06 Jan 2016
WiGig Certification & Gigabit Connectivity
Mark Barrett CMO of Blu Wireless Technology looks at WiGig, its Gigabit data rate capability and the need for certification to ensure correct operation of devices.
Releasing the promise of gigabit wireless connectivity at 60GHz is not simple. Whilst the technology has been around for several years, creating reliable, interoperable systems that provide ultrahigh bandwidth data links is not trivial, and there have been many steps necessary in the last few years to bring this technology to the market.
The 60GHz band has attracted much attention over the years. The band is unlicensed around the world and provides the opportunity for very high bandwidth gigabit links.
However, the amount of bandwidth available varies in different regions, the technical challenges of operating at such high frequencies are significant, and connections are generally limited by line-of-sight as millimetre wave wireless signals are easily blocked by walls and even people.
IEEE 802.11ad standard
That said, the IEEE has developed the IEEE 802.11ad standard for operating at 60GHz, which specifies operation up to 7Gbit/s. This also includes a mode of operation for the media access controller to support co-operative operation with existing WiFi 802.11a,b,g and ac MACs, as well as a new physical layer (PHY) that has several different modes.
These include a low power mode for transfers at around 1Gbit/s for mobile phones as well as a full multi-channel mode for the full 7Gbit/s link. This is aimed at replacing wires in the home such as the HDMI cable from a set to box to an Ultra HD TV screen with a typical range of up to 10m within a room. Moreover, it is possible to use the 802.11ad standard for longer range high bandwidth line-of-sight applications such as the backhaul from small mobile phone radio basestations – together with suitable modifications to the radio and array antenna sub-systems.
Using the 60GHz band also brings some key benefits to the antenna design. Due to the small wavelength (5mm) these links can be achieved with significantly smaller antennas, and this also makes a phased array, beam steering antenna design practical for the backhaul applications. When combined with closed loop electronic control such a beamforming antenna potentially eliminates the alignment challenges of setting up such links as the antenna can automatically converge on the optimum direction connection.
However, the steps to implementing this technology have been significant. In 2013 the WiGig Alliance merged with the WiFi Alliance in order to create a tri-band specification where the MAC is common to all the WiFi standards and in order to create the necessary industry wide interoperable standard necessary for a high volume chip market for 60GHz implementations.
The specification recommends the use of four channels, each 2.16GHz wide, and there are three modem protocols specified for use in the 802.11ad PHY – Control PHY, Single Carrer PHY and an OFDM PHY. The Control PHY and certain elements of the SC PHY are mandatory whilst other modes are optional. Data channel of 1.76 GHz bandwidth is sampled using a IQ sample rate of 2.64GHz.
The Control PHY (CPHY) has to be extremely reliable and so uses differential encoding with spread spectrum coding and BPSK modulation, coupled with high levels of error correction to provide the control signals at 27.5Mbit/s for the link. The Single Carrier PHY (SCPHY) mode uses a single carrier modulation such as BPSK, QPSK or 16-QAM for a simple link with a fixed data rate of 1.76 Gsymbols/s that translates to a raw bit rate from 385Mbit/s to 4620Mbit/s.
For higher data rates, Orthogonal Frequency Division Multiplex (OFDM) with up to 64QAM modulation is used in the optional OFDM PHY. This uses multiple carriers and Spread QPSK modulation with paired OFDM carriers. This reduces the risk of errors from channel fading and provides data rates from 693Mbit/s to 6756.75Mbit/s.
The Low Power Single Carrier PHY (LPSCPHY) is a variant of the single carrier PHY optimised for low power applications such as mobile phone handsets and other battery-powered devices. Depending on whether BPSK or QPSK coding is used, this provides raw data rates from 625.6Mbit/s to 2503Mbit/s. This can be used for ‘casting’ video from a phone to a larger screen, or for transferring large, gigabyte files quickly.
This latter mode can be important in maintaining battery life in a terminal as the energy used can be lower than using a lower bit rate technology for a considerable longer period. This allows large video files to be downloaded in a few seconds and played locally, rather than streamed across the network with a constant wireless network connection. This also reduces the congestion on the network and improves the experience for other users.
While the 60GHz band is unlicensed around the world, there are variations in the bands that are actually available (see table 1).
|Table 1 Global WiGig band Allocations|
|Europe||57.00 - 66.00 (4 channels)|
|North America||57.05 – 64.00 (3 channels)|
|South Korea||57.00 - 64.00 (3 channels)|
|Japan||59.00 – 66.00 (4 channels)|
|Australia||59.40 – 62.90 (2 channels)|
|China||59.00 – 64.00 (2 channels)|
The default channel centred at 60.48 GHz (CH2) is the only one that falls within all the regional spectrum allocations, but this allows a system to join a network and then determine which region it is operating in to use the relevant channels.
The small size of an antenna at 60GHz and the accompanying low-cost manufacturing techniques make phased array antenna systems viable. This uses an array of small antennas that can be electronically ‘steered’ by changing the phase of the signal at each antenna element in order to focus the possible beam in the right direction to get the best possible link with the optimum gain. The beamforming training specified in 802.11ad uses a bi-directional sequence of training frame transmissions that are added to each transmission type. These shape the transmit and receive antenna patterns in real time to account for local movement and interruptions to line-of-sight communication. Either the transmitter or the receiver can ask for a ‘beam refinement transaction’ to improve the link. This set of beam refinement frames consisting of beam refinement requests and responses, and the training is complete when one terminal receives a beam refinement frame with no training requests from the other device.
This combination of multiple wideband PHYs and beam forming for 802.11ad places a significant demand on the processing in the chip Since the typical clock rates of wireless baseband processor are in the region 500MHz to 1GHz, a sophisticated parallel processing architecture is needed to process IQ streams from arriving from the radio at a rate of 2.6 GHz or higher. Morever, the total processing load required to implement the complex modulation requirements is in the region of 1 Teraop – hence multiple parallel processing units are required to process the PHY and MAC streams in a power and area (cost) efficient manner. Whilst it is possible to implement the standard entirely in hardware such an approach lacks flexibility.
A more sophisticated solution to solving this baseband uses combination of fixed function Digital Signal Processing (DSP) blocks with highly optimised parallel vector DSPs in order to providea pool of DSP capability that can be reconfigured into different clusters for the different PHY modes. Each cluster has its own controller that automatically optimises the units, switching off execution units off between tasks to reduce the power consumption. This provides the best trade-off between the high performance required for 60GHz PHY processing, the die area, which relates directly to the cost of the chip, and the power consumption.
This keeps the utilisation of the processing units high and minimises data buffering, and has been shown to be four times more efficient in area and power compared to more general SDR baseband designs.
Following the merger in 2013 of the WiGig Alliance with the WiFi Alliance, providing interoperability testing and certification has become viable. With first pre-certified prototypes of commercial silicon released in 2015 to support all the different modes of operation, equipment builders have been able to start interoperability testing with a the objective of validating the WiGig certification plan This will allow WiGig interoperabiliy certification during 2016 for equipment on the market so that buyers can be reassured that systems will work together.
With prototype silicon and systems being developed and testing in 2015, the promise of high bandwidth, gigabit wireless links at 60GHz is emerging. With interoperability testing moving forward, manufacturers expect to have systems on the market through 2016 for both consumer and industrial applications. Although there is highly complex silicon, software and antenna designs involved, the technology has evolved sufficiently to start rolling out in living rooms around the world.
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About the author
Mark Barrett is CMO, Blu Wireless Technology. He began his career with Philips Research working on millimetre wave radar and signal processing. During the 1990’s, Mark led the development of several applications of array antennas and digital beamforming to satellite, radar and mobile communications (Smart Antennas) applications. He led the TSUNAMI series of multi company European projects, which demonstrated the use of Smart Antennas for 2G and 3G mobile systems.
Blu Wireless is a leader in 60GHz intellectual property. The company designs and licences its technology for inclusion on 802.11ad next generation WiFi (WiGig), tri-band WiFi and 4G mobile network backhaul chipsets.
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