EFFICACITE AMELIOREE DE TRANSMISSION PAR PAQUETS POUR METHODES ET SYSTEMES APPLICABLES AUX SIGNAUX DE TRANSMISSION DE BLOCS

IMPROVED PACKET EFFICIENCY FOR BLOCK TRANSMISSION SIGNALS METHODS AND SYSTEMS

Abrégé français

Cette invention a pour objet un dispositif de communication configuré pour l'utilisation du transport d'un signal de communication ayant un préambule spécialisé permettant un rendement de bande passante amélioré. Le dispositif de communication comprend un premier dispositif configuré pour manipuler un schéma de transmission en bloc, tel qu'un signal OFDM ou SCBT, ayant une taille de bloc égale à N, où N est un entier supérieur à 1, le signal de transmission en bloc ayant un préambule avec une configuration de symbole tel qu'un pourcentage de tous les symboles du préambule peut être utilisé pour toute l'estimation de décalage en fréquence, une synchronisation d'horloge et une estimation de canal.

Abrégé anglais

A communication signal having a specialized preamble (410) allowing for increased bandwidth efficiency is disclosed. The specialized preamble consist of a serie of repeated blocks (412), wherein each block consist of a serie of symbols a0,...,aN with each symbol an defined as Formula (I),n=0,...,N. Said serie of symbols is also referred to as the "complex quadric" (CQ) sequence. The application further discloses a communication device adapted for using the specialized preamble for performing frequency offset estimation, clock synchronization and channel estimation.

Revendications

CLAIMS
1. A communication device configured for the use with a communication signal
having a specialized preamble that allows for increased bandwidth efficiency,
the
communication device comprising:
a first device configured to manipulate a block transmission signal having a
block size
of N, wherein N is an integer greater than 1;
wherein the block transmission signal has a preamble with a symbol
configuration such
that at least one symbol of all symbols of the preamble can each be used for
all of frequency
offset estimation, clock synchronization and channel estimation.
2. The communication device according to claim 1, wherein the block
transmission signal has a preamble with a symbol configuration such that at
least 50% of all
symbols of the preamble can each be used for all of frequency offset
estimation, clock
synchronization and channel estimation.
3. The communication device according to claim 2, wherein the block
transmission signal has a preamble with a symbol configuration such that
substantially all
symbols of the preamble can each be used for at least two of frequency offset
estimation, clock
synchronization and channel estimation.
4. The communication device according to claim 1, wherein the preamble is
cyclically orthogonal.
5. The communication device according to claim 4, wherein the preamble uses
have no zero padding or no cyclic prefix.
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6. The communication device according to claim 4, wherein the preamble has a
symbol configuration such that each symbol has equal magnitude and has a
substantially flat
frequency response.
7. The communication device according to claim 1, wherein the communication
signal is an orthogonal frequency division multiplexed (OFDM) signal.
8. The communication device according to claim 6, wherein the preamble
consists
of a repeating block of symbols, and wherein each symbol value a n of the
repeating block is
determined by the following equation:
<IMG>
wherein n is a symbol number.
9. The communication device according to claim 8, wherein the first device is
a
portion of a receiver.
10. The communication device according to claim 9, wherein the first device
includes a frequency offset estimation device for estimating frequency offset,
a synchronization
device for estimating the timing of a received signal and a channel estimation
device for
estimating the channel response of a received signal, and wherein the
synchronization device is
configured to operate in parallel with at least one of the frequency offset
estimation device and
the channel estimation device.
11. A method for the reception and data extraction of block transmission
communication signals, the method comprising:
receiving a block transmission communication signal having a block size of
length N,
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wherein N is an integer greater than 1;
performing at least two of frequency offset estimation, clock synchronization
and
channel estimation for the first block transmission communication signal using
a common set
of symbols in a first preamble of the block transmission communication signal.
12. The method for the reception and data extraction according to claim 11,
further
comprising performing all three of frequency offset estimation, clock
synchronization and
channel estimation using a common set of symbols in a first preamble.
13. The method for the reception and data extraction according to claim 12,
wherein the common set of symbols in the first preamble includes a repeating
block of
symbols.
14. The method for the reception and data extraction according to claim 13,
wherein each symbol value a n of the repeating block is determined by the
following equation:
<IMG>
wherein n is a symbol number.
15. The method for the reception and data extraction according to claim 12,
wherein the step of clock synchronization is performed in parallel with at
least one of the steps
of frequency offset estimation and channel estimation.
16. The method for the reception and data extraction according to claim 12,
wherein the step of clock synchronization includes detecting a large peak
during a running
power spectrum detection process.
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17. The method for the reception and data extraction according to claim 16,
wherein the step of clock synchronization includes detecting multiple large
peaks at a common
location during a running power spectrum detection process on multiple blocks
of a series of
repeating blocks of symbols.
18. The method for the reception and data extraction according to claim 13,
wherein the step of clock synchronization is required to use at least one more
block than either
of the steps of frequency offset estimation and channel estimation.
19. The method for the reception and data extraction according to claim 13,
wherein first preamble contains no zero padding or cyclic prefix.
20. The method for the reception and data extraction according to claim 13,
wherein the step of channel estimation includes averaging noise over a
plurality of preamble
blocks.
21. An electromagnetic wave propagating through a transmission medium, the
electromagnetic wave comprising:
an block transmission communication signal having a block length equal to N,
wherein
N is an integer greater than 1, wherein the preamble includes a repeating
block of symbols, and
each symbol value a n of the repeating block is determined by the following
equation:
<IMG>
wherein n is a symbol number.
22. The electromagnetic wave extraction according to claim 21, wherein the
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preamble contains no zero padding or cyclic prefix.
23. The electromagnetic wave extraction according to claim 21, wherein the
electromagnetic wave consists of an orthogonal frequency division multiplexed
(OFDM)
communication signal.

Description

CA 02656184 2008-12-23
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IMPROVED PACKET EFFICIENCY FOR BLOCK TRANSMISSION SIGNALS
METHODS AND SYSTEMS
FIELD OF THE DISCLOSURE
[0001] This disclosure pertains to the field of packet-based communication
systems.
BACKGROUND
[0002] Typically, for conventional block transmission methods, such as
Orthogonal Frequency
Division Multiplexing (OFDM) or Single Carrier Block Transmission (SCBT),
transmission
systems using a packet-based protocol, each packet sent and received consists
of a data field
preceded by a preamble. Each data field will generally include a stream of
data bits, a header and
some form of data check. Each preamble will include a series of two or three
separate portions
devoted to: (1) synchronization, (2) frequency offset estimation and (3)
channel estimation. In
such block transmission schemes, the preamble is also typically transmitted in
blocks with each
block separated by some form of buffer, such as a Zero Padding (ZP) buffer or
a Cyclic Prefix
(CP) buffer, i.e., a buffer formed from cyclically redundant symbols.
[0003] While the above-described packet structures have been in use for a long
time, the
increased demands of certain data communication systems have put increased
pressure to improve
system performance to transfer more data using the same available bandwidth.
Accordingly, new
technology related to the efficient transmission and reception of packetized
information is
desirable.
SUMMARY
[0004] In a first embodiment, a communication device configured for the use of
transporting a
communication signal having a specialized preamble allowing for increased
bandwidth efficiency.
The communication device includes a first device configured to manipulate a
block transmission
scheme, such as OFDM or SCBT signal, having a block size equal to N, wherein N
is an integer
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greater than 1, wherein the block transmission signal has a preamble with a
symbol configuration
such that a percentage of all symbols of the preamble can each be used for all
of frequency offset
estimation, clock synchronization and channel estimation.
[0005] In a second embodiment, a method for the reception and data extraction
of block
transmission communication signals includes receiving a block transmission
communication signal
having a block size equal to N, wherein N is an integer greater than 1, and
performing at least two
of frequency offset estimation, clock synchronization and channel estimation
using a common set
of symbols in the preamble.
[0006] In a third embodiment, an electromagnetic wave propagating through a
transmission
medium is presented. The electromagnetic wave includes block transmission
signal having a block
size equal to N, wherein N is an integer greater than 1, wherein each channel
has a preamble that
includes a repeating block of symbols, where each symbol is derived from a
Complex Quadratic
sequence.
DESCRIPTION OF THE DRAWINGS
[0007] The example embodiments are best understood from the following detailed
description
when read with the accompanying drawing figures. It is emphasized that the
various features are
not necessarily drawn to scale. In fact, the dimensions may be arbitrarily
increased or decreased
for clarity of discussion. Wherever applicable and practical, like reference
numerals refer to like
elements.
[0008] FIG. 1 is an exemplary communication system according to the present
disclosure;
[0010] FIG. 2 is a block diagram of an exemplary receiver;
[0011] FIG. 3 is a block diagram outlining various exemplary operations
directed to the
reception, processing and data extraction of block transmission packets; and
[0012] FIG. 4 depicts an exemplary communication waveform for use with the
various
methods and systems of the present disclosure.
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DETAILED DESCRIPTION
[0013] In the following detailed description, for purposes of explanation and
not limitation,
example embodiments disclosing specific details are set forth in order to
provide a thorough
understanding of an embodiment according to the present teachings. However, it
will be apparent
to one having ordinary skill in the art having had the benefit of the present
disclosure that other
embodiments according to the present teachings that depart from the specific
details disclosed
herein remain within the scope of the appended claims. Moreover, descriptions
of well-known
apparatus and methods may be omitted so as to not obscure the description of
the example
embodiments. Such methods and apparatus are clearly within the scope of the
present teachings.
[0014] Typically, in packet-based block transmission systems, such as an OFDM
or SCBT
transmission system, time-domain and frequency-domain training sequences are
transmitted at the
beginning of each packet. These training sequences are used by a respective
receiver for signal
synchronization (SYNC), frequency offset estimation (FOE) and Channel
Estimation (CE). For
example, the time domain sequence of a MB-OFDM UWB communication system has a
length
equal to 24 OFDM symbols while the respective frequency domain sequence has a
length equal to
6 OFDM symbols. The time domain sequence is used for synchronization and
frequency offset
estimation while the frequency domain sequence is used for channel estimation.
Typically these
OFDM symbols are separated using a Cyclic Prefix (CP) or Zero Padding (ZP).
While this
approach follows a simple paradigm, it requires a long preamble, which in turn
reduces the
bandwidth efficiency of the system. In high rate communication systems it can
be beneficial to
reduce such preamble overhead in order to improve the bandwidth efficiency of
the system.
[0015] The present methods and systems can increase efficiency by reducing
preamble
overhead, i.e., by reducing the number of symbols required in a preamble, as
well as shorten the
time required to process a packet's preamble once the packet is received.
[0016] FIG. 1 is an exemplary communication system 100 according to the
present disclosure.
As shown in FIG. 1, the communication systan 100 has a signal source 140 and a
signal
destination 160 coupled by an intermediate transmission media 150. The
intermediate
transmission media 150 has an inherent channel response h[t] with inherent
delay tTAu and added
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noise source rlo. The exemplary communication system 100 communicates using a
packet-based
block transmission method.
[0017] However, unlike traditional packet-based block transmission systems,
the exemplary
communication system 100 can communicate using packets having a special
preamble that lends
itself to both increased bandwidth efficiency and parallel processing.
[0018] FIG. 4 depicts an example of an exemplary block transmission packet 400
for use with
the disclosed methods and systems. As shown in FIG. 4, the block transmission
packet 400
includes a preamble 410 and a data field 420. The preamble 410 includes a
repeating block 412 of
symbols. The data field includes alternating blocks of data 424 and zero or
cyclic prefixes 422.
[0019] As further shown in FIG. 4, each preamble block 412 can consist of a
series of symbols
ao...aN_i with each symbol a defined by EQ. 1 below:
-J~ J~ n 2
a,z =e ge N,n=0,...,N-1 EQ. 1
[0020] This equation, sometimes referred to as the "complex quadratic" (CQ)
sequence, is
known in the communication arts, but has never been applied in the various
manners developed by
the inventors of the disclosed methods and systems.
[0021] A first advantage of the complex quadratic sequence is that it is
circularly orthogonal.
That is, the complex quadratic sequence is orthogonal to any sequence based on
a cyclic shift of
itself. This property of the complex quadratic sequence makes it a very good
choice for
correlation-based synchronization for block transmission systems as such
sequences eliminate the
need for any cyclic prefix or zero padding between blocks. This in itself can
substantially reduce
preamble overhead.
[0022] Yet another advantage to using the complex quadratic sequence is that
it has constant
power in time, i.e. I aõ I = 1. This property of the complex quadratic
sequence can allow one to
transmit the preamble at higher power without running into power amplifier non-
linearity at the
receiver side.
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[0023] Still another advantage of the complex quadratic sequence can be found
by looking at
the Discrete Fourier Transform (DFT) of the complex quadratic sequence, which
is shown below
in EQ. 2:
7C 7C Z
- -J-k
Ak =ege N ,k=0,...,N-l, EQ.2
[0024] An analysis of EQ. 2 reveals that the complex quadratic sequence also
has constant
power over frequency, i.e. I Ak I = 1. For OFDM communication systems, this
property enables
one to sense a channel across the whole bandwidth, i.e., across all sub-
carriers.
[0025] Hence, the CQ sequence can be a good choice for the purpose of channel
estimation.
[0026] Note that each preamble block does not need to consist of N symbols,
but can
alternatively have fewer symbols for more practical applications. Furthermore,
the length of the
preamble blocks may not be fixed. That is, CQ sequences with different lengths
may be used in
the same preamble. Good block lengths may be expected to vary from embodiment
to
embodiment depending on a variety of factors.
[0027] FIG. 2 is a block diagram of an exemplary receiver 160. As shown in
FIG. 2, the
exemplary receiver includes a controller 210, a memory 220, a correlation
device 230, a
synchronization device 240, a frequency offset estimation device 250, a
channel estimation device
260 and an input/output device 290. The various components 210-290 are linked
via a
control/data bus 202.
[0028] Although the exemplary receiver 160 of FIG. 2 uses a bussed
architecture, it should be
appreciated that any other architecture may be used as may be known to those
of ordinary skill in
the art. For example, in various embodiments, the various components 210-290
can take the form
of separate electronic components coupled together via a series of separate
busses or a collection
of dedicated logic arranged in a highly specialized architecture.
[0029] It also should be appreciated that some of the above-listed components
230-290 can
take the form of software/firmware routines residing in memory 220 and be
capable of being
executed by the controller 210, or even software/firmware routines residing in
separate memories

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in separate servers/computers being executed by different controllers.
[0030] In operation, a detected/demodulated block transmission packet can be
received via
the input/output device 290 and stored in the memory 220 under control of the
controller 210.
Next, the received packet can correlated with a training sequence using the
correlation device 230
in order to determine whether a valid packet has arrived.
[0031] Once a valid packet is detected, the controller 210 can extract the
preamble from the
packet and provide identical copies of the preamble to the synchronization
device 240, the
frequency offset estimator 250 and the channel estimator 260.
[0032] While there is no specific requirement that the receiver 160 perform
any parallel
processing, as mentioned above the preamble of the exemplary packet 400 of
FIG. 4 uniquely
lends itself to parallel processing. That is, when each channel's preamble
consists of the repetition
of blocks containing a cyclically orthogonal sequence, different time-domain
and frequency-
domain sequences do not need to be used for synchronization, frequency offset
estimation and
channel estimation. Accordingly, frequency offset estimation and correction,
as well as channel
estimation, can be performed in parallel with synchronization using the
identical blocks of
symbols. For the present embodiment, it should be appreciated that
synchronization can be
performed in parallel with one or both of frequency offset estimation and
channel estimation.
[0033] To perform proper channel estimation, however, frequency offset can
first be taken
into consideration. Accordingly, the frequency offset estimation device 250
can perform a
frequency offset estimation on the preamble. Any frequency offset can be
estimated by measuring
the phase rotation between similar peaks (generated by the correlation device)
in two consecutive
blocks. For a more accurate estimate, the estimated value from different pairs
of blocks can be
averaged. Typically, frequency offset takes only two repeated blocks, but of
course performance
and performance requirements can vary widely depending on a plethora of
circumstances.
[0034] Once the frequency offset estimation device 250 has provided the
appropriate
frequency offset information to the channel estimation device 260, the channel
estimation device
260 can correctly estimate a preliminary channel estimate.
[0035] Note that when a cyclically orthogonal sequence is used, when in the
absence of
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frequency offset noise, the output of the correlator should represent the
communication channel
through which the packet traveled. In other words, in the absence of noise and
frequency offset,
any block of M consecutive samples in the output of the correlator can
resemble the exact channel
impulse response with an unknown cyclic shift. Accordingly, when no noise is
present, the task of
the channel estimation device 260 can be made simple.
[0036] However, when noise is present, the channel estimation device 260 can
derive a better
channel estimate can by averaging a number of consecutive blocks (assuming
that frequency offset
is corrected).
[0037] While the frequency offset estimation device 250 and channel estimation
device 260
are working together, the synchronization device 240 independently can perform
a
synchronization procedure by looking for large peaks during a time
correlation. Assuming typical
channel models (e.g. with exponential decay), this approach can provide a good
estimate. To
ensure a higher probability of synchronization success, more than one peak
(and typically 3-4
peaks) in the same relative location in sequential repeated blocks can be
required. In other words,
if the system observes that three consecutive blocks produce a large peak in
the same location, it
can assume with a high degree of confidence that the location of these peaks
is the correct
synchronization time.
[0038] After the synchronization device 240 derives the correct
synchronization time, the
synchronization device 240 can provide the correct synchronization time to
channel estimation
device 260.
[0039] In turn, assuming that the channel estimation device 260 has produced a
correct
preliminary channel estimate accounting for frequency offset and (optionally)
noise, the channel
estimation device 260 can cyclically shift the preliminary channel estimate to
produce a true
channel estimate.
[0040] Notice that as long as the number of blocks used for synchronization is
greater than
the number of blocks used for either frequency offset estimation or channel
estimation, one can be
reasonably sure that the received data used for channel estimation and
frequency offset estimation
contains the transmitted training sequence (as opposed to garbage). Typically
channel and
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frequency offset estimates can be obtained using 2 blocks, and the
synchronization can be
confirmed after 3 or 4 blocks with good peaks.
[0041] Once the channel estimation device 260 has estimated a true channel
estimate, the
controller 210 can use this channel estimate to extract data from the data
portion of the received
packet.
[0042] FIG. 3 is a block diagram outlining various exemplary operations
directed to the
reception, processing and data extraction of block transmission packets. The
process starts in
step 302 where a block transmission packet, such as the block transmission
packet 400 of FIG. 4,
is received. Next, in step 304, the received packet is correlated with a
predetermined training
sequence in order to assure, among other things, that a valid packet has been
received. Then, in
step 306, the preamble is extracted from the received packet, and the first
block of the preamble is
identified. Control continues to step 310.
[0043] In step 310, the first packet is processed according to a number of
intermediate steps
312-320, which can (optionally) be performed in a parallel fashion.
[0044] In a first line of processing, control starts with step 312 where a
frequency offset
estimation procedure can be performed. Next, in step 314, a frequency offset
correction
procedure can be conditionally performed assuming that the correct frequency
offset can be
estimated in step 312. Then, in step 316, a channel estimation procedure can
performed with the
caveat that frequency offset and noise should be accounted for before a proper
preliminary
channel estimate can be derived. Control continues to step 330.
[0045] In a second line of processing, control starts with step 312 where a
synchronization
procedure is performed. Control continues to step 330.
[0046] In step 330, a determination is made as to whether the synchronization
procedure of
step 320 was successfully performed. As discussed above, synchronization may
be determined
when a strong output pulse is found in the output of a correlator for a
particular location within a
block. However, as a higher level of confidence may be had by processing
multiple blocks,
synchronization may by definition require the processing of multiple blocks.
If a successful
synchronization is determined to be produced; control continues to step 332;
otherwise, control
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jumps to step 340.
[0047] In step 340, which assumes an unsuccessful synchronization, a
determination is made
as to whether the last available block in the preamble was processed in step
310. If the last
available block in the preamble was processed, control continues to step 342,
where a failure
report is issued to some relevant control circuitry, and the process stops at
step 390.
[0048] If the last available block in the preamble was not processed, control
jumps to step
350, where the next sequential block in the preamble is identified. Control
then jumps back to
step 310 wherein the above-described frequency offset estimation, frequency
offset correction,
channel estimation and synchronization steps 312-320 are performed on the next
identified block.
[0049] In step 332, which assumes a successful synchronization process at step
330, the
synchronization offset produced by step 320 can be applied to the preliminary
channel estimation
output of step 316 to cyclically shift the channel estimation output - thus
producing a true channel
estimate. Next, in step 334, the true channel estimate can be used to extract
data from the data
portion of the received packet, and control continues to step 390 where the
process stops.
[0050] In various embodiments where the above-described systems and/or methods
are
implemented using a programmable device, such as a computer-based system or
programmable
logic, it should be appreciated that the above-described systems and methods
can be implemented
using any of various known or later developed programming languages, such as
"C", "C++",
"FORTRAN", Pascal", "VHDL" and the like.
[0051] Accordingly, various storage media, such as magnetic computer disks,
optical disks,
electronic memories and the like, can be prepared that can contain information
that can direct a
device, such as a computer, to implement the above-described systems and/or
methods. Once an
appropriate device has access to the information and programs contained on the
storage media,
the storage media can provide the information and programs to the device, thus
enabling the
device to perform the above-described systems and/or methods.
[0052] For example, if a computer disk containing appropriate materials, such
as a source file,
an object file, an executable file or the like, were provided to a computer,
the computer could
receive the information, appropriately configure itself and perform the
functions of the various
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systems and methods outlined in the diagrams and flowcharts above to implement
the various
functions. That is, the computer could receive various portions of information
from the disk
relating to different elements of the above-described systems and/or methods,
implement the
individual systems and/or methods and coordinate the functions of the
individual systems and/or
methods described above.
[0053] The many features and advantages of the present teachings are apparent
from the
detailed specification, and thus, it is intended by the appended claims to
cover all such features
and advantages of the present teachings which fall within the true spirit and
scope of the present
teachings. Further, since numerous modifications and variations will readily
occur to those skilled
in the art, it is not desired to limit the invention to the exact construction
and operation illustrated
and described, and accordingly, all suitable modifications and equivalents may
be resorted to,
falling within the scope of the invention.

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