KR101164318B1 - Carrier switching in a multi-carrier wireless communication network - Google Patents

Abstract

Techniques for performing carrier switching in a multi-carrier access network are disclosed. The terminal may be assigned a carrier among a plurality of carriers having different transmit power levels, for example by the access network during system access or handoff. The terminal may receive a switch threshold from the access network. The terminal may periodically measure the received signal strength of the assigned carrier and compare the switch threshold with the received signal strength. The terminal may prohibit switching to a stronger carrier if the received signal strength exceeds the switch threshold and may switch to a stronger carrier if the received signal strength is less than the switch threshold. This carrier switching scheme may prohibit the terminal from switching to the strongest carrier when the assigned carrier can provide satisfactory performance. The access network may also switch the terminal to another carrier by sending a carrier switch message.

Description

Carrier Switching in Multi-Carrier Wireless Communications Networks

TECHNICAL FIELD This disclosure relates generally to communications and, more particularly, to techniques for operating a terminal in a wireless communication network.

This application is filed May 14, 2007, and is claimed by US Patent Provisional Application No. 60 / 917,926, entitled "RATE PREDICTION IN FRACTIONAL REUSE SYSTEMS," which is assigned to the assignee and incorporated herein by reference. do.

Wireless communication networks are widespread for providing a variety of communication content such as voice, video, packet data, messaging, broadcast, and the like. Such wireless networks can be multiple-access networks that can support multiple users by sharing the available network resources. Examples of such multiple-access networks are code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, and single-carrier It includes FDMA (SC-FDMA) networks. A wireless communication network may be referred to as an access network (AN), a radio access network (RAN), a radio network (RN), or the like.

An access network can be a multi-carrier network that supports operation on a plurality of carriers. A carrier may refer to a range of frequencies used for communication or transmission over the range of frequencies. The carrier may be referred to as a frequency channel, a radio frequency (RF) channel, a CDMA channel, or the like. A base station can transmit data over a plurality of carriers to multiple terminals, and can use different transmit power levels for different carriers. It is required that each terminal operate on an appropriate carrier so that good performance can be achieved for all terminals.

Techniques for performing carrier switching in a multi-carrier access network are described herein. The terminal may be assigned one carrier among a plurality of carriers having different transmit powers, for example, by the access network during system access or handoff. The terminal may receive a switch threshold from the access network. The terminal may periodically measure the received signal strength of the assigned carrier and compare the switch threshold with the received signal strength. The terminal may prohibit switching to a stronger carrier if the received signal strength of the assigned carrier exceeds the switch threshold. The terminal may switch to a stronger carrier if the received signal strength of the assigned carrier is less than the switch threshold. This carrier switching scheme may prohibit the terminal from switching to the strongest carrier when the assigned carrier can provide satisfactory performance.

The terminal may mobile-initiated handoff and autonomously switch to a stronger carrier if the received signal strength of the assigned carrier falls below the switch threshold. The access network may control mobile-initiated handoff using switch thresholds to mitigate performance degradation to other terminals assigned to strong carriers. The access network may also switch the network-initiated handoff and terminal to another carrier by sending a carrier switch message to the terminal. The access network may perform network-initiated handoff to balance the load of different carriers and / or to ensure proper quality of service (Qos) for the terminal.

Various aspects and features of the invention are disclosed below in more detail.

1 illustrates an access network.

2 shows the transmission of three carriers on the forward link.

3 shows a processor for performing carrier switching by a terminal.

4 shows an apparatus for performing carrier switching.

5 shows a process for supporting carrier switching by an access network.

6 shows an apparatus for supporting carrier switching.

7 shows a block diagram of a base station and a terminal.

The techniques presented herein can be used in a variety of wireless communication networks, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and other networks. The terms "network" and "system" as used herein are often used interchangeably. CDMA networks may implement radio technologies such as cdma2000, Universal Terrestrial Radio Access (UTRA), and the like. cdma2000 includes IS-2000, IS-95, and IS-856 standards. UTRA includes wideband-CDMA (WCDMA) and various other CDMA. TDMA networks can implement wireless technologies such as Global System for Mobile Communications (GSM). OFDMA networks can implement wireless technologies such as ultra mobile broadband (UMB), evolved UTRA (E-UTRA), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash OFDM®, and the like. UTRA and E-UTRA are part of the Universal Mobile Telecommunications System (UMTS). 3GPP Long Term Evolution (LTE) is the next release of UMTS that uses E-UTRA, which uses OFDMA on the downlink and SC-FDMA on the uplink. UTRA, E-UTRA, UMTS, LTE and GSM are presented in documents of the " Third Generation Partnership Project (3GPP) ". cdma2000 and UMB are presented in the documents of "3rd Generation Partnership Project 2 (3GPP2)". For clarity, certain aspects of the techniques are described below for UMB, and UMB terminology is used in much of the description below. UMB is disclosed in 3GPP2 C.S0084-001, August 2007, entitled "Physical Layer for Ultra Mobile Broadband (UMB) Air Interface Specification," which is publicly available.

1 illustrates an access network (AN) 100, which may include any number of base stations, network controllers, and other network entities. For simplicity, only one base station 120 and one network controller 130 are shown in FIG. 1. A base station is generally a fixed station that communicates with the terminals and can also be referred to as an access point, a Node B, an evolved NodeB, and the like. The base station provides communication coverage for a particular geographic area. To improve capacity, the entire coverage area of the base station can be divided into a plurality of (eg, three) smaller areas. In 3GPP, the term “cell” may refer to the smallest coverage area of the base station and / or the base station subsystem serving this coverage area. In 3GPP2, the term “sector” may refer to the smallest coverage area of the base station and / or the base station subsystem serving this coverage area. For clarity, the 3GPP2 concept of sector is used in the specification below.

Network controller 130 may be connected to a set of base stations, may provide coordination and control for base stations under its control, and may route data to terminals served by such base stations. Access network 100 may include other network entities not shown in FIG. 1.

Terminals 110 may communicate with access network 100 to obtain communication services. The terminal may be fixed or mobile and may also refer to an access terminal (AT), mobile station, user equipment, subscriber unit, station, or the like. The terminal may be a cellular telephone, a personal digital assistant (PDA), a wireless modem, a handheld device, a laptop computer, or the like. The terminal may communicate with the base station via forward and reverse links. The forward link (or downlink) refers to the communication link from the base station to the terminal, and the reverse link (or uplink) refers to the communication link from the terminal to the base station. The terms "terminal" and "user" are used interchangeably herein.

The access network may support operation over a plurality of carriers for the forward link and / or reverse link. The base station may transmit data via a plurality of carriers to the terminals over the forward link. Terminals may transmit data through a plurality of carriers to the base station via the reverse link. Multi-carrier operation can be supported in various ways.

2 shows an example transmission of three carriers on the forward link for multi-carrier operation. Each carrier may have a bandwidth f _BW , which may be a fixed or configurable value. Carrier 1 has a center frequency f _c1 , carrier 2 has a center frequency f _c2 , and carrier 3 has a center frequency f _c3 . The center frequencies can be selected so that the carriers are far enough apart to eliminate intercarrier interference. In general, N carriers can be supported for a given link, and N can be any integer. The N carriers may have the same or different bandwidths and may have a center center at frequencies apart by appropriate amounts.

Base station 120 may transmit N forward link signals on the N carriers. Each forward link may carry a pilot for traffic data, signaling, and a set of terminals. Different terminals may be in different locations throughout the access network and may observe different channel conditions. In one design, terminals may be assigned to different carriers based on their channel conditions. For example, terminals located near the base station may be assigned to one carrier (eg, carrier 3 of FIG. 2), and terminals located in the center of the cell may be assigned to another carrier (eg, carrier 1 of FIG. 2). And terminals located at sector edges may be allocated to other carriers (eg, carrier 2 of FIG. 2). The base station may use different transmit power levels or settings for different carriers, as shown in FIG. For example, the base station may use high power for carrier 2 for sector-edge terminals, medium power for carrier 1 for center range terminals, and low power for carrier 3 for nearby terminals. . Since the path loss is generally greater the greater the distance from the base station, this transmission scheme can ensure that all of the terminals located across the sector can achieve good performance even though they may have different path losses. have.

The terminal may wish to access the access network and measure the received signal strength of each of the N carriers. The received signal strength indicates the strength of a received signal or transmission and may be referred to as received power, received strength, received signal strength indicator (RSSI), and the like. Received signal quality may also be used in place of received signal strength, indicating the quality of the received signal or transmission. As used herein, the term "receive signal strength" may generally refer to reception strength or reception quality.

The terminal may send received signal strength measurements for the N carriers to the access network. The access network may assign the terminal to one of the N carriers based on various factors such as received signal strength measurements for the N carriers, load on each carrier, QoS and data requirements of the terminal, and the like. have. For example, an access network can allocate a terminal to a high power carrier (eg, carrier 2) if the terminal is located far from the base station, and only the received signal strength of this carrier is strong enough. The access network can allocate the terminal to a low power carrier (eg, carrier 3) if the terminal is located close to the base station, and the received signal strength of this carrier is sufficiently strong. In any case, the access network can allocate the terminal to the appropriate carrier during system access, so that the terminal can obtain satisfactory performance. As a result, the terminal may receive data through the assigned carrier.

The access network may support handoff initiated by the terminal, which may be referred to as mobile-initiated handoff, AT-controlled handoff, and the like. During normal operation, the terminal may periodically acquire received signal strength measurements for the N carriers. The terminal may then determine whether to stay on the assigned carrier, whether to switch to another carrier of the same base station, or whether to switch to another base station based on received signal strength measurements. If N carriers are transmitted at different power levels, for example as shown in FIG. 2, the terminal can select the carrier with the strongest received signal strength. Even if the terminal is located close to the base station, the terminal may attempt to switch to the strongest carrier. This may cause performance degradation for sector-edge terminals assigned to the strongest carrier.

In one aspect, the terminal is prohibited from switching to a stronger carrier of the same base station if the received signal strength of the assigned carrier is greater than the switch threshold. This switch threshold may be referred to as ATChannelSwitchThreshold and may be given in units of decibels (dB). The terminal may receive a switch threshold from the access network. The access network can control mobile-initiated handoff using switch thresholds to mitigate the loss of performance for sector-edge terminals.

In one design, the same switch threshold may be used for all N carriers. In other designs, different switch thresholds may be used for different carriers. For both designs, the switch threshold for each carrier can be determined based on various factors such as the QoS requirements of the terminals, the data rates of the terminals, the load of each carrier, and the like. The supported data rate may be dependent on the received signal strength. The higher switch threshold may allow the terminal to switch to a stronger carrier when the received signal strength of the assigned carrier is at a higher level, which may ensure that the terminal can support higher data rates. . The switch threshold may thus be selected to ensure a particular minimum data rate for the terminal during normal operation. The default value may be used for the switch threshold unless specified by the access terminal.

3 shows one design of a process 300 for performing carrier switching by a terminal. The terminal may be assigned to a first carrier among a plurality of carriers having different transmit power levels, for example, by the access network during system access or handoff (block 312). The terminal may receive the switch threshold from the access network, for example, via a unicast message sent to the terminal or a broadcast message sent to all terminals (block 314). The switch threshold may be configurable by the access network. During normal operation, the terminal may periodically measure received signal strength of the first carrier and possibly other carriers (block 316). For example, the terminal can measure the received power of the pilot transmitted on the first carrier and can use the received pilot power as the received signal strength of this carrier. In general, the terminal may measure the received signal strength of the carrier based on pilot, data and / or other transmissions transmitted on the carrier.

The terminal may compare the switch threshold with the received signal strength of the first carrier (block 318). As determined at block 320, if the received signal strength of the first carrier meets or exceeds the switch threshold, the terminal may prohibit switching to a stronger carrier of the same base station (block 322). The terminal may stay on the first carrier, even when there is a stronger carrier, if the received signal strength of the first carrier exceeds the switch threshold (block 324). The terminal can switch to a weaker carrier that can provide satisfactory performance if certain conditions are met.

As determined at block 320, if the received signal strength of the first carrier is less than the switch threshold, if a stronger carrier is available, the terminal may switch from the first carrier to a stronger carrier of the same or another base station. May be (block 326). In one design, the terminal may determine a difference between the received signal strength of the first carrier and the received signal strength of the stronger carrier. The terminal may switch from the first carrier to the stronger carrier if the difference exceeds the delta threshold. This delta threshold can be used to provide hysteresis, so that the terminal is between carriers with similar received signal strength due to fluctuations in channel conditions and / or measurement variability. Does not continue to switch.

If the received signal strength of the assigned carrier falls below the switch threshold, the terminal can automatically switch to a stronger carrier. The access network may also switch the terminal to another carrier by sending a carrier switch message to the terminal. The access network may perform network-initiated handoff to balance the load of different carriers and / or to ensure proper QoS for each terminal. As determined at block 328, if the terminal receives a carrier switch message to switch to the second carrier, the terminal may switch from the first carrier to the second carrier in response to the message (block 330).

4 shows a design of an apparatus 400 for performing carrier switching. The apparatus 400 includes a module 412 for receiving an assignment of a first carrier among a plurality of carriers having different transmit power levels, a module 414 for receiving a switch threshold from an access network, a received signal of the first carrier. Module 416 for measuring strength, module 418 for comparing the switch threshold with the received signal strength of the first carrier, and if the received signal strength of the first carrier exceeds the switch threshold, to a stronger carrier of the same base station. Module 420 for inhibiting switching, module 422 for switching from a first carrier to a stronger carrier of the same base station or another base station if the received signal strength of the assigned carrier is less than the switch threshold, a second from the access network A module 424 for receiving a message for switching to a carrier, and from the first carrier to the second carrier in response to the message It includes a module 426 for switching.

5 shows a design of a process 500 for supporting carrier switching. Process 500 may be performed by an access network, such as a base station, a network controller, and / or some other entity in the access network.

The access network may assign the terminal to the first carrier among the plurality of carriers having different transmit power levels, for example, during system access or handoff (block 512). The access network may send the switch threshold to the terminal, for example, in a unicast or broadcast message (block 514). The access network may set the switch threshold based on the QoS requirements and / or other factors of the terminals. The access network may determine whether signaling is received from the terminal to switch from the first carrier to the stronger carrier (block 516). The switch can be initiated by the terminal only when the received signal strength of the first carrier is less than the switch threshold, which can prevent the terminal from switching to a stronger carrier when the first carrier can provide satisfactory performance. . If signaling is received from the terminal, the access network may switch the terminal from the first carrier to the stronger carrier in response to the signaling (block 518).

The access network may determine whether to move the terminal from the first carrier to the second carrier, for example, to balance the load among the plurality of carriers and / or to satisfy the QoS for the terminal (block 520). If the answer is yes, the access network may send a message to the terminal to switch to the second carrier (block 522). The access network may then switch the terminal from the first carrier to the second carrier (block 524).

6 shows a design of an apparatus 600 for supporting carrier switching. The apparatus 600 includes a module 612 for assigning a terminal to a first carrier among a plurality of carriers having different transmit power levels, a module 614 for transmitting a switch threshold to the terminal, for switching to a stronger carrier. A module 616 for receiving signaling from the terminal, a module 618 for switching the terminal from the first carrier to the stronger carrier in response to the signaling, eg, balancing load among a plurality of carriers and / or A module 620 for determining whether to move the terminal from the first carrier to the second carrier to satisfy the QoS for the terminal, a module 622 for sending a message to the terminal for switching to the second carrier, And a module 624 for switching the terminal from the first carrier to the second carrier.

The modules in FIGS. 4 and 6 may include processors, electronic devices, hardware devices, electronic components, logic circuits, memories, and the like, or any combination thereof.

The techniques described herein may allow the terminal to automatically switch to a stronger carrier if the received signal strength of the assigned carrier suddenly drops. While mitigating the negative impact on terminals on stronger carriers, this can enable robust operation and ensure good performance for the terminal under variable channel conditions. Network initiated handoff can be used for load balancing and to ensure QoS.

FIG. 7 shows a block diagram of one design of base station 120 and terminal 110, which may be one of the terminals in FIG. 1. In this design, base station 120 has T antennas 734a through 734t, and terminal 110 has R antennas 752a through 752r, where T ≧ 1 and R ≧ 1.

At base station 120, transmit processor 720 receives traffic data for one or more terminals at data source 712 and for each terminal based on one or more modulation and coding schemes selected for the terminal. It can process traffic data and provide data symbols for all terminals. The transmit processor 720 may also receive signaling from the controller / processor 740, process the signaling, and provide signaling symbols. The signaling may include switch thresholds, allocation of carriers during system access or handoff, carrier switch messages, and the like. The transmit processor 720 may also generate pilot symbols, which may be used to measure received signal strength. The transmit (TX) multiple-input multiple-output (MIMO) processor 730 can multiplex data symbols, signaling symbols, and pilot symbols, and if possible, spatial processing (eg, performing multiplexed symbols on the multiplexed symbols). Precoding), and provide T output symbol streams to T modulators (MODs) 732a through 732t. Each modulator 732 may process each output symbol stream (eg, for OFDM) to obtain an output chip stream. Each modulator 732 may further process (eg, convert to analog, amplify, filter, and upconvert) the output chip stream to obtain a forward link signal. T forward link signals from modulators 732a through 732t may be transmitted via T antennas 734a through 734t, respectively.

At terminal 110, antennas 752a through 752r may receive forward link signals from base station 120 and may provide received signals to demodulators (DEMODs) 754a through 754r, respectively. Each demodulator 754 may condition (eg, filter, amplify, downconvert, and digitize) each received signal to obtain samples, and to obtain received symbols (eg, to OFDM). Samples may be further processed. The MIMO detector 760 may obtain received symbols from all R demodulators 754a through 754r, perform MIMO detection on the received symbols if possible, and provide the detected symbols. Receive processor 770 processes (eg, demodulates, deinterleaves, and decodes) the detected symbols, provides decoded data for terminal 110 to data sink 772, and provides a controller / processor ( 790 may provide decoded signaling. In general, the processing by the MIMO detector 760 and the receiving processor 770 is complementary to the processing by the TX MIMO processor 730 and the transmitting processor 720 of the base station 120.

For the reverse link, at terminal 110, traffic data from data source 778 and signaling from controller / processor 790 are sent to transmit processor 780 (eg, to switch to a stronger carrier). And, if possible, further processed by TX MIMO processor 782, conditioned by modulators 754a through 754r, and transmitted to base station 120. At base station 120, reverse link signals from terminal 110 are received by antennas 734, conditioned by demodulators 732, processed by MIMO detector 736 if possible, and It may be further processed by the receiving processor 738 to obtain traffic data and signaling sent by the terminal 110.

The controllers / processors 740 and 790 may direct the operation at the base station 120 and the terminal 110, respectively. Controller / processor 790 may perform and / or direct process 300 in FIG. 3 and / or other processes for the techniques described herein. Controller / processor 740 may perform and / or direct process 500 in FIG. 5 and / or other processes for the techniques described herein. The memories 742 and 792 may store data and program codes for the base station 120 and the terminal 110, respectively. The carrier measurement unit 794 can measure the received signal strength of each carrier of interest and provide the received signal strength measurements for all the carriers to the controller / processor 790. The controller / processor 790 may determine whether to switch the carrier based on the received signal strength measurements and, as described above, may initiate switching to the stronger carrier if appropriate conditions are met. The scheduler 744 may schedule terminals for transmission on the forward and / or reverse link and provide allocations of resources to the scheduled terminals.

Those skilled in the art will appreciate that information and signals may be represented using different types of different technologies. For example, the data, instructions, commands, information, signals, bits, symbols, and chips presented herein may be voltage, current, electromagnetic waves, magnetic fields or particles, light fields or particles, or any combination thereof. It can be expressed as.

Those skilled in the art will appreciate that the various exemplary logical blocks, modules, circuits, and algorithm steps described above may be implemented as electronic hardware, computer software, or combinations thereof. In order to clarify the interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement these functions in varying ways for each particular application, but such implementation decisions are not necessarily outside the scope of the invention.

The various illustrative logic blocks, modules, and circuits described herein in connection with this specification may be used in a general purpose processor, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate array (FPGA), or other programming. Possible logic devices, discrete gate or transistor logic, discrete hardware components, or a combination of those designed to perform the functions described herein may be implemented or performed. A general purpose processor may be a microprocessor, but in alternative embodiments, such processor may be a conventional processor, controller, microcontroller, or state machine. A processor may be implemented as a combination of computing devices, such as, for example, a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or a combination of such configurations.

The steps of the method or algorithm described herein in connection with this specification can be implemented directly in hardware, in a software module executed by a processor, or by a combination of the two. Software modules include RAM memory, flash memory, ROM memory; It may exist as an EPROM memory, EEPROM memory, register, hard disk, portable disk, CD-ROM, or any form of known storage medium. An exemplary storage medium is coupled to the processor such that the processor reads information from the storage medium and writes the information to the storage medium. In the alternative, the storage medium may reside inside of a processor. The processor and the storage medium may be located in an ASIC. The ASIC may be located at the user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

In one or more example designs, the described functions may be implemented through hardware, software, firmware, or a combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. The storage medium may be a general purpose computer or any available medium that can be accessed by a special computer. For example, such computer-readable media may be any program code required in the form of RAM, ROM, EEPROM, CD-ROM or other optical disk storage media, magnetic disk storage media or other magnetic storage devices, or instructions or data structures. And may be used to convey or store means, and include, but are not limited to, a general purpose computer, special purpose computer, general purpose processor, or any other medium that can be accessed by a special purpose processor. In addition, any connection may be properly termed as a computer-readable medium. For example, if software is transmitted from a website, server, or other remote source via coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, wireless, and microwave Coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, wireless, and microwaves may be included within the definition of such media. The discs and discs used here include compact discs (CDs), laser discs, optical discs, DVDs, floppy discs, and Blu-ray discs where disc plays the data magnetically, As shown in FIG. The combinations may also be included within the scope of computer readable media.

The description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. have. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features presented herein.

Claims (41)

As a method of performing carrier switching, Receiving a switch threshold from an access network; Measuring received signal strength of a first carrier among a plurality of carriers having different transmit power levels; Comparing the switch threshold with the received signal strength of the first carrier; Determining a difference between the received signal strength of the first carrier and the received signal strength of the stronger carrier when the received signal strength of the first carrier is below the switch threshold; Switching from the first carrier to the stronger carrier if the difference exceeds a delta threshold; And Inhibiting switching to the stronger carrier when the received signal strength of the first carrier exceeds the switch threshold Method of performing carrier switching comprising a. The method of claim 1, If the received signal strength of the first carrier exceeds the switch threshold, further comprising staying in the first carrier, even when the stronger carrier is present, How to perform carrier switching. delete delete The method of claim 1, Receiving a message from the access network to switch to a second carrier; And Switching from the first carrier to the second carrier in response to the message; How to perform carrier switching. The method of claim 1, Receiving an assignment of the first carrier from the access network during system access or handoff; How to perform carrier switching. The method of claim 1, The switch threshold is configurable by the access network, How to perform carrier switching. An apparatus for wireless communication, Receive a switch threshold from an access network, measure a received signal strength of a first carrier among a plurality of carriers having different transmit power levels, compare the switch threshold with the received signal strength of the first carrier, and determine the first Determine a difference between the received signal strength of the first carrier and the received signal strength of the stronger carrier if the received signal strength of the carrier is below the switch threshold; and from the first carrier if the difference exceeds the delta threshold. At least one processor configured to switch to a strong carrier and prohibit switching to the stronger carrier when the received signal strength of the first carrier exceeds the switch threshold Apparatus for wireless communication comprising a. The method of claim 8, The at least one processor is configured to stay in the first carrier, even when the stronger carrier is present, if the received signal strength of the first carrier exceeds the switch threshold, Device for wireless communication. delete The method of claim 8, The at least one processor is configured to receive a message from the access network to switch to a second carrier and to switch from the first carrier to the second carrier in response to the message; Device for wireless communication. An apparatus for wireless communication, Means for receiving a switch threshold from an access network; Means for measuring a received signal strength of a first carrier among a plurality of carriers having different transmit power levels; Means for comparing the switch threshold with a received signal strength of the first carrier; Means for determining a difference between the received signal strength of the first carrier and the received signal strength of the stronger carrier when the received signal strength of the first carrier is below the switch threshold; Means for switching from the first carrier to the stronger carrier if the difference exceeds a delta threshold; And Means for inhibiting switching to the stronger carrier when the received signal strength of the first carrier exceeds the switch threshold Apparatus for wireless communication comprising a. 13. The method of claim 12, Means for staying in the first carrier, even when the stronger carrier is present, if the received signal strength of the first carrier exceeds the switch threshold, Device for wireless communication. delete 13. The method of claim 12, Means for receiving a message from the access network to switch to a second carrier; And Means for switching from the first carrier to the second carrier in response to the message; Device for wireless communication. As a computer-readable medium, Code for causing at least one computer to receive a switch threshold from an access network; Code for causing the at least one computer to measure a received signal strength of a first carrier among a plurality of carriers having different transmit power levels; Code for causing the at least one computer to compare the switch threshold with a received signal strength of the first carrier; Code for causing the at least one computer to determine a difference between the received signal strength of the first carrier and the received signal strength of the stronger carrier when the received signal strength of the first carrier is below the switch threshold; Code for causing the at least one computer to switch from the first carrier to the stronger carrier when the difference exceeds a delta threshold; And Code for causing the at least one computer to inhibit switching to the stronger carrier when the received signal strength of the first carrier exceeds the switch threshold Computer-readable media comprising a. 17. The method of claim 16, Code for causing the at least one computer to stay in the first carrier, even when the stronger carrier is present, when the received signal strength of the first carrier exceeds the switch threshold, Computer-readable media. delete 17. The method of claim 16, Code for causing the at least one computer to receive a message from the access network to switch to a second carrier; And Code for causing the at least one computer to switch from the first carrier to the second carrier in response to the message; Computer-readable media. As a method of supporting carrier switching, Transmitting a switch threshold to a terminal; Receiving signaling from the terminal to switch from a first carrier to a stronger carrier among a plurality of carriers having different transmit power levels, wherein the switching is performed with the received signal strength of the first carrier and the received signal of the stronger carrier. Initiated by the terminal only if the difference between the strengths exceeds a given delta threshold while the received signal strength of the first carrier is less than the switch threshold; And Switching the terminal from the first carrier to the stronger carrier in response to the signaling from the terminal How to support carrier switching comprising a. 21. The method of claim 20, Setting the switch threshold based on quality of service (QoS) requirements of the terminals; How to Support Carrier Switching. 21. The method of claim 20, The switch threshold is used to prohibit the terminal from switching to the stronger carrier when the first carrier can provide satisfactory performance. How to Support Carrier Switching. 21. The method of claim 20, Sending a message to the terminal to switch to a second carrier; And Switching the terminal from the first carrier to the second carrier; How to Support Carrier Switching. 24. The method of claim 23, Moving the terminal from the first carrier to the second carrier to balance load among the plurality of carriers, or to satisfy a quality of service for the terminal. doing, How to Support Carrier Switching. 21. The method of claim 20, Allocating the terminal to the first carrier during system access or handoff; How to Support Carrier Switching. An apparatus for wireless communication, Send a switch threshold to a terminal; Receiving from the terminal signaling for switching from a first carrier to a stronger carrier among the plurality of carriers having different transmit power levels, wherein the switching is for receiving a signal strength of the first carrier and a signal strength of the stronger carrier; Initiated by the terminal only if the difference between is greater than a given delta threshold and the received signal strength of the first carrier is less than the switch threshold; And at least one processor configured to switch the terminal from the first carrier to the stronger carrier in response to the signaling from the terminal. Apparatus for wireless communication comprising a. 27. The method of claim 26, The at least one processor is configured to set the switch threshold based on quality of service (QoS) requirements of terminals; Device for wireless communication. 27. The method of claim 26, The at least one processor is configured to send a message to the terminal for switching to a second carrier and to switch the terminal from the first carrier to the second carrier, Device for wireless communication. 29. The method of claim 28, The at least one processor is configured to load the terminal from the first carrier to the second carrier to balance load among the plurality of carriers or to satisfy a quality of service for the terminal. Configured to move, Device for wireless communication. The method of claim 1, Wherein the switch threshold is a first switch threshold for a first carrier among a plurality of carriers having different transmit power levels, the method further comprising: Receiving, from the access network, for the plurality of other carriers of the plurality of carriers, a plurality of corresponding different switch thresholds, each corresponding to a different carrier among the plurality of other carriers, How to perform carrier switching. 31. The method of claim 30, Setting a default switch threshold for a carrier among the plurality of carriers that does not have a corresponding receive switch threshold; How to perform carrier switching. The method of claim 8, The switch threshold is a first switch threshold for a first carrier among a plurality of carriers having different transmit power levels, and the at least one processor is further configured to receive a plurality of different different switch thresholds from the access network, and Each of the other switch thresholds corresponds to a different carrier among other carriers of the plurality of carriers, Device for wireless communication. 33. The method of claim 32, Further configured to set a default switch threshold for a carrier among the plurality of carriers that does not have a corresponding receive switch threshold, Device for wireless communication. 13. The method of claim 12, The switch threshold is a first switch threshold for a first carrier among a plurality of carriers having different transmit power levels, and the apparatus differs among the plurality of carriers, for a plurality of other carriers among the plurality of carriers. Means for receiving from the access network a plurality of corresponding different switch thresholds, each corresponding to a carrier, Device for wireless communication. 35. The method of claim 34, Means for setting a default switch threshold for a carrier among the plurality of carriers that does not have a corresponding receive switch threshold, Device for wireless communication. 17. The method of claim 16, The switch threshold is a first switch threshold for a first carrier among a plurality of carriers having different transmit power levels, and the computer-readable medium causes the at least one computer to cause a plurality of different carriers among the plurality of carriers. Further comprising: code for receiving from the access network a plurality of corresponding different switch thresholds, each corresponding to a different one of the plurality of carriers, Computer-readable media. 37. The method of claim 36, Code for causing the at least one computer to set a default switch threshold for a carrier among the plurality of carriers that does not have a corresponding receive switch threshold, Computer-readable media. 21. The method of claim 20, The switch threshold is a first switch threshold for a first carrier among a plurality of carriers having different transmit power levels, and the method further comprises transmitting a plurality of different switch thresholds to the terminal. Each of the switch thresholds corresponds to a different one of the plurality of carriers, How to Support Carrier Switching. 39. The method of claim 38, Setting at least one of the plurality of other switch thresholds based on quality of service (QoS) requirements of the terminals; How to Support Carrier Switching. 27. The method of claim 26, The switch threshold is a first switch threshold for a first carrier among a plurality of carriers having different transmit power levels, and the at least one processor is configured to generate a plurality of different switch thresholds each corresponding to a different carrier among the plurality of carriers. Further configured to transmit to the terminal, Device for wireless communication. 41. The method of claim 40, The at least one processor is further configured to set at least one of the plurality of other switch thresholds based on quality of service (QoS) requirements of the terminals, Device for wireless communication.

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