Multiple access techniques for wireless communications

MULTIPLE ACCESS TECHNIQUES FOR WIRELESS COMMUNICATIONS UNIT - IV

CONTENTS ,[object Object],[object Object],[object Object],[object Object]

Introduction ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Frequency division duplexing (FDD) ,[object Object],[object Object],[object Object],[object Object],[object Object],frequency seperation reverse channel forward channel f

Time division duplexing (TDD) ,[object Object],[object Object],[object Object],[object Object],[object Object],time seperation t forward channel reverse channel

Multiple Access Techniques ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Narrowband systems ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Wideband systems ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Multiple Access Techniques in use Multiple Access Technique Advanced Mobile Phone System (AMPS) FDMA/FDD Global System for Mobile (GSM) TDMA/FDD US Digital Cellular (USDC) TDMA/FDD Digital European Cordless Telephone (DECT) FDMA/TDD US Narrowband Spread Spectrum (IS-95) CDMA/FDD Cellular System

Frequency-division Multiple Acess

Frequency division multiple access FDMA ,[object Object],[object Object],[object Object],[object Object],[object Object]

FDMA compared to TDMA ,[object Object],[object Object],[object Object],[object Object],[object Object]

Nonlinear Effects in FDMA ,[object Object],[object Object],[object Object],[object Object],[object Object]

Number of channels in a FDMA system ,[object Object],[object Object],[object Object],[object Object],N= B t - B guard B c

Example: Advanced Mobile Phone System ,[object Object],[object Object],[object Object],[object Object],[object Object],N= 12.5 E 6 - 2*(10 E 3) 30 E 3 = 416 channels

Time Division Multiple Access ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Repeating Frame Structure Slot 1 Slot 2 Slot 3 … Slot N Preamble Information Message Trail Bits One TDMA Frame Trail Bits Sync. Bits Information Data Guard Bits The frame is cyclically repeated over time.

Features of TDMA ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Number of channels in a TDMA system ,[object Object],[object Object],[object Object],[object Object],[object Object],N= m*(B tot - 2*B guard) B c

Example: Global System for Mobile (GSM) ,[object Object],[object Object],[object Object],[object Object],[object Object],N= 8*25E6 200E3 = 1000 simultaneous users

Efficiency of TDMA ,[object Object],[object Object],[object Object],[object Object],[object Object]

Efficiency of TDMA ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],b OH = N r *b r + N t *b p + N t *b g + N r *b g

Efficiency of TDMA ,[object Object],[object Object],[object Object],b T = T f * R

Efficiency of TDMA ,[object Object],[object Object],[object Object], f = (1-b OH /b T )*100%

Space Division Multiple Access ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Space Division Multiple Access ,[object Object],[object Object]

Reverse link problems ,[object Object],[object Object],[object Object],[object Object],[object Object]

Solution by SDMA systems ,[object Object],[object Object],[object Object],[object Object],[object Object]

Disadvantage of SDMA ,[object Object],[object Object]

SPREAD SPECTRUM MULTIPLE ACCESS ,[object Object],[object Object],[object Object],[object Object]

Frequency Hoping Spread Spectrum

Frequency Hopping Spread Spectrum

Frequency Hopping Spread Spectrum ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Code-Division Multiple Access (CDMA) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

CDMA for Direct Sequence Spread Spectrum

CAPACITY of CELLULAR SYSTEMS .

Spreading in Cellular CDMA Systems ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Capacity of Cellular Systems ,[object Object],[object Object],[object Object],[object Object],[object Object]

Co-Channel Reuse Ratio Q ,[object Object],[object Object],[object Object],Q=D/R

Forward channel interference ,[object Object],[object Object],[object Object]

Carrier-to-interference ratio C/I ,[object Object],C = I D 0 -n 0 M k=1 D K -n k ,[object Object],[object Object]

Carrier-to-interference ratio C/I ,[object Object],[object Object],[object Object],[object Object],C I = D 0 -n 6*D -n

Worst Case Performance ,[object Object],[object Object],[object Object],1/6 * (R/D) (C/I) min = > -n

Co-Channel reuse ratio Q ,[object Object],[object Object],[object Object],[object Object],Q = D/R = (6*(C/I) min ) 1/n

Radio Capacity m ,[object Object],[object Object],[object Object],m = B t B c * N radio channels/cell

Radio Capacity m ,[object Object],Q = (3*N) 1/2 m= B t B c * (Q²/3) = B t Bc * 6 C I 3 n/2 ( * ( ) min ) 2/n

Radio Capacity m for n = 4 ,[object Object],[object Object],[object Object],[object Object],m = B t B c * 2/3 * (C/I) min

Compare different Systems ,[object Object],[object Object],[object Object]

Compare different Systems ,[object Object],[object Object],[object Object],[object Object],C I = C I B c B c’ ( ) ( ) min )² eq * (

C/I in digital cellular systems ,[object Object],[object Object],[object Object],[object Object],C E b *R b E c *R c I I I = =

C/I in digital cellular systems ,[object Object],(C/I) (E c *R c )/I B c ’ (C/I) eq (E c ’*R c ’)/I’ B c = = ( )² ,[object Object]

C/I in digital cellular systems ,[object Object],[object Object],E c B c ’ E c ‘ B c = ( )³

Compare C/I between FDMA and TDMA ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Example ,[object Object],[object Object],[object Object]

Example ,[object Object],C’ = E b *R b ’ = 1/3*(E b *10 E 4 bits) = 3*R b *E b =3*C I’ = I0*Bc’ = I0*30kHz = 3*I ,[object Object]

Example ,[object Object],[object Object]

Capacity of SDMA systems ,[object Object],[object Object],[object Object],[object Object],[object Object]

Capacity of SDMA systems ,[object Object],[object Object],[object Object]

Capacity of SDMA ,[object Object],[object Object],I = E {  G(  i ) P r;I } K-1 i=1

Capacity of SDMA systems ,[object Object],P r;I = P c ,[object Object],I = P c E {  G(  i ) } K-1 i=1

Capacity of SDMA systems ,[object Object],I = P c *(k -1) * 1/D ,[object Object],[object Object]

Capacity of SDMA systems ,[object Object],P b = Q ( ) 3 D N K-1 ,[object Object],[object Object],[object Object],[object Object]

Multiple access techniques for wireless communications

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Multiple access techniques for wireless communications