4Motion Alvarion Advanced Antenna Systems Leveraging MIMO and diversity schemes to take WiMAX infrastructure to the next level of wireless broadband White Paper SentieM TM
Contents Abstract 3 AAS Enables WiMAX Network Efficiency 3 Antenna Diversity and Down Link (DL) Transmit Diversity Schemes 4 Delay Diversity 4 Cyclic Delay Diversity 4 Delay Diversity over Beams 5 MIMO Technology 5 Down Link (DL) Technologies: Matrix A and Matrix B 5 Up-Link (UL) Technologies: MRC and CSM 7 Beamforming (BF) 8 Alvarion SentieM Technologies 8 Alvarion s AAS Business Benefits and Technical Features 9 Business Benefits 9 Technical Features 9 Summary 10 Glossary of Acronyms 11 2
Abstract Alvarion Advanced Antenna Systems (AASs) use Multi-Input-Multi-Output (MIMO) technology and diversity schemes that deliver wireless service level agreements (SLAs) efficiently and cost effectively. The unique characteristics of each multi-antenna technology are highlighted in relation to operator-specific needs for Quality of Service (QoS), coverage and capacity. To operators, this means a whole new level of reliability and affordability when delivering next-generation wireless broadband services over WiMAX. This paper briefly covers the enabling technologies of Alvarion s AAS technologies. AAS Enables WiMAX Network Efficiency In addition to being a leading-edge technology, Mobile WiMAX has also emerged as a business driver addressing the ever escalating needs of operators. One of the primary requirements is the demand for lowcost, wireless broadband to mobile stations, such as cell phones, Mobile Internet Devices (MIDs), laptops, smartphones and PDAs. However, the challenge still hinges on the capability to deliver reliable and consistent service to these networks while meeting the low price point demanded by consumers. This has become even more apparent when operators attempt to maximize Average Revenue per User (ARPU) and lower Capital Expenditures (CAPEX) and Operating Expenses (OPEX) in order to remain competitive. Alvarion s AASs refer to a class of intelligent antenna technologies that use multiple antennas at both transmission and reception ends of the wireless link. AASs generate multi-channel systems, increasing the carrier-to-interference plus noise ratio (CINR), significantly improving the radio signal and therefore impacting QoS for the customer. This greatly enhances the performance of WiMAX networks, while reducing the number of required base stations and cell sites. At the same time, it increases overall system reliability, improves data rates, and boosts capacity and coverage. Alvarion s AAS technologies demonstrate that WiMAX can successfully meet and even exceed operator expectations, providing operators with the differentiation they need to succeed. Alvarion s AASs go beyond WiMAX-based standard rules to integrate hybrid, best-in-class solutions that leverage innovative, proprietary signal processing functionalities embedded with standard WiMAX multi-antenna schemes. 3
Antenna Diversity and Down Link (DL) Transmit Diversity Schemes Antenna Diversity plays a major role in WiMAX implementations. Diversity greatly improves the quality and reliability of a wireless link line, utilizing more than one antenna element. Simply defined, Down Link (DL) Transmit Diversity is comprised of a number of schemes for reducing the effects of fading by transmitting identical information from two or more different antenna elements, generally with different transmission characteristics. Delay Diversity Alvarion s Delay Diversity exploits an antenna array by applying different delays to each antenna element. As the multiple channels are spectrally different, due to different multipath fading, combining these channels at the receiver end increases the frequency selectivity. Cyclic Delay Diversity In OFDM systems, Alvarion s Delay Diversity takes the form of Cyclic Delay Diversity (CDD) where instead of simple time delay to each stream, every transmission element contains a cyclic shifted version of the OFDM data transmission. As CDD only builds a different Single-Input-Single-Output (SISO) channel, it requires no additional effort from the receiver. This is an important feature, as it enables using this application with no specific equipment from the receiver. Consequently, CDD improves WiMAX coverage by dramatically decreasing the outage probability, especially for users close to the cell edge. Cyclic Delay Diversity 4
Delay Diversity over Beams Alvarion s unique implementation of CDD, namely Delay Diversity over Beams (DDOB), enables increased diversity gain relative to standard CDD, resulting in improved performance and enhanced robustness for a larger number of users. This maximizes the extent of the cell with enhanced performance and improved coverage, and allows operators to deploy fewer base stations, reducing CAPEX and OPEX for a better business case. MIMO Technology In radio access networks, Multi-Input-Multi-Output (MIMO) refers to the use of multiple antennas at both transmitter and receiver ends in order to improve communication performance. MIMO benefits include the ability to provide a significant increase in coverage and capacity while leveraging bandwidth through higher spectral efficiency and link reliability. AAS technologies represent Alvarion s unique approach to MIMO implementation, and are fundamental building blocks in any successful WiMAX-based network deployment and in the successful delivery of customer-centric services and solutions. Down Link (DL) Technologies: Matrix A and Matrix B MIMO Matrix A In an Alvarion MIMO Matrix A implementation, a single data stream is transmitted from multiple antennas and encoded using a mathematical manipulation known as Space Time Block Code (STBC) or Alamouti Code. This improves a receiver s capability to detect information. Implementing multiple receiver antenna elements increases the diversity order and improves the decoding performance of STC transmissions. Additionally, using more than two transmit (TX) antenna elements at the base station side allows for the combination of STC with CDD, or with beamforming (BF). MIMO Matrix A Some of the benefits provided by MIMO Matrix A include the provision of improved coverage for Mobile WiMAX stations; maximization of the cell extent for enhanced performance and allowing operators to deploy fewer base stations; and the reduction of network deployment CAPEX and OPEX. Space Time Code (STC) Receiver Implementation STC requires support from a decoding receiver; however, this is easy to implement since a receiving mobile station uses the two pilot patterns that are orthogonal and unique to each transmission (TX) antenna in order to estimate the channel paths of each antenna. STC provides improved reliability as a result of the better diversity; higher TX effective antenna gain; and the increased link budget and coverage realized. 5
MIMO Matrix B An Alvarion MIMO Matrix B implementation leverages Spatial Multiplexing (SM) utilizing two (or more) multiple antenna elements at the base station and the mobile station for processing independent data streams. Data bits are split between two antennas and transmitted simultaneously as separate (non-redundant) streams. A receiver separates the independent data streams via space-time processing techniques, leveraging two orthogonal pilot patterns. As a result, MIMO Matrix B positively affects throughput capacity. Although it entails added complexity at both the transmitter and receiver ends, a carrier s allocated frequency bandwidth capacity can be enhanced by up to 60%. MIMO Matrix B Alvarion s implementation of MIMO Matrix B, efficiently employs two data streams over two antenna elements, thereby easing mobile station implementations in such a way that even basic receivers realize substantially higher performance. In addition, it increases throughput for user terminals, raising aggregate capacity and facilitating mobile station implementations. MIMO Business Benefits Reduced amount of cell sites resulting in fewer base stations, fewer antennas, less space to rent, and easier location of regulatorapproved sites Implementing MIMO Matrix B for Downlink Improved capacity which better utilizes the spectrum, resulting in improved QoS and more subscribers on a single sector, thereby allowing operators to offer higher speed packages Enhanced coverage, allowing operators to better utilize base stations and cover greater distances 6
Up-Link (UL) Technologies: MRC and CSM Maximal-ratio Combining (MRC) Alvarion Maximal-ratio Combining (MRC) is a receive diversity scheme. Each signal from a receiver (RX) antenna array is multiplied by a weight proportional to the incoming signal level, and inversely proportional to the noise level, after which all the signals are combined. Alvarion s technology features a unique MRC algorithm which achieves exceptional results for operators, while greatly enhancing system coverage. The robust nature of MRC provides operators with a value-added methodology for realizing optimal performance in terms of the Signal-to-Noise Ratio (SNR). MRC s lack of interference mitigation is compensated by the abilities of other more advanced and more complex receivers, in tandem with UL beamforming techniques. Employing UL MRC in a WiMAX base station receive chain increases the UL budget; expands coverage while improving operator network performance; and delivers an improved business case by lowering the number of required base stations to cover the same area. Collaborative Spatial Multiplexing (CSM) Alvarion s CSM is an antenna scheme whereby multiple mobile stations simultaneously send transmission signals, thereby acting like a multi-antenna transmitter. The mobile stations feature one or two transmit antennas, while the base station is multi-antennaed. MIMO in the UL direction utilizes two transmit (TX) channels to send data to multiple receive (RX) antennas located at the base station. The scheme uses two mobile stations paired for Spatial Multiplexing (SM), which transmit data simultaneously, while utilizing the same frequency allocation. Implementing MIMO for Uplink (Pairing) Alvarion s proprietary technology features smart algorithms, which couple geographically-separated mobile stations (also known as pairing) in such a way that two transmitters are spatially diverted, so that the base station receiver can resolve the two incoming data streams. Implementing CSM can maximize the spectral efficiency; increase the aggregate sector capacity, especially in small cells; and improve the business case due to efficient usage of spectrum, allowing operators to connect more subscribers to one sector. 7
Beamforming (BF) Alvarion s beamforming focuses the radio signals of the antenna arrays, acting as a powerful directional antenna. By being aimed towards signal sources, beamforming can reduce interference and fading, while significantly enhancing signal quality. Different beamforming schemes are currently in use; however Alvarion utilizes Adaptive Beamforming, which is the most effective scheme for specific applications. For more information, refer to Alvarion s beamforming white paper. Alvarion Adaptive Beamforming Alvarion SentieM Technologies WiMAX networks are dependent on standards-based technologies which enhance both coverage and capacity. However, superior networks require unique technologies extending beyond WiMAX standards, enabling enhanced coverage and capacity for better service quality and improved user experience. These three fundamentals of mobile WiMAX networks are built into Alvarion s innovative SentieM technologies, providing substantial benefits in terms of better coverage, capacity, and Quality-of-Service (QoS). SentieM technologies offer considerable improvement in the utilization of AAS technologies, Radio Resource Management (RRM), Radio Network Architecture and Media technologies. Designed to comply with the IEEE 802.16e-2005 standard, SentieM technologies deliver and leverage superior technological advantages. Alvarion s AASs leverage the widest range of diversity schemes, combining them to achieve better capacity and coverage. Alvarion s SentieM technologies are able to intelligently determine whether wireless conditions call for the use of beamforming, MIMO, or the use of both combined, for best-in-class wireless broadband transmit/ receive (TX/RX) delivery. A good example of Alvarion s technological AAS superiority is the Mode Selection algorithm. This algorithm selects the right AAS scheme by instantly learning the mobile station noise level, signal strength, mobility (speed that the device is traveling), distance from the base station, mobile station receive (RX) antenna configuration (type, amount), burst length, traffic type (voice, data), system limitation, QoS and other critical factors needed for best-in-class WiMAX. The above examples, as well as Alvarion s additional methods of combining and implementing intelligent and dynamic schemes, maximize overall WiMAX network spectral efficiency, increasing capacity up to 70%, while leveraging an exact combination of multi-antenna schemes for meeting the needs of WiMAX operators, determined on a case-by-case, and user-by-user business basis. 8
Alvarion s AAS Business Benefits and Technical Features Business Benefits Increase the probability that subscribers will receive service according to their SLA Provide on-the-fly solutions to meet the dynamic needs of any wireless environment Provide even basic receivers with substantially enhanced performance Enable enhanced base station coverage and capacity, resulting in reduced system costs and better performance Increase system reliability, utilizing AASs that allow retention of SLAs in hard-to-reach areas Technical Features Deliver a full range of robust, MIMO-based transmission schemes, reducing fading and interference while adaptively managing air interfaces Deliver on-demand collaborative MIMO and beamforming, enhancing coverage and capacity by intelligently selecting the right, operator-specific, multi-antenna technology Deliver optimal performance in terms of SNR Employ UL MRC at the base station receive chain, increasing link budget while enhancing coverage Maximize spectral efficiency, significantly increasing aggregate sector capacity, especially in small cells Provide proprietary CDD, improving network coverage, while greatly decreasing outages close to the cell edge Provide STC, a robust method for delivering extensive diversity gain 9
Summary Alvarion s AASs play a strategic, critical role for ensuring the delivery of best-in-class, WiMAX solutions for operators. Whether Delayed Diversity, MIMO Matrix A, MIMO Matrix B or a combination of any of the schemes, operators must be provided with the WiMAX deliverables they require to satisfy their business case demands. For operators, selecting the right vendor for the provision of WiMAX technologies is a process which must be executed meticulously and methodically, with a partner that fully understands the industry while adapting to the operator s own business case. In a competitive marketplace which allows no room for errors, this is imperative. Alvarion, the global leader in WiMAX solutions, is the vendor of choice for many operators worldwide, who are successfully expanding their businesses on the crest of today s Mobile WiMAX wave. Furthermore, as operators position themselves for the technological challenges materializing on a daily basis, and WiMAX increasingly impacts the world of communications, Alvarion provides operators with the best-in-class open solutions they require, in order to meet the challenges of tomorrow, today. Capacity SISO MIMO B CDD MIMO A Alvarion Intelligent AAS Combining Schemes Coverage Antenna Technologies Comparison Graph 10
Glossary of Acronyms AAS Adaptive Antenna Systems BF CAPEX CINR CPE CDD CSM DL HARQ MISO MRC MRRC MS MID MIMO OFDM OFDMA OPEX QoS PDA RX SD SDMA SISO SNR STBC STC SM TX UL WiMAX Beamforming Capital Expenditures Carrier-to-Interference plus Noise Ratio Customer Premise Equipment Cyclic Delay Diversity Collaborative Spatial Multiplexing Down Link Hybrid Automatic Repeat Request Multiple-Input-Single-Output Maximal-ratio Combining Maximal-ratio Receive Combining Mobile Station Mobile Internet Device Multi-Input-Multi-Output Orthogonal Frequency-division Multiplexing Orthogonal Frequency-division Multiple Access Operating Expenses Quality of Service Personal Digital Assistant Receiver Spatial Diversity Spatial Division Medium Access Single-Input-Single-Output Signal-to-Noise Ratio Space Time Block Code Space Time Code Spatial Multiplexing Transmitter Up Link Worldwide Interoperability for Microwave Access 11
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