 a function of the number of active users. The Layer 1 (L1) and Layer 2 (L2) overhead are accounted for in time, frequency, or space for calculation of system performance metrics such as spectral efficiency, user throughput, VoIP capacity, etc. Examples of L1 overhead include synchronization channel (preambles), guard sub-carriers and DC sub-carrier, guard time (in TDD systems), reference signals, and cyclic prefix. Examples of L2 overheads include common and dedicated control channels, HARQ ACK/NACK feedback, channel quality feedback, random access channels, packet headers, and sub-headers, as well as CRC. The power allocation/boosting should also be accounted for in modeling resource allocation for control channels. Based on the example two-dimensional time-frequency model shown in Figure 12-1, the L1 and L2 overhead can be calculated as: OL1+L2 = lim (12-9) where B denotes the system bandwidth and T is the radio frame size, Bk is the resource occupied by the kth L1 (or L2) overhead channel across the frequency dimension and Tk denotes the required time resource for transmission of the kth L1 (or L2) overhead channel in time. Using this model, the total resources consumed by the L1 overhead over relatively long period of time is given as: BKTk, (12-10) ke S(L1) where S(L1) denotes the set of resources used for static L1 overhead channels. The total resources consumed by the L2 overhead over relatively long period of time is given as: (12-11) Note that the amount of resources that have already been used by the L1 overhead must not be recounted in the calculation of OL2 and that OL1+2 # OL1 + OL2. Also S(L2) denotes the set of resources used for L2 overhead channels The average spectral efficiency inclusive of the effect of the L1/L2 overhead can be obtained as SE(1 OL1+2), where SE denotes the spectral efficiency that has 12.2 Calculation of static and dynamic overhead Static Available Dynamic Overhead Overhead Resources Radio Frame (T) FIGURE 12-1 An illustration of the static and dynamic overhead been obtained