Recently, our colleague Petrut Ionel Romeo, Technical Project Manager, Lasting Software held the presentation entitled Satellite Communication solution for Cellular backhaul, as part of Codecamp Timişoara, the autumn edition.
In what is actually a solid business case for satellite – based mobile communications, he outlined the importance of this technology and its 2 main current key purposes, in a way that would make it clear and palatable by non-specialists and technical people altogether.
We will briefly recap the main ideas, leaving aside the more technical content. Nevertheless, let your imagination add to this material the context of a busy, dynamic conference, and you will have the image of a great day…
Satellite – related facts
Satellites (communication and weather), are situated in the geostationary orbit. This is to make it easier for the Earth-based antennae to maintain continuous communication. A geostationary orbit allows for the position of the orbiting object to remain constant. To a stationary observer from Earth, it seems motionless.
In time, the number of satellites placed in the geostationary orbit became high enough to justify the new ring system made by all these devices being called the Geostationary Satellite Belt.
Having to control and maintain sophisticated pieces of technology at such a remote distance is a huge task. There are specific challenges linked to the system of satellites surrounding the Earth. Although by developing the technology at an impressive rate, the previous reach, maneuver and management issues have been solved in ways that were not possible a while ago, the physical premises (and not only) make satellite technology a highly demanding field.
Satellites operate in extreme thermal conditions, risk being hit by space debris, face the hostility of radiation belts and so on. Perhaps the simplest challenge to understand of them all would be that satellites are remote devices, with a specific procedure in place in order to access, maintain and repair.
By taking a look at the distance-related communication challenges, we may consider how:
- The Clarke belt (the part of space in the plane of the equator, designated implementation area for near-geostationary orbits) is about 36.000km above sea level;
- When speaking of communication back and forth, we are dealing with 72000km
- Taking into consideration the speed of light, the resulting delay in transmissions is of approximately 250-270ms
However, despite these challenges, communication satellites also have a few particular traits that put them above any other communication-enabling technology located on Earth.
The unmatchable advantages of the communication satellites
Satellites are extremely important because in certain locations and/or circumstances, the terrestrial communication infrastructure is inefficient or even completely out of range/function.
There are 2 major (and we may add critical) situations where only satellite-enabled communications can support the flow of necessary data and messages.
- Geographically-isolated or architecturally-isolated spots
- Often in rural and remote areas fiber and microwave transmissions are unavailable, as there is no business interest
- Satellite communications are also efficient in mountains, deserts, islands, in other areas difficult to reach due to the landforms and/or structure
- This type of communications may be of use in order to relieve congested urban areas: stadiums, malls, markets, academic centers
- Situations that require a solid communication infrastructure for emergency response
Satellite can act as a trustworthy fiber backup, since fiber is not that reliable. Faced with earthquakes or other cataclysms, both landline and fiber systems are easily down, unlike satellite-enabled communications, which become crucial for keeping in touch, monitoring and intervening in such moments.
Communication Satellites Architecture Options
In accordance with their type and with the communication needs they have to meet, satellites usually feature one of the following main architectural types, when it comes to data transmissions:
- Point to point links
- When there is a limited number of links
- For nb interface, for example
- For very high speed trunks: +300 mbps
- Hub and Star architecture
- Multiplex on forward and return
- Smaller remote equipment
Mobile backhaul: key considerations
Mobile backhaul (MBH) is the process of data and voice transportation from distributed network sites to the network core. It enables mobile users to access the main data centers that host the content and applications.
Terrestrial backhaul is the traditional method. For a long while mobile and satellites existed in parallel, due to the costs involved in satellite operations. Once the more recent advances in satellite technology reduced the bandwidth costs – for example High Throughput Satellites (HTS) managed to bring an up to 70 % saving – satellite backhaul became a viable, attractive solution which is about to gain traction.
What does the shift towards satellite backhaul involve, as far as the mobile communications are concerned?
- Mobile networks: Quality of Service (QoS) and Service Level Agreements (SLAs) are key for Voice traffic, Data traffic, Signaling, Management
- The mobile equipment: configured to accept higher satellite delay
- Mobile traffic: needs to be optimized to lower the cost of satellite bandwidth
Mobile traffic optimization
As mentioned above, traffic needs optimization, in order to make the most efficient use of the satellite bandwidth. To that avail, here are a few possible methods for each of the following telecommunication infrastructure types:
- 2G TDM: remove silence and idle channels
- Optimization on Abis can bring up to 50% bandwidth gain
- Gains on Ater, A link and nb interface as well
- 2G IP, 3G, 4G: leverage compression for headers (small packets), and payload (data)
- VoLTE: compression of internal stacks as well (within GTP tunnel)
*Additional feature: accelerating TCP in 4G
- TCP traffic – captured transparently within GTP tunnel, by using “protocol spoofing”
- A mechanism that tries to send as much data as possible, as soon as possible
- The protocol uses the alternative window size mechanism, with a larger window – to increase throughput (RFC 1323)
- The protocol implements alternative acknowledgment mechanism, reducing number of ACKs.
The importance and requirements of the satellite solution
Mobile network operators considered satellite backhaul as an attractive option for a long time. This is due to it being the only option in extreme situations, either permanent (remote or congested spots), or temporary (cataclysms, catastrophes, major downtime incidents). While it used to be a cost-prohibitive solution, the advances in technology now open up this option.
The new opportunities come with their own specific traits and requirements:
- Spectral efficiency is essential in reducing the cost of satellite bandwidth
- Quality of Service (QoS) is the key to being able to fulfil the mobile operators’ tight requirements
- Flexibility is important. It accommodates the multiple mobile technologies (2G, 3G, 4G), and the various network configurations (including the rural low power consumption phenomenon)
- The technology allows for bandwidth sharing and dynamic adjustment to real-time traffic and weather conditions
- Scalability, which is critical for:
- Typical mobile backhaul network: 20 to 100 remote sites
- Typical small cell network: 1000 sites
- Increasingly, mobile operators also want other services to be hosted on the same satellite solution, e.g. enterprise service, thus resulting more remotes