The Quest for Wireless Gigabit Recent Advances in the Wireless Physica 1 of 10 file F www cse574 06 ftp phy trends index html Brandon Heller Abstract A number of recent advances in the physical layer are enabling wireless communications devices to reach ever greater speeds These developments in modulation techniques coding and radio architecture enable better spectrum allocation more power efficient errorresistant transmissions and more flexible architectures for receiving signals Many of the advances are being included in upcoming standards like 802 16 and 802 11n and will likely improve the already fast adoption of wireless networking equipment See Also A Review of Key Wireless Physical Layer Concepts Wireless Networking Issues and Trends Table of Contents 1 Introduction 2 Advanced Modulation Techniques 2 1 Ultrawideband 2 1 1 IEEE 802 15 3a 2 1 2 WiMedia Alliance 2 1 3 UWB Forum 2 2 Orthogonal Frequency Division Multiplexing OFDM 3 Multi Antenna Techniques 3 1 Multiple Input Single Output MISO 3 2 Multiple Input Multiple Output MIMO 3 3 Space time Codes 4 Turbo Codes 5 Radio Architecture Summary References List of Acronyms Keywords Networking wireless physical layer gigabit signal transmission signal coding information theory radio architecture ultrawideband UWB OFDM MIMO space time block codes STBC turbo codes Description Covers recent developments in wireless physical layer including modulation techniques multi antenna techniques coding and radio architecture 1 0 Introduction Recent advances allow smarter more complex transmitters and receivers to pack more bits into the same spectrum by using a wider slice of spectrum ultrawideband a more narrow set of frequency bands orthogonal frequency division multiplexing more directional use of spectrum smart antennas and more intelligent encoding of transmissions coding In addition to higher bit rates more flexible radio architectures are now out there software defined radio These developments provide wireless users a better experience including greater range better bit rates greater battery life and increased reliability Upcoming standards will integrate these techniques yielding better wireless devices that are getting closer to gigabit speeds Section 2 discusses advanced modulation techniques Section 3 describes different ways to use multiple antennas to achieve additional 11 27 2013 2 10 AM The Quest for Wireless Gigabit Recent Advances in the Wireless Physica 2 of 10 file F www cse574 06 ftp phy trends index html throughput or reduced bit error rates Section 4 describes options for more reliably encoding data Section five discusses recent advances in radio architecture specifically software defined radios 2 0 Advanced Modulation Techniques Modulation techniques concern the way spectrum is used to deliver a wireless signal from receiver to transmitter Here we discuss ultrawideband UWB Orthogonal Frequency Division Multiplexing OFDM and the commercial status and implications of these technologies 2 1 Ultrawideband Ultrawideband UWB is a wireless transmission technology fundamentally different from other radio technologies With UWB data is represented by impulses rather than carrier modulation The Defense Advanced Research Projects Agency DARPA a prime financial supporter of UWB research defines UWB as any wireless technology where the signal is 25 or more of the frequency used McCorkle02 UWB signals can spread over a spectrum range of up to 7 GHz while carrier based systems might have a 40 MHz or smaller bandwidth Time modulation pulse position modulation and pulse polarity modulation pulse amplitude modulation are two modulation techniques used WikipediaUWB UWB applications thus far have focused on extremely high speed shorter distance personal area networks PANs UWB is also called impulse baseband zero carrier or modulated wavelet technology UWB proponents note its potential for increased signal quality at reduced transmission power The pulse duration of a UWB transmission often as short as 1 ns enables the transmitter to be on for a brief period of time saving battery life in energy constrained devices Obstructions that prevent narrowband signals from reaching their intended targets are inconsequential to UWB as its wideband nature ensures at least some part of the signal will pass through most obstacles The extremely wide signal resists fading and jamming while saving additional power through reduced retransmissions and higher coding density UWB systems consume very little power around one ten thousandth of that of cell phones Geier03 The simple nature of pulse based transmissions combined with the falling costs of silicon may lead to highly integrated UWB transceivers that are cheaper than equivalent carrier based radios due to the reduced need for complex analog modulation circuitry These purported cost benefits have yet to be seen primarily due to a lack of economies of scale Early UWB implementations encountered significant opposition from military and civil services who were worried about interference effects from UWB Aviation fire police and rescue services use radios in which the UWB signal overlaps their narrow spectrum This overlap could create a safety conflict if the extra noise due to UWB were significant enough to those emergency service transmissions The FCC evaluated the issue decided it was not a threat and passed a resolution in Feb 2002 enabling permission for low power use of the 3 1 to 10 6 GHz spectrum area Paulson03 All UWB radios with FCC approval right now are considered to operate under the noise floor of carrier based radios In the near future the FCC is expected to reevaluate their UWB findings for higher power transmissions The lack of FCC approval for high power and long range applications as well as competing industry standards may delay the technology s eventual application UWB has been primarily seen as a high speed replacement for slow Bluetooth Personal Area Networks PANs An initial target is 480 Mbps vs the 1 2 Mbps currently specified for Bluetooth devices An IEEE task group 802 15 3a was created to standardize this application but was dissolved in January 2006 after failing to unite the two largest industry players Griffith06 2 1 1 IEEE 802 15 3a Task Group 3a TG 3a the IEEE 802 15 3a working group was created in mid 2003 with the hopes of uniting competing wireless standards and producing a high speed Bluetooth replacement The working group did have an initial success in reducing the
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