Protocol parameter selection for fiber-supported IEEE 802.16m networks

In this paper we investigate protocol issues that might arise due to the extra fiber propagation delay in fiber-fed IEEE 802.16m networks. Our study indicates that although the fiber delay might affect network performance, an informed choice of protocol parameters, such as the guard times and the ranging channel structure, can minimize the reduction in efficiency and allow for relaxation of some of the constraints imposed on the optical distribution network architecture

Subcarrier and Power Allocation in WiMAX

Worldwide Interoperability for Microwave Access (WiMAX) is one of the latest technologies for providing Broadband Wireless Access (BWA) in a metropolitan area. The use of orthogonal frequency division multiplexing (OFDM) transmissions has been proposed in WiMAX to mitigate the complications which are associated with frequency selective channels. In addition, the multiple access is achieved by using orthogonal frequency division multiple access (OFDMA) scheme which has several advantages such as flexible resource allocation, relatively simple transceivers, and high spectrum efficient. In OFDMA the controllable resources are the subcarriers and the allocated power per subband. Moreover, adaptive subcarrier and power allocation techniques have been selected to exploit the natural multiuser diversity. This leads to an improvement of the performance by assigning the proper subcarriers to the user according to their channel quality and the power is allocated based on water-filling algorithm. One simple method is to allocate subcarriers and powers equally likely between all users. It is well known that this method reduces the spectral efficiency of the system, hence, it is not preferred unless in some applications. In order to handle the spectral efficiency problem, in this thesis we discuss three novel resources allocation algorithms for the downlink of a multiuser OFDM system and analyze the algorithm performances based on capacity and fairness measurement. Our intensive simulations validate the algorithm performances.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Investigation of efficient resource allocation schemes for WiMAX networks

This thesis was submitted for the degree of Master of Philosophy and was awarded by Brunel University on 9 July 2008.WiMax (Worldwide Interoperability for Microwave Access) is a promising wireless technology with the aim of providing the last mile wireless broadband access designed for both fixed and mobile consumers as an alternative solution to the wired DSL and cable access schemes. The purpose of this research project is to investigate efficient resource allocation algorithms for WiMax. To achieve this goal, we investigate efficient PHY layer Partial Usage of SubCarriers (PUSC) allocation as well as MAC layer piggyback bandwidth request mechanisms. At the PHY layer we proposed improvements on the Uplink and Downlink PUSC subcarrier allocation scheme. For the Uplink PUSC we suggested a method by allocating different frequencies to neighbouring cells in combination with the Integer Frequency Reuse (IFR) and Fractional Frequency Reuse (FFR) in order to reduce interferences and collisions. The simulation results exhibit that collision rates can be reduced to zero for both IFR and FFR patterns with the proposed improvement by assuming that perfect power control is used in the system. In addition, there is no collision at cell edges. The results also show that FFR patterns achieve lower inter-cell interference and higher capacities as compared to the IFR patterns. For the Downlink PUSC we introduced an offset scheme with the purpose of increasing the number of users in the system. At the MAC layer we propose an improvement on the piggyback bandwidth request mechanism by increasing the size of the piggyback bandwidth request in order to reduce the number of bandwidth requests and hence improve the resource utilisation. The simulation results demonstrate that our improved scheme achieves higher throughput, less delay and packet loss rates as compared to the standardised piggyback bandwidth request mechanism

Performance evaluation of fixed WiMax physical layer under high fading channels

This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University.A radio channel characteristic modelling is essential in every network planning. This project deals with the performance of WiMax networks in an outdoor environment while using fading channel models. The radio channels characteristics are analyzed by simulations have been done using Matlab programming. Stanford University Interim(SUI) Channels set was proposed to simulate the fixed broadband wireless access channel environments where IEEE 802.16d is to be deployed. It has six channel models that are grouped into three categories according to three typical different outdoor Terrains, in order to give a comprehensive study of fading channels on the overall performance of the system, WiMax system has been tested under SUI channels that modified into account for 30o directional antennas, with 90% cell coverage and with 99.9% reliability in its geographical covered area. Furthermore, in order to combat the fading which occurs in urban areas and improve the capacity and the throughput of the system, multiples antennas at both ends of communication link are used, the transmission gain obtained when using multiple antennas instead of only a single antenna. Space-time coding and maximum ratio combining for more than one transmit and receive antenna is implemented to allow performance investigations in various MIMO scenarios. It has been concluded that uses multiple antennas at the receiver offers a significant improvement of 3 dB of gain in the channel SNR. This thesis also contain implementation of all compulsory features of the WiMax OFDM physical layer specified in IEEE 802.16-2004 using Matlab coding. In order to combat the temporal variations in quality on a multipath fading channel, an adaptive modulation technique is used. This technique employs multiple modulation schemes to instantaneously adapt to the variations in the channel SNR, thus maximizing the system throughput and improving BER performance. WiMax transceiver has been tested with and without encoding and studied the effect of encoding on multipath channel. Testing the system with flexible channel bandwidth has been part of this thesis. Finally it has been explained in this thesis the affect of increasing the size of cyclic prefix on overall performance of WiMax system

Real-time validation of a SDR implementation of TDD WiMAX standard

[Abstract]: This paper focuses on the validation of an innovative software- defined radio architecture for a WiMAX system based on commercially available field-programmable gate array and digital signal processor modules. We provide a realtime implementation of a standard-compliant time-division duplex physical layer including a mobile and a base station as well as downlink and uplink communications, thus obtaining a full-featured physical layer. Additionally, a set of different configurations are supported as described in the standard and in the WiMAX Forum. The main contribution of the paper consists in a reproducible and repeatable validation of the implementation in representative scenarios. At the same time, a characterization of the performance exhibited by the system is provided based on bit error rate measurements carried out using a custom-made, real-time channel emulator.This work has been partially supported by Indra Sistemas S.A. and the Spanish Ministry of Defence with the technical direction of PEC/ITM under grant DN8644-COINCIDENTE. The authors wish to thank J. M. Camas- Albar from Indra Sistemas S.A. for his help. This work has been additionally funded by Xunta de Galicia, Ministerio de Ciencia e Innovación of Spain, and FEDER funds of the European Union under grants with numbers 10TIC003CT, 09TIC008105PR, TEC2010-19545- C04-01, and CSD2008-00010.Xunta de Galicia; 10TIC003CTXunta de Galicia; 09TIC008105P

The Most Possible Scheme of Joint Service Detection for the Next Wireless Communication Technologies

 The era of beyond third generation wireless communication is highly heterogeneous in that it comprises several radio access technologies that need to be joined into a single multimode terminal. In this respect, this paper introduces a common service recognition system for the next wireless communication technologies i.e. Long Term Evolution (LTE), WiMAX or IEEE 802.16, and Wireless Local Area Network (WLAN) or IEEE 802.11.It is done in physical layer as one of multimode terminal ability regardless network cooperation existence. We investigation the preamble and synchronization signals as indicators of the available services instead of carrier frequency detection. To detect these signals, we proposed a time domain detection system consisting of auto-correlation, cross-correlation, and a peak period detection. Based on complexity analysis, this paper proposes the most possible scheme with lower complexity than cross-correlation implementation. Moreover, the fixed point simulation results show that the proposed system satisfies the minimum receiver sensitivity requirements that specified in the standards