U.S. patent number RE47,259 [Application Number 14/877,494] was granted by the patent office on 2019-02-26 for method and apparatus for supporting multiple reference signals in ofdma communication systems.
This patent grant is currently assigned to Samsung Electronics Co., Ltd. The grantee listed for this patent is Samsung Electronics Co., Ltd.. Invention is credited to Joon-Young Cho, Jin-Kyu Han, Ju-Ho Lee, Aris Papasakellariou.
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United States Patent |
RE47,259 |
Papasakellariou , et
al. |
February 26, 2019 |
Method and apparatus for supporting multiple reference signals in
OFDMA communication systems
Abstract
Methods and apparatuses are described for a Node B to transmit
Reference Signals (RS) from multiple antennas to enable User
Equipments (UEs) to perform demodulation of received information
signals and to estimate Channel Quality Indication (CQI) metrics.
To minimize overhead and enable backward compatible operation with
legacy systems, RS from a first set of Node B antennas are
transmitted in every transmission time interval and substantially
over the whole operating BandWidth (BW). RS from a second set of
Node B antennas serving for CQI estimation are periodically
transmitted, substantially over the whole operating BW, with
transmission period informed to UEs through broadcast signaling by
the Node B and starting transmission sub-frame determined from the
identity of the cell served by the Node B. RS from the second set
of antennas, and new RS from the first set of antennas, serving for
demodulation of information signals have substantially the same BW
as the information signals which can be smaller than the operating
BW.
Inventors: |
Papasakellariou; Aris (Houston,
TX), Cho; Joon-Young (Gyeonggi-do, KR), Lee;
Ju-Ho (Gyeonggi-do, KR), Han; Jin-Kyu (Seoul,
KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Samsung Electronics Co., Ltd. |
Gyeonggi-do |
N/A |
KR |
|
|
Assignee: |
Samsung Electronics Co., Ltd
(KR)
|
Family
ID: |
65410593 |
Appl.
No.: |
14/877,494 |
Filed: |
October 7, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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14842548 |
Sep 1, 2015 |
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61088886 |
Aug 14, 2008 |
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Reissue of: |
12541475 |
Aug 14, 2009 |
8634385 |
Jan 21, 2014 |
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Reissue of: |
12541475 |
Aug 14, 2009 |
8634385 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L
5/0048 (20130101); H04L 5/0092 (20130101); H04W
72/042 (20130101); H04L 25/0226 (20130101); H04L
5/0026 (20130101); H04L 25/02 (20130101); H04L
25/0206 (20130101); H04L 5/0082 (20130101); H04L
5/006 (20130101); H04L 5/0023 (20130101); H04J
11/0069 (20130101); H04L 5/005 (20130101); H04L
5/0082 (20130101); H04J 11/00 (20130101) |
Current International
Class: |
H04W
4/00 (20180101); H04L 5/00 (20060101); H04W
72/04 (20090101); H04L 25/02 (20060101); H04J
11/00 (20060101) |
Field of
Search: |
;370/350,503,208,210,344,347,342,498,334,328,329
;375/260,299,295 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2011-528887 |
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Nov 2011 |
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JP |
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WO 2006/034577 |
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Apr 2006 |
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WO |
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WO 2007/024935 |
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Mar 2007 |
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WO |
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WO 2008/050964 |
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May 2008 |
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WO |
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WO 2009/157167 |
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Dec 2009 |
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WO |
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WO 2010/017628 |
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Feb 2010 |
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WO |
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Other References
Chinese Office Action dated Nov. 8, 2016 issued in counterpart
application No. 201410211310.8, 8 pages. cited by applicant .
U.S. Office Action dated Mar. 20, 2017 issued in counterpart U.S.
Appl. No. 14/842,548, 8 pages. cited by applicant .
U.S. Office Action dated Aug. 24, 2016 issued in counterpart
application No. 14/842,548, 22 pages. cited by applicant .
U.S. Office Action dated Aug. 24, 2016 issued in counterpart
application No. 14/877,458, 12 pages. cited by applicant .
Motorola: "Common Reference Symbol Mapping/Signaling for 8 Transmit
Antennas," R1-083224. 3GPP TSG Ran1 #54, Aug. 18, 2008. cited by
applicant .
Samsung: "Issues on DL RS Design for Higher Order MIMO," R1-084169,
3GPP TSG RAN WG1 #55, Nov. 10, 2008. cited by applicant .
Nortel Networks: "RS Design Considerations for High-Order MIMO in
LTE-A", R1-083157, TSG-RAN1 #54, Aug. 18, 2008. cited by applicant
.
NTT DoCoMo, "Support of DL Higher-Order MIMO Transmission in
LTE-Advanced", R1-083685, 3GPP TSG RAN WG1 Meeting #54bis, Oct. 3,
2008. cited by applicant.
|
Primary Examiner: Sager; Mark
Attorney, Agent or Firm: The Farrell Law Firm, P.C.
Parent Case Text
.Iadd.More than one Reissue Application has been filed for U.S.
Pat. No. 8,634,385. This application is a Continuation Reissue of
U.S. application Ser. No. 14/842,548, which is a Reissue
Application of U.S. Pat. No. 8,634,385. Additionally, Continuation
Reissues application Ser. Nos. 14/877,458 and 14/877,482 have been
filed, which are also Continuation Reissues of U.S. application
Ser. No. 14/842,548, which is a Reissue Application of U.S. Pat.
No. 8,634,385..Iaddend.
Claims
What is claimed is:
.[.1. A method for transmitting first and second sets of Reference
Signals (RSs) from a set of Node B antennas, the set of Node B
antennas also transmitting control data signals in a Physical
Downlink Control Channel (PDCCH) and information data signals in a
Physical Downlink Shared Channel (PDSCH) over a transmission time
interval having transmission symbols, the PDCCH being located in
different transmission symbols than the PDSCH, the method
comprising: transmitting the first set of RSs, from the set of Node
B antennas, using frequency division multiplexing and time division
multiplexing, in both PDCCH transmission symbols and PDSCH
transmission symbols of consecutive transmission time intervals;
and periodically transmitting the second set of RSs, from the set
of Node B antennas, using code division multiplexing in a time
domain and in a frequency domain, in PDSCH transmission symbols of
the transmission time interval, wherein a transmission period is
received from the Node B..].
.[.2. The method of claim 1, wherein the first set of RSs is used
for demodulation of the control data signals or for demodulation of
the information data signals and for obtaining channel quality
estimates, and the second set of RSs is used for obtaining the
channel quality estimates..].
.[.3. The method claim 1, wherein the second set of RSs is used for
obtaining a channel quality estimate..].
.[.4. The method of claim 1, further comprising: transmitting the
first set of RSs from the set of Node B antennas over an entire
operating bandwidth; and transmitting the second set of RSs from
the set of Node B antennas over a portion of the operating
bandwidth that is less than the entire operating bandwidth..].
.[.5. A method for transmitting first and second sets of Reference
Signals (RSs) from a set of Node B antennas, over a transmission
time interval in a set of transmission time intervals and over an
entire operating bandwidth in a cell, the method comprising:
transmitting the first set of RSs from the set of Node B antennas
in all sub-frames in consecutive transmisson time intervals using
frequency division multiplexing and time division multiplexing; and
periodically transmitting the second set of RSs from the set of
Node B antennas in one sub-frame among a set of sub-frames in
transmission time intervals using code division multiplexing in a
time domain and in a frequency domain, a number of the sub-frames
in the set being greater than 1, wherein a sub-frame comprises a
plurality of symbols, and wherein a transmission period is received
from the Node B..].
.[.6. The method of claim 5, wherein the second set of RSs is used
for obtaining a channel quality estimate..].
.[.7. The method of claim 5, wherein the one sub-frame in the set
of sub-frames for the second set of RSs is determined from a cell
identity..].
.[.8. The method of claim 5, wherein the Node B communicates with a
first category and a second category of User Equipments (UEs) and
the second category of UEs interprets the broadcast signaling from
the Node B..].
.[.9. The method of claim 5 wherein the second set of RSs is used
for obtaining channel quality estimates..].
.[.10. The method of claim 5, further comprising: combining at the
Node B the first set of RSs or the second set of RSs for
demodulation of information control signals; and transmitting the
first set of RSs and the second set or RSs separately for
demodulation of information data signals..].
.[.11. The method of claim 10, wherein a number of RSs used for the
demodulation of the information data signals is eight, and a number
of RSs used for the demodulation of the information control signals
is four..].
.[.12. The method of claim 5, wherein the number of the sub-frames
in the set is transmitted to a user equipment..].
.[.13. An apparatus for transmitting first and second sets of
Reference Signals (RSs) from a set of Node B antennas, the set of
Node B antennas also transmitting control data signals in a
Physical Downlink Control CHannel (PDCCH) and information data
signals in a Physical Downlink Shared CHannel (PDSCH) over a
transmission time interval having transmission symbols, the PDCCH
being located in different transmission symbols than the PDSCH, the
apparatus comprising: a first transmitter for transmitting the
first set of RSs, from the set of Node B antennas, using frequency
division multiplexing and time division multiplexing, in both PDCCH
transmission symbols and PDSCH transmission symbols of consecutive
transmission time intervals; and a second transmitter for
periodically transmitting the second set of RSs, from the set of
Node B antennas, using code division multiplexing in a time domain
and in a frequency domain, in PDSCH transmission symbols of the
transmission time interval, wherein a transmission period is
received from the Node B..].
.[.14. The apparatus of claim 13, wherein the first set of RSs is
used for demodulation of the control data signals or for
demodulation of the information data signals and for obtaining
channel quality estimates, and the second set of RSs is used for
obtaining the channel quality estimates..].
.[.15. An apparatus for transmitting first and second sets of
Reference Signals (RSs) from a set of Node B antennas, over a
transmission time interval in a set of transmission time intervals
and over an entire operating bandwidth in a cell, the apparatus
comprising: a first transmitter for transmitting the first set of
RSs from the set of Node B antennas in all sub-frames in
consecutive transmission time intervals using frequency division
multiplexing and time division multiplexing; and a second
transmitter for periodically transmitting the second set of RSs
from the set of Node B antennas in one sub-frame among a set of
sub-frames in transmission time intervals using code division
multiplexing in a time domain and in a frequency domain, a number
of the sub-frames in the set being greater than 1, wherein a
sub-frame comprises a plurality of symbols, and wherein a
transmission period is received from the Node B..].
.[.16. The apparatus of claim 15, wherein the number of the
sub-frames in the set is transmitted to a user equipment..].
.[.17. The apparatus of claim 15, wherein the second set of RSs is
used for obtaining a channel quality estimate..].
.[.18. The apparatus of claim 15, wherein the one sub-frame in the
set of sub-frames for the second set of RSs is determined from a
cell identity..].
.[.19. The apparatus of claim 15, wherein a Node B communicates
with a first category and a second category of User Equipments
(UEs) and the second category of UEs interprets the broadcast
signaling from the Node B..].
.[.20. The apparatus of claim 15, further comprising: combining at
a Node B the first set of RSs or the second set of RSs for
demodulation of information control signals; and transmitting the
first set of RSs and the second set of RSs separately for
demodulation of information data signals..].
.[.21. The apparatus of claim 20, wherein a number of RSs used for
the demodulation of the information data signals is eight, and a
number of RSs used for the demodulation of the information control
signals is four..].
.Iadd.22. A method for receiving, by a terminal, reference signals
(RSs) from a base station including a set of antennas in a wireless
communication system, the method comprising: receiving, by the
terminal, from the base station, a first set of RSs using frequency
division multiplexing and time division multiplexing, in both
physical downlink control channel (PDCCH) transmission symbols and
physical downlink shared channel (PDSCH) transmission symbols of
consecutive sub-frames; and periodically receiving, by the
terminal, from the base station, a second set of RSs using code
division multiplexing in a time domain and in a frequency domain,
in PDSCH transmission symbols of a sub-frame based on a
transmission period of the second set of RSs, wherein the second
set of RSs is used for obtaining a channel quality estimate, and
wherein the transmission period of the second set of RSs is
received from the base station..Iaddend.
.Iadd.23. The method of claim 22, wherein the first set of RSs is
used for demodulation of control data signals or for demodulation
of information data signals and for obtaining channel quality
estimates..Iaddend.
.Iadd.24. The method of claim 22, wherein the first set of RSs are
received over an entire operating bandwidth, and wherein the second
set of RSs are received over a portion of the operating bandwidth
that is less than the entire operating bandwidth..Iaddend.
.Iadd.25. A terminal for receiving reference signals (RSs) from a
base station including a set of antennas in a wireless
communication system, the terminal comprising: a first receiver for
receiving, from the base station, a first set of RSs using
frequency division multiplexing and time division multiplexing, in
both physical downlink control channel (PDCCH) transmission symbols
and physical downlink shared channel (PDSCH) transmission symbols
of consecutive sub-frames; and a second receiver for periodically
receiving, from the base station, a second set of RSs using code
division multiplexing in a time domain and in a frequency domain,
in PDSCH transmission symbols of a sub-frame based on a
transmission period of the second set of RSs, wherein the second
set of RSs is used for obtaining a channel quality estimate, and
wherein the transmission period of the second set of RSs is
received from the base station..Iaddend.
.Iadd.26. The terminal of claim 25, wherein the first set of RSs is
used for demodulation of control data signals or for demodulation
of information data signals and for obtaining channel quality
estimates..Iaddend.
.Iadd.27. The terminal of claim 25, wherein the first receiver
receives the first set of RSs over an entire operating bandwidth,
and wherein the second receiver receives the second set of RSs over
a portion of the operating bandwidth that is less than the entire
operating bandwidth..Iaddend.
.Iadd.28. A method for transmitting reference signals (RSs) by a
base station including a set of antennas in a wireless
communication system, the method comprising: transmitting, by the
base station, a first set of RSs using frequency division
multiplexing and time division multiplexing, in both physical
downlink control channel (PDCCH) transmission symbols and physical
downlink shared channel (PDSCH) transmission symbols of consecutive
sub-frames; and periodically transmitting, by the base station, a
second set of RSs using code division multiplexing in a time domain
and in a frequency domain, in PDSCH transmission symbols of a
sub-frame based on a transmission period of the second set of RSs,
wherein the second set of RSs is used for obtaining a channel
quality estimate, and wherein the transmission period of the second
set of RSs is transmitted, by the base station, to a
terminal..Iaddend.
.Iadd.29. The method of claim 28, wherein the first set of RSs is
used for demodulation of control data signals or for demodulation
of information data signals and for obtaining channel quality
estimates..Iaddend.
.Iadd.30. The method of claim 28, wherein the first set of RSs are
transmitted over an entire operating bandwidth, and wherein the
second set of RSs are transmitted over a portion of the operating
bandwidth that is less than the entire operating
bandwidth..Iaddend.
.Iadd.31. A base station including a set of antennas for
transmitting reference signals (RSs) in a wireless communication
system, the base station comprising: a first transmitter for
transmitting a first set of RSs using frequency division
multiplexing and time division multiplexing, in both physical
downlink control channel (PDCCH) transmission symbols and physical
downlink shared channel (PDSCH) transmission symbols of consecutive
sub-frames; and a second transmitter for periodically transmitting
a second set of RSs using code division multiplexing in a time
domain and in a frequency domain, in PDSCH transmission symbols of
a sub-frame based on a transmission period of the second set of
RSs, wherein the second set of RSs is used for obtaining a channel
quality estimate, and wherein the transmission period of the second
set of RSs is transmitted, by the base station, to a
terminal..Iaddend.
.Iadd.32. The base station of claim 31, wherein the first set of
RSs is used for demodulation of control data signals or for
demodulation of information data signals and for obtaining channel
quality estimates..Iaddend.
.Iadd.33. The base station of claim 31, wherein the first
transmitter transmits the first set of RSs over an entire operating
bandwidth, and wherein the second transmitter transmits the second
set of RSs over a portion of the operating bandwidth that is less
than the entire operating bandwidth..Iaddend.
Description
PRIORITY
The present application claims priority under 35 U.S.C. .sctn.
119(e) to U.S. Provisional Application No. 61/088,886, entitled
"Support of Multiple Reference Signals in OFDMA Communication
Systems", which was filed on Aug. 14, 2008, the contents of which
are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a wireless communication
system and, more specifically, to an Orthogonal Frequency Division
Multiple Access (OFDMA) communication system, in light of the
development of the 3.sup.nd Generation Partnership Project (3GPP)
Evolved Universal Terrestrial Radio Access (E-UTRA) Long Term
Evolution (LTE).
2. Description of the Art
A User Equipment (UE), also commonly referred to as a terminal or a
mobile station, may be fixed or mobile and may be a wireless
device, a cellular phone, a personal computer device, a wireless
modem card, etc. A Node B (or base station) is generally a fixed
station and may also be referred to as a Base Transceiver System
(BTS), an access point, or some other terminology.
Several types of signals should be supported for the proper
functionality of a communication system. The DownLink (DL) signals
consist of data signals, control signals, and reference signals
(also known as pilot signals). The data signals carry the
information content and can be conveyed from the serving Node B to
UEs through a Physical Downlink Shared CHannel (PDSCH). The control
signals may be of broadcast or UE-specific. Broadcast control
signals convey system information to all UEs. UE-specific control
signals convey information related to the scheduling of data signal
transmissions from the serving Node B to a UE or from a UE to the
serving Node B. The signal transmissions from UEs to a serving Node
B occur in the UpLink (UL) of the communication system. The
transmission of UE-specific control signals from the serving Node B
to UEs is assumed to be through a Physical Downlink Control CHannel
(PDCCH).
The DL Reference Signals (RS) can serve for the UEs to perform
multiple functions, as known in the art, such as: channel
estimation in order to perform demodulation of data signals or
control signals; phase reference for Multiple-Input Multiple Output
(MIMO) or beam-forming reception; measurements assisting in a cell
search and a handover; or Channel Quality Indication (CQI)
measurements for link adaptation and channel-dependent
scheduling.
The DL RS transmission can have certain characteristics including:
time multiplexed (transmitted only during certain Orthogonal
Frequency Division Multiplexing (OFDM) symbols); scattered (having
a pattern in both the time and frequency domains); common (can be
received by all UEs in a serving Node B); dedicated (can be
received only by one or a few UEs in a serving Node B); or multiple
antennas (in support of MIMO, beam-forming, or transmission (TX)
diversity).
An exemplary structure for a Common RS (CRS) transmitted from four
antennas of a serving Node B is shown in FIG. 1. FIG. 1 corresponds
to one of the structures used in the 3GPP E-UTRA LTE. The DL data
packet transmission time unit is assumed to be a sub-frame
comprising 14 OFDM symbols 110. Each OFDM symbol is transmitted
over an operating Band Width (BW) comprising OFDM sub-carriers 120
or Resource Elements (REs). Four Node B transmission antennas are
assumed. The DL RS from antenna 1, antenna 2, antenna 3, and
antenna 4 is respectively denoted as RS1 130, RS2 140, RS3 150, and
RS4 160. Each RS has a scattered structure over the DL sub-frame.
If only two Node B antennas exist, the corresponding sub-carriers
occupied by the RS for Node B antennas 3 and 4 may be used for the
transmission of control or data signals or simply left empty. The
same applies for the sub-carriers occupied by the RS for antenna 2
if only one antenna exists. The time density of RS1 and RS2 is
twice the time density of RS3 and RS4 as the frequency density is
the same for all RSs. The former RSs exist in 4 OFDM symbols while
the latter RSs exist in 2 OFDM symbols. The rationale for such a
non-uniformity is that the use of the third and fourth antennas is
typically associated with low to moderate UE velocities, such as,
for example, up to 200 Kilometers per hour, and the time density of
the respective RS can be decreased but remain adequate to capture
the time variations of the channel medium for typical carrier
frequencies while the corresponding RS overhead from Node B
antennas 3 and 4 becomes half that from Node B antennas 1 and
2.
The RS structures illustrated in FIG. 1 correspond to the CRS which
substantially occupies the entire operating BW as opposed to the
UE-Dedicated RS (DRS) which typically occupies only the BW where a
UE is scheduled to receive DL data packet reception in the PDSCH.
This enables the CRS to be used for the reception of signals with
frequency diverse transmission, such as, for example, control
signals, for CQI measurements, or for cell search and handover
measurements. However, if the RS is intended to be used only for
providing a phase reference for beam-forming or MIMO, a DRS
transmitted over the PDSCH data packet transmission BW to a UE
suffices. In FIG. 1 for the PDCCH and PDSCH multiplexing, the PDCCH
170 occupies the first N OFDM symbols while the remaining 14-N OFDM
symbols are typically assigned to PDSCH transmission 180 but may
occasionally also contain transmission of synchronization and
broadcast channels.
An OFDM transmitter is illustrated in FIG. 2. The information data
210 is first encoded and interleaved by coding and interleaving
unit 220, for example, using turbo encoding and block interleaving.
The data is then modulated in modulator 230, for example, using
QPSK, QAM16, or QAM64 modulation. A Serial to Parallel (S/P)
conversion is applied to generate M modulation symbols in S/P
converter 1:M 240 which are subsequently provided to an IFFT unit
250 which effectively produces a time superposition of M orthogonal
narrowband sub-carriers. The M-point time domain blocks obtained
from the IFFT unit 250 are then serialized Parallel to Serial (P/S)
converted M:1 260 to create a time domain OFDM signal 270. The RS
transmission can be viewed as a non-modulated data transmission.
Additional functionalities, such as data scrambling, cyclic prefix
insertion, time windowing, filtering, and others are well known in
the art and are omitted for clarity.
The reverse functions are performed at the OFDM receiver as
illustrated in FIG. 3. The received OFDM signal 310 is provided to
a serial to parallel converter 320 to generate M received signal
samples which are then provided to an FFT unit 330, and after the
output of the FFT unit 330 is serialized in P/S converter 340, the
signal is provided to demodulator 350 and decoding and
deinterleaving unit 360 to produce decoded data. Similarly to the
OFDM transmitter structure in FIG. 2, well known in the art
functionalities such as filtering, time-windowing, cyclic prefix
removal, and de-scrambling are not shown for clarity. Also,
receiver operations such as channel estimation using the RS are
also omitted for clarity.
The total operating BW may consist of elementary scheduling units,
referred to as Physical Resource Blocks (PRBs). For example, a PRB
may consist of 12 consecutive sub-carriers. This allows the serving
Node B to configure, through the PDCCH, multiple UEs to
simultaneously transmit or receive data packets in the UL or DL by
assigning different PRBs for the packet transmission or reception
from or to each UE. For the DL, this concept is illustrated in FIG.
4 where five out of seven UEs are scheduled to receive data in one
sub-frame over 8 PRBs 410. UE1 420, UE2 430, UE4 440, UE5 450, and
UE7 460, are scheduled for PDSCH reception in one or more PRBs
while UE3 470 and UE6 480 are not scheduled for any PDSCH reception
during the reference sub-frame 490. The allocation of PRBs may or
may not be contiguous in the frequency domain and a UE may be
allocated an arbitrary number of PRBs (up to a maximum number as
determined by the operating BW and the PRB size).
The Node B scheduler can select the PRBs used to transmit the data
packet to a scheduled UE based on the CQI feedback from the
scheduled UE over a set of PRBs. The CQI feedback is typically a
Signal-to-Interference and Noise Ratio (SINR) estimate over a set
of PRBs as illustrated in FIG. 5. The Node B scheduler can use this
information to schedule PDSCH transmissions to UEs in the PRBs
where the SINR is the highest, thereby maximizing the system
throughput. In FIG. 5, the SINR 501 of UE1, the SINR 502 of UE2 and
the SINR 503 of UE3 are maximized respectively over the PRB sets
504, 506, and 505 and the corresponding PDSCH transmissions can be
over these PRB sets.
If the set of PRBs is a set corresponding to the entire operating
BW, a RS for the respective Node B transmission antenna port is
needed over the operating BW to obtain the CQI estimate and, as
previously mentioned, requires the use of a CRS. For the sub-frame
structure and the RS structure in FIG. 1, the total RS overhead
from four Node B transmission antennas is equal to 14.3% of the
total overhead, which is significant but not unacceptably
large.
The maximum and average supportable data rates in a communication
system depend, among other factors, on the number of transmission
antennas. In order to increase these data rate metrics, and thereby
more effectively utilizing the BW resource, additional antennas are
often required. To enable gains in system throughput and peak data
rates afforded by increasing the number of transmission antennas to
be realized in practice, it is essential to avoid a substantial
increase in the total RS overhead as required to support signal
transmission from the additional antennas. For example, for eight
Node B transmission antennas, even if antennas 5-8 employed the RS
structure with reduced time density as antennas 3 and 4 in FIG. 1,
the total RS overhead would be 23.8% of the total overhead, which
is unacceptably large.
Additionally, it is often desirable to support PDSCH transmission
to UEs with different capabilities. For example, some UEs may be
able to receive PDSCH transmissions from a maximum of only four
Node B antennas (legacy UEs) while other UEs may be able to receive
PDSCH transmissions from a maximum of eight Node B antennas
(non-legacy UEs). Support for RS transmitted from eight Node B
antennas should not conflict with the capability of legacy UEs to
receive PDSCH transmitted from a maximum of four Node B antennas
without requiring additional receiver operations.
Therefore, there is a need to avoid proportionally increasing the
RS overhead as the number of Node B transmission antennas
increases.
There is another need to support RS transmissions for providing
reliable data scheduling at the Node B, by enabling the UEs to
provide the appropriate CQI feedback, and to enable reliable signal
reception at UEs as the number of Node B transmission antennas
increases.
There is yet another need to support RS transmissions from a number
of Node B antennas without affecting the signal processing at UE
receivers capable of processing only signals transmitted from a
smaller number of Node B antennas.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been designed to solve at
least the aforementioned problems in the prior art, and the present
invention provides methods and apparatus for enabling the
transmission of Reference Signals (RS) from a new subset of Node B
transmission antennas in the set of Node B transmission antennas to
allow the estimation of channel quality indicator metrics while
controlling the associated overhead and minimizing the impact on
the operation on legacy User Equipments (UEs) which utilize only
the legacy subset of Node B transmission antennas from the set of
Node B transmission antennas.
Further, the present invention provides methods and apparatus for
the placement of the RS from the new subset of Node B transmission
antennas.
The present invention also provides methods and apparatus for the
Node B, legacy UEs, and non-legacy UEs, to address the resource
collisions between RS transmissions from the new subset of Node B
transmission antennas and transmissions of information signals.
Additionally, the present invention provides methods and apparatus
for the Node B to multiplex RS transmissions from the new subset of
Node B transmission antennas in a transmission time interval for
the purpose of channel quality indicator estimation.
Additionally, the present invention provides methods and apparatus
for the Node B to multiplex RS transmissions from the new subset of
Node B transmission antennas in a transmission time interval for
the purpose of information data signal demodulation.
Finally, the present invention also provides methods and apparatus
for the Node B to multiplex RS transmissions from the new subset of
Node B transmission antennas for the purpose of channel quality
indicator estimation over multiple transmission time intervals and
to determine which transmission time intervals have RS
transmissions from the new subset of Node B transmission
antennas.
In accordance with an embodiment of the present invention, the RS
transmissions from the new subset of Node B transmission antennas
are located only in the region of the transmission time interval
where data information signals are transmitted, unlike RS
transmissions from the legacy subset of Node B transmission
antennas which are additionally located in the region of the
transmission time interval where control information signals are
transmitted. Moreover, the present invention considers that legacy
UEs treat RS transmissions from the new subset of Node B
transmission antennas as data information signals while non-legacy
UEs puncture the respective resources from the reception of data
information signals.
In accordance with another embodiment of the present invention, RS
transmissions from the new subset of Node B transmission antennas
is code division multiplexed in the time domain and in the
frequency domain while RS transmissions from the legacy subset of
Node B transmission antennas uses time division multiplexing and
frequency division multiplexing.
In accordance with another embodiment of the present invention, RS
transmissions from the new subset of Node B transmission antennas
for the purpose of channel quality indicator estimation can be
periodic in non-consecutive transmission time intervals. The
starting transmission time interval, in a set of transmission time
intervals, can be determined by the identity of the cell served by
the Node B and the transmission period can be signaled by the Node
B through a broadcast channel.
In accordance with another embodiment of the present invention, RS
transmissions from the new subset of Node B transmission antennas
for the purpose of information signal demodulation can be
transmitted over only a portion of the operating bandwidth while RS
transmissions from the legacy subset of Node B transmission
antennas is substantially transmitted over the entire operating
bandwidth.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, features, and advantages of the
present invention will be more apparent from the following detailed
description taken in conjunction with the accompanying drawings, in
which:
FIG. 1 is a diagram illustrating a downlink sub-frame structure for
an OFDMA communication system;
FIG. 2 is a block diagram illustrative of an OFDM transmitter;
FIG. 3 is a block diagram illustrative of an OFDM receiver;
FIG. 4 is a diagram illustrative of scheduling data packet
transmissions in an OFDMA communication system;
FIG. 5 is a diagram illustrative of scheduling data packet
transmissions in an OFDMA communication system based on feedback of
channel quality indicators from user equipments;
FIG. 6 is a diagram illustrating the incorporation of new reference
signals, for the estimation of channel quality indicators, in a
legacy sub-frame structure through frequency division
multiplexing;
FIG. 7 is a diagram illustrating the incorporation of new reference
signals, for the estimation of channel quality indicators, in a
legacy sub-frame structure through code division multiplexing in
the time domain and in the frequency domain;
FIG. 8 is a diagram illustrating the incorporation of new reference
signals, for the estimation of the channel medium and the
demodulation of data information signals, in a legacy sub-frame
structure through code division multiplexing in the time domain and
in the frequency domain;
FIG. 9 is a diagram illustrating the incorporation of new reference
signals, for the estimation of the channel medium and the
demodulation of data information signals, in a legacy sub-frame
structure through code division multiplexing in the time domain and
in the frequency domain; and
FIG. 10 is a diagram illustrative of the periodic transmission of
new reference signals, for the estimation of channel quality
indicators, in an existing sub-frame structure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now 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.
Additionally, although the present invention is described in
relation to a Single-Carrier Frequency Division Multiple Access
(SC-FDMA) communication system, the present invention also applies
to all Frequency Division Multiplexing (FDM) systems in general and
to Orthogonal Frequency Division Multiple Access (OFDMA), OFDM,
FDMA, Discrete Fourier Transform (DFT)-spread OFDM, DFT-spread
OFDMA, Single-Carrier OFDMA (SCOFDMA), and SCOFDM in
particular.
System and methods of the embodiments of the present invention are
related to the need for the Node B to transmit Reference Signals
(RS) to enable User Equipments (UEs) to demodulate information
signals and estimate a Channel Quality Indicator (CQI) metric which
is then fed back to the Node B to enable channel-dependent
scheduling for the transmission of information signals. Supporting
the transmission of information signals from a number of Node B
transmission antennas beyond the one existing in legacy
communication systems, requires RS transmissions from the
additional Node B antennas. However, this should minimize the
associated overhead, the impact to legacy UEs, while enabling
additional transmission features.
The first object of the present invention aims to provide methods
and means for introducing transmission of RS from multiple Node B
antennas while providing the desired reliability for the associated
RS functionalities without proportionally increasing the total RS
overhead.
The second object of the present invention assumes in its exemplary
embodiment that the RS transmission structure from a maximum of
four Node B antennas, for example as described in FIG. 1, is an
existing (legacy) transmission structure and aims to provide
methods and means for introducing RS transmission from additional
Node B antennas while maintaining the capability of legacy UEs
supporting the reception of signals transmitted from a maximum of
four Node B antennas to receive such signals. The goal is for the
insertion of additional RS to be transparent to such legacy
UEs.
FIG. 6 illustrates the introduction of reference signals RS5 670
and RS6 680 transmitted from Node B antennas 5 and 6, respectively,
which represent the only modification relative to FIG. 1 in the RS
transmission structure in a sub-frame. The additional overhead
introduced by RS5 and RS6 is 4.76% of the available overhead
bringing the total RS overhead to about 19% of the available
overhead. Assuming that the PDCCH .[.690.]. is transmitted at most
in the first N OFDM symbols and that the system should support
legacy UEs configured to receive signal transmission from at most
four Node B antennas, RS5 and RS6 should not exist in the PDCCH
region (first N OFDM symbols) because this may require the PDCCH to
extend to the first N+1 OFDM symbols in order to maintain the same
capabilities for control signaling. Then, legacy UEs may not be
able to successfully receive the PDCCH. Additionally, puncturing
sub-carriers where the PDCCH is transmitted in order to insert
additional RS may cause significant degradation in the PDCCH
reception reliability. Unlike the PDSCH 695, the PDCCH does not
typically benefit from the application of Hybrid Automatic Repeat
reQuest (HARQ) and requires better reception reliability than the
PDSCH.
The present invention takes into consideration that RS from
additional Node B antennas, beyond the ones supported for legacy
UEs, are always placed outside the PDCCH region. Note however that
PDCCH transmission from all Node B antennas may still apply for UEs
supporting reception of signals transmitted from all Node B
antennas.
Continuing from FIG. 6, FIG. 7 illustrates the introduction of
reference signals RS7 760 and RS8 770 which are transmitted from
Node B antenna ports 7 and 8, respectively, in addition to the RS1
731, RS2 732, RS3 733, RS4 734, RS5+RS6+RS7+RS8 740, and
RS5-RS6+RS7-RS8 750 which are respectively transmitted from Node B
antennas 1 through 6. Unlike the RS from the four Node B
transmission antennas which are orthogonally multiplexed either by
occupying different sub-carriers 720 (Frequency Division
Multiplexing (FDM)) or different OFDM symbols 710 (Time Division
Multiplexing (TDM)), or both, RS5, RS6, RS7, and RS8 are
multiplexed in the same sub-carriers and the same OFDM symbols
through Code Division Multiplexing (CDM). With CDM, Walsh-Hadamard
(WH) codes apply to the RS in two consecutive OFDM symbols and in
two consecutive sub-carriers having RS transmission. The WH codes
are:
RS5: {1, 1} in the time domain and {1, 1} in the frequency
domain;
RS6: {1, 1} in the time domain and {1, -1} in the frequency
domain;
RS7: {1, -1} in the time domain and {1, 1} in the frequency domain;
and
RS8: {1, -1} in the time domain and {1, -1} in the frequency
domain.
At the UE receiver, the reverse operations are performed to remove
the covering of WH codes. For example, if the {1, 1} WH code is
applied at the Node B transmitter, the UE receiver needs to sum
(average) the RS from two consecutive locations in time or
frequency while if the {1, -1} WH code is applied at the Node B
transmitter, the UE receiver needs to sum (average) the RS from two
consecutive locations in time or frequency after having reversed
the sign of the RS value in the second location. A requirement for
successfully applying CDM is that the response of the channel
medium remains practically the same within two consecutive
locations (in time or frequency) so that orthogonality is
maintained in the received signal.
S.sub.11 and S.sub.12 denote the received signal on odd and even RS
sub-carriers, respectively, in the first OFDM symbol with RS
transmission, and S.sub.21 and S.sub.22 denote the received signal
on odd and even RS sub-carriers, respectively, in the second OFDM
symbol with RS transmission. Ignoring normalization factors, the
respective channel estimates for the signals transmitted Node B
antennas 5 through 8 in each OFDM symbol at sub-carriers at or
between odd and even RS sub-carriers could be obtained as:
Channel Estimate for Antenna 5:
S.sub.11+S.sub.12+S.sub.21+S.sub.22;
Channel Estimate for Antenna 6:
S.sub.11-S.sub.12+S.sub.21-S.sub.22;
Channel Estimate for Antenna 7:
S.sub.11+S.sub.12-S.sub.21-S.sub.22; and
Channel Estimate for Antenna 8:
S.sub.11-S.sub.12-S.sub.21+S.sub.22.
Other averaging methods preserving and restoring orthogonality may
also apply. For example, the channel estimate at an even RS
sub-carrier may incorporate both odd RS sub-carriers at each side
of the even RS sub-carrier and vice versa.
With the use of CDM to transmit the RS from Node B antennas 5
through 8 in FIG. 7, the respective received RS SINR is decreased
by a factor of 2 relative to the SINR obtained for the RS
transmitted from Node B antennas 3 and 4, and by a factor of 4
relative to the SINR obtained for the RS transmitted from Node B
antennas 1 and 2, assuming the same transmission power for all RS.
This is because for the RS from Node B antennas 5 through 8, four
RS share the same sub-carrier while the RS from Node B antennas 3
and 4 has no such sharing and the RS from Node B antennas 1 and 2
is transmitted in twice as many sub-carriers. This SINR reduction
may be less than the previous factors if RS in different cells of a
communication system do not always occupy the same
sub-carriers.
The reduction in the received SINR for the RS from Node B antennas
5 through 8 is offset by the savings in time-frequency resources.
Typically, PDSCH transmission using all eight Node B antennas is
targeted to relatively high SINR UEs with low velocities for which
channel estimation is highly accurate and a small loss in RS SINR
does not lead to noticeably degraded PDSCH reception reliability.
Additionally, legacy UEs capable of supporting reception of signals
transmitted from a maximum of four Node B antennas are not affected
by the transmission of RS from Node B antennas 5 through 8. The
legacy UEs can assume PDSCH transmission in the sub-carriers where
the RS from Node B antennas 5 through 8 are actually transmitted
with the only ramification being a small degradation in the PDSCH
reception reliability which the Node B scheduler can consider in
advance when selecting the modulation and coding scheme. Moreover,
as PDSCH benefits from HARQ, the overall impact on system
throughput is negligible while no change in the receiver processing
is needed for the legacy UEs.
Consequently, the RS transmission structure in FIG. 7 can support
eight Node B antennas with a total overhead of about 19% without
affecting the functionality of legacy UE receivers which are
assumed to be configured for receiving signals transmitted from at
most the four Node B antennas.
The RS transmission from Node B antennas 5 through 8 in FIG. 7
spanned the entire operating BW. This is typically appropriate when
the RS is a Common RS (CRS) that can be received from all UEs. The
second object of the invention considers that Node B antennas 5
through 8 transmit a mixture of CRS and UE-Dedicated RS (DRS). As
it is subsequently analyzed, this can provide another mechanism for
controlling the respective RS overhead.
FIG. 8 illustrates the concept of DRS from Node B antennas 5
through 8 (this can obviously be extended to DRS from Node B
antennas 1 through 4). A reference UE capable of receiving a signal
transmitted from all eight Node B antennas is scheduled to receive
PDSCH in the sub-set 830 of sub-carriers 820 during the portion of
OFDM symbols 810 allocated to PDSCH transmission in a sub-frame.
The CRS from Node B antennas 1 through 4, namely RS1 841, RS2 842,
RS3 843, and RS4 844, remain unchanged. The RS from Node B antennas
5 through 8, namely RS5, RS6, RS7, and RS8, are multiplexed in the
same sub-carriers and OFDM symbols through CDM as described in FIG.
7. In particular, in the odd sub-carriers of the first OFDM symbol
having RS transmission from Node B antennas 5 through 8,
RS5+RS6+RS7+RS8 850 is transmitted while in the even sub-carriers,
RS5-RS6+RS7-RS8 860 is transmitted. In the odd sub-carriers of the
second OFDM symbol having RS transmission from Node B antennas 5
through 8, RS5+RS6-RS7-RS8 870 is transmitted while in the even
sub-carriers, RS5-RS6-RS7+RS8 880 is transmitted. Compared to FIG.
7, the additional RS overhead from Node B antennas 5 through 8 in
FIG. 8 is smaller and the PDSCH reception from legacy UEs remains
entirely unaffected.
An alternative structure for the DRS transmission from Node B
antennas 5 through 8 is illustrated in FIG. 9. The same structure
applies for the DRS from Node B antennas 1 through 4 (not shown for
brevity). The respective DRS overhead is doubled relative to the
DRS overhead in FIG. 8 but there is no constraint for the channel
medium response to effectively remain the same between consecutive
sub-carriers or OFDM symbols with RS transmission as required for
the successful application of CDM. Similarly to FIG. 8, a reference
UE capable of receiving a signal transmitted from all eight Node B
antennas is scheduled to receive PDSCH in the sub-set 930 of
sub-carriers 920 during the portion of OFDM symbols 910 allocated
to PDSCH transmission in a sub-frame. The CRS from Node B antennas
1 through 4, namely RS1 941, RS2 942, RS3 943, and RS4 944, remain
unchanged. The RS from Node B antennas 5 through 8, namely RS5 950,
RS6 960, RS7 970, and RS8 980, are multiplexed in different
sub-carriers or different OFDM symbols using FDM/TDM.
It should be noted that although in all the described RS structures
the separation of sub-carriers and OFDM symbols with RS
transmission from Node B antennas 5 through 8 are shown to be the
same as the ones for the RS transmission from Node B antennas 1
through 4, this is only an exemplary embodiment. The separation of
RS sub-carriers and OFDM symbols with RS transmission can generally
be different between Node B antennas 5 through 8 and Node B
antennas 1 through 4. It is also possible for the RS structure from
Node B antennas 5 through 8 to be configurable. For example, in
channels with small frequency selectivity, CDM may apply as in FIG.
7 or FIG. 8, while in channels with large frequency selectivity,
FDM/TDM may apply as in FIG. 6 or FIG. 9. The multiplexing method
may be blindly determined by the UEs having a reception capability
of signals transmitted from eight Node B antennas or it can be
signaled using 1 bit in a broadcast channel from the serving Node
B.
Although having a DRS transmitted from Node B antennas 5 through 8
is sufficient for PDSCH reception by a UE, this cannot apply for
PDCCH transmission which typically needs to be frequency diverse
and not located only in a sub-set of contiguous sub-carriers, and
cannot apply for CQI estimation enabling scheduling from Node B
antennas 5 through 8. To address the first issue, an embodiment of
the invention considers that a Node B having eight antennas uses
only four of these antennas for PDCCH transmission (for example, by
combining pairs from eight antennas) while the Node B can use all
eight antennas for PDSCH transmission.
To address the second issue, another embodiment of the present
invention considers that a CRS is also transmitted from Node B
antennas 5 through 8 to at least enable UEs to obtain a CQI
estimate from antennas 5 through 8. This CQI estimate can then be
provided by UEs to the serving Node B through the uplink
communication channel in order for the Node B to perform scheduling
of PDSCH transmissions to UEs from Node B antennas 5 through 8
using the appropriate parameters, such as the set of sub-carriers
and the modulation and coding scheme, for each scheduled UE. As
this CRS transmitted from Node B antennas 5 through 8 is intended
to primarily serve for CQI estimation, and not for channel
estimation to perform PDSCH demodulation in each sub-frame, the CRS
does not need to be transmitted in every sub-frame, thereby
avoiding significantly increasing the total RS overhead.
Considering that PDSCH transmissions from Node B antennas 5 through
8 are primarily intended for UEs with low or medium velocities, the
CQI variations in time are slow and the CRS transmission from Node
B antennas 5 through 8 does not need to be frequent. Naturally, in
sub-frames where CRS from Node B antennas 5 through 8 is
transmitted, it can also be used in PDSCH reception and possibly in
the reception of control channels if a method involving all Node B
transmission antennas in the respective sub-frames is used for
their transmission.
FIG. 10 further illustrates an exemplary CRS transmission from Node
B antennas 5 through 8. This CRS transmission is assumed to be once
every 5 sub-frames. The sub-frame structure consists of OFDM
symbols 1010 in the time domain and sub-carriers 1020 in the
frequency domain as it was previously described. The CRS from Node
B antennas 1 through 4, namely RS1 1031, RS2 1032, RS3 1033, and
RS4 1034, is transmitted in all sub-frames. The CRS from Node B
antennas 5 through 8, namely RS5 1045, RS6 1046, RS7 1047, and RS8
1048, are transmitted only in sub-frame 4 1054 and sub-frame 9
1059. DRS transmission from Node B antennas 5 through 8 is not
shown for simplicity.
To minimize the CRS overhead from Node B antennas 5 through 8, an
exemplary embodiment of the invention considers that each of these
CRS is transmitted in only one OFDM symbol. Otherwise, the same
structure with the CRS from Node B antennas 1 through 4 is
maintained to allow for similar processing at a UE receiver.
Nevertheless, the CRS from each of the Node B antennas 5 through 8
may be transmitted in two OFDM symbols or CDM can be used for the
transmission of RS5, RS6, RS7, and RS8 as described in FIG. 7.
Moreover, the CRS from all Node B antennas 5 through 8 are
transmitted in one sub-frame to enable UEs to monitor only the
respective sub-frames, thereby enabling UE power savings, or assist
in the reception of specific control channels transmitted in such
sub-frame.
The sub-frames having CRS transmission from Node B antennas 5
through 8 can be either pre-determined or signaled by the serving
Node B using a broadcast channel. In the former case, CRS
transmission can be pre-determined, for example, that every fifth
sub-frame contains CRS transmission from Node B antenna ports 5
through 8 (at predetermined time-frequency locations). The exact
sub-frames with CRS transmission from Node B antennas 5 through 8
may also be pre-determined, such as sub-frame 0 and sub-frame 4, or
may simply have a predetermined offset with the first sub-frame
depending on the cell identity (Cell-ID). For example, for a first
Cell-ID the first sub-frame is sub-frame 0 while for a second
Cell-ID the first sub-frame is sub-frame 3. This further assumes
that UEs obtain the Cell-ID after initial synchronization with
their serving cell.
With broadcast signaling of the sub-frames where the Node B
transmits the CRS from antennas 5 through 8, several such
configurations can be supported, for example, depending on the
system load. If the cell primarily serves legacy UEs supporting RS
transmission from only Node B antennas 1 through 4, no sub-frames
may contain CRS transmission from Node B antennas 5 through 8. If
the cell primarily serves UEs supporting RS transmission from all
eight Node B antennas, all sub-frames may contain CRS transmission
from Node B antennas 5 through 8. Naturally, intermediate
configurations can also be supported. Table 1 outlines possible
configurations of sub-frames with CRS transmission from Node B
antennas 5 through 8 assuming that 3 bits are included in a
broadcast channel to specify the configuration.
TABLE-US-00001 TABLE 1 Broadcasted 3-bit Field Specifying
Sub-Frames with CRS Transmission from Antennas 5 through 8.
Sub-Frame Configuration with CRS Transmission Broadcasted Value
from Antennas 5 through 8 000 No sub-frame 001 One every 60
sub-frames 010 One every 20 sub-frames 011 One every 10 sub-frames
100 One every 5 sub-frames 101 One every 3 sub-frames 110 One every
2 sub-frames 111 All sub-frames
The starting sub-frame may always be the same, for example, the
first sub-frame every 60 sub-frames, or may depend on the Cell-ID
as previously described. As legacy UEs may not be able to interpret
the broadcasted field specifying the sub-frames with CRS
transmission from Node B antennas 5 through 8, this field may be in
a broadcast channel that is received only by UEs capable of
receiving this CRS transmission.
While the present invention has been shown and described with
reference to certain preferred embodiments thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the present invention as defined by the appended
claims.
* * * * *