Cyclic Delay Transmission for Vector OFDM Systems

TL;DR

This paper introduces cyclic delay diversity transmission for vector OFDM systems with multiple antennas, enhancing diversity and antenna capacity, especially beneficial for massive MIMO systems, with theoretical analysis and simulations.

Contribution

It develops CDD-V-OFDM, combining cyclic delay diversity with vector OFDM, enabling increased transmit antennas and diversity gains in MIMO systems.

Findings

Achieves diversity order based on system parameters and rate.

Allows more transmit antennas than traditional CDD-OFDM.

Simulation results confirm theoretical diversity gains.

Abstract

Single antenna vector OFDM (V-OFDM) system has been proposed and investigated in the past. It contains the conventional OFDM and the single carrier frequency domain equalizer (SC-FDE) as two special cases and is flexible to choose any number of symbols in intersymbol interference (ISI) by choosing a proper vector size. In this paper, we develop cyclic delay diversity (CDD) transmission for V-OFDM when there are multiple transmit antennas (CDD-V-OFDM). Similar to CDD-OFDM systems, CDD-V-OFDM can also collect both spatial and multipath diversities. Since V-OFDM first converts a single input single output (SISO) ISI channel to a multi-input and multi-output (MIMO) ISI channel of order/length $K$ times less, where $K$ is the vector size, for a given bandwidth, the CDD-V-OFDM can accommodate $K$ times more transmit antennas than the CDD-OFDM does to collect all the spatial and multipath diversities. This property will specially benefit a massive MIMO system. We show that with the linear MMSE equalizer at each subcarrier, the CDD-V-OFDM achieves diversity order $d_{\text{CDD-V-OFDM}}^{\text{MMSE}} = \min \{ \lfloor 2^{-R}K \rfloor, N_t L \} +1$, where $R$ is the transmission rate, $N_t$ is the number of transmit antennas, and $L$ is the ISI channel length between each transmit and receive antenna pair. Simulations are presented to illustrate our theory.