he resources for the quick access message unused. As shown in Figure 10-18, the BW-REQ tile 10.3 Uplink control channels UL Tile Frequency FIGURE 10-18 Bandwidth request channel physical structure [2] consists of a preamble (Aij) and data (Bij) sub-carriers. The BW-REQ preamble is transmitted over four sub-carriers and six OFDM symbols. The data portion of the BW-REQ tile occupies two contiguous sub-carriers over six OFDM symbols and is used for transmission of the quick access message for the three-step bandwidth request procedure. In a three-step bandwidth request procedure, 16-bit BW-REQ or BR information is constructed from a 12-bit STID and a 4-bit predefined BR index (i.e., the mapping between Predefined BR Index, BR Size, and QoS Level is performed during DSx procedure. The BR Size and QoS Level are deter- mined based on the QoS parameters of the service flow in the DSx messages. The BR Size is described in number of bytes and is mapped to Maximum Traffic Burst parameter, and QoS Level is mapped to UL Grant Scheduling Type parameter). Let SOS1S2S3S4S5S6S7S8S9S10S1 and S12S13S14S15 denote the STID and predefined BR index, respectively. The 16-bit BW-REQ information is formed by reordering the STID and predefined BR index bits as bob 1b2 where bi=(si + Si+3 + Si+6 + Si+9 + Si+121 mod 2), i = 0,1,2. The 3-bit bob1b2 index is carried in the BR preamble using the preamble index. The remaining physical resources in the BW-REQ channel are used to transmit the other 13 bits of information. The frame number and 16 bits of the bandwidth request message are used to select a 24-bit preamble sequence which is transmitted in the preamble portion of the BW-REQ tiles. The BR preamble sequences are defined as Sp(k,u),0 < k < 24 where k is symbol index and denotes the sequence index [2]. The selected preamble sequence Sp(k,u),0 < k < 24 is BPSK modulated (0 mapped to +1 and 1 mapped -1) and mapped to Aij in the BW-REQ channel (see Figure 10-18). The 16-bit information in the quick access message transmitted in the BW-REQ ch