Femtocells Configuration, Organization, and Installation
- an overview addressing the installation, organization and configuration of femtocells.
One of the key elements of the femtocell its that its installation, organization and configuration should be completely trouble free and without any intervention from the home owner. It is a prime requirement that femtocells must be able to be installed by people with no technical knowledge of their operation and once installed, they should continue to operate without any intervention, even if the surrounding environment changes.
Therefore the installation of the femtocell should be totally plug and play, and it should not require any intervention from the users apart from connecting it to an internet router and plugging it in to a mains supply. This requires a considerable amount of intelligence within the femto cell itself.
Femtocell self-organization requirements
Femtocells are required to be able to completely self organise themselves so that there is no intervention from the user. This can be split into three main areas:
- Femtocell self configuration: This element of femtocell installation requires the femtocell to be able to select the initial parameters required for operation to commence. These will include the channel, neighbour list, power, etc.
- Femtocell self optimisation: Once operational, the femtocell will need to monitor the environment to ensure that it takes account of any changes required including the channel and resources required.
- Femtocell self healing: As problems may occur after set-up, the femtocell will need to be able to resolve any problems that may occur.
Femtocell configuration at start-up
One of the key elements of the femtocell configuration occurs at the first start up when the femtocell equipment is being installed. It is essential that this operates smoothly for the concept to gain acceptance by the user.
After acquiring a femtocell the customer should only need to plug the femtocell intot he power and connect it to the Internet connection to provide the backhaul connection.
With power applied, the first element of the registration is for the femtocell to register within the network. The femtocell will attempt to gain access to the core network via the gateway (HNB-GW in the case of a UMTS femtocell). To achieve this it will utilise the femtocell ID - a unique identifier given to the each femtocell. Additionally the operator is likely to have obtained the address where the user will base the femtocell.
With the femtocell successfully registered, a check for the latest software will be undertaken. This can be downloaded if required, and the femtocell will then verify the correct operation of the new software.
With the backhaul connection successfully operational, the next stage of the femtocell configuration is to configure the radio interface parameters. There are two main elements toth is:
- Primary femtocell configuration information:
- RF channel information (frequencies for uplink and downlink).
- Scrambling codes.
- Network femtocell configuration information:
- Service area code and information.
- Neighbour list.
- Physical cell ID.
- RF parameters including pilot, maximum RF power, etc..
Generally this information is provided by the backhaul channel from the Operation Support Subsystem, OSS of the network. If this cannot be provided by the OSS, then it is possible for the femtocell to be able to detect the conditions and configure itself accordingly. However it is always preferable for the OSS to provide the data so that the femtocell is configured according to the requirements of the network.
Sensing the radio environment
Regardless of whether femtocell configuration information is supplied from the OSS over the backhaul network, it is necessary for the femtocell to sense the radio environment. In this way the femtocell can sense the signal levels of neighbouring cells. The techniques used rely heavily on cognitive radio technology.
There are a number of elements to the radio sensing:
- Listen mode: In order that the femtocell is able to sense the surrounding radio environment it must carefully listen. Accordingly it is necessary for the femtocell to have the capability to listen on its own channels as well as other channels to sense the overall radio environment.
In listen mode, the femtocell uses similar techniques to this of a standard user equipment, listening to the broadcast and control channels of the strongest base station in the vicinity, and synchronise with the base station. It can then distinguish the type of cell and also the estimated signal strengths and path losses.
Using the information obtained from radio environment, the femtocell can adjust its settings accordingly - adjusting parameters such as power level to minimise interference. The femtocell can also record its own figures for elements such as dropped calls, failed handovers and the like. In this way it is able to adjust its performance accordingly, thereby providing part of the femtocell optimisation routines.
- Message exchange: In some instances the femtocells may broadcast information that can be received by neighbouring base stations - either femtocells or even macrocells. In this way, femtocells can cooperate more effectively and improve performance as well as reducing interference.
One of the key features of the femtocell is that it is able to provide configuration, organisation and optimisation without the need for external intervention. The self control capabilities of femtocells exceed those of many macro-cells and as such the femtocell is a very sophisticated network entity. With levels of integration and software capabilities increasing, the facilities available within a femtocell are able to meet the requirements for self configuration, optimisation and healing.
By Ian Poole
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