characterizing wi fi-link_in_open_outdoor_netwo
DESCRIPTION
long distance wifi is really an important concept to deliver internet to remote places in developed countries as well as the poor and developing countries.TRANSCRIPT
CHARACTERIZING WI-FI LINK IN OPEN OUT-DOOR NETWORK
BY:
SALAH AMEAN
OUTLINES
Summary of the paper
scope
Background
802.11n
literature
experiment / preparation
Results and discussion
Conclusion
BACKGROUND
Providing internet to remote areas in developed or developing countries
Unlicensed WiFi spectrum WiFi availability and low cost
These networks typically have long distance point-to-point wireless lin enabled by high-gain directional antennas Several KM
Low throughput
Infrastructure is installed on top of high areas Antennas on tall building or towers
BACKGROUND
Oil and gas exploration Sensors that are deployed to collect seismic data covering a huge geographic space
sensor data needs to be collected and delivered to a centralized command unit
Sensors are buried in the ground to capture seismic data
Access Point (AP) covers a space where the sensors in that space communicate to that AP
APs form aggregation layer
The APs of one aggregation layer communicates to an AP of the next higher layer, and vice versa
CONSECUTIVE SUMMARY
Characterizing Wi-Fi links in open space outdoor environment
A large scale wireless sensor network scenario of seismic data collection from sensors that are buried in ground and
a set of access points (APs) form the hierarchical aggregation layer and the backbone of the network
Oil and gas exploration
Evaluate the links between sensor nodes and a wireless AP using IEEE 802.11a/b/g and then IEEE 802.11n Ieee802.11n high gain directional antenna for high throughput and long distance
Characterize the long distance wireless backhaul links between the Aps 148 Mb/s throughput at 800 meter line-of-sight links
40.8 Mb/s for the 1800 m link
Showing how PHY and MAC enhancement of 802.11n impact performance in outdoor environment
OUTDOOR WIFI ADVANTAGES
Providing internet to remote places
Cheaper assets
Considering the amount of capital investment in developing countries Implement in some developed countries where the number of users are not dense
Variety of applications can used for wifi deployment in resorts, hotels, etc.
deploying service to distant locations in developing countries India(Aravind hospital), Ghana, malawi
802.11B LINKS: PERFORMANCE MEASUREMENT AND EXPERIENCE PAPER (RE-QUIREMENTS)
What are the packet error-rate seen on the long distance links? and how they vary with the RSS?
Is there any dependence of the packet error rate on the link length?
What is effect of packet size and transmit rate (modulation) on the packet error rate?
Is there any time-correlation in the packet errors seen? At what time scales?
What effect do weather conditions (rain/fog) have on the link performance?
Are there any MAC-level ACK timeouts on the long distance links? What effect does this have on the application throughput
What is the effect of inter-link or external interference?
Answers to the above questions have implications on the planning of long-distance links, protocol design, as well as application design.
THERE ARE TWO MAIN REASONS FOR THIS POORPERFORMANCE IN WILD NETWORKS
Shortcoming of Wi-Fi 802.11 that makes it ill-suited for WiLD networks Link recovery mechanism(stop-and-wait) cause low utilization
ACK or retransmit options
With long distance , sender waits for a longer time for the ACKs to return
long distances frequent collisions occur because of the failure of CSMA/CA
Interlink interference
Solution: Using adaptive link recovery mechanism
Using bulk acknowledgment
Application-based parameter configuration
LONG DISTANCE WIFI BASED NETWORKS
Developed countries Least occupied places
E.g., Norway
Developing countries Providing internet facility
India
Malaysia ( Kampung WiFi)
Zambia
Ghana
ARAVIND EYE HOSPITAL AT THENI
Providing eye care to rural areas
Only one nurse working in the clinic
Specialist at the Aravind eye hospital inTheni diagnose patients
RELATED WORK(1)B. Raman 2007 the first to deploy a WiFi based outdoor long
distance network consisting of approximately ten links and lengths ranging from 1 ~ 16 Km
-All these work have infrastructured APs on top of towers or high buildings to create LOS links.
-In addition, their main focus is to provide network connection over long-distance (up to 16 Km) point-to-point link and high throughput is not their major concern. -In contrast, our network requires high bandwidth and has relaying APs every 1~2 Km. -We evaluate 802.11n for long distance links in a rural environment where there is less multipath ef-fect than indoor and urban environments.
K. Chebrolu, 2006 -study of long distance 802.11b link performance-study the behavior of such long links for varying packet sizes, data rates, SNRs and weather conditions-modification to the MAC to
R. Patra 2007 a TDMA based MAC protocol in lossy conditions for long distance links
V. Shrivastava 2008 show that the throughput of an 802.11n link can be severely degraded in presence of an 802.11g link
Constantinos pelechinis
2010 -802.11n produces more loss in high transmission rate(outage) -wider channel are sensitive to interference
RELATED WORK(2)
Ece Gelal et al. 2010 -PHY layer gains due to MIMO diversity do not always carry over to the higher layers,-the use of other PHY layer features such as FEC codes significantly influence the gains due to MIMO diversity- routing metric used may impact the gains possible with MIMO.
-
Arslan et al. 2010 -Channel bonding (CB) exacerbates interference ef-fect-CB does not always provide benefits in interfer-ence-free settings, and can even degrade perfor-mance in some cases-ACORN integrates the functions of user association and channel allocation
-J. P. Kermoal, -I. Sarris and A. R. Nix. -J. M. G. Pardo,
2001,2007,2009 Reporting the gain of polarization antenna diversity on MIMO channel with LOS components-indoor environment -controlled & anechoic chamber -focusing on validating their theoretical model
-this paper is the first measurement report that shows the polarization diversity gain for long distance outdoor communication using commod-ity 802.11n devices
NETWORK ARCHITECTURE CONCEPTUAL DIAGRAM
Two link characterisation Sensor-to-AP
AP-to-AP
SENSOR-TO-AP The link between a sensor node and an AP
High throughput is not required for this link
Range is important for the network design
802.11a/b/g is used for this link
Because of the simplistic design of the sensor node,
it is not possible to use multiple antennas at the sensor node.
Thus, there is no link range benefit by using 802.11n for this link.
BACKHAUL LINK BETWEEN TWO AP
high throughput & distance are required as it transmits the aggregated data from a large number of sensors towards a remote data collection & command center
Consideration of 802.11n for this link because the 802.11n MIMO technique support
Consideration of MAC enhancements provide high throughput without requiring stronger signal power than 802.11a/g
CONTRIBUTION
Studying how different modulation schemes and antenna heights at the sensor nodes af-fect the maximum communication distance
Evaluating the performance of 802.11n in an open outdoor environment , and showing its effectiveness in outdoor desert-like environment
Analyzing how several PHY/MAC enhancements of 802.11n improve the performance in an outdoor network
SET UP OF A WCB NODE ON THE GROUND
Sensor node-HP E-M111 Access point-HP E-MSM422 AP
ANTENNA SETUP AT ONE END OF THE LINK AP is connect to this antenna
12dBi gain antenna
The antenna is mounted on top of tripod 3 m high
Previous works of WiLD networks 24dBi to 14KM
TESTING AREA
SATELITE VIEW OF THE AREA
Nodes are shown in circles Green is fixed
MEASURED RECEIVED SIGNAL STRENGTH
RSS naturally decays over distance
Measured using
Pr power received , Pt is the transmitted power
K is constant depending
transmission frequency, antenna gains, and antenna height
α is 2 or 6 depending on the propagation environment
d transmitter-receiver distance
802.11N FEATURES
Frame Aggregation and Block Acknowledgement Allowing multiple frames to form an aggregated frame(A-MPDU and A-MSDU)
Block ACK for several frames received
Reduces overhead
Channel Bonding Wider channel 40MHz doubles data rate
Reduces the No. of channels
Prone to interferences
reduces received power at the receiver by 3 dB because the transmitted energy spreads over twice the channel widtd
802.11N FEATURES
Guard Interval Theoretically SGI provides 11% increase in PHY data rate
Reduction of inter OFDM symbols from 800ns to 400ns
PHY Layer Diversity MIMO antennas with spatial diversity and spatial multiplexing
Various modulation and coding schemes MCS
MAC and application throughput will be less than the specified PHY data rates mainly due to the
MAC layer overhead including back-off and retransmissions caused by packet losses
sa
PHY LAYER DATA RATES
3 × 3 MIMO streams
combination of channel width and guard interval.
MCS 0 to 7 indicate one data stream,
MCS 8 to 15 indicate two data streams
whereas MCS 16 to 23 indicate three data streams
THROUGHPUT FOR 300M LINK LENGTHS
Shows throughput when enabling/disabling aggregation
Huge improvement in throughput
could not establish link connectivity
for the high MCS rates(above 18)
THROUGHPUT IMPROVEMENT FOR FRAME AGGREGATION FOR 300M LINK
Frame aggregation reduces the MAC layer overhead
%450 through put improvement 40MHz Channel + SGI
Aggregation is necessary To notice significant improvement in throughput
THROUGHPUT IMPROVEMENT FOR CHANNEL BONDING FOR DIFFERENT LINK LENGTHS. FRAME AGGREGATION IS ENABLED AND LONG GI IS USED
Aggregation + SGI (300Meter) Aggregation and LGI
SNR AND ERROR
SNR Error (Aggregation and LGI)
This work is intended for the usage at oil and gas exploration wireless sensor network
This scenario is different from the traditional long distance WiFi network in the sense that nodes are placed closer to ground level and long links also require high bandwidth
present a measurement experimental study of two types of links of this network
First hop-link uses 8 02.11a/b/g to find the maximum link range and construct a path-loss model for our network
We use 802.11n for the backhaul link and evaluate different PHY/MAC layer features pro-vided in 802.11n
CONCLUSION
REFERENCES Paul, U.; Crepaldi, R.; Jeongkeun Lee; Sung-Ju Lee; Etkin, R., "Characterizing WiFi link performance in open outdoor
networks," Sensor, Mesh and Ad Hoc Communications and Networks (SECON), 2011 8th Annual IEEE Communications Society Conference on , vol., no., pp.251,259, 27-30 June 2011.
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http://www.arubanetworks.com/wp-content/uploads/AP_OutdoorPointToPoint.pdf
http://www.niasat.com/q-what-is-the-difference-between-terrestrial-land-based-internet-and-satellite-internet-service/
Rabin Patra, Sergiu Nedevschi, Sonesh Surana, Anmol Sheth, Lakshminarayanan Subramanian, and Eric Brewer. 2007. WiLdnet: design and implementation of high performancewifi based long distance networks. In Proceedings of the 4th USENIX conference on Networked systems design \&\#38; implementation (NSDI'07). USENIX Association, Berkeley, CA, USA, 7-7.
http://www.berkeley.edu/news/media/releases/2006/06/06_telemedicine.shtml
P. Ermanno. Setting Long Distance WiFi Records: Proofing Solutions for Rural Connectivity. http://ci-journal.net/index.php/ciej/article/view/487/402
Antennas: http://www.tp-link.com/lk/products/details/?model=TL-ANT2412D#spec
Arvind case: http://www.youtube.com/watch?v=v-Jog34Ovco