Development is well underway on Gigabit LTE cellular communications systems that promise an order of magnitude increase in data transfer rates and 5G is close behind. Small cell access nodes will form an essential part of both systems but new communications processors are needed to make these a reality.

If there is one thing that the mobile communication revolution has proved it is that people love data. We can’t consume enough of it. And we want to access it across a range of devices in different locations and environments.

This situation has presented network equipment providers and operators with a wealth of business opportunities coupled with an equivalent amount of technological challenges. One way these are being addressed for the current, 4G, generation of devices is through the deployment of small cell radio access nodes such as microcells, picocells and femtocells. In urban areas in developed countries, saturation point is being reached for traditional cellular macrocell base stations due to environmental constraints. Small cells, concealed in lampposts and walls, are becoming the only option here. Tiny and hidden from view, small cells are able to offer similar data capacity to their larger cousins but, owing to lower RF transmit power, provide much smaller areas of coverage and user capacity individually.

While traditional cellular base stations have generally relied on discrete digital signal processors (DSPs) or application-specific ICs, small cells generally use system-on-chip (SoC) devices featuring programmable DSP cores. As an example, Taiwan’s ITRI R&D organization selected the CEVA-XC DSP core to form the basis of its new 4G small cell base station platform. ITRI will deploy the core to enable a software defined radio (SDR) baseband architecture for its small cell platform. This provides a 3GPP release 10 (LTE Advanced) compliant access point solution integrating the core functions of baseband signal processing, RF front-end circuit and software protocols.

 

 

The Next Step

With the rollout of 5G equipment and services planned to occur from 2020, work is under way on the development of the stepping stone to it – LTE-Advanced Pro or Gigabit LTE. This promises mobile broadband with download speeds above 1Gbit/s.

Users increasingly rely on mobile, rather than fixed line, Internet access and utilize this indoors. However, the higher frequency bands used by LTE-Advanced Pro (up to 3.7GHz) – and several preceding cellular communications standards – do not penetrate buildings very well. Consequently, there is a need for small cells within buildings and a corresponding requirement for new semiconductor architectures to support communication processing. CEVA has seen a significant uptake in its communication processor cores, such as the CEVA-XC4500 and CEVA-XC12, for Gigabit LTE applications with tens of cores being designed into some macrocell SoCs and single or dual cores being deployed for small cells. ( See Figure 1).

 

Figure 1. The CEVA-XC12 communication processor core has been adopted in SoCs for eNodeB and gNodeB applications including small cells, Remote Radio Head or RRH, Macrocells and Cloud RAN for LTE-Advanced Pro and 5G. It delivers powerful vector capabilities alongside a general computation engine to supply the performance and flexibility demanded by next generation communication applications.

 

Away from densely populated urban areas, small cells are finding another use serving rural communities. In many rural areas and villages, the lower population density makes the deployment of traditional macrocell base stations economically unattractive for network operators. Small cells may offer a solution here, delivering a more flexible and lower cost method of delivering broadband services in a more targeted manner.

 

Supporting 5G

5G will ratchet up the demands on the network even further to deliver high speed and low latency services. The issue at this point will be responsiveness rather than throughput. This is because download speeds will far exceed the required levels for even the most bandwidth-hungry applications – such as streaming ultra high definition video – but services will be sold on the basis of instant response; for example, the ability to download a full-length HD movie in a few seconds.

In order to support the required multi-Gigabit download speeds to users, extremely high transmission frequencies will be deployed – up to 95GHz. Such microwave bands are commonly used today to connect and backhaul macrocell towers together and to the network. Moving into microwave bands means that signals only have a direct line of sight propagation: in urban outdoor environments signals will be blocked by buildings and indoors they will be blocked by walls. This means that a very large number of small cells will be needed to propagate the signals in a dense urban environment indoor and outdoor. Furthermore, they are likely to be powered over Ethernet, which will be used to provide backhaul for the network. This arrangement limits the power budget of the small cells to a range of 25-90W.

So what does this mean for the underlying electronics? Well, signal processor cores have already evolved into highly flexible, programmable units that can meet the seemingly incompatible requirements of greater performance and lower power consumption demanded by LTE-Advanced Pro. However, to enable the small cell infrastructure that will be essential for the success of 5G, a whole new generation of communication processors must be developed.

 


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