5G NTN is Here – What are the challenges?

Consumers and businesses have had access to satellite-based TV, phones, internet service, and GPS for decades. Yet, recently, there has been a surge in discussions about satellite with new entrants to the market offering non-terrestrial networks and devices touting their ability to connect to these “new” networks. What has changed?

In this 5G-NTN blog series, we’ll discuss the changes that the satellite space is currently undergoing, the key challenges in deploying the networks, use cases that are emerging, and considerations for programmable silicon that help address these issues.

The Change

What has changed is the shift of mobile networks into the realm of space. The satellite industry has long participated in the 3rd Generation Partnership Project (3GPP) mobile standards to integrate their networks in the 5G ecosystem. This not only enables the traditional terrestrial (cellular) mobile market to enjoy easier and more consistent access to non-terrestrial networks (NTN), but it enables access across a much larger ecosystem of IoT devices to connect to satellite as well. This powers new use cases that previously weren’t accessible and creates net new revenue streams across device manufacturers, network operators, chip and module makers, and more.

However, the 5G-NTN market is still in its infancy, and device manufacturers are still struggling with establishing chip-level requirements. To better determine specific requirements,it’s helpful to know the challenges that must be solved that differentiate it from traditional cellular networks.

The Challenges

Integrating satellites into 3GPP-based networks is a tremendous challenge. In this first blog, we’ll look at each challenge in a bit more depth.

The second relates to the type of satellites; in particular, the difficulties posed by those in non-geostationary satellite orbit (NGSO). The third is 3GPP itself, which like all standards efforts has its advantages and drawbacks. Finally, there are several hardware-related considerations, including power.

Challenge #1: Long Propagation Delays

The first challenge is the sheer distance of satellites from gateways and end devices on Earth. Let’s take a look at mobile,for instance. A mobile device must connect to a base station to transmit communications, and that base station may only be up to 10 km away. In this scenario,a one-way message will only take a millisecond to transmit. But in a LEO-enabled NTN, which is typically between 600 and 1,400 km away from the device, that signal may take 30 milliseconds. With a longer roundtrip in message transmissiontime, more variables arise in the channel conditions, which can impact quality of service.

Challenge #2: Doppler Shift, Moving Coverage Areas

There are different types of satellites based, typically classed by their distance from Earth. Those that exist in the LEO zone are up to 2000 km away, cover smaller areas on the ground so there are often many of them,and tend to move in an orbit around the globe. They are not fixed in space. GEO satellites, on the other hand, are over 35,000 km from Earth, cover large geographical areas so there are a few of them, and are fixed in their locations, generally nearthe equator.

The relative movement of LEO satellites creates Doppler shift, which means that the frequency at which a satellite transmits a signal will not be the same as it is received. Failure to compensate for this effect results in incorrect signal sampling. The subsequent cascading effect can lead to a very high error rate. There is also the quasi-fixed nature of a LEO satellite’s steerable beams. With them, a satellite can cover the same area for a time, but eventually it must hand over to the next satellite in the constellation. Managing these handovers poses another challenge.

Challenge #3: Evolving Standards

The primary advantage of the 3GPP standard is that it influences a tremendous base of mobile user equipment. The 3GPP also incorporated NB-IoT and LTE-M in the 4G standards. Yet standards evolve slowly, where every new iteration attempts to reduce limitations and address a broader range of applications. The initial work on 5G-NTN, for instance, has been limited to the transparent mode, in which the satellite acts as a relay point. Some applications, however, are better suited to the regenerative mode, which provides more architectural flexibility and improved performance.

Challenge #4: Form Factors, Power, Radiation

LEO satellites are smaller than their GEO counterparts, but the paradigm has further shifted with mini-, micro-, nano-, and pico-satellites. Satellites that conform to the CubeSat specification weigh less than 2 kg. Small form factor and low power consumption are desirable characteristics in these smaller classes, which are often associated with LTE-M and NB-IoT use cases. The last factor is radiation and regardless of the payload size, satellite components need to be protected from radiation in outer space.

For our next blog in this series, we’ll discuss satellite use cases.

To download our full white paper on 5G Non-Terrestrial Networks and Satellites that includes topics discussed in this blog, click here.

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