Baseband trellis-coded modulation with combined equalization/decoding for high bit rate digital subscriber loops

Orthogonal frequency-division multiplexing (OFDM) is a popular line code scheme that has found application in wideband modem technologies such has asynchronous digital subscriber loop, high bit rate digital subscriber loop, in addition to digital audio broadcast, digital television terrestrial broadcast, and mobile data communication. To prevent interblock interference (IBI), OFDM inserts a guard time sequence, called the cyclic prefix (CP), between each transmitted block. In practice, CP is rarely long enough for the complete elimination of IBI. Understanding the nature of IBI is crucial in subduing its adverse effects. This study characterizes the power spectral density of the IBI in terms of the channel impulse response and the cyclic prefix length. One of the key findings is that the samples of the impulse response tails do not contribute to IBI power uniformly, but rather their contributions grow linearly as the samples move closer to the edges of impulse response. Based on this observation, the study proposes a time of reference computation technique that minimizes the total IBI power as seen by the receiver.

The author presents a proposal for solving the problem of reduced performance of coded modulation due to colored channel noise by whitening the noise with an added noise predictor in the decision-feedback equalizer (DFE). This also has the benefit of increasing the nominal SNR. The resulting equalizer has a structure encompassing as a special case the noise-predictive DFE proposed earlier by others. Several numerical examples are provided to illustrate the digital subscriber line transmission performance with the new noise-predictive DFE. It is shown that the added noise predictor improves the transmission performance in two ways: first, it decorrelates the noise, and second, it decreases the noise power by its prediction gain.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The author reviews modern developments in telecommunications transmission and services offered over the digital subscriber loop. Issues in provision of telecommunications in African low-income urban situations are discussed. Two particular services, the High Density Subscriber Loop (HDSL) and the Asymmetric Digital Subscriber Loop (ADSL), are examined. Their appropriateness for the African urban situation is examined. The HDSL is seen as offering significant pair-gain opportunities and a new approach to planning subscriber cable installations in areas with little or no telephone service penetration. ADSL is argued to have significant potential for delivery of educational material to urban schools.

We investigate detectors for transmultiplexer-based high bit rate transmission over dispersive channels like telephone wires. The transmitter is based on a synthesis stage. At the receiver side, we design, for an MMSE criterion, multiple-input/multiple-output (MIMO) linear detectors applied after an analysis stage and upgraded with a MIMO decision-feedback (DF) section. The performance of the system is investigated for filter banks over copper wires with different noises (AWGN, FEXT and RFI). The influence of the forward section rate is investigated. The potential of these detectors is clearly demonstrated. Besides, reduced complexity solutions are also put forward.

This paper presents various requirements and configurations in the information network system (INS) NTT's version of the integrated services digital network (ISDN)- such as field trials, and technologies and equipment design of the digital subscriber loop using balanced wire pairs. The main aspects characterizing digital subscriber loops, are a customer access structure, a digital transmission system on existing subscriber loops, and customer interface. A configuration of two-wire digital subscriber loops with two customer access channels, which is adopted in the field trials, will be described. The time-shared two-wire digital transmission and power feeding methods on subscriber loops are discussed. The common mode rejection ratio (CMRR) is discussed in detail, since CMRR is one of the main factors which affects the transmission ability of balanced wire pairs. A proposed self-clocked four-wire customer interface utilizes time division multiplexing technique. The digital subscriber loop operates on a call-by-call basis for link establishment to avoid excessive power dissipations as well as to avoid impairments caused by crosstalk from other lines within a cable. Its design objectives and implementation are also discussed.

With the global deployment of wavelength division multiplexing (WDM), many fibre manufacturers are developing new exotic fibre types. These have been designed to support long haul high bit rate transmission as afforded through optical multiplexing. However, high channel rate NRZ WDM transmission is impaired considerably by both the linear and non-linear fibre effects. These effects are further compounded as the channel rates migrate from 10 Gbps to 40 Gbps. The correct choice of fibre type required to support multichannel high bit rate transmission on such systems becomes of critical importance. We report on the performance of the ubiquitous non-dispersion shifted fibre (NDSF) type, SMF28/sup TM/, and in particular its performance with various dispersion compensation schemes. Furthermore we investigate the implications and performance of NZ-DS fibre types. The NZ-DS fibre types considered comprise the large effective area NZ-DSF and the standard NZ-DSF.

The central theme is the study of error propagation effects in decision feedback equalizers (DFEs). The thesis contains: a stochastic analysis of error propagation in a tuned DFE; an analysis of the effects of error propagation in a blindly adapted DFE; a deterministic analysis of error propagation through input-output stability ideas; and testing procedures for establishing correct tap convergence in blind adaptation. To a lesser extent, the decision directed equalizer (DDE) is also treated. Characterizing error propagation using finite state Markov process (FSMP) techniques is first considered. We classify how the channel and DFE parameters affect the FSMP model and establish tight bounds on the error probability and mean error recovery time of a tuned DFE. These bounds are shown to be too conservative for practical use and highlight the need for imposing stronger hypotheses on the class of channels for which a DFE may be effectively used. In blind DFE adaptation we show the effect of decision errors is to distort the adaptation relative to the use of a training sequence. The mean square error surface in a LMS type setting is shown to be a concatenation of quadratic functions exposing the possibility of false tap convergence to undesirable DFE parameter settings. Averaging analysis and simulation are used to verify this behaviour on some examples. Error propagation in a tuned DFE is also examined in a deterministic setting. A finite error recovery time problem is set up as an input-output stability problem. Passivity theory is invoked to prove that a DFE can be effectively used on a channel satisfying a simple frequency domain condition. These results give performance bounds which relate well with practice. Testing for false tap convergence in blind adaptation concludes our study. Simple statistic output tests are shown to be capable of discerning correct operation of a DDE. Similar tests are conjectured for the DFE, supported by proofs for the low dimensional cases.

Introduction Indoor infrared wireless systems using diuse channels are considered as the best form in respect of the network exibility. Infrared wireless system using ono keying code-division multiple-access (OOK-CDMA) has been proposed to realize multiple access in indoor infrared wireless communications, and the performance is analyzed on diuse channels [1]. It is shown in [1] that the bit error rate (BER) of indoor infrared wireless systems using OOK-CDMA on diuse channels is degraded excessively owing to the eects of ISI. To mitigate the eects of ISI, some equalization schemes for infrared wireless systems have been discussed [2]-[5]. The performance of the OOK-CDMA with the decision-feedback equalizer (DFE) and that of the OOK-CDMA with the decision-feedforward-andfeedback equalizer (DFFE) have been evaluated, and it is shown that the system with the DFFE has better performance than that of the system with the DFE [4]. The performance of the DS-CDMA with the feedfo

We have demonstrated that mid-span spectral inversion by four-wave mixing in a semiconductor optical amplifier can be used to effectively eliminate dispersion in high bit rate transmission. The technique has been used to achieve transmission of 1OGb/s signals from a directly modulated DFB over 200km dispersive fibre, and of 25ps gain-switched pulses over 100km dispersive fibre. The results show a complete elimination of degradation resulting from fibre chromatic dispersion. The former result represents more than a 40-fold increase in the bit rate distance product for the directly modulated signals by means of MSSI.

We report a very efficient semianalytical approach for the performance evaluation of differential detection schemes for GMSK signals of the DECT standard. Precisely, for a given channel, the performance is determined by means of an analytical procedure which includes the saddlepoint approximation. We consider both static channels (with impulse response generated by the simulation program SIRCIM) and two-ray Rayleigh and log-normal fading channels. As a departure from previous works, our receiver includes an all-digital part after the analog differential detection scheme. The digital part includes: (1) a block for the estimation of both the optimum sampling phase and the nonlinear channel coefficients (by making use of the DECT training sequence), (2) a one-tap decision feedback (DF) equalizer, and (3) a block for the evaluation of the approximate optimum bias level (/spl gamma//sub e/) in the threshold detector. Both the DF equalizer coefficient and /spl gamma//sub e/ are based on the nonlinear channel coefficients estimate. For channels with a normalized delay spread up to 0.2, the use of the optimum threshold together with the DF equalizer permits a gain of about 2 dB at BER=10/sup -6/ with respect to a receiver without equalization and a zero-level decision threshold. In addition, we discover that, in indoor environments, the 2-bit GMSK detector performs roughly the same as the 1-bit detector. The threshold optimization is also effective in the presence of channels affected by fading. To support this statement, we report the performance of the 1-bit differential detection scheme combined with antenna selection diversity in the presence of a two-ray log-normal and Rayleigh fading channel.

Addresses problems related to the conceptual design of a fully digital synchronous DFE (decision feedback equalizer) and investigates the effects of the necessary quantization of the input signals and coefficients on DFE performance in static and dynamic operation. The analysis is performed taking into account the following topics: the influence of the dynamic range and quantization levels of the input signal and coefficients: the tracking and acquisition algorithm capabilities; comparison of DFE structures; and the extension of robust algorithms to DFEs. An experimental setup including a digital baseband equalizer is described. Results are reported for two kinds of DFE structures and a 16-AQM (quadrature amplitude modulation) modulation format. Specific problems related to the operation of DFEs in digital radio modems are discussed. It is established that the DFE structure is able to track continuous minimum-phase to nonminimum-phase transitions and vice versa without getting out of lock. This is an important result since the DFE outperforms current linear equalizers. >

We investigate the equalization and channel identification for space-time block coded signals over a frequency-selective multiple-input multiple output (MIMO) channels. The equalization is considered by taking into account the cyclostationarity of space-time block coded signals. The minimum mean square error (MMSE) solutions are derived for linear and decision feedback (DF) equalizers. Due to the redundancy induced by space-time block coding, a blind estimation for MIMO channels is investigated by using the subspace method. Together with pilot symbols, the semi-blind channel estimation can be used and it can result in less (bit error rate) performance degradation of the MMSE linear and DF equalizers.

In this paper, the theoretical as well as experimental results of BER characteristics of three different modulation schemes, ASK, FSK and BPSK, in a multi-path Rician channel are addressed. These BER characteristics are analyzed as a function of E b / N o and the power ratio of the line of sight (LOS) component to the Rayleigh scattered component The theoretical as well as computer simulation results shows the ASK is the most suitable modulation scheme for the dedicated short range communication (DSRC) in terms of implemental cost and system complexity. The decision feedback equalizer is proved to be very effective in canceling the multi-path interference in the DSRC channel environment. The simulation result of the equalized ASK, reveals the performance enhancement achievable with decision feedback (DFE) equalizer for the first generation DSRC system. The multi-ray DSRC channel model is also provided to predict the received carrier power and fluctuation, which are quite dependent on the surroundings of a cell.

An efficient MPEG-2 to MPEG-4 video transcoder is presented in this paper. We consider the transcoding from high quality and bit rate MPEG-2 video with larger image size (e.g. 4CIF/4SIF, CIF) to lower quality and bit rate MPEG-4 video with smaller image size (e.g. CIF, QCIF). First, the transcoder needs to down-sample the input MPEG-2 video. Since the motion vectors carried by the MPEG-2 stream will be reused in the transcoding process, they are sub-sampled besides the frame pixels, and the coding mode for each down-sampled macroblock is examined. A new rate control method is proposed to convert the high bit rate MPEG-2 video to the low bit rate MPEG-4 counterpart. The proposed rate control scheme adjusts the frame rate and the frame quantization step size simultaneously according to the channel bandwidth to achieve a good temporal-spatial quality tradeoff. Due to the reuse of motion vectors, key frames (i.e. I and P frames) cannot be skipped to maintain the prediction sequential order, while some B frames containing less temporal information may be skipped in transcoding to save the bit rate. Skipped B frames can be reconstructed at the decoder to ensure the full frame rate playback. The TM7 quadratic Rate-Qtz model is adopted in the proposed rate control scheme to calculate the re-quantization step size from the given target bit. Simulations show that the proposed MPEG-2 to MPEG-4 video transcoder with rate control can out-perform the basic MPEG transcoder that adjusts the re-quantization step size at a constant frame rate. The complexity of the proposed transcoder is low so that it can be used in real-time applications.

The increasing demand for higher bit rates in access networks requires fibre deployment closer to the customer since bit rates in copper based access networks are strictly limited by the length of the copper cables. Besides higher access bit rates optical access network technologies enable extended distances between the network terminal at the customer premise and the line port at the access node due to the lower attenuation of optical fibres: The network operator is able to establish larger service areas resulting in a simplified network structure leading to a cost-efficient re-design of the network. In this paper different architectures for optical access networks with emphasis on network node consolidation are analyzed with respect to optical reach and installation costs. Based on simplified device and cost models the results show that the costs for the feeder fibres between the new central network node and the former node being now de-activated represent a major cost part. In order to economically re-design the access network, technologies with a high multiplexing factor and a cost-efficient operation are necessary.