Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

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.

  • Be the first to comment

  • Be the first to like this

Characterizing wi fi-link_in_open_outdoor_netwo

  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
  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    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.   P. Ermanno. Setting Long Distance WiFi Records: Proofing Solutions for Rural Connectivity.  Antennas:  Arvind case: