Channel Symbol Rate Research Articles

Performance Bounds of ADC-Based Receivers Due to Clock Jitter

The maximum tolerable clock jitter for high-speed ADCs is pessimistically predicted by Nyquist-rate input sinusoidal tests. We prove that the jitter can be greatly relaxed in the presence of lossy channels in wireline systems. We derive compact expressions that allow PLL designers to decide how much jitter can be tolerated for a given channel loss and symbol rate.

Gate-free integrated-optic tunable filter for demultiplexing various capacity optical OFDM signals

Spectrally efficient optical communication with flexible capacity is required in the prospective adaptive photonic network. Optical orthogonal frequency division multiplexing (OFDM) is one of candidates to contribute to this type of photonic network. Here we report on a gate-free integrated-optic tunable filter that can demultiplex optical OFDM signals with various number and symbol rate sub-carrier channels. The filter consists of tunable couplers, an array of delay lines, and a slab star coupler-type optical Fourier transformation circuit. We can tune the number and/or the symbol rate of demultiplexed optical OFDM channels by selecting the delay lines with the tunable couplers. Optical timing gates were normally attached to the filter output ports with a view to extracting the effective time of the filtered channels. In this investigation, we removed the optical gates and substituted a high-speed photodetector for the gate with a view to achieving completely passive demultiplexing of the various capacity optical OFDM signals. Various channel symbol rate and channel number OFDM signals (5 × 10 to 20 Gsymbol/s and 3 × 20 Gsymbol/s) were successfully demultiplexed with this gate-free tunable filter. Our star coupler-type tunable OFDM filter without the gates was used to demultiplex various channel symbol rate optical OFDM signals for the first time.

Relative impact of channel symbol rate on transmission capacity

Through C+L band transmission experiments and theoretical modeling, we investigate the impact of channel symbol rate (30, 40, 60, and 85 GBd) on the performance of data center interconnection, metropolitan, and core network distances. Two different transponder architectures are investigated: (a) single-carrier receiver and (b) multi-carrier receiver, where multiple subcarriers are received together in a single wideband receiver. The architectures of both receivers experience a reduction in the achievable information rate as the channel symbol rate increases due to dominating transceiver noise; this holds over all tested transmission distances. However, the multi-carrier receiver shows a weaker performance dependency on symbol rate, as receiver-related impairments dominate. When testing the single-carrier receiver after 630 km, we find that by increasing the channel symbol rate from 40 to 85 GBd, gross capacity decreases by 16%; however, the required number of transceivers to fill the transmission window decreases by 52%. Using the multi-carrier receiver reduces receiver count further. This potentially impacts the cost and complexity of deploying fully loaded transmission systems.

Estimation and stability over AWGN channel in the presence of fading, noisy feedback channel and different sample rates

This paper is concerned with estimation and stability of control systems over communication links subject to limited capacity, power constraint, fading, noisy feedback, and different transmission rate rather than system sampling rate. A key issue addressed in this paper is that in the presence of noisy feedback associated with channel, which models transmission of finite number of bits over such links as is the case in most practical scenarios, the well-known eigenvalues rate condition is still a tight bound for stability. Based on an information theoretic analysis, necessary conditions are derived for stability of discrete-time linear control systems via the distant controller in the mean square sense. By construction of a specific coding scheme and by the design of a proper controller, the tight sufficient conditions for stability of control systems are also derived for linear discrete-time control systems over both Additive White Gaussian Noise (AWGN) and fading channels. This implies that the proposed coding scheme is efficient. The results are presented with the mismatch assumption between channel symbol and plant sample rates. As one key result of this paper, it is shown that if the channel symbol rate is less than the system sample rate, the control system is still stabilizable via increasing the transmission power.

How 64 GBaud Optical Carriers Maximize the Capacity in Core Elastic WDM Networks With Fewer Transponders per Gb/s

Following the extensive investigations of the research community throughout the last five years regarding transmission performance when roughly doubling the channel symbol rate in WDM systems from generic 32 GBaud to more than 60 GBaud, this evolution is about to appear in the field in the next twelve months. The general sense is that it will reduce the cost per transmitted gigabit per second (Gb/s), once the related faster optoelectronic interfaces become mature enough. This paper refines this consideration by quantifying the related transponders saving per Gb/s on three distinct backbone WDM networks equipped with elastic optoelectronic regenerators. It also reports how much extra network capacity stems from routing individual 64 GBaud subcarriers 75 GHz apart to serve connections, the capacities of which range from 100 Gb/s to 1 Tb/s. It eventually discusses the impact on the network performance when constraining the regenerators' placement along the light paths of the accommodated services or when simplifying the elastic regenerators by avoiding internal electrical traffic regrooming.

Design of realisable optimum post‐detection filters for high data‐rate m ‐PAM systems with clock jitter tolerance

The continual increase in demand for extremely high data-rate systems spans the full range of network systems from local area networks to long-haul systems. While coherent optical systems dominate the long-haul market, there is significant interest in using simpler direct detection systems for application areas, where simplicity and lower-cost is a key driver. Pulse-amplitude modulation (PAM) is appropriate to consider as it enables the reduction of the channel symbol rate for a given data rate, without unduly increasing the complexity of the system. A route to the design of optimum post-detection filter for PAM systems is presented that offers significantly improved robustness to timing jitter, which is an impairment of increasing import as symbol rates are increased.

Single parity check-coded 16QAM over spatial superchannels in multicore fiber transmission.

We experimentally investigate single-parity check (SPC) coded spatial superchannels based on polarization-multiplexed 16-ary quadrature amplitude modulation (PM-16QAM) for multicore fiber transmission systems, using a 7-core fiber. We investigate SPC over 1, 2, 4, 5 or 7 cores in a back-to-back configuration and compare the sensitivity to uncoded PM-16QAM, showing that at symbol rates of 20 Gbaud and at a bit-error-rate (BER) of 10-3, the SPC superchannels exhibit sensitivity improvements of 2.7 dB, 2.0 dB, 1.7 dB, 1.3 dB, and 1.1 dB, respectively. We perform both single channel and wavelength division multiplexed (WDM) transmission experiments with 22 GHz channel spacing and 20 Gbaud channel symbol rate for SPC over 1, 3 and 7 cores and compare the results to PM-16QAM with the same spacing and symbol rate. We show that in WDM signals, SPC over hl1 core can achieve more than double the transmission distance compared to PM-16QAM at the cost of 0.91 bit/s/Hz/core in spectral efficiency (SE). When sharing the parity-bit over 7 cores, the loss in SE becomes only 0.13 bit/s/Hz/core while the increase in transmission reach over PM-16QAM is 44 %.

Fast Wavelength Switching Transceiver for a Virtualized Coherent Optical Network

Fast reconfigurable digital coherent transceivers will become a key subsystem in future virtualized optical networks as they provide the ability to tailor the channel frequency, symbol rate, and modulation format. This transceiver agility is of paramount importance for network resilience, bandwidth on demand applications, and congestion aware routing. We demonstrate a fast wavelength switching coherent transceiver based on semiconductor tunable lasers and a parallelized digital signal processing implementation. The inherent frequency and phase noise associated with semiconductor tunable lasers is analyzed and a dc pilot tone assisted phase noise mitigation technique is proposed for a fast wavelength switching dual-polarization orthogonal frequency-division multiplexed transceiver. This enables the use of commercially available digital supermode distributed Bragg reflector lasers in both the transmitter and receiver in an 800-km wavelength routed coherent network that exhibits a variable path history.

The performance of Reed-Solomon codes on a bursty-noise channel

The performance of a Reed-Solomon coded binary communication system on a bursty-noise channel is considered. Bursty noise is defined to be background Gaussian noise plus burst noise, where burst noise is defined to be a series of finite-duration Gaussian-noise pulses with fixed duration and Poisson occurrence times. Using the noise model, along with ideal symbol interleaving, decoded bit-error probability bounds are derived for the case where the noise bursts are long with respect to the channel symbol rate. Specific performance results are presented for the (31,15,8) Reed-Solomon Joint Tactical Distribution System (JTIDS) code with a binary phase shift keyed (BPSK) modulation scheme. Simulation results are presented and they compare well with the theoretical results. >

Simultaneous estimation of echo path and channel responses using full-duplex transmitted training data sequences

To reduce the system initialization time in high-speed full-duplex data transmission over two-wire lines, we propose an efficient full-duplex fast training algorithm which can simultaneously estimate the impulse responses of echo paths and channels at both ends. Two mutually orthogonal periodic sequences are designed and used to co-estimate the near echo, the far echo with bulk delay, and the channel response. The new algorithm can reduce the tap-setting time to half of that required by the traditional half-duplex fast training schemes. The effects of channel noise and symbol rate offset between two ends are examined in terms of both mean-square error (MSE) and signal-to-noise ratio (SNR). Both the theoretical analysis and computer simulation show that there are three degrading factors due to symbol rate offset. The SNR is inversely proportional to the sum of the estimated coefficients, the half period of the training sequences, and the square of symbol rate offset. If the far-signal-to-channel-noise ratio is 30 dB, then the degradation is significant when the symbol rate offset is more than 10/sup -4/. If it is 40 dB, then the degradation is significant when the symbol rate offset is above 3/spl times/10/sup -5/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Maximum-likelihood decoding of array codes with trellis structure

A new simple algorithm which allows the design of a trellis diagram for array codes is introduced. Based on this algorithm, the trellis decoding of array codes with maximum likelihood decoding (MLD) performance and relatively low complexity is proposed. It is shown that the trellis structure of array codes allows the application of combined coding and modulation (CCM) with higher information digit per channel symbol rate than for conventional CCM methods, based on convolutional codes. The bounds on the transmission rates for different types of CCM signals, based on convolutional and array codes, have been obtained and presented in the paper.

Message waiting time performance for meteor-burst communication systems

The performance is investigated of the meteor-burst channel in terms of the waiting time required to reliably transmit a message of length N bits. Two modulation techniques are considered. The first is the traditional fixed-rate modulation scheme where the modem operates at a constant bit rate whenever the channel is available for message traffic. The second is an adaptive modulation method where the channel symbol rate varies continuously to match the time-varying signal-to-noise ratio at the receiver. Upper and lower bounds on waiting time for the general case are derived using probabilistic arguments. Novel closed-form expressions for waiting time and optimal bit rate are derived for the fixed-rate modem. Bounds on mean waiting time are derived for the adaptive-symbol-rate modem. It is shown that for fixed-rate modems operating at the optimal bit rate and for adaptive modems operating at a minimum bit rate equal to this rate, the improvement in mean waiting time can never exceed a factor of two.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

On Improving Bit Error Probability of QPSK and 4-Level Amplitude Modulation Systems by Convolutional Coding

We consider Amplitude Modulation (AM) systems, PhaseShift-Keying (PSK) and Amplitude-Phase-Keying (APK) systems in which each symbol can take 2nvalues. After a systematic search of (n, n - 1) binary convolutional codes with large values of free distance and minimal number of code words at that distance, simulations have been performed with an 8-symbol modulation system ( n = 3 ). For a bit error probability of less 2 \times 10^{-4} , the saving in average power signal-signal-to-noise ratio over that required for an uncoded system with the same channel symbol rate was more than 2 dB with PSK and APK, and 1.5 dB with AM.