Phase-shift cyclic-delay diversity (PS CDD) scheme and space-frequency-block-code (SFBC) PS CDD are developed for multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. The proposed PS CDD scheme preserves the diversity advantage of traditional CDD in uncorrelated multiantenna channels, and furthermore removes frequency-selective nulling problem of the traditional CDD in correlated multiantenna channels.

It is well known that a multiple-input-multiple-output (MIMO) transmission system can provide benefits on throughput and reliability in multipath fading channels over single-antenna systems [

In particular, transmit diversity (TxD) schemes are utilized to realize the reliability benefits of multi-antenna systems in slow-fading environment without channel state information (CSI) available at the transmitter side, by providing multiple signals conveying the same information over different spatial channels. In OFDM-based systems, Alamouti space-frequency block code (SFBC) [

In this paper, we develop and analyze a new TxD scheme for OFDM systems, phase-shift CDD (PS CDD), which takes advantages from both SFBC and CDD, and at the same time mitigates the issue of frequency-selective nulls. The performance of the introduced transmit diversity scheme is evaluated through numerical simualtion results.

We consider a MIMO OFDM system, with

In this paper, we focus on TxD schemes used for robust transmissions in various channel conditions, such as high-Doppler channels and highly frequency-selective channels. Such TxD schemes transmit only one channel-coded stream to ensure maximum reliability, while sacrificing spectral efficiency. We note that general TxD schemes may transmit multiple streams [

Alamouti SFBC can be described in a 2-transmit and 1-receive antenna system. For an SFBC transmission, two transmit signals at two adjacent subcarriers are paired, which we denote as

When the number of receive antennas is greater that 1, maximal ratio combining (MRC) would produce a received SNR of

On the other hand, CDD is a coded TxD scheme in an OFDM system, which can be designed for arbitrary number of Tx antennas. In two-transmit and one-receive antenna system, at subcarrier

CDD can be easily extended to cases where the number of Tx antennas is grater than 2. For example, when the number of Tx antennas is 4, we have a transmit signal

A well-known drawback of CDD is frequency-selective nulling. As CDD artificially increases frequency selectivity, in some subcarriers, the two component channels of the composit channel,

Reviewing these two TxD schemes of SFBC and CDD, in summary, we realize that SFBC is robust but not extendable to systems with large number of transmit antennas, while CDD is easily extendable and requires only one pilot signal but not robust in correlated channels. In the sequel, we develop new TxD schemes taking the advantages of both schemes while still ensuring robustness in correlated channels.

We recall that a major problem of CDD is nonrobustness in correlated channels when two terms from

To facilitate the analysis of performance of (

To gain some insights on this approach, let

Comparison of powers of composite channels with CDD and PS CDD.

The most general form of PS CDD can be written as

In Section

For an SFBC PS CDD transmission, two transmit signals at two adjacent subcarriers are paired, which we denote

In this section, we present numerical simulation results of block-error rate (BLER, or frame error rate, FER) performance comparing the TxD schemes introduced in this paper and some existing schemes such as CDD and SFBC-FSTD. For the simulation, ITU typical urban 6-path channel model (TU-6) has been used and 120 km/hr is assumed for terminal speed. Furthermore, we consider a MIMO channel with 4-transmit and 2-receive antennas, where 4 transmit antennas are correlated with correlation coefficients 0.9 and 0, while 2 receive antennas are uncorrelated. For channel coding, 3GPP Turbo code [

Figure

BLER performance in correlated channels.

BLER performance in uncorrelated channels.

In this paper, we have introduced phase-shift cyclic delay diversity PS CDD and SFBC PS CDD schemes. The proposed schemes treat frequency-selective nulling problem of traditional CDD. In particular, SFBC PS CDD takes benefits of both SFBC and PS CDD, and achieves robust block-error rate performance in both highly correlated and uncorrelated channels, while requiring only two pilot signals, as opposed to the well-known SFBC-FSTD requiring four pilot signals.