Kouji Ohuchi

Throughput Evaluation of ARQ Scheme for Multi-route Coding in Wireless Multi-hop Networks

For reduction in bit errors on wireless channels, we proposed the multi-route coding scheme on multiple routes for wireless multi-hop networks. In this paper, we introduce ARQ to the multi-route coding. In the multi-route coding, the destination node combines and decodes sub packets which are encoded and divided by the source node. The intermediate node relays a sub packet, that is, only a part of a packet. Therefore, the intermediate node cannot detect packet errors, and only the destination node can do after combining and decoding sub packets. We propose the ARQ scheme between the source node and the destination node. We analyze the proposed ARQ scheme and evaluate the throughput performance

Construction of hierarchical optical broadcasting systems for intelligent transport system

The local broadcast systems, that transmit both the wide-area information and the local-area information, are proposed. A nearby user, which is near to the broadcasting station, demodulates together the wide-area information and local-area information. Even if a distant user, which is far to the station, does not receive the local-area information, it is expected that he receives wide-area information only. In the proposed systems, the broadcast information is hierarchized by combining the two modulation scheme. In particular, the two proposed systems are described; the ASK-CSK system which combines amplitude-shift-keying(ASK) with code-shift-keying(CSK) and the CNK-CSK system which combines code-number-keying(CNK) with CSK. The CNK-CSK system is superior to the ASK-CSK system.

Effect of route diversity by employing turbo coding in multihop ad hoc and mesh networks

Sensor networks have attracted enormous attention in recent years. These networks can form a multiroute multihop structure by the signal relaying via multiple sensor nodes. When the signals are transmitted over multiple routes, route diversity effect becomes possible. This effect can help in preventing performance degradation caused by the quality loss of each route. Forward Error Correction (FEC) schemes and turbo coding can be expected to enhance the route diversity. A turbo encoder generates one message stream and two parity streams whilst the message stream is influential for decoding process rather than the parity streams. Thus by allocating the message stream to a reliable route, the performance degradation could be prevented. In this paper, we examine the effect of the route diversity in multihop networks using turbo codes. The diversity effect against the quality loss of the multiple routes is investigated. We adopt the triangle mesh networks for the evaluation. The results suggest that the multiroute transmissions have high diversity effect. They also suggest that large performance degradation can be prevented by appropriate route assignment of the streams even though the link quality of the multiple routes cannot be guaranteed.

Performance of Channel Information Estimation Method Utilizing Parity Check Bits for Turbo Coded Multi-route Multi-hop Networks

Recently, sensor networks have been drawing many attentions. The networks can be applicable to many communication systems such as emergency communications, intelligent transportation systems, and so on. They could have a multi-route multi-hop structure by the signal relaying via multiple sensor nodes. Since the wireless links have very severe condition for the communications, a method which can maintain the quality of the links is required. Forward error correction techniques and turbo codes are effective ways to prevent performance degradation by the wireless links. In the multi-hop multi-route structure, the route diversity can be enhanced by using the error correction codes. For the decoding process of the turbo codes, the receiver should estimate the channel information to obtain high decoding performance. Although many channel information estimation methods are not applicable to the multi-hop structure, the channel information estimation method utilizing parity bits can be applied. In this paper, we investigate the route diversity effect of the channel information estimation scheme. We also provide performance comparison between the proposed scheme and the pilot aided scheme. The results suggest that the proposed scheme is effective in obtaining the route diversity.

Bit-error-rate Performance Improvement in Wireless Multi-hop Ad Hoc Networks using Route Diversity Considerations

Multi-hop multi-route networks are promising candidate for achieving the high channel capacity. The networks have high applicability to various new communications. Especially sensor networks are one of the attractive applications of the multihop multi-route networks. When the signals are transmitted over multiple routes, a route diversity effect would be possible. The effect can help to prevent performance degradation caused by quality loss of every route. Forward error correction schemes and turbo coding can be expected to enhance the route diversity. As it would be well known, a turbo encoder generates one message stream and two parity streams and the message stream is more important than the parity streams for reliable communications. Thus by allocating the message stream to a reliable route, the performance degradation could be prevented. In this paper, we examine the effect of the route diversity on multi-hop networks using turbo codes. The diversity effect against the quality loss of the multiple routes is investigated. The results suggest that the multi-route transmissions have high diversity effect. They also suggest that large performance degradation can be prevented by appropriate route assignment of the streams even though the link quality of the multiple routes can not be guaranteed.

Performance improvement of turbo coded multi-route multi-hop networks using parity check codes

Wireless multi-hop networks are promising techniques for next generation wireless communications. Multi-hop networks have large channel capacity and can achieve multi-route transmissions. By using multi-route transmissions, we can obtain a route diversity effect at the destination nodes. In order to enhance the diversity effect, we usually adopt forward error correction techniques. Forward error correction techniques and turbo codes effectively work against severe wireless environment including fading channels. The iterative turbo decoder requires accurate channel information to achieve good decoding performance. In multi-hop transmissions, however, the receiver usually measures only the channel information of the last hop and it does not know the channel information of the whole route. In this paper, we propose the turbo coded multi-route multi-hop networks using parity check bits. By using parity bits, we can easily estimate the whole channel information in multi-route multi-hop networks. Using numerical examples, we show that the proposed scheme improves the performance in the fast fading channel conditions.

Effect of parity check bits in turbo coded multi-route multi-hop networks

One technique to provide high data transmission for large number of users in mobile cellular networks is to arrange the network in a multi-hop structure. Multi-hop networks have large channel capacity and can achieve multi-route transmissions. When the information bit streams are transmitted over multiple routes, a route diversity effect would also be possible. In multiroute transmission, we usually require the routing protocols which can make every route condition be equal. The requirement, however, makes the routing algorithm be complex and causes large power consumption. Forward error correction schemes and turbo coding can be far from the strict requirement although they enhance the effect of route diversity. When applying the turbo codes, the receiver should know the channel condition for iterative decoding. Thus we have to consider how to obtain the channel information over the multi-route multi-hop network. Furthermore, the performance would improve when the destination knows the difference of the route reliability. In this paper, we propose the turbo coded multi-route multi-hop networks using parity check bits. By using parity bits, we can easily estimate the channel information in multi-route multi-hop networks. Using numerical examples we show that the proposed scheme improves the performance in additive white Gaussian noise and slow fading channel conditions

Proposal of an iterative channel information estimation scheme on multi-hop networks

In this paper, a new channel information estimation scheme for multi-route multi-hop networks is discussed. Multi-hop network has received much attention recent years because of its large channel capacity. When the information bit streams are transmitted over multiple routes, a route diversity effect would also be possible. In order to improve the route diversity effect the receiver has to obtain the channel information for each route. Therefore we have to consider how to obtain the channel information over the multi-route multi-hop networks. The proposed scheme exploits the number of error-corrected bits in the decoding process to estimate the channel information. In this paper, the bit error rate (BER) performance of the proposed scheme is investigated by computer simulations. As the result, the proposed scheme has a better BER performance than the conventional one which uses parity check bits to obtain the channel information. The advantage of the proposed scheme is maintained even if the route conditions is nonuniform.

Analysis of the bi-orthogonal modulation system using two different inner sequences

In this paper, a frame synchronization method for the bi-orthogonal modulation system is proposed. The bi-orthogonal modulation system is an attractive system because the bit error rate (BER) performance improves as the number of sequences, which is employed in the system, increases under an additive white gaussian noise environment. Frame synchronization of the bi-orthogonal modulation system is difficult, however, because the bi-orthogonal modulation system uses several sequences for data transmission. In this paper, we show a frame synchronization system that utilizes two different inner sequences. This system enables the receiver to extract the frame timing from the received signal by using the conventional delay lock loop in total independence from the transmitted sequence. In this paper, we analyze the tracking performance of the proposed frame synchronization system. Moreover, the BER performance considering the tracking performance is investigated. As the result, it is found that there is a trade-off between the BER performance and the tracking performance. Furthermore, it is shown that the BER performance of the proposed system is better than that of binary phase shift keying by 1 [dB] at 10/sup -5/ BER.

Proposal for superposed ACO-OFDM using several even subcarriers

In this paper, we develop the conventional Asymmetrically Clipped Optical OFDM (ACO-OFDM) to propose a new OFDM for optical wireless communication with Intensity Modulation / Direct Detection (IM/DD). Although the conventional ACO-OFDM multiplexes only odd subcarriers, we reveal that some even subcarriers do not interfere with odd ones even if we clip their negative signal part. Then, we can superpose those even subcarriers on odd ones. In this paper, we show that the proposed system is able to use 1.5 times as many subcarriers as the conventional ACO-OFDM does in the same bandwidth. However, the superposed even subcarriers are affected by the odd ones in the demodulation process. Hence, we introduce an interference canceller to reduce the interference from the odd ones. We investigate the bit error rate (BER) of the proposed system, and compare it with that of the conventional ACO-OFDM. When we apply 8QAM and 4QAM for the conventional ACO-OFDM and the proposed system, respectively to achieve the same data transmission rate, the proposed system has a better BER about 1 dB than that of the conventional ACO-OFDM.