5.9 GHz inter-vehicle communication at intersections: a validated non-line-of-sight path-loss and fading model
© Mangel et al; licensee Springer. 2011
Received: 14 July 2011
Accepted: 23 November 2011
Published: 23 November 2011
Inter-vehicle communication promises to prevent accidents by enabling applications such as cross-traffic assistance. This application requires information from vehicles in non-line-of-sight (NLOS) areas due to building at intersection corners. The periodic cooperative awareness messages are foreseen to be sent via 5.9 GHz IEEE 802.11p. While it is known that existing micro-cell models might not apply well, validated propagation models for vehicular 5.9 GHz NLOS conditions are still missing. In this article, we develop a 5.9 GHz NLOS path-loss and fading model based on real-world measurements at a representative selection of intersections in the city of Munich. We show that (a) the measurement data can very well be fitted to an analytical model, (b) the model incorporates specific geometric aspects in closed-form as well as normally distributed fading in NLOS conditions, and (c) the model is of low complexity, thus, could be used in large-scale packet-level simulations. A comparison to existing micro-cell models shows that our model significantly differs.
Vehicular communication is envisioned to increase range and coverage of location and behavior awareness of vehicles, thus enabling highly developed pro-active safety systems.
The idea is that all vehicles communicate information like position, speed, and heading periodically to other vehicles in cooperative awareness messages to enable the derivation of an environment picture, used as basis for movement prediction. An ad hoc communication technology working on 10 MHz wide frequency bands centered around 5.9 GHz in the U.S./Europe is in development. Medium and physical access is standardized as IEEE 802.11p .
Our analysis of building locations at intersections in the city of Munich  showed a need for NLOS reception: If two cars are approaching an intersection with 50 km/h, only 30% of all intersection corners provide LOS at a desired warning point of 3 s [4, 5] to a potential impact (≈ intersection center). While road side units (RSU) might re-broadcast messages and reduce the need for NLOS reception, urban street crossings with sparse traffic are likely not to be equipped with a dedicated RSU. Such scenarios require robust signal transmission between vehicles approaching a crossing. These situations predominantly exhibit NLOS radio link conditions between vehicles, motivating to investigate NLOS reception.
First measurements on 5.9 GHz NLOS reception were done with channel sounders in  and with off-the-shelf radios in [7–10]. While showing that NLOS reception is generally feasible, they did not investigate the influence of factors like building placement on reception quality. Also, all of them lack a systematic and representative test site selection, questioning the generalizability of results. NLOS path-loss models were--albeit simplistic--deduced in [9, 10].
While NLOS models related to vehicle-to-vehicle (V2V) communication exist in cellular research--for below rooftop base stations [11–16], those were only validated at lower frequencies (0.9-2.1 GHz) and higher transmitter heights (3-4 m). Therefore, a validated 5.9 GHz NLOS model for V2V communication is still missing.
To gain more insight about 802.11p NLOS reception properties, we performed an extensive field test, specifically targeted to measure the quality of NLOS reception and to characterize propagation . Special attention was paid to a well-founded selection of representative test cases and to find a test setup that allows for the derivation of predominant influence factors such as inter-building distance. A comparison of the data to the existing cellular models showed that they cannot be properly applied in the intended scenario.
In consequence, we developed--based on the measurement data--a specific 5.9 GHz NLOS propagation model for inter-vehicle communication. The proposed path-loss and fading model is intended to be used in packet level load simulations.
The article is organized as follows: our measurements will be presented in Section 2. Subsequently, we will deduce the NLOS path-loss model, called VirtualSource11p, and characterize NLOS small-scale fading in Section 3. Afterwards, we will compare our model to existing models in Section 4.
2 NLOS reception measurement campaign
Proper measurements are inevitable to judge existing models and deduce our new specific one. Therefore, a summarization of our measurements as published in  is provided here.
2.1 Test design
2.2 Used hardware
The receiver was integrated into a BMW 5 Series GT. GPS information was taken from the CAN bus, providing a high accuracy position (GPS data are enhanced by vehicle sensor data and map matching). A tripod with 35 × 35 cm metal plate at a height of 1.45 m was used as the transmitter mount as it is well placeable. Also, a vehicle would have blocked other traffic.
We used a LinkBird-MX V3  802.11p communication box by NEC containing two DCMA-82-N1 Mini-PCI cards with Atheros 802.11 radio chips. To resemble a close-to-production system, we used small low-profile puck antennas from Nippon Antenna. They provide a gain of 0 dB at 0° (= horizon) and +5 dB at 15°. Each antenna cable inherits a loss of 2.4 dB. These values are according to the corresponding data sheets.
2.3 Systematic intersection selection
23 m, 21 m
Suburban (main case)
23 m, 19 m
Suburban (main case)
Suburban (main case)
24 m, 21 m
Urban (main case)
27 m, 22 m
Urban increased width
Urban high street width
55 m, 30 m
Urban very wide, non-regular shape
Suburban, buildings at only two corners
Free Space, Country Road
One street, no buildings, no trees, etc.
To check the influence of street width, we selected one urban intersection with 30 m width (ID 20), and another in-between (ID 11). A really wide one (ID 21) and one with only two occupied corners (ID 9) complete the selection.
2.4 Parameters, evaluation and results
We tested, in general, with 3 Mbps and 20 dBm transmission power. The transmission frequency was 100 Hz and payload 200 Bytes. With headers, packets had a size of 258 Bytes.
NLOS reception testing configuration
3.0 Mbps (BPSK modulation)
10 MHz, number 180 (5.9 GHz center freq.)
200 Byte payload + IP/MAC/PHY headers
Tx Dist. to ISect. Center
0, 30, 60 m (optional also 100 m)
1-4 (street legs) + 0 (center of intersection)
Two directions per transmitter position
NEC LinkBird v3 (Atheros Chipset)
Nippon DSRC Puck, 0°: 0 dB gain, 15°:+5 dB
Rx Antenna Position
Roof center (optimal position, evaluated in )
Cable (Box to Antenna)
SUCOFLEX_104, 4 m, data sheet: 2.4 dB loss
Tripod, 35 × 35 cm metal plate at 1.45 m height
BMW 5 Series GT, no sunroof
4 suburban + 4 urban + free space
Figure 6 shows that intersections with same street width and setting (suburban intersections 1, 2, 3) exhibit the same performance, and that path-loss decreases with increased street width (compare urban intersections 10, 11, 20, and 21 with increasing width). Suburban intersections have an estimated 3-4 dB less rcv-power compared to urbans with same width (urban intersection 10 against suburban 1, 2, 3). In general, NLOS reception is well feasible, with 50% or more reception rate at 50 m to center for transmitter and receiver.
3 NLOS propagation model development
Subsequent, we deduce a specific vehicular 5.9 GHz NLOS path-loss model--VirtualSource11p--from the measurements and characterize small-scale fading in NLOS areas.
3.1 Data quality and system loss
There was only one issue: power histograms revealed that there are no packets reported with -69, -68 and -67 dBm. A figure illustrating this can be seen on the website . The same gap can be seen in . We believe that the chipset changes its sensitivity in this power range, and reports values above -69 dBm by 3 dB too strong. We corrected this by subtracting 3 dB from all reported values >-69 dBm. The reported reception sensitivity was not changed by the correction.
We measured received power, where in dBm space: RxPower = Txpower - SystemLoss - PathLoss. To determine path-loss, we need to know system loss. The cables lead to a combined loss of ≈ 4.8dB and the antennas to a gain of two times some value between 0 (0°) and 5 dB (15°).
The fit reveals a loss of 2.75 dB with LE = 2. With SL = 0, it shows a loss exponent of 2.1, being higher as in FSPL. Subsequently, we will assume 1.75 dB system loss, as revealed by fitting both variables. The resulting average gain of 1.5 dB per antenna seems realistic, given its characteristic. Note that such loss determination absorbs the problem that real transmitted power might slightly differ from the configured value.
3.2 NLOS path-loss model development
The model takes the distance of transmitter and receiver to intersection center (d t and d r ), receiver street width (w r ), and distance of transmitter to wall (x t ) as input. Last two values reflect building position influence. Adaption to differing streets is enabled by a street parameter (α). A higher loss is present at high rcv-distances (due to a diffraction, rather than reflection predominance), determined by a break even distance (d b ).
Value i s is specifying suburban (i s = 1) or urban (i s = 0). As d b ≈ 180 m for our setup, which exceeds the highest distance d r with reception, the d r > d b equation is of no use for the fitting.
The fit input values are form the regular shaped (≈90° and w t ≈ w r ) intersections with buildings at each corner: intersection 2, 3, 10, 11, and 20, with w r being 21, 21, 23, 26 and 30 m, respectively, and intersection 2 and 3 having i s = 1. The fitted measurements have d t values of 30 and 60 m (plus 100 m for intersection 11).
Each input value (visualized as a cross in Figure 10) is complemented by the reception rate in the bin and the intersection wide w r and i s values as input to the equation and for pre-selection. w r is set to as w t and w r were selected similar per intersection and we fit intersection wide average values. System loss is set to 1.75 dB and (as this dimension was not tested).
We did not fit intersection 1, 9, and 21 due to differing reasons: intersection 1 was the very first tested intersection. Here, we measured with alternating transmission power (20 dB, 10 dB) and rate (3 Mbps, 6 Mbps) in each second. In consequence, there are spatial gaps in the data for each of the four configurations, leading to empty bins at the 5 m bin width in the fit. Anyhow, the performance is very close to intersection 2 and 3, as shown in . Intersection 9 has missing reflection facades. This dimension was not incorporated in the fit, as it would have complicated the fit by another dimension. Furthermore, we only tested one intersection of such type (as it is rare), leading to insufficient data to provide a reliable fit in this additional dimension. Intersection 21 was excluded due to two reasons: First, one of the street legs has a non 90° angle. Second, the inter-building distance in the two streets differs a lot (55 m against 30 m). It is questionable whether the averaging over the four side street simplification is applicable for this particular intersection. Despite the exclusion of these three intersections, the fit covers 11 data rows from five intersections, stemming from 88 test-runs.
We fitted the median reception power curve, as it is more stable at lower reception rates. The average reception power curve suffers (bin values are too high) from incomplete data as soon as the reception rate sinks below 1.0. The median is technically accurate as long as reception rate is greater than 0.5. However, due to small-scale fading leading to variations and potential measurement inaccuracies around the reception threshold of the radio, median values also turn out to be slightly too high at reception rates close to 0.5. This is visible in plots. To prevent a negative influence on the fit, an exclusion criterion of reception-rate >0.65 was selected.
Despite the no available measurement data for high d r distances, an increased loss at high distances (d r > d b ) due to diffraction rather than reflection being dominant is incorporated (as in [11, 12, 14, 15]).
3.3 NLOS small-scale fading classification
4 Path-loss model comparison
In this section, we compare our model to previously proposed NLOS models. One was measured under Car2X conditions at 790 MHz, the rest are micro-cellular models for urban street canyons where base stations are typically located inside street canyons, for example at signal lights. Note that we do not compare with the models in [9, 10], as they do not take important influence factors such as street-width into account.
Street canyon NLOS model comparison
Claimed validity or verification (V)
# Verific. scenarios/measurem.
Vehicle G-plate antenna
1.5, 1.5 m (V)
Virtual Source 
5-10, 2-3 m (V)
Sai et al.  (Toyota)
1.8-5 m, 1.9 m (V)
Only at Rcv.
ITU-R P1411-5  (4.2.3,0.8-2 GHz)
4-50, 1-3 m
ITU-R P1411-5  (4.2.4,2-16 GHz)
4-50, 1-3 m
w r <10 m
10, 1.5 m (V)
10-40 m (V)
All models except the second ITU-R model are only specified for up to 2 GHz and h t > 4 m. Also, those models are not based on measurements with vehicular ground plate antennas as in our measurements, except the receiver side in . In iTETRIS, the model was not verified with the new environment parameters; in CORNER only very briefly. Our model was derived from measurements in 5 intersections and 11 loss-curves, based upon 88 test runs.
Obviously, the VirtualSource11p model shows a very good accordance to measurements due to its fitting based development. Comparisons to the other tested scenarios reveal similar results and show that our model especially follows changes in the street width better than the P1411-5 2-16GHz and the Toyota model.
With VirtualSource11p, we present a well validated, low complexity NLOS path-loss model for 5.9 GHz V2V communications at intersections. It was deduced from data collected in an extensive measurement campaign, specifically targeted to measure NLOS reception quality. A founded selection of test intersections enabled to quantify the influence of inter-building distance and suburban/urban differences in a single path-loss equation with only a few simple geometric input-values.
Due to its fitting-based generation, the equation corresponds well to measurement data in different scenarios, especially with changing inter-building distances. In contrast, existing street canyon NLOS path-loss models for micro-cellular environments at lower frequencies differ mostly substantially from the measurements when parameterized to 5.9 GHz V2V communication. Of course, our model is also limited in its validity to the measurement environment it is based on. While we certainly did not cover every special case, we selected the test intersections as representative as possible, building upon an own building positioning investigation . To the best of our knowledge, this is a novel approach and has not been done before.
In addition to path-loss, we investigated NLOS fading, finding a normal distributed power variation around average. In conclusion, this article provides a well-founded general framework to include NLOS propagation conditions into packet level simulations of 5.9 GHz inter-vehicle communication, thus enabling large-scale load simulations in intersection environments.
The authors wish to thank Matthias Michl, who worked with us at the underlying measurements during his Bachelor Thesis.
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