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Self-adaptive CSMA/CA for wireless networks Disclosure Number: IPCOM000247103D
Publication Date: 2016-Aug-05
Document File: 5 page(s) / 111K

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This artical describes a self-adaptive CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance) which can be deployed in wireless networks to decrease the latency, increase the throughput and use the battery efficiently. It has the following features: (1) When the priority of the packet is high, then the value of CW (Contention Window) will be decreased exponentially, thus the waiting time is also decreased; (2) When the packet queue becomes long, then the value of CW will be decreased accordingly; (3)When the battery becomes low, the value of CW will be decreased linearly.

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Self-adaptive CSMA/CA for wireless networks

Nowadays, with countless handsets and wireless sensors used in our daily life, the world is more wirelessly connected than ever before. With so many devices exchanging information frequently, the traffic becomes more congested in the wireless networks. How to relieve this problem becomes more prominent.

Due to its simplicity and easy implementation, CSMA/CA is a distributed MAC (Medium Access Control) protocol widely deployed in WLAN, Bluetooth, Zigbee and other wireless networks. However, the performance of CSMA/CA still needs to be improved to adapt to the increasing traffic requirement.

A typical CSMA/CA works as follows:

When one node has packet to send

1. Chose a random integer value N from [1, CW], set N as the value of the backoff counter. CW is short for Contention Window 2. Listen to then channel to check whether it is idle or busy, and begin the countering process (a) If the channel is idle, decrease N by 1 (b) If the channel is busy, freeze the counter till the channel is idle again
3. When the value of the backoff counter reaches 0, send the packet
4. If collision happens in step 3, then repeat step 1

Note that the average waiting time for a node is 1/2*CW if collision doesn't happen frequently

Contrasted with the methods mentioned above, the main idea of self-adaptive CSMA/CA is to adjust the value of CW based on the real-time transmission requirement of the node. Put in more specifically, take three factors into consideration: the priority of the sending packet, the length of the packet queue and the remaining battery capacity of the node.

Next, we will explain why choosing these three factors.

Wireless sensor nodes collects data from nearby environment. Different type of packets may generate during the monitoring process, which can be distinguished by assigning them a priority. Usually, the higher the priority of one packet, the more important data it contains. It should be transmitted immediately. For that purpose, in self-adaptive CSMA/CA, the value of CW will decrease


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as the priority increase.

Since wireless sensor node usually is small in size, memory is limited. That means node can't store many packets. When the length of the packet queue meets the ceiling, some old packets will be discarded to make room for the new packets, which will results in data loss. Besides, the time is relevant for wireless packet, when too much packets stranded in the queue. In self-adaptive CSMA/CA, the value of CW will decrease accordingly.

Another important issue for wireless node is the remaining battery capacity. Due to the inconvenience of changing battery, node dies when battery runs out. So energy should be used efficiently. However, listening to the channel during the backoff process is quite energy-consuming. When the remaining battery becomes lower, the energy becomes more valuable, the unnecessary energy waste should be reduced. To that aim, in self-adaptive CSMA/CA...