Reference [1] first introduced the concept of active IRS and demonstrated that, under the same total power budget PIRS, the achievable rate of an active IRS-assisted wireless communication system is higher than that of a passive IRS-assisted system. The specific achievable rate comparison results are shown in Figure 1. The total power budget for both active and passive IRS is PIRS=10dBm, with the passive IRS having 100 REs. When the maximum allowable amplitude amplification factors are 40dB and 50dB, respectively, the active IRS requires only 13 and 20 REs to achieve optimal performance, which is significantly higher than that of the passive IRS.

Figure 1. Achievable rate versus the number of REs.

Reference [2] points out that active IRS can amplify the amplitude of incident signals, thereby mitigating the “multiplicative fading” losses that affect passive IRS. Figure 2 shows the variation of user sum rate with the horizontal distance L between the users and the base station under two scenarios: strong direct link and weak direct link, with the same total power budget Pmax=10dBm. In both scenarios, active IRS provides a higher sum rate gain compared to passive IRS.

Figure 2. User sum rate versus distance L.

Moreover, reference [2] established a hardware platform for experimental measurements, as illustrated in Figure 3. Using this platform, the measurement results shown in Figure 4 were obtained, demonstrating that the active REs can achieve a reflection gain of up to 25dB.

Figure 3. Experimental setup from [2] validating the reflection gain of active IRS.

Figure 4. Reflection gain G of active RE obtained using the hardware platform depicted in Figure 3.

Reference [3] compared the achievable rates of active IRS and passive IRS-assisted wireless communication systems under the same total power budget (including both the base station and the IRS) Qtot=30dBm. The specific results are shown in Figure 5. Figure 5 illustrates that the achievable rate of the active IRS-assisted wireless communication system is substantially higher than that of the passive IRS-assisted wireless communication system.

Figure 5. System achievable rate versus IRS deployment location.

Reference [4] proves that, with the same total power budget for the system, the total power consumption of an active IRS-assisted system is lower than that of a passive IRS-assisted system. The detailed results are illustrated in Figure 6.

Figure 6. Total system power consumption versus IRS deployment location.

Reference [5] examined the effect of the total system power budget pT on the user sum rate, with detailed results illustrated in Figure 7. Under the same total system power budget pT, the user sum rate of the active IRS-assisted system employing non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) is significantly higher compared to the passive IRS-assisted system.

Figure 7. User sum rate versus total system power budget.

Reference [6] examined the effect of IRS deployment location on the total computational bits (TCB) of an IRS-assisted mobile edge computing system under the same total power budget pT=34dBm. The detailed results are illustrated in Figure 8. From Figure 8, it is evident that the TCB of the active IRS-assisted system employing NOMA and OMA are substantially higher than those of the passive IRS-assisted system.

Figure 8. Total computational bits versus IRS deployment location.

With the same total system power budget, Figure 9 illustrates the performance improvement percentage of active IRS-assisted systems relative to passive IRS-assisted systems in the studies mentioned above. As illustrated in Figure 9, even with varying application scenarios and system performance indicators, the benefits brought by active IRS to the system are consistently significantly higher than those of passive IRS.

Figure 9. Performance enhancement percentage of active IRS relative to passive IRS in existing studies.

(1) In our manuscript, we validate the performance of the proposed joint passive beamforming and IRS deployment mechanism for active IRS-assisted EH-CRSNs through simulation experiments, without constructing a hardware platform for real measurements. In our future work, we will set up a hardware platform to further verify the superiority of the proposed joint mechanism over PIRS.

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