Method of handoff within a telecommunications system containing digital base stations with different spectral capabilities Number:7,151,933 from the United States Patent and Trademark Office (PTO) owispatent The present invention is directed to a digital wireless telecommunications system that includes a plurality of base station of differing spectral capabilities, and a plurality of remote stations capable of transmitting data to and receiving transmissions from the plurality of base stations. The invention herein provides a method for remote station hand-off between base stations of a narrower spectral capacity and base stations of a wider spectral capacity. A method is provided for a wireless telecommunications infrastructure to facilitate a remote station hand-off from a set of narrowband compliant base stations to at least one wideband compliant base station while a remote station is in the coverage area of both types of base stations. Additionally, the invention herein provides remote station apparatus, base station apparatus, and base station controller apparatus for performing the handoff methodology of the present invention.<H telecommunications, capabilities, Method, of, hando, 7151933.html, Patent, pto, 7151933

Title: Method of handoff within a telecommunications system containing digital base stations with different spectral capabilities

Abstract: The present invention is directed to a digital wireless telecommunications system that includes a plurality of base station of differing spectral capabilities, and a plurality of remote stations capable of transmitting data to and receiving transmissions from the plurality of base stations. The invention herein provides a method for remote station hand-off between base stations of a narrower spectral capacity and base stations of a wider spectral capacity. A method is provided for a wireless telecommunications infrastructure to facilitate a remote station hand-off from a set of narrowband compliant base stations to at least one wideband compliant base station while a remote station is in the coverage area of both types of base stations. Additionally, the invention herein provides remote station apparatus, base station apparatus, and base station controller apparatus for performing the handoff methodology of the present invention.

Patent Number: 7,151,933 Issued on 12/19/2006 to Chen, et al.

Inventors: Chen; Tao (San Diego, CA), Jou; Yu-Cheun (San Diego, CA)
Assignee: Qualcomm Incorporated (San Diego, CA)

Appl. No.: 10/969,638

Filed: October 20, 2004

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
10213601	Mar., 2003	6853843
09546219	Apr., 2000	6535739

Current U.S. Class: 455/437 ; 370/331; 370/332; 370/335; 455/552.1; 455/561

Current International Class: H04Q 7/20 (20060101)

Field of Search: 455/436,437,439,442,446,449,450,454,552.1,553.1,560,561,67.11,522 370/331,332,335

References Cited [Referenced By]

U.S. Patent Documents


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5164958	November 1992	Omura
5267261	November 1993	Blakeney et al.
5490165	February 1996	Blakeney et al.
5594718	January 1997	Weaver et al.
5625876	April 1997	Gilhousen et al.
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5754961	May 1998	Serizawa et al.
5848063	December 1998	Weaver, Jr. et al.
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6055428	April 2000	Soliman
6307849	October 2001	Tiedemann, Jr.

Primary Examiner: Vuong; Quochien B.
Attorney, Agent or Firm: Wadsworth; Philip Nguyen; Thien Patel; Rupit

Parent Case Text

CLAIM OF PRIORITY UNDER 35 U.S.C. .sctn.120

The present Application for Patent is a Continuation of patent application Ser. No. 10/213,601, entitled "METHOD OF HANDOFF WITHIN A TELECOMMUNICATIONS SYSTEM CONTAINING DIGITAL BASE STATIONS WITH DIFFERENT SPECTRAL CAPABILITIES" filed Aug. 6, 2002, now U.S. Pat. No. 6,853,843 which is a Continuation of patent application Ser. No. 09/546,219 filed Apr. 7, 2000 now U.S. Pat. No. 6,535,739, entitled "METHOD OF HANDOFF WITHIN A TELECOMMUNICATIONS SYSTEM CONTAINING DIGITAL BASE STATIONS WITH DIFFERENT SPECTRAL CAPABILITIES" issued Mar. 18, 2003, and assigned to the assignee hereof and hereby expressly incorporated by reference herein.

Claims

What is claimed is:

1. A method of facilitating a remote station hand-off, comprising: receiving signals in a first frequency band in accordance with a single carrier protocol at said remote station; transmitting signal strength measurements of various base stations in a first message from said remote station; and receiving a second message at said remote station that indicates that said remote station should begin receiving signals in accordance with a multi-carrier protocol in a second frequency band that is larger than said first frequency band, wherein the second message is responsive to a determination that at least one of various base stations is single-carrier compliant and at least one of various base stations is multi-carrier compliant.

2. The method of claim 1 wherein said first frequency band is contained within said second frequency band.

3. The method of claim 1, wherein said second message also indicates that said remote station should begin transmitting messages in accordance with said multi-carrier protocol on a second frequency band that is larger than said first frequency band.

4. The method of claim 1, further comprising the steps of: receiving at said remote station from said at least one of various base stations that is multi-carrier compliant, signals in accordance with said single carrier protocol in said first frequency band; and monitoring, from said at least one of said various base stations that is multi-carrier compliant, a second frequency band for signals transmitted in accordance with said single carrier protocol in said second frequency band.

5. A remote station, comprising: means for receiving signals in a first frequency band in accordance with a single carrier protocol; means for transmitting signal strength measurements of various base stations in a first message; and means for receiving a second message that indicates that said remote station should begin receiving signals in accordance with a multi-carrier protocol in a second frequency band that is larger than said first frequency band, wherein the second message is responsive to a determination that at least one of various base stations is single-carrier compliant and at least one of various base stations is multi-carrier compliant.

6. The remote station of claim 5, wherein said first frequency band is contained within said second frequency band.

7. The remote station of claim 5 wherein said second message also indicates that said remote station should begin transmitting messages in accordance with said multi-carrier protocol on a second frequency band that is larger than said first frequency-band.

8. The remote station of claim 5 further comprising: means for receiving at said remote station from said at least one of various base stations that is multi-carrier compliant, signals in accordance with said single carrier protocol in said first frequency band; and means for monitoring, from said at least one of said various base stations that is multi-carrier compliant, a second frequency band for signals transmitted in accordance with said single carrier protocol in said second frequency band.

9. A computer readable media embodying a method comprising of facilitating a remote station hand-off, the method comprising: receiving signals in a first frequency band in accordance with a single carrier protocol at said remote station; transmitting signal strength measurements of various base stations in a first message from said remote station; and receiving a second message at said remote station that indicates that said remote station should begin receiving signals in accordance with a multi-carrier protocol in a second frequency band that is larger than said first frequency band, wherein the second message is responsive to a determination that at least one of various base stations is single-carrier compliant and at least one of various base stations is multi-carrier compliant.

10. A computer readable media embodying a method comprising of facilitating a remote station hand-off, the method comprising: receiving signals in a first frequency band in accordance with a single carrier protocol at said remote station; transmitting signal strength measurements of various base stations in a first message from said remote station; and receiving a second message at said remote station that indicates that said remote station should begin receiving messages in accordance with a multi-carrier protocol in a second frequency band that is larger than said first frequency band, and wherein said second message also indicates that said remote station should begin transmitting messages in accordance with said multi-carrier protocol on a second frequency band that is larger than said first frequency band, and further, wherein the second message is responsive to a determination that at least one of various base stations is single-carrier compliant and at least one of various base stations is multi-carrier compliant.

11. A computer readable media of claim 10, wherein the method embodied further comprises: receiving at said remote station from said at least one of various base stations that is multi-carrier compliant, signals in accordance with said single carrier protocol in said first frequency band; and monitoring, from said at least one of said various base stations that is multi-carrier compliant, a second frequency band for signals transmitted in accordance with said single carrier protocol in said second frequency band.

Description

BACKGROUND

1. Field

The present invention relates to wireless telecommunications. More particularly, the present invention relates to a novel method for facilitating handoffs between digital base stations with different spectral capabilities.

2. Background

In a code division multiple access (CDMA) spread spectrum communication system, a common frequency band is used for communication with all base stations within that system. An example of such a system is described in the TIA/EIA Interim Standard IS-95-A entitled "Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System", incorporated herein by reference. The generation and receipt of CDMA signals is disclosed in U.S. Pat. No. 4,901,307 entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEMS USING SATELLITE OR TERRESTRIAL REPEATERS" and in U.S. Pat. No. 5,103,459 entitled "SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM" both of which are assigned to the assignee of the present invention and incorporated herein by reference.

Signals occupying the common frequency band are discriminated at the receiving station through the spread spectrum CDMA waveform properties based on the use of a high rate pseudonoise (PN) code. A PN code is used to modulate signals transmitted from the base stations and the remote stations. Signals from different base stations can be separately received at the receiving station by discrimination of the unique time offset that is introduced in the PN codes assigned to each base station. The high rate PN modulation also allows the receiving station to receive a signal from a single transmission station where the signal has traveled over distinct propagation paths. Demodulation of multiple signals is disclosed in U.S. Pat. No. 5,490,165 entitled "DEMODULATION ELEMENT ASSIGNMENT IN A SYSTEM CAPABLE OF RECEIVING MULTIPLE SIGNALS" and in U.S. Pat. No. 5,109,390 entitled "DIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM", both of which are assigned to the assignee of the present invention and incorporated herein by reference.

U.S. Pat. No. 5,101,501 entitled "METHOD AND SYSTEM FOR PROVIDING A SOFT HANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEM," and U.S. Pat. No. 5,267,261 entitled "MOBILE STATION ASSISTED SOFT HANDOFF IN A CDMA CELLULAR COMMUNICATIONS SYSTEM," both of which are assigned to the assignee of the present invention and are incorporated herein by reference, disclose a method and system for simultaneous communication between a remote station and more than one base station, known as soft handoff. Further information concerning handoff is disclosed in U.S. Pat. No. 5,101,501, entitled "METHOD AND SYSTEM FOR PROVIDING A SOFT HANDOFF IN COMMUNICATIONS IN A CDMA CELLULAR TELEPHONE SYSTEM", U.S. Pat. No. 5,640,414, entitled "MOBILE STATION ASSISTED SOFT HANDOFF IN A CDMA CELLULAR COMMUNICATIONS SYSTEM", and U.S. Pat. No. 5,625,876 entitled "METHOD AND APPARATUS FOR PERFORMING HANDOFF BETWEEN SECTORS OF A COMMON BASE STATION," each of which is assigned to the assignee of the present invention and incorporated in its entirety herein by this reference. The subject matter of U.S. Pat. No. 5,625,876 concerns what is known in the art as "softer handoff." For the purposes of this document, the term "soft handoff" is intended to include both "soft handoff" and "softer handoff."

If a remote station travels outside the boundary of the system with which it is currently communicating, it is desirable to maintain the communication link by transferring the call to a neighboring system, if one exists. The neighboring system may use any wireless technology, examples of which are CDMA, NAMPS, AMPS, TDMA or FDMA. If the neighboring system uses CDMA on the same frequency band as the current system, an inter-system soft handoff can be performed. In situations where inter-system soft handoff is not available, the communication link is transferred through a hard handoff where the current connection is broken before a new one is made. Examples of hard handoffs are those from a CDMA system to a system employing an alternate technology or a call transferred between two CDMA systems which use different frequency bands (inter-frequency hard handoff).

Inter-frequency hard handoffs can also occur within a CDMA system. For example, a region of high demand such as a downtown area may require a greater number of frequencies to service demand than the suburban region surrounding it. It may not be cost effective to deploy all available frequencies throughout the system. A call originating on a frequency deployed only in the high congestion area must be handed off as the user travels to a less congested area. Another example is that of a microwave or other service operating on a frequency within the system's boundaries. As users travel into an area suffering from interference from the other service, their call may need to be handed off to a different frequency.

Handoffs can be initiated using a variety of techniques. Handoff techniques, including those using signal quality measurements to initiate handoff, are found in U.S. Pat. No. 5,697,055 entitled "METHOD AND APPARATUS FOR HANDOFF BETWEEN DIFFERENT CELLULAR COMMUNICATIONS SYSTEMS", issued Dec. 9, 1997, assigned to the assignee of the present invention and incorporated herein by reference. Further disclosure on handoffs, including measurement of round-trip signal delay to initiate handoff, is disclosed in U.S. Pat. No. 5,848,063, entitled "METHOD AND APPARATUS FOR HARD HANDOFF IN A CDMA SYSTEM", issued Dec. 8, 1998, assigned to the assignee of the present invention and incorporated herein by reference. Handoffs from CDMA systems to alternate technology systems are disclosed in U.S. Pat. No. 5,594,718 ('306 application) entitled "METHOD AND APPARATUS FOR MOBILE UNIT ASSISTED CDMA TO ALTERNATIVE SYSTEM HARD HANDOFF", issued Jan. 14, 1997, assigned to the assignee of the present invention and incorporated herein by reference. In the '306 application, pilot beacons are placed at the boundaries of the system. When a remote station reports these pilots to the base station, the base station knows that the remote station is approaching the boundary.

When a system has determined that a call should be transferred to another system via hard handoff, a message is sent to the remote station directing it to do so along with parameters that enable the remote station to connect with the destination system. The system has only estimates of the remote station's actual location and environment, so the parameters sent to the remote station are not guaranteed to be accurate. For example, with beacon aided handoff, the measurement of the pilot beacon's signal strength can be a valid criterion for triggering the handoff. However, the appropriate cell or cells in the destination system which are to be assigned to the remote station (known as the Active Set) are not necessarily known.

The cdma2000 cellular telephone standard proposal issued by the Telecommunications Industry Association (TIA), entitled "cdma2000 Series TIA/EIA/IS-2000," published in August of 1999, hereinafter referred to as cdma2000, uses advanced signal processing techniques to provide efficient and high quality phone service, and is incorporated herein by reference. For example, a cdma2000 compliant cellular telephone system utilizes decoding, error detection, forward error correction (FEC), interleaving, and spread spectrum modulation in order to make more efficient use of the available radio frequency (RF) bandwidth, and to provide robust connections. In general, the benefits provided by cdma2000 include longer talk time and fewer dropped calls when compared to other types of cellular telephone systems.

In the world of cellular telecommunications, those skilled in the art often use the terms 1G, 2G, and 3G. The terms refer to the generation of the cellular technology used. 1G refers to the first generation, 2G to the second generation, and 3G to the third generation. 1G is used to refer to the analog phone system, known as an AMPS (Advanced Mobile Phone Service) phone systems.

2G is commonly used to refer to the digital cellular systems that are prevalent throughout the world, and include cdmaOne, Global System for Mobile communications (GSM), and Time Division Multiple Access (TDMA). cdmaOne, based on a Code Division Multiple Access (CDMA) technology, refers to a digital cellular system that adheres to the family of IS-95 standards. 2G systems can support a greater number of users in a dense area than can 1G systems.

3G is commonly used to refer to the digital cellular systems currently being developed. 3G systems include cdma2000 and Wideband-CDMA (W-CDMA). 3G systems promise higher peak data transfer rates than do their 2G counterparts. Additionally, many 3G systems can support a greater number of users than can 2G systems.

Spreading Rate 3 versions of cdma2000, hereinafter referred to as 3X, use a frequency band of 3.75 megahertz (MHz), comprised of three 1.25 MHz chunks, while the Spreading Rate 1 versions of cmda2000, hereinafter referred to as 1X, uses a frequency band having a width of 1.25 MHz. Wherein 1X is a single carrier protocol, 3X is a multi-carrier protocol. As would be known to one skilled in the art, a single carrier protocol transmits data in a single frequency band, while a multi-carrier protocol, transmits data in multiple [single carrier] frequency bands. For instance, whereas 1X transmits data in a single 1.25 MHz frequency bands, 3X transmits data in three 1.25 MHz frequency bands. The modulation techniques performed by multi-carrier systems, hereinafter referred to as a multi-carrier modulation techniques, differ from those performed by single carrier systems, hereinafter referred to as single carrier modulation techniques. Although the examples of 1X and 3X are used as single carrier and multi-carrier protocols respectively, the invention is not limited to 1X and 3X protocols, and applies equally well to any system that is comprised of both single carrier and multi-carrier base stations, such as may be the case in future versions of W-CDMA that are attempting to support higher data transmission rates.

Any given cdma2000 system need not support 1X (version 1X of cdma2000) exclusively or 3X (version 3X of cdma2000) exclusively. A version of cdma2000 that uses a multi-carrier 3.75 MHz spectrum on the forward link, the wireless link that delivers data from the base station to the remote station, but uses a single carrier 1.25 MHz spectrum on the reverse link, the wireless link that delivers data from the remote station to the base station is described in U.S. patent application Ser. No. 09/382,438 entitled "Method and Apparatus Using a Multi-Carrier Forward Link in a Wireless Communication System" assigned to the assignee of the present invention and incorporated herein by reference. A system such as this, that uses multi-carrier capabilities on the forward link, but uses single carrier capabilities on the reverse link, is hereinafter referred to as a hybrid system. A 3X/1X system is merely used as an example, and a hybrid system is not limited to such an embodiment. A block diagram of an exemplary hybrid system is shown in FIG. 1.

FIG. 1 is a block diagram of an exemplary simplified cellular telephone system that uses multi-carrier transmission on the forward link and single carrier transmissions on the reverse link, wherein a 3X protocol is used on the forward link and a 1X protocol is used on the reverse link. Remote stations such as remote stations 110 (typically cellular telephones, personal digital assistants (PDAs) with wireless capabilities, or laptop computers with wireless capabilities) are located among base stations 120. The remote stations 110a and 110b are in an active mode and are therefore interfacing with at least one base station 120 using radio frequency (RF) signals modulated in accordance with the CDMA signal processing techniques. A system and method for modulating RF signals in accordance with CDMA modulation is described in U.S. Pat. No. 5,103,459 entitled "System and Method for Generating Signal Waveforms in a CDMA Cellular Telephone System" assigned to the assignee of the present invention and previously incorporated herein by reference. The other remote stations 110 are in standby mode and are therefore monitoring either a full paging channel for page messages indicating a request to communicate, or they are monitoring a quick paging channel for indicator bits indicating whether a message is expected on a full paging channel.

Each given base station 120 that is in active mode with at least one remote station 110 transmits data to remote stations 110 across three frequency bands f1, f2, f3, and receives data from remote stations 110 in a single frequency band f4. Each frequency band f1, f2, f3, and f4 has the same bandwidth. Frequency bands f1, f2, and f3 are adjacent frequency bands. For instance, if in the example of the hybrid system each band f1 was the frequency band 1900 MHz 1901.25 MHz, then f2 would be 1901.25 MHz 1902.5 MHz, and f3 would be 1902.5 MHz 1903.75 MHz. Thus, the adjacent frequency bands take up the spectrum 1900 MHz 1903.75 MHz in this example. In such a case, f4 would be a 1.25 MHz band located outside of that frequency range. For example, f4 could be located at 1820 MHz 1821.25 MHz.

Base stations 120 connect to a Base Station Controller (BSC) 114. Base Station Controller 114 controls base stations 120, and exchanges information packets between Mobile Switching Center (MSC) 116 and base stations 120. Mobile Switching Center 116 exchanges information packets between Public Switched Telephone Network 118. In other embodiments, different switches, such as a packet data serving node (PDSN), can be connected to the system. A cellular telephone system can contain more than one Base Station Controller 114 and more than one Mobile Switching Center 116, or conversely, in decentralized systems, such as those disclosed in U.S. Pat. No. 6,215,779, entitled "DISTRIBUTED INFRASTRUCTURE FOR WIRELESS DATA COMMUNICATIONS", issued Apr. 10, 2001, assigned to the assignee of the present invention, and incorporated by reference herein, Base Station Controller 114 or Mobile Switching Center 116 may be absent from the cellular telephone system.

FIG. 2 is a block diagram of an exemplary simplified cellular telephone system that uses single carrier transmissions on the forward link and single carrier transmissions on the reverse link. Remote stations such as remote stations 210 (typically cellular telephones) are located among base stations 220. The remote stations 210a and 210b are in an active mode and are therefore interfacing with at least one base station 220 using radio frequency (RF) signals modulated in accordance with the CDMA signal processing techniques. The other remote stations 210 are in standby mode and are therefore monitoring either a full paging channel for page messages indicating a request to communicate, or they are monitoring a quick paging channel for indicator bits indicating whether a message is expected on a full paging channel.

Each given base station 220 that is in active mode with at least one remote station 210, transmits data to remote stations 210 across a single frequency band f1, and receives data from remote stations 210 in a single frequency band f2. Each frequency band f1 and f2 has the same bandwidth. Frequency bands f1 and f2 can be offset by a predefined amount. If an amount of 80 MHz is used, and f1 is at the frequency band 1900 MHz 1901.25 MHz, then f2 could be located at 1820.00 MHz 1821.80 25 MHz.

Base stations 220 connect to a Base Station Controller 114. Base Station Controller 114 controls base stations 220, and exchanges information packets between Mobile Switching Center 116 and base stations 220. Mobile Switching Center 116 exchanges information packets between Public Switched Telephone Network 118. In other embodiments, different switches, such as a packet data serving node (PDSN), can be connected to the system. A cellular telephone system can contain more than one Base Station Controller 114 and more than one Mobile Switching Center 116, or conversely, in decentralized systems, such as those disclosed in U.S. Pat. No. 6,215,779 entitled "DISTRIBUTED INFRASTRUCTURE FOR WIRELESS DATA COMMUNICATIONS", issued Apr. 10, 2001, applied for by the applicant of the present invention, and incorporated by reference herein, Base Station Controller 114 or Mobile Switching Center 116 may be absent from the cellular telephone system as separate entities, but rather may be integrated into the base stations themselves.

FIG. 3 is a block diagram of an exemplary simplified cellular telephone system that uses multi-carrier transmissions on the forward link and multi-carrier transmissions on the reverse link. Remote stations such as remote stations 310 (typically cellular telephones) are located among base stations 320. The remote stations 310a and 310b are in an active mode and are therefore interfacing with at least one base station 320 using radio frequency (RF) signals modulated in accordance with the CDMA signal processing techniques. The other remote stations 310 are in standby mode and are therefore monitoring either a full paging channel for page messages indicating a request to communicate, or they are monitoring a quick paging channel for indicator bits indicating whether a message is expected on a full paging channel.

Each given base station 320 that is in active mode with at least one remote station 310, transmits data to remote stations 310 across three frequency bands, f1, f2, f3, and receives data from remote stations 310 across three frequency bands f4, f5, f6. Each frequency band f1, f2, f3, f4, f5, f6 has the same bandwidth. Frequency bands f1, f2, and f3 are adjacent frequency bands. For instance, if in the example of the hybrid system each band f1 was the frequency band 1900 MHz 1901.25 MHz, then f2 would be 1901.25 MHz 1902.5 MHz, and f3 would be 1902.5 MHz 1903.75 MHz. Thus the adjacent frequency bands take up the spectrum 1900 MHz 1903.75 MHz in this example. Likewise, frequency bands f4, f5, and f6 are adjacent to one another. Frequency bands f1 and f4 can be offset by a predefined amount. If an amount of 80 MHz is used, and f1 begins at the frequency 1900 MHz, then reverse link bands f4, f5, f6, could take up the 3.75 MHz spectrum located between 1820 MHz 1823.75 MHz.

Although a carrier could upgrade its entire network from a single carrier system to a multi-carrier system all at once, this is often undesirable in light of costs. Economically, it may be more desirable for a carrier to put multi-carrier capabilities in a few areas of their network that will benefit the most from multi-carrier capabilities, and then slowly roll out multi-carrier capabilities into other areas of its network over time. During such a gradual rollout, some of the base stations in the system will be multi-carrier protocol compliant while others will not. Likewise, some carriers may find it desirable to upgrade a portion of its network to support a multi-carrier protocol, without having the intent of ever upgrading the remaining portion of its network to a multi-carrier protocol.

What is needed is a method and apparatus for performing handoff in a wireless telecommunication system that contains digital base stations, some of which comply with a multi-carrier protocol and some of which are not multi-carrier compliant.

SUMMARY

The present invention is directed to a digital wireless telecommunications system that includes a plurality of base stations of differing spectral capabilities, and a plurality of remote stations capable of transmitting data to and receiving transmissions from the plurality of base stations. The invention herein provides a method for remote station handoff between base stations of a narrower spectral capacity and base stations of a wider spectral capacity. A method is provided for a wireless telecommunications infrastructure to facilitate a remote station hand-off from a set of single carrier compliant base stations to at least one multi-carrier compliant base station while a remote station is in the coverage area of both types of base stations.

In one embodiment the handoff is enabled by transmitting a message to a remote station that indicates that the remote station should transmit modulated signals according to a single carrier protocol (e.g., 1X) and should receive modulated signals according to a multi-carrier protocol. In another embodiment, the remote station is instructed to transmit the modulated signals in the same frequency band as was used for transmission prior to the handoff. In another embodiment, the remote station is instructed to transmit the modulated signals in a different frequency band than was used for transmission prior to the handoff. In another embodiment the single carrier compliant base stations transmit in the single carrier frequency a portion of the signal that is generated in accordance with the multi-carrier protocol.

In another embodiment, the handoff is enabled by transmitting a message to a remote station that indicates that the remote station should transmit modulated signals according to a multi-carrier protocol and should receive modulated signals according to a multi-carrier protocol.

In another embodiment, the handoff is enabled by transmitting a message to a remote station that indicates that the remote station should transmit modulated signals according to a single carrier protocol and should receive modulated signals according to a single carrier protocol. In this embodiment, the remote station is instructed that it should receive single carrier modulated signals from at least one multi-carrier compliant base station.

In many of the embodiments, a means to avoid reverse link interference is achieved by performing a two part handoff, the first of which is performed while the remote station is in the coverage of both types of base stations, and the second of which occurs when the remote station travels to an area that is only in the coverage of multi-carrier compliant base stations.

The remote station adjusts its transmit and receive modulation techniques in accordance with the received handoff messages of the above embodiments.

The invention herein also provides remote station apparatus, base station apparatus, and base station controller apparatus for performing the above-described methodology.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify like features correspondingly throughout:

FIG. 1 is a block diagram of an exemplary simplified cellular telephone system that uses multi-carrier transmissions on the forward link and single carrier transmissions on the reverse link, wherein a 3X protocol is used on the forward link and a 1X protocol is used on the reverse link.

FIG. 2 is a block diagram of an exemplary simplified cellular telephone system that uses single carrier transmissions on the forward link and single carrier transmissions on the reverse link.

FIG. 3 is a block diagram of an exemplary simplified cellular telephone system that uses multi-carrier transmissions on the forward link and multi-carrier transmissions on the reverse link.

FIG. 4 is a simplified network diagram of an exemplary embodiment of the coverage of a spread spectrum system in the midst of a hybrid deployment of single carrier services to multi-carrier services.

FIG. 5 diagrams a portion of the simplified network diagram of FIG. 4, and also shows the path of an exemplary remote station traveling throughout the network.

FIG. 6 is an exemplary diagram of the communication path of a remote station that is a multi-carrier handoff candidate communicating with two single carrier base stations BS1.

FIG. 7 is a diagram of an exemplary communication path during the handoff of a first handoff embodiment.

FIG. 8 is a diagram of an exemplary communication path during the handoff of a second handoff embodiment.

FIGS. 9a and 9b contain an illustration of the spectral density and the associated transmission power that would be utilized to transmit N information bits using an exemplary single carrier protocol.

FIG. 10a contains an illustration of the spectral density and the associated transmission power that would be utilized in a first embodiment to simultaneously transmit N information bits using an exemplary single carrier protocol and transmit N information bits using an exemplary multi-carrier protocol.

FIG. 10b contains an illustration of the spectral density and the associated transmission power that would be utilized in a second embodiment to simultaneously transmit N information bits using an exemplary single carrier protocol and transmit N information bits using an exemplary multi-carrier protocol.

FIG. 11 contains an illustration of the spectral density and the associated forward link transmission power that would be utilized to transmit N information bits using an exemplary multi-carrier protocol.

FIG. 12 contains an illustration of the spectral density and the associated forward link transmission power that would be utilized in a first embodiment to simultaneously transmit N information bits using an exemplary single carrier protocol and transmit N information bits using an exemplary multi-carrier protocol.

FIG. 13 is a diagram of an exemplary communication path during the handoff of a third handoff embodiment.

FIG. 14 contains an exemplary illustration of the spectral density and the associated forward link transmission power that would be utilized to transmit N information bits to two remote stations using an exemplary multi-carrier protocol to communicate with each remote station.

FIG. 15 is a diagram of an exemplary communication path during the handoff of a fourth handoff embodiment.

FIG. 16 is a diagram of an exemplary communication path during the handoff of a fifth handoff embodiment.

FIG. 17a contains an exemplary illustration of a transmitted multi-carrier signal.

FIG. 17b contains an exemplary illustration of a portion of the multi-carrier signal shown in FIG. 17a that can be transmitted in a single carrier frequency band.

FIG. 18 is a diagram of an exemplary communication path during the handoff of a sixth handoff embodiment.

FIG. 19 is a diagram of an exemplary communication path during the handoff of a seventh handoff embodiment.

FIG. 20 is a diagram of an exemplary communication path during the handoff of an eighth handoff embodiment.

FIG. 21 is a flowchart of the methodology that can be used to implement the first through the eighth handoff embodiments.

FIG. 22 is an exemplary block diagram of a base station apparatus that can be used to perform the first through the eight handoff embodiments.

FIG. 23. is an exemplary block diagram of a remote station apparatus that can be used to perform the first through the eight handoff embodiments.

FIG. 24. is an exemplary block diagram of a base station controller (BSC) apparatus that can be used to perform the first through the eight handoff embodiments.

DETAILED DESCRIPTION

Although many of the detailed descriptions are discussed in reference to a cdma2000 system containing 1X and 3X base stations, one skilled in the art will appreciate that the invention can be applied to any spread spectrum system and is not limited to the 1X and 3X systems used in many of the exemplary embodiments.

When discussing signal transmissions in a frequency range, the phrase `in a frequency band` is used herein to refer to a spread spectrum signal that is spread across a given frequency. For instance, when stating that a signal is transmitted in frequency band X, wherein frequency band X is defined as the band ranging from 1900 MHz 1903.75 MHz, it is meant that the transmitted signal is spread across the frequency band 1900 MHz 1903.75 MHz.

FIG. 4 is a simplified network diagram of an exemplary embodiment of the coverage of a spread spectrum system in the midst of a hybrid deployment of single carrier services to multi-carrier services.

In the network diagram, each circular footprint labeled BS3 represents a base station that is multi-carrier compliant and its corresponding coverage/footprint. Each circle, itself, is representative of the footprint of a base station BS3. Although the physical base station, BS3, is not diagrammed separately within the figure, it can be assumed that it lays somewhere within the diagrammed footprint. Each multi-carrier compliant base station is capable of both transmitting and receiving spread spectrum signals in accordance with a multi-carrier protocol. Hereinafter, all multi-carrier compliant base stations will simply be referred to as multi-carrier base stations.

In the network diagram, each circular footprint labeled BS1 represents a base station that is single carrier compliant and its corresponding coverage/footprint. Each circle, itself, is representative of the footprint of a base station BS1. Although the physical base station, BS1, is not diagrammed separately within the figure, it can be assumed that it lays somewhere within the diagrammed footprint. Each single carrier compliant base station is capable of both transmitting and receiving spread spectrum signals in accordance with a single carrier protocol (e.g., 1X). Hereinafter, all single carrier compliant base stations will simply be referred to as single carrier base stations.

A carrier (e.g. Vodafone AirTouch) will likely deploy multi-carrier services in small areas, or pockets, wherein multi-carrier services are first needed. FIG. 4 illustrates an example of such a network 410, wherein a small pocket of multi-carrier services is provided by six multi-carrier base stations, BS3, and wherein single carrier services are provided in a large surrounding area by forty-eight single carrier base stations, BS1. Hereinafter, the term non-homogenous network will be used to refer to a network containing both multi-carrier base stations and single carrier base stations, such as network 410. The non-homogenous network is essentially the combination of a single carrier system (the base stations labeled BS1) and a multi-carrier system (the base stations labeled BS3) that share common infrastructure, such as a BSC or MSC.

Multi-carrier base stations BS3 are not necessarily limited to communicating with remote stations by transmitting data to a remote station in compliance with a multi-carrier protocol in a multi-carrier frequency band. Rather, though, multi-carrier base stations BS3 may also be able to communicate with remote stations in accordance with a single carrier protocol in a single carrier frequency.

Having such flexibility in multi-carrier base stations proves useful when a network 410 is created by upgrading a pocket of single carrier base stations to multi-carrier base stations. In such a network 410, many pre-existing remote stations that desire service on the network 410 may only be single carrier compliant. So as not to deny service to non-multi-carrier compliant remote stations that have traveled into these upgraded pockets, the upgraded base stations may continue to provide single carrier compliant services in addition to the newly added multi-carrier services.

Although a multi-carrier base station, as used herein, can mean a base station that is not only multi-carrier compliant, but one that additionally is single carrier compliant, the same does not hold true for the meaning of a single carrier base station. A single carrier base station, as used herein, is a base station that is single carrier compliant and is not fully multi-carrier compliant. Thus, single carrier base stations cannot both transmit data on a multi-carrier forward link in accordance with a multi-carrier protocol and receive data on a multi-carrier reverse link in accordance with a multi-carrier protocol. All base stations that can both transmit data on a multi-carrier forward link in accordance with a multi-carrier protocol and receive data on a multi-carrier reverse link in accordance with a multi-carrier protocol are referred to herein as multi-carrier base stations.

FIG. 5 diagrams a portion of the network 410, and also shows the path of an exemplary remote station traveling throughout the network. Subscripts have been added to each instance of BS1 and BS3 for distinguishment purposes.

In FIG. 5, a remote station is in a call while traveling throughout a portion of network 410. The remote station begins its call at point 510 and terminates its call at point 558. "X"es are placed in the diagram to call to the attention of the reader various points at which the remote station is in different coverage areas.

At points 510 through 518, the remote station is solely in the coverage areas of single carrier base stations. At point 510, the remote station is only in the coverage area of BS1a. At point 518, the remote station is in the coverage area of both BS1d and BS1e. Because the remote station never enters multi-carrier coverage between these points, no handoff is needed between the multi-carrier base stations and the single carrier base stations.

At points 530 through 538, the remote station is solely in the coverage area of multi-carrier base stations. At point 530, the remote station is only in the coverage area of BS3c. At point 538, the remote station is in the coverage area of BS3f. Because the remote station never enters single carrier coverage between these points, no handoff is needed between the multi-carrier base stations and the single carrier base stations between these points.

At points 550 through 558, the remote station is solely in the coverage areas of single carrier base stations. At point 550, the remote station is only in the coverage area of BS1h. At point 558, the remote station is in the coverage area of BS1k. Because the remote station never enters multi-carrier coverage between these points, no handoff is needed between the multi-carrier base stations and the single carrier base stations, between these points.

At points 520 through 528, the remote station is within the coverage areas of both single carrier base stations and multi-carrier base stations. At point 520, the remote station is in the coverage area of single carrier base stations BS1d and BS1e, and it is also in the coverage area of multi-carrier base station BS3b. At point 528, the remote station is in the coverage area of single carrier base station BS1f, and it is also in the coverage area of multi-carrier base station BS3c.

At points 540 through 548, the remote station is within the coverage areas of both single carrier base stations and multi-carrier base stations. At point 540, the remote station is in the coverage area of single carrier base stations BS1i, and it is also in the coverage area of multi-carrier base station BS3f. At point 548, the remote station is in the coverage area of single carrier base stations BS1h and BS1i, and it is also in the coverage area of multi-carrier base station BS3e.

In order to keep the call up, at some point between point 518 and point 530 a handoff must occur between single carrier base stations BS1 and multi-carrier base stations BS3. Likewise, at some point between point 538 and point 550 a handoff must occur between multi-carrier base stations BS3 and single carrier base stations BS1.

Several embodiments of the invention facilitate such a handoff. Some notation will prove helpful in describing these embodiments. Nf will be used hereinafter to represent a particular single carrier frequency band (such as 1900 MHz 1901.25 MHz) used for the forward link, while Nr will be used hereinafter to represent a particular single carrier frequency used for the reverse link. The term multi-carrier frequency band is hereinafter used to refer to the set of single-carrier frequency bands used for a multi-carrier transmission. For instance, if the combination of transmissions on frequency bands 1900 1901.25 MHz, 1901.25 1902.50 MHz, and 1902.50 1903.75 MHz is used to send a multi-carrier signal (e.g. a 3X transmission signal), then the set of these single-carrier frequency bands comprises a multi-carrier frequency band. Wf will be used hereinafter to represent a particular multi-carrier frequency band used for the forward link, while Wr will be used hereinafter to represent a particular multi-carrier frequency band used for the reverse link. Nf can be contained within Wf, or it can be a frequency band outside of Wf, further discussed in reference to FIG. 7. Likewise, Nr can be contained within Wr, or it can be a frequency band outside of Wr.

A remote station that is communicating with at least one base station BS1 via a single carrier protocol on frequencies Nf and Nr, while it is also in the coverage area of at least one multi-carrier base station BS3, is hereinafter referred to as a multi-carrier handoff candidate. Referring to FIG. 5, if the remote station is only communicating with BS1d and BS1e at point 520, it would be considered a multi-carrier handoff candidate at that point, since it is also in the coverage area of a multi-carrier base station BS3b. It should be noted that point 520 is not the only spot at which the remote station could be considered a multi-carrier handoff candidate. At all points 520 528, if the remote station is communicating with at least one single carrier base station BS1, but it is not communicating with any multi-carrier base stations BS3, the remote station would be considered a multi-carrier handoff candidate.

Multiple embodiments of the invention, each for facilitating a handoff in a non-homogenous system, are described below. Following the description of these embodiments is a description of a flow chart that can be used for all handoff embodiments.

In a first handoff embodiment of the present invention, a multi-carrier handoff candidate is sent a handoff message (often referred to as an extended handoff direction message) from at least one single carrier base station BS1, instructing it to cease single carrier communications with single carrier base stations BS1 on Nf and Nr, and to begin multi-carrier communications on frequencies Wf and Wr with multi-carrier base stations BS3. For instance, at point 520, the remote station, which was communicating with BS1d and BS1e on frequencies Nf and Nr using a single carrier protocol, would be instructed to switch its mode of communication to a multi-carrier protocol on frequencies Wf and Wr, and to only communicate with base station BS3b. In such an embodiment, the infrastructure instructs the multi-carrier base stations BS3 to begin communications with the remote station using the multi-carrier protocol on frequencies Wf and Wr. The infrastructure also instructs the single carrier base stations BS1 to cease communications with the remote station. Using point 520 as an exemplary point of handoff, figures used herein will assume a multi-carrier handoff candidate that is in the coverage area of two single carrier base stations BS1 and one multi-carrier base station BS3. However, one skilled in the art will realize that a multi-carrier handoff candidate could be in a coverage area in which there are more or less of either type of base station, as long as it is in the coverage area of at least one single carrier base station and one multi-carrier base station. One skilled in the art will also appreciate that the descriptions of the below embodiments are not limited to coverage areas of exactly two single carrier base stations BS1 and one multi-carrier base station BS3, but that they apply to other coverage mixes as well, such as a point that is in the coverage area of two multi-carrier base stations BS3 and only one single carrier base station BS1.

An exemplary diagram of the communication path of a remote station that is a multi-carrier handoff candidate communicating with two single carrier base stations BS1 is shown in FIG. 6. A diagram of an exemplary communication path after the handoff of a first handoff embodiment appears in FIG. 7, wherein the remote station begins transmitting in frequency band Wr, and begins receiving in frequency band Wf, and wherein transmissions adhering to the multi-carrier protocol are received by a base station BS3, and wherein the base station BS3 begins transmitting in accordance with the multi-carrier protocol in frequency band Wf.

Although this first handoff embodiment succeeds in allowing a remote station to keep up a communications link while traveling throughout a non-homogenous network, it lacks the desirable features of communication path diversity and power control that can be provided by soft handoff.

The lack of being in communication with both single carrier base stations and multi-carrier base stations when in the coverage of both negatively affects path diversity. If the remote station performs a handoff of the first handoff embodiment just prior to point 520, then the remote station will only have communication links established with multi-carrier base station BS3b. Although the remote station is in the coverage areas of both BS1d and BS1e, it will no longer have communication links with these base stations, and will not gain the path diversity that could have been received by being in a soft handoff with these base stations. This is especially evident in instances where Nf is contained within Wf, and where BS1d or BS1e is transmitting at a particularly high power level and is interfering with the signals transmitted from BS3b. If the remote station had been in soft handoff with BS3b, BS1d, and BS1e, it would likely have received a good transmission from the high powered base station, either BS1d or BS1e, whose high transmission power level significantly corrupted the transmission signal transmitted by BS3b. However, in the case that it is not in such a soft handoff, as is the case in the first handoff embodiment, it would only receive the corrupted signal from BS3b.

The lack of such a soft handoff negatively affects reverse link power control as well. For instance, if after a handoff of the first handoff embodiment, at point 520 BS3b instructs the remote station to raise its transmission power, the remote station will do so without regard as whether its transmissions are interfering with base station BS1d or BS1e, as can occur when Nr is contained within Wr. This is the case because the remote station is only receiving power control information from BS3b. However, had the remote station been in soft handoff with all three base stations, it would only raise its transmission power if all three base stations had requested it to do so, thus reducing the chance that the remote station would raise its power level excessively.

Although the above embodiment describes how to facilitate a handoff from a single carrier base station to a multi-carrier base station, one skilled in the art will appreciate that a similar method can be used to handoff from a multi-carrier base station to a single carrier base station. A handoff from a multi-carrier base station to a single carrier base station could be used when a remote station is exiting multi-carrier coverage, such as at point 540 or point 548.

In FIG. 8, in a second embodiment of the present invention, a multi-carrier handoff candidate is sent a soft handoff message that instructs the remote station to continue receiving single carrier signals from the single carrier base stations BS1, but also to additionally begin receiving single carrier communications on frequency Nf from at least one multi-carrier base station BS3. In this embodiment, the infrastructure instructs these multi-carrier base stations BS3 to begin communications with the remote station using the single carrier protocol both on the forward and reverse links in frequency bands Nf and Nr, respectively. For instance, if the soft handoff were to occur at point 520, BS3b would be instructed to begin single carrier communications with the multi-carrier handoff candidate in frequency bands Nf and Nr.

While a remote station is in such a soft handoff, it has communication links both with single carrier base stations BS1 and with multi-carrier base stations BS3, and thus receives the communication path diversity and power control benefits provided by such a soft handoff. Namely, the remote station is receiving data from and transmitting data to multiple base stations along different paths. Additionally, the remote station is receiving power control feedback (commonly received in the form of power control bits) from both the single carrier and multi-carrier base stations whose coverage area it is in, and thus is less likely to raise its power transmission level to a point at which it unnecessarily interferes with one of these base stations. A diagram of the communication path after a handoff of this embodiment appears in FIG. 8, wherein the remote station continues transmitting in frequency band Nr, and wherein the remote station continues receiving single carrier transmissions in frequency band Nf from single carrier base stations BS1. FIG. 8 also illustrates that the remote station begins receiving single carrier transmissions in frequency Nf from a multi-carrier base station BS3. Additionally, remote station transmissions adhering to the single carrier protocol are received by single carrier base stations BS1 and multi-carrier base station BS3.

Although the above describes a handoff from single carrier coverage to mixed coverage (an area that is both in the coverage of a single carrier base station and in the coverage of a multi-carrier base station), which occurs, for instance, at point 520, one skilled in the art will appreciate that a similar method can be used to handoff from multi-carrier coverage to mixed coverage, such as at point 540 or point 548.

In the second handoff embodiment, once the remote station travels to a point at which it is no longer in the coverage of single carrier basestations BS1, such as point 530, the remote station will only be communicating with multi-carrier base stations BS3, but will be communicating with them using the single carrier protocol. At such a point, a subsequent handoff can occur that will switch the mode of communications from single carrier to multi-carrier. This subsequent handoff comprises the infrastructure sending a handoff message to the remote station instructing it to stop single carrier communications with a set of at least one multi-carrier base station BS3 and to begin multi-carrier communications on the same set of base stations in frequency bands Wf and Wr. In other words, the remote station is sent a handoff message instructing it to cease all single carrier communications, and to only communicate using the multi-carrier protocol on the forward and reverse links. In such an embodiment, the infrastructure instructs the set of multi-carrier base stations BS3 to switch its mode of communications with the remote station to the multi-carrier protocol in frequency bands Wf and Wr.

For instance, at point 530, a remote station which had performed a handoff of the second handoff embodiment, and which was communicating with BS3c in frequency bands Nf and Nr, using a single carrier protocol, would be instructed to switch its mode of communication with BS3c to a multi-carrier protocol in frequency bands Wf and Wr. After this subsequent handoff, a diagram of the communication path looks once again as it did in FIG. 7.

Performing such a subsequent handoff is beneficial because it allows the benefits of multi-carrier transmissions to be achieved. Wherein performing multi-carrier transmissions on both the forward and reverse links at a time when a remote station was in the coverage area of both multi-carrier and single carrier base stations, as was done in the first handoff embodiment, could have deleterious effects, performing these transmissions when not in a single carrier coverage area will not have these deleterious effects, and thus should be performed after a remote station exits the single carrier base stations' BS1 coverage areas.

A subsequent handoff that tells the remote station to only communicate with one type of base station in that base station's native protocol (the native protocol of a multi-carrier base station is a multi-carrier protocol, while the native protocol of a single carrier base station is a single carrier protocol) is not limited to a remote station traveling from a mixed coverage area to a multi-carrier coverage area, such as at point 530. Rather, a subsequent handoff message that instructs a remote station to o