r control mechanism that relies on the base station signaling target RACH preamble received power as well as base station transmitted reference signal power to the client for it to be able to estimate initial transmit power. A power ramp-up algorithm is employed beyond this to ensure that in less favorable radio conditions the base station can still end up detecting the RACH preambles. Transmit side 3GPP systems have a limited range TPC. Two 3GPP requirements define the TPC: RE (Radio Equipment) power control dynamic range which is the difference between the power of a single RE and the average RE power for a BS-in effect the dynamic range of the RE level power control. Requirements are specified in 38.104 as maximum of + 4 dB (up) and 6dB (down). The BS total power dynamic range is the difference between the maximum and the minimum transmit power of an OFDM (orthogonal frequency division multiplexing) symbol for a specified set of reference condition, which include transmission over a single RE versus transmission over a full OFDM symbol in the frequency domain. Requirements are specified in 38.141 and are up to 24.3 dB for a 100 MHz <6 GHz channel. Discontinuous transmission and reception A wireless data communication receiver uses a lot of DC energy, associated with digital sig- nal processing (DSP), data conversion, analog demodulation, and so on. While data rates continue to increase, batteries only get incrementally more performance, putting more pres- sure on energy efficiency. Process node advancements help on the (mainly) digital side but there are additional savings to be had at protocol level, where the objective is to define a pat- tern of enabled/disabled regions during which the (mobile phone) receiver knows it cannot expect transmission from the base station. The objective is to turn off the radio for the most time possible while staying connected to the network. The radio modem can be Chapter 2 System components, requirements, and interfaces 67 turned off "most" of the time, while the mobile devic