RTLS Synchronization Schemes Comparison

Introduction

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.

Comparison

Here is a brief comparison table:

Synchronization Scheme

UDP Sync

TCP Sync (KeepSync)

Maturity Level

STABLE

RELEASE CANDIDATE

Backhaul protocol

UDP Broadcast

TCP Unicast

PortUDP/5001TCP/5001
Communication DirectionRTLS Studio - Transmitter / Anchor - ReceiverRTLS Studio - Receiver / Anchor - Transmitter

RTLS Studio location

Must be within the same L2 network - same broadcast domain

Router cannot be on the communication path.

No limitations*

Cannot have NAT on the network path

Ethernet backhaul

Complete

Complete

Wi-Fi backhaul

Limited to only one Access Point

Scalable Access Point topology

Mixed Ethernet/Wi-Fi backhaul

No

Yes

RTLS Studio

>=1.3.2

>=1.6.0

Anchor FW

>=1.000

>=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."
-Segal's law

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