Methods and systems for OFDM using code division multiplexing
In some embodiments of the invention, OFDM symbols are transmitted as a plurality of clusters. A cluster includes a plurality of OFDM sub-carriers in frequency, over a plurality of OFDM symbol durations in time. Each cluster includes data as well as pilot information as a reference signal for channel estimation. In some embodiments, a plurality of clusters collectively occupy the available sub-carrier set in the frequency domain that is used for transmission. In some embodiments of the invention data and/or pilots are spread within each cluster using code division multiplexing (CDM). In some embodiments pilots and data are separated by distributing data on a particular number of the plurality of OFDM symbol durations and pilots on a remainder of the OFDM symbol durations. CDM spreading can be performed in time and/or frequency directions.
1. A method of transmitting comprising:
defining a first plurality of OFDM symbols to contain a plurality of clusters, each cluster comprising a plurality of sub-carriers over a plurality of OFDM symbol durations;
spreading at least one of data and pilots within each cluster using code division multiplexing (CDM);
transmitting the first plurality of OFDM symbols from a first transmit antenna,
further comprising for each of at least one additional transmit antenna:
defining a respective plurality of OFDM symbols to contain a plurality of clusters, each cluster comprising a plurality of sub-carriers over a plurality of OFDM symbol durations;
spreading at least one of data and pilots within each cluster using a respective code division multiplexing (CDM) code;
transmitting the respective plurality of OFDM symbols from the additional transmit antenna.
2. The method of claim 1 wherein, for each respective transmit antenna, a first sub-set of the OFDM symbol durations contain the pilots and a second sub-set of the OFDM symbol durations contain the data, the first sub-set being distinct from the second sub-set.
3. The method of claim 1 , wherein spreading at least one of data and pilots within each cluster using CDM comprises spreading only data in a time direction over multiple OFDM symbol durations or a frequency direction over multiple sub-carriers.
4. The method of claim 1 , wherein spreading at least one of data and pilots within each cluster using CDM comprises spreading only pilots in a time direction over multiple OFDM symbol durations or a frequency direction over multiple sub-carriers.
5. The method of claim 1 further comprising:
for at least one transmit antenna of the first and additional transmit antennas, for each of a plurality of users, spreading the data for the user using a respective CDM code to produce a respective spread data;
adding together the spread data for inclusion in the data locations of the plurality of OFDM symbols.
6. The method of claim 1 , wherein spreading data within each cluster comprises spreading data in a time direction over multiple OFDM symbols.
7. The method of claim 1 , wherein spreading data within each cluster comprises spreading data in a frequency direction over multiple sub-carriers.
8. The method of claim 1 wherein transmitting from the first transmit antenna and the at least one additional transmit antenna comprises transmitting from at least two transmitters each having at least one transmit antenna.
9. The method of claim 1 wherein transmitting from the first transmit antenna and the at least one additional transmit antenna comprises transmitting from one transmitter having the first transmit antenna and the at least one additional transmit antenna.
10. The method of claim 1 , further comprising:
for each transmit antenna, assigning pilots in each sub-carrier of at least one OFDM symbol duration in each of the plurality of clusters and nulls in each sub-carrier of at least one other OFDM symbol duration in the plurality of clusters.
11. The method of claim 1 , wherein transmitting from the first transmit antenna and the at least one additional transmit antenna comprises transmitting from two transmit antennas, the method further comprising:
for the first transmit antenna, assigning pilots in each sub-carrier of at least one OFDM symbol duration in the plurality of clusters and assigning nulls in each sub-carrier of at least one other OFDM symbol duration in the plurality of clusters; and
for the at least one additional transmit antenna, inserting pilots in each sub-carrier of the at least one other OFDM symbol duration in the plurality of clusters and inserting nulls in each sub-carrier of the at least one OFDM symbol duration in the plurality of clusters.
12. The method of claim 1 , wherein transmitting from the first transmit antenna and the at least one additional transmit antenna comprises transmitting from two transmit antennas, the method further comprising:
for the first transmit antenna of the two transmit antennas, for repeating first and second clusters of the plurality of clusters assigning pilots in each sub-carrier of at least one OFDM symbol duration of the first cluster and assigning nulls in each sub-carrier of the at least one OFDM symbol duration of the second cluster; and
for the at least one additional transmit antenna of the two transmit antennas, for the repeating first and second clusters assigning pilots in each sub-carrier of at least one OFDM symbol duration of the second cluster and inserting nulls in each sub-carrier of the at least one OFDM symbol duration of the first cluster.
13. The method of claim 1 , wherein transmitting from the first transmit antenna and the at least one additional transmit antenna comprises transmitting from two transmit antennas, the method further comprising:
for the first transmit antenna of the two transmit antennas, for repeating first and second clusters of the plurality of clusters assigning pilots in each even numbered sub-carrier of at least one OFDM symbol duration of the first cluster and assigning nulls in each odd numbered sub-carrier of the at least one OFDM symbol duration of the second cluster; and
for the at least one additional transmit antenna of the two transmit antennas, for the repeating first and second clusters assigning pilots in each even numbered sub-carrier of at least one OFDM symbol duration of the second cluster and assigning nulls in each odd numbered sub-carrier of the at least one OFDM symbol duration of the first cluster.
14. The method of claim 1 , wherein, for each respective transmit antenna, a subset of the plurality of clusters provides an access channel comprising a particular number of sub-carriers over a particular number of OFDM symbol durations for communication between a mobile terminal and a basestation.
15. The method of claim 14 , wherein the subset of the plurality of clusters that provides the access channel are mapped to locations that are spread out within the combined OFDM sub-carrier set of the plurality of clusters.
16. The method of claim 14 , wherein the plurality of clusters that provide the access channel are contiguous within the combined OFDM sub-carrier set of the plurality of clusters.
17. The method of claim 1 wherein pilots and data share an OFDM sub-carrier set of the cluster in at least one OFDM symbol duration.
18. The method of claim 17 wherein a plurality of pilot groups are arranged in each cluster, each pilot group comprising a plurality of pilot locations, and wherein pilots are spread across pilot locations within each pilot group.
19. The method of claim 18 , wherein the plurality of pilot locations in each pilot group are localized in close proximity and the plurality of pilot groups are distributed within the cluster.
20. The method of claim 17 , performed for at least one user, each of the at least one user being assigned a respective CDM spreading code.
21. A method of transmitting comprising:
defining a first plurality of OFDM symbols to contain a plurality of clusters, each cluster comprising a plurality of sub-carriers over a plurality of OFDM symbol durations;
spreading at least one of data and pilots within each cluster using code division multiplexing (CDM);
transmitting the first plurality of OFDM symbols from a first transmit antenna,
wherein a subset of the plurality of clusters provides an access channel comprising a particular number of sub-carriers over a particular number of OFDM symbol durations for communication between a mobile terminal and a basestation, wherein the plurality of pilot locations in each pilot group are contiguous in at least one of time and frequency.
22. The method of claim 18 wherein the plurality of pilot locations in each group are scattered within the cluster.