NOVEL OFDM FRAME STRUCTURE AND CHANNEL ESTIMATION TECHIQUE FOR DIGITAL TELEVISION TERRESTRIAL BROADCASTING SYSTEM

Abstract

Orthogonal frequency division multiplexing (OFDM) is the most popular technology to transmit data in many wireless communication applications including digital television terrestrial broadcasting (DTTB). Over fast fading channels, iterative padding subtraction (IPS) based time domain synchronous OFDM (TDS-OFDM) has good spectral e ciency, but at a cost of high computational complexity. Dual pseudo noise padding (DPNP) based TDS-OFDM is used to reduce the computational complexity compared to IPS-based TDS-OFDM by compromising with spectral e ciency. An alternate time-frequency- domain (TFD) based frame structure enhances the system performance of TDS-OFDM over fast time-varying channel at a cost of high computational complexity. This dissertation proposes a novel frame structure for OFDM-based DTTB system. The proposed frame structure incorporates pilots in the time domain for channel estima- tion purpose. The cyclic pre x and modulable orthogonal sequence (MOS) in TFD-based frame structure are retained in the proposed frame structure. Since the proposed frame structure is completely de ned in time domain, channel estimation and equalization be- come easier. Estimation and equalization of channel are needed before deploying a DTTB system in practical environment. Using the new frame structure, a novel channel estimation technique is proposed that works in two stages. In the rst stage, the MOS in guard interval is used to estimate the channel delay and gain. Later in the second stage, the channel gain estimated in rst stage are used as initial weights of an adaptive lter. Fur- ther, these weights are tuned by applying least mean square (LMS) or recursive least squares algorithm. The bit-error-rate (BER) performance of proposed technique is bet- ter compared to DPNP-based TDS-OFDM. In addition, computational complexity of proposed LMS-based method is low compared to TFD-based TDS-OFDM system over static, slow and fast time-varying channels. Less than 1.5% of the total sub-carriers are used as redundant pilots, and therefore the loss in spectral e ciency is negligible in the proposed frame structure. Apart from DTTB this frame structure can also be used for other wireless communication applications.