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We propose a new broadcast strategy for a multiple-input multiple-output (MIMO) system with N transmit antennas at the transmitter and M≤N single antenna receivers. The proposed method, based on dirty-paper coding (DPC), spatially separates the M users but does not suffer from the power loss of classical spatial division multiple access (SDMA). For the special case of M=N=2 and when the two single antenna receivers are assumed to be co-located, the proposed scheme produces a 2 transmit, 2 receiver antenna MIMO transmission system that doubles the symbol rate of MIMO space-time block code (STBC) systems from one to two symbol per transmission time. It is proved theoretically and experimentally that the proposed scheme provides the same performance level as that of MIMO STBC systems (i. e., the Alamouti scheme) for the first symbol, and the same performance as the Bell labs layered space-time (BLAST) system for the second symbol. When compared to the BLAST system, the proposed scheme has the same symbol rate, but achieves significantly better performance, since it provides 2 level diversity per symbol on the first symbol while the BLAST system does not provide any diversity.

The paper proposes a new duplexing scheme, which is called the hybrid division duplex (HDD), that is suitable for fourth-generation mobile communication systems. The proposed mobile communication system is much more flexible and efficient in providing asymmetric data service and managing intercell interference by exploiting the advantages of both time division duplex (TDD) and frequency division duplex (FDD) schemes. The HDD scheme has a pair of frequency bands such as the FDD, performing a TDD operation using one of the bands in such a manner that allows for simultaneous FDD and TDD operations. Considering the properties of the HDD system architecture, frequency hopping orthogonal frequency division multiple (OFDM) access is adopted in one band for the TDD operation and code division multiple access (CDMA) in the other band for the FDD uplink operation. The important advantage of the HDD scheme is the robustness against cross time slot interference that is inherent to the TDD system, which is caused by the asynchronous downlink/uplink switching boundaries among all neighbor cells. From the simulation results, the proposed system can achieve approximately 7% and 30% improvement with regard to the downlink and uplink throughput, respectively, as compared to the conventional TDD system under cell-independent downlink/uplink traffic asymmetries. It demonstrates that the HDD scheme is a viable solution for future communication systems that are projected to have a cell-independent asymmetric-traffic-supported hierarchical cell structure.

A random beamforming technique for multiple-input multiple-output (MIMO) systems that simultaneously obtains downlink multiuser diversity gain, spatial multiplexing gain and array gain by feeding back only effective signal-to-noise ratios (SNRs) is described. In addition, power control using waterfilling is employed to improve the throughput of our method in correlated channels. In a slow fading channel, we prove that the throughput of the proposed method converges to that of eigen beamforming when many users are in a cell. The number of users required to achieve capacity bound increases with the number of antennas and SNR was determined. However, the capacity bound is achieved even with a small number of users, e.g., 16 users in a cell, when the SNR is low, e.g., 0 dB, and the number of transmit and receive antenna is small, e.g., two. We also find that the effect of waterfilling is more noticeable in correlated channels.

For the fast fading channels, e.g., fast mobile channels, non-coherent detection scheme is promising because the receiver does not require to measure the channel information, which results in reducing transmission overhead. In this paper, we compare the bit error rate of two non-coherent encoding/decoding schemes for multiple transmit antennas under fast fading environments when the number of antenna varies from two to three. The first approach is a unitary space-time modulation (USTM) that aims to achieve the non-coherent channel capacity. The second one is a differential space-time block code (DSTBC), which projects information symbols to a number of orthogonal bases that consist of the previously sent symbols. We exhibit the fact that the block length of both schemes affects the performance significantly rather than encoding/decoding methods when the channel varies fast. In addition, we present some problems of the DSTBC sending the complex symbols with more than two transmit antennas.

Antenna selection strategies for multiple-input multiple-output (MIMO) wireless systems is presented. In our scheme, both transmit and receive antenna selection is done at the receiver, significantly reducing feedback information to the transmitter. Row/column probability density function (pdf) is used for antenna selection to reduce computational complexity without performance degradation. Unlike other schemes, we used two different antenna selection algorithms both for high SNR and low SNR regime, achieving additional performance gain in comparison with the single antenna selection algorithm. Simulation results show that our scheme nearly approaches to the optimal closed-loop capacity (known as water-filling capacity).

We present a multiple-input multiple-output (MIMO) relay system with hybrid automatic repeat request (HARQ) protocols which can achieve better outage behaviors than simple MIMO cooperative diversity schemes. Using repetition based and Alamouti based HARQ scheme, we can achieve better diversity gains without increasing additional transmit power. This system can be a practical solution for a new system which requires lower deployment costs and limited power in each nodes.

In this paper, we propose a recursive space time decoding method for orthogonal frequency division multiplexing (OFDM) systems exploiting multiple transmit antenna diversity when the channels are fast fading. We first develop a computationally efficient space-time decoding method involving a matrix inversion to mitigate the channel variation effect. We then further reduce the computational complexity of the matrix inversion decoding method via a recursive formulation. Computer simulation results show that the proposed recursive decoding has much better BER performance than Alamouti decoding, requiring much less computation than the matrix inversion decoding. Moreover, the relative advantage in BER performance of the proposed scheme over Alamouti decoding stands out as the Doppler frequency increases

In this paper, we construct a differential spatial multiplexing method that can trade-off spatial diversity for increased transmission rate in differential multi-input multi-output (MIMO) systems. To achieve a desired multiplexing gain while providing simple encoding and decoding, Gram-Schmidt algorithm is used at the transmitter to construct the unitary transmission matrix. In addition, by applying optimum scaling factors to generate transmission matrix, the symbol error rates can be minimized. Because the transmission matrix itself is not the information we are interested in, the equivalent channel parameters for each transmitted information symbols are calculated and the linear signal model for the information symbols is derived. Since that model is exactly the same as that of the coherent spatial multiplexing, all kinds of coherent detection schemes can be directly applied. The advantage of the proposed scheme over the differential space-time block codes (STBC) and the effects of scaling factor are investigated by computer simulation. In high transmission rate regimes, the proposed differential spatial multiplexing method can outperform the differential STBC having the same transmit rate in the signal to noise ratios (SNRs) we are interested in.

The tracking performance of the nonlinear carrier synchronizer in Rician fading channels is discussed. The performance is characterized in terms of the error variance of the estimated phase. Analytic results are provided using the joint probability density function (pdf) between two samples. These results are compared with those obtained by computer simulation in various fading conditions.

In this paper, 60 GHz indoor broadband wireless channels are measured with various configurations in a typical office environment. Measurements are taken at nine positions of the room and the base-station antenna is placed either at the center or at an edge of the measurement room, and the remote-station antenna is of either sharp beam or broad beam type. The RMS delay spread (RDS) and normalized received power (NRP) are estimated from the measurements. Statistical models of the 60 GHz indoor wireless channels are also presented with model parameters from the measured channel data based on the Saleh's (1987) indoor channel modeling method. Bit error rate (BER) simulations are performed using measured and simulated channel impulse responses with DQPSK-OFDM modulation, respectively. Using sharp beam antenna results in superior performances to using broad beam antenna in terms of both bit error rates (BER) and NRP penalty. Also, placing the base-station antenna at the center is superior to placing it at an edge in terms of BER and NRP.