Wimax Efficiency Worldwide Interoperability for

WiMAX Efficiency Worldwide Interoperability for Microwave Access (WiMAX) Efficiency This research proposal provides an overview of the study envisioned herein, as well as relevant background information on Worldwide Interoperability for Microwave Access, or WiMAX. One of the harsh realities of the Age of Information is the limited amount of bandwidth available to service the growing demand for wireless services and the fundamental constraints involved in delivering wireless services in geographically challenging areas.

In this regard, Vucetic and Yuan (2003) report that, "Demands for capacity in wireless communications, driven by cellular mobile, Internet and multimedia services have been rapidly increasing worldwide. On the other hand, the available radio spectrum is limited and the communication capacity needs cannot be met without a significant increase in communication spectral efficiency" (p. 30).

Indeed, the past decade or so has witnessed an explosion in the demand for such services, and wireless access is no longer regarded as a luxury by consumers but rather as an expected part of their day-to-day lives. For instance, in their white paper, "Smart WiMAX -- Delivering personal broadband," Subramanian, Rangarajan and Sergeant (2004) enthuse, "Wireless communications is becoming an inherent part of our everyday life. We now take for granted the ability to make a phone call no matter where we are via a cellular phone.

At the same time the Internet explosion has created a need for access to data and multimedia that is much more than simple voice communication" (p. 2). In this environment, identifying cost-effective and efficient alternatives represents a timely and valuable enterprise, but complex problems require complex solutions and this environment is no exception. According to Mukherjee (2007), "As bandwidth intensive, rich media applications are introduced, larger volumes of subscribers consume ever-growing quantities of data packets while continuing to utilize more minutes of voice.

Simply acquiring more spectrum channels and deploying more sites to resolve capacity issues can be decidedly inefficient and costly" (p. 2). Clearly, a superior approach would use the best of what was available to its maximum advantage within existing service parameters and there have been a number of initiatives to this end in recent years that have met with mixed results.

Consumer and business expectations of reliable and efficient wireless services are becoming increasingly severe, and companies that are able to deliver the goods will be at a distinct competitive advantage over those who plod along with their existing approaches. As Subramanian and his colleagues emphasize, "We expect to be able to access these applications anywhere any time on any device. The end result is personal broadband - a wireless broadband connection that belongs to an individual, like a cell phone.

Achieving the economics of a personal broadband network deployment is the real challenge for next generation wireless networks. Some believe that existing cellular networks and their evolution to 3G and LTE can address this need" (Subramanian et al., p. 2). This evolution to ubiquitous computing is not without its rocky spots, though. Cellular networks that were originally designed for outdoor remain profoundly constrained in their ability to provide simple reliable voice services indoors as well as a fundamental inability to provide media-rich broadband content indoors and out (Subramanian et al.).

Therefore, technologies that can overcome these constraints today can provide consumers and businesses alike with the level of service that they have come to expect. In this regard, Subramanian and his colleagues note that, "As personal broadband devices such as laptops, ultra-mobile computing platforms, PDAs, game devices etc. proliferate, the user expectation is to be able to access broadband content indoors as well as outdoors in a stationary or mobile context.

Given such a requirement it is increasingly becoming clear that we need a different approach to the delivery ubiquitous anytime anywhere broadband" (emphasis added) (p. 2). In fact, as researchers at Intel emphasize, "Recent research indicates that laptop computers are becoming the access devices of choice for broadband wireless data. Personal productivity applications such as email, address books, calendars, and internet browsers, are among the top applications used" (Understanding WiMAX, 2004, p. 4). A wide range of geographical constraints affect the ability of telecommunications providers in servicing this increasing array of applications.

For instance, one industry analysts emphasizes that, "The wireless environment provides significant challenges including attenuation, multipath interference and cell planning. It is also important to consider the client complexity (and costs associated) and cell deployment scenarios" (Understanding WiMAX, p. 5). Multipath is the term used to describe the interference that develops when a transmission is originally transmitted and what happens to it in geographically challenging areas. For instance, Brooks and Hoelzer (2001) report that, "A common problem found in high-speed communication is inter-symbol interference (ISI).

ISI occurs when a transmission interferes with itself and the receiver cannot decode the transmission correctly. For example, in a wireless communication system, the same transmission is sent in all directions. Because the signal reflects from large objects such as mountains or buildings, the receiver sees more than one copy of the signal. In communication terminology, this is called multipath" (p. 2). According to Mukherjee (2007), "One of the greatest challenges to traditional wireless systems has been managing multi-path fading environments.

Multi-path fading is the resulting signal degradation due to obstructions between a wireless transmitter and its intended destination" (p. 2). Because the indirect paths require more time to reach the receiver, the delayed copies of the signal tend to interfere with the direct signal, thereby causing ISI (Brooks & Hoelzer). In fact, this problem was identified early on.

For instance, Cimini (1985) noted that "Severe multipath propagation, arising from multiple scattering by buildings and other structures in the vicinity of a mobile unit, makes the design of a mobile communication channel very challenging. This scattering produces rapid random amplitude and phase variations in the received signal as the vehicle moves in the multipath field. In addition, the vehicle motion introduces a Doppler shift, which causes a broadening of the signal spectrum" (p. 665).

Taken together, these constraints suggest that these problems might in fact be far too complex for a simple approach, but researchers have developed a cost-effective alternative that may be able to overcome these obstacles and provide the level of services needed today and in the short-term in the world's inexorable march to ubiquitous computing, and these issues are discussed further below. WiMAX Background.

Worldwide Interoperability for Microwave Access or WiMAX represents a profound step forward in overcoming the numerous constraints to the delivery of efficient wireless services in geographically challenging areas and provides a number of other valuable benefits as well in the process. According to Salvekar, Sandhu, Li, Vuong and Qian (2004), "WiMAX is a wireless technology that provides broadband data at rates over 3 bits/second/Hz.

In order to increase the range and reliability of WiMAX systems, the IEEE 802.16-2004 standard supports optional multiple-antenna techniques such as Alamouti Space-Time Coding (STC), Adaptive Antenna Systems (AAS) and Multiple-Input Multiple-Output (MIMO) systems" (p. 229). As Strandell, Wennstrm, Rydberg and berg (n.d.) point out, "The use of adaptive antennas in mobile communication systems offers a possibility to increase the system capacity" (p. 1).

Multiple-input multiple-output, or MIMO, is a technique developed for use in multi-antenna communication systems; the MIMO technique depends on the presence of multiple, independent radio frequency (RF) chains and antennas at the cell site as well as on the subscriber device (Hedayat, Guo, Rangarajan, Jin, Sergeant & Subramanian, 2007). The MIMO technique has been shown to be able to provide improved throughput and range, particularly when the technique is implemented together with beamforming (Hedayat et al.).

According to Stine (1997), "Beamforming is another name for spatial filtering where an array of sensors together with appropriate signal processing can either direct or block the radiation or the reception of signals in specified directions" (p. 2). This innovation takes advantage of multipath propagation rather than trying to eliminate its adverse effects.

In this regard, Hedayat and his colleagues point out that, "Wireless MIMO communication exploits environmental phenomena such as multipath propagation to increase data throughput and range, or reduce bit error rates, rather than attempting to eliminate effects of multipath propagation as SISO (Single-Input Single-Output) communication systems seek to do" (p. 7).

In this regard, in their white paper, "A Practical Guide to WiMAX Antennas," researchers at Motorola report that, "Mobile WiMAX has offered the industry a very capable platform by which to deliver the demanding service requirements for wireless access today and tomorrow. With the added support for a variety of advanced multi-antenna implementations, Mobile WiMAX offers the wireless operator considerable relief in meeting their growing network demands with higher performance, fewer sites, less spectrum, and reduced cost" (p. 2). Trends.

According to Salvekar and his colleagues, "Multiple-antenna techniques can greatly enhance the performance of wireless transmission systems. Systems are currently trending towards using multiple antennas at the BS and future systems may evolve to multiple antenna systems at the SS. We have demonstrated that Alamouti reception, circular delay diversity, and selection diversity are simple schemes that can increase performance greatly. More advanced MIMO techniques can increase performance well beyond the current limits of data rate and reach" (p. 238).

It would also appear that a growing number of vendors are recognizing the inherent constraints involved in the previous MIMO configuration and are developing superior alternatives. In this regard, according to Hedayat and his associates (2007), "Many MIMO systems for WiMAX are being developed without beamforming, and although it helps in robustness and can add some capacity, MIMO does nothing for the uplink.

The result will be an uplink limited system that either has very slow uplink and frequent coverage holes, or a system that requires many more base stations and cell sites for universal coverage" (p. 8).

Navini is in the process of introducing a new standards compliant MIMO solution that it calls "Smart MIMO"; Smart MIMO applies adaptive beamforming to MIMO in order to provide additional benefits beyond what simple MIMO can provide (Hedayat et al.) in the case of MIMO-a, the Space Time Coded signals are both beamformed using the adaptive beamforming algorithms based on measurements taken on the uplink channel (Hedayat et al.).

The signals in the MIMO -- a configuration are also managed in phase in order to assure their optimal reception at the mobile station (Hedayat et al.). While the pundits continue to debate the pace at which the world will ultimately reach a truly ubiquitous computing environment, the hand-writing is on the wall for everyone else to see and it appears the time is ripe for WiMAX today.

As Hedayat and colleagues emphasize, "The performance improvements promised by MIMO, and later beamforming in WiMAX deployment scenarios are essential components for the delivery of true broadband services. MIMO equipment is already being deployed in the Wi-Fi market for IEEE802.11n products and has demonstrated massive increases in capacity. Clearly the environment represented by WiMAX is quite different from that of Wi-Fi and interference management is a key concern for WiMAX" (p. 17).

Interference management concerns, though, are not restricted to WiMAX but are equally relevant for other technologies in use and envisioned and there issues are discussed further below. Current Scenario and Importance of Comparison to Other Technology. Because resources are by definition scarce and the costs associated with implementing and maintaining a sophisticated WiMAX system are not small, it just makes good business sense to determine if the WiMAX approach is worthy of the capital investments involved or whether a "wait-and-see" approach might be more prudent.

Nevertheless, the need is great today and experts predict that demand will continue to grow in the future. According to Chen, Ahmad and Hanzo (n.d.)., "The ever-increasing demand for mobile communication capacity has motivated the needs for new technologies, such as space division multiple access, to improve spectrum utilization" (p. 1).

Not surprisingly, there have been a number of approaches developed and tested in recent years in an effort to satisfy this growing demand and generate a profit in the process, but some approaches have clearly been better suited to existing needs than others.

For instance, in their study, "Universal Broadband Access: Going Wireless and Mobile," Hurel, Brouet, Le Gouriellec and Peruyero (2005) ask, "GSM/EDGE, UMTS/HSDPA/HSUPA, WiMAX, CDMA2000, UMTS-TDD-HCR, TD-SCDMA, WiFi, mobile broadcast! What is the best technology to select? Are there any bad technologies that we can forget?" (p. 1). It is easy to become confused in this alphabet of choices, but an increasing number of industry experts suggest that the technology of choice today is WiMAX IEEE 802.16e, and these issues are discussed further below.

WiMAX (IEEE 802.16e) The evolution of the WiMAX system from its 80216a permutation to its current 802.16e approach has been enthusiastically received by the mobile telecommunications industry as a revolution in how cellular services are provided. For instance, in their white paper, Airspan (2007) reports that, "Multiple Antenna Systems in WiMAX," WiMAX, championed by the WiMAX Forum to promote conformance and interoperability of the IEEE 802.16 standard, has revolutionised the wireless wide area broadband communications.

The latest version of the standard, IEEE 802.16e-2005, extends the earlier specifications in order to address the requirements of mobile WiMAX deployments" (p. 3). According to Muquet, Biglieri, Goldsmith and Sari (n.d.), "WiMAX systems are based on the IEEE 802.16-2004 and IEEE 802.16e-2005 standards which define a physical (PHY) layer and the medium access control (MAC) layer for broadband wireless access systems operating at frequencies below 11 GHz. The first of these standards, published in 2004, addresses fixed services, and the second, published in 2005, is intended for mobile services" (p. 4).

According to Airspan (2007), "The underlying WiMAX PHY is ideally suited to multipath operations in demanding mobile and fixed WiMAX deployment scenarios. One of the strengths of the WiMAX PHY is the ease with which it supports and cooperates with multiple antenna technologies" (p. 17).

The initial version of the WiMAX standard operated in the 10-66GHz frequency band and required line of sight towers; however, the 802.16a extension employs the lower frequency of 2-11GHz, which relaxed regulatory requirements and does not require a line of sight configuration as well as providing a 31-mile range compared with Wi-Fi's 200-300 yards, and 70 Mbps data transfer rates (Gabriel, 2003, p. 4).

Nevertheless, because WiMAX is scheduled to operate in the 2.5, 3.5, or 5.8 GHz bands, the system may require more cells than 3G, an approach that generally has frequencies less than 2 GHz because of the higher frequencies involved (Understanding WiMAX). According to analysts at Intel, one of the primary developers and proponents of the WiMAX approach, "The main impact will be to operators planning to deploy in the unlicensed 5.8 GHz spectrum.

However, the costs associated with licensed spectrum for 3G and 2.5/3.5 GHz spectrum may offset the cost for additional cell sites" (Understanding WiMAX, p. 6). According to their white paper, the researchers at Intel advise, "The portable version of WiMAX, IEEE 802.16e utilizes Orthogonal Frequency Division Multiplexing Access (OFDM/OFDMA) where the spectrum is divided into many sub-carriers. Each sub-carrier then uses QPSK or QAM for modulation" (Understanding WiMAX, p. 4). Likewise, Sivaradje and Dananjayan report that, "OFDM allows many users to transmit in an allocated carrier.

Each user is allocated several carriers in which to transmit their data. The transmission is generated in such a way that the carriers used are orthogonal to one another, thus allowing them to be packed together much closer than standard frequency division multiplexing. This leads to OFDM providing a high spectral efficiency" (p. 1). As Muquet and his colleagues advise, "The IEEE 802.16e-2005 specifications actually define three different PHY layers: Single-carrier transmission, orthogonal frequency-division multiplexing (OFDM), and orthogonal frequency-division multiple access (OFDMA) (p. 4).

According to Vasuki (1999), OFDM is a multicarrier transmission technique that is used in both wired and wireless communications; the author notes in the former instance, though, the use of the term "Discrete Multi-Tone" is considered more accurate. In this regard, Vasuki reports that, "The OFDM technique divides the frequency spectrum available into many closely spaced carriers, which are individually modulated by low-rate data streams.

In this sense, OFDM is similar to FDMA (the bandwidth is divided into many channels, so that, in a multi-user environment, each channel is allocated to a user)" (p. 2). The fundamental difference between the two concerns the fact that the carriers selected in OFDM are much more closely spaced than in FDMA (1kHz in OFDM compared to approximately 30 kHz in FDMA); this difference serves to increase its spectral usage efficiency, with the orthogonality between the carriers being responsible for the close spacing of carriers (Vasuki).

According to Hedayat and his colleagues (2007), "There are two forms of MIMO supported by mobile WiMAX (based on the IEEE 802.16e-2005 standard), as part of the wave 2 certification profiles. Called MIMO Matrix a and Matrix B, the two types of MIMO have the potential to improve the performance of personal broadband systems in diverse ways (p. 7).

In their study, "Design and Optimisation of an Antenna Array for WIMAX Base Stations," Mahler and Landstorfer (2005), report that they have developed an intelligent base station antenna with beam- and nullsteering for 360-degree coverage in order to increase the capacity and coverage in broadband data communication according to the IEEE 802.16e WiMAX standard. Efficiency and Its Importance in WiMAX. One of the more compelling advantages of the WiMAX technology is the increased efficiency it provides to existing infrastucture.

As Wu (n.d.) emphasizes, "The WiMAX standard is set to bring the long-awaited spectral efficiency and throughput to meet users' needs for combined mobility, voice services and high data rates" (p. 3). As noted above, there are a number of alternatives available that could, alone or in combination, provide the short-term answer to the exponential growth in wireless telecommunications, but WiMAX represents more than just such a stop-gap solution.

According to Wu, "[WiMAX] will enable access for more users due to its NLOS [non-line of sight] capability, lower deployment costs, wide-range capability and penetration into the mass consumer market. Needless to say, it is the clear path to broadband mobility that will form the basis of 4G" (p. 3). This is not to say, though, that WiMAX also represents an end-all solution to these problems, but rather provides a valuable framework in which they can be administered. In.