U.S. patent application number 12/963262 was filed with the patent office on 2011-04-07 for aggregated transmission in wlan systems with fec mpdus.
This patent application is currently assigned to INTEL CORPORATION. Invention is credited to Dilip Krishnaswamy, Robert Stacey.
Application Number | 20110080887 12/963262 |
Document ID | / |
Family ID | 39261093 |
Filed Date | 2011-04-07 |
United States Patent
Application |
20110080887 |
Kind Code |
A1 |
Krishnaswamy; Dilip ; et
al. |
April 7, 2011 |
AGGREGATED TRANSMISSION IN WLAN SYSTEMS WITH FEC MPDUs
Abstract
In various embodiments, a wireless device may determine the
quality of a channel by transmitting at least one packet to another
device and receiving from that other device an indicator of the
quality of the channel. Based on the quality indicator, the device
may determine an estimated packet error rate, and subsequently
transmit few enough packets that if the estimated percentage of
those packets fail, there will be time to retransmit them.
Inventors: |
Krishnaswamy; Dilip;
(Roseville, CA) ; Stacey; Robert; (Portland,
OR) |
Assignee: |
INTEL CORPORATION
|
Family ID: |
39261093 |
Appl. No.: |
12/963262 |
Filed: |
December 8, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11529986 |
Sep 29, 2006 |
|
|
|
12963262 |
|
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04L 1/0009 20130101;
H04L 1/0007 20130101; H04L 1/008 20130101; H04L 1/1671 20130101;
H04W 72/08 20130101; H04L 1/1809 20130101; H04L 1/1621 20130101;
H04L 1/0003 20130101; H04L 1/0025 20130101; H04L 1/0026
20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 72/00 20090101
H04W072/00 |
Claims
1. A method of communicating, comprising: transmitting at least one
packet over a channel and receiving in return an indicator value of
channel quality based on the at least one packet; selecting a
modulation and coding scheme for subsequent packets transmitted
over the channel that would provide a predetermined statistical
packet error rate based on the indicator value of channel quality;
using the selected modulation and coding scheme to create a data
transmission; and determining a number of subsequent packets to
transmit in the data transmission based on the expected packet
error rate such that there is time available after the transmission
to retransmit expected failed packets.
2. The method of claim 1, further comprising transmitting the
subsequent packets.
3. The method of claim 1, further comprising receiving an
acknowledgement to the subsequent packets.
4. The method of claim 2, further comprising retransmitting the
subsequent packets that actually fail.
5. An apparatus, comprising a wireless device having a transceiver
and a processing device, the wireless device to: transmit at least
one packet over a channel and receive in return an indicator value
of channel quality based on the at least one packet; select a
modulation and coding scheme for subsequent packets transmitted
over the channel that would provide a predetermined statistical
packet error rate based on the indicator value of channel quality;
use the selected modulation and coding scheme to create a data
transmission; and determine a number of subsequent packets to
transmit in the data transmission based on the expected packet
error rate such that there is time available after the transmission
to retransmit expected failed packets.
6. The apparatus of claim 5, wherein the wireless device is further
to transmit the subsequent packets.
7. The apparatus of claim 5, wherein the wireless device is further
to receive an acknowledgement to the subsequent packets.
8. The apparatus of claim 6, wherein the apparatus is further to
retransmit the subsequent packets that actually fail.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. patent application Ser. No.
11/529,986, filed Sep. 29, 2006, and claims priority to that date
for all applicable subject matter.
BACKGROUND
[0002] Recent developments in a number of different digital
technologies have greatly increased the need to transfer large
amounts of data from one device to another or across a network to
another system. Technological developments permit digitization and
compression of large amounts of voice, video, imaging, and data
information, which may be rapidly transmitted from computers and
other digital equipment to other devices within the network.
Computers have faster central processing units and substantially
increased memory capabilities, which have increased the demand for
devices that can more quickly transfer larger amounts of data.
[0003] These developments in digital technology have stimulated a
need for utilizing the spectrum used for wireless interconnection
within these networks and controlling the protocol overheads prior
to actual transmission of a message. Various overheads have been
proposed to provide improved performance in transmission times in
networks that adhere to the emerging protocol standards. Further
improvements in transmissions, such as in data packet
transmissions, are needed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The subject matter regarded as the invention is particularly
pointed out and distinctly claimed in the concluding portion of the
specification. The invention, however, both as to organization and
method of operation, together with objects, features, and
advantages thereof, may best be understood by reference to the
following detailed description when read with the accompanying
drawings in which:
[0005] FIG. 1 is a diagram that illustrates a wireless device that
incorporates circuitry and an algorithm to efficiently transmit
aggregated data packets in accordance with the present
invention;
[0006] FIG. 2 is a timing diagram that illustrates aggregated data
packets in accordance with the present invention; and
[0007] FIG. 3 is a flow diagram that illustrates a method of
determining a number of FEC MPDUs to include with MPDUs to improve
transmission of aggregated data packets in accordance with the
present invention.
[0008] It will be appreciated that for simplicity and clarity of
illustration, elements illustrated in the figures have not
necessarily been drawn to scale. For example, the dimensions of
some of the elements may be exaggerated relative to other elements
for clarity. Further, where considered appropriate, reference
numerals have been repeated among the figures to indicate
corresponding or analogous elements.
DETAILED DESCRIPTION
[0009] In the following detailed description, numerous specific
details are set forth in order to provide a thorough understanding
of the invention. However, it will be understood by those skilled
in the art that the present invention may be practiced without
these specific details. In other instances, well-known methods,
procedures, components and circuits have not been described in
detail so as not to obscure the present invention.
[0010] As shown in FIG. 1, wireless communications device 10
includes a radio to allow communication in an RF/location space
with other devices. Accordingly, communications device 10 may
operate in a wireless network such as, for example, a Wireless
Local Area Network (WLAN), a Wireless Personal Area Network (WPAN),
or a combination thereof. Communications device 10 is any type of
wireless device capable of communicating in an RF/location space
with another device that is capable of using an algorithm that
monitors and controls packet aggregation techniques to improve the
performance and effective throughput in networks.
[0011] The figure illustrates a transceiver 12 that both receives
and transmits a modulated signal from multiple antennas. The
illustrated embodiment for a Multiple-in, Multiple-out (MIMO)
system utilizes multiple antennas at both the transmitter and
receiver side to provide that independent data streams are
simultaneously transmitted from different antennas. The use of this
MIMO system may take advantage of spatial multiplexing to increase
wireless bandwidth and range in providing a significant capacity
gain over conventional single antenna systems. The MIMO system may
comprise a number of types of antenna including an omni-directional
antenna, a directional antenna, or high-gain antennas, among
others, and even a combination of antenna types. The
omni-directional antennas may be used for line-of-sight
communications with mobile stations spread in all directions. The
directional antennas may transmit and receive RF energy more in one
direction, and the higher-gain antennas may provide a narrower
radiation beam width. However, it should be noted that neither the
type of antennas nor the arrangement of antennas used to implement
the MIMO algorithm should be considered a limitation of the present
invention.
[0012] A spectrum management and channel characterization block 14
illustrated in FIG. 1 may be used to monitor characteristics of
selected communications channels and adjacent channels. Block 14
may cognitively monitor channel characteristics such as channel
signal power and other characteristics to gather parameters and
make determinations about the quality of the selected channel and
the adjacent channels. Block 14 may use the channel parameters to
switch transmission energy profiles in accordance with
deteriorating channel conditions. Further, block 14 may calculate
an indicator value of the channel quality directly from a received
packet. Alternatively, at least one packet may be transmitted over
a channel and an indicator value of the channel quality based on
the packet transmitted may be received in return. A modulation and
coding scheme is then selected for data packets transmitted over
the channel that would achieve a desired statistical packet error
rate based on the channel quality indicator value. Data packets may
be collected using the selected modulation and coding scheme to
create an aggregated data transmission.
[0013] In some embodiments the transmitted data may be left
unprotected from random channel impairment and then it is desirable
to include a link adaptation 16 to improve the system performance
and quality of service. Link adaptation in wireless communications
denotes the matching of the modulation, coding and other signal and
protocol parameters to the conditions on the radio link. The
dynamic link adaptation process updates signal and protocol
parameter changes as the radio link conditions change (e.g. the
path loss, the interference due signals coming from other
transmitters, the sensitivity of the receiver, the available
transmitter power margin, etc.).
[0014] Analog front end transceiver 12 may be a stand-alone Radio
Frequency (RF) discrete or integrated analog circuit. Transceiver
12 may also be embedded with a processor as a mixed-mode integrated
circuit. The processor, in general, processes functions that fetch
instructions, generate decodes, find operands, and perform
appropriate actions, then stores results. The processor may include
baseband and applications processing functions and utilize one or
more processor cores 20 and 22 dedicated to handle application
specific functions and allow processing workloads to be shared
across the cores. The processor may transfer data through an
interface 26 to a system memory 28 that may include a combination
of memories such as a Random Access Memory (RAM), a Read Only
Memory (ROM) and a nonvolatile memory, although neither the type
nor variety of memories included in system memory 28 is a
limitation of the present invention.
[0015] Wireless communications device 10 may operate in a network
where a CSMA/CA protocol is used. The Carrier-Sense, Multiple
Access/Collision-Avoidance (CSMA/CA) protocol is a
network-contention protocol that listens to the network to avoid
transmission collisions. Before data signal transmissions and
packet delivery across the network, the CSMA/CA protocol broadcasts
a signal onto the network to listen for collisions in order to
indicate to other devices to refrain from broadcasting.
[0016] The architecture of wireless communications device 10
includes, among other layers, a Media Access Control (MAC) layer
and a PHY layer. The MAC level operates a MAC aggregated management
block 18 to control MAC protocol data units (MPDUs) that dictate
the process for moving data packets to and from an interface across
a shared channel while the PHY layer provides the hardware for
sending and receiving bit stream signals on a carrier through the
network. Wireless communications device 10 employs functional logic
and various methods in the MAC layer to dynamically create and send
information MPDUs in an aggregated transmission along with packet
level FEC MPDUs. Forward Error Correction (FEC) is a system of
error control for data transmission, a technique that allows the
receiver to correct errors in the currently received data.
[0017] Based on channel characteristics gathered in spectrum
management and channel characterization block 14, the MAC layer
generates the MPDUs being aggregated for transmission and a
sufficient number of FEC MPDUs. After transmitting the aggregate
data and receiving acknowledgements for correctly received packets,
the data packets that were not correctly received are retransmitted
in the remaining available time. Thus, the number of packets to
transmit in the aggregated data transmission is based on the
expected packet error rate such that there is time available after
the transmission to retransmit the expected failed packets.
Further, the number of FEC MPDUs transmitted with the aggregate
data may be based on the expected probability of packet errors in
the channel.
[0018] FIG. 2 illustrates one aggregate data packet denoted as an
aggregated MPDU 200 (A-MPDU, Aggregated-MAC Protocol Data Unit).
Individual MPDUs 210, 220 and 230 are each prefixed with an
aggregate framing header and concatenated in one aggregated
protocol data unit denoted as A-MPDU 200 as shown. MPDUs 210, 220
and 230 may be aggregated at the MAC in hardware or in software.
One or more of the aggregated MPDUs may be FEC MPDUs 230.
[0019] In general, the MAC header contains details of the MPDU that
principally include the transmit and receive address that identify
the source and destination of the packet on the wireless link,
miscellaneous control information and payload encryption
information. The payload may contain either a management message or
user data. A payload in a transport connection may contain a MAC
service data unit (MSDU), fragments of MSDUs, aggregates of MSDUs,
aggregates of fragments of MSDUs, bandwidth requests or
retransmission requests according to the MAC rules on bandwidth
requesting, fragmentation, and packing.
[0020] By aggregating data packets, a single block acknowledgement
may to be sent for several messages to eliminate the overhead of
interframe spacings or physical layer preambles and
acknowledgements that accompany each individual packet. However, an
aggressive implementation of aggregation may impact overall
performance, specifically in implementations which use the same
physical layer preamble field which has been used to estimate the
channel for the entire duration of the aggregated packet. Put
another way, a block acknowledgement sent as a response regarding
the proper delivery of the packets that is delayed for a long
duration causes a slow link adaptation compared to traditional
802.11a/b/g MACs where an acknowledgement is expect for each MPDU
that is transmitted as a PHY packet.
[0021] In addition, retransmissions of MPDUs that were not received
successfully may be scheduled. The retransmissions have delays due
to the aggregated delivery of MPDUs because any retransmissions of
an MPDU wait until all MPDUs in the aggregated transmission are
delivered, the block acknowledgement is received, and the next
opportunity for transmission becomes available. Immediate
retransmissions may be attempted in the same TxOP (Transmit
Opportunity) time but it could be demanding on the hardware. It is
also likely that for large aggregated packet sizes, trailing
packets within the aggregated packet may have errors if the channel
estimation becomes invalid as time progresses during data
transmission of the aggregated packet. Thus, it is desirable to
have an aggregated packet length and transmission duration such
that the estimation of the channel continues to remain valid and
packets are not determined to be in error due to an incorrect
estimation of the channel being used for decoding at the
receiver.
[0022] FIG. 3 shows a flowchart in accordance with various
embodiments of the present invention that illustrate an algorithm
in accordance with the present invention that may be used to
improve the performance and effective throughput in WLAN networks
that employ packet aggregation techniques. Method 300 or portions
thereof are performed by the processor/transceiver combination of
an electronic system. Method 300 is not limited by the particular
type of apparatus, software element, or system performing the
method. Also, the various actions in method 300 may be performed in
the order presented, or may be performed in a different order.
Further, in some embodiments, some actions listed in FIG. 3 may be
omitted from method 300.
[0023] Method 300 is shown beginning at block 310. In block 320 the
receiver portion of a device such as, for example, an 802.11 device
or an 802.11 derivative device receives a transmission. The
received transmission includes an aggregate indication as indicated
in the header of the A-MPDU 200. In block 330 a determination is
made as to whether one or more received frames have Ack_Policy
equal to BlockAck. Ack_Policy denotes which type of acknowledgement
is to be used such as, for example, a block acknowledgement, a
regular acknowledgement or no acknowledgement. In block 340 a
determination is made as to whether Block_Ack_Policy is equal to
FECMode. This may be explicitly indicated or inferred by the
presence of FEC MPDUs in the aggregate.
[0024] Method 300 further shows in block 370 that if the number of
received frames in error is less than or equal to the number of
correct FECFrames, a BAack response to indicate a successful
transmission for all frames is sent. The response includes the
number of frames that are in error for feedback information to the
transmitter. In block 380 the response includes a BAck signal that
indicates the latest received error frames that cannot be corrected
with correctly received FEC frames in the response. Again the
response may also indicate the number of frames in error for
feedback information to the transmitter.
[0025] The various embodiments for this invention involve
combinations of link adaptation, aggregation, retransmissions and
FEC in order to provide optimized transmissions at the physical
layer. In some embodiments link adaptation may be done prior to
aggregated transmission. Link quality may be estimated based on the
success or failure of previous transmissions as indicated by the
feedback from the receiver. It is understood that wireless
communications device 10 provides wireless transmissions to the
channel knowing that some packets in the aggregated transmissions
may be received by the receiving device with packet errors. Knowing
that errors may occur, wireless communications device 10 may
include redundant FEC MPDUs along with data MPDUs to match the
expected error rate of transmissions of packets. Thus, wireless
communications device 10 dynamically adjusts the combined number of
redundant FEC MPDUs and data MPDUs to match or exceed the expected
error rate of transmissions of packets in order to alleviate the
need for retransmissions.
[0026] Based on the modulation and coding schemes chosen for
transmission and the available transmit opportunity time TxOP,
wireless communications device 10 may estimate the number of bits
that should be sent in the TxOP time period. Wireless
communications device 10 may use the transmit opportunity time TxOP
to provide flexibility in providing longer access to the medium
while transmitting higher priority traffic across the channel and
shorter access to lower priority traffic. The modulation and coding
schemes chosen by wireless communications device 10 may be used to
decide how many packets may be aggregated based on the packet size.
A block acknowledgement request is sent after the transmission of
the aggregated packets and a block acknowledgement is received in
response.
[0027] As mentioned, based on the expected physical layer packet
error rate, wireless communications device 10 may include FEC MPDUs
along with the MPDUs for transmission in the aggregated packet
transmission. By way of example, if k data MPDUs and (n-k) FEC
MPDUs are transmitted in an aggregated packet (n and k are integer
values), then as long as any k/n MPDUs are received the aggregated
transmission is considered successful. Again, by including
redundant FEC MPDUs based on Reed-Solomon coding in the aggregated
packet, retransmissions may be avoided. The Block Acknowledgement
(BlockAck) signal received in response to the transmitted
aggregated packet provides information about which MPDU's in the
A-MPDUs are in error.
[0028] Method 300 may be extended to include further steps as
illustrated by the following example. The transmitting node may
send 10 MPDUs and 2 FEC MPDUs for a total of 12 MPDUs. Upon
receiving the aggregated transmission the receiving node may
determine that three MPDUs are in error. In the receiving node, the
two FEC MPDUs would cover for two of the MPDUs received with
errors. The receiving node may send a response in its BlockACK
signal to the transmitting node indicating the errors in the three
MPDUs. The transmitting node may create and make available a number
of additional FEC packets/MPDUs that are kept ready during the
transmission of the 12 MPDUs. When the transmitting node receives
the BlockACK that indicates more MPDUs were in error than the
number of FEC MPDUs originally sent, the transmitting node may send
one additional FEC MPDUs if time is available in the transmit
opportunity time TxOP.
[0029] This immediate ability by the transmitting node to respond
to the error message from the receiving node is applicable if the
MAC protocol allows for an immediate retransmission when the
BlockACK signal arrives, otherwise it would not be applicable. In
this example the transmitting node does not have to fetch a
specific packet/MPDU that is in error. Rather, the transmitting
node would send an FEC packet/MPDU that it created and kept
available for transmission in the immediate retransmission phase in
the MAC protocol.
[0030] Note that if the channel coherence time and channel estimate
do not remain valid for the duration of transmission and a burst of
trailing MPDUs are detected to be in error, wireless communications
device 10 may scale back on the number of packets being aggregated.
On the other hand, if the trailing MPDUs are determined to not be
in error during transmission based on the received block
acknowledgement signal, then additional MPDUs may be aggregated
into the A-MPDU. Further, wireless communications device 10 may
receive link adaptation feedback from a receiving device with
suggestions of modulation and coding choices and corresponding PHY
packet error rates.
[0031] By now it should be apparent that cognitive radio networks
may incorporate features of the present invention to improve
over-the-air transmissions. A wireless communications device may
receive an indicator value indicative of the quality of a
communications channel. The received indicator value is used to
calculate an expected error transmission rate in a Media Access
Control (MAC) layer of the wireless communications device. The
wireless communications device selects a modulation and coding
scheme to transmit data packets over the channel based on the
expected error transmission rate. The wireless communications
device dynamically adjusts the number of redundant FEC MPDUs to
transmit in the aggregated data packets based on the expected error
transmission rate and the chosen modulation and coding choices.
[0032] While certain features of the invention have been
illustrated and described herein, many modifications,
substitutions, changes, and equivalents will now occur to those
skilled in the art. It is, therefore, to be understood that the
appended claims are intended to cover all such modifications and
changes as fall within the true spirit of the invention.
* * * * *