Communication system and method

Abstract

A communication system comprises: mobile user equipment; and a communication network adapted to communicate with the user equipment, the communication network comprising: a first base station adapted to communicate with the user equipment using radio signals and according to a first defined radio frame format comprising a first sequence of radio frames each having the same length and each being allocated a respective first system frame number (SFN) such that the radio frames of the first sequence are sequentially numbered; and a second base station adapted to communicate with the user equipment using radio signals and according to a second defined radio frame format comprising a second sequence of radio frames each having said same length and each being allocated a respective second SFN such that the radio frames of the second sequence are sequentially numbered, the user equipment being adapted to receive radio signals from the first base station and to use said received signals to synchronise with the first sequence of numbered radio frames, such that the user equipment can transmit radio signals to the first base station in accordance with the first defined radio frame format, and determine the first SFN of a frame of the first sequence at a particular time, the communication network being further adapted to transmit a radio signal to the user equipment, the radio signal comprising first information indicative of a difference between the first and second SFNs at a particular time and second information usable with said first information to determine unambiguously at least a least significant bit of the SFN in binary form of a frame of the second sequence at a particular time from a knowledge of the SFN of a frame of the first sequence at a particular time, the user equipment being further adapted to receive said radio signal and, when synchronised with said first sequence, to use the first and second information to synchronise with the second sequence, such that the user equipment can transmit radio signals to the second base station in accordance with the second defined radio frame format. A corresponding communication method is provided.

1 - 30 . (canceled) 
     
     
         31 . A communication method in a communication system comprising mobile user equipment and a communication network adapted to communicate with the user equipment, the communication network comprising: a first base station adapted to communicate with the user equipment using radio signals and according to a first defined radio frame format comprising a first sequence of radio frames each having the same length and each being allocated a respective first system frame number (SFN) such that the radio frames of the first sequence are sequentially numbered; and a second base station adapted to communicate with the user equipment using radio signals and according to a second defined radio frame format comprising a second sequence of radio frames each having the same length and each being allocated a respective second SFN such that the radio frames of the second sequence are sequentially numbered, the length of the radio frames of one of the first and second formats being an integer multiple of the length of the radio frames of the other format, the method comprising:
 receiving radio signals from the first base station at the user equipment and using said received signals to synchronise the user equipment with the first sequence of numbered radio frames, such that the user equipment can transmit radio signals to the first base station in accordance with the first defined radio frame format, and to determine the first SFN of a frame of the first sequence at a particular time;   transmitting a radio signal to the user equipment from the communication network, the radio signal comprising first information indicative of a difference between the first and second SFNs at a particular time and second information usable with said first information to determine unambiguously at least a least significant bit of the SFN in binary form of a frame of the second sequence at a particular time from a knowledge of the SFN of a frame of the first sequence at a particular time; and   receiving said radio signal at the user equipment when synchronised with said first sequence, and using the first and second information to synchronise the user equipment with the second sequence, such that the user equipment can transmit radio signals to the second base station in accordance with the second defined radio frame format.   
     
     
         32 . The communication method in accordance with  claim 31 , further comprising transmitting a radio signal from the user equipment to the second base station in accordance with the second defined radio frame format. 
     
     
         33 . The communication method in accordance with  claim 32 , wherein the second base station is an enhanced node B (eNB), and the step of transmitting a radio signal from the user equipment to the second base station comprises transmitting a RACH signal. 
     
     
         34 . The communication method in accordance with  claim 32 , comprising continuing communication between the second base station and user equipment, after transmitting said radio signal from the UE to the second base station, by exchanging radio signals in accordance with the second defined format. 
     
     
         35 . The communication method in accordance with  claim 34 , comprising ceasing communication between the first base station and user equipment after transmitting said radio signal from the UE to the second base station. 
     
     
         36 . The communication method in accordance with  claim 31 , further comprising determining said first information in the communication network from signals received from the first and second base stations. 
     
     
         37 . The communication method in accordance with  claim 31 , further comprising determining a time difference between radio frame boundaries of the first and second sequence, and using said time difference together with an estimate of an accuracy of said time difference to determine said second information. 
     
     
         38 . The communication method in accordance with  claim 37 , comprising determining said second information according to the relative magnitudes of said time difference and said estimate of accuracy. 
     
     
         39 . The communication method in accordance with  claim 38 , comprising determining said second information to indicate that said difference between SFNs applies between a particular frame of the first sequence and the frame of the second sequence having a start time closest to that of said particular frame in the event that the magnitude of said time difference is less than the magnitude of said estimate of accuracy. 
     
     
         40 . The communication method in accordance with  claim 38 , comprising determining said second information to indicate that said difference between SFNs applies between a particular frame of the first sequence and the frame of the second sequence having a start time within said particular frame in the event that the magnitude of said time difference is greater than the magnitude of said estimate of accuracy. 
     
     
         41 . The communication method in accordance with  claim 37 , wherein determining said time difference comprises using the NTP. 
     
     
         42 . The communication method in accordance with  claim 37 , further comprising the step of determining said estimate of accuracy. 
     
     
         43 . The communication method in accordance with  claim 31 , wherein said second information is usable with said first information to determine unambiguously at least two least significant bits of the SFN in binary form of a frame of the second sequence at a particular time from a knowledge of the SFN of a frame of the first sequence at a particular time. 
     
     
         44 . The communication method in accordance with  claim 31 , wherein said second information is usable with said first information to determine unambiguously the SFN of a frame of the second sequence at a particular time from a knowledge of the SFN of a frame of the first sequence at a particular time. 
     
     
         45 . The communication method in accordance with  claim 31 , wherein said step of transmitting a radio signal to the user equipment from the communication network comprises transmitting the radio signal from the first base station. 
     
     
         46 . The communication method in accordance with  claim 31 , wherein the radio signal comprising the first and second information further comprises additional information indicative of frame structure in said second defined radio frame format. 
     
     
         47 . A communication system comprising:
 mobile user equipment; and   a communication network adapted to communicate with the user equipment,   the communication network comprising:   a first base station adapted to communicate with the user equipment using radio signals and according to a first defined radio frame format comprising a first sequence of radio frames each having the same length and each being allocated a respective first system frame number (SFN) such that the radio frames of the first sequence are sequentially numbered; and   a second base station adapted to communicate with the user equipment using radio signals and according to a second defined radio frame format comprising a second sequence of radio frames each having the same length and each being allocated a respective second SFN such that the radio frames of the second sequence are sequentially numbered, the length of the radio frames of one of the first and second formats being an integer multiple of the length of the radio frames of the other format,   the user equipment being adapted to receive radio signals from the first base station and to use said received signals to synchronise with the first sequence of numbered radio frames, such that the user equipment can transmit radio signals to the first base station in accordance with the first defined radio frame format, and determine the first SFN of a frame of the first sequence at a particular time,   the communication network being further adapted to transmit a radio signal to the user equipment, the radio signal comprising first information indicative of a difference between the first and second SFNs at a particular time and second information usable with said first information to determine unambiguously at least a least significant bit of the SFN in binary form of a frame of the second sequence at a particular time from a knowledge of the SFN of a frame of the first sequence at a particular time,   the user equipment being further adapted to receive said radio signal and, when synchronised with said first sequence, to use the first and second information to synchronise with the second sequence, such that the user equipment can transmit radio signals to the second base station in accordance with the second defined radio frame format.   
     
     
         48 . The communication system in accordance with  claim 47 , wherein the second base station is an eNB. 
     
     
         49 . The communication system in accordance with  claim 48 , wherein the user equipment is further adapted to transmit a RACH signal to the eNB in accordance with the second defined radio frame format when synchronised with said second sequence 
     
     
         50 . The communication system in accordance with  claim 48 , wherein the communication network is an E-UTRA network, and the first and second base stations are first and second eNBs respectively, and the user equipment is further adapted to transmit a measurement report to the first eNB, the first eNB is responsive to the measurement report to send a handover request to the second eNB, the second eNB is responsive to the handover request to send a handover request acknowledgement to the first eNB comprising said first and second information, the first eNB is responsive to the handover request acknowledgement to transmit said radio signal comprising first and second information to the user equipment, and the user equipment is then arranged to send a RACH message to the second eNB. 
     
     
         51 . The communication system in accordance with  claim 47 , wherein the communication network is arranged to determine a time difference between radio frame boundaries of the first and second sequences, and to determine said second information according to said time difference and an estimate of an accuracy of said time difference. 
     
     
         52 . The communication system in accordance with  claim 51 , wherein the communication network is adapted to determine said second information according to the relative magnitudes of said time difference and said estimate of accuracy. 
     
     
         53 . The communication system in accordance with  claim 51 , wherein the communication network is arranged to determine said time difference using the NTP. 
     
     
         54 . The communication system in accordance with  claim 51 , wherein the communication network is further adapted to determining said estimate of accuracy using the NTP. 
     
     
         55 . The communication system in accordance with  claim 47 , wherein said second information is usable with said first information to determine unambiguously at least two least significant bits of the SFN in binary form of a frame of the second sequence at a particular time from a knowledge of the SFN of a frame of the first sequence at a particular time. 
     
     
         56 . The communication system in accordance with  claim 47 , wherein said second information is usable with said first information to determine unambiguously the SFN of a frame of the second sequence at a particular time from a knowledge of the SFN of a frame of the first sequence at a particular time. 
     
     
         57 . The communication system in accordance with  claim 57 , wherein the communication network is adapted to transmit said radio signal to the user equipment from the first base station.