Are you measuring the overall capacity of the network during your 5G DSS deployment?

While we have discussed how critical is 5G Dynamic Spectrum Sharing DSS for your company in the previous article, DSS includes also some challenges that need to be considered.

Jose Manuel Alvarez, RAN Expert at Telefonica Spain, said "Dynamic Spectrum Sharing (DSS) between 4G and 5G technologies will play a key role in a smooth 5G introduction, as it can be seen as an efficient and rapid way to have 5G nationwide coverage by using dynamically the existing LTE spectrum, while the C-band 5G network continues to be deployed. It’s true there may be some issues to be addressed in this first wave of NSA networks (customer experience still similar to 4G, slight impact on LTE capacity, challenging technical feature) but the 5G ecosystem is evolving fast and 5G devices supporting DSS technology are already available, as well as demands from the industry for the first applications and services that require from 5G capabilities. 5G is a much anticipated technology that will bring to our connected society a lot of benefits, many of them still to be discovered. Now it’s the time for experiencing the technology, showing its possibilities, and I’m convinced DSS technology can help to explore now and everywhere the 5G new world".

DSS decreases the capacity of the network slightly, the capacity drop must be measured and understood during the initial trial phase to prevent surprises after the rollout. In general, DSS changes the operation of the base station packet scheduler a great deal. Hence, throughout performance evaluation of this critical network function is another important verification area. Both these aspects can be measured using device-based lab and field testing solutions. 

Reduced capacity. Spectral efficiency of the network drops when DSS is deployed. This drop directly reduces network capacity. The fundamental reason for capacity decrease is the increase of control channels. Both LTE and 5G systems have various control and reference channels transmitted in uplink and downlink. These channels are mandatory for coordination and control purposes of the network and without them, the network cannot operate properly. The drawback is that these channels are using share of the spectrum that could be otherwise used for the payload of the users. In DSS this overhead is increased as the control channels of both 5G and 4G need to be transmitted. The overhead can be up to several tens of percent. The exact capacity reduction may vary, depending on the implementation of the DSS. 3GPP allows many distinct ways to implement the DSS.

Scheduling Challenges.

The base station resource scheduler is allocating the available DL and UL radio resources between the users in a cell. In DSS the LTE and 5G schedulers are merged into one function, responsible for allocating the radio resources of both 5G and LTE users. Base station resource scheduler is a key network function impacting the DSS performance. The scheduler operation is not defined 3GPP specifications. Therefore, it gives an opportunity for the network vendors to differentiate among each other. This makes it also an important performance verification area for the network operators. Following challenges or verification areas may exist with DSS

• As the number of NR devices in a network increases: it is important that sufficient scheduling capacity for NR UEs on the shared carriers is ensured.
• The scheduling resolution between LTE and 5G can be 1ms at highest, or anything less depending on the scheduler implementation. Vendors may try to differentiate between each other with the scheduling resolution. Performance impact of the scheduling resolution is not obvious, it can be verified as part of the trials.
• Latency in 5G and LTE.
• VoLTE and VoNR over DSS, voice quality measurement

Technology moves fast. Unfortunately, many of the Testing products available for measuring accurately spectrum, mobility and handovers have not kept pace.

That’s why we at Keysight have been collating feedback and suggestions from chipset and device manufacturers (Keysight has supported the development of about 75% of 5G devices) over many years regarding their technical specifications for implementing the most reliable field and drive testing solutions. I outline a summary of our DSS end to end field and lab testing methodology, which have been specifically designed to meet the needs of communications service providers:

• Two devices (or more) both 5G DSS and LTE only devices.
• Test network, field or lab, with no live traffic, only the test devices. This ensures accurate monitoring of the resource allocations between LTE and 5G devices under test.
• Test devices connected to the Nemo Outdoor for modem diagnostic monitoring, application protocol stack monitoring, and test control.
• Active tests with bulk data transfer (DL and UL) and ping via Nemo Outdoor, tests run inside the phone
• Example test cases: Start data transfer from 5G device, add 4G device data transfer, Previous in opposite order
• Key metrics to be monitored in the test cases: L1 or MAC throughput LTE device and 5G device, Ping, Voice quality MOS, PRB allocations LTE device and 5G device, Total PRB allocation LTE+5G and SS-RSRP, RSRP.

Networks are going to continue evolving rapidly in the coming years, which will increasingly lead to even more challenges. In my opinion, Network Engineering teams need to have accurate information about customer experience in relation to network capacity and latency in real-time, as well as detailed information that can be used to reduce, as much as possible, the troubleshooting process.

This article is based on Keysight DSS Technology Overview specification written by Javier Campos, Binu Mathew, Llaria Massa, Mohit Kanchan and Matti Passoja.

Feel free to ask me if you want to secure a smooth 4G to 5G transition with DSS.

5G Keep Moving!