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mMIMO Enables 5G, GaN on SiC Enables mMIMO

Jan 29, 2020
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The standardization process for 5G communications continues at a rapid rate with the 3rd Generation Partnership Project (3GPP) working to finalize the Release 16 in 2020. A recent report1 by ResearchAndMarkets.com identifies 3.4-3.8 GHz as the primary band for the first 5G launches and estimates that 70 percent of the operators will introduce 5G by 2023.

Among key enabling technologies is massive Multiple-Input Multiple-Output (mMIMO), which is critical to 5G delivering on its promise of a cellular network that, according to Marcus Weldon, CTO of Nokia and President of Nokia Bell Labs, is “permanently always-on, ultra-reliable, ultra-available, low-latency, high-performance, and everywhere.”2

What is mMIMO?

While MIMO, which is already found on some 4G base stations, typically uses two or more transmitters and receivers to send and receive more data at once, mMIMO extends that concept by significantly increasing the number of antennas on a single array.

For instance, Ericsson’s AIR 6468 uses 64 transmit and 64 receive antennas to support 64 feeds in an 8x8 array. Other equipment vendors have demonstrated mMIMO systems going up to 128 antennas.

mMIMO relies on multipath signal propagation due to reflections from structures in the environment. With radio channel estimation and signal processing techniques, the spatial diversity due to multipath propagation is leveraged to enable communication between base stations and multiple users in the same time and frequency resource.

The main benefits of mMIMO are:

  • Network Capacity: mMIMO increases network capacity and data throughput by splitting data packets over multiple signal paths as well as allowing simultaneous multiple users through the use of multi-user MIMO (MU-MIMO).
  • Better Coverage: Beamforming with mMIMO enables dynamic coverage for moving users by adjusting signal paths and, therefore, coverage to suit user location.
Figure 1: Massive MIMO improves both coverage, and network capacity and speed by exploiting multiple signal paths to users.

The challenges

The higher bandwidth of 5G does not linearly translate to higher capacity because it contributes inversely to the signal-to-noise ratio (SNR) as in Shannon’s Equation, which describes the information carrying capacity of a channel. To keep the SNR fixed while increasing bandwidth, the transmit power must be proportionally increased.

mMIMO has a higher number of RF chains and requires additional signal processing resources. This means additional hardware and higher power consumption, potentially leading to space and thermal management challenges. What’s more, given the higher operating frequency, the space between the antennas is much less and leaves less space for thermal management.

The GaN on SiC solution

Until now, silicon-based technologies, such as laterally-diffused metal-oxide semiconductor (LDMOS) devices have been widely used for wireless communications. However, LDMOS devices have power density and high-frequency limitations that cannot suitably meet 5G requirements.

This is where gallium nitride (GaN) transistors shine with their low-loss, high-frequency switching performance because of lower terminal capacitances and lack of a body diode with reverse-recovery loss (see GaN on SiC: The Substrate Challenge). The emergence of GaN on high-thermal conductivity silicon carbide (SiC) substrate has enabled mMIMO implementation and thus 5G.

GaN delivers higher performance than LDMOS at all frequencies and enables higher average power and wideband operation. GaN on SiC can save over 200 W of DC power compared to a system that uses LDMOS power amplifiers (PAs) when operated at maximum average power, according to Wolfspeed.

Besides higher power density, GaN on SiC’s higher thermal conductivity helps reduce die size and, ultimately, system size and weight by requiring less of the thermal management paraphernalia that LDMOS demands. This effectively solves the thermal issues due to hardware density as mentioned earlier.

From a network operator’s standpoint, the reduction in power consumption, and size and weight equate to a reduction in costs (see How GaN on SiC lowers 5G base station costs).

Who leads the GaN on SiC market?

When establishing a long-term 5G base station supply chain for RF components, it is important to choose a reliable GaN on SiC component vendor. The market leader in this area is Wolfspeed.

With over 3,700 patents issued to Wolfspeed, market analysis firm Yole Développement sees the company in the strongest IP position, especially for GaN HEMTs on SiC substrates.3 And the company continues to invest heavily in R&D — their R&D spend rose by 24 percent in fiscal 2019 to reach $157.9 million.

Wolfspeed’s components are field-tested and proven reliable. A trusted RF partner for telecom OEMs for more than 25 years, the company has shipped millions of products for the telecom sector and is part of 5G rollouts in Japan, South Korea and the United States.

References

1. Researchandmarkets.com, 4G to 5G: Worldwide Developments, Deployments, Revenue Models, & Forecasts 2019 to 2025 (https://www.researchandmarkets.com/reports/4791682/4g-to-5g-worldwide-developments-deployments)

2. Marcus Weldon, New value creation in the 5G era (https://www.bell-labs.com/var/articles/new-value-creation-5g-era/)

3. Yole Développement, RF GaN 2019 — Patent Landscape Analysis (https://www.i-micronews.com/products/rf-gan-2019-patent-landscape-analysis/)

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