GB2538946B - Feedback on reception quality over secondary sub-channels of a composite channel in 802.11 networks - Google Patents
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Description
FEEDBACK ON RECEPTION OUALITY OVER SECONDARY SUB-CHANNELS OF A COMPOSITE CHANNEL IN 802.11 NETWORKS
> FIELD OF THE INVENTION
The present invention relates generally to communication networks and more specifically to communication methods having channel feedback to provide or use evaluation of reception quality, and associated devices, for transmitting data over a wireless communication network using Carrier Sense Multiple Access with Collision ) Avoidance (CSMA/CA), the network being accessible by a plurality of stations.
BACKGROUND OF THE INVENTION
Wireless local area networks (WLANs), such as a wireless medium in a communication network using Carrier Sense Multiple Access with Collision Avoidance j (CSMA/CA), are founded on the principles of collision avoidance. Such networks may also conform to a communication standard such as a communication protocol of 802.11 type e.g. Medium Access Control (MAC).
The IEEE 802.11 MAC standard defines the way WLANs must work at the physical and medium access control (MAC) level. Typically, the 802.11 MAC (Medium ) Access Control) operating mode implements the well-known Distributed Coordination Function (DCF) which relies on a contention-based mechanism based on the so-called “Carrier Sense Multiple Access with Collision Avoidance” (CSMA/CA) technique.
The 802.11 medium access protocol standard or operating mode is mainly directed to the management of communication nodes waiting for the wireless medium to j become idle so as to try to access to the wireless medium.
The network operating mode defined by the IEEE 802.11ac standard provides very high throughput (VHT) by, among other means, moving from the 2.4GHz band which is deemed to be highly susceptible to interference to the 5GHz band, thereby allowing for wider frequency contiguous channels of 80MHz to be used, two of which ) may optionally be combined to get a 160MHz channel as operating band of the wireless network.
The 802.11ac standard also tweaks control frames such as the Request-To-Send (RTS) and Clear-To-Send (CTS) frames to allow for composite channels of varying and predefined bandwidths of 20, 40 or 80MHz, the composite channels being made of j one or more sub-channels that are contiguous within the operating band. The 160MHz composite channel is possible by the combination of two 80MHz composite channels within the 160MHz operating band. The control frames specify the channel width (bandwidth) for the targeted composite channel. A composite channel therefore consists of a primary channel on which a j given node performs EDCA backoff procedure to access the medium, and of at least one secondary channel, of for example 20MHz each. The primary channel is used by the communication nodes to sense whether or not the channel is idle, and the primary channel can be extended using the secondary channel or channels to form a composite channel. ) Given a tree breakdown of the operating band into elementary 20MHz channels, some secondary sub-channels are named tertiary or quaternary channels.
In 802.11ac, all the transmissions, and thus the possible composite channels, include the primary channel. This is because the nodes perform full Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) and Network Allocation Vector j (NAV) tracking on the primary channel only. The other channels are assigned as secondary channels, on which the nodes have only capability of CCA (clear channel assessment), i.e. detection of an idle or busy state/status of said secondary channel. A node or station is allowed to use as much channel capacity (or bandwidth, i.e. of (sub-)channels in the composite channel) as is available. The constraint is that the ) combined channels need to be contiguous within the operating band for a node having a single antenna (or single spatial stream).
The node or station may thus use the combined or “composite” channels as a 40 or 80 or 160MHz modulation band for data modulation when transmitting data frames. j However, if there is noise or interference on one of the 20MHz channel within the wider composite channel, the available bandwidth is reduced. The 802.11ac standard only allows a restricted number of composite channel configurations, i.e. of predefined subsets of 20MHz channel that can be reserved by the 802.11ac nodes to wireless communicate and thus transmit data. These configurations correspond to ) contiguous composite channels of 20, 40, 80MHz bandwidth in case of single antenna node devices.
Therefore, noise or interference even on a small portion of the composite channel may substantially reduce the available bandwidth of the composite channel to only 40 or 20 MHz, since the resulting reserved bandwidth must meet the 20MHz, j 40MHz, 80MHz or 160MHz channel configurations allowed by the standard.
More recently, Institute of Electrical and Electronics Engineers (IEEE) officially approved the 802.11 ax task group, as the successor of 802.11ac. The primary goal of the 802.11 ax task group consists in seeking for an improvement in data speed to wireless communicating devices used in dense deployment scenarios. j The huge gigabit throughputs that are often attributerfto 802.11 ac are mainly theoretical. In fact, they represent the overall capacity a Wi-Fi network can support, for Λ instance 1.3 Gbps in today’s most advanced routers. However, they can occur only in the rarest circumstances where any individual device would actually be able to connect at such high rates. ) The existing 802.11ac standard requires that the composite channel width be specified in the 802.11ac frames, resulting in that channels non-contiguous within the operating band cannot be used although they are available. Therefore, in the 802.11 ax research context, there is a need to enhance the efficiency and usage of the wireless channel. j Publication IEEE 802.11-13/1058r0 “Efficient Wider Bandwidth Operation” provided during the 802.11ax task group has raised the benefit of using all available channels, even if no solution to do so has been provided.
An issue with the use of composite channels as defined in the 802.11η or 802.11ac (or 802.11 ax) is that the 802.11η and 802.11ac-compliant nodes (i.e. HT nodes ) standing for High Throughput nodes) and the other legacy nodes (i.e. non-HT nodes compliant only with for instance 802.11a/b/g) have to co-exist within the same wireless network and thus have to share the 20MHz channels.
To cope with this issue, the 802.11η and 802.11ac standards provide the possibility to duplicate control frames (e.g. ACK frames to acknowledge correct or j erroneous reception of the sent data) in an 802.11a legacy format (called as “non-HT”) to establish a protection of the requested TXOP over the whole composite channel.
This is for any legacy 802.11a node that uses any of the 20MHz channel involved in the composite channel to be aware of on-going communications on the 20MHz channel. As a result, the legacy node is prevented from initiating a new ) transmission until the end of the current composite channel TXOP granted to an 802.11n/ac node.
As originally proposed by 802.11η, a duplication of conventional 802.11a or “non-HT” transmission is provided to allow the two identical 20MHz non-HT control frames to be sent simultaneously on both the primary and secondary (sub)channels j forming the used composite channel.
This approach has been widened for 802.11ac to allow duplication over the sub-channels forming an 80MHz or 160MHz composite channel. In the remainder of the present document, the “duplicated non-HT frame” or “duplicated non-HT control frame” or “duplicated control frame” means that the node device duplicates the conventional or j “non-HT” transmission of a given control frame (e.g. ACK frame) over secondary 20MHz (sub)channel(s) of the (40MHz 80MHz or 160MHz) operating band.
In practice, to request a composite channel (equal to or greater than 40MHz) for a new TXOP, an 802.11n/ac node does an EDCA backoff procedure in the primary 20MHz (sub-)channel. In parallel, it performs a channel sensing mechanism, such as a ) Clear-Channel-Assessment (CCA) signal detection, on the secondary channels to detect the secondary channel or channels that are idle (channel state/status is “idle”) during a PIFS interval before the start of the new TXOP (i.e. before the backoff counter expires).
In other words, only frames on the primary 20MHz (sub-)channel are demodulated and decoded by a receiving node, in particular to determine if they are j addressed to it. On the secondary (sub-)channels, no demodulation or decoding of frames is performed.
However, the above explanations show that, in the 802.11ac standard, the transmitter or “source node” determines by itself the bandwidth to use, using channel sensing at its side only. ) This approach is not satisfactory because the choice of the bandwidth does not take into account the channel quality at the receiving side, which may evolve over time, e.g. during current data transmissions.
This deficiency is even more aggravated in the 802.11 ax context since dense wireless environments are more ascertained to suffer from previous limitations. j To improve the situation, the 802.11ac standard defines dedicated messages called “Measurement Report Element’ that can be requested by the source node by sending a “Measurement Request element’.
The mechanism based on these measurement request/report messages has drawbacks. First, it is bandwidth consuming since messages are requested. Second, it ) adds delay between the time at which the measurement is wished and the time at which the measurement is made, due to the need of sending a request and of processing it by the receiving node. Third, it does not allow reacting efficiently on the modifications of the reception quality.
> SUMMARY OF INVENTION
It is a broad objective of the present invention to provide communication methods and devices for transmitting data over an (ad-hoc) wireless network, the physical medium of which being shared between a plurality of communication nodes, often containing a single antenna device. j The present invention has been devised to overcome one or more foregoing limitations.
In this context, the present invention seeks to provide communication methods having enhanced channel feedback to provide or use evaluation of reception quality. ) The invention can be applied to any wireless network where a source node sends data of a data stream to a receiving node using multiple channels. The invention is especially suitable for data transmission in an IEEE 802.11 ax network (and future version), requiring more flexibility in the bandwidth management.
In particular, from the receiving node’s perspective, embodiments of the j invention first provide a wireless communication method between a source node and a receiving node over a composite channel in a wireless network, the composite channel being made of a primary sub-channel and of one or more secondary sub-channel, the method comprising, at the receiving node: receiving, from the source node, a signal modulated on the whole composite ) channel, the modulated signal encoding one or more data frames; applying a decoding process on the modulated signal; generating an acknowledgment frame, the acknowledgment frame being one of an acknowledgment frame acknowledging correct reception of the one or more data frames or an acknowledgment frame acknowledging erroneous reception of the one or j more data frames; sending the acknowledgment frame to the source node on the primary subchannel; the method further comprising, at the receiving node: determining a channel quality for one or more of the secondary sub- ) channels; and sending a duplicate of the acknowledgment frame to the source node only on each secondary sub-channel of a subset of the secondary sub-channels that excludes at least one secondary sub-channel having a low determined channel quality.
From the source node’s perspective, embodiments of the invention also j provide a wireless communication method between a source node and a receiving node over a composite channel in a wireless network, the composite channel being made of a primary sub-channel and of one or more secondary sub-channels, the method comprising, at the source node: transmitting, to the receiving node, a signal modulated on the whole j composite channel, the modulated signal encoding one or more data frames; receiving, from the receiving node in response to the transmitted signal, at least one acknowledgment frame on the primary sub-channel and possibly a duplicated acknowledgment frame on a respective secondary sub-channel; and modifying the composite channel for future transmission, by discarding (i.e. ) excluding) at least one secondary sub-channel of the composite channel on which no duplicated acknowledgment frame is received.
At least one duplicated acknowledgment frame may be received on a respective secondary sub-channel.
The composite channel may be made of a plurality of secondary sub-j channels (in addition to the primary one).
Correlatively, the invention provides a receiving node for wireless communication over a composite channel in a wireless network, the composite channel being made of a primary sub-channel and of one or more secondary sub-channels, the receiving node comprising at least one microprocessor configured for carrying out the ) steps of the method defined above from the receiving node’s perspective.
Also the invention provides a source node for wireless communication over a composite channel in a wireless network, the composite channel being made of a primary sub-channel and of one or more secondary sub-channels, the source node comprising at least one microprocessor configured for carrying out the steps of the j method defined above from the source node’s perspective.
In the specific context of 802.11, the sub-channels are 20Mhz channels that can be combined.
The invention uses the duplication of control frames, for instance 802.11 ACK frames, in a clever way to make it possible to provide channel feedback without ) delay and additional messages.
This is achieved by providing, in response to received frames, such control frames only on secondary sub-channels for which a measured reception quality is for instance satisfactory.
This is made possible because the duplicates of the control frames are not mandatory on the secondary sub-channels for the source node and the receiving node to signal the TXOP.
As a result, the source node is quickly informed on which secondary sub-j channel or sub-channels have low reception quality, and may adjust, if necessary, the composite channel to be used for future communication by removing or discarding low- reception-quality sub-channel or sub-channels.
Optional features of embodiments of the invention are defined in the appended claims. Some of these features are explained here below with reference to a ) method, while they can be transposed into system features dedicated to any device according to embodiments of the invention.
In embodiments regarding the receiving node’s perspective, determining the channel quality for a secondary sub-channel comprises evaluating a quality of signal reception on the secondary sub-channel using the received modulated signal. As a j result, a current reception quality is evaluated, rather than being based on past (and possibly out-of-date) measurements.
In a specific embodiment, the quality of signal reception is evaluated based on a plurality of data frames conveyed by the modulated signal. This approach provides a better evaluation. ) In embodiments, the method further comprises, at the receiving node, comparing the channel quality determined for each secondary sub-channel with a quality threshold to exclude the secondary sub-channel or sub-channels having a determined channel quality below the quality threshold.
In embodiments, the acknowledgment frame and duplicates thereof are j acknowledgment frames acknowledging correct reception of the one or more data frames; and no acknowledgment frame and duplicate thereof are sent in case of erroneous reception of a data frame. The decision may be taken based on the result of the decoding process. It means that the receiving node adapts the sending of ACK duplicates on the secondary sub-channels having good quality of reception, while the ) receiving node is positively acknowledging the reception of the data frames. In case of erroneous reception, the source node will resend the one or more data frames after an acknowledgment waiting time (timeout).
This approach applies particularly to unitary acknowledgment, rather than block acknowledgment.
In embodiments, the acknowledgment frame is an acknowledgment frame acknowledging erroneous reception of the data frame or frames, and the duplicate or duplicates of the acknowledgment frame are sent only on the subset of secondary subchannels. j Furthermore, an acknowledgment frame acknowledging correct reception of a data frame received from the source node and duplicates thereof may be generated and sent respectively on the primary sub-channel and on the one or more secondary sub-channels forming the composite channel.
Again, the decision may be taken based on the result of the decoding ) process. It means that the receiving node adapts the sending of ACK duplicates on the secondary sub-channels having good quality of reception, while the receiving node is negatively acknowledging the reception of the data frames (for instance because one of the sub-channel is too disturbed). As the difference between positive and negative acknowledgment can be made based on which sub-channels an ACK signal is received, j this ACK signal may be reduced to a very short message.
In embodiments, the acknowledgment frame is a block acknowledgment frame acknowledging correct or erroneous reception of respectively each of a plurality of data frames. This is to comply with the Block-ACK (BA) messages as proposed in 802.11ac. BA frames make it possible to identify which data frames have been correctly ) received and which ones have been erroneously received, in order to reduce the number of data frames to be retransmitted. As a consequence, the block acknowledgment frame is generated based on the result of the decoding process on the signal corresponding to each data frame.
In embodiments, the acknowledgment frame and the duplicate or duplicates j thereof are sent substantially simultaneously (i.e. simultaneously given some acceptable tolerance margins) on their respective sub-channels. This may help the source node to efficiently detect the duplicated on the secondary sub-channels as explained below.
From the source node’s perspective, embodiments provide that the wireless communication method further comprises, at the source node, determining whether or ) not transmitted data frame or frames have been correctly received by the receiving node, using the received acknowledgment frame and duplicates thereof; and retransmitting the data frame or frames not correctly received. As mentioned above, the source node can determine that data frame or frames have not been correctly received because an acknowledgment waiting time (timeout) has expired without receiving any ACK frame. In another embodiment, it is because a duplicated ACK frame has not been received on each and every secondary sub-channel of the composite channel.
For completeness, embodiments relying on block-acknowledgment make it possible for the source node to determine precisely which data frame or frames among j a set of data frames have not been correctly received.
In a specific embodiment, the data frame or frames not correctly received are retransmitted as a signal modulated on the modified composite channel. This embodiment takes advantage of both the negative acknowledgment (to identify the data frame or frames to be sent again) and the channel quality feedback according to the ) invention to adjust the composite channel on which the non-received frames are resent.
In embodiments, the wireless communication method further comprises, at the source node, updating, in memory, channel quality history associated with one or more secondary sub-channels, based on whether or not a duplicated acknowledgment frame is received on the respective secondary sub-channel. Having a channel quality j history (for each monitored secondary sub-channel) makes it possible to efficiently decide when removing or deleting a sub-channel from the composite channel. Indeed, systematic removing of a sub-channel on which no control frame is received is thus avoided.
In a corresponding specific embodiment, modifying the composite channel ) for future transmission includes determining at least one secondary sub-channel to discard from the composite channel based on the stored channel quality histories.
While the source node may decode each signal received on the secondary sub-channels to determine whether or not it corresponds to the ACK frame received on the primary sub-channel, 802.11ac has preferred to lighten the process at the nodes by j only providing decoding of the signal received on the primary sub-channel and by only performing CCA signal detection on the secondary sub-channels.
Therefore, there is an issue for such nodes to be able to discriminate between a duplicated ACK frame and a legacy communication and even collision that may occur on the secondary sub-channels at the same time as receiving the ACK frame ) on the primary sub-channel. A need is thus apparent to improve the sensing of duplicated frames on the secondary sub-channels. This would help to improve the bandwidth usage of the wireless network and thus the efficiency of wireless communication over such a network.
In this context, the wireless communication method at the source node may j further comprises determining, for each secondary sub-channel, whether or not a duplicated acknowledgment frame is received on the secondary sub-channel, wherein the determining step for a secondary sub-channel includes: sensing, for the primary sub-channel and the secondary sub-channel, a change of an idle/busy status of the primary and secondary sub-channels, and storing, j in memory, the status changes in association with time information; determining, using the stored time information, whether or not the secondary sub-channel has respective status changes temporally similar to the status changes in the primary sub-channel due to the received acknowledgment frame, to trigger detection of a duplicated acknowledgment frame received on the secondary sub-channel in case ) of temporal similarity between the status changes.
According to a specific feature, the time information includes a time instant at which the status change for the primary or secondary sub-channel occurs or a time difference between the status change thus sensed and the preceding sensed status change in the same primary or secondary sub-channel. Timestamps generated by a j clock internal to the node may be used. Such time information takes very little space in memory of the nodes.
According to another specific feature, determining using the stored time information includes determining whether or not the time difference between an idle-to-busy status change in the secondary ) sub-channel and an idle-to-busy status change corresponding to the start of the received acknowledgment frame in the primary sub-channel is less than a first threshold; and the time difference between a busy-to-idle status change in the secondary sub-channel and a busy-to-idle status change corresponding to the end of the received acknowledgment frame in the primary sub-channel is less than a second threshold. j The busy-to-idle status change is the next status change in the sub-channel after the idle-to-busy status change first considered. This is because the channel status usually has only two states: idle and busy.
Given the time information stored in memory of the source node, the above approach for determining the available sub-channels needs low processing resources. ) The first and second thresholds may be identical, but this is not mandatory.
As an example, the thresholds may equal few, tenths or hundredths of nanoseconds (ns) because the sensing (e.g. CCA) sensitivity of the 802.11 nodes has the same error tolerance for each sub-channel and thus there should be little or no drift in status change detection among the various sub-channels. For instance, the thresholds j are substantially less than the aCCATime defined in 802.11ac as being the “maximum time (in microseconds) that the CCA mechanism has available to detect the start of a valid IEEE 802.11 transmission within the primary channel and to assess the energy on the medium within the primary, secondary, secondary40 ... channels”, e.g. substantially less than 1 microsecond. j According to another specific feature, the step of sensing a change of the idle/busy status of each sub-channel includes comparing a signal energy level in the primary or secondary sub-channel to a predefined threshold.
For instance, the step of sensing a change of the idle/busy status of the primary or secondary sub-channel includes performing a Clear Channel Assessment ) (CCA). CCA is a WLAN carrier sense mechanisms defined in the IEEE 802.11-2007 standards as part of the Physical Medium Dependant (PMD) and Physical Layer Convergence Protocol (PLCP) layer. It involves two functions:
Carrier Sense (CCA-CS) which is the ability of the receiving node to detect j and decode an 802.11 frame preamble. From the PLCP header field, the time duration for which the medium will be occupied can be inferred and when such 802.11 frame preamble is detected, the CCA flag is held busy until the end of data transmission.
Energy Detect (CCA-ED) which is the ability of the receiving node to detect non-802.11 energy in the channel and back off data transmission. The ED threshold is ) for instance defined to be 20dB above the minimum sensitivity of the PHY layer of the node. If the in-band signal energy crosses this threshold, CCA is held busy until the medium energy becomes below the threshold anew.
In embodiments, all the secondary sub-channels on which no duplicated acknowledgment frame is received are discarded from the composite channel. This j provision is to optimize the composite channel, in order to minimize any future risk of collision or interference.
In embodiments, the wireless network is defined by an operating band made of an ordered succession of sub-channels, and the composite channel is made of subchannels that are contiguous within the operating band. ) The operating band may correspond to the band defined by the operating mode of the wireless network. In the example of an 802.11ac or the like operating mode, the operating band may be an 80MHz band or a 160MHz band (made of two frequency contiguous or non-contiguous 80MHz sub-bands). Conventionally the operating band is made of successive sub-channels ordered according to their carrier frequencies. It means that the sub-channels of an operating mode are not necessary all frequency contiguous (for instance in the case of the 80+80MHz bandwidth).
According to the above provision, the modulation band or composite channel used to transmit data is made of sub-channels contiguous within the operating band, j therefore complying with 802.11 ac/ax standards.
In a variant, the composite channel may be made of sub-channels that are not contiguous within the operating band. This configuration provides better usage of network bandwidth since the maximum number of available sub-channels is used, contrary to the 802.11ac fallback mechanism. ) Another aspect of the invention relates to a non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a device for wireless communication over a composite channel in a wireless network, the composite channel being made of a primary sub-channel and of one or more secondary sub-channels, causes the device to perform any method as defined j above.
The non-transitory computer-readable medium may have features and advantages that are analogous to those set out above and below in relation to the methods and node devices.
At least parts of the methods according to the invention may be computer ) implemented. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit", "module" or "system". Furthermore, the present invention may take the form of a computer program product j embodied in any tangible medium of expression having computer usable program code embodied in the medium.
Since the present invention can be implemented in software, the present invention can be embodied as computer readable code for provision to a programmable apparatus on any suitable carrier medium. A tangible carrier medium may comprise a ) storage medium such as a hard disk drive, a magnetic tape device or a solid state memory device and the like. A transient carrier medium may include a signal such as an electrical signal, an electronic signal, an optical signal, an acoustic signal, a magnetic signal or an electromagnetic signal, e.g. a microwave or RF signal.
> BRIEF DESCRIPTION OF THE DRAWINGS
Further advantages of the present invention will become apparent to those skilled in the art upon examination of the drawings and detailed description. Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings. j Figure 1 illustrates a typical wireless communication system in which embodiments of the invention may be implemented;
Figure 2 is a timeline schematically illustrating a conventional communication mechanism according to the IEEE 802.11 standard;
Figure 3a illustrates 802.11ac channel allocation that support channel ) bandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz as known in the art;
Figure 3b illustrates an example of 802.11ac multichannel station using a transmission opportunity on an 80 MHz channel as known in the art;
Figure 4 shows a conceptual diagram illustrating a broadband channel usage mechanism employing an 80MHz channel bandwidth as known in the art; j Figure 5 illustrates three examples of dynamic fallback to narrower channel widths in the presence of co-channel interference or noise that only affects a portion of the larger channel;
Figure 6 shows a schematic representation a communication device or station in accordance with embodiments of the present invention; ) Figure 7 shows a schematic representation of a wireless communication device in accordance with embodiments of the present invention;
Figures 8a, 8b, 8c show several schematic representation of acknowledgement packet generation, wherein Figures 8a and 8b illustrate conventional schemes and Figure 8c illustrates an enhanced scheme according to embodiments of j the invention;
Figures 9a and 9b illustrate enhanced wireless communication method according to embodiments of the invention, respectively from the source node’s perspective and from the receiving node’s perspective;
Figures 10a, 10b and 10c illustrate the process of Figure 9b with more ) details according to embodiments of the invention;
Figure 11 illustrates embodiments of some steps of Figure 9b with more details according to embodiments of the invention;
Figure 12 illustrates, using two flowcharts, general steps of an enhanced detecting or sensing method used to detect duplicated acknowledge frames on secondary sub-channels during the method of Figure 9a, according to embodiments of the invention; and
Figure 13 illustrates the profile matching used in the detecting or sensing method of Figure 12.
DETAILED DESCRIPTION
The invention will now be described by means of specific non-limiting exemplary embodiments and by reference to the figures.
Figure 1 illustrates a communication system in which several communication ) nodes exchange data frames over a radio transmission channel 100 of a wireless local area network (WLAN).The radio transmission channel 100 is defined by an operating band, for instance with a bandwidth available for the communication nodes.
Access to the shared radio medium to send data frames is based on the CSMA/CA technique, for sensing the carrier and avoiding collision by separating j concurrent transmissions in space and time.
Carrier sensing in CSMA/CA is performed by both physical and virtual mechanisms. Virtual carrier sensing is achieved by transmitting control frames to reserve the medium prior to transmission of data frames.
Next, a transmitting or source node first attempts through the physical ) mechanism, to sense a medium that has been idle for at least one DIFS (standing for DCF InterFrame Spacing) time period, before transmitting data frames.
However, if it is sensed that the shared radio medium is busy during the DI FS period, the source node continues to wait until the radio medium becomes idle. To do so, it starts a countdown backoff counter designed to expire after a number of timeslots, j chosen randomly between [0, CW], CW (integer) being referred to as the Contention Window. This backoff mechanism or procedure is the basis of the collision avoidance mechanism that defers the transmission time for a random interval, thus reducing the probability of collisions on the shared channel. After the backoff time period, the source node may send data or control frames if the medium is idle. ) One problem of wireless data communications is that it is not possible for the source node to listen while sending, thus preventing the source node from detecting data corruption due to channel fading or interference or collision phenomena. A source node remains unaware of the corruption of the data frames sent and continues to transmit the frames unnecessarily, thus wasting access time.
The Collision Avoidance mechanism of CSMA/CA thus provides positive acknowledgement (ACK) of the sent data frames by the receiving node if the frames are received with success, to notify the source node that no corruption of the sent data frames occurred. j The ACK is transmitted at the end of reception of the data frame, immediately after a period of time called Short InterFrame Space (SIFS).
If the source node does not receive the ACK within a specified ACK timeout or detects the transmission of a different frame on the channel, it may infer data frame loss. In that case, it generally reschedules the frame transmission according to the ) above-mentioned backoff procedure. Even if this can be seen as a bandwidth waste if only the ACK has been corrupted but the data frames were correctly received by the receiving node, this basic mechanism is well fitted for small frames that are quite common in usual traffic.
Figure 2 illustrates the behaviour of three groups of nodes during a j conventional communication over a 20 MHz channel of the 802.11 medium: transmitting or source node 20, receiving or addressee or destination node 21 and other nodes 22 not involved in the current communication.
Upon starting the backoff process 270 prior to transmitting data, a station e.g. source node 20, initializes its backoff time counter to a random value as explained ) above. The backoff time counter is decremented once every time slot interval 260 for as long as the radio medium is sensed idle (countdown starts from TO, 23 as shown in the
Figure).
The time unit in the 802.11 standard is the slot time called ‘aSlotTime’ parameter. This parameter is specified by the PHY (physical) layer (for example, j aSlotTime is equal to 9ps for the 802.11 n standard). All dedicated space durations (e.g. backoff) add multiples of this time unit to the SIFS value.
The backoff time counter is ‘frozen’ or suspended when a transmission is detected on the radio medium channel (countdown is stopped at T1, 24 for other nodes 22 having their backoff time counter decremented). ) The countdown of the backoff time counter is resumed or reactivated when the radio medium is sensed idle anew, after a DIFS time period. This is the case for the other nodes at T2, 25 as soon as the transmission opportunity (transmission 230 of data and reception of acknowledgment 240) used by source node 20 ends and the DIFS period 28 elapses. DIFS 28 (DCF inter-frame space) thus defines the minimum waiting time for a source node before trying to transmit some data. In practice, DIFS = SIFS + 2 * aSlotTime.
When the backoff time counter reaches zero (26) at T1, the timer expires, the corresponding node 20 starts sending data (230) on the medium using a data frame, j and the backoff time counter is reinitialized using a new random backoff value.
An ACK frame 240 is sent by the receiving node 21 after having correctly received the data frame sent, after a SIFS time period 27.
If the source node 20 does not receive the ACK 240 within a specified ACK Timeout (generally within the maximum value for a transmission opportunity TXOP), or ) if it detects the transmission of a different frame on the radio medium, it reschedules the frame transmission using the backoff procedure anew.
Since the DIFS value is higher than the SIFS value, other nodes 22 cannot decrement their backoff counter between the data transmission 230 and the corresponding ACK transmission 240. As a consequence, access to the radio medium j for the other nodes 22 is consequently deferred (the medium is seen as busy 290) until the next backoff countdown period starts at T2.
This prevents the listening nodes 22 from transmitting any data during period 230-240.
As described above, the original IEEE 802.11 MAC always sends an ) acknowledgement (ACK) frame 240 after each data frame 230 received.
The 802.11 backoff procedure was first introduced for the DCF mode as the basic solution for collision avoidance, and further employed by the IEEE 802.11e standard to solve the problem of internal collisions between enhanced distributed channel access functions (EDCAFs). In the emerging IEEE 802.11n/ac/ax standards, j the backoff procedure is still used as the fundamental approach for supporting distributed access among mobile stations or nodes.
The rapid growth of smart mobile devices is driving mobile data usage and 802.11 WLAN proliferation, creating an ever-increasing demand for faster wireless networks to support bandwidth-intensive applications, such as web browsing and video ) streaming. The new IEEE 802.11ac standard is designed to meet this demand, by providing major performance improvements over previous 802.11 generations.
The IEEE 802.11ac standard is an emerging very high throughput (VHT) wireless local access network (WLAN) standard that can achieve physical layer (PHY) data rates of up to 7 Gbps for the 5 GHz band.
The scope of 802.11ac includes single link throughput supporting at least 500 Mbps, multiple-station throughput of at least 1 Gbps and backward compatibility and coexistence with legacy 802.11 devices in the 5 GHz band.
Consequently, this standard is targeted at higher data rate services such as j high-definition television, wireless display (high-definition multimedia interface - HDMI -replacement), wireless docking (wireless connection with peripherals), and rapid sync- and-go (quick upload/download).
In general, 802.11ac could be schematized as an extension of IEEE 802.11η in which the two basic notions of multiple-input, multiple-output (ΜΙΜΟ) and wider ) channel bandwidth are enhanced for greater efficiency.
Using the optional ΜΙΜΟ feature, an access point AP (having multiple antennae) may communicate with several nodes simultaneously using Spatial Division Multiple Access (SDMA). An SDMA multiple access scheme enables multiple streams to be transmitted to different receiving nodes at the same time, resulting in a sharing of j the same frequency channel. However it requires several antennas.
Contrary to 802.11η in which each communication node should support up to two spatial streams (SSs) and an operating band of 40 MHz bandwidth, only one spatial stream (and thus only one antenna par device) is required in 802.11ac or 802.11ax, while operating bands of 80MHz or 160MHz bandwidth are allowed. In ) 802.11ac or 802.11ax, the single antenna of the node is able to modulate on or demodulate from such 80MHz or 160MHz band, referred to as modulation band in the description below.
One reason for such a change in the new versions of 802.11 is that increasing the number of antennas often results in higher costs. Indeed, supporting j multiple Spatial Streams (SS) has been considered as requiring at least the same number of antennas (and as much reception chains behind these antennas), thus important costs. Consequently, a majority of 802.11η devices available on the market could only support a single SS.
In 802.11ac, support for only one SS is required so that devices, and ) especially smartphones, could be labelled as ‘802.11ac compliant’. The operating mode with an 80 MHz operating band is made mandatory as a lower cost alternative to the two SS and 40 MHz operating band. Hence, the operating modes that utilize more than one spatial stream are now become optional in 802.11ac.
As a result, 802.11ac is targeting larger bandwidth transmission through j multi-channel operations, meaning that the single antenna of the nodes modulates on or demodulates from a modulation band that can be made of one or more 20MHz channels, for instance 40MHz or 80MHz or even 160MHz. The wider channel aspect is further described in reference to Figures 3 and Figure 4.
In order to support wider channel bandwidths within the operating band, the j operating band in 802.11ac is made of an ordered succession (or series) of sub-channels 300-1 to 300-8 as shown for instance in Figure 3a. IEEE 802.11ac introduces support of a restricted number of predefined subsets of these sub-channels to form the sole predefined composite channel configurations that are available for reservation by any 802.11ac node on the wireless network to transmit data. ) The predefined subsets are shown in Figure 3a and correspond to 20 MHz, 40 MHz, 80 MHz, and 160 MHz channel bandwidths including the so-called “primary” sub-channel (here 300-3), compared to only 20 MHz and 40 MHz supported by 802.11η. Indeed, the 20 MHz component channels (or sub-channels) 300-1 to 300-8 are concatenated to form wider communication composite channels. j In the 802.11ac standard, the sub-channels of each predefined 40MHz, 80MHz or 160MHz subset are contiguous within the operating band, i.e. no hole (i.e. missing sub-channel) within the sub-channels as ordered in the operating band is allowed, and are defined with respect to the primary sub-channel.
The 160 MHz channel bandwidth is composed of two 80 MHz channels that ) may or may not be frequency contiguous. The 80 MHz and 40 MHz channels are respectively composed of two frequency adjacent or contiguous 40 MHz and 20 MHz channels, respectively. The support of 40 MHz and 80 MHz channel bandwidths is mandatory while the support of 160 MHz and 80 + 80 MHz is made optional in the standard (80+80 MHz means that the operating band is made of two non-frequency- j contiguous wide channels having each a bandwidth of 80 MHz). A multi-channel communication node (accessing an 80 MHz operating band in the illustrated example of Figure 3b) is granted a TxOP through the enhanced distributed channel access (EDCA) mechanism on the “primary sub-channel” (300-3). Indeed, for each channel bandwidth, 802.11ac designates one sub-channel as “primary,” ) meaning that it is used for control of transmission on that bandwidth.
It shall, however, transmit an 80 MHz PPDU (PPDU means PLCP Protocol
Data Unit, with PLCP for Physical Layer Convergence Procedure; basically a PPDU refers to an 802.11 physical frame) only if all other secondary channels have been idle for at least a point coordination function (PCF) inter-frame spacing (PIFS). If at least one j of the secondary sub-channels has not been sensed as idle for a PIFS, then the node must either restart its backoff count, or use the obtained TxOP for 40 MHz or 20 MHz PPDUs (i.e. on 40 MHz or 20 MHz composite channel).
Figure 4 gives a description of the CCA process for an 80Mhz composite channel. During the CCA, all the sub-channels that should be used in the aggregated j composite channel are sensed (the signal and energy levels are evaluated, and a subchannel is considered as idle if the energy level measured on the sub-channel is lower than the CCA threshold of -62dBm and the signal is lower than -82dBm on the primary channel, and -72dBm on the secondary channels).
If all secondary sub-channels have been idle for at least a point coordination ) function (PCF) inter-frame spacing (PIFS), with PIFS = SIFS + aSlotTime, then the secondary channels can also be used. If at least one of the secondary channels has not been idle for a PIFS, then the node must either restart its backoff count, or use the current
TxOP for 40 MHz or 20 MHz PPDUs.
The vertical aggregation scheme of Figure 3b reflects the extension of the j payload 230 to all sub-channels forming the 80MHz composite channel used. If there is only one collision in one of the sub-channels at a given time, the risks of having a corrupted segment of these sequences are very high despite the error-correcting decoding process. All MPDU (MAC Protocol Data Unit) frames inside the PPDU could thus automatically be considered as incorrect. ) In the description below, the words “channel", “20 MHz channel" or “sub channel" mainly refer to the same technical feature, i.e. any channel that complies with 802.11η or older standards. “Composite channel" thus refers to the additional feature according to which a composite channel is made of one or more sub-channels of the operating band of the wireless network. In 802.11ac, the composite channels are 20MHz j wide (if made of only one sub-channel) or 40MHz wide or 80MHz wide or, optionally, 160MHz wide.
Further, Figure 4 gives a description of the CCA process allowing the usage of wide bandwidth. During the backoff countdown period 260, source node STA1 20 senses all the sub-channels forming a wider bandwidth, i.e. a composite channel. When ) the backoff counter reaches 0 (26-1), if the secondary sub-channel have been idle for at least a PIFS period, they are considered idle and can be aggregated and used to modulate data 230-1 on a wider composite channel (in the example of the left-side part of the Figure, an 80Mhz composite channel).
If during the PIFS period, the secondary sub-channel is not idle (for instance j as in the right-side part of the Figure where the backoff counter of source node STA1 20 reaches zero at 26-2), source node STA1 can decide to either restart its backoff counter, or try to use a 40Mhz composite channel and send data 230-2 on this 40Mhz composite channel (using a longer airtime).
The ability of the 802.11ac nodes to fall back to lower bandwidth modes, and j thus to narrower modulation band for transmission, in case not all the targeted bandwidth is available is known as a fallback mechanism.
As addressed above, the IEEE 802.11ac standard enables up to four, or even eight, 20 MHz sub-channels to be bound. Because of the limited number of channels (19 in the 5 GHz band in Europe), channel saturation becomes problematic. ) Indeed, in densely populated areas, the 5 GHz band will surely tend to saturate even with a 20 or 40 MHz bandwidth usage per Wireless-LAN cell.
As a result, the fallback mechanism currently provided in the 802.11ac standard is too limitative. For instance, channel interferences will occur more often: contrary to the example of Figure 4, the fallback mechanism currently provided in the j 802.11ac standard will suffer from misleading detection of channel occupation, as further shown in regards to Figure 5.
Channel interference (Figure 5) is typically caused by a legacy 802.11a or 802.11η node transmitting on a 20 MHz channel. Indeed, the 802.11ac node may transmit over a fraction of the original desired bandwidth: depending of which 20Mhz ) channels (300) are busy, the channel width of resulting composite channel is reduced from 80MHz to a predefined channel width of the 802.11ac channel bonding scheme, namely to 40MHz (cases 510 and 511) or to 20Mhz (case 520), whereas a 60Mhz (i.e. additional 20MHz or40MHz respectively) bandwidth is potentially available.
One can note the 802.11ac standard has not envisaged using such lost j bandwidth, as the VHT preamble in the 802.11 ac frames embeds a bandwidth indication only supporting predefined channel widths and thus predefined modulation bands, namely 20, 40, 80 or 160 Mhz.
This bandwidth allocation deficiency can be especially problematic with personal devices on which a central organization has little or even no control to select ) the wireless channels of the 5GHz or the like band. This is ascertained in distributed environments, which are by essence not managed at all.
However, the 802.11 ax task group has raised the benefit of using all available sub-channels of the operating band to form a composite channel, even if some are non-contiguous within the operating band.
In the 802.11ac standard, the source node determines by itself the bandwidth to use, using channel sensing at its side only.
This approach is not satisfactory because the choice of the bandwidth does not take into account the channel quality at the receiving side, which may evolve over j time, e.g. during current data transmissions. For instance legacy hidden nodes around the receiving node cannot be detected by the source node and can thus interfere with any communication between the source node and the receiving node.
As no acknowledgment of the data is received by the source node, the latter may then decrease the bandwidth used or modify its modulation to obtain a better ) reception quality at the receiving node. However, the global throughput is highly decreased.
To slightly improve the situation, the 802.11ac standard defines dedicated messages called “Measurement Report Element’ that can be requested by the source node by sending a “Measurement Request element’. j The mechanism based on these measurement request/report messages has drawbacks. First, it is bandwidth consuming since messages are requested. Second, it adds delay between the time at which the measurement is wished and the time at which the measurement is made, due to the need of sending a request and of processing it by the receiving node. Third, it does not allow reacting efficiently on the modifications of the ) reception quality.
The present invention finds a particular application in enhancements of the 802.11ac standard, and more precisely in the context of 802.11 ax wherein dense wireless environments are more ascertained to suffer from previous limitations.
The present invention provides enhanced channel feedback mechanisms to j provide evaluation of reception quality by the receiving node. Such evaluation may be used by the source node to efficiently adjust the composite channel to be used for future communication. Thus, the enhanced channel feedback mechanisms contribute to enhanced wireless communication methods between a source node and a receiving node over a composite channel in a wireless network, the composite channel being made ) of a primary sub-channel and of one or more (usually more) secondary sub-channels.
An exemplary ad-hoc wireless network is an IEEE 802.11ac network (and upper versions). However, the invention applies to any wireless network in which a source node 101-107 sends data of a data stream to a receiving node 101-107 using a composite channel. The invention is especially suitable for data transmission in an IEEE 802.11ax network (and future versions) requiring more flexibility in the bandwidth management.
The behaviour of communication nodes during a conventional communication over an 802.11 medium has been recalled above with reference to j Figures 1 to 5.
From the receiving node’s perspective, a wireless communication method includes: receiving, from the source node, a signal modulated on the whole composite channel, the modulated signal encoding one or more data frames; ) applying a decoding process on the modulated signal; generating an acknowledgment frame to acknowledge correct or erroneous reception of the one or more data frames; sending the acknowledgment frame to the source node on the primary sub channel. j From the receiving node’s perspective, a wireless communication method includes: transmitting, to the receiving node, a signal modulated on the whole composite channel, the modulated signal encoding one or more data frames; receiving, from the receiving node in response to the transmitted signal, at ) least one acknowledgment frame on the primary sub-channel and possibly a duplicated acknowledgment frame on a respective secondary sub-channel.
One aspect of embodiments of the present invention provides, from the receiving node’s perspective, the additional steps of: determining a channel quality for one or more of the secondary sub-j channels; and sending a duplicate of the acknowledgment frame to the source node only on each secondary sub-channel of a subset of the secondary sub-channels that excludes at least one secondary sub-channel having a low determined channel quality.
This approach uses the duplication of control frames, for instance 802.11 ) ACK frames, in a clever way to make it possible to provide channel feedback without delay and additional messages.
This is achieved by providing, in response to received frames, such control frames only on secondary sub-channels for which a measured reception quality is for instance satisfactory.
This is made possible because the duplicates of the control frames are not mandatory on the secondary sub-channels for the source node and the receiving node to signal the TXOP.
Thanks to the duplicate of the acknowledgment frame on some sub-channels j only, the source node is quickly informed on which secondary sub-channel or sub channels have low reception quality.
Aspects of the present invention thus provide, from the source node’s perspective, the step of modifying the composite channel for future transmission, by discarding (i.e. excluding) at least one secondary sub-channel of the composite channel ) on which no duplicated acknowledgment frame is received.
In other words, the source node can adjust, if necessary, the composite channel to be used for future communication by removing or discarding low-reception-quality sub-channel or sub-channels as sensed by the absence of acknowledgment frame on those sub-channels. j Figure 6 schematically illustrates a communication device 600 of the radio network 100, configured to implement at least one embodiment of the present invention. The communication device 600 may preferably be a device such as a micro-computer, a workstation or a light portable device. The communication device 600 comprises a communication bus 613 to which there are preferably connected: ) · a central processing unit 611, such as a microprocessor, denoted CPU; • a read only memory 607, denoted ROM, for storing computer programs for implementing the invention; • a random access memory 612, denoted RAM, for storing the executable code of methods according to embodiments of the invention as well as the registers j adapted to record variables and parameters necessary for implementing methods according to embodiments of the invention; and • at least one communication interface 602 connected to the radio communication network 100 over which digital data packets or frames are transmitted, for example a wireless communication network according to the 802.11ac protocol. ) The data frames are written from a FIFO sending memory in RAM 612 to the network interface for transmission or are read from the network interface for reception and writing into a FIFO receiving memory in RAM 612 under the control of a software application running in the CPU 611.
Optionally, the communication device 600 may also include the following j components: • a data storage means 604 such as a hard disk, for storing computer programs for implementing methods according to one or more embodiments of the invention; • a disk drive 605 for a disk 606, the disk drive being adapted to read data from the j disk 606 or to write data onto said disk; • a screen 609 for displaying decoded data and/or serving as a graphical interface with the user, by means of a keyboard 610 or any other pointing means.
The communication device 600 may be optionally connected to various peripherals, such as for example a digital camera 608, each being connected to an ) input/output card (not shown) so as to supply data to the communication device 600.
Preferably the communication bus provides communication and interoperability between the various elements included in the communication device 600 or connected to it. The representation of the bus is not limiting and in particular the central processing unit is operable to communicate instructions to any element of the j communication device 600 directly or by means of another element of the communication device 600.
The disk 606 may optionally be replaced by any information medium such as for example a USB key or a memory card and, in general terms, by an information storage means that can be read by a microcomputer or by a microprocessor, integrated ) or not into the apparatus, possibly removable and adapted to store one or more programs whose execution enables a method according to the invention to be implemented.
The executable code may optionally be stored either in read only memory 607, on the hard disk 604 or on a removable digital medium such as for example a disk 606 as described previously. According to an optional variant, the executable code of j the programs can be received by means of the communication network 603, via the interface 602, in order to be stored in one of the storage means of the communication device 600, such as the hard disk 604, before being executed.
The central processing unit 611 is preferably adapted to control and direct the execution of the instructions or portions of software code of the program or programs ) according to the invention, which instructions are stored in one of the aforementioned storage means. On powering up, the program or programs that are stored in a nonvolatile memory, for example on the hard disk 604 or in the read only memory 607, are transferred into the random access memory 612, which then contains the executable code of the program or programs, as well as registers for storing the variables and j parameters necessary for implementing the invention.
In a preferred embodiment, the apparatus is a programmable apparatus which uses software to implement the invention. However, alternatively, the present invention may be implemented in hardware (for example, in the form of an Application Specific Integrated Circuit or ASIC). j To provide or use the enhancement channel quality feedback as introduced above, the communication nodes include specific functionalities.
Figure 7 is a block diagram schematically illustrating the architecture of a communication device also called node (or station) 600 adapted to carry out, at least partially, the invention. As illustrated, node 600 comprises a physical (PHY) layer block ) 703, a MAC layer block 702, and an application layer block 701. Between PHY block 703 and MAC block 702, node 600 comprises block 706 containing the interface functions (also known as primitives) allowing the communication of data and parameters between the MAC and PHY layers.
The PHY layer block 703 (here an 802.11 standardized PHY layer) has the j task of formatting, modulating on or demodulating from any 20MHz sub-channel or the composite channel, and thus sending or receiving frames over the radio medium used 100, such as 802.11 data frames (over the composite channel) or 802.11 acknowledgment frames (over a 20MHz sub-channel).
The PHY layer block 703 optionally includes CCA capability to sense the idle ) or busy state of sub-channels and to report the result to the MAC 702 according to 802.11 standard. Upon detecting a PLCP preamble of a received frame, the PHY layer block 703 generates and transmits a PHY_CCA.indication primitive to the MAC layer block 702. This primitive shall be issued for reception of a signal with significant received signal strength (for the primary channel, it is typically issued prior to correct reception of the j PLCP preamble of an 802.11 frame).
Next after having demodulating and Viterbi-decoded a frame header, it generates and transmits another primitive, namely the PHY_RXSTART.indication primitive, to the MAC layer block 702.
In more details, every frame transmission begins with a PLCP training ) sequence broadcast on the shared channel(s). The PHY layer block 703 generates a PHY-RXSTART.indication when it has successfully validated the PLCP header error check CRC at the start of a new PLCP frame.
The RXVECTOR associated with this primitive represents a list of parameters that the PHY layer provides the local MAC layer upon receipt of a valid PLCP j header or upon receipt of the last PSDU data bit in the received frame. This vector contains both MAC and MAC management parameters. It includes the SIGNAL field, the SERVICE field, the MAC Protocol Data Units (MPDU) length in bytes (calculated from the LENGTH field in microseconds), the antenna used for receive (RX_ANTENNA), the received signal strength indicator (RSSI) and signal quality. j The MAC layer block or controller 702 preferably comprises a MAC 802.11 layer 704 implementing conventional 802.11 MAC operations, and an additional block 705 for carrying out, at least partially, the invention. The MAC layer block 702 may optionally be implemented in software, which software is loaded into RAM 612 and executed by CPU 611. ) Preferably, the additional block, referred to as the measurement feedback module 705, implements the part of the invention that regards node 600, i.e. feedback generation for a receiving node, feedback use for a source node invention. These feedback capabilities relate to handling the dedicated acknowledgment packet generation or analysis. j From receiving node’s perspective, measurement feedback module 705 obtains a channel quality measurement for the secondary sub-channels; forming the composite channel currently used, and drives the sending of duplicates of the ACK frame to appropriate secondary sub-channels to provide the signalling as mentioned above.
From source node’s perspective, measurement feedback module 705 ) determines on which secondary sub-channels, a duplicated ACK frame is received, in order to drive any modification of the composite channel to be used for future transmission, by discarding (i.e. excluding) appropriate secondary sub-channel or subchannels.
On top of the Figure, application layer block 701 runs an application that j generates and receives data packets, for example data packets of a video stream. Application layer block 701 represents all the stack layers above MAC layer according to ISO standardization.
Figures 8a, 8b, 8c show several schematic representations of acknowledgement packet generation. ) Figures 8a and 8b illustrate conventional schemes.
Source node STA1 (accessing an 80 MHz operating band in the illustrated example of Figure 3b) is granted a TxOP through the enhanced distributed channel access (EDCA) mechanism on the “primary sub-channel” (300-3) as described above with reference to Figure 2. Indeed, for each channel bandwidth, 802.11ac designates one sub-channel as “primary,” meaning that it is used for control of transmission on that bandwidth.
To do so, source node STA1 initiates a backoff mechanism 810 on the primary sub-channel while (during a PIFS time 811 before the end of the backoff j mechanism) the secondary sub-channels are sensed as idle. Next, source node STA1 is able to transmit 80MHz PPDUs (PHY Protocol Data Unit - data frames) 812 during the obtained TxOP, by modulating the data on the whole granted 80MHz composite channel (as illustrated by the vertical aggregation scheme, reflecting the extension of the payload 230 to all sub-channels). ) Note that if only one collision occurs in one of the sub-channels during the data transmission, the risks of having a corrupted segment of the data are very high despite the error-correcting decoding process. In case of data corruption, all MPDU (MAC Protocol Data Unit) frames inside the PPDU are automatically considered as incorrect and rejected. j Upon receiving the 80MHz PPDUs, receiving node STA2 has to acknowledge the received 80MHz PPDUs. According to the 802.11ac standard, a corresponding ACK packet or frame is built and transmitted. Two transmission schemes to transmit the ACK frame exist: - a non-HT duplicate scheme, in which the ACK packet or frame is modulated ) on a 20MHz channel and is sent in the primary 20MHz sub-channel and duplicated for sending on each secondary 20MHz sub-channel (813 - Figure 8a). - a non-HT scheme, in which the ACK packet or frame is modulated on a 20MHz channel and is sent in the primary 20MHz sub-channel only (823 - Figure 8b).
To handle the reception of the non-HT and non-HT duplicate frames, the j PHY layer (703) of the source node STA1 notifies the MAC layer (702) using a PHY-CCA.indication related to a frame reception. Afterwards a PHY-RXSTART.indication primitive is generated when the PHY layer (703) has successfully validated the PLCP header error check CRC at the start of a new PLCP frame. This primitive includes RXVECTOR parameters enabling the format of the received frame to be identified. ) Figure 8c illustrates an enhanced scheme according to the invention, wherein channel quality feedback is provided based on the non-HT duplicate scheme described above.
In this illustration, before generating the ACK packet, the MAC layer of the receiving node STA2 retrieves an evaluation of reception quality over each secondary j sub-channel from the PHY layer.
The reception quality can be an SNR value (Signal-To-Noise Ratio) retrieved through additional parameters of the RXVECTOR. The reception quality can be any other metrics mirroring the reception quality over each sub-channel.
Next, if this retrieved reception quality for a secondary sub-channel is lower j than a predefined threshold, receiving node STA2 notifies source node STA1 that transmission conditions are really bad on this identified secondary sub-channel.
The threshold value depends on the modulation and coding rate used for the frame transmission. For instance, the 802.11 standard defines the MCSO code when a BPSK modulation and a % coding rate are used for frame transmission. In that exemplary ) case, the predefined SNR threshold may be 7dB, corresponding to a packet error rate of 1%.
The bad-transmission-condition signaling is performed by duplicating the generated ACK frame only on the secondary sub-channels for which the retrieved reception quality is greater than the predefined threshold (834). Correspondingly, no j duplicate of the generated ACK frame is sent on the secondary sub-channels for which the retrieved reception quality is lower than the predefined threshold (833).
By detecting on which secondary sub-channels a duplicated ACK frame is received (and thus on which secondary sub-channels no duplicated ACK frame is received), source node STA1 is now aware of which secondary sub-channels have poor ) or the lowest transmission conditions. In response, source node STA1 may implement communication policy in which the composite channel to be used is reduced by removing one or more secondary sub-channels having poor or the lowest transmission conditions.
Figures 9a and 9b illustrate enhanced wireless communication method according to embodiments of the invention, respectively from the source node’s j perspective and from the receiving node’s perspective.
At the source node, the method starts at step 910 in which the source node publishes the acknowledgement mode that is to be used during the coming communication, i.e. the acknowledgement mode to be used by the receiving node upon receiving data frame or frames. ) The publication of the acknowledgement modes used by a node can be made during the association of the node with the 802.11 wireless network. Indeed, as defined in the 802.11 standard, a node transmits all its functionality during its association with the network.
Two acknowledgement modes are proposed in this example: • a first mode “mode 1” which is based on the conventional acknowledgment mode in which any ACK frame (in non-HT duplicate format) actually acknowledges (positive acknowledgment) the associated received data frame. When a data frame is erroneously received, no ACK frame is sent by the receiving node, and j the source node decides to retransmit the already-sent data frame when an associated timeout elapses; • a second mode “mode 2” in which the ACK frame is interpreted as a positive acknowledgment only if it (including its duplicates) is received over all subchannels forming the composite channel. On the other hand, the ACK frame is ) considered as being a negative acknowledgment if one of its duplicates is missing on at least one of the secondary sub-channels of the composite channel.
Another way to acknowledge data frames in the 802.11 standard is to use the Block Ack (BA) frame. An ACK frame acknowledges only one data frame, while a BA frame acknowledges a set of data frames. Since the BA frame indicates (for instance j through a bitmap) the reception status (correct/erroneous) of each data frame of the considered set of data frames, there is no need to discriminate two behaviors as for the two modes above. For BA mode, mode 1 above without timeout (and no ACK frame behavior) can be used.
Next to step 910, the source node transmits one data frame or more data ) frames (in case of BA mode) by modulating them on the whole composite channel made of multiple sub-channels (including the primary sub-channel). This is step 911.
The remainder of the Figure depends on the reception of the ACK frames sent by the receiving node. It is described below after the method performed at the receiving node, which is now described with reference to Figure 9b. j At the receiving node, the method starts at step 920 in which the receiving node received a modulated signal encoding the one or more data frames sent by the source node at step 911. The signal received on the whole composite channel is demodulated and the receiving node tries to decode it to obtain the data frames (step 921). ) At step 922, an ACK frame is generated with a view to positively or negatively acknowledge the receipt of the data frame or frames.
Next, at step 923, the MAC layer retrieves the channel reception quality for each secondary sub-channel of the composite channel used, from the PHY layer.
As mentioned above, the channel reception quality can be a SNR value j (Signal-To-Noise Ratio) retrieved through additional parameters of the RXVECTOR. In that case, the channel reception quality for a secondary sub-channel comprises evaluating a quality of signal reception on the secondary sub-channel using the received modulated signal.
At step 924, if the acknowledgment mode requires the ACK frame to be sent, j the ACK frame and the duplicate or duplicates thereof are transmitted to the source node only over the primary sub-channel and the secondary sub-channels of the composite channel for which the obtained reception quality is above a predetermined threshold. More generally, the duplicate or duplicates are sent only on each secondary sub-channel of a subset of the secondary sub-channels that excludes at least one secondary sub-) channel having a low determined channel quality, for instance the lowest-quality secondary sub-channel.
This mechanism allows the secondary sub-channels with a bad reception quality to be signaled with no overhead.
In addition, the transmission also remains fully compliant with the 802.11ac j standard because the ACK frame is transmitted over the primary sub-channel.
Figures 10a, 10b and 10c illustrate the process of Figure 9b with more details, in particular by discriminating among the acknowledgment modes.
Figure 10a illustrates the mode 1 in which any ACK frame (in non-HT duplicate format) actually acknowledges (positive acknowledgment) the associated ) received data frame.
Upon receiving one data frame modulated over a composite channel made of a primary sub-channel and of secondary sub-channels and upon applying a decoding process to it (step 1010), a channel reception quality is obtained for each sub-channel of the composite channel (optimally for each secondary sub-channel only). This is step > 1011.
The channel reception quality is retrieved from the PHY layer where values representative of such quality are evaluated. Details of such step have been provided above for step 923. Note that the evaluation of the channel reception quality may be made for the time being since the last acknowledgment frame has been sent (for instance ) the MAC layer may calculate a means value of SNR values received from the PHY layer since the last acknowledgment frame has been sent).
Next, step 1012 consists to check whether or not the data frame has been correctly received (including the decoding thereof).
In case an erroneous reception/decoding of the data frame is detected, the j receiving node does not acknowledge reception of the data frame to the source node, to drive the latter to resend the data frame upon expiry of a timeout. In other words, no acknowledgment frame and duplicate thereof are transmitted in case of erroneous reception of data frames.
In case the data frame has been correctly received and decoded, the j receiving node determines, at step 1013, the secondary sub-channels of the composite channel having good reception quality. For instance, those sub-channels are the secondary sub-channels for which the channel reception quality retrieved at step 1011 is higher than a predefined quality threshold. The result of this step forms a subset of secondary sub-channels that excludes at least one low quality sub-channel. ) In a variant, the one or more secondary sub-channels having the lowest channel reception quality may be discarded to keep a subset of secondary sub-channels that excludes at least one low quality sub-channel.
Next, an ACK frame is built using the non-HT duplicate format, meaning that a main ACK frame is generated and duplicate or duplicates thereof (if any) are also j generated (step 1014). It means that the sending of the acknowledgment frame and possibly of its duplicates acknowledges correct reception of the data frame.
Next, the generated ACK frame is sent on the primary sub-channel of the composite channel, and the duplicates thereof are sent only on the secondary subchannels of the subset as determined at step 1013. However, no duplicate of the ACK ) frame is sent on the secondary channels having bad reception quality. This is step 1015.
Thus, in the mode 1, sent ACK frames positively acknowledge received data frames. Thus, modulating the ACK frames on a secondary sub-channel or not is a means to transmit information related to channel reception statistics of this secondary subchannel (obtained at step 1011) to the source node. j Figure 10b illustrates the mode 2 in which the ACK frame is interpreted as a positive acknowledgment only if it (including its duplicates) is received over all the subchannels of the composite channel. On the other hand, it is considered as being a negative acknowledgment if one of its duplicates is missing on at least one of the secondary sub-channels of the composite channel. ) In other words, the duplicate or duplicates of the acknowledgment frame are sent only on a subset of secondary sub-channels (excluding low quality secondary subchannels) to acknowledge erroneous reception of the data frame; and an acknowledgment frame and duplicates thereof are transmitted on all the sub-channels forming the composite channel to acknowledge correct reception of the data frame.
Upon receiving one data frame modulated over a composite channel made of a primary sub-channel and of secondary sub-channels and upon applying a decoding process to it (step 1030), a channel reception quality is obtained for each sub-channel of the composite channel (optimally for each secondary sub-channel only). This is step 5 1031.
The channel reception quality is retrieved from the PHY layer where values representative of such quality are evaluated. Details of such step have been provided above for step 923. Note that the evaluation of the channel reception quality may be made for the time being since the last acknowledgment (possibly BA) frame has been ) sent (for instance the MAC layer may calculate a means value of SNR values received from the PHY layer since the last acknowledgment frame has been sent).
Next, step 1032 consists to check whether or not the data frame has been correctly received (including the decoding thereof).
In case an erroneous reception/decoding of the data frame is detected, the j receiving node determines, at step 1033, the secondary sub-channels of the composite channel having good reception quality. For instance, those sub-channels are the secondary sub-channels for which the channel reception quality retrieved at step 1031 is higher than a predefined quality threshold. In a variant, the one or more secondary sub-channels having the lowest channel reception quality may be discarded to keep a ) subset of secondary sub-channels that excludes at least one low quality sub-channel. This variant makes it possible to negatively acknowledge a received data frame, even if all the secondary sub-channels have correct channel reception qualities (i.e. above or slightly above the predefined quality threshold).
Next, an ACK frame is built using the non-HT duplicate format, meaning that j a main ACK frame is generated and duplicate or duplicates thereof (if any) are also generated (step 1034).
Next, the generated ACK frame is sent on the primary sub-channel of the composite channel, and the duplicates thereof are sent only on the secondary subchannels of the subset as determined at step 1033. However, no duplicate of the ACK ) frame is sent on the secondary sub-channels having bad reception quality. This is step 1035.
Thus, in the mode 2, sent ACK frames negatively acknowledge received data frames when at least one secondary sub-channel does not convey a duplicate of the ACK frame. And, modulating the ACK frames on a secondary sub-channel or not is a means to transmit information related to channel reception statistics of this secondary sub-channel (obtained at step 1031) to the source node.
Back to test 1032, if the data frame has been correctly received and decoded, an ACK frame is built using the non-HT duplicate format, meaning that a main ACK frame j is generated and duplicates thereof are also generated (step 1036).
Next, the generated ACK frame and its duplicates are sent on the primary sub-channel and on all the secondary sub-channels of the composite channel, meaning that the sending of the ACK frame is made regardless of the reception quality of each sub-channel. This is step 1037. ) Thus, ACK frames sent on all the sub-channels forming the composite channel positively acknowledge received data frames. No feedback about reception statistics over the secondary sub-channels of the composite channel is sent.
Figure 10c illustrates the BA mode in which a Block Ack frame is used to acknowledge a set of data frames, instead of an ACK frame acknowledging a single data j frame.
Upon receiving a predefined number of data frames modulated over a composite channel made of a primary sub-channel and of secondary sub-channels and upon applying a decoding process to it (step 1050/1051), a channel reception quality is obtained for each sub-channel of the composite channel (optimally for each secondary ) sub-channel only). This is step 1052.
The channel reception quality is retrieved from the PHY layer where values representative of such quality are evaluated. Details of such step have been provided above for step 923. Note that the evaluation of the channel reception quality may be made for the time being since the last BA frame has been sent (for instance the MAC j layer may calculate a means value of SNR values received from the PHY layer since the last acknowledgment frame has been sent).
Next, at step 1053, the receiving node determines the secondary subchannels of the composite channel having good reception quality. For instance, those sub-channels are the secondary sub-channels for which the channel reception quality ) retrieved at step 1011 is higher than a predefined quality threshold. In a variant, the one or more secondary sub-channels having the lowest channel reception quality may be discarded to keep a subset of secondary sub-channels that excludes at least one low quality sub-channel.
Next, a BA frame is built using the non-HT duplicate format, meaning that a j main BA frame is generated and duplicate or duplicates thereof are also generated (step 1054). It means that the BA frame acknowledges correct reception of one or more data frames. The BA frame also indicates, for instance using a bitmap, those data frames that are erroneously received.
Next, the generated BA frame is sent on the primary sub-channel of the j composite channel, and the duplicates thereof are sent only on the secondary subchannels of the subset as determined at step 1053. However, no duplicate of the BA frame is sent on the secondary sub-channels having bad reception quality. This is step 1055.
Based on any mode described above with reference to Figure 10a, 10b or ) 10c, the source node receiving an ACK frame or a BA frame and its possible duplicates sent by the receiving node is now aware of some channel reception information.
Back to Figure 9a, the source node determines, at step 912, whether or not one or more duplicated ACK frames associated with the data frames sent at step 911 are received. j At step 913, the source node determines on which secondary sub-channels the duplicates of the ACK frame (received on the primary sub-channel) are received.
In a simple embodiment in which the source node has capabilities to receive and decode the signals received through all the sub-channels, step 913 may consist in comparing the frames received through the secondary sub-channels to the ACK frame ) received through the primary sub-channel to check they are duplicates.
In a more sophisticated embodiment which may apply when the source node has capabilities only to decode the signal received through the primary sub-channel and to perform CCA on the secondary sub-channels, the source node performs the following steps: j sensing, for the primary sub-channel and the secondary sub-channel, a change of an idle/busy status of the primary and secondary sub-channels, and storing, in memory, the status changes in association with time information; determining, using the stored time information, whether or not the secondary sub-channel has respective status changes temporally similar to the status changes in ) the primary sub-channel due to the received acknowledgment frame, to trigger detection of a duplicated acknowledgment frame received on the secondary sub-channel in case of temporal similarity between the status changes.
An idea of this approach is that, since all the sub-channels supporting the communication are known, the PHY layer may timestamp each status change for the j sub-channels of the frequency operating band. The MAC layer can then retrieves all these items of information (status changes and associated timestamps) to build a timing profile for all the sub-channels. Next, the timing profile of the primary sub-channel is considered as the reference for the received ACK frame because this is that ACK frame the node analyzes. j A verification of profile matching is thus performed between the primary sub channel profile and each secondary sub-channel profile to determine whether or not temporal similar status changes occurred. That is to say both the respective rising and falling edge timestamps should match between the two profiles compared (the drift is negligible and may be set to a few nano-seconds). ) Finally, one can conclude that the matching profiles belongs to the same communication, in which case the source node infers that a duplicated ACK frame has been received on the secondary sub-channel considered. On the other hand, a profile different from the primary sub-channel profile is considered either as a distinct communication or as a collided secondary sub-channel, in which case no duplicated j ACK frame has been received on the secondary sub-channel considered, and the latter can be rejected.
Figure 12 illustrates, using two flowcharts, a detecting or sensing method as briefly explained above, to enhance channel usage detection for multi-channel transmission in an 802.11ac wireless medium. ) Figure 12b illustrates, using a flowchart, continuous monitoring of the sub channels that compose the operating band.
By default, the PHY layer 703 is configured to sense wireless signal, to demodulate it in order to receive incoming packet headers (CS/CCA state). Whenever the PHY layer 703 senses the status of a wireless medium changing from channel idle j to channel busy or from channel busy to channel idle, it sends a PHY-CCA.indication to the MAC indicating the current state of the medium.
As recalled, CCA is physical carrier sense which listens to received energy on the radio interface with the same energy threshold set over all sub-channels (including the primary one). ) At step 1210, measurement feedback module 705 receives a PHY- CCA. indication from PHY layer 703.
For instance, upon receiving the transmitted 802.11 PLCP preamble (i.e. beginning of a control frame) in the primary 20 MHz sub-channel, the PHY layer measures a receive signal strength. The CCA mechanism detects a “medium busy” j condition for the primary sub-channel and the medium status activity is indicated by the PHY to the MAC via the PHY-CCA.indication primitive with STATUS=busy, prior to correctly receiving the whole PLCP frame.
Similarly, when the PHY stops detecting a signal on the sub-channel, the PHY notifies the MAC by issuing the PHY-CCA.indication primitive with STATUS=idle. j For multi-channel PHY as in 802.11η or ac, the PHY-CCA.indication(STATE, channel-list) primitive is issued as an indication of reception/end-of-reception of a signal in the sub-channels (anyway if the packet will be further decoded or not). The STATE parameter is either “busy” or “idle” depending on the state detected by CCA.
The channel-list is a parameter indicating a list of one or more sub-channels ) corresponding to the “STATE” parameter. For example, if it is determined that the secondary sub-channel is IDLE, the indication is generated as PHY-CCA.indication(IDLE, Secondary). As another example, if it is determined that a composite channel including the primary sub-channel, the sub-secondary channel and the tertiary sub-channel is BUSY, the indication is generated as PHY-j CCA.indication(BUSY, Primary, Secondary, Tertiary). As another example, if it is determined that, over a composite channel composed of four sub-channels, only the tertiary sub-channel is BUSY, the indication is generated as PHY-CCA.indication(BUSY,
Tertiary).
One can note that the CCA sensitivity (in terms of wireless signal level ) detection and detection time) of the PHY layer has the same error tolerance for each 802.11 channel, thus there should be little or no drift in PHY-CCA.indication assertions among various channel (taking into account the non-HT duplicate frame to analyse is simultaneously duplicated over several channels by a unique PHY transmitter). Most of the time, a single PHY-CCA.indication is captured for several channels through the use j of the channel-list parameter.
Next, at step 1211, using the received PHY-CCA.indication, module 705 identifies the sub-channels concerned by the received PHY-CCA.indication primitive using the channel-list parameter and their state or status using the STATE parameter. This information is stored in memory 604. ) Next, at step 1212, module 705 generates a timestamp for every item of information stored at step 1211, and stores the timestamps in memory 604 in association with their respective sub-channel and status information.
In a slight variant that reduces use of memory, module 705 generates timestamps only for status change in a sub-channel, and saves such information in j memory. For instance, module 705 detects for a sub-channel whether or not the status identified in the last processed PHY-CCA.indication is different from the previous one stored in memory. In other words, the status changes correspond to rising and falling edges in the busy signal indication (meaning both idle and busy notification by the PHY layer). j The time information stored in memory may include the (absolute) time instant (i.e. timestamp) at which the status change for the sub-channel occurs or may include a (relative) time difference between the status change thus sensed and the preceding sensed status change in the same sub-channel. A method for triggering the required timestamps is to link the PHY- ) CCA.indication with a simple local clock counter. Alternatively, the counter could be driven by the PHY’s existing high-precision reference oscillator and equipped with a means for generating precise timestamps at the moment that a PHY-CCA.indication passes through the PHY-MAC interface. The module 705 could later access the stored timestamp values simply by reading the content of a register without degrading its value j because of some uncontrolled notification and/or access delays between PHY-MAC.
In embodiments, the timestamps of at least the current TXOP are stored in memory 604, meaning that the stored values are erased when a new backoff procedure starts.
Knowing the subchannel status changes and corresponding timestamps, ) module 705 is able to generate CCA profiles, an example of which is shown in Figure 13.
Figure 12a illustrates, using a flowchart, the algorithm performed to determine which secondary sub-channel(s) of the operating band also convey a duplicate of the ACK frame received in the primary sub-channel. As apparent from the j explanation below, this determination is made relative to the status changes (for instance CCA status profile) of the primary sub-channel. The idea of this process is to determine, using the stored time information or timestamps, one or more other sub-channels of the operating band that have status changes temporally similar to the status changes in the primary sub-channel due to the received ACK frame. ) Note that the determination process of Fig. 12a is asynchronous to the one of Fig.12b, as the determination process is raised upon demodulation of an 802.11 frame on the primary sub-channel.
The determination process starts at step 1200 in which source node 600 receives the ACK frame on its primary sub-channel. The PHY-CCA.indication notifications related to the reception of this ACK frame have already been captured by the process of Fig. 12b.
Next, at step 1201, the source node determines whether or not the ACK mode is a non-HT duplicate ACK mode. It is the case if the source node has published j an acknowledgment mode at step 910, in which case the next step is step 1202.
Otherwise, the process ends.
At step 1202, the stored timestamp values of each sub-channel composing the composite channel are retrieved from memory 604. These stored values for a given sub-channel form the CCA timing profile which displays that channel’s usage. ) Next, at step 1203, the CCA timing profile of the primary sub-channel is selected as a reference for the received ACK frame.
Next, at steps 1204 and 1205, the source node 600 determines the real subchannels that have successfully conveyed a duplicate of the ACK frame received through the primary sub-channel. j This determination includes checking a CCA profile matching (for instance
by comparison) between the CCA profile of the primary sub-channel (used as reference) and the CCA profile of each secondary sub-channel of the composite channel. The check is made on the portion of the profile that regards the reception of the ACK frame on the primary sub-channels (for instance a temporal portion with an additional PIFS or 2xPIFS ) margin). This is because it is considered that the ACK frame on the primary sub-channel and a duplicate of the same ACK frame on any secondary sub-channel have the same temporal signature.
The check of a profile matching may include determining whether or not the rising and falling edge timestamps are close enough between the two profiles, so that j the drift is negligible (for instance less than a few nano-seconds).
The check for the rising edge may include determining whether or not the time difference between an idle-to-busy status change (i.e. a change from idle status to busy status due to the sensing) in the sub-channel considered and an idle-to-busy status change corresponding to the start of the received ACK frame in the primary sub-channel ) is less than a first threshold.
Similarly, the check for the falling edge may include determining whether or not the time difference between a busy-to-idle status change in the sub-channel considered and a busy-to-idle status change corresponding to the end of the received ACK frame in the primary sub-channel is less than a second threshold.
Of course, to have the same temporal signature through the considered subchannels, the analysis of step 1204 is based on two consecutive edges: a rising edge quite simultaneous to the rising edge due to the received ACK frame in the primary subchannel, and the next falling edge. j Based on the time drift between the rising and falling edges for the sub channels with respect to the primary sub-channel, module 705 consider the subchannels having a matching profile as pertaining to the same communication, i.e. has having received a duplicated ACK frame.
On the contrary, when the profile matching is not obtained, the corresponding ) secondary sub-channel is considered as belonging to a distinct communication or as being a collided channel. Thus, this non-matching secondary sub-channel is rejected at step 1205.
Figure 13 illustrates the profile matching for a composite channel made of four 20MHz channels. j The source node retrieves the CCA time profiles for all the sub-channels as explained above. Four exemplary CCA time profiles are shown in the Figure.
Based on these CCA time profiles where the CCA time profile for the primary sub-channel is used as a reference, the source node detects (using the process of Fig. 12a) that the falling edge (1300) for the third sub-channel does not temporally match ) the falling edge of the primary (reference) profile. Even if the rising edge timing is considered as correct, the difference of timing 1300 informs the source node that no duplicate of the ACK frame has been received on this third sub-channel.
On the other hand, the CCA profiles of the second and fourth sub-channels perfectly match the CCA profile of the primary sub-channel. The source node thus infers j that duplicates of the ACK frame have been received on the second and fourth sub channels.
Back to Figure 9a, next to step 913, steps 914 and 915 are performed.
At step 914, the source node determines the data frames that are to be retransmitted. This is based on the acknowledgment mode used (mode 1 or 2 or BA) ) and on the outcome of step 913 (in the mode 2, no duplicate of the ACK frame means that the data frame has not been correctly received). Note that the BA frame makes it possible to identify, within a set of sent data frames, the one or ones that have not been correctly received. A first option for step 915 is for the source node to directly modify the j composite channel for future transmission, by discarding (i.e. excluding) at least one secondary sub-channel of the composite channel on which no duplicated acknowledgment frame is received, i.e. the secondary sub-channels having bad reception quality according to the receiving node. It is not a requirement but using bad reception quality channels may imply additional error transmissions and extra bandwidth j overhead.
A more sophisticated embodiment for step 915 uses channel quality history associated, in memory, with all 20MHz sub-channels of the operating band. For instance, the channel quality history for a secondary sub-channel may count how many times a receiving node has signalled bad reception quality (by not sending a duplicate of ACK ) frame on this secondary sub-channel) over the last N TXOPs.
The source node may thus use the channel quality histories associated with the current composite channel to adjust its transmission conditions for the next data transmission, i.e. to update the composite channel (or modify it). For instance, it may discard therefrom the secondary sub-channels for which the associated channel quality j history indicates a high number of bad reception quality occurrences.
As the number of secondary sub-channels tends to decrease over time, the source node is able to perform a conventional access to the wireless medium in order to determine a fully new composite channel, on which the present invention may be applied anew. ) Next to steps 914 and 915, the data frame or frames determined at step 914 are retransmitted using the composite channel as possibly modified at step 915. This is step 916. Note that the data frames to be retransmitted are modulated over the whole composite channel.
Figure 11 illustrates embodiments of steps 912-916 of Figure 9b with more j details, in particular by discriminating among the acknowledgment modes.
Step 1110, similar to step 912, consists to receive an ACK frame in a non-HT duplicate format. Upon reception thereof, the source node determines on which secondary sub-channels of the composite channel a duplicated ACK frame is received. This is step 1120 similar to step 913. In addition, step 1120 may flag each secondary ) sub-channel of the composite channel on which no duplicated ACK frame is received, if any.
Note that the source node may receive no duplicate at all, for instance if the receiving node may indicate that each of the secondary sub-channels forming the composite channel have low reception quality. Thanks to the declaration of step 910, the source node will be able to determine that this lack of duplicated ACK frame should be processed according to the teachings of the present invention.
In mode 1 (as described in step 910), the received ACK frame positively acknowledges the data frame, meaning that no retransmission is needed. In mode BA, j the received ACK frame positively acknowledges some data frames and negatively acknowledges some other data frames. The secondary sub-channels determined at step 1120 may be used to restrict the composite channel for the next data transmission: only the determined secondary sub-channels (if any) combined with the primary sub-channel may be used. This is step 1140 in which the composite channel is updated. ) In mode 2 (as described in step 910), it is determined whether or not a secondary sub-channel has been flagged (i.e. no duplicated ACK frame has been received). It is recalled that, in this mode 2, if the ACK frame is not duplicated on all the secondary sub-channels, it means that a data frame was not correctly received. This is step 1150. j If test 1150 is negative, the ACK frame positively acknowledges the reception of the data frame. Neither update of the composite channel nor retransmission of data frames is needed since no new reception quality statistics is received. The process loops back to step 1110.
If test 1150 is positive, the ACK frame negatively acknowledges the reception ) of the data frame.
These data frames can be retransmitted at step 1160 using the composite channel.
In addition, the channel reception quality statistics of the sub-channels of the operating band are updated at step 1170. For instance, a counter may be increased for j each flagged secondary sub-channel, i.e. the sub-channels of the composite channel on which no duplicated ACK frame has been received. If the reception quality over a flagged sub-channel becomes lower than a predetermined threshold (for instance the associated counter over the last N transmissions is higher than a threshold), the source node can decide to no longer use this sub-channel for the next data transmission. The composite ) channel is thus updated by removing the “bad quality” sub-channels from the composite channel.
In other words, the composite channel is modified for future transmission by determining at least one secondary sub-channel to discard from the composite channel based on the stored channel quality histories.
Note that steps 1160 and 1170 may be inverted so that the data frame or frames not correctly received are retransmitted as a signal modulated on the modified (updated) composite channel.
Note that the updated composite channel may be made of sub-channels that j are not contiguous within the operating band. In such a case, the modulation of a data frame on the BW band can be made by turning off the carriers (OFDM tones) corresponding to the unused sub-channels “k” in the modulation band (i.e. not used according to the ACM map). This modulation may involve the formula, as mentioned above: ) where N is the FFT size.
To turn off the carriers of non-active sub-channels, the D(k) components for these unused sub-channels “k” are set to 0.
This is explained in document IEEE 802.11-15/0035r1, entitled “Scalable j Channel Utilization Scheme".
Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications will be apparent to a skilled person in the art which lie within the scope of the present invention. ) Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention, that being determined solely by the appended claims. In particular the different features from different embodiments may be interchanged, where appropriate. j In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used.
Claims (24)
1. A wireless communication method between a source node and a receiving node over a composite channel in a wireless network, the composite channel being made of a primary sub-channel and of one or more secondary sub-channel, the method comprising, at the receiving node: receiving, from the source node, a signal modulated on the whole composite channel, the modulated signal encoding one or more data frames; applying a decoding process on the modulated signal; generating an acknowledgment frame, the acknowledgment frame being one of an acknowledgment frame acknowledging correct reception of the one or more data frames or an acknowledgment frame acknowledging erroneous reception of the one or more data frames; sending the acknowledgment frame to the source node on the primary subchannel; the method further comprising, at the receiving node: determining a channel quality for one or more of the secondary sub channels; and sending a duplicate of the acknowledgment frame to the source node only on each secondary sub-channel of a subset of the secondary sub-channels that excludes at least one secondary sub-channel having a low determined channel quality.
2. The wireless communication method of Claim 1, wherein determining the channel quality for a secondary sub-channel comprises evaluating a quality of signal reception on the secondary sub-channel using the received modulated signal.
3. The wireless communication method of Claim 2, wherein the quality of signal reception is evaluated based on a plurality of data frames conveyed by the modulated signal.
4. The wireless communication method of Claim 1, further comprising, at the receiving node, comparing the channel quality determined for each secondary subchannel with a quality threshold to exclude the secondary sub-channel or sub-channels having a determined channel quality below the quality threshold.
5. The wireless communication method of Claim 1, wherein the acknowledgment frame and duplicates thereof are acknowledgment frames acknowledging correct reception of the one or more data frames, and no acknowledgment frame and duplicate thereof are sent in case of erroneous reception of a data frame.
6. The wireless communication method of Claim 1, wherein the acknowledgment frame is an acknowledgment frame acknowledging erroneous reception of the data frame or frames, wherein the duplicate or duplicates of the acknowledgment frame are sent only on the subset of secondary sub-channels; and an acknowledgment frame acknowledging correct reception of a data frame received from the source node and duplicates thereof are generated and sent respectively on the primary sub-channel and on the one or more secondary subchannels forming the composite channel.
7. The wireless communication method of Claim 1, wherein the acknowledgment frame is a block acknowledgment frame acknowledging correct or erroneous reception of respectively each of a plurality of data frames.
8. The wireless communication method of Claim 1, wherein the acknowledgment frame and the duplicate or duplicates thereof are sent substantially simultaneously on their respective sub-channels.
9. A wireless communication method between a source node and a receiving node over a composite channel in a wireless network, the composite channel being made of a primary sub-channel and of one or more secondary sub-channels, the method comprising, at the source node: transmitting, to the receiving node, a signal modulated on the whole composite channel, the modulated signal encoding one or more data frames; receiving, from the receiving node in response to the transmitted signal, at least one acknowledgment frame on the primary sub-channel and possibly a duplicated acknowledgment frame on a respective secondary sub-channel; and modifying the composite channel for future transmission, by discarding at least one secondary sub-channel of the composite channel on which no duplicated acknowledgment frame is received.
10. The wireless communication method of Claim 9, further comprising, at the source node, determining whether or not transmitted data frame or frames have been correctly received by the receiving node, using the received acknowledgment frame and duplicates thereof; and retransmitting the data frame or frames not correctly received.
11. The wireless communication method of Claim 10, wherein the data frame or frames not correctly received are retransmitted as a signal modulated on the modified composite channel.
12. The wireless communication method of Claim 9, further comprising, at the source node, updating, in memory, channel quality history associated with one or more secondary sub-channels, based on whether or not a duplicated acknowledgment frame is received on the respective secondary sub-channel.
13. The wireless communication method of Claim 12, wherein modifying the composite channel for future transmission includes determining at least one secondary sub-channel to discard from the composite channel based on the stored channel quality histories.
14. The wireless communication method of Claim 9, further comprising determining, for each secondary sub-channel, whether or not a duplicated acknowledgment frame is received on the secondary sub-channel, wherein the determining step for a secondary sub-channel includes: sensing, for the primary sub-channel and the secondary sub-channel, a change of an idle/busy status of the primary and secondary sub-channels, and storing, in memory, the status changes in association with time information; determining, using the stored time information, whether or not the secondary sub-channel has respective status changes temporally similar to the status changes in the primary sub-channel due to the received acknowledgment frame, to trigger detection of a duplicated acknowledgment frame received on the secondary sub-channel in case of temporal similarity between the status changes.
15. The wireless communication method of Claim 14, wherein the time information includes a time instant at which the status change for the primary or secondary sub-channel occurs or a time difference between the status change thus sensed and the preceding sensed status change in the same primary or secondary subchannel.
16. The wireless communication method of Claim 14, wherein determining using the stored time information includes determining whether or not the time difference between an idle-to-busy status change in the secondary sub-channel and an idle-to-busy status change corresponding to the start of the received acknowledgment frame in the primary sub-channel is less than a first threshold; and the time difference between a busy-to-idle status change in the secondary sub-channel and a busy-to-idle status change corresponding to the end of the received acknowledgment frame in the primary sub-channel is less than a second threshold.
17. The wireless communication method of Claim 14, wherein the step of sensing a change of the idle/busy status of each sub-channel includes comparing a signal energy level in the primary or secondary sub-channel to a predefined threshold.
18. The wireless communication method of Claim 17, wherein the step of sensing a change of the idle/busy status of the primary or secondary sub-channel includes performing a Clear Channel Assessment (CCA).
19. The wireless communication method of Claim 9, wherein all the secondary sub-channels on which no duplicated acknowledgment frame is received are discarded from the composite channel.
20. The wireless communication method of Claim 9, wherein the wireless network is defined by an operating band made of an ordered succession of subchannels, and the composite channel is made of sub-channels that are contiguous within the operating band.
21. The wireless communication method of Claim 9, wherein the composite channel is made of sub-channels that are not contiguous within the operating band.
22. A receiving node for wireless communication over a composite channel in a wireless network, the composite channel being made of a primary sub-channel and of one or more secondary sub-channels, the receiving node comprising at least one microprocessor configured for carrying out the steps of: receiving, from the source node, a signal modulated on the whole composite channel, the modulated signal encoding one or more data frames; applying a decoding process on the modulated signal; generating an acknowledgment frame, the acknowledgment frame being one of an acknowledgment frame acknowledging correct reception of the one or more data frames or an acknowledgment frame acknowledging erroneous reception of the one or more data frames; sending the acknowledgment frame to the source node on the primary subchannel; determining a channel quality for one or more of the secondary subchannels; and sending a duplicate of the acknowledgment frame to the source node only on each secondary sub-channel of a subset of the secondary sub-channels that excludes at least one secondary sub-channel having a low determined channel quality.
23. A source node for wireless communication over a composite channel in a wireless network, the composite channel being made of a primary sub-channel and of one or more secondary sub-channels, the source node comprising at least one microprocessor configured for carrying out the steps of: transmitting, to the receiving node, a signal modulated on the whole composite channel, the modulated signal encoding one or more data frames; receiving, from the receiving node in response to the transmitted signal, at least one acknowledgment frame on the primary sub-channel and possibly a duplicated acknowledgment frame on a respective secondary sub-channel; and modifying the composite channel for future transmission, by discarding at least one secondary sub-channel of the composite channel on which no duplicated acknowledgment frame is received.
24. A non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a device for wireless communication over a composite channel in a wireless network, the composite channel being made of a primary sub-channel and of one or more secondary sub-channels, causes the device to perform the method of Claim 1 or 9.
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| EP2253852A1 (en) * | 2009-05-19 | 2010-11-24 | Siemens Aktiengesellschaft | Compressor assembly with an active magnetic bearing |
| EP2289196A1 (en) * | 2008-06-19 | 2011-03-02 | Telefonaktiebolaget L M Ericsson (PUBL) | Method and apparatus in a telecommunications network |
| WO2012047643A2 (en) * | 2010-10-04 | 2012-04-12 | Marvell World Trade Ltd. | Determining a communication channel from a plurality of possible channel bandwidths |
| EP2692187A2 (en) * | 2011-03-31 | 2014-02-05 | Telefonaktiebolaget L M Ericsson (publ) | Ensuring reception quality for non-adjacent multi-carrier operation |
| EP2801167A1 (en) * | 2012-01-06 | 2014-11-12 | Samsung Electronics Co., Ltd. | Method for transmitting harq-ack information based on transmission diversity priority |
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| EP2289196A1 (en) * | 2008-06-19 | 2011-03-02 | Telefonaktiebolaget L M Ericsson (PUBL) | Method and apparatus in a telecommunications network |
| EP2253852A1 (en) * | 2009-05-19 | 2010-11-24 | Siemens Aktiengesellschaft | Compressor assembly with an active magnetic bearing |
| WO2012047643A2 (en) * | 2010-10-04 | 2012-04-12 | Marvell World Trade Ltd. | Determining a communication channel from a plurality of possible channel bandwidths |
| EP2692187A2 (en) * | 2011-03-31 | 2014-02-05 | Telefonaktiebolaget L M Ericsson (publ) | Ensuring reception quality for non-adjacent multi-carrier operation |
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| GB2538946A (en) | 2016-12-07 |
| GB201507848D0 (en) | 2015-06-17 |
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