## 3 Overview of Video Delivery in 4G Mobile Cellular Networks
### Mobile Video Delivery in 4G LTE  
**Video Coding Standards:** Video codecs are under constant evolution due to ever increasing performance requirements and novel use cases. The current video coding standards, H.265/HEVC [36], replaced the previous one, H.264/AVC [37], due to requirements for higher coding efficiency, higher spatial resolution (4K/8K video), color resolution and dynamic range. Extensions of HEVC include scalable (SHVC), multi-view (MV-HEVC), range (RExt) and 3D video coding (3D-HEVC) [38].  
Details of HEVC compression are beyond the scope of this paper. We assume compressed video is packetized and organized into source blocks compatible with RLNC coding approach in Section 2. Typically, source blocks represent compressed group of frames (GOFs). Layered source block structure can be obtained via scalable video coding (SVC) or using specific codec features such as slicing or data partitioning [23; 39]. Finally, we note that, besides H.264/AVC and H.265/HEVC, other popular video codec are in use such as VP9 and AV1 codecs.  
**Mobile Video Streaming/Downloading over 4G LTE:** Most prevalent techniques for online video delivery are progressive downloading (PD) [24] and adaptive bitrate streaming (ABR) [25]. Chronologically, progressive downloading was first implemented and aimed to enable video users watching the video before the entire video content is downloaded. Video players download first metadata which describes video details and as soon as the first video data has been downloaded the rendering can start. ABR streaming also provides users capability to watch video content before the download is complete, however, this streaming technique provides multiple representations of the same video on the content server. These representations are encoded in different resolutions and bitrates thus allowing video clients to adapt delivered video resolution by switching between different representations according to the bandwidth available on the client side. Multiple ABR implementations are available but the most dominant ones are Apple HLS (HTTP Live Streaming), DASH (Dynamic adaptive streaming over HTTP), Microsoft Smooth Streaming and Adobe HTTP Dynamic streaming. Analysis shows that around 80% of total mobile streamed video is delivered in ABR format while therest is delivered in PD format. 70% out of total mobile streamed video is delivered in encrypted format by using HTTPS or QUIC transport, where e.g., QUIC protocol is used for Youtube content.  
**Mobile Video Multicasting/Broadcasting over 4G LTE:** LTE network support for a point-to-multipoint (PtM) services is defined in 3 GPP as evolved Multimedia Broadcast/Multicast Service (eMBMS) [9]. The service is initially designed for mobile TV and radio broadcasting use case, however, other push-based services such as popular content caching (e.g., podcasts, news, ads, updates), live streaming of popular events (e.g., sport events such as olympics) and mobile network emergency alerts contributed to eMBMS development. eMBMS is delivered via PtM radio bearers thus providing for efficient usage of radio resources for the price of using fixed (i.e., non-adaptive) and conservative transmission configuration targeting improved cell coverage. In the context of this paper, eMBMS provides support for application-layer forward error correction (AL-FEC) [40], where Raptor codes are recommended, although potentially, RLNC could also be used as an alternative. Despite rising interest in LTE broadcasting, eMBMS has not yet been massively deployed at mobile network operators, while significant experience and promising prospects are gained via service trials [41].