The Institute of Electrical and Electronics Engineers published an extensive white paper, “IEEE 5G and Beyond Technology Roadmap,” which holds some information, forecasts and predictions relevant for the wireless infrastructure business that AGL Magazine covers. Published with permission from the IEEE 5G Initiative, what follows are verbatim excerpts from the white paper about multiple-input multiple output (MIMO) technology and millimeter-wave technology that will play an important role in the deployment of antenna sites for 5G wireless communications.
MIMO technology has been considered a vital approach to improving spectral efficiency for wireless communications systems over the past 20 years. In 4G systems, the number of the antennas supported at the base station (BS) cannot be larger than 64 and, thus, the performance gain from MIMO is quite limited. For 5G systems and beyond, to further improve spectral efficiency and energy efficiency, a new technique named as large-scale antennas has been proposed to serve multiple users in the same time-frequency resource. Massive MIMO uses hundreds, if not thousands, of antennas.
However, technical challenges escalate as the number of antennas at base stations increases. Firstly, the performance gain from massive MIMO largely depends on the accuracy of channel state information (CSI), which is used for precoding design, modulation and coding scheme decision, and signal demodulation. Therefore, channel estimation accuracy is critical for MIMO realization. Traditional MIMO utilizes orthogonal pilot sequences to acquire CSI. However, this approach encounters great difficulties in the massive MIMO case.
Network operators spend as much as half of their operating expenses on energy costs. As the number of RF chains at a base stations increase to support 5G massive MIMO, the energy costs are likely to go up. There will be a need to create adaptive power management systems. During low usage periods, by using adaptive radio network designs perhaps enabled by machine learning, will significantly lower operator costs and CO2 emissions.
Although many researchers have studied massive MIMO techniques, how to apply them into high-speed scenario and how to achieve a low complexity yet accurate channel estimation and detection remain big research challenges. Furthermore, system layer views and applications, such as cell virtualization or cell shaping, will require further attention.
The U.S. Federal Communications Commission (FCC) has freed approximately 30 times more bandwidth at millimeter-wave (mmWave) frequencies than is available at cellphone bands for commercial use. Millimeter-wave spectrum would allow orders of magnitude greater throughput, opening important application spaces such as virtual reality, in which what a user sees is relayed as high-definition video back to a server, processed, and augmented with high-definition overlays sent back to the user, all in real time. Applications like this cannot be supported without the availability of instantaneous bandwidths of 500 MHz (or even wider) and low latencies that cannot be achieved at current cellphone bands. Additional advantages include reducing the need for carrier aggregation and reducing the need to be as spectrally efficient so that modulation waveforms with lower complexity can be used (i.e., 256 QAM instead of 1024 QAM).
However, mmWave hardware for 5G has unique challenges and required characteristics as compared to hardware for below-6-GHz operation. The following examples of challenges are identified for 5G mmWave hardware with some suggested solutions and standards that will apply. More detailed discussions of these topics will be addressed in the IEEE 5G and Beyond Technology Roadmap.
○ Possible solutions include high-density femto/pico cells, beamforming arrays, scalable and massive array concepts, and conformal antenna integration.
○ Related hardware needs include sensitive low-power receivers with robust immunity to interference; low-cost, compact integrated antenna arrays; new conformal materials for antennas; efficient, low-cost active and passive devices (e.g., combiners, phase shifters, filters, and other passives); and large-signal measurements at mmWave frequencies.
○ Semiconductor technologies considered include SiGe, GaN, GaAs, CMOS, heterogeneous integration, and wafer-level packaging.
○ Potential standards activities include the following: IEEE 287, IEEE Standard for Precision Coaxial Connectors (DC to 110 GHz); IEEE P1770, Draft IEEE Recommended Practice for The Usage of Terms Commonly Employed in the Field of Large-Signal Vector Network Analysis; and the development of IEEE P1785, IEEE Frequency Bands and Waveguide Dimensions, and others25.
○ Possible solutions include time division multiple access (TDMA), hybrid architectures with subarrays, mmWave MIMO technologies, code division multiple access (CDMA), and frequency division multiple access (FDMA).
○ Related hardware needs include high-power mmWave amplifiers; integrated high-order phase shifters; new active antenna technologies; and measurement traceability for dynamic free-field modulated signals.
○ Potential standards activities include IEEE P149™, Draft IEEE Recommended Practice for Antenna Measurements; IEEE 1720™-2012, IEEE Recommended Practice for Near- Field Antenna Measurements; and others
○ Possible solutions include indoor repeaters and collaboration with gigabit Wi-Fi networks.
○ Related hardware needs include handsets with diversity RF-front-ends that can switch between mmWave, below 6 GHz, Wi-Fi, and Li-Fi networks.
Migration from 1G to 4G has been facilitated by the availability of readily usable or at least known technologies that required a limited amount of development. The migration from the operating frequency of 800 MHz of 1G to the 1800-MHz range of 4G did not have a major influence on signal propagation properties in air. The migration to digital technologies, introduction of new, more efficient protocols, and the extensive coverage provided by deployment of repeaters were the main contributors to enhanced performance. However, the use of frequencies beyond 6 GHz will impose drastic restrictions on signal propagation distance. Furthermore, the inability of signals to circumvent obstacles will progressively become an even greater problem as higher frequencies are under consideration for future generations.
The IEEE 5G Initiative is mobilizing across industry, academia, R&D organizations, application developers, and the standards, policy and regulatory communities globally to enable the historic transformation promised by 5G and future generations of connectivity.
Executive Editor and Associate Publisher
Don Bishop joined AGL Media Group in 2004. He helped to launch and was the founding editor of AGL Magazine, the AGL Bulletin email newsletter (now AGL eDigest) and DAS and Small Cells magazine (now AGL Small Cell Magazine). He served as host for AGL Conferences from 2010 to 2012, appearing at 12 conferences. Bishop writes and otherwise obtains editorial content published in AGL Magazine, AGL eDigest and the AGL Media Group website. Bishop also photographs and films conferences and conventions. Many of his photographs have appeared on the cover, in articles and in the “AGL Tower of the Month” center spread photo feature in AGL Magazine. During his time with Wiesner Publishing, Primedia Business Information and AGL Media Group, he helped to launch several magazines and edited or managed editorial departments for a dozen magazines and their associated websites, newsletters and live event coverage. He is a former property manager, radio station owner and CEO of a broadcast engineering consulting firm. He was elected a Fellow of the Radio Club of America in 1988, received its Presidents Award in 1993, and served on its board of directors for nine years. Don Bishop may be contacted at: [email protected]