Next Previous Post link in WordPress with previous post title / next post title?

single.php

<nav id="nav-single">
    <?php
        $prev_post = get_previous_post(); 
        $id = $prev_post->ID ;
        $permalink = get_permalink( $id );
    ?>
    <?php 
        $next_post = get_next_post();
        $nid = $next_post->ID ;
        $permalink = get_permalink($nid);
    ?>
       <span class="nav-previous"><?php previous_post_link( '%link', __( '<span class="meta-nav">&larr;</span> Previous', 'twentyeleven' ) ); ?> 
            <h2><a href="<?php echo $permalink; ?>"><?php echo $prev_post->post_title; ?></a></h2>
       </span>

       <span class="nav-next"><?php next_post_link( '%link', __( 'Next <span class="meta-nav">&rarr;</span>', 'twentyeleven' ) ); ?>
            <h2><a href="<?php echo $permalink; ?>"><?php echo $next_post->post_title; ?></a></h2>

      </span>
</nav>