U.S. patent application number 13/617629 was filed with the patent office on 2013-03-21 for frequency division duplexing and half duplex frequency division duplexing in multihop relay networks.
The applicant listed for this patent is Israfil Bahceci, Nimal Senerath, Wen Tong, Derek Yu, Hang Zhang, Peiying Zhu. Invention is credited to Israfil Bahceci, Nimal Senerath, Wen Tong, Derek Yu, Hang Zhang, Peiying Zhu.
Application Number | 20130070662 13/617629 |
Document ID | / |
Family ID | 44341597 |
Filed Date | 2013-03-21 |
United States Patent
Application |
20130070662 |
Kind Code |
A1 |
Bahceci; Israfil ; et
al. |
March 21, 2013 |
Frequency Division Duplexing and Half Duplex Frequency Division
Duplexing in Multihop Relay Networks
Abstract
In methods of operating a relay station in a multi-hop wireless
relay network, the relay station in communication with a
superordinate station and a subordinate station, a downlink
transmission to/from the superordinate station is
transmitted/received at a first frequency. An uplink transmission
to/from the subordinate station is transmitted/received at a second
frequency. Communications between the relay station and the
superordinate station may be scheduled using frames, each frame
including a downlink portion at the first frequency, and an uplink
portion at the second frequency. The downlink portion includes
first and second downlink subframes for communication between the
superordinate station and first and second pluralities of stations,
respectively. The uplink portion includes first and second uplink
subframes for communication between the superordinate station and
the first and second pluralities of stations, respectively. The
downlink transmission occurs in the first downlink subframe, and
the uplink transmission occurs in the first uplink subframe.
Inventors: |
Bahceci; Israfil; (Nepean,
CA) ; Senerath; Nimal; (Nepean, CA) ; Zhang;
Hang; (Nepean, CA) ; Zhu; Peiying; (Kanata,
CA) ; Yu; Derek; (Kanata, CA) ; Tong; Wen;
(Ottawa, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bahceci; Israfil
Senerath; Nimal
Zhang; Hang
Zhu; Peiying
Yu; Derek
Tong; Wen |
Nepean
Nepean
Nepean
Kanata
Kanata
Ottawa |
|
CA
CA
CA
CA
CA
CA |
|
|
Family ID: |
44341597 |
Appl. No.: |
13/617629 |
Filed: |
September 14, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12875516 |
Sep 3, 2010 |
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13617629 |
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12806204 |
Sep 3, 2009 |
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12875516 |
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Current U.S.
Class: |
370/315 |
Current CPC
Class: |
H04J 3/08 20130101 |
Class at
Publication: |
370/315 |
International
Class: |
H04W 72/04 20090101
H04W072/04; H04B 7/14 20060101 H04B007/14 |
Claims
1. A method of operating a relay station in a multihop wireless
relay network, said relay station in communication with a
superordinate station and a subordinate station, said method
comprising: receiving a downlink transmission from said
superordinate station at a first carrier frequency; receiving an
uplink transmission from said subordinate station at a second
carrier frequency; transmitting a downlink transmission to said
subordinate station said first carrier frequency; and transmitting
an uplink transmission to said superordinate station at said second
carrier frequency.
2. The method of claim 1, wherein said communication between said
relay station and said superordinate station is scheduled using
frames, each said frame comprising: a downlink portion at said
first carrier frequency, said downlink portion comprising a first
downlink subframe for communication between said superordinate
station and a first plurality of stations, and a second downlink
subframe for communication between said superordinate station and a
second plurality of stations; and an uplink portion at said second
carrier frequency, said uplink portion comprising a first uplink
subframe for communication between said superordinate station and
said first plurality of stations, and a second uplink subframe for
communication between said superordinate station and said second
plurality of stations; wherein said first downlink subframe
corresponds with a first time interval, said first uplink subframe
corresponds with a second time interval, and said first time it and
said second time interval do not overlap; and wherein said relay
station is one of said first plurality of stations, whereby said
receiving said downlink transmission occurs in said first downlink
subframe, and said transmitting said uplink transmission occurs in
said first uplink subframe.
3. The method of claim 2, wherein: said first downlink subframe is
divided into a downlink access zone and a downlink transparent
zone, and said first uplink subframe is divided into an uplink
access zone and an uplink relay zone; and wherein said receiving
said downlink transmission occurs in said downlink access zone, and
said transmitting said uplink transmission occurs in said uplink
relay zone.
4. The method of claim 2, wherein said second uplink subframe
corresponds with said first time interval, and said second downlink
subframe corresponds with said second time interval.
5. The method of claim 2, wherein said downlink portion comprises a
third downlink subframe for communication between said
superordinate station and a third plurality of stations, and said
uplink portion comprises a third uplink subframe for communication
between said superordinate station and said third plurality of
stations.
6. The method of claim 5, wherein: said second uplink subframe
corresponds with said first time interval; said second downlink
subframe and said third uplink subframe correspond with a third
time interval; and said third downlink subframe corresponds with
said second time interval.
7. The method of claim 6, wherein: said first plurality of stations
are in idle state during said third time interval, said second
plurality of stations are in idle state during said second time
interval, and said third plurality of stations are in idle state
during said first time interval; and for each said frame, said
first time interval occurs before said third time interval, and
said third time interval occurs before said second time interval,
whereby respective receive-to-transmit transition gaps for said
first and third plurality of stations are absorbed by said
respective idle states.
8. The method of claim 5, wherein: said second downlink subframe
corresponds with said second time interval; said second uplink
subframe and said third downlink subframe correspond with a third
time interval; and said third uplink subframe corresponds with said
first time interval.
9. The method of claim 8, wherein; said first plurality of stations
are in idle state during said third time interval, said second
plurality of stations are in idle state during said third time
interval, and said third plurality of stations are in idle state
during said second time interval; and for each said frame, said
first time interval occurs before said second time interval, and
said second time interval occurs before said third time interval,
whereby respective transmit-to-receive transition gaps for said
first and third plurality of stations are absorbed by said
respective idle states.
10. A multihop relay system comprising: a relay station in
communication with a superordinate station and a subordinate
station, said relay station comprising: receive circuitry for
receiving a downlink transmission from said superordinate station
at a first carrier frequency, and for receiving an uplink
transmission from said subordinate station at a second carrier
frequency; and transmit circuitry for transmitting a downlink
transmission to said subordinate station at said first carrier
frequency, and for transmitting an uplink transmission to said
superordinate station at said second carrier frequency.
11. The system of claim 10, wherein said communication between said
relay station and said superordinate station is scheduled using
frames, each said frame comprising: a downlink portion at said
first carrier frequency, said downlink portion comprising a first
downlink subframe for communication between said superordinate
station and a first plurality of stations, and a second downlink
subframe for communication between said superordinate station and a
second plurality of stations; and an uplink portion at said second
carrier frequency, said uplink portion comprising a first uplink
subframe for communication between said superordinate station and
said first plurality of stations, and a second uplink subframe for
communication between said superordinate station and said second
plurality of stations; wherein said first downlink subframe
corresponds with a first time interval, said first uplink subframe
corresponds with a second time interval, and said first time
interval and said second time interval do not overlap; and wherein
said relay station is one of said first plurality of stations,
whereby said receiving said downlink transmission occurs in said
first downlink subframe, and said transmitting said uplink
transmission occurs in said first uplink subframe.
12. The system of claim 11, wherein: said first downlink subframe
is divided into a downlink access zone and a downlink transparent
zone, and said first uplink subframe is divided into an uplink
access zone and an uplink relay zone; and wherein said receiving
said downlink transmission occurs in said downlink access zone, and
said transmitting said uplink transmission occurs in said uplink
relay zone.
13. The system of claim 11, wherein said second uplink subframe
corresponds with said first time interval, and said second downlink
subframe corresponds with said second time interval.
14. The system of claim 11, wherein said downlink portion comprises
a third downlink subframe for communication between said
superordinate station and a third plurality of stations, and said
uplink portion comprises a third uplink subframe for communication
between said superordinate station and said third plurality of
stations.
15. The system of claim 14, wherein: said second uplink subframe
corresponds with said first time interval; said second downlink
subframe and said third uplink subframe correspond with a third
time interval; and said third downlink subframe corresponds with
said second time interval.
16. The system of claim 15, wherein: said first plurality of
stations are in idle state during said third time interval, said
second plurality of stations are in idle state during said second
time interval, and said third plurality of stations, are in idle
state during said first time interval; and for each said frame,
said first time interval occurs before said third time interval,
and said third time interval occurs before said second time
interval, whereby respective receive-to-transmit transition gaps
for said first and third plurality of stations are absorbed by said
respective idle states.
17. The system of claim 14, wherein: said second downlink subframe
corresponds with said second time interval; said second unlink
subframe and said third downlink subframe correspond with a third
time interval; and said third uplink subframe corresponds with said
first time interval.
18. The system of claim 17, wherein: said first plurality of
stations are in idle state during said third time interval, said
second plurality of stations are in idle state during said third
time interval, and said third plurality of stations are in idle
state during said second time interval; and for each said frame,
said first time interval occurs before said second time interval,
and said second time interval occurs before said third time
interval, whereby respective transmit-to-receive transition gaps
for said first and third plurality of stations are absorbed by said
respective idle states.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 61/239,514, filed in the United States
Patent Office on Sep. 3, 2009, the contents of which are
incorporated by reference herein.
[0002] This application is a continuation-in-part of the
non-provisional application (serial number TBD) resulting from
conversion under 37 C.F.R. .sctn.1.53(c)(3) of U.S. Provisional
Patent Application No. 61/239,514, filed on Sep. 3, 2009, which
claims the benefit of U.S. Provisional Patent Application No.
61/096,495, flied on Sep. 12, 2008.
FIELD OF THE INVENTION
[0003] The present invention relates to wireless communications and
more particularly to a method and system for providing frequency
division duplexing ("FDD") and half-duplex frequency division
duplexing ("H-FDD") support in multihop relay networks.
BACKGROUND
[0004] Wireless communication networks, such as cellular networks,
operate by sharing resources among mobile terminals operating in
the communication network. As part of the sharing process,
resources are allocated by one or more controlling devices within
the system. Certain types of wireless communication networks are
used to support cell-based high speed services such as those under
the family of IEEE 802.16 standards. The IEEE 802.18 standards are
often referred to as WiMAX or less commonly as WirelessMAN or the
Air Interface Standard. Another emerging standard that has not yet
been ratified is referred to as Long Term Evolution (LTE). Other
wireless networking technologies include Third Generation (3G),
Third Generation Partnership Project (3GPP), and 802.11, popularly
known as WiFi.
[0005] More specifically, IEEE 802.16e extends the 2004 version of
IEEE 802.16 for fixed Broadband Wireless Access so as to support
the mobility of users and provide Quality of Service (QoS)
guarantees to enable multimedia services. From a system-level
perspective, an IEEE 802.16e cell includes a number of Mobile
Stations (MSs) served by a Base Station (BS), which controls the
access to the wireless medium in a centralized manner. Before
transmitting to (or receiving from) the BS, a MS must request the
admission of a new connection. If accepted, the BS is then
responsible for meeting the requested QoS guarantees.
[0006] The shared wireless medium demands co-ordinated transmission
of multiple traffic flows over it. Duplexing refers to the way
two-way communication is carried on the transmission medium. There
are two commonly used duplexing techniques: Time Division Duplex
(TDD), and Frequency Division Duplex (FDD). In TDD, the DL and UL
traffic is typically transmitted on the same carrier frequency at
different times. The time allocations for the DL and UL portions
can be adaptive, which makes it suitable for asymmetric
connections. In FDD, the UL and DL traffic is transmitted on
different carrier frequencies, and may thus be transmitted/received
simultaneously. An FDD hybrid known as Half-duplex Frequency
Division Duplex (H-FDD), adds the restriction that a terminal
cannot transmit and receive at the same time. H-FDD is cheaper to
implement and less complex than full-duplex FDD, though the system
throughout is lower.
[0007] Access to the shared wireless medium is scheduled using
Orthogonal Frequency-Division Multiple Access (OFDMA) frames that
extend over two dimensions; time, in units of OFDMA symbols, and
frequency, in units of logical sub-channels. Data bursts are
conveyed into two-dimensional (i.e. time and frequency) data
regions, which identify regions within the frame and are advertised
by the BS via specific control messages. Each frame is divided into
downlink (DL) and uplink (UL) subframes. The former is used, by the
BS to transmit data to the MSs, whereas the MSs transmit to the BS
in the latter.
[0008] FIG. 12 shows an example TDD frame structure. As shown, a DL
subframe starts with a preamble followed by a Frame Control Header
(FCH), a downlink MAP (DL-MAP), and an uplink MAP (UL-MAP). The
preamble helps MSs perform synchronization and channel estimation.
The FCH specifies a burst profile and the length of one or more
downlink bursts that immediately follow the FCH in the current
frame. The DL-MAP and UL-MAP notify MSs of the corresponding
resources allocated to them in the downlink and uplink direction,
respectively, within the current frame. In general, the BS is free
to define the shape and position of any data region. Based upon the
schedule received from the BS, each MS can determine when (i.e.,
OFDMA symbols) and where (i.e., subchannels) it should receive from
and transmit to the BS. Proper time gaps, namely
receive-to-transmit trans ti gap (RTG) and transmit-to-receive
transition gap (TTG, also referred to herein as TRG), have to be
inserted between consecutive subframes in order to give wireless
devices sufficient time to switch from transmission mode to
reception mode, or vice versa.
[0009] FIG. 13 shows an example FDD frame structure. IEEE 802.16
specifics that BSs of FDD systems shall operate in full-duplex
mode, while MSs shall be either full-duplex (FDD) or half-duplex
(H-FDD). The FDD frame structure shown in FIG. 13 supports the
concurrent operation of H-FDD and FDD MSs. The frame structure
supports a coordinated transmission arrangement of two groups of
H-FDD MSs (Group-1 and Group-2) that share the frame at distinct
partitions of the frame. As shown, the DL frame contains two
subframes. DL Subframe 1 comprises a preamble region, a MAP region
(MAP1) and a data regio (DL1). DL Subframe 2 comprises a MAP region
(MAP2) and a data region (DL2). Similarly, the UL frame contains
two subframes, UL2 and UL1. FIG. 13 shows the timing relationship
of the UL subframes relative to the DL subframes. The four
parameters TTG1, TTG2, RTG1 and RTG2 are sufficiently large to
accommodate the H-FDD MSs transmit receive switching time plus the
round trip propagation delay. Group-1 H-FDD MSs listen to DL
Subframe 1 and transmit in uplink subframe UL1. Group-2 H-FDD MSs
listen to DL Subframe 2 and transmit in uplink subframe UL2. The
MAP regions--MAP1 and MAP2--are independent and include FCH, DL-MAP
and UL-MAP.
[0010] IEEE 802.16j adds multihop relay capabilities to IEEE 802.16
systems. Relay-based systems typically comprise low-cost relays,
which are associated with specific base stations (BSs). The relays
can be used to extend the coverage area of a BS and/or increase the
capacity of a wireless access system. The relays can repeat
transmissions to/from the BS so that MSs within communication range
of a relay can communicate with the BS through the relay. The
relays do not need a backhaul link because they communicate
wirelessly with both BSs and MSs. This type of network may be
referred to, as a multihop network because there may be more than
one wireless connection between the MS and a hardwired connection.
Depending upon the particular network configuration, particular MS
may gain network access via one or more neighbour relays and/or one
or more neighbour BSs. In addition, relays themselves might have
one or more available path options to connect to a particular BS.
IEEE 802.16j requires that from the perspective of the MS any
communications with a Multihop Relay Base Station (MR-BS) which are
relayed through a Relay Station (RS) appear to be the same as if
they had come directly from the BS. The radio link between a MR-BS
or RS and en MS is called an access link, while the link between a
MR-BS and an RS or between a pair of RSs is called a relay
link.
[0011] IEEE 602.16j defines two different RS modes of operation
transparent and non-transparent. A Transparent RS (T-RS) does not
transmit control information such as preamble, FCH, and MAP. An MS
connected to a T-RS receives control information directly from the
MR-BS, and the T-RS relays only data traffic. A Non-Transparent RS
(NT-RS) transmits a preamble and other broadcast messages and
relays data traffic as well.
[0012] IEEE 802.16j specifies a TDD frame that is divided into DL
and UL subframes, much like the IEEE 602.16 TDD frame structure
shown in FIG. 12. However, IEEE 802.16j subframes are further
divided into zones to support BS-RS communications and RS-MS
communications in addition to BS-MS communications. In both
transparent and non-transparent modes, so-called "access zones" are
defined that support BS/NT-RS communications with the MS/T-RS, in
the transparent mode a so-called "transparent zone" is defined for
T-RS communications with the MS. In non-transparent mode "relay
zones" are defined for BS/NT-RS communications with NT-RS. FIG. 14
shows an example configuration for a T-RS frame structure. FIG. 15
shows an example configuration for a T-RS frame structure in which
MR-BS and RS have partitioned the UI subframe in the frequency
domain. FIG. 16 shows an example of a minimum configuration for a
NT-RS frame structure. FIG. 17 shows an example of configuration
for NT-RS frame structure where MR-BS and RS have partitioned the
UL subframe in the frequency domain.
[0013] Presently, the available standards for relay operation such
as the IEEE 802.16j standard support only a TDD frame structure,
and therefore, only the TDD mode of operation. However, systems
such as WiMax, IEEE 802.16e and LTE support FDD, H-FDD and TDD
capable mobile terminals.
[0014] A need exists for FDD and H-FDD support in multihop relay
networks such that the coverage and other performance enhancements
of relay systems can be extended to the FDD-based systems.
SUMMARY OF THE INVENTION
[0015] In accordance with an aspect of the present invention, there
is provided a method of operating a relay station in a multihop
wireless relay network, where the relay station is in communication
with a superordinate station and a subordinate station. The method
comprises: receiving a downlink transmission from the superordinate
station at a first carnet frequency; receiving an uplink
transmission from the subordinate station at a second carrier
frequency; transmitting a downlink transmission to the subordinate
station at the first carrier frequency; and transmitting an uplink
transmission to the superordinate station at the second carrier
frequency. The communication between the relay station and the
superordinate station may be scheduled using frames, where each
frame comprises: a downlink portion at the first carrier frequency,
the downlink portion comprising a first downlink subframe for
communication between the superordinate station and a first
plurality of stations, and a second downlink subframe for
communication between the superordinate station and a second
plurality of stations; and an uplink portion at the second carrier
frequency, the uplink portion comprising a first uplink subframe
for communication between the superordinate station and the first
plurality of stations, and a second uplink subframe for
communication between the superordinate station and the second
plurality of stations. The first downlink subframe may correspond
with a first time interval, and the first uplink subframe may
correspond with a second time interval, where the first time
interval and the second time interval do not overlap. The relay
station may be one of the first plurality of stations, whereby the
receiving the downlink transmission occurs in the first downlink
subframe, and the transmitting the uplink transmission occurs in
the first uplink subframe.
[0016] In accordance with a further aspect of the present
invention, there is provided a multihop relay system comprising a
relay station in communication with a superordinate station and a
subordinate station. The relay station comprises: receive circuitry
for receiving a downlink transmission from said superordinate
station at a first carrier frequency, and for receiving an uplink
transmission from said subordinate station at a second carrier
frequency; and transmit circuitry for transmitting a downlink
transmission to said subordinate station at said first carrier
frequency, and for transmitting an uplink transmission to said
superordinate station at said second carrier frequency. The
communication between the relay station and the superordinate
station may be scheduled using frames, where each frame comprises:
a downlink portion at the first carrier frequency, the downlink
portion comprising a first downlink subframe for communication
between the superordinate station and a first plurality of
stations, and a second downlink subframe for communication between
the superordinate station and a second plurality of stations; and
an uplink portion at the second carrier frequency, the uplink
portion comprising a first uplink subframe for communication
between the superordinate station and the first plurality of
stations, and a second uplink subframe for communication between
the superordinate station and the second plurality of stations. The
first downlink subframe may correspond with a first time interval,
and the first uplink subframe may correspond with a second time
interval, where the first time interval and the second time
interval do not overlap. The relay station may be one of the first
plurality of stations, whereby the receiving the downlink
transmission occurs in the first downlink subframe, and the
transmitting the uplink transmission occurs in the first uplink
subframe.
[0017] Other aspects and features of the present invention will
become apparent to those ordinarily skilled in the art upon review
of the following description of specific embodiments of the
invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] In the figures which illustrate embodiments of the invention
by example only,
[0019] FIG. 1 is a block diagram of a cellular communication
system;
[0020] FIG. 2 is block diagram an example base station that might
be used to implement some embodiments of the present
application;
[0021] FIG. 3 is a block diagram of an example mobile terminal that
might be used to implement some embodiments of the present
application;
[0022] FIG. 4 is a block diagram of an example relay station that
might be used to implement some embodiments of the present
application;
[0023] FIG. 5 is a block diagram of a logical breakdown of an
example OFDM transmitter architecture that might be used to
implement some embodiments of the present application;
[0024] FIG. 6 is a block diagram of a logical breakdown of an
example OFDM receiver architecture that might be used to implement
some embodiments of the present application;
[0025] FIG. 7 is a block diagram of an example overall network
architecture that might be used to implement some embodiments of
the present application;
[0026] FIG. 8 is a block diagram of a portion of the overall
network architecture of FIG. 7;
[0027] FIG. 9 is a block diagram illustrating the operation of a
relay station using two carrier frequencies at half-duplex;
[0028] FIG. 10 is a block diagram illustrating the operation of a
relay station using two carrier frequencies at full-duplex;
[0029] FIG. 11 is a block diagram illustrating the operation of a
relay station using four carrier frequencies;
[0030] FIG. 12 is a block diagram of an example TDD frame
structure;
[0031] FIG. 13 is a block diagram of an example FDD frame
structure;
[0032] FIG. 14 is a block diagram of an example configuration for a
T-RS frame structure;
[0033] FIG. 15 is block diagram of an example configuration for a
T-RS frame structure in which MR-BS and RS have partitioned the UL
subframe in the frequency domain;
[0034] FIG. 16 is a block diagram of an example minimum
configuration for a NT-RS frame structure;
[0035] FIG. 17 is a block diagram of an example configuration for
NT-RS frame structure where MR-BS and RS have partitioned the UL
subframe in the frequency domain;
[0036] FIG. 18a, 18b and 18c are block diagrams of example H-FDD
frame structures adapted to support multihop relaying;
[0037] FIGS. 19a and 19b are block diagrams of additional example
H-FDD frame structures adapted to support multihop relaying;
[0038] FIG. 20 is a block diagram of an example H-FDD frame
structure defining three groups of users with three different
regions;
[0039] FIG. 21 is a block diagram of are example H-FDD frame
configuration for a three-hop case.
DETAILED DESCRIPTION
[0040] Referring now to the drawing figures in which like reference
designators refer to like elements. FIG. 1 shows a base station
controller (BSC) 10 which controls wireless communications within
multiple cells 12, which cells are served by corresponding base
stations (BS) 14. In some configurations, each cell is further
divided into multi pie sectors 13 (not shown). In general, each
base station 14 facilitates communications using OFDM with mobile
terminals 16, which are within the cell 12 associated with the
corresponding base station 14. The movement of the mobile terminals
16 in relation to the base stations 14 results in significant
fluctuation in channel conditions. As illustrated, the base
stations 14 and mobile terminals 16 may include multiple antennas
to provide spatial diversity for communications. As described in
more detail below, relay stations 15 may assist in communications
between base stations 14 and mobile terminals 16. Mobile terminals
16 can be handed off 18 from any cell 12, sector 13 (not shown),
base station 14 or relay 15 to an other cell 12, sector 13 (not
shown), base station 14 or relay 15, in some configurations, base
stations 14 communicate with each and with another network (such as
a core network or the internet, both not shown) over a backhaul
network 11, in some configurations, a base station controller 10 is
not needed.
[0041] FIG. 2 depicts an example of a base station 14. Base station
14 generally includes a control system 20, a baseband processor 22,
transmit circuitry 24, receive circuitry 26, antennas 28, and a
network interface 30. The receive circuitry 26 receives radio
frequency signals bearing information from one or more remote,
transmitters provided by mobile terminals 16 (illustrated in FIG.
3) and relay stations 15 (illustrated in FIG. 4). A low noise
amplifier and a filter (not shown) may cooperate to amplify and
remove broadband interference from the signal for processing.
Downconversion and digitization circuitry (not shown) will then
downconvert the filtered, received signal to an intermediate or
baseband frequency signal, which is then digitized into one or more
digital streams.
[0042] The baseband processor 2 processes the digitized received
signet to extract the information or data bits conveyed in the
received signal. This processing typically comprises demodulation,
decoding, and error correction operations. As such, the baseband
processor 22 is generally implemented in one or more digital signal
processors (DSPs) or application-specific integrated circuits
(ASICs). The received information is then sent across a wireless
network via the network interface 30 or transmitted to another
mobile terminal 16 serviced by the base station 14, either directly
or with the assistance of a relay 15.
[0043] On the transmit side, baseband processor 22 receives
digitized data, which may represent voice, data, or control
information, from the network interface 30 under the control of
control systems 20, and encodes the data for transmission. The
encoded data is output to the transmit circuitry 24, where it is
modulated by one or more carrier signals having a desired transmit
frequency or frequencies. A power amplifier (not shown) will
amplify the modulated carrier signals to a level appropriate for
transmission, and deliver the modulated carrier signals to the
antennas 28 through a matching network (not shown). Modulation and
processing details are described in greater detail below.
[0044] FIG. 3 illustrates an example of a mobile terminal 16.
Similarly to the base station 14, the mobile terminal 16 will
include a control system 32, a baseband processor 34, transmit
circuitry 38, receive circuitry 38, antennas 40, and user interface
circuitry 42. The receive circuitry 38 receives radio frequency
signals bearing information from one or more base stations 14 and
relays 18. A low noise amplifier and a filter (not shown) may
cooperate to amplify and remove broadband interference from the
signal for processing. Dow conversion and digitization circuitry
(not shown) will then downconvert the filtered, received signal to
an intermediate or baseband frequency signal, which is then
digitized into one or more digital streams.
[0045] Baseband processor 34 processes the digitized received
signal to extract the information or data bits conveyed in the
received signal. This processing typically comprises demodulation,
decoding, and error correction operations. The baseband processor
34 is generally implemented in one or more digital signal
processors (DSPs) and application specific integrated circuits
(ASICS).
[0046] For transmission, baseband processor 34 receives digitized
data, which may represent voice, video, data, or control
information, from the control system 3 which it encodes for
transmission. The encoded data is output to the transmit circuitry
36, where it is used by a modulator to modulate one or more carrier
signals that is at a desired transmit frequency or frequencies. A
power amplifier (not shown) will amplify the modulated carrier
signals to a level appropriate for transmission, and deliver the
modulated carrier signal to the antennas 40 through a matching
network (not shown). Various modulation and processing techniques
available to those skilled in the art are used for signal
transmission between the mobile terminal and the base station,
either directly or via the relay station.
[0047] In OFDM modulation, the transmission band is divided into
multiple, orthogonal carrier waves. Each carrier wave is modulated
according to the digital data to be transmitted. Because OFDM
divides the transmission band into multiple carriers, the bandwidth
per carrier decreases and the modulation time per carrier
increases. Since the multiple carriers are transmitted in parallel,
the transmission rate for the digital data, or symbols, on any
given carrier is lower than when a single carrier is used.
[0048] OFDM modulation utilizes the performance of an Inverse Fast
Fourier Transform (IFFT) on the information to be transmitted. For
demodulation, the performance of a Fast Fourier Transform (FFT) on
the received signal recovers the transmitted information. In
practice, the IFFT and FFT are provided by digital signal
processing carrying out an Inverse Discrete Fourier Transform
(IDFT) and Discrete Fourier Transform (DFT), respectively.
Accordingly, the characterizing feature of OFDM modulation is that
orthogonal carrier waves are generated for multiple bands within a
transmission channel. The modulated signals are digital signals
having a relatively low transmission rate and capable of staying
within their respective bands. The individual carrier waves are not
modulated directly by the digital signals. Instead, all carrier
waves are modulated at once by IFFT processing.
[0049] In one embodiment, OFDM is preferably used for at least
downlink transmission from the base stations 14 to the mobile
terminals 16. Each base station 14 is equipped with "n" transmit
antennas 28 (n>=1), and each mobile terminal 16 is equipped with
"m" receive antennas 40 (m>=1). Notably, the respective antennas
can be used for reception and transmission using appropriate
duplexers or switches and are so labelled only for clarity.
[0050] When relay stations 15 are used, OFDM is preferably used for
downlink transmission from the base stations 14 to the relays 15
and from relay stations 15 to the mobile terminals 16.
[0051] FIG. 4 illustrates en example relay station 15. Similarly to
the base station 14, and the mobile terminal 16, the relay station
15 includes a control system 132, a baseband processor 134,
transmit circuitry 136, receive circuitry 138, antennas 130, and
relay circuitry 142. The relay circuitry 142 enables the relay 14
to assist in communications between a base station 16 and mobile
terminals 16. The receive circuitry 138 receives radio frequency
signals bearing information from one or more base stations 14 and a
mobile terminals 16. A low noise amplifier and a filter (not shown)
may cooperate to amplify and remove broadband interference from the
signal for processing. Downconversion and digitization circuitry
(not shown) will then downconvert the filtered, received signal to
an intermediate or baseband frequency signal, which is then
digitized into one or more digital streams.
[0052] Baseband processor 134 processes the digitized received
signal to extract the information or data bits conveyed in the
received signal. This processing typically comprises demodulation,
decoding, and error correction operations. Baseband processor 134
is generally implemented in one or more digital signal processors
(DSPs) and application specific integrated circuits (ASICs).
[0053] For transmission, baseband processor 134 receives digitized
data, which may represent voice, video, data, or control
information, from control system 132, which it encodes for
transmission. The encoded data is output to the transmit circuitry
136, where it is used by a modulator to modulate one or more
carrier signals that is at a desired transmit frequency or
frequencies. A power amplifier (not shown) will amplify the
modulated carrier signals to a level appropriate for transmission,
and deliver the modulated carrier signal to the antennas 130
through a matching network (not shown). Various modulation and
processing techniques available to those skilled in the art are
used for signal transmission between the mobile terminal and the
base station, either directly or indirectly via a relay station, as
described above.
[0054] With reference to FIG. 5, a logical OFDM transmission
architecture will be described. Initially, base station controller
10 will send data to be transmitted to various mobile terminals 16
to base station 14, either directly or with the assistance of a
relay station 15. Base station 14 may use the channel quality
indicators (CQIs) associated with the mobile terminals to schedule
the data for transmission as well as select appropriate coding and
modulation for transmitting the scheduled data. The CQIs may be
directly from the mobile terminals 16 or determined at the base
station 14 based on information provided by the mobile terminals
16. In either case, the CQI for each mobile terminal 16 is a
function of the degree to which the channel amplitude (or response)
varies across the OFDM frequency band.
[0055] Scheduled data 44, which is a stream of bits, is scrambled
in a manner reducing the peak-to-average power ratio associated
with the data using data scrambling logic 46. A cyclic redundancy
check (CRC) for the scrambled data is determined and appended to
the scrambled data using CRC adding logic 48. Next, channel coding
is performed using channel encoder logic 50 to effectively add
redundancy to the data to facilitate recovery and error correction
at the mobile terminal 16. Again, the channel coding for a
particular mobile terminal 18 is based on the CQI. In some
implementations, the channel encoder logic 50 uses known Turbo
encoding techniques. The encoded data is then processed by rate
matching logic 52 to compensate for the data expansion associated
with encoding.
[0056] Bit interleaver logic 54 systematically reorders the bits in
the encoded data to minimize the loss of consecutive data bits. The
resultant data bits are systematically mapped into corresponding
symbols depending on the chosen baseband modulation by mapping
logic 56. Preferably, Quadrature Amplitude Modulation (QAM) or
Quadrature Phase Shift Key (QPSK) modulation is used. The degree of
modulation is preferably chosen based on the CQI for the particular
mobile terminal. The symbols may be systematically reordered to
further bolster the immunity of the transmitted signal to periodic
data loss caused by frequency selective fading using symbol
interleaver logic 58.
[0057] At this point, groups of bits have been mapped into symbols
representing locations in an amplitude and phase constellation.
When spatial diversity is desired, blocks of symbols are then
processed by space-time block code (STC) encoder logic 60, which
modifies the symbols in a fashion making the transmitted signals
more resistant to interference and more readily decoded at a mobile
terminal 16. The STC encoder logic 60 will process the incoming
symbols and provide "n" outputs corresponding to the number of
transmit antennas 28 for the base station 14. The control system 20
and/or baseband processor 22 as described above with reference to
FIG. 5 will provide a mapping control signal to control STC
encoding. At this point, assume the symbols for the "n" outputs are
representative of the data to be transmitted and capable of being
recovered by the mobile terminal 16.
[0058] For the present example, assume the base station 14 has two
antennas 28 (n=2) and the STC encoder logic 60 provides two output
streams of symbols. Accordingly, each of the symbol streams output
by the SIC encoder logic 60 is sent to a corresponding IFFT
processor 62, illustrated separately ease of understanding. Those
skilled in the art will recognize that one or more processors may
be used to provide such digital signal processing, alone or in
combination with other processing described herein. The IFFT
processors 62 will preferably operate on the respective symbols to
provide an inverse Fourier Transform. The output of the TUFT
processors 62 provides symbols in the time domain. The time domain
symbols are grouped into frames, which are associated with a prefix
by prefix insertion logic 64. Each of the resultant signals is
up-convened in the digital domain to an intermediate frequency and
converted to an analog signal via the corresponding digital
up-conversion (DUG) and digital-to-analog (DIA) conversion
circuitry 66. The resultant (analog) signals are then
simultaneously modulated at the desired RF frequency, amplified,
and transmitted via the RE circuitry 68 and antennas 28. Notably,
pilot signals known by the intended mobile terminal 16 are
scattered among the sub-carriers. The mobile terminal 16, which is
discussed in detail below, will use the pilot signals for channel
estimation.
[0059] Reference is now made to FIG. 6 to illustrate reception of
the transmitted signals by a mobile terminal 16, either directly
from base station 14 or with the assistance of relay 16. Upon
arrival of the transmitted signals at each of the antennas 40 of
the mobile terminal 16, the respective signals are demodulated and
amplified by corresponding RF circuitry 70. For the sake of
conciseness and clarity, only one of the two receive paths is
described and illustrated in detail. Analog-to-digital (AID)
converter and down-conversion circuitry 72 digitizes and
downconverts the analog signal for digital processing. The
resultant digitized signal may be used by automatic gain control
circuitry (AGC) 74 to control the gain of the amplifiers in the RE
circuitry 10 based on the received signal level.
[0060] Initially, the digitized signal is provided to
synchronization logic 76, which includes coarse synchronization
logic 78, which buffers several OFDM symbols and calculates an
auto-correlation between the two successive OFDM symbols. A
resultant time index corresponding to the maximum of the
correlation result determines a fine synchronization search window,
which is used by fine synchronization logic 80 to determine a
precise framing starting position based on the headers. The output
of the fine synchronization logic 80 facilitates frame acquisition
by frame alignment logic 84. Proper framing alignment is important
so that subsequent PET processing provides an accurate conversion
from the time domain to the frequency domain. The fine
synchronization algorithm is based on the correlation between the
received pilot signals carried by the headers and a local copy of
the known pilot data. Once frame alignment acquisition occurs, the
prefix of the OFDM symbol is removed with prefix removal logic 86
and resultant samples are sent to frequency offset correction logic
88, which compensates for the system frequency offset caused by the
unmatched local oscillators in the transmitter and the receiver.
Preferably, the synchronization logic 76 includes frequency offset
and clock estimation logic 82, which is based on the headers to
help estimate such effects on the transmitted signal and provide
those estimations to the correction logic 88 to properly process
OFDM symbols.
[0061] At this point, the OFDM symbols in the time domain are ready
for conversion to the frequency domain using EFT processing logic
90. The results are frequency domain symbols, which are sent to
processing logic 92. The processing logic 92 extracts the scattered
pilot signal using scattered pilot extraction logic 94, determines
a channel estimate based on the extracted pilot signal using
channel estimation logic 98, and provides channel responses for all
sub-carriers using channel reconstruction logic 98. In order to
determine a channel response for each of the sub-carriers, the
pilot signal is essentially multiple pilot symbols that are
scattered among the data symbols throughout the OFDM sub-carriers
in a known pattern in both time and frequency. Continuing with FIG.
6, the processing logic compares the received pilot symbols with
the pilot symbols that are expected in certain sub-carriers at
certain times to determine a channel response for the sub-carriers
in which pilot symbols were transmitted. The results are
interpolated to estimate a channel response for most if not all of
the remaining sub-carriers for which pilot symbols were not
provided. The actual and interpolated channel responses are used to
estimate an overall channel response, which includes the channel
responses for most, if not all, of the sub-carriers in the OFDM
channel.
[0062] The frequency domain symbols and channel reconstruction
information, which are derived from the channel responses for each
receive path are provided to an STC decoder 100, which provides STC
decoding on both received paths to recover the transmitted symbols.
The channel reconstruction information provides equalization
information to STC decoder 100 sufficient to remove the effects of
the transmission channel when processing the respective frequency
domain symbols. The relay station could act as another base station
or as a terminal in the context of this invention.
[0063] The recovered symbols are placed back in order using symbol
de-interleaver logic 102, which corresponds to the symbol
interleaver logic 58 of the transmitter. The de-interleaved symbols
are then demodulated or de-mapped to a corresponding bitstream
using de-mapping logic 104. The bits are then de-interleaved using
bit de-interleaver logic 106, which corresponds to the bit
interleaver logic 54 of the transmitter architecture. The
de-interleaved bits are then processed by rate de-matching logic
108 and presented to channel decoder logic 110 to recover the
initially scrambled data and the CRC checksum. Accordingly, CRC
logic 112 removes the CRC checksum, checks the scrambled data in
traditional fashion, and provides it to the de-scrambling logic 114
for de-scrambling using the known base station de-scrambling code
to recover the originally transmitted data 116.
[0064] In parallel to recovering the data 116, a CQI, or at least
information sufficient to create a CQI at the base station 14, is
determined and transmitted to the base station 14 As noted above,
the CQI may be a function of the carrier-to-interference ratio
(CIR), as well as the degree to which the channel response varies
across the various sub-carriers in the OFDM frequency band. For
this embodiment, the channel gain for each sub-carrier in the OFDM
frequency band being used to transmit information is compared
relative to one another to determine the degree to which the
channel gain vanes across the OFDM frequency band. Although
numerous techniques are available to measure the degree of
variation, one technique is to calculate the standard deviation of
the channel gain for each sub-carrier throughout the OFDM frequency
band being used to transmit data.
[0065] FIGS. 1 to 6 provide one specific example of a communication
system that could be used to implement embodiments of the
application, it is to be understood that embodiments can be
implemented with communications systems having architectures that
are different than the specific example, but that operate in a
manner consistent with the implementation of the embodiments as
described herein.
[0066] FIG. 7 is a block diagram illustrating a logical
representation of an overall network architecture 700 that might be
used to implement some embodiments of the present application. As
shown, overall network architecture 700 consists of the following
functional entities: mobile stations (MS) 702, access service
networks (ASN) 706 comprising base stations (BS) 704 and
ASN-gateways (ASN-GW) 705, and a number of connectivity service
networks (CSN) 708. Network architecture 700 may be based on the
framework defined in WiMAX Network Architecture (The WiMAX Forum
Network Architecture Stage 2-3: Release 1, Version 1.2, the ant
contents of which are incorporated by reference herein).
[0067] ASN 706 may be IEEE 802.16m/e compliant, ASN 706 provides a
complete set of network functions needed to provide radio access to
an IEEE 802.16e/m subscriber, ASN 706 provides at least the
following functions: IEEE 802.16e/m Layer-1 (L1) and Layer-2 (L2)
connectivity with IEEE 802.16e/m MS transfer of AAA messages to
IEEE 802.16e/m subscriber's Home Network Service Provider (H-NSP)
for authentication, authorization and session accounting for
subscriber sessions; network discovery and selection of the IEEE
802.16e/m subscriber's preferred NSP; relay functionality for
establishing Layer-3 (L3) connectivity with an IEEE 802.16e/m MS
(i.e. IP address allocation); and Radio Resource Management.
[0068] in addition to the above functions, for a portable and
mobile environment, ASN 706 further supports the following
functions: ASN anchored mobility; CSN anchored mobility; paging;
and ASN-CSN tunneling.
[0069] Each CSN 708 is a set of network functions that provide IP
connectivity services to IEEE 802.16e/m subscriber(s). A given ASN
706 may be shared by more than one CSN 708. A CSN 708 may provide
the following functions: MS IP address and endpoint parameter
allocation for user sessions; Internet access; AAA proxy or server;
policy and Admission Control based on user subscription profiles;
ASN-CSN tunneling support; IEEE 802.16e/m subscriber billing and
inter-operator settlement; inter-CSN tunneling for roaming; and
inter-ASN mobility. A CSN 708 may further comprise network elements
(not shown) such as routers, AAA proxy/servers, user databases,
Interworking gateway MSs.
[0070] As shown in FIG. 8, relay stations (RS) 802 may be deployed
in the network to provide improved coverage and/or capacity. When
RSs 802 are present, communications between a BS 704 and a MS 702
can occur directly or via a RS 802.
[0071] IEEE 802.16j defines two relay station types according to
the number of carriers they can support during relaying: [0072] (1)
Single radio relay: A relay station that uses the same carrier
frequency as the MR-BS DL/UL carrier for its downlink and UL
transmissions, e.g., the MR-BS transmits to the RS at frequency f1
in interval T1, and the RS forwards the signals to its subordinate
stations at f1 in interval T2, where T1 and T2 do not have any
overlapping period. [0073] (2) Dual-radio relay: A relay station
that uses a different frequency from the MR-BS DL/UL carrier for
its downlink and uplink transmissions, e.g., the MR-BS transmits to
the RS at frequency f1, and the RS forwards the signals at f2 to
its subordinate stations.
[0074] Note that the above, definitions assume TDD operation, that
is, the same frequency is being used for both DL and UL
communication on any given interface.
[0075] As previously noted, in FDD the UL and DL traffic is
transmitted different carrier frequencies. In accordance with
embodiments of the present application, for FDD operation a RS may
use the same carrier f1 for its DL transmission that its
superordinate station uses for its DL, and the same carrier f2 for
its UL transmission that its superordinate station uses for its UL.
This option requires two carrier frequencies, and as described in
more detail below the frame structure may have to be split into
access and relay zones. FIG. 9 illustrates the case where the relay
is half-duplex (i.e., it does not receive and transmit
simultaneously on a given interface) and the relay operation occurs
in a time division fashion. FIG. 10 illustrates the case where the
relay is full-duplex (i.e., it receives and transmits
simultaneously at the same interface).
[0076] Alternatively, for FDD operation a RS may use a different DL
(UL) frequency from the DL (UL) frequency of its super ordinate
station. Not that this option requires 4 carriers (2 for odd hops
and 2 for even hope). FIG. 11 depicts this case.
[0077] The cases depicted in FIGS. 10 and 11 are similar to each
other except that a relay that can operate according to FIG. 10 may
require more complex antenna deployment and interference
cancellation circuitry for receiving, and transmitting
simultaneously at the same time at the frequencies. From
configuration point of view, they can be treated as being the
same.
[0078] The relay system depicted in FIG. 9 is more practical in
terms of hardware implementation and design, and in addition, the
operation suits well to the H-FDD operation already defined in the
IEEE 802.16e/Rev2 standard. For example, according to the H-FDD
frame structure defined in IEEE 802.16e/Rev2/D6, both DL and UL
frames are split into 2 intervals T1 and T2, one for Group 1
MSs/SSs and one for Group 2 MSs/SSs. During T1 (T2) interval, Group
1 (Group 2) MSs/SSs receive the DL signals from the BS, and during
T2 (T1) interval, Group 1 (Group 2) MSs/SSs transmit their UL
signals to the BS. As described in more detail below, this frame
structure may be modified for use in a multi-hop relay network, for
example, by inserting the optional relay amble (R-amble), replacing
FCH/DL-MAP with R-FCH/R-MAP, etc. In addition, it is also desirable
to seek a single-frame approach where more than one relay zone is
allowed to appear in a single frame to support FDD multi-hop relay
networks. Otherwise, where only one relay zone is allowed to appear
in a single frame, multiple frames would be required for multiple
relays.
Existing FDD and H-FDD Mode Operation in IEEE 802.16e/Rev2
[0079] As specified in IEEE 802.16e/Rev2, parameters related to
frame configuration are signalled in DL Channel Descriptor (DCD),
UL Channel Descriptor (UCD) and DL-MAP. During network entry, an MS
first synchronizes to an available channel and reads DL-MAP1 (FIG.
13) to receive DCD/UCD. Initially, MS performs its ranging
operation as part of Group 1. There may be one or two DCD/UCD. If
there is one DCD/UCD and the same type/length/value (TLV) is
repeated twice, the first one belongs to user Group 1 and the
second belongs to user Group 2.
[0080] MS receives the length of T1 (T2) interval in the current
(next) frame from DL-MAP 1 (DL MAP 2), and the UL carrier frequency
from UCD, DCD/UCD provides parameters such as DL_gap size,
DL_residue gap size and its location, TTGs and RTGs, etc. so that
MS/SS can locate exactly the DL and UL intervals within the
frame.
[0081] MS performs initial ranging assuming itself in Group 1. BS
can switch the MS user group any time by transmitting an H-FDD
Group switch Information Element (IE). If the group switch IE is
received at frame n, it becomes effective at frame n+switch
delay+m, where switch delay parameters is specified in UCD, and m
is the group number (e.g., for group 1 user, m=1).
[0082] In both FDD and TDD, DL MAP refers to allocations in the
current frame while UL MAP refers to a region in the next frame. In
H-FDD, the DL MAP 1 or DL MAP 2 refers to a region in the current
frame, while UL MAP 1 refers to the next frame, end UL MAP 2 refers
to the next-next frame.
[0083] If full-duplex and half-duplex MSs operate at the same time,
BB can transmit FDD Paired Allocation IE to schedule the
full-duplex MSs to all H-FDD resources available. The FDD Paired
Allocation IE contains UL MAP IEs that refer to allocations in the
other UL region. This IE may also contain a UL Zone Switch IE and a
UL Allocation Start IE, in which case those IEs refer to
configuration related to the other UL allocation region.
RS and MR-BS Operation in FDD and H-FDD Mode
[0084] In accordance with embodiments of the present invention, the
FDD frame structure shown in FIG. 13 may be modified to support
multihop relaying. As shown in FIG. 18A, the DL1, DL2, UL1 and UL2
subframes may each be divided into two zones in order to support
BS-RS and RS-MS communications in addition to BS-MS communications.
As with the FDD frame structure of FIG. 13, the frame structure of
FIG. 18A supports a coordinated transmission arrangement of two
groups of H-FDD stations (Group-1 and Group-2) that share the frame
at distinct partitions of the frame.
[0085] For transparent RS (T-RS) operation, the DL1 and DL2
subframes may each be divided into an access zone and a transparent
zone, and the UL1 and UL2 subframes may each be divided into an
access zone and a relay zone, as shown in FIG. 18B. A T-RS can be
assigned to one of Group-1 and Group-2 in the same way as a MS is
assigned. MR-BS can simultaneously assign multiple T-RSs to each
Group since T-RSs can be treated as if they are MSs. A T-RS
assigned to Group 1 (Group 2) can relay data in the DL1/UL1
(DL2/UL2) regions. For simplicity, all RSs may be assigned to the
same Group so that the FCH/MAP for that Group may contain only
optional FCH/R-MAP.
[0086] For non-transparent RS (NT-RS) operation, the DL1, DL2, UL1
and UL2 subframes may each be divided into an access zone and a
relay zone, as shown in FIG. 18C. A capable NT-RS in Group 1 (Group
2) can use the entire UL zone except for UL 1 (UL 2).
[0087] The R-link Channel Description (RCD) MAC message can be
employed to signal the access and relay zones. The access zones may
be contiguous and fall within one of the subframes of the H-FDD
frame, while the relay zones may be contiguous and fall within the
other subframe. The FCH/MAP and R-FCH/RMAP can be transmitted in
the first tx access zone and relay zone, respectively.
[0088] The RS may obtain the UL carrier from the UCD during network
entry. For single radio RSs, the same carrier frequencies used at
the first hop may be used at other hops. For dual-radio RSs, the
second carrier frequency signalled in the RS Config CMD message can
refer to the DL carrier in FDD mode. In FDD mode, an additional TLV
may be signalled to configure the UL carrier for RS to use in
communicating with subordinate stations.
[0089] In non-transparent RS systems, all of the half-duplex
MSs/SSs may set as Group 1 users, and all of the RSs may be set as
Group 2 users (or vice versa) in FDD mode. An RS can still operate
in full-duplex mode, e.g., it may be allocated resources at all
available H-FDD resources via FDD Paired Allocation IE. A
transparent RS can monitor both DL MAP 1 and DL MAP 2, and perform
relaying according the forwarding rules it has. In systems where
all RSs are transparent, MSs/SSs can be switched between
groups.
[0090] FIGS. 19A and 19B illustrate alternative frame
configurations for T-RS and NT-RS operation, respectively, wherein
the second subframe of the H-FDD frame structure is used as the
transparent zone or the relay zone, as the case may be. That is,
rather than divide DL1, DL2, UL1 and UL2 into zones, relays are
assigned to only one Group (say, Group 2; i.e. DL2 and UL2, as
shown in FIGS. 19A and 19B). For nontransparent RS operation,
advantage is taken off the MAP2, since the relay would need its own
(R-AMP).
[0091] One of the advantages of TDD over FDD is that TDD fits
better to the asymmetric characteristics of DL-UL transmissions.
The conventional H-FDD frame shown in FIG. 13 assumes only two
groups of users, leading to limited flexibility on varying the
DL-UL ratio and resulting in about two OFDM symbols being wasted
due to the RTG/TRG and/or DL_gap/UL_gap requirement.
[0092] FIG. 20 illustrates an H-FDD frame configuration having
three user group regions. As shown, by using three groups of users
with three different regions in the frame, the DL_gap/UL_gap
requirement may be eliminated, and the RTGs for MS Groups 1 and 3
may be absorbed by their respective radio idle states. It is noted
that if TRG, instead of RTG, takes a longer time, by reordering the
UL group transmission the TRG for the three MS Groups can be
absorbed instead. Flexibility is also gained in varying the DL-UL
ratio since radio idle state can be explored.
[0093] FIG. 21 illustrates a three-hop case for the H-FDD frame
configuration of FIG. 20. As shown, given more hops more
flexibility can be expected, however a higher number of groups of
MSs are required.
[0094] Other modifications will be apparent to those skilled in the
art and, therefore, the invention is defined in the claims.
* * * * *