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.

1. CHARACTERIZING WI-FI LINK IN OPEN OUTDOOR
NETWORK
BY:
SALAH AMEAN

2. OUTLINES
 Summary of the paper
 scope
 Background
 802.11n
 literature
 experiment / preparation
 Results and discussion
 Conclusion

3. 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

4. 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

5. 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

6. 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

7. 802.11B LINKS: PERFORMANCE MEASUREMENT AND EXPERIENCE PAPER (REQUIREMENTS)
 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 app
lication 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.

8. THERE ARE TWO MAIN REASONS FOR THIS POOR
PERFORMANCE 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

9. LONG DISTANCE WIFI BASED NETWORKS
 Developed countries
 Least occupied places
 E.g., Norway
 Developing countries
 Providing internet facility
 India
 Malaysia ( Kampung WiFi)
 Zambia
 Ghana

10. 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

11. RELATED WORK(1)
B. Raman 2007 the first to deploy a WiFi based outdoor long distance netw
ork consisting of approximately ten links and lengths rangi
ng from 1 ~ 16 Km
-All these work have infrastructured APs on top of towers o
r high buildings to create LOS links.
-In addition, their main focus is to provide network connect
ion over long-distance (up to 16 Km) point-to-point link an
d high throughput is not their major concern.
-In contrast, our network requires high bandwidth and has r
elaying APs every 1~2 Km.
-We evaluate 802.11n for long distance links in a rural envir
onment where there is less multipath effect than indoor an
d urban environments.
K. Chebrolu, 2006 -study of long distance 802.11b link performance
-study the behavior of such long links for varying packet siz
es, data rates, SNRs and weather conditions
-modification to the MAC to
R. Patra 2007 a TDMA based MAC protocol in lossy conditions for long di
stance links
V. Shrivastava 2008 show that the throughput of an 802.11n link can be severel
y degraded in presence of an 802.11g link
Constantinos pelec
hinis
2010 -802.11n produces more loss in high transmission rate(outa
ge)
-wider channel are sensitive to interference

12. RELATED WORK(2)
Ece Gelal et al. 2010 -PHY layer gains due to MIMO diversity do not always carry o
ver to the higher layers,
-the use of other PHY layer features such as FEC codes signific
antly influence the gains due to MIMO diversity
- routing metric used may impact the gains possible with MIM
O.
-
Arslan et al . 2010 -Channel bonding (CB) exacerbates interference effect
-CB does not always provide benefits in interference-free setti
ngs, and can even degrade performance in some cases
-ACORN integrates the functions of user association and chan
nel allocation
-J. P. Kermoal,
-I. Sarris and A. R. N
ix.
-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 th
e polarization diversity gain for long distance outdoor co
mmunication using commodity 802.11n devices

13. NETWORK ARCHITECTURE CONCEPTUAL DIAGRAM
 Two link characterisation
 Sensor-to-AP
 AP-to-AP

14. 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.

15. 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

16. CONTRIBUTION
 Studying how different modulation schemes and antenna heights at the sensor nodes affect the maximu
m communication distance
 Evaluating the performance of 802.11n in an open outdoor environment , and showing its effectiveness i
n outdoor desert-like environment
 Analyzing how several PHY/MAC enhancements of 802.11n improve the performance in an outdoor net
work

17. SET UP OF A WCB NODE ON THE GROUND
Sensor node-HP E-M111 Access point-HP E-MSM422 AP

18. 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

19. TESTING AREA
 SATELITE VIEW OF THE AREA
 Nodes are shown in circles
 Green is fixed

20. 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

21. 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 wi
dtd

22. 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

23.  sa

24. 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

25. 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)

26. 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

27. THROUGHPUT IMPROVEMENT FOR CHANNEL BONDING FOR DIFFERENT LI
NK LENGTHS. FRAME AGGREGATION IS ENABLED AND LONG GI IS USED
Aggregation + SGI (300Meter) Aggregation and LGI

28. SNR AND ERROR
SNR Error (Aggregation and LGI)

29. CONCLUSION
 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 provided in 802.11n

30. 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.
 Kameswari Chebrolu, Bhaskaran Raman, and Sayandeep Sen. 2006. Long-distance 802.11b links: performance measurements and experience. In Proceedings
of the 12th annual international conference on Mobile computing and networking (MobiCom '06). ACM, New York, NY, USA, 74-85.
DOI=10.1145/1161089.1161099 http://doi.acm.org/10.1145/1161089.1161099
 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 & implementation (NS
DI'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