Method for allocating physical hybrid automatic repeat request indicator channel
A method for allocating a physical hybrid ARQ indicator channel (PHICH) includes allocating a CDM group according to a cyclic prefix type in consideration of a ratio of the numbers of necessary CDM groups according to spreading factors, and allocating a PHICH to the allocated CDM group. The PHICH includes an ACK/NACK signal multiplexed by code division multiplexing (CDM). Therefore, resources for PHICH transmission are efficiently allocated and a transmission structure can be maintained irrespective of a spreading factor.
1. A method for transmitting a spread signal by a transmitting end in a wireless communication system, the method comprising:
selecting spreading codes of a spreading factor among spreading codes set having a plurality of spreading factors, according to a length of a cyclic prefix in an orthogonal frequency division multiplexing (OFDM) symbol;
spreading a plurality of signals using the spreading codes of the spreading factor;
multiplexing the spread plurality of signals into one or more physical hybrid automatic repeat request indicator channel (PHICH) groups; and
transmitting the one or more PHICH groups to a receiving end through one or more transmit structures which are configured in the OFDM symbol,
wherein the number of PHICH groups when the OFDM symbol has an extended cyclic prefix is determined as multiples of the number of PHICH groups when the OFDM symbol has a normal cyclic prefix.
2. The method of claim 1 , wherein the transmit structure includes L neighboring subcarriers, wherein L denotes a positive integer.
3. The method of claim 2 , wherein the spreading factor when the OFDM symbol has the normal cyclic prefix is the same as the number of subcarriers in the transmit structure.
4. The method of claim 3 , wherein the number of subcarriers in the transmit structure is 4.
5. The method of claim 1 , wherein the spreading codes of spreading factor 4 is selected if the OFDM symbol has the normal cyclic prefix, and the spreading codes of spreading factor 2 is selected if the OFDM symbol has the extended cyclic prefix.
6. The method of claim 1 , wherein a product of the number of PHICH groups and the spreading factor is always constant.
7. The method of claim 1 , wherein the number of PHICH groups (G M ) when the OFDM symbol has the extended cyclic prefix is determined by equation 1:
G M =G N *( N/M ) equation 1
where N denotes a spreading factor when the OFDM symbol has the normal cyclic prefix, M denotes a spreading factor when the OFDM symbol has the extended cyclic prefix, and G N denotes the number of PHICH groups when the OFDM symbol has the normal cyclic prefix.
8. The method of claim 1 , wherein the number of PHICH groups (G M ) the OFDM symbol has the extended cyclic prefix is determined by equation 2:
G M =G N *ceil ( N/M ) equation 2
where N denotes a spreading factor when the OFDM symbol has the normal cyclic prefix, M denotes a spreading factor when the OFDM symbol has the extended cyclic prefix, and G N denotes the number of PHICH groups when the OFDM symbol has the extended cyclic prefix, and ceil(•) denotes the ceiling function.
9. The method of claim 1 , wherein the one or more PHICH groups are repeatively transmitted a total of 3 times in one or more OFDM symbols.
10. The method of claim 1 , wherein the one or more PHICH groups are transmitted via multi-antennas.
11. The method of claim 10 , wherein the one or more PHICH groups are transmitted via a plurality of antenna pairs, where space frequency block coding (SFBC) is applied to same antenna pair and frequency switching transmit diversity (FSTD) is applied between different antenna pairs.
12. The method of claim 1 , wherein the number of PHICH groups when the spreading codes of spreading factor 2 is selected is twice of the number of PHICH groups when the spreading codes of spreading factor 4 is selected.
13. The method of claim 5 , wherein the number of PHICH groups when the OFDM symbol has the extended cyclic prefix is twice of the number of PHICH groups when the OFDM symbol has the normal cyclic prefix.
14. A method for receiving a spread signal by a receiving end in a wireless communication system, the method comprising:
receiving one or more physical hybrid automatic repeat request indicator channel (PHICH) groups from a transmitting end through one or more transmit structures which are configured in an orthogonal frequency division multiplexing (OFDM) symbol, each PHICH group carrying multiplexed spread signals,
wherein the spread signals are generated by using spreading codes of a spreading factor which are selected from spreading code sets having a plurality of spreading factors, according to a length of a cyclic prefix in the OFDM symbol; and
determining a PHICH group index and a spreading code index for identifying a spread signal designated to the receiving end by using the number of PHICH groups,
wherein the number of PHICH groups when the OFDM symbol has an extended cyclic prefix is determined as multiples of the number of PHICH groups when the OFDM symbol has a normal cyclic prefix.
15. The method of claim 14 , wherein the transmit structure includes L neighboring subcarriers, wherein L denotes a positive integer.
16. The method of claim 15 , wherein the spreading factor when the OFDM symbol has the normal cyclic prefix is the same as the number of subcarriers in the transmit structure.
17. The method of claim 16 , wherein the number of subcarriers in the transmit structure is 4.
18. The method of claim 14 , wherein the spreading codes of spreading factor 4 is selected if the OFDM symbol has the normal cyclic prefix, and the spreading codes of spreading factor 2 is selected if the OFDM symbol has the extended cyclic prefix.
19. The method of claim 18 , wherein the number of PHICH groups when the OFDM symbol has the extended cyclic prefix is twice of the number of PHICH groups when the OFDM symbol has the normal cyclic prefix.
20. The method of claim 14 , wherein product of the number of PHICH groups and the spreading factor is always constant.
21. The method of claim 14 , wherein the number of PHICH groups (G M ) when the OFDM symbol has the extended cyclic prefix is determined by equation 1:
G M =G N *( N/M ) equation 1
where N denotes a spreading factor when the OFDM symbol has the normal cyclic prefix, M denotes a spreading factor when the OFDM symbol has the extended cyclic prefix, and G N denotes the number of PHICH groups when the OFDM symbol has the normal cyclic prefix.
22. The method of claim 14 , wherein the number of PHICH groups (G M ) when the OFDM symbol has the extended cyclic prefix is determined by equation 2:
G M =G N *ceil ( N/M ) equation 2
where N denotes a spreading factor when the OFDM symbol has the normal cyclic prefix, M denotes a spreading factor when the OFDM symbol has the extended cyclic prefix, and G N denotes the number of PHICH groups when the OFDM symbol has the extended cyclic prefix, and ceil(•) denotes the ceiling function.
23. The method of claim 14 , wherein the one or more PHICH groups are repeatively transmitted a total of 3 times in one or more OFDM symbols.
24. The method of claim 14 , wherein the one or more PHICH groups are transmitted via multi-antennas.
25. The method of claim 14 , wherein the one or more PHICH groups are transmitted via a plurality of antenna pairs, where a space frequency block coding (SFBC) is applied to same antenna pair and frequency switching transmit diversity (FSTD) is applied between different antenna pairs.
26. The method of claim 14 , wherein the number of PHICH groups when the spreading codes of spreading factor 2 is selected is twice of the number of PHICH groups when the spreading codes of spreading factor 4 is selected.