The advent of Femto Cells

Home base station solutions, also called Femto cells have recently attracted a lot of attention. The idea is to give the mobile user a small box similar to wireless routers, which provides mobile cellular coverage at home. But why would mobile operators want to do that?

In order to answer this question, one has to look at what mobile operators are competing against. Fixed line carriers and DSL service providers are seriously threatening the mobile business by offering new products centered around Fixed Mobile Convergence, which in essence utilises wireless access technology to capture mobile users when at home, and divert their mobile originated voice and data calls to the fixed line network.

Mobile operators found themselves in a predicament: the traditional Macro cellular networks are not able to compete with what DSL service providers can offer, neither from a cost structure point of view, nor in terms of access speeds. (of course the mobile operators are partly to blame because they picked the wrong battle by trying to compete on the basis of access speeds rather than mobile centric applications).

A home base station or femto cell can help mobile operators in many ways. First they can compete directly with other home access solutions which rely on other types of access technology such as WiFi or WiMax. This is because low cost mobile handsets are widely available, whereas dual mode handsets with WiFi capabilities are pricey and still limited in variety.

The femto cell will also enable the operator to cater for subscribers where the service is most needed. Compare this with traditional macro deployment where the infrastructure is first built in places where subscribers are "likely" to appear and even before subscribers start using the network. A femto cell also circumvents the issue of outdoor-to-indoor propagation which typically kills the capacity of 3G and 3.5G systems.

The deployment costs associated with a femto cell are marginal in comparison with Macro cell deployment. This is because the customer is providing the "real estate" to keep the box, the power, as well as the backhaul (e.g. DSL subscription). I don't assume here that Femto cells will replace the macro layer, nevertheless the extent of investment in the macro layer will be considerably less.

Femto cells will also enable the operator to offer creative and disruptive tariffs to directly compete with fixed line. Home zone offers can also be more effective than traditional home zone offers using macro cells which extend for kilometers sometimes (because they rely on a cell ID parameter).

So where is the catch? I will discuss the downside in a future post.

Advanced Cellular Technologies Episode 3: Continuous Packet Connectivity (CPC)

CPC is a large 3GPP R7 work item. What is the motivation for it, what does it do and what should we expect out of it? We'll find out in this post.

Motivation:
When a handset is activated it is usually put in Idle state until the user decides to transmit or receive data, at which point the system transfers the handset from the Idle state to a "connected" state. If the user is inactive for a number of seconds, the handset is put again in Idle state in order to save network resources. This turns out to be problematic with certain types of applications that require continuous connectivity, such as IM, hence the motivation for Continuous Packet Connectivity. The vision is to make the mobile bradband experience similar to the DSL experience in terms of network response time.

The main concern with CPC is the amount of battery power required to maintain connectivity. There are various concepts and schemes that, together, will enable CPC. Some of these concepts are:

DPCCH gating:
DPCCH is a control channel which is typically always on. This will change such that control channels have a discontinuous pattern, which reduces the amount of interference and increases battery life.

Modified HS-SCCH operation:
HS-SCCH is a channel that carries HSDPA signaling in the downlink. This channel typically consumes large amount of power which eats up a part of the cell capacity. Therefore 3GPP came with various suggestions to reduce its effects by restricting it, or eliminate it altogether.

CQI reporting reduction:
CQI stands for Channel Quality Indicator, which is a message sent by the terminal to the bas station reporting the channel quality so that the base station can decide what to send to the terminal. Reducing the rate of CQI signaling will reduce overheads. This means that more bandwidth is available for traffic packets instead of overhead.