What is the difference between handover and roaming

As a result, we have seen a growing number of wireless technologies and services providers in order to fulfill users' needs. Wireless networks enable users to roam seamless in areas that are covered by network providers with which the user does not have any prior arrangements. While users are roaming between different network providers there is a handoff process that takes place, but ensuring the security and efficiency of this process is challenging. Mainly, because during the handoff process, a user has to wait for some time before it can communicate with an Access Point AP of the network provider with which it has no preceding arrangement.

As a result, during this period of delay, certain applications and services are interrupted. In the case of call pending, the scanning rate preferably has to be faster than in the waiting or idle mode of a communication unit, i.

For making a list as to a suitable number of radio links available for handover, a full scan of all the available radio links is not always necessary.

The scan can be stopped or limited if, for instance, a sufficient number of adequately radio links has been found, i. When the radio communication unit is switched on, or has been out of range for a longer time, an initial locking procedure has to be performed.

It is preferred to scan first the entire radio environment. Synchronisation should be performed with respect to the strongest radio access unit. When a radio communication unit is synchronised or locked or has a call pending, scanning for synchronous radio links can be performed more often than scanning for asynchronous systems.

This to enhance the possibility of retrieving a synchronous link to ensure as much as possible a seamless handover, if applicable. In the flow chart diagram shown in FIG. The method according to the present invention for handover of a call in progress from a first radio link to a second radio link is generally illustrated in FIGS. Arrows 13 and 14 represent a first duplex radio link carrying a call in progress between the radio communication unit 10 and the first radio access unit The radio communication unit 10 comprises a timing reference 17 which is synchronised or locked to the radio access unit 11 , as indicated by a dashed line.

The radio communication unit 10 is also in the range of the second radio access unit It is assumed that the radio access units 11 and 12 do not operate time synchronous. Further, it is assumed that the radio communication unit 10 has to perform an inter-cell handover of the call from the first radio access unit 11 to the second radio access unit This because the user of the radio communication unit 10 is moving in the direction of the second radio access unit 12 or that the radio path between the radio communication unit 10 and first radio access unit 11 is suddenly blocked, for example.

From the list of available radio links retrieved from a previous scan of the radio environment, a suitable second duplex radio link 15 , 16 is selected by the radio communication unit 10 and it starts to occupy this second radio link, however not before transmitting by the radio communication unit 10 at the first radio link 13 , 14 is suspended. The first radio access unit 11 , however, continues to transmit on the first radio link, indicated by arrow In order to establish the second radio link 15 , 16 the radio communication unit 10 synchronizes its timing reference 17 to the second radio access unit, as indicated by the dashed line.

If the second radio link 15 , 16 is successfully established the call can be resumed and the first radio access unit 11 can cease its transmitting at the first radio link, either via a time out or upon receipt of message from the second radio access unit 12 indicating that the call has been taken over. As shown in FIG. During handover, i. By receiving the first radio link, for which the timing reference 17 of the radio communication unit 10 has not to be synchronised to the first radio access unit 11 , a simplex radio link is maintained.

Note that a wide scan window can be used for receiving the first radio link which is now asynchronous to the radio communication unit In case the call has a strong simplex character, i. For the purpose of indicating handover to a user or device involved in a call in progress, a transmit suspension message may be forward by the remote radio communication unit 10 before transmitting at the first radio link is suspended.

This message can be used for signalling purposes to the end users and may take the form of a spoken message, a special tone or tone sequence, a text displayed at a terminal display etc. In the case of a remote radio communication unit 10 still receiving at the first radio link, this message can also received back by the radio communication unit Whenever the second radio link 15 , 16 cannot be established it is preferred to resume the call at the first radio link 13 , 14 , if applicable.

Otherwise a third radio link connecting to the first radio access unit has to be established. When a call is resumed all the call control features, such as encryption and the like particular to the call, are started on the new radio link as well. In case of an inter-system handover the same procedure will be followed as outlined above in connection with inter-cell handover.

However, switching between different radio communication systems may be subject to additional access rights and the like. The radio telephone set 20 has four essential building blocks, i. The timing and synchronisation control unit 23 receives data over the air interface 25 and the radio unit 22 from a base station 3 FIG. Signalling and synchronisation information are removed from the received data by the unit 23 and received speech data are fed to the speech processing unit The speech processing unit 24 , among others, takes care of the deciphering of received data.

A codec 26 decodes the received digitised speech data into a form for making it audible to a user of the handset via a loudspeaker 27 connected to the codec Speech produced by the user is received by a microphone 28 and encoded into a suitable digital format by the codec This encoded speech data is fed to the speech processing unit 24 which, among others, takes care of encryption of the speech data.

The timing and synchronisation control unit 23 adds suitable synchronisation and signalling information to the encrypted speech data.

The radio unit 22 transmits this signalling and speech data via the air interface 25 for reception by a base station 3 FIG. The central control and application logic unit 21 comprises a microprocessor or microcontroller and memory means, and connects to the timing and synchronisation control unit The central control unit 21 essentially controls the system data and the communication with the user of the radio telephone set 20 via a keypad means 29 , display means 33 and ring generator means 30 , all connected to the central control unit Further, an external interface 35 connects to the central control unit 21 for external control and data processing purposes.

Frame and time slot allocation and, in the case of a multi-carrier multi-time-slot technology such as DECT, also the various combinations of carrier frequencies and time-slots are controlled by the central control unit 21 and stored in the memory means. The ring generator means 30 connect to a buzzer 31 for producing a ringing or alerting sound at the arrival of a call. The display means 33 , such as an LCD device, are operatively connected to the central control unit 21 for displaying call information and other user and system data.

For the overall powering of the telephone set 20 a battery and powering unit 34 is included. In accordance with the present invention, the timing and synchronisation control unit 23 is controlled such to perform handover and roaming to synchronous as well asynchronous radio links. The access unit 40 has a wired connection 41 to a radio exchange 2 shown in FIG. The different connections and time slots are merged via a multiplexer The radio access unit 40 has a frame and slot synchronisation unit 44 which controls slot reception and transmission timing.

With antenna diversity, if a radio connection provides no good communication, the control logic first tries the other antenna before changing the radio communication channel. Synchronisation and control information is stripped from received data by unit 49 , whereas such information is added to the data to be transmitted by unit 50 , connected as shown.

The frame and slot synchronisation unit 44 is controlled such to support handover in accordance with the present invention. Although the present invention is generally illustrated with respect to a DECT radio telephone communication system, it is not restricted thereto. The present invention can be used with other communication devices, such as data communication equipment, as well as in other wireless multicell communication systems. What is claimed is: 1.

A method according to claim 1 , wherein at step a said remote communication unit synchronizes its timing reference to retrieved synchronisation data. A method according to claim 1 , wherein at step b said scan window having a width and position in time such to include said predetermined time period, and wherein synchronous radio links and asynchronous radio links are distinguished on the basis of time difference between the receipt of synchronisation data and said predetermined time period.

A method according to claim 3 , wherein said time difference is used by said remote communication unit to adjust its timing reference. A method according to claim 1 , wherein step a and step b are performed at different rates. A method according to claim 5 , wherein step a is performed at a higher rate than step b if a number of synchronous radio links adequately for handover is detected, said number and rate may be adoptively set subject to predetermined radio link criteria.

A method according to claim 1 , wherein at step a and step b the number of radio links to be scanned is limited if a number of radio links adequately for handover is detected, said number may be adoptively set subject to predetermined radio link criteria.

A method according to claim 1 , further comprising the steps of:. A method according to claim 9 , wherein said first and second radio access units are operated in a mutually time asynchronous manner, and wherein said first and second radio access units may form part of first and second time independently operated radio communication networks, respectively.

A method according to claim 9 , wherein during steps e and 0 said first radio access unit maintains transmitting said call at said first radio link, and said remote radio communication unit maintains receiving said call at said first radio link. A method according to claim 9 , wherein at the start of a handover said remote communication unit forwards a transmit suspension message to said first radio access unit.

A method according claim 12 , wherein upon receipt of said transmit suspension message by said first radio access unit a signaling message is exchanged for the purpose of indicating that said call is subjected to handover, which message at a terminal side may take the form of but not limited to a voice signal, an audio tone signal or a visual display signal, and wherein said signaling message is released if said call is resumed. A method according to claim 9 , wherein if said call is resumed at said second radio link, said first radio link is released after a predetermined time period following suspension of transmitting by said remote communication unit.

A method according to claim 9 , wherein if said call is resumed at said second radio link, a release message is forwarded to said first radio access unit via its corresponding radio communication network in order to release said first radio link.

A method according to claim 9 , wherein if said second radio link cannot be established, said call is resumed at said first radio link. A method according to claim 16 , wherein if said call cannot be resumed at said first radio link, a third radio link between said remote communication unit and said first radio access unit is established and said call is resumed at said third radio link.

A method according to claim 9 , wherein said call is resumed maintaining call control features particular to said first radio link. A communication unit comprising:. The communication unit of claim 19 , wherein said communication unit is a radio telephone.

The communication unit of claim 19 , wherein said communication unit is a base station. A method for performing handover and roaming in a radio communication environment. Method for performing handover and roaming in a radio communication environment. USB1 en. EPB1 en. JPB2 en. KRB1 en. Wireless Networks - Catching the Mobile Future, , pp. Bosch, P. Pereira, A.

Petter Nielsen, Introduction of the third generation of mobile communication system in Norway, Department of informatics, University of Oslo, Norway. Issac 1 Email author 1. Personalised recommendations.

Cite paper How to cite? ENW EndNote.