【正文】 onnected via BNs (. E → BN 2 → C → D). Mobile nodes between remote areas can also be connected via BNs (. A → B → BN 1 → BN 2 → C → D). Thus, whenever a remote mobile node has a request to connect to 2 another node, the BNs function both as normal mobile nodes and also forward connection requests to the desired remote destination node. This implies that the works can establish more and better routes, and are able to deliver more packets without extra routing overhead. The effectiveness of this approach in enhancing work connectivity can be proved by simulation in different work configurations, that is, with different node densities, velocities, and transmission power. We used the Javabased scalable wireless ad hoc work simulator (SWANS) to simulate a MANET with IEEE medium access control protocol and transmission of UDP traffic. The BNs possess all the properties of normal mobile nodes, but they possess larger transmission power and remain stationary during the simulation. The ad hoc ondemand vector routing (AODV) protocol is used. Two criteria are used to assess work connectivity: the packet delivery ratio (the total number of data packets received over the total number of packets sent by all nodes) and the average path length (the average number of mobile hops a packet takes to reach its destination). Results show that our approach performs better than the normal MANET in all simulated work scenarios. Performance is significantly improved (see Figure 2) when work node density is lower. In the case of 50 nodes, our approach can deliver more than 89% of packets, an increase of 28% pared with the normal MANET. This is because, without the assistance of BNs, many nodes are out of the reach of each other when the node density is lower. In parison with the normal work, the average packet length is shorter, with our work consistently establishing routes about one hop less than the normal work in all scenarios. Figure 2. In paring packet delivery ratios as a function of node density when nodes are stationary, the work with BNs provides better performance, especially in lower node density situations. High connectivity, extremely important for MANET to be feasible in critical situations, can be greatly enhanced by selecting a few nodes to serve as backbone nodes. This approach is relatively easy to deploy inasmuch as output power of many wireless devices can be customconfigured. It can also be used to improve user or node connectivity in other works, such as sensor works and mobile munication systems. Authors 3 Xiyu Shi, Ahmet Kondoz Centre for Communication Systems Research, University of Surrey， Guildford， UK Christopher Adams Department of Information Systems, University of Buckingham， Buckingham， UK References: 1. C. Perkins, E. BeldingRoyer, S. Das, Ad hoc ondemand distance vector (AODV) routing, IETF RFC, Vol: 3561, 2020. 2. D. Johnson, D. Maltz, Y. Hu, The dynamic source routing protocol for mobile ad hoc works (DSR), IETF Interdrafts, 2020. 3. D. B. Johnson, D. A. Maltz, Dynamic source routing in ad hoc wireless works, Mobile Computing, pp. 153181, 1996. 4. Z. Haas, M. Pearlman, P. Samar, The zone routing protocol (ZRP) for ad hoc works, IETF Interdrafts, , 2020. 5. J. Broch, D. A. Maltz, D. B. Johnson, Y. C. Hu, J. Jetcheva, A performance parison of multihop wireless ad hoc work routing protocols, Proc. Fourth Annual ACM/IEEE Int. Conference on Mobile Computing and Networking (MobiCom39。98), 1998. 6. B. Freisleben, R. Jansen, Analysis of routing protocols for ad hoc works of mobile muters, Proc. of the 15th IASTED International Conference on Applied Informatics, 1997. 7. X. Shi, F. Li, C. Adams, The impact of backbone nodes on MANET routing performance, Proc. of the MultiService Networks 2020 Conference, 2020. DOI: Chirp signaling offers modulation scheme for underwater munications Edit J. Kaminsky Information contained in the slope of chirp signals can be employed for digital underwater acoustic munications across a broad range of applications. Wireless munication can be conducted in the underwater acoustic (UWA) channel through sonar signalling. We propose using the frequencyvstime slope of sonar ?chirps‘ to transmit information in a robust scheme for a spreadspectrum underwater munications system. Digital data can be represented by the slope of chirp signals. In the simplest binary case, an ?up‘ chirp (., a signal with instantaneous frequency that linearly increases with time) represents a ?1‘ and a ?down‘ chirp represents a ?0‘. Higherdimensional constellations can easily be obtained by 4 using a larger number of up/down slopes. The wide bandwidth should provide immunity from signal degradation in the channel. Underwater munications Using a cable to establish munication between two remote underwater sites has several disadvantages. It is expensive to install and maintenance and repair are difficult, especially for munication in deep water. In addition, drag on the cable can be a problem if the user is small and mobile. Sound propagated through water is a better solution. However, the UWA channel is an unfiving wireless medium that poses numerous challenges to reliable, high data rate and longdistance munications. Four aspects of the UWA channel are of primary concern: ambient noise, transmission loss due to geometrical spreading and absorption, reverberation due to multiple paths, and Doppler spreading due to relative motion. Each of these must be considered in modeling the appropriate UWA ,2 Multipath propagation, for instance, could restrict munication in the channel to noncoherent modulation schemes and low data rate transmission. In the past, underwater acoustic munications received much attention, mainly from the military, and the field was closely associated wit