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Wi-Fi has been a fixture of road-warrior mobility and migratory computer use for a long time in wireless network planning. In fact, hotspots predate any significant use of cellular data plans as a way to support wireless connectivity to the Internet. Even after cellular data came along, operators found it attractive to support Wi-Fi as a way to offload data traffic from cells in congested areas.
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Even though 4G reduces cell congestion problems, congestion is still there, and some mobile operators, cable companies and even cities are turning to Wi-Fi as a complete replacement for 4G services. Replacing 4G with Wi-Fi isn't an attractive option for an operator investing heavily in LTE services, although some operators still like to use Wi-Fi for offloading traffic and to give cost-conscious customers a way to commit to heavy data use without expecting all-you-can-eat pricing.
It seems obvious that for Wi-Fi to provide maximum value for mobile operators, it has to be considered in the context of complementing 4G. That's possible if you organize the approach and execution of a Wi-Fi strategy carefully and answer three important questions.
The first question in wireless network planning is, which devices are you targeting? Most operators have three classes of 4G user devices: phones, tablets and laptops. The earlier your target devices are on this list, the more important it is that Wi-Fi appears as an extension of the 4G mobile services your customers buy. Nearly all phone users and some tablet users will see "wireless without boundaries" as their objective.
Next up, what about session continuity? A seamless wireless service would have to preserve at least some sessions across a wireless transition from cellular to Wi-Fi networks. The question is, which sessions? For phone services, even the current shift from voice to SMS means that call continuity is essential, while tablet or laptop voice services are less critical simply because they are used less frequently and because users are more accepting of a temporary break in the session flow when a switchover to a different wireless network is needed.
Finally, are 4G and Wi-Fi both perceived as multi-cell networks? Operators need to know whether users believe they should be able to roam between Wi-Fi hotspots just as they do between 4G cells, in addition to being able to move between Wi-Fi and 4G.
While all of these mobility models are important, Wi-Fi becomes almost a parallel cellular strategy, and supporting that the Wi-Fi model is technically challenging.
Viewing 4G and Wi-Fi separately. Once you've considered these three questions, you can lay out a basic strategy for Wi-Fi. The primary goal is balancing hotspot autonomy and Wi-Fi roaming in your design. If users operate with continuous 4G and islands of Wi-Fi for a protracted period of time (the "migratory" model of use), it's easiest to simply support Wi-Fi hotspots and authentication in the traditional way. If users can reconnect their sessions after they transition between 4G and Wi-Fi, it may not be critical to support roaming into or out of Wi-Fi. Instead, let the user pick up in the new hotspot. This model works where users view Wi-Fi and 4G separately, with each linked to their own applications or experiences.
Viewing Wi-Fi hotspots as a single virtual network. The opposite situation occurs where a user is likely to roam among hotspots with little or no reliance on 4G services, using 4G either as a bridge between hotspots or as a supplement to Wi-Fi for conversational services like voice calls. In this situation, operators need to view their entire Wi-Fi hotspot network as a single virtual network, just like the virtual network 4G cells create. As a result, operators have to support migration between hotspots, at least to the extent of automatic sign-on and sign-off during roaming. Where voice is likely to be supported over multiple Wi-Fi hotspots, operators need session continuity as well. All of this leads to treating Wi-Fi hotspots as cells in a manner so similar to that of 4G that it would be best to think of Wi-Fi as operating under IMS and Evolved Packet Core, or EPC, control. The RF is different, but the service model is the same.
Operators that don't have 4G licenses or deployments are likely to fit into the second model, where operators support migration between hotspots. Most 4G-mobile operators fit into the first model, which uses continuous 4G with Wi-Fi hotspot islands. Operators that believed their Wi-Fi commitments would somehow put them into the middle ground have found too many forces pulling them toward the integrated Wi-Fi-4G model. Unlicensed Mobile Access, or UMA, is the basis for tight Wi-Fi-4G integration.
Addressing the technical issues. Most operators that want to use Wi-Fi to supplement 4G services also plan to allow traditional hotspot access. If so, the real question may be whether to design for IMS authentication or build parallel Wi-Fi sign-on screens to allow for guests. The solution depends on the operator's Wi-Fi scope, both for today and in the future. In general, it's probably smartest to assume that if you have both Wi-Fi and 4G services, your model will eventually look like 4G, not like Wi-Fi. Going to an IMS-based solution from the beginning would save time and offer more service flexibility.
Lightweight versions of IMS could be used to authenticate and manage Wi-Fi users, avoiding the overhead of full IMS. This means treating your Wi-Fi network as a roaming partner, which could provide the added value of letting you control policies for Wi-Fi use by class of customer. Even operators that never plan to use 4G but plan instead to deploy Wi-Fi as a cellular-like mobile architecture could benefit from a lightweight model of IMS (Project Clearwater is an example) to support not only registration but session services and VoIP. For this class of user, planning to use Web Real-Time Communications, or WebRTC, for all conversational services could be the best move of all.
A national Wi-Fi network with full roaming and the ability to sustain sessions across hotspot switches could look like a 4G network to users. Even a local network or series of local networks can provide valuable offload capabilities to operators and improve user data performance, particularly for streaming video. Wi-Fi can be a valuable addition to an operator's 4G plans.
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