FDD Sub-3GHz Massive MIMO Radios Will Play A Critical Role Enabling Operators To Maximise Opportunities Offered By 5G Advanced

Over the next few years, 5G Advanced will provide networks with enhanced capabilities, including improved uplink, lower latency and better coverage resulting in higher network performance and increased reliability. This will enable operators to enhance existing services while generating additional sources of revenues via new services. However, to do this operators will need to maximise their spectrum assets across all bands, particularly their legacy Sub-3GHz spectrum.

Benefits of Sub-3GHz Bands

While higher TDD spectrum bands are being used to provide 5-10Gbps downlink speeds required for premium customer experiences, FDD Sub-3GHz spectrum is also needed to extend high-speed 5G mobile broadband coverage across urban, suburban and rural regions and to provide reliable coverage for IoT services. In particular, Sub-1GHz spectrum is vital for indoor coverage. In addition, FDD spectrum offers lower latency than TDD as different channels are used for the uplink and downlink channels.

Most operators have around 80-120MHz of Sub-3GHz spectrum as this was the primary spectrum used by previous cellular generations and most of this spectrum is becoming available for 5G as operators switch-off legacy 2G and 3G networks. Refarming existing FDD spectrum bands will allow operators to quickly build up their 5G footprint. However, as there is less spectrum available in the Sub-3GHz bands compared to higher bands, operators will need to introduce advanced radio technologies with much improved spectrum efficiencies, throughputs and latencies. In addition, this must be done using compact, cost-efficient radio solutions in order to keep capex and opex costs to a minimum.

FDD Triple-band MIMO and Massive MIMO

Several vendors offer 4T4R and 8T8R ultra-wideband modules for low-band (700MHz, 800MHz and 900MHz) and mid-band (1.8GHz, 2.1GHz, and 2.6GHz) frequencies. As a result, only two multi-antenna, single RAN RF modules are required to cover both spectrum bands – instead of six as with conventional radios. In addition, some vendors offer 32T32R massive MIMO modules which can be deployed in a compact radio/antenna enclosure for the mid-band spectrum bands.

FDD triple-band massive MIMO radios significantly boost capacity and coverage compared to conventional 4T4R radios. This enables operators to improve the spectrum efficiency of their existing Sub-3GHz resources, while at the same time, satisfying higher traffic demands and improving user experience. From an investment viewpoint, FDD massive MIMO radios also reduce operators’ overall capex and opex costs.

Key Radio Technologies

Key technologies at the heart of state-of-the-art FDD RF modules include FDD Beamforming, GigaBand multi-band fusion technology plus innovative energy-saving features enabled primarily by innovations in power amplifier technologies.

  • FDD Beamforming

To date, beamforming has primarily been used in TDD spectrum as operators initially deployed 5G in TDD bands. However, beamforming can also be used in FDD spectrum which has been supported since 3GPP’s Release 15 specification. As with TDD spectrum bands, the main benefit is increased spectrum efficiency as the directional beams focus the radio signals where they are needed rather than distributing them across the entire cell. This increases radio capacity and coverage while reducing interference. Increasing the number of transmit antenna – and hence the number of beams – means narrower and more focused beams, resulting in even higher capacity and better spectral efficiency.

  • Multi-Band Power Amplifier Technology

Multi-band technology allows the functionality of several radios to be combined into a single radio unit with a single transceiver accommodating two or three bands. A tri-band radio therefore only requires one power amplifier and one filter rather than three power amplifiers/filters as required in a conventional radio. This significantly increases the level of integration thereby reducing tower footprint. As traffic rarely peaks in all bands simultaneously, a multi-band power amplifier allows power to be dynamically shared between different bands. This means that it is possible to provide full power output for each band but without designing the power amplifier for simultaneous peak power in all bands.

  • GigaBand Technology

Compared to wide-band TDD spectrum, 700-900MHz low-band FDD spectrum is limited, fragmented and consists of narrow bandwidth channels. The same is true of 1.8-2.1/2.6GHz spectrum. GigaBand technology is a multi-band fusion technology that converts these disparate spectrum assets into a single 100MHz-wide FDD carrier. Using carrier aggregation and Multi-Band Serving Cell (MBSC) technology, six Sub-3GHz spectrum bands can be combined into a single carrier which maximises spectral efficiency.

  • Energy Saving AI Software

Service requirements are higher with 5G, which means that peak-to-average traffic ratios are also higher. As a result, the requirements for higher energy efficiency at peak hours and low power consumption in idle time are more urgent. AI software solutions are playing a major part to help reduce energy consumption in 5G networks by enabling shutdowns at network, cell and at radio levels coupled with fast wake-up capabilities, with AI/ML being used in real-time to optimise network parameters according to traffic demands.

In the radios, state-of-the-art AI-based software solutions can achieve “deep sleep dormancy” with very low power consumption in an idle state coupled with fast on-demand wake-up. For an operator using multiple frequency bands at a single cell, smart algorithms can progressively shut down different frequency bands depending on traffic loads until only one band is operating, with all other frequencies being in a dormant state.

Huawei FDD MIMO and massive MIMO Radios

In 2022, Huawei launched the industry’s first FDD triple-band MIMO modules supporting GHz-level bandwidths contained in a single radio box. The modules are available in 4T4R, 8T8R and 32T32R configurations.

  • GigaBand RF Modules – Huawei’s FDD ultra-wideband RF modules have an instantaneous bandwidth (IBW) in excess of 800MHz per module. This is a major advantage for operators with fragmented spectrum as one ultra-wideband radio can replace two or even three narrower band radios. Alternatively, ultra-wideband radios can be used for RAN sharing, which means that two operators can share one radio, again reducing capex and opex costs.
  • Advanced Power Amplifiers – key to this ultra-wideband capability is Huawei’s advanced power amplifier technology, which leverages breakthroughs in several technologies, including AI-based DPD[1] beamforming algorithms, advanced power amplifier architectures, RF filter materials and improved passive cooling via bionic heat sinks. Huawei claims that its power amplifiers are 10% more efficient than industry rivals and that its innovative filter materials generate 1dB less filter loss compared to industry rivals.
  • GigaGreen Platform – at the heart of the GigaGreen platform is Huawei’s “0-bit, 0-Watt” and “More-bit, Less-Watt” solutions, which leverage breakthroughs in materials technology, energy saving policy orchestration and smart algorithms. With millisecond level carrier and channel shutdown, Huawei’s “0-bit, 0-Watt” solution can achieve 99% “super deep sleep dormancy” enabling RF modules to consume almost zero power under low load, while its “More-bit, Less Watt” solution continuously minimizes energy consumption under medium and high loads – without compromising user experience. Achieving these low power consumption levels requires independent shutdown of individual power amplifiers and full power sharing across all carriers, frequency bands and Radio Access Technologies (RATs).

FDD sub-3GHz Deployment Example

FDD Sub-3GHz triple band radios are designed from the outset to simplify deployments at cell sites while reducing power consumption. For operators, this translates into capex and opex savings. For example, many operators use four or five FDD frequency bands at a single tower site. Traditionally, this would require four or five radios, i.e. one RF module per frequency band. However, with ultra-wideband 4T4R, 8T8R and 32T32R massive MIMO modules, only two radios are required. In addition, the operator has the option to add one (or two) additional frequency bands.

By combining an active massive MIMO radio/antenna with a six-band passive antenna into a single package, the number of “boxes” per sector can be reduced from seven to two (Exhibit 1). This enables new frequency bands to be added without increasing the number of base stations or power consumption while opex is also reduced.


Exhibit 1:  Leveraging Ultra-Wideband Radios To Enable Site Simplification

Analyst Viewpoint

FDD technology at Sub-3GHz frequency bands is set to play a critical role as 5G Advanced is rolled out over the next few years. To fully leverage the opportunities offered by 5G Advanced, Counterpoint Research believes that it is imperative that operators maximise their existing FDD Sub-3GHz spectrum assets in order to ensure seamless coverage across urban, suburban and rural regions. Not only will this provide an enhanced user experience for customers, it will also enable operators to offer a range of new high-data, low-latency services with guaranteed service levels across their entire network footprint.

As less spectrum is available at Sub-3GHz, however, operators will need to boost the spectrum efficiencies of their RAN equipment at these FDD frequencies. In practice, this will involve investing in the latest, advanced massive MIMO radios, which offer significant spectral efficiency gains compared to conventional radios. For example, Huawei claims that its Sub-3GHz 32T32R massive MIMO radio can offer operators up to 10X more capacity, 10X more data downlink throughput, a 10dB increase in coverage and a 30% reduction in power consumption compared to a 4T4R radio.

Counterpoint Research believes that this transition to advanced massive MIMO radios must be done without substantially increasing capex and opex costs for operators, particularly power consumption. RAN operations are typically a trade-off between radio performance and power consumption. Despite their higher throughputs and superior spectrum efficiencies, massive MIMO radios can also help minimise capex and opex costs. As seen in Exhibit 1, replacing multiple single-band radios with a single multi-band radio leads to considerable site simplification and thus a lowering of tower leasing costs. In many cases, using radios with higher spectral efficiencies can also result in a reduction in the number of cell sites required and may even lower operators’ investments in new spectrum bands. In addition, by leveraging state-of-the art radio technologies, including the latest power amplifiers coupled with the latest AI-driven power saving techniques, smart algorithms, etc., massive MIMO radios can also reduce overall power consumption on a cell site basis, thus reducing opex costs for operators, while helping to minimise their carbon footprint.

This blog was sponsored by Huawei

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Gareth has been a technology analyst for over 20 years and has compiled research reports and market share/forecast studies on a range of topics, including wireless technologies, AI & computing, automotive, smartphone hardware, sensors and semiconductors, digital broadcasting and satellite communications.

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