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Power Control for CDMA Macro-Micro Cellular System

Power Control for CDMA Macro-Micro Cellular System. Date: 27 Aug 2000 Advisor: Dr. Wang Speaker: Chih-Wen Chang. Content of this speech Introduction Motive Solution: Hierarchical Cell Structure (HCS) The proposed method System Description Macro/Micro-cells SIR power control (up link)

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Power Control for CDMA Macro-Micro Cellular System

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  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 • Motive • Solution: Hierarchical Cell Structure (HCS) • The proposed method • System Description • Macro/Micro-cells • SIR power control (up link) • 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: • Maximum power constraint: • Required SIR: • The Distributed convergent power control takes the form of (3) (6) (7)

  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 • Minimize the transmission power in mobiles: • 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)

  12. Simple Example:

  13. 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…??

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