As the wireless world prepares for 5G, many aspects of the next generation of wireless networks remain uncertain. However, there is consensus around one major change. The boundaries between licensed and unlicensed spectrum will break down. 5G will be bigger than one new radio, but will provide a migration path for all the current wireless technologies, including Wi-Fi, LTE and low power machine-to-machine (M2M) connections. Already, the coexistence and increasing interworking between licensed and unlicensed spectrum technologies has driven considerable change, and will continue to do so on the road to 5G – which for some players will lead to trials as early as 2017, while for others, will be a decade or more away.
Key trends leading towards convergence include:
• Wi-Fi offload and onload The ability to offload data from cellular networks to Wi-Fi was the first significant step towards use of converged spectrum. This allowed mobile operators to increase their overall wireless capacity without the cost of additional spectrum, offloading some types of traffic to Wi-Fi in order to maximize efficiencies on their core 3G or 4G systems. As the movement of traffic between the two types of networks became more seamless, thanks to developments in the network core and in the devices, the strategic value of this approach increased and also included other types of operator. In particular, wireline service providers were able to add a wireless element to their offerings in order to create a quad play service. Cable and broadband operators, and some start-ups, have adopted a Wi-Fi-first approach, in which subscribers stay on the Wi-Fi connection by default, and only transfer to a cellular link when a strong Wi-Fi signal is unavailable. This minimizes the fees which the provider needs to pay the MNO (mobile network operator), reducing the cost of delivery and enabling it to offer very low tariffs to subscribers.
• Next Generation Hotspot and Hotspot 2.0 Key enablers of the seamless access and hand-off which makes a combined Wi-Fi/cellular offering attractive are Next Generation Hotspot (NGH) on the infrastructure side, and Hotspot 2.0 or Passpoint in the device. These complementary standards emerged from the Wireless Broadband Alliance and the Wi-Fi Alliance respectively and have started to enjoy significant adoption over the past two years. This has often gone hand-in-hand with Wi-Fi providers’ moves to upgrade their infrastructure to fully carrier-class capabilities in order to support the same quality of experience (QoE) on Wi-Fi as on cellular.
• Voice and enterprise Voice has been a particularly challenging issue for companies deploying services over integrated cellular and Wi-Fi networks. This is especially true in the enterprise, where high quality wireless voice is seen as a ‘killer app’ as many companies adopt a mobile-first strategy. The emergence of Voice over Wi-Fi (also known as Wi-Fi Calling) has been critical, providing a voice platform which is managed by the operator’s core network and IMS, in the same way as the cellular solution, VoLTE. This allows for hand-off between Wi-Fi and cellular voice calls.
• Carrier aggregation The greatest challenge for users of any type of spectrum is to make the most efficient possible use of a precious resource. Wi-Fi offload was just a first step towards this goal but new ways to harness spectrum will enhance the efficiencies of using both licensed and unlicensed spectrum in tandem. One technique is carrier aggregation, which allows different channels to be bonded either in the same band or separate ones. Initially aggregation has been between carriers in either licensed or unlicensed spectrum (for instance, two- or three-carrier LTE-Advanced, or the 802.11ac standard for Wi-Fi). But the ability to bond licensed and unlicensed bands will be critical to next generation wireless. First steps have been taken with supplemental downlink (SDL), which aggregates an unlicensed carrier to provide additional downlink capacity for an anchor network in a licensed band (LTE-Unlicensed is an example).
• Proliferation of unlicensed technologies for the Internet of Things If the data demands of mobile broadband will require convergence of several technologies to keep up with demand, the emerging requirements of the Internet of Things (IoT) will be even more challenging. There are several specialized technologies already supporting low power M2M connectivity, over the wide area (e.g. Sigfox and LoRa) or the personal area (e.g. Bluetooth, ZigBee and Thread). The Wi-Fi community has HaLOW for the wide area, which is especially targeted at smart city applications, while the 3GPP has the NB-IoT standard in licensed spectrum. Most of these options run in sub-GHz bands, where capacity is limited, so ways for the various technologies to coexist and interwork will be essential to avoid interference and to allow optimal connectivity for the very diverse services of the IoT.