Zero-forcing (ZF) beamforming, an efficient technique for multiuser MIMO systems, requires perfect channel state information to be available at the base station. This is achieved by quantizing the channel and feeding back the information with a limited number of bits. A challenge of this method is the large downlink signaling overhead, which is due to the large size of the codebook that can be used at the base station for ZF beamforming. In this paper, we first analyze this problem and then present a technique designing codebooks with reduced size and minimal performance degradation. We also define the associated procedures required for the system implementation. Simulation results show that the size of the eNodeB codebook can be substantially reduced with only a small (5%) penalty in performance.

In this paper a multiple-input multiple-output (MIMO) scheme proposed for a single carrier frequency division multiple access (SC-FDMA) system is described. Transmit and receive algorithms are developed for SC-FDMA MIMO systems. A spatial precoding closed-loop transmit beamforming (TxBF) algorithm for SC-FDMA MIMO system which uses singular value decomposition (SVD) at the transmitter and linear minimum mean square error (LMMSE) equalization at the receiver is described. Quantization and feedback schemes to support closed-loop operation are discussed. The PAPR effects and a mitigation approach are presented. Simulation results are shown for throughput vs. signal-to-noise ratio (SNR). The performance for the new TxBF algorithm is compared to Single-Input-Multiple Output (SIMO). Also, single and dual- codeword performance is compared.

A salient advantage of single carrier frequency division multiple access (SC-FDMA) is low peak-to-average power ratio (PAPR) which is lower than that of OFDMA. Precoding using transmit beamforming (TxBF) is a MIMO spatial multiplexing method that increases the data throughput significantly. However, when applied to SC-FDMA, it increases the PAPR. In this paper, we describe how we can apply TxBF to an SC-FDMA system and show its effect on PAPR We then consider the effects of precoder averaging across subcarriers and quantization, typically used to reduce feedback overhead, on the PAPR Comparisons are made with single antenna, non-precoded spatial multiplexing (SM) and space-frequency block coding (SFBC) systems. Lastly, we show that a modest amount of amplitude clipping can reduce PAPR to an acceptable level with virtually no harmful effects on performance or spectral growth.

An efficient feedback design for single carrier frequency division multiple access (SC-FDMA) multiple input multiple output (MIMO) communication systems is described. We consider a codebook-based approach for MIMO pre-coding and quantization of feedback information. Differential processing is used to generate the updates iteratively for the feedback information between feedback instances. An approach of combined differential and non-differential feedback is considered for reduced feedback overhead and improved performance. A differential feedback with periodic error reset for differential processing is described. The performance of MIMO communication systems using pre-coding/transmit beamforming and the described feedback design is evaluated for SC-FDMA systems. The effects of pre-coding and feedback quantization, sub-carrier grouped feedback and feedback delay are investigated.

This paper presents computational complexity and memory counts for various data detection algorithms for TD-SCDMA. The algorithms include joint detection (JD) using Cholesky decomposition, successive interference cancellation based joint detection (SIC-JD), JD using fast Fourier transform (FFT-JD), single-user detection (SUD) and matched-filter based SIC (MF-SIC).

Broadband code division multiple access (B-CDMA) using direct sequence spread spectrum can be used as an overlay to an existing analog or narrowband digital cellular system to provide increased capacity and new data services. In order to achieve significant capacity, it has been shown that both transmit and receive notch filters should be used at the base station. This paper addresses whether the B-CDMA overlay concept can be applied to creating a CDMA microcell underlaying an existing analog macrocell. It is shown that indeed high capacity can be achieved in the microcell on both forward and reverse links, largely independently of the separation between microcell and macrocell bases. Furthermore, in the forward link the effect of neighboring base stations is shown to be negligible. In order to achieve maximum capacity, it is found that transmit and receive notch filters at the microcell base station are invaluable at small separations between micro and macrocells. It is also shown that key parameters which must be properly controlled are the powers of the CDMA base and mobile transmitters relative to their analog counterparts.>