diff --git a/CHANGELOG.md b/CHANGELOG.md
index ace39f8..2c46d59 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## v2.1.5 - 2024-12-24
+- [upgrade] apply multithread to process several pointclouds parallely
+- [upgrade] store pointclouds with `std::deque`
+- support for one single pointcloud input
+
 ## v2.1.4 - 2024-12-24
 - [upgrade] set `queue_size` of `Subscriber` to `boost::thread::hardware_concurrency()`
 - [upgrade] check if both `frame_id`s are the same
diff --git a/include/merge_pcl/merge_pcl.h b/include/merge_pcl/merge_pcl.h
index b218d54..f746e87 100644
--- a/include/merge_pcl/merge_pcl.h
+++ b/include/merge_pcl/merge_pcl.h
@@ -5,6 +5,9 @@
 #ifndef MERGE_PCL_H
 #define MERGE_PCL_H
 
+#include <thread>
+#include <deque>
+#include <mutex>
 #include <ros/ros.h>
 #include <ros/rate.h>
 #include <pcl_ros/point_cloud.h>
@@ -16,9 +19,6 @@
 #include <pcl/point_types.h>
 #include <pcl/kdtree/kdtree_flann.h>
 #include <message_filters/subscriber.h>
-#include <message_filters/sync_policies/approximate_time.h>
-#include <message_filters/sync_policies/exact_time.h>
-#include <message_filters/time_synchronizer.h>
 #include <sensor_msgs/PointCloud2.h>
 
 using namespace std;
@@ -28,23 +28,30 @@ class PointCloudMerger {
     PointCloudMerger();
     ~PointCloudMerger() = default;
 
-    void mergeCallback(const sensor_msgs::PointCloud2ConstPtr& pcl2_0,
-                       const sensor_msgs::PointCloud2ConstPtr& pcl2_1);
+    // Method to process buffers
+    void processBuffers();
 
 private:
-    typedef message_filters::sync_policies::ApproximateTime<sensor_msgs::PointCloud2, sensor_msgs::PointCloud2>
-            SyncPolicy;
-    typedef shared_ptr<message_filters::Synchronizer<SyncPolicy>> Synchronizer;
-
     ros::NodeHandle nh;
 
     int pcl2_source_num;
+    size_t queue_size;
+    double timeout;
+
     std::string pcl2_topic_0, pcl2_frame_0;
+    ros::Subscriber pcl2_sub_0;
+    void pcl2Callback0(const sensor_msgs::PointCloud2ConstPtr& pcl2);
+
     std::string pcl2_topic_1, pcl2_frame_1;
-    shared_ptr<message_filters::Subscriber<sensor_msgs::PointCloud2>> pcl2_sub_0, pcl2_sub_1;
-    int queue_size;
-    Synchronizer synchronizer_;
+    ros::Subscriber pcl2_sub_1;
+    void pcl2Callback1(const sensor_msgs::PointCloud2ConstPtr& pcl2);
+
+    // Buffers to store point clouds
+    std::deque<pcl::PointCloud<pcl::PointXYZ>::Ptr> buffer_0;
+    std::deque<pcl::PointCloud<pcl::PointXYZ>::Ptr> buffer_1;
+    std::mutex buffer_mutex;
 
+    // Transform listeners
     tf::TransformListener listener0, listener1;
     double tf_duration;
 
diff --git a/package.xml b/package.xml
index 88646b3..8eeb33a 100644
--- a/package.xml
+++ b/package.xml
@@ -1,7 +1,7 @@
 <?xml version="1.0"?>
 <package format="2">
     <name>easondrone_mapping</name>
-    <version>2.1.4</version>
+    <version>2.1.5</version>
     <description>
         A ROS package for mapping via octomap
     </description>
diff --git a/src/merge_pcl/merge_pcl.cpp b/src/merge_pcl/merge_pcl.cpp
index a293543..c6c26b2 100644
--- a/src/merge_pcl/merge_pcl.cpp
+++ b/src/merge_pcl/merge_pcl.cpp
@@ -2,75 +2,108 @@
 
 using namespace std;
 
-PointCloudMerger::PointCloudMerger() : nh("~"){
+PointCloudMerger::PointCloudMerger() : nh("~") {
     nh.param<int>("pcl2_source_num", pcl2_source_num, 2);
+    queue_size = boost::thread::hardware_concurrency();
+    nh.param<double>("timeout", timeout, 0.5);
+
     nh.param<string>("pcl2_topic_0", pcl2_topic_0, "");
     nh.param<string>("pcl2_frame_0", pcl2_frame_0, "");
+    pcl2_sub_0 = nh.subscribe<sensor_msgs::PointCloud2>
+    (pcl2_topic_0, queue_size, &PointCloudMerger::pcl2Callback0, this);
+
     nh.param<string>("pcl2_topic_1", pcl2_topic_1, "");
     nh.param<string>("pcl2_frame_1", pcl2_frame_1, "");
+    pcl2_sub_1 = nh.subscribe<sensor_msgs::PointCloud2>
+    (pcl2_topic_1, queue_size, &PointCloudMerger::pcl2Callback1, this);
+
     nh.param<double>("tf_duration", tf_duration, 0.1);
+    listener0.waitForTransform(pcl2_frame_out, pcl2_frame_0, ros::Time(0), ros::Duration(tf_duration));
+    listener1.waitForTransform(pcl2_frame_out, pcl2_frame_1, ros::Time(0), ros::Duration(tf_duration));
+
     nh.param<string>("pcl2_topic_out", pcl2_topic_out, "");
     nh.param<string>("pcl2_frame_out", pcl2_frame_out, "");
+    pcl2_pub = nh.advertise<sensor_msgs::PointCloud2>
+    (pcl2_topic_out, queue_size);
 
-    queue_size = boost::thread::hardware_concurrency();
-
-    pcl2_sub_0.reset(new message_filters::Subscriber<sensor_msgs::PointCloud2>
-    (nh, pcl2_topic_0, queue_size));
-    pcl2_sub_1.reset(new message_filters::Subscriber<sensor_msgs::PointCloud2>
-    (nh, pcl2_topic_1, queue_size));
-
-    synchronizer_.reset(new message_filters::Synchronizer<SyncPolicy>(SyncPolicy(100), *pcl2_sub_0, *pcl2_sub_1));
-    synchronizer_->registerCallback(boost::bind(&PointCloudMerger::mergeCallback, this, _1, _2));
-
-    pcl2_pub = nh.advertise<sensor_msgs::PointCloud2>(pcl2_topic_out, queue_size);
+    ROS_INFO("[merge_pcl] Initialized!");
+}
 
-    listener0.waitForTransform(pcl2_frame_out, pcl2_frame_0, ros::Time(0), ros::Duration(tf_duration));
-    listener1.waitForTransform(pcl2_frame_out, pcl2_frame_1, ros::Time(0), ros::Duration(tf_duration));
+void PointCloudMerger::pcl2Callback0(const sensor_msgs::PointCloud2ConstPtr& pcl2) {
+    pcl::PointCloud<pcl::PointXYZ>::Ptr pclxyz_0(new pcl::PointCloud<pcl::PointXYZ>());
+    pcl::fromROSMsg(*pcl2, *pclxyz_0);
+
+    if (pcl2->header.frame_id != pcl2_frame_out) {
+        try {
+            pcl_ros::transformPointCloud(pcl2_frame_out, *pclxyz_0, *pclxyz_0, listener0);
+        } 
+        catch (...) {
+            ROS_ERROR("Transform failed for pcl2_0!");
+            return;
+        }
+    }
 
-    ROS_INFO("[easondrone_mapping] merge_pcl initialized!");
+    std::lock_guard<std::mutex> lock(buffer_mutex);
+    buffer_0.push_back(pclxyz_0);
+    if (buffer_0.size() > queue_size) {
+        buffer_0.pop_front();
+    }
 }
 
-void PointCloudMerger::mergeCallback(const sensor_msgs::PointCloud2ConstPtr& pcl2_0, const sensor_msgs::PointCloud2ConstPtr& pcl2_1) {
-    pcl::PointCloud<pcl::PointXYZ>::Ptr pclxyz_0, pclxyz_1, pclxyz_output;
-
-    pclxyz_0.reset(new pcl::PointCloud<pcl::PointXYZ>());
-    pcl::fromROSMsg(*pcl2_0, *pclxyz_0);
-    // check if both frames are the same
-    if(pcl2_0->header.frame_id != pcl2_frame_out){
-        try{
-            pcl_ros::transformPointCloud(pcl2_frame_out, *pclxyz_0, *pclxyz_0, listener0);  
-        }
-        catch(...){
-            ROS_ERROR("pcl_ros::transformPointCloud failed!");
+void PointCloudMerger::pcl2Callback1(const sensor_msgs::PointCloud2ConstPtr& pcl2) {
+    pcl::PointCloud<pcl::PointXYZ>::Ptr pclxyz_1(new pcl::PointCloud<pcl::PointXYZ>());
+    pcl::fromROSMsg(*pcl2, *pclxyz_1);
+
+    if (pcl2->header.frame_id != pcl2_frame_out) {
+        try {
+            pcl_ros::transformPointCloud(pcl2_frame_out, *pclxyz_1, *pclxyz_1, listener1);
+        } 
+        catch (...) {
+            ROS_ERROR("Transform failed for pcl2_1!");
+            return;
         }
     }
 
-    pclxyz_1.reset(new pcl::PointCloud<pcl::PointXYZ>());
-    pcl::fromROSMsg(*pcl2_1, *pclxyz_1);
-    // check if both frames are the same
-    if(pcl2_1->header.frame_id != pcl2_frame_out){
-        try{
-            pcl_ros::transformPointCloud(pcl2_frame_out, *pclxyz_1, *pclxyz_1, listener1);  
-        }
-        catch(...){
-            ROS_ERROR("pcl_ros::transformPointCloud failed!");
-        }
+    std::lock_guard<std::mutex> lock(buffer_mutex);
+    buffer_1.push_back(pclxyz_1);
+    if (buffer_1.size() > queue_size) {
+        buffer_1.pop_front();
     }
+}
 
-    pclxyz_output.reset(new pcl::PointCloud<pcl::PointXYZ>());
+void PointCloudMerger::processBuffers() {
+    while (ros::ok()) {
+        pcl::PointCloud<pcl::PointXYZ>::Ptr pclxyz_0, pclxyz_1, pclxyz_output;
+
+        {
+            std::lock_guard<std::mutex> lock(buffer_mutex);
+            if (!buffer_0.empty()) {
+                pclxyz_0 = buffer_0.front();
+                buffer_0.pop_front();
+            }
+            if (!buffer_1.empty()) {
+                pclxyz_1 = buffer_1.front();
+                buffer_1.pop_front();
+            }
+        }
 
-    pclxyz_output->header.seq = pclxyz_1->header.seq;
-    pclxyz_output->header.stamp = pclxyz_1->header.stamp;
-    pclxyz_output->header.frame_id = pcl2_frame_out;
+        if (pclxyz_0 || pclxyz_1) {
+            pclxyz_output.reset(new pcl::PointCloud<pcl::PointXYZ>());
+            if(pclxyz_0){
+                *pclxyz_output += *pclxyz_0;
+            }
+            if(pclxyz_1){
+                *pclxyz_output += *pclxyz_1;
+            }
 
-    *pclxyz_output += *pclxyz_1;
-    *pclxyz_output += *pclxyz_0;
+            sensor_msgs::PointCloud2 pcl2_output;
+            pcl2_output.header.frame_id = pcl2_frame_out;
+            pcl::toROSMsg(*pclxyz_output, pcl2_output);
 
-    sensor_msgs::PointCloud2 pcl2_output;
-    pcl::toROSMsg(*pclxyz_output, pcl2_output);
+            pcl2_pub.publish(pcl2_output);
+        }
 
-    if(pcl2_pub){
-        pcl2_pub.publish(pcl2_output);
+        ros::Duration(tf_duration).sleep();  // Small delay to avoid excessive CPU usage
     }
 }
 
@@ -78,6 +111,10 @@ int main(int argc, char** argv) {
     ros::init(argc, argv, "merge_pcl");
     PointCloudMerger pc_merger;
 
+    boost::thread processing_thread(&PointCloudMerger::processBuffers, &pc_merger);
+
     ros::spin();
+    processing_thread.join();
+
     return 0;
 }