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Latest News || 27 October 2026: Dr Soumava Mukherjee's invited talk at Queen's University Belfast joined device-level hardware innovation with channel-level control. || 22 October 2026: I received a Certificate of Appreciation for serving as a reviewer for IEEE IMAS 2026. || 15 October 2026: I presented a poster on beam-domain ML fingerprinting for RIS-aided mmWave localisation at the Centre for Wireless Innovation's annual symposium. || 15 October 2026: CWI's annual symposium brought research and industry perspectives on 6G, ISAC, optical wireless, AI, and future networks to Queen's University Belfast. || 14 October 2026: Erik Nordell of Ericsson visited our Keysight Lab for a live RIS-assisted video streaming demonstration.
Tarek Hassan
Knowledge Hubris assisted isac system1. How ISAC Connects to RIS

ris assisted isac system learning note

1. How ISAC Connects to RIS

Follow a waveform from data transmission to a controlled reflection and a target echo, then recover the correct path distance.

At a glance

  • Two jobs, one waveformISAC carries user data and extracts target information from echoes; RIS controls a propagation path.
  • A known detourA reciprocal RIS echo measures BS–RIS plus RIS–target distance, not the straight BS–target distance.
  • Visibility is only the startA geometrically open reflected path still needs enough received power and a calibrated receiver.

The Connection in One Sentence

ISAC measures the world while carrying data; RIS changes a path through that world. Integrated sensing and communication (ISAC) uses radio resources for both tasks. A reconfigurable intelligent surface (RIS) applies programmed phase changes to incident waves.

A base station (BS) can send data toward a user while illuminating a target. The user decodes the message; the sensing receiver looks for a delayed, Doppler-shifted echo. Doppler is the frequency shift caused by radial motion. A passive RIS redirects incident energy without regenerating the waveform.

References for this section3

What Each Part Provides

  • ISAC waveform: a known transmitted signal from which a receiver can estimate delay, direction and motion.
  • RIS configuration: a controlled pattern of element phases that changes constructive and destructive interference.
  • Known surface location: geometry that helps interpret a reflected path, provided timing and path identity are known.

Non-line-of-sight (NLoS) means that the direct path is blocked. A RIS can offer an indirect path when both BS–RIS and RIS–target segments are visible. It does not see through an opaque obstacle: a building blocking either of those segments can still defeat the route.

References for this section3

What the Echo Delay Measures

Consider the reciprocal route BS → RIS → target → RIS → BS. Let d1d_1 be BS–RIS distance, d2d_2 RIS–target distance, cc propagation speed and τ\tau calibrated round-trip delay:

τ=2(d1+d2)c,d2=cτ2−d1.\tau=\frac{2(d_1+d_2)}{c},\qquad d_2=\frac{c\tau}{2}-d_1.

The quantity cτ/2c\tau/2 is the one-way path length, not straight-line distance to the BS. At 40 m and 20 m, the full echo travels 120 m and returns after approximately 400 ns.

With waveform bandwidth BB, nominal separation of two echoes along this path is Δd2=c/(2B)\Delta d_2=c/(2B). Bandwidth does not remove clock bias, resolve every multipath ambiguity or automatically supply a second spatial coordinate.

What distance does the echo actually measure?

1. Formula and symbols
τ=2(d1+d2)/c\tau=2(d_1+d_2)/c
d2=cτ/2−d1,Δd2=c/(2B)d_2=c\tau/2-d_1,\quad\Delta d_2=c/(2B)
  • d1d_{1}: known BS–RIS distance
  • d2d_{2}: RIS–target distance
  • τ\tau: reciprocal four-leg echo delay
  • cc: wave speed
  • BB: bandwidth

This is a total-path timing measurement, not an ordinary direct range.

BuildingBSRIS panelTargetd₁ = 50 md₂ = 30 mSolid: outward pathDashed: return echo
2. Work with the current inputs
τ=2(d1+d2)c=2(50+30)299792458=533.7 ns\tau=\frac{2(d_1+d_2)}{c}=\frac{2(50+30)}{299792458}=533.7\ \mathrm{ns}
d2=cτ2−d1=30 m,Δd2=c2B=1.50 md_2=\frac{c\tau}{2}-d_1=30\ \mathrm{m},\qquad \Delta d_2=\frac{c}{2B}=1.50\ \mathrm{m}
3. Result
Round-trip delay533.7 ns
Recovered RIS–target range30 m
Nominal range resolution1.50 m
Reciprocal BS–RIS–target–RIS–BS timing with a known BS–RIS distance. The sketch is schematic. This delay model ignores hardware delay and multipath; the c/(2B) result is nominal path-range resolution, not guaranteed position accuracy.
References for this section3

One Surface, Coupled Objectives

  • User-focused phases: can strengthen data reception while reducing illumination elsewhere.
  • Target-focused phases: can strengthen a selected echo while reducing user signal quality.
  • Shared control: must account for the BS beam, user requirements, clutter and surface hardware together. Clutter means unwanted echoes from the environment.

A target is an object being sensed; it need not be the communication user. A strong user signal therefore does not establish that a different target is detectable.

References for this section3

Passive, Active and Sensing Surfaces

SurfaceCapabilityMain question
PassiveRedirects incident wavesIs the echo strong enough?
ActiveAdds amplificationDoes signal improvement exceed added noise and power cost?
STARTransmits and reflectsHow is available power shared across both sides?
Hybrid or multifunctionalAdds receiving or other hardware functionsWhat sensing and control can the actual hardware support?

STAR means simultaneous transmitting and reflecting. These categories describe capabilities; they do not guarantee a particular improvement.

References for this section3

Takeaway

A RIS supplies a controllable route, while ISAC supplies the waveform and processing. Next, calculate the four-hop echo budget: visibility is useful only when enough energy returns.

References for this section3

Check your understanding

0 of 4 answered

  1. The BS–RIS leg is 40 m and the RIS–target leg is 20 m. What is the complete reciprocal echo path length?

  2. Using c ≈ 3 × 10⁸ m/s, an echo delay is 600 ns and the known BS–RIS leg is 40 m. What is the RIS–target range?

  3. What is nominal path-range resolution at B = 100 MHz, using c ≈ 3 × 10⁸ m/s?

  4. How many propagation legs are in BS–RIS–target–RIS–BS?

Complete references and further reading