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The existing transmit diversity schemes for time domain synchronous OFDM (TDS-OFDM) is only suitable either for fast time-varying but weakly frequency-selective channels, or strongly frequency-selective but slow fading channels. In this paper, the space-time shifted constant amplitude zero autocorrelation (CAZAC) sequence based TDS-OFDM transmit diversity scheme is proposed for doubly selective channels...
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...
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...
To reduce the cost and complexity of receiver without losing much diversity gain, we propose an antenna selection scheme for MIMO systems employing non-constant envelope mapping. By detection of the received signal and a simplified process without any knowledge of channel statement information, this scheme can approach the ideal selection strategy. Single carrier system and STC-OFDM (space-time-code...
We consider multi-hop decode-and-forward relaying OFDM systems in this paper. All the relay nodes are assumed to be regenerative and working in half-duplex mode. We propose adaptive power allocation (PA) algorithms to maximize the overall system capacity and minimize the system outage probability, respectively. Simulation results show that the proposed algorithms outperform the existing PA algorithms...
Energy efficiency is increasingly important for wireless cellular systems due to the limited battery resources of mobile clients. While modern cellular standards emphasize low client battery consumption, existing techniques do not explicitly focus on reducing power that is consumed when a client is actively communicating with the network. Based on high data rate demands of modern multimedia applications,...
Performances and capacity of MIMO-OFDM systems are enhanced with adaptive MIMO techniques such as Demmel condition number based switching algorithm. In this paper we show that the complexity of this algorithm can be reduced by using the 2-norm condition number of the channel matrix as the selection metric. Simulation results show that using this selection criterion, the switching algorithm offers...
One major Disadvantage of OFDM is the high peak-to-average Power ratios (PAPR). There is a procedure for Selected Mapping (SLM) is PAPR reduction techniques for Orthogonal Frequency Division Multiplexing (OFDM). But these reduction techniques produce high computation complexity which is costly and time consuming. In this paper we proposed a scheme to reduce the computational complexity of SLM technique...
In this paper we present two strategy to maximize user's throughput in Cooperative MU-OFDM network while considering fairness of users. Our strategy is proposed to improve throughput and fairness of users only with limited feedback. With perfect instantaneous channel state information(CSI) at receiver, the resource allocating strategy not only decided in base station, but also decided in users of...
In this paper, an area-efficient FFT processor is proposed for IEEE 802.16m mobile WiMAX systems. The proposed scalable FFT processor can support the variable length of 512, 1024, 2048 and 4096. By reducing the required number of non-trivial multipliers with mixed-radix (MR) and multi-path delay commutator (MDC) architecture, the complexity of the proposed FFT processor is dramatically decreased without...
In this paper, a new low-complexity partial transmit sequence (PTS) scheme is proposed, which generates alternative signal sequences by adding mapping signal sequences of each subblock to each signal subsequence. The proposed scheme considerably reduces the computational complexity without sacrificing BER and PAPR reduction performance, especially for the OFDM system with quadrature amplitude modulation...
Linear constellation precoded orthogonal frequency division multiplexing (LCP-OFDM) requires a maximum likelihood (ML) decoder to fully collect multipath diversity gain. However, the complexity of ML increases exponentially with the channel memory, signal constellation size, and the number of transmit/ receive antennas. Therefore, linear equalizers are highly desirable. This paper mainly analyzes...
The use of decision directed (DD) channel estimation in a MIMO-OFDM downlink receiver with a LTE pilot structure is studied in this paper. The space-alternating generalized expectation-maximization (SAGE) algorithm is used to improve the receiver performance from the one obtained by using the pilot symbol based least-squares (LS) channel estimator. The DD channel estimation improves the performance...
A novel cell search scheme based on coherent sequence detection and sign decision is proposed in this paper. The given structure of the SCH (synchronization channel) allows the UE (user equipment) to detect cell ID with low complexity, and the adverse effects of the channel fading and frequency offset are eliminated in the three search steps. The performance of the scheme is investigated in various...
Employing OFDMA and scalable bandwidth scheme in Long Term Evolution (LTE) downlink access impact on increasing complexity in frequency domain physical layer identity detection. Therefore, in this paper, we propose time domain detection instead of frequency domain using finite impulse response (FIR) filter and partial cross-correlation. Moreover, we implement RAM based architecture instead of multipliers...
In the frame of block pilot channel estimation, an ameliorated version of the Least Squares (LS) algorithm is here proposed for OFDM systems. Former studies use the fact that the cyclic prefix (CP) duration upper bounds the length of the channel impulse response (CIR) to cancel the estimation noise lying outside the CIR first taps, equal in number to the CP samples. However, if the channel is sparse,...
When the cyclic prefix is less than channel memory or under clipping noise in Orthogonal Frequency Division Multiplexing (OFDM) detection, a good Bit Error Rate (BER) performance is achieved using the Maximum Likelihood Block Detector (MLBD). However, the computational load at the receiver is high under this condition. It is well known that conventional GA based approach offers less computation for...
High Peak to Average Power Ratio (PAPR) is a critical issue in multi-carrier communication systems using Orthogonal Frequency Division Multiplexing (OFDM), as Second Generation Terrestrial Digital Video Broadcasting (DVB-T2) system. This problem can result in large performance degradation due to the non-linearity of the High Power Amplifier (HPA) or in its low power efficiency. In this paper, we evaluate...
In this paper we study the performance and complexity tradeoff of filtered multitone modulation (FMT) in statistically representative indoor radio channels. We consider two design approaches. The first one is based on the use of long prototype pulses with high sub-channel frequency confinement. The second one follows an orthogonal design with minimal length pulses (down to the length of one transmitted...
This paper considers the use of precoding in MIMO-OFDM systems based on deterministic channel state information at the transmitter (CSIT). The proposed technique combats subcarrier fading using a linear spreading of the source information in the spatial and frequency domains. Unlike previous works, it is assumed that the receiver does not necessarily has to rely on linear processing, allowing in this...
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