\begin{array}{l} \mathop {\max }\limits_p \;t\\ s.t.\;t \le SIN{R_i}\\ 0 \le p \le {p_{\max }}\\ SIN{R_i} \ge SIN{R_{i,\min }}\\ SIN{R_i} = \frac{{{p_i}}}{{\sum\limits_{j = 1,j \ne i}^6 {{p_j}} + N}} \end{array}

where p_{\max}, N and SINR_{i, min} are three constants. It seems this is a geometric programming. Yet the first constraint can not be changed in to a convex one. Can anyone help me?