Showing papers on "Bit error rate published in 1997"

A new rate control scheme using quadratic rate distortion model

Abstract: A new rate control scheme is used to calculate the target bit rate for each frame based on a quadratic formulation of the rate distortion function. The distortion measure is assumed to be the average quantization scale of a frame. The rate distortion function is modeled as a second-order function of the inverse of the distortion measure. We present a closed form solution for the target bit allocation which includes the MPEG-2 TM5 rate control scheme as a special case. The model parameters are estimated using statistical linear regression analysis. Since the estimation uses the past encoded frames of the same picture prediction type (I, P, B pictures), the proposed approach is a single pass rate control technique. Because of the improved accuracy of the rate distortion function, the fluctuations of the bit counts are significantly reduced by 20-65% in the standard deviation of the bit count while the picture quality remains the same. Thus, the buffer requirement is reduced at a small increase in complexity. This technique has been adopted by the MPEG committee as part of VM5.0 in November 1996.

Adaptive, performance-optimizing communication system for communicating with an implanted medical device

Abstract: An adaptive, performance-optimizing communication system for communicating with an implanted medical device in which signals are transmitted and received in accordance with predetermined, interrelated operational parameters, such as transmission rate, transmitter power, and the like. Various aspects of system performance, including bit error rate in received signals, the strength of received signals, the signal-to-noise ratio of received signals, the presence of local RF noise and non-telemetry related RF signals, and the like, are dynamically monitored by the communication system, to determine whether predetermined system performance goals are being met. If it is determined that one or more system performance goals are not being met, one or more operational parameters may be automatically adjusted so that desired performance can be achieved.

Tree-structured generation of orthogonal spreading codes with different lengths for forward link of DS-CDMA mobile radio

Abstract: Tree-structured generation of orthogonal spreading codes with different lengths is presented for orthogonal multiplexing of forward-link code-channels of different data rates in direct sequence code division multiple access DS-CDMA mobile radio. The bit error rate performance under a multi-user environment suffering multipath Rayleigh fading is evaluated by computer simulation.

Progressive image coding for noisy channels

Abstract: We cascade an existing image coder with carefully chosen error control coding, and thus produce a progressive image compression scheme whose performance on a noisy channel is significantly better than that of previously known techniques. The main idea is to trade off the available transmission rate between source coding and channel coding in an efficient manner. This coding system is easy to implement and has acceptably low complexity. Furthermore, effectively no degradation due to channel noise can be detected; instead, the penalty paid due to channel noise is a reduction in source coding resolution. Detailed numerical comparisons are given that can serve as benchmarks for comparisons with future encoding schemes. For example, for the 512/spl times/512 Lena image, at a transmission rate of 1 b/pixel, and for binary symmetric channels with bit error probabilities 10/sup -3/, 10/sup -2/, and 10/sup -1/, the proposed system outperforms previously reported results by at least 2.6, 2.8, and 8.9 dB, respectively.

Effects of clipping and filtering on the performance of OFDM

Abstract: Orthogonal frequency division multiplexing (OFDM) is an attractive technique for wireless communication applications. However, an OFDM signal has a large peak-to-mean envelope power ratio (PMEPR), which can result in significant distortion when transmitted through a nonlinear device, such as a transmitter power amplifier. We investigate, through extensive computer simulations, the effects of clipping and filtering on the performance of OFDM, including the power spectral density, the bit error rate, and the PMEPR. Our results show that clipping and filtering is a promising technique for the transmission of OFDM signals using realistic linear amplifiers.

Power control of an integrated cellular communications system

Abstract: A cellular communications system is provided having both surface and satellite nodes which are fully integrated for providing service over large areas. Two-way adaptive power control and signal quality monitoring and power control responsive thereto are provided for controlling the power output levels of transmitters to the minimum necessary for satisfactory communications. Each transmission includes a code representative of the transmitter output power level. Receivers compare this code to the received signal strength and adjust their associated transmitter power output level accordingly. Bit error rate and SNR are monitored by receivers to develop a measure of signal quality. A signal quality code is transmitted to remote units and transmission output power level is adjusted in response. Timing signals are provided by one or more nodes to obtain user position information. Preferably, the invention provides power control of a cellular communications system using code division multiple access (CDMA) employing forward error correction coding (FECC) and spread spectrum waveforms to enhance the effective gain and selectivity of the system.

Pilot assisted channel estimation for OFDM in mobile cellular systems

Abstract: The use of pilot symbols for channel estimation introduces overhead and it is thus desirable to keep the number of pilot symbols to a minimum. The number of needed pilot symbols for a desired bit error rate and Doppler frequency is highly dependent on the pilot pattern used in orthogonal frequency division multiplexed, OFDM, systems. Five different pilot patterns are analysed by means of resulting bit error rate, which is derived from channel statistics. Rearrangement of the pilot pattern enables a reduction in the number of needed pilot symbols up to a factor 10, still retaining the same performance. The analysis is general and can be used for performance analysis and design of pilot patterns for any OFDM system.

A novel ARQ technique using the turbo coding principle

Abstract: A novel automatic repeat request (ARQ) technique based on the turbo coding principle is presented. The technique uses the log-likelihood ratios generated by the decoder during a previous transmission as a priori information when decoding retransmissions. Simulation results show a significant decrease in frame error rate, especially at low-to-moderate E/sub b//N/sub 0/.

Apparatus and method for adaptive forward error correction in data communications

Abstract: An apparatus (101, 110) and method for adaptive forward error correction in a data communication system (100) provides for dynamically changing forward error correction parameters based upon communication channel conditions. Data having a current degree of forward error correction is received (305), and a channel parameter is monitored (310). A threshold level for the channel parameter is determined (315), and the monitored channel parameter is compared to the threshold level (320). When the channel parameter is not within a predetermined or adaptive variance of the threshold level, a revised forward error correction parameter having a greater or lesser degree of forward error correction capability is selected (330, 340, 350, 360), and the revised forward error correction parameter is transmitted (370). The device receiving the revised forward error correction parameter, such as a secondary station (110), then transmits data encoded utilizing the revised error correction parameter (425).

Standard compatible extension of H.263 for robust video transmission in mobile environments

Abstract: In this paper we address the problem of robust video transmission in error prone environments. The approach is compatible with the ITU-T video coding standard H.263. Fading situations in mobile networks are tolerated and the image quality degradation due to spatio-temporal error propagation is minimized utilizing a feedback channel between transmitter and receiver carrying acknowledgment information. In a first step, corrupted group of blocks (GOB's) are concealed to avoid annoying artifacts caused by decoding of an erroneous bit stream. The GOB and the corresponding frame number are reported to the transmitter via the back channel. The encoder evaluates the negative acknowledgments and reconstructs the spatial and temporal error propagation. A low complexity algorithm for real-time reconstruction of spatio-temporal error propagation is described in detail. Rapid error recovery is achieved by INTRA refreshing image regions (macroblocks) bearing visible distortion. The feedback channel method does not introduce additional delay and is particularly relevant for real-time conversational services in mobile networks. Experimental results with bursty bit error sequences simulating a Digital European Cordless Telephony (DECT) channel are presented with different combinations of forward error correction (FEC), automatic repeat on request (ARQ), and the proposed error compensation technique, Compared to the case where FEC and ARQ are used for error correction, a gain of up to 3 dB peak signal-to-noise ratio (PSNR) is observed if error compensation is employed additionally.

Error concealment based on directional interpolation

Abstract: Compressed bitstreams are, in general, very sensitive to channel errors. For instance, a single bit error in a coded video bitstream may cause severe degradation on picture quality. When bit errors occur during transmission and cannot be corrected by an error correction scheme, error concealment is needed to conceal the corrupted image at the receiver. Error concealment algorithms attempt to repair damaged portions of the picture by exploiting both the spatial and the temporal redundancies in the received and reconstructed video signal. We discuss several temporal, spatial, and transform-domain error concealment techniques for MPEG coded pictures, and propose a new scheme based on directional interpolation. We also compare the performance of these techniques by computer simulation.

A New Type

Abstract: The areal density of magnetic disk is expected to grow to over 20Gb/in 2 by the end-1990s. In the INTERMAG'96, the authors demonstrated high areal density of 5Gbit/in 2 with PR4ML channel. The thermal instability can not be neglected at higher areal density than 5Gb/in 2 . It indicates the necessity to use the code which expand bit length such as (1,7) RLL code. We consider the best combination of (1,7) RLL code and a partial response channel. The partial response system of the polynomial (1+D)(1-D 2 ) called modified E 2 PR4(MEEPR4) exhibits the best performance. We performed this partial response simulation model with white noise and media - noise and examined the architectural consideration in the design of the experimental prototype.

Interference mitigation in spread spectrum communication systems using time-frequency distributions

Abstract: The capability of the time-frequency distributions (TFDs) to properly represent a single as well as multiple component signals in time and frequency permits the application of a new approach for interference excision in spread spectrum communication systems. The instantaneous frequency (IF) estimate from the TFD is used to construct a finite impulse response filter that reduces the interference power with a minimum possible distortion of the desired signal. The proposed technique is therefore a case of open-loop adaptive filtering. Three- and five-coefficient zero-phase excision filters are considered. Closed-form expressions of the improvement of SNR at the receiver correlator output using the TFD-based adaptive filtering are derived for two extreme cases of time-varying interferers, namely, those of fixed frequency sinusoids and randomly changing instantaneous frequencies. Simulation results including the bit error rates are presented for both swept and frequency hopping jammers.

Simultaneous quantum cryptographic key distribution and conventional data transmission over installed fibre using wavelength-division multiplexing

Abstract: Wavelength division multiplexing (WDM) is used to add a secure quantum key distribution channel (/spl lambda/=1300 nm) to a conventional 1.2 Gbit/s data channel (/spl lambda//spl sim/1550 nm) operating over 28 km of installed fibre in BT's London and East Anglia multiservice network testbed (LEANET). Error-free operation of the data channel is demonstrated with no degradation of the quantum channel performance.

Ultra wideband receiver with high speed noise and interference tracking threshold

Abstract: An UWB receiver utilizing a microwave tunnel diode as a single pulse detector for short pulse, impulse, baseband or ultra wideband signals. The tunnel diode detector's bias point is set at system start-up, through an automatic calibration procedure to its highest sensitivity point relative to the desired bit error rate performance (based upon internal noise only) and remains there during the entire reception process. High noise immunity is achieved through the use of a high speed, adaptive dynamic range extension process using a high speed, Gallium Arsenide (GaAs) voltage variable attenuator (VVA) whose instantaneous attenuation level is determined by a periodic sampling of the ambient noise environment. Microprocessor-controlled detector time-gating is performed to switch the tunnel diode detector to the receiver front end circuitry for reception of an incoming UWB pulse, and alternately to ground through a resistor to discharge stored charge on the tunnel diode detector. In a second embodiment, two tunnel diode detectors are utilized in parallel, one biased for data detection and the other biased for noise detection, such that data detection can be interpreted based on simultaneous comparison to both a data threshold and a noise threshold.

A 700-Mb/s/pin CMOS signaling interface using current integrating receivers

Abstract: A high speed CMOS signaling interface for application in multiprocessor interconnection networks has been developed. The interface utilizes I-V push-pull drivers, a delay line phase-locked loop (PLL), and sampling of the data on both edges of the clock. In order to increase the noise immunity of the reception, a current-integrating input pin sampler is used to receive the incoming data. Chips fabricated in a 0.8 /spl mu/m CMOS technology achieve transfer rates of 740 Mb/s/pin operating from a 3.3 V supply with a bit error rate of less than 10/sup -14/.

DCT coefficients recovery-based error concealment technique and its application to the MPEG-2 bit stream error

Abstract: This paper presents a novel error concealment technique based on the discrete cosine transform (DCT) coefficients recovery and its application to the MPEG-2 bit stream error. Assuming a smoothness constraint on image intensity, an object function which describes the intersample variations at the boundaries of the lost block and the adjacent blocks is defined, and the corrupted DCT coefficients are recovered by solving a linear equation. Our approach can be regarded as a special case of Wang et al.'s (1991). However, we show that the linear equation in the proposed algorithm can be decomposed into four independent subequations, requiring much lower computational load and simpler hardware structure than existing algorithms, while providing adequate performances. To develop a generic error concealment (EC) system, the blocks corrupted by the random bit errors are identified by a multistage error detection algorithm. Thus, the proposed EC system can be applied to more realistic environments, such as concealment of random bit error in MPEG-2 bit stream. Computer simulation results show that the quality of a recovered image is significantly improved even at a bit error rate as high as 10/sup -5/.

Symbol-by-symbol MAP demodulation of CPM and PSK signals on Rayleigh flat-fading channels

Abstract: Demodulation using the symbol-by-symbol maximum a posteriori probability (MAP) algorithm is presented. The algorithm is derived for the case of continuous phase modulation (CPM) signals transmitted over Rayleigh flat-fading channels, and a corresponding receiver structure is specified. It is shown that the MAP algorithm requires computing, for each trellis branch, the sum of the products of the weights of all paths through the trellis which pass through that branch, and that this generic computational problem can be solved efficiently by an approach that uses a forward and backward recursion through the trellis. Simulation results are presented which show both the hard and soft decision performance of the MAP receiver to be robust, even in the presence of fade rates of up to 30% of the symbol rate. The application of the receiver concept to phase-shift keying (PSK) signals is also discussed, and then evaluated via simulation. The concept of joint demodulation and decoding using iterative processing techniques is introduced. It is shown that the MAP receiver is well suited for iterative processing applications due to its use of a priori symbol probabilities and its production of optimal soft decisions. Simulation results for the reception of quaternary PSK (QPSK) show that the bit error rate (BER) performance of the iterative MAP receiver can approach that of a receiver operating with perfect knowledge of the fading process.

Laser satellite communication network-vibration effect and possible solutions

Abstract: A number of serious consortiums develop satellite communication networks. The objective of these communication projects is to service personal communication users almost everywhere on Earth. The intersatellite links in those projects use microwave radiation as the carrier. Free-space optical communication between satellites networked together can make possible high-speed communication between different places on Earth. Some advantages of an optical communication system over a microwave communication system in free space are: (1) smaller size and weight, (2) less transmitter power, (3) larger bandwidth, and (4) higher immunity to interference. The pointing from one satellite to another is a complicated problem due to the large distance between the satellite, the narrow beam divergence angle, and vibration of the pointing system. Such vibration of the transmitted beam in the receiver plane decreases the average received signal, which increases the bit error rate. We review: (1) the present status of satellite networks, (2) developing efforts of optical satellite communication around the world, (3) performance results of vibration effects on different kinds of optical communication satellite networks, and (4) seven approaches to overcome the problems caused by transmitter pointing vibration.

Combined turbo equalization and turbo decoding

Abstract: In this paper, the subject of turbo coding in the presence of intersymbol interference channel is investigated. An iterative decoder structure is presented, which combines the channel equalization and the turbo decoding. At each iteration extrinsic information from the channel detector is fed into the turbo decoders, and then their extrinsic information is fed back to the channel detector. Simulation results are presented for turbo code with BPSK and and PSK modulations, transmitted over several ISI channels having severe frequency distortion. The performances are about 1 dB from the ISI channel capacity at bit error rate of 10/sup -5/.

Multi-carrier CDMA with iterative decoding and soft-interference cancellation

Abstract: A novel multi-user detection scheme applying iterative soft-interference cancellation in multi-carrier code division multiple access (MC-CDMA) systems is proposed and investigated. The novel detection scheme cancels the interference from the other users by taking into account reliability information about the detected interference. For this purpose, we do not use the decisions from the inner decoder (despreader) but the more reliable soft-values from the outer soft-in/soft-out decoder to reduce error propagation. It can be shown that the iterative soft-interference cancellation scheme clearly outperforms an MC-CDMA system with inner joint detection based on maximum likelihood sequence estimation (MLSE) which is followed by an outer channel decoder. Furthermore, the bit error rate (BER) obtained with the proposed scheme closely approaches the single-user bound. Hence, iterative soft-interference cancellation is able to eliminate almost all multiple access interference.

A video compression scheme with optimal bit allocation among segmentation, motion, and residual error

Abstract: We present a theory for the optimal bit allocation among quadtree (QT) segmentation, displacement vector field (DVF), and displaced frame difference (DFD). The theory is applicable to variable block size motion-compensated video coders (VBSMCVC), where the variable block sizes are encoded using the QT structure, the DVF is encoded by first-order differential pulse code modulation (DPCM), the DFD is encoded by a block-based scheme, and an additive distortion measure is employed. We derive an optimal scanning path for a QT that is based on a Hilbert curve. We consider the case of a lossless VBSMCVC first, for which we develop the optimal bit allocation algorithm using dynamic programming (DP). We then consider a lossy VBSMCVC, for which we use Lagrangian relaxation, and show how an iterative scheme, which employs the DP-based solution, can be used to find the optimal solution. We finally present a VBSMCVC, which is based on the proposed theory, which employs a DCT-based DFD encoding scheme. We compare the proposed coder with H.263. The results show that it outperforms H.263 significantly in the rate distortion sense, as well as in the subjective sense.

Effective evaluation of link quality using error vector magnitude techniques

Abstract: Bit error rate (BER) is an accepted figure of merit in the industry for the characterization of transmission link quality and communications systems in general. While useful as a conceptual figure of merit, it suffers from a number of practical drawbacks that compromise its value as a standard test in manufacturing or maintenance. This paper discusses the use of error vector magnitude (EVM) and its relationship to BER to develop a foundation that will help in formulating and implementing a sound and cost-effective test strategy for component, sub-system and system test in communications systems, such as mobile cellular, satellite and wireless data networks.

Reduced complexity bit allocation to subchannels in a multi-carrier, high speed data transmission system

Abstract: A communications system employing the Discrete Multitone (DMT) line code divides the used frequency band W into a large number of subchannels, each with a bandwidth Δf=W/N. The signal in each subchannel is independently modulated at the symbol rate 1/Δf. Because of noise and the non-ideal characteristics of the transmission channel, the signal-to-noise ratio (SNR) varies for different subchannels across the frequency band. Each subchannel is used to transmit an integer number of bits in a two-dimensional signal constellation, the susceptibility to noise increasing with the size of the constellation assuming that the same signal energy is used. In order to use the transmission channel optimally, subchannels are assigned different numbers of bits depending on their specific SNR values, i.e., a subchannel with a high SNR value is assigned a large number of bits and vice versa. An optimal bit allocation is determined that ensures a certain bit error rate (BER) is obtained for all subchannels. In order to simplify numerical computations, thresholding is employed to make initial bit assignments. Further simplification of the bit loading procedures is obtained by ending bit allocation optimization efforts after a targeted BER is achieved.

Error detection and correction code for data and check code fields

Abstract: A method and apparatus for detecting and correcting single bit errors, detecting double bit errors, and detecting multiple bit errors within a nibble of a data field comprising 135 data bits and 9 check bits. 9 check bits are generated based on 135 data bits. The 9 check bits are appended to the data bits and the cumulative data field is checked for errors. An error detection syndrome is generated that indicates whether an error has occurred and whether the error is correctable. Check bit generation and error detection syndrome generation is accomplished based on the ordering in an ECC code matrix.

A constrained optimization approach to multiuser detection

Abstract: Interference cancellation or multiuser detection schemes are of great interest to the CDMA community because of their potential ability to treat the near-far problem and significantly reduce interference levels. A linear adaptive multiuser detection scheme based on constrained optimization is presented, constraints are constructed from knowledge of users' codes and associated timing. Both single- and multiple-constraint detectors are derived and shown to have interesting relationships to existing detectors. Simulation results, presented in the form of bit error rate curves, demonstrate the receiver's performance in an additive white Gaussian noise (AWGN) channel.

Performance analysis of coherent DS-CDMA systems in a Nakagami fading channel with arbitrary parameters

Abstract: A new expression for the bit error rate (BER) of an asynchronous direct-sequence code-division multiple-access (DS-CDMA) system with coherent BPSK demodulation in a multipath Nakagami (1960) fading channel is derived. The analysis assumes an arbitrary number of independent, but nonidentical resolvable paths combined by the RAKE receiver. The results obtained show that in such systems, the effect of nonidentical fading on system performance cannot be ignored.

A digital communications system having an automatically selectable transmission rate

Abstract: A system and method for maintaining communication between a paging base station (13) and a mobile paging unit (14) when the signal reception is below a level that would otherwise be unacceptable The system changes from one data transmission rate to another depending upon the quality of the communication channel In particular, the symbol rate of the transmissions remains the same, but the number of modulation states and bits per symbol is decreased or increased depending upon the bit error rate of the received signal In some arrangements, the transceiver (13) transmits at the highest bit rate (46) for that particular system If no response is received from the paging unit or the paging unit sends a response signal back to the transceiver (13) indicating the signal sent is unacceptable (43), the transceiver (13) retransmits at a lower bit rate (45) In other arrangements, the receiver (14) determines the highest data rate within the group of data rates available and transmits a signal representative of that data rate to the base station (13) In response to such a signal, the base station transmits at the requested data rate until a different data rate is requested (51)

Interference cancelling equalizer (ICE) for mobile radio communication

Abstract: This paper proposes an adaptive interference cancelling equalizer (ICE), which not only equalizes intersymbol interference (ISI), but also cancels cochannel interference (CCI) in the received signal in Rayleigh-fading environments, ICE is an adaptive multiuser detector for the frequency-selective fading environment commonly experienced by mobile communication channels. ICE employs a novel detection scheme: recursive least-squares maximum-likelihood sequence estimation (RLS-MLSE), which simultaneously estimates time-varying channel parameters and transmitted signal sequences. Diversity reception is used to enhance the signal detection performance of ICE. A computer simulation of a 40-kb/s QPSK time-division multiple-access (TDMA) cellular mobile radio system demonstrates the possibility of improving system capacity with ICE. Simulations of ICE with and without diversity are carried out under various fading conditions. For the maximum Doppler frequency of 40 Hz, ICE can attain an average bit-error rate (BER) of 10/sup -2/ under a single CCI carrier-to-interference ratio (CIR) of /spl sim/14 dB. Moreover, ICE for two independent CCI signals can attain the average BER of 1.5/spl times/10/sup -2/ with average CIR/spl ges/-10 dB.

Theory of burst-mode receiver and its applications in optical multiaccess networks

Abstract: In this paper, a unified theory for the newly developed optical burst-mode receiver is presented. Based on this theory, an analysis of the performance of the receiver is given both theoretically and experimentally. The theoretical model agrees well with the experimental results. This theory can quantitatively explain the bit error rate (BER) performance of burst-mode receivers. Several potential applications of burst-mode receivers are also illustrated, including applications in supervisory system for erbium-doped fiber amplifier (EDFA) trans-oceanic optical links and various high-speed all-optical multiaccess packet networks.