5G promises to deliver dramatic improvements in spectral efficiency, effectively maximizing the ability of operators to deliver the required capacity over scarce spectrum resources. These improvements will be achieved by spatial multiplexing in one form or another. For millimeterwave deployments, this will rely on beamforming, where the signal is coherently beamed from the basestation to the user equipment, while for sub-6GHz deployments, multiple input multiple output “MIMO” technology is expected to prevail.
MIMO, and particularly Massive MIMO (“M-MIMO”), takes advantage of the combination of communications channels in rich scattering environments, such as an urban environment, and an increased number of antenna elements (typically 64 or greater). The increased number of antennae allows the basestation to turn the challenge of urban channel environment into an asset, essentially using the fading characteristics to de-correlate end users.
Theoretically M-MIMO can then deliver the full channel capacity to multiple users simultaneously, reusing the same frequency and time resources. This theory has been extended to successful lab technology demonstrations, with universities such as Bristol and Lund recently demonstrating a capacity of 2.9Gbps over a 20MHz channel, equivalent to 145bps/Hz, an extraordinary improvement compared to 1-2bps/Hz in commercially deployed LTE networks today.
The Challenge of 5G
The challenge today lies within converting the theory and demonstrations to tangible deployment scenarios. To date, several operators have announced results of early trials showing performance of 300-700Mbps over the same channel bandwidths. Although this is impressive compared to the 1bps benchmark, a challenge remains, since in demonstrations the user terminals are optimally placed to maximize the headline figures. The practical use case gains are much more modest, perhaps achieving 2-4bps/Hz. Some of the considerations limiting achieved performance are inter-cell interference at the cell edge, pilot tone contamination, and sub-optimal channels. It remains to be seen whether enhancements to signal processing, cell planning and resource scheduling will help M-MIMO to reach its potential, or whether beamforming solutions will play a role in complementing where channel conditions are favorable.
Aside from achieving the technology’s potential, there are challenges in the path of 5G deployment into mature markets. In many markets, operators are operationally limited in their ability to deploy new antennas by leasing agreements with site landlords, which can limit the number, size and weight of antennas on a mast. It is common for an operator to have an allocation of two antennas per sector, tracing back well over 20 years to when a second antenna was used to support GSM uplink diversity to address the challenges of fading within the channel. Today, these two antennas cover a multitude of bands from 700MHz to 2.6GHz, with multiple columns of antenna elements per band to deliver diversity and up to 4T4R MIMO, while also featuring up to 12 or 14 RF ports. Adding an active antenna to deliver 5G over 3.5GHz will complicate the situation even further, either requiring all bands to be integrated into a single antenna, or combining the 3.5GHz Active Array with passive antennas in a single radome.
Achieving the Promise of 5G
Despite the many challenges facing the mainstream deployment of 5G, the promised benefits continue to excite and bring together an industry dedicated to achieving its execution. Recently at the IWPC workshop, multiple operators, OEMs and technology vendors gathered to debate antenna innovation and evolution, where the challenges and progress toward commercially viable 5G employments were candidly addressed, and potential solutions debated. This continued dedication to innovation will make strides toward fulfilling the full potential of 5G, and meriting the benefits of this technology.
As the path to 5G deployment continues, MACOM is bringing to bear our full portfolio of RF to Light technologies to address the challenges of 5G with cost effective, compact, highly efficient and integrated front-end solutions. These solutions leverage MACOM’s GaN-on-Silicon power amplifiers and proprietary switch technologies, combined with our high speed optical interconnects to facilitate the dataflow within the radio head required for M-MIMO signal processing. MACOM is committed to enabling 5G by providing the high-performance product solutions required to better enable the necessary wireless infrastructure.
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