Ádám Knapp

A survey of handover management in LTE-based multi-tier femtocell networks

Ubiquitous mobile communication requires increased capacity and appropriate quality guarantee for services. To meet these demands next-generation mobile network operators will deploy small cells next to conventional base station structure intensively to enhance capacity and service coverage for customers. Implementation of seamless handover between first tier (macrocell layer) and second tier (small cells) is one of the key challenges to fulfill the QoS requirements. In this paper we introduce the reader to the details of the handover procedure: information gathering, decision strategies and the base station exchange process. All these three phases face difficulties in multi-tier networks. High dense femtocell deployment makes handover related information gathering very hard, efficient handover decision mechanisms are vital to reduce the number of unnecessary handovers and avoid ping-pong effect. Last but not least base station exchange has to be accelerated to achieve appropriate system performance. Next a comprehensive survey of state of the art handover optimization solutions in 3GPP LTE/LTE-A Home eNodeB handover management is presented which includes the actual version of 3GPP LTE/LTE-A HeNB handover procedure.

Average system capacity in a two-tier LTE environment with random waypoint mobile users

Delivery of multimedia transmission in mobile networks requires appropriate coverage and enough capacity to provide Quality of Service. Femtocell systems can be suitable network components to handle these challenges. State of the art mobile and wireless networks introduce MIMO transmitters and receivers to increase available capacity significantly in exchange of very sophisticated signal processing algorithms. In this paper we present a new system model for OFDM-based femtocell systems which allows computing the average system capacity for mobile users using multimedia applications.

Performance analysis of pulse position based chirp spread spectrum technique for multiple access

The paper presents a new wireless communication system using Chirp Spread Spectrum (CSS) transmission. The applied modulation scheme is extended with Pulse Position Modulation (PPM) to transmit data for multiple mobile terminals simultaneously. The proposed system is a Low-Power Wide-Area Network (LPWAN) providing very reliable and robust transmission, especially for terminals moving with high speeds or at long range, but has limited throughput. These features makes it a perfect candidate for such communication environments, where transmitting control or other critical information is necessary. The extensive analytical investigations are also presented regarding to the instantaneous and average symbol-error rate (SER) in Rayleigh fading channel. The numerical results show that the Pulse Position based Chirp Spread Spectrum for Multiple Access (PP-CSS-MA) technique is able to provide higher data rates comparing to the original CSS transmission, while only a slight increase of SNR is requied to achieve the same Symbol-Error Rate (SER). Furthermore, the average transmission power barely increases when applying higher data rates of PP-CSS-MA.

Statistical based optimization of number of pilot signals in LTE/LTE-A for higher capacity

LTE/LTE-A systems use pilot or reference signals for channel estimation occupying a significant part of the time-frequency grid. In this paper the efficiency of channel equalization over a flat-fading channel is analysed taking into account the estimation error. Closed form formulas are provided to calculate symbol-to-error ratio depending on the estimation error using QPSK modulation. Then, a trade-off is proposed based on the statistical behaviour of estimation error to maximize the effective channel capacity by tuning the number of pilot signals on subcarrier level. Higher amount of reference signals improves the channel equalization, but occupies unnecessary resource slots reducing the effective channel capacity. Numerical results confirm that choosing the appropriate number of reference symbols is able to maximize the effective channel capacity. Furthermore, the results are compared to the LTE/LTE-A standard and it is found that the effective channel capacity is better in every investigated scenario.

A New Synchronization Method for Direct Sequence Spectrum Spread Based Systems

Abstract For precise indoor localization accurate synchronization is necessary. In this paper we propose a new synchronization method for direct sequence spread spectrum modulation based systems, which enables a more accurate correlation peak detection. We provide comprehensive statistical analysis and numerical results for the decision error probability assuming both coherent and non-coherent receiving via an AWGN channel. The essence of the proposed method is the two overlapping correlators, which allows taking into account the statistically not independent noise components to reduce the error probability of the correlation peak detection.

The effect of a new hybrid decision handover algorithm on QoS in two-tier LTE-A network

New sophisticated solutions are required in next generation networks to provide appropriate quality of service for users. The introduction of small cells in Long Term Evolution (LTE) raises numerous problems along with undoubted advantages to the engineers and researchers. In this paper a new handover decision algorithm is described for two-tier macrocell-small cell LTE-Advanced (LTE-A) using network map, i.e. positioning service and additional network provided information. The proposed algorithm processes information on the reported RSSI, the speed of users and the actual load of cells extended with a sliding averaging window on RSSI. Simulation results focus on QoS parameters and show that the new decision procedure ensures higher system throughput and lower delay than the legacy, strongest cell algorithm in most scenarios.

Improving wireless network throughput with constant dimension subspace codes

The application of network coding in wireless environment provides a new horizon for throughput enhancement. By means of network coding the throughput of a network can be increased very efficiency. In this paper we use a family of constant dimension subspace codes called lifted rank-metric coding (LRMC) and investigate its performance in a general wireless environment. LRMC process reduces the number of packet transmissions and packet delivery time, thus improves the throughput of the network. Firstly, we investigate the gain on deterministic grid structure, afterwards on a random topology, where the node locations are modeled by spatial Poisson point process (PPP). Simulations were evaluated for error-free and lossy packet network scenarios.

Application of LTE small cells in urban environments for higher capacity

Extending conventional LTE systems with small cells offer new horizon in mobile communications to provide better coverage and enhance capacity. OFDM-based air interfaces allow sharing this capacity in a very flexible way. MIMO transmitters and receivers introduce significant increase in capacity in exchange of very sophisticated signal processing algorithms. In this paper we present a new system model for OFDM-based LTE small cell systems which allows computing the overall system capacity when mobile MIMO users move along edges of a graph, e. g. roads.