Multiple transmit (Tx) and multiple receive (Rx) antennas systems, referred to as multiple-input multiple-output (MIMO) systems, have been proposed to achieve higher data rates in wireless communication systems. In this paper, we investigate joint design of transmitter and receiver for the MIMO system when the channel information is available at both transmitter and receiver. We discuss the problem concerning the design of Tx and Rx filters with the aim of minimizing the bit-error probability (BEP). We derive the optimum Tx and Rx filters when the number of data symbols is two. For a general number of data symbols, we derive a Tx and Rx filters design criterion referred to as equal signal-to-noise plus interference ratio (SNIR) criterion, and propose Tx and Rx filters based on this equal SNIR criterion. The performance of the proposed filter is compared with that of the conventional minimum mean-squared error (MMSE) filter. Performance analysis shows that the proposed filter provides a significant improvement over the MMSE filter in BEP and spectral efficiency.

In this paper, resource allocation for heterogeneous services is studied in multiuser orthogonal frequency division multiplexing (OFDM) systems. We propose a resource allocation algorithm, which is designed to improve the system throughput while satisfying the quality of service (QoS) requirements of both the real-time and nonreal-time services. In the proposed algorithm, the resources, composed of subcarriers and transmit power, are adaptively allocated to the users based on their service types and channel states over two sequential steps: (1) resource allocation for the real-time users that minimizes the resource usage required to satisfy the data rate requirement, and (2) resource allocation for the nonreal-time users that maximizes the system throughput using the remaining resource. The performance of the proposed resource allocation algorithm is evaluated in a frequency-selective fading channel, and compared with that of a simple resource allocation algorithm. Numerical results show that the proposed algorithm provides a significant throughput gain over the conventional algorithm.

Abstract — Resource management in wireless networks is an important issue because of the scarceness of communication resource. So optimization schemes for efficient resource usage have been extensively researched. Throughput maximization under the condition of limited total power or power minimization under the condition of minimum bit rate are usually considered objective in many papers. These researches focused on the power allocation, but they did not consider time slot allocation which can be also used to improve the efficiency. In this paper, we introduce a time slot allocation problem for multi-user wireless networks to achieve minimum rate guarantee under the condition of fixed total power. We solve the allocation problem by using dynamic programming method, which has the complexity of where is the number of users. This complexity is lower than the non-polynomial complexity of exhaustive searching for the optimal solution. The performance of our proposed algorithm is compared with that of the waterfilling algorithm. An advantage of using the time slot optimization approach is that it can support high mobility users with QoS requirements. From simulation results, we demonstrate that our proposed algorithm shows better performance than a conventional scheme that does not use any time slot allocation. I.

For a closed-loop transmit (Tx) diversity, the Tx weights are calculated at a receiver, and fed back to a transmitter. As the number of Tx antennas increases, the potential gain of closed-loop Tx diversity may be significant. However, the amount of feedback information, which is the number of Tx weights that should be fed back, linearly increases, and the performance improvement of a closed-loop Tx diversity system may not be as significant as expected due to delay in the feedback process. Thus, an efficient Tx weight representation, which can reduce the amount of feedback information, is needed. In this letter, a Tx weight vector representation is presented, and its performance is analyzed. Analysis shows that this weight vector representation, referred to as basis selection, significantly reduces the amount of feedback information with little performance degradation.

For a closed-loop transmit (Tx) diversity, the Tx weights are calculated at a receiver, and fed back to a transmitter. As the number of Tx antennas increases, the potential gain of closed-loop Tx diversity may be significant. However, the amount of feedback information linearly increases, and the performance improvement of a closed-loop Tx diversity system may not be as significant as expected due to delay in feedback process. Thus, an efficient Tx weight representation, which can reduce the amount of feedback information, is needed. A Tx weight vector representation is presented, and its performance is analyzed.

We investigate the performance of coherent direct-sequence code division multiple access (DS/CDMA) systems with antenna diversity in Rayleigh fading channels. For a DS/CDMA system operated in fading channels, the multiple access interference (MAI) is affected by fading. We determine the distribution of multiple access interference (MAI) in Rayleigh fading channels. Two simple approximation methods for MAI distribution are proposed, and compared with the exact MAI distribution. Using the exact and approximated MAI distributions, we evaluate the bit error probability (BEP) expression for coherent DS/CDMA systems with antenna diversity. Moreover, the BEP accuracy of the standard Gaussian approximation is investigated as the number of users, processing gain, and the number of antennas are varied.