Optimal Transmission Range for Wireless Ad Hoc Networks Based on Energy Efficiency

The transmission range that achieves the most economical use of energy in wireless ad hoc networks is studied for uniformly distributed network nodes. By assuming the existence of forwarding neighbors and the knowledge of their locations, the average per-hop packet progress for a transmission range that is universal for all nodes is derived. This progress is then used to identify the optimal per-hop transmission range that gives the maximal energy efficiency. Equipped with this analytical result, the relation between the most energy-economical transmission range and the node density, as well as the path loss exponent, is numerically investigated. It is observed that when the path loss exponent is high (such as four), the optimal transmission ranges are almost identical over the range of node densities that we studied. However, when the path loss exponent is only two, the optimal transmission range decreases noticeably as the node density increases. Simulation results also confirm the optimality of the per-hop transmission range that we found analytically

Performance evaluation of packet radio networks

The first ground wireless packet switching radio network, named the ALOHA network, was implemented in the early 1970s at University of Hawaii. The most distinct features of a packet radio network are: (1) the absence of physical connections between users, (2) the sharing of a common transmission medium, and (3) the broadcasting capability of each user. Today, the packet radio network technology is widely used in a variety of civilian as well as military applications;The throughput of a packet radio network is defined as the percentage of time the channel carries good packets. It is largely determined by the channel access method, the signal propagation characteristics, and the capture effect at a receiver. In this dissertation, we present two packet radio network models under the Slotted ALOHA channel access method and a capture model which is based on the relative strength of signal powers of the desired packet and the interfering packets;The first model is a single-hop network with a central station and finite number of users randomly distributed in a limited area. All the users communicate with each other through the central station, which is within one hop distance of all users. Given a density distribution function for the distance of a user, we show that there is an optimal transmission probability which maximizes the throughput of the network. Also, under a light traffic load, the throughput of a remote user is relatively insensitive to its distance from the station;The second model is a multi-hop network where a user is equipped with a directional antenna and not every user can directly communicate with every other else. As a result, a user communicates with another user either directly in a single hop or through some intermediate users in multiple hops. The location of all users is modeled by a two-dimensional Poisson process with an average of [lambda] users per unit area. By balancing the transmission probability and the antenna beam width, we show that the maximum hop-by-hop progress of a packet can be achieved when the transmitter and the receiver are separated by an optimal distance

Collision-free Time Slot Reuse in Multi-hop Wireless Sensor Networks

To ensure a long-lived network of wireless communicating sensors, we are in need of a medium access control protocol that is able to prevent energy-wasting effects like idle listening, hidden terminal problem or collision of packets. Schedule-based medium access protocols are in general robust against these effects, but require a mechanism to establish a non-conflicting schedule. In this paper, we present such a mechanism which allows wireless sensors to choose a time interval for transmission, which is not interfering or causing collisions with other transmissions. In our solution, we do not assume any hierarchical organization in the network and all operation is localized. We empirically show that our localized algorithm is successful within a factor 2 of the minimum necessary time slots in random networks; well in range of the expected (worst case) factor 3-approximation of known first-fit algorithms. Our algorithm assures similar minimum distance between simultaneous transmissions as CSMA(/CD)-based approaches