U.S. patent application number 12/647442 was filed with the patent office on 2010-10-28 for harq buffer management and feedback design for a wireless system.
Invention is credited to Jong-Kae Fwu, Tom Harel, Yuval Lomnitz, Hongmei Sun, Hujun Yin, Yuan Zhu.
Application Number | 20100272033 12/647442 |
Document ID | / |
Family ID | 42992059 |
Filed Date | 2010-10-28 |
United States Patent
Application |
20100272033 |
Kind Code |
A1 |
Fwu; Jong-Kae ; et
al. |
October 28, 2010 |
HARQ BUFFER MANAGEMENT AND FEEDBACK DESIGN FOR A WIRELESS
SYSTEM
Abstract
A method is disclosed for performing HARQ buffer management. The
HARQ buffer management method is a new approach to buffer overflow
management that allows the mobile station, rather than the base
station, to control the size of its buffer. The HARQ buffer
management reports buffer size, buffer occupancy status, and buffer
overflow to the base station, to facilitate efficient communication
between the base station and the mobile station.
Inventors: |
Fwu; Jong-Kae; (Sunnyvale,
CA) ; Sun; Hongmei; (Beijing, CN) ; Yin;
Hujun; (Saratoga, CA) ; Harel; Tom; (Shfaim,
IL) ; Lomnitz; Yuval; (Herzelia, IL) ; Zhu;
Yuan; (Beijing, CN) |
Correspondence
Address: |
CARRIE A. BOONE, P.C.;c/o CPA Global
P.O. Box 52050
Minneapolis
MN
55402
US
|
Family ID: |
42992059 |
Appl. No.: |
12/647442 |
Filed: |
December 26, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61173204 |
Apr 28, 2009 |
|
|
|
Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04L 1/1812 20130101;
H04W 72/04 20130101; H04L 1/1835 20130101; H04L 5/0053 20130101;
H04L 5/0055 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 72/00 20090101
H04W072/00 |
Claims
1. A method to manage a hybrid automatic repeat request (HARQ)
buffer, the method comprising: transmitting a buffer size to a base
station, the buffer size indicating the size of the HARQ buffer,
wherein the buffer size is transmitted when the size of the HARQ
buffer changes; if the HARQ buffer overflows, transmitting a buffer
overflow indicator to the base station; and managing the size of
the HARQ buffer without input from the base station.
2. The method of claim 1, further comprising: if occupancy of the
buffer exceeds a predetermined threshold, transmitting a buffer
occupancy notification to the base station.
3. The method of claim 1, transmitting a buffer size to a base
station further comprising: transmitting the buffer size in a
secondary fast feedback channel to the base station.
4. The method of claim 2, transmitting a buffer occupancy
notification to the base station further comprising: transmitting
the buffer occupancy notification as a code word using a primary
fast feedback channel to the base station.
5. The method of claim 2, transmitting a buffer occupancy
notification to the base station further comprising: transmitting
the buffer occupancy notification as a bit using a bandwidth
request channel.
6. The method of claim 2, further comprising: transmitting the
buffer occupancy notification and buffer overflow indicator as a
code word using a primary fast feedback channel to the base
station.
7. The method of claim 2, further comprising: transmitting the
buffer size, buffer occupancy notification, and buffer overflow
indicator using an uplink feedback channel.
8. The method of claim 1, managing the size of the HARQ buffer
without input from the base station further comprising: evacuating
correctly decoded forward error correction blocks from the HARQ
buffer.
9. The method of claim 1, managing the size of the HARQ buffer
without input from the base station further comprising: evacuate
soft parity bits from the HARQ buffer; and store systematic bits in
the HARQ buffer, wherein the systematic bits positively affect
decoder performance.
10. The method of claim 1, managing the size of the HARQ buffer
without input from the base station further comprising: not storing
mother coded bits in the HARQ buffer.
11. The method of claim 1, managing the size of the HARQ buffer
without input from the base station further comprising: storing
some blocks received from the base station into the HARQ buffer in
a compressed manner that enables HARQ combining gain while using
fewer memory bits; and not storing some other blocks received from
the base station into the HARQ buffer; wherein the stored blocks
are sufficient to decode as a lossy version of data transmitted by
the base station.
12. A method to manage a hybrid automatic repeat request (HARQ)
buffer, the method comprising: receiving a buffer size from a
mobile station, the buffer size indicating the size of the HARQ
buffer within the mobile station, wherein the buffer size is
received when the size of the HARQ buffer changes; if the HARQ
buffer overflows, receiving a buffer overflow indicator from the
mobile station; and managing the traffic rate to the mobile station
without managing the HARQ buffer.
13. The method of claim 12, further comprising: if occupancy of the
HARQ buffer exceeds a predetermined threshold, receiving a buffer
occupancy notification from the mobile station.
14. The method of claim 12, receiving a buffer size from a mobile
station further comprising: receiving a buffer size from a
secondary fast feedback channel, wherein the secondary fast
feedback channel comprises up to twenty-four bits.
15. The method of claim 13, further comprising: receiving the
buffer overflow indicator and buffer occupancy notification as a
code word in a primary fast feedback channel.
16. The method of claim 12, further comprising: receiving the
buffer overflow indicator as a bit in a bandwidth request
channel.
17. The method of claim 13, further comprising: receiving the
buffer occupancy notification as a bit in a bandwidth request
channel.
18. A method, comprising: managing a hybrid automatic repeat
request (HARQ) buffer for use in a wireless system, wherein the
management comprises: sending a size of the HARQ buffer to a
serving base station when the size of the HARQ buffer changes;
sending a buffer overflow indication to the base station if the
buffer is full; and sending a buffer occupancy indicator to the
base station if the buffer contents exceed a predetermined
threshold.
19. The method of claim 18, managing a HARQ buffer further
comprising: receiving blocks from the base station, the blocks
comprising both decode bits and receive bits; storing the decode
bits in the HARQ buffer; and not storing the receive bits in the
HARQ buffer.
20. The method of claim 19, not storing the receive bits in the
HARQ buffer further comprising: not storing forward error
correction bits in the HARQ buffer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. 119(e) to
U.S. Provisional Patent Application No. 61/173,204, entitled,
"ADVANCED WIRELESS COMMUNICATION SYSTEMS AND TECHNIQUES", filed on
Apr. 28, 2009.
TECHNICAL FIELD
[0002] This application relates to hybrid automatic repeat request
(HARQ) buffer management under the advanced air interface
standard.
BACKGROUND
[0003] IEEE 802.16 is a set of wireless broadband standards
promulgated by the Institute of Electrical and Electronics
Engineers (IEEE). IEEE 802.16m is known as the advanced air
interface standard. Hybrid automatic repeat request (HARQ) is
widely supported in current state-of-the-art wireless communication
standards. Under automatic repeat request (ARQ), error detection
information is added to data before transmission, ensuring that the
receiver is able to decode the data. With HARQ, additional forward
error correction (FEC) bits are also added to the data.
[0004] Several wireless communication standards are defined by the
Institute of Electrical and Electronics Engineers (IEEE), including
802.16e (broadband wireless access) and 802.16m (advanced air
interface standard). IEEE 802.16e is referred to herein as
"802.16e" or "broadband wireless access standard"; IEEE 802.16m is
referred to herein as "802.16m" or "advanced air interface
standard".
[0005] Also under this standard, there are two types of uplink fast
feedback channels: a primary fast feedback channel (PFBCH),
supporting up to six bits of information; and a secondary fast
feedback channel (SFBCH), supporting up to twenty-four bits of
information. The SFBCH potentially has up to three times as much
storage as the PFBCH. The availability of either the PFBCH, the
SFBCH, or both fast feedback channels, will vary, depending on a
number of criteria.
[0006] In practical implementations, the mobile station saves
information from bursts that were not decoded correctly in a buffer
known as the HARQ buffer. This buffer has a limited size, and
additional bursts cannot be further saved when the buffer is full.
The size and management scheme of this buffer affects both the
maximum throughput of the mobile station and the performance of
HARQ. Since large buffers are required in order to handle the
traffic rates supported in 802.16m, the buffer management scheme
should balance the buffer utilization with HARQ performance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The foregoing aspects and many of the attendant advantages
of this document will become more readily appreciated as the same
becomes better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein like reference numerals refer to like parts
throughout the various views, unless otherwise specified.
[0008] FIG. 1 is a schematic diagram of a HARQ buffer management
method, according to some embodiments;
[0009] FIG. 2 is a schematic diagram showing how a mobile station
buffers blocks received from a base station, according to some
embodiments;
[0010] FIG. 3 is a schematic diagram showing how a base station can
keep track of the buffer size of the mobile station, according to
some embodiments;
[0011] FIG. 4 is a graph showing the probability of having a fully
occupied buffer when there are x failures in sixteen trials,
assuming a fail probability of 0.3 in each transmission, according
to some embodiments;
[0012] FIG. 5 is a diagram showing four ways in which a mobile
station increase the size of its buffer, according to some
embodiments;
[0013] FIG. 6 is a table showing a possible code word sequence
defined for reporting HARQ buffer status to the base station using
the HARQ buffer management method of FIG. 1, according to some
embodiments; and
[0014] FIG. 7 is a table showing possible channel reporting of the
buffer overflow, buffer occupancy status, and buffer size by the
HARQ buffer management method of FIG. 1, according to some
embodiments.
DETAILED DESCRIPTION
[0015] In accordance with the embodiments described herein, a
method is disclosed for performing HARQ buffer management. The HARQ
buffer management allows the mobile station, rather than the base
station, to control the size of its own buffer. The HARQ buffer
management reports buffer overflow, buffer occupancy status, and
buffer size to the base station, to facilitate efficient
communication between the base station and the mobile station.
[0016] FIG. 1 is a block diagram of a HARQ buffer management method
100, according to some embodiments. The HARQ buffer management
method 100 includes buffer overflow management and buffer occupancy
feedback reporting. The HARQ buffer management method 100 reports
buffer overflow 30, buffer occupancy 40, and buffer size 50 to a
base station 70 by a mobile station 60. The operations of the HARQ
buffer management method 100 are described in more detail in the
following paragraphs.
[0017] The mobile station 60 includes a HARQ buffer 200. Because
the base station 70 may transmit encoded data in multiple blocks,
the mobile station 60 stores some of the blocks until all blocks
have been received from the base station. The mobile station 60
then decodes the blocks together. If one of the blocks is
transmitted in error, the mobile station 60 requests retransmission
from the base station 70 of the erroneously transmitted block.
[0018] These operations are depicted schematically in FIG. 2,
according to some embodiments. In FIG. 2, a data transmission
consists of four separate blocks 80.sub.A, 80.sub.B, 80.sub.C, and
80.sub.D (collectively, "blocks 80"), or partial transmissions,
which may vary in size. The blocks 80 are encoded at the base
station 70 before transmission to the mobile station 60. Three of
the four blocks 80.sub.A, 80.sub.B, and 80.sub.D are successfully
transmitted to the base station 70, and the mobile station 60
transmits an acknowledgement ("ACK") to the base station for each
of the successful transmissions. The block 80.sub.C, however, is
erroneously transmitted, and the mobile station 60 transmits a
negative acknowledgement ("NACK") to notify the base station 70 to
retransmit the block 80.sub.C. Thus, the base station 70
retransmits the block 80.sub.C to the mobile station, after which
the mobile station 60 acknowledges the successful transmission.
[0019] The HARQ buffer 200 located at the mobile station 60 stores
the blocks 80 as they are received from the base station 70. In
FIG. 2, the HARQ buffer 200 is a first-in-first-out (FIFO) memory
buffer, but the mobile station may have other types of buffer
storage as well. The four-block data transmission is not decoded
until all blocks 80 of the original data transmission are received.
Thus, the HARQ buffer 200 saves the portions of the transmission
that were successfully received (blocks 80.sub.A, 80.sub.B, and
80.sub.D) until all blocks have been received (block 80.sub.C).
Then, the mobile station 60 is able to decode the data.
[0020] FIG. 2 shows the general principles in which the HARQ buffer
200 is used. As long as there is storage available for the blocks
80 being transmitted, the mobile station 60 will only have to
request retransmission ("NACK") whenever a block is transmitted
erroneously. Another way in which retransmissions will be needed is
when the buffer 200 overflows, preventing the mobile station 60
from being able to store the partial transmission. The HARQ buffer
200 is said to overflow when the buffer is full of data such that
no additional data can be stored therein. Until the buffer 200 is
available to store blocks 80 received from the base station 70 (not
overflowed), the mobile station 60 is forced to request
retransmission.
[0021] The availability of a buffer of sufficient size in the
mobile station 60 relates directly to the throughput of
transmissions between the mobile station and the base station 70.
If the size of the HARQ buffer 200 (given by HARQ buffer size 50)
is very small, the buffer will fill up quickly, and the mobile
station 60 will force retransmission by the base station 70.
Therefore, traditionally, the buffer has been managed
conservatively, with the base station 70 controlling the HARQ
buffer 200 in the mobile station 60.
[0022] The HARQ buffer management method 100 takes a different
approach than the traditional buffer management methods. In some
embodiments, the HARQ buffer management method 100 gives control of
the buffer size to the mobile station 60, with the mobile station
60 giving the base station 70 sufficient status information about
the HARQ buffer 200 to enable the base station to intelligently
transmit data to the mobile station.
[0023] Buffer Overflow Management
[0024] As used herein, buffer overflow is defined as the reception
of more (erroneously decoded) data into the HARQ buffer 200 than
the buffer is capable of processing. When the buffer overflows, the
HARQ performance deteriorates. Put another way, the throughput of
transmissions between the base station 70 and the mobile station 60
is undermined when the HARQ buffer 200 overflows.
[0025] The throughput problem becomes more severe for incremental
redundancy HARQ (IR-HARQ or HARQ-IR) and adaptive HARQ, for two
reasons. First, in HARQ-IR, the re-transmission might include only
parity bits. Channel-to-channel (CTC) decoder performance, in the
absence of some initial information on systematic bits, is
undesirable. Further, in some cases, it is impossible to decode a
re-transmission without using the original transmission, even
without noise (SNR.fwdarw..infin.). Also, in adaptive HARQ, the
size of the re-transmission may be quite small, assuming most of
the information needed for decoding was received in the previous
transmissions.
[0026] Accordingly, in some embodiments, under the HARQ buffer
management method 100, the overflow of the HARQ buffer 200 is
managed by the base station's scheduler, which manages the data
transmission to the mobile station 60. The mobile station 60
reports its HARQ buffer size 50 to the base station 70, and the
base station thereafter tracks the occupancy level in the mobile
station's buffer 200 (until the next reporting of the HARQ buffer
size). By knowing the buffer size 50 and keeping track of
transmissions to the mobile station 60, the base station 70
controls the transmission of data to the mobile station 60, in some
embodiments, such that improved throughput is realized.
[0027] FIG. 3 schematically depicts buffer overflow management by
the HARQ buffer management method 100, according to some
embodiments. The mobile station 60 reports the HARQ buffer size 50
to the base station 70. The base station 70 has a scheduler 300
that keeps track of various data and operations performed by the
base station, including data about each mobile station serviced by
the base station. The scheduler 300 also has a processor 90, to
keep track of data transmissions to the mobile station 60 that will
affect the size of the HARQ buffer 200. (The processor 90 may be a
simple counter or timer to keep track of transmissions to the
mobile station.) Since the mobile station 60 only receives
transmission from the base station 70 (known as its "serving base
station"), the base station is able to keep track of the size of
the HARQ buffer 200 by first obtaining the size information (buffer
size 50) from the mobile station 60, then keeping track of
transmissions made by the base station to the mobile station,
transmissions that will affect the fullness or emptiness of the
buffer. In some embodiments, the mobile station 60 periodically
transmits the buffer size 50 to the base station 70. Each time the
mobile station 60 sends the buffer size 50 to the mobile station
70, the scheduler 300 restarts the processor 90.
[0028] Maximum Throughput and HARQ Buffer Occupancy
[0029] A conservative buffer management scheme that avoids overflow
limits the maximum throughput that can be achieved by the mobile
station 60 with a given HARQ buffer size. One of the goals for the
advanced air interface standard (802.16m) is to support high
throughput traffic, about 180 Mbits/sec for 2.times.2 MIMO
(multiple-input-multiple-output schemes) with a 20 MHz bandwidth. A
conservative design, such as was applied in the mobile broadband
wireless standard (802.16e), may be used for 802.16m, but such an
implementation is likely to use large buffers to support such
throughput, as depicted in the following calculation. Large
buffers, however, add to the expense of the mobile station and are
inefficient when they are not fully utilized.
[0030] The maximum supported throughput is given by:
thput .ltoreq. Buf f erSiz * e R max R T T ##EQU00001##
where R.sub.max the maximum code-rate (e.g., ) and RTT (round trip
time) is the time from a transmission to its retransmission or new
transmission. A new transmission includes receiver processing time,
(N)ACK channel signaling, and scheduling of re-/new transmission,
in 802.16m, is at least one sub-frame (5 ms), and BufferSize is the
number of soft bits or metrics in the buffer.
[0031] The reason for the higher bound on this throughput is that
the base station 70 cannot send more coded bits than the mobile
station 60 buffer size before receiving an acknowledgement that
some bursts were received and decoded correctly, making room for
new information.
[0032] This worst case approach ensures that the HARQ buffer is
never overflowed (unless there are errors in control signaling).
Actually, however, this approach makes poor usage of the buffering
capability. Assume the information in one frame is divided into
sixteen bursts of equal size, each one on a different HARQ channel,
and the probability of error is 0.3 for each burst and independent
among them. Then, the probability of having a fully occupied buffer
by the end of the frame is as small as 4*10.sup.-9. This shows that
more information could have been sent to the mobile station 60 with
negligible error probability. FIG. 4 is a graph showing the
probability of having a fully occupied buffer when there are x
failures in sixteen trials, assuming a fail probability of 0.3 in
each transmission (0<=x<=16). FIG. 4 shows that, with a
probability of 10.sup.-2, up to one half of the buffer (eight
bursts) is occupied at the end of the frame.
[0033] The conservative buffer management protocol of avoiding
overflow wastes resources and limits the maximum user throughput.
Therefore, the base station 70 might over-use the mobile station 60
buffer by transmitting more information than the declared mobile
station buffer size, using statistical assumptions on the maximum
number of failures in the frame (that do not cause buffer
overflow). However, the statistical assumption for the buffer
over-usage depends on mobile station buffer management.
[0034] In contrast to prior art solutions in which the base station
70 controls the size of the HARQ buffer 200, the HARQ buffer
management method 100 allows the mobile station 60 to control its
buffer size, larger or smaller, therefore allowing more efficient
buffer usage.
[0035] In some embodiments, the HARQ buffer management method 100
enables the mobile station 60 to enlarge its buffer size 50 in
several ways. The options are depicted schematically in FIG. 5,
according to some embodiments, with items excluded from the buffer
200 being denoted using dashed lines. For example, the mobile
station 60 may evacuate correctly decoded forward error correction
(FEC) blocks 82 from the buffer 200. Forward error correction
encoding encodes the "data bits" as well as error detection bits
such as cyclic redundancy check (CRC) or checksum bits. Thus, the
FEC encoding inflates the number of transmitted bits. For example,
if the code rate is 1/2, then 100 "data bits" are transmitted by
200 "coded bits." The coded bits are obtained during demodulation
at the mobile station 60, typically with many errors. The coded
bits are saved in the form of "metrics," in which each metric is a
guess of the transmitted coded bits together with its reliability.
For example, a metric of .infin. means the coded bit surely is a
"0" while a metric of -.infin. means the coded bit surely is a "1".
A metric of zero means that the coded bit might be a "1" or a "0"
with equal probability. These metrics are sometimes called "soft
bits." The metrics are quantized and saved, as one example, in
8-bit form.
[0036] For example, if there are 100 data bits and the code rate is
1/2, then the mobile station 60 would need to save 100/1/2 or 200
soft bits (one for each coded bit), which require 200 times 8, or
1600 bits in the buffer 200 (for the current decoding as well as
for HARQ combining). However, if only the data bits are stored in
the buffer 200, then only 100 bits of space in the buffer are
needed. Furthermore, if the data bits contain error detection bits
(e.g., CRC), then their savings is not required, but the potential
savings is relatively small.
[0037] Alternatively, the mobile station 60 may perform smart
handling of buffer overflow events, such as on-the-fly allocation
of more buffering resources, using a buffer overflow handler 210,
as shown in FIG. 5. In some embodiments, the buffer overflow
handler 210 is invoked if the mobile station 60 gets stuck and must
be reset, due to a buffer overflow or if the buffer 200 is full.
Or, the buffer overflow handler 210 may ensure that the buffer 200
always has room to decode new transmissions by evacuating old
transmissions in random order or according to some criteria. For
example, the buffer 200 may delete the oldest transmissions first
(FIFO buffer), since the base station 70 may no longer retransmit
the older data.
[0038] Under a more sophisticated approach, the buffer overflow
handler 210 may evacuate only parity soft bits and try to save the
metrics of systematic bits. Systematic bits are coded bits that are
more important to the decoder performance than other bits. Thus, it
makes sense to evacuate other bits before the systematic bits. As
another option, the buffer overflow handler 210 may save each
metric with fewer bits, e.g., two bits per metric instead of eight
bits per metric, to recover more space in the buffer 200. These
options are ways to trade off the performance (HARQ combining gain)
with a limited buffer size.
[0039] As yet another option, the mobile station 60 may refrain
from reserving buffer space for mother code bits 84 and save
metrics only for actually received coded bits 86. In incremental
redundancy HARQ, new coded bits are transmitted in a
retransmission, necessitating a larger buffer size after
retransmission. A naive implementation is to allocate sufficient
buffer size for all of the subsequent transmissions during the
reception of the first transmission. The size of the buffer is
determined according to a minimal effective code rate, or "mother
code rate." In 802.16m systems, the mother code rate is 1/3, while
the actual code rate of a transmission might be 1/2 or , for
example, and use a significantly smaller buffer. Under the HARQ
buffer management method 100, the mother code bits 84, i.e., the
newly coded bits used for retransmission, would not be stored in
the HARQ buffer 200, in contrast with prior art
implementations.
[0040] Or, the mobile station 60 may trade off performance for
buffer size (lossy compression of received information).
[0041] As can be observed from the above list, it may be difficult
and undesirable to fully standardize the internal buffer management
of a mobile station. For example, to fully specify the removal of
FEC blocks 82 from the buffer 200 to the base station 70, the
mobile station 60 would need to report the size of the soft bit
buffer, the size of the decoded bit buffer, and some parameters
regarding the delay of evacuating correctly received blocks to the
base station. Even with this information, the base station 70 lacks
sufficient information to decide on the maximum traffic to send,
since the utilization of these buffers ultimately depends on the
channel behavior.
[0042] Accordingly, the HARQ buffer management method 100 operates
under a different approach. The mobile station internal buffer
management is not exposed to the base station 70. Instead, the base
station 70 receives metrics from the mobile station 60 that will
allow the base station 70 to manage the traffic rate. These metrics
will encompass the channel behavior as well as the specific mobile
station implementation.
[0043] In some embodiments, according to the HARQ buffer management
method 100, the mobile station 60 judiciously stores bits in the
HARQ buffer 200. When some received bits are decoded correctly
while others cannot be decoded, HARQ retransmission is initiated.
In prior art solutions, all of the soft bits are saved in the
buffer 200 for combining with the HARQ retransmission. In the HARQ
buffer management method 100, the mobile station 60 saves the
correctly decoded FEC blocks as data bits, while the coded soft
bits are evacuated from the buffer 200. Only FEC blocks that were
not decoded correctly are saved in the form of soft bits.
[0044] Buffer Occupancy Feedback
[0045] In order to allow the base station 70 to optimally use the
HARQ buffer 200, the HARQ buffer management method 100 uses two
kinds of feedback from the mobile station 60 to the base station
70, as shown in FIG. 1. First, the HARQ buffer size 50 is reported
by the mobile station 60 to the base station. In some embodiments,
the mobile station 60 reports as a capability the number of coded
soft bits that can be saved in its HARQ buffer 200. Also, the
buffer occupancy notification 40 is reported by the mobile station
60 to the base station 70. The buffer occupancy 40 is a measure of
the buffer usage efficiency. In some embodiments, the buffer
occupancy 40 is reported to the base station 70 either upon request
(on demand) or periodically.
[0046] On-Demand Buffer Occupancy Feedback Reporting Mechanism
[0047] Since HARQ buffer overflow happen irregularly, it is more
efficient to feed back buffer management-related information on
demand. The HARQ buffer management method 100 reports two kinds of
status, in some embodiments. For the buffer occupancy 40, a ratio
threshold, BufThr, is predefined. When the buffer occupancy 40
exceeds the BufThr threshold, the mobile station 60 sends a
notification to the base station 70.
[0048] For example, assume that the buffer threshold, BufThr, is
40%. When the buffer occupancy 40 exceeds 40% (meaning that at
least 40% of the buffer 200 is occupied, or full, of data), the
mobile station 60 will notify the base station 70. The notification
can thus be accomplished with a single bit, in some embodiments.
While the buffer occupancy 40 is less than 40%, no notification
will be sent.
[0049] Second, the HARQ buffer management method 100 feeds back
buffer overflow information 30 to the base station 70. In this
case, the mobile station 60 sends a notification to the base
station 70 when the HARQ buffer 200 overflows since last being
reported.
[0050] There are different ways to report on-demand buffer
occupancy 40 and buffer size 50 mentioned above. In some
embodiments, the HARQ buffer management method 100 uses a primary
fast feedback channel (PFBCH) to feed back the buffer occupancy 40
and overflow notification on demand by reserving two code-words in
the PFBCH, one code word to represent buffer occupancy and the
other code word to represent buffer overflow on demand.
[0051] FIG. 6 is a table 24 showing a possible code word sequence
for reporting buffer overflow 30 and buffer occupancy 40 using the
PFBCH by the HARQ buffer management method 100, according to some
embodiments. Some of the sequences are reserved for channel quality
indicator (CQI) reporting. Two code words, denoted X+1 and X+2, are
defined to report buffer information to the base station 70 by the
mobile station 60. The code word, X+1, indicates the buffer
occupancy 40, whether the buffer 200 exceeds the predefined
threshold, BufThr, or not. The code word, X+2, notifies the base
station 70 of an overflow of the HARQ buffer 200 (buffer overflow
30).
[0052] As another option, a bandwidth request channel (BWRCH) may
be used to send a one-bit message to represent the buffer occupancy
40 and the buffer overflow 30 on demand. Thus, instead of the code
words defined in the table 24 (FIG. 6), a single bit may be defined
for each of these buffer status indicators. Additionally, the
secondary fast feedback channel (SFBCH) may be used to feed back
the buffer size 50. FIG. 7 has a table showing the various options
for reporting this data to the base station 70 by the mobile
station 60.
[0053] Thus, the buffer size 50, the buffer overflow indicator 30
and the buffer occupancy status 40 may be reported using an uplink
feedback channel, such as the PFBCH, the SFBCH, the BWRCH, or other
channels. In still other embodiments, the buffer size 50, the
buffer overflow indicator 30, and the buffer occupancy status 40
may be reported using a single type feedback channel, such as the
physical uplink control channel (PUCCH) in long-term evolution
(LTE) systems.
[0054] While the application has been described with respect to a
limited number of embodiments, those skilled in the art will
appreciate numerous modifications and variations therefrom. It is
intended that the appended claims cover all such modifications and
variations as fall within the true spirit and scope of the
invention.
* * * * *