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A Study on Coexistence of WLAN and WPAN with PAN-coordinator using

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					A Study on Coexistence of WLAN and WPAN
     with PAN-coordinator using Array Antenna


Yuta NAKAO, Kotaro WATANABE, Tadatomo SATO, Ryuji KOHNO
            Yokohama National University, Japan

     2007 Software Defined Radio Technical Conference
                    November 7 Wed



                     SDR'07 Techical Conference         1
Presentation Outline

  Introduction
     Background
     Conventional DAA mechanism
     Aim of Study
  Proposal
     Configuration of an array antenna
     Access control of WPAN with array antenna
     Estimation of SINR
  Performance Evaluation
     Simulation model
     Evaluation criterion
     Total throughput
     Interference rate
  Conclusions
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1.1 background

Many various wireless communication systems
Broadband wireless communication

                                                2G,3G,WLAN,UWB
The shortage of assignable                      Blue tooth, etc...
                 radio spectrums
                                                    Bandwidth
                                               PDC:25kHz
Sharing frequency                              CDMA2000: 1.25MHz
                                               Blue tooth: 1MHz
   with several systems                        IEEE 802.11a: 20MHz
       based on Cognitive Radio                UWB: more than 500MHz

 Dynamic Spectrum Access
 Low Duty Cycle
 Detect and Avoid
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   1.2 Conventional DAA technologies

   Temporal DAA
     Strategy such as carrier sense multiple access
                                          with collision avoidance
Frequency
                                             Advantages: Low-complex
  Band                                       Drawbacks: Risk of losing
                                                   communication opportunities
                                 Time
   Frequency DAA(DSA)
     Adaptive frequency hopping             Secondary System Primary System
 Frequency                                  (Cognitive Radio)

   Band1
                                             Advantages:
                                               Flexible frequency bands selection
   Band2
                                             Drawbacks: Deep impact
                                                    when frequency band overlaps
   Band3
                                              Time
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 1.3 Aim of Study

Objective
 Avoiding interference to WLAN and keeping communication
 opportunities
Assumptions
 WPAN system is assumed as UWB system
 WLAN system is assumed as 802.11a for indoor environments
 The coexistence network of these systems is considered


Proposal
 Spatial DAA   -Access control of WPAN with an array antenna
 Flexible frequency characteristics
              -subband signal processing on an array antenna-


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      2.1 Configuration of An Array Antenna

  Linear array
  WPAN bandwidth: 3.1-10.6GHz
  Subband bandwidth: 300MHz
  The number of BPF: 25

    Steering vector
     for considering subband processing
a( f i , θWPAN )
  ⎡ − j 2πf i d sin(θWPAN )       −j
                                     2πf i
                                           d ( L −1) sin(θWPAN ) ⎤
= ⎢1, e  c
                            ,L, e     c
                                                                 ⎥
  ⎣                                                              ⎦
  θWPAN: DOA of WPAN signal
  fi: central frequency of each subband
  d: distance between two elements=Λ/2
  Λ: the WLAN carrier wavelength
  c: light velocity
                                               SDR'07 Techical Conference   6
  2.2 An example of Beam Pattern


DOA of WPAN signal: 20[degrees]
SNR of WPAN:20[dB]

DOA of WLAN signal: -40[degrees]
SNR of WLAN:20[dB]

The number of elements:3



The wideband beam is steered to
WPAN incoming direction
A null is formed to the WLAN
signal’s direction and its frequency
band only



                           SDR'07 Techical Conference   7
  2.3 Access Control of WPAN with Array Antenna

   Arrival traffic

                               Yes
Other WPAN terminals
 are communicating                           Drop traffic

   No                                                           Arrival traffic
   WLAN terminals        Yes
 are communicating
                        Estimation DOA
                          θWLAN, θWPAN
                     Generate beam pattern
     No
                        Estimate SINR

                                                 No
                        Estimation SINR                  Estimation SINR>Threshold SINR
                          >Threshold SINR

Start to communicate                                WPAN terminals       WLAN terminals
                                  Yes
                            SDR'07 Techical Conference                            8
 2.4 Estimation of SINR

The calculation procedure of estimating SINR
 Bandwidth of the each system is different
        SINR is calculated taking the difference
                               of the bandwidths into account
                          f high

                            ∫ PD | wa (θ D , f ) |2 L(rD , f )df
      SINR=
                           f low
                 '
              f high

               ∫ PI | wa (θ I , f ) |2 L(rI , f )df + Pn ( f D ,high − f D ,low )
                 '
              f low


PD: Transmission power density of desired signal
PI: Transmission power density of interference signal
PD: Thermal noise power density
                                                                            ⎛ 4πrf ⎞
                                                                                       2
L(r,f): Free space propagation loss channel                               )=⎜
                                                L(r , f                            ⎟
w: weight vector (MMSE criterion)                                           ⎝ c ⎠
                                   SDR'07 Techical Conference                              9
 3.1 Simulation model

WPAN system
PAN coordinator: 1
WPAN terminal: 4
All WPAN terminals have
               DAA technologies
PAN coordinator only equip
              the array antenna
Star topology


WLAN system
WLAN terminal: 5
Infrastructure mode
Access control: CSMA/CA




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  3.2 Criterion for evaluation


 Total throughput
                                                 Ti: a summation of time
                            N ,M                    communicated on each terminals
                          W ∑t j                 W: bit rate of the each systems
                             j =1                Tsim: time to simulate
            
Throughput [bit / s ] =              
                                    [bit / s ]                    the DAA mechanism
                           Tsim                  N: the number of
                                                               the all WPAN terminals
                                                 M: the number of
                                                               the all WLAN terminals

 Interference rate
                                    countint: the number of communications
                     countint
Interference rate =                            in which the desired SINR
                                                of the each systems is not obtained
                    countcomm       countcomm: the number of communications
                                                                   of each systems


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 3.3 Simulation parameters

                                             The number of
Bit rate of WPAN    100 [Mbps]             antennas elements    3

                                            WPAN bandwidth      3.1-10.6[GHz]
Bit rate of WLAN    10 [Mbps]
                                            WLAN bandwidth      5.19-5.21[GHz]

                                           Transmission power
 Simulation time    200 [s]                     of WPAN         -2.85[dBm]

                    Free space             Transmission power
  Propagation                                   of WLAN         15[dBm]
                    propagation loss
    channel
                    channel

                    Poisson
                                               Desired SINR     20 [dB]
Packet occurrence
                    random process

 Average arrival
     rate λ
                    0.1~1 [1/s]


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3.4 Performance evaluations(1)
Total throughput
Proposed DAA shows the best performance
                      compared to the existing DAA techniques
     Communication opportunity of WPAN system is increased
           Effect of space division and subband signal processing
   WPAN Total throughput                     WLAN Total throughput




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3.5 Performance evaluations(2)
Interference rate
 WPAN Interference rate of Spatial DAA mechanism can be about half
 of that of temporal DAA
 WLAN Interference rate of all DAA mechanism is alike
      Avoid interference from WLAN
                         without increasing the interference for WLAN

    WPAN Interference rate                     WLAN Interference rate




                        SDR'07 Techical Conference                      14
4.1 Conclusions

  We propose DAA mechanism with an array
  antenna
     The access control which can not only avoid interference to
     WLAN system but also make an environment in which
     WPAN terminals can communicate actively
     The beam pattern for flexible frequency characteristic is
     obtained by subband signal processing
  We evaluate the performance by computer
  simulation
     Performance of the proposal can be improved in total
     throughput
  Further study
     Theoretical analysis based on the distribution of
     terminals
     Comparison with the performance of DAA mechanism
     on frequency domain
                     SDR'07 Techical Conference               15
end




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