U.S. patent application number 15/022893 was filed with the patent office on 2016-08-04 for synchronization of device to device communication.
The applicant listed for this patent is INTEL IP CORPORATION. Invention is credited to Debdeep Chatterjee, Alexey Khoryaev, Sergey Panteleev, Mikhail Shilov.
Application Number | 20160227496 15/022893 |
Document ID | / |
Family ID | 52995317 |
Filed Date | 2016-08-04 |
United States Patent
Application |
20160227496 |
Kind Code |
A1 |
Panteleev; Sergey ; et
al. |
August 4, 2016 |
SYNCHRONIZATION OF DEVICE TO DEVICE COMMUNICATION
Abstract
A wireless communication device is configured to perform
synchronization of device-to-device (D2D) communication.
Device-to-device communication circuitry in the wireless
communication device searches for a synchronization signal and
determines if a received synchronization signal satisfies a signal
metric. A synchronization signal for D2D communication is broadcast
depending upon a result of the search. Radio resource information
circuitry is configured to broadcast information about D2D radio
resources. Other embodiments may be described and claimed.
Inventors: |
Panteleev; Sergey; (Nizhny
Novgorod, RU) ; Shilov; Mikhail; (Nizhny Novgorod,
RU) ; Khoryaev; Alexey; (Nizhny Novgorod, RU)
; Chatterjee; Debdeep; (Mountain View, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INTEL IP CORPORATION |
Santa Clara |
CA |
US |
|
|
Family ID: |
52995317 |
Appl. No.: |
15/022893 |
Filed: |
September 26, 2014 |
PCT Filed: |
September 26, 2014 |
PCT NO: |
PCT/US14/57895 |
371 Date: |
March 17, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61898425 |
Oct 31, 2013 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 76/10 20180201;
H04W 74/0833 20130101; H04W 76/19 20180201; H04W 36/305 20180801;
H04W 56/001 20130101; H04W 88/16 20130101; H04W 4/023 20130101;
H04W 28/08 20130101; H04W 72/10 20130101; H04W 92/20 20130101; H04W
4/02 20130101; H04W 36/0069 20180801; H04J 3/1694 20130101; H04W
8/06 20130101; H04W 76/18 20180201; H04W 88/18 20130101; H04B
7/0413 20130101; H04L 5/001 20130101; H04W 48/08 20130101; H04W
76/15 20180201; H04W 28/0215 20130101; H04L 5/0098 20130101; H04W
8/005 20130101; Y02D 30/70 20200801; H04L 5/0007 20130101; H04W
52/346 20130101; H04W 72/085 20130101; H04W 74/004 20130101; H04W
88/02 20130101; H04W 36/0055 20130101; H04W 72/0486 20130101; H04W
48/18 20130101; H04W 60/00 20130101; H04B 17/318 20150115; H04W
88/08 20130101; H04W 48/12 20130101; H04W 56/002 20130101; H04W
72/0453 20130101; H04W 8/04 20130101; H04W 8/183 20130101; H04W
60/02 20130101; H04W 76/14 20180201; H04W 4/60 20180201; H04W
72/048 20130101; H04W 84/12 20130101; H04W 48/06 20130101; H04W
4/90 20180201; H04W 24/10 20130101; H04W 4/80 20180201 |
International
Class: |
H04W 56/00 20060101
H04W056/00; H04W 8/00 20060101 H04W008/00; H04W 76/02 20060101
H04W076/02 |
Claims
1. Device-to-device communication circuitry, for use in a device of
a wireless communication network, the device being configured to
transmit and receive device-to-device communications, the circuitry
comprising: scanning circuitry configured to search for a
device-to-device synchronization signal and to determine if a
received synchronization signal satisfies a signal quality metric;
synchronization signal broadcasting circuitry configured to
broadcast, depending upon a result of the search performed by the
scanning circuitry, a synchronization signal for synchronizing data
communication on at least one device-to-device communication link
between any transmitting device and any receiving device within a
synchronization range of the device-to-device communication
circuitry; and radio resource information circuitry, configured to
broadcast information about radio resources for device-to-device
operation.
2. The device-to-device communication circuitry of claim 1, wherein
the radio resource information circuitry is configured to recommend
at least a subset of wireless radio resources for allocation to the
at least one device-to-device communication link.
3. The device-to-device communication circuitry of claim 2, wherein
the radio resource information circuitry indicates a subset of
recommended wireless radio resources comprising a subset of time
resources.
4. The device-to-device communication circuitry of claim 2, wherein
the radio resource information circuitry is one of: (i)
preconfigured to store the recommended subset of wireless radio
resources; and (ii) configured to dynamically allocate the subset
of wireless radio resources depending upon the result of the
scanning circuitry search.
5. The device-to-device communication circuitry of claim 1, wherein
the synchronization signal broadcasting circuitry is configured to
trigger broadcast of an independent synchronization signal if no
received device-to-device synchronization signal is detected by the
scanning circuitry.
6. The device-to-device communication circuitry of claim 1, wherein
when the scanning circuitry determines that an existing
synchronization signal, which fails to satisfy the signal quality
metric, is present without a synchronization signal that satisfies
the signal quality metric also being present, the synchronization
signal broadcasting circuitry is configured to establish a gateway
synchronization source by broadcasting a propagated synchronization
signal, the propagated synchronization signal deriving timing from
the existing synchronization signal.
7. The device-to-device communication circuitry of claim 6, wherein
the gateway synchronization source is configured to broadcast the
propagated synchronization signal on radio resources orthogonal in
time to radio resources used to convey the existing synchronization
signal.
8. The device-to-device communication circuitry of claim 6, wherein
the radio resource information circuitry is configured to recommend
for device-to-device communications that derive synchronization
from the gateway synchronization source, a set of time resources
different from an existing set of time resources currently
recommended for to device-to-device communications that derive
synchronization from the existing synchronization signal.
9. The device-to-device communication circuitry of claim 6, wherein
the radio resource information circuitry of the gateway
synchronization source is configured to recommend for
device-to-device communications that derive synchronization from
the gateway synchronization source, a set of frequency resources
different from an existing set of frequency resources currently
recommended for to device-to-device communications deriving
synchronization from the existing synchronization signal.
10. The device-to-device communication circuitry of claim 1,
wherein the received signal metric comprises at least one: of
synchronization hop count, received signal power, received signal
arrival time and Signal to Interference plus Noise Ratio (SINK),
taken jointly and severally in any and all combinations.
11. The device-to-device communication circuitry of claim 1,
wherein the scanning circuitry is configured such that when a
plurality existing synchronization signals are present, the
scanning circuitry selects one of the existing synchronization
signals to camp-on to depending upon the signal metric and
suppresses broadcast of the synchronization signal by the
synchronization signal broadcast circuitry.
12. The device-to-device communication circuitry of claim 1,
wherein the scanning circuitry is configured to compare a received
synchronization signal with a threshold corresponding to the signal
quality metric and wherein broadcast of the synchronization signal
depends upon the threshold comparison.
13. The device-to-device communication circuitry of claim 12,
wherein the scanning circuitry is configured to set the threshold
for the synchronization signal quality metric depending on at least
one of: pre-configured settings and an interference estimate
providing an indication of in-band interference on at least one
device-to-device communication link of the wireless communication
network.
14. The device-to-device communication circuitry of claim 6,
wherein the synchronization signal broadcasting circuitry of the
gateway synchronization source is configured to broadcast to other
devices a synchronization hop count providing an indication of a
hierarchical level of the gateway synchronization source relative
to a master synchronization source.
15. One of a UE, a picocell, a femtocell and a relay node
comprising the device-to-device communication circuitry of claim
1.
16. A method of performing synchronization of peer-to-peer
communication signals between wireless equipments at the same
hierarchical level of a wireless communication network, the method
comprising: searching at a wireless equipment for receipt of a
peer-to-peer synchronization signal and determining if a received
synchronization signal satisfies a required signal characteristic;
broadcasting from the wireless equipment a synchronization signal
having a timing derived independently from any synchronization
source corresponding to an eNB, the broadcast synchronization
signal defining a common timing for peer-to-peer communications
between any transmitting wireless equipment and any receiving
wireless equipment within a synchronization range of the
broadcasting wireless equipment and wherein broadcasting of the
synchronization signal is suppressed depending upon whether a
received signal satisfying the required signal characteristic is
found during the search.
17. The method of claim 16, comprising broadcasting a derived
synchronization signal when a received synchronization signal not
satisfying the required signal characteristic is detected in the
absence of detection of a received synchronization satisfying the
required signal characteristic, the derived synchronization signal
deriving synchronization timing from the received synchronization
signal.
18. The method of claim 17, wherein the derived synchronization
signal uses different time resources from time resources occupied
by the received synchronization signal.
19. The method of claim 17, comprising broadcasting a preferred
radio resource allocation for peer-to-peer data communications that
utilize the derived synchronization signal, the preferred radio
resource allocation being orthogonal in time to radio resources
corresponding to peer-to-peer communication links that utilize the
received synchronization signal.
20. The method of claim 16, wherein the wireless equipment
comprises one of: a UE, a picocell, a femtocell and a relay
node.
21. A computer program product embodied on a non-transitory
computer-readable medium comprising program instructions configured
such that when executed by processing circuitry cause the
processing circuitry to implement the method of claim 16.
22. Device-to-device communication circuitry, for use in a device
of a wireless communication network, the device being configured to
transmit and receive device-to-device communications, the circuitry
comprising: means for searching for a device-to-device
synchronization signal and to determine if a received
synchronization signal satisfies a signal quality metric; means for
synchronization signal broadcasting, configured to broadcast,
depending upon a result of the search performed by the scanning
circuitry, a synchronization signal for synchronizing data
communication on at least one device-to-device communication link
between any transmitting device and any receiving device within a
synchronization range of the device-to-device communication
circuitry; and means for broadcasting information about radio
resources for device-to-device communication.
23. The device-to-device communication circuitry of claim 22,
wherein the means for broadcasting information is configured to
indicate a subset of recommended wireless radio resources for
allocation to D2D communications comprising a subset of time
resources.
24. A UE for use in a wireless communication network, the UE
comprising: a touchscreen configured to receive input from a user
for processing by the UE; a transceiver module configurable to
enable device-to-device communication; a scanning module configured
to search for a device-to-device synchronization signal and to
determine if a received synchronization signal satisfies a signal
quality metric; a synchronization signal broadcasting module
configured to broadcast, depending upon a result of the search
performed by the scanning circuitry, a synchronization signal for
synchronizing data communication on at least one device-to-device
communication link between any transmitting device and any
receiving device within a synchronization range of the
device-to-device communication circuitry; and a radio resource
information module, configured to broadcast information about radio
resources for device-to-device operation.
25. The UE of claim 24, wherein the synchronization signal
broadcasting module is configured to broadcast the synchronization
signal using radio resources orthogonal in time to a received
synchronization signal corresponding to a different synchronization
source.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Patent Application No. 61/898,425, filed 31 Oct. 2013, entitled
"ADVANCED WIRELESS COMMUNICATION SYSTEMS AND TECHNIQUES", the
entire disclosure of which is hereby incorporated by reference.
TECHNICAL FIELD
[0002] Embodiments described herein generally relate to the field
of communications, and more particularly, to device-to-device (D2D)
or peer-to-peer communication in wireless communication
networks.
BACKGROUND
[0003] It is known in wireless communication systems to provide
data communication services such as Internet access and local
services through license exempt radio resource bandwidths using
wireless local-area network (WLAN) technologies such as Wi-Fi and
Wi-Fi Direct, which are based on Institute of Electrical and
Electronics Engineers (IEEE) 802.11 standards or using wireless
personal area network (WPAN) technologies such as Bluetooth and
Ultra Wideband technologies. WLAN and WPAN technologies allow for
higher data rates and lower energy consumption by exploiting short
distances between a transmitter and receiver. However, Wi-Fi and
Bluetooth are susceptible to sources interference from other
communications in the unlicensed band and there is no network-based
interference management available for these technologies. In the
third generation partnership project (3GPP) long term evolution
(LTE) and LTE-Advanced (LTE-A) licensed radio band, femtocells,
picocells and relays also make use of short distances between
transmitter and receiver to perform efficient communication with
user equipments (UEs), but these systems require that the data
communications pass through the picocell/femtocell base station or
relay rather than passing directly between transmitting and
receiving UEs and they also require a backhaul connection to an LTE
or LTE-A eNodeB of a wireless cellular system. D2D communications
utilizing the LTE/LTE-A spectrum offer the possibility of extending
the maximum transmission distance (possibly up to around 1000 m)
relative to technologies such as Bluetooth (10-100 m approximate
range) and Wi-Fi direct (200 m approximate range) and can reduce
the costs and scalability problems potentially associated with the
backhaul connection required for picocell/femtocell/relay
infrastructure-based networks. D2D communications according to the
present technique may also comprise Peer-to-Peer (P2P)
communications involving direct communication between network
entities or wireless equipment(s) at the same hierarchical level of
the wireless network, for example direct communications between
picocells, femtocells and relays as well as direct communications
between wireless devices such as UEs. A wireless equipment includes
at least a UE, a picocell, a femtocell and a relay node, but is in
no way limited to these examples.
[0004] D2D/P2P communications allow offloading of some network
traffic, but there is a need to carefully manage interference
arising from the D2D layer to protect both cellular and D2D
communication links from in-band emission interference. In-band
emission interference corresponds to leakage in a given transmitter
within the channel bandwidth, and the resulting leakage can
interfere with other transmitters. Out-of-band interference
originates from a neighboring transmitter configured to transmit in
a different frequency bandwidth, but which still produces energy in
the frequency bandwidth of the given transmitter. One of the many
potential applications of D2D wireless communication is in public
safety scenarios when cellular infrastructure may be partially or
completely damaged or dysfunctional. In such public safety
scenarios it is desirable for D2D communication to be maintained
when UEs are out of network coverage, although they should still be
able to take advantage of cellular network control when the
cellular infrastructure remains intact. There is a need for
out-of-coverage D2D communication techniques that provide for
effective interference management, and which promote energy
efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] Embodiments described herein are illustrated by way of
example, and not by way of limitation, in the figures of the
accompanying drawings in which like reference numerals refer to
similar elements:
[0006] FIG. 1 schematically illustrates a wireless communication
network implementing D2D/P2P communication;
[0007] FIG. 2 schematically illustrates a wireless communication
system capable of out-of-coverage D2D transmission;
[0008] FIG. 3 schematically illustrates voice data
transmission/reception using a D2D link between two UEs;
[0009] FIG. 4 is a flow cart schematically illustrating
hierarchical synchronization source assignment as implemented by a
D2D-enabled device such as a UE;
[0010] FIG. 5 is a signal timing diagram schematically illustrating
how two different UE pairs in different partially overlapping
transmission regions establish synchronization;
[0011] FIG. 6 schematically illustrates time and frequency
resources allocated to a pair of D2D transmitters deriving
synchronization timing from an independent synchronization
source;
[0012] FIG. 7 schematically illustrates a block diagram of radio
frame resources corresponding to an uplink or downlink LTE radio
frame structure;
[0013] FIG. 8 schematically illustrates time-frequency resource
allocation of a pair of D2D transmitters deriving timing from a
master synchronization source and a pair of D2D transmitters
deriving timing from a subsidiary synchronization source;
[0014] FIG. 9 schematically illustrates a time-frequency resource
grid for D2D resource allocations for transmissions controlled a
master synchronization source and five surrounding transmission
ranges controlled by respective subsidiary synchronization
sources;
[0015] FIG. 10 schematically illustrates how frequency division
multiplexing may be applied between two different Independent
Synchronization Sources having no common synchronization
timing;
[0016] FIG. 11 illustrates an example system according to some
embodiments; and
[0017] FIG. 12 shows an embodiment in which the system of FIG. 11
implements a wireless device such as UE.
DESCRIPTION OF EMBODIMENTS
[0018] Illustrative embodiments of the present disclosure include,
but are not limited to, methods, systems and apparatuses for
performing wireless device-to-device communication.
[0019] FIG. 1 schematically illustrates a wireless communication
network 100 implementing D2D/P2P communication both in and out of
cellular wireless network coverage from a cellular network such as
an LTE or LTE-A network. The network 100 comprises a node 110 and
UEs 132, 134, 136, 138. In 3GPP radio access network (RAN) LTE and
LTE-A systems, the node 110 can be an Evolved Universal Terrestrial
Radio Access Network (E-UTRAN) Node B (also commonly denoted as an
evolved Node B, enhanced Node B, eNodeB, or eNB) or a combination
of a node and one or more Radio Network Controllers (RNCs), The
node/eNB 110 communicates with one or more wireless device, known
as a user equipment (UE). Examples of a UE include a mobile
terminal, a tablet computer, a personal digital assistant (PDA) and
a machine-type communication (MTC) device. The downlink (DL)
transmission can be a communication from the node (or eNB) to the
wireless device (or UE), and the uplink (UL) transmission can be a
communication from the wireless device to the node.
[0020] A first D2D cluster 130 comprises a first UE 132 and a
second UE 134, which are each within network coverage because they
are both located in a cell 120 associated with the eNB 110. A
cluster may include more than two UEs. A direct communication path
141 exists between the first UE 132 and the second UE 134, allowing
data to pass between a transmitting UE and a receiving UE without
being routed via the eNB 110. However, in this embodiment, control
of the D2D data path, Ud, 141 is performed via the eNB 110 using
cellular communication paths 143 and 145. Thus data passes directly
between the transmitting and receiving UEs 132, 134 whereas control
of the D2D link is performed via the eNB 110. The eNB 110 performs
setup control, radio bearer control and resource control of the D2D
communication 141. In the embodiment of FIG. 1, both UEs 132, 134
of the first D2D cluster 130 are in direct communication with the
eNB 110, but in alternative embodiments only a subset of at least
one UE in a D2D cluster may be in direct communication with the eNB
110 while other UEs of the cluster are capable of performing D2D
communication with other cluster devices without having a direct
cellular communication link to the eNB 110.
[0021] In such alternative embodiments, one UE having contact with
the eNB 110 may serve as a D2D coordinator of the cluster 130. A UE
that performs D2D coordination within a cluster may be denoted a
"Peer Radio Head" (PRH) or "cluster head". The D2D cluster 130
corresponds to an in-coverage D2D communication scenario, where at
least one UE 132, 134 has connectivity to the wireless cellular
infrastructure via the eNB 110 for control of the D2D
communications. For the in-coverage D2D cluster 130, cellular
spectrum (e.g. LTE or LTE-A spectrum) can be used for both the D2D
link 141 and the cellular links 143, 145. In some embodiments
communication may be configured in "underlay" mode, where D2D links
and cellular links dynamically share the same radio resources and
in other embodiments in "overlay" mode may be used, where D2D
communication links are allocated dedicated cellular wireless
resources.
[0022] A further D2D cluster 150 comprising a third UE 136 and a
fourth UE 138 corresponds to an out-of-coverage D2D cluster, in
which neither of the UEs 136, 138 is able to form a connection with
an eNB of the wireless cellular infrastructure. In this
out-of-coverage D2D communication cluster 150, the UEs themselves
should be configured to perform peer discovery, interference
management and power control without network support. In public
safety scenarios it is likely that D2D clusters will have network
support prior to any public safety incident and thus some network
pre-configuration of UEs may be performed, but after a public
safety incident there could be partial or no network coverage as
illustrated in the second D2D cluster 150 of FIG. 1.
[0023] In the first D2D cluster 130, which is in-coverage, the two
UEs 132, 134 of the cluster pair are synchronized with the eNB 110
and they acquire frequency synchronization from the eNB 110 and
also slot and frame timing. The in-coverage UEs 132, 134 also have
access to system parameters such as cyclic prefix length and
duplexing mode and are synchronized to each other before a D2D
radio bearer is established. Synchronization of a D2D communication
link in time and frequency between the UEs can thus be performed by
each UE 132, 134 repeatedly synchronizing with the serving eNB 110
or alternatively using reference signals in every timeslot similar
to LTE demodulation reference signals (DMRS).
[0024] Performing D2D communications as shown in FIG. 1 allows for
reuse of radio resources between D2D communications and cellular
communications. The D2D communication link 141 uses a single hop
between UEs 132, 134, unlike a cellular link between the UEs 132,
134 that would require a two-hop link (the first hop being from
transmitting UE to eNB and the second hop being from eNB to
receiving UE) for data transfer via the eNB 110. There is a
proximity gain due to the close proximity between UEs 132, 134 with
potentially favorable propagation conditions allowing for higher
peak data rates than might be achieved when data is routed via the
more distant eNB 110. Latency can also improve by implementing a
D2D link rather than a cellular link between the UEs 132, 134,
because processing performed by the eNB is effectively
bypassed.
[0025] For in-coverage data communication as illustrated in FIG. 1,
Voice Over Internet Protocol (VoIP) can be used to communicate
voice data in real-time. As shown in FIG. 1, the eNB 110 has access
to a Session Initiation Protocol (SIP) server 160, which is in
communication with an IP Multimedia subsystem (IMS) 162. The SIP
server 160 and IMS 162 manage VoIP connections and separate data
bearers with different Quality-of-Service (QoS) specifications are
used for the SIP signaling and voice information. As shown in FIG.
1, the eNB 110 also provides the UE with access to the Internet 164
via a Packet Data Network (PDN) gateway 166. Thus VoIP for the
in-coverage scenario of FIG. 1 requires support both in the UE and
from the cellular network. By way of contrast, for the UEs 136, 138
belonging to the out-of-coverage cluster 150, voice services have
to be fully supported by the UEs themselves. FIG. 3, described
below, schematically illustrates processing performed by two
out-of-coverage UEs to support communication of voice data on a D2D
communication link.
[0026] Setting up D2D communication may be considered to include
two stages: proximity discovery, and subsequent initialization and
initiation of the D2D communication. Proximity discovery may be
achieved, for example, based on positioning information using e.g.,
Global Positioning Satellite (GPS) or Assisted-GPS information. The
second stage includes allocation of network resources (e.g.
bandwidth) to the D2D communication.
[0027] Most D2D schemes can be classified as belonging to one of
two types, termed normal (commercial) D2D and public safety D2D.
Some devices may be arranged to operate according to both schemes,
while other devices may be arranged to operate according to only
one of these schemes.
[0028] According to normal D2D, the D2D-enabled UEs (i.e. UEs that
support proximity-based discovery and communication) are able to
communicate directly with each other only within commercial
cellular LTE/LTE-A network coverage, i.e. with the help of network
elements such as eNBs, mobility management entities (MME), serving
gateways (S-GW), etc. This scheme allows the eNB (or other elements
of the core network) to exercise control over the network resources
that are used during the D2D communication, to minimize
interference with nearby devices, for example.
[0029] In contrast, public safety D2D is intended to be usable when
commercial and/or public safety infrastructure based (cellular)
network coverage is not available, e.g. when a network is suffering
from outage (due to natural disaster, power outage, network energy
saving, incomplete network deployment, etc.). The public safety
D2D-enabled UEs (i.e. UEs that support proximity-based discovery
and communication within public safety or both commercial and
public safety cellular LTE/LTE-Advanced network coverage) can
communicate with each-other even when the infrastructure based
network elements are not available to participate in the setup of
the D2D communication.
[0030] The following lists summarize scenarios in which D2D
communication is to be enabled or disabled.
[0031] A. Normal (commercial) D2D
[0032] A1. Enabling D2D for new communication [0033] Establishing
D2D direct path
[0034] A2. Enabling D2D for ongoing communication [0035] Switching
from cellular path to D2D direct path
[0036] A3. Disabling D2D while session is active (for ongoing
communication) [0037] Switching from D2D direct path to cellular
path
[0038] A4. Disabling D2D at the end of session [0039] Ongoing
direct communication is completed. [0040] Network should be made
aware of this (e.g. for charging purposes) [0041] Network should
update resource inventory.
[0042] B. Public Safety D2D
[0043] B1. Enabling D2D for new communication [0044] Establishing
D2D direct path with and without network coverage [0045] Ability of
autonomous discovery in absence of network coverage [0046] Ability
of autonomous communication in absence of network coverage
[0047] B2. Enabling D2D for ongoing communication [0048] Switching
from cellular path to D2D direct path with and without network
coverage [0049] Ability of autonomous fail-safe and seamless
switching in absence of network coverage
[0050] B3. Disabling D2D while session is active (for ongoing
communication) [0051] Switching from D2D direct path to cellular
path within network coverage [0052] Switching from D2D direct path
to cellular path when network is available again after outage
[0053] B4. Disabling D2D at the end of session [0054] Ongoing
direct communication is completed. [0055] Network should be made
aware of this for charging purposes [0056] Network should update
resource inventory [0057] D2D coordinator, if exists, should be
made aware for updating resources inventory
[0058] B5. Enabling/disabling D2D due to route
modification/rediscovery [0059] For public safety D2D supporting
multi-hop communication. [0060] For UE mobility [0061] Direct
switching from D2D to D2D path.
[0062] There are similarities between the normal and public safety
scenarios, with differences being mainly due to the (possible) lack
of network support in public safety scenario (e.g. in the event of
network outage). Scenarios B2 and B3 can be applied to transitions
between D2D communication and cellular communication due to network
failure/recovery.
[0063] According to some embodiments, an enabling (admission)
decision for normal D2D direct path communication should be made by
the network (e.g., by the eNB if both UEs are served by the same
eNB, or by MME/S-GW if the UEs belong to different eNBs). For
public safety D2D communication, the eNB may perform some
pre-configuration of D2D communications whilst the UEs are still in
coverage. This pre-configuration may be performed, for example, by
the network layer.
[0064] Embodiments may improve broadcast D2D communication for
public safety use cases in out of network coverage scenarios based
on, for example, LTE technology. One of the major requirements for
public safety communication is to support Voice over Internet
Protocol (VoIP) services over large transmission ranges. According
to one proposed D2D evaluation methodology, receivers interested in
reception of the VoIP traffic from the transmitter may be located
in up to, for example, a 135 decibels (dB) transmission range.
Moreover, a number of the associated receivers are likely to have a
low pathgain to the transmitter (i.e. are far from the broadcasting
transmitter of interest).
[0065] In a given geographical area there may be several
transmitters that may want to transmit the VoIP traffic. In order
to allow distant receivers to be reached by transmitted signals,
each transmitter may have to transmit VoIP packets in a narrow part
of the spectrum (i.e. several Physical Resource Blocks (PRBs)) over
multiple sub-frames in order to accumulate energy per information
bit and to reach a signal quality metric, such as, for example, a
2% Block Error Rate (BLER) at 135 dB maximum coupling loss.
Analysis has shown that transmission over two to three PRBs and at
least four Transmission Time Intervals (TTIs) may be appropriate to
achieve a target maximum coupling loss. In LTE one TTI corresponds
to one millisecond (ms), which is one subframe or two timeslots of
a 10 ms radio frame. LTE resources are allocated on a per-TTI
basis.
[0066] However the following issues may be addressed to improve the
efficiency of D2D wireless broadcasts in public safety
scenarios:
1) Transmitters, if not synchronized, may often collide with each
other leading to an asynchronous type of interference, which can
degrade performance. 2) Transmitters can be synchronized and
orthogonalized in time and frequency in order to avoid co-channel
interference. 3) Even synchronized transmitters may cause
significant interference issues at the receiver side when they
transmit simultaneously on orthogonal resources in frequency due to
unavoidable (or at least difficult to avoid) in-band emissions. The
in-band emission effect may significantly degrade performance if
several transmitters occupy the same time slot.
[0067] The combination of these effects may significantly degrade
performance of VoIP Public Safety services in out of network
coverage scenarios especially taking into account the broadcast
nature of D2D operation and no physical layer feedback from the
receivers.
[0068] In-band and out-of-band interference arise as a result of
transmitter imperfections. Out-of-band (or adjacent channel)
interference can be controlled by a spectral shaping filter.
However, the shaping filter cannot control in-band interference
corresponding to leakage in a given transmitter within the channel
bandwidth, and the resulting leakage can interfere with other
transmitters. The effects of in-band interference are likely to be
more pronounced when a resource block allocation size associated
with a communication link is small, and when the interfering signal
is received at a higher power spectral density.
[0069] FIG. 2 shows a wireless communication system 200 capable of
out-of-coverage D2D transmission. The system comprises a first UE
210 having an associated first transmission range 212 and a second
UE 220 having an associated second transmission range 222. In this
embodiment, the first and second UEs 210, 220 are cluster heads,
which coordinate D2D communications within their respective
transmission ranges, but in other embodiments there are no cluster
heads. The cluster heads 210, 220, may have some radio resource
scheduling responsibilities. The two UEs 210, 220 are arranged to
transmit substantially simultaneously using orthogonal frequency
resources. The first transmission range 212 and the second
transmission range 222 partially overlap such that there is an
intersection 230 of transmission ranges.
[0070] All receiving UEs located within the intersection 230 will
receive transmissions from both the first UE 210 and the second UE
220. However, the quality of a received signal from the first UE
210 is likely to diminish on a periphery of the first transmission
range 212. Similarly, the quality of a received signal from the
second UE 220 is likely to diminish on a periphery of the second
transmission range 212. Accordingly, even if the first UE 210 and
the second UE 220 are transmitting using different frequency
resources, in-band interference corresponding to a signal from the
second UE 220 can be comparable in strength at the location of a UE
242, which is on the periphery of the first transmission range 212,
to a communication signal received at the UE 242 from the first UE
210. Accordingly, in-band interference effects are likely to be
more pronounced when a UE is located such that it is receiving a
weak signal from one transmitter and a strong signal from another
transmitter.
[0071] All UEs in the intersection 230 of the transmission ranges
will receive transmission from both first and second UEs 210, 220
but a subset of those UEs located in the intersection 230 will be
able to effectively receive a signal from only one of the first and
second UEs 210, 220 due to the adverse effects of in-band emission
interfering with the weaker of the two transmitted signals. The UEs
242, 244, 246, 248 and 250 in FIG. 2 each have difficulty in
receiving signals from both first and second UEs 210, 220. Note
that receiving UEs should ideally be capable of receiving and
discriminating between signals transmitted from each and every
transmitter of which they are in range. This is because when the
signals are received in the physical layer, the UE has no knowledge
of which transmission a user seeks to tune in to. Thus all signals
should be received in the physical layer and only in the upper
layers upon decoding of the received signals will the payloads
become apparent to the UE.
[0072] In-band emission can be harmful for broadcast communication
when receivers (UEs) attempt to process signals from multiple
transmitters, transmitting in the same time resource. FIG. 2, as
described above, illustrates the problem of in-band emission when
transmission ranges of two UEs are partially overlapped.
[0073] The following observations can be made assuming simultaneous
transmissions on orthogonal frequency resources: [0074] In the case
of non-overlapping transmission areas, transmitters have disjoint
sets of associated receivers. Receivers can successfully receive
data from corresponding transmitters within a respective
transmission range. [0075] In case of fully overlapping
transmission areas, transmitters have almost the same set of
associated receivers. Due to proximity of the transmitters to the
UEs in the transmission range, there may be no significant
de-sensing problems and a majority of associated receivers within
the transmission range may successfully receive data from both
transmitters. De-sensing is the effect of a strong signal from a
transmitter on the detection of a weak signal by a receiver. [0076]
In case of partially overlapping areas as illustrated in FIG. 2,
there may be UEs interested in reception from both transmitters
(UEs 210, 220) but are able to receive a signal only from one
transmitter because of in-band emission and de-sensing
problems.
[0077] Accordingly, when two substantially simultaneous D2D
transmissions derive from UEs that are either sufficiently distant
that their transmission ranges do not overlap or are sufficiently
close that their transmission ranges fully overlap, in-band
interference effects are not likely to be problematical when the
two transmitters are transmitting in the same time resource.
However, for partially overlapping transmission ranges where
transmitters are using orthogonal frequency resources but the same
time resources, in-band interference can interfere with signal
reception.
[0078] Accordingly, a mechanism is proposed to effectively manage
in-band emission interference by establishing synchronization.
[0079] The basic principle to avoid or at least ameliorate an
in-band emission issue is to transmit in orthogonal time resources.
Therefore synchronization between UEs such as, for example, public
safety terminals operating in out of coverage scenarios using D2D
communication needs to be established first. Once synchronization
is established, several "nodes" (not cellular network nodes), in
this case UEs acting as D2D public safety coordinators,
periodically transmit synchronization signals and the public safety
terminals (other D2D enabled UEs) associate to one of these
synchronization sources based on, for example, a maximum received
power or other signal quality criteria or signal metric. The
synchronization sources are synchronized with each other and each
"owns" (i.e. reserves or is dynamically allocated) a part of the
time resources of an LTE frame and/or other radio resources. Any UE
transmitter that wants to broadcast the data should select one or
be assigned by a D2D public safety coordinator to one of the
frequency channels and transmit on the time resources that are
indicated by the given synchronization source, to which the UE has
"camped-on" (i.e. derives timing from).
[0080] Embodiments implement at least one of the following
technical features: [0081] Hierarchical synchronization reference
propagation from a master (I-SS) to a subsidiary synchronization
source (G-SS) to maximize or at least expand a synchronous area
[0082] Time division multiplexing between derived synchronization
references (i.e. between different UEs or peer devices in a
peer-to-peer communication, each of which is broadcasting a
synchronization signal) [0083] Frequency division multiplexing on
the bounds of synchronous areas (e.g. where received power of
synchronization signals falls below a predetermined threshold) to
avoid strong co-channel asynchronous collisions.
[0084] Previously-known solutions to the problem of out-of-coverage
D2D communication are either not synchronous or do not take into
account the in-band emission effect because they transmit in the
whole bandwidth and thus are limited by transmission range or
co-channel interference. Other communication technologies allowing
for short distance communication between transmitter and receiver,
such as WiFi, use collision detection type schemes such as Carrier
Sense Multiple Access (CSMA) for data communication and do not use
a transmitting/receiving terminal such as a UE as a synchronization
source for direct communication.
[0085] FIG. 3 schematically illustrates voice data
transmission/reception using a D2D link between two UEs. LTE/LTE-A
uses OFDMA on the DL and SC-FDMA on the UL. OFDMA is not typically
used on the UL due to its associated high peak-to-average
power-ratio which corresponds to loss of efficiency. SC-FDMA has a
lower peak-to-average power-ratio and yet offers similar multipath
protection to that offered by OFDMA. For D2D communications
according to embodiments either OFDMA (DL) or SC-FDMA (UL) radio
resources can be used. SC-FDMA and OFDMA use very similar
transmitter and receiver architecture and have a virtually
identical radio frame structure (see FIG. 7). The FIG. 3 embodiment
assumes that an UL LTE channel is used for a D2D VoIP
communication, but this is only one of many possible channel types.
A transmitting UE 310 sends voice data to a receiving UE 350 via a
D2D channel 390. An incoming bit stream is passed to a VoIP codec
and compression module 312 where the voice data is encoded and
compressed. The encoded and compressed data is supplied to a
packetiser 314 and then to a modulation unit 316.
[0086] The modulated packet data is then supplied to a Discrete
Fourier Transform (DFT) module 318 which converts time domain
single carrier symbol blocks into discrete frequencies. Output from
the DFT module 318 is supplied to a subcarrier mapping module 320
which maps DFT output frequencies to specified subcarriers for
transmission. An Inverse DFT (IDFT) module 322 converts the mapped
subcarriers back into the time domain for transmission. The
subcarrier mapping module 320 performs a mapping to LTE radio
resources (or alternative radio resources) depending upon how the
D2D channel 390 is configured. Output from the IDFT module 322 is
supplied to a cyclic prefix and pulse shaping module 324, which
prepends a cyclic prefix to the composite SC-FDMA symbol to provide
multipath immunity and pulse shaping is performed to prevent
spectral regrowth (out-of-band interference). An RF front end 326
converts from a digital to an analogue signal and up converts to a
radio frequency for transmission.
[0087] In the receiver side chain the process is reversed, with
received data being processed in turn by: an RF front end 352; a
cyclic prefix removal module 354; a DFT module 356; an equalization
module 358; an Inverse Discrete Fourier Transform (IDFT) module
360, a demodulation unit 362; a de-packetiser 364; and a VoIP
decompression and decoding module 366. According to the present
technique, the subcarrier mapping module 320 maps the D2D payload
and control data to a particular subset of radio resources
depending upon which synchronization source the transmitting and
receiving UEs 310, 350 are relying upon to synchronize the D2D
communication link 390. The synchronization signal itself may be
received by the transmitting UE 310 from another UE serving as a
synchronization source. Alternatively, the transmitting UE 310 may
itself serve as a synchronization source for other UEs in the
vicinity (synchronization signal transmission range). The
synchronization signal according to the present technique may be
included in the LTE/LTE-A radio frames similarly to the Primary
Synchronization Signal (PSS) and the Secondary Synchronization
Signal (SSS) specified as part of the LTE standard 3GPP TS 36.211
V11.4.0 (see section 6.11), published September 2013. The LTE PSS
and SSS are described in more detail below.
[0088] When UEs are in-coverage and have access to the cellular
network, network-assisted synchronization of D2D communications can
be performed using an eNB. In such network-assisted scenarios, the
two UEs of a D2D pair are synchronized with an eNB such that radio
slot and frame timing as well as frequency synchronization are
acquired. The UEs are also configured to store other system
parameters such as duplexing mode and cyclic prefix length. The UEs
can repeatedly synchronize with their serving eNB and the D2D pair
are synchronized to each other prior to D2D radio bearer
establishment. However, in out-of-coverage scenarios, the eNB
cannot be used as a synchronization source, but in order to achieve
synchronization, according to the present technique a common timing
may be established among multiple terminals (such as UEs) with
independent oscillators. This is a departure from a CSMA type
scheme for out-of-coverage short distance communication, as
implemented by WIMAX or WiFi, for example. Multiple approaches may
be used to achieve synchronization in time for out-of-coverage D2D
communication.
[0089] One of the solutions is to use a distributed synchronization
approach in which terminals periodically transmit synchronization
signals and adjust their timing. Such approaches can have a large
convergence time. An alternative solution, as implemented by at
least some embodiments, is to use a hierarchical approach for
synchronization of D2D communications such as out-of-coverage D2D
communications. In this approach one of the terminals may
autonomously take the role of Independent Synchronization Source
(I-SS) generating an independent synchronization source
signal--these terminals that serve as synchronization sources may
alternatively be denoted "Peer Radio Heads" (PRHs). Other terminals
can scan the air and synchronize to the independent synchronization
source which periodically broadcast D2DSS signals as illustrated in
the flow chart of FIG. 4. The Peer Radio Head is independent at
least because it does not derive the timing for transmission of D2D
signals from any other synchronization source operating using
LTE/LTE-A cellular network air interface. However, the PRH may
derive synchronization timing from other external sources, such as,
for example, Global Positioning Satellites (GPS).
[0090] Once the Peer Radio Head has started transmission of
synchronization signals the common timing is established among
neighborhood devices, synchronized to this PRH within
synchronization range that is up to, for example, -135 dB in
pathgain if Primary Synchronization Signals and Secondary
Synchronization Source Signals (PSS and SSS) are used as
Device-to-Device Synchronization Signals (D2DSS).
[0091] With further regard to the type of signals to be used for
the D2DSS, in LTE, there are two types of physical signals:
reference signals used to determine a channel impulse response and
synchronization signals which convey network timing information.
Physical signals use assigned radio resource elements of the LTE
radio frame. A specified reference signal is assigned to each cell
within a network and acts as a cell-specific identifier. Physical
channels convey information to/from higher layers but physical
signals, such as synchronization signals do not. Synchronization
signals use pseudo-random orthogonal sequences.
[0092] There are two types of synchronization signals in LTE: PSS
and SSS. The PSS is broadcast twice during every radio frame and
both transmissions are identical, so the UE cannot detect which is
the first and which is the second. This means that the PSS cannot
be used to achieve radio frame synchronization. However, the PSS is
used to obtain sub-frame, slot and symbol synchronization in the
time domain. The SSS is also broadcast twice within every radio
frame, but the two transmissions are different allowing the UE to
discriminate between the first and the second SSS. The SSS is used
to achieve radio frame synchronization.
[0093] The resource elements used to broadcast the PSS and SSS in
LTE differ depending upon whether FDD mode or TDD mode of LTE is
used. In FDD mode two separate RF carriers (different frequency
bands) are used for UL and DL transmission. In TDD mode, the same
RF carriers are used for UL and DL, but the UE and eNB cannot
transmit substantially simultaneously. An LTE radio frame has
twenty timeslots (see FIG. 7), which can be sequentially labeled as
slot 0 to slot 19. In the case of FDD mode, the PSS is broadcast
using the central 62 subcarriers of the last symbol of timeslots 0
and 10 and the SSS is broadcast in the 62 central subcarriers of
the penultimate symbol of timeslots 0 and 10. In the case of TDD
mode the PSS is broadcast using the central 62 subcarriers of the
third symbols of timeslots 2 and 12. Timeslots 2 and 12 correspond
respectively to sub-frame 1 and sub-frame 6. The SSS is broadcast
using the central 62 subcarriers of the last symbols of timeslots 1
and 11. Timeslots 1 and 11 correspond to sub-frames 0 and 5
respectively. In FDD the PSS and SSS are in adjacent symbols of
timeslots 0 and 10 whereas in TDD mode the PSS and SSS, are not
allocated to adjacent symbols and occupy adjacent time slots,
rather than the same time slot.
[0094] According to the present technique, the physical structure
of LTE PSS and SSS signals may be used for the D2DSS in out-of
coverage and in-coverage scenarios, but the timeslots allocated to
the PSS SSS may differ from the LTE timeslot allocation for the
out-of-coverage implementation. In particular, according to some
embodiments, more than one synchronization source (e.g. different
UEs or different picocells) is likely to be used and it may be
convenient to allocate different radio frame time slots to
different synchronization sources. Different SC-FDMA/OFDMA codes
and/or frequencies may also be allocated to different
synchronization sources. In alternative embodiments, the D2DSS is
defined differently from the LTE PSS and SSS, at least for the
purposes of out-of-coverage D2D communications.
[0095] A further task that may be accomplished by the PRH (I-SS) is
to find or instantiate additional sources of synchronization
signals that derive timing from the PRH and further propagate the
timing of the I-SS over a geographical area of a public safety
accident. The master synchronization source may be denoted an
Independent Synchronization Source (I-SS) or Master synchronization
source (M-SS). The new sources of D2DSS signals, which derive
signal timing from the I-SS are here denoted as Gateway
Synchronization Sources (G-SS) or subsidiary synchronization
sources and they correspond to propagated or replicated versions of
the master synchronization source. In some embodiments, selection
of these new Gateway Synchronization Sources may be done in a
distributed way, based on a distributed protocol for
synchronization source selection (which may be implemented
independently of network control) or, alternatively, can be
directly assigned by the independent synchronization source (PRH).
For example, synchronization source gateways may scan the spectrum
resources in order to detect the D2DSS signals and/or PD2DSCH
(Physical D2D Synchronization Channel), which is a broadcast
channel transmitted by an I-SS and the gateways may start
transmitting their own synchronization signals and channels when
the received power from the I-SS or from another G-SS is below a
predetermined threshold. Alternatively, the G-SSs may be directly
assigned by a PRH that serves as an I-SS. The I-SS may be
considered to be a primary or master synchronization source.
[0096] These new gateways (G-SS) may also transmit D2DSS
synchronization signals periodically and may also keep
synchronization with the independent synchronization source (PRH
I-SS) in order to keep synchronous operation in given geographical
area. The D2DSSs transmitted by independent synchronization source
(PRH I-SS) and synchronization source gateway (PRH G-SS) may be
carried on orthogonal time resources so that they can receive
synchronization and process synchronization signals from each
other. Alternatively, D2DSS muting patterns may be defined to allow
processing of the D2DSS signals between synchronization sources,
which means that the same radio resources can be used for
synchronization signals broadcast by the I-SS and G-SS. In general,
the I-SS may use a different synchronization signal (e.g. different
symbols and/or timeslots of the LTE radio frame) compared to the
G-SS. In some embodiments, the I-SS may use the LTE PSS and SSS
radio resource allocation. The use of time division multiplexing
for the I-SS and G-SS means that the G-SS can detect and predict
where or when the I-SS is transmitting and occupy, for example, the
subsequent time intervals (e.g. time slots) for its own
transmission.
[0097] Alternatively, an additional synchronization channel can be
transmitted jointly with synchronization signal. Recall that a
channel conveys payload information to higher layers whereas a
signal does not. This synchronization channel may carry, for
example, information about hop count used by the corresponding
synchronization source. In some embodiments the hop count=0 could
be used to denote the I-SS, whilst a hop count=1 could be used to
denote a synchronization source deriving timing directly from the
I-SS and so on. The G-SS can derive the hop count information by
decoding the synchronization channel of a received synchronization
signal. In alternative embodiments, the hop count may be used as a
signal to uniquely identify a synchronization signal, similarly to
the use of an LTE reference signal as a cell-specific identifier.
In this case when a device such as a UE synchronizes to
synchronization source (i.e. detects and camps on to a particular
synchronization signal) it derives information about hop count.
[0098] The other terminals (UEs) surrounding the PRH I-SS and PRH
G-SS may track synchronization signals from these nodes/devices and
select the best node/device for synchronization. A criterion that
can be used to select a synchronization source (via a signal
metric) is to select the one that results in the maximum received
power. In many cases, this criterion will result in selection of
the best and closest synchronization source. Following this
procedure the synchronization should be established among all
public safety terminals (UEs or other wireless devices) in the
geographical area of accident. In a general case, more than two-hop
timing propagation may be established by selecting additional PRHs
that derive synchronization timing from the PRH G-SSs rather than
directly from the I-SS. However in the majority of the cases two
hop timing propagation may be sufficient.
[0099] This hierarchical synchronization using a D2D device as an
I-SS to establish common synchronization with nearby devices and
extending the physical area of common synchronization using one or
more G-SS, which propagate the same timing as the G-SS is a first
step in gaining control over interference effects such as in-band
interference. A next step in order to minimize (or at least
ameliorate) the in-band emission effect is to assign different time
slots to different PRHs (I-SS and G-SS) for data transmission. For
example, different time and/or frequency resources of the LTE radio
frames may be allocated for transmission of voice data using
VoIP.
[0100] It will be appreciated that D2D communication is not limited
to communication of voice data, but may include one or more of a
number of different data types although communications involving a
single UE, such as Internet browsing, are not typically suitable
for D2D communication. D2D data may include user files such as
image files or contact information, game data, voice/video data
relating to a phone call or text/chat data associated with a
messaging service. The D2D connection may support one-way data
transfer such as a file transfer as well as two-way data transfer
such as a voice call. In public safety scenarios, voice data is
likely to be a common payload.
[0101] Where D2D radio resource allocation is recommended for a
corresponding synchronization source, the UEs that are associated
with the particular PRH (e.g. UEs within a transmission range of
the particular PRH and camped-on to that PRH as a synchronization
source) can preferentially use the allocated time and/or frequency
resources for data transmission. However, use of the recommended
time-frequency resources corresponding to a given synchronization
source is not mandatory. The use of additional radio resources
outside the recommended resources may sometimes be permitted to
meet, for example, particular QoS requirements for a high data rate
for a requested D2D connection. Thus time-division multiplexing of
payload data transmission for UEs associated with different
synchronization sources may not be performed in certain
circumstances, but is recommended to reduce interference.
[0102] FIG. 4 is a flow cart schematically illustrating
hierarchical synchronization source assignment as implemented by a
D2D-enabled device such as a UE. The method begins at process
element 410. At process element 412 the UE performs proximity
detection to detect any other D2D-capable devices currently in a
D2D transmission range of the given device. For in-coverage
scenarios, the eNB may control peer device discovery by controlling
a UE that has requested to initiate a D2D communication to transmit
a discovery beacon using a given time/frequency/power resource and
may also specify a recipient UE for the discovery beacon.
Alternatively, the eNB may periodically broadcast radio resources
to be used for discovery beacons.
[0103] In the case of out-of-coverage D2D, peer device discovery
may be performed without network support by a UE broadcasting a
discovery beacon on preconfigured radio resources. Also at process
element 412, D2D functionality of the UE is switched on, but a
synchronization source should be identified prior to any D2D data
transmission.
[0104] Next, at process element 414, the given device scans the
radio resources in search of an existing synchronization signal. If
the device is in-coverage then a PSS signal and an SSS signal from
an eNB will be detected and these signals can be used for
synchronization of subsequent D2D communications with other devices
camped-on to the same eNB. However, where the given device (e.g.
UE) is out-of-coverage, there will be no eNB synchronization
signal, although there may be an existing synchronization signal
broadcast by another device in the proximity. If at process element
414, no synchronization signal is detected by scanning the radio
spectrum resources, the process proceeds to process element 416,
where the given device assumes the role of a master synchronization
source (I-SS) and broadcasts a master synchronization signal, which
derives its timing independently from any synchronization source
corresponding to the LTE/LTE-A air interface. The I-SS may derive
timing independently of an eNB for example. The master
synchronization signal in some embodiments may use the radio
resources typically allocated to the PSS or SSS by the cellular
network. In other embodiments different radio resources may be
allocated to the master synchronization signal.
[0105] The master synchronization signal is broadcast periodically,
for example, at least twice per radio frame. Broadcast of the
master synchronization signal having been established at process
element 416, the device which has assumed the role of the I-SS also
broadcasts at process element 418, radio resources recommended for
any D2D communications that derive synchronization from the I-SS.
The D2D communications concerned may, but need not necessarily
involve the given device as a transmitter/receiver, but may be D2D
communications between a different pair or cluster of D2D devices
that are within a transmission range of the master synchronization
signal and that are camped-on to the master synchronization signal.
The given device may be preconfigured with the D2D resource
information to broadcast. This pre-configuration could, for
example, be performed by the cellular network whilst the device is
still in coverage. Alternatively the resource information
corresponding to the I-SS could be dynamically allocated by the
device depending upon, for example, channel conditions and/or
interference measurements.
[0106] Returning to process element 414, if it is determined that
there is in fact an existing synchronization signal on the air
interface then the process proceeds to process element 420, where
each received candidate synchronization signal is checked against a
synchronization signal quality metric to see if the signal quality
metric is satisfied. It will be appreciated that the signal quality
metric could be any type of signal metric, but in some embodiments,
the signal quality metric comprises at least one of: a received
synchronization signal power; a synchronization signal hop count; a
received signal arrival time and a Signal to Interference plus
Noise Ratio (SINR). In the embodiment of FIG. 4, the signal metric
used is a synchronization signal power threshold, Pthr. If the
received synchronization signal has a power greater than or equal
to Pthr, then the process proceeds to process element 422. The same
happens if more than one synchronization signal satisfying the
signal quality metric is encountered at process element 420.
[0107] However, if it is determined at process element 420 that the
received synchronization signal, whilst present, does not satisfy
the signal quality metric, meaning in this example that the
received signal power is less than Pthr, then the process proceeds
to process element 430, whereupon the given device performing the
scanning assumes the role of a G-SS and broadcasts a propagated or
replicated version of the received synchronization signal. The
propagated/replicated synchronization signal derives its timing
from the received synchronization signal. In this embodiment, the
G-SS synchronization is broadcast using different time resources of
the radio frame relative to the resources used for the received
(sub-threshold power) synchronization signal. This means that there
is time division duplexing performed between synchronization
signals corresponding to different geographical regions.
[0108] At process element 432, the given device, having been
designated as a G-SS, is triggered to broadcast radio resource
information recommending to devices using its broadcast
synchronization signal as a synchronization source, radio resources
to be used for D2D communications such as VoIP voice calls, file
transfers, text messaging and such like. In this embodiment the
radio resources recommended for use by the G-SS are orthogonal in
at least time to the radio resources recommended for use by the
I-SS and/or the synchronization source corresponding to the
received synchronization signal. Note that at process element 430,
the hop count of the given device may be determined based upon hop
count information corresponding to the received synchronization
signal, which may be encoded in the signal itself or may be derived
from a separate synchronization channel. The received
synchronization signal need not itself correspond to an I-SS (hop
count 0), but may correspond to a G-SS (hop count 1 or greater). In
some embodiments the hop count increases successively each time an
I-SS is replicated by a further device.
[0109] Returning to process element 420, if at least one received
synchronization signal does in fact satisfy the power threshold
condition, indicating that its signal strength is acceptable, then
the process proceeds to process element 422, where the given device
camps-on to the best candidate synchronization signal. The best
signal is determined with reference to the particular signal
metric. In this embodiment the device camps on to the highest power
received synchronization signal at process element 422. The process
of camping-on proceeds to process element 424, where a radio
resource allocation associated with the selected received
synchronization signal is determined by the given device. The radio
resource allocation may be a recommendation of a set of radio
resources available for use by any D2D communications adopting the
corresponding synchronization signal as a synchronization
reference. In this embodiment, the given device establishes a D2D
connection (e.g. a voice call) with a proximal device using the
synchronization signal, to which it has camped-on for radio frame
synchronization and sub-frame, slot and symbol synchronization in
the time domain. The device also uses at least a subset of the
corresponding recommended radio resource allocation for the
synchronization source.
[0110] FIG. 5 is a signal timing diagram schematically illustrating
how two different UE pairs in different transmission regions of the
partially overlapping transmission regions illustrated in FIG. 2
establish synchronization and set up respective D2D communication
channels. It is assumed that a first D2D pair 510, 512 (shown in
FIG. 2 and FIG. 5) camp-on to a synchronization signal broadcast by
the first synchronization source UE 210. A second D2D pair 520, 522
(also shown in FIG. 2 and FIG. 5) are located outside the
transmission range of the first cluster head UE 210, but achieve
synchronization by camping on to a second synchronization source UE
220. The first synchronization source UE 210 derives its timing
independently of any LTE synchronization source and independently
of any other UE in the wireless communication network and thus
corresponds to an I-SS according to the present technique and
broadcasts, at signal timing element 550, a master synchronization
signal to the first UE 510 and the second UE 512, which are both in
its transmission range 212 and which require establishment of a D2D
connection between them.
[0111] The second synchronization source UE 220, although capable
of receiving the master synchronization signal broadcast by the
first synchronization source 210, determines at timing element 552
that this received synchronization signal does not satisfy a signal
metric, which may be used to control in-band interference between
substantially simultaneous D2D communications. In particular, the
second synchronization source UE 220 determines that the master
synchronization signal upon receipt has a power that is less than a
predetermined threshold power. At timing element 554, the UE 220
assumes the role of a G-SS by broadcasting to UEs in its own
transmission region, a second (propagated) synchronization signal
deriving timing from the master synchronization signal. The second
synchronization signal is received by a third UE 520 and a fourth
UE 522, which are both located in the transmission region of the
G-SS 220, and which have requested establishment of a D2D
communication between them. Prior to setting up a D2D communication
channel between the first and second UEs 510, 512, the I-SS sends
D2D resource allocation information 556 and 558 to each of the two
UEs 510, 512. Similarly, after the third UE 520 and the fourth UE
522 have camped-on to the G-SS, the G-SS sends D2D resource
allocation information to each of the third UE 520 and the fourth
UE 522.
[0112] Note that although the G-SS may also be broadcasting
resource information within its transmission region prior to the
UEs 520, 522 camping on to the G-SS, the UEs need only utilize this
radio resource information after camping on as shown in FIG. 5. In
some embodiments only the transmitting UE of a D2D pair has access
to the D2D resource information of the corresponding
synchronization source. The G-SS UE 220 is configured to broadcast
a D2D radio resource allocation that is orthogonal in time to the
D2D resource allocation currently being used by the I-SS. The fact
that the I-SS and the G-SS have synchronization signals based on
the same timing (i.e. the hierarchical synchronization) make it
possible to implement the orthogonality in time for the two D2D
channel communications. Establishing temporal orthogonality may be
implemented dynamically by the synchronization sources, or
alternatively they may be pre-configured to allocate temporally
orthogonal radio resources.
[0113] FIG. 6 schematically illustrates time and frequency
resources allocated to a pair of D2D transmitters deriving
synchronization timing from an I-SS. A UE 602 and a UE 604 derive
synchronization timing from an I-SS UE 612. The I-SS 612
periodically broadcasts D2D synchronization signals (D2DSS) and in
addition broadcasts information about spectrum resources to be used
for data transmission (e.g. recommended/advertised time
transmission interval). The recommended Time Transmission Interval
(TTI) may be composed from a set of LTE subframes, e.g. four TTIs.
The UEs 602, 604 camp-on to the I-SS 612, since the D2DSS received
signal power exceeds an inter synchronization source received power
threshold SSTHR. The UEs 602, 604 utilize information about
recommended/advertised spectrum resources broadcast by the I-SS 612
and use these resources if there are no transmit data rate and/or
half-duplex constraints (or alternative constraints) that override
the use of the advertised spectrum resources.
[0114] A further UE 622 represents a G-SS and it broadcasts D2DSS
and propagates the timing of the I-SS 612, because its D2DSS
received power is measured as being below the inter synchronization
source received power threshold. The G-SS 622 selects and
advertises/broadcasts recommended spectrum resources not occupied
by other proximate synchronization sources (e.g. time transmission
intervals and/or frequency resources that do not overlap with those
used by proximate synchronization sources).
[0115] FIG. 6 also shows a time-frequency resource grid 660 in
which the two UEs 602, 604 within the same synchronization group
(using the same synchronization source) transmit in the same time
resources but on different frequency sub-channels. A time/frequency
allocation corresponding to a row of the time frequency resource
grid when frequency is represented on the vertical grid axis and
time is represented on the time grid axis, represents a "frequency
sub-channel" 670 that can be composed from different LTE physical
resource blocks (PRBs) and frequency hopping can be applied from
one transmission index to another transmission index (i.e. from one
transmitting UE to another transmitting UE), where each
transmission index corresponds to a different UE deriving
synchronization from the I-SS 612.
[0116] The I-SS 612 has recommended spectrum resources
corresponding to two distinct time resources 672, 674 as shown on
the time-frequency resource grid 660. A time resource 672 or 674 in
this example is assumed to correspond to a TTI. Considering the TTI
672, a first resource unit 682a corresponds to the UE (TX1) 604 and
a second resource unit 684a corresponds to the UE (TX2) 602.
Additional spectrum resource units 682b and 684b are allocated
respectively to the UE (TX1) 604 and the UE (TX2) 602 in a
subsequent TTI 674. The resource units 682a, 682b allocated to the
UE 604 are in the same frequency sub-band as each other but in
different TTIs 672, 674. The resource units 684a, 684b allocated to
the UE 602 are in the same frequency sub-band as each other but in
different TTIs 672, 674 from each other. The UE (TX1) 602 is
allocated resource units 682a, 682b in a different frequency
sub-band from the resource units allocated to the UE (TX2) 684a,
684b. The recommended allocation may be periodic. The radio
resources may be configured in a number of different ways and each
resource unit 682, 684 may comprise a single LTE physical resource
block or may alternatively comprise a plurality of LTE resource
blocks. The radio resources may be unlicensed and/or unused radio
resources and is not limited to LTE radio resources.
[0117] FIG. 7 schematically illustrates a block diagram of radio
frame resources corresponding to an uplink or downlink LTE radio
frame structure according to some embodiments. In LTE, downlink
communications use OFDMA whereas uplink communications use SC-FDMA.
A radio frame 700 has a duration of 10 milliseconds and is composed
of twenty contiguous 0.5 millisecond slots. A subframe 710 is
formed from two adjacent slots and thus has a one millisecond
duration. FIG. 7 shows slot #18, which is the penultimate slot of
the frame, in more detail. A single resource block 730 can be seen
to comprise a number of OFDM/SC-FDMA symbols N.sub.symbol=7 on a
time axis 752 and a plurality of subcarriers N.sub.SC.sup.RB=12 on
a frequency axis 754. Each OFDM/SC-FDMA symbol occupies a shorter
time duration (seven symbols per timeslot) within the 0.5 ms slot
720 of the radio frame 700. The resource block 730 comprises a
total of N.sub.symbol.times.N.sub.SC.sup.RB constituent resource
elements.
[0118] A single resource element 740 is characterized by a single
subcarrier frequency and a single OFDM/SC-FDMA symbol. In FIG. 7,
although only one complete resource block 230 is shown, a plurality
of resource blocks N.sub.BB are associated with each of the twenty
slots of the radio frame 700. The resource block 730 in the FIG. 7
example is mapped to eighty-four resource elements 740 (12
subcarriers times 7 symbols) using short or normal cyclic
prefixing. In one alternative arrangement (not shown) the resource
block is mapped to seventy-two resource elements using extended
cyclic prefixing.
[0119] Each resource element 740 can transmit a number of bits
depending upon the particular type of modulation scheme employed
for the channel with which the resource element is associated. For
example, where the modulation scheme is quadrature phase-shift
keying (QPSK), each resource element 740 can transmit two bits. For
a 16 quadrature amplitude modulation (QAM) or 64 QAM more bits can
be transmitted per resource element. However, for binary phase
shift keying (BPSK), a single bit is transmitted in each resource
element. The resource block 730 can be configured either for
downlink transmission from the eNodeB to the UE or for uplink
transmission from the UE to the eNodeB. As mentioned earlier, LTE
DL transmission used OFDMA whereas UL transmission used SC-FDMA.
SC-FDMA differs from OFDMA in that in the SC-FDMA subcarriers are
not independently modulated whereas the OFDMA subcarriers are
independently modulated. According to some embodiments, resource
elements 740 of the LTE physical resource block 730 for particular
sub-carriers can be used to convey a D2D synchronization signal,
similarly to the LTE PSS SSS synchronization signal. However, the
OFDMA/SC-FDMA symbols and/or timeslots used may differ for
different D2D synchronization sources (I-SSs and G-SSs) and may
differ from those used by the LTE PSS and SSS synchronization
signals. Furthermore, physical resource blocks of the LTE radio
frames can be allocated to D2D communications such as voice
calls.
[0120] FIG. 8 schematically illustrates time-frequency resource
allocation on a time-frequency resource grid 802 to a pair of D2D
transmitters that are camped-on to an I-SS and to a pair of D2D
transmitters that are camped-on to a G-SS having a partially
overlapped transmission range with the I-SS. As shown in FIG. 8, an
I-SS 810 controls D2D transmission timing of a first UE (TX1) 812
and a second UE (TX2) 814. A G-SS 820 controls D2D transmission
timings of a third UE (TX3) 822 and a fourth UE (TX4) 824. The
first UE (TX1) 812 is allocated a radio resource unit 852a in a
first time resource of the grid 802 and is allocated a radio
resource unit 852b in a subsequent time resource. Similarly, the
second UE (TX2) 814 is allocated a radio resource unit 854a in the
first time resource of the grid 802 and a radio resource unit 854b
in the subsequent time resources. Thus the first and second UEs
812, 814 are allocated radio resources occupying the same time
resources but different frequency sub-channels of the
time-frequency resource grid 802.
[0121] FIG. 8 shows a TTI 860 that is the second column from the
left of the time-frequency grid 802 and this TTI 860 is the
recommended time resource corresponding to the G-SS 820. The first
column of the time-frequency resource grid 802, which contains the
resource units 852a, 852b is a TTI recommended for the I-SS 810.
The third UE 822 has an associated recommended a resource unit 856a
in the TTI 860 and the fourth UE 824 has an associated resource
unit 856a in the same TTI 860. This pattern is repeated in a
subsequent TTI associated with the G-SS 820, which shows a
recommended allocation of resource units 856b and 858b for the
third UE 822 and the fourth UE 824 respectively. Thus the third and
fourth UEs 822, 824 are allocated adjacent (thus different) time
resources to the first and second UEs 812, 814 in the example
time-frequency grid 802 of FIG. 8 and also occupy different
frequency sub-channels from each other in the recommended
allocation. D2D communications under control of the G-SS 820 are
both time division multiplexed (occupy a different recommended
transmission time interval) and orthogonal in sub-channel
frequencies relative to D2D communications controlled by the I-SS
810. The D2D transmitter UEs 822, 824 camp-on to the G-SS 820
according to a synchronization source selection rule (e.g. maximum
D2DSS received power) and they utilize information about
recommended spectrum resources (e.g. time transmission interval)
broadcast by the G-SS 820. The recommended resources are used for
establishing D2D communication links if there are no constraints on
transmission data rate and/or half-duplex constraints that preclude
using the recommended resource allocation.
[0122] FIG. 9 schematically illustrates a time-frequency resource
grid 900 for D2D resource allocations for an I-SS 912 and five
surrounding G-SSs 922, 932, 942, 952, 962 having synchronization
source transmission ranges 920, 930, 940, 950, 960 respectively,
each of which is partially overlapping with an I-SS transmission
range 910 centered on the I-SS 912. Each of the six distinct
transmission ranges 910, 920, 930, 940, 950, 960 corresponds to a
different time resource of the time-frequency resource grid as
shown in FIG. 9. In particular the I-SS 912 and its associated
transmission range 910 are allocated a TTI 916a and a subsequent
TTI 916b. The G-SS 922 and its associated transmission range 920
are allocated a TTI 926a and a subsequent TTI 926b. The G-SS 932
and its associated transmission range 930 are allocated a TTI 936a
and a subsequent TTI 936b. The G-SS 942 and its associated
transmission range 940 are allocated a TTI 946a and a subsequent
TTI 946b. The G-SS 952 and its associated transmission range 950
are allocated a TTI 956a and a subsequent TTI 956b. The G-SS 962
and its associated transmission range 960 are allocated a TTI 936a
and a subsequent TTI 936b. Different transmitters deriving
synchronization from the same synchronization source (the I-SS or
one of the five G-SSs) have recommended resource allocations
corresponding to different frequency sub-channels.
[0123] For example, a transmitter (TX1) 911 occupies a first
frequency sub-channel 981 and a transmitter (TX4) 923 that is
camped-on to the G-SS 922 occupies a second frequency sub-channel
984. The transmitter (TX1) 911 and a transmitter (TX2) 913, which
are both camped-on to the I-SS 912 occupy different frequency
sub-channels within the same TTI 916a. Similarly, a transmitter
(TX3) 921 and the transmitter (TX4) 923, which are both camped-on
to the G-SS 922, occupy different frequency sub-channels within the
TTI 926a as shown. In alternative embodiments, the time resource of
the time-frequency grid 900 may have a different duration from a
TTI.
[0124] Each of the G-SSs 922, 932, 942, 952 is a UE selected as a
derived or propagated (i.e. non-master) synchronization source
because the I-SS, which serves as a master synchronization signal,
although received at the given UE, has failed to satisfy the signal
quality metric that would allow the UE to camp-on to the I-SS
912.
[0125] FIG. 10 schematically illustrates how frequency division
multiplexing may be applied between two different I-SSs that are
asynchronous (i.e. have no common synchronization timing), but
which implement frequency division multiplexing between the
independently synchronized regions. A first region having a first
synchronization timing comprises a synchronization area 1011 of a
first I-SS 1010 and synchronization areas 1013, 1015 associated
respectively with a G-SS 1012 and a G-SS 1014 deriving timing from
the first I-SS. A second region having a second synchronization
timing, different from the first synchronization timing, comprises
a second I-SS 1020 and an associated synchronization area 1021
together with a G-SS 1022, a G-SS 1024 and their associated
synchronization areas 1023, 1025.
[0126] A time-frequency resource grid 1000 in FIG. 10 schematically
illustrates how a bandwidth 1070, allocated to a D2D channel,
comprises a first frequency sub-channel 1080 comprising time
resources allocated to the first I-SS 1010 and the corresponding
two G-SSs 1012, 1014. A second frequency sub-channel 1082 of the
bandwidth 1070 is allocated to the second I-SS 1020 and its two
associated G-SSs 1022, 1024.
[0127] Resource units of the first frequency sub-channel 1080 are
time division multiplexed between the I-SS 1010, the G-SS 1012 and
the G-SS 1014. Each resource unit along the time axis in FIG. 10
may correspond to a TTI. Similarly, resource units of the second
frequency sub-channel 1080 are time division multiplexed between
the I-SS 1020, the G-SS 1022 and the G-SS 1024. In the first
frequency sub-channel 1080, a first resource unit 1052 is allocated
to the I-SS 1010, a subsequent resource unit 1054 is allocated to
the G-SS 1012 and an adjacent resource unit on the time axis is
allocated to the G-SS 1014, whereupon a repeating sequence returns
to allocating to the I-SS 1010 again and so on. In the second
frequency sub-channel 1082, a first resource unit 1062 is allocated
to the I-SS 1020, a subsequent resource unit 1064 is allocated to
the G-SS 1022 and an adjacent resource unit on the time axis is
allocated to the G-SS 1024, whereupon the repeating sequence
returns to allocating to the I-SS 1020 again and so on. The two
frequency sub-channels 1080, 1082 have no common synchronization
timing so the time boundaries of the radio frames and timeslots are
asynchronous for the two different I-SSs.
[0128] In practice multiple accidents may happen in close
geographical areas. In order to avoid global propagation of
synchronization timing, asynchronous operation may be considered.
In this case, frequency division multiplexing may be applied
between different independent synchronization sources I-SSs 1010,
1020 that are not synchronous with each other. The first I-SS 1010
and the second I-SS 1020 may achieve orthogonality in frequency by
performing scanning of the radio resources to detect other
synchronization signals and implementing frequency orthogonality
where appropriate. For example if the UE that becomes the second
I-SS 1020 scans the radio resources and detects a synchronization
signal from I-SS 1010, it can switch to a new carrier or select an
orthogonal frequency resource in the same carrier frequency band.
The carriers and shift in frequency may be preconfigured or may be
dynamically assigned.
[0129] The proposed synchronization techniques may improve D2D
communication performance such as VoIP performance in, for example,
out of coverage public safety specific use cases and can allow
multiple receivers to receive VoIP traffic from multiple active
transmitters.
[0130] FIG. 11 illustrates an example system 1100 according to some
embodiments. System 1100 includes one or more processor(s) 1140,
system control logic 1120 coupled with at least one of the
processor(s) 1140, system memory 1110 coupled with system control
logic 1120, non-volatile memory (NVM)/storage 1130 coupled with
system control logic 1120, and a network interface 1160 coupled
with system control logic 1120. The system control logic 1120 may
also be coupled to Input/Output devices 1150.
[0131] Processor(s) 1140 may include one or more single-core or
multi-core processors. Processor(s) 1140 may include any
combination of general-purpose processors and dedicated processors
(e.g., graphics processors, application processors, baseband
processors, etc.). Processors 1140 may be operable to carry out the
above described methods, using suitable instructions or programs
(i.e. operate via use of processor, or other logic, instructions).
The instructions may be stored in system memory 1110, as system
memory portion (D2D module) 1115, or additionally or alternatively
may be stored in (NVM)/storage 1130, as NVM instruction portion
(D2D module) 1135. D2D modules 1115 and/or 1135 may include program
instructions to cause a processor 1140 to generate a
synchronization signal and/or broadcast radio resource information
for D2D communications deriving timing from the generated
synchronization signal. D2D module 1115 and/or 1135 may form part
of a communication section, including circuitry to cause broadcast
of a D2D new synchronization signal having independent timing, a
propagated synchronization signal adopting timing from a received
synchronization signal and radio resource information recommending
radio resources to be used for a D2D communication such as a voice
call.
[0132] Processors(s) 1140 may be configured to execute the
embodiments of FIGS. 2-10. The processor(s) may comprise scanning
circuitry 1142 and synchronization signal circuitry 1144,
configured to generate and trigger broadcast of a D2D
synchronization signal either independently or deriving timing from
a received synchronization signal. The processor(s) may also
comprise resource information circuitry 1146 for storing and/or
dynamically allocating radio resources for recommendation to D2D
devices within the transmission range of the device. A transceiver
module 1165 also comprises scanning circuitry 1166 configured to
search the air interface for synchronization signals and
broadcasting circuitry 1168 configured to broadcast a D2D
synchronization signal and/or radio resources recommended for
allocation to D2D communications deriving timing from the
associated synchronization source. It will be appreciated that the
scanning, synchronization signal generation/broadcast and resource
allocation information broadcast functionality may be distributed
or allocated in different ways across the system involving one or
more of the processor(s) 1140, transceiver module 1165, system
memory 1110 and NVM/Storage 1130.
[0133] System control logic 1120 for one embodiment may include any
suitable interface controllers to provide for any suitable
interface to at least one of the processor(s) 1140 and/or to any
suitable device or component in communication with system control
logic 1120.
[0134] System control logic 1120 for one embodiment may include one
or more memory controller(s) to provide an interface to system
memory 1110. System memory 1110 may be used to load and store data
and/or instructions, for example, for system 1100. System memory
1110 for one embodiment may include any suitable volatile memory,
such as suitable dynamic random access memory (DRAM), for
example.
[0135] NVM/storage 1130 may include one or more tangible,
non-transitory computer-readable media used to store data and/or
instructions, for example. NVM/storage 1130 may include any
suitable non-volatile memory, such as flash memory, for example,
and/or may include any suitable non-volatile storage device(s),
such as one or more hard disk drive(s) (HDD(s)), one or more
compact disk (CD) drive(s), and/or one or more digital versatile
disk (DVD) drive(s), for example.
[0136] The NVM/storage 1130 may include a storage resource
physically part of a device on which the system 1100 is installed
or it may be accessible by, but not necessarily a part of, the
device. For example, the NVM/storage 1130 may be accessed over a
network via the network interface 1160.
[0137] System memory 1110 and NVM/storage 1130 may respectively
include, in particular, temporal and persistent copies of, for
example, the instructions portions 1115 and 1135, respectively.
Instructions portions 1115 and 1135 may include instructions that
when executed by at least one of the processor(s) 1140 result in
the system 1100 implementing a one or more of methods of any
embodiment, as described herein. In some embodiments, instructions
1115 and 1135, or hardware, firmware, and/or software components
thereof, may additionally/alternatively be located in the system
control logic 1120, the network interface 1160, and/or the
processor(s) 1140.
[0138] The transceiver module 1165 provides a radio interface for
system 1100 to communicate over one or more network(s) (e.g.
wireless communication network) and/or with any other suitable
device. The transceiver 1165 may perform the various communicating;
transmitting and receiving described in the various embodiments,
and may include a transmitter section and a receiver section. In
various embodiments, the transceiver 1165 may be integrated with
other components of system 1100. For example, the transceiver 1165
may include a processor of the processor(s) 1140, memory of the
system memory 1110, and NVM/Storage of NVM/Storage 1130. Network
interface 1160 may include any suitable hardware and/or firmware.
Network interface 1160 may be operatively coupled to a plurality of
antennas to provide a multiple input, multiple output radio
interface. Network interface 1160 for one embodiment may include,
for example, a network adapter, a wireless network adapter, a
telephone modem, and/or a wireless modem. For example, where system
1100 is an eNB, network interface 1160 may include an Ethernet
interface, an S1-MME interface and/or an S1-U interface. The system
1100 of FIG. 11 may be implemented in a UE, but may alternatively
be implemented in a station such as a picocell, femtocell or relay
node for the purposes of implementing peer-to-peer communication
and synchronization.
[0139] For one embodiment, at least one of the processor(s) 1140
may be packaged together with logic for one or more controller(s)
of system control logic 1120. For one embodiment, at least one of
the processor(s) 1140 may be packaged together with logic for one
or more controllers of system control logic 1120 to form a System
in Package (SiP). For one embodiment, at least one of the
processor(s) 1140 may be integrated on the same die with logic for
one or more controller(s) of system control logic 1120. For one
embodiment, at least one of the processor(s) 1140 may be integrated
on the same die with logic for one or more controller(s) of system
control logic 1120 to form a System on Chip (SoC). Each of the
processors 1140 may include an input for receiving data and an
output for outputting data.
[0140] In various embodiments, the I/O devices 1150 may include
user interfaces designed to enable user interaction with the system
1100, peripheral component interfaces designed to enable peripheral
component interaction with the system 1100, and/or sensors designed
to determine environmental conditions and/or location information
related to the system 1100.
[0141] FIG. 12 shows an embodiment in which the system 1100
implements a wireless device 1200, such as user equipment (UE), a
mobile station (MS), a mobile wireless device, a mobile
communication device, a tablet, a handset, or other type of
wireless device. The wireless device can include one or more
antennas 1210 configured to communicate with a node, macro node,
low power node (LPN), or, transmission station, such as a base
station (BS), an evolved Node B (eNB), a baseband unit (BBU), a
remote radio head (RRH), a remote radio equipment (RRE), a relay
station (RS), a radio equipment (RE), or other type of wireless
wide area network (WWAN) access point. The wireless device can be
configured to communicate using at least one wireless communication
standard including 3GPP LTE, WiMAX, High Speed Packet Access
(HSPA), Bluetooth, and Wi-Fi. The device is capable of performing
D2D communication with other proximal wireless devices both when
in-coverage and out-of-coverage with respect to the wireless
cellular network. The wireless device can communicate using
separate antennas for each wireless communication standard or
shared antennas for multiple wireless communication standards. The
wireless device can communicate in a wireless local area network
(WLAN), a wireless personal area network (WPAN), and/or a WWAN.
[0142] The wireless device 1200 of FIG. 12 also provides an
illustration of a microphone 1290 and one or more speakers 1230
that can be used for audio input and output from the wireless
device. In various embodiments, the user interfaces could include,
but are not limited to, a display 1240 (e.g., a liquid crystal
display, a touch screen display, etc.), a speaker 1230, a
microphone 1290, one or more cameras 1280 (e.g., a still camera
and/or a video camera), a flashlight (e.g., a light emitting diode
flash), and a keyboard 1270.
[0143] In various embodiments, the peripheral component interfaces
may include, but are not limited to, a non-volatile memory port, an
audio jack, and a power supply interface.
[0144] In various embodiments, the sensors may include, but are not
limited to, a gyro sensor, an accelerometer, a proximity sensor, an
ambient light sensor, and a positioning unit. The positioning unit
may also be part of, or interact with, the network interface 1260
to communicate with components of a positioning network, e.g., a
global positioning system (GPS) satellite.
[0145] In various embodiments, the system 1200 may be a mobile
computing device such as, but not limited to, a laptop computing
device, a tablet computing device, a netbook, a mobile phone, etc.
In various embodiments, system 1200 may have more or less
components, and/or different architectures.
[0146] In embodiments, the implemented wireless network may be a
3rd Generation Partnership Project's (3GPP) long term evolution
(LTE) advanced wireless communication standard, which may include,
but is not limited to releases 8, 9, 10, 11 and 12, or later, of
the 3GPP's LTE-A standards.
[0147] Various techniques, or certain aspects or portions thereof,
may take the form of program code (i.e., instructions) embodied in
tangible media, such as floppy diskettes, CD-ROMs, hard drives,
non-transitory computer readable storage medium, or any other
machine-readable storage medium such that when the program code is
loaded into and executed by a machine, such as a computer, the
machine becomes an apparatus for practicing the various techniques
according to the above described embodiments. In the case of
program code execution on programmable devices such as a UE or a
wireless device, the computing device may include a processor, a
storage medium readable by the processor (including volatile and
non-volatile memory and/or storage elements), at least one input
device, and at least one output device. The volatile and
non-volatile memory and/or storage elements may be a RAM, EPROM,
flash drive, optical drive, magnetic hard drive, or other medium
for storing electronic data.
[0148] One or more programs that may implement or utilize the
various techniques described herein may use an application
programming interface (API), reusable controls, and the like. Such
programs may be implemented in a high level procedural or object
oriented programming language to communicate with a computer
system. However, the program(s) may be implemented in assembly or
machine language, if desired. In any case, the language may be a
compiled or interpreted language, and combined with hardware
implementations.
[0149] It should be understood that the functional units described
in this specification have been labeled as modules, to highlight
their implementation independence. Note that a module may be
implemented, for example, as a hardware circuit comprising custom
VLSI circuits or gate arrays, off-the-shelf semiconductors such as
logic chips, transistors, or other discrete components. A module
may also be implemented in programmable hardware devices such as
field programmable gate arrays, programmable array logic,
programmable logic devices or the like.
[0150] Modules may also be implemented in software for execution by
various types of processors. An identified module of executable
code may, for instance, comprise one or more physical or logical
blocks of computer instructions, which may, for instance, be
organized as an object, procedure, or function. Nevertheless, the
executables of an identified module need not be physically located
together, but may comprise disparate instructions stored in
different locations which, when joined logically together, comprise
the module and achieve the stated purpose for the module.
[0151] Indeed, a module of executable code may be a single
instruction, or many instructions, and may even be distributed over
several different code segments, among different programs, and
across several memory devices. Similarly, operational data may be
identified and illustrated herein within modules, and may be
embodied in any suitable form and organized within any suitable
type of data structure. The operational data may be collected as a
single data set, or may be distributed over different locations
including over different storage devices, and may exist, at least
partially, merely as electronic signals on a system or network. The
modules may be passive or active, including agents operable to
perform desired functions.
[0152] Where functional units have been described as circuitry, the
circuitry may be general purpose processor circuitry configured by
program code to perform specified processing functions. The
circuitry may also be configured by modification to the processing
hardware. Configuration of the circuitry to perform a specified
function may be entirely in hardware, entirely in software or using
a combination of hardware modification and software execution.
Program instructions may be used to configure logic gates of
general purpose or special-purpose processor circuitry to perform a
processing function.
[0153] Reference throughout this specification to "an example"
means that a particular feature, structure, or characteristic
described in connection with the example is included in at least
one embodiment. Thus, appearances of the phrases "in an example" in
various places throughout this specification are not necessarily
all referring to the same embodiment.
[0154] As used herein, a plurality of items, structural elements,
compositional elements, and/or materials may be presented in a
common list for convenience. However, these lists should be
construed as though each member of the list is individually
identified as a separate and unique member. Thus, no individual
member of such list should be construed as a de facto equivalent of
any other member of the same list solely based on their
presentation in a common group without indications to the contrary.
In addition, various embodiments may be referred to herein along
with alternatives for the various components thereof. It is
understood that such embodiments, examples, and alternatives are
not to be construed as de facto equivalents of one another, but are
to be considered as separate and autonomous representations of the
embodiments.
[0155] Furthermore, the described features, structures, or
characteristics may be combined in any suitable manner in one or
more embodiments. In the following description, numerous specific
details are provided, such as examples of layouts, distances,
network examples, etc., to provide a thorough understanding of
embodiments. One skilled in the relevant art will recognize,
however, that embodiments can be practiced without one or more of
the specific details, or with other methods, components, layouts,
etc. In other instances, well-known structures, materials, or
operations are not shown or described in detail to avoid obscuring
aspects of the embodiments.
[0156] While the forgoing examples are illustrative of the
principles of embodiments in one or more particular applications,
it will be apparent to those of ordinary skill in the art that
numerous modifications in form, usage and details of implementation
can be made without the exercise of inventive faculty, and without
departing from the principles and concepts of embodiments.
[0157] Embodiments provide a convenient and efficient way of
managing in-band interference in D2D communications, particularly
where the communicating devices are out-of-coverage of the cellular
network. Alternative short distance communication technologies such
as WiFi and WIMAX typically implement a collision detection data
transmission policy such as Carrier Sense Multiple Access (CSMA)
and do not rely upon a common synchronization signal in the
physical layer. D2D communications can conveniently control
transmission timing using eNB control when the wireless devices
performing the D2D communication are in-coverage (i.e. in
communication with the eNB), but for out-of coverage D2D
communication, control of the D2D communications cannot rely upon
network control.
[0158] Interference, such as in-band emission interference is
likely to be stronger when a wireless receiver receives one
comparatively strong signal and one comparatively weak signal i.e.
where there is a discrepancy in received signal strengths. This
potentially problematical interference scenario is likely to arise
where two transmitters have partially overlapping transmission
ranges. In this case, UEs located in the intersection of the two
transmission ranges that are able to receive both transmissions,
and which are also located close to the periphery of one of the
transmission ranges are likely to be most susceptible to the
effects of in-band emission interference on the D2D communication.
If the two transmitters are in close proximity to each other with
substantially coincident transmission ranges then the signals from
the two different transmitters should be of comparable strength and
thus easy to distinguish from interference. Similarly, if the two
transmitters are sufficiently far apart that there is no overlap in
their transmission ranges then interference between signals from
the two transmitters should not occur.
[0159] Embodiments may implement a check of whether or not a
received synchronization signal satisfies a signal metric and this
can be used to identify indirectly if partial overlap between two
or more different transmission regions currently exists. For
example, if a received synchronization signal is detected, but
evaluation of the signal metric by the scanning circuitry detects
that the synchronization signal has a power or signal quality below
a certain threshold (or at or above a threshold depending upon the
system configuration), this indicates that the receiving UE is
likely to have a transmission area that partially overlaps with the
source of the received synchronization signal. Accordingly,
evaluation of the synchronization signal metric can be used to
indirectly determine when a receiving UE is likely to be
susceptible to in-band emission interference.
[0160] In embodiments, the in-band emission interference can be
ameliorated by designating as gateway synchronization sources
devices determined via the signal metric to be likely to be in a
partial overlap scenario. The gateway synchronization sources may
propagate the same timing the master synchronization signal,
resulting in a higher power signal in the vicinity of the source of
the gateway synchronization signal. Furthermore, radio resources of
the master synchronization sources and gateway synchronization
sources can be adapted to reduce the effects of in-band emission
interference, for example, by time division multiplexing radio
resources for D2D transmissions corresponding to neighboring
synchronization sources.
[0161] Furthermore D2D communications can be directed, via
appropriate radio resource allocation such that the transmissions
are in a subset of the full available bandwidth, for example, 1 MHz
(one LTE PRB has around 180 kHz bandwidth) rather than a full 10
MHz bandwidth. This allows the UE power to be focused upon a subset
of the frequency spectrum rather than being distributed across a
wider frequency bandwidth. According to some embodiments, devices
can be configured to become new synchronization sources propagating
timing of other synchronization sources enabling common
synchronization over a larger geographical area than would be
possible using a single synchronization source. Furthermore, a
synchronization signal metric implemented by the scanning circuitry
may optionally be preconfigured or dynamically adapted to
compensate for interference such as in-band emission
interference.
EXAMPLES
[0162] The following examples pertain to further embodiments.
[0163] Example 1 is device-to-device communication circuitry, for
use in a device of a wireless communication network, the device
being configured to transmit and receive device-to-device
communications, the circuitry comprising: [0164] scanning circuitry
configured to search for a device-to-device synchronization signal
and to determine if a received synchronization signal satisfies a
signal quality metric; [0165] synchronization signal broadcasting
circuitry configured to broadcast, depending upon a result of the
search performed by the scanning circuitry, a synchronization
signal for synchronizing data communication on at least one
device-to-device communication link between any transmitting device
and any receiving device within a synchronization range of the
device-to-device communication circuitry; and [0166] radio resource
information circuitry, configured to broadcast information about
radio resources for device-to-device operation.
[0167] Example 2 may be the subject matter of example 1, wherein
optionally the radio resource information circuitry is configured
to recommend at least a subset of wireless radio resources for
allocation to the at least one device-to-device communication
link.
[0168] Example 3 may be the subject matter of example 1 or example
2, wherein optionally the radio resource information circuitry
indicates a subset of recommended wireless radio resources
comprising a subset of time resources.
[0169] Example 4 may be the subject matter of example 2 or example
3, wherein optionally the radio resource information circuitry
indicates a subset of a full frequency bandwidth of the wireless
radio resources.
[0170] Example 5 may be the subject matter of any one of examples 2
to 4 wherein optionally the radio resource information circuitry is
one of: (i) preconfigured to store the recommended subset of
wireless radio resources; and (ii) configured to dynamically
allocate the subset of wireless radio resources depending upon the
result of the scanning circuitry search.
[0171] Example 6 may be the subject matter of any one of examples 1
to 5 wherein optionally the synchronization signal broadcasting
circuitry is configured to trigger broadcast of an independent
synchronization signal if no received device-to-device
synchronization signal is detected by the scanning circuitry.
[0172] Example 7 may be the subject matter of any one of examples 1
to 6, wherein optionally the synchronization signal broadcasting
circuitry is configured to suppress broadcast of the
synchronization signal if the scanning circuitry determines that at
least one received synchronization signal satisfies the signal
quality metric.
[0173] Example 8 may be the subject matter of any one of examples 1
to 7, wherein optionally, when the scanning circuitry determines
that an existing synchronization signal which fails to satisfy the
signal quality metric is present without a synchronization signal
that satisfies the signal quality metric also being present, the
synchronization signal broadcasting circuitry is configured to
establish a gateway synchronization source by broadcasting a
propagated synchronization signal, the propagated synchronization
signal deriving timing from the existing synchronization
signal.
[0174] Example 9 may be the subject matter of example 8 wherein
optionally the propagated synchronization signal provides
synchronization for device-to-device communications between devices
in a secondary synchronization range different from a primary
synchronization range corresponding to the existing synchronization
signal.
[0175] Example 10 may be the subject matter of example 8 or example
9, wherein optionally the gateway synchronization source is
configured to broadcast the propagated synchronization signal on
radio resources orthogonal in time to radio resources used to
convey the existing synchronization signal.
[0176] Example 11 may be the subject matter of any one of examples
8 to 10, wherein optionally the radio resource information
circuitry is configured to recommend for device-to-device
communications that derive synchronization from the gateway
synchronization source, a set of time resources different from an
existing set of time resources currently recommended for to
device-to-device communications that derive synchronization from
the existing synchronization signal.
[0177] Example 12 may be the subject matter of any one of examples
8 to 11, wherein optionally the radio resource information
circuitry of the gateway synchronization source is configured to
recommend for device-to-device communications that derive
synchronization from the gateway synchronization source, a set of
frequency resources different from an existing set of frequency
resources currently recommended for to device-to-device
communications deriving synchronization from the existing
synchronization signal.
[0178] Example 13 may be the subject matter of any one of examples
1 to 12, wherein optionally the received signal metric comprises at
least one: of synchronization hop count, received signal power,
received signal arrival time and Signal to Interference plus Noise
Ratio (SINR), taken jointly and severally in any and all
combinations.
[0179] Example 14 may be the subject matter of any one of examples
1 to 13, wherein optionally the scanning circuitry is configured
such that when a plurality existing synchronization signals are
present, the scanning circuitry selects one of the existing
synchronization signals to camp-on to depending upon the signal
metric and suppresses broadcast of the synchronization signal by
the synchronization signal broadcast circuitry.
[0180] Example 15 may be the subject matter of any one of examples
1 to 14, wherein optionally the scanning circuitry is configured to
compare a received synchronization signal with a threshold
corresponding to the signal quality metric and wherein broadcast of
the synchronization signal depends upon the threshold
comparison.
[0181] Example 16 may be the subject matter of example 15, wherein
optionally the scanning circuitry is configured to set the
threshold for the synchronization signal quality metric depending
on at least one of: pre-configured settings and an interference
estimate providing an indication of in-band interference on at
least one device-to-device communication link of the wireless
communication network.
[0182] Example 17 may be the subject matter of any one of examples
8 to 16, wherein optionally the synchronization signal broadcasting
circuitry of the gateway synchronization source is configured to
broadcast to other devices a synchronization hop count providing an
indication of a hierarchical level of the gateway synchronization
source relative to a master synchronization source.
[0183] Example 18 is one of a UE, a picocell, a femtocell and a
relay node comprising the device-to-device communication circuitry
of any one of examples 1 to 17.
[0184] Example 19 is a method of performing synchronization of
peer-to-peer communication signals between wireless equipment at
the same hierarchical level of a wireless communication network,
the method comprising: [0185] searching at a wireless equipment for
receipt of a peer-to-peer synchronization signal and determining if
a received synchronization signal satisfies a required signal
characteristic; [0186] broadcasting from the wireless equipment a
synchronization signal having a timing derived independently from
any synchronization signal corresponding to an eNB, the broadcast
synchronization signal defining a common timing for peer-to-peer
communications between any transmitting wireless equipment and any
receiving wireless equipment within a synchronization range of the
broadcasting wireless equipment and wherein broadcasting of the
synchronization signal is suppressed depending upon whether a
received signal satisfying the required signal characteristic is
found during the search.
[0187] Example 20 may be the subject matter of example 19
optionally comprising broadcasting a derived synchronization signal
when a received synchronization signal not satisfying the required
signal characteristic is detected in the absence of detection of a
received synchronization satisfying the required signal
characteristic, the derived synchronization signal deriving
synchronization timing from the received synchronization
signal.
[0188] Example 21 may be the subject matter of example 20, wherein
optionally the derived synchronization signal uses different time
resources from time resources occupied by the received
synchronization signal.
[0189] Example 22 may be the subject matter of example 20 or
example 21, optionally comprising broadcasting a preferred radio
resource allocation for peer-to-peer data communications that
utilize the derived synchronization signal, the preferred radio
resource allocation being orthogonal in time to radio resources
corresponding to peer-to-peer communication links that utilize the
received synchronization signal.
[0190] Example 23 may be the subject matter of example 22, wherein
optionally the peer-to-peer communications comprise Voice Over
Internet Protocol (VoIP) communications.
[0191] Example 24 may be the subject matter of any one of examples
19 to 23, wherein the wireless equipment comprises one of: a UE, a
picocell, a femtocell and a relay node.
[0192] Example 25 is computer program product embodied on a
non-transitory computer-readable medium comprising program
instructions configured such that when executed by processing
circuitry cause the processing circuitry to implement the method of
any one of examples 19 to 24.
[0193] Example 26 is device-to-device communication circuitry, for
use in a device of a wireless communication network, the device
being configured to transmit and receive device-to-device
communications, the circuitry comprising: [0194] means for
searching for a device-to-device synchronization signal and to
determine if a received synchronization signal satisfies a signal
quality metric; [0195] means for synchronization signal
broadcasting, configured to broadcast, depending upon a result of
the search performed by the scanning circuitry, a synchronization
signal for synchronizing data communication on at least one
device-to-device communication link between any transmitting device
and any receiving device within a synchronization range of the
device-to-device communication circuitry; and [0196] means for
broadcasting information about radio resources for device-to-device
communication.
[0197] Example 27 may be the subject matter of example 26, wherein
optionally the means for broadcasting information is configured to
indicate a subset of recommended wireless radio resources for
allocation to D2D communications comprising a subset of time
resources.
[0198] Example 28 is UE for use in a wireless communication
network, the UE comprising: [0199] a touchscreen configured to
receive input from a user for processing by the UE; [0200] a
transceiver module configurable to enable device-to-device
communication; [0201] a scanning module configured to search for a
device-to-device synchronization signal and to determine if a
received synchronization signal satisfies a signal quality metric;
[0202] a synchronization signal broadcasting module configured to
broadcast, depending upon a result of the search performed by the
scanning circuitry, a synchronization signal for synchronizing data
communication on at least one device-to-device communication link
between any transmitting device and any receiving device within a
synchronization range of the device-to-device communication
circuitry; and [0203] a radio resource information module,
configured to broadcast information about radio resources for
device-to-device operation.
[0204] Example 29 may be the subject matter of example 28, wherein
optionally the synchronization signal broadcasting module is
configured to broadcast the synchronization signal using radio
resources orthogonal in time to a received synchronization signal
corresponding to a different synchronization source.
[0205] Example 30 is a computer readable medium comprising
instructions, which, when executed, cause a processor to carry out
the method of any one of examples 19 to 24.
[0206] Example 31 may be the subject matter of example 30, the
medium optionally being one of a storage medium and a transmission
medium.
[0207] Example 32 is device-to-device communication circuitry
substantially as hereinbefore described with reference to the
accompanying drawings.
[0208] Example 33 is a device-to-device communication method
substantially as hereinbefore described with reference to the
accompanying drawings.
[0209] Example 34 is a UE substantially as hereinbefore described
with reference to the accompanying drawings.
* * * * *