Time Compression Multiplexing Research Articles

MDM-TDM PON Utilizing Self-Coherent Detection-Based OLT and RSOA-Based ONU for High Power Budget

A cost-effective mode-division-multiplexing and time-division-multiplexing passive optical network (MDM-TDM PON) utilizing a self-coherent detection for upstream signal at optical line terminal (OLT) and a high-gain reflective semiconductor optical amplifier (RSOA) as an optical amplifier for a downstream signal at optical network units (ONUs) to enhance bidirectional power budget is proposed. Meanwhile, to further reduce the cost of ONU, RSOA is also used as upstream on–off keying (OOK) signal modulator by time compression multiplexing. A novel dual-modulus algorithm is proposed for OOK signal detection at the OLT. We experimentally verify the proposed MDM-TDM PON architecture with an upstream 1-Gb/s OOK signal and a downstream 10-Gb/s orthogonal frequency division multiplexing (OFDM) signal. Due to the high gain of RSOA and high receiver sensitivity of self-coherent detection, a 30-dB bidirectional power budget is achieved after 10-km few-mode fiber and a 20-km standard single-mode fiber at the bit error rate (BER) of 10−3. Optimal seed power and signal power that input to the RSOA are investigated in this paper.

Cost-effective TCM-based WDM-PON for highly asymmetric traffic conditions.

A time compression multiplexing (TCM)-based wavelength division multiplexing passive optical network (WDM-PON) using a reflective semiconductor optical amplifier (RSOA) is proposed, and its feasibility is experimentally demonstrated. In the proposed system, the RSOA pre-amplifies a 10 Gb/s downstream signal and modulates the RSOA output, wavelength-locked to the downstream signal, with a 1.25 Gb/s upstream signal simultaneously. The sensitivity of the downstream signal is improved by about 3 dB through the RSOA. The downstream and upstream signals have power penalties of about 0.1 dB and 1.1 dB, respectively, at bit error rates (BERs) of 10(-9) after 20 km transmission.

Design and dynamic properties of an optical transceiver diode with a bulk detection layer

We clarify the impact of a bulk detection layer in an optical transceiver diode for low-cost time compression multiplexing (TCM) transmission systems. By optimizing the detection layer for both transmitter and receiver operations, we obtain temperature- and wavelength-insensitive responsivity, and the power penalty of sensitivity is within 0.55 dB over a wide-wavelength range in the receiver mode. The pulsation due to the detection layer is also effectively suppressed in the transmitter mode. We demonstrate a switching operation for 156-Mb/s nonreturn-to-zero burst signals, which is indispensable for TCM transmission systems.

An instantaneous response CMOS optical receiver IC with wide dynamic range and extremely high sensitivity using feed-forward auto-bias adjustment

An instantaneous response CMOS optical-receiver IC is described with wide input dynamic range and high sensitivity. In a TCM (time compression multiplexing)-TDMA (time division multiple access) fiber-optic subscriber system, a receiver should be able to handle burst-data packets with different amplitude. This requires quick response and a wide dynamic range. Instantaneous response is achieved with a new feed-forward auto-bias adjustment technique. In addition, multistaged offset compensation provides a wide dynamic range without any external elements and adjustments. Using these design techniques, an optical receiver IC was fabricated in a standard 0.8-/spl mu/m CMOS technology. The receiver has a wide dynamic range of more than 25 dB for burst-mode optical input at 29 Mb/s. It has high transimpedance gain of 150 dB/spl Omega/ and high sensitivity of -42 dBm with stable operation for FET threshold voltage and power supply voltage fluctuation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Switching characteristics of LD transceivers for optical TCM transmission

LD transceivers for a TCM (time-compression multiplexing) scheme are promising for bidirectional transmission and economical optical subscriber networks. This paper describes LD switching characteristics when cycling between transmitter and receiver states. An LD equivalent circuit model is discussed based on detailed observations of the LD discharge properties during switching operations. It Is confirmed that the LD current-blocking layers significantly affect switching characteristics. In addition, a "reverse-bias method" for high-speed switching is proposed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of laser diodes as transmitter and preamplifiers in time compression multiplexing systems

It is proposed that a laser diode used as a transmitter in the transmission mode be used as a low bias current preamplifier in the receiving mode for time compression multiplexing transmission. By adopting the low bias current approach, the preamplifier is wavelength and polarization independent. The maximum bias current is determined to be about 0.5 I/sub th/ (I/sub th/=threshold current) by experiments. A transmission experiment at 3.5 Mb/s reveals that about 4 dB of improvement in receiver sensitivity can be obtained by using a laser preamplifier at I=0.54 I/sub th/ when compared to an unbiased laser. The receiver sensitivity of the proposed configuration (laser amplifier at low bias current and photodiode) is estimated by considering the laser preamplifier noise and circuit noise. The laser preamplifier noise is calculated by treating the laser as a traveling wave amplifier with highly reflecting facets. >

Time compression multiplex transmission system using a 1.3 mu m semiconductor laser as a transmitter and a receiver

A bidirectional system using 1.3 mu m lasers as a transmitter and a receiver are investigated. The lasers considered are commercially available Fabry-Perot and distributed-feedback lasers. It is found that the poor performance of a laser receiver, compared to a PIN receiver, stems from three factors: low responsivity, high capacitance, and polarization dependence of responsivity, high capacitance, and polarization dependence of responsivity. The effect of each factor is evaluated. It has been clarified that the polarization dependence of sensitivity originates from the TE and TM modes dependence of both mode confinement factor and reflection at a facet. Using the measured parameters, 1.3- mu m laser receiver sensitivity for a 10/sup -9/ error rate is estimated. Burst data transmission experiments show that estimated sensitivities agree well with the measured values. Optical ping-pong transmission distance of narrowband services is determined based on estimated sensitivity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Properties of commercial 1.3- mu m Fabry-Perot laser modules in a time compression multiplexing system

The practical properties of nine types of 1.3- mu m Fabry-Perot laser modules were determined so as to construct a bidirectional transmission system. Time compression multiplexing (TCM) transmission is employed and the modules must act as both transmitter and receiver. Many modules are tested and it is found that the responsivity of a laser module is roughly proportional to the module's output power. The main source of variation in responsivity is determined to be due to coupling effects. Optical characteristics are measured over the range -15 to +65 degrees C. The maximum transmission distance for narrow-band ISDN (integrated services digital network) services over single-mode fibers is determined for a bit rate of 3.5 Mb/s.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Error correction performance in digital subscriber loop transmission systems

The author describes an error correction system for digital subscriber loop transmission systems which use time compression multiplexing (TCM). An interleaved block code is used to correct the burst errors due to impulse noise from analog telephone circuits. This interleaving method requires no extra hardware and contributes no additional delay. To evaluate the transmission performance of this error correction system, the bit error rate after decoding is derived on the basis of a burst error model for 200 kb/s digital subscriber transmission using the alternate mark inversion (AMI) line code. The experimental results for a 200 kb/s TCM system show that burst errors are substantially reduced.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A new approach to an optical attenuator for a time compression multiplex system using a laser diode as both transmitter and receiver

A novel method of constructing an optical attenuator for a time compression multiplex system with a laser transceiver is proposed and investigated. The main purpose is to achieve wide dynamic range in a receiver. The transceiver consists of a laser diode backed by a photodiode. At average power levels, the laser diode is the main photodetector. At higher than average levels, the laser diode acts as an optical attenuator for the photodiode. The laser diode is called the laser attenuator (LATT). Basic properties of the proposed LATT, such as wavelength and polarization dependence, are clarified. The LATT is confirmed to have an optical dynamic range of over 37 dB. >

Performance analysis of a low-cost time compression multiplex receiver with a recursive algorithm for timing recovery

A private communication system for two-wire full-duplex transmission at an information rate of 144 kb/s that uses time compression multiplex (TCM) over short cables is considered. A low-cost receiver without pulse-shaping prefilter or equalizer that derives its timing from the estimated start-bit arrival times is presented and analyzed. The worst-case analysis involves the derivation of the timing error distribution and the bit error rate, along with an accurate approximation for the timing error variance. It is shown that the bit error rate degradation due to timing errors can be limited to less than 1.5 dB in signal-to-noise ratio by using a recursive start-bit detection algorithm instead of a conventional memoryless algorithm.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A DSP line equalizer VLSI for TCM digital subscriber-line transmission

The architecture of a line equalizer using digital-signal-processing (DSP) techniques is described. The equalizer is utilized in 320-kb/s time-compression multiplexing (TCM) subscriber-line transmission systems in the integrated services digital network (ISDN). It consists of two digital filter blocks, called the square root f equalizer and the bridged-tap equalizer, and gain- and timing-control blocks. The square root f equalizer achieves the processing speed of 20 MOPS by a powerful arithmetic unit composed of multipliers and adders. It provides an FIR filter with nine taps which satisfies an accurate equalization for the 1.92-Msample/s data. The bridged-tap equalizer performs both the adaptation algorithm of the square root f equalizer and the decision-feedback algorithm. The microprogram control enables the hardware to be shared between these functions and assures flexibility. Algorithm-oriented instructions implemented in the ALU realize high-speed execution of the decision-feedback algorithm with a simple architecture. The 11.3-mm*8.5-mm chip with 61 K transistors has been implemented using 1.5- mu m double-metal-layer CMOS technology. >

Loop Transmission Aspects of ISDN Basic Access

The status of the formulation of standards for loop transmission to provide Basic Access in the North American loop plant is reviewed. The impact of loop plant bridged taps on performance is discussed, the reasons for preferring echo canceller technology over time compression multiplexing are reviewed, and issues involved in the specification of echo canceller requirements are discussed. This includes line code selection and receiver design, including linear and decision feedback equalizer design. Some of the possible methods of timing recovery are reviewed, and future directions for the evolution of Basic loop access are considered.

Modeling and Analysis of Error Probability Performance for Digital Transmission Over the Two-Wire Loop Plant

We describe a methodology for the characterization of the 2-wire twisted-pair subscriber loop plant for high-speed digital communications typical of evolving integrated service digital networks (ISDN's). Through use of this analytical/numerical approach it is possible to predict the resulting error probability performance as a function of signal-to-noise ratio for a given set of input parameters representing a particular subscriber loop and its noise environment, including such effects as intersymbol interference, crosstalk and impulse noise. The results are useful in penetration assessment studies of the loop plant population at a fixed grade of service measured objectively in terms of operating bit error probability. This approach is in contrast to simulation-based methodologies leading to subjective performance assessment criteria, such as eye opening measurements. In the present paper we describe the modeling assumptions together with the analytical/numerical techniques underlying this approach. Attention is restricted to time-compression multiplexing (TCM) schemes with bipolar line coding, although the approach is much more general. Numerical results are illustrated through sample graphical output of an extensive computer program implementing this approach. Finally, we illustrate the application of this approach to objective penetration assessment of the GTE subscriber loop plant utilizing data collected as part of an extensive recent survey.

The Loop Coverage Comparison Between TCM and Echo Canceller Under Various Noise Considerations

This paper describes loop coverage evaluations of two-wire digital subscriber transmission systems to support the CCITT recommended 1-430 interface. Several range-limiting factors are discussed and a cable utility design for two representative two-wire digital subscriber transmission systems is presented. The two transmission systems are time compression multiplexing (TCM) and echo canceller (EC), utilizing the AMI line code and full cosine rolloff line equalization for both systems. A new impulse noise evaluation is applied to cable utility design, because impulse noise is one of the most stringent range-limiting factors, especially for TCM in utilizing existing subscriber loops. Comparison of TCM with EC is also carried out according to various range-limiting factors. As a result, it is noted that the 320 kbit/s line bit rate TCM is more applicable in NTT's exchange area coverage than the 160 kbit/s EC to achieve the 2B + D basic interface transmission.

Truncation and threshold noise effects for TCM DBTV signals

The threshold effects which occur for two DBTV transmission formats using time compression multiplexing to achieve increased capacity, by combining two TV signals on one FM carrier, are compared with the currently proposed single TV system. The effect of limiting the pre-emphasised signals on the C/N level at which truncation noise occurs is investigated.

Timing Recovery in Digital Subscriber Loops

Tradeoffs in the design of the timing recovery functions in a subscriber loop receiver are analyzed. The techniques considered are applicable to both the echo cancellation (EC) and time compression multiplexing (TCM) methods of full duplex transmission. Emphasis is on those techniques that lend themselves to implementation in MOSLSI technology, where the objective requirement is that timing recovery be implemented on a sampled-data signal (with the minimum possible sampling rate where EC is used). The wave difference method (WDM) for timing recovery appears to be the best candidate. A detailed study of its performance is carried out analytically and by computer simulation for the case of binary and alternate mark-inversion (AMI) line coding. A closed form expression describing the binary jitter performance of the WDM and its continuous time counterpart, the spectral line technique, is used to compare the two techniques. Analytical and simulation results for recovered phase and jitter are presented for various cable pulse responses carefully chosen to represent worst-case or nearly worst-case conditions. Two methods for including frequency detection in the WDM, the quadricorrelator and the rotational detector, are also simulated.

Design and Performance Study of a Microprocessor-Based Two-Wire Full Duplex Baseband Modem

The design and implementation of a microprocessor-based two-wire full duplex baseband modem is presented. The modem uses the time compression multiplexing technique in implementing a full duplex digital data transmission over a two-wire facility. The line signal used is a baseband bipolar signal. Measurements have been carried out on two prototypes in the lab, and results on the performance of such a modem are reported.

An experimental time-compression system for satellite television transmission

We describe an experimental system for demonstrating time-compression multiplexing (TCM) of two NTSC color television signals in a satellite channel of 36 MHz. The system employs digital processing to derive line or field differentials from each picture. The television signals are then converted into interleaved lines (or fields) of unimpaired baseband video and companded line (or field) differentials. These signal components are finally time compressed and multiplexed into a combined signal for single-carrier FM transmission. With 4.5-m earth stations, the field-differential technique offers extremely good transmission quality suitable for TV distribution to cable head-ends (weighted signal-to-noise ratio, WSNR ≈ 51.5 dB), while the line-differential method provides a slightly lower WSNR ( ≈ 49 dB). We recommend the field-differential approach because of its superior overall picture quality. For larger receive stations (7m), higher picture quality (WSNR ≈ 56 dB) could be obtained. If 10-m earth stations are employed, the received video performance is practically indistinguishable from the corresponding one in the one-television-per-transponder case, and we infer that three pictures can indeed be sent with a graceful degradation as previously suggested. By choosing the parameters properly, the current TCM system can be optimized for a wide variety of applications with higher channel capacity.

Time-Compression Multiplexing (TCM) of Three Broadcast-Quality TV Signals on a Satellite Transponder

We describe how Time-Compression Multiplexing (TCM) might enable the transmission of three National Television System Committee (NTSC) color TV signals through a satellite transponder of 36-MHz bandwidth. The input TV signals are processed such that three fields from each TV source are compressed into an ordinary field period. This is accomplished by sending one field as is but time compressed; the other two fields are sent as differential signals, also time compressed such that all three fit into a single field period. The resultant compressed waveforms are then time multiplexed between the three sources and have a combined baseband bandwidth of 7.52 MHz for an optimal case, or 8.4 MHz for a practical version. In either case, both the transmitter-multiplexer and the receiver-demultiplexer require only three field memories for (digital) signal processing. Performance is expected to be of network broadcast quality (i.e., weighted signal-to-noise ratio, s/n ≥ 56 dB) for the optimal case of 7.52-MHz baseband if 12-meter receive earth stations are employed in a system such as COMSTAR. The practical version, on the other hand, would yield an s/n ≈ 54 dB.