ECE 5221 Personal Communication Systems

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

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

3. Number or resources in FDMA • Example: GSM deployment in A block PCS • A block PCS: 1850-1865 –UL; 1930-1945 – DL • A block: 2 times 15MHz (15MHz UL, 15 MHz DL) • Guard bands: 100KHz on each side of the band • GSM channel is 200KHz wide • Total number of available channels • FDMA uses FDD and paired spectrum allocation • UL and DL bands are segmented into channels • Two types of channels • Control channels • Always on • Carry signaling • Traffic channels • On only on demand • Carry user information and in-band signaling • Control channels carry broadcast information Note: there are very few pure FDMA systems in operation today. However, FDMA Is part of all access schemes.

4. Number of FDMA resources per cell • The number of resources depends on • Reuse cluster size • Type of the cells • Reuse cluster size depends • Ability of technology to tolerate interference • Propagation (environment and frequency) • Cells may be • Sectored (majority of cells) • Omni directional • GSM deployment with C/I = 12dB and n = 4 in A block • Reuse cluster size: N = 4 • Number of channels per sector: Number of channels per sector is integer. Some sectors would have 6 and some would have 7. Note: Majority of deployed cells are in tri-sector configuration

5. 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 • Most basic – one time slot per user • Lower – less than one slot per frame (ex. one slot every other frame) • Higher – more slots per frame • GSM deployment with C/I = 9dB and n = 4 in A block of PCS • Reuse cluster size N = 3 • Number of FDMA channels per sector in three sector deployment is • Average number of time slots per sector is Note: if users use one slot per frame there can be on average ~ 66 users per sector

6. Number of resources in CDMA • CDMA – users separated by orthogonal codes • Number of users depends on • Distribution of users • Data rate of users • Chip rate (channel bandwidth) • Activity of users • There is no hard number on available resources • CDMA – has interference limited “soft – capacity” Softy capacity of CDMA systems Note 2: In CDMA the number of users that can be accommodated fundamentally depends on interference in the system

7. Nominal number of CDMA resources • Nominal number of CDMA resources is specified by pole point • Assumptions of the pole point equation • Uniform distribution of users • Cells of the same design • Hexagonal grid layout • Perfect power control • Users 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 1.2288Mcps, vocoder rate 14.4kbps, Eb/Nt = 6dB and voice activity of 0.5 in A block of PCS • There can be 11 CDMA channels in A block • Number of users at 50% pole point • With 11 CDMA the number of resources is Multi cell pole point Note: some of CDMA capacity is used to support soft handoff

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