Contributed Paper Original manuscript received January 4, 2010 Revised manuscript received March 18, 2010 Current version published 06 29 2010 Electronic version published A Novel Time-Domain Synchronous Block Transmission Frame Structure for Broadcasting Return Channel Guanping Lu, Jun Wang, Zhaocheng Wang, Chao Zhang, and Zhixing Yang Abstract—In time-domain synchronous (TDS) block transmission systems, known symbols are padded in the guard interval between data blocks using some specific patterns. The complexity of channel estimation is relatively high for the time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) system. As a result, original TDS- OFDM is only used for downlink broadcasting. This paper proposes a new frame structure based on TDS block transmission. The proposed frame structure can simplify the channel estimation and support the multiuser scenarios, due to the proposed padding sequence and its specific time and frequency allocation pattern. It supports the variable number of frames in one superframe, which provides the flexibility to combat various channel conditions and maintains the system efficiency. Because of these characters, it can be used in wireless uplink channel as an alternative orthogonal frequency division multiple access (OFDMA) structure. Simulation results show that the performance of the proposed frame structure is almost the same as the conventional OFDMA scheme, but has better spectrum efficiency. Therefore, it is preferred to be used in the return channel of terrestrial broadcasting systems. 1 Index Terms—Return Channel, TDS-OFDM, Equalization, Channel Estimation. I. INTRODUCTION Time domain synchronous (TDS) block transmission is widely used in terrestrial broadcasting. Time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM), which has been adopted as China digital television terrestrial multimedia broadcasting (DTMB) standard [1][2], is a typical TDS block transmission system. Conventional terrestrial broadcasting systems only have downlink channel. However, in modern digital television systems, return channel is required to support the interactive services [3]. Previously, orthogonal frequency division multiplexing access (OFDMA) technology has been investigated and used for the wireless uplink broadcasting channel. OFDMA was originally suggested by Sari and Karam for cable television (CATV) networks [4] and lately 1 This work was supported by the National Natural Science Foundation of China under Grant No. 60902003. All the authors are with the Department of Electronic Engineering as well as the Tsinghua National Laboratory of Information Science and Technology (TNList), Tsinghua University, Beijing 100084, P.R. China (e-mail: lugp08@mails.tsinghua.edu.cn). adopted in the uplink of the interaction channel for digital terrestrial television (DVB-RCT) [5]. It is also used in IEEE 802.16 standard [6] for wireless metropolitan area networks (WMANs). Fig. 1. TDS-OFDM frame structure In a TDS block transmission system, known symbols are padded in the gap between data blocks in time domain using some specific patterns. The correlation property and padding patterns of these symbols are important to the system performance. In a conventional TDS-OFDM system, pseudo- random (PN) sequence with cyclic prefix (CP) is padded in the guard interval (GI), as depicted in Fig. 1. Benefited from the PN’s good cross-correlation property, TDS-OFDM system outperformes the traditional coded orthogonal frequency division multiplexing (C-OFDM) system in time synchronization, spectrum efficiency and some other features [7]. However, in conventional TDS-OFDM systems, the inter- symbol interference (ISI) introduced from PN to the following data block is difficult to be removed. [8] has proposed a method based on iterative padding subtraction (IPS) with the increase of hardware complexity. In multiuser scenarios, the ISI mitigation becomes more difficult. On the other hand, the PN sequence is orthogonal in time domain but difficult to be differentiated in frequency domain. That’s why the conventional TDS-OFDM structure can’t be used directly to frequency division multiple access (FDMA) scenarios. Therefore, the upgrade of TDS-OFDM is necessary to accommodate the multiuser access. The new scheme should support high user access peak and hold the good performance of TDS-OFDM in spectrum efficiency and receiver sensitivity. At the same time, the algorithm should be kept as simple as possible. This paper outlines a new frame structure, which is based on the principle of TDS-OFDM but employs several new design concepts. Compared with original TDS-OFDM, the new scheme has three main features. First, the padding sequence is PNMC sequence, which is generated by inverse discrete Fourier transform (IDFT) of padded PN sequence in frequency domain. This sequence has the advantage of 366 IEEE Transactions on Consumer Electronics, Vol. 56, No. 2, May 2010 07 06 2010. 0098 3063/10/$20.00 © 2010 IEEE