Finite-State Markov Chain Models for the Intensity of Nakagami Fading

MILCOM 2015 - 2015 IEEE Military Communications Conference

2015

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We employ a four-node network to obtain preliminary comparisons between two forms of network coding when they are used for broadcast distribution of files in tactical packet radio networks. Each of the four nodes in the network has a half-duplex packet radio, and the nodes are connected by radio links that have time-varying fading. We present two methods for network-coded broadcast distribution. One method uses fountain coding and the other employs random linear network coding. Packet-by-packet adaptations of modulation and channel coding are employed to mitigate the effects of fading on the links. Our networkcoded distribution methods are able to exploit the broadcast nature of the wireless medium for improved throughput, and they require only a single frequency band that is used for all packet transmissions in the network.

Section: Channel Modelmentioning

confidence: 99%

Broadcast file distribution in a four-node packet radio network with network coding and code-modulation adaptation

Borkotoky

MILCOM 2015 - 2015 IEEE Military Communications Conference

2015

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“…Consider a packet with QPSK modulation, a turbo product code (TPC) of rate 0.495, 64 subcarriers, and 16,384 binary code symbols (8,192 modulation symbols). For each modulation symbol, M 2 M 4 ordering requires one complex multiplication to compute |Z k | 2 and one real multiplication to get |Z k | 4 from |Z k | 2 .…”

Section: Ordering By Subcarrier Error Ratesmentioning

confidence: 99%

Subcarrier Ordering for OFDM Packet Radio Systems

Juang

2015

IEEE Commun. Lett.

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Subcarrier ordering is a ranking of the subchannels of a multicarrier communication system according to a quality criterion. We describe and evaluate two techniques for subcarrier ordering in half-duplex packet radio systems, including OFDM dynamic spectrum access systems. The ordering techniques require no estimates of subchannel gains or subcarrier signal strengths. The performance of each technique is evaluated for channels with fading and for channels with interference and fading.

“…Our investigation employs equal step-size, finite-state Markov-chain models where each state corresponds to a specific value of channel gain in dB due to fading. They are modeled according to the method given in [7]. These models allow any positive integer value or any non-integer value greater than 1/2 for the parameter m; in addition, channel transitions are not restricted to adjacent states alone.…”

Section: Adaptation Of the Code Rate Andmentioning

confidence: 99%

Preliminary Results on the Performance of an Adaptive Protocol for Packet Relay with Fountain Coding

Borkotok

2014 IEEE Military Communications Conference

2014

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We present our initial findings in the investigation of an adaptive protocol for relaying of information in tactical packet-radio networks. Our protocol employs fountain codes to facilitate a relaying scheme involving two relays for improved throughput. In addition, the protocol adapts the modulation format and error-control code for each packet transmission in response to the time-varying propagation loss in the channel. The adaptation is carried out with the help of simple statistics that can be easily derived from the decoder. I. INTRODUCTIONWe investigate a scenario in which a file must be sent from a source to a destination in a distributed tactical packet radio network. All nodes in the network are halfduplex packet radios. The file is divided into a set of information packets, and the transfer of the file occurs by means of a sequence of packet transmissions. The source and destination are not connected by a reliable radio link, so some form of packet relaying is required.In such situations, it is common to use intermediate radios for relaying packets from the source to the destination. We focus our attention on a situation in which two relays are available to forward packets from the source to the destination. A conventional store-andforward relaying scheme would normally select the single relay that provides the best route to the destination. With normal procedures, the use of multiple relay nodes produces duplicate packets and may cause packet collisions or scheduling conflicts at the destination. Our suggested protocol employs fountain coding in a way that does not create any duplicate packets, yet it permits a second relay node to take part in the file transfer. We show that our approach provides a significant increase in throughput over packet relaying by a single node.Our approach also uses adaptive modulation and channel coding to mitigate the effects of fading on the radio links. The control information needed for adaptive transmission is derived from a simple statistic that is computed in each radio's receiver as it demodulates and decodes each incoming packet. This control information is employed for packet-by-packet adaptation of the channel code and the modulation on each radio link.