KR20230125961A - SC-OFDM radar transmitter, transmission method and system - Google Patents

Abstract

A transmitter for an OFDM radar, comprising: a first transmitter capable of transmitting independent signals; and a second transmitter, wherein a signal transmitted from the first transmission and a signal transmitted from the second transmitter overlap in time.

Description

SC-OFDM radar transmitter, transmission method and system

The present invention relates to an SC-OFDM radar transmitter, transmission method and system, and more particularly, can solve the problem of lower speed performance of maximum ambiguity, slow settling time of stepped LO, and phase discontinuity between LO frequency steps, SC-OFDM radar transmitter, transmission method and system.

In order to obtain high range resolution in OFDM (orthogonal frequency-division multiplexing) radar, wide-band signal processing is required, which requires a fast analog-to-digital converter (ADC) and digital-to-digital converter (DAC). analog converter).

In particular, this situation burdens larger and larger systems in the expansion to multiple input multiple output (MIMO) radars, and to solve this bandwidth issue, several types of OFDM radars have been proposed worldwide. , Among them, the SC-OFDM (Stepped-carrier OFDM) radar is expected to be widely used in future OFDM radars due to its simple signal processing and operation method.

However, the SC-OFDM radar has several disadvantages. First, the speed performance of the reduced maximum ambiguity, the stabilization time of the stepped local oscillator (LO), and the phase discontinuity between LO frequency steps correspond to these problems.

Among them, phase discontinuity is a problem that must be solved because of low-range side lobe performance in SC-OFDM radar. In the existing literature, the stabilization time of the stepped LO is reduced by using a dual-PLL (phase-locked loop) structure, in this case The phase discontinuity was resolved using a pre-correction method through measurement of a reference object. However, since it is difficult to perform pre-correction for each operation, a method for resolving the phase discontinuity irrespective of the distance and speed of objects is required.

1 is a diagram showing a signal structure of an SC-OFDM radar using a dual-PLL structure in Prior Art 1.

Referring to FIG. 1, in the signal structure, two LOG (LO generators) alternately operate in each subband (subband), and the stepped LO is stabilized by the sum of CP (cyclic prefix) and subsymbol (subsymbol) time can be secured. This is a structure in which subbands or subsymbols do not overlap, and since CP is excluded during signal processing in RX (receiver) of the radar, there is a problem that the efficiency of time is reduced by T _cp , and during T _block , T _cp Time wasted by x number of steps, resulting in loss of maximum ambiguity time performance.

Therefore, the problem to be solved by the present invention is to provide a technique capable of solving the problems of the low speed performance of maximum ambiguity, slow settling time of stepped LO, and phase discontinuity between LO frequency steps.

In order to solve the above problems, the present invention is an SC-OFDM radar transmitter, a first transmitter capable of transmitting an independent signal; and a second transmitter, wherein a signal transmitted from the first transmitter and a signal transmitted from the second transmitter overlap in time by a predetermined time.

In one embodiment of the present invention, subsymbols transmitted step by step from the first transmitter and the second transmitter include two adjacent subbands UB and LB, and one of the two subbands UB has a CP ( Cyclic prefix) information, and the other one does not include CP information.

In one embodiment of the present invention, the subband LB not including the CP information is a copy of the subband including CP (Cyclic Prefix) information in the previous step, and the predetermined time is CP (Cyclic Prefix) transmission. is time (T _cp ).

The present invention is a signal transmission method using an SC-OFDM radar transmitter, including generating signals from a first transmitter and a second transmitter, wherein the signals are transmitted from the first transmitter and transmitted from the second transmitter. signals are overlapped in time by a predetermined time, subsymbols transmitted step by step from the first transmitter and the second transmitter include two adjacent subbands, and cyclic prefix (CP) information is included in one of the two subbands. and the other one does not contain CP information, and the subbands that do not contain CP information are duplicates of the subbands that contain Cyclic Prefix (CP) information in the previous step. It provides a signal transmission method using.

In one embodiment of the present invention, the predetermined time is a cyclic prefix (CP) transmission time (T _cp ).

The present invention is the transmitter for the OFDM radar described above; and an OFDM radar receiver corresponding thereto, wherein the SC-OFDM radar transmitter comprises: a first transmitter; and a second transmitter, wherein the first transmitter and the second transmitter are coupled to one power combiner to independently transmit transmission signals.

In one embodiment of the present invention, the receiver is a single-pole double-throw (SPDT) switch.

The present invention is a phase discontinuity compensation method of an SC-OFDM radar signal,

Calculating a cross-correlation between a subband (LB) not including CP information and a subband (UB) including CP (Cyclic Prefix) information in a previous step; extracting gain and phase values of subbands from the calculated results; performing subband phase/gain correction from the extracted gain and phase values; and a step of performing subsymbol phase/gain correction in the subsymbol with the extracted gain and phase values, wherein the phase discontinuity compensation method is provided. The steps described above in the step may be performed serially.

The transmitter according to the present invention has a dual transmission structure capable of generating overlapping signal structures in time and frequency domains. Thereby, three effects can be obtained: 1) improved speed performance of maximum ambiguity, 2) reduced stabilization time of stepped LO, and 3) compensation for phase discontinuity between LO frequency steps. Furthermore, by changing only the structure of the transmitter other than the receiver, it is possible to secure economic feasibility in installation and replacement of the transmission/reception system.

1 is a diagram showing a signal structure of an SC-OFDM radar using a dual-PLL structure in Prior Art 1.
2 and 3 are block diagrams of a transmitter for an OFDM radar according to an embodiment of the present invention and diagrams explaining overlap between signals generated therefrom.
4 is an RF transceiver structure of an SC-OFDM radar according to the present invention, (a) is a transmitter, and (b) is a receiver structure.
5 is a diagram explaining a method of compensating for phase discontinuity at each frequency step.
6 is a simulated range-Doppler map result of a transmitter structure using a transmitter according to the present invention.
7 is a phase plot according to subcarriers as a result of measuring a delay line capable of confirming phase discontinuity according to the present invention.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. However, this is only an example and the present invention is not limited thereto.

In describing the present invention, if it is determined that a detailed description of the known technology related to the present invention may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted. In addition, terms to be described later are terms defined in consideration of functions in the present invention, which may vary according to the intention or custom of a user or operator. Therefore, the definition should be made based on the contents throughout this specification. In addition, the technical spirit of the present invention is determined by the claims, and the following examples are only one means for efficiently explaining the technical spirit of the present invention to those skilled in the art to which the present invention belongs.

As described above, in the present invention, in addition to the dual-PLL structure, the transmitter (TX) also has a dual signal structure in which the time and frequency domains overlap.

In this case, unlike the conventional Dual-PLL structure, in the dual-TX structure according to the present invention, the SC-OFDM radar can be overlapped by T _cp in the time domain, which can be transmitted in the receiver (Receiver, RX) In signal processing, time efficiency can be increased by T _cp x number of steps compared to conventional methods. This has an advantage in maximum ambiguity time performance.

2 and 3 are block diagrams of a transmitter for an OFDM radar according to an embodiment of the present invention and diagrams explaining overlap between signals generated therefrom.

2 and 3, a transmitter for an OFDM radar according to the present invention includes a first transmitter (100, TX1) capable of transmitting independent signals; and a second transmitter (200, TX2), wherein a signal transmitted from the first transmission and a signal transmitted from the second transmitter overlap in time.

That is, it can be seen that the transmitter according to the present invention is composed of two or more multiplexes, and the time of each transmitter overlaps by T _cp . Accordingly, time efficiency can be increased by T _cp x number of steps compared to the conventional method.

In addition, in FIGS. 2 and 3, the subsymbol of each step is composed of two adjacent subbands. At this time, the upper subband is UB (upper band) and the lower subband is LB ( lower band). A cyclic prefix (CP) in one subsymbol can be obtained from a UB signal, and at this time, LB becomes a copy of the signal of UB in the subsymbol generated in the previous step. Accordingly, one of the subbands (UB) of the subsymbol according to an embodiment of the present invention includes cyclic prefix (CP) information, and the other (LB) does not include CP information. Among them, the subband LB that does not include CP information becomes a copy of the subband UB that includes cyclic prefix (CP) information in the previous step.

In the present invention, in particular, due to the characteristics of an OFDM signal, UB in a specific subsymbol and LB in the next subsymbol, which is a copy thereof, can be connected without the presence of a CP. , overlapping subbands are generated, and in RX, phase discontinuity between LO frequency steps can be compensated for under the assumption that the signals of the corresponding subbands are almost the same.

4 is an RF transceiver structure of an SC-OFDM radar according to the present invention, (a) is a transmitter, and (b) is a receiver structure.

Referring to FIG. 4, the receiver operates in the same manner as in the prior art, and alternately operates two LOGs using an SPDT switch. At this time, in the conventional case, two LOGs are alternately operated using an SPDT switch in the same way as RX in TX, but in the present invention, each LOG is connected to each up-mixer chain, thereby configuring two independent transmitters do.

Subsequently, the signals are combined with a power combiner and operated by connecting to one front-end, and since there are two independent TX stages, as shown in FIG. 2, overlapping transmission operations are possible. do. However, since the receiving unit does not need to receive signals in the CP interval, it is possible to receive the overlapped signal structure proposed with the same structure as the conventional RX structure.

On the other hand, it is possible to compensate for the phase discontinuity between LO frequency steps by using the transmitters of FIGS. 2 and 3 through the independent multi-transmitter structure according to the present invention and the time-overlapped signal structure generated therefrom. explained in detail.

As described above, each TX signal from the multi-transmitter structure consists of two adjacent subbands such as UB and LB per frequency step, and there are as many subsymbols as the number of steps in one block. For example, although four are exemplified in FIG. 2, the scope of the present invention is not limited thereto.

That is, subbands overlapping adjacent subsymbols in the frequency domain are generated, and in RX, the phase discontinuity between LO frequency steps can be compensated for under the assumption that the signals of the corresponding subbands are almost the same. It is a step diagram and diagram illustrating a method of compensating for phase discontinuity in a step.

Referring to FIG. 5, a method for compensating for phase discontinuity of an SC-OFDM radar signal according to an embodiment of the present invention utilizes a signal structure overlapping in time and performs temporal comparison-subband phase/gain correction-subsymbol phase/gain correction. perform consecutively. In FIG. 5, payload data allocated to each subcarrier (subcarrier frequency) is represented by a different color, and operates serially in all steps. Also, since data in UB in a specific subsymbol and data in LB in the next subsymbol are configured to be the same, each color is the same. .

Referring to FIG. 5, in a step referred to as “temporal comparison”, cross-correlation between the two bands is calculated, and gain and phase values at the maximum value are extracted (Fig. 5 ①).

Based on this extracted value, subband phase/gain correction (compensation within the same subband) is performed (② in FIG. 5), and then subsymbol phase/gain correction (compensation within the same subsymbol) is performed (FIG. 5 of ③). After that, the value of the compensated UB is used to compensate for the LB (same as the UB of the previous subsymbol) in the subsymbol in the next step, so as a result, a continuous compensation method is performed in all steps in a chain. , whereby the phase discontinuity can be continuously compensated for each block.

In order to verify the signal structure according to the present invention, MATLAB simulation was performed. In this simulation, a bandwidth of 1.024 GHz and carrier frequency (f _c ) of 79 GHz were assumed, and five targets with arbitrary radar cross section, range, radial velocity, and angle information were assumed.

The MIMO OFDM radar simulation platform used here generates a range-Doppler map, and free space path loss and distance-dependent additive white Gaussian noise (AWGN) are also considered in this simulation.

The FFT size (N _FFT ) used for signal processing to obtain the distance-Doppler map was set to 1024 x 256 and a Taylor window was used for the results. 64 synchronized blocks were used, there were 32 steps in one block, and 64 subcarriers in one step. The gain and phase dispersion of the dual transmitter (Dual-TX) according to the present invention were set to ± 0.5 dB and ± 180 °, respectively, and uniformly and randomly set for each step.

Since twice as many subbands are used within one subsymbol than the conventional technology, the sampling frequency (f _s ) was required twice as much, but as described in FIG. 2 for maximum ambiguity, speed, and performance, T _cp x steps Since the efficiency of time can be increased by the number, the performance is further increased.

Table 1 below shows MIMO OFDM radar parameters for MATLAB simulation.

Parameter Value Remark Number of frequency steps 32 Number of coherent radar blocks 64 Number of subcarriers per step 64 Subcarrier spacing 500 kHz Total OFDM bandwidth (BW _OFDM ) 1.024 GHz range resolution: 14.64 cm OFDM subsymbol period (T _{OFDM symbol} ) 2 us CP length (T _cp ) 0.5 us 75m: maximum detectable range Total pulse duration (T _block ) prior art proposed technology Maximum ambiguity rate of the prior art (V _unamb ) Maximum ambiguity rate of the proposed technique (V _unamb ) 80 us 64 us 11.79 m/s 14.74 m/s Carrier frequency (f _c ) 79 GHz Gain variation ± 0.5 dB Uniformly random Phase variation ± 180˚ Uniformly random Modulation scheme (D _n ) 16QAM Sampling frequency (f _s ) prior art proposed technology 32 MHz 64 MHz FFT size (N _FFT ) 2048x128 Range-Doppler map Target information n ^th target RCS (dBm ² ) Range (m) Velocity (m/s) One -28 10 0 2 -24 15 42 3 -12 37.75 -10.09 4 -12 38.50 -10.09 5 -4 53.70 0

6 is a transmitter structure using a transmitter according to the present invention. This is the simulated distance-Doppler map result. Here, (a) the prior art method using one frequency step, (b) the prior art method using all frequency steps (inter-subsymbol-discontinuity), (c) in the situation of (b), the inter-block- When discontinuity is added, (d) it is the result of solving the phase discontinuity using the proposed technique (using a signal structure overlapped in time and frequency domains). Referring to FIG. 6, in the case of (a), since the result is derived using one frequency step, the distance resolution is inferior to that of the SC-OFDM radar. And, since the processing gain is also lowered, it can be seen that the noise floor also has poor performance. Cases (b), (c), and (d) are the results when SC-OFDM radar is applied, and (b) and (c) are simulated with conventional techniques in the presence of phase discontinuity of dual-TX. (d) is the result when the proposed phase discontinuity compensation method is applied, and the signal structure overlapped in the time and frequency domains is applied.

In the case of (b), the discontinuity that occurs between subsymbols is applied in one block called inter-subsymbol-discontinuity, and in the case of (c), a block called inter-block-discontinuity and It is assumed that the discontinuity in the corresponding step between blocks is random.

In the case of (b), it was confirmed that the side lobe increased a lot on the distance axis, and it was confirmed that the adjacent objects No. 3 and No. 4 could not be distinguished. In the case of (c), it can be seen that additional Doppler component extraction is not possible in addition to the result of (b) due to inter-block-discontinuity. However, in the case of (d) according to the present invention, it can be seen that the side lobe goes down a lot on the distance axis, and the distance and Doppler components are easily extracted even in the inter-subsymbol-discontinuity and inter-block-discontinuity situations. In addition, it was confirmed through objects 2, 3, and 4 that the performance of the maximum ambiguity rate also increased. That is, in the case of object 2, it was confirmed that the processing method for compensating for the phase discontinuity works well regardless of its existence, although it is a fast object that exceeds the maximum ambiguity speed.

As described above, the present invention uses a signal structure overlapped in time and frequency domains, thereby 1) improving speed performance of maximum ambiguity, 2) reducing stabilization time of stepped LO, and 3) compensating for phase discontinuity between LO frequency steps. 3 effects can be obtained. Furthermore, by changing only the structure of the transmitter other than the receiver, it is possible to secure the economic feasibility of installing and replacing the signal structure.

An experiment was conducted to confirm the compensation effect of the signal structure and phase discontinuity of the SC-OFDM radar according to the present invention. To this end, a commercial communication board (V3 WARP) that operates in the 5.52 ~ 5.72 GHz band and provides a sampling rate of 40 MHz was used. 64 subcarriers exist in one subband, and a total of 10 frequency steps are used. At this time, the length of CP was set to 0.4 us. By connecting a 30 dB attenuator with a 2.6 m line and measuring the delay, the radar operation and phase discontinuity were confirmed. The results thereof can be seen in FIG. 6 .

7 is a phase plot according to subcarriers as a result of measuring a delay line capable of confirming phase discontinuity according to the present invention.

Referring to FIG. 7, there are 64 subcarriers in one subband in this experiment. 640 virtual subcarriers can be obtained through 10 frequency steps. 76 is the measurement result for a point target of about 13.3m including the internal delay of this system, and the phase value should decrease with a constant slope as the order of subcarriers increases, which is due to the Fourier This is because a time difference in the time domain appears as a phase difference in the frequency domain due to the nature of the transformation. In FIG. 6, it can be seen that the slope is the same in 10 steps due to the phase discontinuity, but the offset (intercept) is different (see purple and orange in FIG. 6).

However, when processed through the signal structure according to the present invention and the phase discontinuity compensation method through this, it can be seen that a straight line is connected (purple → yellow, orange → blue). At this time, the phase discontinuity is compensated by aligning all the offsets to the first frequency step.

The phase discontinuity compensation method according to the present invention will be described as described in FIG. 4 as follows.

Taking the first step and the second step as an example, ① temporal comparison is performed between overlapping subbands (UB in the first step and LB in the second step). Since 64 subcarriers are included in the subband, a cross-correlation is calculated using each of the 64 subcarriers and the maximum value is extracted.

The maximum value is output as gain and phase values. These values are memorized, and based on these memorized values, the subband overlapped in the second step, that is, all subcarriers in LB ② Perform phase/gain correction, and then, the UB of the second step also performs ③ phase/gain correction on all subcarriers with this memorized value.

At this time, in the case of ②, it is named 'subband phase/gain correction' because it is the compensation of subbands overlapping on the frequency side, and in case of ③, it is named 'subsymbol phase/gain correction' because it is the compensation of subsymbols overlapping on the time side.

Subsequently, since the subcarriers of UB compensated in the second step are also used to compensate for the subcarriers of LB in the corresponding subsymbol in the third step, as a result, a sequential compensation method is performed in all steps.

Simply put, these compensating actions then continue between the second step and the third step, and finally to the ninth step and the tenth step, and thus, as mentioned above, the subcarriers in the subsymbols corresponding to the first step represent The phase discontinuity is solved by aligning the subcarriers in the subsymbols corresponding to all steps to the phase offset of the present phase offset.

Claims (12)

As an SC-OFDM radar transmitter,
a first transmitter capable of transmitting independent signals; and
a second transmitter;
The SC-OFDM radar transmitter, characterized in that the signal transmitted from the first transmitter and the signal transmitted from the second transmitter overlap by a predetermined time in time. According to claim 1,
The SC-OFDM radar transmitter, characterized in that the subsymbols transmitted step by step from the first transmitter and the second transmitter include two adjacent subbands (UB, LB). According to claim 2,
The SC-OFDM radar transmitter, characterized in that one (UB) of the two subbands includes cyclic prefix (CP) information, and the other does not include CP information. According to claim 3,
The SC-OFDM radar transmitter, characterized in that the subband (LB) not including the CP information is a duplicate of the subband including CP (Cyclic Prefix) information in the previous step. According to claim 3,
The predetermined time is a Cyclic prefix (CP) transmission time (T _cp ) SC-OFDM radar transmitter, characterized in that. As a signal transmission method using an SC-OFDM radar transmitter,
generating signals from a first transmitter and a second transmitter;
The signal transmitted from the first transmitter and the signal transmitted from the second transmitter are overlapped in time by a predetermined time,
Subsymbols transmitted step by step from the first transmitter and the second transmitter include two adjacent subbands,
One of the two subbands includes cyclic prefix (CP) information, and the other does not include CP information;
The signal transmission method using an SC-OFDM radar transmitter, characterized in that the subband not including the CP information is a duplicate of the subband including CP (Cyclic Prefix) information in the previous step. According to claim 6,
The predetermined time is a signal transmission method using an SC-OFDM radar transmitter, characterized in that the CP (Cyclic prefix) transmission time (T _cp ). a transmitter for an OFDM radar according to any one of claims 1 to 5; and
An SC-OFDM radar transmission/reception system including a receiver for OFDM radar corresponding thereto. According to claim 8,
The SC-OFDM radar transmitter includes a first transmitter; and a second transmitter, wherein the first transmitter and the second transmitter are coupled to one power combiner to independently transmit transmission signals. According to claim 8,
The receiver is an SC-OFDM radar transmission and reception system, characterized in that the SPDT (single-pole double-throw) switch. As a phase discontinuity compensation method of an SC-OFDM radar signal,
Calculating a cross-correlation between a subband (LB) not including CP information and a subband (UB) including CP (Cyclic Prefix) information in a previous step;
extracting gain and phase values of subbands from the calculated results;
performing subband phase/gain correction from the extracted gain and phase values; and
and performing subsymbol phase/gain correction in the subsymbol with the extracted gain and phase values. According to claim 11,
In the phase discontinuity compensation method, the phase discontinuity compensation method characterized in that the step of claim 11 is performed in succession in successive steps.