# Literature Review — verified sources

Each reference below was checked against its Crossref DOI record (title, authors, venue, year,
volume, pages). Summaries are based on the abstracts; skim the PDF of any paper before the viva.

## A. Broadcast storm problem and mitigation
[1] S.-Y. Ni, Y.-C. Tseng, Y.-S. Chen, and J.-P. Sheu, "The broadcast storm problem in a mobile ad hoc network," in Proc. 5th ACM/IEEE MobiCom '99, Seattle, WA, USA, 1999, pp. 151–162, doi: 10.1145/313451.313525.
— Names the broadcast storm (redundant rebroadcasts, contention, collisions). Compares probabilistic, counter, distance, location and cluster suppression. Generic MANET; ignores road geometry and direction. Basis of our flooding baseline.

[2] N. Wisitpongphan, O. K. Tonguz, J. S. Parikh, P. Mudalige, F. Bai, and V. Sadekar, "Broadcast storm mitigation techniques in vehicular ad hoc networks," IEEE Wireless Commun., vol. 14, no. 6, pp. 84–94, Dec. 2007, doi: 10.1109/MWC.2007.4407231.
— Weighted p-persistence, slotted 1-persistence, slotted p-persistence; farther receivers get earlier slots. Up to ~70% less packet loss. Uses distance only, no directional cancellation.

## B. Distance / contention-based multi-hop broadcast
[3] G. Korkmaz, E. Ekici, F. Özgüner, and Ü. Özgüner, "Urban multi-hop broadcast protocol for inter-vehicle communication systems," in Proc. 1st ACM VANET '04, Philadelphia, PA, USA, 2004, pp. 76–85, doi: 10.1145/1023875.1023887.
— UMB: farthest-segment forwarder chosen via MAC-level handshake/ACK. Not possible over plain UDP broadcast.

[4] E. Fasolo, A. Zanella, and M. Zorzi, "An effective broadcast scheme for alert message propagation in vehicular ad hoc networks," in Proc. IEEE ICC, Istanbul, Turkey, 2006, pp. 3960–3965, doi: 10.1109/ICC.2006.255700.
— "Smart Broadcast": position-based backoff so farther vehicles win contention. Idealised channel, one direction. Closest prior work to our contention timer.

[5] O. K. Tonguz, N. Wisitpongphan, and F. Bai, "DV-CAST: A distributed vehicular broadcast protocol for vehicular ad hoc networks," IEEE Wireless Commun., vol. 17, no. 2, pp. 47–57, Apr. 2010, doi: 10.1109/MWC.2010.5450660.
— Handles dense/sparse/disconnected highways with hello beacons and store-carry-forward. Depends on beacons for neighbour knowledge.

[6] H. Füßler, J. Widmer, M. Käsemann, M. Mauve, and H. Hartenstein, "Contention-based forwarding for mobile ad hoc networks," Ad Hoc Netw., vol. 1, no. 4, pp. 351–369, Nov. 2003, doi: 10.1016/S1570-8705(03)00038-6.
— Beaconless greedy forwarding with progress-based timers; shows duplicate suppression is the hard part. Unicast, not area broadcast.

## C. Probabilistic / gossip
[7] Z. J. Haas, J. Y. Halpern, and L. Li, "Gossip-based ad hoc routing," IEEE/ACM Trans. Netw., vol. 14, no. 3, pp. 479–491, Jun. 2006, doi: 10.1109/TNET.2006.876186.
— Fixed-probability forwarding; bimodal behaviour (dies early or reaches almost all). p = 0.6–0.8 typical. Basis of our gossip baseline.

[8] X. Zeng, M. Yu, and D. Wang, "A new probabilistic multi-hop broadcast protocol for vehicular networks," IEEE Trans. Veh. Technol., vol. 67, no. 12, pp. 12165–12176, Dec. 2018, doi: 10.1109/TVT.2018.2872998.
— Distance-dependent forwarding probability plus clustering. Needs clusters; no directional cancellation.

## D. IEEE 802.11p / DSRC
[9] D. Jiang and L. Delgrossi, "IEEE 802.11p: Towards an international standard for wireless access in vehicular environments," in Proc. IEEE VTC Spring, Singapore, 2008, pp. 2036–2040, doi: 10.1109/VETECS.2008.458.
— Overview of 802.11p: communication outside a BSS, no association; justifies our ad hoc broadcast set-up.

[10] M. Torrent-Moreno, D. Jiang, and H. Hartenstein, "Broadcast reception rates and effects of priority access in 802.11-based vehicular ad-hoc networks," in Proc. 1st ACM VANET '04, Philadelphia, PA, USA, 2004, pp. 10–18, doi: 10.1145/1023875.1023878.
— Nakagami fading sharply lowers broadcast reception vs two-ray ground; recommends repetition / multi-hop. Supports our fading + beacon-load + repeated-alert design.

## E. Surveys
[11] H. Hartenstein and K. P. Laberteaux, "A tutorial survey on vehicular ad hoc networks," IEEE Commun. Mag., vol. 46, no. 6, pp. 164–171, Jun. 2008, doi: 10.1109/MCOM.2008.4539481.

[12] S. Latif, S. Mahfooz, B. Jan, N. Ahmad, Y. Cao, and M. Asif, "A comparative study of scenario-driven multi-hop broadcast protocols for VANETs," Veh. Commun., vol. 12, pp. 88–109, Apr. 2018, doi: 10.1016/j.vehcom.2018.01.009.

## F. Recent emergency-message schemes
[13] S. S. Shah, A. W. Malik, A. U. Rahman, S. Iqbal, and S. U. Khan, "Time barrier-based emergency message dissemination in vehicular ad-hoc networks," IEEE Access, vol. 7, pp. 16494–16503, 2019, doi: 10.1109/ACCESS.2019.2895114.

[14] W. Benrhaiem, A. Hafid, and P. K. Sahu, "Reliable emergency message dissemination scheme for urban vehicular networks," IEEE Trans. Intell. Transp. Syst., vol. 21, no. 3, pp. 1154–1166, Mar. 2020, doi: 10.1109/TITS.2019.2902850.

[15] D. Cao, B. Zheng, B. Ji, Z. Lei, and C. Feng, "A robust distance-based relay selection for message dissemination in vehicular network," Wireless Netw., vol. 26, no. 3, pp. 1755–1771, 2020, doi: 10.1007/s11276-018-1863-4.

## G. ns-3 evaluation
[16] F. Raviglione, C. M. Risma Carletti, M. Malinverno, C. Casetti, and C. F. Chiasserini, "ms-van3t: An integrated multi-stack framework for virtual validation of V2X communication and services," Comput. Commun., vol. 217, pp. 70–86, Mar. 2024, doi: 10.1016/j.comcom.2024.01.022.

## Verified extras
- L. Briesemeister and G. Hommel, "Role-based multicast in highly mobile but sparsely connected ad hoc networks," in Proc. 1st MobiHOC, 2000, pp. 45–50, doi: 10.1109/MOBHOC.2000.869212.
- K. Bilstrup, E. Uhlemann, E. G. Ström, and U. Bilstrup, "Evaluation of the IEEE 802.11p MAC method for vehicle-to-vehicle communication," in Proc. IEEE VTC Fall, 2008, pp. 1–5, doi: 10.1109/VETECF.2008.446.
- C.-M. Wu et al., "Emergency message broadcast mechanism in vehicular ad-hoc networks based on reinforcement learning with contention estimation," IEEE Trans. Intell. Veh., vol. 10, no. 2, pp. 819–831, Feb. 2025, doi: 10.1109/TIV.2024.3418778.

## Research gaps (from the review)
1. Distance-based deferral ([2],[4],[8],[13],[15]) lacks directional cancellation; cancellation in [3],[6] needs MAC handshakes/ACKs.
2. Most suppression needs MAC changes or control traffic; few work purely at the application layer over UDP broadcast on unmodified 802.11p.
3. Evaluations often use idealised channels; few compare schemes under Nakagami fading + periodic beacon load ([10],[12]).
4. Repetition ([10],[14]) and suppression are studied separately.
5. Fixed-p gossip [7] is fragile; distance-weighted variants [8] need clusters.
6. ns-3 frameworks ([16]) exist but are rarely used for head-to-head broadcast-storm benchmarks.

**Selected gap (our project):** an application-layer, directional, distance-contention relay over standard
UDP broadcast on IEEE 802.11p, evaluated against flooding and gossip in ns-3 with fading, beacon load and repeated alerts.