05-07-2012, 11:36 AM
OFDM Basics
OFDM Basics.docx (Size: 104.82 KB / Downloads: 84)
OFDM stands for Orthogonal Frequency Division Multiplexing. OFDM is a technique that allows a base station to split a chunk of radio spectrum into sub-channels. The signal strength of the sub-channels and the number of channels assigned to different devices can be varied as needed. OFDM allows high data rates, even far from a base station, and it copes well with the type of radio interference that is common in urban areas, where signals reflect off walls to produce confusing echoes.
This is a method to transmit data using a large number of carriers that are separated on different frequencies to carry one data stream which has been broken up into many signals.
Speeds that are lower are easier to detect. It was discovered that by using multiple subcarriers the receiver could detect signals easier in environments with interference. Subcarriers transmit a lower speed signal which is converted by to its original high-speed signal at the other end. The subcarriers for OFDM are modulated by several methods including QAM and QPSK.
The basic principle of OFDM is to split a high-rate datastream into a number of lower rate streams that are transmitted simultaneously over a number of subcarriers. Because the symbol duration increases for lower rate parallel subcarriers, the relative amount of dispersion in time caused by multipath delay spread is decreased. Intersymbol interference is eliminated almost completely by introducing a guard time in every OFDM symbol. In the guard time, the symbol is cyclically extended to avoid intercarrier interference.
What is OFDM?
• Orthogonal FDM – it’s multiplexing
• It’s more: – Multi Carrier – Digital modulation (PSK, QAM) – Digital processing
• Demultiplexing
In a conventional serial data system, the symbols are transmitted sequentially, with the frequency spectrum of each data symbol allowed to occupy the entire available bandwidth. A When the data rate is sufficient high, several adjacent symbols may be completely distorted over frequency selective fading or multipath delay spread channel.
OFDM Basics.docx (Size: 104.82 KB / Downloads: 84)
OFDM stands for Orthogonal Frequency Division Multiplexing. OFDM is a technique that allows a base station to split a chunk of radio spectrum into sub-channels. The signal strength of the sub-channels and the number of channels assigned to different devices can be varied as needed. OFDM allows high data rates, even far from a base station, and it copes well with the type of radio interference that is common in urban areas, where signals reflect off walls to produce confusing echoes.
This is a method to transmit data using a large number of carriers that are separated on different frequencies to carry one data stream which has been broken up into many signals.
Speeds that are lower are easier to detect. It was discovered that by using multiple subcarriers the receiver could detect signals easier in environments with interference. Subcarriers transmit a lower speed signal which is converted by to its original high-speed signal at the other end. The subcarriers for OFDM are modulated by several methods including QAM and QPSK.
The basic principle of OFDM is to split a high-rate datastream into a number of lower rate streams that are transmitted simultaneously over a number of subcarriers. Because the symbol duration increases for lower rate parallel subcarriers, the relative amount of dispersion in time caused by multipath delay spread is decreased. Intersymbol interference is eliminated almost completely by introducing a guard time in every OFDM symbol. In the guard time, the symbol is cyclically extended to avoid intercarrier interference.
What is OFDM?
• Orthogonal FDM – it’s multiplexing
• It’s more: – Multi Carrier – Digital modulation (PSK, QAM) – Digital processing
• Demultiplexing
In a conventional serial data system, the symbols are transmitted sequentially, with the frequency spectrum of each data symbol allowed to occupy the entire available bandwidth. A When the data rate is sufficient high, several adjacent symbols may be completely distorted over frequency selective fading or multipath delay spread channel.