Link aware clear channel assessment

A pair of Clear Channel Assessment (CCA) rules are presented that protect an initiator's transmission at the responder, and the responder's transmission at the initiator, using additional fields transmitted in a preamble (header) of a Physical Layer Convergence Procedure (PLCP) Protocol Data Unit (PPDU) or in a Media Access Control (MAC) header, if unencrypted and robustly modulated. These techniques enable more parallel/simultaneous transmissions between devices that might otherwise interfere with each other, subject to ensuring an adequate Signal-to-Interference and-Noise Ratio (SINR) for the initiator's transmission at the responder and ensuring an adequate SINR for the responder's transmission at the initiator.

TECHNICAL FIELD

The present disclosure relates to wireless networks.

BACKGROUND

Clear Channel Assessment (CCA) is a technique by which devices detect energy on a channel before initiating a transmission, so as to avoid or minimize interference with other transmissions that may be occurring in the channel. For example, there are CCA rules defined in the IEEE 802.11 wireless local area network (WLAN) standard.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Overview

A pair of Clear Channel Assessment (CCA) rules are presented that protect an initiator's transmission at the responder, and the responder's transmission at the initiator, using additional fields transmitted in a preamble (header) of a Physical Layer Convergence Procedure (PLCP) Protocol Data Unit (PPDU) or in a Media Access Control (MAC) header, if unencrypted and robustly modulated. These techniques enable more parallel/simultaneous transmissions between devices that might otherwise interfere with each other, subject to ensuring an adequate Signal-to-Interference and-Noise Ratio (SINR) (e.g., 15-30 dB) for the initiator's transmission at the responder and ensuring an adequate SINR (e.g., 10-30 dB) for the responder's transmission at the initiator.

Detailed Description

Reference is first made toFIG. 1.FIG. 1shows a block diagram of a wireless network environment10, such as an IEEE 802.11 WLAN. In this diagram, the blocks or boxes represent wireless communication devices or devices with wireless communication capabilities. More specifically, initiating stations (STAs) (called “ISTAs”) transmit data units (e.g., PPDUs) that contain unicast frames desired by a responder STA (called “RSTA”). Other overlapped STAs (called “OSTAs”) may want to transmit data units (e.g., PLCP protocol data unit (PPDUs)) at the same time as the desired PPDUs (e.g., to the “any STA” (referred to as ASTA), or to the RSTA shown inFIG. 1). ISTAs and OSTAs are not disjoint sets since, for example, if the RSTA is an access point (AP), then its clients are both ISTAs and potential OSTAs.

A goal of the techniques presented herein is to protect both an initiating PPDU70sent by ISTA20and a response PPDU72sent by RSTA30, but allow parallel/simultaneous transmissions by other devices, e.g., transmission80by OSTA40, which are not going to interfere with the exchange between the ISTA20and RSTA30. Transmissions by the ISTA20, RSTA30or OSTA40can induce interference on other STAs, as indicated by the dashed lines shown inFIG. 1.

Existing CCA rules can lead to unnecessarily higher signal-to-interference-plus-noise ratio (SINR) at the receiver (when the two devices are very close together), or inadequate protection at the receiver (when the two devices are very far away). Conversely, existing CCA rules may prevent parallel/simultaneous transmissions that could both succeed.

Initiating Transmission

Reference is made toFIGS. 2 and 3for a description of a new Clear Channel Assessment (CCA) rule for an initiating PPDU. First inFIG. 2, the RSTA30can successfully receive PPDUs from ISTA20if either power from a colliding PPDU shown at reference numeral82associated with the PPDU80OSTA sends to ASTA50is received at the RSTA30at no greater than rssi(desiredPpdu,IR)−Margin, or the OSTA does not transmit. This requires the Initiating CCA rule:
rssi(desiredPpdu,IR)−Margin>omniEirp(txPpdu,O)−pathloss(RO)
pathloss(RO)=omniEirp(txPpdu,R)−rssi(snoopedPpdu,RO)
So:rssi(desiredPpdu,IR)−Margin>omniEirp(txPpdu,O)−omniEirp(txPpdu,R)+rssi(snoopedPpdu,RO)

rssi(desiredPpdu,IR) is receive signal strength information at the RSTA30for the initiating transmission70sent by the ISTA20. rssi(desiredPpdu,IR) could be a maximum/mean/X-percentile (e.g. X=95) over a recent window (e.g. 5 sec) of transmissions previously sent by the ISTA and received by the RSTA, and perhaps include higher weighting of more recent data (e.g. via an exponentially weighted filter).

omniEirp(txPpdu,O) is an expected power of the transmission by the OSTA. To be more precise, “omniEirp” is the expected Equivalent Isotropically Radiated Power (EIRP) from a transmission;

omniEirp(txPpdu,R) is an expected power of the initiating transmission70sent by the ISTA to the RSTA; and

rssi(snoopedPpdu,RO) is the RSSI received at the OSTA of a PPDU transmitted by the RSTA, as shown at reference numeral84. The PPDU may or may not be intended for reception by the OSTA (i.e. it may be a snooped PPDU).

Margin may be an agreed and standardized value (e.g. in the range of 15-30 dB), or in another embodiment may be defined by an associated AP, or may be transmitted in a field by the RSTA30either as a distinct parameter or in combination with other parameters, such as omniEirp(txPpdu,R)+rssi(desiredPpdu,IR)−Margin. It may further be adjustable by an overlapping device, e.g., OSTA40or ASTA50.

Reference is now made toFIG. 3, with continued reference toFIG. 2. For the OSTA40to implement the Initiating CCA rule, it needs several pieces of information. omniEirp(txPpdu,O) is already known to the OSTA40because it knows the power at which it will send the transmission80. The omniEirp(txPpdu,R) and rssi(snoopedPpdu,RO) parameters need to come from the same PPDU (or the signaling of the omniEirp(txPpdu,R) parameter in one PPDU needs to indicate that the parameter also characterizes the omniEirp(txPpdu,R) of other PPDUs that might not carry omniEirp(txPpdu,R)), and be reasonably recent (e.g., within 5 sec). The ISTA20needs to send some information out, accessible by the OSTA40, and the RSTA30needs to send some information out, again to be accessible by the OSTA40.

More specifically, the ISTA20needs to send out information indicating to which device it is transmitting, and this information is referred to as the compressed receiver identity (cR), shown at reference numeral90inFIG. 3. The RSTA30sends information out non real-time concerning recent PPDUs it received from the ISTA20, as shown at reference numeral92. When the OSTA40receives that information transmitted by the RSTA30, it measures the receive signal strength (RSSI). If not recently measured, the OSTA40can fall back to conventional CCA such as the CCA for Very High Throughput (VHT) STAs defined in 802.11. The EIRP and transmitter identity (=R) parameters in omniEirp(txPpdu,R) is snooped information, so it needs to be carried in an unencrypted and robustly modulated field (e.g., Signal (SIG) field) of a PPDU from the RSTA30. Thus, a compressed omniEirp and a compressed RSTA identity are needed. These may be added as an IEEE 802.11 preamble by a new IEEE 802.11 amendment (e.g., High Efficiency Wireless (HEW)). As used herein, “robustly modulated” refers to modulation such as or similar to Binary Phase Shift Keying (BPSK)/Quadrature Phase Shift Keying (QPSK) modulation with a rate ½ up to ¾ convolution code, beyond which is non-robust.

Both the RSSI and receiver identity (=R) parameters in rssi(desiredPpdu,IR) need to be advertised by the RSTA30and reach the OSTA40. Both the RSSI and receiver identity information are snooped information, which need to be carried in a SIG field. The receiver identity is the same as the transmitter identity above.

The SIG fields transmitted by the RSTA30(or any other HEW STA) should contain:

omniEirp(txPpdu,cR)+rssi(desiredPpdu,worstCasecR) (e.g., 6-7 bits), where “worstCase” refers to the situation where multiple stations are attempting to transmit to the RSTA (e.g., the RSTA is an AP), in which case the RSTA30reports the RSSI of its worst-situated ISTA (or some approximation thereof: e.g. 95-percencile worst ISTA, 95-percencile worst ISTA within its coverage area; and within the last 5 sec or 24 hours or 1 week; or some filtered average). In other words, the value for omniEirp is a value for a situation where multiple devices are attempting to transmit to the second device (RSTA) and represents weakest receive signal strength information among the multiple devices attempting to transmit to the second device, or an approximation thereof.

Moreover, implicitly, when the ISTA20transmits a PPDU to the RSTA30, the PPDU needs to include the compressed identity of RSTA (cR), (e.g., 5-10 bits).

Responding Transmission

Reference is now made toFIGS. 4 and 5for the CCA for the responding PPDU. The ISTA20can successfully receive PPDUs from the RSTA30if either a colliding PPDU from the OSTA40, shown at reference numeral94(associated with the PPDU80sent to the ASTA50) is received at no greater than rssi(desiredPpdu,RI)−Margin, or the OSTA40does not transmit. This involves a Responding CCA rule:
rssi(desiredPpdu,RI)−Margin>omniEirp(txPpdu,O)−pathloss(IO)

As shown inFIG. 5, for the OSTA40to implement the Responding CCA rule, it needs omniEirp(txPpdu,O), which is already known to the OSTA40, and rssi(snoopedPpdu,IO), which can be directly measured by the OSTA40from the initiating PPDU70(FIG. 2). The omniEirp(txPpdu,I) needs to come from the same PPDU and be signalled by the ISTA20(or the signaling of the omniEirp(txPpdu,I) parameter in one PPDU needs to indicate that the parameter also characterizes the omniEirp(txPpdu,I) of other PPDUs that might not carry omniEirp(txPpdu,I)). Also, the rssi(desiredPpdu,RI) needs to be advertised by the ISTA20as shown at reference numeral96.

Initiating CCA and Responding CCA Rules

Collecting the requirements described above, the SIG field transmitted by the RSTA30(or any other HEW STA) should contain:RSTA indication (1 bit)Compressed RSTA identity (cR) (5-10 bits)omniEirp(txPpdu,R)+rssi(desiredPpdu,R) (6-7 bits)

Other fields may also be included, such as a compressed indication of the RSTA30identity, so that omniEirp(txPpdu, X)+rssi(desiredPpdu, X), X=I or R, is available to snoopers whether the transmitter is currently an ISTA or an RSTA (i.e. snooping collects 2× the information in the same time). Since the responding PPDU typically contains a short frame (e.g., Acknowledgment or Block Acknowledgment), there is little penalty—and some advantages—if the responding PPDU is sent using a more robust modulation and coding scheme. Accordingly, the Margin may be relatively high for the Initiating CCA compared to the Margin for the Responding CCA (via standardization, associated AP control, etc.).

As mentioned above, Margin might also be explicitly included in the SIG field, or combined with the omniEirp(txPpdu,X)+rssi(desiredPpdu, X) terms, X=I or R.

The SIG field may be used to transmit the information for the Initiating CCA and the Responding CCA because the SIG field is in the preamble of a frame and uses the lowest modulation, making it readily detectable by nearby devices. Nevertheless, these fields consume SIG time, so terseness is vital. As proposed herein, these fields consume 50%-100% of a whole SIG OFDM symbol. For the compressed R, too few bits implies station ambiguity. OSTAs would lump omniEirp(txPpdu,cR)+rssi(desiredPpdu,IcR) into the same cR bin for different RSTAs. Since rssi(desiredPpdu,IcR) would typically be 10-20-30 dB different for two random STAs, this degrades the benefit of this enhanced CCA.

As long as an OSTA receives/detects all RSTAs, this is not fatal. For each bin, the maximum received over the past 5 sec is selected, and at worst the system gracefully degrades back to the current fixed CCA currently in use. However, if two RSTAs, one near and one far, map to the same cR, and an OSTA has recent information about just the far RSTA, but the near RSTA transmits, then the OSTA could transmit and collide with a near RSTA. This motivates more bits for identity, to avoid ambiguity.

For example, assume there are 10000 STAs in range across 10 channels. Then 10 bits of compressed identity would be sufficient to (mostly) uniquely identify STAs. A larger cR likely implies more storage at every OSTA: i.e. 2#bits*storage for omniEirp(txPpdu,R)+rssi(desiredPpdu,IR), i.e. up to 7 kbit.

In another embodiment, an AP monitors omniEirp(txPpdu,R)+rssi(desiredPpdu,IR) and omniEirp(txPpdu,I)+rssi(desiredPpdu,RI) for all STAs in its Basic Service Set (BSS), plus probing STAs that associate shortly thereafter, determines a collective value of omniEirp(txPpdu,R)+rssi(desiredPpdu,IR) for the BSS, publishes it to all associated STAs, which in turn echo this in their SIG field, with a compressed indication of the BSS identity in place of a compressed indication of the RSTA's identity. In this embodiment, storage is proportional to the number of overlapping BSSs, which is rarely more than 128.

Given that many physical APs support different BSSs/BSSIDs, still further storage reduction is possible if the physical AP monitors omniEirp(txPpdu,R)+rssi(desiredPpdu,IR) and omniEirp(txPpdu,I)+rssi(desiredPpdu,RI) for all STAs in any of its BSSs. Additionally, probing STAs that associate shortly thereafter determine a collective value of omniEirp(txPpdu,R)+rssi(desiredPpdu,IR) for all of its BSSs, publishes it to all STAs associated with any of its BSSs, which in turn echo this in their SIG field, with a compressed indication of the multiple-BSSID identity in place of a compressed indication of the RSTA's identity. In this embodiment, storage is proportional to the number of overlapping physical APs, which is rarely more than 32.

Further Considerations

Values for omniEirp and RSSI may not be known. It would not be unusual for devices to have a +−5 dB measurement tolerance. Especially for non-isotopic antennas (including omnidirectional antennas), omniEirp may be set to conducted power plus some antenna efficiency.

Reusing 5 second old measurements may be acceptable, depending on device speed. This period of time could be longer if measurements are sparse. As well, some level of weighting/prediction can be incorporated: e.g., if RSSIs are increasing, a higher value is used, if RSSIs are decreasing, then the most recent measurement value is used.

Margin is a critical parameter to select. Optimal modulation to maximize system throughput is closer to Quadrature Phase Shift Keying (QPSK) with higher spatial reuse than 256QAM with lower spatial reuse, i.e., lower margin. The Margin value may be controllable by an access point, and not a fixed value.

If multiple OSTAs transmit at the same time, they raise the interference floor. This can be readily mitigated by adding a few dB extra to Margin.

In general, these CCA rules are more relaxed than the CCA rules defined for VHT STAs in IEEE 802.11, but not always (e.g., protection of long-range links).

Bandwidth can be easily accounted for if the advertised omniEirp and RSSI parameters report energy per unit of bandwidth (e.g. 20 MHz). The system is most robust if the RSTA can be uniquely identified with high probability by its cR field.

Neither legacy PPDUs nor groupcast messages are addressed. In this case, the default is pre-existing CCA rules such as the CCA rules defined for VHT STAs in IEEE 802.11. Probe Requests may use legacy PPDUs. Alternatively, these techniques may be applied to broadcast frames, and an access point would use a different encoding (to identify itself) for broadcast frames. That is, the access point would encode an identity of itself to indicate that the frame is global, and indicating the CCA threshold to be used for the broadcast frame.

With Orthogonal Frequency Division Multiple Access (OFDMA) techniques and multi-user multiple-input multiple-output (MU-MIMO), it is difficult to find sufficient SIG bits to indicate each RSTA. The parameters sent by the ISTA need to be sent in a SIG field (since the ISTA will send at a higher modulation coding scheme/number of spatial streams (MCS/NSS)). Therefore, it may be desirable to default to pre-existing CCA rules in this case, or treat the PDDU as containing a groupcast frame.

By contrast, the parameters sent by the RSTA do not have to be sent in a SIG field. They can be sent in low rate frames, such as Request-to-Send, Clear-to-Send, Acknowledgement, Block Acknowledgment frames.

In the field, an RSTA may be configured to over-report its desired RSSI by a few dB (or more) to give it a higher Signal-to-Interference Plus Noise Ratio (SNR). omniEIRP+RSSI can be compared against measurements made by test equipment using nearby/co-located antennas. Similarly, an access point with desired clients intermittently probing/associating from long range might always report a very high omniEirp(txPpdu,cR)+rssi(desiredPpdu,IcR). This is not unreasonable behavior. APs in high density environments are highly motivated to report low-and-correct rssi(desiredPpdu,cR) values.

The protection time could and should be different for the ISTA and RSTA. The Initiator CCA rule only applies for 0 to TXTIME(thisPPDU)+smallGuardTime from the beginning of the initiating PPDU, and the responder CCA rule only applies from TXTIME(thisPPDU)+SIFS−smallGuardTime to TXTIME(thisPPDU)+SIFS+max(TXTIME(Ack),TXTIME(BA))+smallGuardTime, where SIFS is the short inter-frame spacing interval. In other words, a first time interval during which the third device (OSTA) determines whether or not to send a transmission that may overlap with the transmission from the first device (ISTA) is different from a second time interval during which the third device (OSTA) determines whether or not to send a transmission that may overlap with the response transmission from the second device (RSTA) to the first device (ISTA).

Moreover, the cR could be deliberately selected so as not to collide with a nearby STA.

FIG. 6illustrates a block diagram of a wireless device200(e.g., STA, meaning an access point or a client device) configured to perform the CCA techniques presented herein. The wireless device includes a transmitter210(or multiple transmitters), a receiver220(or multiple receivers), an antenna230(or multiple antennas, each for a corresponding receiver and/or transmitter), a baseband processor (e.g., a modem)240and a controller250. The baseband processor240may perform media access control (MAC) functions as well as physical layer (PHY) functions. The controller250is connected to a memory260and to a wired network interface unit270to provide connectivity to a wired network.

The CCA techniques presented herein may be implemented by CCA logic280in the baseband processor. The CCA logic280may take the form of fixed or programmable digital logic gates. In another form, the CCA logic280may be implemented by instructions stored/encoded in the memory260, and executed by the controller (e.g., a microprocessor)250. To this end, the memory may comprise read only memory (ROM), random access memory (RAM), magnetic disk storage media devices, optical storage media devices, flash memory devices, electrical, optical, or other physical/tangible memory storage devices. Thus, in general, the memory may comprise one or more tangible (non-transitory) computer readable storage media (e.g., a memory device) encoded with software comprising computer executable instructions and when the software is executed (by the controller) it is operable to perform the operations described herein.

Reference is now made toFIG. 7.FIG. 7illustrates a flow chart depicting operations of a method300performed by an ISTA in accordance with the embodiments presented herein. At310, a wireless communication environment is provided that includes a first device seeking to initiate a transmission to a second device and a third device in proximity to the first device and the second device such that signals wirelessly transmitted by the third device could impact ability of the second device to receive the transmission from the first device, and of the first device to receive a response transmission from the second device. At320, the first device wirelessly transmits a message including: (a) information indicating that the message is being transmitted by the first device that is to send a transmission to the second device; (b) an identifier of the second device; (c) a value for a first parameter [omniEirp(txPpdu,I)] that is an expected power of the transmission to be transmitted by the first device; and (d) a value for a second parameter [rssi(desiredPpdu,I)] that is receive signal strength information at the first device for one or more transmissions previously sent by the second device and received by the first device. Moreover, as explained above, the message may be contained in a field of a preamble of a PPDU formatted in accordance with the IEEE 802.11 standard, or in a field of a MAC header that is unencrypted (and robustly modulated).

Similarly,FIG. 8illustrates a flow chart depicting operations for a method400performed by an RSTA in accordance with the embodiments presented herein. At410, a wireless communication environment is provided that includes a first device seeking to initiate a transmission to a second device and a third device in proximity to the first device and the second device such that signals wirelessly transmitted by the third device could impact ability of the first device to receive a response transmission from the second device. At420, the second device wireless transmits a message including: (a) information indicating that the message is being transmitted by the second device that is to send the response transmission to the first device in response to an initiating transmission received from the first device; (b) an identifier of the second device, (c) a value for a first parameter [omniEirp(txPpdu,R)] that is a power of a current transmission by the second device; and (d) a value for a second parameter [rssi(desiredPpdu,R)] that is receive signal strength information at the second device for one or more transmissions previously sent by the first device and received by the second device. The message may include information indicating a value for the first parameter for each of one or more other transmissions made by the second device, e.g., of other PPDUs that are covered by the same value for the first parameter. Moreover, as explained above, the message may be contained in a field of a preamble of a PPDU formatted in accordance with the IEEE 802.11 standard, or in a field of a MAC header that is unencrypted (and robustly modulated).

Turning now toFIG. 9, a flow chart is shown for a method500performed by an OSTA according to the embodiments presented herein. At510, a wireless communication environment is provided that a first device seeking to initiate a transmission to a second device and a third device in proximity to the first device and the second device such that signals wirelessly transmitted by the third device could impact ability of the second device to receive the transmission from the first device. At520, the third device receives from the first device receiver identity information indicating to which device the first device is sending the transmission. At530, the third device receives from the second device a message containing identity information of the second device, a value for a first parameter that is an expected power transmitted by the second device [e.g., the aforementioned omniEirp(txPpdu,R)] and a value for a second parameter that is receive signal strength information at the second device for one or more transmissions previously sent by the first device and received by the second device [e.g., the aforementioned rssi(desiredPpdu,IR)]. The message may be contained in a field of a preamble of a PPDU formatted in accordance with the IEEE 802.11 standard, or contained in a MAC header that is unencrypted (though robustly modulated). At540, the third device determines whether to initiate a transmission based on the information received from the first device, information contained in the message received from the second device and a margin quantity.

The determining operation540may be based further on a value of a third parameters that is an expected power for the transmission to be sent by the third device [e.g., the aforementioned omniEirp(txPpdu,O)] and a value of a fourth parameter that is receive signal strength information for a transmission sent by the second device and received at the third device [e.g., the aforementioned rssi(snoopedPpdu,RO)].

Moreover, the determining operation540may further involve determining whether a sum of the value for the first parameter and the value for the second parameter minus the value for the fourth parameter and the margin quantity is greater than the value for the third parameter [omniEirp(txPpdu,O)<omniEirp(txPpdu,R)+rssi(desiredPpdu,IR)−rssi(snoopedPpdu,RO)−Margin] Furthermore, instead of performing this in the dB domain with addition and subtraction operations, this may be performed with multiplication and division operations in the linear power or magnitude domain. The transmission from the first device is initiated if the sum of the value for the first parameter and the value for the second parameter minus the value for the fourth parameter and the margin quantity is greater than the value for the third parameter and otherwise not the transmission from the third device is not initiated. As explained above, the margin quantity may be a predetermined value or may be contained in the message received from the second device.

To summarize, a pair of CCA rules are presented herein that protect an initiator's PPDU at the responder, and the responder's PPDU at the initiator, using additional fields transmitted in a preamble (header) of a PPDU or in a MAC header, if unencrypted. These techniques enable more parallel/simultaneous transmissions between devices that would otherwise interfere with each other, subject to ensuring an adequate SINR (15-30 dB) for the initiator's PPDU at the responder and ensuring an adequate SNR (15-30 dB) for the responder's PPDU at the initiator.

In addition to the various methods described above (such as in connection with the flowcharts ofFIGS. 7-9), the techniques may be embodied in an apparatus and/or non-transitory computer readable storage media form. For example, an apparatus may be provided that comprises a wireless network interface unit and a processor. The wireless network interface unit is configured to transmit wireless signals and receive wireless signals in wireless communication environment that includes a first device seeking to initiate a transmission to a second device and the first device to receive a response transmission from the second device, and further to: receive from the first device a signal containing receiver identity information indicating to which device the first device is sending the transmission; and receive from the second device a signal containing identity information of the second device and a value for a first parameter that is an expected power transmitted by the second device and a value for a second parameter that is receive signal strength information at the second device for one or more transmissions previously sent by the first device and received by the second device. The processor is coupled to the wireless network interface unit and is configured to determine whether to initiate a transmission based on information contained in the signal received from the first device, information contained in the signal received from the second device and a margin quantity.

The above description is intended by way of example only.