Robust frequency offset estimation for pilot symbol assisted packetCDMA with MIMO antenna systems

We propose frequency offset estimation and combining techniques for pilot symbol assisted (PSA) packet downlink code-division multiple access (CDMA) with multiple-input and multiple-output (MIMO) antenna systems. Orthogonal Walsh codes are used for dedicated pilot symbols at the transmit antennas. The discrete Fourier transform (DFT)-based frequency offset estimation is used for simple implementation. In addition, simple interpolation is also used for resolution improvement of the DFT. When identical frequency offset is assumed, the frequency offset estimates for each single-input single-output (SISO) sub-stream (i.e., transmit/receive antenna pair) can be combined at the receiver. Simulation results show that the estimation and combining techniques proposed deliver improvement in the frequency offset estimation performance     

Acoustic damping characterization of a double-perforated liner in an aero-engine combustor

Journal of Mechanical Science and Technology - Double-perforated liners are widely used in gas turbine combustors because of their improved thermal load characteristics and broader acoustic damping...     

Performance analysis for multistage interference cancellers in asynchronous DS-CDMA systems

The authors propose an accurate analytical method for an asynchronous direct-sequence code-division multiple-access system using a multistage interference cancellation technique. In this analysis, the RAKE receiver is considered over uplink fading channels. Monte Carlo simulations show that the proposed analysis agrees more closely with simulation results than previous analyzes.     

Thread‐Like CMOS Logic Circuits Enabled by Reel‐Processed Single‐Walled Carbon Nanotube Transistors via Selective Doping

The realization of large‐area electronics with full integration of 1D thread‐like devices may open up a new era for ultraflexible and human adaptable electronic systems because of their potential advantages in demonstrating scalable complex circuitry by a simply integrated weaving technology. More importantly, the thread‐like fiber electronic devices can be achieved using a simple reel‐to‐reel process, which is strongly required for low‐cost and scalable manufacturing technology. Here, high‐performance reel‐processed complementary metal‐oxide‐semiconductor (CMOS) integrated circuits are reported on 1D fiber substrates by using selectively chemical‐doped single‐walled carbon nanotube (SWCNT) transistors. With the introduction of selective n‐type doping and a nonrelief photochemical patterning process, p‐ and n‐type SWCNT transistors are successfully implemented on cylindrical fiber substrates under air ambient, enabling high‐performance and reliable thread‐like CMOS inverter circuits. In addition, it is noteworthy that the optimized reel‐coating process can facilitate improvement in the arrangement of SWCNTs, building uniformly well‐aligned SWCNT channels, and enhancement of the electrical performance of the devices. The p‐ and n‐type SWCNT transistors exhibit field‐effect mobility of 4.03 and 2.15 cm² V^?1 s^?1, respectively, with relatively narrow distribution. Moreover, the SWCNT CMOS inverter circuits demonstrate a gain of 6.76 and relatively good dynamic operation at a supply voltage of 5.0 V.     

Effect of multiple antennas at the source on outage probability for amplify-and-forward relaying systems

The amplify-and-forward (AF) relaying system considered here consists of a source node with M transmit antennas, and relay and destination nodes with a single antenna each. The closed-form expressions for the outage probabilities for maximum-ratio-transmission (MRT) at the source are presented for some specific values of M. Numerical results show that increasing M from 1 to 2 can achieve roughly a 3dB SNR gain, guaranteeing the same outage probability. However, we discover that for M ≥ 3, the additional gain compared to M = 2 decreases quickly as the SNR increases. Therefore, increasing M above 3 does not achieve significantly greater gain over M = 2 at high SNR.     

A New Multistage Whitener-Based Detector for MIMO Systems

We propose a new multistage whitener-based detector (MWD) to guarantee low complexity and high performance for multiple-input multiple-output systems. The proposed MWD reduces complexity by detecting two out of N _T transmitted symbols in each stage of the whitening process. Furthermore, it can enhance performance by adopting a norm-based selection criterion that considers the instantaneous channel state and interference cancellation using C ⁱ local solutions at the i-th stage of the whitening process. Accordingly, the proposed MWD can achieve the optimum maximum likelihood detector (MLD) while having a considerably reduced computational complexity compared with the optimal MLD.     

Cooperative diversity performance for OFDM transmission over partially jammed channels

Cooperative diversity is a transmission technique, where multiple terminals share their resources to form a virtual antenna array that realizes spatial diversity gain in a distributed fashion. In this paper, we focus on a performance evaluation for orthogonal frequency division multiplexing (OFDM) transmission in cooperative networks under partial-band jamming (PBJ) environments. We present a bit error rate (BER) analysis for a cooperative diversity system with amplifying-and-forward (AF) relays over partially jammed Rayleigh fading channels. In addition, a simple jamming mitigation technique, called relay-based sub-band shifting method, is proposed. Through this approach, each sub-band of the amplified OFDM symbol at the relay can be changed by the predefined shifting rule of each relay, and the jamming effects at the destination are partially removed. Simulation results show that the proposed method improves significantly the BER performance at a low signal-to-jamming ratio.     

Average SNR and Ergodic Capacity Analysis for Opportunistic DF Relaying with Outage over Rayleigh Fading Channels

In the paper, we deal with a single-selection opportunistic relaying with the decode-and-forward (DF) protocol over Rayleigh fading channels. The exact end-to-end average signalto- noise ratios (SNR) and ergodic capacities of both proactive and reactive opportunistic relaying are derived as a closed-form for arbitrary link SNR. In addition, the effective ergodic capacity satisfying the minimum required data rate without outage is also identified for both relaying schemes. The analysis results are used to demonstrate which relaying scheme outperforms the other for given system parameters.     

Forced and self-excited oscillations in a natural gas fired lean premixed combustor

An experimental study of the flame response in a premixed gas turbine combustor has been conducted at room temperature and under atmospheric pressure inlet conditions using natural gas. The fuel is premixed with the air upstream of a choked inlet to avoid equivalence ratio fluctuations. Therefore the observed flame response is only the result of the imposed velocity fluctuations, which are produced using a variable-speed siren. Also, a variable length combustor is designed for investigating characteristics of self-excited instabilities. Measurements are made of the velocity fluctuation in the mixing section using hot wire anemometry and of the heat release fluctuation in the combustor using chemiluminescence emission. The results are analyzed to determine the phase and gain of the flame transfer function.The results show that the gain of flame transfer function is closely associated both with inlet flow forcing conditions such as frequency and amplitude of modulation as well as the operating conditions such as equivalence ratio. In order to predict the operating conditions where the combustor goes stable or unstable at given combustor and nozzle designs, time-lag analysis was tried using convection time delay measured from the phase information of the transfer function. The model prediction was in very good agreement with the self-excited instability measurement. However, spatial heat release distribution became more significant in long flames than in short flames and also had an important influence on the system damping procedure.     

Pilot to data channel power allocation for PCA-DS/CDMA withinterference canceler

The purpose of this letter is to examine channel power assignment for multiuser direct sequence/code division multiple access (DS/CDMA) uplinks. The channels under consideration are pilot channels and data channels. A multiuser detector is also included. The pilot channel estimates are used for multiple access interference (MAI) regeneration, as well as for data channel detection. Simulation results allowed us to pinpoint optimum pilot-to-data channel power ratios (PDRs) for the best bit error rate (BER) performance. In addition, the optimum PDRs of the receivers with the multiuser detector are high compared with those of conventional receivers without the multiuser detector. This study may prove helpful in the effort to optimize the channel power assignment for channel estimation and coherent detection of systems with the multiuser detector