Abstract
In this article, we propose a multiple-input-multiple-output, orthogonal frequency division multiplexing, code-division multiple-access (MIMO OFDM-CDMA) scheme. The main objective is to provide extra flexibility in user multiplexing and data rate adaptation, that offer higher system throughput and better diversity gains. This is done by spreading on all the signal domains; i.e, space-time frequency spreading is employed to transmit users' signals. The flexibility to spread on all three domains allows us to independently spread users' data, to maintain increased system throughput and to have higher diversity gains. We derive new accurate approximations for the probability of symbol error and signal-to-interference noise ratio (SINR) for zero forcing (ZF) receiver. This study and simulation results show that MIMO OFDM-CDMA is capable of achieving diversity gains significantly larger than that of the conventional 2-D CDMA OFDM and MIMO MC CDMA schemes.
Highlights
Modern broadband wireless systems must support multimedia services of a wide range of data rates with reasonable complexity, flexible multi-rate adaptation, and efficient multi-user multiplexing and detection
The Bit error rate (BER) and Block error rate (BLER) performance of the orthogonal frequency-division multiplexing (OFDM)-code-division multiple-access (CDMA) system using space-time-frequency spreading (STFS) has been evaluated taking into consideration diversity/
We showed that our proposed system gives the advantage of maintaining maximum achievable spatial diversity on the receiver side in the case of slow frequency-selective Rayleigh-fading channels
Summary
Modern broadband wireless systems must support multimedia services of a wide range of data rates with reasonable complexity, flexible multi-rate adaptation, and efficient multi-user multiplexing and detection. Each user will be allocated with one orthogonal code and spread its information data over the frequency and time domain uniformly In this study, it was not mentioned how this approach will perform in a MIMO environment, specially in a downlink transmission. We propose an open-loop MIMO OFDM-CDMA system using space, time, and frequency (STF) spreading [10]. Time-frequency mapping is applied to ensure signal independency when transmitted and maximizing achievable diversity [14] on the receiver side. 1) Spatial spreading Lets denote xk as the transmitted symbol from user k It will be first spread in space domain using orthogonal code such as Walsh codes or columns of an FFT matrix of size Nt, as they are efficient short orthogonal codes.
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