A Comparison between Ook/ask and Fsk Modulation Techniques for Radio Links

Short range unlicensed radio links, with typical ranges of 1 to 100 meters, are becoming more and more popular. Millions of these radios are used today in such applications as automotive keyless entry, tire pressure monitoring, gate openers, wireless security systems, data links, remote meter reading and too many other applications to enumerate. With the number of short range devices (SRD’s) increasing daily, the potential for interference by competing nearby SRD’s or other wireless services has increased dramatically over the last few years. It is becoming more and more important for SRD’s to be capable of reusing the same spectrum shared by other SRD’s. To share the same spectrum, radio receivers must ignore co-channel interfering signals that are weaker than the desired signal. Such a receiver exhibits what is commonly referred to as the “capture effect”. The term “capture effect” is commonly associated with FM or FSK receivers and not with OOK/ASK by the industry in general. The industry also believes that FSK receivers are more sensitive than OOK receivers. This paper will show that, when properly implemented, OOK can actually outperform FSK in both the areas of sensitivity and co-channel interference tolerance.