 are called a subframe and 10 of such subframes create a frame, which is of 10-ms length. The scheduler can assign resource blocks only in pairs of two consecutive RBs (in time); that is, the smallest unit of resource that can be assigned is two RBs. There is, however, one important difference between the feasible assignments on the UL and DL shared channels. Because in the UL the modulation uses the single carrier FDMA (SC-FDMA) concept, the allocation of RBs per UE has to be on consecutive RBs in frequency. The SC-FDMA modulation basically corresponds to a discrete Fourier transform (DFT) precoded OFDM signal, where the modulation symbols are mapped to consecutive OFDM carriers. The primary motivation for using the SC-FDMA scheme in the UL is to achieve better peak-to-average power ratios. For more details on the layer 1 (L1) radio interface parameters, modulation, and coding schemes, see reference 5. Because the LTE physical layer is defined such that it supports various multi- antenna MIMO schemes [7] such as transmit diversity and spatial multiplexing, the virtual space of radio resources is extended with a third dimension correspond- ing to the antenna port, in addition to the classical time and frequency domains. This essentially means that a time-frequency resource grid is available per antenna port. In the downlink, the system supports multistream transmission on up to four transmit antennas. In the uplink, no multistream transmission is supported from the same UE, but multiuser MIMO transmission is possible. Based on the preceding discussion, we can define the abstract resource element in LTE as the three tuple of [time, frequency, antenna port]. Thus, the generic radio resource assignment problem in LTE can be formulated as finding an opti- mal allocation of the [time, frequency, antenna port] resource units to UEs so that the QoS requirements of the radio bearers are satisfied while minimizing the use of the radio resources. A closely related function to resource assignment is link © 2009 by Taylor & 