What is NOMA: Non-Orthogonal Multiple Access
NOMA, Non-Orthogonal Multiple Access, that uses the power domain to separate signals from each other. NOMA gives a new dimension in which signals can be separated and given access to a base station.
NOMA is an additional form for providing a multi-user access scheme.
NOMA uses the power domain to separate signals, a technique that has not been used within 2G, 3G or 4G before.
What is NOMA?
The key to NOMA, non-orthogonal multiple access is to have signals that possess significant differences in power levels. It is then possible to totally isolate the high level signal at the receiver and then cancel it out to leave only the low level signal. In this way, NOMA exploits the path loss differences amongst users, although it does need additional processing power in the receiver.
Looking at NOMA in a little more detail, non-orthogonality is intentionally introduced either in time, frequency or code.Then as the signal is received demultiplexing is obtained as a result of the large power difference between the two users. To extract the signal, successive interference cancellation is used within the receiver. The channel gain consisting of elements including the path-loss and received signal to noise ratio difference between users is translated into multiplexing gains. Although power sharing reduces the power allocated to each user, both users - those with high channel gains and those with low channel gains benefit by being scheduled more frequently and by being assigned more bandwidth. This means that NOMA enables system capacity and fairness of allocations to be improved for all users.
In addition to this NOMA, non-orthogonal multiple access is able to support more connections than other systems and this will become particularly useful in view of the massive projected increase in connectivity for 5G materialises.
By Ian Poole
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