Modulo precoding for 11ac
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January 2011. Modulo Precoding for 11ac. Authors:. Date: 2011-01-17. January 2011. Introduction. Precoding Techniques for MU-MIMO Linear precoding - Low complexity , Low data rate (capacity) Channel Inversion MMSE Precoding Block Diagonalization

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Modulo Precoding for 11ac

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Modulo precoding for 11ac

January 2011

Modulo Precoding for 11ac

Authors:

Date: 2011-01-17


Introduction

January 2011

Introduction

Precoding Techniques for MU-MIMO

  • Linear precoding - Low complexity, Low data rate (capacity)

    • Channel Inversion

    • MMSE Precoding

    • Block Diagonalization

  • Non-linear precoding – High Complexity, High data rate (capacity)

    • Vector Perturbation

      • Sphere encoding (NP-hard)

      • Lattice reduction aided (Suboptimal but still full diversity)

    • Tomlinson Harashima Precoding

      • Equivalent to a low complexity vector perturbation but the diversity order is the same as Linear Precoding


Introduction1

January 2011

Introduction

  • The main disadvantage of Linear Precoding is that the normalization constant g (to maintain constant average power) is often very large.

  • This happens when the transmit vector lies along the singular vectors of the precoding matrix H-1 with high singular value [1].

  • Solution

    • Make sure the transmit signal does not lie along the singular vectors associated with large singular value of H-1.

    • Vector Perturbation can provide such transmit signal

  • This presentation is a proposal for non-linear precoding method like Vector Perturbation.

    • This technique can minimize the quantity γ


Simulation result

January 2011

Simulation Result

  • Vector Perturbation : BER Performance (Channel :Rayleigh)

Note: Perfect CSI, Ideal Conditions


Simulation result1

January 2011

Simulation Result

  • Vector Perturbation : Signal Power

Modulation =64 QAM

Channel Model = Rayleigh

4 x [1 1 1 1] MU-MIMO case

Vector Perturbation can reduce the unnormalized transmit power which increases the effective receive SNR.


Vector perturbation mu mimo system model

AP

User 1

MIMO

Decoder

modulo

VP algorithm

User 2

MIMO

Decoder

modulo

User k

MIMO

Decoder

modulo

User K

MIMO

Decoder

modulo

January 2011

Vector PerturbationMU-MIMO System Model

  • VP is analogous to doing MLD in the receiver.

  • The AP is free to use any algorithm to find the perturbing vector. Complexity can range from a simple O(n) modulo operation to MLD-like complexity

  • Regardless of the algorithm used by the transmitter, the receiver needs

  • only a predefined modulo lattice operation.

STAs doesn’t need to know how the perturbing vector was generated

Manufacturer specific


Review vector perturbation

Review-Vector Perturbation-

January 2011

Im

-1+1j

0+1j

1+1j

τ

Re

-1+0j

0+0j

1+0j

τ

n th stream’s decoded symbol :

-1-1j

0-1j

1-1j

Modulo operation :

  • This technique can minimize the quantity γ

  • Choose l in such a way that x=H-1 has smaller unnormalized transmit power than x=H-1u

    • τ: positive real value

    • l : Perturbation vector

      • each element is composed of

        a + jb(a and b are integers)

  • Receiver use modulo operationbecause a constellation is expanded


Proposals for tgac

January 2011

Proposals for TGac

  • Allow the AP to perform vector perturbation to prevent huge attenuation of transmit signals

  • Add one bit in the VHT-SIG-A Field to indicate that vector perturbation was performed.

    • all modulo decode-capable STAs will modulo decode if the bit is set.

    • The element of l corresponding to modulo decode-incapable STAs canbe forced to zero.

    • Alternatively, the AP will not use VP when one user doesn’t support modulo lattice decoding.


Reference

January 2011

Reference

  • [1] Christian B. Peel, Bertrand M. Hochwald and A. Lee Swindlehurst, “A Vector-Perturbation Technique for Near-Capacity Multiantenna Multiuser Communication -Part II: Perturbation, ” IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 53, NO.3, MARCH 2005


Strawpoll 1

January 2011

Strawpoll #1

  • Would you support to allot one bit in the VHT-SIG-A to indicate that modulo lattice decoding is needed after channel equalization?

  • Yes

  • No

  • Abstain


Strawpoll 2

January 2011

Strawpoll #2

  • Would you support allowing the AP to have the capability of reducing the signal attenuation by doing vector perturbation ?

  • Yes

  • No

  • Abstain


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