The present invention relates generally to communication networks and in particular, to medium access control in communication networks.
The Medium Access Control (MAC) data communication protocol layer provides addressing and channel access control mechanisms for several network nodes to communicate within a multipoint network. Such a network can be a local area network (LAN) as in a wired or wireless network. For a wireless network, the MAC layer manages and maintains communications between wireless communication stations by coordinating access to a shared wireless (e.g., radio frequency) channel utilizing MAC protocols for communications over the wireless channel.
In a contention-based MAC protocol without channel sensing, all stations contend for the access to a shared channel, wherein a packet transmission is successful when only one station attempts to transmit the packet. When multiple nodes attempt transmitting packets over the shared channel simultaneously, packet collisions occur.
In a Pure Aloha MAC protocol for packet radio networks, a station transmits a packet over the channel whenever a new packet arrives into the transmission queue of that station. Packet collision occurs if more than one station transmits at the same time, resulting in a retransmission of the packet at some time in the future, independent of other stations. As a result, the communication system throughput of a network using a Pure Aloha MAC protocol is about 18%.
However, the Slotted Aloha MAC protocol has several disadvantages. Each slot should be long enough to accommodate the largest size packet. If packets are of variable length, then unused slot durations lead to channel bandwidth waste or lower channel utilization. Even if a packet is transmitted successfully, the transmitting station (the sender) has no information about the success of the transmission. Thus, an explicit acknowledgement (ACK) is required from a receiving station (the receiver) in a different time slot. This further consumes channel bandwidth. Further, upon receiving the ACK, the transmitting station must acknowledge such receipt to the receiving station, further consuming channel bandwidth. In addition, the latency from the instant a data packet is transmitted from a transmitting station to the instant following receipt of a corresponding ACK from a receiving station can be quite large. Such a large latency is a disadvantage for transmission of delay sensitive packets.
The present invention provides a method and a system for medium access control among devices in a communication system. One embodiment involves selecting a contention-based control period for access to a shared communication medium; dividing the contention-based control period into multiple time slots, wherein each slot has a duration that is a function of one or more of the duration of transmission of a request to send (RTS) frame, the duration of transmission of a clear to send (CTS) frame, and an inter frame space (IFS) duration therebetween; and transmitting an RTS frame in a selected slot for allocating a reservation period for accessing the medium for data transmission.
In one implementation, the RTS frame includes a duration field indicating the number of slots desired for the reservation period. A reservation period is allocated by receiving the RTS frame, and transmitting a CTS frame in response during said selected slot to indicate successful allocation of the reservation period for accessing the medium. The CTS frame includes a duration field indicating the number of slots in the reservation period. Upon successfully receiving the CTS frame, transmission of data via the medium during the reservation period is initiated.
These and other features, aspects and advantages of the present invention will become understood with reference to the following description, appended claims and accompanying figures.
In the drawings, like references refer to similar elements.
The present invention provides a method and a system for media access control in communication systems. One embodiment provides a RTS/CTS Slotted Aloha MAC protocol (RCSA protocol) for controlling access to a shared channel for a contention-based control period. The RCSA protocol according to the present invention, does not require channel sensing for channel access, simplifying transmitter/receiver (transceiver) implementation and reducing hardware costs.
The RCSA protocol can be used with both omni-directional and directional modes of wireless station antennas. An implementation of such an RCSA protocol is described below in conjunction with a wireless network for communication of video information such as high definition (HD) video. An example of an RCSA protocol for a 60 GHz frequency band wireless network is provided which is useful with WirelessHD (WiHD) applications. WirelessHD is an industry-led effort to define a wireless digital network interface specification for wireless HD digital signal transmission on the 60 GHz frequency band, e.g., for consumer electronics (CE) and other electronic products. An example WiHD network utilizes a 60 GHz-band mmWave (millimeter-wave) technology to support a physical (PHY) layer data transmission rate of multi-Gbps (gigabits per second), and can be used for transmitting uncompressed high definition television (HDTV) signals wirelessly. The wireless devices can have multiple antennas, wherein directional beams are formed for transmitting/receiving HD video information using orthogonal frequency division multiplexing (OFDM). The present invention is useful with other wireless communication systems as well.
A video frame is divided into multiple scan lines, each scan line including an integer number of pixels, wherein each pixel comprises multiple components (e.g., color, luminance). In one example, pixel components include either a color component (chrominance) or a luminance component of the video. Quantization for pixel depth, or bits per component (bitplane), may be 8-bit, 10-bit, 12-bit or 16-bit values. Considering an 8-bit quantization, one 1080p scan line includes 46,080 bits. And, considering 60 frames/second, one second of uncompressed video (1080p) comprises 60×3×8×1920×1080=2.98 Gbits.
In this example, the WiHD coordinator 12 is a sink of video information (hereinafter “receiver 12”), and a WiHD station 14 is a sender of the video information (hereinafter “sender 14”). For example, the receiver 12 can be a sink of video and/or audio data (e.g., an HDTV set in a wireless network environment). The sender 14 can be a source of uncompressed video or audio. Examples of the sender include a set-top box, a DVD player, etc. In another example, the coordinator 12 can be a source of a video stream. In yet another example, the coordinator provides channel coordination functions for wireless communication between a sink station and a source station. The coordinator functions can also be implemented in a stand-alone device, in a sink device and/or in a source device.
The asymmetric HR data channel is a directional (beamformed) channel which is used for the transmission of uncompressed video from the WiHD sender 32 to the WiHD receiver 34. An example scenario in
The network 30 is a type of personal area network (PAN). The device 34 acts as the coordinator (such as the coordinator 12 in
During the entire CBCP 42, the sender and the receiver devices remain awake. During a mini-slot 44, a sender transmits an RTS 46 with the MAC address of a particular receiver. When a particular receiver receives an RTS 46 that has the MAC address of the receiver, that receiver then replies with a CTS 48 during the same mini-slot 44 as transmission of the RTS 46, as shown by example in
In many wireless communication systems, a frame structure is used for data transmission between a transmitter and a receiver. For example, the IEEE 802.11 standard uses frame aggregation in a Media Access Control (MAC) layer and a physical (PHY) layer. In a typical transmitter, a MAC layer receives a MAC Service Data Unit (MSDU) and attaches a MAC header thereto, in order to construct a MAC Protocol Data Unit (MPDU). The MAC header includes information such as a source address (SA) and a destination address (DA). The MPDU is a part of a PHY Service Data Unit (PSDU) and is transferred to a PHY layer in the transmitter to attach a PHY header (i.e., PHY preamble) thereto to construct a PHY Protocol Data Unit (PPDU). The PHY header includes parameters for determining a transmission scheme including a coding/modulation scheme. Before transmission as a packet from a transmitter to a receiver, a preamble is attached to the PPDU, wherein the preamble can include channel estimation and synchronization information. According to the IEEE 802.11b specification (IEEE 802.11, Part II: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specification, ANSI/IEEE std. 802.11 edition, 1999), the typical size of an RTS is 20 bytes, and the typical size of a CTS is 14 bytes.
Compared to the conventional RTS 50 and the CTS 55, in the modified RTS 60 and CTS 65 (modified formats) the following changes are made. Instead of using a 6-byte transmitter address (TA) and a 6-byte receiver address (RA) fields, a 1-byte RA field is used in the modified formats. The frame control field which indicates the type of the frame is reduced to 4-bits in the modified formats. Since the modified RTS 60 is shorter than the conventional RTS 50, instead of using 4-bytes for a frame check sequence (FCS) field, a 4-bit CRC field is used for the FCS field of the modified RTS 60. The conventional TA address field is removed from the modified RTS 60. The conventional RA and TA addresses are removed from the modified CTS 65 because the CTS 65 is always transmitted in response to the RTS, which dispenses with the need for RA and TA addresses. Further, no CRC field is included in the CTS frame 65.
The duration field in the modified RTS 60 and CTS 65 frames represents the number of mini-slots the sender is trying to reserve using an RTS/CTS exchange. The value of the duration field in the RTS 60 and CTS 65 is the number of mini-slots a sender is requesting to reserve (i.e., the reservation period). This reservation period is used for transmitting a data packet including any ACKs. The base time unit of the duration field is N mini-slots. For example if the value of the duration field in the RTS 65 is “0011”, the actual number of mini-slots being reserved is 3*N mini-slots. The RTS sender compares the duration field in the CTS 65 with the duration field in the RTS 60, and if the two duration fields match, then the sender assumes that the correct CTS 65 is received, otherwise not.
Referring back to
Each device (communication station) in the network maintains a network allocation vector (NAV) timer which is used for virtual carrier sensing. A device updates its NAV timer based on the duration field of a received CTS 65. A device will not start a RTS/CTS exchange if its NAV timer has a value which is greater than the current time, indicating that the channel is reserved by some other device.
After deferring for B mini-slots, if the sender determines that its NAV timer is greater than the current time, indicating that the channel is busy, then the sender defers for a number of mini-slots 44, which is the difference between the NAV timer and the current time (step 74). Thereafter, if the NAV timer is less than the current time, the sender backs off for a selected number of mini-slots 44 between 1 and CurrBW (as explained above) before sending another RTS. The sender attempts a number of retries (e.g., maxRTSTries) before discarding the data packet. The number of retries is implementation dependent.
The flowchart 75 in
The flowchart 80 in
The flowchart 85 in
The duration field can also be utilized to handle a hidden terminal problem (the hidden terminal problem is described in the IEEE 802.11b protocol). Any device receiving an RTS and CTS pair in a mini-slot for which it is not the sender or receiver, updates its NAV timer to the duration field of the received RTS and CTS. Due to hidden terminal problems or for other reasons, a few devices may update their NAV timers based on an RTS received in a mini-slot without properly receiving the pairing CTS. This can lead to potential channel waste because although the sender of the RTS cannot transmit its data packet as it did not receive a paring CTS, other devices assume that the channel is busy and refrain from accessing the channel while the channel idles.
This is diagrammatically shown in the example network 100 in
In another implementation, an optimized CTS includes a special PHY preamble so that upon receiving that preamble the sender knows that it is a RTS reply (i.e., CTS). This further reduces the CTS size, wherein transmitting said preamble indicates successful receipt of an RTS. The length of the special PHY preamble is the same as the PHY preamble used for the RTS. However, the CTS does not include any MAC or PHY payload. Using such an optimized CTS, the mini-slot duration can be selected based on the time required to transmit the RTS/CTS pair.
Further, assuming an RTS/CTS exchange reserves a fixed number of mini-slots for a sender (i.e., a fixed length reservation), the duration field in the RTS can be eliminated in an optimized RTS 110 as shown in
The time required to transmit RTS/CTS pair=(RTS PHY preamble duration+RTS size in bits/PHY transmission rate in Mbps)+(CTS PHY preamble duration)+IFS.
In another implementation, when both the LR and HR channels use a similar type of PHY layer technology (e.g., OFDM), the LR channel can use the HR rate steering vectors for beamforming or directional transmissions. In that case, a separate beamtracking for the LR channel becomes unnecessary. Referring to the examples in
Referring to
The time required to transmit an RTS=PHY preamble duration+RTS size in bits/PHY transmission rate in Mbps.
For a fixed length reservation scheme in the RCSA protocol 90, the mini-slot duration is the same as the time required to transmit an RTS, as described above.
An RCSA protocol according to the present invention allows higher channel utilization, accommodates variable length packets, reduces delay for transmitting time sensitive packets, reduces hardware costs since transceivers do not require supporting channel sensing, and supports both omni-directional and directional transmission modes.
The sender 202 includes a PHY layer 206 and a MAC layer 208. The MAC layer 208 implements a reservation module 208A and a packet communication module 208B.
The receiver 204 includes a PHY layer 212 and a MAC layer 214. The MAC layer 214 implements a reservation module 214A and a packet communication module 214B. The PHY layers 206, 212, may implement functions as the PHY layer in the IEEE 802.11 standard. Each PHY layer 206, 212, may comprise one or multiple antennas.
The MAC layers 208, 214 together implement an RCSA protocol, according to the present invention as described hereinabove. The MAC layers 208, 214 comprise several modules, however, in
Although the above examples of the present invention have been described in conjunction with wireless networks, the present invention is useful with other networks, such as wired networks, as those skilled in the art will recognize.
Further, as is known to those skilled in the art, the aforementioned example architectures described above, according to the present invention, can be implemented in many ways, such as program instructions for execution by a processor, as logic circuits, as an application specific integrated circuit, as firmware, etc. The present invention has been described in considerable detail with reference to certain preferred versions thereof; however, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.
Number | Name | Date | Kind |
---|---|---|---|
5574938 | Bartow et al. | Nov 1996 | A |
6363062 | Aaronson et al. | Mar 2002 | B1 |
6374085 | Saints et al. | Apr 2002 | B1 |
6438723 | Kalliojarvi | Aug 2002 | B1 |
6611231 | Crilly, Jr. et al. | Aug 2003 | B2 |
6640087 | Reed et al. | Oct 2003 | B2 |
6662321 | Collin | Dec 2003 | B1 |
6813260 | Fogle | Nov 2004 | B1 |
6947409 | Iwamura | Sep 2005 | B2 |
7145871 | Levy et al. | Dec 2006 | B2 |
7283832 | Jia et al. | Oct 2007 | B2 |
7321580 | Ramanathan et al. | Jan 2008 | B1 |
7433648 | Bridgelall | Oct 2008 | B2 |
7508834 | Berkman et al. | Mar 2009 | B2 |
7522618 | Hamamoto et al. | Apr 2009 | B2 |
7558249 | Hamamoto et al. | Jul 2009 | B2 |
7558854 | Nakahara et al. | Jul 2009 | B2 |
7720036 | Sadri et al. | May 2010 | B2 |
7804842 | Malik et al. | Sep 2010 | B2 |
7822440 | Park et al. | Oct 2010 | B2 |
7852791 | Nakajima et al. | Dec 2010 | B2 |
7889701 | Malik et al. | Feb 2011 | B2 |
7920885 | Singh et al. | Apr 2011 | B2 |
7925297 | Zhu et al. | Apr 2011 | B2 |
7945680 | Logalbo et al. | May 2011 | B2 |
7990997 | Wang et al. | Aug 2011 | B2 |
8005003 | Miyazaki et al. | Aug 2011 | B2 |
8060447 | Hamid et al. | Nov 2011 | B2 |
8145182 | Rudolf et al. | Mar 2012 | B2 |
8175043 | So | May 2012 | B2 |
8190136 | Pucar Rimhagen et al. | May 2012 | B2 |
8416720 | Hiben et al. | Apr 2013 | B2 |
8503339 | Nakajima et al. | Aug 2013 | B2 |
20020146023 | Myers | Oct 2002 | A1 |
20030084162 | Johnson et al. | May 2003 | A1 |
20030125932 | Wang et al. | Jul 2003 | A1 |
20030227934 | White et al. | Dec 2003 | A1 |
20040047314 | Li | Mar 2004 | A1 |
20040258006 | An | Dec 2004 | A1 |
20050013238 | Hansen | Jan 2005 | A1 |
20050089002 | Shin et al. | Apr 2005 | A1 |
20050141545 | Fein et al. | Jun 2005 | A1 |
20050147112 | Sugaya | Jul 2005 | A1 |
20050249121 | Matsunaga | Nov 2005 | A1 |
20060013176 | De Vos et al. | Jan 2006 | A1 |
20060067283 | So et al. | Mar 2006 | A1 |
20060114867 | Du et al. | Jun 2006 | A1 |
20060153105 | Jia et al. | Jul 2006 | A1 |
20060159003 | Nanda et al. | Jul 2006 | A1 |
20060168343 | Ma et al. | Jul 2006 | A1 |
20060209772 | Fang et al. | Sep 2006 | A1 |
20060209876 | Liu et al. | Sep 2006 | A1 |
20060239293 | Vasil'evich et al. | Oct 2006 | A1 |
20070153916 | Demircin et al. | Jul 2007 | A1 |
20070204205 | Niu et al. | Aug 2007 | A1 |
20070223412 | Lott | Sep 2007 | A1 |
20070240191 | Singh et al. | Oct 2007 | A1 |
20070258541 | Yamaura | Nov 2007 | A1 |
20080002636 | Gaur et al. | Jan 2008 | A1 |
20080080553 | Hasty et al. | Apr 2008 | A1 |
20080186895 | Shang et al. | Aug 2008 | A1 |
20080273600 | Singh et al. | Nov 2008 | A1 |
20080298310 | Hu | Dec 2008 | A1 |
20090207769 | Park et al. | Aug 2009 | A1 |
20090286116 | Matsumoto et al. | Nov 2009 | A1 |
20100115090 | Petersen et al. | May 2010 | A1 |
20100172296 | Singh et al. | Jul 2010 | A1 |
20110009051 | Khedouri et al. | Jan 2011 | A1 |
20110122853 | Hirano et al. | May 2011 | A1 |
20110170511 | Chen | Jul 2011 | A1 |
20120020257 | Urabe et al. | Jan 2012 | A1 |
20120099576 | Li et al. | Apr 2012 | A1 |
20120263137 | Walton et al. | Oct 2012 | A1 |
20130021366 | Khedouri et al. | Jan 2013 | A9 |
20130022185 | Khedouri et al. | Jan 2013 | A9 |
20130142080 | So | Jun 2013 | A1 |
Entry |
---|
Maruhashi, K.; Kishimoto, S.; Ito, M.; Ohata, K.; Hamada, Y.; Morimoto, T.; Shimawaki, H., “Wireless uncompressed-HDTV-signal transmission system utilizing compact 60-GHz-band transmitter and receiver”, Microwave Symposium Digest, 2005 IEEE MTT-S International, Jun. 12-17, 2005, pp. 1867-1870. |
802.15.3™ IEEE Standard for Information Technology-Telecommunications and information exchange between systems-Local and metropolitan area networks-Specific requirements, Part 15.3: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for High Rate Wireless Personal Area Networks (WPANs), IEEE Std 802.15.3-2003, IEEE Computer Society, Sep. 29, 2003, 324 pages. |
“Distributed Medium Access Control (MAC) for Wireless Networks,” WiMedia Alliance, Draft 0.99, Nov. 1, 2005, 182 pages. |
Hitachi, Ltd. et al., High-Definition Multimedia Interface (HDMI) Specification Version 1.2, Aug. 22, 2005, pp. 1-214. |
IEEE 802.11, Part II: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, ANSI/IEEE Std. 802.11, 1999 Edition, 528 pages. |
WirelessHD, LLC., “WirelessHD Specification, Revision 0.1,” WirelessHD, LLC., Jul. 12, 2006, pp. i-167, United States. |
Hachman, M. “CE Giants Back Amimon's Wireless HDTV Tech,” www.pcmag.com, Jul. 23, 2008, p. 1, United States, downloaded from http://www.pcmag.com/article2/0,2817,2326277,00.asp on Feb. 2, 2011. |
Physorg.Com, “NEC Develops Compact Millimeter-wave Transceiver for Uncompressed HDTV Signal Transmission,” www.physorg.com, Apr. 5, 2005, pp. 1-2, United States, downloaded from www.physorg.com/ news3569.html on Sep. 29, 2006. |
LG Electronics Inc. et al., “WirelessHD Specification Version 1.0 Overview,” wirelesshd.org, Oct. 9, 2007, pp. 1-77, United States. |
Villasenor-Gonzalez, L. et al., “HOLSR: A Hierarchical Proactive Routing Mechanism for Mobile Ad Hoc Networks,” IEEE Communications Magazine, Jul. 2005, pp. 1-8, United States. |
Ros, F. et al., “Cluster-based OLSR Extensions to Reduce Control Overhead in Mobile Ad Hoc Networks,” International Wireless Communications and Mobile Computing Conference (IWCMC 2007), Aug. 12-16, 2007, pp. 1-6, Honolulu, United States. |
Ramachandran, K.N. et al., “Interference-Aware Channel Assignment in Multi-Radio Wireless Mesh Networks,” INFOCOM 2006 25th IEEE International Conference on Computer Communications, Apr. 2006, pp. 1-22, United States. |
Perahia, E. et al., “Next Generation Wireless LANs: Throughput, Robustness, and Reliability in 802.11n,” 2008, pp. 1-10, Cambridge University Press, Cambridge, United Kingdom. |
U. Madhow, “MultiGigabit millimeter wave communication: System concepts and challenges,” Information Theory and Applications Workshop 2008, Jan. 2008, pp. 1-4, United States. |
IST Broadway, “A 5/60GHz Hybrid System Concept,” IST BroadWay, 2008, pp. 1-12, United States. |
802.11 Working Group of the 802 Committee, “IEEE P802.11nTM/D3.00 Draft Standard for Information Technology—Telecommunications and Information Exchange Between Systems—Local and Metropolitan Area Networks-Specific Requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: Amendment 4: Enhancements for Higher Throughput,” IEEE, Sep. 2007, pp. 1 -544, United States. |
Choi, S. et al., “IEEE 802.11e Contention-Based Channel Access (EDCF) Performance Evaluation,” IEEE International Conference on Communications, 2003, vol. 2, IEEE, pp. 1-6, United States. |
Iannone, L. et al., “Can Multi-Rate Radios Reduce End-to-End Delay in Mesh Networks? A Simulation Case Study,” MESH Networking: Realizing the Wireless Internet (Meshnets'05), Jul. 2005, pp. 1-10, Budapest, Hungary. |
Heinzelman, W.R. et al., “Energy-Efficient Communication Protocol for Wireless Microsensor Networks,” Proceedings of the 33rd Hawaii International Conference on System Sciences, Jan. 2000, pp. 1-10, Hawaii, United States. |
Draves, R. et al., “Routing in Multi-Radio, Multi-Hop Wireless Mesh Networks,” MobiCom '04, Sep. 26, 2004 to Oct. 1, 2004, pp. 1-15, Philadelphia, United States. |
Courville, M. et al., “Evaluation of Centralized Adhoc Network Architecture (CANA),” BAI Cluster Workshop 2004-03, IST BroadWay Project, Jun. 1, 2004, pp. 1-17, United States. |
IEEE Computer Society, “802.11 IEEE Standard for Information Technology—Telecommunications and Information Exchange Between Systems—Local and Metropolitan Area Networks—Specific Requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications—(Revision of IEEE Std 802.11-1999),” IEEE, Jun. 12, 2007, pp. i-1184, United States [Part 1—pp. i-251]. |
IEEE Computer Society, “802.11 IEEE Standard for Information Technology—Telecommunications and Information Exchange Between Systems—Local and Metropolitan Area Networks—Specific Requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications—(Revision of IEEE Std 802.11-1999),” IEEE, Jun. 12, 2007, pp. i-1184, United States [Part 2—pp. 252-551]. |
IEEE Computer Society, “802.11 IEEE Standard for Information Technology—Telecommunications and Information Exchange Between Systems—Local and Metropolitan Area Networks—Specific Requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications—(Revision of IEEE Std 802.11-1999),” IEEE, Jun. 12, 2007, pp. i-1184, United States [Part 3—pp. 552-950]. |
IEEE Computer Society, “802.11 IEEE Standard for Information Technology—Telecommunications and Information Exchange Between Systems—Local and Metropolitan Area Networks—Specific Requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications—(Revision of IEEE Std 802.11-1999),” IEEE, Jun. 12, 2007, pp. i-1184, United States [Part 4—pp. 951-1184]. |
U.S. Non-Final Office Action for U.S. Appl. No. 11/743,013 mailed Jan. 29, 2013. |
U.S. Final Office Action for U.S. Appl. No. 12/626,527 mailed Feb. 6, 2013. |
U.S. Non-Final Office Action for U.S. Appl. No. 12/626,527 mailed Aug. 27, 2012. |
U.S. Final Office Action for U.S. Appl. No. 11/743,013 mailed Dec. 21, 2011. |
U.S. Non-Final Office Action for U.S. Appl. No. 11/743,013 mailed Nov. 2, 2012. |
U.S. Non-final Office Action for U.S. Appl. No. 11/743,013 mailed Sep. 13, 2011. |
U.S. Final Office Action for U.S. Appl. No. 11/743,013 mailed May 13, 2013. |
U.S. Non-Final Office Action for U.S. Appl. No. 12/626,527 mailed Aug. 26, 2013. |
U.S. Notice of Allowance for U.S. Appl. No. 12/626,527 mailed Mar. 17, 2014. |
Number | Date | Country | |
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20090109938 A1 | Apr 2009 | US |