CN1254144C - Network estimated handover assisted by mobile station and base station - Google Patents

Abstract

In the described telecommunications system a handover is determined and defined based on uplink and downlink conditions between a mobile radio station and a base station of a neighbouring cell. The mobile radio reports downlink conditions for the neighboring cell to the network, which instructs the base station of the neighboring cell to report uplink conditions from the mobile station. The network reports handover specifications and mobile station power levels based on the uplink and downlink condition information.

Description

Network estimated handover assisted by mobile station and base station

Field of Invention

The present invention relates to wireless communication systems, and more particularly, to methods and apparatus for efficiently handing over mobile radio stations between adjacent cells.

Background and Summary of the Invention

In a typical cellular radio system, a geographical area is divided into cells served by base stations connected to the radio network. Each subscriber (mobile subscriber) in a cellular radio system is equipped with a portable, pocket, hand-held, or vehicle-mounted mobile station which communicates voice and/or data with the mobile network. Each base station consists of a plurality of channel units containing transmitters, receivers and controllers, and is equipped with omnidirectional antennas for transmitting equally in all directions, or with directional antennas, each directional antenna serving a Specific sector-shaped cells. Each mobile station also includes a transmitter, receiver, controller and user interface, and is identified by a specific mobile station identifier. The first public mobile wireless systems were proposed in the late 1970s and early 1980s. As a group, those systems that are now well known are referred to as "first generation" systems. They include the Advanced Mobile Phone System (AMPS) in the US, the Nordic Mobile Phone System (NMT) in Scandinavia, the Total Access Communications System (TACS) in the UK, and the Japan Mobile Telephone System" (NAMTS). They usually share some common transmission characteristics, such as wireless analog frequency modulation and digital control in the network. However, each system uses unique communication standards relative to the other systems.

In conventional analog cellular systems, when a mobile station is idle (not using a traffic channel), it tunes to and constantly monitors the control channel corresponding to its current cell in the network. Thus, the mobile station can constantly determine whether a paging message destined for it has been received on the control channel. If yes, the mobile station sends a paging response on the control channel to the base station, and the base station forwards the paging response to the wireless network. After receiving the paging response, the wireless network selects an available voice channel in the cell from which the paging response was received, and requests the base station in the cell to instruct the mobile station to establish a direct connection via the control channel.

Alternatively, a mobile station can access the network to initiate a call by dialing a telephone number and pressing the "send" button on the telephone handset. Control signals, including the mobile station identification number and dialed telephone number, are sent over the control channel to the base station and forwarded to the wireless network, which authenticates the mobile station, assigns a traffic channel, and establishes a direct connection.

If a mobile station moves between cells while a connection is established, a "handover" of the connection occurs between cells. Handovers may occur due to various changes that may occur in communications between the mobile station and the network. A typical handoff occurs when a mobile station is communicating with a single base station serving the cell in which the mobile station is located. When the mobile station travels from that cell to a new cell served by the new base station, the first base station handovers communications to the new base station. Thus, when a mobile station moves out of a cell served by a respective base station, the mobile station ends communication with a first base station and begins communication with a second base station.

In another type of handoff, the mobile station may be receiving redundant communications from multiple base stations in order to ensure the quality of the transmission. For example, in FIG. 1, a radio network core 100 receives a communication 102 from a network (not shown). And it is intended to direct the communication 102 to the mobile station MS via the established traffic channel TCH for the communication. The radio network core 100 passes the communication 102 to a diversity handover DHO entity 101, which splits the signal into redundant messages destined for base station BS1 and base station BS2. The base stations BS1 and BS2 pass the communication to the mobile station MS via the same traffic channel TCH. Various techniques are known for providing the diversity handover described above. Because mobile stations receive messages via redundant communications on traffic channels, reception (and delivery) can be improved by having the opportunity to select signals from traffic channels or by combining signals received on traffic channels according to known protocols the quality of.

When the mobile station moves from point A to point B, the quality of transmission and reception to and from base stations BS1 and BS2 changes. From a communication point of view, the mobile station MS and the current base stations BS1 and BS2 can benefit from the additional base station BS3 in a diversity communication scheme. That is, the mobile station MS can be seen as communicating with a current set of base stations (BS1 and BS2), and has neighboring base stations (BS1 and BS2) available as promising candidates for future communication links BS3).

During movement from point A to point B, base station 2 maintains communication with mobile station MS throughout the travel of the mobile station, and base stations BS1 and BS3 may or may not maintain communication depending on signal quality. In FIG. 1, a mobile station communicates by using a traffic channel TCH irrespective of the base station with which it is communicating.

A mobile station keeps a record of its current base station, and can test (or be instructed to test) neighboring cells for inclusion in the record. The currently communicating base stations are added to or removed from the current record as specified by the conditions.

Handovers can occur even within the range of a single base station, as shown in Figure 2. In the figure, the base station is shown with four antennas A1-A4 defining four geographical service areas. The mobile station MS at position A communicates with the base station via a traffic channel TCH. At location A, the mobile station communicates with the base station by redundant reception/transmission to antennas A1 and A4. However, after moving to location B, mobile station MS can start receiving and transmitting to antennas A1 and A2. Switching between antennas A1/A4 and antennas A1/A2 occurs when the mobile station moves from point A to point B.

The benefit of diversity reception/segmentation as shown in Figures 1 and 2 is that the communication between the base station and the mobile station (the situation of Figure 2) and between the radio network core and the mobile station (the situation of Figure 1) is never interruption. That is, in the situation of Fig. 1, even when the mobile station moves from point A to point B and even when it is handed over from base station 1 to base station 3, mobile station MS always maintains communication with the core of the wireless network via base station 2 . Likewise, in the situation of FIG. 2, the mobile station MS maintains communication with the antenna A1 even when the mobile station moves from point A to point B and even when it switches from antenna A4 to antenna A2.

Handover situations occur due to the occurrence of specified conditions, such as signal strength between the mobile station and the receiver. In the situation of FIG. 1, for example, when the mobile station moves from point A to point B (shown by the undulating line on the figure), a decision can be made that the signal strength between the mobile station MS and the base station BS3 is preferably suitable for for communication with the mobile station MS, not with BS1. In previous handover situations, the current radio conditions (often measured and reported by the MS) and resource conditions (often measured and reported by the MS) and resource conditions (find out Free channels in the indicated cell are measured by the MS). At present, the MS generally measures cell conditions and reports the result to the network, and the network estimates the handover according to the required resources. However, this is problematic because: as the same condition, a handover may be expected from the network's point of view, but may not be expected from the mobile station's point of view. That is, the network may wish to perform a handover due to some signal conditions, but the mobile station may perceive the handover conditions to be different, and vice versa. If the handover decision is made by the network, it will do so regardless of mobile station conditions. On the other hand, if the handover is performed by the network mobile station, it will do so regardless of network conditions.

In the present invention, both uplink and downlink signals to and from the mobile radio station and the radio network are involved in handover estimation. The invention is particularly useful whenever uplink and downlink conditions are different in a network, or when a mobile station is close to the border of two different network operators. In such a situation, the handover-related measurement reports from the mobile station may be passed to the wireless network and used by the network to determine when the base station should measure the uplink transmission quality from the mobile station. These two measurements are used to make handover decisions.

The invention allows the BS to make certain measurements of the MS simultaneously with the MS's measurements of the BS. In addition, some BSs listen to the uplink without transmitting on the downlink, rather than using existing downlink transmit power control commands from other BSs.

The present invention also allows the network to correct channel and/or power level uplink conditions before a wireless station switches to a new cell broadcast area.

Brief description of the attached drawings

The above and other objects, features, and advantages of the present invention will become apparent from the following description of the preferred embodiments and from the accompanying drawings in which reference characters refer to the same parts throughout. Although various functional blocks and components are shown in many of the figures, those skilled in the art will appreciate that these functions can be implemented by individual hardware circuits, by a suitably programmed digital microprocessor, by an application-specific integrated circuit (ASIC), and/or Or implemented by one or more digital signal processors (DSP).

FIG. 1 is a schematic diagram of a simplified mobile wireless communication system;

FIG. 2 is a schematic diagram of a simplified mobile station-base station communication system;

Figure 3 is a schematic representation of a mobile station-base station communication link;

Figure 4 is a schematic representation of a simplified mobile station communication network;

Figure 5 is a schematic representation of a simplified radio network controller connected to a base station;

Figure 6 is a schematic representation of a simplified mobile station;

Figure 7 is a graphical representation of thresholds for the current group and adjacent groups employed by an exemplary embodiment of the present invention;

Figure 8 is a schematic representation of a simplified mobile communication system in which a mobile station communicates with different base stations via uplink and downlink; and

Figure 9 is a schematic representation of an exemplary embodiment of the invention for use at a border between different operators.

Detailed description with attached drawings

In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular embodiments, data flows, signaling implementations, protocols, techniques, etc., in order to provide an understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods, interfaces, devices, and signaling techniques are omitted so as not to obscure the description of the present invention with unnecessary detail.

The present invention is illustrated in the non-limiting example of Universal Mobile Telecommunications (UMTS) 10 shown in FIG. 4 . A representative connection-oriented external core network is shown as cloud 12, which may be, for example, the public switched telephone network (PSTN) and/or the integrated services digital network (ISDN). Another representative connectionless-oriented external core network is shown as cloud 14, which can be the Internet, for example. The two core networks are coupled to respective service nodes 16 . The PSTN/ISDN connection-oriented network 12 is connected to connection-oriented service nodes, such as Mobile Switching Center (MSC) nodes 18, for providing circuit switched services. In the existing GSM model, the MSC 18 is connected via interface A to a base station subsystem (BSS) 22, which in turn is connected to a radio base station 23 via interface A'. The Internet connectionless-oriented network 14 is connected to a general packet radio service (GPRS) node 20, which is customized to provide packet-switched type services and is sometimes referred to as a Serving GPRS Service Node (SGSN). Each core network service node 18 and 20 is connected to a UMTS Terrestrial Radio Access Network (UTRAN) 24 through a Radio Access Network (RAN) interface. UTRAN 24 includes one or more radio network controllers 26. Each RNC 26 is connected to a plurality of base stations (BS) 28 and any other RNC in the UTRAN 24.

Preferably, the wireless access is based on Wideband Code Division Multiple Access (WCDMA), wherein individual wireless channels are allocated by using CDMA spreading codes. Of course, other access methods may also be used. WCDMA provides wide bandwidth for multimedia services and other high transmission rate requirements as well as reliable features such as diversity handover and RAKE receiver, thereby ensuring high quality. Mobile stations 30 use transmission codes so that base station 28 can identify transmissions from a particular mobile station 30 . In the current WCDMA standard, it is assumed that codes are assigned to dedicated channels as follows:

(a) Uplink and downlink transmissions use a channelization code and a scrambling code on top of it;

(b) the channelization code determines the spreading factor, and the spreading factor determines the maximum bit rate;

(c) mobile stations using the same frequency and the same spreading factor in the same cell will use different channelization codes for the downlink channel, but the same scrambling code;

(d) Mobile stations in other cells use the same channelization code but different scrambling codes.

The scrambling code ensures integrity between downlink transmissions using the same channelization code in different cells. The scrambling code used in the uplink ensures integrity between uplink transmissions from different mobile stations in the same or different cells.

Thus, the MS gets its own scrambling code, while BS transmissions on dedicated channels to a particular mobile station will use a common scrambling code but a unique channelization code. The MS has the ability to combine downlink transmissions using different scrambling codes and different channelization codes (one limitation today is that the spreading factors of the channelization codes from all cells must be the same).

The radio network controller 26 and the base station 28 shown in Fig. 5 are radio network nodes, and each node comprises corresponding data processing and control unit 32 and 33, is used for carrying out the communication required between RNC 26 and mobile station 30 extensive wireless and data processing operations. A portion of the equipment controlled by the base station data processing and control unit 33 includes a plurality of radio frequency transceivers 34 connected to one or more antennas 35 . The mobile station 30 shown in FIG. 6 also includes a data processing and control unit 36 for controlling various operations required by the mobile station. A data processing and control unit 36 of the mobile station provides control signals as well as data to a radio frequency transceiver 37 connected to an antenna 38 . The data processing and control unit 36 and the transceiver 37 are powered by voltage supplied by a battery 39 . The amount of power supplied by the battery 39 to the data processing and control unit 40 and the transceiver 37 may be adjusted by one or more of its control signals from the data processing and control unit 36 .

The present invention can be employed in the context of the example mobile communication system 10 shown in FIG. net. In previous handover scenarios, the mobile station performed radio condition assessment, and the network performed resource assessment, in order to determine whether a handover should occur. The main problem that occurs as a result of this is an over- or under-power condition, where the MS broadcasts a signal strength that is too strong or too weak for the conditions that exist in neighboring handover cells. On the other hand, the invention allows measurements to be taken by the network before the network sends a handover command, which operation will replace the operation of receiving measurement reports from the mobile station, or which operation will (in the more likely case) The operation of receiving the measurement report by the station is performed in parallel.

Figure 3 shows these conditions in more detail. When the mobile station MS is in position A, the traffic channel TCH provides an uplink from the mobile station MS to the base station BS1 and a downlink from the base station BS1 to the mobile station MS. Communication quality between a mobile station and a base station is specified by referring to uplink conditions and downlink conditions. When the mobile station moves to location B, a handover decision between base station BS1 and base station BS2 has to be made. In order to ensure high quality communication, a handover decision is made by comparing the uplink and downlink communication quality between the mobile station and base station BS1 with that of the mobile station in base station BS2.

In particular, if the handover between base station BS1 and base station BS2 is only made by the network, the network does not know with certainty the downlink conditions between mobile station MS and base station BS1 relative to mobile station MS and base station BS2. Current protocols allow the network to make resource estimates regardless of whether the MS or BS makes radio condition estimates. That is, the MS can report radio condition information for use by the network to estimate handovers, or the BS can provide radio condition estimates based on uplink conditions. The radio condition information can be estimated by using the path loss measured by the MS, but this information can obviously be measured by the BS to a more precise degree.

Referring now to Figures 1-3, the preferred embodiment of the present invention causes the mobile station to report to the RNC 100 about the downlink profile, and the RNC uses this profile to order the handover operation. The MS will use the BCCH channel to make measurements on the cells it communicates with (ie the cells included in the active set). In location A, the MS keeps a record of the current base station with which it communicates. The MS also continuously monitors the quality of downlink signals of adjacent cells based on the reception quality of the common pilot channel. Alternatively, any channel containing pilot bits with constant output power and covering the entire cell can be used for neighbor cell measurements. Therefore, when the MS moves from location A to location B, the MS measures the BCH downlink condition from the base station BS3. The MS reports these measurement profiles from the downlink to the RNC 100 whenever profiles from neighboring cells exceed the criteria. The RNC informs the base station (eg base station BS3) that the MS identifies the base station as the intended base station for current and near future communications. When the mobile station moves from location A to location B, the RNC 100 instructs the BS3 to measure the uplink transmission power received from the MS. RNC 100 uses The existing link between MS-BS1 and MS-BS2 instructs the mobile station to reduce its power level to an appropriate interference-free level for the cell defined by BS3. By temporarily reducing the MS output power, the BS3 uplink is protected from excessive interference until the wireless link between the MS and BS3 is established in a manner that sufficiently supports fast power control.

The base stations BS1 and BS2 continue to communicate with the mobile station MS on the previously established transport channel TCH. First, only control power is provided between MS and BS3 until BS3 reports to RNC 100 that the uplink from MS is at an appropriate level. At this point, the RNC 100 notifies the MS: it should set up a handover to include BS3 in its current communication report on TCH (or, if the mobile station capacity can no longer accept the base station, remove the weakest from the current report base station and replace it with BS3). Of course, the RNC 100 will inform the mobile station MS to reduce its transmit power to an appropriate level when it includes BS3 in the current report of the base stations communicating with the mobile station on the TCH.

It is also possible to have BS3 receive the uplink and combine this uplink with BS1 and BS2 long before BS3 is ordered to start its transmission on the downlink. As a result of combining the uplinks from BS1, 2 and 3, the MS may be instructed to reduce its power. This is typically achieved by changing the signal-to-interference ratio target in BS1 and BS2 since BS1 and BS2 have a fast power control connection with the MS on the downlink.

In general, the preferred embodiment of the present invention removes any link in situations where both the downlink and uplink are weak. A mobile station maintains communication within its active communication group with base stations in which a strong uplink, i.e. low path loss and low interference (factors that make it possible to use low power to achieve quality goals ) will be associated with a weak downlink (or vice versa). Finally, strong uplink and downlink signals will ensure continuity of communication between the mobile station and any base station with possible power reduction instructions provided by the RNC to the MS.

According to an exemplary embodiment of the present invention, the mobile station reports the BCH power level for all neighboring cells, whether the signal is weak or strong. The RNC uses the measurements from the mobile station to determine from the reported downlink information when neighboring base stations should measure the uplink information transmitted by the mobile station. When the uplink information satisfies the threshold value, the handover will be triggered. Other reasons for initiating BS measurements could also be: the BS is compromised by high interference levels, the MS output power is about to reach its limit, or the BS members in the active set will run out of power. Another reason: the frequency used by the MS will reach overload and the MS will have to be switched to another frequency. The BS can then make measurements on the MS and estimate which BS the UE should use after the frequency change (assuming other frequencies are not supported by all cells in the area). When the BS makes measurements on the MS, the MS is identified by its unique scrambling code. As a result of the BS measurements, the MS is identified by its unique scrambling code. Additionally, the system should be able to make more reliable inter-frequency handover decisions.

Figure 7 shows a comparison of signal quality received at a mobile station from various base stations as the mobile station moves over time through geographical areas close to BS1, BS2 and BS3. At earlier times, the mobile station is only in voice communication with BS 1 (and possibly monitoring downlink conditions from BS2 and BS3). Neither BS2 nor BS# are included in the mobile station's current active set of base stations. Regardless, the mobile station continues to report to the RNC 100 about the downlink signal strength situation for the neighboring cells BS2 and BS3. At time t1, the downlink signal strength for BS2 reaches a threshold value that can be included in the current communication active set) CS. This can be seen as a request for an update. (In IS-95, the request is more explicit, such as "The MS makes an offer to the network that it cannot refuse").

The mobile station continues to test the downlink signal strength from base station BS3. When the downlink signal strength from BS3 exceeds the neighbor cell group threshold) NS, the mobile station reports that BS3 is now a candidate to be included in the current group. For hard handover, RNC informs BS3 to estimate uplink conditions and report about possible interference and power level conditions. The RNC returns a report to the MS when and at what power level the connection with BS3 can be started. When the RNC notifies the MS that there is an appropriate handover specification (and an appropriate power level), and that the MS detects a CS downlink threshold from BS3, then BS3 is added to the current report. For soft handover, the MS does not adjust its power explicitly; it adjusts its power when the power control bits transmitted on the downlink of the active set indicate that the MS power should be reduced.

Figure 8 shows another exemplary embodiment in which the present invention provides an advantageous application. In FIG. 8, mobile station MS1 starts communicating at location A with uplink and downlink on TCH from three base stations BS1, BS2 and BS3. Thus, the MS has a current communication group equal to BS1, BS2 and BS3. Mobile station MS1 monitors the BCHs from BS4 and BS5 and eventually adds them to its proposed neighbor cells. However, there is a problem with adding BS4 and BS5 to the current report. For BS4, the signal strength is too large and should be reduced as quickly as possible. If BS4 detects a strong signal, BS4 can instruct BS1, 2, 3 to reduce their signal interference goals, thereby forcing the MS to reduce power quickly by using the fast power control bit so that it does not interfere with BS4. It is also advantageous if the BS4 uplink is included in the DHO combination to compensate for the reduced uplink power of the UE. The BS4 downlink can be activated and the MS active set can be updated later as the network sees fit. For BS5, the MS's communication on TCH will cause unacceptable interference to the established communication between MS1 and BS5 on channel TCHp.

If the mobile station MS1 makes the handover decision independently of the network based only on the comparison of the downlink signal strength between BS1, BS2, BS3 versus BS4 and BS5, the communication will be blocked on the uplink side because the network MS power floods BS4 and interferes with existing communications in BS5. On the other hand, according to the preferred embodiment of the present invention, when MS1 moves to position B, MS1 detects BCH downlinks from BS4' and BS5', and when for each adjacent base station, )NS is exceeded, MS1 reports to the network. When the threshold value is reached, the network does not order the handover process immediately, but notifies the base station to perform uplink estimation. After doing so, the base station BS4 or BS5 will detect power level problems or interference conditions, and will report the conditions to the network. If BS4 and BS1, 2, 3 are operating on the same frequency, the handover should be seen as an earlier power control to condition this MS in favor of all other MSs using BS4. If the MS power is reduced, BS5 is no longer obstructed by this MS. The RNC then waits for further downlink information input from the mobile station for other neighboring cells.

Figure 9 shows yet another exemplary embodiment in which the present invention can be used advantageously. In Figure 9, the mobile station is served by operator 1 to the left of the indicated boundary, and once moved to position B, the mobile station is served by a different operator (operator 2) to the right of the boundary. On the other hand, in the cell 1 of the operator 1, the mobile station MS performs uplink communication on the frequency F1. If the mobile station moves to the cell of operator 2, the mobile station may communicate uplink on frequency F1, thereby interfering with other transmissions. After applying the invention, a current list of those base stations) for operator 1 (exceeding) the CS threshold) is created by the mobile station MS, and created for operator 2 ( )Ns-threshold) the contiguous list. This information is reported to the RNC of the operator 2, which instructs the base station 2 in the cell 2 to measure the uplink from the mobile station MS. This uplink measurement may show a high signal strength from this particular MS, so, as long as the MS is not connected to cell 2, cell 2 suffers from interference from this MS. The RNC for operator 2 then reports to the RNC for operator 1 that the neighbor list does not allow uplink communication of the mobile station in cell 2 on frequency F1 . After receiving this information from Operator 2, there are at least three options to do.

1. Perform an internal operator switch from cell 1 (operator 1) to cell 2 (operator 2).

2. Perform internal frequency switching, but still reside at operator 1.

3. Limit the output power.

If the method according to 1 is chosen, the RNC for operator 1 will request to perform a handover from cell 1 to cell 2, and the RNC operator 2 will order the BS in cell 2 to perform measurements on the user entity, and according to the measurement results to Answer the request for a switch.

While the invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but rather the invention is intended to cover the spirit contained in the appended claims. and various modifications and equivalent arrangements within the scope.

Claims (7)

1. changing method that is used to have the network of a plurality of base stations, one of them mobile radio station and at least one base station communicate, and the method is characterized in that:

Receive the downlink measurement data of network from mobile radio station, and determine according to the downlink measurement data whether one or more base stations should measure the one or more characteristics from the ul transmissions of travelling carriage;

One or more characteristics of the radio up-line transmission of measurement from mobile radio station to one or more adjacent base stations;

The idle channel of estimating one or more base stations according to the down link of measuring and uplink feature is so that determine which idle channel is applicable to this mobile radio station;

According to up link and the downlink characteristics measured, give travelling carriage the power level reporting of handover event technical conditions and travelling carriage; And

Power level according to handover event technical conditions and travelling carriage is switched mobile radio station.

2. the process of claim 1 wherein that switching is soft handover.

3. the process of claim 1 wherein that switching is direct-cut operation.

4. the process of claim 1 wherein that switching is to switch between the network operator.

5. the process of claim 1 wherein that mobile radio station keeps and the communicating by letter of present base station after switching.

6. the process of claim 1 wherein that the downlink measurement of regulation is data based relates to the relation between the threshold value of the down link signal reference level between this mobile radio station and the base station and is reported to network measurement data and one.

7. the process of claim 1 wherein that in down link and the uplink measurement data at least one is at least one numerical value in the following:

-signal strength signal intensity,

-signal noise ratio,

-path loss,

-the time difference and

The time-delay of-round trip.

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