5G NR-Unlicensed (NR-U)

I have been talking about unlicensed LTE since 2013. With all the debate around LTE-U and LAA now non-existent, the technology has evolved with every new release. As can be seen from this picture by Ericsson above, 5G NR-U in Release-16 supports:

• License-exempt Downlink (DL)
• License-exempt scheduled Uplink (UL)
• License-exempt autonomous UK
• Standalone license-exempt operation

5G New Radio Unlicensed (NR-U): Challenges and Evaluation - https://t.co/RFyhHHddzh #Free5Gtraining #3G4G5G #5G #5GNR #NRU #NRunlicensed #UnlicensedSpectrum #5GNetworks #5GTechnology #Release16 pic.twitter.com/aiTg2RCECR

— Free 5G Training (@5Gtraining) October 17, 2021

The Release-16 work item summary details the following deployment scenarios for NR-based access to unlicensed spectrum:

• Scenario A: Carrier aggregation between NR in licensed spectrum (PCell) and NR in shared spectrum (SCell);
• A.1: SCell is not configured with UL (DL only); 
• A.2: SCell is configured with UL (DL+UL). 
• Scenario B: Dual connectivity between LTE in licensed spectrum and NR in shared spectrum (PSCell);
• Scenario C: NR in shared spectrum (PCell);
• Scenario D: NR cell in shared spectrum and uplink in licensed spectrum;
• Scenario E: Dual connectivity between NR in licensed spectrum (PCell) and NR in shared spectrum (PSCell)

5G New Radio Unlicensed: Challenges and Evaluation, available on arXiv here provides a lot of useful information on different kind of operations within the unlicensed band and the challenges of co-existence with Wi-Fi

Finally, Qualcomm has quite a few resources on this topic. Last year, they hosted a webinar on the topic, "How does unlicensed spectrum with NR-U transform what 5G can do for you?". The slides from that are available here and a video of that is available here. RCR Wireless also has this short article from one of the webinar presenters here.

Related Posts: 

• The 3G4G Blog: 3GPP Release 16 Description and Summary of Work Items
• The 3G4G Blog: Introduction to 5G Reduced Capability (RedCap) Devices
• The 3G4G Blog: Positioning in 5G networks
• The 3G4G Blog: Qualcomm Explains 5G Millimeter Wave (mmWave) Future & Integrated Access and Backhaul (IAB)
• The 3G4G Blog: '5G RAN Release 18 for Industry Verticals' Webinar Highlights
• The 3G4G Blog: Qualcomm Demoes Sub-band Half Duplex (SBHD)
• The 3G4G Blog: Reducing 5G Device Power Consumption Using Connected-mode Discontinuous Reception (C-DRX)
• The 3G4G Blog: Positioning Techniques for 5G NR in 3GPP Release-16
• The 3G4G Blog: 5G Enhanced URLLC (eURLLC) 

R&S Webinar on LTE-A Pro and evolution to 5G

Rohde & Schwarz recently uploaded a webinar video on their YouTube channel. I found it really useful. It's embedded below.

Topics covered:

• LTE-M / NB-IoT
• feMTC
• UE Category M2
• OTDOA based positioning
• UE Categories
• Unlicensed Spectrum Overview
• LTE in Unlicensed Spectrum
• LWA, LWIP
• LAA, eLAA
• Wi-Fi
• LBT
• LWA mobility
• Carrier Aggregation Enhancements
• Multi-user superposition transmission (MUST)
• Single cell - point to multipoint transmission (SC-PTM)
• SC-PTM Channel Structure
• SC-PTM Channel Flow
• Massive MIMO
• V2X Overview
• eNB scheduling - transmission mode 3
• Distributed scheduling - transmission mode 4
• Direct communication
• LTE Advanced Pro (Release 15)
• Further NB-IoT Enhancements
• Even further enhanced MTC - eMTC4 (Rel-15)

Related Posts:

• LTE-Advanced Pro (a.k.a. 4.5G)
• New LTE UE Categories (Downlink & Uplink) in Release-13
• Mission Critical Services update from 3GPP - June 2017

Second thoughts about LTE-U / LAA

Its been a while since I wrote about LTE-U / LAA on this blog. I have written a few posts on the small cells blog but they seem to be dated as well. For anyone needing a quick refresher on LTE-U / LAA, please head over to IoTforAll or ShareTechNote. This post is not about the technology per se but the overall ecosystem with LTE-U / LAA (and even Multefire) being part of that.

Lets recap the market status quickly. T-Mobile US has already got LTE-U active and LAA was tested recently. SK Telecom achieved 1Gbps in LAA trials with Ericsson. AT&T has decided to skip the non-standard LTE-U and go to standards based LAA. MTN & Huawei have trialled LAA for in-building in South Africa. All these sound good and inspires confidence in the technology however some observations are worrying me.

Couple of years back when LTE-U idea was conceived, followed by LAA, the 5GHz channels were relatively empty. Recently I have started to see that they are all filling up.

The 5GHz spectrum is already getting congested, how will #MulteFire fit in this? #WGCLon pic.twitter.com/cqNkBwJZN4

— Zahid Ghadialy (@zahidtg) May 10, 2017

Any malls, hotels, service stations or even big buildings I go to, they all seem to be occupied. While supplemental downlink channels are 20MHz each, the Wi-Fi channels could be 20MHz, 40MHz, 80MHz or even 160MHz.

On many occasions I had to switch off my Wi-Fi as the speeds were so poor (due to high number of active users) and go back to using 4G. How will it impact the supplemental downlink in LTE-U / LAA? How will it impact the Wi-Fi users?

On my smartphone, most days I get 30/40Mbps download speeds and it works perfectly fine for all my needs. The only reason we would need higher speeds is to do tethering and use laptops for work, listen to music, play games or watch videos. Most people I know or work with dont require gigabit speeds at the moment.

Once a user that is receiving high speeds data on their device using LTE-U / LAA creates a Wi-Fi hotspot, it may use the same 5GHz channels as the ones that the network is using for supplemental downlink. How do you manage this interference? I am looking forward to discussions on technical fora where users will be asking why their download speeds fall as soon as they switch Wi-Fi hotspot on.

The fact is that in non-dense areas (rural, sub-urban or even general built-up areas), operators do not have to worry about the network being overloaded and can use their licensed spectrum. Nobody is planning to deploy LTE-U / LAA in these areas. In dense and ultra-dense areas, there are many users, many Wi-Fi access points, ad-hoc Wi-Fi networks and many other sources of interference. In theory LTE-U / LAA can help significantly but as there are many sources of interference,its uncertain if it would be a win-win for everyone or just more interference for everyone to deal with.

Further reading:

• Unlicensed LTE Explained – LTE-U vs. LAA vs. LWA vs. Multefire
• LTE-U(LTE-Unlicensed) / LAA / LWA / MultiPath / MulteFire /LTE-R (LTE-Railway)
• Ruckus Wireless LTE Operation in Unlicensed Spectrum [Video]
• 160 MHz channels in 802.11ac wave 2
• MulteFire: A double-edged sword

LTE-Hetnet (LTE-H) a.k.a. LTE Wi-Fi Link Aggregation (LWA)

We have talked about the unlicensed LTE (LTE-U), re-branded as LTE-LAA many times on this blog and the 3G4G Small Cells blog. In fact some analysts have decided to call the current Rel-12 non-standardised Rel-12 version as LTE-U and the standardised version that would be available as part of Release-13 as LTE-LAA.

There is a lot of unease in the WiFi camp because LTE-LAA may hog the 5GHz spectrum that is available as license-exempt for use of Wi-Fi and other similar (future) technologies. Even though LAA may be more efficient as claimed by some vendors, it would reduce the usage for WiFi users in that particular spectrum.

As a result, some vendors have recently proposed LTE/WiFi Link Aggregation as a new feature in Release-13. Alcatel-Lucent, Ruckus Wireless and Qualcomm have all been promoting this. In fact Qualcomm has a pre-MWC teaser video on Youtube. The demo video is embedded as follows:



The Korean operator KT was also involved in demoing this in MWC along with Samsung and Qualcomm. They have termed this feature as LTE-Hetnet or LTE-H.

The Korean analyst firm Netmanias have more detailed technical info on this topic.

Link aggregation by LTE-H demonstrated at MWC 2015 (Source: Netmanias)

As can be seen the data is split/combined in PDCP layer. While this example above shows the practical implementation using C-RAN with Remote Radio Head (RRH) and BaseBand Unit (BBU) being used, the picture at the top shows LTE Anchor in eNodeB. There would be a need for an ideal backhaul to keep latency in the eNodeB to minimum when combining cellular and WiFi data.

Comparison of link level Carrier Aggregation technologies (Source: Netmanias)

The above table shows comparison between the 3 main techniques for increasing data rates through aggregation; CA, LTE-U/LAA and LTE-H/LWA. While CA has been part of 3GPP Release-10 and is available in more of less all new LTE devices, LTE-U and LTE-H is new and would need modifications in the network as well as in the devices. LTE-H would in the end provide similar benefits to LTE-U but is a safer option from devices and spectrum point of view and would be a more agreeable solution by everyone, including the WiFi community.

A final word; last year we wrote a whitepaper laying out our vision of what 4.5G is. I think we put it simply that in 4.5G, you can use WiFi and LTE at the same time. I think LTE-H fulfills that vision much better than other proposals.

LA-LTE and LAA

Recently came across a presentation by Ericsson where they used the term LA-LTE. I asked a few colleagues if they knew or could guess what it means and they all drew blank. I have been blogging about Unlicensed LTE (a.k.a. LTE-U) on the Small Cells blog here. This is a re-branding of LTE-U

LA-LTE stands for 'Licensed Access' LTE. In fact the term that has now been adopted in a recent 3GPP workshop (details below) is Licensed Assisted Access (LAA).

Couple of months back I blogged in detail about LTE-U here. Since then, 3GPP held a workshop where some of the things I mentioned got officially discussed. In case you want to know more, details here. I have to mention that the operator community is quite split on whether this is a better approach or aggregating Wi-Fi with cellular a better approach.

The Wi-Fi community on the other hand is unhappy with this approach. If cellular operators start using their spectrum than it means less spectrum for them to use. I wrote a post on the usage of Dynamic Spectrum Access (DSA) Techniques that would be used in such cases to make sure that Wi-Fi and cellular usage does not happen at the same time, leading to interference.

Here is a presentation from the LTE-U workshop on Use cases and scenarios, not very detailed though.

Finally, the summary presentation of the workshop. As it says on the final slide "The current SI proposal focuses on carrier aggregation operations and uses the acronym LAA (Licensed Assisted Access)", you would be seeing more of LAA.

3GPP workshop on LTE in unlicensed spectrum, June 13, 2014: Chairman Summary from Zahid Ghadialy