Published on August 14th, 2012
Emerging WiFi and long-term evolution (LTE) standards require gigabit per second speeds to address the growing consumer demand for higher data transfer between their mobile devices, TVs, BluRay players and desktop computers. The WiFi and LTE wireless standards are implemented on systems on chip (SoCs) that are not and will not be fully integrated into a larger SoC. WiFi and LTE chips require complex RF and analog technology that must be carefully laid out separately from the CPU or mobile applications processor. To connect the wireless SoC to the main SoC, CPU, PC chipset, or mobile applications processor, designers use either USB or PCI Express (PCIe). While not visible on the outside of a product, some PCs use PCIe, but most PCs, tablets and smart phones use USB to connect the wireless chip to the main SoC.
Designers implementing WiFi and LTE SoCs are switching from USB 2.0 to USB 3.0 because USB 2.0 effective throughputs are only about 0.350 gigabits per second (Gbps), and USB 2.0 consumes more power per megabyte than USB 3.0. Today’s USB 2.0 runs at a maximum effective throughput of 0.32 to 0.35 Gbps, much less than the theoretical speed of 0.48 Gbps because of latencies in the PC’s hardware, operating system, drivers, or the PC peripheral’s hardware, OS, or firmware. For example, a USB 2.0 flash drive made with slow NAND flash memory will never achieve even 0.32 Gbps if the flash can only be read at 0.17 Gbps. This is a hardware limitation on the USB 2.0 speed.
|Table 1: Comparison of throughput speeds for current and coming standard deployments|
This article describes three important forces that are driving designers to incorporate USB 3.0 into WiFi and LTE products that are scheduled to hit the market in 2014 and 2015:
WiFi Reaching Super Speeds
The need to keep up with increasing WiFi/LTE speeds is the first driver of USB 3.0 into WiFi and LTE products is. The current generation of WiFi is the fourth generation, called WiFi-N. With a single antenna, WiFi-N runs up to 0.15 Gbps, and with multiple-in multiple-out antennas, WiFi-N runs even faster. Two antennas for receive and two for transmit, commonly called 2x2, offer twice the speed, or 0.30 Gbps. A small number of companies make products with 3x3 antennas which enable speeds up to 0.45 Gbps. This is much faster than the USB 2.0’s effective throughput of 0.35 Gbps. In this case, the 3x3 chip must implement USB 3.0 to take full advantage of the WiFi throughput.
WiFi Super-Charged with WiFi-AC
Currently, the number of WiFi-N 3x3 products is small. Greater leaps in speed are being made in the fifth generation of WiFi, called WiFi-AC. While the AC standard has not yet been finalized, manufacturers are already shipping products that support the draft of the AC standard, or “draft-AC.” NetGear and Buffalo shipped the first draft WiFi-AC products, based on Broadcom’s 802.11ac chipset, in early 2012. In fact, NetGear demonstrated a commercially available draft WiFi-AC Residential Gateway with a 1.2 Gbps download speed. Marvell also announced availability of its own WiFi-AC chipset in May 2012.
|Figure 1: WiFi-AC routers enable download speeds of up to 1.2 Gbps|
WiFi-AC products will operate at 1 Gbps or higher, of which USB 2.0 can only support 0.35 Gbps. The AC products are backward compatible so they work with all existing WiFi products, but products with USB 3.0 will be able to take advantage of the full WiFi-AC product speeds.
LTE Advanced Super Charges LTE
LTE Advanced (LTE-A) modems will also begin shipping in 2014 or earlier. LTE-A will deliver data at over 0.50 Gbps, allowing mobile users to synchronize data, music, pictures, videos stored in the internet cloud. A big initial market for LTE-A modems will be USB 3.0 dongles. The dongle is widely used worldwide because it is easy to deliver to customers, easy to set up and is easy to switch from one USB 3.0-ready PC to another.
Access to Personal, In-Home Cloud
The second driver of USB 3.0 into WiFi and LTE products is consumer demand for faster data access from peripheral devices. For example, WiFi-AC routers that create WiFi networks will soon have one or more USB 3.0 host ports. This will allow users to connect USB 3.0 hard drives to the network, as shown in Figure 2.
|Figure 2: WiFi-AC routers with multiple USB 3.0 ports and drives will allow consumers to create an expandable, in-home, personal cloud|
With USB 3.0 hard drives hooked up to a network, consumers can create their own in-home Internet cloud for storage. Consumers can store all their photos, videos, music and other data in their USB 3.0 hard drives and access them wirelessly. All users in the home can access the same data, without a full server or PC. The flexibility of multiple ports allows users to add storage as their needs grow; for example, today a user could connect a 3 terabyte (TB) hard drive and a year later add a 4 TB hard drive. Using WiFi-AC will allow data transfers at gigabit per second speeds between a laptop and personal cloud.
USB 3.0 for Wireless Connectivity on PCs
Some laptop users will purchase a USB 3.0 dongle with faster WiFi to eliminate the need for a gigabit Ethernet cable. These dongles are simply plugged into the laptop’s USB 3.0 port or attached to a host port in a USB 3.0 docking station. Even with this simple installation, dongles can outperform the current option of WiFi miniPCIe cards that require the semi-professional installation of opening up a PC, plugging the card into the miniPCIe slot, and connecting the antenna cable.
WiFi-AC for TVs and Set-Top Boxes
In addition to USB dongles for laptops, an ideal market for WiFi-N 3x3 and WiFi-AC is consumer electronics, smart phones and tablets.
In consumer electronics, many mid-range and high-end TVs connect to the Internet using wired Ethernet or WiFi. WiFi is connected in one of two ways, and usually via USB. The first kind of WiFi USB connection is inside the TV and hidden from the consumer. TV manufacturers use this inside port to connect to a USB card reader. The card reader is exposed so the consumer can insert an SD card and view stored photos or videos. Most consumers are familiar with the second kind of USB connection, which is the exposed USB port on the outside of the TV that is used to plug in a USB flash drive, USB web cam, or USB WiFi dongle. The consumer can plug a USB dongle, like the 3G HSUPA dongle shown in Figure 3, into an external USB port. Most new TVs now include at least two USB ports, and often some additional internal ports. One port is used for connecting to USB storage and the other port is used for connecting to a USB dongle. High-end TVs will soon include USB 3.0 ports.
|Figure 3: Today’s TVs include USB 2.0 ports that can accept WiFi dongles for wireless connectivity. Tomorrow’s TVs will include USB 3.0 ports for faster WiFi or LTE connectivity.|
To take advantage of the faster speeds WiFi-AC will offer, high-end TVs have already started to migrate from USB 2.0 and upgrade to USB 3.0. This upgrade allows users to stream content from either a remote home gateway or a media source withfaster WiFi speed transfer of data between sources of video.
In the U.S., set-top boxes currently include digital video recording (DVR) functionality, and video stored in one room can be viewed in another room. This flexibility requires a fast WiFi or networking connection to improve the delivery of video between rooms, especially for high-definition (HD) content.
Reduce power consumption with SSIC and USB 3.0
The third driver of USB 3.0 in WiFi and LTE products is the availability of M-PHYs supporting SSIC. A MIPI M-PHY is typically used with MIPI protocols and has the advantage of running at gigabit speeds, but it is smaller in size and power consumption than a USB 3.0 PHY. USB 3.0 is used outside the box between a host and device. SuperSpeed Interchip (SSIC) brings USB from outside the box to inside the box and on the printed circuit board (PCB). SSIC communicates between chips on the PCB, and in this case, between the WiFi or LTE chip and a main processor chip, CPU, or mobile application processor.
SSIC reuses existing USB 3.0 protocol and software drivers and exchanges the USB 3.0 PHY for a smaller, lower power MIPI M-PHY. While a USB 3.0 PHY sends data across a 3 meter cable, the smaller MIPI M-PHY executes USB 3.0 communication between chips across only a few millimeters, and with lower power consumption. Instead of a USB cable, metal lines on the PCB connect the two chips.
|Figure 4: A USB 3.0 Host Controller with SSIC can reduce power consumption.|
To reduce power consumption, mobile applications (apps) processors that run smart phones use a USB 3.0 host controller with an SSIC interface. The SSIC pins on the apps processor connect to the SSIC pins on the USB 3.0 device controller on an LTE modem. SSIC enables the USB 3.0 data transfer speed between chips to match the speed of the wireless protocols. This also reduces power consumption to about one-fifth of the power of USB 3.0. SSIC lets product makers reuse their existing software drivers and digital controllers. Drivers can be shared, because the same USB 3.0 drivers can be reused with SSIC. As a result, every WiFi chip and every LTE modem chip developed beginning in 2012 will use SSIC to save power.
Designers working on consumer electronics products that are scheduled to go to market in 2014 and 2015 must be cognizant of the three forces driving USB 3.0 into WiFi and LTE products: increasing WiFi and LTE speeds, consumer demand for faster data access, and the desire for lower power consumption that USB 3.0/SSIC offers. Choosing an IP solution such as Synopsys’ DesignWare® USB 3.0 controller and PHY enables SoC designers to develop high-quality USB 3.0 silicon solutions to meet these growing market demands with fast time-to-market.
Eric Huang, Senior Product Marketing Manager for Semiconductor USB Digital IP, Synopsys, Inc.
In his role as senior product marketing manager for semiconductor USB digital IP at Synopsys, Eric Huang is responsible for managing USB 3.0 and USB 2.0 IP. Huang worked on USB at the beginning in 1995 with the world's first BIOS that supported USB keyboards and mice while at Award Software. After a departure into embedded systems software for real-time operating systems, Huang returned to USB cores and software at inSilicon, the world’s leading supplier of USB IP at the time. inSilicon was later acquired by Synopsys in 2002. Huang served as chairman of the USB On-The-Go Working Group for the USB Implementers Forum from 2004-2006.
Huang received an M.B.A. from Santa Clara University, an M.S. in Engineering from University of California Irvine, and a B.S. in Engineering from the University of Minnesota. He is a licensed professional engineer in civil engineering in the State of California.