# Beacon Success Rate versus Gateway Density in Sub-GHz Sensor Networks
## 7 Conclusions  
This paper demonstrates that DL-beacon performance under interference depends on several factors, such as the PHY bit-rate available, the protocol parameters (including the number of channels, the beacon duration and its periodicity, and the number of devices such as the number of GWs and ENs), and the environment (urban, sub-urban, or rural areas, which provide different path-loss environment and different levels of interference from other networks).  
This study demonstrates that, with large beacon intervals and an ample number of channels for frequency hopping, a considerable number of GWs can coexist in a WAN IoT network. For instance, a beacon interval of 10.08 s was analyzed along with 69 channels and a 152 ms beacon duration. Under such system settings, the expected number of colliding GWs (or beacons) in the DL is 1 out of 2000 GWs (Figure 18). This result corresponds to the performance of the MAC layer. According to the results with the path-loss model, 1000 GWs can coexist (at \(\sim\)1225 GWs/km\({}^{2}\) density) with an average beacon success rate of 95% (ref. Figure 21). This capacity result corresponds to the combined performance of the MAC and PHY layers. The performance relies on the protocol settings and HW settings. Due to the large beacon interval, the results indicate that the mean beacon acquisition latency is 10.5 s with only one GW. This latency significantly decreases when multiple GWs are within the reach of a given EN (Figure 19). The availability of GW diversity enhances the coverage area and reduces beacon acquisition latency.  
Future works as next steps to this study include, but are not limited to, the following. 1. Conducting an analysis of the capacity of a multi-rate GW capable of supporting different types of ENs, ranging from those that support higher bitrates to those supporting lower bitrates. 2. Assessing the performance versus beacon interval to identify the optimal balance between latency and network capacity under interference. 3. Proposing a next generation system design where GWs are coordinated in the cloud and employ a frequency reuse mechanism to minimize the interference impact of neighboring GWs. 4. Providing a performance evaluation of UL and DL data links with LBT and determining the maximum number of packets per beacon interval that can be supported in the network. 5. Conducting a performance evaluation for urban dense and rural environments.  
Conceptualization, B.C., B.K., A.B., F.Z., S.P. and U.B.; methodology, B.C., B.K., A.B., F.Z., S.P., M.F.G., J.H., P.P. and U.B.; software, A.B., F.Z., S.P., B.C. and M.F.G.; validation, B.C., A.B., F.Z., S.P., J.H., P.P. and M.F.G.; formal analysis, B.C., F.Z., S.P., J.H., P.P. and A.B.; investigation, B.C., B.K., A.B., F.Z., S.P. and M.F.G.; data curation, B.C., B.K., A.B., F.Z. and S.P.; writing--original draft preparation, B.C.; writing--review and editing, B.C., A.K., F.Z. and A.B.; visualization, B.C., S.P., F.Z. and A.B.; supervision, B.C., B.K., A.B., U.B., R.S., S.M., A.K. and V.S.K.V.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Amazon.com, Inc., and performed by the employees of the same. This research received no external funding.  
Not applicable.  
Data Availability Statement: Data are contained within the article.  
The authors extend their appreciation to [PERSON] and [PERSON] for their initial revisions of the WAN-FSK NS-3 sub-module code development. Additionally, the authors would like to recognize [PERSON] for conducting field measurements using the SX-1262 chipset, and [PERSON] for assisting in estimating the path loss exponent based on the field measurements. Special gratitude is extended to [PERSON] for her guidance with pre-submission paper review.  
Authors were employed by the company Amazon Lab126.