nd OFDM symbols for the ranging channel. The BS can separate colliding codes and extract timing information and power. In the process of user code detection, the BS obtains the Channel Impulse Response (CIR) of the code, thus acquiring information about the user's channel condition. The timing and power measurements allow the system to compensate for the near/far problem, as well as the propagation delay caused by transmission over large cells. The ranging channel for non-synchronized users in IEEE 802.1 16m is formed using one or three uplink subframes known as Initial Ranging Channel Format 0 or Format 1, respectively. The ranging preamble RP is repeated twice in non-synchronized initial ranging Format 0, as shown in Figure 10-16, to increase ranging opportunity and to avoid phase discontinuity at the OFDM symbol boundaries. The RCP is a copy of the last portion of the ranging preamble. The beginning of the transmission time in the ranging channel is aligned with that of the uplink subframe at the MS. There is a time gap at the end of uplink subframes containing the ranging channel to prevent interference between the adjacent subframes. A non-synchronized MS does not transmit any other uplink burst or uplink control channel signal in the subframe where a ranging channel is transmitted. The ranging channel for synchronized mobile stations is used for periodic ranging. The mobile stations that are already synchronized with the target BS are allowed to transmit a periodic ranging signal. The synchronized ranging channel occupies 72 sub-carriers over six OFDM symbols, starting from the first OFDM symbol within the uplink subframe. There are two repeated signal waveforms, a basic unit which is generated by the ranging preamble code over 72 sub-carriers, three OFDM symbols, and a repeated basic unit. In the Initial Ranging Channel Format 0 (i.e., the default format), the ranging preamble is repeated to increase ranging opportunity. The non-synchronized mobile stations can only use one instance of the ranging preamble