This document discusses different types of modulation techniques for carrier signals. It describes modulation as altering properties of carrier signals, including amplitude, frequency, and phase. It then explains three spread spectrum techniques: Frequency Hopping Spread Spectrum (FHSS), Direct Sequence Spread Spectrum (DSSS), and Orthogonal Frequency Division Multiplexing (OFDM). It provides details on how each technique works and compares their strengths, such as resistance to interference, and weaknesses, such as limited data rates or sensitivity to synchronization issues.

1. Justin Andrews
ACSG 525
Carrier signals are waveforms that have been modulated in some way in order to convey information,
whether to transmit information through electromagnetic waves or allow for several carriers at varying
frequencies to share a common physical transmission medium.
Modulation is a process that alters one or more properties of carrier signals. It can be done in three
specific ways: amplitude modulation, frequency modulation, and phase modulation, which alter the
volume, pitch, and timing of a given waveform.
Frequency Hopping Spread Spectrum (FHSS) is a method for transmitting radio signals, done by rapidly
switching a carrier across many different channels. Depending on how it’s used, it can result in a heavy
resistance to deliberate jamming and have also been used to create a specific kind of walkie-talkie that
employs such technology. OFDM itself has benefits due to its ability to cope with severe channel
conditions.
Direct Sequence Spread Spectrum (DSSS) is another technique that uses the full bandwidth of a given
device’s transmitting frequency, with carrier signals.It’s seen use with IEEE and radio-controlled vehicles,
for example.
Orthogonal Frequency Division Multiplexing (OFDM) is a method of encoding data on multiple
frequencies. It can work with various kinds of digit communications, with just digital television and 4G
mobiles being a couple of examples. It’s also used as a digital multi-carrier modulation method, just like
the other two techniques.
FHSS itself is known for being highly resistant to noise, with signals that are difficult to intercept. It does
have a limited data rate, however. DSSS on the other hand is very flexible in regards to data rates, with
higher capacities possible. It can be compared to FHSS as well with its resistance to outside factors. DSSS
has its own issue though, with a near-far effect.OFDM has a high spectral efficiency in comparison to
other means of modulation, along with efficient implementation. OFDM drawbacks include sensitivity to
frequency synchronization problems and a Doppler shift.