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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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Presentation Transcript
slide1

Power Control for CDMA Macro-Micro Cellular System

Date: 27 Aug 2000

Advisor: Dr. Wang

Speaker: Chih-Wen Chang

slide2

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
slide3

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.

slide4

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.
slide5

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.
slide6

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)

slide8

2. SIR power control

The uplink SIR’s measured by both the macrocell and microcell base stations:

(4)

(5)

slide9

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)

slide10

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)

slide11

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)

slide18

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…??