# Is Satellite Ahead of Terrestrial in Deploying NOMA for Massive Machine-Type Communications?
## 4 Developed E-SSA-Based NOMA System Elements
### Digital Phased Array Antennas and Compact Terminals  
The spread spectrum nature of F-SIM also makes it an interesting choice for being used in conjunction with small antennas. The use of small antennas has, in general, a strong impact on the system performance:  
* In the forward link, the received SNR degrades both for the gain loss due to the reduced antenna size and for the increased interference received from adjacent satellites in the GEO arc. Therefore, negative SNR values are typically used, with modulation such as DVB-S2X very low signal-to-noise ratio (down to \(-9\) dB) modes (VL-SNR);
* In the return link, the limiting factor becomes the aggregate power flux density (PFD) limitation towards adjacent satellites, which translates into a low aggregate achievable spectral efficiency and requires a good terminal pointing. This throughput efficiency still makes the solution attractive compared to the current commercial offer from satellite mobile operators.  
The large spreading factors supported by F-SIM reduce the emitted power density from each terminal under the thermal noise level, making it easier to comply with emission masks. As a matter of fact, a badly pointed terminal (e.g., due to a fast mobile platform movement) will generate a very low PFD to the adjacent position, and it can be assumed that the aggregate PFD is well centered around the satellite orbital location actually used.  
Another interesting factor is that the same band can be shared with large (fixed) terminals, both in the forward link using DVB-S2X adaptive coding and modulation and in the return link using different spreading factors--therefore, the global system efficiency is only marginally reduced.  
Small antennas with electronic steering had a high cost in the past, but recent developments open the way to full terminals well under the USD 1000 threshold, which  
Figure 8: Egated terminal mounted in a KNS maritime antenna.  
can target use cases with low volume requirements where the higher transmission cost (due to reduced efficiency) is justified. Some experiments are ongoing with flat panel manufacturers, in order to develop solutions both for fixed use (20 \(\times\) 20 cm antenna easy to point) or mobile use (flat panel with electronic steering), using different technologies.  
Satixfy has developed an integrated antenna/modem that supports F-SIM, including the DVB-S2X VL-SNR modes required in the forward link for such a small antenna. The \"Diamond\" Ku-band antenna shown in Figure 9 has 256 elements with electronic steering, a nominal EIRP of 32 dBW and a G/T of 2 dB/K at boresight and embeds GPS, Wi-Fi and Bluetooth. Its size is 30 \(\times\) 35 cm, and its power consumption ranges from 0.5 (sleep) to 60 (receive only) to 90 W (transmit mode).  
The antenna works in the time-division multiplex mode, i.e., it cannot receive data while transmitting. Work is ongoing to extend the DVB-S2 protocol by adopting some time slicing techniques--this will, at the same time, reduce the average power consumption to a few watts, according to the use case, and prevent any potential transmit/receive packet collisions.  
The integrated antenna/modem is therefore an appropriate solution for (a) fixed installations where no space is available, or ease of installation is required; and (b) mobility environments such as trucks and small boats.