Adaptive QoS Framework for Wireless Sensor Networks Lucy He Honeywell Technology & Solutions Lab No. 430 Guo Li Bin Road, Pudong New Area, Shanghai, P.R.C., 201203
2 Proposed Adaptive QoS Framework for WSN • 2.1 Basic Architecture
2.2 Data Communication between Head and Sensor Nodes • The cluster nodes communicate with the cluster head via the Time division multiple access (TDMA) scheme. • Packet reservation multiple access (PRMA) is integrated with TDMA scheme to schedule the sharing channel dynamically. The TDMA frame consists of two phases: basic slots and reserved slots. • The basic slots are used for transmitting control messages of each node, • Each node is allocated a basic time slot to communicate with the cluster head initially. • The reserved slots are used for transmitting real-time data of requested nodes.
2.3 Dynamic Time Slot Scheduling(1/2) • When a node finds that it has not enough time to transmit its data during its own slot, the node sends a request-to-send message (RTS) to the cluster head for reserving more slots. • If two RTS have the same priority, they will be inserted into the priority queue via FIFO scheme. • The head allocates time slots to the cluster nodes according to their priority and requested slots, and broadcasts acknowledgementmessage (ACK) with allocated time slots in its control slots. • The other nodes also know that these slots are reserved and will not try to contend. Thus contention is avoided among them.
2.4 Periodic Listening and Sleeping (1/2) • When its time slot comes, the node is required to wake up and send keep-alive message to the cluster head. • Otherwise, the cluster head will assume the node is dead and deleted it from its neighbor table if it does not receive any keep-alive messages from the node after some predefined maximum interval.
2.6 Head Selection • The cluster heads should be rotated among sensor nodes. • a Backup Head is needed. • Head updates Backup Head with the changes at every time frame.
2.7 Data Communication between Cluster Head and Base Station • TDMA scheme is implemented to allow channels to be shared among the cluster heads without contention. • As the bandwidth of base stations is much larger than that of the sensor nodes, the bandwidth can be divided to more small channels via the frequency division multiple access (FDMA).
3 The Clock Synchronization Protocol • The cluster head prepares the control message with timestamp (t1) and broadcasts it (t2) to the nodes in this cluster in slot 0. • Each slave receives the message (t3) and adjusts their local clocks (t4). The protocol works as follows (see Figure 5).
4 System Self-organization • Node entry: It then sends its join message to Head at a free slot. the cluster head will add the node into its neighbor table and assign it a basic time slot for further communications. • Node failure: If the cluster head hasn’t received any message from a node for a predefined period the cluster head will delete it from the neighbor table, set its time slot to be a free slot.
5 Discussion • WSN can mainly be used in the following two kinds of application backgrounds: • 1. Sensing events. • 2. Tracking mobile objects. This framework is mainly designed for the first case in which sensor nodes are immobile. How to support QoS in these ad hoc networks is still a difficulty. This is one research direction of our future work.
6 Conclusion • An adaptive framework for QoS support • Time synchronization in wireless sensor networks based on TDMA and PRMA scheme. • A rule engine is designed at the application layer to differentiate the importance of data packet • The simulation results for bandwidth calculation and reservation, resource scheduling and time synchronization will be presented in future work. • QoS support in mobile ad-hoc networks without centralized base-stations is still under further study and investigation
comment 1.The contribution of this paper is not clear. Because of Basic Architecture, DataCommunication between Head and Sensor Nodes, Periodic Listening and Sleeping,Data Communication between Cluster Head and Base Station, The Clock Synchronization Protocol are not your originality. 2.Your references is not enough. 3.In Section 2.3 "Dynamic Time Slot Scheduling" , your proposed dynamic time Slot Scheduling scheduling is not specific. How heads dose adjust the queue according to the elapsed time of RTSs. 4.In Section 2.6 “Head Selection" , the actual values in equation 1 is not clear. how to evaluate "C- computation ability" ? And location is not considered in equation 1. 5.You don't guarantee that your adaptive QoS framework is better than other QoS frameworks in WSN.