Interference-Aware Accurate Signal Recovery in UHF Band Reuse-1 Cellular
OFDMA Downlinks
Abstract
Reuse-1 systems operating in the sub-1 GHz UHF band are limited by
substantial co-channel interference (CCI). In such orthogonal frequency
division multiple access (OFDMA) cellular systems, the inter-sector or
inter-tower interference (ITI) makes accurate signal recovery quite
challenging as sub-1 GHz bands only support single-input single-output
(SISO) links. Interference-aware receiver algorithms are essential to
mitigate the ITI in such low-frequency bands. Such algorithms enable
ubiquitous mobile broadband access over the entire homeland, say with
>95% geographical coverage with quality of service
guarantees. One element of the interference-aware signal recovery is the
least-squares-based joint channel estimation scheme that uses
non-orthogonal pilot subcarriers. This estimator is then compared with a
variant that uses orthogonal pilot subcarriers to bring out the
advantage of this joint estimator. It is shown that the proposed joint
estimator requires fewer pilots to be well-determined when compared to
its under-determined orthogonal counterpart. Moreover, it is easy to
implement and does not require any knowledge of channel statistics. This
work also derives a compensation factor needed for the
interference-aware detector in the presence of inter-carrier
interference (ICI) originating from multiple transmitters. Simulation
results show that the proposed joint channel estimator outperforms
traditional estimators at moderate to high frequency selectivity. The
proposed compensation factor to the joint detector is found to be
essential for recovering the transmitted signal in the absence of
phase-tracking pilots.