1 Power Control for CDMA Macro-Micro Cellular System Date: 27 Aug 2000 Advisor: Dr. Wang Speaker: Chih-Wen Chang

2 Content of this speech Introduction 1.Motive 2.Solution: Hierarchical Cell Structure (HCS) 3.The proposed method System Description 1.Macro/Micro-cells 2.SIR power control (up link) 3.Micro-cell size control (down link) Simulation Results Conclusions Problems & Discussion

3 Motive The increasing demand for cellular communications access and the evolution of wireless networks toward personal communications systems require a substantial increase of traffic capacity and full coverage of the service area. Solution(micro-cellular systems with an overlay structure) Micro-cells are capable of providing more capacity than macro-cell per unit area and are also attractive. Combining a macro-cell and micro-cell with a two-tier overlaying and underlaying structure for a CDMA system is to become an increasingly popular trend in the near future. *Macro-cell provides full coverage.

4 The Hierarchical Cell Structure (HCS) HCS is needed for different requirements: For large cell: Guarantee continuous coverage Serve high mobility and low capacity terminals. For small cell: Achieve good spectrum efficiency and high capacity. Serve low mobility and high capacity terminals. Two approaches for HCS in DS/CDMA system: Co-existing hierarchy layers operate in the same frequency band. Users operating on different layers are separated by handovers and signal fading. Different hierarchy levers are separated in the frequency domain. Problem: Non-uniform traffic distribution degrades communications quality at BS and the disparity in communications quality between BS and lowers system capacity.

5 The proposed power control method for downlink Controlling cell size according to time-varying traffic distribution in macro/micro overlaid cell environment. The aims is to bring communications quality in both macro-cell and micro-cell to a target quality level. Microcell base station controls the pilot signal transmission power to change its radius. The two control schemes: 1. Minimize the transmission power in mobiles. 2. Minimize the mean square error of received SIR.

6 Systems Description 1. Macro/Micro-cells The received power from a transmitter is: and are the height of the mobile antenna and the base station antenna. is the transmitted power and is the wave length. The ratio of transmission powers from central macro-cell and micro-cell base station is (1) (2)

7 Fig.1 Macro-cell/micro-cell structure.

8 2. SIR power control The uplink SIR’s measured by both the macrocell and microcell base stations: (4) (5)

9 Power control is to find a nonnegative power values satisfying: 1.Maximum power constraint: 2.Required SIR: The Distributed convergent power control takes the form of (7) (3) (6)

10 3. Micro-cell size control Since a mobile determines its cell from which the highest power pilot is received, variations in the transmitted power level of the pilot signal may control the coverage area of the cells. The Practical pilot power control algorithm is: (8) (9)

11 Two control scheme --- two decision varible 1.Minimize the transmission power in mobiles: 2.Minimize the mean square error of received SIR: If => pilot power variation in previous control time causes the reduction of transmission power. =>the system performance was improved by the previous cell size control. If in current time,pilot power is varied in the same direction (increase or decrease) with the variation of previous time. (10) (11)

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13 Simple Example:

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18 Problems & Discussion Q1: (Page4) Why “signal fading” can separate users operating on different layers? Q2: The simulation of non-uniform traffic distribution is Gaussian with mean corresponding to the micro-cell center. What’s the meaning and how to simulate …? Q3: How to decide ? Q4: In [2], the author said:” The micro-cell hot spot can be treated as the aggregation of multiple micro-cells. Thus, some phenomena exhibited in this structure can be applied to the hierarchical structure of multiple macro- cells and micro-cells.”…?? What’s the meaning…??