NLOS Infinet Version 1.0.1

R5000 series - NLOS

Software Version: MINTv1.90.5

Last updated: 4/1/2014

Whitepaper

Infinet NLOS whitepaper

Document structure

This document consists of the following chapters:

Purpose of this document - This chapter presents the information about this

documents purpose and structure

Introduction to NLOS - This chapter provides descriptions to non line of sight

scenarios and to challenges for such scenarios

Technology overview - This chapter provides descriptions to radio technology

features to improve signal reception and recognition in NLOS scenarios

Theoretical estimations - This chapter provides descriptions how to estimate

and evaluate NLOS scenarios

Infinet Unique features - This chapter provides descriptions solutions specific

to Infinet Wireless to improve data transfer with NLOS scenarios

Practical example - This chapter provides the description of one of the NLOS

installation in England

Conclusion - This chapter provides the brief summary of the NLOS scenarios

with Infinet Wireless equipment

Abbreviations

The following abbreviations are used in this document:

MINT - mesh interconnection networking technology

FDD frequency division duplex

LoS line-of-sight

NrLoS near line of sight

NLoS non line-of-sight

OFDM orthogonal frequency division multiplexing

TDD time division duplex

BWA broadband wireless access

MIMO - Multiple-Input and Multiple-Output

MISO - Multiple-Input and Single-Output


Purpose of this document

Infinet Wireless is one of the leading manufacturers of Broadband Wireless Access

equipment mostly for carrier grade fixed installations. The majority of wireless

installations using Infinet equipment have clear visibility from one end of the link to the

other with no obstacles in the first Fresnel Zone. However, for many requirements,

especially backhauls for LTE, clear line-of-sight is not possible.

This document shows that high capacity and high availability, non line of sight wireless

links are achievable for just such an application.

The purpose of this document is to define a wireless link which is operates in line of

sight, near line of sight and non line of sight. It will explain the effects on the RF

signal caused by different obstructions and how the radios overcome these to provide a

high capacity and reliable wireless link. Moreover, the document provides configuration

tips specific for Infinet Wireless equipment that are very useful with 'near line of sight'

and 'non line of sight' installations. It also gives an example of a non line of sight link

that achieved 100Mb/s aggregate throughput.


Introduction to NLOS

A Fresnel zone is one of a theoretical infinite number of concentric ellipsoids which

define volumes in the radiation pattern of an antenna. Or simply put; the RF energy

collected at a radio receiver is the sum of the energy transmitted which had traveled

in both a straight line and an infinite number of elliptical paths from transmitter to

receiver. Energy that has traveled along odd Fresnel zones is in phase with the direct

path but energy that has traveled along an even Fresnel zone is out of phase with

the direct path. The widest radius of the nth Fresnel zone is dependent on the radio

frequency (or wavelength) and the path length. Radio frequency engineers are

primarily interested in the 1st Fresnel zone only. The radius of this can be calculated

using the following formula

LoS is a link where the 1st Fresnel zone is completely unobstructed.

NrLoS is a link where the 1st Fresnel zone is partially obstructed (


Diffraction

Every radio wave changes when it encounters an obstacle. When an

electromagnetic wave reaches the edge of a sharp obstruction, diffraction occurs

the process of signal deformation and change in direction.

In reality, the energy of the wave is scattered in the plane perpendicular to the edge

of the building. The energy loss which can be considerable is proportional to

both the sharpness of the shift and the frequency of the wave. The effect on the

signal depends on the obstacle. If it is a knife edge obstruction, for example a

building which is perpendicular to the wireless link, then the signal is more likely to

experience diffraction and hence attenuation but not reflection.

Reflection

Wireless links with optical line of sight and a good RF reflector off-axis at the optimal

angle will perform reliably on the direct beam or a reflected beam. During

alignment, it is possible to see the received signals amplitude and cross polarization

isolation vary as the receiver collects RF energy from the direct path or a reflection.

If the link passes down a narrow street lined with tall buildings, the energy will

reflect off the front of the buildings even around corners, and can still be received

at the remote end reliably. If both an in-direct and direct signal are received with

similar amplitudes, the time delayed reflected signal could be received out of phase

to the direct signal. This echo could cancel out the direct signal causing errors in

the decoded signal.

Absorption

Penetration occurs when radio waves pass through an object or building that

completely or partially obstructs the line of sight. Path loss resulting from

penetration is highly dependent on frequency and the obstruction material, this

normally prevents the ability to operate NLoS links experiencing absorption at

frequencies above 5 GHz. However, some research has shown that in reality path

loss due to penetration is only slightly dependent on frequency, and that in fact it is

the type and thickness of the object itself that creates the impact on throughput.


If the link is partially obstructed by a tree, then many factors affect the link:

absorption reflection and diffraction. The key factor affecting the loss in NLOS

scenarios is diffraction losses from buildings and tree lines. The main parameter is

the ratio between obstruction depth and the Fresnel zone radius. The attenuation

as a function of clearance is indicated below:

Fresnel zones Attenuation

0.5 zone clear -2 dB

0 (touching) -6 dB

0.5 zone obstructed -10 dB

1.0 zone obstructed - 16 dB

1.5 zone obstructed -19.5 dB



3.0 zone obstructed -25.5 dB

Note that at deeply obstructed LOS, additional factors may come in, such as the

shape of the obstruction (edges of the building) or penetration through trees, in the

case of tree line.


Technology overview

OFDM

The OFDM modulation concept is to create a wideband signal consisting of a

number of independent or orthogonal subcarriers, each carrying a low bit rate data

stream. The low data rate bit stream allows for a sizeable guard band at the

beginning of each symbol, effectively isolating the symbols from each other and

neutralizing the effect of delay spread. In addition, the subchannelized operation in

conjunction with the proper error correction system proves to be very tolerant of

narrowband multipath fades. In most cases, only a limited number of subcarriers

may be affected by a fade, causing the loss of symbols. With the remainder of the

wideband signal unaffected, the error correction system takes over and is able to

reconstruct the small percentage of missing data bytes.

OFDM and NLOS

OFDM is a key element in the NLoS solution. The significant amplitude of the signal

loss between a transmitter and NLoS receiver, due to obstructions and multipath

fading, mandate additional measures be taken to increase system gain.

The most obvious way to increase the system gain is by increasing the transmitters

RF output power or the receivers sensitivity. Due to strict linearity requirements for

an OFDM system, a high power OFDM transmitter is difficult to achieve. Improving

the receivers sensitivity is also difficult to achieve without sacrificing data

throughput.


MIMO

There have been recent successes to combat link attenuation involving

sophisticated methods of spatial and time diversity.

Space-time coding and multi-input / multi-output (MIMO) radio systems are able to

access the real time channel conditions to adjust how the data is sent to multiple

transmit antennas and how best to extract symbols from multiple receive antennas.

MIMO (Multiple Input and Multiple Output)

Use of multiple antennas at both the transmitter and receiver side to improve

communication performance. Data is sent on both the horizontal and vertical

polarizations. Data is space-time coded (spatial multiplexing) to improve the

reliability of data transmission. Infinet MIMO 2x2 technology effectively doubles

spectrum efficiency and allows to achieve real throughput up to 280 Mbps in 40

MHz band (please see picture below).

Data transmission path in Infinet Wireless MIMO products

MULTIPATH PROPAGATION

Multiple reflections results in signal multipath propagation. Multipath appears

when obstacles exist between the units locations. In such conditions the

transmitted signal experiences reflection, diffraction and scattering, which causes

multiple echoes of the same signal to arrive at the receiver at different times.


ISI

The effect of multipath phenomenon on wireless communication is ISI - InterSymbol

Interference. The echoes of a certain symbol (namely symbol n), resulting from the

multi path nature of an NLOS link, are seen as interference to the subsequent

symbol (namely symbol N+1). OFDM technology overcomes the ISI problem by using

a Guard Interval (GI) period at the beginning of symbol. The Guard Interval period is

actually the part of the symbol that is corrupted by the ISI. The data period that

follows the Guard Interval carries the data payload.

The use of OFDM accounts for high data rates and high spectral efficiency. This is

achieved by parallel transmission of multiple sub-carriers over-the-air, each capable

of carrying modulated data (up to QAM 64 5/6 with Infinet Wireless units). The sub-

carriers are placed on orthogonal frequencies. Orthogonality means that the central

frequency of a certain sub carrier coincides with the nulls of the other sub carriers.

The use of orthogonal frequencies avoids interference between the different sub

carriers, therefore enabling usage of QAM modulation on each carrier, thus

achieving very high spectral efficiency.


Theoretical estimations

System properties

A simplified NLoS link budget can be obtained by adding the additional NLoS path

attenuation (Lnlos) to the traditional LoS link budget, as shown below:

Prx=Ptx +Gtx+Grx 20log (d ) 20log ( f ) Lf Lnlos

Here,

Prx + Ptx are the received and transmitted power (dBm ratio of power in decibels

referenced to 1 milliwatt)

Gtx and Grx are antenna gain (in decibels referenced to an isotropic radiator dBi) for

the transmitter and receiver respectively

d is the link distance (in kilometers)

f is the frequency (in GHz)

Lf is atmospheric loss (in dB)

Lnlos is the additional loss (in dB) resulting from the deployment of a NrLoS or NLoS

link

For example: Infinet Wireless units for 3.5 GHz frequencies could use up to 64QAM

modulation in a 40MHzwide TDD channel with a 2x2 MIMO (dual-polarized)

configuration providing full duplex peak throughput of 150Mbps (300Mbps

aggregate).


Diffraction

It is commonly believed that the diffraction losses occurring at frequencies around

3 GHz are prohibitively high, and consequently, deploying a system using this effect

for NLoS propagation at such frequencies is not feasible. However, even if the

absolute loss can be relatively high, 34dB for (with a diffraction angle of 30 degrees),

in comparison the relative difference will be only 6dB much less than the

difference in gain for comparable antenna sizes.

Reflection

Reflection loss is strongly dependent on the material of the reflecting object. It is

possible to cover areas that are difficult to reach using multiple reflections in

principle. However, taking advantage of more than two reflections is in practice

problematic due to limited link budget and the difficulty of finding suitably aligned

reflective surfaces. Lnlos predictions for a single reflection can be expected to vary

between 5dB and 20dB.

Penetration

As with the case for NLoS reflection, the path loss resulting from penetration is

highly dependent on the material of the object blocking the line of sight.

Consequently, the excess path loss for the single-tree scenario varied between 0

and 6dB. In the double-tree case excess path loss varied from 8dB to 20dB. It must

be noted that trees obstructing the path cause an additional problems primarily

that the channel behavior can vary rapidly over time, thus preventing the radio from

compensating.


Infinet Unique Features

Adaptive Polling (Dynamic TDD)

To prevent over-the-air collisions Infinet Wireless uses polling (marker access),

where one of the devices plays the role of the communications master. This master

device consequentially gives the right for transmission and reception to every slave

device in the wireless network. Using polling effectively lowers delay and jitter and

allows the use of wireless networks for real-time traffic delivery.

Infinet Wireless devices use a single frequency for transmitting and receiving data

over the wireless links. In this case Dynamic Time Division Duplex (Dynamic TDD)

multiplexing technology is used to enable full duplex data transmission. Dynamic

time slots are allocated for data going in both directions, allowing any ratio for

upstream/downstream data flow, depending on the demand in free bandwidth. The

size of the allocated time slots depends on the amount of traffic, priority, number

of retries and errors on the link, thus allowing Infinet Wireless effectively serve any

kind of data streams Internet, VoIP, CCTV, etc., as the timeslot structure adapts to

the data flow, resulting in the most effective data transmission with the lowest

latency and packet loss rate.

Classical TDD systems (Exalt, Orthogon) allow only fixed ratio for incoming/outgoing

data flow (50:50, 30:60, etc.). Some systems (e.g. Winlink and most microwaves)

allow fixed 50:50 ratio only without the capability to alter ratios. Other TDD systems

can be statistically adjusted from the base ratios.


MISO

Reflections could cause vertical polarization outputted from one unit could be

received by horizontal transceiver of other unit. Also, such polarization swap could

happen constantly all the time. However, this effect could be easily solved by

switching Infinet units to special 'multiple-input-single-output ' (MISO) mode. MISO

mode with Infinet Wireless results in simultaneous transmission of the same data

signal using both (vertical and horizontal) polarizations, hence on the reception side

the unit receives the same data to both (vertical and horizontal) transceivers. The

effect is immediately twice less data, however such mode significantly improves

signal reception quality and doesn't care about polarization swap effect. MISO mode

is extremely helpful to 'stabilize' the link especially when the units works with

reflected signals.

MISO (Multiple Input Single output)

Special mode of operation of MIMO devices. It is used in nLOS conditions or in a

noisy RF environment. In MISO mode the same data is transmitted over both

polarizations, lowering the performance of the link, but enhancing the ability to

transmit data in case of interference or obstacles in transmission path (please see

picture below)

Data transmission path in Infinet Wireless MIMO products in MISO mode


MINT

MINT stands for Mesh Interconnection Network Technology which points to the

technology for networks based on arbitrary connections. Therefore MINT allows to

create networks combines from any inner topology (mesh, ring, star, ptp, etc.).

Meanwhile it is guaranteed the customer traffic delivery would be done using the

fastest route available between any MINT supported nodes at every single time

period.

The route will be selected with account to:

Current links load between MINT supported nodes

Throughput available

Wireless link quality

Error rate

Optimal route consistency is being checked in real-time. The most important criteria

for route selection are:

Minimal RTT

Maximum throughput

Route switch will be performed seamlessly and immediately due to link quality

change. There will be no packet or sessions lost during route switch process.

Route switch to backup route will take fraction of second in case of instant main

route failure. Redundant connection increase network reliability, also MINT

protocol is loop free protocol. MINT algorithms exclude loop creation and are

suitable for transmission of multicast traffic, video surveillance.

MINT has one important principle at its basis:

No matter the complexity of inner network structure, MINT would provide the best

quality data transfer service.


MINT features

Architecture - Virtual Ethernet

All units are treated as independent peers. It is possible to assign different

peer roles using configuration settings.

Any topology connection possible: PtP, PtMP, Mesh, Tree, Ring, Full Mesh

Independence from IP level (Layer 3) protocols

Unified MINT network via interconnection between different MINT

domains, between different PtMP (with different frequencies), etc.

Interconnection tools - using JOIN, PRF, MINT-over-IP, MINT-over-Ethernet

Multiple connections to unlimited number of MINT nodes with optimal

transport path selection

Frequency roaming support

Mobile CPE connection support

Built-in QoS policies, Automatic QoS

MINT resides between Data Link Layer and Network Layer in accordance with OSI

network model

Another approach to solve the NLOS issue is to adopt to ever-changing radio

communication medium (air) by using at least 2 radio units at one installation point

with possibility to utilize better Signal-to-Noise signal levels of one or other unit for

every data transmission. The idea is to configure each unit to different central

frequency hence to different Base Station or any other neighboring unit. Next, we

interconnect both units to each other by MINT protocol through wired switch using

special Pseudo Radio Interface (Logical interface). After it we interconnect both

wireless MINT domains through wired MINT domain using JOIN command. The

diagram below illustrates such scenario.


Practical results

One early NLoS scenario occurred during installation of a wireless video surveillance

system in Bishop's Waltham, Hampshire, England. Additional relay installations

were restricted. The results were obtained using Infinet Wireless link test

procedure.

Example output of the Infinet Wireless link test:

Achieved link test results are shown below:

Required RF bitrate

ltest rf5.0 000e8e19ce50 -tb 15

Bidirectional throughput test to 000E8E19CE50 via rf5.0 with no priority

packet size 1536, bitrate 52000, reply bitrate 52000

Please wait...............

=============================================================================

Direction | Kbit/s | Pkt/s | Retries | Errors | min/avg/max/stddev (usec)

=============================================================================

Transmit | 26221 | 2185 | 2.93% | 0.00% | 35/457/49250/1638

Receive | 13599 | 1133 | 1.99% | 0.00% | 19/882/59101/3012

-----------------------------------------------------------------------------

Total | 39820 | 3318 |

-----------------------------------------------------------------------------


Maximum RF bitrate

ltest rf5.0 000e8e19ce50 -r 130 -tb 15

Bidirectional throughput test to 000E8E19CE50 via rf5.0 with no priority

packet size 1536, bitrate 130000, reply bitrate 130000

Please wait...............

=============================================================================

Direction | Kbit/s | Pkt/s | Retries | Errors | min/avg/max/stddev (usec)

=============================================================================

Transmit | 47593 | 3966 | 3.08% | 0.00% | 30/252/29485/1491

Receive | 47469 | 3955 | 2.58% | 0.00% | 15/252/53173/1189

-----------------------------------------------------------------------------

Total | 95062 | 7921 |

-----------------------------------------------------------------------------


Both NLoS links can be seen in this map:

BW Camera to BW Relay at only 129m, then onto BW Police Station at 332m. Both

points are located very non line of sight.

Camera to relay obstructions


Relay to Police Station obstructions

BW Camera location


BW Relay location

View from BW Relay to BW Camera


View from BW Relay to BW Police Station


Conclusion

The short link length helped boost system gain and enabled reliable NLoS link

performance even at high data throughput.

In both of these links, the obstructions were quite stable and will have primarily

caused diffraction and absorption.

The ability to operate in near line of sight and non line of sight conditions is crucial

to the future use of Broadband Wireless Access (BWA) as an access technology.

Understandably, operators need to know that BWA can be deployed anywhere, and

can overcome obstacles such as mountains and trees in rural areas, and buildings in

suburban and dense urban areas. Such capabilities allow for various deployment

scenarios from private residential homes in suburban areas to offices and

businesses in central urban areas, thus giving operators the advantage of catering

for the whole broadband access market with a single BWA system. The benefits of

having BWA systems with NLOS capabilities are:

Better coverage and penetration, which enables the provision of BWA services

to previously unserved customers, thus increasing the revenue potential for

the Operator/Service Provider.

Reduced operation and installation costs, resulting from faster and simpler

installation procedures that do not dictate mandatory LOS conditions and may

save the need to install additional accessory equipment such as high masts,

etc.

NLOS Infinet Version 1.0.1

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