Voice over Wi-Fi can be a compelling option for mobile operators and cable providers, but a strong deployment model is critical for service quality.
Voice calling over mobile networks has been around for a long time, so why is there so much discussion in the industry around voice over Wi-Fi? The big deal with VoWi-Fi is that it’s fast becoming a critical tool in operators’ armory for both cable and cellular operators alike. It has moved from a nice-to-have status to being considered a necessity by several operators – but why?
VoWi-Fi has created a paradigm shift in the way mobile carriers can provide indoor voice coverage. Operators can offset spotty cellular in-home coverage by running voice calls over Wi-Fi. Better indoor coverage means improved call completion rates and call quality in the home, facilitating a better customer experience and increasing customer retention.
There are other benefits for mobile carriers too. Wi-Fi has been used by mobile operators to offload data when users have Wi-Fi access. Offloading reduces the amount of data being carried on cellular bands, freeing bandwidth for other users. With VoWi-Fi, voice will similarly be offloaded onto Wi-Fi networks, further liberating cellular capacity.
VoWi-Fi can also be exploited to facilitate lower cost roaming, allowing subscribers to make cheaper voice calls while traveling abroad. Operators can offer the same set of services to users whether they are on Wi-Fi or LTE. And mobile operators can do all this while leveraging their core network investments, using voice-over-LTE infrastructure to provide the service.
VoWi-Fi becomes even more critical for cable operators. For them, it’s the main course, not an appetizer or side dish. These companies are increasingly seeking to get into the mobile wireless business – starting with Wi-Fi in the home and expanding externally with outdoor access points, filling in gaps in wide-area coverage with mobile virtual network operator relationships. It’s essentially an “in-to-out” strategy. For these players to offer a quad-play service, VoWi-Fi becomes critical since Wi-Fi is the wireless asset they have access to. And MVNO arrangements can be expensive, so it makes great sense for these carriers to keep their users on Wi-Fi as much as possible.
This is the world of operator-provided VoWi-Fi, different from voice-over-IP apps that have been around for a while – such as Skype, Viber, WhatsApp and the like. While these apps run over-the-top and enable calling via dialers built into the apps, operator-provided VoWi-Fi can use the native dialer built into the mobile device, giving the user a consistent look-and-feel whether making a call over a cellular network or over Wi-Fi. Calls are also made using users’ regular mobile phone numbers as opposed to an app-specific user id.
To make a VoWi-Fi call, you need a capable device, access points and a core network. Many popular smartphone brands support Wi-Fi calling, and in some cases service providers have issued standalone Wi-Fi phones. The access point can be a retail router or an operator-supplied access point. The problem with a user-purchased router is the service provider may not be able to manage the quality of voice calls delivered over it – in essence it becomes a best-effort service for the user. Many operators are preferring to supply their own access points, ones they will be able to manage in order to shape the service delivered to the user. The core network is typically IP multimedia subsystem-based and can also be used to deliver VoLTE if the operator is also a cellular provider.
Delivering high-quality voice is key to the success of VoWi-Fi – voice has been around for a while and users expect no less. There are three metrics that significantly impact voice quality: latency, jitter and packet loss. High latencies can cause echo and interactivity issues. It is generally accepted that a delay in excess of 150 milliseconds causes noticeable difficulty in carrying on a conversation. Jitter compounds this issue. Packet loss results in voice clipping, skips and garbled speech. Latency, jitter and packet loss can be impacted by three issues in a Wi-Fi system – congestion, interference and coverage.
Let’s take congestion first. Wi-Fi embraces a resource sharing philosophy where all manner of devices – stations, access points, etc. – contend for the resource democratically, on equal terms. When one device is using a channel, others on the channel wait. Even in a perfectly behaved network, if a large number of devices congest a channel, a long line of waiting devices can build up. The result? Each device has to wait longer for its turn to transmit and latencies rise dramatically. This is akin to a choked motorway.
And if the network isn’t quite as well behaved, devices can step on one another to create interference. For example, in a dense network, two access points may not hear each other and may therefore simultaneously transmit data on a channel. A client device that can hear both access points can end up getting both transmissions, one clobbering the other. This can be worse than a slow traffic lane – this is more like a traffic accident. In voice quality terms, interference can result in high packet error rates and packet loss, which can cause clipped and garbled speech, and even call drops.
Coverage is the other make-or-break factor. If the calling device is in a part of the house that sees a weak Wi-Fi signal from the access point, voice quality will be affected. And the coverage situation changes as the user moves around the house, complicating the issue further. There’s no point in having a clear Wi-Fi channel if you don’t have the coverage to access the capacity. The highway might be carrying light traffic, but that doesn’t help if access to the highway is in poor condition.
Surmounting these issues will require intelligent radio frequency management solutions that maximize the quality of services such as VoWi-Fi. The ability to move access points and client devices to cleaner channels in the face of congestion or interference becomes critical. It’s like changing from the crowded right lane on a highway to a less congested middle lane. Clever use of bands and management of power to limit interference are as important.
Simplicity has been the name of the Wi-Fi game from its very beginning. From the outset Wi-Fi has been designed for low cost, lightweight operation, simple interoperability and ease of deployment. It has been designed with connectivity as the primary goal. Wi-Fi doesn’t inherently come with tools to manage congestion, interference and coverage, which means radio management solutions will need to come in “behind the back of Wi-Fi” to ensure services like VoWi-Fi work well.
Editor’s Note: The RCR Wireless News Reality Check section is where C-level executives and advisory firms from across the mobile industry share unique insights and experiences.
