Milica Pejanovic-Djurisic

SDN Based Mobile Networks: Concepts and Benefits

Mobile Internet traffic is expected to grow faster than the fixed Internet traffic in a near future. Since, today’s broadband networks are approaching theoretical limits in terms of spectral efficiency per link, mobile operators are compelled to seek for new solutions that will be able to accommodate the expected traffic growth and improve their position in the competitive market. Addressing those challenges with current inflexible, not scalable and complex architecture is very hard, if possible at all. Software defined networking (SDN) is a new networking architecture paradigm that holds great promise to overcome many of mentioned limitations and provides required improvements in performance by decoupling control functions from underlying physical infrastructure. In this paper, we explain key reasons for transition to SDN based mobile networks and briefly describe several proposals of design scenario. Special emphasis is placed on SDN’s contribution to more efficient inter-cell interference management, traffic control and network virtualization.

A Novel Method for Performance Analysis of OFDM Polarization Diversity System in Ricean Fading Environment

OFDM (Orthogonal Frequency Division Multiplexing) is proven to be a very effective modulation and multiple access technique that enables high data rate transmission. Due to its good performance it is already implemented in several standardized technologies, and it is very promising technique for the next generation wireless communication systems. Still, further system performance improvements under severe frequency selective fading conditions are necessary, and they can be obtained implementing diversity, at either transmit or/and receive end of a wireless link. Since polarization diversity can be realized using only one compact, dual polarized antenna, it can be considered as an attractive, space and cost effective solution. Analysis presented in this paper shows that implementation of dual polarized antenna at the receiver can lead to significant performance improvement, under certain propagation conditions. In order to calculate BER (Bit Error Rate) for the considered OFDM polarization diversity system with a certain level of the received signals correlation, we propose a novel analytical method. The obtained results are compared with the ones attained by simulation.

On the optimal subcarrier mapping scheme in OFDM decode-and-forward relay systems

BER performance of the DPSK (Differentially Phase Shift Keying) modulated dual-hop OFDM based DF (Decode and Forward) relay system, implementing subcarrier mapping (SCM) at the relay (R) station, is examined. Closed form BER expressions are derived for the two SCM schemes, denoted as BTB SCM (Best-to-Best Subcarrier Mapping) and BTW SCM (Best-to-Worst Subcarrier Mapping) in the scenario with Rayleigh fading on both hops. The accuracy of the obtained analytical results is verified through comparison with the simulation results. It is shown that BTB SCM scheme achieves the lowest BER results for all SNRs (Signal-to-Noise Ratios) of interest, which approves it to be the optimal SCM scheme in dual-hop OFDM DF relay systems, as it has already been known that the same SCM scheme maximizes the capacity.

BER performance of OFDM Amplify-and-Forward relaying system with subcarrier permutation

We perform error probability analysis of the uncoded OFDM fixed gain Amplify-and-Forward (AF) relaying system with subcarrier permutation (SCP). Two SCP schemes, named: the best-to-best SCP (BTB SCP) and the best-to-worst SCP(BTW SCP) are considered. Closed-form expressions for the bit error rate (BER) of the above SCP methods are derived. Numerical results manifest that these SCP schemes may outperform one another, depending on the average channel conditions of the links involved. That is, BTB SCP is better in the low signal-to-noise ratio (SNR), while BTW SCP prevails in the medium and high SNR regime. Thus, it could be concluded that OFDM AF relaying systems may switch from the BTB SCP to BTW SCP in order to achieve optimum BER performance.

On the ergodic capacity of dual-hop OFDM based DF relay system with subcarrier mapping

In this paper ergodic capacity analysis of the dual-hop OFDM decode-and-forward (DF) relay system implementing subcarrier mapping (SCM) at the relay station (R) has been conducted. A scenario with no direct communication between the source of information (S) and destination terminal (D), with Rayleigh fading statistics on both hops is considered. Closed form expression for the achievable ergodic capacity in the case of equal average signal-to-noise ratios (SNRs) on both hops is derived, while for the case of unequal average SNRs on hops a tight upper bound is obtained. Comparison with the simulation results has confirmed the accuracy of the undertaken analytical approach. The obtained results have shown that significant capacity enhancement is achieved through implementation of best-to-best SCM (BTB SCM) scheme, even in the case when the average SNRs on hops are significantly different. Having in mind that this SCM scheme also improves bit error rate (BER) performance of the considered system, then it can be recognized as a very interesting solution for 4G cellular systems.

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.

Dual-Hop Amplify-and-Forward Relay System Over Non-identical Ricean Fading Channels

Motivated by the importance of the Ricean statistical model in describing communication channels, in this paper we study the performance of a dual-hop amplify-and-forward relay transmission over non-identical Ricean fading channels. A complete analytical model for the performance evaluation of the analyzed system is presented. The probability density function, cumulative distribution function and moment generating function of the total received signal-to-noise ratio are derived in a form of rapidly converging infinite sum. Based on the derived expressions, we further proceed with the calculation of the outage probability and the average bit error rate performance of the system under study. Numerical and simulation results confirm the validity of the proposed analytical model. Additionally, we analyzed the impact of unbalanced SNRs of the two hops on the error performance of the considered relay system.

SDN-based concept of QoS aware heterogeneous wireless network operation

Software defined networking (SDN) is a new paradigm for wired networks which cleanly decouples control and the date plane, leaving all control functionality to logically centralized entity. By centralizing network intelligence it provides better visibility of the network conditions, and hence allows more sophisticated traffic management. In this paper, we investigate how the adoption of SDN concept can improve efficiency of heterogeneous wireless environments. We present architectural solution for SDN-based wireless networks, and elaborate on opportunities it provides from various perspectives. In order to exploit benefits of scalable cloud infrastructure, integration of Network Function Virtualization (NFV) is proposed. In particular, the proposed architectural solution allows fast deployment of new services for network operators, gives flexible content delivery options for application providers, and provides improved quality of experience (QoE) for end users.

Performance improvement of two-hop cooperative relay system under correlated Ricean fadings

This paper studies performance of two-hop cooperative relaying system employing regenerative decode-and-forward (DF) technique. Infrastructure based relay equipped with dual-polarized antenna is assumed, performing maximal ratio combining of the received signals. Link between the source and the relay is characterized as two correlated and non-identical Ricean fading channels. There is also direct communication between the source and the destination. In order to determine the level of improvement introduced through the implementation of polarization diversity, performances of the considered system are compared with the DF relay system with single antenna relay. The obtained results show that, using polarization diversity, the same BER (Bit Error Rate) values can be obtained with significantly lower SNR (Signal to Noise Ratio), despite a certain level of correlation and power unbalance between the diversity branches. In that manner, compared to the system with no diversity, the total needed transmit power for achieving the same level of system performances is reduced, and thus more energy efficient communication is enabled.

Ergodic capacity of OFDM AF fixed gain relay system with subcarrier mapping

In this paper ergodic capacity of dual-hop OFDM amplify-and-forward (AF) fixed gain (FG) relay system, implementing capacity maximizing best-to-best subcarrier mapping (BTB SCM) scheme at the relay (R) station, is examined. Scenario without direct communication between the source of information (S) and destination terminal (D) is considered, with Rayleigh fading statistics on both hops. A closed form relation for the tight lower bound of the system ergodic capacity is derived. Comparisons of the obtained ergodic capacity results with the simulation results have confirmed the accuracy of the undertaken analytical approach. Thus, the derived analytical expression presents very useful and most accurate available tool for the performance assessment of the OFDM AF FG relay system with BTB SCM, considered to be interesting solution for the next generation of mobile cellular systems.