Design of a Baseband Transceiver for Multicarrier CDMA Communications
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Design of a Baseband Transceiver for Multicarrier CDMA Communications Pei-Yun Tsai Graduate Institute of Electronics Engineering and Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan Email: [email protected]
Hsin-Yu Kang Graduate Institute of Electronics Engineering and Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan Email: [email protected]
Tzi-Dar Chiueh Graduate Institute of Electronics Engineering and Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan Email: [email protected] Received 29 February 2004; Revised 30 July 2004 Multicarrier systems have become popular for their spectral efficiency and robustness against frequency-selective fading. Multicarrier code-division multiple access (MC-CDMA) is a technique that combines the advantage of multicarrier modulation with that of code-division multiple access (CDMA) to offer reliable high-data-rate downlink cellular communication services. In this paper, we present the architecture of a downlink baseband transceiver using the MC-CDMA technology under the same bandwidth requirement and channel condition as the third-generation wideband CDMA system. In the transmitter, a scrambling code is applied in order to reduce the peak-to-average power ratio (PAPR) of the transmitter output. In the receiver, we use a joint weighted least-squares (WLS) synchronization error estimation algorithm and a novel channel estimator. Both algorithms greatly enhance the system error-rate performance, as indicated by functional simulation. Simulation results also verify maximum aggregate coded data rates of 5.4/10.8 Mbps from 32/64 users in mobile/stationary multipath fading channel with a 3/4 convolutional code, respectively. Keywords and phrases: multicarrier CDMA, baseband transceiver, peak-to-average power ratio, channel estimation, weighted least squares.
1.
INTRODUCTION
Direct-sequence spread-spectrum (DSSS) CDMA has been adopted in the third-generation (3G) mobile communication standard to provide high capacity and high transmission rate over conventional schemes such as frequencydivision multiple access (FDMA) and time-division multiple access (TDMA). However, it is also well known that due to inherent wide bandwidth of the spread-spectrum systems, severe frequency-selective fading degrades system performances. Moreover, multiple-access interference (MAI) can limit its application if there is no diversity or forward-errorcorrection coding. Recently, one type of multicarrier modulation, known as orthogonal frequency-division multiplexing (OFDM) has drawn much attention due to its ability to combat frequency-selective multipath fading and to
utilize spectrum resource efficiently. In an OFDM system, a frequency-selective-faded wideband channel is partitioned into a large number of flat-faded narrowband subchannels, each of which allows simple yet effective equalization. In addition, the signals in these subchannels (subcarriers) overlap with one another,
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