We describe an improved version of simple polling protocol employed in a wireless sensor network proposed in [4]. Although this simple wireless sensor network works efficiently, it is very limited in computing capability. Simple polling protocol works well in situation where every sensor node shares heavy traffic. However, when a few sensor nodes contribute to the traffic, most of the time slots allocated are not occupied and wasted. We propose in this work a hybrid protocol that can switch from polling protocol to slotted Aloha when traffic is low. The result obtained with the protocol switch is that those sensor nodes will not have to wait for its time slot and be able to access time slot any time when free. The network transmission time is therefore reduced overall as a result. A new criterion in selecting polling protocol or slotted Aloha is proposed. This criterion is very simple in that it is based on sensor node traffic that can be calculated locally on the sensor node. The information is sent over to the server together with data packet so it takes very small amount of extra resources.
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