Browsing by Subject "WiMAX"

Now showing 1 - 4 of 4

Open Access
A Performance comparision of polar codes with convolutional turbo codes
(2009) Özgür, Üstün
Polar codes introduced recently by Arıkan are the first low-complexity codes achieving symmetric capacity for arbitrary binary-input discrete memoryless channels (B-DMCs). Although being theoretically significant, their practical significance is an issue that has not yet been fully explored. Previous studies have compared polar codes with Reed-Muller codes, where it was found that polar codes can outperform them. In this thesis, to investigate how polar codes perform against state-of-the-art forward error correction (FEC) codes used in practice, we implement a IEEE 802.16 based link-level Worldwide Interoperability for Microwave Access (WiMAX) simulator which incorporates several WiMAX FEC options, and polar codes. IEEE 802.16 standards family define standards for current and next generation broadband wireless access, which will make high data rate multimedia applications in mobile environments a reality. Next generation broadband access standard, pursued by the IEEE 802.16 Task Group m is a work in progress, and requires even more sophisticated error correction schemes so that higher throughput, better QOS, higher mobilities, wider ranges and lower latencies are supported. We perform performance comparison simulations with the convolutional turbo codes (CTC) configurations defined in IEEE 802.16e to see how much of a performance gap exists between polar codes and CTCs. The main findings of the thesis are that, although the polar codes achieve capacity for specific conditions, as expected, for the code lengths and channel conditions we have simulated, the performance of them cannot compete with that of the CTCs with equivalent rates and lengths. It remains a task to see whether polar codes can achieve similar performances with CTCs when used as component codes in other configurations and aid in the advancement of new communication technologies.
Open Access
Performance of static and adpative subchannel allocation schemes for fractional frequency reuse in WiMAX networks
(2011) Kar, Görkem
We study the downlink performance of WiMAX under fractional frequency reuse (FFR) model. Conventional cellular planning methods can be used for broadband wireless access systems that operate in point-to-multipoint (PMP) configuration based on OFDMA/OFDM such as WiMAX. As an alternative planning method, FFR has been recently proposed for OFDMA/OFDM based cellular systems. FFR divides the cell into two regions: the inner and outer cell. Mobile Stations (MS) inside the inner cell can use the entire frequency band (achieving full frequency reuse), while MSs in the outer ring use a fraction of the band (having fractional frequency reuse). Transmissions in the inner and outer cells occur during different time periods so that users at the cell edge experience less interference. In this thesis, we investigate the effect of dynamically changing the number of subcarriers allocated to inner and outer cells. We use two metrics: total cell throughput and Jain’s fairness index for the distribution of cell throughput among MSs. As the ratio of subcarriers allocated to inner cell increases, the total cell throughput increases while the fairness index decreases. We use the product of cell throughput and fairness index in order to study the trade-off between the two metrics. We show that by dynamically adjusting the ratio of subcarriers allocated to the inner cell based on the user distribution, the throughput
Open Access
A survey on scheduling in IEEE 802.16 mesh mode
(Institute of Electrical and Electronics Engineers, 2010) Kas, M.; Yargicoglu, B.; Korpeoglu, I.; Karasan, E.
IEEE 802.16 standard (also known as WiMAX) defines the wireless broadband network technology which aims to solve the so called last mile problem via providing high bandwidth Internet even to the rural areas for which the cable deployment is very costly. The standard mainly focuses on the MAC and PHY layer issues, supporting two transmission modes: PMP (Point-to-Multipoint) and mesh modes. Mesh mode is an optional mode developed as an extension to PMP mode and it has the advantage of having an improving performance as more subscribers are added to the system using multi-hop routes. In 802.16 MAC protocol, mesh mode slot allocation and reservation mechanisms are left open which makes this topic a hot research area. Hence, the focus of this survey will mostly be on the mesh mode, and the proposed scheduling algorithms and performance evaluation methods. © 2010 IEEE.
Open Access
A system level simulation study of WiMAX
(2010) Başçiftçi, Yüksel Ozan
In this thesis, we implement a WiMAX system level simulator compliant with the evaluation methodology document published by the IEEE 802.16m Task Group. We study the PHY abstraction of polar codes and integrate polar codes into the simulator. We compare the system level performances of polar code and convolutional turbo code (CTC) and observe that CTC outperforms polar code. On the simulator, we study the downlink (DL) performance of WiMAX under various configurations such as scheduling methods, subchannelization methods, and frequency reuse models. We study there types of scheduling methods, namely round robin (RR) scheduling, proportional fair (PF) scheduling, and maximum sum rate (MSR) scheduling. We observe that MSR scheduling has the best throughput performance but does not support the users far from the base station. We study three frequency reuse models, namely 1×3×1, 1×3×3, and 3×3×1. We observe that 1 ×3×1 reuse model has the best throughput performance and maximum spectral efficiency is obtained in 1 × 3 × 3 reuse model. We study two subchannelization methods, namely PUSC and band AMC. We observe that in low mobility cases, band AMC outperforms PUSC and in high mobility cases, PUSC is better than band AMC.