r footprint, and it is installed at a lower height, for example, on a lamppost. Therefore, a large number of antennas is not desirable. This reduces the maximum throughput and small cell processing requirements. 4.6 Small Cells Table 4.6.1 Typical cell dimensioning. Parameter Macro cell Small cell <6 GHz Small cell nmWave Channel 3 sectors of 100 MHz 100 MHz N X 100 MHz bandwidth Users/transmission time interval (TTI) Number layers 8 downlink, 4 uplink 4 downlink, 2 uplink 4 downlink, 4 uplink Number antennas Small cells often use a smaller channel bandwidth than macro cells. For example, an operator may allocate a specific portion of their frequency spectrum to indoor coverage. This also reduces the maximum throughput and small cell processing requirements. While at sub-6 GHz frequencies a mobile operator can choose the size of the cell they wish to deploy, at the new nmWave frequencies the cell will always be small. The propagation characteristics of mmWave frequencies limit the size of the cell up to 100 m. In order to maximize the cell size multiple antennas, also called massive MIMO, are used and since antenna size is directly related to transmission frequency these antennas are small enough to be deployed with a small cell sited at street level. The final dimension for frequency spectrum is whether the spectrum is licensed or unli- censed. Licensed is the standard operating model with the spectrum available for the exclu- sive use of the mobile operator. This means the operator chooses where specific frequencies are used and the interference levels within the cell will be dependent on the cell planning performed by the network operator. The alternate is unlicensed spectrum, typically at either 2.4 GHz or 5 GHz, where the spectrum can be used by multiple technologies (e.g. Wi-Fi and Bluetooth) or multiple instances of the same technology. Unlicensed access was first used in 4G with two different modes - unlicensed (LTE-U) where a cell operates entirely in unli- censed spectrum and licensed assisted access (L