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BLIND DETECTION OF MODULATION TYPE AND NUMBER OF ACTIVE USERS IN CDMA WITH BOTH QPSK DATA MODULATION AND SPREADING Siavash Ghavami, Seyed Ali-Asghar Beheshti Shirazi Iran University of Science and Technology Electrical Engineering Department May 2009

MOTIVATIONS |

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In conventional multi-user DS-CDMA systems, y , the spreading sequence is typically known to the receiver for the despreading operation and data detection [2]. In non cooperative contexts such as spectrum surveillance and eavesdropping, the spreading sequence used by the transmitter is unknown. It is i almost l t impossible i ibl to t estimate ti t the th data d t sequence when it is very difficult even to detect the presence of the signal and to synchronize the receiver without k knowledge l d off the h spreading di sequence. QPSK spreading increases resistance against of signal g eavesdropping pp g and enhance system y security. y

OUTLINES System y Model | Joint Modulation Type and Number of Active User Estimation | Blind Synchronization for QPSK Spreading | Simulation Results | Conclusions C l i |

SYSTEM MODEL |

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uplink scenario of the asynchronous CDMA systems BPSK/QPSK spreading and data modulations. channel model y y

slow flat Rayleigh fading, channel coefficients are likely constant in a p processing g window duration.

received signal K

r (t ) =

+∞

∑∑A d k

k

[i ]hk (t − iT s − τ k ) + n (t ),

k =1 i =−∞

hk (t ) = N

−1/ 2

N −1

∑c m =0

in , k

[m ]p (t − mT T c ) + jc j qu , k [m ] p (t − mT T c ), )

COVARIANCE MATRIX OF THE RECEIVED SIGNAL K −1 ⎧ ⎪ R = σ n2 ⎨ (1 − α k ) βin, k v in# , k ( v in# , k )* + β qu , k v #qu , k ( v #qu , k )* ⎪⎩ k = K s

∑

(

(

)

) }

+α k βin, k v †in, k ( v †in, k )* + β qu , k v †qu , k ( v †qu , k )* + I , ⎧λin# , k = σ n2 ( β in, k (1 − α k ) + 1) ⎪ # ⎪ λqu , k = σ n2 ( β in, k (1 − α k ) + 1) ⎪⎪ † 2 ⎨ λin, k = σ n ( β qu , k α k + 1) ⎪ † 2 λ = σ ⎪ qu , k n ( β qu , k (1 − α k ) + 1) ⎪ 2 ⎪⎩ λk = σ n

k = 0,1,...,K -1 k = 0,1,...,K -1 k = 0,1,...,K -1 k = 0,1,...,K -1 k = K ,...,M − 1

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JOINT MODULATION TYPE AND NUMBER OF ACTIVE USER ESTIMATION modulation type yp of received signal g is recognized g and number of active users is estimated jointly. | an adaptive threshold is introduced for di i i ti discriminating signal i l eigenvalues i l f from th those off noise. | This adaptive threshold update, based on delay situation relative to the beginning of the processing window. |

λnormalized (i + 1) − λnormalized (i ) > mean ( λ j +1 − λ j ) + μ

j = 0,... M − 2

std ( λ j +1 − λ j )

j = 0,... M − 2

⇒ λnormalized (i + 1) : signal ,

JOINT MODULATION TYPE AND NUMBER OF ACTIVE USER ESTIMATION μl =1 = 1

μl + 4

μl +1

l

μl

Flow chart of determining of adaptive threshold

BLIND SYNCHRONIZATION FOR QPSK SPREADING Blind synchronization for QPSK signal with BPSK spreading based on FSNB and MEVB have been considered respectively in [10] and [11], in equal power scenario. scenario | For QPSK Spreading our analyses shows that FSNB and MEVB can be used for blind synchronization |

FROBENIUS square norm behavior (FSNB) F(d f ) =

{

K −1

∑ ( βin2 ,k + βqu2 ,k ) ( mod [(d f − τ k ),) T s ]) k =0

2

− mod [ (d f − τ k ),T s ]}.

Maximum eignenvalue behavior (MEVB) C (d f

)=τ

max

k ≤ d f ≤τ k +1

(λ

# in , k

)

, λqu# , k , λin† , k +1 , λqu† , k +1 ,

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SIMULATION RESULTS |

Simulation Parameters y

y y y y y y y y y y y

spreading di sequences off the h users is i random d BPSK or QPSK (e.g. different spreading sequence in in-phase and quadrate components). Processing gain of 18dB (N = 63) Chi time Chip i = 200 nsec Sampling frequency = 200 MHz length of the processing window is assumed 200 symbols with the duration of 315 usec Bit duration is 1.575 usec Channel Model : Slow flat fading Maximum tolerable Doppler frequency of less than 316.5 Hz Number of Active User : 3 All of them are asynchronous relative to the beginning of the processing window ( 0.2 usec, 0.8 usec, 1.4 usec) Users power are same. R i d signal Received i l SNR iis considered id d -11 11 dB before b f d despreading di

SIMULATION RESULTS

(a) eigenvalues of the total received signal covariance matrix with QPSK data modulation and BPSK Spreading, (b)is similar to (a), except that the covariance matrix is calculated for inphase component of signal, Fig. 2-c is similar to Fig. 2-b, except that the covariance matrix is calculated for quadrate component of signal.

‫آزﻣﻮن ﻛﺎراﻳﻲ اﻟﮕﻮرﻳﺘﻢ اراﺋﻪ ﺷﺪه ﺑﺎ اﺳﺘﻔﺎده از ﺷﺒﻴﻪ ﺳﺎزي ﻫﺎي ﻛﺎﻣﭙﻴﻮﺗﺮي‬

(a) eigenvalues of the total received signal covariance matrix with QPSK data modulation (a). and QPSK Spreading, (b)is similar to Fig. 3-a, except that the covariance matrix is calculated for in-phase component of signal, (c) is similar to (a), except that the covariance matrix is calculated for quadrate component of signal.

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s as a function of µ with QPSK data modulation and different spreading sequence in in-phase and quadrate components, Fig. 4-b. it is similar to Fig. 4-a. with QPSK data modulation and same spreading s

‫آزﻣﻮن ﻛﺎراﻳﻲ اﻟﮕﻮرﻳﺘﻢ اراﺋﻪ ﺷﺪه ﺑﺎ اﺳﺘﻔﺎده از ﺷﺒﻴﻪ ﺳﺎزي ﻫﺎي ﻛﺎﻣﭙﻴﻮﺗﺮي‬

(a). Number of estimated signal eigenvalues as a function of µ with QPSK data modulation and QPSK Spreading, (b). It is similar to Fig. 4 a with QPSK data modulation and BPSK Spreading 4-a.

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(a). MEVB in terms shifts of beginning of the processing window, (b). FSNB in terms shifts of beginning g g of the p processing g window.

CONCLUSIONS | |

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A new algorithm is proposed for modulation type and number of active users estimation. Two blind synchronization methods, which used for BPSK spreading by [10] and [11], are analyzed for the case of QPSK spreading without any prior knowledge about spreading sequences in asynchronous multi-user direct sequence spread spectrum t (DS SS) systems. (DS-SS) t Simulation results show that modulation type and number of active users is estimated using the proposed d adaptive d ti th h ld in threshold i SNR off -11 11 dB for f spreading factor of 18 dB. Computer simulations confirm that our analysis about b t both b th blind bli d synchronization h i ti methods th d for f QPSK spreading in SNR of -11 dB.

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