Method and apparatus for multiple access communication

Abstract

A virtual FDD base station comprises two base station sub-units each of which comprise a base station transmitter and a base station receiver. The first base station sub-unit transmits base-to-user messages to user stations only during a first half of a repeating time frame, and receives user-to-base messages from the user stations only during a second half of the time frame. The second base station sub-unit is preferably collocated with the first base station sub-unit and synchronized thereto, and transmits base-to-user messages to user stations only during half of the time frame, while receiving user-to-base messages from the user stations only during the other half of the time frame. Duplex communication channels are preferably defined by correlating a base transmit time slot with a user transmit time slot, which are separated by a sufficient amount of time to allow transmit/receive switching by a user station. The base station sub-units may be configured so that one of the sub-units transmits continuously and the other receives continuously, thereby providing full FDD functionality. In another embodiment, a TDD base station is adapted to support FDD communication. An over-the-air controller switches the transmit and receive operating frequency in accordance with a defined time slot communication pattern comprising base transmit time slots and user transmit time slots, and at the same time ensures that the base transmitter and base receiver are appropriately switched back and forth for connection with the base station antenna.

What is claimed is:  
     
       1. A communication system for virtual FDD communication, comprising: 
       a first base station sub-unit, said first base station sub-unit comprising a first transmitter for transmitting a first plurality of base-to-user messages to a first plurality of user stations only during a first half of a repeating time frame, said first base station sub-unit further comprising a first receiver for receiving a first plurality of user-to-base messages from said first plurality of user stations only during a second half of said repeating time frame; and  
       a second base station sub-unit collocated with said first base station sub-unit, said second base station sub-unit comprising a second transmitter for transmitting a second plurality of base-to-user messages to a second plurality of user stations only during said second half of said repeating time frame, said second base station sub-unit further comprising a second receiver for receiving a second plurality of user-to-base messages from said second plurality of user stations only during said first half of said repeating time frame.  
     
     
       2. The communication system of  claim 1 , further comprising means for synchronizing said first base station sub-unit and said second base station sub-unit. 
     
     
       3. The communication system of  claim 2 , wherein said means for synchronizing comprises a synchronization unit connected to said first base station sub-unit and said second base station sub-unit, said synchronization unit providing a time frame marker and a time slot marker to said first base station sub-unit and said second base station sub-unit. 
     
     
       4. The communication system of  claim 2 , wherein said means for synchronizing comprises a master-slave clock connection between said first base station sub-unit and said second base station sub-unit. 
     
     
       5. The communication system of  claim 2 , wherein said means for synchronizing comprises a time frame marker signal from a base station controller connected to both said first base station sub-unit and said second base station sub-unit. 
     
     
       6. The communication system of  claim 1 , wherein said first base station sub-unit and said second base station sub-unit share at least one common antenna. 
     
     
       7. The communication system of  claim 1 , further comprising a backhaul interface connected to said first base station sub-unit and said second base station sub-unit, said backhaul interface providing multiplexing and de-multiplexing of communication channels over a backhaul signal line. 
     
     
       8. The communication system of  claim 1 , wherein said first base station sub-unit communicates with each of said first plurality of user stations in a duplex time slot assigned to the user station, and wherein said second base station sub-unit communicates with each of said second plurality of user stations in a duplex time slot assigned to the user station. 
     
     
       9. The communication system of  claim 8 , wherein said first plurality of base-to-user messages are interleaved with said second plurality of base-to-user messages, and wherein said first plurality of user-to-base messages are interleaved with said second plurality of user-to-base messages. 
     
     
       10. The communication system of  claim 8 , wherein said first plurality of base-to-user messages are consecutive without any intervening base-to-user message of said second plurality of base-to-user messages, wherein said second plurality of base-to-user messages are consecutive without any intervening base-to-user message of said first plurality of base-to-user messages, wherein said first plurality of user-to-base messages are consecutive without any intervening user-to-base message of said second plurality of user-to-base messages, and wherein said second plurality of user-to-base messages are consecutive without any intervening user-to-base message of said first plurality of user-to-base messages. 
     
     
       11. A method for FDD communication, comprising: 
       generating a repeating time frame;  
       generating a first plurality of duplex time slots and a second plurality of duplex time slots in said time frame, each duplex time slot of said first plurality of duplex time slots comprising a base transmit time slot within a first half of said time frame and a user transmit time slot within a second half of said time frame, and each duplex time slot of said second plurality of duplex time slots comprising a base transmit time slot within said second half of said time frame and a user transmit time slot within said first half of said time frame, and wherein the base transmit time slot of each duplex time slot bears the same temporal relationship with its respective user transmit time slot;  
       assigning, on demand, said first plurality of duplex time slots and said second plurality of duplex time slots to user stations for communication with the base station;  
       transmitting, over a base transmit frequency band and from a first base station sub-unit, a first plurality of base-to-user messages during the base transmit time slots of said first plurality of duplex time slots;  
       receiving said first plurality of base-to-user messages at a first plurality of said user stations;  
       transmitting, over a base transmit frequency band and from a second base station sub-unit, a second plurality of base-to-user messages during the base transmit time slots of said second plurality of duplex time slots;  
       receiving said second plurality of base-to-user messages at a second plurality of said user stations;  
       transmitting, over a user transmit frequency band and from said first plurality of user stations, a first plurality of user-to-base messages during the user transmit time slots of said first plurality of duplex time slots;  
       receiving said first plurality of user-to-base messages at said first base station sub-unit;  
       transmitting, over said user transmit frequency band and from said second plurality of user stations, a second plurality of user-to-base messages during the user transmit time slots of said second plurality of duplex time slots; and  
       receiving said second plurality of user-to-base messages at said second base station sub-unit.  
     
     
       12. The method of  claim 11 , wherein said first half of said time frame and said second half of said time frame each comprise a contiguous portion of said time frame. 
     
     
       13. The method of  claim 11 , wherein said first half of said time frame and said second half of said time frame each comprise non-contiguous portions of said time frame, such that base transmit time slots of said first plurality of duplex time slots are interleaved with base transmit time slots of said second plurality of duplex time slots, and user transmit time slots of said first plurality of duplex time slots are interleaved with user transmit time slots of said second plurality of duplex time slots. 
     
     
       14. The method of  claim 13 , wherein said base transmit time slots of said first plurality of duplex time slots alternate with the base transmit time slots of said second plurality of duplex time slots, and wherein said user transmit time slots of said first plurality of duplex time slots alternate with the user transmit time slots of said second plurality of duplex time slots. 
     
     
       15. The method of  claim 14 , wherein the base transmit time slot and user transmit time slot of each duplex time slot are separated by at least one time slot. 
     
     
       16. The method of  claim 11 , wherein generating a repeating time frame comprises synchronizing said first base station sub-unit and said second base station sub-unit. 
     
     
       17. A method for FDD communication, comprising: 
       generating a repetitive time frame;  
       allocating a first portion of said time frame to a first base station sub-unit for transmitting a first plurality of base-to-user messages to a first plurality of user stations over a base transmit frequency band;  
       allocating a second portion of said time frame to a second base station sub-unit for transmitting a second plurality of base-to-user messages to a second plurality of user stations over said base transmit frequency band, said first portion of said time frame and said second portion of said time frame comprising substantially the entirety of said time frame;  
       allocating said second portion of said time frame to said first base station sub-unit for receiving a first plurality of user-to-base messages from said first plurality of user stations over a user transmit frequency band; and  
       allocating said first portion of said time frame to said second base station sub-unit for receiving a second plurality of user-to-base messages from said second plurality of user stations over said user transmit frequency band.  
     
     
       18. The method of  claim 17 , wherein generating a repetitive time frame comprises synchronizing said first base station sub-unit and said second base station sub-unit. 
     
     
       19. The method of  claim 17 , wherein said first base station sub-unit and said second base station sub-unit each transmit base-to-user messages and receive user-to-base messages in duplex time slots assigned to said first plurality of user stations and said second plurality of user stations. 
     
     
       20. A method for communication, comprising: 
       generating a time frame at a base station;  
       generating a plurality of time slots within said time frame;  
       assigning pairs of said time slots for duplex communication to a plurality of user stations on demand, each pair of time slots comprising a user transmit time slot and a base transmit time slot, such that no more than half of said time slots are assigned as user transmit time slots and no more than half of said time slots are assigned as base transmit time slots, and wherein each user transmit time slot from each pair of time slots is separated temporarily from its respective base transmit time slot in the pair by the same amount;  
       transmitting, over a base transmission frequency band, base-to-user messages from the base station to said user stations during said base transmit time slots;  
       receiving said base-to-user messages at said user stations, each user station receiving a base-to-user message in its assigned base transmit time slot;  
       transmitting, over a user transmission frequency band separate and distinct from said base transmission frequency band, user-to-base messages from said user stations to the base station during said user transmit time slots, each user station transmitting a user-to-base message in its assigned user transmit time slot; and  
       receiving said user-to-base messages at the base station.  
     
     
       21. The method of  claim 20  wherein said base transmit time slots alternate with said user transmit time slots. 
     
     
       22. The method of  claim 20  wherein all of said base transmit time slots are consecutive without any intervening user transmit time slots, and wherein all of said user transmit time slots are consecutive without any intervening base transmit time slots. 
     
     
       23. A base station, comprising: 
       a radio transceiver, said radio transceiver comprising a base transmitter and a base receiver selectably connected to at least one base antenna by a transmit/receive switch, and said radio transceiver further comprising a voltage controlled oscillator whereby a transmission/reception frequency of said radio transceiver is set;  
       a memory buffer connected to said radio transceiver, said memory buffer partitioned into a plurality of memory segments according to separate time division duplex communication channels, one memory segment for each such time division duplex communication channel;  
       an over-the-air controller connected to said radio transceiver, said over-the-air controller comprising a time frame counter and a time slot counter;  
       a toggle signal output from said over-the-air controller to said transmit/receive switch, said toggle signal causing said base transmitter and base receiver to be alternately connected to said at least one base antenna;  
       a frequency selection signal output from said over-the-air controller to the voltage controlled oscillator of said radio transceiver, said frequency selection signal causing said radio transceiver to alternate between a base transmit frequency band and a base receive frequency band, said base transmit frequency band being selected when said base transmitter is connected to said at least one base antenna, and said base receive frequency band being selected when said base receiver is connected to said at least one base antenna; and  
       a backhaul interface connected to said memory buffer, said backhaul interface multiplexing information from said memory buffer for transmission over a backhaul line, and demultiplexing information received over said backhaul line for storage in said memory buffer.  
     
     
       24. The base station of  claim 23 , wherein said toggle signal switches states with each change in state of said time slot counter. 
     
     
       25. The base station of  claim 23 , wherein said toggle signal switches states in response to said time slot counter, each time a predetermined number of time slots are counted. 
     
     
       26. A method for frequency division duplex (FDD) communication, comprising: 
       generating a repeating time frame;  
       generating a first plurality of duplex time slots and a second plurality of duplex time slots in the time frame, each duplex time slot of the first plurality of duplex time slots comprising a base transmit time slot within a first half of the time frame and a user transmit time slot within a second half of the time frame, each duplex time slot of the second plurality of duplex time slots comprising a base transmit time slot within the second half of the time frame and a user transmit time slot within the first half of the time frame;  
       assigning at least a portion of the first plurality of duplex time slots and the second plurality of duplex time slots to user stations;  
       transmitting a first plurality of base-to-user messages to a first plurality of the user stations from a first base station sub-unit over a base transmit frequency band during the base transmit time slots of the first plurality of duplex time slots;  
       transmitting a second plurality of base-to-user messages to a second plurality of the user stations from a second base station sub-unit over the base transmit frequency band during the base transmit time slots of the second plurality of duplex time slots;  
       receiving a first plurality of user-to-base messages from the first plurality of user stations at the first base station sub-unit over a user transmit frequency band during the user transmit time slots of the first plurality of duplex time slots; and  
       receiving a second plurality of user-to-base messages from the second plurality of user stations at the second base station sub-unit over the user transmit frequency band during the user transmit time slots of the second plurality of duplex time slots.  
     
     
       27. A method for communication, comprising: 
       generating a time frame;  
       generating a plurality of time slots within the time frame;  
       assigning pairs of the time slots for duplex communication to a plurality of user stations, each pair of time slots comprising a user transmit time slot and a base transmit time slot, no more than half of the time slots assigned as user transmit time slots and no more than half of the time slots assigned as base transmit time slots;  
       transmitting base-to-user messages from a base station to the user stations over a base transmission frequency band during the base transmit time slots; and  
       receiving user-to-base messages from the user stations at the base station over a user transmission frequency band separate and distinct from the base transmission frequency band during the user transmit time slots.