REVIEW 4 major objections 5 minor 13 references
On-Demand Routing for Urban VANETs using Cooperating UAVs
T0 review · 4 major / 5 minor · reviewed 2026-08-14 · deepseek-v4-flash
Pith's one-line read A new reactive routing protocol that makes UAVs full members of discovered paths and uses them as bridges for fragmented ground segments can extend connectivity in sparse urban VANETs, reducing end-to-end delay and raising packet delivery…
desk verdict Plausible protocol, unenforced UAV-coverage assumption, and a conclusion that contradicts its own delay plot. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is a routing path represented as a sequence of fixed zone IDs, where each zone is roughly the size of the vehicle communication range (about 300 m). During route discovery, a RREQ packet accumulates each transited zone ID and the vehicle count in that zone, so the destination can compute the average zone density and the standard deviation of zone densities for every discovered path. The selection score combines those computed metrics with the raw delay and the number of UAV hops, and the winning path is returned to the source greedily. The maintenance machinery stores all discovered paths in the data-packet header, so an intermediate node can switch to an alternative path without re-running discovery, and when no ground alternative exists, a UAV is designated as the next forwarder to bridge disconnected clusters.
What would settle it
Run the same protocol in a simulator where drone coverage is not guaranteed over every four road segments, or where building obstacles attenuate air-to-ground links, and measure whether the packet-delivery-ratio advantage over ground-only routing vanishes below a threshold such as fewer than the assumed 16 UAVs.
Extended reading notes
Core claim
The paper claims that a heterogeneous network in which UAVs are full members of on-demand routing paths, rather than mere data mules, keeps urban vehicular networks connected when ground traffic is sparse. The destination scores each candidate path by $$\mathrm{Score}=\frac{\mathrm{NB_{vehicles}}}{\mathrm{Delay}}\times \frac{1}{1+\mathrm{Sdeviation}+\mathrm{Hops_{UAV}}}$$ where NB_vehicles is the number of vehicles along the path, Delay is the RREQ traversal time, Sdeviation is the standard deviation of per-zone vehicle counts, and Hops_UAV is the number of UAV hops in the path. Paths with more vehicles, lower delay, balanced vehicle distribution, and fewer UAV hops are preferred; all discovered paths are stored in the data-packet header, and when the selected path breaks, the current forwarder switches to an alternative path, or calls on a UAV to bridge the gap. In NS-2 simulations over a 4 km x 4 km grid with up to 200 vehicles and 16 UAVs, the protocol reports higher packet delivery ratio and lower end-to-end delay than RBVT-R and AGP at low vehicle densities, though at high densities RBVT-R achieves lower delay.
Load-bearing premise
The scheme needs a sufficient number of UAVs that each area of four road segments always has at least one UAV overhead, and it assumes drone-to-vehicle wireless links are long-range and unaffected by buildings; without those two conditions the connectivity gain disappears.
Editorial extensions
If this is right
- In sparse urban traffic, routing paths need not be confined to ground vehicles: UAV hops extend connectivity and reduce the average number of hops.
- Storing all discovered paths in the data-packet header lets intermediate nodes switch paths without a new route discovery as long as at least one alternative remains.
- Density balance, not just shortest distance or fewest intersections, is a workable route-selection criterion for city VANETs.
- At high vehicle densities, ground-only reactive routing can match or beat the UAV-assisted approach in end-to-end delay, because UAV mobility triggers route rediscovery.
- When alternatives are exhausted, the protocol falls back to a route-error message and a fresh discovery, so failures degrade to standard reactive behavior.
Reading between the lines
- The protocol assumes blanket drone coverage over every group of four road segments; a more economical design would reposition UAVs toward predicted disconnection points rather than hovering everywhere.
- The score weights vehicle density, delay, density balance, and UAV hops equally; changing those relative weights could trade path stability against delay and could be tuned separately for highway or rural settings.
- If air-to-ground links suffer the same building blockage as ground-to-ground links, the bridge advantage shrinks, so a simulation varying building height and link budget would test the core connectivity claim.
- The zone-density scoring idea could be reused in non-urban settings, which the paper itself names as a possible extension.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a reactive routing protocol for urban VANETs in which UAVs participate in route discovery, path scoring, and path maintenance. Paths are scored using a multi-criteria formula that rewards vehicle count, penalizes delay, density imbalance, and the number of UAV hops, and the best path is selected from multiple discovered routes. When a route breaks, an alternative pre-discovered path is used, and UAVs are employed to bridge disconnected ground clusters. The protocol is evaluated in NS-2 with VanetMobiSim/MobiSim mobility against RBVT-R and AGP, reporting packet delivery ratio, end-to-end delay, hop count, and routing overhead. The abstract claims reduced end-to-end delay and high delivery ratio, supporting the conclusion that heterogeneous vehicle-UAV communication extends network connectivity.
Significance. If the claimed results hold, the paper would make a moderate contribution to UAV-assisted VANET routing by combining zone-density-aware path scoring with UAV relaying and pre-computed alternative paths. The comparison against RBVT-R and AGP is appropriate, and the scoring rule in Eq. (3) is a constructive, parameter-free heuristic rather than a fit to the reported outcomes. However, the central claim rests entirely on simulation evidence that conflicts with the paper's own coverage assumption and with its internal delay statements; no statistical support is provided. The idea is plausible and worth pursuing, but the current manuscript does not establish the load-bearing connectivity claim.
major comments (4)
- [III.A, Table II] The coverage assumption in Section III.A that the network has a sufficient number of UAVs so that at each moment at least one UAV hovers over an area of four road segments is never enforced or verified in the simulation. Table II specifies only 16 UAVs moving at 50–120 km/h, and the conclusion lists making UAV mobility more controllable as future work. Since the claimed connectivity gain depends on a UAV being within communication range of two disconnected ground segments at the instant a path is needed, the simulation results may reflect random UAV placement rather than the routing protocol itself. The authors should either implement a UAV control/placement model that realizes the hovering assumption or evaluate the protocol under conditions where the assumption is relaxed.
- [IV.C, Fig. 7(b), Conclusion] The results text in Section IV.C explicitly states that for more than 140 vehicles, RBVT-R outperforms the proposed approach in end-to-end delay, and that UAV-composed routes are unstable due to high mobility. The Conclusion, however, claims the protocol outperforms existing routing in terms of end-to-end delay 'especially the high densities,' and the abstract states an unqualified 'reduced end-to-end delay.' These statements are internally contradictory and overstate the findings. The claims must be restricted to the density range where the data support them.
- [IV.A, IV.C] The evaluation reports 15 simulation repeats per scenario, but no error bars, confidence intervals, or statistical tests are presented for any metric. This is particularly important because the end-to-end-delay advantage appears only below roughly 140 vehicles, and the crossover is a central point of the paper's claims. Without statistical evidence, the differences shown in Fig. 7 could be within simulation noise.
- [III.C, Eq. (3)] The score in Eq. (3) depends on a Delay value carried in the RREQ, but the manuscript does not specify how this delay is estimated during route discovery, which nodes update it, or how the destination obtains the values shown in Table I. The RREQ description says UAVs add only their IDs to the transited-zones list, so it is unclear how UAV-involved paths accumulate the delay metric. Without a defined delay estimator, the scoring rule is not reproducible.
minor comments (5)
- [IV.B] The definition of average number of hops, 'the number of successfully delivered data packets divided by the total number of hops,' is the inverse of the intended quantity; the figure axes and the surrounding text indicate the metric is hops per delivered packet. Please correct the definition.
- [IV.C] The phrase 'RBVT-R performs well than AGP' should read 'RBVT-R performs better than AGP.'
- [III.C] The word 'undiserable' should be 'undesirable.'
- [II] Reference [12] is cited as a 2016 publication for VanetMobiSim; please verify the correct year and version, as the mobility generator is widely known from earlier releases.
- [IV.A] The simulation map is described only as 4000 m × 4000 m with 9 intersections; the road lengths, block sizes, and segment structure are not given, which makes it difficult to interpret the meaning of the zone sizes and vehicle densities.
Circularity Check
No circular dependency: the protocol's scoring rule is defined independently of the reported simulation outcomes, and comparisons are against external baselines.
full rationale
The paper presents a reactive routing protocol with a fixed, explicitly stated path-scoring formula (Eq. 3) that combines measured RREQ information: NBvehicles, Delay, Sdeviation, and HOPs_UAV. No parameters were fitted to the NS-2 results, and no reported performance metric is defined as an output of that formula. The central claim, that cooperative UAVs extend connectivity in sparse urban VANETs, is evaluated by comparing the protocol against external baselines RBVT-R and AGP in simulation, rather than derived from the protocol's own assumptions. The only self-citation, reference [1] in the list [1]–[9], is used as contextual related-work support and is not load-bearing for any step of the proposed mechanism. The assumption in Section III.A that a UAV hovers over every four road segments is a design premise, not a quantity produced by the protocol, and any mismatch with the simulated UAV mobility is an experimental validity concern, not circularity. No self-definitional, fitted-input, self-citation-chain, or ansatz-smuggling reduction is present in the paper's derivation chain.
Assumptions & free parameters
free parameters (3)
- Zone size =
≈300m
- Number of UAVs =
16
- Communication range =
≈300m
assumptions (4)
- domain assumption UAVs can communicate with vehicles through wireless interfaces up to a large transmission range and are not affected by obstacles.
- domain assumption Each node has GPS, a map, and maintains an updated neighbor table.
- domain assumption There is no energy constraint for vehicles or UAVs.
- ad hoc to paper The network has a sufficient number of UAVs so that at each moment at least one UAV hovers an area of four road segments.
invented entities (1)
-
fixed zone
Cite this review
Pith. "Pith review of On-Demand Routing for Urban VANETs using Cooperating UAVs." pith.science (2026). https://pith.science/paper/NTB7RK7E
@misc{pith2026190805905,
author = {Pith},
title = {Pith review of: On-Demand Routing for Urban VANETs using Cooperating UAVs},
year = {2026},
howpublished = {\url{https://pith.science/paper/NTB7RK7E}},
note = {Machine review of arXiv:1908.05905}
}
read the original abstract
Vehicular ad hoc networks (VANETs) are characterized by frequent routing path failures due to the high mobility caused by the sudden changes of the direction of vehicles. The routing paths between two different vehicles should be established with this challenge in mind. Stability and connectedness are a mandatory condition to ensure a robust and reliable data delivery. The idea behind this work is to exploit a new reactive routing technique to provide regulated and well-connected routing paths. Unmanned Aerial Vehicles (UAVs) or what are referred to as drones can be both involved in the discovery process and be full members in these discovered paths in order to avoid possible disconnections on the ground when the network is sparsely connected. The different tests of this technique are performed based on NS-2 simulator and the outcomes are compared with those of related on-demand routing protocols dedicated for VANETs. Interesting results are distinguished showing a reduced end-to-end delay and a high delivery ratio, which proving that this heterogeneous communication between vehicles and UAVs is able to extend the network connectivity.
Figures
Figures from the paper (3 more)
Reference graph
Works this paper leans on
-
[1]
Intelligent UA V-Assisted Routing Protocol for Urban V ANETs,
O. S. Oubbati, A. Lakas, F. Zhou, M. G ¨unes ¸, N. Lagraa, and M. B. Yagoubi, “Intelligent UA V-Assisted Routing Protocol for Urban V ANETs,”Computer communications , vol. 107, pp. 93–111, 2017
work page 2017
-
[2]
D. K. N. Venkatramana, S. B. Srikantaiah, and J. Moodabidri, “SC- GRP: SDN-enabled connectivity-aware geographical routing protocol of V ANETs for urban environment,”IET Networks, vol. 6, no. 5, pp. 102– 111, 2017
work page 2017
-
[3]
MoZo: a moving zone based routing protocol using pure V2V commu- nication in V ANETs,
D. Lin, J. Kang, A. Squicciarini, Y . Wu, S. Gurung, and O. Tonguz, “MoZo: a moving zone based routing protocol using pure V2V commu- nication in V ANETs,”IEEE Transactions on Mobile Computing , vol. 16, no. 5, pp. 1357–1370, 2017
work page 2017
-
[4]
V ANET routing on city roads using real-time vehicular traffic information,
J. Nzouonta, N. Rajgure, G. Wang, and C. Borcea, “V ANET routing on city roads using real-time vehicular traffic information,” IEEE Transac- tions on V ehicular Technology,, vol. 58, no. 7, pp. 3609–3626, 2009
work page 2009
-
[5]
Real-Time Intersection-Based Segment Aware Routing Algorithm for Urban Vehicular Networks,
Y . R. B. Al-Mayouf, N. F. Abdullah, O. A. Mahdi, S. Khan, M. Ismail, M. Guizani, and S. H. Ahmed, “Real-Time Intersection-Based Segment Aware Routing Algorithm for Urban Vehicular Networks,” IEEE Trans- actions on Intelligent Transportation Systems , 2018
work page 2018
-
[6]
A Traffic Aware Segment-based Routing protocol for V ANETs in urban scenar- ios,
S. Khan, M. Alam, M. Fr ¨anzle, N. M ¨ullner, and Y . Chen, “A Traffic Aware Segment-based Routing protocol for V ANETs in urban scenar- ios,” Computers & Electrical Engineering , vol. 68, pp. 447–462, 2018
work page 2018
-
[7]
S. Yan, X.-y. JIN, and S.-z. CHEN, “AGP: an anchor-geography based routing protocol with mobility prediction for vanet in city scenarios,” The Journal of China Universities of Posts and Telecommunications , vol. 18, pp. 112–117, 2011
work page 2011
-
[8]
Delay analysis and routing for two-dimensional V ANETs using carry-and-forward mechanism,
J. He, L. Cai, J. Pan, and P. Cheng, “Delay analysis and routing for two-dimensional V ANETs using carry-and-forward mechanism,” IEEE Transactions on Mobile Computing, vol. 16, no. 7, pp. 1830–1841, 2017
work page 2017
Show all 13 references
-
[9]
MURU: A multi-hop routing protocol for urban vehicular ad hoc networks,
Z. Mo, H. Zhu, K. Makki, and N. Pissinou, “MURU: A multi-hop routing protocol for urban vehicular ad hoc networks,” in Proceedings of the 3rd Annual IEEE International Conference on Mobile and Ubiquitous Systems: Networking & Services , 2006, pp. 1–8
2006
-
[10]
UA V assisted disruption tolerant routing,
M. Le, J.-S. Park, and M. Gerla, “UA V assisted disruption tolerant routing,” in Proceedings of IEEE Military Communications Conference (MILCOM), 2006, pp. 1–5
2006
-
[11]
Simulation and Comparative Analysis of Packet Delivery in Flying Ad Hoc Network (FANET) Using AODV,
A. V . Leonov, G. A. Litvinov, and E. V . Shcherba, “Simulation and Comparative Analysis of Packet Delivery in Flying Ad Hoc Network (FANET) Using AODV,” in Proceedings of the 19th International Con- ference of Young Specialists on Micro/Nanotechnologies and Electron Devices (...
2018
-
[12]
VanetMobiSim: generating realistic mobility patterns for V ANETs,
J. Haerri, M. Fiore, F. Fethi, and C. Bonnet, “VanetMobiSim: generating realistic mobility patterns for V ANETs,” 2016
2016
-
[13]
Mobi-sim: A simulation en- vironment for mobile wireless sensors network,
O. Mezghani and P. M. Abdellaoui, “Mobi-sim: A simulation en- vironment for mobile wireless sensors network,” in Proceedings of the International Conference on Control, Decision and Information Technologies (CoDIT). IEEE, 2016, pp. 192–197
2016
Reviewed August 14, 2026 · model on record in the stance chip above.
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