KEYWORDS: Modulation, Signal detection, Signal to noise ratio, Signal processing, Optical engineering, Computer programming, Digital signal processing, Wavelength division multiplexing, Sensors, Transmitters
Three soft-input-soft-output (SISO) detection methods for dual-polarized quadrature duobinary (DP-QDB), including maximum-logarithmic-maximum-a-posteriori-probability-algorithm (Max-log-MAP)-based detection, soft-output-Viterbi-algorithm (SOVA)-based detection, and a proposed SISO detection, which can all be combined with SISO decoding, are presented. The three detection methods are investigated at 128 Gb/s in five-channel wavelength-division-multiplexing uncoded and low-density-parity-check (LDPC) coded DP-QDB systems by simulations. Max-log-MAP-based detection needs the returning-to-initial-states (RTIS) process despite having the best performance. When the LDPC code with a code rate of 0.83 is used, the detecting-and-decoding scheme with the SISO detection does not need RTIS and has better bit error rate (BER) performance than the scheme with SOVA-based detection. The former can reduce the optical signal-to-noise ratio (OSNR) requirement (at BER=10−5) by 2.56 dB relative to the latter. The application of the SISO iterative detection in LDPC-coded DP-QDB systems makes a good trade-off between requirements on transmission efficiency, OSNR requirement, and transmission distance, compared with the other two SISO methods.
DP-QDQ is a partial-response shaping modulation based on 16QAM, which has been proposed in our previous research paper. In this paper, the power spectral density (PSD) of the DP-QDQ signal is analyzed and compared with DP-16QAM, DP-64QAM, and DP-256QAM signals, and the simulation setup is presented. The analysis results show the DP-QDQ signal has high spectral efficiency. In addition, the optical coherent DP-QDQ system is discussed in compared with DP-16QAM, DP-64QAM, and DP-256QAM systems in terms of the tolerance to optical signal to noise ratio (OSNR), transmission distance at 100G/s by simulations. It is revealed that DP-QDQ not only achieves high spectral efficiency, but also obtains a good compromise of the performances on spectral efficiency, OSNR tolerance and transmission distance.
The IEEE 802.17 Working Group has taken another step forward in providing standards to Resilient Packet Ring (RPR) architectures by approving draft 2.4 of the RPR standard. Some companies have already had their RPR equipments for good market perspectives before the final standardization of RPR specifications. These equipments can supply services such as Ethernet Private Line (EPL), Transparent LAN Service (TLS), Ethernet Line Aggregation (ELA) and so on. Quality of Service (QoS) is an important part implemented in these equipments. Only when there is promise of QoS for RPR equipment, can commercial clients put their key applications to its network. Both the edge and the ring of RPR equipment need take QoS into effect to get QoS guarantees. This paper mainly deals with edge QoS study of RPR equipment. Policing, classification, shaping, and scheduling that are used for edge QoS process are introduced in the paper. And a QoS process method for traffic across rings is discussed at the same time.
In this paper, two wireless broadband access and accounting schemes were introduced. There are some differences in the client and the access router module between them. In one scheme, Secure Shell (SSH) protocol is used in the access system. The SSH server makes the authentication based on private key cryptography. The advantage of this scheme is the security of the user's information, and we have sophisticated access control. In the other scheme, Secure Sockets Layer (SSL) protocol is used the access system. It uses the technology of public privacy key. Nowadays, web browser generally combines HTTP and SSL protocol and we use the SSL protocol to implement the encryption of the data between the clients and the access route. The schemes are same in the radius sever part. Remote Authentication Dial in User Service (RADIUS), as a security protocol in the form of Client/Sever, is becoming an authentication/accounting protocol for standard access to the Internet. It will be explained in a flow chart. In our scheme, the access router serves as the client to the radius server.
This research mainly focuses on the performance evaluation and the improvement of the IEEE 802.11 DCF. The basic access method in the IEEE 802.11 MAC protocol is the distributed coordination function (DCF), which is a carrier sense multiple access with collision avoidance (CSMA/CA) MAC protocol. In this paper, we first evaluate the performance of DCF using the classical Markov analytical model proposed by Bianchi, and then present an improvement named TDCF. Both the theoretical computation and the simulation in our research prove that TDCF has better performance than DCF.
This paper evaluates the performances of the contention-based channel access mechanism of IEEE 802.11e, called enhanced distributed coordination function (EDCF), compared with the 802.11 legacy MAC in supporting voice, video and data applications through network simulation of a scenario of 802.11e. Then we discuss the effects of Contention Window (CW) and Arbitration Inter-Frame Space (AIFS) on service differentiation and total throughput. We also consider an optional feature of the EDCF, called contention-free burst (CFB). Through our simulation study, we can draw a conclusion that the EDCF with TXOP can provide better-differentiated channel access for different traffic types than EDCF without TXOP especially at high traffic load conditions. But the movements caused by the parameters in CFB seem a lot bouncing and instability when in different application and configuration.
This paper firstly introduces the basic framework and the character and then makes analysis and design to the WDM network's management, which is using optical control channel to transmit network management information on the basis of comparing several existing transport methods of network management information.
Resilient Packet Ring (RPR) is a newly developed Layer 2 access technology for ring topology based high speed network. Fairness Algorithm (FA), one of its key technologies, takes responsibility for regulating each station access to the ring. Since different methods emphasize particularly on different aspects, the RPR Work Group have tabled several proposals. This paper will discuss two of them and propose an improved algorithm, which can be seen as a generalization of the two schemes proposed in  and . The new algorithm is a distributed algorithm, and uses a multi level feedback mechanism. Each station calculates its own fair rate to regulate its access to the ring, and sends fairness control message (FCM) with its bandwidth demand information to the whole ring. All stations keep a bandwidth demand image, which update periodically based on the information of received FCM. The image can be used for local fair rate calculation to achieve fair access. In the properties study section of this paper, we compare our algorithm with the two existing one both in theoretical method and in scenario simulation. Our algorithm has successfully resolve lack of the awareness of multi congestion points in  and the drawback of weakness of fault tolerance in .
The Resilient Packet Ring (RPR) IEEE 802.17 standard is under development as a new high-speed backbone technology for metropolitan area networks (MAN) . Bandwidth reclamation has been concerned in RPR specifications from draft 0.1 to draft 2.4. According to specifications, allocated bandwidth can be reused, or reclaimed, by a lower priority service class whenever the reclamation does not effect the service guarantees of any equal or higher priority classes on the local station or on any other station on the ring . The class-based queuing (CBQ) algorithm is proposed to implement link-sharing . A hierarchical link-sharing structure can be used to specify guidelines for the distribution of 'excess’ bandwidth  and it can rate-limit all classes to their allocated bandwidth. There is some sameness between the link-sharing of CBQ and bandwidth reclamation of RPR. The CBQ is a mature technology while RPR is a new technology. Given CBQ improvement and full use so as to make its thought suitable for bandwidth reclamation of RPR is the focus of our work. In this paper, we present the solution that can solve the reclamation problem, which proves to be effective by simulation.
Resilient Packet Ring is a new technology being standardized by IEEE 802.17 working group. This paper describes the ways to accomplish uniform traffic handling and spatial traffic handling by comparison. Since uniform shaping cannot avoid head of line blocking or decrease the jitter of bandwidth utilization on multiple chock point ringlet, this paper proposes a solution for shaping of spatial traffic handling. Virtual destination queues are introduced to the shaper to avoid HOL, and a special kind of dynamic priority is added to the scheduler to optimize bandwidth utilization. A simulation model is set up to exam the performance of VDQ aware shaper, which is the first phase to accomplish spatial shaping.
The information format in the experimental underwater laser system is discussed. Two-pulse modulation for the laser is proposed. This method clearly reduces the modulated laser pulse's vibration range which is caused by the random change of Q switch's trigger of the laser. Thus the reliability of the communication is increased. The hardware and software flow chart of the modulator are shown in this paper.