# Experimental Demonstration of Terahertz-Wave Signal Generation for 6G Communication Systems
## 2 Simulation Model for THz Generation
\begin{table}
\begin{tabular}{c c} \hline \hline
**Modulation Parameters** & **Value** \\ \hline Modulation order & QPSK \\ RF carrier frequency & 12.5 GHz \\ RF amplitude & 1 a.u \\ Signal data rate & 4 Gbps \\ CW laser 1 frequency & 193.1 THz \\ CW laser 1 power & 1 mW \\ CW laser 1 linewidth & 100 kHz \\ SRRC roll-off factor & 0.18 \\ Responsivity of PD & 1 A/W \\ Thermal noise & \(10\times 10^{-12}\) A/Hz\({}^{(1/2)}\) \\ \hline \multicolumn{2}{c}{**SOA’s Parameters**} \\ \hline Injection current (IC) & 0.25 A \\ Height & 80 μm \\ Length & 500 μm \\ Width & 3 μm \\ Optical confinement factor & 0.99 \\ Index to gain coupler & 3.8 \\ Waveguide loss coefficient & 4000 1/m \\ \hline \multicolumn{2}{c}{**DD-MZM’s Parameters**} \\ \hline Extinction ratio & 35 dB \\ \(V_{p}DCV_{p}RF\) & 0.5 V \\ Insertion loss & 6 dB \\ Operation temperature & 25 degC \\ Extinction ratio & 35 dB \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation parameters’ values. Figure 6: BER measurements versus optical power for different types of modulation orders. timation errors under high Doppler spread. To evolve toward 6G's high-capacity demands, we propose future enhancements, including: advanced DSP using neural-network-based equalizers to compensate nonlinearities/phase noise; hybrid ARQ combined with LDPC coding for robust 256-QAM; hardware upgrades integrating GaN-based PAs and high-resolution ADCs to improve SNR by \(>\)6 dB; and multi-antenna MIMO techniques to mitigate fading. These steps align with 3 GPP's 6G study items (e.g., AI-native air interfaces and sub-THz support), enabling our platform to scale beyond 100 Gbps. We will incorporate these solutions in the next hardware revision and validate them against 3 GPP Rel-21 requirements. In 6G communications, which aim for ultra-high data rates, extremely low latency, high spectral efficiency, and reliable connectivity, the performance metrics such as BER and EVM are critical indicators of the system's capability to meet these demanding requirements. The correlation with practical applications:  
**Quality of Service (QoS):** Low BER and EVM values are necessary to guarantee QoS in applications like remote surgery, holographic communications, or autonomous driving, where errors can have critical consequences. **Spectral Efficiency:** High-order modulation schemes used in 6G require precise signal quality; thus, low EVM is crucial to prevent error propagation and to maximize data throughput. **Robustness and Reliability:** Maintaining these metrics within acceptable thresholds ensures the system can operate reliably under varying channel conditions, multipath effects, and interference, which are common in real-world environments. **Energy Efficiency:** Systems with low BER and EVM reduce the need for retransmissions and complex error correction, saving power a vital aspect for battery-powered IoT devices and mobile terminals. Achieving low BER and EVM directly supports the core objectives of 6G--high reliability, efficiency, and low latency--making these metrics not just performance indicators but essential parameters for ensuring that the communication system can meet the stringent demands of next-generation applications. In the stage of measuring the performance of the generated THz signal, we simulated the bit error rate (BER), which refers to comparing the recovered data from the received signal to the original transmitted data. The BER for the generated optical vector THz signal as a function of optical received power is depicted in Figure 7a. The results show that the BER decreases as the optical received power increases. At the HD-FEC threshold value of \(3.8\times 10^{-3}\), the corresponding optical received power is \(-16.5\) dBm. Subsequently, we included the error vector magnitude (EVM) metric in our performance assessment, as it serves as an important measure of the radio transmitter or receiver's performance in digital communications.