tributed resource units. This is different from the legacy system, where each permutation zone could only accommodate localized or distributed sub-channels. The frequency partitions can be used for different purposes, such as Fractional Frequency Reuse (FFR). The downlink/uplink resource petitioning and mapping procedure is illustrated in Figure 9-22). In the example shown, three frequency partitions are defined, where some of them include both localized and distributed resource units. A Physical Resource Unit (PRU) is the basic physical unit for resource allocation that comprises Psc consecutive sub-carriers by Nsym consecutive OFDM symbols. The default value for Psc is 18 sub- carriers, and Nsym can be 6, 7, or 5 OFDM symbols for type-1, type-2, and type-3 subframes, respectively. A Logical Resource Unit (LRU) is the basic logical unit for localized or distributed resource allocations. An LRU comprises Ps Nsym sub-carriers, inclusive of the pilot sub-carriers that are embedded in a PRU. A Distributed Resource Unit (DRU) is defined to achieve frequency diversity gain in multipath fading channels. The DRU contains a group of sub-carriers which are physically spread across the distributed resources within a frequency partition. The size of the DRU is the same size as the PRU. The minimum unit for forming a DRU is equal to one sub-carrier or a pair of sub- carriers, also known as a tone-pair. A localized resource unit, alternatively known as Contiguous Resource Unit (CRU), is used to achieve frequency-selective scheduling gain. The CRU contains a group of sub-carriers which are physically contiguous across the localized resource allocations within a frequency partition. The size of the CRU is the same as the size of the PRU. The physical sub-carriers associated with an OFDM symbol are grouped into Nguard-left left guard sub-carriers, Nguard-right right guard sub-carriers, and Nused used sub-carriers. The DC sub-carrier is not used. The Nused sub-carriers are divided into an integer number of PRUs. Each PRU contains