Access Technologies and Microwave Radio Systems

O.Bat-Erdene(J.TC08D027) G.Uranchimeg(J.TC08D718)A.Ulziisuren(J.TC08D702)

Access Technologies

Small business and residences use one of thetechnologies described in this chapter: DSL , cable, or wireless.

DSL-Digital Subscriber Line

DSL operates over the ILECs’ copper wire local loop. Although the loop is not ideal for broadband communications, it is widely available, inexpensive, and does the job effectively. ILEC – Incumbent Local Exchange Carrier

DSL standards

•HDSL – High Bit-Rate Digital Subscriber Line•ADSL – Asymmetric Digital Subscriber Line•SDSL – Single-Pair Digital Subscriber Line•VDSL – Very High Bit Rate Digital Subscriber

Line•G.Lite – Splitter less Digital Subscriber Line

Asymmetric Digital Subscriber Line (ADSL)

ADSL is the most common type and is most attractive for casual users.

Rate (downstream) – 1.5Mbps

Rate (upstream) – 64-640Kbps

Very High Bit-Rate Digital Subscriber Line (VDSL)

VDSL was developed to support video or high-speed data.

High rate – 52Mbps , range -1000ft(330m)

Drop rate – 13Mbps , range -4500ft(1500m)

High-Speed Digital Subscriber Line (HDSL)

ILECs use HDSL to provide T1/E1 service over two twisted pair wires up to 12,000 ft (4000 m) long.

This service is not sold to subscribers as DSL service, but as T1/E1 point-to-point service.

Single-Pair Digital Subscriber Line (SDSL)

SDSL, also known as symmetric DSL, provides T1/E1 service on a single cable pair and derives a POTS line under the data signal. It transmits and receives in the same band of frequencies using an echo-canceling protocol.

Cable Access TechnologyCable operators inject information and entertainment

channels at the head end.Standard TV channel:• 6MHz wide• QAM modulation• 1channel= 27Mbps of downstream data

The service provider decides how many subscribers will share the bandwidth. There are 2 streams:

Upstream Downstream

Data Over Cable System Interface Specification(DOCSIS)

DOCSIS is an international Telecommunication Standard. Consortium of equipment manufacturers developed DOCSIS as a standard method of providing Internet access.

•In Europe=>Euro-DOCSIS(USA’s version) •Over a 6 MHz Radio Frequency channel

DOCSIS is designed for cable but it can also be used in Wireless Multipoint Multichannel Distribution Service(MMDS)

Link security layer consists of 3 security protocols:•Baseline Privacy Interface(BPI) =>encrypt data traffic between the user’s modem

•Security System Interface(SSI)•Removable Security Module Interface(RSMI)

DOCSIS compared to OSI

• TCP-Transmission Control Protocol

• UDP-User Diagram Protocol• IEEE 802.2 – protocol of

LLC(Logical Link Control) standard

• TDMA-Time Division Multiple Access

• MPE-2 – Motion Picture Experts Group 2

• QPSK- Quadrature Phase Shift Keying

Wireless AccessWireless is the broadband access method to provide many users as Internet.Service: - Licensed(Satellite, Cellular) -Unlicensed (802.11)

Wireless has a cable with medium is shared.Downstream Upstream

o FDMA(Frequency Division Multiple Access)o TDMA(Time Division Multiple Access)o CDMA (Code Division Multiple Access)

oWhy wireless access?

Wi-Fi 802.11 and WiMAX 802.16

Wi-Fi 802.11(Wireless Fidelity)- standard for unlicensed frequencies

Wi-Fi frequency Ranges: 2.4GHz band(older)

•2.4-2.4835GHz•11unlicensed communications channels

5GHz band(newer)• 5.1GHz; 5.3GhH; 5.4GHz; 5.8GHz• 24 unlicensed bands

Wi-Fi benefit: Wide range It covers airport, coffee shops, some street corners

• WiMAX 802.16 (Worldwide Interoperability for Microwave Access)

• WiMAX range is around 16km.• WiMAX benefits:

High security Low cost Open standards Wide coverage

• WiMAX Applications:1. Gaming with many players2. Video Conferencing3. Streaming Media4. Web browsing and Instant Message5. Media content Downloads

MMDS(Multipoint Multifrequency

Distribution Service)

MMDS was originally intended as a wireless replacement for cable television with 200 MHz of spectrum allocated between 2.5 and 2.7 GHz.

CDPD (Cellular Digital Packet Data)

CDPD is a packet overlay on cellular sites.

3G: Third Generation Cellular

Third generation (3G) cellular is intended to support Internet access from a cell phone or equivalent.

• Regulatory Issues:In the United States, Congress and the FCC have a major

role to play in broadband development and the outcome is difficult to predict.

• Choice of Medium:Cable access is available in localities in which the cable

operator has upgraded the facility to two-way and provides access service over the cable.

Voice and Video ServiceInternet access is asymmetric in nature, so the

limited upstream bandwidth of cable, wireless, and DSL are appropriate.

Micro radio system is included in access technology.

Microwave Radio Systems

Microwave Technology

Radio Signal Propagation

• When designing microwave systems, engineers take into account the following conditions that affect signals:

Free-space lossAtmospheric attenuationReflectionDiffractionRain attenuation

Microwave systems

Parabolic Horn Antennas

The general principles of microwave radio are the same as those of lower frequency radio.

A second cause of fading is heavy rain, which absorbs part of the transmitted power. The effect is most detrimental at frequencies higher than about 10 GHz. Diversity, as described in a later section, alleviates the two primary causes of microwave path disruption, which are fading and equipment failures.

Microwave Repeaters

Point-to-point microwave routes are established by connecting a series of independent radio paths with repeater stations. Line of sight is required between the transmitting and receiving antennas for all microwave systems except MIMO and those that use forward scatter techniques to transmit beyond the horizon.

Multipath Fading and Interferences

• Multipath reflection

• Adjacent channels

• Cross polarization- 20to 30dB

Microwave antennas

Microwave antennas’ features:

Parabolic dishesHornsDiameters

•Less than 1m for short distance

•30m for Earth Station Satellite Systems

Connected by coaxial cable

Microwave tower

Some troubles(because of our environment)

• When microwave signal radiates into free spaces, it is attenuated by losses.

Losses are:Temperature inversionsRainFogSnowLightning so on….

Thank you for your

attention!