SCIENCE CHINA Information Sciences, Volume 64 , Issue 9 : 192304(2021) https://doi.org/10.1007/s11432-020-2991-1

Optical true time delay pool based hybrid beamformer enabling centralized beamforming control in millimeter-wave C-RAN systems

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  • ReceivedMar 19, 2020
  • AcceptedJul 20, 2020
  • PublishedAug 18, 2021



This work was supported by National Key RD Program of China (Grant No. 2018YFB1801302) and Project for Zhongshan Social Public Welfare Science (Grant No. 2019B2007).


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  • Figure 1

    (Color online) (a) Structure of the proposed OTTDP-HBF for mmWave 5G C-RAN systems with eCPRI-based fronthaul; (b) PHY-layer with brief processing stages in downlink direction, and a promising eCPRI split II$_D$. OTTDP-HBF: optical true time delay based hybrid beamforming.

  • Figure 2

    (Color online) Framework of the proposed OTTDP-HBF enabling centralized beamforming control in a mmWave 5G C-RAN system with eCPRI-based fronthaul.

  • Figure 3

    (Color online) Implementation of the proposed OTTDP-HBF in a mmWave 5G C-RAN system with eCPRI-based fronthaul. TOF: tunable optical filter; E/O: electro-optic conversion; MLS: multi-wavelength laser source; Muxer: multiplexer; Demuxer: demultiplexer; PD: photodetector.

  • Figure 4

    An example of $9\times10$ optical wavelength matrix ${\boldsymbol~W}_{\rm~OW}$ designed based on (1), and its corresponding weight matrix ${\boldsymbol~F}_w^{\rm~OW}$. CW: codeword.

  • Figure 5

    (Color online) Spectral efficiency versus SNR ($\rho/\sigma^2$) for the single user channel via fully-digital precoding (red color), OMP-based hybrid precoding (blue color), and OTTDP-based hybrid precoding (green color).

  • Figure 6

    (Color online) Averaged achievable rates achieved by optimal multi-user precoder without interference (red color), two-stage multi-user hybrid precoder (green color), and OTTDP-based multi-user precoder (blue color).


    Algorithm 1 OTTDP-based sparse precoding via orthogonal matching pursuit

    Require:${\boldsymbol~F}_{\rm~opt}$, ${\boldsymbol~W}_{\rm~OW}$, and ${\boldsymbol~F}^{\rm~OW}_w$.

    Output: ${\boldsymbol~F}^{\rm~OW}_{\rm~RF}$ and ${\boldsymbol~F}^{N}_{\rm~BB}$.

    Initialize ${\boldsymbol~F}^{N}_{\rm~RF}$ and ${\boldsymbol~F}^{N}_{\rm~BB}$;


    for $i=1~\to~N^{\rm~RF}_{t}$




    ${\boldsymbol~R}_{\rm~res}=\frac{{\boldsymbol~F}_{\rm~opt}-{\boldsymbol~F}^{N}_{\rm~RF}{\boldsymbol~F}^{~N}_{\rm~BB}} {\|{\boldsymbol~F}_{\rm~opt}-{\boldsymbol~F}^{N}_{\rm~RF}{\boldsymbol~F}^{N}_{\rm~BB}\|_\mathrm{F}}$;

    end for

    Select ${\boldsymbol~F}^{\rm~OW}_{\rm~RF}$ from ${\boldsymbol~W}_{\rm~OW}$ according to ${\boldsymbol~F}^{N}_{\rm~RF}$.


    Algorithm 2 OTTDP-based hybrid precoding for multi-user scenarios

    Require:${\boldsymbol~V}_{\rm~opt}$, ${\boldsymbol~F}^{\rm~OW}_{w}$, and ${\boldsymbol~W}_{\rm~OW}$.

    Output:${\boldsymbol~V}^{\rm~OW}_{\rm~RF}$, ${\boldsymbol~V}_{\rm~RF}$, and ${\boldsymbol~V}_{\rm~BB}$.

    Calculate fully-digital zero-forcing precoder ${\boldsymbol~V}_{\rm~opt}$ by (7);

    Calculate weight vector ${\boldsymbol~h}$ by (9);

    Generate analog precoder ${\boldsymbol~V}_{\rm~RF}$ by (10);

    Select columns from ${\boldsymbol~W}_{\rm~OW}$ to form ${\boldsymbol~V}^{\rm~OW}_{\rm~RF}$;

    Calculate digital precoder ${\boldsymbol~V}_{\rm~BB}$ by (11).


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