WordPress ajax problem need wordpress expert?

i want to call a function using wordpress ajax and i have done a code for that also. but when i fire a ajax call it always retrun -1. i dont know what is the problem can any body help me to solve.

Here is my code

function.php

 function my_AJAX_processing_function(){
   //echo  $getLetter = $_GET['post_id'];
   print_r($_GET);
   exit;
    global $wpdb;
    global $post;

    $result = $wpdb->get_results('SELECT * FROM wp_posts where post_title LIKE "'.$getLetter.'%" AND post_status = "publish" AND post_type="post"');
    while($row = $result)
    {
      echo '<a href="' . $row["guid"] . '">' . $row['post_title'] . '</a><br>';
    }
    die();
}
add_action('wp_ajax_nopriv_download_track_resources', 'my_AJAX_processing_function');

footer.php

    <script type="text/javascript">
jQuery(function($) {
    $(document).ready(function() {
        $(".downloadtrack").bind('click', function(){
            console.log(this.name);
            var siteurl = '<?php echo esc_url( home_url( '/' ) ); ?>';
            alert(siteurl);
            var val = this.name;
            alert(val);
            var data = {action: 'download_track_resources', post_id: val};
            $.ajax({
                 url:siteurl+'wp-admin/admin-ajax.php',
                 success:function(data){
                   alert(data);
                 }
            });
        });
    });
});
</script>

Html code

<td height="25"><a href="javascript:void(0);" title="Download <?php the_title(); ?>" class="downloadtrack" name="<?php echo $post->ID;?>"><?php the_title(); ?></a></td>

Thanks