l message. If the MS receives an AAI-UL-POWER-ADJUST message at the ith frame, the local value is updated according to the BS instruction applies from the (i+1)th frame. For initial ranging, the MS sends an initial ranging code at a randomly selected ranging oppor- tunity. The initial transmission power is decided according to the Received Signal Strength (RSS) measured on the downlink reference signals such as the secondary advanced preamble. If the MS does not receive a response, it may increase the transmit power level by APIR = 2 dB or may send a new 10.3 Uplink control channels y=0.2 y=0.4 y=0.6 y=0.8 y=1.2 y=1.4 y=1.6 y=1.8 Interference over Thermal loT(dB) FIGURE 10-20 Distribution of loT for different values of Y One Control Command every 250 ms One Control Command every 5 ms Cell Edge Spectral Efficiency Cell Spectral Efficiency FIGURE 10-21 Effect of open-loop power control on cell edge and cell spectral efficiencies initial ranging code, where APIR is the power step size. The MS can repeatedly increase the power on failure until the maximum transmit power is reached. The initial transmit power of the MS in the initial ranging channel is given as PTX-IRmin = PRX-IRmin + EIRPBS - RSS + (GMS-RX - GMS-TX) where PRX-IRmin EIRPBS, GMS-TX, and GMS-RX denote the minimum BS detectable power for receiving CHAPTER 10 The IEEE 802. 16m Physical Layer (Part II) the initial ranging preamble, Effective Isotropic Radiation Power of the BS, the MS receiver and transmitter antenna gains, respectively. If the MS receiving and transmitting antenna gains are equal, the last term of latter equation vanishes. The other terms in the latter equation are obtained from S-SFH SP2 and SP1. Power control for the sounding channel is supported to ensure the quality of channel measure- ments. The mobile station's transmit-power for the sounding channel is controlled separately according to the target SINR value for the corresponding sounding channel. The power per sub-carrier is adjusted according to Equation (10-19) for uplink soundi