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.

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