Romeo Giuliano

WiMAX fractional frequency reuse for rural environments

WiMAX paves the way for wireless DSL to play a significant role in the broadband wireless access market, especially for rural areas with low population density. Conventional cellular planning methods can be used for point-to-multipoint network design. As an alternative, the Fractional Frequency Reuse (FFR) planning strategy has been recently proposed for cellular systems based on the OFDMA/OFDM radio interface (e.g., WiMAX). In this article we analyze the FFR scheme in rural areas evaluating the increase of the overall system capacity. FFR performances are reported in terms of the average number of bits that can be transmitted per symbol in the area. Finally, comparisons with classical frequency reuse planning are analyzed taking into consideration rural environment characteristics. We show that the FFR scheme can provide extra capacity, slightly penalizing the users at the cell edge.

On the coexistence of power-controlled ultrawide-band systems with UMTS, GPS, DCS1800, and fixed wireless systems

Ultrawide bandwidth (UWB) wireless technology will play a key role in short-range wireless connectivity supporting very high bit rates availability, low power consumption, and location capabilities. UWB can be conveniently deployed in the design of wireless local and personal area networks, providing advanced integrated multimedia services to nomadic users within hot-spot areas. The very large bandwidth required by the UWB signals cannot be exclusively allocated; thus, UWB band overlaps with the bands allocated to many other narrow-band systems. Therefore, the assessment of the interference caused by UWB devices on already-existing systems is of primary importance to ensure coexistence and, therefore, to guarantee acceptance of UWB technology worldwide. We study the coexistence issues between an UWB-based system and universal mobile telecommunication systems, global positioning systems, DCS1800, and fixed wireless access systems and point-to-point (PP) links terminals. UWB interference is evaluated accounting for the UWB signal model, a realistic UWB master/slave system architecture with power-controlled terminals. Furthermore, we analyze the dependence of the UWB interference from the UWB signal parameters and demonstrate through computer simulation that, in all practical cases, a UWB system can coexist with the selected victim terminals without causing any dangerous interference.

Exponential effective SINR approximations for OFDM/OFDMA-based cellular system planning

Classical single carrier cell planning is extended to multi-carrier systems operating over frequency selective channels. Extension is achieved by expressing the link outage probability in terms of the statistics of the effective SINR. Two approximations for the link outage probability are obtained by considering log-normal and Gaussian assumptions for the derivation of the statistics of the exponential effective SINR. A simplified planning procedure is presented and applied to the calculation of the network parameters for the typical two cells interference scenario. Results having accuracy within one dB are obtained for a number of sub-carriers greater than six and for an outage target of 5%.

Performance Evaluation of Detect and Avoid Procedures for Improving UWB Coexistence with UMTS and WiMAX systems

Detect and avoid procedures (DAA) aim at improving ultra-wideband (UWB) coexistence with existing narrowband-wideband systems operating at the same time and in the same area. We assess the interference caused by UWB devices implementing DAA on UMTS, as well as on WiMAX systems, by estimating the time percentage where UWBs interferer with these systems. Both UMTS and WiMAX are supposed to provide primary services with respect to UWB. As a consequence, UWB is not allowed to influence their operations, i.e. no cooperation is assumed between UWB and UMTS, WiMAX devices. In this paper we present and discuss the performances of two DAA techniques, analyzing their dependence on some key UWB transmission parameters, such as the bit rate and emitted power. The proposed DAA procedures are simple to be implemented and their parameters can be selected so to arbitrarily reduce the average percentage of time the UWB interferes with the two considered victim systems

Algorithms for dynamic frequency selection for femto-cells of different operators

The self-installation nature of femtocells sharing the same frequency band can lead to harmful femto-to-femto interference levels. The possibility for operators to share its licensed spectrum allows femtocells of one operator to exploit the frequency resources of other operators. In this paper we propose and analyze the performance of two dynamic frequency selection algorithms that permit to the generic femtocell the smart selection of its operating band, among those available from every operator, starting from the measurements of local interference. The performance of the proposed techniques are analyzed by simulation in terms of outage probability and the achievable Signal-to-Interference Ratio (SIR). It is observed that, in a multi-operator scenario this approach offers significant improvement in terms of achievable network capacity and quality of service to customers.

Fractional Frequency Reuse Planning for WiMAX over Frequency Selective Channels

Fourth generation broadband wireless access systems based on OFDMA/OFDM techniques operate in point-to-multipoint (PMP) configuration so that conventional cellular planning methods can be used for network design. As an alternative planning method fractional frequency reuse (FFR) strategy has been recently proposed for OFDMA/OFDM cellular systems such as WiMAX. For what concerns the determination of the system outage prediction, planning procedures for multi-carrier systems are usually based on bit error rate curves as a function of the average signal-to-interference plus noise ratio (SINR). Such curves are obtained after simulating the entire transmitter-receiver chain including multipath channel. However these approaches do not explicitly evidence the role of the number of M sub-carriers allocated to each user and are computationally intensive. In order to avoid such inconveniences we express the outage probability as a function of the effective SINR which is a function of the M SINRs (one for each sub-carrier). Such function already includes the decoding effects thus avoiding the re-simulation of the decoder behavior. Furthermore, this approach allows to explicitly evidence the role on planning of the number of sub- carriers allocated for one user. For evaluation purposes we apply the procedure in a simple two cell FFR interference scenario. It is shown that the number of sub-carriers can play a significant role in the entire planning process i.e. the reuse distance can be lowered at the expense of an increased number of sub-carriers to be allocated per block.

Adaptive cell sectorization for UMTS third generation CDMA systems

Cell sectorization is commonly used to increase system capacity in cellular systems and is easily implemented. We propose a technique to improve system capacity based on adaptive sectorization. Sectors are rotated and/or resized adaptively in order to equalize the uplink C/I or the total downlink transmitted power in each sector The performance of the proposed procedure is analyzed for both uplink and downlink transmissions. Noticeable performance improvements are obtained when traffic is not uniformly distributed both spatially and in terms of data rate.

Ultra-wideband detect and avoid procedure for WiMAX victims

Detect and avoid (DAA) procedures aim at improving ultra-wideband (UWB) coexistence with existing narrowband/wideband licenced/unlicenced victim terminals operating in the same band at the same time and area. The authors propose a DAA procedure that can be used to reduce the percentage of time the UWB interferes with victims operating in a time division duplexing (TDD) mode. The authors consider a system scenario where a TDD terminal has a primary role and UWB devices create a secondary network on a local area basis. A DAA procedure is implemented only in the UWB devices that adapt their transmissions in order to avoid or reduce interference on primary device(s) in the same area. The performance of the proposed DAA procedure is presented and discussed and its dependence on some key UWB transmission parameters, bit rate and the emitted power is evidenced. It is shown that the DAA timeout parameters can be tuned so as to arbitrarily reduce the average percentage of time the UWB interferes with the considered victim systems even well below the limits imposed by regulatory bodies. It is shown that interference reduction is obtained at the expense of reduced performance of the UWB transmission. The proper selection of DAA timeouts for a desired percentage of UWB interference and UWB link efficiency is discussed.

Consumed power analysis for mobile radio system dimensioning

Cellular mobile radio networks are expected to increase the energy requirements due to their massive deployment. Then, it is required to improve their energy efficiency in order to favor the eco-sustainability and not to obstacle their economic impact. In this paper we study the impact of the power consumption in the design of mobile networks. The evaluation has been performed for GSM and LTE systems. The main aim is the analytical evaluation of the optimal cell radius accounting for the network sustainability and for both coverage and traffic constraints. Overall power consumption is expressed as the sum of static and dynamic terms. The former is due to BSs switch on and signaling, the latter is function of the traffic in the cell. The beneficial effects of power control on energy consumption are evaluated and compared with the non-power controlled case. Finally, reduction in power consumption for LTE respect to GSM is analyzed.

On the UWB coexistence with UMTS terminals

Ultra wide bandwidth (UWB) spread-spectrum techniques will play a key role in short range wireless connectivity providing high bit rates, low power consumption and location capabilities. UWB can be used in the design of advanced wireless local and personal area networks providing integrated multimedia services to nomadic users within hot-spot areas. Due to the very large UWB signal bandwidth, the assessment of the possible interference caused by UWB devices on already existing narrowband systems is important to ensure not conflicting coexistence and, therefore, to guarantee acceptance of UWB technology worldwide. This paper investigates on the coexistence between an UWB-based system and WCDMA-UMTS terminals. UWB interference on the UMTS terminal is evaluated accounting for the UWB signals characteristics and the UWB network architecture. The dependence of the interference from the UWB signal parameters is analyzed through computer simulation and demonstrates that, in all practical cases, UWB system can coexist with UMTS terminals without causing any dangerous interference.