Effect of worst case multiple partial-band noise and tone jammerson coded FH/SSMA systems

The author characterizes and evaluates the effect of simultaneous multiple partial-band noise or tone jammers and other user interference on a single communication link employing frequency-hopped spread-spectrum (FH/SS) signaling, M-ary frequency-shift keying (FSK) modulation with noncoherent demodulation, and Reed-Solomon coding. For the symbol error probability of these systems, the author derives exact expressions in the absence of multiple-access interference and tight upper bounds in the presence of other-user interference. Although the analytical methods are valid for any number of multiple jammers, the numerical study is restricted to the cases of two and three-partial-band noise and tone jammers. For fixed values of the spectral densities of noise jammers, or the energies per symbol of tone jammers, the worst-case fraction of the band that each jammer should use in order to maximize the error probability of the FH/SS or FH/SSMA system is evaluated. For the range of the signal-to-jammer power ratios examined, multiple-noise or multiple-tone jammers appear to have no advantage over single-tone jammers of equivalent spectral density or energy per symbol, but achieve approximately the same worst-case performance by jamming smaller fractions of the band     

Performance analysis of time-hopping spread-spectrum multiple-access systems: uncoded and coded schemes

An ultra-wide bandwidth time-hopping spread-spectrum code division multiple-access system employing a binary PPM signaling has been introduced by Scholtz (1993), and its performance was obtained based on a Gaussian distribution assumption for the multiple-access interference. In this paper, we begin first by proposing to use a practical low-rate error correcting code in the system without any further required bandwidth expansion. We then present a more precise performance analysis of the system for both coded and uncoded schemes. Our analysis shows that the Gaussian assumption is not accurate for predicting bit error rates at high data transmission rates for the uncoded scheme. Furthermore, it indicates that the proposed coded scheme outperforms the uncoded scheme significantly, or more importantly, at a given bit error rate, the coding scheme increases the number of users by a factor which is logarithmic in the number of pulses used in time-hopping spread-spectrum systems.     

Hermitian codes for frequency-hop spread-spectrum packet radio networks

Hermitian codes are an attractive alternative to Reed-Solomon codes for use in frequency-hop spread-spectrum packet radio networks. For a given alphabet size, a Hermitian code has a much longer block length than a Reed-Solomon code. This and other considerations suggest that Hermitian codes may be superior for certain applications. Analytical results are developed for the evaluation of the packet error probability for frequency-hop transmissions using Hermitian coding. We find there are several situations for which Hermitian codes provide much lower packet error probabilities than can be obtained with Reed-Solomon codes. In general, as the code rate decreases or the symbol alphabet size increases, the relative performance of Hermitian codes improves with respect to Reed-Solomon codes. Performance evaluations are presented for an additive white Gaussian noise channel and for certain partial-band interference channels, and the packet error probability is evaluated for both errors-only and errors-and-erasures decoding.     

Error Analysis of Grouped Multilevel Space-Time Trellis Coding with the Combined Application of Massive MIMO and Cognitive Radio

In today’s scenario, demand for error-correcting codes with minimal error constraints for wireless communications. Multilevel coding scheme with trellis codes as component codes provides flexible data transmission rates, coding gain, diversity gain with improved spectral efficiency and low decoding complexity. This paper investigates the potential improvements by using the Multilevel coding scheme with massive Multiple-Input Multiple-Output in Cognitive Radio Networks with trellis codes as component codes. This paper discussed space-time coding with beamforming and antenna grouping according to the channel state information. Multilevel Space-time coding is based on multi-level Quadrature Amplitude Modulation signaling and beamforming to mitigate the effect of primary users for the enactment of secondary users in Cognitive Radio. The primary users provide channels dynamically to the secondary user for an unknown duration. Our transmission use Quadrature Amplitude Modulation based signals, with an adaptive grouping of antenna which weight according to the optimization, which inherently depends upon the resource allocation of the secondary user. The results show that the proposed coded system achieves Bit error rate/Symbol error rate/Frame error rate and Signal to noise ratio varies according to sources sensing time.

     

Error probabilities of fast frequency-hopped MFSK withnoise-normalization combining in a fading channel with partial-bandinterference

An error probability analysis performed for an M-ary orthogonal frequency-shift keying (MFSK) communication system employing fast frequency-hopped (FFH) spread-spectrum waveforms transmitted over a frequency-nonselective, slowly Rician fading channel with partial band interference is discussed. Diversity is obtained using multiple hops per data bit. Noise-normalization combining is employed by the system receiver to minimize partial-band interference effects. The partial-band interference is modeled as a Gaussian process. Thermal noise is also included in the analysis. Forward error correction coding is applied using convolutional codes and Reed-Solomon codes. Diversity is found to dramatically reduce the degradation of the noise-normalization receiver caused by partial-band interference regardless of the strength of the direct signal component. Diversity offers significant performance improvement when channel fading is strong, and performance improvement is obtained for high modulation orders (M>2). Receiver performance is improved when diversity, higher modulation orders, and coding are combined     

An Analysis of the MIMO–SDMA Channel With Space–Time Orthogonal and Quasi-Orthogonal User Transmissions and Efficient Successive Cancellation Decoders

We consider space–time transceiver architectures for space-division multiple-access (SDMA) fading channels with simultaneous transmissions from multiple users. Each user has up to four transmit antennas and employs a space–time orthogonal or a quasi-orthogonal design as an inner code. At the multiple-antenna receiver, efficient successive group interference cancellation strategies based on zero-forcing or minimum mean-square error (MMSE) filtering are employed in some fixed or channel-dependent order. These strategies are efficient in the sense that they exploit the special structure of the inner codes to yield much higher diversity orders than would be otherwise possible, while at the same time preserving what we call the decoupling property of the constituent inner codes which enables the use of low-complexity outer encoders/decoders for each user. Motivated by the special structure of the effective channel matrix induced by the inner codes, we obtain several new distribution results on the QR and eigenvalue decompositions of certain structured random matrices. These results are the key to a comprehensive performance analysis of the proposed multiuser transceiver architectures including the characterization of diversity–multiplexing tradeoff (DMT) curves and exact per-user bit-error rates (BERs) without making simplifying assumptions about error propagation.      

Coded Error Probability for DS Spread-Spectrum Systems with Periodic Pulsed Multiple-Tone Interference

The coded error probability for direct sequence (DS) BPSK or QPSK spread-spectrum systems, used with or without interleaving, and operating in the presence of pulsed multiple-tone interference, is investigated. We consider the worst-case channel error probability under conditions of pulsed multiple-tone jamming for the various systems, and present coded error probability as a function of interleaving delay for(n, k)block codes with hard-decision decoding. It is shown that when the maximum level of continuous multiple-tone interference does not exceed the level of the desired signal, the duty cycle of the corresponding pulsed interference which yields the worst-case error probability is usually small, and that the smaller the duty factor of the jamming, the more considerable is the performance improvement due to the use of interleaving in conjunction with the coding.     

Optimum transmission ranges in a direct-sequence spread-spectrummultihop packet radio network

The authors obtain the optimum transmission ranges to maximize throughput for a direct-sequence spread-spectrum multihop packet radio network. In the analysis, they model the network self-interference as a random variable which is equal to the sum of the interference power of all other terminals plus background noise. The model is applicable to other spread-spectrum schemes where the interference of one user appears as a noise source with constant power spectral density to the other users. The network terminals are modeled as a random Poisson field of interference power emitters. The statistics of the interference power at a receiving terminal are obtained and shown to be the stable distributions of a parameter that is dependent on the propagation power loss law. The optimum transmission range in such a network is of the form CK^α where C is a constant, K is a function of the processing gain, the background noise power spectral density, and the degree of error-correction coding used, and α is related to the power loss law. The results obtained can be used in heuristics to determine optimum routing strategies in multihop networks     

A joint source coding-power control approach for video transmission over CDMA networks

We consider future generation wireless code-division multiple-access (CDMA) cellular networks supporting heterogeneous compressed video traffic and investigate transport schemes for maximizing the number of users that can be supported in a single cell while simultaneously maximizing the reconstructed video quality of individual users. More specifically, we demonstrate that the network resources consumed by an individual user in a spread-spectrum CDMA network can be taken as the product of the allocated source-coding rate R/sub s/ and the energy per bit normalized to the multiple-access interference noise density /spl gamma//sub b/. We propose a joint source coding and power control (JSCPC) approach for allocating these two quantities to an individual user, subject to a constraint on the total available bandwidth, to simultaneously maximize the per-cell capacity while maximizing the quality of the delivered video to individual users. We demonstrate the efficacy of this approach using the ITU-T H.263+ video source coder, although the approach is generally applicable to other source-coding schemes as well. The results indicate a significant improvement in delivered quality-of-service (QoS), measured in terms of the end-user average peak signal-to-noise ratio, that can be achieved at a given level of network loading. Furthermore, we demonstrate that without an appropriate JSCPC strategy the traditional soft-capacity limit associated with CDMA networks is no longer present. Indeed, a precipitous decrease in performance can be expected with increasing load. We show that this behavior can be avoided with the proposed JSCPC approach, thereby significantly extending the useful capacity of the CDMA network while exhibiting a more graceful degradation pattern under increasing load.     

Performance analysis of multicarrier frequency-hopping (MC-FH) code-division multiple-access systems: uncoded and coded schemes

In this paper, we provide multiuser performance analysis of a multicarrier frequency-hopping (MC-FH) code-division multiple-access system as first introduced in the work of Lance and Kaleh. We propose to use a practical low-rate convolutional error-correcting code in this system, which does not require any additional bandwidth than what is needed by the frequency-hopping spread-spectrum modulation. We provide multiuser exact performance analysis of the system for both uncoded and coded schemes in additive white Gaussian noise and fading channels for a single-user correlator receiver. We also derive the performance analysis of the system based on a Gaussian distribution assumption for multiuser interference at the receiver output. Our numerical results first indicate that the coded scheme significantly increases the number of users supported by the system at a fixed bit error rate, in comparison with the uncoded MC-FH scheme. Moreover, it shows that the Gaussian analysis in some cases does not accurately predict the number of users supported by the system.     

Bandwidth‐efficient turbo coding over Rayleigh fading channels

Introduced in 1993, turbo codes can achieve high coding gains close to the Shannon limit. In order to design power and bandwidth‐efficient coding schemes, several approaches have been introduced to combine high coding rate turbo codes with multilevel modulations. The coding systems thus obtained have been shown to display near‐capacity performance over additive white Gaussian noise (AWGN) channels. For communications over fading channels requiring large coding gain and high bandwidth efficiency, it is also interesting to study bit error rate (BER) performance of turbo codes combined with high order rectangular QAM modulations. To this end, we investigate, in this paper, error performance of several bandwidth‐efficient schemes designed using the bit‐interleaved coded modulation approach that has proven potentially very attractive when powerful codes, such as turbo codes, are employed. The structure of these coding schemes, termed ‘bit‐interleaved turbo‐coded modulations’ (BITCMs), is presented in a detailed manner and their BER performance is investigated for spectral efficiencies ranging from 2 to 7 bit/s/Hz. Computer simulation results indicate that BITCMs can achieve near‐capacity performance over Rayleigh fading channels, for all spectral efficiencies considered throughout the paper. It is also shown that the combination of turbo coding and rectangular QAM modulation with Gray mapping constitutes inherently a very powerful association, since coding and modulation functions are both optimized for operation in the same signal‐to‐noise ratio region. This means that no BER improvement is obtainable by employing any other signal constellation in place of the rectangular ones. Finally, the actual influence of the interleaving and mapping functions on error performance of BITCM schemes is discussed. Copyright © 2002 John Wiley & Sons, Ltd.     

Combined power control and error-control coding in multicarrier DS-CDMA systems

We propose truncating the transmission power (allocating no power) for symbols with low channel gain, and tagging erasures on the corresponding symbols at the receiver. The motivation is that symbols with low channel gain are highly likely to be in error and yet, if transmitted, consume the energy resource and generate interference to other users. Truncating the power for those symbols has the effect of reducing the interference to other users and allocating more power on symbols with high channel gain (thereby reducing the error probability). Since block codes can correct twice as many erasures as errors, the coded performance can be improved by properly combining the power control with the error-control coding. In this letter, we analyze the performance of the Reed-Solomon-coded multicarrier direct-sequence code-division multiple-access systems with two power-control schemes. We show that the probability of incorrect decoding can be significantly improved by properly combining the power control with the error control coding.     

Very low rate convolution codes for maximum theoretical performanceof spread-spectrum multiple-access channels

A spread-spectrum multiple-access (SSMA) communication system is treated for which both spreading and error control is provided by binary PSK modulation with orthogonal convolution codes. Performance of spread-spectrum multiple access by a large number of users employing this type of coded modulation is determined in the presence of background Gaussian noise. With this approach and coordinated processing at a common receiver, it is shown that the aggregate data rate of all simultaneous users can approach the Shannon capacity of the Gaussian noise channel     

Progressive transmission of images over memoryless noisy channels

An embedded source code allows the decoder to reconstruct the source progressively from the prefixes of a single bit stream. It is desirable to design joint source-channel coding schemes which retain the capability of progressive reconstruction in the presence of channel noise or packet loss. Here, we address the problem of joint source-channel coding of images for progressive transmission over memoryless bit error or packet erasure channels. We develop a framework for encoding based on embedded source codes and embedded error correcting and error detecting channel codes. For a target transmission rate, we provide solutions and an algorithm for the design of optimal unequal error/erasure protection. Three performance measures are considered: the average distortion, the average peak signal-to-noise ratio, and the average useful source coding rate. Under the assumption of rate compatibility of the underlying channel codes, we provide necessary conditions for progressive transmission of joint source-channel codes. We also show that the unequal error/erasure protection policies that maximize the average useful source coding rate allow progressive transmission with optimal unequal protection at a number of intermediate rates     

A general scheme for spectral efficiency evaluation ofdirect-sequence spread-spectrum systems

Typically, spectral efficiency, the throughput in bits/second/hertz, has been evaluated for fixed values of the bit error probability. We introduce a cutoff-rate-based approach to evaluation of the spectral efficiency of direct-sequence spread-spectrum schemes so that the results are independent of specific bit error rates or channel codes. Results are shown for M-ary phase-shift keyed modulation on the slow-fading Rician channel     

Frequency-hopped multiple access communications with coding andside information

The authors consider frequency-hopped spread-spectrum multiple-access communications using M-ary modulation and error-correction coding. The major concerns are multiple-access interference and the network capacity in terms of the number of users that can transmit simultaneously for a given level of codeword error probability. Block coding is studied in detail. The authors first consider the use of Q-ary Reed-Solomon (RS) codes in combination with M-ary modulation with mismatched alphabets so that Q>M. It is shown that the network capacity is drastically reduced in comparison with the system with matched alphabets. As a remedy, the use of matched M-ary BCH codes is proposed as an alternative to mismatched RS codes. It is shown that when the number of users in the system is large, a BCH code outperforms an RS code with a comparable code rate and decoding complexity. The authors consider the use of a robust technique for generation of reliable side information based on a radio-threshold test. They analyze its performance in conjunction with MFSK and error-erasure correction decoding. It is shown that this nonideal ratio-threshold method can increase the network capacity in comparison with the system with perfect side information     

Operational rate-distortion performance for joint source andchannel coding of images

This paper describes a methodology for evaluating the operational rate-distortion behavior of combined source and channel coding schemes with particular application to images. In particular, we demonstrate use of the operational rate-distortion function to obtain the optimum tradeoff between source coding accuracy and channel error protection under the constraint of a fixed transmission bandwidth for the investigated transmission schemes. Furthermore, we develop information-theoretic bounds on performance for specific source and channel coding systems and demonstrate that our combined source-channel coding methodology applied to different schemes results in operational rate-distortion performance which closely approach these theoretical limits. We concentrate specifically on a wavelet-based subband source coding scheme and the use of binary rate-compatible punctured convolutional (RCPC) codes for transmission over the additive white Gaussian noise (AWGN) channel. Explicit results for real-world images demonstrate the efficacy of this approach.     

Maximum-Likelihood Decoding of Binary Convolutional Codes on Band-Limited Satellite Channels

Viterbi decoding of binary convolutional codes on bandlimited channels exhibiting intersymbol interference is considered, and a maximum likelihood sequence estimator algorithm is derived. This algorithm might be applied either to increase the allowable data rate for a fixed power transmitter or to reduce the required power for a fixed data rate. Upper and lower bounds on the bit error rate performance of several codes are found for selected values of the ratio of information rate to channel bandwidth, and results are compared against both conventional equalization techniques and the Shannon capacity limit. Results indicate that this algorithm can provide the power saving associated with low rate (highly redundant) codes without suffering the noise enhancement of linear equalization techniques.     

Soft multiuser demodulation and iterative decoding for FH/SSMA with a block turbo code

The number of users that can be supported by frequency-hopped, spread-spectrum multiple-access systems can be increased greatly by using multiuser demodulation and iterative decoding. In the receiver employed hard-decision multiuser demodulation followed by iterative decoding, users exchange decoded information with each other. Additional information from multiuser demodulation in the first decoding iteration is limited by the hard-decision output of the multiuser demodulator. The error-correction used was an errors-and-erasures Reed-Solomon (RS) decoder. We revisit hard-decision demodulation and conventional RS decoding. Hard-decision multiuser demodulation is modified to provide a soft output, which is then given to a nonbinary block turbo code with shortened RS codes as the constituent codes. An iterative multiuser decoding algorithm is developed to do soft multiuser interference cancellation. This soft receiver with soft demodulation and decoding is shown to be more resistant to multiuser interference and channel noise, especially at lower values of signal-to-noise ratio. The results show a great improvement in the ability of the system to support more users (more than three times in some cases), as compared with systems that erase all hits or employ hard-decision multiuser demodulation followed by RS code. We examine the proposed method for synchronous as well as asynchronous frequency-hopped systems in both AWGN and fading channels.     

Optimum rate Reed-Solomon codes for frequency-hoppedspread-spectrum multiple-access communication systems

The authors consider a multiple-access frequency-hopped spread-spectrum communication system with Reed-Solomon codes. The performance measures of interest are an achievable region and the channel throughput. The achievable rate region is the set of all pairs of code rate and number of users for which communication is possible with error probability below a fixed value. The throughput measures the expected number of successful codeword transmissions per unit bandwidth. Two models of interference are considered. For these two models, the authors determine the optimal number of users for a given bandwidth and the optimal rate Reed-Solomon code that maximize the throughput. They also determine the achievable region for these models