is slightly better than that of the long-term covariance matrix that is fed back every four frames. 12.10 3GPP LTE-ADVANCED LINK-LEVEL AND SYSTEM-LEVEL PERFORMANCE The 3GPP LTE-Advanced is another candidate for IMT-Advanced whose performance was fully characterized based on the same evaluation methodology that was applied to the IEEE 802.16m. The following sections summarize the performance characterization of the 3GPPLTE-Advanced as part of the IMT-Advanced submission. Although the performance of the two candidate technologies, i.e., IEEE 802.16m and 3GPP LTE-Advanced, are not directly compared, it can be generally concluded that the two technologies perform similarly, and have the same level of functionality and performance in various test environments. 12.10.1 Cell Spectral Efficiency and Cell Edge Spectral Efficiency Cell and cell edge spectral efficiencies were evaluated through extensive simulations conducted by a number of 3GPP member companies. The simulation results were reported based on specific 3GPP LTE-Advanced configurations, i.e., downlink and uplink MU-MIMO, downlink and uplink CoMP, and uplink SU-MIMO, for both FDD and TDD duplex schemes in various test scenarios. The performance differences among contributing sources can be explained by implementation-specific functionalities at the transmitter and the receiver that are not explicitly specified by the standard, such as receiver type, scheduling algorithms, etc. In the results reported for the downlink, the size of the control channel (L OFDM symbols) and the number of the MBSFN subframes are the factors that affect the overhead. Note that in the 3GPP submission, the control channel overhead is statically modeled, i.e., the downlink control channels occupy a fixed number of OFDM symbols irrespective of the number of users, although it is expected that the size of the PDCCH varies dynamically with the number of active users in the cell. In the MBSFN subframes, there are no common reference signals in data regions, which effectively reduce the over