SUMMARY In this paper, a two‐phase algorithm for the spectrum sensing and power/rate control of a secondary user (S‐user) or cognitive radio is proposed. In the first phase, the primary base station (P‐BS), which is conscious of both the number and the data rate of primary active users (P‐user), broadcasts theitusage capacity percentage (UCP) of its cell. Since knowing only the UCP is not enough to guarantee that the total load (of P‐users and S‐users) is less than a maximum permissible load, the S‐user must measure the total interference received from both the P‐users and other S‐users. In this direction, using both the UCP and measurement of the interference received from the P‐users and the S‐users by the S‐user or secondary base station (S‐BS), we mathematically derive an equation for issuing data transmission permission, which if it is held then the second phase of the algorithm: the transmit power/rate control starts. In this phase, the S‐user and the S‐BS look for feasible values for the transmit power level and transmission rate. If there are feasible values, it starts its transmission at these feasible transmit power and rate. Since both the location of the S‐user and the channel condition vary in time, the whole algorithm is iterated periodically with a period faster than the coherence time of the channel. Furthermore, we consider the down link of the above system with cooperation among neighboring S‐users to overcome fading channels and we investigate the amount of improvement in the reliability of the issuing data transmission permission. As well, we consider the uplink of the system with multiple antennas in the S‐BS to investigate the improvement in the same parameter over spatially correlated and independent fading channels. Theoretical analysis is validated using computer simulations. Both theoretical analysis and computer simulations show that the proposed cooperative spectrum sensing algorithm performs properly at SNR = −5dB in flat Nakagami‐m fading channels with m = 1 even in correlated fading channels. We also address the improvement of the reliability of the issuing data transmission permission in the uplink in case of using multiple antennas only in the S‐BS. Copyright © 2011 John Wiley & Sons, Ltd.

SUMMARYIn this paper, we propose two new power loading schemes for an OFDM cognitive radio (CR). The novelty of this paper is that the CR has no knowledge about the interference power introduced by primary users (PUs). In the first scheme, we maximize the total received signal power on all CR subcarriers as the objective function with the two constraints: (i) keeping the interference to the PUs below a given threshold, and (ii) allocating less than peak transmit power as the total power levels on all CR subcarriers. The second proposed scheme is similar to the first one with one more constraint, which is more power loading to the CR subcarriers experiencing higher ratio of channel power gain to the noise power. This third constraint results in increasing CR throughput (similar to the water‐filling scheme). Performances of these schemes are analyzed by numerical and simulation results, which illustrate that the two proposed schemes achieve relatively close to the optimal scheme (in which the secondary transmitter has full knowledge about PUs’ interference power) and outperform the scheme based on estimation of this interference power with an estimation error higher than a given threshold. Copyright © 2012 John Wiley & Sons, Ltd.

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In this paper, we investigate joint optimization of power allocation factors (PAFs) and decoding order of users in the downlink of a non-orthogonal multiple access (NOMA) system over Nakagami-m fading channels. The objective is to guarantee fairness among the users in terms of outage probability (or its complement success probability). To this end, we maximize the minimum success probability (Max-MSP) among the users when only statistical channel state information (CSI) is available at the transmitter side. We solve such a problem by first proving that at the optimal solution, all the users have a common success probability (CSP), and then proposing an efficient algorithm for finding CSP of the users. The optimal PAFs and optimal decoding order are derived in closed form based on the CSP and statistical CSI of the users. It is proved that the proposed algorithm always converges to a unique optimal solution. Furthermore, we show that in contrast to Rayleigh fading channels, in Nakagami-m fading channels, the optimal decoding order not only depends on the average signal-to-noise ratio (SNR) of each user but also depends on the variance of the SNR and data rate of that user.INDEX TERMS Non-orthogonal multiple access (NOMA), Nakagami-m fading, outage probability, fairness, power allocation factor, decoding order.

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In this paper, a new practical dirty paper coding scheme and its extension is proposed for interference mitigation of a single TV broadcast station in uplink and downlink of a cognitive radio network using both a single secondary user (SU) and multiple SU scenarios. In the single SU scenario, which is called interference cognitive radio channel, derived simulation results show that the transmission rate of the SU archives the capacity of an AWGN channel with the cost of a 2.5 dB extra signal-to-noise ratio. In the sequel, the proposed scheme is extended to a multiple SU scenario using direct sequence spread spectrum technique in both uplink and downlink considering a TV band. Derived simulation results show that the number of supportable SUs in our proposed scheme increases to a fully loaded scenario of the same multiuser direct sequence spread spectrum system. KEY WORDS: cognitive radio; dirty paper coding; interference suppuration; lattice quantizer R 2 ; meanwhile, S 2 knows the transmitted message of S 1 . To derive achievable rate, authors in [3] used the following ideas: Gel'fand and Pinsker's coding for channel with known interference in the transmitter [8], Costa's dirty paper coding (DPC) [9], achievable scheme for IFC [2] and capacity of Gaussian MIMO channel [10]. Also, achievable rate region for the IFC, which has been described by Han and Kobayashi [11], is used widely by the authors in [3]. Implementation of Costa's DPC idea [9] based on nonrandom codes has been made in [12] and [13] using lattice precoding for a single user scenario. In [12], authors used parallel concatenated code (PCC) or turbo code as a channel

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