Abstract:
A method of providing uplink and downlink transmissions between a mobile terminal and a base station in a mobile communication system is provided. The method increases the flexibility and efficiency of a mobile communication system utilizing one or more relay entities and provides new frame structures to support legacy and new transmissions in a mobile communication system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Pursuant to 35 U.S.C. §120, this application claims the benefit of U.S. Provisional Application Ser. No. 61/020,689 filed on Jan. 11, 2008, the contents of which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to mobile communication systems, and particularly, to the use of an enhanced Time Division Duplex (“TDD”) frame structure capable of supporting both legacy and advanced frame structures. 
     DESCRIPTION OF THE RELATED ART 
     In communication systems utilizing a Time Division Duplex (“TDD”) scheme, the downlink (“DL”) transmission from a base station (also referred to in the art as “an access point”) to one or more mobile stations (are also referred to in the art as an “access device” or “access terminal”) and the uplink (“UL”) transmission from a mobile station to a base station are duplexed in the time domain. In the TDD scheme, the DL and UL transmissions are in the same frequency band. However, the TDD scheme can also be implemented using different frequency bands. 
     In the TDD scheme, one or more UL transmissions are initiated only after one or more DL transmissions are completed, and one or more DL transmissions are initiated only after one or more UL transmissions are completed. An example of a TDD transmission frame structure for mobile Worldwide Interoperability for Microwave Access (WiMAX) IEEE 802.16e is shown in  FIG. 1 . 
     With reference to transmission frame  101  in  FIG. 1 , the period between a DL transmission, such as DL transmission  102 , and a UL transmission, such as UL transmission  104 , within a single frame is a DL/UL switching point, such as DL/UL switching point  106 . In order to minimize the interference between a DL transmission from a base station of one cell and a UL transmission from a base station of a different cell, the DL/UL switching points of the base stations of the cells are typically synchronized. An example of such synchronization is shown in  FIG. 2 . 
       FIG. 2  shows “Cell  1 ,” which includes base station  210 , and “Cell  2 ,” which includes base station  214 . As also shown in  FIG. 2 , “Cell  1 ” has a communication range  208  and “Cell  2 ” has a communication range  212 . 
     In  FIG. 2 , base station  210  of “Cell  1 ” is configured to communicate with mobile station  216  via a sequence of frames, such as frame  220 , and base station  214  of “Cell  2 ” is configured to communicate with mobile station  218  via a sequence of frames, such as frame  222 . As shown in  FIG. 2 , the DL/UL switch point  224  in frame  220  of “Cell  1 ” and the DL/UL switch point  226  in frame  222  of “Cell  2 ” occur at the same time. Otherwise, the DL transmission of one cell, such as DL  228  of “Cell  1 ”, would affect the UL transmission of another cell, such as UL  230  of “Cell  2 .” 
     In designing a new communication system or standard, backward compatibility is critically important. One example is that two or more different systems or different types of signals are transmitted from one or multiple base stations in a communications system. An example of such a scenario is shown in  FIG. 3 . 
       FIG. 3  shows an exemplary frame structure  300  for accommodating a legacy system frame structure, as indicated by portions  332  and  334 , and a new advanced mode frame structure, as indicated by portions  336  and  338 . 
     As shown in  FIG. 3 , the frame structure  300  comprises 3 switching points, such as switching points  340 ,  342 , and  344 . One approach is to fix one of the switching points, such as switching point  342 , across the entire network. The other two switching points, such as switching points  340  and  344 , can be configured on a frame by frame basis. In the frame structure  300 , with respect to the legacy transmission, the DL transmission indicated by portion  332  is configured so as not to exceed the first switching point, that is, switching point  340 , and the UL transmission indicated by portion  334 , is configured so as not to begin before the last switching point, that is, switching point  344 . 
       FIG. 4  shows the compatibility of the frame structure  300  described above, with a legacy frame structure  400 . As show in  FIG. 4 , “Cell  1 ” can be configured to utilize frame structure  300  while “Cell  2 ” can be configured to utilize legacy frame structure  400 . Although the frame structure  300  and the legacy frame structure  400  may coexist in the same network, the abovementioned fixed switching point  342  for the entire network can limit the DL and UL transmission flexibility of the frame structure  300 . 
       FIG. 5  shows a mobile communication system  10  that includes a base station (“BS”)  12 , a relay station (“RS”)  14 , and one or more mobile stations (“MS”)  16 . 
     As shown in  FIG. 5 , RS  14  is configured to receive a downlink (DL) transmission  18  from BS  12  and an uplink (UL) transmission  20  from MS  16 . As also shown in  FIG. 5 , RS  14  is configured to encode the received DL transmission  18  and the UL transmission  20  by performing an EXCLUSIVE OR operation on the DL transmission  18  and the UL transmission  20  to generate a singe network-coded DL and UL transmission  22 . As further shown in  FIG. 5 , the RS  14  is configured to broadcast the network-coded DL and UL transmission  22  to the BS  12  and the MS  16 . 
     For example, as illustrated in  FIG. 6A , the mobile communication system  30  may include a base station (“BS”)  32 , a relay station (“RS”)  34 , a first mobile station (“MS 1 ”)  36   a  having transmission range  38 , a second mobile station (“MS 2 ”)  36   b  having a transmission range  40 , and a third mobile station (“MS 3 ”)  36   c  having a transmission range  42 . As shown in  FIG. 6A , each mobile station, such as MS 2   36   b , maintains a mobile station group (“MSG”) comprising any neighboring mobile stations that can be detected by the mobile station via the UL transmissions of the neighboring mobile stations. 
     For example, the MSG of MS 2   36   b  in  FIG. 6A  comprises MS 1   36   a , MS 2   36   b , and MS 3   36   c  because MS 2   36   b  is within the transmission range  38  of MS 1   36   a  and the transmission range  42  of MS 3   36   c , and therefore can detect the UL transmissions of MS 1   36   a  and MS 3   36   c . Each mobile station, such as MS 2   36   b , periodically reports its MSG to a base station, such as BS  32 . 
     The scheduling of uplink and downlink transmissions by a base station according to an MSG will now be discussed with reference to  FIG. 6B .  FIG. 6B  shows the mobile communication system  30  in  FIG. 6A , with MS 3   36   c  omitted in order to simplify the following discussion. 
     With reference to  FIG. 6B , the base station scheduler (not shown in  FIG. 6B ) of BS  32  pairs a transmission of a DL packet to MS 2   36   b , such as DL_MS 2   44 , and a UL packet from MS 1   36   a , such as UL_MS 1   46 , in the same frame since MS 1   36   a  is in the MSG of MS 2   36   b . It should be noted that MS 1   36   a  and MS 2   36   b  can be the same mobile station. 
     With reference to  FIG. 6C , the relay station  34  is configured to receive a transmission of a DL packet to MS 2   36   b  from BS  32  and a transmission of a UL packet from MS 1   36   a  to BS  32  and to encode the DL transmission and the UL transmission to generate a singe network-coded DL and UL transmission  48 . As shown in  FIG. 6C , the RS  34  is configured to multicast the network-coded DL and UL transmission  48  to the BS  32  and the MS 2   36   b.    
       FIG. 7  shows a relay station (“RS”), such as RS  34  in  FIGS. 6A through 6C , that provides cooperative relay support by re-encoding the packets in the UL and DL transmissions and transmitting the result of an EXCLSUIVE OR operation of the parity bits, instead of transmitting separate coded physical layer (“PHY”) packets. For example, as shown in  FIG. 7 , an RS decodes the first DL and UL subpackets and re-encodes both the DL and UL subpackets by performing an EXCLUSIVE OR operation on, for example, the second, third, or other subsequent subpacket of the first packet and, for example, the second, third, or other subsequent subpacket of the second packet. 
     A base station (“BS”), such as BS  32  in  FIGS. 6A through 6C , and a mobile station (“MS”), such as MS 1   36   a  in  FIGS. 6A through 6C , each use their own parity bits, which are not transmitted, to descramble the received parity bits and to decode the received packets. Therefore, the receiver, which can be the BS or the MS, combines the information from both the source, which can be the BS or the MS, and the RS after descrambling is performed in order to decode the packet, and to thereby reduce bandwidth consumption of the RS. 
     SUMMARY OF THE INVENTION 
     Features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     In one aspect of the invention, a method of providing uplink and downlink transmissions between a mobile terminal and a base station in a mobile communication system is provided. The method includes a relay entity of a first zone of the mobile communication system receiving an uplink transmission from at least one mobile station in the first zone and a downlink transmission from at least one base station in the first zone, the relay entity of the first zone broadcasting first information in the first zone, the first information comprising both the received uplink transmission and received downlink transmission from the first zone, wherein while the relay entity in the at least a first zone is broadcasting the first information, uplink and downlink transmissions are allowed only for good geometry mobile terminals in any communication zone of the mobile communication system in which the corresponding relay entity does not broadcast information. 
     It is contemplated that a relay entity of a second zone of the mobile communication system receiving an uplink transmission from at least one mobile station in the second zone and a downlink transmission from at least one base station in the second zone and the relay entity of the second zone broadcasting second information in the second zone, the second information comprising both the received uplink transmission and received downlink transmission from the second zone, wherein the broadcast of the second information is synchronized with the broadcast of the first information. 
     It is contemplated that the relay entity of the first zone broadcasts the first information during a predefined time period. 
     In another aspect of the invention, a method of transmitting uplink data bursts in a mobile communication system comprising a plurality of mobile terminals, at least a first of the plurality of mobile terminals operating according to a first communications standard and at least a second of the plurality of mobile terminals operating according to a second communications standard is provided. The method includes receiving first information indicating correspondence between the at least a first of the plurality of mobile terminals and information to be transmitted in at least a first uplink data burst and a correspondence between the at least a second of the plurality of mobile terminals and information to be transmitted in at least a second uplink data burst, and transmitting information in the at least first uplink data burst or the at least second uplink data burst according to the first information, wherein the at least first uplink data burst or the at least second uplink data burst comprises only information from the at least a second of the plurality of mobile terminals. 
     It is contemplated that the at least first uplink data burst comprises information from both the at least a first of the plurality of mobile terminals and the at least a second of the plurality of mobile terminals. 
     It is contemplated that the at least first uplink data burst is transmitted before the at least second uplink data burst. It is further contemplated that the at least second uplink data burst is transmitted before the at least first uplink data burst. It is still further contemplated that the at least first uplink data burst and the at least second uplink data burst are transmitted during the same time interval. 
     It is contemplated that the time period during which the at least first uplink data burst and the at least second uplink data burst are transmitted may be utilized by both the at least a first of the plurality of mobile terminals and the at least a second of the plurality of mobile terminals for providing information or making requests to the network. 
     The method can further include receiving second information identifying at least one point in time at which the at least first uplink data burst or the at least second uplink data burst should be transmitted. It is further contemplated that transmitting information in the at least first uplink data burst or the at least second uplink data burst comprises utilizing the first information to determine a start point of the at least first uplink data burst or the at least second uplink data burst. 
     In another aspect of the invention, a method of receiving downlink data bursts in a mobile communication system comprising a plurality of mobile terminals, at least a first of the plurality of mobile terminals operating according to a first communications standard and at least a second of the plurality of mobile terminals operating according to a second communications standard is provided. The method includes receiving first information indicating correspondence between the at least a first of the plurality of mobile terminals and information in at least a first downlink data burst and a correspondence between the at least a second of the plurality of mobile terminals and information in at least a second downlink data burst, receiving the at least first downlink data burst and the at least second downlink data burst, processing information in the at least first downlink data burst or the at least second downlink data burst according to the first information, wherein the at least first downlink data burst or the at least second downlink data burst comprises information that only the at least a second of the plurality of mobile terminals can process. 
     It is contemplated that the at least first downlink data burst comprises information that both the at least a first of the plurality of mobile terminals and the at least a second of the plurality of mobile terminals can process and the at least second downlink data burst comprises information that only the at least a second of the plurality of mobile terminals can process. 
     The method can further include receiving second information identifying at least one point in time at which the at least first downlink data burst or the at least second downlink data burst should be received. 
     It is contemplated that processing information in the at least first downlink data burst or the at least second downlink data burst comprises utilizing the first information to determine a start point of the at least first downlink data burst or the at least second downlink data burst. It is further contemplated that the at least first uplink data burst is received before the at least second uplink data burst. 
     In another aspect of the invention, a method of transmitting uplink data bursts in a mobile communication system comprising a plurality of mobile terminals, at least a first of the plurality of mobile terminals operating according to a first communications standard and at least a second of the plurality of mobile terminals operating according to a second communications standard is provided. The method includes receiving first information indicating correspondence between the at least a first of the plurality of mobile terminals and information to be transmitted in a first uplink data burst, receiving second information indicating correspondence between the at least a second of the plurality of mobile terminals and information to be transmitted in a second uplink data burst, and transmitting information in either the first uplink data burst or the second uplink data burst according to the first information or the second information, where the second uplink data burst comprises only information from the at least a second of the plurality of mobile terminals. 
     It is contemplated that the first uplink data burst is transmitted before the second uplink data burst. It is further contemplated that the second uplink data burst is transmitted before the first uplink data burst. It is still further contemplated that the first uplink data burst and the second uplink data burst are transmitted during the same time interval. 
     The method can further include receiving third information identifying at least one point in time at which the first uplink data burst or the second uplink data burst should be transmitted. 
     It is contemplated that transmitting information in either the first uplink data burst or the second uplink data burst comprises utilizing the first information to determine a start point of at least the first uplink data burst or the second uplink data burst. 
     It is contemplated that the time period during which the first uplink data burst and the second uplink data burst are transmitted may be utilized by both the at least a first of the plurality of mobile terminals and the at least a second of the plurality of mobile terminals for providing information or making requests to the network. 
     In another aspect of the invention, a method of receiving downlink data bursts in a mobile communication system comprising a plurality of mobile terminals, at least a first of the plurality of mobile terminals operating according to a first communications standard and at least a second of the plurality of mobile terminals operating according to a second communications standard is provided. The method includes receiving first information indicating correspondence between the at least a first of the plurality of mobile terminals and information in a first downlink data burst, receiving second information indicating correspondence between the at least a second of the plurality of mobile terminals and information in a second downlink data burst, receiving the first downlink data burst and the second data burst, and processing information in either the first downlink data burst or the second downlink data burst according to either the first information or the second information, wherein the second downlink data burst comprises information that only the at least a second of the plurality of mobile terminals can process. 
     It is contemplated that the first uplink data burst is received before the second uplink data burst. 
     The method can further include receiving third information identifying at least one point in time at which the first downlink data burst or the second downlink data burst should be received. It is contemplated that processing information in at least the first downlink data burst or the second downlink data burst comprises utilizing the first information to determine a start point of at least the first downlink data burst or the second downlink data burst. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     These and other embodiments will also become readily apparent to those skilled in the art from the following detailed description of the embodiments having reference to the attached figures, the invention not being limited to any particular embodiments disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. Features, elements, and aspects of the invention that are referenced by the same numerals in different figures represent the same, equivalent, or similar features, elements, or aspects in accordance with one or more embodiments. 
         FIG. 1  shows an example of a Time Division Duplex (“TDD”) transmission frame structure for mobile Worldwide Interoperability for Microwave Access (WiMAX) IEEE 802.16e. 
         FIG. 2  shows an example of synchronization of uplink and downlink switching points in a mobile communication system. 
         FIG. 3  shows a frame structure for accommodating a legacy system frame structure and a new advanced mode frame structure. 
         FIG. 4  shows the compatibility of the frame structure in  FIG. 3  with a legacy frame structure. 
         FIG. 5  shows an example of network coding in a mobile communication system. 
         FIG. 6A  shows a mobile communication system comprising a mobile station group. 
         FIG. 6B  shows a mobile communication system showing the scheduling of packets by a base station based on a mobile station group. 
         FIG. 6C  shows a mobile communication system comprising a relay station multicasting a network-coded sub-frame. 
         FIG. 7  shows the encoding of packets by a relay for providing cooperative relay support. 
         FIG. 8  shows a frame structure pattern in accordance with one embodiment of the present invention. 
         FIG. 9  shows an exemplary implementation of a frame structure in accordance with one embodiment of the present invention. 
         FIG. 10  shows an exemplary implementation of a frame structure in accordance with one embodiment of the present invention. 
         FIG. 11  shows an exemplary implementation of a frame structure in accordance with one embodiment of the present invention. 
         FIG. 12  shows an exemplary implementation of a frame structure in accordance with one embodiment of the present invention. 
         FIG. 13  shows a frame structure supporting legacy and new transmissions in accordance with one embodiment of the present invention. 
         FIG. 14  shows a frame structure supporting legacy and new transmissions in accordance with one embodiment of the present invention. 
         FIG. 15  shows a frame structure supporting legacy and new transmissions in accordance with one embodiment of the present invention. 
         FIG. 16  shows a frame structure supporting legacy and new transmissions in accordance with one embodiment of the present invention. 
         FIG. 17  shows a frame structure supporting legacy and new transmissions in accordance with one embodiment of the present invention. 
         FIG. 18  shows a frame structure supporting legacy and new transmissions in accordance with one embodiment of the present invention. 
         FIG. 19  shows a frame structure comprising a network coded (“NC”) subframe in accordance with one embodiment of the present invention. 
         FIG. 20  shows a frame structure comprising a network coded (“NC”) subframe in accordance with one embodiment of the present invention. 
         FIG. 21  shows a frame structure comprising a network coded (“NC”) subframe in accordance with one embodiment of the present invention. 
         FIG. 22  shows a frame structure comprising a network coded (“NC”) subframe in accordance with one embodiment of the present invention. 
         FIG. 23  shows an example of a HARQ time line in accordance with one embodiment of the present invention. 
         FIG. 24  shows a mobile communication network in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention relates to an apparatus and method for an enhanced Time Division Duplex (“TDD”) frame structure capable of supporting both legacy and advanced frame structures, while providing increased downlink (“DL”) and uplink (“UL”) transmission flexibility. Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 8  shows a frame structure pattern  500  in accordance with one embodiment of the present invention. As shown in  FIG. 8 , frame structure  500  comprises downlink zone  544 , flexible zone  546 , and uplink zone  548 . 
     The downlink zone  544  is typically used for transmitting data or additional control/signaling information from a base station to one or more mobile stations. The downlink zone  544  can be configured to include a legacy downlink subframe or a burst transmission, a legacy broadcast/multicast subframe or a burst transmission, a new/advanced downlink subframe or a burst transmission, and/or a new/advanced broadcast/multicast subframe or burst transmission. Where the numerology for the advanced subframe is compatible with the numerology of the legacy subframe, the advanced subframe and the legacy subframe can be mixed in the frequency domain or can utilize the same symbols. For example, a legacy transmission and an advanced signal transmission can share the same Orthogonal Frequency Division Multiplexing (“OFDM”) symbols. 
     The uplink zone  548  is typically used for transmitting data or additional control/signaling information from one or more mobile stations to a single base station. The uplink zone  548  can be configured to include a mix of a legacy uplink subframe or burst and an advanced uplink subframe or burst. Where the numerology for the advanced subframe is compatible with the legacy subframe, the advanced uplink burst and the legacy uplink burst can share the same symbols, such as the same OFDM symbols. 
     The flexible zone  546  can be configured to transmit any possible downlink or uplink subframe or bursts. As shown in  FIG. 8 , the flexible zone  546  is defined between two switching points, such as switching points  550   a  and  550   b . In one embodiment, switching points  550   a  and  550   b  can be configured with respect to an entire network. In another embodiment, switching points  550   a  and  550   b  can be configured on a frame by frame basis or based on multiple frames. Due to the flexibility of the transmissions inside the flexible zone  546 , co-channel interference may occur between neighbor cells. However, with proper network planning and appropriate configuration of the switching points  550   a  and  550   b , a balance can be achieved between interference and flexibility. 
       FIG. 9  shows an exemplary implementation of the frame structure  500  in  FIG. 8  in accordance with one embodiment of the present invention. 
     As shown in  FIG. 9 , “Cell  1 ” of a mobile communication network can be configured to use the frame structure  652  and “Cell  2 ” can be configured to use the frame structure  654 . As further shown in  FIG. 9 , the first switching point  650   a  located between the flexible zone  646  and the downlink zone  644  and the second switching point  650   b  located between the flexible zone  646  and the uplink zone  648  are fixed with respect to frame structures  652  and  654 . 
     As also shown in  FIG. 9 , the frame structures  652  and  654  allow flexible transmissions within flexible zone  646 . For example, the frame structure  652  of “Cell  1 ” can comprise a different configuration of uplink and downlink subframes within flexible zone  646  than frame structure  654  of “Cell  2 .” As another example, the switching points in the flexible zone  646  in the frame structure  652  of “Cell  1 ” can be different than the switching points in the flexible zone  646  in the frame structure  654  of “Cell  2 .” 
       FIG. 10  shows an exemplary implementation of the frame structure  500  in  FIG. 8  in accordance with one embodiment of the present invention. 
     As shown in  FIG. 10 , “Cell  1 ” of a mobile communication network can be configured to use the frame structure  756  and “Cell  2 ” can be configured to use the frame structure  758 . As further shown in  FIG. 10 , the first switching point  750   a  located between the flexible zone  746  and the downlink zone  744  and the second switching point  750   b  located between the flexible zone  746  and the uplink zone  748  are fixed with respect to the frame structures  756  and  758 . 
     As also shown in  FIG. 10 , the frame structures  756  and  758  allow flexible transmissions within the flexible zone  746 . For example, the frame structure  758  of “Cell  2 ” can comprise a different configuration of the uplink and downlink subframes within the flexible zone  746 , including one or more new subframes, such as the relay subframe  760 , than the frame structure  756  of “Cell  1 .” As another example, the switching points in the flexible zone  746  in the frame structure  756  of “Cell  1 ” can be different than the switching points in the flexible zone  746  in the frame structure  758  of “Cell  2 .” 
       FIG. 11  shows an exemplary implementation of the frame structure  500  in  FIG. 8  in accordance with one embodiment of the present invention. 
     As shown in  FIG. 11 , “Cell  1 ” of a mobile communication network can be configured to use the frame structure  862  and “Cell  2 ” can be configured to use the frame structure  864 . As further shown in  FIG. 11 , the first switching point  850   a  located between the flexible zone  846  and downlink zone  844  and the second switching point  850   b  located between the flexible zone  846  and the uplink zone  848  are fixed with respect to the frame structures  862  and  864 . 
     As also shown in  FIG. 11 , the frame structures  862  and  864  allow flexible transmissions within the flexible zone  846 . For example, the frame structure  864  of “Cell  2 ” can comprise a different configuration of uplink and downlink subframes within the flexible zone  846 , including one or more new subframes, such as the relay subframe  860 , than the frame structure  862  of “Cell  1 .” For another example, “Cell  2 ” can be configured to utilize compatible numerologies between the legacy system and the new system within the flexible zone  846 . For still another example, the switching points in the flexible zone  846  in the frame structure  862  of “Cell  1 ” can be different than the switching points in the flexible zone  846  in the frame structure  864  of “Cell  2 .” 
       FIG. 12  shows an exemplary implementation of the frame structure  500  in  FIG. 8  in accordance with one embodiment of the present invention. 
     As shown in  FIG. 12 , “Cell  1 ” of a mobile communication network can be configured to use the frame structure  966  and “Cell  2 ” can be configured to use the frame structure  968 . As further shown in  FIG. 12 , the first switching point  950   a  located between the flexible zone  946  and the downlink zone  944  and the second switching point  950   b  located between the flexible zone  946  and the uplink zone  948  are fixed with respect to the frame structures  966  and  968 . 
     As also shown in  FIG. 12 , the frame structures  966  and  968  allow flexible transmissions within the flexible zone  946 . For example, the frame structure  968  of “Cell  2 ” can comprise a different configuration of uplink and downlink subframes within the flexible zone  946 , including one or more new subframes, such as the relay subframe A  960 , than the frame structure  966  of “Cell  1 .” As another example, the switching points in the flexible zone  946  in the frame structure  966  of “Cell  1 ” can be different than the switching points in the flexible zone  946  in the frame structure  968  of “Cell  2 .” In the embodiment of  FIG. 12 , “Cell  2 ” can be configured to transmit one or more new subframes in uplink zone  948 , such as the relay subframe B  970 . 
       FIG. 13  shows a frame structure  1000  supporting legacy and new transmissions in accordance with one embodiment of the present invention. 
     Frame structure  1000  includes a preamble  1072 , a frame control header (“FCH”)  1074 , a downlink MAP message (“DL-MAP”)  1076 , an uplink MAP message (“UL-MAP”)  1078 , a downlink burst  1  (“DL Burst  1 ”)  1080 , a downlink burst  2  (“DL Burst  2 ”)  1082 , a receive/transmit transmission gap (“RTG”)  1084 , a ranging channel  1086 , an uplink burst  1  (“UL Burst  1 ”)  1088 , an uplink burst  2  (“UL Burst  2 ”)  1090 , and a transmit/receive transmission gap (“TTG”)  1092 . 
     As shown in  FIG. 13 , frame structure  1000  maintains the same number of switching points, that is, one RTG and one TTG, as the frame structure of the IEEE 802.16e standard. The frame structure  1000  shown in  FIG. 13  supports the same or different numerologies for legacy and new transmissions. In one embodiment, legacy systems and new systems may use the same numerologies. 
     In the frame structure  1000 , new mobile stations can be assigned to DL Burst  1   1080 , DL Burst  2   1082 , UL Burst  1   1088 , and UL Burst  2   1090 , whereas legacy mobile stations can be assigned to DL Burst  1   1080  and UL Burst  1   1088 . It should be understood that the DL Burst  2   1082  and the UL Burst  2   1090  are transparent to legacy mobile stations. In one embodiment, the locations of the DL Burst  1   1080  and the DL Burst  2   1082  in frame structure  1000  can be switched. As shown in  FIG. 13 , the UL Burst  1   1088  and the UL Burst  2   1090  can each have a ranging channel, such as ranging channel  1086 . 
     The times at which the DL Burst  2   1082  and the UL Burst  2   1090  begin can be adjusted depending on various factors, such as the number of legacy and new mobile stations involved, and the amount of network traffic. In order to support the DL Burst  1   1080 , DL Burst  2   1082 , UL Burst  1   1088 , and UL Burst  2   1090 , the DL-MAP  1076  and the UL-MAP  1078  are appropriately modified. 
     In the frame structure  1000 , a new mobile transmission in the DL Burst  1   1080  can be acknowledged in either the UL Burst  1   1088  or the UL Burst  2   1090 . For example, a delay sensitive transmission from a new mobile in the DL Burst  1   1080  can be acknowledged in the UL Burst  1   1088 . As another example, a delay tolerant transmission from a new mobile station in the DL Burst  1   1080  can be acknowledged in either the UL Burst  2   1090  or in the UL Burst  1  or the UL Burst  2  in a subsequent super-frame (not shown in  FIG. 13 ). 
     In the frame structure  1000 , a new mobile transmission in the DL Burst  2   1082  can be acknowledged in either the UL Burst  2   1090 , or the UL Burst  1  or the UL Burst  2  in a subsequent super-frame (not shown in  FIG. 13 ). The legacy mobile transmission in DL Burst  1   1080  can be acknowledged in either the UL Burst  1   1088  or in the UL Burst  1  in a subsequent super frame. 
       FIG. 14  shows a frame structure supporting legacy and new transmissions in accordance with one embodiment of the present invention. 
     Frame structure  1100  in  FIG. 14  comprises a preamble  1172 , a frame control header (“FCH”)  1174 , a DL-MAP  1176 , a UL-MAP  1178 , a DL Burst  1   1180 , a DL Burst  2   1182 , an RTG  1184 , a ranging channel  1186 , a UL Burst  1   1190 , a UL Burst  2   1188 , and a TTG  1192 . 
     As shown in  FIG. 14 , frame structure  1100  maintains the same number of switching points, that is, one RTG and one TTG, as the frame structure of the IEEE 802.16e standard. The frame structure  1100  shown in  FIG. 14  supports the same or different numerologies for legacy and new transmissions. In one embodiment, legacy systems and new systems may use the same numerologies. 
     In the frame structure  1100 , new mobile stations can be assigned to the DL Burst  1   1180 , DL Burst  2   1182 , UL Burst  1   1190 , and UL Burst  2   1188 , whereas legacy mobile stations can be assigned to the DL Burst  1   1180  and UL Burst  1   1190 . It should be understood that the DL Burst  2   1182  and the UL Burst  2   1188  are transparent to legacy mobile stations. As shown in  FIG. 14 , the UL Burst  1   1190  and UL Burst  2   1188  can each have a ranging channel, such as ranging channel  1186 . In one embodiment, the positions of the DL Burst  1   1180  and the DL Burst  2   1182  in the frame structure  1100  can be switched with one another. 
     The time at which the DL Burst  2   1182  begins and the time at which the UL Burst  2   1188  ends can be adjusted depending on various factors, such as the number of legacy and new mobile stations involved, and the amount of network traffic. In order to support the DL Burst  1   1180 , DL Burst  2   1182 , UL Burst  1   1190 , and UL Burst  2   1188 , the DL-MAP  1176  and the UL-MAP  1178  are appropriately modified. 
     In the frame structure  1100 , a new mobile transmission in the DL Burst  1   1180  can be acknowledged in either the UL Burst  1   1190  or the UL Burst  2   1188 . In the frame structure  1100 , a new mobile transmission in the DL Burst  2   1182  can be acknowledged in either the UL Burst  1   1190 , or the UL Burst  1  or the UL Burst  2  in a subsequent super-frame (not shown in  FIG. 14 ). The legacy mobile transmission in the DL Burst  1   1180  can be acknowledged in either the UL Burst  1   1190  or in the UL Burst  1  in the subsequent super frame. 
       FIG. 15  shows a frame structure supporting legacy and new transmissions in accordance with one embodiment of the present invention. 
     Frame structure  1200  includes a preamble  1272 , an FCH  1274 , a DL-MAP  1276 , a UL-MAP  1278 , a DL Burst  1   1280 , new uplink and downlink MAP messages (MAP for Advanced)  1281 , a DL Burst  2   1282 , an RTG  1284 , a ranging channel  1286 , a UL Burst  1   1288 , a UL Burst  2   1290 , and a TTG  1292 . 
     As shown in  FIG. 15 , frame structure  1200  maintains the same number of switching points, that is, one RTG and one TTG, as the frame structure of the IEEE 802.16e standard. The frame structure  1200  shown in  FIG. 15  supports the same or different numerologies for legacy and new transmissions. In one embodiment, legacy systems and new systems may use the same numerologies. 
     In the frame structure  1200 , new mobile stations can be assigned to the DL Burst  2   1282  and the UL Burst  2   1290 , whereas legacy mobile stations can be assigned to the DL Burst  1   1280  and the UL Burst  1   1288 . It should be understood that the DL Burst  2   1282  and the UL Burst  2   1290  are transparent to legacy mobile stations. As shown in  FIG. 15 , the UL Burst  1   1288  and the UL Burst  2   1290  can each have a ranging channel, such as ranging channel  1286 . 
     In the frame structure  1200 , legacy transmissions in the DL Burst  1   1280  and the UL Burst  1   1288  are supported by the legacy DL-MAP  1276  and UL-MAP  1278 , and new transmissions in the DL Burst  2   1282  and the UL Burst  2   1290  are supported by the MAP for Advanced  1281 . The times at which the MAP for Advanced  1281  and the UL Burst  2   1290  begin can be adjusted depending on various factors, such as the number of legacy and new mobile stations involved, and the amount of network traffic. 
     In the frame structure  1200 , a new mobile transmission in the DL Burst  2   1282  can be acknowledged in either the UL Burst  2   1290  or the UL Burst  2  in a subsequent super-frame (not shown in  FIG. 15 ). In the frame structure  1200 , the legacy mobile transmission in the DL Burst  1   1280  can be acknowledged in either the UL Burst  1   1288  or in the UL Burst  1  in the subsequent super frame. 
       FIG. 16  shows a frame structure supporting legacy and new transmissions in accordance with one embodiment of the present invention. 
     Frame structure  1300  includes a preamble  1372 , an FCH  1374 , a DL-MAP  1376 , a UL-MAP  1378 , a DL Burst  1   1380 , new uplink and downlink MAP messages (MAP for Advanced)  1381 , a DL Burst  2   1382 , an RTG  1384 , a ranging channel  1386 , a UL Burst  1   1388 , a UL Burst  2   1390 , and a TTG  1392 . 
     As shown in  FIG. 16 , frame structure  1300  maintains the same number of switching points, that is, one RTG and one TTG, as the frame structure of the IEEE 802.16e standard. The frame structure  1300  shown in  FIG. 16  supports the same or different numerologies for legacy and new transmissions. In one embodiment, legacy systems and new systems may use the same numerologies. 
     In the frame structure  1300 , new mobile stations, such as mobiles communicating at high speeds, can be assigned to the DL Burst  2   1382  and the UL Burst  2   1390 , whereas legacy mobile stations can be assigned to the DL Burst  1   1380  and the UL Burst  1   1388 . It should be understood that the DL Burst  2   1382  and the UL Burst  2   1390  are transparent to legacy mobile stations. As shown in  FIG. 16 , the UL Burst  1   1388  and the UL Burst  2   1390  can each have a ranging channel, such as ranging channel  1386 . 
     In the frame structure  1300 , legacy transmissions in the DL Burst  1   1380  and the UL Burst  1   1388  are supported by the legacy DL-MAP  1376  and UL-MAP  1378 , and new transmissions in the DL Burst  2   1382  and the UL Burst  2   1390  are supported by the MAP for Advanced  1381 . The time at which the MAP for Advanced  1381  begins and the time at which the UL Burst  2   1390  ends can be adjusted depending on various factors, such as the number of legacy and new mobile stations involved, and the amount of network traffic. 
     In the frame structure  1300 , a new mobile transmission in the DL Burst  2   1382  can be acknowledged in either the UL Burst  2   1390  or in the UL Burst  2  in a subsequent super-frame (not shown in  FIG. 16 ). The legacy mobile transmission in the DL Burst  1   1380  can be acknowledged in either the UL Burst  1   1388  or in the UL Burst  1  in the subsequent super frame. 
       FIG. 17  shows a frame structure supporting legacy and new transmissions in accordance with one embodiment of the present invention. 
     Frame structure  1400  includes a preamble  1472 , an FCH  1474 , a DL-MAP  1476 , a UL-MAP  1478 , a DL Burst  1   1480 , a DL Burst  2   1482 , an RTG  1484 , a ranging channel  1486 , a UL Burst  1   1488 , a UL Burst  2   1490 , and a TTG  1492 . 
     As shown in  FIG. 17 , frame structure  1400  maintains the same number of switching points, that is, one RTG and one TTG, as the frame structure of the IEEE 802.16e standard. The frame structure  1400  shown in  FIG. 17  supports the same or different numerologies for legacy and new transmissions. In one embodiment, legacy systems and new systems may use the same numerologies. 
     In the frame structure  1400 , new mobile stations can be assigned to the DL Burst  1   1480 , DL Burst  2   1482 , UL Burst  1   1488 , and UL Burst  2   1490 , whereas legacy mobile stations can be assigned to the DL Burst  1   1480  and the UL Burst  1   1488 . It should be understood that the DL Burst  2   1482  and the UL Burst  2   1490  are transparent to legacy mobile stations. As shown in  FIG. 17 , the UL Burst  1   1488  and the UL Burst  2   1490  can each have a ranging channel, such as ranging channel  1486 . In one embodiment, the positions of DL Burst  1   1480  and the DL Burst  2   1482  in frame structure  1400  can be switched with one another. 
     The time at which the DL Burst  2   1482  begins and the time at which the UL Burst  1   1488  and the UL Burst  2   1490  begin can be adjusted depending on various factors, such as the number of legacy and new mobile stations involved, and the amount of network traffic. In order to support the DL Burst  1   1480 , DL Burst  2   1482 , UL Burst  1   1488 , and UL Burst  2   1490 , the DL-MAP  1476  and the UL-MAP  1478  are appropriately modified. 
     In the frame structure  1400 , a new mobile transmission in the DL Burst  1   1480  can be acknowledged in either the UL Burst  1   1488  or the UL Burst  2   1490 . For example, a delay sensitive transmission from a new mobile in the DL Burst  1   1480  can be acknowledged in the UL Burst  1   1488 . As another example, a delay tolerant transmission from a new mobile in the DL Burst  1   1480  can be acknowledged in either the UL Burst  2   1490 , or in the UL Burst  1  or the UL Burst  2  in a subsequent super-frame (not shown in  FIG. 17 ). 
     In the frame structure  1400 , a new mobile transmission in the DL burst  2   1482  can be acknowledged in the UL Burst  2   1490  if the Acknowledged/Not Acknowledged (“ACK/NACK”) segment for the UL Burst  2   1490  is located in the later portion of the UL Burst  1   1488  and the UL Burst  2   1490 , or the UL Burst  1  or the UL Burst  2  in a subsequent super-frame. Such acknowledgment depends on receiver complexity (time) of decoding the subpacket and generating the ACK/NAK. 
     The legacy mobile transmission in the DL Burst  1   1480  can be acknowledged in either the UL Burst  1   1488  or in the UL Burst  1  in a subsequent super frame (not shown in  FIG. 17 ). 
       FIG. 18  shows a frame structure supporting legacy and new transmissions in accordance with one embodiment of the present invention. 
     Frame structure  1500  includes a preamble  1572 , an FCH  1574 , a DL-MAP  1576 , a UL-MAP  1578 , a DL Burst  1   1580 , new uplink and downlink MAP messages (MAP for Advanced)  1581 , a DL Burst  2   1582 , an RTG  1584 , a ranging channel  1586 , a UL Burst  1   1588 , a UL Burst  2   1590 , and a TTG  1592 . 
     As shown in  FIG. 18 , frame structure  1400  maintains the same number of switching points, that is, one RTG and one TTG, as the frame structure of the IEEE 802.16e standard. The frame structure  1500  shown in  FIG. 18  supports the same or different numerologies for legacy and new transmissions. In one embodiment, legacy systems and new systems may use the same numerologies. 
     In the frame structure  1500 , new mobile stations can be assigned to the DL Burst  2   1582  and the UL Burst  2   1590 , whereas legacy mobile stations can be assigned to the DL Burst  1   1580  and the UL Burst  1   1588 . It should be understood that the DL Burst  2   1582  and the UL Burst  2   1590  are transparent to legacy mobile stations. As shown in  FIG. 18 , the UL Burst  1   1588  and the UL Burst  2   1590  can each have a ranging channel, such as ranging channel  1586 . 
     In the frame structure  1500 , legacy transmissions in the DL Burst  1   1580  and the UL Burst  1   1588  are supported by the legacy DL-MAP  1576  and UL-MAP  1578 , and new transmissions in the DL Burst  2   1582  and the UL Burst  2   1590  are supported by the MAP for Advanced  1581 . The times at which the MAP for Advanced  1581  and the UL Burst  2   1590  begin can be adjusted depending on various factors, such as the number of legacy and new mobile stations involved, and the amount of network traffic. 
     In the frame structure  1500 , a new mobile transmission in the DL Burst  2   1582  can be acknowledged in either the UL Burst  2   1590  if the Acknowledged/Not Acknowledged (“ACK/NACK”) segment for the UL Burst  2   1590  is located in the later portion of the UL Burst  1   1588  and the UL Burst  2   1590 , or in the subsequent super-frame (not shown in  FIG. 18 ). The legacy mobile transmission in the DL Burst  1   1580  can be acknowledged in either the UL Burst  1   1588  or in the UL Burst  1  in the subsequent super-frame. 
     A network coded (“NC”) subframe in accordance with one embodiment of the present invention will now be discussed. 
       FIG. 19  shows a frame structure comprising a network coded (“NC”) subframe in accordance with one embodiment of the present invention. As shown in  FIG. 19 , frame structure  1920  comprises a provisioned relay station (“RS”) resource  1922 . 
     In one embodiment and as shown in  FIG. 19 , the provisioned RS resource  1922  can comprise an NC subframe  1924  and a relay station MAP (“RS-MAP”)  1926 , a relay station receive/transmit transmission gap (“RSRTG”)  1928 , and a base station receive/transmit transmission gap (“BSRTG”)  1930 . 
     Alternatively, the provisioned RS resource  1922  can comprise supplementary UL subframe  1934 , relay station MAP (“RS-MAP”)  1937 , NC subframe  1936 , supplementary DL subframe  1938 , relay station receive/transmit transmission gap (“RSRTG”)  1940 , and base station receive/transmit transmission gap (“BSRTG”)  1942 . Supplementary UL subframe  1934  enables an uplink transmission by a mobile station (“MS”) having good geometry to a base station (“BS”) and supplementary DL subframe  1938  enables a downlink transmission by a BS to an MS having good geometry. 
       FIG. 20  shows a frame structure comprising a network coded (“NC”) subframe in accordance with one embodiment of the present invention. As shown in  FIG. 20 , frame structure  2021  comprises a provisioned relay station (“RS”) resource  2023 . 
     As shown in  FIG. 20 , provisioned RS resource  2023  can comprise NC subframe  2048 , relay station MAP (“RS-MAP”)  2052 , supplementary UL subframe  2050 , supplementary DL subframe  2044 , and base station receive/transmit transmission gap (“BSRTG”)  2056 . 
     Alternatively, the provisioned RS resource  2023  can comprise NC subframe  2058 , RS-MAP  2057 , supplementary UL subframe  2060 , supplementary DL subframe  2062 , relay station receive/transmit transmission gap (“RSRTG”)  2064 , and base station receive/transmit transmission gap (“BSRTG”)  2066 . Supplementary UL subframes  2050  and  2060  enable an uplink transmission by a mobile station (“MS”) having good geometry to a base station (“BS”) and supplementary DL subframes  2044  and  2062  enable a downlink transmission by a BS to an MS having good geometry. 
       FIG. 21  shows a frame structure comprising a network coded (“NC”) subframe in accordance with one embodiment of the present invention. As shown in  FIG. 21 , frame structure  2168  comprises a provisioned relay station (“RS”) resource  2170 . 
     As shown in  FIG. 21 , the provisioned RS resource  2170  can comprise a relay station receive/transmit transmission gap (“RSRTG”)  2172 , an RS preamble  2174 , a relay station MAP (“RS-MAP”)  2176 , an NC subframe  2178 , and a base station receive/transmit transmission gap (“BSRTG”)  2180 . 
     Alternatively, the provisioned RS resource  2170  can comprise a relay station receive/transmit transmission gap (“RSRTG”)  2182 , an RS preamble  2184 , an RS-MAP  2186 , an NC subframe  2188 , a supplementary UL subframe  2190 , a base station receive/transmit transmission gap (“BSRTG”)  2192 , and a supplementary DL subframe  2194 . In one embodiment, a transmit/receive transmission gap (TTG) can be inserted after the supplementary DL subframe  2194  if the particular base station supports legacy mobile stations. The supplementary UL subframe  2190  enables an uplink transmission by a mobile station (“MS”) having good geometry to a base station (“BS”) and the supplementary DL subframe  2194  enables a downlink transmission by a BS to an MS having good geometry. 
       FIG. 22  shows a frame structure comprising a network coded (“NC”) subframe in accordance with one embodiment of the present invention. As shown in  FIG. 22 , frame structure  2059  comprises a provisioned relay station (“RS”) resource  2261 . 
     As shown in  FIG. 22 , provisioned RS resource  2261  can comprise a relay station preamble  2263 , relay station MAP (“RS-MAP”)  2265 , NC subframe  2267 , supplementary UL subframe  2269 , a base station receive/transmit transmission gap (“BSRTG”)  2271 , and a supplementary DL subframe  2273 . 
     Alternatively, the provisioned RS resource  2261  can comprise relay station receive/transmit transmission gap (“RSRTG”)  2275 , a relay station (“RS”) preamble  2277 , an RS-MAP  2279 , an NC subframe  2281 , a supplementary UL subframe  2283 , a base station receive/transmit transmission gap (“BSRTG”)  2285 , and a supplementary DL subframe  2287 . In one embodiment, a transmit/receive transmission gap (TTG) can be inserted after the supplementary DL subframe  2273  or  2287  if the particular base station supports legacy mobile stations. The supplementary UL subframes  2269  and  2283  enable an uplink transmission by a mobile station (“MS”) having good geometry to a base station (“BS”) and the supplementary DL subframes  2273  and  2287  enable a downlink transmission by a BS to an MS having good geometry. 
     Each NC subframe described above may further comprise network coded hybrid automatic repeat-request (“HARQ”) transmissions to a base station or a mobile a station, downlink hybrid automatic repeat-request (“DL HARQ”) retransmissions to a mobile station, uplink hybrid automatic repeat-request (“UL HARQ”) retransmissions to a base station, and hybrid automatic repeat-request (“HARQ”) acknowledge/not acknowledged (“ACK/NAK”) of a base station or a mobile station. An example of a HARQ time line is shown in  FIG. 23 . 
       FIG. 24  shows a mobile communication network in accordance with one embodiment of the present invention. 
     In  FIG. 24 , mobile communication system  2400  includes cells  2402 ,  2404 , and  2406 . As shown in  FIG. 24 , cell  2402  comprises base station  2408  with base station transmission range  2410 , mobile station  2414 , and relay station  2412 . As also shown in  FIG. 24 , cell  2404  comprises base station  2418  with base station transmission range  2420 , mobile station  2424 , and relay station  2422 . As further shown in  FIG. 24 , cell  2406  comprises base station  2428  with base station transmission range  2430 , mobile station  2434 , and relay station  2432 . 
     In the mobile communication system  2400 , the need for a relay station, such as relay station  2412 , can vary from time to time based on the hybrid automatic repeat-request (“HARQ”) acknowledge/not acknowledged (“ACK/NAK”) of a base station, such as base station  2408 , or a mobile station, such as mobile station  2414 . Accordingly, a fixed relay station (“RS”) resource, such as the provisioned RS resource of the present invention described with respect to the embodiments in  FIGS. 19 through 22 , is provisioned for each frame. 
     In one embodiment, the provisioned RS resource can be used for transmission of an NC subframe. In another embodiment, the provisioned RS resource can be used for a downlink (“DL”) transmission and/or an uplink (“UL”) transmission for mobile stations having good geometry where the relayed traffic is small. 
     For example, as shown in  FIG. 24 , during the time period of the provisioned RS resource, RS  2412  in cell  2402  broadcasts a transmission  2416  of a received DL transmission from base station  2408  and a received UL transmission from MS  2414 , between BS  2408  and MS  2414 . While RS  2412  is transmitting within cell  2402 , DL and UL transmissions can be performed during the provisioned RS resource time period for mobile terminals having good geometry in other cells, such as cell  2404  and  2406 , in which the corresponding relays, such as RS  2422  and  2432 , do not broadcast information. 
     Depending on the type of implementation, it is possible that the present invention can take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment containing both hardware and software elements. A software embodiment may include, but not be limited to, firmware, resident software, microcode, etc. 
     As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims. Therefore, all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are intended to be embraced by the appended claims.