• ETRI Journal
• /
• 제20권1호
• /
• pp.16-27
• /
• 1998

In this paper, we consider the acquisition performance of an IS-95 reverse link access channel slot as a function of system design parameters such as postdetection integration length and the number of access channel message block repetitons. The uncertainty region of the reverse link spreading codes compared to that of forward link is very small, since the uncertainty region of the reverse link is determined by a cell radius. Thus, the parallel acquisiton technique in the reverse link is more efficient than a serial acquisition technique in terms of implementation and of acquisition time. The parallel acquisition is achieved by a bank of N parallel I/Q noncoherent correlator are analyzed for band-limited noise and the Rayleigh fast fading channel. The detection probability is derived for multiple correct code-phase offsets and multipath fading. The probability of no message error is derived when rake combining, access channel message block combining, and Viterbi decoding are applied. Numerical results provide the acquisition performance for system design parameters such as postdetection integration length and number of access channel message block repetitions in case of a random access on a mobile station.

• 한국가시화정보학회지
• /
• 제5권1호
• /
• pp.37-42
• /
• 2007

Reverse flow occurs in a channel when there is an obstruction at the entry. However it has been shown recently that reverse flow can be realized without an obstruction, by staggering the sides of the channel and placing it at an angle of attack to the oncoming flow. In this study the latter flow is computationally investigated. Studies have been carried out for different widths (gap between the two walls forming the channel), and at an angle of attack of 30. The results have captured all the essential features of this complex phenomenon and show the time dependent pumping mechanism which leads to the occurrence of reverse flow.

• 한국통신학회논문지
• /
• 제22권3호
• /
• pp.562-570
• /
• 1997

In Direct Sequence Code Division Multiple Access(DS/CDMA) communication systems, it is important to contraol the power of reverse link channel evenly for overall channel capacity. To control the reverse link powers efficiently, it is necessary to estimate signal quality of each reverse link channel. In this paper, we discuss a method to estimate the signal-to-noise ratio(SNR) for each channel by measuring the powers of pilot and noises. Computer simulations are done to show the effectiveness of the scheme.

• 한국가시화정보학회:학술대회논문집
• /
• 한국가시화정보학회 2006년도 추계학술대회 논문집
• /
• pp.11-16
• /
• 2006

Reverse flow occurs in a channel when there is an obstruction at the entry, However it has been shown recently that reverse flow can be realized without an obstruction, by staggering the sides of the channel and placing it at an angle of attack to the oncoming flow. In this study the latter flow is computationally investigated. And the mechanism is investigated using PIV (Particle Image Velocimetry) method. The results have captured all the essential features of this complex phenomenon and show the time dependent pumping mechanism which leads to the occurrence of reverse flow.

• 한국가시화정보학회:학술대회논문집
• /
• 한국가시화정보학회 2006년도 추계학술대회 논문집
• /
• pp.36-41
• /
• 2006

Reverse flow (i.e. flow in the direction opposite to the free stream) inside a channel occurs when an obstruction is placed at certain positions near the near to the channel, placed in another wider channel. In this paper the reverse flow in a duct (diameter D) with an obstruction at the front (which is a disc), is investigated using PIV. The gap g between the obstruction and the entry to the duct is systematically varied and it is found that maximum reverse flow occurs at a g/D value of 0.5. The flow is stagnant around g/D of 1.25 and forward flow occurs for g/D values of 1.5 and above.

• 대한전기학회논문지:전기물성ㆍ응용부문C
• /
• 제51권3호
• /
• pp.99-104
• /
• 2002

lateral insulated gate bipolar transistors(LIGBTs) are extensively used in high voltage power IC application due to their low forward voltage drops. One of the main disadvantages of the LIGBT is its scow switching speed when compared to the LDMOSFET. And the LIGBT with reverse channel structure is lower current capability than the conventional LIGBT at the forward conduction mode. In this paper, the LIGBT which included p+ ring and p-channel gate is presented at the reverie channel structure. The presented LIGBT structure is proposed to suppress the latch up, efficiently and to improve the turn off time. It is shown to improve the current capability too. It is verified 2-D simulator, MEDICI. It is shown that the latch up current of new LIGBT is 10 times than that of the conventional LIGBT Additionally, it is shown that the turn off characteristics of the proposed LIGBT is i times than that of the conventional LIGBT. It is net presented the tail current of turn off characteristics at the proposed structure. And the presented LIGBT is not n+ buffer layer because it includes p channel gate and p+ ring.

• 융합신호처리학회논문지
• /
• 제2권2호
• /
• pp.55-61
• /
• 2001

본 논문에서는 cdma2000 규격을 채용한 역방향 링크 동기식 DS-CDMA 시스템을 시뮬레이션 하여 시스템의 성능을 분석하였고, 파일롯 채널과 정보 채널 즉, 기존의 트래픽 채널간의 최적 전력비를 구하였다. cdma2000 시스템은 기존의 IS-95와는 달리 파일롯 채널을 이용하여 페이딩 채널을 추정하고 이를 이용하여 채널 환경에 의한 수신신호의 위상변화를 보강해 준다. 채널 추정길이 31pcg 심볼에서 파일롯 채널과 트래픽 채널의 최적 전력비를 구하였다. 또한 시스템에 전력 제어를 적용하여 목표 FER을 만족시키기 위한 required Eb/No를 구하였고, 다중의 사용자가 고속의 데이터를 동시에 전송할 때의 성능을 분석하였다.

• 한국정보통신학회:학술대회논문집
• /
• 한국해양정보통신학회 2000년도 춘계종합학술대회
• /
• pp.222-225
• /
• 2000

본 논문에서는 차세대 멀티미디어 통신인 IMT-2000 시스템의 엑세스 방식으로 제안되고 있는 cdma2000 규격을 채용한 동기식 CDMA 시스템을 시뮬레이션하여 최적의 역방향 채널 전력비와 채널 추정 길이를 구하였다. 제안된 시스템은 기존의 IS-95와는 달리 Pilot 채널을 이용하여 페이딩 채널을 추정하며, 이에 따라 최적의 추정 길이(Estimation Lengths)가 요구된다. 따라서 본 논문에서는 Pilot Channel과 Fundamental Channel의 전력비에 따라 요구되는 최적의 추정 길이를 구하였고, 또한 고정된 추정 길이에서 전력비의 변화에 따른 FER을 구하였다.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 2000년도 ITC-CSCC -2
• /
• pp.982-985
• /
• 2000

This paper presents channel estimation of an asynchronous W-CDMA reverse link using the interpolation and moving average algorithm in frequency-selective Rayleigh fading channel. The proposed algorithm is an interpolated decision-directed (IDD) block-wise moving average (BWMA) algorithm. The IDD-BWMA algorithm performs two- stage processes. The first stage performs data decision to make a virtual pilot channel by using linear interpolation channel estimation scheme. Then, the second stage performs the channel estimation of the “block-wise moving average” type by using a virtual pilot channel obtained in the first stage. By using Monte-Carlo computer simulations, we show that the proposed channel estimator is superior to other estimation schemes such as the WMSA(K=1) and DD-RAKE at higher Doppler frequencies, especially.

• Journal of Mechanical Science and Technology
• /
• 제17권6호
• /
• pp.879-887
• /
• 2003

The flow in a parallel walled test channel, when obstructed with a geometry at the entrance, can be forward, reverse and stagnant depending on the position of the obstruction. This interesting flow phenomenon has potential benefit in the control of energy and various flows in the process industry In this experiment, the flat plate obstruction geometry was used as an obstruction at the entry of the test channel. The parameters that influence the flow inside and around the test channel were the gap (g) between the test channel and the obstruction geometry, the length (L) of the test channel and the Reynolds number (Re). The effect of the gap to channel width ratio (g/w) on the magnitude of the velocity ratio (V$\_$i/ / V$\_$o/ : velocity inside/ velocity outside the test channel) was investigated for a range of Reynolds numbers. The maximum reverse flow observed was nearly 20% to 60% of the outside velocity for Reynolds number ranging from 1000 to 9000 at g/w ratio of 1.5. The maximum forward velocity inside the test channel was found 80% of the outside velocity at higher g/w ratio of 8. The effect of the test channel length on the velocity ratio was investigated for different g/w ratios and a fixed Reynolds number of 4000. The influence of the Reynolds number on the velocity ratio is also discussed and presented for different gap to width ratio (g/w). The flow visualisation photographs showing fluid motion inside and around the test channel are also presented and discussed.