| Traffic Balancing | ||
| Based on reactive routing protocol (can also deployed for proactive routing protocol) | ||
| Each node records the medium usage around itself and put this information into route request (inrease overThresholdCounter if measured medium usage is over the certain threshold) | ||
| Sender chooses the path with smallest overThresholdCounter | ||
| Defect | ||
| Traffic Balancing verifies if the medium is busy just by the measured medium usage (using a constant threshold) | ||
Traffic Balancing and On-demand Routing Protocol
| Traffic Balancing determines the medium state only by the percentage of time that the measured signal strength is over the constant threshold | |
| Some important issues such as node mobility and congestion state are not considered even though these issues also influence the medium state | |
| As mobility that causes collisions and transmission loss, the measured medium usage under the busy state may vary (backoff period) | |||
| Examples (5.3 Kbps with packet size of 64 bytes): | |||
| 0 m/s (max. moving speed) | |||
| (0.06+0.06+0.32+0.06)/(0.06+0.01+0.06+0.01+0.32+0.01+0.06+0.01)=92.59% | |||
| 5 m/s | |||
| (0.06+0.06+0.32+0.06)*10/((0.06+0.01+0.06+0.01+0.32+0.01+0.06+0.01)*9+(0.06+0.02*15+0.06+0.02*15+0.32+0.02*15+0.06+0.02*15))=76.22% | |||
| Transmission rate is 2 Mbps and it takes around 0.06 ms to transmit a RTS or CTS or ACK. The data packet needs 0.32 ms to be sent and the interframe period is 0.01 ms | |||
| The number of collisions that can be seen by a node over a certain period can indicate the node mobility or medium usage condition more precisely than other parameters | ||
| The faster nodes move, the larger number of collisions can be observed by nodes | ||
| The larger number of collision happens, the more backoff periods are and less medium usage is detected | ||
| Method | ||
| Nodes measure the medium usage and number of collisions over a certain period | ||
| Based on the number of collisions, a suitable threshold is set | ||
| Simulation Environment | ||
| Network Simulator 2 (NS2) | ||
| IEEE 802.11 MAC | ||
| Constant Bit Rate Traffic (CBR) at 5.3 Kb/s | ||
| 100 nodes in a 1000*1000 m2 area | ||
| Implementation of Adaptive Traffic balancing | ||
| The node checks the number of collisions in the past 2 seconds | ||
| <10, the medium usage threshold = 0.9 | ||
| >10 and <50, the medium usage threshold = 0.7 | ||
| >50, the medium usage threshold = 0.5 | ||
| Adaptive Traffic Balancing improves system performance further by dynamically changing the medium usage threshold according to the number of observed collisions | |
| The number of collisions partly reflects the node mobility | |
| The network state is divided into three levels that limit the benefits of adaptive Traffic Balancing | |
| Some other parameters such as bit error rate to reflect the wireless environment need also be included to estimate the network state |