g-term covariance matrix is not fed back via dedicated uplink control CHAPTER 12 Performance of IEEE 802. 16m and 3GPP LTE-Advanced TABLE 12-8 Summary of Control Overhead for Various Test Environments [2] Duplex Mode Direction Downlink 9.19% 12.33% 11.17% 11.15% Uplink 7.85% 12.60% 9.23% 8.34% Downlink 9.74% 16.28% 13.77% 13.63% Uplink 6.02% 10.58% 8.01% 6.51% channel, rather through a regular MAC management message, its overhead is included in the calcu- lation of the UL control overhead. A fixed overhead for the long-term covariance matrix feedback is taken into consideration assuming a reporting period of 20 ms for both the UMa and the RMa scenarios. Furthermore, a fixed overhead of one OFDM symbol per long TTI in both TDD and FDD modes is accounted for in the transmission of the sounding sequences in the uplink. The initial ranging channel is assumed to have occupied four LRUs per superframe in both TDD and FDD modes, while the overhead due to bandwidth request channel is four LRUs per superframe. Table 12-8 summarizes the downlink and uplink control overhead for various test environments. 12.9.1 Cell Spectral Efficiency and Cell Edge User Spectral Efficiency Cell spectral efficiency SEcell is defined as the aggregate throughput of all users, i.e., the number of correctly received bits delivered to the upper layers at the MAC SAP over a certain period of time, divided by the channel bandwidth divided by the number of cells. The channel bandwidth is defined as the effective bandwidth multiplied by the frequency reuse factor, where the effective bandwidth is the operating bandwidth that is appropriately scaled by the uplink/downlink ratio. The cell spectral effi- ciency is measured in bits/s/Hz/cell. If di denotes the number of correctly received bits by user i (in the downlink) or from user i (in the uplink) in a system comprising N active users and M cells, and if B denotes the channel bandwidth and T the time over which the data bits are received, the cell spectral efficiency can be expressed as follows: (12