With the rapidly increasing demand of data traffic in fifth-generation (5G) wireless systems, various sophisticated techniques have been developed to cope with the demand. New radio-unlicensed (NR-U) technology is one of the most promising techniques to address the exponential growth of data traffic. At the same time, NR base stations are densely deployed in 5G. Therefore, large numbers of NR-U base stations attempt to access the unlicensed spectrum. Although listen before talk (LBT) with random backoff can guarantee fairness, it can also increase the collision probability. For the IEEE 802.11 Wi-Fi networks, a contention-based random access protocol is adopted, which cannot guarantee the Quality of Service (QoS).To overcome these problems, a new LBT protocol, referred to as cooperative LBT, is designed, in which zero forcing (ZF) precoding is applied to suppress the multi-user interference. Based on the new LBT protocol, a (N + 3)-state semi-Markovian model is established to characterize the effective capacity of NR-U in unlicensed bands, where N is the number of NR-U base stations. An expression for the effective capacity is obtained, which is a function of QoS, instantaneous transmit rate, the number of Wi-Fi nodes, and NR-U base stations. The influences of the finite backhaul and transmit power on the effective capacity are also analyzed in this paper. The simulation results show that the usage of cooperative communication can reduce the collision probabilities from 0.4928 to 0.1632 and increase the effective capacities by 220.04%. The cooperative LBT protocol has a more compelling advantage for 5G NR ultradense deployment scenarios.INDEX TERMS Effective capacity, new radio-unlicensed (NR-U), cooperative network, quality of service (QoS), listen before talk (LBT).

Joint transmission (JT)-based Coordinated Multipoint (CoMP) systems achieve high performance gains by allowing full coordination among multiple cells, transforming unwanted intercell interference into useful signal power. In this paper, we present an analytical model to perform adaptive modulation for a typical JT CoMP system, consisting of three transmission points, under a target bit error rate (BER) constraint. Probability density functions of the signal-to-interference-plus-noise ratio (SINR) are derived for different JT CoMP schemes, and based on them, closed-form expressions for the average spectral efficiency (ASE) are obtained when adopting continuous-rate adaptive modulation. The study of ASE is also extended for the case of discrete-rate modulations, where the performance comparison of different practical quantized modulation schemes is carried out. Index Terms-Average spectral efficiency (ASE), continuous-rate adaptive modulation, Coordinated Multipoint (CoMP), discrete-rate adaptive modulation, joint transmission (JT).

Dynamic point selection/dynamic point blanking (DPS/DPB)-based coordinated multipoint (CoMP) has attracted lots of interest because of the significant performance improvement with a particular low complexity. In this paper, we first investigate the average spectral efficiency (ASE) of M-ary quadrature amplitude modulation (M-QAM) satisfying instantaneous bit error rate constraint for DPS/DPB CoMP system with 3 different adaptive modulation strategies. Closed-form expressions of the ASE for continuous-rate M-QAM are obtained in which calculus of variations is used to obtain the optimal power allocation policy. We also analyze the ASE for discrete-rate M-QAM which is more useful for the practical DPS/DPB CoMP wireless communication systems. Average bit error rate for DPS/DPB CoMP discrete-rate M-QAM is also investigated in this paper. Monte Carlo simulations are used to verify the correctness of our analysis. The results reveal that in M-QAM DPS/DPB CoMP systems, when the channel condition is unfavorable, the transmit power is the crucial parameter to enhance the ASE, otherwise the transmit rate is the key parameter. We can also notice that by using adaptive modulation, DPS/DPB CoMP has an obvious channel capacity improvement compared to the case without coordination among different transmission points.

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