Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J3/00—Time-division multiplex systems
  • H04J3/02—Details
  • H04J3/06—Synchronising arrangements
  • H04J3/0635—Clock or time synchronisation in a network
  • H04J3/0682—Clock or time synchronisation in a network by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
  • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
  • H04B7/2662—Arrangements for Wireless System Synchronisation
  • H04B7/2671—Arrangements for Wireless Time-Division Multiple Access [TDMA] System Synchronisation
  • H04B7/2678—Time synchronisation
  • H04B7/2687—Inter base stations synchronisation
  • H04B7/2696—Over the air autonomous synchronisation, e.g. by monitoring network activity

Definitions

• the present invention relates to improvements in or relating to mobile telecommunications systems.
• UTRA TDD The UMTS terrestrial radio access time division duplex (UTRA TDD) mode is based on a combination of code division multiple access (CDMA) and hybrid time division multiple access (TDM A).
• CDMA code division multiple access
• TDM A hybrid time division multiple access
• UMTS is an acronym for universal mobile telecommunication system as will be understood by persons skilled in the art.
• Reliable operation in the UTRA TDD mode requires synchronisation between base stations within a compliant telecommunications system.
• the mode also requires the provision of position information for the mobile stations affiliated to each base station. Synchronisation between base stations is also desirable in order to maximise system capacity.
• the synchronisation of base stations must be achieved at the levels of time slots, frames and multi-frames, where a multi-frame is a repeating cycle of a number of frames.
• Co-pending British patent application nos. 0007143.1 and 0007144.9 describe a method of providing synchronisation between a plurality of base stations in a telecommunications system which comprises providing a random access channel in each cell.
• a mobile station receives a resource unit via the random access channel and a base station uses the random access channel in one cell to transmit a synchronisation signal to other base stations within the system.
• the base stations are synchronised together by means of transmissions between base stations. This involves measuring timing differences or offsets between the base stations in both directions to remove the effect of propagation delays. The timing differences or offsets are reported back to a central radio network controller (RNC) which computes the necessary timing updates and signals these back to the base stations.
• RNC central radio network controller
• a method of synchronising measurements of propagation delay between two base stations comprising the steps of:- a) achieving synchronisation between the two base stations; b) calculating an initial propagation delay; c) storing the initial propagation delay; d) calculating a subsequent propagation delay; e) determining if the subsequent propagation delay falls within predetermined limits; f) using the subsequent propagation delay if within the predetermined limits; g) storing the subsequent propagation delay if within the predetermined limits and below the initial propagation delay; and h) repeating steps d) to g).
• step c) comprises determining if the initial propagation delay meets the requirements of:-
• ⁇ TM and TTM are respectively the minimum and maximum predetermined limits of acceptable propagation delays; and di j and d ⁇ are respectively the time differences between base stations i and 7 in opposite directions.
• the RNC can filter the measurements for consistency and thus significantly reduce the utilisation of erroneous measurements.
• two way measurements are taken between two base stations and the result comprises a component relating to propagation delay and a component relating to time difference.
• a two way measurement should cancel out the propagation delay component, but this is only possible if the same path is measured in both cases as the only way to be consistent is to make the measurements on the earliest path.
• ⁇ itj is bounded. Simplistically, ⁇ itj > 0 and ti j ⁇ d ma Jc where d max is the maximum range between base stations and c is the speed of light. It may be necessary to increase d max artificially to cover the case where the line of sight path is unavailable. Alternatively, if the location of base stations i and 7 are known, as might be necessary for providing location services, the bounds on -zj can be more tightly specified.
• the probability of a measurement in error falling within the test window is greatly reduced.
• its impact is small because the error itself must be relatively small.
• this process can be used to detect when the timing measurement detects a path later than the earliest path. This is achieved by storing previous values of ⁇ N , and when a new measurement is performed and the test becomes ⁇ ⁇ m , ⁇ in ⁇ ⁇ ⁇ m , ⁇ . ⁇ ⁇ ", ⁇ . + ⁇
• ⁇ typically corresponds to 0.25 chips. If the test is true, then the stored value of r" y is replaced with ⁇ " y . and the measurement is used. If the test is not true, then the stored value of ⁇ ". is not replaced with ⁇ " y . and the measurement is not used.
• the stored value tends towards being based upon the earliest path so that only measurements based on the earliest paths are used.
• the method may be too stringent to perform during the early stages of synchronisation. In this case, wider limits (or no limits, if appropriate) can initially be used. When a reasonable degree of synchronisation is detected, then the more stringent test can be applied. This reasonable degree of synchronisation can be detected, for example, by evaluating the magnitude of the computed timing updates.
• the method of the present invention allows the measured propagation delay which is used to determine the earliest path to decrease, but not to increase.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Mobile Radio Communication Systems (AREA)

Applications Claiming Priority (5)

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• 2000
  • 2000-11-07 EP EP00973079A patent/EP1232582A1/en not_active Withdrawn
  • 2000-11-07 WO PCT/GB2000/004268 patent/WO2001039400A1/en not_active Application Discontinuation
  • 2000-11-07 CN CNB008160171A patent/CN1157870C/zh not_active Expired - Fee Related

Non-Patent Citations (1)

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