Error statistics of real-time power measurements in cellular channels with multipath and shadowing

Real-time power measurements performed by cellular receivers are essential for power control, handoff, and dynamic channel allocation. For best results, the measurement filter bandwidth must be sufficiently narrow to average out multipath fluctuations, yet sufficiently wide to follow shadow fading fluctuations. Our study considers two measurement methods (filtering the squared envelope, and filtering the logarithm of the squared envelope), and two filter types (integrate-and-dump and RC). We show, using standard models for the multipath and shadow fadings, that the dB measurement error tends to be Gauss-distributed, and can readily be made unbiased (zero mean) by proper amplitude calibration. The performance metric then becomes the standard deviation (Δ) of the dB error, which can be minimized by proper choice of the filter bandwidth. We find that Δ can be kept to values of 3 dB or lower over a wide range of mobile velocities and shadow fading characteristics. Also, we discuss the potential gains in measurement accuracy associated with diversity reception and broad-band channels