U.S. patent application number 11/043230 was filed with the patent office on 2005-10-13 for hand-off between ultra-wideband cell sites.
Invention is credited to Arrieta, Rodolfo T., Jolly, Donald W., Santhoff, John H..
Application Number | 20050226188 11/043230 |
Document ID | / |
Family ID | 26944719 |
Filed Date | 2005-10-13 |
United States Patent
Application |
20050226188 |
Kind Code |
A1 |
Santhoff, John H. ; et
al. |
October 13, 2005 |
Hand-off between ultra-wideband cell sites
Abstract
Briefly, the present invention provides a dynamic channel
re-assignment capability between mobile units, base stations and
sectors within base station coverage areas. The wireless devices
used in the present invention may include ultra-wideband radio
communication devices. Ultra-wideband bandwidth and channel
allocation can be effectively managed, even though link quality
generally deteriorates near the outer boundary of the base station.
By maintaining dual communications with an adjoining base station,
the present invention reduces the bit error rate and maintains
signal strength.
Inventors: |
Santhoff, John H.; (Panama
City Beach, FL) ; Arrieta, Rodolfo T.; (Panama City
Beach, FL) ; Jolly, Donald W.; (Smithtown,
IL) |
Correspondence
Address: |
PULSE-LINK, INC.
1969 KELLOGG AVENUE
CARLSBAD
CA
92008
US
|
Family ID: |
26944719 |
Appl. No.: |
11/043230 |
Filed: |
January 25, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11043230 |
Jan 25, 2005 |
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09804110 |
Mar 12, 2001 |
|
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6907244 |
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60255469 |
Dec 14, 2000 |
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Current U.S.
Class: |
370/335 |
Current CPC
Class: |
H04B 1/1027 20130101;
H04W 36/18 20130101; H04W 36/30 20130101; H04L 1/08 20130101; G01S
13/878 20130101; H04B 1/7176 20130101; H04L 1/203 20130101; H04L
1/1816 20130101; H04B 1/7174 20130101; H04L 1/1829 20130101; H04B
17/309 20150115 |
Class at
Publication: |
370/335 |
International
Class: |
H04B 007/216 |
Claims
What is claimed is:
1. A method for performing a soft hand-off in an ultra-wideband
code-based cellular communication system, wherein the soft hand-off
is from a first mobile unit to a second mobile unit to a base
station, the method comprising the steps of: monitoring signal
strength and the bit error rate from a first base station and
determining that either is unacceptable; attempting to locate an
adjacent base station with an acceptable signal strength and bit
error rate and determining that no adjacent base station has an
acceptable signal strength and bit error rate; transmitting a
hand-off request from a first mobile device that is linked to the
first base station to a second mobile device: receiving; a response
from the second mobile device: and using the second mobile device
as a temporary repeater to pass data to a second base station.
2. A computer program product for performing a soft hand-off in an
ultra-wideband code-based cellular communication system, wherein
the soft hand-off is from a first mobile unit to a second mobile
unit to a base station, comprising: computer code for monitoring
signal strength and the bit error rate from a first base station
and determining that either in unacceptable; computer code for
attempting to locate an adjacent base station with an acceptable
signal strength and bit error rate and determining that no adjacent
base station has an acceptable signal strength and bit error rate;
computer code for transmitting a hand-off request from a first
mobile device that is linked to the first base station to a second
mobile device; computer code for receiving a response from the
second mobile device; and computer code for using the second mobile
device as a temporary repeater to pass data to a second base
station.
3. A system for performing a soft hand-off in an ultra-wideband
code-based cellular communication system, wherein the soft hand-off
is from a first mobile unit to a second mobile unit to a base
station, the system comprising: means for monitoring signal
strength and the bit error rate from a first base station and
determining that either is unacceptable; means for attempting to
locate an adjacent base station with an acceptable signal strength
and hit error rate and determining that no adjacent base station
has an acceptable signal strength and bit error rate; means for
transmitting a hand-off request from a first mobile device that is
linked to the first base station to a second mobile device; means
for receiving a response from the second mobile device; and means
for using the second mobile device as a temporary repeater to pass
data to a second base station.
4. A mobile unit for an ultra-wideband code-based cellular
communication system, wherein mobile unit performs a soft hand-off
to a second mobile unit to a base station, the mobile unit
comprising: means for monitoring signal strength and the bit error
rate from a first base station to which it is linked sod
determining that either is unacceptable; means for attempting to
locate an adjacent base station with an acceptable signal strength
and bit error rate and determining that no adjacent base station
has an acceptable signal strength and bit error rate; means for
transmitting a hand-off request to a second mobile device; means
for receiving a response from the second mobile device; and means
for using the second mobile device as a temporary repeater to pass
data to a second base station.
5. A base station system for an ultra-wideband code-based cellular
communication system, wherein there is a soft hand-off from a first
mobile unit to a second mobile unit to the base station, the base
station comprising: means for monitoring signal strength and the
bit error rate from the first base station and determining that
either is unacceptable; and means for attempting to locate an
adjacent base station with an acceptable signal strength and bit
error rate and determining that no adjacent base station has an
acceptable signal strength and bit error rate.
Description
[0001] This application is a divisional of, and claims priority
from, U.S. non-provisional application Ser. No. 09/804,110, filed
Mar. 12, 2001, entitled: "HANDOFF BETWEEN ULTRA-WIDEBAND CELL
SITES," which claims priority from U.S. provisional patent
application Ser. No. 60/255,469, filed Dec. 14, 2000, and entitled
"Ultra-Wideband Communication System and Method", which is
incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to the field of ultra-wideband
communication systems. More particularly, the present invention
relates to hand-offs between cell sites in an ultra-wideband
communication system.
BACKGROUND OF THE INVENTION
[0003] Wireless communication systems are changing the way people
work, entertain, and communicate. For example, portable phones and
other mobile devices have enabled highly mobile individuals to
easily communicate. Such devices can transmit and receive both
voice and data signals. As more features are added to these mobile
wireless devices, users are able to receive a wider variety of
information. This enhances the user's entertainment and more
efficiently solves the user's business problems.
[0004] Data, such as computer files, graphics, video, and music may
be sent from a remote location and received by mobile wireless
devices located throughout a large (or "wide") area. Such wide area
uses generally require a series of fixed transceivers arranged to
communicate with the mobile wireless devices. The wireless device
is able to communicate only as long as it remains in contact with
at least one of the transceivers.
[0005] While the use of such wide area systems is expanding, the
use of local wireless communication systems is also growing. A
local wireless communication system, for example, may configure the
wireless devices in a single building, such as a residence, to
share information. Such local wireless communication systems may
enable computers to control peripherals without physical
connections, stereo components to communicate, and almost any
appliance to send and receive information to the Internet.
[0006] The amount of data being sent on both wide area and local
communication systems is mushrooming, and it may quickly exceed the
bandwidth available in the traditional communication bands. A
relatively new communication technology (termed "ultra-wideband"
technology) may provide assistance in meeting the ever-increasing
bandwidth demands. An example of ultra-wideband technology is the
communication system using an impulse radio system that is
disclosed in U.S. Pat. No. 6,031,862, entitled "Ultra-Wideband
Communication System and Method". Impulse radio uses individually
pulsed monocycles emitted at fractions of nanosecond intervals to
transmit a digital signal. For many applications, the pulses are
transmitted at extremely low power density levels, for example, at
less than -30 dB. The generated pulses are so small that they
typically exist in the noise floor of other more traditional
communication systems.
[0007] Ultra-Wide band communication systems enable communication
at a very high data rate, such as 100 megabits per second or
greater, when operated in a small local area. Ultra-Wideband
systems, however, must operate at extremely low power, typically
transmitting signals at the noise level. These systems must operate
at low power because they need to avoid interfering with the more
established communication frequencies. The low power requirement
restricts the size of each ultra-wideband cell Thus, ultra-wideband
cells generally are smaller than the cells in the more traditional
continuous wave or carrier based systems.
[0008] The relatively small size of a cell in an ultra-wideband
communication system necessitates a relatively dense placement of
base station antennas. This high density of antennas may, under
some circumstances, lead to cross-talk between the channels
assigned to different users. This is especially true if the users
are highly mobile. In this case, they will often travel across cell
boundaries where the signals of two or more base stations overlap.
Since this event will be relatively frequent with such small cells,
user channels must be geographically separated to minimize the
occurrence of channel interference. For example, if a particular
channel is used in a cell, that channel should not be used in any
other cell within several miles. Accordingly, since only relatively
few of the communication channels can be allocated to each cell,
the reuse distance determines the total capacity of the overall
cell communication system.
[0009] The utilized bandwidth in conventional cells varies as a
function of user demand. Since user demand can vary greatly from
one time period to another, there are likely to be times when a
particular cell is greatly under-utilized. There are also likely to
be other times when that same cell is saturated, thereby causing
undesirable drops in transmissions, connection refusals, and
quality degradation. When a cell's bandwidth utilization exceeds
system quality standards in a conventional communication system,
the system operator typically will add another cell in the area to
move some of the user traffic from the over-utilized cell to the
new cell. Adding cells and antennas, however, can be a costly and
time-consuming process.
[0010] Although ultra-wideband technology has the ability to
decrease the impact of multipath interference, it is still subject
to attenuation of the received signal as the signal passes between
transmitter and receiver. For a point RF source, received signal
strength varies as the inverse of the squared distance for open
line of sight communications. In cluttered and mobile environments,
the attenuation is more closely proportional to the inverse of the
fourth power of the distance. This is due to multipath
cancellation, which is present even in ultra-wideband signals. In
either scenario, the attenuation of the signal can decrease the
signal level to a value that is unsuitable for reliable data
transfer.
[0011] Due in part to the deficiencies described above,
conventional ultra-wideband communication systems risk poor quality
of service, especially as a mobile unit moves from one location to
another. Such systems also do not enable entirely efficient
utilization of bandwidth and system resources.
SUMMARY OF THE INVENTION
[0012] It is an object of the present invention to provide mobile
ultra-wideband methods and devices for effectively linking and
maintaining an acceptable level of service and coverage while
simultaneously handling multiple data streams and multiple users.
It is also an object of the present invention to efficiently
utilize bandwidth and system resources. To meet the stated
objectives, and to overcome or greatly alleviate the disadvantages
in known ultra-wideband units, the present invention provides
methods, systems, software and related devices for performing a
"soft hand-off" between and within ultra-wideband cells.
[0013] Briefly, the present invention provides a dynamic channel
re-assignment capability to mobile units, base stations and sectors
within base station coverage areas. The wireless devices may
include impulse radio communication devices such as ultra-wideband
radio (also known as digital pulse wireless) communication devices.
The bandwidth and channel allocation of these devices and sectors
can be effectively managed with the present invention despite the
fact that link quality generally deteriorates near the outer
boundary of the base station. This effective management is achieved
by having the mobile unit maintain dual communication with a linked
base station and an adjoining base station. The present invention
thereby reduces the bit error rate and maintains signal strength
(e.g., RF signal strength). This dual communication procedure is
termed a "soft-handoff.backslash.
[0014] In the present invention the mobile units and base stations
constantly monitor both signal strength and the bit error rate in
order to determine whether there is a need for a hand-off. When the
data integrity of a mobile unit drops below a minimum acceptable
bit error rate (BER), and/or the signal strength drops below a
pre-determined minimum acceptable level, a soft hand-off that
maintains acceptable service will be initiated. FIG. 1 lists the
typical minimum acceptable bit error rates for video, audio and
data.
[0015] Advantageously, the present invention efficiently insures
that a soft hand-off is performed for a mobile device as it moves
from one location to another. This greatly enhances the
desirability of the associated ultra-wide band system by minimizing
or eliminating interruptions in communication. High quality
communication is thus maintained and at the same time the ability
to accommodate additional traffic is provided.
[0016] In one aspect the present invention features a method for
performing a soft hand-off in a cellular communication system
(preferably a code-based cellular communication system) and a
corresponding computer program product. The method involves the
steps of: (a) monitoring signal strength and the bit error rate
from a primary source (preferably an ultra-wideband primary
source); (b) monitoring signal strength and the bit error rate from
a secondary source (preferably an ultra-wideband secondary source);
(c) comparing the strength of the signal and the bit error rate
from the primary source to the strength of the signal and the bit
error rate from the secondary source; and (d) transferring data
reception and transmission from the primary source to the secondary
source when the strength of the signal from the secondary source is
greater than the strength of the signal of the primary source, or
when the bit error rate of the secondary source is less than the
bit error rate of the primary source, or when either signal
strength or bit error rate is below a pre-determined level.
Monitoring signal strength may involve determining signal strength
and storing the information in memory.
[0017] In one embodiment, the hand-off is from a first base station
to a second base station to a mobile unit. In this case: (a) the
first base station is linked to the mobile unit and selects an
adjoining second base station; (b) the first base station contacts
the second base station to request initial hand-off sequence; (c)
the second base station acknowledges the request, provides a
channel assignment to the mobile unit and links to the mobile unit;
(d) the mobile unit transmits a hand-off release to the first base
station; and (e) the first base station releases the mobile unit
and completes the soft hand-off.
[0018] In another embodiment, the soft hand-off is from a mobile
unit to a first base station to a second base station. In this
case: (a) the mobile unit is linked to the first base station and
detects an increase in bit error rate and/or a reduction in signal
strength; (b) the mobile unit sends a request to the first base
station for a hand-off; (c) the first base station receives the
request, selects the second base station and contacts the second
base station to request an initial hand-off sequence; (d) the
second base station acknowledges the request for an initial
hand-off sequence; (e) the second base station contacts the mobile
unit, provides a channel assignment to the mobile unit and links to
the mobile unit; (f) the mobile unit transmits a hand-off release
request to the first base station; and (g) the first base station
releases the mobile unit, and thereby completes the soft
hand-off.
[0019] In still another embodiment, the soft hand-off involves
dynamic power range linking. In this embodiment: (a) a mobile
device is linked to a first base station and requests the position
of a plurality of base stations; (b) the plurality of base stations
reply; (c) the mobile unit determines and stores the location of
each of the base stations; (d) each of the base stations transmits
an associated rating to the mobile device; (e) the mobile device
calculates the data integrity of each base station and establishes
a link with a base station having the highest data integrity; and
(f) the mobile device transmits a link curtailment to the first
base station.
[0020] In another aspect, the invention provides a method for
performing a soft hand-off in a code-based cellular communication
system. The soft hand-off is from a first mobile unit to a second
mobile unit to a base station. The method involves the steps of:
(a) monitoring signal strength and the bit error rate from a first
base station and determining that either in unacceptable; (b)
attempting to locate an adjacent base station with an acceptable
signal strength and bit error rate and determining that no adjacent
base station has an acceptable signal strength and bit error rate;
(c) transmitting a hand-off request from a first mobile device that
is linked to the first base station to a second mobile device; (d)
receiving a response from the second mobile device; and (e) using
the second mobile device as a temporary repeater to pass data to a
second base station.
[0021] In yet another aspect, the present invention provides an
adaptive link controller. The adaptive link controller includes:
(a) logic for monitoring the signal strength and bit error rate of
a mobile unit and a plurality of base stations; (b) logic for
performing dual link coordination and maintenance with a linked
base station and a hand-off base station; and (c) logic for
performing hand-off initiation and link curtailment.
[0022] For each of the methods of the invention described above, a
corresponding computer program product is also provided. The
invention also features ultra-wideband code based cellular
communications systems capable of performing each of the methods of
the invention. The present invention also features mobile units and
base stations that are configured and structured to operate in such
systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The nature, goals, and advantages of the invention will
become more apparent to those skilled in the art after considering
the following detailed description when read in connection with the
accompanying drawing in which like reference numerals identify like
elements throughout, wherein:
[0024] FIG. 1 lists typical minimum acceptable bit error rates for
video, audio and data in accordance with the present invention;
[0025] FIG. 2 shows base station architecture with overlapping
coverage in accordance with the present invention;
[0026] FIG. 3 shows a single base station with connectivity to six
other base stations for handoff and channel coordination in
accordance with the present invention;
[0027] FIG. 4 shows sectorization at an ultra-wide band base
station in accordance with the present invention;
[0028] FIG. 5 is a flowchart for scenario one (a soft hand-off from
base station to new base station to mobile unit) in accordance with
the present invention;
[0029] FIG. 6 is a flowchart for scenario two (a soft hand-off from
mobile unit to base station to new base station) in accordance with
the present invention;
[0030] FIG. 7 is a flowchart for soft handoff scenario number three
that performs dynamic power range linking in accordance with the
present invention;
[0031] FIG. 8 is a power range linking model for soft handoff with
a mobile unit leaving the coverage of base station 2 in accordance
with the present invention;
[0032] FIG. 9 shows scenario four (a soft hand-off from mobile unit
to mobile unit to base station with emergency geo-locating) in
accordance with the present invention;
[0033] FIG. 10 is a flow chart for soft hand-off procedures for
scenarios one through four in accordance with, the present
invention; and
[0034] FIG. 11 depicts an adaptive link controller in accordance
with the present invention.
[0035] It will be recognized that some or all of the figures may be
schematic representations for purposes of illustration and do not
necessarily depict the actual relative sizes or locations of the
elements shown.
DETAILED DESCRIPTION OF THE INVENTION
[0036] In the following paragraphs, the present inventions will be
described in detail by way of example with reference to the
attached drawings. Throughout this description, the preferred
embodiment and examples shown should be considered as exemplars,
rather than as limitations on the present invention. As used
herein, "the present invention" refers to any one of the
embodiments of the invention described herein.
[0037] I. Soft Hand-Off and Mobile Ultra-Wideband Dynamic Linking
Architecture
[0038] FIG. 2 illustrates a preferred base station 10 hexagonal
topology 100 that will provide overlapping coverage 30 for
ultra-wideband base stations 10. Other configurations may also be
used, such as a micro pico-network on a daisy chain backbone,
placed like emergency call boxes along a highway, for separate
routing of signals, but this configuration will allow an effective
soft hand-off, which is essential for code-based cellular
communications. Base station topologies can be hexagonal or linear.
The hexagonal topology covers disperse user density environments
whereas the linear topology mainly covers linear features such as
roads. The concept is the same but the number of sectors per base
station differs. Given this preferred arrangement, or other
suitable arrangements, the present invention may be used in
conjunction with the methods, devices, and systems described in
U.S. patent application, number to be assigned, entitled "Ultra
Wideband Communication System And Method", filed Dec. 13, 2000,
which is incorporated herein by reference in its entirety.
[0039] The overall base station 10 architecture 100 includes a
plurality of base stations 10. Each base station 10 has an
associated coverage area 20, for example a substantially circular
coverage area 20 as shown in FIG. 2. The coverage areas 20 of
adjacent base stations 10 may overlap, thereby creating overlapping
coverage areas 30. The spacing and configuration of the base
stations 10 and the size and shape of the coverage areas 20 will
determine the size and shape of the overlapping coverage areas 30.
In the hexagonal configuration shown in FIG. 2, each base station
10 on the interior of the architecture 100 has six adjacent base
stations 10, while each base station 10 on the exterior of the
architecture 100 has three adjacent base stations 10.
[0040] FIG. 3 shows a single base station 10 with connectivity 40
to six other adjoining base stations 10. The station in the center
60 links with the other base stations 10 to coordinate allocated
channels so that adjoining base station 10 sectors 50 do not use
the same channels. The suitability of the channels may be managed
using the methods and devices described in U.S. patent application
Ser. No. 09/746,348 entitled "System for Pre-testing and
Certification of Multiple Access Codes," filed Dec. 21, 2000, which
is incorporated herein by reference in its entirety.
[0041] The linked architecture 200 also provides an inter-connected
communications system that is necessary to provide a "soft
hand-off" as a mobile unit 70 moves from the coverage area of one
base station 10 to the coverage area of another. Mobile unit 70 may
be a handheld-type mobile device. Alternatively, it may be an
ultra-wideband component in a mobile phone, a mobile internet
device, a portable radio, a personal data assistant, a desktop
computer or appliance located in a home, an automobile, or office
environment or a device for similar applications.
[0042] During the "soft hand-off," the mobile unit 70 will maintain
a link with both base stations 10 until the hand-off is complete.
FIG. 3 also demonstrates the "sectorization" within the coverage
area 20 of the base station 10. Each base station 10 is sub-divided
into six coverage sectors 50. The sub-division provides greater
bandwidth management in the base station's coverage area 20.
[0043] FIG. 4 demonstrates that when a mobile unit 70 passes from
one sector 50 to another 80 within the coverage area 20 of a single
base station 10, the base station 10 will complete a "soft hand-off
as channel re-assignment is accomplished. In this case, the base
station 10 will allocate a new channel for the mobile unit 70 as it
moves into another sector 80, and will maintain the current
allocated channel until the hand-off is complete.
[0044] II. Soft Hand-Off Scenarios
[0045] A. Scenario #1: Base Station to Receiving Base Station to
Mobile Unit
[0046] FIG. 5 illustrates a preferred soft hand-off technique 500.
In step 510, a base station 10 detects an increase in bit error
rate and/or a reduction in signal strength (e.g., RF signal
strength) using known methods. The base station 10 that is linked
to the mobile unit 70 monitors the bit error rate and signal
strength between all of it's linked mobile units 70, as well as
their relative geo-locations. When the bit error rate exceeds the
acceptable bit error rate limit or the signal strength drops below
the predetermined acceptable level, the base station 10 initiates
the hand-off with an adjoining base station 10. The hand-off
procedure begins with the linked base station 10 selecting the most
suitable adjoining base station 10. This selection is based on the
calculated relative geo-positional data (obtained using known
methods or as described herein) that the currently linked base
station 10 has for the mobile unit 70 in relation to the best
suited base station 10 within the hexagonal coverage scheme.
[0047] In step 520 the currently linked base station 10 (base
station 810) contacts the selected adjoining base station 10 (base
station 820) to request an initial hand-off sequence. Step 530
determines if the first adjoining base station 10 has replied using
known methods. If not, then in step 540 base station 810 contacts
the next available base station 10 in the hexagonal coverage
scheme. Alternatively, if the first adjoining base station 10, here
base station 820, has replied, then the initial hand-off sequence
is given by base station 820 in step 550. This initial hand-off
sequence consists of the acknowledgment to base station 810 for
requested hand-off, the channel assignment selection for the mobile
unit 70 and the initial contact with the mobile unit 70 by base
station 820. At this time the mobile unit 70 is in communication
with both base station 810 and base station 820.
[0048] After base station 820 links with the requesting mobile unit
70 in step 560 and both calculate and "acceptable" bit error rate
and signal strength, the mobile unit 70 will transmit in step 570 a
hand-off release request to base station 810. In step 580, base
station 810 then releases the mobile unit 70, and in step 590 the
soft hand-off is complete.
[0049] B. Scenario #2: Initiation by Mobile Unit in Contact with
Base Station
[0050] FIG. 6 illustrates that when a mobile ultra-wideband unit 70
moves from one coverage area 20 to another, the hand-off process
happens in multiple steps. FIG. 6 illustrates the process 600 when
a base station 10 or mobile unit 70 detects, in step 620, an
increase in bit error rate and/or a reduction in signal strength.
In step 630, the mobile unit 70 initiates the hand-off request to
the linked base station 810 if the mobile unit 70 detects the
quality of service changes. When the bit error rate has exceeded
the acceptable limit (e.g., see FIG. 1) or the signal strength
drops below the predetermined acceptable level, the mobile unit 70
sends a request in step 640 to the linked base station 10 for a
hand-off to an adjoining base station 10.
[0051] After the linked base station 10 has received the request,
the hand-off procedure starts with the linked base station 10
selecting the most suitable adjoining base station 10. This
selection is based on the base station 10 sector 50 occupied by the
mobile user or, as in step 650, the known geo-location of the
mobile unit 70 in relation to the best suited base station 10
within the hexagonal coverage scheme. Thus, at this time the base
station 10 has, from step 650, an up-to-date geo-location on the
mobile unit 70, and the six nearest neighbor base stations 10.
[0052] In step 640, the currently linked base station 10 (base
station 810) contacts the selected adjoining base station 10 (base
station 820) that it predicts to be within range of the mobile unit
70 (based on the mobile's position and direction) to request an
initial hand-off sequence. Step 660 determines if the new base
station 10 is able to take the mobile unit 70. If not, then in step
665 base station 810 contacts the next closest base station 10 in
the hexagonal coverage scheme.
[0053] If base station 820 can accept the mobile unit 70, it sends
an acknowledgement in step 670 to base station 810 and proceeds to
link with the mobile unit 70. In step 670, the initial hand-off
sequence by base station 820 includes the acknowledgment to base
station 810 for requested hand-off, the channel assignment
selection for the mobile unit 70 and the initial contact with the
mobile unit 70 by base station 820. At this time the mobile unit 70
is data linked to both base station 810 and base station 820. The
mobile unit 70 will remain linked to base station 810 until a
confirmed Quality of Service (QOS) link with base station 820 or
another base station 10 is established.
[0054] After base station 820 links with the requesting mobile unit
70, a dialogue ensues that leads to a calculation of a bit error
rate and signal strength. If this bit error rate and signal
strength are belter than that achieved through base station 810, as
determined in step 675, then, in step 680 base station 820 will
link with the mobile unit 70 and establish a data channel. Then,
the mobile unit 70 will, in step 685, transmit a hand-off release
request to base station 810. Base station 810 then releases the
mobile unit 70 in step 690, and, as shown in step 695, the soft
hand-off is complete.
[0055] B. Scenario #3: Mobile Ultra-Wideband Dynamic Power Range
Linking
[0056] FIG. 7 demonstrates the principles of the ultra-wideband
dynamic power range linking and soft hand-off technique 700. In
this technique a mobile ultra-wideband unit 70 can determine and
select a base station 10 that will provide optimum signal
integrity. The process includes not only the initial "handshake"
with the base station 10 providing the mobile unit 70 with optimum
capability, but also provides a coordinated "soft hand-off" as
required with the previously linked base station 10.
[0057] In step 710 a mobile device 70 is linked to a first base
station 10 and requests the position of a plurality of base
stations 10. In steps 715 and 725 it is determined if the plurality
of base stations 10 reply. Once the plurality of base stations 10
reply, then in steps 730 an! 735 the mobile unit 70 determines and
stores the location of each of the base stations 10. The
determination of the location may be done by conventional
triangulation or it may be done using the methods and/or devices
described in U.S. patent application Ser. No. 09/745,498, entitled
"Use of Third-Party Ultra-Wideband Devices to Establish
Geo-Positional Data," filed Dec. 22, 2000, which is incorporated
herein by reference in its entirety.
[0058] In steps 740 and 745 the projected bit error rate (PBER)
algorithms are performed. In steps 750 and 755 each of the base
stations 10 transmits an associated rating to the mobile device 70.
In step 760 the mobile device 70 calculates the data integrity of
each base station 10 and establishes a link with a base station 10
having the highest data integrity. In step 770 the mobile device 70
transmits a link curtailment to the fiistbase station 1.0.
[0059] This process is accomplished in a fashion that is
transparent to the mobile user. FIG. 8 illustrates a mobile
ultra-wideband device 70 that is within transmission range of two
ultra-wide band towers 810 and 820 and is in a location that would
benefit from a hand-off. In this diagram, the transmission distance
to base station 810 is a.sub.1, and the transmission distance to
base station 820 is b.sub.1. The mobile ultra-wideband device 70
will require less power (e.g., RF power) to transmit to base
station 820 at distance b.sub.1 than to base station 810 at
distance a.sub.1.
[0060] The present invention additionally manages system bandwidth
by restricting power level such as RF power levels, in mobile
ultra-wideband devices 70 to the smallest amount necessary to
maintain a data link with an acceptable level of service. In FIG.
8, the limited RF power output would keep the mobile unit 70
primarily within the broadcast range of base station 820. Since the
mobile ultra-wideband device's transmission is limited to base
station 820, only bandwidth from base station 820 is utilized and
no adjoining base station's bandwidth is encumbered. As the mobile
ultra-wideband 70 moves away from the base station 10, the bit
error rate will increase and the signal strength will drop to the
predetermined point where data is unacceptable and a soft hand-off
will be initiated. Power level can be further minimized by
combining the present invention with the technology described in
U.S. patent application Ser. No. 09/677,082, entitled
"Communication System", filed Sep. 29, 2000, which is incorporated
herein by reference in its entirety.
[0061] C. Scenario #4: Mobile Unit to Mobile Unit to Base
Station
[0062] FIG. 9 illustrates the process when a mobile unit 70 detects
an increase in bit error rate and/or a reduction in RF signal
strength. The mobile unit 70 also has been unable to contact
another base station 10 directly and the currently linked base
station 10 (base station two (820) in this case) is unable to
initiate a hand-off routine to another adjoining base station 10.
In this case the mobile unit 70 (mobile unit two (920)) initiates
the "mobile unit to mobile unit link hand-off request" to any
mobile unit 70 that will respond. The mobile unit 70 that responds
to this request (mobile unit one (910)) will then perform, as a
temporary repeater to pass mobile unit 2 (920) geo-location data to
base station one (810). This may be useful, for example, for
emergency 911 linking.
[0063] III. Hand-off Procedure Cycle
[0064] FIG. 10 shows the procedural flow 1000 for conducting a soft
hand-off. This shows the four scenarios and the situations in which
they would be conducted. When the bit error rate or the signal
strength has reached the level where the quality of service is no
longer acceptable, the base station 10 or the mobile unit 70 will
initiate the procedures for a hand-off to an adjoining base station
10. Due to various field conditions, both the base station 10 and
the mobile unit 70 have the individual capability to "request" a
hand-off to another base station 10 to maintain quality of service.
In the event that a mobile unit 70 cannot contact a base station
10, including the previous linked base station 10, the mobile unit
70 will conduct a "Tower Range Linking" procedure. This procedure
will locate and link with a neighboring mobile unit 70 for the
purpose of using the contacted mobile unit 70 as a temporary
repeater and as an emergency "911" link back to a base station
10.
[0065] The overall scheme 1000 begins in step 1010 when the mobile
unit 70 link to base station 10 degrades, either due to an
increased bit error rate or a signal decrease. In step 1020 it is
determined, whether the base station 10 detects the degraded link.
If yes, then the hand-off procedures are initiated in step 1040. If
no, then in step 1030 the mobile unit 70 detects the degraded
link.
[0066] Then, in step 1050, it is determined whether the mobile unit
70 has successfully conducted a soft hand-off through the linked
base station 10. If yes, then the hand-off procedures arc initiated
in step 1040. If no, then in step 1060, the mobile unit 70
initiates power range linking.
[0067] In step 1070 it is determined whether the mobile unit 70 has
conducted a soft hand-off through, power range linking. If yes,
then the hand-off procedures are initiated in step 1040. If no,
then the mobile unit 70 initiates power range linking with the
nearest mobile unit 70 for an emergency repeater link to a base
station 10.
[0068] IV. Adaptive Link Controller
[0069] An adaptive link controller (ALC) is structured to provide
at least one of the following acts at a mobile unit, a base station
or some combination thereof: (a) constantly monitoring the Bit
Error Rate (BER); (b) after reaching a predetermined threshold,
searching active cells for a link with a greater signal strength
based on a minimum acceptable level; (c) monitoring signal
strengths of other signals within the cell; (d) maintaining a
two-way link between base stations and mobile units in hand-off
process; (e) performing hand-off request and hand-off actions; (f)
performing emergency link management; (g) creating emergency
message set; (h) performing an overall data link coordination;
and/or (i) performing vector manipulation beam tracking.
[0070] Thus, for example, the ALC may provide the hand-off
coordination and execution. As indicated in steps 1110 and 1120,
the adaptive link controller monitors the bit error rate and the
overall "quality of service" in both the mobile ultra-wideband unit
70 and the base stations 10. When the channel quality has dropped
below acceptable level and the quality of service is diminished,
the adaptive link controller in either the base station 10 or the
mobile unit 70 performs the steps necessary to conduct a
hand-off.
[0071] FIG. 11 illustrates how the adaptive link controller
monitors the channel quality with the assigned mobile units 70 and
the adjoining base stations 10, As a mobile unit 70 traverses
through, the coverage area 20 of a base station 10, the mobile
unit's adaptive link controller maintains the status of the link
with the base station 10. Additionally, in step 1130 the base
station 10 adaptive link controller monitors the link status of the
mobile units 70 in its coverage area 20, as well as the "local"
adjoining base stations 10 that would be us ed for hand-off. The
adaptive link controller provides and maintains a dual link (i.e.,
the mobile unit 70 is in communications with two base stations 10
on two separate channels) during the hand-off process. In step 1140
the adaptive link controller initiates a link curtailment after the
hand-off has effectively transferred control to the receiving base
station 10.
[0072] While various embodiments have been described above, it
should be understood that they have been presented by way of
example only, and not limitation. Thus, the breadth and scope of a
preferred embodiment should not be limited by any of the
above-described exemplary embodiments, but should be defined only
in accordance with the following claims and their equivalents.
* * * * *