Mediums of Communication may be categorized broadly as

Electro Magnetic Spectrum1.Radio

Frequency- 300Hz to 300GHz, Wave length - >10 cm,Energy- < 10 ^ -7 eV

2.Microwave3.Infrared4.Visible light5.UV rays6.X-rays7.Gamma rays WL -10^-9 cm, E - >10^5 eV.

• 1. Coverts wire propagated wave to space propagated wave

• Basic condition – Height = Lamda/2• Frequency range• Gain• VSWR• Horizontal / Vertical Beam width

Antenna Basics

Properties of EM wave

• 1. Carries Energy and momentum• 2. Propagates by oscillating electric and magnetic fields right angles to each other • 3. Travels at a speed of Light• 4. Transverse waves – Oscillations occurs

perpendicular to the direction of energy transfer

• * Ground / space / sky wave propagation

1.AM/FM & TV ( Simplex)2.Walkie-Talkie (Half Duplex)3.GSM (Full Duplex)4.WiFi and Wi-MAX5. Satellite (DTH and VSAT)6.WLL ( Wireless in local loop)

Examples of Radio communication Services

Emergence of WLL concept

Problem in “Last mile Connectivity” (That is in Copper based Local Loop)

1. Copper is Costly 2. Installation is time consuming3. Fault Prone/EM Interference4.Mntce difficult and time consuming5. Cost per line depends on Distance

Multiple Access Techniques

Multiple Access Technique s1.TDMA2.FDMA3.CDMA

Evolution of CDMA1.IS95-A2.IS95-B3.2001X4.1X-EVDO –Release 0 1X-EVDO-Revision A (EVDV)

Difference between GSM and CDMA

Sl No Parameters GSM CDMA

1 Access technology FDMA & TDMA CDMA only

2 Modulation / Coding technique

GMSK / RPE-LTP (Regular pulse Excited long term prediction)

QPSK or OQPSK / QCELP or EVRC

3 Frequency band 890-915 / 935-960 824-849 / 869-894

4 Channel BW 200 KHz 1.25 MHz

5 Planning requires Frequency planning Power planning

Advantages of CDMA

• 1. Large Coverage – for 1000sq km GSM- 200BTS , CDMA-50BTS.• 2. High spectrum capacity – 4 to 6 times GSM• 3.High security• 4.Soft handoff – make before break• Good voice quality – 13k –QCELP• Mean power- 2mw to 200mw GSM – 125mw to 2W

Disadvantages of CDMA

• 1 Proprietary nature ( Qualcom- US)

• Can not offer International roaming

• New network ( Not familier)

Shannon’s Equation

• C = W x log2(1 + S/N)

whereC = Channel CapacityW = Bandwidth availableS/N = Signal to Noise Ratio

• Increasing the Bandwidth and thereby increasing the Channel Capacity forms the basis of CDMA.

• S/N can be increased by devising proper Power Control methods.

Spread Spectrum Techniques

• 1. DSSS

• 2. FHSS

• 3. THSS

Spread spectrum principle

Direct Sequence Spread using Walsh code Consist of 64 orthogonal codes each 64 bits long Spreads spectrum to 1.2288 M bps from 9.6 Kbps

Channel Capacity C=W log (1+S/N) Increasing BW improves Signal Transmission with lower S/N

Frequency

Power

Spectral

Density-------------------------------------------------------------------------------------- Noise Level

Narrow Band Waveform

Spread Waveform

PN CODES

• 1. Short PN – 2 ^15• Long PN – 2 ^ 42 ( takes 41 days for a cycle)• Walsh Code 64 codes of 64 bits length

Walsh Code GenerationOrthogonal Property ( XOR ing the codes Equal

nos of 0’s and 1’s.

MSC Based WLL Architecture

CDMA / WLL – 2001X

• Architecture

1.Mobile Station(MS)2.Base Station Subsystem(BSS) 3.Mobile switching Subsystem(MSS)4.Packet Data Switching Subsystem(PDSS)5.Operation and maintenance subsystem(OSS)

OMCS and OMCR