Broadband OFDM Radar System at Reduced Sampling Rates Using Frequency Combs (BORA)

• Applicants: Professor Dr.-Ing. Ahmet Ulusoy; Professor Dr.-Ing. Thomas Zwick
• Subject Area: Communication Technology and Networks, High-Frequency Technology and Photonic Systems, Signal Processing and Machine Learning for Information Technology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 467104011

In the BORA project, a novel concept for the generation and processing of broadband OFDM radar signals with reduced sampling rates is to be investigated and implemented in integrated circuits. A high bandwidth is required in radar applications in order to achieve a good range resolution for the separation of closely spaced targets. In digital radar modulation schemes, such as OFDM, the challenge arises that, along with the high instantaneous bandwidth, high sampling rates are required for the digital-to-analog (DAC) and analog-to-digital converters (ADC). However, since these converters are very expensive and power hungry, alternative options are currently being investigated to enlarge the bandwidth without increasing the sampling rates. Here we propose a unique method, which is to be further developed and implemented in BORA. It is based on the mixing of a narrowband OFDM baseband signal with a frequency comb, whose frequency spacing is identical to the bandwidth of the baseband signal. The concatenation of several subbands results in a broadband OFDM radar signal that can be emitted. Here, each of the subbands results from the up-conversion of the baseband signal with one of the comb frequencies. Only some of the possible subcarriers are used in the baseband, which creates gaps in the spectrum into which the subcarriers of the remaining subbands can be inserted on the receiving side. This creates a common narrow-band frequency band that contains the information of all received subbands. After appropriate filtering, the associated signal can be sampled at the same low rate at which the baseband signal was generated in the transmitter. The interleaving of the subbands in the receiver is achieved by mixing the received signal with a second frequency comb, whose carrier spacing is slightly smaller than that in the transmitter. Since in OFDM all subcarriers are orthogonal to one another, the information of the interleaved subcarriers can be separated and the broadband radio-frequency signal can be virtually reconstructed.In the BORA project, the frequency comb OFDM radar scheme is to be further developed and requirements regarding a hardware implementation are to be derived. Based on this system analysis, a suitable hardware architecture is to be designed and implemented on an MMIC (monolithic microwave integrated circuit) at 140 GHz. Finally, with the help of the MMICs, a demonstrator is to be set up and put into operation. With its help, the results of the system analysis can be validated and, for example, the influence of different comb generation methods and forms can be examined. When successful, BORA will enable a very efficient digital high-resolution radar for fast moving targets (e.g. for crash avoidance or some industrial applications).

• DFG Programme: Research Grants