Extension mode for wireless LANs complying with short interframe space requirement

This present disclosure is a continuation of U.S. application Ser. No. 12/151,185, filed on May 5, 2008, which is a continuation of U.S. application Ser. No. 11/824,993 (now U.S. Pat. No. 7,468,990), filed Jul. 3, 2007, which is a continuation of U.S. application Ser. No. 10/080,454 (now U.S. Pat. No. 7,239,648), filed Feb. 21, 2002, which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 60/333,579, filed Nov. 27, 2001.

The present invention relates to wireless local area networks (WLANs), and more particularly to transmitters, receivers and/or transceivers of WLANs.

A wireless local area network (WLAN) uses radio frequency (RF) signals to transmit and receive data between electronic devices. WLANs provide all of the features and benefits of traditional hard-wired LANs without requiring cable connections between the devices. Referring now to FIG. 1 , an infrastructure-based WLAN 10 includes a wireless access point 11 that provides a transparent connection between stations 12 - 1 , 12 - 2 , . . . , and 12 - n and a network 14 . The network 14 typically includes a distributed communication system 16 such as an Ethernet and one or more servers 18 .

The access point 11 is the wireless equivalent of a hub. The access point 11 communicates with the wireless stations 12 using antennas 22 . The access point 11 maintains the connections to the stations 12 that are located in a coverage area 24 . The access point 11 also typically handles security by granting or denying access to the network 14 . Similarly, a wireless access point 32 provides a transparent connection between stations 34 - 1 , 34 - 2 , . . . , and 34 - n and the network 14 . The access point 32 also communicates with the wireless stations 34 using antennas 42 . The wireless access point 32 maintains the connections to stations 34 that are located in a coverage area 42 .

Referring now to FIG. 2 , an independent WLAN 38 supports direct wireless communications between stations 40 - 1 , 40 - 2 , . . . , and 40 - n in a coverage area 42 . Referring now to FIG. 3 , stations 50 include a controller 52 , and a transceiver 54 that is connected to one or more antennas 56 . The stations 50 include additional circuits 58 for processing transmit/receive signals and for performing various other common functions of stations 50 . Referring now to FIG. 4 , access points 60 also include a transceiver 64 that is connected to one or more antennas 66 . Likewise, the access point 60 includes additional circuits 68 for processing transmit/receive signals and for performing various other common functions of access points 60 .

Referring now to FIG. 5 , a WLAN architecture 70 for stations 50 and the access point 60 is shown. The architecture 70 includes a media access control (MAC) sublayer 72 that communicates with a MAC layer manager 74 . A physical layer convergence protocol (PLCP) sublayer 76 and a physical medium dependent (PMD) sublayer 78 communicate with a physical layer manager 80 . IEEE sections 802.11, 802.11(a), and 802.11(b), which are hereby incorporated by reference, set forth other specifications and operating details of the WLAN architecture 70 .

When multiple stations are located in a coverage area, they compete for access to a medium. In other words, only a single station can transmit data or acknowledge receipt of data at a time. Standards such as IEEE sections 802.11, 802.11(a), and 802.11b set forth a specific protocol for WLAN communications to accommodate contention between the devices for the medium.

Referring now to FIG. 6 , a source station 90 transmits data 92 . Following a short interframe space (SIFS), a destination station 96 generates an acknowledgment (ACK) 98 . IEEE section 802.11 and other related sections set forth a maximum time interval for the destination station 96 to respond with the ACK 98 . Other stations 100 must defer access during the transmission of the data 92 and for a period that is longer than the SIFS to avoid contention.

Referring now to FIG. 7 , the SIFS is shown in further detail. The SIFS is defined as a nominal time that the MAC and PHY require to receive the last symbol of a frame, to process the frame, and to respond with a first symbol of a response frame. In other words, aSIFSTime=aRXRFDelay+aRXPLCPDelay+aMACProcessingDelay+aRxTxTurnaroundTime. For both 802.11 and 802.11(b), the nominal aSIFSTime is defined as 10 microseconds (μs).

In FIG. 7 , D 1 is equal to aRXRFDelay+aRXPLCPDelay, which corresponds to a receiver delay and a receiver processing delay, respectively. M 1 is equal to aMACProcessingDelay, which is the processing delay of the MAC layer. RxTx is equal to the RxTxTurnaroundTime, which is the delay associated with a transition between receiver and transmitter modes.

In implementations that comply with IEEE section 802.11 and related sections, aSIFSTime must not vary from the defined nominal. SIFS time value by more than 10% of the slot time. For both sections 802.11 and 802.11(b), aSIFSTime must be between 8 and 12 μs as measured on the medium to be compatible. These limitations on aSIFSTime prevent the use of advanced signal processing techniques. For example, Turbo coding, Reed-Solomon coding, convolutional code concatenated with Reed-Solomon coding, and other advanced error coding techniques are not possible when backward compatibility is required. These advanced signal processing techniques allow higher data rates and/or provide other advantages. However, the advanced signal processing techniques also require receiver processing time that is typically longer than the nominal aSIFSTime that is defined by IEEE 802.11 and related sections.

In general, in one aspect, this specification describes, a first wireless device comprising: a transmitter configured to transmit, in accordance with a first mode of operation or a second mode of operation, a packet to a second wireless device, wherein the packet includes a header portion and a data portion. A maximum time interval for the second station to respond to the packet is as follows: (i) in response to the packet being transmitted to the second device in accordance with the first mode of operation, the second device is to respond to the packet within a predetermined time period, and (ii) in response to the packet being transmitted to the second device in accordance with the second mode of operation, the second device is to respond to the packet in a time greater than the predetermined time period.

In response to the packet being transmitted to the second device in accordance with the first mode of operation, the transmitter is configured to encode the header portion of the packet to indicate that the packet is being sent in accordance with the first mode of operation, and in response to the packet being transmitted to the second device in accordance with the first mode of operation, the transmitter is configured to i) encode the header portion of the packet to indicate that the packet is being sent in accordance with the second mode of operation, and ii) insert dummy data into the data portion of the packet, wherein the dummy data sent to the second device during the time greater than the predetermined time period.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of an infrastructure-based WLAN according to the prior art;

FIG. 2 is a functional block diagram of an independent WLAN according to the prior art;

FIG. 3 is a functional block diagram of a station according to the prior art;

FIG. 4 is a functional block diagram an access point according to the prior art;

FIG. 5 is a functional block diagram of a WLAN architecture according to the prior art;

FIG. 6 illustrates timing of data and acknowledgment signals according to the prior art;

FIG. 7 illustrates timing of a short interframe space (SIFS) according to the prior art;

FIG. 8 illustrates a physical layer convergence protocol (PLCP) header followed by data according to the present invention;

FIG. 9 is a functional block diagram of a station according to the present invention;

FIG. 10 is a functional block diagram of an access point according to the present invention;

FIG. 11 is a functional block diagram of an infrastructure-based WLAN according to the present invention;

FIG. 12 is a functional block diagram of an independent WLAN according to the present invention; and

FIG. 13 illustrates timing of data, dummy data, D 1 , SIFS, and acknowledgment (ACK) according to the present invention.

The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

Referring now to FIG. 8 , a PLCP header 120 precedes data 122 . The PLCP header 120 includes a signal portion 126 , a service portion 128 , a length portion 130 , and a CRC portion 132 . The signal portion 126 is typically 8 bits, the service portion 128 is typically 8 bits, the length portion is typically 16 bits, the CRC portion 132 is typically 16 bits, and the data 122 typically has a length between 64-2300 bytes.

Allowed values for the signal portion 126 are currently defined by the IEEE section 802.11 and other related sections as follows: “0A” (in hexadecimal) is for 1 Mbps; “14” is for 2 Mbps, “37” is for 5.25 Mbps, and “6E” is for 11 Mbps. According to the present invention, an additional code “XX” is used to indicate an extension mode. The additional code “XX” is a predetermined code that can be set equal to any unused hexadecimal code. For example, the additional code can be set to “8E” (hexadecimal).

A length portion 130 is typically used to define the number of microseconds that are required to transmit a PLCP service data unit (PSDU) or the data 122 when the signal portion 126 is set equal to “0A”, “14”, “37”, or “6E”. According to the present invention, the length portion 130 is set equal to a number of microseconds that are required to transmit the data 122 and an additional extension time T ext when the signal portion 126 is set equal to “XX”.

Referring now to FIG. 9 , a station 150 according to the present invention includes a transceiver 152 , a controller 154 , an advanced coding and decoding circuit 156 , an antenna 158 and other circuits 159 that perform common station functions. Referring now to FIG. 10 , access point 160 includes a transceiver 162 , a controller 164 , an advanced coding and decoding circuit 166 , an antenna 168 and other circuits 169 that perform common functions of access points 160 .

Referring now to FIG. 11 , the present invention will be described in the context of a wireless RF signal that is originated by the access point 160 and that is intended for the station 150 - 1 in FIG. 11 . Reference numbers from FIGS. 1 and 2 have been used in FIG. 11 to identify similar elements. Skilled artisans can appreciate that the RF signal can be initiated by the station 150 - 1 and be intended for the access point 160 . In FIG. 12 , the RF signals can also be generated between stations 150 - 1 and 150 - 2 .

Referring now to FIG. 13 , when the transmitter 162 is operating in the extension mode, the transmitter 162 sets the signal portion 126 equal to “XX”. In addition, the length portion 130 is set equal to the number of microseconds for the data 122 and the extension time T ext . Dummy data 170 is inserted at the end of the data 122 . The dummy data 170 is sent during the extension time T ext . The extension time T ext is used to extend the duration of D 1 and to allow advanced signal processing such as advanced error coding for extension mode capable devices.

The transceiver 152 receives the PLCP header 120 with the signal portion 126 and the length portion 130 that specify the extension mode. Upon receiving the PLCP header correctly, the transceiver knows from the length portion 130 that there is a packet being transmitted and that the transmission requires the time that is specified in the length portion. The target station or access point knows that valid data ends a period T ext before the time that is specified in the length field of the PLCP header 120 .

As can be appreciated, other stations and/or access points are not impacted by the extension mode. For stations and access points without the extension mode capability, the data 122 ends after the dummy data 170 . In other words, the physical carrier sense or energy detection of other stations or access points will indicate a clear channel assessment (CCA) busy signal during the period T ext . This CCA busy state remains until after the transmission of the dummy data 170 ends. Therefore, the SIFS time requirements of IEEE section 802.11 and other related sections are still met while providing backward compatibility.

The present invention provides a solution for advanced signal processing that is transparent to the MAC layer. Therefore, there is no need to change IEEE section 802.11 MAC layer specifications to accommodate the extension mode. The dummy data 170 causes a negligible efficiency loss because the length of the dummy data 170 is much smaller than a typical length of the data 122 .

Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.