Analytic Evaluation of a Hybrid Broadcast-Unicast TV Offering

Today mobile TV services in cellular spectrum are delivered over unicast radio bearers as offered by 3G technologies like WCDMA and HSDPA. Since unicast transmission does not scale very well if mobile TV becomes a true mass service, 3GPP has defined a broadcast extension for UMTS, called multimedia broadcast multicast service (MBMS). MBMS introduces radio broadcast bearers serving all users in common, thus providing true broadcast capabilities. A not so well known feature of MBMS is its support for hybrid broadcast-unicast transmission. In this mode the more popular channels are broadcasted over point- to-multipoint radio bearers while the less popular channels are delivered over point-to-point bearers only on request. In this paper we will present a theoretical framework which allows an analytic evaluation of the capacity limits when delivering mobile TV services over hybrid broadcast-unicast transmission schemes provided by MBMS.