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This paper proposes a channel-dependent adaptive spreading code selection method in downlink multicarrier code division multiple access (MC-CDMA). The proposed method is compared to the conventional MC-CDMA and orthogonal frequency division multiple access (OFDMA). First we show that the signal-to-noise and interference power ratio (SINR) after minimum mean squared error (MMSE)-based equalization...
Adaptive bit and power loading is a constraint optimization problem with generally two cases of practical interest, where the objectives are the achievable data rate maximization (RM) and system margin maximization (MM) \cite{Ni-2008}. In this paper, we propose a different optimization model for underwater acoustic (UWA) channels, which is achieved by two algorithms: one is the bandwidth-efficient...
This paper derives a simulation based comparison for UWBOFDM with different multipath channel models. Several multipath channel models such as (AWGN, Rayleigh and Rician) has been simulated and compared with a proposed hybrid combination of Rayleigh, Rician and AWGN to observe a realistic multipath faded environment. These cases are based on no fading and flat Rayleigh- fading, multiple-diversity...
In this paper, we consider the symbol-wise beamforming with limited feedback for MIMO-OFDM systems in the presence of co-channel interference. We propose a non-iterative algorithm for the symbol-wise beamforming with limited feedback, which provides the considerable performance with low computational complexity. We also propose the codebook for the symbol-wise beamforming with limited feedback under...
A novel adaptive Orthogonal Frequency-Division Multiplexing (OFDM) system with multi-layered (ML) transmission is proposed for mobile multimedia networks to support transmission of multiple data streams with flexible Quality-of-Service (QoS) adjustment capability and therefore can accommodate users with different QoS requirements or link conditions. The enhanced layers (ELs), formulated by parallel...
This paper studies QoS-guaranteed fair resource allocation and packet scheduling for OFDMA networks. We start with non-traffic-aware weighted generalized proportional fair (WGPF) scheduler and make it a delay-fair scheduler. Delay-fair objective is to equalize delay dissatisfaction measures among users. In this paper the focus is on mean queuing delay. We show how the WGPF objectives are connected...
In this paper, we propose an improved adaptive receiver in order to overcome the performance degradation problem encountered by the existing conjugate transmission schemes due to a time-varying frequency offset. We apply two different phase rotations on the two receiving paths instead of employing only one common phase rotation for both paths in the previous work. The two phase rotations are chosen...
This paper addresses the problem of resource allocation in a multiple access channel where several mobile terminals (MT's) are transmitting simultaneously to a single receiving base station, all of them with multiple antennas and exploiting beamforming. A multi-carrier modulation is assumed, either orthogonal frequency division multiplexing (OFDM) or filter bank multi-carrier (FBMC). The main advantage...
This paper elaborates on self-organized and distributed interference management for femtocells that share the available radio resources with macrocells. A multi-agent learning approach is examined, based on distributed Q-learning, where femtocell base stations control their transmit power, such that the femtocell capacity is maximized, while the aggregated downlink interference generated at macro...
Distributed Omni Antenna Systems (OASs) have been proposed to increase the capacity of Broadband Wireless Access (BWA) systems. We investigate the extension of such systems by employing distributed Directive Antenna Arrays (DAAs) to support high speed users also employing multiple antenna configurations. The problem of beamforming in a single sector is considered where remote Base Stations (BS's)...
Multiuser MIMO vector perturbation precoding facilitates multiple representations of the transmit symbols in order to improve transmit power normalization. When reference symbols (pilots) are considered, they must remain unperturbed. For conventional dedicated pilot schemes, where reference and data symbols are separated, the pilot vector is effectively linearly precoded, which degrades the performance...
In this paper, we briefly describe four modulation schemes (Orthogonal Frequency Division Multiplexing (OFDM), DFT-spread OFDM, Constant Envelope OFDM (CEOFDM)and Filter Bank Multicarrier (FBMC)) for Cognitive Radios (CR) in white space. In the first part, we give a short overview of the main signal processing blocks and signal properties. Then, we compare them by means of sensitivity to various synchronization...
The energy balancing is one of the main concerns in wireless sensor networks (WSNs). Different from current methods, this paper attempts to solve the unbalanced energy consumption problem in the orthogonal frequency division multiplexing (OFDM) system for a WSN. The objective is to increase the sum throughput with almost equal energy consumption among the sensor nodes. Inspired by this goal, we formulated...
Link adaptation is an important technique in achieving good system spectral efficiency. However, due to the effect of frequency selective fading, the SNRs of adjacent sub-carriers in an OFDMA system can potentially be different. To provide a reasonable signalling overhead, the smallest unit of channel quality feedback is represented in terms of a group of sub-carrier SNRs, or effective SNR for short...
In this paper the joint effects of the inter-cell macrodiversity schemes combined with intra-cell spatial multiplexing are investigated for MIMO-OFDM systems. We compare the SINR and throughput performances of cellular Alamouti, cellular cyclic delay diversity (CDD) schemes and pure macrodiversity at the cell edge. Our simulation results indicate that cellular Alamouti scheme outperforms cellular...
This paper Presents information channel capacity as a fundamental measure of estimating the quality of digital communication channel which is possible with vanishingly small probability of bit error. This work presents that the capacity of a stationary channel with intersymbol interference (ISI) is achievable by both the techniques:1) single carrier modulation with ideal MMSE-DFE receiver and 2)multicarrier...
The problem of sparse channels structured estimation is here addressed in the frame of Orthogonal Frequency Division Multiplexing (OFDM) communications. In our approach, the Channel Impulse Response (CIR), to be estimated, is constrained to fit a beforehand detected structure specifying the nonzero valued taps positions. In this contribution, a newly proposed thresholding based scheme, used for CIR...
In this paper, we investigate the interference caused by Non Linear (NL) power amplifiers together with timing errors for multicarrier OFDM/FBMC transmissions. This kind of interference will be found in Cognitive Radio systems where users are non synchronized. We found that the global interference can be computed by adding the NL effect with the unsynchronized one. Finally, simulation results are...
In orthogonal frequency division multiplexing (OFDM) underwater acoustic (UWA) communications, some subcarriers may be subject to deep fading. If the channel state information (CSI) is available at the transmitter, adaptive transmission techniques can be applied to mitigate the deep fading effect and increase the system's overall performance. Therefore, it is more valuable to analyze the UWA channel...
Next generation cellular mobile communication systems require cell-edge throughput improvement as well as performance improvement of peak throughput and system throughput. Recently, coordinated multi-cell MIMO technologies have been receiving considerable attention due to their cell-edge throughput improvement. Unfortunately, these technologies have difficulty in improving both cell-edge throughput...
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