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Transmission power control (TPC) leads to heterogeneous transmission power levels of the nodes in multi-hop wireless ad hoc networks. This eventually results in a quite complicated collision scenario due to hidden and exposed terminal problems, and brings a big challenge for analyzing the saturation throughput of the flows. This paper presents a saturation throughput model for IEEE 802.11 multi-hop ad hoc networks with heterogeneous transmission powers. In the model, one tagged node goes through with three processes, i.e., backoff, freezing and transmission, and each of which is composed of a certain number of continuous fixed length time slots. We put forward a four-dimensional Markov chain model for the behavior of the tagged node in each fixed-length time slot. Under the condition of heterogeneous transmission powers, we consider two types of collisions, i.e., the instantaneous and persistent collisions. Their probabilities are characterized by the one-step transition probability matrix of the Markov chain. The per-flow saturation throughput of the flow is eventually derived through an iterative way. Finally, the accuracy of our model is validated by comparing the analytical values and the simulation results, and the impact of the heterogeneous power levels on the performance of the wireless multi-hop ad hoc networks is effectively analyzed.

Contention-based distributed synchronization (CDS) protocols, which first standardized in the IEEE 802.11 power saving mode (PSM), have been widely used in wireless ad hoc networks. The time required to complete the synchronization progress, i.e., synchronization efficiency, is obviously an important performance metrics for CDS protocols. However, few attempts have been focusing on modeling and analyzing the synchronization efficiency of the CDS protocols. In this letter, we present a 2-D Markov chain model for the CDS scheme of the IEEE 802.11 PSM. The purpose of our model is to determine the relationship between the time required to complete the synchronization process and the value of the contention parameter, i.e., the contention window size. Through modeling, we derive the optimal values of the contention window size to achieve the minimum synchronization time at different network scales. We also validate the accuracy of our model by comparing the analytical results with that obtained by means of simulations.

Directional antennas have numerous advantages over omnidirectional antennas in CSMA/CA ad hoc networks. However, estimating the available bandwidth of a flow in the medium access process in such a network is very challenging. In this paper, we present a passive available bandwidth estimation algorithm for directional ad hoc networks, termed PABE-D. The estimation process consists of two phases, i.e., the preliminary and refined estimation phases. In the preliminary phase, the available transmission/reception duration in each beam of the node and the available bandwidth of the directional link are obtained by analyzing the available duration of both the sender and receiver. In the refined phase, we analyze the effect of the directional hidden terminal and deafness problems to further improve the estimate accuracy. The performance of our proposed PABE-D algorithm is evaluated in two typical topologies, i.e., the parallel and random grid topologies. The simulation results demonstrate that our algorithm can effectively estimate the available bandwidth in directional ad hoc networks.

In wireless ad hoc networks, a suitable MAC protocol can provide better QoS (Quality of Service) guarantees. However, in modern warfare environment, the combat missions change rapidly. A fixed MAC protocol may be not suitable for the highly changeable environments and combat missions. To solve this problem, we propose a neural network-based MAC protocol-selection mechanism to select the optimal MAC protocol for new missions based on the real-time environment information of the battlefield, i.e., the intelligent selection (IS) algorithm. In IS, we prepare the empirical data set with massive mission data, and construct the learning model through making use of the neural network. Experimental results demonstrate that the prediction accuracy of the proposed IS algorithm is over 0.93.

This paper analyzes the limitation of IEEE 802.11 protocol using a single power for node communication. On the basis of IEEE 802.11protocol and the basic power backoff protocol which introduces the idea of power backoff, a CSMATPB protocol with time and space backoff is proposed. The protocol increases the time competition window, while making the power backoff reduce the interference between nodes. Then, the three dimensional Markov chain model is established for this protocol. Through the results of numerical calculation and simulation analysis, it is proved that the protocol mechanism can effectively solve the problem that the lower space reuse rate of IEEE 802.11 protocol and the problem that the basic power backoff protocol discards the packet prematurely. So CSMA-TPB protocol can effectively improve the saturation throughput and energy utilization of the network.

This paper presents DT-MAC, a dynamic TDMA based medium access control (MAC) protocol designed to offer collision-free transmissions while providing QoS guarantees for different services in scalable fully connected ad hoc networks. In DT-MAC, a new time frame structure which consists of synchronization, request, assignment and data slots is put forward. In each frame, the number of slots and their lengths are adaptively adjusted according to the number of nodes and their services in the network. Meanwhile, a distributed frame synchronization method is proposed to provide synchronization guarantee for the nodes and generate a manager node for each frame to dynamically allocate the slots according to the QoS requirements of different services. Besides, by introducing request slot, DT-MAC can make nodes join or leave the network without conflicts. Simulation results show that DT-MAC performs better in providing QoS guarantees and accommodating the change of network scale compared with conventional TDMA-based MAC protocols.

The aeronautical ad hoc network (AANET) is an application of the mobile ad hoc networking technology to aeronautical communications. As the airliners move at a very high speed, one critical issue for improving the performance of AANET is to select reliable route that can address the frequent link breakage problem induced by the unpredicted network topology changes. In this paper, we focus on developing a link availability estimation based reliable routing protocol which considers the unpredicted network topology change problem to improve the performance of AANET. The link availability indicates the probability that a link will be continuously available for a given period of time. We first propose a novel Semi-Markov Smooth mobility model to mimic the behavior of the airliners in the sky. On the basis of the mobility model, we obtain the probability density function of the relative speed of two nodes, and further derive the expectation of the link lifetime. The accuracy of our analysis is validated by comparing the analytical results with that obtained by means of simulations. Moreover, we define the link availability factor and use it as the path selection metric to design a reliable routing protocol for AANET. Simulation results show that a gain in performance can be obtained by our protocol compared with the traditional routing strategy.

In this paper, we focus on improving MACA-P performance in multi-hop ad hoc networks. Based on the analysis of the collision problems of the distributed coordination function (DCF) and MACA-P in multi-hop ad hoc networks, we propose an adaptive collision avoidance scheme (ACAS). ACAS mainly improves MACA-P by adaptively adjusting the control gap of the master transmission based on the conditions of the master transmission. Also, a new hybrid confirmation mechanism is presented, which, together with the adjustment of the control gap, decreases the energy consumption of the nodes. Simulation results show that our scheme can obtain higher overall throughput and lower energy consumption in comparison with the DCF and MACA-P protocols.