ANSI C63.27:2017 pdf free download – American National Standard for Evaluation of Wireless Coexistence
5.7 Unintended signals
The test signals are the unintended signals (see Figure 2) to be used in evaluating the ability of the EUT to coexist with devices using such signals. Test signals (unintended signals) shall be selected based on the RAT, operating frequency of the EUT, and the intended use environment. The test signals to be used shall be documented in the test plan. If the unintended signals are similar to the signals of the EUT, measures shall be taken to prevent the EUT from receiving and processing the unintended signals, because this can affect test results. Transmission parameters of the unintended signals shall be documented in the test plan and test report, such as frequency, bandwidth utilization, transmission power, and channel utilization.
The failure characteristics of the EUT shall be used in selecting the unintended signals to be used. Where there are several differing sets of failure modes or the characteristics of the failure modes are unknown, a wider variation in the test signals might be necessary to ensure that there is a high probability that a weakness will be detected by the testing. In some cases, the failure characteristics of the EUT are well known and can be used in planning a test. However, it is common that exploratory testing is useful and part of the test plan development process. Exploratory testing is useful for refining the specific details of the evaluation and getting experience with the EUT. In some cases, the failure characteristics will become evident during the exploratory testing process and can support the development of a more effective test plan. In this process, the three basic coexistence parameters (frequency, range, and time) of the unintended signal can be varied to identify the failure characteristics. For example, 1) the channel utilization of the unintended signal can be increased until the EUT is unable to coexist, 2) the intended-to-unintended signal (I/U) ratio (of the EUT signal to the unintended signal) can be decreased until the EUT is unable to coexist, or 3) the separation of the carrier frequencies between the EUT signal and unintended signal can be decreased until the FWP is unable to be maintained by the EUT.
Annex A provides RAT and band-specific test guidance for some of the most commonly used RATs and frequency bands. The carrier frequency of the EUT and unintended signal are fixed to decrease test variables and limit test time. 24 The test plan shall specify the coexistence parameters of the unin tended signals to investigate during testing. The two possible parameters to determine in coexistence testing are 1) the I/U ratio and 2) the channel utilization of the unintended signal. The intended test deliverables will determine the combination of the test parameters to investigate. In some cases, only one parameter will need to be changed for the FWP to maintained acceptable performance. For example, if the test deliverable is to find the I/U ratio for coexistence (or minimum separation distance) between the EUT and the unintended signal, the channel utilization of the unintended signal is set to its maximum, and the I/U ratio is found experimentaly such that the FWP can maintain acceptable performance. If the test deliverable is to find the channel utilization of the unintended signal, the I/U ratio is fixed, and the channel utilization of the unintended signal is decreased until the FWP can maintain acceptable performance. Figure 2 ilustrates the relationship between an intended signal and an unintended signal in the co-channel and adjacent channel I/U ratios. Characteristics of the unintended signals shall be documented in the test plan and test report. Communication systems can often operate in multiple modulation and coding states (MCS), and the test plan shall document the MCS for both the intended signals and the unintended signals. It is important to know the failure responses of the EUT for each MCS, or to know that the unintended signals will maximize the probability of detecting susceptibility, should one exist.