Nonexposure Accurate Location 𝐾-Anonymity Algorithm in LBS

Algorithm 1

Optimal ASR.

(1) function optimal ASR (𝑘, 𝐴_min, ID_now(𝑋,𝑌))

(2)  if (𝑁 >= 𝑘)  // 𝑁 indicates the number of the user’s grid-area.

(3)  𝑆 = the area of ID_now(𝑋,𝑌);    //ID_now(𝑋,𝑌) is the user’s grid-area; 𝑆 is cloaked set of grid-areas.

(4)  else     {

(5)     int 𝑑 = 1; //the distance from the grid-area of ID_now(𝑋,𝑌).

(6)     while all the useful areas have not yet been searched {.

(7)         d++;    // Extends the distance to search, for the first time, 𝑑=2, so there are 24 grid-areas can be chosen.

(8)          if (total number of the users in all the grid-areas nearby whose distance from ID_now(𝑋,𝑌) <= 𝑑 is less

(9)              than 𝑘−𝑁) continue;

(10)           𝑆 = the grid-area of ID_now(𝑋,𝑌);

(11)         Adds the grid-area which has the highest QoS into 𝑆 until the total users in 𝑆 is not less than 𝑘;

(12)         // the QoS of the grid-area can be calculated by Formula (3).

(13)         break;

(14)          }  //end while

(15)    }    //end else

(16)   if (𝑆 is null) 𝑆 = the grid-area of ID_now(𝑋,𝑌);

(17)  // Not enough users, so reduce the degree of anonymity.

(18)   if (the total square measure of 𝑆 < 𝐴_min)

(19)       adds the grid-area which has the highest QoS into 𝑆 until the total square measure of 𝑆

(20)       is not less than 𝐴_min;    // the QoS of the grid-area can be calculated by Formula (2).

(21)   if  (there are grid-areas which are adjacent in 𝑆)

(22)       Combines the adjacent grid-areas to one single area;

(23)   replaces the ID(𝑋,𝑌) to Rec⟨(𝑥_ul,𝑦_ul),(𝑥_dr,𝑦_dr)⟩ for grid-areas in 𝑆 to get the ASR;

(24)    return ASR;