U.S. patent application number 10/430151 was filed with the patent office on 2003-12-18 for method and system of channel analysis and carrier selection in ofdm and multi-carrier systems.
This patent application is currently assigned to ENIKIA L.L.C.. Invention is credited to Durfee, Lawrence F., Logvinov, Oleg, Walvis, Dirk J.M..
Application Number | 20030231582 10/430151 |
Document ID | / |
Family ID | 29420369 |
Filed Date | 2003-12-18 |
United States Patent
Application |
20030231582 |
Kind Code |
A1 |
Logvinov, Oleg ; et
al. |
December 18, 2003 |
Method and system of channel analysis and carrier selection in OFDM
and multi-carrier systems
Abstract
The invention presents a novel method to channel estimation in
OFDM systems. The embodiment of this invention is a block of new
logic and modifications performed to other components of the
system, added to any existing OFDM receiver, which utilizes
information available from other blocks as found in the receiver.
This logic would improve the units' error rate because of the
improved channel quality estimations it makes available. This
improvement is made possible because both channel noise data and
channel signal data are used in the estimation process. This data
goes through a learning process over time and multiple data blocks
for further improvements in the quality of the estimate. This
improvement is possible without any direct communications with
other remote units, but it could be used in a multi-node
environment to improve the performance of the system as the
whole.
Inventors: |
Logvinov, Oleg; (East
Brunswick, NJ) ; Durfee, Lawrence F.; (Washington,
NJ) ; Walvis, Dirk J.M.; (Santa Cruz, CA) |
Correspondence
Address: |
CHRISTINA HILDEBRAND
NORRIS, MCLAUGHLIN & MARCUS
220 EAST 42ND STREET - 30TH FLOOR
NEW YORK
NY
10017
US
|
Assignee: |
ENIKIA L.L.C.
North Plainfield
NJ
|
Family ID: |
29420369 |
Appl. No.: |
10/430151 |
Filed: |
May 6, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60378196 |
May 6, 2002 |
|
|
|
Current U.S.
Class: |
370/208 ;
370/210 |
Current CPC
Class: |
H04L 27/2657 20130101;
H04L 1/20 20130101; H04L 5/0048 20130101; H04L 25/0226 20130101;
H04L 27/2655 20130101; H04L 25/0208 20130101; H04L 25/03299
20130101; H04L 5/006 20130101; H04L 27/2662 20130101 |
Class at
Publication: |
370/208 ;
370/210 |
International
Class: |
H04J 011/00 |
Claims
What is claimed:
1. An orthogonal frequency division multiplexing receiving system
comprising: a noise analysis logic unit (NAL) for receiving FFT
data including at least one of channel noise data and channel
signal data, wherein the channel signal data is transmitted on a
channel by a transmitter, wherein the NAL includes inputs for
receiving protocol data and predetermined synchronization data, and
wherein the NAL processes the FFT data to identify channel noise
data and channel signal data based on the protocol data and the
synchronization data.
2. The system according to claim 1, wherein the NAL is coupled to a
data processing block which processes the received signal and noise
data to identify and provide for learning of noise characteristics
of the channel and to generate an enhanced channel quality
estimate, providing for an improved error rate for data
transmission on the channel.
3. The system according to claim 1, further comprising: at least
one carrier selection device which utilizes the enhanced channel
quality estimate to select a channel for data signal exchange.
4. The system according to claim 1, further comprising: again
control device which utilizes the enhanced channel quality estimate
to control signal gain processing.
5. The system according to claim 1, further comprising: a data
signal synchronization device which utilizes the enhanced channel
quality estimate as part of synchronization processing.
6. The system according to claim 1, further including a distributed
intelligence built into a plurality of nodes that allows the system
to process the information collected from all nodes to optimize the
operation of the system.
7. The system according to claim 3, further including a waiting
factor to the at least one carrier to improve the accuracy of
synchronization.
8. A method for providing an orthogonal frequency division
multiplexing receiving system comprising the steps of: providing a
noise analysis logic unit (NAL) for receiving FFT data including at
least one of channel noise data and channel signal data, wherein
the channel signal data is transmitted on a channel by a
transmitter, and wherein the NAL includes inputs for receiving
protocol data and predetermined synchronization data, and further,
wherein the NAL processes the FFT data to identify channel noise
data and channel signal data based on the protocol data and the
synchronization data.
9. The method according to claim 8, further comprising the step of
providing silent interval data to derive channel quality assessment
data.
10. The method according to claim 8, wherein the noise data are
utilized to detect the presence further narrow-band signals.
11. The method according to claim 8, further comprising the step of
utilizing the noise data to detect the presence of a wide-band
signals.
12. The method according to claim 8, further comprising the step of
utilizing the noise data to select carriers for the pilot tone
insertion.
13. The method according to claim 8, further comprising the step of
exchanging data gathered among all nodes.
14. The method according to claim 13, further providing a dedicated
node to process the information collected from all nodes to
optimize the operation of the system.
15. The method according to claim 8, further comprising the step of
including a distributed intelligence built into a plurality of
nodes that allows the processing of the information collected from
all nodes to optimize the operation of the system.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/378,196 filed May 6, 2002, which is incorporated
by reference herein.
FIELD OF THE INVENTION
[0002] The present invention relates to data communications using
Orthogonal Frequency Division Multiplexing (OFDM) techniques. It is
not restricted to any one application, but can enhance any OFDM
(Orthogonal Frequency Division Multiplexing) implementation
including those for single frequency networks, wireless networks
and powerline networks.
BACKGROUND OF THE INVENTION
[0003] OFDM is a very effective technique for data communications
in several environments because of its ability to reduce the
negative effects of channel distortions such as selective fading
and narrow band interference. ("OFDM for Wireless Multimedia
Communications"; by R. van Nee, R. Prasad; Artech House Publishers;
2000; ISBN 0-89006-530-6. OFDM uses a multi-carrier transmission
scheme (i.e., sub-channels or tones) for both synchronization and
data transfer. Examples of communications systems using OFDM
include IEEE 802.11a (IEEE Standard for Wireless LAN Medium Access
Control (MAC) and Physical Layer (PHY) specifications and
supplements (wireless LAN applications), DAB ("Digital Audio
Broadcast, Guide to DAB Standards; Guidelines and Bibliography",
ETSI, TR 101 495 V1.1.1), DVB-T ("Digital Video Broadcasting (DVB);
Framing structure, channel coding and modulation for digital
terrestrial television", ETSI, EN 200,744), HPA ("Home Plug
Alliance", Home Plug Special Interest Group website:
http://www.homeplug.org) and others. The above-listed references
are incorporated herein by reference.
[0004] In a network of one or more OFDM transmitters, the channel
is used to communicate between units and there are time segments
when transmitter signals are present and times when there are no
transmitter signals on the channel as illustrated FIG. 1. The time
durations when transmitters occupy the channel vary depending on
parameters such as the block size of the data being sent (payload
data or control data). Segments of time when no transmitters occupy
the channel have different durations that can vary based on
situations such as: a single transmitter sending consecutive blocks
of data with gaps between blocks, multiple transmitters contending
for access to the channel and a channel idle condition. The lengths
of these time segments are predictable (except for the situation
where no units are communicating) and can be determined based on
knowledge of the appropriate communications standard (e.g.,
802.11a, DVB-T, etc.). Knowledge of the communications standard
also provides information about the structure of transmitter
signals (e.g., preamble structure, priority resolution structure,
etc.). Knowing the structure of the signal, especially preset
information such as transmission structure, provides data that can
be used to estimate the quality of the received signal and the
channel itself. Information gathered when no transmitters occupy
the channel can be used to estimate channel noise. This approach
could be used on the power up of the system or during operation.
The information this process would result to may provide a viable
input related to the following:
[0005] Allocation of pilot tones when necessary;
[0006] Detection of other narrow-band signals;
[0007] Detection of other wide-band systems;
[0008] Detection of beacons, etc.
[0009] The quality of each sub-channel at any given time determines
how well the overall system can transport data. A good quality
sub-channel provides good synchronization information, which is
then used to recover data correctly. A poor quality sub-channel
could mean data loss due to errors in synchronization or
unrecoverable errors in the data itself. Furthermore, time taken to
evaluate sub-channel quality as part of the transmission process,
time taken to retransmit data due to channel related errors or time
taken to regularly distribute estimated channel quality all tend to
reduce the overall data rate. Improvements in channel quality
estimates used at the local receiver, without direct cooperation
with any remote transceivers, would therefore improve the quality
of communications (i.e., facilitate higher data rates and reduce
error rates).
[0010] One of the first steps an OFDM receiver must perform in
order to extract data from the channel, is to perform
synchronization. Two types of synchronization are required: OFDM
symbol boundary identification/timing and sub-carrier
frequency/phase offset estimation/correction. FIG. 2 illustrates
the blocks in a typical OFDM transceiver (PHY layer). The
highlighted blocks in the following list are directly involved in
synchronization:
1 Transmitter Receiver Serial data input Serial data output [1]
Coding (FEC, [15] Decoding (FEC, Encryption, etc.) Encryption,
etc.) [2] Interleaving [14] De-interleaving [3] Mapping/ [13]
Demapping/ Pilot insertion Channel correction [4] Modulation [12]
Demodulation [5] iFFT [11] FFT [6] Cyclic extension, [10] Timing
and windowing & frequency sync & cyclic filtering extension
removal [7] DAC, RF Tx & [9] Coupler, coupler [8] Powerline RF
Rx & ADC Channel
[0011] The transmitter, in some implementations (e.g., 802.11a),
inserts several fixed pilots (performed by block #3: Mapping/Pilot
Insertion) on particular sub-channels to be used by the receivers
channel estimator (sub-channel time and frequency estimations).
While on other implementations (notably HPA) this block enables and
disables sub-channels in cooperation with remote units (known as
tone mapping). Part of the function of block #6 (Cyclic Extension,
Windowing and Filtering) is to insert preset synchronization
information before the transmission of the data block to be used by
the receiver to estimate the timing and frequency offset of each
OFDM symbol.
[0012] The two key receiver blocks, block #10 (Timing and Frequency
Sync & Cyclic Extension Removal) and block #13
(Demapper/Channel Correction), correspond to block #6 and block #3
respectively on the transmit side and are responsible for, among
other tasks, synchronization.
[0013] The other key receiver component is block #11 that performs
FFT's on the channel signal. The output of this block contains
amplitude and phase information at every OFDM carrier
frequency.
[0014] Block #9, although not directly involved in synchronization
and data recovery contains AGC circuits, which have an important
role in acquiring good signals from the channel.
[0015] It is evident from the previous discussion that much of the
mechanism needed to gather channel signal and channel noise data is
already available within OFDM receivers. This invention focuses on
improving both synchronization and data transfer of any OFDM system
through the independent and continuous estimation of channel
quality for use by the local receiver.
SUMMARY OF THE INVENTION
[0016] This invention improves the error rate of an OFDM receiver
and the system as the whole by providing the receiver with an
improved estimate of channel quality. The system wide benefit is
derived from the ability to select the best carriers for the pilot
tome insertion as well as the detection and avoidance of already
occupied frequencies. The receiver uses the data to improve data
synchronization and data recovery. Channel data is gathered during
periods when transmitters occupy the channel as well as times when
the channel is idle or "silent". The data that is gathered is used
in a learning process to improve its effectiveness over time and
multiple blocks.
[0017] This channel quality estimate is better for several
reasons:
[0018] 1. The best estimate is always ready when the receiver needs
it, there is no delay and the estimate is constantly being updated
and improved
[0019] 2. The estimate uses noise data gathered from the idle or
"silent" channel as well as data generated by remote unit
transmissions
[0020] 3. In addition to the remote units it is communicating with,
channel signal data from all remote transmitters is used in the
estimating process
[0021] 4. The channel noise data used in the estimate goes through
a learning process over time
[0022] 5. The channel signal data used in the estimate goes through
a learning process over multiple blocks and multiple
transmitters
[0023] The improved channel quality estimate can be used by the
OFDM receiver in many ways that include, but is not limited
to--improved carrier selection, improved AGC and so on.
BRIEF DESCRIPTION OF THE FIGURES
[0024] Other objects and advantages of the present invention will
be apparent from the following detailed description of the
presently preferred embodiments, which description should be
considered in conjunction with the accompanying drawings in
which:
[0025] FIG. 1 is a diagram showing any OFDM communications between
two stations which will have periods of silence when there is no
transmitter using the channel and this concept is shown in the
figure. The diagram shows further the three key processing blocks
involved in an implementation of this patent idea.
[0026] FIG. 2 shows a simplified set of processing blocks (i.e.,
PHY layer) that would be present in any OFDM transceiver
implementation. Interactions with other parts of a complete system
(e.g., protocol layer, etc.) are not shown to make the diagram more
straightforward.
[0027] FIG. 3 shows in addition to the previous figure of a noise
analysis logic (NAL) block (item #16), connected as shown in the
figure, to an existing OFDM transceiver gives the receiver better
performance.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION
[0028] This invention improves OFDM receivers by adding information
derived from silent intervals to estimates for the quality of the
channel using both channel noise and channel signal data. In the
preferred embodiment this process may have a continues nature or
may be performed in the predetermined fashion. Further in the
preferred embodiment the enhanced channel estimation data may be
used for the following purposes:
[0029] Improving accuracy of the channel estimation;
[0030] Improving accuracy of the synchronization;
[0031] Allocation of pilot tones when necessary;
[0032] Detection of other narrow-band signals;
[0033] Detection of other wide-band systems;
[0034] Detection of beacons, etc.
[0035] It is especially important to note that the main benefit in
the systems similar to HPA the accuracy of synchronization may be
improved through the novel method introduced in this invention; by
adding a waiting factor to each carrier the preferred embodiment of
the system can greatly improve the accuracy of synchronization.
[0036] As an example, data from the PHY blocks and information from
the protocol layer are used. Block #16 (Noise Analysis Logic) in
FIG. 3 is the primary element to carry out the process. The inputs
to the NAL (Noise Analysis Logic) block are the FFT data (block
#11) and data from block #10 (Timing and Frequency Synchronization
and Cyclic extension Removal Block) and information from the
protocol layer. The outputs include, but are not limited to channel
map updates sent to block 13 (Demapper/Channel Correction Block),
gain adjustments sent to block #9, and others.
[0037] The process proceeds by acquiring FFT data and alternately
saving it as either signal data or noise data where the choice is
controlled by processed data from block #10 and the protocol layer.
These two elements have the necessary information that is used to
determine when there are transmitters on the channel or when the
channel is idle. The FFT data contains both amplitude and phase
information for each of the OFDM carriers (e.g., there are 84
carriers in an HPA system; there can be 1705 carriers in a DVB-T
system; etc.). The FFT channel signal data along with the FFT
channel noise data then go through a separate learning process over
multiple data blocks. The results are processed into a channel
quality estimate.
[0038] There may be occasions when the channel is idle for long
periods of time (i.e., no units are actively involved in
communications with other units). During these time periods,
estimates of signal quality cannot be made. One possible system
level improvement would be to require transceivers to send short,
"heart beat" messages from time to time for the express purpose of
maintaining a good estimate of channel signal quality. This message
would be defined such that no response is required and that it is
sent only afterthe channel has been idle for long periods. This
message is not required for this patent, but it would improve
performance by allowing channel signal data to be acquired even if
the channel remains unused for long periods of time.
[0039] Thus, the invention uses channel noise data as well as
channel signal data to improve the error rate of any OFDM receiver.
Further, the invention uses channel data from the transmitter it is
communicating with as well as all transmitters. In addition, the
invention applies a learning process on the collected signal and
noise data to further improve the error rate of any OFDM receiver.
Also, the invention provides an improved estimate of channel
quality without the need to directly contact any other
transmitters. The receiver can use the enhanced channel quality
estimate in at least the following ways:
[0040] the receiver's carrier selection process can be improved
with the use of the data provided by this invention; the gain
control process can be improved with the use of the data provided
by this invention; and the receiver's synchronization process can
be improved with the use of the data provided by this
invention.
[0041] Improvement of the accuracy of the channel quality
assessment is greatly beneficial to the operation of a single node
that uses the method described in this invention. In the multi-node
system the ability to analyze the channel may be used to improve
the operation of the system as the whole. The information that is
gathered by the means of the proposed method can be shared among
the nodes in the system. In this cases it becomes possible to use
this information to optimize the operation of the system. The
following exemplifies the use of the information.
[0042] In the system that uses pilot tones for synchronization and
the media access control it is important to keep the number of
pilot tones to the minimum to avoid excessive bandwidth penalties.
In the channels with the high level of diversity such as powerline
channel exits number of tones required to achieve good
synchronization may be very large. The described in this invention
method allows the system to analyze the channel and select a
minimum number of pilot tomes required in such way that most of the
tones are received by all nodes of the system. After such
determination the system may reallocate pilot tones.
[0043] The same approach is applicable for determining the presence
of narrow and wide band interferers. Such interferers could be
other communication systems. The application of the above describe
method would allow to configure the system to avoid the
interference and improve the reliability of the communication.
[0044] Such system wide optimization may be performed in the
centralized component of the system that may be residing on one of
the nodes or standalone. Or in the different version of the
preferred embodiment such intelligence may be distributed across
multiple nodes in the system.
* * * * *
References