The Second meeting of satrc working Group on Spectrum 12-13 December 2011 Colombo, Sri Lanka

OFDM is a spectrally efficient version of multi-carrier modulation where the sub-carriers are selected such that they are all orthogonal to one another over the symbol duration, thereby avoiding the need to have non overlapping sub-carrier channels to eliminate inter-carrier interference .

• Orthogonal Frequency Division Multiple Access (OFDMA)

• OFDM is a spectrally efficient version of multi-carrier modulation where the sub-carriers are selected such that they are all orthogonal to one another over the symbol duration, thereby avoiding the need to have non overlapping sub-carrier channels to eliminate inter-carrier interference .
• Guard intervals are used between OFDM symbols. By making the guard intervals larger than the expected multi-path delay spread, ISI can be completely eliminated

• The Second meeting of SATRC Working Group on Spectrum
• 12-13 December 2011 Colombo, Sri Lanka

OFDM can be used as a multi-access scheme, where the available sub-carriers may be divided into several groups of sub-carriers called sub-channels. Different sub channels may be allocated to different users as a multiple access mechanism. This type of multi access scheme is called OFDMA.

• Orthogonal Frequency Division Multiple Access (OFDMA)

• OFDM can be used as a multi-access scheme, where the available sub-carriers may be divided into several groups of sub-carriers called sub-channels. Different sub channels may be allocated to different users as a multiple access mechanism. This type of multi access scheme is called OFDMA.
• OFDMA is essentially a hybrid of FDMA and TDMA. Users are dynamically assigned sub-carriers (FDMA) in different time slots (TDMA).
• OFDMA is a flexible multiple access technique that can accommodate many users with widely varying applications, data rates and QoS requirements.

• The Second meeting of SATRC Working Group on Spectrum
• 12-13 December 2011 Colombo, Sri Lanka