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# System prepended metadata

title: Index

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# Index
- [Papers](#papers)
    1) [*A survey of techniques and challenges in underwater localization*](#survey_techiques)
- [Documentation](#docs)

# Papers <a name="papers"></a>

## a) *A survey of techniques and challenges in underwater localization* <a name="survey_techiques"></a>

**1. Challenges towards design localization schemes**
- High accuracy
- Fast convergence
- Wide coverage
- Low communication costs
- Good scalability

**2. Range-based underwater localization**
- Step 1a: Range measurement (within communication range)
- Step 1b: Range measurement (outside communication range)
- Step 2: Location estimation
- Step 3: Calibration

    **2.1. Challenges**
    - 2.1.1. Underwater environment
        - Reference deployment in deep sea
        - Node mobility
        - Inter-node time synchronization
        - Signal reflection due to obstacles and reflective surfaces
    - 2.1.2. Underwater acoustic propagation
        - Long propagation delay
        - Multipath fading and shadowing
        - Sound speed variation
        - Low bit rate
        - Highly unreliable and asymmetric signal-to-noise ratio
    **TL($d_{ij}$)=10$\lambda$$log_{10}$$\frac{d_{ij}}{1m}$+$\alpha$$d_{ij}$ dB**
            - TL is the transmission loss
            - $\lambda$ is the propagation loss parameter
            - $\alpha$ is the absorption loss parameter 
                - $\uparrow$ with carrier frequency
                - affected by salinity and water temperature)
            - ambient noise level 
                - depth dependent
                - $\downarrow$ with frequency $\rightarrow$ 50-log(f)[dB]

    **2.2. Single-stage, static references**
    - 2.2.1 UPS
    - 2.2.2 Model-based localization

    **2.3. Multi-stage, static references**
    - 2.3.1. Localization for hierarchical UWSNs
    - 2.3.2. Projection-based localization

    **2.4. Mobile References**
    - 2.4.1. AUV-assisted localization
    - 2.4.2. DNR-enabled localization

**3. Range-free underwater localization schemes**
- does not depend on the accuracy of range measurement

    **3.1. Schemes based on area localization**
    **3.2. Schemes based on directional beaconing**

**4. Commercial underwater positioning system**
-  Based on the distance between the baseline stations
    **4.1. Long baseline systems**
    **4.2. Short baseline systems**
    **4.3. Ultra short baseline systems**

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## Documentation <a name="docs"></a>

- [Writing Mathematic Formulas in Markdown](https://csrgxtu.github.io/2015/03/20/Writing-Mathematic-Fomulars-in-Markdown/)
- [List of Greek letters and math symbols](https://www.overleaf.com/learn/latex/List_of_Greek_letters_and_math_symbols)



