EXHIBIT A

Case 6:20-cv-00488-ADA Document 37 Filed 11/06/20 Page 1 of 8
United States Patent 

US007489929B2 

(12) (10) Patent No.: US 7489,929 B2 

Das et al. (45) Date of Patent: Feb. 10, 2009 

(54) HARD HANDOFF PROCEDURE FOR 2003/0060230 A1 3/2003 Soliman ..................... 455,556 

DEDICATED AND HIGH SPEED SHARED 2003/0147370 A1 8, 2003 Wu 

CHANNELS 2005/0266847 A1* 12/2005 Tinnakornsrisuphap et al. .. 455/ 

436 

(75) Inventors: Suman Das, Scotch Plains, NJ (US); Ali 2006/0135075 A1 6/2006 Tee et al. ................. 455/67.13 

Masoomzadeh-Fard, Marlboro, NJ 

(US); Martin H. Meyers, Montclair, NJ FOREIGN PATENT DOCUMENTS 

Nstarish Viswanathan, Morristown, EP 1377 101 A1 1, 2004 

EP 1432.262 A1 6, 2004 

(73) Assignee: Alcatel-Lucent USA Inc., Murray Hill, WO WOO1,992.91 A2 12/2001 

NJ (US) OTHER PUBLICATIONS 

(*) Notice: Subj ect to any site the still PCT International Search Report for International Application No. patent is extended or adjusted under 35 pottisooooooo715, filed Mar 17, 2006. 

U.S.C. 154(b) by 314 days. Written Opinion of the International Searching Authority relating to 

International Application No. PCT/US2006/009715, filed Mar. 17, (21) Appl. No.: 11/095,043 2006. 

(22) Filed: Mar. 31, 2005 * cited by examiner 

(65) Prior Publication Data Primary Examiner David Q Nguyen 

US 2006/0223535A1 Oct. 5, 2006 (57) ABSTRACT 

(51) Int. Cl. A wireless communication network (20) utilizes a hard hand 

H04O 7/20 (2006.01) off procedure for switching between cells serving a mobile 

(52) U.S. Cl. ....................... 455/436: 455/439; 455/442: station (40). In a disclosed example, the existing link between 

455/443; 455/444; 455/432.1; 455/433:455/435.1; the mobile station (40) and a serving base station (38) is not 

455/.435.2 released until a new link between a target base station (32) and 

(58) Field of Classification Search ................. 455/439, a mobile station (40) is established. At the same time, how 

455/438,436,437, 442, 443, 444, 67.13 ever, the mobile station maintains only one base station or link 

See application file for complete search history. within its active set at all times. The disclosed example is 

useful for dedicated channel and shared channel communi (56) References Cited 

U.S. PATENT DOCUMENTS 

6,609,003 B1* 8/2003 Park et al. ................... 455,436 

52 

58 N SET 

RECEIVEMEASUREMENTREPORTFROMMOBILESTATION OWEREXISTINGLINK 

HANDOFF 

NETWORKSIGNALSTARGETBASESTATIONTO 

cations in CDMA systems, for example. 

15 Claims, 2 Drawing Sheets 

DESRED 

SEND ACTIVESETUPDATEMESSAGETOMOBILESTATION 

UPNEWLINK 

- 

OWEREXISTINGLINK 

- TARGETBASESATIONBEGINSUPLINK SYNCHRONAON 

TRANSMTPHYSICALLAYERCONTROLINFORMATIONOWER 

- 

EXISINGLINKFOR psy 

H 

ScroNATON FOR 

62- TARGETBASESTATIONAND NEW LINKACHIEVES UPLNKSYNCHRONIZATION 

MOBILESTATIONUPDATES ACTIVESETBASEDON MESSAGERECEIVEDOWEREXISTINGLINK 

66- MOBILESTATIONACHIEVESDOWNLINK SYNCHRONATION 

68- MOBILESTATIONPROVIDESACTIVESET UPDATECONFIRMAON 

70-N NETWORKRELEASESTHE EXISTINGBASESTATION AND THE EXISTINGLINK 

72- EXISTINGINKSTOPSTRHANDOFF TOTHENEWINKCOMPTE 

64 

 

 

Case 6:20-cv-00488-ADA Document 37 Filed 11/06/20 Page 2 of 8
U.S. Patent US 7489,929 B2 

40 38 32 

MOBILE OLD LEG NEWLEG 

 

 

Case 6:20-cv-00488-ADA Document 37 Filed 11/06/20 Page 3 of 8
U.S. Patent Feb. 10, 2009 Sheet 2 of 2 US 7489,929 B2 

52 RECEIVE MEASUREMENTREPORT FROMMOBILESTATION 

OVEREXISTING LINK 

HANDOFF - 

DESIRED 

YES 

58 NETWORKSIGNALSTARGET BASE STATION TO 

SETUPNEW LINK 

60a SEND ACTIVE SETUPDATE MESSAGETOMOBILESTATION 

OVEREXISTING LINK 

60b TARGETBASE STATION BEGINSUPLINK 

SYNCHRONIZATION 

TRANSMTPHYSICALLAYER CONTROL INFORMATION OVER 

60C EXISTING LINKFOR by CHRONATON FOR 

62 TARGET BASE STATION AND NEW LINKACHIEVES 

UPLINKSYNCHRONIZATION 

64 MOBILESTATIONUPDATES ACTIVE SETBASED ON 

MESSAGE RECEIVED OVEREXISTING LINK 

66 MOBILESTATIONACHIEVESDOWNLINK 

SYNCHRONIZATION 

68 MOBILESTATION PROVIDES ACTIVE SET 

UPDATE CONFIRMATION 

70 NETWORKRELEASES THE EXISTINGBASE STATION 

AND THE EXISTING LINK Fig.2 2 

72 EXISTING LINKSTOPSTXRx HANDOFF 

TO THE NEW LINK COMPLETE 

 

Case 6:20-cv-00488-ADA Document 37 Filed 11/06/20 Page 4 of 8
US 7,489,929 B2 

1. 

HARD HANDOFF PROCEDURE FOR 

DEDICATED AND HIGH SPEEDSHARED 

CHANNELS 

FIELD OF THE INVENTION 

This invention generally relates to telecommunications. 

More particularly, this invention relates to wireless commu 

nication systems. 

DESCRIPTION OF THE RELATED ART 

Wireless communication systems are well known and in 

widespread use. Typical systems include a plurality of base 

stations arranged to serve specific geographic areas or cells. 

An individual can use a mobile station to communicate 

through the wireless communication system as their mobile 

station communicates with a base station serving the cell in 

which they are currently located. 

As a mobile station moves from one cell to another, com 

munications for that mobile station should be handled by 

different base stations at different times. As a mobile station 

moves from one cell to another cell, the communications for 

that mobile station are transferred from the base station serv 

ing the one cell to the base station serving the other cell. The 

process of transferring communications for a mobile station 

between base stations is known as “handoff.” 

Typically, a mobile station monitors a pilot signal or other 

signal strength indicator to determine what base station is 

providing a useful signal for communications. As the mobile 

station approaches the edge of the cell in which it is currently 

located, the signal from the base station serving that cell 

typically weakens while a signal from a base station in an 

adjacent cell typically becomes stronger. In many instances, a 

mobile station recognizes these conditions and requests a 

handoff to the next base station. The requested base station is 

often called a target base station. According to existing com 

munication protocols, mobile stations may request a handoff 

to one or more base stations based upon the relative measured 

strengths of the pilot signals of the base stations. 

Wireless communication networks can also trigger handoff 

procedures based upon periodic measurement reports from 

mobile stations or for other reasons such as bearer traffic 

management in one or more cells. 

One type of wireless communication system is known as a 

Code Division Multiple Access (CDMA) system. Handoffs 

used in CDMA systems are known as “soft' handoffs. A 

mobile station and a wireless network that use soft handoff 

procedures establish communication with a target base sta 

tion before terminating communication with an existing or 

currently serving base station. During a soft handoff proce 

dure, a mobile station is in simultaneous communication with 

more than one base station. Soft handoff procedures typically 

are employed to ensure that there is no interruption of com 

munication between the mobile station and the wireless net 

work through at least one base station. Eventually, a soft 

handoff process is completed and the mobile station commu 

nicates only through the target base station, which becomes 

the existing or serving base station after the handoff is com 

plete. 

Soft handoff in CDMA systems is facilitated based on the 

pilot signal strength of several sets of base stations as deter 

mined by the mobile station. The sets of base stations typi 

cally maintained by a mobile station in a CDMA system 

include an active set, a neighbor set, a candidate set and a 

remaining set. The active set for a typical mobile station is the 

set of base stations through which active communication is 

10 

15 

25 

30 

35 

40 

45 

50 

55 

60 

65 

2 

established. The neighbor set is a set of base stations sur 

rounding the active base stations and includes base stations 

that have a high probability of having a pilot signal strength of 

sufficient level to establish communication, but through which active communication is not yet established. The sur 

rounding base stations that have such a pilot signal strength 

are members of the candidate set. Any one or more of the base 

stations within the candidate set may become the target base 

station for a handoff procedure. The remaining set is a set of 

base stations that are not included in any of the other three 

SetS. 

The network and the mobile station use the different sets of 

base stations to control a handoff procedure. During a typical 

Soft handoff procedure, the active set contains more than one 

base station. The mobile station monitors the pilot signal 

strengths of the base stations in the active set, the candidate 

set, the neighbor set and the remaining set. During a soft 

handoff procedure, when a pilot signal strength of a base 

station in the neighbor or remaining set reaches a defined 

threshold level, that base station is added to the candidate set 

and removed from the neighbor or remaining set, for 

example. 

In one example, a mobile station triggers the handoff pro 

cedure when the mobile station detects a relatively strong candidate pilot signal strength. The mobile station in Such an 

example transmits a measurement report to a radio network 

controller by sending appropriate signals to the serving base 

station. The measurement report may be accompanied by a 

request to add the base station having the detected strong 

candidate pilot to the mobile station’s active set. In other 

situations, handoff requests are transmitted along with peri 

odic measurement reports provided by the mobile station. 

The radio network controller of the wireless communication 

network evaluates the mobile station measurement report to 

coordinate the processing of a soft handoff with the base 

stations associated with strong detected pilot signals. 

The mobile station measurement report contains the mea 

Sured pilot strength for a target base station that the mobile is 

requesting to be included in its active set. The radio network 

controller determines if that target base station has the appro 

priate resources available to serve that mobile station. If the 

target base station has appropriate resources (i.e., Sufficient 

transmit power, bandwidth and data rate), the radio network 

controller sends a message to the mobile station informing the 

mobile station that the requested target base station can be 

added to the mobile station's active set. The mobile station 

responds by sending a confirmation message back to the radio 

network controller confirming that the active set has been 

updated and communication with that target base station, 

which has been added to the active set, can then begin. 

In soft handoff procedures, the mobile station is in simul 

taneous communication, using a communication link com 

prising one or more communication channels, with the active 

set members. Eventually, the handoff process transfers com 

munication to only one of the base stations in the active set. At 

that point, the mobile station has one communication link 

with the one base station within the active set. Such a com 

munication link is also referred to as a “leg. Typical soft handoff procedures may include adding a new 

leg to the active set, removing an existing leg from the active 

set or, if the active set is full, replacing an existing member of 

the active set with a new member. For each of these events 

during a handoff procedure, there is a hysteresis for a handoff 

decision. Typical hysteresis thresholds are on the order of 1 

dB. If a member of the active set has a pilot signal strength, for 

example, that is 1 dB less than a candidate base station, the 

latter may become a member of the active set to replace an 

Case 6:20-cv-00488-ADA Document 37 Filed 11/06/20 Page 5 of 8
US 7,489,929 B2 

3 

existing member when that threshold difference, which is 

specified by the selected replacement hysteresis, occurs. 

Soft handoff procedures are used for dedicated channels in 

CDMA systems. High speed shared channels (SCH) are Sup 

ported in 3G CDMA systems to increase throughput, reduce 

delay and achieve high peak rates. Soft handoff is typically 

avoided over such shared channels to decrease interference 

and increase system capacity. By avoiding soft handoff, strict 

latency requirements for Such channels can also be relaxed. 

The signaling associated with Such a handoff goes through a 

dedicated channel. Dedicated channels in CDMA systems utilize soft handoff procedures. Therefore, the handoff of the 

service over the SCH using signaling over the dedicated chan 

nel is generally considered reliable because the soft handoff 

procedure used on the dedicated channel allows for providing macrodiversity transmission. 

A drawback associated with the current approach is that 

there is a cost associated with the dedicated channel being used in the Soft handoff process for the higher layer signaling 

related to serving the SCH. With such procedures, more 

Walsh codes are used and strict synchronization between cells 

is required. 

It has not previously been possible to complete a handoff 

for dedicated channels in CDMA systems without using soft 

handoff procedures with sufficient reliability. In the absence 

of soft handoff for a dedicated channel, the Switch from one 

cell to another should be very quick to avoid dropping a call. 

The signaling associated with the handover should be reliable 

to avoid retransmissions that introduce additional delay. 

Moreover, when a current or existing cell signal quality is not 

good, it is possible for handoff signaling to fail to get through 

quickly enough before the current link quality becomes unre 

liable. Under some circumstances, this may result in a 

dropped call because Switching to a better-situated base sta 

tion depends upon fast and reliable handoff signaling between 

the mobile station and the wireless communication network. 

As mobile stations move at higher speeds, this problem 

becomes more prevalent. 

There is a need for an improved technique for completing 

handoffs in CDMA systems. It would be beneficial to be able 

to avoid the use of resources required for soft handoff proce 

dures. At the same time, any hard handoff procedure should 

be reliable enough to avoid dropped calls. 

SUMMARY OF THE INVENTION 

This invention addresses the need for an improved tech 

nique for completing handoffs in CDMA systems. A dis 

closed example method of communicating includes a hard 

handoff procedure that can be used for dedicated channels or 

high speed shared channels in CDMA systems. 

An exemplary disclosed embodiment includes establishing 

a link between a target base station and a mobile station 

before releasing an existing link between the mobile station 

and another base station without having more than one base 

station in the mobile station’s active set. In other words, the 

exemplary embodiment provides a make-before-break hard 

handoff that does not use soft combining in a mobile station 

and does not require frame selection. 

One example method of communicating includes deter 

mining that a handoff is desired between a serving base sta 

tion and a target base station. A new link between a mobile 

station and a target base station is then initiated. An active set 

update message is transmitted to the mobile station using an 

existing link between the serving base station and the mobile 

station. Uplink synchronization for the target base station for 

communicating with the mobile station is then achieved. At 

10 

15 

25 

30 

35 

40 

45 

50 

55 

60 

65 

4 

least one signal is eventually received over the new link 

indicating that the mobile station has processed the transmit 

ted active set update message. After this, the existing link is 

released by the network and communication between the 

target base station and the mobile station over the new link 

begins. 

In one example, an active set for the mobile station includes 

only one active link at all times. 

One example method includes receiving an active set 

update message over an existing link between a mobile sta 

tion and a serving base station. The active set update message 

indicates a handoff from the serving base station to a target 

base station. Physical layer control information is then 

received over the existing link for downlink synchronization 

between the mobile station and the target base station. Down 

link synchronization is then achieved with the target base 

station responsive to the received physical layer control infor 

mation. An active set update confirmation is transmitted 

through the new link and communication over the existing 

link is terminated after the active set update confirmation has 

been received by the target base station. 

With such an example, an active set for the mobile station 

includes only one active link at all times. 

The various features and advantages of this invention will 

become apparent to those skilled in the art from the following detailed description. The drawings that accompany the 

detailed description can be briefly described as follows. 

BRIEF DESCRIPTION OF THE DRAWINGS 

FIG. 1 schematically shows selected portions of a wireless 

communication network that utilizes a handoff procedure designed according to an embodiment of this invention. 

FIG. 2 is a flowchart diagram Summarizing an example 

handoff procedure. 

FIG. 3 is a timing diagram Schematically showing various 

portions of an example handoff procedure. 

DETAILED DESCRIPTION 

FIG. 1 schematically shows selected portions of a wireless 

communication network 20. A plurality of cells 22, 24, 26 and 

28 are served by base stations 32, 34, 36 and 38, respectively. 

The base stations 32-38 communicate with a radio network 

controller and other portions of a wireless communication 

network in a known manner. 

A mobile station 40 is schematically shown within the 

geographic region or area of coverage of the cell 28. Com 

munications between the mobile station 40 and another 

device using the wireless communication network occurs 

over an existing link between the base station 38 and the 

mobile station 40. The base station 38 in this instance is 

considered a serving base station or an existing base station 

for purposes of this description. The communication link 

between the mobile station 40 and the base station 38 under 

Such circumstances is an existing leg or an existing link. 

Eventually the mobile station 40 moves into another region 

corresponding to another one of the cells. As such movement 

occurs, a handoff between the existing base station 38 and a 

new or target base station serving the cell that the mobile 

station 40 is entering should occur. In traditional CDMA 

systems, a soft handoff procedure would have been used. 

With the disclosed example, a hard handoff procedure that 

includes making a connection over the new link before break 

ing the connection over the existing link allows the mobile 

station to have only one base station or link within an active 

set of the mobile station at all times. In other words, with the 

Case 6:20-cv-00488-ADA Document 37 Filed 11/06/20 Page 6 of 8
US 7,489,929 B2 

5 

disclosed example, the mobile station 40 does not need to use 

Soft combining and the base stations do not need to use frame 

selection. 

FIGS. 2 and 3 illustrate an example handoff procedure designed according to an embodiment of this invention. The 5 

flow chart diagram 50 in FIG. 2 begins at 52 where the 

wireless network (i.e., a radio network controller) receives a 

measurement report from the mobile station 40 over the exist 

ing link (i.e., with the serving base station 38) as the mobile 

station 40 is in the cell 28. Depending on the conditions at that 10 

time, the measurement report may include a handoffrequest 

from the mobile station. At 54 (in FIG.3) the network receives 

the measurement report from the mobile station 40 over the 

existing link through the serving base station 38. 

At 56, the network determines whether a handoff is 15 

desired. In some examples, the handoff is triggered by the 

mobile station request for a handoff. In other circumstances, 

the network may initiate a handoff to better manage network 

resources using known selection criteria for Such situations. 

Once a handoff decision is made, the network communicates 20 

with a target base station (i.e., base station32, for example) to 

setup a new link between the target base station 32 and the 

mobile station 40. Such communication is schematically 

shown at 58 in FIG. 3 to represent communications between 

the network components and the target base station. Such 25 

communications include, for example, a radio link setup 

request to the target base station, a response from the target 

base station, information regarding a packet data convergence 

protocol, which in one example is a data link layer protocol 

for packet Switch data whose main function is header com- 30 

pression, and a radio link control signal, whose functions 

correspond to segmentation and retransmission. A variety of 

known signals or information to meet the needs of a particular 

situation may be used for setting up the new link with the 

target base station. 35 

Based on information regarding the target base station, the 

network sends an active set update message to the mobile 

station 40 over the existing link with the serving base station 

38. This is shown at 60A in FIG. 2. In one example, at the 

same time, the target base station (or the new link) begins the 40 

process of uplink synchronization at 60B and starts transmit 

ting on a physical control channel (i.e., pilot signal, etc.). The 

uplink synchronization is based upon the received physical 

layer control information provided by the network at 58. 

In one example, at the same time, physical layer control 45 

information for the mobile station 40 to accomplish downlink 

synchronization is transmitted over the existing link to the 

mobile station 40. 

At 62, the new linkachieves uplink synchronization. At 64, 

the mobile station 40 receives the active set update message, 50 

updates the active set to replace the existing link with the new 

link and transmits an active set update confirmation message 

to the network over the new link. 

In one example, the mobile station begins downlink syn chronization at essentially the same time using the physical 55 

control information regarding the new link that was received 

by the mobile station over the existing link. At 66 in FIGS. 2 

and 3, the mobile station 40 achieves downlink synchroniza 

tion. 

At 68, the active set update confirmation from the mobile 60 

station 40 is received by the network. Signaling between the 

network and the old link for releasing the old link is sche 

matically shown at 70. At 72, the existing link has been 

released and no longer receives or transmits any communica 

tions between the network and the mobile station 40. 65 

By not releasing the old link until after receiving a confir 

mation message regarding the new link in a sequence as just 

6 

described, the hard handoff process of this example includes 

making the new link connection before breaking the existing 

link connection. This represents an improvement over other 

hard handoff procedures where the making and breaking of 

the new and existing links occurred simultaneously. At the 

same time, however, the mobile station 40 in this example 

only maintains one member in its active set at all times. That 

is, the mobile station 40 replaces the existing link with the new link in the active set. 

In one example, if the network does not receive the active 

set update confirmation from the mobile station 40 within a 

selected time after transmitting the active set update message, 

then the network proceeds as if the new link could not be 

established and utilizes the existing link to send another 

active set update message regarding the same target base 

station or a different target base station, for example. By not 

releasing the existing link until after receiving confirmation 

that the mobile station has updated the active set, the dis 

closed example avoids potential call drops associated with 

other hard handoff procedures. 

The speed with which the example handoff process is com 

pleted is important. One example includes using a prediction 

algorithm on the network side to expedite the hard handoff 

process. Based upon periodic measurement reports from the 

mobile station, the network predicts the relative strength of 

pilot signals in a next measurement period. This prediction 

allows the network to make a faster handoff decision and to be 

able to switch to the strongest possible link when the link 

quality of an existing link between the mobile station and a 

serving base station degrades quickly. Given this description, 

those skilled in the art will be able to develop the detailed 

workings of such a prediction algorithm to meet their particu 

lar needs. 

Another feature of the disclosed example is that all user 

data for a mobile station involved in the example handoff 

process is buffered during the handoff process. In other 

words, all data from the mobile station is buffered at the 

mobile station and all data at the network side is buffered at 

the network side until the handoff process is complete. This 

further allows fast and reliable switching to the strongest 

target base station while avoiding soft handoff for high speed 

shared channels and the associated dedicated channels. 

Another feature of the disclosed example includes mini 

mizing replacement hysteresis associated with replacing the 

existing link with the new link. In one example, a lower 

hysteresis threshold than that used in a typical soft handoff 

procedure facilitates the example hard handoff process. In 

one example, a replacement hysteresis threshold of approxi 

mately 0.25 dB is used as the threshold for deciding when to 

handoff between an existing link and the target base station or 

new link. Other examples use thresholds between about 0.2 

dB and about 0.5 dB. The replacement hysteresis threshold 

level in the illustrated example is set high enough to avoid the 

so-called ping-pong effect when the pilot signal strengths of 

two base stations vary repeatedly over time. At the same time, 

using a smaller threshold compared to soft handoff thresh 

olds, which typically are on the order of 1 dB, speeds up the 

hard handoff process of the disclosed example. 

The disclosed example handoff process allows for quickly 

Switching between base stations and utilizes simplex opera 

tion. Avoiding soft handoff for dedicated channels in CDMA 

systems, for example, resolves the problem of tight synchro 

nization between cells, which is otherwise needed to satisfy latency requirements. The disclosed example reduces the 

number of Walsh codes per user since each mobile station is 

connected to only one cell using only one link and one base 

station in an active set at all times. Accordingly, simplex 

Case 6:20-cv-00488-ADA Document 37 Filed 11/06/20 Page 7 of 8
US 7,489,929 B2 

7 

operation is used for the dedicated channels and high data rate 

shared channels, which provides the advantage of potentially decreasing interference and increasing system capacity. 

The disclosed example includes making the new link 

before breaking the existing link but no soft combining is 

used in the downlink (i.e., by the mobile station) and no frame 

selection is used in the uplink (i.e., by the radio network 

controller). 

The disclosed example allows for switching between cells 

or base stations while avoiding soft handoff. This eliminates 

the need for tight synchronization between cells and framing protocol between nodes to guarantee latency requirements. 

The disclosed example is less costly in terms of the required 

number of Walsh codes used per mobile station. Moreover, 

the disclosed example maintains link quality during a fast 

hard handoff procedure by establishing the new leg before 

releasing the old leg without using soft combining in the 

downlink and without frame selection in the uplink, both of 

which have been used for typical soft handover procedures. The preceding description is exemplary rather than limit 

ing in nature. Variations and modifications to the disclosed 

examples may become apparent to those skilled in the art that 

do not necessarily depart from the essence of this invention. 

The scope of legal protection given to this invention can only 

be determined by studying the following claims. 

We claim: 

1. A method of communicating between a mobile station, a 

serving base station and a target base station comprising: 

establishing a new link between the target base station and 

the mobile station before releasing an existing link 

between the mobile station and the serving base station 

while having only the existing linkin an active set for the 

mobile station before releasing the existing link by 

(A) determining ifa handoff is desired between the serving 

base station and the target base station; 

(B) initiating the new link between the mobile station and 

the target base station; 

(C) transmitting an active set update message to the mobile 

station using the existing link between the serving base 

station and the mobile station; 

(D) achieving uplink synchronization for the target base 

station to communicate with the mobile station; 

(E) receiving at least one signal over the new link indicat 

ing that the mobile station has processed the transmitted 

active set update message; and 

(F) releasing the existing link responsive to the at least one 

signal of step (E). 

2. The method of claim 1, comprising communicating 

between the mobile station and the target base station using the new link only after completing step (F). 

3. The method of claim 1, wherein step (A) comprises receiving a handoffrequest from the mobile station and com 

prising selecting the target base station based at least in part 

on the received request from the mobile station. 

5 

10 

15 

25 

30 

35 

40 

45 

50 

8 

4. The method of claim 1, wherein step (B) comprises providing the target base station with physical layer control 

information comprising at least a radio link setup request, a 

packet data convergence protocol and a radio link control. 

5. The method of claim 4, wherein step (D) comprises initiating the uplink synchronization responsive to the physi 

cal layer control information. 

6. The method of claim 1, comprising 

providing physical layer control information for downlink 

synchronization between the target base station and the 

mobile station from the target base station to the serving 

base station; and 

transmitting the provided physical layer control informa 

tion from the serving base station to the mobile station. 

7. The method of claim 6, comprising transmitting the 

provided physical layer control information to the mobile 

station prior to completing step (D). 

8. The method of claim 1, comprising 

receiving a plurality of measurement reports from the 

mobile station over the existing link; and 

predicting the desired handoff based on the received mea 

Surement reports. 

9. The method of claim 8, comprising predicting the target 

base station. 

10. The method of claim 1, comprising receiving at least 

one signal from the mobile station over the existing link that 

is indicative of a desire of the mobile station for a handoff and 

performing step (A) responsive to the received at least one 

signal. 

11. The method of claim 1, comprising buffering bearer 

traffic between the mobile station and the serving base station 

while performing steps (A) through (F). 

12. The method of claim 1, comprising achieving downlink 

synchronization between the mobile station and the target base station prior to performing step (F). 

13. The method of claim 12, comprising receiving down 

link physical layer control information over the existing link, 

the downlink physical layer control information originating 

from the target base station for downlink synchronization 

between the target base station and the mobile station. 

14. The method of claim 1, comprising 

determining a characteristic of the existing link; 

determining the characteristic of the new link: 

determining a difference between the determined charac 

teristics; and 

performing step (A) if the determined difference exceeds a 

threshold that is selected to minimize replacement hys 

teresis. 

15. The method of claim 1, comprising providing at least 

one signal indicating a desire for the mobile station to handoff 

from the existing base station using the existing link. 

k k k k k 

Case 6:20-cv-00488-ADA Document 37 Filed 11/06/20 Page 8 of 8