• The Journal of the Korea institute of electronic communication sciences
• /
• v.2 no.2
• /
• pp.129-135
• /
• 2007

In this paper, we present hybrid ARQ techniques to improve the throughput performance in high speed packet transmission such as Internet or multimedia services in Hospital. In order to evaluate the performance of the three different types of hybrid ARQ schemes, systemized link level simulations based on WWW traffic model are considered. In this paper, we also consider the simulated performance for an average link throughput and a normalized packet delay to compare the hybrid ARQ with link adaptation scheme in GPRS.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.8 no.6
• /
• pp.73-81
• /
• 2009

Wireless media communication has lower robustness and stability than wired communication because of narrow bandwidth and unstable channel state. To make up for the deficient points of wireless communication, we used the diversity effect of cooperation communication and the error correction effect of channel coding schemes. In this paper, the cooperative communication system with RCPC codes and Hybrid ARQ transmission scheme is proposed for improving reliability on wireless communication, and we executed these simulations. From the simulation results, proposed system is showed lower BER performance than legacy system. In addition, we confirm the fact that the channel state of Relay-node and source-node is more important than the channel state of Relay-node and destination-node.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.1A
• /
• pp.9-12
• /
• 2007

In this paper, we propose and analyze a scheme for wireless channels, which is a combination of a type I hybrid-automatic repeat request (H-ARQ) scheme and a power ramping. The power ramping is considered for more reliable downlink data transmission, in which the transmission power is gradually changed from a small level to a large level when the number of retransmissions increases. The simulation results demonstrate that, when the power ramping step size is 0.5dB, the average throughput gain may be as high as 2% to 5% with properly selected parameters.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.24 no.9B
• /
• pp.1616-1623
• /
• 1999

This paper describes error resilient coding scheme is added in WLL system and its application for robust low-bit rate still image transmission over power controlled W-CDA system Rayleigh fading channels. The baseline JPEG compressing methods are uses in image coding over wireless channel. The channel uses Reed-Solomon(RS) outer codes concatenated with convolutional inner codes, and truncated type I hybrid ARQ protocol based on the selective repeat strategy and the RS error detection capability. Simulation results are proved for the statistics of the frame-error bursts of the proposed system in comparison with conventional WLL system. it gains the 2 dB of the Eb/No in same BER.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.7 no.1
• /
• pp.9-18
• /
• 2003

In this paper, we analyzed the throughput of DS/CDMA system applying packet combining scheme combined with Type- I Hybrid ARQ scheme over AWGN channel and Nakagami fading channel with RAKE receiver. As the parameter for analysis, we used number of combined packet(L), number of diversity branch$({L_c})$, fading index(m), and length of packet(N), and used CRC-12 error detection code and (2,1,3) convolutional code. As a results, we found that throughput of system over Nakagami fading channel with RAKE receiver was superior to throughput over AWGN channel, and throughput of system decreases rapidly as channel degrades when number of combined packet(L) was increased. However throughput of system with the combining scheme was achieved even at low ${E_b}/{N_o}$. Also, we found that throughput of system was increased when fading index(m) and number of diversity branch$({L_c})$ were increased, but it was decreased when number of user(K) and length of packet(N) were increased.

• Journal of Communications and Networks
• /
• v.8 no.2
• /
• pp.212-219
• /
• 2006

In this paper, a new turbo codes-based hybrid automatic repeat request (TC-HARQ) scheme with segment selective repeat (SSR) is proposed. The main strategy is, upon retransmission, to repeat the data that are most important for the next round of decoding based on the distribution of residual errors after current decoding. The performance in terms of reliability and throughput is analyzed. To adapt to correlated fading channels where an inter-leaver is always employed before transmission, we further modify the SSR strategy so that data having experienced correlated deep fading are selected for retransmission. Finally, this proposed scheme is applied to the wideband code division multiple access (WCDMA) system under frequency selective fading channels. Simulation results demonstrate that in all single and multiple user cases, SSR-based TC-HARQ leads to significant throughput improvement with similar bit error rate (BER) performance as compared to type-I TC-HARQ.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2001.10a
• /
• pp.693-696
• /
• 2001

본 논문에서는 무선 홈네트워킹 시스템으로 대두되고 있는 Wireless LAN(802.11), HomeRF, Bluetooth 성능을 간섭이 고려되지 않는 경우의 실내 무선 환경하에서 시스템의 변조 방식만을 고려하였으며 실내환경에서 발생되는 에러에 대한 제어 기술로 Truncated Type-B Hybrid ARQ를 적용하였다. 무선 홈네트워킹 시스템의 채널 수 및 주파수 대역은 동일하며 실내 무선 환경을 라이시안 페이딩 환경으로 고려하였을 경우, 직직접파 대 반사파 전력비(K)가 6[dB]인 라이시안 페이딩 환경하에서 오율 $10^{-3}$을 기준으로 할 때 2FSK가 DQPSK보다는 E$_{b}$ /N$_{o}$ 가 약 3[dB] 정도 우수하며 오율 $10^{-6}$을 기준으로 비교하여 보면, DPSK 방식이 4FSK 보다 약 E$_{b}$ /N$_{o}$ 가 5[dB] 우수하였다. 또한 K=6인 라이시안 환경하에서 변조 방식만을 고려한 경우보다 성능 개선 기법을 채용한 무선 홈네트워킹 시스템의 E$_{b}$ /N$_{o}$ 가 더 우수함을 알 수 있었다.

• Journal of Communications and Networks
• /
• v.2 no.1
• /
• pp.76-84
• /
• 2000

Communication systems, including cell-based mobile communication systems, multiple satellite communication systems of multi-beam satellite systems, require reliable handoff methods between cell-to-cell, satellite-to-satellite of beam-to-team, respectively. Recent measurement of a CDMA cellular system indicates that the system is in handoff at about 35% to 70% of an average call period. Therefore, system reliability during handoff is one of the major system performance parameters and eventually becomes a factor in the overall system capacity. This paper presents novel and improved techniques for handoff in cellular communications, multi-beam and multi-satellite systems that require handoff during a session. this new handoff system combines the soft handoff mechanism currently implemented in the IS-95 CDMA with code and packet diversity combining techniques and an iterative decoding algorithm (Turbo Coding). the Turbo code introduced by Berrou et all. has been demonstrated its remarkable performance achieving the near Shannon channel capacity [1]. Recently. Turbo codes have been adapted as the coding scheme for the data transmission of the third generation international cellular communication standards : UTRA and CDMA 2000. Our proposed encoder and decoder schemes modified from the original Turbo code is suitable for the code and packet diversity combining techniques. this proposed system provides not only an unprecedented coding gain from the Turbo code and it iterative decoding, but also gain induced by the code and packet diversity combining technique which is similar to the hybrid Type II ARQ. We demonstrate performance improvements in AWGN channel and Rayleigh fading channel with perfect channel state information (CSI) through simulations for at low signal to noise ratio and analysis using exact upper bounding techniques for medium to high signal to noise ratio.