Good Channel Conditions Research Articles

Throughput Maximization by Adaptive Switching with Modulation Coding Scheme and Frequency Symbol Spreading

It is required to realize higher transmission rate and higher reliability for mobile communication due to the increase in Internet use. However, wireless channel capacity can not be used with maximum efficiency due to fluctuating channels affected by shadowing, multipath fading and mobility. Adaptive modulation and coding (AMC) scheme is now commonly implemented to maximize the throughput performance under the given link qualities. Forward Error Correction (FEC) based link adaptation is effective to improve throughput in a lower SNR regime, however, it immolates maximal throughput in good channel condition. Frequency symbol spreading (FSS) has been proposed that can improve BER even without FEC. It fully exploits the frequency diversity gain by spreading symbol per subcarrier to all frequency components. This paper proposes a new adaptation control scheme for OFDM by switching FSS and legacy AMC. Simulation result verifies its maximized throughput performance harvesting both of frequency diversity gain and coding gain.

NOMA-Based Cooperative Opportunistic Multicast Transmission Scheme for Two Multicast Groups: Relay Selection and Performance Analysis

The orthogonal frequency division multiple access (OFDMA)-based cooperative multicast (CM) technology realizing the intra-cooperation of multicast group (MG) has improved the performance in throughput and coverage. In the MG scenario, users are uniformly distributed. Due to the small effective transmission range of relay user (RU), the cooperation is hindered, which limits the performance of CM. Therefore, non-orthogonal multiple access (NOMA)-based two MGs joint cooperative opportunistic multicast scheme (termed as COM-NOMA) is proposed. In COM-NOMA scheme, two MGs are served as one quasi-MG. First, on the same frequency band, base station (BS) opportunistically multicasts the superposition signal, which is formed by two MGs’ signals, to the users with good channel conditions in the two MGs using NOMA way. Second, some successfully receiving users are selected as RUs. The superposition signal is forwarded to the other users by Device-to-Device multicast way. Then, according to the coverage ratio of BS and the decode condition of NOMA, the signal to interference and noise ratio threshold for RU selection is given. Finally, the spectral efficiency of COM-NOMA is analyzed and the approximate expression of system coverage ratio is derived. The simulation results show that, spectral efficiency at unit transmit power (spectral efficiency per watt) and system coverage ratio is improved in comparison with other OFDMA-based CM schemes.

A Zero-Sum Game Approach for Non-Orthogonal Multiple Access Systems: Legitimate Eavesdropper Case

In this paper, secure communication in non-orthogonal multiple access (NOMA) downlink system is considered wherein two NOMA users with channel gain difference are paired in each transmission slot. The user with poor channel condition (weak user) is entrusted, while the user with good channel condition (strong user) is a potential eavesdropper. The weak user data can be intercepted by the strong user since the strong user needs to decode the weak user’s message for successive interference cancellation operation in NOMA. To impair strong user’s eavesdropping capability, weak user’s information-bearing signal is merged with an artificial signal (AS). Thus, the eavesdropping process requires extra decoding step at higher power level. The secrecy outage probability of the weak user is derived and provided in closed-form expression. The weak user faces a choice between transmitting the information-bearing signal with the total power and the deploying the AS technique, whereas the strong user can choose whether to eavesdrop the weak user’s message or not. To investigate users’ power-secrecy tradeoffs, their interactions are modeled as a non-cooperative zero-sum game. The existence of Nash equilibria (NEs) of the proposed game is first analyzed, and pure and mixed-strategy NE profiles are provided. In addition, numerical simulations are conducted to validate the analytical results and to prove that AS-Aided proposed scheme enhances the secrecy performance of NOMA systems while maintaining the NOMA superiority over OMA systems.

On the Performance of NOMA-Based Cooperative Relaying Systems Over Rician Fading Channels

Non-orthogonal multiple access (NOMA) is a promising technique for the fifth generation (5G) wireless communications. As users with good channel conditions can serve as relays to enhance the system performance by using successive interference cancellation (SIC), the integration of NOMA and cooperative relaying has recently attracted increasing interests. In this paper, a NOMA-based cooperative relaying system is studied, and an analytical framework is developed to evaluate its performance. Specifically, the performance of NOMA over Rician fading channels is studied, and the exact expression of the average achievable rate is derived. Moreover, we also propose an approximation method to calculate the achievable rate by using the Gauss-Chebyshev Integration. Numerical results confirm that our derived analytical results match well with the Monte Carlo simulations.

User Pairing for Downlink Non-Orthogonal Multiple Access Networks Using Matching Algorithm

In this paper, we study the user pairing in a downlink non-orthogonal multiple access (NOMA) network, where the base station allocates the power to the pairwise users within the cluster. In the considered NOMA network, a user with poor channel condition is paired with a user with good channel condition, when both their rate requirements are satisfied. Specifically, the quality of service for weak users can be guaranteed, since the transmit power allocated to strong users is constrained following the concept of cognitive radio. A distributed matching algorithm is proposed in the downlink NOMA network, aiming to optimize the user pairing and power allocation between weak users and strong users, subject to the users’ targeted rate requirements. Our results show that the proposed algorithm outperforms the conventional orthogonal multiple access scheme and approaches the performance of the centralized algorithm, despite its low complexity. In order to improve the system’s throughput, we design a practical adaptive turbo trellis coded modulation scheme for the considered network, which adaptively adjusts the code rate and the modulation mode based on the instantaneous channel conditions. The joint design work leads to significant mutual benefits for all the users as well as the improved system throughput.

An improved multicast based energy efficient opportunistic data scheduling algorithm for VANET

A road side unit in VANET is capable of providing various infotainment services. With the increase in demand for data download amongst the vehicular users, power consumption, both at vehicle end and the road side unit is also increasing proportionally. Hence, there is a need for improving energy efficiency as well as the throughput of the system. In this work, we focus on improving energy efficiency and throughput of the road side unit. We propose an improved multicast based energy efficient opportunistic data scheduling algorithm. We estimate optimum data rate and optimum number of users having good channel conditions, thus obviating the need to know the channel state information at the transmitter. The group of users so selected is served by multicasting the service at optimal data rate. Results show that the proposed algorithm is not only energy efficient but also throughput optimal. It is also possible to estimate the maximum throughput accurately and with low search complexity (O(N)) using the proposed method. Simulations are done for two different cases in order to test the flexibility of the algorithm—one, when no new user is entertained until all the initial users get served; two, new users can enter the system in every time slot.

Asymptotically Optimal Pilot Allocation Over Markovian Fading Channels

We investigate a pilot allocation problem in wireless networks over Markovian fading channels. In wireless systems, the channel state information (CSI) is collected at the base station, in particular, this paper considers a pilot-aided channel estimation method (TDD mode). Typically, there are less available pilots than users, hence at each slot the scheduler needs to decide an allocation of pilots to users with the goal of maximizing the long-term average throughput. There is an inherent tradeoff in how the limited pilots are used: assign a pilot to a user with up-to-date CSI and good channel condition for exploitation , or assign a pilot to a user with outdated CSI for exploration . As we show, the arising pilot allocation problem is a restless bandit problem and thus its optimal solution is out of reach. In this paper, we propose an approximation based on the Lagrangian relaxation method, which provides a low-complexity Whittle index policy. We prove this policy to be asymptotically optimal in the many users regime (when the number of users in the system and the available pilots for channel sensing grow large). We evaluate the performance of Whittle’s index policy in various scenarios and illustrate its remarkably good performance for small number of users, where it is not guaranteed to be optimal.

Achievable sum rate analysis of relay aided overlay device to device communication among multiple devices

In this paper, we consider device to device (D2D) communication overlaying cellular network where a group of D2D users exchange messages among themselves. We investigate the case when the channel conditions of the direct links among these D2D users are not strong enough to support direct communication and hence, an intermediate relay node assists the communication among the D2D users. Here we consider capacity achieving lattice codes at the D2D users along with compute-and-forward protocol at the relay. Based on these, we derive the received signal to noise ratio (SNR) at the relay, as well as the D2D users and formulate upper bounds on the achievable sum rate. We also investigate the achievable sum rate when the devices communicate using the direct links and compare with that of the relay aided D2D communication. We find that when the D2D users are closer to the relay, relay aided communication achieves better performance compared to direct communication. However, for the same distances, the sum rate degrades more for relay aided communication. It is also shown that when the links between most of the D2D users and the relay have good channel conditions compared to the direct links, relay aided communication can achieve better sum rate performance than the direct communication.

Application of Non-Orthogonal Multiple Access in Cooperative Spectrum-Sharing Networks Over Nakagami- $m$ Fading Channels

This paper proposes a novel non-orthogonal multiple access (NOMA)-based cooperative transmission scheme for a spectrum-sharing cognitive radio network (CRN), whereby a secondary transmitter (ST) serves as a relay and helps transmit the primary and secondary messages simultaneously by employing NOMA signaling. This cooperation is particularly useful when the ST has good channel conditions to a primary receiver but lacks the radio spectrum. To evaluate the performance of the proposed scheme, the outage probability and system throughput for the primary and secondary networks are derived in closed forms. Simulation results demonstrate the superior performance gains for both networks thanks to the use of the proposed NOMA-based cooperative transmission scheme. It is also revealed that NOMA outperforms conventional orthogonal multiple access (OMA) and achieves better spectrum utilization.

On the Performance Gap between ML and Iterative Decoding of Finite-Length Turbo-Coded BICM in MIMO Systems

As real-time applications typically require short length code words, this paper analyzes the minimum achievable code word error rate of the given finite-length code words, namely, maximum likelihood (ML) decoding error probability. For coding schemes ML decoding is too complex, the key contribution of this paper is to analytically assess the performance gap between ML decoding and a practical decoding scheme. We analyze the combination of turbo codes and bit-interleaved coded-modulation that is a spectrally efficient coding scheme adopted in 3GPP long term evolution (LTE). In single-input single-output (SISO) systems, it was shown in the literature that turbo decoding delivers near-ML decoding performance. In this paper, we extend the analysis to a multi-input multi-output (MIMO) system. In contrast to the SISO case, the turbo principle-based iterative decoding scheme is subject to appreciable performance loss compared with the ML decoding, even in good MIMO channel conditions. For this reason, we further analyze potential reasons and examine possible improvements. By means of simulation, it is shown that convergence to a non-ML code word rather than non-convergence is the key reason for the observed performance loss in good channel conditions.

Uplink Scheduling and Link Adaptation for Narrowband Internet of Things Systems

Narrowband Internet of Things (NB-IoT) is a new narrow-band radio technology introduced in the Third Generation Partnership Project release 13 to the 5th generation evolution for providing low-power wide-area IoT. In NB-IoT systems, repeating transmission data or control signals has been considered as a promising approach for enhancing coverage. Considering the new feature of repetition, link adaptation for NB-IoT systems needs to be performed in 2-D, i.e., the modulation and coding scheme (MCS) and the repetition number. Therefore, existing link adaptation schemes without consideration of the repetition number are no longer applicable. In this paper, a novel uplink link adaptation scheme with the repetition number determination is proposed, which is composed of the inner loop link adaptation and the outer loop link adaptation, to guarantee transmission reliability and improve throughput of NB-IoT systems. In particular, the inner loop link adaptation is designed to cope with block error ratio variation by periodically adjusting the repetition number. The outer loop link adaptation coordinates the MCS level selection and the repetition number determination. Besides, key technologies of uplink scheduling, such as power control and transmission gap, are analyzed, and a simple single-tone scheduling scheme is proposed. Link-level simulations are performed to validate the performance of the proposed uplink link adaptation scheme. The results show that our proposed uplink link adaptation scheme for NB-IoT systems outperforms the repetition-dominated method and the straightforward method, particularly for good channel conditions and larger packet sizes. Specifically, it can save more than 14% of the active time and resource consumption compared with the repetition-dominated method and save more than 46% of the active time and resource consumption compared with the straightforward method.

Multi-Stage Partial Parallel Interference Cancellation Algorithm for MUSA Systems

Multi-User Shared Access is a non-orthogonal multiple access scheme of 5G,which has a high computational complexity and a large time delay due to the usage of successive interference cancellation detection algorithm. This paper proposes a multi-stage partial parallel interference cancellation detection algorithm, which does not require repeated ordering and repeated matrix inversion. In the first stage of detection, the bits of these users with good channel conditions will be outputted, and the influence of multiple access interference on users with bad channel conditions in the second stage will be decreased. Theoretical analysis and simulation results show that the symbol error rate of the proposed algorithm is slightly better than that of the two-stage MMSE-PIC, and the complexity is reduced. In the meanwhile, the computational complexity is significantly reduced without SER performance degradation when compared with MMSE-SIC algorithm.

QC2LinQ: QoS and Channel-Aware Distributed Link Scheduler for D2D Communication

We study a distributed link scheduling problem for device-to-device (D2D) communication considering the quality-of-service (QoS) requirements and time-varying channel conditions of D2D links. To this end, we first study an optimal centralized link scheduling problem maximizing the total average sum-rate while satisfying the QoS requirements of D2D links. We then abstract the important scheduling principles of the optimal link scheduling, i.e., giving more chance to be scheduled to the links which have a good channel condition and do not satisfy the QoS requirement, in order to utilize them to develop distributed link scheduling algorithms. With the scheduling principles, we develop a procedure with which D2D links can share their degree of QoS unsatisfaction and channel condition with each other and generate their scheduling priorities according to the shared information in a distributed manner. We also develop a novel distributed link scheduling criterion with which D2D links determine their link scheduling. By using them, we propose distributed link scheduling algorithms, QCLinQ and QC $^{2}$ LinQ, which have significantly smaller signaling overhead and low computational complexity compared with the centralized optimal link scheduling algorithm. Moreover, they closely meet the QoS requirements of D2D links while achieving significant sum-rate improvement over conventional distributed algorithms.

Multicast Resource Allocation Enhanced by Channel State Feedbacks for Multiple Scalable Video Coding Streams in LTE Networks

The growing demand for mobile multicast services, such as Internet Protocol television (IPTV) and video streaming, requires effective radio resource management (RRM) to handle traffic with strict quality-of-service constraints over Long-Term Evolution (LTE) and beyond systems. Special care is needed to limit system performance degradation when multiple multicast streams are simultaneously transmitted. To this aim, this paper proposes an RRM policy based on a subgrouping technique for the delivery of scalable multicast video flows in a cell. Our proposal enhances the legacy multicast transmission over LTE systems by exploiting multiuser diversity and the users' channel quality feedbacks. Moreover, it is designed to take advantage of the frequency selectivity in the subgroup formation. Simulation results demonstrate the effectiveness of the proposed scheme, which outperforms existing approaches from the literature. It succeeds in achieving higher spectral efficiency and guaranteeing adequate video quality to all multicast receivers and improved quality to those with good channel conditions.

An efficient hierarchical 16‐QAM dynamic constellation to obtain high PSNR reconstructed images under varying channel conditions

Startling growth in multimedia services over wireless channels emphasizes the need for bandwidth and power efficient modulation techniques. This study investigates the suitability of hierarchical quadrature amplitude modulation (HQAM) for image transmission over erroneous wireless Gaussian channels. HQAM provides unequal error protection, to compressed and coded image data, transmitted without increasing the required bandwidth, unlike channel coding. A discrete cosine transform based image coder is used to divide the image data bit stream into high-priority (HP) and low-priority (LP) sub-streams for significant and non-significant data respectively. The ratios between the constellation distances are then dynamically adjusted with the objective to achieve an acceptable bit-error rate (BER) for HP sub-stream over varying channel conditions at the cost of increased BER for LP sub-stream. The work highlights HQAM implementation using conventional quadrature amplitude modulation (QAM) demodulator at the receiver which does not require the knowledge of varying constellation distance ratios at the transmitter. An analysis of 16-HQAM transmission for different values of distance ratios is presented to obtain high peak signal-to-noise ratio (PSNR) values of reconstructed images under poor as well as good channel conditions and the performance is compared qualitatively and quantitatively with 16-QAM.

Channel Aware Scheduling Algorithm for LTE Uplink and Downlink

In the past two decades, there has been a drastic increase in the mobile traffic, which is caused by the improved user experience with smart phones and its applications. In LTE system, the packet scheduler plays a vital role in the effective utilization of the resources. This field is not standardized and has immense scope of improvement, allowing vendor-specific implementation. LTE scheduling can be categorized into two extremes, namely, Opportunistic scheduling and Fairness scheduling. The Best Channel Quality Indicator (BCQI) algorithm falls under the former category while Proportional Fairness (PF) algorithm under the later. BCQI algorithm provides high system throughput than PF algorithm, however, unlike BCQI algorithm, PF algorithm considers users with poor channel condition for allocation process. In this work, a new scheduling algorithm called as Opportunistic Dual Metric (ODM) Scheduling Algorithm is proposed for LTE uplink and downlink.The objective of the algorithm is to prioritize the users with good channel condition for resource allocation, at the same time not to starve the users with poor channel conditions. The proposed algorithm has two resource allocation matrices, one being throughput-centric and the other being is fairness-centric. The uplink algorithm uses the two resource allocation matrices to allocate the resources to the users and to ensure contiguous resource allocation. The downlink algorithm is an extension of the proposed uplink algorithm avoiding uplink constraints. The downlink algorithm employs the two resource distribution matrices to provide an efficient resource allocation by expanding the allocation for the users considering intermittent resources. The performance of ODM is measured in terms of throughput, fairness. Additionally, the uplink algorithm is analyzed in terms of transmit power. From the results it is observed that the proposed algorithm has better trade-off in terms of all the performance parameters than PF scheduler and BCQI scheduler.

Multi-Sensor Detection with Particle Swarm Optimization for Time-Frequency Coded Cooperative WSNs Based on MC-CDMA for Underground Coal Mines.

In this paper, a wireless sensor network (WSN) technology adapted to underground channel conditions is developed, which has important theoretical and practical value for safety monitoring in underground coal mines. According to the characteristics that the space, time and frequency resources of underground tunnel are open, it is proposed to constitute wireless sensor nodes based on multicarrier code division multiple access (MC-CDMA) to make full use of these resources. To improve the wireless transmission performance of source sensor nodes, it is also proposed to utilize cooperative sensors with good channel conditions from the sink node to assist source sensors with poor channel conditions. Moreover, the total power of the source sensor and its cooperative sensors is allocated on the basis of their channel conditions to increase the energy efficiency of the WSN. To solve the problem that multiple access interference (MAI) arises when multiple source sensors transmit monitoring information simultaneously, a kind of multi-sensor detection (MSD) algorithm with particle swarm optimization (PSO), namely D-PSO, is proposed for the time-frequency coded cooperative MC-CDMA WSN. Simulation results show that the average bit error rate (BER) performance of the proposed WSN in an underground coal mine is improved significantly by using wireless sensor nodes based on MC-CDMA, adopting time-frequency coded cooperative transmission and D-PSO algorithm with particle swarm optimization.

ORS-FA: An Opportunistic Relay Selection Scheme for Frame-Aggregated Environments

In conventional opportunistic relay selection schemes, one or multiple relays with better channel condition are selected. However, if frame aggregation is supported for improving MAC throughput, each relay can have different amounts of data and thus conventional selection schemes may choose a worse relay node only with good channel condition but little data. In this paper, we propose a novel opportunistic relay selection scheme when frame aggregation is adopted. In the proposed scheme, a relay node is selected in a distributed manner by considering the amount of data as well as channel condition, and therefore the most appropriate relay node can be chosen. Simulation results demonstrate that the proposed scheme outperforms other relay selection schemes, especially when the number of relay nodes is large.

Energy-Efficient Layered Video Multicast over OFDM-Based Cognitive Radio Systems

An energy-efficient layered video multicast (LVM) scheme for “bandwidth-hungry” video services is studied in OFDM-based cognitive radio (CR) systems, where the video data is encoded into a base layer and several enhancement layers with the former intended for all subscribers to guarantee the basic quality of reconstructed video and the latter aiming at the quality improvement for the promising users with good channel conditions. Moreover, in order to balance user experience maximization and power consumption minimization, a novel performance metricenergy utility(EU) is proposed to measure the sum achieved quality of reconstructed video at all subscribers when unit transmit power is consumed. Our objective is to maximize the system EU by jointly optimizing the intersession/interlayer subcarrier assignment and subsequent power allocation. For this purpose, we first perform subcarrier assignment for base layer and enhancement layers using greedy algorithm and then present an optimal power allocation algorithm to maximize the achievable EU using fractional programming. Simulation results show that the proposed algorithms can adaptively capture the state variations of licensed spectrum and dynamically adjust the video transmission to exploit the scarce spectrum and energy resources adequately. Meanwhile, the system EU obtained in our algorithms is greatly improved over traditional spectrum efficiency (SE) and energy efficiency (EE) optimization models.

Reducing power consumption in LTE data scheduling with the constraints of channel condition and QoS

3GPP has developed the Discontinuous Reception (DRX) power saving mechanism, which periodically turns off the radio interface to reduce the power consumption. However, packets cannot be received during the turn-off duration, as a result that the Quality of Services (QoS) may be violated. Therefore, optimal DRX parameters should be configured to satisfy QoS and minimize power consumption. In addition, channel condition may be unstable during the transmission, so the DRX parameters should also be dynamically adjusted. In this paper, we propose the Dynamic Scheduling with Extensible Allocation and Dispersed Offsets (DXD) scheme, which is composed of two algorithms, DRX parameters decision, to determine DRX period by considering channel condition and QoS constraints, and DRX-aware scheduling, to determine whether to extend the on duration so that QoS would not be affected by DRX. Simulation results demonstrate that the proposed DXD approach can reduce power consumption up to 96.7% compared to No-DRX scheme and guarantee QoS as good as No-DRX scheme. In addition, the power consumption can be reduced by 70.1% and 45.7% compared to the Fixed-DRX (100ms), start-offset scheme and TS scheme in good channel condition. Our approach effectively reduces power consumption in varied channel conditions and high loading system and still achieves better delay satisfaction ratio than others.