U.S. patent application number 13/204753 was filed with the patent office on 2013-02-14 for system and method to increase link adaptation performance with multi-level feedback.
This patent application is currently assigned to RESEARCH IN MOTION LIMITED. The applicant listed for this patent is Ozgur Ekici, Muhammad Khaledul Islam. Invention is credited to Ozgur Ekici, Muhammad Khaledul Islam.
Application Number | 20130039266 13/204753 |
Document ID | / |
Family ID | 47677508 |
Filed Date | 2013-02-14 |
United States Patent
Application |
20130039266 |
Kind Code |
A1 |
Ekici; Ozgur ; et
al. |
February 14, 2013 |
SYSTEM AND METHOD TO INCREASE LINK ADAPTATION PERFORMANCE WITH
MULTI-LEVEL FEEDBACK
Abstract
A method and apparatus for explicit adaptive modulation and
coding scheme selection, the method receiving, at a mobile device,
a transport block targeted to the mobile device, and if a quality
of the received transport block exceeds a threshold, providing an
acknowledgment or negative acknowledgment to a network element; and
if the quality of the received transport block is below the
threshold, suppressing the acknowledgment or negative
acknowledgement.
Inventors: |
Ekici; Ozgur; (Ottawa,
CA) ; Islam; Muhammad Khaledul; (Ottawa, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ekici; Ozgur
Islam; Muhammad Khaledul |
Ottawa
Ottawa |
|
CA
CA |
|
|
Assignee: |
RESEARCH IN MOTION LIMITED
Waterloo
CA
|
Family ID: |
47677508 |
Appl. No.: |
13/204753 |
Filed: |
August 8, 2011 |
Current U.S.
Class: |
370/328 |
Current CPC
Class: |
H04L 1/0003 20130101;
H04L 1/0007 20130101; H04L 1/1854 20130101 |
Class at
Publication: |
370/328 |
International
Class: |
H04W 28/04 20090101
H04W028/04 |
Claims
1. A method of explicit adaptive modulation and coding scheme
selection comprising: receiving, at a mobile device, a transport
block targeted for the mobile device; if a quality of the received
transport block exceeds a threshold, providing an acknowledgment or
negative acknowledgment to a network element; and if the quality of
the received transport block is below the threshold, suppressing
the acknowledgment or negative acknowledgement.
2. The method of claim 1, wherein the transport block is received
over a high speed downlink packet access channel.
3. The method of claim 2, wherein the acknowledgement or negative
acknowledgement are hybrid automatic repeat request responses.
4. The method of claim 1, wherein the network element is an element
within a long term evolution network.
5. The method of claim 1, wherein the quality is determined to be
below the threshold based on a Yamamato bit that provides a binary
indication of quality of the transport block.
6. The method of claim 1, wherein, due to the suppressing, the
network element chooses a new modulation and coding scheme to send
data from the transport block to the mobile device.
7. The method of claim 1, wherein the threshold is chosen based on
a probability of successfully decoding a subsequent transport block
utilizing an existing modulation and coding scheme.
8. The method of claim 1, wherein the threshold is set higher if
the network element uses chase combining rather than incremental
redundancy.
9. A mobile device comprising: a processor; a communications
subsystem; and memory, wherein the processor, communications
subsystem and memory cooperate to: receive a transport block
targeted for the mobile device; if a quality of the received
transport block exceeds a threshold, providing an acknowledgment or
negative acknowledgment to a network element; and if the quality of
the received transport block is below the threshold, suppressing
the acknowledgment or negative acknowledgement.
10. The mobile device of claim 9, wherein the transport block is
received over a high speed downlink packet access channel.
11. The mobile device of claim 10, wherein the acknowledgement or
negative acknowledgement are hybrid automatic repeat request
responses.
12. The mobile device of claim 9, wherein the mobile device
operates in a long term evolution network.
13. The mobile device of claim 9, wherein the quality is determined
to be below the based on a Yamamato bit that provides a binary
indication of quality of the transport block.
14. The mobile device of claim 9, wherein, due to the suppressing,
the network element chooses a new modulation and coding scheme to
send data from the message to the mobile device.
15. The mobile device of claim 9, wherein the threshold is chosen
based on a probability of successfully decoding a subsequent
message utilizing an existing modulation and coding scheme.
16. The mobile device of claim 9, wherein the threshold is set
higher if the network element uses chase combining rather than
incremental redundancy.
Description
FIELD OF THE DISCLOSURE
[0001] The present disclosure relates to hybrid automatic repeat
request retransmission and in particular relates to adaptive
modulation and coding schemes for hybrid automatic repeat request
retransmission.
BACKGROUND
[0002] Automatic Repeat reQuest (ARQ) is a method for packet data
transmission that uses positive or negative acknowledgement by the
receiving party to indicate to the sending party whether the data
packet has been successfully received or not. If the sender does
not receive an acknowledgment or receives negative acknowledgment,
it usually retransmits until an acknowledgment is received from the
receiving party or the number of re-transmissions exceeds a
predefined threshold. The term "Hybrid ARQ" (HARQ) is used to
describe any scheme that combines forward error correction (FEC)
with ARQ in which data received in unsuccessful attempts are used
by receiving party in FEC decoding instead of being discarded. The
simplest form of HARQ is called Chase Combining (CC) wherein each
retransmission repeats the first transmission, or part of it, and
the receiver combines multiple received copies of the coded packet
prior to decoding. Incremental redundancy (IR) is another HARQ
technique wherein instead of sending simple repeats of the entire
coded packet, additional redundant information is incrementally
transmitted if the decoding fails on the first attempt. HARQ is
used in a number of wireless technologies such as 3GPP High Speed
Packet Access (HSPA) and Long Term Evolution (LTE), 3GPP2 High Rate
Packet Data (HRPD).
[0003] Successful reception may depend on the modulation and coding
scheme (MCS) used to send the data packet. A lower order modulation
scheme, meaning less number of bits transmitted per modulated
symbol, typically provides better performance than higher order
modulation in a given radio channel condition, but yields lower
data throughput. For example, QPSK (quadrature phase shift keying)
is more robust and can tolerate higher levels of communication
errors than 16QAM (quadrature amplitude modulation). However, 16QAM
provides a higher data rate than QPSK.
[0004] Link adaptation is a term used in wireless communications to
indicate dynamic matching of the modulation and coding scheme to
the radio channel conditions. For example, in case of 3GPP high
speed downlink packet access (HSDPA), rate control is implemented
by the medium access control high speed (MAC-hs) entity that
configures the transport format of a high speed downlink shared
channel (HSDSCH) in every 2 milliseconds of transmit time interval
(TTI). This results in fast adaptation of both the modulation
scheme and instantaneous code rate to provide a data rate suitable
for current radio conditions.
[0005] Rate control is not applicable during retransmission
attempts. This means that that the transport block size and the
modulation scheme as well as the number of channelization codes
cannot change during retransmission. Thus, in degrading channel
conditions, the retransmission of a data packet that was
unsuccessfully received uses the same modulation scheme and
instantaneous code rate as the first transmission. In such
scenario, the data packet is never successfully received, and
retransmission will continue until a maximum retry count has been
reached on the physical layer and eventually the data
retransmission has to be performed on the higher layers such as the
radio link control (RLC) level.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The present disclosure will be better understood with
reference to the drawings, in which:
[0007] FIG. 1 is a block diagram illustrating transport block
processing at a mobile device in a sample HSDPA operation;
[0008] FIG. 2 is a process diagram illustrating a method in
accordance with the present disclosure;
[0009] FIG. 3 is a block diagram illustrating transport block
processing in a sample HSDPA operation using the process of FIG. 2;
and
[0010] FIG. 4 is a block diagram of an exemplary mobile device
capable of being used with the embodiments of the present
disclosure.
DETAILED DESCRIPTION OF THE DRAWINGS
[0011] The present disclosure provides a method of explicit
adaptive modulation and coding scheme selection comprising:
receiving, at a mobile device, a transport block targeted to the
mobile device; if a quality of the received transport block exceeds
a threshold, providing an acknowledgment or negative acknowledgment
to a network element; and if the quality of the received transport
block is below the threshold, suppressing the acknowledgment or
negative acknowledgement.
[0012] The present disclosure further provides a mobile device
comprising: a processor; a communications subsystem; and memory,
wherein the processor, communications subsystem and memory
cooperate to: receive a transport block targeted to the mobile
device; if a quality of the received transport block exceeds a
threshold, providing an acknowledgment or negative acknowledgment
to a network element; and if the quality of the received transport
block is below the threshold, suppressing the acknowledgment or
negative acknowledgement.
[0013] The transport block size, modulation scheme as well as a
number of channelization codes are typically kept the same during
HARQ retransmission of data packets. If channel conditions remain
bad during such retransmission attempts, the mobile device will not
be able to decode the transmitted packet successfully. As will be
appreciated, this may happen frequently in practice, especially
when the serving cell providing high speed downlink shared channel
(HSDSCH) cell to the mobile device changes.
[0014] In a typical HSPA network configuration, 5 HARQ processes
are configured for the HSDSCH with a packet retransmission time of
10 ms and a maximum retransmission count configured in Node-B as 5
to 6. These configuration parameters translate to an additional
latency of 50 to 60 ms due to retransmission using the same
modulation which is expected to fail in deteriorating channel
conditions. The high latency increases the round trip time almost
twice the expected value provided that the next round of
transmission is successful. A typical round trip time in HSDPA
systems is about 70 ms and with the above scenario the round trip
time increases to around 130 ms, which negatively affects data
throughput due to the acknowledged transmission nature of data
calls.
[0015] Increased latency that occurs as an artifact of
retransmission using the same modulation scheme may have a serious
adverse impact on certain applications that use packet data
services. For example, increased latency may make the circuit
switched (CS) voice over HSPA channels (as described in the Third
Generation Partnership Project (3GPP) Technical Specification
25.331, "Radio Resource Control; Protocol specification" Change
Request 3214, the contents of which are incorporated herein by
reference) not viable as voice service requires certain acceptable
delay requirements.
[0016] Example of another feature that may suffer degradation as
result of increased latency is operation of signaling radio bearer
(SRB) when mapped to HSPA channels, as described in 3GPP, Technical
Specification 25.331, "Radio Resource Control; Protocol
specification" Change Request 2600, the contents of which are
incorporated herein by reference. SRB is used for exchanging
control messages and timely reception of the control messages is
very important--e.g. increase latency may delay allocation of the
radio resources.
[0017] Similar problems exist in the Long Term Evolution (LTE)
non-adaptive retransmission. The present disclosure is not meant to
be limited to HSDPA or LTE but these are merely used as examples
below to provide examples of methods that are provided to force a
non-adaptive modulation scheme to become an adaptive modulation
scheme during HARQ retransmission.
[0018] Reference is now made to FIG. 1, which shows a plurality of
HARQ process blocks 110 in a HSDPA operation at a mobile device. In
the example of FIG. 1, six HARQ processes exist, and are labeled
within blocks 110 as "1", "2", . . . "6". As will be appreciated by
those in the art having regard to the above, after HARQ process 6
is used, HARQ process 1 is then utilized.
[0019] The labels in blocks 110 further show the transport block
that is being sent from Node-B (NB) during the HARQ process
block.
[0020] As seen in FIG. 1, a first HARQ process block 112 is used to
send a first transport block on the downlink from the network to a
mobile device. This is shown by arrow 130.
[0021] A device receives the first transport block and processes
the block, as shown by reference 132.
[0022] In the example of FIG. 1, the device was unable to
successfully receive and demodulate the first transport block and
therefore sends a NAK on the uplink back to the network, as shown
by arrow 134. The network then requires rescheduling, as shown by
arrow 136.
[0023] Subsequently, during the next HARQ process 1 block 114, the
first transport block is re-sent. Transport blocks 112 and 114
carry the same information content and use the same modulation
scheme as well as block size.
[0024] Conversely, in the second HARQ process, as shown as block
116, the second transport block is transmitted to a mobile device,
as shown by arrow 140. The device then processes the second
transport block as shown by block 142 and is able to successfully
receive and demodulate the second transport block. Thus, an
acknowledgement, shown at arrow 144 is sent back to the network. At
the next HARQ process 2 block, shown by reference 118, a new
transport block is sent to the mobile device.
[0025] Similarly, for the remaining HARQ processes, transport
blocks are sent and acknowledged, resulting in new transport blocks
being provided in the next HARQ process time slot.
[0026] From FIG. 1, the transmit time interval is approximately 2
ms. Thus, with 6 HARQ processes, the retransmission time is
approximately 12 ms.
[0027] One exemplary situation could be the attempt to send a large
packet to a mobile device utilizing 16QAM modulation and a high
code rate. This may be TrBlk1 from block 112 in FIG. 1. The
sending, in the present example, is being done as wireless channel
conditions degrade.
[0028] The sending of the large packet results in a NAK being
provided to the network, shown by arrow 134. The network then needs
to reschedule the next HARQ transmission block to re-send the large
packet again. Since the HARQ process is continuing, the next
retransmission will utilize 16QAM modulation and the high code
rate, even though a lower data rate with QPSK modulation would have
been better for retransmission due to the degraded channel
conditions.
[0029] Such circumstances often require multiple retransmission
attempts. For example, typically six attempts are observed in
commercial HSPA networks. This results in lower throughput as well
as unacceptable delay performance for certain applications such as
CS over HSPA or SRBs mapped on HSPA.
[0030] In existing HSPA networks, the use of a higher order
modulation and coding scheme may be common when the serving HSDSCH
cell changes and the new serving HSDSCH cell may not know the
channel quality of the mobile device or the mobile device is in an
active set with non-serving pilots, among other situations.
[0031] Table 1 below shows an example mobile device log on an
exemplary commercial HSPA network.
TABLE-US-00001 TABLE 1 Sample log Number Row Time sub- Transport
Modulation of # (s) frame CRC block size HAP type Codes 1 25.880 2
FAIL 4115 1 16QAM 5 2 25.880 3 N/A 3 25.880 4 N/A 4 25.890 0 N/A 5
25.890 1 N/A 6 25.890 2 PASS 3090 0 QPSK 5 7 25.890 3 FAIL 4115 1
16QAM 5 8 25.890 4 FAIL 3762 2 16QAM 5 9 25.900 0 FAIL 1380 3 QPSK
4 10 25.900 1 N/A 11 25.900 2 N/A 12 25.900 3 N/A 13 25.900 4 FAIL
4115 1 16QAM 5 14 25.910 0 FAIL 3762 2 16QAM 5 15 25.910 1 N/A 16
25.910 2 N/A 17 25.910 3 N/A 18 25.910 4 N/A 19 25.920 0 FAIL 4115
1 16QAM 5 20 25.920 1 FAIL 3762 2 16QAM 5 21 25.920 2 PASS 1380 3
QPSK 4 22 25.920 3 N/A 23 25.920 4 N/A 24 25.930 0 N/A 25 25.930 1
FAIL 4115 1 16QAM 5 26 25.930 2 FAIL 3762 2 16QAM 5 27 25.930 3 N/A
28 25.930 4 N/A 29 25.940 0 N/A 30 25.940 1 N/A 31 25.940 2 FAIL
4115 1 16QAM 5 32 25.940 3 FAIL 3762 2 16QAM 5
[0032] As is seen in Table 1 above, the block sent in row 1 is not
properly decoded by a mobile device, even after 60 ms, as shown in
row 31. This results in upper layers such as the radio link control
(RLC) requiring retransmission.
[0033] From Table 1, it can be seen that packets that are
transmitted with QPSK modulation have a higher chance of proper
decoding due to its robustness to channel imperfections, as seen in
rows 6 and 21 of the table.
[0034] In particular, Table 1 shows 5 HARQ processes, with each
sub-frame being shown in column 3 of the table. The modulation
scheme is shown in the second last column and the number of codes
allocated to the mobile device is shown in the last column.
[0035] The hybrid ARQ process (HAP) for each transmission is shown
in the 8th column.
[0036] Thus, for row 1, at time 25.880, a transport block of 4115
bits is sent on sub-frame 2 using HARQ process 1. The modulation
scheme is 16QAM with 5 codes allocated to the mobile device.
[0037] Moving down the table to row 7, the same HARQ process is
shown again. The 4115 bits are transported utilizing 16QAM with 5
codes allocated to the mobile device and this again fails. The same
HARQ process is then shown in rows 13, 19, and 31 and continues to
fail.
[0038] Conversely, in row 6, 3090 bits are transported utilizing
QPSK modulation with 5 codes allocated to the mobile device. In
this case, the bits are successfully received and decoded and
therefore this process passes.
[0039] As will be appreciated, the resending of the HARQ process 1
over 60 ms makes CS voice over HSPA or SRBs mapped on HSPA not
viable. For a typically conversational class application such as
voice, the packet delay should be strictly maintained under
reasonable time limits. The maximum mount-to-ear delay is in the
order of 250 ms. Assuming that the delay for the radio network
controller plus core network is approximately 100 ms, the total
delay for HARQ processes on the physical and MAC layers should be
strictly below 150 ms. Hence, assuming that both end users are
HSDPA users, the tolerable one way delay for HARQ should be under
75 ms. The addition of 50 to 60 ms delay on top of regular
performance would exceed the delay budget designed for voice over
Internet protocol (VoIP) or CS voice over HSPA and cause a
sub-optimal user experience.
[0040] Reference is now made to FIG. 2, which shows an exemplary
method in accordance with the present disclosure.
[0041] The process of FIG. 2 starts at block 210 and proceeds to
block 212 in which a mobile device receives a transport block. The
transport block is received and associated with a specific HARQ
process.
[0042] The process then proceeds from block 212 to block 214 in
which the quality of the transmission is checked against a
threshold.
[0043] The check in block 214 can use any thresholds to evaluate
the level of reliability of decodability of the received transport
block. In one embodiment, this may be achieved by setting a
Yamamoto bit to remember if, at any stage in a Viterbi trellis, the
distance between the survivor path and the discarded path is
smaller than a Yamamoto threshold. In one embodiment, this method
is similar to the decision making process of reception of the high
speed shared control channel (HS-SCCH) at the mobile device to
determine whether the transmission is intended for the mobile
device.
[0044] In other embodiments the threshold may be determined based
on signal quality or other determining factors, and the present
disclosure is not meant to be limited to any specific determination
in block 214.
[0045] From block 214, if the channel quality is greater than a
threshold, the process proceeds to block 220 in which an ACK or a
NAK is sent based on the received transport block. The ACK would be
sent if the transport block was received correctly and properly
decoded. The NAK would be sent if the transport block could not be
properly decoded but the quality was greater than a threshold.
[0046] From block 220 the process proceeds to block 240 and
ends.
[0047] Conversely, from block 214, if the quality is less than a
threshold the process proceeds to block 230. At block 230 the
mobile device suppresses the sending of a response to the received
transport block. In other words, since the channel quality is less
than a threshold, the mobile device suppresses the sending of an
ACK or a NAK at block 230 to the Node B which acts as a Base
Station Transceiver in a HSPA network.
[0048] From block 230 the process proceeds to block 240 and
ends.
[0049] The network (Node B) does not receive either an ACK or a NAK
in response to block 230 and the initial transmission attempt, and
will assume that the mobile device may have missed the initial
transmission on the downlink. In other words, the network will
assume that either the mobile device could not decode the HS-SCCH
on the downlink or the ACK or NAK response on the uplink on the
high speed physical dedicated control channel (HS-PDCCH) was lost
due to bad channel conditions.
[0050] With such assumptions, the node B will stop the current HARQ
process, flush the HARQ process buffer and start a fresh HARQ
process from scratch with a modulation and transport block size
more suitable for current channel conditions.
[0051] Thus, based on the suppression of the ACK or NAK at block
230, the network element exits a redundant implicit link adaption
stage (where the modulation scheme and the transport block size are
kept the same) and instead uses an explicit link adaption where a
new transport block is transmitted with a more suitable modulation
and coding scheme.
[0052] As will be appreciated by those in the art having regard to
the above, a benefit of exiting the HARQ process and thus entering
explicit link adaption is reduced delay. While relying on implicit
link adaption alone may be sufficient from a system throughput
point of view, the end user service quality may not be acceptable
from a delay perspective. The implementation on the device side to
evaluate the level of reliability or decodability of the received
transport block as described above with regard to block 214 ensures
that the mobile device can determine whether or not the received
transport block is good enough.
[0053] Since the mobile device is at the receiving end of the
downlink transmission, only the mobile device has information on
whether the received initial transport block has a very poor
quality or the device has almost decoded it. At one end of the
spectrum, if the transport block is received with very poor quality
or not at all, then the mobile device and network are better off
with a fresh HARQ process with a more suitable modulation and
coding scheme that match current channel conditions. On the other
hand, if the mobile device has almost decoded the packet and just
needs a few more parity bits to pass the cyclic redundancy check
(CRC), then another HARQ retransmission would suffice. This can be
done regardless of whether the HARQ utilizes incremental redundancy
or chase combining.
[0054] At present, the mobile device responds with a NAK in both
the scenarios described earlier. Therefore, the network has no
information whether to change the modulation and coding scheme or
not. The method shown in FIG. 2, provides a mechanism to the mobile
device to inform the network so that the network can make a proper
decision to mitigate the above-mentioned problems.
[0055] Reference is now made to FIG. 3. FIG. 3 shows the example of
FIG. 1 in which block 132 determines, through device processing,
that the quality of the received transport block is below a
threshold. In this case, the NAK 134 from FIG. 1 is suppressed.
[0056] In response, the network receives neither an ACK or a NAK
and at the next HARQ process 1, shown by block 310, the example of
FIG. 3 shows the transmission of transmit block 7. As will be
appreciated, transport block 7 may contain some or all of the data
of transport block 1, and is encoded with a modulation and coding
scheme more appropriate to meet channel conditions.
[0057] The method of FIG. 3 can increase the overall network
throughput as it minimizes avoidable unnecessary retransmissions.
In networks with packet acknowledgement schemes such as TCP/IP, the
maximum effective data throughput is not necessarily equal to the
system's peak rate. The latency can reduce the overall throughput
to the time required to acknowledge the data packet. In other
words, large peak bit rates do not result in better user experience
when the latency is too large.
[0058] As an example, throughput performance of a typical mobile
device is illustrated below. The physical layer peak data rate of
HSPA category 10 is 14 mega bits per second (Mbps), which is
computed as 27952/2 or 13.9 Mbps assuming transmission of maximum
transport block size of 27952 bits transmitted in 2 ms TTI. This
peak data rate is calculated with the assumption of all HARQs being
fully utilized and no retransmission is triggered. If 6 HARQ
processes are configured on the device, then the retransmission
behavior can be illustrated in the example of FIG. 1 above.
[0059] As can be seen, the mobile device can assist yielding
improved throughput by proactively adapting to channel conditions
in a timely manner compared to conventional scheme. Reference is
now made to Table 2 below.
TABLE-US-00002 TABLE 2 Data Throughput of category 10 HSDPA with
packet re-transmissions Transport block Transmission Data rate size
(bits) duration (ms) (Mbps) No re-tx with 16QAM 27952 2 13.976 1
re-tx with 16QAM 27952 12 2.329 2 re-tx with 16QAM 27952 24 1.165 3
re-tx with 16QAM 27952 36 0.776 4 re-tx with 16QAM 27952 48 0.582 5
re-tx with 16QAM 27952 60 0.465 1 re-tx with QPSK 14115 12
1.176
[0060] As seen from Table 2, utilizing 16QAM modulation coding with
a 27952 bit transport block requiring no retransmissions provides a
data rate of almost 14 Mbps.
[0061] If one retransmission is required with 16QAM and the same
transport block size is utilized, then the overall packet
transmission duration is 12 ms and throughput decreases to 2.3
Mbps.
[0062] If two retransmissions with 16QAM are required with the
transport block size of 27952, the overall packet transmission
duration is 24 ms and the throughput is 1.165 Mbps.
[0063] Similarly, with three retransmissions at the same transport
block size the transmission duration is 36 ms and the throughput is
0.77 Mbps. With four retransmissions the transmission duration is
48 ms and the throughput is 0.582 Mbps. With five retransmissions
the transmission duration is 60 ms with a data rate of 0.465
Mbps.
[0064] Conversely, with one retransmission and the changing of the
modulation and coding scheme to QPSK and the transport block size
to 14115, the transmission duration is 12 ms and the throughput is
1.176 Mbps.
[0065] Thus, as can be seen from Table 2 above, if more than one
retransmission is required then it is better to move directly to
the modulation and coding scheme that will more likely be
successfully received at the mobile device.
[0066] Further, as will be appreciated by those skilled in the art
having regard to the above, if the initial transmission is received
with very poor quality, the probability of the occurrence of
increased retransmission attempts is higher if full incremental
redundancy (IR) is used as implicit rate adaptation compared to
chase combining (CC) for soft decoding. This is due to the fact
that during retransmission, not all redundancy versions provide the
same amount of information about the transport block. For instance,
for turbo codes, the systematic bits are of higher importance that
the parity bits. Therefore, the initial transmissions typically
have all systematic bits and some parity bits. If full IR is
implemented in a network, all the retransmissions will have highly
punctured systematic bits and therefore include mostly parity bits.
During HSDPA transmission, if mobile device cannot decode the
initial transmission it will respond to the network with negative
acknowledgement (NAK) on the uplink, triggering the retransmission
of the transport block with new redundancy versions.
[0067] In a current implementation, if a network uses full IR as
the HARQ method and if the mobile device receives a first
transmission that it is unable to decode, then triggering a NAK and
repeatedly receiving retransmitted parity bits would not help
decode the transport block.
[0068] If chase combining is implemented on the network side, then
retransmissions will include the same coded bits as the initial
transmission (systematic bits are prioritized). This may increase
the chance of decoding the transmitted transport block.
[0069] The above can be implemented on any mobile device and the
present disclosure is not meant to be limited to any particular
mobile device. One example of a mobile device on which the above
could be implemented is shown below with regard to FIG. 4.
[0070] Mobile device 400 is a two-way wireless communication
device. Depending on the exact functionality provided, the wireless
device may be referred to as a data messaging device, a two-way
pager, a wireless e-mail device, a cellular telephone with data
messaging capabilities, a wireless Internet appliance, or a data
communication device, as examples.
[0071] Where mobile device 400 is enabled for two-way
communication, it can incorporate a communication subsystem 411,
including both a receiver 412 and a transmitter 414, as well as
associated components such as one or more, antenna elements 416 and
418, local oscillators (LOs) 413, and a processing module such as a
digital signal processor (DSP) 420 The particular design of the
communication subsystem 411 depends upon the communication network
in which the device is intended to operate.
[0072] When required network registration or activation procedures
have been completed, mobile device 400 may send and receive
communication signals over the network 419. As illustrated in FIG.
4, network 419 can comprise of multiple base stations communicating
with the mobile device.
[0073] Signals received by antenna 416 through communication
network 419 are input to receiver 412, which may perform such
common receiver functions as signal amplification, frequency down
conversion, filtering, channel selection and the like, and in the
example system shown in FIG. 4, analog to digital (A/D) conversion.
A/D conversion of a received signal allows more complex
communication functions such as demodulation and decoding to be
performed in the DSP 420. In a similar manner, signals to be
transmitted are processed, including modulation and encoding for
example, by DSP 420 and input to transmitter 414 for digital to
analog conversion, frequency up conversion, filtering,
amplification and transmission over the communication network 419
via antenna 418. DSP 420 not only processes communication signals,
but also provides for receiver and transmitter control. For
example, the gains applied to communication signals in receiver 412
and transmitter 414 may be adaptively controlled through automatic
gain control algorithms implemented in DSP 420.
[0074] Network access requirements will also vary depending upon
the type of network 419. In some networks network access is
associated with a subscriber or user of mobile device 400. A mobile
device may require a removable user identity module (RUIM) or a
subscriber identity module (SIM) card in order to operate on a
network. The SIM/RUIM interface 444 is normally similar to a
card-slot into which a SIM/RUIM card can be inserted and ejected.
The SIM/RUIM card hold many key configurations 451, and other
information 453 such as identification, and subscriber related
information.
[0075] Mobile device 400 includes a processor 438 which controls
the overall operation of the device. Communication functions,
including at least data and voice communications, are performed
through communication subsystem 411. Processor 438 also interacts
with further device subsystems such as the display 422, flash
memory 424, random access memory (RAM) 426, auxiliary input/output
(I/O) subsystems 428, serial port 430, one or more keyboards or
keypads 432, speaker 434, microphone 436, other communication
subsystem 440 such as a short-range communications subsystem and
any other device subsystems generally designated as 442. Serial
port 430 could include a USB port or other port known to those in
the art.
[0076] Some of the subsystems shown in FIG. 4 perform
communication-related functions, whereas other subsystems may
provide "resident" or on-device functions. Notably, some
subsystems, such as keyboard 432 and display 422, for example, may
be used for both communication-related functions, such as entering
a text message for transmission over a communication network, and
device-resident functions such as a calculator or task list.
[0077] Operating system software used by the processor 438 can be
stored in a persistent store such as flash memory 424, which may
instead be a read-only memory (ROM) or similar storage element (not
shown). Specific device applications, or parts thereof, may be
temporarily loaded into a volatile memory such as RAM 426. Received
communication signals may also be stored in RAM 426.
[0078] As shown, flash memory 424 can be segregated into different
areas for both computer programs 458 and program data storage 450,
452, 454 and 456. These different storage types indicate each
program can allocate a portion of flash memory 424 for their own
data storage requirements. Processor 438, in addition to its
operating system functions, can enable execution of software
applications on the mobile device. A predetermined set of
applications which control basic operations, including at least
data and voice communication applications for example, will
normally be installed on mobile device 400 during manufacturing.
Other applications could be installed subsequently or
dynamically.
[0079] A software application may be a personal information manager
(PIM) application having the ability to organize and manage data
items relating to the user of the mobile device such as, but not
limited to, e-mail, calendar events, voice mails, appointments, and
task items. Naturally, one or more memory stores would be available
on the mobile device to facilitate storage of PIM data items. Such
PIM application can have the ability to send and receive data
items, via the wireless network 419. In an embodiment, the PIM data
items are seamlessly integrated, synchronized and updated, via the
wireless network 419, with the mobile device user's corresponding
data items stored or associated with a host computer system.
Further applications may also be loaded onto the mobile device 400
through the network 419, an auxiliary I/O subsystem 428, serial
port 430, short-range communications subsystem 440 or any other
suitable subsystem 442, and installed by a user in the RAM 426 or a
non-volatile store (not shown) for execution by the microprocessor
438. Such flexibility in application installation increases the
functionality of the device and may provide enhanced on-device
functions, communication-related functions, or both.
[0080] In a data communication mode, a received signal such as a
text message or web page download will be processed by the
communication subsystem 411 and input to the microprocessor 438,
which further processes the received signal for element attributes
for output to the display 422, or alternatively to an auxiliary I/O
device 428.
[0081] A user of mobile device 400 may also compose data items such
as email messages for example, using the keyboard 432, which can be
a complete alphanumeric keyboard or telephone-type keypad, in
conjunction with the display 422 and possibly an auxiliary I/O
device 428. Such composed items may then be transmitted over a
communication network through the communication subsystem 411.
[0082] For voice communications, overall operation of mobile device
400 is similar, except that received signals would be output to a
speaker 434 and signals for transmission would be generated by a
microphone 436. Alternative voice or audio I/O subsystems, such as
a voice message recording subsystem, may also be implemented on
mobile device 400. Although voice or audio signal output is
accomplished primarily through the speaker 434, display 422 may
also be used to provide an indication of the identity of a calling
party, the duration of a voice call, or other voice call related
information for example.
[0083] Serial port 430 in FIG. 4 would normally be implemented in a
personal digital assistant (PDA)-type mobile device for which
synchronization with a user's desktop computer (not shown) may be
desirable, but is an optional device component. Such a port 430
would enable a user to set preferences through an external device
or software application and would extend the capabilities of mobile
device 400 by providing for information or software downloads to
mobile device 400 other than through a wireless communication
network. The alternate download path may for example be used to
load an encryption key onto the device through a direct and thus
reliable and trusted connection to thereby enable secure device
communication. Serial port 430 can further be used to connect the
mobile device to a computer to act as a modem.
[0084] WiFi Communications Subsystem 440 is used for WiFi
Communications and can provide for communication with access point
440.
[0085] Other communications subsystem(s) 441, such as a short-range
communications subsystem, are further components that may provide
for communication between mobile device 400 and different systems
or devices, which need not necessarily be similar devices. For
example, the subsystem(s) 441 may include an infrared device and
associated circuits and components or a Bluetooth.TM. communication
module to provide for communication with similarly enabled systems
and devices.
[0086] The embodiments described herein are examples of structures,
systems or methods having elements corresponding to elements of the
techniques of the present application. The above written
description may enable those skilled in the art to make and use
embodiments having alternative elements that likewise correspond to
the elements of the techniques of the present application. The
intended scope of the techniques of the above application thus
includes other structures, systems or methods that do not differ
from the techniques of the present application as described herein,
and further includes other structures, systems or methods with
insubstantial differences from the techniques of the present
application as described herein.
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