This study shows a fast simulation method for turbo codes over an additive white class A noise (AWAN) channel. The reduction of the estimation time is achieved by applying importance sampling (IS) which is one of the variance reduction simulation methods. In order to adapt the AWAN channel, we propose a design method of a simulation probability density function (PDF) utilized in IS. The proposed simulation PDF is related to the Bhattacharyya bound to evaluate wider area of the signal space than the conventional method. Since the mean translation method, which is a conventional design method of the simulation PDF used in IS, is optimized for an additive white Gaussian noise channel, the evaluation time of the error performance of turbo codes over the AWAN channel can not be reduced. To evaluate BER of 10-8, the simulation time of the proposed method can be reduced to 1/104 under the condition of the same accuracy of the traditional Monte Carlo simulation method.

Parallel concatenated convolutional codes, turbo codes, are very attractive scheme at a point of view of an error probability performance. An bit error rate (BER) evaluation for turbo codes is done by a uniform interleaver bound calculation and/or a computer simulation. The former is calculated under the assumption of uniform interleaver, and is only effective for an BER evaluation with a pseudo random interleaver. The latter dose not have any interleaver restrictions. However, for a very low BER evaluation, it takes enormous simulation time. In this paper, a new error probability evaluation method for turbo codes is proposed. It is based on the error event simulation method. For each evaluation for the predetermined error sequence, importance sampling, which is one of the fast simulation methods, is applied. To prove the effectiveness of the proposed method, numerical examples are shown. The proposed method well approximates the BER at the error floor region. Under the same accuracy, the IS estimation time at BER = 10-7 is reduced to 1/6358 of the ordinary Monte-Carlo simulation time.

This paper shows a fast estimation method of very low error rate of low-density parity-check (LDPC) codes. No analytical tool is available to evaluate performance of LDPC codes, and the traditional Monte Carlo simulation methods can not estimate the low error rate of LDPC codes due to the limitation of time. To conquer this problem, we propose another simulation method which is based on the optimal simulation probability density function (PDF). The proposed simulation PDF can also avoid the dependency between the simulation time and the number of dominant trapping sets, which is the problem of some fast simulation methods based on the error event simulation method. Additionally, we show some numerical examples to demonstrate the effectiveness of the proposed method. The simulation time of the proposed method is reduced to almost less than 1/10 of that of Cole et al.'s method under the condition of the same accuracy of the estimator.

The decorrelating detector is one of the detecting methods in a direct sequence code division multiple access systems. We investigate the blind adaptive decorrelating detector (BADD) using only the signature of the desired user (DU) according to the assumption that the algorithm is used in downlink. When the BADD is constructed with an antenna array, both the spatial and temporal signature must be taken into consideration for signal detection. We propose the BADD incorporated with the blind estimation of spatial signature (SS) of the DU only from the received signals. As the estimation procedure of SS, the orthogonal projection approximation and subspace tracking algorithm is adopted. The proposed BADD presented the BER improvement with using antenna array. The BER performance has a lower limit with increasing the number of antenna array elements.

This study shows a fast simulation method of turbo codes over slow Rayleigh fading channels. The reduction of the simulation time is achieved by applying importance sampling (IS). The conventional IS method of turbo codes over Rayleigh fading channels focuses only on modification of additive white Gaussian noise (AWGN) sequences. The proposed IS method biases not only AWGNs but also channel gains of the Rayleigh fading channels. The computer runtime of the proposed method is about 1/5 of that of the conventional IS method on the evaluation of a frame error rate of 10-6. When we compare with the Monte Carlo simulation method, the proposed method needs only 1/100 simulation runtime under the condition of the same accuracy of the estimator.

The evaluation of a error probability of a trellis-coded modulation scheme by an ordinary Monte-Carlo simulation method is almost impossible since the excessive simulation time is required to evaluate it. The reduction of the number of simulation runs required is achieved by an importance sampling method, which is one of the variance reduction simulation methods. The reduction of it is attained by the modification of the probability density function, which makes errors more frequent. The error event simulation method, which evaluates the error probability of finite important error events, cannot avoid a truncation error. It is the fatal problem to evaluate the precision of the simulation result. The reason of it is how to design the simulation probability density function. We propose a evaluation method and the design methods of the simulation conditional probability density function. The proposed method simulates any error event starting at the fixed time, and the estimator of it has not the truncation error. The proposed design method approximate the optimum simulation conditional probability density function. By using the proposed method for an additive non-Gaussian noise case, the simulation time of the most effective case of the proposed method is less than 1/5600 of the ordinary Monte-Carlo method at the bit error rate of 10-6 under the condition of the same accuracy if the overhead of the selection of the error events is excluded. The simulation time of the same bit error rate is about 1/96 even if we take the overhead for the importance sampling method into account.

Multiple access interference (MAI) due to many simultaneous users is the main factor that limits the performance of DS-CDMA system. Multiuser detection is a method to avoid performance degradation due to MAI. We propose a blind multiuser detection method based on the algorithm consisting of two-stage decoding process, i.e., linearly constrained constant modulus (LCCM) and iterative least squares (ILS). The computer simulations confirmed that the algorithm is near-far resistant and that the proposed method is effective in the application to the slow fading channels.

This paper shows the method of theoretical analysis for the bit error probability of the trellis-coded partial response continuous phase modulation (TCM-PR-CPM) over the correlated Rician fast frequency nonselective fading channel. In the analysis, the fading correlation of the channel and the effect due to finite interleaver are taken into account. By applying the method to the rate 1/2 (7, 2) trellis code with the raised cosine pulse of length 2 (2RC) partial response signaling, we show that the tighter upper bounds of the bit error rate are obtained than those in the preceding report.

We study the performances of a synchronous chip-interleaved, block spread (CIBS) code division multiple access (CDMA) with space-time block-coding (STBC) in the presence of frequency-selective fading. For providing the space diversity gain due to STBC, we introduce the optimum precoding for the STBC. Zero-forcing and minimum mean square error equalizers for CIBS-CDMA are derived. Simulation results confirm that the proposed precoder is valid under the frequency selective fading.

This study shows the effectiveness of the simulation probability density function (p. d. f. ) based on the Bhattacharyya bound from the point of view of the twisted distribution. As a result, the simulation p. d. f. related to the Bhattacharyya bound is asymptotically optimal for the trellis coded modulation scheme under some practical conditions. And the optimality is also confirmed by a numerical example.

Blind channel estimation algorithm which is applicable to the time-variant channel under frequency-selective fading is proposed. The condition on the blind channel identifiability using temporally and spatially oversampled data is shown. The proposed algorithm consists of two stages. At the first stage, the channel equalization matrix is estimated by taking account of the time-variant characteristics of the channel. At the second stage, the signals and the channel matrix are alternately estimated by using the finite alphabet property of the transmitted symbols. Periodical return from the second stage to the first makes the blind estimation algorithm feasible for the time-variant channel with fast fading. The simulation results confirm the fast convergence property and the effectiveness of the proposed algorithm in coping with the frequency-selective fading.

When bit error probability of a trellis-coded modulation (TCM) scheme becomes very small, it is almost impossible to evaluate it by an ordinary Monte-Carlo simulation method. Importance sampling is a technique of reducing the number of simulation samples required. The reduction is attained by modifying the noise to produce more errors. The low error rate can be effectively estimated by applying importance sampling. Each simulation run simulates a single error event, and importance sampling is used to make the error events more frequent. The previous design method of the probability density function in importance sampling is not suitable for the TCM scheme on an additive non-Gaussian noise channel. The main problem is how to design the probability density function of the noise used in the simulation. We propose a new design method of the simulation probability density function related to the Bhattacharyya bound. It is reduced to the same simulation probability density function of the old method when the noise is additive white Gaussian. By using the proposed method for an additive non-Gaussian noise, the reduction of simulation time is about 1/170 at bit error rate of 106 if the overhead of the calculation of the Bhattacharyya bound is ignored. Under the same condition, the reduction of the simulation time by the proposed method is 1/65 of the ordinary Monte-Carlo method even if we take the overhead for importance sampling into account.

We research on an importance sampling (IS) simulation to estimate a low error probability of turbo codes. The simulation time reduction in IS depends on another probability density function (p.d.f.) called simulation p.d.f. The previous IS simulation method can not evaluate the error probability on the low SNR and waterfall region. We derive the optimal simulation p.d.f. which gives the perfect estimator. A new simulation p.d.f. design, which is related to the optimal one, is proposed to overcome the problem of the previous IS method. The proposed IS simulation can evaluate all possible error patterns. Finally, some computer simulations show that the proposed method can evaluate the error probability on the low SNR, waterfall, and error floor regions. At the evaluation of the BER of 10-7, the simulation time of the proposed method is about 1/350 times as short as that of the Monte-Carlo simulation. When the BER is less than 710-8, the proposed method requires shorter simulation time than the conventional IS method.

We present a design method of the simulation probability density function for a trellis-coded modulation (TCM) in an impulsive noise environment. The upper bound evaluation method for the TCM scheme cannot be applied to the lognormally distributed impulsive noise, since the Chernoff bound cannot be defined. Thus the error probability can only be estimated by a computer simulation. For an evaluation of a low error probability, importance sampling (IS) is an efficient technique. A design method of the simulation probability density function, which plays an important role in IS, is proposed for the noise. The effectivity is shown by a numerical example.

We propose bit error rate (BER) evaluation methods for a trellis coded modulation (TCM) scheme over a Rayleigh fading channel by using importance sampling (IS). The simulation probability density function for AWGN and Rayleigh fading is separately designed. For efficient simulation of a system model with finite interleaver, frequency of the generation of fading sequences is reduced. The proposed method gives a good BER estimates over a Rayleigh fading channel.