Cooperative systems based signal processing techniques with applications to three-dimensional video transmission

Three-dimensional (3-D) video has recently emerged to offer an immersive multimedia experience that can not be offered by two-dimensional (2-D) video applications. Currently, both industry and academia are focused on delivering 3-D video services to wireless communication systems. Modern video communication systems currently adopt cooperative communication and orthogonal frequency division multiplexing (OFDM) as they are an attractive solution to combat fading in wireless communication systems and achieve high data-rates. However, this strong motivation to transmit the video signals over wireless systems faces many challenges. These are mainly channel bandwidth limitations, variations of signal-to-noise ratio (SNR) in wireless channels, and the impairments in the physical layer such as time varying phase noise (PHN), and carrier frequency offset (CFO). In response to these challenges, this thesis seeks to develop efficient 3-D video transmission methods and signal processing algorithms that can overcome the effects of error-prone wireless channels and impairments in the physical layer. In the first part of the thesis, an efficient unequal error protection (UEP) scheme, called video packet partitioning, and a new 3-D video transceiver structure are proposed. The proposed video transceiver uses switching operations between various UEP schemes based on the packet partitioning to achieve a trade- off between system complexity and performance. Experimental results show that the proposed system achieves significantly high video quality at different SNRs with the lowest possible bandwidth and system complexity compared to direct transmission schemes. The second part of the thesis proposes a new approach to joint source-channel coding (JSCC) that simultaneously assigns source code rates, the number of high and low priority packets, and channel code rates for the application, network, and physical layers, respectively. The proposed JSCC algorithm takes into account the rate budget constraint and the available instantaneous SNR of the best relay selection in cooperative systems. Experimental results show that the proposed JSCC algorithm outperforms existing algorithms in terms of peak signal-to-noise ratio (PSNR). In the third part of the thesis, a computationally efficient training based approach for joint channel, CFO, and PHN estimation in OFDM systems is pro- posed. The proposed estimator is based on an expectation conditional maximization (ECM) algorithm. To compare the estimation accuracy of the proposed estimator, the hybrid Cram´er-Rao lower bound (HCRB) of hybrid parameters of interest is derived. Next, to detect the signal in the presence of PHN, an iterative receiver based on the extended Kalman filter (EKF) for joint data detection and PHN mitigation is proposed. It is demonstrated by numerical simulations that, compared to existing algorithms, the performance of the proposed ECM-based estimator in terms of the mean square error (MSE) is closer to the derived HCRB and outperforms the existing estimation algorithms at moderate-to-high SNRs. Finally, this study extends the research on joint channel, PHN, and CFO estimation one step forward from OFDM systems to cooperative OFDM systems. An iterative algorithm based on the ECM in cooperative OFDM networks in the presence of unknown channel gains, PHNs and CFOs is applied. Moreover, the HCRB for the joint estimation problem in both decode-and-forward (DF) and amplify-and-forward (AF) relay systems is presented. An iterative algorithm based on the EKF for data detection and tracking the unknown time-varying PHN throughout the OFDM data packet is also used. For more efficient 3-D video transmission, the estimation algorithms and UEP schemes based packet portioning were combined to achieve a more robust video bit stream in the presence of PHNs. Applying this combination, simulation results demonstrate that promising bit-error-rate (BER) and PSNR performance can be achieved at the destination at different SNRs and PHN variance. The proposed schemes and algorithms offer solutions for existing problems in the techniques for applications to 3-D video transmission

Multiple Access for Massive Machine Type Communications

The internet we have known thus far has been an internet of people, as it has connected people with one another. However, these connections are forecasted to occupy only a minuscule of future communications. The internet of tomorrow is indeed: the internet of things. The Internet of Things (IoT) promises to improve all aspects of life by connecting everything to everything. An enormous amount of effort is being exerted to turn these visions into a reality. Sensors and actuators will communicate and operate in an automated fashion with no or minimal human intervention. In the current literature, these sensors and actuators are referred to as machines, and the communication amongst these machines is referred to as Machine to Machine (M2M) communication or Machine-Type Communication (MTC). As IoT requires a seamless mode of communication that is available anywhere and anytime, wireless communications will be one of the key enabling technologies for IoT. In existing wireless cellular networks, users with data to transmit first need to request channel access. All access requests are processed by a central unit that in return either grants or denies the access request. Once granted access, users' data transmissions are non-overlapping and interference free. However, as the number of IoT devices is forecasted to be in the order of hundreds of millions, if not billions, in the near future, the access channels of existing cellular networks are predicted to suffer from severe congestion and, thus, incur unpredictable latencies in the system. On the other hand, in random access, users with data to transmit will access the channel in an uncoordinated and probabilistic fashion, thus, requiring little or no signalling overhead. However, this reduction in overhead is at the expense of reliability and efficiency due to the interference caused by contending users. In most existing random access schemes, packets are lost when they experience interference from other packets transmitted over the same resources. Moreover, most existing random access schemes are best-effort schemes with almost no Quality of Service (QoS) guarantees. In this thesis, we investigate the performance of different random access schemes in different settings to resolve the problem of the massive access of IoT devices with diverse QoS guarantees. First, we take a step towards re-designing existing random access protocols such that they are more practical and more efficient. For many years, researchers have adopted the collision channel model in random access schemes: a collision is the event of two or more users transmitting over the same time-frequency resources. In the event of a collision, all the involved data is lost, and users need to retransmit their information. However, in practice, data can be recovered even in the presence of interference provided that the power of the signal is sufficiently larger than the power of the noise and the power of the interference. Based on this, we re-define the event of collision as the event of the interference power exceeding a pre-determined threshold. We propose a new analytical framework to compute the probability of packet recovery failure inspired by error control codes on graph. We optimize the random access parameters based on evolution strategies. Our results show a significant improvement in performance in terms of reliability and efficiency. Next, we focus on supporting the heterogeneous IoT applications and accommodating their diverse latency and reliability requirements in a unified access scheme. We propose a multi-stage approach where each group of applications transmits in different stages with different probabilities. We propose a new analytical framework to compute the probability of packet recovery failure for each group in each stage. We also optimize the random access parameters using evolution strategies. Our results show that our proposed scheme can outperform coordinated access schemes of existing cellular networks when the number of users is very large. Finally, we investigate random non-orthogonal multiple access schemes that are known to achieve a higher spectrum efficiency and are known to support higher loads. In our proposed scheme, user detection and channel estimation are carried out via pilot sequences that are transmitted simultaneously with the user's data. Here, a collision event is defined as the event of two or more users selecting the same pilot sequence. All collisions are regarded as interference to the remaining users. We first study the distribution of the interference power and derive its expression. Then, we use this expression to derive simple yet accurate analytical bounds on the throughput and outage probability of the proposed scheme. We consider both joint decoding as well as successive interference cancellation. We show that the proposed scheme is especially useful in the case of short packet transmission

Network Coding with Multimedia Transmission and Cognitive Networking: An Implementation based on Software-Defined Radio

Network coding (NC) is considered a breakthrough to improve throughput, robustness, and security of wireless networks. Although the theoretical aspects of NC have been extensively investigated, there have been only few experiments with pure NC schematics. This paper presents an implementation of NC under a two-way relay model and extends it to two\ua0non-straightforward scenarios: (i) multimedia transmission with layered coding and multiple-description coding, and (ii) cognitive radio with Vandermonde frequency division multiplexing (VFDM). The implementation is in real time and based on software-defined radio (SDR). The experimental results show that, by combining NC and source coding, we can control the quality of the received multimedia content in an on-demand manner. Whereas in the VFDM-based cognitive radio, the quality of the received content in the primary receiver is low (due to imperfect channel estimation) yet retrievable. Our implementation results serve as a proof for the practicability of network coding in relevant applications

Exposing a waveform interface to the wireless channel for scalable video broadcast

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 157-167).Video broadcast and mobile video challenge the conventional wireless design. In broadcast and mobile scenarios the bit-rate supported by the channel differs across receivers and varies quickly over time. The conventional design however forces the source to pick a single bit-rate and degrades sharply when the channel cannot support it. This thesis presents SoftCast, a clean-slate design for wireless video where the source transmits one video stream that each receiver decodes to a video quality commensurate with its specific instantaneous channel quality. To do so, SoftCast ensures the samples of the digital video signal transmitted on the channel are linearly related to the pixels' luminance. Thus, when channel noise perturbs the transmitted signal samples, the perturbation naturally translates into approximation in the original video pixels. Hence, a receiver with a good channel (low noise) obtains a high fidelity video, and a receiver with a bad channel (high noise) obtains a low fidelity video. SoftCast's linear design in essence resembles the traditional analog approach to communication, which was abandoned in most major communication systems, as it does not enjoy the theoretical opimality of the digital separate design in point-topoint channels nor its effectiveness at compressing the source data. In this thesis, I show that in combination with decorrelating transforms common to modern digital video compression, the analog approach can achieve performance competitive with the prevalent digital design for a wide variety of practical point-to-point scenarios, and outperforms it in the broadcast and mobile scenarios. Since the conventional bit-pipe interface of the wireless physical layer (PHY) forces the separation of source and channel coding, to realize SoftCast, architectural changes to the wireless PHY are necessary. This thesis discusses the design of RawPHY, a reorganization of the PHY which exposes a waveform interface to the channel while shielding the designers of the higher layers from much of the perplexity of the wireless channel. I implement SoftCast and RawPHY using the GNURadio software and the USRP platform. Results from a 20-node testbed show that SoftCast improves the average video quality (i.e., PSNR) across diverse broadcast receivers in our testbed by up to 5.5 dB in comparison to conventional single- or multi-layer video. Even for a single receiver, it eliminates video glitches caused by mobility and increases robustness to packet loss by an order of magnitude.by Szymon Kazimierz Jakubczak.Ph.D

Performance analysis of OFDM technology on radio-over-fiber systems

Dissertação de mest., Engenharia Eletrónica e Telecomunicações, Faculdade de Ciências e Tecnologia, Univ. do Algarve, 2011Nowadays, the demand for high speed, high quality and diversity in distributed services presents a challenge for telecommunication technology. Wireless systems provide the accessibility to end-user, but are not the solution for long distance links. Currently, the ideal technology for long-range transmissions at high data rates is optical fiber. Hence, a new concept for high capacity networks emerges, with centralized services into Base Stations (BS) engineered to provide flexibility and control over the system, and to perform operations such as electrical to optical domain conversion and modulation. Such Radio-over-Fiber (RoF) networks also appear as an attractive technology because they are efficient and cost effective. Orthogonal Frequency Division Multiplexing (OFDM) technology is widely used in a number of standards. For instance, it is actually the Multi-Carrier Modulation (MCM) technique applied in 802.11a/g/n wireless standards and in Digital Video Broadcasting-Terrestrial (DVB-T), among other prevailing systems, which makes this subject one particularly pertinent to study. OFDM systems are an appealing choice for waveform modulation, as they are very bandwidth efficient comparing to others MCM, and provide flexibility in data transmission rates. Additionally, an important advantage dwells in its natural robustness against severely interfering environments. In this thesis, fundamentals on OFDM technology are extensively described, and its application to wireless and optical fiber networks is introduced. The combined channel effects of these technologies on OFDM signals are investigated. In terms of performance analysis, this exposition focuses on understanding the importance of OFDM modulation parameters, and explores some OFDM signal properties. To achieve this, a simulator was implemented with Matlab to create arbitrary OFDM waveforms and emulate channel effects. This study also investigates the efficiency of OFDM technology over a real Radio Frequency (RF) system with an ideal communication channel. Finally, an experimental RoF configuration is implemented and its performance is assessed

Physical Layer Techniques for Wireless Communication Systems

The increasing diffusion of mobile devices requiring, everywhere and every time, reliable connections able to support the more common applications, induced in the last years the deployment of telecommunication networks based on technologies capable to respond effectively to the ever-increasing market demand, still a long way off from saturation level. Multicarrier transmission techniques employed in standards for local networks (Wi-Fi) and metropolitan networks (WiMAX) and for many years hot research topic, have been definitely adopted beginning from the fourth generation of cellular systems (LTE). The adoption of multicarrier signaling techniques if on one hand has brought significant advantages to counteract the detrimental effects in environments with particularly harsh propagation channel, on the other hand, has imposed very strict requirements on sensitivity to recovery errors of the carrier frequency offset (CFO) due to the resulting impact on correct signal detection. The main focus of the thesis falls in this area, investigating some aspects relating to synchronization procedures for system based on multicarrier signaling. Particular reference will be made to a network entry procedure for LTE networks and to CFO recovery for OFDM, fltered multitone modulation and direct conversion receivers. Other contributions pertaining to physical layer issues for communication systems, both radio and over acoustic carrier, conclude the thesis

Network Coding with Multimedia Transmission and Cognitive Networking: An Implementation based on Software-Defined Radio

Network coding (NC) is considered a breakthrough to improve throughput, robustness, and security of wireless networks. Although the theoretical aspects of NC have been extensively investigated, there have been only few experiments with pure NC schematics. This paper presents an implementation of NC under a two-way relay model and extends it to two non-straightforward scenarios: (i) multimedia transmission with layered coding and multiple-description coding, and (ii) cognitive radio with Vandermonde frequency division multiplexing (VFDM). The implementation is in real time and based on software-defined radio (SDR). The experimental results show that, by combining NC and source coding, we can control the quality of the received multimedia content in an on-demand manner. Whereas in the VFDM-based cognitive radio, the quality of the received content in the primary receiver is low (due to imperfect channel estimation) yet retrievable. Our implementation results serve as a proof for the practicability of network coding in relevant applications

Wi-Fi의 신뢰성 및 에너지 효율성 향상을 위한 MAC/PHY 기법

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 8. 최성현.Over the last quarter century, wireless local area network (WLAN) technology has become an essential and indispensable part of our daily lives. Recently, a tremendously growing number of portable devices, such as smartphones, tablets and laptops, are being equipped with Wi-Fi, the hallmark of the IEEE 802.11 WLAN, in order to meet ever-increasing traffic demands at extremely low cost. Encouraged by this remarkable success, Wi-Fi is facing two trends. First, the state-of-the-art IEEE 802.11 specifications, e.g., IEEE 802.11n and 802.11ac, have focused on improving physical layer (PHY) rate by enabling multiple antennas, called multiple-input multiple-output (MIMO), and bandwidth widening, known as chan- nel bonding [1, 2]. Second, to achieve high throughput and transmission efficiency at medium access control (MAC) layer, IEEE 802.11n/ac standards have defined two types of frame aggregation techniques: MAC service data unit (MSDU) aggregation and MAC protocol data unit (MPDU) aggregation which amortize PHY/MAC proto- col overhead e.g., binary random backoff, physical layer convergence protocol (PLCP) preamble, and acknowledgement (ACK), over multiple frames by packing several MS- DUs and MPDUs into a single aggregate MSDU (A-MSDU) and aggregate MPDU (A-MPDU), respectively. Apparently, there is no doubt that these state-of-the-art features meet and fulfill i the requirements of Wi-Fi equipped device users by offering several hundred-fold in- creases in PHY rate and ubiquitous access. However, with respect to the demands of the battery-powered portable device users, the belief is easily broken from two per- spectives. First, since using higher PHY rate and longer A-MPDU are more vulnerable to channel errors especially for mobile users, the significant throughput performance degradation can be observed. Second, the emerging Wi-Fi chipsets, based on IEEE 802.11n/ac, consume much more energy than its legacy IEEE 802.11a/b/g counterparts due to the usage of MIMO and channel bonding. Nowadays, as the battery-powered portable device users place increasingly complex demands on the functionality of their devices which have strict power limitation, satisfaction with robust communication and battery life time is becoming increasingly important. In this dissertation, to address these challenges, we propose robust and energy efficient MAC/PHY layer strategies of Wi-Fi. First of all, to confirm those changes, we have conducted extensive experiments using state-of-the-art commercial IEEE 802.11n/ac-equipped devices and Microsofts Software Radio (Sora) platform. Our experiment results have revealed strong evidence that the use of long A-MPDU frames seriously deteriorates the Wi-Fi performance, i.e., throughput, especially for the pedestrian mobile users. Besides, we have found that the use of channel bonding remarkably consumes more energy, thus making Wi- Fi a primary energy consumer in the battery-powered portable devices. Especially, the energy cost is dominated by excessive and unnecessary listening and receiving operations. We begin an intra-frame rate control algorithm (Intra-RCA) design, called SNR- aware Intra-frame Rate Adaption (SIRA), which enhances the system performance of Wi-Fi in fast time-varying environments [3]. Widely used inter-frame rate control algorithms (Inter-RCAs), which select the PHY rate of each frame based on the time- ii averaged frame loss rate and the signal strength statistics, perform poorly for a long A-MPDU due to the channel variation in mobile environments. Unlike the previous ap- proaches, SIRA adapts the PHY rate on intra-frame basis, i.e., the PHY rate is updated in the middle of a frame according to user mobility. The performance of the proposed scheme is also evaluated by a trace-driven link level simulator employing the collected channel traces from real measurements. The simulation results show that SIRA outper- forms a standalone Inter-RCA in all tested traces. Despite its enhanced performance and considerable frame error reduction, the performance degradation caused by the impact of user mobility still remains due to the inherent limitation of IEEE 802.11 PHY design. Therefore, we conclude that this challenge should be solved with the assistance of PHY modification, and propose Channel-Aware Symbol Error Reduction (ChASER), a new practical channel estimation and tracking scheme for Wi-Fi receivers [4]. ChASER utilizes re-encoding and re-modulation of the received data symbol to keep up with the wireless channel dynamics at the granularity of orthogonal frequency division multi- plexing (OFDM) symbols. In addition, its low-complexity and feasibility of standard compliance is demonstrated by Microsofts Sora prototype implementation and experi- mentation. To our knowledge, ChASER is the first IEEE 802.11n-compatible channel tracking algorithm since other approaches addressing the time-varying channel con- ditions over a single (aggregated) frame duration require costly modifications of the IEEE 802.11 standard. Even though the above proposed approaches enhance the Wi- Fis throughput performance and robustness over conventional technique, the rest re- quirement of the portable device user, i.e., energy efficient Wi-Fi system design, should be addressed as ever. Accordingly, we propose a new power save operation as well as the corresponding protocol, called WiFi in Zizz (WiZizz), which judiciously exploits the characteristic iii of the channel bonding defined in IEEE 802.11ac and efficiently handles the channel bandwidth in an on-demand manner to minimize the traumatic energy spent by IEEE 802.11ac devices [5]. Our extensive measurement and simulation show significant per- formance improvement (as high as 73% energy saving) over a wide range of commu- nication scenarios. In addition, the feasibility of easy implementation is demonstrated by a prototype with a commercial 802.11ac device. To the best of our knowledge, WiZizz is the first IEEE 802.11ac-congenial energy efficient bandwidth management while other existing approaches require costly modifications of the IEEE 802.11ac specification. In summary, we propose a number of compelling algorithms and protocols to im- prove the robustness and energy efficiency in accordance with the paradigm shift of Wi-Fi. Moreover, our evaluation results show that the proposed schemes in this disser- tation are effective and yield considerable performance gain based on both the trace- driven link level simulation and the network level simulation which well reflects the wireless channel characteristics of the real world and the operation of IEEE 802.11 WLAN, respectively. We demonstrate the feasibility of our approaches by implement- ing prototypes in off-the-self IEEE 802.11n/ac devices and software-defined radio.Abstract Contents List of Tables List of Figures 1 Introduction 1.1 Paradigm Shift of Wi-Fi 1.2 DevelopmentTrend of IEEE802.11 1.2.1 MAC Features 1.2.2 PHY Features 1.3 Overview of Existing Approaches 1.3.1 Rate Adaptation 1.3.2 MPDU Length Optimization 1.3.3 Channel Estimation 1.3.4 Demystifying Wi-Fi Power Consumption 1.3.5 Minimizing Energy Consumption of Wi-Fi 1.4 Main Contributions 1.4.1 Impact of Mobility Analysis 1.4.2 Intra-frame Rate Adaptation 1.4.3 Enhanced Channel Estimation and Tracking 1.4.4 802.11ac Power Consumption Analysis 1.4.5 Energy Efficient Bandwidth Management 1.5 Organization of the Dissertation 2 Impact of Mobility 2.1 Introduction 2.2 Background 2.2.1 Channel Estimation and Compensation 2.2.2 Role of Pilot Subcarriers 2.2.3 Frame Aggregation 2.3 Measurement Study 2.3.1 Experimental Settings 2.3.2 Temporal Selectivity 2.3.3 Unreliability of A-MPDU in Mobile Environments 2.3.4 Relation between Symbol Dispersion and Mobility 2.4 Summary 3 SIRA: SNR-aware Intra-frame Rate Adaptation 3.1 Introduction 3.1.1 Revisit of Rate Adaptation Algorithms 3.1.2 Channel and Mobility Condition 3.2 ProposedAlgorithm 3.2.1 Pilot-based SNR Estimation 3.2.2 Mobility Detection 3.2.3 Unequal Modulation and Coding Scheme 3.2.4 Zero-overhead Feedback 3.2.5 SIRA Structure 3.3 Simulation 3.3.1 Trace-drivenLinkLevelSimulation 3.3.2 Mobility Detection Accuracy 3.3.3 Performance Comparison 3.4 Summary 4 ChASER: Channel-Aware Symbol Error Reduction 4.1 Introduction 4.2 Revisit of Channel Estimation Algorithms 4.3 ChASER Design 4.3.1 Channel Estimation using Unknown Data Symbols 4.3.2 Adaptive Filter 4.3.3 Adaptive Filter for MIMO 4.3.4 CRC-assisted Channel Correction 4.3.5 Summary of ChASER Operation 4.3.6 Impact of Step Size μ 4.4 Testbed Experiments 4.4.1 Prototype Implementation on SDR Platform 4.4.2 Testbed Settings 4.4.3 Performance Comparison 4.5 Simulation 4.5.1 Simulation Methodology 4.5.2 Estimation Accuracy 4.5.3 Impact of the A-MPDU Duration 4.5.4 Throughput Performance 4.6 Summary 5 Power Consumption of Wi-Fi: Modeling and Testbed Validation 5.1 Introduction 5.2 Revisit of IEEE 802.11ac Features 5.2.1 Wider Bandwidth Channel 5.2.2 MIMO and Higher Order Modulation 5.2.3 Relation between 802.11ac Features and Power 5.3 Modeling 802.11ac Power Consumption 5.3.1 Power Model of IEEE 802.11ac Receiver 5.3.2 Power Model of IEEE 802.11ac Transmitter 5.4 Power Consumption Measurement 5.4.1 Experimental Setting 5.4.2 Idle State Power Consumption 5.4.3 Receive State Power Consumption 5.4.4 Transmit State Power Consumption 5.4.5 PowerModelVerification 5.4.6 Summary 6 WiZizz: Energy Efficient Bandwidth Management 6.1 Introduction 6.2 WiFi Need to Zizz 6.3 WiZizz Design 6.3.1 Dynamic Mode 6.3.2 Pseudo-dynamic Mode 6.3.3 PHY-level Filtering 6.4 Testbed Experiments 6.4.1 Prototype Implementation and Testbed Setting 6.4.2 Bandwidth Switching Delay 6.4.3 Performance Evaluation 6.5 SimulationResults 6.5.1 Simulation Methodology 6.5.2 Constant Traffic Source with FixedMCS 6.5.3 Comprehensive Traffic Patterns 6.5.4 Collaboration with SMPS 6.6 Summary 7 Conclusion and Future Work 7.1 Research Contributions 7.2 Further Research Plans Abstract (In Korean) 감사의 글Docto