DL/UL TDD slot configuration: DDDSU, DDSUU, patterns and impact

TDD Slot Patterns Explained

In TDD (Time Division Duplex) systems like 5G NR on n78 (3.5 GHz), the same frequency is shared between downlink and uplink by alternating in time. The TDD slot pattern determines how many slots are allocated to DL vs UL, directly impacting throughput ratio, latency, and capacity. The most common pattern is DDDSU — 3 full downlink slots, 1 special slot (partially DL plus guard period plus partially UL), and 1 full uplink slot per 5-slot period. This gives approximately 75-80% DL and 20-25% UL resources, optimized for the typical consumer traffic profile where downloads dominate. DDSUU…