Capacity of Generalized UTRA FDD Closed-Loop Transmit Diversity Modes

Abstract

Transmit diversity techniques have received a lot of attention recently, and open-loop and closed-loop downlink transmit diversity modes for two transmit antennae have been included into universal terrestrial radio access (UTRA) frequency division duplex (FDD) specification. Closed-loop modes provide larger system capacity than openloop modes, but they need additional side information of the downlink channel in the transmitter. In FDD systems this requires a separate feedback channel. Quantization of channel state information (CSI) in closed-loop transmit diversity schemes decreases the performance when compared to a closed-loop system where the transmitter has access to complete CSI. In this paper, we analyze the effect of quantization of CSI and deduce approximate capacity formulae for closed-loop transmit diversity schemes that are generalizations of the closed-loop schemes included in UTRA FDD specification. Moreover, we calculate approximation error and show by simulations that our approximation is tight for flat Rayleigh fading environments with and without fast transmit power control.

Performance Analysis of Hierarchically Combined Practical Beamforming Methods

“…We then compute PDF for Z sc using known expression for distribution of maximum over two independent random variables given in [34] and approximations in (12) …”

“…Some of these methods have been adopted to practical systems, for instance, into the 3rd generation partnership project (3GPP) high speed packet access (HSPA) and long term evolution (LTE) systems, to be used in either co-located or distributed transmission modes. In the colocated scenario, closely-spaced antennas transmit the same information exploiting channel state information (CSI) to maximize the received signal-to-noise ratio (SNR) [8][9][10][11][12]. For the distributed beamforming scenario techniques such as coordinated multipoint (CoMP) joint transmission (JT) have been introduced and incorporated into the practical systems mainly to improve link reliability and data rate of cell-edge users [13][14][15][16][17].…”

“…In general, the more there is feedback capacity, the better the link performance, see e.g. [4,5,12,[17][18][19]. The performance degradation due to feedback errors is presented in [20] while [21] shows that it is possible to design efficient codebooks even under imperfect feedback system.…”

Combined transmit beamforming and channel-aware scheduling for interference mitigation in femtocells

“…In [30], the authors used this approximation to evaluate the effect of limited CSI in a MIMO broadcast channel, when spatial multiplexing is implemented in transmission using similar codebook structures (e.g., closed-loop mode 1). The justification for such an approach can be found in [29], and is based on the fact that the Nakagami distribution shows good fitting when modeling the received SNR that various multi-antenna techniques provide. In practice, the degrees of freedom for the corresponding χ 2 approximation depend on the value that the fading figure parameter takes (by definition, the fading figure of a Nakagami RV is the ratio of its squared mean value to http://jwcn.eurasipjournals.com/content/2012/1/293 its variance).…”

Power imbalance induced BER performance loss under limited-feedback CoMP techniques

“…Various limited-feedback precoding methods with different implementation requirements for practical CoMP scenarios have been studied [9][10][11][12]. Most analytical studies rely on the conventional assumption that antenna branches are homogeneous and antenna channels seen by the receiver admit the same statistical properties.…”