Dynamic Spectrum Access (DSA) provides a new opportunity for last-mile and rural connectivity. However, the nature of DSA and varying environmental conditions means that desired spectrum is not always available. To that end, we have deployed a testbed using both DSA-enabled TV White Space devices and fixed spectrum WiFi (5GHz) in parallel to support communication between and within townships. Using this testbed, we will develop new algorithms to support wireless mesh routing in DSA networks

Densmore, Dr Melissa

Johnson, Dr David

Maliwatu, Mr Richard

Zlobinsky, Ms Natasha

UCT Computer Science Research Document Archive

A road map for wireless mesh routing with DSARichard Maliwatu#, Natasha ZlobinskyΨ, Melissa Densmore¥, David Johnson*Department of Computer Science, University of Cape Town#rmaliwatu@cs.uct.ac.za, ¥mdensmore@cs.uct.ac.zaMeraka Institute, CSIR, South Africa*djohnson@csir.co.za, Ψnzlobinsky@csir.co.za Abstract—Dynamic  Spectrum  Access  (DSA)  provides  a  newopportunity for last-mile  and rural  connectivity. However, thenature of DSA and varying environmental conditions means thatdesired spectrum is not always available. To that end, we havedeployed  a  testbed  using  both  DSA-enabled  TV White  Spacedevices and fixed spectrum WiFi (5GHz) in parallel to supportcommunication  between  and  within  townships.   Using  thistestbed, we will develop new algorithms to support wireless meshrouting in DSA networks.  Keywords— wireless mesh routing, dynamic spectrum access, multi-radio systems, rural connectivityI.  INTRODUCTIONTraditionally,  regulators  assign  frequencies  forelectromagnetic  radio  spectrum  users  to  operate  in.  Usershave  exclusive  access  and  these  assignments  remainunchanged  over  the  license  validity  period.  In  line  withregional  or  national  regulation,  manufacturers  pre-set  thespectrum band in which wireless devices operate. Owing tothe shortcomings of the Fixed Spectrum Assignment (FSA)method,  numerous  proposals  [1,  2,  3]  have  been  maderecently   that  propose  Dynamic  Spectrum  Access  (DSA)techniques.  DSA is  a  new  spectrum  assignment  approachwhere devices make real-time adjustment of spectrum usageto  adapt  to  changes  in  the  spectral  environment  orperformance objective. DSA has also been suggested as oneof  the  techniques  to  be  used  in  5G  networks.  DSA  haspotential to allow unlicensed users to access licensed parts ofthe spectrum on a secondary basis when not in use by theprimary/licensed  users.  The  term  white  space  is  used  todescribe the parts of spectrum that are vacant either spatiallyor  temporarily.  Though  present  in  any  spectrum band,  thecurrent  emphasis  is  on  the  television  band  because  this  iswhere the most significant white space is found. We refer tothis spectrum as television white space (TVWS).II. RELEVANCE OF WIRELESS COMMUNICATION TO EMERGINGMARKETSAmong the available options for the last mile, the roll-outcost  of  wired  links  is  comparatively  high.  In  addition,  theinfrastructure  might  be  targeted  by  thieves  because  of  thehigh  value  of  copper  cables.  Fibre-optic  communication  isanother possible alternative but for low-income communitiesthe  capital  required  to  set  it  up  renders  it  less  viable  forextension beyond the Point-of-Presence (POP).  In  addition,the terrain in some cases makes the implementation of wiredinfrastructure in rural areas impractical. Very Small ApertureTerminal (VSAT) is capable of covering remote areas but therequired initial and recurring costs are prohibitive. Therefore,open  spectrum wireless  access  technology  offers  the  mosthope in extending connectivity to rural areas [4]. For DSA to work, it requires provisioning across at leasttwo dimensions:  regulation  and  hardware/software  support.With the continued increase in the development of wirelessapplications in the recent past, a trend that has shown no signsof slowing down, DSA is the preferred approach because itpromises  efficient  spectrum  utilisation  and  eliminates  thecomplexities  associated  with  static  frequency  assignmentplanning that would otherwise be required for large scale ad-hoc  networks.  The  benefits  of  DSA based  communicationbuild on the advantages that  wireless  mesh networks  hold,which  includes  comparatively  low  upfront  costs,  self-configuration,  robustness,  and  easy  set-up,  expansion  andmaintenance.III. PROBLEM STATEMENTA network is to be designed and built that makes optimal useof  spectrum  and  routes  traffic  over  optimal  paths.  Thenetwork must be self-configuring, require little maintenanceand extend connectivity at low-cost.IV. NODE DESIGNFIGURE 1 shows the node used in the outdoor testbed. Thenodes have the following features: Multi-radio: 2.4GHz WiFi for access, 5GHz WiFi andTVWS for the back-haul. Support for Protocol to Access White Space (PAWS). Inbuilt GPS to determine position required by PAWSfor querying the spectrum database. Inbuilt spectrum analyser for clean channel selection.FIGURE 1: white space mesh node.Page 46 Southern Africa Telecommunication Networks and Applications Conference (SATNAC) 2016V. APPLICATION SCENARIO AND TESTBED DESCRIPTION One major challenge in rural communities is the extensionof connectivity from the nearest POP to the houses. The areasare  characterised by sparse population and rugged terrain,which makes cabling or laying down optical fibre impracticalin  both  technical  as  well  as  economic  terms.  This  workfocuses on the application of white space spectrum to extendbroadband connectivity to rural communities as illustrated inFIGURE 2. Vegetation and other obstacles along the signalpropagation path results in obstructed line-of-sight. FIGURE3 shows the actual  node placement  of  the outdoor testbed.The nodes are placed at sites in a way that provides a diverseset of available TV white space spectrum, which is useful forresearch. Distances between the nodes is 1-12 km.FIGURE 2: white space for rural broadband connectivity.FIGURE 3: outdoor mesh node placement. VI. DESIGN MOTIVATION AND CHALLENGESThe nodes consist of a 5 GHz WiFi and a TVWS radio.The idea is to use 5 GHz where we have perfect line of sight,and use a TVWS link where we have a near line-of-sight. Inaddition,  the  nodes  are  equipped  with  a  2.4  GHz   WiFiinterface for access as illustrated in FIGURE 2. Though thereis  a  significant  amount  of  white  space  especially  in  thetelevision  band,  it  is  not  guaranteed  to  be  available  at  alltimes  and  at  all  locations.  Therefore,  in  order  to  maintainconnectivity in the absence of white space, our nodes consistof dual transit links i.e. a TVWS link and a fixed spectrum (5GHz  WiFi)  link.  The  other  reason  for  the  dual-link  radiodesign  is  that  we  envisage  mesh  deployments  over  anextensive area with varying environmental conditions such asdistance, vegetation, buildings and other elements bound toaffect  radio  signal  propagation  between  the  nodes.  Theintention  is  to  auto-switch  between  WiFi  and  TVWSdepending on which one thrives under the conditions at hand.Therefore,  the  two links can be used  alternately when onefails or they can be used in concert to achieve real full-duplex.We define full-duplex from the node perspective as the use ofone link for outbound traffic and the other for inbound traffic.The  challenge  is,  to  determine  a  standard  of  comparisonbetween links operating in different spectrum bands so trafficcan be routed over the optimal link.VII. OBJECTIVE AND EXPECTED OUTCOMEThis work aims to develop new mesh networking algorithmsthat are suited to DSA networks. The objective is to enhanceconnectivity and increase throughput. The expected outcomeof this research includes improved metrics for TVWS meshand routing algorithms for selection of TVWS or WiFi links.ACKNOWLEDGMENTThis  work  is  supported  by  Council  for  Scientific  andIndustrial  Research  Council  (CSIR)  Meraka  Institute,Pretoria,  South  Africa,  and  Hasso  Plattner  Institute  (HPI)Research School at UCT.REFERENCES[1] Michael J. Marcus. Unlicensed cognitive sharing of TV spectrum: Thecontroversy  at  the  Federal  Communications  Commission, IEEECommunications Magazine, 43(5):24–25, 2005.[2] Marja Matinmikko, Miia Mustonen, Dennis Roberson, et al. Overviewand comparison of recent spectrum sharing approaches in regulationand research: From opportunistic unlicensed access towards licensedshared access, In 2014 IEEE International Symposium on DynamicSpectrum Access Networks, DYSPAN 2014, pages 92–102, McLean,VA, 2014.[3] M. Nekovee. Current Trends in Regulation of Secondary Access to TVWhite  Spaces  Using  Cognitive  Radio, In  2011  IEEE  GlobalTelecommunications  Conference  -  GLOBECOM  2011,  pages  1–6,Houston, TX, 2011.[4] Amit Kumar and David Lloyd Johnson. White Space Communication:advances,  developments  and  engineering  challenges.  SpringerInternational Publishing, 2014Richard Maliwatu received his MSc in Computer Science at theUniversity  of  Cape Town (UCT) in  2014.  He is  currently a  PhDstudent in the Computer Science Department and a member of theComputer Science for Africa (CS4A) research center at UCT.David  Johnson is  a  Principal  Researcher  at  the  CSIR  MerakaInstitute  and an adjunct  Senior Lecturer  in the Computer  ScienceDepartment of the University of Cape Town. He received his PhD inComputer Science at the University of California, Santa Barbara in2013 and he currently leads the UCT Net4D research group studyingnetwork solutions for developing regions.Natasha  Zlobinsky  received  her  BSc  degree  in  ElectricalEngineering  in  2011  from  the  University  of  the  Witwatersrand,Johannesburg and  is  completing  her  MSc in  TelecommunicationsEngineering at Wits. She has worked as an Engineer for Eskom andis currently at the CSIR Meraka Institute.Melissa  Densmore  is  a  Senior  Lecturer  in  the  Department  ofComputer  Science at  UCT, and a  member of  the UCT Centre  inInformation and Communications and Technology for Development.She holds a PhD in Information, Management and Systems from theUniversity of California Berkeley. Her research looks at the design,deployment,  and  uptake  of  new  information  technologies  in  thecontext of socio-economic development.5GHz WiFiUHF TVWS2.4GHz WiFiSouthern Africa Telecommunication Networks and Applications Conference (SATNAC) 2016 Page 47

A Road Map for Wireless Mesh Routing with DSA

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A Road Map for Wireless Mesh Routing with DSA

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