Data Transmission and Multiplexing Techniques
Data Transmission Methods
Synchronization
Asynchronous Transmission: The issuer informs the receiver about the transmission instants. The receiver interprets the asynchronous information.
Synchronous Transmission: Transmission occurs at a constant cadence without needing character discrimination. This method aims to modulate the signal and adapt it to the channel, utilizing frequencies with the best channel response.
Modulation Techniques
Amplitude Modulation (AM): Modifies the wave’s amplitude (height) to encode digital signals. A maximum amplitude represents bit 1, and a minimum amplitude represents bit 0.
Frequency Modulation (FM): Modifies the wave’s frequency (number of waves in a given time) to encode digital signals. A maximum frequency represents bit 1, and a minimum frequency represents bit 0.
Phase Modulation (PM): Uses variations in the wave’s phase (direction) to encode the digital signal. Bit 0 is encoded with the initial phase, and bit 1 with the inverse phase.
Cabling
Unshielded Twisted Pair (UTP) Cable: A twisted pair cable without external metallic shielding, making it susceptible to interference. However, the twisting compensates for electromagnetic induction.
Shielded Twisted Pair (STP) Cable: Similar to UTP but with added metallic shielding to reduce external interference. Offers better protection against interference and allows for longer data lines.
Coaxial Cable: Available in thin and thick variations. Suitable for most installations due to its flexibility and ease of installation. Can transmit signals over long distances before attenuation becomes significant.
Multiplexing
Multiplexing allows a single channel to carry signals from different sources to different receivers.
Frequency Division Multiplexing (FDM): Each signal is assigned a specific frequency band within the spectrum.
Time Division Multiplexing (TDM): Logical channels are allocated specific time slots on the physical channel.