Adaptive OFDM Radar for Target Detection in

最前沿的ofdm国外研究成果

78IEEE TRANSACTIONS ON SIGNAL PROCESSING,VOL.59,NO.1,JANUARY2011 Adaptive OFDM Radar for Target Detection in

Multipath Scenarios

Satyabrata Sen,Student Member,IEEE,and Arye Nehorai,Fellow,IEEE

Abstract—We develop methods for detecting a moving target in the presence of multipath re?ections,which exist,for example,in urban environments.We take advantage of the multipath prop-agation that increases the spatial persity of the radar system and provides different Doppler shifts over different paths.We employ a broadband orthogonal frequency pision multiplexing (OFDM)signal to increase the frequency persity of the system as different scattering centers of a target resonate variably at different frequencies.To overcome the peak-to-average power ratio(PAPR)problem of the conventional OFDM,we also use constant-envelope OFDM(CE-OFDM)signaling scheme.First, we consider a simple scenario in which the radar receives only a?nite number of specularly re?ected multipath signals.We develop parametric measurement models,for both the OFDM and CE-OFDM signaling methods,under the generalized multi-variate analysis of variance(GMANOV A)framework and employ the generalized likelihood ratio(GLR)tests to decide about the presence of a target in a particular range cell.Then,we propose an algorithm to optimally design the parameters of the OFDM transmitting waveform for the next coherent processing interval. In addition,we extend our models to study the aspects of temporal correlations in the measurement noise.We provide a few numer-ical examples to illustrate the performance characteristics of the proposed detectors and demonstrate the achieved performance improvement due to adaptive OFDM waveform design.

Index Terms—Adaptive waveform design,asymptotic perfor-mance analysis,multipath,OFDM radar,target detection,urban scenarios.

I.I NTRODUCTION

T HE problem of detection and tracking targets in the pres-ence of multipath,particularly in urban environments, are becoming increasingly relevant and challenging to radar technologies.In[1],we have shown that the target detection capability can be signi?cantly improved by exploiting multiple Doppler shifts corresponding to the projections of the target velocity on each of the multipath components.Furthermore,the multipath propagations increase the spatial persity of the radar system by providing extra“looks”at the target and thus enabling target detection and tracking even beyond the line-of-sight(LOS)

Manuscript received January04,2010;accepted October04,2010.Date of publication October11,2010;date of current version December17,2010.This work was supported by the Department of Defense under the Air Force Of-?ce of Scienti?c Research MURI Grant FA9550-05-1-0443and ONR Grant N000140810849.The associate editor coordinating the review of this manu-script and approving it for publication was Dr.Deniz Erdogmus.

The authors are with the Department of Electrical and Systems Engineering, Washington University in St.Louis,St.Louis,MO63130USA(e-mail: ssen3@ese.wustl.edu;nehorai@ese.wustl.edu).

Color versions of one or more of the?gures in this paper are available online at http://doc.guandang.net.

Digital Object Identi?er10.1109/TSP.2010.2086448[2],[3].Other areas of application in which multipath effects are of primary interest are in low-angle tracking(sea-skimmers) [4]–[7],height?nding[8],[9],and radar-aided navigation and landing systems[10].Similar problems have been addressed in sonar literature due to bottom bounce in shallow waters[11], [12].Note that in[13]we have demonstrated that the direction-?nding capability of a radar system can be improved also by exploiting multipath re?ections close to the sensors.

To resolve and exploit the multipath components it is gener-ally common to use short pulse,multi-carrier wideband radar signals.We consider the orthogonal frequency pision multi-plexing(OFDM)signaling scheme[14],[15],which is one of the ways to accomplish simultaneous use of several subcarriers. The use of OFDM signal mitigates the possible fading,resolves the multipath re?ections,and provides additional frequency di-versity as different scattering centers of a target resonate at dif-ferent frequencies.

Although OFDM has been elaborately studied and com-mercialized in the digital communication?eld[16],it has not so widely been studied by the radar community apart from a few recent efforts[17]–[19].One of major reasons of such unpopularity is that OFDM has a time-varying envelope and that originates a potentially high peak-to-average power ratio (PAPR)[20],[21].A high value of PAPR demands for system components(e.g.,transmitter’s power ampli?er)with a large linear region of operation.However,practical power ampli?ers operate over limited linear region,beyond which they saturate causing nonlinear distortion to the signal[22].

Over the years,a number of approaches have been proposed to deal with the PAPR problem.A comprehensive survey of PAPR reduction techniques can be found in[20]and[23,Ch. 6].One of such methods is to apply the phase modulation transform that achieves the lowest possible PAPR(0dB).In this work,besides considering conventional OFDM,we also include the constant-envelope OFDM(CE-OFDM)signaling scheme[21],[24]–[27],which is based on using a real-valued baseband OFDM signal to phase modulate the carrier.

First,we discuss a detection problem in which the radar has the complete knowledge of the?rst-order(or single bounce) specularly re?ected multipath signals.We also assume that the clutter and measurement noise are temporally white.In Section II,we develop the measurement models,for both the OFDM and CE-OFDM signaling schemes,under the generalized multivariate analysis of variance(GMANOV A) framework[28],[29].Based on these models,in Section III,we formulate the detection problem as a hypothesis test to decide about the presence …… 此处隐藏：4021字，全部文档内容请下载后查看。喜欢就下载吧 ……