Note: Descriptions are shown in the official language in which they were submitted.
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COMMUNICATIONS SYSTEM AND PROTOCOL FOR MEDICAL ENVIRONMENT
100011 This is a divisional stemming from Canadian Patent Application No.
2,675,938.
FIELD OF THE INVENTION
[0001a] This invention relates generally to the field of communications and
more specifically
to the field of medical communications devices.
BACKGROUND OF THE INVENTION
[00021 Modem health care environments place heavy burdens on medical
personnel
responsible for a continuously growing number of patients. Nursing shortages
and heavy
workloads continue to be the norm in most modern hospitals. Nursing and other
front line
medical caregivers are typically responsible for monitoring and reporting
patient conditions. A
patient's post-operative recovery, for example, often requires monitoring and
restricting patient
movement. This task is frequently complicated when dealing with patients who
are confused or
unable to understand the caregiver's instructions and are at risk of injury
due to their propensity
for excessive movement.
[0003] Patient movement and bed position detection systems provide
monitoring and alerting
capabilities by conveying to care giving personnel a patient's movement and/or
position on the
bed. These systems provide for remote monitoring and alerting by employing
sensors
incorporated into hospital beds or other patient supporting equipment that
interface with a nurse
call system to relay the sensor data to a nursing station or a telemetry unit.
When the system
detects that a patient has left the bed, changed positions and/or moved the
bed controls in a way
that does not comply with an allowed range of motion, nursing personnel are
alerted to take
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appropriate action. Typically, patient movement and position sensors mounted
in the bed
interface with a control unit located on the bed. The control unit transmits
the patient data to the
nursing station via a cable that connects the control unit and a nurse call
system interface located
in the patient's room.
[0004] Patient beds and other patient equipment are often moved
about a hospital. Upon
moving the bed to another location, the cable connecting the bed to the nurse
call system is
disconnected for transport of the bed and then reconnected when the bed is
prepared at its new
location. Because the cable is a physical tether, it is easy for hospital
personnel to forget to
disconnect the cable before moving the bed or any other equipment cabled to
the wall, causing
damage to the cables and to the connectors on the bed and the wall
Additionally, when the bed is
being prepared at a new location, hospital personnel do not have the physical
reminder to
= connect the cable.
= BRIEF SUMMARY OF THE INVENTION
[0005] A wireless communications link and associated protocol
interconnect a pair of bed
and wall units that communicate patient information, including bed exit
alerts, from a patient
supporting equipment to a hospital nurse call system. In one embodiment, the
bed/wall unit pair
operates within unlicensed spectrum and, therefore, takes into account
possibility of congestion
and interference in order to provide safe and reliable connection to the nurse
call system.
Specifically, a linking procedure aids the establishment of a communications
link between the
bed and wall units and prevents unintended cross linking of the paired units
to other nearby bed
and wall units. During the linking procedure, the establishment of the
communications link fails
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upon detection of a third communications device such as a bed or wall unit
attempting to
participate in the linking process.
[0006] Once established, the communications link is maintained by
periodically exchanging
link status or check-in message sequences between the linked bed/wall pair.
The processing of
the messages includes detecting collisions with link status messages generated
by other linked
bed/wall pairs. Early detection of collisions or interference among links is
achieved by
monitoring corruption of an end-of-packet or tail-feather byte within the
periodic messages. As
link status messages from different links slowly drift toward one another, the
end-of-packet byte
in one of the two messages will corrupt first. By responding to corruption of
the end-of-packet
byte, the data in the packet is saved so that the integrity of the link status
message remains intact.
Early detection of the collision enables the message to be adjusted either in
time or frequency to
avoid corruption of the links' integrity.
[0007] In one embodiment, the periodic link messages are time shifted upon
detection of a
collision of link status messages, which moves the messages away from the
colliding messages
that are also periodic. Although the interfering messages may share the same
or a similar
repetition period, by shifting the timing of one of the messages, the messages
of one link no
longer overlap messages of the other link detected by the collision. Other
features include
monitoring for combinations of first-try check-in message failure and first-
resend success, as
strong indications of colliding units, and adjusting the nominal time slot of
periodic check-in
messages. Alternatively, the linked bed/wall unit pair shifts to another
operating channel upon
detection of link status message collisions. To prevent interference from
other devices sharing
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the same spectrum, the system also provides for monitoring channel noise and
moving to a
different operating channel to evade other interfering devices.
[0008] Preferably, the bed unit includes a local power source
such as a battery. To
ensure long lasting operation, the bed unit enters an idle sleep mode by
temporarily powering
down its transceiver circuitry.
[0009] To ensure prompt interconnection of units, embodiments of
the invention
provide for a link reminder to alert the health care provider to initiate the
steps for linking the
bed and wall units whenever two or more unlinked units are in proximity. The
system
broadcasts link reminder messages to elicit reply messages from one or more
nearby unlinked
units and activates a link reminder alert upon receipt of multiple replies
from the same
unlinked unit. When the system operates on multiple frequencies, unlinked
units transmit link
reminder messages on each of the system channels.
[0009a] According to one aspect of the present invention, there is
provided a method
for alerting personnel to establish a communications link between a mobile
hospital apparatus
' 15 and a stationary point, the method comprising: transmitting a link
reminder message between
the mobile hospital apparatus and the stationary point; transmitting a link
response message in
response to the link reminder message; and signaling the personnel after
transmission of the
link reminder and link response messages that the communications link between
the mobile
hospital apparatus and the stationary point is not established.
[0009b] According to another aspect of the present invention, there is
provided a
system for reminding personnel to establish a wireless communications link
between a pair of
transceivers, the system comprising: a first transceiver for generating one or
more signals
indicating it is available for establishing the wireless communications link
with another
device; a second transceiver responsive to the signals from the first
transceiver for generating
complementary signals indicating the second transceiver is available for
establishing the
wireless communications link; and a signaling device for alerting the
personnel that the first
and second transceivers are available for establishing the wireless
communications link.
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[0009c] According to still another aspect of the present invention,
there is provided a
medical communications device in a pair of devices for transmitting patient
information via a
wireless communications link, the medical communications device comprising: a
user
interface for receiving user inputs; a transceiver for establishing the
wireless communications
link with another device forming the pair of devices for transmitting the
patient information;
and a controller responsive to the transceiver for detecting a presence of the
other device in
the pair; and a signal generator responsive to the controller for prompting
action by personnel
responsible for establishing the wireless communications link.
[0009d] According to yet another aspect of the present invention,
there is provided a
medical communications device in a pair of devices for transmitting patient
information via a
wireless communications link between a hospital bed and a stationary base, the
medical
communications device comprising: a user interface for receiving user inputs;
a transceiver
for establishing the wireless communications link with another device in the
pair of devices
for transmitting the patient information between the hospital bed and the
stationary base; a
controller responsive to the transceiver for detecting a presence of the other
device in the pair
and informing the other device that the transceiver is available for
establishing the wireless
communications link such that an alerting signal prompts action by personnel
responsible for
establishing the wireless communications link.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0010] While the appended claims set forth the features of the present
invention with
particularity, the invention and its advantages are best understood from the
following detailed
description taken in conjunction with the accompanying drawings, of which:
[0011] FIGURE 1 is a schematic diagram illustrating a hospital
facility environment
having multiple hospital beds each wirelessly connected to a hospital
monitoring and alerting
system via a pairs of bed and wall units;
100121 FIGS. 2 and 3 are front and side views of the bed unit of FIG.
1;
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[0013] FIGS. 4 and 5 are front and side views of the wall unit of FIG. 1;
[0014] FIG. 6 is a schematic diagram of the RF and controller circuitry in
the bed unit
of FIGS. 1-3;
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[0015] FIG. 7 is a schematic diagram of the RF and controller circuitry in
the wall unit of
FIGS. 1, 4 and 5;
[0016] FIG. 8 illustrates the format of a communications frame in
accordance with the
communications protocol of the invention;
[0017] FIG. 9 is a timing diagram illustrating the successful completion of
the linking
process to establish a communications link between a bed/wall unit pair of
FIG. 1;
[0018] FIGS. 10 and 11 are timing diagrams illustrating different scenarios
leading to failure
of the linking process of FIG. 9;
[0019] FIG.12 is a timing diagram illustrating the adjustment of a time
window in which a
bed unit of FIGS. 1-3 periodically communicates with its mated wall unit to
maintain the
communications link, where the time window is adjusted pursuant to advanced
detection of
collisions of check-in message sequences associated with a bed/wall unit pair
of FIG. 1;
[0020] FIG. 13 is a timing diagram illustrating the operation of the link
reminder to alert the
health care provider to initiate the linking process of FIG. 9;
[0021] FIG. 14 is a state diagram showing the relationship among various
operating states of
the bed and wall units, including Linking Process, Linked Idle, Check-in
Message, Call Message
and Unlinked Idle states;
[0022] FIG. 15 is a flowchart illustrating the detailed operation of the
Linking Process State
of Fig. 14;
[0023] FIG. 16 is a flowchart illustrating the detailed operation of the
Linked Idle State of
Fig. 14;
[0024] FIG. 17 is a flowchart illustrating the detailed operation of the
Check-in Message
State of Fig. 14;
[0025] FIG. 18 is a flowchart illustrating the detailed operation of the
Call Message State of
Fig. 14; and
[0026] FIG. 19 is a flowchart illustrating the detailed operation of the
Unlinked Idle State of
Fig. 14.
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DETAILED DESCRIPTION OF THE INVENTION
[0027] Turning to the drawings and referring first to Figure 1, a typical
hospital facility
environment has multiple hospital beds connected to a hospital monitoring and
alerting system.
In Figure 1, only two hospital rooms 10a and 10b are illustrated. Each of the
rooms 10a and 10b
are identically equipped.
[0028] For ease of explanation, whenever detailed reference is made
hereinafter to the
equipment in one of the rooms 10a and 10b, the description applies equally
well to the other
room in Figure 1, unless indicated otherwise. Moreover, Figure 1 is
representative of a larger
environment such as a hospital that may include many more rooms such as the
two illustrated in
Figure 1 that are also equipped in the same or similar manner. All of the
rooms may be
connected to a common nurse call system as suggested by Figure 1 or there may
be several nurse
call systems with each of them connecting a group of rooms. All such
networking architectures
and others are contemplated by the detailed description set forth herein.
[0029] To communicate patient information from the hospital room 10a to a
monitor 12 at a
remote nursing station, a bed and wall unit pair 14 and 16, respectively, is
associated with a
mobile hospital bed 26 through a wireless communications link 22. Preferably,
the
communications link 22 operates within an unlicensed frequency band, such as
Industrial,
Scientific, and Medical (ISM) frequencies allocated by the United States
Federal
Communications Commission (FCC) to be employed for low-power/short-range
wireless
communications. To reduce the chance of interference from other devices
sharing the ISM
frequencies, the communications link 22 preferably operates within the 902 ¨
928 MHz ISM
frequency band and complies with the corresponding maximum transmit power
limitations
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designated by the FCC for devices operating within this frequency range. Other
contemplated
frequency bands include other available ISM frequency bands, such as 2.4 GHz
and 5.8 GHz
bands. In the illustrated embodiment, the bed unit 14 is attached to the
mobile hospital bed 26
for collecting the patient information, which includes patient occupancy,
nurse call, call
assurance, and system status signaling.
[0030] To convey the nurse call and call assurance signaling,
the bed unit 14 interfaces with
the patient communications module 46, which is located within the siderail 50.
To communicate
with the health care provider 54, a patient initiates a nurse call via the
communications module
46. Once the patient places a nurse call, the communications module 46
generates a call
assurance signal by activating a visual indicator (not shown), such as a
status LED, to indicate
that a nurse call has been placed. Similarly, when the maintenance of the
communications link
22 is in jeopardy due to low battery power at the bed unit 14, or when the
communications link
=
22 is lost, such as due to poor signal conditions or movement of the bed 26,
the bed unit 14 or the
wall unit 16 generates a "bed out" signal reflecting the system status.
[0031] Furthermore, to collect the patient occupancy
information, a bed sensor 30 measures
the interaction of the patient's body with the bed frame 34 and conveys the
collected information
to the bed unit 14 via a cable 42. Alternatively, there may be a wireless
connection between the
bed unit 14 and the bed sensor 30. An example of a bed sensor equipped
hospital bed is a
Chaperone center of gravity bed exit system manufactured by Stryker
Corporation located at
2825 Airview Boulevard, Kalamazoo, Michigan 49002. A typical bed exit system
includes one
or more occupancy sensors 30 distributed along a bed frame 34 to collect and
analyze the weight
information and determine the patient's occupancy status, such as whether the
patient has left the
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bed 26 and/or the patient's position on the bed 26. In the illustrated
embodiment, the bed sensor
30 is a pad type sensor placed on top of the mattress 38, while other
embodiments include load
cell sensors incorporated into the bed frame 34. The patient occupancy
information generated by
the bed exit system also includes a bed exit alarm signal generated by the
occupancy sensor 30
when the patient moves off the bed frame 34. The patient occupancy information
further
includes patient weight, bedrail height, bed height, brake status, and bed
support elevation angle.
[0032] Upon collecting the patient information, the bed unit 14
communicates with the wall
unit 16 via the communications link 22. While the bed unit 14 is capable of
mobility due to its
attachment to the mobile hospital bed 26, each wall unit 16 remains stationary
in its associated
hospital room 10a. Therefore, the wall unit 16 is able to communicate with the
bed unit 14 when
the bed unit 14 moves in its proximity. The wall unit 16, in turn, conveys the
collected
information to the health care provider 54 via the nurse call system 56. The
nurse call system 56
connects a plurality of rooms 10a, 10b, each having a bed 26, 28 and a
corresponding bed/wall
unit pairs 14/16,and 18/20 to one or more nursing station monitors 12 for
allowing the health
care provider 54 to monitor the patient information. Exemplary nurse call
systems include any
one of a line of Responders integrated health care communications systems
manufactured by the
Rauland Borg Corporation located at 3450 West Oakton Street, Skokie, Illinois
60076. In one
embodiment, the nurse call system 56 integrates with an IP-based local area
network to
accumulate the patient information from a plurality of mobile hospital beds
26, 28 via
connections 58, 60. To provide a local indication of on-going bed exit and
nurse call events to
the health care provider 54, the wall unit 16 additionally connects to an
external room transducer
15, which is mounted to one of the internal or external walls of each room 10a
and 10b. The
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room transducer 15 provides an audio alert, such as a speaker or a bn77er
tone, for the health care
provider 54 to check on the patient within the room. Alternatively, the
transducer 15 provides a
visual alert, such as a flashing light, or a combination of audio and visual
alerts.
[0033] To establish the communications link 22, the health care provider
interacts with user
interfaces at each of the bed and wall units, such as by pressing a button on
each of the units. As
illustrated in Figures 2 and 3, to link the bed unit 14 with the wall unit 16,
the health care
provider presses a link button on one or both of the user interfaces 64 and 78
of the bed and wall
units 14 and 16, respectively. Preferably, it does not matter whether the
health care provider first
presses the link button 62 or the link button 76 to initiate the linking
process. Pressing a link
button on either the bed unit 14 or the wall unit 16 initiates a timer during
which the health care
provider is required to press the corresponding link button on the other unit
of the pair to be
linked. In one embodiment, the linking process timer is set to five (5)
seconds from the time the
health care provider activates the link button 62 or the link button 76. Each
unit's link indicator
66, 80 flashes during the linking process. Once the linking process is
complete and the
communications link 22 between the linked bed/wall unit pair is established,
the wall unit's link
indicator 80 lights up continuously. Since the bed unit is preferably battery
operated, while the
wall unit is powered through its connection to the nurse call system, the bed
unit's link indicator
66 turns off to save battery power after the communications link 22 is
established.
[0034] If the link attempt is unsuccessful, one or both of the bed unit 14
and the wall unit 16
sounds a continuous tone for a predetermined duration. In the illustrated
embodiment, the unit
that initiates the link attempt signals a failure since the other unit may not
be aware of the
attempt.
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[0035] To immediately silence the link failure tone, the health care
provider presses the bed
unit's unlink button 68 and the wall unit's cancel button 82. Similarly, when
the bed 26 is
moved to another hospital room, the health care provider manually unlinks a
linked bed/wall unit
pair by pressing the unlink button 68 on the bed transceiver unit 14.
Unlinking the units also
generates a "bed out" signal, which the wall unit 16 relays to the nursing
station monitor 12 to
alert the caregiver personnel that the communications link 22 between the two
units is lost. The
bed unit also generates a "bed out" signal and activates the low battery
indicator 70 when its
battery level drops below a predetermined threshold. When the bed unit 14 is
linked to the wall
unit 16, the wall unit 16 similarly activates its low battery indicator 84
upon relaying the "bed
out" signal and the associated low battery warning to the nursing station. The
low battery
threshold is preferably set so as to allow continued operation of the bed unit
14 for a number of
days or weeks after the activation of the low battery indicators in order to
provide the caregiver
with sufficient time to change the batteries.
[0036] Preferably, the bed and wall units include a link reminder feature
that alerts the health
care personnel to initiate the linking process whenever an unlinked bed unit
14 moves in
proximity of the unlinked wall unit 16. The bed unit 14 emits an audio
reminder, such as a short
chirp, to prompt the health care personnel to initiate the linking process and
press the link button
62 or the link button 76. Alternatively, the wall unit 16 can provide the
reminder or even both
units 14 and 16 can provide reminders, including a visual reminder, such as
flashing the link
status LEDs 66, 80 at one or both units, instead of or in addition to the
audio reminder.
[0037] If the caregiver decides that the communications link 22 should not
be established
between the two units, he or she presses the unlink button 68 on the bed unit
14 in order to
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silence the link reminder alarm. Preferably, the link reminder returns after a
predetermined time,
such as one hour, if the two unlinked units still remain unlinked and in
proximity. However, to
provide a link reminder with respect to a new pair of unlinked units, such as
when a previously
silenced unlinked bed unit is moved in proximity of a different unlinked wall
unit, the link
reminder returns before the one hour period. Additional aspects of operation
of the link reminder
feature are discussed in more detail below in connection with the state
diagrams and flowcharts
of Figures 13 and 19.
[0038] As illustrated in Figure 4, to convey the patient information from
the mobile hospital
bed 26 to a nearby wall unit 16, the bed unit 14 attaches to the bed frame 34
via fasteners 72, 74
and interfaces with the bed sensor 30 and the communications module 46 via a
connector 96.
Specifically, the bed unit connector 96 mates with a bed interface connector
97 for routing the
patient occupancy information (e.g., bed exit alarms), as well as nurse call
and call assurance
signaling, to the bed unit 14 via cables 42 and 95 respectively. The connector
pair 96 and 97
uses a DB37 pin type connection. Similarly, as shown in Figure 5, the wall
unit 16 interfaces
with the nurse call system 56 and room transducer 15 via a connector pair 93
and 94, which also
employs a DB37 pin type connection. Preferably, the wall unit 16 is powered
through the
connector 94 via a corresponding pin connection to the nurse call system 56.
To provide an
alternative power source, which can be used during the maintenance of the
nurse call system 56,
for example, the wall unit 16 includes an external power port 86. Wall
fasteners 88, 90 ensure
that the connector 94 does not come loose from its wall receptacle, while the
chain pin 92
provides an attachment point for a small wall chain to ensure that the wall
unit 16 is not
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misplaced when it is disconnected from the wall receptacle, such as during the
system
maintenance.
[0039] Circuitry comprising each of the bed unit 14 and wall unit 16
includes radio
frequency (RF) and controller components to manage the establishment and
maintenance of the
communications link 22. The RF component is a transceiver for supporting the
wireless
communications link 22. The controller component cooperates with the
transceiver to support
the processes described herein.
[0040] Referring to Figures 6 and 7, the bed interface circuitry 98 of the
bed unit 14 collects
the patient information from the bed sensor 30, as well as the communications
module 46 (Fig.
1), and provides it to the controller 100 for processing. In turn, the bed
unit controller 100, as
well as the wall unit controller 114, manage the establishment, operation, and
status reporting of
the communications link 22, 24, via their respective RF circuitry components,
namely the
transceivers 102, 112, in order to relay the collected patient information
between the units and to
the nurse call system 56 and/or the room transducer 15. An exemplary
embodiment of the
controllers 100, 114 is a model CY8C27443 manufactured by Cypress
Semiconductor
Corporation located at 198 Champion Ct., San Jose, California 95134. An
exemplary
embodiment of the transceiver circuitry 102, 112 is a model XE1203F
transceiver module
manufactured by Semtech Corporation, located at 200 Flynn Road, Camarillo,
California 93012.
Preferably, each of the bed and wall units 14 and 16 includes an internal
antenna 104, 116,
respectively, coupled to the transceiver circuitry 102, 112 for transmitting
the patient information
between the units.
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[0041] When the bed
unit 14 is in its unlinked state and its controller 100 detects a nearby
unlinked wall unit 16, the controller drives the link reminder signal
generator 106 by outputting
an activation signal to the link reminder signal generator, which responds by
generating a link
reminder alarm that can be a sound generated by a transducer 108 and/or a
visual prompt at the
user interface 64. Although in the illustrated embodiment the link reminder
signal generator 106
is external to the controller 100, the generator and the controller may be a
single component. In
the illustrated embodiment, the transducer 108 provides an audio alert and may
be a piezoelectric
13117.7er that emits short chirping sounds, while other embodiments include
visual link reminders
at the interface 64, such as flashing LEDs, as well as combinations of audio,
visual, and other
types of alert indicators. In yet another embodiment, the wall unit 16 also
includes the link
reminder signal generator and transducer circuitry for alerting the health
care personnel of its
unlinked status.
[0042] In order for
the communications link 22 to be a completely wireless connection, the
bed unit 14 includes a local power source such as one or more batteries 110.
Battery operation
enables the unlinked bed unit 14 to operate continuously and without relying
on hospital
personnel to attach a power source. However, external power sources can also
provide power to
the bed unit 14. For example, power can be derived from a power source
primarily intended for
the bed 26. If total power consumption is very low, the bed unit 14 may even
be powered by an
electromagnetic source remote from the unit and the bed in a manner similar to
passive
transponders. When powered by batteries 110, power consumption is minimized by
including a
sleep mode for the electronics wherein the controller 100 periodically directs
the bed unit 14 to
enter a partially powered down state. Unlike the bed unit 14, however, the
wall unit 16 is usually
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fixed in the hospital room and, therefore, has access to the hospital's
primary power resources.
Thus, the wall unit need not require power conservation techniques although it
still may
incorporate them if desired. As illustrated in Figure 7, the wall unit 16
draws power from the
nurse call system power source 55 via a pin connection at its connector
interface 94 (Figure 5).
[0043] To provide for message transmission between the bed and wall
units, the message
format employed by the communications link 22 includes a plurality of message
fields
corresponding to message routing, data payload, and error detection signaling.
In Figure 8, a
message packet for transmission by the communications link 22 is a message
frame 118
comprising a 22 byte sequence preceded by a preamble 120 to allow the
transceiver 102, 112 in
each of the bed and wall units 14 and 16 to lock onto the incoming message
data stream in a
conventional manner. The preamble 120 is a known or expected bit sequence that
the receiving
bed or wall unit 14, 16 discards after locking onto the message stream. Thus,
the receiving bed
or wall unit 14, 16 does not include the preamble 120 in the message decoding,
cyclic
redundancy code (CRC), and message byte count calculations.
[0044] Proceeding down the message byte sequence, message bytes 1 - 4
include a fixed
pattern block 122, which comprises the same four hexadecimal bytes within each
message frame
118. During system testing and maintenance, the fixed pattern block 122
enables a test receiver
to log all message traffic on a given channel without concern for the source
address 126 in the
transmission packet, which is exchanged by the bed and wall units during the
establishment of
the communications link 22. When a health care provider initiates the linldng
process by
pressing the link button 68, 76 at either the bed or the wall unit 14, 16, the
bed unit transmits a
message packet with a Link Request Broadcast Code (LRBC) within the field 124
corresponding
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to bytes 5 through 8 of the message frame 118. Alternatively, when the bed and
wall units 14, 16
are linked, the message field 124 includes a destination address of the bed or
wall unit,
depending on the originating unit, that is the address of the intended
recipient of the message
frame 118. During the setup of the communications link 22, the bed and wall
units exchange
their unique addresses, which correspond to device serial numbers. Similarly,
the message field
126 (bytes 9-12) contains the source address, or serial number, of the
transmitting device. Other
embodiments include exchanging Media Access Control (MAC) addresses between
the units to
designate destination and source addresses among the devices.
[0045] To keep
track of the message exchange and to identify the communicating devices,
the message frame 118 includes a message sequence number counter 128 and a
device type field
130 (bytes 13, 14). The message sequence number counter 128 keeps track of the
message
session number for the corresponding device within the communications link 22.
When the
communications link 22 is established between a bed/wall unit pair, the device
type field 130
identifies each communicating device as a bed or wall unit, respectively. The
device type field
130 also identifies additional device types when the communications link 22
includes other
devices, such as a wall-mounted emergency push button station and/or a pull
cord station for
generating a nurse call signal.
[0046] The status
bytes field 132 (bytes 15-17) relays additional message data and patient
information, such as a nurse call signal indicator, a bed exit alarm
indicator, a bed out alarm
indicator, link reminder signaling, and various link status indicators,
including periodic link
status request or "check-in" signaling between the linked units. The message
type field 134
(byte 18), in turn, includes "Ace indicators sent in response to a successful
receipt of certain
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messages, as well as "Nak" indicators sent in response to messages having CRC
errors identified
by comparing the received message CRC to the transmitted CRC bytes 136 (bytes
19-21).
Message type field 134 also relays link connection commands between the bed
and wall units.
As discussed in more detail in connection with Figure 12 below, the
transmission protocol also
provides advanced collision detection by monitoring for corruption of the last
byte (byte 22),
called the end-of-packet (EOP) or "tail feather" byte 138, in transmission of
Ack messages sent
in response to periodic check-in messages. The tail feather byte 138 is not
used to calculate the
CRC value. Therefore, Ack messages having good CRC values and uncorrupted data
payloads,
but having a corrupted tail feather byte 138, provide an early indication of
collisions of periodic
check-in message sequences between multiple bed/wall unit pairs. Upon
detection of corruption
of the tail feather byte 138, the transmission protocol includes time or
frequency shifting the next
= periodic transmission of check-in or link status messages by a random
delay in order to prevent
data corruption.
[0047] To reduce the overall number of messages exchanged
between the linked bed/wall
unit pairs and, consequently, extend each bed unit's battery life, the message
protocol further
provides for transmission of full frames at all times between both units
within the pair, including
when the message type byte 134 contains an Ack or a Nak indicator. This allows
inclusion of
additional data within the message frames containing the Ack or Nak signaling,
thereby reducing
the need for separate data transmissions.
[0048] The timing diagrams of Figures 9-11 are exemplary
scenarios related to establishing
the communications link 22. Figure 9, for example, depicts a transmission
protocol that results
in successfully establishing the communications link 22, where the health care
provider initiates
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the linldng process by pressing each of the link buttons 62, 76 on the
bed/wall unit pair 14/16
within a predetermined amount of time 140. The timer 140 is set to allow the
health care
provider sufficient time, such as five (5) seconds, to press the link button
on the second unit after
pressing the link button on the first unit. During this time period, the bed
unit 14 transmits a link
request broadcast code (LRI3C) 142, labeled "Link Request BUI" to indicate a
link request from
a first bed unit, and waits to receive an acknowledgment 144, labeled "Ack WW"
to indicate an
acknowledgement from a first wall unit, from a nearby wall unit 16.
[0049] Since the bed and wall units 14, 16 exchange their unique addresses
to establish the
communications link 22, the bed unit is initially unaware of which wall unit
will reply to its link
request. Therefore, when the communications link 22 is between only one wall
unit and one bed
unit, it is desirable to prevent the occurrence of inadvertently cross linking
the pairs of units in
two different rooms 10a and 10b (Figure 1). For example, if the two bed units
14, 18 in the
adjacent hospital rooms 10a, 10b initiate the linking process at about the
same time, there is an
opportunity for each of the units to link to the wall unit in the other room.
Therefore, after
exchanging their unique addresses included in the initial link request
broadcast code and
acknowledgement messages 142, 144, the bed and wall units 14, 16 wait for
another
predetermined duration 146 in Figure 9 to receive link requests or
acknowledgements from other
nearby units, such as the units 18 and/or 20 in the other room in Figure 1, in
order to ensure that
cross linking of two pairs of units has not occurred.
[0050] In one embodiment, the timer 146 is also set to five (5) seconds. If
the timer 146
expires without detection of a link request or an acknowledgement having an
address different
from either of the original addresses within the pair 14, 16, the
communications link is
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established after the bed unit 14 transmits a link confirmation message 148
and receives an
acknowledgement 150 from its corresponding wall unit 16. Otherwise, the link
fails when, prior
to the expiration of the linking timer 146, the wall unit 16 receives a link
request 152 having a
bed unit address different from that in the original link request 142 (Figure
10), or when the bed
unit 14 receives an acknowledgement 154 having a wall unit address different
from that in the
original acknowledgment 144 (Figure 11).
[0051] Instead of establishing one-to-one communication links 22 between
bed and wall
units, the communications link can also be one-to-many in that one of the wall
units 16 can
support communications links 22 to several bed units 14. In this case, when
the health care
provider presses the wall unit's 16 link button, the wall unit sends out a
periodic linking beacon
message and listens for reply messages from one or more nearby bed units 14
once the health
care provider presses their corresponding link buttons. In this scenario, the
wall unit 16 remains
in the linking mode for a predetermined duration, such as 5 seconds, during
which it listens for
bed unit replies. Upon receipt of one or more bed unit reply messages, the
wall unit 16 sends out
link confirmation messages addressed specifically to each of the bed units 14
that replied,
thereby forming multiple bed/wall unit pairs 14, 16, where all of the
communications links 22
have a common wall unit and a unique bed unit. In this embodiment, to prevent
cross linking the
bed units 14 with more than one wall unit, such as when multiple wall units 16
are located in
adjacent hospital rooms, each of the bed units 14 fails the linking process if
it receives linking
beacon messages from more than one wall unit 16.
[0052] Once the bed and wall units 14, 16 are linked, the units
periodically exchange check-
in message sequences in order to check the integrity of the communications
link 22 between the
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units. When multiple linked pairs of units are in proximity, such as when a
bed/wall unit pair 14,
16 in hospital room 10a is adjacent to another linked bed/wall unit pair in
room 10b, each pair of
units undergoes its own periodic exchange of check-in message sequences, as
illustrated in
Figure 12.
[0053] Either the bed unit 14 or the wall unit 16 may originate the
periodic check-in message
transmissions, though it is preferable in this embodiment for the bed unit to
initiate all
communications. Since the bed unit 14 is preferably battery operated, its
transceiver circuitry
102 is temporarily powered down to save battery power after its communications
link 22 is
established. In the absence of other transmissions, such as bed exit and/or
bed out alarms, the
controller 100 of each bed unit 14 periodically wakes up the transceiver
circuitry 102 to ensure
the communications link 22 is alive at the other unit by sending a check-in
message 156, 158
(Figure 12) to its corresponding wall unit 16 and waiting for the subsequent
acknowledgement
(Ack) message 160, 162 from its wall unit 16.
[0054] There is a tendency for the endpoints of the periodic check-in and
Ack message
transmissions in one link 22 to gradually drift in time with respect to the
same signals in another
link due to inherent differences in each unit's timing circuitry. This gradual
drift 164 in the
check-in message transmissions, for example, in a communications link 22 may
result in a
message collision 166 due to a temporal overlap between the end of one of the
periodic check-in
transmission sequences 168, 170 for one pair and the beginning of a
corresponding check-in
transmission sequence 172, 174 for another co-channel pair. Therefore, the
message protocol
provides advanced collision detection by monitoring for corruption of the end-
of-packet (FOP)
or "tail feather" byte 138 (Figure 8), in transmission of messages from the
wall unit 16.
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[0055] Specifically, when the bed unit 14 receives an Ack message 170 from
the mated wall
unit 16 with good CRC but with a corrupted EOP byte 138, the message protocol
assumes the
leading edge 176 of another check-in message 172, belonging to a different
communications link
22, is beginning to overlap the trailing edge 178 of the Ack message 170.
Since all linked bed
units 14 normally transmit the initial check-in messages at a fixed period 180
in Figure 12, there
is a high probability that the collision will reoccur during the next periodic
transmission of the
check-in message sequences in each of the links 22. To prevent reoccurrence of
collisions, the
bed unit 14 that detected the corrupted EOP byte 138 adds a one-time random
delay interval 182
to its next check-in period 180, thereby permanently shifting the nominal time
slot of its periodic
check-in message sequences with respect to another bed/wall unit pair. After
the random delay
182, transmissions of check-in message sequences 184, 186 and 188, 190
continue according to
the original check-in period 180. While the illustrated embodiment allocates a
single byte 138
for the EOP marker, other embodiments include allocating a plurality of EOP
bytes at the tail
end of the message frame 118 (Figure 8) in order to enhance the ability to
detect another
impending collision before the data payload is affected.
[0056] In the scenario illustrated in Figure 12, the collision 166
corrupted the data payload
within the leading edge of the check-in message 176, thereby resulting in a
CRC error at the
corresponding wall unit. To indicate a CRC error, the wall unit 16 receiving
the corrupted
check-in message 176 transmits a Nak message 174. Upon receipt of the Nak
message 174, the
bed unit 14 within this pair initiates a retry transmission of the check-in
message 192 after a
random delay 194. In this case, the bed unit receives an Ack message 196,
indicating a
successful receipt of the check-in message 192 by its corresponding wall unit
16. In this
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illustrated embodiment, unlike the situation in which a message is received
having good CRC
but corrupted EOP or tail feather byte 138, which provide an early indication
of a collision prior
to data corruption, when the bed unit 14 receives a transmission having bad
CRC or including a
Nak message, it resends the check-in message after a random delay 194. In this
case, however,
the bed unit 14 does not add the random delay 194 to the next check-in message
period 180. In
other words, the bed unit 14 still transmits the next check-in message 198
after a check-in period
180 referenced from the corrupted check-in message 172. In this case, the bed
unit does not
change its nominal time slot for subsequent check-in message transmissions
because the CRC
error also could have been caused by reasons other than a collision with
another bed/wall unit
pair's periodic check-in message sequence, such as due to a signal fade.
[0057] In addition to detecting gradual collisions by monitoring corruption
of the end-of-
packet byte, the communications link 22 is also managed so that the bed unit's
nominal time slot
for transmission of periodic check-in messages is monitored for sudden
collisions. The
monitoring detects successive occurrences of check-in message retries followed
by successful
receipt of Ack messages. This method of check-in message time slot management
detects a
sudden and recurring collision of check-in message sequences that occur after
one of the
bed/wall unit pairs resets its check-in message period 180 due to transmission
of nurse call or
bed exit signaling. Specifically, a collision between the check-in messages of
two nearby bed
units results in a bad CRC to either or both pairs of units. In this case,
either or both bed units 14
in the two communications links 22 receive a Nak message from their
corresponding wall units
or do not receive any reply at all. This prompts the bed unit 14 to retry the
transmission of the
check-in message after a random delay. If the second transmission of the check-
in message is
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successful, the bed unit 14 receives an Ack message from the wall unit 16 in
response. The
combination of first-try failure of the check-in sequence and first-resend
success is a strong
indication of colliding bed units 14 since other possible causes of packet
corruption are not likely
to appear and disappear quickly. Therefore, each bed unit 14 keeps a count of
successive
occurrences of the combination of successive first-try failures followed by
first-resend successes.
If this count reaches a predetermined limit, such as 3 such combinations for
example, the bed
unit makes a permanent shift in its nominal check-in message sequence time
slot by adding a
random delay to its next periodic check-in message transmission.
[0058] In response to detection of check-in message sequence collisions
among multiple
communications links 22, whether via detection of EOP byte corruption or via
monitoring the
described combination of successive first-try check-in message failures
followed by first-resend
successes, at least one of the bed/wall unit pairs whose communications link
22 is colliding
initiates a change in its operating channel frequency to avoid future
collisions.
[0059] Turning to Figure 13, should a communications link 22 fail or the
responsible hospital
personnel forgets to link the two nearby bed and wall units 14, 16, one of the
unlinked units
sends out periodic link reminder messages to the other nearby unlinked unit(s)
on each of the
multiple operating channels and listens for corresponding acknowledgement
(Ack) messages
from one or more other unlinked units. Preferably, the bed unit 14 sends out
the link reminder
messages 200 ¨206 on each of the system operating channels and logs the wall
IDs, or wall unit
serial numbers, from which it receives acknowledgement replies 208 ¨212 in the
memory of its
controller 100. Since the bed unit 14 is battery operated where its
transceiver circuitry 102
periodically enters an idle sleep mode, the bed unit includes a periodic
reminder timer 216 to
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wake up its transceiver circuitry and begin the link reminder message cycle
220. In this
embodiment, the system operates on 3 channels, therefore during each link
reminder message
cycle 220 the bed unit 14 transmits the link reminder messages 200 ¨ 204 on
each operating
channel because the bed unit 14 is not aware of the current operating channel
of a nearby
unlinked wall unit. Transmission of link reminder messages on multiple
operating channels also
takes into account possible collisions with other nearby bed units in the link
reminder mode.
Pursuant to each transmission of link reminder messages 200 ¨ 206, the bed
unit 14 listens for
incoming acknowledgement messages 208 ¨ 212 for a corresponding listen period
214, which, in
one embodiment, is set to 100 milliseconds. Once the full 3 channel cycle 220
is complete, the
bed unit resumes transmitting additional link reminder messages 206 during
another link
reminder message cycle 220, which begins when the periodic reminder cycle 216
expires. In
embodiments, the periodic reminder cycle 216 is set to 45 and 60 seconds,
respectively. When
the bed unit 14 detects a second acknowledgment message 212 originating from
the same wall
ID or serial number as one of the previous acknowledgments 208, the bed unit
14 activates the
link reminder alert 218 to prompt the caregiver to initiate the linking
process.
[0060] Figures 14¨ 19 illustrate the detailed operation of embodiments of
various operating
states of the system in accordance with the invention. Specifically, Figure 14
is a state diagram
generally illustrating the transition between various operational states of
each bed/wall unit pair,
while Figures 15 - 19 are flowcharts illustrating the operation of each of the
states in Figure 14 in
more detail. Figures 15 - 19 simultaneously depict operation of the bed and
wall units by
representing the steps associated with the bed unit on the left side, while
representing the steps
associated with the wall unit on the right side of each figure. It should be
noted that the steps
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referenced throughout Figures 15 -19 are performed by programmable firmware of
each unit's
controller 100, 114 (Figures 6 and 7).
[0061) As illustrated in Figure 14, after going through the linking process
state 222, the
linked bed/wall unit pair enters the linked idle state 224 where the bed unit
enters into the linked
idle sleep mode by temporarily powering down its transceiver circuitry to
extend the battery life
when no patient information is transmitted, while the wall unit enters into a
linked idle receive
mode to continuously listen for messages from one or more of its associated
bed units. When the
linked bed/wall unit pair needs to communicate patient information, such as
bed exit alarms or
bed out calls, the units enter the call message state 228 to relay the
information to the nurse call
system. Upon completion of the call message transmissions, the units reenter
the linked idle
state 224. Similarly, during periodic check-in message sequences, the linked
unit pair enters the
check-in message state 226 and returns to the linked idle state 224 when check-
in message
transmission is successful. However, when the communications link 22, 24 is
lost or when the
linking process fails, the bed and wall units enter the unlinked idle mode,
which includes
periodic link reminder alerts to prompt the health care provider to
(re)establish the
communications link 22, 24.
[0062] Turning to Figure 15, detailed operation of an embodiment of the
linking process
state 222 is illustrated, wherein the bed unit initially powers down its
transceiver circuitry in its
unlinked idle sleep mode 232, while the wall unit is in the unlinked idle
receive mode 234 for
receiving link reminder messages from the bed unit. When the health care
provider activates the
bed unit's link button, the bed unit begins transmitting link request (LRBC)
messages for a
predetermined duration, such as five (5) seconds, step 236. Similarly, in step
238, when the
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health care provider activates the wall unit's link button, the wall unit
listens for the bed unit's
link request messages for the five (5) second period. It should be noted that
after transmitting a
link request message, the bed unit switches to receive mode, for example for
70 milliseconds, to
wait for an Ack message from a receiving wall unit, step 240. If, in step 242,
the wall unit
receives a link request message with good CRC, in step 244, the wall unit
transmits an Ack with
random delay to the bed unit and switches to receive mode for another five
seconds to wait for
additional link requests from nearby bed units undergoing the linking process.
As discussed
above in connection with Figures 9-11, detection of additional bed/wall unit
pairs simultaneously
undergoing the linking process with the current pair, as well as the
associated link failure,
prevents unintended cross linking of the units located in adjacent rooms.
Alternatively, in step
246, when the wall unit receives a link request message with a CRC error, or,
in step 248, when
the wall unit does not receive any link request messages from the bed unit,
the wall unit
continues to listen, in step 250, for the bed unit's link requests for the
duration of its link button
activation timer 238.
[0063] Correspondingly, in step 252, when the bed unit receives a first Ack
message from a
given wall unit, it includes the associated wall ID or serial number in all
subsequent link request
messages, which the bed unit continues to send out on all operating channels
for another five
seconds. Alternatively, in step 254, the bed unit does not yet receive any
acknowledgments from
the nearby wall unit(s).
[0064] If, in step 256, the wall unit receives link request messages that
include its ID or serial
number in the destination address field, it continues listening for link
request messages
originating from bed unit IDs other than the source of original link request
message until the
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expiration of the linking period timer 244. Specifically, in step 258, if the
wall unit receives a
link request, containing its ID in the destination field, from a second bed
unit ID designated as
the source device, the link attempt immediately fails and the wall unit enters
the unlinked idle
receive mode, step 262, to prevent unintended cross linking of multiple
bed/wall unit pairs.
Alternatively, in step 260, if the wall unit receives link request messages
that do not contain its
ID in the destination device field, the wall unit continues sending Ack
messages until the 5
second linking period timer 244 expires. In step 264, at the end of the five
second linking period
timer 244, the wall unit listens for an additional second for a link
confirmation message from the
original bed unit and, in step 266, sends the corresponding acknowledgement
message to
establish the communications link and enters the linked idle receive mode,
step 268. Otherwise,
if the wall unit does not receive the final link confirmation message, step
270, the wall unit
= reenters the unlinked idle receive mode in step 272.
[0065] As with the wall unit, if, in step 274, the bed unit
receives an Ack message from a
second wall unit ID designated as the source device, the link attempt
immediately fails and the
bed unit enters an unlinked idle sleep mode, step 276, to prevent unintended
cross linking of
multiple bed/wall unit pairs. Otherwise, in step 278, the bed unit
continuously transmits link
request messages three (3) times on each of the operating channels until the
expiration of the five
(5) second timer 252. At the end of the five (5) second timer 252, the bed
unit transmits a final
link confirmation message and awaits a corresponding Ack message from the wall
unit, step 280.
To ensure successful completion of the linking process, the bed unit is able
to retry transmission
of the final link confirmation message until it receives an acknowledgement
from the wall unit.
Once the bed unit receives the acknowledgement to the link confirmation
message, step 282, the
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bed unit enters the linked idle sleep mode in step 284 where it temporarily
powers down its
transceiver circuitry until either receiving patient information, such as bed
out and bed exit
alarms, or until the next periodic transmission of check-in messages.
Otherwise, in steps 286,
288, the bed unit enters the unlinked idle sleep mode where it initiates
periodic link reminder
messages and link reminder alerts to prompt the health care provider to
reinitiate the linking
process with a nearby unlinked wall unit.
[0066] Turning to Figure 16, detailed operation of an embodiment of the
linked idle state 224
is illustrated. The bed/wall unit pair enters the linked idle state 224 after
successful completion
of the linking process and pursuant to successfully relaying the patient
information between the
units, including the nurse call signaling initiated by the patient, bed exit
and bed out alarms, as
well as periodic check-in or link status message transmissions, steps 290 ¨
300. In this case, the
bed unit remains in a linked idle sleep mode 302 wherein it temporarily powers
down its
transceiver circuitry until it is time to transmit periodic check-in messages
to the wall unit, steps
304, 306, or the bed unit needs to relay the patient information to the wall
unit, for example
when the bed unit detects that the patient activated a nurse call button via
the siderail
communications module, steps 308, 310.
[0067] Correspondingly, the wall unit remains in the idle receive mode 312
where it listens
for bed unit transmissions and subsequently enters the check-in message state,
steps 314, 316, or
the call message state, steps 318, 320, upon receipt of periodic check-in
messages or other
patient information from the wall unit. It should be noted that, in step 322,
the wall unit
monitors noise on its operating channel in order to detect and evade
interference from other
bed/wall units, as well as from other devices occupying the same spectrum,
such as cordless
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phones operating in Direct Sequence Spread Spectrum mode, for example.
Therefore, in this
embodiment, if the wall unit detects noise after a few consecutive noise
readings, it moves to the
next operating channel and switches to receive mode, while waiting for the
linked bed unit to
attempt a new transmission, accumulate a plurality of Missed Wall Unit events,
and rejoin the
wall unit on the new channel. Finally, when the health care provider activates
the unlink button
at either unit, the bed unit enters the unlinked idle sleep mode, where it
periodically wakes up its
transceiver circuitry to send out the link reminder messages to nearby
unlinked wall units, while
the wall unit enters the unlinked idle receive mode to listen for the bed
unit's link reminder
transmissions, steps 324 ¨ 330.
[0068] Turning to Figure 17, detailed operation of an embodiment
of the check-in message
state 226 is illustrated. In this embodiment, when the linked bed/wall units
are in their respective
linked idle modes, steps 332, 334, the bed unit periodically transmits check-
in, or link status,
=
messages to the associated wall unit and temporarily switches to receive mode
in order to await
for corresponding acknowledgments from the wall unit, steps 336, 338. In an
embodiment, the
bed unit periodically transmits the check-in messages every 45 seconds and
thereafter switches
to the receive mode for a 70 millisecond duration.
[0069] If the wall unit receives a check-in message with good
CRC value, the wall unit
transmits an Ack message and, in this embodiment, listens for another 200
milliseconds for any
incoming retry transmissions from the bed unit prior to completing the check-
in process by
returning to the linked idle receive mode until the onset of the next check-in
message period in
45 seconds, steps 340 ¨ 344. Alternatively, if the wall unit receives a check-
in message having a
CRC error, the wall unit replies with a Nak message and listens for subsequent
retry
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transmissions by the bed unit, steps 346, 348. In yet another scenario, if the
wall unit does not
yet receive the check-in message, whether due to poor RF conditions or
otherwise, the wall unit
remains in the linked idle receive mode to await the incoming check-in message
transmission,
step 350. During the check-in message state, the wall unit also monitors the
current channel for
noise conditions and, upon detecting presence of RF noise, the wall unit
changes the operating
frequency, step 352.
[0070] When the bed unit receives an Ack message indicating successful
receipt of the
check-in message by the wall unit, the bed unit returns to the linked idle
sleep mode until the
next check-in message period, steps 354, 356. Alternatively, if the bed unit
receives a Nak
message from the wall unit, indicating a CRC error in a check-in message
received by the wall
unit, the bed unit retries the transmission of the check-in message after a
random delay after the
receipt of the Nak message and awaits for a successful acknowledgement, steps
358, 360.
Further, if the bed unit does not receive any reply messages from the wall
unit, the bed unit
retries transmitting another check-in message and listens for wall unit's
replies, steps 362, 364.
[0071] In this embodiment, upon transmitting three (3) consecutive
acknowledgements to the
same bed unit within the check-in period, the wall unit changes to another
operating channel,
step 366, since repeated retries of check-in message transmission by the bed
unit indicate a
reception problem at the bed unit. Similarly, if the bed unit transmits three
(3) consecutive
check-in message retries without receiving an Ack from the wall unit, the bed
unit changes to
another operating channel to retry the transmission since the wall unit
already moved to a
different channel after transmitting three (3) consecutive Ack messages missed
by the bed unit,
step 368. Signal degradation at the wall unit is the likely reason for the
wall unit transmitting 3
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consecutive Nalc messages to the same bed unit within the same check-in
message period without
receiving a check-in message with a good CRC value. In this case, the wall
unit moves to
another operating channel and switches to receive mode to listen for check-in
messages from the
bed unit once it follows the wall unit to the new channel, step 370. The wall
unit also moves to
another channel if it is overdue for receiving the next periodic check-in
message transmission,
such as when the periodic check-in timer has expired by two (2) seconds, step
371.
[0072] In step 372, the bed unit receives 3 consecutive Nak messages and
follows the wall
unit by moving to another one of the operating channels to retry the
transmission of check-in
messages. The bed unit repeats transmission on each new channel until it fmds
the wall unit's
channel by receiving an acknowledgment message. Otherwise, the bed unit
retries transmitting
the check-in messages on different channels until some predetermined time from
last receiving
an Ack message. In one embodiment, the communications link fails and the bed
unit enters the
unlinked idle sleep mode when 60 seconds elapse from receipt of the last Ack
message, steps
374, 376. Similarly, the wall unit listens for bed unit's check-in messages
for one (1) second on
each of the operating channels until the expiration of the one minute timer.
Thereafter, the wall
unit enters the unlinked idle receive mode, steps 378, 380.
[0073] As discussed above in connection with Figure 12, to provide for
early detection of
check-in message collisions between check-in message sequences of multiple
bed/wall unit pairs
and prevent data corruption, the bed unit shifts its nominal time slot for
periodic transmission of
check-in messages by adding a random delay to the next scheduled check-in
message
transmission when it detects corruption of the end-of-packet byte in
acknowledgement messages
having good CRC values, step 382. Additionally, the bed unit shifts its
nominal time slot for
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transmission of periodic check-in messages by monitoring for successive
occurrences of check-
in message retries followed by successful receipt of Ack messages. This method
of check-in
message time slot management detects a sudden and recurring collision of check-
in message
sequences, which occur after one of the bed/wall unit pairs resets its check-
in message timer due
to transmission of nurse call or bed exit signaling. In this embodiment, if
the bed unit receives 3
consecutive Ack messages in response to three (3) consecutive retries of check-
in message
transmissions, the bed unit similarly shifts its nominal check-in message time
slot by adding a
random delay to the next periodic check-in message transmission time, step
384.
[0074] Turning to
Figure 18, detailed operation of an embodiment of the call message state
228 is illustrated. In the illustrated embodiment, the linked bed/wall unit
pair relays patient-
initiated nurse call signaling to the hospital nurse call system, however it
should be understood
that the following steps also apply to transmission of other patient
information, including bed out
and bed exit alerts. While the linked bed/wall unit pair is in the linked idle
mode, steps 386, 388,
the bed unit detects activation of the nurse call button and transmits the
nurse call message to the
associated wall unit, steps 390, 392.
[0075] If the wall
unit receives the nurse call signal with good CRC, the wall unit places a
call on the nurse call system, transmits an Ack message, and listens for
another 200 milliseconds
for any incoming retry transmissions from the bed unit in case the bed unit
does not receive the
Ack message due to a signal reception problem, steps 394, 396. If the wall
unit does not receive
a retry transmission from the bed unit, the wall unit completes the
transmission process by
returning to the linked idle receive mode, steps 398. Alternatively, if the
wall unit receives a
nurse call message having a CRC error, the wall unit replies with a Nak
message and listens for
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subsequent retry transmissions by the bed unit, steps 400, 402. If, however,
the wall unit does
not yet receive any message, whether due to poor RF conditions or otherwise,
the wall unit
remains in the linked idle receive mode, step 404. While in the call message
state, the wall unit
also monitors the current channel for noise conditions and, upon detecting
presence of RF noise,
changes the operating frequency, step 406.
[0076] When the bed unit receives an Ack message, the bed unit returns to
the linked idle
sleep mode until either the next check-in message period or the next
transmission of patient
information between the linked units, steps 408, 410. Alternatively, if the
bed unit receives a
Nak message from the wall unit, indicating a CRC error, the bed unit retries
the transmission of
the nurse call message with a random delay after the receipt of the Nak
message and awaits for a
successful acknowledgement, steps 412, 414. Further, if the bed unit does not
receive any reply
messages from the wall unit, the bed unit retries transmitting another nurse
call message and
listens for the wall unit's replies, steps 416, 418.
[0077] Upon transmitting three (3) consecutive acknowledgements to the bed
unit, the wall
unit changes to another operating channel, step 420, since repeated retries by
the bed unit
indicate that it is having a reception problem. Similarly, if the bed unit
transmits three (3)
consecutive retries without receiving an Ack from the wall unit, the bed unit
changes to another
operating channel since the wall unit already moved to a different channel
after transmitting
three (3) consecutive Ack messages missed by the bed unit, step 422. Signal
degradation at the
wall unit is the likely reason for the wall unit transmitting three (3)
consecutive Nak messages to
the same bed unit without receiving a message with a good CRC value. In this
case, the wall
unit moves to another operating channel and switches to receive mode to listen
for retry
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messages from the bed unit when it follows the wall unit to the new channel,
step 424. Thus, in
step 426, the bed unit follows the wall unit when it receives three (3)
consecutive Nak messages
and moves to another one of the operating channels to retry the transmission.
The bed unit
repeats transmission on each new channel until it finds the wall unit's
channel by receiving an
acknowledgment message. Otherwise, the bed unit retries transmitting the
messages on different
channels until some predetermined time from last receiving an Ack message. In
one
embodiment, the communications link fails and the bed unit enters the unlinked
idle sleep mode
when 60 seconds elapse from receipt of the last Ack message, steps 428, 430.
Similarly, the wall
unit listens for the bed unit's message for one (1) second on each of the
operating channels until
the expiration of the one minute timer. Thereafter, the wall unit enters the
unlinked idle receive
mode, steps 432, 434.
[0078] Turning to
Figure 19, detailed operation of an embodiment of the unlinked idle state
230 is illustrated. The bed and wall units enter the unlinked idle state
either due to failure of the
communications link between a bed/wall unit pair, failure of the linking
process, or when the
health care provider activates the unlink button on one of the units, steps
436 ¨ 446. While in the
unlinked idle sleep mode, the bed unit completes periodic link reminder
cycles, wherein it sends
out a link reminder message on each of the operating channels and waits for
acknowledgments
from nearby unlinked wall units, steps 448, 450. Since an unlinked bed unit is
not aware of the
nearby wall unit's current operating channel, the bed unit repeats the link
reminder cycle on each
operating channel after a predetermined period. In embodiments, the bed unit
repeats the link
reminder cycle every 45 or 60 seconds. When the wall unit receives the link
reminder message
with correct CRC value, it responds with an Ack message, steps 452, 454.
Alternatively, if the
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wall unit receives a link reminder message with a CRC error, or when the wall
unit does not yet
receive any link reminder messages, the wall unit remains in the idle receive
mode, steps 456 ¨
460. While in the idle receive mode, the wall unit scans the current channel
for noise and moves
to another operating channel if it detects interference from nearby bed or
wall units and/or other
devices sharing its spectrum, step 462.
[0079] Upon receipt
of the Ack messages from one or more nearby unlinked wall units, the
bed unit logs each wall unit's unique identifier, which in this embodiment is
the device serial
number, in a list of wall IDs, step 464. If the bed unit is not in vicinity of
an unlinked wall unit,
it does not receive any Acks, step 466. After logging the wall IDs associated
with the incoming
Ack messages for 100 milliseconds, the bed unit moves to another channel to
transmit the next
link reminder message, step 468. If, in steps 470 ¨ 476, the caregiver decides
to activate the
units' respective link buttons, both units transition to the linking process
state 222. In steps 478,
480, the wall unit continues to respond with acknowledgement messages upon
receipt of link
reminders with correct CRC values. Otherwise, in step 482, the wall unit
remains in the idle
receive mode. When the bed unit receives two consecutive acknowledgments from
the wall ID
that is already on its wall ID list 464, the bed unit activates a link
reminder alert to prompt the
health care provider to initiate the linking process of the two nearby units,
step 484. In this
embodiment, the link reminder alert is an audio alarm, such as a short chirp.
Other embodiments
include using visual alerts, such as flashing one or more LEDs. If the health
care provider
wishes to deactivate the link reminder alert, the health care provider
activates the bed unit's
unlink button, which moves the list of wall IDs to a silence list for a
predetermined duration,
such as one hour, step 486. Consequently, the bed unit does not sound the link
reminder alert if
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it subsequently receives acknowledgements from wall unit IDs already on the
silent list, step
488.
[0080]
[0081] The use of the terms "a" and "an" and "the" and similar referents
in the context of
describing the invention (especially in the context of the following claims)
are to be construed to
cover both the singular and the plural, unless otherwise indicated herein or
clearly contradicted
by context. The terms "comprising," "having," "including," and "containing"
are to be
construed as open-ended terms (i.e., meaning "including, but not limited to,")
unless otherwise
noted. Recitation of ranges of values herein are merely intended to serve as a
shorthand method
of referring individually to each separate value falling within the range,
unless otherwise
indicated herein, and each separate value is incorporated into the
specification as if it were
individually recited herein. All methods described herein can be performed in
any suitable order
unless otherwise indicated herein or otherwise clearly contradicted by
context. The use of any
and all examples, or exemplary language (e.g., "such as") provided herein, is
intended merely to
better illuminate the invention and does not pose a limitation on the scope of
the invention unless
otherwise claimed. No language in the specification should be construed as
indicating any non-
claimed element as essential to the practice of the invention.
[0082] Preferred embodiments of this invention are described herein,
including the best
mode known to the inventors for carrying out the invention. Variations of
those preferred
embodiments may become apparent to those of ordinary skill in the art upon
reading the
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foregoing description. The inventors expect skilled artisans to employ such
variations as
appropriate, and the inventors intend for the invention to be practiced
otherwise than as
specifically described herein. Accordingly, this invention includes all
modifications and
equivalents of the subject matter recited in the claims appended hereto as
permitted by applicable
law. Moreover, any combination of the above-described elements in all possible
variations
thereof is encompassed by the invention unless otherwise indicated herein or
otherwise clearly
contradicted by context.
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