Why Phase Synchronization is Critical for JCAS Localization

In the world of Joint Communication and Sensing (JCAS), achieving precise localization is a game-changer. Whether it’s enabling autonomous vehicles to navigate complex environments or powering smart infrastructure, accuracy in localization is critical. One of the most fundamentally essential aspects in this domain is phase synchronization.

 

The Power of Phase in Localization

Phase information locates at the heart of JCAS localization. While many are familiar with amplitude-based approaches, phase-based localization can offer significantly higher accuracy. This becomes particularly evident in scenarios involving multiple transmitters and receivers—often referred to as bistatic configurations.

When signals travel from a transmitter to a target and then to a receiver, the exact phase of the signal contains critical information about the distance (i.e., position) of the target. The delay associated with the signal, denoted as τₙₘ in our equations, depends on the total path length from the transmitter to the target and then to the receiver.

 

But There’s a Catch: Clock Mismatches

Now, imagine each transmitter (Tx) and receiver (Rx) running on separate, unsynchronized clocks. Even tiny discrepancies in timing can introduce significant phase misalignments. These mismatches—commonly referred to as Tx and Rx time errors—distort the received signal , leading to incorrect localization estimates.

In our simplified model, the phase misalignment stems from  and , representing the time errors at the transmitter and receiver respectively. Without synchronization, these subtle shifts can have major consequences.

 

A Visual Example

To visualize the impact, consider the two heatmaps shown below. Both visualize localization results from a bistatic setup.

• The left heatmap assumes perfect time synchronization. The result is a sharp and focused peak that clearly indicates the target’s location.
• The right heatmap, by contrast, includes time synchronization errors. Here, the peak becomes smeared and less distinct, and the surrounding artifacts obscure the true location.

 

Why This Matters

In real-world JCAS applications—such as vehicle-to-everything (V2X) communications, drone swarms, or collaborative robotics—phase errors caused by clock mismatches can lead to degraded performance, increased latency, or even safety risks. Designing systems with robust phase synchronization isn’t just an optimization—it’s a necessity.

As we move toward increasingly distributed and cooperative sensing architectures, understanding and mitigating phase errors will define the next frontier of localization performance in JCAS.

Stay tuned as our project continues to explore innovative synchronization methods that bridge communication and sensing for a safer, smarter future.

 

An article by Qing Zhang.

 

Reference

D. Tagliaferri et al., “Cooperative Coherent Multistatic Imaging and Phase Synchronization in Networked Sensing,” in IEEE Journal on Selected Areas in Communications, vol. 42, no. 10, pp. 2905-2921, Oct. 2024, doi: 10.1109/JSAC.2024.3414609