U.S. patent application number 15/722688 was filed with the patent office on 2018-03-29 for physical layer (phy) design for a low latency millimeter wave (mmw) backhaul system.
This patent application is currently assigned to InterDigital Patent Holdings, Inc.. The applicant listed for this patent is InterDigital Patent Holdings, Inc.. Invention is credited to Tao DENG, Philip J. PIETRASKI, Ravikumar V. PRAGADA, Onur SAHIN.
Application Number | 20180092116 15/722688 |
Document ID | / |
Family ID | 50190754 |
Filed Date | 2018-03-29 |
United States Patent
Application |
20180092116 |
Kind Code |
A1 |
PIETRASKI; Philip J. ; et
al. |
March 29, 2018 |
PHYSICAL LAYER (PHY) DESIGN FOR A LOW LATENCY MILLIMETER WAVE (MMW)
BACKHAUL SYSTEM
Abstract
A method and apparatus are disclosed for establishing a low
latency millimeter wave (mmW) backhaul connection. A base station
may receive a mmW relay schedule from an evolved Node B (eNB)
within one Long Term Evolution (LTE) scheduling interval. The base
station may decode the mmW relay schedule, and initialize a mmW
radio transmission resource according to the mmW relay schedule.
The base station may receive a data packet from a second base
station in a mmW transmission time interval (TTI) based on the mmW
relay schedule using the initialized mmW radio transmission
resource, and may transmit the data packet to a third base station
based on the mmW relay schedule using the initialized mmW radio
transmission resource. The transmitting may begin before the
reception of the data packet is complete.
Inventors: |
PIETRASKI; Philip J.;
(Jericho, NY) ; DENG; Tao; (Roslyn, NY) ;
SAHIN; Onur; (Brooklyn, NY) ; PRAGADA; Ravikumar
V.; (Collegeville, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
InterDigital Patent Holdings, Inc. |
Wilmington |
DE |
US |
|
|
Assignee: |
InterDigital Patent Holdings,
Inc.
Wilmington
DE
|
Family ID: |
50190754 |
Appl. No.: |
15/722688 |
Filed: |
October 2, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14766696 |
Aug 7, 2015 |
9781738 |
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PCT/US2014/015141 |
Feb 6, 2014 |
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15722688 |
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61762181 |
Feb 7, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 72/1289 20130101;
H04L 5/0091 20130101; H04L 5/0044 20130101; H04W 72/1263 20130101;
H04B 7/15528 20130101; H04B 7/155 20130101; H04L 5/0053 20130101;
H04W 72/0426 20130101; H04W 72/046 20130101; H04W 88/08
20130101 |
International
Class: |
H04W 72/12 20090101
H04W072/12; H04W 72/04 20090101 H04W072/04; H04L 5/00 20060101
H04L005/00; H04B 7/155 20060101 H04B007/155 |
Claims
1. A method for use in a base station for establishing a low
latency millimeter wave (mmW) backhaul connection, the method
comprising: receiving a mmW relay schedule from an evolved Node B
(eNB) within one Long Term Evolution (LTE) scheduling interval;
decoding the mmW relay schedule; steering a receive beam and a
transmit beam according to the mmW relay schedule; receiving a data
packet from a second base station in a mmW transmission time
interval (TTI) based on the mmW relay schedule using the receive
beam; and transmitting the data packet to a third base station
based on the mmW relay schedule using the transmit beam, wherein
the transmitting begins before reception of the data packet is
complete.
2. The method of claim 1, wherein a length of the mmW TTI is based
on a length and structure of the LTE scheduling interval.
3. The method of claim 1, wherein receiving the mmW relay schedule
further comprises decoding downlink control information (DCI) in a
Physical Downlink Control Channel (PDCCH) region of an LTE
sub-frame.
4. The method of claim 3, wherein the mmW relay schedule is
received in a mmW control channel, and wherein the DCI indicates at
least one of a frequency allocation of the mmW control channel, a
transport format of the mmW control channel, and at least one of a
plurality of OFDM symbols in a Physical Downlink Shared Channel
(PDSCH) region of the LTE sub-frame.
5. The method of claim 4, wherein the at least one of the plurality
of OFDM symbols includes relay scheduling information for one mmW
TTI and a frequency allocation for a mmW data channel, wherein the
relay scheduling information includes at least one of a reception
time, a receive antenna pattern, a frequency channel for reception,
a transmission time, a transmit antenna pattern, a frequency
channel for transmission, and a transmit power.
6. The method of claim 1, further comprising: receiving, from the
eNB, an eNB neighbor list that indicates a plurality of neighbor
base stations of the eNB; and receiving, from the eNB, a plurality
of base station neighbor lists that indicate a plurality of
neighbor base stations of each of a plurality of base stations.
7. The method of claim 6, wherein the mmW relay schedule indicates
a plurality of links, and wherein each link is identified by a
transmitting base station and a receiving base station, wherein
each of the transmitting base station and receiving base station is
indicated by an index associated with one of the plurality of
neighbor base stations on the eNB neighbor list or on one of the
plurality of base station neighbor lists.
8. The method of claim 1, wherein the mmW relay schedule indicates
a delay between receiving the mmW relay schedule and receiving the
data packet.
9. The method of claim 1, further comprising: receiving a sounding
schedule; performing a sounding procedure based on the sounding
schedule; and transmitting a sounding report to an eNB via the LTE
link.
10. The method of claim 9, further comprising: receiving an updated
mmW relay schedule based on the sounding report.
11. A base station for establishing a low latency millimeter wave
(mmW) backhaul connection, the base station comprising: a receiver
configured to receive a mmW relay schedule from an evolved Node B
(eNB) within one Long Term Evolution (LTE) scheduling interval; a
processor configured to decode the mmW relay schedule; the
processor configured to steer a receive beam and a transmit beam
according to the mmW relay schedule; the receiver configured to
receive a data packet from a second base station in a mmW
transmission time interval (TTI) based on the mmW relay schedule
using the receive beam; and a transmitter configured to transmit
the data packet to a third base station based on the mmW relay
schedule using the transmit beam, wherein the transmitting begins
before reception of the data packet is complete.
12. The base station of claim 11, wherein a length of the mmW TTI
is based on a length and structure of the LTE scheduling
interval.
13. The base station of claim 11, wherein receiving the mmW relay
schedule further comprises decoding downlink control information
(DCI) in a Physical Downlink Control Channel (PDCCH) region of an
LTE sub-frame.
14. The base station of claim 13, wherein the mmW relay schedule is
received in a mmW control channel, and wherein the DCI indicates at
least one of a frequency allocation of the mmW control channel, a
transport format of the mmW control channel, and at least one of a
plurality of OFDM symbols in a Physical Downlink Shared Channel
(PDSCH) region of the LTE sub-frame.
15. The base station of claim 14, wherein the at least one of the
plurality of OFDM symbols includes relay scheduling information for
one mmW TTI and a frequency allocation for a mmW data channel,
wherein the relay scheduling information includes at least one of a
reception time, a receive antenna pattern, a frequency channel for
reception, a transmission time, a transmit antenna pattern, a
frequency channel for transmission, and a transmit power.
16. The base station of claim 11, wherein: the receiver is further
configured to receive, from the eNB, an eNB neighbor list that
indicates a plurality of neighbor base stations of the eNB; and the
receiver is further configured to receive, from the eNB, a
plurality of base station neighbor lists that indicate a plurality
of neighbor base stations of each of a plurality of base
stations.
17. The base station of claim 16, wherein the mmW relay schedule
indicates a plurality of links, wherein each link is identified by
a transmitting base station and a receiving base station, and
wherein each of the transmitting base station and receiving base
station is indicated by an index associated with one of the
plurality of neighbor base stations on the eNB neighbor list or on
one of the plurality of base station neighbor lists.
18. The base station of claim 11, wherein the mmW relay schedule
indicates a delay between receiving the mmW relay schedule and
receiving the data packet.
19. The base station of claim 11, wherein: the receiver is further
configured to receive a sounding schedule; the processor is further
configured to perform a sounding procedure based on the sounding
schedule; and the transmitter is further configured to transmit a
sounding report to an eNB via the LTE link.
20. The base station of claim 19, wherein: the receiver is further
configured to receive an updated mmW relay schedule based on the
sounding report.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/766,696 filed Feb. 6, 2014, which claims
the benefit of U.S. provisional application No. 61/762,181 filed
Feb. 7, 2013, the contents of which is hereby incorporated by
reference herein.
BACKGROUND
[0002] The third generation partnership program (3GPP) introduced
long term evolution (LTE) to increase cellular network bandwidth
for anticipated mobile data demand. However, it is projected that
the mobile data demand growth will soon outpace the capacity
introduced by even the next generation of LTE, the LTE-Advanced
(LTE-A).
SUMMARY
[0003] A method and apparatus are disclosed for establishing a low
latency millimeter wave (mmW) backhaul connection. A base station
may receive a mmW relay schedule from an evolved Node B (eNB)
within one Long Term Evolution (LTE) scheduling interval. The base
station may decode the mmW relay schedule, and initialize a mmW
radio transmission resource according to the mmW relay schedule.
The base station may receive a data packet from a second base
station in a mmW transmission time interval (TTI) based on the mmW
relay schedule using the initialized mmW radio transmission
resource, and may transmit the data packet to a third base station
based on the mmW relay schedule using the initialized mmW radio
transmission resource. The transmitting may begin before the
reception of the data packet is complete.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] A more detailed understanding may be had from the following
description, given by way of example in conjunction with the
accompanying drawings wherein:
[0005] FIG. 1A is a system diagram of an example communications
system in which one or more disclosed embodiments may be
implemented;
[0006] 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;
[0007] FIG. 1C is a system diagram of a small cell backhaul in an
end-to-end mobile network infrastructure;
[0008] FIG. 1D is a system diagram of a mmW backhaul applied to
both a 3GPP cellular network and a non-3GPP network access
infrastructure;
[0009] FIG. 2 illustrates a low latency mmW system overview;
[0010] FIG. 3 shows an exemplary low latency mmW backhaul
system;
[0011] FIG. 4 is an example mmW access link frame structure;
[0012] FIG. 5 shows an example of the scheduling of the mmW data
channel;
[0013] FIG. 6 shows an example of the scheduling of the mmW
Physical Downlink Control Channel (mmPDCCH);
[0014] FIG. 7 shows a synchronized amplify-and-relay operation;
[0015] FIG. 8 shows a mmW base station initialization
procedure;
[0016] FIG. 9 illustrates end-to-end channel sounding over a
scheduled route; and
[0017] FIG. 10 illustrates sounding of individual backhaul
links.
DETAILED DESCRIPTION
[0018] FIG. 1A is a diagram of 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 system 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), and the like.
[0019] As shown in FIG. 1A, the communications system 100 may
include wireless transmit/receive units (WTRUs) 102a, 102b, 102c,
102d, a radio access network (RAN) 104, a core network 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 may be configured to
transmit and/or receive wireless signals and may include user
equipment (UE), a mobile station, a fixed or mobile subscriber
unit, a pager, a cellular telephone, a personal digital assistant
(PDA), a smartphone, a laptop, a netbook, a personal computer, a
wireless sensor, consumer electronics, and the like.
[0020] The communications system 100 may also include a base
station 114a and 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 core network 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 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.
[0021] 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 within a particular geographic region, which may
be referred to as a cell (not shown). 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 another
embodiment, the base station 114a may employ multiple-input
multiple-output (MIMO) technology and, therefore, may utilize
multiple transceivers for each sector of the cell.
[0022] 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, infrared (IR), ultraviolet (UV), visible
light, etc.). The air interface 116 may be established using any
suitable radio access technology (RAT).
[0023] 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 Packet Access (HSDPA)
and/or High-Speed Uplink Packet Access (HSUPA).
[0024] In another 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).
[0025] In other embodiments, the base station 114a and the WTRUs
102a, 102b, 102c may implement radio technologies such as 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.
[0026] 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, 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
another 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, 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 core network 106.
[0027] The RAN 104 may be in communication with the core network
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. For
example, the core network 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 core network 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 an E-UTRA radio technology,
the core network 106 may also be in communication with another RAN
(not shown) employing a GSM radio technology.
[0028] The core network 106 may also serve as a gateway for the
WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet
110, and/or 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 the internet
protocol (IP) in the TCP/IP internet protocol suite. The networks
112 may include wired or wireless communications networks owned
and/or operated by other service providers. For example, the
networks 112 may include another core network connected to one or
more RANs, which may employ the same RAT as the RAN 104 or a
different RAT.
[0029] Some or all of the WTRUs 102a, 102b, 102c, 102d in the
communications system 100 may include multi-mode capabilities,
i.e., 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.
[0030] FIG. 1B is a system diagram of 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 other peripherals 138. It will be
appreciated that the WTRU 102 may include any sub-combination of
the foregoing elements while remaining consistent with an
embodiment.
[0031] 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 Array (FPGAs) circuits, any other type of
integrated circuit (IC), 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.
[0032] 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 another
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
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.
[0033] In addition, 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.
[0034] 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 UTRA and IEEE 802.11, for example.
[0035] 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).
[0036] 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.
[0037] 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.
[0038] 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 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, and
the like.
[0039] FIG. 1C is a system diagram of a small cell backhaul in an
end-to-end mobile network infrastructure according to an
embodiment. A set of small cell (SC) nodes 152a, 152b, 152c, 152d,
and 152e and aggregation points 154a and 154b interconnected via
directional millimeter wave (mmW) wireless links may comprise a
"directional-mesh" network and provide backhaul connectivity. For
example, the WTRU 102 may connect via the radio interface 150 to
the small cell backhaul 153 via small cell 152a and aggregation
point 154a. In this example, the aggregation point 154a provides
the WTRU 102 access via the RAN backhaul 155 to a RAN connectivity
site 156a. The WTRU 102 therefore then has access to the core
network nodes 158 via the core transport 157 and to internet
service provider (ISP) 160 via the service LAN 159. The WTRU also
has access to external networks 161 including but not limited to
local content 162, the Internet 163, and application server 164. It
should be noted that for purposes of example, the number of SC
nodes 152 is five; however, any number of nodes 152 may be included
in the set of SC nodes.
[0040] FIG. 1D is a system diagram of a mmW backhaul applied to
both a 3GPP cellular network and a non-3GPP network access
infrastructure according to an embodiment. In this example, the
non-3GPP network is IEEE 802.11 based. The WTRUs 102a, 102b, 102c,
102d, and 102e may have access via millimeter wave base stations
(mBs) 172a, 172b, and 172c in an 802.11 network 170 to a millimeter
wave base station aggregator (mBA) 172d. The mBA 172d may provide
access to external networks such as the Internet 192, and to the
cellular network via a trusted WLAN gateway (TWAG) 191.
[0041] Also, in this example, WTRU 102f in the 3GPP network 180 may
have access via mBs 182a and 182c to a mobility management entity
(MME) 183 and a serving gateway (SGW) 184, which may provide access
to public data network gateway (PGW) 190 and the Internet 192.
[0042] WTRUs 102f and 102g may also have access via mBs 182a and
182b via mBA 182d to SGW 184, which may provide access to public
data network gateway (PGW) 190 and the Internet 192.
[0043] WTRUs 102f and 102g may also have access via an evolved Node
B (eNB) 185 to the MME 183 and SGW 184, which may provide access to
the public data network gateway (PGW) 190 and the Internet 192.
[0044] As shown in the examples of FIG. 1C and FIG. 1D, wireless
mesh networks (WMNs) operating at mmW frequencies may be used, for
example, to serve as backhaul networks for cellular or WLAN SCs
such as those based on, for example, LTE or IEEE 802.11. An mmW
directional mesh network may be an economical solution to provide
backhaul connectivity to several cheaply deployed SCs. Directional
links using highly directional antennas may be used to close the
link budget at mmW frequencies. A directional mesh network may also
provide a flexible topology by requiring Line-Of-Sight (LOS) with
only immediate neighbors. A directional mesh network may provide
easy scalability in that new nodes may be added with minimal
network planning. A directional mesh network may provide robustness
in redundancy provided by multiple connectivity paths between
mesh-nodes. A directional-mesh network may be configured with fully
distributed scheduled, multi-hop, and time division multiple access
(TDMA) based directional mesh MAC features to ensure fast
scheduling and short queue times.
[0045] The millimeter wave (mmW) hot-spot underlay and backhaul
system deploys a mmW mesh network with an overlay traditional
cellular system. The resulting hybrid wireless system consists of a
cellular layer and an mmW layer. Referring to FIG. 2, the mmW mesh
network 200 may consist of mmW base stations (mBs) 202, 204, 206
that may bidirectionally relay transmissions on the mmW layer
between a source eNB 208 and a target UE 210 via a scheduled route
over a number of peer mBs.
[0046] The scheduling of the mmW backhaul links 212 and the mmW UE
access link 214 may be centralized at the eNB 208, and may be
communicated via cellular signaling 216. Alternatively, a mmW
gateway (mGW) 218 may be responsible for routing and higher layer
access stratum (AS) processing of user data that is carried on the
mmW layer, and may communicate with the mBs 202, 204, 206 via the
mmW layer 220, as indicated in FIG. 2.
[0047] The edge mB 206, i.e., the mB directly communicating with
the target UE 210, may serve as a hot spot base station covering a
local group of UEs to increase the system capacity and alleviate
the cellular system load. The hot spot base station may have
several different modes of operation.
[0048] The envisioned relaying may apply amplify and forward (AF)
technology (including full duplex and small/zero duplex distances),
and the resulting latency through the mesh network may be
considered small enough to be negligible in view of the overall
latency budget in the end-to-end transmission, which may be
analogous to fiber transmission latencies. In addition, the
backhaul links may remain relatively static over the course of the
mmW data transmission. Thus the AF-based low latency mmW system may
be also referred as a fiber parity system.
[0049] Alternatively, the edge mB 206 may employ decode and forward
(DF) technology and retransmit the packet at a lower modulation
and/or code rate to the target UE 210. This is seen as useful since
the mmW access link quality may be lower than the quality of the
backhaul (BH) links since the UE is more likely to have physically
worse channel conditions, and because UE antennas are likely to
have lower capabilities than BH antennas. With small enough slot
sizes, the one additional DF process may add only a small
additional end-to-end delay, and only in the access link. The eNB
may still have complete scheduling control of the mmW resources in
the access link. In this case the system may become a backhaul-only
mmW system, consisting of the mB nodes with mmW backhaul links.
[0050] The mBs and UEs of a mmW hot spot system may be covered by
and associated with a cellular network and may potentially operate
on both cellular and mmW layers. The coordination, scheduling, and
routing of the system may be performed by a centralized entity,
e.g., an entity residing in the eNB and signaled to all other nodes
on the cellular layer. Thus the higher layer and physical layer
control signaling may be exclusively communicated via the cellular
layer signaling between all nodes and the mmW layer signaling may
carry traffic data only. Accordingly, the mmW layer scheduling may
be performed and conveyed by the cellular layer, i.e., cross layer
scheduling. In the case of the backhaul-only low latency mmW
system, some control and coordination information may be exchanged
over the X2 interface between small cells.
[0051] Referring to FIG. 3, the low latency mmW system may provide
backhaul transmissions 302 to an edge mB 304 that may be, for
example, a remote radio unit (RRU). The AF mmW data may thus carry
multi-user data traffic for some or all of the UEs 306-314 that are
associated with the edge mB/RRU 304. This may be equivalent to the
current RRU solution, but with the fiber between the edge mB/RRU
304 and the eNB 316 being replaced by the low latency mmW system.
The data multiplexing over the fiber may be realized over the AF
link, because the mmW bandwidth may be much larger than the
cellular access link bandwidth, e.g., in an LTE system. In this
option, the access links 318 between the edge mB/RRU 304 and the
UEs 306-314 may be either mmW or cellular, and the UEs 306-314
associated with the edge mB/RRU 304 may not have cellular links to
the eNB 316.
[0052] A brief summary of the low latency mmW system nodes is now
provided.
An eNB is a traditional cellular node performing the centralized
control, scheduling, and routing of the mmW hot-spot underlay
system. An eNB may communicate with neighbor mBs via mmW links. An
mB is a mmW base station that may communicate with its neighbor mBs
via mmW links and may register at the eNB via a cellular link as an
advanced user device with enhanced capabilities associated with the
underlay system, for example certain reduced eNB functionalities. A
mB may apply AF via mmW backhaul links to relay a transmission to
another mB according to a route scheduled by the eNB. A mB may
communicate with multiple UEs and mUEs and may serve as a hot spot
base station via mmW access links. A mUE is a traditional cellular
node with mmW capability that may communicate with its associated
eNB via a cellular access link and with a mB via a mmW access
link.
[0053] The overlay system may be a cellular system such as a R10
LTE network or another network based on WiFi or WiMAX systems. The
overlay system may also operate in a different spectrum space such
as TV white space (TVWS). The mmW BH link and mmW access link may
be based on the IEEE 802.11ad network, the new 60 GHz band system
discussed in the subsequent paragraphs, or on another system in a
different frequency band.
[0054] An example of a single-carrier mmW access link frame
structure is shown in FIG. 4. One transmission time interval (TTI)
in this example is one time slot of 100-.mu.s length. In order to
facilitate the cross layer scheduling, the frame structure 400 has
a 1-ms sub-frame 402 that aligns with the LTE sub-frame structure.
The number of TTIs per mmW access link sub-frame may be tied to the
number of scheduling instances in the cellular link, and
accordingly the length of the frame structure may depend on the
cross layer scheduling scheme.
[0055] In this example, each mmW access link time slot may be
scheduled via a mmW Physical Downlink Control Channel (mmPDCCH)
mapped at one symbol location in the LTE sub-frame. Thus, the ten
time slots shown in FIG. 4, Time Slot #0-9, may require ten
mmPDCCHs transmitted in ten consecutive symbol locations. The
mmPDCCH may be multiplexed with the regular Physical Downlink
Shared Channel (PDSCH) and with different types of LTE reference
signals in the frequency domain at the same symbol location. More
details of the scheduling scheme are provided herein.
[0056] The mmW access link TTI may be also 1 ms, which is the
length of the sub-frame. In this case the scheduling instance
required in one LTE sub-frame is reduced to one symbol location.
The advantage of a longer TTI is that the mmW scheduling may
require fewer LTE resources. Given the large bandwidth that a mmW
access link may apply, however, the transport block size may become
too large to handle.
[0057] The frame structure may apply a sampling frequency of about
1760 MHz, which is about the same as the 802.11ad system, and the
resulting base time unit is about 0.57 ns. However, to provide more
flexibility in the cross layer scheduling scheme and to enable a
common block sharing between the LTE link and the mmW link in one
device, the sampling frequency may be a common multiple of the LTE
sampling frequency of 30.72 MHz and the cross layer scheduling
instances. For example, when the LTE DL has ten mmPDCCHs in one
sub-frame, the mmW access link may use a sampling frequency of
30.72.times.572=1757.184 MHz. It should be noted that the 802.11ad
sampling frequency is 1760 MHz. The sampling frequency of 1757.184
MHz can certainly align with 10 mmPDCCH instances in one LTE
sub-frame.
[0058] Furthermore, in order to accommodate a set of possible
scheduling instances in one LTE sub-frame, the number of TTIs per
mmW access link sub-frame may be based on the least common multiple
of the set and the LTE sampling frequency (15000.times.2048) and a
sampling factor so that the single carrier bandwidth occupies a
good part of the available 2 GHz. For example, considering a set of
scheduling instances of {8, 9, 10, 11, 12}, the least common
multiple of the set is 3960. The least common multiple of 3960 and
the LTE sampling frequency of 30720000 is 126720000. Thus a
sampling frequency of 1774.08 MHz (K at 14) may be used.
[0059] As described above, each OFDM symbol time of the LTE PDSCH
may correspond to one mmW end-to-end scheduling event. For
illustration, the first 10 PDSCH OFDM symbols may be used for
scheduling the mmW layer. Other variations are possible and may
adapt to varying numbers of PDSCH symbols. The timing offset from
the end of the first BH/mmPDCCH message (i.e., the end of first
PDSCH OFDM symbol) to the start of the corresponding mmW slots
(To,1) at the PoP node may be signaled to all other nodes via RRC
signaling in the cellular layer.
[0060] The timing offset from the end of the kth BH/mmPDCCH message
to the start of the corresponding mmW slots (To,k) at the PoP node
may be larger for increasing k. This is because the first ten OFDM
symbols of the PDSCH may be used for the ten BH/mmPDCCH messages
corresponding to 1 ms worth of mmW TTIs, i.e., the LTE PDCCH (and
possibly some trailing OFDM symbols for the LTE PDSCH if the mmW
slots do not adapt to the PDSCH symbols) may not be used for
scheduling the mmW layer. The timing offset may be defined by the
following equation:
To,k=To,1+(k-1)*(NOFDM-Nmm)/(NOFDM)[ms],
where Nmm is equal to the number of PDSCH symbols used for mmW
scheduling.
[0061] The delay of the mmW time frame may on average be longer
than for the LTE signal (due to a longer path and some AF delay).
Each AF node may start the AF action relative to its LTE timeframe.
A guard period may be added to each mmW packet to allow timing
drift of the mmW time frame relative to the LTE time frame. The
guard period may be at least as long as the maximum difference
between the LTE and mmW timeframes. With Manhattan grid routing,
the propagation distance difference should be approximately equal
to (sqrt(2)-1)*LOS path, which as a 1 km macro radius is
approximately equal to 414 m. This gives a delay of 414
m/3.times.10.sup.8 m/s=1.4 .mu.s. The processing delay per hop may
be approximately 100 ns, giving 500 ns total for five hops. This
time, combined with the 1.4 .mu.s travel time discussed above,
results in about a 2 .mu.s delay. With a 2.times. safety factor, a
4 .mu.s guard period may be reasonable. The above-described
approach for scheduling and synchronization may be applied to other
types of mmW channels with different bandwidths or to a different
overlay system with a different sampling frequency.
[0062] The physical layer information carried in the mmW access
link TTI may be categorized as follows. Referring to FIG. 4, the
automatic gain control (AGC) field 404 may include the fixed
sequence intended for the AGC settling and convergence. The primary
pilot field 406 may include the pilot sequence generated by the
source eNB for the purpose of timing acquisition and channel
estimation. Golay sequences 408 may be considered as shown in FIG.
4. The auxiliary pilot field 410 may include an optional pilot
sequence generated by the edge mB, e.g., in DF application for the
purpose of timing acquisition and channel estimation of the last
hop. The auxiliary control field 412 may include an optional short
message from the edge mB pertaining to the last hop. The header 414
may include optional control information required for reception of
the data field of the last hop, e.g. MCS, packet ID, etc. The data
field 416 may include the traffic data carried in this TTI. The
beam refinement field 418 may include optional control information
for beam refinement. The QCI reporting field 420 may contain QCI
information for backhaul links and access links. The guard period
422 may be a preset period of guard interval to remove timing
impact from propagation. The number of the field, the content
carried in each field, the order of the fields, and the duration of
each field discussed in this section are one example of the mmW
frame structure. Different design parameters may be considered.
[0063] The cross layer scheduling may be performed by the eNB and
transmitted in the downlink control channel on the cellular layer,
e.g., the PDCCH in LTE systems. The scheduled transmissions,
however, may occur on the mmW layer, either on the mmW access link
or the mmW backhaul link. This is the reason that the scheduling is
referred to as cross layer scheduling.
[0064] The cross layer scheduling differs significantly from the
cross carrier scheduling of the LTE R10 system because of the
inequality in the length of the TTI of the mmW backhaul/access link
and the LTE link. The LTE TTI may correspond to multiple mmW TTIs,
and as a result the LTE sub-frame may need to have an equal number
of scheduling instances as mmW TTIs of one mmW sub-frame. As
discussed above in connection with the frame structure, the
cellular layer may schedule mmW transmissions as often in one
sub-frame as the number of TTIs of one mmW sub-frame.
[0065] The LTE R11 standard introduced the Enhanced Physical
Downlink Control Channel (EPDCCH) as specified in TS 36.213. The
EPDCCH is only used for the UE-specific search area and is
multiplexed with the PDSCH and DL reference signals at the same
symbol locations beyond those signaled in the Physical Control
Format Indicator Channel (PFICH). The starting position is
configured by the higher layer parameter of epdcch-StartSymbol in
the RRC dedicated signaling, and a UE may monitor the EPDCCH at
each symbol location from the starting position until the last
position of the sub-frame. A UE may also receive an EPDCCH Physical
Resource Block (PRB) configuration including a PRB set, the number
of PRB pairs, etc., via the dedicated RRC signaling. The UE may
perform EPDCCH candidate monitoring, i.e., blind detection in a
similar manner as it does for the regular PDCCH according to the
pre-defined set of aggregation levels. The EDPCCH carries a
pre-defined set of DCI formats.
[0066] At a high level, the cross layer scheduling schemes may
include the following. The PDCCH may carry new DCIs, e.g., a mmDCl
for the access link and a BHDCI for the backhaul link, that do not
carry mmW data channel resource allocation and scheduling
information, but that do carry information related to a mmW control
channel. The information may point to the location and
configuration of the mmPDCCH or BHPDCCH. Thus, blind detection may
not be applied on the mmPDCCH or BHPDCCH.
[0067] In another possible scheme, RRC dedicated signaling may
convey the resource location and configuration of the mmPDCCH or
BHPDCCH. Blind detection may be applied on the mmPDCCH or BHPDCCH
in a mechanism similar to the EPDCCH. However, one EPDCCH may be
distributed over a span of symbols and may not be decoded
completely until the end of the LTE sub-frame. The mmPDCCH or
BHPDCCH, on the contrary, may need to be decoded completely at each
symbol location.
[0068] In a third possible scheme, RRC dedicated signaling may
convey the resource location and configuration of the mmPDCCH or
BHPDCCH, and no blind detection may be applied. The PDCCH may carry
a new DCI to trigger the decoding of the mmPDCCH or BHPDCCH. Note
that this DCI, unlike the DCI in the first scheme described above,
may not carry any scheduling or grant information for the mmW
control channel. A combination of the above-described schemes may
also be used.
[0069] An example of the first scheduling scheme is depicted in
FIG. 5. An FDD downlink sub-frame 500 has a duration of 1 ms, and
includes a PDCCH region 502 and a PDSCH region 504. In the example
shown in FIG. 5, the PDCCH region 502 includes three OFDM symbols,
OFDM Symbols 0-2. The PDSCH region 504 includes eleven OFDM
symbols, OFDM Symbols 3-13, though other numbers of symbols for the
PDCCH and PDSCH regions may be used. The PDCCH may carry new DCIs,
for example a mmDCl for access link scheduling. The mmDCl may carry
information pointing to the location and configuration of the
mmPDCCH. As shown in FIG. 5, the mmPDCCH, which may be multiplexed
with the PDSCH, may carry scheduling information for the mmPDSCH.
The mmW access downlink sub-frame 506 may have a 1 ms duration
divided into ten time slots, each time slot having a 100 .mu.s
duration. Ten LTE OFDM symbols in the PDSCH region may carry
scheduling information for the ten mmPDSCH time slots.
[0070] The inventive LTE DCIs are discussed in detail in the
subsequent sections. As indicated by the dashed lines in FIG. 6, an
LTE DCI for the mmW access link (mmDCl) may be added to the PDCCH
region 602 of an LTE sub-frame 600 to indicate a region of the
PDSCH 604 (which may be multiplexed with the mmPDCCH). The
indicated region, OFDM Symbols 3-12 in FIG. 6, may be used for the
scheduling of the multiple mmW TTIs in that interval for the UE on
the mmW access link.
[0071] As a mUE is associated with the network, it may use the
designated Radio Network Temporary Identifier (RNTI) in the PDCCH
decoding to detect the PDCCH DCI intended for it. The mmDCl may
include the symbol location, the PRB allocation, the sub-frame
number, etc., that a mUE may need to decode the mmPDCCH. The mmDCl
may also include a frequency allocation of the mmPDCCH, and a
transport format of the mmPDCCH.
[0072] Alternatively or additionally, the mmPDCCH monitoring
configuration, e.g., the symbol location, the region of PRB, etc.,
may be signaled in RRC dedicated signaling so that the mUE may know
where to monitor the mmPDCCH beforehand. The monitoring of the
mmPDCCH, however, may be commanded by the mmDCl.
[0073] In the case in which the edge mB is a type of remote radio
unit (RRU) and the mmW AF operation carries data for multiple users
associated with the RRU, the mmDCl may be intended for a group
including not only the mBs involved in the AF route but all of the
mUEs whose data are multiplexed in the relayed transmission. The
mmDCl may therefore provide further information as to how the user
data is multiplexed in the transmission, e.g., the frequency
resource allocation of each user, in order for each user to
identify its data.
[0074] A mB/mUE may monitor the channel and receive a control
message such as mmW access link scheduling information including
grant and scheduling of the mmW access downlink/uplink
transmissions. The mB/mUE may learn the location of the mmPDCCH
within the PDSCH region via a PDCCH DCI and may decode its complete
mmW control message per LTE OFDM symbol.
[0075] The mmPDCCH may have the following fields with information
required for a mUE to receive on an access link from an mB: an
Uplink/Downlink field (1 bit); a Full mBID field (7 bits); a
UEID_mBID field that includes the index of the mUE associated with
that particular mB (7 bits); an MCS field (5 bits); a Channel field
(2 bits); and an UL Tx power field (this may be a 1-bit field
indicating an increase/decrease relative to the last received Tx
power field, or a 5-bit field to accommodate an absolute value of a
power level with a maximum higher than 20 dBm). In the case of 1/3
rate convolutional coding, roughly five PRBs may be required for
this content. This information may be appended by a number of
cyclic redundancy check (CRC) bits for protection.
[0076] Alternatively, the mmPDCCH may carry the fields below for a
total of about 30-32 bits with eight CRC bits: an Uplink/Downlink
field (1 bit); a mmW UEID in macro cell field that includes maximum
number of UEs in mmW sessions per PoP (8-10 bits); and eNB ID of
edge mB field that includes a maximum of 128 mBs per PoP (7 bits);
an MCS field (4 bits); a Channel field (2 bits); and a CRC field
(8-16 bits).
[0077] The mmPDCCH may be semi-statically scheduled or dynamically
scheduled by the mmDCl in the PDCCH or via dedicated RRC signaling.
The mmPDCCH may be mapped to a contiguous set of PRBs or be
distributed over the PDSCH region (e.g., for frequency diversity).
Therefore the network may stagger the mmPDCCH with the PDSCH and
with downlink reference signals in the frequency domain on a symbol
location. The number of mmPDCCHs one symbol location can
accommodate may thus be variable depending on the mmPDCCH payload,
system bandwidth, reference signal configuration, cell load,
etc.
[0078] FIG. 7 illustrates mmW transmit/receive scheduling for mBs.
One LTE sub-frame 700 includes a PDCCH region 702 and a PDSCH
region 704. The PDSCH region may include scheduling information for
mmPDSCH time slots in a mmW sub-frame 706. As shown in FIG. 7,
there may be a fixed time offset 708 between the control message
and when the mmW transmission/reception occurs, i.e., the type and
time location of the control message may uniquely define the
corresponding mmW TTI. The offset for allocations (mmW DL) may be
different than the offset for grants (mmW UL), e.g., the offset for
grants may be longer than for allocations so that the mUE has time
to prepare the mmW UL packet. The mmPDCCH may also carry timing
information (such as a timing bitmap) for mmW transmission which
may include smaller resolution allocations (mmW slots) compared
with the mmW TTI (e.g. 100 .mu.s). The timing bitmap may schedule
multiple mmW slots in various times.
[0079] The cellular layer may also perform the scheduling and
routing on the mmW layer for the AF operation over the backhaul
to/from the PoP node from/to an edge mB. A new LTE DCI for the
backhaul (BHDCI) may be added to indicate a region of the PDSCH
(BHPDCCH) that is used to perform scheduling for the multiple mmW
TTIs in that interval for the BH. The BHDCI may indicate a
frequency allocation of the BHPDCCH and a transport format of the
BHPDCCH. Alternatively, the BHDCI may be merged with the mmDCl and
may share one type of LTE PDCCH DCI.
[0080] The BHDCI may contain the mB_IDs of the mBs that should
listen to the corresponding BHPDCCH. The mB_IDs may be explicitly
signaled, may be sent as one or more mB group IDs, or may be sent
as a combination of mB group IDs and individual mB_IDs. There may
be multiple BHDCIs that indicate multiple different BHPDCCHs that
different groups of mBs may be listening to.
[0081] A single mB or group of mBs may receive the AF scheduling
information from an eNB in an LTE scheduling interval. The group of
mBs may receive the information in their BHPDCCHs simultaneously,
and may expect the AF packet transmission to occur in the
subsequent same mmW TTI. The latency between the scheduling
instance and the packet transmission may be compensated by a
pre-defined LTE-mmW timing offset 708, as shown in FIG. 7.
Moreover, the difference between the mB's LTE reference timing, the
propagation delay between mBs, and the RF chain processing delay
(on the order of ns) may be dimensioned into the Guard Period
design.
[0082] When each mB, either independently or as part of a group,
has received its scheduling information, it may initialize a mmW
radio transmission resource according to the schedule. This may
include preparing for the AF relay by steering its receive (Rx)
beam to receive from the last mB node and its transmit (Tx) beam to
transmit to the next mB node. The indices of all member mBs of the
route may be included in the scheduling information, as the eNB and
all mBs may maintain a universal mB neighbor list for a common
reference. The scheduling information may also include, for each
link, a reception time, a receive antenna pattern, a frequency
channel for reception, a transmission time, a transmit antenna
pattern, a frequency channel for transmission, and a transmit
power. Each mB may also configure its RF processing chain with
scheduled parameters, e.g., channel and power. The preparation may
ensure that the packet is transmitted from the eNB and received by
the last relay node within the same mmW TTI. This is illustrated in
FIG. 7, wherein a packet 710 is relayed from an eNB 712 to mB4 720
via three other mBs 714-718 within a single TTI (Time Slot 0). As
shown in FIG. 7, each mB may begin transmitting the packet before
it has received the entire packet. Very low latency transmissions
can thus be achieved by the AF relay scheduling occurring on the
cellular layer.
[0083] The BHPDCCH is a sequence of control messages that indicate
to all mBs that are listening to the BHPDCCH when and how to
execute AF actions through the BH network. It may be assumed that
all nodes (mBs) know the topology of the network, and hence their
neighbor IDs. The BHPDCCH may carry the following information: an
mB_ID; a direction of the receive beam, i.e., the ID of the node
from which to receive a transmission; the channel of the receive
transmission; a direction of the transmit beam, i.e., the ID of the
node to which to transmit; a channel on which to transmit; a power
with which to transmit; and an indication of whether or not to add
a training field to the transmission (this may be used by the next
hop receiver for sounding or help with initial timing
recovery).
[0084] Alternatively, the BHPDCCH may carry the information below
assuming that all mBs know the BH topology, and have neighbor lists
for the eNB and mBs in the network. Accordingly, the mB's may know
neighbor indices that are signaled via RRC in LTE. In this case,
the BHPDCCH may carry the following information: an uplink/downlink
indication (1 bit), and a number of hops (2-3 bits; if maximum
allowed hops is 4 then 2 bits. Alternatively, zero bits may be used
and one index value may be reserved to indicate end-of-AF-chain.).
The BHPDCCH information may further include an index into the eNB's
neighbor list that defines the link of hop1 (2-3 bits). Hop1 is the
link between the eNB and the first mB (mB1), and accordingly may be
indicated by mB1's index value in the eNB's neighbor list. The
BHPDCCH information may further include the hop1 channel (2 bits
for the 60 GHz band); an index into the base station neighbor list
of mB1 that defines the link for hop2 (2-3 bits); the hop2 channel
(2 bits for the 60 GHz band); and fields for hop3, hop4, etc.,
until the last BH hop (4-5 bits per hop). The BHPDCCH may also
carry the following additional information: a UE_ID used by the
edge mB (7 bits if the number of supported UEs is less than 128);
padding (0 to 16-20 bits, depending on the number of hops); and a
CRC (8-16 bits). Other possible fields include a link pilot field
and a control field that may be used for link sounding and other
control message passing between links (1 bit); a beam refinement
field (1 bit); an extension field for the UE that indicates that no
mmPDCCH is needed, but implies that BH may be operated below
capacity since the MCS will tend to be lower; an MCS field (4
bits); and a channel field (2 bits). Given four or five neighbors,
the BHDPCCH payload may be 34 bits or 41 bits, respectively, before
encoding.
[0085] The BHPDCCH may be semi-statically scheduled or dynamically
scheduled by the PDCCH or by RRC signaling. Similar to the mmDPCCH,
the BHPDCCH may be mapped to a contiguous set of PRBs or may be
distributed over the PDSCH region (e.g., for frequency
diversity).
[0086] There may be a fixed time offset between the control message
and when the mmW AF action takes place (i.e., the type and time
location of the control message may uniquely define the
corresponding mmW TTI). The offset for the mmW DL AF actions may be
different than the offset for the mmW UL AF actions, and may depend
on whether a UE or mB is the source of the UL traffic. For example,
the offset for UL may be longer than for DL so that the source has
time to create the mmW UL packet. A UE may need a different amount
of time to create such a packet than an mB.
[0087] Alternatively, the BHPDCCH may carry the timing information
(e.g. a timing bitmap) for mmW transmissions which may include
smaller resolution (mmW slots) compared with mmW TTI (e.g. 100
.mu.s). The timing bitmap may schedule multiple mmW slots in
various times.
[0088] The BHDCI and mmDCl may be combined into an end-to-end DCI
(e2eDCI) to provide end-to-end scheduling in a single e2ePDCCH. The
e2ePDCCH may contain the combined information of the BHPDCCH and
the mmPDCCH. The mUE part and mB part may be in different fields so
that each need not decode parts of the message not needed for
delivery of the packet. End-to-end acknowledgment/negative
acknowledgement (ACK/NACK) messaging may be achieved by a mmW
ACK/NACK signaled on the cellular carrier or piggy backed on the
mmW UL. For an ACK/NAK signaled on the cellular carrier (e.g., when
no mmW UL exists), the DL terminal nodes receiving mmW packets may
send the ACK/NACK on the PUCCH (or optionally the PUSCH in the case
that the terminal node is an mUE using the PUSCH for UL). Since
multiple mmW transmissions may have been received since the last
ACK/NACK, the mmW ACK/NACKs may be bundled, and may be further
bundled with cellular ACK/NACKs. If all received mmW packets are
positively acknowledged, the bundled ACKs may indicate the number
of packets so that the sender may determine if a mmPDCCH message
was not detected. For an ACK/NAK signaled on the mmW carrier, if
the terminal node has an UL grant scheduled at the same time that
an ACK/NACK is required to be sent, the ACK/NACK may be added to
the mmW transmission rather than being sent on the PUSCH/PUCCH.
[0089] The initialization process for a mB/BH candidate node is
shown in FIG. 8. When a mB/BH candidate node turns on, it may first
register as a UE and indicate that it has mmW BH capabilities (step
800). The candidate node and/or the network may estimate its
position (step 802). A central node may provide basic information
about the mmW layer, such as channel locations and BWs, a
mmW/cellular TTI ratio, a cellular-mmW TTI offset at an estimated
nearest neighbor, etc. (step 804). The candidate node may provide
capability information relative to the mmW layer configuration
(e.g., which of the channels listed may be supported, the number of
beams that it can form in a beam search, and a number of antenna
arrays) (step 806).
[0090] The central node may estimate the set of BH nodes that might
be within range of the candidate node (a candidate neighbor list).
The central node may provide a beam search schedule to BH nodes and
the candidate node (808). The schedules may be provided by cellular
RRC signaling. The schedule provided to the candidate node may
contain mmW channels and TTIs in which to listen for other BH
nodes, a Tx beam duration, and a beam sweep period (e.g., if the
candidate neighbor nodes will sweep through their Tx beams in T
seconds, then the candidate node should dwell on each of its Rx
beams for T seconds). The schedule provided to the nodes in the
candidate neighbor list may include mmW channels and TTIs in which
to transmit beam sweeps, a Tx power, and beam sweep details (e.g.,
the number of beams to sweep through per mmW TTI, and the total
number of beams to sweep through).
[0091] The candidate node may listen for transmissions according to
the beam search schedule (step 810). After the beam search phase is
completed (i.e., the search schedule expires), the candidate node
may signal the central node via cellular RRC signaling (step 812).
The candidate note may indicate the signal strength of each
detected beam and the associated BH node IDs. Alternatively, a
subset of these may be reported, e.g., the strongest beam from each
BH node that was detected above some threshold, up to a maximum of
K BH IDs.
[0092] The central node may select a subset of the indicated BH
nodes as the neighbor list for the new node (i.e., these are now
links to be added to the topology) and may signal the new node and
the neighbors via cellular RRC signaling (step 814). The message
may include a node ID at each end of the new links, and the
currently preferred beam to use for each link (this may be for
neighbors only).
[0093] After the new links are added, each link may go through an
optional initial beam refinement phase to better align the beam
directions. The new links may be added to sounding schedules (BH
link sounding and end-to-end sounding). Once link metrics and
end-to-end channel qualities are known by the central node, the new
node may be scheduled via mmW control channels (step 816). An
interference matrix may be used to help the central controller
identify routes and possibly to de-rate MCS selections in the case
of anticipated interference. Finally, the candidate node may relay
data packets base on the scheduling via mmW control channels (step
818).
[0094] An edge mB node may have at least one mmW BH link to another
mB, and a mmW access link to a mUE. The edge mB node may receive
data packets, decode the packets, re-encode them, and re-transmit
them. The reception and re-transmission of the data packets may use
different MCSs and different numbers of TTIs per sub-frame. The
following is an example in which twice as many access link TTIs as
BH TTIs are used to deliver data that arrived on the BH links. mUEs
1, 3, 5, 7 may be served by mB1, while mUEs 0, 2, 4, 6, may be
served by mB2.
[0095] The BH link to mB1 may use mmW TTIs 1, 3, 5, 7, to receive
data intended for the UEs served by it (UEs 1, 3, 5, 7). This is
half of the mmW TTIs in the BH. The BH link to mB2 may use mmW TTIs
0, 2, 4, 6, to receive data intended for the UEs served by it (UEs
0, 2, 4, 6). This is also half of the TTIs in the BH. mB1 may use
access link mmW TTIs 2, 3 for UE1, TTIs 4, 5 for UE3, TTIs 6, 7 for
UE5, and TTIs 0, 1 (of the next frame) for UE7. Thus, in the access
link, all TTIs may be used. mB2 may use access link mmW TTIs 1, 2
for UE0, TTIs 3, 4 for UE2, TTIs 5, 6 for UE4, and TTIs 7, 0 (of
the next frame) for UE6. Again, all access link TTIs may be
used.
[0096] In this example, the BH resources are shared between the 2
mBs (with 50% of the duty cycle each) and each mB uses 100% of its
access link resources to forward the data to its UEs. Thus, the
code rate in the access link may be half of what it was in the
BH.
[0097] As described above, channel quality indexing (CQI) may be
part of the initialization of a new mB, and as detailed above, may
also play a role in scheduling mmW BH links after initialization.
The following paragraphs consider end-to-end sounding, and
modulation and coding scheme (MCS) selection in mmW backhaul
systems. Channel quality may be based on data transmissions or on
sounding signals. In the AF technique, the training/pilot symbols
transmitted by the source are amplified and forwarded in the same
manner as the data, and therefore are a good reference for
end-to-end channel quality estimation. In an end-to-end
transmission (either UE to PoP or PoP to UE for the BH plus access
link case, or mB to PoP or PoP to mB in the BH only case) the
pilots are used for reception of the data, but may also be used for
CQI estimation. A UE may be configured to send the mmW CQI
corresponding to the last data reception(s) on the PUCCH (or
optionally the PUSCH in the case that the PUSCH is used for UL)
along with the ACK/NACKs of the mmW data. UE or mB transmissions to
the PoP also contain training/pilots that are used for reception of
packets and may be used for channel quality estimation. These
end-to-end channel quality estimations may be used to compute the
MCSs for UL grants.
[0098] Training/pilot signals may also be scheduled explicitly for
end-to-end channel quality estimation. FIG. 9 shows an example of
an end-to-end channel sounding procedure over a scheduled route. An
eNB 900 may send an AF transmission of a pilot to a last relay node
906 via multiple other mBs 902, 904. The pilot may be sent over mmW
BH links 910. The pilot may then be transmitted to the mUE 908 over
the mmW access link 912. The mUE 908 may use a cellular link 914 to
send a sounding report that includes the pilot measurements to the
eNB 900. Once the eNB 900 receives a sounding report, it may
transmit an updated mmW relay schedule based on the report. The
training/pilot signals may contain no user data (some control
information may be included, e.g., when and how to report the
corresponding CQI). The mmW sounding TTI may be shorter than the
mmW data TTI, e.g., there may be multiple mmW sounding TTIs per mmW
data TTI. The sounding (and CQI reporting when appropriate) may be
scheduled with BH AF actions.
[0099] For semi-static mmW sounding/reporting, the mmW sounding
TTIs may be scheduled as background tasks that are overridden by
other higher priority tasks (e.g., data transmission). The
semi-static mmW sounding may be scheduled via RRC messaging in the
cellular layer. For DL channels, sounding may consist of a two-way
exchange (a sounding signal followed by a CQI report). The CQI
report may be sent on the same route as the sounding signal, but in
the opposite direction. The CQI report may in turn be used to
assess the end-to-end channel quality in the UL (i.e., a PoP node
may learn about channel quality in the UL and DL). For UL only
channel sounding, the channel quality estimate may not need to be
reported back to the sounding signal transmitter. UL sounding may
take less time since the response may not be needed. The extra time
may be used for denser sounding or to carry other information. The
UL sounding transmission may include additional control information
like buffer status reports (BSRs).
[0100] For dynamic mmW sounding/reporting, a sounding message in
the mmPDCCH/BHPDCCH may also be used to initiate sounding. The
content of BH AF actions message for sounding may be similar as the
message for data, and may include the following: a mB_ID; a
direction of the receive beam (i.e., the ID of the node from which
to receive a transmission); a channel of the mmW receive
transmission; a direction of the transmit beam (i.e., the ID of the
node to which to transmit); a mmW channel on which to transmit; a
power with which to transmit; an indication of whether or not to
add a training field to the transmission; a sub-TTI (if the
sounding time period is smaller than the data time period, the
sub-TTI may indicate in which part of a corresponding TTI to place
the AF action); and an UL/DL indicator (DL may indicate that the AF
mirror should be reversed to carry the CQI response to
sounding).
[0101] The content of the mmPDCCH for sounding may include a UE_ID,
a mB_ID, a Tx/Rx indicator, a transmit power (for sounding
transmission), a mmW channel indicator, a sub-TTI, and a mmW CQI
report.
[0102] Backhaul link sounding may be used to measure the quality of
mB-mB links, and while it may primarily be used for routing, it may
aid in scheduling and MCS selections as well. FIG. 10 illustrates
channel sounding of individual backhaul links of the mmW mesh
network. The eNB 1000 may schedule the backhaul link sounding over
the cellular links 1020. Pilots may then be transmitted between the
mB's 1002-1018 via AF transmissions over BH links 1022. The mB's
1002-1018 may use the cellular links 1020 to report the pilot
measurements to the eNB 1000. Once the eNB 1000 receives a report,
it may transmit an updated mmW relay schedule based on the
report.
[0103] Backhaul link sounding may be semi-statically scheduled
along with end-to-end semi-static mmW sounding/reporting. The BH
mmW sounding TTIs may be scheduled as background tasks that are
overridden by other higher priority tasks (e.g., data
transmission). Semi-static mmW sounding may be scheduled via RRC
messaging in the cellular layer (this may either not conflict with
end-to-end sounding or one process may be given priority over the
other). A semi-static PUSCH grant on the cellular layer may be
allocated to nodes to provide BH link quality metrics to PoP nodes.
The PUSCH grant may be shared by multiple mBs, and the messages of
multiple PUSCHs may be separated by CDMA/TDMA/FDMA within the PUSCH
RBs.
[0104] Access link sounding may be used to measure the mmW access
link quality at the mmW-capable UEs. For sounding between a serving
mB and a mUE, the serving mB and its mUEs may exchange periodic
control messages even when no messages to or from the PoP are
carried. These messages may be used for the mobile access link
maintenance. The central node (e.g., a PoP node) may provide an
access link beam tracking schedule to each mB. The beam tracking
schedule may indicate which mUEs in which mmW TTIs should be used
to perform beam tracking updates and interference measurements.
Channel quality may be assessed during the beam tracking update.
The most recent channel quality assessments may be used for access
link CQI reporting.
[0105] mBs may report access link CQIs to the PoP via the PUSCH.
The access link CQI reporting may be scheduled via a persistent
PUSCH schedule. A mB may also initiate an access link CQI report,
for example, if a mUE requires a handover before the next scheduled
CQI report. The report may be initiated by a normal service request
(SR) on the cellular link, and may be piggybacked on other UL
transmissions. An eNB that receives a report may transmit an
updated mmW relay schedule based on the report.
[0106] Sounding between a neighbor mB and a mUE may be the same as
between a serving mB and a mUE except that the motivation for
initiating an aperiodic CQI report may be different. For example,
the report may be used to indicate that a mUE with a low CQI should
not be handed off to a particular mB, and the mB might be removed
from the mUE's neighbor list.
[0107] As discussed earlier in connection with FIG. 2, the low
latency mmW system may also act as a pure backhaul solution to
carry multiple-access-user data to the edge mB in a similar way to
fiber transmissions. Depending on the air interface of the access
link between the edge mB and the end user, e.g. a UE or mUE, the
edge node may perform decode-and-forward (DF). The eNB may schedule
the multiple access link user data transmission together with the
scheduling of the backhaul link in the mmDCl, and the scheduled
users may take into account a pre-defined DF-related delay before
starting to receive the de-multiplexed data. Alternatively, the eNB
may only schedule the AF transmission to the edge mB and the edge
mB may apply DF and also flow control, and may schedule the
de-multiplexed data independently.
[0108] In the case of applying the low latency mmW system for a
single user, the access link capacity may be substantially lower
than the backhaul link capacity, and flow control and buffering may
be applied after the DF process. In this scenario, the use of mmW
TTIs in the access link and in the BH links may be decoupled.
[0109] To support DF in the edge mB, the mmPDCCH/BHPDCCH message to
the edge mB may include additional information, or alternatively
the edge mB may listen to the mmPDCCH of the served UEs. The
information may include a BH MCS, an access link MCS, and a number
of access link mmW TTIs per BH TTI. Note that only two of the three
pieces of information (BH MCS, Access MC, Number of access link mmW
TTIs per BH) may be needed. The information may also include a
BH-access offset that indicates the time between the BH and access
TTIs for a given packet.
[0110] In the embodiments described herein, it is also possible for
the last hop to be on the cellular layer when the target UE does
not have mmW capability. In this case, the mmW layer may provide a
backhaul to the mBs, which may also act as small LTE cells. The
edge mB may terminate the backhaul link and may Decode and Forward
(DF) to translate the data from the mmW layer to the cellular
layer. This may increase the latency, and thus may need to be taken
into consideration for the system design. Both the envisioned AF/DF
and AF-only versions of the mmW hot spot underlay systems may share
a bulk of the system design described above. In the case in which
the mmW layer is providing BH, the small cell may be a regular LTE
eNB with its own scheduler, etc. Alternatively, where the mmW layer
is providing backhaul to a small cell, the small cell may be a
remote radio unit (with no local scheduler, etc.).
[0111] The apparatus shown in FIGS. 1A-1D may be configured to
perform the functions described above. In particular, the WTRUs
102a-102e, mBs 172a-172d, and eNB 185 in FIG. 1D may be configured
to perform the functions described herein.
[0112] 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.
* * * * *