Multiple Access Scheme (Custom OFDM)

Default: None

Range: None, SCMA, NOMA, DFT discrete Fourier transform

Multiple Access Scheme specifies how multiple transmitters may simultaneously use the same frequency/time/signal path. These transmitters inherently interfere with each other, but several schemes have been developed which allow the individual transmitter signals to be isolated by the receiver.

None - The default value of None disables multiple access analysis. All analysis is done the same as in previous versions of VSA.
SCMA - When SCMA (Sparse Code Multiple Access) is selected, the received signal contains two signals that use a CDMA Code Division Multiple Access: One of several digital wireless transmission methods in which signals are encoded using a specific pseudo-random sequence, or code, to define a communication channel. A receiver, knowing the code, can use it to decode the received signal in the presence of other signals in the channel. This is one of several "spread spectrum" techniques, which allows multiple users to share the same radio frequency spectrum by assigning each active user an unique code. CDMA offers improved spectral efficiency over analog transmission in that it allows for greater frequency reuse. Other characteristics of CDMA systems reduce dropped calls, increase battery life and offer more secure transmission. See also IS-95.-like scheme to overlay the signals on top of each other. Even though the signals interfere with each other, the receiver can isolate the signals by correlating with the sparse code for each signal. The SCMA Settings section of the Multiple Access tab contains properties to configure the SCMA analysis. Note that SCMA analysis is not supported when the Modulation Scheme is set to FBMC.
NOMA - When NOMA (Non-Orthogonal Multiple Access) is selected, the received signal contains two signals that are simply added together. If the receiver knows the modulation format of the individual signals, it can demodulate both signals if signal-to-noise ratio is large enough. The NOMA Settings section of the Multiple Access tab contains properties to configure the NOMA analysis. Note that NOMA analysis is not supported when the Modulation Scheme is set to FBMC.
DFT - When DFT (Discrete Fourier Transform) is selected, Transform precoding is enabled for the data (DFT spreading). Note that DFT is not supported when the Modulation Scheme is set to FBMC.

When analyzing a signal that uses multiple access, the separate interfering transmitted signals are not displayed in the demodulated traces like OFDM Orthogonal Frequency Division Multiplexing: OFDM employs multiple overlapping radio frequency carriers, each operating at a carefully chosen frequency that is Orthogonal to the others, to produce a transmission scheme that supports higher bit rates due to parallel channel operation. OFDM is an alternative tranmission scheme to DSSS and FHSS. IQ Meas and OFDM IQ Ref. Instead, these traces contain the combination of the two interfering transmitted signals. This allows the overall EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format. to be calculated accurately, but does not provide individual bit values for each of the two interfering transmitted signals.