The Future of WiMAX

Historically, the main usage of wireless data-transfer was voice communication. As wireless communication standards evolved to become digital (Wi-Fi or GSM), voice has become one among several more bandwidth consuming (broadband) applications such as high definition video or games. Many wireless IP (internet protocol) network standards try to satisfy the increasing demand for more bandwidth in more locations while on the move.

Intel’s WiMAX/WiFi Link 5350 chipset (Credit Intel)

Existing cellular networks like 3G or the more advanced 3.5G (based on high speed packet access, or HSPA, a family of standards that extend and improve the performance of existing 3G) can only partially satisfy broadband wireless demands. Cellular networks are continuously connected everywhere, where one base station can cover a small medium sized neighborhood at a range of more than 3 kilometers, but the bandwidth of existing cellular standards is relatively small (up to 3.1Mbps for 3G, compared to Wi-Fi, which can support bandwidth effectively up to 30Mbps in 802.11g), and even more expensive compared to Wi-Fi due to the need for the deployment of expensive cellular base stations and the expensive spectrum of service providers versus the cheap and easy Wi-Fi hotspot deployment and free unlicensed Wi-Fi spectrum.

Intel’s metropolitan Wimax network vision (Credit: Intel)

As a result of these limitations there is a need for a new standard which will enhance the existing standards for wireless broadband and give a broadband experience as it was meant to be: pervasive, mobile, fast, and cheap. This is where WiMAX comes into the picture. WiMAX tries to take the best part of cellular network access – the part that allows you to easily connect anywhere within your service provider’s wide coverage area – and to take the best part of your Wi-Fi experience – the fast speeds and a familiar broadband internet experience – and combine them into a new wireless standard. This new wireless standard is based on the IEEE 802.16 standard (also called WirelessMAN), and was named by the WiMAX Forum which was formed in June 2001 to promote conformance and interoperability of the new wireless standard. It is common to divide WiMAX into two sub-standards, one for fixed wireless data transmission, known as “fixed WiMAX” (based on 802.16d), and the other, known most commonly today as “mobile WiMAX” (based on 802.16e). Mobile WiMAX includes some improvements over fixed WiMAX by also supporting mobility futures. Throughout this article, the notation WiMAX will be used to designate the more advanced mobile WiMAX.

How Does WiMAX Work?

WiMAX blankets large areas with broadband internet. Handover (transition) between WiMAX coverage areas and Wi-Fi hot spot areas enable the best experience whether you are in a Wi-Fi or WiMAX coverage area (Credit: Intel)

The WiMAX network uses an approach that is similar to that of cell phones. A user sends data from a subscriber device to a base station mounted on a tower or tall building to broadcast the wireless signal in a channel called an uplink, and the base station transmits to the same or other user in a channel called a downlink. Unlike the user, who traditionally has limited resources, i.e. very limited transmission power, limited number of antennas, and limited computation capabilities, the base station can use higher transmission power, more antennas, and enhanced computation algorithms. WiMAX service providers deploy a network of towers that enable access over many miles and the WiMAX broadband service will be available anywhere within coverage areas. Coverage for a geographical area is divided into a series of overlapping areas called cells. When the user travels from one cell to another, the wireless connection is transferred from one cell to another.

The transmitted signal in space, frequency, and time. Due to the physical phenomena of reflections from the surrounding objects on the propagation path, the transmitted signal is distorted and split into different multi-paths (Credit: Alvarion.com)

At the heart of WiMAX technology stands several comprehensive concepts that can improve spectral efficiency (the number of information bits transmitted over a given spectrum resource) compared to other technologies.The first important relatively new transmission technique used by WiMAX is orthogonal frequency division multiplexed access (OFDMA), applied in order to efficiently exploit the frequency bands. The WiMAX Forum has defined three licensed “spectrum profiles” (transmission frequencies) of 2.3 GHz, 2.5 GHz, and 3.5 GHz to decrease the cost for manufacturers, as each spectrum profile may require different hardware infrastructures. Additionally, there is more unlicensed spectrum that is less frequently used by most telecom companies that prefer to control the entire available spectrum. Each spectrum profile has a related “bandwidth profile” which determines the channel’s bandwidth. The signal bandwidth is divided in OFDMA to small narrowband, equally and closely-spaced signal carriers used to carry data called sub-carriers. The transmitted data is then divided into several parallel independent data streams where each is allocated to another sub-carrier and all are transmitted at the same transmission interval. In the downlink path, the base station can transmit the data streams for different subscribers efficiently over consecutive sub-carriers. The independency of data streams is an important feature of OFDMA that prohibits several users’ data from interfering with each other and be multiplexed (transmitted in parallel simultaneously). It is obtained by orthogonality of the different sub-carriers carrying the data at different bandwidths. Orthogonality is achieved when the peak of each signal sub carrier (in frequency) coincides with the nulls of other signals (due to the certain equal bandwidth of each sub-carrier) so that they do not interfere with each other. The OFDMA independent sub-carrier transmission enables power prioritization for different subcarriers according to the link quality (the measure of signal quality opposite to its distortion in the wireless channel); good quality sub-carriers will carry more data and bad sub-carriers will carry none. Furthermore, since the subcarriers’ bandwidth is narrow, it can combat better channel degradation caused by multi-paths. Consequently, OFDMA is considered a multi-path resistance.

The independency of data streams can be explained by the orthogonality of the different sub-carriers carrying the data at different bandwidths. Orthogonality is when the peak of each signal sub carrier (in frequency) coincides with the nulls of other signals (due to the certain equal bandwidth of each sub-carrier) so that they do not interfere with each other and can be transmitted simultaneously. (Credit: Alvarion)

WiMAX, unlike WiFi, supports quality of service (QoS) mechanisms, which ensure a certain level of service to enable high-quality levels of applications such as VoIP or real time TV broadcasts. A dedicated data communication protocol centered at the base station is aware of the QoS application requirements and prioritizes the data streams and gives higher priority to data related to service that requires a higher QoS, like video streaming. This high priority is translated into transmission parameters such as higher transmitted power or more sub-carriers per user.

All of the above techniques working together increase coverage, user bandwidth, spectral efficiency (starting at 3.7 bits/sector/Hz), the number of users per WiMAX cell (in macro cells, up to thousands of “normal” subscribers), system stability, and costs. In a typical cell radius deployment of three to ten kilometers, WiMAX Forum Certified systems can be expected to deliver a capacity of up to 40 Mbps per channel for fixed and portable access applications; enough bandwidth to simultaneously support hundreds of businesses or thousands of residences with DSL speed connectivity.

MSI WiMax netbook

Unlike service providers mentioned above, Verizon and Vodafone (the joint owners of U.S. based Verizon Wireless), on the other hand, plan to develop and deploy as their fourth generation mobile broadband network the competing technology – LTE. Which 4G technology will win, WiMAX or LTE? Both technologies have much in common from a technology standpoint and have many architectural similarities. Still, WiMAX has the following advantages over LTE: it benefits from strong allies including Intel and Google, and Network Operators is the largest segment of the WiMAX Forum. People might prefer to use WiMAX as the next generation of free Wi-Fi and in order to rebel against the traditional cell phone companies. WiMAX has already started regional and nationwide deployments while LTE may only enter the market in late 2009 (at the earliest). According to Nokia and Ericsson, their primary market – 3G operators – will be unlikely to adopt LTE until a few years later. LTE operator AT&T reiterated its position that its 3.5 (HSPA) and 3G network technologies still have a lot of life left in them, and that LTE technology would not be rolled out for at least another three years. The WiMAX Forum has already started working on the next backwards-compatible generation of the WiMAX standard, the 802.16m, which will be able to use even higher bandwidths and achieve higher spectral efficiency that will be able to compete with 802.11n in non-rural conditions.

Simens Gigaset SE68 SE68 WiMAX Express Card (Credit: Simens)

Recently, there are signs that the WiMAX and LTE camps are seeking a negotiated settlement to harmonize WiMAX and LTE. Participants from both the WiMAX and LTE camps and standards organizations have recognized the need to collaborate on developing communications. Vodafone is among the operators that have called for the merging of WiMAX and LTE because of the reduction in both conflicts and costs for the industry. The long-term trends in technology, regulation, ecosystem consolidation, and globalization contribute to the rationale that wireless systems should strive to achieve common air interfaces where feasible. Intel CEO Paul Otellini has also called for harmonization between WiMAX and LTE, pointing out the goals of unified broadband communications and common use of technologies. A head-to-head battle over the next few years would require an outlay of billions of dollars in equipment deployment that can be saved with the harmonization of the standards. The primary obstacle to achieving harmonization of WiMAX and LTE is simply the commercial self-interests of competing companies and manufacturers which prevent a common push forward. Intel will eventually provide combined support regardless of whether or not the standards groups achieve official harmonization about providing a multi-mode WiMAX plus LTE chipset for notebooks. Altair Semiconductor, an innovative mobile WiMAX chipset company, also uses the multi-mode WiMAX plus LTE chipset for other portable devices. The first example of standard harmonization comes from the base station manufacturer Freescale Semiconductor, who recently introduced the industry’s first multi-standard device.

A bit of history – Alcatel WiMAX in CeBIT 2007

Infonetics Research, the premier international market research and consulting firm specializing in data networking and telecom, believes that consumers will adopt dual-mode Wi-Fi notepads and phones (Wi-Fi and WiMAX) for use with home wireless networks, public hotspots, and municipal networks. Intel and Nokia are developing technology that is supposed to provide true uninterrupted broadband connectivity based on automatic undetectable switchovers from Wi-Fi to WiMAX. The American municipal wireless networking and intelligent transportation company Azulstar recently launched a high-speed WiMAX service based on Alvarion’s BreezeMAX 3650, which operates in the 3.65 GHz spectrum in New Mexico, which is supposed to support highly reliable services of up to 6 Mbps for home users and up to 100 Mbps for business connections. The launch is supposed to include the complete transition from Wi-Fi to WiMAX technology in Grand Haven, the first Wi-Fi city in the U.S, across New Mexico.

Altair – fabless semiconductor WiMAX

A:

Altair is a fabless chip company developing ultra-low power and high performance 4G/OFDMA silicon solutions. The company was established almost four years ago, by a group of ex-Texas Instruments executives with exceptionally vast experience in the field of broadband semiconductor development. This team has developed during the past 10 years over 25 different complex mixed-signal broadband ICs, which shipped in millions of commercial products in the field. Prior to TI we worked together in a chip startup called “Libit Signal Processing,” which was acquired by TI in 1999, in what is still considered today as one of the most successful semiconductor acquisition in Israel’s tech scene.