In a self-organizing vehicular network, vehicles share and distribute information by rebroadcasting a received information packet to their neighbors. An efficient broadcast technique can offer a high reactivity without sacrificing the communication reliability. Therefore, broadcast techniques are particularly suitable for safety-related vehicular transmissions, whose goal is reaching reliably the widest area in the shortest time. Among the numerous solutions appeared in the literature, the probabilistic broadcast approaches seem to be promising and not yet accurately analyzed. Since the interaction between a high level broadcasting protocol with the lower layers cannot be ignored, in this work we analyze the behavior of a recently proposed broadcast technique, denoted as the Irresponsible Forwarding (IF), in IEEE 802.11 networks. Our attention concentrates on the Medium Access Control (MAC) layer, which is affected by some critical impairments for broadcasting, such as the hidden terminal problem and self-interference. In this work, we evaluate the benefits brought by the use of IF to perform efficient broadcasting in IEEE 802.11 networks.

The frame length is a significant factor which affects the performance of the framed ALOHA-based anti-collision protocols for RFID systems. Using a large frame length can reduce the number of collision slots. However, it also increases the number of wasteful slots. In order to optimize the performance, the frame length must be chosen carefully. In this paper, we present an optimal frame length selection scheme, which maximizes the system throughput. Our scheme requires only minimal information obtained from the tags' responses in the current frame, as opposed to relying on the past information collected in the previous frames. It is shown that the performance of our scheme is close to that of the ideal best-case scheme where the reader has completely accurate knowledge of the number of tags transmitting in each frame.

This paper investigates whether and when route reservation-based (RB) communication can yield better delay performance than non-reservation-based (NRB) communication in ad hoc wireless networks. In addition to posing this fundamental question, the requirements (in terms of route discovery, medium access control (MAC) protocol, and pipelining, etc.) for making RB switching superior to NRB switching are also identified. A novel analytical framework is developed and the network performance under both RB and NRB schemes is quantified. It is shown that if the aforementioned requirements are met, then RB schemes can indeed yield better delay performance than NRB schemes. This advantage, however, comes at the expense of lower throughput and goodput compared to NRB schemes

Power conservation is one of the most important issues in wireless ad hoc and sensor networks, where nodes are likely to rely on limited battery power. Transmitting at unnecessarily high power not only reduces the lifetime of the nodes and the network, but also introduces excessive interference. It is in the network designer's best interest to have each node transmit at the lowest possible power while preserving network connectivity. In this paper, we investigate the optimal common transmit power, defined as the minimum transmit power used by all nodes necessary to guarantee network connectivity. This is desirable in sensor networks where nodes are relatively simple and it is difficult to modify the transmit power after deployment. The optimal transmit power derived in this paper is subject to the specific routing and medium access control (MAC) protocols considered; however, the approach can be extended to other routing and MAC protocols as well. In deriving the optimal transmit power, we distinguish ourselves from a conventional graph-theoretic approach by taking realistic physical layer characteristics into consideration. In fact, connectivity in this paper is defined in terms of a quality of service (QoS) constraint given by the maximum tolerable bit error rate (BER) at the end of a multihop route with an average number of hops

In this paper, we compare the performance of two possible switching techniques for ad hoc wireless networks: namely, reservation-based (RB) and non-reservation-based (NRB) switching. Fundamental network performance metrics, such as throughput and delay, are studied to understand the tradeoffs between the two switching schemes. In particular, we identify the circumstances where each of these two schemes is better than the other.

Power conservation is one of the most important issues for ad hoc wireless networks where nodes are likely to rely on limited battery power. Transmitting at unnecessarily high power not only reduces the lifetime of the nodes and the network, but also introduces excessive interference. It is in the network designer's best interest to have each node transmit at the lowest possible power while preserving network connectivity. In this paper, we investigate the optimal common transmit power, defined as the minimum transmit power used by all nodes necessary to guarantee network connectivity. In particular, we show that for a given route BER and node spatial density, there exists a global optimal data rate at which the transmit power can be globally minimized. Moreover, we also show that there exists a critical node spatial density at which the optimal transmit power is the minimum possible for a given data rate and a given route BER.

In this paper, the performance of two possible switching schemes for ad hoc wireless networks, namely reservation-based (RB) and non-reservation-based (NRB) is investigated. It is shown that route reservation would be the scheme of choice in a scenario where delay is a constraint, the network is dense, and/or nodes move with moderate speed. However, a non-reservation scheme is preferable in a scenario where the network is sparse, there is heavy traffic load, nodes are static, and/or delay is not a major concern.

In this paper, we propose a simple semi-analytical approach for the evaluation of the impact of mobility on the bit error rate (BER) performance of multi-hop ad hoc wireless networks. Analytical expressions, relating the BER at the end of a multi-hop route with the mobility characteristics of the nodes and the routing strategy, are derived. Two node mobility models are considered: direction-persistent (DP) and direction-nonpersistent (DNP). In particular, two network switching scenarios are analyzed: (i) opportunistic non-reservation-based switching (ONRBS), where a message flows from source to destination by opportunistically choosing the available shortest consecutive links; and (ii) reservation-based switching (RBS), where, after the creation of a multi-hop route from source to destination, the message is "forced" to flow over the reserved links, regardless of their actual lengths. The network performance is evaluated in ideal (without inter-node interference, INI) and realistic (with INI) cases. The improved robustness against mobility offered by ONRBS, with respect to RBS, is analyzed and quantified.