Patent Description:
HARQ is a feature widely used in various wireless communication technologies, such as in Universal Mobile Telecommunications System (UMTS) and Long Term Evolution (LTE). Unlike the Automatic Repeat Request (ARQ), wherein incorrectly decoded packets are discarded at the receiver and are then retransmitted by the transmitter, HARQ enables soft combining (or combining of equalized tones). This means that Log Likelihood Ratios (LLRs) respective to incorrectly decoded packets are stored in a memory of the receiver, and are combined at the receiver with retransmissions of the same information bits from the transmitter.

This soft combining increases the probability for correct packet detection (after retransmission).

Due to the improved performance (after applying such HARQ combining), practical wireless communication systems employing HARQ may also use a lower fade margin in the rate selection algorithm. This means that the rate selection mechanism effectively uses a higher Modulation and Coding Scheme (MCS).

This may be especially beneficial in a Carrier Sense Multiple Access / Collision Avoidance (CSMA/CA) system, where the rate selection algorithm uses a larger fade margin (relative to cell coordination systems), because the interference level has big fluctuations (among other issues, due to hidden nodes).

There are several different flavors of HARQ, for instance:.

The existing <NUM> Wi-Fi standards (i.e. specifications (a/g/n/ac/ax)) do not support HARQ for various reasons. Supporting HARQ is particularly problematic for the use case of an Aggregated MAC Protocol Data Unit (A-MPDU). In the existing <NUM> standards (and hence also in the respective implementations) the following restrictions exist:.

Assuming an A-MPDU was transmitted, and some of the MPDUs of the A-MPDU were incorrectly decoded by the receiver, the transmitter will have to retransmit only those MPDUs that failed.

For example, in <FIG> an A-MPDU containing <NUM> MPDUs is transmitted (each MPDU containing <NUM> bits) using a coding rate <NUM>/<NUM>. As shown, the scrambling seed of the scrambler has a periodicity of <NUM> bits, i.e. it includes scrambler blocks of size <NUM> bits. As also shown, the FEC operates on FEC blocks of information bits. The boundaries of the MPDUs, scrambler blocks and FEC blocks are not aligned.

Assuming that the <NUM>nd and <NUM>rd MPDUs fail, these MPDUs are retransmitted as shown in <FIG>. The retransmission of the failed MPDUs will include different coded bits, due to a different setting of the scrambler (now operated with a different scrambling seed) and FEC (different information bits). Thus, the LLRs of the initial transmission and the retransmission cannot be combined. In essence, the misalignment of the MPDUs and the scrambling seed and FEC blocks poses a problem for supporting HARQ.

<CIT> discloses a system and method for scrambling in a wireless communication system.

<CIT> discloses a wireless communication device including a receiver and a transmitter.

<CIT> discloses a method for transmission of media access control (MAC) protocol data units (MPDUs) over a wireless local area network (WLAN) communication channel.

<CIT> discloses a method and an apparatus for transmitting non-decodable packets.

In view of the above-mentioned disadvantages, the present invention aims to enable HARQ in the standard implementation of <NUM> (i.e. for Wi-Fi). In particular, the invention has the objective to provide devices and methods to incorporate HARQ with as few changes as possible into the existing Wi-Fi standards. The changes should specifically be minimal with respect to existing modules and procedures, like FEC, scrambling, MPDU aggregation, etc. The devices and methods of the invention should account for the misalignment of both scrambling and FEC to MPDU boundaries, so that regardless of a location of a MPDU within an A-MPDU, a HARQ procedure can be carried out.

The objective of the present invention is achieved by the solution provided in the enclosed independent claims. In the following, parts of the description and drawings referring to embodiments not covered by the claims, are not part of the invention, but are illustrative examples necessary for understanding the invention.

In particular, the invention proposes a solutions for supporting HARQ in <NUM> (Wi-Fi), by focusing on the most typical case of HARQ with the transmission of an A-MPDU. A single MPDU transmission is of low efficiency in <NUM>. Hence, transmitting an A-MPDU will in many cases be used.

In this document CC HARQ, where the same coded bits are retransmitted and soft bits (LLRs) are combined at the receiver (simplest to implement), is presented as a reference. However, the solution of the invention is applicable to IR HARQ as well.

A first aspect of the invention provides a device for supporting HARQ, the device being configured to transmit to a receiver an A-MPDU according to the IEEE <NUM> standards and including at least two data units, and to transmit to the receiver, together with the A-MPDU, HARQ block information about a division of the A-MPDU into a plurality of determined HARQ Blocks, wherein the device is further configured to scramble and encode the A-MPDU by performing scrambling and by using FEC independently on each of the plurality of HARQ blocks, and to retransmit to the receiver, if a decoding of at least one data unit failed at the receiver, at least a part of the A-MPDU including the at least one failed data unit, wherein each HARQ block includes at least one data unit, wherein the retransmitted part contains each HARQ block that includes a failed data unit, and wherein the device is further configured to scramble and encode the at least one failed data unit in the retransmitted part by performing scrambling based on the same scrambling seed and by using FEC with the same FEC outputs that were used for scrambling and encoding said data unit in the A-MPDU.

By using the same scrambling seed to scramble the data unit in the initially transmitted A-MPDU, and in the retransmitted part, and by using the same FEC outputs, the receiver is able to combine the respective transmissions for an improved decoding. Accordingly, a HARQ procedure can be carried out regardless of a location of the data unit (e.g. MPDU) within the A-MPDU. Thus, the device of the first aspect enables HARQ in Wi-Fi.

A scrambling seed is a sequence of bits, which is used as an input (e.g. to a scrambler) for scrambling the bits of the A-MPDU and the retransmitted part, respectively. The scrambling seed (bit sequence) may be periodic, e.g. after each <NUM> bits the same <NUM> bits may be repeated (i.e. the scrambling seed can be seen as repetitive arrangement of identical scrambling blocks). Using the same scrambling seed for the failed data unit - in the initially transmitted A-MPDU on the one hand, and in the retransmitted part on the other hand - means that the bits of the data unit are in both cases scrambled using the same scrambling bits / scrambling block(s). The same scrambling seed can be achieved, for example, by memorizing it, e.g. for each A-MPDU and/or data unit. Alternatively, by dividing the A-MPDU into determined HARQ blocks, which are then retransmitted as smallest units of the retransmitted part (i.e. the retransmitted part includes at least one HARQ block and an integer number of HARQ blocks), and which may be aligned with the periodicity of the scrambling seed. FEC outputs are the encoded bits output after FEC. Using the same FEC outputs means that encoding yields the same coded bits after performing FEC. To this end, it may be ensured that the FEC performed on the failed data unit is operated based on the same blocks of information bits - for the data unit in the initially transmitted A-MPDU on the one hand, and in the retransmitted part on the other hand. The same FEC outputs can be achieved, for example, by memorizing the FEC outputs for the A-MPDU and/or for the data units, or memorizing FEC parameters that resulted in the FEC outputs. Alternatively, it can be achieved by using the above-described HARQ blocks, and making the HARQ blocks the same size as FEC blocks of information bits, on which the FEC is operated.

In an implementation form of the first aspect, the device is further configured to modify the FEC outputs after encoding the scrambled A-MPDU, particularly by puncturing, and modify the FEC outputs after encoding the at least one failed data unit in the retransmitted part differently than modifying the FEC outputs after encoding the scrambled A-MPDU, particularly by different puncturing.

Accordingly, the device also supports IR HARQ, wherein modifications of the FEC outputs are typically applied. The device may transmit to the receiver an indication of how the puncturing changes between (re)transmissions, i.e. may send puncturing information. Alternatively, there may be a pre-defined agreement between the device and the receiver determining how bits are punctured in each (re)transmission.

In a further implementation form of the first aspect, the device is further configured to receive an ACK and/or a NACK message from the receiver regarding one or more data units that were correctly and/or incorrectly decoded at the receiver.

Thus, the device can derive, which data units could not be decoded at the receiver, and need to be retransmitted.

In a further implementation form of the first aspect, the retransmitted part includes the at least one failed data unit and additional bits.

Adding additional bits helps to ensure that the same FEC outputs are used for encoding the data unit in the retransmitted part.

The use of HARQ blocks leads to a very small overhead, and a retransmission of failed data units only. Further, the same Block Acknowledge operation can be maintained.

In a further implementation form of the first aspect, a HARQ block includes at least one data unit and additional padding bits.

The padding bits allow using HARQ blocks of well-defined size (known at device and receiver), while including into each HARQ block an integer number of data units.

In a further implementation form of the first aspect, a HARQ block has a number of bits that is a multiple of a total number of bits of a scrambling block.

Thus, it is efficiently ensured that the same scrambling seed is used when retransmitting a failed data unit in a HARQ block, such that the scrambler operates continuously and need not be reset after every HARQ block.

In a further implementation form of the first aspect, the HARQ block information comprises a size, number and/or location of the HARQ blocks in the A-MPDU.

"Together" may include that the HARQ block information is transmitted within a signaling part (e.g. preamble) related to the A-MPDU. The HARQ block information can, however, also be included in the A-MPDU. The HARQ block information can be pre-determined, e.g. it can be determined prior to the communication between the device and the receiver.

In a further implementation form of the first aspect, the device is further configured to concatenate multiple data units and/or fragment one or more data units to generate data units of about the size of a HARQ block.

In a further implementation form of the first aspect, the HARQ blocks in the A-MPDU are all of a same determined size.

This provides an easy implementation for both device and receiver.

In a further implementation form of the first aspect, the device is further configured to maintain the scrambling seed and/or FEC parameters that were used for scrambling and encoding the at least one data unit in the A-MPDU, and use the maintained scrambling seed and/or FEC parameters for scrambling and encoding the at least one failed data unit in the retransmitted part.

By memorizing the scrambling seed and/or FEC parameters, the device is efficiently able to use the same scrambling seed and same FEC outputs when scrambling and encoding a failed data unit in the retransmitted part (the same that was used for scrambling and encoding the data unit in the A-MPDU).

FEC parameters may include FEC block sizes. The maintained FEC parameters may further include inputs to each FEC and each output.

In a further implementation form of the first aspect, the device is further configured to maintain the scrambled bits and/or coded bits obtained after performing scrambling and/or after using FEC during the scrambling and encoding of the A-MPDU, and use the maintained scrambled bits and/or coded bits for generating the at least one failed data unit in the retransmitted part.

By memorizing the scrambled and/or coded bits, the device is efficiently able to use the same scrambling seed and same FEC outputs when scrambling and encoding a failed data unit in the retransmitted part.

In a further implementation form of the first aspect, the bits of the at least one failed data unit and the additional bits span the entire FEC outputs that were used for encoding said data unit in the A-MPDU.

Thus, it is ensured that the same FEC outputs can be used for the failed data unit in the retransmitted part.

In a further implementation form of the first aspect, the device is configured to transmit to the receiver, together with the retransmitted part, a retransmission indication.

This provides the receiver with the information that the received transmission is a retransmission. Thus, the receiver is accordingly able to decode the retransmission and combine it with the initial transmission.

A second aspect of the invention provides a device for supporting HARQ, the device being configured to receive from a transmitter a scrambled and FEC encoded A-MPDU according to the IEEE <NUM> standards and including at least two encoded data units, receive from the transmitter, together with the A-MPDU, HARQ block information about a division of the A-MPDU into a plurality of determined HARQ Blocks, decode the at least two data units, send to the transmitter an ACK and/or a NACK message regarding one or more data units that were correctly and/or incorrectly decoded, receive from the transmitter, if a decoding of at least one data unit failed, a retransmission of at least a part of the A-MPDU including the at least one failed data unit, and to decode the at least one retransmitted data unit and soft combine it with the previously received failed data unit, wherein each HARQ block includes at least one data unit, wherein each of the plurality of HARQ blocks in the A-MPDU is scrambled and FEC encoded independently, and wherein the retransmitted part contains each HARQ block that includes a failed data unit.

Thereby, HARQ is enabled for Wi-Fi. The decoding of the data units becomes more reliable.

A third aspect of the invention provides a method for HARQ, the method comprising transmitting to a receiver an A-MPDU according to the IEEE <NUM> standards and including at least two data units, transmitting to the receiver, together with the A-MPDU, HARQ block information about a division of the A-MPDU into a plurality of determined HARQ Blocks, wherein each of the plurality of HARQ blocks in the A-MPDU is scrambled independently and each of the plurality of scrambled HARQ blocks the scrambled A-MPDU is encoded independently by using FEC, and retransmitting to the receiver, if decoding of at least one data unit failed at the receiver, at least a part of the A-MPDU including the at least one failed data unit, wherein each HARQ block includes at least one data unit, wherein the retransmitted part contains each HARQ block that includes a failed data unit, and wherein the at least one data unit in the retransmitted part is scrambled and encoded by performing scrambling based on the same scrambling seed and using FEC with the same FEC outputs that were used for scrambling and encoding said data unit in the A-MPDU.

In an implementation form of the third aspect, the method further comprises modifying the FEC outputs after encoding the scrambled A-MPDU, particularly by puncturing, and modifying the FEC outputs after encoding the at least one failed data unit in the retransmitted part differently than modifying the FEC outputs after encoding the scrambled A-MPDU, particularly by different puncturing.

In a further implementation form of the third aspect, the method further comprises receiving an ACK and/or a NACK message from the receiver regarding one or more data units that were correctly and/or incorrectly decoded at the receiver.

In a further implementation form of the third aspect, the retransmitted part includes the at least one failed data unit and additional bits.

In a further implementation form of the third aspect, this HARQ block includes at least one data unit and additional padding bits.

In a further implementation form of the third aspect, a HARQ block has a number of bits that is a multiple of a total number of bits of a scrambling block.

In a further implementation form of the third aspect, the HARQ block information comprises a size, number and/or location of the HARQ blocks in the A-MPDU.

In a further implementation form of the third aspect, the method further comprises concatenating multiple data units and/or fragmenting one or more data units to generate data units of about the size of a HARQ block.

In a further implementation form of the third aspect, the HARQ blocks in the A-MPDU are all of a same determined size.

In a further implementation form of the third aspect, the method comprises maintaining the scrambling seed and/or FEC parameters that were used for scrambling and encoding the at least one data unit in the A-MPDU, and using the maintained scrambling seed and/or FEC parameters for scrambling and encoding the at least one failed data unit in the retransmitted part.

In a further implementation form of the third aspect, the method comprises maintaining the scrambled bits and/or coded bits obtained after performing scrambling and/or after using FEC during the scrambling and encoding of the A-MPDU, and using the maintained scrambled bits and/or coded bits for generating the at least one failed data unit in the retransmitted part.

In a further implementation form of the third aspect, the bits of the at least one failed data unit and the additional bits span the entire FEC outputs that were used for encoding said data unit in the A-MPDU.

In a further implementation form of the third aspect, the method comprises transmitting to the receiver, together with the retransmitted part, a retransmission indication.

The method of the third aspect and its implementation forms achieve the same advantages and effects as the device of the first aspect and its respective implementation forms.

It has to be noted that all devices, elements, units and means described in the present application could be implemented in the software or hardware elements or any kind or combination thereof.

<FIG> shows a device <NUM> according to an embodiment of the invention. The device <NUM> is configured to support HARQ for (NG) Wi-Fi. The device <NUM> may thereby be a Wi-Fi Access Point (AP), router or the like. The device <NUM> may also by a non-AP Station (STA) such as a smartphone. The device <NUM> may include a scrambler and a FEC unit.

The device <NUM> is configured to transmit, to a receiver <NUM>, an aggregated data unit <NUM> including at least one data unit <NUM>. The aggregated data unit <NUM> is an A-MPDU and the at least one data unit <NUM> may be a MPDU.

The device <NUM> is configured to scramble the aggregated data unit <NUM> by performing scrambling, and to encode the scrambled aggregated data unit <NUM> by using FEC. The scrambling can, for instance, be implemented by the scrambler of the device <NUM>, and the FEC can be implemented by the FEC unit of the device. The scrambling is based on a scrambling seed (bit sequence), particularly a periodic scrambling seed, wherein the periodicity in effect divides the scrambling seed into scrambler blocks containing a determined number of bits (e.g. <NUM> bits each). The scrambling seed is used as input to the scrambler to scramble the bits of the aggregated data unit <NUM>, and thus the bits of each data unit <NUM>.

The device <NUM> is further configured to retransmit, to the receiver <NUM>, if a decoding of at least one data unit <NUM> failed at the receiver <NUM>, at least a part <NUM> of the aggregated data unit <NUM> including the at least one failed data unit <NUM>. That is, only the failed at least one data unit <NUM> can be transmitted, or e.g. the at least one failed data unit <NUM> and some additional bits. The device <NUM> may determine that the decoding of a data unit <NUM> at the receiver <NUM> failed by receiving and analyzing an ACK and/or a Not-Acknowledge (NACK) message from the receiver <NUM> concerning one or more data units <NUM> that were correctly and/or incorrectly decoded at the receiver <NUM>.

When retransmitting the part <NUM> of the aggregated data unit <NUM>, the device <NUM> is configured to scramble and encode the at least one failed data unit <NUM> in the retransmitted part <NUM> by performing scrambling based on the same scrambling seed <NUM> and by using FEC with the same FEC outputs <NUM> that were used for scrambling and encoding said data unit <NUM> in the aggregated data unit <NUM>. That is, the bits of the data unit <NUM> are scrambled in both cases - when transmitted in the aggregated data unit <NUM> and when transmitted in the retransmitted part <NUM> - based on the same scrambling bits of the scrambling seed. FEC is further performed based on the same blocks of information bits. In such a manner, the bits after scrambling and FEC in the retransmission are the same as in the original transmission.

<FIG> shows a device <NUM> according to an embodiment of the invention. The device <NUM> is configured to support HARQ for (NG) Wi-Fi. The device <NUM> may be a Wi-Fi client, STA or the like. The device <NUM> may also be an AP. The device <NUM> may include a descrambler and a FEC unit. The device <NUM> may particularly be the receiver <NUM> described with respect to <FIG>.

The device <NUM> is configured to receive from a transmitter <NUM> an encoded aggregated data unit <NUM> including at least one encoded data unit <NUM>. The transmitter <NUM> may be the device <NUM> described with respect to <FIG>. The aggregated data unit <NUM> is an A-MPDU and the data unit <NUM> may be an MPDU.

The device <NUM> is further configured to decode the at least one data unit <NUM>, and send to the transmitter <NUM> an ACK and/or a NACK message <NUM> regarding one or more data units <NUM> that were correctly and/or incorrectly decoded. The decoding may be performed by the FEC unit, and may include descrambling performed by the descrambler. The descrambling is based on a descrambling seed which corresponds to the scrambling seed used at the transmitter <NUM>.

The device <NUM> is further configured to receive from the transmitter <NUM>, if a decoding of at least one data unit failed <NUM>, and was accordingly reflected in the ACK and/or NACK message, a retransmission of at least part <NUM> of the aggregated data unit <NUM> including the at least one failed data unit <NUM>. The device <NUM> is then able to decode the at least one retransmitted data unit <NUM> and to soft combine it with the previously received failed data unit <NUM>. Thus, it can obtain a more reliable decoding of the data unit <NUM>.

In the following, specific solutions of retransmitting schemes for the at least part <NUM> of the aggregated data unit <NUM> by the device <NUM> are explained in more detail. In particular, the aggregated data unit <NUM> is assumed to be an A-MPDU <NUM>, which includes one or more data units <NUM> that are all MPDUs <NUM>.

A first, very simple solution is retransmitting the entire A-MPDU <NUM>, regardless of which MPDU <NUM> in the initially transmitted A-MPDU <NUM> failed. In this case, the device <NUM> preferably informs the receiver <NUM> that the current transmission is a retransmission, e.g. by sending a retransmission indication. The same scrambling seed <NUM> and FEC outputs <NUM> as for the initial transmission are used for the retransmission of the A-MPDU <NUM>.

A second solution is shown in <FIG>, and bases on the following:.

The second solution may be further supported by the following:.

A third solution is shown in <FIG> and bases on the idea that if the FEC/scrambling would be performed per MPDU <NUM> (instead of for the entire A-MPDU <NUM>), things would be easier. However, there is an inherent problem, namely the receiver's PHY layer does not know in advance what is the size of the MPDU <NUM>, so it cannot compute all LDPC parameters (number of FEC blocks, size, etc.).

Hence, the third solution proposes to pre-define a 'HARQ Block' <NUM>, which is of known size (i.e. known to both device <NUM> and receiver <NUM>), and on which FEC/scrambling is performed independent of other HARQ blocks <NUM>. The size of the HARQ block <NUM> may be defined in the specification (single size, one value per A-MPDU length, etc.) or may be negotiated between the device <NUM> and the receiver <NUM>. For instance, the size of the HARQ block <NUM>, which may contain at least one MPDU <NUM>, a Zero Length Delimiter (ZLD) and padding <NUM>, may be selected such that it is a multiple of scrambler seed period (<NUM> bits). A-MPDU aggregation or MPDU fragmentation can be used to reduce overhead (padding <NUM> to reach HARQ block <NUM> size).

For example, a HARQ block <NUM> of size 1536Bytes may be chosen (as exemplarily shown in <FIG>), which is a multiple of <NUM> bits. It yields <NUM> LDPC codewords of size <NUM>/<NUM> information bits and <NUM>/<NUM> coded bits. MPDUs <NUM> smaller than 1536B shall be first padded with <NUM> to <NUM> zero bytes to align them to <NUM>-bits and then with <NUM>-byte ZLDs to 1536B.

In order to adhere to symbol boundary, anything beyond the last HARQ block <NUM> may be denoted post-FEC bits. Both the device <NUM> and the receiver <NUM> may know in advance the size of a HARQ block <NUM>, so that the location of the first post-FEC bit is easy for them to compute. <FIG> shows particularly an example with several HARQ blocks <NUM>, each containing at least one MPDU <NUM>. In the example, MPDU #<NUM> fails, so that the entire HARQ block #<NUM> is retransmitted, yielding the same coded bits, which can be combined with previous LLRs.

The third solution may be further supported by the following:.

In this scenario, <FIG> shows that there is up to <NUM>% data rate improvement as a function of A-MPDU size for a transmission scheme using HARQ according to the invention.

<FIG> shows a method <NUM> according to an embodiment of the invention, particularly a HARQ method for Wi-Fi. The method <NUM> may be carried out by an access point or router, and/or by the device <NUM> shown in <FIG>.

The method <NUM> includes a step <NUM> of transmitting to a receiver <NUM> and aggregated data unit <NUM> (e.g. an A-MPDU) including one or more data units <NUM> (e.g. MPDUs). In or before this step <NUM>, the method <NUM> includes scrambling the aggregated data unit <NUM> and encoding the scrambled aggregated data unit <NUM> by using FEC. That is, the scrambled and encoded aggregated data unit <NUM> is transmitted to the receiver <NUM>.

The method <NUM> includes further a step <NUM> of retransmitting to the receiver <NUM> at least a part <NUM> of the aggregated data unit <NUM> including at least one failed data unit <NUM>. The failed data unit <NUM> is a data unit <NUM> that the receiver could not decode. In or before this step <NUM>, the method <NUM> includes scrambling and encoding the at least one failed data unit <NUM> based on the same scrambling seed (same scrambling bit sequence) and using the same FEC outputs that were used for scrambling and encoding the same data unit <NUM> in the initially transmitted aggregated data unit <NUM>.

Claim 1:
Device (<NUM>) for supporting Hybrid Automatic Repeat Request, HARQ, the device (<NUM>) being configured to
transmit to a receiver (<NUM>) an Aggregated Media Access Control Protocol Data Unit, A-MPDU (<NUM>), according to the IEEE <NUM> standards and including at least two data units (<NUM>), and to
transmit to the receiver (<NUM>), together with the A-MPDU (<NUM>), HARQ block information about a division of the A-MPDU (<NUM>) into a plurality of determined HARQ Blocks (<NUM>),
wherein the device (<NUM>) is further configured to scramble and encode the A-MPDU (<NUM>) by performing scrambling and by using Forward Error Correction, FEC, independently on each of the plurality of HARQ blocks (<NUM>), and to
retransmit to the receiver (<NUM>), if a decoding of at least one data unit (<NUM>) failed at the receiver (<NUM>), at least a part (<NUM>) of the A-MPDU (<NUM>) including the at least one failed data unit (<NUM>),
wherein each HARQ block (<NUM>) includes at least one data unit (<NUM>),
wherein the retransmitted part (<NUM>) contains each HARQ block (<NUM>) that includes a failed data unit (<NUM>), and
wherein the device (<NUM>) is further configured to scramble and encode the at least one failed data unit (<NUM>) in the retransmitted part (<NUM>) by performing scrambling based on the same scrambling seed (<NUM>) and by using FEC with the same FEC outputs (<NUM>) that were used for scrambling and encoding said data unit (<NUM>) in the A-MPDU (<NUM>).