U.S. patent application number 15/473619 was filed with the patent office on 2017-10-05 for wireless communication system design.
The applicant listed for this patent is MEDIATEK INC.. Invention is credited to Bo-Si Chen, Yih-Shen Chen, Chien-Chang Li, Weidong Yang.
Application Number | 20170289985 15/473619 |
Document ID | / |
Family ID | 59960472 |
Filed Date | 2017-10-05 |
United States Patent
Application |
20170289985 |
Kind Code |
A1 |
Yang; Weidong ; et
al. |
October 5, 2017 |
Wireless Communication System Design
Abstract
Apparatus and methods are provided for low latency an ultra-low
latency (ULL) communications. In novel aspect, short TTIs are
configured for low latency communications. The UE configures one or
more downlink short transmission time interval (sTTI) regions over
a normal TTI region, decodes one or more low latency control
channels, which indicates one or more sTTI regions for one or more
UEs, and obtains one or more sTTI regions for the UE based on the
decoded low latency control channels. In one embodiment, the
location short TTI control channels is determined by detecting a
short TTI control message at a beginning of a TTI and obtaining a
duration of the short TTI in the detected short TTI control
message. In one embodiment, the UE obtains one or more uplink
resources, power control and CSI configurations based on
corresponding downlink short TTI transmissions according to a
mapping rule.
Inventors: |
Yang; Weidong; (San Diego,
CA) ; Chen; Yih-Shen; (Hsinchu County, TW) ;
Li; Chien-Chang; (Penghu County, TW) ; Chen;
Bo-Si; (Keelung City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MEDIATEK INC. |
Hsinchu |
|
TW |
|
|
Family ID: |
59960472 |
Appl. No.: |
15/473619 |
Filed: |
March 30, 2017 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62317447 |
Apr 1, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 52/146 20130101;
H04W 72/0406 20130101; H04L 5/0007 20130101; H04L 5/0044 20130101;
H04W 72/042 20130101; H04W 72/085 20130101; H04L 5/0037 20130101;
H04W 52/16 20130101; H04W 84/042 20130101; H04W 72/0446 20130101;
H04L 5/0087 20130101; H04L 5/0092 20130101; H04W 52/281 20130101;
H04W 72/10 20130101 |
International
Class: |
H04W 72/04 20060101
H04W072/04; H04W 72/10 20060101 H04W072/10; H04W 52/14 20060101
H04W052/14 |
Claims
1. A method comprising: configuring one or more downlink short
transmission time interval (sTTI) regions over a normal TTI region
in a system bandwidth by a user equipment (UE) in a wireless
network, wherein the resources in the sTTI regions have short TTI
length; decoding one or more low latency control channels and one
or more normal latency control channels, wherein each low latency
control channel indicates one or more sTTI regions for one or more
UEs in the wireless network; and obtaining one or more sTTI regions
for the UE based on the decoded one or more low latency control
channels and the one or more normal latency channels.
2. The method of claim 1, wherein locations of the normal TTI
control channels and the short TTI control channels are
preconfigured.
3. The method of claim 1, wherein the location short TTI control
channels is determined by detecting a short TTI control message at
a beginning of a TTI and obtaining a duration of the short TTI in
the detected short TTI control message.
4. The method of claim 1, wherein the one or more short TTI regions
are configured by a short TTI configuration comprising:
configuration through a SIB message, configuration through a
dedicated RRC configuration, configuration through a dynamic
signaling, and a static configuration.
5. The method of claim 4, further comprising: activating the short
TTI region configuration, wherein the one or more short TTI regions
are configured upon successful activation.
6. The method of claim 5, wherein the activating of the short TTI
region configuration involves receiving an activation signal via a
normal latency control command.
7. The method of claim 1, further comprising: obtaining one or more
uplink resources based on corresponding downlink short TTI
transmissions, wherein the one or more uplink resources are mapped
to corresponding downlink short TTI transmissions according to a
mapping rule.
8. The method of claim 7, wherein the mapping rule is to map an
uplink resource transmission time based on the corresponding
downlink short TTI transmission time and a predefined processing
time.
9. The method of claim 7, wherein the mapping rule is to
dynamically map an uplink resource based on corresponding regular
TTI and one or more short TTIs.
10. The method of claim 1, further comprising: mapping uplink
resources in parallel to corresponding a downlink transmission,
wherein the downlink transmission includes one or more short TTIs
within a regular TTI; and adjusting uplink transmission power based
on based a TTI power priority rule, wherein the TTI power
priority.
11. The method of claim 10, wherein the TTI power priority rule
indicates a short TTI with the shortest TTI length has the highest
priority, and a short TTI has higher priority than a normal
TTI.
12. The method of claim 1, wherein a short PDSCH (sPDSCH) is
demodulated based on CRS, and wherein Pa/Pb for downlink power
control is configured with different value than a regular
PDSCH.
13. The method of claim 1, wherein a transmission mode for a short
PDSCH (sPDSCH) is configured differently from a regular PDSCH.
14. The method of claim 1, wherein a CSI feedback for a short PDSCH
(sPDSCH) is configured differently from a regular PDSCH.
15. A method comprising: configuring one or more downlink short
transmission time interval (sTTI) regions over a normal TTI region
in a system bandwidth by a base station in a wireless network,
wherein the resources in the sTTI regions have short TTI length;
encoding one or more low latency control channels and one or more
normal latency control channels, wherein each low latency control
channel indicates one or more sTTI regions for one or more UEs in
the wireless network; and transmitting radio resources, wherein the
radio resources comprises one or more sTTI regions for one or more
user equipment (UE).
16. The method of claim 15, wherein locations of the normal TTI
control channels and the short TTI control channels are
preconfigured.
17. The method of claim 15, wherein the location short TTI control
channels is determined by detecting a short TTI control message at
a beginning of a TTI and obtaining a duration of the short TTI in
the detected short TTI control message.
18. The method of claim 15, wherein the one or more short TTI
regions are configured by a short TTI configuration comprising:
configuration through a SIB message, configuration through a
dedicated RRC configuration, configuration through a dynamic
signaling, and a static configuration.
19. The method of claim 18, further comprising: sending a short TTI
activating signal via a normal latency control command, wherein the
activating signal indicates short TTI regions being configured.
20. The method of claim 15, further comprising: receiving one or
more uplink resources based on corresponding downlink short TTI
transmissions, wherein the one or more uplink resources are mapped
to corresponding downlink short TTI transmissions according to a
mapping rule.
22. A user equipment (UE), comprising: a radio frequency (RF)
transceiver that transmits and receives radio signals in a wireless
communication network; a transmission time interval (TTI)
configurator that configures one or more downlink short TTI (sTTI)
regions over a normal TTI region in a system bandwidth in a
wireless network, wherein the resources in the sTTI regions have
short TTI length; a decoder that decodes one or more low latency
control channels and one or more normal latency control channels,
wherein each low latency control channel indicates one or more sTTI
regions for one or more UEs in the wireless network; and a resource
locator that obtains one or more sTTI regions for the UE based on
the decoded one or more low latency control channels and the one or
more normal latency channels.
23. The UE of claim 22, wherein locations of the normal TTI control
channels and the short TTI control channels are preconfigured.
24. The UE of claim 22, wherein the location short TTI control
channels is determined by detecting a short TTI control message at
a beginning of a TTI and obtaining a duration of the short TTI in
the detected short TTI control message.
25. The UE of claim 22, wherein the one or more short TTI regions
are configured by a short TTI configuration comprising:
configuration through a SIB message, configuration through a
dedicated RRC configuration, configuration through a dynamic
signaling, and a static configuration.
26. The UE of claim 22, further comprising: an uplink encoder that
obtains one or more uplink resources based on corresponding
downlink short TTI transmissions, wherein the one or more uplink
resources are mapped to corresponding downlink short TTI
transmissions according to a mapping rule.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. .sctn.119
U.S. provisional application 62/317,447 entitled "SYSTEM DESIGN FOR
LOW LATENCY COMMUNICATION AND ULTRA-LOW LATENCY COMMUNICATIONS"
filed on Apr. 1, 2016, the subject matter of which is incorporated
herein by reference.
TECHNICAL FIELD
[0002] The disclosed embodiments relate generally to wireless
communication, and, more particularly, to methods and apparatus for
wireless communication system design.
BACKGROUND
[0003] Mobile networks communication continues to grow rapidly. The
mobile data usage will continue skyrocketing. New data applications
and services will require higher speed and more efficient. Large
data bandwidth application continues to attract more consumers.
Today, 3G/4G mobile wireless systems provide connectivity for wide
range of applications and services. In the next generation 5G
network, it is expected that the latency issue will be one of the
key performance indicators (KPIs), which shape the air interface
and network architecture design.
[0004] Short TTIs (Transmission Time Interval) are effective in
reducing end-to-end latency and ultimately improves user
experiences. In the long term evolve (LTE) system, typically eNB
uses downlink control channel to inform UE of the downlink data
transmission. One to three OFDM symbols in a subframe with fourteen
OFDM symbols are set aside for control signaling, including PDCCH,
PHICH, and PCFICH. Even if there is very little control signaling
actually sent in a subframe, the whole control region is still
reserved and the spare resource not taken by downlink control still
cannot be used by downlink data, except that PCFICH can be used to
control the size of the control region. On a short TTI, such a
practice can lead to a severe waste of radio resources. Further,
the data packets for one UE can be of different sizes and can have
different latency requirements, which are best addressed with TTIs
with different lengths. For a UE, if the network can support only
one TTI length at any given time, then eNB cannot address the
different requirements satisfactorily.
[0005] Improvements and enhancements are required to improve system
latency. In particular, enabling resource sharing between downlink
control and downlink data and simultaneous supports for TTIs of
different lengths are desired.
SUMMARY
[0006] Apparatus and methods are provided for low latency an
ultra-low latency (ULL) communications. In novel aspect, short TTIs
are configured for low latency communications. The UE configures
one or more downlink short transmission time interval (sTTI)
regions over a normal TTI region in a system bandwidth. The UE
decodes one or more low latency control channels and one or more
normal latency control channels, wherein each low latency control
channel indicates one or more sTTI regions for one or more UEs in
the wireless network. The UE obtains one or more sTTI regions for
the UE based on the decoded one or more low latency control
channels and the one or more normal latency channels. In one
embodiment, the location short TTI control channels is determined
by detecting a short TTI control message at a beginning of a TTI
and obtaining a duration of the short TTI in the detected short TTI
control message. In another embodiment, the one or more short TTI
regions are configured by a short TTI configuration comprising:
configuration through a SIB message, configuration through a
dedicated RRC configuration, configuration through a dynamic
signaling, and a static configuration. In yet another embodiment,
the short TTI regions are activated when receiving an activation
signal via normal latency control command.
[0007] In one embodiment, the UE obtains one or more uplink
resources based on corresponding downlink short TTI transmissions,
wherein the one or more uplink resources are mapped to
corresponding downlink short TTI transmissions according to a
mapping rule. In another embodiment, a short PDSCH (sPDSCH) is
demodulated based on CRS, and wherein Pa/Pb for downlink power
control is configured with different value than a regular PDSCH. In
yet another embodiment, a CSI feedback for a short PDSCH (sPDSCH)
is configured differently from a regular PDSCH.
[0008] In another novel aspect, the UE is configured for control
overhead reduction. The UE configures one or more short
transmission time interval (sTTI) regions over a normal TTI region
in a system bandwidth. The sTTI regions are shared by the UE and
one or more other, each UE includes a self-contained control
information sPDSCH occupying a control information region. The UE
detects a cover signal, which indicates one or more resource
elements (REs) in the sPDSCH control information region that can be
used for data transmission. The UE obtains data transmission from
the REs in the SPDCCH control information region based on the
detected cover signal. In one embodiment, the cover signal is a
dedicated signal such that the SPDCCH control information for the
UE includes resources by one or more SPDCCH for the one or more
other UEs in the wireless network. In another embodiment, the cover
signal is a common signal, and wherein the common signal comprises
information of radio resource usage for all sPDCCHs. In yet another
embodiment, the cover signal is encoded in a downlink control
information (DCI) intended for the UE, and wherein the cover signal
indicates control channel elements (CCEs) of PDCCHs taken by other
UEs in the wireless network. In one embodiment, the cover signal
indicates one or more CCE REs to be excluded for data
transmission.
[0009] In yet another novel aspect, ULL is configured for the UE.
The UE receives a downlink resource assignment and determines
whether an ultra-low latency (ULL) alert signal exists, wherein the
ULL alert signal indicates a set of soft bits are overridden. The
UE discards the set of soft bits from the overridden resources upon
determining the ULL alert signal exists. The UE performs channel
decoding based of the received downlink resource. In one
embodiment, the ULL alert signal resides in the assignment
subframe, and the overridden soft bits are in the assignment
subframe. The alert timing for the ULL alert signal is
preconfigured. In another embodiment, the ULL alert signal resides
in a subframe that is right after the assignment subframe, and
wherein the overridden soft bits are in the assignment subframe.
The alert signal is enabled through an enabling of an enhanced
mobile broadband (eMBB) and ULL service. In one embodiment, the
alter signal indicates a superset of the overridden soft bits. In
another embodiment, the alter signal indicates part of the
overridden soft bits.
[0010] Other embodiments and advantages are described in the
detailed description below. This summary does not purport to define
the invention. The invention is defined by the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The accompanying drawings, where like numerals indicate like
components, illustrate embodiments of the invention.
[0012] FIG. 1 illustrates a system diagram of a wireless network
that supports low latency and ultra-low latency communications in
accordance with embodiments of the current invention.
[0013] FIG. 2 shows an exemplary diagram of a soft resource
partition including short TTIs in accordance with embodiments of
the current invention.
[0014] FIG. 3 shows an exemplary diagram of candidate locations for
control channels of short TTI and normal TTI in accordance with
embodiments of the current invention.
[0015] FIG. 4 shows an exemplary diagram for the mapping from
logical resource to physical resources in accordance with
embodiments of the current invention.
[0016] FIG. 5 shows exemplary diagrams for mapping of logical
control resources to physical resource in accordance with
embodiments of the current invention.
[0017] FIG. 6 shows exemplary diagrams for the mapping of downlink
and uplink resources with short TTIs configured in accordance with
embodiments of the current invention.
[0018] FIG. 7 shows an exemplary diagram for the uplink power
control, downlink power control, and CSI-feedback transmission mode
configurations in a short TTI configured system in accordance with
embodiments of the current invention.
[0019] FIG. 8 shows exemplary diagrams for efficient multiplexing
of control and data for control overhead reduction in accordance
with embodiments of the current invention.
[0020] FIG. 9 illustrates an exemplary diagram for dedicated
signaling to indicate control resources taken by other UEs for
control overhead reduction in accordance with embodiments of the
current invention.
[0021] FIG. 10 illustrates exemplary diagrams for alert signals for
ULL support in accordance with embodiments of the current
invention.
[0022] FIG. 11 illustrates exemplary flow charts for alter signal
in the same TTI for ULL support in accordance with embodiments of
the current invention.
[0023] FIG. 12 illustrates exemplary flow charts for alter signal
sent in the next TTI for ULL support in accordance with embodiments
of the current invention.
[0024] FIG. 13A illustrates an exemplary flow chart for a UE to
perform a short TTI configuration for low latency communication in
accordance with embodiments of the current invention.
[0025] FIG. 13B illustrates an exemplary flow chart for a base
station to perform a short TTI configuration for low latency
communication in accordance with embodiments of the current
invention.
[0026] FIG. 14A illustrates an exemplary flow chart for a UE to
perform control overhead reduction in accordance with embodiments
of the current invention.
[0027] FIG. 14B illustrates an exemplary flow chart for a base
station to perform control overhead reduction in accordance with
embodiments of the current invention.
[0028] FIG. 15A illustrates an exemplary flow chart for a UE to
perform ultra-low latency (ULL) procedure in accordance with
embodiments of the current invention.
[0029] FIG. 15B illustrates an exemplary flow chart for a base
station to perform ultra-low latency (ULL) procedure in accordance
with embodiments of the current invention.
DETAILED DESCRIPTION
[0030] Reference will now be made in detail to some embodiments of
the invention, examples of which are illustrated in the
accompanying drawings.
[0031] FIG. 1 illustrates a system diagram of a wireless network
that supports low latency and ultra-low latency communications in
accordance with embodiments of the current invention. Wireless
communication system 100 includes one or more wireless networks
each of the wireless communication network has a fixed base
infrastructure units, such as receiving wireless communications
devices or user equipment (UE) 102 103, and 104, forming wireless
networks distributed over a geographical region. The base unit may
also be referred to as an access point, an access terminal, a base
station, a Node-B, an eNode-B, or by other terminology used in the
art. Each of the receiving UE 102, 103, and 104 serves a geographic
area. Backhaul connections 113, 114 and 115 connect the
non-co-located receiving UEs, such as 102, 103, and 104. These
backhaul connections can be either ideal or non-ideal
[0032] A wireless communications device 101 in wireless network 100
is served by base station 102 via uplink 111 and downlink 112.
Other UEs 105, 106, 107, and 108 are served by different base
stations. UEs 105 and 106 are served by base station 102. UE 107 is
served by base station 104. UE 108 is served by base station
103.
[0033] In one novel aspect, wireless communication network 100
supports low latency and ultra-low latency communication using
short TTIs. In one embodiment, the UE configures one or more
downlink short transmission time interval (sTTI) regions over a
normal TTI region in a system bandwidth. The short TTIs have
shorter TTI length than a normal TTI. The UE then decodes the one
or more low latency control channels and one or more normal latency
control channels, which indicates one or more sTTI regions for one
or more UEs in the wireless network. The UE obtains one or more
sTTI regions for the UE based on the decoded one or more low
latency control channels and the one or more normal latency
channels.
[0034] In another novel aspect, wireless communication network 100
supports control and data multiplexing. In one embodiment the UE
transmitting data in the unused control subframes. In one
embodiment, the UE configures one or more short TTI regions over a
normal TTI region in a system bandwidth. The UE detects a cover
signal, which indicates one or more resource elements (REs) in the
sPDCCH control information region that can be used for data
transmission. The UE subsequently, obtains data transmission from
the REs in the SPDCCH control information region based on the
detected cover signal.
[0035] In yet another novel aspect, wireless communication network
100 supports ultra-low latency communications. In one embodiment,
the UE receives a downlink resource assignment and determines
whether an ultra-low latency (ULL) alert signal exists. The ULL
alert signal indicates a set of soft bits are overridden. The UE
discards the set of soft bits from the overridden resources upon
determining the ULL alert signal exists and performs channel
decoding subsequently. In one embodiment, the alert signal is in
the same TTI as the assignment TTI. In another embodiment, the
alert signal is in the next subframe of the assignment TTI.
[0036] FIG. 1 further shows simplified block diagrams of wireless
stations 101 and base station 102 in accordance with the current
invention.
[0037] Base station 102 has an antenna 126, which transmits and
receives radio signals. A RF transceiver module 123, coupled with
the antenna, receives RF signals from antenna 126, converts them to
baseband signals and sends them to processor 122. RF transceiver
123 also converts received baseband signals from processor 122,
converts them to RF signals, and sends out to antenna 126.
Processor 122 processes the received baseband signals and invokes
different functional modules to perform features in base station
102. Memory 121 stores program instructions and data 124 to control
the operations of base station 102. Base station 102 also includes
a set of control modules, such as a short TTI processor 181 that
configures short TTIs for UEs, a control overhead reducer 182 that
reuses control subframes for data transmission, a ULL handler 183
that sends alert signals to UEs for ULL soft bits.
[0038] UE 101 has an antenna 135, which transmits and receives
radio signals. A RF transceiver module 134, coupled with the
antenna, receives RF signals from antenna 135, converts them to
baseband signals and sends them to processor 132. RF transceiver
134 also converts received baseband signals from processor 132,
converts them to RF signals, and sends out to antenna 135.
Processor 132 processes the received baseband signals and invokes
different functional modules to perform features in mobile station
101. Memory 131 stores program instructions and data 136 to control
the operations of mobile station 101.
[0039] UE 101 also includes a set of control modules that carry out
functional tasks. A TTI configurator 191 configures one or more
downlink short TTI (sTTI) regions over a normal TTI region in a
system bandwidth in a wireless network, wherein the resources in
the sTTI regions have short TTI length. A decoder 192 decodes one
or more low latency control channels and one or more normal latency
control channels, wherein each low latency control channel
indicates one or more sTTI regions for one or more UEs in the
wireless network. A resource locator 193 obtains one or more sTTI
regions for the UE based on the decoded one or more low latency
control channels and the one or more normal latency channels. A UL
encoder 194 obtains one or more uplink resources based on
corresponding downlink short TTI transmissions, wherein the one or
more uplink resources are mapped to corresponding downlink short
TTI transmissions according to a mapping rule. A data processor 195
obtains data transmission from the REs in the SPDCCH control
information region based on the detected cover signal. A detector
196 detects a cover signal, wherein the cover signal indicates one
or more resource elements (REs) in the sPDCCH control information
region that can be used for data transmission. A resource allocator
197 receives a downlink resource assignment at an assignment
subframe in the wireless network. An alert detector 198 determines
whether an ultra-low latency (ULL) alert signal exists, wherein the
ULL alert signal indicates a set of soft bits are overridden. A
resource locator 199 discards the set of soft bits from the
overridden resources upon determining the ULL alert signal exists.
A channel decoder 190 performs channel decoding based of the
received downlink resource.
[0040] FIG. 2 shows an exemplary diagram of a soft resource
partition including short TTIs in accordance with embodiments of
the current invention. In one novel aspect, over the system
bandwidth, one or more regions over a normal TTI can be configured
for short TTI transmissions. The time and frequency regions
configured for the short TTI transmission are short TTI regions.
The illustrated time frequency regions are contiguous in the
logical domain. The physical resources are mapped to the logical
domain following predefined rule. The illustrated resources are
virtual resources and are not necessarily contiguous in the
physical domain. A system resource 201 with a normal TTI 202 are
configured with both normal TTI region and two short TTI regions,
short TTI region-1 211, and short TTI region-2 212. A downlink
control 221 points to the time/frequency resource 231 between two
short TTI regions, and that resource is given to UE-1. It is also
possible for a single transmission; a downlink control schedules
resources from parts in the time/frequency resource in the middle,
and in one short TTI region or in two short TTI regions.
[0041] In one embodiment, the UE simultaneously monitors PDCCH and
sPDCCH to support dynamical multiplexing of sTTI(s) and TTI in one
subframe. An eNB can dynamically switch the TTI type for
transmission(s) intended for a UE depending on whether data
transmission is during the slow start stage or congestion avoidance
stage, and only one TTI type is exploited at any given time. In one
embodiment, parallel transmissions on different TTI types are
enabled. One example is when multiple TCP connections are open
between one TCP server or multiple TCP servers and TCP client or
TCP clients associated with the UE. One TCP connection may be in
the slow start stage, while another TCP connection may be in the
congestion avoidance stage, which makes it more difficult for the
eNB to settle down on one TTI type to server the UE. Another use
case for simultaneous use of different TTI types is applications
with different latency requirements can run at the same UE. The UE
are assigned different TTIs for different applications.
[0042] In one embodiment, the configuration of a short TTI region
can static, semi-static, or dynamic, such as through a SIB message,
through a dedicated RRC configuration, or through dynamic
signaling. The configuration can be at various radio interface time
scales such as at a subframe or at a radio frame. The semi-static
or dynamic configuration can be further improved by accompanying
activation mechanism so that the overlapping resource can be normal
TTI or shorter TTI while needed. In another embodiment of
activation mechanism is to transmit activation signal via normal
latency control command through control region 221.
[0043] In one embodiment, the configuration of candidate locations
for a short TTI region or a number of short TTI regions can be
different for different UEs. For example depending on their
processing capabilities, a less capable UE is configured with a
fewer number of candidate locations. The UE can be configured to
handle less time-stringent TTI types based on the UE capacity. The
configuration can also indicate the allowed mixture of TTI types.
In another embodiment, the UE is signaled a set of positions in a
subframe. At each of those positions, the UE searches for a control
channel indicating the start of a TTI. In yet another embodiment,
the UE is also signaled a set of PRBs over which it searches for
the control channels. In LTE, a PDCCH's REG can come from any of
the PRBs in the system bandwidth. For example, a REG of a sPDCCH
may come from one of the PRBs in the signaled set only. The sEPDCCH
can be defined similarly by restricting its duration over the sTTI
and span in the frequency domain to the signed PRB set. As an
example, symbols {0, 1, 4, 7, 8, 11} is the set of positions, and
PRBs {1, 3, 5, 7, 9, 11, . . . , 25} are the PRBs for a UE to
search for control channels. In general, a normal TTI can start at
symbol zero only. A sTTI with seven symbols can start at symbol
zero or symbol seven only. In one embodiment, a sTTI with four
symbols can start at symbol zero or symbol four only. A sTTI with
three symbols can start at symbols 1, 4, 8, 11 only.
[0044] FIG. 3 shows an exemplary diagram of the candidate locations
for control channels of short TTI and normal TTI in accordance with
embodiments of the current invention. A total system bandwidth 301
with a normal TTI 302 is configured to detect downlink control
information at a number of candidate locations: one or more
candidate locations for normal latency control which can schedule
downlink data transmission in the whole system bandwidth including
short TTI regions over a regular TTI, a number of candidate
locations for short TTI control which can schedule downlink data
transmission in a short TTI region. A normal TTI control channel
311 configures normal TTI regions 331 and 332. Region 331, which
includes part of the normal TTI region 330 is assigned to UE-1.
Region 332, which includes part of normal TTI region 330 and all
the short TTI region-2 320 is assigned to UE-4. A short TTI
region-1 310 is controlled by short TTI control channels 321, 322,
323, and 324. Control channel 321 assigns short TTI region 334 to
UE-4, and 335 to UE-5. Control channel 322 assigns short TTI region
336 to UE-6, and 337 to UE-7. Control channel 323 assigns short TTI
region 338 to UE-8, and 339 to UE-9.
[0045] In one embodiment, one or more of the TTI control channels
are not being used and can be used for data transmission. As an
example, region 338 and region 339 extends to the very end of short
TTI region-1. Control channel 324 is not used. eNB does not
transmit any downlink control messages on control channel 324. The
resources 324, which would be used by downlink control messages for
part of the short TTI region-1 can be used for data transmission.
Different types of short TTIs can be supported as shown in FIG.
3.
[0046] In another embodiment, one UE can receive different type of
TTI assignment. UE-4 receives two assignments: one for a sTTI and
another for a regular TTI. The assignment for the sTTI can be used
for a TCP connection in the slow start stage; and the assignment
for the regular TTI can be used for another TCP connection, which
is in the congestion avoidance stage. In one embodiment, the
locations for short TTI controls are preconfigured. In another
embodiment, the locations for short TTI controls are determined
dynamically. UE 4 detects short TTI control message(s) at the
beginning of a TTI in the short TTI region-1 310. The duration of
the short TTI is provided in the detected downlink control
message(s). Then the UE attempts to detect short TTI control
messages(s) after the end of the short TTI.
[0047] FIG. 4 shows an exemplary diagram for the mapping from
logical resource to physical resources in accordance with
embodiments of the current invention. One goal for the soft
partition of system resource is to utilize the fragmented spectrum
under one operator's control, or patch together fragmented spectrum
from two or more operators when they enter a spectrum sharing
agreement. The mapping of physical resources to logical resources
is utilized. Four carriers, carrier-1, carrier-2, carrier-3, and
carrier-4 are configured. A total system resource 401 with a normal
TTI 402 is configured for three UEs, UE-1, UE-2, and UE-3. TTI
control channel 441 configures three regions for each of the UE.
UE-1 is configured with region 431. UE-2 is configured with region
432. UE-3 is configured with region 433. The configured logical
regions are mapped to different carrier. As shown, UE-1 is mapped
to carrier-1 441. UE-2 is mapped to carrier-2-3 442. UE-3 is mapped
to carrier-4 443.
[0048] FIG. 5 shows exemplary diagrams for mapping of logical
control resources to physical resource in accordance with
embodiments of the current invention. One goal is to harvest
frequency diversity gain by mapping a short TTI region over
well-separated frequencies. For both DL and UL, in 1 ms, short TTIs
can be multiplexed with DL/UL normal TTIs in an interleaved fashion
in the frequency domain. Resources can be partitioned among short
TTIs (TTI at 1/3/4/7 OFDM symbol) and a normal TTI (14 OFDM
symbols)). A logical-to-physical mapping can be applied to
determine the PRBs taken by short TTIs. Two types of short TTI,
short TTI-1, and short TTI-2 are multiplexed with normal TTI1. The
five pairs of short TTIs are separated in the frequency domain by
taking the PRB24, PRB19, PRB14, PRB9, and PRB4.
[0049] Based on the short TTI transmission in the downlink, the
uplink resource for data and/or control transmission can be defined
or mapped to the corresponding short TTI transmission. The
relationship between the corresponding DL and UL transmission can
be static, semi-static, or dynamic. In one embodiment, the static
mapping is used. DL resource is received at time T1, uplink
resource is expected to be available at T2, wherein
T2=T1+Tproc_short and Tproc_short is the pre-defined processing
time for a specific short TTI subframe duration. In another
embodiment, dynamic mapping is used. No uplink resource is set
aside specifically for a certain type of downlink short TTI
transmissions. The uplink resource for data and/or control is
created on-demand according to the current downlink usage of a
regular TTI or various short TTIs.
[0050] FIG. 6 shows exemplary diagrams for the mapping of downlink
and uplink resources with short TTIs configured in accordance with
embodiments of the current invention. Two types of sTTIs are used
in the downlink, and two corresponding types of sTTIs are derived
and used in the uplink. Using the derivation or mapping rule from a
downlink resource to an uplink resource, just as in the downlink
case, no hard partition of resources between regular TTIs, short
TTIs, and different levels of short TTIs, such as spanning one half
of a regular TTI or a quarter of regular TTI, is necessary.
Resources for uplink transmission for data, control and channel
sounding, can be derived from a mapping rule on the fly. DL 600 has
multiple subframes with 1 ms, including SF-N, SF-N+1 SF-N+2,
SF-N+3, SF-N+4, and SF-N+8. Each subframes are configured with
different types of TTI resources, including sTTIs of different
types and normal TTIs. The uplink resources UL 610 can be mapped to
the configured DL resource 600 based on different rules. DL
resource 601, which is a short TTI with 1/4 of the normal TT, in
SF-N is mapped to UL resource 611, which is also mapped DL resource
602 in SF-N+2. Similarly, DL resource 603, which is a short TTI
with half of the normal TT, in SF-N is mapped to UL resource 612,
which is also mapped DL resource 604 in SF-N+4. DL resource 605,
which is a normal TT, in SF-N is mapped to UL resource 613, which
is also mapped DL resource 606 in SF-N+8.
[0051] In one novel aspect, for systems configured with short TTIs,
the uplink power control, downlink power control, and CSI feedback
transmission mode are configured and implemented for the low
latency transmission.
[0052] FIG. 7 shows an exemplary diagram for the uplink power
control, downlink power control, and CSI-feedback transmission mode
configurations in a short TTI configured system in accordance with
embodiments of the current invention. At step 701, the UE
determines that the short TTIs are configured. At step 711, UL
power control are configured accordingly. In the case more than on
data transmissions, over either the regular TTI or short TTIs are
sent to one UE within a regular TTI, there can be uplink resources
dynamically mapped in parallel corresponding to the downlink
transmissions. And in this case, the UE needs to adjust its
transmission power over each uplink resource according to the
priority or UE transmit power limit. In the case that there is a
shortage in uplink power and simultaneous transmissions of a short
TTI and regular TTI cannot be maintained with their respectively
desired power level, the transmission of the short TTI has a higher
priority over a regular TTI; and if multiple levels of short TTIs
and regular TTI are present, the shortest TTI has the highest
priority as its transmit power is first guaranteed. In the uplink,
as the operation point of sPUCCH/sPUSCH can be different from that
of PUCCH/PUSCH, for sPUCCH/sPUSCH, power control is configured
separately from those for PUCCH/PUSCH. At step 712, downlink power
control is configured accordingly. For downlink transmission, if
sPDSCH's demodulation is based on CRS, PA/PB for shortened TTIs can
be also set separately from those for regular TTIs. At step 713,
CSI procedures are configured accordingly. CSI feedback for
different TTIs can be introduced considering a number of factors.
The first factor is that the CSI feedback for short TTIs may demand
short feedback latency. The second factor is that the time
diversity for a transmission over a short TTI is much less than
that over a longer TTI, the most suitable transmission for the
short TTI can be different from that for a longer TTI. CSI feedback
mode can be set for each TTI type at a UE. There are also
motivations to configure different transmission modes for sPDSCH
and PDSCH: first to facilitate fast processing of sPDSCH, the
transmit scheme for sPDSCH can be different from that for PDSCH. In
one embodiment, only rank one transmission is used for sPDSCH.
second the justified overhead on a short TTI due to reference
signal and control can be also different from that on a regular
TTI, the suitable reference signal may be different for sPDSCH and
PDSCH; third for a short TTI, not much time diversity exists and it
is more important to harvest frequency diversity. From them, CSI
feedback, transmission mode can be configured differently for
sPDSCH and PDS.
Control Overhead Reduction
[0053] In LTE, two types of control channels are specified: PDCCH
and EPDCCH. With a 20 MHz channel, PDCCH can reside on one to three
OFDM symbols of a 14-OS TTI. Some REs are left unused. These REs
are not occupied by CRS, PDCCH, PCFICH or PHICH. For both PDCCH and
EPDCCH, a UE is not expected to detect the PDCCH and/or ePDCCH
intended for another UE. The unused REs are wasted resources.
[0054] To achieve latency reduction and give network scheduling
flexibility, a short TTI with self-contained control information
(named, sPDCCH) is desirable in general. If the same design
practice as highlighted above for LTE were followed, the overhead
due to wasted resource could be severe. Methods are provided to
multiplex data and control resources. Methods are also provided to
manage the overhead due to control information. In the downlink
control intended to a UE, the information for resources taken by
co-scheduled UEs' control information is provided. In essence, a
cover for the resources taken by co-scheduled UEs' control
information is provided to a UE. The cover does not have to be an
exact cover. In one embodiment, a superset is provided. For
example, it is allowed some REs, which are not used for any UE are
masked by the cover. One reason is a small number of options for
the cover reduces the cover's signaling overhead.
[0055] FIG. 8 shows exemplary diagrams for efficient multiplexing
of control and data for control overhead reduction in accordance
with embodiments of the current invention. System resource 801 and
system resource 802 both have a control region 810 and a data
region 820. For system resource 801, the REs in the first symbol of
the short TTI 810 are either used by control or left un-used as in
LTE (TDM). In general, neither TDM as in PDCCH/PDSCH nor FDM as in
EPDCCH/PDSCH is enough to partition resources between control and
data. As shown, REs 811-818 are used for sPDCCH for UE-1. REs
821-828 are used for sPDCCH for UE-2. Blocks of REs 851-856 of
control symbol 810 for system resource 801 are left unused. For
system resource 802, however, REs in the first symbol of the short
TTI 801 are not all dedicated to control. The unused REs are also
used for data. Hence the basic TDM/FDM rule can be enhanced or
modified according to resource usage at that moment. As seen, some
REs in 801 not used for control are used for data for UE-1,
including RE blocks of 861-864. Similarly, some REs in 801 not used
for control are used for data for UE-2, including RE blocks of 865
and 866.
[0056] To ensure the eNB and the UE have the same understanding of
the resource partition between control and data, dedicated
signaling or common signaling can be used to signal the control
resources taken by others. In one embodiment, dedicated signaling
is used. In another embodiment, common signaling to indicate the
resources used by all sPDCCHs, from this the leftover on the first
symbol can be used for data.
[0057] FIG. 9 illustrates an exemplary diagram for dedicated
signaling to indicate control resources taken by other UEs for
control overhead reduction in accordance with embodiments of the
current invention. The resources for other sPDCCHs are indicated in
each sPDCCH, which also allows the leftover on the first symbol to
be used for data. In one embodiment, in one short TTI, two UEs are
scheduled and each one's sPDCCH provides information about resource
usage of another UE. A control message for UE-1 is illustrated as
PDCCH-1 910. The contents of 910 includes a TTI type 911, a HARQ
process number 912, a new data indicator 913, a resource block
allocation 914, and resource used by PDCCH-2 915. The resource used
by PDCCH-2 915 points to the resource of PDCCH-2 920 for UE-2.
PDCCH-2 920 includes a TTI type 921, a HARQ process number 922, a
new data indicator 923, a resource block allocation 924, and
resource used by PDCCH-1 925. The resource used by PDCCH-1 925
points to the resource of PDCCH-1 910 for UE-1.
[0058] In one embodiment, the consideration in the cover design
considers providing a cover for CCEs of PDCCHs taken for other UEs
in a DCI intended for one UE. A similar procedure can be performed
for sPDCCH or sEPDCCH. In one embodiment, a method is provided to
enumerate all the starting CCE positions for different DCIs. In a
20 MHz LTE system, there are twenty-seven positions for Aggregation
level-1, level-13 positions for aggregation level-2, level-6
positions for level aggregation four, and three positions for
aggregation level-8. A bitmap for the cover is used. Twenty-seven
bits are needed. In another embodiment, a method is provided to
indicate a cover to exclude REs for data. The cover does not have
to be exact: for example, one bit is for a CCE at aggregation
level-2. A bit is set to one if the corresponding CCE is fully or
partially occupied. In total thirteen bits are used for the cover.
It is allowed to cover a DCI with four CCEs with the cover for
eight CCEs. It is allowed to cover a DCI with eight CCEs with the
cover for two resources: each resource is four CCEs.
Support for Ultra-Low Latency (ULL)
[0059] When an eNB has enough processing time to schedule sTTIs and
regular TTIs, the above-provided control channel design allows the
eNB to create sTTIs on the fly and UEs receive the necessary
signaling for sequential processing. Yet in ultra-low latency
communications, it may happen that an eNB may need to interrupt an
ongoing transmission, and allocate radio resources for the
ultra-low latency communication, the resource allocation overrides
the original resource allocation for the interrupted transmission.
The design framework given above can be still used for a UE
involved in the ULL communication. For example, dense candidate
locations are configured for the UE so the UE can be alerted about
ULL transmission with very short latency. However, if another UE,
which was originally instructed to receive a transmission, which is
now interrupted, can suffer catastrophically as its soft buffer
contains erroneous soft bits due to resource over-riding. In one
novel aspect, the eNB can alert the affected UE of the interruption
by signaling after the ULL transmission.
[0060] FIG. 10 illustrates exemplary diagrams for alert signals for
ULL support in accordance with embodiments of the current
invention. A resource 1010 includes a TTI-N and a TTI-N+1, which
follows TTI-N. In one embodiment, symbols in ULL 1011 are hijacked
by other communications. An alert signal 1012 was inserted in the
same TTI-N for 1010 to indicate to the UE assigned with 1010 that
resources are hijacked. In another embodiment, a resource 1020
includes a TTI-N and a TTI-N+1, which follows TTI-N. Symbols in ULL
1021 are hijacked by other communications. An alert signal 1022 was
inserted in the next subframe TTI-N+1 for 1020 to indicate to the
UE assigned with 1020 that resources are hijacked.
[0061] FIG. 11 illustrates exemplary flow charts for alter signal
in the same TTI for ULL support in accordance with embodiments of
the current invention. In one embodiment, the possible alert
timings are configured to a UE. Upon the arrival of the alert
timing, the UE can check if some specific resource regions are
over-ridden for ULL. If indeed that has happened, the UE can
discard the over-ridden resource before performing soft combining
operation. At step 1101, the UE receives downlink assignment for
resources. At step 1102, the UE checks within the same TTI whether
there exists an alert signal for ULL. In one embodiment, (method
1111), the time for the alert signal is preconfigured. If step 1102
determines yes, the UE moves to step 1103, and discards the soft
bits. In one embodiment, (method 1112), a resource which covers the
over-ridden resource is indicated. A superset of the over-ridden
resource is indicated. In another embodiment, a resource, which
covers most of the over-ridden resource while not covering all the
over-ridden resource to the affected UEs is indicated. The UE then
moves to step 1104 and performs channel decoding. If step 1102
determines no, the UE moves to step 1104 and performs channel
decoding.
[0062] FIG. 12 illustrates exemplary flow charts for alter signal
sent in the next TTI for ULL support in accordance with embodiments
of the current invention. In one embodiment, a control channel is
used in the next subframe to indicate the interruption as shown in
FIG. 11. In this case, in the control channel design, a unified
support for enhanced mobile broadband (eMBB) eMBB and ULL can be
enabled. At step 1201, the UE receives downlink assignment for
resources at subframe N. At step 1202, the UE receives control
region at subframe N+1. At step 1203, the UE checks in the control
region at subframe N+1 whether there exists an alert signal for
ULL. In one embodiment, (method 1211), the enabling of the control
region is through the eMBB and ULL service enablement. If step 1203
determines yes, the UE moves to step 1204, and discards the soft
bits. In one embodiment, (method 1212), a resource which covers the
over-ridden resource is indicated. A superset of the over-ridden
resource is indicated. In another embodiment, a resource, which
covers most of the over-ridden resource while not covering all the
over-ridden resource to the affected UEs is indicated. The UE then
moves to step 1205 and performs channel decoding. If step 1203
determines no, the UE moves to step 1205 and performs channel
decoding.
[0063] FIG. 13A illustrates an exemplary flow chart for a UE to
perform a short TTI configuration for low latency communication in
accordance with embodiments of the current invention. At step 1301,
the UE configures one or more downlink short transmission time
interval (sTTI) regions over a normal TTI region in a system
bandwidth in a wireless network, wherein the resources in the sTTI
regions have short TTI length. At step 1302, the UE decodes one or
more low latency control channels and one or more normal latency
control channels, wherein each low latency control channel
indicates one or more sTTI regions for one or more UEs in the
wireless network. At step 1303, the UE obtaining one or more sTTI
regions for the UE based on the decoded one or more low latency
control channels and the one or more normal latency channels.
[0064] FIG. 13B illustrates an exemplary flow chart for a base
station to perform a short TTI configuration for low latency
communication in accordance with embodiments of the current
invention. At step 1311, the base station configuring one or more
downlink short transmission time interval (sTTI) regions over a
normal TTI region in a system bandwidth in a wireless network,
wherein the resources in the sTTI regions have short TTI length. At
step 1312, the base station encodes one or more low latency control
channels and one or more normal latency control channels, wherein
each low latency control channel indicates one or more sTTI regions
for one or more UEs in the wireless network. At step 1313, the base
station transmits radio resources, wherein the radio resources
comprise one or more sTTI regions for one or more UEs.
[0065] FIG. 14A illustrates an exemplary flow chart for a UE to
perform control overhead reduction in accordance with embodiments
of the current invention. At step 1401, the UE configures one or
more short transmission time interval (sTTI) regions over a normal
TTI region in a system bandwidth in a wireless network, wherein the
sTTI regions are shared by the UE and one or more other UEs in the
wireless network, and wherein each UE includes a self-contained
control information sPDCCH occupying a control information region.
At step 1402, the UE detects a cover signal, wherein the cover
signal indicates one or more resource elements (REs) in the sPDCCH
control information region that can be used for data transmission.
At step 1403, the UE obtains data transmission from the REs in the
SPDCCH control information region based on the detected cover
signal.
[0066] FIG. 14B illustrates an exemplary flow chart for a base
station to perform control overhead reduction in accordance with
embodiments of the current invention. At step 1411, the base
station configures one or more short transmission time interval
(sTTI) regions over a normal TTI region in a system bandwidth in a
wireless network, wherein the sTTI regions are shared by one or
more user equipments (UEs) in the wireless network, and wherein one
or more sPDCCHs occupying a control information region is
configured for each corresponding UE. At step 1412, the base
station encodes a cover signal, wherein the cover signal indicates
one or more resource elements (REs) in the sPDCCH control
information region that can be used for data transmission. At step
1413, the base station transmits data information using the REs in
the SPDCCH control information region in accordance to the cover
signal.
[0067] FIG. 15A illustrates an exemplary flow chart for a UE to
perform ultra-low latency (ULL) procedure in accordance with
embodiments of the current invention. At step 1501, the UE receives
a downlink resource assignment at an assignment subframe in a
wireless network. At step 1502, the UE determines whether an
ultra-low latency (ULL) alert signal exists, wherein the ULL alert
signal indicates a set of soft bits are overridden. At step 1503,
the UE discards the set of soft bits from the overridden resources
upon determining the ULL alert signal exists. At step 1504, the UE
performs channel decoding based of the received downlink
resource.
[0068] FIG. 15B illustrates an exemplary flow chart for a base
station to perform ultra-low latency (ULL) procedure in accordance
with embodiments of the current invention. At step 1511, the base
station sends a downlink resource assignment to a user equipment
(UE) at an assignment subframe for a first communication in a
wireless network. At step 1512, the base station interrupts the
first communication by allocating a set of overridden soft bits in
the assigned downlink resource to the UE. At step 1513, the base
station encodes an ultra-low latency (ULL) alert signal, wherein
the ULL alert signal indicates the set of soft bits are overridden.
At step 1514, the base station sends the ULL alert signal to the
UE.
[0069] Although the present invention has been described in
connection with certain specific embodiments for instructional
purposes, the present invention is not limited thereto.
Accordingly, various modifications, adaptations, and combinations
of various features of the described embodiments can be practiced
without departing from the scope of the invention as set forth in
the claims.
* * * * *