Why Mobile TV Doesn’t Use IPTV
Mobile TV can be watched on a smartphone or 3G, such as the LG Vu smartphone or the Samsung SCH u620. Both AT&T Wireless and Verizon Wireless offer cell TV service. For Verizon, it’s VCAST TV and for AT&T, it’s AT&T Mobile TV. Both AT&T and Verizon Mobile TV use Qualcomm’s MediaFLO technology to broadcast VHF digital TV signals (center frequency 719 MHz) to cell phones. Mobile TV services from different operators combine different sets of TV channels in their broadcast (in the range of 10 to 12 TV channels in the basic package).
The Mobile TV service does not use cell phone networks to transmit TV signals. Instead, it uses separate networks to distribute, transmit and broadcast TV signals to cell phones. It only uses the cell phone network to provide user interactivity and authorization with the TV service provider. Since AT&T and Verizon’s 3G cell phone networks are both capable of carrying IP traffic, it seems clear that the simplest application for mobile TV is to use IPTV. A good example is AT&T already using Smart IPTV in its U-verse services (internet, telephone and TV).
In order to understand why mobile TV does not use IPTV, it is necessary to explain the unique properties of mobile networks. Current 3G (UMTS, EVDO) mobile phone networks are designed to carry unicast traffic only, i.e. a point to point connection needs to be established between the user and the Media server for the network to transmit TV traffic to the mobile phone. Since TV is a broadcast service, that is, a point to multipoint connection is required for mobile TV services. To implement a point to multipoint connection, the mobile network needs to set up an IP connection between the Media server and each mobile user who is receiving broadcasts simultaneously. Some of these connections will easily overwhelm the phone’s network capacity and block any other voice and data traffic that needs to use the network.
In order for mobile TV to use IPTV, the IP multicast feature needs to be implemented in the cell phone network. Multicasting is a technique of transmitting a single video signal simultaneously to several end users. All viewers receive the same signal at the same time but there is no separate stream (connection) for each receiver. IP multicast is widely used in the delivery of TV broadcast services over IP networks. This significantly reduces the amount of bandwidth required to transmit high-quality IPTV content over the network. This is because only one copy of each video stream needs to be sent to the router, which in turn creates a copy of that stream for the requesting device. Multicast not only reduces network bandwidth requirements but Media server processing power can also be kept relatively low as it transmits only one copy of the IPTV stream at a time.
Although the current 3G cellular networks from AT&T and Verizon do not have IP multicast, however, the next 3G cellular network upgrade of the two carriers may include the IP multicast feature. For AT&T Wireless, the next network upgrade is HSPA (High Speed Packet Access) which supports MBMS (Multimedia Broadcast Multicast Services) features. For Verizon Wireless, the next upgrade is EVDO Rev A which supports BCMCS (Broadcast and Multicast Services) features. Hence, future mobile TV services from AT&T Wireless and Verizon Wireless could use IPTV implementations.