ub-carriers Fade more than Others for each User is Different Localized Resource Allocation Distributed Resource Allocation FIGURE 9-21 A comparison of localized and distributed allocation schemes (example) comprises N1 adjacent PRUs and a mini-band consists of N2 adjacent PRUs. The sub-bands are suitable for frequency-selective allocations as they provide a contiguous allocation of PRUs in frequency. The mini-bands are suitable for frequency diversity allocation and are permuted in frequency. The downlink sub-carrier to resource unit mapping process is defined as follows and is illustrated in Figures 9-23 to 9-25: 1. An outer permutation is applied to the PRUs in the units of N1 and N2 PRUs where N1 = 4 and N2 = 1. 2. The reordered PRUs are distributed into frequency partitions. 3. The frequency partition is divided into localized and/or distributed resource allocations. The sizes of the distributed/localized groups are flexibly configured per sector. Adjacent sectors do not need to have same configuration for the localized and distributed groups. 4. The localized and distributed resource units are further mapped into LRUs by direct mapping for CRUs and by the use of sub-carrier permutation for DRUs. The sub-carrier permutation defined for the downlink distributed resource allocations spreads the sub- carriers of the DRU across all the distributed resource allocations within a frequency partition. After mapping all pilots, the remaining usable sub-carriers are used to form the DRUs. To allocate the LRUs, the remaining sub-carriers are paired into contiguous sub-carrier pairs. Each LRU consists of a group of sub-carrier pairs. The number of sub-bands depends on the system bandwidth and is broadcast through the Downlink Sub-band Allocation Count (DSAC) parameter in the secondary superframe header [2]. CHAPTER 9 The IEEE 802. 16m Physical Layer (Part I) Distribute Physical Resource Distribute Physical Resource Units to Distribute Sub-carriers to Units to Frequency Partitions Localized and Distributed Groups Logical 