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This paper focuses on the coexistence problem of multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) systems and current radio systems such as IEEE802.11a. Aiming at improving the performance of MB-OFDM UWB, we attempt to avoid interferences from IEEE802.11a systems. The cognitive radio (CR) technology is introduced to detect the distribution of co-channel interferences...
Efficient spectrum sensing ensures cognitive radio users opportunistically use the under-utilized frequency band without causing harmful interference to primary users. However, in practice, owing to the non-zero probability of the missed detection and false alarm of active primary transmission, a certain degree of performance degradation of the primary user is unavoidable. In this paper, we consider...
In this paper, an orthogonal frequency division multiplexing (OFDM) system operating in a fast fading environment modeled by a doubly selective channel (DSC) is considered. The paper first reformulates a commonly adopted system model using the generalized complex exponential basis expansion technique. The resulting model enables the IQ imbalance and DSC to be estimated in the time domain with a small...
Future cognitive radio broadband wireless networks are expected to support a variety of communication services with diverse quality-of-service (QoS) requirements. Multimedia applications such as broadband voice transmission and real-time video streaming are very delay-sensitive and need guaranteed throughput. On the other hand, applications like file transfer and email services are relatively delay...
The low-power and low-cost femtocells can improve indoor coverage and capacity. However, when femtocells are deployed extensively, the serious two-tier interference problem occurs. The method to access the femtocell is the key to manage the interference in the femtocell systems. In this paper, we investigate the impacts of access methods and directional antenna on link reliability and capacity for...
In the MIMO-OFDM system, the carrier frequency offset and phase noise cause loss of orthogonality among subcarriers and leads to intercarrier interference (ICI). This paper considers ICI self-cancellation schemes using space frequency block code (SFBC) in MIMO-OFDM system. In this paper we have analytically derived expression for common phase error (CPE), ICI, carrier to interference (CIR) and BER...
The frequency offset in orthogonal frequency division multiplexing (OFDM) system damages the orthogonality of OFDM sub carriers and cause intercarrier interference (ICI) which in turn quickly reduces the performance of the system. In this paper, the authors have proposed an efficient and new scheme for ICI cancellation that is an improved version of ICI self cancellation technique. Through a detailed...
This paper presents system level downlink performance evaluation results for the TDD based LTE-Advanced networks utilizing some of the most recent technologies for mobile systems. The main enhanced technology components used in the systems include multi-user (MU)-MIMO, intra-site coordinated multipoint (CoMP) transmission and space-time-frequency proportional fair scheduling. Performance comparison...
Uplink scheduling in a multicell OFDMA system is considered. A non-collaborative intercell interference avoidance method is proposed, where base stations shut down certain subcarriers in a probabilistic manner based on the received interference level. Proportional fair scheduling is implemented in order to ensure fairness for cell edge users. A low complexity scheduling algorithm is proposed for this...
A novel coordinated scheduling algorithm for OFDM-based systems in multi-cell scenario is proposed in this paper. The studied algorithm based on the utility function is general for the downlink of networks. The algorithm coordinates the subcarrier assignment over the BS cluster. We first establish the framework for this inter-cell coordinated optimization problem through utility-based method. The...
This paper considers the implementation of a soft-output MMSE detector for packet-based MIMO-OFDM transmission. The paper focuses on channel-matrix preprocessing realized with a QR decomposition which needs to be carried out under tight latency constraints. We discuss how the preprocessing algorithm should be selected to meet the specific requirements of the soft-output MMSE detector. Additionally...
Performance of a single input multiple output (SIMO) orthogonal frequency division multiplexing (OFDM) system is analyzed considering the channel characterized by frequency selective and Rayleigh fading environment with maximal ratio combining (MRC) at the receiver. The analysis includes the effect of inter-carrier interference (ICI) due to frequency offset caused by Doppler frequency shift. The result...
When fast and accurate channel state information (CSI) at the transmitter is available, opportunistic power control (OPC) is an attractive alternative to signal-to-interference-and-noise ratio (SINR) target following approaches, because it maximizes throughput by taking advantage of fast channel variations. On the other hand, in multiple-input multiple-output (MIMO) systems, open loop schemes such...
Offset QAM orthogonal frequency division multiplexing (OFDM/OQAM) is a promising technique for high data rate next generation cellular systems, operating on highly time-frequency dispersive channels. To combat dispersive channel interference, OFDM/OQAM systems allow very well time and frequency localized prototype functions. The good localization of the prototype function results from the separation...
In this paper, we propose a novel algorithm to reduce the out-of-band radiation for the Discrete Fourier Transform (DFT)-based orthogonal frequency division multiplexing (OFDM) cognitive radio (CR) systems. Further, we provide a performance comparison for the proposed and conventional algorithms in terms of power spectral density (PSD), peak to average power ratio (PAPR), and required bandwidth for...
In this paper we analyze the distribution of effective Signal-to-Interference-plus-Noise-Ratio (SINR) in multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) systems with application to 3GPP Long Term Evolution (LTE) Downlink. The asymptotic distribution of effective SINR in case of correlated post-processed SINR is established analytically to obey normal distribution...
The bit error rate performance of orthogonal frequency division multiplexing (OFDM) systems is severely degraded in the presence of phase noise. The effect of phase noise on an OFDM signal has been studied in the literature. The OFDM signal sub-carriers are distorted due to phase noise in two ways. First is the constant phase shift of all the sub-carriers, and second is the inter-carrier interference...
Multiple-input multiple-output (MIMO) communications based on orthogonal frequency division multiplexing (OFDM) are considered for improving the performance and bandwidth utilization of underwater acoustic systems in which cooperation is possible between distributed transmitters. The major challenge in such a framework - and the principal difference from the traditional case where multiple transmitters...
In this paper we propose a blind estimation of fading coefficients without using the pilot symbols in QAM-OFDM systems subjected to carrier frequency offset (CFO), where the phases of the fading coefficients are within ±7r/4. First, under a frequency selective fading channel, the inter-carrier interference (ICI) due to CFO is formulated in the framework of independent component analysis (ICA). Then...
Interference reduces the performance of a correct data signal detection and decoding. This problem becomes severe when interferences exist during the period of channel estimation. This will destroy the accuracy of channel estimation and, will eventually result severe degradation in the performance of signal detection and decoding in the entire data packet/frame. In this article, we propose an improved...
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