• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.10A
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• pp.1123-1130
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• 2004

This paper proposes the fast OVSF code generation method using the multi-stage spreading scheme based on the single code indexing scheme. The conventional OVSF indexing scheme based on the code-tree structure uses two numbers as the codeword indices, the layer number and the code number of the corresponding layer. However, the single code index number implicitly includes the information of the spreading factor as well as the code number. Since the binary representation of the single code indices shows the pattern of the codeword, the orthogonality between two different codewords can be determined by comparing their code indices instead of much longer codewords. The above useful property also makes the codeword can be generated directly kom its single code index. In this paper, the multi-stage spreading scheme is applied to generate the long code by spreading two shorter codewords with the appropriate code indices. The proposed fast code generation algorithm is designed for 3GPP UMTS systems and verified by the simulations.

• Journal of Korea Society of Industrial Information Systems
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• v.11 no.4
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• pp.112-120
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• 2006

Multicarrier code division multiple access(MC-CDMA) system that combines multicarrier modulation with CDMA offers robustness to frequency selective fading and can support higher rate data transmission with higher spectral efficiency. A new asynchronous MC-CDMA system to implement multiple data rate communications is proposed in this paper. In a W-CDMA downlink the orthogonal variable spreading factor(OVSF) code is used for variable spreading factor for various multimedia traffic. Proposed system utilizes the OVSF code that generated by generation property for spreading. The proposed MC-CDMA system use different lengths of OVSF code as a spreading code according to their data rate. The groupwise processing is accomplished by code grouping in OVSF code generation tree. For the analysis of average BER performance, numerical method and computer simulation were used. We also compare the system performance with that of a single rate MC-CDMA system used orthogonal code as a spreading code.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.6
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• pp.9-14
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• 2009

In this paper, we proposed spreading code slicing technique for efficient transmitter detection in AT-DMB system with single frequency network. At the transmitter, the spreading code for transmitter identification inserted using slicing technique on forehead of null symbol and then transmitted. In this point, it requires high correlation characteristic spreading code. At the receiver, peak to peak value calculated by correlation process before signal demodulation. The transmitter information by proposed technique is employed to implement the single frequency network (SFN) which is proposed for solving a frequency inefficiency problem of the MFN. The results of the paper can be applied to wireless multimedia digital broadcasting system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.8A
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• pp.733-738
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• 2002

Zero Cross-correlation Zone (ZCZ) code has a good performance in Multi-user CDMA system to get low correlation zone and reject co-channel interference. In this paper, we do analysis of spreading code design to obtain this kind of property of correlations with a complex spreading scheme and denote their effective performance for mobile communication system. In addition, a Jacket polyphase sequence is an example to show the improved performance and regular properties effective performance for mobile communication system. In addition, a Jacket polyphase sequence is as an example to show the improved performance and regular properties.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9A
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• pp.679-684
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• 2009

A collision dispersion scheme based on orthogonal pre-spreading is proposed to reduce the effect of collisions that occur in orthogonal code hopping multiplexing(OCHM). The OCHM scheme was previously proposed to accommodate a significantly larger number of low-activity bursty channels than the number of orthogonal codewords. The proposed scheme greatly reduces the required SNR in channel decoding. In addition, the proposed scheme can be applied to OFHM based on OFDM.

• ETRI Journal
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• v.23 no.2
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• pp.52-60
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• 2001

In this paper, a medium access control protocol is proposed for integrated voice and data services in wireless local networks. Uplink channels for the proposed protocol are composed of time slots with multiple spreading codes per slot based on slotted code division multiple access (CDMA) systems. The proposed protocol uses spreading code sensing and reservation schemes. This protocol gives higher access priority to delay-sensitive voice traffic than to data traffic. The voice terminal reserves an available spreading code to transmit multiple voice packets during a talkspurt. On the other hand, the data terminal transmits a packet without making a reservation over one of the available spreading codes that are not used by voice terminals. In this protocol, voice packets do not come into collision with data packets. The numerical results show that this protocol can increase the system capacity for voice service by applying the reservation scheme. The performance for data traffic will decrease in the case of high voice traffic load because of its low access priority. But it shows that the data traffic performance can be increased in proportion to the number of spreading codes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12C
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• pp.1135-1142
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• 2006

This article presents a new asynchronous MC-CDMA system to implement multiple data rate communications. In a W-CDMA downlink, the OVSF code is used for spreading code for various multimedia traffic. Proposed system utilizes the OVSF code that generated by generation property for spreading. The proposed MC-CDMA system use different lengths of OVSF code as a spreading code according to their data rate. The groupwise processing is accomplished by code grouping in OVSF code generation tree. Between each group, the code grouping interference canceller is performed to cancel other group interference. At that time the proposed receiver does not require any information about interference users. For the analysis of average BER performance, we propose system model and computer simulation were used. We also compare the system performance with that of a single rate MC-CDMA system used orthogonal code as a spreading code.

• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.11-14
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• 1998

This paper introuces a new efficient method of synchronization acquisition which is the most important element in DS-CDMA system using the phase offset of binary code. This approach uses the binary code function which can easily estimate the phase offset from the received spreading waveforms which respect to the receiver-stored replica of the spreading code. This paper proposes the initial acquisition model with repeat error control device that is good for perfomance. The hardware is implemented by TMS320c30

• Proceedings of the KIEE Conference
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• 2005.10a
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• pp.173-175
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• 2005

Two-dimensional orthogonal variable spreading codes are presented for multiplexing of forward link in direct sequence code division multiple access (DS-CDMA) multiple antennas system And the results of code generation and simulation of 2 dimensional orthogonal variable spreading factors on Jacket matrices are also be investigated. The bit error rate(BER) performance under a multi-user environment for the additive white Gaussian noise (AWGN) channel demonstrated that the proposed scheme could provide flexible rates and lower correlation values

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.1
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• pp.81-86
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• 2008

Fast spreading Internet worms, such as Code Red and Slammer, have become one of the new major throne of the Internet recently. In order to defend against theses worms, it is essential to understand how Internet worms propagate and how different Internet factors affect worm spreading. In this paper, we intend to describe the spread of worms on Internet environments accurately. Therefore we model and analyze the spreading effects by various simulations considering Internet addressing and speed. The results lead to a better prediction of the worm spreading on current and future Internet environments.