U.S. patent application number 10/011221 was filed with the patent office on 2005-10-27 for collaborative mechanism of enhanced coexistence of collocated wireless networks.
Invention is credited to Liang, Jie.
Application Number | 20050239474 10/011221 |
Document ID | / |
Family ID | 21749379 |
Filed Date | 2005-10-27 |
United States Patent
Application |
20050239474 |
Kind Code |
A9 |
Liang, Jie |
October 27, 2005 |
Collaborative mechanism of enhanced coexistence of collocated
wireless networks
Abstract
A digital device 310 with a plurality of collocated wireless
networks encounters inter-network interference if the collocated
wireless networks operate in a common operating frequency. A
coordinator unit 510, coupled to the plurality of wireless
networks, provides a transmission reservation system wherein a
wireless network with a need to transmit can request and receive a
reservation for time to transmit. The coordinator unit 510 provides
a way to schedule transmissions from the plurality of wireless
networks and to reduce the probability of collisions.
Inventors: |
Liang, Jie; (Plano,
TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 0083095 A1 |
May 1, 2003 |
|
|
Family ID: |
21749379 |
Appl. No.: |
10/011221 |
Filed: |
October 25, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60262008 |
Jan 16, 2001 |
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Current U.S.
Class: |
455/454 ;
370/348; 455/41.2; 455/507; 455/63.1 |
Current CPC
Class: |
H04W 72/1215 20130101;
H04W 16/14 20130101 |
Class at
Publication: |
455/454 ;
455/507; 370/348; 455/063.1; 455/041.2 |
International
Class: |
H04B 001/38; H04B
001/00; H04B 015/00; H04B 007/212; H04Q 007/20; H04B 007/00 |
Claims
What is claimed is:
1. A method for controlling access to a wireless communications
medium shared a plurality of collocated wireless networks
comprising: receiving a reservation request at a coordinator unit;
deciding upon the reservation request; and returning the results of
the decision.
2. The method of claim 1, wherein the deciding step further
comprises: determining if a desired time specified in the
reservation request is available; granting the reservation request
if the desired time is available; and rejecting the reservation
request if the desired time is not available.
3. The method of claim 2, wherein the determining step further
comprises: generating a start time and a stop time for the
reservation request based on information provided in the
reservation request; and comparing the start time and the stop time
for the reservation request against a list of granted start and
stop times.
4. The method of claim 1, wherein the receiving step comprises
receiving a single reservation request from one collocated wireless
network.
5. The method of claim 1, wherein the receiving step comprises
receiving a plurality of reservation requests for an overlapping
transmission time from the plurality of collocated wireless
networks.
6. The method of claim 5, wherein the deciding step further
comprises: selecting a random number, D; comparing the random
number against a threshold, DP; and granting a reservation request
from the plurality of reservation requests based on the
comparison.
7. The method of claim 6, further comprises the step of rejecting
all remaining reservation requests from the plurality of
reservation requests.
8. The method of claim 7, wherein the returning step comprises
returning a granted reservation request to a collocated wireless
network whose reservation request was granted and returning
rejected reservation requests to collocated wireless networks whose
reservation requests were rejected.
9. The method of claim 6, wherein there are two collocated wireless
networks, and wherein the threshold, DP, is a number between 0 and
1.
10. The method of claim 6, wherein there are three collocated
wireless networks, and wherein the threshold, DP, is a set of two
numbers between 0 and 1.
11. The method of claim 1, wherein the reservation request
comprises a transmit start time and a transmit duration.
12. The method of claim 1, wherein the reservation request
comprises a transmit start time and a transmit stop time.
13. A method for sharing a wireless communications medium among a
plurality of collocated wireless networks comprising: (a)
determining a need to transmit; (b) sending a reservation request
to a coordinator unit; (c) transmit if the reservation request was
granted; and (d) deferring transmission if the reservation request
was rejected.
14. The method of claim 13, wherein the determining step comprises
decoding a message addressed to self that requires a response.
15. The method of claim 13, wherein the determining step comprises
receiving a message addressed to self that grants permission to
transmit.
16. The method of claim 13, wherein the determining step comprises
the assertion of a transmit indicator for transmission of a
periodic transmission.
17. The method of claim 13, wherein the determining step comprises
servicing a request to grant permission to transmit.
18. The method of claim 13, wherein the determining step further
comprises: determining that the wireless communications medium is
idle; waiting a specified time interval; generating a random
backoff time; loading the random backoff time into a backoff timer;
decrementing the backoff timer each time an idle network slot
expires; and determining when the backoff timer reaches zero.
19. The method of claim 13, wherein the deferring step further
comprises: waiting until a next available transmission time; and
repeating steps (b)-(d).
20. The method of claim 13, wherein the deferring step further
comprises: sending a reservation request to the coordinator unit,
requesting a next available time; and repeating steps (c)-(d).
21. The method of claim 13, wherein the deferring step comprises
repeating steps (a)-(d).
22. A coordinator unit comprising: a reservation request flag line,
the reservation request flag line to denote a status of a pending
reservation request; an arbiter unit coupled to the reservation
request flag line, the arbiter unit containing circuitry to receive
reservation requests and to grant reservation requests based on the
state of the reservation request flag line; and a scheduler unit
coupled to the arbiter unit and the reservation request flag line,
the scheduler unit containing circuitry to maintain a list of
granted reservation requests and to assert the status of a pending
reservation request on the reservation request flag line.
23. The coordinator unit of claim 22, wherein there is a plurality
of wireless networks interfaces collocated in a digital device, and
wherein the coordinator unit is coupled to each wireless network
interface.
24. The coordinator unit of claim 23, wherein the coupling is a
wired connection between the coordinator unit and each wireless
network interface.
25. The coordinator unit of claim 24, wherein each wired connection
is an electrically separate connection.
26. The coordinator unit of claim 23, wherein the coupling is a
wireless connection between the coordinator unit and each wireless
network interface.
27. The coordinator unit of claim 26, wherein each wireless
connection operates at a different operating frequency.
28. The coordinator unit of claim 26, wherein each wireless network
operates on a common operating frequency, and wherein each wireless
connection operates at a different operating frequency the common
operating frequency of the wireless networks.
29. The coordinator unit of claim 22, wherein the coordinator unit
further comprises a random number generator unit coupled to the
arbiter unit, the random number generator unit containing circuitry
to generate a random number in a range of 0 to 1.
30. The coordinator unit of claim 29, wherein the coordinator unit
further comprises a threshold comparator unit coupled to the
arbiter unit, the threshold comparator unit containing circuitry to
compare the random number generated by the random number generator
unit against a prespecified threshold.
31. The coordinator unit of claim 30, wherein the prespecified
threshold is a number in a range of 0 to 1.
32. A digital device containing a plurality of collocated wireless
networks comprising: a plurality of wireless network interface, one
wireless network interface for each of the plurality of collocated
wireless networks, each wireless network interface provides an
connection between the digital device and the wireless network
interface's respective wireless network; a coordinator unit coupled
to each wireless network interface, the coordinator unit further
comprises: a reservation request flag line, the reservation request
flag line to denote a status of a pending reservation request; an
arbiter unit coupled to the reservation request flag line, the
arbiter unit containing circuitry to receive reservation requests
and to grant reservation requests based on the state of the
reservation request flag line; and a scheduler unit coupled to the
arbiter unit and the reservation request flag line, the scheduler
unit containing circuitry to maintain a list of granted reservation
requests and to assert the status of a pending reservation request
on the reservation request flag line.
33. The digital device of claim 32, wherein the digital device is a
personal computer.
34. The digital device of claim 32, wherein the digital device is a
personal digital assistant.
35. The digital device of claim 32, wherein the digital device is a
cellular telephone.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to communications networks
and particularly to enhancing the performance of multiple wireless
communications networks operating in a same frequency band,
collocated in a small area.
BACKGROUND OF THE INVENTION
[0002] Radio frequency (RF) spectrum is a valuable commodity in
today's world. There are more people desiring to use the RF
spectrum than there is spectrum to go around, so use of the
spectrum must be regulated. In many countries, the RF spectrum is
regulated by governmental bodies. The Federal Communications
Commission (FCC) regulates the RF spectrum in the United
States.
[0003] The RF spectrum is regulated usually in one of two ways. A
first way that governmental bodies regulates the RF spectrum is to
sell portions of it to the highest bidder. The winning bidder, then
has exclusive use of the particular portion of the RF spectrum that
he has just purchased. This is way that RF spectrum for cellular
telephones, television and radio channels are allocated. Single
user allocations are the preferred method for applications where
interference from other sources cannot be tolerated.
[0004] A second way that the government regulates RF spectrum usage
is to create certain bands where anyone can use the RF spectrum as
long as they comply with specified spectrum usage rules. For
example, in the United States, the FCC has created three such
bands. These bands are called the industrial, scientific, and
medical (ISM) and the unified national information infrastructure
(UNII) bands and are in the 900 MHz, 2.4 GHz, and 5.7 GHz portions
of the RF spectrum. Anyone may use the spectrum in these bands as
long as they are able to accept interference from other users and
do not cause undue interference to other users.
[0005] The ISM and UNII bands have created a huge market for
wireless consumer electronics products, such as cordless
telephones, wireless computer products, and wireless computer
networks. However, the popularity of the bands has resulted in a
problem that many product developers did not anticipate, namely,
performance degradation due to inter-product interference.
[0006] In wireless computer networks, the performance degradation
is seen mainly in the network's data transfer rates. A wireless
network today is capable of delivering a data transfer rate of 11
Mbps or more in an interference free environment, but if
interference is introduced, the data transfer rate may drop to only
a small fraction of the maximum.
[0007] Interference to a wireless computer network may come from
many different forms. Sources of interference may include large
appliances in the environment, other electronic devices such as
pagers, cordless telephones, and microwave ovens, and other
wireless computer networks. The relatively simple sources of
interference such as appliances and pagers and telephones are
relatively simple to deal with because their interference is
periodic and is usually predictable. Because the interference is
predictable, it is usually easy to avoid.
[0008] When multiple wireless computer networks are collocated, the
wireless networks may interfere with one another. If the wireless
computer networks are of the same type (the networks use a common
technical standard), then there are often built-in mechanisms that
permit the networks to remain operating at near optimal levels.
However, if the wireless computers networks are of differing types,
then there normally no built-in techniques that will permit the
networks to work around each other.
[0009] Interference from wireless networks are more difficult to
deal with due to the bursty nature of computer traffic and the fact
the networks are often adaptive and can adjust their behavior
depending on network conditions. The adaptive behavior often makes
the interference worse because in many cases the network simply
increases its transmission power when it detects a decrease in data
rate. The increased transmission power results in a corresponding
increase in the interference to other networks.
[0010] The collocation problem is at its worst when a single device
has wireless network cards for multiple wireless networks
installed. For example, a personal computer may have two (or more)
wireless network interface cards installed inside it. A first card
may be used with an IEEE 802.11 (802.11) wireless Ethernet network
that permits the personal computer access to a company's corporate
intranet and access to the Internet. A second card may be used with
a Bluetooth (BT) network that permits the personal computer
short-range access to personal digital assistants, printers,
cellular telephones, etc.
[0011] Unfortunately, since the two network cards are often only a
few inches (or less) from one another, when one card transmits, it
often saturates the receiver of the other. This prevents the other
card from receiving any information transmitted in its own network.
A similar problem occurs when one card is receiving information,
where the received information from one network may be so powerful
that it obliterates any information intended for the other
network.
[0012] One proposed solution for the collocation of multiple
wireless computer networks in a single device involves regulating
traffic flow from the networks with fixed priorities. This involves
assigning different traffic classes in each of the networks a
different priority and then allowing the traffic classes with
higher priorities to transmit at the expense of lower priority
traffic. However, with a fixed priority structure, it is very
possible to have the higher priority traffic dominate access to the
networks and starve the lower priority traffic. Additionally, by
using fixed priorities, it is not possible to adjust the priorities
to meet changing network conditions.
[0013] A need has therefore arisen for a solution that allows
multiple wireless computer networks to collocate and at the same
time, permit sufficient flexibility so that the solution itself may
be adjusted to meet changing network conditions.
SUMMARY OF THE INVENTION
[0014] In one aspect, the present invention provides a method for
controlling access to a wireless communications shared by multiple
collocated wireless networks comprising receiving a reservation
request from a collocated wireless network, deciding to grant or
reject the reservation request, and providing the results of the
decision to the requesting wireless network.
[0015] In another aspect, the present invention provides a method
for sharing a wireless communications medium between multiple
collocated wireless networks comprising a wireless network
determining that it needs to transmit and the wireless network
sending a reservation request corresponding to the transmission to
a coordinator unit, the wireless network can transmit if the
reservation request was granted and the wireless network must defer
the transmission if the request was rejected.
[0016] The present invention provides a number of advantages. For
example, a preferred embodiment of the present invention permits
multiple wireless computer networks to collocate on a single
digital device and share the available RF spectrum through the use
of an arbitration unit that schedules usage of the RF spectrum for
the wireless networks. Through the use of scheduling, the
collisions of packets transmitted by the collocated networks are
reduced.
[0017] Also, since present invention uses an arbitration unit that
decides which network is granted permission to transmit, the
present invention has the ability to adjust the decision making
process used by the arbitration unit in a dynamic fashion to
optimize network performance.
[0018] Additionally, the present invention uses an arbitration unit
can be updated via software techniques, so that when additional
networks are supported or changes are made to existing network
technical standards, the arbitration unit can be easily
upgraded.
[0019] Furthermore, in the case when only one of the collocated
wireless networks is operating (transmitting), the wireless network
does not suffer any performance penalties from the present
invention. The wireless network will function as well as if it were
the only wireless network located on the device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The above features of the present invention will be more
clearly understood from consideration of the following descriptions
in connection with accompanying drawings in which:
[0021] FIG. 1 illustrates a typical (prior art) configuration for
an IEEE 802.11 wireless local area network;
[0022] FIG. 2 illustrates a typical (prior art) configuration for a
Bluetooth wireless network;
[0023] FIG. 3 illustrates a digital device with a collocated IEEE
802.11 wireless local area network and a Bluetooth wireless
network;
[0024] FIG. 4 illustrates a collision between a Bluetooth
transmission stream and an IEEE 802.11 frame;
[0025] FIG. 5 illustrates a coordinator unit, coordinating
transmissions between an IEEE 802.11 wireless local area network
and a Bluetooth wireless network according to a preferred
embodiment of the present invention;
[0026] FIG. 6a illustrates a functional view of the coordinator
unit displayed in FIG. 5 according to a preferred embodiment of the
present invention;
[0027] FIG. 6b illustrates a flow diagram detailing a virtual
contention algorithm for collision resolution according to a
preferred embodiment of the present invention;
[0028] FIG. 7a illustrates an algorithm for requesting reservation
requests and processing request rejections when the digital device
contains an 802.11 wireless station as one of the collocated
wireless networks, when the 802.11 wireless local area network is
operating in contention-free mode according to a preferred
embodiment of the present invention;
[0029] FIG. 7b illustrates an algorithm for requesting reservation
requests and processing request rejections when the digital device
contains an 802.11 access point as one of the collocated wireless
networks, when the 802.11 wireless local area network is operating
in contention-free mode according to a preferred embodiment of the
present invention;
[0030] FIG. 8 illustrates an algorithm for requesting reservation
requests and processing request rejections when the digital device
contains an 802.11 access point or 802.11 wireless station as one
of the collocated wireless networks, when the 802.11 wireless local
area network is operating in contention access mode according to a
preferred embodiment of the present invention;
[0031] FIG. 9a illustrates an algorithm for requesting reservation
requests and processing request rejections when the digital device
contains a BT master unit as one of the collocated wireless
networks according to a preferred embodiment of the present
invention; and
[0032] FIG. 9b illustrates an algorithm for requesting reservation
requests and processing request rejections when the digital device
contains a BT slave unit as one of the collocated wireless networks
according to a preferred embodiment of the present invention.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0033] The making and use of the various embodiments are discussed
below in detail. However, it should be appreciated that the present
invention provides many applicable inventive concepts which can be
embodied in a wide variety of specific contexts. The specific
embodiments discussed are merely illustrative of specific ways to
make and use the invention, and do not limit the scope of the
invention.
[0034] Wireless networks have become extremely popular with users
of digital equipment. They allow a degree of mobility and
flexibility that has not been available until recently. A user with
a digital device connected to a wireless network can roam freely
within the operational range of the network without being
encumbered by wires. Additionally, more sophisticated wireless
networks permit configurations wherein multiple networks can be
setup so that the user can transparently roam between the networks
without noticing the change in networks taking place or needing to
make any adjustments to the digital device.
[0035] Unfortunately, the popularity of wireless networks has also
spawned a large number of incompatible wireless networks. In the
majority of cases, a device that is configured to operate on one
wireless network cannot operate on another. One solution for
digital devices that are capable of supporting multiple network
cards is to install multiple wireless network cards onto the
digital device.
[0036] However, since the wireless networks are usually
incompatible and often share the same radio frequency (RF)
spectrum, typically only one network can be operational at one
time. If multiple networks share the same RF spectrum, when one
transceiver (a combination transmitter and receiver) in a digital
device containing multiple transceivers transmits, the transmission
will saturate the receivers in each of the other transceivers. With
their receivers saturated, the other transceivers will not be able
to receive any packets, or if they are currently receiving a
packet, then the packet will be damaged by the transmitted packet
from the transmitting transceiver.
[0037] The present invention discloses a method for permitting
multiple wireless networks to collocate within the same general
area (the same digital device). The method permits the multiple
networks to continuously operate without suffering a large
performance decrease. While the discussion will specifically
discuss two specific types of wireless networks, the ideas
presented in the present invention has application in other types
of wireless networks and to more than two collocated wireless
networks. Therefore, the present invention should not be construed
as being limited solely to the two wireless networks discussed
herein.
[0038] Networks adhering to the IEEE 802.11 technical standard are
among the most widely available wireless network today. The 8 02.11
wireless network operates in the 2.4 GHz ISM RF spectrum band and
provides up to 11 Mbps of data transfer rate and a more advanced
version, IEEE 802.11a, operating in the 5.7 UNII band provides up
to 54 Mbps of data transfer rate. The 802.11 wireless network is
specified in a technical standard, "ANSI/IEEE Std 802.11, 1999
Edition; Information technology--Telecommunic- ations and
information exchange between systems--Local and metropolitan area
networks--Specific requirements. Part 11: Wireless LAN Medium
Access Control (MAC) and Physical Layer (PHY) Specifications" which
is incorporated herein by reference. An 802.11 wireless network is
intended as a wireless replacement to the wired data network,
therefore, it provides a high data transfer rate and a relatively
large operating area (a high transmitted signal power level).
[0039] Referring now to FIG. 1, a diagram (prior art) of a typical
wireless network configuration according to the 802.11 technical
standard. Note that FIG. 1 displays one possible configuration of
an 802.11 wireless network out of the many different configurations
that are possible. FIG. 1 illustrates a wireless network 100
comprised of an access point 110 that is wirelessly connected to a
first station 120 and a second station 130.
[0040] An 802.11 wireless network provides two different modes of
communications. A first mode of communications is known as
contention-free communications. Contention-free communications
occurs during a contention-free period and is controlled by a point
coordinator. The point coordinator is typically located inside an
access point. During contention-free communications, a station can
communicate after it has received a poll-frame from the access
point (the point coordinator). After the station receives the
poll-frame from the access point, it is free to transmit for a time
duration that is specified in the poll-frame.
[0041] A second mode of communications is known as contention
access communications. Contention access communications occurs
during a contention period. Contention access communications is a
distributed communications methodology and there is no controller
to control communications. If a station wishes to communicate, it
must wait until the communications medium is idle. After the
communications medium becomes idle, the station is required to wait
a prespecified amount of time referred to as a Distributed
Coordinating Function (DCF) interframe space (DIFS) period. The
wait of a DIFS period is required to ensure that the stations
involved in the previous communications exchange have completed
their communications. Note that the 802.11 technical standard
defines two types of idle media, a physical idle when there are no
transmissions on the medium, and a virtual idle when there are no
expected transmissions. Both types of idle must be met in order for
the communications medium to be considered idle.
[0042] Once the communications medium becomes idle and the station
waits the requisite DIFS period, a backoff period starts. During
the backoff period, a backoff timer decrements one each time an
idle network slot passes. The station must wait until the backoff
timer reaches zero prior to transmitting. The duration of the
backoff period (the value in the backoff timer) is a randomly
generated value that is specified by a contention window. The
contention window is a range from (0, CW) that specifies the
possible values for the backoff period. When the backoff timer
reaches zero, the station is permitted to transmit. Since
contention access communications is not a controlled form of
communications, there is a non-zero probability that packets
transmitted using contention access communications will collide
with other packets.
[0043] Should a collision take place, the stations involved in the
collision are required to repeat the backoff procedure with larger
values for the contention window. After each collision, the value
CW is doubled, resulting in a doubling of the contention window
size. Should collisions continue to occur, the value of CW will
exceed a maximum permitted value, CWmax. If this is the case, the
CW will remain at the maximum permitted value until the
transmissions succeed or the number of transmission attempts exceed
a specified limit and the transmission is aborted.
[0044] Another wireless network standard is the Bluetooth (BT)
special interest group (SIG) technical standard. Specified in the
"Specification Volume 1: Specification of the Bluetooth System,
Version 1.1, Feb. 22, 2001," which is incorporated herein by
reference. BT wireless networks are intended as replacements for
low data-rate wired connections, such as parallel and serial
connections, and universal serial bus connections between digital
devices. As such, BT wireless networks are typically small area
networks (a low transmission power level).
[0045] Referring now to FIG. 2, a diagram (prior art) of a typical
wireless network configuration according to the BT SIG technical
specifications. Note that FIG. 2 displays one possible
configuration of a BT wireless network out of the many different
configurations that are possible. FIG. 2 illustrates a BT wireless
network 200 comprised of a master unit 210 and three slave units
220, 230, and 240. The master unit 210 is wirelessly connected to
the three slave units. According to the BT SIG specifications, a
slave unit cannot communicate unless it is specifically addressed
in a packet from the master unit.
[0046] A BT network operates in the 2.4 GHz ISM band, along with
802.11 wireless LANs. It uses a frequency hopping, time-division
duplex scheme with a slot length of 625 micro-seconds. The
transmission pattern is as follows: the master unit and the slave
units are granted alternating time slots. If a master unit is
granted a time slot number 1, then the master unit can transmit
during that time slot and all subsequent odd numbered time slots.
Time slots dedicated to the master unit are referred to as
master.fwdarw.slave time slots. The slave unit(s) are then assigned
time slot number 2 and then all subsequent even numbered time
slots. Time slots dedicated to the slave unit(s) are referred to as
slave.fwdarw.master time slots. A unit, either master or slave(s),
cannot transmit outside of its assigned time slots, without using
special provisions provided for transmitting a packet of length
greater than one time slot. A slave unit is only allowed to
transmit after addressed by the master unit in previous
master.fwdarw.slave slot.
[0047] A BT wireless network provides two different communications
modes. A first mode, referred to as synchronous connection oriented
(SCO), simulates a circuit switch connection between a master unit
and a slave unit. SCO communications are scheduled well in advance
of the actual communications instances and occur at regular
intervals. The master unit 210 will setup a SCO link between itself
and a slave unit and at periodic intervals, the master unit 210
will transmit to the slave unit using a master.fwdarw.slave time
slot, who in turn, will transmit a response in the following
slave.fwdarw.master time slot.
[0048] A second mode, referred to as asynchronous connectionless
(ACL), provides packet switched connections between a master unit
and a slave unit(s). The master unit can transmit to a single
slave, a group of slaves or all slaves in a master.fwdarw.slave
time slot. If a slave decodes that the transmission was intended
for it (via decoding its address in the transmission), then it is
permitted to transmit back to the master in the next
slave.fwdarw.master time slot. There is no reply transmission if
the transmission was not addressed to a specific slave, i.e., the
transmission was a broadcast to all slave units.
[0049] Both 802.11 wireless LANs and BT wireless networks operate
in the same 2.4 GHz ISM band. Accordingly, transmissions from an
802.11 wireless LAN will interfere with a BT wireless network and
vice versa. The interference is especially problematic if a single
digital device is simultaneously in both an 802.11 wireless LAN and
a BT wireless network. When a digital device is collocated in both
wireless networks, then when the digital device is transmitting a
packet in one network, the transmission will saturate the receiver
of the other network. This in effect "blinds" the receiver of the
other network.
[0050] Referring now to FIG. 3, a diagram illustrates a digital
device 310 collocated with both an 802.11 wireless LAN and a BT
wireless network. The digital device 310 may be (but not limited
to) personal computers (PCs), personal digital assistants (PDAs),
cellular and personal communications system (PCS) telephones,
computer network gateways, handheld computers, and pen-based
computers, or any other type of digital device that can connect to
wireless networks. The digital device 310, as shown, contains two
network interface cards (NICs). One NIC is for the 802.11 wireless
network (802.11 NIC 320) and a second NIC is for the BT wireless
network (BT NIC 330). In a typical application, the 802.11 NIC 320
is used to provide wireless connectivity to a high data-rate
network and perhaps to the Internet, while the BT NIC 330 provides
a low data-rate connection to devices such as cellular/PCS
telephones, personal digital assistants, printers, etc.
[0051] FIG. 3 displays the digital device 310 communicating with
other stations 340 and 350 from an 802.11 wireless LAN and other
slaves 360 and 370 from a BT network. FIG. 3 does not display an
802.11 access point or a BT master. It is conceivable that the
digital device 310 contain an 802.11 access point or a BT master or
both, although according to the present invention, it does not have
to contain either.
[0052] Although BT networks use a frequency hopping transmission
mechanism that changes transmission frequency after each time slot,
collisions between BT and 802.11 wireless networks can and do
occur. This is in part due to the wide spectral footprint of the
802.11 wireless network, where the entire 2.4 GHz ISM band can only
support three different communications channels. Therefore, at any
given time, an 802.11 wireless network occupies a full one-third of
the communications band.
[0053] Referring now to FIG. 4, a diagram illustrates a collision
between a BT time-division duplex time slot stream and an 802.11
data frame. FIG. 4 displays an alternating sequence of BT
master.fwdarw.slave and slave.fwdarw.master time slots (slots 410,
415, 420, 425, 430, and 435). Also displayed is a single 802.11
frame 440. The frame 440 is transmitted using contention access,
where the station is free to transmit if it senses that the medium
is idle and its back-off timer is at zero. If there had been data
in master.fwdarw.slave time slot 420, the 802.11 frame 440 would
not have been transmitted. But since the 802.11 frame 440 was
transmitted, the BT slots 420, 425, and 430 cannot be used to
transmit or receive data. Additionally, since BT networks do not
require checking medium status prior to transmission, the BT master
may transmit in the master.fwdarw.slave slot 430. If it does, then
chances are high that the 802.11 frame 440 will be corrupted.
Therefore, a mechanism is needed to coordinate transmissions of the
wireless networks, especially when they are collocated in a single
digital device.
[0054] A solution to multiple collocated wireless networks can be
as simple as periodically turning the wireless networks on and off.
While one wireless network is on, the other wireless networks are
off. This solution has an advantage of ease in implementation.
However, turning a network on and off has significant overhead
costs such as in re-training the network when it is powered back
on. Additionally, turning a network off and then turning another
network on can be wasteful if the network being turned on has no
transmissions to send.
[0055] Alternatively, multiple wireless networks can collocate if
they know when they can and cannot transmit. Because when one
wireless NIC in a digital device transmits it often "blinds" any
other wireless NICs in the same digital device, many problems can
be alleviated if wireless NICs know when one another is
transmitting or receiving. A way to share the transmission and
receiving information is to provide it to a centralized controller.
The centralized controller can then maintain a schedule of
transmissions. The centralized controller can be further extended
to include a reservation system where a wireless NIC can request
transmission permission prior to transmitting. If the permission is
not granted, the wireless NIC will not transmit.
[0056] Referring now to FIG. 5, a diagram illustrates a coordinator
unit (CU) 510 for controlling transmissions for collocated wireless
networks according to a preferred embodiment of the present
invention. According to a preferred embodiment of the present
invention, the CU 510 is located in the digital device 310 with the
collocated wireless networks. If the CU 510 is located in the
digital device, then the CU 510 is preferably coupled to the
wireless network NICs via a wired connection. In another preferred
embodiment of the present invention, the CU 510 is coupled to each
of the wireless network NICs by a separate wired connection.
[0057] Alternatively, the CU 510 may be external to the digital
device 310 and coupled to the digital device 310 via some type of
physical connection, either wired or wireless. If the coupling is
wireless, then ideally, the wireless connections should be at a
different operating frequency from the operating frequency of the
collocated wireless networks. In another preferred embodiment of
the present invention, each wireless connection between the CU 510
and the wireless network NICs uses a different operating frequency.
The purpose of being directly connected to the digital device with
multiple collocated wireless networks rather than sharing the same
wireless network connections is that the CU 510 may immediately
receive messages from the wireless network NICs without
encountering the problem of wireless messages colliding, i.e., the
same problems that it is trying to solve.
[0058] The CU 510 is coupled to an 802.11 media access control
(MAC) layer 515, which in turn is coupled to an 802.11 physical
(PHY) layer 520, which is coupled to a wireless medium 525. The CU
510 is also coupled to a BT MAC layer 530. Similarly to the 802.11
side of picture, the BT MAC layer 530 is coupled to a BT PHY layer
535, which in turn is coupled to the wireless medium 525. In
general, a MAC layer is responsible for scheduling protocols and
access control procedures to accomplish the delivery of data units,
while a PHY layer controls such things as physical layer signaling
techniques and interface functions for the wireless medium.
[0059] The CU 510 receives reservation requests from either the
802.11 MAC 515 or the BT MAC 530 or both or any other wireless
network's MAC layer to which it may be coupled. When the CU 510
receives the reservation request, the CU 510 examines the scheduled
transmissions and will grant the reservation request if there are
no scheduled transmissions during the same time period. According
to a preferred embodiment of the present invention, the CU 510
calculates a start time and a stop time for the reservation
request, based on information provided in the reservation request,
and compares the start and stop times with a list of granted
reservation start and stop times.
[0060] In a situation when the wireless networks are busy, multiple
reservation requests may arrive at approximately the same time
(e.g., a subsequent reservation request arrives for an overlapping
time period before a first reservation request can be processed).
Should multiple reservation requests for the same time period
occur, the CU 510 can use a probabilistic virtual contention
mechanism for collision resolution to resolve the conflicting
requests. A discussion of the probabilistic virtual contention
mechanism for collision resolution will be presented below. Once
the CU 510 has scheduled a reservation request, it returns a
reservation to the requesting MAC. If the requesting MAC does not
receive a reservation for its reservation request, the
corresponding wireless network is not able to transmit.
[0061] Referring now to FIG. 6a, a diagram provides a more detailed
view of the CU 510 according to a preferred embodiment of the
present invention. The CU 510 comprises an arbiter unit 610 and a
scheduler unit 620. Not shown, but also part of the CU 510 is a
reservation request flag line. The reservation request flag line is
a status line from the scheduler unit 620 to the arbiter unit 610
and reports the status of the pending reservation request. The
arbiter unit 610 receives the reservation requests from the various
wireless networks and if there are no conflicting requests,
forwards the reservation requests to the scheduler unit 620 where
they are scheduled and granted (if possible) or rejected (if not
possible). The scheduler unit 620 uses the reservation request flag
line to return the results of the pending reservation request to
the arbiter unit 610. The arbiter unit 610 returns the results to
the requesting wireless network.
[0062] The scheduler unit 620 maintains a list of the reservations
that it has granted and when a new reservation comes in, it checks
the new reservation against its list of existing reservations. If
the time requested is free, then the scheduler unit 620 will grant
the reservation and insert the reservation into its list. If the
time requested is not available, then the scheduler unit 620 will
reject the reservation request.
[0063] If there are multiple pending requests for a reservation
that spans a common time period, i.e., a conflicting reservation,
the arbiter unit 610 must decide which request to grant and which
request to reject. According to a preferred embodiment of the
present invention, the arbiter unit 610 uses a probabilistic
mechanism referred to as virtual contention for collision
resolution to decide which reservation request is granted. Virtual
contention follows a specific set of rules and probabilities.
[0064] Referring now to FIG. 6b, a diagram illustrates an algorithm
for granting reservation requests from conflicting reservations
requests according to a preferred embodiment of the present
invention. The algorithm is also referred to as the virtual
contention for collision resolution algorithm. If the reservation
request is from a BT SCO transmission (block 650), then the BT SCO
transmission is granted. Virtual contention gives BT SCO
transmissions the highest priority and grants BT SCO transmission
reservation requests over other requests. For remaining
transmission types, the following decision is performed should
conflicting reservation requests be made. The arbiter unit 610
selects a random number, D, from the range of [0, 1) (block 655).
The arbiter unit 610 then compares the random number, D, with a
prespecified value, D.sub.p (block 660). D.sub.p is a threshold
value ranging from [0, 1]. If D is>=D.sub.p, then grant the BT
request and reject the 802.11 request (block 670). If D
is<D.sub.p, then reject the BT request (block 665).
[0065] According to a preferred embodiment of the present
invention, if there are more than two pending requests in a
conflicting reservation (for the case when there are more than two
collocated wireless networks), then the virtual contention
collision resolution algorithm generates a random number from a
range [0, 1). This random number is then compared with a threshold,
D.sub.p, which has N-1 numbers, where N is the number of wireless
networks involved in the conflicting reservation request. The
reservation request is given to the wireless network based on where
the random number falls in the threshold.
[0066] As an example of the virtual contention collision resolution
algorithm for a situation with more than two conflicting
reservation requests, let there be three conflicting reservation
requests in a digital device with four collocated wireless
networks. The virtual contention collision resolution algorithm
would then generate a random number, D, which lies in the range [0,
1). The random number, D, is then compared against a threshold,
D.sub.p, which has two number, N1 and N2. The values of the numbers
in the threshold, D.sub.p, can be prespecified values and they may
or may not be dynamically adjustable to meet current network
performance conditions. According to a preferred embodiment of the
present invention, a range [0, N1) would be assigned to conflicting
wireless network number 1, a range [N1, N2) would be assigned to
conflicting wireless network number 2, and a range [N2, 0] would be
assigned to conflicting wireless network number 3. Then, depending
on which assigned range the random number, D, lies, the assigned
conflicting wireless network would be granted the reservation. The
above is an example and the actual assignment of the ranges to
conflicting wireless networks may be different based on system
design decisions, current network performance issues, etc.
[0067] According to another preferred embodiment of the present
invention, the value of D.sub.p, though initially prespecified, can
be adjusted to meet changing network conditions and performance
preferences. The CU 510 may be able to monitor network performance
and if it notices an imbalance in one wireless networks'
performance, the arbiter unit 610 can adjust the value of D.sub.p
to more fairly balance the wireless networks' performance.
Alternatively, the CU 510 may be commanded to effectively prevent
one wireless network's transmissions if another wireless network
has a transmission at the same time. The arbiter unit 610 may the
adjust the value of D.sub.p to a value such that it will always
grant a reservation request to the preferred wireless network
should there be a conflicting request.
[0068] As discussed previously, there are two types of wireless
stations in an 802.11 wireless LAN (a wireless station and an
access point) and there are two types of wireless stations in a BT
wireless network (a master unit and a slave unit). Algorithms for
requesting reservation requests and handling request rejections
differ according to the particular type of wireless station the
digital device with the collocated wireless networks happens to be.
Optimally, scheduling would be most readily accomplished and the
best performance would be achieved if the digital device had both
an 802.11 access point and a BT master unit. This is due to the
fact that the 802.11 access point controls communications during
the contention-free period in the 802.11 network and the BT master
unit controls all communications in the BT network. This particular
configuration minimizes the occurrence of receiving unexpected
packets.
[0069] Referring now to FIG. 7a, a diagram illustrates an algorithm
700 for requesting reservation requests and processing request
rejections when the digital device contains an 802.11 wireless
station as one of the collocated wireless networks according to a
preferred embodiment of the present invention. The algorithm 700
executes on the 802.11 wireless station when the 802.11 wireless
network is operating in contention-free mode.
[0070] The wireless station remains idle until it receives a
poll-frame from the 802.11 access point (block 705). As discussed
previously, a wireless station operating in contention-free mode
cannot transmit any frames unless it first receives a poll-frame
from the 802.11 access point. When the wireless station receives
the poll-frame, it will immediately send a reservation request to
the CU 510 (block 710). The reservation request will request a
transmission time that begins immediately and last for a duration
that is specified in the poll-frame from the 802.11 access point.
The CU 51 0, knowing that the wireless station is operating in
contention-free mode, will give the reservation request high
priority and will grant the reservation request unless there is
already some outstanding request for the time period specified in
the request.
[0071] In block 715, the wireless station checks to see if its
request has been granted. If the request has been granted, then the
wireless station can transmit. If the request has not been granted,
the wireless station cannot transmit and the chance to transmit is
wasted. The wireless station must wait until it receives another
poll-frame from the access point prior to requesting another
reservation from the CU 510.
[0072] Referring now to FIG. 7b, a diagram illustrates an algorithm
750 for requesting reservation requests and processing request
rejections when the digital device contains an 802.11 access point
as one of the collocated wireless networks according to a preferred
embodiment of the present invention. The algorithm 750 executes on
the 802.11 access point when the 802.11 wireless network is
operating in contention-free mode.
[0073] In contention-free mode, an 802.11 access point transmits a
poll-frame to a wireless station, granting the wireless station
permission to transmit for a time duration specified in the poll
frame. Due to the fact that the 802.11 access point controls the
initiation of the frame exchange sequence, the 802.11 access point
knows exactly when the transmissions will commence. Hence, prior to
transmitting the poll-frame, the 802.11 access point sends a
reservation request to the CU 510 (block 755) for a reservation
that begins immediately and lasts for a period of time equal to the
amount of time required for the 802.11 access point to transmit the
poll-frame plus the time duration specified in the poll-frame.
[0074] After sending the reservation request in block 755, the
802.11 access point will check to see if its request has been
granted (block 760). If the request has been granted, then the
802.11 access point can transmit the poll-frame (block 765). If the
request has not been granted, the 802.11 access point cannot
transmit the poll-frame and must wait until a next available
transmission time and request another reservation (block 770). The
next available transmission time may be the next time that the
transmission medium becomes idle.
[0075] Referring now to FIG. 8, a diagram illustrates an algorithm
800 for requesting reservation requests and processing request
rejections when the digital device contains an 802.11 wireless
station or an 802.11 access point as one of the collocated wireless
networks according to a preferred embodiment of the present
invention. The algorithm 800 executes on the 802.11 wireless
station or 802.11 access point when the 802.11 wireless network is
operating in the contention period. When the 802.11 wireless
network is operating in the contention period, both the wireless
station and the access point operates in a similar fashion and will
be generically referred to as a station.
[0076] The algorithm 800 begins when the station has some frames to
transmit. When the station has frames to transmit, the station
first checks to see if the medium is idle (block 810). If the
medium is not idle, then the station will continue to wait until
the medium becomes idle. Once the medium becomes idle, the station
must wait an additional DIFS period (block 815). The additional
wait is to ensure that any frames that were delayed due to
processing or signal propagation delays have had a chance to be
detected by all wireless stations in the 802.11 network.
[0077] If the medium remains idle for the additional DIFS period
(block 815), then the station generates a random backoff time
(block 820). The random backoff time is a probabilistic load
distribution method specified for in the IEEE 802.11 technical
standards. The actual methodology used in generating the backoff
time is beyond the scope of the present invention. With the backoff
time in hand, the station sends a reservation request to the CU 510
(block 825) for a reservation starting at the current time plus the
backoff time for a duration equal to the size of the frames that it
wishes to transmit plus some miscellaneous time for overhead.
[0078] After requesting the reservation, the station begins a
backoff process (blocks 830 and 835). The station begins the
backoff process by loading the backoff time into a backoff counter.
The station checks to see if the backoff counter is equal to zero
(block 830). If the backoff counter is not equal to zero, then the
station waits for the expiration of a network time slot and
decrements the value in the backoff counter by one if the expired
network time slot was idle (block 845). The backoff process
continues until the backoff counter reaches zero.
[0079] Once the backoff counter reaches zero, the station checks to
see if its reservation request had been granted (block 840). If the
request was granted, then the station is free to transmit (block
845). If the request was denied, then the station cannot transmit
and station begin the entire backoff procedure once again with a
new random backoff time
[0080] In a BT wireless network, there are two distinct operating
modes, SCO and ACL. Both operating modes are actually quite similar
and only several minor differences differentiate the two modes. In
both SCO and ACL, a BT master unit initiates the transmission and a
slave unit cannot transmit unless it was specifically addressed by
the BT master unit. SCO differs from ACL in that SCO transmissions
are scheduled well in advance and is directed to a single slave
unit. As a result of the similarities, a single algorithm (one for
the master unit and one for the slave units) for requesting
reservation requests and processing request rejections is
sufficient for both operating modes.
[0081] Referring now to FIG. 9a, a diagram illustrates an algorithm
900 for requesting reservation requests and processing request
rejections when the digital device contains a BT master unit as one
of the collocated wireless networks according to a preferred
embodiment of the present invention. The algorithm 900 executes on
the BT master unit when the BT wireless network is operating in
either SCO or ACL modes.
[0082] In a BT wireless network, the master unit initiates all
transmissions. Therefore, if the collocated network device is a
master unit, the scheduling of transmissions is a relatively simple
matter. When the master unit is scheduling SCO transmissions, it
may simply schedule an entire sequence of SCO transmissions at one
time. This is possible because SCO transmissions are periodic.
According to a preferred embodiment of the present invention, BT
SCO transmissions are of the highest priority and will be granted
over any conflicting reservation requests.
[0083] For a SCO transmission, the BT master unit sends a
reservation request to the CU 510 for a master.fwdarw.slave time
slot and a slave.fwdarw.master time slot pair at a specified time
(block 910). The master unit then checks to see if the reservation
request has been granted (block 915). If the request has been
granted, then the master unit is free to transmit when the
requested time slot arrives. If the request was rejected, then the
master unit will request the next available master.fwdarw.slave and
slave.fwdarw.master time slot pair. Since the SCO transmissions are
given the highest priority, the SCO requests are typically
granted.
[0084] For ACL transmissions, there are two possibilities. There is
a directed ACL transmission, where a slave unit is specifically
addressed and a response from the addressed slave unit is expected.
In this case, the algorithm 900 executes in the same manner as for
a SCO transmission as described above. There is also a broadcast
ACL transmission, where no slave unit is specifically addressed and
no response is expected. In this case, the algorithm 900 requests a
reservation for a master.fwdarw.slave time slot only and no
slave.fwdarw.master time slot is requested. However, the steps
taken by the algorithm 900 are the same as described above.
[0085] Referring now to FIG. 9b, a diagram illustrates an algorithm
950 for requesting reservation requests and processing request
rejections when the digital device contains a BT slave unit as one
of the collocated wireless networks according to a preferred
embodiment of the present invention. The algorithm 950 executes on
the BT slave unit when the BT wireless network is operating in
either SCO or ACL modes.
[0086] In a BT wireless network, a slave unit can only transmit
when it decodes a transmission that is specifically addressed to
it. It is expected that the slave unit transmit a response to a
transmission addressed to it in the next slave.fwdarw.master time
slot immediately after the slave receives the initial transmission.
Therefore, there is a certain level of urgency that the slave be
granted a reservation request when it requests for one.
[0087] The algorithm 950 begins after the slave unit decodes a
transmission that is specifically addressed to it (block 955). The
slave unit sends a reservation request to the CU 510 for the next
slave.fwdarw.master time slot (block 960). Since
master.fwdarw.slave and slave.fwdarw.master time slots alternate in
a BT network, the next slave.fwdarw.master time slot is the slot
immediately following the time slot that carried the transmission
to the slave unit. The slave unit checks to see if the request has
been granted in block 965. If the request was granted, then the
slave unit is free to transmit in block 970. If the request was
rejected, then the slave unit will have to wait for being addressed
by the master again before making another reservation.
[0088] According to a preferred embodiment of the present
invention, there is a request counter that maintains a count of how
many times a particular request from a particular requester has
been rejected. Once the count exceeds a specified threshold, then
the request may be marked as a failed request and can no longer be
requested. According to another preferred embodiment of the present
invention, as the request counter increases, the priority is also
increased. By increasing the priority granted a request, the
probability of the request being granted will also increase.
[0089] While this invention has been described with reference to
illustrative embodiments, this description is not intended to be
construed in a limiting sense. Various modifications and
combinations of the illustrative embodiments, as well as other
embodiments of the invention, will be apparent to persons skilled
in the art upon reference to the description. It is therefore
intended that the appended claims encompass any such modifications
or embodiments.
* * * * *