U.S. patent application number 15/095137 was filed with the patent office on 2017-11-16 for system and method for performing high-speed communications over fiber optical networks.
The applicant listed for this patent is Alexander Soto, Walter Soto. Invention is credited to Alexander Soto, Walter Soto.
Application Number | 20170331579 15/095137 |
Document ID | / |
Family ID | 42266303 |
Filed Date | 2017-11-16 |
United States Patent
Application |
20170331579 |
Kind Code |
A9 |
Soto; Alexander ; et
al. |
November 16, 2017 |
SYSTEM AND METHOD FOR PERFORMING HIGH-SPEED COMMUNICATIONS OVER
FIBER OPTICAL NETWORKS
Abstract
Processing a received optical signal in an optical communication
network includes equalizing a received optical signal to provide an
equalized signal, demodulating the equalized signal according to an
m-ary modulation format to provide a demodulated signal, decoding
the demodulated signal according to an inner code to provide an
inner-decoded signal, and decoding the inner-decoded signal
according to an outer code. Other aspects include other features
such as equalizing an optical channel including storing channel
characteristics for the optical channel associated with a client,
loading the stored channel characteristics during a waiting period
between bursts on the channel, and equalizing a received burst from
the client using the loaded channel characteristics.
Inventors: |
Soto; Alexander; (San Diego,
CA) ; Soto; Walter; (San Clemente, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Soto; Alexander
Soto; Walter |
San Diego
San Clemente |
CA
CA |
US
US |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20170026145 A1 |
January 26, 2017 |
|
|
Family ID: |
42266303 |
Appl. No.: |
15/095137 |
Filed: |
April 10, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12512968 |
Jul 30, 2009 |
9337948 |
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15095137 |
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11772187 |
Jun 30, 2007 |
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12512968 |
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10865547 |
Jun 10, 2004 |
7242868 |
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11772187 |
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60477845 |
Jun 10, 2003 |
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60480488 |
Jun 21, 2003 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04J 14/02 20130101;
H04B 10/5161 20130101; H04J 14/0282 20130101; H04J 14/0298
20130101; H04J 14/0227 20130101; H04J 14/0221 20130101; H04J
14/0256 20130101; H04J 14/0267 20130101; H04B 10/2581 20130101;
H04B 10/2507 20130101; H04B 10/40 20130101 |
International
Class: |
H04J 14/02 20060101
H04J014/02; H04J 14/02 20060101 H04J014/02; H04J 14/02 20060101
H04J014/02; H04B 10/40 20130101 H04B010/40; H04J 14/02 20060101
H04J014/02; H04J 14/02 20060101 H04J014/02; H04B 10/516 20130101
H04B010/516; H04B 10/2581 20130101 H04B010/2581; H04J 14/02
20060101 H04J014/02; H04B 10/2507 20130101 H04B010/2507 |
Claims
1. A method for m-ary modulation communication across an optical
network by an optical transceiver module comprising of: receiving a
first electrical binary data signal through a system interface of
the optical transceiver module; converting the first electrical
binary data signal in the optical transceiver module to a first
electrical m-ary modulation signal; amplifying the first electrical
m-ary modulation signal to drive an optical transmitter of the
optical transceiver module; emitting a first optical signal on a
first wavelength responsive to and representative of the amplified
first electrical m-ary modulation signal from the optical
transmitter of the optical transceiver module; receiving a second
optical signal on a second wavelength and producing an electrical
signal from an optical detector of the optical transceiver module;
amplifying the electrical signal to facilitate clock and data
recovery in the optical transceiver module; equalizing the
amplified electrical signal and recovering clock data information
to produce a second m-ary modulation signal in the optical
transceiver module; demodulating the second m-ary modulation signal
according to a second electrical binary signal; and transmitting
the second electrical binary signal through the system interface of
the optical transceiver module.
2. The method of claim 1, whereby the form factor of the optical
transceiver module is selected from the group consisting of: SFP;
SFP+; XFP; X2; XENPAK; XPA; and 300 pin transceiver form
factors.
3. The method of claim 1, whereby the m-ary modulation method is
selected from the group consisting of: quadrature amplitude
modulation (QAM); QAM-32; QAM-256; quadrature phase shift keying
(QPSK); differential QPSK; return-to-zero QPSK; dual-polarized
QPSK; orthogonal frequency division multiplexing (OFDM); pulse
amplitude modulation (PAM); PAM-5; and PAM-17.
4. The method of claim 1, further comprising of: storing a first
set of coefficients which improve processing of the electrical
signal.
5. The method of claim 1, further comprising of: loading a second
set of stored coefficients which improve processing of the
electrical signal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is filed as a 37 C.F.R. 1.53(b) as a
continuation claiming the benefit under 35 U.S.C .sctn.120 of the
pending U.S. patent application Ser. No. 12/512,968, "System and
Method for Performing High-Speed Communications over Fiber Optical
Networks", which was filed by the same inventors on Jul. 30, 2009
claiming the benefit under 37 C.F.R. 1.53(b)(2) of U.S. patent
application Ser. No. 11/772,187 filed on Jun. 30, 2007, which
claims benefit of commonly-assigned U.S. patent application Ser.
No. 10/865,547 filed on Jun. 10, 2004, now U.S. Pat. No. 7,242,868,
which claims the benefit of U.S. Provisional Application No.
60/477,845 filed Jun. 10, 2003, incorporated herein by reference,
and U.S. Provisional Application No. 60/480,488 filed Jun. 21,
2003, incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to optical fiber communications
generally, and more specifically to m-ary modulation in optical
communication networks.
BACKGROUND OF THE INVENTION
[0003] Line coding is a process by which a communication protocol
arranges symbols that represent binary data in a particular pattern
for transmission. Conventional line coding used in fiber optic
communications includes non-return-to-zero (NRZ), return-to-zero
(RZ), and biphase, or Manchester. The binary bit stream derived
from these line codes can be directly modulated onto wavelengths of
light generated by the resonating frequency of a laser.
Traditionally direct binary modulation based transmission offers an
advantage with regard to the acceptable signal-to-noise ratio (SNR)
at the optical receiver, which is one of the reasons direct binary
modulation methods are used in the Datacom Ethernet/IP, Storage
Fiber-Channel/FC and Telecom SONET/SDH markets for transmission
across nonmultiplexed unidirectional fiber links.
[0004] The performance of a fiber optic network can be measured by
the maximum data throughput rate (or information carrying capacity)
and the maximum distance between source and destination achievable
(or reach). For Passive Optical Networks (PONs) in particular,
additional measures of performance are the maximum number of
Optical Networking Units (ONUs) and/or Optical Networking Terminals
(ONTs) possible on a network and the minimum and maximum distance
between the Optical Line Terminator (OLT) and an ONU/ONT. These
performance metrics are constrained by, among other things,
amplitude degradation and temporal distortions as a result of light
traveling through an optical fiber.
[0005] Amplitude degradation is substantially a function of length
or distance between two end points of an optical fiber. Temporal
distortion mechanisms include intramodal (chromatic) dispersion and
intermodal (modal) dispersion. Intramodal dispersion is the
dominant temporal dispersion on Single-mode fiber (SMF), while
intermodal dispersion is dominant on Multi-mode fiber (MMF). Both
types of temporal distortions are measured as functions of
frequency or rate of transmission (also referred as line rate of a
communication protocol) over distance in MHzkm. Temporal
distortions are greater, hence a constraint on network performance,
with increasing frequency transmission.
SUMMARY OF THE INVENTION
[0006] In general, in one aspect, the invention includes a method
for processing a received optical signal in an optical
communication network, the method including: determining a first
set of coefficients to equalize a portion of an optical signal
received over a first optical link including using a blind
equalization method that does not use a known training sequence to
equalize the portion of the optical signal, equalizing the portion
of the optical signal using the determined coefficients, and
demodulating the equalized portion of the optical signal according
to an m-ary modulation format.
[0007] Aspects of the invention may include one or more of the
following features. The method includes determining a second set of
coefficients to equalize a portion of an optical signal received
over a second optical link. The method includes selecting one of
the first or second set of coefficients based on a source of the
portion of optical signal being equalized. The portion of the
optical signal includes a burst within a time slot of the first
optical link. The method includes storing the determined
coefficients. The method includes retrieving the stored
coefficients for equalizing a second portion of the optical signal
corresponding to a portion received from a same source as generated
the first portion of the optical signal. The coefficients are
retrieved between signal bursts on the first optical link. The
stored coefficients are retrieved for respective portions of the
optical signals that correspond to respective signal sources. The
first optical link includes a link in a point-to-multipoint passive
optical network. The m-ary modulation format is selected from the
group consisting of quadrature amplitude modulation, quadrature
phase shift keying, orthogonal frequency division multiplexing and
pulse amplitude modulation. The method includes demodulating a
received first data stream and demodulating a second data stream
received in the optical signal, and multiplexing the first and
second data streams.
[0008] In general, in another aspect, the invention includes
optical communication system including: a first transceiver coupled
by an optical network to a second transceiver and third
transceiver, the first transceiver including an equalization block
and a modulation block, the equalization block operable to
determine a first set of coefficients to equalize a portion of an
optical signal received over the optical network from the second
transceiver and a second set of coefficients to equalize a portion
of the optical signal received over the optical network from the
third transceiver, the equalization block including a blind
equalization routine that does not use a known training sequence to
equalize the portions of the optical signal, the equalization block
operable to equalize the portions of the optical signal using the
determined coefficients, and the modulation block operable to
demodulate equalized portions of the optical signal according to an
m-ary modulation format.
[0009] Aspects of the invention may include one or more of the
following features. The optical network includes a first optical
link for coupling the first and second transceiver, and a second
optical link for coupling the first and third transceivers and
where the equalization block is operable to select one of the first
or second set of coefficients based on a source of the portion of
optical signal being equalized. The equalization block is operable
to store the first and second sets of coefficients for later
retrieval and use to equalize portions of the optical signal. The
portion of the optical signal includes a burst within a time slot
on the optical network. The equalization block is operable to
retrieve the sets of coefficients between signal bursts on the
optical network. The optical network includes a link in a
point-to-multipoint passive optical network. The m-ary modulation
format is selected from the group consisting of quadrature
amplitude modulation, quadrature phase shift keying, orthogonal
frequency division multiplexing and pulse amplitude modulation. The
system includes a multiplexer, the modulation block operable to
demodulating a received first data stream and a second data stream
received in the optical signal, and the multiplexer operable to
multiplex the first and second data streams. The system includes a
transmission convergence layer block for processing data streams
received by the first transceiver, the transmission convergence
layer block operable to control the demultiplexing of data streams
including control of the multiplexer. The optical network is an
optical distribution network. The first transceiver is an optical
line terminator. The second and third transceivers are optical
network terminals or optical network units.
[0010] In general, in another aspect, the invention includes a
method for processing data for transmission in an optical
communication network, the method including: demultiplexing a data
stream into a first demultiplexed data stream and a second
demultiplexed data stream, modulating each of the first and second
data streams according to an m-ary modulation format, transmitting
the first modulated data stream over a first optical link; and
transmitting the second modulated data stream over a second optical
link.
[0011] In general, in another aspect, the invention includes an
optical communication system including: a demultiplexer operable to
demultiplex a data stream into a first demultiplexed data stream
and a second demultiplexed data stream, a modulation block operable
to modulate each of the first and second data streams according to
an m-ary modulation format, transmitting means operable to transmit
the first modulated data stream over a first optical link and the
second modulated data stream over a second optical link.
[0012] In general, in another aspect, the invention includes a
method for processing a received optical signal in an optical
communication network, the method including: equalizing a received
optical signal to provide an equalized signal, demodulating the
equalized signal according to an m-ary modulation format to provide
a demodulated signal, decoding the demodulated signal according to
an inner code to provide an inner-decoded signal, and decoding the
inner-decoded signal according to an outer code.
[0013] Aspects of the invention may include one or more of the
following features. The m-ary modulation format is selected from
the group consisting of quadrature amplitude modulation, quadrature
phase shift keying, orthogonal frequency division multiplexing and
pulse amplitude modulation. Equalizing the received optical signal
includes equalizing the received optical signal using a blind
equalization routine that does not use a known training sequence.
Equalizing the received optical signal includes equalizing the
received optical signal using a known training sequence. The known
training sequence is multiplexed in a frame within the received
optical signal. The inner code includes a trellis code. The outer
code includes an error correction code. The outer code includes a:
Reed-Solomon code; trellis code; Low-density parity-check code, or
a Turbo code.
[0014] In general, in another aspect, the invention includes a
transceiver including: an equalizer for equalizing a received
optical signal to provide an equalized signal, a demodulator in
communication with the equalizer for demodulating the equalized
signal according to an m-ary modulation format to provide a
demodulated signal, an inner-decoder in communication with the
demodulator for decoding the demodulated signal according to an
inner code to provide an inner-decoded signal, and an outer-decoder
in communication with the inner-decoder for decoding the
inner-decoded signal according to an outer code.
[0015] Aspects of the invention may include one or more of the
following features. The transceiver includes an optical module
including a first bi-directional optical fiber interface including
a first detector and a first driver, and a second bi-directional
optical fiber interface including a second detector and a second
driver, and management means for managing data flow across the
first bi-directional optical fiber interface and across the second
bi-directional optical fiber interface. The transceiver includes an
optical module including a first bi-directional optical fiber
interface including a first detector and a first driver, and a
second bi-directional optical fiber interface including a second
detector and a second driver, and a multiplexer for multiplexing a
first demultiplexed data stream received over the first
bi-directional optical fiber interface and a second demultiplexed
data stream received over the second bi-directional optical fiber
interface into a multiplexed data stream for transmission. The
transceiver includes an optical module including a first
bi-directional optical fiber interface including a first detector
and a first driver, and a second bi-directional optical fiber
interface including a second detector and a second driver, and a
queue manager for managing traffic for a first bi-directional link
associated with the first bi-directional optical fiber interface
independently from traffic for a second bi-directional link
associated with the second bi-directional optical fiber
interface.
[0016] In general, in another aspect, the invention includes a
transceiver including: an optical module including a first
bi-directional optical fiber interface including a first detector
and a first driver, and a second bi-directional optical fiber
interface including a second detector and a second driver, and
management means for managing data flow across the first
bi-directional optical fiber interface and across the second
bi-directional optical fiber interface.
[0017] Aspects of the invention may include one or more of the
following features. The management means includes a multiplexer for
multiplexing a first demultiplexed data stream received over the
first bi-directional optical fiber interface and a second
demultiplexed data stream received over the second bi-directional
optical fiber interface into a multiplexed data stream for
transmission. The management means is configured to demultiplex a
data stream over a plurality of fiber links that excludes one or
more failed fiber links. The management means includes a queue
manager for managing traffic across the first bi-directional fiber
interface independently from traffic for the second bi-directional
fiber interface. The management means is configured to change the
alignment of received data bits to adjust for an order of optical
fiber connections to the first bi-directional optical fiber
interface and the second bi-directional optical fiber
interface.
[0018] In general, in another aspect, the invention includes a
method for equalizing an optical channel including: storing channel
characteristics for the optical channel associated with a client,
loading the stored channel characteristics during a waiting period
between bursts on the channel, and equalizing a received burst from
the client using the loaded channel characteristics.
[0019] Aspects of the invention may include one or more of the
following features. The method includes determining that the
waiting period occurs before a burst from the client based on a
schedule. The method includes updating the stored channel
characteristics. The method includes providing a grant window,
transmitting an identification number to the client in response to
receiving a serial number from the client after the grant window.
The method includes determining a distance from an upstream device
to the client. The method includes compensating for communication
delays between the upstream device and the client based on the
determined distance.
[0020] In general, in another aspect, the invention includes a
method for communicating data on a fiber optic network, the method
including: modulating and demodulating data traffic on an optical
link in the network in an m-ary modulation format; encoding and
decoding data traffic on an optical link in the network according
to an inner coding routine and an outer coding routine,
demultiplexing data traffic from an optical link in the network and
transmitting the data traffic across a plurality of optical fiber
links in the network, multiplexing the data traffic from the
plurality of optical fiber links, and equalizing a receive channel
in the network to remove temporal distortions.
[0021] Aspects of the invention may include one or more of the
following features. The method includes equalizing the receive
channel according to a blind equalization routine. The method
includes equalizing the receive channel according to a decision
directed equalization routine. The method includes saving and
loading coefficients for equalizing the receive channel for each of
a plurality of transmitting sources. The method includes conveying
a training sequence for a decision directed equalization routine as
part of an in-use communication protocol. A training sequence for a
decision directed equalization routine is conveyed as part of the
activation process for an optical network terminal or optical
network unit. An incorrect connection of an optical fiber link is
corrected without having to physically change the connection.
[0022] In general, in another aspect, the invention includes a
method for communicating on a passive optical network between a
central transmission point and a plurality of receiving client end
points, the method including: preparing downstream data for
transmission and transmitting an optical downstream continuous mode
signal demultiplexed across a plurality of bi-directional fibers
using a plurality of wavelengths of light, receiving an optical
downstream continuous mode signal demultiplexed from the plurality
of bi-directional fibers using the plurality of wavelengths of
light and recovering a downstream data transmission, preparing
upstream data for transmission and transmitting an optical upstream
burst mode signal demultiplexed across the plurality of
bi-directional fibers using the plurality of wavelengthss of light,
and receiving an optical burst mode signal demultiplexed from the
plurality of bi-directional fibers using the plurality of
wavelengths of light and recovering an upstream data
transmission.
[0023] Aspects of the invention may include one or more of the
following features. The central transmission point includes an
optical line terminal, and the end points are operative as
transceivers in a passive optical network. The upstream and
downstream data for transmission are conveyed by respective
different industry-standard services.
[0024] Implementations of the invention may include one or more of
the following advantages.
[0025] A system is proposed that provides for high-speed
communications over fiber optic networks. The system may include
the use of the one or more of the following techniques either
individually or in combination: m-ary modulation; channel
equalization; demultiplexing across multiple fibers, coding and
error correction. M-ary modulation allows for increased data
throughput for a given line rate due to an increase in the number
of bits per symbol transmitted. Channel equalization reduces the
effects of temporal distortions allowing for increased reach.
Demultiplexing across multiple fibers allows lower lines rates for
a given data throughput rate due to the increased aggregate data
throughput from the multiplexing. Coding and error correction
allows for a greater selection of qualifying optical components
that can be used in the network and complements m-ary modulation
and channel equalization for overall system performance improvement
as measured by transmit energy per bit. These methods when combined
(in part or in total) increase the data throughput and reach for
fiber optic networks. For PONs in particular, these methods may
increase the number of ONU/ONTs and the distance between OLT and
ONU/ONT by decreasing the line rate as compared to a conventional
communication system of equivalent data throughput.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 illustrates a fiber optic data network.
[0027] FIG. 2 illustrates a block diagram of a passive optical
network.
[0028] FIG. 3 illustrates a block diagram of a high-speed
communication system for fiber optic networks.
[0029] FIG. 4 illustrates a block diagram of an alternative
high-speed communication system for fiber optic networks.
[0030] FIG. 5 illustrates a block diagram of an alternative
high-speed communication system for fiber optic networks.
[0031] FIG. 6A illustrates a block diagram of an alternative
high-speed communication system for fiber optic networks.
[0032] FIG. 6B illustrates a block diagram of an alternative
high-speed communication system for fiber optic networks.
[0033] FIG. 7 illustrates a block diagram of an alternative
high-speed communication system for fiber optic networks.
[0034] FIG. 8A illustrates an exemplary flow diagram for upstream
burst mode communication processing.
[0035] FIG. 8B illustrates another exemplary flow diagram for
upstream burst mode communication processing.
[0036] FIG. 9 illustrates an exemplary flow diagram for a
downstream continuous mode communication equalization process.
DETAILED DESCRIPTION
[0037] Referring to FIG. 1, wherein like reference numerals
designate identical or corresponding parts throughout the several
views and embodiments, a high-level fiber optic data network 50
includes a first transceiver 100 in communication with a second
transceiver 101 via a fiber 108. The first transceiver 100 and the
second transceiver 101 include transmitter circuitry (Tx) 134, 135
to convert electrical data input signals into modulated light
signals for transmission over the fiber 108. In addition, the first
transceiver 100 and the second transceiver 101 also include
receiver circuitry (Rx) 133, 136 to convert optical signals
received via the fiber 108 into electrical signals and to detect
and recover encoded data and/or clock signals. First transceiver
100 and second transceiver 101 may contain a micro controller (not
shown) and/or other communication logic and memory 131, 132 for
network protocol operation. Although the illustrated and described
implementations of the transceivers 100, 101 include communication
logic and memory in a same package or device as the transmitter
circuitry 134, 135 and receiver circuitry 133, 136, other
transceiver configurations may also be used.
[0038] First transceiver 100 transmits/receives data to/from the
second transceiver 101 in the form of modulated optical light
signals of known wavelength via the optical fiber 108. The
transmission mode of the data sent over the optical fiber 108 may
be continuous, burst or both burst and continuous modes. Both
transceivers 100,101 may transmit a same wavelength (e.g., the
light signals are polarized and the polarization of light
transmitted from one of the transceivers is perpendicular to the
polarization of the light transmitted by the other transceiver).
Alternatively, a single wavelength can be used by both transceivers
100, 101 (e.g., the transmissions can be made in accordance with a
time-division multiplexing scheme or similar protocol).
[0039] In another implementation, wavelength-division multiplexing
(WDM) may also be used. WDM is herein defined as any technique by
which two optical signals having different wavelengths may be
simultaneously transmitted bi-directionally with one wavelength
used in each direction over a single fiber. In yet another
implementation, coarse wavelength-division multiplexing (CWDM) or
dense wavelength-division multiplexing (DWDM) may be used. CWDM and
DWDM are herein defined as any technique by which two or more
optical signals having different wavelengths are simultaneously
transmitted in the same direction. The difference between CWDM and
DWDM is CWDM wavelengths are typically spaced 20 nanometers (nm)
apart, compared with 0.4 nm spacing for DWDM wavelengths. Both CWDM
and DWDM may be used in bi-directional communications. In
bi-directional communications, e.g. if wavelength-division
multiplexing (WDM) is used, the first transceiver 100 may transmit
data to the second transceiver 101 utilizing a first wavelength of
modulated light conveyed via the fiber 108 and, similarly, the
second transceiver 101 may transmit data via the same fiber 108 to
the first transceiver 100 utilizing a second wavelength of
modulated light conveyed via the same fiber 108. Because only a
single fiber is used, this type of transmission system is commonly
referred to as a bi-directional transmission system. Although the
fiber optic network illustrated in FIG. 1 includes a first
transceiver 100 in communication with a second transceiver 101 via
a single fiber 108, other implementations of fiber optic networks,
such as those having a first transceiver in communication with a
plurality of transceivers via a plurality of fibers (e.g. shown in
FIG. 2), may also be used.
[0040] Electrical data input signals (Data IN 1) 115, as well as
any optional clock signal (Data Clock IN 1) 116, are routed to the
transceiver 100 from an external data source (not shown) for
processing by the communication logic and memory 131. Communication
logic and memory 131 process the data and clock signals in
accordance with an in-use network protocol. Communication logic and
memory 131,132 provides management functions for received and
transmitted data including queue management (e.g., independent link
control) for each respective link, demultiplexing/multiplexing and
other functions as described further below. The processed signals
are transmitted by the transmitter circuitry 134. The resulting
modulated light signals produced from the first transceiver's 100
transmitter 134 are then conveyed to the second transceiver 101 via
the fiber 108. The second transceiver 101, in turn, receives the
modulated light signals via the receiver circuitry 136, converts
the light signals to electrical signals, processes the electrical
signals using the communication logic and memory 132 (in accordance
with an in-use network protocol) and, optionally, outputs the
electrical data output signals (Data Out 1) 119, as well as
optional clock signals (Data Clock Out 1) 120.
[0041] Similarly, the second transceiver 101 receives electrical
data input signals (Data IN 1) 123, as well as any optional clock
signals (Data Clock IN) 124, from an external data source (not
shown) for processing by the communication logic and memory 132 and
transmission by the transmitter circuitry 135. The resulting
modulated light signals produced from the second transceiver's 101
transmitter 135 are then conveyed to the first transceiver 100
using the optical fiber 108. The first transceiver 100, in turn,
receives the modulated light signals via the receiver circuitry
133, converts the light signals to electrical signals, processes
the electrical signals using the communication logic and memory 131
(in accordance with an in-use network protocol), and, optionally,
outputs the electrical data output signals (Data Out 1) 127, as
well as any optional clock signals (Data Clock Out 1) 128.
[0042] Fiber optic data network 50 may also include a plurality of
electrical input and clock input signals, denoted herein as Data IN
N 117/125 and Data Clock IN N 118/126, respectively, and a
plurality of electrical output and clock output signals, denoted
herein as Data Out N 129/121 and Data Clock Out N 130/122,
respectively. The information provided by the plurality of
electrical input signals may or may not be used by a given
transceiver to transmit information via the fiber 108 and,
likewise, the information received via the fiber 108 by a given
transceiver may or may not be outputted by the plurality of
electrical output signals. The plurality of electrical signals
denoted above can be combined to form data plane or control plane
bus(es) for input and output signals respectively. In some
implementations, the plurality of electrical data input signals and
electrical data output signals are used by logic devices or other
devices located outside (not shown) a given transceiver to
communicate with the transceiver's communication logic and memory
131, 132, transmit circuitry 134, 135, and/or receive circuitry
133,136.
[0043] FIG. 2 illustrates an implementation of a passive optical
network (PON) 52, where the functions described above associated
with the first transceiver 100 and the second transceiver 101 of
FIG. 1, are implemented in an optical line terminator (OLT) 150 and
one ore more optical networking units (ONU) 155, and/or optical
networking terminals (ONT) 160, respectively. PON(s) 52 may be
configured in either a point-to-point network architecture, wherein
one OLT 150 is connected to one ONT 160 or ONU 155, or a
point-to-multipoint network architecture, wherein one OLT 150 is
connected to a plurality of ONT(s) 160 and/or ONU(s) 155. In the
implementation shown in FIG. 2, an OLT 150 is in communication with
multiple ONTs/ONUs 160, 155 via a plurality of optical fibers 152.
The fiber 152 coupling the OLT 150 to the PON 52 is also coupled to
other fibers 152 connecting the ONTs/ONUs 160, 155 by one or more
passive optical splitters 157. All of the optical elements between
an OLT and ONTs/ONUs are often referred to as the Optical
Distribution Network (ODN). Other alternate network configurations,
including alternate implementations of point-to-multipoint networks
are also possible.
[0044] FIG. 3 shows a system block diagram for an implementation of
transceiver 100. It will be appreciated that, while not always
shown, one or more elements or blocks in the following embodiments
may be sealed in one or more faraday cages or combined with blocks
in faraday cages already shown. It will also be appreciated that,
while not shown, one or more elements or blocks in the following
embodiments may be combined onto one or more integrated circuits
(IC) or surface mount photonic (SMP) devices. The following is a
description of the functions and responsibilities that are part of
an implementation of the Communication Logic & Memory 131 of
transceiver 100. The Communication Logic & Memory 131 includes
an asynchronous or synchronous system transmit (TX) interface 301
and receive (RX) interface 302 that is supported by the TX Path 303
and RX Path 304 blocks. System interfaces 301,302 and management or
control interfaces can be selected from conventional interfaces
including serial, serial XFI, parallel, GMII, XGMII, SGMII, RGMII
or XAUI or some other interface may be used. TX Path 303 and RX
Path 304 blocks manage the TX and RX interfaces 301,302 and feed
data into and get data from the transmission convergence layer or
media access control (TC-Layer/MAC) block 305. TX Path 303 and RX
Path 304 blocks may perform line code adaptation functions (e.g.,
line coding used outside the transceiver can be terminated by a TX
Path block 303 or sourced by a RX Path block 304 to allow a bit
stream, cell, frame, and/or packet formatted data to be adapted for
processing by a TC-Layer/MAC block 305). The TC-Layer/MAC 305 block
creates the transport system that the data traffic, management and
control agents will exploit. TC-Layer/MAC 305 block includes a
TC-layer protocol stack such as specified in the ITU G.984
specification (incorporated herein by reference), IEEE 802.3ah MAC
protocol stack specification (incorporated herein by reference) or
a derivative thereof. A variety of other protocol stacks may also
be used. The TC-Layer/MAC 305 block may perform the additional
functions of equalizer, coding, queue and demultiplexing
management. The TC-Layer/MAC 305 block sends transmit data to a
DeMux 306 block, which splits the transmitting data into a
plurality of data paths (two paths shown in FIG. 3) for
demultiplexing data across multiple fibers. Some implementations
need not include DeMux 306 block (and hence do not support
demultiplexing data across multiple fibers). DeMux 306 block may
demultiplex data across a subset of fibers to exclude fibers
experiencing link failure to ensure data communications continue.
The exclusion of fiber links experiencing failure is controlled by
the TC-Layer/MAC 305 block as part of the demultiplexing management
function.
[0045] After DeMux 306 block, in one implementation, the transmit
paths have analogous processing blocks. In an alternative
implementation, independent signal processing can be supported in
each path. FIG. 3 shows two transmit paths, though more can be
included. In a transmit path, the transmit data is provided to the
outer coder 307a, 307b block. In one implementation, outer coder
307a performs a reed-solomon coding. The outer coder 307a, 307b
block provides data to the inner coder 308a, 308b block. In order
to improve the energy per bit required to deliver the transmitting
data, an inner coder 308a, 308b is used. Outer coder 307a, 307b may
be used to support forward error correction (FEC) recovery of
bit(s) errors. In one implementation, inner coder 308a, 308b
implements a trellis coding method. Data from the inner coder 308a,
308b is provided to Modulation (MOD) 309a, 309b block.
Alternatively, in some implementations, the outer coder 307a, 307b
and inner coder 308a, 308b blocks are not used, and the output of
the DeMux 306 block is provided directly to the MOD 309a, 309b
block. Other outer coding methods that work on bit or symbol
streams of arbitrary length can be used, for example linear block
codes such as Low-density parity-check (LDPC) and convolutional
codes such as Turbo code may be used. Other inner coding methods
that are complementary to the outer code as well as inner coding
methods that are designed to shape or control the relative
intensity noise (RIN) of the optical transmitter to improve overall
system performance may be used. For example, an inner coder that
dynamically adapts to measured RIN or compensates for measured
temperature or other artifacts of laser design may be used.
[0046] To increase the number of bits per symbol transmitted, m-ary
modulation is performed in the MOD 309a, 309b block. In one
implementation, an m-ary modulation method such as Quadrature
Amplitude Modulation (QAM), QAM-32, QAM-256, Pulse Amplitude
Modulation (PAM), PAM-5, PAM-17, Quadrature Phase Shift Keying
(QPSK), differential QPSK (DQPSK), return-to-zero QPSK (RZ-QPSK),
dual-polarized QPSK (DP-QPSK), or Orthogonal Frequency Division
Multiplexing (OFDM) is used. Other m-ary modulation communication
methods can be used, in particular other coherent modulation
techniques which are known in the art. After processing by the MOD
309a, 309b block, the transmit data is converted to an analog
signal by a Digital to Analog Converter (DAC) 310a, 310b. In one
implementation, DAC 310a, 310b is configured to shape, condition or
emphasize the signal for improved transmission performance. The DAC
310a, 310b passes the transmit data via electrical signals 311a,
311b to the laser driver (Driver) 312a, 312b as part of an
implementation of TX 134 in an Optical Module 326. The driver 312a,
312b drives an optical transmitter, such as the Laser Diode (LD)
313a, 313b, which transmits light in response to transmit data
signals received from the driver 312a, 312b. The light emitted from
LD 313a, 313b is directed into the fibers 314a, 314b with the aid
of a fiber optic interface (not shown). The fiber optic interface
may include the necessary components (e.g., filters) to implement
WDM, CWDM or DWDM functions.
[0047] On the receive side of the transceiver 100 as part of an
implementation of RX 133 in an Optical Module 326, light propagated
across an ODN (not shown in FIG. 3) travels over fibers 314a, 314b
through a fiber optic interface (not shown) and is received by an
optical detector, such as the photo diode (PD) 315a, 315b. In
response, the PD 315a, 315b provides a photocurrent to the
TransImpedance Amplifier (TIA) 316a, 316b that converts the
photocurrent into an electrical voltage signal. The electrical
voltage signal from the TIA 316a, 316b is then transmitted to a
Linear Amplifier (LA) 317a, 317b as a differential signal or a
single-ended signal 318a, 318b. The LA 317a, 317b performs signal
conditioning on the received electrical voltage signal to provide
increased resolution and system performance. The LA 317a, 317b
provides an electrical signal 319a, 319b to a Clock Data Recovery
(CDR) and Equalization (EQ) 320a, 320b block that recovers clock
and data signals and performs equalization on the received data,
which is then provided to a De-Mod & Inner Decoder 323a, 323b.
The CDR & EQ 320a, 320b block may implement a blind
equalization method or decision-directed equalization method. Blind
equalization is discussed further below. Other equalization methods
may be used, particularly those that aid the CDR. The De-Mod &
Inner Decoder 323a, 323b block performs complementary de-modulation
to the m-ary modulation performed in the MOD 309a, 309b block as
well as a complementary decoding method to the coding method
performed in the Inner Coder 308a, 308b block. In one
implementation, De-Mod & Inner Decoder 323a, 323b includes a
Viterbi decoder. Other decoding means may be used. Received data is
then provided to the outer decoder 324a, 324b block, which performs
a complementary decode to the error detection and/or recovery
method chosen in the outer coder 307a, 307b block. After
demodulation and decoding, the received data is then provided to
the Mux 325 block that performs a complementary function to the
DeMux 306 block. The combined received data is then provided to the
TC-Layer/MAC 305. In implementations without Outer Coder 307a, 307b
and Inner Coder 308a, 308b blocks, the output of the CDR & EQ
320a, 320b block is provided directly to the Mux 325 block.
[0048] The RX 133,136 and TX 134,135 circuitry of transceivers
100,101, or portions thereof, for example, PD 315a, 315b and LA
317a, 317b, can be combined within industry standard optical
modules. Common optical module standards are 300pin, XENPAK, X2,
and XPAK transponders and XFP or SFP and SFP+transceivers. These
optical modules include unidirectional fiber links with one fiber
link for transmit path and a second fiber link for the receive
path. However, implementations of optical modules 326, 401, 501
incorporate a plurality of bi-directional fiber links for
transmitting demultiplexed data on separate fiber links. Any of a
variety of optical couplers may be used to separate and/or combine
light propagating into or out of the fiber links. These optical
modules 326, 401, 501 used herein can conform to a form factor of
standard optical modules such as the 300pin, XENPAK, X2, XPAK, XFP
or SFP and SFP+. Other form factors may also be used.
[0049] Alternatively, in other implementations of transceiver 100,
functions described above may be integrated into various different
components. For example, in the implementation of transceiver 100
shown in FIG. 4, various functions may be incorporated into optical
module 401 such as: digital to analog conversion 310a, 310b; analog
to digital conversion 321a, 321b; clock data recovery and
equalization 320a, 320b; m-ary modulation 309a, 309b; m-ary
de-modulation 323a, 323b; inner coder 308a, 308b; inner de-coder
323a, 323b; outer coder 307a, 307b; outer de-coder 324a, 324b, and
the De-Mux 306 and Mux 325 functions that enable demultiplexing
across multiple fibers. The optical module 401 may have an
interface that can connect to existing TC-Layer or MAC
implementations currently produced. In another alternative
implementation the digital to analog conversion 310a, 310b; analog
to digital conversion 321a, 321b, and the clock data recovery 320a,
320b functions are incorporated into an optical module (not shown).
In yet another alternative implementation of the transceiver 100 as
shown in FIG. 5, an optical module 501 includes the De-Mux 306 and
Mux 325 functions enabling demultiplexing across multiple fibers.
The optical module 501 may have an interface that can connect to
existing TC-Layer or MAC implementations currently produced.
[0050] Alternative implementations of transceiver 100 utilizing a
single fiber link 314a (without demultiplexing across multiple
fibers) are illustrated in FIG. 6A-6B. Alternatively, an
implementation of the transceiver 100 may utilize multiple fiber
links 314a, 314b while not performing demultiplexing across
multiple fibers, as illustrated in FIG. 7. In this implementation,
the TC-Layer/MAC 701 block manages the fiber links as independent
fiber links that all connect to the same end point(s) on the
network. In one implementation, TC-Layer/MAC 701 block is a
derivative of the Transmission Convergence Layer specified in ITU
G.984 or MAC specified in IEEE 802.3ah, with the added
functionality of queue management of the traffic across the
plurality of independent fiber links. The TC-Layer/MAC 701 block
may exclude use of one or more fiber links if the fiber link
experiences a failure. This exclusion of failed fiber links enables
the TC-Layer/MAC 701 block (i.e., queue management function) to
continue providing service across a PON using the remaining active
links. Each fiber can be deployed across physically different paths
to provide optical fiber distribution path diversity and improved
protection against failures. Failures may originate in the optical
module or across elements of the ODN such as fiber or connector
breaks.
Channel Equalization
[0051] An implementation for a channel equalization routine
executed in the CDR & EQ 320a, 320b block includes determining
coefficient settings or weights that are applied to the received
data to remove undesired information (e.g. intersymbol interference
(ISI) or noise from the received data and thereby increase the
sensitivity, dynamic range of detecting signals and accuracy of
receiving signals. Channel equalization can include a training or
convergence period in which characteristics of the channel are
learned or accounted for and coefficients, filter variables, or
weights are adapted before or while processing the received data.
Decision-directed equalization is an equalization method in which a
known training sequence is sent during the training period and the
receiver/transceiver uses the knowledge of the training sequence to
learn about the channel characteristics. The training sequence can
be multiplexed within a PON's TC-Layer framing protocol. Blind
equalization is a process during which an unknown input data
sequence is recovered from the output signal of an unknown channel
(i.e., current equalization data for a given channel is unknown or
otherwise unavailable). Other equalization methods may be used,
digital signal processing methods, or methods that improve the
accuracy of processing received data signals or improve the
efficiency of processing received data signals (e.g., reducing data
acquisition time, reducing power consumed) by saving or storing a
first set of settings generated by processing data from a first
ONU/ONT and then load previously saved second set of settings
previously generated by processing data from a second ONU/ONT
before processing another set of data from the second ONU/ONT.
[0052] One mode of communications used by a PON, e.g., for upstream
data traffic (ONU/ONT to OLT direction), is "burst mode"
communications. For example, upstream communications on a PON may
include a link shared among multiple clients or ONUs/ONTs via time
division multiplexing under control by an OLT. The upstream
direction is divided into time slots; each time slot includes a
defined number of bits. A given ONU/ONT is granted some number of
time slots during which to transmit an upstream frame of data to an
OLT. The upstream direction uses an orchestrated collection of
bursts from the different ONU/ONTs, coordinated by the OLT that
tries to maximize upstream traffic bandwidth efficiency by
minimizing empty slots.
[0053] A flow chart for an exemplary upstream burst mode
communication equalization process is shown in FIG. 8A. To read or
interpret the upstream data traffic from a client ONU/ONT, an OLT
trains and/or equalizes the channel for that client ONU/ONT. Since
the ONU/ONTs may be at different distances from the OLT and all do
not share the same fiber, different channel characteristics result.
Communication efficiencies may be obtained by determining 800 a set
of equalization coefficients for a channel during a burst from a
client, saving 801 the determined equalization coefficients,
entering a wait period 802 (also known as a PON's silence period
when no client ONU/ONTs are transmitting upstream), and loading 803
the stored equalization coefficients before a next burst from the
client (during the wait period), to avoid re-training or
re-equalizing on every burst communication. The OLT has prior
knowledge of which ONU/ONT will be transmitting data during which
time slots and can use this knowledge during the time between burst
communications (during the wait period) to load 803 an appropriate
set of coefficients pertaining to the particular ONU/ONT
transmitting prior to receiving 804 its next upstream burst. This
process continues for subsequent bursts. In one implementation,
periodic (though not coincident with each communication burst)
updates to the channel characteristics may be made (and stored).
The OLT can save 801 coefficients that have converged or have been
trained after receiving burst communications from the first ONU/ONT
and load 803 a new set of coefficients during the wait period
between bursts (i.e., before an incoming upstream burst from a
second ONU/ONT). In another exemplary implementation, the OLT can
save or store 801 coefficients or settings during the wait period
802 between burst as shown in FIG. 8B. In one implementation, in
addition to or alternative to storage of coefficient data, the OLT
may also save and load inner and/or outer coding states between
bursts improving the efficiency of communication, similar to the
equalization process of FIG. 8A-8B. Other methods that improve the
accuracy and efficiency of processing burst mode data from specific
ONUs/ONTs may be used following a similar process.
[0054] Another mode of communications used by a PON, e.g., for
downstream data traffic (OLT to ONU/ONT direction), is "continuous
mode" communications. In one implementation, a receiver, such as an
ONU/ONT, equalizes a received data channel using either one of a
blind equalization or a decision directed equalization method.
[0055] A flow chart for an exemplary PON activation process is
shown in FIG. 9. In a PON in which a decision directed method is
used for training an ONU/ONT receiver, a continuous mode
transmitter, such as an OLT transmitter, sends a training sequence
900 multiplexed within a PON's TC-Layer downstream frame protocol.
In a PON in which a blind equalization method is used, the OLT
needed not send this training sequence 900. An ONU/ONT equalizes
its received downstream channel 901 before it is able to receive
and interpret PON network parameters 902. If the OLT has not been
previously informed of the existence of the ONU/ONT then the
ONU/ONT awaits an upstream grant window 903 available for new
ONU/ONTs to respond to the OLT with its serial number 904. After
the ONU/ONT has received an upstream grant window and processed PON
system parameters, the ONU/ONT sends a training sequence 905 and
then its serial number 904 to the OLT. In a PON in which blind
equalization is used the ONU/ONT need not send a training sequence
905. After the OLT has received the ONU/ONT serial number the OLT
will assign and send the ONU/ONT an identification number. If the
ONU/ONT does not receive an identification number 906a, the ONU/ONT
returns to waiting for an upstream grant window for new ONU/ONTs
903. Once the ONU/ONT receives an identification number 906b, the
OLT performs ranging 907 to determine the distance between the OLT
and ONU/ONT and then compensates for the communication timing
delays. The ONU/ONT can perform updates continuously or
periodically depending on the equalization method employed. After
the downstream continuous mode channel and the upstream burst mode
channel have been equalized, both ends of the PON transmission link
are equalized and the ONU/ONT enters its normal operating state
908.
[0056] Link Connection Errors
[0057] A system has been proposed that includes demultiplexing
across multiple fibers as is shown above with reference to FIGS.
3-6. In systems using demultiplexing across multiple fibers, fibers
can be connected incorrectly at installation. For example, a first
transceiver 100, such as is shown in FIG. 3, with fibers 314a and
314b can be connected to a second transceiver 101 with fiber 314b
connected in place of fiber 314a, and fiber 314a connected in place
of fiber 314b. The incorrect connection in this example may cause
the first and second transceivers to not establish communications
due to misalignment of bits during multiplexing of received
data.
[0058] Information in a frame is used to synchronize a receiver
(e.g., transceiver 101) with the beginning of a frame (e.g., a
"frame delimiter"). The process of discovering the beginning of a
frame is called "frame synchronization." In specific protocols such
as G.984, the downstream frame delimiter is called Psync, the
upstream frame delimiter is called Delimiter and the process of
frame synchronization in the downstream is called the HUNT. In one
implementation, TC-Layer/MAC 305 block performs frame
synchronization. In one implementation, specific bit patterns or
values for frame delimiters are used that are unique for each fiber
to differentiate one fiber from another or the order of fiber
connections to correctly multiplex received data. The use of unique
frame delimiters allows the TC-Layer/MAC 305 block to change the
alignment of received data bits during multiplexing to adjust for
the order of the fiber connections, without having to physically
change the connections. Management of the bit alignment in this
implementation forms part of the TC-Layer/MAC's 305 block
demultiplexing management responsibilities and functions.
[0059] Alternatively, the TC-Layer/MAC 305 block may assume an
order for the fiber connections to determine the alignment of bits
for multiplexing the received data and attempt frame
synchronization. After a period of time with no frame
synchronization success, the TC-Layer/MAC 305 block may assume a
different order for the fiber connections and change the alignment
of bits during multiplexing and attempt frame synchronization
again. The process may repeat, including changing the alignment of
bits to reflect other configurations during the multiplexing, and
frame synchronization attempts continue until frame synchronization
succeeds. In yet another alternative implementation, the
TC-Layer/MAC 305 block may assume and attempt frame synchronization
on all possible combinations of bit alignments in parallel, one of
which will succeed in achieving frame synchronization.
[0060] Although the invention has been described in terms of
particular implementations, one of ordinary skill in the art, in
light of this teaching, can generate additional implementations and
modifications without departing from the spirit of or exceeding the
scope of the claimed invention. Accordingly, it is to be understood
that the drawings and descriptions herein are proffered by way of
example to facilitate comprehension of the invention and should not
be construed to limit the scope thereof.
* * * * *