The best outer bound on the capacity region of the two-user Gaussian
Interference Channel (GIC) is known to be the intersection of regions of
various bounds including genie-aided outer bounds, in which a genie provides
noisy input signals to the intended receiver. The Han and Kobayashi (HK) scheme
provides the best known inner bound. The rate difference between the best known
lower and upper bounds on the sum capacity remains as large as 1 bit per
channel use especially around g2=Pβ1/3, where P is the symmetric power
constraint and g is the symmetric real cross-channel coefficient. In this
paper, we pay attention to the \emph{moderate interference regime} where
g2β(max(0.086,Pβ1/3),1). We propose a new upper-bounding technique
that utilizes noisy observation of interfering signals as genie signals and
applies time sharing to the genie signals at the receivers. A conditional
version of the worst additive noise lemma is also introduced to derive new
capacity bounds. The resulting upper (outer) bounds on the sum capacity
(capacity region) are shown to be tighter than the existing bounds in a certain
range of the moderate interference regime. Using the new upper bounds and the
HK lower bound, we show that Rsymββ=21βlog(β£gβ£P+β£gβ£β1(P+1)) characterizes the capacity of the symmetric real
GIC to within 0.104 bit per channel use in the moderate interference regime
at any signal-to-noise ratio (SNR). We further establish a high-SNR
characterization of the symmetric real GIC, where the proposed upper bound is
at most 0.1 bit far from a certain HK achievable scheme with Gaussian
signaling and time sharing for g2β(0,1]. In particular, Rsymββ
is achievable at high SNR by the proposed HK scheme and turns out to be the
high-SNR capacity at least at g2=0.25,0.5.Comment: Submitted to IEEE Transactions on Information Theory on June 2015,
revised on November 2016, and accepted for publication on Feb. 28, 201