Flexible Data Rate Research Articles

Intra super-channel fiber nonlinearity compensation in flex-grid optical networks

We report on the nonlinear transmission limits of various super-channel configurations in a flex-grid network upgrade scenario. In particular, we consider flexible data-rates ranging from 180Gb/s to 1.2Tb/s, employing either single-carrier, dual-carrier, or penta-carrier polarization multiplexed m-state quadrature amplitude modulation (PM-8QAM/PM-16QAM) -termed as super-channels, and establish transmission performance margins for each configuration, both with and without super-channel fiber nonlinearity compensation. Our results show that the benefit of intra super-channel nonlinearity mitigation (nonlinear compensation addressing full super-channel bandwidth) reduces with increasing sub-carrier count within the super-channel, and that single-carrier super-channel achieves the maximum improvement from nonlinearity mitigation (up to ~4.5dB, in Q-factor), better than dual-carrier (up to ~3.5dB) and penta-carrier (up to ~2dB) configurations. Moreover, the maximum reach improvement, compared to linear compensation only, is found to be ~170% (180Gb/s, PM-8QAM), ~150% (240Gb/s, PM-16QAM), ~100% (360Gb/s, PM-8QAM), ~100% (480Gb/s, PM-16QAM), and ~65% (1.2Tb/s, PM-16QAM).

Study of OFDM Technique on RoF Passive Optical Network

The combination of radio over fiber (RoF) and orthogonal frequency division multiplexing (OFDM) techniques has resulted in a high-data-rate at lower cost in the last mile of wireless networks. This paper investigates the use of the OFDM as a modulation technique for radio over fiber (RoF) in passive optical network (PON). A laser source of 1550 nm wavelength was used with 100 km, 140 km and 288 km single mode fiber. In the OFDM-PON a passive optical splitter of ratio 1:2 is used to connect two optical network units (ONUs). A 10 Gbits/sec transmission bit rate is used to simulate the RoF-OFDM-PON system. The proposed system can provide a flexible, cost effective and significant high data rate.

A Novel Hybrid Multiple Access Scheme in Downlink for 4G Wireless Communications

In this paper, we present a hybrid multiple access scheme to increase the data rate and to provide more flexibility for 4G wireless communications. The proposed scheme utilizes a combination of the multiple access techniques TDMA, CDMA and OFDMA. It uses variable time slots, spreading factors and number of subcarriers to provide flexible data rates for different classes of users. The performance analysis of the proposed scheme is carried out for different modulation schemes used in downlink and expressions for multiple access interference (MAI) and bit error rate (BER) are derived. The parameters for this scheme are selected depending on available bandwidth, required data rates, number of users, type of service provided etc. It is found that this scheme provides better scalability and can support more number of users.

Narrow-band interference suppression in wavelet packets based multicarrier multicode CDMA overlay system

The wavelet packets based multicarrier MC multicode MCD code-division multiple-access CDMA transceiver consists of the MCD part, which ensures the transmission for high speed and flexible data rate; the MC part contributing to robustness to frequency-selective fading and flexibility for handling multiple data rates; and wavelet packets WPs modulation technique, which contributes to the mitigation of the interference problems. As WPs have lower sidelobes compared with sinusoidal carriers, this system is very effective in reducing the problem of inter-carrier interference. Of course, like any CDMA system, the system can suppress a given amount of interference. This paper considers an interference suppression scheme which will enhance the performance of the system. The receiver employs suppression filters to mitigate the effect of narrow-band jammer interference. The framework for the system and the performance evaluation are presented in terms of the bit error rate and the outage probability over a Nakagami fading channel. Also, we investigate how the performance is influenced by various parameters, such as the number of taps of the suppression filter and the ratio of narrow-band interference bandwidth to the spread-spectrum bandwidth. Finally, the performance of the system is compared with the performance of sinusoidal based MC/MCD-CDMA system denoted Sin-MC/MCD-CDMA. Copyright © 2012 John Wiley & Sons, Ltd.

Variable power adaptive MIMO OFDM system under imperfect CSI for mobile ad hoc networks

Future high speed mobile applications require diverse Quality of Service (QoS). To provide flexible data rate services while satisfying the low delay requirements, adaptive MIMO OFDM is a promising technique over time varying channels. In this paper a variable power adaptive MIMO OFDM system under imperfect CSI using cross layer design for mobile ad hoc networks is proposed. Data throughput is maximized while maintaining the delay QoS requirements in the presence of channel estimation errors. Numerical results show that the variable power adaptive MIMO OFDM system provides better spectral efficiency than its constant power counterpart.

Running-code optical CDMA at 2 × 10 Gbit/s and 40 Gbit/s

A continuously running-code optical CDMA system useful for secure communications is reported. The system utilises acousto-optic modulator-based pulse shapers as spectral phase en-/decoding devices, which are capable of microsecond-scale code sequence refresh rates. The codes are generated on-the-fly by a stream cipher. Transmit/receive code synchronisation is independent of the data stream, allowing for a flexible data rate. Two multiplexed 10 Gbit/s channels and a single 40 Gbit/s channel are demonstrated.

Performance analysis of quadratic congruence codes using superstructured fiber Bragg gratings for a flexible data rate coherent DS-OCDMA system

The performance of a coherent direct sequence optical code division multiple access (DS-OCDMA) system using quadratic congruence codes implemented with superstructured fiber Bragg gratings is experimentally analyzed. We point out that nonperiodic and sparse quadratic congruence codes reduce multipath beat noise and intersymbol interference, respectively. These two properties of the structure of the quadratic congruence codes are shown to improve the bit-error-rate (BER) performance of the coherent system. As a result, we demonstrate that the performance enhancement of the coherent DS-OCDMA system allows the data bit rate of the system to be varied from 1 Gbit/sto2.5 Gbits/s and the receiver bandwidth to be decreased from 15 GHzto5 GHz respecting the low-cost requirement of the optical access network. These data bit rate and receiver bandwidth performances are achieved with moderate BER penalty.

Performance of a New Premulticoded Multicarrier DS-CDMA System in Nakagami Fading

In this paper, we proposed a new multicarrier, direct sequence code division multiple access, the so-called premulticoded MC-DS-CDMA system. In this scheme, the basic MC-DS-CDMA system is augmented with a precoder and a multicode encoder at the transmitter. The multicode encoder is an inverse Walsh-Hadamard transform (IWHT) unit, while the precoder is a recently suggested ldquoconstant amplituderdquo encoder that guarantees that the IWHT output stream has binary level. While IWHT, multicarrier (MC) transmission, and direct sequence spreading provide us with frequency diversity, the constant amplitude precoder ensures that the transmitted waveform is spread BPSK signal, minimizing peak to average-power ratio (PAPR) problem. The multicode and (MC) combination also addresses the need for flexible high data rate services in present day wireless communications. In the receiver, after matched filtering or correlation demodulation for each subcarrier and WHT operation, a detection strategy based on minimum-mean-square-error (MMSE) criterion is used. We have derived an upper bound for the bit error rate (BER) performance in Nakagami fading channel. Numerical results are compared with those obtained from a single carrier DS-CDMA system (SC-DS-CDMA) and a MC-DS-CDMA scheme without the precoding and IWHT units. We show that our proposed MC-DS-CDMA scheme has a much better BER performance compared with both of these schemes.

Downlink Transmission of Broadband OFCDM Systems—Part II: Effect of Doppler Shift

The orthogonal frequency and code division multiplexing (OFCDM) system with 2-D spreading (time- and frequency-domain spreading) is becoming a promising candidate for future broadband wireless communication systems. OFCDM is more attractive than orthogonal frequency-division multiplexing (OFDM) both by introducing frequency-domain spreading for frequency diversity provision and time-domain spreading for flexible data rate provision. To provide high-speed mobile services, multicode transmission is employed in conjunction with OFCDM. In a Gaussian or flat-fading channel, multicode channels are orthogonal. However, in a realistic wireless channel, the orthogonality no longer maintains. Thus, multicode interference (MCI) is caused. This paper focuses on the investigation of the effect of Doppler shift on the downlink transmission of high-speed mobile OFCDM systems. A practical channel estimation algorithm based on a code-multiplexed pilot channel is employed to track the variations of fading channels. Hybrid MCI cancellation and minimum mean-square error (MMSE) detection proposed by the authors is employed as an efficient way to eliminate the MCI in the frequency domain. The system performance is analytically studied with imperfect channel estimation to show how it is affected by parameters such as the window size in the channel estimation, Doppler shift, the number of stages of the hybrid detection, the power ratio of pilot to data channels, spreading factor, and so on

High Rate Recursive Space-Time Trellis Code Designed for Serially Concatenated Space-Time Codes

Using several high rate recursive convolutional codes as the basic element and the trace criteria as the designing principle, a new kind of recursive space-time trellis code with more flexible and higher data rate is presented for the serially concatenated space-time code. When 2 b -ary modulation and N transmit antennas are used, the data rate of the new code can be arranged from b bps/Hz to Nb-1bps/Hz by modifying the number of recursive convolutional codes and the data rate of each code.

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.

A multicarrier allocation (MCA) scheme for variable-rate 3Gwireless systems

High spectral efficiency and flexible data rate access are the main focus of future wireless networks. Multiple channel allocation schemes have the potential of achieving this goal. By assigning multiple slots and/or multiple carriers to one user, it is possible to provide a flexible data rate with quite low complexity. In this article we propose a simple allocation scheme where each user is assigned a fixed group of carriers. These carriers are adaptively used depending on the interference situation within the system. The system performance in terms of average throughput is investigated for two different types of allocation schemes: a fully centralized scheme and a distributed one that uses frequency diversity as a mean of improving the user link quality. The obtained results show that both schemes improve the system throughput over single carrier allocation without affecting the capacity of the system in terms of number of users per cell.

Adaptive Modulation and Multiple Access for the OFDM Transmission Technique

For the transmission of flexible and high data rates in future mobile communication systems, the multicarrier transmission technique (Orthogonal Frequency Division Multiplexing, OFDM) can be regard...

LOCNET--A local area network using optical switching

A wide-band local area network using optical switching is presently being developed by the Heinrich-Hertz-lnsitut in Berlin (West). To ensure high reliability the system will be implemented as a star type network, divided into two subsystems. All switching within the system will be done by optical switching techniques. The wide-band subsystem will use Lithium-Niobate switching matrix elements, interconnected as a multistage space switch. Thus bit rate independent channels will be available with the ability to establish various wide-band services of the in-house area. The second subsystem makes use of a single-mode star coupler. Distributed circuit switching with fast switching capability and flexible data rates will be implemented, utilizing a TDM frame, that supports 63 narrow-band connections and a capacity of 8 Mbit/s for fast data services. To prevent typical disadvantages of distributed switching like line tapping and system disturbance, caused by malfunctioning system components, LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> switches will be installed in front of and behind the star coupler. The single-mode star coupler will be implemented by cascading 2 × 2 star couplers, which are available as 3-dB couplers.

Digital Frame Storage for Television Video

Storage of a full frame of quantized television video using an all-digital memory has now become practical, thanks to the steady increase over the past few years of the data-rate capabilities of MOS shift register devices (now 5–8 MHz) accompanied by decreasing costs (now less than 0.4 cents per bit). The primary advantages of a digital frame store with real-time input/output capability are flexible data rate (as opposed to the fixed rate of a video disc) and long-term stability (as opposed to storage tubes). The recently-built system described in this paper utilizes digital frame storage to provide a flexible interface between standard television video, an Electron Beam Recorder using non-interlaced scanning, and a computer with a relatively slow input and output rate.