Performance and Optimal Placement Analysis of Intelligent Reflecting Surface-assisted Wireless Networks
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摘要: 当基站(BS)和用户的位置固定,基站到智能反射面(IRS)与IRS到用户的距离和一定时,该文在视距信道和瑞利信道下基于最大化系统可达速率准则对无源和有源IRS的最优放置位置进行分析。首先,运用相位对齐和大数定律推导了无源和有源IRS辅助无线网络可达速率的闭合表达式;然后,分析了基站到IRS的路径损耗指数${\beta _1}$和IRS到用户的路径损耗指数${\beta _2}$对IRS最优部署位置的影响,即当${\beta _{\text{1}}} \gt {\beta _{\text{2}}}$时,无源IRS的最优部署位置始终靠近基站,随着${\beta _1}$和${\beta _2}$的差距逐渐增大,有源IRS的最优部署位置逐渐靠近基站;当${\beta _1} \lt {\beta _2}$时,则得到相反的结论。仿真结果表明:当${\beta _1} = {\beta _2}$且无源IRS到基站和到用户的距离相等时,系统的可达速率性能最差。当固定有源IRS处的噪声功率且增加用户处的噪声功率时,IRS的最优部署位置始终靠近用户;当固定后者增大前者时,IRS的最优部署位置逐渐靠近基站。Abstract: When the locations of the Base Station (BS) and user are fixed and the sum of the distances from BS to the Intelligent Reflecting Surface (IRS) and from the IRS to the user is given, the optimal placement of passive and active IRSs based on the maximizing achievable rate criterion under line-of-sight and Rayleigh channels are analyzed in this paper. First, the phase alignment and the law of large numbers are employed to derive the close-form expressions of the achievable rates of passive and active IRS-assisted wireless networks. Then, the effects of the path loss exponent ${\beta _1}$ from the BS to IRS and the path loss exponent ${\beta _2}$ from the IRS to user on the optimal placement location of the IRS are analyzed. That is, when ${\beta _1} \gt {\beta _2}$, the optimal placement location of passive IRS is always close to the BS, and with the difference between ${\beta _1}$ and ${\beta _2}$ gradually increasing, the optimal placement location of active IRS is gradually close to the BS. The contrary conclusions are obtained when${\beta _1} < {\beta _2}$. Simulation results show that the achievable rate is worst when ${\beta _1} = {\beta _2}$ and the passive IRS is located at equal distances to the BS and user. When fixing the noise power at active IRS and increasing the noise power at user, the optimal placement location of active IRS is always close to the user. When fixing the latter and increasing the former, the optimal placement location of active IRS is gradually closer to the BS.
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表 1 路径损耗指数设置表
无源IRS 有源IRS ${\beta _1}$ ${\beta _2}$ ${\beta _1}$ ${\beta _2}$ ${\beta _1} \gt {\beta _2}$ 3.0 2.2 3.5 2.5 ${\beta _1} = {\beta _2}$ 2.2 2.2 2.5 2.5 ${\beta _1} \lt {\beta _2}$ 2.2 3.0 2.5 3.5 -
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