In this paper, we investigate a downlink non-orthogonal multiple access (NOMA) system consisting of a base station (BS) and two users, where each user decodes its own signal through successive interference cancellation (SIC). When the signal of one user, called the weak user (WU) who has a bad channel, is being decoded, the signal of the other user, called the strong user (SU) who has a good channel, acts as interference. In an interference channel, we can increase the achievable rate by applying improper Gaussian signaling (IGS). Therefore, we apply IGS to SU, aiming to mitigate the interference. We also consider imperfect SIC at SU, which is a more general assumption for a NOMA system. For the considered NOMA system model, we derive the outage probability of each user in a closed form, provide its asymptotic expression, and obtain its diversity order. We also derive the ergodic rate of each of the two users in a closed form. We propose two algorithms to maximize the fairness of the NOMA system based on the primal decomposition method. Through simulation, we verify that our analysis is correct, and confirm that applying IGS improves the fairness of the NOMA system. INDEX TERMS Ergodic rate, fairness, imperfect successive interference cancellation (SIC), improper Gaussian signaling (IGS), non-orthogonal multiple access (NOMA) system, outage probability, primal decomposition.
Cognitive radio network technology is that secondary (unlicensed) users use the spectrum of primary (licensed) users without interfering primary communication. In this paper, we propose multiple access scheme for a cognitive radio network, where multiple secondary users access spectrum of one primary user. We consider two types of multiple access scheme, one is p-persistent and one is non-persistent, and apply these two schemes in the secondary network. For each multiple access scheme, total throughput of secondary network is derived and verified by Monte Carlo simulation. Simulation results show that maximum total throughput of the secondary network is achieved when channel access probability or the number of maximum waiting frames is chosen appropriately.
In this paper, we investigate p-persistent random access used for a spectrum sensing cognitive radio network with multiple secondary users to avoid a collision. Effect of the imperfect sensing, false alarm and miss detection, is considered. We analyze the total throughput of the secondary network and propose throughput optimization algorithm. It is shown that simulation results well match with analysis results.
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