## 4 Performance Evaluation
Neither GHT nor GCLP take account of the query frequency; therefore, the number of repository nodes is fixed in spite of the increased query frequency. This leads to an increase in the number of queries received per node. On the other hand, ASST varies the size of the trajectory in proportion to the query frequency, so that the number of repository nodes in ASST is increased in proportion to the increased query frequency. Therefore, the number of received queries per node in ASST is smaller than that in GHT and GCLP. GHT can be regarded as minimum replication, and GCLP can be regarded as maximum replication. It should be noted that the number of repository nodes in GCLP and ASST is similar when the query frequency is high, but the number of received queries per node in GCLP is higher than that in ASST due to the two  
Figure 9: Number of repository nodes and the number of queries received per repository node. matching points in GCLP. In GCLP, both the publish trajectory and the subscribe trajectory form a cross, making two matching points. Therefore, the number of received queries is higher than that in ASST. The number of queries per node can affect the response time. Figure 10 shows the response time with an increased query frequency. When the query frequency is low, GCLP shows a shorter response time than ASST or GHT because GCLP has more repository nodes than GHT or ASST. Moreover, GCLP forms a trajectory crossing the network so that GCLP occupies a larger area than GHT or ASST, and this leads to a reduction in the hop counts between the repository and query nodes. However, as the query frequency increases, the response time also increases. When the query frequency is very high, the response time is longer than that in ASST. This is caused by the larger number of received queries. However, GHT and ASST have the same number of repository nodes and the same hop counts between the repository and query nodes when the query frequency is low, so that the response times of both is the same. However, when the query frequency is increased, the response time of GHT is increased drastically while the response time of ASST is almost uniform. This is due to the difference between GHT and ASST in terms of the number of received queries per node. GHT always has a fixed number of repository nodes so that the number of received queries per node increases, and this leads to an increased response time. On the other hand, ASST increases the number of repository nodes in proportion to the query frequency so that the number of received queries per node and response time are almost uniform. Replicating data in several sensor nodes requires energy costs for packet transmission. More nodes participate in replication, and more energy is consumed because energy consumption is increased whenever a node transmits a packet. Figure 11 shows the energy consumption for repository construction. As mentioned earlier, the number of repository nodes in GHT and GCLP is fixed in spite  
Figure 10: Response time with increased query frequency. of query frequency change. GHT maintains a minimum number of repository nodes around the target point so that the energy consumption is lower than that with GCLP or ASST. In contrast, GCLP maintains repository nodes between the network boundaries in a cross shape so that energy consumption is higher than that under GHT or ASST. On the other hand, ASST varies the number of repository nodes in proportion to the query frequency so that the energy consumption is low when the query frequency is low, and the energy consumption is increased in proportion to the query frequency. The energy consumption is similar with GHT when the query frequency is low, and the energy consumption is increased towards the GCLP as the query frequency increases.