Algorithm 1: Autonomous power decision.

Require:${\mathbf{p}}_{\max }^j={\mathit{p}}^U$, ${\mathbf{p}}_{\min }^j>\mathbf{0}$$\forall j=1,2,\cdots ,J$; Ensure:$\mathbf{p}$  1: Each user picks up its spreading sequences.  2: Each user selects a random power level $p^j\in [p_{\min }^j,p_{\max }^j]$.  3: The BS detects user signals.  4: The BS calculates the optimal power $p^{j,\mathrm{opt}}$.  5: The BS compares each user power $p^j$ with the nearest power level from $p^{j,\mathrm{opt}}$.  6: The BS sends an acknowledgment to each user:  (a) If $p^{j,\mathrm{opt}}=p^u$⇒$\mathrm{ACK}=3$  (b) If $p^j>p^{j,\mathrm{opt}}$⇒$\mathrm{ACK}=2$  (c) If $p^j<p^{j,\mathrm{opt}}$⇒$\mathrm{ACK}=1$  (d) If $p^j=p^{j,\mathrm{opt}}$⇒$\mathrm{ACK}=0$  7: If the propagation environment is changed, the BS sends a one bit ACK: $\mathrm{Stat}=1$.  8: Each user updates its $p_{\min }^j$ or $p_{\max }^j$:  (a) If $\mathrm{ACK}=3$⇒$p^j=p^u>0$  (b) If $\mathrm{ACK}=2$⇒$p_{\max }^j=p^j\le p^U$ If $\mathrm{Stat}=1$⇒$p_{\min }^j=0$  (c) If $\mathrm{ACK}=1$⇒$p_{\min }^j=p^j>0$ If $\mathrm{Stat}=1$⇒$p_{\max }^j=p^U$  (d) If $\mathrm{ACK}=0$⇒ no update  9: Return to Step 2