Antenna arrays in multi-user detection of spread spectrum signals

Karim, M.R. and Wei, S. (2007) Antenna arrays in multi-user detection of spread spectrum signals. In: Department of Civil Engineering, Faculty of Engineering Building, University of Malaya, 50603 Kuala Lumpur, MALAYSIA, 2007, Orlando, FL.

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Abstract

In a code division multiple access (CDMA) spread spectrum system, each user is assigned a unique scrambling code. If these codes are not mutually orthogonal, the resulting multiple access interference (MAI) causes frame error rates to be unacceptably high. A number of multi-user detection algorithms have been suggested by various authors. Optimal receivers based upon maximum likelihood sequence decoding are quite complex, their complexity increasing exponentially with the number of users in the system. Sub-optimal receivers such as linear detectors or adaptive cancellers are not as complex, but the error rates increase with the number of users. In this paper, we suggest a new multi-user detection procedure using an antenna array at the receiver. First, we provide an upper bound on the minimum mean-squared error due to MAI, and show how the frame error rate increases with the number of users. The transmitted symbols are estimated by inverting the transfer function of the channel, multiplying it with the outputs of matched filters, and then passing the result through a maximum likelihood decoder. Our analysis indicates that if the channel impulse response is known with sufficient accuracy, this procedure leads to an optimal design. In those cases where the impulse response is only approximately known, we estimate the transmitted symbols and compute the resulting baseband SNR. If this SNR is above a threshold, the baseband signal is acceptable and ready for maximum likelihood sequence decoding. Otherwise, the impulse response is adjusted in small steps until the SNR is above that threshold.

Item Type:	Conference or Workshop Item (Paper)
Funders:	UNSPECIFIED
Additional Information:	Conference code: 72625 Export Date: 16 December 2013 Source: Scopus Art. No.: 4454747 CODEN: PMICE doi: 10.1109/MILCOM.2007.4454747 Language of Original Document: English Correspondence Address: Karim, M. R.; CACI, Eatontown, NJ, United States References: Verdu, S., Minimum Probability of Error for Asynchronous Gaussian Multiple-Access Channels (1986) IEEE Trans. Inform. Theory, IT-32, pp. 85-96. , Jan; Verdu, S., Poor, H.V., Abstract Dynamic Programming Models under Commutativity Conditions (1987) SIAM J. Control Optimization, 24, pp. 990-1006. , July; Poor, H.V., Verdu, S., Probability of Error in MMSE Multiuser Dectection (1997) IEEE Trans. Inform. Theory, 43, pp. 858-871. , May; Verdu, S., (1998) Multi-user Detection, , Cambridge, UK: Cambridge University Press; Moshavi, S., Multiuser Detection for DS-CDMA Communications (1996) IEEE Commun. Mag, pp. 124-136. , Oct; Glisic, S., Vucetic, B., (1997) Spread Spectrum CDMA Systems for Wireless Communications, , Chapter 6. Boston: Artech House; Kohno, R.H., Imai, H., Hatori, M., Cancellation Techniques of Co-Channel Interference in Asynchronous Spread Spectrum Multiple Access Systems (1983) Trans. IECE (Electronics and Communications in Japan), 66, pp. 416-423. , May; Kohno, R.H., Imai, H., Hatori, M., Pasupathi, S., Combination of an Adaptive Array Antenna and a Canceller of Interference for Direct-Sequence Spread-Spectrum Multiple Access Systems (1990) IEEE J. Selected Areas Comm, 8 (4), pp. 675-682. , May; Yoon, Y.C., Kohno, R., Imai, H., Spread-Spectrum Multiple Access System with Co-Channel Interference Cancellation for Multipath Fading Channels (1992) IEEE J. Selected Areas Comm, 11 (7), pp. 1067-1075. , May; Patel, P., Holzman, J., Analysis of Simple Successive Interference Cancellation Scheme in DS/CDMA-System (1994) IEEE J. Selected Areas Comm, 12 (5), pp. 796-807. , June; Duel-Hallen, A., Holtzman, J., Zvonar, Z., Multiuser Detection for CDMA Systems (1995) IEEE Personal Commun, pp. 46-58. , Apr; Valenti, M.C., Woerner, B.D., Iterative Multiuser Detection, Macrodiversity Combining and Decoding for the TDMA Cellular Uplink (2001) IEEE J. Selected Areas Comm, 19 (8), pp. 1570-1583. , Aug; Pederson, K., Kolding, T., Seskar, I., Holtzman, J., Practical Implementation of Successive Interference Cancellation in DS/CDMA Systems Proc. ICUPC'96, pp. 321-325. , Cmabridge, MA, pp; Correal, N.S., Buehrer, R.M., Woerner, B.D., A DSP-BASED DS-CDMA Multiuser Receiver Employing Partial Parallel Interference Cancellation (1999) IEEE J. Selected Areas Comm, 17 (4), pp. 613-630. , April; Seskar, I., Mandayam, N.B., Software-Defined Radio Architectures for Interference Cancellation in DS-CDMA Systems (1999) IEEE Personal Commun, 6 (4), pp. 26-34. , Aug; Seskar, I., Mandayam, N.B., A Software Radio Architecture for Linear Multiuser Detection (1999) IEEE J. Selected Areas Comm, 17 (5), pp. 814-823. , May; Samardzija, D., Mandayam, N., Seskar, I., Blind Successive Interference Cancellation for DS-CDMA Systems (2002) IEEE Trans. Commun, 50 (2), pp. 276-290. , Feb; Jakes Jr., W.C., A Comparison of Specific Space Diversity Techniques for Reduction of Fast Fading in UHF Mobile Radio Systems (1971) IEEE Trans. Veh. Tech, VT-20 (4), pp. 81-92. , Nov; Kohno, R., Structures and Theories of Software Antennas for Software Defined Radio (2000) IEICE Trans. Commun, ES3-B (6), pp. 1189-1199. , June; Salvekar, A., Sandhu, S., Li, Q., Vuong, M., Qian, X., Multiple- Antenna Technology in WiMax Systems (2004) Intel Tech. Journal, 8 (3), pp. 229-240. , Aug. 20; Jeruchim, M.C., Balaban, P., Shanmugan, K.S., (1992) Simulation of Communication System, pp. 352-356. , New York: Plenum Press, pp; Cox, D.C., Leek, R.P., Distributions of Multipath Delay Spread and Average Excess Delay for 910-MHz Urban Mobile Radio Paths (1975) IEEE Trans. Ant. & Prop, AP-23 (2), pp. 206-213. , March; Papoulis, A., (1965) Probability, Random Variables, and Stochastic Processes, pp. 390-400. , New York: McGraw-Hill
Uncontrolled Keywords:	Adaptive cancellers, Base band (BB) signals, Baseband (BB), Channel impulse response (CIR), Code division multiple access (CDMA2000), Error Rate (ER), Frame Error Rate (FER), Frame error rates (FER), Linear detectors, Matched filters (MFs), Maximum likelihood (ML) decoder, Minimum mean-squared error (MMSE), Multi-user detection (MUD), Multiple-access-interference (MAI), Optimal designs, Optimal receivers, Spread spectrum (SS) system, Spread-spectrum signals, Transmitted symbols, Upper bounds, Acoustic intensity, Antenna accessories, Antenna arrays, Antennas, Block codes, Channel estimation, Code division multiple access, Codes (standards), Codes (symbols), Decoding, Error analysis, Estimation, Impulse response, Learning systems, Maximum likelihood estimation, Mean square error, Military communications, Military operations, Multiple access interference, Multiuser detection, Radio interference, Signal to noise ratio, Spectrum analysis, Transfer functions, Maximum likelihood
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Divisions:	Faculty of Engineering
Depositing User:	Mr Jenal S
Date Deposited:	03 Jan 2014 02:39
Last Modified:	03 Jan 2014 02:39
URI:	http://eprints.um.edu.my/id/eprint/8787

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