Many of these 5G base stations will use massive MIMO antennas. Thanks to the use of massive MIMO antennas, these new 5G network architectures push the outer edges of the cellular network to always be connected. In this article, we will introduce all the basics related to RF front-ends in massive MIMO base stations.
Definition of Massive MIMO
Massive MIMO uses multiple base station antennas to communicate with multiple users, and uses beamforming technology in phased array adaptive technology. Massive MIMO increases capacity without increasing the design complexity of inter-cell coordination. By using massive MIMO, beams can be formed, ensuring that a single beam can only support one user at almost any time. Therefore, to provide each user with a non-interference, high-capacity base station connection.
Massive MIMO technology uses a large antenna array (generally composed of 16, 32, or 64 array components) to achieve spatial multiplexing (see the figure below). Spatial multiplexing provides multiple parallel data streams in the same resource module. By expanding the total number of virtual channels, it can increase capacity and data rate without adding additional towers and spectrum.
Recall what other blog posts in this series have told:
● Small cell blog, part 1
● Small cell blog, part 2
● How will the carrier network realize 5G
● 5 factors that need to be considered when designing a fixed wireless access system
Figure 1. The advantages of massive MIMO
Massive MIMO 5G and NR standards
The 3GPP version 15 released in the first phase of the 5G New Radio (NR) specification was released in June 2018. The specification focuses on mobile deployments using 5G NR non-standalone (NSA) and standalone (SA) standards. NSA is a transitional step for operators to switch to SA (see Figure 2). The NSA uses the LTE anchor band for control and uses the 5G NR band to provide faster data rates. NSA allows operators to directly provide 5G data rates without building a new 5G core network. Because we are still at the beginning of 5G NR design, most base station applications are NSA. But as 5G continues to evolve, this situation will change after the deployment of SA-type systems.
Figure 2. The road to independent 5G.
5G frequency band suitable for massive MIMO systems
A major challenge faced by base station component suppliers and manufacturers is to provide the minimum number of stock-keeping units (SKU) required in each region. These fragmented frequency band combinations in the higher frequency range force suppliers and manufacturers to provide a diversified product portfolio (see figure below). In addition, the increase in frequency and bandwidth requirements has further increased the design difficulty for RF semiconductor technology providers. For example, the gain and efficiency of a power amplifier (PA) are interrelated, and the silicon LDMOS power technology currently used in the transmit path will have an impact on it. Therefore, system manufacturers have begun to switch from silicon LDMOS to gallium nitride (GaN), which can achieve up to 60% efficiency at an average operating power level and wide bandwidth, making it very suitable for massive MIMO base station systems.
Explore the RF front-end of massive MIMO systems (semiconductor technology perspective and manufacturer perspective)
So, what RF front-end (RFFE) components do 5G massive MIMO base station systems need? Integrated front-end components with high linearity, high efficiency and low power consumption. In order to analyze from a specification point of view, manufacturers hope that semiconductor suppliers can optimize the following parameters to meet their system requirements.
Key RF front-end specifications that manufacturers require semiconductor providers to meet
● High Adjacent Channel Power Ratio (ACPR), also known as Adjacent Channel Leakage Ratio (ACLR)
○ ACPR refers to the ratio of the transmitter power on the allocated channel to the leakage power on the adjacent radio channel. The ACPR of the transmitter mainly depends on the performance of the PA. The higher the linearity of the PA, the better the ACPR, because less distortion will be produced.
● High power added efficiency (PAE)
○ This indicator to measure the efficiency of a power amplifier takes into account the influence of amplifier gain. It is best to choose an amplifier with a higher PAE value. This is because its heat sink is smaller or is not equipped with a heat sink, so it generates less heat, higher reliability, and lighter weight, which can achieve higher overall performance.
● Low noise figure (NF)
○ The low noise amplifier (LNA) is the first active stage in the Rx configuration, and its noise figure has a direct effect on the sensitivity of radio reception. Therefore, RF semiconductor suppliers always try to achieve lower NF because this is one of the most critical specifications in radio design.
○ The noise figure, in dB, is the ratio between the signal-to-noise ratio of Rx (SNRi) input and the signal-to-noise ratio of Rx (SNRo) output.
● Low power consumption
○ Low-power devices have always been a good choice for system applications. They can reduce heat generation, reduce system operating costs and additional hardware costs (such as radiators). Given that massive MIMO has more orders of magnitude antennas in a single radio, reducing power consumption is critical.
● High channel isolation
○ Isolation is to prevent signals from appearing on unnecessary nodes in the circuit. Higher isolation means less interference and clearer communication. Isolation is a measure of the loss between two channel ports: between the transmitter and the transmitter port, or between the transmitter and the receiver port. The higher the isolation, the clearer the signal.
○ After adopting the 5G massive MIMO architecture, channel isolation has suddenly become an important parameter to measure the proximity between multiple antenna chains in a single radio system. Although TDD operation reduces the isolation requirements between Tx-Rx, Tx-Tx and Rx-Rx isolation is still required. As more small signal content is integrated into a single chip package, and multiple Rx front-end paths are set in the same package, isolation compliance can only be achieved through innovative semiconductor circuit design and packaging technology.
Semiconductor suppliers must optimize the above parameters so that manufacturers of massive MIMO systems can more easily meet the specifications. The following system specifications are related to the above-mentioned RF front-end semiconductor parameters.
Key manufacturer system specifications
● Optimize the application of equivalent isotropic radiated power (EIRP)
○ The transmitter power and antenna gain in a given direction are related to the omnidirectional antenna of the radio transmitter.
○ For 5G systems below 6 GHz, 16, 32, or 64 array components will be used, depending on the EIRP required by the application. Since a large number of array components are required, and each component also needs to output power, heat dissipation becomes a major challenge, prompting designs to seek technologies that provide the highest efficiency.
○ The use of technologies such as GaN and GaAs can help reduce the number of active components required for massive MIMO arrays while meeting base station EIRP system requirements.
● High receiver sensitivity
○ Receiving sensitivity measures the ability of the receiver to detect weak signals and process these signals without errors. Noise is the biggest obstacle to achieving the target sensitivity. Therefore, the use of components with excellent noise figure is the key to the receiver system design.
○ Another measure of receiver sensitivity is the error vector magnitude (EVM) of the received signal decoding.To minimize the EVM error, it can only be achieved by using low noise figure and high linearity components to minimize the weakened signal distortion
● Small size
○ Massive MIMO systems must be light enough to be easily installed in locations such as traditional base station towers and streetlight poles. In addition, the front-end components must be placed as close as possible to the radiating antenna, which is crucial. This has also prompted the adoption of front-end integration and energy-efficient semiconductor technology and packaging.
● Low power consumption
○ In order to meet the needs of 5G high-data applications, we will need more infrastructure (such as macro base stations and micro base stations, data centers, servers, and small base stations). This means that network power consumption will increase, and therefore system efficiency needs to be improved to save total energy consumption. In the end, operators can achieve greater output at lower costs. Providing solutions with high output power, higher efficiency and low power consumption is the key.
○ A In addition, massive MIMO systems with 32 or 64 channels can also use more heat sinks. The use of GaN and other technologies can improve the power added efficiency of the system, reduce the need for large radiators, and thus minimize the weight and size of the system.
● Passive cooling, highly reliable
○ Another benefit of low power consumption is that it can reduce the amount of heat generated, so fewer radiators are needed, which in turn reduces size and weight. The Advanced Antenna System (AAS) must have high energy efficiency and robustness in order to passively cool all outdoor tower top Electronic equipment, which is very important. GaN allows manufacturers to use passive cooling in certain applications, reducing the need for fans or air conditioners, and can install the RF front end on the antenna.
The construction of 5G massive MIMO base stations has begun, and operators will continue to expand their deployment. All parts of the world need products with different frequencies and power levels, so suppliers need to choose from a diversified product portfolio supply chain. Because massive MIMO systems have strict requirements on parameters and require higher frequency ranges and bandwidths, new technologies must be adopted. As shown in the table below, Qorvo offers the richest 5G massive MIMO product portfolio on the market. We also use the most suitable technologies for various massive MIMO applications to create products. Qorvo not only provides products that cover all frequencies above 3.5 GHz, these products also use GaN, GaAs, and filter bulk acoustic wave (BAW) technology for excellent performance.
5G massive MIMO and millimeter wave infrastructure designs below 6 GHz are already in use. Technologies such as GaN, GaAs, and BAW all help operators and base station OEMs achieve 5G massive MIMO goals and extend coverage to the edge of the network. As consumers, we have just seen the tip of the iceberg of massive MIMO and 5G capabilities.