This study focuses on visible light communications using a high-speed display and rolling-shutter camera of a smartphone. We aim to achieve high-quality communication imperceptible to the human eye through the high-speed display. The capture rate of an image sensor is generally slow. Then, the image sensor cannot obtain some parts of a transmitted data image because of the high-speed display rate. We employ the rolling shutter camera that reads pixels row by row and propose a receiving scheme in which the camera obtains some transmitted data images in a captured image. The proposed scheme can acquire transmitted data, even if the display rate is higher than the capture rate. We experimentally evaluate the proposed scheme in terms of the quality of the visual information and the communication quality to clarify its superiority.

Root raised cosine roll-off (RRC) filter is one of the most fundamental elements in modern digital communications. This paper proposes a new method to efficiently realize the RRC filter. The method employs cubic Hermite interpolation to obtain a piecewise-polynomial approximation for the impulse response of the RRC filter. Then, the approximated impulse response is efficiently realized by using a transversal filter with a very small number of taps followed by integrators with a simple recursive structure, named cascaded recursive finite impulse response (CR-FIR) filter. As an example, an RRC filter with roll-off factor 0.5 is constructed by using the CR-FIR filter with only nine multipliers. Performance of the RRC filter in matched filtering is examined by computer simulations. Then, it is shown that the constructed RRC matched filter has nearly the same performance as the ideal filter.

In this paper, we focus on a X channel; a system with two transmitters and two receivers each equipped with a single antenna, where independent messages need to be conveyed over channels from each transmitter to each receiver. A key concept of that arises in the context of the X channel is interference alignment (IA) that refers to an overlap of signal spaces occupied by undesired interference at each receiver while keeping desired signal spaces distinct. However, all the channel responses and the precise time synchronization are required at every transmitter and receiver to realize the IA, which are seriously demanding in practice. In this paper, we propose semi-blind IA (S-BIA) scheme exploiting frequency selectivity of wireless channels using orthogonal frequency division multiplexing (OFDM), which only requires channel responses corresponding to each transmitter. Numerical results confirm that proposed S-BIA can achieve the same degrees of freedom as conventional IA even in the presence of time synchronization errors.

In this paper, we propose a new automatic repeat request (ARQ) scheme, named Go-Back-i-symbol (GBi) ARQ scheme, suitable to Meteor Burst Communications (MBC). The scheme realizes symbol-wise ARQ by using the Viterbi decoding algorithm for convolutional codes. We also propose a practical transmission protocol for applying the GBi-ARQ scheme to packet communications over time varying short burst channels such as meteor burst channels. Fundamental performances of the GBi-ARQ scheme in MBC are evaluated by computer simulations. Effectiveness of the GBi-ARQ scheme is shown by comparing the performance with that of a conventional block-wise ARQ scheme.

Recently, collaborative (or cooperative) multi-hop transmissions have gained much attention since they can achieve highly reliable communication and longer life of each node simultaneously. While it is often assumed that each cluster in collaborative multi-hop transmissions has an identical number of nodes in the literature, this assumption is not reasonable since the sensor nodes are not uniformly distributed in practice. In this paper, we analyze the collaborative multi-hop transmission in non-uniformly distributed networks in terms of outage probability. Using analytical results, we provide a design guideline of the networks. We further show that the appropriately designed networks may potentially achieve the superior outage performance compared with conventional uniformly distributed networks.

In this paper, we propose a new ARQ scheme, named Go-Back-i-symbol (GBi) ARQ scheme which is suitable to Meteor Burst Communications (MBC). The scheme is based on the Viterbi decoding algorithm for convolutional codes and can achieve symbol-wise retransmission, so that it has high throughput performance for packet communication systems over time varying short burst channels such as MBC channels. We also propose a practical transmission protocol for applying the GBi-ARQ scheme to MBC systems. Comparing to a conventional block-wise ARQ scheme, the effectiveness of the proposed scheme is shown by computer simulations.

Multi-hop ad-hoc networks are promising candidates for next generation wireless communications. When using HARQ for multi-hop transmissions, each relay node has to decode received messages and request retransmission to its previous node when it detects errors. Thus, every relay node is required to spend extra power and time because of retransmissions and decodes for collaboration of transmission by the source node. We propose a new HARQ scheme that can reduce the load of the relay nodes but maintain high throughput. In this scheme, every relay node neither decodes the received messages nor requests retransmission to reduce the load. Only the destination node decodes messages by using LDPC codes. RC-LDPC codes, which are suitable for Type-II HARQ, are utilized in the proposed ARQ scheme. Throughput performance of the proposed scheme is evaluated to show its effectiveness.

Multi-hop ad-hoc networks are promising candidates for next generation wireless communications. When using HARQ for multi-hop transmissions, each relay node has to decode received messages and request retransmission to its previous node when it detects errors. Thus, every relay node is required to spend extra power and time because of retransmissions and decodes for collaboration of transmission by the source node. We propose a new HARQ scheme that can reduce the load of the relay nodes but maintain high throughput. In this scheme, every relay node neither decodes the received messages nor requests retransmission to reduce the load. Only the destination node decodes messages by using LDPC codes. RC-LDPC codes, which are suitable for Type-II HARQ, are utilized in the proposed ARQ scheme. Throughput performance of the proposed scheme is evaluated to show its effectiveness.

Wireless sensor networks (WSNs) usually have a regular lattice structure and can be considered as multi-hop multi-route networks. In multi-route transmissions, even if the link quality of several routes decreases, the whole performance of the communication would be compensated by the help of the other routes, which is referred to "the route diversity effect". As generally known, forward error correction (FEC) techniques can enhance the route diversity gain. In this paper, route diversity effect in WSNs using turbo codes is investigated. We introduce a WSN having a triangle lattice structure. BER performances of an additive white Gaussian noise channel and a slow Rayleigh fading channel are evaluated in order to show the route diversity effect.

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.

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.

For reduction in transmission errors on wireless links, we proposed the multi-route coding on multiple routes for wireless multi-hop networks. In the proposed coding, a source node encodes a packet, divides it into sub packets, and transmits them on multiple routes. A destination node combines and decodes the arriving sub packets to get coding and diversity gain. In this paper, we propose a hybrid ARQ scheme for the multiroute coding. In a hybrid ARQ, important information is firstly transmitted, and redundant information is retransmitted later. On the other hand, in the multiroute coding, all sub packets should have the same importance because of efficient diversity combining. We investigate the trade-off between hybrid ARQ and multi-route coding

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

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

This paper deals with low density parity check (LDPC) codes on power line communication (PLC). PLC is very attractive for achieving high-rate in-home networks. The noise in power lines is modeled as cyclostationary Gaussian noise processes. In order to achieve reliable communication using power lines, error control techniques need to be taken against the particular noise. We examine the effects of LDPC codes on power line noise environments. The result indicates that LDPC codes have enough capability to limit the influence of the power line noise. It also provides that an accurate SNR estimation technique is required to achieve "good" decoding performance. Furthermore, we find that the performance of LDPC codes is superior to that of turbo codes under the power line noise environments.

Power line communication (PLC) is very attractive for achieving high-rate in-home networks. In order to achieve reliable communication using power lines, effective measures including error control techniques need to be taken against this particular noise. This paper focuses its attention on an effect of turbo codes on PLC. We adopt two noise environments for examining the effect in terms of BER performance. The result of the examination provides that turbo codes have enough capability to limit the effect of the noise. It also provides that the effect depends on the relation between the interleaver size and the period of the AC source. Since an effective SNR estimation scheme should be required to apply turbo codes to PLC, we also examine the effect of the pilot aided SNR estimation scheme in terms of BER performance.

This paper proposes a new initial acquisition method for DS/SS signals with a large carrier frequency offset. In LEO satellite communications, the performance of the initial acquisition is degraded by the effect of a large carrier frequency offset. The proposed method utilizes the property of Walsh functions and is effective against the large carrier frequency offset. The effectiveness of the proposed method is evaluated in terms of mean acquisition time.

We evaluate the bit-error rate performance of direct-sequence spread spectrum (DS/SS) system using /spl pi//4-shift QPSK and /spl pi//2-shift BPSK and observe the effect of the nonlinearity of the high power amplifier (HPA) of transmitters which occurs when the HPA is operated near its saturation region. The hard limiter is chosen as the example of the nonlinear amplifier and the numerical results are reported by using coherent as well as differential detection at the receiving end. With the employment of either /spl pi//4-shift QPSK or /spl pi//2-shift BPSK, the DS/SS signal is not much influenced by the nonlinearity of the HPA as the two modulation schemes have the advantage of nearly constant envelope.