Mixed Data Rate Research Articles

Theoretical and experimental study of performance anomaly in multi-rate IEEE802.11ac wireless networks

IEEE 802.11 wireless local area networks (WLANs) are shared networks, which use contention-based distributed coordination function (DCF) to share access to wireless medium among numerous wireless stations. The performance of the distributed coordination function mechanism mostly depends on the network load, number of wireless nodes and their data rates. The throughput unfairness, also known as performance anomaly is inherent in the very nature of mixed data rate Wi-Fi networks using the distributed coordination function. This unfairness exhibits itself through the fact that slow clients consume more airtime to transfer a given amount of data, leaving less airtime for fast clients. In this paper, we comprehensively examine the performance anomaly in multi-rate wireless networks using three approaches: experimental measurement, analytical modelling and simulation in Network Simulator v.3 (NS3). The results of our practical experiments benchmarking the throughput of a multi-rate 802.11ac wireless network clearly shows that even the recent wireless standards still suffer from airtime consumption unfairness. It was shown that even a single low-data rate station can decrease the throughput of high-data rate stations by 3–6 times. The simulation and analytical modelling confirm this finding with considerably high accuracy. Most of the theoretical models evaluating performance anomaly in Wi-Fi networks suggest that all stations get the same throughput independently of the used data rate. However, experimental and simulation results have demonstrated that despite a significant performance degradation high-speed stations still outperform stations with lower data rates once the difference between data rates becomes more significant. This is due to the better efficiency of the TCP protocol working over a fast wireless connection. It is also noteworthy that the throughput achieved by a station when it monopolistically uses the wireless media is considerably less than 50 % of its data rate due to significant overheads even in most recent Wi-Fi technologies. Mitigating performance anomaly in mixed-data rate WLANs requires a holistic approach that combines frame aggregation/fragmentation and adaption of data rates, contention window and other link-layer parameters.

Real-Time DSP-Enabled Digital Subcarrier Cross-Connect Based on Resampling Filters

A real-time digital signal processing (DSP)- enabled digital subcarrier cross-connect (DSXC) with resampling filters for channel frequency translation is demonstrated in this paper. This circuit-based DSXC supports flexible and fine data-rate subcarrier channel granularities, offering a low-latency data plane, transparency to modulation formats, and the capability of compensating for transmission impairments in the digital domain. The presented 8 × 8 DSXC demonstrator makes use of a Virtex-7 field programmable gate array (FPGA) platform, which supports any-to-any switching of eight subcarrier channels with mixed modulation formats and data rates. Digital resampling filters enable frequency translation of subcarrier channels at the cross-connect with much reduced processing requirements for the FPGA resources in comparison to the traditional technique based on in-phase/quadrature mixing and filtering.

Throughput Estimation with Regard to Airtime Consumption Unfairness in Mixed Data Rate Wi-Fi Networks

The paper discusses throughput unfairness inherent in the very nature of mixed data rate Wi-Fi networks employing random media access control technique CSMA/CA. This unfairness exhibits itself through the fact that slow clients consume more airtime to transfer a given amount of data, leaving less airtime for other clients. This decreases the overall network throughput and significantly degrades performance of high data rate clients. In the paper we propose mathematical models considering airtime unfairness and estimating wireless networks throughput depending on number of network connections and their data rates. These models show that all wireless clients have an equal throughput independently of data rates used by them. We verify our theoretical findings by running natural experiment and show that client's throughput approximates to the data rate of the slowest client.

Research on Mixed Data Rate in WDM Networks

To meet the growing data traffic demands in the telecommunication applications, the number of wavelengths is to be increased in a fiber-optic backbone of the telecommunication network. The exponential growth of internet services, transmission capacity is a tremendous challenge to networks. Nowadays, 10 Gbps transmission systems are being used for commercial applications. At the same time, the non-linear effects such as FWM, SRS, XPM, SPM, and Dispersion are also increased, when the number of wavelengths passing through the single fiber is increased. The analysis of efficient modulation formats for DWDM system and long-haul transmission system, we go for various modulations for DWDM system. The maimum data rate for NRZ-OOK modulation format is 10 Gbps. For RZ-OOK the maximum rate is 50 Gbps. Since RZ-OOK modulation uses twice the band width when compared to NRZ-OOK modulation. The modulation format is partially upgraded from OOK to PSK, the influence of OOK signals on the updated PSK signals must be considered when using multi-channel wavelength conversion. The PSK modulation is also analyzed. DOI: http://dx.doi.org/10.11591/telkomnika.v11i12.2515 Full Text: PDF

Research on Mixed Data Rate and Format Transmission in WDM Networks

Research on Mixed Data Rate and Format Transmission in WDM Networks

Research on Mixed Data Rate and Format Transmission in WDM Networks

To meet the growing data traffic demands in the telecommunication applications, the number of wavelengths is to be increased in a fiber-optic backbone of the telecommunication network. The exponential growth of internet services, transmission capacity is a tremendous challenge to networks. Nowadays, 10 Gb/s transmission systems are being used for commercial applications. At the same time, the non-linear effects such as FWM, SRS, XPM, SPM, and Dispersion are also increased, when the number of wavelengths passing through the single fiber is increased. The analysis of efficient modulation formats for DWDM system and long-haul transmission system, we go for various modulations for DWDM system. The maximum data rate for NRZ-OOK modulation format is 10 Gb/s. For RZ-OOK the maximum rate is 50 Gb/s. Since RZ-OOK modulation uses twice the band width when compared to NRZ-OOK modulation. The modulation format is partially upgraded from OOK to PSK, the influence of OOK signals on the updated PSK signals must be considered when using multi-channel wavelength conversion. The PSK modulation is also analyzed.

Performance Study of Novel Designed Hybrid WDM System

Performance Study of Novel Designed Hybrid WDM System This article presents investigation of the proposed hybrid WDM scheme with mixed data rates (10 and 20 Gbps), different modulation schemes and unequal channel spacing (100 GHz/50GHz). The investigated hybrid system consists of five transmitters and each transmitter has four channels having total capacity of twenty channels. Numerous optical modulators such as linear modulator, DPSK modulator, Sin2 modulator, Dual Arm Balanced and unbalanced MZM have been implemented on the transmission links. The simulated results depicted excellent performance with linear modulator, phase modulator while unbalanced MZM has showed degraded transmission performance for arbitrarily selected transmission distances 200 km, 320 km and 360 km. Hence, the study of hybrid WDM system illustrates that it can be capable scheme for further augment in spectral efficiency and significant viable option for the present and future active, passive optical networks.

Schemes for Compensation of Chromatic Dispersion in Combined HDWDM Systems

Schemes for Compensation of Chromatic Dispersion in Combined HDWDM SystemsThe authors seek best ways to realize chromatic dispersion (CD) compen-sation schemes for differently modulated optical signals in high-speed mixed data rate HDWDM systems. The research is based on OptSim 5.1. simulation software, which numerically solves nonlinear Schrödinger equation using the split-step Fourier method. It is shown that the CD compensation scheme is crucial for the performance evaluation in combined HDWM transmission channels. Therefore, a scheme of the type is proposed that is suited best for a very complicated combined fiber optical transmission system. It is also found that asymmetrical CD compensation schemes in pre- and post-compensation modules are the most efficient, allowing the best BER in a channel to be achieved.

Investigation of Mixed Data Rate and Format Transmission in WDM Networks.

Simultaneous propagation of different modulation formats in WDM systems are evaluated numerically with OptSim simulation software at a bit rate of 2.5 Gbit/s and 10 Gbit/s using 80 km fibre length. The obtained results show the flexibility of mixed WDM networks and usability in futures solutions. Ill. 7, bibl. 5 (in English; summaries in English, Russian and Lithuanian).

Formulation of Distributed Coordination Function of IEEE 802.11 for Asynchronous Networks: Mixed Data Rate and Packet Size

In carrier-sense-multiple-access/collision-avoidance networks in which stations have different data rates, some stations are penalized because slow stations receive more time to transmit. Thus, a single low data-rate station unfairly brings down the throughput of the high data-rate stations. We introduce a simple and standard-compliant algorithm to fairly utilize the channel. We first provide a formulation for the throughput with mixed data-rate connections. To alleviate the low performance of the high data-rate stations, we introduce a mechanism that implements an adaptive scheme to adjust the packet size according to the data rate. With this scheme, stations occupy the channel for equal amounts of time. We then extend the scheme to a frame-aggregation scheme to show how different packet sizes affect performance.

Long-haul DWDM transmission systems employing optical phase conjugation

In this paper, we review the recent progress in transmission experiments by employing optical phase conjugation (OPC) for the compensation of chromatic dispersion and nonlinear impairments. OPC is realized with difference frequency generation (DFG) in a periodically poled lithium-niobate (PPLN) waveguide, for transparent wavelength-division multiplexed (WDM) operation with high conversion efficiency. We discuss extensively the principle behind optical phase conjugation and the realization of a polarization independent OPC subsystem. Using OPC for chromatic dispersion compensation WDM 40-Gb/s long-haul transmission is described. As well, transmission employing both mixed data rates and mixed modulation formats is discussed. No significant nonlinear impairments are observed from the nonperiodic dispersion map used in these experiments. The compensation of intrachannel nonlinear impairments by OPC is described for WDM carrier-suppressed return-to-zero (CSRZ) transmission. In this experiment, a 50% increase in transmission reach is obtained by adding an OPC unit to a transmission line using dispersion compensating fiber (DCF) for dispersion compensation. Furthermore, the compensation of impairments due to nonlinear phase noise is reviewed. An in-depth analysis is conducted on what performance improvement is to be expected for various OPC configurations and a proof-of-principle experiment is described showing over 4-dB improvement in Q-factor due to compensation of nonlinear impairments resulting from nonlinear phase noise. Finally, an ultralong-haul WDM transmission of 22times20-Gb/s return-to-zero differential quadrature phase-shift keying (RZ-DQPSK) is discussed showing that OPC can compensate for chromatic dispersion, as well as self-phase modulation (SPM) induced nonlinear impairments, such as nonlinear phase noise. Compared to a "conventional" transmission link using DCF for dispersion compensation, a 44% increase in transmission reach is obtained when OPC is employed. In this experiment, we show the feasibility of using only one polarization-independent PPLN subsystem to compensate for an accumulated chromatic dispersion of over 160 000 ps/nm

Demonstration of an optical-label switching router with multicast and contention resolution at mixed data rates

This letter experimentally demonstrates a scalable optical-label switching router architecture that supports a limited multicast function. A semiconductor-optical-amplifier-based Mach-Zehnder interferometer wavelength converter performs multiwavelength conversion for multicast at 10 Gb/s by cross-phase modulation. With a 2.5-Gb/s unicast channel, the experiment also demonstrates contention resolution in the wavelength domain at mixed data rates.

Wavelength blocking filter with flexible data rates and channel spacing

This work presents a high-resolution (13.2 GHz) channel-blocking optical filter, suitable for use as a reconfigurable optical add/drop multiplexer (ROADM), which seamlessly supports data rates from 2.5 to 160 Gb/s. The filter consists of a linear array of 64 MEMS micromirrors and a high-dispersion echelle grating. The demonstrated device had an insertion loss of 9 dB, a loss ripple of 1.2 dB, and a group delay ripple of 15 ps. Data transmission through the device with various mixed data rate scenarios ranging from 2.5 to 160 Gb/s showed negligible penalty, except at 40 Gb/s where a maximum penalty of 1.5 dB was observed due to a phase coherence with the blocker filter ripple.

Mixed data rate and format transmission (40-Gbit/s non-return-to-zero, 40-Gbit/s duobinary, and 10-Gbit/s non-return-to-zero) by mid-link spectral inversion

A polarization-diverse subsystem based on periodically poled lithium niobate waveguides is used as an optical phase conjugator for compensation for linear and nonlinear distortion. We show successful transmission formats of 13 x 40 Gbit/s non-return-to-zero mixed with 6 x 10 Gbit/s non-return-to-zero and 40-Gbit/s duobinary over 8 x 100 km of standard single-mode fiber. A single phase conjugator is used to conjugate all data formats, including the alternative duobinary format, simultaneously.