U.S. patent application number 14/965502 was filed with the patent office on 2016-04-07 for time to time-frequency mapping and demapping for ethernet passive optical network over coax (epoc).
This patent application is currently assigned to Broadcom Corporation. The applicant listed for this patent is Broadcom Corporation. Invention is credited to Edward Boyd, Sanjay GOSWAMI, Avi Kliger, Leo Montreuil, Yitshak Ohana.
Application Number | 20160099780 14/965502 |
Document ID | / |
Family ID | 50274577 |
Filed Date | 2016-04-07 |
United States Patent
Application |
20160099780 |
Kind Code |
A1 |
GOSWAMI; Sanjay ; et
al. |
April 7, 2016 |
Time to Time-Frequency Mapping and Demapping for Ethernet Passive
Optical Network over Coax (EPoC)
Abstract
Embodiments include, but are not limited to, systems and methods
for enabling Orthogonal Frequency Division Multiple Access (OFDMA)
in the upstream in an Ethernet Passive Optical Network over Coax
(EPoC) network. Embodiments include systems and methods for
translating Ethernet Passive Optical Network (EPON) upstream time
grants to OFDMA resources represented by individual subcarriers of
an upstream OFDMA frame. In an embodiment, the translation of EPON
upstream time grants to OFDMA resources ensures that Coaxial
Network Units (CNUs) sharing an OFDMA frame do not use overlapping
subcarriers within the frame. Embodiments further include systems
and methods for timing upstream transmissions by the CNUs in order
for the transmissions to be received within the same upstream OFDMA
frame at a Fiber Coax Unit (ECU). Embodiments further include
systems and methods for regenerating a data burst from OFDMA
resources for transmission from the ECU to an Optical Line Terminal
(OLT).
Inventors: |
GOSWAMI; Sanjay; (Santa
Rosa, CA) ; Kliger; Avi; (Ramat Gan, IL) ;
Boyd; Edward; (Petaluma, CA) ; Ohana; Yitshak;
(Givat Zeev, IL) ; Montreuil; Leo; (Atlanta,
GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Broadcom Corporation |
Irvine |
CA |
US |
|
|
Assignee: |
Broadcom Corporation
Irvine
CA
|
Family ID: |
50274577 |
Appl. No.: |
14/965502 |
Filed: |
December 10, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14029180 |
Sep 17, 2013 |
9253554 |
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14965502 |
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61702108 |
Sep 17, 2012 |
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61702113 |
Sep 17, 2012 |
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61702144 |
Sep 17, 2012 |
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61724399 |
Nov 9, 2012 |
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Current U.S.
Class: |
398/58 |
Current CPC
Class: |
H04Q 2213/1301 20130101;
H04Q 2213/13389 20130101; H04B 10/27 20130101; H04L 5/0007
20130101; H04Q 11/0067 20130101; H04L 5/001 20130101 |
International
Class: |
H04B 10/27 20060101
H04B010/27; H04L 5/00 20060101 H04L005/00 |
Claims
1. An Ethernet Passive Optical Network over Coax (EPoC) physical
layer (PHY) chip for use in a Fiber Coax Unit (FCU), comprising: a
PHY controller configured to receive a multi-subcarrier frame
containing first and second transmissions from a first Coaxial
Network Unit (CNU) and a second CNU; identify a first subcarrier
group of the multi-subcarrier frame carrying the first transmission
from the first CNU; and generate a bit stream using the first
subcarrier group.
2. The EPoC PHY chip of claim 1, wherein the PHY controller is
configured to identify the first subcarrier group using a start
marker and an end marker inserted in the first subcarrier group by
the first CNU.
3. The EPoC PHY chip of claim 2, further comprising: a coaxial
media converter (CMC) configured to adapt the bit stream for
optical transmission to generate an adapted bit stream; and an
optical transceiver configured to generate an optical signal using
the adapted bit stream and to transmit the optical signal to an
Optical Line Terminal (OLT).
4. The EPoC PHY chip of claim 1, where the multi-subcarrier frame
comprises multiple time consecutive symbols, and wherein the PHY
controller is further configured to: determine a symbol bit loading
for a subcarrier of the subcarrier group from an upstream bit
loading profile of the first CNU, wherein the symbol bit loading
indicates a number of bits that can be carried by the subcarrier in
one symbol time from the first CNU; and demodulate the subcarrier,
using the symbol bit loading, over the multiple time consecutive
symbols to generate a bit sequence for the subcarrier.
5. The EPoC PHY chip of claim 4, wherein the PHY controller is
further configured to append bit sequences generated by
demodulating subcarriers of the first subcarrier group to generate
the bit stream.
6. The EPoC PHY chip of claim 1, wherein the PHY controller is
further configured to determine first and second upstream bit
loading profiles for the first and second CNUs respectively and to
adjust a subcarrier loading order used by the first CNU based on a
comparison of the first and second upstream bit loading
profiles.
7. A method, comprising: receiving a multi-subcarrier frame
containing first and second transmissions respectively from a first
Coaxial'Network Unit (CNU) and a second CNU; identifying a first
subcarrier group of the multi-subcarrier frame using a start marker
and an end marker inserted in the first subcarrier group by the
first CNU; and generating a bit stream using the first subcarrier
group.
8. The method of claim 7, further comprising: adapting the bit
stream for optical transmission to generate an adapted bit
stream.
9. The method of claim 8, further comprising: generating an optical
signal using the adapted bit stream; and transmitting the optical
signal to an Optical Line Terminal (OLT).
10. The method of claim 7, wherein the multi-subcarrier frame
comprises multiple time consecutive symbols.
11. The method of claim 10, further comprising: determining a
symbol bit loading for a subcarrier of the subcarrier group from an
upstream bit loading profile of the first CNU, wherein the symbol
bit loading indicates a number of bits that can be carried by the
subcarrier in one symbol time from the first CNU; and demodulating
the subcarrier, using the symbol hit loading, over the multiple
time consecutive symbols to generate a bit sequence for the
subcarrier.
12. The method of claim 11, further comprising: appending hit
sequences generated by demodulating subcarriers of the first
subcarrier group to generate the bit stream.
13. The method of claim 7, further comprising: determining first
and second upstream bit loading profiles for the first and second
CNUs, respectively.
14. The method of claim 13, further comprising: adjusting a
subcarrier loading order used by the first CNU based on a
comparison of the first and second upstream bit loading
profiles.
15. An Ethernet Passive Optical Network over Coax (EPoC) physical
layer (PHY) chip. comprising: a PHY controller configured to
receive a multi-subcarrier frame containing a transmission from a
Coaxial Network Unit (CNU); identify a subcarrier group of the
multi-subcarrier frame carrying the transmission from the CNU using
a start marker and an end marker inserted in the subcarrier group
by the CNU; and generate a bit stream using the subcarrier
group.
16. The EPoC PHY chip of claim 15, further comprising: a coaxial
media converter (CMC) configured to adapt the bit stream for
optical transmission to generate an adapted bit stream; and an
optical transceiver configured to generate an optical signal using
the adapted bit stream and to transmit the optical signal to an
Optical Line Terminal (OLT).
17. The EPoC PHY chip of claim 15, wherein the multi-subcarrier
frame comprises multiple time consecutive symbols, and wherein the
PHY controller is further configured to: determine a symbol bit
loading for a subcarrier of the subcarrier group from an upstream
bit loading profile of the CNU, wherein the symbol bit loading
indicates a number of bits that can be carried by the subcarrier in
one symbol time from the CNU; and demodulate the subcarrier, using
the symbol bit loading, over the multiple time consecutive symbols
to generate a bit sequence for the subcarrier.
18. The EPoC PHY chip of claim 17, wherein the PHY controller is
further configured to append bit sequences generated by
demodulating subcarriers of the subcarrier group to generate the
bit stream.
19. The EPoC PHY chip of claim 15, wherein the PHY controller is
further configured to determine first and second upstream bit
loading profiles for the CNU and to adjust a subcarrier loading
order used by the CNU based on a comparison of the upstream bit
loading profiled to an upstream bit loading profile of another
CNU.
20. The EPoC PHY chip of claim 15, wherein the EPoC PHY chip is
implemented in a Fiber Coax Unit (FCU).
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] The present application is a divisional of U.S. patent
application Ser. No. 14/029,180, filed Sep. 17, 2013, which claims
the benefit of U.S. Provisional Application No. 61/702,108, filed
Sep. 17, 2012, U.S. Provisional Application No. 61/702,113, filed
Sep. 17, 2012, U.S. Provisional Application No. 61/702,144, filed
Sep. 17, 2012, and U.S. Provisional Application No. 61/724,399,
filed Nov. 9, 2012, all of which are incorporated herein by
reference in their entireties.
BACKGROUND
[0002] 1. Technical Field
[0003] The present disclosure relates generally to Ethernet Passive
Optical Network over Coax (EPoC), and more particularly to time to
time-frequency mapping/demapping and upstream bit loading profile
balancing for Orthogonal Frequency Division Multiple Access (OFDMA)
support.
[0004] 2. Background Art
[0005] In a hybrid fiber-coax (HFC) network, the Medium Access
Control (MAC) level upstream multi-access method may be different
than the physical layer (PHY) level upstream multi-access method
over the Ethernet Passive Optical Network over Coax (EPoC) portion
of the network. For example, at the MAC level, upstream access is
typically based on Ethernet Passive Optical Network (EPON) Time
Division Multiple Access (TDMA). At the PHY level, however a
multi-subcarrier multiple access technique, such as Orthogonal
Frequency Division Multiple Access (OFDMA) may be used.
BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES
[0006] The accompanying drawings, which are incorporated herein and
form a part of the specification, illustrate the present disclosure
and, together with the description, further serve to explain the
principles of the disclosure and to enable a person skilled in the
pertinent art to make and use the disclosure.
[0007] FIG. 1 illustrates an example cable network architecture
according to an embodiment.
[0008] FIG. 2 illustrates another example cable network
architecture according to an embodiment.
[0009] FIG. 3 illustrates an example coaxial network unit (CNU)
according to an embodiment.
[0010] FIG. 4 is an example that illustrates an Orthogonal
Frequency Division Multiple Access (OFDMA) framing approach
according to an embodiment.
[0011] FIG. 5 is an example that illustrates upstream burst
alignment according to an embodiment.
[0012] FIG. 6 is an example that illustrates the end-to-end
transport of a Medium Access Control (MAC) frame from a Coaxial
Network Unit (CNU) to a Coaxial Line Terminal (CLT) according to an
embodiment.
[0013] FIG. 7 illustrates an example CLT according to an
embodiment.
[0014] FIG. 8A illustrates example upstream bit loading profiles
for CNUs according to an embodiment.
[0015] FIG. 8B illustrates example upstream bit loading profiles
for CNUs according to an embodiment.
[0016] FIG. 9 is an example that illustrates capacity balancing of
an upstream bit loading profile according to an embodiment.
[0017] FIG. 10 is an example that illustrates capacity balancing of
multiple upstream bit loading profiles according to an
embodiment.
[0018] FIG. 11 illustrates an example process according to an
embodiment.
[0019] FIG. 12A illustrates another example cable network
architecture according to an embodiment.
[0020] FIG. 12B illustrates another example cable network
architecture according to an embodiment.
[0021] The present disclosure will be described with reference to
the accompanying drawings. Generally, the drawing in which an
element first appears is typically indicated by the leftmost
digit(s) in the corresponding reference number.
DETAILED DESCRIPTION OF EMBODIMENTS
[0022] For purposes of this discussion, the term "module" shall be
understood to include at least one of software, firmware, and
hardware (such as one or more circuits, microchips, processors, or
devices, or any combination thereof), and any combination thereof.
In addition, it will be understood that each module can include
one, or more than one, component within an actual device, and each
component that forms a part of the described module can function
either cooperatively or independently of any other component
forming a part of the module. Conversely, multiple modules
described herein can represent a single component within an actual
device. Further, components within a module can be in a single
device or distributed among multiple devices in a wired or wireless
manner.
[0023] FIG. 1 illustrates an example cable network architecture 100
according to an embodiment. Example cable network architecture 100
is provided for the purpose of illustration only and is not
limiting of embodiments. Embodiments described herein can be
implemented in a cable network architecture, such as cable network
architecture 100.
[0024] As shown in FIG. 1, example network architecture 100
includes a CLT 102 and a CNU 104, coupled via a distribution
network 106. Distribution network 106 can include a coaxial cable
and optionally other coaxial components (e.g., splitters,
amplifiers, etc.). As would be understood by a person of skill in
the art based on the teachings herein, CLT 102 can serve multiple
CNUs, such as CNU 104, in a point-to-multipoint topology.
[0025] CLT 102 and CNU 104 implement respective Medium Access
Control (MAC) layers 110 and 114. According to embodiments, MAC
layers 110 and 114 can be, without limitation, Data Over Cable
Service Interface Specification (DOCSIS) or Ethernet Passive
Optical Network (EPON) MAC layers. An end-to-end MAC link can be
established between MAC layers 110 and 114 as shown in FIG. 1.
[0026] CLT 102 and CNU 104 implement physical layers (PHYs) 108 and
112 respectively. PHYs 108 and 112 establish a PHY link over
distribution network 106, which can be transparent to upper layers
such as the MAC layer. PHYs 108 and 112, can be, without
limitation, Ethernet Passive Optical Network over Coax (EPoC) PHYs.
In an embodiment, PHY 108 includes a service provider PHY and PHY
112 includes a subscriber PHY.
[0027] FIG. 2 illustrates another example cable network
architecture 200 according to an embodiment. Example cable network
architecture 200 is provided for the purpose of illustration only
and is not limiting, of embodiments. Embodiments described herein
can be implemented in a cable network architecture, such as cable
network architecture 200. Cable network architecture 200 is a
hybrid fiber coaxial (HFC) architecture.
[0028] As shown in FIG. 2, example cable network architecture 200
includes an Optical Line Terminal (OLT) 202, which is coupled via a
fiber optic line 204, to a Fiber Coax Unit (FCU) 212. FCU 212 is
coupled via a coaxial cable 206, and an intervening splitter 208,
to CNU 104 and a CNU 210. FCU 212 can have different configurations
according to embodiments, two of which are described in example
architectures 1200A and 1200B of FIGS. 12A and 12B.
[0029] In example architecture 1200A illustrated in FIG. 12A, FCU
212 is in a managed repeater configuration and includes an EPoC PHY
1202, an optical burst transceiver 1204, and optical burst
transceiver 1206. FCU 212 can also include in this configuration an
EPON MAC (not shown), which can be used for management. In this
configuration, FCU 212 serves to convert at the PHY level between
optical and coax. In an embodiment, ECU 212 includes a media
converter for converting signals at the PHY level from optical to
electrical, and vice versa. According to this configuration, an
upstream transmission request from a CNU, such as CNU 104, is
received by FCU 212, converted from coax to optical, and then
transmitted to OLT 202. OLT 202 issues an EPON time grant in
response to the request. The EPON time grant is converted from
optical to coax at FCU 212 and then forwarded to CNU 104, which
then transmits in the upstream in accordance with the EPON time
grant.
[0030] In example architecture 1200B illustrated in FIG. 12B, FCU
212 is in a bridge configuration and includes a CLT 102 and an EPON
ONU 1208. CLT 102, as described above in FIG. 1, includes an EPON
MAC 110 and an EPoC PHY 108. EPON ONU 1208 includes an EPON MAC and
is used to establish a MAC link between OLT 202 and FCU 212. In
this configuration, the EPON time grant issuance to the CNUs occurs
at FCU 212, particularly at EPON MAC 110. Specifically, an upstream
transmission request from a CNU, such as CNU 104, is received by
CLT 102 of FCU 212. EPON MAC 110 of CLT 102 issues an EPON time
grant in response to the request, and the EPON time grant is sent
to CNU 104. Subsequently, CNU 104 sends data in the upstream in
accordance with the issued EPON time grant. The upstream data is
received by EPON MAC 110 of CLT 102 and then forwarded to EPON ONU
1208 of FCU 212. EPON ONU 1208 can then request an upstream
transmission request from OLT 202, in order to deliver this
upstream data to OLT 202.
[0031] Returning to FIG. 2, OLT 202 can serve multiple ONUs (not
shown in FIG. 2), including EPON ONU 1208 of FCU 212, over the EPON
portion of the network. For example, the multiple ONUs can share a
portion of fiber 204 to communicate with OLT 202. In EPON/EPoC, the
multiple ONUs share the upstream using a Time Division Multiple
Access (TDMA) method, in which OLT 202 assigns each ONU a time slot
in which to transmit its upstream data (upstream EPON time grant).
A guard band time is typically used between upstream transmissions
of different ONUS to avoid overlap of transmissions at OLT 202. In
order to minimize this guard band time (and increase the upstream
bandwidth). OLT 202 uses a ranging, protocol to determine the round
trip delay time (RTT) between itself and each of the ONUs and
grants upstream transmission times for ONUs in accordance with the
determined RTTs.
[0032] CNUs 104 and 210 share the upstream channel to FCU 212.
Specifically, CNUs 104 and 210 use an Orthogonal Frequency Division
Multiple Access (OFDMA) technique, which allows them to share the
same OFDMA symbol or OFDMA frame (the OFDMA frame includes multiple
time consecutive OFDMA symbols) to FCU 212. In an embodiment, a
particular CNU upstream transmission (or burst) can use individual
subcarriers over a portion or all the symbols in the OFDMA
frame.
[0033] But with the EPON and EPoC portions of the network using
different upstream access methods, a translation function is
needed. For example, to transmit a data burst from CNU 104 over the
EPoC portion, there is a need to translate (map) an EPON upstream
time grant assigned by OLT 202 (in example architecture 1200A) or
by CLT 102 (in example architecture 1200B) to OFDMA resources
represented by individual subcarriers of an upstream OFDMA frame.
For upstream transmission of the same data burst from FCU 212 to
OLT 202, the upstream resources need to be identified and
demodulated by FCU 212 to re-generate the data burst for TDMA
transmission to OLT 202. In addition, with FCU 212 supporting
multiple CNUs, such as CNUs 104 and 210, the translation of
upstream EPON time grants to OFDMA resources must not result in
CNUs using overlapping subcarriers in the same OFDMA frame.
Additionally, the CNU upstream transmissions must be timed
appropriately in order for them to be received within the same
upstream OFDMA frame at the FCU. Further, it is desirable that a
given upstream OFDMA frame shared by multiple CNUs be used (i.e.,
its individual subcarriers be used) efficiently among the CNUs to
increase the amount of data carried by the OFDMA frame.
[0034] Embodiments as further described below include, but are not
limited to, systems and methods for enabling OFDMA (or any other
multi-subcarrier multiple access technique) in the upstream in an
EPoC network. For example, embodiments include systems and methods
for translating EPON upstream time grants to OFDMA resources
represented by individual subcarriers of an upstream OFDMA frame.
In an embodiment, the translation of EPON upstream time grants to
OFDMA resources ensures that CNUs sharing an OFDMA frame do not use
overlapping subcarriers within the frame. Embodiments further
include systems and methods for timing upstream transmissions by
the CNUs in order for the transmissions to be received within the
same upstream OFDMA frame at the FCU. Embodiments further include
systems and methods for regenerating a data burst from OFDMA
resources for TDMA transmission from the FCU to an OLT. Further,
embodiments include systems and methods for efficiently allocating
the subcarriers of a given OFDMA frame among multiple CNUs in order
to increase the amount of data carried by frame.
[0035] FIG. 3 illustrates an example coaxial network unit (CNU) 300
according to an embodiment. Example CNU 300 is provided for the
purpose of illustration only and is not limiting of embodiments.
Example CNU 300 can be an embodiment of CNU 104 or CNU 210
described above in FIGS. 1 and 2, and can be used, along with other
similar CNUs, to form and transmit an upstream OFDMA frame to an
FCU, such as FCU 212 for example.
[0036] As shown in FIG. 3, example CNU 300 includes a MAC layer
302, a PHY chip 304, a radio frequency (RF) transceiver 312. MAC
layer 302 can be implemented in a chip or processor and can be an
EPON MAC layer. MAC layer 302 is connected to PHY chip 304 via a
MAC-PHY interface 306. MAC-PHY interface 306 can be a media
independent interface (MII), such as the 10 Gigabit MII (XGMII)
interface. PHY chip 304 includes, among other components, a PHY
controller 308 and an upstream bit loading profile 310. RF
transceiver 312 includes an RF transmitter and an RF receiver and
is coupled to a coaxial cable 318.
[0037] In an embodiment, PHY controller 308 is configured to
receive a MAC bit stream 316 over MAC-PHY interface 306 from MAC
layer 301 MAC bit stream 316 can include one or more EPON MAC
frames that represent a MAC data burst. MAC bit stream 316 can be
transmitted by MAC layer 302 in response to an upstream EPON time
grant, received by MAC layer 302 in response to an upstream
transmission request to an OLT. In an embodiment, PHY controller
308 can determine the bit size of MAC bit stream 316 based on a
start transmission time and an end transmission time of MAC bit
stream 316 over MAC-PHY interface 306.
[0038] PHY controller 308 is configured to determine a transmission
time duration for MAC bit stream 316 over coaxial cable 318. In an
embodiment, PHY controller 308 determines the transmission time
duration for MAC bit stream 316 based on the bit size of MAC bit
stream 316 and upstream bit loading profile 310. Upstream bit
loading profile 310 determines for each available subcarrier of an
OFDMA symbol (which is defined as a plurality of subcarriers for a
defined OFDMA symbol time) the number of bits that can be carried
by the subcarrier in one OFMDA symbol (subcarrier symbol bit
loading) when used by CNU 300 to transmit to the FCU. Typically,
subcarrier bit loading can vary from subcarrier to subcarrier
(especially for subcarriers that are frequency distant) and from
CNU to CNU (e.g., because CNUs can have different Signal-to-Noise
Ratios (SNRs) at the ECU).
[0039] In an embodiment, PHY controller 308 determines a total bit
carrying capacity of an OFDMA frame. The OFDMA frame includes
multiple time consecutive OFDMA symbols having a defined symbol
time duration. The number of OFDMA symbols in an OFDMA frame is
configurable and may be between 8 and 32, for example. PHY
controller 308 then divides the total bit carrying capacity of the
OFDMA frame by the OFDMA frame duration to determine an average
data transmission rate from CNU 300 to the FCU. PHY controller 308
then uses the average data transmission rate to compute the
transmission time duration for MAC bit stream 316 based on the bit
size of MAC bit stream 316, In an embodiment, PHY controller 308
represents the transmission time duration for MAC bit stream 316 in
terms of EPON Time Quantas (TQs) (each EPON TQ is equivalent to 16
nanoseconds).
[0040] PHY controller 308 is then configured to translate the
transmission time duration for MAC bit stream 316 into an OFDMA
frame number and a subcarrier group. In an embodiment, the frame
number identifies an upstream scheduled OFDMA frame and the
subcarrier group identifies a plurality of subcarriers of the
upstream scheduled OFDMA frame. In an embodiment, upstream OFDMA
frames are transmitted consecutively in time (with optionally an
inter-frame gap (IFG)) to the FCU to form an upstream channel. Each
upstream OFDMA frame has a frame number associated with it, which
identifies the frame in time (i.e., identifies the frame start and
end in time) to the FCU and each of the CNUs. As further described
below, the subcarrier group can correspond to consecutive or
non-consecutive subcarriers (in terms frequency) of the OFDMA
frame. Thus, a frame number (e.g., frame #200) and a subcarrier
group (e.g., subcarriers 100-150) within the frame identified by
the frame number indicate unique OFDMA resources of the upstream
channel to the FCU.
[0041] In an embodiment, PHY controller 308 is configured to
translate the transmission time duration into the frame number and
the subcarrier group based at least in part on the start
transmission time of MAC bit stream 316 over MAC-PHY interface 306.
In an embodiment, PHY controller 308 uses a translation function
that implements a one-to-one mapping of start transmission times to
upstream OFDMA resources (i.e., no two different start transmission
times can result in same or overlapping OFDMA resources). In an
embodiment, MAC layer 302 is synchronized with a MAC layer of the
serving OLT (e.g., example architecture 1200A) or the CLT (e.g.,
example architecture 1200B), such that no two CNUs served by the
OLT or CLT can have the same start transmission times over their
respective MAC-PHY interfaces. As a result, the translation of the
transmission time duration based on the start transmission time of
MAC bit stream 316 over MAC-PHY interface 306 results in upstream
OFDMA resources which can only be determined by example CNU
300.
[0042] Having identified the upstream OFDMA resources to carry MAC
bit stream 316, PHY controller 308 is configured to map MAC bit
stream 316 to the determined subcarrier group of the identified
upstream OFDMA frame. In an embodiment, PHY controller 308 is
configured to map MAC bit stream 316 to the subcarrier group based
on upstream bit loading profile 310, assigning to each subcarrier
of the subcarrier group a number of bits of MAC bit stream 316 in
accordance with the symbol bit loading of the subcarrier as
determined in upstream bit loading profile 310. PHY controller 308
then outputs an output signal 320 to RF transceiver 312. Output
signal 320 includes, for each subcarrier of the subcarrier group,
the bits mapped to the subcarrier for the next OFDMA symbol (of the
OFDMA frame) to be transmitted. In an embodiment, RF transceiver
312 includes an Inverse Fast Fourier Transform (IFFT) module, which
modulates each subcarrier of the subcarrier group with the
respective bits mapped to it. The resulting modulated subcarriers
form the OFDMA symbol to be transmitted. The same process is
repeated for each OFDMA symbol in the OFDMA frame. In another
embodiment, PHY controller 308 is further configured to configure
RF transceiver 312 using a control signal 314 to transmit during
the identified upstream OFDMA frame and on the identified
subcarrier group over coaxial cable 318.
[0043] FIG. 4 is an example 400 that illustrates an OFDMA framing
approach according to an embodiment. Example 400 is provided for
the purpose of illustration only and is not limiting of
embodiments. Example 400 shows two upstream OFDMA frames (OFDMA
Frame 1 and OFDMA Frame 2) being transmitted consecutively in time.
In an embodiment, an IFG separates consecutive OFDMA frames. Each
OFDMA frame includes 12 OFDMA symbols, though the OFDMA frame can
be configured to include any number of OFDMA symbols according to
embodiments.
[0044] OFDMA frames are transmitted OFDMA symbol by OFDMA symbol.
However, the mapping of bits (e.g., MAC bit stream 316) to OFDMA
frames is done subcarrier per subcarrier as illustrated by the
arrows shown in FIG. 4. For example. assuming that subcarriers are
filled in an ascending order of frequency, then bits are mapped to
a first subcarrier 402 across all OFDMA symbols of the OFDMA frame,
before the mapping of bits to a second subcarrier 404 is performed.
This mapping approach ensures that any given data codeword (e.g.,
Forward Error Correction (FEC) protected data block) of the MAC bit
stream is spread over multiple OFDMA symbols, which reduces the
effects of burst noise on any transmitted data codeword. In another
embodiment, one or more OFDMA symbols in a given OFDMA frame are
designated as SYNC symbols and are configured to carry a mixture of
data and pilot information. The pilot information can be used by
the FCU to estimate the upstream channels from the CNUs.
[0045] Returning to FIG. 3, in an embodiment, example CNU 300 can
be configured to implement the OFDMA framing approach illustrated
in FIG. 4. Accordingly, PHY controller 308 can be configured, for
each subcarrier of the identified subcarrier group, to determine a
symbol bit loading for the subcarrier from upstream bit loading
profile 310; determine, using the symbol bit loading, a total
number of bits that can be carried by the subcarrier across the
multiple time consecutive symbols of the OFDMA frame; and map bits
from MAC bit stream 316 to the subcarrier in accordance with the
total number of bits. In an embodiment, PHY controller 308 maps the
bits from MAC bit stream 316 to internal registers, each
corresponding to a particular subcarrier. Then, for each OFDMA
symbol, PHY controller 308 outputs an appropriate number of bits
from each of the internal registers (according to the symbol bit
loading of the respective subcarrier) using output signal 320 to RF
transceiver 312.
[0046] As described above, in addition to ensuring that CNUs served
by the same FCU use non-overlapping subcarriers in an OFDMA frame,
transmissions by the CNUs must be timed appropriately such that
they arrive and can be received within the same upstream OFDMA
frame at the FCU. With OFDMA frames having boundaries that are
defined both in time and frequency by the FCU, each CNU must
maintain a local OFDMA frame start time (which identifies, for
example, the start of the next upstream OFDMA frame). As CNUs can
be located at different distances from the FCU, the OFDMA frame
start time for the same OFDMA frame can be different from one CNU
to another, with the difference accounting for the difference in
propagation time to reach the shared medium. This is illustrated in
example 500 of FIG. 5, which illustrates upstream burst alignment
according to an embodiment. Example 500 is provided for the purpose
of illustration only and is not limiting of embodiments. For
simplification purposes only, example 500 is described with
reference to example cable network architecture 200.
[0047] As shown in FIG. 5, CNU 104 and CNU 210 are both served by
FCU 212 using a shared coaxial cable 206. For illustration, CNU 104
is assumed to be closer to FCU 212 than CNU 210 (e.g., CNU 104 is
connected to splitter 208 via a shorter coaxial cable than CNU
210). In order for CNUs 104 and 210 share a same upstream OFDMA
frame 502 to FCU 212 for respective bursts, CNUs 104 and 210 must
transmit on non-overlapping resources 504 and 506, respectively, of
OFDMA frame 502. In addition, CNU 210 must begin its burst
transmission before CNU 104 such that the two transmissions align
in time at splitter 208. Splitter 208 can combine the two
transmissions onto coaxial cable 206 to form upstream OFDMA frame
502.
[0048] In an embodiment, FCU 212 assists each of CNUs 104 and 210
to determine their respective local OFDMA frame start times to
align their transmissions in time at the first component of the
shared upstream medium (splitter 208 in example 500). In an
embodiment, to calibrate its respective local OFDMA frame start
time, a CNU (e.g., via PHY controller 308) is configured to
transmit a signal on an upstream control channel according to its
local OFDMA frame start time. The upstream control channel can be
transmitted on a fixed set of subcarriers outside of the data
channel carrying the OFDMA frame. In an embodiment, the CNU begins
transmitting the signal at its local OFDMA frame start time. When
FCU 212 receives the signal on the upstream control channel, it
computes a time offset between the time that the signal was
received and the time that the start of the corresponding upstream
OFDMA frame was received. FCU 212 then sends the time offset to the
CNU on a downstream control channel. The downstream control channel
can be transmitted on a fixed set of subcarriers outside of the
downstream data channel. The CNU is configured to receive the time
offset on the downstream control channel and to adjust the local
frame start time using the time offset. By adjusting its local
frame start time using the time offset, the CNU can ensure that its
upstream transmissions align with the FCU defined OFDMA frame
boundary.
[0049] In addition to ensuring time alignment at the PHY level such
that the FCU PHY (e.g., EPoC PHY 1202 or 108) receives CNU upstream
transmissions within defined OFDMA frame boundaries, embodiments
are transparent to the MAC layer such that neither the CNU MAC nor
the FCU MAC (e.g., EPON MAC 110) (nor the OLT EPON MAC) needs to be
modified or made aware of the underlying translation of upstream
EPON time grants to OFDMA resources. In an embodiment, to ensure
that the MAC layers are not affected by the underlying PHY level
translation, the CNU PHY maps MAC data to OFDMA resources based on
a fixed delay and the FCU PHY (e.g., EPoC PHY 1202 or EPoC PHY 108)
demodulates OFDMA resources and releases the resulting MAC data to
the CLT MAC (e.g., EPON MAC 110) (e.g., in example architecture
1200B) or OLT MAC (e.g., in example architecture 1200A) based on a
fixed delay. This results in a fixed end-to-end MAC frame delay
between the CNU MAC and the CLT/OLT MAC. This is illustrated in
FIG. 6 below.
[0050] FIG. 6 is an example that illustrates the end-to-end
transport of MAC bit stream 316 from a CNU to a CLT according to an
embodiment. MAC bit stream 316 can include one or more MAC frames,
for example. As shown in FIG. 6. MAC bit stream 316 is placed by
CNU MAC layer 302 on MAC-PHY interface 306. CNU PHY 304 maps MAC
bit stream 316 to a subcarrier group 612 of an upstream OFDMA frame
614 and transmits the subcarrier group 612 over a coaxial cable 318
at a fixed delay 602 relative to when MAC bit stream 316 appeared
on MAC-PHY interface 306. At the CLT, a CLT PHY 606 demodulates the
subcarrier group 612 of OFDMA frame 614 to re-generate MAC bit
stream 316. CLT PHY 606 then places MAC bit stream 316 on a MAC-PHY
interface 610 for CLT MAC 608, at a fixed delay 604 relative to
when OFDMA frame 614 was received. MAC bit stream 316 thus incurs a
fixed end-to-end delay from CNU MAC layer 302 to CLT MAC 608, which
ensures a constant data rate MAC link between the CNU and CLT.
[0051] FIG. 7 illustrates an example FCU 700 according to an
embodiment. Example FCU 700 is provided for the purpose of
illustration only and is not limiting of embodiments. Example FCU
700 can be an embodiment of FCU 212 described above in FIGS. 2,
12A, and 12B. As shown in FIG. 7, example FCU 700 includes a PHY
chip 702, a MAC layer 704, a Coaxial Media Converter (CMC) 706, an
RF transceiver 312, and an optical transceiver 708. In other
embodiments, FCU 700 can include more or less components than shown
in FIG. 7. For example, in accordance with example architecture
1200B, FCU 700 may not include CMC 706. In other embodiments. CMC
706 may be part of PHY chip 702, which along with MAC layer 704 can
form a CLT, such as CLT 102.
[0052] MAC layer 704 can be implemented in a chip or processor and
can be an EPON MAC layer. MAC layer 704 is connected to PHY chip
702 via a MAC-PHY interface 716. MAC-PHY interface 716 can be an
XGMII interface. PHY chip 702 includes, among other components, a
PHY controller 720 and CNU upstream bit loading profiles 722. CNU
upstream bit loading profiles 722 include the upstream bit loading
profiles for CNUs served by FCU 700. CMC 706 can be implemented as
described in U.S. application Ser. No. 12/878,643. filed Sep. 9,
2010, which is incorporated herein by reference in its entirety. In
an embodiment, CMC 706 performs PHY level conversion from EPON to
EPoC, and vice versa. RF transceiver 312 includes an RF transmitter
and an RF receiver and is coupled to a coaxial cable 710. Coaxial
cable 710 can connect FCU 700 to one or more CNUs. Optical
transceiver 708 includes an optical transmitter and an optical
receiver and is coupled to a fiber optic line 712. Fiber optic line
712 can connect FCU 700 to an OLT, such as OLT 202, for
example.
[0053] In an embodiment, example FCU 700 can receive an upstream
OFDMA frame over coaxial cable 710. The upstream OFDMA frame can be
formed from upstream transmissions of one or more CNUs as described
above. For example, the upstream OFDMA frame can contain first and
second upstream transmissions from first and second CNUs, such as
CNUs 104 and 210, to FCU 700. The first and second transmissions
are transmitted from the first and second CNUs at respective first
and second upstream transmission times. The first and second
upstream transmission times are provided to the first and second
CNUs in respective first and second upstream EPON time grants,
issued by an OLT (e.g., OLT 202 in example architecture 1200A) or
by FCU 700 (by MAC layer 704) and delivered to the first and second
CNUs by FCU 700.
[0054] RF transceiver 312 is configured to receive a signal that
carries the upstream OFDMA frame over coaxial cable 710 and to
provide an output signal 724 that represents the upstream OFDMA
frame to PHY controller 720. In an embodiment, PHY controller 720
controls RF transceiver 312 using a control signal 726 in order to
locate the upstream OFDMA frame in time and frequency.
[0055] PHY controller 720 is configured to act on output signal
724, which includes the upstream OFDMA frame, to identify, a first
subcarrier group of the OFDMA frame carrying the first transmission
from the first CNU. In an embodiment, PHY controller 720 identifies
a start marker and an end marker associated with the first
subcarrier group. In an embodiment, the start marker corresponds to
a first subcarrier of the first subcarrier group and is filled by a
sequence of bits that can be identified by PHY controller 720 of
FCU 700. The end marker corresponds to the last subcarrier of the
first subcarrier group and is filled by a sequence of bits that can
be identified by PRY controller 720 of FCU 700. PHY controller 720
then generates a bit stream 718 using the first subcarrier
group.
[0056] In an embodiment, as described above, the upstream OFDMA
frame includes time consecutive OFDMA symbols. Accordingly, PHY
controller 720 is further configured, for each subcarrier of the
first subcarrier group, to determine a symbol bit loading for the
subcarrier from an upstream bit loading, profile of the first CNU
(located in CNU upstream profiles 722), and to demodulate the
subcarrier, using the symbol bit loading, over the multiple time
consecutive OFDMA symbols of the OFDMA frame to generate a bit
sequence for the subcarrier. PHY controller 720 then appends the
bit sequences generated by demodulating the subcarriers of the
first subcarrier group to generate bit stream 718. In an
embodiment, PHY controller 720 eliminates the bits corresponding to
the start and end markers in generating bit stream 718.
[0057] In an embodiment, such as when FCU 700 is used in an
architecture such as example architecture 1200B, bit stream 718 is
delivered over MAC-PHY interface 716 to MAC layer 704. MAC layer
704 can then send an upstream transmission request to the OLT in
order to deliver the MAC data contained in bit stream 718 to the
OLT.
[0058] In another embodiment, such as when FCU 700 is used in an
architecture such as example architecture 1200A, bit stream 718 is
forwarded to CMC 706. In an embodiment, CMC 706 can be part of PHY
702. CMC 706 is configured to adapt bit stream 718 for optical
transmission to generate an adapted bit stream 714. In an
embodiment, CMC 706 is configured to adjust a PHY level encoding
(e.g., line encoding) of bit stream 718 to generate bit stream 714.
Optical transceiver 708 is configured to generate an optical signal
using adapted bit stream 714 and to transmit the optical signal
over fiber optical line 712 to the OLT.
[0059] As mentioned above, embodiments further include systems and
methods for efficiently allocating the subcarriers of a given
upstream OFDMA frame among multiple CNUs in order to increase the
amount of data carried by the frame. In an embodiment, the
allocation takes into account the upstream bit loading profiles of
the multiple CNUs, such that CNUs use subcarriers with larger
symbol bit loading whenever possible. In another embodiment, the
subcarrier loading order (the order of subcarriers used by a CNU to
map a bit stream to the subcarriers) used by one or more CNUs is
adjusted for an upstream OFDMA frame based on the upstream loading
profiles of CNUs transmitting during the upstream OFDMA frame.
These embodiments are further described below with reference to
FIGS. 8A, 8B, 9, and 10.
[0060] FIG. 8A illustrates example upstream bit loading profiles
for CNUs according to an embodiment. Specifically, FIG. 8A shows a
first upstream bit loading profile 802 and a second upstream bit
loading profile 804. First upstream bit loading profile 802 can be
for a first CNU, such as CNU 104, for example, and second upstream
bit loading profile 804 can be for a second CNU, such as CNU 210,
for example. For the purpose of illustration only, it is assumed
that first and second upstream bit loading profiles 802 and 804
include 21 subcarriers, numbered from 1 to 21, which correspond to
the subcarriers of an OFDMA frame. As would be understood by a
person of skill in the art, an OFDMA frame can include more than 21
subcarriers in practice. Subcarrier 21 is assumed to be the lowest
frequency subcarrier, followed by subcarrier 20, and so on until
subcarrier 1, which is the highest frequency subcarrier.
[0061] First upstream bit loading profile 802 has a greater symbol
bit loading per subcarrier than second upstream bit loading profile
804 for each of the subcarriers 1-21. Specifically, for
illustration, it is assumed that the symbol bit loading of first
upstream bit loading, profile 802, for each subcarrier, is twice
that of second upstream bit loading profile 804. For example, for
subcarrier #1, the symbol bit loading is 2 bits per symbol in first
upstream bit loading profile 802 and 1 bit per symbol in second
upstream bit loading profile 804. Similarly, for subcarrier #10,
the symbol bit loading is 4 bits per symbol in first upstream bit
loading profile 802 and 2 bits per symbol in second upstream bit
loading profile 804. Accordingly, the first CNU can load twice as
many bits in the OFDMA frame than the second CNU if each CNU were
to use the OFDMA frame exclusively.
[0062] Because first and second upstream bit loading profiles 802
and 804 are proportional to each other (related by a 2 to 1 ratio
in terms of symbol bit loading per subcarrier), if the subcarriers
1-21 are filled in order (e.g., from the lowest frequency
subcarrier to the highest frequency subcarrier, or vice versa) any
given OFDMA frame usage capacity percentage will be reached at the
same subcarrier location within the OFDMA frame using both first
and second upstream bit loading profiles 802 and 804. For example,
as shown in FIG. 8A, using first upstream bit loading profile 802,
if subcarriers are filled consecutively starting from subcarrier
#1, the OFDMA frame will reach 50% usage capacity (i.e., the OFDMA
frame will be half full) once subcarrier #13 is filled as
illustrated by 50% capacity line 806. Similarly, the 50% capacity
line 808 for second upstream bit loading profile 804 occurs once
subcarrier #13 is filled.
[0063] Because of this alignment of capacity usage percentage lines
between first and second upstream profiles 802 and 804 (due to them
being proportional), the first and second CNUs can be readily
accommodated within the same OFDMA frame. For example, if the first
and second CNUs each requested an upstream transmission equivalent
to 50% capacity of an OFDMA frame, then the first CNU can use a
first half (of the subcarriers) of the OFDMA frame and the second
CNU can use the other half of the OFDMA frame. Similarly, if the
first CNU had requested 20% of the capacity of an OFDMA frame and
the second CNU had requested 30% of the capacity of the OFDMA
frame, then the first CNU can use, for example, the lowest
frequency subcarriers in the frame until the 20% capacity line is
reached and the second CNU can use the next set of subcarriers
until the 50% capacity line is reached.
[0064] In practice, however, upstream bit loading profiles of CNUs
transmitting within the same OFDMA frame are not always
proportional or substantially proportional as illustrated in FIG.
8A. For example, as shown in FIG. 8B, a first CNU and a third CNU
transmitting in the same OFDMA frame can have respectively first
upstream bit loading profile 802 and a third upstream bit loading
profile 810. Third upstream bit loading profile 810 has nulled
subcarriers at subcarriers 1 through 9. As a result, upstream bit
loading profiles 802 and 810 have distributions that are not
proportional, and their respective capacity usage percentage lines
do not match. For example, using first upstream bit loading profile
802, if subcarriers are filled consecutively starting from
subcarrier #1, the OFDMA frame will reach 50% usage capacity once
subcarrier #13 is filled as illustrated by 50% capacity line 806.
In contrast, the 50% capacity line 812 using third upstream bit
loading profile 810 is only reached after subcarrier #15 is
filled.
[0065] Because of this misalignment of capacity percentage lines
between first and third upstream profiles 802 and 810, the first
and third CNUs are more difficult to accommodate within the same
OFDMA frame. For example, if both the first and third CNUs request
an upstream transmission equivalent to 50% capacity of an OFDMA
frame, then the loading order of subcarriers can determine whether
or not both CNUs can be accommodated in the same frame. For
example, if subcarriers are filled consecutively starting from
subcarrier #1 beginning with the third CNU, then the third CNU will
use subcarriers 1-15. The remaining subcarriers 16-21 however do
not provide the first CNU a 50% capacity because the 50% capacity
line 806 for first upstream profile 802 is before subcarrier #15.
Accordingly, the first CNU transmission cannot be fully
accommodated within the same OFDMA frame and additional overhead is
needed in order to spread the first CNU transmission, over multiple
OFDMA frames.
[0066] Embodiments as further described below can be used to
alleviate this problem. Specifically, in an embodiment, the
upstream bit loading profile of a CNU can be capacity balanced by
adjusting the order in which subcarriers are filled by the CNU.
This is illustrated in FIG. 9, which shows the capacity balancing
of an upstream bit loading profile 902.
[0067] As shown in FIG. 9, bit loading profile 902 is unbalanced
with subcarriers 1-10 being nulled and unable to carry any bits,
and subcarriers 11-20 each having a certain bit loading. Because of
this unbalance, the CNU can only use subcarriers 11-20 or a portion
thereof for any upstream transmission, which constrains the use of
the subcarriers between multiple CNUs and may cause overlap between
CNUs. For example, if an upstream time grant of a given start time
and length (in TQs) is mapped to frequency according to profile
902, then the start time may map to some of subcarriers 1-10.
However, because the CNU cannot transmit any bits on those
subcarriers, it may end up transmitting on the subcarriers starting
with subcarrier #11. However, this may overlap with a transmission
of another CNU with the same profile and a different start time.
This problem can be resolved according to two different embodiments
as further described below.
[0068] In one embodiment, bit loading profile 902 can be capacity
balanced by adjusting the order of subcarriers within the profile
to generate a capacity balanced bit loading profile 904.
Specifically. subcarriers 1-10 are interleaved with subcarriers
11-20 as shown in FIG. 9, such that the bit loading, is uniform
over any two consecutive subcarriers of the profile. The CNU uses
bit loading profile 904 according to the adjusted subcarrier
loading order, for example filling subcarrier. #11, then subcarrier
#1, then subcarrier #12, and so on, or vice versa starting from
subcarrier #10.
[0069] In another embodiment, suitable when the CNU(s) have similar
bit loading profiles, a total number of bits per OFDMA frame (frame
capacity) is calculated using the bit loading profile. Each CNU
then maintains a buffer that is equivalent to the OFDMA frame (with
equal capacity to the calculated frame capacity). For every OFDMA
frame, each CNU fills the buffer (as if it was filling the OFDMA
frame, i.e., subcarrier by subcarrier) with actual data, when it
has upstream MAC data to send, and with null data, when it has no
upstream MAC data to send. The CNUs fill their respective buffers
in a time synchronized manner such that each CNU fills the same
buffer element at the same time. Each CNU PHY then maps the
contents of the buffer to subcarriers and only transmits those
subcarriers filled with actual data from the buffer. Because the
upstream time grants from the OLT/CLT are never overlapping, at any
time only one CNU can be filling actual data to subcarriers while
the other CNUs will be filling null data to the same subcarriers.
Additionally, only the one CNU that filled actual data to the
subcarriers transmits on the subcarriers during the OFDMA
frame.
[0070] Capacity balancing can also he used even in situations in
which the CNUs served by the FCU have proportional upstream hit
loading profiles as described above in FIG. 8A. For example, as
shown in FIG. 10, upstream bit loading profiles 1002 and 1004,
while proportional to each other, are unbalanced across
subcarriers. The unbalance can complicate the allocation of
subcarriers to the CNUs within the same OFDMA frame. In an
embodiment, profiles 1002 and 1004 can be capacity balanced to
result in profiles 1006 and 1008. Profiles 1006 and 1008 remain
proportional to each other but are also capacity balanced across
subcarriers.
[0071] In an embodiment, as described above, capacity balancing of
upstream bit loading profiles can be performed by the FCU. As
described above, the FCU PHY has knowledge of the upstream bit
loading profiles of CNUs that it serves. For example, the ECU can
measure the upstream bit loading profile for a CNU, by measuring
the SNR on each subcarrier from the CNU and calculating a symbol
bit loading for each subcarrier based on the SNR measurement. In an
embodiment, the FCU can compare the upstream bit loading profiles
of CNUs that it serves and can decide to adjust one or more the
upstream bit loading profiles to facilitate the sharing of upstream
OFDMA frames by the CNUs. For example, the FCU (e.g., using a PHY
controller, such as PHY controller 720) can adjust the first
upstream bit loading profile of a first CNU based on a comparison
of the first upstream bit loading profile with a second upstream
bit loading profile of a second CNU. The adjustment can be in order
to render the first and second bit loading profiles proportional to
one another across subcarriers in the OFDMA frame. Alternatively or
additionally, the adjustment can be in order to capacity balance
the first bit loading profile across subcarriers in the OFDMA
frame.
[0072] FIG. 11 illustrates an example process 1100 according to an
embodiment. Example process 1100 is provided for the purpose of
illustration only and is not limiting of embodiments. Example
process 1100 can be performed by a CNU, such as example CNU 300, in
order to map a MAC bit stream to an upstream scheduled
multi-subcarrier frame. In an embodiment, the multi-subcarrier
frame includes an OFDMA frame that includes a plurality of time
consecutive OFDMA symbols.
[0073] As shown in FIG. 11, process 1100 begins in step 1102, which
includes receiving a MAC bit stream. In an embodiment, the MAC bit
stream is received from a MAC layer via a MAC-PHY interface, such
as an XGMII interface. Subsequently, process 1100 proceeds to step
1104, which includes determining a transmission time duration for
the MAC bit stream. In an embodiment, step 1104 includes
determining the transmission time duration for the MAC bit stream
based on a bit size of the MAC bit stream and an upstream bit
loading profile. The upstream bit loading profile determines for
each available subcarrier of the multi-subcarrier frame the number
of bits that can be carried by the subcarrier in one symbol of the
frame.
[0074] Process 1100 then proceeds to step 1106, which includes
translating the transmission time duration into a frame number that
identifies an upstream scheduled multi-subcarrier frame and a
subcarrier group, which identifies a plurality of subcarriers of
the multi-subcarrier frame. Then, in step 1108. process 1100
includes determining whether or not all subcarriers of the
subcarrier group have been filled with respective bits of the MAC
bit stream. If the answer is yes, process 1100 proceeds to step
1110, which includes transmitting the multi-subcarrier frame,
symbol per symbol. Otherwise, process 1100 proceeds to step
1112.
[0075] Step 1112 includes identifying the next subcarrier of the
subcarrier to fill with bits from the MAC bit stream. The next
subcarrier may or may correspond to the next subcarrier in
frequency of the subcarrier group. For example, as described above
in FIGS. 9 and 10, the filling order of subcarriers can be shuffled
according to embodiments to result in capacity balanced upstream
bit loading profiles for CNUs.
[0076] Process 1100 then proceeds to step 1114, which includes
determining a symbol bit loading for the subcarrier, where the
symbol bit loading indicates a number of bits that can be carried
by the subcarrier in one symbol time. In an embodiment, the symbol
bit loading is determined from the upstream bit loading profile.
Then, in step 1116, process 1100 includes determining, using the
symbol bit loading, a total number of bits that can be carried by
the subcarrier across the multiple time consecutive symbols of the
multi-subcarrier frame. Process 1100 then proceeds to step 1118,
which includes mapping bits from the MAC bit stream to the
subcarrier in accordance with the total number of bits determined
in step 1116. Process 1100 then returns to step 1108.
[0077] Embodiments have been described above with the aid of
functional building blocks illustrating the implementation of
specified functions and relationships thereof. The boundaries of
these functional building blocks have been arbitrarily defined
herein for the convenience of the description. Alternate boundaries
can be defined so long as the specified functions and relationships
thereof are appropriately performed.
[0078] The foregoing description of the specific embodiments will
so fully reveal the general nature of the disclosure that others
can, by applying knowledge within the skill of the art, readily
modify and/or adapt for various applications such specific
embodiments, without undue experimentation, without departing from
the general concept of the present disclosure. Therefore, such
adaptations and modifications are intended to be within the meaning
and range of equivalents of the disclosed embodiments, based on the
teaching and guidance presented herein. It is to be understood that
the phraseology or terminology herein is for the purpose of
description and not of limitation, such that the terminology or
phraseology of the present specification is to be interpreted by
the skilled artisan in light of the teachings and guidance.
[0079] The breadth and scope of embodiments of the present
disclosure should not be limited by any of the above-described
exemplary embodiments, but should be defined only in accordance
with the following claims and their equivalents.
* * * * *