The Case for Mobile Broadband Offloading - Xchange Magazine

Wi-Fi, Femtocells Can Solve the Mobile Data Capacity Crunch

Arun Handa
03/10/2010

Operators facing increased 3G traffic (thanks to smartphones and the applications explosion) are increasingly considering offloading traffic to Wi-Fi or femtocell networks as a solution to the capacity crunch. There are a few reasons that makes sense.

Data made its foray into cellular networks around 2002 with 2.5G networks. The initial uptake of these GPRS and CDMA-1xRTT networks was slow. There was little that could be done with clunky voice-centric handsets and lack of data services. The BlackBerry changed that and began to whet the consumer’s appetite for a service beyond voice. The iPhone continued to expose consumers to mobile Internet and rich data services such as mobile video. Operators have been compelled to scramble to expand 3G networks to support this phenomenon. Yet this is only the start of the data deluge where the infrastructure is finding it hard to keep up.

Solving this conundrum requires an understanding of certain mobile data realities. For one, the 3G infrastructure required to deliver data services to smartphones is creaking at two main points: radio and backhaul. Wireless spectrum is a limited resource. Radio technology continues to improve the efficiency of transmission and reception, but there are limits to how many bits can be packed into a radio stream.

Further, network congestion is caused disproportionately by users. AT&T for instance has acknowledged a 5000 percent growth in data in the last three years. More importantly, the top 3 percent of smartphone users are consuming 40 percent of network capacity. They are consuming 13 times the data of an average smartphone user.

There are several ways operators can address the challenge. Increasing capacity in underserved areas can be done by building new cell-sites. Addressing traffic demands can be offset by technology upgrade such as HSPA+. However these options come at a high cost to the operator.

Augmenting and improving backhaul capacity can also mitigate this problem. Additional T1/OC3 lines can be linked to cell-sites to increase data capacity. The flow of traffic on the pipe can also be controlled using packet inspection and service level policy. In addition, caching the overall content can also help to smooth the flow of traffic.

Overlay networks offer an orthogonal solution. These exploit an alternate path to deliver data wirelessly to the user at cost-effective price points. Overlay networks exploit the service provider’s licensed spectrum with a femtocell solution or a ubiquitously available unlicensed spectrum for Wi-Fi networks. Both strategies extend the operator’s network footprint.

The Case for Offload

Many contend that scaling network capacity is only masking the problem. While providing a broader delivery pipe, most users realize a fractional benefit as a few consumers will continue to hog the increased bandwidth. Optimization is a promising solution as it helps in flow-control, but it is costly and raises privacy issues.

Offload on the other hand provides an alternate path with a best performance capability. If traffic for a bandwidth-hogging user is offloaded to an alternate overlay network, it will relinquish bandwidth for other consumers on the macro network. Alternately, a user competing for bandwidth from a loaded macro site can be offloaded to an alternate network. These networks can function with the macro-cellular network as an adjunct network either operating independently or as an overlay network. Both femtocells and Wi-Fi networks have their merits as candidates for offloading networks.

Femtocells leverage the licensed spectrum, offer better indoor coverage at lower power and work with common single-radio handsets. The challenge is that they have yet not reached widespread availability. This will take a few more years to reach pervasiveness. Wi-Fi offers the advantage of using the unlicensed spectrum, which means there are fewer spectrum planning and refactoring issues. Access-points and hotspots are ubiquitous, with MNOs such as AT&T, T-Mobile, Orange and Vodafone owning a large footprint. Smartphones have made Wi-Fi availability and ease-of-use an attractive feature to consumers.

Wi-Fi Data Offload

A growing number of smartphone users are already using the Wi-Fi path to access Internet services. Is that not data offload? On the contrary, it is a network bypass from the mobile network. Service providers need to use this to their advantage or risk losing all. The important point to understand is that Wi-Fi simply provides an access transport. The alternate path the service provider uses to deliver data must conform closely to existing service standards.

The difference lies in providing Wi-Fi as an integrated and managed service. This is possible only if the service provider can exercise control over this service. Providing this as an integrated and managed service lets the operator control the alternate path of data services through the unlicensed spectrum and helps monetize this effectively on operator owned hotspots.

The minimal model of providing Wi-Fi as a managed service is to provide an access network. This is what most operators offer as a public WLAN or hotspot service. This service may be managed but not well integrated. Integration refers to interworking with the cellular network, which requires the following:

- Common authentication methods – this implies a common identity which can be authenticated from the subscriber provisioning done in the core network

- Charging – support for postpaid and prepaid charging that conform to the charging entities in the cellular network

- Mobility – seamless movement between a Wi-Fi and cellular network

- Seamless and transparent access without the need to know the underlying radio network

- Easy or zero touch authentication while moving between cellular and Wi-Fi

The 3GPP has introduced the specifications for interworking WLAN with cellular networks. The standards-based infrastructure makes a compelling case to support the Wi-Fi data offload path.

Arun Handa is Chief Technology Officer for IntelliNet Technologies, a global leader in wireless broadband convergence technology for accelerating the deployment of new applications and services in mobile operator networks.