U.S. patent application number 12/245535 was filed with the patent office on 2009-10-08 for method for efficient packet framing in a communication network.
This patent application is currently assigned to NXP B.V.. Invention is credited to Vipin Aggarwal, Rahul Malik.
Application Number | 20090254794 12/245535 |
Document ID | / |
Family ID | 41037659 |
Filed Date | 2009-10-08 |
United States Patent
Application |
20090254794 |
Kind Code |
A1 |
Malik; Rahul ; et
al. |
October 8, 2009 |
METHOD FOR EFFICIENT PACKET FRAMING IN A COMMUNICATION NETWORK
Abstract
Techniques to reduce the transmission overheads in a
communication system are disclosed. In an embodiment, a method
described herein relates to the elimination of redundant padding to
realize an integer number of FEC code-words during the FEC-encoding
process of transmission as well as the reduction/elimination of
redundant padding to realize an integer number of transmission
symbols during the subcarrier modulation mapping process of
transmitting OFDM/ACMT/DMT symbols. The techniques are described in
the context of a communication system based on the MoCA
specification. Furthermore, techniques for channel-profiling,
channel-estimation and bandwidth request/grant signaling that
facilitate the realization of the method of reduction of
transmission overheads in a MoCA system are also described.
Inventors: |
Malik; Rahul; (Bangalore,
IN) ; Aggarwal; Vipin; (Irvine, CA) |
Correspondence
Address: |
NXP, B.V.;NXP INTELLECTUAL PROPERTY & LICENSING
M/S41-SJ, 1109 MCKAY DRIVE
SAN JOSE
CA
95131
US
|
Assignee: |
NXP B.V.
Eindhoven
NL
|
Family ID: |
41037659 |
Appl. No.: |
12/245535 |
Filed: |
October 3, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61042586 |
Apr 4, 2008 |
|
|
|
Current U.S.
Class: |
714/776 ;
714/E11.032 |
Current CPC
Class: |
H04L 5/0046 20130101;
H04L 1/0041 20130101; H04L 27/2602 20130101; H04L 5/006 20130101;
H04L 1/0083 20130101; H04B 2201/709709 20130101; H04L 1/0056
20130101 |
Class at
Publication: |
714/776 ;
714/E11.032 |
International
Class: |
H03M 13/05 20060101
H03M013/05; G06F 11/10 20060101 G06F011/10 |
Claims
1. A method for generating a Forward Error Correction (FEC) encoded
frame for use in communicating data between nodes over a network,
the method comprising: identifying a set of FEC code-words having
different sizes, the set of FEC code-words including a largest size
FEC code-word; encoding as much of a payload as possible into one
or more FEC code-words of the largest size FEC code-word; and
encoding a remainder portion of the payload into a last FEC
code-word, the last FEC code-word being the smallest possible FEC
code-word of the set of FEC code-words; wherein the combination of
the one or more largest size FEC code-words and the last FEC
code-word forms a shortened FEC encoded frame.
2. The method of claim 1 further comprises adding an FEC pad to the
payload, wherein the size of the FEC pad is selected so that the
remainder portion of the payload and the FEC pad fill the last FEC
code-word.
3. The method of claim 2 further comprising removing the FEC pad to
generate a shortened last FEC code-word and using the shortened
last FEC code-word to form the shortened FEC encoded frame.
4. The method of claim 1 wherein the set of FEC code-words
comprises FEC code-words of sizes (32, 40), (36, 44), (64, 74),
(128, 140), and (192, 208) bytes.
5. The method of claim 1 further comprising: reducing the adaptive
constellation multi-tone (ACMT) pad overhead required to ACMT
modulate a data frame to form an ACMT-modulated frame, the
reduction of said ACMT-pad resulting in a shortened ACMT modulated
frame, said method comprising the steps of: determining a number of
ACMT symbols that reduces the medium-occupancy of the associated
ACMT modulated frame; and determining a reduced ACMT pad to be
appended to the data frame, the resultant ACMT padded data frame,
when modulated, resulting in the number of ACMT symbols, the
resultant ACMT symbols being of sizes that reduce medium occupancy,
the aggregate of the ACMT modulated symbols being referred to as a
shortened ACMT modulated frame.
6. The method of claim 1 further comprising generating a shortened
adaptive constellation multi-tone (ACMT) modulated frame from the
shortened FEC encoded frame, wherein generating the shortened ACMT
modulated frame comprises: establishing a set of ACMT modulation
symbols having different sizes, the set of ACMT modulation symbols
including a largest size ACMT modulation symbol; encoding as much
of the shortened FEC encoded frame as possible into one or more
ACMT modulation symbols of the largest size ACMT modulation symbol;
and encoding a remainder portion of the shortened FEC encoded frame
into a tail ACMT modulation symbol, the tail ACMT modulation symbol
being the smallest possible ACMT modulation symbol of the set of
ACMT modulation symbols; wherein the combination of the one or more
largest size ACMT modulation symbols and the tail ACMT modulation
symbol form the shortened ACMT modulated frame.
7. The method of claim 6 further comprising adding an ACMT pad to
the shortened FEC encoded frame, wherein the size of the ACMT pad
is selected so that the remainder portion of the shortened FEC
encoded frame and the ACMT pad fill the tail ACMT modulation
symbol.
8. The method of claim 6 wherein the set of ACMT modulation symbols
comprises ACMT modulation symbols of 32, 64, 128, and 256
tones.
9. A method for generating an adaptive constellation multi-tone
(ACMT) modulated frame for use in communicating data between nodes
over a network, the method comprising: establishing a set of ACMT
modulation symbols having different sizes, the set of ACMT
modulation symbols including a largest size ACMT modulation symbol;
encoding as much of a payload as possible into one or more ACMT
modulation symbols of the largest size ACMT modulation symbol; and
encoding a remainder portion of the payload into a tail ACMT
modulation symbol, the tail ACMT modulation symbol being the
smallest possible ACMT modulation symbol of the set of ACMT
modulation symbols; wherein the combination of the one or more
largest size ACMT modulation symbols and the tail ACMT modulation
symbol form a shortened ACMT modulated frame.
10. The method of claim 9 further comprising adding an ACMT pad to
the payload, wherein the size of the ACMT pad is selected so that
the remainder portion of the payload and the ACMT pad fill the tail
ACMT modulation symbol.
11. The method of claim 9 wherein the set of ACMT modulation
symbols comprises ACMT modulation symbols of 32, 64, 128, and 256
tones.
12. The method of claim 9 further comprising determining a number
of ACMT modulation symbols that reduces the medium-occupancy of the
associated ACMT modulated frame.
13. A method for decoding a Forward Error Correction (FEC) encoded
frame that is used in communicating data between nodes over a
network, the method comprising: inserting an FEC pad of a
predetermined content and size in between the data and parity of a
shortened last FEC code-word of a shortened FEC encoded frame,
resulting in an FEC encoded frame; decoding the FEC encoded frame
to determine an FEC padded data frame; and discarding the FEC pad
to recover an underlying data frame.
14. A method for determining a modulation profile for use in
communicating data between nodes over a network, the method
comprising: transmitting a legacy modulation profiling sequence
from a transmitter to a receiver; using the received modulation
profiling sequence to determine the signal to noise ratio of legacy
tone positions; and determining the signal-to-noise ratio at the
tone positions of a shortened adaptive constellation multi-tone
(ACMT) modulation symbol by interpolation of the signal-to-noise
ratios of the legacy tone-positions.
15. The method of claim 14 further comprising communicating the
determined modulation profile of the reduced-size ACMT symbol from
the transmitter to the transmitter.
16. A method determining a modulation profile for use in
communicating data between nodes over a network, the method
comprising: determining a modulation profile for a shortened
adaptive constellation multi-tone (ACMT) modulation symbol from a
modulation profile of a legacy ACMT modulation symbol, the
determination including applying a common and pre-determined set of
rules to the modulation profile of the legacy ACMT symbol to
determine the modulation profile of the shortened ACMT modulation
symbol.
17. The method of claim 16 wherein the bit-loading capacity of a
tone of a shortened ACMT modulation symbol is determined as the
minimum of the bit-loading capacities of adjacent tones of the
legacy ACMT modulation symbol.
18. The method of claim 16 further comprising communicating a
preamble type in use by a transmitter, the modulation profile used
by the transmitter in transmitting a shortened ACMT modulated
frame, the cyclic-prefix in use by the transmitter for every ACMT
symbol, the duration of the transmission, and the ACMT-pad used by
the transmitter in its transmission.
19. The method of claim 16 further comprising determining channel
estimates at tone positions of the shortened ACMT symbol based on
channel estimates at tone positions of legacy ACMT modulation
symbols as determined from a legacy preamble by determining the
size of the shortened ACMT modulation symbol prior to receiving it
and interpolating the channel estimates at the tone positions of
the legacy ACMT modulation symbol to determine the channel
estimates at the tone positions of the shortened ACMT modulation
symbol.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is entitled to the benefit of provisional
U.S. Patent Application Ser. No. 61/042,586, filed Apr. 4, 2008,
the disclosure of which is incorporated by reference herein in its
entirety.
FIELD OF THE INVENTION
[0002] The invention relates to a communication system and more
particularly to a communication system using adaptive constellation
multi-tone (ACMT) modulation.
BACKGROUND OF THE INVENTION
[0003] Driven by the increasing prevalence of digital content and
multi-media applications, of late there has been a dramatic growth
in the need for home networking. This has fuelled new development
of home networking technology both wired and wireless. One such
technology--Multimedia over Coax Alliance (MOCA) V1.0 Specification
(identified herein as [1] or `the standard`) describes the MAC and
PHY layers for high-rate communications over the coaxial TV-cable
plant that is present in most homes. MoCA makes use of a 256-tone
OFDM based-PHY to provide for a data-rate of up to 310 Mbps at a
range of up to 300 feet on a 50 MHz channel. In order to provide
for reliable communications, the standard specifies the use of a
Reed Solomon (RS) forward error correction scheme drawn from Galois
Field GF(256) with code-words having sizes chosen from the set
{(32,40), (36,44), (64,74), (128,140), (192,208)} as specified in
the standard. The respective byte-error correction capabilities for
these codes are {4, 4, 5, 6, 8} respectively. Thus, the (32,40)
code-word can correct 4 byte-errors in a block of 32
information-bytes using 8 parity-bytes, while the (192,208)
code-word can correct for 8 byte-errors in a block of 192
information-bytes using 16 parity-bytes. Of the code-words
specified in the standard, the (36,44) code is used only for beacon
transmission and not for data transmission.
[0004] FIG. 1 (Prior-art) depicts the steps carried out by a
standard compliant transmitter in converting a MAC-packet to a
PHY-packet for transmission over the channel. MAC-frame 101 depicts
a packet which is handed to the PHY for transmission. The PHY
performs FEC-padding by appending redundant pad information 106 to
the MAC-frame 101 to produce resultant FEC-padded frame 105.
[0005] The FEC-padded frame 105 is encrypted to produce the
encrypted-frame 110. The encrypted-frame 110 is FEC-encoded into
individual code-blocks each code-block constituted of a
data-section and a parity-section. As an example, we depict the
encoding of encrypted-frame 110 into two FEC code-blocks--116 and
117, each of which is constituted of data-section--116a and 117a,
and parity-section--116b and 117b, respectively. The collective
FEC-encoded frame is referred to as FEC-encoded frame 115 in FIG.
1.
[0006] The FEC-pad 106 applied to MAC-frame 101, above is
determined such that the eventual FEC-encoded frame can be
constituted of an integer number of FEC code-words.
[0007] An ACMT-pad 121 comprising of redundant pad information is
appended to FEC-encoded frame 115 to produce an ACMT-padded frame
120, as shown in FIG. 1. The ACMT-padded frame 120 is Byte
scrambled to produce a Byte-scrambled frame 125, as shown in the
Figure.
[0008] The Byte-scrambled frame 125 is further decomposed into an
integer number (three as per this example) ACMT symbols--130a, 130b
and 130c, collectively called the Subcarrier modulation mapped
frame 130.
[0009] The ACMT-pad 121 applied to FEC-encoded frame 115, above is
determined such that the eventual Subcarrier modulation mapped
frame 130 can be constituted of an integer number of ACMT
symbols.
[0010] The Subcarrier modulation mapped frame 130 is bin-scrambled
to produce a bin scrambled frame 135. The PHY performs ACMT
modulation on 135 and inserts the appropriate preamble 141 to
generate the ACMT Modulated frame 140. Frame 140 is further
filtered and up-converted to the appropriate RF-carrier frequency
to generate the final PHY packet 145, which is transmitted over the
channel.
[0011] A MoCA standard compliant receiver receives the transmitted
PHY packet 145 and demodulates, decodes and decrypts the packet to
recover the originally transmitted MAC-frame 101.
[0012] The MoCA PHY makes use of an adaptive constellation
multi-tone (ACMT) modulation scheme whereby a transmitter modulates
each tone of its OFDM-symbol differently in accordance with the SNR
expected for that tone at the receiver, for a particular
(transmitter, receiver) pair. Pre-requisite to using
ACMT-modulation is the profiling of the channel between all-pairs
of nodes in the network. The standard defines a means whereby a
new-node (NN) joining a network performs modulation profiling with
all existing nodes (ENs) in the network, allowing the NN and ENs to
determine the per-tone bit-loading pattern to be used for
communication between them. Additionally, nodes (NN and ENs) also
determine the preamble-type to be used for data communication
between them.
[0013] Nodes refresh their profile information during periodic link
maintenance operations (LMOs) as specified in the standard. In
addition to updating their modulation profiles and preamble-types,
MoCA nodes also determine the delay-spread of the channel between
them and their peer-nodes and correspondingly adjust their
cyclic-prefix in order to compensate for the same.
[0014] The modulation profiling of the channel between two nodes is
performed by the transmitter sounding the channel with a packet
comprising 256-tone ACMT symbols, referred to as a `Type-1 Probe`
in the standard. The receiver determines the per-tone SNR on each
tone and determines its bit-loading capacity. It also determines
the preamble-type to be used for subsequent transmissions from the
transmitter. The determined per-tone bit-loading capacity and
preamble-type are fed-back to the transmitter by means of a `Type-1
Probe Report` as described in the standard. The transmitter uses
this modulation profile to effect subsequent transmissions. The sum
of the per-tone bit-loading capacities across all tones in the
256-tone ACMT symbol is equivalent to the number of bits per ACMT
symbol defined as Nbas in the standard and henceforth referred to
as Nbas256.
[0015] Likewise, the transmission of Type-3 Probes and Type-3 Probe
reports as defined in the standard are used to determine the cyclic
prefix to be used.
[0016] Collectively, the modulation-profile, preamble-type and
cyclic-prefix to be used for a transmission/reception are referred
to as a `PHY-Profile`.
[0017] Depending on the nature of the transmission and its
recipients, the standard specifies the use of different
PHY-profiles between two nodes. In general, the specific
bit-loading pattern, preamble-type and cyclic-prefix to be used for
communication between two nodes may be identified by the 3-tuple
comprising: the source node identifier, the destination node
identifier and the PHY-profile identifier.
[0018] Nodes in a MoCA network exchange data with one another using
a TDMA-based MAC protocol. One of the nodes in the network is
designated as the network coordinator (NC)--which in addition to
transacting data on the network, is responsible for coordinating
medium-access among all nodes on the network, among other functions
defined in [1]; while the other nodes are referred to as
existing-nodes (ENs).
[0019] An EN, with data to transmit to another node first transmits
a reservation-request (RR) to the NC. A RR may consist of a
plurality of Request Elements, each of which reserves bandwidth for
a particular transmission. The standard specifies two types of
Request elements--Asynchronous Data/Control Reservation Request
element and Link-Probe Reservation Request element. The
Asynchronous Data/Control Reservation Request element is used for
reserving bandwidth for upper-layer data and MoCA control frame
transmissions, while the Link Probe Reservation Request Element is
used for reserving bandwidth for probe transmissions.
[0020] As per the standard, the Asynchronous Data/Control
Reservation Request Element comprises information elements as
listed in the structure below:
TABLE-US-00001 Asynchronous Data/Control Reservation Request
Element := { FRAME_SUBTYPE FRAME_TYPE DESTINATION PHY_PROFILE
REQUEST_ID PARAMETERS PRIORITY DURATION }
[0021] The NC computes a schedule for transmission based on the
Reservation Request Elements received from nodes in its network
during a scheduling interval referred to as a `MAP-cycle` in the
standard. The NC further broadcasts a `MAP-frame` which defines the
schedule for all medium activity in the subsequent MAP-cycle to all
ENs in the network. Nodes in the network then transmit and/or
receive data in accordance with the schedule of the MAP-frame.
[0022] A MAP-frame is comprised of a plurality of allocation-units
(AUs), each of which specifies an allocation of time on the medium
to a transmission as requested via a request element. The standard
specifies two types of AUs--Probe Allocation Unit (PAU) and Data
Allocation Unit (DAU) respectively.
[0023] A PAU is used to allocate time/bandwidth to a probe
transmission.
[0024] A DAU is used to allocate bandwidth to data and control
traffic on the network, providing information about the start-time,
the type of transmission to be scheduled and the
profile-identifier, along with the source and destination node IDs
for the transmission. As per the standard, a DAU comprises of
information elements as listed in the structure below:
TABLE-US-00002 Data Allocation Unit := { FRAME_SUB_TYPE FRAME_TYPE
SRC DESTINATION PHY_PROFILE REQUEST_ID IFG_TYPE OFFSET }
[0025] In accordance with the methods of the standard, the process
of computing the FEC-pad 106 at the transmitter is such that the
receiver needs knowledge only of the number of bits per ACMT symbol
and the number of ACMT symbols in the PHY data packet payload in
order to unambiguously determine the number and sizes of the RS
code-words in the packet, thereby setting up the receiver for
correct reception.
[0026] A MoCA receiver may determine the number of ACMT symbols to
be received based on the difference in the OFFSET field between
successive allocation-units in the MAP-frame, as per the method in
the standard. Likewise, a receiver may determine the number of bits
per ACMT symbol, the preamble-type and the length of cyclic-prefix
based on the PHY_PROFILE, SRC and DESTINATION fields specified in
the DAU.
[0027] As per FIG. 1, a MoCA PHY packet comprises of a preamble 141
and the PHY data payload 142. While payload 142 carries the
encrypted, encoded, scrambled and modulated MAC-data, preamble 141
comprises of a known sequence. The various parts of preamble 141
are used to facilitate various aspects of packet acquisition
including AGC gain settling, symbol timing estimation, frequency
offset estimation etc. The channel estimation sequence (CES) is
used by the receiver to derive channel-estimates, which are
subsequently used to equalize the payload ACMT symbols prior to
demodulation and decoding. The MoCA preambles specified in the
standard make use of a CES based on 256-tone ACMT symbols.
[0028] While MoCA [1] was originally designed to provide a usable
MAC-layer throughput of 125 Mbps, it was soon determined that
higher throughputs were required to support the evolving
`bandwidth-hungry` applications on home networks. MoCA V1.1 Draft
Specification (referred to herein as [2]) was defined as a set of
MAC-layer extensions to [1] that among other functionality,
augmented the MAC-layer throughput of [1] to 180 Mbps. However,
this still falls short of requirements set by newer network usage
scenarios, which require even higher PHY data-rates.
SUMMARY
[0029] A method for reducing the FEC-pad overhead required to
encode a data-frame to form an FEC-encoded frame, the reduction of
said FEC-pad resulting in a shortened FEC encoded frame, said
method comprising the step of determining a number of FEC
code-words that minimizes the parity-overhead of the
FEC-encoded-frame, the step of determining an FEC-pad of known
values to be appended to the data-frame, said FEC-pad resulting in
the shortest possible last FEC code-word in resultant FEC-encoded
frame, the step of determining a shortened last FEC code-word from
said last FEC code-word, said shortened last FEC code-word
comprising the data of last FEC code-word without FEC-pad; and the
parity of last FEC-code-word, the step of determining a shortened
FEC-encoded frame, said shortened FEC-encoded frame comprising of a
first group of code-words corresponding to all but the last FEC
code-word of the FEC-encoded frame and a shortened last FEC
code-word. Additionally, the method of the decoding said encoded
frame, said method comprising the step of inserting an FEC-pad of
known values in between the data and parity of the shortened last
FEC-code-word of the shortened FEC-encoded frame, resulting in an
FEC-encoded frame, the step of decoding said FEC-encoded-frame to
determine an FEC-padded data-frame, and the step of discarding said
FEC-pad to recover the under-lying data-frame. Furthermore, the
method can further comprise the step of determining a number of
ACMT-symbols that reduces the medium-occupancy of the associated
ACMT modulated frame, and the step of determining a reduced
ACMT-pad to be appended to the data-frame, the resultant
ACMT-padded data-frame when modulated resulting in the number of
ACMT-symbols determined above, the resultant ACMT symbols being of
sizes that reduce medium occupancy, the aggregate of the ACMT
modulated symbols determined above referred to as a shortened ACMT
modulated frame. In addition, the method can further comprise the
step of determining a reduced ACMT-pad to be appended to the
data-frame the resultant ACMT-padded data-frame when modulated
resulting in the number of ACMT-symbols determined above,
all-but-last of the resultant ACMT symbols being of size
corresponding to the largest ACMT symbol, the last ACMT symbol
being of size less than or equal to the largest ACMT symbol, the
aggregate of the ACMT modulated symbols determined above referred
to as a shortened ACMT modulated frame.
[0030] Another embodiment is a method for generating a PHY-packet
from a data-frame, prior to transmission, said method comprising
the step of determining an FEC-pad of known values that results in
a minimum parity overhead when encoding the data-frame above to
form an FEC-padded frame, the step of FEC-encoding said FEC-padded
frame to determine an FEC encoded frame, the step of determining a
shortened FEC encoded frame by shortening said FEC encoded frame,
the step of determining an ACMT-pad that when appended to said
shortened FEC encoded frame, results in an ACMT-padded frame, the
step of determining a shortened ACMT-modulated frame by modulating
said ACMT-padded frame to the minimum number of ACMT-symbols,
having the minimum medium occupancy, and the step of determining a
PHY-packet from said ACMT-modulated frame. Furthermore the method
can further comprise the step of determining an encryption-pad that
when appended to the MAC-frame results in an encryption-padded
frame, the step of encrypting said encryption-padded frame to
determine an encrypted frame, and the step of determining an
FEC-padded-frame, a FEC encoded frame, a shortened FEC encoded
frame, an ACMT pad, an ACMT-padded frame, a shortened ACMT
modulated frame.
[0031] Additionally, a system comprising a transmitter and a
receiver is disclosed wherein the transmitter and the receiver are
configured to determine the modulation profile for a reduced size
ACMT symbol by the transmitter transmitting a legacy modulation
profiling sequence to the receiver, and the receiver using received
modulation profiling sequence to determine the signal to noise
ratio of the legacy tone-positions, determining the signal to noise
ratio at the tone positions of the reduced size ACMT symbol by
interpolation of the signal to noise ratios of the legacy
tone-positions, and communicating the determined modulation profile
of the reduced-size ACMT symbol to the transmitter.
[0032] Also disclosed is a system comprising a transmitter and
receiver configured to determine the modulation profile for a
reduced size ACMT symbol from the modulation profile of a legacy
ACMT symbol by the transmitter and receiver applying a common and
pre-determined set of rules to the modulation profile of the legacy
ACMT symbol to determine the modulation profile of the reduced-size
ACMT symbol. Furthermore, the transmitter and receiver can apply a
common set of rules where the bit-loading capacity of a tone of a
reduced size ACMT symbol is determined as the minimum of the
bit-loading capacities of the adjacent tones of the legacy ACMT
symbol, as determined from its modulation profile.
[0033] Additionally, a transmitter can be configured to determining
the parameters required by the receiver to receive a data-packet
transmitted using the method for generating a PHY-packet described
above. The transmitter communicates appropriate parameters prior to
transmission of said data-packet, where the parameters comprises
the preamble-type in use by the transmitter, the modulation-profile
used by the transmitter in transmitting the packet, the
cyclic-prefix in use by the transmitter for every ACMT symbol, the
duration of the transmission, and the ACMT-pad used by the
transmitter in its transmission. The transmitter further can be
configured to transmit information to the receiver via a third-node
in the network. The transmitter further can determine the
parameters by selecting the preamble-type, modulation-profile and
cyclic-prefix to be used based on the source, destination and type
of the packet to be transmitted, determining the size of an
encryption-pad to be applied to the packet so that the resultant
encryption-padded packet may be encrypted to form an encrypted
packet, determining the size of a FEC-pad to be applied to the
encrypted-packet so that the resultant FEC-padded packet may be
encoded to obtain a shortened FEC-encoded frame that has a reduced
parity overhead, and determining the size of an ACMT-pad to be
applied to the shortened FEC-encoded frame such that the resulting
ACMT-padded frame may be modulated using the available symbol-sizes
to construct a shortened ACMT modulated frame that when transmitted
minimizes the medium occupancy, the resultant medium occupancy
determined to be the duration.
[0034] The receiver corresponding can be configured to determine
the parameters of a packet to be received based on the information
received from the transmitter by determining the number of ACMT
symbols to be received based on the duration of the packet, the
preamble type and the cyclic-prefix, determining the size of the
various ACMT symbols using the determined duration and the
determined number of ACMT symbols, applying the knowledge of the
methods of the transmitter in determining the ACMT modulated frame,
determining the length of the shortened FEC encoded frame using
knowledge of the modulation-profiles of the various symbol-sizes
along with the sizes of the ACMT-symbols, and determining the size
of the various FEC code-words and the FEC-pad to be inserted in the
shortened FEC code word so as to recover the FEC encoded-frame.
[0035] The receiver can also be configured to determine the
channel-estimates at the tone-positions of a shortened ACMT-symbol
based on channel estimates at the tone positions of legacy ACMT
symbols as determined from the legacy preamble by determining the
size of the shortened ACMT symbol prior to receiving it and
interpolating the channel estimates at the tone positions of the
legacy ACMT symbol to determine the channel estimates at the tone
positions of the shortened ACMT symbol.
[0036] Other systems, methods, features, and advantages of the
present disclosure will be or become apparent to one with skill in
the art upon examination of the following drawings and detailed
description. It is intended that all such additional systems,
methods, features, and advantages be included within this
description, be within the scope of the present disclosure, and be
protected by the accompanying claims.
BRIEF DESCRIPTION OF DRAWINGS
[0037] Many aspects of the disclosure can be better understood with
reference to the following drawings. The components in the drawings
are not necessarily to scale, emphasis instead being placed upon
clearly illustrating the principles of the present disclosure.
Moreover, in the drawings, like reference numerals designate
corresponding parts throughout the several views.
[0038] FIG. 1 depicts a convention method of framing a packet in a
MoCA network;
[0039] FIG. 2 depicts the method of code-shortening;
[0040] FIG. 3 depicts the method of transmitting a shortened
tail-symbol;
[0041] FIG. 4 depicts the method of transmitting a packet across a
MoCA network;
[0042] FIG. 5 depicts the method of determining the
bit-loading/channel-estimates of shortened ACMT symbols;
[0043] FIG. 6 is a flowchart depicting the method of a transmitter
to generate a reservation request element; and
[0044] FIG. 7 is a flowchart depicting the method of a receiver to
determine the receiver parameters.
DETAILED DESCRIPTION
[0045] Nodes are configured to realize a more optimal packet
framing structure, resulting in a reduction (and in some instances,
elimination) of redundant pad information in the MoCA PHY packet.
This leads to an overall reduction in medium occupancy, the
resulting savings being available for other transmissions, thereby
resulting in an overall increase in throughput of the network.
[0046] Furthermore, these nodes are designed to coexist and
interoperate with legacy nodes in the network. It is understood
that legacy nodes are nodes in the network which have not been
configured to realize a more optimal packet framing structure as
described in this disclosure.
[0047] Each of the code-words specified by the standard has a
different error correction capability in terms of number of
byte-errors that can be corrected in a code-word. As a PHY packet
can be constituted of a number of RS code-words above, the
code-word with the lowest error-correction capability per
unit-information is sufficiently robust to meet the transmission
reliability needs of the over-lying MAC and application-layers. The
number of code-blocks to be used is chosen in a manner that
minimizes the overall number of code-blocks and the amount of
parity-information to be associated with a payload frame, while
generating an FEC encoded frame.
[0048] Using the code-words specified in the standard as exemplary
in the ensuing description, the number of code-blocks Brs to be
used to transmit a payload of M-bytes is determined by equation
(1):
Brs=.left brkt-top.M/192.right brkt-bot.. (1)
[0049] A payload may thus be decomposed into a first (Brs-1)
code-words of size (192,208) and a last code-word of size (Klast,
Nlast) determined by equation (2):
( Klast , Nlast ) = { ( 32 , 40 ) if 0 < M mod 192 .ltoreq. 32 (
64 , 74 ) if 32 < M mod 192 .ltoreq. 64 ( 128 , 140 ) if 64 <
M mod 192 .ltoreq. 128 ( 192 , 208 ) otherwise ( 2 )
##EQU00001##
[0050] RS-codes belong to the class of systematic codes i.e., codes
where the resultant encoded code-word comprises of the original
data suffixed by the parity information. Recognizing this property,
the elimination of the FEC-padding of the payload by transmitting a
shortened last code-word is advocated, as described in the
following.
[0051] The amount of FEC-pad i.e. MFECPad that would be required to
be appended to a payload prior to FEC encoding, such that the
resultant FEC-encoded packet is constituted of Brs code words as
determined above, is given by equation (3), below. Consequently,
the amount of information contained in the last code-word KlastAct
is determined in equation (4).
MFECPad=192*(Brs-1)+Klast-M (3)
KlastAct=Klast-MfecPad (4)
[0052] A transmitter pads the information to be placed in the last
code-word--KlastAct-bytes, with MFECPad-bytes of known values
(which are also known to the receiver). The transmitter encodes the
resultant Klast-bytes to determine a code-word of Nlast-bytes.
[0053] However, in order to optimize usage of the medium, the
transmitter transmits a shortened-last code word comprising of the
KlastAct information bytes suffixed with the (Nlast-Klast) parity
bytes determined during the encoding process. Thus the last
code-word has a length of KlastAct+(Nlast-Klast) bytes.
[0054] Correspondingly, a receiver incorporating the methods
embodied herein inserts a pad of MFECPad-bytes equivalent to what
was used as part of encoding by the transmitter in between the
KlastAct bytes of information and the (Nlast-Klast) bytes of
parity. The resultant Nlast bytes code-word is decoded using
conventional RS-decoding methods.
[0055] The length of the shortened FEC-encoded frame L, is thus
given by equation (5).
L=208*(Brs-1)+KlastAct+(Nlast-Klast) (5)
[0056] FIG. 2 depicts an example application of FEC
code-shortening. Frame 201 represents a payload of M=264-bytes. The
amount of FEC-padding MFECPad that aligns the payload M to an
integer number of code-words Brs, while minimizing the overall
parity overhead is determined using equations (1) through (3).
Thus, as per the present example, Brs=2. The payload may be split
into a first block 211 of size 192-Bytes and a second block
212--which comprises of 72-Bytes of data 212a and 56-bytes of
FEC-pad 212b. The split payload is FEC encoded, the first codeword
221 (corresponding to block 211) being of type (192,208), while the
second codeword 222 (corresponding to block 212) being of type
(Klast,Nlast)=(128,140). Codeword 222 comprises of 72-Bytes of
information 222a, 56-bytes of FEC-pad 222b and 12-bytes of parity
222c. The shortened FEC encoded frame 230 may then be represented
by a first code word 231 (corresponding to codeword 221) and a
shortened last codeword 232 comprising the information 232a
(corresponding to information 222a) and the parity 232c
(corresponding to parity 222c).
[0057] While described in the context of a MoCA system [1] using RS
encoding, it would be apparent to one skilled in the art that
similar methods would apply to alternate coding schemes e.g., LDPC;
and alternate communications systems.
[0058] The use of the redundant ACMT-pad which is appended to a
payload prior to subcarrier modulation mapping such that the
resultant subcarrier modulation mapped frame is comprised of an
integer number of 256-tone ACMT symbols, is reduced by means of
adopting variable sized ACMT symbols.
[0059] A transmitter on transforming a MAC packet to a PHY-packet
prior to transmission reduces/eliminates the need for ACMT-pad by
using a shortened ACMT symbol having a reduced number of tones, and
consequently a lower medium occupancy. The shortened ACMT symbol is
selected from a set of sizes known a-priori to both transmitter and
receiver. The same cyclic-prefix is used on both shortened as well
as legacy 256-tone ACMT symbols.
[0060] In another aspect, a transmitter exploits the fact that
larger ACMT symbols are more efficient i.e. have lower
cyclic-prefix overheads than smaller ones. Such a transmitter
performs subcarrier modulation mapping with the objective of using
the largest available and applicable ACMT symbols first, before
attempting to use shorter symbols.
[0061] As an example, we shall consider the use of shortened
symbols whose length is a sub-multiple of the legacy 256-tone
symbol. In the ensuing description, we shall assume a set of
allowable ACMT symbols as given by {32, 64, 128, 256} tones.
However, it would be apparent that the set of allowable ACMT
symbols may be extended to include other symbol sizes as well.
[0062] Continuing with our illustration of a MAC-payload of M-bytes
which was encoded into a shortened FEC-encoded frame of length L,
as per equation (5), a transmitter determines the number of ACMT
symbols Nsym to be transmitted by applying equation (6).
Nsym=.left brkt-top.8*L/Nbas256.right brkt-bot. (6)
Where, Nbas256 refers to the number of bits that can be
accommodated in a 256-tone ACMT symbol. The value Nbas256 is
determined as part of modulation profiling as described in the
standard.
[0063] Additionally, nodes can be further configured to determine
the number of bits per ACMT symbol for all available symbol sizes
during modulation profiling. As per the present example, nodes
predetermine Nbas32, Nbas64, Nbas128 and Nbas256.
[0064] Thus, in the present example, a subcarrier modulation mapped
frame would comprise of a first (Nsym-1) 256-tone ACMT symbols and
a last tail symbol as determined by equations (7) and (8),
below.
modL=(8*L) mod Nbas256 (7)
[0065] where, modL determines the number of bits to be modulated
into the tail ACMT symbol.
Nbaslast = { Nbas 32 if 0 < mod L .ltoreq. N bas 32 // tail A C
M T symbol is 32 - tone Nbas 64 if 32 < mod L .ltoreq. N bas 64
// tail A C M T symbol is 64 - tone Nbas 128 if 64 < mod L
.ltoreq. Nbas 128 // tail A C M T symbol is 128 - tone Nbas 265
otherwise // tail A C M T symbol is 256 - tone ( 8 )
##EQU00002##
where, Nbaslast represents the number of bits per ACMT symbol of
the last/tail ACMT symbol.
[0066] The required ACMT-pad, MACMTpad to be added to the payload
prior to subcarrier modulation mapping is thus determined by
equation (9).
MACMTpad=.left brkt-top.((Nsym-1)*Nbas256+Nbaslast)/8.right
brkt-bot.-L (9)
While it would be apparent that the most efficient subcarrier
modulation mapped frame that minimizes medium occupancy may not be
comprised of a plurality of the longest ACMT symbol followed by a
shortened tail ACMT symbol i.e., a more efficient subcarrier
modulation mapped frame could have been, for example constructed
using a plurality of shorter ACMT symbols, the above-mentioned
mechanism minimizes the additional signaling required in the
Asynchronous data/control reservation request-element and
data-allocation-unit (DAU) that are required by the MoCA MAC
protocol, as described in a subsequent embodiment. However, it is
understood that all such variants of reducing the overhead of the
ACMT-pad by means of using variable-sized ACMT symbols are
applicable as is apparent to one of ordinary skill in the art.
[0067] FIG. 3 depicts an example application of tail-ACMT symbol
shortening. Carrying forward with the previous example of a
264-Byte frame, the length of the shortened FEC-encoded frame L=292
was determined using (5). The number of symbols Nsym is determined
as per equation (6) and the size of the last symbol and the number
of ACMT-pad bytes required is determined by equations (7) through
(9). As, as example, considering Nbas256=1000; Nbas128=500;
Nbas64=250 and Nbas32=125 and applying the described methods, a
292-byte payload 301 would be appended with a 21-byte ACMT-pad 311
to form a padded-frame 310. The padded frame 310 is then split into
an ACMT-modulated frame 320 constituted by two symbols--321 and 322
of the maximum symbol-size and a shortened tail-symbol of 128-tones
323.
[0068] FIG. 4 depicts the steps carried out by a transmitter in
converting a MAC-packet to a PHY-packet for transmission over the
channel. Packet 401 depicts a MAC-frame of m-bytes which is handed
to the PHY for transmission. The PHY performs DES-padding by
appending a DES-pad 406 of up to 7-bytes so as to generate a
DES-padded frame 405 of length M-bytes, where M is a multiple of 8.
This satisfies the requirements of the standards based DES
encryption which operates on multiples of 8-bytes of data. The size
of the DES-pad MDESpad is determined as per equation (10) and the
DES-padded MAC frame has size M, as determined by equation
(11).
MDESpad=8-(m mod 8) (10)
M=m+MDESpad (11)
[0069] The DES-padded frame 405 is encrypted using the DES
encryption scheme to produce an encrypted frame 410. It would be
apparent that the requirement of DES padding to a multiple of
8-bytes is characteristic of the DES algorithm itself and is
performed here in order to integrate the nodes into a MoCA-system.
In a system that does use DES the steps of generating 405 need not
be used.
[0070] The PHY performs FEC-padding by appending MFECpad bytes of a
pre-determined FEC-pad 416 to the encrypted frame 410 to produce an
FEC-padded frame 415. The FEC padded frame 415 is encoded into
individual code-blocks, each code block constituted of a
data-section and a parity section. As an example, we depict the
encoding of 415 into two FEC code blocks 421 and 422, each of which
is constituted of a data section--421a and 422a, and a parity
section--421b and 422b, respectively. The FEC encoded frame is
collectively referred to as 420.
[0071] FEC code block 421 would have the largest code-word size
(lowest parity overhead); while FEC code block 422 may be one of
the available code-words. Additionally, FEC code block 422 may be
transmitted as a shortened code-word, having a data-section 423a of
size KlastAct bytes, as determined in equation (4), and a parity
section 423b (equivalent to parity-section 422b of FEC code block
422) of (Nlast-Klast) bytes. Collectively, the shortened FEC
encoded frame is referred to by literal 424 in FIG. 4.
[0072] An ACMT-pad 426 of length MACMTpad, as determined in
equation (9) is suffixed to the shortened FEC encoded frame 424 to
produce and ACMT padded frame 425. The resultant frame 425 is byte
scrambled to produce the Byte-scrambled frame 430.
[0073] The byte-scrambled frame 430 is decomposed into an integer
number (three as per this example) ACMT symbols--435a, 435b and
435c, collectively called the subcarrier modulation mapped frame
435.
[0074] Symbols 435a and 435b would be the longest available and
applicable ACMT symbol, while symbol 435c may be any one of the
available ACMT symbols. The length of symbol 435c may be determined
as per equation (8).
[0075] The symbols of the subcarrier modulation mapped frame 435
are bin-scrambled to produce a bin-scrambled frame 440. The PHY
performs ACMT modulation on 435 and inserts the appropriate
preamble 446 to generate an ACMT modulated frame 445. Frame 445 is
further filtered and up-converted to the appropriate RF-carrier
frequency to generate the final PHY packet 450, which is
transmitted on the channel.
[0076] Nodes embodying the methods contained herein determine the
bit-loading profile and the number of bits per ACMT symbol for all
supported symbol sizes using the legacy Type-1 Probes as defined in
the standard. For a reduced-size ACMT symbol whose sub-carrier
positions correspond to the sub-carrier positions of the Type-1
Probe's ACMT symbol, the per-tone SNRs (and consequently
bit-loading) may be determined directly. For a reduced-size ACMT
symbol whose sub-carrier positions do not correspond to the
subcarrier positions of the Type-1 Probe's ACMT symbol, the
per-tone SNRs may be estimated by means of interpolation.
[0077] According to one aspect, the per-tone bit-loading pattern as
determined by the recipient of the Type-1 Probe frame may be
communicated back to the transmitter by means of extending the
existing Type-1 Probe Report, as described in the standard by
altering the LENGTH field as specified in the structure below to
accommodate the bit-loading patterns for the newly defined
symbols--SHORT_BL_PATTERNn. Thus, the Type-1 Probe Report may be
redefined to contain the following fields:
TABLE-US-00003 Type-1 Probe Report := { PROBE_TYPE NUM_ELEMENTS
REPORT_SOURCE REPORT_RECEIVER RELAY_FLAG for ( i = 0; i <
NUM_ELEMENTS; i++){ CHANNEL_SOURCE CHANNEL_RECEIVER PHY_PROFILE
PREAMBLE_TYPE CHANNEL_USABLE MAX_BINS NUM_OF_SYMS
BITS_PER_ACMT_SYMBOL CP_LENGTH GCD_BITMASK TPC_BACKOFF_MAJOR
TPC_BACKOFF_MINOR for (j=0; j < 256; j++){ SC_MOD }
SHORT_BL_PATTERNn } PAYLOAD_CRC }
[0078] A Type-1 Probe Report frame may contain a singularity or a
plurality of SHORT_BL_PATTERNn fields, depending on the number of
supported ACMT symbol sizes. In the instance of when a plurality of
SHORT_BL_PATTERNn fields are included, the order of placement of
SHORT_BL_PATTERNn fields in the Type-1 Probe Report should be
predetermined in order to facilitate correct interpretation of the
frame at both transmitter and receiver. As an example, we shall
assume that the various SHORT_BL_PATTERNn fields are arranged in
descending order of symbol size n.
[0079] A single SHORT_BL_PATTERNn field is defined as follows:
TABLE-US-00004 SHORT_BL_PATTERNn := { for j=0; j<n; j++ {
SC_MODj } }
[0080] Where SC_MODj refers to the bit-loading pattern applicable
on tone j for a n-point ACMT symbol.
[0081] It is understood that new frame-type can be defined to carry
bit-loading profiles of specific symbol sizes.
[0082] The recipient of a Type-1 Probe frame determines the
bit-loading pattern for a 256-tone ACMT symbol and communicates
this to the transmitter via the Type-1 Probe Report Frame, as
defined in the context of legacy nodes. Nodes implemented as
described here can further infer the bit-loading pattern of the
available symbol-sizes by applying a common set of rules on the
legacy (256-tone) bit-loading pattern. The fact that transmitter
and receiver use the same rules would guarantee consistency between
their respectively inferred modulation profiles for a given
symbol-size.
[0083] The bit-loading of tone k of a j-tone ACMT symbol may be
determined as the minimum of the bit-loading on the adjacent tones
of the 256-tone ACMT symbol. As an example, the bit loading of tone
551 of a 128-tone ACMT symbol 550, may be determined as the minimum
of the bit-loading of the adjacent tones--511 and 512 of the
256-tone ACMT symbol 510. As a consequence of this method, nodes
implemented as described here require no additional signaling to
effect the exchange of the modulation-profiles for different
ACMT-symbol-sizes in a MoCA network.
[0084] It is understood that there can be several variations to the
common set of rules practiced by the nodes, for example, the
derived bit-loading of a particular tone may be defined to be the
mean of bit-loading across several tones of the 256-tone symbol; or
in another realization, having a back-off from the value determined
above.
[0085] As discussed previously, the MoCA MAC protocol is built
around TDMA where a node with data to transmit, first transmits a
RR to the NC, which computes a schedule and broadcasts a MAP-frame
defining the schedule of transmissions (in terms of AUs) over the
next MAP-cycle. Nodes in the network then schedule their
transmissions and reception for the next MAP-cycle based on the AUs
contained in the MAP-frame.
[0086] In order to correctly demodulate a PHY packet transmitted in
accordance with the method of FIG. 4, the receiver needs to be
aware of the number of ACMT-symbols, their respective symbol-sizes
and modulation capacity (Nbas); the cyclic-prefix; the number and
size of the FEC code-blocks used; and the amount of DES-pad
applied. While MoCA systems of prior-art required knowledge of only
the PHY-profile in use and the number of ACMT symbols to correctly
setup the receiver for reception, nodes embodying the methods
contained herein, further need knowledge of the number of ACMT-pad
bytes--MACMTpad.
[0087] The asynchronous-data/control request element that defines
the bandwidth requirements for a data/control transmission is
modified to additionally contain the MACMT_PAD field which defines
the number of ACMT-pad bytes used in the transmission, as depicted
in the structure below.
TABLE-US-00005 Asynchronous Data/Control Reservation Request
Element := { FRAME_SUBTYPE FRAME_TYPE DESTINATION PHY_PROFILE
REQUEST_ID PARAMETERS PRIORITY DURATION MACMT_PAD }
[0088] The value of MACMT_PAD can be accommodated in the unused
bits (eg: the reserved PARAMETERS field) of the asynchronous
data/control reservation request element as defined in [1].
[0089] The DAU which is used to allocate bandwidth to a node that
requested for it using a corresponding asynchronous data/control
reservation request element, as defined in [1] may similarly be
modified to additionally contain the MACMT_PAD field as depicted in
the structure below:
TABLE-US-00006 Data Allocation Unit := { FRAME_SUB_TYPE FRAME_TYPE
SRC DESTINATION PHY_PROFILE REQUEST_ID IFG_TYPE OFFSET MACMT_PAD
}
[0090] The MACMT_PAD field can be accommodated in the
unused/reserved bits (eg: the excess bits of the SRC and
DESTINATION fields) of the DAU frame as defined in [1].
[0091] FIG. 6 is a flowchart describing the method to be adopted by
a transmitter to determine the DURATION and MACMT_PAD parameters of
the asynchronous data/control reservation request as defined above,
prior to transmission of a packet as per the steps of FIG. 4.
[0092] The flowchart is invoked in step 600, when there is a m-byte
frame to be transmitted. In step 610, the size of the DES-pad and
consequently the DES-padded frame is determined in using equations
(10) through (11). In step 620, the size of the FEC-pad to be
applied and the number and sizes of the various FEC code words is
determined by means of equations (1) through (4). Further the size
of the shortened FEC-encoded frame L is determined using equation
(5).
[0093] In step 630, the amount of ACMT-pad to be applied in order
to construct an ACMT-modulated frame is determined, applying
equations (6) through (9).
[0094] In step 640, the duration of the packet transmission is
determined based on the number and sizes of the ACMT-symbols as
determined in step 630 and the cyclic-prefix and preamble-type in
use, using the method specified in [1].
[0095] The flowchart terminates in step 650.
[0096] FIG. 7 is a flowchart describing the method to be adopted by
a receiver to determine the necessary parameters to correctly
receive a PHY packet described by the DAU, as defined above.
[0097] The flowchart is invoked in step 700, on receiving a
MAP-frame with a DAU indicating an impending reception to the
receiver. In step 710, the duration of the transmission Nsamp is
computed based on the difference in the OFFSET fields of the DAU of
interest and the subsequent AU contained in the MAP-frame. Using
the cyclic prefix CPlen and preamble-length PreambleLen (based on
the PHY-profile indexed by the 3-tuple--{SRC, DESTINATION,
PHY_PROFILE} contained in the DAU), the number of ACMT symbols Nsym
and the length of the tail ACMT symbol Tsym is determined in 720,
as per equations (12) and (13).
Nsym=.left brkt-top.(Nsamp-PreambleLen)/(256+CPlen).right brkt-bot.
(12)
Where, PreambleLen is the length of the preamble in number of
samples appropriately adjusted in accordance with the conventions
of standard.
Tsym=Nsamp-(Nsym-1)*(256+CPlen)-CPlen (13)
Nbaslast is selected form the number of bits per ACMT symbol for
the various symbol-sizes using Tsym. In step 730, the number of
bytes in the shortened FEC-encoded frame L as transmitted in 424 of
FIG. 4 is determined using equation (14):
L=.left brkt-top.((Nsym-1)*Nbas256+Nbaslast)/8.right
brkt-bot.-MACMTpad (14)
In step 740, the number of FEC code-words Brs and the size of the
last FEC code-word FEClast of the received packet are determined as
per equations (15) and (16).
Brs=.left brkt-top.L/208.right brkt-bot. (15)
FEClast=L mod 208 (16)
[0098] As per the method of the transmitter previously described in
FIG. 2, the first (Brs-1) code words are of type (192,208), while
the parameters of the last FEC code-word are determined as in
equations (17) and (18):
( Klast , Nlast ) = { ( 32 , 40 ) if 0 < FEClast .ltoreq. 32 (
64 , 74 ) if 40 < FEClast .ltoreq. 64 ( 128 , 140 ) if 74 <
FEClast .ltoreq. 128 ( 192 , 208 ) otherwise ( 17 ) KlastAct =
FEClast - ( Klast - Nlast ) ( 18 ) ##EQU00003##
[0099] The flowchart of FIG. 7 terminates in step 750, with the
receiver having determined the number and sizes of the ACMT symbols
and the number and sizes of the FEC-code-words from the DAU. The
receiver can then be setup for correct reception of the packet.
[0100] A receiver can determine the size of the last ACMT symbol to
be received by it, prior to actual reception, based on decoding the
AUs of the MAP-frame, as described in a previous embodiment. The
receiver uses this information along with the received (legacy)
256-tone channel estimation sequence to determine an appropriate
set of channel estimates corresponding to the tone positions of the
shortened ACMT symbol, facilitating its subsequent demodulation.
The channel estimates to be applied to the shortened ACMT symbol
may be based on interpolation across tones of the channel estimates
of the 256-tone channel estimation sequence. Thus, as per the
methods embodied herein, the transmission of additional channel
estimation sequences for reduced size ACMT symbols (in addition to
legacy channel estimation sequences) are not required in order to
practice the method of transmitting a shortened ACMT symbol. It is
understood however that additional channel estimation sequences for
the reduced-size ACMT symbol can be used.
[0101] As an example, consider the tones of 256-tone ACMT symbol
510--for example tone-position 511 and tone-position 512 as
representing the channel estimates at two adjacent tones, estimated
from a 256-tone channel estimation sequence. The channel estimate
of a corresponding tone-position 551 of a reduced size 128-tone
ACMT symbol may be determined by interpolating across the channel
estimates 511 and 512. It would be apparent to one skilled in the
art that the channel estimates of other adjacent tones from
256-tone ACMT-symbol 510 may also be used to determine the channel
estimate at tone-position 551.
[0102] The performance enhancements realizable by nodes
incorporating the teachings embodied herein may be greatly enhanced
by an NC not using the `2600-slot limit` between two transmissions
in the network as defined in the standard.
[0103] It would be apparent to one skilled in the MoCA standard
[1], that the methods incorporated herein may be practiced by a
subset of nodes in a MoCA network to achieve reductions in medium
occupancy during transmissions between them. As such, it would be
apparent that a node incorporating the present invention may
communicate with legacy nodes by reverting to means of
communications specified by the standard. It would be apparent that
the operation of these legacy-nodes would not be hampered by the
nodes practicing the present invention. Thus, it is envisioned that
nodes incorporating the present invention would be inter-operable
and could coexist in a network with legacy nodes.
[0104] While certain embodiments of the invention have been
described above, it will be understood that the embodiments are by
way of example only. Accordingly, the invention should not be
limited based on the described embodiments.
* * * * *