EP4581387A1

EP4581387A1 - Waveform design with constellation extension for ofdm dual-functional radar-communications

Info

Publication number: EP4581387A1
Application number: EP23861004.2A
Authority: EP
Inventors: Ebubekir MEMISOGLU; Talha YILMAZ; Huseyin Arslan
Original assignee: Istanbul Medipol Universitesi
Current assignee: Istanbul Medipol Universitesi
Priority date: 2022-08-31
Filing date: 2023-08-28
Publication date: 2025-07-09

Abstract

Invention is a waveform design method for dual-function radar communication (DFRC) systems. Proposed method enhances Cramer-Rao Bound (CRB) of the orthogonal frequency division multiplexing (OFDM) waveform for radar performance, while keeping the transmission transparent to the communication receiver. (Here transparent means a conventional OFDM receiver do not needs to know about the design to be able to receive succesfully.)

Description

DESCRIPTION WAVEFORM DESIGN WITH CONSTELLATION EXTENSION FOR OFDM DUAL- FUNCTIONAL RADAR-COMMUNICATIONS Technical Field The invention is related to a novel waveform design method for dual-function radar communication (DFRC) systems. Proposed method enhances Cramer-Rao Bound (CRB) of the orthogonal frequency division multiplexing (OFDM) waveform for radar performance, while keeping the transmission transparent to the communication receiver. (Here transparent means a conventional OFDM receiver do not needs to know about the design to be able to receive succesfully.) Prior Art Advancement of wireless communication technologies have led to a spectral expansion. Due to this spectral expansion wireless communication systems are expected to work in same operating frequencies as radar systems. This have caused a great congestion in the frequency spectrum. One solution approach for this problem is to design systems that can execute radar and communication services simultaneously, which is called DFRC. There are plenty of proposed DFRC system designs in the literature. However, most of them are not directly compatible with current wireless standards. There are several OFDM-based DFRC system approaches in the literature. All of them involving a solution to some optimization problem to enhance radar and communication performance. Closest approaches involve: In prior art, some documents propose a waveform design by solving an optimization problem constrainted by ISL to improve CRB of range and doppler parameters to improve radar performance and finding the optimum feedforward signaling for the communication receiver. In prior art, some documents propose a waveform design that utilizes empty subcarriers in a low traffic load to minimize range and doppler CRB’s to improve radar performance of OFDM waveform while improving the peak-to-average-power-ratio (PAPR) performance. For the waveform design proposed standards should be revised to support the feedforward signaling authors propose. Moreover, some methods require channel information to obtain the optimum waveform for DFRC. On the other hand, other some documents are an opportunistic waveform design method and it’s performance relies on the traffic load. In situations with large traffic method would not yield a significant performance enhancement. Brief Description and Objects of the Invention In invention, proposed method neither transmitter or receiver requires extra signalling (channel information feedback or feedforward signaling). Also, proposed method is more suitable for real-time applications since it is less computationally complex. Without any changes in receiver operations proposed method can be adapted by a simple software update on transmitter side. Inveniton proposes a design method which is easily adaptable to current wireless communication standards. Any wireless communication system that wants to support radar operations can adopt the proposed method to improve both radar and communication performance of the system. This makes the proposed method valuable for beyond 5G systems. DFRC systems can be used to either decongest the frequency spectrum or to support various sensing applications. However, waveforms developed by both radar and communication literature does not satisfy enough performance for both operations. For this purpose a waveform that can support both radar and communication operations are required. Proposed method yields a waveform that enables a system that can serve both communication and sensing services. Proposed method is expected to enable unified radar and communication system by enhancing both radar and communcation performance. 1. It is a transparent method which requires no feedforward signalling to be executed. 2. Proposed method does not require any feedback signaling from the communication receiver. 3. Compared to the other methods in the literature, proposed method can be applied in any situation (for a given power budget). The proposed power allocation scheme demonstrated in Figure 3 enables these features. The power allocation does not affect process of data symbol demodulation at the receiver side. The power allocation can be done to optimize CRB without any channel feedback from the receiver. Mentioned power allocation is done at the number of references as 510, 511, 512, and 513. Figures Figure 1: System model Figure 2: OFDM frame Figure 3: Constellation diagram for conventional and proposed 16-QAM Figure 4: Algorithm for generation of the weight matrix Figure 5: Algorithm of the proposed waveform design REFERENCE NUMBERS 100 transceiver 101 radar target 102 receiver 103 transmission 104 reflections 200 OFDM subcarriers 201 Subcarrier index 202 OFDM Symbol index 300 Inner symbol 301 Corner symbol 302 Edge symbol 303 Power enhanced corner symbol 304 Power enhanced edge symbol 305 Constellation diagram 400 (400) represents the defining parameters required for weight matrix generation. These parameters include carrier frequency ( ^^_^ ), subcarrier spacing (Δ ^^ ), OFDM symbol duration ( ^^_^௬^), radar SNR ( ^^_^), number of subcarriers in one OFDM symbol ( ^^), number of OFDM symbols in one transmission frame ( ^^), maximum allowed power for one subcarrier ( ^^_^^௫), and a weighting factor for delay-Doppler estimation accuracy ( ^^). 401 (401) initiates the subcarrier counter ( ^^) from zero. 402 (402) is a decision blocks that decides if the following statement is true: ^^ ≤ ^^ − 1 403 In case of (402) is true (403) initiates the OFDM symbol counter (m) from zero. 404 A decision block that decides if the following statement is true: ^^ ≤ ^^ − 1 405 In case of (404) is true (405) initiates power matrix of subcarriers by unit power. Mathematically this can be represented by: ^^ഥ _{^ = ^^ ^^ ^^} where ^^ഥ^ is the power matrix and ^^ _{^^ ^^} is a ^^ ^^ ^^ matrix consists of all ones. 406 (406) sets the n-th subcarrier’s power of the m-th OFDM symbol to ^^_^^௫. ^^ത _{^( ^^, ^^) = ^^^^௫} _{407 vectorizes the ^} ^ഥ _{^ for weight calculation. Vectorized version of ^} ^ഥ _{^ is called ^^.} _{^ഥ^ = ^^ ^^ ^^( ^} ^ഥ _^) 408 Calculates the weight of the n-th subcarrier of the m-th OFDM symbol by: ^^( ^^, ^^) = ^^ ^^_ఛ + (1 − ^^) ^^_ఔ ^^ _^^ ≜ 2 ^^Δ ^^( ^^ _^^ ⊗ ^^ _^^), ^_{^ ^^ ≜ 2 ^^ ^^^ ^^^} ⁽ _{^^ ^^ ⊗ ^^ ^^} ⁾ _, _{^^ ^^ ≜} ⁽ _{^^ ^^ ⊙ ^^ ^^} ⁾ _^^ ^{^} ^^{^} ^_{^^ − ^^ ^^ ^^} ^{^} ^_^ ^{^} _, _{^^ ^^ ≜} ⁽ _{^^ ^^ ⊙ ^^ ^^} ⁾ _^^ ^{^} ^^{^} ^_{^^ − ^^ ^^ ^^} ^{^} ^_^ ^{^} _, _{^^ ^^ ^^ ≜} ⁽ _{^^ ^^ ⊙ ^^ ^^} ⁾ _^^ ^{^} ^^{^} ^_{^^ − ^^ ^^ ^^} ^{^} ^_^ ^{^} _, where ⊗ represents the tensor product and ⊙ represents the Hadamard product. Increments the OFDM symbol counter ( ^^). In case of (404) is false, (410) increments the subcarrier counter ( ^^). (200) starts by defining the parameters of the system to be optimized for DFRC usage. For our method, required parameters include Total power ( ^^_௧), power budget for communication ( ^^_^), number of subcarriers in an OFDM symbol ( ^^), number of OFDM symbols in the transmission frame ( ^^), maximum allowed power for a subcarrier ( ^^_^^௫) and modulation order ( ^^). Initializes the modified subcarriers matrix as the conventionally allocated subcarriers as: ^^^′ = ^^ Here ^^′ and ^^ represents the modified and conventionally allocated subcarrier matrices respectively. An example OFDM frame is given in Figure 2. Calculates the number of subcarriers to be modified by: where ^^_^ is the number of subcarriers to be modified, ^^_ଶ is the number of corner symbols (301) in the given D-QAM constellation, ^^_ଷ is the number of outer edge symbols (302) in the given D-QAM constellation, and ^⌊. ^⌋ represents the floor operation. _{Calculates the weight matrix ^^ to be used. Flow chart in Figure 4 explains how} to obtain this matrix. Initializes the counter for the number of modified subcarriers ( ^^) as zero. A decision block that checks the following statement: ^^ ≤ ^^_^ − 1 506 vectorizes the obtained ^^ from (403) for further processing. Vectorized version of ^^ will be mentioned as ^^. 507 Returns the indices ( ^^) of the sorted ^^. Specifically, values of ^^ gets sorted in an ascending order. Then, the original indices that corresponds to these values are returned as ^^. 508 Obtains the subcarrier index to be modified by: where ^^ ^^ ^^() is the modulus operation. 509 obtains the OFDM symbol index to be modified by: ^_{^ =} ^⌊ _^^ ⁽ _^^ ⁾ _{, ^^} ^⌋ _. 510 A decision block that decides if the symbol at subcarrier ^^( ^^, ^^) is a corner symbol (301). 511 In case (510) is true, (511) modifies the power of the selected subcarrier by: 512 In case (510) is false, (512) is a decision block that decides if the symbol at subcarrier ^^( ^^, ^^) is an outer edge symbol (302) or not. 513 In case (512) is true (513) modifies the power of the selected subcarrier by: ^^^′( ^^, ^^) = ^^( ^^, ^^) + ^^_ௗଷ, where ^^_ௗଷ is a complex value so that ^^^′( ^^, ^^) has the power value of ^^_^^௫. 5¹⁴ _{(514) increments ^^ by one.} Some definitions; DFRC: Dual-function radar communication OFDM: Orthogonal Frequency Division Multiplexing CRB: Cramer-Rao Bound ISL: Integrated Side Lobes PAPR: Peak-to-Average-Power Ratio D-QAM: D-ary Quadrature Amplitude Modulation SNR: Signal-to-Noise Ratio ^^_ఛ: Delay estimation Cramer Rao Lower Bound ^^_௩: Doppler estimation Cramer Rao Lower Bound Detailed Description of the Invention The invention relates to the method proposed in this patent application is an algorithm for waveform design to enhance both radar and communication performance. Proposed method enhances Cramer-Rao Bound (CRB) of the orthogonal frequency division multiplexing (OFDM) waveform for radar performance, while keeping the transmission transparent to the communication receiver. Power extension of conventional QAM constellation diagrams is proposed in this invention. Proposed power allocation is done on the constellation diagram (305) at the DFRC transceiver (100). The algorithms are explained via flowcharts in Figure 4 and Figure 5. System model as shown in Figure 1 consists of a DFRC transceiver (100), radar targets (101) to be detected, and communication receiver (102). The radar targets (101) in the environment that is going to be detected by the DFRC transceiver (100). Note that it is possible to think (102) as a radar target as well. DFRC transceiver (100) transmits a signal that conveys information for the receiver (102). During this transmission (103), DFRC transceiver (100) can also receive reflections (104) of the transmission signal from radar targets (101) and process it to do localization. Proposed method involves the design of the waveform to be used for transmission (103) and radar operation (104). Proposed waveform design is based on OFDM. Figure 2 shows the OFDM frame structure. Proposed method is developed for D-QAM symbols on OFDM subcarriers (200). However, it can be applied for other wireless communicaiton systems. The system model assumes OFDM subcarriers (200) are modulated via D-QAM, which is used in 4G and 5G. Proposed method selects the best OFDM subcarriers (200) for power optimization by generating a weight matrix for any radar performance metric. In this method, CRB is used for illustration purposes. In order to establish communication link (transmission) (103) without any feedforward signaling our method proposes a novel power allocation technique. Proposed power allocation can be seen in Figure 3. Figure 3 consists conventional and proposed constellation points with average symbol energy ^^_^ of the data symbols generated by the selected modulation order. Conventional constellation points can be categorized under three groups. Inner points (300) cannot be used for power allocation. Outer points on the corner symbol (301), and on the edge symbol (302) are suitable for the power allocation. Power of these points can be enhanced to a maximum allowed power value ^^_^^௫. Power enhancement of corner symbol (301) and edge symbol (302) yields proposed constellations (power enhanced corner symbol(303)and power enhanced edge symbol (304) respectively). It is possible to use the proposed waveform design in any communication system that supports sensing applications to improve the radar performance. Proposed algorithms can be integrated into existing and upcoming communication systems easily. Depend on all in formations, the inveniton relates to system which is waveform design for dual- function radar communication (DFRC) systems comprising; • A constellation diagram (305) where power allocation is performed on at the DFRC transceiver (100), • The DFRC transceiver (100) which is the transmitting signal that conveys information for the receiver (102) and which is the part where proposed power allocation described in the constellation diagram (305) takes place, • A communication receiver (102) which demodulates transmitted data symbols of the constellation diagrams (305). The inveniton relates to method which is waveform design method for dual-function radar communication (DFRC) systems comprising; • Defining the parameters of the system to be optimized for DFRC usage by OFDM subcarrier (200), • Initializing the modified subcarriers matrix as the conventionally allocated subcarriers as: ^^^ᇱ = ^^ by subcarrier index (201), _{• Calculating the number of subcarriers to be modified by: ^^^ =} is the number of subcarriers to be modified, ^^_ଶ is the number of corner symbols (301) in the given D-QAM constellation, ^^_ଷ is the number of outer edge symbols (302) in the given D-QAM constellation, • Calculating the weight matrix ^^ to be used, • Initilizing the counter for the number of modified subcarriers ( ^^) as zero, • Checking the following statement: ^^ ≤ ^^_^ − 1 in decision block, • Vectorizing the obtained ^^ from process of initiating of the OFDM symbol counter (m) from zero for further processing, • Returning the indices ( ^^) of the sorted ^^ in an ascending order, • Obtaining the subcarrier index to be modified by: ^^ = ^_{^ ^^ ^^} ⁽ _^^ ⁽ _^^ ⁾ _{, ^^} ⁾ _{, where ^^ ^^ ^^() is the modulus operation,} • Obtaining the OFDM symbol index to be modified by: ^^ = • Checking if the symbol at subcarrier ^^( ^^, ^^) is a corner symbol (301), • In case of the symbol at subcarrier ^^( ^^, ^^) is a corner symbol (301), m_{odifiying the power of the selected subcarrier by: ^^} ^ᇱ( _{^^, ^^} ⁾ ₌ • If the symbol at subcarrier ^^( ^^, ^^) is not a corner symbol (301), that checking if the symbol at subcarrier ^^( ^^, ^^) is an outer edge symbol (302) or not by decision block, • If the symbol at subcarrier ^^( ^^, ^^) is not a corner symbol (301), modifiying of the power of the selected subcarrier by: ^^^ᇱ( ^^, ^^) = c_ompl ^ᇱ _{ex value so that ^^ ( ^^, ^^)} has the power value of ^^_^^௫, •_{Incrementing ^^ by one.} A constellation diagram (305) that only corner symbols (301) and edge symbols (302) are modified to obtain power enhanced corner symbols (303) and power enhanced edge symbols (304) at the transceiver (101) as shown in Figure 3. This constellation design can also be utilized to improve a different perfromance metric than CRB.

Claims

CLAIMS 1. A system which is waveform design for dual-function radar communication (DFRC) systems comprising; • A constellation diagram (305) where power allocation is performed on at the DFRC transceiver (100), • The DFRC transceiver (100) which is the transmitting signal that conveys information for the receiver (102) and which is the part where proposed power allocation described in the constellation diagram (305) takes place, • A communication receiver (102) which demodulates transmitted data symbols of the constellation diagrams (305). 2. A method which is waveform design method for dual-function radar communication (DFRC) systems comprising; • Defining the parameters of the system to be optimized for DFRC usage by OFDM subcarrier (200), • Initializing the modified subcarriers matrix as the conventionally allocated subcarriers as: ^^^ᇱ = ^^ by subcarrier index (201), •_{Calculating the number of subcarriers to be modified by: ^^^ =} where ^^_^ is the number of subcarriers to be modified, ^^_ଶ is the number of corner symbols (301) in the given D-QAM constellation, ^^_ଷ is the number of outer edge symbols (302) in the given D-QAM constellation, • Calculating the weight matrix ^^ to be used, • Initilizing the counter for the number of modified subcarriers ( ^^) as zero, _{• Checking the following statement: ^^ ≤ ^^^ − 1 in decision block,} • Vectorizing the obtained ^^ from process of initiating of the OFDM symbol counter (m) from zero for further processing, • Returning the indices ( ^^) of the sorted ^^ in an ascending order, • Obtaining the subcarrier index to be modified by: ^^ = ^_{^ ^^ ^^} ⁽ _^^ ⁽ _^^ ⁾ _{, ^^} ⁾ _{, where ^^ ^^ ^^() is the modulus operation,} _{• Obtaining the OFDM symbol index to be modified by: ^^ =} ^⌊ _^^ ⁽ _^^ ⁾ _{, ^^} ^⌋ _, • Checking if the symbol at subcarrier ^^( ^^, ^^) is a corner symbol (301), • In case of the symbol at subcarrier ^^( ^^, ^^) is a corner symbol (301), modifiying the power of the selected subcarrier by: ^^^ᇱ( ^^, ^^) = • If the symbol at subcarrier ^^( ^^, ^^) is not a corner symbol (301), that checking if the symbol at subcarrier ^^( ^^, ^^) is an outer edge symbol (302) or not by decision block, • If the symbol at subcarrier ^^( ^^, ^^) is not a corner symbol (301), modifiying of the power of the selected subcarrier by: ^^^ᇱ( ^^, ^^) = ^^( ^^, ^^) + ^^_ௗଷ, where ^^_ௗଷ is an complex value so that ^^^ᇱ( ^^, ^^) has the power value of ^^_^^௫, •_{Incrementing ^^ by one.} 3. The system of according the claim 1 comprising; wherein the constellation diagram (305) that only corner symbols (301) and edge symbols (302) are modified to obtain power enhanced edge symbols (303) and power enhanced outer symbols at the transceiver (101).