Showing papers on "Bit error rate published in 2001"

Degrees of freedom in adaptive modulation: a unified view

Abstract: We examine adaptive modulation schemes for flat-fading channels where the data rate, transmit power, and instantaneous BER are varied to maximize spectral efficiency, subject to an average power and BER constraint. Both continuous-rate and discrete-rate adaptation are considered, as well as average and instantaneous BER constraints. We find the general form of power, BER and data rate adaptation that maximizes spectral efficiency for a large class of modulation techniques and fading distributions. The optimal adaptation of these parameters is to increase the power and data rate and decrease the BER as the channel quality improves. Surprisingly, little spectral efficiency is lost when the power or rate is constrained to be constant. Hence, the spectral efficiency of adaptive modulation is relatively insensitive to which degrees of freedom are adapted.

Error control coding

Abstract: The basic goal in digital communications is to transport bits of information without losing too much information along the way. The level of information loss that is tolerable/acceptable varies for different applications. The loss is measured in terms of the bit error rate, or BER. An interesting application that employs error control coding is a system with a storage medium such as a hard disk drive or a compact disc (CD). We can think of the channel as a block that causes errors to occur when a signal passes through it. Regardless of the error source, we can describe the problem as follows: when the transmitted signal arrives at the receiver after passing through the channel, the received data will have some bits that are in error. The system designer would like to incorporate ways to detect and correct these errors. The field that covers such digital processing techniques is known as error control coding.

SLM peak-power reduction without explicit side information

Abstract: Selected mapping (SLM) peak-power reduction is distortionless as it selects the actual transmit signal from a set of alternative signals, which all represent the same information. The specific signal generation information needs to be transmitted and carefully protected against bit errors. Here, me propose an extension of SLM, which employs scrambling and refrains from the use of explicit side information in the receiver. Some additional complexity and nearly vanishing redundancy is introduced to achieve markedly improved transmit signal statistics. Even though SLM is applicable with any modulation, we concentrate on orthogonal frequency-division multiplexing (OFDM) in this letter.

Design, analysis, and performance evaluation for BICM-ID with square QAM constellations in Rayleigh fading channels

Abstract: We consider bit-interleaved coded modulation with iterative decoding (BICM-ID) for bandwidth-efficient transmission over Rayleigh fading channels. We propose the design criteria that utilize a large Hamming distance inherited in a low-rate code and a new labeling technique designed specifically for fading channels. This results in a large coding gain over noniterative coded modulation and performance close to that of "turbo" coded modulation with less complexity. We also show that BICM-ID designed for fading channels usually has a very good performance over the additive white Gaussian noise (AWGN) channel while the converse is difficult to achieve. When combined with signal space diversity, diversity order can be improved to twice the diversity order of conventional BICM-ID; therefore, the code complexity can further be reduced while maintaining the same level of performance. Specifically, with the bandwidth efficiency of 2 bits/s/Hz over Rayleigh fading channels, a bit error rate (BER) of 10/sup -6/ can be achieved with 16-QAM, a four-state rate 1/2 code at E/sub b//N/sub 0/ of about seven dB. We also derive performance bounds for BICM-ID with and without signal space diversity over Rayleigh fading channels, which can be easily extended for other types of fading channels.

Single-carrier frequency-domain equalization for space-time block-coded transmissions over frequency-selective fading channels

Abstract: We propose an Alamouti-like scheme for combining space-time block-coding with single-carrier frequency-domain equalization. With two transmit antennas, the scheme is shown to achieve significant diversity gains at low complexity over frequency-selective fading channels.

Dynamic channel selection scheme for IEEE 802.11 WLANs

Abstract: Disclosed is a method and system for dynamically selecting a communication channel between an access point (AP) and a plurality of stations (STAs) in an IEEE 802.11 wireless local area network (WLAN). The method includes the steps of: determining whether a new channel between the AP and STAs within a particular basic service set (BSS) is needed; requesting a channel signal quality measure to some of the plurality of stations by the AP; reporting a channel signal quality report back to the AP based on a received signal strength indication (RSSI) and a packet error rate (PER) of all channels detected by the stations within the BSS; selecting a new channel based on the channel quality report for use in communication between the AP and the plurality of stations.

Probability of error calculation of OFDM systems with frequency offset

Abstract: Orthogonal frequency-division multiplexing (OFDM) is sensitive to the carrier frequency offset (CFO), which destroys orthogonality and causes intercarrier interference (ICI), Previously, two methods were available for the analysis of the resultant degradation in performance. Firstly, the statistical average of the ICI could be used as a performance measure. Secondly, the bit error rate (BER) caused by CFO could be approximated by assuming the ICI to be Gaussian. However, a more precise analysis of the performance (i.e., BER or SER) degradation is desirable. In this letter, we propose a precise numerical technique for calculating the effect of the CFO on the BER or symbol error in an OFDM system. The subcarriers can be modulated with binary phase shift keying (BPSK), quaternary phase shift keying (QPSK), or 16-ary quadrature amplitude modulation (16-QAM), used in many OFDM applications. The BPSK case is solved using a series due to Beaulieu (1990). For the QPSK and 16-QAM cases, we use an infinite series expression for the error function in order to express the average probability of error in terms of the two-dimensional characteristic function of the ICI.

Soft digital signal processing

Abstract: In this paper, we propose a framework for low-energy digital signal processing (DSP), where the supply voltage is scaled beyond the critical voltage imposed by the requirement to match the critical path delay to the throughput. This deliberate introduction of input-dependent errors leads to degradation in the algorithmic performance, which is compensated for via algorithmic noise-tolerance (ANT) schemes. The resulting setup that comprises of the DSP architecture operating at subcritical voltage and the error control scheme is referred to as soft DSP. The effectiveness of the proposed scheme is enhanced when arithmetic units with a higher "delay imbalance" are employed. A prediction-based error-control scheme is proposed to enhance the performance of the filtering algorithm in the presence of errors due to soft computations. For a frequency selective filter, it is shown that the proposed scheme provides 60-81% reduction in energy dissipation for filter bandwidths up to 0.5 /spl pi/ (where 2 /spl pi/ corresponds to the sampling frequency f/sub s/) over that achieved via conventional architecture and voltage scaling, with a maximum of 0.5-dB degradation in the output signal-to-noise ratio (SNR/sub o/). It is also shown that the proposed algorithmic noise-tolerance schemes can also be used to improve the performance of DSP algorithms in presence of bit-error rates of up to 10/sup -3/ due to deep submicron (DSM) noise.

VLSI architectures for iterative decoders in magnetic recording channels

Abstract: VLST implementation complexities of soft-input soft-output (SISO) decoders are discussed. These decoders are used in iterative algorithms based on Turbo codes or Low Density Parity Check (LDPC) codes, and promise significant bit error performance advantage over conventionally used partial-response maximum likelihood (PRML) systems, at the expense of increased complexity. This paper analyzes the requirements for computational hardware and memory, and provides suggestions for reduced-complexity decoding and reduced control logic. Serial concatenation of interleaved codes, using an outer block code with a partial response channel acting as an inner encoder, is of special interest for magnetic storage applications.

On the performance of ultra-wide-band signals in Gaussian noise and dense multipath

Abstract: An ultra-wide-band (UWB) signal is characterized by a radiated spectrum with a very wide bandwidth around a relatively low center frequency. In this paper, we study the reduced fading margin property of UWB signals. To evaluate the fading margin, we compare the performance of UWB signals in an environment with only additive white Gaussian noise (AWGN) versus the performance of UWB signals in a dense multipath environment with AWGN. The assumption here is that the presence of multipath causes a small increase in the signal-to-noise ratio required to achieve reasonable levels of bit error rate. A numerical example confirms this assumption, more specifically, the example shows that to achieve a bit error rate equal to 10/sup -5/, we require about 13.5 dB in the AWGN case and about 15 dB in the multipath case, resulting in a fading margin of just 1.5 dB. This small fading margin can be understood by the ability of the UWB signal to resolve the dense multipath.

Orthogonal frequency division multiplex synchronization techniques for frequency-selective fading channels

Abstract: The effect of time-domain and frequency-domain synchronization errors is quantified in the context of various coherently and noncoherently detected 1, 2, and 4 bits/symbol OFDM constellations, in order to demonstrate the wide applicability of the techniques proposed for mitigating the bit error rate (BER) performance degradations inflicted. A reference symbol is proposed and a range of correlation techniques are suggested for coarse and fine synchronization. Their performance is studied over time-dispersive Rayleigh fading channels, with the conclusion that the proposed synchronization techniques result in virtually unimpaired BERs over the range of wideband channels investigated in comparison to a perfectly synchronized system.

Performance of ultrawideband SSMA using time hopping and M-ary PPM

Abstract: Wireless spread spectrum multiple access (SSMA) using time hopping and block waveform encoded (M-ary) pulse position modulated (PPM) signals is analyzed. For different M-ary PPM signal designs, the multiple-access performance in free-space propagation renditions is analyzed in terms of the number of users supported by the system for a given bit error rate, signal-to-noise ratio, bit transmission rate, and number of signals in the M-ary set. The processing gain and number of simultaneous users are described in terms of system parameters. Tradeoffs between performance and receiver complexity are discussed. Upper bounds on both the maximum number of users and the total combined bit transmission rate are investigated. This analysis is applied to ultrawideband impulse radio modulation. In this modulation, the communications waveforms are practically realized using subnanosecond impulse technology. A numerical example is given that shows that impulse radio modulation is theoretically able to provide multiple-access communications with a combined transmission capacity of hundreds of megabits per second at bit error rates in the range 10/sup -4/ to 10/sup -7/ using receivers of moderate complexity.

Performance of wideband CDMA systems with complex spreading and imperfect channel estimation

Abstract: The coherent RAKE reception of wideband code division multiple access (W-CDMA) signals with complex spreading is considered. A general multipath-fading channel model is assumed. A dedicated pilot channel, which is separate from the data channels, is used for the purpose of channel estimation. Based on a digital implementation, the coherent demodulation scheme is presented. Pilot channel estimation error, due to multiple access and multipath interference, is studied. The system performance is evaluated by means of the bit error rate (BER). The analysis shows that the error of channel estimation significantly degrades system performance and can be effectively suppressed by low pass filters (LPFs). A discussion on the envelope variation of complex spread signals is also included, which illustrates that the complex spread signal has a more stable envelope than the dual-channel spread signal. The power ratio of pilot to data channels should be chosen in the range of 0.2 to 0.4 (or -7 to -4 dB), in order to achieve maximum system capacity.

Softbit speech decoding: a new approach to error concealment

Abstract: In digital speech communication over noisy channels there is the need for reducing the subjective effects of residual bit errors which have not been eliminated by channel decoding. This task is usually called error concealment. We describe a new and generalizing approach to error concealment as part of a modified robust speech decoder. It can be applied to any speech codec standard and preserves bit exactness in the case of an error free channel. The proposed method requires bit reliability information provided by the demodulator or by the equalizer or specifically by the channel decoder and can exploit additionally a priori knowledge about codec parameters. We apply our algorithms to PCM, ADPCM, and GSM full-rate speech coding using AWGN, fading, and GSM channel models, respectively. It turns out that the speech quality is significantly enhanced, showing the desired inherent muting mechanism or graceful degradation behavior in the case of extreme adverse transmission conditions.

Mode selection for data transmission in wireless communication channels based on statistical parameters

Abstract: A method and communication system for selecting a mode for encoding data for transmission in a wireless communication channel between a transmit unit and a receive unit. The data is initially transmitted in an initial mode and the selection of the subsequent mode is based on a selection of first-order and second-order statistical parameters of short-term and long-term quality parameters. Suitable short-term quality parameters include signal-to-interference and noise ratio (SINR), signal-to-noise ratio (SNR), power level and suitable long-term quality parameters include error rates such as bit error rate (BER) and packet error rate (PER). The method of the invention can be employed in Multiple Input Multiple Output (MIMO), Multiple Input Single Output (MISO), Single Input Single Output (SISO) and Single Input Multiple Output (SIMO) communication systems to make subsequent mode selection faster and more efficient. Furthermore the method can be used in communication systems employing various transmission protocols including OFDMA, FDMA, CDMA, TDMA.

A new direct millimeter-wave six-port receiver

Abstract: A new direct-conversion wide-band (23-31 GHz) six-port receiver is proposed suitable for millimeter-wave integrated system design. This new hardware receiver is found to be robust, rugged, low cost, and suitable for use in broad-band wireless mass-market QPSK communications. The prototype circuits are fabricated to validate this new concept with our miniaturized hybrid microwave integrated-circuit technology and the proposed receiver topology is also suitable for monolithic-microwave integrated-circuit fabrication. This application-specific integrated receiver is designed on the basis of a wide-band six-port junction and other analogical circuits in the form of a simple multichip module. Bit-error-rate measurements and simulation results are shown and discussed in the presence of noise, adjacent signal interference, local-oscillator (LO) phase shift, and LO phase noise. The maximum bit rate is fundamentally limited by the speed of the video and decoder circuits. Nevertheless, several hundred megabits per second can be achieved at low cost.

Differential modulation using space-time block codes

Abstract: We consider a space-time differential modulation scheme where neither the transmitter nor the receiver has to know the channel. Our scheme is based on the theory of unitary space-time block codes. Compared to the existing differential modulation schemes for multiple antennas our scheme has a much smaller computational complexity. Moreover, our codes have a higher coding gain and lower bit error rate than the codes proposed by other researchers.

Adaptive minimum-BER linear multiuser detection for DS-CDMA signals in multipath channels

Abstract: The problem of constructing adaptive minimum bit error rate (MBER) linear multiuser detectors is considered for direct-sequence code division multiple access (DS-CDMA) signals transmitted through multipath channels. Based on the approach of kernel density estimation for approximating the bit error rate (BER) from training data, a least mean squares (LMS) style stochastic gradient adaptive algorithm is developed for training linear multiuser detectors. Computer simulation is used to study the convergence speed and steady-state BER misadjustment of this adaptive MBER linear multiuser detector, and the results show that it outperforms an existing LMS-style adaptive MBER algorithm presented by Yeh et al. (see Proc. Globecom, Sydney, Australia, p.3590-95, 1998).

Method and system for generating, transmitting and utilizing bit rate conversion information

Abstract: A method and apparatus for generating and transmitting bit rate conversion information to be utilized during bit rate conversion decisions and a method and apparatus for performing bit rate adaptation of media signals to use an available bandwidth of a channel, the media signals being associated with bit rate conversion information, the method for utilizing the bit rate conversion information including the steps of: receiving the media signals and the bit rate conversion information; the bit rate conversion information being indicative of a change in a bit rate of the media signals resulting from bit rate conversion; and converting the multiplexed processed media signals in response to the available bandwidth and the bit rate conversion information.

Transmitter, receiver, and coding scheme to increase data rate and decrease bit error rate of an optical data link

Abstract: Transmitters, receivers, and coding schemes to increase data rate and decrease bit error rate of an optical data link are disclosed. Data is transmitted across the link with a less than nominal bit error rate (BER), by encoding the data using a forward error correction (FEC) code or by requesting retransmission of transmitted packets in error. Data is transmitted at a speed that introduces errors at a rate that is in excess of the nominal BER but that may be corrected using the FEC code or retransmission so that the data may be received with less than the nominal BER. The data rate is increased as the link operating speed is increased beyond the overhead required by the FEC codes or retransmission. High speed FEC encoders and decoders facilitating such transmission are disclosed.

Performance analysis of compact antenna arrays with MRC in correlated Nakagami fading channels

Abstract: This paper presents the average error probability performance of a compact space diversity receiver for the reception of binary coherent and noncoherent modulation signals through a correlated Nakagami (1960) fading channel. Analytical expressions of the average bit error rate (BER) are derived as a function of the covariance matrix of the multipath component signals at the antenna elements. Closed-form expressions for the spatial cross-correlation are obtained under a Gaussian angular power profile assumption, taking account of the mutual coupling between antenna elements. The effects of antenna array configuration (geometry and electromagnetic coupling) and the operating environment (fading, angular spread, mean angle-of-arrival) on the BER performance are illustrated.

Zigzag codes and concatenated zigzag codes

Abstract: This paper introduces a family of error-correcting codes called zigzag codes. A zigzag code is described by a highly structured zigzag graph. Due to the structural properties of the graph, very low-complexity soft-in/soft-out decoding rules can be implemented. We present a decoding rule, based on the Max-Log-APP (MLA) formulation, which requires a total of only 20 addition-equivalent operations per information bit, per iteration. Simulation of a rate-1/2 concatenated zigzag code with four constituent encoders with interleaver length 65 536, yields a bit error rate (BER) of 10/sup -5/ at 0.9 dB and 1.3 dB away from the Shannon limit by optimal (APP) and low-cost suboptimal (MLA) decoders, respectively. A union bound analysis of the bit error probability of the zigzag code is presented. It is shown that the union bounds for these codes can be generated very efficiently. It is also illustrated that, for a fixed interleaver size, the concatenated code has increased code potential as the number of constituent encoders increases. Finally, the analysis shows that zigzag codes with four or more constituent encoders have lower error floors than comparable turbo codes with two constituent encoders.

Performance of trellis-coded CPM with iterative demodulation and decoding

Abstract: Interleaved trellis-coded systems with full response continuous-phase modulation (CPM) are considered. Upper bounds on the bit-error rate performance are derived for coherent detection on the additive white Gaussian noise and flat Rayleigh fading channels by considering the trellis code, interleaver, and CPM modulator as a serially concatenated convolutional code. A coherent receiver that performs iterative demodulation and decoding is shown to provide good bit error performance. Finally, a noncoherent iterative receiver is proposed and is shown to perform close to the coherent iterative receiver.

Performance analysis of maximal ratio combining in the presence of multiple equal-power cochannel interferers in a Nakagami fading channel

Abstract: The effect of cochannel interference on the performance of digital mobile radio systems in a Nakagami (1960) fading channel is studied. The performance of maximal ratio combining (MRC) diversity is analyzed in the presence of multiple equal-power cochannel interferers and additive white Gaussian noise. Closed-form expressions are derived for the average probability of error as well as outage probability of both coherent and noncoherent (differentially coherent) binary frequency-shift keying and binary phase-shift keying schemes in an environment with cochannel interference and noise. The results are expressed in terms of the confluent hypergeometric function of the second kind, a function that can be easily evaluated numerically. The analysis assumes an arbitrary number of independent and identically distributed Nakagami interferers.

Underwater acoustic communication using time reversal

Abstract: Time reversal, or phase-conjugation, refocuses energy back to a probe source location despite the complexity of the propagation channel. A probe source pulse is transmitted and a complicated multipath signal is measured by an array of source/receiver elements. The signal is time reversed and retransmitted into the ocean. The time-reversal process recombines this temporal multipath at the original probe source range and depth. The ability of time reversal to reduce dispersion and its simplicity of implementation makes it ideal for underwater acoustic communications, which must mitigate the inter-symbol interference caused by the time-varying multipath dispersion. Furthermore, time reversal focuses energy at the desired depth, thus mitigating the effects of channel fading. An experiment was conducted in June 2000 demonstrating that the time-reversal process recombined the temporal multipath resulting in reduced bit errors for communication. Communication sequences were transmitted over a distance of 10 km both in range independent and range dependent environments north of Elba Island, Italy. The range independent transmissions were made in 110-m deep water and the range dependent transmissions were made upslope from 110-m deep water into 40-m deep water. Single source transmissions were also measured in the same channels. Quantitative bit error results are shown for BPSK (binary phase shift keying) and QPSK (quadrature phase shift keying).

Interference between Bluetooth networks-upper bound on the packet error rate

Abstract: This paper presents a probabilistic treatment of the performance of a Bluetooth piconet under cochannel interference from other Bluetooth piconets. An upper bound on the packet error rate of a link is given, as well as a lower bound on the aggregated throughput of n collocated piconets.

Broadband packet wireless access appropriate for high-speed and high-capacity throughput

Abstract: This paper evaluates the optimum broadband packet wireless access scheme using a 50-100 MHz bandwidth to achieve highspeed packet transmission taking into consideration the realization of high-speed and high-capacity packet transmission, the accommodation of variable rate services with different quality requirements, and the extendibility for and commonality to the IMT-2000. In the forward link, the presented simulation results associated with the evaluation of key features show that multi-carrier CDMA (MC-CDMA) is the most promising candidate, since it achieves the highest-capacity packet transmission in a severe multipath fading channel due to a lower symbol-rate with numerous sub-carriers and a channel coding gain accompanied by the frequency diversity effect. Meanwhile, single-carrier/DS-CDMA and multi-carrier/DS-CDMA (SC/DS-CDMA and MC/DS-CDMA) are severely degraded due to significantly increasing multipath interference, and orthogonal frequency division multiplexing (OFDM) lacks efficient cell deployment due to the necessity of frequency reuse in a multi-cell environment without complicated dynamic channel assignment (DCA). Furthermore, in the reverse link, we conclude that MC(SC)/DS-CDMA is a promising candidate because it has advantages such as an effective random access method, soft handover, and an inherent property for accurate location detection.

Genetic algorithm assisted joint multiuser symbol detection and fading channel estimation for synchronous CDMA systems

Abstract: A novel multiuser code division multiple access (CDMA) receiver based on genetic algorithms is considered, which jointly estimates the transmitted symbols and fading channel coefficients of all the users. Using exhaustive search, the maximum likelihood (ML) receiver in synchronous CDMA systems has a computational complexity that is exponentially increasing with the number of users and, hence, is not a viable detection solution. Genetic algorithms (GAs) are well known for their robustness in solving complex optimization problems. Based on the ML rule, GAs are developed in order to jointly estimate the users' channel impulse response coefficients as well as the differentially encoded transmitted bit sequences on the basis of the statistics provided by a bank of matched filters at the receiver. Using computer simulations, we showed that the proposed receiver can achieve a near-optimum bit-error-rate (BER) performance upon assuming perfect channel estimation at a significantly lower computational complexity than that required by the ML optimum multiuser detector. Furthermore, channel estimation can be performed jointly with symbol detection without incurring any additional computational complexity and without requiring training symbols. Hence, our proposed joint channel estimator and symbol detector is capable of offering a higher throughput and a shorter detection delay than that of explicitly trained CDMA multiuser detectors.

Analytical modeling and simulation of phase noise interference in OFDM-based digital television terrestrial broadcasting systems

Abstract: This paper deals with the problem of modeling of phase noise in OFDM systems and the impact it may have on the bit error rate performance of such systems subject to a number of system variables and to a number of channel conditions which may be encountered when such systems are deployed for certain applications such as high speed wireless LANs and Digital Television Terrestrial Broadcasting (DTTB). The phase noise processes, the sources of which are the transmitter's and receiver's local oscillator, are modeled using what is believed to be commercially realizable phase noise masks. Such masks represent the long-term averaged power spectral densities of the local oscillator output signal.

Space-time turbo codes with full antenna diversity

Abstract: In attempting to find a spectrally and power efficient channel code which is able to exploit maximum diversity from a wireless channel whenever available, we investigate the possibility of constructing a full antenna diversity space-time turbo code. As a result, both three-antenna and two-antenna (punctured) constructions are shown to be possible and very easy to find. To check the decodability and performance of the proposed codes, we derive non-binary soft-decoding algorithms. The performance of these codes are then simulated and compared with two existing space-time convolutional codes (one has minimum worst-case symbol-error probability; the other has maximal minimum free distance) having similar decoding complexity. As the simulation results show, the proposed space-time turbo codes give similar or slightly better performance than the convolutional codes under extremely slow fading. When fading is fast, the better distance spectra of the turbo codes help seize the temporal diversity. Thus, the performance advantage of the turbo codes becomes evident. In particular, 10/sup -5/ bit-error rate and 10/sup -3/ frame-error rate can be achieved at less than 6-dB E/sub b//N/sub 0/ with 1 b/s/Hz and binary phase-shift keying modulation. The practical issue of obtaining the critical channel state information (CSI) is also considered by applying an iteratively filtered pilot symbol-assisted modulation technique. The penalty when the CSI is not given a priori is about 2-3 dB.