Efficient Detection Algorithm for a Multiple-Input and Multiple-Output MultiuserMulti-Carrier Code Division Multiple Access in Time-Varying Channels

Mardina Abdullah,Fares Sayadi,Norbahiah Misran,Mahamod Ismail,Kasmiran Jumari

doi:10.3844/ajeassp.2009.635.642

Mardina Abdullah, Fares Sayadi + Show 3 more

Open Access

https://doi.org/10.3844/ajeassp.2009.635.642

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Abstract

Problem statement: Maximum Likelihood (ML) decoding has been applied for the uplink of a Multi-Carrier Code Division Multiple Access (MC-CDMA) system based on Orthogonal Frequency Division Multiplexing (OFDM). Multiple-Input Multiple-Output (MIMO) channel from k users, which moves at vehicular speed, to the Base-Station (BS) is time-varying. For time-varying channels, Sphere Decoding (SD) was introduced to perform ML decoding. Whereas, computational complexity of SD (due to a QR-factorization for each symbol), is nevertheless high. Modified SD had been proposed to achieve near optimum solutions that called Subspace-Sphere Decoder (SPSD). Approach: Proposed algorithm was based on subspace and orthogonal projection with very small dimensionality as robustness scheme in an iterative Multi-User Detection (MUD) and Parallel Interference Cancelation (PIC) method. Results: This approach had been achieved intense reduction of computational complexity for time-varying channel via one and more than one order of magnitude at channel estimation and multiuser detection respectively. Furthermore, SPSD was robustness to channel estimation error (about 3.8 dB) as compared to the representative counterparts in literature. Conclusion: Effectiveness of proposed method was demonstrated by simulations.

Highlights

We consider the uplink of a Multi-Carrier CodeDivision Multiple Access (MC-CDMA) system based on Orthogonal Frequency Division Multiplexing (OFDM) with N subcarriers
Complexity of the comprehensive search: We demonstrate the advantage of the QR decomposition by evaluating the computational complexity for comprehensive search subsequent to QR decomposition as[3]: In[12], one QR Decomposition (QRD) of size NR×T, possesses complexity as: CQRD
We focus on the multiuser detector utilizes the subspace-sphere method

Summary

INTRODUCTION

We consider the uplink of a Multi-Carrier CodeDivision Multiple Access (MC-CDMA) system based on Orthogonal Frequency Division Multiplexing (OFDM) with N subcarriers. The time-variant channel model utilizing the subspace and orthogonal projection via DPS sequences and the proposed detection algorithm are detailed as well as the computational complexity. We will omit the time index m the BCJR decoder (i.e., the (M-J) T detected symbols unless necessary, the contribution of transmit antenna (k, t) to the signal at receive antenna r is sɶ b r,(k,t) (k,t). Time-variant channel model: The estimating of timevariant frequency response gr(k,t) [m] demonstrates performance of the iterative receiver structure since the effective spreading sequence sɶr(k,t) truthfully depends on the factual channel realization. >λ, the time-variant frequency selective channel gr(k, t)[m]∈CN for the duration of a single data block JM = {0,...M-1} is projected onto the subspace spanned by linear superposition of the first D Slepian sequences and is approximated as: the received signal of user k after. We exploit the details of the subspace SD structure by using the model (15) to reduce the computational complexity for a MIMO MC-CDMA system

MATERIALS AND METHODS

DISCUSSION

Findings

CONCLUSION