Consensus on LTE Femtocell Layer as starting point

Many people in our industry are now of the opinion that the best way forward with LTE is to roll them out as Femtocells and then when more and more people start using them, then start deploying LTE Microcells/Macrocells.


There is this news in Gigaom:


Will personal cell towers replace the giant monstrosities currently sitting on rooftops and beside highways? Manish Singh, a VP with Continuous Computing, says that may be the case with the 4G buildout. He spoke with me about the company’s new line of software and hardware for carriers deploying LTE networks, noting that those in North America and Europe are asking whether they should deploy citywide — or one consumer at a time, using femtocells.

He said two things are driving this, one being the huge capital expenditure associated with building out a wireless network and the second being the length of time it has taken for widespread use of the 3G data networks. Verizon started deploying its EVDO networks in 2003, but only in the last few months — thanks to better pricing and the iPhone — has 3G data been used by many customers. When it comes to 4G provided by LTE, a controlled femtocell deployment ensures that customers could get LTE speeds of up to 150 Mbps (in theory) while at home or in coffee shops and use the existing 3G network while out and about.

The femtocell strategy will be used in another 4G rollout — this time for WiMAX — as part of the Clearwire joint venture involving Clearwire, Sprint, Google and several cable companies.


And there was this other news in Electronics Weekly by CTO of PicoChip:


Approximately 60% of mobile usage already takes place indoors, yet providing in-building coverage is a technical problem at the gigahertz frequencies used for Wimax and LTE. This is only set to get worse as the mobile continues to replace the home phone. Research indicates that, as “all you can eat” data packages become commonplace, this number is likely to reach 75% by 2011.

As transmission frequency increases, in-building penetration degrades. The additional attenuation reduces throughput for those users indoors, but there is another effect too: if the traditional macrocell allocates more power to reach the indoor user, this increases the interference for other users. Such realities inevitably have a quantifiable, negative impact on cell capacity, making it impossible to deliver 10 times the performance of 3G that is a fundamental requirement of the 4G vision.

Furthermore, the large cell approach is fundamentally less able to provide the benefits for which LTE was intended. As Cooper’s Law identifies, the best way to increase traffic density is via smaller cell sizes. A macrocell gets hit twice in this respect – it has poorer total throughput due to RF conditions and it has to spread that throughput over a much wider area.

Most operators considering the roll-out of LTE already have widespread HSPA networks. If terminal devices are going to be multimode (LTE and HSPA and GSM, for example), there is little point in deploying LTE everywhere and ensuring ubiquitous coverage, since the user experience may be no better than that provided by HSPA (or could be worse). The capital expenditure of a small cell approach need not be prohibitive. Indeed, substantial savings will be available on the back of the technological innovations that are driving down the bill of materials costs for residential femtocells.

A small cell approach also has cost implications for operating expenditure. These networks need to incorporate self-optimising technology to eliminate manual configuration during deployment and throughout the life of the equipment. These self-optimising networks (SONs) will, for instance, dynamically optimise radio network performance in use and provide intelligent backhaul capabilities. Operators are already recognising these requirements and mandating the provision of SONs; the emerging residential femtocell in WCDMA is proving this capability now.

This network architecture change will produce corresponding changes throughout the infrastructure value chain. The network equipment industry will move towards a consumer market approach – in a manner similar to the use of “commercial off-the-shelf” (COTS) technologies in the military equipment market, infrastructure manufacturers can borrow from femtocell innovations to benefit from consumer electronics economics. This will place an onus on IC suppliers to offer unprecedented levels of systems-level expertise and support.


The traditional macrocell approach will flounder at the next stage of network evolution: they are too expensive a solution and do not deliver the required results.

Last month in a blog, I mentioned that the Femtocell issue is becoming urgent because of the Release 8 freeze date in December. Othmar Kyas from Textronix argues the same thing in a different way in Total Telecom:

Currently, 3G femto access points, which are the WLAN-like devices residing at customer premises, are connected to so-called femto gateways via the customers' private DSL links using largely proprietary protocols to provide femto-specific functionalities such as plug and play, self-organising features, guest user management, roaming or charging. The femto gateway, which can connect to thousands of femto access points, translates the femto communication links to the "Iu" interface, which is the standard connection between a 3G core and a 3G access network.

In order to resolve resulting compatibility and interworking issues, 3GPP, the standardisation body behind the GSM family of technologies, has nominated this issue as a study item in the upcoming version of its standard, 3GPP Release 8.

Release 8 is also the first version of the 3GPP standard that contains the long awaited fourth-generation (4G) GSM variant LTE (Long-Term Evolution). Femto aspects in this study cover both 3G (UMTS) and 4G (LTE) infrastructures. 3GPP Release 8 describes the femto architecture in an official standard document for the first time. It introduces the concept of home base stations for 3G and 4G using the nomenclature Home Node B (HNB) and Home eNodeB (HeNB). Additionally, it defines a new interface capable of directly connecting home base stations to 3G and 4G core networks, the 'IuH' interface.

According to the 3GPP specification, all home base stations in the future will have to provide the following functionality:

• HNB and HeNB deployed as small UTRA and EUTRAN cells, respectively, in domestic, small office and similar environments.

• The HNB and HeNB interconnects with the 3G core and Evolved Packet Core, respectively, over a fixed broadband access network (e.g. DSL, cable, etc.).

• Support for full mobility into and out of a HeNB coverage including service continuity where applicable.

• Operators and owners of HeNB and HNB will be able to control access to the resources provided.

The full specification for HNBs, HeNBs and IuH will become available with Release 9 of the 3GPP standard, which probably will not publish before the beginning of 2010. (Release 8 is scheduled to freeze in December 2008 and to publish in early 2009).

The second challenge that needs to be overcome before the 'femto dream' can materialise is the cost of the femto hardware. To be successful in the competitive consumer market, femto access points probably need to sell below US$200. Current chip-set prices for 3G femto base stations still range significantly above $100, indicating that there is still substantial work needed in terms of manufacturing cost reduction.

Will the lack of standardisation or the hardware cost hinder the success of femto? Have equipment manufacturers and operators learned the expensive 3G-lesson? Will the femto equipment be as plug-and-play and as interoperable as claimed? Will the performance live up to the high customer expectations?

Finally, there will need to be attractive tariffs or flat-rate payment plan offers from operators to kick start a 3G business that reaches far beyond early adopters and business users but actually grabs a mass market.

Kick-starting the LTE technology as Femtocells may have its own advantage and will help iron out the initial problems which are bound to cause hiccups otherwise. Yesterday I mentioned that LTE may be far away but it can be rolled out earlier if this approach is taken. As it was mentioned earlier, 60% of the people access data from their homes, LTE based Femtocells may be what may turn this figure into 90%+. What is needed now would be some killer applications ;)