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.
