By Jianliang Zheng and Myung J. Lee
Standard IEEE 802.15.4 is designed for low data rate, low power consumption and low cost wireless networking. The authors develop an NS2 simulator for IEEE 802.15.4 and conduct several sets of experiments, including, 1) beacon enabled mode and non-beacon enabled mode, 2) association, tree formation and network auto-configuration, 3) orphaning and coordinator relocation, 4) carrier sense multiple access with collision avoidance (CSMA-CA), both unslotted and slotted, 5) direct, indirect and guaranteed time slot (GTS) data transmissions.
Wireless networks provide advantages in deployment, cost size, and distributed intelligence. Wireless technology not only enables users to set up a network quickly, but also enables them to set up a network where it is inconvenient or impossible to wire cables. A host of new applications can benefit from new standard IEEE 802.15.4, such as those using sensors that control lights or alarms, smart tags and badges, inventory tracking device, etc. The authors develop an NS2 simulator for simulation and carry out severals states of experiments to evaluate its performances.
A Brief Description of IEEE 802.15.4 :
standard IEEE 802.15.4 defines the physical layer (PHY) and medium access control sublayer (MAC). an 802.15.4 network can simply be a one-hop star, or, when lines of communications exceed 10 meters, a self-configuring, multi-hop network. a device can use either a 64-bit IEEE address or a 16-bit short address assigned during the association procedure, and a single 802.15.4 network can accommodate up to 64k (2^16) devices.
The PHY layer :
The PHY layer provides an interface between the MAC sublayer and the physical radio channel. It provides two services : PHY data service and the PHY management service. PHY layer is responsible for the following task :
– Activation and deactivation of the radio transceiver : turn the radio into three states –> transmitting, receiving, off (sleeping).
– Energy Detection (ED) within the current channel.
– Link Quality Indication (LQI) for received packets.
– Clear channel assessment (CCA) for carrier sense multiple access with collision avoidance (CSMA-CA)
– Channel frequency selection
– Data transmission and reception
The MAC sublayer :
it provides an interface between the service spesific convergence sublayer (SSCS) and the PHY layer. It provides two services : MAC Data service and MAC management service. The MAC sublayer is responsible for the following task :
– Generating network beacons if the device is a coordinator
– Synchronizing to the beacons : this synchronizing is important for data polling, energy saving, and detection of orphanings.
– Supporting personal area network (PAN) association and disassociation.
– Employing the carrier sense multiple access with collision avoidance (CSMA-CA) mechanism for channel access : The new standard does not include the request-to-send (RTS) and clear-to-send (CTS) mechanism, in consideration of the low data rate used in LR-WPNAs.
– Handling and maintaining the guaranteed time slot (GTS) mechanism.
– Providing a reliable link between two peer MAC entities.
General Function – Data Transfer :
data transfer can happen in three different ways : 1) from a device to a coordinator, 2) from a coordinator to a device, 3) from one peer to another peer in a peer-to-peer multi-hop network. but, for their performance study, they classify the data transfer into the following three types :
– Direct data transmission
– Indirect data transmission : this only applies to data transfer from coordinator to its device.
– GTS data transmission
NS-2 Simulator :
The 802.15.4 NS2 simulator developed at the Joint Lab of Samsung and the City University of New York (CUNY) contains these modules :
– Wireless Scenario Definition : it selects the routing protocols, defines the network topology, schedules events such as initializations of PAN coordinator, coordinator and devices, and starting (stopping) applications. It defines radio-propagation model, antenna model, interface queue, traffic pattern, link error model, link and node failures, superframe structure in beacon enabled mode, radio transmission range, and animation configuration.
– Service Specific Convergence Sublayer (SSCS) : This is the interface berween 802.15.4 MAC and upper layer. It provides a way to access all MAC primitives.
– 802.15.4 PHY : It implements all 14 PHY primitives.
– 802.15.4 MAC : This is the main module. It implements all the 35 MAC sublayer primitives.
Performance Metrics :
These are all performance metrics :
– Packet delivery ratio : The ratio of packets successfully received to packets sent in MAC sublayer.
– Hop delay : The transaction time of passing a packet to a one-hop neighbor, including time of all necessary processing, backoff as well as transmission, and averaged all successfull end-to-end transmissions within a simulation run.
– RTS/CTS overhead : the ration of RTS/CTS packets sent to all the other packets sent in 802.11. This metric is not applicable in 802.15.4.
– Successfull association rate : The ration of devices successfully associated with coordinator to the total devices trying to associate with a coordinator.
– Association efficiency : The average number of attempts per successful association.
– Orphaning rate : A device is considered orphaned if it misses aMaxLostBeacons (default value 4) beacon from its coordinator in a row. The orphaning rate is defined as the ratio of devices orphaned at least once to the total devices that are in beacon enabled mode and keep trying beacons.
– Orphaning recovery rate : Two different versions are defined for this metrics. One is the ration of orphaned devices that have successfully relocated their coordinators (i.e, have recovered from orphaning) to the total orphaned devices. The other is the ratio of recovered orphanings to the total orphanings, in which multiple orphanings of a device are counted.
– Collision rate : the total collisions during a simulation run.
– Collision rate between hidden terminals : The total collisions that occur between hidden terminals during a simulation run.
– Repeated collision rate : The total collisions that happen more than once between the same pair of packets during a simulation run.
– Collision distribution : The time distribution, within a superframe, of collision. This metrics is only used in beacon enabled mode.
– Duty cycle : The ratio of active duration, including transmission, reception and carrier sense time, of a transceiver to the whole session duration.
– Set 1 : Comparing 804.15.4 with 802.11
– Set 2 : Association efficiency
– Set 3 : Orphaning
– Set 4 : Collision
– Set 5 : Direct, indirect and GTS data transmissions.
A Comprehensive Performance Study of IEEE 802.15.4
Jianliang Zheng and Myung J. Lee
City University of New York
Note : This resume is created for self-learning only. Author and Publisher hold copyrights
Paper Predator Jutsu [Mode On] – Searching Research Idea
February 18 2008,
High Speed Network Lab