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

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Presentation Outline

     Conventional DAA mechanism
     Aim of Study
     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
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1.1 background

Many various wireless communication systems
Broadband wireless communication

The shortage of assignable                      Blue tooth, etc...
                 radio spectrums
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
                                             Advantages: Low-complex
  Band                                       Drawbacks: Risk of losing
                                                   communication opportunities
   Frequency DAA(DSA)
     Adaptive frequency hopping             Secondary System Primary System
 Frequency                                  (Cognitive Radio)

                                               Flexible frequency bands selection
                                             Drawbacks: Deep impact
                                                    when frequency band overlaps
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 1.3 Aim of Study

 Avoiding interference to WLAN and keeping communication
 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

 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
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  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

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  2.3 Access Control of WPAN with Array Antenna

   Arrival traffic

Other WPAN terminals
 are communicating                           Drop traffic

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

                        Estimation SINR                  Estimation SINR>Threshold SINR
                          >Threshold SINR

Start to communicate                                WPAN terminals       WLAN terminals
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 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
                           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 ⎞
L(r,f): Free space propagation loss channel                               )=⎜
                                                L(r , f                            ⎟
w: weight vector (MMSE criterion)                                           ⎝ c ⎠
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 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
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

                                               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

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4.1 Conclusions

  We propose DAA mechanism with an array
     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
     Performance of the proposal can be improved in total
  Further study
     Theoretical analysis based on the distribution of
     Comparison with the performance of DAA mechanism
     on frequency domain
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