Note: Descriptions are shown in the official language in which they were submitted.
CA 02773945 2015-01-23
TITLE: THE USE OF FIRST AND SECOND PREAMBLES IN WIRELESS
COMMUNICATION SIGNALS
FIELD OF THE INVENTION
[001] The present invention relates generally to the field of data delivery
via a wireless
connection and, more particularly, to the delivery of data via signal frames
that comprise
multiple synchronization preambles.
BACKGROUND OF THE INVENTION
[002] The demand for services in which data is delivered via a wireless
connection has
grown in recent years and is expected to continue to grow. Included are
applications in
which data is delivered via cellular mobile telephony or other mobile
telephony, personal
communications systems (PCS) and digital or high definition television (HDTV).
Though
the demand for these services is growing, the channel bandwidth over which the
data
may be delivered is limited. Therefore, it is desirable to deliver data at
high speeds over
this limited bandwidth in an efficient, as well as cost effective, manner.
[003] A known approach for efficiently delivering high speed data over a
channel is
by using Orthogonal Frequency Division Multiplexing (OFDM). The high-speed
data
signals are divided into tens or hundreds of lower speed signals that are
transmitted in
parallel over respective frequencies within a radio frequency (RF) signal that
are known
as sub-carrier frequencies ("sub-carriers"). The frequency spectra of the sub-
carriers
overlap so that the spacing between them is minimized. The sub-carriers are
also
orthogonal to each other so that they are statistically independent and do not
create
crosstalk or otherwise interfere with each other. As a result, the channel
bandwidth is
used much more efficiently than in conventional single carrier transmission
schemes such
as AM/FM (amplitude or frequency modulation).
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[004] Another approach to providing more efficient use of the channel
bandwidth is to
transmit the data using a base station having multiple antennas and then
receive the
transmitted data using a remote station having multiple receiving antennas,
referred to as
Multiple Input-Multiple Output (MIMO). The data may be transmitted such that
there is
spatial diversity between the signals transmitted by the respective antennas,
thereby
increasing the data capacity by increasing the number of antennas.
Alternatively, the data
is transmitted such that there is temporal diversity between the signals
transmitted by the
respective antennas, thereby reducing signal fading.
[005] In OFDM and MIMO systems, a preamble may be inserted within a signal
frame
in order to provide: base station identification and selection, CIR
measurement, framing
and timing synchronization, frequency synchronization as well as channel
estimation. In
many cases, the preamble search requires a large amount of computation power
at the
subscriber station. For the initial cell search, there is no prior knowledge
about the
synchronization positions for potential base station candidates; hence the
subscriber station
needs to perform the correlations with all possible pseudo noise (PN)
sequences for each
Fourier fast transform window position within the entire searching window.
Such a
window could be large even for the synchronous bases station network. For
handoff, even
with the presence of the adjacent base station list information broadcast from
the anchoring
base station, the preamble search is of excessively high computational
complexity.
[006] Advancements to communication systems such as those standardized in the
evolution of WiMAX have resulted in concepts that build upon the initial frame
structure
found in the original 802.16e standard. These concepts result in new
possibilities for
addressing and synchronizing devices within the communication system. These
concepts
and possibilities also may be applied to any 3GPP or 3GPP2 system.
[007] It is therefore desirable to provide preambles that enable easy, fast
synchronization
between the subscriber station and the base stations and that provide low
complexity and
fast cell search after coarse synchronization.
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[008] Accordingly, there is a need for an improved preamble design, method and
apparatus which are suitable for the mobile, broadband wireless access
systems.
SUMMARY OF THE INVENTION
[009] In accordance with a first broad aspect, the present invention provides
a method
of transmitting data within a signal frame. The method comprises inserting a
first
synchronization preamble into a first location within the signal frame and
inserting a
second synchronization preamble into a second location within the signal
frame, wherein
the first synchronization preamble conveys information indicative of the
second location.
The method further comprises issuing the signal frame towards a receiving
device in a
wireless communication environment.
[010] In accordance with a second broad aspect, the present invention provides
a
method for generating a signal frame. The method comprises determining a first
location within the signal frame for inserting a first synchronization
preamble and a
second location within the signal frame for inserting a second synchronization
preamble, generating the first synchronization preamble at least in part on a
basis of the
determined second location of the second synchronization preamble, inserting
the first
synchronization preamble at the determined first location within the signal
frame,
inserting the second synchronization preamble at the determined second
location within
the signal frame and causing the signal frame to be issued towards a receiving
device in
a wireless communication environment.
[0111 In accordance with a third broad aspect, the present invention provides
a
transmitting device for transmitting a signal frame over a wireless
communication
environment. The transmitting device comprises a control entity operative for
determining
a first location within the signal frame for a first synchronization preamble
and a second
location within the signal frame for a second synchronization preamble,
generating the first
synchronization preamble at least in part on a basis of the determined second
location of
the second synchronization preamble, inserting the first synchronization
preamble at the
determined first location within the signal frame and inserting the second
synchronization
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preamble at the determined second location within the signal frame. The
transmitting
device further comprises transmitting circuitry for causing the signal frame
to be issued
towards a receiving device.
[012] In accordance with a fourth broad aspect, the present invention provides
a
method of receiving a signal frame in a wireless communication environment.
The
method comprises receiving a wireless signal comprising a plurality of signal
frames,
wherein each signal frame comprises a first synchronization preamble and a
second
synchronization preamble, identifying a first synchronization preamble within
a given
signal frame, determining at least in part on a basis of information conveyed
by the first
synchronization preamble a location within the given signal frame of the
second
synchronization preamble and obtaining from a combination of the first
synchronization
preamble and the second synchronization preamble transmission signalling
information.
[013] In accordance with a fifth broad aspect, the present invention
provides a
receiving device for receiving a signal frame in a wireless communication
environment.
The receiving device comprises receiving circuitry and a control entity. The
receiving
circuitry is for receiving a wireless signal comprising a plurality of signal
frames,
wherein each signal frame comprises a first synchronization preamble and a
second
synchronization preamble. The control entity is for identifying a first
synchronization
preamble within a given signal frame of the wireless signal, determining at
least in part
on a basis of information conveyed by the first synchronization preamble a
location
within the given signal frame of the second synchronization preamble and
obtaining from
a combination of the first synchronization preamble and the second
synchronization
preamble transmission signalling information.
[014] In accordance with a further aspect, the present invention provides a
method of
transmitting data within a signal frame, the method comprising: a) inserting a
first
synchronization preamble into a first location within the signal frame; b)
inserting a
second synchronization preamble into a second location within the signal
frame, wherein
the first synchronization preamble conveys information indicative of the
second location
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of the second synchronization preamble within the signal frame; and c) issuing
the signal
frame towards a receiving device in a wireless communication environment.
[015] In a further aspect, the present invention provides a method for
generating a
signal frame, comprising: a) determining a first location within the signal
frame for
inserting a first synchronization preamble and a second location within the
signal frame
for inserting a second synchronization preamble; b) generating the first
synchronization
preamble at least in part on a basis of the determined second location of the
second
synchronization preamble within the signal frame; c) inserting the first
synchronization
preamble at the determined first location within the signal frame; d)
inserting the second
synchronization preamble at the determined second location within the signal
frame; and
e) causing the signal frame to be issued towards a receiving device in a
wireless
communication environment.
[015a] In a further aspect, the present invention provides a transmitting
device for
transmitting a signal frame over a wireless communication environment, the
transmitting
device comprising: a) a control entity operative for: i) determining a first
location within
the signal frame for a first synchronization preamble and a second location
within the
signal frame for a second synchronization preamble; ii) generating the first
synchronization preamble at least in part on a basis of the determined second
location of
the second synchronization preamble within the signal frame; iii) inserting
the first
synchronization preamble at the determined first location within the signal
frame; and iv)
inserting the second synchronization preamble at the determined second
location within
the signal frame; b) transmitting circuitry for causing the signal frame to be
issued
towards a receiving device.
[015b] In a still further aspect, the present invention provides a method of
receiving a
signal frame in a wireless communication environment, the method comprising:
a)
receiving a wireless signal comprising a plurality of signal frames, each
signal frame
comprising a first synchronization preamble and a second synchronization
preamble; b)
identifying a first synchronization preamble within a given signal frame; c)
determining,
at least in part on a basis of information conveyed by the first
synchronization preamble,
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a location within the given signal frame of the second synchronization
preamble; and d)
obtaining, from a combination of the first synchronization preamble and the
second
synchronization preamble, transmission signaling information.
[015c] In a still further aspect, the present invention provides a receiving
device for
receiving a signal frame in a wireless communication environment, the
receiving device
comprising: a) receiving circuitry for receiving a wireless signal comprising
a plurality of
signal frames, each signal frame comprising a first synchronization preamble
and a
second synchronization preamble; and b) a control entity for: i) identifying
the first
synchronization preamble within a given signal frame of the wireless signal;
ii)
determining, at least in part on a basis of information conveyed by the first
synchronization preamble, a location within the given signal frame of the
second
synchronization preamble; iii) obtaining, from a combination of the first
synchronization
preamble and the second synchronization preamble, transmission signaling
information.
[015d] In a further aspect, the present invention provides a receiving device
for
receiving a signal frame in a wireless communication environment, the
receiving device
comprising: a) receiving circuitry for receiving a wireless signal comprising
a plurality of
signal frames, each signal frame comprising a first synchronization preamble
and a
second synchronization preamble; and b) a control entity for: i) identifying
the first
synchronization preamble within a given signal frame of the wireless signal;
ii)
identifying the second synchronization preamble within the given signal frame
at least in
part on a basis of information conveyed by the first synchronization preamble;
and iii)
obtaining, from at least one of the first synchronization preamble and the
second
synchronization preamble, control information.
[0161 These and other aspects and features of the present invention will now
become
apparent to those of ordinary skill in the art upon review of the following
description of
specific embodiments of the invention and the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
[017] In the accompanying drawings:
1018] Figure 1 shows a block representation of a wireless communication
system;
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[019] Figure 2 shows a block representation of a base station according to a
non-limiting
embodiment of the present invention;
[020] Figure 3 shows a block representation of a mobile station according to a
non-limiting
embodiment of the present invention;
[021] Figure 4 shows a block representation of a relay station according to a
non-limiting
embodiment of the present invention;
[022] Figure 5 shows a logical breakdown of a transmitter architecture
according to a non-
limiting embodiment of the present invention;
[023] Figure 6 shows a logical breakdown of a receiver architecture according
to a non-
limiting embodiment of the present invention;
[024] Figure 7 shows Figure 1 of I FEE 802.16m-08/003r1, an example of an
overall
network architecture;
[025] Figure 8 shows Figure 2 of IEEE 802.16m-08/003r1, a relay station in an
overall
network architecture;
[026] Figure 9 shows Figure 3 of IEEE 802.16m-08/003r1, a system reference
model;
[027] Figure 10 shows Figure 4 of IEEE 802.16m-08/003r1, the IEEE 802.16m
protocol
structure;
[028] Figure 11 shows Figure 5 of IFEE 802.16m-08/003r1, the IEEE 802.16m
MS/BS
data plane processing flow;
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[029] Figure 12 shows Figure 6 of IEEE 802.16m-08/003r1, the IEEE 802.16m
MS/BS
control plane processing flow;
[030] Figure 13 shows Figure 7 of IEEE 802.16m-08/003r1, generic protocol
architecture
to support multicarrier system;
[031] Figure 14 shows an example of a signal comprising frames, subframes and
first and
second synchronization sequences;
[032] Figures 15(a)-(c) show non-limiting representations of a synchronization
channel in
relation to primary and secondary carrier frequencies;
[033] Figures 16(a)-(c) show non-limiting representations of primary and
secondary
synchronization channels in relation to primary and secondary carrier
frequencies;
[034] Figure 17 shows a non-limiting example of a method used by a
transmitting device in
order to transmit signals in a wireless communication environment; and
[035] Figure 18 shows a non-limiting example of a method used by a receiving
device in
order to receive signals over a wireless communication environment.
[036] Other aspects and features of the present invention will become apparent
to those
ordinarily skilled in the art upon review of the following description of
specific
embodiments of the invention in conjunction with the accompanying figures.
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DETAILED DESCRIPTION
1037J Referring to the drawings, FIG. 1 shows a base station controller (BSC)
10 which
controls wireless communications within multiple cells 12, which cells are
served by
corresponding base stations (BS) 14. In some configurations, each cell is
further divided
into multiple sectors 13 or zones (not shown). In general, each base station
14 facilitates
communications using OFDM with mobile and/or wireless terminals 16, which are
within
the cell 12 associated with the corresponding base station 14. The movement of
the mobile
terminals (MS) 16 in relation to the base stations 14 results in significant
fluctuation in
channel conditions. As illustrated, the base stations 14 and mobile terminals
16 may
include multiple antennas to provide spatial diversity for communications. In
some
configurations, relay stations 15 may assist in communications between base
stations 14
and wireless terminals 16. Wireless mobile terminals 16 can be handed off from
any cell
12, sector 13, zone (not shown), base station 14 or relay station (RS) 15 to
another cell 12,
sector 13, zone (not shown), base station 14 or relay station 15. In some
configurations,
base stations 14 communicate with each other and with another network (such as
a core
network or the internet, both not shown) over a backhaul network 11. In some
configurations, a base station controller 10 is not needed.
1038] With reference to FIG. 2, an example of a base station 14 is
illustrated. The base
station 14 generally includes a control entity 20, a baseband processor 22,
transmit circuitry
24, receive circuitry 26, multiple antennas 28, and a network interface 30.
The receive
circuitry 26 receives radio frequency signals bearing information from one or
more remote
transmitters provided by mobile terminals 16 (illustrated in FIG. 3) and relay
stations 15
(illustrated in FIG. 4). A low noise amplifier and a filter (not shown) may
cooperate to
amplify and remove broadband interference from the signal for processing.
Downconversion and digitization circuitry (not shown) will then downconvert
the filtered,
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received signal to an intermediate or baseband frequency signal, which is then
digitized into
one or more digital streams.
[039] The baseband processor 22 processes the digitized received signal to
extract the
information or data bits conveyed in the received signal. This processing
typically
comprises demodulation, decoding, and error correction operations. As such,
the baseband
processor 22 is generally implemented in one or more digital signal processors
(DSPs) or
application-specific integrated circuits (ASICs). The received infoimation is
then sent across
a wireless network via the network interface 30 or transmitted to another
mobile terminal 16
serviced by the base station 14, either directly or with the assistance of a
relay 15.
[040] On the transmit side, the baseband processor 22 receives digitized data,
which may
represent voice, data, or control infoiniation, from the network interface 30
under the
control of control entity 20, and encodes the data for transmission, The
encoded data is
output to the transmit circuitry 24, where it is modulated by one or more
carrier signals
having a desired transmit frequency or frequencies. A power amplifier (not
shown) will
amplify the modulated carrier signals to a level appropriate for transmission,
and deliver
the modulated carrier signals to the antennas 28 through a matching network
(not shown).
Modulation and processing details are described in greater detail below.
10411 With reference to FIG. 3, an example of a mobile terminal 16 is
illustrated. Similarly
to the base station 14, the mobile terminal 16 will include a control entity
32, a baseband
processor 34, transmit circuitry 36, receive circuitry 38, multiple antennas
40, and-user
interface circuitry 42. The receive circuitry 38 receives radio frequency
signals bearing
information from one or more wireless transmitters, which could be base
stations 14 and/or
relays 15. A low noise amplifier and a filter (not shown) may cooperate to
amplify and
remove broadband interference from the signal for processing. Downconversion
and
digitization circuitry (not shown) will then downconvert the filtered,
received signal to an
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intermediate or baseband frequency signal, which is then digitized into one or
more
digital streams.
[042] The baseband processor 34 processes the digitized received signal to
extract the
information or data bits conveyed in the received signal. This processing
typically
comprises demodulation, decoding, and error correction operations. The
baseband
processor 34 is generally implemented in one or more digital signal processors
(DSPs) and
application specific integrated circuits (ASICs).
1043] For transmission, the baseband processor 34 receives digitized data,
which may
represent voice, video, data, or control inforrnation, from the control entity
32, which it
encodes for transmission. The encoded data is output to the transmit circuitry
36, where it
is used by a modulator to modulate one or more carrier signals that is at a
desired transmit
frequency or frequencies. A power amplifier (not shown) will amplify the
modulated carrier
signals to a level appropriate for transmission, and deliver the modulated
carrier signal to
the antennas 40 through a matching network (not shown). Various modulation and
processing techniques available to those skilled in the art are used for
signal transmission
between the mobile terminal and the base station, either directly or via the
relay station 15.
[044] In OFDM modulation, the transmission band is divided into multiple,
orthogonal
carrier waves. Each carrier wave is modulated according to the digital data to
be
transmitted. Because OFDM divides the transmission band into multiple
carriers, the
bandwidth per carrier decreases and the modulation time per carrier increases.
Since the
multiple carriers are transmitted in parallel, the transmission rate for the
digital data, or
symbols, on any given carrier is lower than when a single carrier is used.
[045] OFDM modulation utilizes the performance of an Inverse Fast Fourier
Transform
(1FFT) on the information to be transmitted. For demodulation, the performance
of a Fast
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Fourier Transform (FFT) on the received signal recovers the transmitted
information. In
practice, the IFFT and FFT are provided by digital signal processing carrying
out an Inverse
Discrete Fourier Transform (IDFT) and Discrete Fourier Transform (DFT),
respectively.
Accordingly, the characterizing feature of OFDM modulation is that orthogonal
carrier
waves are generated for multiple bands within a transmission channel. The
modulated
signals are digital signals having a relatively low transmission rate and
capable of staying
within their respective bands. The individual carrier waves are not modulated
directly by
the digital signals. Instead, all carrier waves are modulated at once by IFFT
processing.
[046] In operation, OFDM is preferably used for at least downlink transmission
from the
base stations 14 to the mobile terminals 16. Each base station 14 is equipped
with "n"
transmit antennas 28 (n >=1), and each mobile terminal 16 is equipped with "m"
receive
antennas 40 (m>=1).
[047] Notably, the respective antennas can be used for reception and
transmission using
appropriate duplexers or switches and are so labelled only for clarity.
[048] When relay stations 15 are used, OFDM is preferably used for downlink
transmission
from the base stations 14 to the relays 15 and from relay stations 15 to the
mobile terminals
16.
[049] With reference to FIG. 4, an example of a relay station 15 is
illustrated. Similarly to
the 25 base station 14, and the mobile terminal 16, the relay station 15 will
include a
control entity 132, a baseband processor 134, transmit circuitry 136, receive
circuitry
138, multiple antennas 130, and relay circuitry 142. The relay circuitry 142
enables the
relay 15 to assist in communications between a base station 16 and mobile
terminals 16.
The receive circuitry 138 receives radio frequency signals bearing information
from one
or more base stations 14 and mobile terminals 16. A low noise amplifier and a
filter
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(not shown) may cooperate to amplify and remove broadband interference from
the
signal for processing. Downconversion and digitization circuitry (not shown)
will then
downconvert the filtered, received signal to an intermediate or baseband
frequency
signal, which is then digitized into one or more digital streams.
[050] The baseband processor 134 processes the digitized received signal to
extract the
information or data bits conveyed in the received signal. This processing
typically
comprises demodulation, decoding, and error correction operations. The
baseband
processor 134 is generally implemented in one or more digital signal
processors (DSPs) and
application specific integrated circuits (ASICs).
[051] For transmission, the baseband processor 134 receives digitized data,
which may
represent voice, video, data, or control information, from the control entity
132, which it
encodes for transmission. The encoded data is output to the transmit circuitry
136, where it
is used by a modulator to modulate one or more carrier signals that is at a
desired transmit
frequency or frequencies. A power amplifier (not shown) will amplify the
modulated carrier
signals to a level appropriate for transmission, and deliver the modulated
carrier signal to
the antennas 130 through a matching network (not shown). Various modulation
and
processing techniques available to those skilled in the art are used for
signal transmission
between the mobile terminal and the base station, either directly or
indirectly via a relay
station 15, as described above.
[052] With reference to FIG. 5, a logical OFDM transmission architecture will
be
described. Initially, the base station controller 10 will send data to be
transmitted to various
mobile terminals 16 to the transmitting devices, which could be the base
station 14 directly
or the base station 14 with the assistance of a relay station 15. The base
station 14 may use
the channel quality indicators (COIs) associated with the mobile terminals to
schedule
the data for transmission as well as select appropriate coding and modulation
for
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transmitting the scheduled data. The CQIs may be directly from the mobile
terminals
16 or determined at the base station 14 based on information provided by the
mobile
terminals 16. In either case, the CQI for each mobile tenninal 16 is a
function of the
degree to which the channel amplitude (or response) varies across the OFDM
frequency band.
[053] Scheduled data 44, which is a stream of bits, is scrambled in a manner
reducing the
peak-to-average power ratio associated with the data using data scrambling
logic 46. A
cyclic redundancy check (CRC) for the scrambled data is determined and
appended to the
scrambled data using CRC adding logic 48. Next, channel coding is performed
using
channel encoder logic 50 to effectively add redundancy to the data to
facilitate recovery and
error correction at the mobile terminal 16. Again, the channel coding for a
particular mobile
teiminal 16 is based on the CQI. In some implementations, the channel encoder
logic 50
uses known Turbo encoding techniques. The encoded data is then processed by
rate
matching logic 52 to compensate for the data expansion associated with
encoding.
[054] Bit interleaver logic 54 systematically reorders the bits in the encoded
data to
minimize the loss of consecutive data bits. The resultant data bits are
systematically
mapped into corresponding symbols depending on the chosen baseband modulation
by
mapping logic 56. Preferably, Quadrature Amplitude Modulation (QAM) or
Quadrature
Phase Shift Key (QPSK) modulation is used. The degree of modulation is
preferably
chosen based on the CQI for the particular mobile terminal. The symbols may be
systematically reordered to further bolster the immunity of the transmitted
signal to
periodic data loss caused by frequency selective fading using symbol
interleaver logic 58.
[055] At this point, groups of bits have been mapped into symbols representing
locations in
an amplitude and phase constellation. When spatial diversity is desired,
blocks of symbols
are then processed by space-time block code (STC) encoder logic 60, which
modifies the
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symbols in a fashion making the transmitted signals more resistant to
interference and
more readily decoded at a mobile terminal 16. The STC encoder logic 60 will
process the
incoming symbols and provide "n" outputs corresponding to the number of
transmit
antennas 28 for the base station 14. The control system 20 and/or baseband
processor 22 as
described above with respect to FIG. 5 will provide a mapping control signal
to control
STC encoding. At this point, assume the symbols for the "n" outputs are
representative of
the data to be transmitted and capable of being recovered by the mobile
terminal 16.
1056] For the present example, assume the base station 14 has two antennas 28
(n--2) and
the STC encoder logic 60 provides two output streams of symbols. Accordingly,
each of the
symbol streams output by the STC encoder logic 60 is sent to a corresponding
IFFT
processor 62, illustrated separately for ease of understanding. Those skilled
in the art will
recognize that one or more processors may be used to provide such digital
signal
processing, alone or in combination with other processing described herein.
The IFFT
processors 62 will preferably operate on the respective symbols to provide an
inverse
Fourier Transform. The output of the IFFT processors 62 provides symbols in
the time
domain. The time domain symbols are grouped into frames, which are associated
with a
prefix by prefix insertion logic 64. Each of the resultant signals is up-
converted in the
digital domain to an intermediate frequency and converted to an analog signal
via the
corresponding digital up-conversion (DUC) and digital-to-analog (D/A)
conversion
circuitry 66. The resultant (analog) signals are then simultaneously modulated
at the
desired RF frequency, amplified, and transmitted via the RF circuitry 68 and
antennas
28. Notably, pilot signals known by the intended mobile terminal 16 are
scattered
among the sub-carriers. The mobile terminal 16, which is discussed in detail
below, will
use the pilot signals for channel estimation.
10571 Reference is now made to FIG. 6 to illustrate reception of the
transmitted signals by a
mobile teiminal 16, either directly from base station 14 or with the
assistance of relay 15.
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Upon arrival of the transmitted signals at each of the antennas 40 of the
mobile terminal
16, the respective signals are demodulated and amplified by corresponding RF
circuitry 70.
For the sake of conciseness and clarity, only one of the two receive paths is
described and
illustrated in detail. Analog-to-digital (A/D) converter and down-conversion
circuitry 72
digitizes and downconverts the analog signal for digital processing. The
resultant digitized
signal may be used by automatic gain control circuitry (AGC) 74 to control the
gain of the
amplifiers in the RF circuitry 70 based on the received signal level.
[058] Initially, the digitized signal is provided to synchronization logic 76,
which includes
coarse synchronization logic 78, which buffers several OFDM symbols and
calculates an
auto-correlation between the two successive OFDM symbols. A resultant time
index
corresponding to the maximum of the correlation result deteiiiiines a fine
synchronization
search window, which is used by fine synchronization logic 80 to deteilaine a
precise
framing starting position based on the headers. The output of the fine
synchronization
logic 80 facilitates frame acquisition by frame alignment logic 84. Proper
framing
alignment is important so that subsequent FFT processing provides an accurate
conversion
from the time domain to the frequency domain. The fine synchronization
algorithm is
based on the correlation between the received pilot signals carried by the
headers and a
local copy of the known pilot data. Once frame alignment acquisition occurs,
the prefix
of the OFDM symbol is removed with prefix removal logic 86 and resultant
samples
are sent to frequency offset correction logic 88, which compensates for the
system
frequency offset caused by the unmatched local oscillators in the transmitter
and the
receiver. Preferably, the synchronization logic 76 includes frequency offset
and clock
estimation logic 82, which is based on the headers to help estimate such
effects on the
transmitted signal and provide those estimations to the correction logic 88 to
properly
process OFDM symbols.
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10591 At this point, the OFDM symbols in the time domain are ready for
conversion to the
frequency domain using FFT processing logic 90. The results are frequency
domain
symbols, which are sent to processing logic 92. The processing logic 92
extracts the
scattered pilot signal using scattered pilot extraction logic 94, determines a
channel
estimate based on the extracted pilot signal using channel estimation logic
96, and
provides channel responses for all sub-carriers using channel reconstruction
logic 98. In
order to determine a channel response for each of the sub-carriers, the pilot
signal is
essentially multiple pilot symbols that are scattered among the data symbols
throughout the
OFDM sub-carriers in a known pattern in both time and frequency. Continuing
with FIG.
6, the processing logic compares the received pilot symbols with the pilot
symbols that are
expected in certain sub-carriers at certain times to determine a channel
response for the
sub-carriers in which pilot symbols were transmitted. The results are
interpolated to
estimate a channel response for most, if not all, of the remaining sub-
carriers for which
pilot symbols were not provided. The actual and interpolated channel responses
are
used to estimate an overall channel response, which includes the channel
responses for
most, if not all, of the sub-carriers in the OFDM channel.
[060] The frequency domain symbols and channel reconstruction information,
which are
derived from the channel responses for each receive path are provided to an
STC decoder
100, which provides STC decoding on both received paths to recover the
transmitted
symbols. The channel reconstruction information provides equalization
information to the
STC decoder 100 sufficient to remove the effects of the transmission channel
when
processing the respective frequency domain symbols.
10611 The recovered symbols are placed back in order using symbol de-
interleaver logic
102, which corresponds to the symbol interleaver logic 58 of the transmitter.
The de-
interleaved symbols are then demodulated or de-mapped to a corresponding
bitstream using
de-mapping logic 104. The bits are then de-interleaved using bit de-
interleaver logic 106,
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which corresponds to the bit interleaver logic 54 of the transmitter
architecture. The de-
interleaved bits are then processed by rate de-matching logic 108 and
presented to channel
decoder logic 110 to recover the initially scrambled data and the CRC
checksum.
Accordingly, CRC logic 112 removes the CRC checksum, checks the scrambled data
in
traditional fashion, and provides it to the de-scrambling logic 114 for de-
scrambling using
the known base station de-scrambling code to recover the originally
transmitted data 116.
[062] In parallel to recovering the data 116, a CQI, or at least information
sufficient to
create a CQI at the base station 14, is determined and transmitted to the base
station 14. As
noted above, the CQI may be a function of the carrier-to-interference ratio
(CR), as well as
the degree to which the channel response varies across the various sub-
carriers in the
OFDM frequency band. For this embodiment, the channel gain for each sub-
carrier in the
OFDM frequency band being used to transmit information is compared relative to
one
another to determine the degree to which the channel gain varies across the
OFDM
frequency band. Although numerous techniques are available to measure the
degree of
variation, one technique is to calculate the standard deviation of the channel
gain for each
sub-carrier throughout the OFDM frequency band being used to transmit data.
[063] In some embodiments, a relay station may operate in a time division
manner using only
one radio, or alternatively include multiple radios.
[064] FIGs. 1 to 6 provide one specific example of a communication system that
could be
used to implement embodiments of the application. It is to be understood that
embodiments
of the application can be implemented with communications systems having
architectures
that are different than the specific example, but that operate in a manner
consistent with the
implementation of the embodiments as described herein.
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[065] Turning now to Fig. 7, there is shown an example network reference
model, which is
a logical representation of a network that supports wireless communications
among the
aforementioned BSs 14, MSs 16 and RSs 15, in accordance with a non-limiting
embodiment of the present invention. The network reference model identifies
functional
entities and reference points over which interoperability is achieved between
these
functional entities. Specifically, the network reference model can include a
MS 16, an
Access Service Network (ASN), and a Connectivity Service Network (CSN).
10661 The ASN can be defined as a complete set of network functions needed to
provide
radio access to a subscriber (e.g., an IEEE 802.16e/m subscriber). The ASN can
comprise
network elements such as one or more BS s 14, and one or more ASN gateways. An
ASN
may be shared by more than one CSN. The ASN can provide the following
functions:
- Layer-1 and Layer-2 connectivity with the MS 16;
Transfer of AAA messages to subscriber's Home Network Service Provider (H-NSP)
for authentication, authorization and session accounting for subscriber
sessions
- Network discovery and selection of the subscriber's preferred NSP;
Relay functionality for establishing Layer-3 (L3) connectivity with the MS 16
(e.g.,
IP address allocation);
- Radio resource management.
[067] In addition to the above functions, for a portable and mobile
environment, an ASN
can further support the following functions:
ASN anchored mobility;
CSN anchored mobility;
- Paging;
ASN-CSN tunnelling.
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10681 For its part, the CSN can be defined as a set of network functions that
provide IP
connectivity services to the subscriber. A CSN may provide the following
functions:
MS IP address and endpoint parameter allocation for user sessions;
AAA proxy or server;
- Policy and Admission Control based on user subscription profiles;
- ASN-CSN tunnelling support;
- Subscriber billing and inter-operator settlement;
- Inter-CSN tunnelling for roaming;
- Inter-ASN mobility.
[069] The CSN can provide services such as location based services,
connectivity for peer-
to-peer services, provisioning, authorization and/or connectivity to IP
multimedia services.
The CSN may further comprise network elements such as routers, AAA
proxy/servers, user
databases, and interworking gateway MSs. In the context of IEEE 802.16m, the
CSN may
be deployed as part of a IEEE 802.16m NSP or as part of an incumbent WEE
802.16e NSP.
[0701 In addition, RSs 15 may be deployed to provide improved coverage and/or
capacity.
With reference to Fig. 8, a BS 14 that is capable of supporting a legacy RS
communicates
with the legacy RS in the "legacy zone". The BS 14 is not required to provide
legacy
protocol support in the "16m zone". The relay protocol design could be based
on the
design of IEEE 802-16j, although it may be different from IEEE 802-16j
protocols used in
the "legacy zone".
[071] With reference now to Fig. 9, there is shown a system reference model,
which applies
to both the MS 16 and the BS 14 and includes various functional blocks
including a
Medium Access Control (MAC) common part sublayer, a convergence sublayer, a
security
sublayer and a physical (PHY) layer.
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[072] The convergence sublayer performs mapping of external network data
received
through the CS SAP into MAC SDUs received by the MAC CPS through the MAC SAP,
classification of external network SDUs and associating them to MAC SFID and
CID,
Payload header suppression/compression (PHS).
[073] The security sublayer performs authentication and secure key exchange
and
Encryption.
[074] The physical layer performs Physical layer protocol and functions.
[075] The MAC common part sublayer is now described in greater detail.
Firstly, it will be
appreciated that Medium Access Control (MAC) is connection-oriented. That is
to say, for
the purposes of mapping to services on the MS 16 and associating varying
levels of QoS,
data communications are carried out in the context of "connections". In
particular, "service
flows" may be provisioned when the MS 16 is installed in the system. Shortly
after
registration of the MS 16, connections are associated with these service flows
(one
connection per service flow) to provide a reference against which to request
bandwidth.
Additionally, new connections may be established when a customer's service
needs change.
A connection defines both the mapping between peer convergence processes that
utilize the
MAC and a service flow. The service flow defines the QoS parameters for the
MAC
protocol data units (PDUs) that are exchanged on the connection. Thus, service
flows are
integral to the bandwidth allocation process. Specifically, the MS 16 requests
uplink
bandwidth on a per connection basis (implicitly identifying the service flow).
Bandwidth
can be granted by the BS to a MS as an aggregate of grants in response to per
connection
requests from the MS.
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[0761 With additional reference to Fig. 10, the MAC common part sublayer (CPS)
is
classified into radio resource control and management (RRCM) functions and
medium
access control (MAC) functions.
[077] The RRCM functions include several functional blocks that are related
with radio
resource functions such as:
Radio Resource Management
- Mobility Management
- Network Entry Management
- Location Management
Idle Mode Management
Security Management
System Configuration Management
- MBS (Multicast and Broadcasting Service)
- Service Flow and Connection Management
- Relay functions
- Self Organization
Multi-Carrier
Radio Resource Management
[078] The Radio Resource Management block adjusts radio network parameters
based on
traffic load, and also includes function of load control (load balancing),
admission control
and interference control.
Mobility Management
[079] The Mobility Management block supports functions related to Intra-RAT /
Inter-RAT
handover. The Mobility Management block handles the Intra-RAT / Inter-RAT
Network
topology acquisition which includes the advertisement and measurement, manages
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candidate neighbor target BSs/RSs and also decides whether the MS performs
Intra-RAT /
Inter-RAT handover operation.
Network Entry Management
[0801 The Network Entry Management block is in charge of initialization and
access
procedures. The Network Entry Management block may generate management
messages
which are needed during access procedures, i.e., ranging, basic capability
negotiation,
registration, and so on.
Location Management
[0811 The Location Management block is in charge of supporting location based
service
(LBS). The Location Management block may generate messages including the LBS
information.
Idle Mode Management
[0821 The Idle Mode Management block manages location update operation during
idle
mode. The Idle Mode Management block controls idle mode operation, and
generates the
paging advertisement message based on paging message from paging controller in
the core
network side.
S ecurity Management
[0831 The Security Management block is in charge of
authentication/authorization and key
management for secure communication.
System Configuration Management
[0841 The System Configuration Management block manages system configuration
parameters, and system parameters and system configuration infoimation for
transmission
to the MS.
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MB S (Multicast and Broadcasting Service)
[085] The MBS (Multicast Broadcast Service) block controls management messages
and
data associated with broadcasting and/or multicasting service.
Service Flow and Connection Management
10861 The Service Flow and Connection Management block allocates "MS
identifiers" (or
station identifiers ¨ STIDs) and "flow identifiers" (FIDs) during
access/handover/ service
flow creation procedures. The MS identifiers and FIDs will be discussed
further below.
Relay functions
[087] The Relay Functions block includes functions to support multi-hop relay
mechanisms. The functions include procedures to maintain relay paths between
BS and an
access RS.
Self Organization
[088] The Self Organization block performs functions to support self
configuration and self
optimization mechanisms. The functions include procedures to request RSs/MSs
to report
measurements for self configuration and self optimization and receive the
measurements
from the RSs/MSs.
Multi-Carrier
[089] The Multi-carrier (MC) block enables a common MAC entity to control a
PHY
spanning over multiple frequency channels. The channels may be of different
bandwidths
(e.g. 5, 10 and 20 MHz), be on contiguous or non-contiguous frequency bands.
The
channels may be of the same or different duplexing modes, e.g. FDD, TDD, or a
mix of
bidirectional and broadcast only carriers. For contiguous frequency channels,
the
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overlapped guard sub-carriers are aligned in frequency domain in order to be
used for data
transmission.
[090] The medium access control (MAC) includes function blocks which are
related to the
physical layer and link controls such as:
PHY Control
Control Signaling
- Sleep Mode Management
QoS
- Scheduling and Resource Multiplexing
- ARQ
Fragmentation/Packing
MAC PDU formation
Multi-Radio Coexistence
- Data forwarding
Interference Management
Inter-BS coordination
PHY Control
[091] The PHY Control block handles PHY signaling such as ranging,
measurement/feedback (CQI), and HARQ ACK/NACK. Based on CQI and HARQ
ACK/NACK, the PHY Control block estimates channel quality as seen by the MS,
and
performs link adaptation via adjusting modulation and coding scheme (MCS),
and/or power
level. In the ranging procedure, PHY control block does uplink synchronization
with
power adjustment, frequency offset and timing offset estimation.
Control Signaling
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[092] The Control Signaling block generates resource allocation messages.
Sleep Mode
Management block handles sleep mode operation.
Sleep Mode Management
[093] The Sleep Mode Management block may also generate MAC signaling related
to
sleep operation, and may communicate with Scheduling and Resource Multiplexing
block
in order to operate properly according to sleep period.
QoS
[094] The QoS block handles QoS management based on QoS parameters input from
the
Service Flow and Connection Management block for each connection.
Scheduling and Resource Multiplexing
[095] The Scheduling and Resource Multiplexing block schedules and multiplexes
packets
based on properties of connections. In order to reflect properties of
connections Scheduling
and Resource Multiplexing block receives QoS information from The QoS block
for each
connection.
ARQ
[0961 The ARQ block handles MAC ARQ function. For ARQ-enabled connections, ARQ
block logically splits MAC SDU to ARQ blocks, and numbers each logical ARQ
block.
ARQ block may also generate ARQ management messages such as feedback message
(ACK/NACK information).
Fragmentation/Packing
[097] The Fragmentation/Packing block performs fragmenting or packing MSDUs
based on
scheduling results from Scheduling and Resource Multiplexing block.
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MAC PDU folination
[0981 The MAC PDU formation block constructs MAC PDU so that BS/MS can
transmit
user traffic or management messages into PHY channel. MAC PDU formation block
adds
MAC header and may add sub-headers.
Multi-Radio Coexistence
[0991 The Multi-Radio Coexistence block perfoims functions to support
concurrent
operations of IEEE 802.16m and non-IEEE 802.16m radios collocated on the same
mobile
station.
Data forwarding
[01001 The Data Forwarding block performs forwarding functions when RSs are
present on
the path between BS and MS. The Data Forwarding block may cooperate with other
blocks
such as Scheduling and Resource Multiplexing block and MAC PDU formation
block.
Interference Management
[01011 The Interference Management block performs functions to manage the
inter-
cell/sector interference. The operations may include:
MAC layer operation
- Interference measurement/assessment report sent via MAC signaling
- Interference mitigation by scheduling and flexible frequency reuse
- PHY layer operation
- Transmit power control
- Interference randomization
- Interference cancellation
- Interference measurement
Tx beamforming/precoding
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Inter-BS coordination
[0102] The Inter-BS coordination block performs functions to coordinate the
actions of
multiple BSs by exchanging information, e.g., interference management. The
functions
include procedures to exchange infoluiation for e.g., interference management
between the
BSs by backbone signaling and by MS MAC messaging. The information may include
interference characteristics, e.g. interference measurement results, etc.
[0103] Reference is now made to Fig. 11, which shows the user traffic data
flow and
processing at the BS 14 and the MS 16. The dashed arrows show the user traffic
data flow
from the network layer to the physical layer and vice versa. On the transmit
side, a network
layer packet is processed by the convergence sublayer, the ARQ function (if
present), the
fragmentation/packing function and the MAC PDU formation function, to form MAC
PDU(s) to be sent to the physical layer. On the receive side, a physical layer
SDU is
processed by MAC PDU formation function, the fragmentation/packing function,
the ARQ
function (if present) and the convergence sublayer function, to form the
network layer
packets. The solid arrows show the control primitives among the CPS functions
and
between the CPS and PHY that are related to the processing of user traffic
data.
[0104] Reference is now made to Fig. 12, which shows the CPS control plane
signaling
flow and processing at the BS 16 and the MS 14. On the transmit side, the
dashed arrows
show the flow of control plane signaling from the control plane functions to
the data plane
functions and the processing of the control plane signaling by the data plane
functions to
foul, the corresponding MAC signaling (e.g. MAC management messages, MAC
header/sub-header) to be transmitted over the air. On the receive side, the
dashed arrows
show the processing of the received over-the-air MAC signaling by the data
plane functions
and the reception of the corresponding control plane signaling by the control
plane
functions. The solid arrows show the control primitives among the CPS
functions and
between the CPS and PHY that are related to the processing of control plane
signaling. The
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solid arrows between M SAP/C SAP and MAC functional blocks show the control
and
management primitives to/from Network Control and Management System (NCMS).
The
primitives to/from M_SAP/C_SAP define the network involved fiinctionalities
such as
inter-BS interference management, inter/intra RAT mobility management, etc,
and
management related finactionalities such as location management, system
configuration etc.
[0105] Reference is now made to Fig 13, which shows a generic protocol
architecture to
support a multicarrier system. A common MAC entity may control a PHY spanning
over
multiple frequency channels. Some MAC messages sent on one carrier may also
apply to
other carriers. The channels may be of different bandwidths (e.g. 5, 10 and 20
MHz), be on
contiguous or non-contiguous frequency bands. The channels may be of different
duplexing
modes, e.g. FDD, TDD, or a mix of bidirectional and broadcast only carriers.
[0106] The common MAC entity may support simultaneous presence of MSs 16 with
different capabilities, such as operation over one channel at a time only or
aggregation
across contiguous or non-contiguous channels.
[01071 In OFDM and OFDMA wireless communication systems, any mobile station 16
that
intends to enter the system needs to establish time and frequency
synchronization with a
base station 14 that is transmitting signals, as well as obtain identification
information
(such as the cell ID) of the transmitting device, which in most cases is a
base station 14.
The mobile station 16 must thus synchronize to the base station 14 and detect
certain base
station parameters, such as the cell ID. The cell ID is generally obtained by
detecting a
preamble used by the certain base station 14 that is inserted into each signal
frame that is
issued from the base station 14. Although the transmitting device will be
described herein
as being a base station 14, it should be appreciated that the transmitting
device could also
be a relay station 15.
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[0108] In general, preambles may provide at least one of the following
operations: fast base
station access, base station identification/selection and C/I ratio
measurement, framing and
timing synchronization, frequency and sampling clock offset estimation and
initial channel
estimation. Ideally, a frame preamble is designed in order to have minimized
overhead in
order to provide greater spectral efficiency and radio capacity.
[0109] Due to an increase of channel bandwidth in broadband wireless access,
as well as an
increase in FTT size, searching for a preamble in a received signal can
require high
computational complexity by the mobile station 16.
101101 In evolved versions of wireless communication systems such as 802.16m,
the frame
structure is such that new preamble configuration is desirable. It is possible
for this
configuration to provide relative timing of primary secondary preambles, use
of a primary
synchronisation channel to convey other information to the mobile (including
signalling
timing/ location of secondary preamble, group ID (specifically to a group of
localized
cells), bandwidth and/ or multi-carrier structure, legacy system parameters,
other
information useful to the mobile), structure and/ or position of the
synchronization channels
relative to multi-carrier structures, specific code structure for mobile
base/relay stations,
relative timing options for preambles and superframe header.
[0111] In accordance with an embodiment of the present invention, each frame
in an
OFDM signal is provided with at least a first preamble and a second preamble.
The first
preamble is designed such that the overall searching for the first preamble
and the second
preamble is relatively fast and requires less computational complexity than
existing
preamble designs. The first preamble and the second preamble may be used for
coarse
timing and frame synchronization, cell ID identification and frequency
synchronization.
The first and second preambles may also support frequency domain fine
frequency
synchronization. In addition the control information is conveyed on the
preamble, reduced
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ambiguity in timing of primary and secondary synchronization channels is
provided, the
number of total cell IDs is increased, and there is less ambiguity in
multicarrier preamble
placements. Although a first and second preamble will be described for
simplicity below, it
should be appreciated that the present invention could also be implemented
using three or
more preambles within a signal frame.
[0112] As will be described in more detail below, the first preamble and the
second
preamble provide first and second synchronization sequences that enable a
mobile station
to gain access to a base station or to a plurality of base stations. At least
one of the first and
second preambles may coexist with the existing legacy preamble, or replace the
legacy
preamble. The term "legacy preamble" is intended to include the prior art
preamble in an
OFDMA frame, as described in IEEE802.16-2004.
[0113] The first preamble comprises a first synchronization sequence capable
of conveying
information. In accordance with a non-limiting example, at least a portion of
the first
synchronization sequence is capable of conveying a "cell group ID" that is
associated to a
group of base stations. The group of base stations may be grouped together on
the basis of
geography or a common characteristic, such as being mobile base stations,
among other
possibilities.
[0114] As will be described in more detail below, the first synchronization
sequence of the
first preamble may further convey additional information relating to different
attributes or
parameters associated with the transmitting base station 14 or the certain
group of base
stations to which the transmitting base station 14 belongs. The first
synchronization
sequence may also contain certain control info/Illation that is intended to be
conveyed to a
mobile device 16.
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[0115] The second preamble comprises a second synchronization sequence that
conveys
information indicative of a "local ID" associated to the transmitting base
station 14 within
the group of base stations. As such, when combined, the first synchronization
sequence and
the second synchronization sequence convey a unique cell ID of the
transmitting base
station. The combination of the first synchronization sequence and the second
synchronization sequence may also convey certain control information to a
mobile device
16.
[0116] Shown in Figure 14 is a non-limiting example of an OFDM signal 1400
employed
by the present invention. This OFDM signal 1400 is sent as a plurality of
sequential OFDM
frames 1402 or blocks that typically contain 1000 bits of data. Each OFDM
frame 1402
comprises a number of subframes, which have been numbered 1404a-e in the non-
limiting
example illustrated. It should be appreciated that each OFDM frame 1402 could
include a
different number of subframes 1404. The subframes are allocated for preambles,
headers or
OFDM symbols, as will be described in more detail below. Futhremore, the
subframes
could be on different subcarriers. The structure could be similar to, but not
limited by, the
one proposed in 802.16m, which is envisaged to be similar to those that will
be developed
in 3GPP and 3GPP2 technologies.
[0117] In the example shown in Figure 14, subframe 1404a contains the first
preamble,
which comprises the first synchronization sequence 1406 and subframe 1404c
contains the
second preamble which comprises the second synchronization sequence 1408.
Subframe
1404b contains a header. Subframes 1404d and 1404e contain the OFDM symbols,
which
are used to transmit voice data, video data, control information or any other
data of
information intended to be transmitted to a receiving mobile station 16 over
the wireless
network.
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[0118] It should be appreciated that the relative position or location within
the OFDM
frame of the preambles, header and OFDM signals can be fixed for each OFDM
frame or
can vary from one OFDM frame to the next. In some cases, the first preamble
("preamble
1") can be sent on the first subframe and the second preamble ("preamble 2")
can be sent
on the second subframe. Alternatively, it is possible for the second preamble
to be
positioned before the first preamble. For example, in some embodiments, the
first preamble
is sent on a subframe immediately following the subframe containing the second
preamble.
In alternative embodiments, the header is sent on the subframe immediately
following the
second preamble. In some cases, the header is a superframe header, such that
it is not
included within each frame, and instead is only included within every fourth
or fifth frame,
for example. In such a situation, the first preamble and the second preamble
may be
adjacent to one another, or separated by subframes containing OFDM symbols.
[0119] Given that the relative position of the first and second preambles can
vary, in
accordance with the present invention, the first preamble is designed to
convey information
indicative of the location within the frame of the second preamble. In this
manner, when the
OFDM frames are received at a mobile station 16, it is easier and faster for
the receiving
mobile station 16 to search for, and locate, both the first and second
preambles.
[0120] The infomiation indicative of the location, or relative location,
within the OFDM
frame of the second preamble, is generally carried via the first
synchronization sequence of
the first preamble. More specifically, the first synchronization sequence is
able to convey
information indicative of the location of the second preamble within the OFDM
frame. The
first synchronization sequence may convey information indicative of a relative
timing
between the first preamble and the second preamble, or the first
synchronization sequence
may convey information indicative of an offset or relative location between
the first
preamble and the second preamble. Based on this infolination a mobile station
16 that
receives the OFDM signal is able to quickly determine where to look in an OFDM
frame
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for the second preamble, thereby greatly reducing the time and computational
complexity
necessary to find the second preamble and establish synchronization with the
base station
14 and identify the unique Cell ID of the transmitting base station 14.
[0121] As mentioned above, the first preamble carries the information
indicative of the
location within the OFDM frame of the second preamble using a first
synchronization
sequence. In a non-limiting example, the first preamble may use 1 of 40
synchronization
sequences, wherein the synchronization sequence is made up of a first portion
that provides
1 of 10 possible "cell group 1Ds" and a second portion that provides 1 of 4
possible offsets
between the first preamble and the second preamble. As such, the
synchronization sequence
is made up of a first portion that provides a "cell group ID" of a group of
base stations to
which the transmitting base station belongs, and a second portion that provide
an indication
of an "offset" between the first preamble and the second preamble. By
signalling the
"offset", the receiving mobile station 16 will not have to search each
subframe position for
the second preamble. Instead, the mobile station 16 will know exactly where to
look,
thereby reducing the searching complexity.
[0122] It should be appreciated that any number of synchronization sequences
could be
used by the first preamble, and that the first portion is not limited to l of
10 sequences. In
addition, instead of the second portion of the synchronization sequence
providing an
indication of an "offset" between the first preamble and the second preamble,
the second
portion of the synchronization sequence could provide an indication of a
relative timing
between the two preambles.
[0123] The first synchronization sequence may further comprise a third portion
that
conveys other information, which could be control information or infoiniation
indicative of
an attribute or parameter associated with the group of base stations. The
third portion could
also convey information indicative of a relative location of the header or
superframe
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header, or the relative position between the first preamble and a legacy
frame, among other
possibilities.
[0124] As mentioned above, the second preamble comprises a second
synchronization
sequence that conveys a "local ID" associated with the transmitting base
station within the
group of base stations. For example, the second synchronization sequence could
use 1 of
114 sequences (or any other possible number of sequences), that are each
respectively
associated with a different base station in the group of base stations. As
such, when the first
portion of the first synchronization sequence (which indicates a group of base
stations) is
combined with the second synchronization sequence (which indicates the
transmitting base
station within the group) a complete cell ID is obtained.
[0125] The second synchronization sequence may simply carry the local ID of
the
transmitting base station 16, or alternatively may carry additional
information as well. For
example, the second synchronization may comprise a first portion that carries
the "local
ID" of the transmitting base station 16, and a second portion that carries
additional
information, such as control information, or a portion of control information
that when
combined with a portion of the first synchronization sequence conveys control
information.
[0126] In accordance with a non-limiting example, the first synchronization
sequence
belongs to a first set of synchronization sequences and the second
synchronization sequence
belongs to a second set of synchronization sequences. The first set of
synchronization
sequences is preferably smaller than the second set of synchronization
sequences, in order
to facilitate the ease and speed of searching for the first preamble. In the
example given
above, the first synchronization sequence belongs to a set of 40
synchronization sequences
and the second synchronization sequence belongs to a set of 114
synchronization
sequences. This facilitates faster searching for the primary sequence, and
given that the
primary sequence provides the location within the signal frame of the second
preamble, the
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overall time and complexity required for searching for both the first and
second preambles
is greatly reduced.
101271 As mentioned above, the first synchronization sequence includes at
least a portion
that conveys a "cell group ID". As such, a group of base stations (such as a
local cluster of
base stations) share a common portion of the first synchronization sequence.
Moreover, the
"cell group ID" portion of the synchronization sequence is common to every
base station
within that group of base stations. The synchronization of a mobile station 16
with a
transmitting base station 14 can be facilitated by the use of macro-diversity,
wherein all of
the base stations within a group of base stations issue signal frames having
the same "cell
group ID" sequence at the same time over the same resources. By all the base
stations 14
within the group of base stations transmitting the same "cell group ID"
sequence at the
same time, a receiving mobile station 16 is able to identify the commonly
issued sequence,
and thus the first preamble, with greater ease. Once the first preamble has
been identified,
the receiving mobile station 16 can then identify the location of the second
preamble within
the OFDM signal frame, which gives the "local ID" of the transmitting base
station such
that the base stations within the group can be differentiated. The receiving
mobile station
16 then knows the unique Cell ID of the transmitting base station 14.
[0128] Referring back to Figure 1, it is possible for some of the base
stations 14 and/or
relays 15 to be mobile, such that they are moving transmitters. In accordance
with a non-
limiting embodiment, the mobile base stations 14 and/or relays 15 may be
associated with a
dedicated "cell group ID" sequence. Moreover, one or more "cell group IDs"
from the set
of "cell group IDs" may be reserved for these moving transmitters, so as to be
able to
differentiate them from the fixed base stations 14 and relays 15. In this
manner, a mobile
station 16 that receives signals from these moving transmitters can detect
that they are
moving on the basis of the "cell group ID" sequence. A "cell group ID"
sequence may be
associated with both mobile base stations 14 and relays 15, or the mobile base
stations 14
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and mobile relays 15 may be associated with different "cell group ID"
sequences, such that
a receiving mobile station 14 can detect whether it is receiving from either a
base station 14
or a relay 15.
101291 In order to further simplify and facilitate searching and initial
detection or the
preambles, the first and second preambles may be confined to being transmitted
over one or
more carrier frequencies in certain predefined manners. For example, at least
a portion of
one of the first and second preambles may be carried by a synchronization
channel that is
subject to the following conditions:
= the synchronization channel may be confined to a fixed bandwidth within a
carrier
frequency, which may be the minimum carrier frequency. For example, the
synchronization channel may be fixed at 5MHz;
= the synchronization channel may be restricted to being present only over
a primary
carrier frequency that is able to carry control information;
= the synchronization channel may be restricted to being aligned with one edge
of the
carrier frequency; and
= in multi-carrier embodiments, the synchronization channel may be
restricted to being
sent over only the smaller one of the multi-carrier frequencies.
[01301 Shown in Figures 15(a) through 15(c) are some graphical representations
of the
synchronization channel in relation to one or more carrier frequency channels
that illustrate
the above restrictions. As shown in Figure 15(a), the synchronization channel
has the same
bandwidth as the primary carrier frequency (which is restricted to 5MHz), and
is aligned
with both edges of the primary carrier frequency. Shown in Figure 15(b) is a
primary carrier
frequency that has a greater bandwidth than the synchronization channel. The
synchronization channel has a fixed bandwidth and is aligned with one edge of
the primary
carrier frequency. The synchronization channel is carried over the primary
carrier
frequency, which is able to carry control information. The secondary carrier
frequency is
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shown without the synchronization channel. As used herein, the primary carrier
frequency
is able to carry control information, whereas the secondary carrier frequency
is not. Shown
in Figure 15(c) are two primary carrier frequencies. The synchronization
channel is carried
over the smaller of the two primary carrier frequencies, and the secondary
carrier is without
a synchronization channel. In an alternative embodiment, it is possible that
both of the
primary carrier frequencies carry a synchronization channel. In such a case,
the first primary
carrier frequency would have a greater bandwidth that the synchronization
channel.
[0131] In a further embodiment, at least a portion of the first and second
preambles may be
carried by primary and secondary synchronization channels that are transmitted
over one or
more carrier frequencies according to certain predefined conditions. For
example, the
primary and secondary synchronization channels may be subject to the following
conditions:
= the primary synchronization channel may be confined to a fixed bandwidth
that may
be the minimum carrier frequency, such as 5MHz. Whereas, the secondary
synchronization channel can have a wider bandwidth, that includes the entire
bandwidth of the carrier frequency;
= the primary and secondary synchronization channels may be restricted to
being
present only over a primary carrier frequency that is able to carry control
information. However, in alternative embodiments, the secondary
synchronization
channel may be present on all carrier frequencies;
o the primary synchronization channel may be restricted to being aligned
with one edge
of the carrier frequency; and
= in multi-carrier embodiments, the primary synchronization channel may be
restricted
to being sent over only the smaller one of the multi-carrier frequencies,
whereas, the
secondary synchronization channel may be present on all carrier frequencies.
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[01321 Shown in Figures 16(a) through 16(c) are some graphical representations
of the
primary and secondary synchronization channels in relation to one or more
carrier
frequency channels. As shown in Figure 16(a), both the first and second
synchronization
channels have the same bandwidth (which is restricted to 5MHz) as the primary
carrier
frequency. In addition, both the first and second synchronization channels are
aligned with
an edge of the primary carrier frequency. Shown in Figure 16(b) are both the
primary and
secondary synchronization channels carried over the primary carrier frequency.
The primary
synchronization channel is restricted to the 5MHz bandwidth, whereas the
secondary
synchronization channel has a greater bandwidth, which is the bandwidth of the
primary
carrier frequency. Both the primary and secondary synchronization channels are
aligned
with one edge of the primary carrier frequency. Shown in Figure 16(c) is a
multi-channel
embodiment, wherein the secondary synchronization channel is carried over the
larger of
the two primary carrier frequencies and the primary synchronization channel is
carried over
the smaller of the two primary carrier frequencies. The secondary carrier
frequency is
shown without a synchronization channel.
[0133] The manner in which a signal frame is generated in order to include
both the first
preamble and the second preamble will now be described in more detail with
reference to
Figures 2 and 17. Referring back to Figure 2, one or more processing modules
at the control
entity 20 and/or baseband processor 22 are able to determine where within a
signal frame
that first and second preambles should be located, and generate the first and
second
preambles in order to be able to convey at least some of the information
described above to
a receiving device, such as a mobile station 16.
[01341 Shown in Figure 17 is a flow diagram illustrating the process used by
the one or
more processing modules in order to generate and position within a signal
frame the first
and second preambles. Firstly, at step 1702, the process involves determining
a first
location within the signal frame that a first preamble should be located and
determining a
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second location within the signal frame that a second preamble should be
located. This
determination can be done based on a variety of criteria, such as the frame
length, the
channel conditions, weather or not a superframe header is included, etc. As
mentioned
above, the second preamble may be positioned within the signal frame at a
location prior to
the first preamble.
[0135] At step 1704, the process involves generating the first preamble. As
mentioned
above, the first preamble comprises a first synchronization sequence that
includes at least a
first portion that provides a "cell group ID" and a second portion that
provides information
indicative of the location of the second preamble within the signal frame. As
such, the first
preamble is generated at least in part on the basis of the deteiiiiined
location of the second
preamble.
[01361 The first portion of the first synchronization sequence, which provides
the "cell
group ID", may be known to the base station, such that the synchronization
sequence
indicative of the "cell group ID" is included within each signal frame that is
issued by the
base station 14. Alternatively, it is possible that the synchronization
sequence associated
with the "cell group ID" is provided to the base station by the base station
controller. In yet
a further alternative, it is possible that a look-up table (located either
locally or remotely) is
accessed in order to determine the synchronization sequence associated with
the "cell group
ID" to which the transmitting base station belongs. In the case where a look-
up table is
accessed, the synchronization sequence associated with the "cell group ID" may
be
determined on a basis of the cell group ID, a characteristic of the
transmitting base station,
such as the geographical coordinates of the base station, the local ID of the
base station, or
any other possible characteristic or attribute known to the transmitting base
station.
[0137] The second portion of the first synchronization sequence, which
provides
information indicative of a location within the signal frame of the second
preamble, is
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established on the basis of the location determined at step 1702 for the
second preamble.
For example, a different sequence portion is associated with each of the
different possible
locations within the signal frame where the second preamble could be located.
In the
example given above, the second preamble could be located at 1 of 4 different
offset
positions in relation to the first preamble. Each one of the offset positions
can be associated
with a respective one of four possible synchronization sequence portions. As
such, on the
basis of the offset position, the corresponding synchronization sequence
portion is
determined and added to the first synchronization sequence. The corresponding
synchronization sequence portion can be determined on the basis of a look-up
table (located
either locally or remotely) that maps different offset positions to different
synchronization
sequence portions.
[0138] Although the example of an offset between the first preamble and the
second
preamble is provided above, it should be appreciated that other
synchronization sequence
portions could be used in order to convey a relative timing between the first
preamble and
the second preamble.
[0139] The process of generating the first preamble may further comprises
adding
additional information that conveys different attributes and/or properties
relating to the
transmitting base station or the group of base stations to which the
transmitting base station
belongs. The first preamble could also convey control infointation. This
additional
information conveyed by the first preamble could be carried via other
synchronization
sequence portions, among other possibilities.
[0140] At step 1706, the first preamble is inserted within the signal frame at
the first
location determined at step 1702, and at step 1708 the second preamble is
inserted within
the signal frame at the second location determined at step 1702. The second
preamble is
generated in much the same way as the first preamble. As described above, the
second
CA 02773945 2011-12-22
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preamble comprises a second synchronization sequence that conveys a local ID
associated
with the transmitting base station. This second synchronization sequence
indicative of the
local ID may be known by the transmitting base station, such that it is
included within each
signal frame that is issued by the base station 14.
[0141] Finally, at step 1710, once the appropriate signal modulation has taken
place, the
signal frame is caused to be issued towards a receiving mobile station 16 in
the wireless
network.
[0142] The wireless signal that has been issued over the wireless network by
the
transmitting base station is received by a receiving mobile station 16. The
manner in which
the signal frame is handled by the receiving mobile station 16 will now be
described in
more detail with respect to Figures 3 and 18.
[0143] Referring back to Figure 3, the receiving circuitry 38 receives the
signals issued
over the wireless network and passes those signals to the baseband processor
34. One or
more processing modules at the control entity 32 and/or baseband processor 34
are then
able to search for and identify the first and second preambles contained
within a given
signal frame.
[0144] Shown in Figure 18 is a flow diagram illustrating the process of
receiving and
identifying the first and second preambles within a signal frame. Firstly, at
step 1802, the
wireless signal comprising a plurality of signal frames is received at the
receiving circuitry
38. Each of the signal frames comprises a first preamble and a second
preamble. At step
1804, one or more processing modules at the baseband processor 34 and/or
control entity
32 identify the first synchronization preamble within a signal frame. The
identification of
the first synchronization signal may be done by identifying a repetitively
occurring
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synchronization sequence (which will be at least a portion of the first
synchronization
sequence) that is contained in each of the signal frames.
[0145] As mentioned above, the first synchronization sequence may be 1 of 40
possible
synchronization sequences that are known to the receiving mobile station 16.
As such, the
receiving mobile station will "look out" for repetitively occurring ones of
these known
sequences in received signals. Once one of the sequences is detected within a
signal frame,
the receiving mobile station 16 will know that the first preamble has been
detected, such
that frame frequency and timing synchronization can be performed. Furthermore,
once the
first synchronization sequence has been detected, the receiving mobile station
16 can
determine both the "cell group ID" and the location of the second preamble.
[0146] In keeping with the example described above, the first synchronization
sequence
comprises a first portion that provides the "cell group ID", and a second
portion that
provides an indication of the location of the second preamble. In accordance
with a non-
limiting embodiment, the receiving mobile station 16 may compare the first
synchronization sequence (or the first and/or second portions thereof) with
known
sequences contained in a look-up table that map synchronization sequences (or
portions
thereof) to cell group IDs and different offset or timing locations within the
signal frame.
By comparing the detected first synchronization sequence (or portions thereof)
with
sequences contained in the look-up table, the "cell group ID" and the offset
or timing
between the first and second preambles may be determined. Alternatively, the
first portion
of the synchronization sequence itself may be the "cell group ED". The
location of the
second preamble within a signal frame is identified on the basis of
infoimation conveyed by
the first preamble, and specifically on the information carried by at least a
portion of the
first synchronization sequence.
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[0147] In this manner, at step 1806, the location of the second preamble
within a signal
frame can be identified on the basis of information conveyed by the first
preamble. This
greatly reduces the searching complexity associated with identifying the
location of the
second preamble. Once the location has been identified, the receiving mobile
station 16
is able to access the second preamble which conveys information indicative of
a local ID.
More specifically, the information indicative of the local ID of the
transmitting base station
can be carried by a second synchronization sequence. The local ID of the
transmitting base
station may be the second synchronization sequence, or a look-up table can be
accessed
that maps known second synchronization sequences to respective local IDs of
various
transmitting base stations within the group of base stations associated to the
cell group ID.
[0148] At step 1808, once both the first and second preambles have been
identified,
transmission signalling information can be obtained from the combination of
the first
preamble and the second preamble. In accordance with a non-limiting
embodiment, the
transmission signalling information can be the unique Cell ID of the
transmitting base
station 14.
[0149] Although the present invention has been described in considerable
detail with
reference to certain preferred embodiments thereof, variations and refinements
are
possible without departing from the scope of the invention. Therefore, the
scope of the
invention should be limited only by the appended claims and their equivalents.
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