Mobile Communications (KECE425) Lecture Note Prof. Young-Chai Ko

Transcription

1 Mobile ommunications (K425) Lecture Note Prof. Young-hai Ko 1

2 Summary ellular concept o-channel interference ellular size and capacity Path loss model Prof. Y. -. Ko 2

3 ellular oncept... f 3 f 2 f f f 3 f 1 f 2 f 1 + f 2 + f 3 = f = 2 = 3 Total bandwidth f 3 f 1 Key idea of cellular system: frequency reuse Prof. Y. -. Ko 3

4 Prof. Y. -. Ko luster luster size N=3 luster size N=4 3-cell reuse pattern 4-cell reuse pattern 4

5 luster size N=7 7-cell reuse pattern Prof. Y. -. Ko 5

6 xample of requency Reuse KT: 1960 MHz 1980 MHz for uplink and 2150 MHz 2170 MHz xample for N= in MHz: and for UL and L, respectively. in MHz: and for UL and L, respectively. in MHz: and for UL and L, in MHz: and for UL and L, respectively. Prof. Y. -. Ko 6

7 ellular Reuse luster tessellating reuse cluster of size N 3-cell, N =3 4-cell, N =4 N = i 2 + ij + j 2, {i, j 2 I i j} 7-cell, N =7 N = =1 N = =3 N = =4 N = =7... Prof. Y. -. Ko 7

8 Shapes of ellular: Tessellating shapes ell Hexagons are typically used as models for wireless systems. Prof. Y. -. Ko 8

9 o-hannel Reuse actor : Reuse distance R : ell radius N :lustersize R o-channel reuse factor Q = R = p 3N Prof. Y. -. Ko 9

10 o-hannel Interference The cells with same frequency band experiences the co-channel interference! R o-channel interference cells are separated by a reuse distance. Prof. Y. -. Ko 10

11 luster Size and uplex hannels onsider a cluster with N cells with S duplex channels/cluster. - KT: 1960 MHz 1980 MHz for uplink and 2150 MHz 2170 MHz. - ach user needs 1MHz for L and 1MHz for UL. - Then we have 20 duplex channels/cluster. - If N = 4, there are 5 duplex channels/cell. - Hence, we have S = k N where k is the number of duplex channels/cell. Prof. Y. -. Ko 11

12 System apacity If cluster is replicated M times within the system, the total number of channels available for the cellular system is = MkN = MS measure of capacity Prof. Y. -. Ko 12

13 Remark = MkN = MS M "=) " #, M"=) " So choose the cluster size N as small as possible in order to increase capacity. hoose high N (high Q) to improve the QoS due to small level of I. Trade-off between capacity and QoS Prof. Y. -. Ko 13

14 ell Size vs. ell apacity Macro-cell R =1 P t : km 10W overage apacity Micro-cell Pico-cell emto-cell R =0.2 P t : 20mW R = 10 1km R apple 10 m 200 m P t : 10mW P t : 5mW Prof. Y. -. Ko 14

15 International Standards of ellular ommunications 1 (Macro-cell) 2 (Macro/ Micro-cell) 3 (Micro/ Pico-cell) 4 (Pico/ emto-cell) Voice signals only nalogue cellular phones MPS (analog mobile phone system) Voice and data signals igital fidelity cellular phones SM (urope), M (US, Korea), TM (US, Japan) Voice, data, and video signals Video telephony / internet surfing W-M nhanced 3 / Interoperability protocol High-speed & IP-based LT (OM) 9.6/14.4 kbps 3.1 Mbps(peak) kbps 100 ~ 300 Mbps (peak) 3-5 Mbps Prof. Y. -. Ko 15

16 Mobile Radio Propagation Radio signals generally propagate according to three mechanisms: scattering di raction reflection Prof. Y. -. Ko 16

17 Power ttenuation in ree Space Received signal power at d denoted as p (d) in free space 2 c p (d) = t k 4 d where - t : transmit power - c: wavelength where c = c f c. - k: a constant of proportionality - d: distance between the transmitter and the receiver Prof. Y. -. Ko 17

18 In decibel domain, we have p(dm) (d) = 10 log 10 ( p (d) 10 3 ) # 2 c = 10 log 10 " t k d = 10 log 10 t 10 3 c log 10 4 d = t(dm) + 10 log 10 k = t(dm) 20 log 10 (d) + 10 log 10 (k 0 ) where k 0 = 2 c 16 2 Prof. Y. -. Ko 18

19 In free space, the received signals of the locations at the same distance are all the same as p(dm) (d) = t(dm) 20 log 10 (d) + 10 log 10 (k 0 ) location d location Power at = Power at Prof. Y. -. Ko 19

20 Let us assume that the power at the distance d 0 is p(dm) (d 0 ): p(dm) (d 0 )= t(dm) 20 log 10 (d 0 ) + 10 log 10 (k 0 ) or equivalently we can write p(dm) (d 0 ) + 20 log 10 (d 0 )= t(dm) + 10 log 10 (k 0 ) Then we can express the power at a certain distance d as p(dm) (d 0 ) as p(dm) (d) = t(dm) 20 log 10 (d) + 10 log 10 (k 0 ) = p(dm) (d 0 ) + 20 log 10 (d 0 ) 20 log 10 (d) = p(dm) (d 0 ) 20 log 10 (d/d 0 ) Prof. Y. -. Ko 20

21 Path Loss Model in Mobile Radio nvironment ree space propagation does not apply in a mobile radio environment. Instead, the following simple path loss model is often used: p(dm) (d 0 )= t(dm) 20 log 10 (d 0 ) + 10 log 10 (k 0 )+ (d) where (d) is aussian random variable with zero mean and variance 2. Then p(dm) is also aussian random variable such as p(dm) (d 0 ) N µ p(dm) (d 0 ), 2 where µ p(dm) (d 0 )= t(dm) 20 log 10 (d 0 ) + 10 log 10 (k 0 ) Prof. Y. -. Ko 21