Cell-edge Mobile Stations Research Articles

Wireless Environment Aware Adaptive Scheduling Technique For Cellular Networks

<p>It is now well known that employing channel knowledge based on signaling techniques in wireless mobile ad-hoc networks (MANET) system can yield large improvements in almost all performance metric. Here we proposed the adaptive scheduling, in which the work done is based upon the bandwidth information of channel to provide better quality of service (‘QoS’) to the cell-edge mobile stations. Channel information is critical based on which scheduling is carried out. The bandwidth channel information contains estimation delay, the pilot channel noise and pilot contamination. Afterwards, Zero Forcing precoding methodology has applied for removing the interference at user nodes, destination nodes and gateway side. By extending the characteristics of ZF, the modified Zero Forcing (MZF) has proposed to achieve higher throughput rate and higher spectrum efficiency. The achievable-rates of the ZF and MZF has derived under the comprehensive model of imperfect bandwidth information.</p>

Cross-Layer Performance Analysis of Cooperative ARQ With Opportunistic Multi-Point Relaying in Mobile Networks

A cross-layer analysis framework is developed for the design and performance evaluations of cooperative automatic repeat request (ARQ) with opportunistic multi-point relaying (OMPR) in mobile networks. In particular, three exemplar OMPR functions and their combinations are studied for opportunistic distributed space–time coded (ODSTC) retransmissions in time-division duplex long-term evolution advanced systems. According to the complexities and coordination delays of the OMPR functions, the influences of channel fading on the spatial and temporal diversities offered by ODSTC-based ARQ and their impacts on the system throughput, transmission energy consumption, and relays’ queuing delays can be evaluated effectively under this framework. Based on the analytical results, a rate adaptation strategy is also proposed to maximize the system throughput subject to constraints on queuing delays at relay stations (RSs) and packet error rates at mobile stations (MSs). Analysis and simulation results show that in typical vehicular speeds, using maximally two active RSs for ODSTC is a very robust and effective choice to provide near best system throughput with less energy consumptions and lower protocol complexities. The throughput gains over a system without using RS retransmissions range from 16 ~ 80% for cell-edge MSs, with only 25 ~ 45% of the transmission energy consumption.

On the Design of OFDMA-Based FFR-Aided Irregular Cellular Networks With Shadowing

Owing to its high capabilities in terms of spectral efficiency and flexibility, orthogonal frequency division multiple access (OFDMA) has played a crucial role towards the success of 4G cellular systems and an increasing number of actors in the 5G arena strongly advocate for its continuation. OFDMA-based architectures do not introduce intracell interference but, due to the use of very aggressive frequency reuse plans, they must implement some form of inter-cell interference (ICI) control to warrant prescribed levels of quality of service, specially to users located near the cell edge. An efficient technique for mitigating ICI in OFDMA networks is the well-known fractional frequency reuse (FFR) scheme. In FFR, a signal-to-interference-plus-noise ratio threshold is used to categorize mobile stations (MSs) as cell-center or cell-edge MSs. Furthermore, a different number of frequency resources are allocated to cell-center and cell-edge areas according to a prescribed frequency reuse plan. This paper presents an analytical characterization of FFR-aided OFDMA-based multi-cellular networks that, unlike most previous studies, incorporates shadowing effects and, furthermore, considers that base stations are irregularly deployed. This analytical approach can incorporate different scheduling rules and can underpin different designs for which the optimal FFR parameters can be derived. The proposed framework allows the performance evaluation and optimization of any cell in the system by considering the specific network topology, the user association and categorization processes, the spatial density of users and the characteristics of both the fast multipath fading and the spatially correlated slow shadow fading.

Joint Power Allocation at the Base Station and the Relay for Untrusted Relay Cooperation OFDMA Network

The secure communication that multiple OFDMA-based cell-edge mobile stations (MS) can only transmit confidential messages to base station (BS) through an untrusted intermediate relay (UR) is discussed. Specifically, with the destination-based jamming (DBJ) scheme and fixed MS transmission power assumption, our focus is on the joint BS and US power allocation to maximize system sum secrecy rate. We first analyze the challenges in solving this problem. The result indicates that our nonconvex joint power allocation is equivalent to a joint MS access control and power allocation. Then, by problem relaxation and the alternating optimization approach, two suboptimal joint MS access control and power allocation algorithms are proposed. These algorithms alternatively solve the subproblem of joint BS and UR power allocation and the subproblem of MS selection until system sum secrecy rate is nonincreasing. In addition, the convergence and computational complexity of the proposed algorithms are analyzed. Finally, simulations results are presented to demonstrate the performance of our proposed algorithms.

Incidence Coloring-Assisted Frequency Assignment in Two-Hop OFDMA-based Cellular Networks

In this paper, we consider frequency assignment for orthogonal frequency division multiple access-based cellular networks. We develop a new framework for the mathematical modeling of the frequency assignment problem, which aims at suppressing multi-links interference and enhancing spectral efficiency. The concept of incidence coloring from modern graph theory is utilized to recast the original frequency assignment problem and guide the solution from graph theory perspective. In addition, optimal position of relay stations in a hierarchical cluster based two-hop cellular networks is investigated, and proposes an efficient frequency assignment scheme based on the incidence coloring. System-level simulation results demonstrate that the frequency assignment scheme can effectively mitigate inter-cell interference and improve signal-to-interference-plus-noise ratio. Compared with existing frequency assignment schemes, better coverage performance is obtained and throughput of cell-edge mobile stations is greatly improved.

Multi-Cell Multi-Stream Collaborative Transmission Incorporating Closed-Loop and Open-Loop Techniques

Abstract This paper addresses the inter-cell interference (ICI) issue in the multi-cell scenario in modern wireless communications systems which employ factor-one frequency reuse pattern, and proposes an effective solution to deal with the ICI. The proposed transmission structure takes advantage of the cooperation between base stations (BS), and combines both closed-loop and open-loop multiple-input multiple-output (MIMO) techniques. The cases of single-stream transmission and multi-stream transmission are both considered in this work. The proposed schemes can enhance the communications quality of the cell-edge mobile stations considerably while causing no additional system complexity. Analysis and simulation results show the effectiveness of the proposed transmission scheme against the inter-cell interference. In particular, the proposed transmission scheme can obtain comparable performance compared with local precoding of coordinated multipoint (CoMP) in terms of sum rate, and doubly reduce the feedback overhead as well.

Remote Coalition Network Elements for Base Station Cooperation Aided Multicell Processing

Remote coalition network elements (CNEs) are proposed for base station (BS) cooperation, where the CNEs carry traffic in the second hop for the primary BS in support of its cell-edge mobile stations (MSs) by exploiting the unused frequency bands of the main BS network while considering a range of practical impairments. We derive the coalition probability of the CNEs by taking into account both the specific system load and the CNE's greediness factor. Our simulation results demonstrate that the proposed solution is capable of substantially increasing the attainable signal-to-interference-plus-noise ratio (SINR) in a wide range of scenarios, and it is also robust to diverse practical imperfections. We demonstrate that the maximal sum profit of the main BS network and the CNE network is achieved at a greedy factor of 0.45 when the MSs are located in the range of r <; 0.25R of the CNE, where is the cell's radius.

Joint Zero-Forcing Based Precoder Design for QoS-Aware Power Allocation in MIMO Cooperative Cellular Network

We study a cellular system scenario where multiple data streams originating from a base station (BS) targeted to multiple cell-edge mobile stations (MSs) are transmitted via pre-installed cooperative relay stations (RSs) with multiple antennas. Our objective is to guarantee quality-of-service (QoS) in terms of predefined signal-to-noise ratio at such users within the transmit power budgets at BS and RSs while minimizing total transmit power. We propose a novel precoder design method for power allocation between multiple data streams at BS and RS by using joint zero-forcing strategy in order to avoid multiuser interference (MUI) in the signal received by MSs via both the direct and relay links. We also propose low-complexity suboptimal power allocation algorithm. We focus on analyzing the significance of direct link transmission in providing QoS to cell-edge MSs specially when RS is not situated directly between BS and MSs. Simulation results show that considering direct link and using the proposed scheme in such case significantly improves system outage performance compared to existing schemes in the literature which do not consider direct link.

Cell Edge Capacity Improvement by Using Adaptive Base Station Cooperation in Cellular Networks with Fractional Frequency Reuse

The present paper focuses on the application of the base station cooperation (BSC) technique in fractional frequency reuse (FFR) networks. Fractional frequency reuse is considered to be a promising scheme for avoiding the inter-cell interference problem in OFDMA cellular systems, such as WiMAX, in which the edge mobile stations (MSs) of adjacent cells use different subchannels for separate transmission. However, the problem of FFR is that the cell edge spectral efficiency (SE) is much lower than that of the cell center. The BSC technique, in which adjacent BSs perform cooperative transmission for one cell edge MS with the same channel, may improve the cell edge SE. However, since more BSs transmit signals for one cell edge MS, the use of BSC can also increase the inter-cell interference, which might degrade the network performance. In this paper, with a focus on this tradeoff, we propose an adaptive BSC scheme in which BSC is only performed for the cell edge MSs that can achieve a significant capacity increase with only a slight increase in inter-cell interference. Moreover, a channel reallocation scheme is proposed in order to further improve the performance of the adaptive BSC scheme. The simulation results reveal that, compared to the conventional FFR scheme, the proposed schemes are effective for improving the performance of FFR networks.