PDF of this tutorialApplying effective echo control via the echo-cancellation platform is one way of improving the overall call clarity on digital cellular networks. Another derives from improvements that must be made within the handset or terminal itself. There also is considerable room to enhance the network itself, focusing principally on vocoder development.
Recent headlines have charted the ongoing commercial battles regarding which digital technologies will eventually emerge as the winners, as equipment manufacturers fight it out. However, this public battle will soon be overshadowed by another battle concerning handsets. At present, there are four major players in the digital cordless market. Europe has cordless telephony (CT2) and digital European cordless telephony (DECT), while Japan has the personal handyphone system (PHS) and the United States has personal communications services (PCS).
Connecting directly into the plain old telephone system, CT2 was one of the first digital technologies to provide low-cost mobile phones. Although the technology worked well, it had a fundamental problem: it could not handle cell handovers. DECT and GSM have overcome this problem and will eventually dominate European cellular services.
During the development of early cordless telephony, attention was paid to basic and enhanced functions and interworking with different network architectures. While the early generation of handsets looked very elegant and aesthetically pleasing, very little attention was paid to designing the handset with echo suppression/cancellation in mind. The result was that they looked good but were extremely poor at reducing acoustic echo.
In the setting of standards for GSM and PCS, handset design and the impact of different design approaches on call quality was researched. As a result, recommendations stated a range of parameters, including sidetone tolerance and echo return loss performance. With the resultant advent of new recommendations with much tighter requirements for handsets, there is a call for greatly improved designs to be implemented. This, complemented by ongoing improvements in network technology and echo cancellation techniques, will bring digital wireless telephony much closer to matching wireline quality.
