# LAR – Location Aided Routing

## The main problems of previous mechanisms

Node **location changes rapidly**.

**No information** regarding:

* Current **location**.
* **Speed**.
* **Direction**.

Knowing the location.

* **Minimizes the search zone**.
* **No need to flood** the network.

Knowing the speed and/or direction.

* More minimization of the search zone.
* **Increases the probability to find** the necessary node.

## Location-Aided Routing (LAR)

**Each node knows its location** at every moment.

Using location information for route discovery.

**Routing** is done **using** the **last known location** + an assumption.

Route discovery is initiated when.

* S does not know a route to D.
* The previous route from S to D is broken.

Assumptions.

* Location knowledge.
* No error.
* 2D movement.
* Full cooperation.

## Location information

* Alignment of satellites and ground stations.
* Global Positioning System (GPS) - USA.
* Global Navigation Satellite System (GLONASS) - Russia.
* Galileo – EU.
* 3D positioning.
* Accuracy 3-100 meters.
* Can provide further information.
  * Velocity.
  * Time.
* Cutting-edge technology.
* Already in use in many fields.

## Definitions

### Expected Zone

<figure><img src="https://2823298875-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FDVtU9cdYIg5EIwefavH8%2Fuploads%2Fpd3Yh8W8OiAORNaRtrJJ%2Fa.png?alt=media&#x26;token=81bd82a9-9321-4215-a484-6e57f29b105d" alt=""><figcaption></figcaption></figure>

* *S* knows the location *L* of *D* in *t0*.
* Current time *t1*.
* The location of *D* in *t1* is the expected zone.
* Assume Max/Avg speed *v*.

### Request Zone

<figure><img src="https://2823298875-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FDVtU9cdYIg5EIwefavH8%2Fuploads%2FHq5tpz2hRLT1YcihFeoN%2Fa.png?alt=media&#x26;token=1e0b2fa4-aab7-48d4-b851-0d2ad1951a67" alt=""><figcaption></figcaption></figure>

* Flood with a modification.
* Node S defines a request zone for the route request.
* How to determine the size and shape of the request zone?
* Several considerations.
  * If the destination’s EZ does not include the source node, other regions must be included in the RZ.
  * Not always a route will be found using a certain RZ.

## Scheme 1

### Algorithm

Node *I* receives **RREQ**.

* Location of *I* – *(Xi, Yi)*.
* If it is within the rectangular, *I* forwards the RREQ to its neighbors.
* Else *I* discards the RREQ.

Node *D* receives the **RREQ**.

* Replies RREP.
* Adds its current location.

### Some issues

The rectangular size is proportional to:

* Average speed (*v*).
* Time elapsed (*t1-t0*).

Therefore:

* **Low speed** -> small *v* in the same (*t1-t0*) -> **smaller&#x20;*****RZ***.
* **High speed** -> large *v* in the same (*t1-t0*) -> **larger RZ**.

Improvements:

* *D* can add its speed/avg. speed in the **RREP**, this can help other nodes in future route discoveries.
* *D* can piggyback its location in other packets.