Ugljesa Urosevic

A solution for performance improvements of OFDM-CDMA system with pilot tone

In this paper, MIMO OFDM–CDMA downlink scheme is proposed as a solution for improving performance of the OFDM–CDMA downlink system with pilot tone and threshold detection combining (optimum TDC). The new presented system with MIMO included uses space–time block coding applied to two, three and four transmit antennas and it has an arbitrary number of receive antennas. Bit error rate performance in the case of Ricean frequency selective fading is evaluated for the original system as well as for the one with MIMO included. For that reason an adequate simulation model is developed. The results show that the proposed system significantly outperforms the OFDM–CDMA downlink system with pilot tone and optimum TDC.

BER performance of MIMO OFDM-CDMA system in ricean fading channel

In this paper, bit error rate (BER) performance of the MIMO OFDM-CDMA system, in case of Ricean frequency selective fading, is evaluated using originally developed computer simulation. The assumed system uses space-time block coding applied to two, three and four transmit antennas and has arbitrary number of receive antennas. Channel estimation is performed by implementing pilot sequences at each transmit antenna. The results are compared with BER results of the competitive OFDM-CDMA down link system with threshold detection combining (optimum TDC). The results show that the presented system provides lower BER, even when less subcarriers are used for transmitting single data symbol, than its competitive solution.

A New Solution for Simple Cooperative Relaying

In this paper we present a new simple cooperative relaying scheme. The proposed scheme is compared with simple cooperative schemes with virtual orthogonal space time block coding (OSTBC) and quasi orthogonal space time block coding (QOSTBC). Every of these three schemes includes one base station with two antennas, two relay stations each with a single antenna and one mobile station with a single antenna. The aim of the proposed scheme is to preserve, as much as it is possible bit error rate (BER) performance of the cooperative scheme with virtual OSTBC, but with increased code rate. It is shown that the presented scheme obviously outperforms simple cooperative scheme with virtual QOSTBC, while in comparison with simple cooperative scheme with virtual OSTBC has very similar BER performance and increased code rate.

New schemes for increasing code rate of the OFDM based virtual OSTBC

In this paper we propose new schemes for increasing code rate of the orthogonal frequency division multiplexing (OFDM) based virtual orthogonal space time block coding (OSTBC). The proposed schemes are used for creating virtual 4×1 multiple input-single output (MISO) channel. These schemes include one base station (BS), one relay station (RS), both equipped with two antennas and one mobile station (MS) with a single antenna. One of the main disadvantages of the virtual OSTBC is its code rate, so we propose new schemes with greater code rate while preserving bit error rate (BER) of the scheme with virtual OSTBC. We proposed new schemes with greater code rate on the first hop while the code rate on the second hop remains the same. The code rates between BS and RS in the proposed schemes are 1, 4/5, 2/3 and 4/7, while in the scheme with virtual OSTBC the code rate is only 1/2. Also, we proposed subcarriers mapping in best to worst manner (BW) at RS in order to improve BER performance. The simulation results show that the proposed schemes maintain BER performance very close to the scheme with virtual OSTBC.

New simple cooperative relaying schemes

In this paper we propose new schemes for increasing code rate of simple cooperative relaying with virtual orthogonal space time block coding (OSTBC). The proposed schemes are used for creating virtual 4×1 multiple input-single output channel (MISO). These systems include one base station (BS) with two antennas, two relay stations (RS) each with a single antenna and one mobile station (MS) with a single antenna. One of the main disadvantages of the virtual OSTBC is its code rate, so we propose new simple cooperative relaying schemes with greater code rate while preserving BER of the scheme with virtual OSTBC. We proposed new schemes with greater code rate on the first hop while the code rate on the second hop remains the same. The code rates between BS and RSs in the proposed schemes are 1, 4/5, 2/3 and 4/7, while in the scheme with virtual OSTBC the code rate is only 1/2. The simulation results show that the proposed schemes maintain BER performance very close to the scheme with virtual OSTBC.

MISO model for improving performance of OFDM-CDMA system with pilot tone

In this paper, MISO OFDM-CDMA downlink scheme is proposed as a solution for improving performance of the OFDM-CDMA downlink system with pilot tone and threshold detection combining (optimum TDC). Space-time block coding (STBC) applied to two, three and four transmit antennas is implemented in the proposed scheme. Original simulation model is developed for obtaining bit error rate (BER) performance in the case of Ricean frequency selective fading. Evidently better BER performance can be achieved with proposed system, while maintaining the same spectrum efficiency. Besides that, spectrum efficiency can be improved with the proposed system, i.e. proposed scheme with decreased number of subcarriers retains better BER performance. Also, implementation of very complex equalization technique such as optimum TDC is avoided. Instead of that orthogonal restoring combining (ORC), as a considerably simpler equalization technique is implemented.

MISO model for improving BER performance of OFDM-CDMA system with pilot tone

In this paper, MISO scheme is proposed as a solution for improving BER performance of the OFDM-CDMA downlink system with pilot tone and threshold detection combining (optimum TDC). BER (Bit Error Rate) performance is evaluated through originally developed simulation model in the case of Ricean frequency selective fading. The analyzed system uses space-time block coding applied to two, three and four transmit antennas. Channel estimation is performed by implementing pilot sequences at each transmit antenna. The simulation results show that the proposed scheme provides significantly better BER performance.

Distributed MIMO solutions for peer-to-peer communications in future wireless systems

The future generation of wireless networks is expected to support a significantly large amount of mobile data traffic, massive number of wireless connections and devices, achieve better cost, increased energy and spectral efficiency, improved quality of service (QoS) in terms of communication delay, capacity, reliability and security. The main techniques that will enable these features are massive multiple-input, multiple-output (MIMO), utilization of higher frequencies, particularly millimeter-wave (mmWave) frequencies, super dense and deployment of cells, peer-to-peer (P2P) communications, heterogeneous network (HetNet) implementation, etc. Here we present new solutions for implementing distributed MIMO techniques for P2P communications.

Performance improvements of virtual QOSTBC systems

In this paper we propose new solutions for improving performance of the virtual quasi orthogonal space time block coding (QOSTBC). The considered schemes are used for creating virtual 4x1 multiple input-single output (MISO) channel. These schemes include one base station (BS), one relay station (RS), both equipped with two antennas, and one mobile station (MS) with a single antenna. The simulation results show that the proposed solutions can provide evidently better bit error rate (BER) performances and greater energy efficiency.

Performance improvement of OFDM based virtual QOSTBC

In this paper we present a solution for performance improvement of orthogonal frequency division multiplexing (OFDM) based virtual quasi orthogonal space time block coding (QOSTBC). The considered scheme is used for creating virtual 4×1 multiple input-single output (MISO) channel. This scheme includes one base station (BS), one relay station (RS), both equipped with two antennas, and one mobile station (MS) with a single antenna. In this 2-hop scheme, the procedure at the RS is reduced due to omitting the decoding process. The simulation results show that the proposed solution provides evidently better bit error rate (BER) performance.