Energy-efficient scheduling for downlink multi-user MIMO

In the upcoming fifth-generation (5G) wireless communication system, the massive MIMO and mmWave technologies will play a key role to improve the system performance. With the rapid development of the network communications, optimizing radio resources of wireless communication has been one of the challenging issues in 5G networks. In order to effectively improve network performance, an efficient resource allocation and power optimization algorithm is necessary. In this paper, we study joint resource allocation and power optimization (JRAPO) problem in multiuser mmWave massive MIMO system, which target at increasing energy efficiency (EE) and decreasing power consumption of systems. First, the problem of JRAPO is formulated as a multivariate mixed integer nonlinear programming problem. Second, because the non-convexity of this problem, we transformed it into a convex optimization problem by relaxing the resource block (RB) allocation indicator. Finally, we used Lagrangian dual decomposition algorithm and water-filling scheme to resolve this joint optimization problem. Simulation results demonstrated the effectiveness of the proposed algorithm.

This paper outlines the current state of Network MIMO as a viable technique for increasing the performance of wireless communication systems by cancelling the intercell interference in the near future. It also presents the results of a simulation environment designed to compare the BER performance capabilities of a wireless multiuser OFDM systems with and without the use of Network MIMO. Simulations confirm that Network MIMO techniques can result in significant reductions in interference. “Network MIMO” is a family of techniques where each user in a wireless system is served through all the access points within its range of influence. Taking prior information theoretic analyses of MIMO to the next level, this report quantify the spectral efficiency gains obtainable under realistic propagation and operational conditions. The results confirm that Network MIMO stands to provide a multiple fold increase in spectral efficiency by cancelling intercell interference and reducing Bit-Error-Rate under such conditions.

Multiuser MIMO (MU-MIMO) in which the base station transmits multiple streams to multiple users, has received significant importance as a way of achieving spectral efficiency (SE) and energy efficiency (EE). However, these two important design criteria conflict with each other and a careful study of their trade-off is mandatory for designing future wireless communication systems. This paper investigates the trade-off between EE and SE in downlink MU-MIMO system which is adopted by 3GPP Long Term Evolutions (LTE). The EE is measured as, “throughput (bits) per Joule” while both RF transmit power and circuit power consumptions are considered. In this paper, given the SE requirement, a constrained optimization problem where a constraint redefined with cubic inequality is formulated to maximize EE. Then, a novel resource allocation algorithm is proposed to achieve maximum EE. Simulation results demonstrate the effectiveness of the proposed scheme and illustrate the fundamental trade-offs between energy efficient and spectral efficient transmission.

This paper addresses optimal energy-efficient design for uplink (UL) MU-MIMO in a single cell environment. The energy efficiency is measured by throughput per Joule, while both RF transmission power and device electronic circuit power are considered. We define the energy efficiency (EE) capacity for UL MU-MIMO and study the power allocation that achieves this capacity. First we assume all users consume a fixed amount of circuit power and show that user antennas should be used only when the corresponding spatial channels are sufficiently good and using them improves the overall network EE. Mobile devices may have improved circuit management capability and turn off circuit operations when some antennas are not used to reduce circuit power consumption. Therefore we further study energy-efficient UL MU-MIMO with improved circuit management and show that some antennas should not be used even when their channel states are good because turning them on consumes too much circuit power. Based on theoretical analysis, we further develop low-complexity yet globally optimal energy-efficient power allocation algorithms that converge to the optimum exponentially. Simulation results are provided to demonstrate the significant gain in network energy efficiency.

10 - Improving energy efficiency in next-generation IoT networks with beam adjustment technique

The telecommunication industry has changed the way we communicate, work and socialize in a remarkable way since its inception. This change is continuous as new services and applications are being developed and deployed worldwide. In order to confront the requirements of new services, there are still many technical challenges. These include enhanced capacity, high data rate, low latency, spectral and energy efficiency. Therefore, researchers target on 5G wireless communication systems that are scheduled to be rolled out by the year 2020. In this paper, we give an overview of the 5G wireless standard and expected performance characteristics. Promising technologies including Millimeter Wave Technology, Massive MIMO, green Communication, and Cognitive Radio Networks are identified to support the requirements of 5G. Finally, we present numerical results on the path loss characteristics utilizing the SUI model for microwave band and modified SUI model for the mm-wave band.

In multiuser MIMO systems, block diagonalization (BD) eliminates inter-user interference with perfect CSI since the transmitter decomposes a multiuser MIMO channel into multiple parallel independent single-user MIMO channels. For a large number of users, the transmitter selects a subset of users who have good channels to maximize the system throughput. In this paper, a new low complexity scheduling algorithm with BD is proposed since an exhaustive search for the optimal user set is impractical. Simulation results show that the proposed algorithm has much lower complexity while it achieves the total throughput close to the optimal algorithm. It also has lower complexity than previous low complexity scheduling algorithms.

Multi-user MIMO (MU-MIMO) using Tomlinson-Harashima precoding (THP) has great potential to achieve high system capacity in wireless systems. On the other hand, hybrid ARQ (HARQ) is essential to realize the reliable wireless packet transmission and therefore, the combination of THP with HARQ can be seen as a promising approach to achieve reliable high-capacity wireless transmissions. However, this combination has a problem of severe performance degradation due to the accumulation of modulo loss which is the inherent drawback of THP. In this paper, we propose the HARQ scheme to cancel the accumulation of modulo loss in Multi-user MIMO THP systems. The main feature of the proposed approach is to add the same perturbation vector as the initial transmit packet to the retransmit packets in order to prevent the accumulation of modulo loss. The effectiveness of the proposed scheme is demonstrated in comparison with the conventional packet combining scheme by means of computer simulations.

The design procedure of hybrid beamforming is investigated considering multi-user MIMO communication systems taking into account the number of independent data streams for each user. Hybrid precoding and combining are utilized at the transmitter and receiver sides of millimeter-wave multi-user massive MIMO. The obtained results indicate the trade-off in performance based on the ratio of the number of antennas to the number of data streams at the transmitter as well as the receiver. The optimization of the number of parallel data streams per user allows the increase of transmitted data rate while keeping the levels of error vector magnitude (EVM) at acceptable levels.

Research into cutting-edge systems that can satisfy the rising needs for greater data rate and increased reliability is becoming more and more necessary as wireless communication technologies continue to evolve. To enhance the spectral and energy efficiencies, this study examine the performance of massive multiple input multiple output (mMIMO) communication systems using wavelet-order orthogonal frequency division multiplexing (W-OFDM). Also, a communication system was created based on W-OFDM Massive MIMO using MATLAB to model its operation. The simulated system's various stages of operation was examined through detailed analysis and its performance was compare with prior studies and practical networks on OFDM. Key performance metrics, specifically the data throughput, was evaluated to assess the effectiveness and viability of the system. The simulation results indicates that W-OFDM can achieve up to 35% reduction in peak-to-average-power-ratio (PAPR) compared to the traditional OFDM, with a 20% improvement in BER performance under Rayleigh fading conditions. Also, the spectral efficiency of W-OFDM mMIMO outperforms convectional OFDM by 15%, making it a viable technology for future communication networks requiring high data rates and reliability. This implies that, the analytical evaluation confirms that W-OFDM mMIMO provides substantial benefits for improving energy and spectral efficiencies in wireless communication systems, addressing the challenges of increased user demands for high spectrum. This study contributes to the understanding of MIMO systems' performance optimization, highlighting the importance of antenna configuration and cell distance. Comprehensive analysis of spectral efficiency and energy efficiency trade-offs in MIMO systems and identification of optimal antenna configuration for maximum energy efficiency, addressing some of the challenges of future wireless communication systems.

The multi-user MIMO space time scheduling problem is the prime focus of the paper. Optimizing the link level performance of the MIMO system does not always imply achieving scheduling level optimization. Therefore,design optimization across the link layer and the scheduling layer is very important to exploit fully the temporal and spatial dimensions of the communication channel. We address the design of the optimal space time scheduler for a multi-user MIMO system based on an information theoretical approach. We assume a partial feedback channel, namely a scaler rate-feedback channel, is available to the transmitter, but the full channel matrix is unknown to the transmitter. With the partial feedback, we find that the optimal resource allocation strategy is water-filling in both the temporal domain and spatial domain. The optimal scheduler should allocate all the power to at most n/sub R/ users at any particular instant. The optimal scheduler performance depends on the total number of users (K), the number of receive antennas at the base station (n/sub R/), and the number of transmit antennas at the mobile (n/sub T/). The scheduling gain increases with n/sub R/ due to the distributed MIMO configuration formed between mobile users and base station. With a single power feedback channel, the scheduling gain reduces as n/sub T/ increases, illustrating that transmit diversity hurts the scheduling performance in the case of scalar feedback. Finally, scheduling performance improves as K increases due to the multi-user selection diversity.

With tremendous power shortage and raising voice of greener energy usage, energy efficiency (EE) maximization in MIMO systems has received much attention in next generation wireless communications. Within recent years, there has been a lot of great work on power allocation and antenna selection in order to maximize EE under holistic power models. However, it is not a trivial work to derive a closed-form solution for energy efficiency optimization. In this paper, an asymptotic approach is adopted to obtain the analytical solutions of the EE optimal transmission schemes, as well as its performance limits. More specifically, we are interested in the capacity achieving dirty paper coding (DPC) and practical low-complexity zeroforcing beamforming (ZFBF), where EE is optimized with and without total power constraint. Closed-form formulas are given to determine the EE optimal number of antennas and transmit power. The proposed asymptotic analysis matches well with the numerical results when the number of users is moderately large, i.e., over 30.

A null space constraint based block Tomlinson-Harashima preceding technique (NS-BTHP technique) is proposed for the downlink of multi-user MIMO systems. Employing non-linear pre-processing at the base station this technique pre-eliminates multi-user interference (MUI) among different mobiles. Therefore, an equivalent point-to-point MlMO channel is realized for each mobile, and the spatial interference among the multiple data streams directed to each user (self-interference) can be eliminated using signal processing algorithms developed for point-to-point MlMO systems. The proposed nonlinear preceding approach results in an improvement of the null space constraint technique (NS technique), in which linear pre-processing is used to pre-eliminate the MUI at the base station. The advantage of the NS-BTHP technique over the NS technique is explained and demonstrated by simulations.

Significant throughput gains can be achieved in a multi-user MIMO (MU-MIMO) wireless system by exploiting the combination of multi-user scheduling and multi-user diversity. Open-loop MU-MIMO (OL-MU-MIMO) is a codebook based precoding technique where precoders are fixed a priori at the base station (BS) in a known fashion and the user needs to feedback which precoding vector is to be chosen referred to as precoding vector index (PVI) or stream indicator. This scheme feedbacks the channel quality indicator (CQI) which is used by the BS for allocation of modulation and coding scheme (MCS) to the scheduled users. As the precoders used at all the base stations are known a priori, estimation of co-channel interference (CCI) is accurate and there is negligible mismatch between the CQI fed back by the user in present frame and SINR experienced by the user during next frame for low Doppler, resulting in stable CQI modeling. In this paper, an extensive study is made on OL-MU-MIMO and open loop single-user MIMO (OL-SU-MIMO), with an emphasis on how OL-MU-MIMO exploits multi-user diversity to achieve high spectral efficiencies. We also derive the SINR and CQI expressions for such MU-MIMO systems, and provide simulation results which indicate that OL-MU-MIMO outperforms OL-SU-MIMO only when there are large number of users in the system.

In multiuser MIMO uplink, different pairs of transmitter and receiver may have different time delays and carrier frequency offsets (CFOs). This causes the time delay and CFO estimations much more difficult than those for a single input single output (SISO) system. It is a challenging problem to resolve the time delays and CFOs in the MIMO uplink. In this paper, an asynchronous multiuser MIMO system with multipath channels and CFOs is remodeled into another system. A blind method based on second order statistics is then used for estimating the shaped channels with ambiguity. Based on the shaped channels, specially designed pilots are proposed to find the CFOs. The same pilots are also used for resolving the time delays and the ambiguity in the estimated channels. Only upper bounds for the channel orders and time delays are needed for implementing the algorithms, which makes them applicable to practical multiuser MIMO systems.