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We present a novel BCH code based sequences design method for generating large families of ranging sequences. The sequences can be used in an OFDMA network to offer sufficient ranging opportunities and guarantee low probability of false detection. Each derived sequence has low peak to average power ratio (PAPR) and cross-correlations with other sequences. These properties enable a mobile receiver...
In this paper, OFDMA (Orthogonal Frequency Division Multiple Access) access methods based on PF (Proportional Fair) algorithm considering the fairness among MS (Mobile Stations) and the total throughput were studied. Concretely, four types of scheduling methods were proposed. Computer simulations were carried out with four types of proposed methods in order to clarify the performance. As the result...
In this paper we consider cognitive radios (CR) that employ orthogonal frequency division multiplexing (OFDM) modulation at the physical layer and present an algorithm for transmitter adaptation subject to specified quality of service (QoS) constraints. The proposed algorithm explicitly considers multipath channels between the CR transmitter and its intended receiver, and performs joint spectral shaping...
We study the performance of a two-hop full-duplex OFDM relay link, where the relay, or in-band repeater, amplifies and forwards its input signal on the same channel as the main transmitter. We derive new closed-form expressions for the end-to-end signal-to-interference and noise ratio (SINR) when the multipath channels are modeled with clustered exponential power-delay profiles. Our system model incorporates...
Superimposed training (SIT) design for estimating of time-varying multipath channels is investigated for mobile orthogonal frequency division multiplexing (OFDM) systems. The design of sub-optimum SIT consists of two parts: the optimal SIT sequence is derived by minimizing the channel estimates' mean square error (MSE); the sub-optimal power allocation between training and information data is developed...
In this paper, a low complexity ordered successive interference cancellation (OSIC) equalizer based on minimum-mean squared error (MMSE) criterion is proposed for suppressing intercarrier interference (ICI) caused by time-selective channels in OFDM systems. The proposed scheme exploits a low complexity MMSE equalizer and a partial MMSE-OSIC equalizer appropriately, according to symbol selection algorithm...
This work presents a symbol time (ST) synchronization algorithm for orthogonal frequency-division multiplexing systems based on a metric of signal-to-interference-and-noise ratio (SINR) which drops drastically with the increasing ST error. The ST is intuitively estimated by maximizing the SINR metric that exploits the correlation results of the separated-by-N samples. Unlike most existing techniques...
An orthogonal frequency division multiplexing (OFDM) system suffers performance degradation when the length of the cyclic prefix (CP) is less than the channel impulse response. The root cause of this degradation is the inter-carrier interference (ICI) and inter-symbol interference (ISI) introduced by the excessive multipath delay. Generally, MIMO beamforming is helpful in mitigating such interference...
OFDM systems are sensitive to front-end imperfections including CFO, IQ imbalance and phase noise. In practice, these imperfections are inevitable and would lead to significant performance degradation. In this paper, a general closed-form expression on average signal-to-interference-and-noise ratio (SINR) over multipath fading channels is derived for performance evaluation. When additive white Gaussian...
In orthogonal frequency division multiplexing (OFDM) systems, time- and frequency-selective (or doubly-selective) fading leads to the loss of subcarrier orthogonality and the occurrence of inter-carrier interference (ICI), which increases an irreducible error floor in proportional to the normalized Doppler frequency offset. Channel estimation (CE) in rapidly time-varying multi-path scenarios is critical...
Fourth generation broadband wireless access systems based on OFDMA/OFDM techniques operate in point-to-multipoint (PMP) configuration so that conventional cellular planning methods can be used for network design. As an alternative planning method fractional frequency reuse (FFR) strategy has been recently proposed for OFDMA/OFDM cellular systems such as WiMAX. For what concerns the determination of...
Orthogonal frequency division multiplexing (OFDM) is the modulation scheme of choice for digital video broadcasting-handheld (DVB-H), which is required to operate under high mobility conditions resulting in significant Inter-carrier Interference (ICI). To mitigate ICI, several cancellation schemes have been proposed but they require reliable channel information at the receiver which is quite challenging...
Orthogonal frequency division multiplexing (OFDM) is the modulation scheme of choice for digital video broadcasting-handheld (DVB-H) which is required to operate under high mobility conditions resulting in significant Inter-Carrier Interference (ICI). Under these conditions, the conventional one-tap per subcarrier channel estimation and equalization is suboptimal since it does not account for ICI...
In this paper we consider the coexistence issue between OFDM-based WLANs of the 802.11a family and time-hopping ultra wideband (TH-UWB) systems. A general analytical expression is provided for the bit error rate (BER) of the OFDM transceiver operating in the presence of UWB interference and the interferences caused by the multipath propagation phenomenon on the 802.11a OFDM signal, comprising intersymbol...
Time-varying multi path channels lead to the loss of orthogonality among sub-carriers, resulting in inter carrier interference (ICI) in OFDM systems. Different from many schemes which only focus on equalizer design, our paper consider the entire receiver, and propose the semi-blind channel estimation and detection for OFDM systems in time-varying multi path channel. Theoretical analysis and simulation...
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