We will define
a resource consisting of a combination of the following: subframes, power allocation, modulation
scheme, number of multicodes, and FEC rate.
HSDPA does not support handoffs due to a requirement of low latency, forcing the MAC functionality
for the high-speed channels (MAC-hs) to reside in the NodeB. Hence cell reselection or
WCDMA handoffs can cause a reduction in the user throughput.
7.7.1 Physical Channels
In this subsection, we will present the physical channels required for HSDPA operations.
High-Speed??“Downlink Shared Channel (HS-DSCH). The HS-DSCH has a constant SF16, and
can be scrambled by either the primary or secondary scrambling code. The time slot and subframe
structure is given in Fig. 7.109. This HS-DSCH channel carries the packet data mentioned above.
3G WIDEBAND CDMA 429
FIGURE 7.108 HSDPA physical channels.
Node B
UE
HS-DSCH
HS-SCCH
DPCH/F-DPCH
HS-DPCCH
DPCCH/DPDCH
FIGURE 7.109 HS-DSCH time slot and subframe structure.
Data = NData Bits Data
2560 Chips
Slot #1 Slot #0 Slot #2
Subframe = 2 msec
The HS-PDSCH in Fig. 7.109 corresponds to a single channelization code from the set of possible
channelization codes reserved for the HS-DSCH transmission. Total number of possible codes 15.
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