In this paper, the separate coding scheme is applied to space-time turbo-coded modulations (ST-TuCM). The separate coding for ST-TuCM uses the plural number of component encoders, each of which is a binary turbo encoder in the transmitter. The receiver has component decoders corresponding to the component encoders. The likelihood values derived by the component decoders are employed as a-priori information of transmitted signal from other transmit antennas in iterative demodulation-decoding. Simulation results under the fast Rayleigh fading channel show that separate coding and iterative demodulation-decoding improve the bit error rate performance.

We have two goals in this paper. One is the comparison of Spread Spectrum (SS) CDMA and Spread Time (ST) CDMA. The other is to propose a new SS-ST CDMA system, which is an adaptive CDMA with both merits of SS and ST CDMA. SS and ST CDMA are compared from the view point of two dimensional space "frequency (B Hz)-time (T Sec)" together with their communication capacity. A primary modulation is assumed to be PPM in ST CDMA, and FSK in SS CDMA which is regarded as PPM in frequency axis. Both SS and ST CDMA are combined to give the proposed SS-ST CDMA, where transmitted signals are spread both in time and frequency domain. In order to realize the proposed system, a transmitter model is presented, and two receiver structures are discussed. The discrete Fourier transform (DFT) is employed for the system flexibility. Although SS, ST and SS-ST CDMA are shown to have the same capacity of 0.7213, the combined SS-ST CDMA has a merit of adaptability to adjust spreading gain of ST and SS according to property of channels, an impulsive noise dominated or a CW interference dominated channel. Numerical results of DFT are also shown to illustrate the waveform and spectrum of the proposed SS-ST CDMA system. Finally the symbol error probability performance of ST PPM, SS FSK and combined SS-ST systems in CW and impulsive environment is presented.

In this letter, an analysis of bit error probability of 4-state soft decision Viterbi decoding is presented. The bit error probability of recursive systematic convolutional code is also derived.

A model for time spread-pulse position modulation (TS-PPM)/code division multiple access (CDMA) systems is presented. A TS signal is produced by a TS-filter, whose characteristic is a pseudonoise sequence in frequency domain. The error probability performance is analyzed and compared with those of on-off keying (OOK) and binary phase shift keying (BPSK). It is shown that at the same transmission speed TS-PPM is superior to TS-OOK and TS-BPSK due to the dramatic decrease of multiple access interference. The throughput of the network is analyzed, and its relation to the length of pseudonoise sequence and the packet length is also discussed.

Orthogonal frequency division multiplexing (OFDM) is a possible candidate for the modulation used in mobile multimedia communications because of its robustness to fading and flexibility of transmission rate. Partial transmit sequence (PTS) is an effective technique for reducing the peak power of OFDM signals by means of phase rotation. In PTS, side information (SI) is transmitted to correct the effects of the phase rotation. We propose a new method based on rotationally invariant trellis coded modulation for coded OFDM with PTS. In this method, no SI is required and the few information bits affected by the phase rotation are not used as data. (They are regarded as dummy bits). It is shown that the proposed method yields better bit error rate (BER) performance than other methods using side information under the condition of almost the same transmission rate.

This paper investigates fast Packet Classification techniques, where a large routing table is divided into many much smaller tables by an index key at first; the resulting small tables are much easier to search. A traditional way is to use the front bits as the index key, but we show it's not an effective way to divide a routing table. In this paper, we propose three bit selection methods for division. They can be implemented by CAM or hash structure. Simulations show that the bit selection methods decrease the delay of classification 50% compared to the traditional method. We also propose an optimized method which is adapted to the biased traffic pattern, which shows 70% improvement in our simulation.

We consider slotted ALOHA systems with a controlled output power level. The systems were proposed to improve the throughput performance by the capture effect. However widely used linear modulation systems have no capture effect, and a power level distribution dominates the performance in those systems. In this paper we consider linear modulation systems employing PSK. We introduce an average error probability of the highest power signal as a performance measure, and a uniform distribution is applied to the error probability analysis. Numerical results show the superiority of the systems with uniform distribution to a conventional slotted ALOHA in a heavy traffic condition. On the other hand, in a light traffic condition, the optimal power distribution which minimizes the error probability is obtained for 2-level ALOHA. We also propose the power level selection method to search the optimal power level. The validity of analytical results are confirmed by simulations.

Time spread (TS) pulse position modulation (PPM) signals have been proposed for CDMA applications, where the envelope detection is employed instead of coherent detection for easier synchronization of PPM. In this paper, a new method of deriving symbol error probability (SEP) of TS PPM signals in the presence of interference is introduced. The analysis is based on the moment technique. The maximum entropy criterion for estimating an unknown probability density function (PDF) from its moments is applied to the evaluation of PDF of envelope detector output. Numerical results of SEP are shown for 4, 8 and 16PPM in the practical range of signal-to-noise power ratio (SNR) and signal-to-interference power ratio (SIR) of 5, 10 and 20 dB. SEP by the union bound is also given for comparison. From the results it is noted that when PPM multilevel number is small, the union bound goes near to SEP by the proposed method, but when it increases the difference of the SEP by the bound and proposed method becomes larger. The effect of central frequency offset of TS-filter is evaluated as an illustrative example.

It is known that cycle slip due to frequency selective fading causes a burst error by symbol deletion or insertion, and has a serious effect on mobile radio communication systems. In this paper, first, we show that phase rotating modulation is suitable for code synchronization error detection. Next, we consider a code synchronization controller using correlation estimator of received sequence, and the controller combines the estimator with 2π/3-shifted modulation to construct a new code synchronization error control scheme as a cycle slip cancelling system. Furthermore, we apply the scheme to the multilevel trellis coded modulation (TCM). Finally, computer simulation results confirm that proposed scheme is capable of code synchronization error correction.

The end-to-end round trip time (RTT) is one of the most important communication characteristics for Internet applications. From the viewpoint of network operators, RTT may also become one of the important metrics to understand the network conditions. Given this background, we should know how a factor such as a network incident influences RTTs. It is obvious that two or more factors may interfere in the observed delay characteristics, because packet transmission delays in the Internet are strongly dependent on the time-variant condition of the network. In this paper, we propose a modeling method by using mixed distribution which enables us to express delay characteristic more accurately where two or more factors exist together. And, we also propose an inferring method of network behavior by decomposition of the mixed distribution based on modeling results. Furthermore, in experiments we investigate the influence caused by each network impact factor independently. Our proposed method can presume the events that occur in a network from the measurements of RTTs by using the decomposition of the mixed distribution.