Yuteng Wu

Symbol error rate analysis for cooperative diversity networks by distributed embedded space time code

In this paper a special version of cooperative distributed space time coding for the relays network is proposed. According to this system model relays cooperatively collaborate with the sources to transmit the space time code to the destination. Process of the transmission consists of two phases. In the first time phase source broadcast the information to the destination and relay. In the next time phase, the source and relay cooperatively send signals to the destination by using an embedded space time coding. Structure of embedded space time code is based on singular value decomposition of circulant matrix. Relays are assumed to be non-regenerative amplify-and-forward. Theoretical analysis for calculating the bit error rate (BER) has been done based on maximum ratio combining (MRC). Simulation results for the case of one relay, one source and destination through the Rayleigh fading channel has been done and compared with the scenario when transmitter and relay used the Alamouti code.

A circulant based space-time coding for multiple input multiple output system in fading channels

In this paper a new space time coding, which is suitable for high data rate communications is proposed. In this approach data is encoded by using a decomposition of a circulant matrix and the output of encoder is splitted into N streams to be transmitted simultaneously to N transmit antennas. The performance of this multiple input multiple output system is evaluated in a Rayleigh fading channel. Its performance in terms of symbol error rate, diversity gain and complexity is obtained. Simulation results show that with a perfect channel estimator, when channel state information (CSI) is available at the receiver, the Circulant Space Time code (CSTC) has a better symbol error rate via signal to noise ratio in compared to the spatial multiplexing and near to orthogonal space time block code.

Multiuser network coding based on DFT matrices design

Cooperative communications are candidates for emerging distributed Network designs. In this paper, a new design of distributed network coding is introduced. The proposed design are based on algebraic constructions in Finite Fields using the Discrete Fourier Transform (DFT). These set of codes provides an alternative to Generalized Dynamic Network Codes (GDNC) and are based on the Hamming distance metric. Using this metric, the codes have maximum diversity and scales over large networks. In our work, we show that a compromise on the Field Size becomes necessary for enforcing the distributed Network codes over large networks. While the diversity offered by these codes are optimum, a unique feature of these codes are the ease of generation and scalability to larger network sizes. Results are provided and compared with theoretical evaluations.

Embedded space–time codes for multiple-input–multiple-output systems in Rayleigh fading

In this study, novel designs of embedded space–time multiplexing codes are presented. The space–time codes are constructed initially based on the decomposition of normal matrices that produce diagonal structures. The eigenvalue decomposition of circulant matrices, a type of normal matrices, can generate these codes. A key constraint in the design is that only the diagonal matrices are function of data. Since the components of the diagonal matrix are linear combinations of the data, the codes are called embedded. These codes provide an embedded diversity, full rate and enable multi-user applications with reduced interference. Later constructions in Galois fields are used to reduce the constellations expansion introduced by the dependency of the eigenvalues of the diagonal matrix to the data. The pairwise error probability for the codes is derived. Performance of the codes based on simulation and theoretical analysis, are compared with the conventional spatial-multiplexing codes and other complex orthogonal designs. Simulation results demonstrate the advantage of the proposed codes. Simulation has been done for Rayleigh-fading channels with known channel-state information.

Multiuser Network Codes based on symmetric matrices

Cooperative communications is a candidate technology for future network designs. In this paper, a design of distributed network coding is introduced. The proposed design are based on algebraic constructions in Finite Field using symmetric Matrices. These set of codes are an alternative to Generalized Dynamic Network Codes (GDNC). A rich feature of these codes are a high diversity and ease of scalability to larger network designs. Finite fields has a unique feature of constraining the signal energy and its performance does not deteriorate much when transmitted through fading channels. Results are compared with theoretical evaluations.

Space time block code for four time slots and two transmit antennas

In this paper a special space time coding is proposed for communication systems which is equipped with four time slots and two antennas. The launched code has full rate and full diversity and maximum likelihood (ML) decoding requires joint detection of four real symbols. Simulation results for bit error rate (BER) analysis show that the proposed STBC outperforms previously presented schemes.

Signal sets for constellation expansion in NOMA

In this paper, alternative signal set designs for higher order constellations based on combinatorial structures are proposed. These system designs are practical for 5th and future generation of systems. Non-Orthogonal Multiple Access (NOMA) is currently recognized as a promising multi-access technique for fifth generation (5G) networks. NOMA techniques ensure that multiple users share the same spectrum or resource. Sharing the same resource by multiple users results in interference and an expansion in the received constellation. This expansion is driven by the number of users transmitting and the constellation for each user. Solutions for these expansions involved rotations of transmit users constellations, lattice decoding, transmission at orthogonal frequencies with different phases and other solutions. The proposed system, using a non-orthogonal combinatorial structure provides a large signal set that is distinguishable at the receiver. Using a non-orthogonal format, a solution is proposed where large number of users share the channel. Performance is evaluated using upper bounds for their error probability considering the interference between users.

A Multidimensional design for Multi-user communications

In this paper, we propose a Multi-user (Mu)-Multidimensional system in a wireless communication scenario. This design uses precoding and reordering of data in multiple dimensions. Hence it produces an embedded diversity due to the linear combination of all input elements. However, because of this precoding, there is a constellation expansion that needs to be controlled. It is widely known that constellation design is a complex and systematic process. We propose two sub-optimum methods aimed at reducing the constellation expansion and the implementation burden.

Network Codes Based on Symmetric Matrices

The key challenges of future wireless communication are improving data rate and quality of service. However, the challenges posed by having a large number of users such as power control, frequency synchronization and independently faded channels scales with the number of users. Cooperative communications is a candidate technology for high data rate and multi-user communications. In this paper, a new design of distributed network codes is introduced. These network codes are based on algebraic constructions in finite fields. Finite fields have an attractive feature of constraining transmit signal energy and is resilient to fading channels. The codes have high diversity and scale up with an arbitrary number of users. The codes are an alternative to Generalized Dynamic Network Codes without a restriction on the field size. Results are compared to theoretical evaluations and systems with similar configurations.

Impact of channel estimation errors on the performance of space time code

In this paper, we study the performance of space time block code (STBC) under the constraint that the receiver must rely on imperfect channel state information. This is done in order to verify and compare the performance that can be expected in an actual space time code system. The sensitivity and robustness of space-time block codes to varying levels of error in the amplitude and phase of the estimates will be illustrated using a series of simulations. This new information could be used to help design and verify the performance of a channel estimation scheme based on the insertion of pilot sequences into the data stream of each transmit antenna. The imperfect channel estimates will be created by taking the actual fading coefficients introduced into the channel and applying some degree of error into either the magnitude or the phase of those coefficients before decoding. This simulates the inability of an estimation scheme to predict the channel characteristics with perfect accuracy.