This article presents a continuous-time (CT) linear-exponential incremental ADC (IADC) that achieves 15-bit resolution at 250kHz bandwidth with 40 cycles for one conversion. It is based on an energy-efficient CT linear-exponential IADC, which alleviates the requirements of the power-hungry input buffer and loop filter. The proposed IADC employs a coarse 9-bit first-order IADC followed by a fine 8-bit cyclic ADC. The first-order IADC performs the coarse conversion by linearly accumulating input signals, resulting in a small thermal noise penalty. The residual quantization noise is exponentially reduced by the cyclic ADC, significantly shortening the conversion cycle. The cyclic ADC achieves the required accuracy by reconfiguring the loop filter of the coarse IADC and effectively compensating for the excessive loop delay. The prototype CT IADC is fabricated in a 65-nm CMOS process. With a 20MHz clock, it achieves 88.6-dB SNDR, 89.3-dB SNR, 90.1-dB DR, and 103.1-dB SFDR at a conversion rate of 500 kS/s. It consumes only 2.4 mW from a 1.2 V supply. It achieves the Schreier FoM (SNDR) of 168.8dB.

Controllability perception significantly influences motivated behavior and emotion and requires an estimation of one's influence on an environment. Previous studies have shown that an agent can infer controllability by observing contingency between one's own action and outcome if there are no other outcome-relevant agents in an environment. However, if there are multiple agents who can influence the outcome, estimation of one's genuine controllability requires exclusion of other agents' possible influence. Here, we first investigated a computational and neural mechanism of controllability inference in a multi-agent setting. Our novel multi-agent Bayesian controllability inference model showed that other people's action-outcome contingency information is integrated with one's own action-outcome contingency to infer controllability, which can be explained as a Bayesian inference. Model-based functional MRI analyses showed that multi-agent Bayesian controllability inference recruits the temporoparietal junction (TPJ) and striatum. Then, this inferred controllability information was leveraged to increase motivated behavior in the vmPFC. These results generalize the previously known role of the striatum and vmPFC in single-agent controllability to multi-agent controllability, and this generalized role requires the TPJ in addition to the striatum of single-agent controllability to integrate both self- and other-related information. Finally, we identified an innate positive bias toward the self during the multi-agent controllability inference, which facilitated behavioral adaptation under volatile controllability. Furthermore, low positive bias and high negative bias were associated with increased daily feelings of guilt. Our results provide a mechanism of how our sense of controllability fluctuates due to other people in our lives, which might be related to social learned helplessness and depression.

Taking the positions of pico-cell base stations (PBSs) into consideration, a scheme of cell range expansion (CRE) for maximum sum rate is addressed in heterogeneous multi-input multi-output multi-user wireless networks. The optimal CRE bias obtained numerically by the proposed CRE scheme with intercell interference coordination (ICIC) allows us to maximize the sum rate while successfully maintaining the load balance between the macro-cell base station and PBSs. Numerical results confirm that the proposed CRE scheme with ICIC can provide a higher sum rate than conventional schemes while maintaining balanced load.

This paper proposes a novel unambiguous correlation function for sine-phased binary offset carrier (BOC) tracking. Modeling a BOC signal pulse as a sum of multiple rectangular pulses, correlating the multiple rectangular pulses with the received BOC signal, and combining the correlations, we construct an unambiguous correlation function with only a single main-peak. The proposed correlation function is confirmed from numerical results to provide an improved tracking performance over the conventional correlation functions.

This paper presents a comparative study of Schmidl-Cox (SC) and Morelli-Mengali (MM) algorithms for frequency offset estimation in OFDM, along with a new least squares (LS) and a new modified SC algorithm. All algorithms have comparable accuracy approaching asymptotically the Cramer-Rao bound. The complexity of the LS algorithm is between O(N) and O(N log N) operations, where N is the length of the training sequence, while the complexity of the SC algorithm is between O(N log N) and O(N2) operations, and the complexity of the MM algorithm is O(N2) operations. The modified version of the SC algorithm requires only one training sequence as opposed to two required by the original SC algorithm, and significantly reduced O(N log N) complexity. The sensitivity of the three algorithms to quantization of the arg function (the argument of a complex number) is analyzed and quantified. The analysis and simulation results demonstrate that while all considered algorithms can be used with coarse quantization of the arg function, the LS algorithm is least affected and the SC algorithm is most affected by this quantization error.

In this paper, we propose an optical orthogonal code (OOC) acquisition scheme for optical code division multiple access (CDMA) systems. By employing multiple thresholds, the proposed scheme provides a better mean acquisition time (MAT) performance than the conventional scheme. Numerical results demonstrate that the MAT of the proposed scheme is shorter than that of the conventional scheme.

This paper proposes a novel correlation function with no side-peak for synchronization of composite binary offset carrier (CBOC) signals. We first propose novel local signals, and then, propose an unambiguous correlation function by combining the correlations between the received signal and the local signals. Numerical results demonstrate that the proposed correlation function has no side-peak and provides a better power ratio performance than the CBOC autocorrelation.

This paper proposes a novel distance measuring scheme based on repeated PN sequence for ultra wide-band vehicle radar systems. The proposed scheme measures the distance between a vehicle and an obstacle based on repeated use of a single short pseudo random sequence. Simulation results show that the proposed scheme provides a shorter mean distance measuring time while keeping a similar measurement error performance to that of the conventional scheme.

In this paper, a novel pseudo noise (PN) code acquisition scheme based on sequential estimation is proposed, which can not only achieve code acquisition for both inverted and non-inverted PN codes, but also demodulate the spreading data. Simulation results show that the proposed scheme has approximately half the complexity of the conventional scheme while exhibiting a similar mean acquisition time performance to that of the conventional scheme.

This paper proposes a novel two-stage detection scheme based on multiple correlator outputs to enhance the detection performance in ultra-wideband (UWB) signal acquisition. Due to the rich multipath of UWB channels, the signal energy spreads over multiple correlator outputs, which makes each correlator output have only a portion of the signal energy, and thus, degrades the detection performance of the conventional scheme where a single correlator output is used as the decision variable for detection. In the proposed two-stage detection scheme, the decision variable is formed by combining multiple correlator outputs, making it possible to collect the signal energy spread by the multipath. Simulation results show that the proposed scheme can provide a better detection performance over the conventional scheme in various UWB channel environments.

In this paper, we propose a new periodogram-based integer frequency offset (IFO) estimation scheme robust to the fractional frequency offset (FFO) variation. We first observe the reason why the conventional IFO estimation scheme in is sensitive to the variation of the FFO, and then, propose a new IFO estimation scheme using the modified maximum-likelihood (ML) metric. The numerical results demonstrate that the proposed scheme is more robust to the variation of the FFO and has better IFO estimation performance than the conventional scheme in.

In this paper, a low complexity sequential estimation scheme for pseudo noise (PN) code acquisition is proposed, which can not only achieve code acquisition for both inverted and non-inverted PN codes, but also demodulate the spreading data. Numerical results show that the proposed scheme has approximately half the complexity of the conventional scheme while exhibiting a similar mean acquisition time performance to that of the conventional scheme.

This paper addresses a novel Alamouti coding scheme for asynchronous cooperative communication systems over frequency selective fading channels. In the proposed scheme, the Alamouti coded form at the destination node is constructed through a simple combination of symbols at the source node, instead of the time-reversal operation at the relay nodes used in the conventional scheme. Numerical results show that the proposed scheme achieves a higher order cooperative diversity than that of the conventional scheme.

To reduce the influence of interference on the OFDM-based cognitive radio overlaid with narrowband primary users, we consider a scheme called the variable subband nulling (VSN), in which a VSN mode is selected adaptively according to the result of spectrum sensing for the frames following the sensing period. For reliable detection of the VSN mode embedded in the preamble, we consider two types of metrics. The performances of the metrics are analyzed in Gaussian channels with/without narrowband interference (NBI), and are confirmed by simulation results. In fading channels with/without NBI, the detection performance is examined via simulation results. The analysis and simulation results have confirmed that, if the VSN mode is selected appropriately at the transmitter, the proposed metrics provide us with a reliable detection performance even when the NBI is strong.

The conventional ultra-wideband (UWB) synchronization schemes could cause poor performance in receiver operations such as demodulation after the synchronization, since unreliable timing information corresponding to low-power multipath components might be transferred to the next stage. To solve this problem, in this paper, we propose novel synchronization schemes for UWB systems. We first derive an optimal scheme based on the maximum likelihood (ML) criterion and then develop a simpler suboptimal scheme. Simulation results show that both proposed schemes provide a better synchronization performance than the conventional scheme.

This paper proposes two novel schemes for pilot-aided integer frequency offset (IFO) estimation in orthogonal frequency division multiplexing (OFDM)-based digital video broadcasting-terrestrial (DVB-T) systems. The conventional scheme proposed for estimating the IFO uses only partial information of combinations that pilots can provide, which stems from a rigorous assumption that the channel responses of pilots used for estimating the IFO change very rapidly. Thus, in this paper, we propose the novel IFO estimation schemes exploiting additional information of combinations that pilots can provide to improve the performance of the IFO estimation. The simulation results show that the proposed schemes are highly accurate in terms of the IFO detection probability.

This paper deals with the integer frequency offset (IFO) estimation issue for reliable transmission in orthogonal frequency division multiplexing (OFDM)-based digital video broadcasting-terrestrial (DVB-T) systems. To estimate the IFO the conventional scheme uses only partial information of combinations that pilots provide. However, since the conventional scheme exploits a small number of correlations, it does not use sufficient signal energy for the IFO estimation. Thus, in this paper, we propose novel IFO estimation schemes efficiently using the additional correlations between pilots. The simulation results show that the proposed schemes are highly accurate in terms of the IFO detection probability.

This paper proposes a novel asynchronous transmission scheme for cooperative wireless networks using Alamouti coded orthogonal frequency division multiplexing (OFDM) modulation. The proposed scheme obviates the need for the timing synchronization at the relay nodes through a renewal of the cyclic prefix (CP) of the OFDM symbol, and achieves a cooperative diversity gain through some simple complex-valued operations at the relay node. Numerical results demonstrate that the bit error rate (BER) performance of the proposed scheme, unlike that of the conventional scheme, does not degrade even when there exists a timing synchronization error at the relay nodes, and also, that the proposed scheme obtains two times higher cooperative diversity gain compared with that of the conventional scheme at the cost of the symbol transmission rate being reduced by half.

In this paper, a new demapper generating log-likelihood ratio (LLR) is proposed by using a linear approximation for the nonlinear factor of an exact LLR. The exact LLR is sufficient for the probability based decoding, but its calculation requires a large number of computations in the case of high order modulations such as 16 quadrature amplitude modulation (QAM) and 64QAM. To alleviate the computational complexity a piecewise-linear demapper was proposed by neglecting the nonlinear factor of the exact LLR. However, it is observed that the throughput performance of the piecewise-linear demapper in hybrid automatic repeat request (HARQ) system is deficient in low signal-to-noise ratio region. Therefore, the new demapper is proposed which has an equivalent throughput performance to the exact LLR in HARQ system, and at the same time, only needs a few elementary operations for calculating the simplified LLRs. Experimental evidences which show the viability of the proposed demapper are also provided.

Due to multiple side-peaks in the binary offset carrier (BOC) autocorrelation function, BOC signal synchronization is one of the most challenging tasks for global navigation satellite systems (GNSSs) including Galileo and global positioning system (GPS). Recently, a novel correlation function with reduced side-peaks was proposed for BOC signal synchronization by Julien; however, Julien's correlation function still has the side-peaks and can be possible only for sine phased BOC(n, n), where n is the ratio of the pseudo random noise (PRN) code rate to 1.023 MHz. In this paper, we propose a new correlation function for BOC signal synchronization, investigating how multiple side-peaks arise in BOC autocorrelation function. The proposed correlation function does not have any side-peaks and can be generated for any type of BOC signal, sine/cosine phase BOC(n, n), where k is the ratio of a PRN chip duration to the period of a square wave sub-carrier used in BOC modulation. In addition, an efficient correlator structure is presented for generating the proposed correlation function.

Due to its anti-jamming capability, chirp spread spectrum (CSS) technique has attracted much attention in the area of wireless communications. However, there has been little rigorous analysis for the performance of the CSS communication system in the presence of jamming signals. In this paper, we present analytic results on the performance of a CSS system: symbol error rate (SER) expressions are derived for a CSS M-ary phase shift keying (MPSK) system in the presence of broadband and tone jamming signals, respectively. The numerical results show that the empirical SER closely agrees with the analytic result.

We present an OFDM frequency synchronization scheme. The scheme uses periodic OFDM symbols, similar to the algorithms proposed previously by Morelli and Mengali (1999) and Schmidl and Cox (1997). The proposed scheme attains considerably higher accuracy than the scheme by Schmidl and Cox requiring a similar computational load. Compared to the scheme by Morelli and Mengali, the proposed algorithm attains a somewhat inferior accuracy but at a significantly reduced computational complexity, i.e O(N) versus O(N/sup 2/) operations for N-tone OFDM. In addition to that, the scheme proposed here is considerably less sensitive to the accuracy of the involved computations than the other two schemes.

In this letter, we propose a new detector for code acquisition systems in non-Gaussian noise channels. Modeling the acquisition problem as a hypothesis testing problem, a detector is derived for non-Gaussian, symmetric /spl alpha/-stable noise, based on the locally optimum detection technique. Numerical results show that the proposed detector can offer robustness and substantial performance improvement over the conventional schemes in non-Gaussian channels.

We investigate optimal and suboptimal decision rules for parallel code acquisition in chip-asynchronous direct-sequence spread-spectrum (DS/SS) systems. The conventional decision rule for parallel acquisition is to choose the largest correlator output of a receiver. However, such a scheme is optimum only for chip-synchronous models. In this letter, an optimal decision rule is derived based on the maximum-likelihood criterion for chip-asynchronous models. A simpler suboptimal decision rule is also discussed. The performance of the optimum and suboptimum decision rules is compared to that of the conventional decision rule. Numerical results show, that for chip-asynchronous models, both the optimal and suboptimal decision rules outperform the conventional decision rule.