Physical Layer

Physical Layer
The Physical layer provides for the transmission of bits through a communication channel by
defining electrical, mechanical, and procedural specifications.
Modulation, which is a Physical layer function, is a process in which the radio transceiver prepares
the digital signal within the network interface card (NIC) for transmission over the airwaves.
Spread spectrum “spreads” a signal’s power over a wider band of frequencies (see
Figure 2.4), sacrificing bandwidth in order to gain signal-to-noise performance (referred to as
process gain). This contradicts the desire to conserve frequency bandwidth, but the spreading
process makes the data signal much less susceptible to electrical noise than conventional radio modulation techniques. Other transmission and electrical noise, typically narrow in bandwidth,
will interfere with only a small portion of the spread spectrum signal, resulting in much less
interference and fewer errors when the receiver demodulates the signal.