Xmax Technology Full Documentation

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1.INTRODUCTION
1.1 Current Situation:
Wireless operators today are facing a dilemma. Customers are demanding more and
more data applications to be delivered on the go. However, the operator is using scarce
expensive licensed spectrum that is overburdened with delivering core voice services.
Support for voice, data, location awareness, chat and other applications are required for
customers that are very mobile. The operator is facing a choice of acquiring more licensed
spectrum (if any is available) or losing customers due to demand for advanced services. xG
Technology has a solution to this dilemma of overwhelming demand for advanced
applications versus lack of spectrum.
xG Technology is developing an affordable mobile voice and data cellular system that
operates in free unlicensed bands using what is known as cognitive radio technology. Using
cognitive (i.e., smart) radios and advanced system and signal processing capabilities, the xG
system makes unlicensed spectrum communications as reliable as licensed band
communications. This is made possible by effectively mitigating the interference in the
congested and chaotic unlicensed bands. Another advantage of xG’s cognitive radio
approach is the reduction of the RF engineering the operator needs to deploy and maintain the
system.
1.1.1 Cognitive Radio:
Cognitive radio (CR) is a form of wireless communication in which a transceiver can
intelligently detect which communication channels are in use and which are not, and instantly
move into vacant channels while avoiding occupied ones. This optimizes the use of available
radio-frequency (RF) spectrum while minimizing interference to other users.
A third benefit of this system is the ability to reuse all the engineering going into
smartphones, tablets and laptops today. The xG system is designed to support these devices
through a physical or WiFi connection. Finally, the xG system is all-IP protocol based so that
it can utilize COTS (commercial off-the-shelf) infrastructure components for network
connectivity, standard applications and established management interfaces.
1.2 About xG Technology:
xG Technology is a leading developer of innovative and disruptive communications
technologies for wireless networks. Its extensive patented intellectual property portfolio
covers a broad range of applications including cognitive radio networks. The company has
commercialized some of these technologies to create xMax, the world’s first carrier-class
cognitive radio network.
xMax’s standards-based IP architecture minimizes network deployment, management
and operational costs while simplifying the delivery of fixed and mobile services. Using
field-proven cognitive radio technology, xMax enables the delivery of mobile services in
both licensed and unlicensed bands.

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xMax offers unique capabilities to enterprises, utilities, government agencies and
others who require advanced wireless communications to support business operations and
mission critical applications.
Fig:1.1 Logo of xG
1.3 xMax Mobile Voice and Data Overview:
xMax is a mobile voice and data solution from xG Technology that has been designed to address the
issues raised above and more. In particular, it was designed with the following requirements in mind:
 Leverages COTS end user devices including 3G and 4G smartphones, tablets and
netbooks without requiring licensed commercial frequencies.
 Dynamic Spectrum Access (DSA) and advanced interference mitigation to increase
operational and deployment flexibility. 5g
 Full cognitive networking capabilities including dynamic access and optimization of
available spectrum resources, as well as self-Radio Frequency (RF) planning and self-
organizing.
 A single end-to-end IP network architecture supporting mobile voice, wideband data,
real time video, chat and other apps.

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2.xMax NETWORK COMPONENTS
Fig:1.2 xMax cellular Network
2.1 xMax Cellular Architecture:
The xMax mobile cellular solution leverages a standard cellular architecture – with
some notable enhancements. The following are the major components of the system:
xMod
xAp
xMSC
x Monitor/x Drive
2.2 xMod:
The xMod is a small battery or vehicle-powered radio that bridges the COTS end user
device to the wideband transport layer of the xMax system. Devices may be physically
tethered or connected via secure WiFi links to the xMod. The xMod can deliver up to
3.5Mbps to the connected end user device(s) under real world conditions

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Fig:1.3 xMod
2.3 xAP:
The xAP acts as a compact, high-performance base station and wirelessly connects to
the xMod using the xMax cognitive networking waveform. Each xAP can deliver up to 14
Mbps of total user bandwidth to its associated xMods. xAPs may be deployed individually or
in clusters of up to 9 xAPs to increase total throughput.
Fig:1.4 xAP
2.4 xMSC:
The xMSC acts as both a base station controller and aggregation point for the
connected xAPs. It performsrouting and security functions, as well as proprietary mobile
VoIP optimization and compression. The xMSC is typically connected to the worldwide
Internet and one or more VoIP soft switches.

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Fig:1.5 xMSC
2.5 xMonitor/xDrive:
These software tools provide integrated and comprehensive network and element
management for the xMax network, as well as mobile network throughput and coverage
optimization.
Fig:1.6 xMonitor/Drive

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3.WORKING OF XMAX TECHNOLOGY
3.1 End-to-end IP architecture and shared spectrum optimization:
All the components of the xMax system are IP based. COTS routers and switches are
used as network components. The xMax xAP supports both Ethernet and Fibre interfaces.
Voice is transported as mobile-optimized Voice over IP (VoIP), enabling the entire system to
operate as a data packet network – but with full voice calling features. Standard SIP
signalling supports integrated COTS voice switches and gateways, or an external (cloud-
based) switch/gateway service may be utilized.
The air interface between the xMod and xAP is an advanced Physical Layer (PHY)
featuring OFDM modulation and MIMO transmit and receive. This interface, combined with
other xG innovations, was optimized to provide licensed quality service in free, unlicensed
spectrum. Since this is a shared spectrum resource, implementing interference immunity and
spectral efficiency was paramount for commercial applications.
3.2 Cognitive operation including DSA and interference mitigation:
xMax employs advanced cognitive radio and networking techniques, including
Dynamic Spectrum Access to provide reliable operation in unlicensed but interference prone
spectrum. xMax’s Dynamic Spectrum Access technology is frequency agnostic and can be
re-tuned to operate in TV white spaces, unlicensed or licensed commercial bands. Another
benefit of xMax’s cognitive technology is that the network has the ability to self-configure
and self-organize. This is planned to be further enhanced to support full meshing capabilities
in future xMax product releases.
3.3 Advanced cognitive sensing, signal and multi-spatial processing:
Real time RF sensing and dynamic spectrum access are the cornerstones of xMax
radio technology. The commercial xMax system (slated for release in H1 2012) utilizes the
902-928 MHz and the 5.725- 5.825 GHz band for license free operation. Using these freely
available bands allows the xMax system to scan over 125 channels (in release 3) for
interference-free operation. Both the xAP and xMod devices are frequency agile and have
several built-in capabilities to mitigate interference by first employing advanced signal/spatial
processing as well as dynamically switching channels to avoid overwhelming interference or
jamming.

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Fig:1.7 Dynamic channel selection
3.4 Advanced antenna, PHY layer and software radio design:
The xMax PHY layer is designed with a proprietary 2x4 (two transmitters, four
receivers per link) multiple input multiple output (MIMO) antenna and radio configuration.
This MIMO system enables longer range, higher throughput and is a key enabler of the xMax
interference mitigation technology.
The system uses orthogonal frequency division modulation (OFDM) which is found
in other state-of-the-art wireless systems such as LTE, WiMAX, WiFi and other solutions.
The xMax system utilizes proprietary long OFDM symbols, which allow longer cyclic
prefixes. This results in low overhead and high usable throughput (as a percentage of total
over the air bandwidth).
The xMax PHY supports adaptive modulation with BPSK, QPSK, QAM16 and
QAM64 modes that allow the system to dynamically self-configure for the optimal
combination of range, throughput and interference rejection.
This combination of capabilities enables increased performance under dynamic
conditions, in addition to minimizing power consumption for extended battery life and
remote operation.

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3.5 Interference tolerance, frequency reuse and high link reliability:
By applying cognitive capabilities to enhance active interference mitigation, xMax
can operate effectively under higher interference and jamming levels than competing
solutions. This is critical for maximizing reliability as well as increasing the utilization of
scarce spectrum resources. By enabling xMax to tolerate high levels of interference before
requiring the radios to switch channels, more “gray spectrum” (spectrum containing
interference or jamming) can be used in place of white spectrum (clean and interference-free
spectrum). This capability increases the network’s total throughput and capacity greatly –
without consuming additional scarce spectrum resources. Since the technique is primarily
implemented within the receiver chain, the RF environment is not made noisier as would be
the case for mitigation techniques that rely on raising the transmitter power to overcome the
interferer. This technique significantly increases the system capacity of an xMax network.
Fig:1.8 Spatial processing to Jamming and Interference

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4.Wi-Fi
4.1 Wi-Fi:
Wireless networking, also called WiFi or 802.11 networking, is used to connect the
computers at home, and some cities are trying to use the technology to provide free or low-
cost Intrnet access to residents.
Fig:1.9 WiFi Network
4.2 What Is Wi-Fi?
A wireless network uses radio waves, just like cell phones, televisions and radios do.
In fact, communication across a wireless network is a lot like two-way radio communication.
Here's what happens:
1. A computer's wireless adapter translates data into a radio signal and transmits it using an
antenna.
2. A wireless router receives the signal and decodes it. The router sends the information to the
Internet using a physical, wired Ethernet connection.
The process also works in reverse, with the router receiving information from the Internet,
translating it into a radio signal and sending it to the computer's wireless adapter.
The radios used for WiFi communication are very similar to the radios used for walkie-
talkies, cell phones and other devices. They can transmit and receive radio waves, and they
can convert 1s and 0s into radio waves and convert the radio waves back into 1s and 0s. But
WiFi radios have a few notable differences from other radios:
 They transmit at frequencies of 2.4 GHz or 5 GHz. This frequency is considerably higher
than the frequencies used for cell phones, walkie-talkies and televisions. The higher
frequency allows the signal to carry more data.
 They use 802.11 networking standards, which come in several flavors: 802.11a transmits at 5
GHz and can move up to 54 megabits of data per second. It also uses orthogonal frequency-
division multiplexing (OFDM), a more efficient coding technique that splits that radio signal
into several sub-signals before they reach a receiver. This greatly reduces
interference. 802.11b is the slowest and least expensive standard. For a while, its cost made it

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popular, but now it's becoming less common as faster standards become less expensive.
802.11b transmits in the 2.4 GHz frequency band of the radio spectrum. It can handle up to
11 megabits of data per second, and it uses complementary code keying (CCK) modulation
to improve speeds. 802.11g transmits at 2.4 GHz like 802.11b, but it's a lot faster -- it can
handle up to 54 megabits of data per second. 802.11g is faster because it uses the same
OFDM coding as 802.11a. 802.11n is the newest standard that is widely available. This
standard significantly improves speed and range. For instance, although 802.11g theoretically
moves 54 megabits of data per second, it only achieves real-world speeds of about 24
megabits of data per second because of network congestion. 802.11n, however, reportedly
can achieve speeds as high as 140 megabits per second. The standard is currently in draft
form -- the Institute of Electrical and Electronics Engineers (IEEE) plans to formally
ratify 802.11n by the end of 2009.
 Other 802.11 standards focus on specific applications of wireless networks, like wide area
networks (WANs) inside vehicles or technology that lets you move from one wireless
network to another seamlessly.
 WiFi radios can transmit on any of three frequency bands. Or, they can "frequency hop"
rapidly between the different bands. Frequency hopping helps reduce interference and lets
multiple devices use the same wireless connection simultaneously.
As long as they all have wireless adapters, several devices can use one router to
connect to the Internet. This connection is convenient, virtually invisible and fairly reliable;
however, if the router fails or if too many people try to use high-bandwidth applications at the
same time, users can experience interference or lose their connections.
4.3 The name Wi-Fi:
The name of a popular wireless networking technology that uses radio waves to
provide wireless high-speed Internet and network connections. The organization that owns
the Wi-Fi (wireless fidelity) term specifically defines Wi-Fi as any "wireless local area
network (WLAN) products that are based on the Institute of Electrical and Electronics
Engineers' (IEEE) 802.11 standards."
Fig:1.10 Logo of Wi-Fi

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4.4 ComparisonbetweenxMax and Wi-Fi:
As calculated above, the received signal power at the xMax receiver was -120.91
dBW or -90.91 dBm. The Ruckus Wireless 802.11g transceiver specifies a receiver
sensitivity of only -96 dBm at 6 Mb/s. That's 5 dB less power for almost twice the data rate (6
Mb/s Vs 3.7 Mb/s), or 7.1 dB less power for WiFi compared to xMax at the same speed. Note
that this comparison does not require any estimates, while the Eb/N0 calculation above
required that we estimate the noise temperature of the receiving system. This is because
receiver sensitivity figures combine the effects of system noise and demodulator/decoder
Eb/N0.
It is possible that the xMax demo operated with link margin, meaning that it could
have worked on a weaker signal than the one used. But one can reasonably presume that if
this were the case, xG would have lowered the signal level and eliminated the margin to
make its demo seem more impressive. In any event, xG Technology is the one claiming to
have a new and vastly more power-efficient modulation method so it is entirely up to them to
prove it.
The xMax demo may impress those who haven't done the calculations and are
unaware of how little power it actually takes to transmit digital data over a benign line-of-
sight path. But the same demonstrated performance could have been easily achieved with just
about any conventional digital modulation scheme, including an off-the-shelf WiFi
transceiver, and some of these schemes already come very close to the theoretical limits.
Broadcast stations use such powerful transmitters because they cannot assume line of
sight paths; large margins are required to reliably overcome obstacles, fading, reflections and
interference throughout their entire service areas.
This is not to say there can't be any more big developments in digital radio
communications; far from it! But they will not come as fundamental modulation
breakthroughs from xG Technologies or anyone else. Opportunities still abound in frequency
reuse, the basis of modern cellular phones; cooperative ad-hoc networking; improved
spectrum sharing; better adaptivity to changing or hostile radio link conditions; improved
interference mitigation; multiple-in, multiple-out (MIMO) antenna arrays; improvements in
RF hardware that will let us make better use of the underutilized higher frequency bands, and
in other ways but not from breakthroughs in modulation, because there won't be any more.
By way of analogy, dialup modems reached their theoretical limits years ago, but Internet
access speeds continue to rise thanks to cable modems, fibre deployments, radio networking,
and DSL.

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4.5 xMax and Wi-Fi differences:
Table:1.1 Differences between Wi-Fi and xMax technology

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5. ADVANTAGES,LIMITATIONS&APPLICATIONS OF
XMAX TECHNOLOGY
5.1 Advantages:
 Quality of service (QoS) to support long ranges mobile VoIP.
 Deterministic latency on wireless links for voice packets.
 Header compression.
 Zero latency network configuration.
 Soft hand- off mechanism.
 Substantially lower capital requirements for materially more sophisticated product
offering.
 No spectrum license costs.
 Exclusive service territories.
 Network capacity managed through software-defined radio system.
 Path to 4G performance with a revolutionary battery solution for user device.
5.2 Applications:
 The completely new mobile VoIP system that is similar to most popular VoIP service
providers like skype.
 xMax cognitive radio cellular system represents a complete, scalable mobile wide
band solution that is capable of supporting a wide range of smart phones,tablets,net
books and other end –user devices. The coverage and capacity of the network can be
tailored to the market and business model at hand and can be rapidly reconfigured to
support new or expanded applications.
 xMax’s cognitive networking technology is frequency agnostic and can be adapted to
a wide array of TV spaces, unlicensed frequency bands.
 The xMax system’s cognitive networking capability allows it to dynamically access
and optimize available spectrum resources, while also enabling it to optimize its own
RF plan.
 xMax’s end-to-end IP network architecture supports mobile voice,widwband,real
time video, chat and other apps over a single integrated network, unlike typically 3G
and 4G networks that require separate voice and data network equipment and
transport layers.

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5.3 Limitations:
 VoIP technology is great at saving its users money, but it does have some
disadvantages – you have to be connected to a computer to use it, and VoIP calls are
blocked on some networks by cellular companies concerned that they are missing out
on revenues.
 There is also an issue with quality, as cellular networks are not designed for Internet
voice traffic.
 US-based xG Technology has addressed these problems with its xMax system, which
has been specifically designed for mobile VoIP.
 The network uses available free spectrum, rather than licensed spectrum and an all-IP
architecture that is less expensive to operate than traditional networks.
 Although the test was limited in its scope, he used a phone connected to a laptop
while being driven around Fort Lauderdale and reported that the voice quality was
fine.
 There still seems to be issues to address, as the phone eventually overheated, but it
seems that mobile VoIP could not be too far away.

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6.FUTURE SCOPE:
The XMAX™ technology can provide fixed, nomadic, portable solution and with
OFDMA at the heart of the technology, it can also deliver mobile wireless broadband
connectivity across vast open and congested areas, over many kilometres.
With the XMAX™ Customer Premises Equipment, IPaXIom gives businesses,
enterprise and the end customer get more options for broadband connectivity at lower cost.
The XMAX™ comes with its own NMS for comprehensive and user friendly day-to-day
management and support function.

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7.Conclusion:
From my analysis it seems that xG's xMax technology is nothing special. Despite
xG's implications to the contrary, no spectacular results have been demonstrated, certainly
nothing that would call into question the fundamental principles of communication theory
that have been firmly established for six decades. And a reading of xG's published claims and
patents belie a surprising lack of awareness of these principles. Prospective investors should
be very wary.

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References:
 www.xgtechnology.com
 A review of Bobier's TriState Integer Cycle Modulation, added 16 May 2007
 comments on MiCOM lab test of xMax, added 4 June 2007
 comments on Prof. Stu Schwartz's evaluation of xMax added 6 June 2007
 an analysis of xG's claims that xMax requires 3,000,000 times less power than WiFi,
revised 29 June 2007
 Prof. Ben Friedlander's blog on xMax and other wireless fantasies, added 21 June
2007
 Comments on Patent Application 20040196910 from an engineer who wishes to
remain anonymous, added 17 June 2007.