1 research outputs found
Multi-layer Interference Alignment and GDoF of the K-User Asymmetric Interference Channel
In wireless networks, link strengths are often affected by some topological
factors such as propagation path loss, shadowing and inter-cell interference.
Thus, different users in the network might experience different link strengths.
In this work we consider a K-user asymmetric interference channel, where the
channel gains of the links connected to Receiver k are scaled with P^{\alpha_k
/2}}, k=1,2,...,K, for 0< \alpha_1 \leq \alpha_2 \leq \cdots \leq \alpha_K \leq
1. For this setting, we show that the optimal sum generalized
degrees-of-freedom (GDoF) is characterized as dsum = (\sum_{k=1}^K \alpha_k +
\alpha_K -\alpha_{K-1})/2, which matches the existing result dsum= K/2 when
\alpha_1 = \alpha_2 = ... = \alpha_K =1. The achievability is based on
multi-layer interference alignment, where different interference alignment
sub-schemes are designed in different layers associated with specific power
levels, and successive decoding is applied at the receivers. While the converse
for the symmetric case only requires bounding the sum degrees-of-freedom (DoF)
for selected two users, the converse for this asymmetric case involves bounding
the weighted sum GDoF for selected J+2 users, with corresponding weights
(2^{J}, 2^{J-1}, ... , 2^{2}, 2^{1}), a geometric sequence with common ratio 2,
for the first J users and with corresponding weights (1, 1) for the last two
users, for J \in {1,2, ... , \lceil\log (K/2)\rceil }