HetNets for super-concentrated mobile broadband

Heterogenous networks, or HetNets, combine different radio technologies and layers within a mobile network. David Swift, Senior Manager - Product Marketing, Wireless Networks Marketing & Strategy at Alcatel-Lucent explains why they will be needed if rising data demands are to be met

HetNets for super-concentrated mobile broadband

Mobile user expectations are growing and operators need to increase network capacity to keep pace. What approaches will succeed?

When it comes to meeting user expectations, you just have to look at the ever-growing number of smartphones, dongles and tablets that are being used continuously to see where the challenges lie. Users expect to have a broadband data connection ‘on the go’, and resent being let down by the network because ‘regular’ mobile simply isn’t up to the job, especially when it comes to data-hungry applications such as streaming movies. In addition, we are also seeing subscribers starting to use multiple SIMs, adding to the challenges for operators. 

With the unpredictable coverage and frustratingly slow download speeds sometimes offered by patchy 3G networks – delivering blistering average speeds of 2.1Mbps – a reasonable question to ask is: will ‘regular’ 4G be good enough?  

The new spectrum allocation for operators is in higher frequency bands which, correspondingly, come with poorer propagation characteristics and poorer in-building penetration. As a result, the whole industry recognises that the only way to address the issue of network capacity is through the use of small cells – located where the end users are – to provide the next leap in performance.   


What are ‘small cells’ and what are the benefits of bringing the network closer to the user?

A small cell is a radio base station with a smaller footprint that can boost mobile service in the home, in the office, or in a public space (a ‘metro cell’, also known as a ‘femto cell’).

For operators, small cells help overcome the challenge of spectrum exhaustion and site acquisition. Small cells also have a lower power requirement and offer much more flexibility on the backhaul, making it very easy for small cells to be located where the end user is and offload capacity – whether that’s indoor in the home, in an enterprise, in a shopping mall, or outside in the high street or in a railway station. 

Small cells enable users in that locale to enjoy improved throughput and a better experience. By relieving the surrounding macro cells, small cells also provide a corresponding benefit to the performance of the macrocell – a win-win situation.   

For end users, being able to bring the network closer ultimately means a higher quality of service experience. In a HetNet configuration, you can deploy a number of metro cells on the streets, wherever you have lots of people, as virtually invisible boxes.

As an example, on November 2012, we partnered with Australian mobile operator Telstra to provide race-goers at the Melbourne Cup horse racing event with fast mobile broadband coverage. With as many as 100,000 people attending on peak days, demand created by 3G-enabled devices was extremely high, so Telstra augmented its network with Alcatel-Lucent’s 3G lightRadio™ metro cells to extend coverage and capacity in its key hospitality area – effectively doubling the available wireless network capacity. Around the world, we’re currently involved in around 44 trials of this type of metrocell deployment.


What is a HetNet and why is it needed?

A HetNet is where you have a number of radio technologies and layers within the network collaborating to deliver a 3G or LTE operator-grade service. A key part of this is having lower power nodes (small cells) working in the same frequency as – and in synchronisation with – the macro cell (high power) nodes.   

The ‘Heterogeneous Network’ part of it is that there are varying power levels within the deployed nodes. Because spectrum is finite, optimising capacity means making cells smaller so that can you can increase re-use of the frequency. However, to deal effectively with faster-moving (and slower-moving) traffic, the macro and the small cells need to be fully synchronised in order to allow you to make intelligent use of that frequency and aggregate spectrum assets. That’s where heterogeneous networks come in to their own – harnessing different parts of the network in harmony with an overarching macro layer.

Quite simply, the reason that HetNets are needed is sheer data demand. Within a 4G HetNet, for example, speeds and capacity can be much greater, delivering download speeds in excess of 88Mbps – a whopping 45 times faster than 3G.  

If you take the premise that spectrum is like a road with cars representing packets of mobile data moving towards their destination, current 3G could be represented as a single track road and 4G similar to a motorway – offering more lanes and therefore more data.   

With a 4G HetNet encompassing small cells, packets of data can also travel closer together, creating much greater efficiency. So the combination of a wider road and closer cars results in much more data per second on subscribers’ mobile devices.

So what does a 4G HetNet service mean in reality for the end user? Well, at 1.4Gb speed, a full HD film of 1.2Gb takes less than 15 seconds to download. With 4G HetNet, mobile users are also able to do something that nobody could do with 3G – playing a full-on gaming blockbuster on a public mobile network (streaming via the cloud-based gaming service OnLive), without a glitch or buffering status in sight. This is a huge differentiator for mobile subscribers.


How are interference challenges managed within a HetNet?

Metro cells and macro cells in HetNet configurations can boost capacity in a given area ten times by deploying them in a 10:1 small cell–to–macro cell ratio. However, to deliver this capacity in real-life deployments, interference between the macro cell and metro cells has to be effectively managed.   

Small cells for use in the home tend to be low capacity and low power, and are insulated from the macro service by house walls. Similarly, small cells for deployment in offices are just slightly larger, with more channels to service more people and, again, insulated by the building walls. But when you move to public service use of small cells (metro cells) you typically have two configurations – shopping mall environments, where the mall surroundings insulate the radio from the main service, but also ‘blue-sky’ locations such as Wembley Stadium – an area that is dense in people, but completely open to the air.    

Indeed, the most complicated HetNet environments are urban hotspots – whether it’s Plaza Mayor in Madrid, Oxford Street in London or Times Square in New York. These locations are characterised by high-density pedestrian traffic, stationary users and, in the case of Oxford Street, slow-moving traffic. For these metro cells to work well, one of the requirements is that they have omni-directional antennae – directed ‘torchbeams’ to allow them to be put in more locations at the centre of a macro cell.  


Why is multivendor interoperability important for HetNets? 

In building a HetNet, there are unique requirements that come with deploying small cells in the same carrier as the macro network, and it’s important for both operators and customers that any solutions can be selected on a best-in-class basis, without being constrained or ‘locked in’ by the existing macro network.    

In 3G, the flat-IP IuH-based architecture simplifies integration of small cell equipment into an existing 3G system – often leveraging existing backhaul options – and gives operators a choice of vendors. On the LTE side, the architecture for macro cells and metro cells is the same, meaning that metro cells can connect through the S1 interface into other vendors’ Mobility Management Entities (MMEs) or S-gateways and perform S1-based handovers, eliminating the need for the X2 interface between base stations and making X2 communication, essentially, optional. A sensible multi-vendor approach means that it’s therefore possible to deploy metrocells in other vendors’ networks and manage mobility exclusively with an S1 handover.

The open and standards-based nature of the X1 and S1 interfaces is key in terms of enabling a multi-vendor future. Why is that important? Because it is through the availability of open standards that end-users will benefit from greater competition, increased industry-wide innovation, and improved Opex and Capex for operators so that they, in turn, can offer a competitive service. For this reason, we’ll see further standardisation of interfaces as we move forward into this new network architecture.


What are the future challenges and opportunities for HetNets? 

Going forward, networks are going to be built differently – we’re in a period of effectively throwing out the rule book. Operators need to work with local councils so that they understand that the mobile network is no longer a big, radio mast-based solution. These new networks of potentially thousands of metro cells also bring new challenges in terms of management. 

Moreover, there is the challenge of educating the community on what the new network looks like from their perspective, how it delivers the service they want and, for the operators, the wholly different economic model from installing a macrocell (taking into account the different logistics of site location, power, radio, and backhaul – all the while keeping it simplified and low cost). 

Primarily where HetNets will start to happen is within urban locations, since 60% of mobile traffic is generated in cities. Using metrocells that blend unobtrusively into the environment resolves a significant dilemma for local councils – how to provide a mobile service that will attract businesses and offer good communications, but which doesn’t create a city skyline of masts and antennas. 

We’re also seeing a number of new, innovative and shared business models emerging, such as operators striking deals with retail chains to provide Wi-Fi hotspots, and even with planners for public or city-wide Wi-Fi.

Thanks to the capabilities provided by small cells, everyone involved is now thinking differently and a solution is evolving that fits the needs of all the stakeholders. The future is HetNet.

Written by Wireless magazine
Wireless magazine

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