Mobile SEO

I need my site e.g domainname.com will appear as m.domainname.com on serps for mobile device users. How do i do this and will my SEO link juice on domainname.com will be same on m.domainname.com? I saw my competitor is doing this too but i don't really know how. Can someone give some guidance to me

You have to write separate code that serves mobile pages when accessed to mobile browsers.

Apply rel = "alternate" tag from the desktop page to corresponding mobile page.

I think this code will help you.

it would be better if you leave the serp as it is but redirect incoming mobile users to m.yourdomain.com version of your website.