This study proposes an incentive-based femtocell cooperation scheme for indoor macrocell users (MUs) in an underlay two-tier heterogeneous network which helps the indoor MUs to achieve higher data rate through time sharing access from the femtocell. Due to underlay spectrum sharing nature of the femtocell, the network suffers from severe cross-tier interference. To manage this cross-tier interference, a price-based power control scheme is also proposed for the femtocell access point (FAP) whereby the macrocell base station (MBS) controls the transmit power of the FAP by pricing their resulted cross-tier interference power level subject to a maximum tolerable interference limit. A Stackelberg game has been formulated and analysed for joint pricing-based power control and incentive-based cooperation game. Numerical results show the performance of the proposed scheme in terms of achievable rate of indoor users and utilities of both the MBS and the FAP for different locations of the femtocells.

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The paper proposes a scheme to minimize the co-tier and cross-tier interference by properly allocating the sub-channels and power among the femtocell users (FUs) in an OFDMA based cognitive femtocell network. An efficient graph coloring based sub-channel allocation scheme is adapted in which the sub-channels in the uplink band of the macrocell are shared by the femtocells dynamically in an opportunistic way through spectrum sensing. A price-based power allocation scheme using game theory is proposed to assign the transmission power among the FUs, whereby the macrocell base-station (MBS) controls the transmission power of the FUs by pricing their resulted interference power levels at the MBS with the constraint that the total interference created at the MBS in each subchannel is kept below a tolerable threshold. The game theoretic approach ensures that no FUs can improve its utility by changing its own transmission power selfishly. The allocation of sub-channels among the FUs is centrally controlled whereas the power allocation is handled in a distributed way which makes the process efficient. Finally, numerical examples are presented to analyze the proposed scheme. The results show that substantial number of FUs with good quality of services can be accommodated in the macrocell reusing the uplink frequency sub-channels and thereby enhancing the throughput and coverage of the network.

Energy detection is one of the basic schemes of spectrum sensing. In case of energy detection because of the uncertainty in estimating the noise variance there exists a fundamental limit of minimum SNR, called the SNR-wall, below which the signal could not be reliably detected. In this paper, we propose a method to overcome this SNR-wall for OFDM signal by exploiting the autocorrelation property of the cyclic prefix both in AWGN and multipath fading channel. Required SNR for signal detection versus noise uncertainty for a given false alarm probability (0.01) and detection probability (0.99) has been found out in case of both energy detector and the autocorrelation based detector for OFDM signal. Our result shows that there is about 23 dB advantage with our proposed method for AWGN channel and about 12 dB advantage for multipath fading channel over conventional energy detector for noise uncertainty parameter U = 5 with ~ 5,000 signal samples.

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