Forward Error Correction for Reliable e-MBMS Transmissions in LTE Networks

The Long Term Evolution (LTE) project focuses on enhancing the Universal Terrestrial Radio Access (UTRA) and optimizing 3rd Generation Partnership Project (3GPP) radio access architecture. A key new feature of LTE is the possibility to exploit the Orthogonal Frequency-Division Multiplexing (OFDM) radio interface to transmit multicast or broadcast data as a multicell transmission over a synchronized Single Frequency Network (SFN): this is known as Multimedia Broadcast and Multicast Service (MBMS) over Single Frequency Network (MBSFN) operation. MBSFN transmission enables a more efficient operation of the MBMS (3GPP, 2008a), allowing over-the-air combining of multi-cell transmissions towards the User Equipments (UEs). This fact makes the MBSFN transmission appear to the UE as a transmission from a single larger cell. Transmission on a dedicated carrier for MBSFN with the possibility to use a longer Cyclic Prefix (CP) with a sub-carrier bandwidth of 7.5 kHz is supported as well as transmission of MBSFN on a carrier with both MBMS transmissions and point-to-point (PTP) transmissions using time division multiplexing. MBMS service defines two delivery methods: the download and the streaming delivery. There are many ways to provide reliability in multicast transmission. The best-known method that operates efficiently for unicast transmission is the Automatic Repeat re-Quest (ARQ). When ARQ is applied in a multicast session, receivers send requests for retransmission of lost packets over a back channel towards the sender. Although ARQ is an effective and reliable tool for point-to-multipoint (PTM) transmission, when the number of receivers increases, it reveals its limitations. One major limitation is the feedback implosion problem which occurs when too many receivers are transmitting back to the sender. A second problem of ARQ is that for a given packet loss rate and a set of receivers experiencing losses, the probability that every single data packet needs to be retransmitted quickly approaches unity as the number of receivers increases. In other words, a high average number of transmissions are needed per packet. In wireless environments, ARQ has another major disadvantage. On most wired networks the feedback channel comes for free, but on wireless networks the transmission of feedback from the receiver can be expensive, either in terms of power consumption, or due to limitations of the communication infrastructure. Thus, due to its requirement for a bidirectional communication link, the