Jason D. Ellis

Adaptive Capacity-Achieving Channel Coding for Fountain-Coded Multicast Transmission in Packet Radio Systems

For time-varying fading, adaptation of the physical-layer channel code greatly enhances the throughput of a multicast transmission system, even if the system employs an application-layer fountain code for packet erasure correction. Performance evaluations for adaptive channel-coding protocols typically require extensive simulations of the fading channel, the iterative decoding process, and the generation of the control information that is used for the adaptation of the channel code. We present a method for the evaluation of such protocols that avoids a substantial amount of the computation required by traditional simulations, and we demonstrate that some important performance measures can be evaluated entirely by analysis. By the use of capacity-achieving channel codes in our investigation, we also decouple the performance of the adaptive coding protocol from the performance of a particular type of channel code and decoding method, which facilitates comparisons among different protocols. The application of our methods is demonstrated for two adaptive channel-coding protocols that are candidates for fountain-coded multicast transmission in packet radio systems.

Integration of Adaptive Modulation and Channel Coding With Fountain Coding for Packet Radio Systems

We examine the integration of adaptive modulation and channel coding protocols with fountain coding in a packet radio system. We present three modes of operation for the adaptive transmission system, each of which adapts the channel code in a way that accommodates the fixed-length packets produced by the fountain encoder. Each mode works with the fountain coding system to mitigate the effects of time-varying fading on the radio links and provide high throughput.

Adaptive Transmission Protocols for Fountain-Coded Multicast in Packet Radio Networks

Fountain coding is a valuable tool for multicast transmissions in half-duplex packet radio networks if it is supported by an adaptive transmission protocol that compensates for fluctuations in the propagation losses on the radio links. Our goal is to devise low-complexity packet-by-packet adaptive modulation and channel coding protocols that provide high throughput for a broad range of multicast channels and operate with limited feedback and no knowledge of the fade levels or even the probability distribution for the fading on the radio links. The only control information for the protocols is derived from simple receiver statistics that are obtained by the demodulators and channel decoders in the receiving radios. Performance results are presented for practical fountain coding with low-complexity adaptive modulation and channel coding. Results on ideal fountain coding with adaptive transmission based on hypothetical perfect channel-state information are employed as performance benchmarks.

Adaptive Coding and Modulation for Multicast Transmission in Packet Radio Networks

A low-complexity protocol is described and evaluated for adaptation of the modulation and coding for multicast transmission in half-duplex packet radio networks. The adaptive multicast transmission protocol is designed to compensate for changes in propagation conditions that occur from packet to packet during a session with one sender and multiple receivers. The protocol relies on simple receiver statistics to obtain the control information for adapting the modulation and coding, and it also provides scheduling to avoid collisions among acknowledgments from the receivers. The throughput provided by the protocol is compared with performance results for hypothetical ideal adaptive multicast transmission protocols that are given perfect channel state information. We illustrate the importance of adaptive modulation and channel coding in systems that employ fountain coding for packet erasure correction.

Analytical evaluation of adaptive coding for Markov models of Nakagami fading

Packet radio systems that communicate over channels with slow fading experience changes in propagation loss from one packet to the next. In order to maintain high throughput, it is necessary for the packet radios to adapt their transmissions in response to changes in the channel. Practical adaptive coding protocols can respond to such changes by adjusting the code rate to maximize the expected throughput for each packet transmission. Performance evaluations for practical protocols typically require simulation of both the time-varying fading process and the adaptive protocol. We employ recently developed finite-state Markov models of Nakagami-m fading to obtain analytical evaluations of the throughput of an adaptive coding protocol. In our approach, neither the fading processes nor their Markov models are simulated.

New Results on the Performance of a Protocol for Adaptive Modulation and Coding

Adaptive transmission protocols are required for efficient communications in packet radio systems that must transmit over time-varying wireless channels. We present a protocol that employs simple receiver statistics for adapting the error-control code and modulation format from packet to packet in response to changes in the channels propagation loss, such as those caused by fading and shadowing.

Insights from the use of Shannon's codes in adaptive multicast transmission protocols

The methods we present for the evaluation of protocols for adaptive channel coding in multicast packet radio systems require considerably less computation than traditional simulations. Shannon capacity limits and Markov models for fading channels are employed to provide analytical results for a number of performance measures.

Adaptive-rate channel coding for packet radio systems with higher layer fountain coding

We present and evaluate two low-complexity protocols for adaptive transmission in tactical packet radio systems that employ higher layer fountain codes. The adaptive-rate coding protocol is permitted to adjust the rate of the channel code between each pair of consecutive packets. The adaptive modulation and coding protocol can change the modulation between each pair of consecutive packets, but it can adjust the code rate only between consecutive frames of packets. Each protocol responds to dynamic fading and other time-varying propagation losses. For control of the adaptation, the protocols rely solely on a simple statistic derived by the receiver. They require no channel measurements, parameter estimates, pilot symbols, or training. The throughput performance of each protocol is evaluated for a Rayleigh fading channel modeled by a finite-state Markov chain. We show that our adaptive-rate coding protocol in tandem with higher layer fountain coding outperforms fountain coding with fixed-rate channel coding. We also compare the performance of our adaptive-rate coding protocol with the performance of a hypothetical ideal adaptive-rate coding protocol for which the transmitter is given perfect channel state information for the previous packet. We demonstrate that our protocol performs nearly as well as the ideal protocol.

Physical Layer Adaptation for Packet Radio Systems with Higher Layer Fountain Coding

We present low-complexity adaptive transmission protocols for use in tactical packet radio systems that employ higher layer fountain coding. Our protocols respond to fading and other time-varying propagation losses by adapting the modulation and channel coding used to transmit packets over the wireless channel. The operation of our protocols is controlled by simple receiver statistics that can be obtained during the demodulation of received packets. No pilot symbols, training, channel measurements, or channel estimation techniques are required by our protocols.

Adaptive incremental-redundancy transmission for tactical packet radio systems

A low-complexity protocol for the adaptation of incremental-redundancy transmission is described and evaluated for use in tactical packet radio systems that must communicate over channels with fading and other time-varying propagation losses. The protocol responds to variations in channel attenuation by adjusting the number of binary code symbols that are punctured in the first transmission for a packet and saved for subsequent transmissions if they are needed. The protocol relies on simple statistics from the receiver to provide the necessary control information for adapting the amount of puncturing or the rate of the code that is employed from one packet to the next. No channel measurements, parameter estimates, pilot symbols, or training are needed. The protocols throughput performance is evaluated for dynamic channels that are modeled by finite-state Markov chains. Performance benchmarks are obtained from hypothetical ideal protocols that are given perfect channel-state information and are told all the parameters of the channel model. We demonstrate that the new adaptive protocol performs nearly as well as the hypothetical ideal protocols even though the adaptive protocol is given no channel-state information and no information about the channel model or its parameters.