Mi Michael hael Liao ao Advisor : Andy Wu Graduate Institute of - - PowerPoint PPT Presentation

Next Generation Mobile Communication

Graduate Institute of Electronics Engineering National Taiwan University Taipei, Taiwan

Channel State Information (CSI) Acquisition for mmWave MIMO Systems

Mi Michael hael Liao ao

April 7, 2015

Advisor : Andy Wu

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Outline

Recap: Millimeter Wave & Hybrid-Beamforming Why Do We Need “Channel State Information” ? CSI Acquisition in Hybrid Architecture Existing Solutions for CSI acquisition Summary Future work Reference

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Recap: Why mmWave for Cellular ?

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Cellular systems live with a little microwave spectrum

600MHz total (best case) in the U.S. Spectrum efficiency is king (MIMO, MU-MIMO)

Huge amount of spectrum available in mmWave bands

Unlicensed and free spectrum for links of very high data rates mmWave already used in LAN and PAN. mmWave links are used for backhaul in cellular networks

8GHz 11GHz 20GHz

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Recap: Big Challenges from mmWave MIMO (1/3)

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LOS NLOS NLOS

Microwave Transmission mmWave Transmission

X X

Rx Tx

30 GHz shows additional about 20 20 dB dB loss compared to 3 GHz. Issues from large pathloss in mmWave –

Links with unreasonable signal-to-noise ratio (SNR) Rank-deficient MIMO due to reduced spatial dimension

Measurements of Propagation Loss [1]

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Pathloss in mmWave can be compensated through large array antenna and directional transmissions.

Huge be beam amform rming gai gain with compact-sized array antenna Meanwhile multiplexing gain still can be achieved by conventional MIMO techniques (e.g. P2P-MIMO, MU-MIMP)

Wireless Multipath Propagation Measurements of Propagation Loss

Tx Array Antenna Rx Array Antenna Distance (m)

Channel

Tx Rx

Recap: Big Challenges from mmWave MIMO (2/3)

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(1) Large antenna array requires multiple RF/analog chains.

Analog-to-digital/digital-to-analog converters Required power amplifiers are proportional to antennas

(2) Higher dimension information of MIMO channel acquisition

Estimation of channel state information (CSI) Training & controlling resource overhead

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(1) (2)

Number of Total Tx Antennas : M Number of Total Rx Antennas : N Number of Independent Data Stream : K

Recap: Big Challenges from mmWave MIMO (3/3)

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Recap: Hybrid-Beamforming Technique

6 Traditional Beamforming is done at BB

Requiring one RF chain per transmitting antenna.

Hybrid Beamforming relies on RF precoding to reduce the number of RF chains

Two-staged structure:

F BB RF

• pt

BB RF RF BB

F F F F F F F   , min arg ) , (

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Why Do We Need “Channel State Information” ?

In wireless communications, channel state information (CSI) refers to known channel properties of a communication link. CSI needs to be estimated at the receiver and usually quantized and feedback to the transmitter. V1 must be acquired from performing SVD on H. 7

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CSI Acquisition in Hybrid Architecture (1/4)

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Due to the hybrid architecture, CSI cannot be acquired by conventional methods directly. Account for practical assumptions on the hybrid architecture:

RF chains is limited, i.e., less than the number of antennas Phase shifters have constant modulus and quantized phases

H

mmWave MIMO with Hybrid Architecture

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RF beamformers greatly reduces the complexity & cost

Requires fewer RF chains

However, it cannot “see” the whole channel instantaneously

Instead, we have to “scan” the channel with directional beams Controlled by analog switches or phase shifters

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CSI Acquisition in Hybrid Architecture (2/4)

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CSI Acquisition in Hybrid Architecture (3/4)

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CSI Acquisition in Hybrid Architecture (4/4)

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Angular Domain Transform [7]

CSI acquisition can be separated in two parts:

(1) Beamformer Training: Find out the active spatial channel path. (2) Channel Estimation: Estimation each entry (path gain) in the Ha

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Existing Solutions for CSI acquisition (1/2)

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Conventional beam scanning protocol

Exhaustive search over a large space given the large # of antennas Scanned requires fine control and leads to slow adaptation Trading overhead –

BS MS

O(N N )

Exhaustive Search

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Multi-resolution codebook for beamforming vector [8]-[11]

Different granularity of beam patterns from codebook and realize progressive searching Greatly reduces the training overhead for large antenna array

Progressive Search = 3x(2x2) = 12 Exhaustive Search = 8x8 = 64

Quasi-Omni Beam Sector Hi-res Beam

Single Path 8x8 System Multipath 8x8 System by Progressive Search = 12 * (# of paths)

Existing Solutions for CSI acquisition (2/2)

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Issues of Existing Solutions

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• 1. However, multi-resolution codebooks is subject to practical

limitations in our applications.

Existence of quantized phase shifters makes the design of non-overlapping beam patterns difficult The Codebook design of this work relies mostly on 2D array. Hybrid analog-digital training codebook is required

• 2. Existing solutions are not designed for MIMO CSI acquisition

How to estimate the parameters of path gain ? Conventional progressive search is not designed for multipath systems

                                      

MS BS

H MS 1 MS 2 MS N BS 1 BS 2 BS N

| | | | | | a ( ) a ( ) a ( ) a ( ) a ( ) a ( ) | | | | | |

H r a t

H H = U U

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Summary & Future Work

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Introduction to Channel State Information. For CSI acquisition in the hybrid precoding transceiver, we prefer to use:

Channel estimation from angular domain . Hybrid analog-digital training codebook

CSI acquisition can be separated in two parts:

Step I: Beamform Training  Beam Alignment & Beamform Tracking Step II: Channel Estimation

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Z1 Z2 Z3 Z4

MS1

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Beam Tracking in BS

MS1

What is “Beamform Tracking”?

Rapid proliferation of smart phones and tablets. Beam alignment can be easily destroyed by even small variation. Re-estimating the channel causes high overhead. Track the channel variations during user mobility with low overhead.

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• Proc. 2010 IEEE International Conf. Commun (ICC).

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[9] L. Chen, Y. Yang, X. Chen, and W. Wang, “Multi-stage beamforming codebook for 60GHz WPAN,” in Proc. of 6th International ICST Conference on Communications and Networking in China, China, 2011, pp. 361–365. [10] S. Hur, T. Kim, D. Love, J. Krogmeier, T. Thomas, and A. Ghosh, “Millimeter wave beamforming for wireless backhaul and access in small cell networks,” IEEE Transactions on Communications, vol. 61, no. 10, pp. 4391–4403, 2013. [11] Y. M. Tsang and A. S. Poon, “Successive AoA estimation: Revealing the second path for 60 GHz communication system,” 49th Annual Allerton Conference on Communication, Control, and Computing (Allerton), pp. 508–515, 2011. [12] A. Alkhateeb, O. E. Ayach, and G. Leus, “Channel Estimation and Hybrid Precoding for Millimeter Wave Cellular Systems,” submitted to IEEE Journal of Selected Topics in Signal Processing, on Jan 2014

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Reference