U.S. patent application number 10/334858 was filed with the patent office on 2004-01-08 for method for performing wireless switching.
This patent application is currently assigned to InterDigital Technology Corporation. Invention is credited to Hunkeler, Teresa Joanne, Zuniga, Juan Carlos.
Application Number | 20040004951 10/334858 |
Document ID | / |
Family ID | 30002848 |
Filed Date | 2004-01-08 |
United States Patent
Application |
20040004951 |
Kind Code |
A1 |
Zuniga, Juan Carlos ; et
al. |
January 8, 2004 |
Method for performing wireless switching
Abstract
A wireless LAN (WLAN) system for communications among a
plurality of users within a basic service system or cell comprising
a switching access point (SAP) for transmitting and receiving
point-to-multipoint communications to and from the users. A
plurality of ports are available at the SAP, each of which assigned
to a unique carrier frequency for isolating communications among
the users to prevent collisions, with the ability of frequency
assignment to be non-permanent, and a capability of dynamic or
pseudo-random carrier assignment. An alternative embodiment of the
SAP uses beamforming to provide spatial ports for assignments to
the plurality of users.
Inventors: |
Zuniga, Juan Carlos; (St.
Laurent, CA) ; Hunkeler, Teresa Joanne; (Montreal,
CA) |
Correspondence
Address: |
VOLPE AND KOENIG, P.C.
DEPT. ICC
UNITED PLAZA, SUITE 1600
30 SOUTH 17TH STREET
PHILADELPHIA
PA
19103
US
|
Assignee: |
InterDigital Technology
Corporation
Wilmington
DE
|
Family ID: |
30002848 |
Appl. No.: |
10/334858 |
Filed: |
December 31, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60394151 |
Jul 5, 2002 |
|
|
|
Current U.S.
Class: |
370/338 ;
370/352 |
Current CPC
Class: |
H04W 72/042 20130101;
H04W 72/04 20130101; H04L 5/0023 20130101; H04W 72/0453 20130101;
H04W 88/08 20130101; H04B 7/0617 20130101; H04W 72/046 20130101;
H04W 72/08 20130101; H04W 16/14 20130101; H04W 88/02 20130101; H04W
84/12 20130101; H04W 4/06 20130101 |
Class at
Publication: |
370/338 ;
370/352 |
International
Class: |
H04Q 007/24 |
Claims
What is claimed is:
1. A wireless LAN (WLAN) system for communications among a
plurality of users within a basic service system or cell,
comprising: a switching access point (SAP) for transmitting and
receiving point-to-multipoint communications to and from the users;
and a plurality of ports, each of which assigned to a unique
carrier frequency for isolating communications among the users to
prevent collisions; wherein said assignment of frequencies is not
permanent, and instead has capability of dynamic or pseudo-random
carrier assignment.
2. The system of claim 1 wherein said not permanent assignment is
the dynamic carrier assignment which is achieved by request-to-send
signals from the users and clear-to-send signals from the SAP.
3. The system of claim 1 wherein said clear-to-send signals
indicate a frequency assigned to the users.
4. The system of claim 1 wherein said clear-to-send signals
indicate a pseudo-random carrier assignment to the users.
5. The system of claim 1 whereby said pseudo-random carrier
assignment is achieved by frequency hopping of the users along a
sequence of changing carriers, said sequence known a priori by the
users and the SAP.
6. A wireless LAN (WLAN) system for communications among a
plurality of users within a basic service system or cell,
comprising: a switching access point (SAP) for transmitting and
receiving point-to-multipoint communications to and from the users;
and a plurality of ports, each of which assigned to a unique
spatial beam for isolating communications among the users to
prevent collisions; wherein the SAP receives more than one spatial
beam at once.
7. The system of claim 4 wherein beamforming is used to create said
spatial ports.
8. A wireless LAN (WLAN) user terminal comprising: a multiple
frequency transmitter for transmitting a request-to-send message
and for transmitting data over an assigned transmit carrier; a
multiple frequency receiver for receiving a clear-to-send signal
over a first frequency and for receiving data over an assigned
receive carrier; and a frequency controller, operatively coupled to
the multiple frequency receiver, for determining the assigned
transmit and the assigned receive carrier of the user terminal
using the received clear-to-send signal.
9. The WLAN user terminal of claim 8 wherein the clear-to-send
signal indicating a pseudo-random transmit and receive carrier
assignment.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from U.S. Provisional
Application No. 60/394,151, filed on Jul. 5, 2002, which is
incorporated by reference as if fully set forth.
FIELD OF INVENTION
[0002] The present invention relates to a Wireless LAN system
(WLAN) with several users connected. More particularly, switching
of WLAN systems for avoiding collisions.
BACKGROUND
[0003] WLAN systems make use of the unlicensed bands for wireless
communication. Transmissions of a wireless LAN (WLAN) communication
system may be from a particular terminal to a desired destination,
either another terminal within the same Basic Service System (BSS)
or the backbone network, but always within the same carrier. There
are two modes of operation for WLAN systems: ad-hoc and
infrastructure. In the ad-hoc mode, terminals can talk to each
other in a multipoint-to-multipoint fashion. In the infrastructure
mode, an access point (AP) acts as a base station to control the
transmissions among users, thus providing a point-to-multipoint
wireless network. Since all the users share the same medium in a
WLAN, the infrastructure mode becomes more efficient for semi-heavy
to heavy loaded networks.
[0004] In an infrastructure mode, the terminal first communicates
with the AP when sending data to a desired destination terminal.
The AP in turn bridges or routes the information to the desired
destination. Thus, in this mode, an AP of a WLAN communication
system controls the transmissions within a BSS or cell.
[0005] Medium Access Control (MAC) protocols are defined to
coordinate the channel usage for WLAN users sharing the band. These
MAC protocols are based upon avoiding collisions between users as
several users access the channel at the same time. The efficiency
of a protocol is gauged by successful avoidance of collisions.
[0006] Two protocols used by WLAN are CSMA/CA MAC and CSMA/CD
Ethernet protocol. Both protocols can sense the carrier for other
transmissions. An Ethernet can be connected in various manners,
including Ethernet hubs and Ethernet switches. An Ethernet hub
concentrates the connections in a central point as a
point-to-multipoint connection, with no impact on performance. An
Ethernet switch operates every time that there is a packet arrival
from a terminal. The switch reads the destination address, learns
on which port it is connected and makes a direct connection between
the two physical ports. The advantage of the Ethernet switch is
that the MAC does not sense any other user in the medium, which
improves performance through reduced probability of collisions and
enhanced throughput as compared to an Ethernet hub. An Ethernet hub
forwards a received packet to all users, even when there is only
one intended receiver. The hub does not look at address
information. The Ethernet switch only sends the packet directly to
the intended destination, resulting in a more efficient usage of
the available bandwidth.
[0007] A common WLAN AP is not capable of using more than one
carrier frequency at the same time, which results in low protocol
efficiency. Ethernet switches have proven to improve the efficiency
of the Ethernet protocol considerably.
[0008] Therefore, what is needed is a method for improving the
performance of a wireless point-to-multipoint network when the
terminals share the same medium.
SUMMARY
[0009] A wireless LAN (WLAN) system for communications among a
plurality of users within a basic service system or cell comprising
a switching access point (SAP) for transmitting and receiving
point-to-multipoint communications to and from the users. A
plurality of ports are available at the SAP, each of which assigned
to a unique carrier frequency for isolating communications among
the users to prevent collisions, with the ability of frequency
assignment to be non-permanent, and a capability of dynamic or
pseudo-random carrier assignment. An alternative embodiment of the
SAP uses beamforming to provide spatial ports for assignments to
the plurality of users.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0010] FIG. 1A shows a system diagram of a WLAN with frequency
carrier Ethernet ports.
[0011] FIG. 1B shows a simplified diagram of a user terminal and a
switching access point using frequency carrier Ethernet ports.
[0012] FIG. 2A shows a system diagram of a WLAN with spatial beam
Ethernet ports.
[0013] FIG. 2B shows a simplified diagram of a user terminal and a
switching access point using spatial beam Ethernet ports.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] FIG. 1A shows a system that applies the Ethernet switch
principle to an access point (AP), allowing multi-frequency
operation, so that the AP becomes a Switching Access Point (SAP)
106. Frequency carriers f1-f5 are treated as different ports in the
SAP, from which user terminals 101-105 have centralized access to
frequency carriers f1-f5 in a controlled manner.
[0015] As shown in FIG. 1A, each user terminal 101-105 is assigned
to a frequency carrier f1-f5 and SAP 106 is capable of receiving
and transmitting each carrier f1-f5. In order to avoid permanent
assignment of carriers f1-f5 to each user terminal 101-105, two
approaches may be used. In the preferred embodiment, it is
desirable, although not essential, to not permanently assign
carriers to user terminals 101-105. A non-permanent assignment
avoids assigning a frequency to a terminal not sending data. When
there are more terminals than available frequencies, a terminal
that has data to send can be prevented from doing so if the
terminal permanently assigned to a frequency is not using it.
[0016] A dynamic carrier assignation (DCA) scheme can be applied,
in which user terminals 101-105 send a request-to-send (RTS) in a
shared carrier and then the SAP replies with a clear-to-send (CTS)
indicating the carrier that can be used for the transmission.
[0017] Alternatively, a frequency hopping scheme may be used, in
which user terminals 101-105 have a pseudo-random sequence for
changing carriers, known a priori by user terminals 101-105 and SAP
106, to minimize the probability of two user terminals
simultaneously using the same carrier. For a preferred WLAN
developed according to the current 802.11b standard, three carriers
are used for frequency hopping. For the 802.11a standard, eight
carriers are used for frequency hopping. Wireless switching system
100 may employ DCA and frequency hopping either separately or
combined.
[0018] FIG. 1B is an illustration of a preferred user terminal and
SAP using multiple frequencies. The SAP 106 has a frequency
assignment device 120 for assigning frequencies (frequency ports)
to the user terminals 101-105. A multiple frequency receiver 118
receives data sent by the terminals 101-105 using the assigned
frequency port. A multiple frequency transmitter 116 sends data
from one terminal to another using the assigned frequency of the
destination terminal. The multiple frequency transmitter 116
preferably also transmits the frequency assignment to the terminals
101-105. An antenna 122 or antenna array is used to send and
receive data by the SAP 106 over the wireless interface 124.
[0019] The terminals 101-105 have a multiple frequency receiver 114
for receiving the frequency assignment and recovers the transmitted
data over the terminal's assigned frequency. A frequency controller
108 users the received assigned frequencies to control the
transmission and reception frequencies of the terminal 101-105. A
multiple frequency transmitter 110 transmits the data over the
assigned frequency.
[0020] FIG. 2A shows an alternative embodiment of wireless
switching by assigning each user terminal 201-205 to a spatial port
instead of a particular frequency. As shown in FIG. 2A, spatial
beams b1-b5 are created by beamforming and can be used as ports to
isolate user terminals 201-206 from each other. SAP 206 recognizes
the destination address of each user terminal 201-205, and
associates a beam to each address. SAP 206 is capable of receiving
more than one beam at the same time.
[0021] FIG. 2B is an illustration of a preferred user terminal and
SAP using spatial beams. The SAP 206 has a beam controller 220 for
determining which beam (spatial port) is associated with a
particular user. The controller 220 provides a beamforming
transmitter 216 and a beamforming receiver 218 the beam information
so that the appropriate spatial port is used for a given terminal.
An antenna array 214 is used to send and receive data over the
wireless interface 222.
[0022] The terminals 201-205 have a beamforming receiver 210 for
receiving transmitted data using an antenna array 212. A
beamforming transmitter 208 is used to transmit data to the SAP 206
using the array 212.
[0023] Although the system configurations of FIGS. 1A, 1B, 2A and
2B show five user terminals, any number of user terminals may be
used. The intent is to demonstrate and not to limit or restrict the
scope of the system capabilities. The wireless switching systems of
FIGS. 1A and 2A can be used separately or combined. To illustrate,
user terminals 101-105 can be distinguished by a combination of
spatial beam and frequency. The wireless switching systems of FIGS.
1A and 2A can be applied to systems including, but not limited to,
direct sequence (DS) WLAN and orthogonal frequency division
multiplexing (OFDM) WLAN systems.
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