03-11-2016, 12:33 PM
1463992642-MULTIPLEACCESSINGTECHNIQUES.pptx (Size: 419.38 KB / Downloads: 6)
Multiple access is the ability of a large number of earth stations simultaneously interconnect their respective voice,data,TV links through a satellite.A multiple access scheme must be able to optimize the following parameters: 1) satellite capacity2) spectrum utilization3) satellite power4) adaptability to different traffic mixes5) cost 6) user acceptability
WHY MULTIPLE ACCESS TECHNIQUES?
Allows interconnection among various earth stations through satellite.
The interconnection allows communication among various satellites.
Provides wide geography coverage capability.
These allow best utilization of satellite channel.
Multiple Access Techniques used in satellite communication are
FDMA (Frequency Division Multiple Access)
TDMA (Time Division Multiple Access)
CDMA (Code Division Multiple Access)
1) The available bandwidth is divided into frequency bands.2) Each station is allocated a band to send its data.3) Each station also uses a bandpass filter to confine the transmitter frequencies.4) To prevent station interference, the allocated bands are seperated by guard band.
1) In TDMA,the stations share the bandwidth of the channel in time.2) Each station is allocated a time slot during which it can send data.3) Each station transmits its data in its assigned time slot.
1) Different users are allocated to different codes.2) CDMA allows users to share a frequency through a special technique known as spread spectrum.3) CDMA in which each channel is assigned a unique code which is orthogonal to codes used by other users.