Maw-Yang Liu

Quality of service-guaranteed cluster-based multihop wireless ad hoc sensor networks

With the help of prioritised polling token and a local synchronisation scheme, this study proposes a quality of service (QoS)-guaranteed scheduling algorithm. It works based on distributed intelligence and schedules both intra-cluster and inter-cluster connections in a cluster-based multihop wireless ad hoc sensor network. Theoretical analyses are employed to derive the bounds for the jitter and delay of each intra-cluster and inter-cluster connection. Based on the obtained jitter bounds and delay bounds, a connection admission control scheme is proposed as the admission criterion for each newly requested connection. Both numerical and simulation results show that by taking the advantages of proposed polling-based QoS scheduling algorithm and the connection admission control jointly, the QoS requirements of all admitted intra-cluster and inter-cluster connections are guaranteed.

Utilization of LDPC Code and Optical Hard-Limiter in OCDMA Communication Systems

In this paper, we investigate the utilization of low-density parity-check (LDPC) code and optical hard-limiter in OCDMA communication systems. Since the multiple access interference will impose significant penalty on system performance, using optical hard-limiter is an effective countermeasure to relieve this adverse impact. To further increase the aggregate capacity, the LDPC code is employed as an error correction mechanism that can allow more simultaneous users accommodated in the network. As the aggregate capacity and system complexity are the main considerations in practical system design, both of which are mutually trade off. Utilization of LDPC code and optical hard-limiter can effectively reduce the system complexity to reach the maximum aggregate capacity. Our proposed scheme can accommodate large number of users in the network simultaneously and support the traffic asynchronously with each user. Furthermore, the aggregate capacity can reach above 100 Gbps; therefore, it is the preferable way as the platform for fiber distribution network in some applications.

Trellis-coded asynchronous optical CDMA systems

Since optical code division multiple access (CDMA) is an interference-limited system, we propose a system employing trellis-coded scheme and double optical hardlimiters (TC-DHLs) to alleviate the adverse impact of multiple access interference. For asynchronous transmission, optical orthogonal code (OOC) is utilized as signature sequence. System performance is evaluated under the chip synchronous case among different users, and thermal noise, avalanche photodiode (APD) noise, and interference are taken into consideration. Numerical results show that our proposed scheme can further reduce the error floor up to several orders over systems that using only double optical hardlimiters.

A Novel Energy-Efficient Adaptive Routing Protocol for Wireless Sensor Network.

Energy efficiency is one of major issues which must be improved to prolong the lifetime of wireless sensor networks (WSNs). Considering the maintenance of Quality of Service (QoS) and energy consumption, we proposed a novel energy-efficient adaptive routing protocol (EEARP) for WSNs. EEARP is composed by a gradient-based topology generator (GBTG) and a novel energy-efficient adaptive routing algorithm (EEARA). After the sensor nodes were deployed broadly, the topology is constructed by GBTG, and then the information of resulted links among the nodes is provided to EEARA. In order to minimize power consumption and transmission delay, the EEARA with loadbalance capability is utilized for selecting efficient path toward the destination sink (the node that is the data storage center). Two simulation scenarios were considered in this study. The simulation results show that the proposed protocol can balance the burden of all nodes effectively and significantly reduce the overall energy consumption.

Time-spreading wavelength-hopping OCDMA systems using parallel detection scheme

In this paper, we employ the two-dimensional spatial coding scheme to improve system performance in time-spreading wavelength-hopping optical CDMA system. The signature sequence in our proposed system utilizes symmetric code (i.e. single-pulse-per-row) and its shifted version. Based on the zero autocorrelation sidelobes property, we propose a two-dimensional parallel detection scheme using trellis coding architecture. This simple architecture can apply to more complicated trellis structure to further improve system performance. Aside from the multiple access interference, some of the adverse impacts of system performance are taken into consideration, which include thermal noise, shot noise, relative intensity noise, and beat noise.

Throughput Performance Analysis of Asynchronous Optical CDMA Networks With Channel Load Sensing Protocol

In this paper, we propose a channel load sensing protocol (CLSP) to prevent the throughput decrease at heavy traffic conditions in asynchronous optical code-division multiple-access (CDMA) networks. The multiple access-interference (MAI) and beat noise are considered the main deleterious source of the network in addition to thermal, shot, and relative intensity noises. Moreover, we employ optical hard limiters and error correction codes to mitigate the physical channel impairments. However, the packet throughput performance declines severely when the number of active users reaches a certain amount in the network. We employ the proposed CLSP with optimum threshold that successfully mitigates the throughput reduction at heavy load conditions. Numerical results show that the proposed protocol can support a throughput rate above 100 Gb/s, which might be compatible for an eventual standardization for broadband optical access networks.

Investigation of coded OFDM system over Rayleigh fading channel

This paper presents a channel coding scheme for OFDM with 64-QAM and 256-QAM over Rayleigh channel. In our proposed scheme, the OFDM system employs three mode of IFFT with 4k, 16k, and 32k. In addition, the concatenated coding scheme of LDPC and BCH code is utilized as channel code referring to the standard from ETSI EN 302 755. Aside from the simulation, we also measure the system performance via the instrument that using DVB-T2 transmitter and receiver. Finally, the comparison and discussion of the simulation and trial measurement are demonstrated.

Optical CDMA using balanced detection and optical hard-limiters

In this paper, we utilize optical hard-limiters to further enhance the system performance in balanced detection optical CDMA systems. It had been investigated that balanced detection is not superior to the OOK scheme because of the impact of beat noise. The employment of optical hard-limiter is an effective way to completely alleviate the adverse impact of beat noise. The carrier-hopping prime code is utilized as signature sequences whose out of phase autocorrelation is zero and the cross-correlation is at most one. Due to the orthogonality of signature sequence, the correlator of shifted version of carrier-hopping prime code is utilized in the receiver. The numerical results reveal that our proposed scheme can greatly reduce the error floor; also it is superior to that of using OOK scheme with optical hard-limiter.

Optical CDMA using trellis RLL code with coset representative

In this paper, the employment of two-dimensional run-length limited code is investigated for time-spreading wavelength-hopping optical CDMA systems. In the proposed architecture, the carrier-hopping prime code is utilized as signature sequences, and it is a symmetric code whose out of phase autocorrelation is zero and the cross-correlation is at most one. Based on the zero autocorrelation sidelobes property, we can apply the two-dimensional ternary symbols to the trellis run-length limited code. To further enhance the free distance of the proposed trellis code, a coset representative is added to the codeword. The multiple access interference and beat noise are the most detrimental factors of system impairment. Apart from the multiple access interference and beat noise, some of the deteriorating impacts of system performance are also taken into consideration, which include thermal noise, shot noise, and relative intensity noise.

Real-time multimedia broadcasting via direct-detection fiber-optic synchronous CDMA networks

A new coding architecture for M-ary fiber-optic synchronous code division multiple access (CDMA) network is proposed to provide real-time multimedia broadcasting. In contrast with variable bit rate (VBR) transmission, the constant bit rate (CBR; i.e. isochronous) transport is more preferable in view of the networking simplicity. We apply a bit-stuffed unipolar m-sequence and maximum a posteriori (MAP) receiver in the proposed network. The system performance is determined by the following parameters: (1) number of simultaneous access broadcasting hosts K, (2) received laser power, (3) input bit rate, and (4) the dimension of M. Furthermore, the adverse impact (thermal noise, APD noise) in the photodetection process is carefully analyzed. Numerical results reveals that for the binary case, the aggregate capacity can achieve 10.2 Gbps.