wireless communication systems
5G, satellite and Wi-Fi: complex design and scalable testing
A guest post by Eric Hsu*
providers on the subject
More bandwidth for higher data throughput and lower latency: The speed of wireless communication transmission is increasing. But not only GSM networks for mobile communication are being expanded, but also satellite communication. This goes hand in hand with the design and testing of the hardware.
Mobile communications are moving from 4G to 5G to enable higher data throughput with lower latency. At the same time, satellite communications providers are building networks in space to enable fast communications from anywhere on Earth. It is about maximizing high data throughput, stability of the connections and processing of the data. The main technological components of the physical layer of wireless systems are larger bandwidths, higher order modulation methods and multi-antenna techniques.
Due to the limited frequency allocation, standardization organizations are looking for additional bandwidths in higher frequency bands. For example, 5G New Radio (NR) Release 15 specifies frequency range 2 (FR2) from 24.25 GHz to 52.6 GHz and a maximum channel bandwidth of 400 MHz. Release 16 introduces an unlicensed frequency band in the 5 GHz and 6 GHz ranges. In mid-2022, 3GPP Release 17 will expand the frequency range of unlicensed bands up to 71 GHz.
Satellite communication and greater bandwidth
Satellite communications provide connectivity to a range of services: television, telephone and broadband internet as well as military communications. Satellites operate in different frequency bands: from L to Ka band. The International Telecommunication Union (ITU) allocates the 71-76 GHz and 81-86 GHz segments of the W-band for satellite services. These frequency segments are of increasing interest to commercial satellite operators due to the larger bandwidths. On June 30, 2021, a satellite carrying a W-band radio transmitter was successfully launched; further commercial projects in the W-band can be expected in the foreseeable future.
Millimeter wave frequency bands offer more available bandwidth. Large bandwidths enable high data throughput and low latency times. However, larger bandwidths also have disadvantages. They result in more noise that affects system performance. Developers of wireless applications must solve the noise problem in broadband communications. Larger bandwidths in higher frequency bands not only lead to more system noise. Examples include design and test issues such as path loss, frequency response, and phase noise.
Higher order modulation scheme
(Image: Keysight Technologies)
With a higher order modulation scheme, higher data rates are possible without increasing signal bandwidth. This requires tighter symbols that are more sensitive to noise. The devices used require better modulation quality as the modulation density increases. The following table shows the EVM (Error Vector Magnitude) requirements for 5G NR base stations defined in 3GPP Release 16 Technical Specification 38.141. The introduction of 1024 QAM for 3GPP is being considered, which in turn will require tighter design and test margins.
|modulation method||Required EVM (in percentage)|
Both larger signal bandwidths and higher order modulation methods increase throughput. More bandwidth does not necessarily mean more system capacity. In the communication system, the signal-to-noise ratio (SNR) must be taken into account. Sufficient SNR is essential to maintain communication links.
Larger bandwidths introduce more noise into the system, and higher-order modulation systems are more susceptible to noise. To maintain communication links, a high power signal must be transmitted without distortion and system noise must be reduced. Testing a design requires accurate characterization of each component and subsystem (Figure 1).
The effect of multiple antenna techniques
(Image: Keysight Technologies)
Most wireless systems for commercial, aerospace, or defense applications use multiple antenna techniques at the receiver, transmitter, or both. This improves the overall performance of the system. These techniques include spatial diversity, spatial multiplexing and beamforming. Designers use several antenna techniques to achieve diversity, multiplexing, or antenna gain.
Thanks to signal amplification, wireless systems can increase the data throughput and SNR of a receiver. For example, 5G NR uses eight spatial streams for FR1 to improve spectral efficiency without increasing signal bandwidth. Therefore, in Technical Specification (TS) 38.141-1, 3GPP defines multi-spatial stream performance tests for 5G NR base stations.
The tests require up to two transmit antennas and eight receive antennas, and each test case has specific propagation conditions, correlation matrix and SNR. Figure 2 shows a 5G base station with multiple-input multiple-output (MIMO) test configuration for two transmit antennas and four receive antennas with hybrid automatic repeat request (HARQ).
Compared to IEEE 802.11ax, the next-generation Wi-Fi standard, IEEE 802.11be (Wi-Fi 7), offers twice the signal bandwidth, 16 spatial streams, and four times the density of the modulation scheme. Together, this enables data speeds of up to 40 GBit/s. The table illustrates the major changes in the IEEE 802.11 physical layer.
|IEEE 802.11 standard||Maximum signal bandwidth [MHz]||modulation method||Number of spatial flows|
|802.11be (Wi-Fi 7)||320||OFDM, up to 4,096 QAM||up to 16|
|802.11ax (Wi-Fi 6)||320||OFDM, up to 1,024 QAM||up to 8|
(Image: Keysight Technologies)
Testing of multi-antenna systems involving spatial diversity, spatial multiplexing and multiple antenna arrays requires a test system capable of delivering multi-channel signals with stable phase relationships between them. However, a commercial signal generator has an independent synthesizer that upconverts an intermediate frequency (IF) signal to an RF signal. A test system must ensure precise timing synchronization between the channels to simulate the multi-channel test signals. The phase between the test signals must be coherent and controllable. Figure 3 shows a fully integrated, calibrated and synchronized signal generation and analysis solution that can be used to minimize measurement uncertainty in multi-antenna testing.
Effects of higher frequencies on the test
Higher frequencies, larger bandwidths, more complex modulation and multi-antenna designs are required for wireless communication systems such as 5G, satellite and Wi-Fi. However, this requires new approaches in the design of mobile devices, and the test also needs to be reconsidered. Finally, hardware testing becomes more complex, measurement uncertainty increases, and devices are affected by excessive path loss and noise. What is needed is a scalable test solution that enables higher frequency coverage, larger bandwidths and multi-channel applications with simple operation and high accuracy.