PHP Sub-string breaks on words

<?php
$complete_url = "When using wireless sensor networks for real-time data transmission, some critical points should be considered. Restricted computational power, memory limitations, narrow bandwidth and energy supplied present strong limits in sensor nodes. Therefore, maximizing network lifetime and minimizing energy consumption are always optimization goals. To reduce the energy consumption of the sensor network during image transmission, an energy efficient image compression scheme is proposed. The image compression scheme reduces the required memory.";
$length = 114;

echo " ";

echo " ";

if(trim($complete_url)!="" && strlen ($complete_url)>=$length) {
    $pos=strpos($complete_url, " ", $length);
    $substring = substr($complete_url, 0, $pos)." ...";
    echo " ";
}

//FUNCTION //PHP Sub-string breaks on words
function substrbw($complete_text="", $length=0) {
if(trim($complete_text)!="" && strlen ($complete_text)>=$length) {
$pos=strpos($complete_text, " ", $length);
$substring = substr($complete_text, 0, $pos);
return $substring;
}
else {
return $complete_text;
}
} ?>