The following "Directions 2001" article by David W. Allan appeared in the December 2000 issue of GPS World magazine, p. 36. It has been posted with the publisher's permission to www.allanstime.com/Publications/DWA/GPS_World/2000.12.p36.htm =======QUOTE======= As we look to the future, I suggest that there are two major timing opportunities that could greatly benefit systems like GPS and Galileo, as well as many other timing-sensitive systems. These suggestions have not been fully utilized to date, one being a breakthrough invention. I propose a better utilization of clock ensembles and a new invention called "Synchronistic Modulation Detection (SMD)." As an example, both in the application of GPS and in the planning of Galileo, one of the most significant concerns for their use is integrity. In the case of GPS, integrity has been primarily worked from the top down rather than from the bottom-up. By "top down" I mean that integrity is primarily a system responsibility in guaranteeing that all signals transmitted by the system are consistent with specifications as to both position and timing. By 'bottom-up" I mean that the user could also take responsibility for integrity in a very inexpensive, robust, and reliable way. Those working integrity with GPS have brought the response time down to six seconds, during which interval the user would be informed of faulty data coming from the system. Galileo design calls for a one-second response time. Of course, the goal is to have the response time as short as possible while having the highest integrity reasonably attainable as to the validity of that response. We have a great opportunity to increase the integrity and to shorten the response time by utilizing inexpensive, quartz-crystal oscillator ensembles in the user sets. Clock ensembles have the great advantage that they are self-characterizing; hence, they can sense statistical outliers very quickly and with great integrity. This concept was introduced a year ago using theory and simulations demonstrating significant cost-effectiveness. The concept has not been implemented to date. Such ensembles could be made very small as well as inexpensively. We can easily envision high integrity response times well under a second using this "bottom-up" approach. By working the "top-down" and the bottom-up" approaches together, we can produce both a great improvement in integrity as well as a significant decrease in the response time. In a cooperative mode, these two approaches could be integrated and made totally compatible. Legal issues may arise as to where to place responsibility for the data's integrity -- with the system or with the user -- but in a well-designed system that responsibility could be clearly be delineated. The benefits versus the costs for this combined approach are anticipated to be very significant and well worth the effort to bring it about. The first simulations of the new "Synchronistic Modulation Detection" have affirmed the theory allowing effective transfer of time and frequency over various media. In its theoretical limit, SMD shows that the transfer medium does not limit synchronization accuracy and precision. Application opportunities for this approach exist in mobile telephony, synchronization of satellite clocks, and new research experiments. Copyright 2000 GPS World magazine December 2000 issue, p. 36 Advanstar Communications, 859 Willamette Street, Eugene OR 97401, USA