System performance issues will be addressed by the TTI capable to be decoded, for example
40 msec or 80 msec or others. The larger TTI provides better interleaving capability and thus has
improved performance. Since MBMS services are expected to handle mobility, then handoffs should
be supported. The MBMS transmission allows for selective combining and soft combining between
radio links. This is possible since the RLC Protocol Data Units (PDU) are numbered. As long as the
NodeBs are reasonably synchronized and they have the same bit rate, selective combining can be
used. We must also mention this assumes the RLC reordering capability of the UE is not exceeded.
The 3GPP standard states that soft combining is possible given the delay between radio links is less
than 1 TTI plus 1 time slot. Performance and memory requirement trade-offs should be conducted to
determine acceptable QoS delivery to the end user.
Product differentiation issues will be addressed by simultaneous configurations. For example, the
possibility to receive a DPCH/HS-DSCH and S-CCPCH carrying MTCH/MCCH simultaneously is
a UE capability. The minimum MBMS bit rate and combining method are also under the control of
the UE. This information is important and should be conveyed to the Radio Network Controller
(RNC) in order to perform or potentially avoid additional signal processing.
Pages:
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802