Patent Publication Number: US-2007104223-A1

Title: Apparatus and method for supporting multiple links by grouping multiple hops in a multi-hop relay cellular network

Description:
PRIORITY  
      This application claims priority under 35 U.S.C. §119 to an application filed in the Korean Intellectual Property Office on Nov. 4, 2005 and assigned Serial No. 2005-105511 and an application filed in the Korean Intellectual Property Office on Jun. 2, 2006 and assigned Serial No. 2006-49692, the contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates generally to a multi-hop relay cellular network, and in particular, to an apparatus and method for configuring subframes by grouping multiple hops in a multi-hop relay cellular network.  
      2. Description of the Related Art  
      The most critical requirement for deployment of a 4 th  Generation (4G) mobile communication system recently being researched is to build a self-configurable wireless network. The self-configurable wireless network is a wireless network that is configured in an autonomous or distributed manner without control of a central system to provide mobile communication services. The 4G mobile communication system installs cells of very small radiuses for the purpose of enabling high-speed communications and accommodating a larger number of calls. As such, the use of conventional centralized wireless network design is not feasible. Rather, the wireless network should be built to be under distributed control and to actively cope with an environmental change like the addition of a new Base Station (BS). That&#39;s why the 4G mobile communication system requires a self-configurable wireless network configuration.  
      For real deployment of the self-configurable wireless network, techniques used for an ad hoc network should be introduced to the mobile communication system. A major example of these techniques is a multi-hop relay cellular network built by applying a multi-hop relay scheme used for the ad hoc network to a cellular network with fixed BSs.  
      In general, since a BS and a Mobile Station (MS) communicate with each other via a direct link in the cellular network, a highly reliable radio link can be established easily between them.  
      However, due to the fixedness of the BSs, the configuration of the wireless network is not flexible, making it difficult to provide an efficient service in a radio environment experiencing a fluctuating traffic distribution and a great change in the number of required calls.  
      These drawbacks can be overcome by a relay scheme for delivering data over multiple hops using a plurality of neighbor MSs or neighbor Relay Stations (RSs). The multi-hop relay scheme facilitates fast network reconfiguration adaptive to an environmental change and renders the overall wireless network operation efficient. Also, a radio channel in a better channel status can be provided to an MS by installing an RS between the BS and the MS and thus establishing a multi-hop relay path via the RS. What is better, since high-speed data channels can be provided to MSs in a shadowing area or an area where communications with the BS is unavailable, cell coverage is expanded.  
       FIG. 1  illustrates the configuration of a typical multi-hop relay cellular network.  
      Referring to  FIG. 1 , an MS  110  within the service area  101  of a BS  100  is connected to the BS  100  via a direct link. On the other hand, an MS  120 , which is located outside the service area  101  of the BS  100  and thus in a poor channel state, communicates with the BS  100  via a relay link of an RS  130 .  
      The BS  100  provides better-quality radio channels to the MSs  110  and  120  via the RS  130  when they communicate with the BS  100  but in a poor channel state as they are located at a boundary of the service area  101 .  
      Thus, the BS  100  can provide a high-speed data channel to the cell boundary area using a multi-hop relay scheme and thus expand its cell coverage. There are a BS-MS link, a BS-RS link and an RS-MS link in the cellular network.  
      The multi-hop relay scheme illustrated in  FIG. 1  enables establishment of multi-hop relay links by use of a plurality of RSs as illustrated in  FIG. 2 .  
       FIG. 2  illustrates the configuration of a typical multi-hop cellular network.  
      Referring to  FIG. 2 , a BS  201  establishes a communication link with an MS  219  by use of a plurality of RSs  211 ,  213 ,  215  and  217  in order to provide a service to the MS  219 . The RSs  211 ,  213 ,  215  and  217  operate in the manner illustrated in  FIG. 3 .  
       FIG. 3  illustrates multiple one-hop links in the typical multi-hop cellular network.  
      Referring to  FIG. 3 , a two-hop network is comprised of an (M−1)-hop RS  301 , an M-hop RS  303 , an M-hop MS  305 , an (M+1)-hop MS  307 , and an (M+1)-hop RS  309 .  
      The (M−1)-hop RS  301  establishes a communication link with the M-hop RS  303  or the M-hop MS  305 . The M-hop RS  303  establishes a communication link with the (M+1)-hop MS  307  or the (M+1)-hop RS  309 .  
      In the above manner, the communication link between the BS  201  and the MS  219  is extended to multiple hops.  
      To enable the MS with mobility to communicate with the multi-hop RSs as well as with the BS, resources (i.e. channels) available in the air interface should be dynamically distributed to each link across multiple hops. If the RSs are fixed, they can receive energy continuously. Yet, if the RSs support mobility, they use limited-resource batteries as their energy sources. For example, when laptop computers or Personal Digital Assistants (PDAs) move, supplying stable energy to them is difficult. In this context, efficient energy use or saving mechanisms are needed.  
      A frame structure configured to support the typical cellular network is illustrated in  FIG. 4 .  
       FIG. 4  illustrates the structure of a typical Time Division Duplexing (TDD) frame. The horizontal axis represents time and the vertical axis represents frequency.  
      Referring to  FIG. 4 , one TDD frame  400  is divided into a downlink subframe  411  and an uplink subframe  421 . The downlink subframe  411  includes a preamble signal for synchronization acquisition at MSs, control information with the position information of data allocated to downlink bursts, and the downlink bursts carrying the data to the MSs.  
      The uplink subframe  421  includes a BS ranging signal and uplink bursts carrying uplink data from a plurality of MSs.  
      A Transmit/Receive Transition Gap (TTG)  431  intervenes between the downlink subframe  411  and the uplink subframe  421  as a guard region to allow for BS transmission-reception mode transition. A Receive/Transmit Transition Gap (RTG)  441  intervenes between the uplink subframe and the downlink subframe to allow for BS reception-transmission mode transition.  
      To support the multi-hop relay scheme with the thus-configured TDD frame structure, the frame has to be reconfigured such that multiple one-hop links are distinguished by different time slots.  
       FIG. 5  illustrates a conventional subframe structure for a multi-hop link. The horizontal axis represents time and the vertical axis represents frequency.  
      Referring to  FIG. 5 , subframes for multiple one-hop links are defined in different time slots within one subframe. Specifically, different time slots are sequentially allocated to a subframe  501  for an (M−1) th  hop link, a subframe  503  for an M th  hop link, and a subframe  505  for an (M+1) th  hop link in the subframe. An RS transition gap intervenes between each one-hop link subframe pair. For example, the (M−1) th  hop link subframe  501  includes a link on which the (M− 1 )-hop RS  301  communicates with the M-hop RS  303  or the M-hop MS  305 . Also, the M th -hop link subframe  503  includes a link on which the M-hop RS  303  communicates with the (M+1)-hop MS  307  or the (M+1)-hop RS  309 . The M-hop RS  303  receives a signal from the (M−1)-hop RS  301  in the (M−1) th  hop link subframe  501  and sends a signal to the (M+1)-hop RS  307  or the (M+1)-hop MS  309  in the M th  hop link subframe  503 . That&#39;s why a transition gap  511  is required between the (M−1) th  hop link subframe  501  and the M th  hop link subframe  503 . Likewise, a transition gap  513  is provided between M th  hop link subframe  503  and (M+1) th  hop link subframe  505 , and transition gap  515  is provided between (M+1) th  hop link subframe  505  and (M+2) th  hop link subframe  507 .  
      As described above, when different time slots are sequentially allocated to one-hop links, a transition gap is required between adjacent one-hop link subframes in the multi-hop relay cellular network.  
      Generally, the TDD frame is short in length, taking into account feedback delay that significantly affects the performance of Transmit Control Protocol (TCP), throughput, Automatic Repeat reQuest/Hybrid Automatic Repeat reQuest (ARQ/HARQ), and closed loop power control. Therefore, the transition gap between adjacent one-hop links within the short frame adds significantly to overhead. Also, the division of one subframe into a plurality of time slots brings about overhead with respect to the granularity of resource allocation to each hop. As the duration of each time slot is decreased, link budget gain achieved by power concentration is reduced.  
     SUMMARY OF THE INVENTION  
      An object of the present invention is to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, an object of the present invention is to provide an apparatus and method for reducing transmission overhead in a multi-hop relay cellular network.  
      Another object of the present invention is to provide a method of configuring a frame by grouping multiple hops to reduce transmission overhead and an apparatus supporting the same in a multi-hop relay cellular network.  
      The above objects are achieved by providing an apparatus and method for configuring a subframe to support multiple links by grouping multiple hops in a multi-hop relay cellular network.  
      According to one aspect of the present invention, in a method of supporting multiple links by grouping multiple hops in a BS in a multi-hop relay cellular network, the BS collects information about RSs forming relay links to a destination and groups the relay links according to the collected RS information. The BS allocates different resources to the relay link groups and sends information about the allocated resources to the RSs.  
      According to another aspect of the present invention, in a method of configuring a subframe in a multi-hop relay cellular network, a subframe for an n th -hop link group is configured in a first period of the subframe, and a subframe for an (n+1) th -hop link group is configured in a second period of the subframe.  
      According to a further aspect of the present invention, in a method of configuring a subframe in a multi-hop relay cellular network, a subframe for a direct link of a BS is configured in a first period of the subframe. A subframe for an n th -hop link group is configured in a second period of the subframe. A subframe for an (n+1) th -hop link group is configured in a third period of the subframe.  
      According to still another aspect of the present invention, in a method of configuring a superframe in a multi-hop relay cellular network, a subframe for an n th -hop link group is configured in an i th  frame and a subframe for an (n+1) th -hop link group is configured in an (i+1) th  frame.  
      According to yet another aspect of the present invention, in a method of configuring a superframe in a multi-hop relay cellular network, a subframe for a direct link of a BS is configured in an i th  frame, a subframe for an n th -hop link group is configured in an (i+1) th  frame, and a subframe for an (n+1) th -hop link group is configured in an (i+2) th  frame.  
      According to yet further aspect of the present invention, in a frame configuring apparatus in a multi-hop relay cellular network, a timing controller provides a timing signal for transmission of each subframe according to a frame configuration method. A frame generator generates subframes for the predetermined hop link groups according to the timing signal and constructs a frame with the subframe. A resource scheduler maps the subframes to resources allocated to a burst for the hop link groups. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
       FIG. 1  illustrates the configuration of a typical multi-hop relay cellular network;  
       FIG. 2  illustrates the configuration of a typical cellular network with multiple hops;  
       FIG. 3  illustrates multiple one-hop links in the typical multi-hop cellular network;  
       FIG. 4  illustrates the structure of a typical TDD frame;  
       FIG. 5  illustrates a conventional subframe structure for a multi-hop link;  
       FIG. 6  illustrates a subframe structure supporting groups of multiple hops in a multi-hop relay cellular network according to the present invention;  
       FIG. 7  illustrates signal flows and interference paths in the multi-hop relay cellular network according to the present invention;  
       FIG. 8  illustrates signal flows and interference paths in the multi-hop relay cellular network according to the present invention;  
       FIG. 9  illustrates resource allocation to a subframe for a group of multiple hops in a multi-hop relay scheme according to the present invention;  
       FIG. 10  illustrates a multi-hop link structure in the multi-hop relay cellular network scheme according to the present invention;  
       FIG. 11  illustrates a subframe structure supporting groups of multiple hops according to the present invention;  
       FIG. 12  illustrates a subframe structure supporting groups of multiple hops according to the present invention;  
       FIG. 13  is a block diagram of a BS apparatus for grouping multiple hops according to the present invention;  
       FIG. 14  is a flowchart illustrating a BS operation for grouping multiple hops in the multi-hop relay cellular network according to the present invention;  
       FIG. 15  illustrates a subframe structure simultaneously supporting a BS-MS link with grouped hop links and a BS-MS link being a direct link according to the present invention;  
       FIG. 16  illustrates a superframe structure in which a hop link group is provided on a frame basis according to the present invention; and  
       FIG. 17  illustrates a superframe structure for communication links that a BS and an RS provide in a two-hop Broadband Wireless Access (BWA) system according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.  
      The present invention provides a method of configuring subframes by grouping multiple hops and an apparatus supporting the same in a multi-hop relay cellular network. Specifically, subframes are configured for two groups of multiple hops in the multi-hop relay cellular network.  
      While the following description is made in the context of a Time Division Duplexing-Orthogonal Frequency Division Multiplexing (TDD-OFDM) wireless communication system by way of example, it is to be appreciated that the present invention is applicable to any other multiple access scheme.  
       FIG. 6  illustrates a subframe structure supporting multiple links by grouping multiple hops in a multi-hop relay cellular network according to the present invention. The horizontal axis represents time and the vertical axis represents frequency.  
      Referring to  FIG. 6 , one subframe is composed of a subframe  601  for a group of odd-numbered hop links and a subframe  603  for a group of even-numbered hop links. Since a communication system (e.g. an RS) at each hop is not affected by signals on links two hops earlier and two hops later, the multiple hops of the cellular network are grouped into an even-numbered hop link group and an odd-numbered hop link group (i.e. a two-hop earlier link group and a two-hop later link group) and subframes are configured for the two groups such that the links of the same hop link group send signals during the same period.  
      A single transition gap  605  intervenes between the subframe  601  for the odd-numbered hop link group and the subframe  603  for the even-numbered hop link group, thus decreasing transition gap-associated overhead, compared to the existence of a transition gap between every adjacent subframe for adjacent hops. Time slots are not divided for each hop in the subframe of each hop group. The resulting increase in the time lot allocated to one subframe solves the problem of data granularity overhead. Since the subframe  601  or the subframe  603  is configured for each hop, a longer time slot is given to the hop, compared to the subframes illustrated in  FIG. 5 . Therefore, the communication system at each hop occupies a narrower bandwidth and improves link budget with power concentration that a low-power communication system may achieve.  
      The multi-hop relay cellular network configures subframes for an odd-numbered hop link group and an even-numbered hop link group as illustrated in  FIG. 6 . If a direct link between a BS and an MS is established irrespective of the multi-hop relay link established via the RSs, both the direct link and the multi-hop relay link are provided between the BS and the MS as illustrated in  FIG. 15 . The multi-hop relay link includes the odd-numbered and even-numbered hop link groups.  
       FIG. 15  illustrates a subframe structure simultaneously supporting a BS-MS link with grouped hop links and a BS-MS link being a direct link according to the present invention.  
      Referring to  FIG. 15 , a subframe  1501  for an odd-numbered hop link group and a subframe  1511  for an even-numbered hop link group are configured for the multi-hop relay link established by the RSs. The subframes  1501  and  1511  include information about the direct BS-MS link. The subframes  1501  and  1511  and the direct BS-MS link are distinguished by different radio resources (e.g. time, frequency).  
      Aside from configuring the subframes separately for the odd-numbered and even-numbered hop link groups, it can be further contemplated that a frame is configured for each hop link group.  
       FIG. 16  illustrates a superframe structure in which a hop link group is provided on a frame basis according to the present invention.  
      Referring to  FIG. 16 , an (L−1) th  frame  1601  includes an odd-numbered hop link group (a (2n−1) th -hop link group) and the direct BS-MS link, and an L th  frame  1611  includes an even-numbered hop link group (a 2n th -hop link group) and the direct BS-MS link. An (L+1) th  frame  1621  includes an odd-numbered hop link group (a (2n−1) th -hop link group) and the direct BS-MS link.  
      In this way, the multi-hop relay cellular network expands to the superframe structure so as to carry out transmission from each hop group in one frame. One frame is composed of a downlink subframe and an uplink subframe which are consecutive in time. Considered independently of the multi-hop relay link, the direct BS-MS link is included in each frame. Yet, considered to be a one-hop link, the direct BS-MS link is included in the odd-numbered hop link group.  
      In the case of using a superframe as illustrated in  FIG. 16 , a BS and an RS provides communication links illustrated in  FIG. 17 .  
       FIG. 17  illustrates a superframe structure for communication links that a BS and an RS provide in a two-hop BWA system according to the present invention.  
      Referring to  FIG. 17 , the BS provides a direct link to an MS in each frame. Specifically, an (L−1) th  frame  1701  provides the direct BS-MS link and a BS-RS link and an L th  frame  1711  provides the direct BS-MS link. An (L+1) th  frame  1721  is similar to (L−1) th  frame  1701 .  
      On the other hand, the BS-RS link and an RS-MS link are separately provided so that the RS transmits and receives in Time Division Multiplexing (TDM).  
      For example, on the downlink, the RS receives data on the BS-RS link in the (L−1) th  frame  1701  and sends data to the MS on the RS-MS link in the L th  frame  1711 . When time division is considered on a frame basis, each communication link (e.g. the BS-RS link and the RS-MS link) includes the downlink and the uplink.  
      However, if signal transmission and reception are performed in subframes or super frames as illustrated in  FIGS. 6 and 15 , interference occurs as illustrated in  FIGS. 7 and 8 . The following description is made on the assumption of a two-hop link in  FIG. 7  and a 5-hop link in  FIG. 8 .  
       FIG. 7  illustrates signal flows and interference paths in the multi-hop relay cellular network according to the present invention.  
      Referring to  FIG. 7 , when a signal is sent from an (M−1) th  hop  701  to an M th  hop  703 , the signal transmission from an (M+1) th  hop  705  interferes with a receiver at the M th  hop  703  in a first period. Then when data is sent from the M th  hop  703  to the (M+1) th  hop  705 , the signal transmission from the M th  hop  703  interferes with the (M−1) th  hop  701 .  
       FIG. 8  illustrates signal flows and interference paths in the multi-hop relay cellular network according to the present invention.  
      Referring to  FIG. 8 , when signals are sent from RSs  801 ,  805  and  809  (RS 1 , RS 3 , and RS 5 ) of an odd-numbered hop link group to RSs  803 ,  807  and  811  (RS 2 , RS 4 , and RS 6 ) of an even-numbered hop link group on the same channel, they cause interference to RSs at hops other than destination hops. For example, if RS 3  sends a signal to RS 4 , the signal interferes with RS 2  and RS 6 .  
      As described above, when signals are sent and received on a hop link group basis, interference is produced by signals in the same hop link group. To reduce the interference, the subframe of the hop link group is configured as illustrated in  FIG. 9 .  
       FIG. 9  illustrates resource allocation to a subframe for a group of multiple hops in a multi-hop relay scheme according to the present invention.  
      Referring to  FIG. 9 , subframes for each hop link in a hop link group are divided into OFDM bursts and different orthogonal resources are allocated to the subframes in a subframe for the hop link group.  
      For an RS separated from a BS by multiple hops, a direct communication link may be required between the RS and the MS as illustrated in  FIG. 10 .  
       FIG. 10  illustrates a multi-hop link structure in the multi-hop relay cellular network scheme according to the present invention.  
      Referring to  FIG. 10 , RSs  1005  and  1007  or an MS  1009  separated from a BS  1001  by multiple hops may establish direct links as well as relay links with the BS  1001 .  
      To distinguish the direct links from the relay links, a frame is configured as illustrated in  FIG. 11 .  
       FIG. 11  illustrates a subframe structure supporting groups of multiple hops according to the present invention. Subframes for a direct link and a relay link are configured in one frame. The horizontal axis represents time and the vertical axis represents frequency.  
      Referring to  FIG. 11 , one frame is composed of a direct link subframe  1101 , a subframe  1103  for an odd-numbered hop link group, and a subframe  1105  for an even-numbered hop link group.  
      The frame allocates different time slots to the subframes  1101 ,  1103  and  1105  to distinguish the direct link from the relay link. For the relay link, multiple hops are grouped into the odd-numbered hop link group and the even-numbered hop link group (i.e. a two-hop earlier group and a two-hop later group) and the different subframes are configured for the hop link groups. Thus, signal transmission on the direct link and the relay link is performed in time division, not simultaneously. The subframe  1105  may be exchanged with the subframe  1103  in time slot position.  
      A transition gap  1107  intervenes between the subframes  1101  and  1103  and a transition gap  1109  intervenes between the subframes  1103  and  1105 .  
      In the illustrated case of  FIG. 11 , the multi-hop relay cellular network divides one frame into time slots and configures subframes for hop link groups and a subframe for a direct link using the time slots. Herein, it can be further contemplated that a superframe is configured in which the hop link group subframes and the direct link subframe occupy one or more frames.  
       FIG. 12  illustrates a subframe structure supporting groups of multiple hops according to the present invention. In the illustrated case of  FIG. 12 , the subframes for the direct link and the relay link occupy two frames.  
      Referring to  FIG. 12 , an i th  frame  1200  is composed of a direct link subframe  1201  and a subframe  1203  for an odd-numbered hop link group, and an (i+1) th  frame  1210  is composed of a direct link subframe  1211  and a subframe  1213  for an even-numbered hop link group.  
      A direct BS-MS link may be established independently of the multi-hop link established using RSs. The direct BS-MS link subframe may be included in either or both of the subframes  1203  and  1213 . Alternatively, the direct BS-MS link can be configured in a frame other than the two frames  1200  and  1210 .  
      In this subframe structure, a single transition gap is required in one subframe. The resulting decrease of the transition gap-associated overhead increases system capacity. In addition, since one subframe is divided into two time slots, data granularity decreases, compared to division of one subframe into more time slots. Thus spectrum efficiency is high. As a time slot occupied with the same amount of resources is lengthened, the frequency band that can be occupied is reduced. As a result, link budget is improved due to power concentration.  
      Now a description will be made of the structures of a BS apparatus and an RS apparatus for grouping multiple hops and configuring a frame for the hop link groups. Since the BS apparatus and the RS apparatus are identical in configuration, the BS apparatus will be described with reference to  FIG. 13 , by way of example.  
       FIG. 13  is a block diagram of the BS (RS) apparatus for grouping multiple hops for signal transmission according to the present invention.  
      Referring to  FIG. 13 , the BS includes a frame configurer  1301 , a timing controller  1303 , a resource scheduler  1305 , a modulator  1307 , a Digital-to-Analog Converter (DAC)  1309 , and a Radio Frequency (RF) processor  1311 .  
      The frame configurer  1301  generates a subframe with data received from an upper layer. For example, if a signal from the BS is sent on a direct link, the frame configurer  1301  configures a direct link subframe or frame as illustrated in  FIGS. 11, 12 ,  15  or  16 . On the other hand, if the signal is sent on a one-hop link, the frame configurer  1301  configures a subframe or frame for an odd-numbered hop link group as illustrated in  FIG. 6  or  FIG. 15 .  
      The frame configurer  1301  sends the subframe configured in accordance with a timing signal received form the timing controller  1303  to the RS or the MS.  
      The resource scheduler  1305  allocates subframes received from the frame configurer  1301  to bursts for the links of the subframes.  
      The modulator  1307  modulates the subframes allocated to the link bursts in a predetermined modulation scheme. The DAC  1309  converts the digital signal received from the modulator  1307  to an analog signal.  
      The RF processor  1311  upconverts the analog signal to an RF signal and transmits it through an antenna.  
      As to the RS apparatus, the frame configurer  1301  generates a subframe for a hop link group corresponding to the hop of the RS.  
      As described above, in order to configure subframes for an even-numbered hop link group and an odd-numbered hop link group separately, the BS sends resource allocation information required for data transmission from each RS to the RS by searching for a route to a destination in the procedure illustrated in  FIG. 14 .  
       FIG. 14  is a flowchart illustrating a BS operation for grouping multiple hops in the multi-hop relay cellular network according to the present invention.  
      Referring to  FIG. 14 , the BS collects information about RSs in order to establish a relay link to a destination (an MS) in the cellular network in step  1401 .  
      In steps  1403  and  1405 , the BS groups multiple hops into an odd-numbered hop group and an even-numbered hop group, respectively, based on the collected information.  
      The BS allocates time slots to the two hop groups in a subframe through the scheduler in step  1407 .  
      In step  1409 , the BS allocates burst-type resources to the RSs of the two hop groups according to the time slots allocated to the two hop groups. Information about the time slots allocated to each hop group is common control information. The common control information is sent from the BS and can be relayed via the RSs.  
      Then the BS ends the procedure.  
      While it has been described above that a frame or super-frame is so configured as to include subframes for an odd-numbered hop link group and an even-numbered hop link group, it can be further contemplated that the BS further configures a subframe for a direct link in addition to the subframes for the odd-numbered hop link group and the even-numbered hop link group.  
      In accordance with the present invention as described above, multiple hops are grouped and subframes are configured for the hop groups in a multi-hop relay cellular network. The resulting expansion of the coverage area of a BS and the resulting reduction of transition gap-overhead lead to an increase of system capacity and efficiency.  
      While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.