Femtocell network architecture

- an overview of the basics of the femtocell network architecture including that for 3G UMTS including the HNB, Iu-h interface and the HNB gateway, and LTE.

In order to enable femtocells to operate within a variety of networks a standard femtocell network architecture is required. This femtocell network architecture enables a variety of femtocells from different manufacturers to work in the networks of different operators. In this way costs can be reduced by gaining the economies of scale. Also there are greater levels of competition between femtocell manufacturers which also keep the costs under control.

Femtocell network architecture requirements

With different cellular telecommunications systems there will need to be different ways of implementing the actual femtocell network architecture. However there are a number of common requirements for the femtocell network architecture regardless of the cellular system used.

The fundamental requirements for the femtocell network architecture are for the femtocell itself to be located within the users building (although some femtocells may be located externally to provide local coverage in areas where there is no other coverage).

There must be a low cost and accessible form of backhaul. Typically this uses the Internet via the users broadband connection.

Finally there must be a gateway to allow the traffic from femtocells carried by the Internet to then access the operator core network.

3GPP HNB femtocell network architecture

Seeing the need to provide an industry-wide standard for femtocell network architecture, 3GPP worked with vendors, and operators to provide the optimum standard. The new standard developed a new interface and also standardised the elements within the femtocell network architecture.

Femtocell network architecture

3g femtocell network architecture

There are three main elements to the femtocell network architecture as defined by 3GPP:

  • Home NodeB (HNB):   The Home Node B is 3G UMTS terminology for the femtocell access point within the home, or other location. The HNB will incorporate the capabilities of a standard Node B as well as the radio resource management functions found within a Radio Network Controller, RNC.
  • HNB Gateway (HNB-GW):   This is the entry point to the core network. The link into the core network is provided over Iu-cs and Iu-ps interface which are already used for links from Radio Network Controllers to the remaining core network.

    The HNB-GW has the following functions:
    • It provides authentication and certification to allow only data to and from authorised HNBs
    • The HNB-GW aggregates traffic from a large number of HNBs and provides an entry point into the operator core network.
    • The HNB-GW provides a mechanism to support enhanced features such as clock sync distribution, other IP based synchronisation (e.g. IEEE1588, IETF Network Time Protocol, NTP, etc)
  • Iu-h Interface:   The Iu-h interface is used to provide the link or interface that connects the HNB with the HNB-GW. The Iu-h interface includes a new HNB Application Protocol, HNBAP that provides the high level of scalability required for the HNB deployment that will occur in a rather ad-hoc fashion.

LTE femtocell architecture

As the inclusion of femtocell technology is key to the deployment of LTE, it was necessary to develop the standardised LTE femtocell network architecture to take account of the LTE SAE, System Architecture Evolution requirements.

The concept behind the LTE SAE is to provide a much flatter overall network architecture. This has many advantages in terms of network simplification and it is also a key element in enabling much lower levels of latency - a key requirement for LTE.

The femtocell network architecture has been defined to allow maximum flexibility and scalability to ensure that the deployment can be easily incorporated into the existing structures. By its very nature, the deployment of femtocells is achieved on an ad-hoc basis, this forms a large requirement for the system.

By Ian Poole

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