LTE falls back on voice

O2 and Vodafone launched their 800 MHz LTE services at the end of August, adding competition to the LTE landscape that is currently dominated by EE. Understandably, the carriers are keen to inform UK consumers about the benefits of 4G by focusing on download speed and the wealth of exciting new content subscribers will be able to access.

Neither carrier, however, is choosing to focus on coverage – which is often one of the traditional battlegrounds that operators favour when it comes to marketing roll outs. Coverage though, particularly for LTE at 800MHz, may still arise as a contentious issue.

The lower-frequency 800MHz band was part of what was referred to as the ‘digital dividend’ and was freed up when analogue terrestrial TV was switched off. It was highly sought after for the LTE networks because lower frequency signals are able to penetrate building walls with much greater efficiency than higher frequency signals. Therefore an LTE signal at 800MHz will enable significantly improved indoor service coverage over an LTE signal at a higher frequency, such as at 2.6GHz (the other band licensed specifically for LTE in the UK).

Great news you might think, particularly for people in areas where coverage (especially indoor coverage) is suboptimal, and this would be enough of an incentive for some to sign up to expensive two year contracts.  There is just one drawback though, as 4G networks are rolled out, early LTE phones will be enabled for faster 4G data services only. So an early user benefit of 800MHz LTE is to support improved coverage for data services indoors, exactly where most smartphone users may already experience a good data service from their fixed broadband provider. To support voice calling, these devices ‘fall back’ to the older 2G and 3G mobile networks to either make or receive a phone call and this is where the user experience may degrade.

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Put yourself in the position of a user in an area where the 2G/3G indoor coverage from your mobile operator is poor and you are often unable to make or receive a call. You hear about the new 4G network and upgrade your phone to enable you to experience it. Operating at 800MHz, you now receive a great LTE signal in your house or workplace – five bars of coverage in all locations. Now you wish to make a voice call. As soon as you hit ‘send’ the phone will drop the LTE connection and search for a 2G or 3G signal to use for the voice call.

There is little difference between making a voice call in this scenario vs. the non-LTE scenario, with the exception of the additional step for the phone to fall back and lock onto the 2G/3G signal.

Incoming calls fair no better. When a call is received the network alerts the phone over the LTE network, which then drops its LTE connection and again attempts to lock onto a 2G or 3G signal on which the user may then receive the call. If there is no good 2G/3G coverage at the current location, or if the phone cannot lock on to the 2G/3G signal in good time, then the user will experience a missed call even with five bars of LTE service showing just before the call was received.

In practice, therefore, there is potential for the voice calling experience on a 4G LTE data-only phone to be worse than that of the existing 2G/3G network, especially for those mobile operators that do not have 2G/3G services operating in frequencies close to the 800MHz LTE signal in the same location!

The irony here is that subscribers who find themselves in a situation where they’re falling back to poor 2G/3G coverage for circuit switched voice may have more success making a call using a third party OTT VoIP client, such as Skype, over the faster LTE data connection.

The longer term solution to this problem is a technology called Voice over LTE (VoLTE) that will enable telephony services as well as data services to use the LTE 4G signal, but there will be a gap for some period of time before all LTE phones and networks become VoLTE enabled and offer the same diversity of services and options that are available today in the circuit-switched telephony world.

So, what is to be done? Many indoor locations (residential, workplace, transportation and retail) are wifi enabled, with residential and workplace locations accounting for typically greater than 95 percent of all Wi-Fi traffic from smartphones. Perhaps if wifi can simply be re-used to support the mobile operator’s services, then this would provide an excellent interim solution for their customers caught in the LTE technology gap.

Wifi calling solutions do exist and are completely compatible with the same infrastructure that must be deployed in support of longer-term plans for VoLTE. Indeed, several carriers are already familiar with wifi coverage solutions for operator-provided services, Orange’s Signal Boost being one such example. And O2 is also heavily promoting its Tu Go service that enables wifi to be used for voice and SMS on tablets and laptops.

Mobile providers that choose such a solution may make available downloadable apps for Android and iOS smartphones that enable full support for both incoming and outgoing telephone calls and SMS over any wifi access network with some level of transparency to the user.  For the mobile operator and smartphone user alike, using wifi to support critical operator services at locations reachable with 800MHz LTE signals but poorly served by 2G/3G signals may prove to be a smart choice.


Keith Mumford, Vice President of Technology at Kineto

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