Reliability
Reliability relates to the capability of transmitting a given amount of traffic within a predetermined
time duration with high success probability.
Reliability is the success probability of transmitting a layer 2/3 packet within a required maximum
time, which is the time it takes to deliver a small data packet from the radio protocol layer 2/3 SDU
ingress point to the radio protocol layer 2/3 SDU egress point of the radio interface at a certain channel
quality.
The satellite component of IMT-2020 shall be able to support reliability as high as 1-10e-3.
The connection time duration required to meet the reliability target should be provided by the proponent
of the submitted RIT/SRIT.
The following assumptions were used for simulation of HRC-s to evaluate the reliability.
- DL and UL overhead:
- DL overhead is assumed to be
0.14 - UL overhead is assumed to be
0.08
- DL overhead is assumed to be
- For the evaluation metrics that require usage of beam area, a beam area of
1415 km2is assumed. - All the beams are considered for computing the area of connection density.
- For SLS to LLS metric of connection density, “pre-processing SINR” is used
- Elevation angle of 90° is used for determining mean and standard deviation values of K-factor and delay spread for NTN TDL-C Rural channel model.
Below are the parameters for system-level simulation-
Simulation Parameters
| Parameter | Value |
|---|---|
| Satellite altitude | 550 km |
| Satellite antenna pattern | Section 6.4.1 in [1] |
| Satellite antenna polarization | Circular |
| Satellite antenna number | 1 Tx / 1 Rx per beam |
| 3 dB beam width | 4.41 degrees |
| Satellite EIRP density | 34 dBW/MHz |
| Satellite antenna gain | 30 dBi |
| Satellite G/T | 1.1 dB/K |
| Central beam center elevation | 90 deg |
| UE antenna type | Handheld, (1,1,2) with omni-directional antenna element |
| UE antenna polarization | Linear: +/- 45deg X-pol |
| UE Rx Antenna gain | 0 dBi |
| UE antenna temperature | 290 K |
| UE noise figure | 7 dB |
| FRF | 1 or 3 |
| Carrier frequency | 2 GHz |
| SCS | 15 kHz |
| Channel bandwidth | 30 MHz for FRF1, 10 MHz for FRF3 |
| Scenario | Rural-eMBB-s |
| UE deployment | 100% outdoor and uniformly distributed over the area |
| LOS condition | 100% LOS |
| Spot beam pattern and frequency reuse factor | Hexagonal pattern, 19 inner beams, Total beams: 61 beams for FRF=1, 127 beams for FRF=3. |
| UE density | 10 UEs per beam |
| UE mobility | 0 (Stationary) |
| Satellite mobility | 0 (Doppler spread is assumed to be compensated) |
| Large scale channel model | Large scale model of Section 6.6 in 38.811 |
| Small scale channel model | Frequency selective fading model of Section 6.7.2 in 38.811 |
| Handover margin | 0 dB (handover was not simulated) |
| UE attachment | RSRP |
| Traffic model | Full-buffer |
| Scheduling scheme | PF and SU-MIMO |
| Receiver type | MMSE-IRC |
| Channel estimation | Realistic |
| Frequency offset | 0 ppm |
| Frequency drift | 0 ppm |
| DL CSI measurement | CQI only (1 layer / 1-port CSI-RS) |
| PRB bundling | Wideband |
| Codeword (CW) | SCW |
| Transmission scheme | One layer |
| Frame structure | FDD |
| Overhead | 0.14 (same as for peak data rate calculation) |
The results for UL and DL reliability after LLS have been reported in the below table. According to Report ITU-R M.2514, the reliability requirement is 1-10e-3 or 99.9%.
Performance results of reliability
| Parameters | Min. Requirement | Values | |
|---|---|---|---|
| Uplink | Downlink | ||
| FRF | 3 | 3 | |
| 5 percentile SINR | -0.03 dB | 7.79 dB | |
| Scheduled Bandwidth | 0.9 MHz (5 PRBs) | 8 PRBs, 30 PRBs | |
| Reliability | 99.9 % |
99.97 % | 99.98 %, 99.999% |
| Connection Time Duration | 36 ms | 1 ms |
We observe from the above table thatwe can meet the reliability requirements for both UL and DL NR-NTN.