Jung-Mao Lin

Optimal Detector for Multitaper Spectrum Estimator in Cognitive Radios

In this paper, the authors propose an optimal detector for the Thomsons multitaper spectral estimation (MTSE) in cognitive radios for spectrum sensing. The MTSE is used for spectral estimation and then the proposed detector can detect primary users and spectrum holes in cognitive radios. The detector is optimized based on the Neyman-Pearson Theorem. The analytical detection performance (probability of detection) of detecting primary users (PUs) and spectrum holes in spectrum sensing is mathematically formulated and verified by simulations. The proposed detector for the MTSE is non-cooperative in spectrum sensing and can perform blind spectrum sensing without prior knowledge of the primary users. Compared to the conventional energy detector, the proposed detector is more reliable and robust for various multiple Slepian tapers. The proposed detector outperforms the cooperative autocorrelation-based detectors in detection rate by 48% and with 3dB gain in SNR performance. Moreover, the minimum required observation size is smaller than the conventional energy detector by a reduction of 73.3%.

A Power Efficient Baseband Engine for Multiuser Mobile MIMO-OFDMA Communications

In this paper, the authors present a configurable and power efficient multiuser MIMO-OFDMA baseband processor for uplink mobile communications. To solve the carrier frequency offset (CFO) problem in multiuser transmission, an inter-carrier interference-based (ICI-cancellation-based) CFO estimator is implemented based on an iterative search criterion of minimum signal-to-interference-noise (SINR) ratio. Compared to the state-of-the-art methods, the proposed CFO estimator is more robust to transmission configurations (MIMO and multiuser) and CFO variations. Moreover, the authors propose an efficient architecture that saves 78% of the hardware complexity compared to the direct implemented architecture by employing Taylor series expansion for ICI/multiple-access interference (MAI) cancellation. Meanwhile, a 2-D linear channel estimator is also proposed to assist the CFO estimator and track the time-variant multipath channel. Two kinds of MIMO detector, vertical Bell Laboratory layered space-time (V-BLAST) and V-BLAST with maximum likelihood (V-ML), are adopted to minimize output latency and achieve the best ML bit-error-rate (BER) performance. An ASIC fabricated by 0.13 μm 1P8M CMOS technology is measured with 2.31 Mbps/mW power efficiency and less than 1.5 dB implementation loss. In addition, the whole transceiver is integrated and verified by a system-on-chip (SoC) platform to demonstrate its efficacy.

A Baseband Transceiver for IEEE 802.16e-2005 MIMO-OFDMA Uplink Communications

In this paper, a 2times2 multiple-input multiple-output- orthogonal frequency division multiple access (MIMO-OFDMA) uplink transceiver based on IEEE 802.16e-2005 standard is proposed. Carrier frequency offset (CFO) and multipath channel impairments are considered. To mitigate the CFO problems in multiuser environment, an inter-carrier-interference- cancellation-based (ICI-cancellation-based) CFO estimator is proposed. The proposed CFO estimator measures energy dispersion of data compensated by ICI cancellation and channel equalization. With measured energy dispersion, correct CFOs can be obtained by running an iterative search. Compared with other designs, the proposed CFO estimator is more robust in transmission conditions and types of subcarrier allocations. Simulation results demonstrate that the proposed transceiver outperforms others in mean-square-error (MSE) and bit-error- rate (BER) performance.

Linear precoding and adaptive multi-taper spectrum detector for cognitive radios

In recent years, cognitive radios are regarded as a valid solution to solve the problem of inefficient spectrum utilization. A cognitive radio system which has the ability of spectrum sensing and transmission adjustment is proposed in this paper. An optimal detector applied for Thomsons adaptive multitaper spectrum estimation (AMTSE) is presented. The detector is based on Neyman-Pearson Theorem and it can adjust the detection threshold according to the environment change. The simulation shows that the detection rate can outperform energy detection by 40%. On the other hand, adjusting the transmission parameter is required after spectrum sensing. By knowing the interference channel, block diagonalization is applied for canceling the interference when primary user exists. If the primary user is idle, the secondary users Tx may can estimate the channel state information (CSI) due to the channel reciprocity. So the extra antennas can be used to antenna selection to improve the secondary users BER performance. Further, the AMTSE spectral detector is implemented by ASIC and the power consumption of this detector is 30.9 mW at 122 MHz. The core area is 1057 × 1057 jm2 and total chip area is 1557 × 1557 μm2.

A Baseband Transceiver for IEEE 802.16 OFDMA Downlink Communications

A baseband transceiver for IEEE 802.16-2004 OFDMA downlink is proposed. The proposed receiver consists of carrier frequency offset (CFO)/sampling frequency offset (SFO) estimation/compensation, channel estimation/equalization, and sample add/drop function for symbol timing synchronization. A 5.8 GHz center frequency with 10 MHz channel bandwidth is chosen. Both first/second order statistics of preamble and pilot energy detection result in low complexity but accurate enough integer CFO estimations. Residual CFO (RCFO) and SFO estimation is based on least-square (LS) algorithm with moving average on successive symbol phase tracking in frequency domain to reduce noise. The performance of the proposed receiver approaches the ideal one under the simulation scenario of Stanford University Interim (SUI) channel model 4.

A Reliable Adaptive Multitaper Spectral Detector in Wideband Strong Interference Environments

Dramatic increase in demand for spectrum access opportunities has triggered a deficiency of conventional single frequency band sensing. Moreover, methods needing large amounts of observations are also inefficient. This has motivated the proposition of an adaptive multitaper spectral detector (AMTSD) for wideband sensing based on Locally Most Powerful Test (LMPT). By taking advantage of multitaper gains, the proposed detector provides a higher degree of freedom (DoF) for the improvement of detection performance. Besides, the detector performs two phase sensing with adjustable spectral-resolution. This makes the system robust to strong interference environments and compatible with wideband spectrum sensing applications. Numerical simulations show that the proposed detector outperforms the cooperative autocorrelation-based and energy detectors in single band sensing by more than 30% in detection performance under SNR=0 dB and P_{FA}=10^{-3}. Moreover, by the provided detector, weak PU (-5 dB) detection can be achieved with multitaper gains even with adjacent strong interference (30 dB).

Live demonstration: A baseband testbed for uplink mobile MIMO WiMAX communications

Recently, orthogonal frequency division multiple access (OFDMA) systems gain more and more attention because OFDMA systems provide higher data rate, better spectrum efficiency and more flexibility in managing channel bandwidth than other systems. This paper describes the implementation of a multi-input multi-output (MIMO)-OFDMA uplink baseband receiver for 802.16e standard in system-on-chip (SoC) platform. As SoC design methodology becomes commonplace and design complexity continues to increase, designers are faced with the daunting task of meeting escalating design requirements in shrinking time-to-market windows. For solving this problem, design reuse emerged as a possible approach to boost design productivity, and intellectual property (IP)-based design methodology has begun since the 1990s. The development of rapid prototyping testbeds with the SoC design methodology has given communication systems engineers the ability to implement and test their designs on real hardware in concert with the simulation stages.