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AI-RAN, RIS, ISAC and Spectrum Coexistence


AI-RAN, RIS, ISAC and Spectrum Coexistence

AI-RAN, RIS, ISAC, and Spectrum Coexistence are major technologies being developed for advanced 5G and future 6G networks. These technologies aim to improve spectrum efficiency, signal quality, and wireless communication performance.

1. AI-RAN (Artificial Intelligence Radio Access Network)

Concept

AI-RAN integrates artificial intelligence directly into the Radio Access Network (RAN) to optimize wireless communication in real time.

The RAN includes:

  • Base stations
  • Antennas
  • Beamforming systems
  • User scheduling
  • Power control

Instead of fixed algorithms, AI dynamically learns optimal decisions.

Optimization Model

The network tries to maximize system performance:

$$ \max_{\mathbf{x}} R(\mathbf{x}) $$

Where:

  • \(R\) = network throughput
  • \(\mathbf{x}\) = control parameters

Example control variables:

$$ \mathbf{x} = \{P, W, f, B\} $$
  • \(P\) = transmit power
  • \(W\) = beamforming weights
  • \(f\) = frequency allocation
  • \(B\) = bandwidth

AI learns the mapping:

$$ (H, I, S) \rightarrow (P, W, f) $$
  • \(H\) = channel information
  • \(I\) = interference
  • \(S\) = spectrum state

2. RIS (Reconfigurable Intelligent Surface)

Concept

Reconfigurable Intelligent Surface (RIS) is a programmable reflecting surface that can control how radio waves propagate.

Instead of signals reflecting randomly off buildings or obstacles, RIS elements control the phase of reflected signals to improve communication.

A RIS surface may contain hundreds or thousands of passive reflecting elements.

Signal Model

Without RIS:

$$ y = hx + n $$

With RIS:

$$ y = (h_d + h_r \Phi g)x + n $$

Where:

  • \(h_d\) = direct channel
  • \(h_r\) = RIS → receiver channel
  • \(g\) = transmitter → RIS channel
  • \(\Phi\) = RIS phase control matrix

RIS phase matrix:

$$ \Phi = \text{diag}(e^{j\theta_1}, e^{j\theta_2}, ..., e^{j\theta_N}) $$

Each RIS element adjusts the phase \(\theta_i\).

Optimization objective:

$$ \max_{\Phi} |h_d + h_r \Phi g|^2 $$

3. ISAC (Integrated Sensing and Communication)

Concept

ISAC integrates radar sensing and wireless communication into a single system.

Example:

  • A base station communicates with users
  • The same signal is used to detect objects like radar

This improves spectrum efficiency.

Signal Model

Communication signal:

$$ y_c = hx + n $$

Radar echo:

$$ y_r = \alpha x(t-\tau) + n $$

Where:

  • \(\alpha\) = reflection coefficient
  • \(\tau\) = time delay

Distance estimation:

$$ d = \frac{c\tau}{2} $$

Where \(c\) is the speed of light.

Joint optimization objective:

$$ \max_x R(x) + \lambda S(x) $$
  • \(R(x)\) = communication rate
  • \(S(x)\) = sensing accuracy

4. Spectrum Coexistence

Concept

Spectrum coexistence allows multiple wireless systems to share the same spectrum without harmful interference.

Examples include:

  • WiFi
  • 5G networks
  • Radar systems
  • Satellite communication

Signal Model

$$ y(t) = \sum_{k=1}^{K} h_k s_k(t) + n(t) $$

Where:

  • \(s_k(t)\) = signal from system \(k\)

Interference power:

$$ I_m = \sum_{k \ne m} |h_{mk}|^2 P_k $$

Constraint:

$$ I_m \le I_{th} $$

Techniques used include:

  • Beamforming
  • Dynamic spectrum access
  • Cognitive radio
  • AI-driven spectrum sharing

5. Combined System for Future 6G

Future wireless systems combine multiple technologies:

  • RIS controls signal propagation
  • AI-RAN optimizes beamforming and resource allocation
  • ISAC enables radar and communication simultaneously
  • Spectrum coexistence allows multiple systems to share frequencies

Example combined signal model:

$$ y = (H_d + H_r \Phi G)Ws + n $$

Where:

  • \(W\) = beamforming matrix
  • \(\Phi\) = RIS control matrix
  • \(s\) = transmitted signals

Optimization objective:

$$ \max_{W,\Phi,P} R - \lambda I $$

6. Industry Applications

These technologies are actively researched for future communication systems such as:

  • 6G wireless networks
  • Smart cities
  • Autonomous vehicles
  • Satellite-terrestrial communication
  • Radar-communication coexistence systems

Companies working on these technologies include:

  • Ericsson
  • Nokia
  • Samsung
  • Huawei
  • Qualcomm
  • NVIDIA

Summary

Technology Purpose
AI-RAN AI optimizes wireless network operation
RIS Programmable surfaces control radio wave propagation
ISAC Combines radar sensing and wireless communication
Spectrum Coexistence Allows multiple systems to share spectrum efficiently

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