Mathematical Problems in Engineering

Volume 2017 (2017), Article ID 5357187, 9 pages

https://doi.org/10.1155/2017/5357187

## HRR Profiling on Integrated Radar-Communication Systems Using OFDM-PCSF Signals

^{1}Communication Engineering Research Center, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen, China^{2}School of Information Science and Technology, East China Normal University, Shanghai, China

Correspondence should be addressed to Xuanxuan Tian

Received 26 April 2017; Revised 23 August 2017; Accepted 6 September 2017; Published 22 October 2017

Academic Editor: Federica Caselli

Copyright © 2017 Xuanxuan Tian et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

In order to improve both the transmission data rate and the range resolution simultaneously in integrated radar-communication (RadCom) systems, orthogonal frequency-division multiplexing with phase-coded and stepped-frequency (OFDM-PCSF) waveform is proposed. A corresponding high resolution range (HRR) profile generation method is also presented. We first perform OFDM-PCSF waveform design by combining the intrapulse phase coding with the interpulse stepped-frequency modulation. We then give the ambiguity function (AF) based on the presented waveforms. Then, the synthetic range profile (SRP) processing to achieve HRR performance is analyzed. Theoretical analysis and simulation results show that the proposed methods can achieve HRR profiles of the targets and high data rate transmissions, while a relative low computational complexity can be achieved.

#### 1. Introduction

Recently, the integrated radar-communication systems using orthogonal frequency division multiplexing (OFDM) signals have been popular [1, 2], where communication and radar functionalities are operated simultaneously on a single platform to improve the spectrum efficiency and cost-effectiveness. There is a large area of applications that would possibly benefit from such systems. One typical example is the intelligent transportation system, which requires both communication links among vehicles and active environment sensing capabilities. With a unified platform, all vehicles on the road could interact as a cooperative radar sensor network, which provides unique safety features and intelligent traffic routing [1]. Another example would be related to ultrawideband (UWB) radar systems for reconnaissance and navigation purposes [2]. In such networks, each sensor can perform synthetic aperture radar (SAR) imaging and ground moving target indication (GMTI) and then share it with other sensor nodes through its own communication links.

Orthogonal frequency division multiplex (OFDM) waveforms, along with coding schemes, are called multicarrier complementary phase-coded (MCPC) signals [3, 4] to enhance radar capabilities. A UWB digital system to measure the radar cross section (RCS) of targets has been proposed in [5], where the transmitted waveform is called OFDM phase-coded (OFDM-PC) signal. The OFDM-PC signals are able to minimize the peak-to-mean envelope power ratio (PMEPR). Due to the advantages on the high spectral efficiency, thumbtack-like ambiguity function (AF) [3], good Doppler tolerance [6], and flexible waveform characteristics and easy implementations [7], OFDM and its variations [7] are attractive to both academic and industrial researchers.

When considering the presented investigations related to range processing approaches in the integrated systems using traditional OFDM signals, a typical approach of direct match filtering has been presented in [2], where one-bit data is carried on each subcarrier, which results in a low data rate and high range sidelobes. An adaptive pulse compression approach to improve the detection performance has been exploited in [8]. However, a high computational effort will be introduced on the cyclic iterative algorithm. A subspace-based approach based on rotation invariance [9] and a modulation symbol-based processing approach based on element-wise division technique [1] are presented to perform range estimation, which also require high computational complexity due to the high resolution range (HRR) performance.

To improve the transmission data rate, a subspace projection approach using the multi-OFDM chirps-based transmit pulses has been appeared in [10]. However, the approach is based on a two-dimensional parameter-searching method, which suffers from a high computational burden. To improve the data rate and range resolution, OFDM linear frequency modulation (LFM) signals based on fractional Fourier transform (FRFT) [11] and a random stepped-frequency (SF) OFDM signal based on correlation processing [12] have been given. However, both signals are prone to the range-Doppler coupling, which may lead to HRR performance degradation. An OFDM-PC strategy along with the discrete Fourier transform (DFT) and correlation processing [13] has been developed to perform range and velocity estimation. However, one of the main drawbacks for OFDM-PC signals in the radar context is that the larger instantaneous bandwidth usually follows higher sampling rate requirements, resulting in higher computational complexity.

In view of the above, we give an OFDM phase-coded stepped-frequency (OFDM-PCSF) based strategy as an improvement to [13] by combining the intrapulse (within the pulse) phase coding and interpulse (among different pulses) SF modulation. OFDM-PCSF signals can essentially synthesize the instant narrow bandwidth into effective large bandwidth, which provides improved data rate and range resolution, with low Doppler sensitivity and computational complexity. The proposed scheme, taking full advantage of the signal structure to achieve HRR performance with low computational complexity, is also provided on the receiver end.

The rest of this paper is organized as follows. The signal model of OFDM-PCSF integrated system is given in Section 2. The analysis of AF for OFDM-PCSF pulse train is presented in Section 3. The principle of SRP processing approach is explained in Section 4. The simulation results are presented in Section 5. Conclusion of the paper is given in Section 6.

#### 2. Signal Model

##### 2.1. Transmitted Signals

We assume that the OFDM-PCSF signals consist of a coherent burst of pulses. The pulse repetition period is . Each pulse is realized by OFDM-PC signals, which transmit on subcarriers simultaneously. The communication messages on each subcarrier are mapped onto a sequence of bits. Then the transmitted signals can be described aswhere is the complex envelope of OFDM-PC single pulse [13] given bywherewhere is the envelope of the phase-coded signal on the th subcarrier, and are the numbers of subcarriers and chips, respectively, is the chip duration, is the subcarrier separation, , is the transmitted PC sequence on the th subcarrier and the th pulse, and is given by

In (1), represents the carrier frequency of the th pulse, where is the radio frequency (RF) carrier frequency and is the bandwidth of the individual pulse. Therefore, the effective bandwidth of the OFDM-PCSF pulse train is . The structure of the pulse train can be seen in Figure 1, where is the pulse width.