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ABSTRACT: Orthogonal frequency division multiple access (OFDMA) has been adopted by all the proposals which have been considered for the fourth generation (4G) wireless technologies. Specifically, the two main contenders in the 4G marketplace are likely to be evolutions of WiMAX and LTE. In this work, we compare the use of OFDMA in these standards.
Communications (NCC), 2010 National Conference on; 03/2010
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ABSTRACT: In this paper, a low complexity cell search algorithm for mobile OFDMA systems is presented, with IEEE 802.16e as the example. We propose a method, to identify a dominant sector at the sector boundary, using common sync symbol. The information about the dominant sector reduces the complexity of cell search. Extensive simulation results show that the new technique using common sync symbol can achieve better performance than the conventional schemes for achieving initial timing acquisition, fractional frequency offset correction, integer frequency offset estimation and dominant sector identification.
Signal Processing, Communications and Networking, 2008. ICSCN '08. International Conference on; 02/2008
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Int. J. Communication Systems. 01/2007; 20:273-296.
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ABSTRACT: This paper proposes a mechanism that supports always best-connected (ABC) quality of service (QoS) to the application in a heterogeneous network. The heterogeneous network consists of IEEE 802.11e WLAN and IEEE802.16d WiMAX access networks. The user equipment (UE) in the network is enabled with both WLAN and WiMAX access capabilities. The generic virtual link layer (GVLL) is placed above the WLAN and WMAN MAC layer in the UE, decides the best serving access network in terms of QoS support. The best access network is chosen dynamically based on the QoS parameters such as throughput, packet loss, and delay. The main focus of this work is to provide QoS for variable bit rate (VBR) multimedia services in a heterogeneous network. The simulation results show that the performance of the users in the network is improved significantly in terms of throughput, delay, call admission because of the support of heterogeneous nature
Industrial and Information Systems, First International Conference on; 09/2006
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ABSTRACT: In this paper, we propose a QoS guaranteed dynamic scheduler for IEEE 802.16d broadband wireless systems. The dynamic scheduler residing at the base station (BS) dynamically schedules the subscriber stations (SS) based on the present load of the system. The number of slots that has to be allotted to satisfy the QoS requirement of the applications running on each SS is estimated by the BS during each frame. This dynamic scheduler is designed for uplink VBR multimedia services with constraint QoS. An admission controller is also included in the system to avoid the system overload. The performance of the dynamic scheduler at the BS is analyzed with various uplink schedulers at the SS. The simulation is carried out for various scenarios and the system performance is evaluated. The results show that the dynamic scheduler enhances the system performance in terms of throughput and delay
Industrial and Information Systems, First International Conference on; 09/2006
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ABSTRACT: The authors present a performance analysis of orthogonal frequency division multiple access (OFDMA) based cellular systems with dynamic packet assignment (DPA). Most approaches in the current literature for analysing wireless data networks do not take into account the interference conditions on the radio channel. An analytical model based on a two-dimensional continuous-time Markov chain (CTMC), that takes into account the interference conditions on the OFDM subcarriers in addition to the traffic conditions, is proposed. The authors derive expressions for the mean delay and the average system throughput on the uplink and the downlink in OFDMA based cellular systems with data traffic.
IEE Proceedings - Communications 03/2005; · 0.32 Impact Factor
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ABSTRACT: We present a performance analysis of OFDMA based cellular systems with dynamic packet assignment (DPA). Most approaches in the current literature to analyze wireless data networks do not take into account the interference conditions on the radio channel. We propose an analytical model based on a two-dimensional continuous time Markov chain (CTMC), that takes into account, the interference conditions on the OFDMA sub-carriers. We derive expressions for the mean delay and the average system throughput on the downlink in OFDMA based cellular systems with data-only traffic.
Personal, Indoor and Mobile Radio Communications, 2004. PIMRC 2004. 15th IEEE International Symposium on; 10/2004
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ABSTRACT: We propose a new decoding method for multi-user detection when space-time block codes are used at the transmitter. Specifically, we consider an arbitrary number of simultaneous co-channel users and present a decoding method to detect their symbols. Simulation results show that the proposed decoding method gives better performance when compared to existing methods. The extension of the method to 4-antenna transmit diversity schemes is discussed. The effect of the Rician factor of the channel on the system performance is analyzed. Simulation results indicate superior performance with the new decoding method for the 2 and 4-antenna systems.
Communications, 2003. APCC 2003. The 9th Asia-Pacific Conference on; 10/2003
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ABSTRACT: In this paper, we propose a method for reducing the mean delay and enhancing the average system throughput of IEEE 802.11 based wireless local area networks (WLANs). The primary medium access control (MAC) technique of the 802.11 network is the distributed coordination function(DCF). In DCF, carrier sense multiple access with collision avoidance(CSMA/CA) is used with binary slotted exponential backoff. We propose a throughput enhancement mechanism for DCF in which each contending station in the WLAN modifies its set back-off time based on the information obtained from the transmitting station. Simulation results are presented to show the advantages of the proposed method with respect to the mean delay and average system throughput.
Communications, 2003. APCC 2003. The 9th Asia-Pacific Conference on; 10/2003
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ABSTRACT: In this paper, we present a performance analysis of OFDM based cellular systems when using dynamic packet assignment in the uplink. We propose a two dimensional Markov chain to model the state of the traffic in each cell of a cellular system with data-only traffic and solve this Markov chain to compute the buffering probability, mean delay, and the average system throughput. We perform simulations to determine the optimum position of the base station at which we obtain the best system performance in terms of mean delay. We show that dynamic packet assignment provides improved performance compared to dynamic channel assignment in terms of Erlang capacity. We also show that our analytical model is accurate and computationally efficient.
Communications, 2003. APCC 2003. The 9th Asia-Pacific Conference on; 10/2003
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ABSTRACT: In this paper, we analyze the issues involved in developing a system based on the IEEE 802.11e draft proposal, which defines medium access control (MAC) procedures to support wireless LAN with QoS requirements. However, for scheduler design, the standard provides informative and normative guidelines only. This paper concentrates on design of a scheduler that adapts with the varying channel conditions. We describe the interactions of this scheduler with other components in the system. The functionality of the scheduler is extended to include rate adaptation information. Through extensive simulations, we study the performance enhancement in terms of throughput offered by the adaptive scheme for traffic streams. Results also show the suitability of the scheme in offering QoS guarantees for networks handling both integrated and differentiated traffic using hybrid coordination function (HCF) defined in the draft.
Communications, 2003. APCC 2003. The 9th Asia-Pacific Conference on; 10/2003
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ABSTRACT: The need to provide reliable high data rate communication over the wireless channel has led to the development of efficient modulation and coding schemes. Diversity (time, frequency, space, polarization, angle) is an effective method to combat fading and improve the link reliability of the wireless channel. Time and frequency diversity lead to loss in bandwidth efficiency. However, by employing multiple antennas at the transmitter and/or at the receiver, spatial diversity mitigates fading without sacrificing the precious bandwidth resource. It is difficult to implement receive diversity in the downlink because of size and power limitations on the portable/mobile terminal. This has motivated the use of transmit diversity schemes wherein multiple antennas are used at the transmitter for the downlink transmission from the base station to the portable terminal. In space-time coding, intelligent coding of symbols across space and time can be done to reap the advantages due to coding and diversity. The coding in space is obtained by using multiple antennas at the transmitter. The article discusses aspects of space-time coding. This is an important research topic in the design of emerging wireless systems. Deployment of wireless systems using space-time codes is expected in the near future.
IEEE Potentials 09/2003;
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ABSTRACT: In this paper, we study the performance of channelized cellular systems when using dynamic packet assignment (DPA) based Medium Access methodology in the downlink. We present a near-distributed approach to resource allocation with a minimum level of co-ordination between base stations. We have implemented a priority based scheduling scheme at the base stations to provide Quality of Service (QoS) guarantees. We show through extensive simulation results that our scheduling model improves the delay performance of real-time traffic with no significant decrease in the throughput of the system as compared with first come first serve (FCFS) model.
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ABSTRACT: In this paper, we present a performance study to evaluate the mean delay and the average system throughput of IEEE 802.11 based wireless local area networks (WLANs). We consider the distributed co-ordination function (DCF) mode of medium access control (MAC). The current literature provides very few models to analyze the DCF performance. Existing analytical studies of the IEEE 802.11 DCF do not take into account, the effect of freezing the backoff counter at a station, due to channel capture by other stations. We present a stochastic reward net (SRN) based analytical model to evaluate the mean delay and the average system throughput of the IEEE 802.11 DCF. Our model takes into account, the effect of freezing of the backoff counter, and the maximum number of packet retrials. We validate our analytical model by comparison with simulations.
Wireless Ad-Hoc Networks, 2004 International Workshop on;
