Common Myths and Misconceptions Regarding Communication Systems

While there have been great strides forward in the recent past in the field of communication systems and signal processing, it has been difficult for engineers, scientists and academicians to cope up with the vast array of technical advances. In this paper, we show that there are certain basic misconceptions and myths surrounding communication systems such as Orthogonal Frequency Division Multiplexing (OFDM). These myths include incorrect notions such as a) cyclic prefix (CP)OFDM has the same subcarrier bandwidth and orthogonality of subcarriers as OFDM without CP, and b) subcarrier bandwidth in OFDM is same as the subcarrier spacing, which is the inverse of the OFDM symbol duration. We also show that even in such a basic field as bit-error rate (BER) vs signal to noise ratio (SNR) performance evaluation of communication systems, there exist many misconceptions such as a) noise power at the output of a root-raised-cosine (RRC) filter varies when the rolloff factor is changed - it increases with an increase in the rolloff factor, b) probability of bit-error in case of uncoded BPSK is given in terms of SNR by the expression Q(sqrt(2SNR)), and c) the relationship between $\mathrm{E}_{s} / \mathrm{N}_{0}$ (energy per symbol to noise power spectral density ratio) and SNR depends on the number of samples per symbol (i.e., the oversampling factor). Many popular websites such as Keysight webpages and Mathworks online documentation pages are shown to contain wrong information that serves to accentuate these misconceptions and myths.