Explain 4 significant technology of the WLL system. What are the advantages and disadvantages of this methodology?

WLL System

The WLL system can be based on 4 significant technologies. They are:

Satellite-Based Systems:

These systems give communication services to rural networks and isolated territories, for example, islands.

Satellite systems are intended for a Gaussian or Rician station with K factor more prominent than 7 dB.

These systems can be of two kinds:

Technology designed explicitly for WLL applications and Technology piggybacked onto mobile satellite systems as an aide service of these.

The previous offer quality and grade of service equivalent to wireline access, yet it might be costly.

The last promises to be less costly but due to bandwidth capacity limitations, may not offer the quality and grade of service comparable to plain old telephone utility (POTS).

A case of a satellite-based technology explicitly designed for WLL is the HNS telephony earth station (TES) technology.

Advantages:

• The low bit rate for voice and data.

• Low-cost mobile terminals.

• It gives quality and grade of services for WLL applications.

Disadvantages:

• The number of satellites and propagation delay put limitations on the system design.

• Handover capacity is required for example LEO, MEO satellites are in motion comparative with the world's surface, so they need handover capacity for all fixed and cell applications

Cellular-Based Systems:

These systems give large power, an enormous range, middle subscriber density, and middle circuit quality WLL services. Cell WLL technologies are primarily used to expand fundamental telephony services.

This methodology offers both portability and fixed wireless access from the equivalent cell platform.

For relatively scantily populated country and even urban settings, WLL technologies based on existing cell systems can be practical and quickly deployable. They incorporate a much-sophisticated technology (and along these lines overhead bandwidth capacity) not really required for the WLL application. The resultant limited client bandwidth speaks to a major limitation of such systems for WLL.

Advantages:

• They give fixed wireless access and versatility.

• They can be quickly deployed in rural and urban territories.

• They give a huge power and operating range.

• They give medium circuit and medium subscriber density.

Disadvantages:

• They are not suggested for indoor organizations and in Pico cells.

• The air interface is complex.

• The client data bandwidth is limited.

Fixed Wireless Access Systems

These systems are restrictive radio systems designed explicitly for fixed wireless applications, which could conceivably be extensible to PCS or cordless.

The essential disadvantage of the cellular approach is its limitation on toll-quality voice (new toll-quality vocoders designed for cell technologies may take out this issue), and signaling transparency.

The essential disadvantage of low-level PCS and microcellular approaches is their range.

FWA systems for zonal areas are designed to cover the local phone zone directly from the PSTN switches. The systems for rural zones give connection at the remote parts of the rural links to the end clients.

Advantages:

• Less costly

• It can be easily installed

• The installation time need is less.

Disadvantages:

• Limitation on toll-quality and signaling transparency.

Low-Tier PCS or Microcellular-Based Systems:

These systems provide low power, small range, high subscriber density, and high circuit quality WLL services. These technologies are considered to encourage rapid market entry and to expand the limit of the current infrastructure.

They are regularly worked at 800 MHz, 1.5 GHz, 1.8 GHz, and 1.9 GHz frequency groups

Compared with the cell-based WLL, more base stations are required to cover a similar service area. Administrators may consider low-tier WLL technologies when existing infrastructure is set up to support backhaul.

For thickly populated urban situations, WLL technologies dependent on existing low-tier PCS radio technologies.

Advantages:

• High Subscriber density.

• Low power.

• High circuit quality.

Disadvantages:

• Transmission cost is more.