GSM and LTE, 2 technologies in 1 base station

LTE for bandwidth and GSM for voice are a match made in heaven for subscribers. The roll-out however, not so much. Running them both from the same radio equipment (BTS) can be the answer. SatSite can run both YateBTS (GSM) and YateENB (LTE) at the same time, in the same spectrum, using the same radio hardware.

Software-defined BTS

This is made possible by replacing commonly used FPGA and DSP boards with one Intel Atom chipset. Both the GSM YateBTS and the LTE YateENB are modules implemented in software, allowing the base station to be reprogrammed or reconfigured to support new protocols. A base station can run GSM at first, and can be later software-upgradeable to LTE, running multiple air interface protocols using the same radio, at the same time.

Mixed 2G/4G spectrum allocation

From a spectrum point of view, as seen in the image below, the mixed GSM/LTE technology enables a base station to be software-configurable for up to 4-TRX/ARFCN. A base station can use the 850, 900, 1800, and 1900 MhZ bands for both GSM and LTE, meaning that it will allocate two ARFCN to GSM and will use the remaining spectrum for LTE.

ss_mix_spectr_2015-10-6_pic1_version1.1Based on the subscribers’ activity (data vs. voice), operators can assign in software the spectrum priority for either LTE or GSM, so LTE gets a higher priority if there is a lower use of voice services. This optimizes the resources allocation in the network and supplies better access to users.

YateBTS and YateENB – Yate modules

Yate is an underlying part of the software architecture of our mixed 2G/4G RAN. It has a highly expandable architecture that provides unified management and monitoring. Both YateBTS and YateENB are software modules based on Yate. Yate’s SDR architecture enables the LTE and the GSM modules to use the same radio hardware. You can find out more about Yate’s multiple modules here.

ss_mix_spectr_2015-10-6_pic2_version1.1Yate’s SDR architecture also enabled us to replace the conventional, special purpose equipment combination of a baseband unit (BBU) + a remote radio unit (RRU), with a single unit. With this technology we implemented all the functions of both a conventional base station and a base station controller, eliminating the costly Abis interface for traffic and signaling, as well as partial functions of an Mobile Switching Center (MSC), in terms of mobility, power and frequency management and handover.

The mixed 2G/4G RAN technology is embodied in our SatSite base station. SatSite acts more like a conventional eNodeB, even when running on GSM, because it uses IP backhaul for both 2G and 4G. It also contains the IP list of all neighboring SatSite units.

Using off-the-shelf hardware and a generic operating system, SatSite embraces everything SDR stands for, and is the solution for an easy adoption of new standards or technologies, even 5G in the future.

Software-defined radio for frequency reuse in LTE

The expansion of 4G LTE challenges operators who have limited spectrum; as some decide to take down existing 2G (and even 3G) deployments in favor of 4G, bandwidth allocation in an area must be carefully planned to match the quality requirements of LTE.

In 4G LTE, spectrum is a crucial resource. Performance is dependent on the proximity between the radio network and the devices. The closer the radio tower, the higher the data throughput. This means that the more cell towers operators build, the better they can cover the area.

Frequency reuse is a widely adopted solution for LTE; essentially, a given area is served by more cell towers using the same frequency. An easier and more efficient approach to this is software-defined radio.

Cell edge interference management using YateENB

Cell edge interference management using YateENB

Frequency reuse means splitting an area in several new, smaller cells. In LTE, to maintain a high throughput, the same frequency is allocated to all the new cells, at the expense of higher interference at the cell edges. Since all the new cells have equal power, two or more cells meeting causes interference around the cells edges.

Apart from that, building and maintaining additional infrastructure required by frequency reuse results in high capital and operational expenses.

SDR in the LTE base station (eNodeB) can be a solution to these limitations. The fact that SDR implements the communication protocols in software and uses general-purpose hardware has several benefits.

The most important one is the effect on infrastructure costs. Base stations built on special-purpose hardware need heavier equipment and hence larger towers, which are expensive to install and operate. An eNodeB using general purpose hardware relies on more lightweight equipment, meaning that smaller towers can be deployed more densely in an area and provide better coverage. A lower power consumption associated with SDR-based BTS equipment also contributes to reducing the overall RAN costs.

Another major benefit of SDR is flexibility. SDR-based eNodeBs can be configured more easily to manage spectrum use at the edges of the cells, and thus minimize interference. Frequency sub-carriers can be selected at two cell edges in such a way that they do not overlap as in the case of conventional systems.

What’s more, SDR permits an adaptable power management so that different services can be assigned optimal QoS depending on the context.

Another aspect of SDR is the ability to build mixed networks. Base station equipment can be programmed to support different technologies at the same time and using the same hardware, serving more users with virtually no infrastructure investment. You can read more about this topic in this previous blog post.

SDR: the next big thing?

SDR systems can accurately be catalogued as ‘software-defined’ if they run on general purpose hardware, in a context where many existing technologies define themselves as SDR while running on special-purpose equipment.

With the adoption of more demanding technologies such as LTE, operators need to handle more traffic and deliver higher quality, meaning that mobile infrastructure needs to be run more efficiently and more profitably.

How can cost savings, resource efficiency, and flexible management be achieved in the mobile network? Our solution is the software-defined SatSite base station.

The reason for turning to SDR is the inflexibility of special-purpose hardware and software currently used in conventional base stations and what this entails in terms of costs, power consumption, and equipment.


Large expenses to upgrade, reprogram, or add new functions to the network

Because they are physically larger, base stations using conventional DSPs are more difficult to manage. What’s more, DSP boards can’t be modified to perform new functions or improve existing ones, so extending the RAN infrastructure usually requires new equipment to be added, leading to increased capital investment. Used on commodity hardware, SDR systems have lower manufacturing costs, making them more profitable when compared to the current heavy, static network equipment.

Increased power consumption

Special-purpose hardware products designed to perform complex functions come with high power demands. SDR allows more functions to be added to the same board, leading to the use of smaller equipment, with a lower power consumption.

Equipment supplier constraints

Another disadvantage of special-purpose equipment is that it is usually produced, serviced and supported by a particular vendor. In this case, operators are limited in recurring to different suppliers, as new equipment needs to inter-work with existing set-ups. SDR has the advantage of running on commodity hardware to avoid the use of specialized components and allow more flexibility to reconfigure or repurpose the hardware.

Dedicated staff training

Specialized hardware/software usually comes with specific vendor training and support. SDR offers operators more autonomy in configuring and managing base station equipment, relying entirely on their personnel.

SDR allows a high level of flexibility in designing and managing the RAN, with network functions being upgraded or reprogrammed with the simple use of software. While it is not a new concept, most base stations continue to use chip sets like DSPs, which are built on special purpose hardware, keeping equipment heavy, costly, and inflexible for changing traffic needs.

SDR is essential for the expansion of mixed networks to provide access across multiple technologies, such as 2G/4G, and prioritize service allocation depending on the needs. SatSite base station simultaneously provides 2G and 4G coverage using from the same equipment.

Built on general purpose hardware and using a non-proprietary operating system, SatSite allows operators to build smaller cell towers, with lower costs. SatSite cell sites can be suitably disposed to match the traffic needs in any area, and network performance can be improved remotely and easily, with a simple software change.

SatSite uses a high level language which enables it to support more complex functions than a conventional base station using a DSP. In highly populated areas or situations, increasing the network capacity to serve more subscribers usually requires a higher density of cell towers. SatSite can be dynamically reprogrammed to meet higher subscribers capacities by a software configuration for multiple-TRX.

Due to the flexibility, capacity, power and cost efficiency SDR brings to mobile networks design, its future probably holds good news.


Wikipedia contributors. “Software-defined radio.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 24 Jun. 2015. Web. 2 Jul. 2015.