses CTC for FEC. In Figure 20, the BER performance of HS PLC and HPGP are shown for comparison. The STD mode of HPGP has the best performance at BER \(=10^{-3}\), followed by the MINI mode, the DV mode of HS PLC, and the HS mode of HPGP. In terms of the BER, the NORMAL mode of HS PLC shows the worst performance. The BER curves of HPGP are steeper than those of HS PLC. Thus, the difference between the BER values of the MINI mode of HPGP and the DV mode of HS PLC becomes larger as the SNR increases.