Effect of hidden nodes in IEEE 802.15.4/ZigBee Wireless Sensor Networks
Karl Benki · 2009
IEEE 802.15.4/ZigBee is the standard for short range, low data rate Wireless Sensor Networks (WSN). It is targeted for battery powered applications where a long battery life is main requirement. Packet collision caused due to hidden node problem is one of the main sources of unnecessary energy waste. Because of a hidden node problem which is not treated by standard our goal was to find its influences on the overall network performances. Keywords — cluster-tree, hidden node, wireless personal area networks. I. INTRODUCTION ACKET collision is a situation when two nodes simultaneously start transmission, and their packets will collide at recipient node which wouldn't be able to successfully receive any of these packets. Packets will need to be retransmitted again which would cause unnecessary energy waste. It will be also increased packet delivery time. In wired networks this problem was solved using collision detection mechanism where each node listen the transmission medium while sending the packet. If collision occurs, the transmission is aborted immediately. In wireless networks, transmitter and receiver share much of the radio components including antenna, so node could not use them at the same time. Even if we had separate pair of transmitter and receiver, power of radio transmission, would completely overshadow any received signal, since ratio between power of transmitted and received signal is as much as million to one. Common practice is that node listen the medium before any transmission. After ensures that medium is not occupied by other nodes, it can start radio transmission. This kind of medium access operates smoothly only if node is capable to hear all nodes which participate in network. Since this is the rare case, it is possible that two nodes, which don't hear each other, start simultaneous transmission. If nodes A, B and C are located in that manner that nodes A and C are so far away that they are unable to hear each other, Figure 1. Node B is located between these nodes and it's capable to communicate with both of them. Simultaneous transmission from nodes A and C will cause packet collision on node B, and these nodes wouldn't be