How to Configure Wireless Receiver Dynamic Range Tests
The most common wireless receiver test is receiver dynamic range which includes minimum input sensitivity, maximum input level, and channel noise. For different wireless standards, the definition of the receiver’s “dynamic range” test might be different – it can be the range of input levels or signal-to-noise ratios. This post will clarify different receiver dynamic range test cases and how to configure the test set-up.
Range of Input Levels
A wireless receiver’s “dynamic range” test is usually defined as the input power to an RF receiver at a minimum and maximum level where the bit-error-rate (BER) or packet-error-rate (PER) does not exceed specified values. Wireless standards, such as Bluetooth and WLAN, define wireless receiver minimum input sensitivity and maximum input level test cases to determine the upper and lower end of the wireless receiver’s dynamic range.
Wireless receiver minimum input sensitivity
The minimum input level test ensures the wireless device can receive data with a defined maximum packet-error-rate or bit-error-rate and be measured at the antenna port. In this test, a signal generator stimulates the antenna port of the receiver and works as an ideal transmitter as shown in Figure 1.
Wireless receiver maximum input level
The maximum input level specifies a maximum BER or PER at the maximum specified signal input level to the wireless receiver. This test ensures the receiver’s low noise amplifier (LNA) will not be saturated by a high input signal. The difference in test configuration from minimum input sensitivity is the input signal level.
Range of Signal-to-Noise Ratios (SNR)
The dynamic range is specified as a measure of the capability of the wireless receiver to receive a wanted signal in the presence of an interfering signal inside the received channel bandwidth in the 3GPP standard (Technical specification 36.104, section 7.3). Noise is part of all communications channels. To simulate realistic channel conditions in a repeatable manner, you need to add random noise to the wanted signal.
What is additive white gaussian noise (AWGN)?
Additive White Gaussian Noise (AWGN) is a mathematical model to simulate the channel between the transmitter and receiver. The model is a linear addition of wideband noise with a constant spectral density and a Gaussian distribution of amplitude. The interfering signal for the dynamic range test requirement is an AWGN signal.
Figure 2 illustrates a common wireless receiver’s performance test setup for dynamic range. The first signal generator outputs the AWGN and the second generator generates the wanted RF signal. Use a hybrid combiner to mix the signals and connect to a device under test (DUT).
Figure 3 depicts the bandwidth and power between the carrier (wanted signal) and AWGN. Carrier bandwidth is the occupied bandwidth of the carrier. The noise bandwidth is flat noise bandwidth. The actual flat noise bandwidth should be slightly wider than the carrier bandwidth (typically 1.6X the carrier bandwidth). When you combine the carrier and AWGN signal for receiver tests, the carrier now appears larger because of the added noise power.
Simplify AWGN signal generation
When you perform wireless receiver tests, measure the noise power that you observe within the carrier bandwidth as shown in yellow in Figure 3. By knowing the noise power value, you can calculate the carrier-to-noise ratio (C/N). Additionally, some standards use energy-per-bit over noise power density at the receiver (Eb/No) to characterize their receiver as opposed to C/N. You need to know the carrier’s bit rate in order to do this. Below is the conversion equation for C/N and Eb/No.
(Eb/No) dB = C/N dB - 10 log10 (bit rate/carrier bandwidth)
These additional measurements and calculations make receiver measurement set-up more tedious. Luckily, with evolving digital signal processing (DSP) technologies, a signal generator can add real-time noise AWGN to the baseband waveforms digitally, instead of using two signal generators and a hybrid combiner. This provides an accurate amplitude level for both the carrier and noise signal without additional measurements. You also do not need to worry about the correction of external accessories. In addition, you can easily select either C/N or Eb/No as the variable controlling the ratio of the carrier power to the noise power in the carrier bandwidth as shown in Figure 4.
Summary
Receiver tests are designed to quantify the performance of a receiver in the presence of degradations in the signal path between the transmitter and the receiver. Dynamic range test is the ability of the receiver signals that are either very weak or very strong and is subject to the effects of linearity and noise figure. In the recent 3GPP standard, dynamic range test is specified as an SNR for receiver testing. With evolving DSP technologies, adding real-time noise AWGN to the test signal becomes easy and accurate.