Iterative receiver design to combat multiple carrier frequency offsets for DVB-T2 in MISO transmission mode

다국어 초록 (Multilingual Abstract)

In the DVB-T2 system incorporating the option
of a multiple-input single-output (MISO) transmission mode,
Alamouti-coded orthogonal frequency division multiplexing (OFDM)
signals are transmitted simultaneously from two spatially
distributed transmitters in a single frequency network (SFN). In
such systems, each transmit-receive link may have a distinct carrier
frequency offset (CFO) due to the Doppler shift and/or frequency
mismatch between the local oscillators, which means that the
received signal experiences multiple CFOs. In the presence of
multiple CFOs, the CFOs cannot be compensated simultaneously by
merely adjusting the compensation frequency at the receiver, thus
residual inter-carrier interference (ICI) always remains. Our
conjecture is that there may exist an optimal compensation frequency
that minimizes the residual ICI. In this dissertation, we first
derive an optimal compensation frequency for multiple CFOs. We also
propose an algorithm that optimizes the compensation frequency for
the MISO-mode DVB-T2 application. Another problem occurring due to
multiple CFOs is that two distinct phase errors are introduced in
desired data, which results in subcarrier phase rotation. These
multiple phase errors cannot be estimated by using conventional
pilot-aided phase error estimation schemes, because the components
of two distinct phase errors are coupled with channel frequency
responses. However, we noticed that when the CFOs are compensated
with the optimized compensation frequency, the components of the
multiple phase errors become a complex conjugate pair and can be
separated from the channel frequency response matrix in the Alamouti
decoding process. Based on this observation, we present the multiple
phase errors estimating scheme, which exploits the binary
phase-shift keying (BPSK) modulated L1-pre data. In addition, the
dissertation proposes a successive-iterative ICI cancellation
technique. This technique successively eliminates the residual ICI
in the initial iteration by exploiting pre-detected data pairs.
Then, in subsequent iterations, the technique performs a fine
interference cancellation using a priori information,
iteratively fed back from the channel decoder. In contrast to
previous works, the proposed techniques do not require estimates of
multiple CFOs. Corresponding performances are evaluated via a full
DVB-T2 simulator. Simulation results show that the DVB-T2 receiver
equipped with the proposed techniques achieves almost the same
performance as ideal multiple CFOs-free systems, even for large
multiple CFOs. Finally, we present iterative joint processing of
data detection, estimation of channels and multiple CFOs and ICI
cancellation. In this scheme, the joint maximum likelihood (ML)
estimator uses the a priori information from the channel
decoder to produce updated estimates of multiple CFOs and channels,
which will in turn help the data detection and ICI cancellation to
make more reliable decision. The whole process is performed in an
iterative manner and it can achieve good bit error rate (BER)
performance with a few iterations.