Mobile data traffic has grown enormously over the last few years, and several industry reports predict that this trend will continue. According to the latest Cisco Visual Networking Index published in February 2012, around the world mobile data traffic grew 2.3-fold in 2011, more than doubling for the fourth year in a row, and it will increase 18-fold between 2011 and 2016.

Cisco notes that in addition to the growth in the number of connected devices, one of the main reasons for this increase is the proliferation of high-end handsets or smartphones. These devices boost data consumption delivering content and applications not supported by previous generations of mobile devices. For example, according to the same report, mobile video traffic was 52% of traffic by the end of 2011, and it will increase 25-fold between 2011 and 2016, accounting for over 70% of total mobile data traffic by the end of the forecast period.

This high growth in mobile data traffic is placing enormous pressure on operators’ installed network capacity. 3G cellular technologies were born as the next generation of the older cellular voice network, but were never designed to support today’s mobile Internet services. The arrival of new generation networks (LTE, WiMAX) will allow operators to transfer from a voice-centric cellular network to a voice-data centric network. Although these more advanced networks provide additional capacity, it is generally agreed that such technologies cannot scale up to support the exponential growth in mobile data traffic, and they will take years to deploy. Meanwhile, with such massive demands for data, industry stakeholders need to look at alternatives to relieve the cellular network from the pressure on capacity.

With greater competition for consumers and strong pressure on revenue per subscriber, operators need solutions that help them to solve network congestion while also enabling them to manage costs and retain consumers.

Mobile data offloading, also known as data offloading, is an affordable approach that reduces congestion while also addressing operators’ needs for fast delivery. The use of complementary network technologies for delivering data originally intended for cellular networks seems to be the immediate solution to cope with the rapid growth in mobile data traffic.

The concept of data offloading is not new. Generic Access Network (GAN), better known by its commercial name Unlicensed Mobile Access (UMA), is a 3GPP standard released in 2005 and designed to enable access to GSM and GPRS mobile services over unlicensed spectrum, including Bluetooth and Wi-Fi.

The technologies chosen by the industry as the alternatives to offload mobile data are Wi-Fi and femtocells. According to Cisco's report, globally 33% of total mobile data traffic from phones and tablets was offloaded onto the fixed network through dual-mode devices (Wi-Fi) or femtocells in 2011. This clearly shows the significant impact of data offloading and how operators could relieve the pressure on their networks. Given that much of the total mobile data traffic is generated at users' homes, Wi-Fi and femtocells are ideal technologies to address the data congestion problem.

The greatest advantages of Wi-Fi are cost-effectiveness, and that it uses unlicensed spectrum. The costs of building dedicated Wi-Fi capacity from scratch are comparable to those for building new cellular capacity with femtocells. However, the strength of Wi-Fi is that it is already widely available (e.g. in the home, at public places) so the possibility of using the existing capacity makes it a better option from a deployment cost point of view. Also, Wi-Fi networks can be easily and cost-effectively escalated without the need for the site surveys and channel planning essential for femtocells.

Since Wi-Fi uses unlicensed spectrum – which is far more plentiful than licensed spectrum – much more traffic can be offloaded using this technology, leaving the precious and scarce licensed spectrum to serve other mobile services. However, this could be seen as a disadvantage in comparison to femtocell technology, as the use of uncontrolled spectrum may potentially make the service susceptible to interferences from neighbouring radio transmissions, for example.

Femtocell offload is a converged voice and data solution designed primarily to deliver improved indoor coverage for a cellular network through a spectrum re-use strategy. As it is the natural extension of the main cellular network, operators would be able to provide most of their mobile services through this technology. Femtocells use the same wireless interface used by the cellular network, hence handsets do not need to have an additional radio unit, as in the case of Wi-Fi. However, since Wi-Fi is already widely available on many mobile devices, this is not a major advantage. The challenges for femtocells are the additional cost of compatible Customer Premises Equipment (CPE) plus the frequency interference management, as a well planned spectrum allocation is required to avoid interference either with neighbouring femtocells or macrocells.

As mentioned above, femtocells are an extension of the cellular network so they would be capable of delivering services that comply with cellular network standards. However, since in a femtocell environment mobile operators do not necessarily have control of the broadband connection to the home (unmanaged link), some services may be adversely affected by a poor connection between the femtocell and the network.

With Wi-Fi, the operators’ concern is whether this technology is capable of serving as an alternative to offload mobile data traffic offering an architecture which is as secure, controllable and reliable as their 3G networks. Taking into consideration that Wi-Fi is relatively variable in terms of quality of service, enabling multiple services with specified quality levels may be a difficult task.

The challenge for Wi-Fi is harvesting its ubiquitous capacity to be used in a managed and secure way, and industry is working toward this goal. The Wi-Fi Alliance through its Wi-Fi Certified Passpoint program aims to enable operators to offload data in public hotspots. During the Wi-Fi Global Congress held in Korea in June 2012, the Wireless Broadband Alliance (WBA) stated that “many of the world’s largest operators and vendors had signed up to advanced trials of Next Generation Hotspots (NGH) employing the first generation of Wi-Fi Certified Passpoint equipment”.

Mobile data offloading will keep growing and it is also predicted that it could become a new industry segment. A technology that was originally conceived as a temporary solution to deal with the growth of data traffic while awaiting deployment of new generation networks, it is now considered as a potential complement to such networks. Spectrum is a scarce resource and it will remain scarce in the future, and costs of increasing core network and backhaul capacity will decrease operators’ profitability. Therefore, a reliable and well-planned data offload solution could play an important role in extending service support to other next generation technologies such as WiMAX and LTE. Operators need to optimise traffic on the network and cope with congestion issues in order to meet both user needs and their own objectives. Data offloading is taking its place as part of the solution to manage congestion and reduce cost challenges in mobile networks. Its coexistence with next generation networks will depend largely on its capacity to provide mobile data services in a secure and reliable way, and the level of integration with those networks.