Layer Bit Research Articles

The SF12 Well in LoRaWAN: Problem and End-Device-Based Solutions.

LoRaWAN has become a popular technology for the Internet of Things (IoT) device connectivity. One of the expected properties of LoRaWAN is high network scalability. However, LoRaWAN network performance may be compromised when even a relatively small number of devices use link-layer reliability. After failed frame delivery, such devices typically tend to reduce their physical layer bit rate by increasing their spreading factor (SF). This reaction increases channel utilization, which may further degrade network performance, even into congestion collapse. When this problem arises, all the devices performing reliable frame transmission end up using SF12 (i.e., the highest SF in LoRaWAN). In this paper, we identify and characterize the described network condition, which we call the SF12 Well, in a range of scenarios and by means of extensive simulations. The results show that by using alternative SF-management techniques it is possible to avoid the problem, while achieving a packet delivery ratio increase of up to a factor of 4.7.

Inter-layer correlation-based adaptive bit allocation for enhancement layer in scalable high efficiency video coding

To facilitate the diversity of network and end-user devices, bit allocation technology must be combined with scalable high efficiency video coding (SHVC) to achieve continuous bitrate variation. However, to date, the multilayer coding feature in SHVC has not been fully utilized. In this paper, a bit allocation algorithm is proposed for the enhancement layer in SHVC. The algorithm includes two parts: a bit allocation method for the initial frame and another for subsequent frames. The bit allocation method for the initial frame consists of a bit allocation factor model constructed based on investigation of the influence of the initial target bitrate on the overall coding performance. For the bit allocation of the subsequent frames, alternate GOP coding is designed and implemented to fully exploit the inter layer correlation. In addition, an adaptive frame layer bit allocation ratio model is deduced according to the rate distortion optimization theory. Experimental results show that the proposed algorithm can improve PSNR by 0.44 dB and 0.41 dB under low delay and random-access configurations, respectively, and achieve high bitrate control accuracy. The algorithm also outperforms the state-of-the-art algorithms in term of PSNR improvement.

CTU Layer Rate Control Algorithm in Scene Change Video for Free-Viewpoint Video

At present, the rate control algorithm for multiview high-efficiency video coding (MV-HEVC) does not have the capability of efficient coding tree unit(CTU) layer bit allocation, and the video quality varies greatly for sequences with sudden scene changes or large motions. To overcome this limitation, this paper proposes a rate control algorithm for MV-HEVC based on scene detection. Firstly, we established ρ domain rate control model based on multi-objective optimization. Then, it uses image similarity to make reasonable bit allocation among viewpoints. If the video scene is switched, the image similarity is recalculated, and then the correlation between the weights of the interview point rates and the correlation between the viewpoints are analyzed. Finally, the frame layer rate control considers the layer B-frame and other factors in allocating the code rate, and the basic unit layer rate control adopts different quantization methods according to the content complexity of the CTU. Experimental results show that the proposed rate control algorithm can maintain good coding efficiency and decrease the average video quality variation by 25.29%.

Attention region detection based on closure prior in layered bit Planes

An attention region usually possesses a closed contour and a significant color contrast against its surroundings. Inspired by this observation, a novel prior so called closure prior is introduced as an important high-level saliency cue in this paper. Specifically, firstly, the connectivity analysis is used in layered bit planes to extract closed regions based on closure prior. Secondly, the closed regions touching image boundaries are removed based on the assumption that most photographers will not crop attention regions along the view frame. Thirdly, based on the hypothesis that an image region should have a big contrast against its surroundings if it has more chances in all bit planes to be a closed region, the contrast contributions of a closed region in all bit planes are accumulated to obtain color contrast. Meanwhile, by taking account for the characteristics of human visual system according to the perception of small attention region, and the mechanism of human visual resource allocation between attention regions, several morphological filtering technologies are applied to the steps of color contrast calculating. Finally, the saliency map aiming for attention region detection is generated from the contrast map. The experimental results show the presented detection method achieves acceptable performance compared with twelve state-of-the-art models.

ALAVIT: An adaptive layered video transmission for wireless OFDM channels

It is well-known that the layered transmission for video bit-streams generated by a layered coding can gracefully accommodate the receivers' heterogeneity in wireless networks. In this paper, we propose a new layered video transmission scheme employing the subcarrier allocation based on the wireless channel characteristics of orthogonal frequency division multiplexing (OFDM) physical (PHY) layer, leading to an adaptive layered video transmission (ALAVIT). In our scheme, scalable video coding (SVC) is exploited to generate the layered video bit-streams; and the resulting base layer (BL) and enhancement layer (EL) bits are modulated differently to obtain their individual wireless symbols. According to the estimated channel characteristics described by the subcarrier channel gains of a connected wireless receiver, subcarriers with good channel quality are allocated to BL symbols for a better protection of these more important bits. In this unicast case, our ALAVIT scheme is demonstrated to provide a much better performance as compared to the state-of-the-art PHY layer techniques such as s-mod and MixCast. This framework is then generalized from unicast to multicast where the problem is formulated into an optimization involving the average bit-error-rate (BER) over all connected receivers. While the complexity of solving this problem remains extremely high for the current OFDM case of 64 or even more subcarriers, we demonstrate by using a case study of 8 subcarriers that the optimal solution indeed offers a better performance than the heuristic solutions.

HIGHLY SECURE SCALABLE COMPRESSION OF ENCRYPTED IMAGES

A highly secure scalable compression method for stream cipher encrypted images is described in this journal. The input image first undergoes encryption and then shuffling. This shuffling in the image pixels enhances the security. For shuffling, Henon map is used. There are two layers for the scalable compression namely base layer and enhancement layer. Base layer bits are produced by coding a series of non-overlapping patches of uniformly down sampled version of encrypted image. In the enhancement layer pixels are selected by random permutation and then coded. From all the available pixel samples an iterative multi scale technique is used to reconstruct the image and finally performs decryption. The proposed method has high security.

Diversity Analysis of Hierarchical Modulation in Wireless Relay Networks

In communication systems, hierarchical modulation is used to increase system robustness and to send different information flows simultaneously. However, when used in cooperative communication systems, hierarchical modulation is prone to error propagation, which is the most important problem that prevents the achievement of full diversity gains. Depending on the signal-to-noise ratio between the source and the relay, threshold digital relaying can be used to mitigate error propagation. Mitigating error propagation and achieving full diversity depend on setting the thresholds at the relay properly. In this paper, the first and second threshold values are determined so that full diversity gains are attained for both base and enhancement layer bits. Analytical and simulation results are provided to show that the threshold values must depend on the hierarchy parameter.

Optimal Rate Control in H.264 Video Coding Based on Video Quality Metric

The aim of this research is to find a method for providing better visual quality across the complete video sequence in H.264 video coding standard. H.264 video coding standard with its significantly improved coding efficiency finds important applications in various digital video streaming, storage and broadcast. To achieve comparable quality across the complete video sequence with the constrains on bandwidth availability and buffer fullness, it is important to allocate more bits to frames with high complexity or a scene change and fewer bits to other less complex frames. A frame layer bit allocation scheme is proposed based on the perceptual quality metric as indicator of the frame complexity. The proposed model computes the Quality Index ratio (QIr) of the predicted quality index of the current frame to the average quality index of all the previous frames in the group of pictures which is used for bit allocation to the current frame along with bits computed based on buffer availability. The standard deviation of the perceptual quality indicator MOS computed for the proposed model is significantly less which means the quality of the video sequence is identical throughout the full video sequence. Thus the experiment results shows that the proposed model effectively handles the scene changes and scenes with high motion for better visual quality.

Macroblock Layer Rate Control Based on Structural Similarity and Mean Absolute Difference for H.264

In the process of the H.264 video coding, special attention should be paid to the subjective quality of the image. This paper applies the structural similarity (SSIM) based subjective evaluation to the rate control in the H.264 coding and proposes to combine the SSIM and the mean absolute difference (MAD) to perform the macroblock layer bit allocation instead of the MAD. Experimental results show that the proposed method is correlating better with the human visual system and thus achieves better subjective image quality.

Visually Favorable Tone-Mapping With High Compression Performance in Bit-Depth Scalable Video Coding

In bit-depth scalable video coding, the tone-mapping scheme used to convert high-bit-depth to eight-bit videos is an essential yet very often ignored component. In this paper, we demonstrate that an appropriate choice of a tone-mapping operator can improve the coding efficiency of bit-depth scalable encoders. We present a new tone-mapping scheme that delivers superior compression efficiency while adhering to a predefined base layer perceptual quality. We develop numerical models that estimate the base layer bit-rate (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> ), the enhancement layer bitrate (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> ), and the mismatch (Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> ) between the resulting low dynamic range (LDR) base-layer signal and the predefined base layer representation. Our proposed tone curve is given by the solution of an optimization problem which minimizes a weighted sum of R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> , R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> , and Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> . The problem formulation also considers the temporal effect of tone-mapping by adding a constraint to the optimization problem that suppresses flickering artifacts. We also propose a technique with which to tone-map a high-bit-depth video directly in a compression-friendly color space (e.g., one luma and two chroma channels) without converting to the RGB domain. Experimental results show that we can save up to 40% of the total bit-rate (or 3.5 dB PSNR improvement for the same bitrate), and, in general, about 20% bit-rate savings can be achieved.

A verifiable hierarchical circular shift cipher scheme for P2P chunk exchanges

BitTorrent swarms rely on reciprocative chunk exchanges among autonomously participating peers. It has been shown that BitTorrent native tit-for-tat mechanism cannot effectively discourage the peer strategic misbehavior such as free-riding and fake chunk attack. This paper proposes a hierarchical chunk cipher scheme based only on bits circular shifting manipulation. As such, encrypted chunks preserve a fraction of information entropy of original chunks that can be observed by the receiving peers directly, which is used for assuring authenticity of the encrypted chunks. Our hierarchical bits shifting scheme allows more flexibility on the fraction of information entropy exposed directly by the encrypted chunks, when compared to the single layer bits shifting scheme. Further, exact mathematical results between the hierarchical scheme and the single layer scheme are derived and analyzed in detail.

Joint bandwidth allocation, data scheduling and incentives for scalable video streaming over peer-to-peer networks

The overall performance of a peer-to-peer (P2P) scalable streaming system largely depends on the strategies employed in bandwidth allocation, data scheduling and incentives. In this paper, we develop a credit-based content-aware bandwidth auction model for scalable streaming in P2P networks. It formulates multi-overlay multi-layer bandwidth request and allocation problems as auction games. Each peer in the games acts as both auctioneer and player. Being a auctioneer, it maximizes the total revenue (credits) by selling upload bandwidth; Being a player, it uses the credits earned in bandwidth sales to sequentially bid for layer bandwidth so as to maximize the received video quality. Also, a content-aware bidding strategy is proposed, under which the required bandwidth quantity from a peer is determined by the informative video chunks and the marginal net utility that peer could provide, as well as the available credits and the maximum layer bit rate. The convergence of the proposed auction algorithm is mathematically proved. Finally, the performance of the proposed scheme is verified by simulation results.

Dependent R/D Modeling Techniques and Joint T-Q Layer Bit Allocation for H.264/SVC

We investigate dependent rate/distortion (R/D) modeling techniques for H.264/SVC videos. We introduce a self-domain ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -domain) analysis method for characterizing the dependent R/D behaviors, where the R/D characteristics of a base layer are employed as the observation domain for those of dependent layers. Based on <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -domain observations, we propose empirical dependent R/D models and analyze physical implications of the proposed models. As an application of the proposed R/D models, we examine a joint temporal-quality layer bit allocation algorithm formulated as a Lagrange optimization problem. The proposed R/D models enable us to derive an analytical solution to the joint optimization problem. Finally, it is demonstrated by experimental results that our bit allocation algorithm outperforms JSVM benchmark by a significant margin (10%-20%) at various bit rates.

Transmission of Visual Data over Wireless Fading Channel in Real-Time Systems Based on Superposition Coding Scheme

Real-time visual applications are among the most important requirements in the next generation wireless communication systems. In these applications, the transmitted data comprise different layers with different importance levels based on their influence on the reception quality. Furthermore, the real-time transmission nature of these applications makes them sensitive to data losses and transmission delay. To address these issues, an efficient superposition adaptive modulation and coding system, for the optimal system performance, is proposed in this paper. The proposed system switches its modulation and coding scheme adaptively to select the suitable modulation order and coding rate that best match with the instantaneous channel condition. The channel state information is estimated in receiver and fed back to transmitter. In such method, better performances in both data rate and bit error rate (BER) can be attained. Here, the source data are divided into different priority layers with different importance. Each layer bit stream is sent with specific error protection level against channel corruption. The highest error protection level is assigned to the highest priority layer, and vice versa. The modulated bit streams of all layers are then superimposed together and transmitted via Rayleigh fading channel. At the receiver side, a specific multi-stage decoding receiver is used to reconstruct the source data which demodulates the layers in the order of their priorities. Simulation results show that the proposed system provides up to 18 dB SNR and 46 % data rate gains, respectively, compared to the traditional BPSK scheme at BER of 10−4.

Rate control for hierarchical B-frames in H.264/AVC

Hierarchical B-frames can bring high coding performance when introduced into H.264/AVC. However, the traditional rate control schemes can not work efficiently in such new coding framework. This article presents a rate control algorithm for hierarchical B-frames in H.264/AVC. Taking the feature of the dyadic hierarchical coding structure into consideration, the proposed algorithm includes group of pictures (GOP) layer, temporal layer and frame layer bits allocation. After frame layer bits allocation is complete, frame layer quantization parameters (QP) determination strategy is responsible for calculating the final QP. Experimental results show that compared with other rate control algorithms, the proposed one can improve the coding performance and reduce the mismatch of target bit rate and real bit rate.

Bit Allocation for Spatial Scalability Coding of H.264/SVC With Dependent Rate-Distortion Analysis

We propose a model-based spatial layer bit allocation algorithm for H.264/scalable video coding (SVC) in this paper. The challenge of this problem lies in the fact that the rate-distortion (R-D) behavior of an enhancement layer is dependent on its preceding layers because of inter-layer prediction. To solve it, we first focus on the case of two spatial layers, derive the distortion and rate models of the dependent layer analytically, and develop a low-complexity bit allocation algorithm. It is shown by experimental results that the proposed two-layer bit allocation algorithm can achieve the coding performance close to the optimal R-D performance based on the full search method. Then, we extend this result to multilayer bit allocation by performing the two-layer allocation scheme recursively. Finally, we compare the performance of group of pictures-based and frame-based spatial layer bit allocation schemes at a fixed temporal resolution. The superior performance of the proposed spatial layer bit allocation algorithm is demonstrated using Joint Scalable Video Model reference software algorithm and two prior H.264/SVC rate control algorithms as the benchmarks.

Design of SVC-based Multicasting System Preserving Scalable Security

Scalable video coding (SVC) has been standardized as an extension of the H.264/AVC standard. SVC allows straightforward adaptation of video streams by providing layered bit streams. In this paper, we propose a SVC video-based multicasting system preserving scalable security which is able to provide a SVC video service while maintaining information security. In order to maintain information security between a server and a client during all transmission time, the proposed system immediately performs a packet filtering process without decoding with respect to encrypted data received in a routing device, thereby reducing an amount of calculations and latency.

Constant Bit-Rate Multi-Stage Rate Control for Rate-Distortion Optimized H.264/AVC Encoders

H.264/AVC encoder employs rate control to adaptively adjust quantization parameter (QP) to enable coded video to be transmitted over a constant bit-rate (CBR) channel. In this topic, bit allocation is crucial since it is directly related with actual bit generation and the coding quality. Meanwhile, the rate-distortion-optimization (RDO) based mode-decision technique also affects performance a lot for the strong relation among mode, bits, and quality. This paper presents a multi-stage rate control scheme for R-D optimized H.264/AVC encoders under CBR video transmission. To enhance the precision of the complexity estimation and bit allocation, a frequency-domain parameter named mean-absolute-transform-difference (MATD) is adopted to represent frame and macroblock (MB) residual complexity. Second, the MATD ratio is utilized to enhance the accuracy of frame layer bit prediction. Then, by considering the bit usage status of whole sequence, a measurement combining forward and backward bit analysis is proposed to adjust the Lagrange multiplier λMODE on frame layer to optimize the mode decision for all MBs within the current frame. On the next stage, bits are allocated on MB layer by proposed remaining complexity analysis. Computed QP is further adjusted according to predicted MB texture bits. Simulation results show the PSNR improvement is up to 1.13dB by using our algorithm, and the stress of output buffer control is also largely released compared with the recommended rate control in H.264/AVC reference software JM13.2.

Microwave-assisted three-dimensional multilayer magnetic recording

Layer-selective writing of two layer bit patterned media is demonstrated by performing micromagnetic finite element simulations. Selectivity is achieved by controlling the frequency of an oscillating magnetic field in the gigahertz range, applied in addition to the head field. Generation of the microwave field by means of a wire next to the tip of a single pole head is proposed. The Oersted field from the alternating current induces magnetic oscillations in the pole tip which create a high frequency field that is superimposed to the perpendicular write field. The amplitude of the ac field component is in the order of 0.1 T.

Optimization of layered multicast with network coding and genetic algorithm

This article studies the problem of constructing optimal layered multicast with network coding for heterogeneous networks. Based on the flexibility of layered source coding, a global-favorable optimization scheme is proposed, which maximizes the aggregate throughput of heterogeneous sink nodes for layered multicast with network coding by determining the optimal bit rates of the layers. To solve this global-favorable optimization scheme, especially in the large-scale heterogeneous networks, a new problem-specific genetic algorithm (GA) is further proposed. It not only searches efficiently for the optimal allocation of layer bit rates, but also guarantees the validity of candidate solutions in the whole evolutionary process. Simulation results demonstrate that this new GA-based optimization scheme could obtain efficiently the optimal or satisfactorily near-optimal bit rates for layered multicast with network coding, even in the large-scale heterogeneous networks.