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Module 1(Lecture 4)

Design Consideration for wireless

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Main design objective

Maximum data rate.

Minimize expenditure on

Signal power.

Channel bandwidth.

Transmitter and receiver complexity.

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Design of wired transmission

Transmission schemes of Twisted pair, co-axial cable and fibre optical cable are

simple.

Purpose is to provide higher data rate and higher bandwidth efficiency.

High bandwidth efficiency result in:

Reduced connect time.

No need for leasing additional circuitry to support application in hand.

A typical telephone channel is less hostile than radio channel.

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For wireless modems

Radio channels are characterized by multipath fading and Doppler

spread.

Main considerations:

Power.

Bandwidth efficiency.

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Bandwidth efficiency

More bandwidth more usersmore revenue

One example:

Cellular industry. Licensed band. Increased capacity means more users

On the contrary:

WLAN where bandwidth efficiency is not as critical as cellular.

Burst-mode traffic.

WLAN rarely approaches system capacity.

Unlicensed band.

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Power efficiency

Power requirement : Power required by the electronics

in the terminal device. Amount of power required at the

output of power amplifier toradiate signal power from theantenna. Function of :

High data rates need highSNR.

More complex receiverdesign needs less transmittedpower.

A trade-off between complexityof receiver and electronic

power consumption.

Example: some handhelddesign avoids using complexspeed coding to reducebattery consumption.

Source: Principal of Wireless Netwoks: A Unified Approach PHI by Pahlavan

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Adjacent channel interference

An important design parameterthat limits the operation between

two adjacent channels in cellularnetwork.

ACI determines the geographical

area of cell.

ACI indirectly influences systemcost and capacity.

Radio design: keep ACI -60 dBbelow the main lobe in thespectrum.

Source: Principal of Wireless Netwoks: A Unified Approach PHI by Pahlavan

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Wireless transmission technique

First category: Pulsetransmission used for IR

application or ultra-wide-band(UWB) transmission. (Baseband- used for short distance)

Second, basic modulationusing TDMA.

Third, spread spectrum used inCDMA and WLAN.

Source: Principal of Wireless Netwoks: A Unified Approach PHI by Pahlavan

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Short distance baseband

Pulse modulation. Pulse Amplitude

Modulation (PAM) :lesspopular.

Pulse Position Modulation(PPM).

Pulse Width Modulation

(PWM).Example:

wired: IEEE 802.3 Ethernetfor LAN.

wireless: IEEE 802.11High speed IR for WLANand Ultra Wide Band(UWB).

Source: Principal of Wireless Netwoks: A Unified Approach PHI by Pahlavan

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What is Ultra wide Band (UWB)

An impulse in time-domain results in Ultra Wide

band in time domain and essentially looks like a

white noise to other devices.

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Ultra-Wide Band (UWB)

FCC restricts the maximum noise generated by wireless equipment

(0dBm = 1mW, -40 dBm= 0.1 mW.

Very short pulses (in ns).

FCC approved UWB in 2002.

Finds use in short distance wireless

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UWB

Sub-nanoseconds impulses are sent many million time

times per second = 25 to 400 ps.

0.25 ns impulse = 100 Mbps.

Became feasible with high-speed switching

semiconductor devices.

May be position, amplitude or polarity modulated.

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Advantages of UWB

Large bandwidth.

Low signal-to-noise ratio.

Low probability of intercept and detection.

Resistance to jamming.

Superior penetration properties at low frequency spectrum.

Shares spectrum with other applications.

All digital. Low cost.

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Advantages UWB

Very Low energy consumption.

Line-of-Sight not required. Passes through object.

Pulse width much smaller than path delay:

Hence easy to resolve Multipath.

Also can use Multipath.

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