U.S. patent application number 12/072416 was filed with the patent office on 2008-06-19 for dynamic forward error correction in utra systems.
This patent application is currently assigned to InterDigital Technology Corporation. Invention is credited to Christopher Cave, Angelo Cuffaro, Paul Marinier.
Application Number | 20080144571 12/072416 |
Document ID | / |
Family ID | 30448162 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080144571 |
Kind Code |
A1 |
Marinier; Paul ; et
al. |
June 19, 2008 |
Dynamic forward error correction in utra systems
Abstract
In a wireless communication system using multiplexed transport
channels in combinations thereof on a coded composite transport
channel (CCTrCh), a system for dynamically varying the combinations
of transport channels includes configuring means for configuring
mutually exclusive dedicated transport channels based on
semi-static transport parameters, and mapping means for mapping
data to a channel selectively based on a preferred semi-static
transport parameter, wherein the mutually exclusive dedicated
transport channels are not multiplexed together onto the
CCTrCh.
Inventors: |
Marinier; Paul; (Brossard,
CA) ; Cuffaro; Angelo; (Laval, CA) ; Cave;
Christopher; (Candiac, CA) |
Correspondence
Address: |
VOLPE AND KOENIG, P.C.;DEPT. ICC
UNITED PLAZA, SUITE 1600, 30 SOUTH 17TH STREET
PHILADELPHIA
PA
19103
US
|
Assignee: |
InterDigital Technology
Corporation
Wilmington
DE
|
Family ID: |
30448162 |
Appl. No.: |
12/072416 |
Filed: |
February 25, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
11196223 |
Aug 3, 2005 |
7349376 |
|
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12072416 |
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10329308 |
Dec 23, 2002 |
6967940 |
|
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11196223 |
|
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60397360 |
Jul 19, 2002 |
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04L 1/0075 20130101;
H04W 72/085 20130101; H04L 1/0016 20130101; H04L 1/0013 20130101;
H04L 1/0009 20130101; H04L 1/0006 20130101; H04L 1/0061
20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04Q 7/00 20060101
H04Q007/00 |
Claims
1. A method for dynamically varying the combinations of transport
channels, comprising: selecting a transport format combination
(TFC) from a TFC set having a semi-static transport parameter for a
dedicated traffic channel (DTCH); the selected TFC set including
the optimum semi-static transport parameter based on the
transmission power conditions; and mapping the DTCH as a transport
channel in accordance with the selected TFC.
2. The method of claim 1 further comprising repeating said
selection and mapping at every transmission time interval
(TTI).
3. The method of claim 1 wherein said selection and mapping are
performed concurrently with dynamic link adaptation (DLA).
4. The method of claim 1 wherein said parameter is forward error
correction (FEC) coding type and rate.
5. The method of claim 1 wherein said parameter is cyclic
redundancy code (CRC) size.
6. The method of claim 1 wherein said parameter is a rate matching
value.
7. A user equipment comprising a medium access control (MAC) for
selecting a transport format combination (TFC) from a TFC set
having a semi-static transport parameter for a dedicated traffic
channel (DTCH) and mapping the DTCH as a transport channel in
accordance with the selected TFC; the selected TFC set including
the optimum semi-static transport parameter based on transmission
power conditions.
8. The method of claim 7 wherein said parameter is forward error
correction (FEC) coding type and rate.
9. The method of claim 7 wherein said parameter is cyclic
redundancy code (CRC) size.
10. The method of claim 7 wherein said parameter is a rate matching
value.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/196,223, filed Aug. 3, 2005, which, in
turn, is a continuation of U.S. patent application Ser. No.
10/329,308, filed Dec. 23, 2002, which claims priority from U.S.
Provisional Application No. 60/397,360, filed Jul. 19, 2002, which
are incorporated by reference as if fully set forth herein.
BACKGROUND
[0002] The proposed invention relates to UMTS 3rd Generation (3G)
wireless communications. More specifically, it considers the Time
Division Duplex (TDD) mode of operation using dynamic link
adaptation (DLA).
[0003] A variety of services, such as video, voice and data, each
having different Quality of Service (QoS) requirements, can be
transmitted using a single wireless connection. This is
accomplished by multiplexing several transport channels onto a
coded composite transport channel (CCTrCh). The CCTrCH is then
mapped onto physical channels for transport over the air interface.
Each transport channel is associated with a transport format set
(TFS), which defines a set of allowed transport formats (TF).
Parameters such as transport block size and transport block set
size are considered dynamic since they can vary within a TFS. In
contrast, semi-static parameters cannot be dynamically changed for
a given transport channel. Rather, they can only be changed after
Radio Resource Control (RRC) signaling has been exchanged between
the user equipment (UE) and the UMTS Terrestrial Radio Access
Network (UTRAN). The time expenditure of this exchange to adjust
semi-static parameters can have unacceptable consequences with
respect to timely mitigation of an RF propagation failure.
[0004] Forward error correction (FEC) coding type and rate are
semi-static parameters that are identical for each TF within a TFS.
An FEC coding rate of 1/2 indicates roughly 2 times as many bits
are required to transmit 1 bit of information, while a 1/3 rate
means there are about 3 times as many bits. A coding rate of 1/2
allows one extra FEC bit to be added for each data bit. For coding
rate 1/3, two extra FEC bits are added for each data bit. This
allows the timeslot to tolerate a lower SIR.
[0005] There are a variety of possible combinations when
multiplexing several transport channels onto a CCTrCh. A particular
transport format combination (TFC) specifies the transport format
of each of the multiplexed channels. A TFC set is a set of allowed
TFCs.
[0006] A transport format combination indicator (TFCI) is an
indicator of a particular TFC, and is transmitted to the receiver
to inform the receiver which transport channels are active for the
current frame. The receiver, based on the reception of the TFCIs,
will be able to interpret which physical channels and which
timeslots have been used. Accordingly, the TFCI is the vehicle
which provides coordination between the transmitter and the
receiver such that the receiver knows which physical transport
channels have been used.
[0007] FIG. 1A shows a UTRA protocol stack, which contains the
following lower layers: radio link control (RLC), medium access
control (MAC) and physical (PHY).
[0008] The RLC layer delivers logical channels bearing control
information to the MAC layer. These channels are the dynamic
control channel (DCCH), which includes set-up information, and the
dynamic traffic channel (DTCH), which carries user data such as
voice and data.
[0009] The MAC layer maps the logical channels DCCH and DTCH to
different transport channels (DCHs), which are then delivered to
the PHY layer. The MAC layer is responsible for selecting the TFC
for combination of transport channels DCH within the CCTrCH. This
selection occurs at every transmission time interval (TTI), which
is the period of time for one data burst. For example, a 20 ms TTI
represents a transmittal of data specified in the TF every 20 ms
(typically amounting to two 10 ms frames). Typically, there are 15
timeslots in each frame. The TFC selection is based on the amount
of buffered data of each logical channel and the UE transmission
power on the uplink (UL) communication. The TFC defines all of the
dynamic and semi-static parameters for each transport channel
within the CCTrCH. The selected TFC and associated data for each UL
CCTrCH is provided to the physical layer for transmission. If the
physical layer subsequently determines transmission of this TFC
exceeds the maximum or allowable UE transmission power, a physical
status indication primitive is generated to the MAC to indicate
that maximum power or allowable transmission power has been
reached.
[0010] FIG. 1B shows a block diagram of the PHY layer combining
transport channels DCH_A, DCH_B and DCH_C on the CCTrCH and mapping
them into physical channels for transmission over the air
interface. A data burst occurs as one coded packet of data is
mapped in one time slot on the physical channel. The PHY layer is
responsible for performing the channel coding of transport channels
DCH, including any forward error correction (FEC). Among the
parameters contained in the TFC are the defined FEC coding types
and rates. The system chooses, on a TTI basis, which transport
channels will be active and how much data will be transmitted in
each one. That is, the TFC selection is fixed for the duration of
the TTI, and can only be changed at the commencement of the next
TTI period. The TFC selection process takes into account the
physical transmission difficulties, (maximum allowable power being
one), and reduces the physical transmission requirements for some
time duration.
[0011] After the multiple transport channels are combined into a
single CCTrCh, the CCTrCh is then segmented and those segments are
mapped separately onto a number of physical channels. In TDD
systems, the physical channels may exist in one, or a plurality of
different timeslots, and may utilize a plurality of different codes
in each timeslot. Although there are as many as 16 possible codes
in a timeslot in the downlink, it is more typical to have, for
example, 8 codes in a particular downlink in a particular timeslot.
A connection can be assigned as many as 16 codes in a downlink
timeslot. In the UL, the UE is limited to using two codes in any
particular timeslot. There are a number of physical channels
defined by a plurality of codes in a plurality of timeslots. The
number of physical channels assigned per connection can vary.
[0012] In the UL, there are rarely more than two codes in a
particular timeslot. In any event, there are a number of physical
channels defined by a plurality of codes in a plurality of
timeslots. The number of physical channels can vary.
[0013] Dynamic link adaptation (DLA) is a fast adjustment mechanism
performed by the UE to combat difficult RF propagation conditions.
When a UE reaches its maximum transmission power, it can reduce its
data rate, typically by 1/2, in an attempt to correct signal to
interference ratio (SIR), by restricting its TFC set to
combinations having lower power requirements. For example, in a
simple case having a single transport channel, and the TFC
corresponding to the allowed transport formats of the transport
channel DCH, such a transport channel may support data rates of 0,
16, 32, 64, and 128 kbps. In this example the TFC set would be
(TF0, TF1, TF2, TF3, TF4), where TF0=0 kbps, TF1=16 kbps, TF2=32
kbps, TF3=64 kbps, TF4=128 kbps. Since transmitting at a higher
data rate requires more power, the data rate is limited during
times of congestion by restricting the TFC set to (TF0, TF1, TF2,
TF3). This eliminates the possibility of the higher data rate TF4
being used. Blocked TFCs may be later restored to the set of
available TFCs by unblocking them in subsequent periods when the UE
transmission power measurements indicate the ability to support
these TFCs with less than or equal to the maximum or allowed UE
transmission power.
[0014] In the 3GPP UTRAN TDD standard, it is specified that
physical resources (i.e., data) must be assigned in the PHY layer
in sequential order, first by timeslot and then by code. Thus,
during each data burst, the first code of the first timeslot is
assigned, then the second code of the first timeslot and so on
until the first timeslot is completely assigned. The assignment of
data continues with the first code of the next consecutive
timeslot, the second code of that timeslot, and so on for the
necessary number of available timeslots and codes until data
resource requirements are satisfied. Upon degraded RF conditions,
DLA decreases the data rate and hence reduces the amount of
required physical resources per TTI. However, the UE assigns
physical resources to timeslots within the frame in consecutive
order, regardless of RF conditions for a particular timeslot. As a
result, if the first few timeslots are the ones having poor SIR,
the later timeslots with potentially more favorable RF conditions
are not utilized or underutilized.
SUMMARY OF THE INVENTION
[0015] A UE transmitter in a 3G UTRAN wireless communication system
performs dynamic link adaptation (DLA) with dynamic semi-static
parameters for overcoming RF propagation difficulties. Separate
transport channels (DCH) are defined for each semi-static
parameter, including forward error coding (FEC) coding type and
rate. When data rate is decreased during DLA, a TFC is selected
having the desired FEC coding type and rate. Since this adjustment
occurs at each TTI, mapping of data packet codes in each timeslot
on the physical channel includes the benefit of FEC rather than
reduced data rate alone. This permits improved SIR in a timeslot
that may be experiencing RF propagation difficulties during the UL
mapping process.
[0016] In a wireless communication system using multiplexed
transport channels in combinations thereof on a CCTrCh, a system
for dynamically varying the combinations of transport channels
includes configuring means for configuring mutually exclusive
dedicated transport channels based on semi-static transport
parameters, and mapping means for mapping data to a channel
selectively based on a preferred semi-static transport parameter,
wherein the mutually exclusive dedicated transport channels are not
multiplexed together onto the CCTrCh.
DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1A shows a representation of a UTRA protocol stack of
layers and channels.
[0018] FIG. 1B shows a block diagram of transport channels being
mapped in the physical layer.
[0019] FIG. 2 shows a flowchart for a dynamic FEC method.
DETAILED DESCRIPTION
[0020] Although the following description of the present invention
is within the context of TDD, it is applicable to both FDD and TDD
modes of operation. DLA enhanced by dynamic forward error
correction (FEC) is useful to either an FDD or TDD UE that reaches
maximum transmission power.
[0021] The UE transmits both control plane information of the
dedicated control channel (DCCH) and user plane data of the
dedicated traffic channel (DTCH) on the same connection. Table 1
shows a UE's TFC set simplified for illustrative purposes,
comprising five transport channels DCH1, DCH2, DCH3, DCH4 and DCH5.
For this example, the transport channels are mapped by the MAC
layer upon radio access bearer establishment (i.e., UE call setup)
such that the DCCH is mapped to DCH1 and the DTCH is mapped to one
from the group DCH2 to DCH5. The transport channels DCH2 to DCH5
have user plane data that is predefined for semi-static parameters
by a system radio network controller (RNC). These transport
channels DCH2 to DCH5 can easily be stored by the RNC in a lookup
table.
[0022] As shown in Table 1, a TFCI value is assigned to each
possible TFC and the presence of control data for each channel is
indicated by `X`. In this example, DCH2 to DCH5 are mutually
exclusive, and hence, never multiplexed together onto the CCTrCh.
The CCTrCh, therefore, never contains more than one user plane
DCH.
TABLE-US-00001 TABLE 1 TFC Set with mutually exclusive DTCH mapping
DCCH DTCH TFCI DCH1 DCH2 DCH3 DCH4 DCH5 1 X X 2 X X 3 X X 4 X X 5 X
6 X 7 X 8 X
[0023] In this example, the semi-static parameters assigned to
transport channels are forward error correction (FEC) coding type
and rate combinations. In a 3G UTRAN system, there are typically
four FEC coding combinations: no coding, convolutional 1/2 rate,
convolutional 1/3 rate and turbo 1/3 rate. Accordingly, the
transport channels in FIG. 2 are defined as DCH2=no coding;
DCH3=convolutional 1/2; DCH4=convolutional 1/3; and DCH5=turbo
1/3.
[0024] The UE can dynamically change the TFC every TTI, depending
on the desired FEC coding. When a high coding rate is desired, such
as convolutional 1/3, the UE selects a TFC containing DCH4, by
setting TFCI=2 or 6. When a lower rate is desired, such as
convolutional 1/2, the UE selects a TFC containing DCH3, by setting
TFCI=3 or 7. All five channels DCH1, DCH2, DCH3, DCH4 and DCH5 are
defined, but only one of the user plane transport channels DCH2 to
DCH5 will be mapped onto the CCTrCh, depending on the value of
TFCI. The control plane transport channel DCH1 is optionally mapped
onto the CCTrCH.
[0025] When used in conjunction with DLA, the dynamic control of
the FEC coding as described above maintains the same number of
physical resources for active timeslots while reducing their
transmission power requirements. More specifically, the data rate
is reduced by DLA when, due to poor SIR, it is decided that the
current number of PHY channels cannot be supported. Although the
rate is reduced in conventional DLA, there may not be an
improvement in SIR if the timeslot experiencing high interference
is the first timeslot in which the user data is transmitted.
Conventional DIA would continue reducing the rate until the number
of bits transmitted in the first timeslot were reduced. With the
lesser data rate, less timeslots and codes of timeslots are
assigned, leading to under utilized PHY channel capacity. However,
with dynamic adjustment of the FEC coding operating concurrently,
those unassigned timeslots and codes of timeslots are available to
accept the additional FEC bits. Thus, the data mapped on the PHY
channels will have improved SIR as a consequence of the adjusted
FEC coding, in addition to the reduced data rate by the DLA. By
allocating more FEC bits, the required transmission power is
reduced for the same target quality of service (QoS). Furthermore,
the number of PHY channels can be maintained at full capacity,
which takes advantage of all possible timeslots, so that those
having the best RF propagation potential are not eliminated from
contention during mapping on the UL.
[0026] The present invention is not limited to dynamic control of a
single semi-static parameter. Alternative embodiments involving
dynamic control of any semi-static parameter are within the scope
of the present invention. Examples of these parameters are the rate
matching parameter and cyclic redundancy code (CRC) size. The UE
must be configured such that a logical channel can be mapped to one
of many transport channels.
[0027] FIG. 2 shows a flowchart for a dynamic FEC method. In step
201, the various semi-static parameters, such as FEC coding type
and rate, are determined and defined for potential mapping as
transport channels DCH. These are stored in a lookup table in step
202 by the RNC. At step 203, upon UE setup, the RNC creates a set
of TFCs such that each semi-static parameter is represented
mutually exclusive for each TFCI. In step 204, the MAC of the UE
selects the TFC from the TFC set having the optimum semi-static
parameters for the present UE transmission power conditions. At
step 205, the logical channels DTCH and DCCH are mapped as
transport channels DCH to the CCTrCh by multiplexing based on the
decision of step 204, and the appropriate TFCI is mapped onto the
UE's timeslot to indicate the mapped TFC for the UL communication.
Steps 204 and 205 repeat at every TTI on the UL, concurrently with
DLA, to dynamically adjust FEC or other semi-static parameters
within the selected TFC.
* * * * *