BBC R&D Mobile Research
Mobile research is ramping up here in FM&T. A chunk of our work is staying informed on technologies and trends, such as smart phone OSes (Symbian OS, Android ...) and runtime environments (J2ME, Flash Lite ...).
The possibilities and constraints of both browser-based and non-browser based are researched. There is always this tension in balance of breadth of device support versus employing more of the device features.
One upcoming area of work is centred on using the mobile phone as a remote control over other devices, such as digital video recorders, catering for accessibility. Another upcoming area will investigate possibile services around Femtocells deployed in the home. A related area is handover between 3G and WiFi.
The remote control research will investigate suitability of different wireless connectivity options (including Bluetooth, WiFi and mobile cellular networks), device discovery and UI presentation, along with supported accessibility options offered by different mobile runtimes.
Accessibility requirements lead to the possibility of separate media streams, as aids, being delivered over broadband to accompany a broadcast. This raises interesting challenges in media synchronisation between the mobile device and the TV, as the media originate in different networks.
For example, clean audio stripped of background music or sound effects could be delivered to the mobile's headset, for the hearing-impaired, alongside the video broadcast being watched on the TV. We're looking forward to very interesting research in this whole area shortly.
Femtocells aren't exactly a household name, so far. However, they have been in trials around the world including the UK. If deployed in the UK, they can enable some novel in-home mobile services. So here is some background on femtocells, starting with problems they are intended to address, followed by what femtocells do, ending with some possibile service ideas, which we will be experimenting with.
Some key issues for operators with 3G include indoor coverage, radio capacity and core network capacity.
The radio frequencies used for 3G are in the 2 GHz spectrum. Such frequencies have difficulty penetrating buildings etc. resulting in poor indoor coverage. So, a lot of the time, you can't get a signal in your home, and you can't rely 100% on being reachable on your mobile at home. Next, any mobile cell has a maximum (configured) amount of radio traffic that it can accomodate, and once "full" becomes inaccessible to new users until someone stops a voice or data call, or moves to an other cell. This radio capacity is shared across a cell and likely prioritised for voice traffic. High datarate services over 3G can rapidly consume capacity, meaning either a few happy folk per cell or everyone's service getting downgraded to accomodate newcomers. The core mobile network sits behind the radio access network (RAN: all the cells and connectivity to the core). The core has to bear all this traffic between the Internet and the RAN, so its capacity may need growing to support this accumulative traffic. The femtocell addresses these issues. (WiFi is discussed below).
Enter the Femtocell...
It's a complete 3G base station belonging to the operator's radio access network (RAN), located in your home (similar form factor to your wireless router). Don't worry about being fried. It radiates at very low power (a 1/10th of the power of your DECT phone). It gives 5-bar coverage in your home.
There should be no more lost incoming calls and voice/data traffic is seamlessly handed over between an outdoor cell and this indoor cell. Because of the proximity of the mobile phone to the femtocell, the mobile transmits at very low power - it's not trying to "shout" at an external macrocell which eats up battery. So battery life should be extended for your mobile activities (voice and data).
What about capacity and quality of service? An HSDPA-based femtocell, supporting say 4 users, offers peak raw data rates of 1.8 Mbps per user. (As with any cell, "raw" means all data over the air, including overheads with protocol headers, error correction etc. The datarate delivered to the mobile application is less).
That's a lot more than iPlayer needs. This will only improve with time if new versions support the higher datarates available through later modulation techniques. But the key point is that your services are running over licensed spectrum. The operator is in control of who gets to use what and hence can make guarantees on Quality of Service.
What about the backhaul? Femtocells can be integrated with the mobile network to offload data traffic direct to the Internet, without touching the mobile network core. So the net effect is reduced capacity requirements for the operator, and reduced latency for your data services.
Any mobile base station engages in mobility along with the mobile phone. As mobiles come in/out of range of a cell, the mobile network knows, so it can track where to route the mobile traffic. Think about what that means. Suppose software gets notified when you're entering or leaving the house. What could that do for automated media services? How about having your home "system" quietly load up your mobile each evening with stuff for your next day's journey? How about notifying your DVR that you've watched 15 minutes of Spooks on your mobile and the DVR knows to just serve up the remainder? Or vice-versa? You've got 10 minutes to go and the system requests the BBC network to transcode this for your mobile and deliver it back quietly overnight to be transferred to your mobile. What about if your car had 3G and it prep'd for the next day's journey? These are all possibilities.
Since WiFi backhauls direct to the Internet also, the same statements can be made about reduction in mobile core capacity. WiFi operates in the unlicensed spectrum, so competes with other WiFi networks in the area, typically causing increased retransmissions.
Ofcom research has shown that about 90% of WiFi traffic is control traffic, leaving 10% for user data. See http://www.ofcom.org.uk/research/technology/research/exempt/wifi/wfiutilisation.pdf (page 6 especially). QoS guarantees can't be made. There have been various announcements concerning WiFi - 3G seamless handover. So, we will need to investigate this also, again looking at service opportunities triggered around mobility and entering / leaving the home network.
Jerry Kramskoy is a Senior Technologist (Future Media Infrastructure), Research & Development.