VIPULZ

Wi-Fi ON STEROIDSHigh Speed Wi-Fi standards 802.11ac and 802.11ad

CHAPTER 1 INTRODUCTION

Wireless networking is a fundamental technology as important as computing itself. Wi-Fi has pushed the performance and user experience of wireless to guarantee that it is keeping pace with the ever increasing demand of higher speeds and new usage models. With the advent of bandwidth hungry applications, such as large file transfers (e.g., blue-ray HD movie, raw uncompressed images, etc.), HD (High Definition) video streaming, wireless display, and cellular data offload, more bandwidth is sorely needed. Wi-Fi is proliferating in the CE (Consumer Electronics) domain providing a playground for faster media transfer communication applications. Market statistics project number of Wi-Fi enabled devices shipped in year 2012to surpasses 1.5 billion. Extensive effort and work are in progress in IEEE on two emerging standards likely to shake up the wireless world: IEEE 802.11ac and IEEE 802.11ad. These standards target data rates faster than the gigabit Ethernet. The history of initiation and development of these standards up to the year 2011 is presented in.

CHAPTER 2Wi-Fi 802.11

Wi-Fi (or, incorrectly but commonly, WiFi) is a local area wireless technology that allows an electronic device to participate in computer networking using 2.4 GHz UHF and 5 GHz SHF ISM radio bands. The Wi-Fi Alliance defines Wi-Fi as any "wireless local area network" (WLAN) product based on the Institute of Electrical and Electronics Engineers' (IEEE) 802.11 standards". Wi-Fi Alliance is a non-profit organization that promotes Wi-Fi technology and certifies Wi-Fi products if they conform to certain standards of interoperability.IEEE 802.11 is a set of media access control (MAC) and physical layer (PHY) specifications for implementing wireless local area network (WLAN) computer communication in the 2.4, 3.6, 5, and 60 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802). The base version of the standard was released in 1997, and has had subsequent amendments. The standard and amendments provide the basis for wireless network products using the Wi-Fi brand. While each amendment is officially revoked when it is incorporated in the latest version of the standard, the corporate world tends to market to the revisions because they concisely denote capabilities of their products. As a result, in the market place, each revision tends to become its own standard.802.11 technology has its origins in a 1985 ruling by the U.S. Federal Communications Commission that released the ISM band for unlicensed use. In 1991 NCR Corporation/AT&T (now Alcatel-Lucent and LSI Corporation) invented a precursor to 802.11 in Nieuwegein, The Netherlands. The inventors initially intended to use the technology for cashier systems. The first wireless products were brought to the market under the name Wave LAN with raw data rates of 1 Mbit/s and 2 Mbit/s.Vic Hayes, who held the chair of IEEE 802.11 for 10 years, and has been called the "father of Wi-Fi", was involved in designing the initial 802.11b and 802.11a standards within the IEEE. In 1999, the Wi-Fi Alliance was formed as a trade association to hold the Wi-Fi trademark under which most products are sold.The original version of the standard IEEE 802.11 was released in 1997 and clarified in 1999, but is today obsolete. Thereafter various standards namely 802.11 a,b,g,n emerged. They use different technologies. The latest two standards which we use now are 802.11ac and 802.11ad.The use of Wi-Fi includes internet connection, device to device file sharing, local networking etc. it is also notable that the latest mobile communication standards are going to use Wi-Fi for their micro cell based architecture.

CHAPTER 3NEED FOR MULTI-GIGABIT WI-FIWi-Fi speed has proliferated keeping pace with the usage model requirements. As of today, commercially available802.11n-based Wi-Fi products support PHY data rates up to540 Mbps. Wi-Fi use cases have evolved to beyond wireless LAN (Local Area Networking) for access to the Internet. The following use cases justify the need for multi-gigabit Wi-Fi.Sync Data/File Transfer: Multi-gigabit Wi-Fi tremendously reduces the time for data synchronization between two devices. For example, a 1 GB file transfer is at least 10 times faster (1 Gbps vs. 100 Mbps). In home, enterprize, and public kiosk environments, time for completion of the activity is critical for a good user experience.Wireless LAN and Backbone Networks:Multi-gigabit Wi-Fi enables faster access to the Internet by improving the PHY data rate between the device and the AP (Access Point) and between AP-to-AP in wireless backbone networks.Small-Cell Backhaul Network: Mobile broadband data is growing at exponential rates. LTE(Long Term Evolution) and 5G increase the capacity of the network leveraging small cells but it has a major impact on the mobile backhaul network design. Backhaul is the transmission link between the small cell and the mobile network controller. Small cell controllers will be deployed in the streets (lamp-posts, street lights, etc.)and their deployment cost must be minimized. Fiber is not a scalable or cost-efficient way to reach all small cell sites, so a wireless solution will play a dominant role. The 60 GHz technology (802.11ad) is an excellent solution for small cell backhaul since it offers more than one Gbps link with a low cost, particularly no license fee. Thus, mobile broadband technologies and multi-gigabit Wi-Fi complement each other.Multi-media Streaming over IP:Uncompressed video at 1920 1080p, 24 bits/pixel,and 60 frames/second generates 3 Gbps of data and requires at least 3 Gbps PHY data rate for wireless streaming. Conventional Wi-Fi can only stream compressed multi-media contents. Multi-gigabit Wi-Fi enables uncompressed multi-media content streaming, achieving the high quality and low end-to-end latency requirements critical for smooth user experience in wireless display use cases. Wi-Fi is more suitable compared to wireless USB , WHDI (Wireless High Definition Interface) , and WiHD (Wireless High Definition) for wireless display, since the former has a larger deployment and user awareness, besides support for IP-networking, ease of connection, and standardized security mechanism.Cellular Data Offloading: The spectrum available for mobile data applications over cellular networks is limited and even the advent of LTE radio access is reaching the limits of Shannons law. Cellular data offloading is one solution to increase the overall cellular network capacity by offloading mobile data to Wi-Fi in high density places like shopping malls, universities, enterprizes,etc. Multi-gigabit Wi-Fi in this setting provides faster data transfer improving the overall Wi-Fi network performance.

CHAPTOR 4IEEE 802.11ac

IEEE 802.11ac is a wireless networking standard in the 802.11 family (which is marketed under the brand name Wi-Fi), developed in the IEEE Standards Association process, providing high-throughput wireless local area networks (WLANs) on the 5 GHz band. The standard was developed from 2011 through 2013 and approved in January 2014.This specification has expected multi-station WLAN throughput of at least 1 gigabit per second and a single link throughput of at least 500 megabits per second (500 Mbit/s). This is accomplished by extending the air interface concepts embraced by 802.11n: wider RF bandwidth (up to 160 MHz), more MIMO spatial streams (up to eight), downlink multi-user MIMO (up to four clients), and high-density modulation (up to 256-QAM).

Now let us see the features of this standard.

1)Carrier frequency: IEEE 802.11ac is an amendment to the IEEE 802.11 for VHT (Very High Throughput) operation in frequency bands below 6 GHz, excluding 2.4 GHz, i.e., unlicensed bands at 5 GHz band. Plurality of 802.11 a/b/g/n devices is currently operating at 2.4 GHz crowding the channels and causing bandwidth crunch and higher signal interference. The 5 GHz band is comparatively cleaner with lower signal interference. The number of non-overlapping channels (of 20 MHz each) available at 5 GHz band is larger (24 in the US, up to 24 worldwide) as compared to a few non overlapping channels at 2.4 GHz (3 in the US), thus enabling channel bonding of 2 or more channels.2)Channel bandwidth: Spectrum is composed of a number of sub-bands including U-NII (Unlicensed National Information Infrastructure)-1, 2, 2e, and 3 bands. The support of DFS (Dynamic Frequency Selection), originally defined in IEEE 802.11h, is mandatory to use UNII- 2 and 2e. DFS is the mechanism to ensure that channels containing radars are avoided by an AP and the energy is spread across the wireless channel to reduce interference to satellites. IEEE 802.11ac supports 40 MHz, 80 MHz, and 160 MHz channel bandwidth compared to only 20 MHz and 40 MHz supported by 802.11n. The 160 MHz channel bandwidth is composed of two 80 MHz channels that may or may not be contiguous. The 80 MHz and 40 MHz channels are composed of two contiguous 40 MHz and 20 MHz channels, respectively. The support of 40 MHz and 80 MHz channel bandwidth is mandatory while support of 160 MHz and 80+80 MHz is optional. These wide channel bandwidths and minimized co-channel interference are challenging to achieve in a dense WLAN environment (for example, enterprise deployment) with plurality of APs deployed on non-overlapping channels. The 802.11ac provides more spectrum and channel bandwidth by relying on DFS channels, which many Wi-Fi devices do not support today. 80 MHz channel bandwidth allows 5 non-overlapping channels in the U.S. (channels 120-128 are prohibited due to TDWR (Terminal Doppler Weather Radar))and 5 in the UK/EU (channels 149 and higher require light licensing for outdoor use only) when DFS is used, but only 2channels in the U.S. and 1 in the UK/EU without DFS. DFS is mandatory for 160 MHz channel bandwidth with 1 non overlapping contiguous 160 MHz channel in the U.S. and 2in the UK/EU.

3)MIMO: Higher data rate can be achieved with multiple antenna system known as MIMO (Multiple Input Multiple Output) system. Data for transmission is divided into independent data streams to be transmitted through multiple antennas. This is known as spatial multiplexing. Typically, a MIMO system has m transmit and n receive antennas. The number of streams M is always less than or equal to the minimum number of antennas available in an m_nMIMO system. The channel capacity C increases linearly with M,C = M x B x log2(1 + SNR),Where B is the channel bandwidth and SNR is the signal to-noise ratio. The 802.11ac supports up to 8 spatial streams compared to the maximum 4 in 802.11n.IEEE 802.11ac supports MU-MIMO (Multi User-MIMO) as well as SU-MIMO (Single User-MIMO). SU-MIMO is a method by which an AP can transmit multiple independent streams at the same time to a single device. MUMIMO as depicted is a technique by which the AP can transmit multiple independent streams at the same time to multiple devices. In 802.11ac, MU-MIMO system supports 4 users with up to 4 spatial streams per user with the total number of spatial streams not exceeding 8.Typically, many of todays CE devices have one transmit and one receive antenna while the APs have m transmit and n receive antennas. The MU-MIMO system is well suited for downlink from AP in this situation as the network performance is improved keeping the complexity of the device side minimum by using only one receive antenna.

4) Modulation and coding scheme: According to 802.11ac the PHY data sub-carriers are modulated using BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), 16-QAM (Quadrature Amplitude Modulation), 64-QAM, and 256-QAM. Note that 256-QAM is not supported by 802.11n. FEC (Forward Error Correction) coding is used with coding rates of 1/2, 2/3, 3/4, and 5/6. Use of BCC (Binary Convolution Coding) is mandatory, but LDPC (Low-Density Parity-Check Coding) is optional.

5) Backward compatibility: IEEE 802.11ac is backward compatible with 802.11n at 5 GHz ensuring the interoperability of 802.11ac and the already deployed 802.11n devices.

New technologiesNew technologies introduced with 802.11ac include the following

Extended channel binding Mandatory 80 MHz channel bandwidth for stations (vs. 40 MHz maximum in 802.11n), 160 MHz available optionallyMore MIMO spatial streams Support for up to eight spatial streams (vs. four in 802.11n)Downlink Multi-user MIMO (MU-MIMO, allows up to four simultaneous downlink MU-MIMO clients) Multiple STAs, each with one or more antennas, transmit or receive independent data streams simultaneously Space Division Multiple Access (SDMA): streams not separated by frequency, but instead resolved spatially, analogous to 11n-style MIMO Downlink MU-MIMO (one transmitting device, multiple receiving devices) included as an optional modeModulation 256-QAM, rate 3/4 and 5/6, added as optional modes (vs. 64-QAM, rate 5/6 maximum in 802.11n)Other elements/features Beamforming with standardized sounding and feedback for compatibility between vendors (non-standard in 802.11n made it hard for beamforming to work effectively between different vendor products) MAC modifications (mostly to support above changes) Coexistence mechanisms for 20/40/80/160 MHz channels, 11ac and 11a/n devices. Adds four new fields to the PPDU header identifying the frame as a Very High Throughput (VHT) frame as opposed to 802.11n's High Throughput (HT) or earlier. The first three fields in the header are readable by legacy devices to allow coexistence Meru Networks has suggested that 802.11ac makes a wireless network employing the Single Channel Architecture substantially more effective. Traditional 802.11 networks are deployed as a Multiple Channel ArchitectureMandatory and optional features Mandatory features (carried over from802.11a/802.11g) 800ns regularguard interval Binaryconvolutional coding(BCC) Single spatial stream New mandatory features (newly introduced in 802.11ac) 80MHz channel bandwidths Optional features (carried over from802.11n) two to four spatial streams Low-density parity-check code(LDPC) Space-Time Block Coding(STBC) Transmit Beamforming (TxBF) 400ns short guard interval (SGI) Optional features (newly introduced in 802.11ac) five to eight spatial streams 160MHz channel bandwidths (contiguous 80+80) 80+80MHz channel bonding (discontiguous 80+80) MCS 8/9 (256-QAM)

CHAPTER 5IEEE 802.11ad

IEEE 802.11ad is an amendment that defines a new physical layer for 802.11 networks to operate in the 60 GHz millimeter wave spectrum. This frequency band has significantly different propagation characteristics than the 2.4 GHz and 5 GHz bands where Wi-Fi networks operate. Products implementing the 802.11ad standard are being brought to market under the WiGig brand name. The certification program is now being developed by the Wi-Fi Alliance instead of the now defunct WiGig Alliance. The peak transmission rate of 802.11ad is 7 Gbit/s.

The formation of the WiGig alliance to promote the IEEE 802.11ad protocol was announced in May 2009. The completed version 1.0 WiGig specification was announced in December 2009. In May 2010, WiGig announced the publication of its specification, the opening of its Adopter Program, and the liaison agreement with the Wi-Fi Alliance to cooperate on the expansion of Wi-Fi technologies. In June 2011, WiGig announced the release of its certification-ready version 1.1 specification.

The WiGig specification allows devices to communicate without wires at multi-gigabit speeds. It enables high performance wireless data, display and audio applications that supplement the capabilities of previous wireless LAN devices. WiGig tri-band enabled devices, which operate in the 2.4, 5 and 60 GHz bands, deliver data transfer rates up to 7 Gbit/s, about as fast as an 8 antenna 802.11ac transmission, and nearly 50 times faster than the highest 802.11n rate, while maintaining compatibility with existing Wi-Fi devices. The 60 GHz signal cannot typically penetrate walls but can propagate off reflections from walls, ceilings, floors and objects using beamforming built into the WiGig system. When roaming away from the main room the protocol can switch to make use of the other lower bands at a much lower rate, but which propagate through walls.

Features of 802.11ad include1. Carrier frequency: 802.11ad is an amendment to 802.11 for enhancements for multi-gigabit throughput in 60 GHz band. Fig. 3 depicts the spectrum allocation for unlicensed operation at 60 GHz. In this band, typically 7 GHz of spectrum is available for unlicensed usage compared to 83.5 MHz in 2.4 GHz band. This standard defines 4 channels, each with 2.16 GHz bandwidth, for operation at 60 GHz band. These channels are 54 times wider than the 40 MHz bonded channels available in 802.11n.2. Modulation and coding scheme: 802.11ad defines both SC (Single Carrier) modulation and OFDM (Orthogonal Frequency Division Multiplexing) modulation. OFDM enables longer distance communication and greater delay spreads. This provides flexibility in handling obstacles and reflected signals. OFDM allows SQPSK, QPSK, 16-QAM, and 64- QAM modulation with the maximum achievable PHY data rate of 6.756 Gbps. SC PHY is low on power consumption and focusses on small form factor devices like handsets. SC uses /2-BPSK, /2-QPSK, and /2-16-QAM modulation with the maximum achievable PHY data rate of 4.620 Gbps. In this standard, the data is encoded by a LDPC encoder with 1/2, 5/8, 3/4, and 13/16 code rates.3. Beamforming: Signal attenuation is high at 60 GHz band and hence link budgeting is challenging. To improve the signal strength at the receiver, high gain antennas are deployed. These high gain antennas, mostly phased-array antennas, utilize beamforming to create beams in a particular direction allowing the transmitted power to be focused.4. Backward compatibility: The backward compatibility factor is irrelevant as IEEE 802.11ad is the first standard for Wi-Fi operation at 60 GHz.

CHAPTER 6MULTI-GIGABIT MODULATION AND CODING SCHEMES

Multi-gigabit PHY data rates in 802.11ad are achieved by using a large chunk of spectrum (2 GHz) with simple modulation schemes (BPSK, QPSK), while in 802.11ac it is based on sending more bits per symbol (256-QAM) and use of simultaneous data streams (up to 8), because bandwidth is limited to a maximum of 160 MHz (with channel bonding).

Table I illustrates MCSs (Modulation and Coding Schemes)used in 802.11n, 802.11ac, and 802.11ad to achieve multimegabitand multi-gigabit PHY data rates. Note that both 802.11n and 802.11ac support long guard interval of 800ns and optionally short guard interval of 400 ns betweentransmission of two symbols. The guard interval is 48.4 ns in802.11ad. Table I assumes the long guard interval for 802.11nand 802.11ac. With short guard interval, the data rates increaseaccordingly, e.g., 802.11ns maximum data rate increases from540 Mbps to 600 Mbps, and 802.11acs maximum data rateincreases from 6.240 Gbps to 6.933 Gbps.The 802.11n PHY data rates range from 6.5 Mbps to 600Mbps, achieved through various combinations of modulationscheme, code rate, channel bandwidth, guard interval, andnumber of spatial streams. 802.11ac PHY data rates rangefrom 6.5 Mbps to 6.933 Gbps. PHY data rates achieved by802.11ac with 256-QAM modulation scheme and by 802.11nwith 64-QAM modulation scheme, 800 ns guard interval, 40MHz channel bandwidth, and 4 spatial streams is 720 Mbpsand 540 Mbps, respectively, i.e., a 33% increase in the PHYdata rate, thanks to 256-QAM modulation scheme.802.11ad PHY data rates range from 385 Mbps to 6.7Gbps, achieved through combinations of modulation schemeand code rate. For BPSK modulation scheme, PHY data rateachieved by 802.11ad using 2.16 GHz channel bandwidth and802.11n employing 20 MHz channel bandwidth is 385 Mbpsand 6.5 Mbps, respectively, i.e., a 58 times increase in thePHY data rate, leveraging larger channel bandwidth.

CHAPTER 7CHALLENGES FOR MULTI-GIGABIT WI-FI STANDARDS

Table II shows the receiver sensitivity and required transmitterEVM (Error Vector Magnitude) values for some keyMCSs of 802.11n, 802.11ac, and 802.11ad. A higher receivesensitivity means that a higher signal strength (or SNR) isrequired for detection. A lower EVM means that system errorssuch as local oscillator phase noise, transmitter nonlinearities,IQ imbalance, etc. must be controlled more precisely.

A. Hardware Complexity and Power Consumption802.11ad systems require a simpler hardware compared to 802.11ac, due to simpler modulation schemes and use of only one stream of data (SISO vs. MIMO). To have multiple independent data streams in 802.11ac, multiple RF and baseband chains are required. In practice, for better radio link performance, the number of RX and TX chains may be larger than the number of desired streams, NS (i.e., number of independent and separately encoded transmit signals or streams). This implies more than NS times increase in powerand RF chip/device area.Even if intelligent power management is applied to TX,MIMO RX system may consume at least NS times more power compared to a single chain RX. Furthermore, the processing power required to form MIMO streams must be added to the total power budget.

B. Device Form FactorIn a multiple antenna system the adjacent antennas must be separated by a minimum distance, around half wavelength (27mm for 802.11ac), to reduce the coupling between antennas as well as correlation between streams. For applications where size matters, this requirement limits the number of antennas,and consequently, the number of streams and maximum bit rate.At 60 GHz the carrier wavelength is only 5 mm, so relatively high gain antennas can be implemented in a small package.For example, a 13 dB patch array antenna printed on Duroid substrate (r = 2.2) occupies an area of 5 mm 6 mm .So, instead of using a dipole antenna with 2 dBi gain on eachside as in 802.11ac, a compact higher gain antenna can be used at each end to compensate for the extra path loss.

C. Semiconductor CostCMOS technology is used for fabrication of Wi-Fi transceivers. 2.4/5 GHz band Wi-Fi transceivers can be synthesized with more conventional CMOS technologies, which are cheaper whereas 60 GHz Wi-Fi transceivers can only be synthesized with the state-of-the-art CMOS technology (65nm, 40 nm, etc.) As of today, 40 nm CMOS technology is expensive, thus making 802.11ad transceivers costly compared to 802.11ac transceivers.

CHAPTER 8802.11AC AND 802.11AD SUITABILITY FORMULTI-GIGABIT USE CASESConsidering the challenges discussed in Section V an important question is raised: are 802.11ac and 802.11ad suitable for the same type of applications, or there are preferred classes of applications for each one?To answer this question, first we need to get a better idea of wave propagation at 5 GHz and 60 GHz bands. At 60 GHz spectrum, radio signals suffer from higher propagation and atmospheric loss compared to 5 GHz. For the same range,free space loss at 60 GHz is 21 dB more than free space lossat 5 GHz (e.g. for 1 m range free space loss is 68 dB at60 GHz, and 47 dB at 5.5 GHz). Note that general rule of thumb is every 6 dB increase in propagation loss halves the coverage distance. Furthermore, obstruction loss is significant at 60 GHz. For example, a human body loss is between 20-40dB.Therefore, 802.11ad is more appropriate for line-of-sightroom-scale, low-cost, short-range very high throughput applications,such as in-room (i) uncompressed and lightly compressed multi-media wireless display, (ii) sync data/filetransfer, etc. IEEE 802.11ac is proper for longer-range high throughput applications, such as in-home (i) WLAN, (ii)(lightly) compressed multi-media wireless display, etc. Insummary, IEEE 802.11ad leveraging small device form factorand low power consumption characteristics is apt for portablepower-constraint multi-gigabit wireless devices.While 802.11ac seems to be more appropriate for longer range applications, the transmitter power regulatory and powerconsumption requirements limit the applicability to the different use cases. As seen in Tables I and II, 802.11ac requires-48 dBm receive sensitivity with 256-QAM modulation and upto 8 spatial streams to achieve multi-gigabit Wi-Fi. To deploy the highest data rates of 802.11ac AC-powered units are more suitable. Since the obstruction loss at 5 GHz is lower comparedto 60 GHz, multi-gigabit 802.11ac is more appropriate for home-scale (both line-of-sight and non-line-of-sight) wireless applications where portability is not a bottleneck.On a different note, at 60 GHz high gain antennas with low cost and small size can be realized for point to point applications such as small-cell backhaul networks. Despite lower propagation loss at 5 GHz band, strict regulatory requirements limit the transmit power proportional to thetransmitter antenna gain. Thus range extension required for backhaul networks cannot be achieved at 5 GHz.

CHAPTER 9CONCLUSIONIn this seminar the need of multi-gigabit Wi-Fi links is articulated. We introduce two emerging standards likely to shake the wireless world: 802.11ac and 802.11ad, highlight the challenges in the path of multi-gigabit Wi-Fi, and discuss suitability of 802.11ac and 802.11ad for supporting multi- gigabit use cases. Wi-Fi is booming rapidly and is used for wireless connectivity between devices in plethora of scenarios. It remains to be seen how the consumer market responds to multi-gigabit Wi-Fi link capabilities.9