In electronics, modulation can be defined as that process of varying different properties of the carrier signal, usually a high frequency periodic waveform, with respect to a modulating signal. In telecommunications, modulation is the process of transmitting a message signal such as an analogue signal or a digital bit steam together with another physically transmittable signal. A baseband message signal is transformed into a passband signal by modulation of a sine waveform.
An example of a passband signal is a radio-frequency (RF) signal. Modulating a sine wave carrier makes it possible to keep the frequency content of the transmitted signal close to the center frequency. This paper is going to compare and contrast Pulse Code Modulation, Pulse Amplitude Modulation, and Signal Code Modulation signals coding techniques and determine which of the three achieves the most optimum transmission and also look at their advantages and disadvantages. Discussion
Pulse Code Modulation is the digital version of an analog signal where the signal’s magnitude is regularly sampled at uniform intervals, then quantized to a series of symbols in a binary code. Pulse Code Modulation has been widely applied electrical musical keyboards in the 1980s-era and in digital telephone systems. Additionally, it is also the standard form for compact disk ‘red book’ format and digital audio in computers. However, it cannot be typically used for video in standard definition because of its lower bit rate.
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Additionally, an irreversible error commonly known as quantization error is introduced by quantization (Pohlmann, 2005).
Pulse Amplitude Modulation (PAM), a modulation signal technique where the message signal is encoded in the amplitude of a string of signal pulses. Pulse amplitude modulation is widely applied in baseband transmission of digital signals, with non-baseband application having chiefly surpassed by pulse code modulation. PAM is also widely used applied is some versions of the famous Ethernet communication standard.
To be precise, the fast Ethernet 100BASE-T2, which runs at 100Megabits per second, uses five level PAM modulation running at 25 megapulses per second over two pairs of wire. A sophisticated technique is utilized to prevent inter-symbol interference between the unshielded pairs. However, the amplitude of PAM signals variation depends on modulated signal, hence noise interference is maximum and it cannot be easily removed and another disadvantage is that the peak power required by the transmitter varies as a result of variation in PAM signals.
Signal Code Modulation is a technique that is based on the idea of representing analog signal by a quantized component, and san analog signal comprising of quantization error. Both components are transmitted by the communication channel and utilized to reconstruct an approximate of the signal at the receiver. The availability of analog residual permits the performance of the system to improve when excess channel signal to noise ratio is available. The digital component provides a gain in signal to noise ratio and makes it possible to achieve near error free transmission (Waggener, 2002).
Of the three coding techniques, Signal code modulation achieves the most optimum transmission. This is because of its ability to vary the data rate according to available signal to noise ratio, which helps it retransmit a digital communication signal over channels with varying signal to noise ratios, without complete re-modulation and demodulation. The technique is also able to trade off bandwidth for signal to noise ratio, in a special way, and achieves performance close to that of traditional Demod/Remod techniques.
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Conclusion Various modulation signals coding technique have been discussed within the paper. Pulse code modulation, pulse amplitude modulation and signal code modulation have been compared and contrasted and came to a consensus that signal code modulation achieves the most optimum transmission. References Pohlmann, K: (2005).
Principles of Digital Audio: Carmel, Indiana: Sams/Prentice-Hall Computer Publishing. Waggener, B: (2002).
Pulse Code Modulation Systems Design: Boston, MA: Artech House.
