Power spectral density PSD of ASK PSK and

Power spectral density (PSD)… of ASK, PSK and FSK • Note that the bandwidth of FSK is higher than ASK or PSK. • Conclusion is that ; polar signaling is the most efficient scheme from the point of view of the noise immunity. The PSK, being polar, requires 3 d. B less power than ASK or FSK for the same noise immunity i. e. for the same error probability.

M-ary orthogonal pulses Fig. 3. 33 shows just one possible M-ary scheme (multi-amplitude signaling). There are other possible ways to structure M waveforms. For example we may use M orthogonal pulses φ1(t), φ2(t), …, φM(t), with the following property: -

M-ary orthogonal pulses Fig. 3. 34 shows one possible set of M orthogonal signals

M-ary orthogonal pulses… • Cross correlation between any two rows is zero for e. g. . Hadamard matrix 4 x 4: • 1 1 • 1 -1 • 1 1 -1 -1 • 1 -1 -1 1

More on quantization • Block diagram of formatting and transmission of baseband signals Fig. 2. 2.

More on quantization…

More on quantization… • The ordinate in fig. 2. 16 is labeled with quantization levels and their code numbers. • Each sample of the analog signal is assigned to the quantization level closest to the value of sample. • Beneath the analog waveform x(t) are seen four representations of x(t) as follows: • The natural sample values, quantized sample values, the code numbers and the PCM sequence.

More on quantization…

More on quantization… • Suppose that analog signal is a musical, which is sample at a Nyquist rate (fs ≥ 2 fm). • Also suppose that when we listen to the music in digital form, it’s quality is not good. • What could we do to improve the fidelity? • We know that process of quantization replaces the true signal with an approximation (i. e. , adds quantization noise). Thus increasing the number of levels will reduce the quantization noise.

More on quantization… • Now, each sample will be represented by 4 bits, consequently we would have high data rates, improved signal quality or fidelity. • In real time communication message must not be delayed, and bits must move faster. • This is how one can generally obtain better fidelity at the cost of more transmission bandwidth • Next Fig. 2. 18 compares the quantization of a strong versus a weak signal for uniform and

More on quantization…