Abstract:
Disclosed is a method, and system thereof, for controlling other-cell interference by adjusting a transmit power parameter for mobile stations in neighboring cells in order to create, within a serving cell, a low interference zone associated with a set of sub-carriers which may be used by edge mobile stations within the serving cell. Rather than restricting the neighboring cells from using the set of sub-carriers associated with the low interference zone, the goal is to reduce the amount of other-cell interference the mobile stations in the neighboring cells can produce with respect to the low interference zone in the serving cell.

Description:
RELATED APPLICATIONS 
       [0001]    Related subject matter is disclosed in the following application filed Aug. 22, 2006, and assigned to the same assignee hereof: U.S. patent application Ser. No. 11/507874 entitled, “A Method For Adaptively Controlling Other Cell Interference,” inventor Anil Rao. 
     
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to wireless communication systems and, in particular, to controlling reverse link transmit power in a wireless communication system. 
       BACKGROUND OF THE RELATED ART 
       [0003]    Universal Mobile Telecommunication System (UMTS) is migrating from a Code Division Multiple Access (CDMA) based air interface to an Orthogonal Frequency Division Multiple Access (OFDMA) based air interface in order to increase reverse link capacity. Reverse link capacity can be increased by limiting interference caused by mobile stations within a same cell (also referred to herein as “in-cell interference”) or by mobile stations in other cells (also referred to herein as “other-cell interference”). 
         [0004]    In-cell and outer-cell Interference are caused, in part, when mobile stations transmit over a same carrier or sub-carrier frequency simultaneously. In a CDMA system, i.e., wireless communication system utilizing a CDMA air interface, mobile stations produces both in-cell interference and other-cell interference because mobile stations in the same cell and in different cells are simultaneously transmitting on a same carrier frequency. In-cell interference is the main source of interference in a CDMA system. By contrast, the main source of interference in an OFDMA system, i.e., wireless communication system utilizing an OFDMA air interface, is other-cell interference. In an OFDMA system, mobile stations in the same cell transmit on different sub-carrier frequencies and, thus, the in-cell interference produced by the mobile stations should be insignificant. However, other-cell interference is still produced because mobile stations in different cells may be simultaneously transmitting on the same sub-carrier frequencies. Accordingly, OFDMA systems have higher reverse link capacity than CDMA systems because mobile stations in an OFDMA system produce less in-cell interference than mobile stations in a CDMA system. 
         [0005]    In order to increase reverse link capacity in an OFDMA system, other-cell interference needs to be reduced. One way to reduce other-cell interference is to limit mobile stations near the edges of adjacent cells to different sets of sub-carrier frequencies. For example, mobile stations near the edge of a first cell would be restricted to using a first set of sub-carrier frequencies, and mobile stations near the edge of an adjacent second cell would be restricted to using a second set of sub-carrier frequencies, wherein the first set includes different sub-carrier frequencies than those in the second set. Edge mobile stations (i.e., mobile stations near the edge of a cell) in the second cell would not be able to use the first set of sub-carrier frequencies even when there are no edge mobile stations in the first cell using sub-carrier frequencies in the first set, or vice-versa. Such manner of reducing other-cell interference will, however, result in an inefficient use of reverse link resources. Accordingly, there exists a need for a method of managing other-cell interference in a wireless communication system more efficiently. 
       SUMMARY OF THE INVENTION 
       [0006]    An embodiment of the present invention is a method, and system thereof, for controlling other-cell interference by adjusting a transmit power parameter for mobile stations in neighboring cells in order to create, within a serving cell, a low interference zone associated with a set of sub-carriers which may be used by edge mobile stations within the serving cell. Rather than restricting the neighboring cells from using the set of sub-carriers associated with the low interference zone, the present invention reduces the amount of other-cell interference the mobile stations in the neighboring cells can produce with respect to the low interference zone in the serving cell. 
         [0007]    In one embodiment, a method of controlling other-cell interference in a wireless system comprises the steps of determining whether a low interference zone of a neighbor cell is interference overloaded, determining whether a high interference zone of the same neighbor cell is interference overloaded, and transmitting zone overload information indicative of whether the low interference zone and/or high interference zone is interference overloaded. The zone overload information is then used to adjust a transmit power constraint of a mobile station in a serving cell. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
           [0009]      FIG. 1  depicts a wireless communication system used in accordance with the present invention; 
           [0010]      FIG. 2  depicts a flowchart illustrating an adaptive interference control used in accordance with a first embodiment of the present invention; 
           [0011]      FIG. 3  depicts a flowchart illustrating an adaptive interference control used in accordance with a second embodiment of the present invention; and 
           [0012]      FIG. 4  depicts an illustrative reverse link sub-carrier partition chart for a set of adjacent cells. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    For purposes of illustration, the present invention will be described herein with reference to a wireless communication system utilizing an Orthogonal Frequency Division Multiple Access (OFDMA) air interface based on the well-known Universal Mobile Telecommunication System standard.  FIG. 1  depicts a wireless communication system  100  comprising base stations  110 ,  120 ,  130  and  140  and at least one mobile station  150 . Each base station  110 ,  120 ,  130  and  140  is associated with a geographical coverage area comprising a plurality of cells or sectors. Specifically, base station  110  is associated with cells  0 ,  1  and  2 ; base station  120  is associated with cells  3 ,  7  and  8 ; base station  130  is associated with cells  4 ,  5  and  9 ; and base station  140  is associated with cells  6 ,  10  and  11 . Mobile station  150  is being served by cell  0 . 
         [0014]    Each base station serves mobile stations within its respective cells using a same set of orthogonal sub-carrier frequencies. The set of orthogonal sub-carrier frequencies may be partitioned in terms of frequency and/or time for reverse link and forward link usage. For purposes of discussion, a sub-carrier frequency, or time segment thereof, used for a reverse link channel or a forward link channel will be referred to herein as a “reverse link sub-carrier” and a “forward link sub-carrier,” respectively, wherein a reverse link channel comprises one or more reverse link sub-carriers and a forward link channel comprises one or more forward link sub-carriers. 
         [0015]    Reverse link channels include traffic channels and control channels, and forward link channels include pilot channels, broadcast channels, control channels and traffic channels. Reverse link traffic channels are assigned to mobile stations by a scheduling entity (also referred to herein as a “scheduler”) at the base station. A message referred to as a “scheduling grant” indicates to the mobile stations, among other things, the reverse link channel (or associated sub-carriers) being assigned and a maximum transmit power spectral density (Max_TPSD) constraint corresponding to a maximum allowable mobile station transmit power for each of the sub-carriers of the assigned reverse link channel. The scheduling grant is transmitted over a forward link control channel. 
         [0016]    Each base station  110 ,  120 ,  130  and  140  transmits a known sequence of bits, i.e., pilot signal, over the pilot channel in each of its associated cells. The pilot channel for each cell in a set of adjacent cells is defined using a different set of (one or more) forward link sub-carriers, wherein a set of adjacent cells comprises a serving cell and a plurality of neighbor cells which are adjacent to the serving cell. For example, a set of adjacent neighbor cells may comprise of serving cell  0  and adjacent neighbor cells  1 - 6 . The forward link sub-carriers used to define the pilot channel in cell  0  would be different from the forward link sub-carriers used to define the pilot channels in cells  1 - 6 . Similarly, the forward link sub-carriers used to define the pilot channel in cell  1  would be different from the forward link sub-carriers used to define the pilot channels in cells  0  and  2 - 6 , and so on. 
         [0017]    For each cell  01 - 11 , the reverse link sub-carriers are partitioned into two or more sets of reverse link sub-carriers. At least one set would be associated with a “low interference zone.” At least another set would be associated with a “high interference zone.” Reverse link sub-carriers associated with a low interference zone would typically be assigned to edge mobile stations, i.e., mobile stations near the edge of a cell. Reverse link sub-carriers associated with a high interference zone would typically be assigned to non-edge mobile stations, i.e., mobile stations not near the edge of a cell. 
         [0018]    For adjacent cells, such as cells  0 ,  5  and  6 , the low interference zone set (i.e., reverse link sub-carrier associated with the low interference zones) would be mutually exclusive with respect to each other.  FIG. 4  depicts an illustrative reverse link sub-carrier partition chart  400  for adjacent cells  0 ,  5  and  6 . The low interference zone sets for cells  0 ,  5  and  6  include reverse link sub-carriers  0  and  1 , reverse link sub-carriers  2  and  3 , and reverse link sub-carriers  4  and  5 , respectively. All other reverse link sub-carriers not in the low interference zone sets may be included in one or more high interference zone sets (i.e., reverse link sub-carrier associated with the high interference zones) for their respective cells. For example, the high interference zone sets for cells  0 ,  5  and  6  include reverse link sub-carriers  2 - 11 , reverse link sub-carriers  0 - 1  and  4 - 11 , and reverse link sub-carriers  0 - 3  and  6 - 11 , respectively. For purposes of illustration, the present invention will be described herein to cells associated with one low interference zone and one high interference zone. This should not be construed to limit the present invention in any manner. 
         [0019]    In each cell, other-cell interference is measured for the low and high interference zones. The other cell-interference measurements are then compared to interference thresholds. Specifically, for a low interference zone, the associated other-cell interference measurement (i.e., interference on reverse link sub-carriers associated with the low interference zone) is compared to a low interference threshold. For a high interference zone, the associated other-cell interference measurement (i.e., interference on reverse link sub-carriers associated with the high interference zone) is compared to a high interference threshold, wherein the low interference threshold is a lower threshold relative to the high interference threshold. If the other-cell interference measurement is above the associated interference threshold, the zone associated with that other-cell interference measurement is considered to be interference overloaded. 
         [0020]    The low and/or high interference thresholds may be the same or different across all cells, or a subset thereof. If the reverse link sub-carriers are partitioned into two or more low interference zone sets or two or more high interference zone sets, then a different low or high interference threshold may apply to each of the low or high interference zones, respectively. Additionally, the low and/or high interference thresholds may be static (e.g., predetermined) or dynamic (e.g., determined based on how many edge mobile stations are in the cell). 
         [0021]    Information indicating whether a zone is overloaded, hereinafter referred to as “zone overload information,” is used to adaptively control other-cell interference.  FIG. 2  depicts a flowchart  200  illustrating an adaptive interference control method used in accordance with a first embodiment of the present invention. In this embodiment, zone overload information is communicated to mobile station  150 . Such overload information is then used by mobile station  150  to determine whether adjustments should be made to the maximum transmit power spectral density (Max_TPSD) constraints associated with the reverse link sub-carriers assigned to mobile station  150 . In another embodiment, the adjustments may be made to some other mobile station transmit power parameter, such as a constraint relating to a total maximum allowable mobile station transmit power, or to actual mobile station transmit power. 
         [0022]    In step  205 , mobile station  150  is in a call and is monitoring the pilot channels of its neighbor cells, i.e., measuring pilot signal strengths of neighbor cells. While mobile station  150  is in the call, its transmit power is continuously being adjusted in accordance with well-known power control techniques and limited by the Max_TPSD constraints. 
         [0023]    In step  210 , serving base station  110  transmits, over a broadcast channel (or some other communication channel, such as a control channel) in cell  0 , an overload channel list indicating overload channels for at least the adjacent neighbor cells, e.g., cells  1 - 6 . The overload channels can be, for example, a broadcast channel or control channel over which zone overload information is transmitted. Like the pilot channel, the overload channel for each cell in the set of adjacent cells is defined using a different set of (one or more) forward link sub-carriers. 
         [0024]    In one embodiment, each base station transmits zone overload information over two overload channels. One overload channel is used to transmit overload information associated with low interference zones, whereas the other overload channel is used to transmit overload information associated with high interference zones. The overload channel list may also indicate which overload channels are associated with low and high interference zones. 
         [0025]    The zone overload information may be a flag or other message indicating whether the associated zone in the cell is interference overloaded. The zone overload information may also indicate the reverse link sub-carriers associated with the overloaded zone. Alternately, information indicating the sub-carriers associated with each zone at neighbor cells may be provided by some other method. For example, such information may be provided via a broadcast message or a scheduling grant. 
         [0026]    In step  215 , mobile station  150  monitors the overload channels indicated by the overload channel list. In step  220 , mobile station  150  determines whether a zone at any adjacent neighbor cell is interference overloaded based on the monitored overload channels. In an alternate embodiment, mobile station  150  may only determine whether a zone in the adjacent neighbor cell with the strongest pilot signal strength at mobile station  150  is interference overloaded (instead of any adjacent neighbor cell). 
         [0027]    If such a zone is interference overloaded (also referred to herein as an “overloaded zone”), flowchart  200  continues to step  225 . Otherwise flowchart  200  continues to step  240 . 
         [0028]    In step  225 , mobile station  150  decreases the maximum transmit power spectral density (Max_TPSD) constraint associated with an overloaded reverse link sub-carrier assigned to mobile station  150 . For purposes of this application, the term “overloaded reverse link sub-carrier” should be construed to mean a reverse link sub-carrier that corresponds to an overloaded zone, i.e., reverse link sub-carrier is a sub-carrier in the overloaded zone. For example, suppose mobile station  150  has been assigned reverse link sub-carriers  0 ,  3 ,  6 ,  9  and  11  in cell  0 . The low interference zone in cell  5  is interference overloaded. The low interference zone set for cell  5  comprises reverse link sub-carriers  2  and  3 . Thus, with respect to cell  5 , assigned reverse link sub-carrier  3  corresponds to an overloaded zone, i.e., reverse link sub-carrier  3  is an overloaded reverse link sub-carrier, and assigned reverse link sub-carriers  0 ,  6 ,  9  and  11  do not correspond to an overloaded zone, i.e., reverse link sub-carriers  0 ,  6 ,  9  and  11  are non-overloaded reverse link sub-carriers. 
         [0029]    In one embodiment, the Max_TPSD constraint is decreased based on relative received pilot powers at mobile station  150  of the serving cell and the adjacent neighbor cell with the overloaded zone to which the overloaded reverse link sub-carrier corresponds (also referred to herein as an “overloaded adjacent neighbor cell”). Alternately, the Max_TPSD constraint may be decreased based on relative distances mobile station  150  is from the serving cell and the overloaded adjacent neighbor cell. 
         [0030]    Note that this relative received pilot powers (or distances) is indicative of an amount of other-cell interference a mobile station transmission produces in the overloaded adjacent neighbor cell. By using such relative received pilot powers (or distances) as a basis for decreasing the Max_TPSD constraint, the amount of other-cell interference produced by a mobile station in the overloaded adjacent neighbor cell is taken into account. For example, if the relative received pilot powers indicate that a mobile station is producing a high amount of other-cell interference in the overloaded adjacent neighbor cell, the Max_TPSD constraint can be reduced by a large amount, or vice-versa. 
         [0031]    In one embodiment, the relative received powers (or distances) is measured using a down pilot power ratio (Down_PPR) corresponding to a ratio between a received pilot power of the overloaded adjacent neighbor cell (P_overloaded_neighbor) at mobile station  150  and a received pilot power of the serving cell (P_serving) at mobile station  150 , i.e., Down_PPR=P_overloaded_neighbor/P_serving. Note that if there are more than one overloaded adjacent neighbor cell, then the overloaded adjacent neighbor cell with the strongest received pilot power at mobile station  150  (also referred to herein as “strongest overloaded adjacent neighbor cell”) would be used as P_overloaded_neighbor to calculate the Down_PPR. The Down_PPR is used to decrease the maximum mobile station transmit power Max_TPSD constraint associated with the overloaded reverse link sub-carrier in accordance with the following equation: 
         [0000]      Max —   TPSD _current=Max —   TPSD _previous−Down —   PPRx Step_Down   (1) 
         [0000]    where Max_TPSD_current corresponds to a new Max_TPSD constraint, Max_TPSD_previous corresponds to a previous Max_TPSD constraint, and Step_Down corresponds to a reference amount (or down step size) by which the previous Max_TPSD constraint is decreased (i.e., amount Max_TPSD constraint is adjusted down when Down_PPR=1). In an embodiment, the Max_TPSD constraint is not decreased unless the Down_PPR is above a first threshold PPR, e.g., 0.5. 
         [0032]    In step  230 , mobile station determines whether the mobile station transmit power for the overloaded reverse link sub-carriers is greater than the new Max_TPSD constraint, e.g., Max_TPSD_current. If the mobile station transmit power is greater than the new Max_TPSD constraint, then in step  235  the mobile station transmit power is decreased for that reverse link sub-carrier until it is not greater than the new Max_TPSD constraint. From step  235 , or if it is determined in step  230  that the mobile station transmit power is not greater than the new Max_TPSD constraint, or If it is determined in step  220  that no zone at an adjacent neighbor cell is interference overloaded, flowchart  200  continues to step  240 . 
         [0033]    In step  240 , mobile station  150  increases the Max_TPSD constraint for each non-overloaded reverse link sub-carrier assigned to mobile station  150 . In one embodiment, the Max_TPSD constraint is increased based on relative received pilot powers of the adjacent neighbor cell with the strongest received pilot signal strength at mobile station  150  (also referred to herein as &#39;strongest adjacent neighbor cell) and the serving cell. Alternately, the Max_TPSD may be increased based on relative distances mobile station  150  is from the strongest adjacent neighbor cell and the serving cell. From step  240 , flowchart  200  continues to step  245 , where mobile station  150  transmits a message indicating to base station  110  the new Max_TPSD constraint and associated reverse link sub-carrier, for example, as part of a scheduling request message. 
         [0034]    Note that this relative received pilot powers (or distances) is different from the one used to decrease the Max_TPSD constraint. This relative received pilot powers is based on the strongest adjacent neighbor cell. By using such relative received pilot powers (or distances) as a basis for increasing the Max_TPSD constraint, mobile stations farther away from their serving base station may increase its transmit power higher (for the non-overloaded reverse link sub-carriers) and achieve better throughput. Other-cell interference produced by these mobile stations is not a concern since the transmit power which may be increased are associated with reverse link sub-carriers that do not correspond to an overloaded zone at an adjacent neighbor cell. 
         [0035]    In one embodiment, the relative received pilot powers (or distances) is measured using an up pilot power ratio (Up_PPR) corresponding to a ratio between a received pilot power of the strongest adjacent neighbor cell (P_strongest_neighbor) at mobile station  150  and a received pilot power of the serving cell (P_serving) at mobile station  150 , i.e., P_strongest_neighbor/Up_PPR=P_serving. 
         [0036]    The Up_PPR is used to increase the maximum mobile station transmit power (Max_TPSD) constraint in accordance with the following equation: 
         [0000]      Max —   TSPD _current=Max —   TPSD _previous+Up —   PPRx Step_Up   (2) 
         [0000]    where Step_Up corresponds to a reference amount (or up step size) by which the Max_TPSD constraint is increased (i.e., amount Max_TPSD constraint is adjusted up when Up_PPR=1). In one embodiment, the Max_TPSD constraint is not increased unless the Up_PPR is below a second threshold PPR, e.g. 0.7. 
         [0037]    In one embodiment, Step_Up and Step_Down are set such that Step_Up&lt;Step_Down. In another embodiment, Step_Up and Step_Down are set such that a desired interference overshoot rate is achieved, wherein the desired interference overshoot corresponds to a desired fraction of time which interference levels in a zone may exceed a particular threshold value. For example, Step_Up and Step_Down are selected in accordance with the following equation: 
         [0000]      Step_Up/Step_Down=Inter_Overshoot(/1-Inter_Overshoot)   (3) 
         [0000]    where Inter_Overshoot corresponds to the desired interference overshoot. 
         [0038]    Note that, in the embodiment of  FIG. 2 , the Max_TPSD constraints are calculated at mobile station  150  and transmitted to base station  110 . In another embodiment, mobile station  150  transmits the relevant received pilot signal strength (for the strongest overloaded adjacent neighbor cell or strongest adjacent neighbor cell, for example), along with some cell identifier associating the received pilot signal strength with the respective cell, to base station  110  over a control channel, such as a scheduling request channel. Or mobile station  150  transmits the Down_PPR (for the strongest overloaded adjacent neighbor cell) or Up_PPR (for the strongest adjacent neighbor cell), along with some cell identifier associating the Down_PPR or Up_PPR with the respective cell or zone, to base station  110  over a control channel, such as the scheduling request channel. The new Max_TPSD constraints are calculated at base station  110  based on the received information and transmitted to mobile station  150  in a message, such as the scheduling grant. 
         [0039]      FIG. 3  depicts a flowchart  300  illustrating an adaptive interference control method used in accordance with a second embodiment of the present invention. In this embodiment, zone overload information is communicated among base stations  110 ,  120 ,  130  and  140 , and used by the serving base station, i.e., base station of serving cell, to determine whether adjustments should be made to the maximum transmit power spectral density (Max_TPSD) constraints associated with the reverse link sub-carriers assigned to mobile station  150 . In another embodiment, the adjustments may be made to some other mobile station transmit power parameter, such as a constraint to a total maximum allowable mobile station transmit power, or to actual mobile station transmit power. 
         [0040]    In step  305 , mobile station  150  is in a call and is monitoring the pilot channels of its neighbor cells, i.e., measuring pilot signal strengths of neighbor cells. While mobile station  150  is in the call, its transmit power is continuously being adjusted in accordance with well-known power control techniques and limited by the maximum transmit power spectral density (Max_TPSD) constraints. 
         [0041]    In step  310 , mobile station  150  transmits a pilot report indicating to its serving base station  110  the received pilot signal strengths from both the serving base station and the neighboring base stations. The pilot report may, for example, be the Event IA,  1 B,  1 C, and  1 D messages used in UMTS for initiating handoffs. In step  315 , base stations  110 ,  120 ,  130  and  140  transmits zone overload information to each other indicating whether zones in their associated cells are interference overloaded. The zone overload information may be transmitted periodically, transmitted only when interference overload is present, or transmitted when the current overload status of a zone in a cell has changed, e.g., overloaded zone is no longer interference overloaded or vice-versa. 
         [0042]    In step  320 , serving base station  110  determines whether a zone at the strongest adjacent neighbor cell (i.e., adjacent neighbor cell with strongest pilot signal strength at mobile station  150 ) is interference overloaded based on the zone overload information. Alternately, serving base station  110  may determine whether a zone at any adjacent neighbor cell is interference overloaded. 
         [0043]    If a zone at the strongest adjacent neighbor cell is interference overloaded, serving base station  110  decreases in step  325  the Max_TPSD constraints for each overloaded reverse link sub-carriers assigned to mobile station  150 . In one embodiment, the Max_TPSD constraint is decreased based on relative received pilot powers of the strongest adjacent neighbor cell and the serving cell (or based on relative distances mobile station  150  is from the strongest adjacent neighbor cell and the serving cell). For example, the Max_TPSD constraint may be decreased in accordance with the following equation: 
         [0000]      Max —   TPSD _current=Max —   TPSD _previous− PPR 2 x Step_Down   (4) 
         [0000]    where PPR2 corresponds to a ratio between a received pilot power of the strongest adjacent neighbor cell (P_strongest_neighbor) at mobile station  150  and a received pilot power of the serving cell (P_serving) at mobile station  150 , i.e., PPR2=P_strongest_neighbor/P_serving. In one embodiment, the Max_TPSD constraint is not adjusted unless the PPR2 is above a third threshold PPR, e.g., 0.6. 
         [0044]    From step  325 , or if it is determined in step  320  that no zone at the strongest adjacent neighbor cell is interference overloaded, flowchart  300  continues to step  330  where serving base station  110  increases the Max_TPSD constraints for each non-overloaded reverse link sub-carriers assigned to mobile station  150 . In one embodiment, the Max_TPSD constraints are increased based on relative received pilot powers of the strongest adjacent neighbor cell and the serving cell (or based on relative distances mobile station  150  is from the strongest adjacent neighbor cell and the serving cell). For example, the Max_TPSD constraint may be increased in accordance with the following equation: 
         [0000]      Max —   TSPD _current=Max —   TPSD _previous+ PPR 2 x Step_Up   (5) 
       In one embodiment, the Max_TPSD constraint is not increased unless the PPR2 is below a fourth threshold PPR, e.g., 0.5. 
       [0045]    In step  335 , serving base station  110  transmits a scheduling grant or other message to mobile station  150  over a forward link control channel, wherein the scheduling grant or other message indicates the new Max_TPSD constraints, i.e., Max_TPSD_current. In step  340 , mobile station  150  adjusts its transmit power using well-known power control techniques under the limits of the new Max_TPSD constraints. 
         [0046]    Note that, in the embodiment of  FIG. 3 , the new Max_TPSD constraints are calculated by serving base station  150  and then transmitted to mobile station  150 . In an alternate embodiment, serving base station  110  transmits a message to mobile station  150  indicating which zones at adjacent neighbor cells are overloaded. Mobile station  150  can subsequently determine the new Max_TPSD constraints based on this message. 
         [0047]    The present invention have been described herein with reference to certain embodiments. This should not be construed to limit the present invention to these embodiments. Other embodiments and combinations of embodiments are possible. For example, instead of adjusting the Max_TPSD constraints, the actual mobile station transmit power may be adjusted using the PPR. Therefore, the spirit and scope of the present invention should not be limited to the description of the embodiments contained herein.