• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.2
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• pp.97-102
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• 2010

In this paper, an area-efficient FFT processor is proposed for IEEE 802.16e mobile WiMax systems. The proposed scalable FFT processor can support the variable length of 128, 512, 1024 and 2048. By reducing the required number of non-trivial multipliers with mixed-radix (MR) and multi-path delay commutator (MDC) architecture, the complexity of the proposed FFT processor is dramatically decreased without sacrificing system throughput. The proposed FFT processor was designed in hardware description language (HDL) and synthesized to gate-level circuits using 0.18um CMOS standard cell library. With the proposed architecture, the gate count for the processor is 46K and the size of memory is 64Kbits, which are reduced by 16% and 27%, respectively, compared with those of the 4-channel radix-2 MDC (R2MDC) FFT processor.

• Journal of Digital Convergence
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• v.12 no.3
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• pp.249-254
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• 2014

Wireless LAN system is evolving toward high-speed data transmission and more accurate channel estimation is necessarily required to improve communication performance. The PLCP preamble field in IEEE 802.11 based wireless MODEM consists of ten short symbols and two long symbols and is used for synchronization and channel estimation. The existing least square (LS) channel estimation is based on only two long training symbols. After estimating channel response separately by using each long training symbol, the final channel estimation is obtained by the average of each estimation. In this paper, a new channel estimation algorithm is presented to improve the performance of the existing LS channel estimation algorithm. From the fact that the short training symbol consists of 12 non-zero subcarriers, it gives us a clue of being able to additionally estimate at least one fourth of channel coefficients. The new LS algorithm performs channel estimation based on both two long training symbols and a short training symbol. The proposed LS algorithm shows a little bit performance improvement over the existing LS estimation and it will be able to be applied to the IEEE 802.11p WAVE system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.5
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• pp.791-798
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• 2015

It has been grown interests of the convergence technologies about communication systems and vehicular industry. Vehicular communications enable a number of infotainment applications to serve cars under high mobility environments. To achieve this goal, a robust and accurate channel estimation scheme is of great importance. This paper proposes an enhanced Decision-Directed channel estimation scheme called PTAU(Pilot Tone Aided Update) for IEEE 802.11p in vehicular communication environment. Existing approaches which use subsequent data symbols to estimate channel response in time domain will lead to the error propagation. In this paper, we use the pilot subcarriers to get initial channel response, then utilize the correlation characteristics to update channel response in frequency domain. Finally, Analysis and simulation results reveal that the proposed scheme outperforms in bit error rate(BER), significantly improve the performance of the estimation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.7 s.361
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• pp.59-69
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• 2007

In this paper, we propose a MIMO-OFDMA (Multi Input Multi Output-Orthogonal Frequency Division Multiple Access) system based on Grassmannian beamforming for performance improvement of downlink real-time traffic transmission in harsh channel conditions with low CIR (Carrier-to-Interference Ratio). In the proposed system to reduce feedback information for the beamforming, we also apply Grassmannian Beamforming. Furthermore, we propose antenna selection scheme which performs the beamforming with more useful transmit antennas. In the proposed system, the optimal combination of transmit antennas with maximum MRT (Maximum Ratio Transmission) beamforming gain, is selected. Simulation results reveal that the proposed MIMO-OFDMA system achieves significant improvement of spectral efficiency in low CIR region as compared to a typical open-loop MIMO-OFDMA system using pseudo-orthogonal space time block code.

• Information and Communications Magazine
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• v.15 no.11
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• pp.124-142
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• 1998

ETSI BRAN (Broadband Radio Access Network)는 고속 무선 LAN 또는 고정 광대역 무선액세스 네트워크에서의 무선 접촉 계층과 ATM 및 IP(Internet Protocol) 코어 네트워크와의 연동을 위한 일부 기능을 표준화하기 위한 과제이다. 특히, BRAN의 HIPERLAN type-2(HIPERLAN/2)의 경우에는 과제의 범위는 무선 접속면, 무선 부시스템에서의 서비스 인터페이스, 서비스 구현에서 요구되는 연동 및 각종 지원 기능을 표준화하며, 무선 접속면의 경우에는 다수 벤더간의 상호 호환성을 제공할 수 있는 인터페이스를 구현하는 것이다. HIPERLAN/2의 기술 규격은 코어 네트워크와 독립적인 물리계층 및 데이터 링크 제어 (DATA Link Control: DLC) 계층과 서로 상이한 코어 네트워크와의 연동을 위한 네트워크 수렴 부계층을 다루게 될 것이며, 초기 단계에서는 ATM과 IP 코어 네트워크와의 연동 기능을 제시하게 될 것이다. 따라서 HIPERLAN/2기반의 시스템 규격을 제시하기 위해서는 네트워크 계층 및 기타 상위 계층에 대한 규격이 요규되며, 이는 ATM Forum에서의 무선 ATM 신호 방식 규격, IETF(Internet Engineering Task Force)의 IP규격, 그리고 ETSI의 SMG (Special Mobile Group) 프로젝트에서 표준화되고 있는 UMTS (Universal Mobile Telecommunication Service) 규격 등과 접목될 것이다. 결과적으로 무선 ATM 관점에서는 완전한 시스템 규격 작성은 ETSI BRAN과 ATM Forum에서 무선 접속 규격과 이동성 관리 및 신호 방식으로 각각 이원화되어 진행되고 있다. 현재 물리 계층에서의 전송 방식은 OFDM(Orthogonal Frequency Division Multiplexing)으로 확정되었으며, DLC 계층에서는 고정 길이의 TDD (Time Division Duplexing) TDMA 프레임 구조를 기반으로 AP (Access Point)에 의해 동적으로 상향 링크 자원을 예약 할당하는 매체 접근 제어 (Medium Access Control: MAC) 프로토콜이 고려되고 있다. 이와 같은 DLC 계층에서는 기본적으로 짧은 길이의 패킷을 통해 다양한 대역폭의 멀티미디어 트래픽을 효율적으로 수용하면서 ATM 네트워크뿐만 아니라 향후 IP 네트워크에서 요구하는 각 서비스별 QoS (Quality of Service)를 개별적으로 보장할 수 있는 기능을 구현하고자 한다. 향후 이 부문에 대한 표준화가 본격적으로 진행될 것으로 예상되며 HIPERLAN/2의 경우에는 1999년 중반까지 1차 기능 규격을 완료할 예정이며, BRAN 전반에 대한 완전한 규격을 2002년까지 완성하는 것을 목표로 하고 있다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.2
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• pp.154-161
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• 2013

This paper presents the signal-to-interference plus noise ratio (SINR) estimation of IEEE 802.16m WirelessMAN-Advanced mobile station with simulation and implementation results. The downlink signal of IEEE 802.16m has two kinds of A-Preambles: the PA-preamble and the SA-preamble. This paper proposes the efficient method of estimating SINR with A-Preambles, by measuring noise power from PA-preamble and measuring interference power and signal power from SA-preamble. The proposed SINR measurement block contains important features such as subcarrier phase rotation elimination and simplified dB transform. The result of this paper is integrated to ETRI's IEEE 802.16m test mobile station, used for decision of adaptive-modulation-and-coding (AMC) and hand-over. It showed good measurement performance in simulation and unified system link test also.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.7A
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• pp.733-742
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• 2008

In 3GPP LTE downlink system, initial cell search is essential for mobile station to connect to base station. In order to obtain information of the base station, the mobile station detects frame timing, frequency offset, and cell identification using primary synchronization channel(PSC) and secondary synchronization channel(SSC), which are defined in downlink OFDMA specification. In this paper, we analyze various detection algorithms in practical environment of inter-cell-interference, frequency offset, and multi-path fading channel and propose the optimal algorithm. Simulation results show that partial correlation method (for PSC acquisition) and interference cancellation method (for SSC detection) are the most superior algorithms among the applicable algorithms. Employ these two algorithms for receiver design, initial cell search is performed with 99% probability within 70ms in the channel environment considered.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.10
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• pp.156-161
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• 2007

In a TDD system, the length of slots can be unequal, and the number of downlink (DL) and uplink (UL) slots per frame can be different as well. The advantage of using TDD is the capability to accommodate asymmetric high-bit-rate services for the DL and It, which will be one of the prominent features in 4G systems. This paper analyzes the performance of TDD system on mobile channel environments like indoor pedestrian and vehicular channel, and proposes optimum modulation/demodulation method in TDD system. A rectangular QAM (RQAM) used in various communication systems has good BER performance but the much more signal amplitudes also have become one of the barriers to implement receiver. While PSK receiver is implemented easily because it has a constant amplitude, but it's BER performance is worse than RQAM. APSK proposed in this paper integrates merits of RQAM and PSK, and minimizes demerits of then And a simple method is also proposed to demodulate the soft symbol. The results indicate that the proposed APSK has a little worse performance than RQAM but the dynamic range of APSK is about 4 dB, 8 dB better than RQAM at 16-ary, 64-ary modulation/demodulation respectively.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.5
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• pp.117-121
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• 2014

In the orthogonal frequency division multiplexing system, the prefix inserted between data symbols should be eliminated to apply the Fourier transform on the valid symbol interval. This functional procedure should be based on the accurate symbol timing detection. The symbol timing detection at the receiver side provides the reference for determining the beginning time index of each symbol whose initial point is located at the boundary between the preamble and the payload part. Also, the detection error is one of the main factors in the overall system performance. In this paper the effect of the bandwidth of the moving average filter on the symbol timing detection is discussed. Simulations are carried out to analyze the detection performance for the varying values of the window size of the moving average filter which is related to the filter bandwidth.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6A
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• pp.593-602
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• 2006

This paper propose to methodology for deciding suitable bit size that minimizes hardware complexity and performance degradation from floating-point design the fixed-point implementation of downlink traffic channel of IEEE 802.16e OFDMA TDD system. One of the major considering issues for implementing fixed-point design is to select Saturation or Quantization properly with the knowledge of signal distribution by pdf or histogram. Also, through trial and error, we should execute exhaustive computer simulation for various bit sizes, hence obtain appropriate bit size while minimizing performance degradation. We carry out computer simulation to decide the optimized bit size of downlink traffic channel under AWGN and ITU-R M.1225 Veh-A channel model.