Time Slot Assignment Algorithm in WSNs to Reduce Collisions

Abstract

Existing hybrid MAC in wireless sensor networks (WSNs) is to combine TDMA and CSMA MAC techniques to adapt sensor nodes into the environment from low contention state to high contention state. It operates in pure CSMA mode when the traffic requirement is comparably low in WSN. On the other hand, as the sensor data is generated in high rate, hybrid MAC is shifted to TDMA-based operation. The main advantage of pure TDMA is no collision among nodes with pre-allocation of each time slot. Every time slot is allocated to nodes in need and it is owned only by pre-allocated node. Non-owner node may not use any other time slots that are not allocated to it. We propose new time slot assignment method to assign every empty slot to nodes which are not in need currently. Even though they are not in need now, the sensor nodes may get more data to send in some time later. In that case, if more time slots were allocated to nodes in advance, the owner nodes can get empty slots to send without contention resulting of reduction in collision and increase in overall traffic throughput.