Double-directional channel modeling approach for MIMO mobile - - PowerPoint PPT Presentation

Double-directional channel modeling approach for MIMO mobile communication systems

Jun-ichi Takada, Tokyo Institute of Technology Ichirou Ida, Fujitsu Laboratories Ltd.

多次元移動情報通信網自動設計技術研究会 2005年11月18日 朱鷺メッセ

Introduction

Array antenna technologies

– Coverage : beamforming – Link quality : diversity (Tx/Rx) – Channel capacity : space division multiplex

MIMO

– Array antennas at both Tx and Rx

Outline

• MIMO channel and double-directional channel
• Approaches
• Issues for system level simulation

This presentation

• does not present new results
• tries to provide some issues in propagation

modeling

• tries to get the opinions from network engineers

Channel modeling strategy for MIMO transmission systems

Performance of MIMO communication system is heavily dependent on MIMO channel property

• Array antennas

– Part of transceiver – Freedom of design

• Propagation environment

– Natural phenomenon – No control

Different elements

MIMO channel model Double-directional channel model

• Array antennas are included.
• Transfer functions between ports
• Array antennas are excluded.
• Parameters of ray paths

MIMO channel model Double-directional channel model

• Array antennas are included.
• Transfer functions between ports
• Array antennas are excluded.
• Parameters of ray paths

MIMO channel model Double-directional channel model

• Array antennas are included.
• Transfer functions between ports
• Array antennas are excluded.
• Parameters of ray paths

MIMO channel matrix

x y z θ φ ζ, τ at ar

MIMO channel can be modeled by double-directional path model.

Double-directional channel models for system level simulation

Model requirement

• Continuous trace of mobile

– dynamic behavior

• Macroscopic channel parameters

– Ignored in link level model – Path loss – Shadowing

• Multiple base stations

Double-directional channel models for system level simulation

Simulation Measurement Site-specific Ray Tracing Channel Sounding Stochastic 3GPP SCM N/A

Stochastic model

• Described purely mathematically
• Reproducible
• Not so realistic

3GPP-3GPP2 SCM

Taken from [4].

3GPP-3GPP2 SCM

Taken from [4].

Example

• A. Lozano, “The Industrial Embrace of MIMO: Reflections & Perspectives,”

in Panel Session “MIMO Technologies – Since Then,” WPMC '05.

Site-specific model

• Location dependent
• More realistic.
• Question about “typical” and “standard”
• Two different approaches

– Simulation based approach – Measurement based approach

Site-specific simulation model

• Numerical analysis of radiowave propagation
• Ray-tracing technique: high frequency

approximation

Example

Taken from [2]

Disadvantages in the ray tracing simulation

Detailed map for scattering objects

• Commercial GIS database

– Expensive – Other objects (sign board, light pole) not available

High frequency approximation

• Error due to roughness and irregularity of

surfaces

Site-specific measured model

• MIMO channel sounder
• Double-directional parameter estimator
• Synthetic channel for system level simulation

– Measured double-directional channel parameters – Virtual array antennas

Example of channel sounder

Example

• T. Matsumoto, “Iterative (Turbo) MIMO Equalization Techniques,”

Tutorial material in COST 273 MCM, May, 2003.

Issues in double-directional channel measurement

• Special array antennas

– Small antenna spacing

• Parameter estimation techniques (e.g. MLE)

– Influence from array geometry – Insufficient signal model

• Dense multipath within resolution
• Plane wave approximation

Current activities of the authors

Double-directional channel measurement and modeling for beyond-3G mobile communication systems

Center frequency 4.5 GHz Bandwidth 120 MHz Tx power 10 W Maximum delay Tx array 4 x 2 rectangular array, dual pol. Rx array 24 x 2 circular array, dual pol. 6.4 µs

First measurement campaign

Tx

+

• small macrocell
• urban residential area
• Height of BS: 30 m
• Scenario: non-line-of-sight (Red)
• Route length: 625 m
• Snapshots: 7 ss/m

Data analysis

• Still ongoing

– Instantaneous parameters

• Multipath fading
• Not yet started

– Macroscopic parameters

• Shadowing
• Path loss

Issues of the double-directional channel measurement

Some can not be solved...

• Limitation of parameter estimation

– Insufficient parametric model – Finite angular resolution – Bigger problem in indoor

• Limitation of license

– Base station position is strictly limited

• multi-cell measurement is impossible
• Limitation of coverage

– 10 W Tx

Summary

• Double-directional channel modeling approaches

– Most of the researches contribute to the models for

link level only

• Open issue

– Does antenna design really impact to the network

performance in MIMO system?