03-10-2016, 10:37 AM
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Abstract:
The Wireless Gigabit Alliance (WiGig) and IEEE 802.11ad are developing a multigigabit wireless
personal and local area network (WPAN/WLAN) specification in the 60 GHz millimeter wave
band. Chipset manufacturers, original equipment manufacturers (OEMs), and telecom
companies are also assisting in this development. 60 GHz millimeter wave transmission will
scale the speed of WLANs and WPANs to 6.75 Gbit/s over distances less than 10 meters. This
technology is the first of its kind and will eliminate the need for cable around personal
computers, docking stations, and other consumer electronic devices. High-definition
multimedia interface (HDMI), display port, USB 3.0, and peripheral component interconnect
express (PCIe) 3.0 cables will all be eliminated. Fast downloads and uploads, wireless sync, and
multi-gigabit-per-second WLANs will be possible over shorter distances. 60 GHz millimeter
wave supports fast session transfer (FST) protocol, which makes it backward compatible with 5
GHz or 2.4 GHz WLAN so that end users experience the same range as in today’s WLANs. IEEE
802.11ad specifies the physical (PHY) sublayer and medium access control (MAC) sublayer of
the protocol stack. The MAC protocol is based on time-division multiple access (TDMA), and the
PHY layer uses single carrier (SC) and orthogonal frequency division multiplexing (OFDM) to
simultaneously enable low-power, high-performance applications.
1 Introduction
There is a huge amount of unlicensed spectrum available worldwide in the 60 GHz band.
Academia and industry have turned to the 60 GHz spectrum because of the universal
availability of unlicensed spectrum, the ever-growing number of user applications creating
heavy data traffic, and the need to reduce data transfer times. Considerable efforts have been
made to use this spectrum and spur the development of silicon, similar to what happened with
the 2.4 GHz ISM band 15 years ago. 60 GHz millimeter wave technologies offers a way to
provide end users with guaranteed quality of service (QoS) for different applications. Fig. 1
shows the allocation for 60 GHz in different countries
60 GHz millimeter wave technologies create significant problems in designing the radio
frequency (RF) front-end, processing gigabit-per-second data, and migrating to 40 nm and 28
nm low-power technologies in designing the silicon, considerable progress have been made in
making it practical and feasible [4]-[6]. 60 GHz millimeter wave systems are needed to cater for
newer applications, such as streaming video in the home or office, that have flourished as a
result of last-mile access provided by internet service providers (ISPs). Such systems will also
eliminate the need for cables around docking stations, and this will reduce clutter and allow
easier connection between devices. There are multiple industry organizations involved in 60
GHz standardization, the notable ones being Wireless HD [7], IEEE 802.15.3c [8], WiGig [9], and
IEEE 802.11ad [10]. The last two of these organizations involve a large number of silicon, OEM,
and telecom companies that are motivated to have a single worldwide 60 GHz standard.
WiGig began standardization in 2008 and has recently released the WiGig 1.0 standard. IEEE
802.11ad also began standardization in 2008 and has recently released IEEE 802.11ad Draft 9.0
standard. These standards are similar, and in this paper, we will refer to 802.11ad as the
representative of both standards, pointing out when there is a feature that is unique to the
WiGig standard. Similar standardization efforts have been made by ECMA-387 and CMMW
Study Group [2], [3]. 60 GHz millimeter wave is the next wireless networking technology and
will appear in the market around 2014 [11]. It is poised to repeat the successes of Bluetooth
and Wi-Fi [12]. This explosive growth of the wireless industry in such a short time can also be
attributed to the opening of unlicensed bands in 60 GHz by the Federal Communications
Commission (FCC).
802.11ad aims to develop the protocol adaptation layers (PALs) to support a plethora of
applications that will arise from the elimination of cables and from fast wireless sync and transfer. The PALs being considered by WiGig include wireless serial extension (WSE), which
eliminates USB 3.0 cables; wireless bus extension (WBE), which eliminates PCIe 3.0 cables;
wireless display extension (WDE), which eliminates high-definition multimedia interface (HDMI)
and display port cables; and wireless secure digital (WSD), which makes secure digital
input/output card (SDIO) disks wireless. The first important 60 GHz millimeter wave application
to enter the market as wireless docking based on PCIe 3.0—with one second-generation lane
(also called x2)—or USB 3.0. All devices with 802.11ad MAC/PHY/Radio use the corresponding
PALs between the application and MAC layers to seamlessly transfer information between
devices as if the devices were connected by wires. Another 60 GHz application is wireless HDMI
based on WDE, which allows transfer of uncompressed bits from devices such as set top boxes
and blue ray disc players to television screens and from laptops, desktops, or ultrabooks to
monitors via a display port cable replacement. The WDE also supports H264 compressed rates
for handling variations in the wireless channel and to ensure seamless content delivery to the
end users. Performance of the PHY and MAC protocols is analyzed in [13] and [14].
In this paper, we describe the novel features of the MAC and PHY sublayers of the protocol
stack defined in 802.11ad. In section 2, we describe the TDMA protocol and the need for
directionality in 60 GHz. In section 3, we outline the 802.11ad PHY layer, and in section 4, we
outline the MAC layer. In section 5, we outline the beamforming protocol, and in section 6 we
outline the power-saving protocol. In section 7, we describe the fast session transfer, and in
section 8, we show achievable rates using different MAC- and PHY-layer packet transmission
options. Section 9 concludes the paper.
2 TDMA Protocol and the Need for Directionality
Interest in the 30–300 MHz millimeter wave spectrum has increased significantly because of
low-cost, high-performance CMOS technology and because of low-loss, low-cost organic
packaging. A millimeter-wave radio can be empowered for the same cost as a radio operating in
the 5 GHz band or lower. This advantage, combined with wide available bandwidth, makes the
millimeter-wave spectrum more attractive than ever before for supporting new systems and
applications. A millimeter wave signal can propagate over a few kilometers at lower frequencies,
penetrating through different construction materials and deriving advantages from reflection
and refraction; however, they are highly directional and can be sustained only over short
distances. The reason for this directionality is explained by the Friis free space equation:
PR = PTGTGRλ
2
/4πR
2
(1)
where PR, PT, GT, GR, λ and R is the receive power, transmit power, transmit antenna gain,
receive antenna gain, wavelength, and distance between the transmitter and receiver,
respectively. There is a 22 dB loss when we move from 5 GHz to 60 GHz. This loss is due to
lower wavelength and can be offset by using directional antennas with higher gains. If 2 GHz
bandwidth was used in 60 GHz and PT = 10 dBm, the noise figure Nf = 10 dB, and the shadow
fading margin σ = 6 dB, 1 Gbit/s throughput could not be achieved (Fig. 2). Therefore, the gains
of directional antennas must be exploited to achieve higher rates.