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Thursday, June 2, 2011

Radio Resource Management (RRM) in Year 2020

The historical evolution of major wireless access systems shows that there is a major introduction of wireless access technology in each decade. In the 1990s we have witnessed worldwide introduction of 2G wireless systems dominated by the GSM standard and voice/SMS applications. In the beginning of the new millennium many operators have extended existing 2G system for supporting data applications (e.g. GPRS and EDGE) and next to that 3G wireless access systems were introduced such as UMTS (later enhanced with advanced packet-data features such as HSPA). According to the announcements from many wireless operators worldwide from 2010 onwards the existing 3G systems will be upgraded with LTE, which is an intermediate step towards real 4G wireless access systems (according to the ITU categorization) labeled as LTE Advanced. 

Next to these deployments, 3G wireless access systems are deployed worldwide based on the IEEE 802.16e standard (i.e. Mobile WiMAX) and planned for upgrade towards 4G wireless systems 802.16m. As the wireless systems evolve, the supported range of applications is extended from voice only to voice and data applications and towards full multimedia wireless applications support. Additionally, the supported wireless access speed typically used in these systems increases from few hundreds of Kbps toward few Mbps per user.

The RRM in wireless access system in year 2020 will be characterized by three major trends: dynamic and effective usage of the available radio spectrum, providing high bit-rates also for users at cell edge, and reduction of the operational cost (OPEX) for the wireless operators. The dynamic and effective usage of the available radio spectrum will be shaped by the following important evolutionary trends:

(a) The system bandwidth of the advanced HSPA+, LTE and WiMAX systems can be dynamically adjusted based on the availability of wireless spectrum. Note here that HSPA + systems have limited granularity of bandwidth adjustments by 5 MHz chunks.
(b) The newest generation wireless access points will be software reconfigurable in the amount of spectrum that is used for the radio access technologies (RATs) that they support. For example, 3GPP aims to standardize multi-mode base stations that support GSM, UMTS/HSPA + and LTE radio access technologies with adjustable system bandwidths.
(c) As the RF technology becomes advanced and cheaper the end-user terminals can support different RATs with adjustable system bandwidths.

Based on this spectrum usage flexibility the future wireless access systems will abandon the current rather static system bandwidth deployment and adjust the used bandwidth per supported RAT based on current traffic demand. The RRM algorithms will reconfigure the system bandwidth per radio access technology in order to improve its utilization. Currently, this is not the case within the wireless access systems because all RRM algorithms have the given system bandwidth as a fixed starting point. Note here that, based on regulatory limitations, it is expected that in the future, wireless access operators can share spectrum usage among each other in the form of licensing agreements, dynamic spectrum sharing, etc. As the wireless access technology reaches the physical limits (e.g., Shannon capacity bound) of the radio, the deployment of smaller cells (pico and femto), cooperative transmissions, and relaying concepts are seen as major contributors towards increased data rates for the end user. For example, a wireless operator can deploy pico/femto cells in order to increase the signal level at the end-user and also share the available spectrum with smaller number of users due to the rather limited coverage of the pico/femto cells.

An important deployment choice is the spectrum coordination among the different cell layers, i.e., macro layer and the pico/femto layer, as presented below;

The overlap of bandwidth between these different coverage layers will be guided by the spectrum availability, quality targets, and capability of the RRM algorithms to coordinate the resource usage at the different coverage layers. From RRM perspective, having no spectrum overlap between the different coverage layers, seen in the illustration above, is the least challenging deployment scenario. However, for the partial or full overlap the RRM algorithms have to limit the negative interference effects originated from the different coverage layers. Similarly, for relaying concepts the RRM algorithms have to coordinate the usage of the radio resources between the donor Macro cells and the relays/repeaters in order to avoid negative cross-interference effects. In order to facilitate this RRM coordination the necessary measurements and signaling exchange have to be provided between the Macro cells and pico/femto/relay nodes.

Regarding the reduction of OPEX (operational expenditure) there are two important RRM trends that are expected for future wireless access systems. First, reducing the energy consumption in the wireless access part of the network is considered very important due to the OPEX reduction as well as the environmental targets of operators worldwide to reduce the carbon emissions of their wireless networks and increase their energy efficiency. Next to the enhanced energy efficiency of the wireless access points, the operators consider dynamically switching on/off their wireless access points as the traffic demand varies during the time of the day.

Second, as the operators have to operate three wireless access networks (2G, 3G, and 4G) and the complexity of these networks increases it is important that the operational costs are decreased by providing intelligent algorithms for automatic configuration and optimization in the network nodes. This concept is illustrated as self-organizing networks. The standardization bodies such as 3GPP have recognized this important property of the future wireless access systems and introduced various SON functionalities for the LTE system. The illustration shows the concept of self-organisation network.

The self-configuration algorithms take place when new wireless access nodes are introduced in the system or when previously switched off base station is activated. The task of these algorithms is to configure all the necessity parameters in plug-and-play fashion.

The self-optimization algorithms continuously optimize the wireless access network based on measurement data from the wireless access nodes and the end-user terminals. With this concept, the configuration of the wireless access nodes is a continuous and a dynamic process that aims at optimizing the performance of the network as given by the operator’s policy.

The self-healing algorithms are activated when a particular network node is having a failure or partially incapable of supporting traffic. The self-healing algorithms aim at mitigating the negative effects of this failure by readjusting the neighboring wireless access points to absorb as much of the traffic, in the coverage area of the failed node, as possible.

In summary The most important trends in the RRM functions are the dynamic reconfigurations of the system bandwidth domain of the macro cell layer and between the macro and pico/femto cell layer or the repeater/relaying nodes. Additionally, system bandwidths can be reconfigured among the supported 2G, 3G, and 4G systems at the wireless operators. Due to targets of reducing costs, energy consumption, and carbon emissions, RRM functions will dynamically switch on/off parts of the wireless access systems according to the traffic demand and quality targets. The RRM functions in wireless access points will have self-organization capabilities to continuously optimize network performance based on access point and end-user measurements. This self-organization concept will drastically reduce the amount of operational costs

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