Realizing FDD capability by leveraging existing TDD technology
Systems and methods are disclosed for using two TDD carriers in the same paired spectrum by offsetting the DL and UL transmissions in frequency to cause the TDD carriers to behave as two half-duplex FDD carriers. DL and UL transmission and reception periods are predefined such that only one of the TDD carriers is transmitting on the DL at any instant in time while the other TDD carrier is transmitting on the UL.
1. A cellular communication system, comprising:
a base transmission station (BTS), that transmits information on a downlink (DL) frequency band to one or more mobile devices and concurrently receives information on an uplink (UL) frequency band from the one or more mobile devices;
a frequency division duplex (FDD) processor that alternately applies first and second time division duplexed (TDD) carriers to a transmission signal on the DL frequency band with downlink transmissions according to a predefined switching schedule, and employs a receive time gap (RTG) on the UL frequency band immediately preceding each of a plurality of transition gaps to prevent concurrent transmission on the DL frequency band and reception on the UL frequency using the same TDD carrier; and
a memory that stores information related to the predefined switching schedule, TDD carrier identity, and DL and UL frequency bands, wherein the BTS transmits the downlink transmissions on the DL frequency band using the first TDD carrier for a first portion of a downlink transmission frame, and using the second TDD carrier for a second portion of the downlink transmission frame, and wherein the BTS receives uplink transmissions on the UL frequency band using the second TDD carrier for a first portion of an uplink transmission frame, and using the first TDD carrier for a second portion of the uplink transmission frame, wherein TDD carriers are shared between uplink and downlink frequencies in an alternating fashion.
2. The system of claim 1 , wherein the FDD processor applies the first TDD carrier to the transmission signal during the first portion of the downlink transmission frame and applies the second TDD carrier to the transmission signal during the second portion of the downlink transmission frame, and applies a first transition gap during which the FDD processor switches from the first TDD carrier to the second TDD carrier.
3. The system of claim 2 , wherein the BTS does not receive information on the UL frequency band during the first transition gap.
4. The system of claim 3 , wherein the first portion of the downlink transmission frame comprises N symbols, where N is a positive integer, and the second portion of the downlink transmission frame comprises M-N symbols, where M is the number of symbols per frame.
5. The system of claim 4 , wherein the FDD processor applies a second transition gap during which the FDD processor switches from the second TDD carrier to the first TDD carrier for transmission of a first portion of a next transmission frame on the DL frequency band.
6. The system of claim 5 , wherein the second transition gap is shorter than the first transition gap.
7. The system of claim 5 , further comprising a receive time gap (RTG) on the UL frequency band immediately preceding each transition gap to prevent concurrent transmission on the DL frequency band and reception on the UL frequency band using the same TDD carrier.
8. The system of claim 7 , further comprising a transmission time gap (TTG) during a symbol preceding the first transition gap to prevent concurrent transmission on the DL frequency band and reception on the UL frequency using the same TDD carrier.
9. The system of claim 1 , wherein the BTS receives information on the UL frequency band using the second TDD carrier during the first portion of the uplink transmission frame, and receives information on the UL frequency band using the first TDD carrier during the second portion of the uplink transmission frame.
10. The system of claim 1 , wherein the first and second TDD carriers are Worldwide Interoperability for Microwave Access (WiMax) TDD carriers.
11. A method that facilitates wireless communication by causing two time division duplexed (TDD) carriers to behave as half-duplex frequency division duplex (FDD) carriers, comprising:
transmitting a DL signal on a DL frequency band using a first TDD carrier during a first portion of a transmission frame;
receiving a UL signal on a UL frequency band using a second TDD carrier during the first portion of the transmission frame;
transmitting the DL signal on the DL frequency band applying the second TDD carrier during a second portion of the transmission frame;
receiving the UL signal on the UL frequency band applying the first TDD carrier during the second portion of the transmission frame, wherein TDD carriers are shared between uplink and downlink frequencies in an alternating fashion;
switching from the first TDD carrier to the second TDD carrier on the DL frequency band, and from the second TDD carrier to the first TDD carrier on the UL frequency band, during a first transition gap that occurs between the first and second portions of the transmission frame; and
switching from the second TDD carrier to the first TDD carrier on the DL frequency band, and from the first TDD carrier to the second TDD carrier on the UL frequency band, during a second transition gap that occurs at the end of the transmission frame; and
employing a receive time gap (RTG) on the UL frequency band immediately preceding each transition gap to prevent concurrent transmission on the DL frequency band and reception on the UL frequency using the same TDD carrier.
12. The method of claim 11 , further comprising temporarily stopping reception on the UL during first transition gap.
13. The method of claim 12 , wherein the first portion of the transmission frame comprises N symbols, where N is a positive integer, and the second portion of the transmission frame comprises M-N symbols, where M is the number of symbols per frame.
14. The method of claim 11 , wherein the second transition gap is shorter than the first transition gap.
15. The method of claim 11 , further comprising employing a transmission time gap (TTG) during the symbol preceding the first transition gap to prevent concurrent transmission on the DL frequency band and reception on the UL frequency using the same TDD.
16. The method of claim 15 , wherein the RTG has a shorter duration than the TTG.
17. The method of claim 11 , wherein the first and second TDD carriers are Worldwide Interoperability for Microwave Access (WiMax) TDD carriers.
18. A system that facilitates wireless communication by causing two time division duplexed (TDD) carriers to behave as half-duplex frequency division duplex (FDD) carriers during communication with a base station, comprising:
one or more transmitters that transmit a DL signal on a DL frequency band using a first TDD carrier during a first portion of a transmission frame;
one or more receivers that receive a UL signal on a UL frequency band using a second TDD carrier during the first portion of the transmission frame;
wherein the one or more transmitters transmit the DL signal on the DL frequency band using the second TDD carrier during a second portion of the transmission frame;
wherein the one or more receivers receive the UL signal on the UL frequency band using the first TDD carrier during the second portion of the transmission frame;
an FDD processor configured to switch from the first TDD carrier to the second TDD carrier on the DL frequency band, and from the second TDD carrier to the first TDD carrier on the UL frequency band, during a first transition gap that occurs between the first and second portions of the transmission frame; and
wherein the FDD processor is further configured to switch from the second TDD carrier to the first TDD carrier on the DL frequency band, and from the first TDD carrier to the second TDD carrier on the UL frequency band, during a second transition gap that occurs at the end of the transmission frame;
wherein transmission, reception, and carrier switching are performed iteratively across multiple transmission frames during a communication event;
wherein the first and second TDD carriers are 802.16e-based Worldwide Interoperability for Microwave Access (WiMax) TDD carriers.