Synchronization of anchors is essential part of TDoA location system. In order to deliver sub-meter position accuracy (1 ns = 30 cm) precise time synchronization in sub-nanosecond resolution is required. This is done via UWB radio from master anchor to all other anchors within line of sight range. It is a periodic process driven from server through backhaul (Ethernet/WiFi). There could be dozens of master anchors within the RTLS deployment. Therefore, UWB transmission among anchors must be aligned into timeslots with micro-seconds resolution.
There are two driving schemes over the backhaul network available:
- UDP Broadcast Synchronization - anchors are synchronized via UDP single broadcast message.
- TCP Sync aka KeepSync - anchors are synchronized one by one via continuous TCP connection.
Let's discuss both of them in more detail. While UDP Synchronization works great it is disseminated through UDP broadcast, which is limited to L2 network layer. Thus, it cannot pass through the router, therefore anchors and RTLS Studio server must be on the same broadcast domain. Which can be limiting from several practical aspects.
Sewio developing new synchronization scheme TCP Sync with aim to replace UDP Sync for scalable deployments. It is design to be scalable and independent on underlying network topology.
Here is a brief comparison table:
TCP Sync (KeepSync)
|Communication Direction||RTLS Studio - Transmitter / Anchor - Receiver||RTLS Studio - Receiver / Anchor - Transmitter|
RTLS Studio location
Must be within the same L2 network - same broadcast domain
Router cannot be on the communication path.
Cannot have NAT on the network path
Limited to only one Access Point
Scalable Access Point topology
Mixed Ethernet/Wi-Fi backhaul
>=3.002, recommended 3.005
Combination of different synchronization schemes among Anchors within single deployment is not allowed. All Anchors must be set either to TCP Sync or UDP Sync.
UDP Sync Network Topology Example
TCP Sync Network Topology Example
"A man with a watch knows what time it is. A man with two watches is never sure."
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