Boost High-Speed Communication Systems With Receiver Tests
All modern communication networks and consumer devices involve complicated digital interfaces or radio communications to meet the high-speed and high-bandwidth demands of businesses and consumers.
Such fast, reliable communication is only possible because of robust receivers that are embedded in every device to receive and understand wireless or digital signals. The complex performance and compliance requirements on them require systematic and specialized receiver testing.
In this article, understand what receiver tests are, what aspects they test, and which industries use them.
What is receiver testing?
The design of transmitters and receivers is a critical aspect of many electronic and communication technologies, especially in:
- radio frequency (RF) systems like radars
- RF telecommunication systems like 5G/6G mobile networks, non-terrestrial networks, and Wi-Fi
- digital interfaces like the universal serial bus (USB) and the high-definition multimedia interface (HDMI)
- photonics systems like fiber optic networks
Receiver testing is the process of rigorously evaluating the performance of a receiver under a variety of test signals and operating conditions. Its goals are to:
- assess the receiver's ability to accurately detect, acquire, process, and interpret signals
- ensure signal integrity across different communication speeds, signal types, modulation patterns, and interference levels
- validate the functionality and reliability of a receiver across its operating range
- ensure compliance with relevant regulatory and industrial standards
- guarantee interoperability with other hardware and software systems
The scope of receiver testing is illustrated below.
Fig 1. Receiver tests in different domains
What are the key parameters evaluated by receiver tests?
Receiver tests across domains share the same goals listed above and use a common set of metrics and parameters to characterize receiver performance. In the sections below, we explore these metrics and parameters in more detail.
Signal-to-noise ratio (SNR)
SNR is the ratio of signal power to the noise power in a signal. It's a key metric of analog RF receivers and optical receivers. It's also a key metric for digital receivers before the demodulation and decoding phases.
What is the significance of signal-to-noise ratio in receiver testing, and how is it measured?
SNR quantifies the level of the desired signal compared to the background noise. It’s a crucial measure of signal integrity as well as a metric that's used to determine other characteristics like sensitivity and selectivity.
SNR testing involves a signal generator that mixes random or additive white Gaussian noise (AWGN) with a signal. A spectrum analyzer then measures the power of the signal and the noise to determine SNR.
An undisturbed power supply that's not prone to voltage fluctuations or other abnormalities is crucial for accurate SNR testing.
Bit error rate (BER), packet error rate (PER), frame error rate (FER), and symbol error rate (SER)
These error rates are important metrics for digital receivers of all types, including digital RF receivers and digital interface receivers. They characterize the accuracy of the receiver's demodulation and processing circuitry.
BER is the ratio of the number of erroneous bits to the total number of bits sent over a digital communication channel during a specified time interval.
FER is the ratio of the number of frames with at least one erroneous bit to the total number of frames sent. It is typically used in communications where the data is transmitted in frames.
PER is the ratio of the number of incorrectly received packets to the total number of packets sent. It is used for packet-based communication systems.
SER is the error ratio of symbols like the ones used in digital communications with pulse-amplitude modulation (PAM) techniques, like PAM-4 or other PAM-N. The SER metric is especially useful for physical layer (PHY) testing.
What role do the error rates play in assessing the overall performance of a communication receiver?
These three error rate metrics are critical for measuring other receiver characteristics like sensitivity and selectivity. A low BER means the receiver is accurately demodulating the transmitted data under a variety of conditions, which is critical for error-sensitive applications, such as data storage interfaces.
Forward error correction (FEC) in digital communications
FEC algorithms significantly improve data reliability by adding redundancy to the transmitted data, enabling the receiver to recover erroneous frames without retransmission. This also reduces the FER. However, burst errors can overwhelm FEC and render the frames completely unusable.
During receiver testing, error frames and burst errors are simulated to check the resilience of the FEC and optimize it.
Sensitivity
Sensitivity is the minimum discernible signal level at the input that the receiver can process into a usable output. It determines the lower threshold at which the receiver can accurately pick up and demodulate a signal from the background noise.
For RF and optical receivers, the sensitivity is specified in decibel-milliwatts (dBm):
- For analog RF receivers, sensitivity is the minimum signal strength that the receiver needs to achieve a minimum SNR.
- For digital RF and optical receivers, sensitivity is the minimum signal strength that the receiver needs to demodulate the signal while keeping error rate metrics — BER, PER, and FER — below maximum thresholds.
For digital interface receivers, sensitivity is the lowest input amplitude of the digital signal that can still be reliably detected while maintaining the BER below a threshold. Sensitivity is typically specified in microvolts or millivolts for such receivers.
Why is sensitivity crucial?
Measuring the sensitivity is critical because it helps in determining the receiver's usefulness, range, and performance in low-signal conditions. A receiver with high sensitivity can pick up weaker signals, which is valuable in conditions where signal strength can be compromised or is prone to attenuation, such as long-distance transmissions or crowded frequency ranges.
How is sensitivity measured?
Fig 2. Sensitivity test setup
Sensitivity is measured using signal generators, bit error ratetesters, and spectrum or vector analyzers. The test setup involves mixing a signal with generated noise and decreasing the signal level in controlled steps until the receiver's SNR falls below a threshold or its BER goes above a threshold.
Dynamic range
A receiver’s dynamic range is the range of signal power levels over which it can operate effectively and is specified in dBm.
In analog receivers, it ranges from the sensitivity level to the level where the signal is distorted due to factors like amplifier overload.
For digital receivers, it ranges from the sensitivity level to a maximum level beyond which error rates go above a threshold due to various effects, such as saturation of the analog-to-digital converter.
Selectivity
Selectivity is the ability to discriminate the desired signal from other signals in closely spaced adjacent channels.
How is selectivity measured?
A common metric to quantify selectivity is the adjacent channel rejection (ACR) or adjacent channel selectivity (ACS). It's the difference in decibels between the desired signal's strength at which the receiver maintains a minimum acceptable SNR or BER and the adjacent signal's strength that causes the SNR or BER to degrade to an unacceptable level.
Blocking performance
Closely related to selectivity is the blocking performance. A strong interfering blocker signal is generated at a frequency that's slightly offset from the adjacent channel frequency. The blocker's power level is then increased until it degrades the receiver's performance as measured by SNR or BER. The difference in power levels between the desired signal and the blocking signal is a measure of its blocking performance.
Why is it important in real-world scenarios?
The blocking performance is crucial in ensuring that receivers can effectively operate in environments with multiple strong signals. For example, mobile network receivers must discern between multiple strong signals in densely populated areas.
Stress-signal testing
Fig 3. Setup for IEEE-compliant high-speed ethernet receiver testing, using a bit error ratio tester (BERT) with built-in signal generator, an oscilloscope, and optical test equipment
Stress-signal testing is essential to ensure that digital, optical, and RF receivers can reliably decode signals under noise, interference, distortion, and other domain-specific real-world impairments. Such conditions include low SNR, jitter, phase noise, inter-symbol interference, reflections, fading, multipath, frequency offsets, crosstalk, and frequency drifts, among others.
Stress-signal testing also helps to discover and optimize the thresholds of acceptable performance.
Insertion loss
The insertion loss of a receiver is the amount of signal power lost between its input and output as the signal passes through its components. It's measured in dBm. The insertion loss should ideally be very low.
What key standards apply to receivers?
The thresholds of the above parameters are different for different types of receivers and are determined by technical, industry, or regulatory standards.
Some important standards that receivers must comply with include:
- CISPR 16-1-1: It's an international standard for the electromagnetic compatibility (EMC) and electromagnetic interference (EMI) of commercial receivers. It is created by the International Special Committee on Radio Interference (CISPR).
- MIL-STD-461: It's a U.S. military standard for verifying EMC, EMI, and electromagnetic emissions.
- 3GPP: 5G and 6G receivers must comply with the 3GPP standards.
- Optical Internetworking Forum (OIF) standards: These standards specify behaviors and compliance requirements for optical receivers.
- IEEE 802.3bs/cd/df/dj: These standards are for high-speed ethernet electrical receivers.
Among other key standards are the USB test specifications, peripheral component interconnect express (PCIe) standards, and various standards specified by the U.S. Federal Communications Commission (FCC) and the International Organization for Standardization (ISO).
Industry applications of receiver tests
In the following sections, we explore how receiver tests are used in different domains to improve reliability and comply with standards.
Telecommunications
Receiver testing is a critical area in all kinds of wireless communications systems, including mobile networks, Wi-Fi, and Bluetooth.
What is the purpose of receiver testing in telecommunications?
Receiver tests ensure that:
- devices can accurately identify and isolate desired signals even in challenging RF environments
- receivers can handle the complex modulation schemes used by these technologies for scalability and throughput in dense RF environments
- all the equipment in the end-to-end communication system can interoperate
- all devices comply with all the mandatory industry and regulatory standards
- the devices used for compliance testing pass the validation process
What are some key challenges and considerations of receiver tests for different communication standards (e.g., GSM, LTE, Wi-Fi)?
The key challenges of these communication standards include:
- generating their signals with the correct frequency bands
- testing receivers over their entire frequency range
- generating their complex modulation schemes and encoding techniques accurately
- simulating the real-world interference and multi-path conditions faced by these signals in dense RF environments
How does receiver testing contribute to the development and improvement of emerging technologies like 5G?
Receiver testing for technologies like 5G and 6G involves challenges like:
- very high frequencies in the 24-110 GHz mmWave band
- wideband testing to ensure that devices can handle broader frequency ranges
- greater bandwidths and high data rates
- advanced modulation schemes like quadrature amplitude modulation
- ensuring that radio emissions are within regulatory limits
High-speed ethernet and optical communication networks
Receiver tests are used to characterize Optical Internetworking Forum Common Electrical Interface (OIF-CEI) and IEEE 802.3bs/cd/df/dj compliance for high-speed 400G, 800G, and faster ethernet networks that are typically used in data centers.
As data center infrastructure evolves toward 400G, 800G, and 1.6T, rigorous optical and electrical testing of receivers is crucial for efficient and error-free data transmission.
Key steps in high-speed digital receiver testing include:
- Signal calibration: This process adjusts the receiver's ability to accurately decode signals affected by various real-world interferences and distortions.
- Stress-signal testing: This tests the receiver’s resilience, data integrity, and performance under worst-case scenarios.
These aspects are tested based on the OIF-CEI and the IEEE 802.3 family of specifications.
Digital and computing interfaces
Fig 4. Receiver testing setup for digital interfaces using a BERT and real-time oscilloscope
Receiver tests are extensively used for digital and computing interfaces like:
- USB for interconnecting all sorts of consumer devices
- HDMI and DisplayPort receivers for video and audio
- peripheral component interconnect express (PCIe) which is used by non-volatile memory express (NVMe) data storage drives
- mobile industry processor interface (MIPI) receivers for connecting high-speed cameras to mainboards
Avionics and defense
Receiver tests are used to characterize defense radars and avionics digital interfaces.
Automotive applications
Receiver tests are used for testing automotive cameras and radars used in advanced driver assistance systems.
Are there specific test equipment or setups commonly used to test receivers?
Receiver characterization involves the following test systems:
- Signal generators and bit error ratiotesters are used to generate the complex signals required by the specific domain or standards being tested.
- Spectrum analyzers, network analyzers, real-time oscilloscopes, or digital communication analyzingoscilloscopes are used to inspect the waveforms if they are critical. For example, UXR real-time oscilloscopes are recommended for receiver test signal calibration. However, for many digital communication tests, waveforms are not critical and the BERT's visualizations are sufficient.
- Specializedreceiver test solutions, like the M8070B system software and receiver test software, provide fully automated and repeatable compliance test suites. They automatically calibrate and run the tests, record the test results, measure key metrics like SNR and BER, and allow users to visualize the results.
All these instruments must undergo carefulcalibration and certification with traceability to ensure the accuracy and reliability of their measurements.
Qualify your communication equipment with robust receiver tests
In this article, we learned about how receiver tests are crucial to modern high-speed communication networks and digital interfaces.
Receiver testing is a complex area that requires an in-depth understanding of the target industry and its standards. Contact us for expertise in selecting the right hardware and software you need for all your functional and compliance receiver tests.---