When 7.5 KHz sub-carrier spacing is being used it means it is a Single Cell Scenario which is used for dedicated mode to provide the MBMS services. It proves that it is only possible in Multimedia Broadcast Single Frequency Network (MBSFN) area.
Radio cells that shall transmit the same content to multiple users will form a so called MBSFN area.
With 3GPP Release 9 it has been extended to provide also information on MBMS. The new information element (IE) MBSFN-SubframeConfig
MBMS in LTE has certain impacts to the physical layer. Its start with the use of the cyclic prefix. Its an OFDM fundamental that the signal needs to arrive at the receiver within the cyclic prefix to avoid Inter-Symbol Interference (ISI). As we have multiple, but synchronized transmission from different source the expected delay spread is much higher than for generic LTE. Therefore and in order to support the broadcast
effect even further eMBMS uses extended cyclic prefix only, where todays LTE networks are all based on normal cyclic prefix.
As there are different CPs and subcarrier spacing defined for LTE, there are different modes for MBMS that take advantage of these. First, a mixed mode of MBMS and unicast transmission. In this mode the subcarrier spacing is 15 kHz and resources (subframes) are shared between MBMS data and generic LTE.
Second, there is an option for a dedicated mode. This is also called single-cell scenario, where the carrier is only used for MBMS data. In this case a different subcarrier spacing of 7.5 kHz will be used, offering a larger cyclic prefix of 33.3 µs which leads to a further improved broadcast effect.
I found the below link very useful which can answer all doubts about eMBMS. Please follow that for complete information:
eMBMS in LTE
