Issue 3, October 2006

Announcing Unique Worldwide ID Codes and New 64k Sensor IDs

The Need for More Sensor ID Codes
In our May 2006 issue of the VEMCO Monitor newsletter, we announced the Vemco 1.1 2006 51-84 Code Map (see below) to be used in the 2006 season to provide a further 64k Pinger and 256 Sensor ID codes.

As we look to 2007 and beyond, it is becoming clear that the total of 512 sensor IDs that this provides are not nearly enough given the rapidly increasing popularity of these transmitters with the introduction of V9 and V13 versions along with the increasing use of multi-year tags.

There are two major and somewhat conflicting constraints we wanted to meet in providing a solution to the above issue:

1. Ensure that 69 kHz is clear worldwide for migration studies.
   This is in response to user feedback at the recent Passive Acoustic Telemetry Workshop that "tag manufacturers ensure that tag codes provided to researchers will not result in two identical codes ever occurring in the same geographic area, even if only remotely possible". To meet this, we are implementing a strategy (by the start of 2007 at the latest) in which codes would be unique worldwide.



2. Maintain compatibility with existing VR2s as long as possible.
   This is important because of the large installed base and precludes the use of new coding schemes currently under development which would support more than 64k Pinger or 256 Sensor IDs on a single 69 kHz sub map. This constraint does not exist with VR3s and will be removed with an updated VR2 to be released in 2007 but we want to give researchers ample time - at least until the 2009 season - to plan for large collaborative projects.

Providing 64k IDs for Sensor Transmitters
We are introducing a new coding scheme for Sensor Tags in which the tag alternately transmits an R64k ID which uniquely identifies the transmitter and an S256 code which contains an 8 bit ID along with the sensor data. This will be referred to as S64k Coding.

In a simple migration situation, one simply uses the 64k ID to identify the fish and the S256 code provides the sensor data.

The situation is a little more complex in residency situations but the general approach is the same. When an S256 code is detected amongst the various fish, one searches for occurrence of a 64k ID which has been assigned to a sensor tag. This determines which fish the sensor data belongs to. This approach will work perfectly unless two tagged fish simultaneously appear having the same S256 ID code. Two observations can be made with respect to such occurrences:

• The probability of it occurring will be low since Vemco will continue to assign S256 ID codes to maintain as much geographic separation between duplicates as possible.



• Even if the situation does occur, one still knows uniquely (from the 64k ID Codes) which fish were present. It just may not be possible to log the sensor data for the time that the particular tags are simultaneously present.

For more information, please refer to the FAQ on how S64k coding affects detection performance.

Future Direction of Code Map
The new Sensor scheme means that we only need one sub map to support sensor tags and it will support both S64k and Legacy S256 Tags. As a result, the standard Code Map (Vemco 1.1 2006 51-84) will start to evolve in 2007 as shown below.

In summary, this arrangement provides 64k unique tag codes any number of which can be assigned to sensor tags. As sub maps A and B become available, the total number of IDs available will grow to 192k - all compatible with existing VR2s.

Do I Need to Reconfigure My Receiver?

1. No reconfiguration will be required for receivers already set up for the Standard Map (Vemco 1.1 2006 51-84) until such time as Sub Map A or B is reassigned to R64k. This will not occur until 2008 at the earliest. If you are uncertain of your current receiver map configuration, please email the VEMCO Support Group or call 1-902-852-3047.



2. Receivers not already configured for the Standard Map (Vemco 1.1 2006 51-84) will need to be reconfigured to recognize the R64k Sub Map D. Please refer to details under the Support Section of this site.



3. Please note that VRAP and VR28 users will need to reconfigure their maps specifically. Please email the VEMCO Support Group or call 1-902-852-3047.