Error rate analysis of differentially encoded and detected 16APSKunder Rician fading

Mobile radio systems require highly bandwidth efficient digital modulation schemes because of the limited resources of the available radio spectrum. A theoretical analysis of bit error rate (BER) is presented for the differential detection of differentially encoded 16-level amplitude/phase shift keying (16DAPSK) under Rician fading in the presence of Rayleigh faded co-channel interference (CCI) and additive white Gaussian noise (AWGN). Differential detection comprises eight-level differential phase detection (DPD) and two-level amplitude ratio detection (ARD). Exact expressions for probability distributions of differential phase noise and amplitude ratio are derived for the BER calculation. The calculated BER performance of 16DAPSK is presented for various values of Rician fading K factor, Doppler spread of diffused component, and Doppler shift of the specular component, and is compared with that of 4-16DPSK. It is shown that 16DAPSK is superior to 16DPSK and requires 1.7 (1.6) dB less E_b/N₀ (SIR) at BER=10^-3 in Rician channels with K=5 dB     

Pilot symbol-assisted coherent multistage interference cancellerusing recursive channel estimation for DS-CDMA mobile radio

A pilot symbol-assisted coherent multistage interference canceller using recursive channel estimation is proposed for DS-CDMA mobile radio cellular system. Since the channel variation caused by fading is recursively estimated at each interference cancelling stage, the accuracy of channel estimation is improved successively. Computer simulation results show that the required E_b/N₀ at the average BER of 3×10^-2 is improved by ~3.5 dB compared to the matched filter receiver for 10 users and two paths with equal power, and where f_dT=10^-3 (f_d: fading maximum Doppler frequency, T: data symbol duration)     

An implementation of a CMA adaptive array for high speed GMSKtransmission in mobile communications

The hardware implementation of an adaptive array as a technique for compensating multipath fading in mobile communications is described. The number of the antenna elements is four. The target communication system is modulated by 256 kbps Gaussian-filtered minimum shift keying (MSK) and has a time-division multiplexing (TDM) architecture with 24 time slots. Based on the digital beamforming concept, all of the signals and the array weights are digital-signal processed. The constant modulus algorithm (CMA) is employed for weight optimizing. In an additive white Gaussian noise channel, this system has 5.6-dB gain in an energy-per-bit-to-noise-density ratio at a bit error rate (BER) of 1.0×10^-3, compared with a single antenna system. The result of the basic field test shows that the gain at a BER of 1.0×10^-3 reaches 22.3 dB in a nonselective, slow Rayleigh fading channel given a 5 Hz maximum Doppler shift     

BER performance of CMA adaptive array for high-speed GMSK mobilecommunication-a description of measurements in central Tokyo

This paper describes the performance of an adaptive array as a countermeasure to multipath fading for a 256 kbps Gaussian-filtered minimum shift keying (GMSK) mobile communication system operating in the 1.5 GHz band. An adaptive array having four antenna elements is implemented using the digital beam forming concept. The constant modulus algorithm (CMA) is employed for the adaptation process to ease the implementation. Measurements in central Tokyo of the bit error rate (BER) performance and an array pattern arising in the multipath environment are presented. Analysis of the array pattern confirms that the array succeeds in directing nulls to the delayed signals. BER performance shows an improvement in E_b/N₀, compared with that of a single antenna system, of 17.5 to 22 dB at a BER of 1.0×10^-2 in a frequency-selective fading channel     

Bit error rate analysis of reduced-state Viterbi differentialdetection of M-ary DPSK signals

A tight upper bound or bit error rate (BER) is derived for approximate maximum likelihood differential detection (DD) implemented by the reduced state Viterbi algorithm (VA) known as RSVDD. The BER performance of RSVDD is compared with Viterbi DD (VDD) for M-ary DPSK in additive white Gaussian noise (AWGN) channels     

Impact of laser phase noise on the performance of a {3×3}phase and polarization diversity optical homodyne DPSK receiver

An analysis of the impact of laser phase noise on the performance of a {3×3} phase- and polarization-diversity differential phase-shift keying (DPSK) receiver is done for the phase and shot-noise limited case. The results show that, for zero laser linewidths, the maximal signal power penalty of the {3×3} phase- and polarization-diversity DPSK receiver with respect to the conventional heterodyne DPSK receiver is approximately 0.7 dB for P_e =10^-9. For nonzero laser linewidths, it appears that, depending on the laser linewidth, for large signal-to-noise ratios the performance of the analyzed {3×3} phase- and polarization-diversity DPSK receiver is close to that of the ideal conventional heterodyne DPSK receiver. For a rectangular intermediate-frequency filter, the maximum allowable normalized laser linewidth (Δυ×T) for the (3×3) phase and polarization diversity DPSK receiver is found to be approximately 0.46% for a power penalty of 1 dB     

Interference cancelling equalizer (ICE) for mobile radiocommunication

This paper proposes an adaptive interference cancelling equalizer (ICE), which not only equalizes intersymbol interference (ISI), but also cancels cochannel interference (CCI) in the received signal in Rayleigh-fading environments, ICE is an adaptive multiuser detector for the frequency-selective fading environment commonly experienced by mobile communication channels. ICE employs a novel detection scheme: recursive least-squares maximum-likelihood sequence estimation (RLS-MLSE), which simultaneously estimates time-varying channel parameters and transmitted signal sequences. Diversity reception is used to enhance the signal detection performance of ICE. A computer simulation of a 40-kb/s QPSK time-division multiple-access (TDMA) cellular mobile radio system demonstrates the possibility of improving system capacity with ICE. Simulations of ICE with and without diversity are carried out under various fading conditions. For the maximum Doppler frequency of 40 Hz, ICE can attain an average bit-error rate (BER) of 10 ^-2 under a single CCI carrier-to-interference ratio (CIR) of ~14 dB. Moreover, ICE for two independent CCI signals can attain the average BER of 1.5×10^-2 with average CIR⩾-10 dB     

On multilevel codes and iterative multistage decoding

This paper develops an approach to iterative multistage decoding of multilevel codes. This involves passing reliability information to previous and subsequent decoders instead of only hard decisions to subsequent decoders. The paper also develops an adaptive version of the suboptimal soft output decoding algorithm of Picart and Pyndiah (1996). This adaptive algorithm provides a gain of approximately 0.24 dB at a bit error rate (BER) of 10^-5 after four iterations and approximately 0.43 dB after ten iterations over the algorithm of Picart et al. If the adaptive algorithm is used in conjunction with iterative multistage decoding then a gain of approximately 0.62 dB is obtained at a BER of 10^-5 after four iterations and approximately 0.9 dB after ten iterations over the algorithm of Picart et al     

Emission cross sections and spectroscopy of Ho3+ laserchannels in KGd(WO4)2 single crystal

The spectroscopic properties of Ho³⁺ laser channels in KGd(WO₄)₂ crystals have been investigated using optical absorption, photoluminescence, and lifetime measurements. The radiative lifetimes of Ho³⁺ have been calculated through a Judd-Ofelt (JO) formalism using 300-K optical absorption results. The JO parameters obtained were Ω₂=15.35×10^-20 cm², Ω ₄=3.79×10^-20 cm², Ω₆ =1.69×10^-20 cm². The 7-300-K lifetimes obtained in diluted (8·10¹⁸ cm^-3) KGW:0.1% Ho samples are: τ(⁵F₃)≈0.9 μs, τ( ⁵S₂)=19-3.6 μs, and τ(⁵F₅ )≈1.1 μs. For Ho concentrations below 1.5×10²⁰ cm^-3, multiphonon emission is the main source of non radiative losses, and the temperature independent multiphonon probability in KGW is found to follow the energy gap law τ_ph ^-1(0)=βexp(-αΔE), where β=1.4×10^-7 s^-1, and α=1.4×10³ cm. Above this holmium concentration, energy transfer between Ho impurities also contributes to the losses. The spectral distributions of the Ho³⁺ emission cross section σ_EM for several laser channels are calculated in σ- and π-polarized configurations. The peak a σ_EM values achieved for transitions to the ⁵I₈ level are ≈2×10^-20 cm² in the σ-polarized configuration, and three main lasing peaks at 2.02, 2.05, and 2.07 μm are envisaged inside the ⁵I₇→⁵I₈ channel     

DS-CDMA RAKE receiver with time-window control loop (TWCL) inmultipath fading environment

This paper presents a code synchronization scheme-the time-window control loop (TWCL)-for postdetection RAKE receiver systems that offers the path-diversity effect. Laboratory test results from a postdetection RAKE receiver system with TWCL under a frequency-selective fading environment are introduced. RAKE combining methods, a simple integral demodulation method within a time window, and a recursive least squares (RLS) demodulation method within the time window that uses the RLS algorithm to realize maximal ratio combining, are investigated. It is found that TWCL performance with delay paths (double-spike frequency-selective Rayleigh-fading model) surpasses the performance of both acquisition and tracking without delay paths (nonfrequency-selective Rayleigh-fading model) because of the path-diversity effect. The laboratory results show that TWCL provides good acquisition and tracking performance under the fading conditions experienced with maximum Doppler frequencies of 5 or 80 Hz. It is also shown that the signal energy per bit to noise-power spectral-density ratio (E_b/N₀) required to achieve the bit error rate (BER) of 10^-3 under the double-spike frequency-selective Rayleigh-fading model is reduced by 10 dB compared to the nonfrequency-selective Rayleigh-fading model. The difference in path-diversity effect between the two RAKE combining methods is only 1 dB. From a structural viewpoint, the simple integral demodulation method supports miniaturization and high-speed data-transmission     

Iterative Viterbi decoding, trellis shaping, and multilevelstructure for high-rate parity-concatenated TCM

We define and apply a new algorithm called the iterative Viterbi decoding algorithm (IVA) to decode a high-rate parity-concatenated TCM system in which a trellis code is used as the inner code and a simple parity-check code is used as the outer code. With trellis shaping, the IVA can achieve a performance 1.25 dB away from the Shannon limit at a BER of 3×10^-5 with low complexity. By augmenting the system with a binary BCH code, the error floor can be reduced to 10^-9 with very little additional cost     

Reduced state transition Viterbi differential detection of M-aryDPSK signals

A reduced state transition Viterbi differential detection (RST VDD) consisting of conventional one symbol DD (1DD) and 3^L-1 state VDD is proposed for the reception of M-ary differential phase shift keying (MDPSK) signals, where L+1 is the observation time length in symbols. The proposed RST VDD has a significantly lower degree of computational complexity compared with the M^L-1 state VDD. The bit error rate (BER) performance of 8DPSK in additive white Gaussian noise (AWGN) channels is evaluated by computer simulation     

The error performance of CD900-like cellular mobile radio systems

The symbol error performance of CD900-like digital cellular mobile radio systems over narrowband and urban wideband transmission channels was investigated. The basic performance is presented for Gaussian, flat-fading Rayleigh, and log-normal channels in the presence of selection and ratio combining space diversity schemes. For wideband channels having more than one resolvable fading path, a CD900-like system without diversity reception suffers from large residual symbol error probabilities P_R(≈10^-1). The introduction of adaptive correlation diversity (ACD) mitigates the effects of multipath, yielding a P_R of 6×10^-5. Although this P_R value is relatively low, the probability of symbol error (P_e) versus signal-to-noise ratio (SNR) is significantly poorer than for the Gaussian channel. By combining the ACD scheme with space diversity, the P_R is eliminated by P_e >10^-5, and the channel SNR is within 5 dB of the Gaussian channel performance when P_e is 10^-10     

CD3-OFDM: a novel demodulation scheme for fixed and mobilereceivers

This paper describes a novel channel estimation scheme identified as coded decision directed demodulation (CD3) for coherent demodulation of orthogonal frequency division multiplex (OFDM) signals making use of any constellation format [e.g., quaternary phase shift keying (QPSK), 16-quadrature amplitude modulation (QAM), 64-QAM]. The structure of the CD3-OFDM demodulator is described, based on a new channel estimation loop exploiting the error correction capability of a forward error correction (FEC) decoder and frequency and time domain filtering to mitigate the effects of noise and residual errors. In contrast to the conventional coherent OFDM demodulation schemes, CD3-OFDM does not require the transmission of a comb of pilot tones for channel estimation and equalization, therefore yielding a significant improvement in spectrum efficiency (typically between 5-15%). The performance of the system with QPSK modulation is analyzed by computer simulations, on additive white Gaussian noise (AWGN) and frequency selective channels, under static and mobile reception conditions. For convolutional coding rate 1/2, the results indicate that CD3-OFDM allows one to achieve a very fast adaptation to the channel characteristics in a mobile environment (maximum tolerable Doppler shift of about 80 Hz for an OFDM symbol duration of 1 ms, as differential demodulation) and an E_b /N₀ performance similar to coherent demodulation (e.g., E_b/N₀=4.3 dB at bit-error rate (BER)=2·10 ^-4 on the AWGN channel). Therefore, CD3-OFDM can be suitable for digital sound and television broadcasting services over selective radio channels, addressed to fixed and vehicular receivers     

Adaptive frequency-domain equalization and diversity combining forbroadband wireless communications

We introduce a new kind of adaptive equalizer that operates in the spatial-frequency domain and uses either least mean square (LMS) or recursive least squares (RLS) adaptive processing. We simulate the equalizer's performance in an 8-Mb/s quaternary phase-shift keying (QPSK) link over a frequency-selective Rayleigh fading multipath channel with ~3 μs RMS delay spread, corresponding to 60 symbols of dispersion. With the RLS algorithm and two diversity branches, our results show rapid convergence and channel tracking for a range of mobile speeds (up to ~100 mi/h). With a mobile speed of 40 mi/h, for example, the equalizer achieves an average bit error rate (BER) of 10 ^-4 at a signal-to-noise ratio (SNR) of 15 dB, falling short of optimum linear receiver performance by about 4 dB. Moreover, it requires only ~50 complex operations per detected bit, i.e., ~400 M operations per second, which is close to achievable with state-of-the-art digital signal processing technology. An equivalent time-domain equalizer, if it converged at all, would require orders-of-magnitude more processing     

Analysis and design of an integrated silicon ARROW Mach-Zehndermicromechanical interferometer

An analysis and design procedure for an integrated silicon micromechanical (pressure sensitive) interferometer is presented. Optimized layer thicknesses of an SiO₂/Si₃N₄ /SiO₂/Si ARROW yield an attenuation of only 2.7×10^-3 dB/cm. Lateral confinement is accomplished with a rib in the core layer. Sensitivity to mechanical measurands is achieved by having the sensing arm of the interferometer on a thin silicon diaphragm, realized by micromachining a cavity from the back of the wafer. An applied pressure P deflects the diaphragm, causing a change in optical path length, leading to a phase shift φ with respect to the reference arm. Sensitivity is increased by thinning the diaphragm, although this increases the resonant attenuation envelope of the diaphragm. Sensitivity calculations based on a simple, first-order model of diaphragm deflection yield (∂φ)/(φ∂P)=1.29×10^-14 P for a specific diaphragm geometry. BPM simulations show that curvature losses due to the bending of the ARROW under deflection is negligible     

Minimum bit rate of DPSK transmission for semiconductor laser with a long external cavity and strong linewidth reduction

A numerical model for a laser diode, weakly coupled to an external cavity, is presented. Using this model, the actual frequency noise spectrum is considered rather than a white frequency noise for estimating the minimum bit rate in a differential-phase-shift-keying (DPSK)-system. Despite possible linewidth reductions by up to 200 with long external cavities, the minimum bit rate (BER = 10^-9) remains nearly unchanged. However, a longer laser cavity (approx600 mum) connected to an external cavity of moderate length ( ≈10 cm) yields a significant reduction of the minimum bit rate (BER = 10^-9) for DPSK-systems at low feedback levels. If more stringent criteria are applied (e.g., receiver penalty < 1 dB) the minimum bit rate remains high also for longer laser cavities.     

All polarisation maintaining fibre DPSK transmission systemexperiment

An all polarisation maintaining (PM) fibre heterodyne 1.4 Gbit/s DPSK system experiment is demonstrated. Good and stable polarisation extinction ratio (>20 dB) is achieved while using low loss keyed connectors between the various optical components. A bit error rate (BER) lower than 10^-9 is measured for both short (10 m) and long (2.6 km) AT&T PM fibres     

Low-resistance bandgap-engineeredW/Si1-xGex/Si contacts

Bandgap-engineered W/Si_1-xGe_x/Si junctions (p⁺ and n⁺) with ultra-low contact resistivity and low leakage have been fabricated and characterized. The junctions are formed via outdiffusion from a selectively deposited Si_0.7Ge _0.3 layer which is implanted and annealed using RTA. The Si _1-xGe_x layer can then be selectively thinned using NH₄OH/H₂O₂/H₂O at 75°C with little change in characteristics or left as-deposited. Leakage currents were better than 1.6×10^-9 A/cm² (areal), 7.45×10^-12 A/cm (peripheral) for p⁺/n and 3.5×10^-10 A/cm² (peripheral) for n⁺/p. W contacts were formed using selective LPCVD on Si_1-xGe_x. A specific contact resistivity of better than 3.2×10^-8 Ω cm² for p ⁺/n and 2.2×10^-8 Ω cm² for n⁺/p is demonstrated-an order of magnitude n⁺ better than current TiSi₂ technology. W/Si_1-xGe _x/Si junctions show great potential for ULSI applications     

一种基于位反转置换的系统极化码的缩短方法

极化码作为 3GPP 标准制定中的一种信道编码技术方案,具有良好的纠错性能。为了进一步提高删余极化码的误码率性能,将极化码中基于位反转置换的缩短算法应用到系统极化码,提出一种系统极化码的缩短方法。仿真结果表明,在AWGN信道中,在高码率条件下,建议的系统极化码的缩短方法的误码率性能优于系统极化码的准均匀凿孔方法,也优于极化码的缩短方法。当码率为3/4、误码率为10^-4时,系统极化码的缩短方法比极化码的缩短方法约有0.5 dB的增益,比系统极化码的准均匀凿孔方法约有0.25 dB的增益。