SDR Testbed for Data-Driven Reactive Jammer Mitigation

The DTRTF Scheme

Objective

Experimentally validate the DTRTF scheme using an SDR-based hardware testbed.
Analyze the constellation behavior before and after self-interference cancellation under different residual self-interference conditions.
Demonstrate the energy and phase modifications incorporated during cooperative retransmission based on the decoded bit at Charlie.

The hardware implementation of the proposed DTRTF scheme can be divided into three phases.

Fig. 1: Figure shows the three-phase hardware implementation of the proposed DTRTF scheme.

Experimental Setup

Carrier frequency: 2.1 GHz
Bandwidth: 300 kHz
Maximum transmit power: 7 dBm
Antenna gain: 2 dBi (Zenith)
Environment: Indoor quasi-static (LoS + NLoS)
Alice–Bob distance: 0.78 m
Alice–Charlie distance: 0.47 m

This video presents an SDR-based hardware testbed for implementing and evaluating countermeasures against reactive jammers in wireless communication systems. We discuss the threat model, jammer behavior, practical mitigation techniques, and real-time implementation using software-defined radio platforms.

Phase 1: Time-Slot 1

Hardware Testbed Description

Adalm-Pluto devices are used to emulate Alice, Charlie, and Dave.
Alice transmits using OOK signaling.
Charlie transmits QPSK symbols on the fCB band with energy α.
Baseband processing is performed in MATLAB/Simulink.
IQ samples are collected at Dave for:
- α = 0.9877
- α = 0.9901
- α = 0.9964

Results

Fig. 2 shows the representative constellation diagrams for α = 0.9901.

Alice Transmits Bit-1

Simultaneous transmission creates a multiple-access channel.
Superposition of symbols causes constellation distortion.
Charlie’s higher-energy transmission dominates synchronization.
Alice’s low-energy signal appears as interference.

Alice Transmits Bit-0

Only Charlie’s QPSK symbols are observed.
Constellation points remain well clustered.
Stable synchronization is maintained.

Fig. 2: Figure shows the constellation diagrams of the received IQ samples for α=0.9901 of time-slot 1.

Phase 2: Decoding at Charlie

Phase 2.A: Controlled Emulation of Full-Duplex Receiver Conditions

Two Adalm-Pluto devices are used to emulate Alice and Charlie.
Alice transmits information using OOK modulation.
Charlie’s QPSK signal is generated using a pseudorandom generator.
The transmitted waveform consists of the superposition of:
- Alice’s OOK signal.
- Charlie’s QPSK signal.
Parameter β controls the residual self-interference strength.
Different β values emulate different analog-cancellation conditions.

Phase 2.B: DTRTF-Based Self-Interference Cancellation under Residual Self-Interference Conditions

Charlie reconstructs the self-interference using knowledge of the transmitted QPSK signal.
The pseudorandom seed is used for interference reconstruction during SIC.

Effective Analog-Cancellation Regime

Small β values.
Linear RF front-end operation.
Interference modeled as a linear component.
Reconstructed interference matches the received signal.
Successful digital cancellation.

Poor Analog-Cancellation Regime

Large β values.
Nonlinear receiver operation and saturation.
Nonlinear distortion in received IQ samples.
Reconstructed interference mismatches the received signal.
Unsuccessful digital cancellation.

Results

Experimental Setup

Experiments conducted for β = 0.4, 0.6, 0.7, and 10.
Average OOK signal power = 0.5.
Corresponding interference powers:
- β = 0.4 → 0.16
- β = 0.6 → 0.36
- β = 0.7 → 0.49
- β = 10 → 100

Corresponding SIR Values

β = 0.4 → SIR ≈ 4.94 dB
β = 0.6 → SIR ≈ 1.43 dB
β = 0.7 → SIR ≈ 0.09 dB
β = 10 → SIR ≈ −23.01 dB

Constellation Diagram Observation

Fig. 3 shows the constellation diagrams after interference removal for different values of β.

Effective Analog-Cancellation Regime

(β = 0.4, 0.6, 0.7)

Signal power exceeds interference power.
Clear cluster separation is achieved.
Two distinct clusters corresponding to bit-1 and bit-0 are observed.
Reliable decoding is possible.

Poor Analog-Cancellation Regime

(β = 10)

Interference power dominates signal power.
Loss of cluster separability is observed.
Clusters overlap and form a single cluster.
Reliable decoding is not possible.

Key Observation

Higher SIR enables clear separation between clusters.
Low SIR leads to interference dominance and overlapping clusters.

Storage for Cooperative Re-Transmission

Decoded bits at Charlie are stored.
Stored bits are incorporated during time-slot 2.
Energy and phase modifications are applied during cooperative re-transmission.

Fig. 3: Figure shows the constellation diagrams of the received IQ samples before and after removing cancellation for different values of β.

Phase 3: Time-Slot 2

Hardware Testbed Description

Two Adalm-Pluto devices are used to emulate Charlie and Dave.
Charlie transmits QPSK symbols on the fCB band.
Transmission parameters are determined using the decoded bit of Alice at Charlie.

Decoded Bit = 1

Unit-energy QPSK transmission.
Standard constellation formation.

Decoded Bit = 0

QPSK transmission with energy 2−α.
Additional π/4 phase-shift introduced.
Energy and phase modifications incorporated during transmission.

Experimental Parameters

IQ samples are collected at Dave.
Experiments are conducted for:
- α = 0.9877
- α = 0.9901
- α = 0.9964

Results

Fig. 4 shows the representative constellation diagrams for α = 0.9901.

Decoded Bit = 1

Well-clustered QPSK constellation observed.
Stable unit-energy transmission.

Decoded Bit = 0

Phase-rotated constellation observed.
Constellation points remain well clustered.
Since 2−α remains close to unity for α close to 1.

Fig. 4: Figure shows the constellation diagrams of the received IQ samples for α=0.9901 of time-slot 2.

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