MXPA06005279A - Method and system for facilitating inter-system handover - Google Patents

Abstract

A method for facilitating inter-system handover by a multi-mode wireless transmit/receive unit (WTRU) is disclosed. The WTRU is capable of communicating in multiple wireless communication systems using different wireless communication protocols. A first wireless communication system provides a hot spot within the coverage area of a second wireless communication system. A base station in a cell in the second wireless communication system generates and transmits a message to inform the WTRU of the existence of the hot spot located in the vicinity of the cell. The WTRU receives the message and is therefore informed of the existence of the hot spot in the vicinity of the cell.

Description

METHOD AND SYSTEM TO FACILITATE INDOOR-SYSTEM TRANSFER FIELD OF THE INVENTION The present invention relates to a wireless communication system. More particularly, the present invention relates to a method and system for facilitating inter-system handover in a wireless communication system.

BACKGROUND Cell-type wireless communication systems of the prior art, such as universal mobile telecommunications service systems (UMTS), comprise a plurality of cells with a particular coverage area. When a wireless transmit / receive unit (WTRÜ) moves through the cell boundary, the WTRÜ needs to perform handover from one cell to another. Each cell broadcasts information necessary to facilitate the handover procedure within the UMTS system. The information typically includes a list of neighboring cells comprising a list of neighboring cells in the vicinity of the cell in service. The list of neighboring cells allows a WTRU to search through only a limited number of cells, instead of all possible codes. As a result, the WTRU is able to speed up the cell search procedure and execute the handover to a new cell more quickly. Meanwhile, wireless local area networks (WLANs) based on IEEE 802.11 standards have been developed and are widely deployed. These systems are convenient for supporting high-speed data transmissions. An example of deploying a WLAN in compliance with the 802.11 standards is the use of access points, called "hot spots" (high speed wireless network connection terminals), in public spaces. A WTRÜ with an 802.11 interface can connect to a hot spot without physical connections. Once the WTRU is wirelessly associated with the hot spot through the RF interface, the WTRU is capable of transmitting and receiving data through the hot spot, typically at a much faster data rate than that provided in a UMTS system. While a hot spot provides high quality, high data rate connectivity, the service range of the hot spot is typically limited to a relatively short range. Since the transmission power of a WTRU under 802.11 standards is limited to a relatively low power level, it is difficult to achieve sufficient coverage across a large population area. In addition, due to the limited range of 802.11 devices, the WTRUs typically perform a constant search procedure for new hot spots. This is a large processing load and, therefore, a constant wear on WTRÜs batteries. In the absence of a mechanism to inform the existence of the hot spot, the WTRU should look for signals transmitted from the hot spot periodically and continuously. This causes an unnecessary consumption of resources and processing power. It would be convenient to provide a dual-mode WTRU that is configured to communicate in, and perform handover between, a UMTS system and a WLAN system under 802.11 standards, since a WTRU can receive much higher speed services from the hot spot, and Once, keep a connection in a wide coverage area in a UMTS system. However, currently, there is no convenient method for handover from a cellular type communication system, such as UMTS, to a wireless local area network (WLAN) communication system, such as a hot spot. Therefore, it is convenient to provide a method and system for facilitating inter-system handover between two wireless communication systems, such as UMTS and WLAN.

THE INVENTION A method is described for facilitating inten-system handover through a wireless multi-mode transmission / reception (WTRU) unit. The WTRU is able to communicate in multiple wireless communication systems, which use protocols of different wireless communication. A first wireless communication system provides a hot spot within at least a portion of the coverage area of a second wireless communication system. A base station in a cell in the second wireless communication system generates and transmits a message to inform the WTRÜ about the existence of the hot spot located in the vicinity of the cell. The WTRU receives the message and is informed if it knows the existence of the hot spot in the vicinity of the cell. The WTRU is able to initiate a handover procedure more quickly and more efficiently without looking for a signal transmitted from the hot spot.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a wireless communication system in accordance with the present invention. Figure 2 is a flowchart of a method for facilitating inter-system handover according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Hereby, the term "WTRU" includes, but is not limited to, a station, a mobile station, a user equipment, a fixed or mobile subscriber unit, a pager, or any other device able to operate in a wireless environment. The present invention facilitates an inter-system handover between two different wireless communication systems, which use two different communication protocols. The wireless communication systems can be any type of wireless communication systems present or developed in the future that include, but are not limited to, UMTS, multiple access by code division 2000 (CDMA2000), global system for mobile communications (GSM) , general radio packet service (GPRS), IEEE 802.11 systems, and Bluetooth. For simplicity, hereinafter, the present invention will be described with reference to a UMTS system and an IEEE 802.11 WLAN communication system that provides a hot sp * t within the coverage area of the UMTS system. However, as mentioned above, it should be noted that the present invention also applies to any wireless access system other than ÜMTS or WLAN 802.11 systems, also in an appropriate manner. Figure 1 is a block diagram of a wireless communication system 100 in accordance with the present invention. The system 100 comprises two or more communication systems that operate in different communication protocols and have an overlay coverage area. Figure 1 illustrates, by way of example, a UMTS 110 system and a 120 hot spot operating under 802.11 standards. The UMTS system 110 has a wider coverage area and the hot spot 120 has a limited coverage area within the coverage area of the UMTS system 110. The UMTS system 110 comprises a plurality of cells 112, each of which serves a particular coverage area. Each cell 112 is served by a base station 114, and the hot spot 120 is served by an ATP 122. A WTRU 130 is configured to communicate both in the UMTS 110 system and in the hot spot 120. The WTRU 130 monitors messages, constant or periodically, from a plurality of base stations 114 and APs 122. The WTRU 130 performs physical measurements on the messages received from the cells 112 and the hot spot 120, and can perform handover to another cell 112 or to the hot spot 120. In accordance with the present invention each base station 114 of the UMTS system 110 informs the WTRU 130 about the existence of any hot spot, such as the hot spot 120, in the vicinity of the cell 112. The base station 114 of each cell is already aware of the existence of the hct spot 120 located in the vicinity of each cell 112. The way in which the base station 114 obtains information regarding the hot spot 120 is not the object of the present invention. However, by way of example, the base station 114 can obtain the information by detecting signals transmitted from the hot spot 120 or by receiving messages from the UMTS 110 system or from the WLAN system. Alternatively, the base station 114 may be manually configured to include said information when the base station 114 is configured, or when new hot spots are configured. In the UMTS system 110, the base station 114 in each cell 112 generates and broadcasts a list of neighboring cells to support efficient handover between cells 112 in the UMTS system 110. In accordance with the present invention, each cell 112 preferably includes additional information regarding the hot spot 120 in the list of neighboring cells. Alternatively, the cell 112 can transmit a separate message for that purpose. The WTRU 130 receives the list of neighboring cells, or a separate message, from the base station 114 of the cell 112 serving the WTRÜ 130, and is thus informed about the existence of the hot spot 120 in the vicinity of the cell 112. The information about the hot spot 120 includes, but is not limited to, the location of the hot spot 120, the frequency band, security level, or any other information necessary to establish a connection to the hot spot 120. Since the WTRÜ 130 obtains the necessary information for connection to the hot spot 120 in advance, the WTRU 130 can reduce the processing power and any resources that are typically necessary to locate the hot spots and to configure the parameters for connection to a particular hot spot. The information on the hot spot 120 is preferably broadcast from the base station 114 to all the WTRUs 130 in the cell 112. Alternatively, the base station 114 of each cell 112 may transmit the list of neighboring cells, or a separate message, only to a subset of WTRUs 130 through a dedicated channel or a shared / common channel. Figure 2 is a flow diagram of a method 200 for facilitating inter-system transfer, informing a WTRU 130 about the existence of a hot spot 120 according to the present invention. A WTRU 130 is a multi-mode WTRU, so that the WTRU 130 can receive messages both from a UMTS 110 system and from a WLAN (ie hot spot) system 120. A base station 114 in a cell 112 of the UMTS system 110 informs the WTRUs 130 located in the cell 112 about the existence of the hot spot 120 in the vicinity of the cell 112. The information on the hot spot 120 is preferably included in a list of neighboring cells. However, the information can be transmitted through a separate message. Each base station 114 in the UMTS system generates a list of neighbor cells for efficient handover to another cell (step 202). The list of neighboring cells contains information necessary for handover including, but not limited to, code group of neighboring cells, primary identity of scrambling code, or a search window of neighboring cells. Each base station 114 broadcasts the list of cells neighboring the WTRUs 130 through a broadcasting channel. Each base station 114 preferably includes information about the nearby hot spot 120 in the list of neighboring cells, or generates a separate message (step 202), and transmits the list of neighboring cells or the message to the WTRUs 130 located in each cell 112 ( step 204). The information about the hot spot may include, but is not limited to, the location of the hot spot, frequency band, security level, or any other information necessary to establish a connection to the hot spot. The information regarding the hot spot 120 is preferably broadcast. However, a base station can transmit the information about hot spot 120 only to a subset of WTRUs 130, instead of broadcasting it. Isa information can be transmitted through, either a dedicated channel or a shared / common channel. The WTRU 130 receives the list of neighboring cells, or the separate message, and is thus informed about the existence of hot spot 120 (step 206). The WTRU 130 can initiate a handover procedure more quickly and more efficiently without searching for a signal transmitted from the hot spot 120. The WTRU 130 can be either in standby mode or in an active mode when the WTRU 130 receives the signal. list of neighboring cells or the separate message. When the. WTRÜ 130 is in an active mode, the WTRÜ 130 uses the information on the hot spot 120 for transfer to the hot spot 120, and when the WTRU 130 is in a standby mode, the WTRÜ 130 can initiate a new call through the hot spot 120 using the information. Before establishing a connection to the 120 hot spot, the WTRU 130 performs physical measurements on messages transmitted from a base station 114 in the list of neighboring cells and the hot spot 120 (step 208). The physical measurements may be any relevant measurement for measuring and comparing signal qualities between the neighboring cells 112 and the hot spot 120. This may include, but is not limited to, a signal-to-interference (SIR) or power intensity ratio. received signal (RSSI). The WTRÜ 130 determines whether the measurement of messages transmitted from the hot spot 120 satisfies predetermined criteria (step 210). If the measurements meet the criteria, the WTRÜ 130 initiates a handover procedure to the hot spot 120, or initiates a new call through the hot spot 120 (step 212). If the measurements do not meet the predetermined criteria, the WTRU 130 does not attempt to establish a connection to the hot spot 120 (step 214). Although the features and elements of the present invention are described in preferred embodiments in particular combinations, each feature or element can be used without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the invention. the present invention.

Claims (14)

1. CLAIMS 1. A method to facilitate the transfer between systems through a multi-mode wireless transmission / reception unit (WTRÜ) which is able to communicate in two wireless communication systems using different wireless communication protocols, and a first system wireless communication provides an active zone within the coverage area of a second wireless communication system, the second wireless communication system comprises a plurality of base stations and each base station serves at least one cell, the method characterized 'because it comprises the steps of: each base station of the second wireless communication system detects an active zone in the vicinity of each base station and generates a message to inform a WTRU of the existence of an active zone located in the vicinity of each base station; each base station transmits the message to the WTRUs located in the cell covered by each base station; and the WTRU receives the message and recognizes the existence of the active zone in the vicinity of the cell.
2. 2. The method according to claim 1 / further characterized in that it comprises the steps of: the WTRU performs the physical measurements on the messages transmitted from the active zone; the WTRU determines whether the measurement results satisfy a predetermined criterion; and the WTRU establishes a connection to the active zone if the predetermined criteria are satisfied.
3. 3. The method according to claim T characterized in that the base station transmits the message through a broadcast channel.
4. 4. The method according to claim 1, characterized in that the base station transmits the message through a dedicated channel, dedicated to the WTRÜ.
5. The method according to claim 1, characterized in that the base station transmits the message to a subset of WTRÜ located in the cell.
6. 6. The method according to claim 1, characterized in that the message is included in a list of neighboring cells.
7. The method according to claim 1, characterized in that the message includes at least one of uh level of location, identity, frequency band, and security of the active zone.
8. 8. A system for facilitating the transfer between systems between two wireless communication systems using two different wireless communication protocols, the system characterized in that it comprises: a wireless transmission / reception unit (WTRU) configured to communicate with both a first communication system wireless and a second wireless communication system; b the first wireless communication system provides an active zone in a coverage area of the second wireless communication system; and the second wireless communication system comprises a plurality of base stations, each base station 0 serves at least one cell, each base station comprises a means to detect the active zones located in the vicinity of the base station and generates and transmits a message to inform a WTRU of the existence of an active zone located in the vicinity of the base station.
9. 9. The system according to claim 8, characterized in that the WTRU further comprises a means for measuring the messages transmitted from the active area; whereby the WTRÜ establishes a connection to the active zone if the measurement satisfies predefined criteria. 0 10.
10. The system in accordance with the claim 8, characterized in that the message is transmitted by a broadcast channel.
11. The system according to claim 8, characterized in that the message is transmitted by a dedicated channel dedicated to the WTRU.
12. 12. The system according to claim 8, characterized in that the message is transmitted to a subset of WTRU located in the cell. The system according to claim 8, characterized in that the message is included in a list of neighboring cells. The system according to claim 8, characterized in that the message includes at least one of a level of location, identity, frequency band, and security of the active zone.