Abstract:
Systems and methods for wireless networks with inner and outer cells are provided. A base station determines an amount of traffic on an inner and outer cell. When the traffic exceed a predetermined threshold value, traffic is adjusted on the inner or outer cell. Traffic can be adjusted by handing off some of the traffic from the inner cell to the outer cell, from the outer cell to the inner cell, between sectors of the inner or outer cells and/or by handing off traffic to a proximately located base station.

Description:
The present application claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 60/658,370, filed Mar. 4, 2005, the entire disclosure of which is herein expressly incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The popularity of wireless networks has resulted in a desire for wireless network operators to increase the capacity of their networks. One way to increase capacity is to use more frequencies over the air interface between base stations and mobile stations. However, most frequencies are allocated by governments bodies and most, if not all, available frequencies have been allocated. Another way to increase capacity is to add cell stations by decreasing the size of existing cells. However, adding base stations requires time consuming and expensive zoning approvals from local government bodies. It also requires additional costs for the equipment for the additional base stations, as well as costs associated with leasing space for the equipment. 
     SUMMARY OF THE INVENTION 
     One technique for increasing network capacity with minimal increased costs is to deploy a so-called overlay-underlay networks, such as that described in U.S. Pat. No. 5,953,661, the entire contents of which are herein expressly incorporated by reference. In the overlay-underlay networks a base station supports concentric cells, including an inner cell and an outer cell. Exemplary embodiments of the present invention are directed to improvements to overlay-underlay and similar types of networks. 
     In accordance with exemplary embodiments of the present invention, traffic on an inner cell and outer cell is monitored. When traffic on one of the inner or outer cells exceeds a threshold value, the traffic can be adjusted to avoid call blocking. The traffic can be adjusted by handing off calls from the inner or outer cell with traffic exceeding a threshold value to the other of the cells of a base station, or to cells of another proximately located base station. 
     Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         FIGS. 1   a  and  1   b  illustrate exemplary inner and outer cell arrangements in accordance with the present invention; 
         FIGS. 2   a - 2   c  illustrate an exemplary reuse pattern for inner and outer cell frequencies in accordance with the present invention; 
         FIG. 3  illustrates an exemplary base station in accordance with the present invention; and 
         FIG. 4  illustrates an exemplary method in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1   a  and  1   b  illustrate exemplary inner and outer cell arrangements in accordance with the present invention. Specifically,  FIG. 1   a  illustrates an exemplary single sector base station with an outer cell  110  and an inner cell  150 . The inner and outer cells  110  and  150  are generated by a single base station, thereby eliminating the additional expenses associated with adding base stations. Specifically, existing antennas and base station radios can be divided between the inner and outer cells  110  and  150 , further reducing additional equipment costs.  FIG. 1   b  illustrates an exemplary three sector inner and outer cell arrangement in accordance with the present invention. The outer cell includes sectors  112 - 116  and the inner cell includes sectors  152 - 156 . In some implementations the sectors can be supported by three antennas, where two antennas are receiving antennas and one antenna is a transmit/receive antenna. Although  FIGS. 1   a  and  1   b  illustrate only two concentric cells, the base station can support more than two concentric cells. The base station can support dispatch voice, interconnect voice, short message service (SMS), and/or packet data on the inner and/or outer cell. In addition, the base station can handoff dispatch voice, interconnect voice and/or packet data calls from the inner cell to the outer cell, from the outer cell to the inner cell, from one sector of the inner cell to another sector of the inner cell, from one sector of the outer cell to another sector of the outer cell, and to inner or outer cells of other base stations. 
       FIGS. 2   a - 2   c  illustrate an exemplary reuse pattern for inner and outer cell frequencies in accordance with the present invention. As illustrated in  FIGS. 2   a - 2   c , a “tighter” frequency reuse pattern can be deployed for the inner cells than the outer cells. Specifically, the inner cells have a reuse pattern of K=3, while the outer cells employ a reuse pattern of K=9. 
       FIG. 3  illustrates an exemplary base station in accordance with the present invention. The base station  310  is coupled to a mobile switching center  305  and to antennas  315  and  320 . Mobile switching center  305  can be coupled to other base stations (not illustrated). Antenna  315  can be used for the inner cell by downtilting the antenna to control its radiation pattern, while antenna  320  can be used to support the outer cell. Base station  310  includes a memory  325  and processor  330 . Memory can be any type of memory, including a random access memory, read only memory, flash memory, hard disk and/or the like. Processor  330  can be a microprocessor executing programmable code provided by memory  325 , an application specific integrated circuit (ASIC), field programmable gate array and/or the like. Processor  330  includes various logic  335 - 355  which will be described in more detail below in connection with  FIG. 4 . 
     It should be recognized that base station  310  can include hardware in addition to that illustrated in.  FIG. 3 . For example, base station  310  can include a number of base radios, diplexer, baseband processing units, upconverters/downconverters and the like. 
       FIG. 4  illustrates an exemplary method in accordance with the present invention. Logic  335  monitors the inner and outer cells in order to determine the amount of traffic at the cells (steps  405  and  410 ). Logic  340  receives and processes signal quality reports from mobile stations (step  415 ). The signal quality reports can include a received signal strength indicator (RSSI), carrier-to-interference ratio (C/I) and/or the like. The signal quality reports can include signal quality of the inner and outer cells of the base station, as well as signal quality of inner and outer cells of proximately located base stations. Logic  345  compares the traffic of the inner and outer cells to a threshold to determine whether the traffic exceeds a predetermined threshold value (step  420 ). The predetermined threshold value is selected to be some value below where call blocking will occur, and can the same for the inner and outer cells or can be different. When the traffic on the inner or outer cells does not exceed a threshold value (“No” path out of decision step  420 ), then the base station continues to determine the amount of traffic on the inner and outer cells and receive signal quality reports (steps  405 - 415 ). 
     When the traffic on the inner or outer cells exceeds a threshold value (“Yes” path out of decision step  425 ), then logic  350  identifies mobile stations as candidates for handoff (step  430 ). Mobile stations are candidates for handoff when they can receive an acceptable signal from the other of the inner or outer cells and/or from inner or outer cells of another base station. Logic  355  then instructs at least some of the identified mobile stations to handoff to inner or outer cells of the base station or to inner or outer cells of another base station (step  430 ). Additionally, or alternatively, some mobile stations can handoff between sectors of the inner and/or outer cells. The base station then continues monitor the traffic on the inner and outer cells. 
     Although  FIG. 4  illustrates particular acts being performed in particular order, some of these acts need not necessarily be performed in this order. For example, the determination of the amount of traffic on the inner and outer cells and receipt of the signal quality reports from the mobile stations can be performed in parallel, and can also be performed while identifying the mobile stations and/or while instructing the identified mobile stations to handoff. Although the logic of  FIG. 3  are illustrated as separate elements, the logic can be combined in various manners. For example, the logic for identifying mobile stations  350  and logic for instructing mobile stations to handoff  355  can be part of a logic for adjusting traffic of the inner or outer cells. 
     Although exemplary embodiments have been described above with processor  330  of base station  310  determining the amount of traffic, monitoring the traffic to determine whether it exceeds a threshold value and instructing mobile stations to handoff, some or all of this processing can be performed in other network elements, such as the mobile switching center  305 . 
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.