2.1 Overview Intelligent antennas are, in the simplest form, antenna systems that use some sort of computational or electronic resource (intelligence) to enhance system performance. Variances in definitions exist. Most observers don’t consider basic diversity to be an intelligent antenna technology. MIMO is usually classified separately than smart antennas such as beamforming solutions. There are essentially three main enhanced antenna techniques; each varies according to the amounts of intelligence employed. Antenna diversity (switched or combining) represents the simplest form in the progressive complexity chain, followed by basic beamforming, which is the process of narrowing radiated energy, which is then followed by the more complex space-time processing and finally by MIMO (a form of space-time processing) 2.2 Definitions 2.2.1 Active Smart Antennas Active smart antennas are those that use digital electronics to implement beamforming and other techniques. They are considered more expensive than passive systems (those that use passive electronics such as analog phase shifters) initially, but provide greater improvements in performance than passive systems. 2.2.2 Beamforming In beamforming, a group of antennas form one or more narrow beams that are focused on a given user(s) at a given time. They may also form nulls that cancel out interferers. The narrow beam results in less interference to adjacent users and improved signal quality. Spatial multiplexing is achieved if the system creates multiple beams at the same time. In such a case, beamforming can be viewed of as a kind of refined sectorization. One of the criticisms of beamforming is that its benefits diminish in the presence of multipath since multipath effectively reduces the carrier to interference ratio (C/I) There are several ways to implement beamforming. Adaptive systems, which rely on complex digital signal processing, can adapt over time and according to the specific user. Adaptive digital systems offer a virtually unlimited range of coverage patterns and nulls. Passive systems often rely on butler matrices. In this case, the weighing of signals to create beams is done in the analog realm. Such implementations lack the flexibility of digital ones and many have limitations on the amount that they can adapt. Beamforming can also be implemented mechanically or via material properties. For example, an antenna could contain many radiating elements within it, each one or set pointing in a different direction. The antenna would generally have a switch within which would direct a signal to different radiating elements. These are considered switched beam antennas and while they focus the radiated power of the antenna, they do not produce nulls to cancel interference.

2.2.3 Diversity Combining Diversity combining is a technique that relies on antenna diversity (having more than one antenna element either physically separated or employing different polarization). The idea behind this concept is relatively simple. The radio will sample (receive) the signal in more than one space or with antenna elements that have different polarization characteristics and then combine the results from the two or more separate antennas to improve signal gain. Diversity combining is a fairly effective means of increasing signal strength, range, and/or capacity. It is present in most base stations today (spatial diversity), and a number of vendors are now targeting diversity-combining products to CDMA handset vendors. CDMA experiences a particularly attractive boost from diversity combining because self-interference (interference from other users in the cell and on the same channel) accounts for a significant portion of the overall interference that is experienced in CDMA systems. 2.2.4 Diversity (Switched) As is the case with other forms of diversity, switched systems rely on two or more antennas or antenna elements. The system switches to the input that is strongest at any particular point in time. It is does not perform any combining of the received waveforms as is the case in diversity combining, rather it chooses to ignore the least desirable signal 2.2.5 Maximum Ratio Combining Ratio combining is a form of diversity combining. Received signals are multiplied by a given ratio and then combined. The strongest signals are usually multiplied by a larger factor than weak signals are. In effect, this minimizes the impact of weak signals and increases signal to noise ratio as opposed to just gain, as is the case with basic diversity combining. Ratio combining can be done with multiple (more than two) receivers. 2.2.6 MIMO Multiple-in-multiple-out (MIMO) is an intelligent antenna technology that uses multiple antennas or antenna elements at the receiver and the transmitter. Advantages of doing so include ability to implement spatial diversity, spatial multiplexing, and beamforming. The benefits of these techniques include interference cancellation, resistance to fading, lower frequency reuse (lower is better), improvements in S/N ratio and efficient use of amplification devices. It is important to note that MIMO systems can implement a number of “intelligent antenna” techniques depending on the characteristics of the radio channel at a given time or place. 2.2.7 Passive Smart Antennas Passive smart antennas use passive electronics in the analog realm (phase shifters/butler matrices) to combine waves in order to control the radiation of an antenna to create beams. 2.2.8 Polarization Diversity Each radio signal contains both a magnetic and electric field component. The relative orientation of these determines the polarization of the signal. The attributes of an antenna

can be altered to optimize reception of a wave of a given polarization. In polarization diversity, the two antenna elements are usually optimized to receive signals with polarizations that are at right angles (orthogonal) to each other. The advantage of this approach over spatial diversity is that a smaller or single (with two elements) antenna can be used. In spatial diversity, the antenna elements are required to maintain certain spacing, defined in wavelengths. The downside of polarization diversity is that it provides limited results in environments that lack high degrees of multipath, such as suburban and rural settings. Polarization diversity is implemented extensively throughout Europe. 2.2.9 Space-Time Processing Systems that utilize space-time processing take advantage of both the delay (time) in the reception of signals, caused by multipath, and the spatial component of the channel usually via multiple antennas that are positioned in different “space.” Examples of space-time processing include IntelliCell from ArrayComm and BLAST (Bell Labs Layered Space-Time) from Lucent/Bell Labs. 2.2.10 Spatial Diversity Spatial diversity is a form of diversity that is achieved by sampling or transmitting waveforms in different space. It is one of the advantages of multiple-in-multiple-out antenna systems (MIMO); using more than one antenna for transmission and reception, but is also available in beamforming implementations where multiple antenna elements are only available at the base station. Spatial diversity can be used to increase gain, provide improvements in S/N ratio, and reduce the effects of fading. These generally result into greater reliability and improved capacity. Even basic receive diversity provides spatial diversity benefits. 2.2.11 Spatial Multiplexing Spatial multiplexing refers to the use of space to increase capacity. Cell splitting is arguably the simplest form of spatial multiplexing. In this case, frequency and hence capacity can be reused due to the introduction of a spatial component, the cell. The sectoring of cell sites is another form of spatial multiplexing. Intelligent antennas can magnify the impact of the spatial aspect of the wireless environment. Beamforming does this by focusing power via multiple beams on multiple users at a time while reducing interference through the creation of null interferers. The end effect of beamforming can be viewed as fine and often adaptive sectorization that changes over time. Beamforming technology may or may not be used to achieve spatial multiplexing. Some beamforming systems will only produce one beam and perhaps no or a limited number of nulls. In these cases, beamforming is applied to improve the carrier to interference ratio (C/I) of the transmission but not for the purpose of spatial multiplexing. Another form of spatial multiplexing is evident in the case of space-time processing techniques such as BLAST from Bell Labs. In this case, the system effectively uses space (which is implemented via multiple antennas on receive and/or transmission) to achieve different spatial channels. It also uses multi-path to benefit the system.

2.2.12 Switched Beam In a switched beam system, an antenna system is capable of producing a limited number of patterns or beams. The system will switch to the beam that provides for the greatest signal quality. These systems are typically implemented by using butler matrices in the RF realm or via mechanical methods at the actual antenna. Switched beam systems do not actively null out interferers, as is the case with adaptive systems. They provide a smaller increase in capacity compared to adaptive beamforming systems but are easier to implement as an appliqué (overlay). 2.3 Why Intelligent Antennas Intelligent antennas are being considered in order to improve system economics, capacity, range, coverage, and/or availability. Operators can use intelligent antennas to reduce the number of base stations required to cover a given area that translates into a savings in both capital expenditures and operating expenses. They can also have a dramatic impact on service quality, and improvements in capacity can be used to hold off cell splitting or migration to a new air interface such as WCDMA. Consideration of intelligent antennas is also an outgrowth of the growing view that the wireless industry is reaching the limits conventional linear radio technology and in dire need of improved economics. 2.4 Implementation Choices There are generally two means to implement intelligent antennas; either as an appliqué or overlay to existing base stations or by incorporating them into base stations during the design phase. Incorporation results in a lower overall cost but appliqué implementations enable operators to make use of their existing base stations. Appliqué methods vary in complexity. Those that implement digital systems generally require an extensive gutting of the base stations inwards. Passive systems might require changes to the systems RF or physical antenna structure alone. 2.5 Key Smart Antenna Vendors and Technologies 2.5.1 Airgo Networks, Incorporated Palo Alto-based Airgo has succeeded in providing a MIMO chipset for WiFi that is compatible with 802.11b/g. The product currently selling within routers from Compton, California-based Belkin Corporation and it requires use of Airgo-based access points and client terminals in order to unlock its full value. That said use of an Airgo-based access point would enhance network performance even when traditional 802.11 client devices are used. The Airgo product is delivering total payload in excess of 125 mbps, about half of which is used for overhead. The Belkin AP currently retails for about $150, which is representative of the first low-cost MIMO implementation we have seen. 2.5.2 AirNet Communications Corporation Melbourne, Florida-based AirNet is a licensee of ArrayComm’s IntelliCell technology. The company has applied it in its AdaptaCell GSM base stations. A test of the AdaptaCell system in early 2003 demonstrated a 600% increase in system capacity of a macro base station over a conventional GSM macro base station. Perhaps just as notably

was the reuse factor, n=1. This figures means that the same frequency was reused in adjacent cells. AirNet began shipping its AdaptaCell base stations in 2004. 2.5.3 ArrayComm, Incorporated ArrayComm, San Jose, California, has two products, IntelliCell and iBurst. Both utilize similar sets of space-time and beamforming processes. IntelliCell is used as an extension to existing wireless standards, including PHS, GSM, and WCDMA. However, it is integrated into base stations designs; it is not an appliqué or upgrade to existing base stations. iBurst uses ArrayComm’s own TDMA and IP-based air interface coupled with its antenna technology. The technology is offered as a mobile, with hard handoff, capable DSL/cable modem competitor/replacement. ArrayComm is the undisputed leader in smart antenna market share. It licenses IntelliCell and iBurst technology to others including AirNet Communications, Kyocera, and LG. The company recently introduced an iBurst ASIC for use in terminal products. Conversion of existing PHS networks to iBurst is a target for the vendor, one that could prove extremely lucrative. 2.5.4 Bell Labs/Lucent Technologies (BLAST) Bell Labs Layered Space Time (BLAST) available from Murray Hill, New Jersey-based Lucent Technologies is a form of spatial multiplexing that can achieve spectral efficiencies of 20 to 40 bits/sec/hertz. The system communicates via multiple spatial channels, which correspond to separate antenna elements, but on the same frequency by training the receiver to first identify and then distinguish between each spatial channel. The way it does this is by profiling the unique characteristics of each spatial channel, which is a condition of the multipath amongst other things. Those profiles enable the receiver to distinguish different channels that are ultimately a function of space. BLAST uses multiple antenna elements to achieve this effect. Correspondingly, product that is BLAST-enabled will also be able to perform beamforming as well as diversity/maximum ratio combining. BLAST can be implemented with just multiple-ins on the device side that would be enabled for asymmetrical performance. Lucent is offering base stations that are BLAST ready, meaning they are made to be easily upgraded to BLAST and BLAST chipsets have also already been made. Agere Systems, Incorporated, the Lucent spin-off, is slated to be one channel for these devices. BLAST is the research that sparked a flood of interest in space-time processing. MIMO-OFDM, STREAM, and IntelliCell exploit similar concepts, though it was not the first use of multipath. 802.11n, regardless of which proposal is adopted, will exploit similar though not necessarily identical concepts. 2.5.5 CalAmp Corporation (formerly California Amplifier)

Oxnard, California based CalAmp, which has dropped its old moniker of California Amplifier, is offering a butler matrix-based system that is intended for use in the WiFi segment. The company’s product is used to increase C/I and not for spatial multiplexing. 2.5.6 Intel Corporation Santa Clara-based Intel purchased the assets of San Jose-based Iospan Wireless Incorporated, which offered a MIMO-OFDM product that consists of a 3 x 2 system. The 3 x 2 systems utilizes three receive and two transmitter elements on the infrastructure side and a 3 x 1 (three receivers and one transmitter) system on the subscriber side. Like other MIMO systems, Iospan’s is capable of time-space, diversity, and beamforming capability. Intel’s purchase of Iospan’s assets suggests that the technology will find itself in future silicon products. Intel has already announced its intention to offer chips sets for 802.16, and it is already offering 802.11 products, which MIMO could also become a part of as well. 2.5.7 InterDigital Communications Corporation Tantivy introduced an IP-based version of CDMA that incorporates beamforming capabilities. The system was called I-CDMA, with “I” standing for Internet. King of Prussia, Pennsylvania-based InterDigital purchased the technology and is now offering the technology for cellular handsets and WLAN products. The current product is called AIM (Adaptive Interference Management) Antenna. It includes steering software which to maximize performance and InterDigital offers hardware (antennas), reference platforms, engineering services, and licenses of its AIM technologies (software and antennas). 2.5.8 Kyocera Corporation Kyoto, Japan-based Kyocera is a licensee of ArrayComm’s IntelliCell technology, which the infrastructure vendor has incorporated into its PHS base stations. The partnership has made Kyocera the world’s leader in shipments of smart antenna systems. Kyocera also uses the IntelliCell technology for wireless local loop products. 2.5.9 LG Electronics Seoul, Korea-based LG is developing equipment based on ArrayComm’s iBurst system. Trials of iBurst were conducted in Korea by mobile carriers KT and Hanaro, for potential use of the product in the 2.3 GHz band. However, the 802.16e-based WiBro has been selected for use in the 2.3 GHz band. ArrayComm, who is supplying IA technology to LG for iBurst, is also expected to license its technology to 802.16 vendors. 2.5.10 Magnolia Broadband, Incorporated Clinton, New Jersey-based Magnolia Broadband offers its Diversity Plus technology that employs two receivers and two transmitters on the handset side to enable diversity receive and a novel technique that can beamform or alters the phase of a given signal to improve uplink performance. Initial product is targeted to cellular handsets in chip set form. Other markets will be addressed and the uplink technology is expected to be licensed by Magnolia to existing cellular phone chipset makers. Magnolia is unique in its

ability to provide improvements in the uplink without resorting to beamforming or more complex MIMO techniques. 2.5.11 Motia, Incorporated Pasadena, California-based Motia’s product is an RFIC for WiFi access points and client devices that performs beamforming and diversity combining. All of this is done in the analog realm and the RFIC can have up to 4 transceiver paths. The part is sold as an upgrade to existing WiFi chipsets that does not compromise compatibility with the standard in any way. Access points are the first target but client devices are expected to follow. 2.5.12 Navini Networks, Incorporated Navini, with headquarters in Richardson, Texas, uses an antenna array at the base station to implement adaptive beamforming. The system is active and uses digital electronics to create and control the beamforming. It can also create nulls to cancel out interferers, and it implements diversity, and space-time techniques. Customer units employ a standard omni-directional antenna but the base station also filters out noise in order to maintain attractive signal to noise ratios on the uplink. Navini’s smart antenna technology is applied to its version of TD-SCDMA (time division synchronous code division multiple access). The system, called Ripwave, is targeted to the broadband wireless space, fixed and nomadic. Navini is also participating in the 802.16 and 802.20 Groups. 2.5.13 Nortel Networks Corporation Nortel Networks, with headquarters in Brampton, Ontario, Canada, introduced and trialed its CDMA AABS smart antenna solution during 2002 but has released no information that would indicate an actual commercial deployment. The system, which Nortel advertised as adaptive, reportedly achieved capacity gains of one hundred percent in trials. The company has also released information regarding trials of MIMO. In February of 2003, Nortel announced tests that demonstrated 20 Mbps in a 5 MHz channel using its MIMO technology. Nortel also offered a GSM-beamforming solution at one time. The solution was used to create supercells but was discontinued. More recently, Nortel has offered MIMO proposals for 802.16 and 3GPP. 2.5.14 Orthogon Systems Orthogon is an Ashburton, Devon, UK-based startup that also has headquarters in Waltham, Massachusetts and which has applied space-time processing MIMO to the point-to-point market. The product is designed to offer N-LoS links as well as high distance and/or capacity. Notably, the product uses a true software defined radio. 2.5.15 Paratek Microwave, Incorporated Paratek, with headquarters in Columbia, Maryland, has developed a technology that would generally be classified as a passive beamforming or scanning antenna. The company’s now discontinued Darwin product had used passive phase shifters that employed tunable dielectric material to create beams. One of the areas Paratek is now focusing on is proving beamforming solutions for WiFi. The WiFi products will not be used to attain gains in spatial multiplexing.

The company specializes in applying its technology across all frequencies. 2.5.16 Qualcomm Incorporated San Diego-based Qualcomm already offers antenna diversity in its EV-DO (evolution data-only) capable handset ASICs. The company is known to be researching additional implementation of diversity combining (receive and transmit) for its handset ASICs. 2.5.17 Texas Instruments, Incorporated Texas Instruments, with headquarters in Dallas, Texas, has not formerly announced any intelligent antenna products. Yet the company is the leader in handset baseband solutions, mainly for GSM, and it has been involved in numerous smart antenna research projects. It is widely believed that TI will introduce a smart antenna device for handsets. The company is also a pioneer in the use of silicon CMOS as evidence by its recent introduction of a “single chip” GSM radio. PA (power amplifier), power control and memory are still required (disputing the “single chip” claim) but TI has succeeded in integrating an entire transceiver sans the PA into one piece of silicon. RF CMOS is considered a key step towards making MIMO chipsets since the latter requires multiple transceivers that would be extremely costly to implement without significant integration. 2.5.18 Vivato, Incorporated Vivato, with headquarters in San Mateo, California, offers a beamforming solution for WLAN hubs. The product uses a butler matrix and can produce multiple beams at a time, spatial multiplexing. It is intended for corporate, campus, and public WLAN applications. Vivato has been subject to intense criticism since its products use beamforming to enable spatial multiplexing in an environment with high levels of multipath phenomena. The benefits of beamforming diminish in such an environment. However, Vivato executives counter that their solution is intended for large public spaces where multi-path is not as significant an issue as in traditional indoor settings, most which have comparatively low roofs. 2.5.19 WaveRider Communications, Incorporated Avendo Wireless Incorporated, Mississauga, Ontario, Canada, had developed space-time technology that employed MIMO. The company’s efforts targeted the point-to-point market. Avendo is now part of WaveRider Communications Corporation, Toronto, Canada, which has frozen development on the former Avendo projects. WaveRider provides as products both point-to-multipoint last mile products and point-to-point links. 2.5.20 Others There are a number of other companies who have either put their intelligent antenna development efforts on hold or who are now bankrupt. These include Kirkland, Washington-based Metawave Communications Corporation, which filed for Bankruptcy January 31, 2003.

Also the WJ Communications, Incorporated product STREAM (Spatial Transmission with Radio Enhanced Adaptive Modulation) was initially targeted for fixed wireless. Tests achieved data rate of 155 Mbps in a 4.6 MHz channel in the 2.5 GHz band. It relied upon MIMO and space-time techniques.