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.

Description

TECHNICAL FIELD[0001]The present invention relates to communication systems and methods in which mobile user equipment (such as a mobile telephone, personal digital assistant (PDA) or other device) communicates with base stations of a communication network using radio signals in accordance with defined radio frame formats. Certain embodiments of the invention are concerned in particular with communication methods and systems in which user equipment communicates with a Universal Terrestrial Radio Access (UTRA) Network (also known as UTRAN, or UMTS Terrestrial Radio Access Network) or an Evolved Universal Terrestrial Radio Access (E-UTRA) Network (or E-UTRAN).BACKGROUND ART[0002]A variety of communication networks comprising a plurality of base stations with which mobile, portable user equipment can communicate, using radio signals, are known. They include, for example, the GSM network, and the 3rd Generation (3G) network (UTRAN). These networks are typically arranged to provide conne...

AI Technical Summary

Benefits of technology

[0018]Thus, the communication network itself provides information to the UE which enables the UE to synchronise with the second radio frame format (in the sense that it is able to transmit one or more signals, for example a RACH signal, in accordance with that format) without the UE first having to read a signal such as a P-BCH signal from the second (i.e. target) base station. This saves time and / or reduces interruption in service; the UE can synchronise with the target base station from the received information and transmit a signal to the target base station in the next available slot, the UE having been able to determine the position of that next available slot from (using) the received information.

[0032]In certain embodiments, the step of transmitting a radio signal (comprising the first and second information) to the user equipment from the communication network comprises transmitting the radio signal from the first base station. Thus, the transmitted signal will be in the first defined frame format (with which the UE is synchronised). The UE can thus quickly use the information on the received signal to synchronise with the second format and begin sending signals for reception by the second base station.

Problems solved by technology

Clearly, this lack of synchronisation between base station's frame formats poses problems for handover of communications; the UE will be synchronised with the frame format of the base station with which it is currently communicating (the source base station), but cannot communicate with the target base station until it can synchronise with the frame format of that target.

BCH reading delay therefore increases the handover interruption time.

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