Frequency division multiple access

Frequency division multiple access (FDMA) A multiplexing method whereby each channel is assigned... 

The functional diagram in Fig. 16.67 is appropriate to a satellite using frequency-division duplex (FDD), which refers to the fact that the satellites use separate frequency bands for the uplink and downlink and where both finks operate simultaneously. This diagram also illustrates a particular multiple access technique, known as frequency-division multiple access (FDMA), which has been prevalent in mature satellite systems. 

Frequency-division multiple access has been the most prevalent access for satellite systems untQ recently. Individual users being assigned a particular frequency band may communicate at any time. SateUite filters subdivide a broad frequencyband into a number of transponder channels, for example, the 500-MHz upHnk ESS band from 5.925 to 6.425 GHz maybe divided into 12 transponder channels of 36-MHz bandwidth plus guard bands. This Emits the interference among adjacent channels in the corresponding downhnk band of 3.7. 2 GHz. 

When the generator is first turned on the F/F must be set to predetermined states. For a BSR this may be any set of values agreed upon by the transmitter and receiver, except the all 0 state. A BSR initiated to all Os will stay in that state forever. This set of initial values, along with the real-world time at which the generator is set to this state, is known as the PN generator key. Two identical SS systems (same carrier frequency, same modulation format) can share a common channel by simply using different keys. This format is called code division multiple access (CDMA) and is becoming popular in a variety of new communication systems. 

Code division multiple access (CDMA) A multiplexing technique where the signal intelligence is mixed with a randomlike code and then spread over a wide range of frequencies. 

In Europe, digital cellular telephony is more cohesive and advanced. GSM uses both time division multiple access (TDMA) and FDMA to carry digital data (Figures 2, 3a). TDMA allows multiple users to share a channel frequency by time-slotting them in sequence. GSM uses an SHA authentication procedure and a 64-bit symmetrical stream cipher. A US counterpart to GSM, called IS-54, operates at a lower bit rate and narrower channel width. GSM/IS-54 operates at 900 MHz, and other GSM-like cordless standards use... 

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