Comparison of two modulation choices for broadband wireless communications

IEEE Vehicular Technology Conference

2006

-To achieve high spectral and power efficiencies, future broadband wireless systems should combine spatial multiplexing techniques employing multiple transmit and receive antennas with transmission schemes suitable to severely time-dispersive channels such as block transmission techniques, with appropriate CP (Cyclic Prefix) and employing FDE (Frequency-Domain Equalization). Moreover, the signal to be transmitted by the MT (Mobile Terminal) should have a reduced peak power, as well as low envelope fluctuations, so as to allow an efficient power amplification.In this paper we consider the uplink transmission within a DS-CDMA system employing CP-assisted block transmission techniques combined with spatial multiplexing techniques that require multiple antennas at both the transmitter and the receiver. We present an efficient frequency-domain receiver structure with an iterative MUD (MultiUser Detection).It is shown that the performance of the proposed receiver can be close to the single-user MFB (Matched Filter Bound), even for fully loaded systems, in severely time-dispersive channels and/or in the presence of strong interfering signals.

Section: Performance Resultsmentioning

confidence: 99%

Section: B Detection Strategymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Multiuser Detection for the Uplink of Prefix-Assisted DS-CDMA Systems Employing Multiple Transmit and Receive Antennas

IEEE Vehicular Technology Conference

2006

“…INTRODUCTION Prefix-assisted DS-CDMA schemes (Direct SequenceCoded Division Multiple Access) are suitable for broadband wireless systems since they combine the flexibility and capacity of CDMA schemes with the possibility of efficient frequency-domain receiver implementations, making them appropriate for severely time-dispersive channels [1]. Since the transmitted signals have single-carrier nature, they can be designed to have reduced envelope fluctuations, making them particularly interesting for the uplink transmission [i.e., the transmission from the mobile terminals to the base stations (BS)] [2], [3]. However, the receiver design presents some challenges at the uplink transmission since a different channel affects the signal associated to each transmitter.…”

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confidence: 99%

Frequency-Domain Multiuser Detection for Highly Overloaded DS-CDMA Systems

2011 IEEE Vehicular Technology Conference (VTC Fall)

2011

Abstract-A DS-CDMA (Direct Sequence-Coded Division Multiple Access) system has maximum spectral efficiency if the system is fully loaded (i.e., the number of users is equal to the spreading factor) and we employ signals with bandwidth equal to the chip rate. However, due to implementation constraints we need to employ signals with higher bandwidth, decreasing the system's spectral efficiency. In this paper we consider prefixassisted DS-CDMA systems with bandwidth that can be significantly above the chip rate. To allow high spectral efficiency we consider highly overloaded systems where the number of users can be twice the spreading factor or even more. To cope with the strong interference levels we present an iterative frequencydomain receiver that takes full advantage of the total bandwidth of the transmitted signals. Our performance results show that the proposed receiver can have excellent performance, even for highly overloaded systems. Moreover, the overall system performance can be close to the maximum theoretical spectral efficiency, even with transmitted signals that have bandwidth significantly above the chip rate.

IB‐DFE receivers with space diversity for CP‐assisted DS‐CDMA and MC‐CDMA systems

Trans Emerging Tel Tech

Gusmão

2007

SUMMARYMulti-Carrier Code Division Multiple Access (MC-CDMA), currently regarded as a promising multiple access scheme for broadband communications, is known to combine the advantages of an Orthogonal Frequency Division Multiplexing (OFDM)-based, Cyclic Prefix (CP)-assisted block transmission with those of CDMA systems. Recently, it was recognised that DS-CDMA (Direct Sequence) implementations can also take advantage of the benefits of the CP-assisted block transmission approach, therefore enabling an efficient use of Fast Fourier Transform (FFT)-based, chip level Frequency-Domain Equalisation (FDE) techniques. When employing a linear FDE with both MC-CDMA and DS-CDMA, the FDE coefficients can be optimised under the Minimum Mean Squared Error (MMSE) criterion, so as to avoid significant noise enhancement. The residual interference levels can be very high, especially for fully loaded scenarios, since the FDE/MMSE does not perform a perfect channel inversion. This paper deals with CP-assisted DS-CDMA systems and MC-CDMA systems with frequency-domain spreading. We consider the use of Iterative Block Decision Feedback Equalisation (IB-DFE) FDE techniques as an alternative to conventional, linear FDE techniques, and derive the appropriate IB-DFE parameters in a receiver diversity context. Our performance results show that IB-DFE techniques with moderate complexity allow significant performance gains in both systems, with bit error rate (BER) that can be close to the single-code matched filter bound (MFB) (especially for the CP-assisted DS-CDMA alternative), even with full code usage.