Showing papers on "Bit error rate published in 2000"
Dissertation•
1 Jan 2000
TL;DR: The reciprocal-channel approximation, based on dualizing LDPC codes, provides a very accurate model of density evolution for the AWGN channel, and another approximation method, Gaussian approximation, is developed, which enables us to visualize infinite-dimensional density evolution and optimization ofLDPC codes.
Abstract: This thesis proposes two constructive methods of approaching the Shannon limit very closely. Interestingly, these two methods operate in opposite regions, one has a block length of one and the other has a block length approaching infinity.
The first approach is based on novel memoryless joint source-channel coding schemes. We first show some examples of sources and channels where no coding is optimal for all values of the signal-to-noise ratio (SNR). When the source bandwidth is greater than the channel bandwidth, joint coding schemes based on space-filling curves and other families of curves are proposed. For uniform sources and modulo channels, our coding scheme based on space-filling curves operates within 1.1 dB of Shannon's rate-distortion bound. For Gaussian sources and additive white Gaussian noise (AWGN) channels, we can achieve within 0.9 dB of the rate-distortion bound.
The second scheme is based on low-density parity-check (LDPC) codes. We first demonstrate that we can translate threshold values of an LDPC code between channels accurately using a simple mapping. We develop some models for density evolution from this observation, namely erasure-channel, Gaussian-capacity, and reciprocal-channel approximations. The reciprocal-channel approximation, based on dualizing LDPC codes, provides a very accurate model of density evolution for the AWGN channel. We also develop another approximation method, Gaussian approximation, which enables us to visualize infinite-dimensional density evolution and optimization of LDPC codes. We also develop other tools to better understand density evolution. Using these tools, we design some LDPC codes that approach the Shannon limit extremely closely. For multilevel AWGN channels, we design a rate 1/2 code that has a threshold within 0.0063 dB of the Shannon limit of the noisiest level. For binary-input AWGN channels, our best rate 1/2 LDPC code has a threshold within 0.0045 dB of the Shannon limit. Simulation results show that we can achieve within 0.04 dB of the Shannon limit at a bit error rate of 10−6 using a block length of 10 7. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)
429 citations
Patent•
19 Dec 2000TL;DR: In this article, a rate conversion system that converts the bit rate of a pre-compressed video bit stream from one bit rate to another, and that is integrated with a digital communication channel, is described.
Abstract: Digitally compressed video/audio bit streams, when transmitted over digital communication channels such as digital subscriber loop (DSL) access networks, ATM networks, satellite, or wireless digital transmission facilities, can be corrupted due to lack of sufficient channel bandwidth. This invention describes schemes to ensure lossless transmission of bit streams containing pre-compressed video signals within the communication channels. The schemes herein comprises a rate conversion system that converts the bit rate of a pre-compressed video bit stream from one bit rate to another, and that is integrated with a digital communication channel, and a means to convey the maximum channel transmission rate to the rate conversion system to allow satisfactory transmission of the bit stream from the input of the rate converter through the transmission facility.
296 citations
TL;DR: This paper suggests two communication schemes that provide a processing gain in chaos-based communication schemes and studies the performance of these and of the earlier proposed differential chaos shift keying, which shows that, when performance is characterized by the dependence of bit error rate on E/sub b//N/sub 0/, the increase of the spreading sequence length beyond a certain point degrades the performance.
Abstract: Using chaotic signals in spread-spectrum communications has a few clear advantages over traditional approaches. Chaotic signals are nonperiodic, wideband, and more difficult to predict, reconstruct, and characterize than periodic carriers. These properties of chaotic signals make it more difficult to intercept and decode the information modulated upon them. However, many suggested chaos-based communication schemes do not provide processing gain, a feature highly desirable in spread-spectrum communication schemes. In this paper, we suggest two communication schemes that provide a processing gain. The performance of these and of the earlier proposed differential chaos shift keying is studied analytically and numerically for discrete time implementations. It is shown that, when performance is characterized by the dependence of bit error rate on E/sub b//N/sub 0/, the increase of the spreading sequence length beyond a certain point degrades the performance. For a given E/sub b//N/sub 0/, there is a length of the spreading sequence that minimizes the bit error rate.
288 citations
TL;DR: This paper quantifies link performance in terms of the transmitter power required to achieve a bit error rate (BER) not exceeding 10/sup -9/ with 95% probability and discusses the use of multibeam transmitters and imaging receivers to implement space-division multiple access (SDMA).
Abstract: We analyze the improvements obtained in wireless infrared (IR) communication links when one replaces traditional single-element receivers by imaging receivers and diffuse transmitters by multibeam (quasi-diffuse) transmitters. This paper addresses both line-of-sight (LOS) and nonline-of-sight (non-LOS) IR links. We quantify link performance in terms of the transmitter power required to achieve a bit error rate (BER) not exceeding 10/sup -9/ with 95% probability. Our results indicate that in LOS links, imaging receivers can reduce the required transmitter power by up to 13 dB compared to single-element receivers. In non-LOS links, imaging receivers and multibeam transmitters can reduce the required transmitter power by more than 20 dB. Furthermore we discuss the use of multibeam transmitters and imaging receivers to implement space-division multiple access (SDMA). In a representative example with two users transmitting at a power sufficient to achieve a BER not exceeding 10/sup -9/ with 95% probability in the absence of cochannel interference, when SDMA is employed, the system can achieve a BER not exceeding 10/sup -9/ with a probability of about 88%.
257 citations
TL;DR: An effective method for increasing error resilience of video transmission over bit error prone networks is described and rate-distortion optimized mode selection and synchronization marker insertion algorithms are introduced.
Abstract: We describe an effective method for increasing error resilience of video transmission over bit error prone networks. Rate-distortion optimized mode selection and synchronization marker insertion algorithms are introduced. The resulting video communication system takes into account the channel condition and the error concealment method used by the decoder, to optimize video coding mode selection and placement of synchronization markers in the compressed bit stream. The effects of mismatch between the parameters used by the encoder and the parameters associated with the actual channel condition and the decoder error concealment method are evaluated. Results for the binary symmetric channel and wideband code division multiple access mobile network models are presented in order to illustrate the advantages of the proposed method.
249 citations
15 May 2000
TL;DR: To obtain an even higher bit rate and make the system more robust against intersymbol interference, (single-carrier) SDM is successfully applied to the spectrum efficient multi- carrier transmission technique orthogonal frequency division multiplexing (OFDM).
Abstract: A promising solution for significant increase of the bandwidth efficiency and transmission capacity is the exploitation of the spatial dimension, by using space division multiplexing (SDM). SDM algorithms exploit the richly scattered (indoor) wireless channel by using multiple transmit and receive antennas. A new SDM technique, called maximum likelihood decoding (MLD) is proposed. The superior SNR performance of MLD compared to other SDM techniques is proven. To obtain an even higher bit rate and make the system more robust against intersymbol interference, (single-carrier) SDM is successfully applied to the spectrum efficient multi-carrier transmission technique orthogonal frequency division multiplexing (OFDM).
228 citations
TL;DR: In this paper, a saddle point integration method for solving the resulting line integral of a particular moment generating function is adopted, and a closed-form approximation for the bit error probability is also provided, which is within 0.01 dB from the exact numerical results.
Abstract: A novel approach to analytically evaluate the bit error probability in optically preamplified direct-detection systems is presented, which can take into account the effects of pulse shaping, chirping, filtering at the transmitter and the receiver, both pre- and postdetection, chromatic dispersion, and ASE noise. The method is computationally very fast in that the saddle point integration method for solving the resulting line integral of a particular moment generating function is adopted. A closed-form approximation for the bit error probability is also provided, which is within 0.01 dB from the exact numerical results.
201 citations
TL;DR: Those basic characteristics of WCDMA waveforms that make them attractive for high data rate transmission over wireless and mobile channels are discussed and how the choice of spread bandwidth affects the bit error rate of the system is discussed.
Abstract: To satisfy ever-increasing demands for higher data rates, as well as to allow more users to simultaneously access the network, interest has peaked in what has come to be known as wideband code division multiple access (WCDMA). We discuss those basic characteristics of WCDMA waveforms that make them attractive for high data rate transmission over wireless and mobile channels. We emphasize how the choice of spread bandwidth affects the bit error rate of the system, as well as how it affects the reliability of various subsystems, such as those that perform coarse acquisition and adaptive power control. We then discuss how some of the waveforms being considered for cellular WCDMA systems differ from those in use in the narrowband CDMA cellular system, and emphasize, as an example, multicarrier CDMA. Finally, we discuss other potential enhancements to WCDMA systems, such as the use of interference suppression at the receiver, or multiple antennas at the transmitter.
173 citations
19 May 2000
TL;DR: This work reports on the use of broadband chirp signals for spread spectrum systems in indoor applications and presents simulations and measurement results from demonstrator systems which use surface acoustic wave (SAW) devices for the generation and matched altering of the chirP signals.
Abstract: We report on the use of broadband chirp signals for spread spectrum systems in indoor applications. The presented system concepts make use of chirp transmission and pulse compression. Different modulation schemes for the chirp signals resulting in different system performance and complexity are compared in terms of bit error rate for the AWGN channel and for frequency selective indoor radio channels. We present simulations and measurement results from demonstrator systems which use surface acoustic wave (SAW) devices for the generation and matched altering of the chirp signals. The RF and IF frequency and transmission bandwidth of the presented systems are 2.4 GHz, 348.8 MHz, and 80 MHz, respectively. Due to the processing gain of 16 dB-made possible by the use of SAW devices-and the large transmission bandwidth the system is insensitive against frequency selective fading, CW interference and noise.
167 citations
TL;DR: Simulation results show that using a transcoder to optimally adjust the resilience improves video quality in the presence of errors while maintaining the same input bit rate.
Abstract: We describe a method to maintain quality for video transported over wireless channels. The method is built on three fundamental blocks. First, we use a transcoder that injects spatial and temporal resilience into an encoded bitstream. The amount of resilience is tailored to the content of the video and the prevailing error conditions, as characterized by bit error rate. Second, we derive analytical models that characterize how corruption propagates in a video that is compressed using motion-compensated encoding and subjected to bit errors. Third, we use rate distortion theory to compute the optimal allocation of bit rate among spatial resilience, temporal resilience, and source rate. Furthermore, we use the analytical models to generate the resilience rate distortion functions that are used to compute the optimal resilience. The transcoder then injects this optimal resilience into the bitstream. Simulation results show that using a transcoder to optimally adjust the resilience improves video quality in the presence of errors while maintaining the same input bit rate.
155 citations
Patent•
13 Jun 2000
TL;DR: In this paper, a system and method for impulse radio power control wherein a first transceiver transmits an impulse radio signal to a second transceiver is described. And the transmitter power of either transceiver, depending on the particular embodiment, is adjusted according to the power control update.
Abstract: A system and method for impulse radio power control wherein a first transceiver transmits an impulse radio signal to a second transceiver. A power control update is calculated according to a performance measurement of the signal received at the second transceiver. The transmitter power of either transceiver, depending on the particular embodiment, is adjusted according to the power control update. Various performance measurements are employed according to the current invention to calculate a power control update, including bit error rate, signal-to-noise ratio, and received signal strength, used alone or in combination. Interference is thereby reduced, which is particularly important where multiple impulse radios are operating in close proximity and their transmission interfere with one another. Reducing the transmitter power of each radio to a level that produces satisfactory reception increases the total number of radios that can operate in an area without saturation. Reducing transmitter power also increases transceiver efficiency.
TL;DR: A comparison of five of the most discussed receiver structures: the decorrelator, the minimum mean square error (MMSE) receiver, the multistage parallel interference cancellation receivers, the successive interference cancellation receiver, and the decor Relating decision feedback receiver.
Abstract: Multiuser detection has gained significant notoriety as a potential advanced enabling technology for the next generation of CDMA systems. Due to the limitations of the conventional correlation receiver, the capacity of a single cell using CDMA is limited by self-interference and is subject to the near-far problem. To overcome these drawbacks, several advanced receiver structures have been proposed. Unlike the conventional receiver which treats multiple access interference (MAI) as if it were AWGN, multiuser receivers treat MAI as additional information to aid in detection. Although each of the multiuser types have been the subject of much literature, there is little published work comparing all structures on the basis of common assumptions. We present a comparison of five of the most discussed receiver structures: the decorrelator, the minimum mean square error (MMSE) receiver, the multistage parallel interference cancellation receiver, the successive interference cancellation receiver, and the decorrelating decision feedback receiver. Comparisons are based on both theoretical analysis and simulation results, examining bit error rate (BER) performance in AWGN, Rayleigh fading, and near/far channels. Additionally, receiver structures are compared on the basis of computational complexity as well as robustness to code phase misalignment. Finally, we present simulation results for noncoherent architectures of the aforementioned receivers.
Patent•
AT&T1
TL;DR: In this paper, a method and apparatus to transmit turbo-encoded data in a multitone channel assigns the original data and selected parity bits across multitone subchannels allowing transmission of an entire turboencoded block withing one or few symbol time frame.
Abstract: A method and apparatus to transmit turbo-encoded data in a multitone channel assigns the original data and selected parity bits across multitone subchannels allowing transmission of an entire turbo-encoded block withing one or few symbol time frame. Parity bits are selected by a procedure using data derived by optimization using simulation of a single-channel system. The optimization determines, for a specified bit error rate, for each possible number of information bits per symbol, the code rate corresponding to the lowest signal-to-noise ratio. Alternatively, in the simulation non-identical integer values may be applied to the channels to approximate non-integer values of code rate and information bits-per-channel in the aggregate. The optimized data are used to determine an optimal code rate and SNR for each channel. In assigning the respective bits to the channels, the number of parity bits in each channel are shared.
TL;DR: This paper introduces a generalized method of analyzing the performance of various optical CDMA receiver structures and takes into account the effect of all major noise sources.
Abstract: We study the performance of optical code-division multiple access (CDMA) systems using various receivers structures. Two general classes of receivers based on required electronic bandwidth are studied. Optical orthogonal codes (OOCs) are utilized as signature sequences and the performance studied in this paper takes into account the effect of all major noise sources, i.e., quantum shot-noise, dark current noise, and Gaussian circuit noise. Furthermore, this paper introduces a generalized method of analyzing the performance of various optical CDMA receiver structures. Required mean number of photon count per chip time for reliable transmission of data bits for various receiver structures is investigated. Finally, the advantages and disadvantages of various receiver structures are discussed.
1 Apr 2000
TL;DR: The convolutional code, achieving bit error rate (BER) below 10/sup -3/ at bit energy over noise spectral density ratio (E/sub b//N/sub 0/) of 2.4 dB with no phase noise, outperforms the turbo code slightly over AWGN channels due to limited capability of the iterative algorithm in this setting.
Abstract: A family of interleaved systems for communicating over the additive white Gaussian noise (AWGN) channel with noisy or unknown phase is investigated Each system comprises convolutional code or turbo code, interleaver, binary phase shift keying or quaternary phase shift keying modulation and differential or similar encoding The receiver performs jointly and iteratively the decoding and the channel demodulation in the presence of unknown phase utilising an observation interval exceeding two symbols All systems exhibit good performance with various levels of phase noise The convolutional code, achieving bit error rate (BER) below 10/sup -3/ at bit energy over noise spectral density ratio (E/sub b//N/sub 0/) of 24 dB with no phase noise, outperforms the turbo code slightly over AWGN channels due to limited capability of the iterative algorithm in this setting The turbo code is superior in bursty channels, modelling for example a block erasures fading environment When the carrier phase is unknown but constant over an interval of ten symbols, the turbo coded system achieves BER lower than 10/sup -3/ at E/sub b//N/sub 0/ of 26 dB, that is 13 dB away from the capacity limit of this channel
TL;DR: This work considers a hybrid mixture of these two approaches to add channel coding without altering the source coder and demonstrates situations in which the hybrid image coder can outperform either of the two building block methods.
Abstract: One method of transmitting wavelet based zerotree encoded images over noisy channels is to add channel coding without altering the source coder. A second method is to reorder the embedded zerotree bitstream into packets containing a small set of wavelet coefficient trees. We consider a hybrid mixture of these two approaches and demonstrate situations in which the hybrid image coder can outperform either of the two building block methods, namely on channels that can suffer packet losses as well as statistically varying bit errors.
AT&T1
TL;DR: This letter describes an efficient bit allocation algorithm for digital subscriber loop modems that use discrete multi-tone technology that computes the optimum bit allocation profile within all constraints and requires fewer computations than the conventional "water-filling" approach.
Abstract: This letter describes an efficient bit allocation algorithm for digital subscriber loop modems that use discrete multi-tone technology. The algorithm computes the optimum bit allocation profile within all constraints and requires fewer computations than the conventional "water-filling" approach. Conventional algorithms are unable to assign data bits to higher frequency bins over long loops with high level of interference due to the power spectrum mask limitation, even if the total power budget is not expended. We propose a novel scheme to distribute data over multiple bins at correspondingly reduced power in these, otherwise unpopulated bins.
TL;DR: A set of universal operational distortion-rate characteristics is developed which balances the tradeoff between source coding accuracy and channel error protection for a fixed overall transmission rate and provides the basis for the optimal bit allocation approach.
Abstract: There has been an increased interest in the transmission of digital video over real-world transmission media, such as the direct broadcast satellite (DBS) channel. Video transmitted over such a channel is subject to degradation due, in part, to additive white Gaussian noise (AWGN). Some form of forward error-control (FEC) coding may be applied in order to reduce the effect of the noise on the transmitted bitstream; however, determination of the appropriate level of FEC coding is generally an unwieldy and computationally intensive problem, as it may depend upon a variety of parameters such as the type of video, the available bandwidth, and the channel SNR. More specifically, a combined source-channel coding approach is necessary in optimally allocating rate between source and channel coding subject to a fixed constraint on overall transmission bandwidth. In this paper we develop a method of optimal bit allocation under the assumption that the distortion is additive and independent on a frame-by-frame basis. A set of universal operational distortion-rate characteristics is developed which balances the tradeoff between source coding accuracy and channel error protection for a fixed overall transmission rate and provides the basis for the optimal bit allocation approach. The results for specific source and channel coding schemes show marked improvement over suboptimum choices of channel error protection. In addition, we show that our results approach information-theoretic performance bounds which are developed in this work.
28 Mar 2000
TL;DR: This work introduces a multiple-description product code which aims at optimally generating multiple, equally-important wavelet image descriptions from an image encoded by the popular SPIHT image coder.
Abstract: Summary form only given. This work introduces a multiple-description product code which aims at optimally generating multiple, equally-important wavelet image descriptions from an image encoded by the popular SPIHT image coder. Because the SPIHT image coder is highly sensitive to errors, forward error correction is used to protect the image against bit errors occurring in the channel. The error-correction code is a concatenated channel code including a row (outer) code based on RCPC codes with CRC error detection and a source-channel column (inner) code consisting of the scalable SPIHT image coder and an optimized array of unequal protection Reed-Solomon erasure-correction codes. By matching the unequal protection codes to the embedded source bitstream using our simple, fast optimizer, we maximize expected image quality and provide for graceful degradation of the received image during fades. To achieve unequal protection, each packet is split into many Reed-Solomon symbols. The i/sup th/ symbol in each packet forms an (n,k) Reed-Solomon code or "column". A fast, nearly-optimal optimizer, based on Lagrange multipliers and optimal to within convex hull and discretization approximations, chooses k for each Reed-Solomon "column" to minimize the expected mean-square error at the receiver. We validated our use of this structure by evaluating its performance in the context of transmitting images over a wireless fading channel. The performance of this scheme was evaluated by simulating the transmission of the Lena image over a Clarke flat-fading channel with an average SNR of 10 dB and a normalized Doppler frequency of 10/sup -5/ Hz.
TL;DR: This letter is concerned with a frequency offset estimation technique for OFDM based transmission systems that utilizes a repetitive signal structure inside of a OFDM symbol which is used to enlarge the range and increase the accuracy of offset estimation.
Abstract: This letter is concerned with a frequency offset estimation technique for OFDM based transmission systems. The frequency estimation technique utilizes a repetitive signal structure inside of a OFDM symbol which is used to enlarge the range and increase the accuracy of offset estimation. Also, an averaged decision-directed channel estimation (ADDCE) technique suitable for burst data is proposed.
7 Mar 2000
TL;DR: This solution gives 4 dB additional gain margin compared with the existing rs(255,239) with redundancy equal to 28% and is based on soft decoding and soft decision.
Abstract: We present the performance of a foward error correction (fec) scheme for submarine transmission systems using Block turbo code. The decoding is based on soft decoding and soft decision. This solution gives 4 dB additional gain margin compared with the existing rs(255,239) with redundancy equal to 28%.
18 Jun 2000
TL;DR: The simulation results of the radio network performance of a large number of co-located Bluetooth units are presented and it is suggested to use long uncoded packet types for data transmission since they have the largest ideal throughput and therefore generate the least interference power.
Abstract: A new radio interface named Bluetooth has been developed to provide short range connectivity between various consumer devices. The Bluetooth system operates in the unlicensed 2.45 GHz ISM band and applies frequency hopping over 79 carriers. This paper presents the simulation results of the radio network performance of a large number of co-located Bluetooth units. For a capacity-demanding WWW data traffic model, the interference caused by (on average) 100 concurrent sessions in a single room of size 10 m/spl times/20 m results only in a 5% degradation of the aggregate throughput. In general, it is advisable to use long uncoded packet types for data transmission since they have the largest ideal throughput and therefore generate the least interference power. For real-time speech links, frame erasures represent the dominant reason for transmission quality degradation, more than residual payload bit errors. It is thus advisable to use the provided uncoded packet type in order to allow for the largest capacity; a system load of about 30 Erlang yields an average frame erasure rate of 1%.
TL;DR: It is shown that a new code structure for spectral amplitude coding optical code division multiple access (CDMA) can effectively suppress the intensity noise and in turn increase the number of active users and improve the bit error rate performance.
Abstract: A new code structure for spectral amplitude coding optical code division multiple access (CDMA) is proposed and analysed. It is shown that such codes can effectively suppress the intensity noise and in turn increase the number of active users and improve the bit error rate performance.
TL;DR: It is found that for a given network configuration, channel characteristics, and packet length, an optimum RF transmission power level exists which assures a minimum energy expenditure for the actually transmitted bit of information.
Abstract: In this paper we consider the problem of reducing energy consumption during the transmission phase in WLANs. We found that for a given network configuration, channel characteristics, and packet length, an optimum RF transmission power level exists which assures a minimum energy expenditure for the actually transmitted bit of information. Based on this observation, we present a packet length dependent power control mechanism. We performed discrete event simulations of an IEEE 802.11 LAN in ad hoc mode using a two state Markov channel model. The achieved simulation results indicate a significant potential for energy saving. We also present a workable approach for choosing the most energy-saving RF transmit power level which is based on the perceived packet error rate of a single mobile.
Patent•
19 Jul 2000
TL;DR: In this paper, an optical transmission system incorporating a transmitter (70) and a receiver (72) having certain transmission characteristics, such as output power level, decision threshold level, etc., that are adjustable in response to BER.
Abstract: Data transmission apparatus includes optical transmitters (14a, 14b) coupled to an optical link (10). A FEC coder (40) is coupled to the input of transmitter (14b'). A first signal (12a) having a first rate is provided to the first transmitter, and a second signal (12b) having a higher information rate than the first signal, while simultaneously enabling the respective output power levels of the amplifiers (18a, 18b). The transmission apparatus achieves higher transmission capacity while retaining compatibility with pre-existing fiber spans and amplifier nodes. An optical transmission system incorporates a transmitter (70) and a receiver (72) having certain transmission characteristics, such as output power level, decision threshold level, etc., that are adjustable in response to BER. A BER estimator (74) is provided at the receiving end of the link. The estimator estimates the BER of the received signal, and provides BER to the receiver, and/or transmitter, and/or optical link, based on the estimated BER, to optimize performance.
TL;DR: It is shown that the existence of a strong line-of-sight (LOS) component and the use of reception diversity can effectively improve transmission performance.
Abstract: A closed form formula is derived for the bit error rate (BER) of orthogonal-frequency-division-multiplexing (OFDM) with M-ary differential-phase-shift-keying (MDPSK) systems in frequency-selective Rayleigh and Rician fading channels with diversity reception. New BER curves are obtained as a function of the rms delay spread of the diffused component for three different types of delay profiles: (1) one-sided exponential, (2) uniform and (3) double spike profiles. Both slow and fast fading conditions are considered. It is shown that the existence of a strong line-of-sight (LOS) component and the use of reception diversity can effectively improve transmission performance.
Patent•
20 Sep 2000TL;DR: In this paper, an enhanced low-bit rate parametric voice coder that groups a number of frames from an underlying frame-based vocoder, such as MELP, into a superframe structure is presented.
Abstract: An enhanced low-bit rate parametric voice coder that groups a number of frames from an underlying frame-based vocoder, such as MELP, into a superframe structure. Parameters are extracted from the group of underlying frames and quantized into the superframe which allows the bit rate of the underlying coding to be reduced without increasing the distortion. The speech data coded in the superframe structure can then be directly synthesized to speech or may be transcoded to a format so that an underlying frame-based vocoder performs the synthesis. The superframe structure includes additional error detection and correction data to reduce the distortion caused by the communication of bit errors.
TL;DR: An adaptive block based intra refresh algorithm for increasing error robustness in an interframe coding system is described, demonstrating a significant improvement in terms of error recovery time over nonadaptive intra update strategies.
Abstract: An adaptive block based intra refresh algorithm for increasing error robustness in an interframe coding system is described. The goal of this algorithm is to allow the intra update rates for different image regions to vary according to various channel conditions and image characteristics. The update scheme is based on an "error-sensitivity metric," accumulated at the encoder, representing the vulnerability of each coded block to channel errors. As each new frame is encoded, the accumulated metric for each block is examined, and those blocks deemed to have an unacceptably high metric are sent using intra coding as opposed to inter coding. This approach requires no feedback channel and is fully compatible with H.263. It involves a negligible increase in encoder complexity and no change in the decoder complexity. Simulations performed using an H.263 bitstream corrupted by channel errors demonstrate a significant improvement in terms of error recovery time over nonadaptive intra update strategies.
IMEC1
TL;DR: This work assesses the BER performance of the complete WLAN-OFDM link and quantifies in terms of implementation loss the influence of the I/Q imbalance and of the frequency synthesizer phase noise.
Abstract: New OFDM-based WLAN standards target wireless communications in the 5 GHz band for consumer multimedia applications. Given the high data rates with required low bit error rates, and given the nature of the OFDM signal, a conservative analysis of the front-end requirements lead to severe, over dimensioned specifications. Such a design would never meet this market, by necessity low-cost and low-power. To extract more optimal front-end specifications, we assess the BER performance of the complete WLAN-OFDM link. As a result, we first show that the transmitted symbols' word-length can be restricted to 8-bit and the normalized crest factor digitally limited at baseband to 4. Then we show that the power amplifier can operate with only 5.4 dB back-off between the average input power and the input-referred P/sub ldB/. Finally, we quantify in terms of implementation loss the influence of the I/Q imbalance and of the frequency synthesizer phase noise.
Patent•
17 Nov 2000TL;DR: In this article, a method and apparatus for improving channel utilization and throughput in an ad-hoc wireless communication system is provided, where a master unit and one or more slaves units are coupled to a shared communication channel having at least an uplink (UL) channel and a downlink channel (DL) for each master unit-slave unit pair.
Abstract: A method and apparatus for improving channel utilization and throughput in an ad-hoc wireless communication system is provided. A master unit and one or more slave units are coupled to a shared communication channel having at least an uplink (UL) channel and a downlink channel (DL) for each master unit-slave unit pair. A group of active nodes is established corresponding to slave units having UL and/or DL data associated therewith for transfer. The group of active nodes may be polled according to Fair Exhaustive Polling (FEP) and information alternately transferred on a TDD. Accumulated information may be transferred in a batch and feedback information collected and used to adjust polling. One or more links may be identified as lossy links due to increased Bit Error Rate (BER) and accompanying information loss resulting in lower throughput. Virtual active nodes added to the group of active nodes to compensate therefor. A transmission parameter such as number of retransmissions may be evaluated against a predetermined threshold to identify lossy links. If lossy links improve, virtual active nodes may be removed from the group of active nodes. Information associated with the one or more slaves units may be circuit switched synchronous information or non-circuit switched asynchronous information. Feedback information such as timeout information associated with the slave units may be evaluated. If a time out signal associated with a slave unit is received the slave unit may be scheduled for polling responsive to the time out signal.