Regulations and standards for automotive millimeter wave radar (2)

火辣西米秀

Regulations and standards for automotive millimeter wave radar (2) [Copy link]

Frequency bands used by automotive millimeter-wave radars in my country. After consulting the document, we found that the peak power (+antenna gain) of 76-79 GHz radars can reach up to 55dBm. Let's take a closer look at the power limits of the two automotive millimeter-wave radar frequency bands that can continue to be used. Today, we will first look at the 24 GHz frequency band.

01 24-24.25 GHz

In my country's "Catalogue and Technical Requirements for Micropower Short-range Radio Transmitter Equipment", the 24-24.25 GHz frequency band is reserved as Class H equipment, which can be used for automotive radars. Its transmit power limit is: 20mW (eirp), which is approximately 13dBm. In addition to the transmit power, there are also some corresponding spurious limits.

Next, let’s take a look at the power limits of the European standards in similar frequency bands. ETSI EN 302 858 provides technical requirements for narrowband automotive radar equipment operating in the frequency range of 24.05 GHz to 24.25 GHz and wideband low activity mode radar equipment (WLAM) operating in the frequency range of 24.05 GHz to 24.5 GHz.

First, for the 24.05-24.25 GHz narrowband automotive radar, the following power limits are specified. According to different frequency bands, different powers and different spectrum access conditions, the signal types are divided into five types: A, B, C, D, and E. The Peak eirp power limit is 20dBm (100mW) and -10dBm (0.1mW). As shown in the following table:

In the 24.075-24.15 GHz frequency band of Class C and Class D, although the peak EIRP requirement is also 20dBm, it is not unconditional, that is, there are spectrum access conditions. The spectrum access conditions are actually requirements for the residence time, which are divided into the following two types:

Fast modulation:

The requirement is a dwell time of ≤4μs/40kHz, accumulated every 3ms (accumulated dwell time). What does this mean? Let's imagine an FMCW frequency modulated continuous wave signal (as shown in the time vs. frequency diagram below). For fast modulation conditions, "accumulated" means that within the same 40kHz modulation frequency range (such as the range of the vertical axis BW_o in the figure below), the sum of the single dwell times (such as the range of the horizontal axis t_d1 and t_d2 in the figure below) within a 3ms interval (such as the range of the horizontal axis t_o in the figure below) must be less than 4μs. This is also the spectrum access requirement for equipment installed behind a bumper. If there is no bumper installed, the requirement should be a maximum dwell time of 3μs/40kHz every 3ms.

Slow modulation:

The spectrum access requirement for devices mounted behind a car bumper or not mounted on a bumper is: ≤1ms/40kHz dwell time (repeated dwell time) every 40ms. We also look at the figure above, which allows entry into the 40kHz range for a maximum of 1ms, with a minimum repetition time of 40ms. Within the 1ms time, it is possible to leave and re-enter the 40kHz range; outside the 1ms time, entry into the same 40kHz range at any other time is allowed only if it is below -10 dBm eirp or meets fast modulation conditions.

Therefore, the power limit of Class C and Class D automotive radar equipment needs to be based on the time dimension. 20dBm is not a power value that can be frequently transmitted.

02 24.05-24.5GHz

The European standard defines WLAM at 24.05-24.5 GHz, which is a broadband low-activity mode radar. What is this about? Let’s first look at the SM (sub mode) classification included in WLAM:

Submode 1 (SM1): Forward-facing radar, used for frontal calibration submode;

Submode 2 (SM2): Front radar, front emergency APPS (Active Pedestrian Protection System) submode, activated for emergency braking support when the camera detects a collision event, the vehicle speed exceeds 20km/h;

Submode 3 (SM3): rear-facing radar, rear parking submode, activated only when the vehicle is moving backwards to better identify pedestrians, speed < 30 km/h;

The power limits of WLAM are shown in the table below. Peak eirp power ranges from -11 to 20 dBm. There are also restrictions on spectrum access conditions. The spectrum access limits of duty cycle are used in F, G, H, and I signal types. For example, in the 24.250-24.500 GHz band, signal type H, if the observation period is 1s, the duty cycle within the 25MHz bandwidth should be ≤ 5.6%, and the peak eirp should be less than 20dBm.