After the FCC announced the availability of a huge amount of 5G spectrum in 2016, I wrote about it in this blog posting. I was rather impressed with the amount of spectrum made available but I also identified three areas that needed breakthrough innovation for 5G to be successful:
- New channel models
- New air interface
The industry is making progress in all three of these areas and there’s still more work to be done. For a good overview of 5G status, see this article on ElectronicDesign "5G—It’s Not Here Yet, But Closer Than You Think".
The 3GPP standards body has been working on the new air interface, now referred to as New Radio (NR). A major milestone was the release of the first NR standard, known as the Non-Standalone (NSA) Release 15 specification. “Non-Standalone” means that the 5G network is dependent upon the existing LTE evolved packet core (EPC) network and an LTE “anchor” carrier for control signaling aggregated with an NR carrier for data. Industry leaders pushed for and got the NSA early release to expedite their deployments. The full up (Stand Alone) Release 15 using the next generation (NG) core network and NR air interface is due out in June 2018. This phased approach makes a lot of sense for a complex system like 5G.
The wireless network operators are already planning and doing 5G field trials of various forms, including proprietary pre-5G implementations. These early trials are mostly focused on delivering broadband wireless to fixed locations, called Fixed Wireless Access (FWA). These deployments not only deliver immediate value to customers but also allow the industry to gain experience with NR and the higher frequency bands.
The goals of the NR specification are very aggressive, and cover use cases including:
- Very low to very high data rates
- Low latency
- Massive machine-to-machine communication
- High reliability
- Low power operation
Think about those requirements a bit and you’ll see that they are full of contradictions and engineering tradeoffs. But engineers do what they do and the NR spec handles these conflicting requirements via a new highly scalable orthogonal frequency division multiplexing (OFDM) system. I won’t try to describe the complex system of variable subcarrier spacing, symbol length and timing but it is designed to be very flexible to cover all the desired use cases.
Up In Frequency
To achieve high data rates while supporting more users, the plan for 5G is to move up in channel bandwidth and frequency. There’s just more spectrum (as measured in Hz) at higher frequencies. These ranges are now referred to as Frequency Range 1 (FR1) and Frequency Range 2 (FR2).
|Frequency range designation||Corresponding frequency range|
|FR1||450 MHz – 6,000 MHz|
|FR2||24,250 MHz – 52,600 MHz|
FR1 extends somewhat higher than the existing LTE spectrum in use now and will require some incremental improvements in technology and approach for 5G, particularly for the much wider bands and channel bandwidths. FR2 is another ballgame, well into the mmWave range where signal power is more difficult to achieve and much easier to lose to propagation losses.
Throw Your Cables Away
With signal loss a problem, adding some additional antenna gain can certainly help. At these higher frequencies (shorter wavelengths), phased array antennas can be used to improve the gain and steer it to where we want it to go. To keep cost down and performance up, these compact phased-array antennas are being attached directly to the RF Integrated Circuit (RFIC). This tight integration into the system means the usual output connectors are not available for measurement use. All measurements must be made Over The Air (OTA). So, yes, it’s time to throw your cables away.
Accurate connected measurements at FR2 can be a challenge, but decades of measurement science work has made them commonplace. Making accurate OTA measurements is a lot harder, introducing a much larger measurement uncertainty. Think many dB of uncertainty instead of <1 dB for connected measurements! In other words, OTA measurements are going to be less accurate than we have become used to – making everything more difficult.
Enter the Spatial Domain
Mobile wireless devices have always operated in three dimensions…the world tends to be configured that way. When a 3G mobile phone changes location, the system just has to track signal strength and make a handover to the right base station at the right time. Now consider a 5G device working at FR2: the variables now include the base station antenna gain, pattern and direction; the behavior of the channel including fast fading and the mobile antenna gain, pattern and direction. We have moved into the spatial domain.
Let’s consider how the User Equipment (UE) makes and maintains a wireless connection. The UE and base station need to find each other by sweeping their antenna beams around in some organized fashion. Once they lock onto beam settings that work, they’ll need to keep updating the beam directions as the UE moves through the network or changes orientation. Especially at FR2 frequencies, shadowing and blocking can be severe. At some point, the UE will need to switch to another base station, causing the cycle to repeat. Beam management is the key, at the UE and at the base station.
The test challenge is made more difficult by this beamforming operation. How do we ensure that the UE can steer the beam appropriately so that the 5G devices will work? Do we need to test in all 3D directions? Or can we just rely on a few key samples to ensure proper operation?
At our recent 5G Tech Connect Conference, my colleague Moray Rumney spoke about these spatial challenges, "For FR1 the question being asked for the last 100 years was “How good is my signal?” But 5G NR at FR2 brings a new paradigm which is “Where is my signal?” since if it is pointing in the wrong direction its quality is no longer relevant."
These design and test challenges are being worked on every day by Keysight engineers and other technical experts in the industry. Learn more about Keysight 5G technology and solutions here.