Complete Communications Engineering

Video streaming to mobile devices in modern mobile networks, such as 3G, supports high quality video. In many cases, the data transmission rate for streaming video to local area coverage is up to 2 Mbps and for wide area coverage up to 384 Kbps.

The major issues in mobile streaming are: low bandwidth, high error rate, bandwidth fluctuation with time (Dynamic Adaptation is required), bandwidth location dependency, limited battery life, network access, terminal heterogeneity, and content protection. The heterogeneity issue is due to the variety of mobile terminals with a wide range of display sizes, capabilities and different maximum link speeds.

One way to solve the heterogeneity issue is to utilize efficient capability exchange mechanisms that let media streaming servers negotiate with mobile terminals the network capabilities and user preferences. This approach allows the streaming server to send media adapted to the client’s mobile terminal and the network. For example, WCDMA network service clients are able to receive media at a higher bit rate than clients using GSM networks. Also, when a mobile terminal client uses high quality headphones instead of the low quality speaker, a dynamic capability exchange may take place to upgrade the transmission to a high quality audio stream.

Different link speeds (bandwidth) are caused by various radio-access networks with different transmission conditions. The efficient delivery of media streams is achievable only if the media transport protocols incorporate the specific characteristics of wireless links, such as delays due to retransmissions of corrupted data packets. The solution to this issue is to use proxies for caching data packets and optimizing the data transport over the wireless links.

The audio and video data streaming to a mobile handset must be placed in the proper format for streaming. The container format for mobile multimedia streaming is the .3gp file, defined by the 3GPP (Third-Generation Partnership Project) for delivery to mobile devices. Because the bandwidth of video telephony networks are limited, the video and audio data included in a .3gp file is compressed significantly. In a .3gp container, video can be encoded by video codecs specified by the 3GPP such as H.263, MPEG-4, and H.264. Audio streams can be encoded by audio codecs as AMR-NB, AMR-WB, AMR-WB+, AAC-LC, HE-AAC v1 or Enhanced aacPlus (HE-AAC v2).

The 3GPP standard specifies protocols used in mobile communication that are able to use steaming video/audio: real-time streaming protocol (RTSP) and session description protocol (SDP) for session setup and control, synchronized multimedia integration language (SMIL) for session layout description, hypertext transfer protocol (HTTP) and transmission control protocol (TCP) for transporting static media such as session layouts, images, and text, and real-time transfer protocol (RTP) for transporting real-time media such as video, speech, and audio.

The 3G2 standard is similar to 3GP. 3GPP file format was designed for the GSM network, but 3GPP2 file format was designed for CDMA. The 3G2 file format can store the same video streams and most of the audio streams used in the 3GP file format. In addition, 3G2 stores audio streams as EVRC, EVRC-B, EVRC-WB, 13K (QCELP), SMV or VMR-WB.

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