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In particular, we present the principles and implementation of structured dirty paper coding (SDPC) that ap- proaches the capacity limit of dirty paper coding in multilayer broadcast- ing. As an alternative to Tomlinson–Harashima precoding (THP), SDPC eliminates the significant performance loss suffered by THP in the low signal-to-noise ratio (SNR) regime due to the modulo operation. The key idea behind the SDPC scheme is the exploitation of the modulation structure of interference, thereby simplifying the demodulation process in hierarchical reception. We exemplify the SDPC technique by implementing an SDPC-based HB system on a real-time test bed. The experimental results show that SDPC delivers the performance of “superposition coding with successive interference cancellation” without extra computation or memory requirements at the receiver side. Index Terms—Dirty paper coding, hierarchical broadcasting, structured dirty paper coding, Tomlinson–Harashima precoding. I. I NTRODUCTION In digital TV or other wireless/wireline broadcasting applications, users at different locations will experience different channel qualities and signal strengths [1]. Ideally, users with better signal strength should be able to receive more information [e.g., high-definition TV (HDTV)] from the broadcasting source than those with lower signal strength (and, therefore, only the basic program). This can be achieved through the combination of source coding and hierarchical modulation [2]–[5]. The most commonly used hierarchical modulation scheme is hierarchical quadratic-amplitude modulation (QAM), where quaternary phase-shift keying (QPSK) carrying the first data stream is combined with another QAM carrying the second data stream, forming a multilevel superposition code [6]. The first QAM enables the basic program with a relatively low reception threshold, whereas the second QAM delivers additional information that can only be decoded at a higher reception threshold (for example, see Digital Video Broadcasting—Terrestrial (DVB-T) [1]). While hierarchical QAM is intuitively simple, it suffers from some performance loss relative to regular QAM. The prime cause of the degradation is the cross interference between multiple data streams. To achieve the true channel capacity, superposition coding or hierarchical QAM with successive cancellation (HQAM-SC) must be employed to recover the loss in hierarchical QAM with independent demodulation (HQAM-ID). This inevitably leads to an extra cost that is sometimes prohibitive in both computation and memory at the receiver side. Manuscript received December 29, 2006; revised September 8, 2007 and October 12, 2007. First published March 3, 2008; current version published November 12, 2008. The review of this paper was coordinated by Dr. C. Yuen. B. Liu, H. Liu, and S. Roy are with the Department of Electrical Engi- neering, University of Washington, Seattle, WA 98105-2500 USA (e-mail: liub@u.washington.edu; huiliu@u.washington.edu; sroy@u.washington.edu). H. Li was with the Department of Electrical Engineering, University of Washington, Seattle, WA 98105-2500 USA. He is currently with the Depart- ment of Electrical and Computer Engineering, North Dakota State University, Fargo, ND 58105 USA (e-mail: hongxiang.li@ndsu.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TVT.2008.919610 0018-9545/$25.00 © 2008 IEEE Authorized licensed use limited to: University of Washington Libraries. Downloaded on July 9, 2009 at 03:04 from IEEE Xplore. Restrictions apply.