On the Feasibility of the CJ Three-User Interference Alignment Scheme for SISO OFDM Systems

The Cadambe-Jafar three-user interference alignment (CJ-3U-IA) scheme for single-input-single-output (SISO) systems is efficient to deal with wireless interference. The CJ-3U-IA scheme assumes that the channel fading coefficients of different time or frequency slots are independent. However, the independence of channel coefficients is not a necessary condition. For orthogonal frequency-division multiplexing (OFDM) systems, the channel coefficients of different frequency slots are generally not independent. In this letter, the necessary and sufficient conditions for the feasibility of the CJ-3U-IA scheme in three-user SISO OFDM systems are theoretically derived. An example has been shown that in the time domain, if a minimum of three channel impulse responses (CIRs) out of a total of nine CIRs have at least two significant taps while the other CIRs only have one significant tap, the CJ-3U-IA scheme is still feasible.