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mobile devices that require a DCH in the uplink direction, and mobile devices that
support a combination of HSDPA in the downlink and HSUPA in the uplink.
As the E‐DCH concept is an evolution of existing standards, it has triggered the crea-
tion of a number of new documents as well as the update of a number of existing speci-
fications. Most notably, 3GPP TR 25.896 [18] was created to discuss the different
options that were analyzed for HSUPA. Once consensus on the high‐level architecture
was reached, 3GPP TS 25.309 [19] was created to give a high‐level overview of the
selected solution. Among the specification documents that were extended are 3GPP TS
25.211 [4], which describes physical and transport channels, and 3GPP TS 25.213 [20],
which was extended to contain information about E‐DCH spreading and modulation.

3.11.1 E‐DCH Channel Structure
For the E‐DCH concept a number of additional channels were introduced in both
uplink and downlink directions as shown in Figures 3.42 and 3.43. These are used in
addition to existing channels, which are also shown in the figure. For further explana-
tion of these channels, see Section 3.4.3 for Release 99 channels and Section 3.10.1
for HSDPA.
As shown on the left side in Figure 3.42, HSUPA introduces a new transport channel
called the E‐DCH. While still a DCH for a single user, the dedicated concept was
adapted to use a number of features that were already introduced with HSDPA for the
downlink direction. Therefore, the following overview just gives a short introduction to
the feature and the changes required to address the needs of a dedicated channel:
Node‐B scheduling. While standard DCHs are managed by the RNC, E‐DCHs are
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managed by the Node‐B. This allows a much quicker reaction to transmission errors,
which in turn decreases the overall RTD time of the connection. Furthermore, the
Node‐B is able to react much more quickly to changing conditions in the radio envi-
ronment and variations in user demand for uplink resources, which helps to better
utilize the limited bandwidth of the air interface.
HARQ. Instead of leaving error detection and correction to the RLC layer alone, the
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E‐DCH concept uses the HARQ scheme, which is also used by HSDPA in the down-
link direction. This way, errors can be detected on a per‐MAC‐frame basis by the
Node‐B. For further details see Section 3.10.2, which describes the HARQ functional-
ity of HSDPA in the downlink direction. While the principle of HARQ in the uplink
direction is generally the same, it should be noted that the signaling of acknowledge-
ments is done in a slightly different way due to the nature of the DCH approach.
Chase Combining and Incremental Redundancy. These are used in a similar way
●
for E‐DCH as described in Section 3.10.5 for HSDPA to retransmit a frame when the
HARQ mechanism reports a transmission error.
On the physical layer, the E‐DCH is split into two channels. The Enhanced Dedicated
Physical Data Channel (E‐DPDCH) is the main transport channel and is used for user
data (IP frames carried over RLC/MAC‐frames) and layer 3 RRC signaling between the
mobile device on the one side and the RNC on the other. As described below, the
spreading factor used for this channel is quite flexible and can be dynamically adapted
from 64 to 2 depending on the current signal conditions and the amount of data the
mobile device wants to send. It is even possible to use several channelization codes at