Cambium College Webinar

Transmission Schemes and Frequency Bands

David Geitner

Systems Architecture Team

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Cambium College – Topic Summary to date

Foundation3/21 Parts of a radio and PTP/PMP/WLAN

4/04 Radio wave propagation and antennas/reflectors

4/18 Interference and Mitigation techniques

5/02 Transmission Schemes and Frequency bands

5/16 WiFi Networks

Applications6/06 Real world applications – service providers

6/20 Enterprise and IoT applications

7/18 Streaming video and throughput uplink/downlink

8/01 MIMO and MU-MIMO

8/15 Guest Speaker: Network Operator

Optimization09/05 Planning a link and the network

09/19 IPv6 and configuration

10/03 Security and Encryption

10/17 Managing the Network

11/07 Maintaining the Network

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RF Spectrum and Frequency Bands

What is RF Spectrum? Does it really matter?

Whenever we are communicating wirelessly in ANY manner, we need to use some portion of RF Spectrum.

Who determines this?

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RF Spectrum and Frequency Bands

Radio SpectrumRadio spectrum is the part of the electromagnetic spectrum from 3 Hz to 3000 GHz (3 THz).

Electromagnetic waves in this frequency range, called radio waves, are extremely widely used in modern technology, particularly in telecommunication.

The Federal Communications Commission (FCC) is

the government agency that keeps track of who's

using which slivers of spectrum. This agency

grants companies licenses to use the spectrum… but

not all spectrum is Licensed! Unlicensed exits too!

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RF Spectrum – United States Spectrum Allocation Map

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RF Spectrum and Frequency Bands

Lower Frequencies (Less than 1Ghz) HIGH VALUE!

Travels farther distances with less energy

Obstacles (trees, buildings, things) have relatively small effect on attenuating LF RF energy

Relatively limited amount of Spectrum in this Range

Higher Frequencies (Greater than 1Ghz)

Takes more energy to travel far distances

Obstacles (trees, buildings, things) have greater effect on attenuating energy

More available Spectrum in this Range

Radio Spectrum – Key Valuation Points

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RF Spectrum and Frequency Bands

Licensed Spectrum HIGH VALUE!

Application for usage required… can take time!

Usually requires a fee ($$) to use… can be substantial!

Provides protection for the user from Interference

Unlicensed Spectrum Can be used without Application or Fee… Immediate!

With new additional allocations, typically available for use

No Legal protection for the user from Interference

Radio Spectrum – Licensed vs Unlicensed

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RF Spectrum and Frequency Bands

VHF (138-174 MHz) – The original standard for push-to-talk voice

– One of the first frequencies to be widely used is still the go-to for marine, air-to-ground and land mobile radio (LMR) radio users. Licensed spectrum.

UHF (406-470MHz) – A multipurpose performer in urban environments

– Another popular LMR frequency for push-to-talk voice, UHF offers better building penetration and tends to perform better in urban environments. UHF is also used for affordable SCADA applications. Licensed spectrum.

700 MHz – The new spectrum for public safety

– 700 MHz available only for public safety and related organizations. Licensed only for public safety.

800 MHz – Still popular for LMR trunking systems

– Public safety use is declining quickly in favor of 700MHz, but expect to see it continue for commercial applications like oil & gas plants. Licensed spectrum.

900 MHz – Sometimes overused license-free spectrum

– Widely used for everything from your cordless phone (if you still have one) to your rural wireless internet service provider. License-free spectrum.

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RF Spectrum and Frequency Bands

2.4 GHz – The go-to for WiFi

– Another license-free and busy piece of spectrum. License-free

3.65 GHz – Working on the promise of WiMax

– Municipalities and wireless internet providers (WISPs) typically deploying point-to-multipoint with some comfort of more controlled spectrum. Lightly licensed

4.9 GHz – Broadband for public safety

– Set-aside protected for public safety and associate users. Ideal for point-to-point links for public safety applications like backhauling video surveillance and linking public safety towers and sites. Licensed

5.7/5.8 GHz – Broadband for the rest

– Excellent for both point-to-point and point-to-multipoint applications that need bandwidth and now also WiFi. It’s license-free which means spectrum cannot be protected, but good RF planning and design can deliver high-reliability bandwidth for a wide range of public and private sector uses. License-free

6–30 GHz – Microwave spectrum for high-bandwidth high-reliability requirements

– Used for high-performance point-to-point links when big bandwidth and/or high availability is critical. This is licensed spectrum which provides confidence that your deployment will have dedicated frequencies. Licensed

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RF Transmission Schemes

• Simplex vs Duplex

• Time Division Duplex (TDD) vs Frequency Division Duplex (FDD)

• Single Carrier vs Multi-Carrier

• SISO vs MIMO

• Scheduled vs Random Access

• Synchronized vs Non-Synchronized

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Simplex RF Communication Scheme

Simplex means Only One-Direction

Communication

Transmitter

Home

Wireless Examples

OTA Broadcast TV

AM/FM Radio

Public Address System

One-Way AMR

Receiver

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Duplex RF Communication Scheme

Home

Transmitter

& Receiver

Half DuplexOnly One Direction at a Time

WiFi (Wireless LAN)

Two Way Communication

Full DuplexBoth Directions Simultaneously

Cellular Phones (LTE, 3G)

Transmitter

& Receiver

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Time Division Duplex

Uses One Carrier Frequency; “Reverses” Many Times

• Typically “reverses” 200 times per second (5ms)

• The “guard time” separates the direction

TransmitterMediumReceiver

Transmitter Medium Receiver

Time

Time

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Frequency Division Duplex

Uses Two Carrier Frequencies

• Forward/reverse or Downlink/Uplink

• Has “guard band” that separates the channels

TransmitterMediumReceiver

Transmitter Medium Receiver

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Single Carrier vs Multi-Carrier OFDM

Single-carrier QPSK/QAM is proven technology. Time-division systems can

provide fast, dynamic capacity allocation, which is ideal for statistical multiplexing of

bursty sources

Orthogonal Frequency Division Multiplexing (OFDM) is a type of multicarrier

modulation. OFDM uses overlapped orthogonal signals to divide a frequency-selective

channel into a number of narrowband flat-fading channels.

Advantages Disadvantages

Proven and Simple Technology Susceptible to Interference & Multipath

Advantages Disadvantages

More Complex and Costly Can Mitigate Interference & Multipath

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SISO vs MIMO

SISO – Single Input Single Output

MIMO – Multiple Input Multiple Output

These are techniques based on number of antennas

used at the transmitter and the receiver.

Difference between SISO and MIMOIn SISO system only one antenna is used at the Transmitter

and one antenna is used at the Receiver.

In MIMO case multiple antennas are used.

(Figure to the right depicts 2x2 MIMO case)

MIMO system achieves better Bit Error rate compared to

SISO counterpart at the same SNR. MIMO system also

delivers higher data rate due to transmission of multiple

data symbols simultaneously using multiple antennas, this

technique is called as Spatial Multiplexing (SM).

SISO

TX

SISO

RX

MIMO

TX

MIMO

RX

Antenna Polarization (V/H, +45/-45)

MIMO-A (Single Payload)

MIMO-B (Dual Payload)

MU-MIMO

XPIC

Related Concepts:

http://community.cambiumnetworks.com/t5/PMP-

FAQ/Throughput-vs-Range-An-Explanation/td-p/37199

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Scheduled vs Random Access Transmission

Impacting Attributes:

• Latency of Data Transmissions

• Scalability of Radio technology

• Complexity of Configuration

• Flexibility of traffic services offered

• Ability to provide good QoS

• Standards based vs Proprietary

• Price delta

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The Need for Synchronization:Interference Due to non-Synchronization

AP5

AP4 AP3

AP2

AP1AP6

SM

AP1

AP2

AP3

AP4

AP5

AP6

CMM

Each Access

Point is

transmitting at

a different time

AP: Access Point

Synchronization - Why

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Synchronization: Common Sync Source Reduces System Interference

AP5

AP4 AP3

AP2

AP1AP6

SM

AP1

AP2

AP3

AP4

AP5

AP6

CMM

Each AP is

transmitting

at the SAME

time

AP: Access Point

Synchronization - How