Interference-Free OFDM: Rethinking OFDM for Interference Networks with Inter-Symbol Interference

TL;DR

This paper introduces IF-OFDM, a novel multi-carrier scheme that achieves linear sum-spectral efficiency scaling in interference channels with ISI, even without channel state information at the transmitter.

Contribution

The paper proposes a new interference-free OFDM scheme that enables linear spectral efficiency scaling in interference channels with ISI without requiring CSIT.

Findings

Sum-spectral efficiency scales linearly with the number of users K.

Longer desired link impulse response compared to interfering links is beneficial.

Two-stage transmission with CSIT improves spectral efficiency.

Abstract

This paper considers a $K$-user single-input-single-output interference channel with inter-symbol interference (ISI), in which the channel coefficients are assumed to be linear time-invariant with finite-length impulse response. The primary finding of this paper is that, with no channel state information at a transmitter (CSIT), the sum-spectral efficiency can be made to scale linearly with $K$, provided that the desired links have longer impulse response than do the interfering links. This linear gain is achieved by a novel multi-carrier communication scheme which we call \textit{interference-free orthogonal frequency division multiplexing (IF-OFDM)}. Furthermore, when a transmitter is able to learn CSIT from its paired receiver only, a higher sum-spectral efficiency can be achieved by a two-stage transmission method that concatenates IF-OFDM and vector coding based on singular value decomposition with water-filling power allocation. A major implication of the derived results is that separate encoding across subcarriers per link is sufficient to linearly increase the sum-spectral efficiency with $K$ in the interference channel with ISI. Simulation results support this claim.