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Characterizing wi fi-link_in_open_outdoor_netwo

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.

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Characterizing wi fi-link_in_open_outdoor_netwo

  1. 1. CHARACTERIZING WI-FI LINK IN OPEN OUTDOOR NETWORK BY: SALAH AMEAN
  2. 2. OUTLINES  Summary of the paper  scope  Background  802.11n  literature  experiment / preparation  Results and discussion  Conclusion
  3. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 13. NETWORK ARCHITECTURE CONCEPTUAL DIAGRAM  Two link characterisation  Sensor-to-AP  AP-to-AP
  14. 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. 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. 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. 17. SET UP OF A WCB NODE ON THE GROUND Sensor node-HP E-M111 Access point-HP E-MSM422 AP
  18. 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. 19. TESTING AREA  SATELITE VIEW OF THE AREA  Nodes are shown in circles  Green is fixed
  20. 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. 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. 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. 23.  sa
  24. 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. 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. 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. 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. 28. SNR AND ERROR SNR Error (Aggregation and LGI)
  29. 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. 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

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