of a slot. Gains of mini-slot based scheduling diminish rapidly both with increasing load and increasing file size. For a given load, as the file size increases, longer mini-slots would be needed to transmit the file, SO the difference between the two schemes decreases. For a given file size, as the load increases, there is likely some queueing delay which degrades the performance gain from using mini-slots. 10.9 Spectral Efficiency and Capacity 10.9.1 Downlink Spectral Efficiency in 5G Compared to LTE One of the 5G targets is to improve spectral efficiency compared to LTE. Since the single link performance is limited by the Shannon theorem, there are no simple solu- tions to improve the link efficiency. The efficiency improvements must come from more advanced usage of antennas and from system-level efficiency. Table 10.19 illustrates the Table 10.19 5G features improving spectral efficiency compared to LTE. Sub-1-GHz FDD 10 MHz Sub-6-GHz 5G features 4 x 2 MIMO TDD 100 MHz Massive MIMO Spectral usage Lean carrier Wideband carrier MIMO optimization Total Approx. +30% Approx. +60% (=1.04*1.10*1.15) (=1.08*1.10*1.10*1.25) 10.9 Spectral Efficiency and Capacity Table 10.20 Expected downlink spectral efficiency. Spectrum Bandwidth Antennas (bps/Hz/cell) (bps/Hz/cell) Sub-1-GHz 10 MHz FDD 2x2 MIMO 2 GHz 20 MHz FDD 4x4 MIMO 3.5 GHz 100 MHz TDD mMIMO main technologies that can improve the efficiency in 5G radio compared to LTE: spec- tral usage, lean carrier, wideband carrier, and MIMO codebook. More efficient spectral usage in 5G yields a small improvement in efficiency. The LTE transmission bandwidth is 90% of the channel spacing. For example, 10 MHz LTE uses 9 MHz for transmission and 1 MHz for guard bands. 5G is designed to utilize the channel spacing more efficiently. 5G in 10 MHz with 15 kHz subcarrier spacing has 94% utilization, and 5G in 100 MHz with 30 kHz subcarrier spacing has 98% utilization. Lean carrier means that there are no cell-specific reference signals in 5G. The relative impact of reference signals d