Florida Institute of technologies ECE 5221 Personal Communication Systems Prepared by: Dr. Ivica Kostanic Lecture 16: Number of resource calculation in cellular access schemes Spring 2011

Florida Institute of technologies Page 2  Number of resources in FDMA  Number of resources in TDMA  Number of resources in CDMA  Examples Outline Important note: Slides present summary of the results. Detailed derivations are given in notes.

Florida Institute of technologies Number or resources in FDMA  Example: GSM deployment in A block PCS oA block PCS: –UL; – DL oA block: 2 times 15MHz (15MHz UL, 15 MHz DL) oGuard bands: 100KHz on each side of the band oGSM channel is 200KHz wide oTotal number of available channels  FDMA uses FDD and paired spectrum allocation  UL and DL bands are segmented into channels  Two types of channels oControl channels  Always on  Carry signaling oTraffic channels  On only on demand  Carry user information and in-band signaling oControl channels carry broadcast information Page 3 Note: there are very few pure FDMA systems in operation today. However, FDMA Is part of all access schemes.

Florida Institute of technologies Number of FDMA resources per cell  The number of resources depends on oReuse cluster size oType of the cells  Reuse cluster size depends oAbility of technology to tolerate interference oPropagation (environment and frequency)  Cells may be oSectored (majority of cells) oOmni directional  GSM deployment with C/I = 12dB and n = 4 in A block oReuse cluster size: N = 4 oNumber of channels per sector: Page 4 Note: Majority of deployed cells are in tri- sector configuration Number of channels per sector is integer. Some sectors would have 6 and some would have 7.

Florida Institute of technologies Number of resources in TDMA  No pure TDMA systems  It is always combination of FDMA/TDMA  FDMA – channelization  TDMA – time slots on channels  Time slots organized in frames  Users may get different number of slots per frame oMost basic – one time slot per user oLower – less than one slot per frame (ex. one slot every other frame) oHigher – more slots per frame  GSM deployment with C/I = 9dB and n = 4 in A block of PCS oReuse cluster size N = 3 oNumber of FDMA channels per sector in three sector deployment is oAverage number of time slots per sector is Page 5 Note: if users use one slot per frame there can be on average ~ 66 users per sector

Florida Institute of technologies Number of resources in CDMA  CDMA – users separated by orthogonal codes  Number of users depends on oDistribution of users oData rate of users oChip rate (channel bandwidth) oActivity of users  There is no hard number on available resources  CDMA – has interference limited “soft – capacity” Page 6 Softy capacity of CDMA systems Note 2: In CDMA the number of users that can be accommodated fundamentally depends on interference in the system

Florida Institute of technologies Nominal number of CDMA resources  Nominal number of CDMA resources is specified by pole point  Assumptions of the pole point equation oUniform distribution of users oCells of the same design oHexagonal grid layout oPerfect power control oUsers have same data rate, Eb/Nt requirements and activity  Pole point is a maximum theoretical limit  Systems are typically designed to work at 50% of the pole point (engineering capacity)  Example. Consider cdma2000 deployment with chip rate Mcps, vocoder rate 14.4kbps, Eb/Nt = 6dB and voice activity of 0.5 in A block of PCS oThere can be 11 CDMA channels in A block oNumber of users at 50% pole point oWith 11 CDMA the number of resources is Page 7 Multi cell pole point Note: some of CDMA capacity is used to support soft handoff

Florida Institute of technologies Comparison (A block PCS deployment)  CDMA has the largest capacity  The capacity is due to N=1, reuse of spectrum Page 8 Note: CDMA figure assumes 33% soft handoff overhead