482 3G Evolution: HSPA and LTE for Mobile Broadband Furthermore, the different types of information do not need to be reported with the same period. Typically, RI can be reported less often, compared to the reporting of PMI and CQI, reflecting the fact that the suitable number of lay- ers typically varies on a slower basis, compared to the channel variations that impact the choice of precoder matrix and modulation rate, and coding scheme. Normally, periodic channel-status reports are delivered using the PUCCH physi- cal channel. However, similar to hybrid-ARQ acknowledgments normally deliv- ered on PUCCH, channel-status reports are `re-routed' to the PUSCH if the terminal has a valid uplink grant and is anyway to transmit on the PUSCH. 19.3 Uplink power control Uplink power control for LTE is the set of tools by which the transmit power for different uplink physical channels and signals are controlled to ensure that they are received at the cell site with an appropriate power. How to set the trans- mit power for the random-access preamble was briefly discussed in Chapter 18. What will be discussed in this section are the LTE power-control mechanisms for The physical uplink control channel (PUCCH) The physical uplink shared channel (PUSCH) Uplink sounding reference signals (SRS). The uplink demodulation reference signals are always transmitted together with PUSCH or PUCCH and are then transmitted with the same power as the corre- sponding physical channel. Fundamentally, LTE uplink power control is a combination of an open-loop mechanism, implying that the terminal transmit power depends on estimates of the downlink path-loss, and a closed-loop mechanism, implying that the net- work can, in addition, directly control the terminal transmit power by means of explicit power-control commands transmitted in the downlink. 19.3.1 Power control for PUCCH For PUCCH, the appropriate received power is simply the power needed to achieve a sufficiently low error rate in the decoding of the L1/L2 control signal- ing transmitted on the PUCCH. However, it is then important to have the fol- lowing in mind: In general, decoding performance is not determined by the received signal strength but rather by the received signal-to-noise/interference ratio (SINR).