U.S. patent application number 11/622157 was filed with the patent office on 2007-05-17 for cell controller adapted to perform a management function.
This patent application is currently assigned to Symbol Technologies, Inc.. Invention is credited to ROBERT BEACH.
Application Number | 20070109993 11/622157 |
Document ID | / |
Family ID | 46280144 |
Filed Date | 2007-05-17 |
United States Patent
Application |
20070109993 |
Kind Code |
A1 |
BEACH; ROBERT |
May 17, 2007 |
CELL CONTROLLER ADAPTED TO PERFORM A MANAGEMENT FUNCTION
Abstract
A wireless local area network is provided with simplified RF
ports which are configured to provide lower level media access
control functions. Higher level media access control functions and
management functions are provided in a cell controller, which may
service one or more RF ports. Mobile units can also be configured
with the higher level media access control functions being
performed in a host processor.
Inventors: |
BEACH; ROBERT; (Los Altos,
CA) |
Correspondence
Address: |
INGRASSIA FISHER & LORENZ, P.C.
7150 E. CAMELBACK, STE. 325
SCOTTSDALE
AZ
85251
US
|
Assignee: |
Symbol Technologies, Inc.
Holtsville
NY
|
Family ID: |
46280144 |
Appl. No.: |
11/622157 |
Filed: |
January 11, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10037225 |
Oct 25, 2001 |
7173923 |
|
|
11622157 |
Jan 11, 2007 |
|
|
|
09780741 |
Feb 9, 2001 |
7173922 |
|
|
10037225 |
Oct 25, 2001 |
|
|
|
09528697 |
Mar 17, 2000 |
|
|
|
09780741 |
Feb 9, 2001 |
|
|
|
Current U.S.
Class: |
370/328 ;
455/560 |
Current CPC
Class: |
H04W 12/033 20210101;
H04W 16/26 20130101; H04W 74/00 20130101; H04W 84/12 20130101; H04L
69/08 20130101; H04L 69/18 20130101; H04L 29/04 20130101; H04W
88/085 20130101; H04W 88/12 20130101; H04W 88/08 20130101; H04L
12/4625 20130101; H04W 60/00 20130101 |
Class at
Publication: |
370/328 ;
455/560 |
International
Class: |
H04Q 7/00 20060101
H04Q007/00 |
Claims
1. A cell controller adapted for a wireless communication system
and for use with a RF port at least partially housed in a first
housing, comprising: a second housing that is physically separate
from said first housing; a memory housed in said second housing,
said memory adapted to store software for a plurality of functions
of a wireless communication standard protocol and a management
function of said wireless communication system; and a processor
housed in said second housing, said processor receptive of a first
signal received by said RF port and adapted to execute said
software stored in said memory to perform said plurality of
functions of the wireless communication standard protocol for said
first signal and said management function of said wireless
communication system.
2. The cell controller of claim 1, wherein said wireless
communication standard protocol is an Institute of Electrical and
Electronics Engineers (IEEE) 802.11 standard protocol.
3. The cell controller of claim 1, wherein said plurality of
functions are higher level Media Access Control (MAC)
functions.
4. The cell controller of claim 1, wherein said management function
is a bandwidth management function.
5. The cell controller of claim 1, wherein said management function
alters bandwidth based at least partially on a type of device that
originates said signal.
6. The cell controller of claim 1, wherein said management function
at least partially accounts for changing load conditions of said
wireless communication network.
7. The cell controller of claim 1, wherein said management function
alters a frequency of said signal.
8. The cell controller of claim 1, wherein said management function
alters a power of said signal.
9. The cell controller of claim 1, wherein said management function
alters a data rate of said signal.
10. The cell controller of claim 1, wherein said management
function is a compression function.
11. The cell controller of claim 1, wherein said management
function monitors software versions of mobile units within said
wireless communication network.
12. The cell controller of claim 1, wherein said management
function detects interference and adjusts transmit power levels of
said RF port.
13. The cell controller of claim 1, wherein said management
function is a security function.
14. The cell controller of claim 1, wherein said management
function is a soft-roaming function.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
application Ser. No. 10/037,225, filed on Oct. 25, 2001, which is
continuation-in-part application of U.S. application Ser. No.
09/780,741, filed on Feb. 9, 2001, which is a continuation-in-part
application of U.S. application Ser. No. 09/528,697, filed Mar. 17,
2000, which are hereby incorporated in their entirety by
reference.
BACKGROUND
[0002] This invention relates to wireless data communications
networks, and in particular to arrangements for communications
between mobile data handling units and a central computer using
wireless data communications.
[0003] The assignee of the present invention supplies a wireless
data communications system known as the Spectrum 24 System, which
follows the radio data communications protocol of IEEE Standard
802.11. In the system as implemented, mobile units are in data
communication with a central computer through access points. The
access points may communicate with a central computer or computers
over a wired network. Each of the mobile units associates itself
with one of the access points. The access points in this system are
functional to perform all the implemented requirements of the
standard protocol, including, association and roaming functions,
packet formulation and parsing, packet fragmentation and
re-assembly encryption and system access control. In order to
maintain order and reduce radio communications each access point
must determine which of the data communications received over the
wired network from the central computer is destined for a mobile
unit associated with that particular access point. This requirement
adds significant computational capacity to the access point,
increasing the cost thereof.
[0004] In addition, in applications that must support a high volume
of data communications from multiple users, such as systems
supporting a self-service shopping system, hospital systems,
systems that include paging or voice data links to many users, or
systems supporting communicating with electronic shelf labels,
additional access points are required to support the data
communications traffic, increasing the overall system cost.
[0005] The cost of an operational access point is dependent not
only on the complexity thereof and the requirement for high speed
processing of data pockets for purposes of selecting those destined
for mobile units associated with an access point, but the
additional cost of the installation of electrical power to the
location of the access point, and the cost of a power supply to
convert AC electrical power to DC power for the circuits of the
access point. Further cost may be involved in physically mounting
the access point hardware and antenna.
[0006] In prior systems each access point is connected on an
Ethernet wired network to the central computer. The access points
are required to determine the identity of mobile units which have
become associated with them and to extract from the data packets on
the Ethernet network those packets addressed to a mobile unit
associated with the access point. This requirement has led to
significant processing burden for the access points and led to
increased cost for the access points.
[0007] In the system described in my prior published International
Patent Application WO 099 37047, published Jul. 22, 1999, the
central computer communicates over an Ethernet wired network with
an intelligent switching hub. Alternately a token ring network can
be used. The switching hub determines the destination of each
packet and routes packets to an access point if the destination of
the packet is a mobile unit associated with the access point. To
achieve this function, the hub is an intelligent hub which
maintains a routing list of mobile units and their associated
access point according to the port of the hub.
[0008] In practice, the hub need only maintain a source list for
those access points connected to the hub and mobile units
associated with the access points connected to the hub. Thus, if a
packet is received at a hub over the Ethernet with a destination
address which is not associated with that hub, the packet is
ignored. The hub will route the packet to an access point only if
the destination address of the packet is identified on the list.
When a packet is received on a hub port associated with a
communications line connected to an access point, the source
address is associated with the hub port in the list. The packet is
routed either to the Ethernet connection or to another port
according to the destination address.
[0009] By determining destination address in the hub and
maintaining the association of a mobile unit address with an access
point connected to a port of the hub in a routing list of the hub,
the functionality required of the access points is greatly reduced.
The access point acts merely as a conduit sending RF transmissions
of packets received on its communication line, and receiving
transmissions from associated mobile units and providing Ethernet
packets to the hub. In addition, the access point must provide
mobile unit association functions and other 802.11 protocol
functions, as provided in the Spectrum 24 system, and may also
provide proxy polling responses for associated mobile units that
are in power saving mode.
[0010] The prior system may have a large number of access points,
each with a memory containing program instructions for carrying out
the various required functions. This distribution of processing
makes it difficult to upgrade a system or to provide changes in
system configuration because any upgrade or change may require
changes to the program code in each of the access points. Such
distribution of processing functions also makes system management
functions, such as load balancing or access control more
difficult.
[0011] It is therefore an object of the present invention to
provide an improved wireless data communications methods and
systems having lower cost, to enable the economical provision of
reliable wireless data communications with increased capacity in
complex installations or at reasonable cost or simple
installations.
SUMMARY OF THE INVENTION
[0012] In accordance with the invention there is provided a system
for providing wireless data communications between mobile units and
a wired network. The system includes a plurality of RF ports having
at least one data interface and arranged to receive formatted data
signals at the data interface and transmit corresponding RF data
signals and arranged to receive RF data signals and provide
corresponding formatted data signal. There is also provided at
least one cell controller, arranged to receive data signals from
the wired network and to provide formatted data signals
corresponding thereto and to receive formatted data signals and to
provide data signals corresponding thereto to the wired network,
the cell controller controls association of mobile units with one
of the RF ports, provides formatted data signals for said mobile
units to an associated RF port and receives formatted data signals
from the mobile unit from the associated RF port.
[0013] In accordance with the invention there is provided an
improvement in a wireless data communications network coupled to a
data processing system, having a plurality of RF ports and mobile
units, wherein the mobile units associate with one of the RF data
communications ports to conduct data communications with said data
processing system. The mobile units are assigned to one of the RF
ports by a cell controller, and the cell controller is arranged to
receive first data communications from the data processing system
and to relay the data communications to an assigned RF port and to
receive second data communications from the RF ports and relay the
second data communications to the data processing system.
[0014] In accordance with the invention there is provided a method
for operating a wireless local area network having at least one RF
port, a plurality of mobile units and a cell controller coupled to
the RF port. The RF is operated port to relay signals received from
mobile units to the cell controller and to relay signals received
from the cell controller to the mobile units. The cell controller
is operated to control association of the mobile units with the RF
port, including sending and receiving association signals between
the RF port and the cell controller, and to send messages to and
from the mobile unit via the RF ports.
[0015] In accordance with the invention there is provided an
improvement in a mobile unit for use in a wireless data
communications system, wherein the unit has a data processor and
programs for the data processor and a wireless network adapter
having a programmed processor and a radio module. The programmed
processor performs first communications processor functions
including control of the radio module and the data processor
operates under the programs to perform second communications
processor functions, including association with a radio access
location of the wireless data communications system.
[0016] According to the invention there is provided an improvement
in a wireless data communications system for providing data
communications following a standardized protocol, wherein the
protocol includes association of mobile units with radio access
locations. At least one RF port is provided at a radio access
location, which RF port comprises a radio module and an RF port
processor in data communications with a programmed computer. The RF
port processor performs first functions of the standardized
protocol and the programmed computer performs second functions of
the standardized protocol, including the association of mobile
units with said radio access location.
[0017] According to the invention there is provided an RF port for
use in a wireless data communications system comprising a radio
module having a data interface and a transmitter/receiver for
wireless data communications; and a digital signal processor having
first and second data communications ports, random access memory
and read-only memory. The second data communications port is
coupled to the data interface of said radio module. The read-only
memory is provided with a bootloader program for controlling the
digital signal processor to load program instructions to the random
access memory via the first communications port. According to the
invention there is provided a method for operating an RF port
having a radio module, a digital processor, random access memory
and read-only memory. A bootloader program is stored in the
read-only memory. The digital processor is operated to download
instructions from a computer to the random access memory using the
bootloader program and the RF port is operated under the downloaded
instructions to send and receive messages using the radio
module.
[0018] According to the invention there is provided a method for
transmitting signals having a wireless signal format using an RF
port having a wired network interface, a data processor and an RF
module. Signals are provided to the wired network interface having
wireless address data and message data within a data packet
addressed to the RF port using a protocol for the wired network.
The processor is operated to provide wireless data signals having
the wireless signal format for the address data and the message
data to said RF module and operating the RF module is operated to
transmit the wireless data signals as an RF signal modulated with
the wireless signal format.
[0019] According to the invention there is provided a method for
transmitting signals having a wireless signal format using an RF
port having an Ethernet interface, a data processor and an RF
module. An Ethernet data packet is provided to the Ethernet
interface, the Ethernet data packet encapsulating as data a data
message having the wireless signal format. The data processor is
operated to provide the data message to the RF module. The RF
module is operated to transmit the data message as an RF
signal.
[0020] According to the invention there is provided a method for
receiving signals having a wireless signal format including
wireless address data and message data at an RF port having a wired
network interface, a data processor and an RF module. The RF module
is operated to receive RF signals having the wireless signal
format. The data processor is operated to receive wireless data
signals from the RF module and provide data signals to the wired
network interface comprising a data packet having a source address
corresponding to the RF port using a protocol for the wired
network, the data packet including the wireless address data and
the message data.
[0021] According to the invention there is provided a method for
receiving RF message signals having a wireless signal format
including an address data format and message data using an RF port
having an Ethernet interface, a data processor and an RF module.
The RF message signals are received in the RF module and provided
as data signals to the data processor. The data processor is
operated to interpret address data in the data signals and, in
dependence on the address data, said message data and said address
data is encapsulated in an Ethernet packet, which is provided to
the Ethernet interface.
[0022] In accordance with the invention there is provided a
simplified wireless local area network system including a computer
having a data processor and a memory, an RF port having an RF port
data processor, an RF module and a data communications interface
coupled to the computer. A first program is provided in the memory
of the computer for operating the computer data processor to
perform first wireless data communications functions, including
association with mobile units. A second program is provided for
operating the RF port data processor to perform second wireless
data communications functions.
[0023] According to the invention there is provided a wireless
access device for providing wireless access to a communication
system. The device includes a modem for sending and receiving data
messages on the communications system and an RF port, having a data
interface coupled to the modem, a data processor and an RF module.
The data is programmed to receive data messages from the modem, to
format the messages for wireless data communications and to provide
the formatted messages to the RF module for transmission by RF data
signals to at least one remote station, and to receive RF data
signals from the at least one remote station, and to provide data
messages to the modem to be sent on the communications system.
[0024] According to the invention there is provided a method for
providing wireless access to the Internet. A modem having a data
communications interface connected to an RF port is connected to
the Internet. The RF port is configured for wireless data
communication to at least one mobile unit having a predetermined
wireless communications address. A mobile unit configured with the
predetermined wireless communications address is provided for
conducting RF data communications with the RF port. The RF port is
arranged to relay communications between the mobile unit and the
modem.
[0025] The apparatus and methods of the present invention provide
RF ports as radio access locations which are less expensive than
known access points and provide greater system management and
flexibility. Much of the software used for controlling
communications to and from mobile units is performed in a
controller wherein software upgrades and changes are easily
implemented. According to some embodiments, wherein instructions
are downloaded to RF ports, it becomes easy to upgrade RF port
instructions. System control is centralized, making management
easier and enabling changes to access control and encryption
functions. Priority for traffic purposes can also be established to
facilitate digital telephony by giving priority to voice traffic.
Accordingly, a system is provided that has significant flexibility
using common RF port hardware to provide a wireless LAN having from
one to hundreds of radio access locations.
[0026] According to the invention, the same RF port may provide
multiple ESS identifications such that each ESS identification is
associated with a separate virtual wireless local area network
having its own policies and security.
[0027] For a better understanding of the present invention,
together with other and further embodiments thereof, reference is
made to the following description, taken in conjunction with the
accompanying drawings, and its scope will be pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a block diagram of a wireless communications
system in accordance with the present invention.
[0029] FIG. 2 is a block diagram illustrating one example of a
mobile unit arranged to be used in the system of FIG. 1.
[0030] FIG. 3 is a block diagram illustrating one example of an RF
port for the system of FIG. 1.
[0031] FIG. 4 is a more detailed block diagram of a preferred
embodiment of an RF port in accordance with the invention.
[0032] FIG. 5 is a block diagram of an arrangement of a computer
and RF port for providing a simplified wireless local area network
according to the present invention.
[0033] FIG. 6 is a block diagram of an arrangement for providing
wireless access to the Internet using the RF port of the present
invention.
[0034] FIG. 7 is a diagram showing signal format according to one
embodiment of the invention.
[0035] FIG. 8 is a diagram showing a compilation of RF ports having
multiple ESS arrangements for providing overlapping, multiple
wireless networks.
DETAILED DESCRIPTION
[0036] Referring to FIG. 1, there is shown an example of a wireless
data communications system 10 according to the present invention
for providing data communications between a central computer or a
collection of computers on a wired network 16 and a plurality of
mobile units 20. While prior systems used access points at each
radio access location, where the access points are capable of
managing wireless communications with mobile units, the system of
FIG. 1 uses simplified RF ports 18 at each radio access location to
provide radio packet communications with the mobile units 20 using
a wireless communications protocol, such as EEEE Standard 802.11,
whereby the radio modules in the mobile units 20 monitor polling
signals from the RF ports 18, which are originated by the cell
controllers 14 and associate with an RF port 18 for purposes of
data communications. The system arrangement of FIG. 1 is especially
effective in a large wireless local area network (LAN) system
wherein it may be necessary to provide a large number of radio
access locations. Typically such systems, operating at low power
microwave frequencies, require radio access locations at about
every 100 feet. Where the wireless LAN system must operate with
mobile units, for example, portable computers or similar devices,
located throughout a large facility, such as a business, hospital
complex or university campus, many such radio access locations may
be required, possibly several hundred. Accordingly there is an
incentive to reduce the cost of the installation at each radio
access location. According to the present invention the system
configuration and operation are redesigned to reduce the cost of
each individual radio access point. In addition, the system of the
present invention provides a concentration of operational control
in one or more central controllers 14, making management of the
system easier and making modifications and upgrades easier to
install.
[0037] According to the invention, much of the functionality of the
802.11 protocol associated with the conventional access point, is
removed from the device located at the radio access location and
provided in a cell controller 14, which may be located in
conjunction with a switching hub 12, connected to the wired network
16, with which the wireless network 10 is associated. In particular
the usual "access point" device is replaced with a simpler device
18, herein referred to as an "RF port" which contains the RF
module, which may be the same RF module used in the prior art
access point, and simplified digital circuits to perform only a
limited portion of the 802.11 media access control (MAC) functions
performed by the prior art access point. In particular the RF port
18 preferably performs only functions of the access point that
require a lower level of processing resources in terms of processor
capacity and software complexity (memory requirement), and which
are time critical. Other functions that are more processor
intensive and require more complex programming, and which are not
time critical, are relegated to one or more "cell controllers" 14,
which may perform these more complex functions for a plurality of
RF ports 18.
[0038] In order to perform the higher level processing functions of
the access point in the cell controller 14, according to the
present invention, all messages directed to or from mobile units 20
associated with a particular RF port 18 are processed in a cell
controller 14. A system may have one or more cell controllers,
which may comprise, e.g. Pentium-type board level computers, each
of which is arranged and programmed to handle data message traffic
and mobile unit associations for a selected plurality of RF ports
18. A switching hub 12 may be interposed to provide message
switching among the wired network connected to communications line
16, RF ports 18 and cell controllers 14. Each of the one or more
cell controllers 14 acts as a virtual "access point" for traffic
addressed to its associated RF ports 18 and to the mobile units 20
associated with those RF ports. When a message is addressed to a
mobile unit 20 is received on line 16, switching hub 12 directs the
message to the appropriate cell controller 14, which reformats the
message and relays the message to the appropriate RF port 18, again
through switching hub 12. When the message is received by an RF
port 18, it is converted to a radio message and sent to the mobile
unit 20 with a minimum of processing.
[0039] Likewise, when a message is received from a mobile unit 20
by an RF port 18, it is converted to a digital message packet and
relayed to the cell controller 14 associated with the RF port 18
through the switching hub 12. The cell controller 14 parses the
message for further relay in the system.
[0040] An important feature of a preferred embodiment of the
invention is the fact that mobile unit association with the RF
ports 18 is a function handled by the cell controller 14.
Accordingly, when a mobile unit 20 first becomes active, it sends
an association request signal in response to a beacon signal sent
by an RF port 18 (in response to direction by the cell controller).
The association request signal is relayed by the RF port 18 to the
cell controller 14, which performs the processing required for
association, including consideration of RF port loading. Cell
controller 14 generates appropriate response signals to be sent by
the RF port 18 to the mobile unit 20. The cell controller 14 is in
an appropriate position to evaluate the loading of the RF ports 18
under its control, and may therefore easily perform load leveling
functions, for example, by providing a message to RF port 18
accepting or declining an association request. In addition, the
cell controller 14 may receive load messages from other cell
controllers 14 in the system 10 and thereby coordinate overall load
management. As a mobile unit 20 moves from a location serviced by
one RF port 18 to a location serviced by a different RF port 18,
the cell controller 14 receives information from the mobile unit 20
indicative of its reception of beacon signals from the various RF
ports in the system and performs the necessary functions to support
roaming of mobile unit 20.
[0041] While in the system 10 of FIG. 1 the cell controllers 14 are
shown as separate computers connected to switching hub 12, the term
"cell controller" is intended to refer to the logical functions
performed by these computers rather than the computers themselves.
As will become apparent, the cell controller may be implemented in
a variety of ways other than as shown in the exemplary system 10 of
FIG. 1.
[0042] Implementation of a simplified RF port is achieved by
performing "higher level" functions of the 802.11 protocol Media
Access Control (MAC) in the cell controller and performing "lower
level" functions in a simplified RF port.
[0043] The lower level functions are those that are hardware
intensive and often time critical. The higher level functions are
those that are software intensive and not time critical. One
possible division of the exemplary 802.11 MAC functions is as
follows:
[0044] Lower Level Functions (preferably to be performed at RF
port)
[0045] Cyclic Redundancy Check (CRC)
[0046] Network Activity Vector (NAV)
[0047] Ready to Send/Clear to Send (RTS/CTS)
[0048] Header generation/parsing
[0049] Collision Avoidance
[0050] Frequency Hopping
[0051] Ack parsing/generating
[0052] Retransmission timeout
[0053] Higher Level Functions (preferably to be performed at Cell
Controller)
[0054] Association processing
[0055] Roaming
[0056] Retransmission
[0057] Rate Control
[0058] Host Interface
[0059] The following optional (higher or lower) level MAC functions
can be placed in either the higher or lower level categories.
[0060] Wired Equivalent Privacy encryption/decryption (WEP)
[0061] Fragmentation/Reassembly
[0062] Data Movement
[0063] Power Save Polling Support (PSP)
[0064] According to a preferred arrangement of the system of the
invention, the lower level MAC functions are provided at the RF
port, the higher level MAC functions are provided in the cell
controller and the optional level functions can be provided at
either the cell controller or the RF port.
[0065] A major advantage of the invention is a cost savings in
hardware, processor capacity and storage capacity for the RF port.
Since a system with, for example, one hundred or more radio access
locations may be implemented with one or two cell controllers, the
processor hardware and memory required for the higher level MAC
functions need be provided only at the cell controllers. In fact,
the capabilities of the overall system, for WEP encryption and
other special functions, can be increased at modest cost by using a
high performance board level personal computer or even a host
computer as a cell controller.
[0066] By eliminating the higher level MAC functions from the radio
access locations, the cost of the devices installed at those
locations can be significantly reduced because of lower processor
capacity and storage.
[0067] In connection with association and roaming functions the RF
ports 18 provide beacon signals in response to commands generated
by the cell controller 14. When an association sequence is
initiated by a mobile unit, the RF port 18 relays the association
messages between the mobile unit 20 and the cell controller 14
during the association process, which is handled by the cell
controller 14.
[0068] In connection with message traffic to a mobile unit 20 from
a network processor, message packets are routed by switching hub 12
to the cell controller 14 responsible for the mobile unit 20
addressed. The message is buffered and formatted by the cell
controller 14 and in a preferred arrangement encapsulated by the
cell controller 14 as a mobile unit packet within a wired network
packet addressed to the responsible RF port 18. This packet is
routed to the RF port 18. The RF port 18 extracts the mobile unit
packet from the message and sends the packet to mobile unit 20 as a
radio signal. The RF port 14 may also provide a CRC calculation and
generate CRC data to be added to the message. The mobile unit 20
responds with an acknowledgment signal to the RF port 18, which
generates and sends an acknowledgment status message to cell
controller 14.
[0069] In connection with messages for systems connected to the
wired network 16, the mobile unit 20 sends a packet to the RF port
18 by radio signal. The RF port 18 filters received radio message
packets according to the BSS (Basic Service Set) identifier in the
packet and, if the packet has a BSS identifier associated with the
RF port 18, performs the CRC check as the packet is received. The
RF port 14 then generates and sends an acknowledgment signal to the
mobile unit 20 and sends the received packet to cell controller 14.
Cell controller 14 buffers, parses and, if necessary, decrypts the
packet and routes the packet to the host on network 16 through hub
12.
[0070] The arrangement of RF port 18 maybe identical to current
access points used in the Spectrum 24 system with some of the
access point software non-functional. Preferably the RF ports are
simplified to reduce cost and power consumption. To reduce
installation expenses the RF ports are powered via an Ethernet
cable, which also connects RF ports 18 to switching hub 12 or to
cell controller 14. The RF ports can be arranged in a small package
(e.g. portable radio size) with integrated diversity antennas and
arranged for easy mounting, such as by adhesive tape or Velcro.
Connection to the switching hub 12 is by Ethernet cable which is
also provided with D.C. power, such as by use of a choke circuit,
such as Pulse Model PO421 as described in my referenced
International Application. The choke circuit may be built into an
Ethernet connector and is available in this configuration.
[0071] The RF port 18 does not have to perform Ethernet address
filtering and does not have to perform 802.11 association and
roaming functions and can therefore have a lower level of processor
capacity, software support, and memory and power consumption. In
one embodiment shown in FIG. 3 the RF port 18 includes only a
digital signal processor (DSP) 38 which includes internal RAM and
ROM. The DSP 38, which may be one of the Texas Instruments TMS 320
family of DSP processor, such as the 5000 series, specifically the
TMS 320 UC 5402 or the TMS 320 VC 5402. This DSP provides an
interface between the Ethernet cable 46 and the RF module 42 in RF
port 18, as shown in FIG. 3. The RF module 42 is provided in
housing 36 with DSP 38, DC/DC power supply 40 and carrying one or
more antennas 44. RF module 42 includes a 3860 or 3861 baseband
processor, such as HFA 3860B, to interface with the digital portion
of the RF port 18, specifically DPS 38. In one arrangement the ROM
memory of the DSP 38 can be provided with "bootloader" firmware
that downloads the necessary DSP software instructions from the
cell controller 14 upon startup of the RF port 18, and loads the
instruction into the RAM of the DSP 38.
[0072] The processors that are currently preferred as a possible
lower level MAC engine are the TMS320UC5402 and the TMS320VC5402.
These parts are functionally identical except for differences in
power consumption (the VC5402 is currently in production and while
the UC5402 is still being sampled). The basic configuration of the
UC5402/VC5402 is:
[0073] 100 MIPS execution rate
[0074] 8 KB on chip ROM (organized as 4K.times.16 bits)
[0075] 32 KB on chip RAM (organized as 16K.times.16 bits)
[0076] Two 16 bit timers with 1 .mu.s or better resolution
[0077] Two High speed, full duplex serial ports (up to 50 Mbits/sec
each) with smart DMA channel support
[0078] One High speed 8 bit wide host/parallel port (160
Mbits/sec)
[0079] Six DMA channels for general purpose use
[0080] 16 bit external memory/IO Bus with internal wait state
generation
[0081] 16 interrupts with 3 instruction (30 ns) worst case
latency
[0082] 0.54 mW/MHz power consumption (30 mA@1.8 v at 100 MHz)
[0083] Low Power Modes (6 mA, 2 mA, 2 .mu.A depending on
setting)
[0084] Internal PLL that generates the system clock with an
external crystal
[0085] This section will describe the use of a 5402 DSP 38 as a MAC
engine for 11 Mbits/sec 802.11 DS systems. It could clearly be used
in FH systems as well. We will focus on the how the 5402 interfaces
to the Intersil 3860/1 baseband processor in RF module 42 and how
it implements the lower level MAC functions.
[0086] The first issue is how the 5402 DSP 38 interfaces to the
3861 (much of what is said applies to the 3860 as well) and the
rest of the RF module 42. As shown in FIG. 4, the 3861 processor 53
in RF module 52 of RF port 50 has 2 major interfaces, both serial.
The first interface, labeled DATA, is used to transfer data between
the MAC engine comprising DSP 64 and the 3861. It has four lines:
TxD, TxC, RxD, and RxC and operates at up to 11 Mbits/sec. The
exact rate depends on the transfer rate of the packet. The clock
signals of both interfaces are generated by the 3861 and so
transfers are controlled by the 3861. Both can be halted at any
time by the 3861 as well as change rate. The second serial
interface, labeled CONTROL is used to load commands into the 3861
and read status information from the 3861. This interface is a 4
wire bi-directional interface using one data line, one clock line,
one "direction control" line, and a chip select line. This serial
interface also can operate at up to 11 Mbits/sec. In addition to
the serial interfaces, there are additional control and status
lines such as Reset, TX_PE, RX_PE, TX_RDY, etc.
[0087] The 5402 DSP 38 has two sets of full duplex serial
interfaces that are capable of operation up to 50 Mbits/sec (given
a 100 MHz clock). They can be clocked using internal or external
sources. In this design one of the sets of serial interfaces,
labeled SER1, is used to connect to the high speed data lines of
the 3861 interface 53. The 5402 DSP 38 interfaces have the same
basic lines (RxD, RxC, TxD, TxC) as does the 3861 and so they
connect with minimal trouble. Although the 5402 uses 1.8 v for its
core, its I/O lines are 3.3 v tolerant and so can interface to the
3861 without converters. In addition, they are fully static and so
can deal the start/stop operation of the clock lines from the
3861.
[0088] Data transfer will be done under DMA control within the 5402
using what TI calls "Auto Buffering Mode." This provides
essentially dedicated DMA channels for each serial port interface
(two DMA channels per serial port interface). These channels access
an independently operating bank of SRAM and so transfers have no
impact on CPU performance. The CPU can start transfers in either
direction and be notified via interrupt on their completion.
[0089] Interfacing to the control serial port on the 3861 interface
53 can be done in three different ways. The first, illustrated in
FIG. 4, utilizes the second serial port, labeled SER 2 on the 5402
DSP 64 with a small amount of combinatorial logic/buffering to
convert between the single data line of the 3861 and the dual data
lines of the 5402. Another approach is to use an external shift
register that would perform serial/parallel conversion. This
register would sit on the I/O bus of the 5402 and would be
loaded/read by the 5402 and data shifted between it and the 3861.
The third approach is to use an external buffer/latch on the 5402
I/O bus and "bit bang" the clock/data lines to the 3861. The second
or third approaches free up the second serial channel for more
other use such as providing high speed serial interfaces such as
Ethernet or USB and in some applications would be preferred over
the first. All require a small amount of external combinatorial
logic and so the cost of all solutions is about the same.
[0090] The same logic would apply to interfacing to the
synthesizer. It is accessed even less often than the control port
of the 3861 and so a "bit banging" approach would work fine.
[0091] Finally, interfacing to the various control and status lines
presented by the 3861 can be done via simple bidirectional
register/latch connected to the I/O bus of the 5402. The 5402 can
read/write this register as it needs to control and monitor the
3861. It would be possible to combine all control/monitor functions
(including the serial control interface) into a single 16 bit
buffered register latch. Parallel control/status lines would be
connected to particular lines of this latch. Serial control
interfaces would also be connected and "bit banged" as necessary to
move data between the 5402 and 3861.
[0092] The arrangement shown in FIG. 4 uses a Crystal CS 8900 A
Ethernet controller 63 coupled to the parallel port of DSP 64 to
interface to the Ethernet port 58. An Ethernet connector/choke 58
receives cable 60 and provides DC power from cable 60 to DC/DC
power supply 62. The FIG. 4 RF port 50 includes spaced diversity
antennas 54, 56 to improve reception in multipath conditions.
[0093] A premise of this design is that the TI DSP is capable of
implementing all lower level MAC functions without external
hardware assistance. This, of course, is the most demanding model
but we will find that the 5402 is up to the task. The most
computational demanding tasks are the CRC-32 and WEP processing.
The CRC-32 calculation is performed over the entire packet and must
be completed in time to generate an ACK should the CRC turn out to
be correct (or to attach the calculation result to an outgoing
packet on transmission). This means that the CRC calculation must
be performed in near real-time during packet transfer between the
3861 and 5402. TI has shown in an application note that a CRC-32
calculation can be made by a 5000 series DSP in 13 instructions. At
100 MIPS this is about 130 ns. At 11 Mbits/sec, a byte takes about
770 ns to transfer and so we have plenty of time to do the CRC.
When receiving a packet, the serial port would be transferring the
data from the 3861 to SRAM within the 5402. At the same time the
CPU within the 5402 would be reading each received byte from SRAM
and calculating the CRC. It would of course have to make sure that
it did not overrun the receive buffer, but that would be a
relatively simple task. Much the same process would happen during
transmission. In either case, the CPU has lots of time to do the
CRC.
[0094] The WEP processing if performed in the RF port 50, is a
harder function to perform than CRC-32 since it includes both an
RC4 encryption function and a second CRC-32. At the same time it
does not need to be completed prior to ACK generation/reception nor
is performed on every packet (just data packets). The RC4
encryption function consists of two parts: building the encryption
table (a 256 byte table) using the selected key and doing the
encryption/decryption process. Based on sample code, it is
estimated that building the table would require about 1200
instructions (12 ms at 100 MIPS) and the encryption/decryption
process would require about 12 instructions/byte. There is no
difference in this cost for 40 or 128 bit keys. The WEP CRC-32
would require another 13 instructions per byte.
[0095] The per byte computational burden for WEP would thus be
about 25 instructions or about 250 ns at 100 MIPS. When added to
the packet CRC-32, the total load would be around 38
instructions/byte. As we pointed out, at 11 Mbits/sec we have about
77 instructions/byte available, so we are spending about 50% of the
CPU on CRC/WEP tasks. The biggest issue is the 1200 clocks (12 us)
required to build the encryption table during receive (For
transmission, the calculation can be done prior to starting packet
transfer). Pausing to create the table would put the CPU about 18
bytes (12 us at 770 ns/byte) behind in the CRC/WEP/CRC calculation
process. It would require about 40 data bytes to catch up (1200
clocks/30 extra clocks per byte) in both packet CRC and WEP/CRC
functions. Since the minimum TCP/IP header is at least 40 bytes
(plus any user data), we should have enough time. In any case if we
are a little late in WEP/CRC calculation, no harm is done. An
alternative approach would be to catch up first for the packet CRC
calculation and then catch up with WEP/CRC.
[0096] After CRC and WEP/CRC processing, the next most critical
activity is header parsing on receive and generation on transmit.
This is because of the need to identify packets for the station and
generate appropriate responses. On receive, the processor must
parse two or three 48 bit addresses and at least a 16 bit header
command field. After the packet completes, an ACK may need to be
generated.
[0097] The 5402 can easily handle these functions. Since these
functions are performed prior to WEP processing, the CPU has 64
instructions/byte (77-13) to perform these functions. Since many of
them can be performed on a 16 bit or even 32 bit basis (the 5402
supports both 16 and 32 operations), there may be up to 128 or 256
instructions per data item (i.e. 256 instructions to perform a 32
bit address check). These functions are performed at 2 Mbits using
a 1 MIPS 188 CPU. We have a 100 MIPS CPU to do the same tasks at 11
Mbits/sec.
[0098] ACK generation is likewise relatively simple. An ACK frame
is only 14 bytes long, including the 4 CRC-32. Given there is a
long (80 us) preamble, we have 8000 instructions to prepare the
ACK. The same applies to RTS/CTS exchanges.
[0099] There are two 16 bit timers available on the 5402. In this
model, one would be used for TSF timing and the other for all other
functions. There are really only a few other timer functions: NAV,
Retransmission, collision avoidance slot countdown, etc.
Retransmission and collision avoidance activities go on only when
waiting for an ACK or to start a retransmission after detection of
an idle network. In such cases there is no data transfer going on
and so there is lots of CPU cycles available.
[0100] Support for MU PSP function can be done in a variety of
ways, depending on how much, if any, external hardware is provided.
The 5402 provides a variety of means of conserving power. The first
is simply to slow down the CPU clock via the software controlled
PLL within the unit. The 5402 generates internal clocks via a PLL
that is driven by either an external crystal or clock. The PLL
multiplies the base frequency of the crystal/external clock by a
factor determined by software. Hence one means of controlling power
consumption is simply to slow down the CPU clock. Since the CPU
portion of the processor consumes most of the power, slowing it
down has the biggest affect on power consumption.
[0101] The second approach is use one of the IDLE modes of the
processor. IDLE1 stops the CPU clock entirely but leaves everything
else running. Power consumption in this mode is on the order of 6
mA at 100 MHz. The CPU can be restarted by any interrupt (internal
or external). In IDLE2 the system clock is stopped and this reduces
consumption to 2 mA. In IDLE3, all system functions are stopped and
consumption is reduced to around 2 .mu.a. In all cases all state is
retained. In IDLE2 and IDLE3, an external interrupt is required to
restart the CPU. In such cases an external, low power timer would
be required.
[0102] Thus with no external hardware, power consumption could be
reduced to at least 6 mA and perhaps less. With a simple external
timer, one could get down to microamps.
[0103] The bottom line is that the vast CPU power of the 5402
allows all lower level MAC functions to be performed in software.
Furthermore it has sufficient power and memory to handle additional
"higher level" functions such as packet retransmission,
fragmentation, and reassembly that can also be done in a cell
controller.
[0104] The system 10 of the present invention is compatible with
IEEE Standard 820.11 and accordingly will operate with any mobile
units 20, including existing units, which are compatible with the
same standard. However, the improvements applied to the RF ports
18, reducing the complexity and cost of these units can also be
applied to the mobile units 20, which have sufficient main
processor capacity to handle the mobile unit functions
corresponding to the higher order MAC functions.
[0105] Referring to FIG. 2 there is shown a block diagram for a
mobile unit 20 having a mobile unit computer 22 and a WLAN adapter
24 connected thereto to provide wireless communications to the
system 10 of FIG. 1. In the mobile unit 20 of FIG. 2, the lower
level MAC functions are performed in WLAN adapter 24, which also
includes RF module 28 and antenna 29. The configuration of WLAN
adapter 24 may be similar to existing adaptors, but preferably
adapter 24 is simplified to perform only the lower level MAC
functions of the IEEE 802.11 protocol and allow special software 34
in host computer 22 to perform the higher level MAC functions, such
as association and roaming. In a preferred arrangement the MAC
functions of adapter 24 are performed in a digital signal processor
26, as described below, which may be the same type DSP described
with respect to RF port 50.
[0106] This section addresses how the 5402 DSP could be used as a
MAC engine in Mobile Unit configurations. There are two
considerations in building MU WLAN solutions. The first is the
location of those MAC functions, while the second is the physical
interface to the host.
[0107] The location of the upper level MAC functions may vary
considerably. Some possibilities are:
[0108] All functions on MAC engine DSP processor 26
[0109] All functions on host processor 22
[0110] Roaming/association on host processor 22, rest on MAC engine
26
[0111] Roaming/association/retransmission on host 22, rest on MAC
engine 26. The choice of the location of the higher level MAC
functions has a major impact on the cost of MU WLAN adapter. If one
is willing to place at least some of the higher level functions on
a host processor 22, then one could get by with just the 5402 on
the WLAN adapter. Possible functions to place on the host would be
roaming and association control. Higher level functions such as
retransmission and fragmentation/reassemble-y could be left on the
5402. This split would permit significant savings, since another
processor/memory subsystem would not be needed on the WLAN adapter.
There are two reasons for not placing all of the MAC functions on
the 5402. The first is memory space on the 5402 is only 32 KB of
SRAM for both code and data. In some MAC implementations such as
frequency hop, the code space alone exceeds 32 KB. The second
reason is that the software on the 5402 is oriented toward meeting
hard, real-time tasks such as CRC and WEP processing. Trying to add
software intensive tasks would only complicate the process.
[0112] If another processor was required, such as an ARM or perhaps
a second 5000 Series processor, the upper level functions could be
added to it.
[0113] Alternatively one could place all the MAC functions on a
faster and/or bigger version of the 5402 processor. Such a
processor would likely have a higher clock rate (current members of
the 5000 Series can be clocked as high as 160 MIPS) and more memory
(say 64 KB instead of 32 KB).
[0114] Both the second processor as well as a faster/bigger 5402
would consume additional power as well as adding cost.
[0115] This section will describe one approach of how a MU WLAN
adapter can be arranged for various hardware host interfaces using
the 5402. It assumes that enough of the upper level MAC functions
have been offloaded to a host processor so that only the 5402 is
required on the PLAN adapter. A second processor could be added to
any of the solutions outlined below.
[0116] In all of the following solutions, it is assumed that the
runtime code for the 5402 is loaded from an external source (such
as computer 22) via the host interface 32. This eliminates the need
for flash memory on the adapter card, saving several dollars in the
process. It should be pointed out that the 5402 comes with 8 KB of
mask programmable ROM and a bootloader program (required for the
USB and Ethernet host interfaces) would be placed in it. The
bootloader would be smart enough to download the runtime code
instructions over whatever serial interface was available.
[0117] The simplest interface of all would be for a host to use the
Host Port on the 5402. This port operates as a dual port interface
into the memory within the 5402. It would not be a standard
interface but would be quite suitable for dedicated systems. Using
it, computer 22 can read/write memory on a random or sequential
basis. It is an 8 bit interface and can operate as fast as 160
Mbits/sec. When operated in random access mode, the computer 22
generates a 16 bit address using two writes to the port and then
performs either a read or write operation. Such a mode allows a
host to set up command blocks and the like within the memory of the
5402. Sequential mode allows a host to transfer data in and out of
the 5402 memory very quickly (160 Mbits/sec). This would be used
for transferring data.
[0118] If this approach was used, the only digital component on the
WLAN adapter would be the 5402.
[0119] In the system of FIG. 1, the cell controller 14 is a board
level personal computer coupled to the switching hub 12 preferably
by 10 M bit and 100 Mb Ethernet ports. For smaller systems a 350
MHz Pentium computer with 16 MB RAM may be used. For larger systems
having many RF ports a 500 MHz Pentium with 64 MB RAM is
appropriate. Communications to and from the wired network are
preferably carried out at 100 MHz. Communications to and from RF
ports may be carried out at 10 MHz. A second cell controller may be
supplied for larger systems and/or to provide backup in the event
one cell controller fails. Reliability can be enhanced by providing
dual fans and dual power supplies. A flash disk memory may be used
for reliability. Alternately, the cell controller 14 may be built
into the switching hub 12 or into a host processor.
[0120] The operating system for the cell controller 14 may be a
real time operating system, such as VRTX or QNX, which provides
multitasking, a full network stack and utilities. Web based
management utilities, which are client side java based, are
provided for maintaining the configuration of the cell controller
14, the RF ports 18 and status of the mobile units 20.
[0121] The cell controller 14 includes applications to provide
mobile unit association management, roaming and packet buffer
management. These applications are similar to those performed by
current access points in the Spectrum 24 system. The cell
controller 14 may also provide QoS support, user authorization and
configuration management. Placing these functions on a personal
computer cell controller facilitates system management and program
updates using available programming tools. Further, modifications
to authorization or management functions need only be installed
into the cell controller 14, and no modification to the software of
the RF ports 18 is required.
[0122] The cell controllers 14 handle routing of all messages to or
from the mobile unit. The cell controller buffers message packets
received from the wired network and determines the appropriate RF
port 18 with which the addressed mobile unit 20 is associated and
sends the packet to the RF port 18. The cell controller 14 can
additionally perform WEP encryption/decryption and the CAC
associated therewith.
[0123] The cell controller 14 may also the additional function of
maintaining and downloading firmware to the RF ports 18. Upon power
up the RF ports 18 use a bootloader routine stored in ROM to send a
download request to cell controller 14. The cell controller then
downloads firmware to the RF port 18, including configuration
information such as channel assignment, ESS and BSS identification.
The cell controller 14 and RF ports 18 additionally share a common
TSF clock.
[0124] The mobile unit computer 22 of mobile unit 20 is provided
with similar software to perform the higher level MAC functions as
outlined above. Advantageously, the software 34 can be programmed
using the same operating system as provided for the computer, and
thereby provide a user interface, such as Windows, which is
familiar to the user. The mobile unit software 34 provides the MAC
functions of header building, roaming and association. The mobile
unit computer 22 may also download firmware to the processor in the
WLAN adapter 24
[0125] As evident from the forgoing description, the hardware for
RF port 18 and WLAN adapter 24 of mobile unit 20 can be
substantially similar, with the possible exception of the interface
to an Ethernet network or to a mobile unit host. Further, the
logical cell controller function and the higher order MAC functions
performed by the mobile unit host processor can be performed on any
computer system.
[0126] Using the RF port 18 of the present invention coupled to a
computer system, it is possible to provide either a mobile unit or
a wireless network according to the software provided. Since the
software for RF port 18 may be downloaded from a host system a
simple combination of a computer and one or more RF ports can
function as either a WLAN mobile unit as a WLAN host or both, by
providing function selectable firmware to the processor in the RF
port.
[0127] In the arrangement shown in FIG. 5, a personal computer 70
is provided with software 72 and connected to one or more RF ports
50A, 50B to provide a complete host system for wireless data
communications. This arrangement could be used, for example, in a
small business wherein office equipment is connected to server 70
by a wired network for conventional LAN operation and one or more
RF ports 50 are also connected to server 70 on the LAN system to
provide data communications between the server 70 and mobile units.
The server can perform the higher order MAC functions and download
firmware instructions to the RF ports. Alternatively, the firmware
instructions can be installed on PROM memory in the RF ports.
[0128] FIG. 6 shows an arrangement for providing wireless access to
the Internet using the RF port 50 of the present invention.
Internet access over communications line 80 to modem 82 may be
provided by cable, DSL or fiber optical transmission. RF port 50
may be provided with MAC firmware on PROM or may be configured with
a bootloader program to download firmware from an ISP server. When
installed in a home or office, mobile units 20 can associate with
RF port 50 to initiate Internet access. The ISP server may perform
the higher level MAC function, or they may be provided in RF port
50.
[0129] The mobile units 20 may be the personal computers 22 in a
home or office with a WLAN adapter 24 as shown in FIG. 2.
[0130] FIG. 7 illustrates an example of communications formats that
might be used in the various system embodiments of the present
invention. The FIG. 7 example assumes that the configuration
includes a host 90 connected to a dedicated cell controller 14,
which is likewise connected to RF port 18. It should be clearly
understood that the logical cell controller functions may be
performed in host 90, particularly in a simple system.
[0131] In the FIG. 7 example host 90 sends message "A" having 100
data bytes via an Ethernet packet 100 to cell controller 14. Packet
100 has a destination address of the Mobile unit (M1), a source
address of the host (H) and includes data (A). Cell controller 14
formats the data in 802.11 format with the destination
corresponding to mobile unit (MU1) 20. The cell encapsulates this
802.11 packet with data A into an Ethernet packet 104 addressed to
RF port 1 (RF1) from the cell controller (cell controller).
[0132] RF port 18 receives the Ethernet packet 104 from cell
controller 14 and generates and sends an RF packet 112 in 802.11
format to mobile unit 20, including data A. It should be understood
that 802.11 header generation can be provided at either the cell
controller 14 or the RF port 18, but packet 104 must include mobile
unit identification data either as an 802.11 header or otherwise to
enable RF port 18 to generate the header. RF port 18 additionally
performs the CRC computation and adds the result to the 802.11
packet 112.
[0133] A second message "B" having 1500 bytes of data is also shown
as originating as Ethernet packet 102 from host 90 to cell
controller 14. Cell controller fragments data message B into three
fragments B1, B2 and B3 to accommodate the 500 byte data limit of
802.11 packets. These three fragments are sent as Ethernet packets
106, 108, 110 to RF port 18, which transmits RF signal packets 114,
116, 118 to mobile unit 20.
[0134] Reverse communication is similar. Message C has 100 bytes
and is sent by mobile unit 20 to RF port 18 as 802.11 RF signal
packet 200. RF port 18 encapsulates this message into Ethernet
packet 208 and sends it to cell controller 14, which extracts the
destination information and data to provide Ethernet message 216 to
the host 90. A larger message D is sent as message fragments 202,
204, 206 to RF ports 18, relayed as Ethernet packets 210, 212, 214
to cell controller 14 and sent as a reassembled Ethernet packet 218
to host 90.
[0135] Referring now to FIG. 8, shown is an application of the
central controller/RF port model that may be used to set multiple
overlapping ESS LANs for use in the same or overlapping physical
space. Shown in FIG. 8 is a central controller 260 which is
associated with two RF ports, RF port 1 250 and RF port 2 270. The
central controller 260 may be associated with more than two RF
ports, but two are shown for illustration purposes. Each RF port
250, 270 provides coverage for a wireless LAN in the physical areas
240, 310.
[0136] FIG. 8 further illustrates the concept of providing multiple
ESS identifications through the same RF port and cell controller
such that each ESS identification is associated with a separate
virtual wireless local area network having its own policies and
security. Thus, RF port 1 250 may be configured so as to support
separate BSS networks 1A 230, 1B 220 and 1C 210, all of which
occupy the same physical space 240. The RF port may support more
than three BSS networks, but three are shown for illustration
purposes. Similarly, RF port 2 270 may be configured so as to
support BSS networks 2A 300, 2B 290 and 2C 280, all of which occupy
the same physical space 310. Using the configuration as shown in
FIG. 8, multiple ESS LANs may be coordinated by the central
controller 260 in the physical space 240 and 310. ESS A consists of
BSS 1A 230 and BSS 2A 300. ESS B consists of BSS 1B 220 and 2B 290.
BSS C consists of BSS 1C 210 and 2C 280.
[0137] As discussed in further detail above the RF ports 250, 270
preferably performs only functions of the access point that require
a lower level of processing resources in terms of processor
capacity and software complexity (memory requirement), and which
are time critical. Other functions that are more processor
intensive and require move complex programming, and which are not
time critical, are relegated to one or more cell controllers 260,
which may perform these more complex functions for a plurality of
RF ports 250, 270. In the case illustrated in FIG. 8, the central
controller handles the necessary processing of multiple ESS LANs A,
B, C in the same physical space 240 and 310.
[0138] One application of multiple ESS LANs may be found on a
public place, such as an airport where, for example, three levels
of wireless networks may operate. A first public network level with
generally open access to a wireless local area network that might
provide, for example, public wireless telephone or internet access.
A second network level would involve airport operations, such as
luggage handling, aircraft servicing, etc. A third network level
may be reserved for emergencies and security. Devices using the
network can be restricted by the cell controller as to which
virtual network they can access using the same RF port of the
wireless network system. The cell controller would thereby control
communications between mobile units accessing an RF port and the
three or more virtual networks such that, for example, a member of
the public using a publicly available device could only access the
public functions of the system and therefore only have access to
the lowest level of virtual wireless network. Other personnel, such
as airport employees, may have access to the public level and also
have access to the airport operational network. The security-based
network would be available for select airport personnel such as
management and security officers.
[0139] The cell controller performs the function of determining
which ESS network a mobile unit communicating with an RF port
associated with the cell controller is operating on, and thereby
controls the direction of communication from the cell controller to
the network. The cell controller can verify the multiple levels of
security provided in connection with the access by the mobile unit
devices, and in addition can prioritize communications so that
higher priority communications such as security communications are
given greater access to the system during higher traffic
conditions. For example, in the three-tier embodiment discussed
above, the security network could have a feature to disallow all
other network access in an emergency situation.
[0140] A similar multi-virtual LAN network may be also useful in a
health care facility wherein different networks are used for
security, medical care, personal and public information.
[0141] The architecture described herein offers advantages in
several discrete areas of wireless network management.
[0142] Bandwidth Management
[0143] An aspect of functionality that can be realized in
connection with the configuration described herein is to modify the
bandwidth of communications in accordance with the type of device
with which the communication is associated. For example, where a
data set comprises an image, for example retrieved from the
Internet, the resolution of the image can be modified in the cell
controller to accommodate the resolution capacity of a portable
device. Therefore, rather than provide a highly detailed image of
the type that can be displayed on a personal computer, an
image-bearing message can be reduced in resolution in the cell
controller to a lower resolution, compatible with a portable
device, such as a personal digital assistant. By therefore reducing
the resolution of the image being sent, the bandwidth and data
capacity necessary to send the image can be significantly
reduced.
[0144] Another functionality available with the configuration
described herein is to control the individual RF ports according to
the traffic experienced by the system. For example, the cell
controller can assigned an RF port experiencing a high volume of
communication to a different channel, such as a reserve channel on
which no other RF ports are operating. This will minimize
interference in communications conducted with a particular RF port
that is experiencing high volume. In this manner the RF port may be
the only RF port operating on the particular, reserve channel. The
cell controller has real time information available to it in order
to make the changes in the RF port configuration to accommodate
changing load conditions.
[0145] A wireless system may also contain RF ports sending and
receiving overlapping 2.4 GHz, Bluetooth, and 5 GHz signals. These
signals will have differing frequencies, power levels, and data
rates. Because the cell controller will monitor all features of the
frequencies generated by the RF ports and will know the locations
of the RF ports, the cell controller will have the ability to
optimize the frequency, power level and data rates in the physical
space for the best possible performance.
[0146] The cell controller provides a central location for
interfacing the WLAN with WAN features that may be accessed by
users. For example, the cell controller can coordinate the
processing necessary to enable voice over IP (VoIP), i.e.
compression or user allocations. Compression is particularly
enhanced using a cell controller because the cell controller can
maintain the necessary historical dictionaries needed for efficient
compression algorithms in one location that applies to all RF
ports. The cell controller can also proxy to access a SIM database
for WAN users in advance of actually needing this data to perform
operations.
[0147] The cell controller allows additional functionality to the
WLAN at all levels while maintaining the compatibility in the MAC
level necessary for IEEE 802.11 systems. One such example would
network management features that are not present in the 802.11
protocol but would be useful to operate at the cell controller/RF
port level. An embodiment of this is to monitor the software
versions present in the MUs in a WLAN and send out updated versions
when each MU "checks in" with the cell controller. Ultimately this
allows the costs of APs/RF ports to remain relatively
inexpensive.
[0148] Other aspects of routing traffic through the cell controller
is the ability to detect interference and noise and the ability to
control the transmit power of particular RF ports. For example, the
cell controller can command the RF port to provide the signal level
they are receiving when there is no communication (background noise
or interference) to the cell controller. This can be used to
provide an analysis of the system operation or to provide the
detection of background interference and its location.
[0149] Security
[0150] Another available function of this architecture is control
of association, since all association is handled in a cell
controller. Accordingly, where a "public access only" device
attempts to associate with the system in a secure area such as, for
example, an airport control tower, where a member of the public
should not be, the fact of this association attempt can be noted in
the cell controller and automatically give notice to security
personnel. The cell controller can additionally deny or permit
access to a mobile unit attempting to associate with an RF port
according to traffic at the RF port as observed at the cell
controller. The cell controller thereby has a measure of control
over roaming and can command a mobile unit as to which RF port to
become associated with. Indeed, under many WLAN architectures, APs
do not coordinate with each other to determine if they are being
probed in such a way that an attempt to break security may be
occurring. In contrast, a cell controller can monitor all such
probing to determine if an attack may be taking place. Logs of such
probing may be kept. In addition, authentication protocols may be
centralized in the cell controller instead of on a central server,
creating greater efficiency.
[0151] Another important aspect of control of association and
roaming in the cell controller is the fact that the cell controller
can perform a "soft-roaming" function. Soft-roaming takes place
when the cell controller changes ownership of the BSS
identification between RF units. In essence the cell controller has
the ability to tell a mobile unit which RF port it will communicate
through. In connection with doing so it is possible for one RF port
to monitor traffic to another RF port and thereby advise the cell
controller that it has the capability of receiving signals from
that particular mobile unit. The cell controller has the ability to
control the access of the mobile units to RF ports according to
traffic as observed in the cell controller. One aspect of the
system is that the intelligence in the cell controller interacts
with the intelligence in the mobile unit to control association.
The RF port has no part in this and accordingly there is a greater
ability to centrally manage the flow of traffic through the RF
port. Another aspect is to provide an arrangement in the cell
controller wherein only one RF port can perform secure data
communication. When a mobile unit desires a secure link, the cell
controller can switch the mobile unit to a particular RF port for
secure communications. In essence the unit is capable of providing
a virtual RF port. The switching of the BSS identification between
RF ports takes place in the cell controller and the mobile unit has
no idea that it has been given the bait and switch. Another aspect
of the centralized management is security, in that if a mobile unit
which does not have access authorization attempts a number of times
to gain access to the system, the security program in the cell
controller can provide an alert and in essence lock out further
attempts by that mobile unit.
[0152] Location Tracking
[0153] In the architecture described herein, because RF ports are
cheaper than typical APs, there may be more RF ports in a given
area than APs. This proliferation of RF ports will allow location
tracking to take place. Moreover, one RF port has the ability to
"snoop" and listen in to the traffic between another RF port and a
mobile unit. The cell controller can take all this data in and use
time stamping based on the arrival of data. Such information can be
passed through the Ethernet to a processor that can determine
location.
[0154] Diagnostic Capability
[0155] An important capability which the cell controller can also
implement is the diagnostic capability. As an initial calibration
when a system is first brought into operation the cell controller
can cause the RF ports to go through a sequence in which the RF
ports communicate to each other. In this way the signal level of
each RF port, as observed at one or more other RF ports, can be
monitored and the radio location of the RF ports can be mapped, for
example, to create alternative RF ports to which traffic can be
switched in the event of excess traffic on any particular RF port.
Accordingly using RF signals the cell controller can dynamically
discover the RF locations and signal characteristics between RF
ports. Each RF port in this case would provide the cell controller
with an indication of the strength of the signals received. The
cell controller can also record the background noise level.
Following the initial calibration of the system the cell controller
can undertake periodic diagnostics, wherein signals are sent from
one RF port to another and the signal level is relayed to the cell
controller to determine whether if the transmitters and receivers
are operating properly. In this respect, the signals received can
be compared to the base line signal levels which have been recorded
at the cell controller as a calibration level. Changes in
background noise can also be determined and this can be used to
detect a problem with a receiver in the system.
[0156] While there has been described what is believed to be
claimed in the above-identified application those skilled in the
art will recognize that other and further modifications may be made
without departing from the scope of the invention and it is
intended to claim all such changes and modifications as fall within
the true scope of the invention.
* * * * *