IEEE 802.11p DSRC Wireless Model

The IEEE 802.11p DSRC module implements the physical layer and Medium Access Control (MAC) layer of Dedicated Short-Range Communications (DSRC) / ITS-G5 over 10 MHz channels in the 5.9 GHz ITS band.

It provides high-fidelity parity with ns-3 v3.42 and OMNeT++ Veins 5.2.

1. Physical Layer (PHY) Models

The PHY model simulates radio wave propagation, obstacle attenuation, diffraction around occluding corners, cumulative interference, and frame error decoding.

1.1. Dual-Slope Log-Distance Path Loss

In vehicular environments, radio waves reflect off ground asphalt and roadside barriers, producing a distinct two-slope path loss curve with a characteristic breakpoint distance.

Implemented in DualSlopePathLoss:

Carrier Frequency: $f_c = 5.9\,\text{GHz}$.
Reference Loss at $d_0 = 1\,\text{m}$:

$$PL_0 = 20 \log_{10}\left(\frac{4 \pi \cdot 1.0 \cdot f_c}{c}\right) \approx 47.85\,\text{dB}$$

Breakpoint Distance ($d_{break}$): $120.0\,\text{m}$.
Near-field Path Loss Exponent ($\gamma_1$): $2.05$.
Far-field Path Loss Exponent ($\gamma_2$): $3.90$.

\[\text{PL}_{det}(d) = \begin{cases} PL_0 + 10 \gamma_1 \log_{10}(d), & d \le d_{break} \\ PL_0 + 10 \gamma_1 \log_{10}(d_{break}) + 10 \gamma_2 \log_{10}\left(\frac{d}{d_{break}}\right), & d > d_{break} \end{cases}\]

1.2. Log-Normal Shadow Fading

Log-normal shadow fading models slow signal variations caused by foliage and topography:

\[X_\sigma \sim \mathcal{N}(0, \sigma^2)\]

Line-of-Sight ($\text{LoS}$): $\sigma_{LoS} = 3.1\,\text{dB}$.
Non-Line-of-Sight ($\text{NLoS}$): $\sigma_{NLoS} = 8.3\,\text{dB}$.

1.3. Building Obstacle Penetration Attenuation

Using the building polygons parsed from SUMO or OpenStreetMap (osm.poly.xml), the engine performs 2D ray-casting:

Calculates the total internal distance $d_{pen}$ traversed through concrete walls.
Attenuation: $0.85\,\text{dB/m}$ up to a maximum cap of $45.0\,\text{dB}$:

$$\text{PL}_{pen} = \min(d_{pen} \times 0.85\,\text{dB/m}, 45.0\,\text{dB})$$

1.4. ITU-R P.526 Knife-Edge Corner Diffraction

When buildings occlude the direct line of sight between two vehicles, radio signals diffract around the closest building corner.

Implemented in FresnelKnifeEdge:

Fresnel-Kirchhoff Parameter $\nu$:

$$\nu = h \sqrt{\frac{2(d_1 + d_2)}{\lambda d_1 d_2}}$$

where $h$ is the clearance height, $\lambda = c / f_c \approx 0.0508\,\text{m}$, and $d_1, d_2$ are the distances from transmitter and receiver to the corner vertex. 2. Diffraction Loss $J(\nu)$:

$$J(\nu) = \begin{cases} 0\,\text{dB}, & \nu \le -0.78 \\ \left[ 6.9 + 20 \log_{10}\left(\sqrt{(\nu - 0.1)^2 + 1} + \nu - 0.1\right) \right]_{0}^{45\,\text{dB}}, & \nu > -0.78 \end{cases}$$

\[\text{Received Power: } P_{rx} = P_{tx} - (\text{PL}_{det}(d) + X_\sigma + \text{PL}_{pen} + J(\nu))\]

2. Interference Tracking & Reception Decider

Implemented in CumulativeInterferenceTracker, providing strict architectural equivalence to ns-3 v3.42 InterferenceHelper:

2.1. Piecewise Constant SINR Chunking

A packet reception interval $[t_{start}, t_{end}]$ is sliced into distinct temporal chunks at every boundary where concurrent interferers start or stop transmitting:

In each chunk $i$, total interference power $I_i$ is summed in linear Watts:

$$I_i = \sum_{j \in \text{active interferers}} P_{rx, j}(t_{mid})$$

$$\text{SINR}_i = \frac{P_{rx, desired}}{I_i + N_0}$$

(where thermal noise floor $N_0 = -99.0\,\text{dBm} \approx 1.259 \times 10^{-13}\,\text{W}$).

2.2. Receiver Capture Effect ($\gamma_{cap} = 4.0\,\text{dB}$)

If interfering signals overlap with the desired packet:

Evaluates the Signal-to-Interference Ratio: $\text{SIR}_i = \frac{P_{rx, desired}}{I_i}$.
Destructive collision: If $\text{SIR}_i < 4.0\,\text{dB}$ and $\text{SINR}_i < 6.0\,\text{dB}$, capture fails and the packet is lost ($\text{PSR} = 0$).
Successful capture: If $\text{SIR}_i \ge 4.0\,\text{dB}$, the receiver locks onto the desired signal despite the simultaneous interferer.

2.3. Analytical Packet Error Rate (PER) Curve

For each chunk, the PER for IEEE 802.11p OFDM 6 Mbps (QPSK 1/2 with convolutional coding) is computed using the ns-3 NistErrorRateModel logistic curve:

\[\text{PER}_i(\text{SINR}_i) = \begin{cases} 1.0, & \text{SINR}_{i,\text{dB}} < 2.0\,\text{dB} \\ 0.0, & \text{SINR}_{i,\text{dB}} > 12.0\,\text{dB} \\ \min\left(1.0, \frac{1}{1 + \exp\left(1.6 (\text{SINR}_{i,\text{dB}} - 5.5)\right)} \times \text{clamp}\left(\frac{L_{bytes}}{300}, 0.5, 3.0\right)\right), & 2.0 \le \text{SINR}_{i,\text{dB}} \le 12.0 \end{cases}\]

The total Packet Success Rate is the product across all chunks:

\[\text{PSR} = \prod_i (1 - \text{PER}_i)\]

3. MAC Layer & EDCA Contention

Implemented in EdcaChannelAccess according to IEEE 802.11-2016 / 802.11p:

3.1. 4 Access Categories (EDCA ACs)

Access Category	Constant	Traffic Type	$AIFSN$	$CW_{min}$	$CW_{max}$
`VoiceSafety`	`AC_VO` (0)	Emergency / High-Priority Safety (DENM)	2	3	7
`Video`	`AC_VI` (1)	High-throughput video / sensor sharing	3	7	15
`BestEffort`	`AC_BE` (2)	Standard periodic Cooperative Awareness (CAM)	6	15	1023
`Background`	`AC_BK` (3)	Non-safety background telemetry	9	15	1023

3.2. Timing Parameters

Slot Time ($\sigma$): $13\,\mu\text{s}$.
SIFS: $32\,\mu\text{s}$.
AIFS: $AIFS[AC] = SIFS + AIFSN[AC] \times \sigma$.
Backoff Delay: $AIFS[AC] + \text{UniformRandom}(0, CW) \times \sigma$.
Air Duration: $40\,\mu\text{s} + \lceil(16 + 8 L_{bytes} + 6)/24\rceil \times 8\,\mu\text{s}$ at 6 Mbps.

3.3. Internal Contention Resolution

When multiple queues within the same node have frames ready at the same time:

\[\text{VoiceSafety} > \text{Video} > \text{BestEffort} > \text{Background}\]

The winning queue transmits. Subordinate colliding queues double their contention window ($CW \leftarrow \min(2 \times CW + 1, CW_{max})$) and re-enter backoff.

3.4. Channel Monitor (CBR) & DCC

ChannelMonitor calculates the true union of channel busy intervals over a sliding $100\,\text{ms}$ window:

\[\text{CBR} = \frac{T_{busy}}{100\,\text{ms}} \in [0.0, 1.0]\]

The measured CBR is fed every 100 ms into Decentralized Congestion Control (DCC Reactive FSM or LIMERIC) to regulate CAM generation intervals ($T_{off}$).