IEEE TRANSACTIONS ON SIGNAL PROCESSING (ACCEPTED) 1 Parameterized Cancellation of Partial-Band Partial-Block-Duration Interference for Underwater Acoustic OFDM Zhaohui Wang, Student Member, IEEE, Shengli Zhou, Senior Member, IEEE, Josko Catipovic, Member, IEEE, and Peter Willett, Fellow, IEEE Abstract—Despite that underwater acoustic channels are well known to contain various interferences, research on interference mitigation in underwater acoustic communications has been very limited. In this paper, we deal with a wideband orthogonal frequency division multiplexing (OFDM) transmission in the presence of an external interference which occupies partially the signal band and whose time duration is shorter than the OFDM block. We parameterize the unknown interference waveform by a number of parameters assuming prior knowledge of the frequency band and time duration of the interference, and develop an iterative receiver, which couples interference detec- tion via a generalized likelihood-ratio-test (GLRT), interference reconstruction and cancellation, channel estimation, and data detection. In addition to simulation results, we verify the receiver performance using data sets collected from two experiments. In both time-invariant and time-varying channels, the proposed iterative receiver achieves robust performance in the presence of unknown interference. Index Terms—Partial-band short-duration interference, OFDM, underwater acoustic communications, parameterized iterative interference mitigation. I. I NTRODUCTION Interference mitigation in communication systems has been an interesting topic since the advent of communication. As opposed to the internal interference, such as the intersymbol interference (ISI) in single carrier transmissions, or intercarrier interference (ICI) in multicarrier transmissions, interference from the external environment, such as jamming and unin- tentional interference, could result in significant performance degradation. The interference in underwater acoustic (UWA) communications includes both unintentional interference, such as interference from sonar operations and marine mammals, and malicious jamming [1]. Manuscript submitted May 19, 2011, revised September 10, 2011 and November 18, 2011, accepted December 4, 2011. Z.-H. Wang, and S. Zhou are supported by ONR N00014-09-1-0704 (PECASE). This work was presented in part at the 2011 the International Workshop on UnderWater Networks (WUWNet) in Seattle, USA. The associate editor coordinating the review of this manuscript and approving it for publication was Prof. Sofiene Affes. Copyright c 2011 IEEE. Personal use of this material is permitted. How- ever, permission to use this material for any other purposes must be obtained from the IEEE by sending a request to pubs-permissions@ieee.org. Z.-H. Wang, S. Zhou, and P. Willett are with the Department of Elec- trical and Computer Engineering, University of Connecticut, 371 Fair- field Way U-2157, Storrs, CT 06269, USA (email: {zhwang,shengli, wil- lett}@engr.uconn.edu). J. Catipovic is with the Naval Undersea Warfare Center, Newport, RI 02841, USA (email: josko.catipovic@navy.mil). This work was primarily motivated by our observations in an experiment held in March, 2010, over one underwater network deployed at the Atlantic Undersea Test and Evaluation Center (AUTEC) around Andros Island near the Tongue of the Ocean, Bahamas [2], [3]. During the transmission of communication signals, other unknown users were transmit- ting multiple sonar waveforms in the same environment. The received communication signal at certain sensors was thus superimposed with the sonar transmissions as shown in Fig. 1, which leads to significant performance degradation. Although such interference occurs quite often during the UWA communications, limited research results for its mitigation are available. For example, although considerable advancements have been made for OFDM and single-carrier transmissions with frequency domain equalization in recent years; see e.g., [4]–[16] and references therein, all of these are investigated in the absence of interference. On the other hand, various methods for interference sup- pression have been investigated for wireless communications in the last two decades [17], [18]. Mainly, the external in- terferences are divided into two categories according to the time-frequency characteristics: i) impulsive interference with short time duration and large bandwidth; and ii) narrowband interference with small bandwidth and long time duration. A. Impulsive Noise Suppression For impulsive noise suppression in multicarrier transmis- sions, the characteristics of short time duration is usually utilized. Using the time-domain clipping, an erasure/Reed- Solomn (RS) decoding scheme for impulsive noise mitigation was proposed in [19]; the proposed scheme was improved in [20] by performing joint erasure marking and Viterbi decoding, but at the cost of high computational complexity. An iterative interference mitigation strategy was proposed in [21], where the frequency components of the impulsive noise and the in- formation symbols were estimated iteratively, and a threshold detector was used to reconstruct the impulsive noise events in the time domain. The proposed receiver structure was further developed in [22] to increase its convergence rate by employ- ing a syndrome decoder. However, both approaches assume perfect channel knowledge, which is impractical in most cases. For channel estimation in the presence of impulsive noise, a support vector machine based algorithm was proposed in [23] by introducing a ǫ-Huber cost function. An iterative channel