Готовое решение от Freescale:
Last week, at the electronica 2010 show in Munich, Freescale announced shipment of 77 GHz radar chipset samples to select customers for automotive safety applications. This expands the Xtrinsic Sensing brand to encompass active safety issues such as adaptive cruise control, blind spot detection, and side impact avoidance.
Active Safety with Freescale Automotive Radar
Figure 1. Active Safety with Freescale Automotive Radar
Chipsets are partitioned into separate RF transmit and receive devices, allowing one system to have multiple modes of operation. Long range radar covers distances up to 250m and vehicle speeds up to 250km/h. It utilizes a narrow frequency band and narrow beam with a spatial resolution on the order of one half meter. This is the mode that enables adaptive cruise control. Alternately, the same devices can be reconfigured (on the fly) for short range radar to identify objects in the immediate vicinity of the vehicle. In this mode, we’re using a wider frequency band and wider beams to detect objects up to 30m in distance. Vehicle speeds up to 150km/h are supported in this mode.
Transmitter
* Low power consumption
* Extremely low phase noise
* High output power
* Very precise control over frequency (+/-100 ppm)
* No trimming, no adjustments
* Supports RX designs with local oscillator at half of the RF frequency (38.25 GHz)
* Ability to monolithically integrate frequency stabilization (PLL), PA and programmable FMCW modulation.
* SPI interface
Multi-Channel Receiver
* Multi-channels supported
* Best in class channel-to-channel isolation
* Local oscillator at 38.25GHz
* Single-ended/differential IF
* Low noise
* Low residual power levels
* ESD protection (RF and DC)
* Optional SPI interface
I love to dig into the technology behind announcements like this. You’ll notice the acronym FMCW (Frequency Modulated Continuous Wave) in the table above. After reviewing the on-demand radar training on the Freescale web site, as well as FMCW MMW Radar for Automotive Longitudinal Control, I learned that FMCW radar transmits a constant amplitude signal which is linearly changing in frequency (usually in a sawtooth or triangular pattern). The transmitted beam bounces off remote objects and returns to the receiver a short time later. The time lag between transmission and reception ensures that the transmitter and receiver are operating at two different frequencies, resulting in a frequency difference which is directly proportional to the distance of the target. The advantages of FMCW are that it is easy to calculate speed and range, and it has good range accuracy.
Figure 2. FMCW Waveforms for Stationary Transmitter/Target
Figure 2 above shows both transmitted (blue) and received (red) waveforms for FMCW radar with stationary transmitter and target. The propagation time between the two waveforms is simply 2R/c, where R is the range between the transmitter and object being detected, and c is the speed of light.
FB is the difference in frequency between the transmitted and received signals. From the figure, we can see that this is equal to 2RΔF/t1c. Re-arranging, we get the distance from transmitter to target R = t1cFB/2ΔF.
Things get more interesting if the target is moving. In that case, the curves look like those shown in Figure 3.
Figure 3. FMCW Waveforms for Moving Transmitter/Target
The Doppler Effect is responsible for the shift in frequency observed in the received waveform. Recall that the Doppler change in frequency is Δf = -v/l0, where v = the velocity of the target relative to the transmitter and l0 is the wavelength of the transmitted wave. So measuring ΔFD in Figure 3 supplies the information necessary to determine how fast your vehicle is approaching another.
The figures above show equal rising and falling frequency rates. In practice, this is a simplification. Use of different rates on different edges allow multiple range calculations to be made based on multiple rates of frequency shift. This can be useful in eliminating ”ghost readings”.
You can view Freescale’s announcement of the new radar products at the company’s website, or visit our Automotive Radar Millimeter-Wave Technology page for more details. Reference 2 below offers a very nice introduction to the topic of FMCW radar.
References:
1. On-Demand Training: Automotive Front-End Radar and Associated Signal Processing, 2008 Freescale Technology Forum
2. FMCW MMW Radar for Automotive Longitudinal Control, William David, California PATH Research Report UCB-ITS-PRR-97-19
3. Theory of FMCW Radar Waveforms, USA JRG-70
4. Wikipedia page on the Doppler Effect
http://blogs.freescale.com/author/michaelestanley/
Сообщение отредактировал ArtemDement - Dec 16 2010, 15:19
Радиодальномер сантиметровой точности, нужен...
Aug 10 2006, 13:45
