The problem of joint collaborative relay beamforming and linear receiver design is addressed for uplink multi-user relay network where each user transmits independent data streams to a multi-antenna basestation through a decentralized relay network. Two dfferent but related design approaches are proposed with different dsign criteria. In the first approach, the total transmit power of al the relay nodes is minimized under individual SINR constraint. In the second approach,the minimal SINR is maximized subject to the aggegate power constraint on the relay nodes. The optimal linear receivers are derived for each collaborative relay beamforming vector, and the collaborative bemforming vectors are explicitly obtained. We show that both joint optimization problems can be reformulated into a standard semi-definite programming problem by performing relaxation on the feasible region. The resulting problem can be solved optimally by using the interior-point method.