System and method for dividing subchannels in a OFDMA network
A system and method for multiplexing subchannels in an OFDMA network is provided. The subchannels can be multiplexed by splitting the subchannels in the frequency domain. Alternatively, the subchannels can be code division multiplexed using N orthogonal spreading codes. The subchannel multiplexing increases system capacity for low-rate services, such as voice-based services.
1. A method of communicating over a low-rate channel which is multiplexed with a plurality of low-rate channels in subchannels of orthogonal frequency division multiple access (OFDMA) frames, the method comprising the acts of:
receiving, by a mobile station, an OFDMA downlink subframe, the subframe including a channel assignment for access to an uplink subframe;
determining which channel within a subchannel is assigned to the mobile station; and
transmitting low-rate information in the assigned channel within the subchannel, wherein the channel within the subchannel comprises a portion of frequencies assigned to the subchannel, and,
wherein the portion of the subchannel frequencies are selected based on the acts of
ordering a set of tones assigned to the subchannel from lowest to highest frequency; and
assigning every other Nth tone of the ordered tones assigned to the subchannel to the mobile station.
2. A method of communicating over a low-rate channel which is multiplexed with a plurality of low-rate channels in subchannels of orthogonal frequency division multiple access (OFDMA) frames, the method comprising the acts of:
receiving, by a mobile station, an OFDMA downlink subframe, the subframe including a channel assignment for access to an uplink subframe;
determining which channel within a subchannel is assigned to the mobile station; and
transmitting low-rate information in the assigned channel within the subchannel, wherein the channel within the subchannel is defined by one orthogonal spreading code of a set of orthogonal spreading codes, wherein the set of orthogonal spreading codes includes N orthogonal spreading codes, and low-rate information is multiplexed into N channels within the subchannel.
3. The method of claim 2 , wherein the orthogonal spreading codes have a length of N.
4. A method of communicating between a mobile station and a base station, comprising the acts of:
selecting an orthogonal frequency division multiple access (OFDMA) subchannel;
ordering tones assigned to the subchannel from a lowest to highest in frequency; and
respectively assigning every other Nth tone of the ordered tones assigned to the subchannel to N mobile stations independent of assignments of tones for the N mobile stations in subchannels other than the subchannel.
5. The method of claim 4 , further comprising the act of:
transmitting information to one of the N mobile stations over the tones of the subchannel assigned to the one of the N mobile stations.
6. The method of claim 4 , wherein the tones of the subchannel are assigned for voice communications.
7. A method of communicating between a base station and a mobile station, comprising the acts of:
selecting, by a base station, an orthogonal frequency division multiple access (OFDMA) subchannel;
determining a length of a spreading code; and
dividing, by the base station, the subchannel between N mobile stations based on the determined length of the spreading code, wherein the number of mobile stations N is equal to the determined length of the spreading code.
8. The method of claim 7 , wherein the spreading code is a Walsh code.
9. The method of claim 7 , further comprising the act of:
determining transmission parameters of the subchannel.
10. The method of claim 9 , wherein the transmission parameters include a number of tones, type of modulation and coding rate.
11. The method of claim 7 , wherein the divided subchannel carries voice information.