How does the 5G NB-IoT software protocol differ for NGSO and GSO satellites?
Major differences are on the satellites´ infrastructure. One example is the different location of the NodeB functionality.
For help in assessing how your satellite system set-up can support 5G NB-IoT connectivity, please do contact us.
Is 5G NB-IoT not more suitable for NGSOs than GSOs?
The 5G NTN standard is working with two different satellite configurations – the 1) Transparent mode, and 2) Regenerative mode.
The 3GPP 5G standardization group has started with the specification of the transparent mode in Rel-17, where the regenerative mode is planned for future releases. The transparent mode fits to both GEO and NGSO satellites.
The standard also looks into the supported frequencies. E.g. the higher the frequency, the more challenges are expected for the performance, as the frequency influences the antenna size. If you want to assess how your satellite set-up is suitable for supporting 5G NB-IoT, please contact us.
In what frequencies does NTN 5G NB-IoT operate?
Even though current operational satellite frequency bands can be used, from 3GPP directive, the S-band (2-4 GHz) is set as an exemplary band.
That´s why we are currently developing the software with L- and S-band reference. However, with Ka and Ku band present in many traditional GSO satellites, we are also looking into this case. The higher frequencies will require a bigger antenna. We will be happy to support you with understanding and assessing exact requirements and potential use cases.
What link budget is anticipated for NTN NB-IoT?
There will often be direct line-of-sight between satellite and device but the Free-Space-Path-Loss for NTN NB-IoT is higher, due to longer distance. The link budget is calculated separately for up- and downlink. Uplink is favored by the use of single-tone transmission which theoretically adds up to 17 dB gain. Antennas on GSO satellites are typically having a large gain (around 50 dBi) while it is less for LEO satellites. This results in LEO and GSO link-budgets with comparable dB ranges. Calculation on a small-sat LEO case indicates that SNR range for downlink is -5 to 0 dB while for uplink it is -2 to 3 dB (depending on elevation angle and distance between the device and satellite).
What latency level is anticipated with GSO and LEO satellites?
With GSO satellites positioned stationary at 36.000 km from Earth propagation delays up to 541 ms will occur. Comparably for a scenario with a LEO satellite on 600 km distance, this will vary between 4-26 ms depending on the position of the satellite in relation to the device for regenerative systems. For transparent systems, as focused on in 3GPP Rel-17, the LEO propagation delay is doubled (8-52 ms).
How is Doppler effect handled with NB-IoT and non stationary satellites (NGSO)?
Since NGSO satellites (e.g. LEO or MEO satellites) are moving around the earth at very high speeds (can be as fast as 28.000 km/hour), transmission signals are influenced by the Doppler-effect. Mathematical algorithms are helping to reconstruct the transmission signaling by taking into account the (moving) positions of the satellite and device. For this GNSS position information of the satellite will be transmitted within System Information Broadcast messages. The device’s location can either be fixed configured or retrieved via an embedded GNSS module. By doing this, the original signal can be recovered and the uplink transmission can be pre-compensated at the device side.
Will there be a seamless satellite handover in a LEO or GSO scenario?
Devices can stay connected to the same GSO satellite, since the satellite is stationary. LEO satellites are moving in relation to earth, and devices will need to continue reselecting different satellites. Otherwise, connection gaps will be experienced. As NB-IoT currently does not support Handover procedures, a message transfer will need to finish during the pass of a single satellite.
How will the network be managed between satellite operators on the non-terrestrial network side (NTN) and the Mobile Network Operators (MNOs) on the terrestrial network (TN) side?
The expected end-vision of the 5G standardization foresees connectivity provision handled by MNOs. This would mean that IoT customers who need connectivity for their IoT terminals, would approach their local MNO, who offers connectivity for dual mode networks (meaning terrestrial and non-terrestrial connectivity – TN and NTN). In this case, the satellite operator would have an agreement with the MNO. Until the standardization has evolved to this point, we expect satellite operators to offer 5G network directly to their customers, with the MNO brought in case by case.
Will there be spectrum / frequency available in my country?
5G NB-IoT connectivity for NTN and TN networks is expected to be a global standard. Please approach your local ITU, to obtain and apply for spectrum allocation.
What antenna is required for an NTN 5G NB-IoT device?
It is desirable and possible to use the same kind of omnidirectional antennas which are used in terrestrial IoT devices. To compensate for the low device antenna gain, the satellite shall be equipped with a directional antenna with a higher gain. It will still be beneficial and possible for some devices to use a higher gain antenna to obtain a better link-budget.
Which chipsets are expected for TN/NTN dualmode 5G NB-IoT operations?
To support NTN 5G NB-IoT connectivity, common chipsets that can support multiple access technologies, as well control carriers on multiple frequencies, are expected to be used.
For LEO satellites, the chipsets will need to be able to control the timing and frequency drifting, caused by the varying time delay and Doppler due to the satellite’s motion.
How will the regenerative mode help out on LEO networks?
Compared to the transparent mode (Rel-17), the regenerative mode will include enhancements and optimizations for NGSO satellite systems, considering the moving of the non-Geostationary satellites, enabling efficient blind search of user devices, etc. The regenerative will enable UEs to communicate with the NodeB even when a feeder link is not active, and makes communication everywhere on the globe possible. In the regenerative mode, the NodeB will be located on the satellites themselves.
What are your thoughts on power consumption and Line of Sight going to affect hybrid connectivity?
The 3GPP standards specify multimode user terminals that are capable of obtaining service without modifications on both terrestrial and non-terrestrial networks. Tests have been conducted with hardware conforming to earlier releases where only software was modified to obtain service. Hence, power consumption is expected to be equal to previous releases for user terminals working in hybrid mode. To close the link budget user terminals are expected to have line of sight visibility to satellites when used on satellite based networks.
Can you comment on the solutions to the synchronization in the presence of Dopper spread also considering the relatively short satellite visibility time?
With help of the NPSS, NSSS and NRS, a signal can be detected, and during the decoding of it, the frequency offset can be determined. That this frequency offset can be very high, and becomes lower the closer the satellite comes to the UE can be calculated and resolved by the processing algorithm.
Will it be possible to use the satellites for data transmission in connected mode or is connectivity restricted to disconnected mode vie the random access procedure?
There are no changes to the protocol or services available under 3GPP release 17 for non-terrestrial networks. A PDP Context can be established and maintained for data transmission as for terrestrial networks. Hence it is not needed to apply the random access procedure as long as the connection is not broken. For NGSO communication, the transmission will be likely a few minutes, and for GEO transmission the context can be kept longer active.
Will there be issues with the use of transparent mode in NGSO systems?
We see two issues with the use of transparent mode in NGSO systems. 1) As the satellites are only visible from both ground station and user terminals in a relatively short time period it is only possible to obtain service in smaller time intervals. 2) Since ground stations must be located in the same satellite footprint as the user terminals there will be large parts of the earth surface like the oceans where is not possible to obtain services.
The 5G handover from one to the next overflying satellite, is this not something ground users uplinking/downlinking signals needs to handle (maybe by having the 2nd link up before the 1st one is lost)?
Handover of traffic connections resulting from moving NGSO satellites is not supported in release 17 and in transparent mode there is no on-board processing. The procedure and algorithms for handover currently implemented in standard compliant user terminals will not be able to support setting up a 2nd link for handover of the traffic. We expect this to come as part of one of the following releases.
How do you know that your models are performing / simulating “real-life-scenarios”?
In essence, the realism of the feasibility study depends on the configuration of the scenario (input parameters) and the results are generally approximation, worst/best-case results and where applicable they have been compared to similar SoTA results. All modelling is an attempt to deconstruct or approximate reality in a way that we can more easily deal with. In our feasibility-study we have divided the RAN (radio access network) in three major parts the fading channel, the link-level and the system level. We can develop fading channels based on Ray-tracing, which will be very realistic or use a more abstract/generalized model – or 3GPP standardized models depending on choice. On the Link-level we do extensive monte-carlo simulations to find the link performance given the chosen fading model. On the system level we have rigorous analytical models, which account for many protocol aspects and signaling overheads (e.g. the various message sequences) – and this level relies on the realism of the two layers below.
On what frequency band are your simulations derived?
The carrier frequency (band of operation) is a parameter for the configuration of the feasibility study. In general the frequency will change the link budget and the Doppler characteristics.
What bandwidth can be reached (in bits per second)?
The peak throughput is a bit less than for terrestrial NB-IoT around 258 kbits/s in PDSCH(DL) and the same in PUSCH(UL) at the link-level without accounting for propagation time. In reality the obtainable throughput will depend heavily on the link-budget throughout the cell and this is a function of the satellite payload. In our feasibility study we can take this evaluation one step further to account for overhead in terms of static signaling and the dynamic message exchanges (an application payload is embedded in a larger message exchange, eg. RA+)
Does the beam center move with the satellite movement in NGSO or does it “track” the location of the NB-IOT devices in FOV?
There are two scenarios defined by 3GPP in the NGSO case: 1) Earth-fixed cells, where an NGSO satellite steers its beams such that the cell projected on the ground does not move and 2) Earth-moving cells, where an NGSO satellite has a fixed beam direction, such that the cell moves around with the satellite.
Why is this based on 5G? Is there a technical limitation that prevented this NB-IoT to work with 4G standards?
5G is a set of requirements for networks – as was 4G. In 5G one of the targeted use-cases is massive machine type communications (mMTC). The requirement for a 5G mMTC technology is that it must be able to service 1 million devices per km2 sending 32bytes of L2 data every 2 hr. After the requirements had been set, the development of the new technologies for 5G started. It was quickly found that NB-IoT and eMTC were sufficient for this requirement (terrestrially) given enough channels. Therefore these radio access networks are 5G compliant and hence now called 5G. In the backbone of the network there is a core network, here the 5G variant is called 5GC (5G core) and the 4G variant is called EPC (evolved packet core). Even though the RAN remains largely the same (but has developed over the 3GPP releases) there are some differences in base-station depending on whether it is interfacing with 5GC or EPC.
Have you done any study concerning potential interference between terrestrial component and NTN component within the same network?
We have not studied interference between TN and NTN. The networks should be separated in frequency with appropriate guard bands handling Doppler shift in the NGSO case. The bands and channels allocated for NTN and TN are being determined by standardization organizations like ITU, 3GPP and ETSI. As a general rule you can count on interference not being allowed.
Is it possible to emulate 5G NB-IoT network links?
Yes, real life testing w. in-orbit emulator.
How is system coping w. finding satellites when both devices and sats are moving?
3GPP has defined functionality wrt. the channel raster such that UEs will always be able to look for, find and appropriately identify any available channel. The trick is to find an available cell by searching for that particular channel while in coverage of a serving satellite. This can be helped by satellite assistance information, which is a feature that is expected to be settled and included n Rel-17.
How are your simulations handling dynamics of moving sats?
In the case of a GEO sat the cell will have a static link-budget and the elevation angle toward the satellite does not vary throughout the cell. In the case of NGSO earth-fixed cell, the cell has a fixed position and so would a stationary UE within it, but the link-budget and elevation angles are dynamic and change overt time, so we compute these for a satellite pass. In case of a earth-moving cell NGSO we have a cell which moves within the cell the linkbudget and elevation angles are static, but the cell moves over the UE. This is equivalent to a UE travelling within a GEU cell (at approximately 7.3km/s or so 🙂 )
Does 5G NB-IoT work on Ka/Ku band?
Rel-17 will work on the S-band, but preliminary work has already been started on the Ka-band. It is likely that higher bands will be supported in future releases. The higher frequencies are a source of wider spectrum/bandwidth for the NTN networks, but there are major challenges involved with higher frequencies – in particular dealing with the increased signal propagation. It could very well be unfeasible to launch ka/Ku band on cubesat payloads due to the limited power budget.
Apart from UEs and satlinks, is there any need for ground infrastructure to establish 5G IoT communication?
Indeed, the radio access network (RAN) NB-IoT, LTE, LoRaWAN, etc. are just the communication link between UEs and satellites. To make this link useful a link to the core-network on earth should be established. This latter link is known as the feeder link in SatCom terminology and is established between the satellite and large ground-stations. The service link must provide sufficient capacity for the cumulative RAN information (and then some other telemetry) to be exchanged which is why ground-station typically have large steerable antennas and a large transmission power.
What are considerations for latency for IoT use case?
The latency in NTN is larger than in terrestrial networks due to the larger propagation delay. In some satellite constellations coverage can not be provided continuously on the ground either. So IoT devices for NTN must be delay tolerant.
Are there any satellite crosslink capabilities providing global Satcom coverage vice just connectivity within one satellite footprint?
Yes, inter-satellite links (ISL) can be used for networking and routing between satellites. However in Rel-17 the focus has been on bent-pipe satellite payloads, i.e.. satellites that act as relays where the ground-station is the actual base-station – so first the focus in a future release needs to switch to regenerative payloads i.e.. base-stations onboard the satellite – and then to ISL later. Nothing hinders ISL at them moment – it is just not standardized.
What are the typical messages lengths (in kilobytes) that can be sent and received via satellite NB-IoT? Does it compare with cellular NB-IoT?
The transport block sizes in NTN NB-IoT are the same as in NB-IoT so the difference is in the fading model and the link budget. Provided that the link budget of a satellite payload is comparable to that of a satellite cell the typical message lengths will be comparable between TN and NTN. Basically, you should in most cases be able to expect TN-like performance if the satellite payload is well designed.
How does the signaling overhead compare for the satellite assistance SIB in LEO vs GEO configurations?
In short, GEO will have little overhead while NGSO and especially LEO will see more overhead, but we expect at most a few percent overhead on the anchor channel. Two SIBs are defined for NTN IoT, the first being for uplink synchronization and the second (to be defined in May) is for helping UEs to predict coverage in discontinuous coverage scenarios, to better enable mobile originating (MO)-traffic. The fist SIB has a fixed size regardless of the use-case, but in LEO it may be necessary to transmit for example once per second (but this will depend on the Orbit, satellite payload GNSS and the band of interest) where in GEO a UE need only receive it once. Overall this SIB should at most take up a few percent of the anchor channel. The SIB for satellite assistance information (SAI) is not defined yet, but we expect it to be of a variable size with plenty of optional parameters. This SIB-SAI is optional and should not be an overhead in GEO. SIB SAI should be expected as overhead in discontinuous NGSO only. The SIB SAI need only be received by UEs once, but the overhead here will again be larger for LEO where the satellite will move faster – a rate of once per 5 or 10 sec should be feasible.
Do you apply beamforming in reception? If yes how do you keep beams in the right direction elevation and azimuth?
In NTN IoT the goal is to reuse the hardware platforms of terrestrial cellular. So the UEs are essentially similar to handheld devices with an omnidirectional antenna. Beamforming may be applied from the satellite site to orient the beam towards a specific geolocation for the ‘earth-fixed cell’ scenario.
What are the currently considered strategies for dealing with the Doppler drift in the NGSO setting? Are UE supposed to precompensate the Doppler?
Yes, in Rel-17 the UE will handle the compensation. In the downlink the UE will synchronize to the Doppler shifted NPSS/NSSS signals as usual, it will then decode an ephemeris (a description of the serving satellite’s orbit accurate for a moment, say 1 sec) which will allow the UE to precompensate for the Doppler effect when it transmits in the uplink direction (RACH/PUSCH). This will be the way for NTN IoT (NB-IoT and eMTC) and also NTN NR.
Is there a difference between cell size and beam size?
Yes, a ‘beam’ refers to the RF or ‘physical’ power from the TX side, which is a continuous function. A ‘cell’ is a logical entity on the RX side in a cellular network and is determined as an area within the ‘beam’ where certain criteria are met: Synchronization and SNR above threshold.
Can ray tracing be done for different areas, mountains, ocean, desert?
Yes, ray tracing can be done for different terrain and geographic locations. We can also create specific scenarios or use 3GPP fading models.
