Reference

Frequency Bands Modulation
Metric Prefixes IEEE 802 Standards
 
 

Reference : Modulation

Four "old" telecom terms (i.e. modulation, spread spectrum, multiplexing, and multiple access) are discussed here because the concepts are very important in telecom and networking, especially in the process of transmitting and receiving signals. The following paragraphs describe the terms briefly.

Modulation is a technique that puts a baseband signal on a carrier to make it feasible and more efficient for transmission and reception. The baseband signal is the message or information that will be transmitted. With modulation, the carrier is modified by the baseband signal. With demodulation, the baseband signal is taken from the modulated carrier and the modulated carrier is returned to its original form.

Spread spectrum is the spread of signal over much wider bandwidth than is needed for transmission. Spread spectrum technique is used to reduce the effect of interference.

Multiplexing is a technique that puts multiple baseband signals that come from multiple stations in one communication channel to maximize traffic-carrying capacity of the channel. Multiplexing results in more efficient use of bandwidth and faster transmission speed (higher data rate).

Multiple access is a method for accessing and sharing a communication medium by multiple stations.

The table below lists some well-known techniques used in telecom and networking. Click on each technique to see its definition.

Modulation AM, FM, PM, PCM, FSK, PSK, BPSK, QAM, QPSK
Spread Spectrum DSSS, FHSS
Multiplexing FDM, TDM, OFDM, SDM, WDM, FDD, TDD
Multiple Access TDMA, FDMA, CDMA, OFDMA, S-OFDMA, SDMA, CSMA/CD, CSMA/CA