comms research

Broadly papers dealing with various aspects of digital communications.

Keywords: UWB, digital communications, receiver design and modifications to the Viterbi Algorithm.

J. Zhang, T. D. Abhayapala, and R. A. Kennedy, "Performance of Ultra-Wideband Correlator Receiver Using Gaussian Monocycles", Proc. IEEE International Conference on Communications, ICC'03, vol. 3, pp. 2192-2196, May 2003.
Abstract BibTeX
Official: Link DOI: 10.1109/ICC.2003.1204045 PDF: 01204045.pdf Google-Scholar: [30]
Abstract: This paper investigates the performance of ultra-wideband (UWB) correlator receivers for Gaussian monocycles under the condition of equal mean power and provides constructive reference to the selection of pulses. Several channel situations are examined including ideal single user AWGN channel, non-ideal synchronous, multipath fading and multiple access interference. Both numerical and analytical techniques show that the shapes of pulses have notable impact on the performance of correlator receivers, especially on the interference resistance ability and signal-to-noise ratio (SNR) of the output. he results are also extended to the field of fractional bandwidth to better understand the possible relationship between fractional bandwidth and correlator receivers.
@inproceedings{KennedyC2003i,
    title = {Performance of Ultra-Wideband Correlator Receiver Using Gaussian Monocycles},
    author = {Zhang, J. and Abhayapala, T. D. and Kennedy, R. A. },
    booktitle = {Proc. IEEE International Conference on Communications, ICC'03},
    volume = {3},
    pages = {2192-2196},
    month = {May},
    year = {2003}}
J. Zhang, R. A. Kennedy, and T. D. Abhayapala, "Cram\'er-Rao lower bounds for the time delay estimation of UWB signals", 2004 IEEE International Conference on Communications, ICC'04, vol. 6, pp. 3424-3428, June 2004.
Abstract BibTeX
Official: Link DOI: 10.1109/ICC.2004.1313180 PDF: 01313180.pdf Google-Scholar: [23]
Abstract: In this paper, we present the Cramer-Rao lower bounds (CKLBs) for the time delay estimation of UWB signals which could be tight lower bounds for the theoretical performance limits of UWB synchronizers. The CRLBs are investigated for both single pulse systems and time hopping systems in AWGN and multipath channels. Insights are given into the relationship between CRLBs for different Gaussian monocycles. It is found that larger number of multipath signals implies higher CRLBs and inferior performance of synchronizers, and multipath interference on CRLBs can not be eliminated completely except in very special cases. As every estimate of time delay could not be perfect, the least influence of the synchronization error on the performance of receivers is quantified.
@inproceedings{KennedyC2004g,
    title = {Cram\'er-{R}ao lower bounds for the time delay estimation of {UWB} signals},
    author = {Zhang, J. and Kennedy, R. A. and Abhayapala, T. D.},
    booktitle = {2004 IEEE International Conference on Communications, ICC'04},
    volume = {6},
    pages = {3424-3428},
    month = {June},
    year = {2004}}
J. Zhang, R. A. Kennedy, and T. D. Abhayapala, "Performance of RAKE Reception for Ultra Wideband Signals in a Lognormal fading Channel", Proc. 2003 Int. Workshop on Ultra Wideband Systems, IWUWBS'2003, pp. 5, June 2003.
Abstract BibTeX
PDF: KennedyC2003l.pdf Google-Scholar: [22]
Abstract: RAKE reception for Ultra Wideband is crucial as the radiated power is restricted to be very low and there exist many resolvable multipath components. In this paper, the effectiveness of RAKE reception is investigated analytically. First, the conditions under which the interference in the RAKE fingers can be ignored are discussed. Then a method is introduced to derive the explicit expression of RAKE performance for the various combining methods for a lognormal fading channel. Numerical results show that RAKE reception can greatly improve the performance, and equal gain combining has comparable performance with maximal ratio combining.
@inproceedings{KennedyC2003l,
    title = {Performance of {RAKE} Reception for Ultra Wideband Signals in a Lognormal fading Channel},
    author = {Zhang, J. and Kennedy, R. A. and Abhayapala, T. D.},
    booktitle = {Proc. 2003 Int. Workshop on Ultra Wideband Systems, IWUWBS'2003},
    pages = {5},
    month = {June},
    year = {2003}}
N. C. McGinty, R. A. Kennedy, and P. Hoeher, "Parallel Trellis Viterbi Algorithm for Sparse Channels", IEEE Commun. Lett., vol. 2, no. 5, pp. 143-145, May 1998.
Abstract BibTeX
Official: Link DOI: 10.1109/4234.673661 PDF: 00673661.pdf Google-Scholar: [21]
Abstract: The Viterbi algorithm (VA), which normally operates using a single trellis, can be optimally reformulated into a set of independent trellises for a special class of sparse intersymbol interference (ISI) channels. These independent trellises operate in parallel and have less overall complexity than a single trellis. This trellis decomposition can be applied to a more general class of sparse channels approximately resulting in a suboptimal reduced complexity equalizer.
@article{KennedyJ1998d,
    title = {Parallel Trellis {V}iterbi Algorithm for Sparse Channels},
    author = {McGinty, N. C. and Kennedy, R. A. and Hoeher, P.},
    journal = {IEEE Commun. Lett.},
    volume = {2},
    pages = {143-145},
    month = {May},
    year = {1998}}
J. Zhang, R. A. Kennedy, and T. D. Abhayapala, "New results on the Capacity of M-ary PPM Ultra- WideBand Systems", Proc. IEEE International Conference on Communications, ICC'03, vol. 3, pp. 2867-2871, May 2003.
Abstract BibTeX
Official: Link DOI: 10.1109/ICC.2003.1204547 PDF: 01204547.pdf Google-Scholar: [15]
Abstract: In this paper, some new results on the capacity of a typical M-ary pulse position modulation (M-PPM) time hopping (TH) ultra-wideband (UWB) systems are presented. Previous results using a 'pure PPM model' are proven to exaggerate the real capacity of a UWB system. Based on an extended model containing correlator and soft decision decoding, the capacity is evaluated in the single-user case and in the case of a system with asynchronous multiple user interference (MUI) when the inputs are equiprobable. It is found that only when bit- signal-to-noise ratio (bit-SNR) is high enough, larger M leads to higher capacity; and for a specific M, the optimal values of PPM time offset parameter T/sub d/, which maximizes the capacity, are independent of bit-SNR. The influence of MUI on capacity is detrimental, especially in the case of high bit-SNR.
@inproceedings{KennedyC2003j,
    title = {New results on the Capacity of {M}-ary {PPM} {U}ltra- {W}ideBand Systems},
    author = {Zhang, J. and Kennedy, R. A. and Abhayapala, T. D.},
    booktitle = {Proc. IEEE International Conference on Communications, ICC'03},
    volume = {3},
    pages = {2867-2871},
    month = {May},
    year = {2003}}
J. Zhang, R. A. Kennedy, and T. D. Abhayapala, "Cram\'er-Rao lower bounds for the synchronization of UWB signals", EURASIP Journal on Applied Signal Processing, vol. 2005, no. 3, pp. 426-438, March 2005.
Abstract BibTeX
Official: Link DOI: 10.1155/ASP.2005.426 PDF: S1110865704404016.pdf Google-Scholar: [14]
Abstract: We present Cram\'er-Rao lower bounds (CRLBs) for the synchronization of UWB signals which should be tight lower bounds for the theoretical performance limits of UWB synchronizers. The CRLBs are investigated for both single-pulse systems and time-hopping systems in AWGN and multipath channels. Insights are given into the relationship between CRLBs for different Gaussian monocycles. An approximation method of the CRLBs is discussed when nuisance parameters exist. CRLBs in multipath channels are studied and formulated for three scenarios depending on the way multipath interference is treated. We find that a larger number of multipaths implies higher CRLBs and inferior performance of the synchronizers, and multipath interference on CRLBs cannot be eliminated completely except in very special cases. As every estimate of time delay could not be perfect, the least influence of the synchronization error on the performance of receivers is quantified.
@article{KennedyJ2005a,
    title = {Cram\'er-{R}ao lower bounds for the synchronization of {UWB} signals},
    author = {Zhang, J. and Kennedy, R. A. and Abhayapala, T. D.},
    journal = {EURASIP Journal on Applied Signal Processing},
    volume = {2005},
    pages = {426-438},
    month = {March},
    year = {2005}}
D. K. Borah, R. A. Kennedy, Z. Ding, and I. Fijalkow, "Sampling and Prefiltering Effects on Blind Equalizer Design", IEEE Trans. Signal Processing, vol. 49, no. 1, pp. 209-218, January 2001.
Abstract BibTeX
Official: Link DOI: 10.1109/78.890364 PDF: 00890364.pdf Google-Scholar: [13]
Abstract: In the development of equalization algorithms for unknown channels, the effects of the sampling rate and the analog receive prefilter prior to discretization of the received signal are often overlooked. In this paper, these effects are investigated. The relationship between the fractionally spaced output samples of a noise-limiting prefilter and the symbol spaced output samples of a matched filter is studied for both the time-invariant and the time-varying channels. It is shown that the prefilter and the sampling rate can have significant effects on blind equalization algorithms. Thus, this paper provides a common framework for comparing different blind algorithms that are studied in the literature with different sampling rates. A case study of the well-known subspace method for blind channel identification is presented. The effects of the noise color due to the prefilter on equalizers is investigated, and the sensitivity of the truncation of the overall channel impulse response in terms of the mean squared error (MSE) performance criterion is investigated through numerical examples.
@article{KennedyJ2001a,
    title = {Sampling and Prefiltering Effects on Blind Equalizer Design},
    author = {Borah, D. K. and Kennedy, R. A. and Ding, Z. and Fijalkow, I.},
    journal = {IEEE Trans. Signal Processing},
    volume = {49},
    pages = {209-218},
    month = {January},
    year = {2001}}
N. C. McGinty and R. A. Kennedy, "Reduced State Sequence Estimator with Reverse-Time Structure", IEEE Trans. Commun., vol. 45, no. 3, pp. 265-268, March 1997.
Abstract BibTeX
Official: Link DOI: 10.1109/26.558678 PDF: 00558678.pdf Google-Scholar: [12]
Abstract: A modified reduced-state sequencer estimator (RSSE) with a reverse-time structure is proposed for postcursor dominated impulse response channels. This structure can provide significant performance improvements over a conventional RSSE of similar complexity for a well-defined and practically motivated class of channels.
@article{KennedyJ1997a,
    title = {Reduced State Sequence Estimator with Reverse-Time Structure},
    author = {McGinty, N. C. and Kennedy, R. A.},
    journal = {IEEE Trans. Commun.},
    volume = {45},
    pages = {265-268},
    month = {March},
    year = {1997}}
Q. Wang, L. Wei, and R. A. Kennedy, "Iterative Viterbi Decoding, Trellis Shaping and Multilevel Structure for High-Rate Concatenated TCM", IEEE Trans. Commun., vol. 50, no. 1, pp. 48-55, January 2002.
Abstract BibTeX
Official: Link DOI: 10.1109/26.975743 PDF: 00975743.pdf Google-Scholar: [8]
Abstract: We define and apply a new algorithm called the iterative Viterbi decoding algorithm (IVA) to decode a high-rate parity-concatenated TCM system in which a trellis code is used as the inner code and a simple parity-check code is used as the outer code. With trellis shaping, the IVA can achieve a performance 1.25 dB away from the Shannon limit at a BER of 3 10 with low complexity. By augmenting the system with a binary BCH code, the error floor can be reduced to 10^-9 with very little additional cost.
@article{KennedyJ2002a,
    title = {Iterative {V}iterbi Decoding, Trellis Shaping and Multilevel Structure for High-Rate Concatenated TCM},
    author = {Wang, Q. and Wei, L. and Kennedy, R. A.},
    journal = {IEEE Trans. Commun.},
    volume = {50},
    pages = {48-55},
    month = {January},
    year = {2002}}
J. Zhang, R. A. Kennedy, and T. D. Abhayapala, "Conditions and Performance of Ideal RAKE Reception for UWB Signals in Lognormal-fading Channels", International Journal on Wireless Information Networks, vol. 10, no. 4, pp. 193-200, October 2003.
Abstract BibTeX
Official: Link DOI: 10.1023/B:IJWI.0000022050.22706.c4 PDF: KennedyJ2003b.pdf Google-Scholar: [8]
Abstract: In this paper, the conditions and performance of ideal RAKE reception for time hopping Ultra-Wideband (UWB) investigated. Owing to the complex propagation phenomena and specific structure of UWB signals, new problems relevant to the operation of RAKE receivers arise. This motivates us to reconsider the conditions under which a RAKE receiver can work effectively with negligible interference between fingers. Key findings are that the conditions not only relate to the property of time hopping codes, but also modulation methods. An analytical technique is introduced to derive explicit expressions of RAKE performance for various combining methods for a lognormal fading channel. Numerical results show that RAKE reception can largely improve the performance, and equal gain combining has comparable performance to maximum ratio combining.
@article{KennedyJ2003b,
    title = {Conditions and Performance of Ideal {RAKE} Reception for {UWB} Signals in Lognormal-fading Channels},
    author = {Zhang, J. and Kennedy, R. A. and Abhayapala, T. D.},
    journal = {International Journal on Wireless Information Networks},
    volume = {10},
    pages = {193-200},
    month = {October},
    year = {2003}}
J. Zhang, T. D. Abhayapala, and R. A. Kennedy, "Role of pulses in ultra wideband systems", IEEE International Conference on Ultra-Wideband, ICU 2005, pp. 565-570, September 2005.
Abstract BibTeX
Official: Link DOI: 10.1109/ICU.2005.1570050 PDF: 01570050.pdf Google-Scholar: [4]
Abstract: UWB pulses are the unique labels of UWB systems. This paper investigates the role of pulse systematically and highlights the central position of the pulse in UWB systems. Four system properties related closely to the pulse are discussed: propagation properties, capacity, interference to existing systems and performance of correlation receivers. The properties of pulses which function directly on every aspect are highlighted. Novel viewpoint is provided for the evaluation of capacity and interference. Suggestions are given on the pulse design, with emphasis on the whole system performance.
@inproceedings{KennedyC2005r,
    title = {Role of pulses in ultra wideband systems},
    author = {Zhang, J. and Abhayapala, T. D. and Kennedy, R. A.},
    booktitle = {IEEE International Conference on Ultra-Wideband, ICU 2005},
    pages = {565-570},
    month = {September},
    year = {2005}}
J. Zhang, T. D. Abhayapala, and R. A. Kennedy, "Principal components tracking algorithms for synchronization and channel identification in UWB systems", IEEE Eighth International Symposium on Spread Spectrum Techniques and Applications, ISSSTA'2004, pp. 369-373, August 2004.
Abstract BibTeX
Official: Link PDF: 01371724.pdf Google-Scholar: [3]
Abstract: We investigate the reduced rank shift invariant techniques in the application of synchronization and channel identification of UWB signals. The proposed reduced rank techniques can track the principal components automatically and reduce the computational complexity significantly by transforming the generalized eigen-problem in an original high dimensional space to a lower dimensional space depending on the number of desired principal signals. Technical details in the application, including the operations of sampling, fast Fourier transform (FFT) and the capture of synchronization delay, are given. Experiments show the performance is only slightly inferior to the general full rank algorithms.
@inproceedings{KennedyC2004l,
    title = {Principal components tracking algorithms for synchronization and channel identification in {UWB} systems},
    author = {Zhang, J. and Abhayapala, T. D. and Kennedy, R. A.},
    booktitle = {IEEE Eighth International Symposium on Spread Spectrum Techniques and Applications, ISSSTA'2004},
    pages = {369-373},
    month = {August},
    year = {2004}}
J. Zhang, R. A. Kennedy, and T. D. Abhayapala, "Reduced Rank Shift Invariant Technique and its Application for Synchronization and Channel Identification in UWB Systems", EURASIP Journal on Wireless Communications and Networking, 2009.
Abstract BibTeX
PDF: 892193v2.pdf
Abstract: In this paper, we investigate reduced rank shift invariant techniques in the application of synchronization and channel identification for UWB systems. General correlator based algorithms confront many limitations in UWB systems. The shift invariant techniques, such as ESPRIT and the matrix pencil method, have high resolution ability, but the associated high complexity makes them less attractive in real time implementations. Aiming at reducing the complexity, we developed novel Reduced-rank Identification of Principal Components (RIPC) algorithms. These RIPC algorithms can automatically track the principal components and reduce the computational complexity significantly by transforming the generalized eigen-problem in an original high dimensional space to a lower dimensional space depending on the number of desired principal signals. Technical details of RIPC algorithms in the application of joint UWB synchronization and channel estimation, including the operations of sampling, fast Fourier transform (FFT) and the capture of synchronization delay, are given. Experiments show the performance is only slightly inferior to the general full rank algorithms.
@article{KennedyJS2009_EURASIP_JWCN,
    title = {Reduced Rank Shift Invariant Technique and its Application for Synchronization and Channel Identification in {UWB} Systems},
    author = {Zhang, J. and Kennedy, R. A. and Abhayapala, T. D.},
    journal = {EURASIP Journal on Wireless Communications and Networking},
    year = {2009}}