Showing papers on "Bit error rate published in 1993"

Near Shannon limit error-correcting coding and decoding: Turbo-codes. 1

Abstract: A new class of convolutional codes called turbo-codes, whose performances in terms of bit error rate (BER) are close to the Shannon limit, is discussed. The turbo-code encoder is built using a parallel concatenation of two recursive systematic convolutional codes, and the associated decoder, using a feedback decoding rule, is implemented as P pipelined identical elementary decoders. >

On information rates for mismatched decoders

Abstract: Reliable transmission over a discrete-time memoryless channel with a decoding metric that is not necessarily matched to the channel (mismatched decoding) is considered. It is assumed that the encoder knows both the true channel and the decoding metric. The lower bound on the highest achievable rate found by Csiszar and Korner (1981) and by Hui (1983) for DMC's, hereafter denoted C/sub LM/, is shown to bear some interesting information-theoretic meanings. The bound C/sub LM/ turns out to be the highest achievable rate in the random coding sense, namely, the random coding capacity for mismatched decoding. It is also demonstrated that the /spl epsiv/-capacity associated with mismatched decoding cannot exceed C/sub LM/. New bounds and some properties of C/sub LM/ are established and used to find relations to the generalized mutual information and to the generalized cutoff rate. The expression for C/sub LM/ is extended to a certain class of memoryless channels with continuous input and output alphabets, and is used to calculate C/sub LM/ explicitly for several examples of theoretical and practical interest. Finally, it is demonstrated that in contrast to the classical matched decoding case, here, under the mismatched decoding regime, the highest achievable rate depends on whether the performance criterion is the bit error rate or the message error probability and whether the coding strategy is deterministic or randomized. >

A spread-spectrum multiaccess system with cochannel interference cancellation for multipath fading channels

Abstract: The authors propose and analyze a direct-sequence spread-spectrum multiaccess (DS/SSMA) receiver that employs a cascade of cochannel interference (CCl) cancellers for communication over multipath fading channels. The receiver first coherently demodulates and despreads the received signal to produce correlator outputs and initial data estimates. Based on these estimates, the cancellation scheme essentially creates replicas of the contributions of the CCl embedded in the correlator outputs and removes them for a second improved hard data decision. By repeating this operation over and over, a cascade of CCl cancellers is derived. Through theoretical analysis and simulation, the authors investigate the canceller's bit error rate (BER) performance in both the absence and presence of errors in the amplitude and phase estimates of each user's received signal. Numerical results show the considerably large improvement in performance that can be attained by the cancellation scheme, even under partially degraded estimates. >

Signal acquisition and tracking with adaptive arrays in the digital mobile radio system IS-54 with flat fading

Abstract: The author considers the dynamic performance of adaptive arrays in wireless communication systems. With an adaptive array, the signals received by multiple antennas are weighted and combined to suppress interference and combat desired signal fading. In these systems, the weight adaptation algorithm must acquire and track the weights even with rapid fading. The author considers the performance of the least-mean-square (LMS) and direct matrix inversion (DMI) algorithms in the North American digital mobile radio system IS-54. He shows that implementation of these algorithms permits the use of coherent detection, which improves performance by 1 dB over differential detection. Results for two base station antennas with flat Rayleigh fading show that the LMS algorithm has large tracking loss for vehicle speeds above 20 mph, but the DMI algorithm can acquire and track the weights to combat desired signal fading at vehicle speeds up to 60 mph with less than 0.2 dB degradation from ideal performance with differential detection. Similarly, interference is also suppressed with performance gains over maximal ratio combining within 0.5 dB of the predicted ideal gain. >

Rayleigh fading compensation for QAM in land mobile radio communications

Abstract: A pilot symbol-aided Rayleigh fading compensation is investigated for M-ary quadrature amplitude modulation (QAM) to achieve highly spectrally efficient land mobile communication systems. The optimum parameters for fading compensation, bit error rate (BER) performance against E/sub b//N/sub 0/ (energy per bit to the noise power spectrum density), adjacent channel interference, and cochannel interference for 16-QAM, 64-QAM, and 256-QAM, and the spectral efficiencies for these modulation schemes in Rayleigh fading environments are investigated by computer simulation. To further verify the effect of pilot symbol-aided fading compensation from a a practical point of view, a 16-QAM modem is implemented, laboratory experiments are executed, and the impact of the dynamic range limitation due to the resolution of the analog-to-digital (A/D) converters is evaluated, along with the imperfection of the analog circuits. It is demonstrated by computer simulation and laboratory experiments that the pilot symbol-aided fading compensation can sufficiently compensate for fast varying Rayleigh fading, and 16-QAM gives the highest spectral efficiency in the case of cellular systems. >

Narrowband land-mobile radio networks

Abstract: VHF and UHF propagation in land-mobile communication probability of signal outage threshold crossing rate and average (non-) fade duration average bit error rate in CW communication random multiple access to mobile radio channels models for receiver capture in mobile random-access networks spatial distributions of traffic in mobile slotted ALOHA networks frequency re-use in wide-area packet-switched networks discussions and conclusions appendices.

OFDM/FM frame synchronization for mobile radio data communication

Abstract: A synchronization scheme enabling the use of orthogonal frequency division multiplexing (OFDM)/FM over a mobile radio channel in a pure ALOHA environment is proposed. The scheme encodes synchronization information in parallel with data in the same manner in which data is encoded in the OFDM/FM frame. The synchronization information is in the form of tones, centered in certain reserved frequency subchannels of the OFDM signal. The receiver uses a correlation detector, implemented in the frequency domain, to acquire synchronization accurately on a packet-by-packet basis. Experimental results indicate that the bit-error-rate performance achievable with the proposed scheme is within 1.5 dB of the performance obtained with ideal synchronization. >

Performance of orthogonal CDMA codes for quasi-synchronous communication systems

Abstract: In this paper, the performance of quasi-synchronous direct-sequence CDMA communication systems based on different sets of orthogonal codes is investigated. The authors search for sets of sequences that minimize the probability of bit detection error, given that there is imperfect synchronization among the signals. Orthogonal sequences based on the Sylvester-type Hadamard matrices (Walsh functions) are shown to provide a large improvement over the case where an orthogonal set is chosen at random. For these sequences closed form expressions are derived for the average bit error rate. Computer searches indicate that this set of codes has special properties with respect to minimizing the average cross-correlations between the different signals for small errors in chip synchronization. It appears that these codes are optimal. A multi-carrier signalling scheme designed to help synchronize the CDMA signals at the chip level is also discussed.

Transmission power control system capable of keeping signal quality constant in mobile communication network

Abstract: In order to provide for a mobile communication network of a cellular type a transmission power control system capable of keeping a signal quality constant, an average bit error rate y is measured on a receiving side in connection with a communication channel being in use (step 100). If the average bit error rate y is not greater than a first rate threshold value LV1, transmission power is decreased by a predetermined amount on a transmitting side (step 102). If the average bit error rate y is not less than a second rate threshold value LV2 which is greater than the first rate threshold value LV1 (step 103), the transmission power is increased by the predetermined amount on the transmitting side (step 104). Preferably, an average reception level is additionally measured to adjust the transmission power when the bit error rate is less or greater than the first or the second rate threshold value. The first and/or the second rate threshold value is adaptively adjusted by counting the number of times by which the bit error rate exceeds a predetermined maximum allowable rate. It is possible to use an average carrier to interference ratio with threshold ratio values substituted for the threshold rate values and with a predetermined minimum allowable ratio used.

Multilevel trellis coded modulations for the Rayleigh fading channel

Abstract: The authors present coded 8-phase-shift-keyed (8-PSK) modulations for the Rayleigh fading channel. The schemes are based on multilevel trellis-coded-modulation constructions and utilize maximum free Hamming distance binary convolutional codes as building blocks. A suboptimal multistage decoder that utilizes interstage interleaving and iterative decoding is proposed and evaluated. Examples are constructed to show that the proposed schemes outperform the best modified codes of the Ungerboeck type due to significantly higher implicit time diversity, yielding seven branches of built-in time diversity, whereas the Ungerboeck code yields four branches of time diversity for a 64-state system. The transmission delay is higher, however. The new schemes can provide three levels of unequal error protection when 8-PSK or 8-differential-phase-shift-keying (8-DPSK) modulations are used. They provide 10-14-dB channel signal-to-noise ratio gain over uncoded 4-DPSK at a bit error rate of 10/sup -3/ for a modest decoding complexity. >

A novel approach to modeling and efficient simulation of frequency-selective fading radio channels

Abstract: A multipath radio channel concept based on channel orthogonalization techniques in two inner product spaces is presented and compared to the conventional approach of modeling each individual Rayleigh or Rice fading multipath ray individually. The proposed simulator can be applied to linear amplitude/phase modulation and linear fading channels including Nyquist filtering. It is shown to be a good approximation to the conventional model in the case of tight rolloff factors. Channels having quasi-or truly continuous delay profiles can now be properly represented at significantly reduced computational complexity. The proposed simulation concept leads to the lowest level of complexity being achieved for the prevailing channel and noise conditions on a particular channel. >

An implementation of a CMA adaptive array for high speed GMSK transmission in mobile communications

Abstract: The hardware implementation of an adaptive array as a technique for compensating multipath fading in mobile communications is described. The number of the antenna elements is four. The target communication system is modulated by 256 kbps Gaussian-filtered minimum shift keying (MSK) and has a time-division multiplexing (TDM) architecture with 24 time slots. Based on the digital beamforming concept, all of the signals and the array weights are digital-signal processed. The constant modulus algorithm (CMA) is employed for weight optimizing. In an additive white Gaussian noise channel, this system has 5.6-dB gain in an energy-per-bit-to-noise-density ratio at a bit error rate (BER) of 1.0*10/sup -3/, compared with a single antenna system. The result of the basic field test shows that the gain at a BER of 1.0*10/sup -3/ reaches 22.3 dB in a nonselective, slow Rayleigh fading channel given a 5 Hz maximum Doppler shift. >

Hanset for a multiple channel communication system and use thereof

Abstract: A handset (24, 25) in a radio communication system (20) determines the quality of a channel (500 and 502) in response to an RSSI signal generated by a receiver (174) in combination with either an eye closure measurement (510) or a bit error rate detected by a CRC codeword in received digital information (502). The battery operated handset is also capable of conserving scanning power while operating in an area having high channel quality (520, 560, 566). The handset also has a method for determining the amount of handovers between base stations (21, 22, 23) by use of dual channel quality thresholds (582, 590) which require a higher quality threshold for establishing communication with a base station and a reduction in channel quality before a handover to a new base station.

Bit error simulation for pi /4 DQPSK mobile radio communications using two-ray and measurement-based impulse response models

Abstract: An accurate software/hardware bit-by-bit error simulator for mobile radio communications is described. Simulation results in indoor and outdoor channels are compared with theoretical results. Bit error rate (BER) results in simulated frequency-selective fading channels generated by several channel models such as two-ray, constant amplitude, and simulated indoor radio channel impulse models (SIRCIMs) are presented. It is shown that BER is not only dependent on the RMS delay spread, but also on the distribution of temporal and spatial multipath components in local areas. An important result is that a two-ray Rayleigh fading model is a poor fit for indoor wireless channels and, if used, can underestimate the BER by orders of magnitude. A real-time bit error simulation of video transmission using the bit-by-bit error simulator is described. The simulator, called BERSIM, is shown to be a useful tool for evaluating emerging data transmission products for digital mobile communications. >

Performance analysis of an all-digital BPSK direct-sequence spread-spectrum IF receiver architecture

Abstract: A VLSI architecture for an all-digital binary phase shift keying (BPSK) direct-sequence (DS) spread spectrum (SS) intermediate frequency (IF) receiver is presented, and an in-depth performance analysis is given. The all-digital architecture incorporates a Costas loop for carrier recovery and a delay-locked loop for clock recovery. For the pseudorandom noise (PN) acquisition block, a robust energy detection scheme is proposed to reduce false PN locks over a broad range of signal-to-noise ratios. The proposed architecture is intended for use in the 902-928 MHz unlicensed spread spectrum radio band. A 100 kbs information rate and a 12.7 Mchips/second PN code rate are assumed. The IF center frequency is 12.7 MHz and the IF sampling rate is 50.8 Msamples/second, which is the Nyquist rate for the 25.4 MHz bandwidth signal. Finite wordlength effects have been simulated to optimize the architecture, thereby minimizing the chip area, and results of the finite wordlength simulations demonstrate that the chip architecture achieves a bit error rate performance within 1 dB of theory in an additive white Gaussian noise channel. >

Simplified Kalman estimation of fading mobile radio channels: high performance at LMS computational load

Abstract: Low-complexity algorithms for channel estimation in Rayleigh fading environments are presented. The channel estimators are presumed to operate in conjunction with a Viterbi decoder, or an equalizer. The algorithms are based on simplified internal modeling of time-invariant channel coefficients and approximation of a Kalman estimator. A novel averaging approach is used to replace the online update of the Riccati equation with a constant matrix. The associated Kalman gain is expressed in an analytical form. Compared with RLS (recursive least squares) tracking, both a significantly lower bit error rate and a much lower computational complexity are achieved. >

Data processor with enhanced error recovery

Abstract: Error detection and recovery is provided in a processor of small size and which can be integrated on a single chip by providing buffers for both data and processor status codes in order to contain errors until a subsequent check point preferably generated at the termination of each instruction is reached without detection of an error. Retry of an instruction can therefore be initiated using the status and data validated at the termination of the previous check point and without placing error correction processing in any critical path of the processor. Error detection is accomplished by comparing outputs of at least a pair of unchecked processors for both memory access requests and output data and status codes. Input to the processors is subjected to a parity check and parity check bits are generated for memory access requests. Error correcting codes are generated for data and status codes to allow correction of single bit errors during transmission within the processor or at a storage system. When an error is detected, all data which has not been validated, preferably by changing the logical value of a flag bit associated with each code, at the most recently generated check point is erased. Data codes in which the flag bit has been changed may be transferred to a storage system autonomously even after an error has occurred.

Pre-RAKE diversity combination for direct sequence spread spectrum communications systems

Abstract: A novel method of multipath diversity signal combination is proposed for mobile direct sequence spread spectrum (DS-SS) communications. Multiple transmissions are made for each spread signal. Each transmission is independently delayed and amplified in the complex domain according to the delay profile and the estimated path strength of the channel. This is done to facilitate reception of a signal at the mobile unit which is already a RAKE combination of the multipath signals. This method is called a pre-RAKE combination system because the RAKE combination function is performed pre-transmission. Using this method the size and complexity of the mobile unit can be kept to a minimum. The pre-RAKE method retains the advantages of diversity reception in a multi-path fading environment. An examination of the SNR for the traditional RAKE and the pre-RAKE systems and computer simulations show that the performance of the pre-RAKE system is equivalent to that of the RAKE system. >

Multilayer perceptron based decision feedback equalisers for channels with intersymbol interference

Abstract: The paper describes the application of multilayer perceptrons to the problem of adaptive channel equalisation in digital communications systems In particular, the use of decision feedback structures is investigated for time-invariant and time-variant bandlimited channels Simulation results show that the equaliser based on the multilayer perceptron provides better bit error rate performance compared with the conventional decision feedback equaliser if the equaliser length corresponds to the time spread of the channel Increasing the equaliser length leads to equivalent bit error rates for the decision feedback and the multilayer perceptron based equaliser Because of the more complex structure of the multilayer perceptron its adaptive behaviour for time-variant channels is inferior compared with the decision feedback equaliser Nonlinearities on the transmission channel can be equalised much better by the multilayer perceptron based equaliser

Multiple hops/symbol FFH-SSMA with MFSK modulation and Reed-Solomon coding for indoor radio

Abstract: A multiple-hopes-per-symbol fast-frequency-hopped spread-spectrum multiple-access (FFH-SSMA) system for indoor radio communication is treated. The data are Reed-Solomon (RS) encoded and then modulate a carrier by means of M-ary frequency-shift-keying (MFSK) The indoor radio channel is described as a multipath (Rayleigh or Rician) slowly fading channel. The receiver uses predetection diversity by linearly combining the squared enveloped of the different hops of the same MFSK symbol. The bit error rate (BER) performane is evaluated, and how the performance is influenced by various parameters, such as the number of hops per symbol, the size of the symbol alphabet, the ratio of specular power to fading power, and the ratio of nonreference user power to reference user power, is investigated. >

Maximum likelihood paths comparison decoder

Abstract: There is described an apparatus and method for decoding signals produced by a communication system employing cascading or concatenation of error control codes that contain, for example, short memory convolution codes. A novel inner decoder and method is described which is a modified Viterbi decoder that generates soft decisions by using a subset of the operations performed by a normal, hard decision, Viterbi decoder. Results of simulation tests show that the performance of the novel decoder provides a bit error rate performance that matches the theoretical bit error rate for the various signal to noise ratios, which performance is better than decoders previously available. Several implementations are described and compared.

Bandwidth efficient concatenated coding schemes for fading channels

Abstract: Concatenated codes consisting of trellis inner codes and Reed-Solomon outer codes are considered to achieve large coding gains with small bandwidth expansion in the presence of frequency-nonselective slow Rician fading. Both errors-only and errors-erasures decoding algorithms for outer codes are applied. New upper bounds on bit error probability performance in the presence of fading are obtained and compared with simulation results for zero channel memory. The effect of interleaving in eliminating channel memory is investigated. The performance gains that are achieved by the coding scheme relative to the reference uncoded systems are illustrated via some examples. >

Performance evaluation for band-limited DS-CDMA communication system

Abstract: The model uses a coherent binary phase shift keying (BPSK) modulation scheme operated in the asynchronous mode. For ease of interpretation of results, raised cosine spectra for filters is assumed. A standard Gaussian approximation is used to derive approximated error probabilities, P/sub e/, in simple form. The effect of imperfect despreading synchronization is shown.

Error and flow control performance of a high speed protocol

Abstract: The performance of the SNR protocol of A. N. Netravali et al. (1990) is studied when it is implemented for end-to-end flow and error control. Using a combination of analysis and simulation, the efficiency with which this protocol uses the network bandwidth and its achievable throughput is evaluated as a function of certain network and protocol parameters. The protocol is enhanced by introducing two windows to decouple the two functions of receiver flow control and network congestion control. This enhancement and the original protocol are compared with go-back-N (GBN) and one-at-a-time-selective-repeat (OSR) retransmission procedures, are shown to have significantly higher throughput for a wide range of network conditions. As an example, for a virtual circuit with 60-ms roundtrip delay and 10/sup -8/ bit error rate, in order to deliver 500 Mb/s throughput, both the GBN and OSR require a raw transmission bandwidth of approximately 800 Mb/s, whereas SNR with two windows needs slightly higher than 500 Mb/s raw bandwidth. Periodic exchange of state can also provide a variety of measures for congestion control in a timely and accurate fashion. >

Automatic adjustment of receiver apparatus based on channel-bit-error-rate-affected parameter measurement

Abstract: Alignment of an antenna and a polarizer for the antenna are automatically adjusted and the frequency setting of a frequency-tunable receiver is automatically adjusted while receiving a broadcast communication signal that is forward-error-correction coded by processing the forward-error-correction code of the received signal to measure a channel-bit-error-rate-affected parameter for the received signal; by realigning the antenna and the polarizer from their respective initial positions in response to the measured parameter until the measured parameter is minimized; and by retuning the receiver from its initial frequency setting in response to the measured parameter until the measured parameter is minimized. A Viterbi decoder processes the forward-error-correction code of the received signal to compute path metrics affected by the bit-error rate of the received signal and normalizes the computed path metrics; and a counter counts the normalizations over fixed intervals to measure a path metric normalization rate as the measured parameter.

A soft-output bidirectional decision feedback equalization technique for TDMA cellular ratio

Abstract: Issues encountered in the design of reliable narrowband time-division multiple access (TDMA) digital cellular mobile communication systems are considered. In particular, the problem of compensating for the harsh multipath fading environment in systems whose transmission bandwidth is commensurate with the coherence bandwidth of the fading channel is considered. A TDMA channel characterization parameter, the slot-normalized fade rate, is introduced, and an adaptive bidirectional equalization technique, which estimates the location of a deep fade within a time slot, is proposed. The simulation results show that the carrier-to-noise ratio requirement is only 15.5 dB when this equalization technique is used. This is achieved without diversity, and with low complexity. An equivalent equalized land mobile radio channel model and the analytical solution for the optimal bit likelihood calculation for pi /4-shift quadrature differential phase-shift keying (QDPSK) modulation are also derived under certain channel conditions. The results are used as soft decisions for the convolutional decoder. >

Apparatus and method for transmitting bit synchronous data over an unreliable channel

Abstract: Data transmission with bit synchronism over an unreliable channel is accomplished by assigning a unique number to each data byte transmitted in a data packet From this unique number, each data bit may be identified at the packet receiver When a data packet is missing or uncorrected, the missing data bits are identified and a fill data bit is supplied to the data sink at the time each missing data bit would have been supplied

Bit-rate flexible all-optical demultiplexing using a nonlinear optical loop mirror

Abstract: The nonlinear optical loop mirror is shown to be capable of demultiplexing 20 Gbit/s pulses from a continuous 40 Gbit/s data stream. Bit error rate measurements are presented for a demultiplexed 10Gbit/s channel, and the sensitivity of the error rate to timing jitter between the signal and clock pulses is examined. Bit-rate flexible demultiplexing can be achieved.

An all feedforward synchronization unit for digital radio

Abstract: The complete structure of a fully digital all feed forward synchronization unit is presented, establishing clock and carrier synchronization. Although the basic synchronization concept is able to operate solely on random data, a structure is presented which is tailored to spontaneous packet transmission and time division multiple access (TDMA) applications, where additional frame synchronization has to be performed. It is shown that frame and frequency synchronization can be efficiently combined. The key features of the scheme, which are presented in terms of estimation error variances and bit error rate (BER), ensure high speed synchronization with negligible decoder performance degradation.