Stepped-Carrier OFDM-Radar Processing Scheme to Retrieve High-Resolution Range-Velocity Profile at Low Sampling Rate

Abstract

Recent publications show the potential of using orthogonal frequency division multiplexing (OFDM) waveforms as radar signals. Since the range resolution is proportional to the RF bandwidth, the major obstacle that obstructs the practical use in automotive and other low cost radars is the requirement to sample the received signal at sampling rates that span the whole RF signal bandwidth requiring ADCs with sampling rates in the order of GHz. This paper presents a method to achieve the high range resolution induced by a large RF bandwidth but with a much lower baseband bandwidth, consequently requiring a much slower ADC while at the same time delivering a velocity profile for each subcarrier. Additionally, the processing scheme induces a range migration compensation, independent of the number of targets. This is achieved with barely increased computational effort. The scheme is verified with simulations and measurements at 77 GHz.

Radar Sensors for Autonomous Driving: Modulation Schemes and Interference Mitigation

“…Since such hardware is expensive and hard to realize, only a fraction of the required bandwidth is achievable with reasonable effort, making it unusable for automotive applications as the range resolution would not meet the requirements. A solution is to use a smaller bandwidth that is realizable with low-cost hardware and to regain the full resolution of the large RF bandwidth by using different carrier frequencies in a single frame and applying suitable signal post-processing [64][65][66].…”

“…The same RF bandwidth and range resolution is reached using proper signal processing.Fig. takenfrom[64].…”

Expanding the Unambiguous Velocity Limitation of the Stepped-Carrier OFDM Radar Scheme

“…to generate a larger measurement bandwidth in the channel, as explained in detail in [6]. M such subsymbols form a block and B blocks are transmitted consecutively, as illustrated in Fig.…”

“…Thus, the ambiguous velocity v 2 is visible at v 2 * =v 2 −2v ua =−5.39 m/s. The behavior can be explained with the result of the velocity calculation via a modified DFT for a target that has an ambiguous velocity of v=v 0 +ξ2v ua , where ξ describes the D nmb e −j2πk(m+bM )T • e j2πξm/M , (6) depending on η=n+mN , as there exists a velocity profile for each virtual subcarrier.…”

“…The practical limitation of a conventional OFDM system [3] is the requirement of analog-to-digital (ADC) and digital-to-analog converters (DAC) with sampling rates of some gigahertz, depending on the desired range resolution. However, it is introduced in [4], [5] and extended in [6] that a stepped-OFDM scheme with an agile carrier that alters after each symbol, forming a regular pattern, can solve this constraint at the cost of reduced unambiguity in velocity. In this paper, a method is proposed that allows to determine the velocity of a target even if it is above the unambiguous velocity limitation of the stepped-carrier OFDM scheme.…”