• Journal of Communications and Networks
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• v.2 no.1
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• pp.5-17
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• 2000

cdma2000 offers several enhancement as compared to TIA/EIA-95, although it remains fully compatible with TIA/EIA-95 systems and allows for a smooth migration from one to the other-Major new capability include:1)connectivity to GSM-MAP in addition to IP and IS-41 networks; 2) new layering with new LAC and MAC architectures for improved service multiplexing and QoS management and efficient use of radio resource ;3) new bands and band widths of operation in support of various operator need and constraints, as well as desire for a smooth and progressive migration to cdma 2000; and 4) flexible channel structure in support of multiple services with various QoS and variable transmission rates at up to 1 Mbps per channel and 2 Mbps per user. Given the phenomenal success of wireless services and desire for higher rate wireless services. improved spectrum efficiency was a major design goal in the elaboration of cdma2000. Major capacity enhancing features include; 1) turbo coding for data transmission: 2)fast forward link power control :3) forward link transmit diversity; 4) support of directive antenna transmission techniques; 5) coherent reverse link structure; and 6) enhanced access channel operation. As users increasingly rely on their cell phone at work and at home for voice and data exchange, the stand-by time and operation-time are essential parameters that can influence customer's satisfaction and service utilization. Another major goal of cdma2000 was therefore to enable manufacturers to further optimize power utilization in the terminal. Major battery life enhancing features include; 1) improved reverse link performance (i.e., reduced transmit power per information bit; 2) new common channel structure and operation ;3) quick paging channel operation; 4) reverse link gated transmission ; and 5) new MAC stated for efficient and ubiquitous idle time idle time operation. this article provides additional details on those enhancements. The intent is not to duplicate the detailed cdma2000 radio access network specification, but rather to provide some background on the new features of cdma2000 and on the qualitative improvements as compared to the TIA/EIA-95 based systems. The article is focused on the physical layer structure and associated procedures. It therefore does not cover the MAC, LAC, radio resource management [1], or any other signaling protocols in any detail. We assume some familiarity with the basic CDMA concepts used in TIA/EIA-95.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.12A
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• pp.1009-1018
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• 2003

A new fading channel estimation technique is proposed for an OFDM based modem In the ITS system. The algorithm is based on the transfer function extraction of the channel using the pilot signals and compensated the channel preceding the equalization. The newly derived algorithm is division-free arithmetic operations allows the faster circuit operation and the smaller circuit size. Proposed techniques compensate firstly the distortion which is generated at fading channels and secondly eliminate inter-symbol interference. All algorithms are suitability estimated and improved for a system implementation using digital circuits. As the results, the circuit size is reduced by 20% of the conventional design and achieved about 10% performance improvement at low SNR under 10dB in case of ITS system adapted 16-QAM mode.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.6B
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• pp.1082-1091
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• 2000

In this paper, the efficient equalization method for OFDM(Orthogonal Frequency Division Multiflexing) System using the QAM(Quadrature Amplitude Modulation) in multipath fading channel is proposed in order to faster and more efficiently equalize the received signals that are sent over real channel. In generally, the one-tap linear equalizers have been used in the frequency-domain as the existing equalization method for OFDM system. In this technique, if characteristics of the channel are changed fast, the one-tap linear equalizers cannot compensate for the distortion due to time variant multipath channels. Therefore, in this paper, we use one-tap non-linear equalizers instead of using one-tap linear equalizers in the frequency-domain, and also use the linear equalizer in the time-domain to compensate the rapid performance reduction at the low SNR(Signal-to-Noise Ratio) that is the disadvantage of the non-linear equalizer. In the frequency-domain, when QAM signals, consisting of in-phase components and quadrature (out-phase) components, are sent over the complex channel, the only in-phase and quadrature components of signals distorted by the multipath fading are changed the same as signals distorted by the noise. So the cross components are canceled in the frequency-domain equalizer. The time-domain equalizer and the adaptive algorithm that has lower-error probability and fast convergence speed are applied to compensate for the error that is caused by canceling the cross components in the frequency-domain equalizer. In the time-domain, To compensate for the performance of frequency-domain equalizer the time-domain equalizes the distorted signals at a frame by using the Gold-code as a training sequence in the receiver after the Gold-codes are inserted into the guard signal in the transmitter. By using the proposed equalization method, we can achieve faster and more efficient equalization method that has the reduced computational complexity and improved performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.3A
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• pp.271-280
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• 2007

This paper presents a power control scheme for OFDM based wireless communication systems in a multicell environment with co-channel interference which enables each system to achieve its target level of transmission bit rate. Generally, the optimal or near optimal power control scheme for multicarrier systems is Down to control the power level of each subcarrier in accordance with the associated channel status, which may be found in WF(waterfilling) and WF(iterative waterfilling) schemes. However, this requires the channel state information associated with every subchannel to be fed back from the receiver to its transmitter for successful power control. If the wireless channel exhibits relatively fast fading or the number of subcarriers is large, this may result in a considerable overhead. Here, in order to alleviate this problem, we propose a power control strategy for an OFDM systems maintaining the same power level over all the subcarriers. Also we prove its convergence, compare its complexity with that of the existing IWF algorithm, and examine its convergence characteristic through computer simulations.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.7
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• pp.646-652
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• 2013

EU's Galileo project is a market-based GNSS (Global Navigation Satellite System) that is under development. It is expected that Galileo will provide the positioning services based on new technologies in 2020s. Because Galileo E1 signal for OS (Open Service) shares the same center frequency with GPS L1 C/A signal, CBOC (Composite Binary Offset Carrier) modulation scheme is used in the E1 signal to guarantee interoperability between two systems. With E1 signal consisting of a data channel and a pilot channel at the same frequency band, there exist several options in designing signal acquisition for Assisted-Galileo receivers. Furthermore, compared to SNR worksheet of Assisted-GPS, some factors should be examined in Assisted-Galileo due to different correlation profile and code length of E1 signal. This paper presents SNR worksheets of Galileo E1 signals in E1-B and E1-C channel. Three implementation losses that are quite different from GPS are mainly analyzed in establishing SNR worksheets. In the worksheet, hybrid long integration of 1.5s is considered to acquire weak signal less than -150dBm. Simulation results show that the final SNR of E1-B signal with -150dBm is 19.4dB and that of E1-C signal is 25.2dB. Comparison of relative computation shows that E1-B channel is more profitable to acquire the strongest signal in weak signal environment. With information from the first satellite signal acquisition, fast acquisition of the weak signal around -155dBm can be performed with E1-C signal in the subsequent satellites.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.8 s.350
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• pp.59-68
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• 2006

The study on the uniform error property of codes has been restricted to additive white Gaussian noise (AWGN) channel, which is generally referred to as geometrical uniformity. In this paper, we extend the uniform error property to space-time codes in multiple-input multiple-output (MIMO) channel by directly treating the probability density functions fully describing the transmission channel and the receiver. Moreover, we provide the code construction procedure for the geometrically uniform space-time trellis codes in fast MIMO channels, which consider the distance spectrum. Due to the uniform error property, the complexity of code search is extensively reduced. Such reduction makes it possible to obtain the optimal space-time trellis codes with high order states. Simulation results show that new codes offer a better performance in fast MIMO channels than other known codes.

• Journal of Broadcast Engineering
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• v.18 no.3
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• pp.474-480
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• 2013

In orthogonal frequency division multiplexing system (OFDM), rapid channel variation caused by fast moving receiver leads to a loss of subcarrier orthogonality which results in inter-carrier interference (ICI) and receiver performance degradation. In conventional receivers, performance is enhanced by estimating ICI and removing it from received signals. In this paper, an ICI reduction scheme using a time-domain mask and adding is proposed. The proposed scheme is applied to DVB-T receiver to prove the Doppler mobile performance enhancement.

• Proceedings of the IEEK Conference
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• 1999.11a
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• pp.67-70
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• 1999

DS-CDMA is used to widely spread spectrum for a cellular mobile digital communication that maximizing users- capacity at the limited frequency bandwidth, solving technical matters with the channel. Especially, the capability of a spread spectrum receiver relied on fast code acquisition time at the demodulation. In this paper, we considered that fast code acquisition time when a spread spectrum system is designed, and existed code acquisition system set up one code epoch on a position at initial processing, but the proposed code acquisition system improved that two code epoch are set up at the same time, therefore code acquisition time is diminished in effect. The structure modeling to VHDL language. Its synthesized the synthesized and, is implemented FPGA chip

• Journal of Advanced Navigation Technology
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• v.21 no.6
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• pp.659-665
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• 2017

In this paper, a low complexity fast Fourier transform(FFT) processor is proposed for multiple input multiple output(MIMO) systems. The IEEE 802.11ac standard has been adopted along with the demand for a system capable of high channel capacity and Gbps transmission in order to utilize various multimedia services using a wireless LAN. The proposed scalable FFT processor can support the variable length of 64, 128, 256, and 512 for 8x8 antenna configuration as specified in IEEE 802.11ac standard with MIMO-OFDM scheme. By reducing the required number of non-trivial multipliers with mixed-radix(MR) and multipath delay commutator(MDC) architecture, the complexity of the proposed FFT processor was dramatically decreased. Implementation results show that the proposed FFT processor can reduced the logic gate count by 50%, compared with the radix-2 SDF FFT processor. Also, compared with the 8-channel MR-2/2/2/4/2/4/2 MDC processor and 8-channel MR-2/2/2/8/8 MDC processor, it is shown that the gate count is reduced by 18% and 17% respectively.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.43 no.3 s.309
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• pp.9-16
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• 2006

Many image and video compression algorithms work by splitting the image into blocks and producing variable-length code bits for each block data. If variable-length code data are transmitted consecutively over error-prone channel without any error protection technique, the receiving decoder cannot decode the stream properly. So the standard image and video compression algorithms insert some redundant information into the stream to provide some protection against channel errors. One of redundancies is resynchronization marker, which enables the decoder to restart the decoding process from a known state in the event of transmission errors, but its usage should be restricted not to consume bandwidth too much. The Error Resilient Entropy Code(EREC) is well blown method which can regain synchronization without any redundant information. It can work with the overall prefix codes, which many image compression methods use. This paper proposes EREREC method to improve FEREC(Fast Error-Resilient Entropy Coding). It first calculates initial searching position according to bit lengths of consecutive blocks. Second, initial offset is decided using statistical distribution of long and short blocks, and initial offset can be adjusted to insure all offset sequence values can be used. The proposed EREREC algorithm can speed up the construction of FEREC slots, and can improve the compressed image quality in the event of transmission errors. The simulation result shows that the quality of transmitted image is enhanced about $0.3{\sim}3.5dB$ compared with the existing FEREC when random channel error happens.