Yi Zhao Raviraj Adve Teng Joon Lim Beamforming with limited feedback in amplify-and-forward cooperative networks - [transactions letters]. 5145-5149 2008 7 IEEE Transactions on Wireless Communications 12-2 http://dx.doi.org/10.1109/T-WC.2008.070675 db/journals/twc/twc7.html#ZhaoAL08