Flexible two-way telecommunication system

Abstract

A flexible two-way telecommunications system comprises a plurality of geographically distributed primary stations (PS 1 to PS 3 ) whose coverage areas (CA 1 to CA 3 ) define contiguous cells. Secondary stations (SS 1 to SS 3 ) are capable of roaming between and within the coverage areas of the primary stations. Downlink communications from the primary stations comprise TDMA transmission and uplink transmissions from the secondary stations comprise CDMA/TDMA transmissions. Data packets transmitted on the downlink are modulated to suit the quality of the link between the primary station and the addressed secondary station. A header applied to the downlink transmission includes information about the location of the respective data packets relative to a reference point and the modulation scheme applied to each data packet.

1 . A method of transmitting a signal between a primary station and a secondary station, each said station comprising transceiving means and control means, at least the control means of the primary station being capable of determining the quality of a signal received on an uplink, characterised by modulating a signal to be transmitted on a downlink and by selecting the characteristics of the transmission in response to information concerning the quality of the uplink and/or downlink.  
     
     
         2 . A method as claimed in  claim 1 , characterised by further selecting the said characteristics on the basis of at least one of bit rate, bit error rate and end-to-end delay.  
     
     
         3 . A method as claimed in  claim 1  or  2 , characterised in that downlink transmission comprise time frames and in that each time frame includes a header having indicia indicating the transmission characteristics and timing of each data burst in the time frame.  
     
     
         4 . A method as claimed in  claim 1 ,  2  or  3 , characterised in that downlink transmissions are TDMA.  
     
     
         5 . A method as claimed in any one of  claims 1  to  4 , characterised in that uplink transmissions are CDMA and/or TDMA.  
     
     
         6 . A two-way telecommunications system comprising a primary station and at least one secondary station comprising transceiving means, the primary station comprising transmitting means for transmitting signals on a downlink, receiving means for receiving signals transmitted by the transceiving means of the secondary station on an uplink and control means, said control means including means for determining the quality of a signal received by the receiving means from the uplink and means for modulating a signal to be transmitted on the downlink, said modulating means selecting the characteristics of the uplink and/or downlink transmission in response to information obtained concerning the quality of the uplink and/or downlink.  
     
     
         7 . A system as claimed in  claim 6 , characterised in that the primary station transmits downlink signals in accordance with a TDMA format comprising a succession of time frames each including a frame header.  
     
     
         8 . A system as claimed in  claim 7 , characterised in that the frame header includes indicia indicating the location of data bursts intended for one or more of the secondary stations.  
     
     
         9 . A system as claimed in  claim 8 , characterised in that the frame header includes indicia indicating the format and timing of each data burst.  
     
     
         10 . A system as claimed in  claim 8  or  9 , characterised in that training sequences are embedded in the data bursts.  
     
     
         11 . A system as claimed in any one of  claims 7  to  10 , characterised in that the at least one secondary station effects power saving by adopting a sleep mode whenever the secondary station determines that data bursts are directed to other secondary stations.  
     
     
         12 . A system as claimed in any one of  claims 7  to  11 , characterised in that the time frames are of a substantially fixed duration.  
     
     
         13 . A system as claimed in anyone of  claims 6  to  12 , characterised in that the modulating means applies a high order modulation scheme to signals to be transmitted to secondary stations relatively close to the primary station and low bit rate orthogonal codes when transmitting signals to relatively distant secondary stations.  
     
     
         14 . A system as claimed in any one of  claims 6  to  13 , characterised in that traffic data is transmitted on the downlink with a modulation scheme and power level determined to ensure reliable receipt by a secondary station.  
     
     
         15 . A system as claimed in any one of  claims 6  to  14 , characterised in that uplink signals are transmitted as CDMA signals.  
     
     
         16 . A system as claimed in any one of  claims 6  to  15 , characterised in that uplink signals are transmitted in accordance with a TDMA format.  
     
     
         17 . A system as claimed in  claim 16 , characterised in that TDMA uplink signals comprise at least two data bursts and in that a guard space is provided between adjacent data bursts.  
     
     
         18 . A system as claimed in  claim 16  or  17 , characterised in that TDMA uplink signals comprise data bursts, and in that each data bursts comprises at least one training sequence.  
     
     
         19 . A system as claimed in  claim 16 , 17  or  18 , characterised in that TDMA uplink signals comprise data packets, and in that the bit rates of at least two of the data packets are different.  
     
     
         20 . A system as claimed in any one of  claims 6  to  19 , characterised in that timing for uplink signals is derived from the downlink signals.  
     
     
         21 . A system as claimed in any one of  claims 6  to  20 , characterised in that the system is a cellular system comprising a plurality of cells, each cell having a primary station defining a respective coverage area.  
     
     
         22 . A system as claimed in  claim 21 , characterised in that primary stations have means for handing over secondary station participating in a call from one cell to another cell.