Recently, extreme demand of mobile communication, small cells in millimeter wave bands within macro-cell network is attracting the attention in academics as well as the industries. Evolution of 4G is essential in keeping up with the exponential growth of mobile data network traffic. Up to 7GHz bandwidth has been allocated worldwide for license-free 60GHz radio frequency. Multiple giga-bites per second can be transmitted by utilizing the huge unlicensed bandwidth using mmWave communication in the 60GHz band. Numerous amount of spectrum available in micro frequencies are able to provide cost effective communication between the nodes in small cell via high capacity backhaul. Wireless backhaul is an attractive option for small cells as it provides a less expensive and easy-to-deploy over fiber. However, there are multitude of bands and features (e.g. LOS/NLOS, spatial multiplexing etc.) connected to wireless backhaul that need to be used smartly for small cells. Candidate bands include: sub-6 GHz band that is useful in non-line-of-sight (NLOS) scenarios, microwave band (6�42 GHz) that is used in point-to-point line-of-sight (LOS) scenarios, and mmWave bands (e.g. 60, 70 and 80 GHz) that are recently being commercially used in LOS scenarios. In many deployment topologies, it is more beneficial to use aggregator nodes, located at the roof tops of tall buildings near small cells. The protocol supports concurrent transmission in minimum frequency to the greater extent. Further to enhance the efficiency of network, performance analysis and different parameters will be calculated.

Device-to-Device communication (D2D), Heterogeneous cellular network, millimeter wave, MAC scheduling, spatial re-use

[1]. �Exploiting Device-to-Device Communication in Joint Scheduling of access and Backhaul for mmWave Small Cells� Yong Niu; Chuhan Gao; Yong Li; Li Su; Depeng Jin; Athanasios V. Vasilakos, 2015
[2]. �Exploiting Device-to-Device Communications to Enhance Spatial Reuse for Popular Content Downloading in Directional mmWave Small Cells� Yong Niu, Li Su, Chuhan Gao, Yong Li, Member,IEEE, Depeng Jin, and Zhu Han, Fellow, IEEE, 2016
[3]. White_paper_c11-481360, �Cisco Visual Networking Index: Forecast and Methodology,� June 2010
[4]. �Directional MAC protocol for millimeter wave based wireless personal area networks�. Xueli An and Ramin Hekmat Faculty of Electrical Engineering, Mathematics, and Computer Science Delft University of Technology, Delft, The Netherlands {X.An, R.Hekmat}@ewi.tudelft.nl 2008
[5]. �Millimeter-wave propagation channel characterization for short-range wireless communications�. Suiyan Geng, Jarmo Kivinen, Xiongwen Zhao, and Pertti Vainikainen, Member, IEEE 2009
[6]. C. Sum et al., �Virtual time-slot allocation scheme for throughput enhancement ina millimeter-wave multi-Gbps WPAN system,� IEEEJ. Sel. Areas Commun., vol. 27, no. 8, pp. 1379�1389, Oct. 2009.
[7]. C.-S. Sum et al., �A multi-Gbps millimeter-wave WPAN system based on STDMA with heuristic scheduling,� in Proc. IEEE GLOBECOM, Honolulu, HI, USA, Nov. 30�Dec. 4, 2009, pp. 1�6
[8]. L. X. Cai, L. Cai, X. Shen, and J. W. Mark, �REX: A randomized exclusive region based scheduling scheme for mmWave WPANs with directional antenna,� IEEE Trans. Wireless Commun., vol. 9, no. 1, pp. 113�121, Jan. 2010.
[9]. J. Qiao, L. X. Cai, X. Shen, and J. W. Mark, �Enabling multi-hop concurrent transmissions in 60 GHz wireless personal area networks,� IEEE Trans. Wireless Commun., vol. 10, no. 11, pp. 3824�3833, Nov. 2011.
[10]. S. Singh, F. Ziliotto, U. Madhow, E. M. Belding, and M. Rodwell, �Blockage and directivity in 60 GHz wireless personal area networks: From cross-layer model to multi hop MAC design,� IEEE J. Sel. Areas Commun., vol. 27, no. 8, pp. 1400�1413, Oct. 2009.
[11]. I. K. Son, S. Mao, M. X. Gong, and Y. Li, �On frame-based scheduling for directional mmWave WPANs,� in Proc. IEEE INFOCOM, Orlando, FL, USA, Mar. 25�30, 2012, pp. 2149�2157
[12]. A. Lebedev et al., �Feasibility study and experimental verification of simplified fiber-supported 60-GHz picocell mobile backhaul links,� IEEE Photon. J., vol. 5, no. 4, Aug. 2013, Art. ID. 7200913.
[13]. Y. Zhu et al., �Demystifying 60 GHz outdoor picocells,� in Proc. 20th Annu. Int. Conf. Mobile Comput. Netw., Maui, HI, USA, Sep. 7�11, 2014, pp. 5�16.
[14]. M. X. Gong, R. J. Stacey, D. Akhmetov, and S. Mao, �A directional CSMA/CA protocol for mmWave wireless PANs,� in Proc. IEEE WCNC, Sydney, NSW, Australia, Apr. 18�21, 2010, pp. 1�6.
[15]. V. Chandrasekhar, J. G. Andrews, and A. Gatherer, �Femtocell networks: A survey,� IEEE Commun. Mag., vol. 46, no. 9, pp. 59�67, Sep. 2008.