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- Published on Wednesday, 14 December 2011
- Written by David Chambers
Qualcomm have published a research paper comparing LTE femtocells operating in close co-ordination with the macrocell network (a so-called HetNet or Heterogeneous Network) and secondly macrocells augmented by uncontrolled Wi-Fi. Perhaps not unsurprisingly, the results favoured the operator controlled femtocell scenario. But for me the surprise was just how much more effective LTE was than Wi-Fi, showing a capacity gain of 920% from just 4 LTE femtocells. The question is - does this present the full picture?
It's not the first time concerns expressed about Wi-Fi congestion in areas of heavy use
If my own experience with Wi-Fi at busy airports and other transport hubs is anything to go by, I'm not surprised to hear some in the industry express concern with issues around Wi-Fi congestion. There are several places where my PC or handset can see (too) many different Wi-Fi hotspots, but getting anything like a stable or useful connection is patchy at best.
This contrasts with my experience at home or in less congested office environments, where my iPhone or laptop connect easily and efficiently. Wi-Fi has the added advantages of low cost, wide availability and plenty of spectrum (especially at 5GHz). It is present in more than 1 billion devices today, and will be standard in most of the 700 million new smartphones forecast to be manufactured during 2012.
Some unfortunate misreporting?
Virgin Media, a UK cable network, were recently (mis)reported to be pondering a solution to this problem themselves. The Guardian newspaper suggested they might bid for LTE spectrum and build out large numbers of LTE residential femtocells, offering a more reliable and consistent service to their customers. This report was quickly refuted by their PR department the following day, saying it was just some blue-sky thinking from one of their executives. So while this specific example might not be taken seriously, there is some evidence that the industry is trying to figure out how to find the balance between so-called "uncontrolled" Wi-Fi and the more predictable commercial wireless data service over managed mobile networks.
As always, there is a balance between what the end consumers value (always on access to high speed data everywhere they go) and what they want to pay (only where they perceive value).
What the research uncovered
Some very clever people at Qualcomm have simulated several scenarios and compared the capacity gain between adding Wi-Fi and LTE femtocells. Their report is freely available from their website. They've done this for an exclusive LTE network, where in practice most networks would also have considerable amounts of 3G as part of the full HetNet (Heterogeneous Network) mix. As with today's 3G femtocells/macrocells, the LTE femtocells and small cells would share and reuse the same frequencies as the LTE macrocells.
The study took into account some of the latest features of LTE, specified in Release 10 and known as LTE Advanced. In particular, IC (Interference Cancellation) and eICIC (enhanced Inter-Cell Interference Co-ordination), which provides planning guidelines and interworking between the femtocells and macrocells to enhance the performance of sharing the same spectrum.
Two main scenarios were modelled, one where the users were randomly distributed and a second where they were clustered closer to where the small cells/Wi-Fi hotspots were.
The most dramatic result was for a suburban scenario where an astonishing 920% capacity gain was achieved with just 4 LTE femtocells positioned close to the users, considerably more efficient that the 230% gain from Wi-Fi in the same scenario.
In more dense environments, where the picocells and femtocells are closer to the macro, the capacity gain from 4 small cells is a more modest 150%, still higher than the Wi-Fi figure of 70%.
In all cases, the LTE small cells outperformed similar numbers of Wi-Fi hotspots.
Other factors at play
There are some constraints with this approach of course. Wi-Fi is already embedded in a large and growing proportion of smartphones and laptops today, although many featurephones may not. It will take time for LTE smartphones to become widely deployed and consume a significant proportion of data traffic. Operators will want to make full use of their extensive 3G and HSPA investments in both network and handset subsidies. Today's Wi-Fi hotspots are seen as low cost, but I expect the hardware costs are probably over
The report also discusses three elements affecting the end user experience:
- Mobility, where handover within the mobile network is well specified and implemented
- Quality of Service, where LTE includes a range of QoS capabilities
- Security, where authentication and encryption procedures may vary
At face value, this technical research confirms that the capacity delivered through small cells can be considerably more than using more traditional macrocells, with a 10x capacity gain from just 4 additional femtocells. It also reinforced how much more effective a fully co-ordinated wireless system can be compared with a network of best effort Wi-Fi hotspots.
The challenge will be for network operators to translate this capability into added value perceived by the end users who fund it.
The report can be downloaded from Qualcomm's website here
Do you agree with these findings - feel free to comment below (anonymously if you prefer).
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