U.S. patent application number 16/361390 was filed with the patent office on 2019-08-22 for unified flexible radio access technology (rat) for 5g mobile communication systems.
The applicant listed for this patent is National Instruments Corporation. Invention is credited to Nikhil U. Kundargi, James Wesley McCoy, Karl F. Nieman.
Application Number | 20190260549 16/361390 |
Document ID | / |
Family ID | 59962220 |
Filed Date | 2019-08-22 |
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United States Patent
Application |
20190260549 |
Kind Code |
A1 |
McCoy; James Wesley ; et
al. |
August 22, 2019 |
UNIFIED FLEXIBLE RADIO ACCESS TECHNOLOGY (RAT) FOR 5G MOBILE
COMMUNICATION SYSTEMS
Abstract
Embodiments are disclosed for a new unified and flexible frame
structure for 5G (5.sup.th generation) mobile telecommunications
standard and related radio access technology (RAT). The disclosed
embodiments use communication frames with multiple partition types
and are able to span a wide range of 5G deployment scenarios in a
flexible and scalable manner.
Inventors: |
McCoy; James Wesley;
(Leaner, TX) ; Kundargi; Nikhil U.; (Austin,
TX) ; Nieman; Karl F.; (Austin, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
National Instruments Corporation |
Austin |
TX |
US |
|
|
Family ID: |
59962220 |
Appl. No.: |
16/361390 |
Filed: |
March 22, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15270181 |
Sep 20, 2016 |
10243715 |
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16361390 |
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62317134 |
Apr 1, 2016 |
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62317371 |
Apr 1, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 5/0055 20130101;
H04L 27/26 20130101; H04L 5/0051 20130101; H04L 27/2602 20130101;
H04L 5/0007 20130101; H04W 72/1289 20130101; H04L 5/005
20130101 |
International
Class: |
H04L 5/00 20060101
H04L005/00; H04W 72/12 20060101 H04W072/12 |
Claims
1-30. (canceled)
31. A method, comprising: configuring, by a base station, a user
equipment (UE) with first and second partition types having
respective first and second numerologies of configuration
parameters; wherein the first and second partition types are
assigned to different types of communications; and wherein the
first and second numerologies comprise at least a subcarrier
spacing configuration parameter and a number of occupied
subcarriers configuration parameter.
32. The method of claim 31: wherein the types of communication
comprise two or more types from the list: control messages;
sounding reference signals (SRS) or sounding pilots; data
communications; hybrid automatic repeat request (HARD)
communications; and transmit acknowledgements.
33. The method of claim 31: transceiving, between the base station
and the UE, orthogonal frequency division multiplex (OFDM) symbols
using the configured first and second partition types.
34. The method of claim 31: using, by the UE, a common sampling
rate for the first and second partition types.
35. The method of claim 31: wherein the different partition types
are semi-statically configurable.
36. The method of claim 31: configuring, by the base station, other
UEs with other partition types having respective numerologies of
configuration parameters.
37. The method of claim 36: wherein said configuring, by the base
station, the other UEs with the other partition types having the
respective numerologies of configuration parameters comprises the
base station communicating control messages to the other UEs.
38. The method of claim 37: scheduling, by the base station,
uplink/downlink (UL/DL) messages to/from the base station and the
UEs to create a multi-resolution frame schedule that includes the
different partition types.
39. The method of claim 38: dynamically changing, by the base
station, the multi-resolution frame schedule that includes the
different partition types by communicating frame scheduling
messages to the UEs.
40. The method of claim 36: wherein the different partition types
compose a time frequency grid.
41. The method of claim 36: wherein the base station assigns the
partition types to the UEs based on a delay spread distribution of
the UEs in a cell serviced by the base station.
42. A base station, comprising: one or more antennas; one or more
radios coupled to the one or more antennas; and one or more
processors coupled to the one or more radios and programmed to:
configure a user equipment (UE) with first and second partition
types having respective first and second numerologies of
configuration parameters; wherein the first and second partition
types are assigned to different types of communications; and
wherein the first and second numerologies comprise at least a
subcarrier spacing configuration parameter and a number of occupied
subcarriers configuration parameter.
43. The base station of claim 42: wherein the types of
communication comprise two or more types from the list: control
messages; sounding reference signals (SRS) or sounding pilots; data
communications; hybrid automatic repeat request (HARD)
communications; and transmit acknowledgements.
44. The base station of claim 42: wherein the one or more
processors are further programmed to: transceive, between the base
station and the UE, orthogonal frequency division multiplex (OFDM)
symbols using the configured first and second partition types.
45. The base station of claim 42: wherein the different partition
types are semi-statically configurable.
46. The base station of claim 42: wherein the one or more
processors are further programmed to: configure other UEs with
other partition types having respective numerologies of
configuration parameters.
47. The base station of claim 46: wherein the base station
communicates control messages to the other UEs to configure the
other UEs with the other partition types having the respective
numerologies of configuration parameters.
48. The base station of claim 47: wherein the one or more
processors are further programmed to: schedule uplink/downlink
(UL/DL) messages to/from the base station and the UEs to create a
multi-resolution frame schedule that includes the different
partition types.
49. The base station of claim 48: wherein the one or more
processors are further programmed to: communicate frame scheduling
messages to the UEs to dynamically change the multi-resolution
frame schedule that includes the different partition types.
50. The base station of claim 46: wherein the different partition
types compose a time frequency grid.
51. The base station of claim 46: wherein the base station assigns
the partition types to the UEs based on a delay spread distribution
of the UEs in a cell serviced by the base station.
52. A user equipment (UE), comprising: one or more antennas; one or
more radios coupled to the one or more antennas; and one or more
processors coupled to the one or more radios and programmed to: be
configured, by a base station, with first and second partition
types having respective first and second numerologies of
configuration parameters; wherein the first and second partition
types are assigned to different types of communications; and
wherein the first and second numerologies comprise at least a
subcarrier spacing configuration parameter and a number of occupied
subcarriers configuration parameter.
53. The UE of claim 52: wherein the types of communication comprise
two or more types from the list: control messages; sounding
reference signals (SRS) or sounding pilots; data communications;
hybrid automatic repeat request (HARD) communications; and transmit
acknowledgements.
54. The UE of claim 52: one or more antennas; one or more radios
coupled to the one or more antennas; and one or more processors
coupled to the one or more radios and programmed to: transceive,
between the base station and the UE, orthogonal frequency division
multiplex (OFDM) symbols using the configured first and second
partition types.
55. The UE of claim 52: wherein the UE is configured to use a
common sampling rate for the first and second partition types.
56. The UE of claim 52: wherein the different partition types are
semi-statically configurable.
57. The UE of claim 52: wherein the one or more processors are
further programmed to: transceive uplink/downlink (UL/DL) messages
with the base station, along with other UEs, within a
multi-resolution frame schedule that includes the different
partition types.
58. The UE of claim 57: wherein the one or more processors are
further programmed to: communicate frame scheduling messages to the
UEs to dynamically change the multi-resolution frame schedule that
includes the different partition types.
59. The UE of claim 52: wherein the different partition types
compose a time frequency grid.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/270,181, filed Sep. 20, 2016, which claims
priority to provisional applications: U.S. Provisional Patent
Application Ser. No. 62/317,134, filed Apr. 1, 2016, and entitled
"UNIFIED FLEXIBLE RADIO ACCESS TECHNOLOGY (RAT) FOR 5G MOBILE
COMMUNICATION SYSTEMS," and U.S. Provisional Patent Application
Ser. No. 62/317,371, filed Apr. 1, 2016, and entitled "UNIFIED
FLEXIBLE RADIO ACCESS TECHNOLOGY (RAT) FOR 5G MOBILE COMMUNICATION
SYSTEMS," each of which is hereby incorporated by reference in its
entirety.
TECHNICAL FIELD
[0002] The disclosed embodiments relate to mobile
telecommunications.
BACKGROUND
[0003] The new radio definition in 3GPP (3.sup.rd Generation
Partnership Project) for mobile systems will encompass a variety of
deployment scenarios such as Rural, Urban Macro, Dense Urban,
Indoor, etc. with a gamut of requirements. For example, Rural will
require up to 5 kilometers (km) ISD (international subscriber
dialing) and high channel delay spread while Urban Macro has a 200
meter (m) ISD with pedestrian or stationary users.
SUMMARY
[0004] As described herein, a new unified and flexible frame
structure is disclosed for 5G (5.sup.th generation) mobile
telecommunications standard and related radio access technology
(RAT). The disclosed embodiments use communication frames with
multiple partition types and are able to span a wide variety of 5G
deployment scenarios in a flexible and scalable manner.
[0005] The disclosed embodiments include one or more of the
following features: [0006] A plurality of partition types with each
partition type having its own numerology. [0007] The numerology of
each partition type includes its unique set of parameters including
one or more of the following parameters: [0008] slot size, [0009]
number of symbols per slot, [0010] number of subcarriers, [0011]
number of occupied subcarriers, [0012] CP (cyclic prefix) length,
[0013] Pilot spacing, [0014] Modulation (OFDM (orthogonal frequency
division multiplexing), SC (suppressed carrier)), [0015] UL/DL
(uplink/downlink) periodicity, and/or [0016] Other parameters.
[0017] A method for coexistence and combination of these partition
types by aligning the numerologies at the type transition
boundaries in time and including the following feature: [0018] All
partition types will have a common baseline sampling rate, and/or
[0019] Other features. [0020] A multi resolution frame schedule
which includes these partition types and includes one or more of
the following features: [0021] The time frequency grid is composed
of a plurality of such partitions, [0022] In time domain, the
partitions are structured so that an integer number of slots of the
shortest one fits in one slot of the longest partition, and/or
[0023] Other features. [0024] A method for static, semi static or
dynamic changing of this multi resolution frame schedule; [0025] A
control channel to support the configuration of the unified
flexible RAT (radio access technology), and/or [0026] Other
features.
[0027] For one embodiment, an apparatus is disclosed including one
or more antennas, one or more radios coupled to the one or more
antennas, and one or more processors coupled to the one or more
radios and programmed to receive communication frames including
OFDM (orthogonal frequency division multiplex) symbols from a
plurality of wireless devices through the one or more radios and
the one or more antennas and to transmit communication frames
including OFDM symbols to the plurality of wireless devices through
the one or more radios and the one or more antennas. Each
communication frame includes a plurality of partition types having
a common baseline sampling rate. The plurality of partition types
include partition parameters including one or more of the
following: size of the time slots, number of symbols per time slot,
number of subcarriers, number of occupied subcarriers, cyclic
prefix length, pilot spacing, and uplink and downlink periodicity.
And each partition type has a unique set of configuration
parameters.
[0028] In additional embodiments, the one or more processors are
further configured to communicate control messages with the
plurality of wireless devices through the one or more radios and
the one or more antennas, and the control messages include
configuration parameters for the plurality of partition types. In
further embodiments, the control messages are communicated through
a control channel. In further embodiments, the control messages
include frame scheduling messages to determine time slots for
communications with the plurality of wireless devices. In still
further embodiments, the frame scheduling messages include
reconfiguration messages to reconfigure time slots for
communications with the plurality of wireless devices.
[0029] In additional embodiments, each partition type includes a
plurality of time slots, and each time slot includes a plurality of
OFDM symbols. In further embodiments, each OFDM symbol has a symbol
type, and the symbol type includes at least one of an uplink pilot,
a downlink pilot, uplink data, downlink data, sync, or guard. In
further embodiments, the time slots for each partition type have a
predetermined time length, and the predetermined time lengths are
different for different partition types. In still further
embodiments, the partition type having the shortest predetermined
time length for its time slots represents the shortest partition
type; the partition type having the longest predetermined time
length for its time slots represents the longest partition type;
and an integer number of time slots for the shortest partition type
fits within one time slot for the longest partition type. In other
embodiments, the plurality of partition types include two or more
partition types including a first partition type having times slot
with a predetermined time length of 0 1 milliseconds and a second
partition type having times slot with a predetermined time length
of 0.5 milliseconds. In other embodiments, the longest time slot
for the plurality of partition types is 0.5 milliseconds.
[0030] In additional embodiments, the plurality of partition types
include two or more partition types including a first partition
type and a second partition type; the first partition type is
shorter in time than the second partition type; and different types
of communications use different partition types. In further
embodiments, transmit and acknowledge messages communicated with
the plurality of wireless devices are configured to use the first
partition type. In further embodiments, sounding pilot
communications with the plurality of wireless devices are
configured to use the first partition type, and data communications
with the plurality of wireless devices are configured to use the
second partition type. In further embodiments, the plurality of
wireless devices include one or more first wireless devices having
a first cyclic prefix (CP) length and one or more second wireless
devices having a second cyclic prefix (CP) length with the first CP
length being shorter than the second CP length; the communications
with the one or more first wireless devices are configured to use
the first partition type; and the communications with the one or
more second wireless devices are configured to use the second
partition type.
[0031] For one embodiment, a method for wireless communications is
disclosed including receiving communication frames including OFDM
(orthogonal frequency division multiplex) symbols from a plurality
of wireless devices through one or more radios coupled to one or
more antennas and transmitting communication frames including OFDM
symbols to the plurality of wireless devices through the one or
more radios and the one or more antennas. Each communication frame
includes a plurality of partition types having a common baseline
sampling rate. The plurality of partition types include partition
parameters including one or more of the following: size of the time
slots, number of symbols per time slot, number of subcarriers,
number of occupied subcarriers, cyclic prefix length, pilot
spacing, and uplink and downlink periodicity. And each partition
type has a unique set of configuration parameters.
[0032] In further embodiments, the method also includes
communicating control messages with the plurality of wireless
devices through the one or more radios and the one or more
antennas, and the control messages include configuration parameters
for the plurality of partition types. In further embodiments, the
method further includes communicating the control messages through
a control channel. In further embodiments, the control messages
include frame scheduling messages to determine time slots for
communications with the plurality of wireless devices. In still
further embodiments, the frame scheduling messages include
reconfiguration messages to reconfigure time slots for
communications with the plurality of wireless devices.
[0033] In further embodiments, each partition type includes a
plurality of time slots, and each time slot includes a plurality of
OFDM symbols. In further embodiments, each OFDM symbol has a symbol
type, and the symbol type includes at least one of an uplink pilot,
a downlink pilot, uplink data, downlink data, sync, or guard. In
further embodiments, the time slots for each partition type have a
predetermined time length, and the predetermined time lengths are
different for different partition types. In still further
embodiments, the partition type having the shortest predetermined
time length for its time slots represents the shortest partition
type; the partition type having the longest predetermined time
length for its time slots represents the longest partition type;
and an integer number of time slots for the shortest partition type
fits within one time slot for the longest partition type. In other
embodiments, the plurality of partition types includes two or more
partition types including a first partition type having times slot
with a predetermined time length of 0 1 milliseconds and a second
partition type having times slot with a predetermined time length
of 0.5 milliseconds. In other embodiments, the longest time slot
for the plurality of partition types is 0.5 milliseconds.
[0034] In additional embodiments, the plurality of partition types
include two or more partition types including a first partition
type and a second partition type; the first partition type is
shorter in time than the second partition type; and different types
of communications use different partition types. In further
embodiments, the method also includes communicating transmit and
acknowledge messages using the first partition type. In further
embodiments, the method also includes communicating sounding pilots
using the first partition type and communicating data using the
second partition type. In further embodiments, the plurality of
wireless devices include one or more first wireless devices having
a first cyclic prefix (CP) length and one or more second wireless
devices having a second cyclic prefix (CP) length with the first CP
length being shorter than the second CP length, and the method
further includes using the first partition type to communicate with
the one or more first wireless devices and using the second
partition type to communicate with the one or more second wireless
devices.
[0035] Other variations can also be implemented while still taking
advantage of the dynamic and flexible frame structure embodiments
and related components described herein.
DESCRIPTION OF THE DRAWINGS
[0036] It is noted that the appended drawings illustrate only
exemplary embodiments and are, therefore, not to be considered
limiting of the scope of the present inventions, for the inventions
may admit to other equally effective embodiments.
[0037] FIG. 1 is a diagram of an example embodiment for the frame
structure of two consecutive slots of a partition.
[0038] FIG. 2 is a diagram of an example embodiment for a structure
for a UL Pilot symbol for the two slots shown in FIG. 1.
[0039] FIG. 3 is a diagram of an example embodiment for a frame
structure for a single partition type.
[0040] FIGS. 4-5 are diagrams of example embodiments for variations
of the frame structure shown in FIG. 1.
[0041] FIG. 6 is a diagram of an example embodiment for Partition
Type I.
[0042] FIG. 7 is a diagram of an example embodiment for Partition
Type II.
[0043] FIG. 8 is a diagram of an example embodiment for a unified
flexible frame structure with mixed Partition types.
[0044] FIG. 9 is a swim lane diagram of an example embodiment for
multi-partition frame configuration and scheduling between a base
station and multiple UEs.
[0045] FIG. 10 is a diagram of an example embodiment for electronic
components that can be used to implement a base station, user
equipment (UE) and/or other processing systems for the disclosed
embodiments.
[0046] FIG. 11 is a block diagram illustrating MIMO communications
in a wireless propagation environment, according to some
embodiments.
[0047] FIG. 12 is a block diagram illustrating exemplary send and
receive processing chains for reciprocity-based MIMO, according to
some embodiments.
[0048] FIG. 13 is a block diagram illustrating a portion of an
exemplary massive MIMO system configured to distribute processing,
according to some embodiments.
[0049] FIG. 14 is a block diagram illustrating an exemplary
software radio peripheral, according to some embodiments.
[0050] FIG. 15 is a block diagram illustrating a hardware system
configured to implement a massive MIMO base station, according to
some embodiments.
[0051] FIG. 16 is a flow diagram illustrating a method for MIMO
processing according to some embodiments.
[0052] FIG. 17 is a diagram illustrating exemplary LTE TDD frame
configurations, according to some embodiments.
[0053] FIG. 18 is a diagram illustrating an exemplary frame
structure for reciprocity-based massive MIMO communications,
according to some embodiments.
DETAILED DESCRIPTION
[0054] A new unified and flexible frame structure for 5G (5.sup.th
generation) mobile telecommunications standard and related radio
access technology (RAT) is disclosed that is able to span a wide
variety of deployment scenarios (e.g., Rural, Urban Macro, Dense
Urban, Indoor, etc.) in a flexible and scalable manner.
[0055] Massive MIMO (multiple input, multiple output) communication
systems can be used for 5G dynamic TDD (time division duplex) air
interfaces. In particular, massive MIMO reciprocity-based TDD air
interfaces allow for symbol-level switching and potential
configurability that in turn allow for features to support three
primary aspects of 5G air interfaces, namely enhanced Mobile
BroadBand (eMBB), massive Machine Type Communications (mMTC) and
Ultra-Reliable and Low Latency Communications (URLLC). Example
embodiments for massive MIMO communication systems and related
signaling and frame structures are described within U.S. Published
Patent Application 2015/0326291, entitled "SIGNALING AND FRAME
STRUCTURE FOR MASSIVE MIMO CELLULAR TELECOMMUNICATION SYSTEMS,"
which is hereby incorporated by reference in its entirety.
[0056] The disclosed unified and flexible frame structure described
herein with respect to FIGS. 1-10 can be used as a new dynamic and
flexible signaling and frame structure for dynamic TDD air
interfaces, such as for example the massive MIMO cellular
telecommunication systems described in U.S. Published Patent
Application 2015/0326291. FIGS. 11-18 described below provide
example embodiments also described within U.S. Published Patent
Application 2015/0326291. Example system objectives, components,
and features are now described in more detail. It is further noted
that different and/or additional features can also be implemented
as desired and related systems and methods can be utilized as
well.
Dynamic TDD Radio Interface Description
[0057] A new proposed frame structure for the New Radio (NR)
includes one or more of the following features: (1) faster TDD
switching, (2) symbol level reconfigurable dynamic TDD, and (3)
higher UL sounding pilot periodicity contained within a flexible
numerology, as well as other advantageous features.
[0058] Faster TDD switching--Typical channel coherence time for
Rural and Urban macro deployment scenarios with high mobility UEs
(user equipment) can be on the order of 500-1000 microseconds
(.mu.s). The legacy TDD LIE (long term evolution) systems can
switch at either 5 milliseconds (ms) or 10 ms. Channel reciprocity
based systems use UL (uplink) channel estimates as proxy for
downlink CSI (channel state information) and this is accurate only
within the channel coherence time. The legacy 5 ms switching
periodicity is not fast enough to enable channel reciprocity based
operation. The new frame structure disclosed herein advantageously
supports UL-DL switching periodicity faster than the channel
coherence times.
[0059] Symbol level reconfigurable Dynamic TDD--With legacy Dynamic
TDD in LTE, the frame type can be reconfigured from mostly DL
(downlink) to mostly UL depending on traffic in cell. For low
latency applications and high flexibility, the new frame structure
disclosed herein advantageously extends this Dynamic TDD to support
the designation of UL and DL on a per symbol basis.
[0060] Higher UL sounding pilot periodicity--The frame structure
disclosed herein is scalable to Massive MIMO communication systems.
It supports channel reciprocity based beamforming for Massive MIMO
if UL sounding signals are sent at least once within the worst case
channel coherence time. In addition, for the new frame structure
disclosed herein, one UL pilot symbol can be sent every 0.5 ms.
This UL pilot symbol implementation for the new frame structure
advantageously enables support of high mobility scenarios.
[0061] FIGS. 1-10 provide example embodiments for a new dynamic and
flexible frame structure that provides one or more of these
features: (1) faster TDD switching, (2) symbol level reconfigurable
dynamic TDD, and (3) higher UL sounding pilot periodicity, as well
as other advantageous features.
[0062] The UL/DL switching time is configurable and, in certain
embodiments, the fastest supported switching periodicity is once
every symbol. Every symbol can be defined as either UL Pilot, DL
Pilot, UL Data, DL Data, Sync or Guard, and signalling support is
provided to redefine the symbol type. The UE-specific UL Pilots are
transmitted with a periodicity of once every 0.5 ms to support
channel reciprocity and high mobility of UEs. DL pilots can be
embedded in DL data or in a dedicated DL Pilot symbol. One guard
symbol can also be included in every frame for timing
adjustment.
[0063] The new radio interface described herein is configured to
have a higher bandwidth per component carrier (CC). For certain
embodiments, a bandwidth of 100 MHz can be used as the basic unit
per CC. Two example embodiments are provided below that partition
the time and frequency domain resources of the channel both loosely
based on the LTE Advanced numerology.
[0064] In particular, the following are two example embodiments
that partition channels for the dynamic frame structure embodiments
described herein: [0065] Partition I: 75 kHz subcarrier spacing
(5.times. legacy .DELTA.f, 1/5.sup.th of legacy symbol duration)
[0066] Partition II: 15 kHz subcarrier spacing, legacy symbol
duration [0067] For each, we choose a FFT (Fast Fourier Transform)
size to satisfy the following constraints: (1) FFT size is a power
of 2, and (2) Target occupied bandwidth of 90%.
[0068] TABLE 1 below provides example numerology including field
types and parameters for Partition I and Partition II.
TABLE-US-00001 TABLE 1 EXAMPLE FIELD TYPES AND PARAMETERS FOR
PARTITIONS FOR DYNAMIC FRAME STRUCTURE Field Description of type
Parameter Partition I Partition II f.sub.SC Sub-carrier spacing 75
kHz 15 kHz T.sub.Sym Symbol duration 13.3 .mu.s 66.66 .mu.s F.sub.s
Sampling rate 153.6 MS/s 153.6 MS/s N.sub.FFT FFT length 2048 10240
(2048*5) N.sub.CP Cyclic prefix length Short: 160 for 800 for
symbol 0 symbol 0 and and 720 for symbol 144 for symbol 1-6 1-6
Long: 512 N.sub.OccupiedSC Number of occupied 1200 6000
sub-carriers T.sub.slot Slot duration 0.1 ms 0.5 ms
[0069] It is noted that in Partition I, the sampling rate is
increased by 5.times. but the legacy number of subcarriers per
symbol is maintained. The symbol duration is scaled down by
5.times. to 13.3 microseconds. In Partition II, the legacy
subcarrier spacing is maintained but the number of subcarriers is
increased by 5.times.. Hence, the sampling frequency is also scaled
up 5.times. to oversample the 100 MHz bandwidth by an oversampling
factor of 1.53.
[0070] FIGS. 1-10 will now be described in more detail.
[0071] FIG. 1 is a diagram of an example embodiment 10 for the
frame structure of two consecutive slots of a partition. A subframe
includes two consecutive slots as indicated by subframe duration 12
and slot duration 14 and associated maximum (max) coherence time
16. Each slot has an Uplink (UL) Pilot symbol as its first symbol
(and FIG. 2 below provides details for the structure of this UL
Pilot symbol). Following the UL pilot, the 2.sup.nd, 3.sup.rd, and
4.sup.th symbols are UL Data symbols, and the 5.sup.th, 6.sup.th,
and 7.sup.th symbols are Downlink (DL) Data symbols. For the
Massive MIMO deployment where a UL channel estimate is derived from
the UL Pilot, the 1.sup.st symbol for each slot is used to compute
the precoded DL data symbols starting from the 5.sup.th symbol as
indicated by arrow 18.
[0072] FIG. 2 is a diagram of an example embodiment 20 for a
structure for the UL Pilot symbols for the two slots shown in FIG.
1. The UL Pilot symbol 22 includes N RBs (Resource Blocks) where
each RB includes 12 subcarriers 24. As an example, for a 100 MHz
bandwidth with 2048 subcarriers and 1200 Occupied subcarriers,
there are N=1200/12=100 RBs. Within each RB, every UE gets a
dedicated subcarrier to transmit its pilot symbol, and there is one
RE (Resource Element) per UE pilot. All UEs transmit orthogonal
pilots as they are separated in frequency. This particular
structure supports 12 UEs. It is noted, however, that different
numbers of UEs could also be supported, as desired. For example,
where 24 UEs are supported, each UE can be allocated a reserved
subcarrier in every alternate RB. Other variations could also be
implemented.
[0073] FIG. 3 is a diagram of an example embodiment 30 for a frame
structure for a single partition type where the frame includes 20
slots, each slot including 7 symbols. As compared to prior
solutions, this frame structure has increased frequency of
transmission of UL pilots, for example, once every 7 symbols which
is once for each slot. This increased periodicity of UL pilots
enables operation based on channel reciprocity as this precoding
happens within the channel coherence time.
[0074] FIGS. 4-5 are diagrams of example embodiments for variations
of the frame structure shown in FIG. 1. FIGS. 4-5 shows that the
ratio of UL to DL traffic can change (dynamically or in a static
way). For the example embodiment 40 of FIG. 4, only UL data
transmissions are included within the two-slot subframe 12 along
with the UL pilot without any DL data traffic. For the example
embodiment 50 of FIG. 5, one UL data transmission and 5 DL data
transmissions are included along with the UL pilot for each slot
within the two-slot subframe 12.
[0075] It is noted that for the example embodiment of FIG. 5, the
DL data traffic has been maximized under a channel reciprocity
based operation for Massive MIMO deployment. It is also noted that
there is at least one symbol between the UL pilot and the DL
symbols. This one symbol gap is shown as a UL Data symbol in the
example of FIG. 5; however, this symbol could also be a guard
symbol or other desired symbol type. This one symbol gap allows for
channel estimation and precoding to happen.
[0076] FIG. 6 is a diagram of an example embodiment 60 for
Partition Type I with the numerology shown in TABLE 1 above.
[0077] FIG. 7 is a diagram of an example embodiment 70 for
Partition Type II with the numerology shown in TABLE 1 above.
[0078] FIG. 8 is a diagram of an example embodiment 80 for a
unified flexible frame structure. In this example embodiment, 5
slots of Partition I are followed by 3 slots of Partition II which
is in turn followed by 10 slots of Partition I. Each partition type
includes a plurality of time slots (e.g. 7 slots), and each time
slot includes a plurality of symbols such as OFDM symbols.
Further Description of New Frame Structure
[0079] CP Overhead--The new frame structure is designed with a CP
(cyclic prefix) duration that addresses the Rural and Urban macro
deployment scenarios, which can have an ISD of up to 5 km. TABLE 2
below compares CP overhead for the example frame types, under the
assumption of legacy CP duration of .about.5 .mu.s (microseconds).
Partition I with a long CP has higher CP overhead than Partition
II. Partition I with a short CP has a CP duration which is reduced
by the same factor as the symbol duration reduction as in TABLE 1
above, at an adverse cost to the delay spread supported.
[0080] As one observation, it is noted that Partition I increases
the CP length enabling use in rural and urban macro scenarios while
maintaining low latency operation required for eMBB operation.
TABLE-US-00002 TABLE 2 EXAMPLE PARAMETERS FOR CP OVERHEAD FOR
DYNAMIC FRAME STRUCTURE Partition Type I Partition Type I Partition
Frame Type (Short CP) (Long CP) Type II CP Overhead 6.6% 20%
6.6%
[0081] Latency Reduction--Layer 1 latency is determined to a large
extent by HARQ (hybrid automatic repeat request) round trip delay
and the TTI. Reducing the symbol duration to 13.3 .mu.s from 66.6
.mu.s will support shorter TTI (transmission time interval) and
also reduce the HARQ RTT (round trip time) latency. Frames for
Partition Type I are superior to frames for Partition Type II from
a latency reduction perspective due to its 5.times. shorter symbol
and slot duration. Other channel coding techniques not requiring
HARQ may also be considered.
[0082] As another observation, it is noted that the flexible frame
structure embodiments described herein allow for control of the
latency based on the selected numerology for a given
allocation.
[0083] Flexible Dynamic RAT--Partition Types I & II are two
example partitions. The new radio interface described herein
provides for seamless coexistence of a multitude of such partitions
optimized for different deployment scenarios. In particular, the
framework described herein is a flexible dynamic RAT that provides
this seamless coexistence. For this framework, each partition
numerology is chosen such that an integer number of slots fits in
the longest partition slot (0.5 ms). Further, a frame schedule of
different partition types can be applied on a static, semi-static
or dynamic basis. FIG. 8 shows an example frame schedule that
includes a mix of Partition Types I & II.
[0084] It is also noted that the uplink/downlink (UL/DL) interval
for transmit and acknowledge (ACK) can be shrunk by using a short
partition type (e.g., Partition Type I above). In this case,
latency is reduced along with a simultaneous reduction in per OFDM
symbol throughput. This reduction may be helpful, for example, to
shorten transmit to ACK turnaround.
[0085] In addition, it is noted that channel state information
obtained using a sounding pilot or SRS (sounding reference signal)
can be compressed in time (and frequency) to reduce link overhead
by using a short partition type (e.g., Partition Type I above). By
using a short partition type, there is some loss in frequency
resolution. However, high resolution is not needed, for example,
with respect to downlink beamforming. As such, short partition
types can be used in such circumstances to reduce the SRS overhead
in a radio frame.
[0086] Further, it is noted that different types of communications
can be configured to use different partition types, and this
configuration can be dynamically assigned. For example, control
messages and SRS or sounding pilots can be assigned to one
partition type, and data communications can be assigned to a
different partition type. In other words, different partition types
within a multi-partition frame can be assigned to different
communication types as part of frame scheduling.
[0087] Still further, it is noted that different partition types
can be used when there are different CP (cyclic prefix)
requirements for different UEs. Some UEs may have long delay
spreads whereas others may have short delay spreads. The short
delay spread UEs can be scheduled into a short partition type
(e.g., Partition Type I above) to reduce CP overhead of the link.
The long delay spread UEs can be scheduled into a long partition
type (e.g., Partition Type II above). These partition types can
also be dynamically assigned as needed depending on the delay
spread distribution of the UEs in a cell.
[0088] FIG. 9 is a swim lane diagram of an example embodiment 90
for multi-partition frame configuration and scheduling between a
base station 92 and first UE 94 and between the base station 92 and
a second UE 96. For the example embodiment 90 shown in FIG. 9,
connection requests are sent from UE 94 to the base station 92 and
from UE 96 to the base station 92. Connection responses are then
sent from the base station 92 to the UE 94 and from the base
station 92 to the UE 96. Control messages are then communicated
between the base station 92 and the UE 94 that include
configuration (CONFIG) parameters for a first partition type (e.g.,
Partition Type I described above). Control messages are
communicated between the base station 92 and the UE 96 that include
configuration (CONFIG) parameters for a second partition type
(e.g., Partition Type II described above). Frame scheduling
messages are communicated from the base station 92 to the UEs 94/96
to schedule UL/DL messages within a multi-partition frame. UL/DL
messages are then communicated between the base station 92 and the
UEs 94/96 within the multi-partition frame as indicated by arrows
98. In addition, the frame scheduling can be reconfigured through
additional reconfiguration messages communicated from the base
station 92 to the UEs 94/96 that reconfigure the frame scheduling
for the multi-partition frame. It is noted that FIG. 9 provides one
example embodiment and that other variations could also be
implemented while still taking advantage of the dynamic and
flexible frame structure embodiments and related components
described herein.
[0089] FIG. 10 is a diagram of an example embodiment 1000 for
electronic components that can be used to implement a base station,
user equipment (UE), and/or other processing systems for the
disclosed embodiments. For the example embodiment 1000 shown in
FIG. 10, one or more processors 1008 communicate with other
components through system bus interconnect 1002. For example, the
one or more processors 1008 communicate with input/output (I/O)
circuitry 1004 and transmit/receive (TX/RX) circuitry 1006 through
the system bus interconnect 1002. Additional circuitry can also be
included such as power supply circuitry and/or other desired
circuitry. The TX/RX circuitry 1006 can be used to provide, for
example, a 5G cellular MIMO radio and/or other desired radios. The
I/O circuitry 1004 can be used to provide one or more interfaces
for users and/or peripherals. The memory 1110 is also coupled to
the system bus interconnect 1002 and can be used by the one or more
processors 1008 to load and/or store instructions, data, and/or
other information during operation. One or more data storage
device(s) 1112 are also connected to the system bus interconnect
1002 and can store software or program instructions and/or other
desired data or information for the operation of the processing
system. For example, computer-readable instructions stored in the
data storage devices 1112 can be loaded within the memory 1110 and
then executed by the processor(s) 1008 to carry out the functions
described herein.
[0090] It is noted that different and/or additional components from
those depicted in FIG. 10 could also be used to implement one or
more processing systems for the embodiments described herein while
still taking advantage of the dynamic and flexible frame structure
embodiments and related components described herein. It is further
noted that the system bus interconnect 1002 can be implemented as
multiple interconnection buses with our without additional
intervening circuitry such as routing or switching circuitry.
Further, the processor(s) 1008 can be implemented using one or more
processing devices including controllers, microcontrollers,
microprocessors, hardware accelerators, configurable logic devices
(e.g., field programmable gate arrays), and/or other programmable
integrated circuits that are programmed to carry out the function
described herein. Further, the one or more processor(s) 1008 can
execute instructions stored in a non-transitory tangible
computer-readable medium to perform the functions described herein.
In addition, data storage device(s) 1112 can be implemented as any
desired non-transitory tangible medium that stores data, such as
data storage devices, FLASH memory, random access memory, read only
memory, programmable memory devices, reprogrammable storage
devices, hard drives, floppy disks, DVDs, CD-ROMs, and/or any other
non-transitory data storage mediums. The memory 1110 can be any
data storage medium configured to maintain data storage when
powered. Other variations could also be implemented.
[0091] As described herein, therefore, a new flexible and dynamic
frame structure is disclosed that is suitable for Massive MIMO.
This frame structure is also suitable for ITU (International
Telecommunication Union) IMT-2020 deployment scenarios. A number of
extensions were also presented for numerology to 100 MHz channels
based on this new flexible and dynamic frame structure. Other
variations are described and can also be implemented.
[0092] It is noted that the functional blocks described herein can
be implemented using hardware, software, or a combination of
hardware and software, as desired. In addition, one or more
processors or programmable integrated circuits running software
and/or firmware can also be used, as desired, to implement the
disclosed embodiments. It is further understood that one or more of
the operations, tasks, functions, or methodologies described herein
may be implemented, for example, as software or firmware and/or
other program instructions that are embodied in one or more
non-transitory tangible computer readable mediums (e.g., memory)
and that are executed by one or more controllers, microcontrollers,
microprocessors, hardware accelerators, and/or other processors or
programmable integrated circuits to perform the operations and
functions described herein.
[0093] It is further noted that the functional blocks, devices,
and/or circuitry described herein can be implemented using
hardware, software, or a combination of hardware and software. In
addition, one or more processors (e.g., central processing units
(CPUs), controllers, microcontrollers, microprocessors, hardware
accelerators, programmable integrated circuitry, FPGAs (field
programmable gate arrays), ASICs (application specific integrated
circuits), and/or other programmable processing circuitry) can be
programmed to perform the operations, tasks, functions, or actions
described herein for the disclosed embodiments. For example, the
one or more electronic circuits can be configured to execute or
otherwise be programmed with software, firmware, logic, and/or
other program instructions stored in one or more non-transitory
tangible computer-readable mediums (e.g., data storage devices,
flash memory, random access memory, read only memory, programmable
memory devices, reprogrammable storage devices, hard drives, floppy
disks, DVDs, CD-ROMs, and/or any other tangible data storage
medium) to perform the operations, tasks, functions, or actions
described herein for the disclosed embodiments.
[0094] It is still further noted that the functional blocks,
components, systems, devices, and/or circuitry described herein can
be implemented using hardware, software, or a combination of
hardware and software. For example, the disclosed embodiments can
be implemented using one or more programmable integrated circuits
that are programmed to perform the functions, tasks, methods,
actions, and/or other operational features described herein for the
disclosed embodiments. The one or more programmable integrated
circuits can include, for example, one or more processors and/or
PLDs (programmable logic devices). The one or more processors can
be, for example, one or more central processing units (CPUs),
controllers, microcontrollers, microprocessors, hardware
accelerators, ASICs (application specific integrated circuit),
and/or other programmable integrated circuits. The one or more PLDs
can be, for example, one or more CPLDs (complex programmable logic
devices), FPGAs (field programmable gate arrays), PLAs
(programmable logic array), reconfigurable logic circuits, and/or
other integrated logic devices. Further, the programmable
integrated circuits, including the one or more processors, can be
configured to execute software, firmware, code, and/or other
program instructions that are embodied in one or more
non-transitory tangible computer-readable mediums to perform the
functions, tasks, methods, actions, and/or other operational
features described herein for the disclosed embodiments. The
programmable integrated circuits, including the one or more PLDs,
can also be programmed using logic code, logic definitions,
hardware description languages, configuration files, and/or other
logic instructions that are embodied in one or more non-transitory
tangible computer-readable mediums to perform the functions, tasks,
methods, actions, and/or other operational features described
herein for the disclosed embodiments. In addition, the one or more
non-transitory tangible computer-readable mediums can include, for
example, one or more data storage devices, memory devices, flash
memories, random access memories, read only memories, programmable
memory devices, reprogrammable storage devices, hard drives, floppy
disks, DVDs, CD-ROMs, and/or any other non-transitory tangible
computer-readable mediums. Other variations can also be implemented
while still taking advantage of the reciprocity compensation
techniques described herein.
[0095] FIGS. 11-18 will now be described in more detail and provide
example embodiments from U.S. Published Patent Application
2015/0326291.
[0096] As indicated above, massive MIMO (multiple input, multiple
output) communication systems can be used for 5G dynamic TDD (time
division duplex) air interfaces. In particular, massive MIMO
reciprocity-based TDD air interfaces allow for symbol-level
switching and potential configurability that in turn allow for
features to support three primary aspects of 5G air interfaces,
namely enhanced Mobile BroadBand (eMBB), massive Machine Type
Communications (mMTC) and Ultra-Reliable and Low Latency
Communications (URLLC). Example embodiments for massive MIMO
communication systems and related signaling and frame structures
are described within U.S. Published Patent Application
2015/0326291, entitled "SIGNALING AND FRAME STRUCTURE FOR MASSIVE
MIMO CELLULAR TELECOMMUNICATION SYSTEMS," which is hereby
incorporated by reference in its entirety.
[0097] Looking first to FIGS. 11-16, example embodiments are
provided for a massive MIMO communication system described in U.S.
Published Patent Application 2015/0326291.
[0098] FIG. 11 shows an exemplary MIMO system 100 that includes
base station 102 and M mobile devices 106A-M (which may also be
referred to as user equipment devices or UEs 106A-M). In the
illustrated embodiment, base station 102 includes N antennas
configured to transmit and receive data with mobile devices 106
using time-division duplexing (TDD). In other embodiments, other
transmission techniques may be used including frequency-division
duplexing (FDD), for example.
[0099] In system 100, mobile devices 106 may concurrently
communicate with base station 102 via wireless propagation
environment. The paths taken by different signals may vary among
the mobile devices, e.g., based on their location in the
environment. Therefore, using MIMO techniques to precode signals
transmitted by the base station, for example, may greatly improve
overall radio capacity, performance, and/or range. Thus, base
station 102 may allocate multiple antennas (e.g., as many as ten or
more in some massive MIMO systems) to a given mobile device 106. To
configure allocation, in some embodiments, mobile devices may
concurrently transmit a known pattern to the base station in a
particular time or frequency slot. Base station 102 may compare the
pattern across a number of antennas to determine the unique channel
characteristics to each spatially diverse path for the different
UEs. Subsequently, the base station may apply the inverse of
channel characteristic parameters as a form of precoding, such that
each mobile device 106 receives its intended messages.
[0100] Speaking generally, MIMO techniques may increase capacity,
performance, and/or range of wireless communications. Although
various embodiments are discussed herein in the context of cellular
communications, these embodiments are not intended to limit the
scope of the present disclosure. Rather, the disclosed techniques
may be used in various wireless communication contexts, such as
WIFI, for example.
[0101] FIG. 12 shows exemplary send and receive chains for
reciprocity-based MIMO for two antennas, which may be included in
MIMO base station 102, for example. In the illustrated embodiment,
analog-to-digital (A/D) converters 212A-N demodulate and digitize
received uplink signals from RF. Down-samplers 214A-N down-sample
the digital samples to a desired sampling rate, e.g., that is some
fraction of the A/D sampling rate. Subsequently, units 216A-N,
218A-N, 220A-N, and 222A-N perform OFDM signal processing,
including removing the cyclic prefix (CP), performing a Fast
Fourier Transform (FFT) after serial-to-parallel conversion,
removing guard subcarriers, and de-allocating uplink data and
pilots to the resource map. Base station 102 may then pass pilot
and data symbols for all N receive chains to channel estimator
250.
[0102] Channel estimates generated by channel estimator 250, in the
illustrated embodiment, are used by MIMO decoder 240 to decode M
uplink data streams and by MIMO precoder 260 to precode M downlink
data streams.
[0103] The precoded downlink data streams, in the illustrated
embodiment, are then processed by units 224A-N, 226A-N, 228A-N, and
230A-N, including resource mapping, adding guard symbols, serial-to
parallel conversion, performing an inverse FFT, and adding the
cyclic prefix. Subsequently, units 232A-N up-convert the data from
the baseband rate and digital to analog converters (D/As) 234A-N
convert the result for transmission via the antennas.
[0104] Various disclosed techniques address challenges when adding
a large number of receive and transmit chains to a system, as in
massive MIMO. In some embodiments, software defined radios are used
to implement a massive MIMO system that is configurable, modular,
meets I/O requirements for distributed processing, and supports
real-time processing for large numbers of antennas.
[0105] FIG. 13 is a block diagram illustrating a subsystem of one
embodiment of a massive MIMO system 300. System 300 may be included
in base station 102, for example. In some embodiments, system 300
is configured to perform at least a portion of the processing
described above with reference to FIG. 12 in a distributed manner.
In the illustrated embodiment, the subsystem includes front-end
TX/RX units 302A-N, antenna combiner 310, antenna splitter 315,
bandwidth splitter 320, bandwidth combiner 325, channel estimator
330, MIMO detector 340, and MIMO precoder 345. In the illustrated
embodiment, link quality evaluator 350 and data source 360 are
included in a central control unit that is shared among multiple
subsystems (as indicated by the vertical dashed lines, delineating
units included in the central controller, according to this
embodiment).
[0106] Other subsystems of system 300 (not shown), in the
illustrated embodiment, include additional MIMO detectors, MIMO
precoders, bandwidth splitters, and bandwidth combiners. For
example, in an embodiment in which the subsystem of FIG. 13
includes eight TX/RXs 302 and the system includes six subsystems,
96 antennas may be used. MIMO processing, in the illustrated
embodiment, is distributed among various processing elements. This
may allow baseband processing to be partitioned across multiple
FPGAs, for example. This may facilitate scaling of massive MIMO
systems far beyond what a single centralized processing unit could
achieve for real-time baseband processing.
[0107] TX/RX units 302A-N, in some embodiments, are included in
software defined radio modules, which may also include processing
elements configured or configurable to perform the functionality of
various other units shown in FIG. 13. For example, TX/RX 302A and
antenna combiner 310 may be implemented by the same SDR element. An
exemplary embodiment of a peripheral configured to implement an SDR
is discussed in further detail below with reference to FIG. 14.
[0108] For uplink symbols, as previously discussed with reference
to FIG. 12, each TX/RX 302 may be configured to digitize the
received RF signals, perform analog front-end calibration and
time/frequency synchronization, remove the cyclic prefix (CP), and
perform FFT OFDM demodulation and guard-band removal. This may
result in frequency domain pilot and unequalized data symbol
vectors, which is provided to antenna combiner 310 in the
illustrated embodiment. Note that, at this point, the OFDM symbols
may contain the superposition of transmitted signals by all users.
For downlink symbols, each TX/RX 302 may be configured to perform
ODFM processing as described above with reference to FIG. 12 for
signals received from antenna splitter 315.
[0109] In one embodiment, antenna combiner 310, bandwidth, splitter
320, MIMO precoder 345, bandwidth combiner 325, and antenna
splitter 315 are each located on a different SDR element that also
implements one of TX/RXs 302. In one embodiment, channel estimator
330 and MIMO detector 340 are located on another SDR element that
also implements one of TX/RXs 302. In various embodiments, the
various elements of FIG. 13 may be partitioned among various
hardware elements configured to perform the disclosed
functionality. The hardware elements may be programmable and/or
include dedicated circuitry.
[0110] Antenna combiner 310, in the illustrated embodiment, is
configured to receive the yet unequalized OFDM symbols from each
TX/RX 302 and combines them into a signal sent to bandwidth
splitter 320. This combines the signals from up to N antennas in
the subsystem. Combining this information before further processing
may allow the system to stay within throughput constraints and may
reduce the number of peer-to-peer connections between SDRs, for
example. In some embodiments, the number of antennas for which
signals are combined by each antenna combiner 310 is dynamically
configurable.
[0111] Bandwidth splitter 320, in the illustrated embodiment, is
configured to split the received signals into separate bandwidth
portions and send the portions to MIMO detectors in different
subsystems. Thus, in the illustrated embodiment, processing is
distributed across different processing elements that each process
data for a different frequency band. Each bandwidth portion may
include one or more subcarriers and the portions may or may not be
non-overlapping. In some embodiments, the number of bandwidth
portions and the size of each portion is configurable, e.g., based
on the number of antennas, current number of users in
communication, etc. In other embodiments, processing may be
distributed among processing elements across different time slices
in addition to and/or in place of splitting by frequency. In some
embodiments, bandwidth splitter 320 is replaced with a time-slice
splitter. Post-FTT subcarrier processing in OFDM may be inherently
independent, allowing subsequent processing to be performed in
parallel by different processing elements.
[0112] In the illustrated embodiment, the output of TX/RX 302B is
provided directly to bandwidth splitter 320 and an output of
bandwidth combiner 325 is provided directly to TX/RX 302D. In other
embodiments, these outputs may be provided to antenna combiner 310
and antenna splitter 315 similarly to the other signals. In
embodiments in which TX/RX 302B and bandwidth splitter 320 share
the same SDR element and TX/RX 302D and bandwidth combiner 325
share the same SDR element, however, the illustrated coupling may
conserve I/O resources.
[0113] MIMO detector 340, in the illustrated embodiment, is
configured to use an estimated channel matrix (e.g., based on
uplink pilot symbols) to cancel interference and detect
frequency-domain symbols from each mobile device 106. As shown, in
some embodiments MIMO detector 340 is configured to process signals
in a given bandwidth from multiple subsystems of system 300. In the
illustrated embodiment, MIMO detector 340 is configured to send the
detected signals to channel estimator 330 and to link quality
evaluator 350 (included in a central controller in some
embodiments) for further processing.
[0114] Channel estimator 330, in the illustrated embodiment, is
configured to perform channel estimation for its frequency portion
for a number of mobile devices, e.g., to produce soft-bits (also
referred to as log-likelihood ratios (LLRs)) and provide them to
link quality evaluator 350 (coupling not shown). In some
embodiments, multiple decoders are implemented, including a turbo
decoder, for example.
[0115] For downlink symbols, data source 360, in test system
embodiments, is configured to generate test data, which may be
pseudo-random or may be explicitly specified for a particular test.
In these embodiments, data source 360 may be located in a central
control unit. In production systems, data source 360 may provide
data from various networks to be transmitted to mobile devices
106.
[0116] MIMO precoder 345, in the illustrated embodiment, is
configured to receive downlink data from data source 360 and
precode the data based on channel estimates (e.g., estimated
reciprocity calibration weights) from channel estimator 330. In
some embodiments, the MIMO precoders in system 300 are configured
to perform precoding on different frequency portions of the
downlink data. In some embodiments (not shown), the MIMO precoders
in system 300 are configured to perform precoding on different time
portions of the downlink data.
[0117] Exemplary precoders, according to some embodiments, include
maximum radio transmission (MRT) and zero forcing (ZF) precoders.
In other embodiments, any of various appropriate precoding
techniques may be implemented. Depending on the precoding technique
implemented, varying amounts of processing for the precoding may be
performed by at a central controller or distributed among MIMO
precoders 345.
[0118] Bandwidth combiner 325, in the illustrated embodiment, is
configured to combine signals at different bandwidths from multiple
MIMO precoders and send the data to antenna splitter 315. This may
result in a complete set of precoded data for transmission from the
separately processed bandwidth portions. In other embodiments,
bandwidth combiner 325 is configured to combine data corresponding
to separately-processed time slices in place of or in addition to
combining separately-processed frequency portions.
[0119] Antenna splitter 315, in the illustrated embodiment, is
configured to split the received signal and provide the split
signal to TX/RXs 302 for OFDM processing and transmission to mobile
devices 106. The set of antennas to which antenna splitter 315 is
configured to provide signals is dynamically configurable, in some
embodiments (e.g., the number of antennas and/or the particular
antennas in the set). Thus, in some embodiments, the set of
processing elements configured to perform distributed processing
for particular antennas and/or users is dynamically
configurable.
[0120] Link quality evaluator 350, in the illustrated embodiment,
is included in a central control unit and is configured to measure
link quality using one or more of various metrics such as bit error
rate (BER), error vector magnitude (EVM), and/or packet-error rate
(PER).
[0121] In various embodiments, system 300 is highly configurable,
e.g., based on user input and/or current operating conditions. In
some embodiments, various disclosed configuration operations are
performed automatically. In some embodiments, the number of
processing elements used at a given time to perform distributed
processing for a set of users or a set of antennas is configurable.
In some embodiments, the number of antennas used to communicate
with each UE is configurable and/or dynamically determined. In some
embodiments, the processing elements configured to perform
different functionality described above is configurable. For
example, the antenna combiner function may be moved from one FPGA
to another FPGA or performed by multiple FPGAs. In some
embodiments, the routing of data between processing elements is
configurable, e.g., to avoid malfunctioning antennas and/or
processing elements. In various embodiments, system 300 is
configured to adjust these configurable aspects dynamically based
on current operating conditions. In some embodiments, system 300
includes a large number of antennas, e.g., more than 8. In some
embodiments, for example, system 300 includes 16, 32, 64, 100, 128,
256, or more antennas. In some embodiments, components of system
300 are modular such that the number of antennas may be increased
by adding additional components.
[0122] In some embodiments, a software library is provided with
system 300 and is configured with example test scenarios for
configuring system 300. In some embodiments, a graphical
programming language such as LabVIEW is used to configure
programmable hardware devices in system 300. Thus, various
functionality described herein may be configured using a graphical
programming interface.
[0123] Exemplary high-level system parameters, according to some
embodiments, include a system bandwidth of 20 MHz, a carrier
frequency of 3.7 GHz, a sampling rate of 30.72 MS/s, and FFT size
of 2048, 1200 used subcarriers, a 0.5 ms slot time, a 1 ms subframe
time, a 10 ms frame time, and 100 antennas. These parameters are
exemplary only and are not intended to limit the scope of the
present disclosure. In some embodiments, the parameters are user
configurable and/or are dynamically configurable by the system
itself.
[0124] In the illustrated embodiment, bandwidth splitter 320 is
configured to separate and provide bandwidth portions of the
incoming signals from multiple antennas in order to distribute
processing load. In other embodiments, the incoming signals maybe
split in other dimensions in addition to and/or in place of the
frequency dimension. Processing for downlink signals may be
similarly distributed. Thus, in various embodiments, the disclosed
system is highly configurable and provides high-performance
distributed processing to meet real-time performance requirements
for massive MIMO systems.
[0125] FIG. 14 shows one embodiment of a software radio peripheral
400. The National Instruments USRP (Universal Software Radio
Peripheral) is one exemplary embodiment of a software radio
peripheral 400. In some embodiments, a software radio peripheral
400 is configured to implement one or more of TX/RXs 302 and one or
more of antenna combiner 310, bandwidth splitter 320, channel
estimator 330, MIMO detector 340, MIMO precoder 345, bandwidth
combiner 325, and antenna splitter 315 of FIG. 13. In some
embodiments, multiple software radio peripherals 400 are coupled
via one or more interconnects to implement a massive MIMO base
station.
[0126] Software radio peripheral 400, in the illustrated
embodiment, includes radio frequency transceivers RFO 412A and RF1
412B, ADCs 414A-B, DACs 416A-B, memory 420, field-programmable gate
array (FPGA) 430, timing and clock distribution unit 440, and
GPS-disciplined clock 435.
[0127] RF transceivers RFO 412A and RF1 412B, in the illustrated
embodiment, are configured to send and receive transmissions to one
or more mobile devices 106 via one or more antennas. In one
embodiment, each transceiver is configured to utilize up to 40 MHz
of radio frequency bandwidth at center frequencies of 1.2-6 GHz and
is configured to transmit with up to 15 decibel-milliwatts
(dBm).
[0128] ADCs 414A-B and DACs 416A-B may be configured similarly to
A/D 212A-N and D/A 234A-N as described above with reference to FIG.
12. In some embodiments, these elements are respectively configured
to convert received analog data to digital form and received
digital information to analog form for wireless transmission.
[0129] FPGA 430, in some embodiments, is a programmable hardware
element configured to and/or configurable to perform various radio
processing functionality. In some embodiments, FPGA 430 is
configured to perform various MIMO processing described above with
reference to FIG. 13. For example, FPGA 430 may be configured to
perform one or more of OFDM front-end processing (e.g., as
discussed with reference to units 214, 216, 218, 220, 222, 224,
226, 228, 230, and 232 of FIG. 12), antenna combining, bandwidth
splitting, MIMO detection, channel estimation, MIMO precoding,
bandwidth combining, antenna splitting, etc. In the illustrated
embodiment, FPGA 430 is coupled to ADCs 414A-B and DACs 416A-B, a
digital I/O port, and a Peripheral Component Interconnect Express
(PCIe) connection. In some embodiments, software radio peripheral
400 is coupled to other software radio peripherals and/or a central
control unit via PCIe (or any of various other appropriate
couplings).
[0130] With reference to various operations disclosed herein, a
program may be used that is capable of causing or configuring a
computing system to perform various operations. This encompasses
both instructions that are executable by the computing system to
cause the system to perform the operation(s) and instructions that
are usable to configure the computing system (e.g., by configuring
FPGA 430) such that it is capable of performing the operation(s)
(note that the latter type of instructions may not be executed, but
may be used to configure programmable circuitry, for example, which
is then configured to perform the operation(s)).
[0131] In other embodiments, FPGA 430 may be replaced or
supplemented with any of various appropriate processing elements.
Inclusion of a programmable hardware element in software radio
peripheral 400 in some embodiments, however, may increase
configurability and flexibility of the system. In test systems, for
example, test engineers may modify the configuration of FPGA 430 to
develop and test different MIMO software radio processing
techniques. In production systems, programmable hardware elements
may facilitate system reconfiguration and/or updates in various
contexts.
[0132] Memory 420, in some embodiments, is configured to facilitate
programming of FPGA 430 and/or storing of values (e.g., sampled and
processed uplink signals) during processing operations by FPGA 430.
Memory 420 may include multiple different storage elements or a
single storage element and may be implemented using various
different memory technologies as appropriate.
[0133] Timing and clock distribution unit 440, in the illustrated
embodiment, is configured to receive information from
GPS-disciplined clock 435, a reference signal input "ref in,"
and/or a trigger input signal. In the illustrated embodiment, unit
440 is also configured to provide a reference output signal "ref
out" and a trigger output signal. In some embodiments, described in
further detail below with reference to FIGS. 7-10, one or more of
these signals may be used to synchronize sampling and/or other
operations by multiple software radio peripherals.
[0134] GPS-disciplined clock 435, in the illustrated embodiment, is
configured to receive global positioning system (GPS) signals and
generate a clock signal for timing and clock distribution unit 440
that is disciplined to a GPS time. GPS is provided as one example
of a reference clock, but in other embodiments, any of various
appropriate reference clocks may be used, including clocks
generated by satellite navigation systems other than GPS, etc. In
some embodiments, the reference signal input may be configured to
receive a reference clock signal and the GPS-disciplined clock 435
is omitted, disabled, or ignored.
[0135] Software radio peripheral 400 is provided as one example of
a hardware module configured or configurable to implement a portion
of the functionality of system 300. In other embodiments, other
processing elements such as a central processing unit or a non-FPGA
programmable hardware element in addition to or in place of an FPGA
may be used to perform similar operations. Further, although unit
400 is referred to as a "software" radio peripheral 400 in
disclosed embodiments, it may also be a hardwired radio peripheral
configured to perform similar functionality. In some embodiments,
software radio peripheral 400 is a plug-in module or card
configured to be inserted into a chassis (such as a PCIe chassis
for example) for communication with other modules. In other
embodiments, processing elements configured to perform similar
functionality may be integrated or coupled into a massive MIMO
system using other techniques.
[0136] Software radio peripheral 400 is provided as one example of
a hardware module configured to implement functionality of system
300. In other embodiments, other processing elements such as
processors or other programmable hardware elements in addition to
or in place of an FPGA may be used to perform similar operations.
Further, although unit 400 is referred to as a "software" radio
peripheral 400 in disclosed embodiments, it may also be a hardwired
radio peripheral configured to perform similar functionality. In
some embodiments, software radio peripheral 400 is a plug-in module
or card configured to be inserted into a chassis (such as a PCIe
chassis for example) for communication with other modules. In other
embodiments, processing elements configured to perform similar
functionality may be integrated or coupled into a massive MIMO
system using other techniques.
[0137] In some embodiments, the disclosed massive MIMO system
performs within practical hardware I/O limits while providing a
low-latency path for time-critical processing. In some embodiments,
the critical signal path is from receipt of OFDM symbols through
channel estimation, MIMO precoding, and OFDM transmission. This
path may be especially important for reciprocity-based MIMO. In
some embodiments, this path includes RX front-end delay, CP
removal, FFT, guard subcarrier removal, channel estimation,
precoder calculation, guard subcarrier interleave, IFFT, CP
addition, and TX front-end delay. Additional sources of latency may
include overhead in data routing, packing, unpacking, and hops
across the PCIe backplane. In disclosed embodiments, this latency
is reduced by using efficient routing mechanisms over a high speed
communication bus (such as PCIe, for example). Further, a high
degree of pipelining (which may be enabled by packing data
antennas-first) and the disclosed combining data from multiple
antennas and then splitting it based on bandwidth before
distributing the data for processing, as shown in FIG. 13, allows
the number of antennas and the overall system bandwidth to be
scaled upwards almost indefinitely. Pipelining, in various
embodiments, may allow different sets of data (e.g., data sampled
from the antennas at different times) to reside in different
processing stages. For example, one FPGA may perform bandwidth
splitting, then pass the data on to another FPGA for MIMO detection
before splitting a subsequent set of data, in a pipelined fashion.
Referring back to FIG. 13, various units may be configured to
operate in a pipelined and distributed manner.
[0138] FIG. 15 shows one embodiment of a system 500 that includes
hardware configured to implement a massive MIMO base station. In
the illustrated embodiment, system 500 includes clock module(s)
510, chassis 520A-N, SRPs 400A-Q, and central controller 530.
[0139] Clock module(s) 510 are configured to distribute clock
and/or trigger signals, in some embodiments, e.g., to the reference
and/or trigger terminals of each SRP.
[0140] In one embodiment, each SRP 400 is included in or coupled to
a chassis 520 and is configured to handle up to 800 MB/s
bidirectional via a PCI eXtensions for Instrumentation Express
(PXIe) backplane. In other embodiments, any of various appropriate
backplane protocols may be implemented.
[0141] Chassis 520, in the illustrated embodiment, are configured
to include or couple to multiple SRPs 400 via PCIe connections. In
some embodiments, each chassis 520 includes one or more switches
configured to route communications. In one embodiment, each chassis
520 includes two switches. Each switch may be configured to stream
up to 3.2 GB/s of bidirectional traffic for each slot in the
chassis, with a total of 12 GB/s shared between devices on the
switch, for example. In the illustrated embodiment, the chassis 520
are coupled via a PCIe daisy chain connection. In some embodiments,
daisy chain connections in star configurations may be used to build
higher channel-count systems. In one embodiment, the daisy-chain
cables between chassis are configured to stream up to 5.6 GB/s
unidirectional or 2.8 GB/s bidirectional. In other embodiments, any
of various appropriate communications protocols may be implemented.
The bandwidths discussed above are exemplary only, and are not
intended to limit the scope of the present disclosure. They
illustrate, however, that the disclosed distributed processing
results in a scalable system configured to operate within bandwidth
constraints of various components.
[0142] Central controller 530, in some embodiments, is configured
to implement the functionality of link quality evaluator 350 and
data source 360. In some embodiments, central controller 530
provides a user interface for radio configuration, deployment of
FPGA configuration code, system visualization etc. In some
embodiments, central controller 530 is configured to source and
sink user data, e.g., with other networks with as the Internet. In
some embodiments, central controller 350 is configured to measure
link quality using metrics such as bit error rate (BER), packet
error rate (PER), and/or error vector magnitude (EVM), for
example.
[0143] In one embodiment, five types of FPGA images are used to
configure the SRPs 400 of system 500. In this embodiment, the first
type is OFDM TX/RX only, used to implement one or more front-end
TX/RXs 302. In some embodiments, this type may be allocated among
available processing elements after allocation of the four other
types. In this embodiment, the second type is OFDM TX/RX with
antenna combiner and bandwidth splitter. In some embodiments, this
type is spread evenly across chassis segments, e.g., with one per
PXI switch segment. In one embodiments, each FPGA of this type is
associated, at least initially, with sixteen antennas. In these
embodiments, the third type is OFDM TX/RX with MIMO detector. In
some embodiments, the MIMO detector may output channel estimates
and/or LLR outputs. In these embodiments, the fourth type is OFDM
TX/RX with MIMO precoder, which may output precoded data bits. In
these embodiments, the fifth type is OFDM TX/RX with bandwidth
combiner and antenna splitter, which may distributed similarly to
the second type, as discussed above. In other embodiments,
processing may be distributed among various types of processing
elements (e.g., in addition to and/or in place of FPGAs) using any
of various appropriate distributions.
[0144] FIG. 16 shows a flow diagram illustrating one exemplary
embodiment of a method 600 for massive MIMO processing. The method
shown in FIG. 16 may be used in conjunction with any of the
computer systems, devices, elements, or components disclosed
herein, among other devices. In various embodiments, some of the
method elements shown may be performed concurrently, in a different
order than shown, or may be omitted. Additional method elements may
also be performed as desired. Flow begins at 610.
[0145] At 610, wireless signals are received via a plurality of
antennas. For example, the illustrated subsystem of FIG. 13 may
receive wireless signals via the 2N antennas coupled to TX/RXs
302A-N. In some embodiments, the signals are OFDM signals, but in
other embodiments, other modulation schemes may be implemented.
[0146] At 620, the received signals are combined. In some
embodiments, antenna combiner 310 is configured to combine the
signals. The signals combined may be from all antennas in a given
massive MIMO system or for a portion of the antennas in a massive
MIMO system (e.g., for the subsystem shown in FIG. 13 or for a
portion thereof). The combined signals may include information from
multiple different users.
[0147] At 630, different portions of the combined signals are
provided to different processing elements. In some embodiments, the
different portions are mutually exclusive (e.g., the information
provided to a given processing element is not provided to other
processing elements). In other embodiments, there may be some
overlap between the information provided to the different
processing elements. In some embodiments, bandwidth splitter 320 is
configured to provide frequency portions of the combined signals to
different software radio peripherals 400. In some embodiments, one
or more processing elements are configured to split the combined
signals into different time slices and provide the time slices to
different software radio peripherals 400. In some embodiments, the
combined signals are split in both the time and frequency dimension
to further distribute processing.
[0148] At 640, signals are transmitted via the plurality of
antennas. In the illustrated embodiment, the signals are generated
based on processing of the portions of the combined signals by the
plurality of processing elements. For example, the processing may
generate channel information used to precode the transmitted
signals for massive MIMO communications. The distributed nature of
the processing may allow system 300 to operate in real time and
provide reciprocity-based precoding before the channel changes
significantly.
[0149] In some embodiments, each processing element is configured
to operate on a different frequency portion of signals received by
multiple antennas. In some embodiments, each processing element is
configured to operate on a different time portions of signal
received by multiple antennas. In some embodiments, the number of
processing elements in the subset is dynamically configurable based
on current communication conditions. In some embodiments, the
operating includes detecting one or more uplink pilot symbols and
generated channel information based on the pilot symbols. In some
embodiments, similar techniques are used for distributed processing
for precoding downlink data then combining the different portions
for transmission via multiple antennas.
[0150] Further, the disclosed techniques may facilitate dynamic
configurability of the massive MIMO base station. For example, if
elements of system 300 are malfunctioning or otherwise unavailable,
system 300 is configured, in some embodiments, to alter the set of
software radio peripherals assigned to a given set of antennas to
route around the unavailable elements. In some embodiments, the
number of processing elements assigned to a given set of antennas
at a given time is also configurable. For example, the size of the
bandwidth and/or time portions processed by each processing element
is also configurable, in some embodiments. Further, the number of
antennas used for a given user device may also be dynamically
configurable. Various dynamic configuration may be performed by
system 300 in response to current operations conditions, e.g.,
power conditions, the state of the wireless communication
environment, number of user devices in communication, etc.
[0151] Looking now to FIGS. 17-18, example embodiments of frame
structures are provided for the massive MIMO communication system
described in U.S. Published Patent Application 2015/0326291.
[0152] In some embodiments, the disclosed system is configured to
utilize conventional signaling (e.g., 3GPP LTE signaling). In other
embodiments, the LTE frame structure is modified or a different
frame structure is used to improve massive MIMO processing,
especially in the reciprocity-based systems.
[0153] FIG. 17 shows an exemplary LTE time division duplexing (TDD)
frame. In the illustrated embodiment, the frame covers ten
milliseconds (ms) in the time dimension and includes ten subframes,
each covering one ms. In the illustrated embodiment, each subframe
is used either for downlink (DL) data, as a guard subframe, or for
uplink (UL) data. LTE TDD defines several frame configurations, two
of which are shown in FIG. 17. The guard frames may include pilot
time slots such as DwPTS and UpPTS.
[0154] In some embodiments, the LTE frame structure is problematic
for reciprocity-based MIMO. Generally, to allow for
reciprocity-based MIMO the following events must occur within the
coherence time of the channel: process received samples, measure
uplink channels, and precode downlink samples. In some embodiments,
the turnaround time between receiving an uplink pilot symbol to
transmitting a downlink symbol is specified to be less than 0.5 ms
to ensure that it is less than the coherence-time, even for UEs
that are moving relatively quickly. As shown in FIG. 17, this is
not typically achieved using a typical LIE TDD frame, because a
full 1 ms subframe is dedicated to UL or DL data.
[0155] FIG. 18 shows an exemplary data frame according to some
embodiments. In the illustrated embodiment, each frame covers ten
ms and includes ten subframes which each cover one ms in the time
dimension. In contrast to the LTE frame of FIG. 17, however, in the
illustrated embodiment each subframe (and each slot) includes both
uplink and downlink data, as well as a switch guard symbol. In the
illustrated embodiment, each slot (corresponding to half of a
subframe) includes 7 OFDM symbols, one of which is used for an
uplink pilot symbol, two of which are used for uplink data, two of
which are used for downlink data, and two of which are used as
guard symbols for switching between uplink and downlink In the
illustrated embodiment, the uplink pilot symbol and switch guard
periods each consist of a single OFDM symbol.
[0156] In some embodiments, uplink pilot symbols are sequentially
interleaved in the frequency dimension for users in the system. For
example, each user's pilot data may be distributed across multiple
separate subcarrier chunks. In some embodiments, pre-coded pilot
information is also inserted into DL OFDM symbols to allow for
compensation of RF chain responses.
[0157] In some embodiments, each frame starts with a down-link
broadcasting subframe to set up initial network synchronization
(e.g., for mobile devices 106 to synchronize carrier and/or
sampling frequency with the base station). In some embodiments, the
remaining nine subframes are used for UL and DL data
transmission.
[0158] In various embodiments, different frame sizes, subframe
sizes, number of OFDM symbols per slot, etc. may be implemented. In
various embodiments, the turnaround time between receiving an
uplink pilot symbol and transmitting the last downlink data that is
encoded based on the uplink pilot symbol is less than 0.5 ms. In
some embodiments, the turnaround time between receiving an uplink
pilot symbol and transmitting the last downlink data that is
encoded based on the uplink pilot symbol is less than the coherence
time of the channel, which may vary over time, e.g., based on
movement of source or receiver.
[0159] As used herein, the "coherence time" of a channel quantifies
the similarity of the channel response at different times and
refers to a time interval over which the impulse response to the
channel is considered to be not varying. Coherence time is
inversely proportional to doppler spread and is often estimated
using the equation 0.423 times the maximum doppler frequency (e.g.,
as determined based on movement of the source and/or receiver). For
example, the maximum doppler frequency of a transmitter moving
directly towards a receiver is the frequency of the carrier wave
times the velocity of movement divided by the speed of light.
[0160] Thus, in some embodiments, frame structures with short
turnaround between uplink pilot receipt and downlink data
transmission allow reciprocity to be used reliably even for
fast-moving mobile devices 106. As discussed above, the distributed
processing techniques disclosed herein may provide a short critical
path for signals and processing needed to meet such a short
turnaround time.
[0161] Further, the disclosed time dimension duplexing (TDD)
techniques may be advantageous relative to frequency division
duplexing (FDD) techniques because FDD systems may run out of
unique pilot tones for a receiver to effectively resolve channel
conditions, given the large number of antennas.
[0162] Further modifications and alternative embodiments of this
invention will be apparent to those skilled in the art in view of
this description. It will be recognized, therefore, that the
present invention is not limited by these example arrangements.
Accordingly, this description is to be construed as illustrative
only and is for the purpose of teaching those skilled in the art
the manner of carrying out the invention. It is to be understood
that the forms of the invention herein shown and described are to
be taken as the presently preferred embodiments. Various changes
may be made in the implementations and architectures. For example,
equivalent elements may be substituted for those illustrated and
described herein, and certain features of the invention may be
utilized independently of the use of other features, all as would
be apparent to one skilled in the art after having the benefit of
this description of the invention.
* * * * *