Manish Singh, VP Product Line Management at Continuous Computing explains what they've been doing on 4G LTE femtocells, proposes a two layer solution with LTE TDD mode femtocells and tells us of the different LTE femtocell system architecture choices still open.
What progress has Continuous Computing made on LTE femtocells?
We've developed a full reference design based on our commercial software. We support both FDD and TDD modes with channel bandwidth from 5MHz up to 20MHz. This complies with the 3GPP Release 8 specifications (March 2009). We are upgrading this to the latest Release 9 at the moment which will be ready before the end of 2010.
This software has been demonstrated over the air with the picoChip physical layer, allowing us to take performance measurements and be confident of meeting the throughput and response times required.
How do you expect network operators to launch LTE femtocells initially and in what format?
Most of our LTE femtocell customers are looking at 16-32 user capacity with open access. These would be used in the so-called Metro-Femto model, directly deployed by the network operator to provide coverage and capacity in hotspot areas.
Can you tell us of any customers you are working with?
We have a number of customer engagements to date, but no announced wins for residential LTE femtocells.
Continous Computing also supply software for use in macrocell basestations, and we have won business in 15 LTE networks so far. These are in early operator trials undergoing field hardening. This will give us the practical experience and insight to improve performance for both macro and femtocell LTE software.
What is the market potential for LTE? Will WiMAX operators consider switching to it?
Across the board, network operators from cdma2000, HSPA and WiMAX are all looking to adopt LTE in the future. Verizon and KDDI are leading the charge from CDMA operators and are expected to launch within 6-12 months.
Clearwire, Yota and some of the Indian WiMAX operator also want to have LTE in their solution and are actively saying they have LTE as an open option. They see that the ecosystem will be much bigger for LTE than WiMAX in the long term.
Some of the WiMAX operators have been looking at complementary solutions, such as LTE TDD mode. These operators have been asking their vendors to prove their kit is LTE capable.
Will there be clear and common spectrum available for LTE?
Spectrum harmonization for LTE worldwide is just not going to happen. The US has adopted 700MHz. Many European countries are looking at 2.3GHz and 2.6GHz, with Germany also auctioning off their Digital TV Dividend.
A single common frequency band won't happen as it did for 3G at 2100MHz.
Additionally, many operators are still debating whether to refarm their GSM spectrum. Some are already doing this for 3G, such as in Scandinavia.
What will LTE mean for the lifetime of GSM and UMTS?
I don't believe GSM sunset will happen for a very long time – perhaps it's more likely that the 3G sunset will happen first. These are complex issues involving regulatory policy, the large installed base of existing handsets, support for roaming and the actions of other network operators.
So why should network operators invest in LTE anyway?
The primary reason is the competitive threat that WiMAX and LTE can offer much higher data rates which puts pressure on those who can't match it.
The danger is that the industry will overmarket/overhype the possible peak data rates from LTE, which won't be achievable in congested or difficult environments.
I expect the industry battleground to shift from a focus on voice coverage to data capacity. Consumers may churn on their experience of data rates, something that can only be optimised in congested areas by using small cells.
3G femtocells are quite standalone from the macrocell network. How will this change for LTE?
The LTE system is designed from the ground up for very close real-time integration between the macro/micro and femtocell. Residential femtocells can directly affect the configuration and interworking of outdoor LTE macrocells.
One approach for network operators to consider is a clearer two-layer system architecture, what we call a heterogeneous network. This could use LTE FDD in the macro/micro layer and have a separate LTE TDD femtocell layer operating in a separate frequency band.
What are the product requirements for LTE femtocells?
The key software requirements for femtocells are interoperability, field hardness and device interoperability. This is true for all 3G and 4G femtocells. The software must be carrier grade.
There are some addition interoperability tests required for LTE, including the S1 interface which connects to both the MME (Mobility Management Entity) and SGW (Serving Gateway).
There is currently a lack of agreement within the 3GPP by operators to select a single architecture for S1 femtocell implementation. One option is to use an LTE femtocell gateway, another to directly connect all LTE femtocells to the MME. Avoiding a femtocell gateway can create some very challenging signaling plane requirements for the MME, which needs to terminate some 100,000 or more SCTP connections – which is why we developed Trillium SCTP FastPath software.
Finally, can you predict when we might expect to see significant volume of LTE femtocells in use?
Our current prediction is for LTE femto trials to begin in 2011 and volumes to start ramping in 2012 and 2013. Time will tell...
The interview below was recorded at Femtocell World Summit in June 2009.
In the first minute Manish explains their LIPA (Local IP Access) demo and the second minute followed by his views on LTE.
It should be embedded below or can be viewed directly on YouTube.