On the Degrees of Freedom of $K$-User SISO Interference and X Channels   with Delayed CSIT
  The $K$-user single-input single-output (SISO) AWGN interference channel and $2\times K$ SISO AWGN X channel are considered where the transmitters have the delayed channel state information (CSI) through noiseless feedback links. Multi-phase transmission schemes are proposed for both channels which possess novel ingredients, namely, multi-phase partial interference nulling, distributed interference management via user scheduling, and distributed higher-order symbol generation. The achieved degrees of freedom (DoF) values are greater than the best previously known DoFs for both channels with delayed CSI at transmitters. 
Mohammad Javad Abdoli, Akbar Ghasemi, Amir Keyvan Khandani
cs.IT math.IT