1. The 5G (NR) time slot structure is flexible and dynamic, where each time slot contains 14 OFDM symbols that can be allocated to uplink (UL), downlink (DL), or a combination of the two; in addition, the UL/DL allocation within the time slot can be changed dynamically, and a Mini-Slot shorter than a full time slot can be used to further enhance the flexibility of low-latency applications. The specific length of the time slot depends on the subcarrier spacing (parameter set). The larger the spacing, the shorter the time slot.
2. Mini-Slot 5G (NR) needs to achieve Urllc (ultra-low latency and high reliability), which is crucial for applications such as autonomous vehicles, industrial automation, and mission-critical IoT. To meet this function, the system introduces Mini-Slot transmission technology; unlike traditional full-slot scheduling, Mini-Slot can transmit data immediately without waiting for the next time slot boundary.
3. Slot and Mini-Slot: In 5G (NR), the figure below shows how the PDSCH (Physical Downlink Shared Channel) utilizes symbols 2 and 4 in various time slot structures. This flexibility and efficiency are the new design features that 5G (NR) brings to downlink communications.
4. Mini-Slot Transmission: Mini-slots use fewer OFDM symbols and have a shorter TTI (Transmission Time Interval). While a time slot typically contains 14 OFDM symbols, a mini-slot can consist of 2, 4, or 7 OFDM symbols. This allows for immediate data transmission, eliminating latency. As shown in Figure 1, a Mini-Slot can transmit 2, 4, or 7 OFDM symbols within a single Time Slot. Traditional scheduling starts at the Time Slot boundary, resulting in higher latency. However, starting at any time (depending on the time slot timing) allows for very low latency (immediate transmission). Practical use cases include eMBB, mMTC, and URLLC (low-latency, highly flexible applications). Figure 1 shows a Mini-Slot of 2 and 4 OFDM symbols, which can be scheduled at different times. Each Mini-Slot is located within the time slot structure labeled Time Slot #n and Time Slot #1. This also demonstrates how 5G supports asynchronous and independent downlink transmission scheduling.
5. Mini-Slot Features:
Reduced Latency: Data can be sent immediately without waiting for a time slot boundary.
Efficient Scheduling: Ideal for time-sensitive traffic such as URLLC (Ultra-Reliable Low Latency Communication).
Flexibility: Dynamic and mixed parameter sets can be accommodated within the same cell.
Enhanced Coexistence: Allows for simultaneous management of eMBB and URLLC traffic.
