Moreover, the scheduling operation has been moved from the RNC to the NodeB to provide quick
turnaround response times.
The basic HSDPA operation is as follows: The NodeB transmits packets of data at a high rate to
the UE. The data rate highly depends on the UE capability, channel conditions, and NodeB capability.
If the UE successfully receives them, then an ACK is transmitted and the NodeB continues to flush
its data buffers. On the other hand, if a NACK is transmitted by the UE, then the NodeB will retransmit
the packet with either the same information or additional information in order to help the UE successfully
detect the packet of data.
The ACK/NACK information is carried in the uplink HS-DPCCH channel. In parallel to this loop,
the UE is sending Channel Quality Indication (CQI) to the NodeB, giving the NodeB scheduler an
428 CHAPTER SEVEN
FIGURE 7.107 PRACH retransmission statistics.
1
6
11
16
21
26
0
10
20
30
40
50
60
70
80
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100
Frequency %
Frames Retransmitted
Eb/No
(dB)
RACH Mean Retransmission
5
7
10
15
20
25
30
5 71015202530
indication of how good the channel is for that particular UE at that particular time instant. At this
point, the NodeB can dynamically adjust its transmit resources to send data to the UE.
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