A directional MAC protocol for MANET

In a typical mobile ad hoc network (MANET), all nodes contend for a single channel access using carrier sense multiple access with collision avoidance (CSMA/CA). Thus, a fundamental limitation of MANET is that, as the number of nodes increases, the performance of the system will dramatically degrade due to the large number of collisions. This, in turn, results in an overall low system throughput. Several researchers have focused on the potential throughput gains achieved using directional antennas in ad hoc networks. When compared to omnidirectional antennas, directional antennas are more attractive option in terms of power and bandwidth efficiency. On the other hand, when used in ad hoc networks, directional MAC (DMAC) protocols usually require all nodes, or part of nodes, to be aware of their exact locations. The location information is typically provided to the DMAC protocol from upper network layers, for example, by using a Global Positioning System (GPS). Other problems that face these DMAC protocols are the deafness problem and the hidden terminal problem. Solving these problems is at the core of designing any DMAC protocol. At the same time, DMC protocols should not sacrifice channel bandwidth to deal with theses problems. In this thesis, we propose an efficient 2-channel 2-mode DMAC protocol. In particular, our protocol employs two frequency division multiplexed channels: Channel one is used for omni mode packets transmission and channel two is used for directional mode packets transmission. Estimation of Signal Parameter via Rotational Invariance Technique (ESPRIT) is used for direction of arrival (DOA) estimation. By avoiding the reliance on GPS for obtaining the position information, our protocol is also suitable for indoor environments. Under different operating conditions and channel models, our simulation results clearly show the improved throughput of our protocol compared to IEEE 802.1

Fixed Rank Kriging for Cellular Coverage Analysis

Coverage planning and optimization is one of the most crucial tasks for a radio network operator. Efficient coverage optimization requires accurate coverage estimation. This estimation relies on geo-located field measurements which are gathered today during highly expensive drive tests (DT); and will be reported in the near future by users' mobile devices thanks to the 3GPP Minimizing Drive Tests (MDT) feature~\cite{3GPPproposal}. This feature consists in an automatic reporting of the radio measurements associated with the geographic location of the user's mobile device. Such a solution is still costly in terms of battery consumption and signaling overhead. Therefore, predicting the coverage on a location where no measurements are available remains a key and challenging task. This paper describes a powerful tool that gives an accurate coverage prediction on the whole area of interest: it builds a coverage map by spatially interpolating geo-located measurements using the Kriging technique. The paper focuses on the reduction of the computational complexity of the Kriging algorithm by applying Fixed Rank Kriging (FRK). The performance evaluation of the FRK algorithm both on simulated measurements and real field measurements shows a good trade-off between prediction efficiency and computational complexity. In order to go a step further towards the operational application of the proposed algorithm, a multicellular use-case is studied. Simulation results show a good performance in terms of coverage prediction and detection of the best serving cell

Location Spoofing Detection for VANETs by a Single Base Station in Rician Fading Channels

In this work we examine the performance of a Location Spoofing Detection System (LSDS) for vehicular networks in the realistic setting of Rician fading channels. In the LSDS, an authorized Base Station (BS) equipped with multiple antennas utilizes channel observations to identify a malicious vehicle, also equipped with multiple antennas, that is spoofing its location. After deriving the optimal transmit power and the optimal directional beamformer of a potentially malicious vehicle, robust theoretical analysis and detailed simulations are conducted in order to determine the impact of key system parameters on the LSDS performance. Our analysis shows how LSDS performance increases as the Rician K-factor of the channel between the BS and legitimate vehicles increases, or as the number of antennas at the BS or legitimate vehicle increases. We also obtain the counter-intuitive result that the malicious vehicle's optimal number of antennas conditioned on its optimal directional beamformer is equal to the legitimate vehicle's number of antennas. The results we provide here are important for the verification of location information reported in IEEE 1609.2 safety messages.Comment: 6 pages, 5 figures, Added further clarification on constraints imposed on the detection minimization strategy. Minor typos fixe

Collaborative Beamforming for Distributed Wireless Ad Hoc Sensor Networks

The performance of collaborative beamforming is analyzed using the theory of random arrays. The statistical average and distribution of the beampattern of randomly generated phased arrays is derived in the framework of wireless ad hoc sensor networks. Each sensor node is assumed to have a single isotropic antenna and nodes in the cluster collaboratively transmit the signal such that the signal in the target direction is coherently added in the far- eld region. It is shown that with N sensor nodes uniformly distributed over a disk, the directivity can approach N, provided that the nodes are located sparsely enough. The distribution of the maximum sidelobe peak is also studied. With the application to ad hoc networks in mind, two scenarios, closed-loop and open-loop, are considered. Associated with these scenarios, the effects of phase jitter and location estimation errors on the average beampattern are also analyzed.Comment: To appear in the IEEE Transactions on Signal Processin