Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SYSTEMS AND METHODS FOR WIRELESS
COMMUNICATIONS
s
This case claims priiority to kJnited States Application No. 60/071,48s,
entitled
"Virtual Radio" and filed 13 January 1998, the contents of which are herein
incorporated by
reference.
The invention relaters in general to communication systems and in particular
to
wireless communication systems that can communicate audio, video and data
signals.
B ~ ~ ro and of h Invention
The field of wireless teleconununications has grown rapidly in recent years,
and the
demand for wireless telecommunication services and equipment continues to
grow. This
notable growth is due, in pout, to the proliferation of new communication
standards and the
development of new hardware technologies. For example, the successful adoption
of cellular
telecommunication standards has promoted the growth of the cellular telephone
industry and
driven the development of smaller and more power efficient cellular telephones
that
incorporate new hardware technologies that provide for greater conversion
rates between the
2s analog and digital domain, and greater digital signal processing power.
Although the new these new standards and hardware technologies have provided a
slew of new devices that often work. exceptionally well, these devices are
generally dedicated
to a specific application and are based on application specific hardware
designs are almost
always restricted in the functionality they can provide. Specifically, the new
hardware
devices generally employ application specific hardware architectures,
including proprietary
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bus architectures, components, and other proprietary elements, that reduce the
flexibility of
these systems and make the systems difficult to upgrade, difficult to extend,
and difficult to
scale.
In part to address the extensibility issues that arise from the use of
proprietary
hardware architectures, digital radios, or software radios, have been
developed. Software
radios employ analog to digital converters and digital signal processors to
process a broadcast
band signal and generate a stream of data that is representative of the
information being
transmitted on a selected channel. R'rannon, Brad, Wide-Dynamic-RangeAlD
Converters
Pave the Way for Widebanu!Digital-Radio Receivers, EDN (November l, 1996). The
datastream can then be passed to a software application that further processes
the datastream
to perform the application at hand. l?or example, a software radio application
that
implements an FM radio receiver can process an incoming datastream to decode
the signal
transmitted on a particular radio frequency assigned to a particular radio
station and can play
the music or voice signals that were encoded on that RF signal.
Software radios, therefore, provide greater flexibility by providing a
datastream to a
computer system that can employ an application program to process the
datastream as the
program dictates. Accordingly, by changing the software that processes the
datastream, a
user can upgrade, or extend., the functionality that is being implemented by
the software
radio. This provides greater flexibility and therefore more powerful
telecommunication
devices.
Moreover, software radios exist today that provide the datastream of the
modulated or
demodulated data into an application program that can be run on a general
purpose
workstation. This use of general purpose workstations more readily integrates
wireless
communication functions with data processing functions and more easily allows
wireless
communications to be integrated into other data processing systems. For
example, this
increased level of integration allows software radios to leverage the power of
wireless
communications along with the resources available on a data processing
platform, such as
network communications, greater data storage, and other such capabilities.
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Although software radios provide increased flexibility over application
specific
hardware architectures, software radios still employ application specific
digital hardware or
digital signal processors (>riSPs) for performing the signal processing that
develops the
datastream that represents the information encoded within a broadcast signal.
Accordingly,
in a software radio the signal processing happens largely within dedicated
signal processing
hardware, typically on a application specific platform, and little to no
opportunity is provided
to adapt or alter the way in which signal processing takes place to generate
the datastream.
For example, even in a software radio, dedicated hardware will still perform
the basic signal
processing that determines the width of a channel, the number of channels that
can be
processed at once by the software application, and other similar parameters.
Accordingly, software radios still place a boundary of an application specific
hardware architecture between a user's application software and the
demodulated data
available from the RF signal. This in turn limits the flexibilty of the
software radio and
reduces the ability to provide teleconununication functions across the data
processing
environment.
Accordingly, it is are object of the invention to provide wireless
telecommunication
devices that can adapt or all:er the signal processing being carried out by
the wireless
communication device.
It is yet another object of the invention to provide wireless communication
systems
and methods that provide greater flexibility over the datastream generated by
the wireless
communication device.
Other objects of the invention will, in part, be obvious, and, in part, be
shown from
the following description of the systems and methods shown herein.
The invention provides systems and methods that include, inter alia, wireless
communication systems that integrate wireless receivers and transmitters with
general
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purpose processing platforms and that include a data access channel that
delivers into the
memory space of an application program digital data that is representative of
a modulated
signal. Accordingly, these systems can employ wide band digitization of an
incoming signal,
such as an RF signal, direct the digitized data into the application memory
space of a general
purpose processing platform and allow an application program operating on the
general
purpose processing platforn to perfbrm the digital signal processing that
obtains the
information encoded within the digitized signal.
E
The foregoing and other objects and advantages of the invention will be
appreciated
more fully from the followiing further description thereof, with reference to
the accompanying
drawings wherein;
Figure 1 depicts a functional block diagram of a wireless communication system
that
includes an application program for processing a modulated signal;
Figure 2 depicts a fimctional. block diagram of one interface card such as
that depicted
in Figure 1;
Figures 3A-3C depict in diagrammatic form the flow of data between the
components
of the system depicted in Figure 1;
Figure 4 depicts as a functional block diagram one embodiment of a cellular
receiver
process that processes digitized IF samples delivered into the memory space of
the process;
Figure 5 depicts an alternative embodiment of a downconverting module that can
be
employed with the cellular receiver process depicted in Figure 4;
Figure 6 depicts the network layers of a network interface card according to
the
invention; and
4
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Figure 7 depicts as a functional block diagram, the software components of an
application for transmitting; packets of network data.
Detailed Description of t-he Illestrated Rm
To provide an overall understanding of the invention, certain illustrative
embodiments
will now be described, incbuding a cellular receiver wireless communication
system.
However, it will be understood by one of ordina 'ry skill in the art that the
systems and
methods described herein can be adapted and modified for other applications
and that
additions and modifications can be made to the embodiments described herein
without
departing from the scope of the invention.
The systems and mc;thods described herein include, inter alia, wireless
communication systems that integrate wireless receivers and transmitters with
host computer
platforms and that include a data access channel that delivers into the memory
space of an
application program digital data thal: is representative of a modulated
signal. Accordingly,
these systems can employ vvide band digitization of an incoming signal, such
as an RF signal,
provide the digitized data to the application memory space of a general
purpose processing
platform and allow an application program operating on the general purpose
workstation to
perform the digital signal processing that obtains the information encoded
within the
digitized signal. To this end, the systems and methods described herein
optionally include a
data interface board for exchanging data between a wireless
receiver/transmitter and an
input/output bus of the genc;ral purpose processing platform, as well as
optionally include a
programming environment that provides libraries of software routines as well
as a framework
that includes a class or set of classes that can embody an abstract design for
a solution to a
wireless communication application.
Figure 1 depicts a wireless communication system 10 that includes a
receiver/transmitter 12, a converter 14, a host platform 1 b, a persistent
memory device 18,
and an input/output device a0. The depicted system 10 provides a platform on
which
processes can be run to perform a desired wireless communication operation. As
shown in
Figure 1, the receiver/transrnitter 12 couples through a bidirectional
transmission path to the
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converter unit 14, which in turn couples through a bidirectional transmission
path to the host
platform 16. The host platform 16 couples through a bidirectional transmission
path to the
persistent memory device 1;8, and through a bidirectional transmission path to
the
input/output device 20. Simply for the purpose of describing the systems and
methods of the
invention, the system 10 will described as including an application program
that implements
a cellular receiver for processing the U.S. cellular band. However, it will be
understood that
the systems described herein are in no way limited to any particular
application, and that
other application programs can be run on the system 10 for implementing other
applications,
including cellular modems, radio receivers, television receivers, wireless
network interface
cards, remote control devices, such as garage door openers, and channel
selection devices, or
any other type of wireless communication service, virtual device or
application.
In one embodiment, the depicted receiver/transmitter 12 comprises an RF
receiver
unit that can act as a front and for thE; system 10 to collect and translate a
selected broadcast
band of interest to a baseband or a substantially base band signal. To this
end, the
receiver/transmitter 12 depicted in Figure 1 includes an antenna element 22
that couples to a
preamplifier 24, which couples to a vvideband filter 28. The functional
components depicted
within the receiver/transmitter unit 12 illustrate that the receiver can
collect an RF signal and
generate from that ItF signal a wideband 1F signal that can be transmitted to
the con~:~erter
unit 14. In one embodiment, the receiver/transmitter unit 12 can include a
commercially
available IZF receiver, such .as the type manufactured and sold by the Tellabs
Company of
Lisle, Illinois. However, it will be apparent to one of ordinary skill in the
art that other
receiver/transmitters, or tuners can be employed, and the receiver/transmitter
device selected
depends in part on the application. For example, the unit 12 depicted in
Figure 1 is described
as a receiver/transmitter. However, it should be apparent that depending upon
the application
the receiver/transmitter 12 can be soYely a receiver unit, or alternatively
solely a transmitter
unit. Moreover, the system 10 can include a plurality of receiver/transmitter
devices thereby
allowing a plurality of trans:mitter/receiver devices to be coupled to the
host platform 16, and
wherein each receiver/transmitter device can be capable of receiving or
transmitting along
different portions of the 1ZF spectrum, including 10 kI-Iz to 1 Ghz, or
alternatively, along
portions of the microwave spectrum, infrared spectrum, visible light spectrum,
or any other
suitable communication spectrum or channel.
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Figure 1 further depicts that the system 10 includes a converter element 14.
In the
embodiment depicted in Figure 1, the converter element 14 is a high
performance analog to
digital converter of the type: manufactured and sold by the Analog Devices
Corporation of
Norwood, Massachusetts. 'The analog to digital converter functions to convert
data from the
analog domain into the digital domain, and conversely to translate data
between the digital
domain and the analog domain.
The design and use ~of converters such as the converter 14, are well known in
the art
of electrical engineering, and any suitable converter can be employed by the
system 10 for
translating signals between the analog domain and the digital domain.
Moreover, it will be
understood that the sampling rate at which the converter 14 is driven normally
depends on the
bandwidth of interest and, typically the highest frequency in the selected
band and the
amount of oversampling that is desired for purposes of improving the signal to
noise ratio in
the digital domain.
The converter element 14 couples through a bidirectional path to the host
platform 16,
shown in Figure 1. The host platform 16 can be a general purpose computer work
station,
such as for example an IBNf compatible personal computer running a Pentium
class
microprocessor having MMX capabilities and operating at a clock frequency of
200
megahertz, with a 33 megahertz internal PCI bus, and at least 64 megabytes of
internal
random access memory (R~~1VI). The host platform 16 is shown diagrammatically
in Figure
1, and includes an interface device 30, the CPU 32, the operating system 34,
computer
memory 36 that can maintain a memory space 38 for data and a program memory
space 40
for application processes and an output controller 48 that couples to the
output device 20.
The host platform 16 is merely one embodiment of a general purpose processing
platform,
and it will be understood by one of ordinary skill in the art that the term
general purpose
platform encompasses computing platforms that are designed for providing a
flexible
architecture to facilitate the loading and naming of different application
programs.
In this example, the host platform 16 operates to perform signal processing on
the
digitized wideband IF data <ielivered from the converter 14. To this end, the
host processor
16 can run the depicted process 44 within the program memory space 40. The
operating
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system 34, which controls resources on the host platform 16, such as the
memory resource
provided by the computer memory 36, can allocate to the process 44 a portion
42 of the
memory space 38 for use by the process 44. As will be described below, the
operating
system 34 can control the flow of data between the interface 30 and the
portion 42 of the data
memory 38 that has been al:Iocated to the process 44, and can allow high
bandwidth data
transfers between the process 44 and the interface 30. The direct data
transfer between the
process 44 and the interface 30 provides to the process 44 a constant stream
of data samples,
or blocks of data samples to process, and reduces or eliminates the time
delays and transfer
fitter than can arise from the' virtual memory operations of the operating
system 34, multiple
levels of caching and competition for input/output resources.
Figure 1 further depicts that the host platform 16 can couple to a persistent
storage
device 18, which can be a herd disk drive, a tape drive, a flash memory or any
other type of
memory device that can provide persistent storage of data. The system 10 can
employ the
storage device 18 for storm~; wideba~id IF data, demodulated data, or any
portion of the data
processed by the signal processing application program operating on the host
platform 16.
Figure 1 further depicts that the host processor 16 can include an output
controller 48 that
couples to the input/output device 20. In one embodiment, the output
controller 48 can be a
sound card, such as the Sound Blaster~ card manufactured and sold by Creative
Labs of
Stillwater, Oklahoma. For trus example, the sound card can couple to one or
more audio
input/output devices such as a microphone and a pair of amplified speakers of
the type
commonly employed with commercial personal computers, In other applications,
the
input/output device can include a data display for displaying data transmitted
over the
wireless channel, as well as .a video display such as a television monitor.
Moreover, the
input/output device can also comprise a device, such as a remote control
device, that can be
employed for generating or responding to a command signal transmitted over a
wireless
channel.
Figure 2 depicts one embodiment of an interface card, such as the interface
card 30
shown in Figure 1. More particularly, Figure 2 depicts an interface card 60
that can be
formed as a plug-in card, or a daughter card, that can be inserted into an
expansion slot on the
motherboard of the host platform 16. As shown in Figure 2, the interface card
60 can include
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a PCI/PCI bridge 62, a conlnguration memory 64, a PCI controller component 68,
an output
page address memory 70, and input page address memory 72, an output data
memory 74 and
an input-data memory 78. '.Che interface card 60 depicted in Figure 2 can
connect through the
PCI/PCI bridge 62 to the P(~I bus of the host platform I6, and can connect
through the
outputJinput data memories 74 and 78 to the analog front end of the system,
such as the
converter 14 depicted in Figure 1.
More specifically, the interface card 60 depicted in Figure 2 can be a full-
size PCI
card that is compliant with version 2.0 of the PCI specification. The
interface 60 acts as a bus
master to perform direct memory access, off loading the transfer of data from
the CPU 32,
and can act as a target when accessing its control and status registers.
The PCI/PCI bridge 62 can be any commercially available PCI bridge device
suitable
for interfacing a PCI card to the PCI bus of a work station, such as the host
platform 16. One
such PCI/PCI bridge component is the 21050-AA, manufactured and sold by the
Intel
Corporation. The PCI/PCI bridge 62 can couple via a transmission path to a PCI
controller
element 68. The PCI controller element 68 can be any suitable element for
controlling the
actions of the interface board 62, and in one embodiment is a field
programmable gate array
(FPGA) such as the type manufactured by the Xilinx Corporation of Millipata;s,
California.
The FPGA can be programnned to contain the PCI controller and DMA engine, to
provide a
high bandwidth interface between the analog front end and the computer memory
36.
Configuration data can be stored in the configuration memory 64, and accessed
by the
controller 68 at start-up or during operation.
In an optional embodiment, the interface card 60 can have a daughter card
interface to
which the converter 14 can connect. A daughter card can carry the converter
14, as well as
any additional components that can be employed for generating data to be sent
to the
interface card 60. The depicted interface 60 includes a pair of data buffer
memories, such as
FIFO memories, each of which exist in the input and output directions for
those systems that
couple to both receiver and lxansmitter units. Optionally, a single buffer can
be provided for
systems which connect only to a receiver or a transmitter unit. The buffers
absorb fitter that
arises from the bursty access to the PCI bus of the host platform 16. In the
input direction,
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the buffer can hold incomvng samples until the interface device 60 acquires
the PCI bus and
can transfer the data into the memory 36 of the host computer 16. In the
output direction, the
buffer can hold excess samples that have been transferred from memory 36 but
are waiting to
be accepted by the converter 14. The buffers 74 and 78 also serve to
temporally decoupie the
timing of the interface cart. 60, which typically operates using the PCI
clock, from
converter 14 or from a daughter card, which typically would operate using the
converter
sampling clock. This reduces, or eliminates, the need for designs that must
take into
consideration synchronization or metastability issues. It also separates the
data transfer and
processing from the fixed rate realrr~ of the analog front end, allowing it to
be bursty, or
sporadic, as is common wil:h shared data transfer resources.
The PCI interface between the interface card 60 and the PCI bus, in the
depicted
embodiment, has a capacihr of about one Gbit/sec. There are also specified
upgrade paths for
increasing the PCI bus bandwidth by doubling the width from 32 to 64 bits and
doubling the
1 S speed from 33 megahertz to 66 megahertz, enabling greater bandwidth.
Although the
interface card 60 depicted in Figure 2 contemplates interfacing to a PCI bus,
it will be
understood by one of ordinary skill in the art that in other embodiments, an
interface to an
ISA bus, an S-bus, or any other data bus capable of transferring information
from an interface
card to the host workstation 16 can be practiced with the systems described
herein.
The depicted interface card 60 acts as a PCI bus master and initiates
transfers on the
PCI bus. Accordingly, the interface card 60 can perform DMA sample streams to
or from the
computer memory 36 at a high speed with minimal intervention from the CPU 32.
In one
embodiment, the interface card 60 implements a variant of scatter/gather DMA
that streams
pages of data between the computer memory 36 and the interface card 60. To
that end, the
interface card 60 includes t,wo page address memories, 70 and 72, which can be
FIFO
memories, one being assigned for input and one being assigned for output. The
memories
can hold physical page addresses associated with buffers in a memory space,
such as the
virtual memory space that i,s organized by the operating system 34. For
example, at the end
of a page transfer, the interface 60 can read the next page address from the
head of the
appropriate page address memory and begin to transfer data to or from the
memory 36. The
interface card 60 can trigger an interrupt when the supply of page addresses
runs low, and the
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page addresses can be replenished by the interrupt handler in the device
driver associated
with the interface card 60. Accordingly, the interface card 60 stores physical
page addresses
within the memories 70 and 72, directly on board the interface card 60.
Optionally, the page
addresses could be stored in a memory table maintained within the computer
program
memory 36. The interface card 60 depicted in Figure 2 can transfer complete
pages of data
between the computer memory 36 and the interface card 60. The transfer of
complete pages
is understood to result in pa;~e aligned, integral page length buffers that
are more easy for the
operating system 34 to manipulate.
The interface card 60 operates in cooperation with the operating system 34 to
achieve
the direct memory access tr2msfer of a data buffer into the application data
memory 38. In
one embodiment, the operatiing system 34 can be an implementation of the Unix
operating
system that provides a multitasking operating system that includes a virtual
memory system
for controlling memory resources on the platform 16. In one specific
embodiment, the
operating system 34 is the Linux operating system that provides a Unix-like
operating system
for the Intel processor architecture. Other versions of Unix, or other
operating systems can be
employed without departing from the scope of the invention. Continuing with
the example of
a Unix operating system, the; operating system can be modified to include a
device driver and
an enhanced virtual memory system, each of which operate to achieve the direct
memory data
transfers of pages of data. The device driver allows for continuous data
transfer between the
interface card 60 and the application data memory 38. To this end, the system
can employ a
ring of buffers into which samples can be transferred. These buffers can be
part of the
operating system kernel virh.~al memory space, and can be locked down in
physical memory.
Portions of the memory can be locked down using any suitable technique,
including the
m lock system call. The device driver can initially fill the input page
address memory 72
with addresses from buffers at the head of the ring of buffers. When this
memory 72 empties
to a certain, programmable, level, the interface card 60 generates an
interrupt, and the
interrupt handler transfers more buffers from the head of the ring. The level
that can trigger
the intemzpt can be set such that there are sufficient pages remaining to
absorb samples
arriving before the interrupt handler can provide new addresses.
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Figures 3A-C depict schematically the flow of data that occurs as the data
travels
through the receiver/transmitte~r 12, into the ring of buffers and then onto
the application
memory 38. Specifically, Figure 3A depicts that an RF data transmission can be
picked up
by a receiver unit, such as the receiver/transmitter 12 depicted in Figure 1.
In Figure 3A, the
receiver comprises a mufti-band front end that can be software controlled to
select a center
frequency and a width of aJn RF band. For example, the 95X family of wideband
receivers
manufactured by the Rockwell Company provide mufti-band front ends that can be
configured through softwwe to select a center frequency and a width of an RF
band in the
range spanning between 2 MHz to 2 GHz. Such front ends allow for mufti-band,
mufti-mode
radio systems. In another example, the front end can operate in the 2.5 GHz
ISM band. As
further shown by Figure 3A, the wideband signal from the receiver/transmitter
12 can be
passed to a converter, such as the converter 14, that can perform direct
sampling, band pass
sampling, or any other suitable sampling process to provide a stream of
digitized IF data. In
one embodiment, the IF signal can be digitized by a 12 bit converter such as
the AD9042
converter manufactured by the Analog Devices Company. This converter is
capable of
digitizing signals at a rate of 40 MSPS. This provides a 20 MHz IF bandwidth.
As shown in
Figure 3A, the stream of digitized IF data can be provided to an interface
with the host
computer, such as the depicted PCI interface 30.
The PCI interface can perform a data transfer into the memory 34 of the host
platform 16 at a transfer rate that is sufficiently high to meet the timing
demands of the
process that is performing signal processing on the data, such as the process
44. For
example, to transfer a strewn of 16 bit samples of a 10 MHz wide IF band
(i.e., a minimum
20 MHz sampling rate) to the application process, a 320 Mbits/sec data rate is
required.
Figure 3A depicts this transfer of data into the memory 34, by showing the
transfer of pages
of digitized IF data into a ring buffer SO that is maintained within the
virtual memory space of
the kernel. In Figure 3A, the ring buffer 50 includes four buffers, 52, 54, 56
and 58, each of
which as a plurality of page, capable of storing data. However, it will be
apparent to one of
ordinary skill in the art that the number of buffexs provided by the ring
buffer 50 can depend
upon the application and each buffer can optionally include hundreds of pages
of memory
space. As discussed above, the interface card 30 has a list of page addresses
that designate the
memory locations into whi<;h the interface card 30 is to provide data. As the
interface card
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operates, pages of data are transferred into the buffers of the ring buffer
50, and the ring
buffer 50 can begin to fill. Accordingly, the ring buffer 50 stores data to be
transferred to the
application memory 38, anal optionally provides sufficient storage of data to
accommodate
those times when the application program is not able to process data at the
rate at which data
is being delivered, thereby allowing the application can catch-up by, from
time to time
processing the buffer faster than it fills.
To transfer data to »he applic;ation memory space 38, the enhanced virtual
memory
system can act to swap buffers from the application's virtual memory space
with buffers in
the kernel's virtual memory space. For example, when an application makes a
request to read
data from the device driver, the application program can be transferred the
buffer at the tail of
the buffer ring 50. To deliver this buffer at the tail of the ring 50 across
the kernel-
application boundary, the system 1 Ct performs a buffer swap operation.
Figures 3B and 3C
depict the transfer of data from the kernel virtual memory space to the memory
space of the
application program.
Specifically, Figures 3B and 3C depict the kernel virtual memory space and the
buffer
ring 50 maintained therein, as well as the application memory space with a
buffer 66 stored
therein. Each of the buffer; depicted in Figures 3B and 3C provide storage for
a certain
amount of data. Associated with this storage are both virtual addresses,
depicted on the left-
hand side of the buffer 58 ass numbers 0-5, and physical addresses, depicted
on the right-hand
side of the buffer 58 by the numbers 6, 3, 58, 467, 2 and 94. As will be
apparent to one of
ordinary skill in the art, a physical memory address is representative of the
actual physical
memory location within the; computer memory 34 that is storing the data.
Similarly, in the
application memory space the buffer 66 has a plurality of pages with these
pages having
associated virtual memory addresses and physical memory addresses. For buffer
66 the
virtual memory addresses are depicted by numbers 0-5, and the physical memory
addresses
are depicted by numbers 2, 5, 98, 105, 3 and 6. To achieve the transfer of
data between the
kernel virtual memory space and the memory space of the application program,
the physical
memory of the buffer being; transferred from the kernel virtual memory space
is swapped out
fiom underneath the virtual address of the buffer 66 in the application memory
space, thereby
swapping the buffer provided by the process 44 for the buffer in the system
kernel. In one
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practice, each page in the user buffer is faulted into a distinct physical
page. The physical
addresses in the page table entries for the kernel and user buffers are then
swapped, and
therefore, the system affects a data Transfer into the application data space
by altering the
page table within the virtual memory system. The manipulation of Page tables
follows from
principles well known in the art, including principles set forth in Bach,
Maurice, J., The
Design of the Unix Operating System, Prentice-Hall, Inc. (1986). Moreover, it
will be
apparent to one of ordinary skill, that any system for swapping a buffer from
the kernel
memory space with a buffer in the application memory space can be practiced
with the
system described herein.
To facilitate the sw<~pping ofbuffers, the application program, such as the
process 44
can, upon initialization, identify or define the size and number of buffers in
the buffer
ring 50, therefore allowing the process 44 to be aware of the size of the
buffer to be provided
to any READ system calls made by the operating system. Accordingly, once the
application
program performs a malloc~() systems call, a memory allocation will occur that
allocates a
memory space that is coordinated with the size of a buffer in the buffer ring
50.
Consequently, the buffers swapped between the kernel memory space and the
application
memory space are the same size.
When outputting data, the process 44 can write to the interface card 60,
treating the
card 60 as an I/O device. Optionally, the device driver can maintain a queue
of buffers that
the process 44 has written to the device driver. The size of the queue can be
bounded to keep
processes in applications from employing all of the physical memory available
on the host
platform 16. In operation, the device driver can first store within the output
page address
FIFO 70 with addresses of buffers at the head of the queue. When the output
page address
FIFO 70 empties, or empties to a certain, optionally programmable, level, an
interrupt can be
triggered by the interface 60 and the interrupt handler of the operating
system can replenish
the FIFO memory 70 from buffers at the head of the queue, if they are
available.
In one embodiment, a system as described herein and running on a 200 MHz
pentium
pro platfonm running Linux with a 33 MHz, 32 bit-wide PCI bus, the IO system
has been
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shown to support continuo~~us sample stream rates at up to 512 Mbits per
second. The peak
burst rates are 933 Mbits per second for input and 790 Mbits per second for
output.
Returning to Figure; 1, it can be seen that with the digitized IF data in the
program
memory 36, the process 44 can then perform signal processing on the digitized
IF samples to
demodulate the transmitted. signal. In one embodiment, the process 44
comprises a cellular
receiver process that demodulates the wideband digitized IF data to provide a
wideband
digital receiver capable of operating in the "A-side" of the U.S. cellular
band. This cellular
receiver process provides a receiver that can continuously monitor 10 MHz of
the cellular
band and provide the capability to demodulate FM signals anywhere in that
band. In this
embodiment, the receiver/hransmittc,~r 12 and converter 14 can be integrated
into a single unit
that comprises a Tellabs Rlj receiver that translates the 825-835 MHz band to
a baseband
signal and then samples the: signal at 25.6 MSPS. The 12-bit sample stream is
fed to the
interface card 30 which performs direct memory access to deliver the samples
into the
memory 36 of the host 16 for processing by the process 44. The process 44 can
control the
system parameters, such as channel filter size and the various sample rates.
This allows
parameters to be modified even while the receiver is operating.
Figure 4 provides a function block diagram of one cellular receiver process
that can
demodulate the sampled IF data being provided to the program memory 36. The
cellular
receiver process can be an executing computer program that operates in the
program space 40
of the computer memory 3fi. The computer program can be written in C, C++,
Java, or in any
suitable computer language;, and developed using standard software debugging
tools. The
pmgram can also include routines from commercially available components, such
as the
FFTW package developed by Matteo Frigo and Steven G. Johnson, and freely
distributed,
which provides routines of signal processing algorithms. Other commercially
available
libraries of routines or sets of classes for building user interfaces, or for
other functionality
can be employed. As is known to those of ordinary skill in the art, the
program can comprise
a plurality of routines, classes or modules, each of which perform a portion
of the processing
that is carried out by the cellular receiver process 80. As depicted in Figure
4, the cellular
receiver process 80 can incilude a channel selection stage 82, a quadrature
demodulator stage
84, a low pass filter and decimation stage 88 and an audio band pass filter 90
and an output
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controller 48. As discussed. above, the IF samples can be provided through DMA
transfer
into the memory space of the application program. The IF samples can be
transferred at the
system tiansfer rate, and the; cellular receiver 80 can be responsible for
operating at sufficient
speed to process incoming ;samples, thereby avoiding the dropping of samples.
As depicted by Figure 4, the cellular receiver process 80 can employ a "data
pull"
architecture. While the flow of data is from input to output, the flow of
control is from
output to input. By placing control downstream, the architecture facilitates
the construction
of systems that can aggressively employ lazy evaluation and adapt to the
requirements of the
downstream modules. The total amount of processing that needs to be done is
reduced
because downstream components can request just the data they need from
upstream modules.
Consider, for example, an audio system to which a variety of output devices
can be attached.
The driver for the output controller 48 can control the amount of data
required depending
upon the application, for example telephone quality, at 8 kHz sampling rate
with 8 bit
quantization, or CD quality audio, at 44 Khz sampling rate with 16 bit
quantization.
The depicted cellular receiver process 80 employs an upstream communication
path
for controlling data transfer between the stages of the process. In one
practice, each module is
capable of requesting data fi-om the next upstream module. Accordingly, each
module can
call the immediately upstream module (or modules) requesting the needed data.
The data
delivered between modules can be done on a sample by sample basis.
Alternatively, the
process 80 can operate on bllocks of data, or payloads. The data payloads,
such as the
depicted payloads 92, 94 and 98 can be made large enough to take advantage of
data and
instruction caching effects, but small,enough to avoid introducing
unacceptable latency. To
process the data payloads, the signal processing applications can employ
algorithms designed
to work on blocks of data rather than. on single samples, which for example
would include
signal processing algorithms such as the fast Fourier transform. The
development of other
such algorithms follows from principles well known in the art, including
principles set forth
in Oppenheim et al, Digital Signal Processing, Prentice-Hall, Ins. (1975).
To process the data, the cellular receiver process 80 includes the channel
selection
filter stage 83. This stage, o~r module, has the task of extracting from the
digitized IF samples
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a narrowband FM signal (AMPS channel bandwidth is 30 kHz) from a 10 MHz wide
frequency band. This depicted stage 83 accomplishes this task using a filter
design that
combines three steps of translating the signal to baseband, lowpass filtering
and decimating
to an intermediate sample rate. This step of processing comprises the largest
portion of the
computational load. The clhannel selection filter 82 employs the raw samples
from the RF
frontend at Rs = 25.6 MSPS as input and produces a complex baseband signal at
a variable
intermediate sample rate, R'D.
Separating narrowband channels in a wideband receiver is a computationally
intensive
task that is usually done usiing special purpose hardware, such as a digital
down-converter
(DDC) implemented in dedicated hardware. Rupert Baines, the DSP Bottleneck,
IEEE
Communications Magazine:, 33(5): 46-54 (May 1995). The wideband signal is
translated to a
complex baseband signal b;y the qua.drature multiplier and then lowpass
filtered to prevent
aliasing due to decimation. Special purpose FIR filters for decimation exist
that do this
operation efficiently-which is important since the sample rates for a wideband
receiver could
be in excess of 30 MSPS. 1?stimates have been made that a channel selection
filter can
require about 100 operations per input sample for a total of 3000 MOPS.
In one embodiment, the channel selection filter 82 follows the structure of a
hardware
DDC. Multiple threads could be employed to implement in software the structure
of the
hardware DDCS, wherein tlhe separate steps of the down-conversion process,
that is, the
generation of the sine/cosine multiplication factors, frequency translation,
and filtering, are
done in separate physical locations in the DDC, and a high degree of pipeline
parallelism is
achieved. Furthermore, there can be additional fine grained parallelism within
the FIR filter.
Figure 5 depicts an ;alternative embodiment of a software DDC, that operates
to
perform reduced processing; of samples at the high sample rate and reduce the
rate early in the
processing chain. As shovv~n in Figure 5, the software DDC intakes samples of
the digitized
wideband IF signal and provides the samples to two routines, represented
functionally by
blocks 102 and 104, for performing frequency translation and decimating low
pass filtering,
to produce in phase and quadrature signals. Both the in phase and quadrature
signals are
provided to the logic block 106. Logic block 106 can collect the data and
provide any
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formatting and transfer fiu:~ctions required for delivering the data payload
to another module.
In this embodiment, an FIIt filter is employed (versus a lower-order IIR
filter) to allow the
production of an output si~~al that depends upon the filter input samples,
x~nJ, and therefore
to compute only those ouput samples, y~nJ, that will be required after
decimation. This is
understood to reduce the computation load by taking advantage of the large
decimation
factors that will exist when processing a narrowband signal in a wideband
receiver.
Furthermore, the precomputed frequency shift factors can be incorporated into
a composite
FIR filter and will then require only a phase correction after each output
sample is calculated.
This feature makes this a time-varying FIR filter, but all of the variation
can be combined
into a single, time-varying multiplicative factor which is applied after the
filtering.
In a particular embodiment, the steps of multiplication and convolution that
perform
the frequency shift and filtc;ring have been combined to produce the composite
filter. To this
end, the process performs a~ first step in the selection of a specific channel
that translates (in
frequency) the real-valued :received signal samples, r~nJ, to baseband by
multiplication with
the appropriate complex exponential:
x[n] = r[n]e'2"f~Ts = r[n]{cos(2nf~nTs) - jsin(2~f~nTs)} (1)
where f is the Garner frequency before translation to baseband and Ts is the
sample interval.
Next, the result is filtered v~rith an order-M FIR filter h~mJ:
M M
y[n] = E h[m]x[n - m] = E h[m]r[n - m]e -~2"fc(n-m)Ts (2)
m=0 m~
At this point, the two steps of frequency translation and filtering can be
combined:
M M
y[n] = eJ2afcnTs ~ h[m]r[n - m]e ~2~~'"'S = el2afcnTs ~: c[m]r[n - m] (3)
m~ m~
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where c[mJ = h[m]e ~Z~f~Ts me the composite filter coefficients. This process
is understood
to reduce the number of computations, as well as eliminate the need to compute
the unfiltered
baseband signal, x[n], whic:h includes the burden of writing the intermediate
results to
memory only to recall them in the next step. Also, while many techniques are
available to
design real-valued FIR filters to meet desired specifications with minimum
order, the use of
complex-valued filter coefficients for h[m] is understood to impose no
additional
computational cost. Accoralingly, the process can take advantage of recent
advances in the
design of complex-coefficient FIR filters to reduce the required filter order
M of the original
LPF, relative to a real-valued h~mJ, without increasing the required
computation load for the
final composite filter.
This above described process is only one process capable of downconverting the
incoming signal, and other techniques that, depending upon the application,
may be less
complicated to set-up and naay employ less memory to store filter
coefficients, can be
I S employed. The above described process also requires knowledge of the
desired carrier
frequency to compute the filter coefficients, c~mJ, and to recompute the
coefficients when a
change in the frequency to which the filter is tuned (or else precompute and
store separate
filters for any desired frequencies) is desired. However, as each set of
filter coefficients may
be employed many thousands or millions of times, the cost of precomputing or
recomputing
can yield improved efficiency. This technique is similar to the idea of using
an analytic filter
to select only the positive fi-equency components of the real-valued signal
for the passband of
interest and decimating, bul: the combination of translation and lowpass
filtering in Figure 5
allows the filter to be quickly redesigned to select a different f . Moreover,
the overhead
incurred by storing these coefficients is minimal given that processing occurs
on a general
purpose processing platforn:i, and that data structures are available as
options/means for
storing data. Other filter deaigns caii include employ randomized algorithms
as an efficient
way to prevent aliasing duriing the decimation process. Additionally, it will
be appaxent from
the above description, that the wideband processing systems dscribed herein
can be employed
to process multiple channels within the wideband signal, wherein each channel
can be
processed by a separated process or module, or by a single process that seeks
transmissions
that are 8. Moreover, the system can be employed to perform channel selection
according to
any method including FDMA, TDMA, CDM:A or spread spectrum.
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Turning again to Figure 4, in a complex FM signal, the desired information
(the voice,
in the case of a cellular telcphone) is carried by the instantaneous
frequency, which is the
time derivative of the phase of the complex signal. This signal is therefore
demodulated
S using a simple quadrature demodulation algorithm that approximates the
derivative of the
signal phase by the phase difference between successive samples, appropriately
scaled. This
quadrature demodulation is carried out by stage 84 of the process 80.
The two final steps of processing are implemented as finite impulse response
(FIR)
filters. The first can be simply a lowpass decimating filter that removes high
frequency
components that would cause aliasi:ng when the sample rate is reduced to the
audio rate, RA,
typically 8K samples/sec. ':Chis is carned out in stage 88. The final step,
carried out in stage
90, is an optional bandpass filter that removes out-of band noise from the
voice signal.
To facilitate the development of signal processing programs, such as the above
described cellular receiver process 80, the system optionally can include a
programming
environment that supports the development of application programs that process
the digitized
IF samples to provide, for example, portable, adaptive signal processing
systems with real-
time constraints. The programming environment can include a library of
routines, or a class
or set of classes, written in a computer programming language, such as the C,
C++ or Java
language. Optionally, the programming environment can include an object-
oriented
application framework that consists of a library of classes that are designed
to be extended
and subclassed by the appliication programmer, packaged along with several
illustrative
sample applications that use those classes and which are designed to be
modified by the
application programmer. The sample applications generally constitute a system
that is useful
in its own right. Frameworks can provide functionality and "wired-in"
interconnections
between the object classes that provide an infrastructure for the application
developer. The
inter-connections can provide the architectural model and design for
developers and free
them to apply their effort on the problem domain. By providing an
infrastructure, the
framework can decrease the amount of standard code that the developer has to
program, test,
and debug. In general, the basic concept of a framework is well known to one
skilled in the
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art. Some example frameworks include X Toollcit, Motif Toolkit, Smalltalk
Model-View-
Controller GUI, and MacA.pp.
Optionally, the programming environment can support adaptive signal
processing,
including adaptive progranuning for achieving adaptation to environment
factors, such as for
example, an application program that implements a modem capable of equalizing
for the
channel. To this end, the system can provide algorithms to detect environment
changes, such
as channel estimation algorithms, and a mechanism for specifying system
modifications
based on the detected changes. Similarly, the programming environment can
support
adaption to the user to allow for user requirements that may change
dynamically and
necessitate changes in the ;system, or in operating parameters of the system.
For example, the
programming environment can pro~ride for user changes such as a user changing
a parameter
representative of the station on a radio. Similarly, the programming
environment can allow
for activating a control representative of a push button for selecting between
AM/FM
broadcasts. The change between A.M and FM broadcasts requires a change in
algorithms
employed by the appiicatio~n program to demodulate the digitized IF data. The
programming
environment can further include routines or classes for allowing fimctional
adaptation.
Functional adaption provides for signal processing techniques, such as a phase-
locked loop,
that are inherently adaptive;. These techniques typically adapt to the signal,
and may modify
system parameters or functionality t;o meet specified requirements. For
example, a receiver
attempting to lock on to the; start frequency of a hopping sequence can adapt
the system to
examine different frequencies until a start code is found. This type of
adaptation can be
driven by a specified constraint, without the need for an external change, or
in cooperation
with an external change. Additionally, the system can provide for adaption in
response to the
availability of resources. F'or example, the application program can detect if
there are spare
CPU cycles available. If C'PU processing power is determined to be available
under the
current system conditions, then running a more computationally intensive
channel estimation
algorithm can be employed. to seek 'better overall system performance.
Conversely, if the
resources suddenly become; scarce due to a burst of activity by other
processes, the system
can adapt, perhaps by running less demanding algorithms and sacrificing some
robustness or
accuracy. This form of adaptability also enables applications to transparently
improve
performance as faster procE;ssors become available.
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The system described above, allows for the transmission and reception of
cellular
communications using the US cellular band. However, an advantage of performing
processing in software is treat the transmission process can be separated from
the reception
process, and therefore, the systems and methods described herein allow for
virtual
communication patch systems, wherein the same device can receive and decode
transmission
under one protocol, and broadcast transmission under another protocol. This
allows for
forming a patch between diisparate wireless systems. In another example, a
radio
transmission broadcast using frequency modulation, could be received and
decoded, and then
encoded using amplitude modulation and rebroadcast, thereby allowing AM
receivers to
receive the same data as FDrI receivers.
In another embodiment, the systems described herein can include network
interface
cards (rIICS) that implement signal processing in software, thereby providing
a wireless
network interface functionality that can be dynamically modified. The software
wireless
network interface can be compatible with a commercial frequency hopping radio
operating in
the 2.4 GHz ISM band employing FSK modulation. Parameters such as the FSK
frequency
deviation and the spacing o~f the hopping channels can be dynamically modified
in software,
with the constraints imposed by the hardware being the width of the IF band
and the RF band
to which the signal is converted. The ability to dynamically modify the
channel width,
channel spacing and the hopping sequence allows the system to adapt to its
environment and
provide better noise rejection and immunity from hostile jamming attacks.
The software network interface architecture can be a refinement of the OSI
layering
model, which subdivides the existing Link and Physical layers as shown in
Figure 6. As
shown, the software NIC can connect to a hardware device that implements the
processing of
layer 102, the frequency conversion, and layer 104, conversion between the
analog domain
and the digital domain. Once data is in the digital domain, the software IVIC
can implement
those other layers that are to be performed for network data transfers. As
shown in Figure 6,
these layers include the multiple access layer 108, the modulation layer 110
and the line
coding layer 112. The multiple access layer 108 can be implemented according
to perform
suitable protocol that sharers the data transfer medium. In layer 110, the
modulation of the
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selected IF data can occur to collect the data transmitted over the wireless
channel. In Iayer
112, the data can be codedl as required for transmission. The data link layers
116 and 114 can
also be implemented by any suitable technique that can perform the data
encapsulation and
decapsulation and the transmit/receive media-access management.
The sequence of processing modules for the transmission application is shown
in
Figure 7. The system interfaces with the host at the IP layer, through a
device driver 126 that
can appear to the kernel asp just another network device driver. However,
instead of handing
the packets off to a hardw;rre device, this driver hands them up to user space
122, where the
software radio processing is performed. The first level of processing is the
network framing.
For this example, the packets can be framed and byte stuffed to carry the
data. A length
code, indicating the total length of the packet including the stuffed values,
can be inserted
after the start code. The next module takes the sequence of bits output by the
network
framing layer and performs byte framing, inserting start, stop and parity
bits.
The conversion of each bit into a discrete signal is performed by the FSK
module 132
and the frequency hopping modulf; 134 then assigns this waveform to the
appropriate
frequency. All of the possible transmission waveforms can be known a priori.
There are two
possible waveforms, corresponding to 1 or 0, for each hop frequency. All of
these
waveforms can be pre-computed and stored at startup, significantly reducing
the computation
required to produce the transmitted. wavefonm. On a 180 MHz Pentium Pro 2.2
microseconds
were required for producing the IF waveform corresponding to a single bit.
This corresponds
to a possible transmit data rate of ~ 450 kbps.
To generate continuous phase waveforms the pre-computed waveforms are actually
oversampled, and a sub-sampled set, corresponding to the output sampling rate,
are copies
into the output buffer. The oversampling allows for indexing into the buffer
to match the
phase, and the pattern can be treated as a circular buffer, allowing the
generation of
waveforms for any bit period. After copying the samples to the output buffer,
the phase value
is updated and used as the index for the waveform corresponding to the next
bit. In a similar
manner, the system can maintain continuous phase between hops, even when the
hop occurs
in the middle of the bit.
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Reception is essentially the reverse of the transmission system shown in
Figure 7.
The receiver detects the presence of a valid transmission and synchronizes to
it, as well as
perforrris the inverse function of each of the transmission layers. Again,
combining the
parameters of the frequency hopping and the FSK demodulation, the system can
constrain the
receiver to look for one of the two valid waveforms at a given hop frequency.
Separate
functions were implemented to track the hopping sequences, and to lock onto
and demodulate
the bits. These bits are de-framed, and then the IP packets is extracted. The
driver then
hands the packet off to the host IP Layer for processing.
Those skilled in thE; art will know or be able to ascertain using no more than
routine
experimentation, many equivalents to the embodiments and practices described
herein. For
example, it will be understood that the systems and methods described herein
can be
employed for developing baseband communication systems, as well as system for
developing
baseband applications. It will also be understood that the systems described
herein provide
advantages over the prior art including the ability to select one or more
channels from a
wideband IF signal, and selectively process the channel.
Accordingly, it will be understood that the invention is not to be limited to
the
embodiments disclosed herein, but is to be understood from the following
claims, which are
to be interpreted as broadh~ as allowed under the law.
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