GB2322999A - Handing Over During Low Voice Activity - Google Patents

Abstract

A handover method comprises the steps of determining when a handover is required, monitoring voice activity to determine a period during which the voice activity is relatively low or zero and initiating handover during the period. In this way a user does not experience any interruption to a conversation caused by handover.

Description

A Cell Handover Method For Use In A Cellular Communication Svstem And Apparatus Field Of The Invention This invention relates to a cell handover or transition method, for use in a cellular communication system particularly, but not exclusively, for use in a cellular radio communication system. It also relates to apparatus.

Background To The Invention In trunked cellular systems (whether digital or analogue) there are call handovers during cell transitions as a result of the mobility of subscriber units (SU). Whilst these handovers are unavoidable they cause disruption to the voice communication which may be perceived by a user. the number of these interruptions depends on how quickly a user passes through the geographical area served by the system and the number of cells through which the user passes. The problem becomes more significant as the size of the cells decreases and is thus most significant in modern low power systems employing so-called microcells because of the frequent cell transitions.

Summarv Of The Invention In accordance with the invention there is provided a cell handover method comprising the steps of determining when a handover is required, monitoring voice activity to determine a period during which the voice activity is relatively low or zero and initiating handover during the period.

By monitoring the voice activity and initiating the handover during a period of low or zero activity it is possible to ensure that a user does not experience any interruption to a conversation caused by handover.

Brief Description Of The Drawings A specific embodiment of the invention will now be described, by way of example only, with reference to the drawings in which: Figure 1 shows in schematic block diagram form a hand-held radio transmitter receiver operating in accordance with the invention; and Figure 2 shows an explanatory diagram illustrating the method of operation of the radio of Fig.1.

Detailed Description Of A Preferred Embodiment As is shown in Fig 1, a handheld radio 1 comprises a transmitter section 2, a receiver section 3 and a processor 4 and associated memory 5.

The receiver section 3 comprises a receiver 6 coupled to an antenna(not shown), a demodulator 7 coupled to the receiver 6 and further coupled to a speech recovery section 8. The speech recovery section is coupled to a speaker via a voice activity detector (VAD) 9.

The transmitter section 2 comprises a microphone 11, into which a user of the radio speaks, coupled via a voice activity detector 12 to a modulator 13. The modulator 13 is coupled to a transmitter 14 which in turn is coupled to the antenna (not shown).

As will be seen from Fig 1, the transmitter 14 and the receiver 6 operate under the control of the processor 4 by means of control lines 16 and 17.

further the processor 4 has a data input 18 from the receiver 6 and a further data input 19 from the VAD 9 and 12.

The conventional aspects of the operation of the receiver will now be briefly described for the nature of this conventional operation will be readily understood by a man skilled in the art.

An incoming signal is coupled by the antenna to the receiver 6. The receiver 6 detects the signals and passes them to the demodulator 7. The demodulator 7 demodulates the signals and passes the demodulated signal to the speech recovery module 8 where the encoded speech present on the demodulated signals is recovers. The speech is then amplified and fed via the VAD 9 to the speaker 10 where it is output to a user.

An outgoing signal is generated in the following way. A user speaks into the microphone 11 which converts the sound into electrical signals. The signals are coupled by the VAD 12 to the modulator 13 where the speech is encoded and modulated. The modulated speech is then coupled to the transmitter 14 and then coupled to the antenna and transmitted to other radios in the system.

The processor 4 is a microprocessor programmed to control the function of the radio 1 (the program being held in part of the memory 5). It provides a number of functional blocks and in this case two of the blocks are illustrated. The blocks that are shown are a signal quality block 20 and a cell transition block 21.

The signal quality block 20 is coupled to the signal derived by the receiver 6. The block assesses the strength of the signal ( or other parameter indicative of signal quality ) received from the present cell and compares it with the strength of the signal received from other cells. The cells are then ordered in a table held in memory in memory 5, the order being in accordance with the received signal strength. When the current cell is not the one offering the highest strength then an output indicative of this condition is then passed to the cell transition block 21.

The cell transition block 21 initiates handover of the radio from the current cell to the next cell offering the best reception strength. This block receives outputs form the VADs 9 and 12 indicative of there being speech received in the reception path or speech present on the transmission path. In a manner to be described later the block makes the decision as to whether to initiate a handover between cells controlling the transmitter 14 and receiver 6 by means of control lines 16 and 17.

As is shown in Fig 2, a first step in the method is for the cell transition block to consider whether or not a cell handover is required as represented by decision diamond 22. This is done in conjunction with the signal quality block 20, that is to say, when the signal quality offered by the current cell is less than that available from another cell then a handover is desirable.

If no cell transition is required then step 22 is repeated.

If a cell transition is desirable then a clock (within the processor) is started in step 23. The next step 24 is to consider whether or not the speech activity detected on both the transmission and reception paths is zero that is to say there is no speech. If the speech is zero then the next step is to proceed to handover procedure 25.

If the speech is not zero that is to say there is speech either on the reception or transmission path then the clock is monitored in step 26. If the clock is less than a threshold then the method returns to step 24. If the clock exceeds a threshold then the method proceeds to the handover procedure 25.

In the above described embodiment consideration is given to speech activity on the reception and the transmission path. In alternative embodiments consideration may be given to just one of those paths or to the paths alternately.

Whilst in the described embodiment the intelligence for operating the method is provided in the handhold radio it could be provided in other parts of the system such as the base-station of the current cell or a relay or distributed over more than one component of the system.

The invention may also find application in cellular telephony systems.

Claims (4)

Claims

1. A cell handover method for use in a cellular communications system comprising the steps of determining when a handover is required, monitoring voice activity to determine a period during which the voice activity is relatively low or zero and initiating handover during the period.

2. A cell handover method substantially as hereinbefore described with reference to or as illustrated by anyone of the drawings.

3. Apparatus for use in a cellular communications system which apparatus comprising: a processor for determining when a handover is required; a voice activity determiner for determining a period when the voice activity is relatively low or zero and means responsive to an output from the voice activity determiner to initiate a handover when required during a period of relatively low or zero voice activity.

4. Apparatus for use in a cellular communications system substantially as hereinbefore described with reference to or as illustrated by any one of the drawings.