# Averting BER Floor with Iterative Source and Channel Decoding for Layered Steered Space-Time Codes
## 3 Source Encoding and Soft-Bit Source Decoding  
We have used the 45 (176 \(\times\) 144)-pixel quarter common intermediate format (QCIF) Akiyo video as test sequence and encoded the frames using the HM reference software for the H.265, also known as HEVC Test Model. The Akiyo video sequence is about a newscaster with few details in the backdrop and having minimal fluctuations. The Akiyo video test sequence is freely redistributed and publicly available at the Xiph.Org Foundation's website. [[https://media.xiph.org/video/derf/](https://media.xiph.org/video/derf/)]([https://media.xiph.org/video/derf/](https://media.xiph.org/video/derf/)). The rates of 15 frames-per-second (fps) and 64 kbps as the overall bitrate of Akiyo video after the encoding operation are considered for our simulations. Moreover, the H.265 standard is particularly designed for achieving the goals of parallel-processing, resilience to data-loss and coding efficiency [43], to say the least. This state-of-the-art compression standard can be extended to network interfacing and implementation, and to the compressed video layer with its high-level syntax providing encapsulation for the compressed video data [44]. Additionally, the H265 standard is useful for bit depth enhancement, configurability, and expandability of the set bits, and for multi-view and multimodal representations of 3D objects as discussed in [44]. There are some features in the H.265 standard which were also deployed in the H.264 architecture [44], namely:  
* The picture parameter set used in H.264 stores shareable information which is rarely changed and is mostly used for decoding operation. The H.265 standard refers to this as the video parameter set (VPS). * For the purpose of enabling video telephony and broadcast or streaming applications, the network abstraction layer (NAL) is designed which is an integral part of both the H.264 and H.265 standards. * The concept of slices is adopted in both the H.264 and H.265 video standards. Slicing is normally used to avoid data losses by recovering the affected segments. * Supplemental enhancement information (SEI) and video usability information (VUI) metadata are supported in both the H.264 and H.265 standards. These are put into the coded video as additional information and indicate the timing information, identify the colour space in the content, and provide other display related statistics. Apart from above features, the H.265 standard also makes use of the inter/intra-prediction and 2D transform techniques, originally deployed in the H.261 standard. The inter and intra prediction techniques assist in determining a prediction residual, undergoing through block transformation, quantization, and entropy coding respectively for correcting the erroneous segments [43; 44; 45]. Traditionally, in all video standards, MacroBlocks (MBs) were used to enhance the performance of iteratively decoded systems by advocating larger interleaver lengths [23; 45]. HEVC has replaced the MBs with Coding Tree Units (CTUs) supporting block structures ranging from (8 \(\times\) 8 to 64 \(\times\) 64) sizes, and sub-partitions the CTUs into Coding Tree Blocks (CTBs) [43]. Each CTB has its associated chroma and luma parts with sizes 16, 32, or 64 for providing better compression. Moreover, intra-prediction (I-slice) and inter-prediction constituting Bi-prediction (B-slice), and Previous-prediction (P-slice) are adopted in HEVC as slice segmentation techniques for mitigating the effects of errors in video transmission [39]. Slicing segments assist in recovering the affected slice using the correctly received segments but often increase the associated overhead. The H.265 video codec has the capability to support all the H.264 applications [46], although it primarily emphasizes on ultra-high-definition transmission without asking for considerable bandwidth. About 50% more compression of the image or video source was attained with the H.265 codec in comparison to the H.264, for the consistent quality [28; 46].