In this paper, the bit error rate (BER) performance of the Spread Spectrum communication with Constrained Spreading Code system is studied under the synchronous CDMA system. Particularly, BER considering the tracking error is derived by theoretical analysis. The synchronizing spreading sequence is employed to track the signals in the receiver. As the result, the BER performance is degraded by increasing the number of users. However, the BER performance can be improved by canceling the co-channel interference and by suppressing the cross-correlation value between the information spreading sequence and the synchronizing spreading sequence.

M-ary/SS systems are compared with DS/SS systems applied the multicarrier systems and the RAKE receiver in the presence of AWGN, frequency selective Rayleigh fading and partial-band interference. In particular, the BER performance and SSMA capability are evaluated. Consequently, the M-ary/SSMA system using the multicarrier techniques is subject to the M-ary/SSMA system with the RAKE receiver in the presence of partial-band interference. The BER performance of the M-ary/SSMA system is better than that of the DS/SSMA system when the number of users is smaller than 20. And the spectral efficiency of the multicarrier M-ary/SSMA system is best in the four systems when JSR=20 [dB] and BER=10-3.

In this paper, to obtain higher spectral efficiency than a conventional M-ary/Spread Spectrum (SS) communication system using an orthogonal code, we propose Double M-ary/SS communication systems in which transmitting sequences are produced by multiplying two sequences obtained from different M-ary/SS systems. First, we estimate the system performance of a Double M-ary/SS in which transmitting sequences are composed of two kinds of sequences which have the same chip duration and the same sequence length in AWGN environment by theoretical analysis and computer simulations using random sequences. And we show that the bit error rate (BER) of the system can be improved, compared to that of the conventional M-ary/SS. Next, we propose two concrete examples of the Double M-ary/SS systems. We investigate the performance of these systems in AWGN environment by computer simulations, and show that the BER and spectral efficiency can be improved by the two systems compared to those of the conventional M-ary/SS. Further, we consider a modified method of the demodulation for one of the examples of Double M-ary/SS systems, and show that we can reduce quantity of calculations by the method.

Two families of rapidly synchronizable spreading codes are compared using the same component codes. The influence of component code choice is also discussed. It is concluded that correlation, code-division multiple-access (CDMA) and information security (measured by the value of linear complexity) properties of Kronecker sequences are considerably better than those of Combination sequences. Combination sequences cannot be recommended for CDMA use unless the number of active users is few. CDMA performance of Kronecker sequences is almost comparable with that of linear pseudonoise (PN) code families of equal length when a Gold or Kasami code is used as the innermost code and the Barker code is used as the outermost code to guarantee satisfactory correlation and CDMA properties. Kronecker sequences possess a considerably higher value of linear complexity than those of the corresponding non-linear Geffe and majority logic type combination sequences. This implies they are highly non-linear codes due to the Kronecker product construction method. It is also observed that the Geffe type Boolean combiner resulted in better correlation and CDMA performance than with majority logic. The use of the purely linear exclusive-or combiner for considerable reduction of code synchronization time is not found recommendable although it results in good CDMA performance.

Millimeter-wave propagation characteristics are measured in the outdoor environments. Especially, specific features in the urban area and the open meadowland are compared.

We have developed a new type of phase interpolation DDS with a digitally controlled delay generator. The new DDS is similar to a sine output DDS in that it produces low spurious signals, but it does not require a sine look-up table. Periodic jitter in the MSB of the DDS accumulator is reduced with the digitally controlled delay generator. Experimental results confirm successful frequency synthesizer operation in which the spurious signal level is successfully reduced to less than that the MSB of the accumulator.

This paper presents a novel transmission diversity scheme for code division multiple access system. Conventional diversity receivers in mobile stations require space and complicated circuits, however, the proposed diversity schemes present significant diversity effect without any diversity equipment at the mobile station. It is possible to use the transmitter diversity at the base station by using the feature of time division duplex (TDD) which has strongly correlated fading patterns in both forward and reverse link. Computer simulation is performed to evaluate the performance of the proposed systems for single user environment. The performance of the system 1, which select best situated antenna, is analyzed and the BER performance for multiple access is presented.

A multimedia coding standard, MPEG4 has frozen its Committee Draft (CD) as the MPEG4 version 1 CD, last October. It defines Audio-Visual (AV) coding Algorithms and their System Multiplex/Composition formats. Founding on Object-base concept, Video part adopts Shape Coding technology in addition to conventional Texture Coding skills. Audio part consists of voice coding tools (HVXC and CELP core) and audio coding tools (HILN and MPEG2 AAC or Twin VQ). Error resilience technologies and Synthetic and Natural Hybrid Coding (SNHC) technologies are the MPEG4 specific features. System part defines flexible Multiplexing of audio-visual bitstreams and Scene Composition for user-interactive re-construction of the scenes at decoder side. The version 1 standardization will be finalized in 1998, with some possible minute changes. The expected application areas are real-time communication, mobile multimedia, internet/intranet accessing, broadcasting, storage media, surveillance, and so on.

This paper presents a generation method of orthogonal spreading codes with different spreading factors (SFs), which are called orthogonal multi-SF spreading codes in this paper, for DS-CDMA mobile radio. The generated orthogonal multi-SF spreading codes have a tree structure and the codes are applied to the forward link such that all users, who transmit data at different rates, are orthogonalized. A group spreading modulator that simplifies the base station transmitter structure is also described. The transmission performance of the orthogonal multi-SF forward link under multi-user and frequency selective Rayleigh fading environments is evaluated by computer simulation to show that its performance is identical to that achieved by using multiple orthogonal spreading codes in parallel (orthogonal multicode forward link). Unlike the orthogonal multicode forward link, only a single Rake combiner is required at a mobile receiver which significantly simplifies the mobile receiver structure.

We have developed a half-duplex spread spectrum-direct sequence (SS-DS) 2. 4 GHz band transceiver (T/R) unit having a smaller size and lower power consumption. A highly efficient elastic SAW convolver with chirp interdigital transducers (IDTs) has been used in the correlation circuit of receiver unit. The code shift keying (CSK) modulation is used in the T/R unit. The size of T/R unit is 90 50 11 mm and the weight is 75 grams. The power consumption of T/R unit is 1. 4 watts. We found that the bit error rate (BER) was less than 10-6 over the range of 0-150 m outdoors and 0-80 m indoors without a digital error detection and correction method. In this case, the data rate was 102 kbps and the transmit RF power was 2. 5 mW/MHz. The electrical characteristics, anti-interference and anti-multipath fading were also evaluated.

Gold on connector contacts is superior in environmental resistance. However, pores existing gold film are source to trigger the corrosion reaction between gold and base metal. For examination of the contacts, it has been popular to apply "Salt Spray Test" and "Sulfur Dioxide Test. " There are some differences of the corrosion products between two tests. Main metal forming the product in Salt Spray is Copper, and main metal in Sulfur Dioxide is Nickel. To investigate the reason, we tried to employ an electro-chemical method. As a result, it was found that there was the difference between the respective galvanic cell combinations generated through pores.

The symbol basis side information generated by Viterbi's ratio threshold test technique is proposed to improve the performance of the asynchronous slow-frequency-hopped multiple access system with BFSK signaling in the frequency non-selective fading channel. By properly setting the ratio threshold to produce erasure decisions for the received symbols, the system performances are optimized. The relationship among the hit symbols in a hop duration is exploited by this symbol basis side information to greatly reduce the packet error probability. This packet error rate improvement can be as large as two order of magnitude, compared with perfect hop basis side information systems.

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.

A slotted ALOHA direct sequence spread spectrum system with random signatures is considered. The system is applicable in cases where a large number of terminals transmit to a single hub station like in cellular digital radio, personal mobile systems and wireless LANs. It is shown that significant improvements in packet throughput capacity are obtained if the adaptive receiver structures are used. Systems for the comparison are the spread spectrum slotted ALOHA system and the conventional slotted ALOHA system.

This paper presents a new CLSP/CC (Channel Load Sensing Protocol/Channel Clearance) in order to obtain better performances in spread slotted ALOHA networks. This protocol can decrease a wasteful utilization of channel by prohibiting continuous transmission of the packets destroyed in previous slot, with little added network complexities. For channel clearance technique, hub station broadcasts NAK to all mobile stations when the number of packets transmitted in a slot exceeds the channel capacity, and mobile stations cease own packet transmissions at NAK broadcast. The performances of the proposed CLSP/CC are obtained and compared with those of conventional CLSP by simulations. The performances include network throughput, average processing time and the number of mobile stations in backlogged state. As simulation results, the proposed CLSP/CC outperforms conventional CLSP, especially in highly offered load environment. Also as the proposed CLSP/CC obtain maximum throughputs at higher offered loads and the larger number of mobile stations in backlogged state than the conventional CLSP, it is found that our protocol can support more mobile stations and higher occurrence probabilities.

It is well known that M-ary/spread spectrum (M-ary/SS) system is superior to direct-sequence spread spectrum system under AWGN, and can achieve high spectral efficiency. On the other hand, however, the main drawback of this system is that the synchronization acquisition is difficult. In this paper, we propose a new synchronization acquisition method of M-ary/SS system. This method acquires the code synchronization by introducing a symmetrical property in spreading sequences, and detecting this property with the differential decoding technique. As spreading sequences, a set of orthogonal sequences and a set of non-orthogonal sequences are considered. The strong features of proposed systems are that the systems can acquire the code synchronization in carrier band and can reduce the complexity of calculation greatly. Among the comparison results of the systems with newly proposed orthogonal and some specific non-orthogonal spreading sequences, it is especially noted that the latter can reduce the mean acquisition time and calculation complexity much greater than the former.

In this paper, we study and analyze the overall acquisition performance of the combined acquisition-tracking synchronization loop for direct-sequence spread-spectrum (DS-SS) signals in the presence of Doppler shift. We consider both the change of effective search rate and the impact on the detection probability due to Doppler for the acquisition loop. We also determine the acquisition behavior of the digital delay lock loop (DDLL) in the presence of code Doppler. As a result, the influence of the DDLL's acquiring capability on the complete acquisition process is investigated and some numerical results are presented to demonstrate the acquisition performances of this combined loop which are quite different from the previous reports.

In this paper, a simple frame synchronization system for M-ary Spread Spectrum (M-ary/SS) communication system is analyzed. In particular, synchronization performance, bit error rate performance, and Spread Spectrum Multiple Access (SSMA) performance are analyzed. The frame synchronization system uses the racing counters. The transmitted signal contains framing chips that are added to spreading sequences. In the receiver, the framing chips are detected from several frames. The authors have proposed the simple frame synchronization system that detects framing chips from consecutive 2 frames. In this system, as the number of framing chips increases, synchronization performance improves and bit error rate performance degrades. In this paper a frame synchronization system that improves bit error rate performance is treated and analyzed. As the rusult, when the number of reference frames is 3, the bit error rate is much improved than the conventional system.

Considering that the application of the direct-sequence slotted spread ALOHA communications system to access/control channel is effective in communications systems with traffic channels operating at CDMA mode, the spread ALOHA communications system is discussed in terms of the system configuration and transmission efficiency. The transmission efficiency of the spread ALOHA communications system using a unified spread code is derived by means of two methods. One is based on the simulation of demodulation algorithm, and the other is based on the approximation by modeling. It becomes obvious from quantitative evaluation in terms of the probability of packet success and the throughput performance that the approximated results coincide with the simulated results, and that the modeling is very effective to estimate the transmission efficiency of the spread ALOHA communications system.

This paper proposes and investigates a vehicular radar system that can measure the distance to, the relative speed of and the direction of arrival (DOA) of the reflected waves from multiple targets or vehicles using the direct-sequence spread spectrum (DS-SS) technique. In particular, we propose a DOA estimation scheme using a multi-beam antenna. In order to show that the proposed system can accurately measure the above mentioned quantities, the performance is evaluated numerically in a multipath environment. Moreover, optimal multi-beam pattern is derived to minimize error probability of DOA estimation.