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In an orthogonal frequency division multiple access (OFDMA) system such as LTE and WiMAX, EESM provides an efficient way to estimate the link performance of a resource block/sub-channel contains a number of sub-carriers by a single value (effective SNR). In order to learn the performance of an OFDMA system involving EESM, it is of interest to investigate the statistics of effective SNR over frequency...
In this paper parametric tracking of channel and synchronization errors for an adaptive multi-dimensional channel estimator for uplink Orthogonal Frequency Division Multiplex Access (OFDMA) communication systems is proposed. The estimator consists of a two-dimensional LMMSE filter. In real world scenarios, channel estimation should work not only in a wide range of terminal velocities and delay spread...
Cognitive radio is a new concept of reusing licensed spectrum in an unlicensed manner. The spectrum must be sensed to detect primary user signals, in order to allow cognitive radios in a primary system. Spectrum sensing is to be done over a wide range of the electro-magnetic spectrum. While many of the signals of interest are similar in terms of the modulation techniques used, the characteristics...
This paper studies the frame synchronization of Orthogonal Frequency Division Multiple Access-Time Division Duplexing (OFDMA-TDD) systems and proposes a new method for downlink of IEEE 802.16 to improve frame synchronization performance. In this paper, we adapt three existing timing metrics for frame synchronization in OFDM mode of WiMAX. Among the methods considered, it is shown that direct application...
Timing and frequency synchronization are the important task in receiver. In this paper, an efficient timing and carrier frequency offset (CFO) estimation method for orthogonal frequency division multiple access/ time division duplexing (OFDMA/TDD) mode in IEEE 802.16-2004 standard (WiMAX) is represented. This method has high performance and jointly estimates timing error and CFO. The performance is...
Synchronization for both time and frequency is a well-known issue in OFDM systems. In order to avoid signal distortion, synchronization is the major job to be completed generally in the receiver end. Especially, the timing error compensation is the first task to be done. This paper proposes two modified preamble patterns with insertion of zero padding for timing synchronization by using the correlation...
Cognitive radio is an enabling technology for efficient utilization of radio spectrum. In this paper, an orthogonal frequency division multiple access (OFDMA) based cognitive (opportunistic) network is considered, which co-exists with a macrocell network through utilizing its unused subcarriers. We particularly consider the uplink opportunity detection problem by the opportunistic network, where accurate...
In this paper, we present low complexity down-sampled MMSE channel estimation. We reduced MMSE channel estimation complexity by downsampling the MMSE weight matrix. The simulation results show that the bit error rate (BER) performance significantly improved over the least square channel estimation and has comparable BER performance with MMSE channel estimation at low SNR with significant decrease...
In this paper, we propose a coarse and fine frequency synchronization method which is suitable for the 3rd Generation Partnership Project (3GPP) long term evolution (LTE) orthogonal frequency division multiple access (OFDMA) system in time division duplexing (TDD) mode. In general, primary synchronization signal (PSS) correlation based estimation method and cyclic prefix (CP) correlation based tracking...
In the OFDMA downlink, obtaining channel state information (CSI) from users is necessary for the base station (BS) to optimize network performance by intelligently allocating resources and scheduling mobile stations (MS). However, the overhead of obtaining CSI is a large burden and therefore, schemes to reduce CSI are necessary for a realizable system. By considering a MS's coherence time Deltatcoh...
This paper proposes a novel lightweight mechanism for a secure physical (PHY) layer in cognitive radio network (CRN) using orthogonal frequency division multiplexing (OFDM). User's data symbols are mapped over the physical subcarriers with a permutation formula. The PHY layer is secured with a random and dynamic subcarrier permutation which is based on a single pre-shared information and depends on...
The emerging smart grid system requires high speed sensing of data from all the sensors on the system within a few power-cycles. The Advanced Metering Infrastructure is a simple example of such a system where all the meters on a certain grid must be able to provide the necessary information to the master head end within a very short duration (fraction of a second for real time load control). Wireless...
Ranging is one of the most important processes in the uplink of the IEEE 802.16e OFDMA system. A ranging process includes initial ranging, periodic ranging, handover ranging, and contention bandwidth request. Initial ranging provides network entry, uplink synchronization, and system coordination. In the initial state of the transmission process, multiple users transmit randomly selected ranging code...
Mobile WiMAX is a wireless protocol for broadband wireless access that utilizes TDD OFDMA. The WiMAX frame begins with a preamble symbol that establishes frame timing and initial symbol timing for the mobile. In a mobile, the preamble symbol detection is often accomplished by a delay correlation detector. Delay correlation detectors take advantage of the preamble symbols redundancy. Previous detection...
Orthogonal frequency division multiplexing (OFDM) systems are sensitive to timing and frequency estimation errors, which cause inter-symbol-interference (ISI) and inter-carrier-interference (ICI), leading to degradation in the system performance. In this paper, optimized implementation of synchronization algorithm for cellular reuse-1 OFDMA systems, compatible with IEEE 802.16d/e wireless MAN standard...
Orthogonal Frequency Division Multiple Access (OFDMA) gains increasing attention for broadband, high data rate fixed/mobile communications. As the basic modulation technique in OFDMA is orthogonal frequency division multiplexing (OFDM), it is severely affected by carrier frequency offset (CFO). The CFO causes loss of orthogonality among the subcarriers. In this paper, we propose a method for joint...
This paper is dedicated to better understanding of the achievable sum rate in the single carrier FDMA (SC-FDMA) system. We investigate the achievable sum rate in a two-user SC-FDMA system, where a mix of SIMO (single input multiple output) and SDMA (space division multiple access) transmission mode is assumed for the wideband communication. The problem is formulated which appears to be non-convex...
In this paper, we adapt four existing timing metrics for frame synchronization in OFDMA mode of WMAN. Among the methods considered, first method uses cyclic prefix information present in the symbol, second method uses the symmetry in the time domain preamble data, third method exploits a priori knowledge of the preamble PN sequence, and the fourth method exploits the conjugate symmetry in the time...
In this paper, the interleaved frequency division multiple access (IFDMA) scheme is considered as a special case of Discrete Fourier Transform (DFT)-precoded Orthogonal Frequency Division Multiple Access (OFDMA) with interleaved subcarrier allocation. The redundancy that is characteristic for an IFDMA-signal is exploited in order to estimate the channel without pilot symbols and, thus, overcome the...
In OFDMA systems, channel quality information (CQI) feedback is used to determine the modulation and coding level of a mobile station (MS). When the MS uses diversity, it transmits the CQI feedback information which contains channel condition which is averaged over all the sub-bands allocated to itself. In conventional CQI feedback scheme, every MS should send its own CQI feedback. So, as the number...
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