U.S. patent application number 14/708476 was filed with the patent office on 2015-08-27 for wireless radio access network control channel capacity management.
The applicant listed for this patent is APPLE INC.. Invention is credited to Giri Prassad DEIVASIGAMANI, Gaurav R. NUKALA, Venkatasubramanian RAMASAMY.
Application Number | 20150245368 14/708476 |
Document ID | / |
Family ID | 47178280 |
Filed Date | 2015-08-27 |
United States Patent
Application |
20150245368 |
Kind Code |
A1 |
NUKALA; Gaurav R. ; et
al. |
August 27, 2015 |
Wireless Radio Access Network Control Channel Capacity
Management
Abstract
Transmission capacity for a control channel sent to multiple
mobile wireless devices in a wireless network is increased by
transmitting the control channel using multi user multiple input
multiple output transmissions (MU MIMO). Received signal quality
measured at mobile wireless devices in a radio sector are
communicated to a radio node and used to determine one or more sets
of mobile wireless devices to share transmission of control channel
elements on the same time and frequency resource element. The radio
node indicates the use of MU MIMO and the selection of precoding
matrices to each of the mobile wireless devices in the each set of
mobile wireless devices.
Inventors: |
NUKALA; Gaurav R.;
(Cupertino, CA) ; RAMASAMY; Venkatasubramanian;
(Cupertino, CA) ; DEIVASIGAMANI; Giri Prassad;
(Cupertino, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
APPLE INC. |
Cupertino |
CA |
US |
|
|
Family ID: |
47178280 |
Appl. No.: |
14/708476 |
Filed: |
May 11, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13246810 |
Sep 27, 2011 |
9031033 |
|
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14708476 |
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Current U.S.
Class: |
370/330 |
Current CPC
Class: |
H04L 5/0023 20130101;
H04L 5/0053 20130101; H04W 72/044 20130101; H04L 1/0072 20130101;
H04L 1/001 20130101; H04W 24/08 20130101; H04W 72/085 20130101;
H04W 4/08 20130101; H04B 7/0452 20130101; H04B 7/0417 20130101;
H04W 72/042 20130101; H04L 1/007 20130101 |
International
Class: |
H04W 72/08 20060101
H04W072/08; H04W 4/08 20060101 H04W004/08; H04W 72/04 20060101
H04W072/04; H04B 7/04 20060101 H04B007/04; H04W 24/08 20060101
H04W024/08 |
Claims
1-23. (canceled)
24. A method, comprising: at a base station: estimating a received
downlink signal quality for each mobile wireless device of a
plurality of mobile wireless devices connected to the base station;
determining a number of control channel elements to be transmitted
to each mobile wireless device based on the received downlink
signal quality of each mobile wireless device; grouping a portion
of the plurality of mobile wireless devices into a first group
based on the received downlink signal quality of each mobile
wireless device and a number of receive antennas for each mobile
wireless device; and transmitting control channel information
comprising the number of control channel elements to each of the
first group of mobile wireless devices, wherein the control channel
information is simultaneously transmitted to each of the first
group of mobile wireless devices using the same frequency and time
resource elements based on multi-user multiple-input
multiple-output (MU-MIMO) transmissions.
25. The method of claim 24, wherein the base station is an LTE or
LTE-Advanced compliant base station.
26. The method of claim 24, further comprising: grouping a portion
of the plurality of mobile wireless devices into a second group
based on the received downlink signal quality of each mobile
wireless device and the number of receive antennas for each mobile
wireless device; and transmitting control channel information
comprising the number of control channel elements to each of the
second group of mobile wireless devices, wherein the control
channel information is simultaneously transmitted to each of the
second group of mobile wireless devices using the same frequency
and time resource elements based on multi-user multiple-input
multiple-output (MU-MIMO) transmissions.
27. The method of claim 26, wherein the base station transmits one
of a same number of control channel elements to the first group and
second group of mobile wireless devices or a different number of
control channel elements to the first group and second group of
mobile wireless devices.
28. The method of claim 26, wherein the first group of mobile
wireless devices has one of a same number of receive antennas as
the second group of wireless devices or a different number of
receive antennas as the second group of wireless devices.
29. The method of claim 26, wherein the received downlink signal
quality of the first group of mobile wireless devices exceeds a
first predetermined threshold and the received downlink signal
quality of the second group of mobile wireless devices exceeds a
second predetermined threshold, wherein the first and second
predetermined thresholds are one of a same value and a different
value.
30. The method of claim 24, wherein the number of control channel
elements is one of 1, 2, 4 or 8.
31. The method of claim 24, wherein the number of receive antennas
is one of 2, 4, 6 or 8.
32. The method of claim 24, wherein the number of receive antennas
for each of the first group of mobile wireless devices is the
same.
33. A base station, comprising: a processor; a transceiver; a
plurality of antennas; and a non-transitory computer readable
storage medium comprising a set of instructions that are executable
by the processor, wherein the instructions causes the processor to:
estimate a received downlink signal quality for each mobile
wireless device of a plurality of mobile wireless devices connected
to the base station; determine a number of control channel elements
to be transmitted to each mobile wireless device based on the
received downlink signal quality of each mobile wireless device;
group a portion of the plurality of mobile wireless devices into a
first group based on the received downlink signal quality of each
mobile wireless device and a number of receive antennas for each
mobile wireless device; and transmit, via the transceiver and one
or more of the plurality of antennas, control channel information
comprising the number of control channel elements to each of the
first group of mobile wireless devices, wherein the control channel
information is simultaneously transmitted to each of the first
group of mobile wireless devices using the same frequency and time
resource elements based on multi-user multiple-input
multiple-output (MU-MIMO) transmissions.
34. The base station of claim 33, wherein the base station is an
LTE or LTE-Advanced compliant base station.
35. The base station of claim 33, wherein the instructions further
cause the processor to: group a portion of the plurality of mobile
wireless devices into a second group based on the received downlink
signal quality of each mobile wireless device and the number of
receive antennas for each mobile wireless device; and transmit, via
the transceiver and one or more of the plurality of antennas,
control channel information comprising the number of control
channel elements to each of the second group of mobile wireless
devices, wherein the control channel information is simultaneously
transmitted to each of the second group of mobile wireless devices
using the same frequency and time resource elements based on
multi-user multiple-input multiple-output (MU-MIMO)
transmissions.
36. The base station of claim 33, wherein the number of receive
antennas is one of 2, 4, 6 or 8.
37. The base station of claim 33, wherein the base station
transmits the control channel information on a number of the
plurality of antennas that corresponds to the number of receive
antennas of the first group of mobile wireless devices.
38. The base station of claim 33, wherein the transceiver comprises
a plurality of transceivers, wherein a first of the plurality of
transceivers has one corresponding antenna and a second of the
plurality of transceivers has more than one corresponding
antenna.
39. The base station of claim 33, wherein the control channel
information is transmitted via a physical downlink control channel
(PDCCH).
40. The base station of claim 33, wherein the base station
estimates the received downlink signal quality for each mobile
wireless device based on a channel quality indicator (CQI) received
from each mobile wireless device.
41. A mobile wireless device, comprising: a processor; a
transceiver; a plurality of antennas; and a non-transitory computer
readable storage medium comprising a set of instructions that are
executable by the processor, wherein the instructions causes the
processor to: receive an indicator that indicates transmissions on
a control channel are encoded using MU MIMO transmission; receive
and decode signals transmitted on a the control channel, wherein
the signals on the control channel comprise a number of control
channel elements corresponding to a received downlink signal
quality for the mobile wireless device and wherein the number of
control channel elements are simultaneously transmitted to at least
one other mobile wireless device using the same frequency and time
resource elements.
42. The mobile wireless device of claim 41, wherein the
instructions further cause the processor to: receive a further
indicator that indicates transmissions on the control channel are
encoded using a transmission scheme that is different from MU MIMO
transmission; and switch decoding of signals received on the
control channel to the transmission scheme.
43. The mobile wireless device of claim 41, wherein the
instructions further cause the processor to: calculate a downlink
signal quality for transmissions received from a base station of a
wireless network; and transmit, via the transceiver and one or more
of the plurality of antennas, the downlink signal quality using
channel quality indicators to the base station of the wireless
network.
Description
TECHNICAL FIELD
[0001] The described embodiments generally relate to methods and
apparatuses for control channel communication between mobile
wireless devices and a wireless network. More particularly, the
present embodiments describe increasing capacity of a control
channel between a radio access portion of a wireless network a
multiple mobile wireless devices using multi-user multiple-input
multiple-output communication.
BACKGROUND
[0002] Wireless networks continue to evolve to support new services
and increased transmission rates as new communication technologies
develop and standardize. A representative wireless network for a
wireless network service provider can include support for one or
more releases of the Third Generation Partnership Project (3GPP)
Long Term Evolution (LTE) wireless communication standard and
LTE-Advanced wireless communication standard. This representative
wireless network can support packet switched connections (voice or
data) through an LTE or LTE-Advanced network.
[0003] An LTE (LTE-Advanced) wireless network can support high rate
packet communication to multiple mobile wireless devices
simultaneously within a geographic area. The radio frequency
spectrum used for communication to the multiple mobile wireless
devices can be shared among the multiple mobile wireless devices
using an orthogonal frequency division multiplexing (OFDM)
transmission method. A transceiver (transmitter/receiver) in a
mobile wireless device can adapt to radio frequency spectral
variation using the OFDM transmission method, which can divide the
occupied radio frequency spectrum into a set of parallel narrower
bandwidth and lower data rate communication sub-channels
transmitted on parallel subcarriers, and each sub-channel can
experience approximately flat frequency spectrum fading. An OFDM
communication system can divide transmissions into a series of
successive OFDM symbols in time, with each OFDM symbol providing
multiple sub-channels centered at different frequencies
simultaneously. A transmission "resource element" (RE) can be
considered a unit of transmission capacity on a single sub-channel
within a single OEDM symbol, and, the wireless network can allocate
multiple RE across multiple sub-channels among multiple wireless
devices dynamically over time. The wireless network can regularly
broadcast control information about the allocation of the RE to the
multiple wireless devices within a geographic area served by a
radio frequency access system of the wireless network. The control
information itself can be transmitted using a subset of the total
available RE, and the number of RE available to support
communication of control information can limit the total number of
mobile wireless devices that can be connected simultaneously to the
wireless network.
[0004] Communication systems can be sensitive to errors that can
occur in the control information received at the wireless devices,
and the wireless network can use different rates of error
correction coding to protect the control information during
transmission and reception by the mobile wireless device in the
presence of noise and interference. Received signal quality at a
mobile wireless device can vary significantly based on the location
of the mobile wireless device with respect to a transmitting radio
frequency access system located in an access network portion of the
wireless network and also based on the amount of noise and
interference received by the mobile wireless device. Mobile
wireless devices located at a greater distance, such as nearer the
edge of a geographic coverage area of the access network
transmitter, can receive weaker signals than mobile wireless
devices located closer to the access network transmitter. As the
control information can be broadcast simultaneously to all of the
multiple wireless devices served by the access network transmitter,
the transmit power used for control channel transmissions can be
the same for the different multiple wireless devices, while the
amount of error correction coding applied can be varied to better
protect transmissions to the different mobile wireless devices.
Specifically more RE can be allocated for communication of control
information to mobile wireless devices with lower received signal
quality, and fewer RE can be allocated to control channel messages
sent to mobile wireless devices with higher received signal
quality. The same RE can be allocated to multiple mobile wireless
devices by sharing the same frequency band/time slot occupied by
the RE using a form of spatial division multiplexing. Multi-user
multiple input multiple output (MU-MIMO) transmission methods can
be applied to transmissions of the control information to share
selected RE among multiple mobile wireless devices and to increase
the total number of mobile wireless devices that can be
simultaneously supported by a radio sector of the wireless
network.
SUMMARY OF THE DESCRIBED EMBODIMENTS
[0005] In one embodiment, a method of increasing transmission
capacity for a control channel in a wireless network is described.
The method includes at least the following steps. In a first step,
a radio node in a radio access network of the wireless network
estimates a received downlink signal quality for each mobile
wireless device in a plurality of mobile wireless devices connected
to the radio node. The radio node selects a first set of mobile
wireless devices in the plurality of mobile wireless devices. Each
selected mobile wireless device has an estimated downlink signal
quality exceeding a first threshold. The radio node transmits
simultaneously to the first set of mobile wireless devices on the
control channel through a plurality of antennas using multi-user
(MU) multiple-input multiple-output (MIMO) transmission. In a
representative embodiment, the radio node assigns at least two
mobile wireless devices in the first set of mobile wireless devices
to a first control channel element that occupies a first set of
time and frequency resource elements in a transmission time
interval. The transmission capacity of the control channel is
limited by the number of control channel elements scheduled for
each transmission time interval.
[0006] In another embodiment, a mobile wireless device including a
receiver and a configurable processor is described. The receiver is
configured to receive and decode signals transmitted on a first
control channel. The receiver is also configured to receive an
indicator transmitted on a separate second control channel. The
transmitted indicator indicates when transmissions on the first
control channel are encoded using MU MIMO transmission. The
receiver is further configured to switch decoding of signals
received on the first control channel between using and not using
MU MIMO transmission based on the indicator. The processor is
configured to calculate a downlink signal quality for transmissions
received from a radio node in a wireless network. The processor is
also configured to transmit the calculated downlink signal quality
using channel quality indicators to the radio node in the wireless
network. The wireless network determines to use MU MIMO
transmission on the first control channel based at least in part on
the communicated calculated downlink signal quality.
[0007] In a further embodiment, non-transitory computer program
product encoded in a non-transitory computer readable medium for
increasing transmission capacity for a control channel in a
wireless network is described. The non-transitory computer program
product in a radio node in a radio access network of the wireless
network includes the following non-transitory computer program
code. Non-transitory computer program code for estimating a
received downlink signal quality for each mobile wireless device in
a plurality of mobile wireless devices connected to the radio node.
Non-transitory computer program code for selecting a first set of
mobile wireless devices in the plurality of mobile wireless
devices, each selected mobile wireless device having an estimated
downlink signal quality exceeding a first threshold. Non-transitory
computer program code for transmitting simultaneously to the first
set of mobile wireless devices on the control channel through a
plurality of antennas using multi-user (MU) multiple-input
multiple-output (MIMO) transmission.
[0008] Although described in terms of an LTE or LTE-Advanced
network, the embodiments disclosed herein can be extended to other
wireless networks that can support multi-user multiple-input
multiple-output transmissions as well.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The described embodiments and the advantages thereof may
best be understood by reference to the following description taken
in conjunction with the accompanying drawings.
[0010] FIG. 1 illustrates components of a generic wireless
communication network.
[0011] FIG. 2 illustrates components of a LTE wireless
communication network.
[0012] FIG. 3 illustrates components of an OFDM transmission frame
in an LTE wireless network.
[0013] FIG. 4 illustrates constituent components of a transmission
time interval for OFDM transmissions in the LTE wireless
network.
[0014] FIG. 5 illustrates several architectures for select
components in a mobile wireless device that supports receive
diversity.
[0015] FIG. 6 illustrates an organization of resource elements for
transmission on multiple antennas within a transmission time
interval across multiple subcarriers.
[0016] FIG. 7 illustrates transmission paths for a multiple input
multiple output. transmission.
[0017] FIG. 8 illustrates multiple mobile wireless devices arrayed
in a radio sector for a radio access subsystem in the LTE wireless
network.
[0018] FIG. 9 illustrates a representative method to increase
transmission capacity for a control channel in a wireless
network.
[0019] FIG. 10 illustrates another representative method to
increase transmission capacity for a control channel in a wireless
network.
DETAILED DESCRIPTION OF SELECTED EMBODIMENTS
[0020] In the following description, numerous specific details are
set forth to provide a thorough understanding of the concepts
underlying the described embodiments. It will be apparent, however,
to one skilled in the art that the described embodiments may be
practiced without some or all of these specific details. In other
instances, well known process steps have not been described in
detail in order to avoid unnecessarily obscuring the underlying
concepts.
[0021] The examples and embodiments provided below describe various
methods and apparatuses for increasing control channel capacity in
a wireless network for communication with multiple wireless mobile
devices. More specifically, methods and apparatuses are described
that use multi-user multiple-input multiple-output (MU MIMO)
transmission in an LTE network. It should be understood, however,
that other implementations of the same methods and apparatuses can
apply to mobile wireless devices used in other types of wireless
networks that support MU MIMO transmission.
[0022] Mobile wireless devices continue to evolve and offer more
advanced features that can benefit from higher data throughput
rates. The 3GPP LTE and LTE-Advanced communication protocols
standardize packet communication to provide a broad variety of
services varying from high speed data to basic voice communication.
The LTE protocols use a flexible communication method known as
orthogonal frequency division multiplexing (OFDM) that divides the
occupied frequency spectrum into multiple parallel low rate
sub-channels. A downlink transmitted OFDM symbol can contain
information intended for multiple users by assigning different
sub-channels to different users in the OFDM symbol. Assignments of
individual sub-channels for one or a set of OFDM symbols can be
communicated using a control channel broadcast to all wireless
mobile devices connected to a particular radio sector of a radio
access subsystem in a wireless network. As the performance of a
mobile wireless device can be particularly sensitive to errors on a
control channel, on which errant control message can affect
multiple data packets, the control channel can be protected using
various levels of error correction capability. Mobile wireless
devices that are located in areas of weak signal quality can
require greater levels of error protection for the control channel
than those mobile wireless devices with strong signal quality.
Higher levels of error protection can require more bandwidth to
communication the same amount of information; and thus, mobile
wireless devices having weaker signal quality can require greater
allocations of control channel resources. The total number of
control channel resources for allocation among all mobile wireless
devices simultaneously served by the radio access subsystem within
a geographical area covered by a radio sector can be limited in
number. As such, the total number of mobile wireless devices that
can be served simultaneously can be limited by the total amount of
control channel resources available.
[0023] The LTE and LTE-Advanced communication protocols include
provisions for transmission and reception of signals between the
radio access subsystem and the mobile wireless device using
multiple antennas. Transmission techniques known as multiple-input
multiple-output (MIMO) can be used to increase the capacity and/or
improve the reliability of transmission. One MIMO transmission
technique known as spatial multiplexing can allow control channel
communication to be shared among multiple users on the same
sub-channels in the same OFDM symbol, i.e. to re-use the same
frequency/time resources for multiple independent mobile wireless
devices. Transmissions to one mobile wireless device can be
separated by transmission to another mobile wireless device by
sending the transmissions on multiple antennas at the same time and
in the same frequency band. The different transmissions can be
separated from one another by each receiver in the mobile wireless
devices by using multiple receive antennas and sophisticated signal
processing techniques. Transmissions to other mobile wireless
devices can be considered "noise" with respect to the "signal"
transmission intended for a particular mobile wireless device. The
receiver in the mobile wireless device can separate the "signal"
from the "noise" when the mobile wireless device receives
sufficiently high quality signals. By using such techniques, the
capacity of the control channel can also be increased, i.e. the
number of mobile wireless devices that can served simultaneously
can be increased. Determining with which mobile wireless device to
use MIMO spatial multiplexing can be based on knowledge of the
respective received signal quality at the multiple mobile wireless
devices. Devices with higher receive signal quality can share the
same frequency/time resources more readily than those mobile
wireless devices that have lower receive signal quality. Control
elements in the radio access subsystem of the wireless network that
communicates with the mobile wireless devices can determine to
which mobile wireless devices to use MIMO spatial multiplexing (and
in which OFDM frequency subchannels and time symbols to use MIMO as
well.) The use of MIMO spatial multiplexing on the control channel
can be communicated in advance to the mobile wireless devices and
can be adapted as receive signal quality changes over time.
[0024] These and other embodiments are discussed below with
reference to FIGS. 1-10. However, those skilled in the art will
readily appreciate that the detailed description given herein with
respect to these figures is for explanatory purposes only and
should not be construed as limiting.
[0025] FIG. 1 illustrates a representative generic wireless
communication network 100 that can include multiple mobile wireless
devices 102 connected by radio links 126 to radio sectors 104
provided by a radio access network 128. Each radio sector 104 can
represent a geographic area of radio coverage emanating from an
associated radio node 108 using a radio frequency carrier at a
selected frequency. Radio sectors 104 can have different geometric
shapes depending on antenna configuration, such as radiating
outward in an approximate circle or hexagon from a centrally placed
radio node 108 or cone shaped for a directional antenna from a
corner placed radio node 108. Radio sectors 104 can overlap in
geographic area coverage so that the mobile wireless device 102 can
receive signals from more than one radio sector 104 simultaneously.
Each radio node 108 can generate one or more radio sectors 104 to
which the mobile wireless device 102 can connect by one or more
radio links 126.
[0026] In some wireless networks 100, the mobile wireless device
102 can be connected to more than one radio sector 104
simultaneously. The multiple radio sectors 104 to which the mobile
wireless device 102 is connected can come from a single radio node
108 or from separate radio nodes 108 that can share a common radio
controller 110. A group of radio nodes 108 together with the
associated radio controller 110 can be referred to as a radio
access subsystem 106. Typically each radio node 108 in a radio
access subsystem 106 can include a set of radio frequency
transmitting and receiving equipment mounted on an antenna tower,
and the radio controller 110 connected to the radio nodes 108 can
include electronic equipment for controlling and processing
transmitted and received radio frequency signals. The radio
controller 110 can manage the establishment, maintenance and
release of the radio links 126 that connect the mobile wireless
device 102 to the radio access network 128. Each mobile wireless
device 102 connected to the radio access subsystem 106 can be
located at a different distance from the radio node 108 from which
it can receive radio frequency signals for the radio links 126. The
radio controller 110 and/or the radio node 108 can control monitor
and control the strength of transmitted and received signals to
each mobile wireless device 102 to manage performance of the radio
link 126 connections. The radio access subsystem 106 can use a
combination of signal strength, data rate encoding, error
correction capability and multiple antenna transmission to improve
the performance of signal reception at the mobile wireless device
102 in the presence of variable noise and interference in the
wireless network 100.
[0027] The radio access network 128, which provides radio frequency
air link connections to the mobile wireless device 102, connects
also to a core network 112 that can include a circuit switched
domain 122, usually used for voice traffic, and a packet switched
domain 124, usually used for data traffic. Radio controllers 110 in
the radio access subsystems 106 of the radio access network 128 can
connect to both a circuit switching center 118 in the circuit
switched domain 122 and a packet switching node 120 in the packet
switched domain of the core network 112. The circuit switching
center 118 can route circuit switched traffic, such as a voice
call, to a public switched telephone network (PSTN) 114. The packet
switching node 120 can route packet switched traffic, such as a
"connectionless" set of data packets, to a public data network
(PDN) 116.
[0028] FIG. 2 illustrates a representative Long Term Evolution
(LTE) wireless network 200 architecture designed as a packet
switched network exclusively. A mobile terminal 202 can connect to
an evolved radio access network 222 through radio links 226
associated with radio sectors 204 that emanate from evolved Node
B's (eNodeB) 210. The eNodeB 210 includes the functions of both the
transmitting and receiving base stations (such as the radio node
108 in the generic wireless network 100) as well as the radio
access network subsystem radio controllers (such as the radio
controller 110 in the generic wireless network 100). The equivalent
core network of the LTE wireless network 200 is an evolved packet
core network 220 including serving gateways 212 that interconnect
the evolved radio access network 222 to public data network (PDN)
gateways 216 that connect to external internet protocol (IP)
networks 218. Multiple eNodeB 210 can be grouped together to form
an evolved UTRAN (eUTRAN) 206. The eNodeB 210 can also be connected
to a mobility management entity (MME) 214 that can provide control
over connections for the mobile terminal 202.
[0029] The radio links 226 between the eNodeB 210 in the eUTRAN 206
of the evolved radio access network 222 can include transmissions
that use multiple antennas at the transmitting end, at the
receiving end and/or at both ends. Transmission and reception using
multiple antennas can improve signal reception in the presence of
variable noise and interference between the mobile terminal 202 and
the eNodeB 210 with the radio sector 204. Multiple antenna
transmission can occur in several different forms, including
transmit diversity, single user spatial diversity and multiple user
spatial diversity. With transmit diversity, the same information
can be sent through two different paths, which can provide
redundancy for recovering the information at the receiver of the
mobile terminal 202. With single user spatial diversity, different
information can be sent through two different paths, which provides
for increased throughput to an individual mobile terminal 202. With
multiple user spatial diversity, different information can be sent
to different mobile terminals 202, thereby increasing the aggregate
amount of information that can be transmitted to a set of mobile
terminals 202. The number of mobile terminals 202 that can served
simultaneously by the eUTRAN 206 in the evolved radio access
network 222 can depend on the available transmission capacity to
send control information to the set of mobile terminals 202. As
will be described further herein, the transmission capacity for
control information can be increased through spatial diversity by
using multiple user multiple input multiple output transmissions
with multiple antennas in the LTE network 200.
[0030] Transmission on the LTE network 200 can use a form of
orthogonal frequency division multiple access (OFDMA) in the
downlink direction, i.e. from the eNodeB 210 to the mobile terminal
202, and single carrier frequency division multiple access
(SC-FDMA) in the uplink direction. With OFDMA, data can be
transmitted on multiple parallel sub-channels, each sub-channel
centered at a different sub-carrier frequency, to multiple mobile
terminals 202 at the same time. The allocation of sub-channels to
the multiple mobile terminals 202 can vary for different OFDM
symbols, and control information can be transmitted to the mobile
terminals 202 to indicate the allocation of radio frequency
resources over time. Each mobile terminal 202 can be allocated a
number of sub-channels for a specified period of time, i.e. a set
of frequencies across a number of successive OFDM symbols.
Allocation of the radio frequency resources can be scheduled by the
eNodeB 210 in the eUTRAN 206 of the evolved radio access network
222.
[0031] LTE transmissions can be organized into a succession of OFDM
symbols 308 as illustrated in FIG. 3. An LTE frame 302 can span a
period of 10 ms and can include 10 transmission timer intervals
(TTI) 304 that each span a time period of 1 ms. Each TTI 304 can
include two time slots 306 that each span 0.5 ms, and each time
slot 306 can include seven OFDM symbols 308. The OFDM symbol 308 as
shown in FIG. 3 can include a cyclic prefix 310 that can provide a
time domain guard interval to minimize inter-symbol interference
between successive OFDM symbols 308.
[0032] Each OFDM symbol 308 can include data transmitted on
multiple sub-channels, each sub-channel on a separate frequency. An
aggregate of a set of sub-channels (sub-carriers) for a set of
successive OFDM symbols can be considered a resource block 406 as
shown in FIG. 4. In a representative embodiment, the resource block
406 can include a set of twelve adjacent frequency subcarriers
during a time slot 306 of seven OFDM symbols 308. Two successive
resource blocks can span a transmission time interval (TTI) 306 and
can include fourteen OFDM symbols 308 divided into a set of control
402 OFDM symbols and a set of data 404 OFDM symbols. The total
number of frequency sub-carriers used for an OFDM symbol can depend
on the bandwidth allocated. With a sub-carrier spacing of 15 kHz,
each resource block 406 can span 180 kHz of bandwidth, and the
total bandwidth occupied can depend on the number of available
resource blocks 406. For example, an LTE transmission system that
uses fifty resource blocks 406 can span a bandwidth of 9 MHz
(lowest to highest sub-carrier center frequency) and can fit within
a 10 Mhz radio frequency total bandwidth (including side
lobes).
[0033] Each transmission on a single frequency subcarrier within a
single OFDM symbol 308 can be considered an individual resource
element (RE) 408 of a physical layer transmission. In general, the
RE 408 can be referred to as a frequency/time resource. The
resource elements 408 in the data portion 404 of a TTI 304 can be
allocated among multiple mobile terminals 202, and the allocation
of the RE 408 an be communicated to the mobile terminals 202 using
resource elements 408 in the control portion 402 of the TTI 304.
Four different resource elements 408 within a single OFDM symbol
308 can form a resource element group (REG) 410, and nine different
REGs 410 can form a control channel element (CCE). A physical
downlink control channel (PDCCH) message in the LTE transmission
system to one of the mobile terminals 202 can use one, two, four or
eight CCEs depending on a format selected for the PDCCH message.
The PDCCH message format can be based on received downlink signal
quality conditions measured at the mobile terminal 202 and reported
to the eNodeB 210 of the LTE wireless network 200. With a high
receive signal quality at the mobile terminal 202, one CCE can
suffice for the PDCCH message, while with a low receive signal
quality, up to eight CCE can be required to minimize decoding
errors of the PDCCH message at the mobile terminal 202.
[0034] The total number of mobile terminals 202 that can be
supported simultaneously in a given TTI 304 can depend on the
available signal quality at each of the mobile terminals 202 and on
the number of OFDM symbols 308 available for control channel
transmission. For each TTI 304, a total of fourteen OFDM symbols
308 can be available and can be divided between control
transmission and data transmission. One, two or three OFDM symbols
308 of the fourteen total OFDM symbols 308 in the TTI 304 can be
used for control 402, while the remaining OFDM symbols 308 in the
TTI 304 can be used for data 404. Some of the resource elements 408
in each resource block 406 can be reserved to carry reference
signals 412, as indicated by select RE 408 labeled with the letter
"R" in the resource block 408 of FIG. 4. The reference signal 412
resource elements 408 can provide a pre-determined known signal to
which the mobile terminal 202 can locate and synchronize as well as
characterize the downlink communication channel to the mobile
terminal 202 from the eNodeB 210 in the evolved radio access
network 222 of the wireless network 200. Within a resource block
406, which can have three OFDM symbols available for control 402
channel transmissions, two of the thirty six resource elements 408
can be used for reference signals 412. As a minimum allocation of
one CCE (36 RE) can be required for control channel communication
for each mobile terminal 202 for a given TTI 304, even with three
OFDM symbols 308 assigned for transmission of control 402
information, a maximum of less than fifty independent mobile
terminals 202 can be accommodated in an LAE transmission system
that occupies 10 MHz of frequency bandwidth. Each mobile terminal
202 that requires more than one CCE; for control channel
transmissions, i.e. when a mobile terminal 202 can have poor
receive radio frequency signal quality and can require 2, 4 or 8
CCE, can reduce the total number of mobile terminals 202 that can
be supported simultaneously per TTI 304, As LTE systems can be
expected to transport both high speed data and numerous lower rate
voice connections, increasing the number of mobile terminals 202
that can be simultaneously supported in each TEl 304 can prove
beneficial.
[0035] FIG. 5 illustrates select elements for several different
architectures that can be used in a mobile wireless device 102 (or
mobile terminal 202). A mobile terminal 202 can include multiple
antennas to improve downlink received signal performance, such as
increased robustness in the presence of noise and interference as
well as higher data rates. The architecture for a mobile terminal
202 can include an application processor (AP) 502, one or more
transceivers and multiple antennas. In a first architecture 500,
the mobile terminal 202 can include one transceiver 504 connected
to the AP 502 and also connected to two antennas. The AP 502 of the
mobile terminal 202 can initiate and terminate connections with the
wireless network 200 in response to application level services
active in the mobile terminal 202. The AP 502 can provide "higher
layer" processing that can establish packet level connections
through the wireless network 200, while the transceiver 504 can
provide "lower layer" signal processing that can translate the
higher layer packet messages into a format suitable for
transmission over the radio links 226 in the radio sector 204
supported by the eNodeB 210 of the eUTRAN 206 in the evolved radio
access network 222. The transceiver 504 can receive downlink
transmissions from the eNodeB 210 through one of the two antennas,
e.g. by selecting among the antennas having a stronger signal
strength or a higher signal quality, or through both antennas
simultaneously and combine the received signals to improve signal
reception.
[0036] In a basic form of diversity, the mobile terminal 202 with
configuration 500 can receive signals transmitted by a single
antenna at the eNodeB 210 through one of the antennas, either
antenna 0 or antenna 1, where the antenna used is switched into
service by the mobile terminal 202 (switch not shown). This form of
diversity can be considered "antenna diversity" in which one of the
antennas can provide better performance, e.g. based on signal
strength and/or signal quality, and the antenna used can be chosen
dynamically for a connection. Alternatively, when the transceiver
504 in the mobile terminal 202 can process signals from both
antennas simultaneously, the transceiver 504 can combine signals
transmitted on each of the different frequency sub-channels in an
OFDM symbol to improve signal strength and/or signal quality
throughout a received frequency spectrum. This combining of signals
received through multiple antennas simultaneously can be considered
"receiver diversity". With these basic forms of diversity, the
receive signal quality reported to the eNodeB 210 in the wireless
network 200 can be higher than without diversity, and the number of
CCE assigned for PDCCH transmissions can be lower, thereby freeing
up some CCE to be used for other mobile terminals 202.
[0037] A more advanced form of diversity can use simultaneous
transmission through multiple antennas at the eNodeB 210 and
simultaneous reception through multiple antennas at the mobile
terminal 202. This form of diversity can be referred to as multiple
input multiple output (MIMO) transmission and can be used to
increase transmission data rates to a single mobile terminal 202,
i.e. single user (SU) MIMO or to transmit data simultaneously to
multiple mobile terminals 202, i.e. multiple user (MU) MIMO.
Sharing the same frequency/time resources using MU MIMO across
multiple mobile terminals 202 can increase the number of mobile
terminals 202 that can be served simultaneously by the limited
number of CCE available per TTI 304, thereby increasing the
capacity of control channel communication in the LTE system. The
number of transmit and receive antennas used for MIMO can be two,
as shown for the architecture 500, as well as four as shown for
architecture 520 or even more (not shown). The LTE and LTE-Advanced
communication protocols include options for one, two, four and
eight antenna configurations. The mobile terminal 202 can determine
the number of transmit antennas used by the eNodeB 210 in the
wireless network 200 by using the transmitted reference signals
412.
[0038] While the description herein covers several different
architectures for mobile terminals 202 that can use multiple
antennas with one or more transceivers, some mobile wireless
devices 102 can include multiple receivers to support connections
to wireless networks that offer different wireless communication
protocols. The evolution of wireless network deployment can result
in periods of overlapping technologies that use different wireless
communication protocols that can require different transceivers,
The architecture 540 for a mobile wireless terminal 102 shown in
FIG. 4 includes a first transceiver 504 that can support multiple
antenna communication and a second transceiver 542 that can support
single antenna communication. The description provided herein
outlined in terms of a mobile wireless terminal 102 having multiple
antennas and a single transceiver block 504 can apply equally to
dual transceiver mobile wireless terminals 102. In some
embodiments, the single transceiver block 504 can also include
multiple parallel transceivers or configurable blocks that can
support reception through multiple antennas in parallel. No loss of
generality is intended by the depiction of a "single" transceiver
block 504 as shown for architecture 504 of the mobile wireless
terminal 102 in FIG. 5.
[0039] With MEMO transmission, the eNodeB 210 in the wireless
network 200 can send signals through multiple antennas. FIG. 6
illustrates how reference signals 412 can be divided between two
different antennas of the eNodeB 210. The resource blocks 610 for
one TTI 304 output by a first antenna 0 can include reference
signals 412 in select frequency/time resource elements 408 and can
exclude sending signals in other resource elements 408 (labeled as
"unused" RE 602). Similarly the resource blocks 620 for one TTI 304
output by a second antenna 1 can include reference signals 412 in
the same frequency/time resource elements 408 that were "unused" by
the first antenna 0. Thus, distinct reference signals 412 can be
transmitted by each antenna, and the mobile terminal 202 can
measure transmission channel characteristics for each antenna
separately using the distinct reference signals 412.
[0040] FIG. 7 illustrates four distinct transmission paths that can
be characterized by the mobile terminal 202 using reference signals
412 sent from transmit (TX) processing 702 at the eNodeB 210.
Receive (RX) processing 704 in the mobile terminal 202 can be used
to receive reference signals 412 transmitted by TX antenna 0 at the
eNodeB 210 through each of the receive antennas separately. The
TX0/RX0 transmission path can be characterized separately from the
TX0/RX1 transmission path by the RX processing 704 of the mobile
terminal 202 using reference signals 412 transmitted in specific
time/frequency resource elements 408 by the TX antenna 0. Similarly
the TX1/RX1 and TX1/RX0 transmission paths can be characterized
separately using reference signals 412 transmitted in a different
set of frequency/time resource elements 408 by the TX antenna 1 to
RX antenna 0 and RX antenna 1. As the reference signals from TX
antenna 0 and TX antenna 1 can be sent in separate time/frequency
resource elements 408 as shown in FIG. 6, the separate transmission
paths can be characterized independently. Once the transmission
paths are characterized, constituent component transmissions for
each of two different transmitting antennas can be determined from
the linear combinations of the transmitted signals received at each
antenna. MIMO transmission as shown in FIG. 7 can be used to
increase the amount of information transmitted to an individual
mobile terminal 202 by sending twice the amount of data using the
two transmitting antennas simultaneously for the same
frequency/time resource element. MIMO transmission can also be used
to transmit to two different mobile terminals 202, e.g. by
increasing the data throughput rate, with half of the data used for
One mobile terminal 202 and the other half of the data used for
another mobile terminal 202 simultaneously.
[0041] The LTE and LTE-Advanced communication protocols specify
several different MIMO transmission methods that can be applied to
downlink data channels; however, for downlink control channels only
a transmit diversity method is specified. Transmit diversity can
improve signal integrity but does not directly share the same
frequency/time radio frequency resource element between multiple
users. By applying MU MIMO for control channel communication from
the eNodeB 210, the wireless network 200 can increase the capacity
of the control channel and thereby serve more mobile terminals 202
simultaneously. Using MU MIMO and two spatially separated
transmitting antennas, the eNodeB 210 can transmit two parallel
control channel data streams simultaneously to two different mobile
terminals 202 sharing the same frequency/time resource elements.
Each of the parallel control channel data streams can be separately
encoded so that control channel data intended for one mobile
terminal 202 can be separated from control channel data intended
for another mobile terminal 202. This encoding at the eNodeB 210
can be referred to as "precoding" and can map control channel data
streams into suitable control channel data symbols for transmission
by the multiple antennas.
[0042] In a representative embodiment, the control channel data
stream for one mobile terminal 202 can be precoded using one "rank
1" vector, while the control channel data stream for a second
mobile terminal 202 can be precoded using a separate "rank 1"
vector. A representative set of four different "rank 1" vectors
from which to select precoding vectors for each mobile terminal 202
can include the following complex valued vectors:
{ 1 2 [ 1 1 ] , 1 2 [ 1 - 1 ] , 1 2 [ 1 j ] , 1 2 [ 1 - j ] , }
##EQU00001##
where the upper entry in each vector can signify the precoding
applied for data transmitted on a first antenna and the lower entry
in each vector can signify the precoding applied for data
transmitted on a second antenna. Each mobile terminal 202 in a set
of mobile terminals that can share frequency/time resources through
MU MIMO can be assigned a different one of the precoding vectors
and can use that knowledge to correctly decode signals received
through its two antennas and to reconstruct its own intended
original data stream. When using four transmit antennas, the set of
precoding vectors can include vectors of length four instead of
length two as shown above for two transmit antennas.
[0043] FIG. 8 illustrates a partition 800 of a radio sector 104 for
a wireless network 100 into three distinct regions nominally based
on distance from a radio access subsystem 106 of the wireless
network 100. A set of mobile wireless devices 102 in a far region
806 can be located at a farthest distance from the radio access
subsystem 106, and signals transmitted by the radio access
subsystem 106 to a mobile wireless device 102 in the far region 806
can incur significant amounts of attenuation. As such, mobile
wireless devices 102 in the far region can have the weakest receive
signal strength and/or the weakest signal quality of mobile
wireless devices 102 served by the radio access subsystem 106 in
the radio sector 104 of the wireless network 100. As mobile
wireless devices 102 can report periodically a channel quality
indicator (CQI) to the radio access subsystem 106, and the radio
access subsystem 106 can categorize the mobile wireless devices 102
based on the CQI (or other performance information) to determine
the number of CCE to assign for a downlink control channel (e.g.
the physical downlink control channel PDCCH) to each mobile
wireless device 102 served by the radio access subsystem 106.
[0044] For mobile wireless devices with a relatively high signal
strength and/or high signal quality, e.g. located in a near region
802 relatively close to the radio access subsystem 106, a minimum
of only one CCE can be used for the control channel information. As
the number of mobile wireless devices 102 in the radio sector that
can be served simultaneously can be limited by the total number of
CCE available, the radio access subsystem 106 can group together
one or more sets of mobile wireless devices 102 located in the near
region 802 of the radio sector 104. Each mobile wireless device 102
in the set can have comparable signal strength and/or signal
quality and can share one CCE among of the set of mobile wireless
devices 102 in the near region 802 using MU MIMO transmission for
the control channel information. When transmitting from the radio
access system 106 with two antennas to mobile wireless devices 102
having two antennas, the radio access subsystem 106 can pair up
mobile wireless devices 102 in the near region 802 in sets of two
mobile wireless devices 102 with comparable signal
strength/quality. When transmitting with four antennas to mobile
wireless devices 102 that can receive MU MIMO transmissions with
four antennas, the radio access subsystem 106 can group the mobile
wireless devices 102 in the near region 802 into sets of up to four
mobile wireless devices 102 to share a single ME.
[0045] The radio access subsystem 106 can use different strategies
to add control channel capacity with MU MIMO transmission depending
on one or more factors such as the number of mobile wireless
devices 102 associated with the radio access subsystem 106, the
number of mobile wireless devices 102 actively connected to the
radio access subsystem 106, the number of transmit antennas at the
radio access subsystem 106, the number of receive antennas at each
of the mobile wireless devices 102, measured receive signal
strength and/or signal quality communicated from each mobile
wireless device 102 to the radio access subsystem 106, and
selection and use of MU MIMO on data channels for a particular
mobile wireless device 102.
[0046] FIG. 9 illustrates a representative method 900 to increase
transmission capacity for a control channel in a wireless network
100. The method can be executed at a radio node 108 in a radio
access network 128 of the wireless network 100. In step 902, the
radio node 108 can estimate downlink signal quality for a plurality
of mobile wireless devices 102. In a representative embodiment, the
downlink signal quality can be reported by one or more of the
plurality of mobile wireless devices 102 to the radio node 108
using channel quality feedback indicators. In step 904, the radio
node 108 can select a set of mobile wireless devices 102 each
having an estimated downlink signal quality that exceeds a first
pre-determined threshold. In a representative embodiment, the first
pre-determined threshold can be set the wireless network 100 and
can be communicated to the mobile wireless device 102. In step 906,
the radio node 108 can transmit simultaneously to the set of mobile
wireless devices 102 on the control channel using MU MIMO
transmission. In a representative embodiment, at least two of the
mobile wireless devices 102 in the set of mobile wireless devices
102 can be assigned to a common control channel element (CCE) that
occupies a set of time and frequency resource elements during a
transmission time interval for the control channel. The
transmission capacity of the control channel can be limited by the
number of control channel elements that can be scheduled for each
transmission time interval. In a representative embodiment, the
radio node can transmit an indication to the mobile wireless device
102 when MU MIMO transmission is used for transmission of the
control channel. The number of mobile wireless devices 102 that
share a common CCE using MU MIMO transmission can depend on the
estimated receive downlink signal quality. Higher receive downlink
signal quality can support sharing of the common CCE among more
mobile wireless devices 102 simultaneously than lower receive
downlink signal quality.
[0047] FIG. 10 illustrates another representative method 1000 to
increase transmission capacity for a control channel in a wireless
network 100. The method can be executed at a mobile wireless device
102 in the wireless network 100. In step 1002, the mobile wireless
device 102 can calculate a received downlink signal quality. In
step 1004, the mobile wireless device 102 can transmit the
calculated downlink signal quality using channel quality indicators
to a radio node 108 in the wireless network 100. In step 1006, the
mobile wireless device 102 can receive and decode signals on a
first control channel. In step 1008, the mobile wireless device 102
can receive an indicator on a second control channel that can
indicate when transmissions on the first control channel can use MU
MIMO. In step 1010, the mobile wireless device can switch decoding
of signals received on the first control channel between using and
not using MU MIMO based on the received indicator from the wireless
network 100. In a representative embodiment, the mobile wireless
device 102 can receive from the wireless network 100 notification
of an assigned rank one pre-coding matrix used for MU MEMO
transmission on the first control channel. The mobile wireless
device 102 can decode the signals received on the first control
channel using the assigned rank one pre-coding matrix.
[0048] In a representative embodiment, the first control channel,
on which the mobile wireless device 102 can receive MU MIMO
transmissions, and the second control channel, on which the mobile
wireless device 102 can receive indications when transmissions on
the first control channel use MU MIMO transmissions, can be the
same physical control channel. An exemplary physical control
channel can be the PDCCH control channel. The mobile wireless
device 102 can receive the physical control channel initially
without using MU MIMO and can switch to using MU MIMO based on a
message transmitted in the physical control channel. The message
can indicate a switch to MU MIMO transmission at a particular
frame. Messages in the physical control channel can use MU MIMO
transmission from that particular indicated frame onward until a
subsequent message can indicate a switch to not use MU MIMO
transmission. In another embodiment, the mobile wireless device 102
can detect when MU MIMO transmission is used and can appropriately
decode the received transmissions on the PDCCH control channel
based on the detection. In another embodiment, the mobile wireless
device 102 can decode transmissions on the PDCCH control channel
trying different transmission modes, such as with MU MIMO and
without MU MIMO, to achieve a best decoding of the PDCCH control
channel.
[0049] In another representative embodiment, the first control
channel and the second control channel can be separate physical
control channels. Separate physical control channels can be, for
example, a first PDCCH and a second PDCCH. Messages on the first
control channel can switch between using and not using MU MIMO
based on messages transmitted on the second control channel. The
second control channel can use a fixed transmission method with
high reliability, such as with transmission diversity.
[0050] In another representative embodiment, the first control
channel and the second control channel can be separate logical
channels on the same physical control channel. Separate logical
channels can be two different logical channels that share the same
PDCCH. A PDCCH can use multiple control channel elements (CCEs)
that span multiple time/frequency resource elements, a two
different blocks of time/frequency resource elements that are used
by the PDCCH can be grouped into separate control channels
(effectively separate control sub-channels within the PDCCH control
channel).
[0051] The various aspects, embodiments, implementations or
features of the described embodiments can be used separately or in
any combination. Various aspects of the described embodiments can
be implemented by software, hardware or a combination of hardware
and software.
[0052] The foregoing description, for purposes of explanation, used
specific nomenclature to provide a thorough understanding of the
described embodiments. However, it will be apparent to one skilled
in the art that the specific details are not required in order to
practice the described embodiments. Thus, the foregoing
descriptions of the specific embodiments described herein are
presented for purposes of illustration and description. They are
not target to be exhaustive or to limit the embodiments to the
precise forms disclosed. It will be apparent to one of ordinary
skill in the art that many modifications and variations are
possible in view of the above teachings.
[0053] The advantages of the embodiments described are numerous.
Different aspects, embodiments or implementations can yield one or
more of the following advantages. Many features and advantages of
the present embodiments are apparent from the written description
and, thus, it is intended by the appended claims to cover all such
features and advantages of the invention. Further, since numerous
modifications and changes will readily occur to those skilled in
the art, the embodiments should not be limited to the exact
construction and operation as illustrated and described. Hence, all
suitable modifications and equivalents can be resorted to as
falling within the scope of the invention.
* * * * *