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Monday, February 21, 2011

Data Capabilities of a HSDPA Network for Video Streaming


Before discussing HSDPA Network data capabilities for video streaming let me highlight some Video Coding Requirements for Transmission on 3G Networks. Let’s not forget that Mobile networks present a challenging environment for the transmission of video to individual users in a 3G (or cellular network). The carriage of video over 3G networks falls into the following categories:







 Video in multimedia message services (MMS): Messages are sent from the server by streaming to the mobile receiver.
 Video in live or streaming mode: Video is transferred in a unidirectional mode (half-duplex).
 Video in conversational services, including video conferencing: This requires the transfer of video and audio in full-duplex mode.

The carriage of video on 3G requires a channel on which the bit rate can be sustained to meet the minimum video carriage requirements. In 3G networks there is only limited capacity to support streaming video as it is very bandwidth intensive.

HSDPA is a feature added in release 5 of the 3GPP specifications. HSDPA extends the DSCH, allowing packets destined for many users to be shared on one, higher bandwidth channel called the high-speed DSCH. To achieve higher raw data rates, HSDPA uses, at the physical layer, higher level modulation schemes such as 16-point quadrature amplitude modulation (16QAM), together with an adaptive coding scheme. The HSDPA also changes the control of the medium access control (MAC) function from the radio network controller to the base station. This allows the use of fast adaptation algorithms to improve channel quality and throughput under poor reception conditions. On the average download speeds for DSCH can be 10 Mbps (total shared among the users). However, lab tests and theoretical predictions suggest the rates can be as high as 14.4 Mbps. Of course the maximum data rate falls as the users move outward in the cell and can fall to 1–1.5 Mbps at the cell edge. HSDPA also uses IPv6 in the core network, together with improved protocol support for bursty traffic.

Under normal conditions the HSDPA network can deliver 384 kbps to up to 50 users in a cell area, which is a 10-fold improvement over the release ’99 WCDMA, with which only 5 users could be provided such throughput as indicated in the illustration below;

As per an analysis (Ericsson) of HSDPA networks with 95% of satisfied users, 128 kbps streaming service can be provided at 12 erlangs of traffic. Under low usage conditions (i.e., 2 - 5 min per day) all the users in the cell area (assumed user density per cell of 600) can get satisfactory service. For medium usage (assumed 5 _ 10 min per day) the users that can be catered to within the satisfaction level falls to 171 per cell or 28%, while for high usage (e.g., 4 - 20 min) the usage falls to 108 users per cell or 18%. The unicast services do have the advantage that the number of content channels can be virtually unlimited (including the video on-demand channels) as no resource is used in the idle condition. When a user sets up a connection with the server the content is delivered and resources are used. However, as the figure above indicate, the unicast service does not scale well with the number of users or high-usage patterns. Other disadvantages (advantage for network operators) is that the users incur the data transmission charges.








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