14-07-2012, 04:31 PM
Orthogonal Frequency Division Multiple Access(OFDMA) For 4G
OFDMA for 4G.ppt (Size: 4.24 MB / Downloads: 52)
Non-contention-based Multiple Access (MA)
A logic controller (BS or AP) is needed to coordinate the transmissions of all the terminals
The controller informs each device when and on which channel it can transmit
Collisions can be avoided entirely
Two Subdivisions
Code Division Multiple Access (CDMA)
IS-95
Orthogonal Walsh codes
64 codes (channels)
One pilot channel
Seven paging channels
55 traffic channels
Each carrier 1.25 MHz
Frequency Division Multiple Access (FDMA)
American Mobile Phone System (AMPS)
Total Bandwidth 25 MHz
Each Channel 30 KHz
Orthogonal frequency-division multiplexing (OFDM)
It is a method of encoding digital data on multiple carrier frequencies.
OFDM has developed for wideband digital communication, whether wireless or over copper wires
A large number of closely spaced orthogonal sub-carrier signals are used to carry data.
The data is divided into several parallel data streams or channels, one for each sub-carrier.
Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase-shift keying) at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.
Receiver(OFDM)
This returns parallel streams, each of which is converted to a binary stream using an appropriate symbol detector. These streams are then re-combined into a serial stream, , which is an estimate of the original binary stream at the transmitter.
OFDMA for 4G.ppt (Size: 4.24 MB / Downloads: 52)
Non-contention-based Multiple Access (MA)
A logic controller (BS or AP) is needed to coordinate the transmissions of all the terminals
The controller informs each device when and on which channel it can transmit
Collisions can be avoided entirely
Two Subdivisions
Code Division Multiple Access (CDMA)
IS-95
Orthogonal Walsh codes
64 codes (channels)
One pilot channel
Seven paging channels
55 traffic channels
Each carrier 1.25 MHz
Frequency Division Multiple Access (FDMA)
American Mobile Phone System (AMPS)
Total Bandwidth 25 MHz
Each Channel 30 KHz
Orthogonal frequency-division multiplexing (OFDM)
It is a method of encoding digital data on multiple carrier frequencies.
OFDM has developed for wideband digital communication, whether wireless or over copper wires
A large number of closely spaced orthogonal sub-carrier signals are used to carry data.
The data is divided into several parallel data streams or channels, one for each sub-carrier.
Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase-shift keying) at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.
Receiver(OFDM)
This returns parallel streams, each of which is converted to a binary stream using an appropriate symbol detector. These streams are then re-combined into a serial stream, , which is an estimate of the original binary stream at the transmitter.