PREVIOUS TECHNIQUES Wireless equipments, such as mobile phones, laptop, PDAs and sensor networks need to use suitable transmitting power that guarantees good communication's quality while maximizing battery's lifetime.

Wireless mobile equipments have power control devices that allow them to operate adequately with the telecommunication infrastructure where they work.

Typically, such devices adjust their transmission power in an increasing and gradual way, based on the receiver distance, which is estimated through the signal level that the transmitter receives from the receiver and vice-versa, that is, the longer is the distance, the lower is the level of the signal that the receiver acknowledges.

According to the communication infrastructure type, the transmission power is adjusted following one of the following three methods.

The first method is used when there are radio base stations or access points for mobile computing, with preinstalled infrastructure. In this case, the device uses only the signal received from de base station or from the access point.

The second method is used in mobile ad-hoc networks. In this environment, the device increases or decreases the signal level until it makes the contact with the other equipment.

The third method uses a combination of data that come from GPS systems and a Geographic Information System.

This last method can estimate precisely the transmission distance and the obstacles present on the terrain, allowing the device to operate very close to the ideal transmission power.

Generally, mechanisms based on precise localization methods demand high processing and need also embedded localization devices, which are expensive.

SUMMARY OF THE INVENTION The present invention refers to a method of power adjustment for wireless mobile equipments.

This invention is based on the terrain's obstacle spatial distribution where the equipments will work, as well as the probability of occupation of the transmitters and receivers (transceivers for short) across the terrain.

Specifically, the method first produces statistical information about the electromagnetic interference of the terrain, considering both its obstacles and the transceiver's spatial distribution. Based on the statistical information, it generates two metrics, namely the terrain blockage rate and the useful transmission rate,

that are used to adjust the transmission power by the transceivers.

The terrain blockage rate (BT) for a determined range is defined as the ratio between the area that would be reached but was shadowed by the obstacles, divided by the sum of this same area plus the area that was not affected by the obstacles for a given range of transmission.

The useful transmission rate (UT) for a determined range is defined by the rate between the effective reachable area and the theoretical reachable area without obstacles for a given range of transmission.

These characteristics, other goals and advantages of the present invention will be easier to understand and will be better describe if these document will be read with the following figures.

Figure 1 : Probability spatial distribution map (for transmitters and receivers).

Figure 2: Blockage Terrain Rate (BT) and Useful Transmission Rate (UT).

Figure 3: Distribution of the coefficients (BT and UT) for the equipments in open environments.

Figure 4: Distribution of the coefficients (BT and UT) for the equipments in close environments (such as offices).

DETAILED DESCRIPTION OF THE INVENTION Probabilistic spatial distribution map for transceivers.

Mobile computing equipments moving inside an area tend to form an occupation profile for that area. For example, pedestrians normally walk in sidewalks, gardens or parks, vehicles move along the roads, and so on. Thus, according to the features of terrain occupation, a mathematic model is possible to be constructed.

[Figure 1] shows an example of a receivers' probabilistic spatial distribution map based on the relative weights of the transceiver's occupation across the terrain. These weights are obtained from a given probability density.

The distribution is function of time, of the transceiver's number and can be conditional (P (AlB)).

As an example, the [figure 1] represents a scenario where the area with p=4 corresponds to streets, p=2 represents sidewalks, p=l corresponds to gardens and p=0 represents a lake.

Terrain blockage rate (BT) The blockage terrain rate (BT) is the metric that indicates the transmission interference in percent that the geographic obstacles of a given scenario harm electromagnetic propagation, thus degrading or blocking transmissions.

Using the probabilistic spatial distribution map [figure 11, the blockage terrain rate is computed by the following formula: 2 t=blockedp, B¢ (R, s, l) r pomts Points t=blocked, B R, s I +r r=rcached. F R, s, y. po'ntsPO'ntbyS EP, Where: R: the range of the transmission. This is the main parameter of the metric. s: Geographic coordinates of the source (in 2D or 3D) ps : source's occupation probability of the point s. t: Geographic coordinates of the target (in 2D or 3D). The sum function corresponds to all geographic point that will be reached by the source's electromagnetic transmission in a terrain without obstacles.

pt : target's occupation probability of the point t.

Bco : a function that returns 1 if there is at least one obstacle that blocks the transmission between s and t.

Otherwise, returns 0 Fco : the inverse function of Bco.

A: the domain of the metric. It represents the region where the coefficient is computed.

This intuitive idea is clarified in [figure 2], where we also show the notion of UT.

So, the terrain blockage metric for a determined range is defined as the ratio between the area that would be reached but was shadowed by the obstacles, divided by the sum of this same area plus the area that was not affected by the obstacles for a given range of transmission.

We have to compute a weighted sum of each point, by considering the probability of each geographic position holding either a source or a target. To do so, we use the map we described previously.

This computation must be done in advance, considering also other statistical data such as variance, standard deviation, median, maximum, and minimum.

Useful transmission rate (UT) The useful transmission rate (UT) corresponds to the electromagnetic transmission effectively used, in a scenario with obstacles. With this metric is possible to compute how much of the transmission is effectively used.

The main idea of UT is also illustrated in [figure 2].

The useful transmission metric for a determined range is defined by the rate between the effective

reachable area and the theoretical reachable area without obstacles, i. e., wR2.

Similarly to BT, the UT coefficient is computed using a probabilistic map.

The formula of UT is shown above: t=points 7rFolR, s, t) reached by s I P"- t=Po L s y. F (R s t) TU (A) = reached 17y s U Ps The variables of this equation are the same of BT. The only difference is that the function Fso represents the interaction between s and t, without the obstacles.

Similarly to BT, UT is also a function of the range of the transmission and also computes other statistical variables, such as variance, standard deviation, median, maximum and minimum value.

The computation of UT, as BT, must to be done in advance.

BT and UT distribution The present invention can be used in open areas as well in close areas, such as offices and buildings.

[figure 3] and [figure 4] show two schema of information distribution. [figure 3] applies to open areas and [figure 4] applies to close areas.

In open areas, with telecommunication infrastructure, the radio base station transmits the statistics data about BT and UT. This radio base station (RBS) works similarly to mobile phones, where the RBS is responsible for broadcasting the statistics information about BT and UT.

In close environments, with infrastructure, the distribution nodes are wireless equipments that will have

the database of BT and UT and thus are responsible for broadcasting the statistics information about BT and UT.

In environment without infrastructure, the nodes with greater data processing capability and localization capability would be the distribution nodes. These devices with special capability will broadcast the BT and UT information to their closest neighborhoods.

Power adjustment mechanism BT and UT are combined in order to select the best transmission power.

Once data about BT and UT are available, wireless equipments can choose to operate at the most suitable level of transmission power while saving most energy. The best level is the one that combines efficient transmission with lower power usage.

In addition, BT and UT provide information about any large transmitting rates if such that can overcome obstacles that cause negative effects such as reflection.

An intuitive use of UT is to estimate the area effectively reached. This is possible through the following formula: Reachable area = UT. n. R2 By using BT and UT parameters, the transmitters can decide which power is more suitable to use.

Also, localization algorithms that have to choose ranges in order to compute transceiver positions, can select the most convenient range according to the transmission profile of the scenario.

Routing algorithms can also be benefited by these metrics because they can estimate, in average, how many hops in a given range will be necessary to send packet between two different nodes.

Finally, it is possible to use this invention in telecommunication devices such as sensor networks, mobile phones, tracking and localization devices and so on.