Resource Management and Cell Planning in LTE Systems

Abstract

Future 4G cellular systems will address the need for capacity increase for the support of diverse services. It is therefore of fundamental importance to design innovative 4G cellular systems able to support the increase in the traffic demand. This Chapter deals with LTE systems and the design of a new reuse scheme, called Soft Frequency Reuse (SFR), that is able to increase the cell capacity that is studied, considering the impact of different scheduling schemes and of different user mobility patterns. A consistent SFR scenario has been implemented in both Ns-3 and OMNeT++ environments. An analytical approach is proposed to evaluate the cell capacity with SFR that has been validated by means of Ns-3 simulations. Finally, OMNeT++ simulations have permitted to highlight the significant impact of the scheduling scheme and user mobility on cell capacity; different mobility patterns have been taken into account.for carrying all traffic types, LTE is expected to provide support for IP-based traffic with end-to-end Quality of Service (QoS) [3].In the LTE architecture, E-UTRAN consists of a single node, i.e., the eNode B (eNB) that interfaces with the User Equipment (UE). The protocol architecture of the LTE air interface can be separated between control and user planes. In the user plane, the application creates data packets that are processed by protocols such as TCP, UDP and IP; instead, in the control plane, the Radio Resource Control (RRC) protocol generates the signalling messages (radio resource management, admission control, enforcement of QoS negotiated, ciphering/deciphering of user and control plane data, compression/decompression of downlink/uplink user plane packet headers, etc.) that are exchanged between eNB and UE. In both cases, the information is processed by the Packet Data Convergence Protocol (PDCP), the Radio Link Control (RLC) protocol, and the Medium Access Control (MAC) protocol, before being passed to the physical layer (PHY) for transmissions. IP packet segmentation is performed at the RLC layer.The aim of this Chapter is to analyse a special frequency reuse scheme proposed for LTE and called Soft Frequency Reuse (SFR). The interest is to study SFR with both analysis and simulations in order to determine the configuration that permits us to maximize cell capacity. This work represents a significant improvement with respect to the study carried out in [3], where we have adopted a less accurate modelling of SFR and where we have not conducted a simulation study to validate the analysis proposed. We expect that the present work can help network planners when designing 4G LTE systems based on SFR.

Soft frequency reuse schemes for heterogeneous LTE systems

“…We can see that 3B-ISFR has always a lower macro cell outage probability than 3B-SFR. The macro cell outage probability of 3B-ISFR depends on the selected R s value: the best results are achieved with R s = 3 kb/s for 1000 UEs/macro cell, when 3B-ISFR outperforms 2B-SFR for a wide range of 3 SINR has deterministic values since in this study we do not consider fading variations, but just a shadowing margin is included in the path loss model [1]. α values.…”

“…Hence, the total number of messages exchanged in this first round from steps #2 to #4 is N r + 2. At the next run from steps #4 to #6 we have N r − 1 + 2 message exchanges, then N r − 2 + 2 1 In this algorithm, we do not consider to coordinate the FRP with micro cells of adjacent macro cells: micro cells belonging to different macro cells are decoupled in the FRP allocation phase to simplify the problem and not to consider the feedback effects in a macro cell due to the FRP decisions taken in micro cells of adjacent macro cells. This limitation will be removed in the simulations in Sec.…”

“…According to Table 1 in [1], let us assume that the eNB uses the i-th LTE modulation and coding level for the transmissions to a generic UE u depending on its SINR value (downlink) above the threshold of the i-th mode. The corresponding efficiency η i is written below where r i and M i denote the code rate and modulation size of the i-th mode:…”

“…This simulator takes several aspects of a real LTE system into account, using different modules for path loss, SINR calculation, etc. In particular, we use the Stanford University Interim (SUI) model [8] for the propagation loss in macro nodes (path loss exponent of 4.16 for the intermediate scenario and shadowing margin of 15.8 dB [1]) and the WINNER II model [9] for micro nodes (path loss exponent of 2.5 and extra attenuations due to walls so that there is a 15 dB wall attenuation at 150 m from micro cell eNB). The basic settings of our simulator are [1]: honeycomb regular macro cell tessellation (macro cell radius R = 1664 m and distance between two neighboring macro cell eNBs d = R× √ 3), macro cell (micro cell) transmission power P a = 46 dBm (P b = 30 dBm), and system bandwidth of 20 MHz.…”

“…The exponential growth of mobile data traffic is a pressing need that evolving 4G cellular networks (e.g., Long Term Evolution -Advanced, LTE-A) need to address [1]. In this context, Heterogeneous cellular Networks (HetNets) comprising of conventional high-power macro cell base stations (eNB) overlaid by low power nodes, also known as small cells, are considered to be an efficient solution to improve resource reuse and spectral efficiency, while offloading user traffic from macro cells towards small ones.…”