Patent Description:
The IEEE (Institute of Electrical and Electronics Enignecrs) <NUM> Working Group is developing <NUM>. 11ax HE (High Efficiency) WLAN (Wireless Local Area Network) air interface in order to achieve a very substantial increase in the real-world throughput achieved by users in high density scenarios. OFDMA (Orthogonal Frequency Division Multiple Access) multiuser transmission has been envisioned as one of the most important features in <NUM>. OFDMA is a multiple access scheme that performs multiple operations of data streams to and from the plurality of users over the time and frequency resources of the OFDM (Orthogonal Frequency Division Multiplexing) system.

Fequency scheduling is generally performed for OFDMA multiuser transmission in <NUM>. According to frequency scheduling, a radio communication access point apparatus (hereinafter simply "access point" or "AP") adaptively assigns subcarriers to a plurality of radio communication station apparatuses (hereinafter simply "terminal stations" or "STAs") based on reception qualities of frequency bands of the STAs. This makes it possible to obtain a maximum multiuser diversity effect and to perform communication quite efficiently.

Frequency scheduling is generally performed based on a Resource Unit (RU). A RU comprises a plurality of consecutive subcarriers. A RU may have different types depending on the number of constituent subcarriers per RU. The RUs are assigned by an AP to each of a plurality of STAs with which the AP communicates. The RU assignment result of frequency scheduling performed by the AP shall be reported to the STAs as RU assignment information. In addition, the AP shall also report other control signaling such as common control information and per-user allocation information to STAs.

Document <NPL>, relates to a two-step padding method of the last OFDM symbol, using pre-FEC and post-FEC.

Patent Application <CIT> relates to wireless communication, in particular to group resource allocation GRA, with groups of users being associated according to group-specific parameters. Users within a group may share common parameters, such as MCSs, resource sizes, burst sizes, and MIMO modes.

The transmission for all the STAs in downlink OFDMA shall end at the same time. Padding is a straightforward method for achieving this goal. In addition, packet extension may be applied to an HE packet in order for the receiver to have enough time to process the last OFDM symbol of the received HE packet since <NUM>. 11ax has an OFDM symbol duration which is four time larger than <NUM>1n/ac. Packet extension increases system overhead and but reduces implementation complexity of the receiver. Studies are underway to perform efficient padding and packet extension for downlink OFDMA multiuser transmission in <NUM>. 11ax to compromise implementation comolexity and system overhead.

The present invention is defined by the features of the independent claim, with preferred embodiments being specified in the dependent claims.

Various embodiments of the present disclosure will now be described in detail with reference to the annexed drawings. In the following description, a detailed description of known functions and configurations has been omitted for clarity and conciseness.

<FIG> illustrates a format of an HE (High Efficiency) packet <NUM> complying with the <NUM>. 11ax SFD (Specification Framework Document) [see NPL1]. The HE packet <NUM> includes: a leagcy preamble comprising a legacy short training field (L-STF) <NUM>, a legacy long training field (L-LTF) <NUM> and a legacy signal field (L-SIG) <NUM>; an HE preamble comprising a repeated L-SIG field (RL-SIG) <NUM>, a first HE signal field (HE-SIG-A) <NUM>, a second HE signal field (HE-SIG-B) <NUM>, an HE short training field (HE-STF) <NUM> and an HE long training field (HE-LTF) <NUM>; a HE data field <NUM>; and a packet extension (PE) field <NUM>.

The legacy preamble (<NUM>, <NUM>, <NUM>) is used to facilitate backwards compatibility with the legacy <NUM>. 11a/g/n/ac standards. The L-STF <NUM> and L-LTF <NUM> are primarily used for packet detection, AGC (Automatic Gain Control) setting, frequency offset estimation, time synchronization and channel estimation. The L-SIG <NUM>, together with the RL-SIG <NUM> in the HE preamble which is duplicated from the L-SIG <NUM>, is used to assist in differentiating the HE packet <NUM> from the legacy <NUM>. 11a/g/n/ac packets. In addition, the L-SIG <NUM> comprises a Length field which indicates the transmission time of the HE packet <NUM>.

The HE-SIG-A <NUM> in the HE preamble carries common control information required to interpret the remaining fields of the HE packet <NUM>. In case of the HE packet <NUM> for single user transmission, the HE-SIG-A <NUM> comprises signaling fields such as bandwidth, MCS (Modulation and Coding Scheme), the number of spatial streams (Nss), coding, STBC (Space Time Block Coding), a-factor, PE Disambiguity and LDPC Extra Symbol, etc. The coding field indicates whether the FEC (Forward Error Correction) applied to the HE data field <NUM> is BCC (Binary Convolutional Code) or LDPC (Low Density Parity Code). The STBC field indicates whether STBC is applied to the HE data field <NUM>. The usage of the a-factor field, the PE Disambiguity field and the LDPC Extra Symbol field will be explained later. In case of the HE packet <NUM> for downlink multiuser transmission, the HE-SIG-A <NUM> comprises signaling fields such as bandwidth, SIGB MCS, SIGB Number of Symbols, a-factor, PE Disambiguity and LDPC Extra Symbol, etc..

The HE-SIG-B <NUM> in the HE preamble comprises a common field followed by a user specific field. The common field contains RU assignment information (e.g., the RU arrangement in frequency domain and the number of users multiplexed in each RU). If a RU is designated for single user transmission, the number of users multiplexed in the RU is one. If a RU is designated for MU-MIMO (Multiuser Multiple Input Multiple Output) transmission, the number of users multiplexed in the RU is two or more. The user specific field comprises a plurality of user specific subfields. Each of the user specific subfields carries per-user allocation information. For each RU designated for single user transmission, there is only a single corresponding user specific subfield, which contains signaling fields such as STA identifier, MCS, coding and the number of spatial streams (Nss), etc. For each RU designated for MU-MIMO transmission with K multiplexed users, there are K corresponding user specific subfields, each comprising signaling fields such as STA identifier, MCS, coding and spatial configuration, etc. The ordering of the user specific subfields in the user specific field is compliant with the RU arrangement signalled by the common field. The HE-SIG-B <NUM> does not exist in the HE packet <NUM> if it intends to be used for single user transmission or for uplink triggered based multiuser transmission. For uplink triggered based multiuser transmission, RU assignment information and per-user allocation information for designated transmitting STAs are preset at the AP and transmitted in a trigger frame by the AP to the designated transmitting STAs.

The HE-STF <NUM> in the HE preamble is used to reset AGC and reduces the dynamic range requirement on the ADC (Analog-to-Digital Converter). The HE-LTF <NUM> in the HE preamble is provided for MIMO channel estimation for receiving and equalizing the HE data field <NUM>.

When BCC encoding is used for a STA, the HE data field <NUM> for the STA comprises the SERVICE field, the PSDU (Physical Layer Service Data Unit), the PHY (Physical Layer) padding bits and the tail bits. Note that the PSDU includes the MAC (Media Access Control Layer) padding bits. When LDPC encoding is used for a STA, the HE data field <NUM> for the STA comprises the SERVICE field, the PSDU and the PHY padding bits. The HE data field <NUM> for a STA is transmitted on its designated RU spanning all of OFDM symbols in the HE data field <NUM>.

The PE field <NUM> carries null data, which is purely used to allow the receiver to have enough time to process the last OFDM symbol of the HE data field <NUM>.

Details of transmission processing for the L-STF <NUM>, the L-LTF <NUM>, the L-SIG <NUM>, the RL-SIG <NUM>, the HE-SIG-A <NUM>, the HE-SIG-B <NUM>, the HE-STF <NUM>, the HE-LTF <NUM>, the HE data field <NUM> and the PE field <NUM> can be found in the <NUM>. 11ax SFD [see NPL1].

According to the <NUM>. 11ax SFD [see NPL1], a two-step padding process is applied to the HE data field <NUM> of the HE packet <NUM>. A pre-FEC padding with both MAC and PHY padding is applied before conducting FEC coding, and a post-FEC PHY padding is applied on the FEC encoded bits (including information bits, pre-FEC padding bits and FEC parity bits). The pre-FEC padding may pad torward four possible boundaries in the last one or two OFDM symbols of the HE data field <NUM> of the HE packet <NUM> depending on whether STBC is applied to the HE data field <NUM>. If no STBC is applied to the HE data field <NUM>, the pre-FEC padding may pad torward four possible boundaries in the last OFDM symbol of the HE data field <NUM>. Otherwise the pre-FEC padding may pad torward four possible boundaries in the last two OFDM symbols of the HE data field <NUM>. The four possible boundaries are represented by a so-called a-factor parameter, which partition the FEC enocded bit stream of the last OFDM symbol(s) into four symbol segments.

<FIG> illustrates various examples of padding and PE for the HE packet <NUM> for single user transmission in case of no STBC according to a prior art [see NPL1 & NPL2]. In this example, for the a-factor having a value of <NUM>, <NUM> or <NUM>, the pre-FEC padding pads torward the first boundary, the second boundary or the third boundary in the last OFDM symbol of the HE data field <NUM>. For the a-factor having a value of <NUM>, the pre-FEC padding pads torward the end of the last OFDM symbol of the HE data field <NUM>. The duration of the PE field <NUM> is a function of the pre-FEC padding bounday in the last OFDM symbol of the HE data field <NUM>. Details of how the transmitter calculates the duration of the PE field <NUM> can be found in the <NUM>. 11ax SFD [see NPL1 & NPL2]. If the LDPC is applied to the HE data field <NUM>, the receiver needs not to process post-FEC padding bits in the last OFDM symbol of the HE data field <NUM>. As a result, even if the duration of the PE field <NUM> is reduced for the smaller a-factor (e.g., as illustrated in <FIG>, the duration of the PE field <NUM> in case of the a-factor having a value of <NUM> is smaller than that in case of the a-factor having a value of <NUM>, <NUM> or <NUM>), the receiver still has enough time to process the last OFDM symbol of the HE data field <NUM>. In this way, implementation complexity of the receiver is minimized while an increase of the system overhead due to packet extension is suppressed.

<FIG> illustrates an example method <NUM> for determining the padding and PE related parameters for single user transmission according to a prior art [see NPL2]. The method <NUM> starts at step <NUM> based on the following parameters:
<MAT>
where NSD,short is the number of data subcarriers for each of the first three symbol segments, determined by the bandwidth which is indicated in the HE-SIG-A <NUM>; Nss is the number of spatial streams which is indicated in the HE-SIG-A <NUM>; R is the code rate, determined by the MCS which is indicated in the HE-SIG-A <NUM>; and NBPSCS is the number of coded bits per subcarrier, determined by the MCS which is indicated in the HE-SIG-A <NUM>.

At step <NUM>, an initial number of OFDM symbols in the HE data field <NUM> and an initial a-factor value are computed. The initial number of OFDM symbols in the HE data field <NUM> is computed by the following formula:
<MAT>
where APEP LENGTH is the A-MPDU (Aggregate MAC Protocol Data Unit) length prior to end-of-frame MAC paddding; Ntail is the number of tail bits and has a value of <NUM> for BCC and <NUM> for LDPC; NES is the number of BCC encoders and has a value of either <NUM> or <NUM>, determined by the MCS, NSS and bandwidth which are indicated in the HE-SIG-A <NUM>; Nservice is the length of the SERVICE field and has a value of <NUM>; mSTBC has a value of <NUM> for STBC and <NUM> for no STBC; and NDBPS the number of data bits per OFDM symbol, determined by the MCS and bandwidth which are indicated in the HE-SIG-A <NUM>. The initial a-factor is computed by the following formula:
<MAT>
where the number of excess information bits in the last OFDM symbol(s) of the HE data field <NUM> is shown by the following formula.

At step <NUM>, the number of pre-FEC padding bits is computed based on the initial number of OFDM symbols in the HE data field <NUM> and the initial a-factor value by the following formula
<MAT>.

At step <NUM>, the final a-factor value and the final number of OFDM symbols in the HE data field <NUM> are computed based on the initial number of OFDM symbols in the HE data field <NUM> and the initial a-factor value. In case of BCC, the final number of OFDM symbols in the HE data field <NUM> is NSYM = NSYM_init, and the final a-factor is a = ainit. In case of LDPC, it is necessary to go through the LDPC encoding process in order to compute the final a-factor value and the final number of OFDM symbols in the HE data field <NUM>. Starting from
<MAT>.

At step <NUM>, the number of post-FEC padding bits in each of the last symbol(s) is computed based on the final a-factor value by the following formula
<MAT>.

At step <NUM>, the duration of the PE field <NUM> is computed according to the final a-factor value. Notice that the PE Ambiguity field in the HE-SIG-A <NUM> and the Length field in the L-SIG <NUM> can be set according to the final number of OFDM symbols in the HE data field <NUM> and the duration of the PE field <NUM>. Details can be found in the <NUM>. 11ax SFD [see NPL1]. The method <NUM> stops at step <NUM>.

<FIG> illustrates the example padding and PE for the HE packet <NUM> for downlink multiuser transmission in case of no STBC according to a prior art [see NPL1 & NPL2]. For downlink multiuser transmission, all the users share the same duration of the PE field <NUM>, the common a-factor value and the common number of OFDM symbols in the HE data field <NUM>. The common a-factor value is determined from the user with the longest encoded packet duration. In this example, the common a-factor has a value of <NUM> according to the STA2 which has the longest encoded packet duration. For each user, the pre-FEC padding pads torward the second boundary in the last OFDM symbol of the HE data field <NUM>.

However, there is no concrete method available for determining the padding related parameters for downlink multiuser transmission (e.g., the common a-factor, the common number of OFDM symbols in the HE data field <NUM>, per-user number of pre-FEC padding bits and per-user number of post-FEC padding bits, etc). Next, according to a first aspect of the present disclosure, various embodiments of the method for determining the padding and PE related parameters for downlink multiuser transmission will be explained in further details.

<FIG> illustrates an example method <NUM> for determining the padding and PE related parameters for downlink multiuser transmission according to a first embodiment of the first aspect of the present disclosure. The method <NUM> starts at step <NUM> based on the following parameters:
<MAT>
where NSD, short, u is the number of data subcarriers for each of the first three symbol segments for user u, determined by the size of the RU assigned to user u which is indicated in the HE-SIG-B <NUM>, NSD, u is the number of spatial streams for user u which is indicated in the HE-SIG-B <NUM>, Ru is the code rate for user u, determined by the MCS for user u which is indicated in the HE-SIG-B <NUM>, and NBPSCS, u is the number of coded bits per subcarrier for user u, determined by the MCS for user u which is indicated in the HE-SIG-B <NUM>.

At step <NUM>, an initial user-specific number of OFDM symbols in the HE data field <NUM> and an initial user-specific a-factor value are computed for each user. The initial user-specific number of OFDM symbols in the HE data field <NUM> for user u is computed by the following formula
[Math. <NUM>]
<MAT>
where APEP_LENGTH, is the A-MPDU length prior to end-of-frame MAC padding for user u; NES,u is the number of BCC encoders for user u, determined by the MCS for user u, NSS for user u and the size of the RU assigned to user u which are indicated in the HE-SIG-B <NUM>; and NDBPS,u is the number of data bits per OFDM symbol, determined by the MCS for user u and the size of the RU assigned to user u which are indicated in the HE-SIG-B <NUM>. The initial user-specific a-factor for user u is computed by the following formula
[Math. <NUM>]
<MAT>.

At step <NUM>, an initial user with the longest encoded packet duration is determined based on the initial user-specific number of OFDM symbols in the HE data field <NUM> and the initial user-specific a-factor value for each user by the following formula
<MAT>
and Nuser is the total number of users. The initial largest number of OFDM symbols in the HE data field <NUM> is shown by the following formula
<MAT>
and the initial common a-factor value is shown by the following formula.

At step <NUM>, the number of pre-FEC padding bits for each user is computed based on the initial largest number of OFDM symbols in the HE data field <NUM> and the initial common a-factor value. For example, the number of pre-FEC padding bits for user u is given by the following formula
<MAT>.

At step <NUM>, the final common number of OFDM symbols in the HE data field <NUM> and the final common a-factor value are computed based on the initial largest number of OFDM symbols in the HE data field <NUM> and the initial common a-factor value. At first, the user-specific a-factor value and the user-specific number of OFDM symbols in the HE data field <NUM> are computed for each user based on the initial largest number of OFDM symbols in the HE data field <NUM> and the initial common a-factor value. For a user using LDPC, it is necessary to go through the LDPC encoding process in order to compute the user-specific a-factor value and the user-specific number of OFDM symbols in the HE data field <NUM>. For example, if user u uses LDPC, starting from
<MAT>.

Otherwise the final user with the longest encoded packet duration is shown by the following formula.

Finally, the final common number of OFDM symbols in the HE data field <NUM> is N SYM = NSYM,umax and the final common a-factor is a=aumax. It should be noted that the a-factor field in the HE-SIG-A <NUM> is set according to the final common a-factor value.

According to the above descriptions of step <NUM>, if all the users use BCC or if the condition for setting the LDPC Extra Symbol field in the HE-SIG-A <NUM> to <NUM> is not met for any user using LDPC , the final common number of OFDM symbols in the HE data field <NUM> is NSYM= NSYM_max,int and the final common a-factor is a=ainit. Otherwise the final common number of OFDM symbols in the HE data field <NUM> is shown by the following formula
<MAT>
and the final common a-factor is shown by the following formula.

In addition, some LDPC encoding parameters for the users using LDPC need to be updated based on the final common a-factor value and the final common number of OFDM symbols in the HE data field <NUM>. For example, for user u using LDPC, the number of available bits is updated by the following formula
<MAT>.

And the number of bits to be punctured is updated by
<MAT>.

At step <NUM>, the number of post-FEC padding bits in each of the last symbol(s) for each user is computed based on the final common a-factor value. For exmple, the number of post-FEC padding bits in each of the last symbol(s) for user u is given by the following formula.

At step <NUM>, the common duration of the PE field <NUM> is computed based on the final common a-factor value. Notice that the PE Ambiguity field in the HE-SIG-A <NUM> and the Length field in the L-SIG <NUM> can be set according to the final common number of OFDM symbols in the HE data field <NUM> and the common duration of the PE field <NUM>. Details can be found in the <NUM>. 11ax SFD [see NPL1]. The method <NUM> stops at step <NUM>.

<FIG> illustrates an example method <NUM> for determining the padding and PE related parameters for downlink multiuser transmission according to a second embodiment of the first aspect of the present disclosure. The method <NUM> starts at step <NUM>.

At step <NUM>, an initial user-specific number of OFDM symbols in the HE data field <NUM> is computed for each user. For example, the initial user-specific number of OFDM symbols in the HE data field <NUM> for user u, NSYM_init,u, is computed according to Equation (<NUM>). Next an initial largest number of OFDM symbols in the HE data field <NUM> is computed based on the initial user-specific number of OFDM symbols in the HE data field <NUM> for each user by the following formula. <NUM>]
<MAT>.

At step <NUM>, an initial common a-factor value is computed based on the initial largest number of OFDM symbols in the HE data field <NUM>. At first a subset of users, S, with the initial largest number of OFDM symbols in the HE data field <NUM> is determined by the formula below.

Then an initial user-specific a-factor value is computed for each user in the subset. For example, an initial user-specific a-factor value for user u in the subset, ainit,u, is computed according to Equation (<NUM>). Finally the initial common a-factor is shown by the formula below.

Step <NUM> to step <NUM> of the method <NUM> are the same as step <NUM> to step <NUM> of the method <NUM>, respectively. The method <NUM> stops at step <NUM>.

According to step <NUM> and step <NUM> of the method <NUM>, in order to calculate the initial common a-factor value and the initial largest number of OFDM symbols in the HE data field <NUM>, the initial user-specific a-factor values only for a subset of users need to be computed. As a result, the method <NUM> is more efficient than the method <NUM> in terms of computational complexity.

<FIG> illustrates an example method <NUM> for determining the padding and PE related parameters for downlink multiuser transmission according to a third embodiment of the first aspect of the present disclosure. The method <NUM> starts at step <NUM>.

At step <NUM>, an initial user with the longest encoded packet duration is determined by the following formula.

At step <NUM>, an initial largest number of OFDM symbols in the HE data field <NUM> and an initial common a-factor value are computed according to the initial user with the longest encoded packet duration. The initial largest number of OFDM symbols in the HE data field <NUM> is computed by NSYM_max_init = NSYM_init,umax_init, where the initial number of OFDM symbols in the HE data field <NUM> for user umax_init, NSYM_init,umax_init , can be computed according to Equation (<NUM>). The initial common a-factor is ainit = ainit, umax_init, where the initial user-specific a-factor for user umax_init, ainit,umax_init, can be computed according to Equation (<NUM>).

According to step <NUM> and step <NUM> of the method <NUM>, in order to calculate the initial common a-factor value and the initial largest number of OFDM symbols in the HE data field <NUM>, the initial user-specific a-factor value only for a single user needs to be computed. As a result, the method <NUM> is even more efficient than the method <NUM> in terms of computational complexity.

With reference to <FIG>, according to the prior arts [see NPL1 & NPL2], even if the last OFDM symbol in the HE data field <NUM> may not contain information bits for some users (e.g., STA3 and STA4), these users are still required to process the last OFDM symbol in the HE data field <NUM>, which leads to increased power consumption.

According to a second aspect of the present disclosure, all users are grouped into two groups. The first group comprises at least one user that has FEC encoded bits spanned over all of the OFDM symbols in the HE data field <NUM>. The second group comprises the users that have FEC encoded bits spanned over only a part of the OFDM symbols in the HE data field <NUM>.

<FIG> illustrates an example method for user grouping according to the second aspect of the present disclosure. The method <NUM> starts step <NUM>. At step <NUM>, an initial number of OFDM symbols in the HE data field <NUM> for each user is computed. For example, an initial number of OFDM symbols in the HE data field <NUM> for user u, N SYM init,u, can be computed according to Equation (<NUM>). Then an initial largest number of OFDM symbols in the HE data field <NUM>, N SYM max init, can be computed according to Equation (<NUM>) based on the initial number of OFDM symbols in the HE data field <NUM> for each user.

At step <NUM>, the users multiplexed in RUs designated for single user transmission are grouped into the first group and the second group. For user u multiplexed in a RU designated for single user transmission, it will be grouped into the second group if
<MAT>
where M is a positive integer (e.g., M = <NUM>) and its value is predetermined or configurable. Otherwise it will be grouped into the first group.

At step <NUM>, the users multiplexed in RUs designated for MU-MIMO transmission are grouped into the first group and the second group. For a cluster of users multiplexed in a RU designated for MU-MIMO transmission, at first the initial largest number of OFDM symbols in the HE data field <NUM> among the cluster of users is determined by the following formula
<MAT>
where C stands for the cluster of users multiplexed in the RU designated for MU-MIMO transmission. The whole cluster of users will be grouped into the second group if the following condition is met.

Otherwise the whole cluster of users will be grouped into the first group. In other words, the whole cluster of users multiplexed in a RU designated for MU-MIMO transmission shall be grouped into the same group. The method <NUM> stops at step <NUM>.

According to the user grouping method <NUM> illustrated in <FIG>, the initial largest number of useful OFDM symbols in the HE data field <NUM> for the second group is shown by the following formula. <NUM>]
<MAT>.

According to the second aspect of the present disclosure, all the users share the common number of OFDM symbols in the HE data field <NUM> and the common duration of the PE field <NUM>. The common number of OFDM symbols in the HE data field <NUM> and the common duration of the PE field <NUM>, together with other padding related paramters specific to the first group (e.g., the a-factor for the first group), can be determined according to the user in the first group with the longest encoded packet duration using one of the methods according to the abovementioned three embodiments of the first aspect of the present disclosure. For each of the users in the first group, the pre-FEC padding pads towards the boundary in the last OFDM symbol(s) in the HE data field <NUM>, specified by the a-factor value for the first group.

According to the second aspect of the present disclosure, the padding related paramters specific to the second group (e.g., the number of useful OFDM symbols in the HE data field <NUM> for the second group and the a-factor for the second group) are determined according to the user in the second group with the longest encoded packet duration. The methods for determining the padding related parameters specific to the second group will be detailed later. The useful OFDM symbols in the HE data field <NUM> for the second group refer to those OFDM symbols in the HE data field <NUM> that contain FEC encoded bits for at least one of the users in the second group. For each of the users in the second group, the pre-FEC padding pads towards the boundary in the last useful OFDM symbol(s) in the HE data field <NUM> for the second group, specified by the a-factor value for the second group.

<FIG> illustrates example padding and packet extension for the HE packet <NUM> for downlink multiuser transmission in case of no STBC according to the second aspect of the present disclosure. In this example, the first group comprises STA1 and STA2 while the second group comprises STA3 and STA4. The a-factor for the first group has a value of <NUM> and the a-factor for the second group has a value of <NUM>. The number of useful OFDM symbols in the HE data field <NUM> for the second group is one symbol less than the common number of OFDM symbols in the HE data field <NUM>. In other words, for each of the users in the first group (i.e., STA1 and STA2), the pre-FEC padding pads towards the second boundary in the last OFDM symbol in the HE data field <NUM>; while for each of the users in the second group (i.e., STA3 and STA4), the pre-FEC padding pads towards the third boundary in the second last OFDM symbol in the HE data field <NUM>. As a result, the users in the second group (i.e., STA3 and STA4) need not to process the last OFDM symbol in the HE data field <NUM> and therefore power consumption is reduced compared with the prior arts [see NPL1 & NPL2].

<FIG> illustrates an example method <NUM> for determining the padding related parameters specific to the second group according to the first embodiment of the second aspect of the present disclosure. The method <NUM> starts at step <NUM>. At step <NUM>, an initial user-specific a-factor value is computed for each user in the second group. For example, the initial user-specific a-factor for user u, ainit,u, in the second group can be computed according to Equation (<NUM>).

At step <NUM>, an initial user in the second group with the longest encoded packet duration is determined based on the initial user-specific a-factor value for each user in the second group and the initial largest number of useful OFDM symbols in the HE data field <NUM> for the second group, NSYM_max_init,G2, which can be obtained according to Equation (<NUM>) during the user grouping. At first a subset of users, U, in the second group with the initial largest number of useful OFDM symbols in the HE data field <NUM> is determined by the following formula
<MAT>
where Nuser,G2 is the number of users in the second group. The initial user in the second group with the longest encoded packet duration is determined by the following formula.

Then the initial common a-factor value for the second group is shown by the following formula.

At step <NUM>, the number of pre-FEC padding bits for each user in the second group are computed based on the initial largest number of useful OFDM symbols in the HE data field <NUM> for the second group and the initial common a-factor value for the second group. For example, the number of pre-FEC padding bits for user u in the second group is computed by the following formula
<MAT>.

At step <NUM>, the final common number of useful OFDM symbols in the HE data field <NUM> for the second group and the final common a-factor value for the second group are computed based on the initial largest number of useful OFDM symbols in the HE data field <NUM> for the second group and the initial common a-factor value for the second group. Similar to step <NUM> of the method <NUM> as illustrated in <FIG>, it is necessary to go through the LDPC encoding process in order to compute the final common number of useful OFDM symbols in the HE data field <NUM> for the second group and the final common a-factor value for the second group if at least one user in the second group uses LDPC. If all the users in the second group use BCC or if the condition for setting the LDPC Extra Symbol for the Second Group field in the HE-SIG-A <NUM> to <NUM> is not met for any user in the second group using LDPC , the final common number of useful OFDM symbols in the HE data field <NUM> for the second group is NSYM,G2 = NSYM_max_init,G2 and the final common a-factor for the second group is aG2 = ainit,G2. Otherwise the final common number of useful OFDM symbols in the HE data field <NUM> for the second group is shown by the following formula
<MAT>
and the final common a-factor for the second group is shown by the following formula.

At step <NUM>, the number of post-FEC padding bits for each user in the second group is computed based on the final common a-factor value for the second group, the final common number of useful OFDM symbols in the HE data field <NUM> for the second group and the common number of OFDM symbols in the HE data field <NUM>. For example, the number of post-FEC padding bits for user u in the second group is computed by the following formula.

<FIG> illustrates the content of the HE-SIG-A <NUM> of the HE packet <NUM> according to the first embodiment of the second aspect of the present disclosure. The following signalling fields are required in the HE-SIG-A <NUM>:.

Notice that in case of a single user group, the a-factor for the Second Group field, the LDPC Extra Symbol for the Second Group field and the Value of M field are reserved. In addition, if the value of M is predetermined, the Value of M field can be ignored.

<FIG> illustrates the content of each user-specific subfield of the HE-SIG-B <NUM> of the HE packet <NUM> according to the first embodiment of the second aspect of the present disclosure. A Group Indication field shall be present in each user-specific subfield of the HE-SIG-B <NUM> to indicate which one of the first group and the second group each user belongs to.

According to a second embodiment of the second aspect of the present disclosure, the condition for setting the LDPC Extra Symbol for the Second Group field in the HE-SIG-A <NUM> to <NUM> is assumed to be met for at least one user in the second group. As a result, the LDPC Extra Symbol for the Second Group field in the HE-SIG-A <NUM> can be ignored, which leads to reduced signaling requirement in the HE-SIG-A <NUM>. Furthermore, unlike the first embodiment of the second aspect of the present disclosure, there is no need of going through the LDPC encoding process in order to compute the final common a-factor value for the second group and the final common number of useful OFDM symbols in the HE data field <NUM> for the second group.

<FIG> illustrates an example method <NUM> for determining the padding related parameters for the second group according to the second embodiment of the second aspect of the present disclosure. The method <NUM> starts at step <NUM>. Step <NUM> to step <NUM> of the method <NUM> are the same as step <NUM> to step <NUM> of the method <NUM>, respectively.

At step <NUM>, the final common number of useful OFDM symbols in the HE data field <NUM> for the second group and the final common a-factor value for the second group are computed based on the initial largest number of useful OFDM symbols in the HE data field <NUM> for the second group and the initial common a-factor value for the second group. If LDPC is used by at least one of the users in the second group, the final common number of useful OFDM symbols in the HE data field <NUM> for the second group is shown by the following formula.

The final common a-factor value for the second group is shown by the following formula.

If BCC is used by all of the users in the second group, the final common number of useful OFDM symbols in the HE data field <NUM> for the second group is shown by the following formula.

The method <NUM> of the method <NUM> is the same as step <NUM> of the method <NUM>. The method <NUM> stops at step <NUM>.

According to a third embodiment of the second aspect of the present disclosure, the final common a-factor value for the second group aG2 has a value of <NUM> and the condition for setting the LDPC Extra Symbol for the Second Group field to <NUM> is met for at least one user in the second group. As a result, the a-factor for the Second Group field and the LDPC Extra Symbol for the Second Group field in the HE-SIG-A <NUM> can be ignored, which leads to reduced signaling requirement in the HE-SIG-A <NUM>. Furthermore, similar to the second embodiment of the second aspect of the present disclosure, there is no need of going through the LDPC encoding process in order to compute the final common a-factor value for the second group and the final common number of useful OFDM symbols in the HE data field <NUM> for the second group.

<FIG> illustrates an example method <NUM> for determining the padding related parameters for the second group according to the third embodiment of the second aspect of the present disclosure. The method <NUM> starts at step <NUM>. At step <NUM>, the number of pre-FEC padding bits for each user in the second group are computed based on the initial largest number of useful OFDM symbols in the HE data field <NUM> for the second group group, NSYM_max_init,G2, which can be obtained according to Equation (<NUM>) during the user grouping. For example, the number of pre-FEC padding bits for user u in the second group is computed by the following formula.

At step <NUM>, the final common number of useful OFDM symbols in the HE data field <NUM> for the second group is computed based on the initial largest number of useful OFDM symbols in the HE data field <NUM> for the second group by the following formula.

At step <NUM>, the number of post-FEC padding bits for each user in the second group is computed based on the final common number of useful OFDM symbols in the HE data field <NUM> for the second group and the common number of OFDM symbols in the HE data field <NUM>. For example, the number of post-FEC padding bits for user u in the second group is computed by the following formula.

<FIG> is a block diagram illustrating an example configuration of the AP according to the present disclosure. The AP comprises a controller <NUM>, a scheduler <NUM>, a message generator <NUM>, a message processor <NUM>, a PHY processor <NUM> and an antenna <NUM>.

The antenna <NUM> can comprise one antenna port or a combination of a plurality of antenna ports. The controller <NUM> is a MAC protocol controller and controls general MAC protocol operations. For downlink transmission, the scheduler <NUM> performs frequency scheduling under the control of the controller <NUM> based on channel quality indicators (CQIs) from STAs and assigns data for STAs to RUs.

The scheduler <NUM> also outputs the resource assignment results to the message generator <NUM>. The message generator <NUM> generates corresponding control signaling (i.e., common control information, resource assignment information and per-user allocation information) and data for scheduled STAs, which are formulated by the PHY processor <NUM> into the HE packets and transmitted through the antenna <NUM>. In particular, the controller <NUM> computes the padding and PE related parameters according to the above mentioned embodiments of the various aspects of the present disclosure, which are provided to the PHY processor <NUM> to guide the formulation of the HE packet, including padding and packet extension according to the above mentioned embodiments of the various aspects of the present disclosure.

On the other hand, the message processor <NUM> analyzes the received CQIs from STAs through the antenna <NUM> under the control of the controller <NUM> and provides them to scheduler <NUM> and controller <NUM>. These CQIs are received quality information reported from the STAs. The CQI may also be referred to as "CSI" (Channel State Information).

<FIG> is a block diagram illustrating an example configuration of the STA according to the present disclosure. The STA comprises a controller <NUM>, a message generator <NUM>, a message processor <NUM>, a PHY processor <NUM> and an antenna <NUM>.

The controller <NUM> is a MAC protocol controller and controls general MAC protocol operations. The antenna <NUM> can comprise one antenna port or a combination of a plurality of antenna ports. For downlink transmission, the antenna <NUM> receives downlink signal including HE packets, and the message processor <NUM> identifies its designated RUs and its specific allocation information from the control signaling included in the received HE packet, and decodes its specific data from the received HE packet at its designated RUs according to its specific allocation information. Padding and packet extension applied to the received HE packet was formulated by the AP according to the above mentioned embodiments of the various aspects of the present disclosure. The message processor <NUM> estimates channel quality from the received HE packet through the antenna <NUM> and provides them. to controller <NUM>. The message generator <NUM> generates CQI message, which is formulated by the PHY processor <NUM> and transmitted through the antenna <NUM>.

In the foregoing embodiments, the present disclosure is configured with hardware by way of example, but the present disclosure may also be provided by software in cooperation with hardware.

In addition, the functional blocks used in the descriptions of the embodiments are typically implemented as LSI devices, which are integrated circuits. The functional blocks may be formed as individual chips, or a part or all of the functional blocks may be integrated into a single chip. The term "LSI" is used herein, but the terms "IC," "system LSI," "super LSI" or "ultra LSI" may be used as well depending on the level of integration.

In addition, the circuit integration is not limited to LSI and may be achieved by dedicated circuitry or a general-purpose processor other than an LSI. After fabrication of LSI, a field programmable gate array (FPGA), which is programmable, or a reconfigurable processor which allows reconfiguration of connections and settings of circuit cells in LSI may be used.

Should a circuit integration technology replacing LSI appear as a result of advancements in semiconductor technology or other technologies derived from the technology, the functional blocks could be integrated using such a technology. Another possibility is the application of biotechnology and/or the like.

This disclosure can be applied to a method for formatting and transmitting data in a wireless communications system.

As such, the embodiments are limited only by the enclosed claims. Additional embodiments are summarized in the following clauses.

The transmission apparatus according to clause <NUM>, wherein in case that the one or more terminal stations are grouped into the first group and the second group, for each of the one or more terminal stations in the first group, pre-FEC padding included in the data field pads towards the boundary in the last OFDM symbol(s) in the data field, specified by the a-factor value for the first group; while for each of the one or more terminal stations in the second group, the pre-FEC padding included in the data field pads towards the boundary in the last useful OFDM symbol(s) in the data field for the second group, specified by the a- factor value for the second group, and wherein the useful OFDM symbols in the data field for the second group refer to those OFDM symbols in the data field that contains FEC encoded bits for at least one terminal station in the second group.

The transmission apparatus according to clause <NUM>, wherein in case that the one or more terminal stations are grouped into a single group, for each of the one or more terminal stations, the pre-FEC padding pads towards the boundary in the last OFDM symbol(s) in the data field, specified by the common a-factor value.

The transmission apparatus according to clause <NUM>, wherein the first signal field contains a signaling subfield to indicate whether the one or more terminal stations are grouped into a single group or two groups.

The transmission apparatus according to clause <NUM>, wherein in case that the one or more terminal stations are grouped into the first group and the second group, per-user allocation information carried in the second signal field contain a signaling to indicate which one of the first group and the second group each of the one or more terminal stations belongs to.

The transmission apparatus according to clause <NUM>, wherein in case that the one or more terminal stations are grouped into a single group, the transmission apparatus further comprises
a control circuitry, which, in operation, computes padding and packet extension related parameters by:.

The transmission apparatus according to clause <NUM>, wherein in case that the one or more terminal stations are grouped into a single group, the transmission apparatus further comprises
a control circuitry, which, in operation, computes padding and packet extension related parameters by:
computing an initial user-specific number of OFDM symbols in the HE data field for each user and compute an initial largest number of OFDM symbols in the HE data field based on the initial user-specific number of OFDM symbols in the HE data field for each user; and computing an initial common a-factor value based on the initial largest number of OFDM symbols in the HE data field.

The transmission apparatus according to clause <NUM>, wherein the computing includes:.

The transmission apparatus according to clause <NUM>, wherein in case that the one or more terminal stations are grouped into the first group and the second group, the transmission apparatus further comprises
a control circuitry, which, in operation, computes padding and packet extension related parameters by:.

The transmission apparatus according to clause <NUM>, wherein in case that the one or more terminal stations are grouped into the first group and the second group, the transmission apparatus further comprises a control circuitry, which, in operation, computes padding and packet extension related parameters by:.

The transmission apparatus according to clause <NUM>, wherein the computing of the final common number of useful OFDM symbols in the HE data field for the second group and the final common a-factor value for the second group based on the initial largest number of useful OFDM symbols in the HE data field for the second group and the initial common a-factor value for the second group may not require going through the LDPC encoding process even if at least one user in the second group uses LDPC.

Claim 1:
A transmission apparatus comprising,
circuitry (<NUM>) and at least one antenna (<NUM>),
the circuitry configured to generate a transmission signal for each of a plurality of users,
the transmission signal including a plurality of Orthogonal Frequency Division Multilpexing, OFDM, symbols for a data field which contains an encoded bit stream of information bits, wherein the last OFDM symbol of the plurality of OFDM symbols is partitioned into four segments, the four segments ending with four boundaries, respectively, and
the at least one antenna configured to transmit the transmission signal,
the circuitry configured to generate the transmission signal by:
- computing (<NUM>), for each of the plurality of users, an initial padding factor value, and computing, for each of the plurality of users, an initial number of OFDM symbols for the data field, wherein the padding factor value represents one of the four boundaries;
- determining (<NUM>) a user with longest encoded packet duration among the plurality of users;
- determining (<NUM>) a common padding factor value that is the initial padding factor value of the determined user with the longest encoded packet duration;
- determining (<NUM>) a common number of OFDM symbols that is the initial number of OFDM symbols for the data field of the determined user with the longest encoded packet duration;
- adding, for each of the plurality of users, pre-Forward Error Correction, pre-FEC, padding bits to the information bits so that the encoded bit stream fills at least one of the four segments until one of the four boundaries specified by the determined common padding factor value; and
- adding post-FEC padding bits after the encoded bit stream of the last OFDM symbol, wherein
the transmission apparatus comprises a scheduler (<NUM>) configured to perform frequency scheduling under control of the circuitry; and
the user with the longest encoded packet duration is determined based on both the initial number of OFDM symbols and the initial padding factor value of each of the plurality of users.