non-orthogonal multiple access (NOMA)
Non-Orthogonal Multiple Access (NOMA) is a future concept for multiple radio access to be used in 5th generation(5G) mobile networks. It differs from the method used in Long Term Evolution( LTE).
The NOMA method aims to improve spectral efficiency in the existing frequency bands and incorporates transmit and receive power and deliberately generates non-orthogonalities via radio signal levels in time division multiplex, frequency division multip lex and code division multiplex from different user signals.
In the NOMA method, the signals from multiple users are superimposed, although the underlying waveform may be based on Orthogonal Frequency Division Multiple Access( OFDMA) or on a Discrete Fourier Transform( DFT) of OFDM. The user signals are separated at the transmitter end via the power domain, where the individual user signals are transmitted with large differences in signal levels. To increase the transmission capacity and data rate, two methods are used on the receive side: Successive Interference Cancellation (SIC) and Maximum Likelyhood Detection (MLD). The SIC method extracts the user signals based on the different signal levels. Level losses and degradations in the signal-to- noise ratio are compensated by gain components.
The NOMA method supports more connections than other radio methods and is therefore of particular interest for the 5th generation of mobile networks.