5G by 2020: Realising rapid 5G system development

The goals for the so-called 5G Radio Access Network (RAN) are lofty indeed and have been discussed at length by industry experts. What has received far less airtime is the question: "What exactly is the best path to 5G?" This article lays out some of the challenges of the 5G RAN and ways in which ideas can be implemented in hardware—both for prototyping, which needs to happen over the next three years, and ultimately for production deployment, which is slated to commence in 2020.

5G: Evolution, revolution, or both?
The goal of 5G is to provide a 1,000x increase in capacity, supporting 100+ billion connections with data rates up to 10Gbps and less than 1ms latency. However, these new networks will not just support the fastest links and fattest data pipes; they also aim to improve upon the capabilities of current networks. For example, today's wireless networks lack support for the low data rates and long battery life required for M2M (machine-to-machine) and sensor-type technologies.

Developing 5G networks that meet these goals will require a combination of existing systems such as LTE-Advanced and WiFi, combined with revolutionary technologies designed to support new uses such as the Internet of Things (IoT), augmented reality, immersive gaming, and UHD (ultra-high-definition) streaming video.

Major innovation is also needed at the lowest levels to accommodate broad requirements for both video and augmented reality. The needs of M2M networks will drive innovation in the physical layer, air interface definition, and control plane structures.

New frequency bands
5G will see some of the spectrum below 6GHz being re-purposed for use with newer technologies, particularly for non-line-of-sight (NLOS) requirements. Existing cellular bands will be augmented with new spectrum allocations above 6GHz that are able to supply much wider contiguous spectrum. Additionally, carrier aggregation techniques will be used to combine chunks of spectrum that are not co-located within the same band to further improve peak data rates. The core bands will provide up to 100MHz of instantaneous bandwidth, and the new extended bands will provide contiguous chunks of spectrum with as much as 500MHz in bandwidth—perhaps more.

Massive MIMO
Release 12 of the 3GPP standard, slated for freeze in 2015, provides for early massive MIMO (multiple-input and multiple-output) systems. These systems take active antennas to a new level. Large arrays of radiating elements (16x16 to 256x256 MIMO) require horizontal and vertical beam-forming to significantly increase capacity and coverage. In turn, massive MIMO requires significantly more processing power.

Advanced physical layer
Current 4G OFDM (orthogonal frequency-division multiplexing) air interfaces deliver high-speed data with limited support for low-power M2M communications. As a result, air interface technology and the 5G physical layer will be augmented using new bands of spectrum as they become available. Many new candidate air interfaces are being considered to provide support for sub-1ms latency with 10Gbps throughput. Other interfaces that can cater to the needs of simple sensor data transmission will not require such low latency or high data throughput, so it's likely that 5G will not employ a single air interface technology. Equipment will need to support multiple air interfaces—potentially simultaneously.

In addition, the physical layer will require new coding and modulation schemes, protocols, and framing structures brought about by disparate end-user requirements. The 5G infrastructure must automatically determine the type of channel needed, and adapt based on conditions (such as precipitation) or moving objects (such as trains, airplanes, or cars) affecting line-of-sight (LOS). Cognitive radio techniques and advanced adaptive coding and modulation schemes will allow equipment to provide the best possible connections.

Evolving architectures
Existing basestation architectures consist of a cabinet housing radio units, power amplifiers, and base band cards along with control and backhaul access. More recent architectures move the radio units to the mast, adjacent to the antennas, to eliminate lossy coaxial feeder cables and improve energy-related OpEx (operational expenditure).