How femtocells will solve data capacity
If we project these sustained rates of data growth to future mobile network capacity, the current network capacity will represent less than 10 per cent of what is needed by 2016. Future network deployments will, in fact, be handling the vast majority of data capacity requirements for mobile network operators. If we were to scale today’s mobile network architectures to handle this tsunami of data, the cost to deploy would be too high. Future mobile network architecture therefore needs to change, by not only scaling to handle the much higher data loads, but also by scaling cost effectively so that mobile operators can afford to deploy it.
Why Femtocells?
They deliver on the promise of providing the next leap in performance for wireless networks by bringing cell sites closer together, providing coverage, capacity and service delivery platform to subscribers. To realize this vision the industry has had to address the challenges of interference mitigation and mobility requirements from operators and subscribers. But to make this transition, what are the issues that this technology faces? What innovations need to take place? How will they alter the topology of mobile networks and, what will this landscape look like when the roll out of femtocells reaches its apogee?
It is the rapidly rising rate of mobile data which has propelled the development and deployment of femtocells. By 2014, monthly worldwide mobile data traffic will exceed the total for 2008. The pattern of usage has equally inspired this technology with 70 per cent of all mobile use in 2008 done whilst at home or in the office. But the most important factor today impacting mobile broadband performance and use is coverage, particularly in rural areas, and the differences between the performances of operators’ 3G networks. The mass deployment of femtocells should solve this problem resulting in ubiquitous coverage, indoors and out, with faster connection and download speeds.
For operators, the key advantage of femtocells is that they are able to offload resource-intensive over-the-air data traffic onto an IP backbone, reducing both capital (less macro sites) and operational (less backhaul costs) expenditures while creating a branded operator point of presence in either the home or the work environment. As femtocells increase signal strength and provide excellent coverage indoors, they also contribute to a better user experience, with improved coverage/peak data rates and quality of service. As mobile users are offloaded to femtocells, data traffic load and signaling load on the macrocell reduces.
Interference management
Since femtocells are being deployed in configurations and topologies that were not originally anticipated by 3G standards, one of the challenges that has required additional research and development to overcome is how to minimize downlink and uplink interference to macrocells and neighbouring femtocells when femtocell RF frequency channel overlaps with that of macro cellular transmissions. Femtocells are therefore now being designed to self-configure so that they seamlessly integrate and operate satisfactorily with the existing femtocell-macro network and provide excellent performance irrespective of their location in the residence, enterprise or the macro network. Femto solution providers, Qualcomm included, have developed algorithms for 3G femtocells to enable co-existence with macro network. These advanced interference mitigation technologies minimize the impact of the femtocells on the macro network. They use RF measurements by the femtocell and associated handsets to adapt their operations (e.g. channel of operation, femto transmit power, associated handset transmit power cap) to minimize impact on the macro network.
Qualcomm has had an active R&D program in this area for four years, resulting in the UltraSON suite of algorithms that provide for interference as well as mobility management of femtocells. The UltraSON algorithms provide effective downlink power calibration and uplink interference management as well as reliable mobility between macrocells and femtocells. In addition to using mobile handset measurements, femtocells that use UltraSON algorithms require a key additional hardware function, network listen. Network listen is an RF receiver module which resides in the femtocell and “sniffs” the surrounding RF environment, to provide inputs to the UltraSON algorithms which then compute the initial downlink transmit power, frequency channel and scrambling code prior to the femtocell transmitting its RF signal. Subsequent to initialization, the network listen can continuously monitor the RF environment to make dynamic changes as needed to avoid transient interference scenarios.
3G small cell interference management has had to be performed in an isolated cell environment without explicit co-ordination with the macro network, since these small cells were not anticipated as part of the original macro network deployments. LTE, the next-generation mobile air interface network technology, however has incorporated support for interference management of small cells in the Release 10 and Release 11 versions of the LTE standard. As operators upgrade their LTE networks from the initial Release 8 macro deployments, they can support femtocell deployments in a coordinated fashion utilizing the X2 and other signalling messages defined in the subsequent releases of the LTE specification.
A cellular access point in every home
The femtocell landscape is changing as operators develop new business cases for femtocell deployment. One trend that we anticipate is the integration of femtocell technology into existing consumer networking products, such as Wi-Fi access points, set-top boxes and integrated access devices. Every operator will have their own business model for deploying femtocells and these will evolve over time, depending on the operator’s technical and business needs. Some may choose to subsidise the full cost as they are off-loading capacity.
Others will seek to share the cost with the consumer and provide them with additional service benefits such as free talk time or data downloads in the home/enterprise in exchange. Some will use femtocells to enable replacing the wire line phone service in the home. What’s clear is that femtocells are being established as part of a very sophisticated network topology, whether it is indoors in combination with afore mentioned wireline and Wi-Fi solutions, or outdoors, incorporating metro-femtocells and carrier grade Wi-Fi solutions into the macro network and picocells, to become a natural extension of the operators’ network.
Femtocell discovery
Another challenge requiring some attention is a reliable method for legacy mobiles to discover and camp on femtocells in idle mode and to perform handover from a macrocell to a femtocell in active mode. Operators however, have been reluctant to modify the configuration and planning of their macro networks to accommodate femtocells. Even if the macrocell has good channel quality or the handset is operating on a different carrier on macrocell, it is still desirable to move the device from macrocell to femtocell in order to continue the network service as seamlessly as possible. The reason being that heavy traffic users can be connected on the macro network for a very long time, continuing to consume significant amount of macro network resources before transitioning to idle mode. This kind of adaptability and efficiency is important to ensure the migration of as many users as possible to the femtocell and reduce the traffic pressure off the macro network. This is why Qualcomm recommends that a beacon signal is transmitted on the macro carrier that redirects the mobile user to the femtocell carrier frequency. Beacons work reliably with legacy handsets and do not require any macro changes.
Femtocell power-saving advancements
The power-efficiency of femtocells has also been recognised as a challenge which will impact both residential and enterprise uptake and needs to be considered as part of refining the user experience. Qualcomm has developed its femtocell chipset to be small and consume less than 5 W for a residential deployment, which meets EU green guidelines and enables Power–over–Ethernet (PoE) so you don’t have to route power from a wall socket.
One device to rule them all
With M2M and the Internet of Everything just around the corner, the next step in this already game-changing technology is merging Wi-Fi and femtocells to create one single intelligent gateway and coordinate the services delivery via either access technology. Recently, we announced the availability of a Femto-Wi-Fi hardware incorporating our FSM9216 enterprise chipsets, fully-integrated system-on-chip (SoC) solution for femtocell development, with the Qualcomm Atheros 802.11n Wi-Fi AR9350 and AR9344 access point solutions.
This will allow operators to design access points that let their enterprise customers connect to both Wi-Fi and cellular networks. Currently designed to support 32 active users, it can be scaled down to support residential and home applications or scaled up to suit outdoor urban metro-femto-Wi-Fi combinations or cover larger areas. With over 90 per cent of smart phones equipped with Wi-Fi accessibility, the fusion of Wi-Fi and femtocells onto one platform will help with a variety of service issues: improve connection management and solve mobility issues that plague Wi-Fi handsets; aid network side management, resulting in a combined interactive secure gateway into the home.
This advance will see the ability to manage Wi-Fi as well as cellular traffic. Based on RF channel quality and QoS requirements of different applications, the system can select the most suitable technology (Wi-Fi or femtocell) for each traffic flow. As an example, files transfer may be offloaded to Wi-Fi while a voice call is still made through the femtocell.
Within the home environment, if the femtocell is equipped with location based services, it can recognise individual users and offer them personalised content and apps. The femtocell home zone could know what your favourite TV program is, and automatically download it onto your mobile when you enter the zone, or allow users to use their phone to control appliances around the home from lights, air conditioning to the TV — all through the femtocell which could also be accessed remotely. The femtocell location-based services can also be used in retail environments where the users can trigger a personalized offer based on their proximity with the store. The major benefit for using femtocells in this use case is that virtually all handsets could be supported without requiring certain applications to be installed or run on the handsets.
Disruptive models for deployment are enabled by the fact that existing wireless networks need new topologies to handle the anticipated demand. The solution of using smaller cells closer to the subscriber results in the incorporation of a large number of smaller cells, with each small cell requiring a backhaul. Since wire line backhaul is a crucial ingredient in this network topology shift, one could argue that we are closing the circle from a wire-line telecom era to a wireless telecom era and now back to a mainly wire-line with last link being a short wireless hop.
Steven Brightfield is Director of Product Management at Qualcomm CDMA Technologies — www.qualcomm.com.
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