The heterogeneous cognitive radio networks are playing the most important role in the future generation wireless networks in order to address the problem of spectrum scarcity and to satisfy the demand of multiple coexistence networks. . In a country like India the deployment of CRN is possible on television network with the help of TV White Spaces (TVWS) as its capacity is quite high due to digital transmission of TV channel. The use of multiple wireless standards such as IEEE 802.11a, IEEE 802.22, IEEE 802.19.1 and many more wireless networks operating in the same frequency band of TVWS creates the coexistence scenario which involves the heterogeneous networks. The interference mitigation is the most important issue in such heterogeneous networks. In literature, the issue of interference mitigation is addressed mainly at the medium access layer; however, very limited work is presented at physical layer. In this paper, an interference mitigation problem of heterogeneous cognitive radio network at physical layer is addressed. The spatial diversity based techniques are proposed to mitigate the interference in heterogeneous CRN. The coexistence of different wireless networks in secondary CRN is considered for analysis. The characterization of aggregate interference is carried out for different interference scenarios. The proposed system outperform for heterogeneous CRN network over TVWS network

After the advent of cellular standards for mobile wireless voice telephony and data transfer, IEEE 802.11 and IEEE 802.16 standards evolved for wireless broadband data transfer. The IEEE 802.11 replaced the wired LAN and IEEE 802.16 was to wireless point-to-point provide broadband data transfer. IEEE 802.11 operates in 2.4 GHz and 5 GHz bands whereas IEEE 802.11, which was initially designed to operate on a licensed band, later switched to a 2-11 GHz band. However, both these standards used a 5 GHz unlicensed band for transmission causing the possible overlap of channels. The designed protocols fairly allow the sharing on an ad-hoc basis. IEEE 802.11 operated in distributed coordination mode using Distributed Coordination Function (DCF) and point coordinated mode using a dedicated coordinator node called Point Coordination Function (PCF). However, DCF mode allows spectrum sharing for multiple users. Both standards were not designed for coexistence and thereby they may cause interference to each other, degrading their performance. Mechanisms can be designed at various layers such as MAC or PHY to enable the coexistence with desired QoS. In this paper, a performance analysis of the impact of possible interference between IEEE 802.11 and IEEE 802.16 devices is presented. Therefore, this paper presents the approaches for allowing a reliable operation between IEEE 802.16 and IEEE 802.11 when both are sharing unlicensed spectrum 5GHz. In this paper, we propose advancements to the MAC of IEEE 802.16 Base Station (BS) where IEEE 802.11 frame transmissions are not required by an IEEE 802.16 system. Here, Co-existence between IEEE 802.11 and IEEE 802.16 is permitted without any exchange of data between both standards, and also it provides quality of service for both systems operating at unlicensed spectrum 5GHz.

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