Discrete rate and variable power adaptation for underlay cognitive networks

We consider the problem of maximizing the average spectral efficiency of a secondary link in underlay cognitive networks. In particular, we consider the network setting whereby the secondary transmitter employs discrete rate and variable power adaptation under the constraints of maximum average transmit power and maximum average interference power allowed at the primary receiver due to the existence of an interference link between the secondary transmitter and the primary receiver. We first find the optimal discrete rates assuming a predetermined partitioning of the signal-to-noise ratio (SNR) of both the secondary and interference links. We then present an iterative algorithm for finding a suboptimal partitioning of the SNR of the interference link assuming a fixed partitioning of the SNR of secondary link selected for the case where no interference link exists. Our numerical results show that the average spectral efficiency attained by using the iterative algorithm is close to that achieved by the computationally extensive exhaustive search method for the case of Rayleigh fading channels. In addition, our simulations show that selecting the optimal partitioning of the SNR of the secondary link assuming no interference link exists still achieves the maximum average spectral efficiency for the case where the average interference constraint is considered.

[1]  Mikael Skoglund,et al.  On the Expected Rate of Slowly Fading Channels with Quantized Side Information , 2005, ASILOMAR 2005.

[2]  AlouiniMohamed-Slim,et al.  Rate and power allocation for discrete-rate link adaptation , 2008 .

[3]  Amir Ghasemi,et al.  Fundamental limits of spectrum-sharing in fading environments , 2007, IEEE Transactions on Wireless Communications.

[4]  Roy D. Yates,et al.  Adaptive transmission with discrete code rates and power levels , 2003, IEEE Trans. Commun..

[5]  Mohamed-Slim Alouini,et al.  Rate and Power Allocation for Discrete-Rate Link Adaptation , 2007, EURASIP J. Wirel. Commun. Netw..

[6]  Sennur Ulukus,et al.  Channel Estimation and Adaptive M-QAM in Cognitive Radio Links , 2008, 2008 IEEE International Conference on Communications.

[7]  A. Goldsmith,et al.  Capacity of Rayleigh fading channels under different adaptive transmission and diversity-combining techniques , 1999, IEEE Transactions on Vehicular Technology.

[8]  Pravin Varaiya,et al.  Capacity of fading channels with channel side information , 1997, IEEE Trans. Inf. Theory.

[9]  Sonia Aïssa,et al.  Capacity and power allocation for spectrum-sharing communications in fading channels , 2009, IEEE Transactions on Wireless Communications.

[10]  Bang Chul Jung,et al.  Opportunistic Underlay Transmission in Multi-Carrier Cognitive Radio Systems , 2009, 2009 IEEE Wireless Communications and Networking Conference.

[11]  Ying-Chang Liang,et al.  Optimal power allocation for fading channels in cognitive radio networks: Ergodic capacity and outage capacity , 2008, IEEE Transactions on Wireless Communications.

[12]  Joseph Mitola,et al.  Cognitive radio: making software radios more personal , 1999, IEEE Wirel. Commun..