U.S. patent application number 09/823589 was filed with the patent office on 2002-02-14 for method and apparatus for variable power control in wireless communications systems.
Invention is credited to Sharony, Jacob.
Application Number | 20020018451 09/823589 |
Document ID | / |
Family ID | 27396435 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020018451 |
Kind Code |
A1 |
Sharony, Jacob |
February 14, 2002 |
Method and apparatus for variable power control in wireless
communications systems
Abstract
A wireless communications system that has variable power levels
in communications frames may be provided. The wireless
communication system may include a plurality of cells that include
transmitters for providing communications services to a geographic
area. Each cell may be assigned a channel selected from a limited
number of available channels. Communications frames may be
transmitted in the cells using a plurality of data rates. Each
communications frame may include a portion that is to be
transmitted at one of the data rates. The power level used for
transmitting that portion of a communications frame may be selected
(e.g., lowered) to limit at what distances that portion may be
properly received. Locations of cells in the geographic area may be
partly determined based on the power levels.
Inventors: |
Sharony, Jacob; (Dix Hills,
NY) |
Correspondence
Address: |
FISH & NEAVE
1251 AVENUE OF THE AMERICAS
50TH FLOOR
NEW YORK
NY
10020-1105
US
|
Family ID: |
27396435 |
Appl. No.: |
09/823589 |
Filed: |
March 30, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60217588 |
Jul 12, 2000 |
|
|
|
60245834 |
Nov 3, 2000 |
|
|
|
Current U.S.
Class: |
370/329 ;
455/522 |
Current CPC
Class: |
H04W 52/24 20130101;
H04W 52/267 20130101; H04W 52/325 20130101 |
Class at
Publication: |
370/329 ;
455/522 |
International
Class: |
H04Q 007/00 |
Claims
What is claimed is:
1. A method for use in wireless communications systems, comprising:
providing a communications frame for transmission in the wireless
communications system; and transmitting a first portion of the
communications frame at a first data rate and at a first power
level and a second portion of the communications frame at a second
data rate that is different from the first data rate and at a
second power level that is different from the first power
level.
2. The method of claim 1 wherein said transmitting comprises
transmitting the communications frame at a transmitter that is part
of a wireless local area network communications system.
3. The method of claim 1 wherein said providing comprises providing
in the communications frame a set of digital information that is
directed to a receiver in the wireless communications system.
4. The method of claim 1 wherein said transmitting comprising
transmitting the communications frame over air for a receiver in
the wireless communication system.
5. The method of claim 1 wherein said providing comprising
providing the communications frame in a format that is for
transmission in a wireless local area network communications
system.
6. The method of claims 1 further comprising: listening to a
particular frequency band to determine whether the frequency band
is available for transmission; and said transmitting comprising
transmitting the communications frame on that particular frequency
band.
7. The method of claim 1 wherein said transmitting comprising
providing the first data rate for the first portion to be lower
than the second data rate for the second portion.
8. The method of claim 7 wherein said transmitting comprises
providing the first power level of the first portion to be lower
than the second power level for the second portion.
9. The method of claim 1 wherein said transmitting comprising
providing the first data rate for the first portion to be
substantially lower than the second data rate for the second
portion.
10. The method of claim 9 wherein said transmitting comprises
providing the first power level of the first portion to be lower
than the second power level for the second portion.
11. The method of claim 1 wherein said transmitting comprising
transmitting the communications frame using direct sequence spread
spectrum communications techniques.
12. The method of claim 1 wherein said transmitting comprises
providing the first portion to be a preamble portion of the
communications frame.
13. The method of claim 1 wherein said transmitting comprises
providing the second portion to be a data portion of the
communications.
14. The method of claim 1 wherein said transmitting comprising
providing the first and the second portions to substantially
comprise the communications frame.
15. The method of claim 1 further comprising providing a plurality
of communications cells in the wireless communications system.
16. The method of claim 15 further comprising repeating said
transmitting for different communications frames in each cell.
17. The method of claim 16 further comprising providing a plurality
of frequency bands with one of the frequency bands being assigned
to each of the communications cells for carrying transmissions.
18. The method of claim 17 wherein said providing a plurality of
frequency bands comprises providing more communications cells than
frequency bands.
19. The method of claim 17 further comprising: providing wireless
communications services to a substantially contiguous geographic
area using the plurality of cells; positioning the communications
cells that have been assigned the same frequency band at locations
in the geographic area at which the cells operate substantially
without interference from the other cells.
20. The method of claim 19 wherein said transmitting comprises:
providing the first data rate for the first portion to be lower
than the second data rate for the second portion; and providing the
first power level of the first portion to be lower than the second
power level for the second portion.
21. The method of claims 20 further comprising listening in each of
the communications cells to the frequency band assigned to that
cell to determine whether that frequency band is available for
transmission by the transmitter that is operating in that cell.
22. A transmitter for use in wireless communications systems,
comprising: a transmitter configured to provide a communications
frame for transmission in the wireless communications system, and
configured to transmit a first portion of the communications frame
at a first data rate and at a first power level and a second
portion of the communications frame at a second data rate that is
different from the first data rate and at a second power level that
is different from the first power level.
23. The transmitter of claim 22 wherein said transmitter is
configured to operate in a wireless local area network
communications system.
24. The transmitter of claim 22 wherein said transmitter is
configured to include in the communications frame a set of digital
information that is directed to a receiver in the wireless
communications system.
25. The transmitter of claim 22 wherein said transmitter is
configured to transmit the communications frame over air for a
receiver in the wireless communication system.
26. The transmitter of claim 22 wherein said transmitter is
configured to provide the communications frame in a format that is
for transmission in a wireless local area network communications
system.
27. The transmitter of claims 22 wherein said transmitter is
configured to listen to a particular frequency band to determine
whether the frequency band is available for transmission, and to
transmit the communications frame on that particular frequency
band.
28. The transmitter of claim 22 wherein said transmitter is
configured to have the first data rate for the first portion be
lower than the second data rate for the second portion.
29. The transmitter of claim 28 wherein said transmitter is
configured to have the first power level of the first portion be
lower than the second power level for the second portion.
30. The transmitter of claim 22 wherein said transmitter is
configured to have the first data rate for the first portion be
substantially lower than the second data rate for the second
portion.
31. The transmitter of claim 30 wherein said transmitter is
configured to have the first power level of the first portion be
lower than the second power level for the second portion.
32. The transmitter of claim 22 wherein said transmitter is
configured to transmit the communications frame using direct
sequence spread spectrum communications techniques.
33. The transmitter of claim 22 wherein said transmitter is
configured to have the first portion be a preamble portion of the
communications frame.
34. The transmitter of claim 22 wherein said transmitter is
configured to have the second portion be a data portion of the
communications.
35. The transmitter of claim 22 wherein said transmitter to have
the first and the second portions substantially comprise the
communications frame.
36. A wireless communications system comprising: a plurality of
communications cells; a plurality of the transmitters of claim 22
that are each to operate in one the communications cells.
37. The system of claim 36 wherein each transmitter is configured
to transmit communications frames having the first portion at the
first data rate and the first power level and the second portion at
the second data rate and second power level.
38. The system of claim 37 wherein a plurality of frequency bands
are assigned to the cells with the transmitters in each cell being
configured to communicate on the frequency bands assigned to the
cell in which the transmitter is operating.
39. The system of claim 38 wherein the number of communications
cells is more than the number of frequency bands.
40. The system of claim 38 wherein the system is configured to
provide wireless communications services to a substantially
contiguous geographic area using the plurality of cells with the
communications cells that have been assigned the same frequency
band being positioned at locations in the geographic area at which
the cells operate substantially without interference from the other
cells.
41. The system of claim 40 wherein said transmitters are configured
to have the first data rate for the first portion be lower than the
second data rate for the second portion and have the first power
level of the first portion be lower than the second power level for
the second portion.
42. The system of claims 41 wherein said transmitters are
configured to listen to the frequency band assigned to the cell to
determine whether that frequency band is available for
transmission.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 60/217,588, filed Jul. 12, 2000, and the
benefit of U.S. Provisional Patent Application No. 60/245,834,
filed Nov. 3, 2000, which are hereby incorporated by reference
herein in their entirety.
BACKGROUND OF THE INVENTION
[0002] This invention relates to wireless communications systems,
and more particularly, to wireless communications systems having
variable power communications frames.
[0003] Some known communications systems may comprise
communications cells in which transmitters may transmit information
at a data rate that is selected from a plurality of fixed data
rates that are available to the system. In such systems,
information may be transmitted in communications frames that
include a preamble portion. The preamble portion of communications
frames may always be transmitted at a specific data rate. The
preamble portion may be transmitted at the lowest one of the
available data rates to accommodate receivers in the system that
may not be capable of operating at the higher data rates that are
available. Data rates for other portions of communications frames
may be transmitted at any of the fixed data rates that are
available in the system. Known techniques for implementing such
systems have been deficient in meeting communications services
demands (e.g., high speed throughput, low inter-cell interference,
etc.) without substantially adding complexity, cost, circuitry,
etc.
[0004] Such known systems include some wireless local areas network
communications systems. Wireless local area network communications
systems ("wireless LANs") are typically used in applications that
involve mobile computers, in applications where wireline
installation is not feasible, etc. Such applications include
warehouse inventory tracking, portable point of sale, shipping and
receiving, package tracking, etc.
[0005] The IEEE 802.11 communications standard has been used by
some vendors to provide interoperability between wireless LAN
equipment. The 802.11 standard specifies a protocol in which
information is transmitted in frames. The standard specifies
features such as frame size, frame content information, data rates,
roaming, etc. The primary type of information that was initially
transmitted in systems that were designed to the 802.11 standard as
published was information such as barcode information, point of
sale information, package tracking information, etc. In such known
systems, several remote terminals may be in communications with a
single access point to receive and transmit information such as bar
code information, point of sale information, package tracking
information, etc. The standard as published specifies a
communications medium that is shared by transmitters (e.g., an
access point and one or more remote terminals).
SUMMARY OF THE INVENTION
[0006] In accordance with the principles of the present invention,
variable power level communications for wireless communications
systems may be provided. A wireless communications system, such as
a wireless LAN, may be provided. Transmitters (e.g., remote
terminals) and receivers (e.g., access points) in the
communications system may communicate using communications frames.
Communications services may be provided for a substantially
contiguous geographic area with a plurality of transmitters and
receivers in a plurality of cells. Communications frames may be
transmitted in two substantially contiguous portions that are at
two power levels. A first portion of a communications frame may be
transmitted at one data rate (e.g., the lowest data rate supported
by the system) and at one power level. The remaining portion of a
communications frame may be transmitted at one data rate (e.g.,
other supported data rates) and at another power level. The power
level for the remainder portion may be greater than the power level
for the first portion. The first portion may be a preamble portion
of a communications frame. A plurality of cells and a plurality of
channels may be used. Each cell may be assigned one channel from
the plurality of channels. The number of cells may be greater than
the number of available channels. Positions of cells in a
communications system may be determined based on the variable power
levels of the communications frames, number of channels, and the
data rates. A power level for a first portion that is at a lowest
data rate may be selected so that the first portion may have
approximately the same signal propagation characteristics as a
remainder portion that is at the next lowest data rate at another
power level (e.g., higher power level). Transmitters may be
configured to operate using a spread spectrum communications
technique, such as direct sequence spread spectrum techniques.
Transmitters may listen to a channel or frequency band on which the
transmitter is configured to transmit and may determine whether the
channel is available for transmission.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Further features of the invention, its nature and various
advantages will be more apparent from the following detailed
description, taken in conjunction with the accompanying drawings in
which like reference characters refer to like parts throughout, and
in which:
[0008] FIG. 1 is a diagram of an illustrative communications
network that includes an illustrative wireless local area network
in accordance with the present invention;
[0009] FIG. 2 is a diagram of an illustrative communications frame
for use in wireless communications systems in accordance with the
present invention;
[0010] FIG. 3 is a diagram of illustrative communications cells for
a geographic area in accordance with the present invention; and
[0011] FIG. 4 is a flow chart of illustrative steps involved in
providing communications services having variable power
communications frames.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The present invention improves communications in wireless
communications systems. In a country or particular geographic area,
specific frequency bands or channels may be licensed or designated
for use to different types of wireless communications systems. For
example, in the United States, three bands may have been set aside
for use by wireless LANs. Wireless communications systems may be
implemented in groups of communications cells to provide
communications services for a substantially contiguous geographic
region. One criterion in determining locations of cells in the
geographic region may be channel re-use. A cell may be assigned one
channel for providing communications in that cell. Positions of
cells in a geographic area may be determined based on interference
that may be caused by the use of that channel in other cells in
that area (e.g., channel re-use factor).
[0013] Interference between cells that use the same channel may be
partly dependent on the data rate. An inverse type relationship may
exist between the signal propagation characteristics of
communications (e.g., communications frames) and the data rate used
for the communications. For example, lower data rates (e.g., the
lowest available data rate), rather than higher data rates of a
system, may factor in to determining how far apart cells using the
same channel (e.g., frequency band) may be positioned to allow
those cells to operate substantially without interference from each
other.
[0014] In cells that include receivers that support higher (raw)
data rates of the system, actual data rates in the cells may depend
on the distance between a transmitter (e.g., a terminal) and a
receiver (e.g., an access point). For example, when the transmitter
and receiver support data rates of 1, 2, 5.5, and 11 mbps at one
transmission power level, the raw bit rate may be 11 mbps at a
distance of 50 ft or less; the raw bit rate may be 5.5 mbps at a
distance of 100 ft to 50 ft; the raw bit rate may be 2 mbps at a
distance of 100 ft to 250 ft; and the raw bit rate may be 1 mbps at
a distance of 250 ft to 400 ft. Where there are a limited number of
communications bands, for example three communications bands,
adjacent cells may be assigned different bands with a reuse factor
of three to cover a given area with cells. The following table
shows how the total number of interfering cells assigned to one of
the three bands may increase as distance between the cells is
increased when frames are transmitted at one power level.
1 At distance No. of interfering cells .RTM. = Cell Radius) 6 3R 6
3{square root}3R 6 6R 12 3{square root}7R 6 9R
[0015] Communications frames may be transmitted in two portions at
differing data rates. Different power levels may be used to
transmit the two portions of a communications frame. One portion of
the frame may be transmitted at one level and another portion of
the frame may be transmitted at a different level. In each frame,
one portion of the frame (e.g., a preamble portion) may have to be
transmitted at the lowest supported data rate. The power level for
the portion that is to be transmitted at the lowest supported data
rate may be selected to be lower than the power level for the
remaining portions of the frame. Lowering the power level for the
low data rate portion of the frame allows cells to be positioned
more closely together to meet desired demands on communications
services (e.g., by providing actual data rates that are closer to
raw data rates).
[0016] With reference to FIG. 1, wireless LAN 20 may include a
plurality of cells 22. Cell 22 may include an access point 24
(which is sometimes referred to as a wireless local bridge or a
base station). Cell 22 may include remote terminals 26. Access
point 24 and remote terminals 26 may be the transmitters and
receivers of the system. Each terminal 26 may be a mobile,
portable, or stationary terminal. Each terminal 26 may be a desktop
workstation, laptop computer, palm top computer, handheld personal
computer, pen-based computer, personal digital assistant, handheld
scanner, data collector, handheld printer, etc. Each terminal 26
may include wireless-network-interface resources that are
configured to provide two-way radio or infrared signal
communications. Such resources may include an interface card (or an
external modem), a software driver, and an antenna. Other suitable
resources may also be used, but for clarity and brevity, the
wireless network interface resources will be discussed primarily in
the context of an interface card, a software driver, and an
antenna. The interface card may have been configured to use a
standard computer-bus interface (e.g., ISA, PCMCIA, etc.) or
standard computer port (e.g., RS232, RS422, etc.) to provide
convenient access to terminal equipment.
[0017] A network-operating-system may be implemented on each
terminal 26. In each terminal 26, the interface card may be coupled
to the network-operating-system application using the software
driver. The interface card for each remote terminal 26 may be a
network-communications interface. The network interface card for
each terminal 26 are typically implemented to use a carrier sense
access protocol and to modulate communications signals with a
spreading sequence. Access point 24 may be an interface for
communicating between wireless network 20 and a wireline network.
Access point 24 may be configured to provide a communications
gateway between terminals 26 that are in cell 22 and between a
wireline network and the terminals 26. Access point 24 may include
a resource(s) (e.g., software, hardware, or a combination thereof)
that is configured to connect the access point to a wireline
network (e.g., on ethernet network, a token ring network, etc.).
Access point 24 is typically configured to convert signals between
wireline and wireless communications mediums. The conversion may
allow the access point to pass communication information between
the wireline network and wireless remote terminals 26.
[0018] Access points are typically provided with sufficient
processing, hardware, software, etc. to operate in compliance with
the IEEE 802.11 (e.g., to provide 802.11 roaming, standard 802.11
data rates, etc.) and to provide additional features that are
developed by a vendor. Access point 24 may be implemented using a
personal computer (e.g., a Power PC, an IBM compatible computer),
server, workstation, etc., having an appropriate operating system,
wireless-network-interface resources, wireline-network-interface
resources, network-operating-system applications, etc.
[0019] Access point 24 and remote terminals 26 may be configured to
communicate using spread spectrum modulation techniques (e.g.,
direct sequence spread spectrum modulation, frequency hopping
spread spectrum modulation, etc.).
[0020] The IEEE 802.11 standard specifies the format and content of
communications frames. Communications frames that may also be
sometimes referred to as messages or packets may be of variable
size with the size of each frame being identified in frame header
information. In some embodiments, the body of each frame may vary
from 0 to 2312 octets. Communications frames may comprise digital
information that is for a receiver (e.g., a terminal or access
point) in the system.
[0021] In operation, initially when one of the terminals 26 is
powered, that terminal 26 may seek to join cell 22 by associating
with access point 24. Remote terminal 26 may become associated with
access point 24 after a preliminary exchange of communications
between access point 24 and terminal 26. A plurality of terminals
26 may be associated with each access point 24. Each terminal 26
may have different communications capabilities and requirements.
Access point 24 may manage the communications traffic between
terminals 26 and the wireline network. Access point 24 may manage
the communications traffic by controlling when frames are
transmitted to each remote terminal 26 in cell 22. The
communications traffic in cell 22 may include data frames (e.g.,
signals that carry frames to provide data communications), voice
frames (e.g., signals that carry frames to provide voice
communications), real-time frames (e.g., signals that carry frames
to provide real-time communications such as multimedia or voice
communications), management frames (e.g., signals that carry frames
to provide network management communications), etc.
[0022] The wireline network that is coupled to access point 24 may
include equipment 23 that is configured to implement the wireline
network. The wireline network may be coupled to an external network
(e.g., PBX, PSTN, Internet, etc.).
[0023] With reference now to FIG. 2, communications frame 30 may
show the structure of a communications frame that may be
transmitted in communications systems, such as wireless LAN 20 of
FIG. 1. Communications frame 30 may include preamble portion 32
that may be used for purposes such as synchronization. Remainder
portion 34 of communications frame 30 may be a data portion.
Together preamble portion 32 and remainder portion 34 may
substantially comprise a communications frame. For synchronization
or other reasons (e.g., requirements of communication standard),
preamble portion 32 may have to be transmitted at a particular data
rate. For example, communications in a system may be specified to
be at one of four data rates with the data rate for preamble
portion 32 being fixed to the lowest one of the data rates, and
remainder portion 34 may be transmitted at one of the four data
rates. Typically transmitters capable of operating at higher data
rates may operate at these rates to obtain high data
throughput.
[0024] With reference now to FIG. 3, a plurality of cells 22, such
as the cell shown in FIG. 1, may be positioned in a substantially
contiguous geographic area to provide communications services to
that area. For clarity and brevity, cells 22 may be discussed
primarily in the context of three channels (e.g., channels A, B,
and C) that are assignable to the cells for communications. The
number of available channels may be less than the number of
communications cells. In each cell, a transmitter, such as access
point 24 or terminals 26 of FIG. 1, may operate using
communications frames, such as communications frame 30 of FIG. 2.
Communications frames may be transmitted with a first portion
(e.g., preamble portion 32) being transmitted at one data rate
(e.g., the lowest specified data rate in the system) and at one
power level. The other portion (e.g., remainder portion) may be
transmitted at any one of the available data rates in the system at
a different power level. The power level for the other portion
(e.g., remainder portion) may be the conventional or system
specified power level for transmitting frames in such systems and
the power level for the first portion may be at a power level that
is lower than the conventional or system specified power level.
[0025] For example, in a system that uses data rates of 1, 2, 5.5
and 11 Mbps, the first portion may be transmitted at 1 Mbps and the
remainder portion may be transmitted at 1, 2, 5.5 or 11 Mbps. The
first potion may be transmitted at a power level that is lower than
the power level for the remainder portion.
[0026] If desired, transmitters and receivers in cells 22 may use
direct sequence spread spectrum communications techniques. If
desired, transmitters in cells 22 may use a communication technique
in which transmitters listen (e.g., monitor) to a particular
channel to determine whether that channel is available for
transmission (e.g., the channel is clear for transmission of a
frame by the transmitter). For clarity and brevity, cells 22 in
FIG. 3 have been illustrated in equal size hexagons. In
application, shapes and size of cells may be irregular.
[0027] With reference now to FIG. 4, illustrative steps involved in
providing high throughput communications for communications systems
having a plurality of data rates are shown in FIG. 4. At step 52, a
plurality of channels may be provided for a communications system.
At step 53, transmitters may be provided that are configured to
transmit communications frames by transmitting one portion of the
communications frame at one data rate and at one power level and
transmit another portion of the communications frame at one data
rate (e.g., another data rate) and another power level.
Communications services may be provided using the channels in a
group of communications cells. At step 54, locations of the cells
in the geographic area may be determined based on the number of
assignable channels, the data rates, and the power levels.
Transmitting some portions of frames that are at a lowest one of
the available data rates (e.g., the preamble portion) at a lower
power level than the remainder portions of frames may allow cells
to be spaced more closely together. Closer spacing may provide
higher total data rates.
[0028] By reducing power to a portion of the frames (e.g., preamble
portion), interference from nearby cells using the same channel may
be reduced and therefore, the sharing of data bandwidth between a
number of nearby cells using that same channel may be limited which
may result in an effective user throughput that may be up to the
throughput that may be achieved in a single cell
infrastructure.
[0029] If desired, a preamble portion for each frame may be
transmitted at 1 mbps (the lowest data rate) regardless of the
communications data rate of the remainder portion. If operating
without variable power control, transmitters (e.g., access points)
using the same channel (in different cells) may be within "hearing"
distance of each other at 400 ft or less and may refrain from
transmitting at the same time based on a clear channel assessment
function by listening to the channel to determine whether that
channel is available (i.e., all the cells within 400 ft of each
other are sharing the same band). By transmitting the 1 Mbps
preamble portion, at a lower power level than other portions of the
communications frame, the "hearing" distance of transmitters using
the same channel may be reduced. Reducing the "hearing" distance
may then allow locations of cells to be determined based on the
reduced "hearing" distance. If desired, the power level for the
preamble portion at 1 Mbps may be selected to have the preamble
portion have a "hearing" distance that is approximately the same as
the "hearing" distance for the next lowest data rate (e.g., 2
Mbps). The determination of "hearing" distances, which may be
determined by one of ordinary skill in the art based on the
plurality of factors discussed above, may be used to position
communication cells at locations in a geographic area at which the
cells may operate substantially without interference from other
cells on the same channel.
[0030] Thus, cells in a wireless communications system may have
actual data rates that are closer to raw data rates that are
supported by a system by selectively reducing power when
transmitting portions of frames that are at lower data rates.
[0031] If desired, tuning threshold of receivers in the cells may
be adjusted. For example, the threshold for the receivers may be
raised (e.g., from 20 db to 50 db). With higher receiving
thresholds, receivers may receive transmissions that have the
strongest signals and reject other transmissions. Receiving the
strongest transmissions may reduce the sharing of bandwidth between
a group of nearby cells that are using the same channel. If
desired, receiver thresholds may be adjusted in combination with
variable power control of frames.
[0032] The foregoing is merely illustrative of the principles of
this invention and various modifications can be made by those
skilled in the art without departing from the scope and spirit of
the invention.
* * * * *