CN1663300A - Handovers of user equipment connections in wireless communication systems - Google Patents

Abstract

An inter-frequency handover of a UE connection is performed in which the frequency of the uplink connection from the UE to a base station remains the same and the frequency of the downlink connection from the base station to UE changes from a first downlink frequency to a second downlink frequency (figure 4). A request for the handover is transmitted from the base station (401). The request containing information indicating the second downlink frequency and information indicating that the uplink frequency remains the same. In response to the request, the physical layer of the uplink connection is maintained while changing the downlink frequency from the first downlink frequency to the second downlink frequency (403).

Description

Handover of user equipment connection in wireless communication system

technical field

[0001] The present invention relates generally to wireless communications. More specifically, the present invention relates to handover of User Equipment (UE) under the control of a Radio Network Controller (RNC) in a wireless communication system.

Background technique

[0002] In wireless communication systems, soft handover is used to gradually transfer a user equipment (UE) connection from one base station to another without requiring the user to experience any interruption in communication. For example, hard handover is used for switching between modes of operation or switching between base stations when soft handover cannot be performed. Specifically, inter-frequency hard handover is used to switch the connection between the UE and the radio access network from one frequency carrier or frequency band to another. Although it may not necessarily be obvious to the user, a hard handover usually involves some kind of interruption of the connection between the UE and the base station.

[0003] The connection between the UE and the radio access network includes an uplink (UL) connection on a first carrier frequency and a downlink (DL) connection on a second carrier frequency different from the first carrier frequency. A UL connection may be accompanied by a first base station independent of the second base station used for the DL connection. (See WO93/19537 for an example of such a system.) However, most wireless communication systems, including Global System for Mobile Communications (GSM) and IS-95, are fixed duplex systems in which UL and DL Both connections are to the same base station and use one of several predetermined duplex UL-DL pairs. Each 1:1 pair of UL and DL carriers has a constant fixed offset between UL and DL frequencies in order to prevent interference between base stations and between user equipments.

[0004] When the radio network controller wishes to perform an inter-frequency hard handover for a particular UE for any reason (e.g. interference, load, etc.), it identifies a new UL-DL duplex pair, and the UL and DL frequencies for that particular UE At the same time jointly change to a new UL-DL duplex pair. This handover procedure is performed and the entire duplex pair is changed, even if it is desired to change only one of the UL frequency or the DL frequency. For example, it is impossible to keep the uplink connection uninterrupted and only change the downlink connection.

[0005] Prior art Figure 1 illustrates an inter-frequency hard handover procedure performed in a network according to Release 4 of the specification developed by the Third Generation Partnership Project ( www.3gpp.org ). For a complete description of hard handover, see subsection 7.11 of 3GPP TS 25.931 v4.1.0 (2001-06). As shown in steps 7 and 10, the inter-frequency hard handover process includes the physical channel reconfiguration process, which itself is an extended process. See subsection 8.2.2 of 3GPP 25.331 v4.1.0 (2001-06). Prior art Figure 2 illustrates the messages taken by a UE in an inter-frequency hard handover. See also subsection 6.4 of 3GPP TS 25.303 v4.2.0 (2001-09). Inter-frequency hard handover according to Release 4 of the 3GPP specification always assumes a new allocation of uplink carriers due to pairing of UL and DL carriers. Even when only the carrier frequency of one of the UL and DL connections needs to be changed, all the steps shown in prior art Figures 1 and 2 (including physical channel reconfiguration) are still performed, and the carrier frequency of the other connection is still changed. reallocate. Therefore, a disadvantage of the 3GPP handover procedure is that there are unnecessary interruptions in reallocating the two carrier frequencies.

Contents of the invention

[0006] An object of a method according to a preferred embodiment of the present invention is to provide a handover procedure which does not contain the disadvantages of prior art procedures when only one of the UL and DL connections is changed in the handover. Specifically, the preferred embodiments enable the UL connection to be maintained and remain uninterrupted while only the DL connection is changed and resynchronized to the new carrier frequency. Thus, the preferred embodiments solve the problems associated with unnecessary allocation of carrier frequencies that do not change during handover.

[0007] Speeding up the handover in the case where one of the uplink or downlink frequencies remains constant and the other frequency is changed is a particular advantage of the handover process. For example, in a handover where only the downlink connection changes but the uplink connection remains unchanged, the method maintains the uplink connection and supports physical resource processing of the uplink connection.

[0008] A first aspect of the present invention relates to a method for performing inter-frequency handover of a UE connection, wherein the frequency of the uplink connection from the UE to the base station remains unchanged, while the frequency of the downlink connection from the base station to the UE changes from The first downlink frequency is changed to a second downlink frequency, the method includes: sending a request for switching from the base station, the request including information indicating the second downlink frequency and information indicating that the uplink frequency remains unchanged; and responding Upon request, maintain the physical layer of the uplink connection while changing the downlink frequency from the first downlink frequency to the second downlink frequency.

[0009] A second aspect of the present invention relates to a method for performing inter-frequency handover of a UE connection, wherein the frequency of the downlink connection from the UE to the base station remains unchanged, while the frequency of the uplink connection from the base station to the UE changes from The first uplink frequency is changed to a second uplink frequency, the method includes: sending a request for switching from the base station, the request including information indicating the second uplink frequency and information indicating that the downlink frequency remains unchanged; and responding to the request request, maintain the physical layer of the downlink connection, and at the same time change the uplink frequency from the first uplink frequency to the second uplink frequency.

[0010] A third aspect of the present invention relates to a method for triggering inter-frequency handover of a UE connection, wherein the frequency of the uplink connection from the UE to the base station remains unchanged, while the frequency of the downlink connection from the base station to the UE changes from The first downlink frequency is changed to the second downlink frequency, and the method includes: directly measuring the signal strength of the adjacent uplink carrier; determining whether there is interference from the adjacent uplink carrier according to the measurement; if it is determined that there is interference on the adjacent uplink carrier If there is interference, a request for switching is sent from the base station, the request includes information indicating that the second downlink frequency and information indicating that the uplink frequency remains unchanged; The frequency is changed from the first downlink frequency to the second downlink frequency.

Description of drawings

[0011] The foregoing description of the invention will become apparent and the invention better understood by reading the following detailed description of exemplary embodiments of the invention and the claims in conjunction with the accompanying drawings which constitute a part of the disclosure of the invention. While the foregoing and the following written disclosure focus on disclosing example embodiments of the invention, it should be clearly understood that these same are by way of illustration and example only and the invention is not limited thereto.

[0012] FIG. 1 illustrates the steps performed by a UTRAN network according to an inter-frequency hard handover procedure according to the prior art.

[0013] FIG. 2 shows the steps taken by the UE according to the prior art inter-frequency hard handover procedure shown in FIG. 1 .

[0014] FIG. 3 illustrates an exemplary 3GPP wireless communication system in which the present invention may be implemented.

Preferred embodiment of the invention.

[0015] FIG. 4 is a flowchart showing the steps of a handover procedure according to a preferred embodiment of the present invention.

[0016] FIG. 5 illustrates the proposed allocation of extended frequency bands to which the preferred embodiment can be applied.

[0017] FIG. 6 illustrates a second allocation of proposed extended frequency bands.

[0018] FIG. 7 illustrates the problem of UE-UE interference.

[0019] FIG. 8 illustrates a method of detecting adjacent channel interference to trigger handover to avoid interference.

[0020] In all drawings, like parts are identified with like symbols.

Detailed ways

[0021] Before beginning the detailed description of the preferred embodiment of the invention, the following description is appropriate. Preferred embodiments of the present invention are described with reference to an exemplary wireless communication system in accordance with Release 4 of the Specifications developed by the Third Generation Partnership Project. However, these preferred embodiments are not limited to implementation in 3GPP wireless communication systems. They may be implemented in any wireless communication system including, but not limited to, FDMA, CDMA or TDMA type systems. Configurations and embodiments of an exemplary 3GPP wireless communication system are represented in block diagram form and described in this application without excessive detail so as not to obscure the invention, and also in view of the fact that specific details about the implementation of such a system The details can be largely related to the environment. In other words, these specific details may vary, but should be well within the scope of one skilled in the art. While specific details have been set forth in order to describe example embodiments of the invention, it will be readily apparent to one skilled in the art that the invention may be practiced without these specific details or with variations thereof.

[0022] FIG. 3 is a block diagram of an exemplary 3GPP wireless communication system architecture. A first user equipment (UE) 11 and a second UE 12 are connected to respective first and second base stations 21 , 22 (called Node Bs in 3GPP specifications) of the UTRAN 40 via the Uu radio interface. The base station participates in radio resource signaling and management, and provides UL and DL connections with UEs 11 and 12 . The UTRAN 40 comprises at least one base station controller 30 (referred to as a radio network controller (RNC) in the 3GPP specifications) connected to the base stations 21, 22 via an Iub interface, responsible for the radio resources in its domain (i.e. the base station controllers 21 connected to it) , 22) Management and control. RNC 30 may be the service access point for all services provided by UTRAN 40 to the core network (not shown). Figure 3 also shows a second RNC 35 connected to the base stations 23 and 24 via the Iub interface. An Iur interface is provided between RNC30 and RNC35. For ease of illustration, only two base station controllers are shown in FIG. 3 . There can of course be any number of base stations and base station controllers in a mobile communication system.

[0023] Current 3GPP (Third Generation Partnership Project) specifications define signaling protocols such as RANAP (Radio Access Network Application Part). RANAP is a signaling protocol in the Iu interface that contains all control information specified for the radio network layer for UTRAN related issues.

[0024] According to 3GPP TS 25.331 v4.1.0, the RRC management of RNC30 can independently indicate the new target channel frequency of the uplink and downlink in handover. The RRC signaling message may contain separate information elements, which respectively indicate uplink frequency, downlink frequency, etc. However, as described in this application, the uplink connection cannot be kept uninterrupted during the time required to change the downlink carrier frequency and perform resynchronization of the downlink connection.

[0025] Returning to the previous hard handover process, subsection 8.2.2 of 3GPP TS 25.331 v4.1.0 stipulates that when inter-frequency hard handover is performed, UE11 should implement the physical channel reconfiguration proposed in subsection 4.3.2.3 of 3GPP TS25.214 Configuration process A. Applying this procedure to the case where only the downlink is changed, the procedure requires the UE 11 to terminate downlink transmission, tune to the new downlink frequency, and attempt to synchronize with it. However, UE 11 must first break the uplink connection and must not transmit on the uplink connection while this is in progress. Therefore, an inter-frequency hard handover always results in an interruption of the uplink by default. After UE 11 starts to transmit again on the uplink connection, Node B21 has to re-acquire the uplink connection.

[0026] The sequence of steps in the previous handover process is that the network starts downlink transmission on the new downlink frequency, UE 11 stops transmitting on the uplink connection and tries to synchronize with the new downlink connection. Once the UE11 has found a new downlink connection and confirmed that the downlink connection is working normally, the transmission on the uplink connection can be resumed, and the base station 21 tries to reacquire the uplink transmission from the UE11, and if the uplink transmission is found, the base station 21 returns a message to the UE11 order to confirm the upstream transmission.

[0027] As mentioned above, the 3GPP specification does not specify a special case where the frequency and other parameters of the uplink or downlink connection remain unchanged during inter-frequency handover. According to this specification, whenever one of the uplink or downlink frequencies is changed, by default, the network must perform a specified inter-frequency hard handoff process. There is no way to avoid unnecessary extra steps in this process.

[0028] The current 3GPP specification does not indicate what happens when one of the uplink or downlink remains unchanged. Only a single hard handover procedure is invoked whenever one of the upstream or downstream frequencies needs to be changed. This is always the case once the hard handover procedure has been invoked and started, and it involves the same steps. The network establishes new physical resources on Node B21 for new uplink and downlink transmissions, and then signals UE11 to switch to the new frequency. The synchronization process begins, in which the UE 11 attempts to establish a new downlink connection, terminate an uplink connection, and search the network for an uplink connection, and so on. In network signalling, new resources will be established for the uplink connection, even though the frequency remains the same and old physical resources may be used.

[0029] The preferred embodiment of the present invention provides a handover process, wherein, in the case of only changing the frequency of the downlink connection, the uplink connection is maintained during the handover process, so that the physical layer of the connection is not interrupted or terminated. The physical hardware resources of the base station are still allocated to the uplink connection. In this way, the base station remains able to receive transmissions for the uplink connection at the physical layer, even though the UE may not be transmitting.

[0030] FIG. 4 is a flow chart illustrating the overall steps of a handover process applicable to the preferred embodiment of the present invention. Firstly, RNC30 decides to perform an inter-frequency handover, wherein the uplink frequency remains unchanged and the downlink frequency changes (step 401) and provides a handover request signaling message to UE11. The handover request preferably contains two separate items of information. The first information indicates that the uplink frequency remains unchanged, and the second information indicates a new downlink frequency. As described above, the physical layer of the uplink is maintained (402), while the downlink frequency is changed (403). After changing the downlink frequency, UE 11 resynchronizes with the new downlink connection (406). The UE 11 is preferably synchronized to the new downlink connection using the same synchronization procedures already established in the UE 11 for the other procedures. This synchronization process can be as described in U.S. Provisional Patent Application No. 60/375,811, entitled "A Fast Process When (Chip) Synchronizes Co-located Carriers," filed April 29, 2002, which is incorporated herein by reference . During the resynchronization process, uplink transmissions from UE 11 may be suspended (405) or resumed (406). After the resynchronization is complete, the feedback loop lost during the handover is restored (407).

[0031] Even though the UE 11 may continue or suspend transmissions on the uplink, it is subject to lost feedback during periods of time in which transmission on the downlink is not possible due to changing carrier frequencies and the need for resynchronization of the downlink The effect of the loop. The handover may apply an optimized power control feature to minimize the recovery period after this downlink transmission gap. The switching optimized power control features may be similar to known compressed mode power control mechanisms, or may be quite different. For example, if transmissions from UE 11 on the uplink continue, the network may estimate changes in radio propagation in order to allow faster utilization of the best working of the feedback loop. The interruption time in the handover according to the preferred embodiment is shorter than conventional inter-frequency handover, and the path loss of the target cell is known due to co-location of base stations.

[0032] A new downlink connection will have a new chip synchronization signal from the base station, and the UE 11 has to re-synchronize with the new signal. Resynchronization of downlink connections preferably follows the same rules as for asynchronous base stations established in 3GPP TS 25.214. In particular, it utilizes the System Frame Number (SFN) timing method to achieve resynchronization. In 3GPP systems, eg in the Global Positioning System (GPS), there is no synchronization of all base stations. Base stations each run on their own clock and have their own system frame numbering and timing and associated drift. The SFN is used when performing handovers between different cells in order to determine drift between base stations. Signaling information is then sent back to the network so that it positions the frame boundaries accordingly and the UE can demodulate the transmission on the downlink.

[0033] Unlike previous procedures, transmission on the upstream connection remains available during and shortly after the time period in which the downstream connection is interrupted and changed. Uplink transmissions can be continued or suspended (this option can be set by the UE or the network), but they are not fully usable and are affected by eg lost feedback loops in downlink connections for power control. This option for uplink transmission during this time period may be set by the UE or the network or by some cooperation of the two. The first option is to interrupt the upstream transmission, preferably in a manner similar to how this is done in compressed mode gaps. The second option is to continue the uplink transmission, preferably in a manner similar to that done for downlink only compressed mode gaps. Additionally, another method of adjusting UE power on the uplink may also be employed, such as slowing down the power reduction for uplink transmission. UE 11 preferably ignores additional downlink measurements until these uplink transmissions.

[0034] It is desirable to prevent triggering of radio link (RL) failure messages. This can be achieved, for example, by temporarily tolerating a higher number of out-of-sync indications than normally tolerated. For example, according to 3GPP TS 25.433: "N_OUTSYNC_IND" = 1..256 frames, i.e. 2.56 seconds)

[0035] There are many advantages to the handover procedure according to the preferred embodiment of the present invention. Most notably, handover is achieved faster than the previous handover process. The physical layer of the uplink does not need to be terminated, and transmission can continue on the uplink. New downlink connections are available sooner, and power control for uplink connections can resume when synchronization of new downlink connections is achieved. Additionally, power control for the downlink on the new carrier frequency can start immediately when downlink synchronization is achieved - no downlink measurements prior to uplink transmission. The power control preamble can be replaced by a power recovery algorithm. Unlike previous handover procedures, no new uplink channel estimation is required.

[0036] The limited availability of spectrum is always a concern for wireless communications. Operators of cellular systems carefully plan their systems to provide the maximum performance possible in the fixed frequency bands allocated to them.

[0037] In a particular embodiment of the invention, the handover procedure is advantageously applied to additional available spectrum. Specifically, among the new extended frequency bands is the extended frequency band between 2500 and 2690 MHz identified by ITUS5.AAA in FIG. 5 . Different scenarios using this additional extended frequency band are possible. Note that the extended band is not wide enough to support multiple duplex pairs with traditional duplex separation of 190Mhz, the first case is that all carriers in the extended band are used for additional downlink carriers only. In this case, UE connections related to one specific core-band UL carrier may be carried over one or more DL carriers. However, each radio link uses at most one carrier (either in one of the core frequency bands or in the extension frequency band) at any point in time. As shown in Figure 5, variable duplexing in the UE is used to access additional DL carriers in extended frequency bands outside the core frequency band. The switching according to the above embodiments can be used together with the variable duplex technology to change the downlink frequency from the core frequency band to the extended frequency band.

[0038] In the second case shown in Figure 6, the figure shows that there are multiple subbands for UL and DL carriers that are adjacent to each other in the extended frequency band. It is assumed that the (missing) UL part in the extension band to the FDD (outer) DL carrier is realized by utilizing the UL carrier from the core band and variable duplexing. Therefore, only existing UMTS core band operators will be able to use that part of the extended band. The UL/DL "inner part" of the spectrum will be used autonomously, ie without having to use core band carriers, eg by new (or possibly also existing) operators.

[0039] It has been suggested that the new extended frequency bands may be used by UTRAN for load balancing or coverage areas. In either case, inter-frequency band switching becomes an essential element for efficient operation and use of spectrum. In particular, the handover according to the preferred embodiment can be used as an efficient interference avoidance mechanism in the second case since it is faster than the previous handover procedure.

[0040] This handover can be triggered by a unique method of detecting UE-to-UE adjacent channel interference. This interference can occur on the boundary between FDD UL (inner) and FDD DL (outer). Such interference does not occur in conventional fixed-duplex wireless communication systems because the fixed distance between carriers avoids the problem. In addition, the interference is small enough not to be identified as a quiet zone area by current methods, but large enough to cause inefficient use of base station resources. Adjacent UE-UE interference creates a large area of interference due to the fact that there are many mobile stations, ie many sources of interference. Therefore, coupled with the inefficient use of base station resources, the number of significantly interfered mobile stations can also be high. Therefore, early UE-to-UE interference detection and subsequent handover improves spectral efficiency.

The problem is shown in Figure 7. A first UE 12 transmitting on an uplink carrier frequency adjacent to another UE 11's downlink carrier frequency would interfere with that adjacent downlink frequency and possibly establish a dead zone. The result would be an inefficient use of base station resources, ie additional base station transmit power, until the quiet zone is reached. UE11 cannot distinguish between the quiet zone and the edge of the cell of the base station. But in case of a dead zone, by performing handover to a non-interfering downlink carrier according to the preferred embodiment, it is easy to avoid inefficient utilization of base station resources around the dead zone. Efficient utilization of base station resources allows high throughput and signal-to-interference ratio in packet-switched traffic. It also allows more UEs to be served with the available base station transmit power.

[0042] A variant of the compressed mode measurement can be used to detect interference and trigger interference avoidance switching, but a preferred method is shown in FIG. 8 . A preferred triggering method for handover involves separate UE measurements directly on adjacent UL carriers. The UE 11 on carrier "B" directly measures the signal strength (RSSI) of the adjacent UL carrier "A". (The term "adjacent" here may include the second adjacent carrier, the third adjacent carrier, and any one or more of the second adjacent carrier, the third adjacent carrier and/or the guard band separation is also In case of interference, carrier-dependent guard band separation is optionally included.) UE 12 can optionally take measurements at the midpoint of two adjacent carriers (or any point in between) instead of separately Both are measured so that the required measurement time is reduced. RSSI measurements are extremely fast (1-2 slots) and can be done efficiently without switching to compressed mode.

[0043] This triggering method allows timely detection of UE-to-UE interference ("Mobile Quiet Zone") and allows early interference avoidance handover to a non-interfering DL carrier. Therefore, from the perspective of UE-UE interference, the adjacent operation of FDD UL and DL is realized without inefficient utilization of downlink carriers. The switching according to the preferred embodiment is fast and efficient (no CM measurements required). In addition, guard bands are not necessary from a UE-UE interference perspective, resulting in higher spectral efficiency.

[0044] In conclusion, the handover according to the preferred embodiment can be done faster than an inter-frequency hard handover (due to path loss of comparable co-located DL carriers, DL synchronization, known SFN), thus minimizing lost feedback. The path loss of the target cell can be estimated because the new downlink channel with which the UE must synchronize comes from the same site (base station); there is only one different frequency for the channel. For example, a radio transmission at 2.5 GHz experiences about 3 dB higher attenuation than a radio transmission at 2.1 GHz. Transmissions from the exact same base station can be synchronized, which means that the UE can be provided with information indicating the synchronization status of the new cell, including the System Frame Number (SFN). This process can be done very fast because the channel estimates for all parameters in the UE will converge very fast since the parameters are the same. The handover according to the preferred embodiment is also faster than previous inter-frequency hard handovers, since no uplink connection is interrupted, and physical hardware resources in the network for uplink demodulation do not have to be reallocated and reserved. Furthermore, the handover according to the preferred embodiment avoids the problem of time consuming reallocation of terrestrial connections between the base station and the uplink radio network controller if those connections exist. They rule out unnecessary situations occurring in the network, such as signaling, resource reservations, etc. that occur with previous handovers. By maintaining the uplink physical resources on the connection, the handover process will be accelerated.

[0045] While the invention has been described in terms of its preferred embodiments, it should be understood that various modifications could be made thereto without departing from the spirit and scope of the invention. All such modifications are intended to fall within the scope of the appended claims.

Claims (35)

1. A method for performing inter-frequency handover of a UE connection, wherein the frequency of the uplink connection from the UE to the base station remains unchanged, and the frequency of the downlink connection from the base station to the UE changes from the first downlink changing the frequency to a second downlink frequency, the method comprising: sending a request for the handover from the base station, the request including information indicating the second downlink frequency and information indicating that the uplink frequency remains unchanged; and In response to the request, maintaining the physical layer of the uplink connection while changing the downlink frequency from the first downlink frequency to the second downlink frequency. 2. The method according to claim 1, wherein the information indicates a second downlink frequency in a frequency band different from the first downlink frequency. 3. The method according to claim 1, wherein both the downlink connection on the first downlink frequency and the downlink connection on the second downlink frequency include synchronization information. 4. The method of claim 3, wherein the synchronization information is used by the UE to save measurements and to speed up the handover. 5. The method of claim 3, wherein the synchronization information includes a system frame number. 6. The method according to claim 3, wherein the synchronization information includes chips and frames indicating that the downlink connection on the second downlink frequency and the downlink connection on the first downlink frequency synchronized information. 7. The method of claim 2, wherein the different frequency band is an extended frequency band including frequencies of at least 2.5 GHz. 8. The method according to claim 1, wherein the first downlink connection and the second downlink connection have the same cell coverage. 9. The method of claim 1, wherein transmission on the uplink connection is suspended when the downlink connection changes from the first downlink frequency to the second downlink frequency. 10. The method of claim 1, wherein transmission on the uplink connection continues when the downlink connection changes from the first downlink frequency to the second downlink frequency. 11. The method of claim 1, wherein a feedback control loop is interrupted during said handover and resumed after said handover is complete. 12. The method according to claim 1, wherein the base station maintains processing resources related to the uplink connection during the execution of the handover. 13. The method according to claim 1, wherein the base station maintains a UL terrestrial connection to the RNC related to the uplink connection during the execution of the handover. 14. A method for performing inter-frequency handover of a UE connection, wherein the frequency of the downlink connection from the UE to a base station remains unchanged, and the frequency of the uplink connection from the base station to the UE changes from a first uplink frequency Changing to a second uplink frequency, the method includes: sending a request for the handover from the base station, the request including information indicating the second uplink frequency and information indicating that the downlink frequency remains unchanged; and In response to the request, maintaining the physical layer of the downlink connection while changing the uplink frequency from the first uplink frequency to the second uplink frequency. 15. The method of claim 14, wherein the information indicates a second uplink frequency in a frequency band different from the first uplink frequency. 16. The method according to claim 14, wherein both the uplink connection on the first uplink frequency and the uplink connection on the second uplink frequency include synchronization information. 17. The method of claim 16, wherein the synchronization information is used by the UE to save measurements and to speed up the handover. 18. The method of claim 16, wherein the synchronization information includes a system frame number. 19. The method according to claim 16, wherein the synchronization information includes information indicating that the downlink connection on the second downlink frequency is synchronized with the downlink connection chip and frame on the first downlink frequency. 20. The method of claim 15, wherein the different frequency band is an extended frequency band including frequencies of at least 2.5 GHz. 21. The method according to claim 14, wherein the first uplink connection and the second uplink connection have the same cell coverage. 22. The method of claim 14, wherein transmission on the downlink connection is suspended when the uplink connection changes from the first uplink frequency to the second uplink frequency. 23. The method of claim 14, wherein transmission on the downlink connection continues when the uplink connection changes from the first uplink frequency to the second uplink frequency. 24. The method of claim 14, wherein a feedback control loop is interrupted during said handover and resumed after said handover is complete. 25. A method for triggering inter-frequency handover of a UE connection, wherein the frequency of the uplink connection from the UE to the base station remains unchanged, and the frequency of the downlink connection from the base station to the UE changes from the first downlink changing the frequency to a second downlink frequency, the method comprising: Directly measure the signal strength of adjacent uplink carriers; determining that there is interference from the adjacent uplink carrier according to the measurement; If it is determined that there is interference on the adjacent uplink carrier, sending a request for the handover from the base station, the request including information indicating the second downlink frequency and information indicating that the uplink frequency remains unchanged; and In response to the request, maintaining the physical layer of the uplink connection while changing the downlink frequency from the first downlink frequency to the second downlink frequency. 26. The method of claim 25, wherein the information indicates a second downlink frequency in a frequency band different from the first downlink frequency. 27. The method according to claim 25, wherein both the downlink connection on the first downlink frequency and the downlink connection on the second downlink frequency include synchronization information. 28. The method of claim 27, wherein the synchronization information is used by the UE to save measurements and to speed up the handover. 29. The method of claim 27, wherein the synchronization information includes a system frame number. 30. The method according to claim 27, wherein the synchronization information includes information indicating that the downlink connection on the second downlink frequency is synchronized with the downlink connection chip and frame on the first downlink frequency. 31. The method of claim 26, wherein the different frequency band is an extended frequency band including frequencies of at least 2.5 GHz. 32. The method according to claim 25, wherein the first downlink connection and the second downlink connection have the same cell coverage. 33. The method of claim 25, wherein transmission on the uplink connection is suspended when the downlink connection changes from the first downlink frequency to the second downlink frequency. 34. The method of claim 25, wherein transmission on the uplink connection continues when the downlink connection changes from the first downlink frequency to the second downlink frequency. 35. The method of claim 25, wherein a feedback control loop is interrupted during said handover and resumed after said handover is complete.

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