Patent Publication Number: US-2010113050-A1

Title: Carrier aggregation for optimizing spectrum utilization

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 61/198,121 which was filed on Nov. 3, 2008. 
    
    
     FIELD OF THE INVENTION 
     This invention generally relates to communication. More particularly, this invention relates to wireless communication. 
     DESCRIPTION OF THE RELATED ART 
     Wireless communication systems are well known and in widespread use. A variety of system configurations are known. With such systems there are various challenges associated with providing wireless communication service to a variety of users. 
     For example, it is necessary to avoid interference among different users and different communication links. In the current LTE specification, for example, there is a guard band provided for out-of-band emission control. In some scenarios, the designed guard band is not sufficient. For example, some scenarios include uplink and downlink co-existence in a specific carrier band. The guard band is usually specified as a fixed spectrum block and is intended to address co-existence between mobile stations or co-existence between base stations. Adjacent uplink and downlink co-existence typically requires a larger guard band and an associated spurious emission because the downlink transmission power from a base station is normally much higher than that from the mobile station on the uplink. Even with known guard band approaches, there are scenarios in which improvements are required. 
     SUMMARY 
     An exemplary method of allocating bandwidth to a call for at least one network includes allocating 10 MHz of the bandwidth for a downlink between a base station and at least one user. 5 MHz of the bandwidth is allocated for an uplink between the at least one user and the base station. A selected amount of bandwidth is aggregated to the allocated 5 MHz for the uplink. The amount of bandwidth that is aggregated is at least one of an additional 3 MHz band or two additional 1.4 MHz bands. 
     The various features and advantages of disclosed examples will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows selected portions of an example communication system. 
         FIG. 2  is a flowchart diagram summarizing one example approach. 
         FIG. 3  schematically illustrates an example frequency band. 
         FIG. 4  schematically illustrates an example bandwidth allocation technique. 
         FIG. 5  schematically illustrates another example bandwidth allocation technique. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically shows selected portions of a wireless communication system  20 . A user can utilize a mobile station  22  for a variety of wireless communication features. A base station  24  including a cell tower  26  and base station controller (BSC)  28  communicates with the mobile station  22  over a downlink and an associated uplink. The base station  24  in the example of  FIG. 1  is associated in a known manner with a core network  32 , which includes known devices for facilitating communications between a mobile station  22  and another device. 
     One feature of the illustrated example is that it utilizes a carrier aggregation technique for optimizing the utilization of a frequency spectrum to facilitate co-existence with strong interference from a neighboring downlink public safety band transmission. A particular example that is useful with the LTE specification is described below. The carrier aggregation technique optimizes spectrum utilization and uplink system performance. 
       FIG. 2  includes a flowchart diagram  40  that summarizes one example approach for allocating bandwidth to a user of the mobile device  22 , for example. At  42 , a 10 MHz band is allocated for the downlink between the base station  24  and the mobile station  22 . A 5 MHz band is allocated for an uplink between the base station  24  and the mobile station  22 . This is shown at  44  in  FIG. 2 . At  46 , a selected band is aggregated with the allocated 5 MHz band for the uplink. The allocated 5 MHz and the aggregated band are managed as a unit and they are associated with the 10 MHz band allocated for the downlink. 
       FIG. 3  schematically shows a frequency spectrum  50  that includes the 700 MHz spectrum (i.e., between 700 MHz and 800 MHz). The frequency spectrum  50  is segmented with some portions being dedicated to particular use. For example, a band  52  between 763 MHz and 768 MHz is dedicated to public safety broadband downlink transmissions. A band  54  between 769 MHz and 775 MHz is dedicated to public safety narrow band downlink transmissions. Another band  56  between 793 MHz and 798 MHz is dedicated to public safety broadband uplink transmissions. Another band  58  between 799 MHz and 805 MHz is dedicated to public safety narrow band uplink transmissions. 
     In the example of  FIG. 3 , a band  60  between 746 MHz and 757 MHz can be used for downlink traffic between the base station  24  and the mobile station  22 . A band  62  between 776 MHz and 787 MHz can be used for uplink transmissions between the mobile station  22  and the base station  24 . 
     One challenge associated with using the band  62  for such uplink transmissions is that the band  62  is adjacent the band  54 . The closeness of those two bands requires special accommodations to ensure an appropriate out-of-band emission control to deal with interference from downlink transmissions on the public safety band  54 . 
     One example technique for allocating bandwidth for the uplink between the mobile station  22  and the base station  24  is schematically shown in  FIG. 4 . The band  60  in this example is between 746 MHz and 756 MHz and the band  62  is between 777 MHz and 787 MHz. There is a 31 MHz separation between the center  64  of the downlink band  60  and the center  66  of the uplink band  62 . 
     In this example, the entire 10 MHz bandwidth at  68  is allocated to the downlink between the base station  24  and the mobile station  22 . 5 MHz shown at  70  is allocated to the uplink communications between the mobile station  22  and the base station  24 . In this example, the 5 MHz allocated to the uplink as shown at  70  is in the upper portion of the band  62 . In the illustrated example, the allocated 5 MHz is between 782 MHz and 787 MHz. Allocating the 5 MHz shown at  70  to the uplink allows the system to operate with sufficient guard band to reject interference from the neighboring public safety band downlink transmissions in the band  54  of  FIG. 3 . 
     There is additional unused uplink spectrum within the band  62 . In the example of  FIG. 4 , a selected amount of that bandwidth is aggregated to the allocated 5 MHz for the uplink. In this example, an additional 3 MHz band  72  is aggregated to the 5 MHz  70  for the uplink. According to the LTE R-8 specification, bandwidth allocations can be in the amount of 20 MHz, 15 MHz, 10 MHz, 5 MHz, 3 MHz or 1.4 MHz. The allocated and aggregated bandwidth  70  and  72  in this example utilizes bandwidth allocation amounts according to the specification. Therefore, this example can be utilized without requiring any change to this standard. 
     The example of  FIG. 4  includes utilizing 4.5 MHz of the allocated 5 MHz  70  for the uplink traffic. As schematically shown in  FIG. 4 , the portions  70 A and  70 B of the allocated 5 MHz band are utilized for traffic. This leaves an additional 0.25 MHz on either side of those portions. A similar technique is implemented for the 3 MHz band  72  such that 2.7 MHz is utilized for the uplink traffic as shown at  72 A and  72 B. This particular configuration provides guard band portions at  74  (in the amount of 0.25 MHz),  76  (in the amount of 0.15 MHz) and  78  (in the amount of 2 MHz). The technique of  FIG. 4 , therefore, provides for additional guard band at each end of the allocated bandwidth actually utilized for uplink traffic. In this example, 0.25 MHz guard band is provided at  74  on one side of the allocated uplink band width and a 2.15 MHz guard band is provided on an opposite side at  78 . 
     The allocated 5 MHz  70  and the aggregated band  72  are managed as a unity and associated together with the resource of the allocated 10 MHz for the downlink. 
     Another carrier allocation and aggregation technique is shown in  FIG. 5 . In this example, a 5 MHz band  80  is allocated to the uplink traffic. The allocated 5 MHz band  80  in this case is centered within the 10 MHz band  62 . This leaves 2.5 MHz on each side of the 5 MHz band  80 . Two 1.4 MHz bands  82 A and  82 B are aggregated to the 5 MHz band  80  and allocated for the uplink traffic. This is another example that utilizes acceptable band sizes for the LTE specification. 
     As schematically shown in  FIG. 5 , not all of the allocated bandwidth is utilized for the uplink traffic. 4.5 MHz of the 5 MHz band  80  is actually utilized for uplink traffic leaving additional guard band frequency. The portions shown at  80 A and  80 B are utilized for the uplink traffic leaving 0.25 MHz on either side of those portions. The 1.4 MHz bands are also segmented and only a portion at  82 A′,  82 A″,  82 B′ and  82 B″ are actually utilized for uplink traffic. This leaves additional frequency available for the guard band. In this example, a guard band at  88  is 2.75 MHz wide (i.e., 2.5 MHz+0.25 MHz) and a guard band at  89  is 0.16 MHz wide. 
     In the examples of  FIGS. 4 and 5 , the guard band between the allocated 5 MHz band and the aggregated 3 MHz band or 1.4 MHz bands is shared to reduce the overhead on the guard band. 
     The examples illustrated above provide carrier aggregation to improve spectrum efficiency. One downlink 10 MHz carrier is associated with multiple uplink carriers. The initial uplink 5 MHz band  70 ,  80  has an LTE release 8 frame structure and associated PUCCH control channels. Downlink control signaling indicates the resource allocation on the initial uplink 5 MHz carrier  70 ,  80 , the growth carrier  72 ,  82  or both. 
     The aggregated or growth carriers  72 ,  82  in one example include PUCCH on each component carrier to allow the aggregated carrier to associate with the downlink 10 MHz carrier  68  as a backward compatible LTE release-8 carrier. In another example, there is no PUCCH in the aggregated component carrier. In such an example, all CQI/PMI/RI and ACK/NAK are allocated at the original 5 MHz uplink carrier  70 ,  80 . Such an example allows the system to fully utilize the additional or aggregated carrier  72 ,  82  for traffic. 
     A hybrid automatic repeat request (HARQ) processor in one example accommodates the above-described carrier aggregation by having one HARQ processor per component carrier. This example is backward compatible to LTE release-8 for all carriers. Another example includes one HARQ processor for aggregate multiple carriers scheduled for at least one user. This example provides a downlink control channel design that includes one ACK/NAK feedback only. Another example includes dynamic HARQ processors such that one or more HARQ processors are assigned based on demand. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this invention. The scope of legal protection given to this invention can only be determined by studying the following claims.