Wireless Secrecy in Cellular Systems with Infrastructure--Aided   Cooperation
  In cellular systems, confidentiality of uplink transmission with respect to eavesdropping terminals can be ensured by creating intentional inteference via scheduling of concurrent downlink transmissions. In this paper, this basic idea is explored from an information-theoretic standpoint by focusing on a two-cell scenario where the involved base stations are connected via a finite-capacity backbone link. A number of transmission strategies are considered that aim at improving uplink confidentiality under constraints on the downlink rate that acts as an interfering signal. The strategies differ mainly in the way the backbone link is exploited by the cooperating downlink- to the uplink-operated base stations. Achievable rates are derived for both the Gaussian (unfaded) and the fading cases, under different assumptions on the channel state information available at different nodes. Numerical results are also provided to corroborate the analysis. Overall, the analysis reveals that a combination of scheduling and base station cooperation is a promising means to improve transmission confidentiality in cellular systems. 
Petar Popovski and Osvaldo Simeone