In this paper, we propose a general framework to analyze the performance of multiband UWB-MIMO systems regardless of specific coding schemes. A combination of space-time-frequency (STF) coding and hopping multiband OFDM modulation is also proposed to fully exploit all of the available spatial and frequency diversities, richly inherent in UWB environments. We quantify the performance merits of multiband UWB-MIMO systems in case of Nakagami-m frequency-selective fading channels. We show that the maximum achievable diversity of the proposed system is the product of the number of transmit and receive antennas, the number of multipath components, and the number of jointly encoded OFDM blocks. Interestingly, theoretical result shows that the diversity gain does not severely depend on the fading parameter m.. Finally, simulation results are presented to support the theoretical analysis.

The performance of a multiuser wireless network using orthogonal frequency-division modulation (OFDM), combined with power control and adaptive beamforming for uplink transmission is presented here. A network-wide adaptive power control algorithm is used to achieve the desired signal-to-interference-and-noise-ratio at each OFDM subcarrier and increase the power efficiency of the network. As a result, we can achieve a better overall error probability for a fixed total transmit power. With the assumption of fixed-modulation for all subcarriers, transmit powers and beamforming weight vectors at each subcarrier are updated jointly, using an iterative algorithm that converges to the optimal solution for the entire network. Unlike most of the loading algorithms, this approach considers fixed bit allocation and optimizes the power allocation and reduces the interference for the entire network, rather than a single transmitter. We also propose joint time-domain beamforming and power control to reduce the complexity resulting from the number of beamformers and fast Fourier transformed blocks. The proposed algorithm is also extended to COFDM and we show that it improves the performance of those systems.

In this paper, we investigate scheduling in multiuser OFDMA systems. The objective is to maximize the resource utilization in a network, while a required quality of service (QoS) per user is satisfied. A notion of revenue maximization is used to determine the optimal OFDMA subcarrier allocation to different users based on their required QoS. The optimal solution for the problem is presented and its performance and complexity are studied. An iterative low complexity algorithm is also proposed to achieve near optimal performance.

In this paper, we analyze the performance of ultra-wideband (UWB) multiple-input multiple-output (MIMO) systems employing various modulation and multiple access schemes, including time hopping (TH) binary pulse position modulation (BPPM), TH binary phase shift keying (BPSK), and direct sequence (DS) BPSK. We quantify the performance merits of UWB space-time (ST) systems regardless of the specific coding technique. We introduce a framework that enables us to compare UWB-MIMO systems with conventional UWB single-antenna systems in terms of diversity and coding gains. We show that the combination of ST coding and Rake architecture is capable of exploiting spatial diversity as well as multipath diversity, richly inherent in UWB environments. We find the upper bound on the average pairwise error probability (PEP) under the hypothesis of quasi-static Nakagami-m frequency selective fading channels. Finally, simulation results are presented to support the theoretical analysis.

We consider downlink transmission in a multi-user environment, where each base station transmits multiple data streams to its corresponding mobiles using multiple input multiple output (MIMO) OFDM. Using distributed schemes, we find the optimal transmit and receive weight vectors to maximize the total data rate for each user. We consider two scenarios, where in one the total power per user and in the other total power per subcarrier is fixed. In each case, we propose iterative algorithms to maximize the allocated rate per user. We discuss the convergence of our schemes and compare their performances with those of previous work.

The objective of scheduling algorithms in wireless networks is to provide quality of service (QoS) for mobile users in a shared environment and at the same time utilize the system resources efficiently. We have introduced a notion of income maximization to increase throughput for multimedia wireless systems and to maintain the QoS for each user above an agreed level. We have proposed greedy and dynamic programming approaches to solve the optimization problem. The simulation results reveal that our scheduling algorithms provide high network throughput, support QoS even under heavy network loads, and generate high income for service provider.

In this paper, the cyclic shifts of low peak to average power ratio (PAPR) codes used in OFDM transmission is proposed. They comprise a superclass of Golay complementary codes (GCC) with the same level of PAPR (viewed by the discrete OFDM symbols). These codes achieve higher information rate with the expense of lower error correction capabilities. We have proposed a framework for constructing these codes out of GCC. The framework can be applied to obtain the cyclic shift of any code represented by Boolean algebraic functions. An efficient transmission scheme is proposed such that the coding scheme can be switched between the Golay and cyclic Golay codes, based on a feedback from the receiver to perform a better trade-off between the coding rate and bit error rate (BER).

In this paper, we analyze the performance of ultra-wideband (UWB) multiple-input multiple-output (MIMO) systems employing various modulation and multiple access schemes, including time hopping (TH) M-ary pulse position modulation (MPPM), TH binary phase shift keying (BPSK), and direct sequence (DS) BPSK. We quantify the performance merits of UWB space-time (ST) systems regardless of the specific coding scheme. For each modulation scheme, we introduce a framework that enables us to compare UWB MIMO systems with conventional UWB single-antenna systems in terms of diversity and coding gain. Moreover, we adopt the real orthogonal design (ROD) as the engine code for UWB ST codes. We find the closed form expressions of the average pairwise error probability (PEP) bound for all of the schemes under the hypothesis of Nakagami flat fading channels. The extension to frequency-selective fading case is also briefly addressed. Finally, simulation results are presented to support the theoretical analysis.

In this paper, the peak to mean envelope power (PMEPR) of the OFDM codes generated from a 16-QAM constellation is discussed. Maintaining the same level of error correction properties, these codes achieve higher information rate. A new set of 16-QAM Golay sequences having PMEPR bounded up to 3 dB is defined. Many recursive structures are found to generate Super Golay sequences. The recursive algorithm is started by a generalized realization of a 16-QAM sequence as a weighted sum of two QPSK sequences. The coding rate and information rate of the generated code is compared to similar works.

In this paper, the performance of a multiuser wireless network using OFDM, combined with power control and adaptive beamforming for uplink transmission is presented. An adaptive power control algorithm is exploited to achieve the desired signal to noise and interference ratio (SINR) at each subchannel and increase the power efficiency of the mobile transmitter. Therefore, we can achieve a better overall error probability with a fixed total power. A distributed iterative algorithm is used to jointly update the transmission power and the beamformer weights at each subchannel so that it can converge to the optimal solution for both power and beamforming vectors at each subchannel. Another algorithm has been proposed to decrease the complexity resulting from the number of beamformers and FFT blocks. The algorithms use only the interference measured locally by the transmitter. Unlike most of the loading algorithms which optimize the bit distribution and subchannel power allocation for a single transmitter, this approach tries to optimize the power allocation and decrease the interference for the whole network.