Bandwidth Utilization: Multiplexing and Spreading Chapter 6

Bandwidth Utilization It is the wise use of available bandwidth to achieve specific goals. Categories of Bandwidth utilization: Multiplexing Spreading Multiplexing: It is used to enhance the efficiency of transmission system by combining several low bandwidth channels to make one channel with larger bandwidth. Spreading: Expansion of bandwidth used to achieve Privacy and anti-jamming.

Multiplexing Multiplexing: One Link Many Channels It is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link. Used when the bandwidth of a medium linking two devices is greater than their requirement. One Link Many Channels Link: Physical Path Channel: Portion of link, that carries a transmission.

Multiplexing At sender end, multiplexer (MUX) collects and combines the lines into a single stream (Many to One). At receiving end, demultiplexer (DEMUX) separate the stream back into the component transmission (One to many).

Multiplexing

Categories of multiplexing

1. Frequency Division Multiplexing FDM is an analog multiplexing technique that combines analog signals.

1. Frequency Division Multiplexing Frequency Division Multiplexing (FDM) It is used when the bandwidth of the link is greater than the combined bandwidth of the signals to be transmitted. In FDM, signals generated by each sending device modulate different carrier frequencies. These modulated signals are combined into a single composite signal that can be transported by a single link.

1. Frequency Division Multiplexing Channel: Bandwidth range to accommodate a modulated signal. Channels can be separated by strips of unused bandwidth (guard band) to prevent overlapping. Filters: Separate different signals from modulated signal. Modulator: Perform the function of combining carrier signals with data signals. De-modulator: Separate data signals with carrier signals.

1. Frequency Division Multiplexing (Multiplexing)

Analog Hierarchy In analog hierarchy, 12 voice channels are multiplexed onto a higher-bandwidth line to create a group. Further grouped as a super- group, master group and jumbo group.

1. Frequency Division Multiplexing (Applications) AM (530 to 1700KHz) Each channel needs 10 KHz of Bandwidth FM Radio (88 to 108 MHz) Each channel needs 200 KHz of Bandwidth Television Broadcasting Each TV channel has its own bandwidth of 6MHz First Generation Cellular Telephones Each user is assigned by two 30 KHz channels (one  sending, one  Receiving)

1. Frequency Division Multiplexing (Guard Bands) Channels can be separated by strips of unused bandwidth called as Guard Bands.

2. Wavelength Division Multiplexing Wave-Division Multiplexing [WDM] is an analog multiplexing technique to combine optical signals Optical fiber data rate is higher than the data rate of metallic transmission cable. Using a fiber-optic cable for one single line wastes the available bandwidth.

2. Wavelength Division Multiplexing

2. Wavelength Division Multiplexing Multiple light signals are combined at sender side and separated at receiver end. The combining and splitting of light source are easily handled by a prism, which bends a beam of light. Multiplexer combine different beams of light having small band and form a wider band of frequencies. Demultiplexer do the reverse job.

3. Time Division Multiplexing TDM is a digital multiplexing technique to combine data Instead of sharing a portion of the bandwidth, time is shared. Each connection occupies a portion of time in the link.

3. Time Division Multiplexing