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Energy Optimization for Hybrid ARQ
Hybrid automatic repeat request (HARQ) \cite{costello1983error} plays an important role in providing reliable and efficient data transmission. In wireless communications, the wireless channel may vary fast, due to the mobility of the transmitter/receiver and the channel. Forward error correction (FEC) and automatic repeat request (ARQ) are two basic techniques to control errors. FEC employs error correction coding, by adding parity bits to the information bits, to combat channel errors. ARQ allows the receiver to request a retransmission of the packet when an error is detected in the received packet. HARQ gives protection to the wireless transmission by combining FEC and ARQ. In typical HARQ systems, redundancy is added to the information bits, and a retransmission is performed until either the packet is successfully decoded, or a maximum number of transmissions is reached.The motivation to optimize the energy consumption of HARQ is the high energy consumption of wireless communications on mobile devices. Wireless devices usually have a limited battery life, and wireless communications consume the majority of the battery energy of mobile devices. One example is that 3G and Wifi units consume more than 50\% of the energy for some smart phones \cite{tawalbeh2016studying}. Another example is that battery depletion has been identified as one of the primary factors that limit the lifetime of wireless sensor networks \cite{verdone2010wireless}.Previous works on HARQ mainly use information-theoretic approach, which assumes that the number of bits in each transmission round is sufficiently large. This assumption does not necessarily hold for actual codes with finite length. Therefore, in this dissertation, we consider HARQ with actual codes. We use turbo-coded HARQ, since turbo codes are well-known capacity-approaching codes \cite{berrou1993near} and widely used in standards such as 3GPP Long-Term Evolution (LTE) \cite{3gpp2007mulltiplexing}. We study the energy optimization for HARQ in two scenarios: the energy optimization for incremental redundancy (IR) HARQ, and the energy optimization for HARQ in wireless video transmission. For IR HARQ, each retransmission contains additional parity bits beyond those of the previous transmissions. For the first scenario, we consider different cases of channel state information (CSI) at the transmitter: the transmitter has no knowledge of any CSI, or knows the CSI in previous transmission rounds through a perfect feedback channel, or knows both current and previous CSI. The transmitter decides the forward error correction code rate based on the CSI it has. We minimize the energy consumption of turbo-coded HARQ, subject to a packet loss rate constraint. Numerical results show that the energy consumption of HARQ decreases when more CSI information is available at the transmitter. We also compare IR combining with both Chase combining and the system without combining, and IR combining yields the least energy consumption.For the second scenario, we formulate the problem as maximizing the video quality, subject to a constraint on the wireless transmission energy consumption. We consider multiple parameters in multiple layers in a wireless video transmission system: transmit power, alphabet size, FEC code rate, maximum number of transmissions and unequal video data importance. An analytical framework is proposed to include these parameters, which allows us to divide this problem into two sub-problems: data transmission and unequal error protection (UEP) for video content. The problem is tackled by solving the two sub-problems, which are done by exhaustive search and convex optimization, respectively. Simulations of different videos show that the proposed scheme outperforms methods using conventional data transmission and/or unequal error protection. For example, in the low SNR region, there is a total gain of 4.8 to 5.6dB on the peak signal-to-noise ratio of the received video compared to video transmission using conventional HARQ without any video UEP
The Telecommunications and Data Acquisition Report
Archival reports on developments in programs managed by JPL's Office of Telecommunications and Data Acquisition (TDA) are presented. Activities of the Deep Space Network (DSN) and its associated Ground Communications Facility (GCF) related to DSN advanced systems, systems implementation, and DSN operations are addressed. In addition, recent developments in the NASA SETI (Search for Extraterrestrial Intelligence) sky survey are summarized
Scalable Video Streaming with Prioritised Network Coding on End-System Overlays
PhDDistribution over the internet is destined to become a standard approach for live broadcasting
of TV or events of nation-wide interest. The demand for high-quality live video
with personal requirements is destined to grow exponentially over the next few years. Endsystem
multicast is a desirable option for relieving the content server from bandwidth bottlenecks
and computational load by allowing decentralised allocation of resources to the users
and distributed service management. Network coding provides innovative solutions for a
multitude of issues related to multi-user content distribution, such as the coupon-collection
problem, allocation and scheduling procedure. This thesis tackles the problem of streaming
scalable video on end-system multicast overlays with prioritised push-based streaming.
We analyse the characteristic arising from a random coding process as a linear channel
operator, and present a novel error detection and correction system for error-resilient decoding,
providing one of the first practical frameworks for Joint Source-Channel-Network
coding. Our system outperforms both network error correction and traditional FEC coding
when performed separately. We then present a content distribution system based on endsystem
multicast. Our data exchange protocol makes use of network coding as a way to
collaboratively deliver data to several peers. Prioritised streaming is performed by means
of hierarchical network coding and a dynamic chunk selection for optimised rate allocation
based on goodput statistics at application layer. We prove, by simulated experiments, the
efficient allocation of resources for adaptive video delivery. Finally we describe the implementation
of our coding system. We highlighting the use rateless coding properties, discuss
the application in collaborative and distributed coding systems, and provide an optimised
implementation of the decoding algorithm with advanced CPU instructions. We analyse
computational load and packet loss protection via lab tests and simulations, complementing
the overall analysis of the video streaming system in all its components
Video transmission over wireless networks
Compressed video bitstream transmissions over wireless networks are addressed in this work. We first consider error control and power allocation for transmitting wireless video over CDMA networks in conjunction with multiuser detection. We map a layered video bitstream to several CDMA fading channels and inject multiple source/parity layers into each of these channels at the transmitter. We formulate a combined optimization problem and give the optimal joint rate and power allocation for each of linear minimum mean-square error (MMSE) multiuser detector in the uplink and two types of blind linear MMSE detectors, i.e., the direct-matrix-inversion (DMI) blind detector and the subspace blind detector, in the downlink. We then present a multiple-channel video transmission scheme in wireless CDMA networks over multipath fading channels. For a given budget on the available bandwidth and total transmit power, the transmitter determines the optimal power allocations and the optimal transmission rates among multiple CDMA channels, as well as the optimal product channel code rate allocation. We also make use of results on the large-system CDMA performance for various multiuser receivers in multipath fading channels. We employ a fast joint source-channel coding algorithm to obtain the optimal product channel code structure. Finally, we propose an end-to-end architecture for multi-layer progressive video delivery over space-time differentially coded orthogonal frequency division multiplexing (STDC-OFDM) systems. We propose to use progressive joint source-channel coding to generate operational transmission distortion-power-rate (TD-PR) surfaces. By extending the rate-distortion function in source coding to the TD-PR surface in joint source-channel coding, our work can use the ??equal slope?? argument to effectively solve the transmission rate allocation problem as well as the transmission power allocation problem for multi-layer video transmission. It is demonstrated through simulations that as the wireless channel conditions change, these proposed schemes can scale the video streams and transport the scaled video streams to receivers with a smooth change of perceptual quality
CONVERGENCE IMPROVEMENT OF ITERATIVE DECODERS
Iterative decoding techniques shaked the waters of the error correction and communications
field in general. Their amazing compromise between complexity and performance
offered much more freedom in code design and made highly complex codes, that were
being considered undecodable until recently, part of almost any communication system.
Nevertheless, iterative decoding is a sub-optimum decoding method and as such, it has
attracted huge research interest. But the iterative decoder still hides many of its secrets,
as it has not been possible yet to fully describe its behaviour and its cost function.
This work presents the convergence problem of iterative decoding from various angles
and explores methods for reducing any sub-optimalities on its operation. The decoding
algorithms for both LDPC and turbo codes were investigated and aspects that contribute
to convergence problems were identified. A new algorithm was proposed, capable of providing
considerable coding gain in any iterative scheme. Moreover, it was shown that
for some codes the proposed algorithm is sufficient to eliminate any sub-optimality and
perform maximum likelihood decoding. Its performance and efficiency was compared to
that of other convergence improvement schemes.
Various conditions that can be considered critical to the outcome of the iterative decoder
were also investigated and the decoding algorithm of LDPC codes was followed
analytically to verify the experimental results
Error resilient stereoscopic video streaming using model-based fountain codes
Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Science of Bilkent University, 2009.Thesis (Ph.D.) -- Bilkent University, 2009.Includes bibliographical references leaves 101-110.Error resilient digital video streaming has been a challenging problem since
the introduction and deployment of early packet switched networks. One of
the most recent advances in video coding is observed on multi-view video coding
which suggests methods for the compression of correlated multiple image
sequences. The existing multi-view compression techniques increase the loss sensitivity
and necessitate the use of efficient loss recovery schemes. Forward Error
Correction (FEC) is an efficient, powerful and practical tool for the recovery of
lost data. A novel class of FEC codes is Fountain codes which are suitable to be
used with recent video codecs, such as H.264/AVC, and LT and Raptor codes are
practical examples of this class. Although there are many studies on monoscopic
video, transmission of multi-view video through lossy channels with FEC have
not been explored yet. Aiming at this deficiency, an H.264-based multi-view
video codec and a model-based Fountain code are combined to generate an effi-
cient error resilient stereoscopic streaming system. Three layers of stereoscopic
video with unequal importance are defined in order to exploit the benefits of Unequal
Error Protection (UEP) with FEC. Simply, these layers correspond to intra frames of left view, predicted frames of left view and predicted frames of right
view. The Rate-Distortion (RD) characteristics of these dependent layers are de-
fined by extending the RD characteristics of monoscopic video. The parameters
of the models are obtained with curve fitting using the RD samples of the video,
and satisfactory results are achieved where the average difference between the
analytical models and RD samples is between 1.00% and 9.19%. An heuristic
analytical model of the performance of Raptor codes is used to obtain the residual
number of lost packets for given channel bit rate, loss rate, and protection
rate. This residual number is multiplied with the estimated average distortion
of the loss of a single Network Abstraction Layer (NAL) unit to obtain the total
transmission distortion. All these models are combined to minimize the end-toend
distortion and obtain optimal encoder bit rates and UEP rates. When the
proposed system is used, the simulation results demonstrate up to 2dB increase
in quality compared to equal error protection and only left view error protection.
Furthermore, Fountain codes are analyzed in the finite length region, and
iterative performance models are derived without any assumptions or asymptotical
approximations. The performance model of the belief-propagation (BP)
decoder approximates either the behavior of a single simulation results or their
average depending on the parameters of the LT code. The performance model of
the maximum likelihood decoder approximates the average of simulation results
more accurately compared to the model of the BP decoder. Raptor codes are
modeled heuristically based on the exponential decay observed on the simulation
results, and the model parameters are obtained by line of best fit. The analytical
models of systematic and non-systematic Raptor codes accurately approximate
the experimental average performance.Tan, A SerdarPh.D
The deep space network, volume 2 Progress report, Jan. - Feb. 1971
Deep Space Network, Ground Communications Facility, Space Flight Operations Facility, and Deep Space Instrumentation Facility research and development - Vol.
Layered Wyner-Ziv video coding: a new approach to video compression and delivery
Following recent theoretical works on successive Wyner-Ziv coding, we propose
a practical layered Wyner-Ziv video coder using the DCT, nested scalar quantiza-
tion, and irregular LDPC code based Slepian-Wolf coding (or lossless source coding
with side information at the decoder). Our main novelty is to use the base layer
of a standard scalable video coder (e.g., MPEG-4/H.26L FGS or H.263+) as the
decoder side information and perform layered Wyner-Ziv coding for quality enhance-
ment. Similar to FGS coding, there is no performance di®erence between layered and
monolithic Wyner-Ziv coding when the enhancement bitstream is generated in our
proposed coder. Using an H.26L coded version as the base layer, experiments indicate
that Wyner-Ziv coding gives slightly worse performance than FGS coding when the
channel (for both the base and enhancement layers) is noiseless. However, when the
channel is noisy, extensive simulations of video transmission over wireless networks
conforming to the CDMA2000 1X standard show that H.26L base layer coding plus
Wyner-Ziv enhancement layer coding are more robust against channel errors than
H.26L FGS coding. These results demonstrate that layered Wyner-Ziv video coding
is a promising new technique for video streaming over wireless networks.
For scalable video transmission over the Internet and 3G wireless networks, we
propose a system for receiver-driven layered multicast based on layered Wyner-Ziv video coding and digital fountain coding. Digital fountain codes are near-capacity
erasure codes that are ideally suited for multicast applications because of their rate-
less property. By combining an error-resilient Wyner-Ziv video coder and rateless
fountain codes, our system allows reliable multicast of high-quality video to an arbi-
trary number of heterogeneous receivers without the requirement of feedback chan-
nels. Extending this work on separate source-channel coding, we consider distributed
joint source-channel coding by using a single channel code for both video compression
(via Slepian-Wolf coding) and packet loss protection. We choose Raptor codes - the
best approximation to a digital fountain - and address in detail both encoder and de-
coder designs. Simulation results show that, compared to one separate design using
Slepian-Wolf compression plus erasure protection and another based on FGS coding
plus erasure protection, the proposed joint design provides better video quality at the
same number of transmitted packets
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