5G Testing: 3GPP Beam Management
2020-02-28 | 7 min read
Multiple-input multiple-output (MIMO), beam steering, and beamforming are among the most talked-about technologies in 5G. They are essential to delivering the 100x data rates and the 1000x capacity goals specified in the International Mobile Telecommunications-2020 (IMT-2020) vision.
Throughput is one of the key elements to making 5G communications successful. 5G boosts throughput in multiple ways:
• Wider overall channel bandwidths enable sending more data through the air interface
• Spatial multiplexing sends multiple independent streams of data through multiple antennas at a given time and frequency. The use of enhanced channel feedback enables 5G to better exploit this technique and achieve higher data rates than previous technologies.
Spatial Diversity and Spatial Multiplexing
Massive MIMO and beam steering technologies improve throughput. Understanding MIMO challenges requires a basic knowledge of the techniques used to deliver high quality, robust signals to and from a 5G device. Many different techniques can be used for implementing MIMO. Each one offers distinct benefits and compromises.
Spatial diversity is commonly used to improve reliability in many forms of RF communication. This technique consists of sending multiple copies of the same signal via multiple antennas. Spatial diversity increases the chances of properly receiving the signal, improving reliability.
Spatial multiplexing is a different multiple-antenna technique that feeds independent data into each antenna, with all antennas transmitting at the same frequency and time. This technique exploits the wireless channel characteristics allowing the transmission of independent streams over multiple channels, which increases overall data capacity.
Beam Management Techniques
Beam steering and beamforming are additional techniques that use multiple antennas to create directional transmissions that must accurately point at the receiving device. Beam steering is a set of techniques used to focus the direction and width of a radiation pattern. In wireless communications, beam steering changes the direction of the signal while beam refinement narrows the width of the transmitted signal. Both actions are typically performed by manipulating the phase shift of the signal through an array of multiple antenna elements.
Beamforming applies different phase shifts to each antenna element to shape and provide discrete control of the direction of a transmitted beam. Beamforming requires communication channel feedback to implement real-time control of the beam. Both beamforming and beam steering incorporate channel feedback to manipulate the beam shape and direction in real time. Spatial multiplexing with beamforming increases signal robustness with the added advantage of improved throughput.
3GPP Beam Management Procedures
3rd Generation Partnership Project (3GPP) 5G New Radio (NR) Release 15 specifies frequency use up to 52.6 GHz with up to 400 MHz bandwidth per carrier, and aggregation of multiple carriers for up to 800 MHz channel bandwidth. Operating at millimeter-wave (mmWave) frequencies introduces new challenges in path loss, blockage, and signal propagation. Beam steering is a key technology to overcome these issues. 5G NR specifies new initial access procedures to ensure alignment of the directional transmissions used in beam steering.
As shown in Figure 1, new initial access techniques use beam sweeping to have the base station transmit multiple beams and then identify the strongest beam and establish a communication link.
Figure 1. Beam sweeping and initial access
Validating initial access, beam management, and throughput achieved through the wireless link are key factors for successful beam steering implementation in 5G.
Long Term Evolution (LTE) systems use antennas covering large angular areas to cast a wide net for potential users. 5G uses narrow beams to overcome mmWave signal propagation issues. Therefore, special care must be taken in order for the user equipment (UE) to find the beams from the base station. Maintaining link quality is also an issue, especially when the device is in motion.
5G NR Release 15 specifies new procedures for initial access and attach when establishing the wireless link connection. Since neither the device nor the base station knows the other’s location, the base station uses beam sweeping to transmit channel information in sync blocks across the spectrum as shown in Figure 2. The UE determines the strongest match and transmits back to the base station. Once the base station knows the direction of the UE, it establishes a communication link.
Figure 2. 5G initial access and beam management
Beam acquisition and tracking, beam refinement, beam feedback, and beam switching procedures exist. These procedures may have an impact on the time it takes to establish connections or on the quality of service observed in those connections. Designers need to implement, validate, and optimize all these functions, or the user will experience dropped calls or poor performance.
Testing the protocol early in the development cycle ensures the device can establish and maintain a call. A network emulator with a built-in protocol state machine emulates network signals and tests the resulting device signals to verify and optimize initial access and beam management.
You can find more information on beam management and other 5G NR topics in Keysight’s recently published Engineering the 5G World eBook.