Whitepaper Clear Impact v1p0

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ReVerb Networks, Inc

White Paper

Beamforming with Clear Impact

Rick Cuthill

VP Product Management

Document Number: MKT-2007-0002Version 1.0

September 24, 2007



White Paper Version 1.0

Beamforming with Clear Impact September 24, 2007

ReVerb Networks, Inc 2

Introduction

Beamforming and adaptive antennas have been discussed, developed and trialed as part

of mobile networks since the beginning of mobile network deployments. While severalcompanies have tried to create commercial solutions, many have failed – not typically for

technical reasons, but more often for economic ones, or simply the readiness of themarket to accept the candidate solutions. Simply put, the problem to be solved was quiteoften not big enough to justify the expense and risk of an adaptive antenna solution when

better-known alternate solutions were available, such as cell splitting. ReVerb Networks

products address both driving down the cost, and increasing the benefits of adaptive

beamforming solutions.

Today there is much broader awareness of adaptive antennas in communication systems

than there was in the past. This is true even at the consumer level with the introduction

of 802.11n. This is only one of the indicators that the market is becoming open to the

acceptance of different adaptive antenna techniques versus traditional solutions. Anotherstrong indicator is the consumer market introduction to mobile music, video and general

web access with today’s technology, with forecasted increasing demand for such

services. This consumer uptake of mobile broadband data will stress the wirelessnetworks in which they operate, and equipment manufacturers are knowingly including

the adoption of short-range adaptive methods such as Multiple Input Multiple Output

(MIMO) antennas for Orthogonal Frequency Division Multiplexing (OFDM)technologies with the knowledge that OFDM itself will not be enough to meet future

demand.

The choice of MIMO in future mobile broadband networks as an adaptive antenna

technology is obvious, since there is a need to implement smaller cells to support theanticipated bandwidth. But there are a number of places that beamforming based adaptive

solutions will also play in these future technologies.This paper describes the ReVerb Networks approach to adaptive beamforming. It

outlines how the ReVerb approach is different to the typical beamforming approachdesigned specifically for mobile networks, how and where ReVerb Networks solutions

can be applied today and how the technology will scale to future mobile networks.

Specifically, this work outlines how ReVerb Networks’ approach condenses the

geographic frequency reuse dynamically. As a result of our beamforming-based adaptivesectorization, more frequency resource is available; hence, more traffic is supported at the

same time using the same cell site, as compared with traditional fixed sectorization.

How the ReVerb Solution Differs from OthersA typical problem faced by small companies producing beamforming technology is in

which form to sell it. It can be sold purely as intellectual property (IP) or as a softwaresale to Original Equipment Manufacturers (OEMs), or complete systems can be sold to

operators, or a hybrid of these approaches can be used. Versatile beamforming solutions

require specialized RF hardware, but typically “the secret sauce” is a software algorithmrunning at baseband using digital signal processing hardware. The cost of the specialized

radio frequency (RF) hardware is usually more than fifty percent of the system cost.






With the selling IP or software scenarios, each of your customers has to take on the

burden of developing or acquiring the RF hardware. With selling complete systems youmust develop the modem, traffic management, network management and wireline

interface functions. However if your expertise is adaptive beamforming technology (and

because it is a complete proprietary, somewhat specialized RF system), you are then

forced to compete in a market with established general purpose wireless systems.ReVerb Networks takes a unique approach to solving this problem that addresses the

complexity and cost of the digital signal processing, and the cost of the RF, while

achieving the same or better network performance benefits compared to conventionalmethods.

Early applications of beamforming used analog processing of the RF signal, which had

limited versatility, but today beamforming predominately uses digital signal processing

methods, typically integrated into the base station modem. Quite often these basestations create beams on a per user basis. That is, for every user a beam is

instantaneously created, for every Time Division Multiplexing (TDM) voice channel or

every data packet interchange, resulting in thousands of beams created per second.Although this method can work very well, there is a high data processing cost and it

requires that beamforming be done at baseband, therefore must be integrated into the base

station modem.

To address costs issues ReVerb Networks’ solution

Creates beams for groups of users and adapts these beams based on sector andnetwork criteria,

Applies beamforming at intermediate frequencies (IF),

Uses commercial off-the-shelf (COTS) base station modems,

Integrates beamforming with the RF and antenna into a single cost effectivesubsystem.






Figure 1 ReVerb Network’s rV100i Solution Overview

Creating beams for groups of users, or sub-sectorization is certainly not new, but

adapting these sub-sectors based on link and network level parameters in a commerciallyavailable product is new and has significant impact on costs.

The speed of adaptation for groups of users is orders of magnitude lower when compared

to the per-user approach. This results in an overall cost reduction in the digital signalprocessing portion of the system. The use of link and network level optimization allowsReVerb’s solutions to achieve between 2 and 4+ times capacity gain, similar to per user

beamforming, however, with a far simpler implementation.

Because ReVerb’s optimization algorithms do not require an intimate integration with

protocol processing, beamforming can be applied digitally at an intermediate frequency,based on the company’s patented digital IF beamforming method, allowing the ReVerb

product to interface with numerous COTS base station modem products. The ability to

interface to COTS base station modems provides equipment vendors without adaptiveantenna technology a way to easily add this capability for new deployments and enables

the cost effective retrofit of exiting sites.

The challenge of reducing beamforming solution costs has always been the cost

associated with the RF portion of the system. ReVerb Networks attacks this problemhead on by integrating the antenna panel, RF transceivers and beamformer in a single,

easily-installed panel.






Applying ReVerb Solutions Today

One of the additional benefits of the ReVerb Networks approach is the versatility andrelevance to today’s networks.

High data rate mobile technologies and networks are emerging but have not yet fully

arrived. All of the broadband mobile networks will be based on Orthogonal Frequency-Divisional Multiplexing (OFDM) technology whether the specific technology isWiMAX, Long Term Evolution (LTE), or Ultra Mobile Broadband (UMB).

ReVerb Networks has chosen to apply its beamforming methods to OFDM signals and

specifically to WiMAX for its initial products. WiMAX is being used today in backhaul

and fixed wireless access networks whereas LTE and UMB will not be used until thesenetworks are rolled out for mobile.

Today, beamforming and adaptive beamforming are valuable in numerous applications in

markets such as:

Public Safety – Emergency Response, Fire and Rescue, Law Enforcement

Wireless Carriers – WiMax, Mesh, Backhaul, Tower Operators, BroadbandProviders

National Security – Border Patrol, Surveillance and Monitoring, Mission Support

Public Works – Water, Utility, Sanitation, Security

Industrial – Manufacturing, Construction, Fleet

Municipal Networks – Public Wireless Access From Local Governments

The application sweet spot for beamforming are those applications characterized by:

Limited spectrum

High data rates

Nomadic remote users

The combination of current WiMAX technology provided by COTS base station modemsand ReVerb’s versatile beamforming products allows specialized backhaul and access

needs to be addressed cost effectively today.

Current high bandwidth, nomadic applications are best served by the versatility of

beamforming. The performance of the basic building block of beamformed sectorizationis described in the following section.

TDD and FDD ConsiderationsThe Frequency Division Duplex (FDD) and Time Division Duplex (TDD) environments

have significantly different adaptation and interference environments. Considering

adaptation, TDD has a significant advantage in that the Uplink and Downlink propagation factors are reciprocal at any instance in time. Thus weights calculated on the

Uplink channel can be applied to the downlink channel without modification and achieve

identical signal improvements assuming that the uplink/downlink switching rates are fastcompared with changes to the path. This is the case for most TDD broadband






applications. For FDD the weights have to be corrected to allow for the frequency offset

and the lack of channel reciprocity. For this reason the majority of FDD systems trialedor deployed have only used uplink adaptation. Systems have been built and tested in the

cellular bands that have demonstrated that moderate downlink system gains can be

achieved for a cost. For bidirectional adaptive performance gain TDD wins.

For other than isolated deployments when the interference environment is considered, thestory is reversed. For FDD it is only necessary to consider base to remote and remote to

base station interference since different transmit and receive frequencies can be used. For

TDD, however, the same frequencies are used for uplink and downlink in a time sharedmanner. Thus base station to base station, base station to remote, remote to base station

and remote to remote interference are all pertinent. TDD advocates claim that networks

are synchronized and thus time is used to eliminate interference, timing advance is usedto ensure that signals arrive at the base station at their allotted times. This is true and

works for a single cell or sufficiently isolated cells. In the case of a typical macro cell

network (high towers and large number of remotes) with predominant non line of sightpropagation paths to the remotes, these additional base station to base station interference

modes can be significant and in the majority of cases cannot be solved by network synchronization. In these cases base station to base station interference can well represent

a limiting factor. For instance the path loss for a non line of sight remote at 4 km may be30 to 40 dB greater than the path loss from an interfering base station at 10 km. Thus the

ability to null out such interfering base stations will be essential for such multicell

deployments.

Since the majority of WiMAX, 802.16-2004 networks are TDD implementations, and thecurrent outlook is that mobile WiMAX (802.16g) will also be TDD, ReVerb Networks’

ability to implement null steering as one of the capabilities of our adaptive beamforming

solutions, will clearly provide significant performance improvement for tomorrow’smobile networks.

ReVerb Fundamental Performance Simulation

Given a scenario where groups of users occupy a 120 degree sector and each group is

spatially isolated from each other, measured in an angular fashion, then all the users will

share the bandwidth or data rate available in this sector as shown in Figure 2. Under thisscenario where the coverage need not be uniform within the 120 degrees but can be

spatially partitioned into a number of beams at the same frequency with each beam

dedicated to each user group, the total throughput or capacity of the 120 degree sector canbe increased 2 to 4 times. Using the Reverbs Networks approach to beamforming, we

can dynamically change the angular position of each beam center and each beam width to

maximize the data throughput to each user group. The three beam case is shown in Figure3.






Figure 2 Three User Groups Serviced by a 120 degree Sector

Figure 3 Three User Groups Serviced by Three Optimized Beams






A fundamental simulation is performed to show the performance of partitioning into 2 to

4 sub-sectors with various beamwidths and angular positions. This simulation is based onthe 3rd Generation Partnership Project (3GPP) spatial MIMO channel model for an urban

macrocell environment, and only considers an isolated base station deployment, which is

typical of the markets currently being addressed by ReVerb Networks.

The plots in Figure 4 illustrate the probability of achieving a certain signal-to-interference-plus-noise ratio (SINR) from beam to beam for various beam positions and

beam widths. Specifically we compare the performance for

Two 30 degree wide beams, positioned at 15 and 105 degrees,

Three 30 degree wide beams positioned at 15, 60 and 105 degrees,

Three 18 degree wide beams positioned at 9, 60 and 111 degrees,

Four 18 degree wide beams positioned at 9, 43, 77 and 111 degrees,

As seen from the plots, under a general power control scheme, 60% of bursts in the two

30 degree beam case can experience a SINR of 16dB or above, while more than 90% of

bursts have a SINR above 11dB. The most extreme case of four 18 degree beams showsthat 70% of bursts will experience a SINR of 11 dB or more. According to WiMax,11dB SINR can support 13.35Mbps throughput with QPSK and rate ¾ coding, while

16dB SINR can support 17.8Mbps throughput with 16QAM with rate ½ coding.

These probabilities illustrate that the 120 degree sector, under the given scenario typical

of many applications in ReVerb Networks’ markets, can be partitioned into 2 to 4 sub-sectors while maintaining high data throughput, thus increasing the capacity of the

available spectrum up to 4 times of what was previously available.






Figure 4 Cumulative Distribution Function of SINR for Various Beam Scenarios

Ready for Tomorrow

With industry acceptance of open interface standards such as Open Base StationArchitecture Initiative (OBSAI) and other radiohead interface standards, the ReVerb

solution will interface to growing numbers of base station modems providing more

opportunity for manufacturers and operators to take advantage of ReVerb Networksversatile beamforming products.

As broadband mobile networks roll out and capacity solutions are sought, ReVerb

Networks will be ready with field proven solutions and technology. Our RF panels willevolve to meet the size and cost requirements of tomorrow’s picocell networks. Thelower complexity beamforming techniques coupled with network level optimization will

better fit these future networks than today’s typical per-user beamforming methods; and

Reverb Networks methods will be as applicable to LTE and UMB as they are to

WiMAX.

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Whitepaper Clear Impact v1p0