Abstract
Effective suppression of multiuser interference (MUI) and mitigation of frequency-selective fading effects within the complexity constraints of the mobile constitute major challenges for broadband cellular downlink transceiver design. Existing wideband direct-sequence (DS) code division multiple access (CDMA) transceivers suppress MUI statistically by restoring the orthogonality among users at the receiver. However, they call for receive diversity and multichannel equalization to improve the fading effects caused by deep channel fades. Relying on redundant block spreading and linear precoding, we design a so-called multicarrier block-spread-(MCBS-)CDMA transceiver that preserves the orthogonality among users and guarantees symbol detection, regardless of the underlying frequency-selective fading channels. These properties allow for deterministic MUI elimination through low-complexity block despreading and enable full diversity gains, irrespective of the system load. Different options to perform equalization and decoding, either jointly or separately, strike the trade-off between performance and complexity. To improve the performance over multi-input multi-output (MIMO) multipath fading channels, our MCBS-CDMA transceiver combines well with space-time block-coding (STBC) techniques, to exploit both multiantenna and multipath diversity gains, irrespective of the system load. Simulation results demonstrate the superior performance of MCBS-CDMA compared to competing alternatives.
Highlights
The main drivers toward future broadband cellular systems, like high-speed wireless internet access and mobile multimedia, require much higher data rates in the downlink than in the uplink direction
To cope with the challenges of broadband cellular downlink communications, we have designed a novel multicarrier code division multiple access (CDMA) transceiver that enables significant performance improvements compared to 3G cellular systems, yielding gains of up to 6.8 dB in full load situations
Our multicarrier block-spread- (MCBS-)CDMA transmission technique capitalizes on redundant block spreading and linear precoding to preserve the orthogonality among users and to enable full multipath diversity gains, regardless of the underlying multipath channels
Summary
The main drivers toward future broadband cellular systems, like high-speed wireless internet access and mobile multimedia, require much higher data rates in the downlink (from base to mobile station) than in the uplink (from mobile to base station) direction. Due to the increasing success of future broadband services, more users will try to access the common network resources, causing multiuser interference (MUI) Both ISI/ICI and MUI are important performance limiting factors for future broadband cellular systems, because they determine their capabilities in dealing with high data rates and system loads, respectively. By CP or zero padding (ZP) the block-spread symbol blocks, our MCBSCDMA transceiver preserves the orthogonality among users, regardless of the underlying time-dispersive multipath channels. This property allows for deterministic (as opposed to statistical) MUI elimination through low-complexity and channel-independent block despreading. Hatted letters xdenote soft estimates, whereas hatted and underlined letters xdenote hard estimates
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