U.S. patent application number 16/324408 was filed with the patent office on 2019-07-18 for methods for flexible reference signal transmission with single carrier frequency domain multiple access (sc-fdma) and ofdma.
This patent application is currently assigned to IDAC HOLDINGS, INC.. The applicant listed for this patent is IDAC HOLDINGS, INC.. Invention is credited to Erdem Bala, Alphan Sahin, Rui Yang.
Application Number | 20190222455 16/324408 |
Document ID | / |
Family ID | 59684083 |
Filed Date | 2019-07-18 |
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United States Patent
Application |
20190222455 |
Kind Code |
A1 |
Sahin; Alphan ; et
al. |
July 18, 2019 |
METHODS FOR FLEXIBLE REFERENCE SIGNAL TRANSMISSION WITH SINGLE
CARRIER FREQUENCY DOMAIN MULTIPLE ACCESS (SC-FDMA) AND OFDMA
Abstract
A method for transmitting a discrete fourier transform (DFT)
DFT-S-OFDM signal including frequency domain reference symbols is
disclosed. The method comprises: determining to null a plurality of
data symbols prior to DFT-spreading; performing DFT-spreading
including the determined null data symbols; puncturing an
interleaved output of the DFT-spreading; inserting reference
symbols in a frequency domain of the punctured and interleaved
DFT-S-OFDM signal; and transmitting the DFT-S-OFDM signal with
inserted reference symbols to a receiver. The transmitted
DFT-S-OFDM signal enables the receiver to apply zeros corresponding
to the reference symbols to an interleaved input of
DFT-despreading, and cancel interference due to the puncturing by
using all outputs of the DFT-despreading.
Inventors: |
Sahin; Alphan; (Westbury,
NY) ; Yang; Rui; (Greenlawn, NY) ; Bala;
Erdem; (East Meadow, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IDAC HOLDINGS, INC. |
Wilmington |
DE |
US |
|
|
Assignee: |
IDAC HOLDINGS, INC.
Wilmington
DE
|
Family ID: |
59684083 |
Appl. No.: |
16/324408 |
Filed: |
August 10, 2017 |
PCT Filed: |
August 10, 2017 |
PCT NO: |
PCT/US2017/046195 |
371 Date: |
February 8, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62373126 |
Aug 10, 2016 |
|
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62479792 |
Mar 31, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 27/2636 20130101;
H04L 1/0071 20130101; H04L 1/0069 20130101; H04W 4/70 20180201;
H04L 5/0051 20130101; H04L 5/0007 20130101 |
International
Class: |
H04L 27/26 20060101
H04L027/26; H04L 1/00 20060101 H04L001/00; H04L 5/00 20060101
H04L005/00; H04W 4/70 20060101 H04W004/70 |
Claims
1. A method for transmitting a Discrete Fourier
Transform-Spread-Orthogonal Frequency Division Multiple Access
(DFT-S-OFDM) signal, the method comprising: setting at least one
input of a DFT to zero; performing DFT-spreading including the at
least one input set to zero; puncturing an at least one output of
the DFT-spreading; replacing the punctured outputs of the DFT
spreading with additional frequency domain symbols; and
transmitting a DFT-S-OFDM signal including the additional frequency
domain symbols to a receiver.
2. The method of claim 1, wherein the additional frequency domain
symbol is a reference symbol (RS).
3. The method of claim 1, wherein a number of additional frequency
domain symbols inserted is based on a channel condition associated
with the receiver.
4. The method of claim 3, wherein on a condition that the channel
condition is relatively poor, the number of additional frequency
domain symbols inserted is increased.
5. The method of claim 1, wherein the punctured output of the DFT
spreading is interleaved.
6. A wireless communication device configured to transmit a
discrete Fourier transform (DFT) spread signal (DFT-S-OFDM) signal,
the device comprising: A processor configured to: set at least one
input of a DFT to zero; perform DFT-spreading including the at
least one input set to zero; puncture an at least one output of the
DFT-spreading; replace the punctured outputs of the DFT spreading
with additional frequency domain symbols; and a transmitter
configured to transmit a DFT-S-OFDM signal including the additional
frequency domain symbols to a receiver.
7. The device of claim 6, wherein the additional frequency domain
symbol is a reference symbol (RS).
8. The device of claim 6, wherein a number of additional frequency
domain symbols inserted is based on a channel condition associated
with the receiver.
9. The device of claim 8, wherein on a condition that the channel
condition is relatively poor, the number of additional frequency
domain symbols inserted is increased.
10. The device of claim 1, wherein the punctured output of the DFT
spreading is interleaved.
11.-15. (canceled)
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the U.S. National Stage, under 35 U.S.C.
.sctn. 371, of International Application No. PCT/US2017/046195
filed Aug. 10, 2017, which claims the benefit of U.S. provisional
application No. 62/373,126 filed on Aug. 10, 2016 and U.S.
provisional application No. 62/479,792 filed on Mar. 31, 2017 the
contents of which are hereby incorporated by reference herein.
BACKGROUND
[0002] In typical single-carrier frequency division multiple access
(SC-FDMA) communications, such as is used in Long Term Evolution
(LTE) uplink transmission, the reference signal (RS) for data
transmission can only be allocated in two time-domain symbol
locations and no data symbols can be transmitted in those
locations. This overhead in terms of resource usage is fixed for
all users, regardless how different the channel conditions are
among them, and cannot be changed dynamically based on channel
conditions and the need of services. For example, in low SINR and
ultra-reliable application scenario, adding more RS will allow the
receiver to estimate the channel more accurately so the data can be
detected with a low error rate. On the other hand, in high SINR and
high data rate requirement scenario, some of the resources, which
otherwise would be used for transmitting RS, can be used to
transmit the data. Therefore, it is desirable to design a
transmitter and receiver scheme that allows flexibly in inserting
the reference signal depending on each users link condition.
SUMMARY
[0003] A method for transmitting a Discrete Fourier
Transform-Spread-Orthogonal Frequency Division Multiple Access
(DFT-S-OFDM) signal including frequency domain reference symbols is
disclosed. The method comprises: determining to null a plurality of
data symbols prior to DFT-spreading; performing DFT-spreading
including the determined null data symbols; puncturing an
interleaved output of the DFT-spreading; inserting reference
symbols in a frequency domain of the punctured and interleaved
DFT-S-OFDM signal; and transmitting the DFT-S-OFDM signal with
inserted reference symbols to a receiver. The transmitted
DFT-S-OFDM signal enables the receiver to apply zeros corresponding
to the reference symbols to an interleaved input of
DFT-despreading, and cancel interference due to the puncturing by
using all outputs of the DFT-despreading.
[0004] The number of reference symbols inserted may be based on a
channel condition associated with the receiver. For example if the
channel condition is relatively poor, the number of reference
symbols inserted may be increased.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] A more detailed understanding may be had from the following
description, given by way of example in conjunction with the
accompanying drawings wherein:
[0006] FIG. 1A is a system diagram of an example communications
system in which one or more disclosed embodiments may be
implemented;
[0007] FIG. 1B is a system diagram of an example wireless
transmit/receive unit (WTRU) that may be used within the
communications system illustrated in FIG. 1A;
[0008] FIG. 10 is a system diagram of an example radio access
network and an example core network that may be used within the
communications system illustrated in FIG. 1A;
[0009] FIG. 2 shows an example uplink frame format for one subframe
in accordance with an embodiment;
[0010] FIG. 3 shows a generic structure for the DFT-S-OFDM
including multiple DFT-spread blocks;
[0011] FIG. 4 shows an example of resource allocation of reference
signals for two users;
[0012] FIG. 5 shows an example of Transmitter and Receiver
structures for dynamic RS insertion;
[0013] FIG. 6 shows the details of the IC block shown in FIG.
5;
[0014] FIG. 7 shows a different numerology within a subframe with a
single carrier waveform;
[0015] FIG. 8 shows a different numerology within a subframe with
an OFDM waveform; and
[0016] FIG. 9 shows a transmitter and receiver block diagram for
DFT-S-OFDM with generalized frequency domain reference symbols.
DETAILED DESCRIPTION
[0017] FIG. 1A is a diagram illustrating an example communications
system 100 in which one or more disclosed embodiments may be
implemented. The communications system 100 may be a multiple access
system that provides content, such as voice, data, video,
messaging, broadcast, etc., to multiple wireless users. The
communications system 100 may enable multiple wireless users to
access such content through the sharing of system resources,
including wireless bandwidth. For example, the communications
systems 100 may employ one or more channel access methods, such as
code division multiple access (CDMA), time division multiple access
(TDMA), frequency division multiple access (FDMA), orthogonal FDMA
(OFDMA), single-carrier FDMA (SC-FDMA), zero-tail unique-word
DFT-Spread OFDM (ZT UW DTS-s OFDM), unique word OFDM (UW-OFDM),
resource block-filtered OFDM, filter bank multicarrier (FBMC), and
the like.
[0018] As shown in FIG. 1A, the communications system 100 may
include wireless transmit/receive units (WTRUs) 102a, 102b, 102c,
102d, a RAN 104/, a CN 106/, a public switched telephone network
(PSTN) 108, the Internet 110, and other networks 112, though it
will be appreciated that the disclosed embodiments contemplate any
number of WTRUs, base stations, networks, and/or network elements.
Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device
configured to operate and/or communicate in a wireless environment.
By way of example, the WTRUs 102a, 102b, 102c, 102d, any of which
may be referred to as a "station" and/or a "STA", may be configured
to transmit and/or receive wireless signals and may include a user
equipment (UE), a mobile station, a fixed or mobile subscriber
unit, a subscription-based unit, a pager, a cellular telephone, a
personal digital assistant (PDA), a smartphone, a laptop, a
netbook, a personal computer, a wireless sensor, a hotspot or Mi-Fi
device, an Internet of Things (IoT) device, a watch or other
wearable, a head-mounted display (HMD), a vehicle, a drone, a
medical device and applications (e.g., remote surgery), an
industrial device and applications (e.g., a robot and/or other
wireless devices operating in an industrial and/or an automated
processing chain contexts), a consumer electronics device, a device
operating on commercial and/or industrial wireless networks, and
the like. Any of the WTRUs 102a, 102b, 102c and 102d may be
interchangeably referred to as a UE.
[0019] The communications systems 100 may also include a base
station 114a and/or a base station 114b. Each of the base stations
114a, 114b may be any type of device configured to wirelessly
interface with at least one of the WTRUs 102a, 102b, 102c, 102d to
facilitate access to one or more communication networks, such as
the CN 106/, the Internet 110, and/or the other networks 112. By
way of example, the base stations 114a, 114b may be a base
transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a
Home eNode B, a gNB, a NR NodeB, a site controller, an access point
(AP), a wireless router, and the like. While the base stations
114a, 114b are each depicted as a single element, it will be
appreciated that the base stations 114a, 114b may include any
number of interconnected base stations and/or network elements.
[0020] The base station 114a may be part of the RAN 104/, which may
also include other base stations and/or network elements (not
shown), such as a base station controller (BSC), a radio network
controller (RNC), relay nodes, etc. The base station 114a and/or
the base station 114b may be configured to transmit and/or receive
wireless signals on one or more carrier frequencies, which may be
referred to as a cell (not shown). These frequencies may be in
licensed spectrum, unlicensed spectrum, or a combination of
licensed and unlicensed spectrum. A cell may provide coverage for a
wireless service to a specific geographical area that may be
relatively fixed or that may change over time. The cell may further
be divided into cell sectors. For example, the cell associated with
the base station 114a may be divided into three sectors. Thus, in
one embodiment, the base station 114a may include three
transceivers, i.e., one for each sector of the cell. In an
embodiment, the base station 114a may employ multiple-input
multiple output (MIMO) technology and may utilize multiple
transceivers for each sector of the cell. For example, beamforming
may be used to transmit and/or receive signals in desired spatial
directions.
[0021] The base stations 114a, 114b may communicate with one or
more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116,
which may be any suitable wireless communication link (e.g., radio
frequency (RF), microwave, centimeter wave, micrometer wave,
infrared (IR), ultraviolet (UV), visible light, etc.). The air
interface 116 may be established using any suitable radio access
technology (RAT).
[0022] More specifically, as noted above, the communications system
100 may be a multiple access system and may employ one or more
channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA,
and the like. For example, the base station 114a in the RAN 104/
and the WTRUs 102a, 102b, 102c may implement a radio technology
such as Universal Mobile Telecommunications System (UMTS)
Terrestrial Radio Access (UTRA), which may establish the air
interface 116_using wideband CDMA (WCDMA). WCDMA may include
communication protocols such as High-Speed Packet Access (HSPA)
and/or Evolved HSPA (HSPA+). HSPA may include High-Speed Downlink
(DL) Packet Access (HSDPA) and/or High-Speed uplink (UL) Packet
Access (HSUPA).
[0023] In an embodiment, the base station 114a and the WTRUs 102a,
102b, 102c may implement a radio technology such as Evolved UMTS
Terrestrial Radio Access (E-UTRA), which may establish the air
interface 116 using Long Term Evolution (LTE) and/or LTE-Advanced
(LTE-A) and/or LTE-Advanced Pro (LTE-A Pro).
[0024] In an embodiment, the base station 114a and the WTRUs 102a,
102b, 102c may implement a radio technology such as NR Radio
Access, which may establish the air interface 116 using New Radio
(NR).
[0025] In an embodiment, the base station 114a and the WTRUs 102a,
102b, 102c may implement multiple radio access technologies. For
example, the base station 114a and the WTRUs 102a, 102b, 102c may
implement LTE radio access and NR radio access together, for
instance using dual connectivity (DC) principles. Thus, the air
interface utilized by WTRUs 102a, 102b, 102c may be characterized
by multiple types of radio access technologies and/or transmissions
sent to/from multiple types of base stations (e.g., a eNB and a
gNB).
[0026] In other embodiments, the base station 114a and the WTRUs
102a, 102b, 102c may implement radio technologies such as IEEE
802.11 (i.e., Wireless Fidelity (WiFi), IEEE 802.16 (i.e.,
Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,
CDMA2000 1.times., CDMA2000 EV-DO, Interim Standard 2000 (IS-2000),
Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global
System for Mobile communications (GSM), Enhanced Data rates for GSM
Evolution (EDGE), GSM EDGE (GERAN), and the like.
[0027] The base station 114b in FIG. 1A may be a wireless router,
Home Node B, Home eNode B, or access point, for example, and may
utilize any suitable RAT for facilitating wireless connectivity in
a localized area, such as a place of business, a home, a vehicle, a
campus, an industrial facility, an air corridor (e.g., for use by
drones), a roadway, and the like. In one embodiment, the base
station 114b and the WTRUs 102c, 102d may implement a radio
technology such as IEEE 802.11 to establish a wireless local area
network (WLAN). In an embodiment, the base station 114b and the
WTRUs 102c, 102d may implement a radio technology such as IEEE
802.15 to establish a wireless personal area network (WPAN). In yet
another embodiment, the base station 114b and the WTRUs 102c, 102d
may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,
LTE-A, LTE-A Pro, NR etc.) to establish a picocell or femtocell. As
shown in FIG. 1A, the base station 114b may have a direct
connection to the Internet 110. Thus, the base station 114b may not
be required to access the Internet 110 via the CN 106.
[0028] The RAN 104/ may be in communication with the CN 106/, which
may be any type of network configured to provide voice, data,
applications, and/or voice over internet protocol (VoIP) services
to one or more of the WTRUs 102a, 102b, 102c, 102d. The data may
have varying quality of service (QoS) requirements, such as
differing throughput requirements, latency requirements, error
tolerance requirements, reliability requirements, data throughput
requirements, mobility requirements, and the like. The CN 106/ may
provide call control, billing services, mobile location-based
services, pre-paid calling, Internet connectivity, video
distribution, etc., and/or perform high-level security functions,
such as user authentication. Although not shown in FIG. 1A, it will
be appreciated that the RAN 104/ and/or the CN 106/ may be in
direct or indirect communication with other RANs that employ the
same RAT as the RAN 104/ or a different RAT. For example, in
addition to being connected to the RAN 104/, which may be utilizing
a NR radio technology, the CN 106/ may also be in communication
with another RAN (not shown) employing a GSM, UMTS, CDMA 2000,
WiMAX, E-UTRA, or WiFi radio technology.
[0029] The CN 106/ may also serve as a gateway for the WTRUs 102a,
102b, 102c, 102d to access the PSTN 108, the Internet 110, and/or
the other networks 112. The PSTN 108 may include circuit-switched
telephone networks that provide plain old telephone service (POTS).
The Internet 110 may include a global system of interconnected
computer networks and devices that use common communication
protocols, such as the transmission control protocol (TCP), user
datagram protocol (UDP) and/or the internet protocol (IP) in the
TCP/IP internet protocol suite. The networks 112 may include wired
and/or wireless communications networks owned and/or operated by
other service providers. For example, the networks 112 may include
another CN connected to one or more RANs, which may employ the same
RAT as the RAN 104/ or a different RAT.
[0030] Some or all of the WTRUs 102a, 102b, 102c, 102d in the
communications system 100 may include multi-mode capabilities
(e.g., the WTRUs 102a, 102b, 102c, 102d may include multiple
transceivers for communicating with different wireless networks
over different wireless links). For example, the WTRU 102c shown in
FIG. 1A may be configured to communicate with the base station
114a, which may employ a cellular-based radio technology, and with
the base station 114b, which may employ an IEEE 802 radio
technology.
[0031] FIG. 1B is a system diagram illustrating an example WTRU
102. As shown in FIG. 1B, the WTRU 102 may include a processor 118,
a transceiver 120, a transmit/receive element 122, a
speaker/microphone 124, a keypad 126, a display/touchpad 128,
non-removable memory 130, removable memory 132, a power source 134,
a global positioning system (GPS) chipset 136, and/or other
peripherals 138, among others. It will be appreciated that the WTRU
102 may include any sub-combination of the foregoing elements while
remaining consistent with an embodiment.
[0032] The processor 118 may be a general purpose processor, a
special purpose processor, a conventional processor, a digital
signal processor (DSP), a plurality of microprocessors, one or more
microprocessors in association with a DSP core, a controller, a
microcontroller, Application Specific Integrated Circuits (ASICs),
Field Programmable Gate Arrays (FPGAs) circuits, any other type of
integrated circuit (10), a state machine, and the like. The
processor 118 may perform signal coding, data processing, power
control, input/output processing, and/or any other functionality
that enables the WTRU 102 to operate in a wireless environment. The
processor 118 may be coupled to the transceiver 120, which may be
coupled to the transmit/receive element 122. While FIG. 1B depicts
the processor 118 and the transceiver 120 as separate components,
it will be appreciated that the processor 118 and the transceiver
120 may be integrated together in an electronic package or
chip.
[0033] The transmit/receive element 122 may be configured to
transmit signals to, or receive signals from, a base station (e.g.,
the base station 114a) over the air interface 116. For example, in
one embodiment, the transmit/receive element 122 may be an antenna
configured to transmit and/or receive RF signals. In an embodiment,
the transmit/receive element 122 may be an emitter/detector
configured to transmit and/or receive IR, UV, or visible light
signals, for example. In yet another embodiment, the
transmit/receive element 122 may be configured to transmit and/or
receive both RF and light signals. It will be appreciated that the
transmit/receive element 122 may be configured to transmit and/or
receive any combination of wireless signals.
[0034] Although the transmit/receive element 122 is depicted in
FIG. 1B as a single element, the WTRU 102 may include any number of
transmit/receive elements 122. More specifically, the WTRU 102 may
employ MIMO technology. Thus, in one embodiment, the WTRU 102 may
include two or more transmit/receive elements 122 (e.g., multiple
antennas) for transmitting and receiving wireless signals over the
air interface 116.
[0035] The transceiver 120 may be configured to modulate the
signals that are to be transmitted by the transmit/receive element
122 and to demodulate the signals that are received by the
transmit/receive element 122. As noted above, the WTRU 102 may have
multi-mode capabilities. Thus, the transceiver 120 may include
multiple transceivers for enabling the WTRU 102 to communicate via
multiple RATs, such as NR and IEEE 802.11, for example.
[0036] The processor 118 of the WTRU 102 may be coupled to, and may
receive user input data from, the speaker/microphone 124, the
keypad 126, and/or the display/touchpad 128 (e.g., a liquid crystal
display (LCD) display unit or organic light-emitting diode (OLED)
display unit). The processor 118 may also output user data to the
speaker/microphone 124, the keypad 126, and/or the display/touchpad
128. In addition, the processor 118 may access information from,
and store data in, any type of suitable memory, such as the
non-removable memory 130 and/or the removable memory 132. The
non-removable memory 130 may include random-access memory (RAM),
read-only memory (ROM), a hard disk, or any other type of memory
storage device. The removable memory 132 may include a subscriber
identity module (SIM) card, a memory stick, a secure digital (SD)
memory card, and the like. In other embodiments, the processor 118
may access information from, and store data in, memory that is not
physically located on the WTRU 102, such as on a server or a home
computer (not shown).
[0037] The processor 118 may receive power from the power source
134, and may be configured to distribute and/or control the power
to the other components in the WTRU 102. The power source 134 may
be any suitable device for powering the WTRU 102. For example, the
power source 134 may include one or more dry cell batteries (e.g.,
nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride
(NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and
the like.
[0038] The processor 118 may also be coupled to the GPS chipset
136, which may be configured to provide location information (e.g.,
longitude and latitude) regarding the current location of the WTRU
102. In addition to, or in lieu of, the information from the GPS
chipset 136, the WTRU 102 may receive location information over the
air interface 116 from a base station (e.g., base stations 114a,
114b) and/or determine its location based on the timing of the
signals being received from two or more nearby base stations. It
will be appreciated that the WTRU 102 may acquire location
information by way of any suitable location-determination method
while remaining consistent with an embodiment.
[0039] The processor 118 may further be coupled to other
peripherals 138, which may include one or more software and/or
hardware modules that provide additional features, functionality
and/or wired or wireless connectivity. For example, the peripherals
138 may include an accelerometer, an e-compass, a satellite
transceiver, a digital camera (for photographs and/or video), a
universal serial bus (USB) port, a vibration device, a television
transceiver, a hands free headset, a Bluetooth.RTM. module, a
frequency modulated (FM) radio unit, a digital music player, a
media player, a video game player module, an Internet browser, a
Virtual Reality and/or Augmented Reality (VR/AR) device, an
activity tracker, and the like. The peripherals 138 may include one
or more sensors, the sensors may be one or more of a gyroscope, an
accelerometer, a hall effect sensor, a magnetometer, an orientation
sensor, a proximity sensor, a temperature sensor, a time sensor; a
geolocation sensor; an altimeter, a light sensor, a touch sensor, a
magnetometer, a barometer, a gesture sensor, a biometric sensor,
and/or a humidity sensor.
[0040] The WTRU 102 may include a full duplex radio for which
transmission and reception of some or all of the signals (e.g.,
associated with particular subframes for both the UL (e.g., for
transmission) and downlink (e.g., for reception) may be concurrent
and/or simultaneous. The full duplex radio may include an
interference management unit to reduce and or substantially
eliminate self-interference via either hardware (e.g., a choke) or
signal processing via a processor (e.g., a separate processor (not
shown) or via processor 118). In an embodiment, the WRTU 102 may
include a half-duplex radio for which transmission and reception of
some or all of the signals (e.g., associated with particular
subframes for either the UL (e.g., for transmission) or the
downlink (e.g., for reception)).
[0041] FIG. 10 is a system diagram illustrating the RAN 104 and the
CN 106 according to an embodiment. As noted above, the RAN 104 may
employ an E-UTRA radio technology to communicate with the WTRUs
102a, 102b, 102c over the air interface 116. The RAN 104 may also
be in communication with the CN 106.
[0042] The RAN 104 may include eNode-Bs 140a, 140b, 140c, though it
will be appreciated that the RAN 104 may include any number of
eNode-Bs while remaining consistent with an embodiment. The
eNode-Bs 140a, 140b, 140c may each include one or more transceivers
for communicating with the WTRUs 102a, 102b, 102c over the air
interface 116. In one embodiment, the eNode-Bs 140a, 140b, 140c may
implement MIMO technology. Thus, the eNode-B 140a, for example, may
use multiple antennas to transmit wireless signals to, and/or
receive wireless signals from, the WTRU 102a.
[0043] Each of the eNode-Bs 140a, 140b, 140c may be associated with
a particular cell (not shown) and may be configured to handle radio
resource management decisions, handover decisions, scheduling of
users in the UL and/or DL, and the like. As shown in FIG. 10, the
eNode-Bs 140a, 140b, 140c may communicate with one another over an
X2 interface.
[0044] The CN 106 shown in FIG. 10 may include a mobility
management entity (MME) 142, a serving gateway (SGW) 144, and a
packet data network (PDN) gateway (or PGW) 146. While each of the
foregoing elements are depicted as part of the CN 106, it will be
appreciated that any of these elements may be owned and/or operated
by an entity other than the CN operator.
[0045] The MME 142 may be connected to each of the eNode-Bs 140a,
140b, 140c in the RAN 104 via an S1 interface and may serve as a
control node. For example, the MME 142 may be responsible for
authenticating users of the WTRUs 102a, 102b, 102c, bearer
activation/deactivation, selecting a particular serving gateway
during an initial attach of the WTRUs 102a, 102b, 102c, and the
like. The MME 142 may provide a control plane function for
switching between the RAN 104 and other RANs (not shown) that
employ other radio technologies, such as GSM and/or WCDMA.
[0046] The SGW 144 may be connected to each of the eNode Bs 140a,
140b, 140c in the RAN 104 via the S1 interface. The SGW 144 may
generally route and forward user data packets to/from the WTRUs
102a, 102b, 102c. The SGW 144 may perform other functions, such as
anchoring user planes during inter-eNode B handovers, triggering
paging when DL data is available for the WTRUs 102a, 102b, 102c,
managing and storing contexts of the WTRUs 102a, 102b, 102c, and
the like.
[0047] The SGW 144 may be connected to the PGW 146, which may
provide the WTRUs 102a, 102b, 102c with access to packet-switched
networks, such as the Internet 110, to facilitate communications
between the WTRUs 102a, 102b, 102c and IP-enabled devices.
[0048] The CN 106 may facilitate communications with other
networks. For example, the CN 106 may provide the WTRUs 102a, 102b,
102c with access to circuit-switched networks, such as the PSTN
108, to facilitate communications between the WTRUs 102a, 102b,
102c and traditional land-line communications devices. For example,
the CN 106 may include, or may communicate with, an IP gateway
(e.g., an IP multimedia subsystem (IMS) server) that serves as an
interface between the CN 106 and the PSTN 108. In addition, the CN
106 may provide the WTRUs 102a, 102b, 102c with access to the other
networks 112, which may include other wired and/or wireless
networks that are owned and/or operated by other service
providers.
[0049] Although the WTRU is described in FIGS. 1A-1C as a wireless
terminal, it is contemplated that in certain representative
embodiments that such a terminal may use (e.g., temporarily or
permanently) wired communication interfaces with the communication
network.
[0050] In representative embodiments, the other network 112 may be
a WLAN.
[0051] A WLAN in Infrastructure Basic Service Set (BSS) mode may
have an Access Point (AP) for the BSS and one or more stations
(STAs) associated with the AP. The AP may have an access or an
interface to a Distribution System (DS) or another type of
wired/wireless network that carries traffic in to and/or out of the
BSS. Traffic to STAs that originates from outside the BSS may
arrive through the AP and may be delivered to the STAs. Traffic
originating from STAs to destinations outside the BSS may be sent
to the AP to be delivered to respective destinations. Traffic
between STAs within the BSS may be sent through the AP, for
example, where the source STA may send traffic to the AP and the AP
may deliver the traffic to the destination STA. The traffic between
STAs within a BSS may be considered and/or referred to as
peer-to-peer traffic. The peer-to-peer traffic may be sent between
(e.g., directly between) the source and destination STAs with a
direct link setup (DLS). In certain representative embodiments, the
DLS may use an 802.11e DLS or an 802.11z tunneled DLS (TDLS). A
WLAN using an Independent BSS (IBSS) mode may not have an AP, and
the STAs (e.g., all of the STAs) within or using the IBSS may
communicate directly with each other. The IBSS mode of
communication may sometimes be referred to herein as an "ad-hoc"
mode of communication.
[0052] When using the 802.11ac infrastructure mode of operation or
a similar mode of operations, the AP may transmit a beacon on a
fixed channel, such as a primary channel. The primary channel may
be a fixed width (e.g., 20 MHz wide bandwidth) or a dynamically set
width via signaling. The primary channel may be the operating
channel of the BSS and may be used by the STAs to establish a
connection with the AP. In certain representative embodiments,
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)
may be implemented, for example in in 802.11 systems. For CSMA/CA,
the STAs (e.g., every STA), including the AP, may sense the primary
channel. If the primary channel is sensed/detected and/or
determined to be busy by a particular STA, the particular STA may
back off. One STA (e.g., only one station) may transmit at any
given time in a given BSS.
[0053] High Throughput (HT) STAs may use a 40 MHz wide channel for
communication, for example, via a combination of the primary 20 MHz
channel with an adjacent or nonadjacent 20 MHz channel to form a 40
MHz wide channel.
[0054] Very High Throughput (VHT) STAs may support 20 MHz, 40 MHz,
80 MHz, and/or 160 MHz wide channels. The 40 MHz, and/or 80 MHz,
channels may be formed by combining contiguous 20 MHz channels. A
160 MHz channel may be formed by combining 8 contiguous 20 MHz
channels, or by combining two non-contiguous 80 MHz channels, which
may be referred to as an 80+80 configuration. For the 80+80
configuration, the data, after channel encoding, may be passed
through a segment parser that may divide the data into two streams.
Inverse Fast Fourier Transform (IFFT) processing, and time domain
processing, may be done on each stream separately. The streams may
be mapped on to the two 80 MHz channels, and the data may be
transmitted by a transmitting STA. At the receiver of the receiving
STA, the above described operation for the 80+80 configuration may
be reversed, and the combined data may be sent to the Medium Access
Control (MAC).
[0055] Sub 1 GHz modes of operation are supported by 802.11af and
802.11ah. The channel operating bandwidths, and carriers, are
reduced in 802.11af and 802.11ah relative to those used in 802.11n,
and 802.11ac. 802.11af supports 5 MHz, 10 MHz and 20 MHz bandwidths
in the TV White Space (TVWS) spectrum, and 802.11ah supports 1 MHz,
2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non-TVWS spectrum.
According to a representative embodiment, 802.11ah may support
Meter Type Control/Machine-Type Communications, such as MTC devices
in a macro coverage area. MTC devices may have certain
capabilities, for example, limited capabilities including support
for (e.g., only support for) certain and/or limited bandwidths. The
MTC devices may include a battery with a battery life above a
threshold (e.g., to maintain a very long battery life).
[0056] WLAN systems, which may support multiple channels, and
channel bandwidths, such as 802.11n, 802.11ac, 802.11af, and
802.11ah, include a channel which may be designated as the primary
channel. The primary channel may have a bandwidth equal to the
largest common operating bandwidth supported by all STAs in the
BSS. The bandwidth of the primary channel may be set and/or limited
by a STA, from among all STAs in operating in a BSS, which supports
the smallest bandwidth operating mode. In the example of 802.11ah,
the primary channel may be 1 MHz wide for STAs (e.g., MTC type
devices) that support (e.g., only support) a 1 MHz mode, even if
the AP, and other STAs in the BSS support 2 MHz, 4 MHz, 8 MHz, 16
MHz, and/or other channel bandwidth operating modes. Carrier
sensing and/or Network Allocation Vector (NAV) settings may depend
on the status of the primary channel. If the primary channel is
busy, for example, due to a STA (which supports only a 1 MHz
operating mode), transmitting to the AP, the entire available
frequency bands may be considered busy even though a majority of
the frequency bands remains idle and may be available.
[0057] In the United States, the available frequency bands, which
may be used by 802.11ah, are from 902 MHz to 928 MHz. In Korea, the
available frequency bands are from 917.5 MHz to 923.5 MHz. In
Japan, the available frequency bands are from 916.5 MHz to 927.5
MHz. The total bandwidth available for 802.11ah is 6 MHz to 26 MHz
depending on the country code.
[0058] Another example of a communications system including the RAN
104 and the CN 106 is described herein. As noted above, the RAN 104
may employ an NR radio technology to communicate with the WTRUs
102a, 102b, 102c over the air interface 116. The RAN 104 may also
be in communication with the CN 106.
[0059] The RAN 104 may include gNBs (not shown), though it will be
appreciated that the RAN may include any number of gNBs while
remaining consistent with an embodiment. The gNBs may each include
one or more transceivers for communicating with the WTRUs 102a,
102b, 102c over the air interface 116. In one embodiment, the gNBs
may implement MIMO technology. For example, the gNBs may utilize
beamforming to transmit signals to and/or receive signals from the
gNBs. Thus, a gNB, for example, may use multiple antennas to
transmit wireless signals to, and/or receive wireless signals from,
the WTRU 102a. In an embodiment, the gNBs may implement carrier
aggregation technology. For example, a gNB may transmit multiple
component carriers to the WTRU 102a. A subset of these component
carriers may be on unlicensed spectrum while the remaining
component carriers may be on licensed spectrum. In an embodiment,
the gNBs may implement Coordinated Multi-Point (CoMP) technology.
For example, WTRU 102a may receive coordinated transmissions from
multiple gNBs.
[0060] The WTRUs 102a, 102b, 102c may communicate with the gNBs
using transmissions associated with a scalable numerology. For
example, the OFDM symbol spacing and/or OFDM subcarrier spacing may
vary for different transmissions, different cells, and/or different
portions of the wireless transmission spectrum. The WTRUs 102a,
102b, 102c may communicate with the gNBs using subframe or
transmission time intervals (TTIs) of various or scalable lengths
(e.g., containing varying number of OFDM symbols and/or lasting
varying lengths of absolute time).
[0061] The gNBs may be configured to communicate with the WTRUs
102a, 102b, 102c in a standalone configuration and/or a
non-standalone configuration. In the standalone configuration,
WTRUs 102a, 102b, 102c may communicate with the gNBs without also
accessing other RANs (e.g., such as eNode-Bs 140a, 140b, 140c). In
the standalone configuration, WTRUs 102a, 102b, 102c may utilize
one or more of the gNBs as a mobility anchor point. In the
standalone configuration, WTRUs 102a, 102b, 102c may communicate
with the gNBs using signals in an unlicensed band. In a
non-standalone configuration WTRUs 102a, 102b, 102c may communicate
with/connect to the gNBs while also communicating with/connecting
to another RAN such as eNode-Bs 140a, 140b, 140c. For example,
WTRUs 102a, 102b, 102c may implement DC principles to communicate
with one or more gNBs and one or more eNode-Bs 140a, 140b, 140c
substantially simultaneously. In the non-standalone configuration,
eNode-Bs 140a, 140b, 140c may serve as a mobility anchor for WTRUs
102a, 102b, 102c and the gNBs may provide additional coverage
and/or throughput for servicing WTRUs 102a, 102b, 102c.
[0062] Each of the gNBs may be associated with a particular cell
and may be configured to handle radio resource management
decisions, handover decisions, scheduling of users in the UL and/or
DL, support of network slicing, dual connectivity, interworking
between NR and E-UTRA, routing of user plane data towards User
Plane Function (UPF), routing of control plane information towards
Access and Mobility Management Function (AMF) and the like. As
described herein, the gNBs may communicate with one another over an
Xn interface.
[0063] The CN 106 may include at least one AMF, at least one UPF,
at least one Session Management Function (SMF), and possibly a Data
Network (DN). While each of the foregoing elements are may be part
of the CN 106, it will be appreciated that any of these elements
may be owned and/or operated by an entity other than the CN
operator.
[0064] The AMF may be connected to one or more of the gNBs in the
RAN 104 via an N2 interface and may serve as a control node. For
example, the AMF may be responsible for authenticating users of the
WTRUs 102a, 102b, 102c, support for network slicing (e.g., handling
of different PDU sessions with different requirements), selecting a
particular SMF, management of the registration area, termination of
NAS signaling, mobility management, and the like. Network slicing
may be used by the AMF in order to customize CN support for WTRUs
102a, 102b, 102c based on the types of services being utilized. For
example, different network slices may be established for different
use cases such as services relying on ultra-reliable low latency
(URLLC) access, services relying on enhanced massive mobile
broadband (eMBB) access, services for machine type communication
(MTC) access, and/or the like. The AMF may provide a control plane
function for switching between the RAN 104 and other RANs that
employ other radio technologies, such as LTE, LTE-A, LTE-A Pro,
and/or non-3GPP access technologies such as WiFi.
[0065] The SMF may be connected to an AMF in the CN via an N11
interface. The SMF may also be connected to a UPF in the CN 106 via
an N4 interface. The SMF may select and control the UPF and
configure the routing of traffic through the UPF. The SMF may
perform other functions, such as managing and allocating UE IP
address, managing PDU sessions, controlling policy enforcement and
QoS, providing downlink data notifications, and the like. A PDU
session type may be IP-based, non-IP based, Ethernet-based, and the
like.
[0066] The UPF may be connected to one or more of the gNBs in the
RAN 104 via an N3 interface, which may provide the WTRUs 102a,
102b, 102c with access to packet-switched networks, such as the
Internet 110, to facilitate communications between the WTRUs 102a,
102b, 102c and IP-enabled devices. The UPF may perform other
functions, such as routing and forwarding packets, enforcing user
plane policies, supporting multi-homed PDU sessions, handling user
plane QoS, buffering downlink packets, providing mobility
anchoring, and the like.
[0067] The CN 106 may facilitate communications with other
networks. For example, the CN 106 may include, or may communicate
with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server)
that serves as an interface between the CN 106 and the PSTN 108. In
addition, the CN may provide the WTRUs 102a, 102b, 102c with access
to the other networks 112, which may include other wired and/or
wireless networks that are owned and/or operated by other service
providers. In one embodiment, the WTRUs 102a, 102b, 102c may be
connected to a local Data Network (DN) through the UPF via the N3
interface to the UPF and an N6 interface between the UPF and the
DN.
[0068] As described herein and in view of FIGS. 1A-1C, and the
corresponding description of FIGS. 1A-1C, one or more, or all, of
the functions described herein with regard to one or more of: WTRU
102a-d, Base Station 114a-b, eNode-B 140a-c, MME 142, SGW 144, PGW
146, the gNB(s), the AMF(s), the UPF(s), the SMF(s), the DN(s),
and/or any other device(s) described herein, may be performed by
one or more emulation devices. The emulation devices may be one or
more devices configured to emulate one or more, or all, of the
functions described herein. For example, the emulation devices may
be used to test other devices and/or to simulate network and/or
WTRU functions.
[0069] The emulation devices may be designed to implement one or
more tests of other devices in a lab environment and/or in an
operator network environment. For example, the one or more
emulation devices may perform the one or more, or all, functions
while being fully or partially implemented and/or deployed as part
of a wired and/or wireless communication network in order to test
other devices within the communication network. The one or more
emulation devices may perform the one or more, or all, functions
while being temporarily implemented/deployed as part of a wired
and/or wireless communication network. The emulation device may be
directly coupled to another device for purposes of testing and/or
may performing testing using over-the-air wireless
communications.
[0070] The one or more emulation devices may perform the one or
more, including all, functions while not being implemented/deployed
as part of a wired and/or wireless communication network. For
example, the emulation devices may be utilized in a testing
scenario in a testing laboratory and/or a non-deployed (e.g.,
testing) wired and/or wireless communication network in order to
implement testing of one or more components. The one or more
emulation devices may be test equipment. Direct RF coupling and/or
wireless communications via RF circuitry (e.g., which may include
one or more antennas) may be used by the emulation devices to
transmit and/or receive data.
[0071] FIG. 2 provides an example of an LTE uplink frame format for
one subframe. LTE Uplink uses a SC-FDMA scheme based DFT-s-OFDM
modulation. Similar to the downlink (DL) in LTE, each subframe or
transmission time interval (TTI) for the UL is partitioned into 14
symbols (including cyclic prefix (CP)) and the whole system
bandwidth is shared by scheduled users for UL transmissions. The
frequency domain resources (RBs) at the edges of the system
bandwidth are used for transmitting a control channel (PUCCH) and
its reference channel, PUCCH RS. The rest of the bandwidth is used
for transmitting the data channel (PUSCH) or reference channel
(PUSCH RS). For example, in FIG. 2, the 4.sup.th and 11.sup.th
symbols are dedicated to the PUSCH RS, which may be used for
channel estimation at a receiver, while the remaining symbols are
used for the PUSCH.
[0072] FIG. 3 shows an example structure for performing DFT-S-OFDM
wherein multiple DFT-spread blocks are equipped in the waveform
structure. In conventional CP DFT-S-OFDM (sometimes referred to
SC-FDMA with multiple accessing), the data symbols are first spread
with a DFT block, and then mapped to the input of an IDFT block.
The CP is prepended to the beginning of the symbol in order to
avoid inter-symbol interference (ISI) and allow one-tap frequency
domain equalization (FDE) at the receiver.
[0073] The DFT-S-OFDM is an example of a precoded OFDM scheme,
where the precoding with DFT aims to reduce the PAPR. t DFT-S-OFDM
is also an example of a scheme which upsamples the data symbols by
a factor equal to the ratio of the IDFT and DFT block sizes, and
applies a circular pulse shaping with a Dirichlet sinc function
before the CP extension. A benefit of DFT-S-OFDM is that it
exhibits lower PAPR than the plain CP-OFDM symbols.
[0074] In FIG. 3 DFT blocks 305 are used to spread incoming data d.
Generally, it is desirable to have on DFT block per user in order
minimize or reduce PARP. The spread data is then mapped to
subcarriers and sent to the IDFT block at 310. Next a cyclic prefix
(CP) is added to the output of the IDFT block 310, at 315.
[0075] After a set of resources (e.g. resource blocks) is allocated
to a WTRU, the WTRU may choose, or be signaled, to use some
resources elements within the allocated set of resources for
sending reference signals in a subframe. For example, each user may
use a few subcarriers within an OFDM/DFT-S-OFDM symbol for RSs and
the rest of the subcarriers may be used to transmit DFT spread data
symbols. The number of resource elements and times may be specific
to each user so that different users may use different numbers of
resource elements at different times to transmit their RSs.
[0076] In the embodiment shown in FIG. 4, two users are allocated
for uplink transmission, and each user is granted a portion of the
system bandwidth. The reference signals (shaded elements) are used
in different patterns on different symbols between these two users.
The channel condition from the first user (user 1) to the eNB may
be well enough so that a few reference symbols are needed to
achieve reliable channel estimation. While for user 2, the channel
may vary fast or be noisy so that more reference symbols are
desired to achieve more reliable channel estimation. To achieve
dynamic allocation of the reference signal for DFT-s-OFDM, a
special DFT-S-OFDM symbol may be used.
[0077] FIG. 5 shows an example transmitter 510 and receiver 560
structures that are capable of transmitting and receiving the
proposed special DFT-S-OFDM symbol. The transmitter 510 (for
example, a UE) may have K DFT blocks, each with size M.sub.1 518.
KM.sub.2 reference symbols (or pilots) need to be transmitted in
the frequency domain, i.e., at the input of IDFT operation 520. To
achieve this, the M.sub.2 input of DFT block 523 may be set to
zeroes to enable interference cancellation and the M.sub.1 input
518 may be a modulated data symbol, where M.sub.1+M.sub.2=M. The
locations of the zero symbols and the data symbols may be
randomized and maybe different than those shown in this figure. The
location of the zero samples may be chosen such that the receiver
observes at least M.sub.3+1 samples. At the output of each DFT
block, every other M.sub.3 samples may be discarded and replaced by
the reference symbols 530, where M.sub.3=M.sub.1/M.sub.2. This may
be done by puncturing the interleaved outputs. For example, one or
more outputs of the DFT block 523 may be punctured and each
punctured output may be replaced with an RS symbol. The punctured
outputs may be chosen such that they have an interleaved pattern,
(e.g. every n.sup.th output is selected (n=M3)).
[0078] After replacing those samples with RS symbols, the new
vector is fed to the input of IDFT block 520. For example, when M=8
and M.sub.2=2 reference symbols {r.sub.1,r.sub.2} are needed for 8
subcarriers. Then, the input of the DFT block may be {d.sub.1,
d.sub.2, . . . , d.sub.6, 0,0} (in this case M.sub.1=6). When
{x.sub.1, x.sub.2, . . . , x.sub.8} is the output of DFT, after
discarding every other M.sub.3=8/2=4 DFT outputs and replacing them
by {r.sub.1,r.sub.2}, one gets
{r.sub.1,x.sub.2,x.sub.3,x.sub.4,r.sub.2,x.sub.6,x.sub.7,x.sub.8},
which will be fed to IDFT block to generate time domain signals.
Note that the reference symbols may also be inserted with an
offset, e.g.,
{x.sub.1,r.sub.1,x.sub.3,x.sub.4,x.sub.5,r.sub.2,x.sub.7,x.sub.8}
when S=1. Finally, a CP 535 is appended to the output of the IDFT
block 520.
[0079] At the receiver side 560, up to the IDFT operations 564, the
signal processing is similar to the receiver for DFT-S-OFDM
signals. The subcarriers that carry the reference signals at the
output of DFT blocks may be used for channel estimation. In
addition, if the subcarriers that are discarded at the transmitter
side are not replaced by reference signals (i.e., replaced by
zeros), the corresponding subcarriers at the receiver DFT output
570 may be used for noise or interference power estimation.
[0080] Since some of the DFT block outputs are replaced by the
reference symbol or pilots at the transmitter side, the output of
the IDFT at the receiver side is interfered with due to "nulling"
operation 575. However, the interference may be recovered from the
M.sub.2 outputs 577 of the IDFT blocks and may be used to remove
the interference at the other output of the IDFT blocks. This
process may be done in the "IC" blocks 580. As an example, the
structure of the IC block 580 is given in FIG. 6 for a zero offset
(i.e., S=0). The IC block 580 may also be improved with an
iterative receiver architecture.
[0081] In another exemplary embodiment, the reference symbols
r.sub.ij shown in FIG. 5 may also be replaced by data symbols if
some of the data symbols need to be transmitted in frequency
domain. Therefore, the system architecture shown in FIG. 5 allows
transmitting DFT-S-OFDM and OFDM signals simultaneously.
[0082] In another embodiment, consider a single-user scenario
consisting of a transmitter and a receiver communicating over a
wireless channel. Data symbols to be transmitted within one
DFT-s-OFDM symbol may be the elements of vector d.di-elect
cons..sup.N.sup.d.sup..times.1, where N.sub.d is the number of data
symbols. In basic DFT-s-OFDM, first, data symbols are mapped to the
input of a DFT matrix denoted by D.di-elect cons..sup.M.times.M via
a mapping matrix M.sub.t .di-elect cons..sup.M.times.M, where M is
the DFT size and M=N.sub.d as a special case. The output of the DFT
is then mapped to a set of subcarriers in the frequency domain via
another mapping matrix M.sub.f.di-elect cons..sup.N.times.M.
Without loss of generality, the mapping matrix M.sub.f can be
constructed such that it allocates M localized or interleaved
subcarriers to achieve low PAPR. Finally, the output of the matrix
M.sub.f is converted to time domain via F.sup.H as:
x=F.sup.HM.sub.fDM.sub.td, Equation (1)
where F.sup.H.di-elect cons..sup.N.times.N is the inverse DFT
(IDFT) matrix and N is the number of subcarriers.
[0083] Let the channel impulse response (CIR) between the
transmitter and the receiver be a vector h=[h.sub.0 h.sub.1 . . .
], where +1 is the number of taps. Assuming that the size of the
cyclic prefix is larger than , the received signal vector y can be
expressed as:
y=Hx+n, Equation (2)
where H.di-elect cons..sup.N.times.N is the circular convolution
matrix that models the interaction between the transmitted signal x
and the channel h, and n.di-elect
cons..sup.N.times.N.about.(O.sub.N.times.1, .sigma..sup.2I.sub.N)
is the additive white Gaussian noise (AWGN) with variance
.sigma..sup.2.
[0084] At the receiver, the operations applied at the transmitter
are reversed by considering the impact of the multipath channel.
The receiver operation can be expressed as:
{tilde over (d)}=M.sub.t.sup.HD.sup.HQMP.sub.f.sup.HFy, Equation
(3)
here {tilde over (d)}.di-elect cons..sup.N.sup.d.sup..times.1 is
the estimated data symbol vector and Q.di-elect cons..sup.M.times.M
is the equalizer, which removes the impact of the multipath
channel. The equalizer Q is a diagonal matrix and may be derived by
using the minimum mean square error (MMSE) criterion.
[0085] As can be seen in Equation (1), data symbols are spread
across frequency by the matrix D in DFT-s-OFDM. Therefore, legacy
DFT-s-OFDM does not leave any room for frequency domain RSs in
M-dimensional subspace spanned by M columns of F.sup.H. To allow
the receiver to estimate the channel, the RSs may be transmitted
with another DFT-s-OFDM symbol by using a fixed sequence (e.g.,
Zadoff-Chu sequences, as in LTE). However, adopting two separate
DFT-s-OFDM symbols reduces the data rate substantially as the
number of estimated coefficients needed to extrapolate channel
frequency response may be significantly less than M.
[0086] In order to insert RSs at some frequency tones, one may
follow different strategies including the following. One option is
to puncture the information in the frequency domain by relying on
the redundancy introduced by channel coding. However, it may not
yield recoverable DFT-s-OFDM signals at the receiver as the number
of unknowns, i.e., N.sub.d(=M), is greater than the number of
observations, i.e., M-N.sub.p, within one symbol after the
puncturing, i.e., N.sub.d=M>M-N.sub.p, where N.sub.p>0 is the
number of punctured samples in frequency.
[0087] In another option, the number of data symbols may be reduced
as N.sub.d<M and the size of D may be changed from M to N.sub.d
to accommodate the reference symbols within M-dimensional subspace.
However, reference symbols are generally not needed for all of the
symbols in a frame or subframe. Thus, this option causes both
transmitter and receiver to need to employ a DFT block with
variable sizes, likely not suitable with radix-2 FFT
implementation.
[0088] In the third option, the number of data symbols
N.sub.d.ltoreq.M is reduced while keeping the size of DFT as M so
that the number of unknowns is less than or equal to the number of
observations after the puncturing, i.e., N.sub.d.ltoreq.M-N.sub.p.
This option does not increase the transmitter complexity. However,
the puncturing implicitly causes interference to the data symbols
and it is not straightforward to recover the data symbols with a
low-complexity receiver. In the following description, this
challenge is overcome and it is shown that the data symbols can be
recovered with a low-complexity receiver by employing the certain
puncturing pattern and inserting zeros to certain locations before
a DFT-spreading block at the transmitter.
[0089] FIG. 7 shows an example of a transmitter 710 and receiver
760 for generalized DFT-S-OFDM with frequency domain reference
symbols is described. In this scheme,
N.sub.z=M-N.sub.d.gtoreq.N.sub.p null symbols are introduced 715
before DFT spreading 720 so that the number of observations is
greater than or equal to the number of unknowns after puncturing
N.sub.p samples in frequency. The puncturing operation 730 may be
expressed with the matrix P.di-elect
cons..sup.(M-N.sup.p.sup.).times.M considering that P punctures one
symbol every other N.sub.I symbols at the output of the DFT 720
with an offset. Due to its periodic structure, the matrix P can be
expressed as:
P = I N p [ I S O S .times. N i - S O N i .times. 1 O N i - S
.times. S I N i - S ] , Equation ( 4 ) ##EQU00001##
where
N p = M N i + 1 ##EQU00002##
and N.sub.i+1 is integer multiple of M. Without loss of generality,
the punctured vector is mapped to another vector in M-dimensional
space by inserting N.sub.p zeros via a nulling matrix N.di-elect
cons..sup.M.times.M-N.sup.p to accommodate frequency domain
reference symbols denoted by c.sub.l where l=1, 2, . . . , N.sub.p
(940). The reference symbols can be distributed uniformly in
frequency by the IDFT block (950) to improve channel estimation
performance at the receiver 950). In this case, one may choose the
matrix N as:
N=I.sub.N.sub.p[I.sub.N.sub.iO.sub.N.sub.i.sub..times.1].sup.T.
Equation (5)
The overall transmit operation can finally be expressed as:
x = .alpha. F H M f NPDM t [ d 0 N z .times. 1 ] . Equation ( 6 )
##EQU00003##
where
.alpha. = N d N d - N p ##EQU00004##
is scalar which scales the energy of x to be N.sub.d after the
puncturing. A CP may be affixed prior to transmission of the
symbols (755).
[0090] As discussed above, the puncturing operation distorts the
output of DFT-spreading implicitly and causes significant
interference on data symbols. The interference on the data and null
symbols can be expressed as:
r=D.sup.HP.sup.HPDd.sub.e-d.sub.e, Equation (7)
where d.sub.e .di-elect cons..sup.M.times.1 is the mapped data
symbols and can be obtained as d.sub.e=M.sub.t [d.sup.H
O.sub.N.sub.z.sub..times.1.sup.H].sup.H and r.di-elect
cons..sup.M.times.1 is the interference vector. The interference
vector is not arbitrary as every other N.sub.I output of the
DFT-spread block is nulled. By using the lemma given below, one can
obtain the structure of the interference vector r.
[0091] Lemma 1 given below has two important results. First, by
using Lemma 1, one can deduce that the kth element of the vector r
is
r k = p k e 2 .pi. k S M ##EQU00005##
and p.sub.k=p.sub.k+N.sub.p. Secondly, it shows that the degrees of
freedom of the interference vector r is N.sub.p as
p.sub.k=p.sub.k+N.sub.p. Hence, one can regenerate the vector r by
observing only N.sub.p elements of r that correspond to the samples
within one period of p.sub.k and inferring the rest of the vector r
by using the relation of p.sub.k=p.sub.k+N.sub.p. In other words,
M.sub.t should be chosen such that the location of the null symbols
captures the samples at least for one period of p.sub.k. Hence,
Lemma 1 enlightens where to insert null symbols to allow the
receiver to recover the data symbol without any distortion. For
example, let M=8, S=0, and N.sub.p=2, and assume that one chooses
the input of the DFT block to be (d.sub.1, d.sub.2, d.sub.6, 0, 0)
(i.e., N.sub.z=2, M.sub.t=I.sub.8). Let (x.sub.1, x.sub.2, . . . ,
x.sub.8) be the output of DFT. After discarding every N.sub.I=4 DFT
outputs and replacing them by (c.sub.1,c.sub.2), one gets
{c.sub.1,x.sub.2,x.sub.3,x.sub.4,c.sub.2,x.sub.6,x.sub.7,x.sub.8},
which will be fed to IDFT block 750 to generate a time domain
signal. At the receiver side, there are only 6 samples related to
data symbols at the output of IDFT block. By neglecting the impact
of noise for the sake of clarity and by using Lemma 1, one can show
that the IDFT of the equalized vector d.sub.e is (d.sub.1+p.sub.1,
d.sub.2+p.sub.2, d.sub.3+p.sub.1, . . . , d.sub.5+p.sub.1,
d.sub.6+p.sub.2, p.sub.1, p.sub.2) where the last two samples
reveal the interference vector r as p.sub.k=p.sub.k+2. On the other
hand, the selection of the data vector as (0, d.sub.1, 0, d.sub.2,
. . . d.sub.6) does not allow the receiver to regenerate r as first
and third samples carry the same interference sample after the
puncturing.
[0092] At the receiver side 760, up to the frequency domain
de-mapping operation, i.e., M.sub.f.sup.H, 763 the signal
processing is the same for both the legacy DFT-s-OFDM and the
proposed scheme described herein. As opposed to the legacy
DFT-s-OFDM, the subcarriers that carry the reference signals at the
output of DFT can be used for channel estimation (CHEST) 765 with
the proposed scheme. By using the estimated channel, the data
bearing subcarriers are first equalized 770 via Q.di-elect
cons..sup.M-N.sup.p.sup..times.M-N.sup.p and the symbols at the
output of equalizer are then mapped to the input of IDFT via
P.sup.H 775. The output of IDFT D.sup.H 780 can be expressed
as:
d ~ e = 1 .alpha. D H P H QN H M f H Fy , Equation ( 8 )
##EQU00006##
where {tilde over (d)}.sub.e .di-elect cons..sup.M.times.1 is the
received vector which includes the impacts of noise, equalization,
and puncturing. Considering the structure of the interference due
to the puncturing, a simple way to recover the data symbols is:
{tilde over (d)}=M.sub.t.d.sup.H{tilde over
(d)}.sub.e-RM.sub.t.r.sup.H{tilde over (d)}.sub.e Equation (9)
where M.sub.t.d.di-elect cons..sup.M.times.N.sup.d and
M.sub.t.r.di-elect cons..sup.M.times.N.sup.z are the submatrices of
M.sub.t as M.sub.t=[M.sub.t.d M.sub.t,r], and R.di-elect
cons..sup.N.sup.d.sup..times.N.sup.z is the reconstruction matrix
that calculates the distortion due to the puncturing based on the
relation of
r k = p k e 2 .pi. k S M ##EQU00007##
and p.sub.k=p.sub.k+N.sub.p dictated by Lemma 1. As a special case,
when S=0 and M.sub.t=I.sub.M, R becomes a repetition matrix given
by
R=1.sub.N.sub.I.sub..times.1I.sub.N.sub.z, Equation (10)
which simplifies the receiver structure substantially. For example,
if d.sub.e is (d.sub.1+p.sub.1, d.sub.2+p.sub.2, d.sub.3+p.sub.1, .
. . , d.sub.5+p.sub.1,d.sub.6+p.sub.2,p.sub.1,p.sub.2), R
replicates the last two samples by N.sub.I=3 times and one can
recover the data symbols by subtracting the replicated vector from
the rest of the samples of {tilde over (d)}.sub.e as expressed in
Equation (9).
[0093] Although the method discussed in above enables a
low-complexity receiver, it enhances the noise by 3 dB as two noisy
observations are added by Equation (9). One effective way of
mitigating the noise enhancement is to use an iterative receiver
which aims to remove the noise on the second part of Equation (9),
i.e., distortion due to the puncturing. To this end, for the ith
iteration, the data symbols are estimated by:
{tilde over (d)}.sup.(i)=M.sub.t.d.sup.H{tilde over
(d)}.sub.e-RM.sub.t.r.sup.H{tilde over (d)}.sub.e.sup.(i-1),
Equation (11)
where {tilde over (d)}.sub.e.sup.(0)={tilde over (d)}.sub.e. The
estimated data symbols {tilde over (d)}.sup.(i) are then mapped to
closest symbol in the constellation by a non-linear function f ( ),
i.e., demodulation, and {tilde over (d)}.sub.e.sup.(i+1) is
prepared for the next iteration as:
d ~ e ( i + 1 ) = D H P H PDM t [ f ( d ~ ( i ) ) 0 N I .times. 1 ]
. Equation ( 12 ) ##EQU00008##
Since {tilde over (d)}.sub.e.sup.(i+1) is generated after the
decision is made by f ({tilde over (d)}.sup.(i)), it removes the
noise from the second part of Equation (11) effectively and leads
to a better estimate of {tilde over (d)} for the (i+1)th
iteration.
[0094] It is important to emphasize that the proposed schemes
described herein introduce some conditions on the puncturing
pattern, the number of reference signals N.sub.p, the number of
null symbols N.sub.z, and the pattern of the null symbols. First,
the receiver structures discussed above exploit the fact that every
N.sub.i other output of the DFT with an offset S are punctured.
Second, N.sub.z.gtoreq.N.sub.p must hold and the pattern of N.sub.z
null symbols at input of DFT-spread block should capture at least
one period of distortion due to the puncturing to yield a
recoverable a DFT-s-OFDM symbol. One simple way of doing is to
consider N.sub.z adjacent null symbols.
[0095] There is also room to increase the performance of the
receiver. For example, one simple way of improve the receiver
performance is to increase the number of null symbols more than the
number of punctured symbols, i.e., N.sub.z>N.sub.p. In this
case, the receiver can combine the samples to calculate a more
reliable interference vector at the expense of less spectral
efficiency. The receiver structures described above may also be
improved by including the channel coding decoder along with
demodulation on the feedback branch.
[0096] Without loss of generality, the schemes described herein can
be expended to multiple DFT blocks. In addition, if the subcarriers
that are discarded at the transmitter side are not replaced by RSs
(i.e., replaced by zeros), the corresponding subcarriers at the
receiver DFT output can also be used for noise or interference
power estimation.
[0097] As mentioned above, lemma 1 will now be described. Lemma 1
(Periodic Interference): Let (X.sub.n) be a sequence of size
M.di-elect cons. for n=0, 1, . . . , M-1 and let (Y.sub.n) be
another sequence obtained by zeroing every other N.sub.i,
N.sub.i.di-elect cons. elements of (X.sub.n) with an offset of S,
S.ltoreq.N.sub.i, S.di-elect cons..sub.0. Then, it is possible to
decompose the IDFT of Y.sub.n as:
y.sub.k=x.sub.k+r.sub.k, for n=0, . . . ,M-1, Equation (13)
where (y.sub.k) is the IDFT of (Y.sub.n), (x.sub.k) is the IDFT of
(X.sub.n), and (r.sub.k) is a sequence of size M given by
r k = p k e 2 .pi. k S M , ##EQU00009##
for k=0, . . . , M-1 where (p.sub.k) is period sequence with the
period of
M N i + 1 . ##EQU00010##
[0098] The elements of the sequence (Y.sub.n) can be expressed by
using an auxiliary sequence (R.sub.n) as:
Y n = X n + R n , where : Equation ( 14 ) R n = .DELTA. { - X n n -
S N i + 1 .di-elect cons. 0 otherwise . Equation ( 15 )
##EQU00011##
Since IDFT operation is linear, the IDFT of (Y.sub.n) can be
expressed as (y.sub.k)=(x.sub.k)+(r.sub.k), where (r.sub.k) is the
IDFT of (R.sub.n). The elements of (r.sub.k) can be calculated
as:
r k = n = 0 M - 1 R n e 2 .pi. k n M = ( a ) m = 0 M N i + 1 - 1 -
X ( N i + 1 ) m + S e 2 .pi. k ( N i + 1 ) m + S M = ( b ) s mod (
M N i + 1 ) p k e 2 .pi. k S M Equation ( 16 ) ##EQU00012##
where (s.sub.m) is the IDFT of (-X.sub.(N.sub.I.sub.+1)m+S) for
m = 0 , , M N i + 1 - 1. ##EQU00013##
In Equation 16, (a) is true because r.sub.n is zero when
n - S N i + 1 ##EQU00014##
is not an integer and (b) is true due to the periodicity of the
exponential function
e - 2 .pi. k ( N i + 1 ) m M , ##EQU00015##
which results in
p k = p k + M N i + 1 . ##EQU00016##
[0099] In certain scenarios, when a single carrier waveform such as
DFT-s-OFDM is used, all of the subcarriers within the allocated
bandwidth may be used to transmit reference signal (pilot) symbols.
In such a transmission mode, it may be possible to dynamically
change the number of the waveform symbols (for example DFT-s-OFDM
symbols) that carry reference signals. As an example, in LTE uplink
data transmission, one subframe consists of 14 DFT-s-OFDM symbols
and two of these symbols are used to transmit pilots. If a WTRU
needs better channel estimation, for example, due to mobility, it
may be possible to increase the number of symbols for RS
transmission from two to three or more.
[0100] Changing the number of pilot symbols would change the amount
of resources allocated for data transmission. As a result, the
transport block size and/or coding rate may need to be modified. In
one solution, the number and location of pilot symbols may be
configured by a central controller such as the eNB, and/or signaled
dynamically in the control channel for each transmission. For each
of the possible number of pilot symbols, corresponding values for
the transport block size may be defined.
[0101] FIG. 8 shows an example subframe in which, some of the
symbols transmitted within a specific time interval are generated
by using different waveform numerology than the remaining symbols.
In FIG. 8, the time interval used for the first PUSCH symbol 810 is
used to transmit two DFT-s-OFDM symbols, where each DFT-s-OFDM
symbol has half the symbol duration of the remaining symbols. One
of the two new DFT-s-OFDM symbols is used for reference signal
transmission while the other symbol is used for data
transmission.
[0102] When the waveform is not a single carrier waveform, for
example, when it is OFDM, it may be possible to dynamically or
semi-statically configure certain subcarriers of certain OFDM
symbols as data or pilot subcarriers. The subcarriers that were
used for data transmission may be configured to carry reference
symbols, or subcarriers that were used for pilot transmission may
be configured to carry data. It may be possible to transmit a
number of OFDM symbols within a specific time interval where some
of the OFDM symbols may be generated by using different waveforms
and numerologies than the remaining OFDM symbols.
[0103] In FIG. 9, an example is provided where some of the
subcarriers in the last OFDM symbol of the subframe are configured
to transmit reference symbols, in addition to the subcarriers that
were originally configured to transmit reference symbols. In
addition, the first two OFDM symbols have half the duration of the
remaining OFDM symbols and some subcarriers of the first OFDM
symbol are also configured for reference symbol transmission. It
should be noted that due to the different waveform numerologies,
the first two OFDM symbols may have larger subcarrier spacing than
the remaining OFDM symbols. Also, although a cyclic prefix (CP) is
not shown in the figure, a CP may precede each OFDM symbol. These
techniques may apply to other multicarrier waveforms such as
Windowed-OFDM, Filtered OFDM, Filterbank Multicarrier, and the
like.
[0104] Although features and elements are described above in
particular combinations, one of ordinary skill in the art will
appreciate that each feature or element can be used alone or in any
combination with the other features and elements. In addition, the
methods described herein may be implemented in a computer program,
software, or firmware incorporated in a computer-readable medium
for execution by a computer or processor. Examples of
computer-readable media include electronic signals (transmitted
over wired or wireless connections) and computer-readable storage
media. Examples of computer-readable storage media include, but are
not limited to, a read only memory (ROM), a random access memory
(RAM), a register, cache memory, semiconductor memory devices,
magnetic media such as internal hard disks and removable disks,
magneto-optical media, and optical media such as CD-ROM disks, and
digital versatile disks (DVDs). A processor in association with
software may be used to implement a radio frequency transceiver for
use in a WTRU, UE, terminal, base station, RNC, or any host
computer.
* * * * *