task2 implemented

lab_4/link_level_measurements.md

@@ -56,3 +56,38 @@ The CFR magnitude of the representative packet is relatively flat over the activ
 ![Complete CFR Magnitude over all representative Packets by first MCS](complete_packet_cfr_magnitudes_by_first_mcs.svg)
 
 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
+
+![PER over SNR for APEP](per_snr_apep.svg)
+
+###### 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.
+
+![PER over SNR with focus on 600 and 800 APEP and 250 and 1000 APEP contrast plot](per_snr_apep_t22.svg)
+
+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.