Abstract
A multicode direct-sequence code-division multiple-access system experienceslarge envelope variations as a result of a sum of many independently spreadsignals. However, large envelope variations is problematic because it reducesthe spectral efficiency, the efficiency of the power amplifiers and theperformance. All these effects depend on the non-linear amplifiers thatgenerally are used in handsets. It would of course be possible to use a linearamplifier but then the power efficiency is drastically reduced. In this paperwe analyze the envelope variations of a multicode signal in terms of thecrest factor and find that it increases as the square root of thenumber of used codes. As a consequence it is only possible to use themulticode scheme for a few parallel codes. To reduce the envelope variationsa precoder is introduced. This precoder is a non-linear high-rate block codeespecially designed for the set of spreading codes used. However, the precodercan be made independent of the spreading codes if a user-specific spreadingcode is concatenated with a set of Hadamard or Conference sequences. Theresulting spreadig codes are orthogonal. Also, the precoder is independent ofthe user-specific spreading code, and can thus be used for all users. Afterprecoding the crest factor is significantly reduced and the performance, dueto introduced coding gain, improved. Algorithms for the design of precoderswith both reduced envelope variation and good performance are presented.Furthermore, simulations show that a precoded multicode system outperforms anuncoded multicode system in a single-user as well as in a multiuserenvironment.
Similar content being viewed by others
References
R.H. Katz, “Adaption and Mobility in Wireless Information Systems”, IEEE Personal Communications, Vol. 1, No.1, pp. 6–17, 1994.
P.W. Baier, P. Jung and A. Klein, “Taking the Challenge of Multiple Access for Third-Generation Cellular Mobile Radio Systems – A European View”, IEEE Communications Magazine, Vol. 34, No.2, pp. 82–89, 1996.
D.D. Falconer, F. Adachi and B. Gudmundson, “Time Division Multiple Access Methods for Wireless Personal Communications”, IEEE Communications Magazine, Vol. 33, No.1, pp. 50–57, 1995.
T. Ottosson and A. Svensson, “On Schemes forMultirate Support in DS-CDMA Systems”, Wireless Personal Communications, Vol. 6, No.3, pp. 265–287, 1998.
T. Ottosson and A. Svensson, “Multi-Rate Schemes in DS/CDMA Systems”, in Proc. IEEE Vehicular Technology Conference, Chicago, U.S.A., 1995, pp. 1006–1010.
S. Ariyavisitakul and T.T. Liu, “Characterizing the Effects of Nonlinear Amplifiers on Linear Modulation for Digital Portable Radio Communications”, IEEE Transactions on Vehicular Technology, Vol. 39, No.4, pp. 383–389, 1990.
T.S. Rappaport, Wireless Communications: Principles and Practice, Prentice Hall: Upper Saddle River, NJ, 1996.
V. Soula and F. Gourgue, “Linearization of Power Amplifiers Modelling and Simulations”, in Proc. IEEE Global Telecommunications Conference, San Francisco, U.S.A., 1994, pp. 1456–1461.
T.A. Wilkinson and A.E. Jones, “Minimisation of the Peak to Mean Envelope Power Ratio of Multicarrier Transmission Schemes by Block Coding”, in Proc. IEEE Vehicular Technology Conference, Chicago, U.S.A., 1995, pp. 825–829.
S. Boyd, “Multitone Signals with Low Crest Factor”, IEEE Transactions on Circuits and Systems, Vol. CAS-33, No.10, pp. 1018–1022, 1986.
B.M. Popović, “Synthesis of Power Efficient Multitone Signals with Flat Amplitude Spectrum”, IEEE Transactions on Communications, Vol. 39, No.7, pp. 1031–1033, 1991.
D.W. Bennet, R.J. Wilkinson and P.B. Kenington, “Determining the Power Rating of a Multichannel Linear Amplifier”, IEE Proceedings-Communications, Vol. 142, No.4, pp. 274–280, 1995.
J.a. Davis and J. Jedwab, “Peak-to-Mean Power Control and Error Correction for OFDM Transmission Using Golay Sequences and Reed-Muller Codes”, IEE Electronic Letters, Vol. 33, pp. 267–268, 1997.
H. Ochiai and H. Imai, “Block Coding Scheme Based on Complementary Sequences for Multicarrier Signals”, IEICE Trans. Fundamentals, pp. 2136–2143, 1997.
R.D.J. van Nee, “OFDM Codes for Peak-to-Average Power Reduction and Error Correction”, in Proc. IEEE Global Telecommunications Conference, London, 1996, pp. 740–744.
A.E. Jones and T.A. Wilkinson, “Combined Coding for Error Control and Increased Robustness to System Nonlinearities in OFDM”, in Proc. IEEE Vehicular Technology Conference, Atlanta, U.S.A., 1996, pp. 904–908.
T. Ottosson, “Precoding in Multicode DS-CDMA Systems”, in Proc. IEEE International Symposium on Information Theory, Ulm, Germany, 1997, p. 351.
L. Ljung, System Identification: Theory for the User, Prentice Hall: Upper Saddle River, NJ, 1987.
F.J. MacWilliams and N.J.A. Sloane, The Theory of Error-Correcting Codes, North-Holland: Amsterdam, 1977.
S. Kirkpatrick Jr., C.D. Gelatt and M.P. Vecchi, “Optimization by Simulated Annealing”, Science, Vol. 220, No.4598, pp. 671–680, 1983.
A.A. El Gamal, L.A. Hemachandra, I. Shperling and V.K. Wei, “Using Simulated Annealing to Design Good Codes”, IEEE Transactions on Information Theory, Vol. IT-33, No.1, pp. 116–123, 1987.
N. Farvardin, “A Study of Vector Quantization for Noisy Channels”, IEEE Transactions on Information Theory, Vol. 36, No.4, pp. 799–809, 1990.
E. Biglieri, D. Divsalar, P.J. McLane and M.K. Simon, Introduction to Trellis-Coded Modulation with Applications, Macmillian Publishing Company, 1991.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Ottosson, T. Precoding for Minimization of Envelope Variations in Multicode DS-CDMA Systems. Wireless Personal Communications 13, 57–78 (2000). https://doi.org/10.1023/A:1008835513858
Issue Date:
DOI: https://doi.org/10.1023/A:1008835513858