Note: Descriptions are shown in the official language in which they were submitted.
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Description
APPARATUS AND METHOD FOR SUPPORTING RELAY
SERVICE IN A MULTI-HOP RELAY BROADBAND WIRELESS
ACCESS COMMUNICATION SYSTEM
Technical Field
[11 The present invention relates generally to a multi-hop relay
Broadband Wireless
Access (BWA) communication system, and in particular, to an apparatus and
method
for synchronously providing a direct link service and a relay link service in
a multi-hop
relay BWA communication system.
Background Art
[2] One of the most critical requirements for deployment of a 4th
Generation (4G)
mobile communication system is to build a self-configurable wireless network.
The
self-configurable wireless network refers to a wireless network configured in
an
autonomous or distributed manner without control of a central system to
provide
mobile communication services. For the 4G mobile communication system, cells
of
very small radii are defined for the purpose of enabling high-speed
communications
and accommodating a larger number of calls. The conventional centralized
wireless
network design is not self-configurable. Rather, the wireless network should
be built to
be under distributed control and to actively cope with an environmental change
like
addition of new Base Stations (BSs). That is why the 4G mobile communication
system requires the self-configurable wireless network.
[31 For real deployment of the self-configurable wireless network,
techniques used for
an ad hoc network should be introduced to a wireless access communication
system.
Such a major example is a multi-hop relay BWA communication system configured
by
applying a multi-hop relay scheme used for the ad hoc network to a BWA network
with fixed BSs.
[4] In general, since a BS and a Mobile Station (MS) communicate with
each other via
a direct link, a highly reliable radio link can be established easily between
the BS and
the MS in the BWA communication system. However, due to the fixedness of the
BSs,
the configuration of a wireless network is not flexible, making it difficult
to provide an
efficient service in a radio environment experiencing a fluctuating traffic
distribution
and a great change in the number of required calls.
[51 The above drawback can be overcome by a relay service that delivers
data over
multiple hops using a plurality of neighbor MSs or neighbor Relay Stations
(RSs). The
use of the multi-hop relay scheme facilitates fast network reconfiguration
adaptive to
an environmental change and renders the overall wireless network operation
efficient.
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WO 2007/100232 PCT/KR2007/001081
Also, a radio channel in a better channel status can be provided to an MS by
installing
an RS between the BS and the MS and thus establishing a multi-hop relay path
via the
RS. High-speed data channels can be provided to MSs in a shadowing area or an
area
where communications with the BS are unavailable, and cell coverage can be
expanded.
[6] FIG. 1 illustrates the configuration of a typical multi-hop relay BWA
com-
munication system.
[71 Referring to FIG. 1, in the multi-hop relay BWA communication system,
MSs 140,
150, 160 and 170 (MS1 to M54) can receive BWA services through a BS 100, a
primary RS (RS1) 110, and secondary RSs (R52) 120 and 130.
[8] MS1 and M52 within the coverage area 101 of the BS 100 communicate
with the
BS 100 via direct links Li. M52, which is located at the cell boundary of the
BS 100
and thus placed in a poor channel state, can receive a higher-speed data
channel via an
RS-MS link L2 provided by R52 130 compared to the speed via the direct link
Li.
[91 M53 and M54 outside the coverage area 101 of the BS 100 communicate
with the
BS 100 via RS-MS links L3 provided by RS1 110. The communication links between
the BS 100 and M53 and M54 via RS1 110 expand the cell coverage. M54, which is
located at the cell boundary of RS1 110 and thus placed in a poor channel
state, can
increase its transmission capacity using an RS-MS link LA provided by R52 120.
[10] As described above, when an MS is in a poor channel state at a cell
boundary of a
BS or in a shadow area suffering from a severe shielding effect due to, for
example,
buildings, the BWA communication system enables the MS to communicate with the
BS by providing a better-quality radio channel to the MS via an RS. In other
words, the
BS can provide a high-speed data channel to the cell boundary and the shadow
area
and expand its coverage area by the multi-hop relay scheme.
[11] The RSs 110, 120 and 130 are classified into RS1 (RS 110) that expands
cell
coverage and R52 (the RSs 120 and 130) that increases capacity according to
their
operation capabilities.
[12] As stated above, RS1 110 serves to expand the cell coverage of the BS
100.
Because M53 and M54 have difficulty in receiving services directly from the BS
100,
they acquire synchronization to the BS 100 and perform network entry to the BS
100
via RS1 110. Therefore, RS1 110 provides functionalities for the initial
access of the
MSs 160 and 170, that is, provides a control channel (or traffic channel) and
a random
access channel to M53 and M54.
[13] R52 120 and R52 130 relay services to M52 and M54 within their cell
coverage
area, for the purpose of increasing service capacity. M52 receives a control
channel
and a random access channel from the BS 100 and a traffic channel from R52
130.
M54 receives a control channel and a random access channel from RS1 110 and a
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traffic channel from RS2 120.
[14] Typically, transmission/reception is carried out between a BS and an
MS in frames
having the configuration illustrated in FIG. 2 in the BWA communication
system. FIG.
2 illustrates a Time Division Duplex (TDD) frame structure compliant with the
Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard, for
data
transmission/reception between the BS and the MS.
[15] Referring to FIG. 2, a TDD frame 200 is divided into a DownLink (DL)
subframe
210 and an UpLink (UL) subframe 220 with a guard region called
Transmit/receive
Transition Gap (TTG) in between. A guard region called Receive/transmit
Transition
Gap (RTG) is interposed between TDD frames.
[16] A preamble and a common control channel are included in mandatory
slots of the
DL subframe 210 and broadcast to the cell coverage area of a BS. MSs within
the
coverage area of the BS acquire synchronization and control information from
the
preamble and the common control channel.
[17] As described above, RS1 provides BWA services to MSs or RSs which have
difficulty in establishing direct links with the BS as they are located
outside the
coverage area. Therefore, RS1 must provide control information and initial
ranging
slots to the MSs or the RSs, for network entry as well as user traffic
service.
Especially, RS1 must provide a service via an indirect link in the same
configuration as
via a direct link as illustrated in FIG. 3, in order to ensure backward
compatibility for
the MSs.
[18] For a relay service, after receiving a control channel or a traffic
channel from a BS
or an MS, an RS relays them. That is why the RS carries out both transmission
and
reception within a single-directional subframe.
[19] FIG. 3 illustrates a TDD frame structure in a conventional multi-hop
relay BWA
communication system.
[20] Referring to FIG. 3, a single-directional subframe 300 is divided into
a direct link
zone 301 and an indirect link zone 303, and another single-directional
subframe 310 is
divided into a direct link zone 311 and an indirect link zone 313. For a relay
service,
predetermined parts of the subframes 300 and 310 are allocated to the indirect
link
zones 303 and 313. Thus, an RS receives information and data for relaying in
the direct
link zones 301 and 311 and relays them in the indirect link zones 303 and 313.
[21] For instance, RS1 receives control information and a traffic burst to
be relayed from
the BS or an MS in the direct link zone 301 or 311 and then relays them to the
BS or
the MS in the indirect link zone 303 or 313.
[22] R52 receives unicast traffic bursts to be relayed from an MS or the BS
in the direct
link zone 311 or 301 and then relays them to the MS or the BS in the indirect
link zone
303 or 313.
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[23] When communications are conducted in the frame structure illustrated
in FIG. 3, a
different node that provides a BWA service has a different frame timing, i.e.
different
nodes operate asynchronously in the BWA communication system, as illustrated
in
FIG. 4.
[24] FIG. 4 is a diagram illustrating transmission and reception timings of
MSs in the
conventional multi-hop relay BWA communication system.
[25] Referring to FIG. 4, an MS that receives a direct link service from a
BS has the
timing of a BS frame 421 because communications are made in direct link zones
401
and 411. On the other hand, an MS that receives a relay link service from an
RS has
the timing of an RS frame 423 because communications are made in indirect link
zones
403 and 413.
[26] Typically, synchronization and handover are carried out based on
control in-
formation and preamble transmitted to a fixed position in a frame in the BWA
com-
munication system. However, since MSs operate asynchronously depending on the
subject that provides them with service as illustrated in FIG. 4, the handover
and syn-
chronization are very difficult as illustrated in FIG. 5.
[27] FIG. 5 illustrates signal flows when MSs move in the conventional
multi-hop relay
BWA communication system.
[28] Referring to FIG. 5, when an MS 520 (MS1) moves from a BS 500 to the
coverage
area of RS 1 510 while receiving a service from the BS 500, MS1 must receive a
preamble and control information from RS1 510.
[29] When an MS 530 (M52) moves from RS1 510 to the BS 500 during receiving
a
service from RS1 510, M52 must receive a preamble and control information from
the
BS 500.
Disclosure of Invention
Technical Problem
[30] As illustrated in FIG. 3, however, the BS 500 and RS1 510 operate
asynchronously,
thereby making it difficult for MS1 and M52 to acquire the preamble and the
control
information after the handover.
[31] Moreover, since the BS provides a service to the MSs and the RS
simultaneously in
a direct link subframe, as illustrated in FIG. 3, the freedom of configuring a
system in
which the BS supports the RS is low.
[32]
Technical Solution
[33] An aspect of the present invention is to substantially solve at least
the above
problems and/or disadvantages and to provide at least the advantages below. Ac-
cordingly, an aspect of the present invention is to provide a frame
configuration
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method for enabling an MS to perform handover and acquire synchronization ef-
ficiently and an apparatus supporting the same in a multi-hop relay BWA com-
munication system.
[34] Another aspect of the present invention is to provide a frame
configuration method
for increasing the freedom of configuring relay links and an apparatus
supporting the
same in a multi-hop relay BWA communication system.
[35] A further aspect of the present invention is to provide an apparatus
and method for
synchronizing between a direct link service and a relay link service by
configuring a
subframe including a connection-link subframe and a relay-link subframe in a
multi-
hop relay BWA communication system.
[36] According to an aspect of the present invention, there is provided
amethod for
configuring a subframe to support a relay service in a multi-hop relay BWA com-
munication system, in which a first zone of the subframe is configured for at
least one
of communication between a BS and a first MS within the coverage area of the
BS and
communication between each RS and a second MS within the coverage area of the
RS,
and a second zone of the subframe is configured for at least one of
communication
between the BS and the each RS and communication between the RS and another
RS.
[37] According to another aspect of the present invention, there is
provided a method for
configuring a subframe to support a relay service in a multi-hop relay BWA com-
munication system, in which a first zone of the subframe is configured for at
least one
of BS-MS communication and RS-MS communication, a second zone of the subframe
is configured for at least one of BS-RS communication, RS-RS communication,
and
RS-MS communication, and a third zone of the subframe is configured for at
least one
of BS-MS communication and RS-RS communication.
[38] According to a further aspect of the present invention, there is
provided a method of
a BS for supporting a relay service in a multi-hop relay BWA communication
system,
in which the BS communicates with an MS in a first zone of a subframe
according to a
predetermined subframe configuration, and communicates with an RS in a second
zone
of the subframe.
[39] According to still another aspect of the present invention, there is
provided a
method of an RS for supporting a relay service in a multi-hop relay BWA com-
munication system, in which the RS performs network entry based on control in-
formation received from a higher node and acquires subframe configuration in-
formation for supporting the relay service, receives a synchronization
channel, control
information, and a traffic burst from the higher node for a second zone of a
subframe
in an nth frame, and sends asynchronization channel and the received control
in-
formation and traffic burst to an MS for a first zone of the subframe in an
(n+1)th
frame.
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[40] According to yet another aspect of the present invention, there is
provided an
apparatus for supporting a relay service in a multi-hop relay BWA
communication
system, in which a timing controller provides a transmission and reception
timing
signal for a signal for an MS-communication zone for communicating with an MS
and a signal for an RS-communication zone for communicating with an RS
according to a frame configuration, an RF duplexer separates the signal for
the MS-
communication zone from the signal for the RS-communication zone, and a
transceiver communicates with one of the MS and the RS according to the
transmission and reception timing signal.
According to an aspect of the present invention, there is provided a method
for
configuring a subframe to support a relay service in a multi-hop relay
wireless
communication system including at least one Mobile Station (MS), at least one
Base
Station (BS), and at least one Relay Station (RS), the method comprising:
configuring a BS-MS link subframe for at least one of communication between a
BS and a first MS within the coverage area of the BS and an RS-MS link
subframe
for communication between at least one RS and a second MS within the coverage
area of the at least one RS in a first zone of a downlink subframe;
if the wireless communication system includes two hops, configuring a BS-RS
link subframe for communication between the BS and the at least one RS in a
second zone of the downlink subframe;
if the wireless communication system includes three or more hops, configuring
a
BS-RS link subframe for communication between the BS and the at least one RS
and an RS-RS link subframe for communication between the at least one RS and
another RS in the second zone of the downlink subframe;
configuring a BS-MS link subframe for at least one of communication between
the BS and the first MS within the coverage area of the BS and an RS-MS link
subframe for communication between at least one RS and the second MS within
the
coverage area of the at least one RS in a first zone of a uplink subframe;
if the wireless communication system includes two hops, configuring a BS-RS
link subframe for communication between the BS and the at least one RS in a
second zone of the uplink subframe; and
if the wireless communication system includes three or more hops, configuring
a
BS-RS link subframe for communication between the BS and the at least one RS
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and an RS-RS link subframe for communication between the at least one RS and
another RS in the second zone of the uplink subframe,
wherein the first zone and the second zone are distinguished in the downlink
subframe and uplink subframe by time resource,
wherein the first zone and the second zone are located consecutively in the
downlink subframe and uplink subframe,
wherein a guard region is inserted between the first zone and the second zone
of
the downlink subframe and uplink subframe,
wherein the downlink subframe and the uplink subframe are distinguished by
time resources, and
wherein a preamble and a map are positioned at a start of the first zone of
the
downlink subframe.
According to another aspect of the present invention, there is provided a
method
for configuring a subframe to support a relay service in a multi-hop relay
wireless
communication system including at least one Mobile Station (MS), at least one
Base
Station (BS), and at least one Relay Station (RS), the method comprising:
configuring a BS-MS link subframe for BS-MS communication and an RS-MS
link subframe for the RS-MS communication in a first zone of a downlink
subframe;
if the wireless communication system includes two hops, configuring a BS-RS
link subframe for BS-RS communication in a second zone of the downlink
subframe;
if the wireless communication system includes three or more hops, configuring
at
least one of a BS-RS link subframe for BS-RS communication, an RS-RS link
subframe for RS-RS communication, and an RS-MS link subframe for RS-MS
communication in the second zone of the downlink subframe;
if the wireless communication system includes two hops, configuring a BS-MS
link subframe for BS-MS communication in a third zone of the downlink
subframe;
if the wireless communication system includes three or more hops, configuring
a
BS-MS link subframe for at least one of BS-MS communication and an RS-RS link
subframe for RS-RS communication in the third zone of the downlink subframe;
configuring a BS-MS link subframe for BS-MS communication and an RS-MS
link subframe for the RS-MS communication in a first zone of a uplink
subframe;
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if the wireless communication system includes two hops, configuring a BS-RS
link subframe for BS-RS communication in a second zone of the uplink subframe;
if the wireless communication system includes three or more hops, configuring
at
least one of a BS-RS link subframe for BS-RS communication, an RS-RS link
subframe for RS-RS communication, and an RS-MS link subframe for RS-MS
communication in the second zone of the uplink subframe;
if the wireless communication system includes two hops, configuring a BS-MS
link subframe for BS-MS communication in a third zone of the uplink subframe;
if the wireless communication system includes three or more hops, configuring
a
BS-MS link subframe for at least one of BS-MS communication and an RS-RS link
subframe for RS-RS communication in the third zone of the uplink subframe,
wherein the first zone and the second zone and third zone are distinguished in
the
downlink subframe and uplink subframe by time resource,
wherein the first zone and the second zone and third zone are located
consecutively in the downlink subframe and uplink subframe,
wherein the downlink subframe and the uplink subframe are distinguished by
time resources, and
wherein a preamble and a map are positioned at a start of the first zone of
the
downlink subframe.
According to a further aspect of the present invention, there is provided a
method
of a Base Station (BS) for supporting a relay service in a multi-hop relay
wireless
communication system including at least one Mobile Station (MS), at least one
BS,
and at least one Relay Station (RS), the method comprising:
configuring a subframe into a first zone and a second zone;
communicating with an MS in the first zone of the downlink subframe and uplink
subframe according to a predetermined subframe configuration; and
communicating with an RS in the second zone of the downlink subframe and
uplink subframe,
wherein, the first zone includes a BS-MS link subframe and an RS-MS link
subframe, if the wireless communication system includes two hops, the second
zone
includes BS-RS link subframe, if the wireless communication system includes
three
or more hops, the second zone includes BS-RS link subframe and RS-RS link
subframe,
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wherein the first zone and the second zone are distinguished in the downlink
subframe and uplink subframe by time resources,
wherein the first zone and the second zone are located consecutively in the
downlink subframe and uplink subframe,
wherein the downlink subframe and the uplink subframe are distinguished by
time resources,
wherein a preamble and a map are positioned at a start of the first zone of
the
downlink subframe, and
wherein a guard region is inserted between the first zone and the second zone
of
the downlink subframe and uplink subframe.
According to a further aspect of the present invention, there is provided a
method
of a Relay Station (RS) for supporting a relay service in a multi-hop relay
wireless
communication system including at least one Mobile Station (MS), at least one
Base
Station (BS), and at least one RS, the method comprising:
performing network entry based on control information received from a higher
node and acquiring subframe configuration information for supporting the relay
service;
receiving a synchronization channel, control information, and a traffic burst
from
the higher node in a second zone of a downlink subframe in an nth frame;
sending a synchronization channel and the received control information and
traffic burst to an MS in a first zone of a downlink subframe in an (n+1)th
frame;
receiving a synchronization channel, control information, and a traffic burst
from
the higher node in a second zone of the downlink subframe in the (n+1)th
frame; and
if the wireless communication system includes three or more hops,
communicating with another RS in a second zone of the downlink subframe and a
uplink subframe in the (n+ 1)th frame,
wherein the subframe configuration information includes information of a
downlink subframe and an uplink subframe divided into a first zone and a
second
zone,
wherein, the first zone of the downlink subframe and an uplink subframe
includes
a BS-MS link subframe and an RS-MS link subframe, if the wireless
communication system includes two hops, the second zone of downlink subframe
and an uplink subframe includes BS-RS link subframe, if the wireless
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communication system includes three or more hops, the second zone of downlink
subframe and an uplink subframe includes BS-RS link subframe and RS-RS link
subframe,
wherein the first zone and the second zone are distinguished in the downlink
subframe and uplink subframe by time resources,
wherein the first zone and the second zone are located consecutively in the
downlink subframe and uplink subframe,
wherein the downlink subframe and the uplink subframe are distinguished by
time resources,
wherein a preamble and a map are positioned at a start of the first zone of
the
downlink subframe, and
wherein a guard region is inserted between the first zone and the second zone
of
the downlink subframe and uplink subframe.
According to a further aspect of the present invention, there is provided an
apparatus for supporting a relay service in a multi-hop relay wireless
communication system including at least one Mobile Station (MS), at least one
Base
Station (BS), and at least one Relay Station (RS), the method comprising:
a timing controller for providing a transmission and reception timing signal
for a
signal for an MS-communication zone for communicating with an MS and a signal
for an RS-communication zone for communicating with an RS according to a frame
configuration;
a Radio Frequency (RF) duplexer for separating the signal for the MS-
communication zone from the signal for the RS-communication zone; and
a transceiver for communicating with one of the MS and the RS according to the
transmission and reception timing signal,
wherein the frame configuration includes information of a downlink subframe
and
an uplink subframe divided into a first zone and a second zone,
wherein the first zone of the downlink subframe and an uplink subframe
includes
a BS-MS link subframe and an RS-MS link subframe, if the wireless
communication system includes two hops, the second zone of the downlink
subframe and an uplink subframe includes BS-RS link subframe, if the wireless
communication system includes three or more hops, the second zone of the
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downlink subframe and an uplink subframe includes BS-RS link subframe and RS-
RS link subframe,
wherein the first zone and the second zone are distinguished in the downlink
subframe and uplink subframe by time resource,
wherein the first zone and the second zone are located consecutively in the
downlink subframe and uplink subframe,
wherein the downlink subframe and the uplink subframe are distinguished by
time resources,
wherein a preamble and a map are positioned at a start of the first zone of
the
downlink subframe, and
wherein a guard region is inserted between the first zone and the second zone
of
the downlink subframe and uplink subframe.
Advantageous Effects
[41] In accordance with the present invention as described above, a multi-hop
relay
BWA communication system multiplexes a connection-link zone and a relay-link
zone in time division in a signal transmission period. As a result, a direct
service
and a relay service are transparently provided to MSs in synchronized frames.
Hence, handover and synchronization are facilitated for the MSs. Also, since
the
relay-link zone in which an RS receives a service is configured to be
independent of
the connection-link zone, the freedom of configuring the relay link can be
increased
according to the number of hops and a channel environment.
[42]
Brief Description of the Drawings
[43] The above and other objects, features and advantages of the present
invention will
become more apparent from the following detailed description when taken in
conjunction with the accompanying drawings in which:
[44] FIG. 1 illustrates service provisioning by a multi-hop relay scheme in a
typical
BWA communication system;
[451 FIG. 2 illustrates a TDD frame structure in the typical BWA communication
system;
[46] FIG. 3 illustrates a TDD frame structure in a conventional multi-hop
relay BWA
communication system;
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[47] FIG. 4 is a diagram illustrating transmission and reception timings of
MSs in the
conventional multi-hop relay BWA communication system;
[48] FIG. 5 illustrates signal flows when MSs move in the conventional multi-
hop
relay BWA communication system;
[49] FIG. 6 illustrates a subframe structure in a multi-hop relay BWA
communication
system according to the present invention;
[50] FIG. 7 illustrates a frame structure in the multi-hop relay BWA
communication
system according to the present invention;
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[511 FIG.
8 and FIG. 9 illustrate relay-link subframe structures in the multi-hop relay
BWA communication system according to the present invention;
[52] FIG. 10 illustrates timings of a BS, an MS, and RSs in the multi-hop
relay BWA
communication system according to the present invention;
[53] FIG. 11 illustrates a frame structure in the multi-hop relay BWA
communication
system according to the present invention;
[54] FIG. 12 illustrates a frame structure in a 3 or more-hop BWA
communication
system according to the present invention;
[55] FIG. 13 illustrates a frame structure for a BS and RS1 in the 3 or
more-hop relay
BWA communication system according to the present invention;
[56] FIG. 14 illustrates a frame structure for R52 and an MS in the 3 or
more-hop relay
BWA communication system according to the present invention;
[57] FIG. 15 is a flowchart illustrating an operation of the BS in the
multi-hop relay
BWA communication system according to the present invention;
[58] FIG. 16 is a flowchart illustrating an operation of an RS in the multi-
hop relay
BWA communication system according to the present invention; and
[59] FIG. 17 is a block diagram of the BS in the multi-hop relay BWA
communication
system according to the present invention.
Best Mode for Carrying Out the Invention
[60] Preferred embodiments of the present invention will be described
herein below with
reference to the accompanying drawings. In the following description, well-
known
functions or constructions are not described in detail since they would
obscure the
invention in unnecessary detail.
[61] The present invention provides a technique for synchronizing between
services
provide from a BS and an RS to MSs and increasing the freedom of configuring
relay-
link areas in a frame in a multi-hop relay BWA communication system.
[62] The following description will be made in the context of a Time
Division Duplex
(TDD)-Orthogonal Frequency Division Multiple Access (OFDM) wireless com-
munication system, while the present invention is also applicable to a
communication
system using any other multiple access scheme or a Frequency Division Duplex
(FDD)
communication system. Herein, the term a primary RS or RS1 is defined as a
high-
capability RS that provides a control signal to an expanded coverage area, and
the term
a secondary RS or R52 is defined as a low- capability RS that relays mainly
traffic
bursts for an increase in capacity.
[63] In the BWA communication system, a subframe is divided into a
connection-link
subframe and a relay-link subframe in order to send a direct link service and
a relay
link service with the same timing, synchronously, as illustrated in FIG. 6.
The direct
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link is a link via which a BS or an RS communicates with an MS, and the relay
link is
a link via which the BS communicates with the RS or the RS communicates with a
lower RS. The connection-link subframe is configured in compliance with IEEE
802.16.
[64] FIG. 6 illustrates a subframe structure in a multi-hop relay BWA
communication
system according to the present invention.
[65] Referring to FIG. 6, a subframe 600 is divided into a connection-link
subframe 610
and a relay-link subframe 620. The connection-link subframe 610 and the relay-
link
subframe 620 are distinguished by time division.
[66] On the downlink, the connection-link subframe 610 is distinguished
from the relay-
link subframe 620 according to signal destinations. BS-MS transmission or RS-
MS
transmission takes place in the connection-link subframe 610, while BS-RS or
higher
RS-lower RS transmission takes place in the relay-link subframe 620.
[67] On the uplink, the connection-link subframe 610 is distinguished from
the relay-
link subframe 620 according to signal sources. MS-BS transmission or MS-RS
transmission occurs in the connection-link subframe 610, while lower RS-higher
RS
transmission or RS-BS transmission occurs in the relay-link subframe 620.
[68] In the connection-link subframe, a BS and an RS transparently
communicate with
the MS. In other words, the BS and the RS provide services such that the MS is
not
aware of a distinction between a direct link service and a relay link service
and the MS
is aware of communication with the BS. If information travels over multiple
hops in
the BWA communication system, the relay-link subframe 620 may be separated
into a
plurality of areas according to the number of multiple-hop links.
[69] Based on the subframe structure illustrated in FIG. 6, a frame can be
configured in
the fashion illustrated in FIG. 7.
[70] FIG. 7 illustrates a frame structure in the multi-hop relay BWA
communication
system according to f the present invention.
[71] Referring to FIG. 7, a frame is divided into a DL subframe 700 and a
UL subframe
710. According to the subframe structure illustrated in FIG. 6, a connection-
link
subframe 701 and a relay-link subframe 703 are time-multiplexed in the DL
subframe
700, while a connection-link subframe 711 and a relay-link subframe 713 are
time-
multiplexed in the UL subframe 710.
[72] In each of the subframes 700 and 710, the connection-link subframe 701
or 711
precedes the relay-link subframe 703 or 713 in order to transparently notify
MSs of the
preamble-based start of the frame and the position of a TTG.
[73] A BS 720 and RS1 730 communicate with MSs that they serve in the
connection-
link subframes 701 and 711. Notably, a direct link service from the BS 720 and
a relay
link service from RS1 730 are provided in the connection-link subframes 701
and 711
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by Frequency Division Multiplexing (EDM), Spatial Division Multiplexing (SDM),
or
Orthogonal Frequency Division Multiplexing (OFDM).
[74] For transparent relaying, RS1 730 provides control information and a
traffic burst to
an MS in the same manner as the BS 720 provides the direct link service to an
MS.
R52 is allocated a predetermined burst zone 705 or 707 from the BS 720 or RS1
730
and provides a unicast traffic channel to an MS in the burst zone 705 or 707.
[75] In the relay-link subframes 703 and 713, the BS 720 communicates with
RS1 730
or RS 1730 communicates with its lower RS. The relay-link subframes 703 and
713
have a fixed length or a variable length according to a cell environment. An
advanced
technology may applied, which can define a new function and usage for the
relay-link
subframes 703 and 711, and thus the configuration of the relay-link subframes
703 and
711 is not be specified in FIG. 7.
[76] In the case where the BWA communication system is expanded to multiple
hops,
the relay-link subframes 703 and 713 may be time-divided according to the
number of
multi-hop links, as illustrated in FIGs. 8 and 9.
[77] FIGs. 8 and 9 illustrate relay-link subframe structures in the multi-
hop relay BWA
communication system according to the present invention. A relay-link subframe
may
be configured to include control channels and traffic channels of various
structures.
[78] Referring to FIGs. 8 and 9, relay-link subframes 803 and 813 each are
divided
according to the number of multiple hops.
[79] In FIG. 8, zones for relay links are multiplexed in the relay-link
subframes 803 and
813 in a descending hop number order. Specifically, the link between an (n-1)-
hop RS
and an n-hop RS precedes the link between the BS and a one-hop RS in the
multiplexed relay-link subframes 803 and 813.
[80] In FIG. 9, zones for relay links are multiplexed in the relay-link
subframes 803 and
813 in an ascending order of hop number. Specifically, the link between the BS
and the
one-hop RS precedes the link between the (n-1)-hop RS and the n-hop RS in the
multiplexed relay-link subframes 803 and 813. Herein, the number of hops in
the
system refers to the number of RSs.
[81] As illustrated in FIGs. 7, 8 and 9, the BS provides a service to RS1
or an MS, and
RS1 provides a service to an MS or R52 in the separate connection-link
subframe and
relay-link subframe of a single-directional subframe. The BS and the RSs start
frames
at the same timing as illustrated in FIG. 10. That is, the BS and the RSs
synchronously
(with the same timing) provide a connection link service to the MSs.
[82] FIG. 10 illustrates timings of a BS, an MS, and RSs in the multi-hop
relay BWA
communication system according to the present invention. The following
description is
made in the context of a 2-hop relay system. Hence, RS1 and R52 provide a one-
hop
relay service to different MSs.
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[83] Referring to FIG. 10, a BS 920 sends control information and a traffic
burst to an
MS that it serves in a connection-link subframe 901 of a DL subframe 900
during time
period D_t 1. The BS 920 also sends control information and a traffic burst to
RS1 940
and RS2 930 in a relay-link subframe 903 during time period D_t3.
[84] RS1 940 sends control information and a traffic burst to an MS that it
serves in the
connection-link subframe 901 during time period D_t 1, and receives control in-
formation and a traffic burst for relaying from the BS 920 in the relay-link
subframe
903 during time period D_t3. If the BWA communication system is expanded to
three
or more hops and includes a 2-hop relay system, RS1 940 divides the time slots
of the
relay-link subframe 903 and sends control information and a traffic burst to
an RS at
the next hop in a predetermined time slot of the relay-link subframe 903. The
size of
time slots multiplexed in the relay-link subframe 903 is adaptively decided
according
to the number of multiple hops and the channel status.
[85] A control channel period D_t2 is null for R52 930 in the connection-
link subframe
901 and R52 930 sends a unicast traffic burst to an MS during the remaining
period,
i.e. D_tl-D_t2. In the relay-link subframe 903, R52 930 receives control
information
and a traffic burst for relaying from the BS 920 during time period D_t3.
[86] An MS 950 receives a control channel and a traffic burst from the BS
920 or an RS
in the connection-link subframe 901. In the relay-link subframe 903, the MS
950
neglects the relay-link subframe 903, having determined that the subframe 903
is not
allocated to itself and thus is placed in idle mode.
[87] During the period of the UL subframe 910, the BS 920 receives initial
ranging in-
formation and a traffic burst from the MS in the connection-link subframe 911
during
time period U_t1 and receives initial ranging information and traffic bursts
from RS1
940 and R52 930 in the relay-link subframe 913 during time period U_t3.
[88] RS1 940 receives the initial ranging information and a traffic burst
for relaying
from the MS during time period U_t1 in the connection-link subframe 911. RS1
940
also sends the initial ranging information and the traffic bursts to the BS
920 during
time period U_t3 in the connection-link subframe 913. RS1 940 compensates for
the
delay of a radio channel before the signal transmission.
[89] In the connection-link subframe 911, a control channel period U_t2 is
null for R52
930 and R52 930 receives a traffic burst for relaying from the MS during the
remaining period U_tl-U_t2. R52 930 sends the unicast traffic bursts to the BS
920
during time period U_t3 in the relay-link subframe 913. R52 930 compensates
for the
delay of a radio channel before the signal transmission.
[90] In the connection-link subframe 911, the MS 950 sends initial ranging
information
and traffic bursts to the BS 920 or the RS during time period U_t 1. the MS
950
compensates for the delay of a radio channel before the signal transmission.
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[91] The MS 950 neglects the relay-link subframe 913, having determined
that the
subframe 913 is not allocated to itself.
[92] As described above, the RSs are switched between transmission and
reception in the
single-directional subframes. Accordingly, guard regions (e.g. RS TTG and RS
RTG)
are required in the DL subframe 900 and the UL subframe 910. For example, each
of
the guard regions can be formed by setting a short preamble in the first
symbol of the
relay-link subframe, so that the RSs can operate in a switched operation mode
during
the remaining period of the relay-link subframe. The short preamble can be
created by
reducing the number of repeated sequences that form the preamble of the frame.
[93] Alternatively, the BS forms a predetermined gap between the connection-
link
subframe 901 and the relay-link subframe 903 so that the RS can operate in a
switched
operation mode.
[94] FIG. 11 illustrates a frame structure in the multi-hop relay BWA
communication
system according to another embodiment of the present invention. This
embodiment is
characterized in that the configuration of a connection-link subframe is
identical to the
configuration of a relay-link subframe.
[95] Referring to FIG. 11, in a 2-hop relay system, a DL subframe 1000 is
divided into a
connection-link subframe 1001 and a relay-link subframe 1003, and a UL
subframe
1010 is divided into a connection-link subframe 1011 and a relay-link subframe
1013.
[96] A direct link service from a BS and a relay link service from an RS
are provided in
FDM, SDM, or OFDM in the connection-link subframes 1001 and 1011.
[97] The BS communicates with the RS in the relay-link subframes 1003 and
1013.
[98] The above embodiment illustrates a frame structure for supporting a
relay service in
a two-hop relay BWA communication system. If the BWA communication system is
expanded to three or more hops, the frame structure illustrated in FIG. 8 may
be
constructed in the specific form illustrated in FIG. 12. With reference to
FIG. 12, mul-
tiplexing of two relay-link zones in a relay-link subframe to provide a relay
service
over multiple hops will be described.
[99] FIG. 12 illustrates a frame structure for a 3 or more-hop relay BWA
communication
system according to an embodiment of the present invention. The following de-
scription is made with the appreciation that a BS, RSs, and MSs communicate in
spatially multiplexed frames sharing one frequency. Herein, RS1 is a one-hop
RS that
receives data directly from the BS and relays the data, and R52 is a two-hop
RS that
receives data from the BS via RS1 and relays the data.
[100] Referring to FIG. 12, a jth frame 1100 is divided into a DL subframe
1110 and a UL
subframe 1120. The DL subframe 1110 is further divided into a first zone 1111,
a
second zone 1113, and a third zone 1115. The UL subframe 1120 is further
divided
into a first zone 1121, a second zone 1123, and a third zone 1125. The second
and third
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zones 1113 and 1115 correspond to the multiplexed relay-link subframe 803
illustrated
in FIG. 8, and the second and third zones 1123 and 1125 correspond to the
multiplexed
relay-link subframe 813 illustrated in FIG. 8.
[101] The first zones 1111 and 1121 include BS-MS link subframes for
communications
between a BS 1130 and a first MS 1160 (MS1) and RS-MS link subframes for commu-
nications between RS1 1140 and a second MS 1170 (M52) and between R52 1150 and
a third MS 1180 (M53). The second zones 1113 and 1123 include BS-RS link
subframes and RS-MS link subframes. If the system operates over four or more
hops,
the second zones 1113 and 1123 include BS-RS link subframes, RS-RS link
subframes, and RS-MS link subframes. The third zones 1115 and 1125 include BS-
MS
link subframes and RS-RS link subframes.
[102] A TTG exists between the DL subframe 1110 and the UL subframe 1120.
[103] When a multi-hop relay service is supported by the jth frame 1100,
the BS 1130
sends downlink data to MS1 that BS 1130 serves in the first and third zones
1111 and
1115. The BS 1130 also sends downlink data to RS1 1140 in the second zone
1113.
[104] The BS 1130 receives uplink data from MS lin the first zone 1121 and
the third
zone 1125 of the UL subframe 1120. The BS 1130 also receives uplink data from
RS1
1140 in the second zone 1123.
[105] R51 1140 sends downlink data to M52 that it serves in the first zone
1111 of the
DL subframe 1110. RS1 1140 also receives downlink data from the BS 1130 in the
second zone 1113. In the third zone 1115, RS1 1140 sends downlink data to R52
1150.
[106] In the UL subframe 1120, RS1 1140 receives uplink data from M52 in
the first zone
1121 and sends uplink data to the BS 1130 in the second zone 1123. In the
third zone
1125, RS1 1140 receives uplink data from R52 1150.
[107] In the DL subframe 1110, R52 1150 sends downlink data to M53 that R52
1150
serves in the first and second zones 1111 and 1113 and receives downlink data
from
RS1 1140 in the third zone 1115.
[108] In the UL subframe 1120, R52 1150 receives uplink data from M53 in
the first and
second zones 1121 and 1123 and sends uplink data to RS1 1140 in the third zone
1125.
If the system operates over four or more hops, R52 1150 can communicate with a
lower RS instead of M53 in the second zones 1113 and 1123. That is, for the
three-hop
system, R52 1150 is a last-hop RS and thus R52 1150 communicates with M53
instead
of a lower RS.
[109] MS1, M52 and M53 receive downlink data from nodes to which they are
linked in
the DL subframe 1110 and send uplink data to the nodes in the UL subframe 1120
of
the jth frame 1100.
[110] For example, MS1 receives downlink data from the BS 1130 in the first
and third
zones 1111 and 1115 of the DL subframe 1110 and sends uplink data to the BS
1130 in
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the first and third zones 1121 and 1125 of the UL subframe 1120.
[111] MS2 receives downlink data from RS 1140 in the first zone 1111 of the
DL
subframe 1110 and sends uplink data to RS1 1140 in the first zone 1121 of the
UL
subframe 1120.
[112] MS3 receives downlink data from RS2 1150 in the first and second
zones 1111 and
1113 of the DL subframe 1110 and sends uplink data to RS2 1150 in the first
and
second zones 1121 and 1123 of the UL subframe 1120.
[113] In the case where the BWA communication system operates in the manner
il-
lustrated in FIG. 12 and each subframe is constructed in compliance with the
IEEE
802.16 standard, frame structures for the BS and RS1 are illustrated in FIG.
13 and
frame structures for RS2 and an MS are illustrated in FIG. 14.
[114] FIG. 13 illustrates a frame structure for the BS and RS1 for the 3 or
more-hop relay
BWA communication system according to the present invention.
.
[115] Referring to FIG. 13, the j th frame is divided into a DL subframe
1200 and a UL
subframe 1220. The DL subframe 1200 is the configuration of into first, second
and
third zones 1211, 1213 and 1215, and the UL subframe 1220 is the configuration
of
into first, second and third zones 1221, 1223 and 1225. A TTG is interposed
between
the DL subframe 1200 and the UL subframe 1220.
[116] A BS 1230 and RS1 1240 configure DL subframes to be sent to MSs
within their
coverage zones in the first zone 1211 of the DL subframe 1210. The DL
subframes
each sequentially include a preamble for synchronization, control information,
and DL
bursts. The preamble and the control information reside at fixed positions.
[117] In the second zone 1213, the BS 1230 configures a DL subframe to be
sent to RS1
1240. The DL subframe sequentially includes a synchronization channel for syn-
chronization of RS1 1240, control information, and downlink bursts.
[118] Thus, RS1 1240 receives the signal from the BS 1230 in the second
zone 1213.
[119] In the third zone 1215, the BS 1230 transitions to an idle mode or
configures a DL
subframe to be sent to MS1. The DL subframe includes downlink bursts only.
Also in
the third zone 1215, RS1 1240 configures a DL subframe to be sent to R52, i.e.
a
higher RS configures a DL subframe for a lower RS. The DL subframe includes a
preamble for synchronization of the lower RS, control information, and
downlink
bursts.
[120] In the UL subframe 1220, the BS 1230 and RS1 1240 receive control
information
(e.g. ranging signal) and uplink bursts from MSs within their coverage zones
in the
first zone 1221.
[121] RS1 1240 configures a UL subframe to be sent to the BS 1230 in the
second zone
1223. Thus the BS 1230 receives the signal from RS1 1240.
[122] In the third zone 1225, the BS 1230 is in the idle mode or receives a
signal from
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MS1. Also, RS1 1240 receives a signal from RS2. That is, the higher RS
receives a
signal from the lower RS in the third zone 1225.
[123] FIG. 14 illustrates a frame structure for RS2 and an MS in the 3 or
more-hop relay
BWA communication system according to an embodiment of the present invention.
[124] Referring to FIG. 14, the jth frame is divided into a DL subframe
1300 and a UL
subframe 1320. The DL subframe 1300 is divided into first, second and third
zones
1311, 1313, and 1315, and the UL subframe 1320 is divided into first, second
and third
zones 1321, 1323, and 1325. A TTG is interposed between the DL subframe 1300
and
the UL subframe 1320.
[125] R52 1350 configures DL subframes for M53 within its coverage zone in
the first
and second zones 1311 and 1313 of the DL subframe 1310. The DL subframe
created
in the first zone 1311 sequentially includes a preamble for synchronization of
M53,
control information, and downlink bursts. The DL subframe created in the
second zone
1313 includes only downlink bursts for M53.
[126] R52 1350 receives a signal from RS1 1340 in the third zone 1315.
[127] In the DL subframe 1310, the MSs receive DL subframes from nodes that
serve the
MSs.
[128] In the first and second zones 1321 and 1323 of the UL subframe 1320,
R52 1350
receives control information (e.g. ranging signal) and uplink bursts from M53.
[129] In the third zone 1325, R52 1350 configures a UL subframe for RS1
1340. The UL
subframe sequentially includes control information and uplink bursts.
[130] The MSs configure UL subframes to be sent to the nodes serving the
MSs in the
first zone 1321. The UL subframes each sequentially include control
information and
uplink bursts.
[131] The MSs configure UL subframes according to their serving nodes in
the second
zone 1323 and the third zone 1325. For example, MS1 communicating with the BS
1330 configures a UL subframe for the BS 1330 in the third zone 1325. M53 com-
municating with R52 1350 configures a UL subframe for R52 1350 in the second
zone
1323.
[132] If the BWA communication system is a 3 or more-hop system and thus
R52 1350 is
connected to a lower RS, R52 1350 communicates with the lower RS instead of
M53
in the second zones 1313 and 1323.
[133] In the above embodiment, a synchronization channel resides at the
start of each of
the first, second and third zones. It can be further contemplated as another
embodiment
that the synchronization channel is positioned at the end of each of the
second and
third zones.
[134] Now a description will be made of operations of a BS and an RS for
communicating
using the above-described frame structure in the BWA communication system.
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[135] FIG. 15 is a flowchart illustrating an operation of the BS in the
multi-hop relay
BWA communication system according to the present invention.
[136] Referring to FIG. 15, the BS allocates resources for the connection-
link subframe
701 and the relay-link subframe 703 that form a frame in step 1401. The
periods of the
connection-link subframe 701 and the relay-link subframe 703 are fixed or
changed
adaptively according to a service environment. If there is no RS within the
coverage
zone of the BS, the relay-link subframe 703 may not be used. In step 1403, the
BS
communicates with MSs in the connection-link subframe 701.
[137] The BS also communicates with RSs in the relay-link subframe 703 in
step 1405.
For example, on the downlink, the BS sends control information and traffic
bursts to
the MSs in the connection-link subframe 701 and then sends control information
and
traffic bursts to the RSs in the relay-link subframe 703.
[138] On the uplink, the BS receives initial ranging information and
traffic bursts from
the MSs in the connection-link subframe 701 and then receives initial ranging
in-
formation and traffic bursts from the RSs in the relay-link subframe 703. Then
the BS
ends the algorithm.
[139] FIG. 16 is a flowchart illustrating an operation of an RS in the
multi-hop relay
BWA communication system according to the present invention.
[140] Referring to FIG. 16, upon power-on, the RS monitors reception of a
preamble and
control information from the BS in step 1501. Upon receipt of a preamble and
control
information, the RS performs network entry using the preamble and the control
in-
formation in step 1503. In the same manner as an MS, the RS performs the
network
entry via a connection link rather than via a relay link. Then the RS
establishes a relay
link based on relay link information acquired from the initialization.
Alternatively, the
RS may perform the initialization via the relay link rather than via the
connection link.
[141] In steps 1505 and 1507, the RS supports a broadband service via the
relay link and
the connection link established according to the operational capability of the
BS and
the relay capability of the RS. For instance, the RS receives control
information and
traffic bursts for a relay service from the BS or a higher RS in the relay-
link subframe
703 and then sends the control information and the traffic bursts to an MS in
the
connection-link subframe 701 of the next frame. If a lower RS exists under the
RS, the
RS can send the control information and the traffic bursts to the lower RS in
the relay-
link subframe 703. The RS then ends the algorithm.
[142] While how the RS communicates with the BS has been described above,
the same
description holds true also for communications between the RS and its higher
RS.
[143] The BS is so configured as to have a connection-link transceiver for
communicating
with an MS and a relay-link transceiver for communicating with an RS. Yet, the
BS
can support the relay link and the connection link with use of a single
transceiver.
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[144] FIG. 17 is a block diagram of the BS in the multi-hop relay BWA
communication
system according to the present invention.
[145] Referring to FIG. 17, the BS includes a first transceiver 1601 for a
relay link, a
second transceiver 1603 for a connection link, a timing controller 1605, an RF
duplexer 1607, and an antenna 1609. The first transceiver 1601 and the second
transceiver 1603 have the same configuration and thus only the first
transceiver 1601
will be described.
[146] The first transceiver 1601 is comprised of a transmitter 1611, a
receiver 1621, and
an RF switch 1631. The transmitter 1611 has a frame generator 1613, a resource
mapper 1615, a modulator 1617, and a Digital-to-Analog Converter (DAC) 1619.
[147] The frame generator 1613 configures a relay-link subframe to deliver
control in-
formation and traffic bursts to an RS. A frame generator 1643 of the second
transceiver
1641 configures a connection-link subframe to deliver the control information
and
traffic bursts to an MS.
[148] The resource mapper 1615 maps the relay-link subframe received from
the frame
generator1613 to bursts of a link allocated to the relay-link subframe. The
modulator
1617 modulates the mapped subframe according to a predetermined Modulation and
Coding Scheme (MCS) level. The Digital-to-Analog Converter (DAC) 1619 converts
the digital signal to an analog signal, upconverts the analog signal to an RF
signal, and
provides the RF signal to the RF switch 1631. The receiver 1621 has an Analog-
to-
Digital Converter (ADC) 1623, a demodulator 1625, a resource demapper 1627,
and a
frame extractor 1629.
[149] The ADC 1623 downconverts RF signals received from RSs through the RF
switch
1631 in a relay-link subframe to baseband signals and converts the analog
baseband
signals to digital signals. The demodulator 1625 demodulates the digital
signals
according to a predetermined MCS level. The resource demapper 1627 extract
actual
subframes from the bursts of links received from the demodulator 1625. The
frame
extractor 1629 extracts a subframe for the receiver 1621 among the subframes
received
from the resource demapper 1627. For example, the frame extractor 1629
extracts
relay-link subframes from UL subframes received from the RSs. A frame
extractor
1659 of the second transceiver 1641 extracts relay-link subframes from UL
subframes
received from the MSs.
[150] The RF switch 1631 switches one of the transmitter 1611 and the
receiver 1621 to
an RF duplexer 1607 under the control of a timing controller 1605.
[151] The timing controller 1605 controls a transmission and reception
timing for a relay
link service period or a connection link service period.
[152] The RF duplexer 1607 sends an RF signal received through the antenna
1609 to the
transceiver 1601 or 1603 depending on a relay link service period or a
connection link
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service period.
[153] While the invention has been shown and described with reference to
certain
preferred embodiments thereof, it will be understood by those skilled in the
art that
various changes in form and details may be made therein.
[154]
