Transmission apparatus and transmission method for padding and packet extension for downlink multiuser transmission

1. A transmission method comprising:

generating a transmission signal for each of a plurality of users, the transmission signal including a plurality of OFDM symbols for a data field, wherein a last OFDM symbol of the plurality of OFDM symbols can be partitioned into four segments, and wherein the generating of the transmission signal includes:

computing, for each of the plurality of users, an initial padding factor value that is associated with one of the four segments and computing, for each of the plurality of users, an initial number of OFDM symbols for the data field;

determining a user with a longest packet duration among the plurality of users;

determining a common padding factor value that is the initial padding factor value of the determined user with the longest packet duration;

determining 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 packet duration;

adding, for each of the plurality of users, pre-FEC padding bits toward one of four possible boundaries of the last OFDM symbol, the one of four possible boundaries being represented by the determined common padding factor value; and

adding post-FEC padding bits in remaining segment(s) of the last OFDM symbol; and

transmitting the generated transmission signal.

2. The transmission method according to claim 1 , wherein a number of the pre-FEC padding bits is determined for each of the plurality of users based on the determined common padding factor value.

3. The transmission method according to claim 1 , wherein information bits and the added pre-FEC padding bits in the data field are encoded using either a Binary Convolutional Code (BCC) or a Low Density Parity Check (LDPC).

4. The transmission method according to claim 1 , wherein the data field includes information bits, and the initial padding factor value for each of the plurality of users is determined based on the information bits.

5. The transmission method according to claim 1 , wherein a number of the post-FEC padding bits is determined based on the common padding factor value.

6. The transmission method according to claim 1 , wherein

when the plurality of users are grouped into a first group and a second group, and the second group of users has a shorter packet duration than the first group of users,

the pre-FEC padding bits are added toward the end of one of four segments of the last OFDM symbol in the transmission signal for the first group; and

the pre-FEC padding bits are added toward the end of one of four segments of an OFDM symbol other than the last OFDM symbol and the pre-FEC padding bits are not included in the last OFDM symbol in the transmission signal for the second group.

7. A transmission apparatus comprising:

a transmission signal generator which, in operation, generates a transmission signal for each of a plurality of users, the transmission signal including a plurality of OFDM symbols for a data field, wherein a last OFDM symbol of the plurality of OFDM symbols can be partitioned into four segments, and wherein the transmission signal generator generates the transmission signal by:

computing, for each of the plurality of users, an initial padding factor value that is associated with one of the four segments and computing, for each of the plurality of users, an initial number of OFDM symbols for the data field;

determining a user with a longest packet duration among the plurality of users;

determining a common padding factor value that is the initial padding factor value of the determined user with the longest packet duration;

determining 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 packet duration;

adding, for each of the plurality of users, pre-FEC padding bits toward one of four possible boundaries of the last OFDM symbol, the one of four possible boundaries being represented by the determined common padding factor value; and

adding post-FEC padding bits in remaining segment(s) of the last OFDM symbol; and

a transmitter which, in operation, transmits the generated transmission signal.

8. The transmission apparatus according to claim 7 , wherein a number of the pre-FEC padding bits is determined for each of the plurality of users based on the determined common padding factor value.

9. The transmission apparatus according to claim 7 , wherein information bits and the added pre-FEC padding bits in the data field are encoded using either a Binary Convolutional Code (BCC) or a Low Density Parity Check (LDPC).

10. The transmission apparatus according to claim 7 , wherein the data field includes information bits, the initial padding factor value for each of the plurality of users is determined based on the information bits.

11. The transmission apparatus according to claim 7 , wherein a number of the post-FEC padding bits is determined based on the common padding factor value.

12. The transmission apparatus according to claim 7 , wherein

when the plurality of users are grouped into a first group and a second group, and the second group of users has a shorter packet duration than the first group of users,

the pre-FEC padding bits are added toward the end of one of four segments of the last OFDM symbol in the transmission signal for the first group; and

the pre-FEC padding bits are added toward the end of one of four segments of an OFDM symbol other than the last OFDM symbol and the pre-FEC padding bits are not included in the last OFDM symbol in the transmission signal for the second group.