Roaming in LTE – facing challenges with new opportunities

With LTE, operators are now able to offer their subscribers huge bandwidths and significantly improved quality of service, but they also have to face new challenges. LTE drastically changed the mobility architecture and led to the adoption of new interfaces, frequencies, protocols, which ultimately impacted on the state of roaming.

A 2013 Informa report on the market status of LTE Roaming found that most operators hadn’t even finished their roaming strategy. By 2015, operators who deployed LTE networks had data roaming only in a few countries.

Our answer to the LTE roaming dilemma is YateUCN.

So what’s different?

Roaming allows subscribers to use voice and data services when they are abroad. There are two main aspects to keep in mind when discussing roaming:

  • commercial  roaming agreements between operators
  • technical implementation SS7 (Camel/MAP) protocol in the case of 2.5G and 3G networks, and Diameter in 4G networks

Each roaming protocol requires new roaming and interconnect agreements, even with existing partners. Therefore, once an operator deploys a 4G network, it will need new roaming agreements for their LTE subscribers.

Operators who want to add an LTE network will have to face two challenges related to:

  • deploying a network with a radically different infrastructure, including new interfaces and protocols
  • setting up new roaming agreements for Diameter, since LTE roaming requires it

Our solution

YateUCN, our core network solution, allows 4G devices to authenticate to foreign partners over SS7 roaming agreements, to an HLR.

YateUCN is a mixed 2.5G/4G core network server, capable of replacing all the core network equipments associated to both networks, while also using both Camel/MAP and Diameter for roaming.



YateUCN also makes it possible for 4G devices to be registered to a 2.5G network and a 4G network at the same time, if necessary.

With the innovative YateUCN, MNOs will tap the great opportunity LTE roaming is, while also using the standing roaming agreements with their partners. Operators will gain time to set up the right agreements, and at the same time will garner new revenues by encouraging their customers to use data roaming.

Off to greener networks

Going green is not just good for the environment, it’s also good for mobile operators.

It is common knowledge that the share of energy drives the largest costs in mobile network deployments – about 50% of the total OPEX in emerging markets. While diesel power systems play a large part in the high level of expenditure, according to a 2014 GSMA Green Power for Mobile report, they account today for nearly 90% of power solutions used in off-grid and unreliable grid sites.

Operational fuel costs, logistics (transportation, depositing), diesel pilferage – which alone increases costs with about 15%-20%, the need for continual service in areas where power outages are frequent, all add up to operators’ investment and operational expenditure, reflecting eventually in a higher service cost for users and therefore in a drop in use of mobile services.

green power SatSite

60% of the overall network infrastructure costs is attributable to building and powering cell towers [1], so saving on energy requires the choice of equipment that uses makes a more efficient use of power resources.

Deploying cell sites using green energy is easy when using a base station like SatSite, which requires a low power input (45W) and is ideal for installing in remote areas with unstable or no electrical grids. Cell towers using SatSite in either single or 3-sector configuration are a lightweight deployment which allows it to serve isolated or remote locations, relying only on the existing natural resources.

SatSite’s design differentiates from that of traditional base station by integrating a passive cooling system that makes its use independent from air conditioning or ventilation units. The power required for air conditioning makes up for a large part of the overall input needed to run operate a site. Eliminating air conditioning also frees up space to make cell towers more resilient.

Over diesel power systems, solar panels and wind turbines, for example, have a much longer life expectancy, that can range to 20-25 years. Combined with diesel power in hybrid energy systems, operators can achieve a longer and more reliable operation of cell towers, driving down fuel costs to save more than $10 billion annually.

Shifting to green towers has major implications. First, it reduces operators’ costs and allows them to extend mobile networks in places in areas that are completely deprived of coverage due to the lack of an adequate infrastructure. Then, it reduces the negative effects on environment; GSMA reports that an off-grid site in Africa has an average annual consumption of 13,000 litres of diesel, adding as much as 35 tons of CO2 emissions to the environment.

If they choose green energy for telecom towers in remote areas, operators must move to smaller, more autonomous cell sites; profitability will come not only from power savings and a rise in service use, but also from reshaping the overall network infrastructure to better manage power factors.


[1] Telecom infrastructure sharing, (last visited June 10, 2015).

Off-grid technologies for sustainable mobile network deployments

Energy costs amount to 15% up to 50% of the total OPEX of deploying mobile networks in areas without power grid. Operators in developing countries, as those in the Sub-Saharan Africa region, need cost-effective solutions to face this issue, otherwise they will find it impossible to install new networks.

When we first heard about Tesla’s latest innovation we were impressed. It seemed the perfect solution for what households need right now. But then we gave it more thought and realized that Powerwall batteries are also an answer for mobile operators. We now know they would make a great match with our SatSite base stations.

Depending on the type of deployment, cell sites equipped with SatSite units have the following average consumption levels:

  • lightweight site, with omni antenna – approximately 45 Watts
  • three-sector site – less than 150 Watts
  • three-sector site with tower mounted booster – approximately 350 Watts


A Tesla Powerwall battery offers either 7 or 10 kWh power output, is rechargeable with aid from solar panels and can be mounted indoors and outdoors. It also has a 10 years warranty and requires no additional maintenance costs. A single 7 kWh battery is enough for running 3 SatSite units.

Recent initiatives, like GSMA’s Green Power for Mobile, have stressed the importance of deploying network infrastructures powered by green energy (in most cases solar) in developing areas and regions beyond the electrical grid.

Since both equipments can be powered by solar panels we consider this pairing an easy and seamless solution, particularly in areas where connection to the electricity grid is an issue. It can also successfully replace diesel-powered telecom towers, reducing costs and environmental pollution.

Not only does this solution work well in rural or isolated areas, but it would be a great fit for urban areas in developing nations that have an unreliable power grid. Cell towers equipped with SatSite base stations could use Powerwall batteries as a dependable and renewable backup plan in case of power outage. National blackouts affecting hundreds of millions of people, like those in India (2012), Turkey (2015) or United States (2003), will no longer restrict vital mobile communications if operators choose self-sustaining power alternatives.

The Case for the Unconnected Billions

Sending text messages, going on hour-long calls, or live-streaming videos are such an integral part of our lives that most of us take them for granted. And yet around 3 billion people live, today, in areas without access to basic infrastructure – be it remote islands in the Pacific, developing extra-urban areas, or isolated rural areas everywhere around the world.

Mobile communication can connect these people with one another and with technologies that can prove to be vital. Mobile data enables job seeking in wider area ranges, instantly accessing health care information in case of emergency or risk, or keeping farmers in line with market prices and trends.

In remote, unconnected markets, bringing voice and data coverage can be best achieved using GPRS, which provides wider coverage than 3G, and is easier to adapt to rural, remote, or low density areas. In such places, traditional cellular networks have the disadvantage of being economically counterproductive to deploy, and operators are unlikely to invest in hefty infrastructures that generate relatively little revenue from usage compared to the networks’ lifespan maintenance costs.

The YateBTS technology addresses these issues differently than most other approaches to mobile networks. 2.5G networks using SatSite and YateUCN are a simplified, flexible, and low-cost solution that can be adopted anywhere in the world.

Lightweight, low-power sites

SatSite is smaller than typical base stations which makes it easy to build lightweight cell sites that are especially profitable in higher density networks. SatSite’s low power requirements allow operators to plan self-sustaining mobile networks running on solar or wind energy, avoiding the use of costly power grids or diesel systems.

Bandwidth-efficient backhaul

Unlike traditional networks, a YateBTS/YateUCN mobile network allows bandwidth savings of up to 60%, by using the GTP protocol across the entire network.

bring_cov_2015-6-4_version1.2SatSite acts as a BTS/BSC communicating with the YateUCN core network over GTP, without using any additional network nodes, to simplify the network architecture and minimize the backhaul load. Data sessions in networks using YateBTS SatSite can be established either locally, by assigning the IP directly in the SatSite, or in the YateUCN core network, adapting to the constraints of each location.

SatSite unifies the BTS and the BSC from traditional radio access networks architecture, to eliminate the Abis radio interface used to direct traffic between the BTS and the BSC. In conventional cellular networks, the BSC handling all the communication between the core network and the devices leads to high costs and a substantial load on the network. SatSite base station can communicate with YateUCN over satellite, using GTP to replace the signalling interfaces normally used inside the radio access network and to/from the core network.

A satellite backhaul architecture is adapted particularly to sparse networks in areas with a low density populations, where cell sites are far from the core network; satellite allows operators to serve any location, and improve bandwidth performance for both voice and data services. Combined with the light design and an autonomous operation of the SatSite base station, backhaul over satellite makes YateBTS/YateUCN networks ideal for extending connectivity to uncovered areas.

What we talk about when we talk about coverage

There are a multitude of factors operators take into account before deploying their networks in order to provide us with the best possible coverage. Since the radio communication of mobile networks is peer-to-peer, the most significant aspect of coverage is that the device sees the mobile mast. To bring some clarity to what coverage means, and how to calculate it, we will introduce: the elements that influence coverage for both operators and their subscribers, coverage planning and our coverage and range estimation tool.

Coverage varies from cell site to cell site, and depends on the type of terrain, the equipment used, the type of buildings around the site, the radio frequency but also, very importantly, on the sensitivity and transmit efficiency of the subscriber’s equipment.

The coverage level also relies heavily on the antenna type or the amplifier power levels. The further you get from the cell site, the weaker the signal gets, as the ground clutter standing in the signal’s way increases. This makes coverage drop exponentially. ground_clutter_2015-3-5_draft1.2.1

Operators can increase the strength of the signal and the coverage, through higher power transmissions, taller antenna masts, a higher antenna gain etc. Antenna gain is, in fact, a crucial factor in getting a broader coverage, as it accounts for the losses and the directivity of an antenna. The relation between the antenna gain and the coverage is directly proportional, i.e. the higher the antenna gain, the more coverage the cell site will deliver.

Network planners use propagation models like Hata, Cost231 or Walfisch-Ikegami, to roughly calculate, in a quantitative manner, what can be expected in a specific environment. They also utilize more accurate tools that take into account the exact type of environment where their cell sites will be deployed, as the Radio Mobile RF propagation simulation software.

We created a tool that uses a very specific coverage propagation model, so do check out how it works with our SatSite. For more information on SatSite’s coverage area, click here.

For mobile subscribers, coverage depends on their devices’ capabilities, since they are not all the same. Also, the coverage level will not be the same if they use their device attached to a car kit, handheld or with an external antenna.

As an important note, always keep in mind that most times, coverage depends on both the device’s ability to “see” the antenna and the antenna’s capability to reach the device.

YateBTS in the age of IoT

These days, everybody’s talking about the Internet of Things. And it’s no surprise that everybody loves it; from operators, who see a chance to attack new markets and better retain customers, to urban consumers who can connect a whole range of devices to an app on their smartphones, and farmers who can use technology to optimize their activities and maximize production.

Bringing IoT to such different audiences while maintaining a high quality of service and an efficient use of network resources is a challenge for most carriers’ current infrastructure capabilities and cost strategies. In fact, a critical concern when it comes to creating IoT infrastructure for new areas is laying the ground for that infrastructure – that is, mobile network coverage.

The number of IoT applications designed for farming and livestock breeding is on the rise, but their actual penetration in rural areas is limited to regions with existing GSM/GPRS infrastructure. Remote and rural areas offer mobile operators enticing prospects not only in terms of IoT coverage, but also in terms of connecting these new customers to their entire range of services such as voice, SMS, or data. But due to the high investment requirements for equipment, civil infrastructure, or maintenance, operators are still reluctant in building mobile networks in there areas.

The success of carriers setting up new networks in remote locations depends greatly on keeping investment and operational costs down, as well as on basing their network equipment choices on redundancy, power efficiency, and flexibility. A reliable IoT infrastructure amounts to operators providing continual service, seamlessly, and in very variable weather and terrain conditions. The geography of each area and the specific needs of communities influence every decision going from civil infrastructure to power supplying and equipment maintenance. In areas with low infrastructure where grid power isn’t available, for instance, carriers must rely on alternative power sources to successfully deploy new networks.


YateBTS-powered IoT applications

A base station like the YateBTS SatSite offers a reliable and flexible solution for carriers to bring mobile coverage to remote rural areas. SatSite is a 2.5G low-power, lightweight base station that allows it to be easily installed anywhere from hill tops to outlying crop fields. Practical for lightweight cell sites, it can be operated in single or three-sector sites using a single solar panel. This generates a substantial reduction in operators’ initial investment costs but also in operating cell sites in the long-run.

SatSite’s low operating costs make it a particularly suitable solution for small farms and rural households, where resources are more scarce and used less efficiently. Access to IoT applications can support these communities in rendering farming activities more productive and sustainable. The flexibility of SatSite’s architecture suits the requirements of specific IoT solutions. Used for any range of applications and devices, from water pumps and soil measurement sensors, to herd tracking and monitoring, SatSite optimizes resource allocation to allow carriers to efficiently adapt their networks to the specific demands of each location.

In rural areas, access to IoT infrastructure can make it possible to attain better farming results, optimize productivity, and increase the overall quality of life. Basic mobile services can create new standards for health care, education, as well as social and economic development of these areas. Operators can play the leading role in this process, provided that their decisions successfully combine cost effectiveness for themselves, and service quality for consumers.

OFDM – the science behind LTE

No one wants the kitten video they’re watching on Youtube to stop and reload endlessly. We all want to send big chunks of data very fast, while still keeping the integrity of said data. Nevertheless, the faster you send data, the more likely it is to experience transmission problems, especially due to interference or weak signal.

OFDM (Orthogonal Frequency Division Multiplexing) is the radio science behind huge bandwidth capabilities we see in LTE. OFDM splits data into small sub-carriers, also known as data streams, on neighboring frequencies, over a single channel. It allows sending more data than through single carrier modulation techniques, and at a higher rate. OFDM also handles phenomena such as interference, noise or multipath significantly more efficiently than other modulation methods.

How it works

The following explanation is for non-engineers and is meant to shed some light on OFDM, so keep in mind that we are leaving out many details that are not critical for understanding what OFDM is or why we use it.

We’ll use a theoretical example: a bandwidth of 1 MHz and round numbers, which are easier to remember and apply to real-life scenarios.

Traditional single carrier modulation uses only one frequency to send the bits, as seen below.


In OFDM, the bandwidth of 1 MHz band is split into, say, 1000 sub-carriers of 1 kHz, and each of them sends one symbol per millisecond.


Next, OFDM uses the FFT (fast Fourier transform) algorithm and its inverse to effectively retrieve the original data bits from the symbols and vice versa.

Last, but not least, OFDM has a special property called orthogonality, which essentially means that sub-carriers are spaced in such a way that they only partially overlap, as the peak of each sub-carrier intersects the zero crossing of the neighboring sub-carrier. This characteristic is perfectly illustrated in the image below, where you can see 5 of the 1000 1 kHz sub-carriers in the frequency domain, in a single channel.

Orthogonality is what allows us to pack sub-carriers really tight, without wasted frequencies between them as in traditional cases, which require using guard bands.


Let’s go back to the example used earlier. The data rate obtained using OFDM is the same as in the case of single-carrier modulation, so you might wonder why we use it so enthusiastically in LTE, which is what we’ll explain below.

Effective against multipath propagation and interference

Multipath propagation occurs the moment a radio signal bounces-off obstacles that appear in its path: water sources, hills and mountains, buildings, trees etc. Multipath causes the transmitted signal to be sent on two or more paths to the receiver, making it difficult for the receiver to interpret what it receives. Only some frequencies are prone to experience multipath. In single carrier modulation systems, it has a damaging impact throughout the whole frequency and affects all of the data symbols.


Take a look at the image below: only one carrier experiences multipath, but since all sub-carriers transport redundant copies of the sent symbols, data loss is minimal.


OFDM is also effective against interference because only some of the data streams will be affected by this phenomenon and data can be more easily recovered with redundant error-correction coding.

Spectral efficiency

When using OFDM, LTE can tailor the modulation to make the best possible use of the available radio path to and from the UEs. Because of the OFDM carrier structure, LTE can take advantage of the changes in channel conditions and uses different modulations depending how close or far the UEs are from the transmitter.

Because it uses OFMD, LTE can dynamically change the symbol alphabet, depending on the radio conditions, for each individual sub-carrier. For example, if you’re sending data close to the transmitter, LTE will apply a 64-QAM modulation scheme, that is 6 bits/symbol. But if you are moving further from the transmitter, and the radio conditions are unreliable, LTE will dynamically adapt to either 16-QAM or QPSK, sending 4 or 2 bits/symbol. In extreme cases, LTE can even use BPSK (1 bit/symbol).

Some disadvantages

OFDM also has its downsides.

OFDM has a high peak-to-average power ratio, and requires a highly linear and oversized power amplifier that usually has a low efficiency. In the image below, you can see a typical OFDM peak-to-average power ratio. This occurs because multiple sub-carriers with different phases combine constructively in the time domain.

Typically, to obtain a 5 W average output power, an OFDM system requires a 100 W power amplifier, representing an increase by a factor of 20 from the actual 5 W output. Otherwise, the distortion is far too destructive to allow OFDM to function normally.


OFDM is also very sensitive to Doppler shift. This phenomenon occurs when the UE is moving, thus making the frequency of the signal received different from the frequency of the initially transmitted signal. Among its effects in OFDM, Doppler shift deteriorates synchronization, data recovery, and destroys the orthogonality of sub-carriers.

Unified Core Network Demo with iPhone 6

Recently, we verified the interoperability of the new iPhone 6 with the Unified Core NetworkTM, by performing the industry’s first VoLTE call from a GSM mobile phone to iPhone 6, through a single unified switch. This is a Big Deal. Why?

First, Some Background on the Problem

One of the changes 4G LTE is forcing on mobile operators is the elimination of older SS7 MAP core networks of 2G and 3G in favor of IMS. However, many critical services, like roaming are not yet “fully baked” in IMS, so operators will probably continue to run 2G and 3G networks for the foreseeable future. In fact, mixed 2G/4G deployments are happening in many places right now and those operators are in the situation of installing and managing two nearly independent core networks.

The Solution

SS7Ware’s Unified Core Network (UCN), along with YateBTS is the answer to the 2G/4G mixed network problem. The UCN provides a “packet core” for routing internet traffic and an IMS/VoLTE core for handling calls and text messages. It works with YateBTS to support 2.5G GSM/GPRS handsets and with any standard eNodeB to support 4G LTE devices . We first introduced it with this video. (In that first video we referred to “OpenSAE” and “OpenVoLTE” as two different things, but we have since combined them into a single UCN server.)

Unified Core Network The switching, routing and mobility management functions of the core network (4G SAE/IMS and 2G Mobile Switching Center/Visitor Location Register/GPRS support node) are implemented in a single UCN server. This approach offers many advantages:

  • Simplified architecture; even a large network is just many copies of an identical box.
  • Simple scalability; just add more servers.
  • Increased network resiliency: there is a many-to-many relationship between radio sites and UCN servers, with seamless failover and load balancing.

And now the Demos!

Most recently, we have been testing the UCN with the IMS client in the new iPhone 6. (Unlike  over-the-top applications like Skype, a true IMS client is implemented in the baseband processor, so using a true VoLTE-capable handset is critical.) We used the UCN with an an off-the-shelf LTE eNodeB to provide a 4G radio network for the iPhone and we used YateBTS to provide a 2G radio network for a second test phone. In this first demo video, the iPhone registers to the UCN through the 4G radio network and the GSM phone registers to the UCN through the 2G radio network.

The two phones register to the same HLR using SS7-MAP. Then, we exchanged text messages between the two handsets. If you are a hardcore techie, here is a ladder diagram: 2g_4g_register_sms_sip_map-video And here is the signaling trace from the UCN server console. If you look at the ladder diagram, you see that we are using conventional SS7-MAP to register an LTE iPhone6 to the HLR. This solves the LTE roaming problem, and we can do it thanks to the Yate messaging engine, which is the basis of the UCN server.

In the second demo video, we make phone calls between the two handsets.

For the 2G phone, this is an ordinary circuit-switched GSM call. For the 4G phone, this is a VoLTE call. What is special here is that these calls are being handled by a single switch in the UCN, behaving as a 4G IMS and a 2G MSC at the same time. We can do this because the UCN server is built on Yate, which combines one of the most solid SIP implementations in the industry with carrier-certified SS7-MAP support, and because YateBTS gives us a very LTE-like RAN for 2.5G.

We have already had the opportunity to present this technology to mobile operators. Their first reaction is disbelief, followed by a lot of excitement. “You mean we can use CAMEL on a VoLTE call?”  “You mean we can authenticate 4G handsets in an ordinary HLR?” “You mean we can run GSM and LTE out of the same core network?” And to this we say, “Yes, you can!”

YateBTS and YateUCN™ make a perfect match for SDMN

YateBTS and YateUCN can be used together to build complete software-defined mobile networks.

YateBTS is a software implementation of the GSM/GPRS radio network. It runs on any Linux and uses a generic digital radio board, the Nuand BladeRF. The entire physical layer is implemented in software, which is different from the usual FPGA- or DSP-based radio design.

For the core network there’s YateUCN, the unified core network based on Yate. YateUCN is a Linux application that can run on commodity servers. It implements the functions of 2.5G and 4G core networks and is easy to integrate in existing mobile operator infrastructure. Like YateBTS, YateUCN replaces hardware routers and transcoders with pure software.
Together, YateBTS and YateUCN form complete software-defined mobile networks, networks that are affordable to build and operate, and networks that can support 2.5G, 4G or even both at the same time.
There are several advantages to the YateBTS+YateUCN approach:
  • Upgradable – We can add new features, like EDGE, with software upgrades or even replace 2.5G GSM/GPRS with 4G LTE using the same hardware.
  • Manageable – Because the entire system is Linux, we can monitor and manage every aspect of the software in a flexible way.
  • Affordable – A pure software approach has much lower development costs and relies on commodity computing hardware.
  • Flexible – The hardware is protocol-agnostic and can be reconfigured to support any mix of technologies.
  • Scalable – The capacity of the core network can be increased just by adding more servers.
Compare this to a conventional mobile network, with its hardwired base stations in the field and big iron like the Cisco AR550 or an Ericsson Mobile Switching Center in the core. It’s all single-purpose equipment, expensive or impossible to upgrade, and all based on proprietary software and hardware with big licensing fees, special training and support requirements.

Software Defined Mobile Networks

Since the inception of telephony, hardware drove the technological progress. In the early 2000s, generally available CPU’s became cheap enough to enable the development of software-defined radio (SDR) technology and software telephony switches (softswitches). However, it took nearly 10 more years to combine these two technologies and create the first software-defined mobile network (SDMN).

A mobile network can be called “software-defined” if it uses SDR base stations and a software defined core network for both telephony and packet data. A software-defined mobile network needs to be implemented on commodity, non-proprietary hardware, including the radio and network infrastructure hardware. In addition, an SDMN should use off-the-shelf, non-proprietary operating systems.

We may be the first company to offer a complete software-defined mobile network, and we are convinced that this is the future of mobile infrastructure.

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