Performance of a quasi-synchronous four-dimensional super-orthogonal WCDMA modulator for next generation wireless applications

Introduction The success whereby variants of multi-carrier orthogonal frequency division multiplexing (Mc-OFDM), including Mc-CDMA, have been introduced in WLAN standards such as 802.11a and g (WiFi), as well as in broadband wireless access standards such as 802.16-2004 (WiMax), has spawned the idea of extending their application to next generation single-carrier wireless cellular systems that have been based primarily on WCDMA modulation. The spectral efficiency and data throughput advantages that Mc-OFDM-related modulation schemes exhibit over existing 3G single-carrier UMTS and WCDMA-2000 modulation standards are hampered, however, by the weak power efficiency of the former schemes, as manifested by their high peak-to-average power ratios (PAPR), as well as their sensitivity to mobility and fast fading. The high OFDM PAPR requires power amplifier (PA) back-offs of typically 6 to 9 dBs to prevent signal amplitude saturation and corresponding spectral regrowth, resulting in limited communication range due to inefficient utilization of available handset battery power. The OFDM performance and power inefficiency is further jeopardized by the use of multi-quadrature amplitude modulation (M-QAM) of individual orthogonal subcarriers in an effort to achieve improved spectral efficiency. The performance degradation due to the use of these modulation schemes cannot be neutralized or improved without the inclusion of sophisticated forward error correction (FEC) and/or PAPR control coding mechanisms. This paper proposes an alternative low-complexity, upwards-expandable generic single carrier (Mc = 1) QS-4D-SO-WCDMA multi-layered-modulation (MLM) scheme with the potential to overcome the PAPR problems (even with MD ≥ 4 dimensions), while achieving significant BER performance gains which are QPSK-like, compared to singlecarrier and Mc-OFDM and Mc-CDMA M-QAM modulation standards. The BER performances of the latter systems degrade significantly compared to QPSK, when the number of signal levels (or symbols) increases beyond ML = 4 (i.e. M = 16).