Transcript
US 20050021864A1
(19) United States (12) Patent Application Publication (10) Pub. No.: US 2005/0021864 A1 Sherman et al. (43) Pub. Date: Jan. 27, 2005 (54)
4X DESIGN FOR WIRELESS LOCAL AREA NETWORK THROUGHPUT ENHANCEMENT
Publication Classi?cation
(76) Inventors: Itay Sherman, Tel Aviv (IL); Lior Ophir, Kfar Yona (IL); Igor Royzis, HarZeliya (IL); Fredy Rabih, Tel Aviv
G06F 15/16
709/247
(IL) Correspondence Address:
(57)
TEXAS INSTRUMENTS INCORPORATED P O BOX 655474, M/S 3999
ABSTRACT
DALLAS, TX 75265
(21) Appl. No.:
10/760,535
(22) Filed:
Jan. 21, 2004
A system and method for wireless local area network throughput enhancement includes an access point and an
endpoint station in a wireless computer network transmitting data packets over radio frequency signals, and reordering the data packets into a megapacket in the access point using concatenation of the data packets. The method provides a signi?cant throughput enhancement on wireless networks including IEEE 802.11 networks.
Related US. Application Data (60)
Provisional application No. 60/441,544, ?led on Jan. 21, 2003.
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Patent Application Publication Jan. 27, 2005 Sheet 8 0f 17
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Patent Application Publication Jan. 27, 2005 Sheet 9 0f 17
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Patent Application Publication Jan. 27, 2005 Sheet 10 0f 17
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Patent Application Publication Jan. 27, 2005 Sheet 11 0f 17
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Patent Application Publication Jan. 27, 2005 Sheet 15 0f 17
US 2005/0021864 A1
FIG. 14_ 274 RX Wtarget TCP DATA
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Patent Application Publication Jan. 27, 2005 Sheet 16 0f 17
US 2005/0021864 A1
FIG. 15 308 TX Wtarget
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Patent Application Publication Jan. 27, 2005 Sheet 17 0f 17
US 2005/0021864 A1
FIG. 16
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Jan. 27, 2005
US 2005/0021864 A1
4X DESIGN FOR WIRELESS LOCAL AREA NETWORK THROUGHPUT ENHANCEMENT
amble, a PLCP header, a MAC header, a SIFS duration,a dn
an acknowledgment (ACK) time (Which comprises a PLCP preamble, a PLCP header, and the ACK MPDU). Such an
CROSS-REFERENCE TO RELATED APPLICATIONS
overhead amounts up to 764.2 us on an 802.11b PHY With
long PLCP preamble an 11 Mbps data rate.
[0001] This application claims priority to US. Application Ser. No. 60/441,544 ?led on Jan. 21, 2003. FIELD OF THE INVENTION
[0002] The present invention relates generally to features for a Wireless local area netWork
that increase the
Wireless link reliability and boost throughput. More speci? cally, the preferred embodiment relates to boosting through
throughput enhancement to 802.11 devices. Each one of these algorithms can be used by itself or in combination With
one another. Usage of large packets improves the ef?ciency of 802.11 netWorks. The 4x frameWork uses large packets
BACKGROUND OF THE INVENTION
(e.g., Mega Packets) that are compliant to the 802.11 b/g/a PHY speci?cation (up to 4095 bytes). These packets are also using 802.11 MAC compliant headers, but their payload is proprietary. These packets should be recogniZed by standard
WLANs utiliZe RF signals or light signals to con
ing the packets length. Standard equipment Will not be able
put of an IEEE 802.11 Wireless local area netWork.
[0003]
SUMMARY
[0007] The 4x frameWork of the preferred embodiment includes multiple algorithms that provide a signi?cant
802.11 equipment, that Will defer from transmission accord
nect mobile devices to each other or to a centraliZed gateWay
to extract the MPDU content as it is using a proprietary
and transmit data betWeen the physical devices. In 1997 the IEEE published standards for WLANs under the title of 802.11. The 802.11 standards contain different protocols that
encapsulation, but this is not an issue, since these packets Will only be used betWeen tWo STA/APs that support 4x features of the preferred embodiment.
may use unlicenced 2.4 GHZ and 5 GHZ radio bands to
transmit packet data. IEEE 802.11 enables mobile stations (e. g., endpoints) to communicate through a Wireless netWork interface card directly With each other or With other stations through an access point. An access point
is a central
iZed gateWay providing message and poWer management and access to an external LAN and/or the Internet. IEEE
802.11 access products are sold With personal computers
[0008]
In order to create Mega packets, the 4x frameWork
uses tWo different techniques, Extended MTU and Concat enation. Extended MTU is a technique that is used in cases Where both the source and target as Well as all the route betWeen them are on the WLAN netWork. Ad-Hoc mode is
one example. The source TCP/IP max MTU is simply modi?ed to match the siZe of the 802.11 Mega Packet.
(e.g., Wireless NICs), computer peripherals, print servers,
[0009]
and mobile devices such as laptops and personal digital
Where either the source, destination or any point on the route betWeen them is not on the WLAN (Infrastructure mode as an example). In this case the data source concatenates
assistants (PDAs). [0004] There are a plurality of 802.11 standards that each use different frequency bands and have varying data trans mission speeds. The original IEEE 802.11 standard sup ported Wireless interfaces operating at speeds of up to 2
megabyte per second (Mbps) in the 2.4 GHZ radio band. By using different modulation techniques, IEEE 802.11b raised
Concatenation is a technique that is used in cases
multiple MPDUs in to one 802.11 packet. The implemen tation on a STA is identical With the exception that the link list used to hold the buffered packets is a single linked list (all packets from an STA in Infrastructure mode are destined to the AP, so there is no need for multiple queues according
the data transmission rates to 11 Mbps, While 802.11a supports up to 54 Mbps transmission rates at a 5 GHZ
to destination). [0010] Various features are implemented by the preferred
frequency. The IEEE 802.11g is developing standards for
embodiment to implement 4x concatenation. The concat enation process reduces delay and does not add delay to the system. Packets are being concatenated only if natural congestion is occurring in the AP or STA. This ensures that no packet Will be delayed more then it Would have been
data transmission rates of 54 Mbps at the 2.4 GHZ frequency. [0005]
WLANs under 802.11 use media access control
(MAC) protocols to transmit betWeen Wired and Wireless devices. Each Wireless netWork card is assigned a MAC address used to identify the station. The basic protocol of an IEEE 802.11 netWork is the Basic Service Set (BSS), Which is merely a number of endpoint stations that communicate
Without 4x. In most cases the delay Will be reduced as multiple MPDUs are being transmitted on a single access
opportunity to the channel.
With one another. The access to Wireless netWorks is con
[0011] Further, in order to maximiZe the throughput and
trolled by coordination functions. The distributed coordina tion function (DCF) provides access similar to Ethernet CSMA/CA access. The DCF determines if the RF link betWeen devices is clear prior to transmitting. Stations use a random backoff after every frame to avoid collisions. End
use the largest packets possible, the source MTU is modi ?ed. For example: for a maximum Mega Packet siZe of 4095 bytes, the source MTU is modi?ed to approximately 1300 bytes to alloW for 3 concatenated MPDUs in a single Mega packet. Leaving the MTU in it’s standard value for Ethernet
point stations provide MAC Service Data Units (MSDUs)
(1500 bytes) Would yield packets of maximum siZe of
after detecting no current transmissions. The MSDUs func tions to transmit data frames to the proper endpoint station.
approximately 3000 bytes only).
Under the DCF access method of 802.11, each
[0012] The 4x frameWork includes a mechanism to reorder packets in the AP in order to make sure that the 4x STA Will
MSDU transmission incurs an overhead that includes a
enjoy the throughput enhancements offered by the usage of
distributed interface space (DIFS) duration, a backoff inter
Mega Packets also in a mixed environment that includes non 4x STAs so that bandWidth sharing is controlled.
[0006]
val, a Physical Layer Convergence Procedure (PLCP) pre
Jan. 27, 2005
US 2005/0021864 A1
[0013] Acknowledgment (ACK) Emulation is also per formed by the preferred embodiment. TCP/IP protocol
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
involves the sending of ACK packets from a connection
[0032] The preferred embodiment of the present invention
destination to the source. The ACK emulation algorithm can
comprises a set of features for an IEEE 802.11 Wireless local
eliminate the need to send most of these TCP/IP packets.
This is achieved by compressing the information conveyed in the TCP/IP packets and appending it to the 802.11 ACK packets. The receiver of these 802.11 ACK packets Will eXtract the information and Will recreate the TCP/IP ACK
packets that Where eliminated. The implementation pre sented maintains the structure of the 802.11 ACK packets and uses reserved bits in 802.11 PLCP headers to convey the
TCP/IP ACK information. This implementation is fully
area netWork (WLAN), called “4X” that Will increase the
Wireless link reliability and boost the throughput of WLAN BSS and Infrastructure (IBSS) nodes supporting 4X. The preferred embodiment is applied to both IBSS and Ad-Hoc. The 4X features comprise 4X protocol, 4X concatenation, and 4X ACK Emulation techniques. [0033] Referring to FIG. 1, an eXemplary embodiment of the present invention may be implemented using a host
interoperable With eXisting 802.11 equipment.
system 100 connected to a Wireless PCI/Cardbus/USB
[0014] The 802.11 protocol uses a random back off algo rithm to reduce collisions. The Zero collision method imple mented in the preferred embodiment enables a WLAN to achieve a collision free implementation by usage of different Contention WindoW (CW) values for different ST/IAP in a
106, and host random access memory (RAM) 108. The CPU 104 includes an operating system 110 and possibly softWare applications 112. The CPU 104 interfaces With system bus hardWare 106 through driver 118. Driver 118 interfaces With
BSS.
the CPU’s OS 110 through Application Program Interface
adapter card 102. The host system 100 comprises a host central processing unit (CPU) 104 host system bus hardWare
(API) 114 and a NetWork Driver Interface Speci?cation BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Preferred embodiments of the invention are dis cussed hereinafter in reference to the draWings, in Which:
[0016]
FIG. 1 illustrates hardWare architecture of the
preferred embodiment;
(NDIS) 116. [0034] Host system bus 106 connects to adapter card 102 through host interface 120 and PCI/Cardbus/USB host inter face hardWare 122, located on a TeXas Instruments ACX 100
Wireless netWork chip 126 in adapter card 102. NetWork chip 126 is timed With a 44-MhZ clock 127 and is connected to
light emitting diodes 140. Host interface 120 may also
[0017] FIGS. 2A-2C illustrate protocols of the preferred
connect to an IEEE 802.3 netWork interface card 124 and an
embodiment;
IEEE 802.3 netWork connection in host system 100. ACX100126 also includes a local internal RAM 128,
[0018]
FIG. 3 illustrates an access point and station;
[0019] FIGS. 4A-4C illustrate MSDU formats;
embedded CPU130 that are connected to MAC controller
through a local bus. Adapter card 102 may also comprise ?ash RAM 134, eXternal RAM 136, and an IEEE 802.3
[0020] FIGS. 5A-5C illustrate MSDU formats; [0021]
FIG. 6 illustrates concatenation transmission
queues
[0022]
FIGS. 7A-7C illustrate concatenation transmission
queues;
[0023] queue;
[0024]
netWork interface card 138 connected to ACX100126 com
ponents through the local bus. MAC 132 is connected to
Extended Erasable Programmable Read Only Memory (EEPROM) 142 and baseband processor physical layer (PHY). A radio 148 is connected to PHY 146 and MAC 132 on ACX100 chip 126. Radio 148 transmits and receives
radio frequency signals through antenna 150 on adapter card FIG. 8 illustrates a concatenation transmission
102. [0035]
FIGS. 9A-9C illustrate concatenation transmission
queues;
[0025] FIGS. 10A-10C illustrate preparing MSDUs for
sending;
The preferred embodiment uses a “4X frameWork”
that includes multiple algorithms that provide a signi?cant throughput enhancement to 802.11 devices. Each one of these algorithms can be used individually or in combination. The eXemplary embodiment uses algorithms that create large, or Mega, packets for transmission in an 802.11
netWork. Usage of Mega packets improves the efficiency of
[0026]
FIG. 11 illustrates a received concatenation
MPDU; [0027] FIG. 12 illustrates acknowledgment emulation
architecture; [0028] FIG. 13 illustrates the acknoWledgment emulation
802.11 netWorks. The 4X frameWork uses Mega packets that
are compliant to the 802.11b/g/a PHY speci?cation (up to 4095 bytes). These large packets are also using 802.11 MAC compliant headers, but the payloads on the large packets is
proprietary. These packets should be recogniZed by standard 802.11 equipment, that Will defer from transmission accord
steps;
ing the packets length. Standard equipment Will not be able
[0029] FIG. 14 illustrates the Wtarget receive ?oWchart;
encapsulation. HoWever, extracting the MDPU content is not required to practice the eXemplary embodiment since the Mega packets Will be used betWeen tWo station (STA) and Access Points (AP), or STA/AP, that support 4X. [0036] In order to create Mega packets, the 4X frameWork
to eXtract the MPDU content as it is using a proprietary
[0030]
FIG. 15 illustrates the Wtarget transmission ?oW
chart; [0031] chart.
FIG. 16 illustrates the Wsource transmission ?oW
of the eXemplary embodiment uses tWo different techniques.
