In this letter, a novel pilot-aided inter-carrier interference (ICI) self-cancellation scheme is proposed for use in orthogonal frequency division multiplexing (OFDM) systems. The proposed scheme maps both modulated data symbols and pre-defined pilot symbols onto non-neighboring sub-carriers with weighting coefficients of +1 and -1. With the aid of pilot symbols, a more accurate estimation of frequency offsets can be obtained, and the ICI self-cancellation demodulation can be operated properly.

A space-time RAKE (ST-RAKE) receiver with a blind interference-blocking (IB) pre-processor, termed as the IB-RAKE receiver, is proposed for spread spectrum communications systems. The design of the proposed architecture consists of three components. A blind IB transformer is first constructed based on the received data, and then applied on the undespread data for the suppression of strong interference. After despreading, optimal beamforming is then performed on the IB despread data to extract the signals of interest (SOIs) from the desired user. Finally, a RAKE receiver with a maximum ratio combining technique is employed to constructively collect all the SOI energies. Since strong interference has been removed in the first stage, the RAKE receiver combines only those SOIs plus negligible interference, leading to robustness against strong interference. Numerical results have shown that substantial improvement can be obtained from the proposed ST-RAKE receiver with the blind IB pre-processing scheme.

This investigation proposes a virtual-FIFO (VFIFO) back-off algorithm for wireless networks. The proposed scheme takes advantage of the central unit (CU) in a wireless network to broadcast a common back-off window size to all the users, significantly alleviating the unfairness of bandwidth utilization in conventional binary exponential back-off (BEB) algorithms. The proposed scheme exploits the CU's capability for collision detection to estimate the number of simultaneously competing users. Additionally, packets generated in a given cycle are split into groups according to their times of arrivals and are guaranteed to be serviced one after another within the next cycle. Although the proposed algorithm is not strictly first come fist served, the FIFO principle is virtually accomplished. Simulation results demonstrate that the standard deviation of delay can be improved by more than two orders and the throughput can be maintained at 0.42 when the number of users approaches infinity. The capture effect even further improves system performance.

One of the major drawbacks of orthogonal frequency division multiplexing (OFDM) systems is their vulnerability to synchronization errors. To remedy the inter-carrier interference (ICI) effect caused by carrier frequency offset (CFO) estimation errors, this paper proposes a weighted linear parallel ICI cancellation (WLPICIC) equalizer. The optimal weights in the WLPICIC scheme are derived in closed-form expressions by maximizing the average signal-to-interference ratio (SIR) at the WLPICIC output of each sub-carrier. The simulation results show that the WLPICIC equalizer significantly improves the performance of OFDM systems with frequency estimation errors in both AWGN channels and frequency selective fading channels.

This paper presents the baseband receiver design and implementation for the ultra-wideband (UWB) wireless personal area networks (WPAN). In particular, the receiver algorithms, which include frame detection, timing/frequency synchronization, and channel estimation, are designed and implemented. Simulation results demonstrate that the receiver has a packet error rate of less than 8% when Eb/N0 = 4.7 dB, link margin = 10.7 dB, and data rate = 200 Mb/s. The proposed design has been designed using 0.13 µm single-poly eight-metal CMOS process. The overall power dissipation is 132 mW at a 132 MHz system clock, while the core area is 5.62 mm2.

This letter examines the problem of allocating the subcarrier power of the relayed signal in orthogonal frequency division multiplexing (OFDM) based dual-hop systems in which the relay terminal is operated in an Amplify-and-Forward (AF) mode and the source node transmits its signal with a uniform power distribution. In AF relaying systems, both the modulation order and the error control scheme are fixed at the relay node, and thus the potential for increasing the data rate via a suitable allocation of the subcarrier power at the relay node does not exist. Therefore, this study proposes an alternative subcarrier power allocation scheme in which the objective is to scale the power assigned to each of the relayed signal sub-carriers in such a way as to minimize the equivalent average noise power at the destination terminal.