... approximation in (20), weconsider a hexagonal cellular layout with cell sectoring. Byusing 120-degree sectoring in each cell, every 3 neighboringcells can coordinate with each other to serve users in ... Karakayali, R. Yates, G. Foschini, and R. Valenzuela, “Opti-mum zero-forcing beamforming with per-antenna power con-straints,” in Proceedings of the IEEE International Symposiumon Information Theory ... Signal Processing,submitted.[9] T. Tamaki, K. Seong, and J. M. Cioffi, “Downlink MIMOsystems using cooperation among base stations in a slowfading channel,” in P roceedings of the IEEE InternationalConference...