 of the sounding signal from one or multiple antennas and multiple users are supported to provide MIMO channel information for DL and UL transmission. The sounding signal occupies the first OFDM symbol in the uplink subframe. Each subframe can contain only one sounding symbol. In uplink subframes with six OFDM symbols, the sounding signal is not transmitted in the LRUs containing other control channels. The sounding signals can be transmitted in any resource unit when using uplink subframes with seven OFDM symbols. The remaining OFDM symbols in subframes containing sounding signals are used for data trans- mission, as shown in Figure 10-15. Multiple uplink subframes in a radio frame can be used for sounding. The uplink sounding channels of multiple users and multiple antennas per mobile station can be multiplexed, and thereby simultaneously transmitted through decimation or cyclic shift in each sounding channel allocation. When multiple uplink subframes are used for sounding, time-division separation can be applied by assigning different mobile stations to different uplink subframes. When the sounding channels of multiple mobile stations are multiplexed using cyclic shifts, each mobile station occupies all the sub-carriers that are allocated to the sounding channel using different sounding 10.3 Uplink control channels TDD Radio Frame = 5 ms TDD Radio Frame = 5 ms Narrowband Sub-band based Sounding Structure of narrowband/wideband uplink sounding channel in TDD mode FIGURE 10-15 decimated waveforms. In a frequency-decimation separation with scheme, different each frequency mobile station offsets. utilizes The sounding signal sounding allocation carrier transmitted sets by from the the MS in the uplink is described as follows: (10-13) decimated starting multiple users based on decimation, (k = the 0). occupied The occupied sub-carriers sub-carriers are for from each the user Golay or with When offset separating are g modulated relative to using the first BPSK used modulation sub-carrier and the coefficients are ext