The pace of wireless innovation is accelerating, enabling faster, more sensitive, and more reliable connectivity across the globe. The wireless industry is poised for significant technological change in multiple systems. Cellular communications are being upgraded from 4G to 5G to increase data throughput, while satellite providers are building networks in space with the aim of providing high-speed communications to every corner of the globe. Wireless engineers want to achieve technological breakthroughs to maximize system throughput and build robust links and data processing capabilities. For the physical layer of a wireless system, the key technologies involve larger bandwidth, higher-order modulation scheme, and multi-antenna technology in a wireless system.
Greater signal bandwidth
With a limited spectrum to allocate, standards development groups want to provide more bandwidth at higher frequencies. For example, the frequency range 2 (FR2) specified in 5G New AirPort (NR) REL-15 is 24.25ghz to 52.6ghz, and the maximum channel bandwidth is 400 MHz. The REL-16 introduces license-free bands in the 5 GHz and 6 GHz frequency ranges. By mid-2022, 3GPP REL-17 will extend the spectrum of the license-free band to 71 GHz.
Satellite communications provide connectivity for television, telephone, broadband Internet services, and military communications. Satellites can operate in many bands from L to Ka. The International Telecommunication Union (ITU) has allocated 71 to 76 GHz and 81 to 86 GHz in the W-band to satellite services. Commercial satellite operators want more bandwidth in these bands. On June 30, 2021, a satellite carrying a W-band radio transmitter was successfully launched into space. We can expect to see more commercial projects in the W-band in the near future.
The millimeter-wave band provides more available bandwidth. Large bandwidth can achieve high throughput data and low latency, but the increased bandwidth also brings more noise, which affects system performance. Wireless engineers need to manage the noise problems of broadband communications. In addition to generating more system noise, expanding bandwidth at higher frequencies presents other challenges for design and testing, such as path losses, frequency response, and phase noise.
Higher-order modulation schemes
Higher-order modulation schemes can increase data rates without increasing signal bandwidth, and the symbols are more closely spaced and thus more sensitive to noise. As modulation density increases, devices require better modulation quality. Table 1 lists the EVM requirements of 3GPP Rel-16 specification 38.141 for 5G NR base stations. 3GPP is also considering adopting a 1,024 QAM with more stringent design and test margins.
|Modulation Schemes||EVM (%)|
Greater signal bandwidth and higher-order modulation schemes can improve throughput. However, more bandwidth does not necessarily mean more system capacity. You must consider the signal-to-noise ratio (SNR) of your communication system. Proper SNR is critical to maintaining communication links. The larger the bandwidth is, the more noise it brings to the system. The higher the modulation scheme is, the more susceptible it is to noise. You need to transmit high-power signals without distortion and reduce system noise to maintain the performance of communication links. To test your design, you need to accurately characterize each of the components and subsystems are shown in Figure 1.
Most wireless systems used in commercial applications and aerospace and defense use multi-antenna technology on receivers and/or transmitters to improve overall system performance. These techniques include spatial diversity, spatial multiplexing, and beam shaping. Engineers use multi-antenna technology to achieve diversity, multiplexing, or antenna gain. Such techniques help improve the data throughput and SNR of wireless system receivers. For example, 5G NR uses eight spatial streams in FR1 to improve spectral efficiency without increasing signal bandwidth. 3GPP has therefore defined in Technical Specification (TS) 38.141-1 how to perform performance tests using multi-spatial streams for 5G NR base stations. The tests required up to two transmitter antennas and eight receiver antennas, and specific propagation conditions, correlation matrices, and SNR were applied to each test case. Figure 2 shows a 5G base station performance multiple-input multiple-output (MIMO) test configuration for two transmitter antennas and four-receiver antennas to provide mixed automatic repeat request (HARQ) feedback.
Compared to IEEE 802.11AX, the next-generation WI-FI standard IEEE 802.11BE (Wi-Fi 7) provides twice the signal bandwidth, 16 spatial streams, and four times the modulation scheme density. Together they provide data rates of up to 40 Gbps. Table 2 lists the significant changes to the IEEE 802.11 physical layer.
|IEEE 802.11 standard||Maximum signal broadband||Modulation Schemes||Spatial flow quantity|
|802.11be (Wi-Fi 7)||320 MHz||OFDM, more than 4096QAM||16|
|802.11ax (Wi-Fi 6)||160 MHz||OFDM, more than 1024QAM||8|
To test multi-antenna systems using spatial diversity, spatial multiplexing, and multiple antenna arrays, you need a test system that can provide multi-channel signals with stable phase relationships between the signals. However, commercial signal generators use a separate synthesizer to up-convert an IF signal into an RF signal. The test system must provide precise timing synchronization between channels to simulate multi-channel test signals. The phase between test signals must be coherent and controllable. Figure 3 shows a fully integrated, calibrated, and synchronized signal generation and analysis solution that helps you minimize measurement uncertainty for multi-antenna testing.
The new generation of wireless communication systems, such as 5G, satellites, and Wi-Fi, require higher frequencies, greater bandwidth, more sophisticated modulation schemes, and multi-antenna designs. This will help you deal with new design and test challenges, such as increased test complexity, measurement uncertainty, excessive path losses, and noise, which can affect device performance.
To meet these challenges, you need a scalable test solution that accurately and easily supports greater frequency coverage, greater bandwidth, and multi-channel applications. With a fully integrated, calibrated, and synchronized solution, you can reduce test complexity and quickly get repeatable, accurate results.