24,487 research outputs found
Diversity-Multiplexing Tradeoff of Asynchronous Cooperative Diversity in Wireless Networks
Synchronization of relay nodes is an important and critical issue in
exploiting cooperative diversity in wireless networks. In this paper, two
asynchronous cooperative diversity schemes are proposed, namely, distributed
delay diversity and asynchronous space-time coded cooperative diversity
schemes. In terms of the overall diversity-multiplexing (DM) tradeoff function,
we show that the proposed independent coding based distributed delay diversity
and asynchronous space-time coded cooperative diversity schemes achieve the
same performance as the synchronous space-time coded approach which requires an
accurate symbol-level timing synchronization to ensure signals arriving at the
destination from different relay nodes are perfectly synchronized. This
demonstrates diversity order is maintained even at the presence of asynchronism
between relay node. Moreover, when all relay nodes succeed in decoding the
source information, the asynchronous space-time coded approach is capable of
achieving better DM-tradeoff than synchronous schemes and performs equivalently
to transmitting information through a parallel fading channel as far as the
DM-tradeoff is concerned. Our results suggest the benefits of fully exploiting
the space-time degrees of freedom in multiple antenna systems by employing
asynchronous space-time codes even in a frequency flat fading channel. In
addition, it is shown asynchronous space-time coded systems are able to achieve
higher mutual information than synchronous space-time coded systems for any
finite signal-to-noise-ratio (SNR) when properly selected baseband waveforms
are employed
A Proximity based Retransmission Scheme for Power Line Ad-hoc LAN
Power line as an alternative for data transmission is being explored, and
also being used to a certain extent. But from the data transfer point of view,
power line, as a channel is highly dynamic and hence not quite suitable. To
convert the office or home wiring system to a Local Area Network (LAN),
adaptive changes are to be made to the existing protocols. In this paper, a
slotted transmission scheme is suggested, in which usable timeslots are found
out by physically sensing the media. Common usable timeslots for the
sender-receiver pair are used for communication. But these will not ensure safe
packet delivery since packets may be corrupted on the way during propagation
from sender to receiver. Therefore, we also suggest a proximity based
retransmission scheme where each machine in the LAN, buffers good packet and
machines close to the receiver retransmit on receiving a NACK.Comment: Already published in IJDP
Performance analysis of a Master/Slave switched Ethernet for military embedded applications
Current military communication network is a generation
old and is no longer effective in meeting the emerging
requirements imposed by the next generation military embedded applications. A new communication network based upon Full Duplex Switched Ethernet is proposed in this paper to overcome these limitations. To allow existing military subsystems to be easily supported by a Switched Ethernet network, our proposal consists in keeping their current centralized communication scheme by using an optimized master/slave transmission control on Switched Ethernet thanks to the Flexible Time Triggered (FTT) paradigm. Our main objective is to assess the performance
of such a proposal and estimate the quality of service we
can expect in terms of latency. Using the Network Calculus formalism, schedulability analysis are determined. These analysis are illustrated in the case of a realistic military embedded application extracted from a real military aircraft network, to highlight the proposal's ability to support the required time constrained communications
Delay-insensitive pipelined communication on parallel buses
Consider a communication channel that consists of several subchannels transmitting simultaneously and asynchronously. As an example of this scheme, we can consider a board with several chips. The subchannels represent wires connecting between the chips where differences in the lengths of the wires might result in asynchronous reception. In current technology, the receiver acknowledges reception of the message before the transmitter sends the following message. Namely, pipelined utilization of the channel is not possible. Our main contribution is a scheme that enables transmission without an acknowledgment of the message, therefore enabling pipelined communication and providing a higher bandwidth. However, our scheme allows for a certain number of transitions from a second message to arrive before reception of the current message has been completed, a condition that we call skew. We have derived necessary and sufficient conditions for codes that can tolerate a certain amount of skew among adjacent messages (therefore, allowing for continuous operation) and detect a larger amount of skew when the original skew is exceeded. These results generalize previously known results. We have constructed codes that satisfy the necessary and sufficient conditions, studied their optimality, and devised efficient decoding algorithms. To the best of our knowledge, this is the first known scheme that permits efficient asynchronous communications without acknowledgment. Potential applications are in on-chip, on-board, and board to board communications, enabling much higher communication bandwidth
Centralized vs distributed communication scheme on switched ethernet for embedded military applications
Current military communication network is a generation
old and is no longer effective in meeting the emerging
requirements imposed by the future embedded military applications. Therefore, a new interconnection system is needed to overcome these limitations. Two new communication networks based upon Full Duplex Switched Ethernet are presented herein in this aim. The first one uses a distributed communication scheme where equipments can emit their data simultaneously, which clearly improves system’s throughput and flexibility. However, migrating all existing applications into a compliant form could be an expensive step. To avoid this process, the second proposal consists in keeping the current centralized communication scheme. Our objective is to assess and compare the real time
guarantees that each proposal can offer. The paper includes the functional description of each proposed communication network and a military avionic application to highlight proposals ability to support the required time constrained communications
An antenna switching based NOMA scheme for IEEE 802.15.4 concurrent transmission
This paper introduces a Non-Orthogonal Multiple Access (NOMA) scheme to support concurrent transmission of multiple IEEE 802.15.4 packets. Unlike collision avoidance Multiple Access Control (MAC), concurrent transmission supports Concurrent-MAC (C-MAC) where packet collision is allowed. The communication latency can be reduced by C-MAC because a user can transmit immediately without waiting for the completion of other users’ transmission. The big challenge of concurrent transmission is that error free demodulation of multiple collided packets hardly can be achieved due to severe Multiple Access Interference (MAI). To improve the demodulation performance with MAI presented, we introduce an architecture with multiple switching antennas sharing a single analog transceiver to capture spatial character of different users. Successive Interference Cancellation (SIC) algorithm is designed to separate collided packets by utilizing the spatial character. Simulation shows that at least five users can transmit concurrently to the SIC receiver equipped with eight antennas without sacrificing Packet Error Rate
Distributed Partitioned Big-Data Optimization via Asynchronous Dual Decomposition
In this paper we consider a novel partitioned framework for distributed
optimization in peer-to-peer networks. In several important applications the
agents of a network have to solve an optimization problem with two key
features: (i) the dimension of the decision variable depends on the network
size, and (ii) cost function and constraints have a sparsity structure related
to the communication graph. For this class of problems a straightforward
application of existing consensus methods would show two inefficiencies: poor
scalability and redundancy of shared information. We propose an asynchronous
distributed algorithm, based on dual decomposition and coordinate methods, to
solve partitioned optimization problems. We show that, by exploiting the
problem structure, the solution can be partitioned among the nodes, so that
each node just stores a local copy of a portion of the decision variable
(rather than a copy of the entire decision vector) and solves a small-scale
local problem
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