Search

In this paper, we investigate stability region of hybrid uplink non-orthogonal multiple access (NOMA) in conjunction with non-cooperative game, where two users independently send packets with transmit power control according to fading channel gain to the same radio resource so that their packets are received at a base station (BS) with one of two target receive powers (TRPs). The BS then tries to decode the packets with successive interference cancellation (SIC) technique in power domain. We consider a symmetric non-cooperative game where the users (or players) send packets with one of two TRPs or no transmission. We examine the convexity of stability region at the mixed-strategy Nash equilibrium (NE) of the game, where no one's queue grows to infinity. Furthermore, we investigate how the stability region changes depending on the parameters of users’ payoff.

This work proposes a random access system with uplink non-orthogonal multiple access (NOMA), where users transmit their packets by using the space-time line code (STLC) to fully exploit the spatial diversity without channel state information at the receiver. More specifically, users with a single antenna estimate channel gain from the base station (BS) with two antennas, encode the information using the STLC, and then transmit it using transmit power control so that the received power of their packets at the BS can be one of the predetermined values. The BS decodes the received packets via STLC decoding and the successive interference cancellation technique. Owing to spatial diversity, we show that the proposed scheme improves energy efficiency in comparison to the conventional system with a single antenna BS.

In this paper, an $M\times 4$ double space-time line code (D-STLC) is designed for a system with $M$ -transmit and four-receive antennas whose channel state information is available at the transmitter. By delivering two independent STLC data streams simultaneously, both spatial diversity and multiplexing gains are obtained, like a $4\times M$ double space-time transmit diversity (DSTTD) system that transmits two space-time block coded data streams. It is analytically shown that the decoding signal-to-interference-plus-noise ratios of D-STLC and DSTTD are identical to each other, and furthermore, it is numerically verified that the proposed D-STLC significantly outperforms a conventional $M\times 4$ STLC scheme and other existing spatial-diversity and spatial-multiplexing schemes, such as precoded space-time block code and precoded spatial multiplexing, in terms of achievable rate and bit-error-rate performance as the signal-to-noise ratio and/or transmission data rate increase.

In this paper, we propose an enhanced random access (RA) with a distributed pilot orthogonalization (ERA-DPO) for mitigating packet collisions in Step3 during the RA procedure in cellular internet-of-things (IoT) networks. Even though each IoT device experiences a preamble collision in Step1, it can avoid the packet collision in Step3 by differentiating uplink pilot with the proposed technique, which provides an opportunity for the collided packets to be separated in spatial domain by multiple receive antennas. We also mathematically analyze the performance of the proposed scheme in terms of packet collision probability, throughput, and resource efficiency, based on a Markov chain model. Simulation results reveal that the proposed scheme significantly reduces the packet collision probability and increases resource efficiency compared to the conventional scheme.

We mathematically derive an upper bound of bit-error rate (BER) of uplink non-orthogonal multiple access (NOMA) systems with quadrature phase shift keying (QPSK) modulation in fading channels. In particular, we exploit the joint maximum-likelihood (ML) detector at a base station (BS) with multiple antennas since it results in the optimal BER performance of a super-imposed QPSK modulated symbols from multiple users. In particular, we obtain a closed-form integral of Q-function with Erlang distributed random variable to derive the BER. We also obtain diversity order of the uplink NOMA systems. Through extensive computer simulations, we validate that our analytical results match well with the simulation results especially in high signal-to-noise ratio (SNR) regime.

In this correspondence paper, a novel machine learning (clustering) based blind decoding method is proposed for the space–time line code (STLC) systems without the information of modulation size and channels. The number of clusters, which is equivalent to the modulation size, is estimated from the received signals by using a $k$ -mean cluster validation metrics, such as silhouette score and Davies–Bouldin index, and the cluster indices are directly mapped to the transmitted binary information bits. To improve the clustering performance, received signal normalization and the initial centroids of the clusters are designed by exploiting the combined STLC signal structure. From the numerical results, it is verified that the proposed blind decoding method can achieve near-coherent decoding performance with either small-size modulation, low noise at the receiver, or a large number of transmit antennas.

The reactive symbol-level jamming (SLJ) technique is a simple but practical technique to disable or disrupt malicious communication links. After sensing the transmission and detecting the digital modulation scheme of the malicious transmitter, a communication node with the reactive SLJ technique, called a reactive jammer, generates random digital modulation symbols and then sends them to the malicious receiver. In this correspondence, we mathematically analyze both uncoded and coded bit error rate (BER) at the malicious receiver under not only reactive SLJ, but also Gaussian SLJ techniques. In particular, we consider the partial jamming scenario, in which a portion of symbols in a data frame are affected by the SLJ, which is a practical scenario under the reactive jamming techniques. We also consider the effect of imperfect power control and channel estimation error of the reactive jammer on the BER performance at the malicious receiver.

Commercial long-term evolution (LTE) systems adopt an access class barring (ACB) mechanism in the initial random access procedure with multiple preambles in order to accommodate bursty traffic arrivals of machine-type communications. In this paper, we propose two Bayesian ACB algorithms that estimate the number of active machine devices based only on the number of idle preambles in each slot. In the commercial LTE systems, eNodeB cannot instantaneously distinguish if a particular preamble is sent from a single device (i.e., success) or multiple devices (i.e., collision). However, the idle preambles can be instantaneously detected at the base station (BS) in each slot. Numerical results show that the proposed algorithms yield quite similar performance with the ideal ACB algorithm, assuming that the exact number of active devices is known to the eNodeB.

We consider a cellular-aided inband overlay device-to-device (D2D) network, where a base station (BS) and all devices share a frequency band for their communications, but the BS allocates dedicated radio resources to D2D direct communications to avoid the mutual interference between D2D and cellular communications. We first mathematically formulate the optimal sum rate of the D2D network, and provide closed-form approximations of the average sum rate for low and high signal-to-noise ratio (SNR) regimes. Furthermore, we propose two practical D2D link scheduling algorithms: centralized and distributed. The centralized algorithm reduces the computational complexity at the BS, and its performance is shown to be optimal since the SNR of D2D links tends to be either zero or infinity. The distributed algorithm significantly reduces the signaling overhead caused by channel state information feedback from devices to the BS, and the performance loss of the distributed algorithm is marginal compared with that of the centralized algorithm, particularly when the number of D2D pairs is small.

Achievable degrees-of-freedom (DoF) of the large-scale interfering two-way relay network is investigated. The network consists of $K$ pairs of communication nodes (CNs) and $N$ relay nodes (RNs). It is assumed that $K\ll N$ and each pair of CNs communicates with each other through one of the $N$ relay nodes without a direct link between them. Interference among RNs is also considered. Assuming local channel state information (CSI) at each RN, a distributed and opportunistic RN selection technique is proposed for the following three promising relaying protocols: amplify--forward, decode--forward, and compute--forward. As a main result, the asymptotically achievable DoF is characterized as $N$ increases for the three relaying protocols. In particular, a sufficient condition on $N$ required to achieve the certain DoF of the network is analyzed. Through extensive simulations, it is shown that the proposed RN selection techniques outperform conventional schemes in terms of achievable rate even in practical communication scenarios. Note that the proposed technique operates with a distributed manner and requires only local CSI, leading to easy implementation for practical wireless systems., 18 pages, 5 figures, To appear in IEEE Transactions on Vehicular Technology

This paper raises the question of whether the secondary user can attain a nonzero achievable rate without causing capacity loss at the primary user, even when it is utilizing the channel in cognitive radio networks (CRNs). It is assumed that secondary nodes are aware of the channel state information (CSI) of primary nodes and of how the primary nodes operate, whereas the primary nodes operate with no prior knowledge about the secondary nodes. We first propose a full-duplex relaying protocol for the cognitive radio (CR) network with a single relay node shared by both the primary and the secondary networks. In this case, the shared relay is assumed to have full CSI of the primary nodes and to know how the primary and secondary nodes operate. The proposed relaying protocol enables the secondary network to achieve nonzero rates without causing capacity loss at the primary network in a certain channel condition. Then, we also propose three half-duplex relaying protocols for the CR network with two relays, each of which is dedicated to the primary or the secondary network, respectively. It is shown that appropriate combinations of the proposed three half-duplex relaying protocols make it always possible for the secondary network to achieve nonzero rates without causing capacity loss at the primary network. Achievable rates of the proposed full- and half-duplex relaying protocols are evaluated through extensive computer simulations. Simulation results show that the proposed relaying protocols provide nonzero achievable rates of the secondary network over a wide range of signal-to-noise ratios (SNRs).

In this paper, we investigate the effects of heterogeneous mobility on rate adaptation and user scheduling in cellular networks with hybrid automatic repeat request (HARQ). To this end, we first show the performance tradeoff between two extreme scheduling criteria: retransmission-oriented scheduling (ROS) and mixed scheduling (MS) criteria over time-correlated Rayleigh fading channels. Then, we propose an ROS-based joint rate adaptation and user scheduling (JRAUS) policy for cellular networks and compare it with the conventional and reference JRAUS policies. We also evaluate the system-level performance of the proposed ROS-based JRAUS policy in various user distribution and mobility scenarios. In particular, in an asymmetric user distribution and heterogeneous mobility scenario, which is the most general one in practice, the proposed JRUAS policy yields a throughput gain of 49% and a fairness gain of 155% over the conventional JRAUS policies. In this paper, we find that the rate adaptation is significant not only in a single point-to-point link but in multiuser systems with heterogeneous mobility as well.

In this paper, we compare the performance of two downlink capacity-improvement schemes based on orthogonal code-hopping multiplexing (OCHM) and multiple scrambling codes (MSCs). Both OCHM and MSC systems have been proposed to overcome a code-limitation problem in a code division multiple access (CDMA) downlink. We mathematically analyze the user capacity in a general form, considering various factors such as user activity, spreading factor, amount of transmission symbol energy that is allocated to common control channels, amount of outer-cell interference, orthogonality factor, and sectorization factor. Numerical examples show that the capacity gain of the OCHM-based system increases as the other-cell interference decreases and the channel activity decreases. Thus, the OCHM-based system is a more effective scheme than the MSC-based system, considering that a code-limited situation more frequently occurs in the case of low other-cell interference and low channel activity. However, the OCHM-based system is more sensitive to the orthogonality factor.