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Introduction:
High Speed Uplink Packet Access
(HSUPA) is a release 6 feature in 3GPP specifications and is part of HSPA
(High Speed Packet Access) family. HSUPA is more often called as the Enhanced
Uplink Dedicated Channel (E-DCH) by the technically aware people. The main
aim of HSUPA is to increase the uplink data transfer speed in the UMTS
environment and it offers data speeds of up to 5.8 Mbps in the uplink. HSUPA
achieves its high performance through more efficient uplink scheduling in the
base station and faster retransmission control.
Requirements:
HSUPA was designed based on the
following requirements
- The Enhanced Uplink feature
shall aim at providing significant enhancements in terms of user
experience (throughput and delay) and/or capacity. The coverage is an
important aspect of the user experience and that it is desirable to
allow an operator to provide for consistency of performance across the
whole cell area.
- The focus shall be on urban,
sub-urban and rural deployment scenarios.
- Full mobility shall be
supported, i.e., mobility should be supported for high-speed cases also,
but optimisation should be for low-speed to medium-speed scenarios.
- The study shall investigate
the possibilities to enhance the uplink performance on the dedicated
transport channels in general, with priority to streaming, interactive
and background services. Relevant QoS mechanisms shall allow the support
of streaming, interactive and background PS services.
- It is highly desirable to
keep the Enhanced Uplink as simple as possible. New techniques or group
of techniques shall therefore provide significant incremental gain for
an acceptable complexity. The value added per feature/technique should
be considered in the evaluation. It is also desirable to avoid
unnecessary options in the specification of the feature.
- The UE and network complexity
shall be minimised for a given level of system performance.
- The impact on current
releases in terms of both protocol and hardware perspectives shall be
taken into account.
- It shall be possible to
introduce the Enhanced Uplink feature in a network which has terminals
from Release'99, Release 4 and Release 5. The Enhanced Uplink feature
shall enable to achieve significant improvements in overall system
performance when operated together with HSDPA. Emphasis shall be given
on the potential impact the new feature may have on the downlink capacity.
Likewise it shall be possible to deploy the Enhanced Uplink feature
without any dependency on the deployment of the HSDPA feature. However,
a terminal supporting the Enhanced Uplink feature must support HSDPA.
Abbreviations:
It would be important to remember
following abbreviations before proceeding:
- AG: Absolute Grant
- E-AGCH: E-DCH Absolute Grant
Channel
- E-DCH: Enhanced Dedicated
Channel
- E-DPCCH: E-DCH Dedicated
Physical Control Channel
- E-DPDCH: E-DCH Dedicated
Physical Data Channel
- E-HICH: E-DCH Hybrid ARQ
Indicator Channel
- E-RGCH: E-DCH Relative Grant
Channel
- E-RNTI: E-DCH Radio Network
Temporary Identifier
- E-TFC: E-DCH Transport Format
Combination
- HARQ: Hybrid Automatic Repeat
Request
- HSDPA: High Speed Downlink
Packet Access
- RG: Relative Grant
- RLS: Radio Link Set
- RSN: Retransmission Sequence
Number
- SG: Serving Grant
- TSN: Transmission Sequence
Number
HSUPA General Features
- Maximum transmission rate of
5.76Mbps
- BPSK modulation
- No adaptive modulation
- Multicode transmission
- Spreading Factor either 2 or
4
- 10ms and 2ms TTI but
initially only 10ms TTI to be used.
- Hybrid ARQ (HARQ)
- Fast Packet Scheduling in the
uplink
- Soft Handover supported
Protocol Architecture of E-DCH
The following modifications to the
existing nodes are needed to support enhanced uplink DCH:
UE: A new MAC entity (MAC-es/MAC-e) is added in the UE below
MAC-d. MAC- es/MAC-e in the UE handles HARQ retransmissions, scheduling and
MAC-e multiplexing, E-DCH TFC selection.
Node B: A new MAC entity (MAC-e) is added in the Node B to
handle HARQ retransmissions, scheduling and MAC-e demultiplexing.
S-RNC: A new MAC entity (MAC-es) is added in the SRNC to
provide in-sequence delivery (reordering) and to handle combining of data
from different Node Bs in case of soft handover.
HSUPA Physical Layer categories
The following E-DCH UE categories
are defined in the specifications:
|
HSUPA
category
|
Maximum
number of
HSUPA
codes
transmitted
|
Minimum
spreading
factor
|
Support
for 10 and 2 ms
HSUPA TTI
|
Maximum
number of
bits
transmitted
within
a 10 ms
HSUPA
TTI
|
Maximum
number of
bits
transmitted
within
a 2 ms
HSUPA
TTI
|
Maximum
Bit rate
|
|
Category
1
|
1
|
SF4
|
10
ms TTI only
|
7296
|
-
|
0.73
Mbps
|
|
Category
2
|
2
|
SF4
|
10
ms and 2 ms TTI
|
14592
|
2919
|
1.46
Mbps
|
|
Category
3
|
2
|
SF4
|
10
ms TTI only
|
14592
|
-
|
1.46
Mbps
|
|
Category
4
|
2
|
SF2
|
10
ms and 2 ms TTI
|
20000
|
5837
|
2.92
Mbps
|
|
Category
5
|
2
|
SF2
|
10
ms TTI only
|
20000
|
-
|
2.00
Mbps
|
|
Category
6
|
4
|
SF2
|
10
ms and 2 ms TTI
|
20000
|
11520
|
5.76
Mbps
|
New Channels
Dedicated transport channel
E-DCH - Enhanced Dedicated
Channel: The Enhanced Dedicated Channel
(E-DCH) is an uplink transport channel.
Uplink Dedicated Physical channels
E-DPCCH and E-DPDCH:
The E-DPDCH is used to carry the
E-DCH transport channel. There may be zero, one, or several E-DPDCH on each
radio link. The E-DPCCH is a physical channel used to transmit control
information associated with the E-DCH. There is at most one E-DPCCH on each
radio link.
E-DPDCH and E-DPCCH are always
transmitted simultaneously, except for the case that E-DPDCH but not E-DPCCH
is DTXed due to power scaling. E-DPCCH shall not be transmitted in a slot
unless DPCCH is also transmitted in the same slot.
Figure above shows the E-DPDCH and
E-DPCCH (sub)frame structure. Each radio frame is divided in 5 subframes,
each of length 2 ms; the first subframe starts at the start of each radio
frame and the 5th subframe ends at the end of each radio frame. The E-DPDCH
slot formats, corresponding rates and number of bits are specified in Table
A. The E-DPCCH slot format is listed in Table B.
Table
A: E-DPDCH slot formats
|
Slot
Format #i
|
Channel
Bit Rate (kbps)
|
SF
|
Bits/
Frame
|
Bits/
Subframe
|
Bits/Slot
(Ndata)
|
|
0
|
15
|
256
|
150
|
30
|
10
|
|
1
|
30
|
128
|
300
|
60
|
20
|
|
2
|
60
|
64
|
600
|
120
|
40
|
|
3
|
120
|
32
|
1200
|
240
|
80
|
|
4
|
240
|
16
|
2400
|
480
|
160
|
|
5
|
480
|
8
|
4800
|
960
|
320
|
|
6
|
960
|
4
|
9600
|
1920
|
640
|
|
7
|
1920
|
2
|
19200
|
3840
|
1280
|
Table
B: E-DPCCH slot formats
|
Slot
Format #i
|
Channel
Bit Rate (kbps)
|
SF
|
Bits/
Frame
|
Bits/
Subframe
|
Bits/Slot
(Ndata)
|
|
0
|
15
|
256
|
150
|
30
|
10
|
Downlink Dedicated Physical
channels
E-DCH Relative Grant Channel
(E-RGCH):
The E-DCH Relative Grant Channel
(E-RGCH) is a fixed rate (SF=128) dedicated downlink physical channel
carrying the uplink E-DCH relative grants. Figure above illustrates the
structure of the E-RGCH. A relative grant is transmitted using 3, 12 or 15
consecutive slots and in each slot a sequence of 40 ternary values is
transmitted. The 3 and 12 slot duration shall be used on an E-RGCH
transmitted to UEs for which the cell transmitting the E-RGCH is in the E-DCH
serving radio link set and for which the E-DCH TTI is respectively 2 and 10
ms. The 15 slot duration shall be used on an E-RGCH transmitted to UEs for
which the cell transmitting the E-RGCH is not in the E-DCH serving radio link
set.
E-DCH Hybrid ARQ Indicator Channel
(E-HICH):
The E-DCH Hybrid ARQ Indicator
Channel (E-HICH) is a fixed rate (SF=128) dedicated downlink physical channel
carrying the uplink E-DCH hybrid ARQ acknowledgement indicator. Figure above
(same as E-RGCH) illustrates the structure of the E-HICH. A hybrid ARQ
acknowledgement indicator is transmitted using 3 or 12 consecutive slots and
in each slot a sequence of 40 binary values is transmitted. The 3 and 12 slot
duration shall be used for UEs which E-DCH TTI is set to respectively 2 ms
and 10 ms.
Fractional Dedicated Physical
Channel (F-DPCH):
The F-DPCH carries control
information generated at layer 1 (TPC commands). It is a special case of
downlink DPCCH. Figure above shows the frame structure of the F-DPCH. Each
frame of length 10ms is split into 15 slots, each of length Tslot = 2560
chips, corresponding to one power-control period. There are 2 bits/slot.
Common downlink physical channels
E-DCH Absolute Grant Channel
(E-AGCH):
The E-DCH Absolute Grant Channel
(E-AGCH) is a fixed rate (30 kbps, SF=256) downlink physical channel carrying
the uplink E-DCH absolute grant. Figure above illustrates the frame and
sub-frame structure of the E-AGCH. An E-DCH absolute grant shall be
transmitted over one E-AGCH sub-frame or one E-AGCH frame. The transmission
over one E-AGCH sub-frame and over one E-AGCH frame shall be used for UEs for
which E-DCH TTI is set to respectively 2 ms and 10 ms.
HARQ protocol
General Principle
The HARQ protocol has the
following characteristics:
- Stop and wait HARQ is used;
- The HARQ is based on
synchronous downlink ACK/NACKs;
- The HARQ is based on
synchronous retransmissions in the uplink:
- The number of processes
depends on the TTI: 8 processes for the 2ms TTI and 4 processes for the
10ms TTI. For both scheduled and non-scheduled transmission for a given
UE, it is possible to restrict the transmission to specific processes
for the 2ms E-DCH TTI;
- There will be an upper limit
to the number of retransmissions. The UE decides on a maximum number of
transmissions for a MAC-e PDU based on the maximum number of
transmissions attribute (see subclause 11.1.1), according to the
following principles:
- The UE selects the highest
'maximum number of transmissions' among all the considered HARQ
profiles associated to the MAC-d flows in the MAC-e PDU.
- Pre-emption will not be
supported by E-DCH (ongoing re-transmissions will not be pre-empted by
higher priority data for a particular process);
- In case of TTI
reconfiguration, the MAC-e HARQ processes are flushed and no special
mechanism is defined to lower SDU losses.
- Intra Node B macro-diversity
and Inter Node B macro-diversity should be supported for the E-DCH with
HARQ;
- Incremental redundancy shall
be supported by the specifications with Chase combining as a subcase:
- The first transmission shall
be self decodable;
- The UTRAN configures the UE
to either use the same incremental redundancy version (RV) for all
transmissions, or to set the RV according to set of rules based on
E-TFC, Retransmission Sequence Number (RSN) and the transmission
timing;
- There shall be no need, from
the H-ARQ operation point of view, to reconfigure the Node B from upper
layers when moving in or out of soft handover situations.
Error handling
The most frequent error cases to
be handled are the following:
- NACK is detected as an ACK:
the UE starts afresh with new data in the HARQ process. The previously
transmitted data block is discarded in the UE and lost. Retransmission
is left up to higher layers;
- ACK is detected as a NACK: if
the UE retransmits the data block, the NW will re-send an ACK to the UE.
If in this case the transmitter at the UE sends the RSN set to zero, the
receiver at the NW will continue to process the data block as in the
normal case;
- Error cases have been
identified regarding the HARQ operation during soft handover:
- In case the HARQ control
information transmitted on the E-DPCCH could not be detected RSN_max
times in a row for one HARQ process, a soft buffer corruption might
occur. Each HARQ process uses RSN and the transmission time (CFN,
sub-frame) elapsed since storing data in the associated soft buffer in
order to flush the soft buffer and to avoid a wrong combining of data
blocks.
- Duplication of data blocks
may occur at the RNC during soft handover. The reordering protocol
needs to handle the detected duplications of data blocks.
Signaling examples
E-DCH Establishment with TTI
Reconfiguration
This scenario shows an example of
E-DCH configuration. Also TTI reconfiguration is shown in the same scenario.
It is assumed that in this example DCH was established before.
- The SRNC decides there is a
need for a establishing E-DCH for a UE and prepares the RNSAP message
Radio Link Reconfiguration Prepare which is transmitted to the
CRNC.
Parameters: DCHs to Delete IE, E-DPCH Information (TFCS, TTI), Serving
E-DCH RL ID, E-DCH FDD Information.
- The CRNC requests the E-DCH
Node B to perform a synchronised radio link reconfiguration using the
NBAP message Radio Link Reconfiguration Prepare, for the E-DCH radio
link.
Parameters: DCHs to Delete IE, Servine E-DCH RL ID, E-DCH FDD
Information.
- The E-DCH Node B returns a
NBAP message Radio Link Reconfiguration Ready.
Parameters: DCH Information Response , E-DCH FDD Information Response.
- The CRNC returns the RNSAP
message Radio Link Reconfiguration Ready to the SRNC.
Parameters: DCH Information Response, E-DCH FDD Information Response.
- The CRNC initiates set-up of
a new Iub Data Transport Bearers using ALCAP protocol. This request
contains the AAL2 Binding Identity to bind the Iub Data Transport Bearer
to the E-DCH.
- The SRNC initiates set-up of
a new Iur Data Transport bearer using ALCAP protocol. This request
contains the AAL2 Binding Identity to bind the Iur Data Transport Bearer
to the E-DCH.
- The SRNC proceeds by
transmitting the RNSAP message Radio Link Reconfiguration Commit to the
CRNC.
Parameters: SRNC selected activation time in the form of a CFN.
- The CRNC transmits the NBAP
message Radio Link Reconfiguration Commit to the E-DCH Node B including
the activation time.
Parameters: CRNC selected activation time in the form of a CFN.
- The SRNC also transmits a RRC
message Radio Bearer Reconfiguration to the UE.
Parameters: activation time, E-DCH Info and E-RNTI.
- The UE returns a RRC message
Radio Bearer Reconfiguration Complete to the SRNC.
- The CRNC initiates release of
the old Iub Data Transport bearer (DCH) using ALCAP protocol.
- The SRNC initiates release of
the old Iur Data Transport bearer (DCH) using ALCAP protocol.
- The SRNC decides there is a
need for a TTI reconfiguration and prepares the RNSAP message Radio Link
Reconfiguration Prepare which is transmitted to the CRNC.
Parameters: E-DPCH Information (TTI).
- The CRNC requests the E-DCH
Node B to perform a synchronised radio link reconfiguration using the
NBAP message Radio Link Reconfiguration Prepare, for the E-DCH radio
link
- The E-DCH Node B returns a
NBAP message Radio Link Reconfiguration Ready.
Parameters: E-DCH FDD Information Response.
- The CRNC returns the RNSAP
message Radio Link Reconfiguration Ready to the SRNC.
Parameters: E-DCH FDD Information Response.
- The SRNC proceeds by
transmitting the RNSAP message Radio Link Reconfiguration Commit to the
CRNC.
Parameters: SRNC selected activation time in the form of a CFN.
- The CRNC transmits the NBAP
message Radio Link Reconfiguration Commit to the E-DCH Node B including
the activation time.
Parameters: CRNC selected activation time in the form of a CFN.
- The SRNC also transmits a RRC
message Radio Bearer Reconfiguration to the UE.
Parameters: activation time, E-DCH Info and E-RNTI.
- The UE returns a RRC message Radio
Bearer Reconfiguration Complete to the SRNC.
REFERENCES:
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