Friday 2 August 2013

Mobile Relay Nodes (MRN) in Rel-12

Interesting article in IEEE Comms Magazine (embedded below) about the Moving Relay Node (MRN). 3GPP has done a study on a similar topic available in 3GPP TR 36.836. To make the case for the MRN they provide a reference scenario of high speed train

The TGV Eurostar in Europe is 393 m long, moves at speed reaching 300 km/h. The Shinkansen in Japan has similar characteristics, with 480 m long, 300 km/h of commercial speed. The high speed train in China is 432 m long moving at speed reaching 350 km/h.

Due to fast moving and well shield carriage, the network in high speed train scenario faces severe Doppler frequency shift and high penetration loss, reduced handover success rate and increased power consumption of UEs.

To improve the coverage of the train deployment, access devices can be mounted on the high speed train, providing a wireless backhaul connection via the eNBs along the railway by outer antenna e.g. installed on top of the train, and wireless connectivity to the UEs inside carriages by inner antenna installed inside.

MRN is a good solution but when it has to operate alongside with many other technologies can pose challenges. The IEEE article summarises it as follows:

Furthermore, new challenges regarding interference management arise due to the use of MRNs. As the distance between an MRN and the vehicular UE served by it is very short, the MRN and the vehicular UE can communicate with each other using very low power. In addition, the VPL can further help to dampen the signal of the MRN access link that propagates out from the vehicle. Thus, compared to direct transmission, the use of MRNs generates less interference from the access link, for both downlink and uplink, to UE outside the vehicles. This is appreciated in a densely deployed urban scenario where link availabilities are usually dependent on interference rather than coverage. For the backhaul link, however, the problem becomes complicated, as interference is expected both between different MRN backhaul links, and between MRN backhaul links and macro UE. The use of predictor antennas can improve CSI accuracy to enable the use of advanced interference avoidance and cancellation schemes for the backhaul links. Nevertheless, whether enhancements on the current intercell interference coordination (ICIC) framework in LTE are needed to support the use of MRNs still requires further investigation.

I have been thinking of possible use of 8x8 MIMO, this can be one possible scenario where the network may use 8x8 or even 4x4. Anyway, the complete article is embedded below:


Ravi Sinha (Via LTE Evolution group on Linkedin) said...

This whole concept looks very innovative, but I have some concerns other than those discussed in the article:
1. For paging, in case of Class 1 MRN, we need to provide a tracking area and there is no concept of dynamically moving TAC.
2. Consider that for back haul WiFi/ NLOS solution/ LTE UE then S1/X2 is converged on the user plan and due to bad CQI/ CSI reporting how far this link will be alive and in case of recovery how the MRN will behave, since the disturbance is happening on core link. Similarily if IPSEC is enabled, how this whole thing will be handled, if the back haul is also LTE, in case of WiFi most of the concerns are same.
3. How to make sure that the other UE from the same carrier near to the vehicle (MRN) don't select and re-select MRN even if the VPL is considered, but at cell edge it may be possible that the weak signal strength is not masked enough to be considered a target, mainly when the other cell site signals are weaker.
4. What if the WiFi is also available and Donor ENB doesn't have the band width to support the back haul.
5. How to make sure that MRN has got a dedicated number of PRB from the Donor ENB for back haul.

Eric Cummings (Via LTE Evolution group on Linkedin) said...

we just jumped back to 1996 and re-invented the 3 watt booster kit except now its wireless

Thrineshwara M R (Via LTE Advanced group on Linkedin) said...

Thanks Mr. Zahid for highlighting this article. Quite interesting to learn about MRN.

Frank ZHENG (Via LTE (Long Term Evolution) - 3GPP group on Linkedin) said...

Great to learn, high speed train is quite a challenging issuse

juanmorenogl said...

Zahid, could you give us the reference of the IEEE paper where the figure comes from?

Thank you very much.

Zahid Ghadialy said...

Its the same slideshare paper embedded below - from IEEE Communications Magazine, June 2013