Collee of Enineerin Capacity Allocation in Multi-cell UMTS Networks for Different Spreadin Factors with Perfect and Imperfect Power Control Robert Akl, D.Sc. Son Nuyen, M.S. Department of Computer Science and Enineerin
Outline User and Interference Model WCDMA Capacity with Perfect Power Control WCDMA Capacity with Imperfect Power Control Spreadin Factors Numerical Results Conclusions
CDMA with One Class of Users I ji Relative averae interference at cell i caused by n j users in cell j Cell i ri I ji I ji j m r, 10 10 j x y nj E, Cj m 2 da x y r, / Aj i x y i m s 2 nj rj ( x, y) e Aj m r ( x, y) C j i da( x, y) rj Cell j where ln(10) 10 da s is the standard deviation of the attenuation for the shadow fadin m is the path loss exponent
WCDMA with Multiple Classes of Users Inter-cell Interference at cell i caused by n j users in cell j of class r ( x, y) I S v n w( x, y) da( x, y) A r ( x, y) 2 ( ) m s e j ji, j, m j C i j 2 m e rj ( x, y) w( x, y) da( x, y). m A r ( x, y) ( s ) ji, j C j i w(x,y) ji, is the user distribution density at (x,y) is per-user (with service ) relative inter-cell interference factor from cell j to BS i
Total Inter-cell Interference Density in WCDMA M G inter 1 j, ji, W j1, ji 1 I S n M is the total number of cells in the network G total number of services W is the bandwidth of the system
Model User Density with 2D Gaussian Distribution 1 2 2 2 1 y2 1 x 1 2 2 w( x, y) e e 2 1 2 means is a user density normalizin parameter variances of the distribution for every cell own 1 G i, W 1 I S n is the total intra-cell interference density caused by all users in cell i
Sinal-to-Noise Density in WCDMA E I b 0 i, own inter N0 Ii Ii S R S W S R N S n n G M G 0 i, j, ji, W 1 j1, ji 1 where N 0 R is the thermal noise density, is the bit rate for service is the minimum sinal-to-noise ratio required
Simultaneous Users in WCDMA Must Satisfy the Followin Inequality Constraints G M G ( ) ni, n j, ji, ceff 1 j1, ji 1 where c ( ) eff W 1 R R S N 0 S n i, is the minimum sinal-to-noise ratio is the maximum sinal power the number of users in BS i for iven service The capacity in a WCDMA network is defined as the maximum number of simultaneous users ( n1,, n2,,, nm, G) for all services 1,, G. This is for perfect power control (PPC).
Imperfect Power Control Transmitted sinals between BSs and MSs are subject to multi-path propaation conditions E b The received sinals I0 i, vary accordin to a lonormal distribution with a standard deviation on the order of 1.5 to 2.5 db. Thus ( Eb ) i, bin each cell i for every user with service needs to be replaced ( E ) ( E ) b i, b i, b o, b E ( E ) ( E ) b o, b b i, b ( c ) i, I0 I0 c ( ) eff _ IPC c e e ( ) eff ( ) 2 c 2 2
Relationship between Spreadin and Scramblin Channelization codes: separate communication from a sinle source Scramblin codes: separate MSs and BSs from each other
Main differences between WCDMA and IS-95 air interfaces Usae Lenth Number of codes Code family Spreadin Channelization code Uplink: Separation of physical data (DPDCH) and control channels (DPCCH) from same MS Downlink: Separation of downlink connections to different MSs within one cell. Uplink: 4-256 chips same as SF Downlink 4-512 chips same as SF Number of codes under one scramblin code = spreadin factor Orthoonal Variable Spreadin Factor Yes, increases transmission bandwidth Scramblin code Uplink: Separation of MSs Downlink: Separation of sectors (cells) Uplink: 10 ms = 38400 chips Downlink: 10 ms = 38400 chips Uplink: Several millions Downlink: 512 Lon 10 ms code: Gold Code Short code: Extended S(2) code family No, does not affect transmission bandwidth
Spreadin Factor
Orthoonal Variable Spreadin Factor (OVSF) codes
Simulations Network confiuration COST-231 propaation model Carrier frequency = 1800 MHz Averae base station heiht = 30 meters Averae mobile heiht = 1.5 meters Path loss coefficient, m = 4 Shadow fadin standard deviation, σ s = 6 db Bit enery to interference ratio threshold, τ = 9.2 db Activity factor, v = 0.375 Processin ain, W/R = 6.02 db, 12.04 db, 18.06 db, and 24.08 db for Spreadin Factors equal to 4, 16, 64, and 256.
Numerical Results
Numerical Results
Numerical Results
Numerical Results
Results of Optimized Capacity Calculation The SIR threshold for the received sinals is decreased by 0.5 to 1.5 db due to the imperfect power control. As expected, we can have many low rate voice users or fewer data users as the data rate increases. The determined parameters of the 2- dimensional Gaussian model matches well with the traditional method for modelin uniform user distribution.
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