On the face of it these are not good times for satellite operators’ ambitions to play a major role in 5G, even without the COVID-19 effect. The virus was merely a scapegoat for the demise of OneWeb and clearly played no role in Leosat’s folding in November 2019.
Both these companies were in the risky and crowded area of LEO (Low Earth Orbiting) satellites, attempting to build global constellations to provide ubiquitous Internet coverage with special reference to 5G. Although their demise has shaken the industry and discouraged investors, it seems merely to have emboldened those left in the LEO field, notably Elon Musk‘s rocket company SpaceX with its Starlink, and Amazon’s Project Kuiper.
So far, Starlink has launched 300 satellites with plans to reach 12,000 in LEO, while Kuiper has set initial targets just over 3,000. Then in early March 2020 as the scale of the coronavirus crisis was already apparent, Vodafone weighed in with plans to launch LEO satellites specifically to dovetail with the 5G networks it is deploying on the ground. Vodafone is collaborating with Japanese technology group Rakuten with a $25m initial investment into a project called SpaceMobile, named to highlight its complementary role to 5G.
The natural question is how, where and when satellite will complement 5G, at a time when a lot of industry sentiment was negative even before the OneWeb and Leosat failures? There were issues over spectrum contention and also fears voiced over the impact on weather forecasting and astronomy of 5G’s encroachment into frequency ranges previously reserved for satellite. Those issues are beyond our remit here, but they are resolvable with goodwill on both sides, coupled with investment in interference mitigation and coexistence. Whether they will all be resolved properly is another matter, but there is reason to believe satellite can play a significant role in 5G.
It will not be helping 5G meet its headline goals in terms of capacity, multiple device support and low latency, because these are addressed far better on the ground in the RAN, backhaul and IP core. Instead, satellite’s role could be to reinforce 5G’s loftier goal of underpinning ubiquitous global connectivity, ending or at least reducing the geographical bandwidth lottery.
The aim is to fill in those remote areas where cellular coverage is poor, as well as those where it is and will continue to be totally non-existent, which includes serving aircraft and much of the maritime sector. For satellite platform operators, ability to address these sectors is critical for long term success or even survival, as their revenues migrate from DTH (direct-to-home) TV services to general broadband and network carriage. This does not mean they are moving away from video, but switching from direct transmission to over-the-top services over IP, shared with other forms of traffic.
Indeed, apart from filling in remote coverage beyond the reach of cellular signals, satellites can play an important role alleviating core and backhaul bandwidth consumed by ever higher quality video at increasing frame rates, color depths and pixel densities. Satellites are ideally placed to broadcast video over large areas, rather than unicasting separate instances of each channel or stream to every user electing to receive it. This sounds like a repurposing of DTH and in effect it is, but it will also over time be replacing DTT (digital terrestrial) over-the-air broadcasting. 5G itself is moving into this area through overlay models, especially HTHP (high tower high power).
In fact, such overlay models date back to 4G with the ill-fated LTE-Broadcast or -Multicast initiative, which was then revised with some modifications under the FTHP model. This model was first deployed successfully in December 2018 as part of the German Bavarian 5G TODAY research project involving five partners including Bayerischer Rundfunk, Rhode & Schwarz and Kathrein.
The main advance over LTE-Broadcast lay in enabling use of the full signal bandwidth in downlink-only mode for multicast or broadcast video, rather like DTH in fact. It also crucially allowed reception without SIM cards, so could be used for generic broadcast rather than just mobile services to smart phones and other SIM-enabled devices. The HTHP transmission can use existing frequencies without any need for additional spectrum, while coexisting with other mobile applications.
Of course, just as conventional 5G networks will have areas of non-coverage, so will HTHP overlays, so that is where satellite can come in by enabling multicast distribution there. To do this, satellite operators must in the first instance embrace 5G standards and they have been doing that by working with 3GPP.
This has not been a one-way process, with the European Space Agency (ESA) having been successful in creating a work item inside 3GPP through its ‘Satellite for 5G’ project, set up to evaluate how non-terrestrial networks (NTN) in general can be integral to overall global 5G connectivity. This particular 3GPP item has not been just looking at video and other multicast use cases under the enhanced mobile broadband (eMBB) banner, but also the IoT, where the need is for extensive low bit-rate coverage under the flag of massive machine-type communication (mMTC).
5G is unlike its predecessors in going beyond essential standards and protocols for cellular connectivity and service provision, to embrace technologies and architecture for all forms of global communications, both broadband and mMTC. This means aligning infrastructures within the twin pillars of NFV (network functions virtualization) and SDN (software-defined networking). Both of these involve decoupling of activities that were previously closely entwined, in the case of NFV separating specific functions such as IP routing, load balancing and intrusion detection from the hardware on which they resided and executed.
SDN then operates at a broader level by separating the higher layer control plane, where routing decisions are made, from the underlying business of actually getting IP packets from source to destination. It therefore cuts the routing process in two such that the actual forwarding tasks can be distributed to wherever they are needed while the higher level network control can be streamlined and centralized. SDN works at the architectural level, stratifying network control from underlying transport, while NFV enables virtualization within the network through separation of individual functions from hardware. NFV allows lower cost commodity hardware components to be used and increases flexibility or this mythical elasticity because hardware can be scaled independently of the functions.
Satellite operators have been working towards implementing SDN and NFV on their systems, partly in preparation for 5G integration but also to attain the efficiency and scalability benefits directly. This also includes other strands more directly associated with 5G, such as network slicing where spectrum can be partitioned between different services or use cases.
The satellite ground segment in particular has been undergoing this transition and has already entertained hopes or even expectations it will help revive this increasingly moribund sector. Such hopes have been sustained by various reports predicting double digit growth on the back of 5G roll-out, even if such forecasts may have to be put on ice for now.
Naturally such forecasts rest on success of anticipated use cases, which begin with the one that is simplest, in concept if not technically – coverage extension through roaming between terrestrial and satellite networks. In principle this would operate like other any other roaming or offload agreement, with users only accessing the satellite network when their primary 5G network is not available.
This then extends to specific applications, such as broadcast and multicast, where a satellite overlay extends coverage that might be provided on the ground by a HTHP configuration. Then there is the IoT or M2M delivery, where again the satellite network ensures that components such as remote environmental monitors and weather sensors way beyond the reach of any 5G network on the ground can be served by satellite connections.
Most of the other use cases, too numerous to cite individually, revolve around offloading, capacity and backhaul, where the satellite kicks in to deal with peaks in demand, or to carry traffic for which it is best suited, including where low latency is not so critical.
There are also some interesting specific examples of satellite usage for coverage, one called ‘Moving Platform Backhaul’, in which 5G base stations are located on ships or trains that themselves may roam out of coverage. Users can then make calls or access the internet from their devices via 5G as normal.
There is also ‘5G To Premises’, where 5G is proposed as an alternative to fixed broadband in areas where the latter is either unavailable or of poor quality, as when the site is a long way from the nearest exchange point. Here satellite can be used as a backup where in turn 5G is unavailable, to enable more universal service provision. This use case may involve handover to non-3GPP wireless standards in the premise, such as WiFi, or one of the IoT protocols like Bluetooth or Zigbee.
A key point to realize is that while the satellite industry may appear to be the supplicant hanging on grimly to 5G in the hope of fortunes turning up, 5G in turn cannot meet all its promises without satellite, except in the unlikely event one of the other even lower altitude alternatives such as Google’s Loon or drones succeed in providing blanket coverage.