1,742 research outputs found
Enabling Accurate Cross-Layer PHY/MAC/NET Simulation Studies of Vehicular Communication Networks
Vehicle-to-vehicle and vehicle-to-roadside communications is required for numerous applications that aim at improving traffic safety and efficiency. In this setting, however, gauging system performance through field trials can be very expensive especially when the number of studied vehicles is high. Therefore, many existing studies have been conducted using either network or physical layer simulators; both approaches are problematic. Network simulators typically abstract physical layer details (coding, modulation, radio channels, receiver algorithms, etc.) while physical layer ones do not consider overall network characteristics (topology, network traffic types, and so on). In particular, network simulators view a transmitted frame as an indivisible unit, which leads to several limitations. First, the impact of the vehicular radio channel is typically not reflected in its appropriate context. Further, interference due to frame collisions is not modeled accurately ( if at all) and, finally, the benefits of advanced signal processing techniques, such as interference cancellation, are difficult to assess. To overcome these shortcomings we have integrated a detailed physical layer simulator into the popular NS-3 network simulator. This approach aims to bridge the gap between the physical and network layer perspectives, allow for more accurate channel and physical layer models, and enable studies on cross-layer optimization. In this paper, we exemplify our approach by integrating an IEEE 802.11a and p physical layer simulator with NS-3. Further, we validate the augmented NS-3 simulator against an actual IEEE 802.11 wireless testbed and illustrate the additional value of this integration
Channel-access and routing protocols to utilize multiple heterogeneous channels for ad hoc networks
In this thesis, we consider a multi-channel ad hoc network employing frequency-agile radios that utilize direct-sequence spread-spectrum signaling. Two of the key distributed protocols for this type of network control channel access and routing. The channel-access protocol is responsible for controlling access to the channels available to the terminals in the network, and the routing protocol determines how packets are forwarded among the terminals in the network. To achieve reliable and efficient network performance, these protocols should cooperate with one another and take advantage of the multiple channels available to the network. In this thesis, we investigate a number of channel-access strategies for selecting a channel as well as various channel metrics to be used with routing. For our channel-access protocol, one channel is designated the control channel and is used to reserve access to one of the traffic channels. The channel-access protocol selects the traffic channel for a data packet transmission by examining the characteristics of the different traffic channels. New channel metrics are proposed to characterize the channels, and the metric values are used to assign a link resistance value for a link. Least-resistance routing utilizes the link resistances to calculate routes. The performance of the channel metrics for the routing protocol and the channel-access strategies are examined with a discrete-event simulation. From our investigations, we show that a jointly designed protocol that coordinates the channel-access strategies with the channel metrics results in network performance that is better than traditional channel-access and minimum-hop routing protocols
Optimization of the interoperability and dynamic spectrum management in mobile communications systems beyond 3G
The future wireless ecosystem will heterogeneously integrate a number of overlapped Radio
Access Technologies (RATs) through a common platform. A major challenge arising from the
heterogeneous network is the Radio Resource Management (RRM) strategy. A Common RRM
(CRRM) module is needed in order to provide a step toward network convergence. This work
aims at implementing HSDPA and IEEE 802.11e CRRM evaluation tools.
Innovative enhancements to IEEE 802.11e have been pursued on the application of cross-layer
signaling to improve Quality of Service (QoS) delivery, and provide more efficient usage of
radio resources by adapting such parameters as arbitrary interframe spacing, a differentiated
backoff procedure and transmission opportunities, as well as acknowledgment policies (where
the most advised block size was found to be 12). Besides, the proposed cross-layer algorithm
dynamically changes the size of the Arbitration Interframe Space (AIFS) and the Contention
Window (CW) duration according to a periodically obtained fairness measure based on the Signal
to Interference-plus-Noise Ratio (SINR) and transmission time, a delay constraint and the
collision rate of a given machine. The throughput was increased in 2 Mb/s for all the values of
the load that have been tested whilst satisfying more users than with the original standard. For
the ad hoc mode an analytical model was proposed that allows for investigating collision free
communications in a distributed environment.
The addition of extra frequency spectrum bands and an integrated CRRM that enables spectrum
aggregation was also addressed. RAT selection algorithms allow for determining the gains obtained
by using WiFi as a backup network for HSDPA. The proposed RAT selection algorithm
is based on the load of each system, without the need for a complex management system. Simulation
results show that, in such scenario, for high system loads, exploiting localization while
applying load suitability optimization based algorithm, can provide a marginal gain of up to
450 kb/s in the goodput. HSDPA was also studied in the context of cognitive radio, by considering
two co-located BSs operating at different frequencies (in the 2 and 5 GHz bands) in the
same cell. The system automatically chooses the frequency to serve each user with an optimal
General Multi-Band Scheduling (GMBS) algorithm. It was shown that enabling the access to
a secondary band, by using the proposed Integrated CRRM (iCRRM), an almost constant gain
near 30 % was obtained in the throughput with the proposed optimal solution, compared to a
system where users are first allocated in one of the two bands and later not able to handover
between the bands. In this context, future cognitive radio scenarios where IEEE 802.11e ad hoc
modes will be essential for giving access to the mobile users have been proposed
D13.2 Techniques and performance analysis on energy- and bandwidth-efficient communications and networking
Deliverable D13.2 del projecte europeu NEWCOM#The report presents the status of the research work of the
various Joint Research Activities (JRA) in WP1.3 and the results
that were developed up to the second year of the project. For
each activity there is a description, an illustration of the
adherence to and relevance with the identified fundamental
open issues, a short presentation of the main results, and a
roadmap for the future joint research. In the Annex, for each
JRA, the main technical details on specific scientific activities
are described in detail.Peer ReviewedPostprint (published version
Cooperative communication in wireless networks: algorithms, protocols and systems
Current wireless network solutions are based on a link abstraction where a
single co-channel transmitter transmits in any time duration. This model severely
limits the performance that can be obtained from the network. Being inherently an
extension of a wired network model, this model is also incapable of handling the
unique challenges that arise in a wireless medium. The prevailing theme of this
research is to explore wireless link abstractions that incorporate the broadcast and
space-time varying nature of the wireless channel. Recently, a new paradigm for
wireless networks which uses the idea of 'cooperative transmissions' (CT) has garnered
significant attention. Unlike current approaches where a single transmitter transmits
at a time in any channel, with CT, multiple transmitters transmit concurrently after
appropriately encoding their transmissions. While the physical layer mechanisms for
CT have been well studied, the higher layer applicability of CT has been relatively
unexplored. In this work, we show that when wireless links use CT, several network
performance metrics such as aggregate throughput, security and spatial reuse can
be improved significantly compared to the current state of the art. In this context,
our first contribution is Aegis, a framework for securing wireless networks against
eavesdropping which uses CT with intelligent scheduling and coding in Wireless Local
Area networks. The second contribution is Symbiotic Coding, an approach to encode
information such that successful reception is possible even upon collisions. The third
contribution is Proteus, a routing protocol that improves aggregate throughput in
multi-hop networks by leveraging CT to adapt the rate and range of links in a flow.
Finally, we also explore the practical aspects of realizing CT using real systems.PhDCommittee Chair: Sivakumar, Raghupathy; Committee Member: Ammar, Mostafa; Committee Member: Ingram, Mary Ann; Committee Member: Jayant, Nikil; Committee Member: Riley, Georg
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