Le Chung Tran

Space-Time-Frequency Code implementation in MB-OFDM UWB communications: Design criteria and performance

This paper proposes a general framework of space-time-frequency codes (STFCs) for multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra-wide band (UWB) communications systems. A great similarity between the STFC MB-OFDM UWB systems and conventional wireless complex orthogonal space-time block code (CO STBC) multiple-input multiple-output (MIMO) systems is discovered. This allows us to quantify the pairwise error probability (PEP) of the proposed system and derive the general decoding method for the implemented STFCs. Based on the theoretical analysis results of PEP, we can further quantify the diversity order and coding gain of MB-OFDM UWB systems, and derive the design criteria for STFCs, namely diversity gain criterion and coding gain criterion. The maximum achievable diversity order is found to be the product of the number of transmit antennas, the number of receive antennas, and the FFT size. We also show that all STFCs constructed based on the conventional CO STBCs can satisfy the diversity gain criterion. Various baseband simulation results are shown for the Alamouti code and a code of order 8. Simulation results indicate the significant improvement achieved in the proposed STFC MB-OFDM UWB systems, compared to the conventional MB-OFDM UWB ones.

Complex Orthogonal Space-Time Processing in Wireless Communications

Complex Orthogonal Space-Time Processing in Wireless Communications incorporates orthogonal space-time processing using STBCs in MIMO wireless communication systems. Complex Orthogonal STBCs (CO STBCs) are given emphasis because they can be used for PSK/QAM modulation schemes and are more practical than real STBCs. The overall coverage provides general knowledge about space-time processing and its applications for broad audiences. It also includes the most up-to-date review of the literature on space-time processing in general, and space-time block processing in particular. The authors also examine open issues and problemsfor future research in this area.

Antenna Selection Strategies for MIMO-OFDM Wireless Systems: An Energy Efficiency Perspective

In this paper, we investigate antenna selection strategies for multiple-input-multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) wireless systems from an energy efficiency (EE) perspective. We first derive closed-form expressions of the EE and the energy efficiency-spectral efficiency (EE-SE) tradeoff in conventional antenna selection MIMO-OFDM systems. The obtained results show that these systems suffer from a significant loss in EE. To achieve a better EE performance, we propose an adaptive antenna selection method where both the number of active radio-frequency chains and the antenna indexes are selected depending on the channel condition. This selection scheme could be implemented by an exhaustive search technique for a small number of antennas. Moreover, we develop a greedy algorithm that achieves a near-optimal performance with much lower complexity compared with the (optimal) exhaustive search method when the number of antennas is large. In addition, the efficacy of power loading across subcarriers for improved EE in the conventional and proposed antenna selection MIMO-OFDM systems is considered. Monte Carlo simulation results are provided to validate our analyses.

Space-Time-Frequency Codes in MB-OFDM UWB communications: advanced order-8 STFC and its performance

The paper examines the potential of the implementation of high-order Space-Time-Frequency Codes (STFCs) in recently proposed STFC Multi-Band OFDM Ultra Wideband (MB-OFDM UWB) communications systems, and compares the performance of two different code structures of order-8 to that of the Alamouti code and of the conventional MB-OFDM UWB system (without STFCs). It is shown that an order-8 STFC provides significantly better error performance, compared to the Alamouti STFC, and much better error performance, compared to the conventional MB-OFDM, without increasing the total transmission power. It is also shown that, for the same total transmission power, the order-8, fully structured code that we proposed previously for conventional wireless Multiple-Input Multiple-Output (MIMO) Space-Time Block Codes (STBCs) communications is an advanced code, providing the best error performance.

A generalized algorithm for the generation of correlated Rayleigh fading envelopes in wireless channels

Although generation of correlated Rayleigh fading envelopes has been intensively considered in the literature, all conventional methods have their own shortcomings, which seriously impede their applicability. A very general, straightforward algorithm for the generation of an arbitrary number of Rayleigh envelopes with any desired, equal or unequal power, in wireless channels either with or without Doppler frequency shifts, is proposed. The proposed algorithm can be applied to the case of spatial correlation, such as with multiple antennas in multiple-input multiple-output (MIMO) systems, or spectral correlation between the random processes like in orthogonal frequency-division multiplexing (OFDM) systems. It can also be used for generating correlated Rayleigh fading envelopes in either discrete-time instants or a real-time scenario. Besides being more generalized, our proposed algorithm is more precise, while overcoming all shortcomings of the conventional methods.

Novel Constructions of Improved Square Complex Orthogonal Designs for Eight Transmit Antennas

Constructions of square, maximum rate complex orthogonal space-time block codes (CO STBCs) are well known, however codes constructed via the known methods include numerous zeros, which impede their practical implementation. By modifying the Williamson and Wallis-Whiteman arrays to apply to complex matrices, we propose two methods of construction of square, order-4n CO STBCs from square, order-n codes which satisfy certain properties. Applying the proposed methods, we construct square, maximum rate, order-8 CO STBCs with no zeros, such that the transmitted symbols are equally dispersed through transmit antennas. Those codes, referred to as the improved square CO STBCs, have the advantages that the power is equally transmitted via each transmit antenna during every symbol time slot and that a lower peak-to-average power ratio (PAPR) is required to achieve the same bit error rates as the conventional CO STBCs with zeros.

Cooperative Communication in Space-Time-Frequency Coded MB-OFDM UWB

Though cooperative communication has been intensively examined for general wireless systems, such as mobile and ad-hoc networks, it has been almost unexplored in the case of space-time-frequency coded multi-band OFDM ultra-wideband (STFC MB-OFDM UWB). This paper proposes a framework of cooperative communication in such systems where nodes are equipped with only one antenna. Simulation results show that cooperative communication might, in some cases, provide better error performance than non-cooperative communication without any additional transmission power.

A generalized algorithm for the generation of correlated Rayleigh fading envelopes in radio channels

Although generation of correlated Rayleigh fading envelopes has been intensively considered in the literature, all conventional methods have their own shortcomings, which seriously impede their applicability. In this paper, a very general, straightforward algorithm for generation of an arbitrary number of Rayleigh envelopes with any desired, equal or unequal power, in wireless channels either with or without Doppler frequency shifts, is proposed. The proposed algorithm can be applied in case of spatial correlation, such as with antenna arrays in multiple input multiple output (MIMO) systems, or spectral correlation between the random processes like in orthogonal frequency division multiplexing (OFDM) systems. It can also be used for generating correlated Rayleigh fading envelopes in either discrete-time instants or a real-time scenario. Besides being more generalized, our proposed algorithm is more precise, while overcoming all shortcomings of the conventional methods.

Performance analysis of STFC MB-OFDM UWB in WBAN channels

This paper investigates the performance of the space-time-frequency coded (STFC) multiband orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) system over wireless body area network (WBAN) channels, using the Alamouti code. Different MIMO configurations and different modulations are used for comparison. The effect of body directions is also assessed by simulation in this paper. Simulation results show that the proposed STFC MB-OFDM UWB system provides a significantly better BER performance, compared to the conventional MB-OFDM system, even from a reasonably low Eb/No range. The simulations also confirm that the body direction affects the system performance significantly due to the availability of line-of-sight (LOS) or partial LOS paths. Overall, the STFC MB-OFDM UWB system can provide an energy efficient and robust, high data rate transmission for WBAN applications.

Quasi-orthogonal space-time-frequency codes in MB-OFDM UWB

This paper examines the application of Quasi- Orthogonal Space-Time-Frequency Codes (QOSTFCs) to advance either data rate or error performance in recently proposed Space-Time-Frequency Coded Multiband OFDM Ultra- Wideband (STFC MB-OFDM UWB) communications systems. It is shown that QOSTFCs can provide significantly better error performance, compared to the conventional MB-OFDM UWB (without STFCs) and to the Orthogonal STFCs (OSTFCs) of the same order, at the same data rate, without increasing the total transmission power. In other words, QOSTFCs can provide higher data rates with the same error performance, compared to OSTFCs.