The most critical issue of IEEE 802.15.4 WPAN is the capability of dealing with real-time or near real-time
services, which required limited latency and delay jitter. SO and BO are defined to control the length of superframe and the active and inactive in superframe. However, using two parameters is very difficult to achieve deliver smooth and constant data stream from device nodes to coordinator. The author proposes an adaptive interleaving access scheme (IAS) with parameter Interleaving Order (IO)) toadjust the superframe structure such that the active portion is spread over entire superframe in order to control the access latency as well as the bandwidth wastage.
The coordinator control the interval of active and inactive periods in a superframe by setting two parameters : Beacon Order (BO) and Superframe Order (SO). The BO affects the length of superfrmae and the SO controls the active period in superfrmae. The inactive period is the period of superframe minus the active period. The BO is larger than or equal to SO. The intervals of an active period and an active period are equal to 48*(2^SO) UBPs and 48*(2^SO-2^BO) UBPs respectively. 1 UBPs = 20 symbol times. If the WPAN coordinator extends the inactive period to save power, the latency of sending time-sensitive reports to coordinator is also extended.
Contrarily, if the WPAN coordinator extends both the active and inactive interval ()i.e superframe length, the delay jitter of data frames arriving coordinator will become much worse.
The active period is divided as CAP and CFP. Consequently, without contention overhead, the CFP is able to provide a better channel utilization and shorter transmission latency than the CAP.Based on standard protocol, The proposed interleaving access scheme adds a new parameter Interleaving Order (IO) to adaptively adjust the superframe structure. Read more the paper for detail :).
If coordinator decreases the value of BO, the more frequent beacon frmae broadcatings definitely consume much more bandwidth and node’s battery power. Decreasing values of BO and SO is able to reduce ata renewal intervals but that disobeys the low-power consumption requirement and scrifies the channel bandwidth.
By queueing theory, if the amount of arriving data is more than or equal to the amount of delivering data, the
channel performance would get saturation even become worse.
compare the performance of proposed scheme [IAS(BO6,SO5)] and standard protocol [BO6,SO5 and BO2,SO1] :
– Comparison of derived goodputs
– Comparison of derived average data renew
– Comparison average battery lifetimes of nodes
An Adaptive Interleaving Access Scheme (IAS) For IEEE 802.15.4 WPAN
By Shiann-Tsong, Yun-Yen Shih, LuWei Chen
Note : This resume is created for self-learning only. Author and Publisher hold copyrights
October 25, 2008
High Speed Network Lab