3GPP Broadband Evolution to IMT-Advanced - 4G Americas

Figure 40: High-Speed Forward Access Channel 108R99-R6 solutionDelay >0.5 sR7/R8 solutionSeamless transitionCell_FACH Cell_DCH Cell_FACH Cell_DCHRACH +FACHHSDPA +HSUPAHSDPA + HSUPA6-32 kbps >1 Mbps>1 MbpsR99-RC RRC StatesR7/8 RRC StatesRB reconfigurationPCHFACHCell update andC-RNTI allocationtakes >300 msPCHeFACHImmediate transmission w/ocell update. No PCHrequired.RB reconfigurationDCH/HSPANo data flowduring transition>500 msHSPAData flows on HS-FACH also duringtransition.DCH – Dedicated ChannelFACH – Forward Access ChannelRACH – Reverse Access ChannelPCH – Paging ChannelHS-FACH – High Speed FACHRB – Radio BearerRRC – Radio Resource ControlHS-RACHIn Release 8, the concept above extends to the uplink by activating the E-DCH inCELL_FACH to reduce the delay before E-DCH can be used. This feature is called High-Speed Reverse Access Channel (HS-RACH), and together with HS-FACH, is referred to asthe enhanced CELL_FACH operation.The RACH is intended for small amounts of data and thus has a limited data rate and canonly support transmission of a single transport block. For larger amounts of data,terminals must transmit multiple time on the RACH or transition to the dedicated108 Source: "LTE for UMTS, OFDMA and SC-FDMA Based Radio Access,” Harri Holma and Antti Toskala,Wiley, 2009.Transition to 4G: 3GPP Broadband Evolution to IMT-Advanced, Rysavy Research/3G Americas, Aug 2010 Page 95