Sunday 19 July 2015

Small Cells on the Train - A 2 hop solution

An Ericsson blog post some time back talked about the 2 hop solution for trains. Thinking about it, I quite like the idea. The post talks about 3 main challenges on high speed trains:

There are mainly three reasons communication services on high-speed trains is challenging:

  • First, large penetration loss via the shield of the train. This penetration loss is expected to be 20 to 30 dB.
  • Second, large numbers of handovers in very short time. This is due to hundreds or thousands of users needing handover from one site to another concurrently/sequentially. This phenomenon affects system stability and eats up capacity.
  • Third, high power consumption of user equipment (UE). This is because UE-s on the train need higher power to overcome the large penetration loss in uplink as well.

  • A common currently adopted solution for high speed trains is to densify the network along the railway to combat the large penetration loss. However, this will make the second issue more severe, as handover frequency is increased due to smaller site- to-site distance. Another way is to increase the transmission power of the base stations, which helps to solve the large penetration loss as well. However this cannot solve the third issue. And neither of these solutions are cost-effective.

    Another solution I have discussed before is the Mobile Relay Node which was designed with avoiding multiple handovers when the vehicle moves between different macro cells. Not sure about its status in the standardisation process right now.

    Anyway, coming back to the Ericsson post on Small cells on the train, while the Macro cells provide the TD-LTE backhaul outside, Radio Over Fiber (ROF) is used inside the tunnels to provide the same coverage.

    Within the train Small cells (I guess multiple small cells will be needed in practical deployments, one for each carriage) can provide good coverage to the users and avoid the need for handovers.

    Embedded is the video from Ericsson Taiwan that provides more details about this trial

    Saturday 4 July 2015

    Disguising Small Cells in Rural areas

    Bethlehem Middle School student Jeremy Luzinski, center, holds a sign Sunday to protest the planned construction of a cell phone tower a few hundred feet from the Eagle Elementary School, which is behind him, in Bethlehem. ( Philip Kamrass / Times Union ) Photo: PHILIP KAMRASS

    We all want good mobile coverage but we do not want the cell towers in our backyard. The main reason being that somehow this can affect our health and maybe cause cancer. There is absolutely no link between cellphone radiation and cancer as I have discussed in an earlier post here. With more studies having been done, any possible links between cellphone tower and existence of cancer seems to diminish. On the WHO list, exposure to radio emissions is now category 2b (possible carcinogens), along with coffee, talcum powder and many other substances to which we all expose ourselves.

    As a result, the mobile operators have started disguising cell phone towers. A cellphone tower inside the bell tower, rear right, is seen over the Resurrection Lutheran Church in Ankeny, Iowa. In rural areas disguising also doesn't affect the scenery.

    The cactus cell tower in Arizona is another great example of coverage by stealth.

    Small cells on the other hand is a whole new ball game. We are so used to seeing WiFi routers that people will probably not bat an eyelid with the small cell above by Vodafone in Cranborne.

    Another disguise is the bird box cell booster, also by Vodafone. It picks up the mobile signal from the nearest network mast, and boosts it to provide better coverage in the surrounding area. This would definitely fit with the surrounding but getting power can sometimes be tricky.

    Do you know of any disguised small cells, please let us know.