Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND SYSTEM FOR PROVIDING AN UPLINK STRUCTURE AND
IMPROVED CHANNELIZATION SCHEME IN A WIRELESS
COMMUNICATION NETWORK
FIELD OF THE INVENTION
The present invention relates to the field of wireless communications and more
particularly to a method and system for providing an uplink structure and a
channelization
scheme that allocates resource blocks or basic channel units to corresponding
zones for
transmission in the wireless communication network.
BACKGROUND OF THE INVENTION
Wireless communication networks, such as cellular networks, operate by sharing
resources among the mobile terminals operating in the communication network.
As part
of the sharing process, one or more controlling devices allocate system
resources relating
to channels, codes, among other resources. Certain types of wireless
communication
networks, e.g., orthogonal frequency division multiplexed ("OFDM") networks,
are used
to support cell-based high speed services such as those under the IEEE 802.16
standards.
The IEEE 802.16 standards are often referred to as WiMAX or less commonly as
WirelessMAN or the Air Interface Standard.
OFDM technology uses a channelized approach and divides a wireless
communication channel into many sub-channels which can be used by multiple
mobile
terminals at the same time. These sub-channels can be subject to interference,
which may
cause data loss.
A system and method are needed for providing an uplink structure and a
channelization scheme having improved voice over Internet Protocol (VoIP)
capabilities
and advanced interference mitigation techniques, among providing other
benefits. A
system and method are disclosed below providing an uplink structure and
channelization
schemes that utilize resource blocks and frequency zones to provide improved
voice over
Internet Protocol (VoIP) capabilities and advanced interference mitigation
techniques.
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SUMMARY OF THE INVENTION
The invention advantageously provides a method and system for providing an
uplink structure and a channelization scheme that allocates resource blocks or
basic
channel units to corresponding zones for transmission in the wireless
communication
network.
A method is provided for performing channelization in a wireless communication
network, wherein the wireless communication network including at least one
base station
that is communicatively coupled to at least one mobile terminal. A bandwidth
of the
wireless communication network is divided into a plurality of zones at the
base station.
Resource blocks are provided at the base station to receive data symbols
transmitted in the
wireless communication network. A plurality of resource blocks are combined at
the base
station to form a physical basic channel unit which are allocated to one of
the plurality of
zones at the base station. A permutation is performed on the physical basic
channel unit to
form a logical basic channel unit. A channel is provided to communicatively
couple the
base station and the mobile terminal so that the mobile terminal may send an
access grant
message and a user identification to the base station to transmit data in the
logical basic
channel unit.
The invention provides another method of performing channelization in a
wireless
communication network, the wireless communication network including at least
one base
station that is communicatively coupled to at least one mobile terminal. A
bandwidth of
the wireless communication network is divided into a plurality of zones at the
base station.
Physical resource blocks are formed at the base station to receive data
symbols transmitted
in the wireless communication network. The physical resource blocks are
allocated to one
of the plurality of zones at the base station and a permutation is performed
on the physical
resource blocks to form logical resource blocks. A plurality of logical
resource blocks are
combined at the base station to form a logical basic channel unit. A channel
is provided to
communicatively couple the base station and the mobile terminal so that the
mobile
terminal may send an access grant message and a user identification to the
base station to
transmit data in the logical basic channel unit.
The invention provides a base station for use in a wireless communication
system,
the base station being communicatively coupled to at least one mobile
terminal. The base
station includes a control system that divides a bandwidth of the wireless
communication
network into a plurality of zones and forms resource blocks to receive data
symbols
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transmitted in the wireless communication network. The control system combines
a
plurality of resource blocks to form a physical basic channel unit and
allocates the
physical basic channel unit to one of the plurality of zones at the base
station. The control
system performs a permutation on the physical basic channel unit to form a
logical basic
channel unit. The base station has an antenna that communicatively couples the
base
station and the mobile terminal. The antenna receives an access grant message
and a user
identification from the mobile terminal and transmits data in the logical
basic channel unit,
wherein the wireless communication system is configured to transmit data
having different
frame sizes.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present invention, and the attendant
advantages and features thereof, will be more readily understood by reference
to the
following detailed description when considered in conjunction with the
accompanying
drawings wherein:
FIG. 1 is a block diagram of an exemplary cellular communication system
constructed in accordance with the principles of the present invention;
FIG. 2 is a block diagram of an exemplary base station constructed in
accordance
with the principles of the present invention;
FIG. 3 is a block diagram of an exemplary mobile terminal constructed in
accordance with the principles of the present invention;
FIG. 4 is a block diagram of an exemplary relay station constructed in
accordance
with the principles of the present invention;
FIG. 5 is a block diagram of a logical breakdown of an exemplary OFDM
transmitter architecture constructed in accordance with the principles of the
present
invention;
FIG. 6 is a block diagram of a logical breakdown of an exemplary OFDM receiver
architecture constructed in accordance with the principles of the present
invention;
FIG. 7 illustrates resource blocks having uplink pilot designs for two
transmitter
systems in accordance with the principles of the present invention;
FIG. 8 illustrates one channelization scheme in accordance with the principles
of
the present invention;
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FIG. 9 illustrates another channelization scheme in accordance with the
principles
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
As an initial matter, while certain embodiments are discussed in the context
of
wireless networks operating in accordance with the IEEE 802.16m broadband
wireless
standard, which is hereby incorporated by reference, the invention is not
limited in this
regard and may be applicable to other broadband networks including those
operating in
accordance with other OFDM orthogonal frequency division ("OFDM")-based
systems,
including the 3rd Generation Partnership Project ("3GPP") and 3GPP2
evolutions.
Similarly, the present invention is not limited solely to OFDM-based systems
and can be
implemented in accordance with other system technologies, e.g., CDMA.
Referring now to the drawing figures in which like reference designators refer
to
like elements, there is shown in FIG. 1, an exemplary communication system 10
is
provided in accordance with the principles of the present invention.
Communication
system 10 includes a base station controller ("BSC") 12 that controls wireless
communications within multiple cells 14, which cells are served by
corresponding base
stations ("BS") 16. In some configurations, each cell is further divided into
multiple
sectors 18 or zones (not shown). In general, each base station 16 facilitates
communications using orthogonal frequency division multiplexing ("OFDM") with
mobile and/or mobile terminals 20, which are within the cell 14 associated
with the
corresponding base station 16. The movement of the mobile terminals 20 in
relation to the
base stations 16 results in significant fluctuation in channel conditions. As
illustrated, the
base stations 16 and mobile terminals 20 may include multiple antennas to
provide spatial
diversity for communications. In some configurations, relay stations 22 may
assist in
communications between base stations 16 and mobile terminals 20. Mobile
terminals 20
can be handed off from any cell 14, sector 18, zone (not shown), base station
16 or relay
22 to another cell 14, sector 18, zone (not shown), base station 16 or relay
22. In some
configurations, base stations 16 communicate with each other and with another
network
(such as a core network or the Internet, both not shown) over a backhaul
network 24. In
some configurations, a base station controller 12 is not needed.
With reference to FIG. 2, an example of a base station 16 is illustrated. The
base
station 16 generally includes a base control system 26, e.g. a CPU, a baseband
processor
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28, transmit circuitry 30, receive circuitry 32, multiple antennas 34a, 34b
and a network
interface 36. The receive circuitry 32 receives radio frequency signals
bearing information
through a receive antenna 34a from one or more remote transmitters provided by
mobile
terminals 20 (illustrated in FIG. 3) and relay stations 22 (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. Down-conversion and digitization
circuitry
(not shown) may down-convert the filtered, received signal to an intermediate
or baseband
frequency signal, which is digitized into one or more digital streams.
The baseband processor 28 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 28 is generally implemented in one or more digital signal
processors
("DSPs") and/or application-specific integrated circuits ("ASICs"). The
received
information is sent across a wireless network via the network interface 36 or
transmitted to
another mobile terminal 20 serviced by the base station 16, either directly or
with the
assistance of a relay 22.
On the transmit side, the baseband processor 28 receives digitized data, which
may
represent voice, data, or control information, from the network interface 36
under the
control of the base control system 26, and encodes the data for transmission.
The encoded
data is output to the transmit circuitry 30, where it is modulated by one or
more carrier
signals having a desired transmit frequency or frequencies. A power amplifier
(not
shown) amplifies the modulated carrier signals to a level appropriate for
transmission, and
delivers the modulated carrier signals to the transmit antennas 34b through a
matching
network (not shown). Modulation and processing details are described in
greater detail
below.
With reference to FIG. 3, an example of a mobile terminal 20 is illustrated.
Similarly to the base station 16, the mobile terminal 20 includes a mobile
control
system 38, e.g. a CPU, a baseband processor 40, transmit circuitry 42, receive
circuitry 44,
multiple antennas 46a, 46b and user interface circuitry 48. The receive
circuitry 44
receives radio frequency signals bearing information through a receive antenna
46a from
one or more base stations 16 and relays 22. A low noise amplifier and a filter
(not shown)
may cooperate to amplify and remove broadband interference from the signal for
processing. Down-conversion and digitization circuitry (not shown) down-
convert the
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filtered, received signal to an intermediate or baseband frequency signal,
which is
digitized into one or more digital streams.
The baseband processor 40 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 40 is generally implemented in one or more DSPs and/or ASICs.
For transmission, the baseband processor 40 receives digitized data, which may
represent voice, video, data, or control information, from the mobile control
system 38,
which it encodes for transmission. The encoded data is output to the transmit
circuitry 42,
where it is used by a modulator to modulate one or more carrier signals at a
desired
transmit frequency or frequencies. A power amplifier (not shown) amplifies the
modulated carrier signals to a level appropriate for transmission, and
delivers the
modulated carrier signal to the transmit antennas 46b 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.
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.
OFDM modulation utilizes the performance of an Inverse Fast Fourier Transform
("IFFT") on the information to be transmitted. For demodulation, the
performance of a
Fast 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.
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In operation, OFDM is preferably used for at least downlink transmission from
the
base stations 16 to the mobile terminals 20. Each base station 16 is equipped
with "n"
transmit antennas 34b (n >=1), and each mobile terminal 20 is equipped with
"m" receive
antennas 46a (m>=1). Notably, the respective antennas can be used for
reception and
transmission using appropriate duplexers or switches and are so labeled only
for clarity.
When relay stations 22 are used, OFDM is preferably used for downlink
transmission from the base stations 16 to the relays 22 and from relay
stations 22 to the
mobile terminals 20.
With reference to FIG. 4, an example of a relay station 22 is illustrated.
Similarly
to the base station 16, and the mobile terminal 20, the relay station 22
includes a relay
control system 50, e.g. a CPU, a baseband processor 52, transmit circuitry 54,
receive
circuitry 56, multiple antennas 58a, 58b and relay circuitry 60. The relay
circuitry 60
enables the relay 22 to assist in communications between a base station 16 and
mobile
terminals 20. The receive circuitry 56 receives radio frequency signals
bearing
information through a receive antenna 58a from one or more base stations 16
and mobile
terminals 20. A low noise amplifier and a filter (not shown) may cooperate to
amplify and
remove broadband interference from the signal for processing. Down-conversion
and
digitization circuitry (not shown) down-convert the filtered, received signal
to an
intermediate or baseband frequency signal, which is digitized into one or more
digital
streams.
The baseband processor 52 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 52 is generally implemented in one or more DSPs and/or ASICs.
For transmission, the baseband processor 52 receives digitized data, which may
represent voice, video, data, or control information, from the relay control
system 50,
which it encodes for transmission. The encoded data is output to the transmit
circuitry 54,
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 transmit antenna 58b through a matching
network (not
shown). Various modulation and processing techniques available to those
skilled in the art
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are used for signal transmission between the mobile terminal 20 and the base
station 16,
either directly or indirectly via a relay station 22, as described above.
With reference to FIG. 5, a logical OFDM transmission architecture is
provided.
Initially, the base station controller 12 (See FIG. 1) sends data destined for
transmission to
various mobile terminals 20 to the base station 16, either directly or with
the assistance of
the relay station 22. The base station 16 may use channel quality indicators
("CQIs")
associated with the mobile terminals 20 to schedule the data for transmission
as well as
select appropriate coding and modulation for transmitting the scheduled data.
The CQIs
may be obtained directly from the mobile terminals 20 or may be determined at
the base
station 16 using information provided by the mobile terminals 20. In either
case, the CQI
for each mobile terminal 20 is a function of the degree to which the channel
amplitude (or
response) varies across the OFDM frequency band.
The scheduled data 62, which is a stream of bits, is scrambled in a manner
that
reduces the peak-to-average power ratio associated with the data using data
scrambling
logic 64. A cyclic redundancy check ("CRC") for the scrambled data is
determined and
appended to the scrambled data using CRC adding logic 66. Channel coding is
performed
using channel encoder logic 68 to effectively add redundancy to the data to
facilitate
recovery and error correction at the mobile terminal 20. Again, the channel
coding for a
particular mobile terminal 20 is based on the CQI. In some implementations,
the channel
encoder logic 68 uses known Turbo encoding techniques. The encoded data is
processed
by rate matching logic 70 to compensate for the data expansion associated with
encoding.
The bit interleaver logic 72 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 74. 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 20. 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 76.
At this point, groups of bits are mapped into symbols representing locations
in an
amplitude and phase constellation. When spatial diversity is desired, blocks
of symbols
are processed by space-time block code ("STC") encoder logic 78, which
modifies the
symbols in a fashion making the transmitted signals more resistant to
interference and
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more readily decoded at the mobile terminal 20. The STC encoder logic 78
processes the
incoming symbols and provide "n" outputs corresponding to the number of
transmit
antennas 34b for the base station 16. The base control system 26 and/or
baseband
processor 28, as described above with respect to FIG. 2, 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 are capable of being
recovered by the
mobile terminal 20.
For the present example, assume the base station 16 has two transmit antennas
32b
(n=2) and the STC encoder logic 78 provides two output streams of symbols.
Accordingly, each of the symbol streams that are output by the STC encoder
logic 78 is
sent to a corresponding IFFT processor 80a, 80b (referred to collectively
herein as
IFFT 80), 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 80 preferably operate on the respective symbols to provide an
inverse Fourier
Transform. The output of the IFFT processors 80 provides symbols in the time
domain.
The time domain symbols are grouped into frames, which are associated with a
prefix-by-
prefix insertion logic 82a, 82b (referred to collectively herein as prefix
insertion 82). 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 84a, 84b (referred to
collectively herein
as DUC + D/A 84). The resultant (analog) signals are simultaneously modulated
at the
desired RF frequency, amplified, and transmitted via the RF circuitry 86a, 86b
(referred to
collectively herein as RF circuitry 86) and antennas 34b. 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, uses the pilot signals for
channel
estimation.
Reference is now made to FIG. 6 to illustrate reception of the transmitted
signals
by a mobile terminal 20, either directly from base station 16 or with the
assistance of
relay 22. Upon arrival of the transmitted signals at each of the antennas 46a
of the mobile
terminal 20, the respective signals are demodulated and amplified by
corresponding RF
circuitry 88. 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-
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conversion circuitry 90 digitizes and down-converts the analog signal for
digital
processing. The resultant digitized signal may be used by automatic gain
control circuitry
(AGC) 92 to control the gain of the amplifiers in the RF circuitry 88 based on
the received
signal level.
Initially, the digitized signal is provided to synchronization logic 94, which
includes coarse synchronization logic 96, 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 determines a
fine
synchronization search window, which is used by fine synchronization logic 98
to
determine a precise framing starting position based on the headers. The output
of the fine
synchronization logic 98 facilitates frame acquisition by frame alignment
logic 100.
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 102 and resultant samples are sent to frequency offset correction logic
104, which
compensates for the system frequency offset caused by the unmatched local
oscillators in
the transmitter and the receiver. Preferably, the synchronization logic 94
includes
frequency offset and clock estimation logic 106, which is based on the headers
to help
estimate such effects on the transmitted signal and provide those estimations
to the
correction logic 104 to properly process OFDM symbols.
At this point, the OFDM symbols in the time domain are ready for conversion to
the frequency domain using FFT processing logic 108. The results are frequency
domain
symbols, which are sent to processing logic 110. The processing logic 110
extracts the
scattered pilot signals using scattered pilot extraction logic 112, determines
a channel
estimate based on the extracted pilot signals using channel estimation logic
114, and
provides channel responses for all sub-carriers using channel reconstruction
logic 116. 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.
FIG.7 illustrates resource blocks ("RB") 70,70a-70n (hereinafter "RB 70")
having
uplink pilot designs. Two or more RBs 70a-70n may be combined to form a basic
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unit (BCU). The RB 70 includes pilot symbols arranged in a pattern. The pilot
symbol
pattern may be employed for channel estimation, data demodulation, and
sounding, among
other purposes.
The RB 70 may include a plurality of rows and columns. For example, the RB 70
may include twelve rows and six columns. Six symbols or tones may be provided
in each
row, such as OFDM symbols among other symbol types. One of ordinary skill in
the art
will readily appreciate that any number of row and columns may be used. For
example,
the RB 70 may be configured of various sizes, including 12x6, 18x6, and 6x4,
among
other sizes. The RB 70 may be optimized for channelization and for small
packet
transmission (VoIP). FIG. 7 illustrates the RB 70 having a time axis across
the columns
and a frequency axis along the rows.
FIG. 7 illustrates multiple RB configurations having pilot symbol patterns
with
different density configurations for a two transmitter system. The pilot
symbol density
and pilot symbol pattern may be configured in time and frequency to
accommodate
different contiguous resource sizes. The pilot symbol for the first
transmitter is identified
by "1," the pilot symbol for the second transmitter is identified by "2." The
RB 70
includes areas for pilot symbols and areas for data signals. The pilot symbol
pattern and
density value may be chosen based on the size of the contiguous resource and a
multi-
antenna transmission and reception (MIMO) mode.
The frequency domain symbols are provided to an STC decoder 118, which
provides STC decoding on both received paths to recover the transmitted
symbols. The
recovered symbols are placed back in order using symbol de-interleaver logic
120, which
corresponds to the symbol interleaver logic 76 of the base station 16
transmitter.
The de-interleaved symbols are then demodulated or de-mapped to a
corresponding bit stream using de-mapping logic 122. The bits are then de-
interleaved
using bit de-interleaver logic 124, which corresponds to the bit interleaver
logic 72 of the
base station 16 transmitter architecture. The de-interleaved bits are then
processed by rate
de-matching logic 126 and presented to channel decoder logic 128 to recover
the initially
scrambled data and the CRC checksum. Accordingly, the CRC logic 130 removes
the
CRC checksum, checks the scrambled data in traditional fashion, and provides
it to the de-
scrambling logic 132 for descrambling using the known base station de-
scrambling code
to recover the originally transmitted data 134.
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While recovering the data 134, a CQI 136 or at least information sufficient to
create a CQI at the base station 16 is determined by channel variation
analysis logic 138
and transmitted to the base station 16. As noted above, the CQI 134 may be a
function of
the carrier-to-interference ratio ("CIR") 140, 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
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.
An uplink ("UL") control structure for OFDM systems may be provided that
enables mobile terminals 20 to communicate with the base stations 16. The
control
structure may include an uplink acknowledge (UL ACK) channel and a dedicated
control
channel that feeds information back, such as channel quality indicator (CQI)
information,
pre-coding matrix index (PMI) information and rank information, among other
information. The mobile terminals 20 may employ the UL ACK channel for initial
access
to the OFDM system, for bandwidth requests, to trigger continuation of
negotiated service,
and for proposed allocation of a re-configuration header, among other
purposes.
Furthermore, a downlink acknowledge (DL ACK) channel may be provided to
acknowledge UL data transmission. The DL ACK channel may include n tones that
are
spread over the entire band. The DL ACK channel may be power controlled for an
intended user, wherein power control may be provided by assigning a channel to
each
user.
A fixed number of resources maybe allocated to control channels, including UL
ACK channels, DL ACK channels, UL power control channels and multi-case
control
channels. The fixed number of resources may be signaled from a super-frame
control. A
set of ACK channels may be defined for all unicast assignments and a separate
set of ACK
channels may be defined for group assignments. The ACK channels that are used
for a
given packet transmission are determined by the partition number and the
layer. The ACK
signals are transmitted over several ACK tiles, where an ACK tile is defined
as a group of
contiguous tones or sub-carriers. The value of the ACK signals may be
determined by
either non-coherent detection or coherent detection. An orthogonal spreading
code may be
used to multiplex multiple ACK signals onto the same ACK tile.
An uplink control channel structure supports UL ACK channels for both unicast
assignments and group assignments. The UL control channel structure also
supports
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multiple ACKs for different packets that are transmitted on the same
resources, as in
multi-codeword MIMO ("MCW-MIMO") or multi-user MIMO ("MU-MIMO"). The UL
control channel also provides feedback for frequency selective scheduling and
pre-coding,
including for simple diversity assignments.
For MU-MIMO, separate unicast messages are provided for each user that is
assigned to a same partition. A unicast control segment may include a MU-MIMO
header
or a multicast message that is targeted to the lower geometry user in an
assignment. The
header may include a message type that indicates a number of layers that are
multiplexed
on the same resources. Furthermore, the header may include a PMI used for the
transmission in the case of codebook based pre-coding feedback. The PMI is a
matrix
having a number of columns equal to a number of layers, wherein each column
includes a
pre-coding vector for the corresponding layer.
A fixed number of resources may be allocated for the UL dedicated control
channel. The resources are divided into UL control tiles, wherein the number
of tiles
allocated to a user depends on the amount of feedback requested. The allocated
tiles may
be spread over the band to obtain frequency diversity. The UL control
information is CRC
protected and is scrambled by the user ID. The content of the information can
change
each feedback instance to accommodate event driven control information such as
a
bandwidth request.
A UL random access ("RA") channel may be provided to enable the user to
initially gain access to the system through one of several physical control
structures.
According to one embodiment, the UL random access channel is a designated
resource.
The UL random access channel may be a contention based channel for multiple
mobile
terminals 20 to request access/bandwidth. A designated resource may be
allocated for
these access requests. The access request may be spread or repeated across the
resources
that are used exclusively for random access and bandwidth requests. The mobile
station
20 may randomly select from one sequence and location if multiple
possibilities are
available.
According to one embodiment, the mobile terminal 20 may randomly select from
one of L sequences, which spans N RBs 70. Alternatively, the sequence length L
may be
chosen to confine a full sequence within an RB 70. By confining the spreading
sequence
to one RB 70, the spreading sequences maintain orthogonality as the RB 70 is
virtually
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frequency flat as the RB contains physical contiguous tones. The spreading
sequences
may be repeated in each RB 70 to gain diversity.
If many resources are assigned for uplink control, the resources may be
divided
into M time-frequency blocks for random access. In this case, the number of
distinct
codes/resource per sub frame is LM, where the value of M may be dynamically
specified
by the base station 16. In some embodiments, a sub-frame within a superframe
(or
otherwise specified as set of F frames) is also randomly selected, wherein the
number of
distinct codes/resource/sub frames per superframe is defined as LMF.
Another physical control structure includes overlaying the random access
requests
with UL control signals. The access request may be spread or repeated across
the
resources used for uplink control, such as CQI, among other uplink control.
The mobile
terminal 20 may randomly select from one sequence and location if multiple
possibilities
are available. For example, the mobile terminal 20 may randomly select from
one of L
sequences, where L is less than or equal to the RB size. By confining the
spreading
sequence to one RB 70, the spreading sequences maintain orthogonality as the
RB 70 is
virtually frequency flat as the RB 70 includes physical contiguous tones or
sub-carriers.
The length-L sequence is completely repeated on each of the N RBs 70. Coherent
combining of each sequence repetition may improve detection at the base
station 16.
While overlaying the RA request and UL signals, the resources may be divided
into M time-frequency blocks for random access if many resources are assigned
for uplink
control. A number of distinct codes or resources per sub-frame is LM. The
values of N
and M may be dynamically specified by the base station 16. In some
embodiments, a sub-
frame within the superframe (or otherwise specified as a set of F frames) is
also randomly
selected. In some embodiments, the sequences span the N RBs 70. The sequence
length
in these cases is LN and the number of distinct codes or resource per sub
frame is LNM.
In some embodiments, the L sequences are an orthogonal set of spreading
sequences, wherein the L-sequences may be divided into two types of
indications. A first
type includes a system access request without a previously assigned mobile
terminal ID
and a second type includes a system access request with an assigned mobile
terminal ID.
If a mobile terminal 20 is granted access to the system, a down link (DL)
control segment
access grant may be scrambled by the sequence/resource block ID. An access
grant
message may include a user identification of the mobile terminal 20 that
initiated a request
for access. The access grant message may be provided in the UL control
segment. The
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access grant message may be scrambled by a sequence that the mobile terminal
20 used in
the UL random access channel. The UL control segment may include an MCCS
having a
combination index and/or permutation index and a RAB if persistent resources
have been
allocated, including unicast assignment messages for individual assignments
and group
assignment messages for group assignments. Persistent resources may be
allocated using
a persistent assignment message, which are different for UL and DL
assignments. Each
message may include a resource identification for the basic channel unit (BCU)
and a
number of resources assigned. Alternatively, a bitmap may be provided that
indicates the
assigned resources. For the bitmap, the length of the bitmap may be the length
of the
persistent zone. The length may be signaled in the super-frame control. The UL
persistent
assignment message may be included in the UL control segment. Alternatively,
the UL
persistent assignment message may be included in a separate partition. The
UL/DL
persistent assignment messages may be scrambled by a user identification of an
intended
user. The base station 16 may attempt interference cancellation to remove the
RA channel
from UL control.
Another physical control structure includes overlaying the RA channel over the
wideband UL resources. The request is spread or repeated across the UL
channel,
possibly across the entire bandwidth. The random access operation for users
may be
assigned to one length L sequence and one location, if multiple possibilities
are available.
A random access channel may be assigned one length L sequence for use by all
users. The total resources NT may be divided into M time-frequency blocks for
random
access. The access sequence, through spreading and repetition, may span NT /M
= N
RB's (e.g. N=3). The mobile terminal 20 may randomly select one of the M,
wherein the
number of distinction resource per sub frame is M. The sub frame for a request
is also
randomly selected.
The sequences for random access may be an orthogonal set of spreading
sequences. Two sequences may be defined for two types of indications. A first
type
includes a system access request without a previously assigned mobile terminal
ID and a
second type includes a system access request with an assigned mobile terminal
ID. If a
mobile terminal 20 is granted access to the system, a down link (DL) control
segment
access grant may be scrambled by the sequence/resource block ID. The base
station 16
may attempt interference cancellation to remove the RA channel from UL
control. The
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base station 16 may attempt to decode UL control and traffic transmissions
with and
without an assumption that an RA was sent.
The invention provides an improved channelization and control channel design
for
sub-frames, such as WiMAX sub-frames. The WiMAX basic frame structure includes
super-frames, frames, sub-frames and symbols. Each super-frame may span 20ms
and
may be divided into four equally-sized 5ms radio frames. According to one
embodiment,
each 5ms radio frame may include eight sub-frames. A sub-frame may be assigned
for
either DL or UL transmission. Three types of sub-frames may be employed: a sub-
frame
having six OFDM symbols; a sub-frame having five OFDM symbols and a sub-frame
having seven OFDM symbols.
Channelization for control and traffic may be provided within each sub-frame
and
may span across the symbols within the corresponding sub-frame. The invention
uses a
separate zone to support extended sub-frames for both UL and DL. The extended
sub-
frames may be defined to concatenate sub-channel resources across multiple sub-
frames,
to reduce control overhead resources and improve UL coverage.
The bandwidth may be divided into a plurality of zones, including a diversity
zone,
a localized zoned and an extended frame zone. The zones include a one-
dimensional
ordered list of resources, in units of a basic channel unit ("BCU"). In other
words, the
partitioning of resources between the diversity zone, the localized zones and
the extended
frame zone is performed using BCUs. The diversity zone may be used to support
diversity
assignments. The localized zone may be used to support localized assignments,
or
frequency selective scheduling, to optimize a connection quality based on
relative signal
strengths of specific users. The zones also may apply fractional frequency
reuse ("FFR")
to control co-channel interference and support universal frequency reuse, with
minimal
degradation in spectral efficiency. With FFR, mobile terminals 20 located near
the base
station 16 may operate on zones having all sub-channels available.
Alternatively, with
FFR, mobile terminals 20 located near the edge of the cell (i.e., far from the
base station
16) may operate on zones having less than all sub-channels available.
According to one embodiment, the BCU may include three resource blocks. The
resource blocks may include 12 sub-carriers and 6 OFDM symbols. Defining a BCU
size
to include three RBs provides several advantages. Three RBs provide sufficient
granularity and flexibility for VoIP assignments, whereas for non-VoIP
assignments, the
resource unit does not have granularity constraints. In other words, a BCU
having three
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RBs provides a trade-off between channel estimation performance and pilot
overhead
resources. For group assignments, such as VoIP, the groups are allocated in
units of
BCUs. By contrast, individual VoIP users may receive resources in units of
RBs.
Furthermore, three RBs correspond to 394kHz, which provide acceptable
frequency
selective scheduling performance.
FIG. 8 illustrates one channelization procedure wherein band 802 is divided
into a
plurality of resource blocks 804a-804n having contiguous tones, which are
identified by
sub-carriers A, B, C and D. Three contiguous RBs are grouped together to form
physical
BCUs 806a-806n. The physical BCUs 806a-806n are allocated to one of a
Diversity Zone
1 (808), a Diversity Zone 2 (810), a Diversity Zone 3 (812) and a Localized
Zone (814).
The physical BCUs 806a-806n in zones 808, 810, 812 and 814 are evenly spread
throughout the band 802. The physical BCUs 806a-806n within each zone are
permuted at
820, 822 and 824 using a sector specific BCU permutation to form logical BCUs.
FIG. 9 illustrates another channelization procedure wherein band 902 is
divided
into a plurality of resource blocks ("RBs") 904a-904n having contiguous tones,
which are
identified by sub-carriers A, B, C and D. Each physical resource block 904a-
904n is
allocated to one of a Diversity Zone 1 (908), a Diversity Zone 2 (910), a
Diversity Zone 3
(912) and a Localized Zone (914). The physical RBs 904a-904n in zones 908,
910, 912
and 914 are evenly spread throughout the band 902. The physical RBs 904a-904n
within
each zone are permuted at 920, 922 and 924 using a sector specific BCU
permutation to
form logical RBs. Three RBs are grouped together to form logical BCUs.
Basic channel units ("BCU") in the extended frame zone may use the same
channelization as in the non-extended frame zone. According to one embodiment,
the
control channel for the extended frame zone may occur every k-frames and the
assignments in the extended frame zone may be defined for k-frames. The
control channel
may support multi-cast and unicast control. The unicast control information
may be
contained within an associated partition in a first sub-frame. According to
one
embodiment, transmission using extended sub-frames may co-exist with
transmissions
using non-extended sub-frames. Thus, only mobile terminals 20 that use the
extended
zone are affected by the increased latency.
Once a mobile terminal 20 accesses the system, the mobile terminal 20 may
request resources on the UL to transmit information to the base station 16.
The mobile
terminal 20 may be provided with several options for performing the UL
resource request.
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Parameters for a first transmission may be specified by a bandwidth request,
the
parameters may be set to default based on capability negotiation, the
parameters may be
set to a previous configuration based on renewal, or the parameters may be set
in some
other manner. The mobile terminal 20 may change the assignment parameters by
including an additional re-configuration message encoded with data that takes
effect at the
start of the next packet transmission. This takes advantage of HARQ for the
control
message.
The mobile terminal 20 may randomly select an RA signaling ID. A signaling ID
may be a specific spreading sequence, a time-frequency location, a time slot,
an interlace,
or other signaling ID. The set of signaling ID options are known to users and
also the
index associated with each signaling ID option.
In response to a random access channel signal, the base station 16 may assign
one
or more of a user ID to the user, an initial UL resource for the mobile to
provide
information, user equipment capabilities, a DL resource assignment requesting
information from the mobile terminal and additional details, such as group
assignment,
base station procedures, among other parameters. The assignment message may
carry user
ID information.
A message sent to the mobile terminal 20 from the base station 16 may identify
the
base station 16 using a randomly selected signaling ID option that is selected
by the user
for the RA. For example, if the control channels are generally scrambled in
some manner
by the user ID in response to a RA, the base station 16 will send a control
message
scrambled by the index of the randomly selected signaling ID, such as sequence
index,
sequence location, etc.
In another embodiment, some signaling IDs may be reserved for users that have
been assigned user IDs. For example, a user may be in a hand-off operation and
may be
accessing a new serving sector. A user may select from a set of random access
signaling
IDs if an assigned user ID is not provided. Alternatively, a user may select
from a
different subset of signaling options if the user does have a user ID. In
response, the base
station 16 may send a control message that is scrambled by the RA signal index
and
includes a user ID if the mobile terminal 20 has sent a signaling option
indicating a user
ID is not provided. Alternatively, if the mobile terminal 20 has sent a
signaling option
indicating it does have a user ID, then the base station 16 may send a control
message that
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is scrambled by the RA signal index without a user ID. The mobile terminal 20
may
indicate the user ID in the next UL transmission for user equipment
capabilities, etc.
According to one embodiment, the header and optionally a message body may be
added to a first packet transmission. Alternatively, the header and optionally
a message
body may be added to a first packet transmission and every Nth packet
afterwards, where
N can be from 1 to infinity. The base station 16 may provide the mobile
terminal 20 with
an ACK/NAK of packet transmission to indicate that a re-configuration message
was
correctly received.
During an assignment of the mobile terminal 20, users may embed a header on a
data packet transmission that provides details on configuration or re-
configuration. The
request by the mobile terminal 20 for UL resources may be made on dedicated
resources
within UL control tiles. These resource sizes may be different for different
frames
according to a pre-determined pattern. The sizes may be known at the mobile
terminal 20
and the base station 16, so signaling is not needed after configuration.
According to one embodiment, the resource request may occupy a field that is
reserved for another message (CQI, ACK/NAK, precoder index, etc.). The
presence of a
request may be specified by the UL control message type. The mobile terminal
20 may set
this type to a message configuration that includes space for a resource
assignment. As a
result, the size of the message may not be changed from the specified size for
that sub
frame. The presence of the request field may be dynamic, but may not affect
the pre-
determined size of the user's UL control. A resource request may be encoded
with other
UL control data so that resource requests may be reliably received.
The request may have multiple forms for a given system. In a first embodiment,
the resource request may be a single "on/off' indication. Details of an
assignment may be
given in a re-configuration message or may be known from previous or default
configurations. Alternatively, the resource request may be a message, where
details of
assignments are indicated, such as delay constraints, QoS, packet backlog, and
resource
size, among other assignments. Details of an assignment may be given in a re-
configuration message or may be known from previous or default configurations.
For
example, resources may be specified by a secondary broadcast channel, UL
resources may
be allocated across distributed RB blocks, bandwidth requests may be 4-10 bits
indicating
QoS and a first transmission spectral efficiency or a mobile terminal 20
buffer size, a
bandwidth request may occupy a field otherwise assigned for another purpose,
such as DL
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CQI feedback, or UL resources may be encoded with other UL control data for
users so
that a bandwidth request may be reliably received.
According to an alternative embodiment, users may be assigned one of the
random
access signaling IDs (e.g., channel sequences or location) after accessing a
system. A
resource request may use the same sequence or channel configurations. As with
the RA
channel, users also may be assigned specific sub frames for resource request
opportunities.
The assigned signaling may be a unique identifier for a user's resource
request. In a first
example, a set of signaling IDs may be reserved for resource requests and may
not be used
for RA requests. The assigned sequence or location may be a unique identifier
for a user's
resource request. A user may be assigned signaling IDs to identify a bandwidth
request or
a resource request. Alternatively, users may be assigned signaling IDs from a
full set of
RA signaling IDs. The sequence may be scrambled by resource request ID to
identify as
BW or resource request. The assigned sequence, location, or scrambling may be
a unique
identifier for a user's resource request. Users may be assigned multiple
signaled IDs for
different configured services, such as VoIP and http traffic resource
requests, among other
configured services. If the user has another mechanism for obtaining resource
requests,
and opportunities for resource requests are frequent, the user may not be
assigned
signaling for transmitting resource requests in this manner.
According to yet another embodiment, a UL bandwidth or resource request may
use resources that are specified persistently. One or more RBs and multiple
RBs may be
distributed to provide diversity. A UL bandwidth or resource may be overlaid
with other
traffic on a same resource as a traffic signal or a control signal. If the
user has another
mechanism for resource requests and opportunities for requests are frequent,
the user may
not be assigned signaling for transmitting resource requests in this manner.
UL bandwidth
and resource requests for the mobile terminal 20 may include 4-10 bits, with
an initial
message containing limited fields, such as QoS and a first transmission
spectral efficiency
or a mobile terminal buffer size including CRC. The UL bandwidth requests and
resource
requests for a mobile terminal 20 are intended to be reliable signaling with
diversity, with
interference cancellation used at the base station 16. Users may be separated
by locations
of RBs, sub frame, and assigned sequences. Regarding sequences, each user may
be
assigned a sequence block to use. In other embodiments, users may be assigned
a same
set of sequences to facilitate detection at the base station 16.
Alternatively, orthogonal
sequences such as Zadoff-Chu or Walsh sequences may be used. The sequence
length
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may be less than the length of the RB. If N RBs are assigned for each resource
request
channel, it may be repeated over all RBs. Alternatively, the sequence may be
spread over
all N RBs.
The mobile terminal 20 may send a request for a service signal. The message
size
may be minimal as it indicates a renewal or continuation of a configured
service.
According to a first option, the service may be renewed through a single
message after the
mobile terminal receives a UL assignment for a given type of service. The
message may
be a simple ON/OFF toggle to renewal service with previous or existing
parameters. The
message may be sent in a persistently assigned UL control resource space and
the message
type may indicate that the service renewal is being signaled. The mobile
terminals 20 may
be assigned multiple messages to toggle multiple services, parameters of
renewal for first
transmission may be set to a default and a re-configuration signal in first
transmission may
provide parameter changes.
Alternatively, a scrambled ID may be provided to the mobile terminal 20 for a
UL
renewal request. After the mobile terminal 20 receives a UL assignment for a
given type
of service, the service may be renewed through a single message. The message
may be a
simple ON/OFF toggle to renew service with previous or existing parameters.
The
message may be sent using resource requests in random access space to renew
service to
last configuration parameters. The mobile terminals 20 may be assigned
multiple
messages to toggle multiple services. The parameters of renewal for a first
transmission
may be set to a default.
The invention may be realized in hardware, software, or a combination of
hardware and software. Any kind of computing system, or other apparatus
adapted for
carrying out the methods described herein, is suited to perform the functions
described
herein.
A typical combination of hardware and software could be a computer system
having one or more processing elements and a computer program stored on a
storage
medium that, when loaded and executed, controls the computer system such that
it carries
out the methods described herein. The invention can also be embedded in a
computer
program product, which comprises all the features enabling the implementation
of the
methods described herein, and which, when loaded in a computing system is able
to carry
out these methods. Storage medium refers to any volatile or non-volatile
storage device.
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It will be appreciated by persons skilled in the art that the present
invention is not
limited to what has been particularly shown and described herein above. In
addition,
unless mention was made above to the contrary, it should be noted that all of
the
accompanying drawings are not to scale. A variety of modifications and
variations are
possible in light of the above teachings without departing from the scope and
spirit of the
invention, which is limited only by the following claims.
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