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2 Adaptive Modulation and Coding
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2.1 Introduction (1/3)
..........................................................................32.1
Introduction (2/3)
..........................................................................42.1
Introduction (3/3)
..........................................................................52.2
Channel
Coding............................................................................62.3
Multiple Code Operation
..............................................................72.4
Transport Format & Resource Combining
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2.1 Introduction (1/3)
UMTS Rel.99 networks assure a proper downlink stability using a
fast power control
mechanisms between Node B and the UE. With respect to other
mobiles in the same cell theminimum necessary power is radiated on
the Uu interface. Fast power control is performed inloops of 0.666
ms.
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2.1 Introduction (2/3)
HSDPA uses a fixed transmission power between Node B and the UE
and modifies
modulation type and channel coding in real-time to achieve a
certain quality of service. Themobile supports this downlink
adaptation by sending so-called uplink channel qualityindication
reports (CQI).
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2.2 Channel Coding
Both modulation types can be used with different channel coding
algorithms. A 0.25 ChannelCode rate only allows for 119 kbps user
bit rate with very high protection and QPSK as arobust modulation
type. In contrast, 16 QAM and a 0.75 Channel Code rate provides a
higherbit rate with less protection. It would require less
interfered radio conditions.
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2.3 Multiple Code Operation
HSDPA can assign up to 15 channel codes in parallel to increase
data downlink throughput.
All codes have a fixed spreading factor of 16. These codes can
be distributed among severalmobiles on a time division multiplex
access scheme.
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2.4 Transport Format & Resource Combining
This combination of modulation type, Channel Coding type and
number of simultaneouslyallocated Channel Codes provides very
flexible counter-measures to cope with air interfaceinterference.
HSDPA uses a dedicated expression for this mechanism named
TransportFormat & Resource Combining (TFRC).The table shows a
variety of TFRCs and the resulting user bit rates. They range from
119kbps using QPSK, very high protection and only 1 assigned code
to 10.8 Mbps using 16QAM, low protection and 15 codes in
parallel.
