COMMUNICATION SYSTEMS
This is a Divisional Specification drawn fi-om the Original Indian Patent Application No. 1775/CHE/2007 filed on W' August 2007.
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 3 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.
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 4 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 4 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 4 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 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 + \On\ogd (A)
Where d (metres) is the transmitter-receiver separation, b(db) and n are the
pathloss parameters and the absolute pathloss is given by / = 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 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 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 IEEE802.1 la/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/A/ 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 = (co, CI..CN.I) is a vector of N 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 simuhaneous 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 5 illustrates the single hop TDD frame structure used in the OFDMA physical layer mode of the IEEE802.16 standard (WiMAX). 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.
This Patent Application is related to co-pending Indian Patent Applications (i)1774/CHE/2007 dated 10-08-07 having Priority Application GB0616477.6 (ii)1775/CHE/2007 dated 10-08-07 having Priority Application GB0616481.8 (iii)1778/CHE/2007 dated 10-08-07 having Priority Application GB0616482.6 (iv)1779/CHE/2007 dated 10-08-07 having Priority Application GB0616479.2 (v)1777/CHE/2007 dated 10-08-07 having Priority Application GB0610474.3
This Indian Patent Application is also related to the corresponding co-pending UK Patent Applications (i) GB0616478.4 dated 18-08-06 (ii) GB0616471.9 dated 18-08-06 (iii) GB0616472.7 dated 18-08-06 (iv) GB0616475.0 dated 18-08-06 (v)

GB0616476.8 dated 18-08-06. Copies of these UK Patent Applications are filed herewith.
These co-pending Patent Applications describe interrelated inventions proposed by the present inventors relating to communication techniques.
Accordingly, the present invention provides 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 information 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 information from a previous apparatus along the path and to transmit the received information 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 different 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 of said apparatuses for use in transmission, the method comprising: employing said format for one or more such transmission intervals to transmit data and control information together along at least two consecutive said links as a set of successive transmission signals, link by link, each said signal being transmitted in an available transmission window of said interval(s) and at least two of said signals being transmitted during the same said transmission interval such that said information is transmitted along said consecutive links in fewer transmission intervals than said number of consecutive links.
In an embodiment of the present invention, wherein the frequency bandwidth profiles of at least two of said transmission windows encompass a common part of the available transmission frequency bandwidth.
In another embodiment of the present invention, 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.

It is also an embodiment of the present invention, wherein the transmission method for use in a multi-hop wireless communication system further comprising the steps of; prior to said transmission, employing said format to assign a particular transmission window of a particular transmission interval to a first said apparatus along said consecutive links, for transmission of the data and control information to a second said apparatus along said consecutive links being a subsequent said apparatus one link along the path from the first apparatus, and to assign a subsequent transmission window of the particular transmission interval to the second apparatus for transmission of the data and control information to a third said apparatus along said consecutive links being a subsequent said apparatus one link along the path from the second apparatus. In another embodiment of the present invention, wherein said system comprises at least two said intermediate apparatuses, and wherein said particular transmission interval is a first transmission interval and transmission method further comprising, prior to said transmission, employing said format to assign a particular transmission window of a second transmission interval subsequent to said first transmission interval to said third apparatus for transmission of the data and control information to a fourth said apparatus along said consecutive links being a subsequent said apparatus one link along the path from the third apparatus.
In yet another embodiment of the present invention, the transmission method wherein the system comprises at least three said intermediate apparatuses, the method further comprising, prior to said transmission, employing said format to assign a subsequent transmission window of the second transmission interval to the fourth apparatus for transmission of the data and control information to a fifth said apparatus along said consecutive links being a subsequent said apparatus one link along the path from the fourth apparatus.
In further embodiment of the present invention, wherein said particular and subsequent transmission windows of each of said first and/or second transmission intervals, as the case may be, are either side in time of a further transmission window of the transmission interval concerned.
It is also an embodiment of the present invention, wherein the method of particular and subsequent transmission windows of each of said first and/or second transmission intervals, as the case may be, are either side in time of a further transmission window of

the transmission interval concerned, said method further comprising; performing
processing in said second and/or fourth apparatus, as the case may be, during the part of
the particular transmission interval corresponding to the further transmission window
of the transmission interval concerned, so as to configure the information for
transmission in the subsequent transmission window of that transmission interval based
upon the information received in the particular transmission window of that
transmission interval.
In further embodiment of the present invention, wherein the or each particular or
subsequent transmission window comprises two component transmission windows, one
of those component transmission windows being for transmission of the control
information and the other one of those component transmission windows being for
transmission of the data information.
It is also an embodiment of the present invention wherein said communication path is
an indirect communication path, and wherein the system comprises at least a further
destination apparatus, and wherein said source apparatus or any said intermediate
apparatus is operable to transmit information directly to the or each further destination
apparatus along a corresponding single link forming a direct communication path.
In yet another embodiment of the present invention wherein a space division multiple
access technique in one or more of said transmission windows of said transmission
interval(s), as the case may be is employed.
In further embodiment of the present invention, wherein the time-frequency format is a
format for a downlink or uplink sub-frame in a time-division-duplex communication
system.
In another embodiment of the present invention, 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.
In yet another embodiment of the present invention, wherein each said discrete
transmission interval is a sub-frame period.
In yet another embodiment of the present invention, wherein each said transmission
window comprises a region in an OFDM or OFDMA frame structure.

It is also an embodiment of tlie present invention, wherein each said transmission
window comprises a zone in an OFDM or OFDMA frame structure.
In further embodiment of the present invention, wherein said source apparatus is a base
station.
It is also an embodiment of the present invention, wherein said source apparatus is a
user terminal.
In yet another embodiment of the present invention, wherein the or each destination
apparatus is a base station.
In further embodiment of the present invention, wherein the or each destination
apparatus is a user terminal.
It is also an embodiment of the present invention, wherein the or each said intermediate
apparatus is a relay station.
In the multi-hop wireless communication system of the present invention, the system
comprising; a source apparatus, a destination apparatus and one or more intermediate
apparatuses, said source apparatus being operable to transmit information 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 information from a previous apparatus
along the path and to transmit the received information 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 different 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 of said apparatuses for use in transmission; and transmission means operable to
employ said format for one or more such transmission intervals to transmit data and
control information together along at least two consecutive said links as a set of
successive transmission signals, link by link, transmitting each said signal in an
available transmission window of said interval(s) and transmitting at least two of said
signals during the same said transmission interval such that said information is

transmitted along said consecutive links in fewer transmission intervals than said number of consecutive links.
The present invention also provides 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 information 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 information from a previous apparatus along the path and to transmit the received information 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 different 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 of said apparatuses for use in transmission, the method comprising; employing said format for one or more such transmission intervals to transmit data and control information together along at least two consecutive said links as a set of successive transmission signals, link by link, each said signal being transmitted in an available transmission window of said interval(s) and at least two of said signals being transmitted during the same said transmission interval such that said information is transmitted along said consecutive links in fewer transmission intervals than said number of consecutive links. The present invention further provides an intermediate apparatus for use in a multi-hop wireless communication system, the system further comprising a source apparatus, and a destination apparatus, said source apparatus being operable to transmit information along a series of links forming a communication path extending from the source apparatus to the destination apparatus via the intermediate apparatus, and the intermediate apparatus being operable to receive information from a previous apparatus along the path and to transmit the received information to a subsequent apparatus along the path the intermediate apparatus comprising; 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 different 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 of said apparatuses for use in transmission; and transceiver means operable to employ said format for one such transmission interval to receive data and control information together in an available transmission window of said interval and to transmit said data and control information together in a later available transmission window during the same said transmission interval such that said data and control information passes along two said consecutive links in a single transmission interval.
In an embodiment of the present invention, which is a method for use in an intermediate apparatus of a multi-hop wireless communication system, the system further comprising a source apparatus, and a destination apparatus, said source apparatus being operable to transmit information along a series of links forming a communication path extending from the source apparatus to the destination apparatus via the intermediate apparatus, and the intermediate apparatus being operable to receive information from a previous apparatus along the path and to transmit the received information to a subsequent apparatus along the path, the method comprising; accessing 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 different 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 of said apparatuses for use in transmission; and employing said format for one such transmission interval to receive data and control information together in an available transmission window of said interval and to transmit said data and control information together in a later available transmission window during the same said transmission interval such that said data and control information passes along two said consecutive links in a single transmission interval.

The present invention further provides a computer program which, when executed on a computing device of an intermediate apparatus in a multi-hop wireless communication system, causes the intermediate apparatus to carry out a transmission method, the system further comprising a source apparatus, and a destination apparatus, said source apparatus being operable to transmit information along a series of links forming a communication path extending from the source apparatus to the destination apparatus via the intermediate apparatus, and the intermediate apparatus being operable to receive information from a previous apparatus along the path and to transmit the received information to a subsequent apparatus along the path, the method comprising; accessing 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 different 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 of said apparatuses for use in transmission; and employing said format for one such transmission interval to receive data and control information together in an available transmission window of said interval and to transmit said data and control information together in a later available transmission window during the same said transmission interval such that said data and control information passes along two said consecutive links in a single transmission interval.
Preferred features of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which:-
Figure 1 shows a frame structure;
Figure 2 shows node activity within each zone;
Figure 3 shows a two-hop system;
Figure 4 shows applications of relaying; and
Figure 5 shows a TDD frame structure used in OFDMA.
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.

Embodiments of this invention provide a frame structure for a multihop communication system that is an extension of the standard TDD frame structure (see IEEE802.16 standard for an example) that provides support for any number of hops in the system. The proposed frame structure has numerous benefits, as described later in this description.
The proposed frame structure makes the assumption that the MS cannot reliably receive the control information originating from the head node or that a network that incorporates relays that will perform some degree of local connection management and/or medium allocation management. This local management could be based on decisions being made at the RS independent of all other nodes in the communication system or network, or with some degree of co-operation between the various nodes that incorporate some control functionality. Further, it could be that whilst the RS has the capability to transmit control information, that all management decisions are made at a node other than the RS from which the signals are transmitted.
It is also assumed that the modified frame TDD structure should provide support for legacy mobile devices that have no knowledge of a relay station such that they can operate within the communication system or network.
The proposed generic TDD frame structure is shown in Figure 1.
It is composed of a number of transmission and reception zones for both the downlink and uplink sub-frames. The zone types are either:
B Broadcast of control related information such as: synchronization sequences, commands, information and details of the structure or layout of the frame.
C Dedicated control information that is transmitted in a non-broadcast zone (i.e. either to individual or a group of receivers)
T Dedicated user-data transmission
The 9 different zones are described in Table 1, below.



within eacii of tiie zones described in Table 1.
Whilst Figure 2 only illustrates the case of a BS-RS1-RS2-RS3-MS link (i.e. a four hop link), it is possible to use the frame structure to support any number of hops. As shown for the case of RS3, the generalisation is that last relay in the hop (RSn) is not required to transmit the RP or RSn to RSn+1 zones in the DL sub-frame or receive the RSn+1 to RSn in the uplink. Due to the fact that the RS transmits the MAP information after reception of control information from the previous transmitter (i.e. BS or RS), two hop relaying will always incur at least an extra frame latency.
However, due to the fact it is possible to relay control information within a frame from RS to RS, if more than two-hop relaying is undertaken then the proposed frame structure keeps the relaying induced latency to a minimum, where the latency is given by:

In order to enable implementation, the frame structure may also need to incorporate some gap times to allow a node to turn around (i.e. change from transmitting to receiving mode, or vice versa). In this case, some of the zones may also

incorporate a gap region or a gap zone maybe inserted in-between two adjacent zones that require the change in operation mode of the node.
It is further preferably that in such a case that a BS is transmitting information to the RS in the MAP zone that it schedules transmission to the RS first, before transmission to any MS. The BS could then indicate in the MAP zone when there is no more information pending for the RS so that it can stop receiving whilst the BS transmits MAP information to other receivers and use this time as an opportunity for turn around.
In summary the benefits of invention embodiments are:
o Enables the construction of relays that incorporate some degree of local
management of medium access o Maximises spectral efficiency by making sure that the BS does not have any
time in the frame when it is idle o Minimal latency: two or three-hop relaying incurs 1 frame latency; 4 or 5 hop relaying incurs a 2 frame latency, 6 or 7 hop relaying incurs a 3 frame latency, etc. o Enables the relaying enabled system to provide support to a legacy single-hop TDD user o The possibility to further improve spectral efficiency through using SDMA based techniques to enable the same transmission resource (frequency & time) to be used between the BS and the RSs and MSs within a cell. o Is extendable to any number of hops o Defines a special synchronization interval to enable synchronization of the
relay with other relays or base stations
o Enables an RS to transmit a standard preamble or synchronization sequence
(similar to that transmitted by a BS) that a legacy (non-relay aware) user can
decode.
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
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.

We claim:
1. A communication method used in a multi-hop radio communication system
including a base station apparatus, intermediate apparatuses and a user equipment, said
communication method comprising:
providing a first transmission window and a second transmission window in a radio frame;
transmitting data from an intermediate apparatus which is an odd number of hops from said base station apparatus using said second transmission window and transmitting data from an intermediate apparatus which is an even number of hops from said base station apparatus using said first transmission window.
2. The communication method according to claim 1, wherein said user equipment receives data from an intermediate apparatus corresponding to the last hop.
3. The communication method according to claim 1 or 2, wherein said base station apparatus transmits data to an intermediate apparatus in the first hop of a downlink transmission using said first transmission window.
4. The communication method according to any of the preceding claims, wherein said user equipment transmits data to an intermediate apparatus in the first hop of an uplink transmission.
5. The communication method according to any of the preceding claims, wherein said base station apparatus receives data from an intermediate apparatus using said first transmission window in the last hop of an uplink transmission.
6. The communication method according to any of the preceding claims, wherein said base station apparatus and said intermediate apparatuses except for an intermediate apparatus corresponding to the last hop of a downlink transmission transmit preamble, frame structure information or relay amble using corresponding transmission windows.
7. The communication method according to any of the preceding claims, wherein an intermediate apparatus which is the furthest intermediate apparatus from the base station

apparatus receives a downlink transmission using said first transmission window or said second transmission window but does not use said first transmission window and second transmission window for transmission to said user equipment.
8. The communication method according to any of the preceding claims, wherein an
intermediate apparatus which is the furthest intermediate apparatus from the base station
apparatus does not transmit any relay amble.
9. A multi-hop radio communication system comprising:
a base station apparatus;
intermediate apparatuses;
a user equipment,
wherein a first transmission window and a second transmission window are provided in a radio frame and an intermediate apparatus, which is an odd number of hops from said base station apparatus is configured to transmit data using said second transmission window and an intermediate apparatus, which is an even number of hops from said base station apparatus is configured to transmit data using said first transmission window.
10. A base station apparatus used in a multi-hop radio communication system
including intermediate apparatuses, said base station apparatus comprising:
a transmitting unit configured to transmit data to an intermediate apparatus in a first hop using a first transmission window in a radio frame wherein an intermediate apparatus, which is an odd number of hops from said base station apparatus, transmits data using a second transmission window in said radio frame and an intermediate apparatus, which is an even number of hops from said base station apparatus transmits data using said first transmission window in said radio frame.
11. An intermediate apparatus used in a multi-hop radio communication system
including intermediate apparatuses, said intermediate apparatus comprising:
a transmitting unit configured to transmit data using either a first transmission window or a second transmission window in a radio frame in accordance with a hop

number from a base station apparatus to said intermediate apparatus wherein an intermediate apparatus, which is an odd number of hops from said base station apparatus transmits data using said second transmission window in said radio frame and an intermediate apparatus, which is an even number of hops from said base station apparatus, transmits data using said first transmission window in said radio frame.
12. A user equipment used in a multi-hop radio communication system including intermediate apparatuses, said user equipment comprising:
a receiving unit configured to receive data from either an intermediate apparatus which is an odd number of hops from a base station and transmits data to the next intermediate apparatus using a second transmission window in a radio frame or an intermediate apparatus which is an even number of hops from a base station and transmits data to the next intermediate using a first transmission window in said radio frame, the intermediate apparatus transmitting said data to be received by said receiving unit being the furthest intermediate apparatus from the base station and transmitting to the user equipment in a further transmission window of said radio frame.