Introduction to Vsat Networks

INTRODUCTION TO

VSAT NETWORKS

Presented by Dr. Ashraf Eltholth

Introduction

Very Small Aperture Terminal (VSAT) networks

provide affordable access to communications

services.

Basic VSAT concepts defined in this lecture include

VSAT terminology, the main components of a VSAT

network, and the cost comparison between VSAT and

terrestrial networks.

This lecture shows the advantages of VSAT networks

and the typical topologies used by VSAT operators.

Introduction

Outline

What Is a VSAT?

VSAT Networks Versus Terrestrial Communications.

VSAT Satellite Network Topology.

Satellite Frequency Bands.

Overview of VSAT Applications.

Benefits of VSAT Networks.

What Is a VSAT?

A (VSAT) is a micro-Earth station to allow user's access to

reliable satellite communications.

VSATs provide users with services comparable to large

gateways and terrestrial networks, at a fraction of the cost.

A typical VSAT consists of communications equipment and

a small antenna with a diameter less than 3.5 meters.

VSAT networks provide users with simple equipment that

requires minimal installation and repair. They are easy to

operate and simple to troubleshoot. VSAT installations do

not require staff with extensive expertise.

What Is a VSAT?

Typical VSAT Terminal

VSAT :STATIONS

L-Band BUCs versus 70 MHz

Transceivers

A typical has the antenna mounted outside, with the transceiver mounted as close to the

antenna feed as possible. The modem and other electronics are connected by cable from the

operations center out to the antenna. If this cable had to carry the original RF frequency of 4

to 6 GHz it would need to be thick and very expensive. In order to cut down costs, satellite

engineers designed transceivers that would take the high frequencies from the antenna and

then convert them into a much lower frequency. They called this new frequency

Intermediate Frequency (IF). IF frequencies can be carried over long distances between

the antenna and indoor equipment using cheap cables.

Orders for this newer technology - L-Band modems and Block Up Converters (BUCs) - has

surpassed sales of the traditional modem and transceiver package, mainly because of price.

What Is a VSAT?


The antenna and ODU provide the

radio frequency conversion and

amplification for the satellite uplink

and downlink.

The ODU is often called the

transceiver because it includes the

up converters (U/Cs); the Solid State

Power Amplifier (SSPA); the Low

Noise Amplifier (LNA), and the down

converter (D/C).

What Is a VSAT?


The IDU

provides the baseband

interfacing required to

carry the users services.

The power requirement

for each VSAT is low and

in some cases solar cells

supply the power.

What Is a VSAT?

Hub Earth Station

VSAT terminals are

generally part of a

network, with a larger

Earth station that serves

as a network hub.

The hub contains the

intelligence to control

the network operation,

configuration, and traffic.

The hub also records the performance, status and activity levels of each

VSAT terminal. Databases generated by the hub are also used for billing

purposes. Hubs are usually located where the bulk of network traffic

originates and/or terminates.

VSAT Installation

Installation of a VSAT system can be a challenge unless the installer has

considerable experience in performing the task. An experienced installer

will be able to unpack the equipment, assemble the antenna, modem and

transceiver, line up the satellite and get a signal lock in 5 to 7 working

days.

There are several stages involved in building a VSAT facility:

1.Inspection of the VSAT equipment

2.Preparation of the site for VSAT installation

3.VSAT equipment installation

4.VSAT antenna alignment

5.Commissioning and start of VSAT service

VSAT Installation

VSAT Vs. Terrestrial Comm.

Cost effectiveness of VSAT

VSAT Terrestrial

Long distance prices do not apply to

VSAT networks.

The cost per lease line increases in

proportion to the distance

The equipment and installation costs of

VSATs is higher than

terrestrial alternatives.

The installation fee is directly related

to the required data rate.

VSAT had a flat performance,

independent of distance.

The same data rate is not available at

all the branches because the terrestrial

network is not equally developed

throughout the country

A VSAT network can be managed

independently of the terrestrial

network.

If a cable connection breaks, they have

to rely on the phone

company to fix the problem.

VSAT Vs. Terrestrial Comm.

Cost effectiveness of VSAT


There are three types of VSAT network topologies:

star, mesh, and hybrid.


The majority of VSAT networks use star topology

because the large antenna gain at the hub optimizes the

use of the space segment and minimizes the size of the

VSAT terminal.

The drawback of star topology is that the delay for

VSAT to VSAT communication doubles in comparison

to single hop transmission.

VSAT NETWORK OPTIONS

Star or mesh? The answer depends on three factors:

The structure of information flow within the network;

The requested link quality and capacity;

The transmission delay.


The structure of information flow :

Broadcasting: a central site distributes information to many remote sites with no back flow of information.

Corporate network: most often companies have a centralized

structure with administration and management performed at a

central site.

Interactivity between distributed sites


Link quality and capacity

1. Overall Radio Frequency Link

Measured by (C/N0) where C is the received

carrier power and N0 the power spectral

density of noise

2. User-to-user Baseband Link

measured by the information (BER) vs.

Eb/N0 value at the receiver input, where

Eb (J) is the energy per bit and N0 is the

noise power spectral density.


Transmission Delay

VSAT Services OPTIONS


Currently, in the VSAT networks, two frequency

bands are used for VSAT services, C-band and Ku-Band.

For C-band operations, the antennas transmit at 6

GHz and receive at 4 GHz. Ku-band requires

transmission at 14 GHz and reception at 11-12 GHz.


Which frequency band is better?

VSAT operators prefer Ku-band to C-band because it allows

them to reduce the capital investment by using smaller antennas.


VSATs are suited to many applications which broadly

fall into two categories

Broadcasting or one-way applications

Voice, video, or data is transmitted from a central station

and broadcast to VSATs within the satellite beam coverage.

Interactive or two-way applications

Allow two-way communication via the VSAT terminal. The

carrier from the hub station to the VSAT is called outbound,

while the carrier from the VSAT to the hub is called inbound


One-Way Applications

Often, broadcast VSAT applications use a return channel via the PSTN.

For requesting services


Internet Broadcast with Terrestrial Return Link

Often, broadcast VSAT applications use a return channel via the PSTN.

For requesting services


Interactive or two-way applications:

1. Interactive data service

Involving an inquiry from one terminal and a subsequent

response from another terminal

2. Interactive voice services

Several telephone lines which, in turn, can be connected to a

local PBX. Furthermore, a VSAT terminal can be connected to a

base station to extend the service using Wireless Local Loop

(WLL).


Interactive or two-way applications:

3. Interactive video services

Enable video conferencing at data rates as low as 64 kbit/s.

VSAT users generally implement outbound video at 384 kbit/s

and inbound video at 64 kbit/s.

4. High-speed, point-to- point services.

These networks typically have a small number of VSATs, in a

point-to-point configuration, and can handle up to 1.544 Mbit/s

(T1) or 2.048 Mbit/s (E1) carriers in a bidirectional fashion.


VSAT-WLL Network Architecture Diagram

VSAT equipped with 8 satellite

channels and a WLL base

station can serve a population

of 500 telephones. The

telephones can be wireless pay

phones powered by solar cells

or fixed wireless.

The coverage radius for the WLL unit is typically 12 to 20 miles. This application

makes rural telephony affordable with per-line costs of about 1,000 to 1,500 dollars.

Benefits of VSAT Networks.

Wide range of data, voice, and video applications.

Proven and robust technology, (user satisfaction)

Quick network deployment.

Rapid response to market needs, (ease of expansion).

Elimination of the last mile connection problem.

Reliability and ease of maintenance.

ITU Recommendations

General Recommendation ITU-R S.725

Recommendation on spurious emissions S.726-1

Other Recommendations are available.

ETSI Recommendations

Questions?

MULTIPLE-ACCESS PROTOCOLS

Introduction

In implementing VSAT networks, three different layers

of protocols have to be considered:

Satellite Access Protocol, Network Access Protocol,

User Data Protocols.

Capacity Access

Satellite Capacity Access Protocol:

There are three techniques to divide satellite capacity among

multiple users: Frequency Division Multiple Access (FDMA),

Time Division Multiple Access (TDMA), and Code Division

Multiple Access (CDMA).

Network Access

Satellite Network Access Protocol:

By using a network access protocol, efficiency improves.

Network access protocols assign capacity to a particular

terminal based on traffic demand.

Capacity is requested by the VSATs and is assigned by the

network controller at the hub, either on-demand, at random,

or permanently.

Network Access

Satellite Network Access Protocol:

Multiple Access

Controlled

Demand Assigned

SCPC-DAMA DA-TDMA FTDMA-DAMA

Permanent Assigned

FDMA TDMA CDMA

Contention

Access Options

FREQUENCY DIVISION MULTIPLE ACCESS

FDMA shares a common transponder bandwidth by

dividing it into sub-bands and assigning these sub-bands

among the users.

Pre-assigned FDMA (MCPC)

Each earth station transmits

one uplink carrier modulated

with a 60-channel super-group.

The 60 voice channels are

FDM multiplexed, the

multiplexed signal is then FM

modulated : FDM/FMFDMA

FDMA (MCPC)

Sub-band allocated to each channel depends on the Power

capability and required services

FDMA (SCPC)

A pilot frequency is transmitted for the purpose of frequency control,

and the adjacent channel slots on either side of the pilot are left vacant

to avoid interference.

The 45 kHz, which includes a guard-band, is required for each digitized

voice channel, which utilizes (QPSK) modulation.

The scheme therefore provides a total of 399 full-duplex voice circuits.

the frequency pairs are separated by 18.045 MHz.

FDMA efciency

What are the reasons of

efficiency degradation as the

number of carriers increase?

1. Guard bands; increase as

the number of subcarriers

increase, thus the effectively

used BW will be decreased.

2. Non-linear effect of HPA

on multicarrier signal.

The efciency, , of a multiple access scheme is:

= Multiple Access Capacity / Single Access Capacity

at transponder saturation

Inter-Modulation Products

In HPA is the amplifier operated in the

nonlinear region, to gain a maximum power

output, there will be inter-modulation

products that forms a strong interference.

Practically it is required to maintain the

Carrier to IM noise power ratio below a

certain threshold level, this is done by

operating the amplifier at a lower point that

the maximum input power will not drive the

amplifier into the nonlinear region (Back

Off)

Inter-Modulation Products

The back off required depends on the threshold C/IM value and the

number of subcarriers

Increasing the BO and consequently BI, will decrease the total C/N

of the satellite link, that will affect directly on the spectral efficiency

of the system.

TIME DIVISION

MULTIPLE ACCESS

TDMA shares a common

transponder Frequency by

sharing time periods in a

time frame (eg. 2 msec)

and assigning these time

periods among the users.

Size of the time periods

depend on the number of

channels transmitted by

each user.

TIME DIVISION

MULTIPLE ACCESS

Why do we need a guard time band in TDMA?

Guard bands are included to prevent overlap and to

Account for different transmission times for each of the

stations, based on their range to the satellite.

TDMA efciency

Sample Calculation for Frame Efciency

Consider a TDMA frame time of 2ms The relevant, overhead element bit

sizes are:

br = 576 bits

bp = 560 bits

bg = 128 bits

Assume that there are two reference stations, each transmitting a reference burst

in the frame (nr = 2).

Evaluate the TDMA network for a desired frame efficiency of 95%, in terms of

the maximum number of traffic terminals and the operating TDMA data rate.

Sample Calculation for Frame Efciency

Code Division Multiple Access

CDMA efciency

CDMA & TDMA operate

only with digital signals.

FDMA operate with both

analog or digital signals

TDMA & FDMA can

operate permanently or on

demand.

CDMA is Random in

nature

DEMAND ASSIGNED

MULTIPLE ACCESS

In DAMA method single communication paths are allocated

to earth stations on demand. Communication path between

earth stations are provided on request, from an idle pool of

communication paths. When the use of communication path

is completed it returns to the idle pool for reassignment.

DAMA is analogous to PSTN, when a subscriber goes off-

hook, a line is seized to dial and make the voice connection.

When the call is completed with on-hook, the voice path is

returned idle, to be used by another subscriber

DEMAND ASSIGNED

MULTIPLE ACCESS

DAMA TDMA SCPC/FDMA

FTDMA

Resources are reserved either via

Common Signaling Channel or by Contention

In most cases the CSC is used in FDMA based systems, while Contention is used in TDMA systems

Random Access

Pure ALOHA

Star Connection

Mesh Connection

Satellite Access Control Channels

Factors Affecting DAMA

DAMA Connection

VSAT Network

Planning and Implementation

Introduction

Planning and implementing a VSAT

network involves a decision making

process. In some cases the process

requires more than one iteration to reach

to the most economic solution.

How to choose a suitable network

Configuration

Defining the service requirements

Defining expected network objectives, Performance, Quality,

and Availability

Defining network size and design

Comparing the design against available equipment

Evaluating the costs

Preparing an implementation plan

Determining the space segment capacity required


Configuration

Before planning begins, it is important to identify the menu of

services that defines all the potential users that the VSAT network

will require.

An analysis of the current telecommunications infrastructure will also

help to discover the niches not reached, and which the VSAT

network can provide.

This information will define what is needed, why it is needed and

what criteria the clients will use to evaluate the results.

Defining the service requirements


Configuration

Before proceeding in the planning process, it is important to define

the minimum performance expected from the network.

This can be derived from the clients responses and must be defined.

Defining expected network objectives, Performance, Quality,

and Availability


Configuration

The network design will seek to balance the requirements in the

Earth segment and space segment to find the, overall, cost-effective

solution.

Optimum network design minimizes the capital and operating costs

while meeting all service requirements, and involves a trade-off

among available satellite capacity, antenna sizes, proposed

connectivity, network topology, availability, quality, and growth over

time.

Defining network size and design


Configuration

Once link budgets has been performed, the planner needs to

compare the results with the available equipment. This must be done

in terms of antenna, SSPA, carrier rates, coding, and modulation

schemes.

Comparing the design against available equipment

The Request For Proposal RFP

Key aspects to consider for the procurement include:

Clients traffic profile;

Targeted BER and availability;

Equipment location;

Test plan and expected results; (Acceptance Test Plan)

Criteria for network acceptance

Options needed for future expansion;

Schedule for deliverables;

Required technical support and response time from vendor;

Spare equipment;

Service Requirements

A description of the clients service

Clients have different requirements, including voice, data, voice and data,

interactive data, one-way broadcast, video-conferencing, or Internet.

Estimation of the traffic in the peak busy hour (PBH)

As realistic information as possible must be gathered on:

Traffic Erlang, message sizes, call duration, service priority, response time, set-up

time, application protocols (i.e., Ethernet, TCP/IP, etc.).

The estimated traffic growth per year:

Number of new nodes per year, services per node, new services to

existing nodes, priority of services per node.

Any constraint sites that may affect the VSAT operations:

Obstacles, building projects, roads, radio links operating in the same frequency,

and zoning restrictions.

Traffic Estimation

Voice traffic: For voice traffic, most of the information is given in the

number of channels or phone extensions per site.

For example: Client A needs to provide voice services to 250 sites in

a 3-year period. These sites will be part of a rural communications

project. The project plan indicates that every year 85 sites will be added

to the network. In the first year the client requires 2 trunk lines for 60

sites, and 4 trunk lines for the remaining 25 sites.

Calculated Traffic Intensity

(in Erlang)

The VSAT service provider needs to convert this number of channels to

Erlang to derive the number of satellite channels.

For trunk lines, it is common to use a traffic level value between 0.1 to

0.25 erlangs per line in the PBH.

Calculated Traffic Intensity

(in Erlang)

The number of satellite channels is the number of duplex channels

needed to carry the entire network traffic, and is calculated using the

Erlang B tables and a probability of loss Blocking probability Typical

values range from 1 percent to 5 percent .

Voice Traffic

The primary application of the network is to support voice traffic:

1 Call duration is about 3 to 5 minutes.

2 Call setup time is about 5 seconds.

3 The voice calls are susceptible to changes in the connection

delays, but are resilient to errors.

Therefore, the satellite access technique has to allocate a free voice

channel in less than 5 seconds. Then it must run the channel over a

permanent connection to avoid the changes in the connection delay, and

must reduce the satellite bandwidth by allocating the calls on-demand.

SCPC/DAMA is a technically feasible solution.

Data Traffic

Data traffic is more difficult to model because there are several different

protocols with different characteristics. Suppose then, that as VSAT

service provider, you collected the information from a group of clients.

Data Traffic

Data Traffic

Network Traffic Calculation.

Data Traffic

Number of Carriers Calculation.

Network Performance

1) Response time: The elapsed time between the moment an inquiry is

received from the user by the hub or VSAT and the moment when the

response is delivered by the VSAT or hub to the user.

2) Throughput: For the clients, throughput represents time within

which they expect their applications to achieve a given response.

For VSAT service providers it indicates the efficiency of the network.

3) Bit Error Rate: The typical BER tolerated depends upon the

application. Voice tolerates higher BER, while data need lower BER.

Typical values are 10-5 to 10-7 for voice networks and 10-7 to 10-9 for

data.

Network Performance

4) Network availability: Network availability is defined as the

percentage of the time in which the network operates above the BER

threshold. The availability of the ground equipment and the availability of

the satellite link influence the total network availability.

Network Size and Design

Satellite and frequency band: Determine which satellite covers the

desired network geographical area. This is done after identifying the

nodes and the physical locations for each. Then will determine whether

the C- or Ku-band.

Topology and access alternatives: The goal in defining the network

topology is to balance the Earth segment costs with the required satellite

resources.

Link budgets: Will be used to optimize network parameters.

Network Cost Model

VSAT Network Architecture

Top Level Specifications

Top-level specifications, drawing a top-level diagram of the network.

The diagram should indicate all the sites that will require services.

Next, a matrix of traffic requirements must be prepared. This must

contain data suitable for traffic analysis and link budget calculations. This

traffic table can also form an integral part of the RFP documents.

Even though the proposed network may be simple or complex, the

methods suggested for the requirements document and the traffic matrix

are similar.


Shared Hub Configuration.

CUG : Closed User Group

SCC: Sub-Network Control Center

NMCC: Network Monitoring and Control Center

FEP: Frame Encapsulation Protocol


Distributed Hub Configuration.


Distributed vs. Shared Hub

QUESTIONS? Thank You?

Documents

Introduction to Vsat Networks