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DPC-Based Hierarchical Broadcasting: Coding for Wireless Communications: Performance Results,” IEEE J IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 57, NO. 6, NOVEMBER 2008 3895 [3] V. Tarokh, H. Jafarkhani, and A. R. Calderbank, “Space–time block DPC-Based Hierarchical Broadcasting: coding for wireless communications: Performance results,” IEEE J. Sel. Design and Implementation Areas Commun., vol. 17, no. 3, pp. 451–460, Mar. 1999. [4] T. A. Tran and A. B. Sesay, “A generalized linear quasi-ML decoder of OSTBCs for wireless communications over time-selective fading Bin Liu, Student Member, IEEE, channels,” IEEE Trans. Wireless Commun., vol. 3, no. 3, pp. 855–864, Hongxiang Li, Student Member, IEEE, May 2004. Hui Liu, Senior Member, IEEE, and Sumit Roy, Fellow, IEEE [5] A. Vielmon, Y. Li, and J. R. Barry, “Performance of Alamouti transmit diversity over time-varying Rayleigh-fading channels,” IEEE Trans. Wire- less Commun., vol. 3, no. 5, pp. 1369–1373, Sep. 2004. Abstract—This paper discusses interference precancellation in digital [6] D.-B. Lin, P.-H. Chiang, and H.-J. Li, “Performance analysis of two- hierarchical broadcasting (HB). In particular, we present the principles branch transmit diversity block-coded OFDM systems in time-varying and implementation of structured dirty paper coding (SDPC) that ap- multipath Rayleigh-fading channels,” IEEE Trans. Veh. Technol., vol. 54, proaches the capacity limit of dirty paper coding in multilayer broadcast- no. 1, pp. 136–148, Jan. 2005. ing. As an alternative to Tomlinson–Harashima precoding (THP), SDPC [7] P.-H. Chiang, D.-B. Lin, and H.-J. Li, “Performance analysis of two- eliminates the significant performance loss suffered by THP in the low branch space–time block-coded DS-CDMA systems in time-varying mul- signal-to-noise ratio (SNR) regime due to the modulo operation. The tipath Rayleigh fading channels,” IEEE Trans. Veh. Technol., vol. 56, key idea behind the SDPC scheme is the exploitation of the modulation no. 2, pp. 975–983, Mar. 2007. structure of interference, thereby simplifying the demodulation process in [8] J. Kim, R. W. Heath, Jr., and E. J. Powers, “Receiver designs for hierarchical reception. We exemplify the SDPC technique by implementing Alamouti coded OFDM system in fast fading channel,” IEEE Trans. an SDPC-based HB system on a real-time test bed. The experimental Wireless Commun., vol. 4, no. 2, pp. 550–559, Mar. 2005. results show that SDPC delivers the performance of “superposition coding [9] X. Ma, G. Leus, and G. B. Giannakis, “Space–time-Doppler block cod- with successive interference cancellation” without extra computation or ing for correlated time-selective fading channels,” IEEE Trans. Signal memory requirements at the receiver side. Process., vol. 53, no. 6, pp. 2167–2181, Jun. 2005. [10] I. S. Gradshteyn and I. M. Ryzhik, Table of Integrals, Series, and Prod- Index Terms—Dirty paper coding, hierarchical broadcasting, structured ucts, 5th ed. San Diego, CA: Academic, 1994. dirty paper coding, Tomlinson–Harashima precoding. [11] P. Bello, “Characterization of randomly time-variant linear channels,” IEEE Trans. Commun., vol. COM-11, no. 4, pp. 360–393, Dec. 1963. [12] C. E. Shannon, “Communication in the presence of noise,” Proc. IRE, I. INTRODUCTION vol. 37, pp. 10–21, 1949. [13] L. Zheng and D. N. C. Tse, “Diversity and multiplexing: A fundamental In digital TV or other wireless/wireline broadcasting applications, tradeoff in multiple-antenna channels,” IEEE Trans. Inf. Theory, vol. 49, users at different locations will experience different channel qualities no. 5, pp. 1073–1096, May 2003. [14] R. U. Nabar, H. Bolcskei, and A. J. Paulraj, “Diversity and outage perfor- and signal strengths [1]. Ideally, users with better signal strength mance in space–time block coded Ricean MIMO channels,” IEEE Trans. should be able to receive more information [e.g., high-definition Wireless Commun., vol. 4, no. 5, pp. 2519–2532, Sep. 2005. TV (HDTV)] from the broadcasting source than those with lower [15] W. Su, Z. Safar, and K. J. R. Liu, “Diversity analysis of space–time signal strength (and, therefore, only the basic program). This can be modulation over time-correlated Rayleigh-fading channels,” IEEE Trans. Inf. Theory, vol. 50, no. 8, pp. 1832–1840, Aug. 2004. 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: [email protected]; [email protected]; [email protected]). 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: [email protected]). 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. 3896 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 57, NO. 6, NOVEMBER 2008 Fig. 1. (a) DPC implementation with THP. (b) DPC implementation with known interference structure. Dirty paper coding (DPC) provides an intriguing alternative to and its performance are introduced in Section V. Finally, a conclusion receiver-end successive cancellation with interference precancellation is drawn in Section VI. at the transmission side [7]. Based on the results from Costa’s ground- breaking paper in 1983, the capacity of a power-constrained channel with known interference is the same as that without interference. II. DPC AND HB The hierarchical broadcasting (HB) situation can be precisely cast into a DPC framework, where multiple data streams are character- A. DPC ized as known interference to each other. The significant advantage DPC was introduced by Costa in [7]. In Fig. 1(a), an AWGN of DPC over superposition coding, particularly in TV broadcast- channel is corrupted by interference s, which is noncausally known ing, is that interference is presubstracted at the transmitter. There- at the transmitter. The source output v is the input to the precoder, 2 fore, only independent decoding is needed to decode different data whose output x obeys the transmitter power constraint: E|x| ≤ Px. streams. Interference s and noise are assumed to be Gaussian independent At a high signal-to-noise ratio (SNR), DPC can be approximated by identically distributed. Pn is the power of noise. Costa’s result shows Tomlinson–Harashima precoding (THP) [8], [9]. Unfortunately, THP that the capacity of this channel is the same as if interference were has been shown to suffer from a 1.53-dB shaping loss in the high SNR absent, i.e., CDPC =(1/2) log(1 + (Px/Pn)). regime [10]. In the low SNR regime, where broadcasting normally op- In the high SNR regime, DPC can be approximated by THP [15]. erates, the THP performance loss is even more significant, typically in THP was originally introduced in the context of ISI channel [8], [9]. the range of 4–5 dB [11]. The cause of this degradation is quantization The basic idea is illustrated in Fig. 1(a). In the first stage, interference s (i.e., modulo operations) at the transmitter and the receiver. Several is directly subtracted from source v to compensate the interference in trellis precoding-based algorithms have been developed to recover the the channel. However, the power of v − s may exceed the transmitter losses of THP [11], [14]. While in principle these algorithms can be power constraint. A modulo operator is applied to enforce the power applied to HB, the added complexity makes them less desirable in constraints at the transmitter. The quantizer level Λ is chosen to broadcasting applications. meet the power constraints without causing any ambiguity in v.At Motivated by the promises of DPC and HB, this paper discusses the receiver, another modulo operation is performed to recover the DPC-based HB. Our focus is on the design of low-cost high- intended message v. performance DPC techniques that can be used in practical broadcasting In [10], the capacity of the THP channel is shown to be systems. In particular, we seek to develop low-complexity approaches that can reduce or eliminate the modulo loss at a low SNR. Toward this I(ˆv; v)=h ((v + n)modΛ)− h(n mod Λ). end, we observe that in most communication systems [e.g., wireless (1) broadcasting and vector Digital Subscriber Line (DSL)], the inter- ference structure is available to all receivers.
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