$1$Consider $4$ stations A$,$ B$,$ C$,$ and D share a communication link during one bit interval.$$ For encoding, the following rules should be followed:$$

a$-$ If a station needs to send a $0$ bit, it sends a $-1.$

b$-$ If it needs to send a $1$ bit, it sends a $+1.$

c$-$ When a station is idle, it sends no signal $(0).$

d$-$ Assume stations A and B are sending a $0$ bit and station C is sending a $1$ bit while station D is silent for that period.$$

$$Draw the multiplexer and the de$-$multiplexer and the W$1=[-1].$