WirelessNetworkingTechnologies/lab_4/link_level_measurements.md

This PDF will be a bit more 'well defined'

Reproducibility

Reproducibility factor	Task 1 value	Task 2 value	Task 3 value	Task 4.1 value	Task 4.2 value
MATLAB Version	26.1.0.3251617 (R2026a) Update 2	-	-	-	-
5G Toolbox Version	26.1	-	-	-	-
WLAN Toolbox Version	26.1	-	-	-	-
Communications Toolbox Version	26.1	-	-	-	-
Parallel Computing Toolbox Version	26.1	-	-	-	-
Random stream	mt19937ar with seed	-	-	-	-
Random seed	666	-	-	-	-
SNR vector	0:1:40 dB	-	-	-	-
Packet budget	1024 packets per SNR point	-	-	-	-
maxNumErrors	50	-	-	-	-
NTN profile	NTN-TDL-C	-	-	-	-
Carrier frequency	2.4 GHz	-	Task 3.2: [1 2.4 5 5.8 6 12 24 60] GHz	-	-
LEO altitude	600 km	-	-	-	-
Elevation sequence	10° to 90° to 10° over the packet sequence	-	-	-	-
Mean elevation angle	50°	-	-	-	-
Mean slant range	906.32 km	-	-	-	-
Mean satellite Doppler shift	32.73 kHz	-	changes with carrier frequency	-	-
Normalized CFO	0.419	-	changes with carrier frequency	-	-
Channel bandwidth	20 MHz	-	-	-	[20 40 80 160 320] MHz
MCS	2	-	-	[0 2 4 8 10 12 13]	3
APEP length	1000 B	[250 1000 4000 8000 12000] B	Task 3.1: [250 1000 4000 8000 12000] B; Task 3.2: 8000 B	-	-
TX/RX antennas	1-by-1 SISO	-	-	-	-
Pilot tracking	disabled	-	enabled	-	-
Parallelization	parfor over SNR points	-	-	-	-

Task1

1.1

See code lab_4.m, create_baseline_configuration.m and simulateTransmission.m.

1.2

The plot shows the packet error rate significantly decreasing as the signal to noise ration increases. This behavior can be observed when the snr reaches a value of 25, at that simulation point the signal significantly overweights the noise and the PER also significantly decreases in an negative exponential manner. At link level, PER is the fraction of transmitted PHY-layer packets that are not received correctly for a given channel model and SNR.

1.3

For the baseline configuration with f_c = 2.4GHz, LEO altitude 600km, orbital shifted elevation angle (Elevation sequence: 10° to 90° to 10° over the packet sequence, mean: 50°), and static receiver. The mean slant range is 906.32km, the computed mean satellite Doppler shift is approximately 32.73kHz. With the IEEE 802.11be subcarrier spacing of 78.125kHz, this corresponds to a normalized CFO of \epsilon \approx 0.419. Therefore, the Doppler shift is below one subcarrier spacing but still represents 41.9% of the OFDM subcarrier spacing.

1.4

CFR Magnitude single representative Packet:

The CFR magnitude of the representative packet is relatively flat over the active subcarriers. Only moderate variations are visible, without deep frequency-selective fades. Therefore, for the baseline 20 MHz NTN-TDL-C configuration, the channel appears mostly frequency-flat to mildly frequency-selective.

Complete CFR Magnitude over all representative Packets by first MCS:

The complete CFR collection is included as a consistency check. The collected packet CFRs show similar magnitude variations over the active subcarriers, indicating that the selected representative packet is typical for this baseline run. No strong deep fades are visible across most packets, so the 20 MHz NTN-TDL-C baseline appears mostly frequency-flat to mildly frequency-selective.

Task 2

2.1

Visual analysis:

The plots packet error rate to signal to noise ratio curve shifts to higher SNR values for larger APEP values. In contrast to the other graphs APEP = 250 has the highest rate of successful transmitted packets.

Analyzing by meaning:

Smaller APEP values perform better than larger APEP values. In particular, APEP = 250 reaches low PER at lower SNR than the larger payload sizes. As the payload size increases, the plot shifts to the right, so larger packets need a higher SNR to achieve the same packet error rate. Using a small APEP results in more successfully transmitted packets, but also increases the needed network usage, more smaller packets mean more packet headers, resulting in more data that needs to be transferred in sum. Increasing APEP increases the number of payload bits and therefore the number of EHT-Data OFDM symbols. Larger APEP increase the packet duration. Since pilot tracking is disabled, residual CFO and common phase error are not continuously corrected during the data field. The longer the packet lasts, the more residual phase error can accumulate, which increases the probability that the packet is decoded incorrectly. The residual CFO is more harmful to longer packets because the phase error accumulates over the packet duration.

Summary:

Increasing APEP increases the number of payload bits and therefore the number of EHT-Data OFDM symbols. This increases the packet duration. Since pilot tracking is disabled, residual CFO and common phase error are not continuously corrected during the data field. The longer the packet lasts, the more residual phase error can accumulate, which increases the probability that the packet is decoded incorrectly.

2.2

Target PER	Reasonable SNR	Practical maximum APEP
10^{-1}	23dB	600

The target PER for this task is 10^{-1}. I use 23dB as a practical SNR limit, because it is close to the beginning of the low-PER region while still avoiding the very high-SNR tail of the simulation. From the focused APEP comparison, APEP = 600B reaches PER \leq 10^{-1} at approximately 23dB. Larger payloads require a higher SNR to reach the same target PER. Therefore, under the chosen practical SNR limit, APEP = 600 is selected as the practical maximum payload size.

This choice is a compromise between robustness and overhead. Smaller packets such as APEP = 250B are more robust, but require more packets and therefore more protocol overhead to transmit the same amount of user data. Larger packets reduce overhead, but are more sensitive to residual CFO because of their longer packet duration.

As a practical motivation, this SNR limit can be interpreted as a conservative design choice for difficult deployment scenarios, for example remote or terrain-challenged areas. This was not explicitly simulated in this lab, since the channel model does not include blockage, vegetation, or terrain shadowing. However, such scenarios often involve small battery-powered devices with limited energy availability. Therefore, choosing a payload size that reaches the target PER without relying on the very high-SNR tail is useful, because it leaves more link margin and can reduce the need for retransmissions. In this sense, APEP = 600 is a practical compromise between robustness, packet overhead, and energy-aware operation.

For applications where higher data rates are more important than robustness, a larger payload such as APEP = 4000 may still be attractive because it reduces relative packet overhead. In the simulated range, this requires operating closer to the high-SNR end of the sweep, approximately around 40dB for the target PER.