U.S. patent application number 09/919120 was filed with the patent office on 2002-01-03 for hybrid spread spectrum method and system for wirelessly transmitting and receiving wideband digital data.
This patent application is currently assigned to Interair Wireless, Inc.. Invention is credited to Chauncey, David C., Doane, James R., Hoen, Christopher P..
Application Number | 20020001337 09/919120 |
Document ID | / |
Family ID | 22472009 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020001337 |
Kind Code |
A1 |
Chauncey, David C. ; et
al. |
January 3, 2002 |
Hybrid spread spectrum method and system for wirelessly
transmitting and receiving wideband digital data
Abstract
A "software" radio in the form of a system is completely
configurable and controllable in real-time by software and has a
coordination capability to enable scaling to network aggregate data
rates in the 10s of megabits per second per base station with no
interference among the multiple radios. Base stations can, in turn,
be time and frequency coordinated. Scalability is provided by the
addition of substantially identical relay radios at each base
station. A hybrid spread spectrum method and system of the
invention include a protocol which facilitates coordinated
frequency hopping. The system does not dwell more than a few
milliseconds at any frequency center to achieve high scalability of
the system in, for example, a metropolitan area. A single coaxial
cable feeds control signals, electrical power signals and RF
signals to a microwave antenna to reduce system hardware and
installation costs.
Inventors: |
Chauncey, David C.; (Alden,
NY) ; Doane, James R.; (Grand Island, NY) ;
Hoen, Christopher P.; (Hamburg, NY) |
Correspondence
Address: |
David R. Syrowik
Brooks & Kushman P.C.
22nd Floor
1000 Town Center
Southfield
MI
48075-1351
US
|
Assignee: |
Interair Wireless, Inc.
485 Cayuga Road
Buffalo
NY
14225
|
Family ID: |
22472009 |
Appl. No.: |
09/919120 |
Filed: |
July 31, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09919120 |
Jul 31, 2001 |
|
|
|
09136247 |
Aug 19, 1998 |
|
|
|
Current U.S.
Class: |
375/132 |
Current CPC
Class: |
H04L 5/003 20130101;
H04K 1/02 20130101; H04K 3/25 20130101 |
Class at
Publication: |
375/132 |
International
Class: |
H04K 001/00 |
Claims
What is claimed is:
1. A hybrid spread spectrum method for wirelessly transmitting
wideband digital, the method comprising the steps of: formatting
the digital data based on a predetermined protocol; dynamically
allocating bandwidth to the formatted digital data based on a
predetermined set of conditions; coding the formatted digital data
with a signal to obtain encoded digital data; transmitting the
encoded digital data at a plurality of different frequency bands,
each of which has a center frequency so that each bit of digital
data is sent at each of the different frequency bands substantially
simultaneously; and dynamically changing the center frequencies in
real-time in less than 100 milliseconds.
2. The method of claim 1 wherein the step of dynamically changing
is performed in less than 10 milliseconds.
3. A hybrid spread spectrum method for receiving wideband digital
data by reversing the steps of the method of claim 1.
4. A hybrid spread spectrum system for wirelessly transmitting
wideband digital data, the system comprising: means for formatting
the digital data based on a predetermined protocol to obtain
formatted digital data; means for dynamically allocating bandwidth
to the formatted digital data based on a predetermined set of
conditions; means for coding the formatted digital data with a
signal to obtain encoded digital data; means for transmitting the
encoded digital data at a plurality of different frequence bands,
each of which has a center frequency so that each bit of digital
data is sent at each of the different frequencies substantially
simultaneously; and means for dynamically changing the center
frequencies in real-time in less than 100 milliseconds.
5. The system as claimed in claim 4 wherein the means for
dynamically changing changes the center frequencies in less than 10
milliseconds.
6. A hybrid spread spectrum system for wirelessly receiving encoded
formatted wideband digital data, the system comprising: means for
decoding the encoded formatted digital data with a signal to obtain
decoded formatted digital data; means for deformatting the decoded
formatted digital data based on a predetermined protocol to obtain
the digital data; means for dynamically deallocating bandwidth to
the encoded formatted digital data based on a predetermined set of
conditions; means for receiving the wideband encoded formatted
digital data at a plurality of different frequency bands, each of
which has a center frequency so that each bit of digital data is
received at several different frequency bands substantially
simultaneously; and means for dynamically changing the center
frequencies in real-time in less than 100 milliseconds.
7. The system as claimed in claim 6 wherein the means for
dynamically changing changes the center frequencies in less than 10
milliseconds.
8. In a hybrid spread spectrum system including an indoor unit and
an outdoor unit for wirelessly transmitting and receiving wideband
digital data, a method is provided for transmitting power, control
and RF signals between the indoor and outdoor units, the method
comprising the steps of: coupling a single coaxial cable between
the indoor unit and the outdoor unit; and transmitting the control,
power and RF signals between the indoor unit and the outdoor unit
over the single coaxial cable.
Description
TECHNICAL FIELD
[0001] This invention relates to hybrid spread spectrum methods and
systems for wirelessly transmitting and receiving wideband digital
data and, in particular, to spread spectrum methods and systems for
wirelessly transmitting and receiving wideband digital data
utilizing direct sequence and frequency hopping spectrum
techniques.
BACKGROUND ART
[0002] Most interference, deliberate or accidental, affects
communication because the information transmitted is condensed to a
relatively small range of frequencies. An interference source
active at the same frequency would produce signals that would mix
with the actual communication channel to create errors. If,
however, the information bearing signal is dispersed over a wider
range of frequencies, the noise impulses can interference affect
only a portion of the total information channel and can be
filtered.
[0003] Spread spectrum technology increases the channel bandwidth
of the signal to make it less vulnerable to interference. It refers
to the transmission of a signal using a much wider bandwidth than
would normally be required or to the use of narrow signals that are
frequency-hopped through the various frequency segments available
to the transponder. This approach is called spread spectrum
multiple access (SSMA) or code-division multiple access (CDMA).
[0004] Spread spectrum technology was first adopted for military
communication to prevent deliberate jamming or interference
resulting from battle conditions. CDMA operates in three modes:
direct sequence, frequency hopping, and time hopping.
[0005] For commercial applications, spread spectrum technology
permits the use of small antennas (1.2 to 1.8 m in diameter). FCC
regulations governing interference are related to power per unit
bandwidth (power density). Either increasing the antenna size or
the signal bandwidth would reduce the power density to acceptable
levels. Rather than use a large antenna (which increases costs by a
factor proportional to at least the square of the diameter), signal
bandwidth is increased to reduce power density and, thus,
interference.
[0006] With direct sequence spectrum spreading, transmitted
information is mixed with a coded signal that, to an outside
listener, sounds like noise. In this alternative to frequency
hopping, each bit of data is sent at several different frequencies
simultaneously, with both the transmitter and receiver
synchronized, of course, to the same coded sequence.
[0007] More recently, further advances in chip technology have
produced digital signal processors that can crunch data at high
speed, use little power and are relatively inexpensive. The
improved hardware allows more sophisticated spread-spectrum
techniques, including hybrid ones that leverage the best features
of frequency hopping and direct sequence, as well as other ways to
code data. The new methods are particularly resistant to jamming,
noise and multipath--a frequency-dependent effect in which a signal
reflects off buildings, the earth and different atmospheric layers,
introducing delays in the transmission that can confuse the
receiver.
[0008] The U.S. patent to Ben-Efraim (U.S. Pat. No. 5,630,212)
provides for a microwave system with software configuration of
operating parameters. Substantially all parameters in a radio are
available and configurable using a network management system.
[0009] The U.S. patent to Monahan-Mitchell et al. (U.S. Pat. No.
5,381,346) provides for a radio transceiver with a microcomputer
which controls hardware dependent components. Software control of
the microprocessor allows interaction with channel assignment,
channel maintenance and other signaling.
[0010] The U.S. patent to Delprat et al. (U.S. Pat. No. 5,583,870)
provides for a cellular radio base station with software control of
transceiver means.
[0011] The U.S. patent to Sandvos et al. (U.S. Pat. No. 5,490,275)
provides for a virtual radio interface and radio operating system
for a communication device. A radio operating system is described
which controls functioning of a radio through a MC68HC11
microcontroller.
[0012] The U.S. patent to Dunn et al. (U.S. Pat. No. 5,625,877)
provides for a wireless variable bandwidth air-link system. An
apparatus which dynamically aggregates radio channels comprises a
transceiver, microprocessor, and software.
[0013] The U.S. patent to Crosby (U.S. Pat. No. 5,694,138) provides
for a single coaxial cable which carries downlink signals from a
satellite antenna and power signals to operate the antenna and an
attached heating element.
[0014] The U.S. patent to Snow (U.S. Pat. No. 4,115,778) provides
for an electronic solid state FM dipole antenna. An amplified RF
signal and DC power signal share a coaxial cable.
[0015] The U.S. patent to Mead (U.S. Pat. No. 3,843,922) provides
for a television preamplifier power source. The preamplifier is
attached to an antenna mast and power is supplied through a coaxial
cable which also transmits RF signals.
[0016] The U.S. patent to Dumbauld et al. (U.S. Pat. No. 4,823,386)
provides for a cable TV distribution system which uses a single
coaxial cable to power subscriber frequency converters and carry
video and control signals.
[0017] Other relevant U.S. patents include the U.S. Pat. No.
5,459,474 to Mattioli et al.; U.S. Pat. No. 5,548,813 to Charas et
al.; U.S. Pat. No. 5,502,715 to Penny; and U.S. Pat. No. 5,612,652
to Crosby.
[0018] The non-patent literature entitled "Welcome to WIMAN",
describes a wireless MAN that allows an ISP to offer wireless
Internet access.
[0019] The non-patent literature entitled "Base Unit Systems",
lists Mikro-Tik wireless ISP routers and systems.
[0020] The non-patent literature entitled "Microcomm Digital
Communication Products", describes spread spectrum digital radio
offerings and provides for an indoor/outdoor antenna unit to reduce
cable loss. This literature appears on a web site.
SUMMARY OF THE INVENTION
[0021] An object of the present invention is to provide a hybrid
spread spectrum method and system for wirelessly transmitting and
receiving wideband digital data wherein channels can be quickly
changed in a coordinated fashion so that multiple systems can be
incorporated into networks without the fear of message collision
between the different systems.
[0022] Another object of the present invention is to provide a
hybrid spread spectrum method and system for wirelessly
transmitting and receiving wideband digital data wherein the system
includes an indoor unit and an outdoor unit with an antenna and
wherein control, power and radio frequency signals are combined in
a single cable run between the indoor and outdoor units, thereby
eliminating the need for wide temperature range circuits in the
outdoor unit.
[0023] In carrying out the above objects and other objects of the
present invention, a hybrid spread spectrum method for wirelessly
transmitting wideband digital data is provided. The method includes
the steps of formatting the digital data based on a predetermined
protocol and dynamically allocating bandwidth to the formatted
digital data based on a predetermined set of conditions. The method
also includes the steps of coding the formatted digital data with a
signal to obtain encoded digital data and transmitting the encoded
digital data at a plurality of different frequency bands, each of
which has a center frequency so that each bit of digital data is
sent at each of the different frequency bands substantially
simultaneously. The method further includes the step of dynamically
changing the center frequencies in real-time in less than 100
milliseconds.
[0024] Preferably, a hybrid spread spectrum method is provided for
receiving wideband digital data by reversing the steps of the above
method.
[0025] Further in carrying out the above objects and other objects
of the present invention, a hybrid spread spectrum system for
wirelessly transmitting wideband digital data is provided. The
system includes means for formatting the digital data based on a
predetermined protocol to obtain formatted digital data, means for
dynamically allocating bandwidth to the formatted digital data
based on a predetermined set of conditions, means for coding the
formatted digital data with a signal to obtain encoded digital
data, means for transmitting the encoded digital data at a
plurality of different frequence bands, each of which has a center
frequency so that each bit of digital data is sent at each of the
different frequencies substantially simultaneously, and means for
dynamically changing the center frequencies in real-time in less
than 100 milliseconds.
[0026] A hybrid spread spectrum system for wirelessly receiving
wideband encoded and formatted digital data is also provided to
carry out the above objects and other objects of the invention. The
system includes means for decoding the encoded formatted digital
data with a signal to obtain decoded formatted digital data, means
for deformatting the decoded formatted digital data based on a
predetermined protocol to obtain the digital data, means for
dynamically deallocating bandwidth to the encoded formatted digital
data based on a predetermined set of conditions, means for
receiving the wideband encoded, formatted digital data at a
plurality of different frequency bands, each of which has a center
frequency so that each bit of digital data is received at each of
the different frequency bands substantially simultaneously, and
means for dynamically changing the center frequencies in real-time
in less than 100 milliseconds.
[0027] Further in carrying out the above objects and other objects
of the present invention, in a hybrid spread spectrum system
including an indoor unit and an outdoor unit for wirelessly
transmitting and receiving wideband digital data, a method is
provided for transmitting power, control and RF signals between the
indoor and outdoor units. The method includes the steps of coupling
a single coaxial cable between the indoor unit and the outdoor
unit, and transmitting the control, power and RF signals between
the indoor unit and the outdoor unit over the single coaxial
cable.
[0028] The above objects and other objects, features, and
advantages of the present invention are readily apparent from the
following detailed description of the best mode for carrying out
the invention when taken in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a schematic block diagram of a hybrid spread
spectrum system for wirelessly transmitting and receiving wideband
digital data and constructed in accordance with the present
invention;
[0030] FIG. 2 is a block diagram illustrating epochs, frames and
slots of the protocol of the present invention;
[0031] FIG. 3 is a block diagram illustrating the components of a
time interval slot used to transmit/receive a packet of digital
data;
[0032] FIG. 4 is a schematic block diagram of the direct sequence
spread spectrum processor and encode and decode circuits of FIG.
1;
[0033] FIG. 5 is a schematic block diagram of the RF module of FIG.
1;
[0034] FIG. 6 is a schematic block diagram of the outdoor unit of
FIG. 4;
[0035] FIG. 7 is a schematic diagram illustrating a configuration
of subscriber sites, a central relay base station with three relay
radio units, inband backhaul and an ISP site;
[0036] FIG. 8 is a schematic diagram of a simple network including
units at a subscriber site, units at a central base station and
units at an ISP;
[0037] FIG. 9 is a schematic diagram of a simple network with a
single subscriber wherein all time slots are allocated to the
single subscriber;
[0038] FIG. 10 is a schematic diagram of a simple network which can
support several users from each of several subscribers on a single
physical channel;
[0039] FIG. 11 is a schematic diagram of a more complicated network
with three additional radios (i.e., systems) of the present
invention at the base station and at the ISP;
[0040] FIG. 12 is a schematic diagram of a network wherein backhaul
is accomplished by N T1 lines;
[0041] FIG. 13 is a schematic diagram of a base station which
supports 12 sectors each of which has two radios or systems of the
present invention;
[0042] FIG. 14 is a schematic diagram illustrating a coordinated
network of cellular base stations;
[0043] FIG. 15 is a schematic diagram of a cellular topology
wherein a subscriber may use a "surrounding" base station; and
[0044] FIG. 16 is a graph of cost versus system capacity which
illustrates four distinct phases of capacity growth based on one
central relay base station.
BEST MODE FOR CARRYING OUT THE INVENTION
[0045] Referring now to the drawing Figures, there is illustrated
in FIG. 1 a hybrid spread spectrum system or "software radio",
generally indicated at 10, for wirelessly transmitting and
receiving wideband digital data constructed in accordance with the
present invention. The method and system 10 of the present
invention are based on a frequency-tunable, direct sequence spread
spectrum (DSSS) waveform. The method and system 10 use this
frequency tunability for interference rejection. The direct
sequence spread spectrum rejects multipath and some inband
interference and encodes the wideband digital data.
[0046] The system 10 is a "software radio" in that the system 10 is
completely configurable and controllable in real-time by software
via a processor 16. Specifically, the bandwidth, modulation and
frequency tuning and data bit rate are under software control, and
may be changed in real-time.
[0047] Each system 10 transmits in the unlicensed Industrial,
Scientific and Medical (ISM) radio frequency band from 2.4000 to
2.4835 GHz and 5.725 to 5.850 GHz under FCC Regulation Part 15.247.
The method and system 10 are based on a frequency agile direct
sequence spread spectrum waveform. The direct sequence spread
spectrum rejects multipath and some inband interference. The
frequency agility capability is an excellent interference rejection
technique which acts to spread transmission opportunities over the
entire ISM 2.4 GHz band. The system 10 does not dwell more than a
few milliseconds on any frequency center. And, again, the direct
sequence spectrum spreading is sufficient to enable coordinated
frequency hopping under FCC regulations. This coordinated hopping
is necessary to achieve high scalability of system capacity in a
metropolitan area, as described in greater detail hereinbelow.
[0048] Bandwidth
[0049] The system 10 preferably has three data bandwidths
available. Obviously, other bandwidths could be used. These are
expressable as chip rates developed by a DSSS digital signal
processor (DSP):
[0050] Wide band 45 MHZ/4=11.25 Mchips/second
[0051] Medium band 45 MHZ/8=5.625 Mchips/second
[0052] Narrow band 45 MHZ/10=4.5 Mchips/second
[0053] Frequency Tuning
[0054] The system 10 has frequency centers assigned for the above
bandwidths:
1 Wide band 2419.8750, 2431.1250, 2442.3750, 2453.6250 MHZ Medium
band 2405.8125, 2411.4375, 2417.0625, 2422.6875, 2428.3125,
2433.9375, 2439.5625, 2445.1875, 2450.8125, 2456.4375, 2462.0625,
2467.6875 MHZ Narrow band 2404.1250, 2408.6250, 2464.8750,
2469.3750 MHZ
[0055] Modulation, Data Rate
[0056] The system data rate is determined by the selection of 11
chips per symbol for data symbols. This gives the system a
processing gain greater than the 10 dB required by FCC Part 15
rules. DQPSK modulation is used to code each symbol into two bits
as described herein below.
[0057] Therefore, the data rates available to the system 10 are
2.045 Mbps for Wideband, 1.023 Mbps for the Medium bandwidth and
818 Kbps for Narrowband.
[0058] Multiple access is not based on CDMA, rather it is achieved
by time division and is made efficient by the unique time/range
tracking processing and dynamic bandwidth allocation as described
hereinbelow.
[0059] Referring again to FIG. 1, the system 10 includes an indoor
unit (IDU), generally indicated at 12, and a remote outdoor unit
(ODU) with an antenna 76, generally indicated at 14. The IDU 12 is,
in general, a computation capable radio, and the ruggedized ODU 14
is the final stage of RF power amplification as well as the first
stage preamplifier in an RF receiver subsystem.
[0060] The IDU 12 includes a flash RAM 11 and a DRAM 13 which
support a processor 16 which is a high speed communications engine
capable of running standard TCP/IP and Ethernet protocol stacks as
well as processing its node's role in the protocol described below.
The processor 16 may be an Intel 960, 32 bit processor. Processing
also includes precision timing, error control, and radio
configuration/control. The processor 16 communicates with the other
circuits of the IDU 12 by means of a system bus 17.
[0061] The IDU 12 also includes two standard interfaces: a 10base-T
10 MHZ 802.3 Ethernet interface 18 and RS-232C interface 20. A fast
(100Base-T) Ethernet interface may also be included.
[0062] In general, the processor 16 deconstructs Ethernet packets,
reassembles and delivers the enclosed TCP/IP packets over the
protocol and delivers TCP/IP packets to an ISP network.
[0063] The processor 16, together with a precision clock 22,
establishes and maintains time synchronization within microseconds.
This precision enables coordinated use of multiple radios or
systems 10 to obtain scalable capacity with no interference with
any other equipment in the network.
[0064] The IDU 12 also includes error correction encoding and
decoding processing at blocks 24 and 26, respectively, to detect
and correct data errors, both random noiselike and bursty
interference. Most important, this coding guarantees that if a data
block is declared "correct", it is, in fact, error free.
[0065] The IDU 12 further includes a direct sequence spread
spectrum modulator and demodulator as indicated at block 28 and
described in detail hereinbelow.
[0066] The IDU 12 still further includes an RF module coupled to
the block 28 and having a transmitter circuit, a receiver circuit
and a digital frequency synthesizer, all indicated at block 30 as
described in detail hereinbelow.
[0067] In general, the protocol of the method and system of the
present invention is optimized for minimum latency and scalable
bandwidth sharing in a connectionless network. This protocol is a
mix of contention opportunity slots, wideband data transfer and
control slots and supports dynamic bandwidth allocation in a
multipoint network. The protocol enables dynamic data bandwidth
allocation by continuously measuring status of the multipoint
subscriber LAN input queues, and traffic from the Internet destined
for the network. Based on the nature of the packets in these
queues, an optimum trade off of latency for payload rate is made
and transmit slots are reallocated essentially continuously.
[0068] Strict time synchronization facilitated by the protocol
enables reservation of certain slots for permanent virtual channels
if required or for isosynchronous applications such as voice and
video-conferencing. These virtual channels can be quickly released
for general reuse when the application is completed.
[0069] The computation capability of the hardware of FIG. 1 enables
the implementation of the protocol. The protocol is optimized for
minimum latency and scalable bandwidth sharing in a connectionless
network. FIG. 2 illustrates three types of time intervals, Epochs,
Frames and Slots, in the protocol.
[0070] In FIG. 2, Epochs provide structure for bandwidth
allocations and represent the highest level of time interval. The
Epoch structure is used to dynamically allocate bandwidth. Over one
Epoch, status statistics are measured and user requests are
gathered. The following Epoch is used to process these real-time
parameters using the subscriber class of service as a guideline to
optimally allocate the available bandwidth among those subscribers
currently "on air". The next Epoch is used to communicate the
allocation to the subscribers and relay units, and finally, in the
next Epoch, the allocation is used. The duration of these Epochs
are on the order of hundreds of milliseconds, so that bandwidth is
dynamically reallocated in real-time over ones of seconds.
[0071] The allocation itself is represented by the time interval
structure called Frames. All frames in an Epoch have the same
format. Each Frame in an Epoch is identical, and all relay or
subscriber units must "hear" the Frame structure as it is
communicated to each Epoch or the software will preclude it from
transmitting in the corresponding Epoch. Naturally, more than one
transmission of this Frame structure representation is made to each
Epoch to minimize the chances of it being missed. Only one
reception of these structure representations is required of each
Epoch to enable transmission. The Frame is an assigned mix of
"slots": contention slots, wideband data transfer slots, and
control slots. Assignments are made for each physical channel.
[0072] In the lower part of FIG. 2, columns represent time slots,
frame descriptor blocks, pseudo random status messages, ACK/NAK/ELN
and data-payload. Rows represent physical channels, one physical
channel per relay radio. The time slots are on the order of ones of
milliseconds and represent the point-to-point transfer of packets
of data. Two kinds of slots alternate in time in the Frame: relays
slots and subscriber slots. Relay units at a base station tower
transmit in relay slots, subscriber units and ISP units transmit in
subscriber slots. In the case of out-of-band backhaul, all ISP to
relay communication is continuous full duplex.
[0073] FIG. 3 illustrates the components of the time slot interval
which is used to transmit/receive a packet of data. Each packet
consists of one or more (typical max is four) blocks of data:
2 Tuning Time Time to set frequency, spread spectrum codes, ECC
parameters, etc. Typically 100 uS. Guard Allocation of time to
allow for synchronization errors. This allocation is approximately
200 uS. Acquisition Symbol 64 chip Gold Code symbol used each data
block in the packet. At 11.25 Mchips/second this takes 5.7 uS.
Transmitted with DBPSK modulation. Header Bytes 16 to 235 bytes of
header ID, and data transmitted and Data per data block, wherein B
means blocks per slot. ECC Bytes Error correction and coded
redundant bytes (0 to 20 bytes per block) for the detection and
correction of byte errors in receive. Range Delay Allocation of 150
uS to allow for the speed of light over 25 miles.
[0074] As a result of the rule for the relay unit not to transmit
during subscriber slots, no unit transmits in more than half of the
time slots . The worst case transmit duty cycle is at a relay unit
(subscribers don't necessarily transmit in all subscriber
slots).
[0075] Referring again to FIG. 1, once the data processor 16 has
formatted the data into the above-described TDMA protocol, it is
sent to the spread spectrum processor and modulator/demodulator
module 28 after the encoding step described immediately below. In
general, the spread spectrum processing is based on the Stanford
Telecom STEL-2000A ASIC.
[0076] Referring now to FIG. 4, initially, Error Correction Coding
(ECC) is applied to the transmit data at encode block 24 using the
Reed-Solomon burst error correction algorithm. It is then
differentially encoded at block 32 and spread at logic gates 34
with the Pseudo Noise (PN) codes (64 chips for acquisition symbols,
11 chips for data) generated at block 36 to create the I and Q
signals to be applied to a transmit or vector modulator 38 as shown
in FIG. 5. These I and Q signals represent a Differential
Quadrature Phase Shift Key (DQPSK) signal.
[0077] On the receive side, the 35 MHZ received IF is first
demodulated at block 40 into the baseband I and Q signals by a
quadrature demodulator with a 70 MHZ Local Oscillator (LO) 42. The
I and Q signals are each digitized by a high speed A/D converter
(not shown) and applied to a digital tap delay line matched filter
44. This filter 44 correlates the received signal with the
appropriate PN code from block 46 and de-spreads the signal back
into differential dibit symbols. Subsequent digital circuitry 48
recovers the bit clock and converts symbols into data bits. These
bits are processed by the Reed-Solomon ECC circuitry 26 which
determines the syndrome information to both correct and detect bit
errors.
[0078] The next stage in the IDU 12 is the RF module 30. Still part
of the Indoor Unit (IDU) 12, in general, this module 30 contains a
receiver, a transmitter and digitally synthesized LOs. It is
designed for half duplex operation.
[0079] Referring now to FIG. 5, the transmitter portion of the
module 30 operates by modulating at the block 38 a 915 MHZ signal
with the I and Q signals from the spread spectrum processor and
upconverting to 2.4 GHz at a mixer 53. The 915 MHZ signal is
synthesized by mixing a 1025 MHZ signal of a LO 52 and a 110 MHZ
signal of a LO 50 together at a mixer 54. This is done so there is
no 915 MHZ LO running when in the receive mode that could interfere
or quiet the receiver portion of the module 30.
[0080] The receiver portion of the module 30 down converts a
received 2.4 GHz signal to 915 MHZ at a mixer 56, filters at block
58, then down converts to 35 MHZ by mixing with the 880 MHZ signal
from the LO at block 60. The IF stage is dual bandwidth, as
indicated at blocks 62 and 64, 7 MHZ wide for the 5.625 and 4.5
Mchip/second channels and 15 MHZ wide for the 11.25 Mchip/second
channels. The final stages of the IF amplifier is a log amp 66 to
yield high dynamic range.
[0081] The up and down conversion between 915 and 2.4 GHz is made
with a digital synthesizer 1500 MHZ LO 68. This LO 68 can tune
across the ISM band in 100s of microseconds, giving the system 10
its frequency agility.
[0082] The RF transmit and receive signals are coupled together
with a switch 70 to yield the half duplex operation. The RF signal
is combined with a DC voltage and a control signal which signals
are sent over a coaxial cable 74 to power and control the outdoor
unit 14, as indicated at block 72.
[0083] Referring now to FIG. 6, the ODU 14 comprises a
transmit/receive (TIR) module. The ODU 16 has two benefits, it
enables long range wideband communications and it enables easy
installation at all ISP, relay base station and user sites. The ODU
16 is mounted to the back of an antenna 76 (FIG. 1) and includes
the receiver front end at blocks 78, 79, 80 and 81 and the final
stage of transmit power amplification at block 82.
[0084] The ODU 14 makes long RF path lengths possible in the ISM
frequency bands by maximizing the radiated ERP and minimizing the
system noise figure. The unique design feature including the
control signals and power in the coaxial cable 74 as extracted by
block 84 also reduces the system hardware and installation
costs.
[0085] In order for the communications system 10 to achieve long
radiated path lengths, the transmit power must be maximized and the
receiver noise figure must be minimized. Since the transmit power
in the ISM bands is limited, the system noise figure must be
minimized. In addition, it is important that the transmitter output
power use a leveling loop to be as close to the maximum allowed
EiRP as possible.
[0086] The absorptive loss of the cable which runs between the
antenna 76 and the receiver front end can have a significant effect
on the transmit EiRP and the system noise figure. All cable has an
absorptive loss per unit length. This loss must be carefully
controlled to assure maximum radiated path length. Many systems
account for the cable loss by using low-loss cable as the cable
runs get long. The low-loss cable is significantly more expensive
than the standard cable 74. The ODU 14 eliminates the need for
expensive, low-loss cable by placing the transmitter and receiver
front end after/before the cable run.
[0087] The ODU 14 also allows the receiver/transmitter 30 in the
indoor unit 12 to be placed in an environmentally controlled
location. This reduces the cost of the receiver/transmitter unit by
eliminating the need for wide temperature range circuits which
include industrial temperature range components.
[0088] It is necessary to send power and control signals to the
antenna 76 along with the RF signal. The ODU design is unique
because all power and control signals, as well as the RF signal are
transmitted to the ODU 14 and antenna 76 using the single coaxial
conductor 74. It is not necessary to make a separate cable run for
the power and control signals.
[0089] The T/R module 14 is preferably permanently attached to the
antenna 76. Its output is set at the factory to the maximum
allowable EiRP.
[0090] Installation
[0091] Since system 10 does not require any licenses, nor is there
any telco involvement for laying dedicated lines or configuring
ISDN ports, it is perfect for temporary, special event, portable or
emergency installations.
[0092] FIG. 7 illustrates a configuration of: a typical
subscribers' site, generally indicated at 84, including a LAN 86
with a subscriber unit 88, and other units 90; a central relay site
or base station, generally indicated at 92, with three relay radio
units or transceivers 94 and a radio hub 96; inband backhaul 98;
and an ISP site having an ISP server 100, a network manager 102, a
router 104 and transceivers 106 connected on an ethernet 108.
[0093] The system 10, as previously mentioned, involves two units,
the indoor unit 12 and the outdoor unit 14, for each radio at each
site (subscriber, relay, and ISP):
[0094] Indoor Unit 12
[0095] Referring again to FIG. 1, the indoor unit 12 typically has
three connections:
[0096] Power:
[0097] 120V, 60 Hz AC power into a power adapter unit or converter
85.
[0098] LAN Connection:
[0099] RJ-45 10Base-T interface 18 into the indoor unit 12
[0100] CPE--serves as the IP router connection point for routing N
IP addresses over the wireless network.
[0101] Relay units in base station do not use this connection
unless out of band backhaul is used.
[0102] ISP facility--Ethernet connection of N (the number of radios
at the central relay base station to the ISP router.
[0103] Event In/Out--Timing using GPS time synch pulses (PPS) or
self-generated pulses.
[0104] RF Connection to Outdoor Unit:
[0105] Outdoor Unit 14
[0106] The outdoor unit 14 (T/R module and antenna 76) installation
is simplified by the ability to remote it from the indoor unit 12
by several hundred feet to the top of the building of its side, if
necessary. Power, signal and control all flow through the single
thin coax cable 74. As a result, no separate (or outdoor) source
for power for this unit need be found. For very remote outdoor unit
installation, thicker coax may be used.
[0107] Antenna pointing at the subscriber and ISP site is
facilitated by embedded software which helps find the optimum
pointing angle quickly. Antennas at the central base station relay
tower are omnidirectional and need not be "pointed".
[0108] Network Management/Security
[0109] Relay and subscriber units are IP addressable and SNMP
manageable. The system 10 is fully compliant with SNMPv2 and has
registered custom MIB. The SNMP operates with any SNMP workstation
such as Sun, HP, IBM or AT&T.
[0110] The windows based network manager supports the following
capabilities:
[0111] Remote configuration;
[0112] Remote monitoring of status and faults, triggering
diagnostics and alarms together with the appropriate personnel
paging;
[0113] Accounting--bytes, packets delivered; and
[0114] Passing security parameters.
[0115] As previously mentioned, the protocol involves code
diversity, direct sequence spread spectrum and frequency agility,
changing frequency in ones of milliseconds and its configuration
completely each Epoch (ones of seconds). As a result, eavesdropping
requires InterAir unit hardware and a significant work factor to
hack the software in order to "read" a subscribers' packets. Theft
of services is made extremely difficult by the cooperative
synchronization process which exactly identifies the subscriber
hardware, checks with current account data for validity and even
measures range to the subscriber site. Anomalies in any of these
safeguards precludes assignment of virtual channels to transmit
TCP/IP data.
[0116] Metropolitan Area Network
[0117] The system 10 has been designed to operate with a high (20
dB) fade margin at long range (up to 25 miles) in order to cover a
large (2,000 square mile) metropolitan area in this unlicensed
radio environment from a single base station.
[0118] The number of systems 10 in a network is scalable. An ISP
can start up with an individual radio (i.e., system 10) at a
central base station and add additional radios at this base station
site as required by subscriber demand, up to a network aggregate
data rate of 10s of megabits per second. Furthermore, base stations
can be time and frequency coordinated in a cellular topology to
provide network aggregate data rates in the 100s of megabits per
second in a metropolitan area.
[0119] Network Topologies
[0120] A network consists of units or systems at the subscriber
site, units at the central base station, and units at the ISP. The
simplest case is shown in FIG. 8.
[0121] In FIG. 8 and the following FIGS. 9-12 described below, a
subscriber unit at location A supports several users doing TCP/IP
applications. TCP/IP packets are delivered to the subscriber unit
over an Ethernet, where they are packaged into time slots and
transmitted to the relay unit. There is no restriction on packet
size, and all TCP/IP packets are reassembled in the network before
transmission to the ISP network.
[0122] The packets are relayed from the central base station to the
ISP completing the wireless connection. Since, in this case, there
is only one subscriber, A, all time slots can be allocated to A, as
shown in FIG. 9, whether A's users have data to send/receive or
not. The single row of time cells or slots represents the capacity
of one radio at the base station--one physical channel.
[0123] In fact, base station radios can support several users from
each of several subscribers on a single physical channel. In FIG.
10, one radio at the central base station has dynamically divided
its physical channel into "virtual channels" for subscribers A, B
and C based on real-time usage. The processing required for this
real-time bandwidth allocation is performed by the computation
capable network. The scalability is continued by addition of
identical relay radios (i.e., system 10) at the base station.
[0124] In FIG. 11, three radio pairs have been added; three
additional radios at the base station and three additional radios
at the ISP. The network thereby obtained three more physical
channels which are represented as rows in the time division matrix,
one row for each radio pair. The multiple subscribers may be
re-assigned as needed by the bandwidth allocation processing since
the relay antennas at the base station are omni directional. With
four radios at the base station and "inband" backhaul (i.e., a
radio link back to the ISP), the systems can deliver a half duplex
network aggregate data rate of 4 Mbps. As a point of reference, an
ISDN BRI channel is 128 Kbps half duplex and is connection
oriented--not "shareable" as last mile connectivity.
[0125] Fully populated with eight omni antennas, a single base
station can support 6 Mbps half duplex network aggregate data
rate.
[0126] As previously mentioned, the radios or systems 10 are
computation capable and process both the standard TCP/IP and
Ethernet protocol stacks as well as InterAir proprietary protocol
stack optimized for multi-subscriber/multi-channel use in an
interference medium. This protocol provides very fine time
synchronization and coordinated frequency hopping so that no data
is lost to collision. All bandwidth is dynamically allocated by
this protocol although any or all slots may be reserved as required
by the ISP or by future interaction with Internet reservation
protocols.
[0127] The next step in the scalability of network capacity is to
replace the "inband" backhaul with a direct dedicated connection
(leased line or microwave link) from the centralized base station
back to the ISP network connection.
[0128] In FIG. 12, the backhaul is accomplished by N T1 lines where
N is the number required to support the network capacity. The time
division slots are single hop--half as long to deliver the same
number of data bytes--which immediately doubles the network
aggregate data rate of this base station to a maximum of 12 Mbps
half duplex or approximately 93 ISDN equivalents, network
engineered for maximum data rate and reuse as dedicated by the
ISP.
[0129] Again, because the radios 10 meet the FCC regulations for
coordinated use, a single base station can be scaled even further
using directional antennas at this central site to develop a
"sector" topology.
[0130] In FIG. 13, the example base station supports 12 sectors,
each with two radios for a 25 mile range. The radios have
directional antennas and service only those subscribers in the
sector. There is no requirement to build out all sectors. If some
sections cover an area with no subscribers, no radios need to be
installed for those sectors. Out of band backhaul is required in
this topology and the maximum network aggregate data rate
obtainable from a single base station is 48 Mbps half duplex. The
cross-hatched sectors are 2 Mbps: A, C; 1 Mbps: e,g. The white
sectors are 2 Mbps: B, D; 1 Mbps: f, h. FIG. 16, as described
hereinbelow, provides an example of the capacity/cost scalability
for a single base station.
[0131] Ultimately, an entire metropolitan area may be covered with
a coordinated (tiled) network of cellular base stations, as FIG. 14
illustrates.
[0132] In the cellular base station case of FIG. 14, there are 6
sectors per cell each sector with two radios (one at 2 Mbps and one
at 1 Mbps). Again, directional antennas are used at the base
station, and out-of-band backhaul is required. The network
aggregate data rate for each of these cellular base stations is 18
Mbps. All transmissions are coordinated in time and frequency. The
same sectors represent identical frequency pairs. The cells can be
any size from one mile up to a 25 mile radius, making it possible
to extend coverage to fit a variety of market densities and
topographies.
[0133] FIG. 15 illustrates the capability to provide spatial
diversity through a cellular topology. In this topology, a
subscriber may use whichever "surrounding" base station that
provides the easiest access. This is particularly valuable in a
metropolitan business district (urban canyon) setting in which
gaining rooftop access is a potential impediment to quick
installations. Spatial diversity may afford the end user access to
the network through a window mounted antenna. A subscriber may have
a better RF path or easier installation if a more distant relay is
used.
[0134] Cost/Capacity Scalability
[0135] System capacity scales up directly with cost incurred. An
ISP can start with a very low cost infrastructure with a single
central relay base station. Increased capability can be easily and
quickly added as required.
[0136] FIG. 16 illustrates four distinct phases of capacity growth
based on one central relay base station:
[0137] Inband backhaul: In this phase, the ISP starts with 1 radio
on the central relay base station and grows to 8 radios and a
capacity of approximately 40 ISDN equivalents (simultaneous full
128 Kbps half duplex).
[0138] Out-of-band backhaul: Adding out-of-band backhaul
immediately doubles the network capacity. In this phase, one adds
backhaul capacity to get from 40 to 120 ISDN equivalents.
[0139] Start Sectoring: In this phase, the antennas are changed to
directional sector antennas. At 12 radios, it makes economic sense
to change to T3 class backhaul. This represents a capacity of
approximately 190 ISDN equivalents.
[0140] Add T3 class backhaul: Adding radios up to a total of 24
obtains a final single base station capacity of 400 ISDN
equivalents.
[0141] For capacity beyond 400 ISDN equivalents, the system scales
to a cellular configuration, in which each cell has approximately
180 ISDN equivalents and covers an area from 25 square miles (3
mile radius) to over 1,900 square miles.
[0142] The system 10 is typically an Internet Service Provider
(ISP) owned (zero telco involvement) last mile connectivity
infrastructure for up to several hundred wideband service
subscribers in a large metropolitan area.
[0143] The system 10 enables the ISP to offer wideband services:
Internet applications including e-mail, web browser/server, file
transfer, voice, fax, videoconferencing over IP, advanced ISP value
add applications including push, multicasting, . . . , limited only
by imagination.
[0144] The system extends the concept of ISP back office (modem,
bandwidth, . . . ) resource reselling to the last mile subscriber
connectivity resource.
[0145] The system is also affordable: very low initial investment.
The network can be built out as needed, and the system 10 is easy
to install, operate and maintain. It can also provide a completely
independent back-up to a subscriber with a landline based
connection.
[0146] In summary, the system 10 provides for a wireless, wideband,
metropolitan area network for facility based connection to
subscribers, wholly owned by Internet Service Provides (ISP).
[0147] No license is required by the ISP before use of the
equipment in any metropolitan area in the U.S. and Canada. The 2.4
GHz ISM band is available worldwide.
[0148] The equipment and cables are shielded to resist interference
from indoor wireless LANs and microwave ovens. Military strength
anti-interference and anti-intercepting technology is preferably
built in to ensure reliable, secure digital connections.
[0149] Also, the system 10 offers high signal rates (1 and 2 Mbps)
and has been designed to FCC spread spectrum regulations to
legitimately coordinate radios. This coordination capability
enables scaling to network aggregate data rates in the 10s of
megabits per second per base station.
[0150] While the best mode for carrying out the invention has been
described in detail, those familiar with the art to which this
invention relates will recognize various alternative designs and
embodiments for practicing the invention as defined by the
following claims.
* * * * *