Sistemas de tratamiento municipales e industriales

We consider a typical Mobile Satellite System (MSS) operating in L-band where a GEO multibeam and multifeed satellite covers with hundreds of beams a wide geographical area. In particular, we refer to an INMARSAT- like payload as described in [53, 54, 55] and depicted in Figure 2.9. Of inter- est is the flexibility that the system can achieve at the payload level, while all the other segments are similar as in case of the reference Ka-band ar- chitecture. This flexibility is achieved thanks to the capability of assigning dynamically channels within the spot beams. In detail, the assignment is according to the traffic demand and a granularity of 200 KHz is considered for the channels. In terms of power, we assume the system can assign to each channel a reference EIRP (Equivalent Isotropic Radiated Power) pro- portional to the maximum attainable EIRP per spot beam, which is 67 dBW.

2.3. L-band System Architecture and Scenario 19

FIGURE2.9: L-band satellite payload architecture [53]

The channel reference EIRP is not fixed and the payload can flexibly adjust the power within a wider dynamic range of values depending on the num- ber of active channels. In particular, the number of 200 KHz channels that can be processed in parallel by the payload, is assumed to be limited to 630. This constraint apart from the on board processing capability, may be also driven by the fact that the feeder bandwidth is limited.

2.3.2 Scenario 3: Limited downlink user bandwidth

An unbalanced rate demand is present within the coverage, even more no- ticeable due to the increasing and changing requests of the market. In this scenario, the system has to cope both with low and very high rate demands areas along the coverage. In particular, the focus is on these latter, which can be the bottleneck of the system and are called hot spots. The hot spot is, in general, a limited geographical area, for which the system does not have sufficient resources in terms of spectrum and power to satisfy the users’ high demands. Since the hot spots are few with respect to the whole cov- erage and they are usually surrounded by areas with lower demands, this causes an ineffective functioning of the system with respect its overall ca- pabilities. Assuming all the active users of the hot spot limited within the same spot beam, we consider as reference scenario the beam that covers the hot spot plus the six adjacent beams as shown in Figure 2.10a, where differ- ent colors represent their standard coverage. For the considered scenario, the system is limited by a frequency reuse factor of 7. This implies that the available bandwidth can not be reused in different beams within the same cluster. We refer to this frequency allocation plan as reference configuration.

With respect to the spectrum allocation plan in the forward link of L- band mobile systems, the total bandwidth is divided in orthogonal chan- nels of 200 KHz, which can be flexibly allocated among the beams accord- ing to the frequency reuse of the reference configuration. Thus, a different number of channels according to the required bandwidth can be allocated in each beam but obeying the reuse constraint. From the regulatory point of view, the spectrum allocated to L-Band MSS is between 1525 MHz and

(A) Cluster of 7 Beams (B) Zone selection within the central beam coverage.

FIGURE2.10: Representation of the 7 beams cluster and of the 7 zones of the central beam

1559 MHz, i.e., an available bandwidth of 34 MHz, plus an additional band- width of 7 MHz from 1581 MHz to 1525 MHz [37]. Thus, the total available spectrum for the forward downlink in L-Band is equal to 41 MHz, which translates into 205 orthogonal channels of 200 KHz each. This frequency plan, however, faces with some limitation according with the different re- gions. Regulatory bodies give priority to different services within the same bandwidth and, thus, we assume as worst case a limited spectrum avail- ability of only 7 MHz, i.e., 35 orthogonal channels, in some areas [37].

As described in section 4.4.1, the system can achieve high level of flex- ibility even in the reference configuration. However, depending on the de- mands and with particular focus on hot spots, limitations occur. Either spectrum or power availability can affect the performance of the system. The following scenarios, which take into account the main constraints posed by the system, have been identified and addressed.

Spectrum limited scenarios:

- scenarios limited due to regulatory issues. In some regions only part of the total available spectrum, which is 41 MHz, is allocated to L- band satellite systems. The minimum allocated bandwidth in these regions is assumed to be equal to 7 MHz.

Power limited scenarios:

- scenarios limited by the capability of the system. The total EIRP, which is 67 dBW, has to be shared among each channel and the beams.

These limitations penalize the reference configuration in the hot spot sce- nario. However, the flexibility of the considered system can be exploited according to a new framework aiming at improving spectrum efficiency and system performance. This new framework, as will be explained in 4.4.1 and assessed in 4.4.3, identifies new configurations, namely flexible configurations, able to better exploit the flexibility of the system based on a higher frequency reuse and the application of interference management techniques.

21

Chapter 3

Spectrum Awareness

3.1

Introduction

Spectrum awareness techniques provide improved knowledge of other sys- tems’ spectrum activities. This knowledge enables the following phases of the cognitive cycle exploiting those available spectrum opportunities. With respect to the scenario in which the cognitive user operates, different tech- niques can be designed according to the constraints, the requirements, and the performance to be achieved. Thus, targeting specific Figure of Merits (FoM), spectrum awareness techniques must be designed to satisfy them.

In this chapter, a novel approach for spectrum awareness in cognitive- based scenarios is developed. A complete characterization of the technique, namely SNOIRED, in terms of the common indicators that are used to asses awareness techniques performance, is provided. The proposed technique is based on the joint Signal to Interference plus Noise Ratio (SINR) estima- tion and detection of primary users at the cognitive receiver side and it is particularly effective for underlay scenarios, in which cognitive users are allowed to operate in already deployed frequencies if the interference gen- erated against licensed users does not exceed a predefined threshold [3]. The definition of underlay scenario fits the two scenarios described in 2.2. Thus, in these scenarios, an additional awareness capability is provided to the end-user terminals, which would be able to be autonomously aware of the spectrum activities within the bands of interest. The proposed tech- nique, even if designed focusing on satellite cognitive-based scenarios, has a general applicability. Thus, in the following paragraphs, the technique is first designed from a general point of view and, secondly, specific analysis are carried out for the selected satellite cognitive-based scenarios.

The remainder of the chapter is the following. Paragraphs 3.2 and 3.3 present the motivations that have pushed towards the proposed novel ap- proach and the State of the Art of spectrum sensing techniques, respectively. From a general point of view and applicability, in paragraphs 3.4.1, 3.4.2, and 3.4.3 are presented the system model, the design of the estimation, and the design of the detection stages of the proposed technique. Analysis on its performance are carried out in section 3.5. In the subsequent sections 3.6 and 3.7 the technique is assessed on specific SatCom scenarios under ideal and in presence of impairments conditions, respectively. The results ob- tained are then resumed in 3.8. In the appendix 3.9.1 and 3.9.2 are provided additional and complementary details on the technique design. Finally, a review of the typical spectrum awareness techniques in literature, focussing on their applicability in satellite cognitive-based scenarios, is included in section 3.9.3.