Next Stop: Multi-mode Devices

By TMCnet Special Guest
Renuka Bhalerao, Principal Systems Architect at RadiSys Corp
  |  February 04, 2013

Like never before, users are demanding uninterrupted voice coverage and data access both indoors and on the go; and operators have turned to small cells as a means to increase coverage for their user bases. As a result, the heterogeneous network, or hetnet, is a multi-layer network combining macrocells along with strategically placed small cells, Wi-Fi hotspots and more. The hetnet is now widely accepted as the future of wireless networks, and small cells have evolved into an answer for not only coverage, but the capacity crunch as well.

The turning point came when the number of deployed 3G femtocells surpassed the number of 3G macrocells. So what is next for small cells? Well, as the mobile industry transitions from legacy 2G/3G architectures to LTE (News - Alert), there is an immediate need for dual-mode or multi-mode small cell devices that enable operators to continue to deliver the best user experience as they support their existing 3G users while planning for an LTE rollout.

The small cells or femtocells deployed today started as a solution for indoor coverage in the form of residential and enterprise versions of small cells. These are now rapidly evolving into outdoor open access picocells providing coverage in public areas such as stadiums, hotels, shopping malls and so on. At the same time, Wi-Fi hotspots continue to provide license-exempt spectrum in indoor areas, and offer offload of cellular traffic in a cost-effective way.

This has led to the evolution of a complementary approach where Wi-Fi and small cells jointly address the coverage and capacity challenges for indoor and outdoor network areas.

Due to the lack of new site locations, the cost of new deployment and backhaul-related issues, operators are seeing value in placing these Wi-Fi hotspots and small cells under the same enclosure so that they can share location, backhaul and more. The optimal integration is a multi-mode access point that combines 3GPP (WCDMA and LTE) with the Wi-Fi hotspot, giving users the best of both worlds. 

At its simplest form, a dual-mode or multi-mode device combines multiple radio access technologies while maintaining standard interfaces into the operator network. However, there is a plethora of options to combine the logical functions within a small cell device. The obvious functions to support the multi-mode version of small cells include a common device management, provisioning interface, backhaul options and security. However, the synergies go beyond these basic commonalities. These multi-mode devices will also need enhanced scheduling for effective use of radio resources, SON techniques to support intelligent mobility management and neighbor relations, and all while accounting for the multiple available radio accesses.

Mobile operators can leverage multi-mode devices to manage the efficient utilization of all the available radio resources to handle user traffic. The multi-mode device solution can leverage software-defined radio techniques, solving coverage issues and offering an intelligent load balance among radio accesses.

Optimizing dual-mode support for effective load balancing

By their nature, multi-mode small cell devices help operators increase the available coverage area for subscribers by extending the network and enabling subscribers to leverage the best radio. Going forward, both residential and open access settings will need to support LTE as well as legacy 3G handsets. Operators will need to implement a load balancing mechanism that enables the efficient usage of premium LTE resources by diverting the rest of the traffic to 3G as suitable. In addition, operators can also leverage Wi-Fi offloading for low priority users.

Today, smartphones can select which network they want their handset to use – whether their own cellular network or an in-range Wi-Fi network. As the multiple accesses for 3G, LTE and Wi-Fi are unified and made available to smartphone users as a single access point, there is a need to implement network side policy and management function; this will give control back to the operators to manage the available network resources while monetizing their deployments.

Operators can leverage several techniques to optimize their multi-mode devices. One key technique is to leverage policy management functionality on their multi-mode small cells, which enables them to prioritize traffic on their 3G/LTE and Wi-Fi networks.

Additionally, operators can define a quality of service solution for the backhaul transport that works across 3G/LTE and Wi-Fi services. A unified QoS scheme provides the flexibility to allow similar traffic classes on different technologies to share the same QoS marking. Thus synergies at different levels can improve the efficiency of the multi-mode devices significantly.

Leverage SDR for effective multi-mode

Unlike traditional radio chips that leverage one wireless protocol such as cellular, Wi-Fi or Bluetooth, software-defined radio chips rely on the software to determine which applications to implement. This makes SDR devices extremely versatile, and a good fit for multi-mode devices, as SDR can enable these devices to use the best network available, and allow operators to manage their traffic on the network. In other words, SDR can create virtualized wireless networks that support today’s hetnets combined with Wi-Fi.

Optimized SON techniques for multi-mode devices

A self-organizing network, or SON, offers operators a better way to manage their hetnet and multi-mode devices, providing effective coordination of RF resources suitable for multi-radio, multi-standard small cell networks with automated steps for:

·         self-configuration;

·         self-optimization;

·         self-healing; and

·         enhanced O&M.

By automating these steps, mobile operators can lower deployment and operations costs, mitigate interference, and optimize their networks to boost capacity and throughput.

SON has evolved significantly since its initial introduction; it now acts as an umbrella over the entire coordination of the network. SON amasses information on base station feedback through sniffer functions, user equipment measurements and signaling over the X2 interface between two eNodeBs. It then leverages this combined information to provide insight on neighboring cells, interference levels, geographic locations and more. 

In addition, coordination of a distributed SON application at the eNodeB and a centralized SON serve can optimize the network performance for each of these network nodes. This optimization delivers effective cell coordination for better self-configuration and mobility handling, resulting in capex savings.

SON’s range expansion techniques eliminate frequent handovers of traffic and promote stickiness to the small cells in the network. This provides an effective load balancing and traffic offload solution for the macro network, in addition to mitigating interference. Also, the more UEs served by the small cells, the more capacity there is in the macro network.

A multi-layer self-organizing network controller or network entity offers a multi-mode SON function that helps select the best suitable radio access and can also guide how traffic flows are routed and prioritized, and promotes network sharing.

Thus, SON is a vehicle enabling the effective coordination of time and frequency resources between macro and multi-mode small cells to minimize interference and deliver dynamic optimizations, even with a complex hetnet topology and multi-mode small cells.

Multi-mode device availability

It is clear that multi-mode devices shall play a key role as mobile operators turn to them to help solve their capacity and coverage challenges. Multi-mode SoC platforms are now arriving on the market, supporting collocated RF for 3G/LTE. In addition, mobile devices are already well positioned to support this new multi-mode technology; smartphones and tablets on the market today come with multiple radio accesses including Wi-Fi and 3G, and now LTE.

Renuka Bhalerao is principal systems architect at RadiSys (News - Alert) Corp. (www.radisys.com).

Edited by Stefania Viscusi