Transmission scheme implementing code division multiple access in a radar system

Abstract

A vehicle includes multiple transmitters of a Code Division Multiple Access (CDMA) radar system for simultaneously transmitting a frame of transmitted signals. A first duration between the transmission of a first pair of consecutive transmitted signals increases linearly to a second duration between the transmission of a second pair of consecutive transmitted signals. The vehicle also includes a receiver of the CDMA radar system for receiving reflected energy generated by an object reflecting one or more transmitted signals from one or more of the multiple transmitters. A controller processes the reflected energy to obtain information about the object and controls the operation of the vehicle based on that information.

Description

Technical Field

[0001] This subject matter discloses a transmission scheme for implementing code division multiple access in radar systems. Background Art

[0002] Vehicles (e.g., cars, trucks, construction equipment, agricultural equipment, automated factory equipment) are increasingly using sensors to acquire information about the vehicle and its surrounding environment. This information can be used to control one or more aspects of the vehicle's operation. Exemplary sensors for acquiring information about the vehicle's external environment include cameras, light detection and ranging (LiDAR) systems, and radio detection and ranging (radar) systems. In multiple-input multiple-output (MIMO) radar systems that facilitate simultaneous transmission from multiple transmitting elements, Code Division Multiple Access (CDMA) is a method for separating the resulting reflections. Therefore, it is desirable to provide a transmission scheme for implementing CDMA in a radar system. Summary of the Invention

[0003] In one exemplary embodiment, the vehicle includes multiple transmitters of a Code Division Multiple Access (CDMA) radar system to simultaneously transmit a frame of transmitted signals. A first duration between the transmission of a first pair of consecutive transmitted signals increases linearly to a second duration between the transmission of a second pair of consecutive transmitted signals. The vehicle also includes a receiver of the CDMA radar system for receiving reflected energy generated by an object reflecting one or more transmitted signals from one or more of the multiple transmitters. A controller processes the reflected energy to obtain information about the object and controls the operation of the vehicle based on that information.

[0004] In addition to one or more features described herein, the frames of the transmitted signals transmitted by each of the multiple transmitters are based on the same chirp, which is a frequency modulated continuous wave (FMCW) signal.

[0005] In addition to one or more features described herein, a frame of transmitted signals transmitted by each of the plurality of transmitters comprises M transmitted signals repeated at sequential intervals constituting the frame, and M is greater than or equal to the number of the plurality of transmitters.

[0006] In addition to one or more features described herein, each of the multiple transmitters has M transmitted signals obtained by multiplying a chirp by M symbols, and the M symbols are different for each of the multiple transmitters.

[0007] In addition to one or more of the features described here, the M symbols are Hadamard code sequences or pseudo-random sequences.

[0008] In addition to one or more features described herein, the first pair of consecutively transmitted signals are the last transmitted signal of the first sequence interval in the sequence interval constituting the frame and the first transmitted signal of the second sequence interval in the sequence interval, and the second pair of consecutively transmitted signals are the last transmitted signal of the second sequence interval in the sequence interval and the first transmitted signal of the third sequence interval.

[0009] Apart from one or more of the features described herein, the duration between the transmissions of consecutively transmitted signals within the same sequence interval is a constant duration for all sequence intervals.

[0010] In addition to one or more features described herein, the first pair of consecutively transmitted signals and the second pair of consecutively transmitted signals are within the same sequence interval in the sequence interval that constitutes the frame.

[0011] In addition to one or more features described herein, processing the reflected energy involves obtaining an element vector from the reflected energy and, based on the repetition of M transmitted signals at each sequence interval, decoding each of the M elements of the vector together.

[0012] In addition to one or more features described herein, the vehicle also includes one or more additional receivers for a CDMA radar system.

[0013] In another exemplary embodiment, a method of configuring a radar system in a vehicle includes arranging multiple transmitters of a Code Division Multiple Access (CDMA) radar system to simultaneously transmit a frame of transmitted signals. A first duration between the transmission of a first pair of consecutive transmitted signals increases linearly to a second duration between the transmission of a second pair of consecutive transmitted signals. The method also includes arranging a receiver of the CDMA radar system to receive reflected energy generated by an object reflecting one or more transmitted signals from one or more of the multiple transmitters. A controller processes the reflected energy to obtain information about the object and controls the operation of the vehicle based on that information.

[0014] In addition to one or more features described herein, the method also includes basing frames of transmitted signals transmitted by each of a plurality of transmitters on the same chirp, which is a frequency modulated continuous wave (FMCW) signal.

[0015] In addition to one or more features described herein, the method also includes, in a frame of a transmitted signal transmitted by each of a plurality of transmitters, M transmitted signals repeated at a sequence interval constituting the frame, wherein M is greater than or equal to the number of the plurality of transmitters.

[0016] In addition to one or more features described herein, the method also includes obtaining M transmitted signals for each of a plurality of transmitters by multiplying the chirp by M symbols, wherein the M symbols are different for each of the plurality of transmitters.

[0017] In addition to one or more features described herein, the method also includes selecting M symbols as either a Hadamard code sequence or a pseudo-random sequence.

[0018] In addition to one or more features described herein, the first pair of consecutively transmitted signals are the last transmitted signal of the first sequence interval in the sequence interval constituting the frame and the first transmitted signal of the second sequence interval in the sequence interval, and the second pair of consecutively transmitted signals are the last transmitted signal of the second sequence interval in the sequence interval and the first transmitted signal of the third sequence interval.

[0019] In addition to one or more features described herein, the method also includes configuring the duration between the transmissions of consecutively transmitted signals within the same sequence interval as a constant duration for all sequence intervals.

[0020] In addition to one or more features described herein, the method also includes configuring a first pair of consecutively transmitted signals and a second pair of consecutively transmitted signals to be within the same sequence interval in the sequence interval constituting the frame.

[0021] In addition to one or more features described herein, the method also includes processing the reflected energy, including obtaining an element vector from the reflected energy, and decoding each of the M elements of the vector together based on the repetition of the M transmitted signals at each sequence interval.

[0022] In addition to one or more features described herein, the method also includes deploying one or more additional receivers for the CDMA radar system.

[0023] The above-described features and advantages, as well as other features and advantages, of this disclosure will become apparent when taken in conjunction with the accompanying drawings and the following detailed description. Attached Figure Description

[0024] Other features, advantages, and details appear by way of example only in the following detailed description, which refers to the accompanying drawings, wherein:

[0025] Figure 1 It is a block diagram of a vehicle employing a transmission scheme using Code Division Multiple Access (CDMA) in a radar system according to one or more embodiments;

[0026] Figure 2 An exemplary transmission scheme for implementing CDMA is shown according to one or more embodiments;

[0027] Figure 3A An exemplary transmission signal according to one or more embodiments is shown;

[0028] Figure 3B Another exemplary transmission signal according to one or more embodiments is shown;

[0029] Figure 4 This is a flowchart of a method for processing reflected energy generated by a transmission scheme for implementing CDMA in a radar system, according to one or more embodiments; and

[0030] Figure 5 It shows the reference Figure 4 The decoding output produced by the processing at each receiver is discussed. Detailed Implementation

[0031] The following description is merely exemplary in nature and is not intended to limit this disclosure, its application, or use. It should be understood that in all the drawings, corresponding reference numerals denote similar or corresponding parts and features.

[0032] As mentioned earlier, a radar system, more specifically a multiple-input multiple-output (MIMO) radar system, is one of the sensors used to acquire information about objects around a vehicle. A MIMO radar system comprises multiple transmitting elements and multiple receiving elements. Simultaneous transmission from multiple transmitting elements increases the total energy of a single transmission, thereby increasing the maximum detection range. When a simultaneously transmitted signal from multiple transmitting elements encounters one or more objects, the reflections of the various transmitted signals are received at the radar system as the sum of all reflected energy. The reflections must be separated according to their corresponding transmitting elements to obtain angular resolution. That is, each part of the received signal must be processed based on the transmitted signal that generated the received signal in order to obtain an accurate estimate of the angle relative to the object (i.e., the direction of arrival (DOA)).

[0033] CDMA refers to a system where each transmitting element transmits a different coded signal, allowing the received signal portion corresponding to each transmitting element to be identified based on the code. Under existing transmission schemes, each transmitting element repeats a different code sequence within a transmission frame. Another existing transmission scheme involves each transmitting element transmitting a different long pseudo-random code. However, each of these existing schemes has drawbacks in vehicle applications, involving a frequency shift (i.e., Doppler frequency) in the received signal compared to the transmitted signal. This frequency shift is caused by the relative motion between the vehicle and the object generating the received signal (e.g., another vehicle) and is used to determine the rate of change of distance to the object, known as the Doppler.

[0034] Embodiments of the systems and methods detailed herein relate to transmission schemes for implementing CDMA in radar systems. Objects (e.g., other vehicles) travel at similar speeds but at different distances from the radar system, and these distances can be distinguished. Similarly, objects at similar distances but different speeds quickly reveal differences in distance, which helps distinguish the two objects. A scenario where the aforementioned existing schemes are problematic involves two objects at similar distances to the radar system and also traveling at similar speeds. In this case, reflections from the objects will mutually occlude each other for a duration during which the objects remain within a similar range. As detailed herein, the linear delay introduced by the transmission scheme according to one or more embodiments helps detect each object traveling at similar speeds within a similar range.

[0035] According to an exemplary embodiment, Figure 1 This is a block diagram of a vehicle 100 that uses a CDMA transmission scheme in radar system 110. Figure 1 The exemplary vehicle 100 shown is a car 101. Vehicle 100 includes a radar system 110 having transmitters 120a to 120n (generally referred to as 120) and receivers 130a to 130m (generally referred to as 130). The number of transmitters 120 and the number of receivers 130 may be the same or different (i.e., n may be equal to or not equal to m). Transmitters 120a to 120n transmit corresponding transmit signals 125a to 125n (generally referred to as 125). As discussed further, each transmit signal 125 is encoded differently. Simultaneous transmission of the encoded transmit signal 125 from each transmitter 120 may encounter one or more objects 160. Figure 1 Exemplary objects 160a and 160b (e.g., other vehicles) are shown. A portion of the transmitted signal 125 encountering object 160 results in reflected energy 135, which is reflected back to radar system 110 and received by one or more receivers 130. Radar system 110 also includes a controller 115 that controls the transmission scheme implemented by transmitter 120 and can process the reflected energy 135 received by receiver 130.

[0036] The vehicle 100 also includes a controller 140 that receives information from the radar system 110 and one or more other sensors 150 to control the operation of the vehicle 100. Exemplary operations include collision avoidance, automatic braking, and adaptive cruise control. For example, the other sensors 150 include cameras and lidar systems. The number and location of the radar system 110 and other sensors 150 are not limited. Figure 1The limitations shown. The controller 115 of the radar system and the controller 140 of the vehicle 100 may include processing circuitry, which may include application-specific integrated circuits (ASICs), electronic circuitry, processors (shared, dedicated, or grouped), and memory for executing one or more software or firmware programs, combinational logic circuitry, and / or other suitable components that provide the functions described.

[0037] Figure 2 , Figure 3A and Figure 3B A CDMA transmission scheme in radar system 110 is shown according to different exemplary embodiments. Figure 2 An exemplary transmission scheme for implementing Code CDMA according to one or more embodiments is illustrated. For illustrative purposes, it is assumed in the illustration that three transmitters 120a, 120b, and 120c transmit three transmission signals 125a, 125b, and 125c. The basis of each transmission signal 125 is... Figure 2 The image shows a linear frequency modulated continuous wave (LFMCW) signal or chirp c. An exemplary chirp c with time t and frequency f is shown on the vertical axis. As shown, the frequency increases linearly with time. Alternatively, the chirp c may exhibit a linear decrease in frequency.

[0038] The repeating sequence of symbols {a0, a1, a2}, {b0, b1, b2}, or {c0, c1, c2} is multiplied by a chirp c on each transmitter 120. The repeating sequence of symbols can be called the original sequence. Therefore, in the exemplary case, {a0, a1, a2} is the original sequence of transmitter 120a, {b0, b1, b2} is the original sequence of transmitter 120b, and {c0, c1, c2} is the original sequence of transmitter 120c. The number of symbols in the original sequence is at least the same as the number of transmitters 120 or more. In the exemplary case of three transmitters 120, as shown, at least three symbols must be in the original sequence.

[0039] Each sequence interval SIi, where i is the index of the interval, includes the chirp multiple sequence. Each chirp multiple is obtained by multiplying a symbol of the original sequence by the chirp c. For example, to generate a frame for transmitted signal 125a, the original sequence of symbols {a0, a1, a2} is multiplied by the chirp c in a repeating pattern, such that the transmission of chirp multiples a0*c, a1*c, a2*c repeats with sequence intervals SI1, SI2, and SI3, as shown. As another example, the chirp multiple sequence of transmitted signal 125c is c0*c, c1*c, c2*c, and is shown as repeating for sequence intervals SI1, SI2, SI3. The frame may include any number of sequence intervals SIi.

[0040] according to Figure 2 In the exemplary embodiment shown, the duration between chirp multiples within sequence interval SIi is constant, but the duration increases linearly from one sequence interval SIi to the next sequence interval SI(i+1). That is, the duration t1 between chirp multiples {a0*c, a1*c, a2*c}, {b0*c, b1*c, b2*c}, or {c0*c, c1*c, c2*c} within the first sequence interval SI1 increases linearly to the duration t2 between chirp multiples within the second sequence interval SI2 and the duration t3 within the third sequence interval SI3. For a given k-th duration tk, the linear increase in duration is expressed as:

[0041] tk=t1+(k-1)Δ (Equation 1)

[0042] The equations for t2 and t3 are as follows: Figure 2 As shown.

[0043] Figure 3A An exemplary transmitted signal 125 according to one or more embodiments is shown. The original sequence {s0, s1, s2} is used. Figure 3A As shown, the duration between each pair of consecutive chirp multiples increases linearly and is independent of the sequence interval. Therefore, duration t1 is used between s0*c and s1*c, and duration t2, which increases linearly from t1 according to Equation 1, is used between s1*c and s2*c in sequence interval SI1. Similarly, duration t7 is used between s0*c and s1*c, and duration t8, which increases linearly from t7 according to Equation 1, is used between s1*c and s2*c in sequence interval SI3.

[0044] Figure 3B Another exemplary transmitted signal 125 according to one or more embodiments is shown. The original sequence {s0, s1, s2} is used again. Figure 3B As shown, the duration between chirp multiples within each sequence interval SIi is the same for all sequence intervals SIi. The duration between sequence intervals increases linearly. That is, regardless of the sequence interval, a duration t1 is used between s0*c and s1*c, and between s1*c and s2*c. However, the duration between sequence intervals SI1 and SI2 is t2, which increases linearly from t1 according to Equation 1, while the duration between sequence intervals SI2 and SI3 is t3, which increases linearly from t2 according to Equation 1.

[0045] Exemplary symbol sequences include orthogonal sequences, such as Hadamard code sequences and pseudo-random sequences. Therefore, for example, Figure 2The exemplary symbol sequences {a0, a1, a2}, {b0, b1, b2}, and {c0, c1, c2} shown can be orthogonal symbols {1, 1, 1}, {1, -1, 1}, and {1, -1, -1}. According to any exemplary embodiment, the repetition of the symbol sequences (i.e., repetition of the chirp multiple in each sequence interval SIi of the frame) and the linear increase in duration both provide advantages. The repetition of the symbol sequences leads to simplified processing of the reflected signal, and the linear increase facilitates control over the frequency range and amplitude of the sidelobes in the Doppler spectrum. Each of these aspects will be described in further detail.

[0046] Figure 4 This is a flowchart of a method 400 for processing reflected energy 135 according to one or more embodiments, which is generated in a CDMA transmission scheme implemented in radar system 110. As previously described, one or more receivers 130 may receive reflected energy 135 based on one or more objects 160. The received reflected energy 135 may be the sum of reflections from two or more transmitted signals 125. Therefore, at the controller 115 of radar system 110, at the controller 140 of vehicle 100, or a combination of both, processing is performed to separate the portions of reflected energy 135 attributable to each transmitted signal 125. This is necessary for the accurate detection of one or more objects 160 that result in reflected energy 135. In block 410, the process includes receiving reflected energy 135 as a vector x of length L, which is the number of received symbols. Vector x comes from known preprocessing, including down-conversion and digitization of reflected energy 135. The original sequence length is M. Therefore, in reference Figure 2 , Figure 3A and 3B In the example discussed, M = 3.

[0047] In box 420, the process includes separating the vector x of reflected energy 135 into M sub-vectors x. i Each subvector corresponds to a repeating instance of a chirp multiple associated with one of the symbols in the original sequence. For example, when M = 3, x1 will include x(1:4:7:10, ...), all associated with the first symbol of the original sequence, and x2 will include x(2:5:8:11, ...), all associated with the second symbol of the original sequence. In general,

[0048] x i = x(i:i+M:i+2M:i+3M:...) (Equation 2)

[0049] To be clear, the separation discussed with reference to Equation 2 does not yet take into account the use of different symbols in the original sequence of each transmitter 120.

[0050] In box 430, the process includes generating an original code matrix C for the original codes of each of the T transmitters 120. For illustrative purposes, it is assumed that the number of transmitters 120 T is the same as the original sequence length M. As previously stated, M can be greater than T.

[0051]

[0052] For example, in reference Figure 2 In the exemplary case discussed, M = T = 3, and c1 = {a0, a1, a2}, c2 = {b0, b1, b2}, and c3 = {c0, c1, c2}. In box 440, the process includes obtaining the Discrete Fourier Transform (DFT) F from the reflected energy 135. The dimension of the Discrete Fourier Transform F is (N, L / M), where N is the number of selected Doppler frequency bins.

[0053] In box 450, obtaining the DFT output matrix Y includes obtaining:

[0054]

[0055] Each vector y in the DFT output matrix Y i It is given by the following formula:

[0056] y i =Fx i (Equation 5)

[0057] Then, in box 460, the symbols are decoded (i.e., the reflections generated by each of the T different transmitters 120 are separated) to produce a decoding matrix Z, which has a dimension of T, assuming the same number of symbols M and the same number of Doppler frequency bins N. The decoding matrix Z is given by the following formula:

[0058] Z = CY (Equation 6)

[0059] As previously mentioned, the decoding complexity at receiver 130 is reduced due to the repetition of the original sequence, thus improving computational efficiency. As shown in Equation 2, each Mth element of the vector x of the reflected energy 135 can be processed together. That is, decoding a conventional code requires a DFT of size L for each transmit antenna code sequence (i.e., M DFTs of length L). According to one or more embodiments, there are M DFTs of size L / M. Therefore, the decoding complexity is reduced by a factor of M compared to conventional non-repetitive codes. Once the decoding matrix Z is obtained, known additional processing, such as beamforming, can be performed to identify one or more objects 160 and obtain information about each object 160 (i.e., range, rate of change of range, direction of arrival).

[0060] Figure 5 It shows the reference Figure 4 The exemplary decoded output 500 (i.e., elements of the decoded matrix Z) produced by the processing at each receiver 130 discussed is shown. The Doppler frequency, in Hertz (Hz), is displayed along one axis, and the amplitude, in Decibels (dB), is displayed along another vertical axis. The amplitude 510 corresponding to the Doppler frequency (i.e., 0 Hz) of object 160 is significantly higher than the amplitude level 520 of the adjacent sidelobe at the Doppler frequency immediately adjacent to the detected object 160. The amplitude level 530 of the sidelobe at a Doppler frequency further away from the detected object 160 (referred to as the more distant sidelobe for interpretive purposes) is higher than the amplitude level 520 of the adjacent sidelobe.

[0061] In other words, the total energy in the sidelobes is the same as that when using the previous transmission scheme. However, due to the repetition of short source codes and the linear increase in duration in the transmission scheme according to one or more embodiments, the distribution of the sidelobes causes adjacent sidelobes (i.e., the sidelobes closest to the main lobe) to decay more than more distant sidelobes (i.e., sidelobes further away from the main lobe than adjacent sidelobes) (i.e., the amplitude level 520 is lower). This contributes to a high detection probability in the case of multiple objects 160. As further detailed, the maximum idle time ta between transmissions (i.e., the maximum value of the duration tk according to Equation 1) can be selected based on the expected decay of adjacent sidelobes and the expected width of more distant sidelobes. According to various embodiments, determining this maximum idle time ta value helps to determine the value of each duration of the transmission scheme based on the linear relationship between the durations (i.e., based on Equation 1).

[0062] The sidelobe attenuation coefficient is determined by the following formula:

[0063]

[0064] In Equation 7, Ns is the number of symbols in a frame (e.g., 256 symbols), M is the number of symbols in the original sequence (e.g., 3 symbols for 3 transmitters 120), and tc is the chirp duration (e.g., 50 microseconds per chirp). The maximum idle time ta is the maximum time delay value before the next transmission 120. Therefore, for the desired adjacent sidelobe attenuation value (i.e., to achieve a given amplitude level 520 relative to the amplitude of object 160), the maximum idle time ta can be determined, and thus the duration value for a given transmission scheme can be determined. However, if the sidelobe attenuation value is too low for adjacent sidelobes, then the propagation of sidelobe energy will be too wide. That is, the adjacent sidelobe attenuation value obtained from the maximum idle time ta must be balanced with the width of the more distant sidelobes. The wider and farther the sidelobes are, the closer they will be to the Doppler frequency of object 160 (that is, the narrower the adjacent sidelobes will become), thus increasing the chance of blurring object 160 without being detected. The width of the more distant sidelobes is given by the following equation:

[0065]

[0066] While the foregoing disclosure has been described with reference to exemplary embodiments, those skilled in the art will understand that various changes can be made without departing from its scope, and its elements can be substituted with equivalents. Furthermore, many modifications can be made to adapt particular situations or materials to the teachings of this disclosure without departing from the basic scope of this disclosure. Therefore, it is intended that this disclosure be limited to the specific embodiments disclosed, but will include all embodiments falling within its scope.

Claims

1. A vehicle equipped with a Code Division Multiple Access (CDMA) radar system, comprising: The CDMA radar system has multiple transmitters configured to simultaneously transmit a frame of transmission signal, wherein a first duration between the transmission of a first pair of consecutive transmission signals increases linearly to a second duration between the transmission of a second pair of consecutive transmission signals. The receiver of the CDMA radar system is configured to receive reflected energy generated by an object reflecting one or more transmitted signals from one or more transmitters among a plurality of transmitters; and A controller is configured to process the reflected energy to obtain information about the object and control the operation of the vehicle based on that information, wherein the frames of the transmitted signals emitted by each of the plurality of transmitters are based on the same chirp, which is a frequency modulated continuous wave (FMCW) signal, and the frames of the transmitted signals emitted by each of the plurality of transmitters comprise M transmitted signals repeated at sequential intervals constituting the frames, and M is greater than or equal to the number of the plurality of transmitters; in, The first pair of consecutively transmitted signals of the transmitted signal are the last transmitted signal of the first sequence interval in the sequence interval constituting the frame and the first transmitted signal of the second sequence interval in the sequence interval, and the second pair of consecutively transmitted signals of the transmitted signal are the last transmitted signal of the second sequence interval in the sequence interval and the first transmitted signal of the third sequence interval, and the duration between the transmissions of the consecutively transmitted signals of the transmitted signal within the same sequence interval in the sequence interval is a constant duration for all sequence intervals.

2. The vehicle according to claim 1, wherein, The M transmitted signals of each of the plurality of transmitters are obtained by multiplying the chirp by M symbols, wherein the M symbols are different for each of the plurality of transmitters and the M symbols are a Hadamard code sequence or a pseudo-random sequence.

3. The vehicle according to claim 1, wherein, The first pair of consecutively transmitted signals and the second pair of consecutively transmitted signals are within the same sequence interval in the sequence interval that constitutes the frame.

4. The vehicle according to claim 1, wherein, Processing the reflected energy includes obtaining an element vector from the reflected energy and decoding each of the M elements of the vector together based on the repetition of the M transmitted signals for each sequence interval.

5. A method for configuring a radar system in a vehicle, the method comprising: Multiple transmitters in a code division multiple access (CDMA) radar system simultaneously transmit a frame of transmission signal, wherein the first duration between the transmission of a first pair of consecutive transmission signals increases linearly to the second duration between the transmission of a second pair of consecutive transmission signals; The receiver of the CDMA radar system is arranged to receive reflected energy generated by an object reflecting one or more transmitted signals from one or more of the plurality of transmitters; Configure the controller to process the reflected energy, thereby obtaining information about the object, and control the operation of the vehicle based on that information; The frames of the transmitted signals transmitted by each of the multiple transmitters are based on the same chirp, which is a frequency modulated continuous wave (FMCW) signal; and A frame of transmitted signals transmitted by each of a plurality of transmitters includes M transmitted signals repeated at sequential intervals constituting that frame, where M is greater than or equal to the number of the plurality of transmitters; Wherein, the first pair of consecutively transmitted signals of the transmitted signal are the last transmitted signal of the first sequence interval in the sequence interval constituting the frame and the first transmitted signal of the second sequence interval in the sequence interval, and the second pair of consecutively transmitted signals of the transmitted signal are the last transmitted signal of the second sequence interval in the sequence interval and the first transmitted signal of the third sequence interval, and the method further includes configuring the duration between the transmissions of the consecutively transmitted signals of the transmitted signal within the same sequence interval in the sequence interval to be a constant duration for all sequence intervals.

6. The method according to claim 5, further comprising: The M transmitted signals of each of the plurality of transmitters are obtained by multiplying the chirp by M symbols, wherein the M symbols are different for each of the plurality of transmitters, and the M symbols are selected as either a Hadamard code sequence or a pseudo-random sequence.

7. The method of claim 5, further comprising configuring a first pair of consecutively transmitted signals of the transmitted signal and a second pair of consecutively transmitted signals of the transmitted signal to be within the same sequence interval in the sequence interval constituting the frame.

8. The method of claim 5, wherein processing the reflected energy comprises obtaining an element vector from the reflected energy and decoding each of the M elements of the vector together based on the repetition of the M transmitted signals for each sequence interval.

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