Relative Performance of BPSK and QPSK in the Presence of Complex Multiuser CDMA Interference

  • Authors:

  • Teng Joon Lim;Lars K. Rasmussen;Hiroki Sugimoto

  • Affiliations:

  • Centre for Wireless Communications, 20 Science Park Road, #02-34/37, TeleTech Park, Singapore 117674 E-mail: cwclimtj@leonis.nus.edu.sg;Centre for Wireless Communications, 20 Science Park Road, #02-34/37, TeleTech Park, Singapore 117674 E-mail: cwclimtj@leonis.nus.edu.sg;Oki Techno Centre Singapore, 20 Science Park Road, #02-06/10, TeleTech Park, Singapore E-mail: hiroki@okigrp.com.sg

  • Venue:
  • Wireless Personal Communications: An International Journal
  • Year:
  • 2000

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Abstract

In a typical mobile communications channel, the multiple accessinterference (MAI) experienced by any user in a multiuser CDMA systemwill be complex-valued due to independent phase offsets betweensignals received from different users. In addition, complex spreadingcodes may also be employed, in which case MAI is complex-valued evenwithout phase offsets. This paper shows that complex MAI substantiallyalters the single-user relationship between BPSK and QPSK modulation,in which QPSK offers twice the bandwidth efficiency of BPSK withoutsacrificing BER versus Eb/N0 performance. Itis shown bothanalytically and through simulations that it is possible to adjustsystem parameters to achieve identical system bandwidth efficiency andBER performance in BPSK and QPSK systems using the conventionaldetector. The performance of the well-known successive interferencecanceller and decorrelating detector are also examined.