question: What are the effects of IRS (Intelligent reflecting surface) phase noise on the achievable rate in IRS-aided communication systems? option 1: IRS phase noise only causes a constant rate loss option 2: IRS phase noise degrades the achievable rate more severely with a large number of reflecting elements option 3: IRS phase noise leads to exponential complexity in the worst case option 4: IRS phase noise introduces round-off errors in the optimized phase shifts option 5: IRS phase noise is captured by a Gaussian noise model 