Femtocell Challenges

In a previous post I talked about the potential benefits of femtocells to the operators as well as consumers. In this post I'd like to investigate the potential hurdles in the road to viable femtocell solutions.

Looking at various analysts remarks I narrowed the list of potential show stoppers to the following items, all of which are not unresolvable, but one has to be aware of:

Cost:
This is the obvious one. There is no doubt that we are well into the cost reduction era. This is by far the number one item on every operator's agenda. The bottom line is that operators want to see a nice dollar savings associated with Femto cells, which increases pressure on femto cell development firms to reduce their price tag. Traditionally, pricing is based on a BOM plus margins. An alternative way for development firms is to price based on potential benefits/savings. My firm has recently been engaged in a similar pricing activity with a potential investor.

The cost challange means that there is a limit to the amount of effort and features developers will bundle in the femto cell box. Deciding what is "sufficient" feature list is a difficult call (check the technology life cycle model proposed by D. Normann in one of my previous posts)

Radio Planning and interference management:
Unlike Wi Fi, the Femto cell is likely to use the licensed spectrum e.g. UMTS band. Although it is my view that the femto network is better have its own carrier, many clients would like the femto cell concept to work on the same carrier frequency used by existing infrastructure be it a macro, micro or pico layer.
Femtocells are expected to coexist with the rest of the network by automatically configuring themselves. Operator or user intervention is undesirable...a femto cell box has to be fully plug and play without the need to setup,configure or optimise it in anyway. Therefore lots of effort is being spent on femto cell radio management features e.g. choosing the right carrier, automatic setting of power levels, protecting other infrastructure from harmful interference, handoff ...etc .

Core Network Integration:
I touched upon this in a previous post (Femtocell Architecture).
In a nutshell, a legacy architecture is too old fashioned, while on the other hand a full flat IP architecture with an IMS core is an expensive undertaking with no sign of becoming available soon.

Interim solutions relying on some kind of concentrator seem to attract some attention. I can't really comment much on this and I'll leave it to the core experts to make their minds.

With converged solutions such as femto cells there is also an increased expectation of a higher level of network intelligence and features at the edges of the network (as opposed to the traditional model of core intelligence).

End user perception:
The consumer will (and has to) ask: "what's in it for me". At the moment most of the promises revolve around cheaper calls as well as using the often over hyped word: "convergence". The fact is that most people do not know what this word means! The operators will find it challenging to convince the consumer that the femtocell is the way to go.
In addition, there is the issue of backward compatibility in terms of usage. Many people have Internet access at home and a big proportion use WiFi routers to have wireless coverage at home. Is the Femtocell going to replace that? if so, then there is a need to have a combined WiFi/Femto router to enable legacy equipment to access the Internet. Alternatively people will end up with a stack of routers, from different suppliers.... hardly a convergent solution!.
Therefore the extent of device convergence will play a significant role in any operator's femtocell strategy.
There are also health concerns about exposure to increased levels of RF waves.

Advanced Cellular Technologies Episode 4: Evolution of UMTS/HSDPA

3GPP is constantly thinking of ways to improve the performance of UMTS to compete with new emerging technologies that promise enhanced performance over legacy systems.

There are two evolution philosophies within 3GPP. One philosophy is start from scratch and design a new system with new architecture and air interface which do not have any legacy constraints. Another philosophy is to fine-tune existing architecture and introduce advanced features to the existing air interface to enhance its performance to the best level possible while maintaining backward compatibility. The driver for this second approach is to capitalize on existing infrastructure investment. While 3GPP is devising strategies to evolve UMTS on the long term to achieve a set of target performance goals, 3GPP is also thinking of ways to develop the existing UMTS standard to reach its full potential.

Near-term 3GPP enhancements
The near-term enhancements to UMTS are addressed in 3GPP Rel’6 and Rel’7. These primarily focus on the issues directly related to market deployment and the customer experience and to fine-tune and incrementally improve the performance of UMTS earlier standard releases to ensure that UMTS/HSDPA products and services are of high quality, perform correctly and are as fully featured as intended. Some of the goals of these enhancements are:

- Call set-up delay reduction for improved end-user experience.
- Signalling flow optimization.
- Support of real-time packet services such as VoIP.
- Increased system efficiency and overhead reduction.

Medium-term HSDPA evolution: HSPA+
HSPA+ is a manifestation of the evolved HSPA philosophy where the existing HSPA implementation is pushed to its limits by introducing various improvements to increase the efficiency of the system while maintaining backward compatibility. Some of these improvements are:
- Higher order modulation
- The use of advanced receiver such as Equalizers and IC.
- Possibly, the introduction of MIMO receivers and Receive diversity.

The main driver for HSPA+ is to capitalize on existing HSPA investment in infrastructure by focusing on backward compatibility and upgrade simplicity.

Long Term Evolution (LTE) of 3GPP
The main objective for LTE is to enhance the 3GPP standard to become a highly competitive packet-based radio access technology. 3GPP promises huge increases in performance and capacity with LTE. From a performance point of view, the main goals of LTE are:

Flexible spectrum usage with scalable system bandwidth from 1.25 MHz up to 20 MHz
Increased spectrum efficiency and peak data rates at cell edge. Target peak rates of 100 Mbps/DL and 50 Mbps/UL.
Reduced latency for both user and control plane: less than 10ms round trip delay for user plane between UE and the serving RAN node, less than 100ms transition time for control plane between inactive state and active state.

LTE philosophy is more “revolutionary” than HSPA+ in scope. In order to achieve the ambitious goals set for it, LTE takes a fresh look at system architecture and air interface access without the constraints of legacy systems. Therefore system architecture will noticeably change with a new radio access layer.

Although many aspects of LTE are still under discussion in 3GPP, some of the main attributes are:

• OFDM-based air interface (OFDM=Orthogonal Frequency Division Multiplexing).
• Flat IP system architecture. (Often this is described as SAE: System Architecture Evolution, and is a separate study item in 3GPP).
• Higher level modulation and state of the art receiver technology.