WiMAX OFDMA Research Articles

Femtocell Interference, SINR and the Probability of Connection at Downlink

A Femtocell (FMC) is a low power cellular home base station, which is low in cost and operating in licensed spectrum. Nowadays, because of the requirement for high data rate and large area coverage indoors, FMC provides the solution to these requirements. FMC is deployed mainly indoors and sometimes outdoors at the cell edge to increase the area of coverage, capacity and in order to enhance the received signal in the user's premises. In this paper, a novel technique and a Monte Carlo simulation is implemented to calculate the interference, the SINR and the probability of connection at the downlink for a varied number of FMCs based on LTE and WiMAX OFDMA range. Moreover, a novel Monte Carlo simulation is used to carry out the comparison of interference, SINR and probability of connection for three different numbers of FMCs. Furthermore, a novel comparison of FMCs at various SINR threshold values is presented. The downlink interference occurs from neighbouring FMCs to the target user equipment (UE) when the signal transmits from the serving FMC to the target UE and the signals which are transmitted from the neighbouring FMCs would have the same subchannels during the downlink transmission. This paper will explore the appropriate number of FMCs that could serve a specific indoor area and the proper number of UEs in the specified area.

Architecture Design of Frequency Domain Processing for Flexible and Re-configurable WiMAX OFDMA Receiver

This paper proposes hardware architecture of WiMAX OFDMA frequency domain processing system. The system mainly consists of channel estimator, equalizer, and subcarrier de-allocator. The system is optimized for flexible and re-configurable WiMAX OFDMA receiver. The flexibility feature is obtained by employing flexible control unit approach using task FIFO. Using this scheme, the designed system can handle various and complex data structure within OFDMA frame. The propesed architecture has been implemented in 0.13 μm CMOS technology. The implementation result shows that chip area is about 0.45 mm2 and able to work in targeted system clock 54 MHz.

Throughput Gain Using Threshold-Based Multiuser Scheduling in WiMAX OFDMA

This paper presents the analysis of the throughput enhancement possible using threshold-based multiuser scheduling in WiMAX OFDMA. We consider a point-to-multipoint (PMP) WiMAX network where base station (BS) schedules downlink packets for simultaneous transmissions to multiple users using the WiMAX OFDMA system. WiMAX OFDMA standard specifies several subcarrier permutation options, such as the partial usage of subcarriers (PUSC), full usage of subcarrier (FUSC), and the band adaptive modulation and coding (band-AMC) among others, for mapping the physical subcarriers into logical subchannels assigned to users by the BS schedulers. In this paper, we propose the use of threshold testing prior to the process of subchannel assignment to users by the BS scheduler, as a means of throughput enhancement. In the proposed threshold-based multiuser scheduling scheme, the BS scheduler selects at any time instant users whose channel gains in the available subchannels equal or exceed a predetermined energy threshold. Thus, only users who can maximize BS throughput on the available subchannels are assigned data transmission opportunities which enhance the BS data rate, albeit at the expense of fairness to users. We quantify the throughput enhancement of the proposed system and illustrate its benefits by numerical simulations.

Performance study of mobile WiMAX network with changing scenarios under different modulation and coding

AbstractWiMAX—the Worldwide Interoperability for Microwave Access is a promising technology for offering high‐speed data, video and multimedia services over mobile platform evolving toward all IP networks. The increasing demand of WiMAX for VoIP and high‐speed multimedia is due to the simplicity of installation and cost reduction compared with the traditional wired DSL cable. The challenges to service providers lie with the Quality of Service (QoS) under varying fading environment while at the same time maximizing for resource utilization. In this paper, a rigorous and comprehensive performance study of mobile WiMAX has been made with respect to adaptive modulation and coding techniques considering the variation in the speed of the mobile, path‐loss, scheduling services and application type for comparing with the fixed type of modulations. The OPNET 14.5.A modeler for WiMAX platform has been used as simulator for adaptation at the physical layer of the transmission in WiMAX OFDMA structure. Observation reveals that dynamic adaptation of modulation and coding schemes based on channel condition enables better QoS while consuming low overall bandwidth of the system. Copyright © 2011 John Wiley & Sons, Ltd.

Greedy scheduling algorithm (GSA) – Design and evaluation of an efficient and flexible WiMAX OFDMA scheduling solution

WiMAX is one of the most promising technologies to provide broadband wireless access in the near future. In this paper we focus on the study of the combined performance of a WiMAX Base Station MAC downlink scheduler and OFDMA packing algorithm which mainly determine the usage efficiency of the available radio resources. We design and analyze an efficient and flexible solution, greedy scheduling algorithm (GSA), and evaluate its performance as compared to several relevant alternative solutions. Specifically, we analyze performance differences with respect to efficiency, flexibility to provide per subscriber station burst shape preferences, interference mitigation and computational load. Our results show that GSA achieves a performance similar to the one of the competing approaches considered in terms of efficiency, even better in some cases, and significantly outperforms them in flexibility to provide per subscriber station burst shape preferences, interference mitigation and computational load. As a conclusion, the proposed GSA solution is a promising candidate to maximize the utilization of the available WiMAX radio resources at a low computational cost while at the same time being able to fulfill a wide range of requirements based on operators' preferences and/or network environment specifics.

Decoding algorithms for shortened-extended turbo product codes in WiMAX systems

The component codes of turbo product codes inWiMAX systems are extended Hamming codes and single parity check codes as well as their shortened forms. In this paper, three novel iterative decoding algorithms based on Chase, MAP algorithms and their combination are proposed for shortened-extended turbo product codes. The iterative decoding algorithm based on Chase algorithm is proposed to reduce the decoding complexity without any performance loss. An efficient MAP algorithm is then proposed to decode the component codes of shortened single parity check codes and shortened-extended Hamming codes. A comprehensive performance comparison of the proposed decoding schemes is conducted for three typical classes of turbo product codes in WiMAX OFDMA systems. The suitable decoding algorithms are recommended for different classes based on the simulation results.

Fairness and QoS Guarantees of WiMAX OFDMA Scheduling with Fuzzy Controls

A fairness and QoS guaranteed scheduling approach with fuzzy controls (FQFCs) is proposed for WiMAX OFDMA systems. The controllers, respectively, adjust priority and transmission opportunity (TXOP) for each WiMAX connection according to QoS requirements and service classes. The FQFC provides intra- and interclass fairness guarantees by making connections within the same class achieve equal degree of QoS while at the same time making those without QoS requirements equally share the remaining resources. Even in dynamic environments such as mobile WiMAX networks with time-variant traffic specifications, the FQFC fairly guarantees delay, throughput, and jitter, which are seldom achieved at the same time by state-of-the-art solutions.