U.S. patent application number 12/783847 was filed with the patent office on 2010-09-09 for method and apparatus for increasing the number of orthogonal signals using block spreading.
Invention is credited to Tarik Muharemovic, Eko N. Onggosanusi, Aris Papasakellariou.
Application Number | 20100226413 12/783847 |
Document ID | / |
Family ID | 38309947 |
Filed Date | 2010-09-09 |
United States Patent
Application |
20100226413 |
Kind Code |
A1 |
Muharemovic; Tarik ; et
al. |
September 9, 2010 |
METHOD AND APPARATUS FOR INCREASING THE NUMBER OF ORTHOGONAL
SIGNALS USING BLOCK SPREADING
Abstract
Embodiments of the invention apply block spreading to
transmitted signals to increase the number orthogonally multiplexed
signals. The principle of the disclosed invention can be applied to
reference signals, acknowledgement signals, and channel quality
indication signals. In any given time interval, the set of
transmitted signals is defined by two sequences: the baseline
sequence, and the block spreading sequence. Different transmitters
using the same baseline sequence can be identified by using
different block spreading sequences.
Inventors: |
Muharemovic; Tarik; (Dallas,
TX) ; Papasakellariou; Aris; (Dallas, TX) ;
Onggosanusi; Eko N.; (Allen, TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
US
|
Family ID: |
38309947 |
Appl. No.: |
12/783847 |
Filed: |
May 20, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11627035 |
Jan 25, 2007 |
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12783847 |
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60762071 |
Jan 25, 2006 |
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Current U.S.
Class: |
375/130 ;
375/E1.001 |
Current CPC
Class: |
H04L 5/0007 20130101;
H04L 5/0048 20130101; H04L 5/0053 20130101; H04J 13/0062 20130101;
H04J 13/0055 20130101; H04L 25/0228 20130101; H04L 1/1607 20130101;
H04L 1/0026 20130101; H04J 13/22 20130101; H04L 27/2613 20130101;
H04L 5/0016 20130101; H04B 1/707 20130101; H04B 2201/70701
20130101 |
Class at
Publication: |
375/130 ;
375/E01.001 |
International
Class: |
H04B 1/69 20060101
H04B001/69 |
Claims
1-24. (canceled)
25. A method of separating transmitters, comprising the steps of:
receiving a signal transmitted by a first transmitter using a first
baseline sequence employing a first block-spreading sequence;
receiving a signal transmitted by a second transmitter using the
first baseline sequence employing a second block-spreading
sequence; and using the first and second block-spreading sequences
to separate the first and second transmitters.
26. The method of claim 25, wherein said first sequence is based on
a constant amplitude zero cyclic auto-correlation (CAZAC)
sequence.
27. The method of claim 26, wherein said CAZAC sequence is a
Zadoff-Chu sequence.
28. The method of claim 25, wherein said signal is one of: a
reference signal; an acknowledgement signal; and a channel quality
indication signal.
29. An apparatus, comprising: circuitry for receiving a signal
transmitted by a first transmitter using a first baseline sequence
employing a first block-spreading sequence; circuitry for receiving
a signal transmitted by a second transmitter using the first
baseline sequence employing a second block-spreading sequence; and
circuitry for using the first and second block-spreading sequences
to separate the first and second transmitters.
30. The apparatus of claim 29, wherein the first baseline sequence
is based on a constant amplitude zero cyclic auto-correlation
(CAZAC) sequence.
31. The apparatus of claim 30, wherein said CAZAC sequence is a
Zadoff-Chu sequence.
32. The apparatus of claim 29, wherein said signal is one of: a
reference signal; an acknowledgement signal; and a channel quality
indication signal.
Description
CLAIM OF PRIORITY UNDER 35 U.S.C. .sctn.119
[0001] The present application for Patent claims priority to U.S.
Provisional Application No. 60/762,071 entitled "Increasing the
Number of Orthogonal Pilot Channels" filed Jan. 25, 2006. All
applications assigned to the assignee hereof and hereby expressly
incorporated by reference herein.
BACKGROUND
[0002] Embodiments of the invention are directed, in general, to
wireless communication systems and can be applied to generation and
multiplexing of signals in multi-user wireless communications
systems based on single-carrier frequency division multiple access
(SC-FDMA) and orthogonal frequency division multiple access
(OFDMA).
[0003] FIG. 1 shows a block diagram of a transmitter 110 and a
receiver 150 in a wireless communication system 100. For
simplicity, transmitter 110 and receiver 150 are each equipped with
a single antenna but in practice they may have two or more
antennas. For the downlink (or forward link), transmitter 110 may
be part of a base station (also referred to as Node B), and
receiver 150 may be part of a terminal (also referred to as user
equipment--UE). For the uplink (or reverse link), transmitter 110
may be part of a UE, and receiver 150 may be part of a Node B. A
Node B is generally a fixed station and may also be called a base
transceiver system (BTS), an access point, or some other
terminology. A UE, also commonly referred to as terminal or mobile
station, may be fixed or mobile and may be a wireless device, a
cellular phone, a personal digital assistant (PDA), a wireless
modem card, and so on.
[0004] At transmitter 110, a reference signal (also referred to as
pilot signal) processor 112 generates reference signal symbols (or
pilot symbols). A transmitter (TX) data processor 114 processes
(e.g., encodes, interleaves, and symbol maps) traffic data and
generates data symbols. As used herein, a data symbol is a
modulation symbol for data, a reference signal symbol is a
modulation symbol for reference signal, and the term "modulation
symbol" refers to a real valued or complex valued quantity which is
transmitted across the wireless link. A modulator 120 receives and
multiplexes the data and reference symbols, performs modulation on
the multiplexed data and reference symbols, and generates
transmission symbols. A transmitter unit (TMTR) 132 processes
(e.g., converts to analog, amplifies, filters, and frequency
up-converts) the transmission symbols and generates a radio
frequency (RF) modulated signal, which is transmitted via an
antenna 134.
[0005] At receiver 150, an antenna 152 receives the RF modulated
signal from transmitter 110 and provides a received signal to a
receiver unit (RCVR) 154. Receiver unit 154 conditions (e.g.,
filters, amplifies, frequency down-converts, and digitizes) the
received signal and provides input samples. A demodulator 160
performs demodulation on the input samples to obtain received
symbols. Demodulator 160 provides received reference signal symbols
to a channel processor 170 and provides received data symbols to a
data detector 172. Channel processor 170 derives channel estimates
for the wireless channel between transmitter 110 and receiver 150
and estimates of noise and estimation errors based on the received
reference signal. Data detector 172 performs detection (e.g.,
equalization or matched filtering) on the received data symbols
with the channel estimates and provides data symbol estimates,
which are estimates of the data symbols sent by transmitter 110. A
receiver (RX) data processor 180 processes (e.g., symbol demaps,
deinterleaves, and decodes) the data symbol estimates and provides
decoded data. In general, the processing at receiver 150 is
complementary to the processing at transmitter 110.
[0006] Controllers/processors 140 and 190 direct the operation of
various processing units at transmitter 110 and receiver 150,
respectively. For example, controller processor 190 may provide
demodulator 160 with a replica of the reference signal used by
reference signal processor 112 in order for demodulator to perform
possible correlation of the two signals. Memories 142 and 192 store
program codes and data for transmitter 110 and receiver 150,
respectively.
[0007] The disclosed invention is applicable, but not restricted
to, frequency division multiplexed (FDM) reference signal
transmission for simultaneous transmission from multiple UEs. This
includes, but is not restricted to, OFDMA, OFDM, FDMA, DFT-spread
OFDM, DFT-spread OFDMA, single-carrier OFDMA (SC-OFDMA), and
single-carrier OFDM (SC-OFDM) pilot transmission. The enumerated
versions of FDM transmission strategies are not mutually exclusive,
since, for example, single-carrier FDMA (SC-FDMA) may be realized
using the DFT-spread OFDM technique. In addition, embodiments of
the invention also apply to general single-carrier systems.
[0008] FIG. 2 is an example of a block diagram showing an OFDM(A)
transmitter of the reference signal (RS). It comprises of the RS
sequence generator 201 and the Modulate block 202, which generate a
reference signal block 203. Samples 203 are transmitted over the
air. Modulate block further consists of a Tone Map 202A, insertion
of zeros or other signals 202B, and the IFFT in 202C. Tone Map 202A
can be arbitrary. Elements of apparatus may be implemented as
components in a programmable processor or Digital Signal Processor
(DSP).
[0009] FIG. 3 is an example of a block diagram showing a DFT-spread
OFDM(A) (bracketed letter "A" means that the statement holds for
both DFT-spread OFDM and DFT-spread OFDMA) reference signal (RS)
transmitter. It comprises of the RS sequence generator 301 and the
Modulate block 302, which generate a reference signal block 303.
Samples 303 are transmitted over the air. Modulate block further
consists of: DFT 302D, Tone Map 302A, insertion of zeros or other
signals 302B, and the IFFT in 302C. Tone Map 302A can be arbitrary.
Elements of apparatus may be implemented as components in a
programmable processor or Digital Signal Processor (DSP).
[0010] Embodiments of the invention will be described using a
family of mathematically well studied sequences, known as CAZAC
sequences, as transmitted reference signals for several purposes
including coherent demodulation of the data signal and possible
channel quality estimation. CAZAC sequences are defined as all
complex-valued sequences with the following two properties: 1)
constant amplitude (CA), implying that magnitudes of all sequence
elements are mutually equal and 2) zero cyclic autocorrelation
(ZAC). Well-known examples-of CAZAC sequences include (but are not
limited to) Chu and Frank-Zadoff sequences (or Zadoff-Chu
sequences), and generalized chirp like (GCL) sequences.
Nevertheless, the use of CAZAC reference signals is not mandatory
for this invention. There is a need to define reference signal (RS)
generation and transmission such that multiple reference signals
can be simultaneously orthogonally multiplexed. Such generation
should allow efficient use of the RS resources, which will in turn
maximize the number of simultaneously multiplexed RS transmitters.
Although the exemplary embodiment considers for brevity RS
generation and multiplexing, exactly the same principles can be
used to orthogonally multiplex other signals and increase their
number, including acknowledgement signals (ACK/NAK) and channel
quality indication (CQI) signals.
SUMMARY
[0011] In light of the foregoing background, embodiments of the
invention provide an apparatus, method and system for generating,
multiplexing and allocating reference signals to multiple
transmitters. The proposed method can produce orthogonally
multiplexed signals among the multiple transmitters thereby
avoiding corresponding mutual interference.
[0012] The exemplary embodiment of the invention considers the
generation of reference signals (RS) using constant amplitude zero
cyclic auto-correlation (CAZAC) sequences, and block spreading, for
multiplexing RS from multiple transmitters. RS can be used for the
purposes of coherent data (and/or control) signal demodulation,
channel quality estimation, and other functionalities discussed
herein. The same exactly principle of block spreading of CAZAC
sequences can be extended to the multiplexing of other signals such
as acknowledgement signals (ACK/NAK) related to a packet
transmission or channel quality indication (CQI) signals. The
proposed generation and multiplexing method of RS can be applied to
all frequency division multiplex (FDM) systems which are used by
multiple UEs, with or without multiple transmit antennas. This
includes, but is not restricted to OFDMA, OFDM, FDMA, DFT-spread
OFDM, DFT-spread OFDMA, single-carrier OFDMA (SC-OFDMA), and
single-carrier OFDM (SC-OFDM) RS transmission.
[0013] System and method of embodiments of the present invention
solve problems identified in prior techniques and provide
additional advantages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Having thus described the invention in general terms,
reference will now be made to the accompanying drawings, which are
not necessarily drawn to scale (for example, the number of
sub-carriers in FIG. 2 through FIG. 7 may be substantially larger
than illustrated, such as tens, hundreds or thousands of
sub-carriers), and wherein:
[0015] FIG. 1 is a diagram illustrative of an exemplary wireless
communication system;
[0016] FIG. 2 is a diagram illustrative of an exemplary OFDM(A)
reference signal transmitter;
[0017] FIG. 3 is diagram illustrative of an exemplary DFT-spread
OFDM(A) reference signal transmitter;
[0018] FIG. 4 is a block diagram showing an apparatus for reference
signal generation in accordance with a first embodiment of the
invention;
[0019] FIG. 5 is a block diagram showing an apparatus for reference
signal generation in accordance with a second embodiment of the
invention;
[0020] FIG. 6 is a block diagram showing an apparatus for reference
signal generation in accordance with a third embodiment of the
invention;
[0021] FIG. 7 is a block diagram showing an apparatus for reference
signal generation in accordance with a fourth embodiment of the
invention;
[0022] FIG. 8 is a block diagram showing an apparatus for reference
signal reception in accordance with the embodiment of the invention
described in FIG. 6.
DETAILED DESCRIPTION
[0023] The invention now will be described more fully hereinafter
with reference to the accompanying drawings. This invention may,
however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein. Rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art.
[0024] This invention will be described using CAZAC sequences as
baseline sequences for RS generation. CAZAC sequences are
well-described in the literature and can be found in several
publications. For example, they are studied in the article by A.
Milewski, "Periodic sequences with optimal properties for channel
estimation and fast start-up equalization", IBM Journal of Research
& Development, vol. 27, No. 5, September 83, pages 426-431.
CAZAC sequences include a category of sequences that are polyphase
sequences. See for example: L. H. Zetterberg "A class of codes for
polyphases signals on a band-limited gaussian channel", IEEE Trans.
on Info. Theory, IT-11, pp 385, 1965; also see, A. J. Viterbi "On a
class of polyphases codes for the coherent gaussian channel", IEEE
Int. Cony. Record, Part 7, pp 209, 1965. D. C. Chu "Polyphase Codes
with Good Periodic Correlation Properties." IEEE Trans. Info.
Theory IT-18, pp. 531-532 (July 1972). CAZAC sequences also include
the so-called generalized chirp like (GCL) sequences, as shown in
the reference B. M. Popovic, "Generalized Chirp-like Polyphase
Sequences with Optimal Correlation Properties," IEEE Trans. Info.
Theory, vol. 38, pp. 1406-1409, July 1992. See also, U.S. Pat. No.
3,008,125 by Zadoff et al.
[0025] As a specific example of a CAZAC sequences, we cite the
formula for the Zadoff-Chu (ZC) family of CAZAC sequences given in
page 53 from K. Fazel and S. Keiser, "Multi Carrier and Spread
Spectrum Systems," John Willey and Sons, 2003. Let L be any
positive integer, and let k be any number which is relatively prime
with L. Also, let q be any integer. Then, according to the provided
reference, the n-th entry of the k-th Zadoff-Chu CAZAC sequence is
given as follows
c k ( n ) = exp [ j 2 .pi. k n ( n + 1 ) / 2 + qn L ] for L odd
##EQU00001## c k ( n ) = exp [ j 2 .pi. k n 2 / 2 + qn L ] for L
even ##EQU00001.2##
[0026] The set of Zadoff-Chu CAZAC sequences has following
desirable properties (regardless of the value of q) [0027] Constant
magnitude (or constant amplitude). This property is valid for
generic CAZAC sequences, and is not specific to the Zadoff-Chu
family. [0028] Zero circular auto-correlation. This property is
valid for generic CAZAC sequences, and is not specific to the
Zadoff-Chu family. [0029] Flat frequency domain response. This
means that the magnitudes of each DFT entry of a CAZAC sequence are
all equal. It can be shown that this property is mathematically
equivalent to zero circular auto-correlation property. Thus, this
property is valid for generic CAZAC sequences, and is not specific
to the Zadoff-Chu family. [0030] Circular cross-correlation between
two sequences is low and with constant magnitude which is
independent of the sequence offset. This property is specific to
the Zadoff-Chu CAZAC sequences (with the integer q being fixed) and
prime L.
[0031] From a base family of CAZAC sequences, additional sequences
can be generated using any of the following operations on each
individual sequence: multiplication by a complex constant, DFT,
IDFT, FFT, IFFT, cyclic shift, and block-repetition (and, under
certain conditions, sequence truncation). With block-repetition,
the zero cyclic auto-correlation property holds only up to a
certain delay. Thus, with block-repetition, the cyclic
auto-correlation is zero in the vicinity of the peak (this property
is also referred to as pseudo-CAZAC). Nevertheless, the disclosed
invention does not preclude the use of such pseudo-CAZAC sequences.
Furthermore, the disclosed invention does not preclude the use of
sequences which are generated from other base CAZAC sequences,
using any of the described operations (multiplication by a complex
constant, DFT, IDFT, FFT, IFFT, cyclic shift, block-repetition,
truncation), or a combination thereof.
[0032] The use of CAZAC sequences in this invention is only
exemplary. Other sequences with desirable auto and
cross-correlation properties can be used as well, in conjunction
with the disclosed invention, as follows.
[0033] FIG. 4 is a block-diagram showing an apparatus in accordance
with an embodiment of the invention. Apparatus 400 comprises from:
baseline RS generator 401, RS Modulate block 402, complex
multiplier block 406, and the block-spreading sequence generator
403. In turn, the block spreading sequence generator 403 comprises
of sub-blocks: 403.0 which generates first entry of the
block-spreading sequence, 403.1 which generates second entry of the
block-spreading sequence, etc, until the 403.(T-1) which generates
the last entry of the block-spreading sequence. Elements of
apparatus may be implemented as components in a programmable
processor or Digital Signal Processor (DSP).
[0034] In one embodiment of the invention, each of RS blocks
(404.0, 404.1, etc, 404.(T-1)), from a time interval 405, is
generated using block spreading, as follows. To generate each RS
block, the baseline RS generator 401 generates an RS sequence.
Generated baseline RS sequence is then passed to the "Modulate"
block 402. The "Modulate" block can be any one of the modulators
shown in the prior art (for example, FIG. 2 or FIG. 3), but this is
not mandatory. Subsequently, the entire modulated RS sequence is
block-multiplied with a block-spreading entry (403.0 or 403.1, etc,
or 403.(T-1)) of the block-spreading sequence 403, using the
complex multiplier block 406. The block spreading sequence 403 may
have elements exclusively comprising of +1 and -1 in which case the
multiplication block 406 may simply be replaced by sign flips or no
flips. To generate RS block 404.0, the block-spreading entry 403.0
is used, to generate RS block 404.1, the block-spreading entry
403.1 is used, etc, and to generate RS block 404.(T-1), the
block-spreading entry 403.(T-1) is used. Obviously, at times, a
number of computations can be saved by performing 401 and 402 only
once per time interval 405. Data and/or control transmission can
occur in between RS blocks.
[0035] FIG. 5 is another block-diagram showing an apparatus in
accordance with an embodiment of the system. In contrast to FIG. 4,
the apparatus from FIG. 5 performs block-spreading prior to the
modulation. Apparatus 500 comprises from: baseline RS sequence
generator 501, complex multiplier 506, block-spreading sequence
generator 503, which generates block-spreading entries (503.0,
503.1, etc, 503.(T-1)) of the block-spreading sequence, and
finally, the series of modulator blocks 502.0, 502.1, etc,
502.(T-1). Each of the modulator blocks can be one of the
modulators shown in the prior art (for example, FIG. 2 or FIG. 3),
but this is not mandatory. Each of the modulator blocks can operate
on a different set of data.
[0036] In another embodiment of the invention, each of RS blocks
503.0, 503.1, etc, 503.(T-1) from the time interval 504 is
generated using block-spreading, as follows. First, the baseline RS
generator block 501 generates the baseline RS sequence. To generate
the RS block "t" (where t take on values 0,1, . . . , T-1), the
entire baseline RS sequence is multiplied by the block-spreading
entry 503.t, using the multiplier 506, and then modulated using the
"Modulate" block 502.t. At times, a number of computations can be
saved by performing 501 only once per transmission time interval.
Data and/or control transmission can occur in between RS blocks. In
a number of different scenarios, embodiment from FIG. 5 can be made
equivalent to the embodiment from FIG. 4.
[0037] To separate different transmitters, prior art methods
consider using a different baseline RS sequence for different
transmitters. The disclosed invention considers that different
transmitters can also be separated when they are using an identical
(or correlated) baseline RS sequence, but with different
block-spreading sequences. These different transmitters can be
either: a) different mobiles, b) different base-stations, c)
different antennas from the same mobile, d) different antennas from
the same base-station, or e) any combination thereof. Thus,
disclosed invention allows a system designer to increase the total
number of different RS signals through orthogonal multiplexing by a
factor which is the total number of used block-spreading sequences.
The block-spreading sequence is denoted as s.sub.m(t), which
further denotes the t-th entry of the m-th block spreading
sequence. Multiple choices for block spreading sequences exist and
any set of sequences with good correlation properties can be used.
For example, the conventional Walsh sequences can provide such a
set of block spreading sequences. It is also possible to use cyclic
shifts of a root CAZAC sequence, to generate different
block-spreading sequences.
[0038] To illustrate how block-spreading can be used to separate
different transmitters, we now turn to FIG. 6, illustrating an
exemplary time interval 605 containing two distinct RS blocks,
namely 604.0 and 604.1. Other blocks can carry data and control,
and all blocks are preceded by cyclic-prefix transmission (CP), as
common in OFDM-based systems. Two different transmitters which use
a common baseline RS sequence [c.sub.k(0), c.sub.k(1), . . . ,
c.sub.k(L-1)], generated by 601, can be separated using orthogonal
block-spreading sequences. For one transmitter, the block-spreading
sequence generator 603.0 and 603.1 can generate entries
s.sub.0=[s.sub.0(0), s.sub.0(1)]=[+1, +1]. For another transmitter,
the corresponding block-spreading sequence generator 603.0 and
603.1 can generate entries using s.sub.1=[s.sub.1(0),
s.sub.1(1)]=[+1, -1]. The previous block spreading sequences are
the well known Walsh sequences with length 2. The modulator block
602 can be one of the modulators shown in the prior art (for
example, FIG. 2 or FIG. 3), but this is not mandatory. The
multiplier block 606 in case of Walsh sequences can be a simple
sign operator according to the corresponding sign of the Walsh
sequence element. In this specific case, the multiplier block 606
only flips the sign bit for the second transmitter in the second RS
block. Also, each transmitter can reduce computation by executing
601 and 602 only once per time interval 605.
[0039] A number of different receiver structures can be applied to
the disclosed invention. For example, the receiver structure in.
FIG. 8 corresponds to a transmitter structure in FIG. 6 (additional
receiver structures corresponding to the remaining transmitter
configurations are straightforward to derive and are omitted for
brevity). Receiver 800 first performs block de-spreading for the
received RS signal which is eventually used for channel estimation.
Block de-spreading is performed on received RS blocks 804.0 and
804.1, using the multiplier 806 and adder 802. Here, the received
blocks are first block-multiplied by complex conjugates of the
corresponding block-spreading sequence (803.0 or 803.1), and then
block-added using 802. Further channel estimation operations are
performed by 801 to arrive at channel estimates 807. Once again, in
case of Walsh block spreading sequences comprising of +1 and -1
values, complex conjugates and multiplication are not needed as the
de-spreading operation is simply the appropriate sign application
followed by addition over the Walsh sequence elements. Finally,
note that an alternate receiver structure can first perform channel
estimation (RS demodulation etc) first, and then follow up by
block-de-spreading.
[0040] To further illustrate how block-spreading can separate
different transmitters, we now turn to FIG. 7, further illustrating
another exemplary structure containing four distinct RS blocks,
namely 704.0, 704.1, 704.2 and 704.3. Other blocks can carry data
and control, and all blocks are preceded by cyclic-prefix
transmission (CP), as common in OFDM-based systems. Two different
transmitters which use a common (or just correlated) baseline RS
sequence [c.sub.k(0), c.sub.k(1), . . . , c.sub.k(L-1)], generated
by 701, can be separated using orthogonal block-spreading
sequences. For one transmitter, the block-spreading sequence
generator 703.0, 703.1, 703.2, 703.3 can generate entries
s.sub.0=[s.sub.0(0), s.sub.0(1) s.sub.0(2), s.sub.0(3)]=[+1, +1,
+1, +1]. For another transmitter, the block-spreading sequence
generator 703.0, 703.1, 703.2, and 703.3 can generate entries
s.sub.1=[s.sub.1(0), s.sub.1(1) s.sub.1(2), s.sub.1(3)]=[+1, -1,
+1, -1]. The previous block spreading sequences are the well known
Walsh sequences with length 4. The modulator block 702 can be one
of the modulators shown in the prior art (for example, FIG. 2 or
FIG. 3), but this is not mandatory.
[0041] Thus, with the proposed block-spreading transmission of the
RS, the entire RS transmission, for a particular mobile, is defined
using two sequences: the baseline RS sequence [c.sub.k(0),
c.sub.k(1), . . . , c.sub.k(L-1)], and the block-spreading sequence
[s.sub.m(0), s.sub.m(1) . . . s.sub.m(T-1)] which in the examples
of FIG. 6 and FIG. 7 is a Walsh sequence. Each of these two
sequences has to be assigned to the mobile. This is done,
explicitly or implicitly, by the base-station serving (or
controlling) the reference mobile.
[0042] To maintain (near) orthogonality among the simultaneously
multiplexed signals through the exemplary block-spreading in FIG. 4
or FIG. 5 or FIG. 6 or FIG. 7, it is assumed that the channel does
not change substantially in the time period between the
transmissions of different RS blocks. Validity of this assumption
can be determined by the assigning Node B though estimation of the
Doppler shift (or Doppler spread) of the mobiles. Thus, the
controlling node-B may multiplex slow-moving mobiles using
block-spreading. Any additional fast moving mobile can then be
multiplexed using a different baseline RS sequence (for example
c.sub.2(n)), or a different cyclic shift, or using a different set
of tones.
[0043] All herein described reference signal transmissions (or
parts of them) may be pre-computed, stored in the memory of the UE
device, and used when necessary. Any such operation (pre-computing
and storage) does not limit the scope of the invention.
[0044] The exemplary embodiment of the invention assumes that the
reference signal is time division multiplexed (TDM) with the data
and/or control signal (from a single UE), that is, transmission of
the reference signal does not occur concurrently with the data
and/or control signal. This assumption only serves to simplify the
description of the invention, and is not mandatory to the
invention. Nevertheless, when the reference signal is TDM
multiplexed with the data signal, the two can use different
modulation. For instance, data signal can use SC-OFDM(A), while the
reference signal can use OFDMA modulation.
[0045] In case of multi-antenna transmission, multiple antennas of
a singe UE can be treated as different UEs (different
transmitters), for the purpose of allocating reference signals. All
herein described designs extend in a straightforward manner to the
case of multi-antenna transmission.
[0046] All herein described multi-user allocations can be trivially
reduced and also applied to the single-user scenario.
[0047] The principle of "block spreading" also applies to the
multiplexing of other signals, such as acknowledgement (ACK/NAK)
and channel quality indicator (CQI) signals from different UEs. In
this case, different UEs can use different sequences [c.sub.k(0),
c.sub.k(1), . . . , c.sub.k(L-1)] or [s.sub.m(0), s.sub.m(1) . . .
s.sub.m(T-1)], that are modulated with an information symbol which
is identical to described embodiments. For example, an ACK
transmission may correspond to the transmission of the same
sequence as for the RS while a NAK transmission may correspond to
its algebraic opposite. For CQI transmission, complex modulation
symbols can be used to scale the transmitted sequence. Thus,
embodiments of the invention can also be applied beyond the RS
transmission.
[0048] Many other modifications and other embodiments of the
invention will come to mind to one skilled in the art to which this
invention pertains having the benefit of the teachings presented in
the foregoing descriptions, the associated drawings, and claims.
Therefore, it is to be understood that the invention is not to be
limited to the specific embodiments disclosed and that
modifications and other embodiments are intended to be included
within the scope of the appended claims. Although specific terms
are employed herein, they are used in a generic and descriptive
sense only and not for purposes of limitation.
[0049] All herein described reference signal transmissions may (or
may not) be preceded by a "cyclic prefix," which is a common
practice in all frequency division multiplex systems (FDM). These
systems include, but are not restricted to, OFDM, OFDMA, FDMA,
DFT-spread OFDM, DFT-spread OFDMA, single-carrier OFDMA (SC-OFDMA),
and single-carrier OFDM (SC-OFDM) pilot transmission. Transmission
(or non-transmission) of the "cyclic prefix" doesn't affect the
scope of the invention.
[0050] Definition of "time interval," during which the above
block-spreading is applied, in the exemplary embodiments, can be
understood as any pre-determined time unit. For example, it "time
interval" can correspond to frame, sub-frame, transmission time
interval, slot, or any other time unit.
[0051] At times, RS block-spreading may simply be performed just to
achieve interference randomization. In this case, RS
block-spreading can be implemented using either "short" or "long"
block-spreading sequences.
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