throughput enhancement through dynamic fragmentation in wireless lans
DESCRIPTION
Throughput Enhancement Through Dynamic Fragmentation in Wireless LANs. Byung-Seo Kim, Yuguang Fang, Tan F. Wong, and Younggoo Kwon IEEE Transactions on Vehicular Technology Vol. 54, No. 4, July 2005. Outline. Introduction Proposed protocol Fragmentation Scheme Fragment burst NAV update - PowerPoint PPT PresentationTRANSCRIPT
Throughput Enhancement Through Dynamic Fragmentation in Wireless LANsByung-Seo Kim, Yuguang Fang, Tan F. Wong, and Younggoo Kwon
IEEE Transactions on Vehicular TechnologyVol. 54, No. 4, July 2005
Outline Introduction Proposed protocol
Fragmentation SchemeFragment burstNAV update
Performance evaluation Conclusion
Introduction
Wireless communication link in a WLAN is time varying
Rate-adaptive MAC protocols have been proposed in the past for WLANsChannel conditionRTS/CTS handshake
Introduction (cont.)
Receiver based rate determinationRTSCTS (selected rate information)DATA
Overhearing nodes update their NAV
ACK
Introduction (cont.) Fragmentation in IEEE 802.11 MAC with r
ate adaption scheme
> aFragmentThreshold
AddPLCP Headerand Preamble
Introduction (cont.)
These proposed protocols only allowed static size of fragmentsHigher overhead of transmitting each
fragmentChannel could not be used effectively
Proposed protocol A dynamic fragmentation scheme to enhanc
e throughputDurations of all fragments, except the last one,
should be set the same in any data rateA Rate-Based fragmentation thresholding sche
me is employedA new fragment is generated only when the rate
is decided for the next fragment transmission Dynamic Fragmentation
Fragmentation Scheme In order to generate fragments with the sa
me time duration, the different aFragmentationThresholds should be used in different data rate R
Fragmentation Scheme (cont.)
The additional overhead of ThresholdB is
Fragmentation Scheme (cont.)
Fragment Burst
CurrentRate (4)
NextRate (4)
Modified format of DSSSPLCP Header
Fragment Burst (cont.)S R
RTS (base rate)
CTS (base rate)next rate is included
DATA is transmitted with selected rateIn aFragmentationThreshold size
ACK (selected rate)next rate is included
DATA is transmitted with selected rateIn aFragmentationThreshold size
˙˙˙
RTS
CTS
Fragment 1
ACK
Fragment 2 ˙˙˙
Next rate Next rate
NAV update Because the durations of all the fragments
are the same, except the last fragmentMoreFragments = 1
NAV update
Failure policy
When the transmission of a fragment failsThe size of the retransmitted fragment may not
be the same as before Channel condition may have changed
Sender only decreases the remaining MSDU size when receives the ACK from the receiver
Performance Evaluation
Single-hop environment No hidden node
Transmission rage : 300 m Rate selection
Performance Evaluation (cont.)
3 different configuration RFT-DF
Rate-based Dynamic
RFT-CF Rate-based Conventional
SFT-CF Single fragmentation threshold Conventional
Throughput vs. number of nodes
4 m/s
Packets per MSDU vs. number of nodesTime overhead vs. number of nodes
PER vs. number of nodesMAC Service Time vs. number of nodes
MSDU dropping rate vs. number of nodes
Throughput vs. Node speed
40 nodes
Throughput vs. Max. MSDU Size
4 m/s
40 nodes
Throughput vs. Predictor Efficiency
4 m/s
40 nodes
Conclusion
This paper proposes a new rate-adaptive MAC protocol with dynamic fragmentation
Nodes with good channels can transmit more data
Constant duration in physical layer simplifies the process of NAV update
Simulations show the throughput gain from the conventional scheme