U.S. patent application number 12/419580 was filed with the patent office on 2009-10-08 for wireless communications network comprising multi-hop relay stations.
This patent application is currently assigned to Alvarion Ltd.. Invention is credited to Mariana GOLDHAMER.
Application Number | 20090252203 12/419580 |
Document ID | / |
Family ID | 40933599 |
Filed Date | 2009-10-08 |
United States Patent
Application |
20090252203 |
Kind Code |
A1 |
GOLDHAMER; Mariana |
October 8, 2009 |
WIRELESS COMMUNICATIONS NETWORK COMPRISING MULTI-HOP RELAY
STATIONS
Abstract
A method is provided for conveying wireless communications in a
radio network using OFDMA or multi-carrier technologies. The
wireless network comprises a first relay station and a subscriber
station that is operative to communicate with that first relay
station. The first relay station is operative to simultaneously
transmit to or receive communications from at least two recipients
along a shared frequency channel. The two recipients are wireless
network entities selected from among: the base station and a
subscriber station; or another relay station and a subscriber
station; or the base station and another relay station. According
to an embodiment of the invention the wireless communications
network further comprises a second relay station, which is
operative to simultaneously transmit to or receive communications
from at least two recipients along a shared frequency channel. The
two recipients are wireless network entities selected from among:
the first relay station and a subscriber stations, or a third relay
station and a subscriber station, or the first relay station and a
third relay station, wherein a third relay station is a relay
station that does not exchange communications directly with either
the base station nor the first relay station.
Inventors: |
GOLDHAMER; Mariana; (Ramat
Gan, IL) |
Correspondence
Address: |
BROWDY AND NEIMARK, P.L.L.C.;624 NINTH STREET, NW
SUITE 300
WASHINGTON
DC
20001-5303
US
|
Assignee: |
Alvarion Ltd.
Tel-Aviv
IL
|
Family ID: |
40933599 |
Appl. No.: |
12/419580 |
Filed: |
April 7, 2009 |
Current U.S.
Class: |
375/211 ;
375/260; 455/15 |
Current CPC
Class: |
H04B 7/026 20130101;
H04W 16/26 20130101; H04B 7/2606 20130101; H04L 1/0618 20130101;
H04L 2001/0097 20130101 |
Class at
Publication: |
375/211 ; 455/15;
375/260 |
International
Class: |
H04B 7/14 20060101
H04B007/14; H04L 27/28 20060101 H04L027/28 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 7, 2008 |
IL |
190659 |
Claims
1. A method for conveying wireless communications in a wireless
communications network comprising at least one base station, at
least one first relay station and a plurality of subscriber
stations, and wherein said at least one first relay station is
operative to simultaneously transmit communications to or receive
communications from at least two recipients along a shared
frequency channel and wherein said at least two recipients are
wireless network entities selected from among: said base station
and at least one subscriber station selected from among said
plurality of subscriber stations; or at least one other relay
station and at least one subscriber station selected from among
said plurality of subscriber stations; or said base station and at
least one other relay station.
2. A method according to claim 1, wherein said wireless
communications network further comprises at least one second relay
station, and wherein said at least one second relay station is
operative to simultaneously transmit communications to or receive
communications from at least two recipients along a shared
frequency channel, and wherein said at least two recipients are
wireless network entities selected from among: said at least one
first relay station and at least one subscriber station selected
from among said plurality of subscriber stations; or at least one
third relay station and at least one subscriber station selected
from among said plurality of subscriber stations; or said at least
one first relay station and at least one third relay station, and
wherein said at least one third relay station is not operative to
exchange communications directly with either one of said base
station and said at least one first relay station.
3. A method according to claim 1, wherein at least one member of
the group consisting of: said base station, said at least one first
relay station and said at least one second relay station, is
operative to simultaneously transmit or receive communications
directed to/from different recipients by transmitting/receiving
said communications along at least one sub-channel selected from
among a plurality of OFDMA sub-channels or along at least one
sub-carrier selected from among a plurality of sub-carriers.
4. A method according to claim 3, wherein said at least one
sub-channel or said at least one sub-carrier is used simultaneously
by two members of the group consisting of: at least two subscriber
stations each connected either to a different relay station or
connected to a base station and a relay station, or a relay station
and said base station; or two relay stations.
5. A method according to claim 1, wherein transmission and
reception intervals for at least one subscriber station to
communicate with said base station, and for at least one other
subscriber station to communicate with said first relay station,
are scheduled at different time intervals.
6. A method according to claim 2, wherein transmission and
reception intervals for at least one subscriber station to
communicate with said first relay station and for at least one
other subscriber station to communicate with said second relay
station, are scheduled at different time intervals.
7. A method according to claim 1, wherein at least one relay
station is operative in accordance with a TDD or FDD modes of
operation.
8. A method according to claim 7, wherein said at least one relay
station is operative during at least one interval while using two
different frequency channels for simultaneously transmit or
simultaneously receive communications to/from at least two wireless
network entities.
9. A method according to claim 2, wherein at least one member of
the group consisting of: said base station, said at least one first
relay station and said at least one second relay station, is
operative to simultaneously transmit or receive communications
directed to/from different recipients by transmitting/receiving
said communications along at least one sub-channel selected from
among a plurality of OFDMA sub-channels or along at least one
sub-carrier selected from among a plurality of sub-carriers.
Description
FIELD OF THE INVENTION
[0001] The present invention relates in general to
telecommunication systems and methods for efficient utilization
thereof, and particularly to systems to relay transmissions in
wireless networks.
BACKGROUND OF THE INVENTION
[0002] The well known use of relays in wireless networks has gained
some further popularity in the recent years with the introduction
of broadband systems, having physical limitation of the cell size.
Classical relays operate at the radio level, by amplifying the
received signal and re-transmitting it, generally at a different
frequency. Newer relays, sometimes referred to as Layer 2 relays,
decode the signal and re-transmit it at a different point in
time.
[0003] U.S. Pat. No. 5,883,884 describes a wireless communication
system in which a base unit transmits outgoing TDM signals within a
base transmission coverage area at a first frequency. Repeaters in
the base coverage area receive the outgoing signal and retransmit
it within respective repeater coverage areas at respective
frequencies, maintaining the same time slot orientation in TDM
format, where several levels of repeaters form a hierarchy covering
the expanded range. The remote subscriber units located in a
coverage area receive the strongest outgoing frequency signal from
a repeater/base unit in a time slot assigned to that unit for a
particular call. Incoming TDMA signals from remote units use the
same time slots used in received outgoing signals. Each repeater
receives outgoing signals from a lower level repeater (or from the
base unit) at the transmission frequency of the lower level
repeater, and immediately retransmits the signal in its own
coverage at a different frequency. Incoming signals transmitted to
any particular repeater from a remote unit in its coverage area, or
from a higher level repeater, are at the outgoing transmission
frequency for that repeater. The solution provided by this
publication to reduce interruption during communications is that
the repeaters and remote units switch between repeaters to
communicate with the base unit depending upon received signal
strength.
[0004] U.S. Pat. No. 7,386,036 discloses a wireless multi-hop
system in which radio links between relays and users are optimized
separately from the links between relays and base stations and in
which multiple simultaneous data streams between relays and base
stations are created. The system includes a base station (BS)
connected to the core network with a link of wire line quality,
relay stations (RS) connected to the BS with a first radio
interface, and to subscriber stations (SS), with a second radio
interface. The first and second radio interfaces can operate, at
least in part, using the same frequency bandwidth, and the SS can
also connect directly to the BS using the second radio interface if
the BS is closer than any RS.
[0005] U.S. Pat. No. 7,218,891 describes a multi-hop relaying
method for use in a frequency division duplexing based wireless in
a cellular network. The multi-hop transmission scheme utilizes
relays within a conventional cellular system by selecting the
strongest pilot signal from among the base stations and the relays,
reporting such to the base station, distributing an active user
list to the relays along with scheduling and routing information
via a relay control channel, and transmitting data according to a
respective active user based upon the pilot signal strength to
maximize coverage and capacity over the cellular system.
[0006] Still, it is required to provide an improved solution for
spectral efficiency based on the utilization of dedicated as well
as shared allocations of resources used while operating under
access mode (BS/RS to SS) operation.
SUMMARY OF THE INVENTION
[0007] It is therefore an object of the present invention to
provide improved methods and means for using relays in a multi-hop
wireless communications network.
[0008] It is a further object of the present invention to provide
methods for allocating OFDMA/multi-carrier resources to achieve the
foregoing.
[0009] Other objects of the invention will become apparent as the
description of the invention proceeds.
[0010] In accordance with an embodiment of the present invention,
there is provided a method for conveying wireless communications in
a wireless communications network comprising at least one base
station, at least one first relay station and a plurality of
subscriber stations, and wherein the at least one first relay
station is operative to simultaneously transmit communications to
or receive communications from at least two recipients along a
shared frequency channel and wherein the at least two recipients
are wireless network entities selected from among: [0011] the base
station and at least one subscriber station selected from among the
plurality of subscriber stations; or [0012] at least one other
relay station and at least one subscriber station selected from
among the plurality of subscriber stations; or [0013] the base
station and at least one other relay station.
[0014] As will be appreciated by those skilled in the art, the
present invention naturally encompasses cases where the at least
one first relay station communicates with more than two such
recipients in accordance with the method described above. For
example, the at least one first relay station may communicate with
the base station, with one or more other relay stations and with at
least one subscriber station.
[0015] According to another embodiment of the invention, the
wireless communications network further comprises at least one
second relay station, and wherein the at least one second relay
station is operative to simultaneously transmit communications to
or receive communications from at least two recipients along a
shared frequency channel, and wherein the at least two recipients
are wireless network entities selected from among: [0016] the at
least one first relay station and at least one subscriber station
selected from among the plurality of subscriber stations; or [0017]
at least one third relay station and at least one subscriber
station selected from among the plurality of subscriber stations;
or [0018] the at least one first relay station and at least one
third relay station,
[0019] and wherein the at least one third relay station is not
operative to exchange communications directly with either with the
base station nor with the at least one first relay station.
[0020] In accordance with another embodiment of the invention, at
least one member of the group consisting of: the base station, the
at least one first relay station and the at least one second relay
station, is operative to simultaneously transmit or receive
communications directed to/from different recipients by
transmitting/receiving the communications along at least one
sub-channel selected from among a plurality of OFDMA sub-channels
or along at least one sub-carrier selected from among a plurality
of sub-carriers.
[0021] By yet another embodiment of the invention, the at least one
sub-channel or the at least one sub-carrier is used simultaneously
by two members of the group consisting of: [0022] at least two
subscriber stations each connected either to a different relay
station or connected to a base station and a relay station, or
[0023] a relay station and the base station; or [0024] two relay
stations.
[0025] According to still another embodiment of the invention, the
transmission and reception intervals for at least one subscriber
station to communicate with the base station, and for at least one
other subscriber station to communicate with the first relay
station, are scheduled at different time intervals.
[0026] In accordance with another embodiment of the invention the
transmission and reception intervals for at least one subscriber
station to communicate with the first relay station and for at
least one other subscriber station to communicate with the second
relay station, are scheduled at different time intervals.
[0027] By still another embodiment of the invention, at least one
relay station is operative in accordance with a TDD or FDD modes of
operation. Preferably, the at least one relay station is operative
during at least one interval while using two different frequency
channels for simultaneously transmit or simultaneously receive
communications to/from at least two wireless network entities.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 illustrates implementation of prior art sub-frame
concept for use in a wireless network comprising relays;
[0029] FIG. 2 demonstrates areas of interferences to a subscriber
station caused by the use of relays;
[0030] FIG. 3 illustrates an example for aggressive frequency
segment reuse;
[0031] FIG. 4 presents usage of dedicated and shared frequency
segments in relay operation;
[0032] FIG. 5 illustrates operation during time partition 1 when a
relay in an odd hop receives transmissions from its neighbors;
[0033] FIG. 6 illustrates operation during time partition 2 when a
relay in an odd hop sends transmissions to its neighbors;
[0034] FIG. 7 presents a frame structure for IEEE 802.16m relay
TDD--according to an embodiment of the invention;
[0035] FIG. 8 presents a TDD Frame structure in accordance with
another embodiment of the invention;
[0036] FIG. 9 illustrates operation in FDD frequency arrangement
during time partition 1, when the relays located at odd hops
receive transmissions from their respective neighbors and relays in
even hops transmit to their neighbors;
[0037] FIG. 10 illustrates operation in FDD frequency arrangement
during time partition 2, when the relays located in odd hops send
transmissions to their respective neighbors and relays in even hops
receive from their neighbors;
[0038] FIG. 11 presents an FDD Frame structure in accordance with
another embodiment of the invention;
[0039] FIG. 12 illustrates operation with no interference
separation in the time domain; and
[0040] FIGS. 13 to 15 illustrate 3 examples of operation with
interference separation in the time domain.
DETAILED DESCRIPTION OF THE INVENTION
[0041] The present invention will be understood and appreciated
more fully from the following detailed examples taken in
conjunction with the drawings.
[0042] Let us consider now FIG. 1 which presents a representative
example of a prior art solution where a communication frame which
complies with the draft P802.16j/D3 submitted for the IEEE
Recommendation 802.16j, is illustrated as having time division for
enabling operation of a relay station. FIG. 1A illustrates the BS
part and the relay part of frame J, and FIG. 1B illustrates the
continuation of these two parts of frame J. The frame comprises two
separated time intervals dedicated to relay-BS communication per
MAC frame. However, if such a solution were to be adopted for the
IEEE 802.16m System Description Document ("SDD") Recommendation,
due to the limitation which stems from the small number of
available sub-frames in the IEEE 802.16m SDD such an approach might
have serious performance limitations. Additionally, it is highly
desired to use the MIMO technology for the RS-BS or RS-RS
communications, which would not be applicable if this solution is
to be adopted, as the number of possible sub-frames and
consequently the zones in a MAC frame is highly limited. Therefore,
this solution is practically impossible for incorporating the use
MIMO while having a relay allocation of resources.
Scarcity of Sub-Frames
[0043] As will be appreciated by those skilled in the art, the
usage of time separation and the short MAC frame duration impose
certain limitations. The limitation, system wise, is generated by
having too many features that should be supported in the time
domain. Many of these features did not exist at the time when
802.16e was drafted. Some examples of features that are supported
by an 802.16e system that evolved to the 802.16m are the following:
[0044] Permutations and Reuse factor: [0045] Partial Usage of
Channels sub-carrier permutation (PUSC) (Reuse 3) [0046] Adjacent
sub-carrier permutation (AMC) [0047] PUSC with all subchannels
permutation (Reuse 1) [0048] Multicast/Broadcast Zone [0049] MIMO
Zone [0050] AMC permutation [0051] Diversity permutation [0052]
Diversity MAP (diversity combined control information sent from
multiple antennae) [0053] Not-diversity MAP (control information
sent from a single antenna) [0054] Matrix A (MIMO pre-coding)
[0055] Matrix B (combined pre-coding) [0056] Matrix C (beam-forming
pre-coding) [0057] 2/3 antennae [0058] Relays [0059] Legacy support
[0060] Coexistence with Bluetooth [0061] Coexistence with 802.11
[0062] Coexistence with UMTS/LTE.
[0063] Therefore, the solution provided by a preferred embodiment
of the present invention to this problem, is, to transfer part of
the time-separated activities into the sub carriers domain (e.g.
into the OFDMA domain), as will be further discussed
hereinafter.
[0064] The relay operation consists of a number (e.g. 4 as
illustrated in FIG. 1A) of different time intervals in a single
frame. If we were to consider for example a partition of sub-frames
with the a frame compatible with the 802.16m SDD Recommendation,
the embodiment of the proposed solution would become clearer when
taken in conjunction with FIG. 1: [0065] 3 sub-frames for BS DL
(3*3=9 slots), access mode; includes the forward Relay Station (RS)
feeding [0066] 2 sub-frames for RS-DL (2*3=6 slots), access mode
[0067] 2 sub-frames for BS-UL (2*2=4 slots), access mode, for the
relay backward traffic [0068] 1 sub-frame for RS-UL, access mode (2
slots, which is not sufficient, but is the whole resource that
remains available).
[0069] Such a partition would lead to a poor spectral efficiency,
especially in the up-link direction, where the MAC and
fragmentation headers of every UL (uplink) transmission take a
considerable portion of the 4 available slots in the BS UL
operation in the above example. For the relay operation it would
become even worse, because there are only two available UL slots.
Additionally, due to the excessive segmentations, there are
important overheads in both DL (downlink) and UL control messages
(MAPs).
[0070] The addition of MIMO (multiple-input-multiple-output) Zones
suitable for BS-RS communication would therefore become impossible
due to the small number of sub-frames (available symbols).
Interference MAP
[0071] In the general case, a Relay Station (RS) will have a number
of RS surrounding it, which, for the highest range and data
traffic, should be separated in frequency domain. Let us consider
for example a case where Layer 2 relays, (i.e. which decode the
signal received and re-transmit it at a different point in time)
have sector antennas in the access mode. In such a configuration
the interference that would be created to one SS located at the
cell edge are illustrated in FIG. 2. If in such an example omni
antennas are used, there would be also 4 interfering cells.
[0072] The term "frequency segment" as used throughout the
specification and claims or "segment" is used to denote a group of
sub-channels, whereas the term "sub-channel" is used to denote a
logical entity formed by a number of sub-carriers. The sub-carriers
may be OFDM/OFDMA sub-carriers or individual carriers.
[0073] In order to separate the 4 interfering cells, 4 segments
(sub-channel groups) are required in the OFDMA domain. These
segments enable the use of a maximum cell size and will be used
essentially for increasing the SINR (signal to interference and
noise ratio) of specific users, typically those located at the
cell's margin. A better spectral efficiency will be obtained if
those links which do not interfere to others will be grouped in a
"shared" allocation built from sub-channels dedicated for this type
of usage.
[0074] For example, a possible SDD deployment scenario is
illustrated in FIG. 3. This "aggressive" deployment scenario
suffers from interference at the intersection of the coverage
prints of different relays, which lead to low data rate or lack of
coverage.
[0075] A better spectral efficiency and coverage may be obtained if
both dedicated and shared segments are introduced. In FIG. 4 there
are areas around the RS cell center which may be reused in
parallel. The reused spectrum can be appreciated from the
illustration provided in FIG. 4.
[0076] If we take the simplified assumption that used spectrum is
reflected by the coverage, the use in FIG. 4 is of 9*2=18 squares
while in FIG. 3--1+1+5=7 squares are used, representing a 18/7=250%
better spectrum efficiency of the FIG. 4 configuration over that of
FIG. 3.
[0077] Therefore, as a may easily be understood from the above, the
use of the shared segment may significantly increase the spectral
efficiency, whereas the use of the dedicated segments will increase
the cell size.
Relay Support in Frame Structure
[0078] Let us consider now the following examples illustrating
several embodiments of carrying out the present invention.
Relay Operation
[0079] The relay access operation is associated with the frequency
channel used by the BS, and instead of having the partition between
the BS operation and the relay operation in the time domain it is
preferably done in the OFDMA domain.
TDD Operation
[0080] Typically, a TDD relay will not both transmit (Tx) and
receive (Rx) at the same time.
[0081] According to some embodiments of the present invention, the
MAC entity may communicate with different segments; for example,
two time-domain partitions of the 802.16m frame, as follows:
Time Partition 1 (BS-Tx, RS Rx)
[0082] This time partition may include the following segments:
[0083] One DL Segment for carrying the BS traffic. This segment
will be able to carry at least two different STC (space-time
coding)/MIMO modes: one for BS-SS communications and one for BS-RS
communications. To accommodate these different STC modes, this
segment may preferably be split into two smaller segments, each one
using a different STC/MIMO mode. During the BS DL transmissions,
the RS is in receiving mode. [0084] One UL Relay Segment for
carrying: [0085] Up-link traffic from the subscribers (relay access
mode) [0086] Backward link of the next hop RS.
[0087] This segment may either be split into dedicated and shared
sub-channel groups or alternatively different segments may be
allocated to the dedicated and shared UL RS traffic. BS downlink
traffic may also be scheduled during the shared part of the relay
segment, if it does not create interference.
[0088] The RS is isolated in the access activity (RS-MS) from the
BS due to the different sub-channel segment used and the
significant distance between the RS and the BS. The isolation may
further be increased by using directional antenna for the relay
access operation and the feeding link (BS-RS link).
[0089] The functional description of the BS/Relay during time
partition 1 is demonstrated in FIG. 5, where the relay is the focal
point of the receiving (Rx) activity.
Time Partition 2 (BS Rx, RS Tx)
[0090] This time partition may include the following segments:
[0091] BS UL Segment carrying: [0092] BS access traffic (SS
transmissions). [0093] BS-RS backward link
[0094] According to one embodiment of the present invention, this
segment may carry at least two different
[0095] STC modes: one for the BS-SS communications (sub-channel
group for the BS access mode) and one for the BS-RS communications.
Different sub-channel groups are allocated for this activity.
[0096] During the BS UL transmissions, the RS is in transmitting
mode. [0097] DL Relay Segment carrying: [0098] Downlink RS access
traffic to the SSs associated with that RS. This segment may be
split into dedicated and shared segments or different segments may
be allocated for the dedicated and shared DL RS traffic. The shared
segment may also be used by the up-link BS activity as long as it
does not create interference to the operation of the relays. [0099]
Forward link to the next hop RS. [0100] There is interference
potential between: [0101] 1. Transmission of communications from
the SS to the BS and the reception of communications sent from the
relay to the SS (SS to SS interference); [0102] 2. Transmission of
communications from the SS to the relay and to the BS (SS to BS
interference). This scenario is less problematic, due to the higher
separation distance.
[0103] The possible isolation for the first scenario is the SS-SS
separation (90-100 dB in NLOS for 100 m) and the segment separation
(25 dB while using adjacent carriers and 40 dB while using
alternate carriers). If the interference is not overcome, the
scheduling of the interfering SSs shall be carried out in such a
way that they are separated in the time domain, even if the penalty
is some delay for such SS. Another possibility could be to schedule
the interfering SSs in different frames. Example 2 discussed
hereinbelow resolves this potential interference.
[0104] FIG. 6 describes the functional operation during time
partition 2. The relay is presented as the central transmitting
point.
Example 1
Frame Structure
[0105] FIG. 7 demonstrates a functional description of the BS/Relay
operation according to some embodiments of the present invention.
The BS is considered to be located at HOP 0, while the first relay
is located at HOP 1. The frame partition starts with the BS DL,
which is also relevant for relay stations located at HOP 2n. In
FIG. 7 the left time partition corresponds to time partition 1,
whereas the right time partition corresponds to time partition
2.
[0106] For each functional behavior a segment in the OFDMA domain
is allocated.
[0107] A relay transmits in two different directions at the same
time. Each transmission uses the suitable segments associated with
a specific antenna.
[0108] UL and DL activities are mixed within the frame. The
permutations used for UL and DL are compatible, but not necessary
identical.
[0109] The Frame Control Header (FCH) is sent in all DL segments
which are intended for different MIMO/STC modes or for different
antennae. The FCH may be sent at the start of a multi-frame only.
Preambles are sent in DL but can be sent also in up-link.
[0110] The above described scheme has the advantage of minimizing
the number of switching points in the relay operation and allows
the same sub-frame duration as in regular TDD operation.
Example 2
Frame Structure
[0111] In this example the transmitting activity for BS/RS in HOP
2n is separated in the time domain from the receiving activity of
the relay located at HOP 2n+1. FIG. 8 is an example of such a frame
structure, in which there is a separation in the time domain of the
SS receiving and transmitting activities.
Multi Hop-Operation
[0112] The following Table 1 illustrates the multi-hop operation
for 6 Hops.
TABLE-US-00001 TABLE 1 Propagation times Frame 1, Frame 1, Frame 2,
Frame 2, Frame 3, Frame 3, Frame 4, BS DL BS UL BS DL BS UL BS DL
BS UL BS DL BS -> RS1 RS1 -> BS RS2 -> RS1 RS3 -> RS2
RS4 -> RS3 RS5 -> RS4 RS6 -> RS5 RS1 -> RS2 RS2 ->
RS3 RS3 > RS4 RS4 -> RS5 RS5 > RS6
[0113] As can be seen from the above table, the propagation time
from BS to RS6 is only 3 MAC frames.
FDD Operation
[0114] The FDD operation makes use of the frequency f1 for Tx of
the BS and frequency f2 for Tx of the SS, where typically
f1>f2.
[0115] An example of operating in time partition 1 is presented in
FIG. 10 whereas operating in time partition 2 is illustrated in
FIG. 11.
[0116] During time partition 1, the relay may transmit on both f1
and f2, while during time partition 2 the relay receives on both f1
and f2. According to some embodiments of the present invention, a
duplexer is not needed, because there is no simultaneous reception
and transmission on different frequencies. The time separation for
the SS transmission and reception is generally not necessary in FDD
mode, because the separation is done in the frequency domain by
using different receiving and transmitting frequencies. The BS may
operate in a full duplex mode.
FDD Frame Structure
[0117] The FDD frame structure is illustrated in FIG. 11. In order
to ease the understanding of the reader, the operation on frequency
channels f1 and f2 is illustrated by using a common frame
structure. However, in practice, the segments which are used only
for f1 shall be extended so as to occupy the full channel operating
on f1. Similarly, the segments which are used only for f2 shall be
extended so as to occupy the full channel operating on f2.
[0118] The main advantages of the solution proposed by this
embodiment of the present invention are: [0119] Lower MAC
overheads; [0120] Better granularity for resource allocations (as
opposed to the time domain where the resources' allocation is more
or less fixed by the sub-frame size and number); [0121] Support for
MIMO in BS-RS communication; [0122] Significant lower data traffic
forward delays. Only one frame is needed for 2 hops; and [0123]
Better spectral efficiency resulting from the usage of "shared
segments".
[0124] It should be understood that various embodiments of the
present invention may relate to any OFDMA/multi-carrier based
systems such as LTE.
[0125] FIGS. 12 to 15 demonstrate different concepts of time
separation which are helpful for reducing the SS-SS interference,
without creating additional time partitions for the relay feeding
traffic (BS-RS or RS1-RS2).
[0126] In the example presented in FIG. 12 the operation of the BS,
RS in odd-hop and RS in even hop on different rows. There are only
two time partitions, with a gap corresponding to Tx-Rx or Rx-Tx
transition. The MSs may be either in a Tx or Rx state during the
same time partition.
[0127] In FIG. 13, the MS transmissions and receptions to/from the
BS and RSs can be time separated. The MS connected to BS and RS in
even hop, receives traffic at the beginning of the frame (time
partition 1), while the transmission of the MS to the RS at odd hop
is scheduled after ending the previous receiving activity. In a
similar mode, during time partition 2, the MS connected to BS and
RS at even hop transmits traffic at the beginning of the frame; the
receiving activity of the MS from the RS at odd hop is scheduled
after ending the previous transmitting activity. The activity along
the feeding link (BS-RS) can take place in parallel with the access
activity, having no reciprocal interference.
[0128] In FIG. 14 the time separation is extended for separating
the interfering receiving and transmitting activities of relays in
different hops.
[0129] In FIG. 15 the access activities are totally separated from
the feeding activities. In addition, the relays and BS transmit to
MS at the same time.
[0130] Although the present invention has been demonstrated
particularly as a solution for IEEE 802.16m, still it should be
appreciated by those skilled in the art that the present invention
should be understood to encompass all similar systems where OFDMA
sub-channel partitions or multi-carriers may be used.
[0131] It is to be understood that the present invention has been
described using non-limiting detailed descriptions of embodiments
thereof that are provided by way of example and are not intended to
limit the scope of the invention. It should be understood that
features and/or steps described with respect to one embodiment may
be used with other embodiments and that not all embodiments of the
invention have all of the features and/or steps shown in a
particular figure or described with respect to one of the
embodiments. Variations of embodiments described will occur to
persons of the art.
[0132] It is noted that some of the above described embodiments
describe the best mode contemplated by the inventors and therefore
include structure, acts or details of structures and acts that may
not be essential to the invention and which are described as
examples. Structure and acts described herein are replaceable by
equivalents which perform the same function, even if the structure
or acts are different, as known in the art. Therefore, the scope of
the invention is limited only by the elements and limitations as
used in the claims. When used in the following claims, the terms
"comprise", "include", "have" and their conjugates mean "including
but not limited to"
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