U.S. patent application number 11/115711 was filed with the patent office on 2005-09-22 for power efficient channel scheduling in a wireless network.
This patent application is currently assigned to Microsoft Corporation. Invention is credited to Adya, Atul, Bahl, Paramvir, Padhye, Jitendra D..
Application Number | 20050208958 11/115711 |
Document ID | / |
Family ID | 28790901 |
Filed Date | 2005-09-22 |
United States Patent
Application |
20050208958 |
Kind Code |
A1 |
Bahl, Paramvir ; et
al. |
September 22, 2005 |
Power efficient channel scheduling in a wireless network
Abstract
A method and system for optimizing channel access scheduling for
multiple wireless computing devices over a wireless network
improves channel access efficiency with respect to a primary
channel. An access point, or host computer, includes a host
transceiver for receiving control information from the wireless
computing devices over a low power channel. Upon receiving the
control information, the access point applies a scheduling
algorithm to schedule channel access for the wireless computing
devices to transmit data over the primary communication channel.
The wireless computing devices include a low power radio for
receiving scheduling information via the low power channel during
idle periods. When the scheduling information is received, the
wireless computing device activates its primary channel network
interface components to communicate data through the primary
channel. When the computing device is idle, the device is
configured to power down all of its components with the exception
of the circuitry required to power the low power channel. As such,
the low power channel is maintained in an active state for
receiving scheduling information, such as an access schedule,
during both idle and non-idle periods.
Inventors: |
Bahl, Paramvir; (Sammamish,
WA) ; Adya, Atul; (Bellevue, WA) ; Padhye,
Jitendra D.; (Kirkland, WA) |
Correspondence
Address: |
Microsoft Corporation
c/o WOLF, GREENFIELD & SACKS, PC
FEDERAL RESERVE PLAZA
600 ATLANTIC AVENUE
BOSTON
MA
02210-2206
US
|
Assignee: |
Microsoft Corporation
Redmond
WA
|
Family ID: |
28790901 |
Appl. No.: |
11/115711 |
Filed: |
April 27, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11115711 |
Apr 27, 2005 |
|
|
|
10124721 |
Apr 17, 2002 |
|
|
|
Current U.S.
Class: |
455/509 |
Current CPC
Class: |
H04W 52/0219 20130101;
H04W 72/14 20130101; Y02D 70/142 20180101; H04W 88/06 20130101;
H04W 84/12 20130101; Y02D 30/70 20200801; H04W 52/0216 20130101;
H04W 52/0241 20130101; Y02D 70/1226 20180101; H04W 88/04 20130101;
H04W 52/46 20130101 |
Class at
Publication: |
455/509 |
International
Class: |
H04B 007/00 |
Claims
1. A hand-held device for acting as a first node on a wireless
network comprising: a high power radio component that communicates
data on a primary wireless channel, wherein the data omits
scheduling information related to scheduling access to the primary
wireless channel; and a low power radio component that communicates
scheduling information related to scheduling access to the primary
wireless channel to a second node on the wireless network.
2. The device according to claim 1 wherein the scheduling
information is derived based at least in part on information
selected from the group consisting of a number of packets waiting
in a queue for transmission over the primary channel, packet
priority information, and data packet transmission deadline
information.
3. The method according to claim 1 wherein the secondary channel is
a low frequency channel having a carrier frequency less than that
of the primary channel.
4. The method according to claim 1 wherein the primary channel
comprises an 802.11 based communication channel.
5. A network interface card comprising: an first interface to a
first wireless channel; and a second interface to a second wireless
channel.
6. The network interface card according to claim 5, wherein the
first interface consumes more power to transmit a bit over the
first channel than the second interface consumes to transmit a bit
over the second channel.
7. The network interface card according to claim 6, wherein the
first channel has a carrier frequency that differs from a carrier
frequency of the second channel.
8. An operating system embodied in a computer-readable medium in
the form of computer-readable instructions for performing a method
comprising: interfacing a host handheld device to a first network
for transmitting and receiving data over the first wireless
network; and interfacing the host handheld device to a second
network for transmitting and receiving scheduling information over
the second wireless network, wherein the scheduling information
comprises information usable to schedule access of the host
handheld device to the first wireless network.
9. The operating system according to claim 8, wherein the first
wireless network uses a higher power wireless signal than the
wireless signal used by the second wireless network.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates generally to wireless
computing devices, and more particularly, to power efficient
channel access scheduling for wireless computing devices using
multiple radios.
BACKGROUND OF THE INVENTION
[0002] Many wireless computing devices, such as laptop computers,
personal digital assistant devices, etc., may act as client devices
in a wireless networking environment. Often these multiple clients
all communicate via the network through shared radio frequency
channels to a shared access point. However, when a large number of
such client devices attempt to access the network, this sharing of
network access points often leads to congestion and a wasting of
bandwidth. Congestion often leads to collisions in the channel
between data signals and hence to delay.
[0003] To overcome these challenges, various control techniques
have been implemented with respect to wireless networks to aid in
scheduling to avoid collisions. For example, clients may engage in
listen-before-transmit ("LBT") mechanisms, such as the CSMA-CA
channel access mechanism, vying for space in the shared channel
before transmitting. LBT techniques are a type of distributed
coordinated function. CSMA-CA is a particular Ethernet LAN access
method. However, with all LBT schemes, if one client device is
currently transmitting signals (i.e. data packets) in the channel,
other senders are forced to back off and wait a random amount of
time before attempting access again. Additionally, even if the
client devices detect that the network is free, two such devices
may access the channel at exactly the same time, causing a signal
collision. When this type of collision is detected, both client
devices are forced to back off and wait a random amount of time
before attempting transmission again. While the client devices are
waiting, channel bandwidth is wasted, packet transmission is
delayed, and battery power on the client machine is wasted.
[0004] Other mechanisms exist for aiding in scheduling and avoiding
collision between data signals over a shared channel. Another
example is a point-coordinated function ("PCF"), which repeatedly
polls the client devices in order to avoid collisions of signals.
However, while PCF techniques avoid the constant back and forth
between the competing data signals, the constant polling on the
primary channel wastes a large amount of bandwidth, thus making
this technique highly inefficient.
[0005] While current wireless channel access techniques do produce
collision avoidance, they also waste bandwidth on the primary
channel used to send data packets because these techniques use the
channel both to transmit control and scheduling information and to
send useful data. Distributed coordinated functions, such as
CSMA-CA, are further inefficient for real-time data because of the
forced waiting period. Real-time audio data may no longer be
useful, or sufficient, after a forced delay, such as a
100-millisecond delay. Additionally, there is no guarantee of
channel access by any of these techniques and there is no mechanism
to assure that high priority data signals are transferred in a
timely manner.
[0006] However, if the access point knows the exact state of every
client it is servicing (e.g. number of packets pending in the
queue, the packets deadlines, and packet priorities), it can
schedule each client independently on the channel. While
researchers have attempted to build true work conserving fair
queuing algorithms based upon this premise, these algorithms have
not been truly work conserving because part of the bandwidth on the
channel is used up in transmitting control information to the
scheduler and in many cases the media-access control (MAC) protocol
has to be changed. Therefore, even with such techniques bandwidth
is wasted.
[0007] Additionally, while largely avoiding signal collisions,
these techniques cause inefficient use of power because they often
use a high-powered channel to send control data in addition to
useful data. A particular component of a wireless device that
consumes a significant amount of power is the network interface
card (NIC), which handles the wireless transmission and reception
of network communication data. It has been estimated that on
average, about 20% of the total power available to a wireless
device is dissipated as a result of the connection of a NIC, or
other wireless LAN interface component. This phenomenon is due to
the fact that the NIC and wireless device must be in a constant
"listening" state in order to receive and transmit data via the
network. Since the amount of power a battery can provide is rather
limited, minimizing the power consumption of a mobile device in
order to extend its operation time is an important consideration in
the design of battery operated wireless devices, and any
communication systems involving such devices.
SUMMARY OF THE INVENTION
[0008] To address the challenges described above, a method and
system are disclosed for power efficient channel scheduling of
wireless client devices in a wireless network using multiple
radios. This method and system lead to optimum use of channel
bandwidth and power in wireless computing devices. Therefore, true
work conserving algorithms can be implemented. Such wireless
computing devices include, but are not limited to, personal data
assistants ("PDAs"), cellular phones, and laptop computers having
network interface capabilities.
[0009] In accordance with an embodiment of the invention, a
wireless computing device enables a low power control channel to
exchange information including control information for a network
interface card (NIC), and other power consuming components of the
computing device, with a host transceiver, referred to as a
smartbrick. Initially, the low power transceiver registers with the
host transceiver, such as a host transceiver located at a network
wireless access point. The low power transceiver operated by the
wireless computing device then sends control information data
signals to the host transceiver. This information may be, but is
not limited to, state information, the number of data packets in a
queue, the packet priority, and/or packet deadline. The host
transceiver then responds by transmitting scheduling information
back to the low power transceiver. This scheduling information may
include, among other things, channel access information.
[0010] Prior to receiving scheduling information from a host
transceiver component, the high power wireless network interface
components, such as associated with an ordinary wireless NIC, are
idle. Idle periods are periods when a low power state of operation
is employed by the wireless computing device, or periods when no
substantive network activity (e.g., sending or receiving of data)
is being engaged in by the wireless computing device via its high
frequency communication channel (e.g., IEEE 802.11 based channel).
After receiving the scheduling information on the low power control
channel, the full power NIC and necessary circuitry are
automatically activated consistent with the scheduling information.
For example, in one embodiment, upon receiving channel access
information, such as a message that the channel is free for
transmission, the NIC and other components of the wireless
computing device are powered up. The network interface component,
such as the NIC, then transmits or receives data over the high
power channel.
[0011] The low power control channel is implemented via an internal
or external radio frequency (RF) transceiver component, referred to
as a minibrick, which preferably operates at a low frequency (such
as lower than that of the full power NIC) and low power level. In
operation, when the computing device is idle, the device is
configured to power down substantially all of its components with
the exception of the circuitry required to power the low power
transceiver. As such, the control channel is maintained in an
active state for receiving signals during both idle and non-idle
periods.
[0012] In accordance with another embodiment of the invention, the
smartbrick is implemented as a host transceiver that operates at a
host computer, or network access point, to communicate with the
minibrick. The host computer may also be equipped with an IEEE
802.11 based NIC for supporting wireless communication to access
the network through a wireless access point (AP). The wireless AP
acts as an interface to a network infrastructure, such as a wired
enterprise LAN. When a requesting device wishes to communicate with
a wireless computing device, it queries a server in order to
determine the location and presence of the wireless computing
device. In response, the server submits the query to the host
computer. The smartbrick operating on the host computer receives
the query from the server, and communicates with the minibrick via
the low power channel to begin scheduling and operation of full
power communications. The wireless computing device receives this
signal and powers up the NIC and other components accordingly,
resulting in activation of the wireless device prior to any actual
transmission of data by the requesting device.
[0013] Additional features and advantages of the invention will be
made apparent from the following detailed description of
illustrative embodiments that proceeds with reference to the
accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] While the appended claims set forth the features of the
present invention with particularity, the invention and its
advantages may be best understood from the following detailed
description taken in conjunction with the accompanying drawings, of
which:
[0015] FIG. 1 is a schematic diagram of an exemplary computer
network within which embodiments of the invention may be
implemented;
[0016] FIG. 2 is a schematic diagram illustrating the architecture
of an exemplary computing device in which an embodiment of the
invention may be implemented;
[0017] FIG. 3 is a schematic diagram illustrating an architecture
of a transceiver component operated by a computing device for
maintaining a low power control channel in an embodiment of the
invention;
[0018] FIG. 4 is a schematic diagram illustrating an exemplary
operating environment for optimum channel scheduling through a low
power control channel according to an embodiment of the
invention;
[0019] FIG. 5 is a flowchart illustrating the operation of a host
transceiver for communicating with a wireless computing device via
a low power control channel according to an embodiment of the
invention;
[0020] FIG. 6 is a schematic diagram illustrating an operating
environment for optimizing channel scheduling wherein the host
transceiver is logically connected to a host computer according to
an embodiment of the invention;
[0021] FIG. 7 is a channel diagram illustrating bi-directional
communications in a two-channel system;
[0022] FIG. 8a is a schematic diagram illustrating a networked
environment wherein the multiple wireless network devices vying for
channel space are out-of-range of the wireless access point;
and
[0023] FIG. 8b is a schematic diagram illustrating a multi-hop
network operating environment for optimizing channel scheduling
when one or more of the multiple wireless devices vying for channel
space are out-of-range, according to an embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The invention relates to a method and system for traffic
handling of computing devices that are capable of communicating
over a wireless link. Wireless computing devices usable within
embodiments of the invention include, but are not limited to,
personal data assistants, cellular phones, and laptop computers
having wireless network interface capabilities. In the context of
the invention, wireless communication is the transmission of data
between computing devices using radio frequency (RF) and
electromagnetic waves rather than wires. To facilitate wireless
communication, a computing device may be equipped with a network
interface component, such as a network interface card (NIC) that
interfaces the device to the network. Typically, the NIC is
implemented as a plug and play device that can be inserted into a
network card slot of the computing device or that can be otherwise
interfaced to the device. Alternatively, the NIC can be built
integrally as part of the circuitry of the computing device.
[0025] To facilitate wireless communication, the NIC supports a
wireless protocol, such as pursuant to the IEEE 802.11 standard.
General reference will be made throughout the course of this
description to 802.11 as a suitable protocol for facilitating
wireless communication between devices. However, those skilled in
the art will recognize that 802.11 is only one protocol for
facilitating wireless communication, and that the invention is not
limited to any particular wireless protocol. Indeed, other wireless
protocols may be utilized alternatively or additionally in
connection with the invention. It will also be recognized by those
skilled in the art that the designation 802.11 refers to other
protocols within the same family, including 802.11a, 802.11b or
802.11 g.
[0026] An example of a networked environment in which the invention
may be used is shown in FIG. 1. The example network includes
several computing devices 20 communicating with one another over a
network 30, such as the Internet, as represented in the figure by a
cloud. Network 30 may include one or more well-known components,
such as routers, gateways, hubs, etc. and may allow the computers
20 to communicate via wired and/or wireless media.
[0027] Referring to FIG. 2, an example of a basic configuration for
a computing device on which the system described herein may be
implemented is shown. In its most basic configuration, the
computing device 20 typically includes at least one processing unit
42 and memory 44 although such is not required. Depending on the
exact configuration and type of the computing device 20, the memory
44 may be volatile (such as RAM), non-volatile (such as ROM or
flash memory) or some combination of the two. The most basic
general configuration is illustrated in FIG. 2 by dashed line 46.
Additionally, the computing device may also have other
features/functionality. For example, computer 20 may also include
additional data storage components (removable and/or non-removable)
including, but not limited to, magnetic or optical disks or tape.
Computer storage media includes volatile and non-volatile,
removable and non-removable media implemented in any method or
technology for storage of information such as computer-readable
instructions, data structures, program modules, or other data.
Computer storage media includes, but is not limited to, RAM, ROM,
EEPROM, flash memory or other memory technology, CD-ROM, digital
versatile disk (DVD) or other optical storage, magnetic cassettes,
magnetic tape, magnetic disk storage or other magnetic storage
devices, or any other medium which can be used to store the desired
information and which can be accessed by the computing device 20.
Any such computer storage media may be part of the computing device
20.
[0028] The computing device 20 also preferably contains
communication connections 48 that allow the device to communicate
with other devices. A communication connection is an example of a
communication medium. Communication media typically embodies
readable instructions, data structures, program modules or other
data in a modulated data signal such as a carrier wave or other
transport mechanism and includes any information delivery media. By
way of example, and not limitation, communication media includes
wired media such as a wired network or direct-wired connection, and
wireless media such as acoustic, RF, infrared and other wireless
media. The term computer readable media as used herein includes
both storage media and communication media.
[0029] A computing device 20 may also have input devices such as a
keyboard, mouse, pen, voice input device, touch input device, etc.
Output devices such as a display 48, speakers, a printer, etc. may
also be included. Furthermore, for wireless mobile devices, the
computing device 20 is preferably provided with a portable power
source 50, such as a battery pack, fuel cell or other power module.
The power source 50 acts as a primary source of power for
computations and wireless data transmissions to be performed by the
device. All the aforementioned components and features are well
known in the art.
[0030] The device 20 preferably supports an operating system, for
example stored in nonvolatile memory and executed by the processing
unit 42 from volatile memory. According to an embodiment of the
invention, the operating system contains instructions for
interfacing the device 20 to a full power wireless network and to a
low power wireless network. In this manner, scheduling information
usable to schedule access of the device 20 to the full power
wireless network may be sent over the low power wireless network,
saving device power and saving bandwidth in the full power channel,
according to the techniques to be more fully discussed elsewhere
herein.
[0031] A device, component or group of components may be described
herein as "powered up" when the relevant device, component or group
of components is in an "ON" state of operation, e.g. operating, or
at least receiving power and immediately ready to operate, in
itsordinary mode of operation. Conversely, when a device, component
or group of components is described as being "powered down," the
relevant device, component or group of components is not operating
in its ordinary mode of operation, and is not receiving power and
immediately ready to operate in its ordinary mode of operation.
[0032] In accordance with an embodiment of the invention, the
computing device 20 is further equipped with a low power
transceiver component 100 for maintaining a RF control channel, as
illustrated in greater detail in FIG. 3. The low power transceiver
component, referred to as a minibrick 100, is comprised of various
components for the receipt and transmission of data, including a
logic device 102 for controlling the operation of the transceiver
and for affecting the operation of the computing device 20 in
response to various network events. Also preferably included is a
voltage regulator 104 for adapting the voltage output of a low
power battery unit 106. The low power battery unit 106 is suitable
for powering the transceiver using minimal power, and can operate
independently of the portable battery source 50. Alternatively, the
primary battery source 50 may be used to implement the same
function as a low power battery unit 106. The low power transceiver
100 also includes a radio frequency (RF) generator 108 for
generating and providing radio frequency signals for transmission.
Other elements 109 for implementing or enhancing the transceiver
functions may also be included as part of the low power transceiver
circuitry and described elements may be altered or replaced.
[0033] Physically, the low power transceiver 100 can be implemented
as an internal component of the computing device 20, such as by
integrating it with the primary circuitry of the computing device
20, or it can be connected to the computing device via a peripheral
connection, such as an RS232 connection (e.g., the input channels
41). Also, the low power transceiver 100 is configured to support a
control channel for receiving and sending data via the radio
component 108. Exemplary operating characteristics for the low
power transceiver 100 for implementing the low power control
channel are shown in TABLE 1.
1TABLE 1 Example operational characteristics for the low power
transceiver 100. Data Rate 19.2 Kbps Modulation 00K Voltage 3 V
Receiver Current 4.5 mA Peak Radio Output Power 0.75 mW
[0034] As illustrated, the various characteristics of the low power
transceiver 100 result in the generation of a low power, and
preferably low frequency data communication channel at 915 MHz,
supporting a data rate of 19 Kbps, which is substantially less than
that of standard wireless NICs. Conventional NICs, such as those
based on the IEEE 802.11 standard, operate at much higher data
rates ranging approximately from 1-20 Mbps. Because of the higher
data rates and ranges associated with standard NICs, the power
consumption for powering up the standard NIC is also higher. The
low power transceiver 100, however, requires less power to operate,
and is configured to remain active even during powered off states
of all or some of the rest of the wireless computing device 20.
While not limited to the operating characteristics of TABLE 1, the
low power transceiver is suitable for generating and receiving RF
signals without requiring significant power usage by the device.
For an explanation of other features and aspects of the enhanced
two-radio network device, please see United States Patent
Application Serial No. Attorney Docket No. 215108, entitled
Reducing Idle Power Consumption in a Networked Battery Operated
Device, filed Apr. 15, 2002, which is herein incorporated by
reference in its entirety for all that it discloses.
[0035] Referring now to FIG. 4, an exemplary network environment
within which a wireless computing device, such as the device of
FIGS. 2-3, may operate is shown in accordance with an embodiment of
the invention. The exemplary network includes a server 200, which
interfaces with a computer network 202 and manages various network
resources including a Brick Server 203 and a presence server 201.
The Brick Server 203 and presence server 201 operate at the server
200 to facilitate specific network tasks. In particular, the
presence server maintains a list of clients that are registered
with the network server 200 in order to have their state of
presence maintained. Presence data or information is any data
received over the network that describes the availability,
proximity, location, activity level or operating state of a
computing device or corresponding user of a device. By registering
with the server 200, client devices connected to the network 202
may query the presence server 201 to detect the presence of other
devices. Similarly, the Brick Server 203 maintains and manages
presence information pertaining to one or more low power
transceivers or host transceivers, which are low power transceiver
components used to implement a low frequency control channel within
the network infrastructure. The operation of the host transceiver
and low power transceiver within the network environment will be
described in greater detail hereinafter.
[0036] While maintaining network resources, the server 200
facilitates communication for one or more computing devices that
communicate over the network 202. A first client device 204 is
configured to the network 202 through a wired connection (e.g., T1
line, modem) or wireless connection. The access point 210 acts as
an intermediate device between a second client device, such as
wireless computing device 220, and the network 202. Additionally,
logically connected to the access point 210 is a host transceiver
212, which generates radio frequency signals for communicating with
low power transceivers 100 and 102. In an alternative embodiment of
the invention, illustrated in FIG. 6, the host transceiver 212 is
logically connected to a host computing device configured through a
wireless connection. In particular, the host computing device 206
connects to the network 202 through a wireless connection 208
(e.g., 802.11 connection) to the wireless access point 210. The
access point, in this embodiment, may act as an intermediate device
between the host computing device 206 and the network
infrastructure 202. Note that the aforementioned architectures are
exemplary and that any other link that comprises a low power RF
link may be used to interface a device, such as devices 220 and
222, to any access controlling entity, such as access point 210
within the invention.
[0037] The host transceiver 212 registers with the Brick Server 203
maintained by the server 200 in order to report its presence. When
the host transceiver is connected to the network via a host
computing device 206, as illustrated in FIG. 6, it is able to
detect, when needed, the occurrence of various network events, such
as, for example, the transmission of a message to the host
computing device 206, an update to presence information maintained
by the Brick Server 203, the transmission of messages intended for
transmission by the access point 210, and any other statistics
relative to the performance of the network 202.
[0038] In accordance with an embodiment of the invention, multiple
wireless computing devices operating low power transceivers 100 and
102 communicate with the host transceiver 212 via a low power
control channel, as illustrated in FIG. 4. The wireless computing
devices are handheld devices 220 and 222 having wireless computing
capabilities. Low power transceivers 100 and 102 are coupled to the
wireless computing devices 220 and 222 for providing low power,
preferably low frequency control channels. The low power
transceivers 100 and 102 are enabled to remain powered up even
during inactive or idle periods when the components of the wireless
computing devices 220 and 222 (other than the circuitry required
for the low power transceiver 100 and 102) are wholly or
substantially powered off. Preferably, the low power transceivers
100 and 102 are capable of activating the wireless computing
devices 220 and 222 (e.g. transferring them from an inactive or
idle state to an active or non-idle state) in response to the
receipt of scheduling information, such as channel access
information.
[0039] To enable either low power transceiver 100, 102 to engage in
communication over the low power control channel, the low power
transceivers 100 and 102 first register with the Brick Server 203
maintained by the server 200. A user of either wireless computing
device 220, 222 can enable the registration process manually, such
as by running a network application on either device 220, 222 that
engages the registration process. Alternatively, the registration
process can be performed without user intervention through a simple
communication scheme engaged in by the host transceiver 212 and
either low power transceiver 100, 102, as described below.
[0040] To determine whether a low power transceiver exists within
radio range and requires registration, the host transceiver 212
periodically broadcasts beacon or detection signals indicating that
the host transceiver is within a suitable range for engaging in
communication via the low power control channel. This periodic
detection signal is sent preferably when the host transceiver 212
is not transmitting other types of control signals or data. When
the appropriate low power transceiver 100, 102 operating at the
appropriate wireless computing device 220, 222 detects the
detection signal, the low power transceiver 100, 102 generates and
sends a message to the host transceiver 212 indicating that it is
within low power radio range of the host transceiver 212. Upon
receiving such a message, the host transceiver 212 determines its
capability to "manage" the relevant low power transceiver 100, 102,
and replies to the low power transceiver 100, 102 with an
acknowledgement message when appropriate. The host transceiver's
212 ability to manage a specific low power transceiver 100, 102 may
be based on the current situation at the access point, including,
but not limited to, the number of clients currently vying for
channel access. A response acknowledgement is subsequently
generated and sent to the host transceiver 212 by the low power
transceiver 100, 102, which results in an association (connection
or link) between the host transceiver 212 and the relevant low
power transceivers 100, 102. Having established an association
between the host transceiver 212 and both low power transceivers
100 and 102, the host transceiver transmits a message to the
presence server 201 to inform the server of the presence of the low
power transceivers 100 and 102. The connection to each low power
transceiver will be made prior to coordinated scheduling, but each
connection may be established independently at any time without
occurring simultaneously with or in a fixed relationship to any
other connection.
[0041] Regardless of the method of registration performed, be it as
described above or by way of another technique, the wireless
computing devices 220 and 222 operating the low power transceivers
100 and 102 must be within a range suitable for receiving low power
signals from and transmitting low power signals to the host
transceiver 212. This range will vary based upon the specific
design characteristics of the low power transceivers 100 and 102
and host transceiver 212. Since the messages passed between the low
power transceivers 100 and 102 and host transceiver 212 (e.g.,
acknowledgement messages) are transmitted over the low power, low
bandwidth, control channel, and not a primary communication channel
(e.g. an 802.11 channel) the standard high power NIC cards of the
wireless computing devices 220 and 222 need not be used for
facilitating the presence detection and registration process,
resulting in less power usage by the devices. Also, because the
registration process is executed via a low power control channel
rather than the high power channel, the wireless computing devices
220, 222 operating the low power transceivers 100, 102 need not be
powered up during the registration.
[0042] In an embodiment of the invention, the low power control
channel of any device may be idled during non-idle periods of
operation by the wireless computing devices 220 and 222 for
reducing power consumption. Thus, for example, when a standard
wireless NIC card is active on a computing device for facilitating
communication between the wireless computing device and the network
202, the low power transceiver 100 can be powered down or placed
into a nominal power mode (e.g., sleep mode of operation) wherein
no transmissions or received signal processing is performed. Once
the standard NIC of the wireless computing device is placed in a
low power state of operation or becomes idle, the low power
transceiver can be powered up to resume its normal operation on the
device. In this way, there is no substantial concurrent power usage
by the wireless computing device in maintaining both the standard
NIC and the low power transceiver in a powered up state.
[0043] When numerous wireless computing devices attempt to access
the network 202 via the access point 210, data transfer congestion
often results. That is, when multiple wireless computing devices,
such as devices 220 and 222 contend for the bandwidth of the same
access point, one or more devices may experience unacceptable
delay, or denial of service. In one embodiment of the invention,
illustrated by the flow chart in FIG. 5 and the schematic
illustrated in FIG. 7, multiple wireless computing devices vying
for communication bandwidth at an access point will have their
access to the channel for data transmission scheduled based upon
control information sent over their low power channel. This
technique avoids wastage of the primary channel bandwidth caused by
sending control and scheduling information over the primary
channel.
[0044] Beginning at step 400, the wireless computing device
registers with the brick server in a fashion such as previously
discussed or otherwise. After registering with the access point,
the low power transceiver transmits control information to the host
transceiver logically connected to the access point, in step 402,
informing the access point that the wireless computing device has
data to transmit over the primary wireless channel. Types of
control information include, but are not limited to, data packet
priority information, data packet transmission deadline
information, channel access information, and the number of data
packets currently in a queue. Based upon this information and a
scheduling algorithm, the access point, in step 404, generates a
sorted list of nodes having data packets to transmit and the packet
priority of each packet. After generating this list, the access
point then transmits the appropriate scheduling information, in
step 406, to each contending low power transceiver to notify the
wireless computing device as to when it should send data over the
primary channel through the standard NIC. Finally, in step 408, a
wireless computing device proceeds to transmit the primary data
over the 802.11 channel according to the received scheduling
information, while the other wireless computing devices vying for
the channel stand by. The scheduling information may also comprise
a "wake-up" signal notifying a wireless computing device to power
up and then to transmit data through the standard NIC. Such
"wake-up" signals may be transmitted based upon the priority of the
data on the list generated in step 404.
[0045] By placing the control information and scheduling
information out of band with respect to the data transmission, the
invention conserves and better utilizes the primary channel
bandwidth. The control information and corresponding scheduling
information is sent via the low power channel, whereas the useful
data is sent via the primary channel. Therefore, true work
conservation can result from proper work conserving algorithms.
[0046] One of skill in the art will recognize that numerous
scheduling algorithms exist, any one or more of which can be used
in conjunction with the present invention. Suitable scheduling
algorithms include, but are not limited to, fair queuing and first
come, first serve scheduling. Examples of fair queuing scheduling
algorithms that can be used in conjunction with the present
invention appear in S. Keshav, On the Efficient Implementation of
Fair Queueing, Journal of Internetworking: Research and Experience,
Volume 2, pages 27-73 (1991), herein incorporated by reference in
its entirety for all that it discloses. Additionally, one of skill
in the art will recognize that while the examples given above
sometimes reference the 802.11 standard family of protocols, any
communication protocols may be used to implement the present
invention. Also note that although specific frequencies are given
in the foregoing examples, any frequency that is supported in any
section of the world may be used as the frequency for data
transmission or control information transmission according to the
present invention. Preferably, frequencies are used that are
available internationally for devices that may be used
internationally, thus avoiding RF interference and channel
failure.
[0047] In another embodiment of the present invention, the
scheduler at the access point is in synchronization with a
scheduled wireless computing device, allowing scheduling of primary
channel access prior to powering up the wireless network device.
For example, if the access point and wireless computing device are
rate synchronized, wherein the clocks of each count time at
substantially the same rate, the access point can coordinate with
the wireless computing device to power up after passage of a
specified interval so that the primary NIC can transmit or receive
data at that time. This is typically facilitated by use of a
network timing protocol (NTP), or any other suitable protocol, over
the low power channel through a low power transceiver that is held
constantly ready to receive and/or transmit data. One of skill in
the art will recognize that there are numerous other timing
protocols and synchronization technologies that will work within
the present invention to provide synchronized behavior.
[0048] Note that the low power control channel and the primary
channel preferably employ different frequencies. In one example,
the low power transceiver employs a carrier at 433 MHz or 915 MHz,
while the standard NIC for the primary channel operates at 2.4 GHz.
As discussed above, the low power transceiver and the standard NIC
have different power usage requirements due in part to differences
in frequency, data rate, and signal strength.
[0049] In a further embodiment, the powering up of the low power
transceiver itself can be scheduled. This embodiment utilizes
precise clock rate synchronization between the low power
transceiver on a wireless device and the host transceiver located
at the access point. When the low power transceiver and the host
transceiver have access to clocks running at essentially the same
rate, neither the low power transceiver nor the standard NIC need
be maintained in a constantly active state. For example, when the
low power transceiver has received an indication that transmission
from its host device will be permitted after a specified interval,
then both the low power transceiver and the standard NIC can be
placed in a non-active mode during that interval after accounting
for a known start-up delay of each. Note that although the clocks
of the low power transceiver and the host transceiver need not
reference identical rate clocks, the rates of both should be close
enough that channel scheduling is not impacted by any inaccuracies
to the extent that it results in transmission collisions or other
detrimental behavior.
[0050] In an alternative embodiment of the present invention,
illustrated in FIG. 6, the aforementioned scheduling function is
performed at a host computer 206 containing a host transceiver 212,
rather than at the wireless access point 210 itself. The host
computer 206 may be connected to the network 202 via the wireless
access point 210 or otherwise. This networking environment is built
in substantially the same way as the environment wherein the
wireless computing devices are connected directly to the access
point 210. Note that in this or other embodiments, it is not
required that both the primary and low power channels connect the
same nodes. Thus, with reference to FIG. 6, a wireless device 220,
222 may communicate with the host computer 206 via the low power
channel while communicating directly with the access point 210 via
the primary (e.g. 802.11) channel.
[0051] While the invention is not limited to any particular radio
range for the low power channel, it is preferable that the low
power transceiver of the wireless computing devices 220 and 222 be
spatially close enough to a host transceiver enabled access point
210 during operation to ensure RF signal reception and data
integrity. However, it is still possible to have such low power
communications even when the relevant low power transceiver is not
within direct communication range of the host transceiver 212
operating at the access point, or at a host computer. Techniques
for facilitating out-of-range communication are discussed in the
following section of the detailed description.
[0052] In FIG. 8a, a first wireless computing device 300 operating
a low power transceiver 302 and a second wireless computing device
304 operating a second low power transceiver 306 are shown to be
out of a suitable direct range for supporting low power
communication with an access point 210 operating a host transceiver
308. As such, with respect to each wireless computing device 300,
304, the low power transceiver 302, 306 is unable to directly
communicate with the access point 210. In accordance with an
embodiment of the invention, however, the first wireless computing
device 300 may be able to communicate with the access point 210
using multi-hop networking, as illustrated in FIG. 8b.
Specifically, when a third wireless computing device 314 operating
a low power transceiver device 316 is within range of the access
point 210, a low power control channel 318 is established between
the third computing device 314 and host transceiver enabled device
210.
[0053] When the third wireless computing device 314 is also within
range of another wireless computing device 300, 304, the low power
transceiver operating on the wireless computing device 300, 304
establishes contact with the third wireless computing device 314
via a low power communication channel. In particular, the low power
transceiver 302, 306 of the wireless computing device 300, 304
sends a message to the low power transceiver 316 of the third
wireless computing device 314 for retransmission to the access
point 210. The low power transceiver 316 of the third wireless
computing device 314 then makes a determination as to whether to
accept this request or not. If the request is accepted, a control
channel is established between the third wireless computing devices
314 and the other device 300, 304. The low power transceiver 302,
306 associated with the out-of-range wireless computing device 300,
304 sends a registration message to the third wireless computing
device 314 via the low power channel. This message is then
forwarded by the third wireless computing device 314 to the host
transceiver 308 operating at the access point 210, via the low
power channel between the two. Once the registration of the low
power transceiver 302, 306 of the out-of-range wireless computing
device 300, 304 is recorded by the server 310, the out-of-range
wireless computing device 300, 304 is able to engage in
communication with other devices over the network 312.
[0054] Once the out-of-range wireless computing devices 300, 304
are registered, either one may then transmit control information,
such as bandwidth requests, through the third wireless network
device 314 to the host transceiver 308 at the access point 210, or
host computer, as previously described above. Upon receiving the
control information, the access point 210 applies a scheduling
algorithm to all request information in order to schedule channel
access for multiple wireless network devices seeking use of the
same high power channel. The access point 210 then transmits the
scheduling information through the host transceiver 308 to the
third wireless network device 314 via a low power channel. When the
scheduling information reaches the third wireless network device
314, it is forwarded to the pertinent out-of-range wireless network
device. For example, if the scheduling information is in the form
of a "wake-up" signal, then it would only be transmitted to the
wireless device that is to be powered up in order to receive or
transmit data, i.e. the device that has access to the channel at
that time. If the scheduling information is in the form of a
schedule of channel access of multiple wireless access devices, the
scheduling information may be sent to any or all out-of-range
devices as needed by the third wireless device.
[0055] Those skilled in the art will recognize that the
above-described processes will often be carried out within an
environment of more than two competing wireless computing devices
although just two such devices are illustrated herein. As will be
appreciated by those skilled in the art, whenever a number of
wireless computing devices are within an appropriate low power
radio range of one another, multi-hop communication can ideally be
engaged by an unlimited number of such devices. This is
particularly advantageous in the case of mobile wireless computing
devices, such as PocketPCs, wherein a direct connection to a host
transceiver enabled host, such as access point 210, may be limited
as the device user roams from one location to another. Note that
although two low power jumps are used in the described examples to
reach an out-of-range device, any number of such jumps may be
utilized without limitation. Furthermore, it is contemplated that
one or more out-of-range devices may need to use multi-hop
connectivity, while another device or devices are either in direct
range, or at least require fewer hops.
[0056] In view of the many possible embodiments to which the
principles of this invention may be applied, it should be
recognized that the embodiments described herein with respect to
the drawing figures are meant to be illustrative only and should
not be taken as limiting the scope of invention. For example, those
of skill in the art will recognize that the elements of the
illustrated embodiments shown in software may be implemented in
hardware and vice versa or that the illustrated embodiments can be
modified in arrangement and detail without departing from the
spirit of the invention. Therefore, the invention as described
herein contemplates all such embodiments as may come within the
scope of the following claims and equivalents thereof.
* * * * *