Speeding the Wireless Way

Wireless access speeds are rising dramatically due to some new technologies and implementations found in the newest manufactured offerings. Intel’s wireless solution for the Centrino® Duo and Centrino® Pro processors, called the Intel® Next-Gen Wireless-N, incorporates some of the pre-ratified 802.11n advances, including channel bonding and MIMO. This paper gives an overview of these features as well as discussing Quality of Service and Wi-Fi Multimedia* (WMM*).

Wireless capabilities multiply with the technologies available in the Intel Centrino Duo and Intel Centrino Pro processors. With the inclusion of Intel Next-Gen Wireless-N WLAN solution Multiple-Input, Multiple-Output (MIMO), channel bonding, and the Quality of Service (QoS) enhancement Wi-Fi Multimedia* (WMM*), speed and range for wireless connections increase and bandwidth is more intelligently negotiated and used. This paper will discuss these features and their impact on internet connections and user interaction. Other features available with the Intel Next-Gen Wireless-N will be presented in addition to an option for improved upload speeds.

In 1997 the wireless protocol 802.11 was introduced with speeds of 1 and 2 Mbps (Megabits per second). The protocol uses three non-overlapping channels in the ISM (Industrial, Scientific, Medical) frequency band at 2.4 GHz. Version 802.11a, released in 1999, introduced data rates of up to 54 Mbps and 12 non-overlapping UNII (Unlicensed National Information Infrastructure) channels in the 5 GHz band. Year 2003 brought us the 802.11g protocol which retained the 54 Mbps speed, but didn’t improve upon it. The latest protocol, 802.11n, not yet ratified by IEEE (Institute of Electrical and Electronics Engineers), is the first to provide the promise of up to 600 Mbps using channel bonding and the MIMO architecture. In addition to increased speeds, 802.11n utilizes channels in the frequency band at both 2.4 GHz and 5 GHz[1]. Manufacturers are already producing products based on this new protocol, identifying them as “Draft-N” or “draft 802.11n” devices.

In the past, wireless systems have used only one 20 MHz wide channel to send and receive data. With 802.11 Draft-N channel bonding, two channels, combined, give more functional bandwidth than two individual channels provide separately[2]. The first of these bonded channels is identified as the control or primary channel while the other channel is named the extension or secondary channel. Both channels are capable of sending and receiving information.

The primary channel is selected first, with the second channel being identified based on its relative position to the first. For instance, if the control channel is 132 and the extension channel is 136, then the connection is noted as: (132, 1), indicating that 132 is the control and 136 is one channel away in the positive direction. A notation of (132,-1) would indicate that the secondary chan nel is 128, or one channel away in the negative direction. Bonded channels are required to be next to each other[3]. Because there are 24 non-overlapping channels for 5 GHz and only 3 for 2.4 GHz, channel bonding is used almost exclusively in the 5 GHz frequency band[4]. Further information on channel bonding can be found at: http://www.intel.com/support/wireless/sb/CS-025343.htm.

Legacy wireless uses Single-Input, Single-Output (SISO) technology to send and receive signals, meaning that there is one transmit antenna and one receive antenna per channel. MIMO provides multiple data streams within a single frequency channel. Each data stream within the channel has its own antenna pair for transmitting and receiving, its own radio frequency (RF) chain, and its own analog-to-digital converter. When a signal is created. it is sent to all receiving antennas and all receivers listen for any transmitted signals. Using this method, two or more transmitted signals can be fused together to improve the quality of reception. As more antennas are added, more data can be collected and as more data is collected, an increase in bandwidth can be achieved. Go to http://www.intel.com/support/wireless/sb/CS-025362.htm for more technical details of MIMO and how it works.

For many years, traditional wired Ethernet LAN has had a packet priority assignment and management system which prioritizes packets being sent on the network. Implementing this system is known as establishing QoS by increasing the speed that higher priority packets are pushed through the network. The protocol 802.1p established eight different levels of priority, including a default priority “0” that is called “best effort”[5]. This number is determined by the media access control (MAC) at layer 2 of the OSI networking model. The assigned level, however, is lost as soon as the packet leaves the LAN.

When connected to the internet by wire, the ethernet cable is one access point (AP). If only one device is connected to the internet by that cable then it is using the entire bandwidth of that AP. A wireless access point is somewhat different, as all devices that connect through that point must share the available resources. As more devices connect, the amount of bandwidth per device shrinks. Without a priority system, all packets have equal status and a first-come, first-served system takes over. VoIP, high-end gaming, and media applications cannot transmit smoothly unless their packets are delivered in a consistent and timely manner. In order to ensure this, another method was needed to prioritize the packets for wireless communication.

Until the newly certified 802.11e standard is in wide use, WMM, certified by the WiFi Alliance has been filling the gap. WMM is defined by the WiFi Alliance as a profile or subset of 802.11e. What WMM does is to set a contention window that is based on the service type of the traffic and the amount of wait time for MAC layer medium access. There are four different contention levels; “voice”, “video”, “best effort ” and “background”. Assignment of levels are set for voice, audio and video packets only. The “voice” category has the lowest wait time and therefore highest priority[6] With WiFi Multimedia, VoIP, videos and music can work more smoothly on wireless connections, reducing delays, jitter, and pauses while providing a superior user experience[7].

Introduced in early 2007, the Intel Next-Gen Wireless-N is a recent 802.11 Draft-N product and is an option for the Intel Centrino Duo platform. It is a quad-mode capable adapter, meaning it is capable of supporting 802.11 a, b, g, and Draft-N networks. Data transport speed has significantly increased. Real-world speeds are typically about half of stated theoretical maximums; however, 100 to 140 Mbps rates have been recorded using a draft 802.11n protocol device. This presents a 4X improvement over the real-world averages of about 22 – 24 Mbps for the previous wireless standards[8]. In order to reduce the impact to any near by legacy devices, the addition of Friendly Neighbor Assurance restricts all bonded channels to 5 GHz. In addition, the Advanced Security features provide AES encryption for WPA2 to provide stronger security options. Extensive testing has been completed between Intel and the access points of leading vendors to assure customer satisfaction[9].

One other advantage that is included in the Intel Next-Gen Wireless-N is Intel® Throughput Enhancement. This feature provides a packet burst mode which can be enabled to improve upload speed. Control of packet burst mode reverts to a WMM association whenever such a connection is available, but in other situations when large amounts of data are required to be posted online, throughput is increased by switching modes[10].

Faster, smoother, stronger: Draft-N technology pushes WLAN expectations to the next level, and seems poised to deliver enhanced user experiences and increased productivity. Channel bonding and MIMO architecture stretch speed and range for wireless connections beyond their previous borders. Quality of Service provides prioritization of the data traffic. Intel Next-Gen Wireless-N is one of the first solutions utilizing draft 802.11n protocols as part of its quad-mode design. Intel Centrino Duo and Intel Centrino Pro processors complete the next generation platform with the speed and power to propel you on your wireless way.

Judy M. Hartley is a Software Applications Engineer working for Intel Corporation’s Software and Solutions Group in Hillsboro, OR. She worked for 5 years in Chandler, Arizona as a Product Development Engineer before transitioning to SSG in November of 2005.

To find out more about 802.11 and all the different versions of this protocol, you might wish to download the actual standards themselves, http://standards.ieee.org/getieee802/802.11.html.

For 802.11n specifics, there are quite a few links listed below in the endnotes, or try this news web site specifically designed to keep up on 802.11n and MIMO news: http://80211n.wifinetnews.com/.

Another link that has a lot of information is the Wireless Glossary: http://www.devx.com/wireless/Door/11409

http://www.intel.com is also a great source for information on all of the features and protocols mentioned in this paper.