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COMMUNICATION SYSTEMS
INTRODUCTION
Currently there exists significant interest in the use of multihop techniques in packet
based radio and other communication systems, where it is purported that such
techniques will enable both extension in coverage range and increase in system
capacity (throughput).
In a multi-hop communication system, communication signals are sent in a
communication direction along a communication path (C) from a source apparatus to a
destination apparatus via one or more intermediate apparatuses. Figure 6 illustrates a
single-cell two-hop wireless communication system comprising a base station BS
(known in the context of 3G communication systems as "node-B" NB) a relay node RN
(also known as a relay station RS) and a user equipment UE (also known as mobile
station MS). In the case where signals are being transmitted on the downlink (DL) from
a base station to a destination user equipment (UE) via the relay node (RN), the base
station comprises the source station (S) and the user equipment comprises the
destination station (D). In the case where communication signals are being transmitted
on the uplink (UL) from a user equipment (UE), via the relay node, to the base station,
the user equipment comprises the source station and the base station comprises the
destination station. The relay node is an example of an intermediate apparatus (I) and
comprises: a receiver, operable to receive data from the source apparatus; and a
transmitter, operable to transmit this data, or a derivative thereof, to the destination
apparatus.
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Simple analogue repeaters or digital repeaters have been used as relays to improve or
provide coverage in dead spots. They can either operate in a different transmission
frequency band from the source station to prevent interference between the source
transmission and the repeater transmission, or they can operate at a time when there
is no transmission from the source station.
Figure 7 illustrates a number of applications for relay stations. For fixed infrastructure,
the coverage provided by a relay station may be "in-fill" to allow access to the
communication network for mobile stations which may otherwise be in the shadow of
other objects or otherwise unable to receive a signal of sufficient strength from the
base station despite being within the normal range of the base station. "Range
extension" is also shown, in which a relay station allows access when a mobile station
is outside the normal data transmission range of a base station. One example of in-fill
shown at the top right of Figure 7 is positioning of a nomadic relay station to allow
penetration of coverage within a building that could be above, at, or below ground level.
Other applications are nomadic relay stations which are brought into effect for
temporary cover, providing access during events or emergencies/disasters. A final
application shown in the bottom right of Figure 7 provides access to a network using a
relay positioned on a vehicle.
Relays may also be used in conjunction with advanced transmission techniques to
enhance gain of the communications system as explained below.
It is known that the occurrence of propagation loss, or "pathloss", due to the scattering
or absorption of a radio communication as it travels through space, causes the strength
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of a signal to diminish. Factors which influence the pathloss between a transmitter and
a receiver include: transmitter antenna height, receiver antenna height, carrier
frequency, clutter type (urban, sub-urban, rural), details of morphology such as height,
density, separation, terrain type (hilly, flat). The pathloss L (dB) between a transmitter
and a receiver can be modelled by:
L = b + 10n1ogd (A)
Where d (metres) is the transmitter-receiver separation, b(db) and n are the pathloss
parameters and the absolute pathloss is given by l = 10(L/10).
The sum of the absolute path losses experienced over the indirect link SI + ID may be
less than the pathloss experienced over the direct link SD. In other words it is possible
for:
L(SI) + L(ID) < L(SD) (B)
Splitting a single transmission link into two shorter transmission segments therefore
exploits the non-linear relationship between pathloss verses distance. From a simple
theoretical analysis of the pathloss using equation (A), it can be appreciated that a
reduction in the overall pathloss (and therefore an improvement, or gain, in signal
strength and thus data throughput) can be achieved if a signal is sent from a source
apparatus to a destination apparatus via an intermediate apparatus (e.g. relay node),
rather than being sent directly from the source apparatus to the destination apparatus.
If implemented appropriately, multi-hop communication systems can allow for a
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reduction in the transmit power of transmitters which facilitate wireless transmissions,
leading to a reduction in interference levels as well as decreasing exposure to
electromagnetic emissions. Alternatively, the reduction in overall pathloss can be
exploited to improve the received signal quality at the receiver without an increase in
the overall radiated transmission power required to convey the signal.
Multi-hop systems are suitable for use with multi-carrier transmission. In a multi-carrier
transmission system, such as FDM (frequency division multiplex), OFDM (orthogonal
frequency division multiplex) or DMT (discrete multi-tone), a single data stream is
modulated onto N parallel sub-carriers, each sub-carrier signal having its own
frequency range. This allows the total bandwidth (i.e. the amount of data to be sent in
a given time interval) to be divided over a plurality of sub-carriers thereby increasing
the duration of each data symbol. Since each sub-carrier has a lower information rate,
multi-carrier systems benefit from enhanced immunity to channel induced distortion
compared with single carrier systems. This is made possible by ensuring that the
transmission rate and hence bandwidth of each subcarrier is less than the coherence
bandwidth of the channel. As a result, the channel distortion experienced on a signal
subcarrier is frequency independent and can hence be corrected by a simple phase
and amplitude correction factor. Thus the channel distortion correction entity within a
multicarrier receiver can be of significantly lower complexity of its counterpart within a
single carrier receiver when the system bandwidth is in excess of the coherence
bandwidth of the channel.
Orthogonal frequency division multiplexing (OFDM) is a modulation technique that is
based on FDM. An OFDM system uses a plurality of sub-carrier frequencies which are
orthogonal in a mathematical sense so that the sub-carriers' spectra may overlap
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without interference due to the fact they are mutually independent. The orthogonality
of OFDM systems removes the need for guard band frequencies and thereby increases
the spectral efficiency of the system. OFDM has been proposed and adopted for many
wireless systems. It is currently used in Asymmetric Digital Subscriber Line (ADSL)
connections, in some wireless LAN applications (such as WiFi devices based on the
IEEE802.11a/g standard), and in wireless MAN applications such as WiMAX (based on
the IEEE 802.16 standard). OFDM is often used in conjunction with channel coding, an
error correction technique, to create coded orthogonal FDM or COFDM. COFDM is
now widely used in digital telecommunications systems to improve the performance of
an OFDM based system in a multipath environment where variations in the channel
distortion can be seen across both subcarriers in the frequency domain and symbols in
the time domain. The system has found use in video and audio broadcasting, such as
DVB and DAB, as well as certain types of computer networking technology.
In an OFDM system, a block of N modulated parallel data source signals is mapped to
N orthogonal parallel sub-carriers by using an Inverse Discrete or Fast Fourier
Transform algorithm (IDFT/IFFT) to form a signal known as an "OFDM symbol" in the
time domain at the transmitter. Thus, an "OFDM symbol" is the composite signal of all
N sub-carrier signals. An OFDM symbol can be represented mathematically as:

where A/ is the sub-carrier separation in Hz, Ts = 1/Df is symbol time interval in
seconds, and cn are the modulated source signals. The sub-carrier vector in (1) onto
which each of the source signals is modulated c e Cn, c = (c0, C1..CN-1) is a vector of N
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constellation symbols from a finite constellation. At the receiver, the received time-
domain signal is transformed back to frequency domain by applying Discrete Fourier
Transform (DFT) or Fast Fourier Transform (FFT) algorithm.
OFDMA (Orthogonal Frequency Division Multiple Access) is a multiple access variant
of OFDM. It works by assigning a subset of sub-carriers, to an individual user. This
allows simultaneous transmission from several users leading to better spectral
efficiency. However, there is still the issue of allowing bi-directional communication,
that is, in the uplink and download directions, without interference.
In order to enable bi-directional communication between two nodes, two well known
different approaches exist for duplexing the two (forward or download and reverse or
uplink) communication links to overcome the physical limitation that a device cannot
simultaneously transmit and receive on the same resource medium. The first,
frequency division duplexing (FDD), involves operating the two links simultaneously but
on different frequency bands by subdividing the transmission medium into two distinct
bands, one for forward link and the other for reverse link communications. The second,
time division duplexing (TDD), involves operating the two links on the same frequency
band, but subdividing the access to the medium in time so that only the forward or the
reverse link will be utilizing the medium at any one point in time. Both approaches
(TDD & FDD) have their relative merits and are both well used techniques for single
hop wired and wireless communication systems. For example the IEEE802.16
standard incorporates both an FDD and TDD mode.
As an example, Figure 8 illustrates the single hop TDD frame structure used in the
OFDMA physical layer mode of the IEEE802.16 standard (WiMAX).
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Each frame is divided into DL and UL subframes, each being a discrete transmission
interval. They are separated by Transmit/Receive and Receive/Transmit Transition
Guard interval (TTG and RTG respectively). Each DL subframe starts with a preamble
followed by the Frame Control Header (FCH), the DL-MAP, and the UL-MAP.
The FCH contains the DL Frame Prefix (DLFP) to specify the burst profile and the
length of the DL-MAP. The DLFP is a data structure transmitted at the beginning of
each frame and contains information regarding the current frame; it is mapped to the
FCH.
Simultaneous DL allocations can be broadcast, multicast and unicast and they can also
include an allocation for another BS rather than a serving BS. Simultaneous ULs can
be data allocations and ranging or bandwidth requests.
GB 0616477.6, GB 0616481.8 and GB 0616479.2 describe interrelated inventions
proposed by the present inventors relating to communication techniques. The entire
contents of each of these applications is incorporated herein by way of reference
thereto and copies of each of these applications are filed herewith.
In order to enable bi-directional communication between two nodes, two well known
different approaches exist for duplexing the two (forward and reverse) communication
links to overcome the physical limitation that a device cannot simultaneously transmit
and receive on the same resource medium. The first, frequency division duplexing,
involves operating the two links simultaneously but on different frequency bands by
subdividing the transmission medium into two distinct bands, one for forward link and
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the other for reverse link communications. The second, time division duplexing,
involves operating the two links on the same frequency band, but subdividing the
access to the medium in time so that only the forward or the reverse link will be utilizing
the medium at any one point in time.
As an example, Figure 8 illustrates the single hop TDD frame structure used in the
OFDMA physical layer mode of the IEEE802.16 standard.
Both approaches (TDD & FDD) have their relative merits and are both well used
techniques for single hop wired and wireless communication systems. For example the
IEEE802.16 standard incorporates both an FDD and TDD mode.
However, when a node is required to support two independent links to two different
nodes, e.g. a relay station communicating with a basestation and a mobile, the existing
TDD or FDD frame structures require some modification in order to make realization of
the relay practical. Numerous proposals have recently been made that provide
solutions to this problem. However, one underlying issue with any proposal that
involves synchronous BS and RS operation (i.e. aligned frame start time) is how to
control the receive to transmit transition point in the RS and also how to prevent extra
Tx/Rx transitions in a frame.
The invention is defined in the independent claims, to which reference should now be
made. Advantageous embodiments are set out in the sub claims.
Preferred features of the present invention will now be described, purely by way of
example, with reference to the accompanying drawings, in which:-
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Figure 1 shows a frame structure;
Figure 2a shows a beyond three-hop frame structure (with internal subdivision);
Figure 2b shows a preferred detailed frame structure for three-hop;
Figure 3 shows a beyond two-hop frame structure (extra transition);
Figure 4 shows a relay link interval;
Figure 5a shows an RP position determination algorithm;
Figure 5b shows an RP position determination algorithm;
Figure 6 shows a simple two-hop wireless communication system;
Figure 7 shows applications for relay stations; and
Figure 8 shows an example TDD frame structure from OFDMA physical layer of the
IEEE802.16 standard.
Frame Structure Description
The first part of the solution according to invention embodiments is to use a modified
frame structure at the BS and RS, as shown in Figure 1.
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This frame structure provides an optimal and scalable solution. In the case of two hop
relaying, it requires subdivision of the subframes into only two zone or transmission
intervals and does not require any extra Tx/Rx transitions at a device than that used in
a single hop system. The first zone in the DL is BS-MS or RS-MS communications.
The second zone is used for BS-RS communications. Whilst in-frame relaying on the
DL is not supported, it could be possible to perform UL in-frame relaying. The benefits
in this embodiment are due to the fact that the transition from transmit to receive is at
the end of the DL subframe, i.e. putting the BS to RS communication at the end of the
subframe, and doing the reverse in the uplink, the number of rx/tx transitions is not
increased.
The solution is scalable to three hop relaying without the need for increasing the
number of transmit to/from receive transitions. However, this will require subdivision of
the subframes into three transmission intervals or zones, as shown in Figure 2a. Note
that Figure 2a shows at least four hop relaying because an extra relay link interval is
provided in the downlink subframe for RS2 to an RS3. If three-hop relaying only were
required, RS2 would have no relay link in the downlink subframe and its access length
would be identical in length to that of RS1. Figure 2b shows a preferred detailed frame
structure for three-hop communication.
It is possible to use this structure to support beyond three hop relaying, and there are
two approaches to facilitating this. The first would be to allow an extra Tx/Rx transition
in the DL subframe and place another relay link interval after the reception operation at
RS2. The alternative is to utilise some of the RS2-MS transmission interval to provide
the relay link interval, effectively increasing the number of zones or intervals in the
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subframe (see Figure 2a). The advantage of this latter over the former being that the
number of Rx/Tx transitions is not increased, the disadvantage is that radio resource at
RS2 is reduced for the RS2-MS communications. The former solution is illustrated in
Figure 3.
Note that the MS ranging, fast-feedback channel and ACK channel transmission can
occur anywhere within the interval, however it is beneficial to place this at the front of
the interval in order to provide this information to the receiver as early as possible.
Preferred details of the transmission within the relay link interval are shown in Figure 4.
The main benefit of this proposal for the relay link interval is that it can essentially be
the same as the access link interval in terms of structure. It is possible to make the
supported signalling, the same, plus some enhanced messages to support the RS
functionality, or alternatively only support a subset of all messages across this link plus
the enhancements. This enables the RS modem to be very similar in design to the MS
modem reducing development cost and time due to being able to reuse much of the
modem required for an MS. The details of a RM (relay midamble) are included in GB
0616474.3 and in agent reference P107330GB00 filed by the same applicant, on the
same date as the present application. Also, a proposed modification to the method for
conveying CQI values in a CQICH (CQI channel) is provided in agent reference
P107331GB00, filed on the same date as the present application, by the same
applicant. These three applications are incorporated by reference.
Relay station operation
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In the first instance when the RS connects to the BS it uses the preamble (P) to locate
the frame start and synchronise to the BS. The BS then signals to the RS through a
broadcast message (FCH/MAP) where the RM is located or will be located if this is the
first RS connecting to the BS in the frame, if RM transmission is to be supported. If RM
is not used by the BS then instead it signals where the FCH/MAP message will be
located in the relay link interval. The RS can then stop receiving the preamble and
FCH/MAP in access link interval and start transmitting its own preamble (P) and
FCH/MAP to be received by the MS or other RS wishing to connect to the network
through this RS. This transition from use of the relay to access link involves in the
frame before transition is complete receiving the information on both links, the
FCH/MAP information in the access link telling the relay where the FCH/MAP
information is in the relay link. Then FCH/MAP information in the relay link then tells
the RS where it will find the relay link in the following DL and UL subframe. The BS (or
RS) then optionally broadcasts the RM symbol that, as described in P107330GB00,
can be used for the connected RS to maintain synchronisation, following this it will
send control information, similar to the FCH & MAP message in the relay link interval,
to the RS followed by data. Part of this FCH/MAP message in the relay link, which is
broadcast to all RSs, will indicate where the relay link interval will be located in the
subsequent frame. Therefore, an RS can track where the relay link interval will move
to. Once the RS begins broadcast of the preamble in the access link interval is in now
fully operational and ready to support connection of devices to it (ie. MS or further RS).
In order to make this relay link interval start information robust in nature when
broadcast in either the FCH/MAP in the access or relay link interval, it is an absolute
value that indicates the number of symbols after the preamble transmission (P) that the
relay link interval starts. This then allows the RS to know when to transition from
receive to transmit.
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Should an RS not be able to receive the relay link FCH/MAP in one frame then it can
recover operation in the subsequent frame by scanning for the RM, or by receiving the
information in the FCH/MAP message on the access link to find the current start point
of the relay specific part of the frame and not transmitting a MAP message or data. As
the RS will have no new data, due to loss of the RFCH/RMAP, the fact it does not
transmit any data in the next frame should not compound the impact of the loss of
RMAP any further.
Method for determining location of relay link in the DL/UL subframe
The ability to change the transition point at an RS can be exploited by the radio
resource management entity. By monitoring the overall QoS provided across the
various links, it can determine how to partition the resource between the various
transmitting entities (i.e. BS and RSs) and by adjusting the start point of the relay link
interval, control the amount of the frame available to the BS for RS/MS and the RS for
RS/MS communication.
For example, consider the simple case of a BS, an RS and a number of MSs
connected directly and through the RS to the BS. If it is found that the QoS for the
directly connected MSs is lower than that of the relayed MSs, then more transmission
resource can be allocated to the BS-MS transmission by moving the relay link interval
start point to later in the frame, enabling more resource for BS MAP and BS-MS data
transmission. However, if the QoS on the BS-RS link is suffering, then the relay link
start point can be moved earlier in the frame.
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However, advancing the relay link transmission interval must always be offset against
potentially limiting the QoS on the RS-MS link. This is because as the capacity
increases on the BS-RS link, then so can the capacity on the RS-MS link, however
there will come a point when further increase in capacity on the BS-RS link will start to
reduce capacity on the RS-MS link due to the increasing size of the BS-RS interval
causing a shrinking in the RS-MS interval. Therefore, a simple algorithm to apply is
that, if in advancing start point of the relay link, it is found no benefit is given to the
connections served across the RS link then no further advancements of the relay link
should be made as it is likely that the RS-MS link is becoming limited in capacity due to
the increase in size. Figure 5a outlines the proposed algorithm and Figure 5b shows
the proposed algorithm in a preferred embodiment including a relay preamble.
The other check is the difference between the end of the RS-MS and start of the BS-
RS region, once they are adjacent then it is not worth advancing the relay link further.
This would require the reporting of the size of the BS-RS and RS-MS region to the
resource management entity and using this to derive the block status.
A further alternative approach to the block approach would be for the RS to report to
the BS (or other RS) the status of its DL usage (this could take many forms, one
example could be maximum possible RP advance by measuring the difference
between the end of the frame and the current RP position). The BS or RS could then
use this information to determine the maximum advancement possible in relay link start
position in the case an advancement is required.
A similar approach can be used on the UL to determine how to select the relative size
for the MS-BS and RS-BS intervals.
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Summary of benefits
In summary the benefits of this proposal are:
o Provides an optimal solution for providing a two-hop BS/RS synchronised
frame structure requiring no extra Rx/Tx transitions beyond that required for
a single hop device and division of a subframe into only two transmission
intervals or zones.
o Solution is extendable to three hop relaying with no further Tx/Rx
transitions and division of the frame into three transmission intervals.
o Solution is extendable beyond three hops by introducing one more Rx/Tx
transition per subframe, or by further division into increasing number of
transmission intervals, depending on which solution fits best with the
operational requirements.
o Provides a robust signalling mechanism for allowing variation in the relay
midamble positioning in the frame
o Provides a mechanism for determining the optimum position for the relay
midamble and overall dimensioning of the transmission intervals, with a
number of variants for controlling the issue of relay link start point
advancement and potential reduction, rather than improvement in
performance.
Embodiments of the present invention may be implemented in hardware, or as
software modules running on one or more processors, or on a combination thereof.
That is, those skilled in the art will appreciate that a microprocessor or digital signal
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processor (DSP) may be used in practice to implement some or all of the functionality
of a transmitter embodying the present invention. The invention may also be embodied
as one or more device or apparatus programs (e.g. computer programs and computer
program products) for carrying out part or all of any of the methods described herein.
Such programs embodying the present invention may be stored on computer-readable
media, or could, for example, be in the form of one or more signals. Such signals may
be data signals downloadable from an Internet website, or provided on a carrier signal,
or in any other form.
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Possible application of the frame structure to IEEE802.16: Frame Structure
contribution
This contribution (which has been changed for the purposes of this patent application
only in terms of the figure numbering and position) contains a technical proposal for a
modified frame structure that enables communications to occur between an MR-BS,
RS and SS. It requires no changes to the existing SS as defined in the IEEE Std.
802.16 and minimal changes to the existing BS. The frame structure is optimized for
two-hop relaying and is extendible to support multihop relaying. The contribution also
defines two new MAP lEs to support operation and a new SBC related TLV.
Introduction
In order to facilitate the introduction of non-transparent relays (i.e. RS that broadcasts
its own preamble and other control messages) operating in the TDD mode of the
OFDMA-PHY, modification to the current text in the standard is required to: define
frame structure that supports multihop relaying; rules of operation in terms of RS
transmission and reception intervals; and also the rules that the RS and MR-BS must
follow in order to allow for turn-around in the RS and SS transceivers.
This contribution introduces a frame structure that is an extension to the existing TDD
mode of the OFDMA-PHY. It enables BS and RS frame synchronous operation and
also supports preamble, FCH and MAP transmission from an RS.
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Whilst the frame structures introduced do require changes to the existing BS
specification, they do not require any changes to the MS/SS as described in IEEE Std.
802.16. Also the frame structure is designed to provide an optimal solution for two-hop
relaying that minimizes the number of changes required at the BS. It also enables the
RS to reuse many of the standards features developed for the BS and SS, only
requiring two new MAP lE's and one TLV to support the modified frame structure.
Proposed Frame Structure
The current TDD frame structure divides the frame into two subframes for downlink and
uplink transmission. In this proposal, a simple extension to the frame structure is
proposed to enable relaying that involves defining the existence of one or more relay
link transmission and reception intervals in the MR-BS DL and UL subframes,
respectively, to facilitate BS-RS communication. For beyond two-hop relaying, it is also
possible to define a further relay link transmission and reception interval using two
different approaches to facilitate RS-RS relaying.
Overview
The proposed frame structure for two-hop relaying is illustrated in Figure 1. The
access link interval at the BS and RS require no changes to the frame structure in IEEE
Std. 802.16 to define them. The new relay link (R-Link) interval does require new text
to define its structure and also methods for allocating a R-Link interval.
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Figure 2 illustrates the composition of the R-Link interval. The first symbol is optionally
used for a relay midamble transmission (see [1] for further details) that can be used by
the RS when operational as it cannot receive the preamble at the frame start. The first
mandatory part of the R-Link interval is the FCH and MAP transmission, followed by
optional data burst transmission. The structure of the FCH and MAP messages are
unchanged from those defined in IEEE Std. 802.16 as used on the access link interval.
The only change is that the MAP lEs supported on this link could be a combination of a
subset of those supported on the access link and some new messages required for
optimizing communications on the R-Link. The set of MAP IE messages supported on
the R-Link are FFS, and at the moment this proposal provides no restriction assuming
that full support of existing lEs is provided. Such discussion is out of scope of this
contribution that focuses solely on frame structure definition.
The only changes required to lEs defined in IEEE Std. 802.16 are an extra IE for use in
the DL-MAP and UL-MAP to indicate where the relay link interval starts at a particular
transmitter. These lEs can also be used in the DL-MAP and UL-MAP in the relay
interval to indicate the location of the relay link interval in the next frame thus allowing
the higher layers to control the relative amount of resource allocated to the access and
relay links. The proposed lEs are shown in detail in the text proposal, in short they
allow the transmitter to define the end of the R-Link interval and also enable indication
of the DIUC used to convey the FCH and MAP messages.
If the RS does not successfully receive the MAP information in the relay link interval in
any one frame, it can refer back to the MAP in the access link to find the location again,
resulting in minimal impact on performance in future frames.
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The two alternative methods for supporting beyond two hop relaying are shown in
Figures 2a and 3.
Both extensions involve further subdivision of the access link interval at the RS to
enable RS to RS communication. In the first technique, the access link is further
subdivided for each additional hop. The second technique involves just one
subdivision of the access link interval with multi-hopping being supported by alternating
the usage of the two R-link intervals within the DL & UL subframes between
transmission and reception.
As a result, in this proposed method the BS and the SS still obey the same frame
structure as defined in IEEE 802.16-2004. Within the DL subframe, the RS may
operate in both transmit and receive modes at different intervals to receive
communications directed in a forward direction from a BS or RS and transmit signals to
other RS or SS in a forward direction. Likewise, in the UL subframe, the RS may
operate in both transmit and receive modes at different intervals to receive
communications directed in a reverse direction from a SS or RS and transmit signals to
other RS or BS in a reverse direction. However, the RS will never be required to
perform simultaneous transmission and reception. Every time the RS transitions
between transmit and receive a transition gap must be allowed for.
Finally, the process of RS network entry when utilizing this frame structure is described
in [2].
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Advantages of the proposal
The proposed frame structure ensures that the frame start times at the BS and RSs are
synchronized. By operating in a time synchronized mode (i.e. transmitting 0b01 or
0b10 in the PHY Profile ID in the MOB_NBR-ADV message) it ensures that in the
single frequency network case the boosted preamble transmissions do not cause
interference with data transmissions, and in the case of time/frequency synchronization
enables support of macro-diversity based communications such as Multi-BS-MBS and
optimized handover. Through the allocation of different segments to the RSs during
network entry [2] it is possible to minimize the interference between broadcast
messages when using a segmented PUSC zone at the start of the frames. Thus for
the SS point-of-view the composite network formed by BS and RSs looks just like a
standard IEEE Std. 802.16 network.
This frame structure enables relaying with only a single frame latency on the DL and
minimizes the number of transmit/receive transitions at the RS, requiring no extra
transitions for two-hop relaying due to the ordering in time of the access link and relay
link intervals. Whilst it could be possible to devise frame structures that theoretically
enable in-frame relaying on the DL, it is considered that the processing time
requirements would impose significant burden on the RS transceiver. This is because
within the period of less than the DL subframe the RS would have to process the
control and data transmission on the access link and construct the control and data
transmission for the relay downlink. Based on the typical TDD realizations this would
provide processing time of the much less than 1ms for the RS to perform such
operations.
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However, the proposed frame structure would enable the RS to perform fast relaying
on the UL (i.e. within the same subframe) and this may be feasible to implement for the
control related messages such as those on the ACK and Fastfeedback channels where
special modulation techniques are used to facilitate fast processing at the receiver.
For three or more hop relaying two variants exist, as described. The first is beneficial
in that it does not require further transceiver transitions, however it requires subdivision
of the DL and UL subframes, such that the available resource for the access link
decreases with increasing hop number. Therefore, this solution is not suitable for large
number of hops. The second is beneficial in that only requires one extra relay link
interval in the DL and UL subframe, however it does require further transceiver
transitions, and hence transition gaps.
Finally, a further benefit is that the RS is the same as the BS from the point of
transmission on the access link. Further, the RS is very similar to the SS on the relay
link, from the point-of-view of the BS. Therefore, all of the existing messages and
information elements defined for the access link can be reused on the relay link.
Conclusion
This proposal provides a simple extension to the existing frame structure defined in
IEEE Std. 802.16 that enables support for non-transparent relaying. It provides an
optimal solution for the two-hop case and is extendible to support multihop relaying. In
order to support this frame structure only two new MAP lEs are required along with one
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TLV. This enables reuse of much of the features already defined for the BS and SS for
the purposes of defining the operation of the RS.
Proposed text changes
Insert the following text at the end of the subclause 6.3.7.2.
If the BS supports multihop relay then the DL and UL subframes shall be subdivided
into a number of transmission intervals to define the time in the subframe that the MR-
BS and RS can expect to be either operating in transmit or receive mode. The ordering
of the different intervals is defined in the OFDMA PHY specific section and the duration
of each of these intervals within the subframe is controlled in the higher layers within
the system.
Change subclause 6.3.7.3 as indicated:
6.3.7.3 DL-MAP
The DL-MAP message defines the usage of the dowlink intervals on the access and
relay links for a burst mode PHY.
Change subclause 6.3.7.4 as indicated:
6.3.7.4 UL-MAP
The UL-MAP message defines the uplink usage on the access and relay links in terms
of the offset of the burst relative to the Allocation Start Time (units PHY-specific).
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Insert a new subclause 8.4.4.2.1.
8.4.4.2.1 TDD frame structure extension for MR
When implementing a TDD system that supports multihop relaying, the frame structure
is built from RS transmissions as well as MR-BS and SS transmissions. In the DL
transmission period the BS and RS may transmit and in the UL transmission period the
SS and RS may transmit.
The OFDMA frame may include one or more R-Link transmission and reception
intervals and the RS may perform both transmission and reception in one subframe. In
general the access link interval shall precede the R-Link interval(s). For two-hop
relaying the DL subframe consists of a DL access link interval followed by one R-DL
interval. The UL subframe consists of an access link interval followed by one R-UL
interval. The details of the R-Link interval are provided later in this section. Figure 1
illustrates the frame structure for the two-hop case.
For the case of more than two hop relaying one extra R-Link interval may be utilized in
the DL and UL subframes at an RS, prior to the R-Link intervals illustrated in Figure 1.
Two different options are available for facilitating more than two hop relaying. The first
is illustrated in Figure 2a and involves using part of the access link to provide an R-Link
when an RS connects to the BS or RS that is not already communicating with another
RS.
The second frame structure option for more than two-hop relaying is illustrated in
Figure 3. It involves two R-Link intervals in both the DL and UL subframes that
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alternate between transmission and reception with increasing number of hops from the
BS.
The frame start time at the BS and RSs shall be synchronized within the timing
tolerance of 1/8 of the CP.
Allowances shall be made by an RSTTG and RSRTG in between transmit and receive
periods to allow the RS to turn around. The capabilities RSTTG and RSRTG will be
provided by the RS during RS network entry (see 11.8.3.7.20).
When the RS transmission and reception operation is not controlled by the RS,
information shall not be transmitted to an RS later than (RSRTG+RTD) before an RS
transmit allocation, and information shall not be transmitted to it earlier than (RSTTG-
RTD) after the end of the an RS transmit allocation, where RTD denotes the round-trip-
delay between the transmitter and the RS.
The RS shall make allowances for the subscriber station by an SSRTG and SSTTG.
The capabilities SSRTG and SSTTG will be acquired by the RS during SS network
entry.
The RS shall not transmit to an SS later than (SSRTG+RTD) before its scheduled
uplink allocation, and shall not transmit downlink information to it earlier than (SSTTG-
RTD) after the end of its scheduled uplink allocation, where RTD denotes the RS to SS
round trip delay.
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The RS shall transmit a preamble signal, FCH and MAP at the start of the DL subframe
on the access link. In order to facilitate the reception of control related information from
the MR-BS, the MR-BS shall make use of the R-Link transmission interval that is
arranged to occur after the RS has completed transmission of the access link to
optionally transmit a MR midamble followed by a mandatory FCH. The FCH contains
the DL Frame Prefix described in Section 8.4.4.3, and specifies the length of the DL-
MAP message that immediately follows the DL Frame Prefix and the coding used for
the DL-MAP message. The FCH and MAP messages in the R-Link interval shall
transmitted in a PUSC zone using the DIUC indicated in the DL-MAP IE that defined
the R-Link interval. The structure of the R-DL interval is illustrated in Figure 4.
The existence of a MR midamble and the start position of the R-DL transmission
interval shall be signaled in the MR_DL_Allocation IE. This message shall also
indicate the DIUC to be used for the FCH and MAP messages and indicates the
duration of the R-DL interval. Once an R-DL transmission interval is defined, the start
position and duration can be changed at any time by altering the values in the
MR_DL_Allocation_IE. A similar MR_UL_Allocation_IE shall be used in the UL-MAP to
define the R-UL reception interval. The MR_DL_Allocation_IE and
MR_UL_Allocation_IE may also be used in the DL-MAP and UL-MAP messages
respectively on the R-DL to indicated the location of the R-Link intervals in the DL and
UL subframes in the next frame.
An RS shall be capable of receiving control information on the R-Link that may impose
restrictions on the resource usage on the access link to prevent the RS performing
resource allocation at certain intervals in time.
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Change the items in Table 277a in Section 8.4.5.3.2.1 as indicated:
09 MR_DL_Allocation_IE
09-0A Reserved
Insert new subclause 8.4.5.3.28:
8.4.5.3.28 MR_DL_Allocation_IE
In the DL-MAP on the access link, an MR-BS or RS may transmit DIUC = 15 with the
MR_DL_Allocation_IE() to indicate the location of the R-DL interval in the DL subframe
as well as whether an MR midamble is present at the start of this interval. The usage
of the of the interval is described by the FCH and DL-MAP located following the MR
midamble in the R-DL transmission interval. In the DL-MAP on the R-Link, an MR-BS
or RS may transmit DIUC = 15 with the MR_DL_Allocation_IE() to indicate the location
of the R-DL transmission interval in the next frame.

Table 286aa - MR DL Allocation
Syntax Size Notes
MR_DL_Allocation_ IE(){
Extended DIUC 4 bits MR_DL_Allocation_IE = 0x09
Length 4 bits
MR midamble present 1 bit 0b0 = No midamble
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0b1 = Midamble is first symbol in the allocation.
R-DL duration present 1 bit ObO = No duration field present, R-DL extends to theend of the subframe0b1 = Duration field is present, R-DL defined by thisIE has a defined duration
FCH and MAP DIUC 4 bits DIUC used to transmit the FCH and MAP messageson the R-Link.
R-DL OFDMA symbol offset 8 bits Location of the R-DL interval relative to the framestart.
if (R-DL duration present = 1) {
R-DL duration 8 bits Duration of the R-DL interval in symbols.
}
}
Change the items in Table 290a in Section 8.4.5.4.4.1 as indicated:
OB MR_UL_Allocation_IE
OBC ... 0F Reserved
Insert new subclause 8.4.5.3.28:
8.4.5.3.29 MR_UL_Allocation_IE
In the UL-MAP on the access link, an MR-BS or RS may transmit UIUC = 15 with the
MR_UL_Allocation_IE() to indicate the location of the R-UL interval in the UL subframe.
The usage of this interval is described by the UL-MAP that follows the DL-MAP in the
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R-DL interval. In the UL-MAP on the R-Link, an MR-BS or RS may transmit UIUC = 15
with the MR_UL_Allocation_IE() to indicate the location of the R-UL receive interval in
the next frame.

Table 286ab - MR UL Allocation
Syntax Size Notes
MRJJL_Allocation_IE(){
Extended UIUC 4 bits MR_UL_Allocation_IE = 0x0B
Length 4 bits
R-UL duration present 1 bit 0b0 = No duration field present; R-UL extendsto the end of the subframe.0b1 = Duration field is present; R-UL definedby this IE has a defined duration.
OFDMA symbol offset 8 bits -
if (R-UL duration present = 1) {
R-UL duration 8 bits Duration of the R-UL interval in symbols.
}
Insert new subclause 11.8.3.7.20:
11.8.3.7.20 RS transition gaps

Type Length Value Scope
TBD 1 Bits #0-3: RSTTG (OFDMA symbols) SBC-REQ
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Bits #4-8: RSRTG (OFDMA symbols) SBC-RSP
References
[1] Hart, M. et al., "Relay midamble", IEEE C802.16j-06/144, IEEE 802.16 meeting
#46, Dallas, November 2006.
[2] Hart, M. et al., "Network entry procedure for non-transparent relay station", IEEE
C802.16j-06/143, IEEE 802.16 meeting #46, Dallas, November 2006.
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CLAIMS
1. A transmission method for use in a multi-hop wireless communication system, the
system comprising:
a source apparatus, a destination apparatus and one or more intermediate
apparatuses, said source apparatus being operable to transmit along a series of links
forming a communication path extending from the source apparatus to the destination
apparatus via the or each intermediate apparatus, and the or each intermediate
apparatus being operable to receive from a previous apparatus along the path and to
transmit to a subsequent apparatus along the path, the system having access to a
time-frequency format for use in assigning available transmission frequency bandwidth
during a discrete transmission interval, said format defining a plurality of transmission
windows within such an interval, each window occupying a part of that interval and
having a frequency bandwidth profile within said available transmission frequency
bandwidth over its part of that interval, each said window being assignable for such a
transmission interval to one or more of said apparatuses for use in transmission, the
transmission windows including an initial control window for control information
transmission, and a relay window for transmission by the source apparatus to the sole
intermediate apparatus or to at least one of the intermediate apparatuses, the relay
window being defined as the last window in the discrete transmission interval
assignable to the source apparatus for transmission, and the method comprising:
employing said format for such a transmission interval to assign the control
window to the source apparatus and to the or each intermediate apparatus for control
information transmission; and to assign the relay window to the source apparatus for
data transmission to the sole intermediate apparatus or to a particular one of said
intermediate apparatuses; so that at least one window between the control window and
the relay window can be assigned to the sole intermediate apparatus or to the
particular intermediate apparatus for data transmission; and
transmitting in the transmission interval.
2. The transmission method according to claim 1, wherein the format further defines
an intermediate window between the control window and the relay window, and the
method further comprises:
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employing said format for the transmission interval to assign the intermediate
window to the particular or sole intermediate apparatus for data transmission.
3. The transmission method according to claim 1 or 2, wherein the system
comprises at least a further destination apparatus, the format additionally defining a
source access window between the control window and the relay window for
transmission to such a further destination apparatus,
further comprising assigning the source access window to said source apparatus
to allow transmission of data directly to such a further destination apparatus along a
corresponding single link forming a direct communication path.
4. The transmission method according to claims 2 and 3, wherein the source
access window encompasses the intermediate window.
5. The transmission method according to any of claims 2 to 4, wherein the control
window, source access window and relay window together occupy the whole or
substantially the whole of a transmission interval.
6. The transmission method according to any of claims 2 to 5, wherein the system
comprises a single intermediate apparatus and the intermediate window is for
transmission to the destination apparatus.
7. The transmission method according to any of claims 2 to 5, wherein the system
comprises at least two said intermediate apparatuses and the format defines two
constituent intermediate windows forming the intermediate window: an intermediate link
window for transmission from the particular intermediate apparatus to the subsequent
intermediate apparatus along the communication path and an intermediate access
window for transmission from the subsequent intermediate apparatus to the destination
apparatus, the method further comprising:
employing said format for the transmission interval to assign the intermediate
access and intermediate link windows to the particular and subsequent intermediate
apparatuses for data transmission.
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8. The transmission method according to claim 8, wherein the system comprises at
least a further destination apparatus and the intermediate access window is also for
transmission from the particular intermediate apparatus to a further destination
apparatus.
9. The transmission method according to claim 7 or 8, wherein the system
comprises at least three said intermediate apparatuses, the particular and subsequent
intermediate apparatuses being the first and second intermediate apparatuses along
the communication path, the intermediate access window encompassing a further
constituent intermediate access window and a further constituent intermediate link
window both for transmission by the third intermediate apparatus in the
communications path; the method comprising:
employing said format to assign the constituent intermediate windows to the
intermediate apparatuses for data transmission.
10. The transmission method according to claim 7 or 8, wherein the system
comprises at least three said intermediate apparatuses, the particular and subsequent
intermediate apparatuses being the first and second intermediate apparatuses along
the communication path and the format further defines an extra window after the
intermediate window for the second intermediate apparatus to transmit to the third
intermediate apparatus along the communication path; the method further comprising:
employing said format to assign the extra transmission window to the second
intermediate apparatus.
11. The transmission method according to claim 10, wherein the system comprises at
least four said intermediate apparatuses, the method further comprising employing said
format to assign the intermediate link window to the first and third intermediate
apparatuses and assign the extra window to the second and fourth intermediate
apparatuses.
12. The transmission method according to claim 10 or 11, wherein the relay window
encompasses the extra window.
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34
13. The transmission method according to claim 2 or any claim dependent thereon,
wherein each window assigned to an intermediate apparatus comprises at least two
component transmission windows, one of those component transmission windows
being for transmission of intermediate apparatus control information, and one of those
component transmission windows being for transmission of data.
14. The transmission method according to claim 13, wherein each window assigned
to an intermediate apparatus comprises three component transmission windows, one
of those component transmission windows being for transmission of a transmission
introduction sequence for that intermediate apparatus.
15. The transmission method according to claim 13 or 14, wherein the component
transmission window for transmission of intermediate apparatus control information
indicates format information relating to the time position of the intermediate apparatus
control information or the time position of the transmission introduction sequence
respectively in a subsequent transmission interval.
16. The transmission method according to claim 13, 14, or 15, wherein the
component transmission window for transmission of intermediate apparatus control
information indicates format information relating to encoding and/or modulation of the
intermediate apparatus control information and/or transmission introduction sequence
in a subsequent transmission interval.
17. The transmission method according to any of the preceding claims, wherein the
control window comprises at least two component windows, one of those component
windows being for transmission of a preamble and another of those component
windows being for transmission of other control information including format
information.
18. The transmission method according to claim 17 when dependent on claim 13 or
14, wherein the format information relates to the time position of the intermediate
apparatus control information or the time position of transmission introduction
sequence respectively in the transmission interval.
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19. The transmission method according to claim 17 or 18 when dependent on claim
13 or 14, wherein the format information relates to encoding and/or modulation of the
intermediate apparatus control information and/or transmission introduction sequence
in the transmission interval.
20. The transmission method according to claim 3 or any claim dependent thereon,
wherein transmission time available in the format is shared between the source access
window and the relay window, further comprising, prior to assigning windows for
transmission, monitoring the quality of service provided by the source access and relay
windows and adjusting the time position of a division between the source access and
relay window interval parts accordingly.
21. The transmission method according to claim 20, further comprising, after
adjusting the division position, checking whether the adjustment has improved quality
of service in the window having the enlarged interval part and blocking further
adjustment in that direction if there has been no such improvement.
22. The transmission method according to claim 21, further comprising unblocking
the further adjustment if the division is subsequently moved in the other direction.
23. The transmission method according to any of the preceding claims, wherein the
frequency bandwidth profiles of at least two of said transmission windows encompass a
common part of the available transmission frequency bandwidth.
24. The transmission method according to any of the preceding claims, wherein the
frequency bandwidth profiles of at least two said transmission windows extend over
substantially the entire transmission frequency bandwidth for the respective interval
parts.
25. The transmission method according to any preceding claim, comprising
employing a space division multiple access technique in one or more of said
transmission windows of said transmission interval(s), as the case may be.
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26. The transmission method according to any preceding claim, wherein the time-
frequency format is a format for a downlink or uplink sub-frame in a time-division-
duplex communication system.
27. The transmission method according to any preceding claim, wherein said system
is an OFDM or OFDMA system, and wherein the time-frequency format is a format for
an OFDM or OFDMA downlink or uplink sub-frame of an OFDM or OFDMA time-
division-duplex frame.
28. The transmission method according to any preceding claim, wherein each said
discrete transmission interval is a sub-frame period.
29. The transmission method according to any preceding claim, wherein each said
transmission window comprises a region in an OFDM or OFDMA frame structure.
30. The transmission method according to any preceding claim, wherein each said
transmission window comprises a zone in an OFDM or OFDMA frame structure.
31. The transmission method according to any preceding claim, wherein said source
apparatus is a base station.
32. The transmission method according to any preceding claim, wherein said source
apparatus is a user terminal.
33. The transmission method according to any preceding claim, wherein the or each
destination apparatus is a base station.
34. The transmission method according to any preceding claim, wherein the or each
destination apparatus is a user terminal.
35. The transmission method according to any preceding claim, wherein the or each
said intermediate apparatus is a relay station.
36. A multi-hop wireless communication system, the system comprising:
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37
a source apparatus, a destination apparatus and one or more intermediate
apparatuses, said source apparatus being operable to transmit along a series of links
forming a communication path extending from the source apparatus to the destination
apparatus via the or each intermediate apparatus, and the or each intermediate
apparatus being operable to receive from a previous apparatus along the path and to
transmit to a subsequent apparatus along the path;
format-access means operable to access a time-frequency format for use in
assigning available transmission frequency bandwidth during a discrete transmission
interval, said format defining a plurality of transmission windows within such an interval,
each window occupying a part of that interval and having a frequency bandwidth profile
within said available transmission frequency bandwidth over its part of that interval,
each said window being assignable for such a transmission interval to at least one of
said apparatuses for use in transmission, the transmission windows including an initial
control window for control information transmission, and a relay window for
transmission by the source apparatus to the sole intermediate apparatus or to at least
one of said intermediate apparatuses, the relay window being defined as the last
window in the discrete transmission interval assignable to the source apparatus for
transmission;
assignment means operable to employ said format for such a transmission
interval to assign the control window to the source apparatus and to the or each
intermediate apparatus for control information transmission; and to assign the relay
window to the source apparatus for data transmission to the sole intermediate
apparatus or to a particular one of said intermediate apparatuses; so that at least one
window between the control window and the relay window can be assigned to the sole
intermediate apparatus or to the particular intermediate apparatus for data
transmission; and
transmission means operable to transmit in the transmission interval.
37. A suite of computer programs which, when executed on computing devices of a
multi-hop wireless communication system, causes the system to carry out a
transmission method, the system comprising a source apparatus, a destination
apparatus and one or more intermediate apparatuses, said source apparatus being
operable to transmit along a series of links forming a communication path extending
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38
from the source apparatus to the destination apparatus via the or each intermediate
apparatus, and the or each intermediate apparatus being operable to receive from a
previous apparatus along the path and to transmit to a subsequent apparatus along the
path, the system having access to a time-frequency format for use in assigning
available transmission frequency bandwidth during a discrete transmission interval,
said format defining a plurality of transmission windows within such an interval, each
window occupying a part of that interval and having a frequency bandwidth profile
within said available transmission frequency bandwidth over its part of that interval,
each said window being assignable for such a transmission interval to at least one of
said apparatuses for use in transmission, the transmission windows including an initial
control window for control information transmission, and a relay window for
transmission by the source apparatus to the sole intermediate apparatus or to at least
one of said intermediate apparatuses, the relay window being defined as the last
window in the discrete transmission interval assignable to the source apparatus for
transmission, and the method comprising:
employing said format for such a transmission interval to assign the control
window to the source apparatus and to the or each intermediate apparatus for control
information transmission; and to assign the relay window to the source apparatus for
data transmission to the sole intermediate apparatus or to a particular one of said
intermediate apparatuses; so that at least one window between the control window and
the relay window can be assigned to the sole intermediate apparatus or to the
particular intermediate apparatus for data transmission; and
transmitting in the transmission interval.

P107297Foreign
Tx/Rx FRAME

A transmission method for use in a multi-hop wireless communication system, the
system comprising a source apparatus, a destination apparatus and one or more
intermediate apparatuses, said source apparatus being operable to transmit along a
series of links forming a communication path extending from the source apparatus to
the destination apparatus via the or each intermediate apparatus, and the or each
intermediate apparatus being operable to receive from a previous apparatus along the
path and to transmit to a subsequent apparatus along the path, the system having
access to a time-frequency format for use in assigning available transmission
frequency bandwidth during a discrete transmission interval, said format defining a
plurality of transmission windows within such an interval, each window occupying a part
of that interval and having a frequency bandwidth profile within said available
transmission frequency bandwidth over its part of that interval, each said window being
assignable for such a transmission interval to one or more of said apparatuses for use
in transmission, the transmission windows including an initial control window for control
information transmission, and a relay window for transmission by the source apparatus
to at least one of said intermediate apparatuses, the relay window being defined as the
last window in the discrete transmission interval assignable to the source apparatus for
transmission, and the method comprising: employing said format for such a
transmission interval to assign the control window to the source apparatus and to the or
each intermediate apparatus for control information transmission; and to assign the
relay window to the source apparatus for data transmission to a particular one of said
intermediate apparatuses; so that at least one window between the preamble window
and the relay window can be assigned to the particular intermediate apparatus for data
transmission; and transmitting in the transmission interval.