Differentially coherent correlation technique for DS-SS codeacquisition in a fast Rayleigh fading channel

A differentially coherent (DC) correlation scheme is proposed for rapid DS-SS code acquisition in a fast Rayleigh fading channel. It is analytically shown that a serial-search DC acquisition system significantly outperforms the conventional parallel-search I-Q system in a highly dynamic environment     

Performance evaluation for multichannel reception of coherent MPSKover frequency selective fading channels

This paper provides a framework for error rate performance analysis of maximal ratio combining multichannel reception of coherent M-ary phase-shift keying (MPSK) systems over slowly fading channels. Each channel is described by a two-sided discrete model with correlated complex Gaussian taps based on bandlimiting an underlying WSSUS physical channel. The resulting “resolved channel” performance evaluation incorporates the inherent multipath resolution taking into account the fact that phase recovery operates on the resolved main path. The received phase-density function is developed. Conditional bit and symbol error probabilities are determined and the cases for which closed-form or acceptable numerical solutions exist are delineated. A new efficient and accurate recursive solution for the Ricean-fading main resolved path case is presented, which is applicable to both the flat and frequency selective cases. A progressive intersymbol interference (ISI) bound is discussed for the frequency selective case to minimize computation. Examples using the maritime high-data rate line-of-sight (LOS) channel model demonstrate the framework versatility and the ability to simultaneously investigate the important parameters in the frequency selective environment     

Code acquisition schemes using antenna arrays for DS-SS systems and their performance in spatially correlated fading channels

We propose parallel and serial code-acquisition schemes using antenna arrays for initial acquisition of direct-sequence spread-spectrum signals, which can lower substantially the range of detectable signal-to-noise ratio (SNR) as compared to the corresponding conventional schemes with a single antenna. The proposed schemes use the sum of all the single-antenna decision samples from antenna arrays, corresponding to an identical subsequence of a given pseudonoise code as a decision variable in order to enhance SNR of the resulting signal. We analyze the mean acquisition time performance under an additive white Gaussian noise channel and spatially correlated time-varying flat Rayleigh fading channels by deriving the expressions for the probabilities of detection, missing, and false alarm. We consider two extreme cases of spatial fading correlation among antenna arrays, the case of uncorrelated diversity antennas and the case of perfectly correlated antennas. From numerical results, we see that the acquisition performance of the proposed schemes using antenna arrays becomes improved continually as the number of antennas increases and the performance improvement depends on the degree of spatial fading correlation.     

Analytic forward link performance of pilot-aided coherent DS-CDMAunder correlated Rician fading

This paper presents a methodology for analyzing the forward link performance of a pilot-aided coherent DS-CDMA system under correlated Rician fading. In the forward link of a CDMA system, orthogonal modulation is usually used to minimize the self-interference. To maintain the orthogonality and reduce the receiver complexity, a common pilot channel (shared by all users) is employed to provide the reference for coherent demodulation. A tradeoff shows that a higher pilot ratio yields good channel estimates but takes away some capacity from traffic users, while a lower pilot ratio results in poorer channel estimates and leads to higher traffic power per user. This paper derives the analytical error performance, which includes (1) imperfect channel estimation by the pilot channel, (2) a very general channel model where correlations between paths as well as Rician fading are considered, and (3) interference patterns due to multiple paths and the surrounding base stations' transmissions. This paper also considers self-interference due to the loss of orthogonality caused by pulse shaping     

On the performance of single frequency networks in correlatedshadow fading

All transmitters in a single frequency network (SFN) simultaneously transmit the same information within the same frequency block. Simulcasting provides a diversity gain which has been shown to yield good coverage. In traditional analysis uncorrelated shadow fading is used. In some cases this assumption does not capture the behaviour of the shadow fading, e.g., when several transmitters are shadowed by a large obstacle. We investigate the changes in coverage due to correlation among the received signals field strength from different transmitters. A spatial shadow fading correlation model is proposed and validated using the Blomquist-Ladell (1974) prediction method on a digital terrain data base. Results for both wide area and local SFN show that the coverage properties depends on the correlation in the shadow fading. This will affect the planning process since strong correlation, due to the structure of the terrain, yields better coverage for high transmitter powers (interference limited systems) and worse coverage for low transmitter powers (noise limited systems)     

Simplifying performance expressions for noncoherent anddifferentially coherent modulations over generalized fading multiplechannels

We further simplify the numerically friendly bit-error rate expression presented by Simon and Alouini (see ibid., vol.46, p.1625-38, 1998) for noncoherent and differentially coherent systems with multichannel reception over additive white Gaussian noise and generalized fading channels     

Partially coherent digital matched filters

The structure and performance of digital matched filters (DMFs) with partial phase estimation, i.e., partial coherent (PC) DMFs, are considered in this paper. The case of a PC-DMF with one-bit digitization and matched to a binary phase modulated signal is investigated. The filter structure is derived as an approximation to Viterbi's optimum PC analog detector structure and is shown to be a generalization of Turin's noncoherent (NC) DMF structure. The performance of the PC-DMF is investigated in detail for three types of interference, namely, the Gaussian noise, the noncoherent constant amplitude interference (NCAI), and the coherent constant amplitude interference (CCAI). The results are compared with those of the two coherence limiting cases, i.e., the NC-DMF and the coherent DMF case.     

Performance of coherent MQAM schemes in the presence of frequency‐selective Rayleigh fading and CCI

Performance of a coherent MQAM system in the presence of frequency-selective Rayleigh fading, co-channel interference (CCI) and additive white Gaussian noise (AWGN) is presented. Square-root raised-cosine filters are used in both the transmitter and receiver for an optimum performance in a band-limited AWGN channel. Frequency-selective Rayleigh fading channel is modeled as a two-ray model. Based on the characteristic functions of the received signals and a discrete Fourier transform (DFT) method, an analytical procedure to compute the error probability is derived. Numerical results for an illustrative example of a 16QAM system are given. Effects of CCI and frequency-selective fading on the system performance are examined. Accuracy of the proposed method is discussed in comparison with other simulation and analytical techniques. This revised version was published online in June 2006 with corrections to the Cover Date.     

部份相干Talbot效应及干涉仪

本文用模糊函数分析了部份相干照明下的光栅Talbot效应,表明光栅的自成像将发生加宽.同时还提出了部份相干Talbot干涉仪,这可采用空间非相干扩展光源.     

BER performance of OFDM system over frequency nonselective fastRicean fading channels

The fast changing frequency nonselective Ricean fading channel introduces a complicated multiple distortion and an extra additive noise component for an OFDM system. The multiple distortion is the average of the sum of N(N⩾3) correlated Ricean random variables. We propose an approximate technique for calculating the probability density function (PDF) of the multiple distortion under the assumption that the channel response changes in a linear fashion during one OFDM symbol. As a result, the bit error rate (BER) formula of a BPSK modulated OFDM system is derived. The results obtained using the derived formula describe well the OFDM performance under the time variant channel and match very well with the simulation results     

Slotted ALOHA performance for FU‐FB in frequency selective fading environment

Slotted ALOHA is a simple and straightforward random multiple access technique, which has been used extensively in data and cellular networks as the protocol for random access. The complexity of state space‐based analysis methods for finite user finite buffer systems increases exponentially with buffer size and number of users. The presence of multipath frequency selective fading channel further adds to the complexity, making the analysis practically intractable. This paper uses an approximate analysis technique called tagged user analysis (TUA) to analyze the performance parameters of slotted ALOHA over multipath and frequency selective fading channels for finite user finite buffer systems. In TUA, the steady state system performance is evaluated from the analysis of a single user. Moreover, the state flow graph of TUA has just four states, thus reducing the complexity of the analysis. Simulation results confirm the validity of the TUA analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Transmission performance analysis of Multi-Carrier Modulation in frequency selective fast Rayleigh fading channel

In this paper, we discuss the transmission performance of Multi-Carrier Modulation (MCM) in frequencyselective fast Rayleigh fading channels. First, we optimize the transmission parameters of MCM withM-ary differential phase shift keying/differential detection (DPSK):the guard duration andthe number of sub-carriers for frequency-selective fast Rayleigh fading channels, and then show the bit error rate (BER) performance of the optimizedM-ary DPSK MCM. Next, we propose an MCM with pilot-assistedM-ary quadrature amplitude modulation/coherent detection (QAM), and discuss the BER performance when we reduce the number of pilot signals from the view-point of frequency-time utilization efficiency. Finally, we propose a two-stage frequency offset compensation method.     

Error probability performance prediction for multichannel reception of linearly modulated coherent systems on fading channels

This paper provides a framework for the analysis of error rate performance of maximal ratio combining multichannel reception of coherent linearly modulated systems over frequency-selective fading channels. Expressions for the error probability are developed, and the special cases for which closed-form or acceptable efficient numerical solutions are possible are delineated. A new efficient and accurate recursive method for the Ricean fading main resolved path case is presented for coherent quadrature amplitude modulation constellations. The effect of automatic gain control error on analysis of modulation schemes is demonstrated. Finally, numerical examples based on the maritime high-data-rate channel model are provided to demonstrate the usefulness of the framework.     

Performance of coherent data transmission in frequency-selectiveRayleigh fading channels

The error probability of digital transmission through a frequency-selective channel with random multipath fading due to uncorrelated scatterers is calculated. The error probability is averaged with respect to the randomly varying delays, with a given delay power spectrum. Two coherent receivers, suboptimum without any knowledge of the channel and optimum with perfectly known channel, are compared. The results are applied to continuous-phase-modulation (CPM) signals     

Decision-directed coherent detection in multicarrier systems onRayleigh fading channels

Novel coherent detectors for DQPSK and π/4-DQPSK on Rayleigh fading channels are presented. The detectors are based on decision feedback and minimum mean-square error (MMSE) channel estimation. The proposed detectors may be used in both single carrier and multicarrier systems. Analytical results in the form of expressions for channel estimation error variance and bit error probability, both with and without diversity, are derived. The MMSE-based detector has a significantly lower irreducible bit error probability floor compared to a conventional differential detector. For most practical applications, the error floor of the MMSE-based detector is negligible. Simulated results are presented to verify the analysis and justify the approximations made     

Capacity of AM-PSK on partially coherent fading channels

This paper presents numerical capacity curves for two discrete complex channels: (1) a slow-fading Rayleigh channel with discrete carrier tracking by a phase-locked loop (PLL), where the PLL SNR is proportional to the fading amplitude squared, and (2) a fast-fading Rician channel with carrier phase estimation for the line-of-sight path only. Both channel models assume independent fading of successively received symbols. Capacity calculations are performed for equiprobable signaling with 8-ary and 16-ary amplitude-modulated phase-shift-keyed (AM-PSK) constellations. On the Rayleigh channel, the AM-PSK constellations give gains between 2 and 9 dB over PSK, at SNRs between 5 and 40 dB. For the Rician channel, AM-PSK gives a capacity gain over PSK of up to 0.75 bit at high SNR     

Pilot-symbol aided coherent M-ary PSK in frequency-selective fastRayleigh fading channels

Pilot-symbol aided coherent M-ary PSK modems in digital cellular mobile radio systems are analyzed theoretically. The error-floors caused by the Doppler spread in a fast fading channel are removed in both flat and selective fading channels. However, the error-floors caused by the delay spread are lower-bounded by those that exist in the ideal coherent detection. The systems are modeled as frequency-selective fast Rayleigh fading channels, corrupted by co-channel interference (CCI) and additive white Gaussian noise (AWGN). In the proposed scheme, pilot symbols are inserted periodically to monitor the channel characteristics. The fading processes experienced by the pilot symbols are used to estimate those suffered by the data symbols using interpolation or filtering. The estimated fade characteristics are used to compensate the random phase variation caused by the Doppler spread, so that the signals can be demodulated coherently. The theoretical performances of the fade compensated coherent modems are evaluated. The results show that the fade compensated coherent demodulation with the least redundancy achieves the same performance as the ideal differential detection in a fading channel. The performance approaches that of the ideal coherent demodulation as more redundancy is allowed. The pilot-symbol-insertion (PSI) scheme is also applicable to M-ary QAM modems and Rician channels. The residual frequency offset can also be compensated by the PSI technique     

多径衰落信道下频域差分检测OFDM系统的误码率分析

在多径衰落信道条件下，分析了正交频分复用系统中频域差分检测的误码率性能，并进行了仿真验证。分析与仿真结果表明，信道相干时间和相干带宽均影响频域差分检测的误码率性能，信道相干带宽对频域差分检测的影响比信道相干时间的影响更大，频域差分检测适合于多径延迟扩展比较小的信道。     

The theoretical BER performance analysis of a cooperative diversity scheme in frequency selective fading channel

A novel cooperative diversity scheme based on Distributed Space-Time Block Coding and Multi-Carrier Code Division Multiple Access (DSTBC-MC-CDMA) is proposed which works well in frequency selective fading channels with multiple single-antenna users. And an analytical error model is established to describe the symbol decoding errors between interusers, based on which a close form expression for theoretical Bit Error Rate (BER) performance of the scheme is derived to analyze the influence of the interuser decoding errors on the BER performance of the scheme. Then simulation is complimented to verify the analytic result above, which also shows that the BER performance of DSTBC-MC-CDMA outgoes that of non-cooperative MC-CDMA with considerable gains. Further- more, the simulations coincide with the theoretical results well.     

Performance of differentially coherent digital communications overfrequency-selective fading channels

The performance of binary differential phase-shift keyed (DPSK) communications over frequency-selective wide-sense-stationary uncorrelated-scattering fading channels is considered. A technique is described for obtaining bounds on the average error probability for DPSK in terms of one or two parameters obtained from multipath spread or frequency-correlation-function channel measurements. A method of approximating the performance of systems using various data-pulse shapes and systems where it is difficult to obtain a complete channel characterization is developed. Numerical examples and comparisons of the most interesting cases are given