Per Hjalmar Lehne

Spectrum micro-trading for mobile operators

Spectrum trading is an important tool for increasing overall and local spectrum utilization, and to enable access to new and additional spectrum for mobile operators. However, the current spectrum trading regimes usually require long times to execute a trade, hence limiting the flexibility over short timescales in addition to limiting the granularity of the bandwidth and geographical units that may be traded. In this article we discuss the concept of spectrum micro-trading to enable trading of spectrum on the micro-scale in at least three dimensions: the micro-spatial, micro-temporal, and micro-frequency scales. An ecosystem for spectrum micro-trading is presented along with the most important metrics for spectrum micro-trading evaluation. Results from a simulation study for mobile operators, where spectrum is traded via auction, show that the market is viable using the proposed spectrum micro-trading model, and that spectrum utilization can be greatly improved.

TVWS regulation and QoSMOS requirements

Regulatory regimes for opportunistic usage is being discussed in many countries for the so called TV White Space channels. The key objective of the regulators is to ensure that opportunistic systems can coexist with incumbent systems without causing harmful interference. However, they do not specify how these opportunistic systems must be designed to guarantee these requirements and to exploit White Spaces in an optimal way. This paper gathers key regulatory rules for opportunistic usage in the TV bands, and illustrates how these rules are turned into technical requirements within the framework of the European FP7 QoSMOS project.

Space diversity measurements for DECT in indoor and outdoor microcells

Diversity measurements have been performed in microcellular environments where DECT typically might be implemented. The intention has been to investigate how well different implementations of antenna space diversity can combat the problems DECT experiences in multipath environments. Diversity with 2 antennas and selection/switching based on signal level and on delay spread has been investigated, and the effect on the delay spread statistics has been studied. Measurements have been performed in three different types of scenarios; both radio base station (RBS) and portable part (PP) indoors (indoor case), RBS outdoors and PP indoors (outdoor to indoor case) and both RBS and PP outdoors (outdoor case). For the indoor case the delay spread values were small. The most severe time dispersion was observed in the outdoor to indoor case, where delay spread values exceeded 100 ns in almost 50% of the cases. In the outdoor scenario delay spread values above 100 ns were observed for approximately 10% of the cases. It seemed that for both the outdoor, and outdoor to indoor cases, where the time dispersion may cause problems for DECT performance, the diversity algorithm should be based on some other selection/switching criterion than signal level, preferably BER or some other quality criterion. In the indoor environment, signal level as a selection/switching criterion should be sufficient. The work presented in this paper is part of an investigation of DECT performance in environments which DECT has not been originally designed for, to possibly extend the usage of DECT for RLL applications and as a public access system.

Finding the Distribution of Users in a Cell from Smart Phone Based Measurements

Mobile users are assumed to be positioned within the cell or sector boundaries of the serving cell in the network. Measurements of location done by the smart phones combined with the network layout show differently. There is a significant amount of users which are actually outside the nominal sector boundaries. Knowledge about the statistical location distribution of users inside or outside the serving cell intended coverage may prove valuable in finding more optimal resource management methods. Another application is the development of over-the-air characterization of base station antennas. Distance and directional statistics are shown for samples of relative positions within the cell sectors of a real network using smart phone based measurements. Samples for LTE in 800 and 1800 MHz non-voice usage and 3G at 2100 MHz voice usage is included. The distance distributions show clearly that the usage density rapidly decrease with the distance, and there is a clear confirmation that lower frequencies have longer range, also in terms of usage density. Mean usage distance for 800 MHz is 1.62 km, while for 2100 MHz it is only 580 m. It also shows that 90% of the usage is within 3.47 and 1.35 km for the two cases, respectively. The directional distributions relative to the sector centre direction shows that 80% of the users are within 153 degrees for lowest frequency, and 109 degrees for the highest.

Spectrum sensing aided long-term spectrum management in cognitive radio networks

Wireless microphones operating in the TV white spaces often appear at specific venues such as schools or churches, and at specific times. Hence, their location and appearance pattern can be predicted from spectrum sensing statistics. In this paper we propose and evaluate three spectrum selection functions that utilize sensing results to provide long-term spectrum usage statistics as basis for channel selection to enhance performance by reducing interference and increasing throughput. To evaluate performance of the spectrum selection functions, these are implemented in a detailed system level simulator for the IEEE 802.22 standard. We find that the spectrum selection function that uses statistics about channel idle and busy periods performs best when primary user activity is high, and that the spectrum selection function that uses predictions about location and distance to primary users performs best when IEEE 802.22 radio users are mobile and the primary user activity is low.

Coverage Estimations in a WLAN-based Open Broadband Access Network (OBAN)

The main idea of the OBAN concept is that the future deployment of broadband access lines and wireless LANs will have so much excess capacity, beyond what will be utilized by the host households, that it also can accommodate public wireless access services. The purpose of this paper is to analyse the viability of this idea with respect to wireless coverage in some typical scenarios. A model for estimating coverage in single and triple frequency wireless networks based on IEEE 802.11g WLAN is presented. A model for interference is established distinguishing between two types of interference, one present between near neighbours leading to reduced traffic capacity due to the CSMA/CA protocol of the WLAN, and one physical layer interference which will be present between far neighbours, beyond detection range. This latter co-channel interference (CCI) leads to reduced coverage compared to single cell operations and the effects are investigated here. A method of using these results as input to traffic simulations is shown. The analysis shows that severe range reductions will occur even for low traffic in the network. Results for coverage in % are given for three different scenarios.

Implementation of spectrum micro-trading for mobile operators in the spatial dimension

Radio spectrum is a limited natural resource. Most spectrum resources are assigned in the form of licenses, but the actual usage of most spectrum bands is limited. Market mechanisms to trade unused spectrum resources is a promising approach to mitigate the spectrum crunch. An extremely flexible approach to this, the spectrum micro-trading pixelation model, has been proposed to trade spectrum on the micro-scale in frequency, time and geography. In this paper we implement this model in a simulator and evaluate its performance in the spatial dimension using different pixel sizes and auction models. Some surprising findings are presented; the auction that assign spectrum to the bidders willing to pay the most does not provide service to most customers, does far from optimally maximize spectrum utilization, and gives far lower profit to the spectrum broker facilitating the market. Furthermore, we demonstrate the critical tradeoff between spectrum exploitation efficiency, allocation overhead and geographical pixel sizes in the market.

The viability of providing mobile broadband with cognitive femtocells

The viability of providing mobile broadband with cognitive femtocells is evaluated by performing a business case analysis for a scenario where a Fixed Broadband Operator (FBO) uses this approach to extend its offering to include a mobile broadband service. The collective coverage provided by randomly located cognitive femtocells is determined and used to estimate how much of the traffic that will go over the cognitive femtocells and therefore generate revenues for the FBO. With the assumptions made, the cognitive femtocell based mobile broadband service is found to be a reasonable business case for the FBO. The investments over the first few years are moderate and the accumulated cash flow becomes positive after four years. The sensitivity analysis shows that the subscription fee and the general Operational Expenditure (OPEX) are the most critical assumptions in the business case analysis, and that the cost of the cognitive femtocells and their coverage range in suburban areas has a significant influence on the profitability.